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Journal Articles

2024

1. 
   Polycaprolactone-Based Zinc Ink for High Conductivity Transient Printed Electronics and Antennas Carol L. Baumbauer, Anupam Gopalakrishnan, Madhur Atreya, Gregory L. Whiting, and Ana C. Arias Advanced Electronic Materials, 2024 , . [Abstract] [Bibtex] [PDF]

   Distributed sensors and electronics can be used in agriculture to optimize crop management and improve environmental outcomes. Electronic devices in these outdoor spaces require medium to long range (>1m) wireless communication of data over several weeks or months, which in turn requires high conductivity (1 × 105 Sm−1) antennas. Printed bioinert or ecoresorbable conductors, comprising carbon, magnesium, or zinc fillers, typically exhibit conductivity on the order of 10–1000 Sm−1 and lifetimes from a few hours to a few days. A print-based fabrication process for chemically treated zinc traces, which achieves conductivity of up to 6 × 105 Sm−1 is reported here. The ink formulation uses a non-water-soluble soil biodegradable polycaprolactone binder. The ink and printing processes reported here led to stable conductive traces that are used in ultra high frequency radio frequency identification (UHF-RFID) folded dipole antennas operating at 915 MHz. The conductivity of the printed traces is maintained for over 70 days in ambient environments when traces are protected by a biodegradable beeswax encapsulation layer.

   @article{Carol_Zinc, author = {Baumbauer, Carol L. and Gopalakrishnan, Anupam and Atreya, Madhur and Whiting, Gregory L. and Arias, Ana C.}, title = {Polycaprolactone-Based Zinc Ink for High Conductivity Transient Printed Electronics and Antennas}, year = {2024}, doi = {10.1002/aelm.202300658}, publisher = {}, url = {https://doi.org/10.1021/acssensors.3c00630}, journal = {Advanced Electronic Materials}, volume = {}, number = {}, thumbnail = {carol2024Zinc.png}, pdf = {carol2024Zinc.pdf} }

2. 
   Wireless ear EEG to monitor drowsiness Ryan Kaveh, Carolyn Schwendeman, Leslie Pu, Ana C. Arias, and Rikky Muller Nature Communications, 2024 15, . [Abstract] [Bibtex] [PDF]

   Neural wearables can enable life-saving drowsiness and health monitoring for pilots and drivers. While existing in-cabin sensors may provide alerts, wearables can enable monitoring across more environments. Current neural wearables are promising but most require wet-electrodes and bulky electronics. This work showcases in-ear, dry-electrode earpieces used to monitor drowsiness with compact hardware. The employed system integrates additive-manufacturing for dry, user-generic earpieces, existing wireless electronics, and offline classification algorithms. Thirty-five hours of electrophysiological data were recorded across nine subjects performing drowsiness-inducing tasks. Three classifier models were trained with user-specific, leave-one-trial-out, and leave-one-user-out splits. The support-vector-machine classifier achieved an accuracy of 93.2% while evaluating users it has seen before and 93.3% when evaluating a never-before-seen user. These results demonstrate wireless, dry, user-generic earpieces used to classify drowsiness with comparable accuracies to existing state-of-the-art, wet electrode in-ear and scalp systems. Further, this work illustrates the feasibility of population-trained classification in future electrophysiological applications.

   @article{Carolyn_drowsiness, author = {Kaveh, Ryan and Schwendeman, Carolyn and Pu, Leslie and Arias, Ana C. and Muller, Rikky}, title = {Wireless ear EEG to monitor drowsiness}, year = {2024}, doi = {10.1038/s41467-024-48682-7}, publisher = {}, url = {https://doi.org/10.1038/s41467-024-48682-7}, journal = {Nature Communications}, volume = {15}, number = {}, thumbnail = {carolyn2024naturecomm.png}, pdf = {carolyn2024naturecomm.pdf} }

2023

1. 
   Placement and drone flight path mapping of agricultural soil sensors using machine learning Payton Goodrich, Omar Betancourt, Ana C. Arias, and Tarek Zohdi Computers and Electronics in Agriculture, 2023 205, . [Abstract] [Bibtex] [PDF]

   Accurate soil data, which can be collected with agricultural sensors spaced at the half-variogram range, is crucial information for precision agriculture. Drones offer a unique advantage over other existing methods to sample data from soil sensors because of the high density of sensors required to gather spatially granular data to capture soil variability. To determine the placement of sensors within an agricultural field, a novel sequential gap-reduction algorithm that minimizes sensor overlap was developed and used to assign sensor placement for four types of agricultural fields. A genetic algorithm optimized multi-agent flight paths for scanning sensors in a simulated agricultural field using a robust agent-based model. The locations of soil sensors for a simulated 400 m center-pivot irrigation field were used to determine flight paths for swarms of 1-8 drones. Increasing the number of drones in the swarm had a negligible effect on total energy expenditure but reduced the time to scan the sensors from 19 min to less than three minutes. The proposed sequential gap reduction algorithm maximizes the coverage of any arbitrarily-shaped agricultural field with fewer sensors than a grid-based distribution in most cases. The proposed multi-agent flight path mapping can effectively and efficiently generate flight paths for variable numbers of drones to scan all sensors. The framework proposed here can be utilized and expanded for variable rate irrigation, precision application of biological control agents, and smart farming.

   @article{Payton_soil_ML, author = {Goodrich, Payton and Betancourt, Omar and Arias, Ana C. and Zohdi, Tarek}, title = {Placement and drone flight path mapping of agricultural soil sensors using machine learning}, year = {2023}, doi = {10.1016/j.compag.2022.107591}, publisher = {Elsevier}, url = {https://www.sciencedirect.com/science/article/pii/S0168169922008997}, journal = {Computers and Electronics in Agriculture}, volume = {205}, number = {}, thumbnail = {payton2022soiML.jpg}, pdf = {payton2022soiML.pdf} }

2. 
   Home-Made, Self-Powered, Skin-Attachable Sensing Platform for Diverse Vital Sign Monitoring Xiaodong Wu, Wenjuan Ren, Yuhan Wen, Seiya Ono, Juan Zhu, James W. Evans, and Ana C. Arias ACS Sensors, 2023 , . [Abstract] [Bibtex] [PDF]

   Wearable electronic sensors that can perform real-time, continuous, and high-fidelity monitoring of diverse biophysical signals from the human body are burgeoning and exhibit great potential to transform traditional clinical healthcare. However, such emerging devices often suffer from strict requirements of special precursor materials and sophisticated fabrication procedures. Here, we present a new paradigm of a self-powered, skin-attachable, and multifunctional sensing platform that can be fully created just at home with daily necessities. Its operating mechanism is based on mechanical/thermal regulation of the potential difference output of a primary electrochemical cell. This proposed sensing platform is totally self-powered and can be conformally attached to the skin for continuous monitoring of both mechanical and thermal stimulations. A wide spectrum of vital physiological signs of the human body, including body temperature, heart/pulse rate, respiratory rate, coughing, and body motions, can be continuously monitored and analyzed with this home-made sensing platform. This study demonstrates that the lab-conducted professional and expensive scientific research can also be accomplished at home, opening up new opportunities for home-centered healthcare in low-resource environments. Moreover, this work can serve as a handy and cost-efficient prototype for classroom education and clinical training purposes.

   @article{Xiaodong_home_sensor, author = {Wu, Xiaodong and Ren, Wenjuan and Wen, Yuhan and Ono, Seiya and Zhu, Juan and Evans, James W. and Arias, Ana C.}, title = {Home-Made, Self-Powered, Skin-Attachable Sensing Platform for Diverse Vital Sign Monitoring}, year = {2023}, doi = {10.1021/acssensors.3c00630}, publisher = {ACS}, url = {https://doi.org/10.1021/acssensors.3c00630}, journal = {ACS Sensors}, volume = {}, number = {}, thumbnail = {Xiaodong2023home.png}, pdf = {Xiaodong2023home.pdf} }

2022

1. 
   Flexible Blade-Coated Optoelectronic Devices: Dual Functionality via Simultaneous Deposition Jasmine Jan, Juan Zhu, Jonathan Ting, and Ana C. Arias Advanced Functional Materials, 2022 , . [Abstract] [Bibtex] [PDF]

   Advances in printing techniques have enabled a new generation of low-cost and large-area flexible electronics. However, in applications where a combination of printed components is required, multiple fabrication processes and subsequent integration can be complex and time consuming. Additionally, these applications require devices to be stacked atop each other, reducing overall mechanical flexibility. In this work, surface-energy-patterning (SEP) is used to enable simultaneous blade coating of organic photodiode (OPD) and organic light-emitting diode (OLED) films side-by-side. The result is dual functionality on a single flexible substrate. Various active layer solution concentrations are investigated to optimize active layer thicknesses and consequently optimize the performance of each device. A peak spectral responsivity of 0.33 A W−1 at 800 nm is achieved for optimized OPDs and a maximum luminance of 7000 cd m−2 is achieved for optimized OLEDs at an applied bias of 8 V. Overall, this technique enables the printing of two functionally distinct devices in a single step without compromising the performance of either device.

   @article{Jasmine_parallelfab, author = {Jan, Jasmine and Zhu, Juan and Ting, Jonathan and Arias, Ana C.}, title = {Flexible Blade-Coated Optoelectronic Devices: Dual Functionality via Simultaneous Deposition}, year = {2022}, doi = {https://doi.org/10.1002/adfm.20211234}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202112343}, journal = {Advanced Functional Materials}, volume = {}, number = {}, thumbnail = {jasmine2022parallelfab.png}, pdf = {jasmine2022parallelfab.pdf} }

2. 
   Rapid and Scalable Fabrication of Low Impedance, 3D Dry Electrodes for Physiological Sensing Ryan Kaveh, Natalie Tetreault, Karthik Gopalan, Julian Maravilla, Michael Lustig, Rikky Muller, and Ana C. Arias Advanced Materials Technologies, 2022 , . [Abstract] [Bibtex] [PDF]

   Abstract Medical electrophysiological sensors that can study the body and diagnose diseases depend on consistently low impedance electrode–skin interfaces. Clinical-standard wet electrodes use hydrogels and skin abrasion to improve the interface and thus the recorded signal quality. These electrodes are challenging to self-administer and impede in-home care. Wearable dry electrodes are more practical; however, they show higher impedances than wet electrodes and are costly to customize. This work presents a fabrication method for rapidly producing low impedance, anatomically fit dry electrodes that do not require hydrogels. By using electroless copper and gold plating with 3D printing, biocompatible electrodes can be optimized for individuals at a fraction of the cost of existing vacuum deposition-based techniques. Example 3D dry electrodes made with this process are evaluated alongside clinical-standard devices in typical scenarios to compare electrical performance and comfort. The resulting dry electrodes exhibit an average electrode-skin impedance of 66.7 kΩ at 50 Hz and DC offset of −20 mV without any hydrogel, which, when area normalized, is within the range achieved by wet electrodes without skin abrasion.

   @article{Ryan_electrode, author = {Kaveh, Ryan and Tetreault, Natalie and Gopalan, Karthik and Maravilla, Julian and Lustig, Michael and Muller, Rikky and Arias, Ana C.}, title = {Rapid and Scalable Fabrication of Low Impedance, 3D Dry Electrodes for Physiological Sensing}, year = {2022}, doi = {https://doi.org/10.1002/admt.202200342}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admt.202200342}, journal = {Advanced Materials Technologies}, volume = {}, number = {}, thumbnail = {ryan2022electrode.png}, pdf = {ryan2022electrode.pdf} }

3. 
   Printed Potentiometric Nitrate Sensors for Use in Soil Carol L. Baumbauer, Payton J. Goodrich, Margaret E. Payne, Tyler Anthony, Claire Beckstoffer, Anju Toor, Whendee Silver, and Ana C. Arias Sensors, 2022 22, 4095. [Abstract] [Bibtex] [PDF]

   Plant-available nitrogen, often in the form of nitrate, is an essential nutrient for plant growth. However, excessive nitrate in the environment and watershed has harmful impacts on natural ecosystems and consequently human health. A distributed network of nitrate sensors could help to quantify and monitor nitrogen in agriculture and the environment. Here, we have developed fully printed potentiometric nitrate sensors and characterized their sensitivity and selectivity to nitrate. Each sensor comprises an ion-selective electrode and a reference electrode that are functionalized with polymeric membranes. The sensitivity of the printed ion-selective electrodes was characterized by measuring their potential with respect to a commercial silver/silver chloride reference electrode in varying concentrations of nitrate solutions. The sensitivity of the printed reference electrodes to nitrate was minimized with a membrane containing polyvinyl butyral (PVB), sodium chloride, and sodium nitrate. Selectivity studies with sulphate, chloride, phosphate, nitrite, ammonium, calcium, potassium, and magnesium showed that high concentrations of calcium can influence sensor behavior. The printed ion-selective and reference electrodes were combined to form a fully printed sensor with sensitivity of −48.0 ± 3.3 mV/dec between 0.62 and 6200 ppm nitrate in solution and −47 ± 4.1 mV/dec in peat soil.

   @article{Carol_nitrate, author = {Baumbauer, Carol L. and Goodrich, Payton J. and Payne, Margaret E. and Anthony, Tyler and Beckstoffer, Claire and Toor, Anju and Silver, Whendee and Arias, Ana C.}, title = {Printed Potentiometric Nitrate Sensors for Use in Soil}, year = {2022}, doi = {https://doi.org/10.3390/s22114095}, publisher = {MDPI}, url = {https://www.mdpi.com/1424-8220/22/11/4095/htm}, journal = {Sensors}, volume = {22}, number = {4095}, thumbnail = {carol2022nitrate.png}, pdf = {carol2022nitrate.pdf} }

4. 
   Vacuum Formed Coils for MRI Karthik Gopalan, Julian Maravilla, Jaren Mendelsohn, Ana C. Arias, and Michael Lustig Magnetic Resonance in Medicine, 2022 , . [Abstract] [Bibtex] [PDF]

   Purpose To describe a digital fabrication method used for custom MRI receive coils with vacuum forming and electroless copper plating. Methods Our process produces intricate copper traces on curved surfaces. A three-dimensional scan of a desired anatomy is obtained and used to design coil elements. The layout is predistorted with a self built simulation of the vacuum forming process and the geometric overlaps are tested with electromagnetic simulation software. The desired coil geometry is patterned onto a polycarbonate sheet by sandblasting through a tape mask. The sandblasted areas are then catalyzed with a palladium-tin solution and vacuum formed. The catalyzed, three-dimensional part is placed into a custom built plating tank and copper plated. Electronic components are attached to the copper traces to form resonant receive coils. The methods described here are demonstrated and tested with an 8 channel visual cortex coil array. Results The prototype coils exhibit quality factor ratios higher than three, indicating body noise dominance. The coil array shows high signal-to-noise ratio (SNR) near the periphery of a head shaped phantom. In vivo images with up to 0.37?0.37?0.67?mm3$ 0.37\times 0.37\times 0.67;\mathrmmm^3 $ spatial resolution were acquired on a human volunteer. Conclusion This work presents the first example of vacuum formed coils with direct electroless copper plating. Our fabrication method results in coil arrays that are in close proximity to the body. This methods described here may enable the rapid development of a set of coils of different sizes for applications including longitudinal fMRI studies and MR-guided therapies.

   @article{Karthik_vacuum_MRM, author = {Gopalan, Karthik and Maravilla, Julian and Mendelsohn, Jaren and Arias, Ana C. and Lustig, Michael}, title = {Vacuum Formed Coils for MRI}, year = {2022}, doi = {10.1002/mrm.29546}, publisher = {Wiley Online Library}, url = {https://doi.org/10.1002/mrm.29546}, journal = {Magnetic Resonance in Medicine}, volume = {}, number = {}, thumbnail = {karthik2022vacuum.png}, pdf = {karthik2022vacuum.pdf} }

5. 
   A Sparse Sampling Sensor Front-End IC for Low Power Continuous SpO2 & HR Monitoring Sina Faraji Alamouti, Jasmine Jan, Cem Yalcin, Jonathan Ting, Ana Claudia Arias, and Rikky Muller IEEE Transactions on Biomedical Circuits and Systems, 2022 16, 6. [Abstract] [Bibtex] [PDF]

   Photoplethysmography (PPG) is an attractive method to acquire vital signs such as heart rate and blood oxygenation and is frequently used in clinical and at-home settings. Continuous operation of health monitoring devices demands a low power sensor that does not restrict the device battery life. Silicon photodiodes (PD) and LEDs are commonly used as interface devices in PPG sensors; however, using of flexible organic devices can enhance the sensor conformality and reduce the cost of fabrication. In most PPG sensors, most of system power consumption is concentrated in powering LEDs, traditionally consuming mWs. Using organic devices further increases this power demand since these devices exhibit larger parasitic capacitances and typically need higher drive voltages.This work presents a sensor IC for continuous SpO _2 and HR monitoring that features an on-chip reconstruction-free sparse sampling algorithm to reduce the overall system power consumption by \sim70% while maintaining the accuracy of the output information. The designed frontend is compatible with a wide range of devices from silicon PDs to organic PDs with parasitic capacitances up to 10 nF. Implemented in a 40 nm HV CMOS process, the chip occupies 2.43 mm^2 and consumes 49.7 \muW and 15.2 \muW of power in continuous and sparse sampling modes respectively. The performance of the sensor IC has been verified in vivo with both types of devices and the results are compared against a clinical grade reference. Less than 1 bpm and 1% mean absolute errors were achieved in both continuous and sparse modes of operation.

   @article{Jasmine_Sina_SpO2, author = {Alamouti, Sina Faraji and Jan, Jasmine and Yalcin, Cem and Ting, Jonathan and Arias, Ana Claudia and Muller, Rikky}, title = {A Sparse Sampling Sensor Front-End IC for Low Power Continuous SpO2 & HR Monitoring}, year = {2022}, doi = {10.1109/ISSCC42614.2022.9731113}, publisher = {IEEE}, url = {https://ieeexplore.ieee.org/abstract/document/9960794}, journal = {IEEE Transactions on Biomedical Circuits and Systems}, volume = {16}, number = {6}, thumbnail = {Sina2022ISSCCSpO2.png}, pdf = {Sina2022ISSCCSpO2.pdf} }

2021

1. 
   Vacuum Formed Coils for Magnetic Resonance Imaging Karthik Gopalan, Julian Maravilla, Jaren Mendelsohn, Ana C. Arias, and Michael Lustig IEEE, 2021 , . [Abstract] [Bibtex] [PDF]

   Magnetic resonance imaging is an important diagnostic tool that uses resonant RF receivers to create an image. Prior work has shown that bringing these receivers closer to the subject dramatically improves the signal to noise ratio. Here, we describe a method of patterning coil arrays on complex three dimensional surfaces using vacuum forming, sandblasting, and electroless copper plating. To account for the deformation of vacuum forming, we developed a graphical simulation to predistort trace designs. Our process produces coils with quality factors similar to coils made with copper tape.

   @article{Karthik_vacuum, author = {Gopalan, Karthik and Maravilla, Julian and Mendelsohn, Jaren and Arias, Ana C. and Lustig, Michael}, title = {Vacuum Formed Coils for Magnetic Resonance Imaging}, year = {2021}, doi = {10.1109/ICEAA52647.2021.9539783}, publisher = {2021 International Conference on Electromagnetics in Advanced Applications (ICEAA)}, url = {https://ieeexplore.ieee.org/document/9539783}, journal = {IEEE}, volume = {}, number = {}, thumbnail = {karthik2021vacuum.png}, pdf = {karthik2021vacuum.pdf} }

2. 
   Quantitative anatomy mimicking slice phantoms Karthik Gopalan, Jonathan I. Tamir, Ana C. Arias, and Michael Lustig Magnetic Resonance in Medicine, 2021 86, 2. [Abstract] [Bibtex] [PDF]

   To present a reproducible methodology for building an anatomy mimicking phantom with targeted T1 and T2 contrast for use in quantitative magnetic resonance imaging. We propose a reproducible method for creating high-resolution, quantitative slice phantoms. The phantoms are created using gels with different concentrations of NiCl2 and MnCl2 to achieve targeted T1 and T2 values. We describe a calibration method for accurately targeting anatomically realistic relaxation pairs. In addition, we developed a method of fabricating slice phantoms by extruding 3D printed walls on acrylic sheets. These procedures are combined to create a physical analog of the Brainweb digital phantom. With our method, we are able to target specific T1/T2 values with less than 10% error. Additionally, our slice phantoms look realistic since their geometries are derived from anatomical data. Standardized and accurate tools for validating new techniques across sequences, platforms, and different imaging sites are important. Anatomy mimicking, multi-contrast phantoms designed with our procedures could be used for evaluating, testing, and verifying model-based methods.

   @article{Karthik_phantom, author = {Gopalan, Karthik and Tamir, Jonathan I. and Arias, Ana C. and Lustig, Michael}, title = {Quantitative anatomy mimicking slice phantoms}, year = {2021}, doi = {10.1002/mrm.28740}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/10.1002/mrm.28740}, journal = {Magnetic Resonance in Medicine}, volume = {86}, number = {2}, thumbnail = {karthik2021phantom.png}, pdf = {karthik2021phantom.pdf} }

3. 
   Characterization and Comparison of Biodegradable Printed Capacitive Humidity Sensors Emma Wawrzynek, Carol Baumbauer, and Ana C. Arias Sensors, 2021 21, 19. [Abstract] [Bibtex] [PDF]

   Flexible and biodegradable sensors are advantageous for their versatility in a range of areas from smart packaging to agriculture. In this work, we characterize and compare the performance of interdigitated electrode (IDE) humidity sensors printed on different biodegradable substrates. In these IDE capacitive devices, the substrate acts as the sensing layer. The dielectric constant of the substrate increases as the material absorbs water from the atmosphere. Consequently, the capacitance across the electrodes is a function of environmental relative humidity. Here, the performance of polylactide (PLA), glossy paper, and potato starch as a sensing layer is compared to that of nonbiodegradable polyethylene terephthalate (PET). The capacitance across inkjet-printed silver electrodes is measured in environmental conditions ranging from 15 to 90% relative humidity. The sensitivity, response time, hysteresis, and temperature dependency are compared for the sensors. The relationship between humidity and capacitance across the sensors can be modeled by exponential growth with an R2 value of 0.99, with paper and starch sensors having the highest overall sensitivity. The PET and PLA sensors have response and recovery times under 5 min and limited hysteresis. However, the paper and starch sensors have response and recovery times closer to 20 min, with significant hysteresis around 100%. The PET and starch sensors are temperature independent, while the PLA and paper sensors display thermal drift that increases with temperature.

   @article{Emma_sensors, author = {Wawrzynek, Emma and Baumbauer, Carol and Arias, Ana C.}, title = {Characterization and Comparison of Biodegradable Printed Capacitive Humidity Sensors}, year = {2021}, doi = {10.3390/s21196557}, publisher = {MDPI}, url = {https://www.mdpi.com/1424-8220/21/19/6557#}, journal = {Sensors}, volume = {21}, number = {19}, thumbnail = {emma2021humidity.png}, pdf = {emma2021humidity.pdf} }

4. 
   Tuning Strain Sensor Performance via Programmed Thin-Film Crack Evolution Juan Zhu, Xiaodong Wu, Jasmine Jan, Shixuan Du, James W. Evans, and Ana C. Arias ACS Applied Materials and Interfaces, 2021 13, 32. [Abstract] [Bibtex] [PDF]

   Stretchable strain sensors with well-controlled sensitivity and stretchability are crucial for applications ranging from large deformation monitoring to subtle vibration detection. Here, based on single-metal material on the elastomer and one-pot evaporation fabrication method, we realize controlled strain sensor performance via a novel programable cracking technology. Specifically, through elastomeric substrate surface chemistry modification, the microcrack generation and morphology evolution of the strain sensing layer is controlled. This process allows for fine tunability of the cracked film morphology, resulting in strain sensing devices with a sensitivity gauge factor of over 10 000 and stretchability up to 100%. Devices with a frequency response up to 5.2 Hz and stability higher than 1000 cycles are reported. The reported strain sensors, tracking both subtle and drastic mechanical deformations, are demonstrated in healthcare devices, human–machine interaction, and smart-home applications.

   @article{Juan_ACS, author = {Zhu, Juan and Wu, Xiaodong and Jan, Jasmine and Du, Shixuan and Evans, James W. and Arias, Ana C.}, title = {Tuning Strain Sensor Performance via Programmed Thin-Film Crack Evolution}, year = {2021}, doi = {10.1021/acsami.1c10975}, publisher = {American Chemical Society}, url = {https://pubs.acs.org/doi/full/10.1021/acsami.1c10975}, journal = {ACS Applied Materials and Interfaces}, volume = {13}, number = {32}, thumbnail = {juan2021strain.jpeg}, pdf = {juan2021strain.pdf} }

5. 
   Multi-cycle testing of commercial coin cells for buffering of harvested energy for the IoT James W. Evans, Bernard Kim, Seiya Ono, Ana C. Arias, and Paul K. Wright IEEE Internet of Things Journal, 2021 , . [Abstract] [Bibtex] [PDF]

   The sensors and microprocessor-radios of the Internet of Things require power and one possibility is a hybrid source consisting of energy harvesting coupled with a rechargeable battery. This paper concerns a system with a low, but near constant, supply of harvested energy that is sufficient to slowly charge a battery, which buffers that energy and can then supply the higher power level necessary at data transmission. The cycle-life of the battery is then significant and this paper describes the cycling of a commercial lithium coin cell, Panasonic ML2020, for small depth of discharge. Initial work was on a Bio-Logic battery tester and cells were successfully tested, without failure, for a few million cycles at very shallow depth of discharge. Thereafter a battery tester was developed, based on the Particle Photon, that was much less expensive than a channel of a commercial battery tester. Four cells have been cycled, using this tester, for more than 50 million times with no deterioration in performance evident. Capacitors and a NiMH cell are being similarly tested.

   @article{Jim_IEEE, author = {Evans, James W. and Kim, Bernard and Ono, Seiya and Arias, Ana C. and Wright, Paul K.}, title = {Multi-cycle testing of commercial coin cells for buffering of harvested energy for the IoT}, year = {2021}, doi = {10.1109/JIOT.2021.3050735}, publisher = {IEEE}, url = {https://ieeexplore.ieee.org/document/9319152}, journal = {IEEE Internet of Things Journal}, volume = {}, number = {}, thumbnail = {Jim2021battery.PNG}, pdf = {Jim2021battery.pdf} }

6. 
   Stencil-printed Lithium-ion micro batteries for IoT applications Anju Toor, Albert Wen, Filip Maksimovic, Abhinav M. Gaikwad, Kristofer S.J. Pister, and Ana C. Arias Nano Energy, 2021 82, . [Abstract] [Bibtex] [PDF]

   A battery design and fabrication process is demonstrated to make Lithium-ion (Li-ion) microbatteries with high capacity to power IoT devices. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide (LCO) respectively. The active area of the electrodes is scaled down to 1 mm2 and the resulting electrochemical performance is evaluated. These miniature batteries demonstrate a significantly higher discharge capacity (6.4 mAh/cm2) and energy density (23.6 mWh/cm2) than thin-film and thick-film, and 3D microbatteries. This work shows a miniaturized Li-ion battery capable of powering a MEMS-based wireless sensor system with peak current requirements as high as 4 mA, demonstrating its effectiveness as a power source for integrated electronics.

   @article{Anju_NanoEnergy, author = {Toor, Anju and Wen, Albert and Maksimovic, Filip and Gaikwad, Abhinav M. and Pister, Kristofer S.J. and Arias, Ana C.}, title = {Stencil-printed Lithium-ion micro batteries for IoT applications}, year = {2021}, doi = {https://doi.org/10.1016/j.nanoen.2020.105666}, publisher = {Elsevier}, url = {https://www.sciencedirect.com/science/article/abs/pii/S2211285520312398}, journal = {Nano Energy}, volume = {82}, number = {}, thumbnail = {Anju_battery.jpg}, pdf = {Anju_battery.pdf} }

7. 
   A Potentiometric Electronic Skin for Thermosensation and Mechanosensation Xiaodong Wu, Juan Zhu, James W. Evans, Canhui Lu, and Ana C. Arias Advanced Functional Materials, 2021 31, 17. [Abstract] [Bibtex] [PDF]

   Electronic skins (e-skins) that mimic the thermosensation and mechanosensation functionalities of natural skin are highly desired for the emerging fields of prosthetics and robotics. Advances in the materials and architecture of e-skins have been made; nevertheless, sensing mechanism innovations are rarely explored. Here, inspired by the skin sensory behaviors, a single potentiometric sensing scheme for both thermosensation and mechanosensation functionalities are presented. Through careful materials selection, component optimization, and structure configuration, the coupling effect between thermosensation and mechanosensation can be significantly minimized. Such a potentiometric sensing scheme enables one to create a new class of energy-efficient e-skin with distinctive characteristics that are highly analogous to those of natural human skin. The e-skin reported here features ultralow power consumption (at nanowatt level), greatly simplified operation (only voltage output), ultrahigh sensitivity (non-contact sensing capability), all-solution-processing fabrication, and, more importantly, good capability for simultaneous monitoring/mapping of both thermal and mechanical stimulations. In addition to proposing a new sensory mechanism, integration of the dual-functional e-skin with a soft robotic gripper for object manipulation is demonstrated. The presented concise yet efficient sensing scheme for both thermosensation and mechanosensation opens up previously unexplored avenues for the future design of skin prosthetics, humanoid robotics, and wearable electronics.

   @article{Xiaodong_eskin, author = {Wu, Xiaodong and Zhu, Juan and Evans, James W. and Lu, Canhui and Arias, Ana C.}, title = {A Potentiometric Electronic Skin for Thermosensation and Mechanosensation}, year = {2021}, doi = {https://doi.org/10.1002/adfm.202010824}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202010824}, journal = {Advanced Functional Materials}, volume = {31}, number = {17}, thumbnail = {xiaodong2021eskin.png}, pdf = {xiaodong2021eskin.pdf} }

2020

1. 
   Coupling in situ atomic force microscopy (AFM) and ultra-small-angle X-ray scattering (USAXS) to study the evolution of zinc morphology during electrodeposition within an imidazolium based ionic liquid electrolyte Jayme S. Keist, Joshua A. Hammons, Paul K. Wright, James W. Evans, and Christine A. Orme Electrochimica Acta, 2020 342, 136073. [Abstract] [Bibtex] [PDF]

   Zinc (Zn) is a low-cost material that is widely used in plating and is under consideration as a reversible deposit for a range of energy storage applications. In recent years, researchers have demonstrated that the Zn morphology can be tuned by electrodepositing from an ionic liquid often leading to morphologies that improve cyclability. However, the underlying mechanisms that control deposition and morphology are not well understood. In this work, we evaluate the evolution of zinc morphology as a function of the deposition thickness using in situ atomic force microscopy (AFM), in situ ultra-small angle X-ray scattering (USAXS) and ex situ electron microscopy. Imaging reveals two dominant features: a hexagonal plate-like morphology associated with individual Zn crystals and larger domains in which the individual crystals appear co-aligned. Analysis of the key features observed by USAXS indicates that the growth of the domain size is non-linear with the charge passed and that at least some of this non-linearity can be attributed to increased coalescence of the individual plates as the deposit thickens. A more detailed analysis suggests that there is little change in the aspect ratio of the individual Zn crystals- this is consistent with a growth mechanism in which previously deposited plates grow in diameter as new plates nucleate on their surface and then coalesce into one crystal.

   @article{Jim_SciDirect, author = {Keist, Jayme S. and Hammons, Joshua A. and Wright, Paul K. and Evans, James W. and Orme, Christine A.}, title = {Coupling in situ atomic force microscopy (AFM) and ultra-small-angle X-ray scattering (USAXS) to study the evolution of zinc morphology during electrodeposition within an imidazolium based ionic liquid electrolyte}, year = {2020}, doi = {https://doi.org/10.1016/j.electacta.2020.136073}, publisher = {Elsevier}, url = {https://www-sciencedirect-com.libproxy.berkeley.edu/science/article/abs/pii/S0013468620304655?via%3Dihub}, journal = {Electrochimica Acta}, volume = {342}, number = {136073}, thumbnail = {Jim2021zinc.PNG}, pdf = {Jim2021zinc.pdf} }

2. 
   A wearable biosensing system with in-sensor adaptive machine learning for hand gesture recognition Ali Moin, Andy Zhou, Abbas Rahimi, Alisha Menon, Simone Benatti, George Alexandrov, Senam Tamakloe, Jonathan Ting, Natasha Yamamoto, Yasser Khan, Fred Burghardt, Luca Benini, Ana C. Arias, and Jan M. Rabaey Nature Electronics, 2020 , . [Abstract] [Bibtex] [PDF]

   Wearable devices that monitor muscle activity based on surface electromyography could be of use in the development of hand gesture recognition applications. Such devices typically use machine-learning models, either locally or externally, for gesture classification. However, most devices with local processing cannot offer training and updating of the machine-learning model during use, resulting in suboptimal performance under practical conditions. Here we report a wearable surface electromyography biosensing system that is based on a screen-printed, conformal electrode array and has in-sensor adaptive learning capabilities. Our system implements a neuro-inspired hyperdimensional computing algorithm locally for real-time gesture classification, as well as model training and updating under variable conditions such as different arm positions and sensor replacement. The system can classify 13 hand gestures with 97.12% accuracy for two participants when training with a single trial per gesture. A high accuracy (92.87%) is preserved on expanding to 21 gestures, and accuracy is recovered by 9.5% by implementing model updates in response to varying conditions, without additional computation on an external device.

   @article{Ting_NatureElectronics, author = {Moin, Ali and Zhou, Andy and Rahimi, Abbas and Menon, Alisha and Benatti, Simone and Alexandrov, George and Tamakloe, Senam and Ting, Jonathan and Yamamoto, Natasha and Khan, Yasser and Burghardt, Fred and Benini, Luca and Arias, Ana C. and Rabaey, Jan M.}, title = {A wearable biosensing system with in-sensor adaptive machine learning for hand gesture recognition}, year = {2020}, doi = {https://doi-org.libproxy.berkeley.edu/10.1038/s41928-020-00510-8}, publisher = {Nature}, url = {https://www.nature.com/articles/s41928-020-00510-8}, journal = {Nature Electronics}, volume = {}, number = {}, thumbnail = {Ting2021emg.PNG}, pdf = {Ting2021emg.pdf} }

3. 
   Pulse Oximetry Using Organic Optoelectronics under Ambient Light Donggeon Han, Yasser Khan, Jonathan Ting, Juan Zhu, Craig Combe, Andrew Wadsworth, Iain McCulloch, and Ana C. Arias Advanced Materials, 2020 5, 5. [Abstract] [Bibtex] [PDF]

   Light absorption in oxygenated and deoxygenated blood varies appreciably over the visible and near-infrared spectrum. Pulse oximeters use two distinct wavelengths of light to measure oxygen saturation SpO2 of blood. Currently, light-emitting diodes (LEDs) are used in oximeters, which need additional components to drive them and negatively impact the overall size of the sensor. In this work, an ambient light oximeter (ALO) is demonstrated, which can measure photoplethysmography signals and SpO2 using various kinds of ambient light, avoiding the use of LEDs. Spectral filters are combined with organic photodiodes to create the ALO with sensitivity peaks at green (525 nm), red (610 nm), and near-infrared (740 nm) wavelengths. Finally, the wearable ALO is used to measure photoplethysmography signals and SpO2 on the index finger in different indoor and outdoor lighting conditions and the measurements are validated with commercial pulse oximeters under normal and ischemic conditions.

   @article{Han_pulse, author = {Han, Donggeon and Khan, Yasser and Ting, Jonathan and Zhu, Juan and Combe, Craig and Wadsworth, Andrew and McCulloch, Iain and and Arias, Ana C.}, title = {Pulse Oximetry Using Organic Optoelectronics under Ambient Light}, year = {2020}, doi = {10.1002/admt.201901122}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/admt.201901122}, journal = {Advanced Materials}, volume = {5}, number = {5}, thumbnail = {han2020pulse.png}, pdf = {han2020pulse.pdf} }

4. 
   Optimization of printed sensors to monitor sodium, ammonium, and lactate in sweat Alla M. Zamarayeva, Natasha A. D. Yamamoto, Anju Toor, Margaret E. Payne, Caleb Woods, Veronika I. Pister, Yasser Khan, James W., and Ana C. Arias APL Materials, 2020 8, 10. [Abstract] [Bibtex] [PDF]

   We describe the optimization of a flexible printed electrochemical sensing platform to monitor sodium ion (Na+), ammonium ion (NH4+), and lactate in human sweat. We used previously reported material systems and adapted them to scalable fabrication techniques. In the case of potentiometric Na+ and NH4+ sensors, ion-selective electrodes (ISEs) required minimum optimization beyond previously reported protocols, while a reference electrode had to be modified in order to achieve a stable response. We incorporated a carbon nanotube (CNT) layer between the membrane and the silver/silver chloride (Ag/AgCl) layer to act as a surface for adsorption and retention of Cl−. The resulting reference electrode showed minimal potential variation up to 0.08 mV in the solutions with Cl concentration varying from 0.1 mM to 100 mM. Increasing the ionophore content in the NH4+ ISE sensing membrane eliminated an offset in the potential readout, while incorporating CNTs into the sensing membranes had a marginal effect on the sensitivity of both Na+ and NH4+ sensors. Na+ and NH4+ sensors showed a stable near-Nernstian response with sensitivities of 60.0 ± 4.0 mV and 56.2 ± 2.3 mV, respectively, long-term stability for at least 60 min of continuous operation, and selectivity to Na+ and NH4+. For the lactate sensor, we compared the performance of the tetrathiafulvalene mediated lactate oxidase based working electrode with and without diffusion-limiting polyvinyl chloride membrane. The working electrodes with and without the membrane showed sensitivities of 3.28 ± 8 A/mM and 0.43 ± 0.11 μA/mM with a linear range up to 20 mM and 30 mM lactate, respectively.

   @article{AnjuAPLmaterials, author = {Zamarayeva, Alla M. and Yamamoto, Natasha A. D. and Toor, Anju and Payne, Margaret E. and Woods, Caleb and Pister, Veronika I. and Khan, Yasser and W., James and and Arias, Ana C.}, title = {Optimization of printed sensors to monitor sodium, ammonium, and lactate in sweat}, year = {2020}, doi = {https://doi.org/10.1063/5.0014836}, publisher = {American Institue of Physics}, url = {https://aip.scitation.org/doi/full/10.1063/5.0014836}, journal = {APL Materials}, volume = {8}, number = {10}, thumbnail = {Anju_sensor.jpeg}, pdf = {Anju_sensor.pdf} }

5. 
   A Single-Mode, Self-Adapting, and Self-Powered Mechanoreceptor Based on a Potentiometric–Triboelectric Hybridized Sensing Mechanism for Resolving Complex Stimuli Xiaodong Wu, Juan Zhu, James W., and Ana C. Arias Advanced Materials, 2020 , 2005970. [Abstract] [Bibtex] [PDF]

   Human skin is equipped with slow adapting (SA) and fast adapting (FA) capabilities simultaneously. To mimic such functionalities, elaborately designed devices have been explored by integrating multiple sensing elements or adopting multimode sensing principles. However, the complicated fabrication, signal mismatch of different modules, complex operation, and high power-consumption hinder their widespread applications. Here, a new both SA and FA via seamless fusion of complementary while compatible potentiometric and triboelectric sensing principles is reported. The resultant potentiometric–triboelectric hybridized mechanoreceptor exhibits distinctive features that are hard to achieve via currently existing methods, including single-mode output (only voltage signal), greatly simplified operation (singlemeasurement setup), ultralow power-consumption (<1 nW), self-adaptive response behavior, and good capability for resolving complex stimuli. Diverse mechanical characteristics, including magnitude, duration, frequency, applying and releasing speed, can be well interpreted with this single-mode and self-powered mechanoreceptor. Its promising application for monitoring object manipulations with a soft robotic gripper is explored. Furthermore, the versatility of the mechanoreceptor for resolving complex stimuli in diverse daily scenarios is demonstrated. This work presents a new design that will significantly simplify the fabrication/operation and meanwhile boost the functionality/energy-efficiency of future electronic devices and smart systems.

   @article{XiaodongMechanoreceptorAM, author = {Wu, Xiaodong and Zhu, Juan and W., James and and Arias, Ana C.}, title = {A Single-Mode, Self-Adapting, and Self-Powered Mechanoreceptor Based on a Potentiometric–Triboelectric Hybridized Sensing Mechanism for Resolving Complex Stimuli}, year = {2020}, doi = {10.1002/adma.202005970}, publisher = {Advanced Materials}, url = {https://onlinelibrary.wiley.com/doi/10.1002/adma.202005970}, journal = {Advanced Materials}, volume = {}, number = {2005970}, thumbnail = {XiaodongMechanoreceptorAM.PNG}, pdf = {XiaodongMechanoreceptorAM.pdf} }

6. 
   Printed, Flexible, Compact UHF‑RFID Sensor Tags Enabled by Hybrid Electronics Carol Baumbauer, Matthew G. Anderson, Jonathan Ting, Akshay Sreekumar, Jan M. Rabaey, Ana C. Arias, and Arno Thielens Scientific Reports, 2020 10, 16543. [Abstract] [Bibtex] [PDF]

   Sensor data can be wirelessly transmitted from simple, battery-less tags using Radio Frequency Identifcation (RFID). RFID sensor tags consist of an antenna, a radio frequency integrated circuit chip (RFIC), and at least one sensor. An ideal tag can communicate over a long distance and be seamlessly integrated onto everyday objects. However, miniaturized antenna designs often have lower performance. Here we demonstrate compact, fexible sensor tags with read range comparable to that of conventional rigid tags. We compare fabrication techniques for fexible antennas and demonstrate that screen and stencil printing are both suitable for fabricating antennas; these diferent techniques are most useful at diferent points in the design cycle. We characterize two versions of fexible, screen printed folded dipoles and a meandered monopole operating in the 915 MHz band. Finally, we use these antennas to create passive sensor tags and demonstrate over the air communication of sensor data. These tags could be used to form a network of printed, fexible, passive, interactive sensor tags.

   @article{Carol2020nature, author = {Baumbauer, Carol and Anderson, Matthew G. and Ting, Jonathan and Sreekumar, Akshay and Rabaey, Jan M. and Arias, Ana C. and Thielens, Arno}, title = {Printed, Flexible, Compact UHF‑RFID Sensor Tags Enabled by Hybrid Electronics}, year = {2020}, doi = {https://doi.org/10.1038/s41598-020-73471-9}, publisher = {Nature}, url = {https://www.nature.com/articles/s41598-020-73471-9}, journal = {Scientific Reports}, volume = {10}, number = {16543}, thumbnail = {Carol2020nature.PNG}, pdf = {Carol2020nature.pdf} }

7. 
   Highly Flexible Transparent Micromesh Electrodes via Blade-Coated Polymer Networks for Organic Light-Emitting Diodes Juan Zhu, Donggeon Han, Xiaodong Wu, Jonathan Ting, Shixuan Du, and Ana C. Arias ACS Applied Materials and Interfaces, 2020 12, 28. [Abstract] [Bibtex] [PDF]

   The availability of transparent conductive thin films that exhibit mechanical flexibility and are adapted to low-cost and large-area fabrication is a major obstacle for high-performance flexible thin-film optoelectronics. Here, by combining printing, thinfilm deposition, and wet-etching processes, interconnected transparent metal micromesh (TMM) electrodes are reported. Bladecoating is used to generate self-assembled polymer micromesh networks on flexible substrates. The network structures are subsequently converted into conductive metal networks. Asfabricated TMM films display a surface roughness of around 20nm with thickness down to 50 nm. A transmittance of 86% and a conductance of 80 Ω sq−1 are achieved at the described optimal blade-coating suspension concentration. The electrodes show mechanical flexibility with no conductivity degradation with the smallest bending radius of 1 mm or at repeated bending over 3000 cycles at a bending radius of 15 mm. We successfully demonstrate organic light-emitting diodes (OLEDs) using TMM electrodes via the blade-coating technique. The printed OLEDs have a low turn-on voltage of 3.4 V and can achieve a luminance of over 4000 cd/m2 at 6.5 V. At a luminance of 100 cd/m2, the OLEDs show a current density of 7.6 mA/cm2, an external quantum efficiency (EQE) of 3.6%, and a luminous efficacy of 1.4 lm/W.

   @article{Juan2020ami, author = {Zhu, Juan and Han, Donggeon and Wu, Xiaodong and Ting, Jonathan and Du, Shixuan and Arias, Ana C.}, title = {Highly Flexible Transparent Micromesh Electrodes via Blade-Coated Polymer Networks for Organic Light-Emitting Diodes}, year = {2020}, doi = {https://doi.org/10.1021/acsami.0c07299}, publisher = {American Chemical Society}, url = {https://pubs.acs.org/doi/10.1021/acsami.0c07299?ref=pdf&}, journal = {ACS Applied Materials and Interfaces}, volume = {12}, number = {28}, thumbnail = {Juan2020ami.PNG}, pdf = {Juan2020ami.pdf} }

8. 
   A potentiometric mechanotransduction mechanism for novel electronic skins Xiaodong Wu, Maruf Ahmed, Yasser Khan, Margaret E. Payne, Juan Zhu, Canhui Lu, James W. Evans, and Ana C. Arias Science Advances, 2020 6, 30. [Abstract] [Bibtex] [PDF]

   Human skin perceives external mechanical stimuli by sensing the variation in the membrane potential of skin sensory cells. Many scientists have attempted to recreate skin functions and develop electronic skins (e-skins) based on active and passive sensing mechanisms. Inspired by the skin sensory behavior, we investigated materials and electronic devices that allow us to encode mechanical stimuli into potential differences measured between two electrodes, resulting in a potentiometric mechanotransduction mechanism. We present here a potentiometric mechanotransducer that is fabricated through an all-solution processing approach. This mechanotransducer shows ultralow-power consumption, highly tunable sensing behavior, and capability to detect both static and low-frequency dynamic mechanical stimuli. Furthermore, we developed two novel classes of sensing devices, including strain-insensitive sensors and single-electrode-mode e-skins, which are challenging to achieve using the existing methods. This mechanotransduction mechanism has broad impact on robotics, prosthetics, and health care by providing a much improved human-machine interface.

   @article{Xiaodong2020sciadvances, author = {Wu, Xiaodong and Ahmed, Maruf and Khan, Yasser and Payne, Margaret E. and Zhu, Juan and Lu, Canhui and Evans, James W. and Arias, Ana C.}, title = {A potentiometric mechanotransduction mechanism for novel electronic skins}, year = {2020}, doi = {10.1126/sciadv.aba1062}, publisher = {American Association for the Advancement of Science}, url = {https://advances.sciencemag.org/content/6/30/eaba1062}, journal = {Science Advances}, volume = {6}, number = {30}, thumbnail = {Xiaodong2020sciadvances.png}, pdf = {Xiaodong2020sciadvances.pdf} }

9. 
   Large-Area Fabrication of High-Performance Flexible and Wearable Pressure Sensors Xiaodong Wu, Yasser Khan, Jonathan Ting, Zhu Juan, Seiya Ono, Xinxing Zhang, Shixuan Du, James W. Evans, Canhui Lu, and Ana C. Arias Advanced Electronic Materials, 2020 , . [Abstract] [Bibtex] [PDF]

   Flexible pressure sensors with high sensitivity, broad working range, and good scalability are highly desired for the next generation of wearable electronic devices. However, manufacturing of such pressure sensors still remains challenging. A large-area compliant and cost-effective process to fabricate high-performance pressure sensors via a combination of meshmolded periodic microstructures and printed side-by-side electrodes is presented. The sensors exhibit low operating voltage (1 V), high sensitivity (20.9 kPa−1), low detection limit (7.4 Pa), fast response/recovery time (23/18 ms), and excellent reliability (over 10 000 cycles). More importantly, they exhibit ultra-broad working range (7.4–1 000 000 Pa), high tunability, large-scale production feasibility, and significant advantage in format miniaturization and creating sensor arrays with self-defined patterns. The versatility of these devices is demonstrated in various human activity monitoring and spatial pressure mapping as electronic skins. Furthermore, utilizing printing methods, a flexible smart insole with a high level of integration for both foot pressure and temperature mapping is demonstrated. The scalable and cost-effective manufacturing along with the good comprehensive performance of the pressure sensors makes them very attractive for future development of wearable smart devices and human–machine interfaces.

   @article{Xiaodong2020advelectronicmat, author = {Wu, Xiaodong and Khan, Yasser and Ting, Jonathan and Juan, Zhu and Ono, Seiya and Zhang, Xinxing and Du, Shixuan and Evans, James W. and Lu, Canhui and Arias, Ana C.}, title = {Large-Area Fabrication of High-Performance Flexible and Wearable Pressure Sensors}, year = {2020}, doi = {10.1002/aelm.201901310}, publisher = {Wiley Online Library}, url = {https://onlinelibrary-wiley-com.libproxy.berkeley.edu/doi/full/10.1002/aelm.201901310}, journal = {Advanced Electronic Materials}, volume = {}, number = {}, thumbnail = {Xiaodong2020advelectronicmat.PNG}, pdf = {Xiaodong2020advelectronicmat.pdf} }

2019

1. 
   A New Frontier of Printed Electronics: Flexible Hybrid Electronics Advanced Materials, 2019 , 1905279. [Abstract] [Bibtex] [PDF]

   The performance and integration density of silicon integrated circuits (ICs) have progressed at an unprecedented pace in the past 60 years. While silicon ICs thrive at low-power high-performance computing, creating flexible and large-area electronics using silicon remains a challenge. On the other hand, flexible and printed electronics use intrinsically flexible materials and printing techniques to manufacture compliant and large-area electronics. Nonetheless, flexible electronics are not as efficient as silicon ICs for computation and signal communication. Flexible hybrid electronics (FHE) leverages the strengths of these two dissimilar technologies. It uses flexible and printed electronics where flexibility and scalability are required, i.e., for sensing and actuating, and silicon ICs for computation and communication purposes. Combining flexible electronics and silicon ICs yields a very powerful and versatile technology with a vast range of applications. Here, the fundamental building blocks of an FHE system, printed sensors and circuits, thinned silicon ICs, printed antennas, printed energy harvesting and storage modules, and printed displays, are discussed. Emerging application areas of FHE in wearable health, structural health, industrial, environmental, and agricultural sensing are reviewed. Overall, the recent progress, fabrication, application, and challenges, and an outlook, related to FHE are presented.

   @article{khan2019new, author = {}, title = {A New Frontier of Printed Electronics: Flexible Hybrid Electronics}, year = {2019}, doi = {10.1002/adma.201905279}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.201905279}, journal = {Advanced Materials}, volume = {}, number = {1905279}, thumbnail = {khan2019new.png}, pdf = {khan2019new.pdf} }

2. 
   Printed, Flexible Lactate Sensors: Design Considerations Before Performing On-Body Measurements Scientific Reports, 2019 9, 13720. [Abstract] [Bibtex] [PDF]

   This work reports the process of sensor development, optimization, and characterization before the transition to on-body measurements can be made. Sensors using lactate oxidase as a sensing mechanism and tetrathiafulvalene as a mediator were optimized for sporting applications. Optimized sensors show linear range up to 24 mM lactate and sensitivity of 4.8 μA/mM which normalizes to 68 μA*cm-2/mM when accounting for surface area of the sensor. The optimized sensors were characterized 3 different ways: using commercially available reference and counter electrodes, using printed reference and counter electrodes, and using a printed reference electrode with no counter electrode. Sensors intended for measuring sweat must be selective in the presence of sweat constituents. Thus, in addition to traditional characterization in pH 7.0 buffer, we characterized sensor performance in solutions intended to approximate sweat. Sensor performance in pH 7.0 buffer solution was not reflective of sensor performance in artificial sweat, indicating that further characterization is necessary between sensor measurement in pH 7.0 buffer and on-body measurements. Furthermore, we performed enzyme activity measurements and sensor measurements concurrently in five different salts individually, finding that while NH4Cl and MgCl2 do not affect enzyme activity or sensor performance in physiologically relevant ranges of salt concentration, NaCl concentration or KCl concentration decreases enzyme activity and sensor current. On the other hand, CaCl2 induced a nonlinear change in sensor performance and enzyme activity with increasing salt concentration.

   @article{maggie2019printed, author = {}, title = {Printed, Flexible Lactate Sensors: Design Considerations Before Performing On-Body Measurements}, year = {2019}, doi = {10.1038/s41598-019-49689-7}, publisher = {Nature Publishing Group}, url = {https://www.nature.com/articles/s41598-019-49689-7}, journal = {Scientific Reports}, volume = {9}, number = {13720}, thumbnail = {maggie2019printed.png}, pdf = {maggie2019printed.pdf} }

3. 
   Organic Multi-Channel Optoelectronic Sensors for Wearable Health Monitoring Yasser Khan, Donggeon Han, Jonathan Ting, Maruf Ahmed, Ramune Nagisetty, and Ana C. Arias IEEE Access, 2019 4, [Abstract] [Bibtex] [PDF]

   Recent progress in printed optoelectronics and their integration in wearable sensors have created new avenues for research in reflectance photoplethysmography (PPG) and oximetry. The reflectionmode sensor, which consists of light emitters and detectors, is a vital component of reflectance oximeters. Here, we report a systematic study of the reflectance oximeter sensor design in terms of component geometry, light emitter and detector spacing, and the use of an optical barrier between the emitter and the detector to maximize sensor performance. Printed red and near-infrared (NIR) organic light-emitting diodes (OLEDs) and organic photodiodes (OPDs) are used to design three sensor geometries: (1) Rectangular geometry, where square OLEDs are placed at each side of the OPD; (2) Bracket geometry, where the OLEDs are shaped as brackets and placed around the square OPD; (3) Circular geometry, where the OLEDs are shaped as block arcs and placed around the circular OPD. Utilizing the bracket geometry, we observe 39.7% and 18.2% improvement in PPG signal magnitude in the red and NIR channels compared to the rectangular geometry, respectively. Using the circular geometry, we observe 48.6% and 9.2% improvements in the red and NIR channels compared to the rectangular geometry. Furthermore, a wearable two-channel PPG sensor is utilized to add redundancy to the measurement. Finally, inverse-variance weighting and template matching algorithms are implemented to improve the detection of heart rate from the multi-channel PPG signals.

   @article{yasser2019organic, author = {Khan, Yasser and Han, Donggeon and Ting, Jonathan and Ahmed, Maruf and Nagisetty, Ramune and Arias, Ana C.}, title = {Organic Multi-Channel Optoelectronic Sensors for Wearable Health Monitoring}, year = {2019}, doi = {10.1109/ACCESS.2019.2939798}, publisher = {IEEE Xplore}, url = {https://ieeexplore.ieee.org/document/8826261}, journal = {IEEE Access}, volume = {4}, thumbnail = {yasser2019organic.png}, pdf = {yasser2019organic.pdf} }

4. 
   A Platform to Study the Effects of Electrical Stimulation on Immune Cell Activation During Wound Healing Kaiping Wang, Udit Parekh, Jonathan K. Ting, Natasha A. D. Yamamoto, Juan Zhu, Todd Costantini, Ana Claudia Arias Aria, Brian P. Eliceiri, and Tse Nga Ng Advanced Biosystems, 2019 1900106. [Abstract] [Bibtex] [PDF]

   Wound healing is a complex process involving diverse changes in multiple cell types where the application of electric fields has been shown to accelerate wound closure. To define the efficacy of therapies based on electric fields, it would be valuable to have a platform to systematically study the effects of electrical stimulation (ES) upon the inflammation phase and the activation of signaling mediators. Here, an in vivo ES model in which flexible electrodes are applied to an animal model for monitoring inflammation in a wound is reported on. Subcutaneous implants of polyvinyl alcohol sponges elicit inflammation response as defined by the infiltration of leukocytes. The wound site is subjected to electric fields using two types of additively fabricated flexible electrode arrays. The sponges are then harvested for flow cytometry analysis to identify changes in the phosphorylation state of intracellular targets. This platform enables studies of molecular mechanisms, as it shows that an application of low‐frequency ES ≤0.5 Hz increases phosphorylation of Erk proteins in recruited leukocytes, identifying a signaling pathway that is activated during the healing process.

   @article{Ting2019advancedbiosystems, author = {Wang, Kaiping and Parekh, Udit and K. Ting, Jonathan and Yamamoto, Natasha A. D. and Zhu, Juan and Costantini, Todd and Aria, Ana Claudia Arias and Eliceiri, Brian P. and Ng, Tse Nga}, title = {A Platform to Study the Effects of Electrical Stimulation on Immune Cell Activation During Wound Healing}, year = {2019}, doi = {10.1002/adbi.201900106}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adbi.201900106}, journal = {Advanced Biosystems}, number = {1900106}, thumbnail = {Ting2019advancedbiosystems.png}, pdf = {Ting2019advancedbiosystems.pdf} }

5. 
   Electrode Composite for Flexible Zinc–Manganese Dioxide Batteries through In Situ Polymerization of Polymer Hydrogel Alla M. Zamarayeva, Akshaya Jegraj, Anju Toor, Veronika I. Pister, Cheryl Chang, Austin Chou, James W. Evans, and Ana Claudia Arias Energy Technology, 2019 , 1901165. [Abstract] [Bibtex] [PDF]

   It remains important to maximize energy density of wearable batteries. In addition, such batteries should be compliant, safe, and environmentally sustainable. Intrinsically safe zinc–manganese dioxide (Zn/MnO2) batteries are great candidates for powering wearables. However, achieving flexibility of these systems is hindered by the absence of a binder that ensures mechanical integrity of the MnO2 electrode composite. Herein, a unique approach to fabricate a mechanically robust MnO2 electrode is presented. Polyvinyl alcohol (PVA)/ polyacrylic acid (PAA) gel cross-linked in situ via thermal treatment is used as a binder for the electrode. Furthermore, energy density and rate capability of the printed battery electrodes are improved by replacing graphite with single-walled carbon nanotubes (CNTs). The batteries retain 93% capacity when the discharge rate is increased from C/10 to C/3, as well as 97% of their capacity after being flexed. In contrast, batteries based on conventional composition retain 60% and 23% of the capacity, respectively. Finally, the battery with the modified electrode has high areal energy density of 4.8 mWh cm
   2 and volumetric energy density of 320 mWh cm
   -3

   @article{zamarayeva2019electrode, author = {Zamarayeva, Alla M. and Jegraj, Akshaya and Toor, Anju and Pister, Veronika I. and Chang, Cheryl and Chou, Austin and Evans, James W. and Arias, Ana Claudia}, title = {Electrode Composite for Flexible Zinc–Manganese Dioxide Batteries through In Situ Polymerization of Polymer Hydrogel}, year = {2019}, doi = {10.1002/ente.201901165}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/ente.201901165}, journal = {Energy Technology}, volume = {}, number = {1901165}, thumbnail = {zamarayeva2019electrode.png}, pdf = {zamarayeva2019electrode.pdf} }

2018

1. 
   Emission Area Patterning of Organic Light-Emitting Diodes (OLEDs) via Printed Dielectrics Donggeon Han, Yasser Khan, Karthik Gopalan, Adrien Pierre, and Ana C Arias Advanced Functional Materials, 2018 28, 37. [Abstract] [Bibtex] [PDF]

   Solution-processibility is one of the distinguished traits of organic light-emitting diodes (OLEDs) compared to existing solid-state LED technologies. It allows new opportunities which can simplify the fabrication and potentially reduce the cost of manufacturing process. Emission area patterning is one of the crucial fabrication steps and it usually involves subtractive methods, such as photolithography or etching. Here, printing techniques are used to pattern the emission area of blade-coated OLED layers. The print qualities of a number of printing schemes are characterized and compared. Spray coating and screen printing are used to deposit dielectrics with desired patterns on the OLED layers. At luminance of 1000 cd m_2 the OLEDs patterned using spray-coated and screen-printed dielectric show current density of 8.2 and 10.1 mA cm_2, external quantum efficiency (EQE) of 2.1% and 2.1%, and luminous efficacy of 5.5 and 6.3 lm W_1, respectively. The OLED characteristics and features of each printing scheme in depositing the dielectric layer are discussed. The printing methods are further applied to demonstrate displays with complex shapes and a seven-segment display.

   @article{han2018emission, title = {Emission Area Patterning of Organic Light-Emitting Diodes (OLEDs) via Printed Dielectrics}, author = {Han, Donggeon and Khan, Yasser and Gopalan, Karthik and Pierre, Adrien and Arias, Ana C}, journal = {Advanced Functional Materials}, volume = {28}, number = {37}, pages = {1802986}, year = {2018}, publisher = {Wiley Online Library}, url = {https://onlinelibrary.wiley.com/doi/full/10.1002/adfm.201802986}, thumbnail = {han2018emission.png}, pdf = {han2018emission.pdf} }

2. 
   Local electrochemical control of hydrogel microactuators in microfluidics Leeya Engel, Chengming Liu, Nofar Mintz Hemed, Yasser Khan, Ana Claudia Arias, Yosi Shacham-Diamand, Slava Krylov, and Liwei Lin Journal of Micromechanics and Microengineering, 2018 [Abstract] [Bibtex] [PDF]

   Due to the complexity of a chemo-electro-mechanical system and the need for a wet environment, to date, few devices fully integrate hydrogels with microelectromechanical systems. In this paper, we demonstrate the use of inkjet-printed gold electrodes integrated in microfluidic channels to alter the morphology of electroactive polymer hydrogels, cross-linked in situ. Microfluidics is a convenient platform for integrating hydrogels with microsystems as it provides a means for encapsulating electrolytic environments, while maintaining UV transparency. Printed electronics provide a new method for rapid prototyping of electrodes on flexible substrates for electrical control of electroactive polymer microsystems. We attribute the observed actuation to electrochemically-induced pH variations in the vicinity of the printed anode and cathode which diffuse into the hydrogel. Response to pH was verified by exposing the hydrogel to various pH conditions in control experiments without applied electrical bias. This work demonstrates a new, integrated, polymer-based, rapid prototyping approach to building flexible electroactive hydrogel systems which can benefit microfluidic valves, biomimetics, electrochemical sensors and artificial muscles.

   @article{engel2018local, title = {Local electrochemical control of hydrogel microactuators in microfluidics}, author = {Engel, Leeya and Liu, Chengming and Hemed, Nofar Mintz and Khan, Yasser and Arias, Ana Claudia and Shacham-Diamand, Yosi and Krylov, Slava and Lin, Liwei}, journal = {Journal of Micromechanics and Microengineering}, year = {2018}, publisher = {IOP Publishing}, url = {http://iopscience.iop.org/article/10.1088/1361-6439/aacc31/meta}, thumbnail = {engel2018local.png}, pdf = {engel2018local.pdf} }

3. 
   Printed Receive Coils with High Acoustic Transparency for Magnetic Resonance Guided Focused Ultrasound Joseph Corea, Patrick Ye, Dongjin Seo, Kim Butts-Pauly, Ana C. Arias, and Michael Lustig Scientific Reports, 2018 8, 3392. [Abstract] [Bibtex] [PDF]

   In magnetic resonance guided focused ultrasound (MRgFUS) therapy sound waves are focused through the body to selectively ablate difficult to access lesions and tissues. A magnetic resonance imaging (MRI) scanner non-invasively tracks the temperature increase throughout the tissue to guide the therapy. In clinical MRI, tightly fitted hardware comprised of multichannel coil arrays are required to capture high quality images at high spatiotemporal resolution. Ablating tissue requires a clear path for acoustic energy to travel but current array materials scatter and attenuate acoustic energy. As a result coil arrays are placed outside of the transducer, clear of the beam path, compromising imaging speed, resolution, and temperature accuracy of the scan. Here we show that when coil arrays are fabricated by additive manufacturing (i.e., printing), they exhibit acoustic transparency as high as 89.5%. This allows the coils to be placed in the beam path increasing the image signal to noise ratio (SNR) five-fold in phantoms and volunteers. We also characterize printed coil materials properties over time when submerged in the water required for acoustic coupling. These arrays offer high SNR and acceleration capabilities, which can address current challenges in treating head and abdominal tumors allowing MRgFUS to give patients better outcomes.

   @article{Corea2018AcousticTransparency, author = {Corea, Joseph and Ye, Patrick and Seo, Dongjin and Butts-Pauly, Kim and Arias, Ana C. and Lustig, Michael}, title = {Printed Receive Coils with High Acoustic Transparency for Magnetic Resonance Guided Focused Ultrasound}, journal = {Scientific Reports}, volume = {8}, number = {3392}, year = {2018}, month = feb, day = {21}, doi = {10.1038/s41598-018-21687-1}, publisher = {Nature Publishing Group}, url = {https://www.nature.com/articles/s41598-018-21687-1}, thumbnail = {Corea2018AcousticTransparency.png}, pdf = {Corea2018AcousticTransparency.pdf} }

4. 
   All-printed full-color pixel organic photodiode array with a single active layer Igal Deckman, P. Balthazar Lechene, Adrien Pierre, and Ana C. Arias Organic Electronics, 2018 56, [Abstract] [Bibtex] [PDF]

   A new fabrication method to realize fully-printed organic photodiode (OPD) arrays capable of RGB light separation is presented. From the photocurrents generated by each pixel type under the light from RGB LEDs, we demonstrate that this "White", "Yellow" and "Red" array can successfully detect and reconstruct colors in the RGB system, with an average accuracy of 98.5%. A flexible broadband OPD array is printed on PEN substrate by blade-coating PEDOT:PSS, a polyethylenimine cathode interlayer and the photo-active layer, and screen-printing on top a patterned PEDOT:PSS anode. The OPD array achieves an average EQE of _37% at _4_V bias over the whole visible spectrum, 5 orders of magnitude of linear dynamic range (LDR), a 0.5_nA/cm2 dark current, and maintains these performances in ambient conditions for more than 30_h. Pixels detecting "White", "Yellow" and "Red" are fabricated by spray-coating two color filters. The substrate is used as a separator between the filters and OPD array. This physical separation allows solution processing of the filters regardless of their electrical properties or of the compatibility of their solvents with the OPD, thus broadening the choice of filter materials while offering a simple fabrication process. The combination of broadband OPD and broadband filters used in this configuration can significantly simplify the fabrication of spectrally-selective photosensors and full-color imagers.

   @article{Igal2018fullcolorpixel, author = {Deckman, Igal and Lechene, P. Balthazar and Pierre, Adrien and Arias, Ana C.}, title = {All-printed full-color pixel organic photodiode array with a single active layer}, journal = {Organic Electronics}, volume = {56}, pages = {139--145}, year = {2018}, doi = {10.1016/j.orgel.2018.02.009}, url = {https://www.sciencedirect.com/science/article/pii/S156611991830051X}, thumbnail = {Igal2018fullcolorpixel.png}, pdf = {Igal2018fullcolorpixel.pdf} }

5. 
   A flexible organic reflectance oximeter array Yasser Khan, Donggeon Han, Adrien Pierre, Jonathan Ting, Xingchun Wang, Claire M. Lochner, Gianluca Bovo, Nir Yaacobi-Gross, Chris Newsome, Richard Wilson, and Ana C. Arias Proceedings of the National Academy of Sciences, 2018 [Abstract] [Bibtex] [PDF]

   The optical method to determine oxygen saturation in blood is limited to only tissues that can be transilluminated. The status quo provides a single-point measurement and lacks 2D oxygenation mapping capability. We use organic printed optoelectronics in a flexible array configuration that senses reflected light from tissue. Our reflectance oximeter is used beyond conventional sensing locations and accurately measures oxygen saturation on the forehead. In a full system implementation, coupled with a mathematical model, we create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. Our skin-like flexible sensor system has the potential to transform oxygenation monitoring of tissues, wounds, skin grafts, and transplanted organs.Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The existing sensor configuration provides only single-point measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff–induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.

   @article{khan2018flexible, author = {Khan, Yasser and Han, Donggeon and Pierre, Adrien and Ting, Jonathan and Wang, Xingchun and Lochner, Claire M. and Bovo, Gianluca and Yaacobi-Gross, Nir and Newsome, Chris and Wilson, Richard and Arias, Ana C.}, title = {A flexible organic reflectance oximeter array}, year = {2018}, doi = {10.1073/pnas.1813053115}, publisher = {National Academy of Sciences}, issn = {0027-8424}, url = {http://www.pnas.org/content/early/2018/11/06/1813053115}, eprint = {http://www.pnas.org/content/early/2018/11/06/1813053115.full.pdf}, journal = {Proceedings of the National Academy of Sciences}, thumbnail = {khan2018flexible.png}, pdf = {khan2018flexible.pdf} }

2017

1. 
   Flexible and stretchable power sources for wearable electronics Alla M. Zamarayeva, Aminy E. Ostfeld, Michael Wang, Jerica K. Duey, Igal Deckman, Balthazar P. Lechêne, Greg Davies, Daniel A. Steingart, and Ana Claudia Arias Science Advances, 2017 3, 6. [Abstract] [Bibtex] [PDF]

   Flexible and stretchable power sources represent a key technology for the realization of wearable electronics. Developing flexible and stretchable batteries with mechanical endurance that is on par with commercial standards and offer compliance while retaining safety remains a significant challenge. We present a unique approach that demonstrates mechanically robust, intrinsically safe silver-zinc batteries. This approach uses current collectors with enhanced mechanical design, such as helical springs and serpentines, as a structural support and backbone for all battery components. We show wire-shaped batteries based on helical band springs that are resilient to fatigue and retain electrochemical performance over 17,000 flexure cycles at a 0.5-cm bending radius. Serpentine-shaped batteries can be stretched with tunable degree and directionality while maintaining their specific capacity. Finally, the batteries are integrated, as a wearable device, with a photovoltaic module that enables recharging of the batteries.

   @article{zamarayeva2017flexible, author = {Zamarayeva, Alla M. and Ostfeld, Aminy E. and Wang, Michael and Duey, Jerica K. and Deckman, Igal and Lech{\^e}ne, Balthazar P. and Davies, Greg and Steingart, Daniel A. and Arias, Ana Claudia}, title = {Flexible and stretchable power sources for wearable electronics}, volume = {3}, number = {6}, year = {2017}, doi = {10.1126/sciadv.1602051}, publisher = {American Association for the Advancement of Science}, url = {http://advances.sciencemag.org/content/3/6/e1602051}, eprint = {http://advances.sciencemag.org/content/3/6/e1602051.full.pdf}, journal = {Science Advances}, thumbnail = {zamarayeva2017flexible.png}, pdf = {zamarayeva2017flexible.pdf} }

2. 
   Flexible Blade-Coated Multicolor Polymer Light-Emitting Diodes for Optoelectronic Sensors Donggeon Han, Yasser Khan, Jonathan Ting, Simon M. King, Nir Yaacobi-Gross, Martin J. Humphries, Christopher J. Newsome, and Ana C. Arias Advanced Materials, 2017 [Abstract] [Bibtex] [PDF] 1606206

   A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light-emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface-energy-patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near-infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, retrieved PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.

   @article{han2017flexible, author = {Han, Donggeon and Khan, Yasser and Ting, Jonathan and King, Simon M. and Yaacobi-Gross, Nir and Humphries, Martin J. and Newsome, Christopher J. and Arias, Ana C.}, title = {Flexible Blade-Coated Multicolor Polymer Light-Emitting Diodes for Optoelectronic Sensors}, journal = {Advanced Materials}, issn = {1521-4095}, url = {http://dx.doi.org/10.1002/adma.201606206}, doi = {10.1002/adma.201606206}, pages = {1606206--n/a}, keywords = {blade coating, flexible electronics, polymer light-emitting diodes (PLEDs), printed sensors, pulse oximetry, organic light-emitting diodes (OLEDs), wearable sensors}, year = {2017}, note = {1606206}, thumbnail = {han2017flexible.png}, pdf = {han2017flexible.pdf} }

3. 
   Flexible photovoltaic power systems: integration opportunities, challenges and advances Aminy E Ostfeld, and Ana Claudia Arias Flexible and Printed Electronics, 2017 2, 1. [Abstract] [Bibtex] [PDF]

   Photovoltaic power systems, consisting of solar modules, energy storage, and power management electronics, are of great importance for applications ranging from off-grid and portable power to ambient light harvesting for sensor nodes. Co-design and integration of the components using printing and coating methods on flexible substrates enable the production of effective and customizable systems for these diverse applications. In this article, we review photovoltaic module and energy storage technologies suitable for integration into flexible power systems. We discuss the design of electrical characteristics for these systems that enable them to power desired loads efficiently, as well as strategies for physically combining the components. Functions and design considerations of power management electronics are presented along with recent progress toward printed and flexible power electronics. We analyze both hybrid and fully flexible photovoltaic systems and the critical role of the application in the choices of materials and architectures for the system components.

   @article{ostfeld2017flexible, author = {Ostfeld, Aminy E and Arias, Ana Claudia}, title = {Flexible photovoltaic power systems: integration opportunities, challenges and advances}, journal = {Flexible and Printed Electronics}, volume = {2}, number = {1}, pages = {013001}, url = {http://stacks.iop.org/2058-8585/2/i=1/a=013001}, year = {2017}, thumbnail = {ostfeld2017flexible.png}, pdf = {ostfeld2017flexible.pdf} }

4. 
   Charge-integrating organic heterojunction phototransistors for wide-dynamic-range image sensors Adrien Pierre, Abhinav Gaikwad, and Ana Claudia Arias Nature Photonics, 2017 [Abstract] [Bibtex] [PDF] Article

   Solution-processed phototransistors can substantially advance the performance of image sensors. Phototransistors exhibit large photoconductive gain and a sublinear responsivity to irradiance, which enables a logarithmic sensing of irradiance that is akin to the human eye and has a wider dynamic range than photodiode-based image sensors. Here, we present a novel solution-processed phototransistor composed of a heterostructure between a high-mobility organic semiconductor and an organic bulk heterojunction. The device efficiently integrates photogenerated charge during the period of a video frame then quickly discharges it, which significantly increases the signal-to-noise ratio compared with sampling photocurrent during readout. Phototransistor-based image sensors processed without photolithography on plastic substrates integrate charge with external quantum efficiencies above 100% at 100 frames per second. In addition, the sublinear responsivity to irradiance of these devices enables a wide dynamic range of 103 dB at 30 frames per second, which is competitive with state-of-the-art image sensors.

   @article{pierre2017charge, author = {Pierre, Adrien and Gaikwad, Abhinav and Arias, Ana Claudia}, title = {Charge-integrating organic heterojunction phototransistors for wide-dynamic-range image sensors}, journal = {Nature Photonics}, year = {2017}, month = feb, day = {20}, publisher = {Nature Publishing Group}, note = {Article}, issn = {1749-4893}, url = {http://dx.doi.org/10.1038/nphoton.2017.15}, thumbnail = {pierre2017charge.png}, pdf = {pierre2017charge.pdf} }

5. 
   Understanding the Effects of Electrode Formulation on the Mechanical Strength of Composite Electrodes for Flexible Batteries Abhinav M. Gaikwad, and Ana Claudia Arias ACS Applied Materials & Interfaces, 2017 0, 0. [Abstract] [Bibtex] [PDF] PMID: 28151639

   Flexible lithium-ion batteries are necessary for powering the next generation of wearable electronic devices. In most designs, the mechanical flexibility of the battery is improved by reducing the thickness of the active layers, which in turn reduces the areal capacity and energy density of the battery. The performance of a battery depends on the electrode composition, and in most flexible batteries, standard electrode formulation is used, which is not suitable for flexing. Even with considerable efforts made toward the development of flexible lithium-ion batteries, the formulation of the electrodes has received very little attention. In this study, we investigate the relation between the electrode formulation and the mechanical strength of the electrodes. Peel and drag tests are used to compare the adhesion and cohesion strength of the electrodes. The strength of an electrode is sensitive to the particle size and the choice of polymeric binder. By optimizing the electrode composition, we were able to fabricate a high areal capacity (_2 mAh/cm2) flexible lithium-ion battery with conventional metal-based current collectors that shows superior electrochemical and mechanical performance in comparison to that of batteries with standard composition.

   @article{abhinav2017understanding, author = {Gaikwad, Abhinav M. and Arias, Ana Claudia}, title = {Understanding the Effects of Electrode Formulation on the Mechanical Strength of Composite Electrodes for Flexible Batteries}, journal = {ACS Applied Materials \& Interfaces}, volume = {0}, number = {0}, pages = {null}, year = {2017}, doi = {10.1021/acsami.6b14719}, note = {PMID: 28151639}, url = {http://dx.doi.org/10.1021/acsami.6b14719}, thumbnail = {abhinav2017understanding.png}, pdf = {abhinav2017understanding.pdf} }

6. 
   Theoretical analysis and characterization of the energy conversion and storage efficiency of photo-supercapacitors P. Balthazar Lechene, Raphael Clerc, and Ana C. Arias Solar Energy Materials and Solar Cells, 2017 172, [Abstract] [Bibtex] [PDF]

   The time-dependent dynamics of the charge and discharge of photo-supercapacitors (PSC), devices which combine a supercapacitor with a solar cell, are investigated using a semi-analytical model. For a given PSC, it is found that the maximum Energy Conversion and Storage Efficiency (ECSE) is a direct function of the Power Conversion Efficiency (PCE) and Fill Factor (FF) of the solar cell. The capacitance, series and shunt resistances of the supercapacitor affect the time constants of the PSC and the value of the maximum ECSE. To experimentally measure the maximum value of ECSE with at most 2 charge-discharge cycles, a simple experimental procedure is proposed, which consists in comparing the power flowing through the supercapacitor and the energy already stored in it. The theoretical results are validated with experiments on a PSC made from an organic solar cell and a commercial supercapacitor.

   @article{Balthazar2017photosupercapacitors, author = {Lechene, P. Balthazar and Clerc, Raphael and Arias, Ana C.}, title = {Theoretical analysis and characterization of the energy conversion and storage efficiency of photo-supercapacitors}, journal = {Solar Energy Materials and Solar Cells}, volume = {172}, pages = {202--212}, year = {2017}, doi = {10.1016/j.solmat.2017.07.034}, url = {https://www.sciencedirect.com/science/article/pii/S0927024817304282}, thumbnail = {Balthazar2017photosupercapacitors.png}, pdf = {Balthazar2017photosupercapacitors.pdf} }

2016

1. 
   Solution-processed image sensors on flexible substrates Adrien Pierre, and Ana Claudia Arias Flexible and Printed Electronics, 2016 1, 4. [Abstract] [Bibtex] [PDF]

   Image sensors are ubiquitous and used in a wide variety of applications ranging from consumer products to healthcare and industrial applications. The signal-to-noise ratio (SNR) of an image increases with larger pixels, which is costly to scale using silicon and wafer-based microfabrication. On the other hand, the performance of solution-processed photodetectors and transistors is advancing considerably. The printability of these devices on plastic substrates can enable low-cost scaling of large-pixel, high SNR image sensors. In addition, the flexibility of the substrates can enable new imaging systems never possible with the rigidity of conventional sensors. In this work we review the progress made towards solution-processed image sensors on flexible substrates. The fundamental operation of image sensors using intra-pixel charge integration is first explained to introduce the figures of merit for these systems. The physics, figures of merit, and state of the art for solution-processed photodiodes and phototransistors is also overviewed. A literature survey is done on solution-processed passive and active pixel image sensors with emphasis on active-switching for intra-pixel charge integration. Finally, optics compliant with large area and flexible image sensors are reviewed.

   @article{pierre2016solution, author = {Pierre, Adrien and Arias, Ana Claudia}, title = {Solution-processed image sensors on flexible substrates}, journal = {Flexible and Printed Electronics}, volume = {1}, number = {4}, pages = {043001}, url = {http://stacks.iop.org/2058-8585/1/i=4/a=043001}, year = {2016}, thumbnail = {pierre2016solution.png}, pdf = {pierre2016solution.pdf} }

2. 
   Flexible Hybrid Electronics: Direct Interfacing of Soft and Hard Electronics for Wearable Health Monitoring Yasser Khan, Mohit Garg, Qiong Gui, Mark Schadt, Abhinav Gaikwad, Donggeon Han, Natasha A. D. Yamamoto, Paul Hart, Robert Welte, William Wilson, Steve Czarnecki, Mark Poliks, Zhanpeng Jin, Kanad Ghose, Frank Egitto, James Turner, and Ana C. Arias Advanced Functional Materials, 2016 , . [Abstract] [Bibtex] [PDF]

   The interfacing of soft and hard electronics is a key challenge for flexible hybrid electronics. Currently, a multisubstrate approach is employed, where soft and hard devices are fabricated or assembled on separate substrates, and bonded or interfaced using connectors; this hinders the flexibility of the device and is prone to interconnect issues. Here, a single substrate interfacing approach is reported, where soft devices, i.e., sensors, are directly printed on Kapton polyimide substrates that are widely used for fabricating flexible printed circuit boards (FPCBs). Utilizing a process flow compatible with the FPCB assembly process, a wearable sensor patch is fabricated composed of inkjet-printed gold electrocardiography (ECG) electrodes and a stencil-printed nickel oxide thermistor. The ECG electrodes provide 1 mVp-p ECG signal at 4.7 cm electrode spacing and the thermistor is highly sensitive at normal body temperatures, and demonstrates temperature coefficient, _ _ -5.84% K-1 and material constant, _ _ 4330 K. This sensor platform can be extended to a more sophisticated multisensor platform where sensors fabricated using solution processable functional inks can be interfaced to hard electronics for health and performance monitoring, as well as internet of things applications.

   @article{khan2016flexible, author = {Khan, Yasser and Garg, Mohit and Gui, Qiong and Schadt, Mark and Gaikwad, Abhinav and Han, Donggeon and Yamamoto, Natasha A. D. and Hart, Paul and Welte, Robert and Wilson, William and Czarnecki, Steve and Poliks, Mark and Jin, Zhanpeng and Ghose, Kanad and Egitto, Frank and Turner, James and Arias, Ana C.}, title = {Flexible Hybrid Electronics: Direct Interfacing of Soft and Hard Electronics for Wearable Health Monitoring}, journal = {Advanced Functional Materials}, issn = {1616-3028}, volume = {}, number = {}, pages = {n/a--n/a}, year = {2016}, url = {http://dx.doi.org/10.1002/adfm.201603763}, doi = {10.1002/adfm.201603763}, keywords = {flexible electronics, inkjet printing, printed electrocardiography electrodes, printed thermistors, wearable sensor patches}, thumbnail = {khan2016flexible.png}, pdf = {khan2016flexible.pdf} }

3. 
   Materials and Methods for Higher Performance Screen-Printed Flexible MRI Receive Coils Joseph R. Corea, P. Balthazar Lechene, Michael Lustig, and Ana C. Arias Magnetic Resonance in Medicine, 2016 [Abstract] [Bibtex] [PDF]

   Purpose To develop methods for characterizing materials used in screen-printed MRI coils and improve signal-to-noise ratio (SNR) with new lower-loss materials. Methods An experimental apparatus was created to characterize dielectric properties of plastic substrates used in receive coils. Coils were fabricated by screen printing conductive ink onto several plastic substrates. Unloaded and sample loaded quality factor (QUnloaded/QLoaded) measurements and scans on a 3T scanner were used to characterize coil performance. An experimental method was developed to describe the relationship between a coils QUnloaded and the SNR it provides in images of a phantom. In addition, 3T scans of a phantom and the head of a volunteer were obtained with a proof-of-concept printed eight-channel array, and the results were compared with a commercial 12-channel array. Results Printed coils with optimized substrates exhibited up to 97% of the image SNR when compared with a traditional coil on a loading phantom. QUnloaded and the SNR of coils were successfully correlated. The printed array resulted in images comparable to the quality given by the commercial array. Conclusion Using the proposed methods and materials, the SNR of printed coils approached that of commercial coils while using a new fabrication technique that provided more flexibility and close contact with the patients body. Magn Reson Med, 2016. _ 2016 International Society for Magnetic Resonance in Medicine

   @article{corea2016materials, author = {Corea, Joseph R. and Lechene, P. Balthazar and Lustig, Michael and Arias, Ana C.}, title = {Materials and Methods for Higher Performance Screen-Printed Flexible MRI Receive Coils}, journal = {Magnetic Resonance in Medicine}, issn = {1522-2594}, url = {http://dx.doi.org/10.1002/mrm.26399}, doi = {10.1002/mrm.26399}, pages = {n/a--n/a}, keywords = {MRI coils, flexible MRI coils, phased arrays, NMR probes, screen printing, plastic substrates}, year = {2016}, thumbnail = {corea2016materials.png}, pdf = {corea2016materials.pdf} }

4. 
   Organic solar cells and fully printed super-capacitors optimized for indoor light energy harvesting Balthazar P. Lechene, Martin Cowell, Adrien Pierre, James W. Evans, Paul K. Wright, and Ana C. Arias Nano Energy , 2016 26, . [Abstract] [Bibtex] [PDF]

   Abstract Flexibility, lightness and printability make organic solar cells (OSC) strong candidates to power low consumption devices such as envisioned for the Internet of Things. Such devices may be placed indoors, where light levels are well below typical outdoors level. Here, we demonstrate that maximizing the efficiency of {OSC} for indoor operation requires specific device optimization. In particular, minimizing the dark current of the solar cells is critical to enhance their efficiency under indoor light. Cells optimized for sunlight reach 6.2% power conversion efficiency (PCE). However when measured under simulated indoor light conditions, the {PCE} is to 5.2%. Cells optimized for indoor operation yield 7.6% of {PCE} under indoor conditions. As a proof-of-concept, the solar cells are combined with fully printed super-capacitors to form a photo-rechargeable system. Such a system with a 0.475 cm2 indoor-optimized solar cell achieved a total energy conversion and storage efficiency (ECSE) of 1.57% under 1-sun, providing 26 mJ of energy and 4.1 mW of maximum power. Under simulated indoor light the system yielded an {ECSE} of 2.9%, while delivering 13.3 mJ and 2.8 mW. Those energy and power levels would be sufficient to power low-consumption electronic devices with low duty cycles.

   @article{lechene2016organic, title = {Organic solar cells and fully printed super-capacitors optimized for indoor light energy harvesting }, journal = {Nano Energy }, volume = {26}, number = {}, pages = {631 - 640}, year = {2016}, note = {}, issn = {2211-2855}, doi = {10.1016/j.nanoen.2016.06.017}, url = {http://www.sciencedirect.com/science/article/pii/S2211285516302002}, author = {Lechene, Balthazar P. and Cowell, Martin and Pierre, Adrien and Evans, James W. and Wright, Paul K. and Arias, Ana C.}, keywords = {Supercapacitor }, thumbnail = {lechene2016organic.png}, pdf = {lechene2016organic.pdf} }

5. 
   High-performance flexible energy storage and harvesting system for wearable electronics Aminy E. Ostfeld, Abhinav M. Gaikwad, Yasser Khan, and Ana C. Arias Scientific Reports, 2016 6, [Abstract] [Bibtex] [PDF]

   This paper reports on the design and operation of a flexible power source integrating a lithium ion battery and amorphous silicon solar module, optimized to supply power to a wearable health monitoring device. The battery consists of printed anode and cathode layers based on graphite and lithium cobalt oxide, respectively, on thin flexible current collectors. It displays energy density of 6.98_mWh/cm2 and demonstrates capacity retention of 90% at 3C discharge rate and  99% under 100 charge/discharge cycles and 600 cycles of mechanical flexing. A solar module with appropriate voltage and dimensions is used to charge the battery under both full sun and indoor illumination conditions, and the addition of the solar module is shown to extend the battery lifetime between charging cycles while powering a load. Furthermore, we show that by selecting the appropriate load duty cycle, the average load current can be matched to the solar module current and the battery can be maintained at a constant state of charge. Finally, the battery is used to power a pulse oximeter, demonstrating its effectiveness as a power source for wearable medical devices.

   @article{ostfeld2016high, title = {High-performance flexible energy storage and harvesting system for wearable electronics}, author = {Ostfeld, Aminy E. and Gaikwad, Abhinav M. and Khan, Yasser and Arias, Ana C.}, issn = {2045-2322}, journal = {Scientific Reports}, volume = {6}, year = {2016}, publisher = {Nature Publishing Group}, url = {http://www.nature.com/srep/2016/160517/srep26122/full/srep26122.html}, doi = {10.1038/srep26122}, thumbnail = {ostfeld2016high.png}, pdf = {ostfeld2016high.pdf} }

6. 
   Screen-printed flexible MRI receive coils Joseph R Corea, Anita M Flynn, Balthazar Lechêne, Greig Scott, Galen D Reed, Peter J Shin, Michael Lustig, and Ana C Arias Nature Communications, 2016 7, [Abstract] [Bibtex] [PDF]

   Magnetic resonance imaging is an inherently signal-to-noise-starved technique that limits the spatial resolution, diagnostic image quality and results in typically long acquisition times that are prone to motion artefacts. This limitation is exacerbated when receive coils have poor fit due to lack of flexibility or need for padding for patient comfort. Here, we report a new approach that uses printing for fabricating receive coils. Our approach enables highly flexible, extremely lightweight conforming devices. We show that these devices exhibit similar to higher signal-to-noise ratio than conventional ones, in clinical scenarios when coils could be displaced more than 18_mm away from the body. In addition, we provide detailed material properties and components performance analysis. Prototype arrays are incorporated within infant blankets for in vivo studies. This work presents the first fully functional, printed coils for 1.5- and 3-T clinical scanners.

   @article{corea2016screen, title = {Screen-printed flexible MRI receive coils}, author = {Corea, Joseph R and Flynn, Anita M and Lech{\^e}ne, Balthazar and Scott, Greig and Reed, Galen D and Shin, Peter J and Lustig, Michael and Arias, Ana C}, journal = {Nature Communications}, volume = {7}, year = {2016}, publisher = {Nature Publishing Group}, url = {http://www.nature.com/ncomms/2016/160310/ncomms10839/full/ncomms10839.html}, doi = {110.1038/ncomms10839}, thumbnail = {corea2016screen.png}, pdf = {corea2016screen.pdf} }

7. 
   Fabrication of a High-Performance Flexible Silver-Zinc Wire Battery Alla M. Zamarayeva, Abhinav M. Gaikwad, Igal Deckman, Michael Wang, Brian Khau, Daniel A. Steingart, and Ana Claudia Arias Advanced Electronic Materials, 2016 , . [Abstract] [Bibtex] [PDF]

   Fabrication of a flexible wire battery assembled by utilizing low-cost fabrication processes and based on silver-zinc chemistry is reported. It offers unique versatility in terms of integration with wearable technologies due to its omnidirectional flexibility and improved performance characteristics. The battery is stable over 170 cycles with capacity retention above 98% and has linear capacity ranging between 1.2 and 1.8 mAh cm_1 at 0.5C discharge rate.

   @article{zamarayeva2016fabrication, author = {Zamarayeva, Alla M. and Gaikwad, Abhinav M. and Deckman, Igal and Wang, Michael and Khau, Brian and Steingart, Daniel A. and Arias, Ana Claudia}, title = {Fabrication of a High-Performance Flexible Silver-Zinc Wire Battery}, journal = {Advanced Electronic Materials}, issn = {2199-160X}, volume = {}, number = {}, pages = {}, url = {http://dx.doi.org/10.1002/aelm.201500296}, doi = {10.1002/aelm.201500296}, keywords = {flexible batteries, flexible electronics, silver-zinc batteries, wire-shaped batteries}, year = {2016}, thumbnail = {zamarayeva2016fabrication.png}, pdf = {zamarayeva2016fabrication.pdf}, publisher = {Wiley-VCH} }

8. 
   Monitoring of Vital Signs with Flexible and Wearable Medical Devices Yasser Khan, Aminy E. Ostfeld, Claire M. Lochner, Adrien Pierre, and Ana C. Arias Advanced Materials, 2016 , . [Abstract] [Bibtex] [PDF]

   Advances in wireless technologies, low-power electronics, the internet of things, and in the domain of connected health are driving innovations in wearable medical devices at a tremendous pace. Wearable sensor systems composed of flexible and stretchable materials have the potential to better interface to the human skin, whereas silicon-based electronics are extremely efficient in sensor data processing and transmission. Therefore, flexible and stretchable sensors combined with low-power silicon-based electronics are a viable and efficient approach for medical monitoring. Flexible medical devices designed for monitoring human vital signs, such as body temperature, heart rate, respiration rate, blood pressure, pulse oxygenation, and blood glucose have applications in both fitness monitoring and medical diagnostics. As a review of the latest development in flexible and wearable human vitals sensors, the essential components required for vitals sensors are outlined and discussed here, including the reported sensor systems, sensing mechanisms, sensor fabrication, power, and data processing requirements.

   @article{khan2016monitoring, author = {Khan, Yasser and Ostfeld, Aminy E. and Lochner, Claire M. and Pierre, Adrien and Arias, Ana C.}, title = {Monitoring of Vital Signs with Flexible and Wearable Medical Devices}, journal = {Advanced Materials}, issn = {1521-4095}, volume = {}, number = {}, pages = {}, year = {2016}, url = {http://onlinelibrary.wiley.com/doi/10.1002/adma.201504366/abstract}, doi = {10.1002/adma.201504366}, thumbnail = {khan2016monitoring.png}, pdf = {khan2016monitoring.pdf}, publisher = {Wiley-VCH}, keywords = {flexible electronics, flexible medical sensors, printed electronics, wearable health monitoring, wearable sensors} }

9. 
   Inkjet-Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces Yasser Khan, Felippe J. Pavinatto, Monica C. Lin, Amy Liao, Sarah L. Swisher, Kaylee Mann, Vivek Subramanian, Michel M. Maharbiz, and Ana C. Arias Advanced Functional Materials, 2016 , . [Abstract] [Bibtex] [PDF] Cover Article.

   Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low-temperature sintering (_200 _C) technique is demonstrated to fabricate gold electrodes. At low-temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 _m and conductivity values of 5 _ 10 6 S m_1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode-to-electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet-printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.

   @article{khan2016inkjet, author = {Khan, Yasser and Pavinatto, Felippe J. and Lin, Monica C. and Liao, Amy and Swisher, Sarah L. and Mann, Kaylee and Subramanian, Vivek and Maharbiz, Michel M. and Arias, Ana C.}, title = {Inkjet-Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces}, journal = {Advanced Functional Materials}, issn = {1616-3028}, volume = {}, number = {}, pages = {}, year = {2016}, url = {http://onlinelibrary.wiley.com/doi/10.1002/adfm.201503316/abstract}, doi = {10.1002/adfm.201503316}, thumbnail = {khan2016inkjet.png}, pdf = {khan2016inkjet.pdf}, publisher = {Wiley-VCH}, keywords = {bioimpedance and biopotential electrodes, gold nanoparticles, inkjet printing, printed electrodes, wearable sensors}, note = {Cover Article.} }

10. 
    Identifying orthogonal solvents for solution processed organic transistors Abhinav M. Gaikwad, Yasser Khan, Aminy E. Ostfeld, Shishir Pandya, Sameer Abraham, and Ana Claudia Arias Organic Electronics, 2016 30, [Abstract] [Bibtex] [PDF] Solvents visualization program is available in the Downloads section.

    Abstract Identification of solvents for dissolving polymer dielectrics and organic semiconductors is necessary for the fabrication of solution-processed organic field effect transistors (OFETs). In addition to solubility and printability of a solvent, orthogonality is particularly important when forming multilayer structure from solutions. Currently, the process of finding orthogonal solvents is empirical, and based on trial-and-error experimental methods. In this paper, we present a methodology for identifying orthogonal solvents for solution-processed organic devices. We study the accuracy of Hildebrand and Hansen solubility theories for building solubility boundaries for organic semiconductor (Poly(2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene (PBTTT) and polymer dielectrics (Poly(methyl methacrylate) (PMMA), Polystyrene (PS)). The Hansen solubility sphere for the organic semiconductor and polymer gate dielectrics are analyzed to identify solvents that dissolve {PMMA} and PS, but are orthogonal to PBTTT. Top gate/bottom contact {PBTTT} based {OFETs} are fabricated with {PMMA} gate dielectric processed with solvents that are orthogonal and non-orthogonal to PBTTT. The non-orthogonal solvents swell the semiconductor layer and increase their surface roughness.

    @article{gaikwad2016identifying, title = {Identifying orthogonal solvents for solution processed organic transistors}, author = {Gaikwad, Abhinav M. and Khan, Yasser and Ostfeld, Aminy E. and Pandya, Shishir and Abraham, Sameer and Arias, Ana Claudia}, journal = {Organic Electronics}, volume = {30}, pages = {18 - 29}, year = {2016}, issn = {1566-1199}, url = {http://www.sciencedirect.com/science/article/pii/S1566119915302299}, doi = {10.1016/j.orgel.2015.12.008}, thumbnail = {gaikwad2016identifying.png}, pdf = {gaikwad2016identifying.pdf}, publisher = {}, note = {Solvents visualization program is available in the Downloads section.} }

2015

1. 
   High Detectivity All-Printed Organic Photodiodes Adrien Pierre, Igal Deckman, Pierre Balthazar Lechene, and Ana Claudia Arias Advanced Materials, 2015 [Abstract] [Bibtex] [PDF]

   All-printed organic photodiode arrays on plastic are reported with average specific detectivities of 3.45 _ 1013 cm Hz0.5 W_1 at a bias of _5 V. The blade-coated polyethylenimine cathode interlayer and active layer and screen-printed anode enable precise device performance tunability and excellent homogeneity at centimetric scales. These devices high operational reverse bias, good linear dynamic range, and bias stress stability make them attractive for implementation in imaging systems.

   @article{pierre2015high, author = {Pierre, Adrien and Deckman, Igal and Lechene, Pierre Balthazar and Arias, Ana Claudia}, title = {High Detectivity All-Printed Organic Photodiodes}, journal = {Advanced Materials}, issn = {1521-4095}, url = {http://dx.doi.org/10.1002/adma.201502238}, doi = {10.1002/adma.201502238}, year = {2015}, thumbnail = {pierre2015high.png}, pdf = {pierre2015high.pdf} }

2. 
   Charge transport model for photovoltaic devices based on printed polymer: Fullerene nanoparticles Natasha A.D. Yamamoto, Margaret E. Payne, Marlus Koehler, Antonio Facchetti, Lucimara S. Roman, and Ana C. Arias Solar Energy Materials and Solar Cells , 2015 141, . [Abstract] [Bibtex] [PDF]

   Abstract The electrical transport properties of films derived from aqueous semiconducting nanoparticle are fully described by a phenomenological model that relates intrinsic film morphology to photovoltaic response. The model is applied to a new bulk heterojunction blend, composed of organic semiconducting nanoparticles formed from the polymer donor poly[2,6-(4,8-didodecylbenzo[1,2-b:4,5-b]dithiophene)-alt-5,5-(2,5-bis(2-butyloctyl)-3,6-dithiophen-2-yl-2,5dihydropyrrolo[3,4-c]57pyrrole-1,4-dione)] (P(TBT-DPP)) and the fullerene indene-C60-bisadduct (ICBA) synthesized by the miniemulsion method. The nanoparticle inks are printed from an aqueous dispersion onto flexible ITO-free substrates yielding power conversion efficiency of 2.6%.

   @article{yamamoto2015charge, title = {Charge transport model for photovoltaic devices based on printed polymer: Fullerene nanoparticles }, journal = {Solar Energy Materials and Solar Cells }, volume = {141}, number = {}, pages = {171 - 177}, year = {2015}, note = {}, issn = {0927-0248}, doi = {10.1016/j.solmat.2015.05.034}, url = {http://www.sciencedirect.com/science/article/pii/S0927024815002457}, thumbnail = {yamamoto2015charge.png}, pdf = {yamamoto2015charge.pdf}, author = {Yamamoto, Natasha A.D. and Payne, Margaret E. and Koehler, Marlus and Facchetti, Antonio and Roman, Lucimara S. and Arias, Ana C.} }
3. Recent Progress on Printed Flexible Batteries: Mechanical Challenges, Printing Technologies, and Future Prospects Abhinav M Gaikwad, Ana Claudia Arias, and Daniel A Steingart Energy Technology, 2015 [Bibtex]

   @article{gaikwad2015recent, title = {Recent Progress on Printed Flexible Batteries: Mechanical Challenges, Printing Technologies, and Future Prospects}, author = {Gaikwad, Abhinav M and Arias, Ana Claudia and Steingart, Daniel A}, journal = {Energy Technology}, year = {2015}, publisher = {WILEY-VCH Verlag} }

4. 
   Impedance sensing device enables early detection of pressure ulcers in vivo Sarah L Swisher, Monica C Lin, Amy Liao, Elisabeth J Leeflang, Yasser Khan, Felippe J Pavinatto, Kaylee Mann, Agne Naujokas, David Young, Shuvo Roy, and others Nature Communications, 2015 6, 6575. [Abstract] [Bibtex] [PDF] Media Coverage: UC Berkeley News Center, Futurity, BBC News, and many more.

   When pressure is applied to a localized area of the body for an extended time, the resulting loss of blood flow and subsequent reperfusion to the tissue causes cell death and a pressure ulcer develops. Preventing pressure ulcers is challenging because the combination of pressure and time that results in tissue damage varies widely between patients, and the underlying damage is often severe by the time a surface wound becomes visible. Currently, no method exists to detect early tissue damage and enable intervention. Here we demonstrate a flexible, electronic device that non-invasively maps pressure-induced tissue damage, even when such damage cannot be visually observed. Using impedance spectroscopy across flexible electrode arrays in vivo on a rat model, we find that impedance is robustly correlated with tissue health across multiple animals and wound types. Our results demonstrate the feasibility of an automated, non-invasive ’smart bandage’ for early detection of pressure ulcers.

   @article{swisher2015impedance, title = {Impedance sensing device enables early detection of pressure ulcers in vivo}, author = {Swisher, Sarah L and Lin, Monica C and Liao, Amy and Leeflang, Elisabeth J and Khan, Yasser and Pavinatto, Felippe J and Mann, Kaylee and Naujokas, Agne and Young, David and Roy, Shuvo and others}, journal = {Nature Communications}, volume = {6}, number = {6575}, year = {2015}, url = {http://www.nature.com/ncomms/2015/150317/ncomms7575/full/ncomms7575.html}, doi = {10.1038/ncomms7575}, thumbnail = {swisher2015impedance.png}, pdf = {swisher2015impedance.pdf}, publisher = {Nature Publishing Group}, note = {Media Coverage: }, media_1 = {UC Berkeley News Center, }, media_1_link = {http://newscenter.berkeley.edu/2015/03/17/smart-bandages-detect-bedsores/}, media_2 = {Futurity, }, media_2_link = {http://www.futurity.org/smart-bandage-bedsores-876942/}, media_3 = {BBC News, }, media_3_link = {http://www.bbc.com/news/health-31903367}, media_4 = {and many more.}, media_4_link = {http://www.altmetric.com/details.php?domain=www.nature.com&citation_id=3798805} }

5. 
   Screen printed passive components for flexible power electronics Aminy E. Ostfeld, Igal Deckman, Abhinav M. Gaikwad, Claire M. Lochner, and Ana C. Arias Scientific Reports, 2015 5, [Abstract] [Bibtex] [PDF]

   Additive and low-temperature printing processes enable the integration of diverse electronic devices, both power-supplying and power-consuming, on flexible substrates at low cost. Production of a complete electronic system from these devices, however, often requires power electronics to convert between the various operating voltages of the devices. Passive components-inductors, capacitors, and resistors-perform functions such as filtering, short-term energy storage, and voltage measurement, which are vital in power electronics and many other applications. In this paper, we present screen-printed inductors, capacitors, resistors and an RLC circuit on flexible plastic substrates, and report on the design process for minimization of inductor series resistance that enables their use in power electronics. Printed inductors and resistors are then incorporated into a step-up voltage regulator circuit. Organic light-emitting diodes and a flexible lithium ion battery are fabricated and the voltage regulator is used to power the diodes from the battery, demonstrating the potential of printed passive components to replace conventional surface-mount components in a DC-DC converter application.

   @article{ostfeld2015screen, title = {Screen printed passive components for flexible power electronics}, author = {Ostfeld, Aminy E. and Deckman, Igal and Gaikwad, Abhinav M. and Lochner, Claire M. and Arias, Ana C.}, journal = {Scientific Reports}, year = {2015}, volume = {5}, pages = {15959}, url = {http://www.nature.com/articles/srep15959}, doi = {10.1038/srep15959}, thumbnail = {ostfeld2015screen.png}, pdf = {ostfeld2015screen.pdf}, publisher = {Nature Publishing Group} }

2014

1. Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer Felippe J Pavinatto, Carlos WA Paschoal, and Ana C Arias Biosensors and Bioelectronics, 2014 [Bibtex]

   @article{pavinatto2014printed, title = {Printed and flexible biosensor for antioxidants using interdigitated ink-jetted electrodes and gravure-deposited active layer}, author = {Pavinatto, Felippe J and Paschoal, Carlos WA and Arias, Ana C}, journal = {Biosensors and Bioelectronics}, year = {2014}, publisher = {Elsevier} }

2. A High Areal Capacity Flexible Lithium-Ion Battery with a Strain-Compliant Design Abhinav M Gaikwad, Brian V Khau, Greg Davies, Benjamin Hertzberg, Daniel A Steingart, and Ana Claudia Arias Advanced Energy Materials, 2014 [Bibtex]

   @article{gaikwad2014high, title = {A High Areal Capacity Flexible Lithium-Ion Battery with a Strain-Compliant Design}, author = {Gaikwad, Abhinav M and Khau, Brian V and Davies, Greg and Hertzberg, Benjamin and Steingart, Daniel A and Arias, Ana Claudia}, journal = {Advanced Energy Materials}, year = {2014} }

3. All-Printed Flexible Organic Transistors Enabled by Surface Tension-Guided Blade Coating Adrien Pierre, Mahsa Sadeghi, Marcia M Payne, Antonio Facchetti, John E Anthony, and Ana Claudia Arias Advanced Materials, 2014 26, 32. [Bibtex]

   @article{pierre2014all, title = {All-Printed Flexible Organic Transistors Enabled by Surface Tension-Guided Blade Coating}, author = {Pierre, Adrien and Sadeghi, Mahsa and Payne, Marcia M and Facchetti, Antonio and Anthony, John E and Arias, Ana Claudia}, journal = {Advanced Materials}, volume = {26}, number = {32}, pages = {5722--5727}, year = {2014} }

4. Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics Aminy E. Ostfeld, Amelie Catheline, Kathleen Ligsay, Kee-Chan Kim, Zhihua Chen, Antonio Facchetti, Sian Fogden, and Ana Claudia Arias Applied Physics Letters, 2014 105, 25. [Bibtex]

   @article{ostfeld2014single, author = {Ostfeld, Aminy E. and Catheline, Amelie and Ligsay, Kathleen and Kim, Kee-Chan and Chen, Zhihua and Facchetti, Antonio and Fogden, Sian and Arias, Ana Claudia}, title = {Single-walled carbon nanotube transparent conductive films fabricated by reductive dissolution and spray coating for organic photovoltaics}, journal = {Applied Physics Letters}, year = {2014}, volume = {105}, number = {25}, eid = {253301}, pages = {-}, url = {http://scitation.aip.org/content/aip/journal/apl/105/25/10.1063/1.4904940}, doi = {http://dx.doi.org/10.1063/1.4904940} }

5. 
   All-organic optoelectronic sensor for pulse oximetry Claire M Lochner*, Yasser Khan*, Adrien Pierre*, and Ana C Arias Nature Communications, 2014 5, 5745. [Abstract] [Bibtex] [PDF] *Equal contribution. Media Coverage: UC Berkeley Grad News, NSF Science 360 News, UC Berkeley News Center, Phys.org, ScienceDaily, and many more.

   Pulse oximetry is a ubiquitous non-invasive medical sensing method for measuring pulse rate and arterial blood oxygenation. Conventional pulse oximeters use expensive optoelectronic components that restrict sensing locations to finger tips or ear lobes due to their rigid form and area-scaling complexity. In this work, we report a pulse oximeter sensor based on organic materials, which are compatible with flexible substrates. Green (532_nm) and red (626_nm) organic light-emitting diodes (OLEDs) are used with an organic photodiode (OPD) sensitive at the aforementioned wavelengths. The sensor’s active layers are deposited from solution-processed materials via spin-coating and printing techniques. The all-organic optoelectronic oximeter sensor is interfaced with conventional electronics at 1_kHz and the acquired pulse rate and oxygenation are calibrated and compared with a commercially available oximeter. The organic sensor accurately measures pulse rate and oxygenation with errors of 1% and 2%, respectively.

   @article{lochner2014all, title = {All-organic optoelectronic sensor for pulse oximetry}, author = {Lochner*, Claire M and Khan*, Yasser and Pierre*, Adrien and Arias, Ana C}, journal = {Nature Communications}, volume = {5}, number = {5745}, year = {2014}, url = {http://www.nature.com/ncomms/2014/141210/ncomms6745/full/ncomms6745.html}, doi = {10.1038/ncomms6745}, thumbnail = {lochner2014all.png}, pdf = {lochner2014all.pdf}, publisher = {Nature Publishing Group}, note = {*Equal contribution. Media Coverage: }, media_1 = {UC Berkeley Grad News, }, media_1_link = {http://grad.berkeley.edu/news/headlines/engineering-team-invents-medical-sensor/}, media_2 = {NSF Science 360 News, }, media_2_link = {http://news.science360.gov/obj/story/d8f7fa4c-4e41-4bcb-8ccd-1939dc4af3da/organic-electronics-lead-cheap-wearable-medical-sensors}, media_3 = {UC Berkeley News Center, }, media_3_link = {http://newscenter.berkeley.edu/2014/12/10/organic-electronics-cheap-wearable-medical-sensors/}, media_4 = {Phys.org, }, media_4_link = {http://phys.org/news/2014-12-electronics-cheap-wearable-medical-sensors.html}, media_5 = {ScienceDaily, }, media_5_link = {http://www.sciencedaily.com/releases/2014/12/141210131356.htm?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+sciencedaily%2Ftop_news+%28ScienceDaily%3A+Top+News%29}, media_6 = {and many more.}, media_6_link = {http://www.altmetric.com/details.php?domain=www.nature.com&citation_id=2972740} }

2013

1. 
   Empirically based device modeling of bulk heterojunction organic photovoltaics Adrien Pierre, Shaofeng Lu, Ian A. Howard, Antonio Facchetti, and Ana Claudia Arias Journal of Applied Physics, 2013 113, 15. [Abstract] [Bibtex] [PDF] Bulk heterojunction device model simulator package is available in the Downloads section.

   We develop an empirically based optoelectronic model to accurately simulate the photocurrent in organic photovoltaic (OPV) devices with novel materials including bulk heterojunction OPV devices based on a new low band gap dithienothiophene-DPP donor polymer, P(TBT-DPP), blended with PC70BM at various donor-acceptor weight ratios and solvent compositions. Our devices exhibit power conversion efficiencies ranging from 1.8% to 4.7% at AM 1.5G. Electron and hole mobilities are determined using space-charge limited current measurements. Bimolecular recombination coefficients are both analytically calculated using slowest-carrier limited Langevin recombination and measured using an electro-optical pump-probe technique. Exciton quenching efficiencies in the donor and acceptor domains are determined from photoluminescence spectroscopy. In addition, dielectric and optical constants are experimentally determined. The photocurrent and its bias-dependence that we simulate using the optoelectronic model we develop, which takes into account these physically measured parameters, shows less than 7% error with respect to the experimental photocurrent (when both experimentally and semi-analytically determined recombination coefficient is used). Free carrier generation and recombination rates of the photocurrent are modeled as a function of the position in the active layer at various applied biases. These results show that while free carrier generation is maximized in the center of the device, free carrier recombination is most dominant near the electrodes even in high performance devices. Such knowledge of carrier activity is essential for the optimization of the active layer by enhancing light trapping and minimizing recombination. Our simulation program is intended to be freely distributed for use in laboratories fabricating OPV devices.

   @article{pierre2013empirically, author = {Pierre, Adrien and Lu, Shaofeng and Howard, Ian A. and Facchetti, Antonio and Arias, Ana Claudia}, title = {Empirically based device modeling of bulk heterojunction organic photovoltaics}, journal = {Journal of Applied Physics}, year = {2013}, volume = {113}, number = {15}, eid = {154506}, pages = {}, url = {http://scitation.aip.org/content/aip/journal/jap/113/15/10.1063/1.4801662}, doi = {10.1063/1.4801662}, thumbnail = {pierre2013empirically.png}, pdf = {pierre2013empirically.pdf}, publisher = {}, note = {Bulk heterojunction device model simulator package is available in the Downloads section.} }

2012

1. Method and structure for establishing contacts in thin film transistor devices Jürgen H Daniel, Ana Claudia Arias, and Michael Chabinyc 2012 [Bibtex] US Patent 20,120,322,214

   @misc{daniel2012method, title = {Method and structure for establishing contacts in thin film transistor devices}, author = {Daniel, J{\"u}rgen H and Arias, Ana Claudia and Chabinyc, Michael}, year = {2012}, month = dec, note = {US Patent 20,120,322,214} }

2. Thin Film Field Effect Transistor with Dual Semiconductor Layers Sanjiv Sambandan, Ana Claudia Arias, and Gregory Lewis Whiting 2012 [Bibtex] US Patent 20,120,007,079

   @misc{sambandan2012thin, title = {Thin Film Field Effect Transistor with Dual Semiconductor Layers}, author = {Sambandan, Sanjiv and Arias, Ana Claudia and Whiting, Gregory Lewis}, year = {2012}, month = jan, note = {US Patent 20,120,007,079} }

3. OPTOELECTRONIC DEVICES AND A METHOD FOR PRODUCING THE SAME Devin J Mackenzie, Ana Claudia Arias, Richard Henry Friend, and Wilhelm Huck 2012 [Bibtex] US Patent 20,120,064,652

   @misc{mackenzie2012optoelectronic, title = {OPTOELECTRONIC DEVICES AND A METHOD FOR PRODUCING THE SAME}, author = {Mackenzie, Devin J and Arias, Ana Claudia and Friend, Richard Henry and Huck, Wilhelm}, year = {2012}, month = mar, note = {US Patent 20,120,064,652} }

4. Thin film field effect transistor with dual semiconductor layers Sanjiv Sambandan, Ana Claudia Arias, and Gregory Lewis Whiting 2012 [Bibtex] US Patent App. 13/426,518

   @misc{sambandan2012thio, title = {Thin film field effect transistor with dual semiconductor layers}, author = {Sambandan, Sanjiv and Arias, Ana Claudia and Whiting, Gregory Lewis}, year = {2012}, month = mar, note = {US Patent App. 13/426,518} }

5. Synthesis and Solar Cell Application of New Alternating Donor–Acceptor Copolymers Based on Variable Units of Fluorene, Thiophene, and Phenylene Natasha AD Yamamoto, Leah L Lavery, Bruno F Nowacki, Isabel R Grova, Gregory L Whiting, Brent Krusor, Eduardo R Azevedo, Leni Akcelrud, Ana C Arias, and Lucimara S Roman The Journal of Physical Chemistry C, 2012 116, 35. [Bibtex]

   @article{yamamoto2012synthesis, title = {Synthesis and Solar Cell Application of New Alternating Donor--Acceptor Copolymers Based on Variable Units of Fluorene, Thiophene, and Phenylene}, author = {Yamamoto, Natasha AD and Lavery, Leah L and Nowacki, Bruno F and Grova, Isabel R and Whiting, Gregory L and Krusor, Brent and de Azevedo, Eduardo R and Akcelrud, Leni and Arias, Ana C and Roman, Lucimara S}, journal = {The Journal of Physical Chemistry C}, volume = {116}, number = {35}, pages = {18641--18648}, year = {2012}, publisher = {American Chemical Society} }

6. Printed Material Constrained By Well Structures And Devices Including Same Jurgen H Daniel, and Ana Claudia Arias 2012 [Bibtex] US Patent 20,120,238,081

   @misc{daniel2012printed, title = {Printed Material Constrained By Well Structures And Devices Including Same}, author = {Daniel, Jurgen H and Arias, Ana Claudia}, year = {2012}, month = sep, note = {US Patent 20,120,238,081} }

7. Printed Material Constrained By Well Structures And Devices Including Same Jurgen H Daniel, and Ana Claudia Arias 2012 [Bibtex] US Patent 20,120,235,145

   @misc{daniel2012printee, title = {Printed Material Constrained By Well Structures And Devices Including Same}, author = {Daniel, Jurgen H and Arias, Ana Claudia}, year = {2012}, month = sep, note = {US Patent 20,120,235,145} }

8. Conformable Active Devices Robert A Street, and Ana Claudia Arias Stretchable Electronics, 2012 [Bibtex]

   @article{street2012conformable, title = {Conformable Active Devices}, author = {Street, Robert A and Arias, Ana Claudia}, journal = {Stretchable Electronics}, pages = {355--378}, year = {2012}, publisher = {Wiley-VCH Verlag GmbH \& Co. KGaA} }

9. Electronic circuit structure and method for forming same Jürgen H Daniel, and Ana Claudia Arias 2012 [Bibtex] US Patent 20,120,302,046

   @misc{daniel2012electronic, title = {Electronic circuit structure and method for forming same}, author = {Daniel, J{\"u}rgen H and Arias, Ana Claudia}, year = {2012}, month = nov, note = {US Patent 20,120,302,046} }

2011

1. All ink-jet printed polyfluorene photosensor for high illuminance detection Leah Lucas Lavery, Gregory Lewis Whiting, and Ana Claudia Arias Organic Electronics, 2011 12, 4. [Bibtex]

   @article{Lavery2011682, title = {All ink-jet printed polyfluorene photosensor for high illuminance detection}, journal = {Organic Electronics}, volume = {12}, number = {4}, pages = {682 - 685}, year = {2011}, note = {}, issn = {1566-1199}, doi = {10.1016/j.orgel.2011.01.023}, url = {http://www.sciencedirect.com/science/article/pii/S1566119911000383}, author = {Lavery, Leah Lucas and Whiting, Gregory Lewis and Arias, Ana Claudia}, keywords = {PFB:F8BT} }
2. Highly Flexible, Printed Alkaline Batteries Based on Mesh-Embedded Electrodes Abhinav M. Gaikwad, Gregory L. Whiting, Daniel A. Steingart, and Ana Claudia Arias Advanced Materials, 2011 23, 29. [Bibtex]

   @article{ADMAADMA201100894, author = {Gaikwad, Abhinav M. and Whiting, Gregory L. and Steingart, Daniel A. and Arias, Ana Claudia}, title = {Highly Flexible, Printed Alkaline Batteries Based on Mesh-Embedded Electrodes}, journal = {Advanced Materials}, volume = {23}, number = {29}, publisher = {WILEY-VCH Verlag}, issn = {1521-4095}, url = {http://dx.doi.org/10.1002/adma.201100894}, doi = {10.1002/adma.201100894}, pages = {3251--3255}, keywords = {flexible batteries, polymer electrolytes, mesh architectures, flexible electronics}, year = {2011} }

2010

1. Fast polymer semiconductor transistor by nano-particle self assembly S. Sambandan, G. Whiting, A. Arias, and R.A. Street Organic Electronics, 2010 11, 12. [Abstract] [Bibtex]

   Polymer semiconductor based field effect transistors promise low cost electronics over rigid and flexible large area substrates using fabrication techniques such as ink-jet printing. However, the low mobility of carriers in these semiconductors does not permit high performance electronics. A primary means to achieve higher speed in spite of the low carrier mobility is to reduce feature size, particularly channel length, of the field effect transistors. In this paper, we use the controlled coffee stain effect in a silver nano-particle colloid along with ink-jet printing to develop a process which helps reduce field effect transistor channel length to about 1-10 _m and improve transistor speed.

   @article{Sambandan20101935, title = {Fast polymer semiconductor transistor by nano-particle self assembly}, journal = {Organic Electronics}, volume = {11}, number = {12}, pages = {1935 - 1941}, year = {2010}, note = {}, issn = {1566-1199}, doi = {10.1016/j.orgel.2010.08.012}, url = {http://www.sciencedirect.com/science/article/pii/S1566119910002843}, author = {Sambandan, S. and Whiting, G. and Arias, A. and Street, R.A.}, keywords = {Coffee stain effect} }
2. Materials and Applications for Large Area Electronics: Solution-Based Approaches Ana Claudia Arias, J. Devin MacKenzie, Iain McCulloch, Jonathan Rivnay, and Alberto Salleo Chemical Reviews, 2010 110, 1. [Bibtex] PMID: 20070114

   @article{doi:10.1021/cr900150b, author = {Arias, Ana Claudia and MacKenzie, J. Devin and McCulloch, Iain and Rivnay, Jonathan and Salleo, Alberto}, title = {Materials and Applications for Large Area Electronics: Solution-Based Approaches}, journal = {Chemical Reviews}, volume = {110}, number = {1}, pages = {3-24}, year = {2010}, doi = {10.1021/cr900150b}, note = {PMID: 20070114}, url = {http://pubs.acs.org/doi/abs/10.1021/cr900150b}, eprint = {http://pubs.acs.org/doi/pdf/10.1021/cr900150b} }

2009

1. Chemically modified ink-jet printed silver electrodes for organic field-effect transistors Gregory Lewis Whiting, and Ana Claudia Arias Applied Physics Letters, 2009 95, 25. [Bibtex]

   @article{whiting253302, author = {Whiting, Gregory Lewis and Arias, Ana Claudia}, collaboration = {}, title = {Chemically modified ink-jet printed silver electrodes for organic field-effect transistors}, publisher = {AIP}, year = {2009}, journal = {Applied Physics Letters}, volume = {95}, number = {25}, eid = {253302}, numpages = {3}, pages = {253302}, keywords = {carrier mobility; electrodes; organic field effect transistors; organic semiconductors; silver}, url = {http://link.aip.org/link/?APL/95/253302/1}, doi = {10.1063/1.3276913} }
2. Degradation mechanisms of organic ferroelectric field-effect transistors used as nonvolatile memory Tse Nga Ng, Beverly Russo, and Ana Claudia Arias Journal of Applied Physics, 2009 106, 9. [Bibtex]

   @article{Tse094504, author = {Ng, Tse Nga and Russo, Beverly and Arias, Ana Claudia}, collaboration = {}, title = {Degradation mechanisms of organic ferroelectric field-effect transistors used as nonvolatile memory}, publisher = {AIP}, year = {2009}, journal = {Journal of Applied Physics}, volume = {106}, number = {9}, eid = {094504}, numpages = {5}, pages = {094504}, keywords = {ferroelectric storage; field effect transistor circuits; hysteresis}, url = {http://link.aip.org/link/?JAP/106/094504/1}, doi = {10.1063/1.3253758} }
3. Compact model for forward subthreshold characteristics in polymer semiconductor transistors S. Sambandan, R. J. P. Kist, R. Lujan, T. Ng, A. C. Arias, and R. A. Street Journal of Applied Physics, 2009 106, 8. [Bibtex]

   @article{sambandan084501, author = {Sambandan, S. and Kist, R. J. P. and Lujan, R. and Ng, T. and Arias, A. C. and Street, R. A.}, collaboration = {}, title = {Compact model for forward subthreshold characteristics in polymer semiconductor transistors}, publisher = {AIP}, year = {2009}, journal = {Journal of Applied Physics}, volume = {106}, number = {8}, eid = {084501}, numpages = {8}, pages = {084501}, keywords = {deep levels; hopping conduction; organic semiconductors; polymers; Poole-Frenkel effect; semiconductor device models; space-charge-limited conduction; thin film transistors}, url = {http://link.aip.org/link/?JAP/106/084501/1}, doi = {10.1063/1.3233927} }
4. Electrical stability of inkjet-patterned organic complementary inverters measured in ambient conditions Tse Nga Ng, Sanjiv Sambandan, Rene Lujan, Ana Claudia Arias, Christopher R. Newman, He Yan, and Antonio Facchetti Applied Physics Letters, 2009 94, 23. [Bibtex]

   @article{Tse233307, author = {Ng, Tse Nga and Sambandan, Sanjiv and Lujan, Rene and Arias, Ana Claudia and Newman, Christopher R. and Yan, He and Facchetti, Antonio}, collaboration = {}, title = {Electrical stability of inkjet-patterned organic complementary inverters measured in ambient conditions}, publisher = {AIP}, year = {2009}, journal = {Applied Physics Letters}, volume = {94}, number = {23}, eid = {233307}, numpages = {3}, pages = {233307}, keywords = {electron mobility; hole mobility; invertors; organic semiconductors; tantalum compounds; thin film transistors}, url = {http://link.aip.org/link/?APL/94/233307/1}, doi = {10.1063/1.3153510} }

2008

1. Gate bias stress effects due to polymer gate dielectrics in organic thin-film transistors Tse Nga Ng, Jurgen H. Daniel, Sanjiv Sambandan, Ana-Claudia Arias, Michael L. Chabinyc, and Robert A. Street Journal of Applied Physics, 2008 103, 4. [Bibtex]

   @article{ng044506, author = {Ng, Tse Nga and Daniel, Jurgen H. and Sambandan, Sanjiv and Arias, Ana-Claudia and Chabinyc, Michael L. and Street, Robert A.}, collaboration = {}, title = {Gate bias stress effects due to polymer gate dielectrics in organic thin-film transistors}, publisher = {AIP}, year = {2008}, journal = {Journal of Applied Physics}, volume = {103}, number = {4}, eid = {044506}, numpages = {6}, pages = {044506}, keywords = {capacitance; charge injection; conducting polymers; dielectric materials; organic semiconductors; thin film transistors}, url = {http://link.aip.org/link/?JAP/103/044506/1}, doi = {10.1063/1.2884535} }
2. Timing Randomly Spaced Events Using the Threshold-Voltage Shift in Disordered Semiconductors S. Sambandan, A.C. Arias, and R.A. Street Electron Devices, IEEE Transactions on, 2008 55, 12. [Abstract] [Bibtex]

   This paper discusses the concept of using the threshold-voltage shift in disordered-semiconductor-based thin- film transistors to measure the time of occurrence of randomly spaced events of interest. We call the experimental circuit an "analog clock." The analog clock is shown to be accurate while, at the same time, being simple in design using just one transistor.

   @article{4674578, author = {Sambandan, S. and Arias, A.C. and Street, R.A.}, journal = {Electron Devices, IEEE Transactions on}, title = {Timing Randomly Spaced Events Using the Threshold-Voltage Shift in Disordered Semiconductors}, year = {2008}, month = dec, volume = {55}, number = {12}, pages = {3367 -3374}, keywords = {analog clock;disordered-semiconductor-based thin-film transistors;randomly spaced events;threshold-voltage shift;organic semiconductors;thin film transistors;}, doi = {10.1109/TED.2008.2006549}, issn = {0018-9383} }
3. High work function materials for source/drain contacts in printed polymer thin film transistors V. Sholin, S. A. Carter, R. A. Street, and A. C. Arias Applied Physics Letters, 2008 92, 6. [Bibtex]

   @article{sholin063307, author = {Sholin, V. and Carter, S. A. and Street, R. A. and Arias, A. C.}, collaboration = {}, title = {High work function materials for source/drain contacts in printed polymer thin film transistors}, publisher = {AIP}, year = {2008}, journal = {Applied Physics Letters}, volume = {92}, number = {6}, eid = {063307}, numpages = {3}, pages = {063307}, keywords = {electrodes; nanoparticles; polymer blends; silver; thin film transistors; work function}, url = {http://link.aip.org/link/?APL/92/063307/1}, doi = {10.1063/1.2857461} }

2007

1. Jet-Printed Active-Matrix Backplanes and Electrophoretic Displays Jurgen Daniel, Ana Claudia Arias, William Wong, Rene Lujan, Steve Ready, Brent Krusor, and Robert Street Japanese Journal of Applied Physics, 2007 46, 3B. [Bibtex]

   @article{JJAP.46.1363, title = {Jet-Printed Active-Matrix Backplanes and Electrophoretic Displays}, author = {Daniel, Jurgen and Arias, Ana Claudia and Wong, William and Lujan, Rene and Ready, Steve and Krusor, Brent and Street, Robert}, journal = {Japanese Journal of Applied Physics}, volume = {46}, number = {3B}, pages = {1363-1369}, numpages = {6}, year = {2007}, url = {http://jjap.jsap.jp/link?JJAP/46/1363/}, doi = {10.1143/JJAP.46.1363}, publisher = {The Japan Society of Applied Physics} }
2. All-additive ink-jet-printed display backplanes: Materials development and integration Ana C. Arias, Jurgen Daniel, Brent Krusor, Steve Ready, Veronica Sholin, and Robert Street Journal of the Society for Information Display, 2007 15, 7. [Abstract] [Bibtex]

   Abstract- Methods used to deposit and integrate solution-processed materials to fabricate TFT backplanes by ink-jet printing are discussed. Thematerials studied allow the development of an all-additive process in which materials are deposited only where their functionality is required. The metal layer and semiconductor are printed, and the solution-processed dielectric is spin-coated. Silver nanoparticles are used as gate and datametals, the semiconductor used is a polythiophene derivative (PQT-12), and the gate dielectric is an epoxy-based photopolymer. The maximum processing temperature used is 150_C, making the process compatible with flexible substrates. The ION/IOFF ratio was found to be about 105_106, and TFT mobilities of 0.04 cm2/V-sec were obtained. The influence of surface treatments on the size and shape of printed features is presented. It is shown that coffee-stain effects can be controlled with ink formulation and that devices show the expected pixel response.

   @article{JSIDJSID1520, author = {Arias, Ana C. and Daniel, Jurgen and Krusor, Brent and Ready, Steve and Sholin, Veronica and Street, Robert}, title = {All-additive ink-jet-printed display backplanes: Materials development and integration}, journal = {Journal of the Society for Information Display}, volume = {15}, number = {7}, publisher = {Blackwell Publishing Ltd}, issn = {1938-3657}, url = {http://dx.doi.org/10.1889/1.2759554}, doi = {10.1889/1.2759554}, pages = {485--490}, keywords = {Display backplanes, organic semiconductors, TFTs, ink-jet printing}, year = {2007} }
3. Solution Based Self-Assembly of an Array of Polymeric Thin-Film Transistors A. Salleo, and A._C. Arias Advanced Materials, 2007 19, 21. [Bibtex]

   @article{ADMADMA200700445, author = {Salleo, A. and Arias, A._C.}, title = {Solution Based Self-Assembly of an Array of Polymeric Thin-Film Transistors}, journal = {Advanced Materials}, volume = {19}, number = {21}, publisher = {WILEY-VCH Verlag}, issn = {1521-4095}, url = {http://dx.doi.org/10.1002/adma.200700445}, doi = {10.1002/adma.200700445}, pages = {3540--3543}, keywords = {Self-assembly, Semiconductors, Thin-film transistors, organic}, year = {2007} }

2006

1. Vertically Segregated Polymer Blends: Their Use in Organic Electronics and Ana Claudia Arias Journal of Macromolecular Science, Part C: Polymer Reviews, 2006 46, 1. [Abstract] [Bibtex]

   In this paper results on the formation and stability of vertically segregated polymer blend structures applied to organic-based electronic devices are reviewed. In all examples illustrated here, phase separation in a direction normal to the substrate was obtained by a combination of surface treatment, viscosity, solvent evaporation, and blend composition control. It is found that vertically segregated blends form the optimized structure for photovoltaic devices, in which exciton dissociation is enhanced by the composition of the phases and transport of charges is improved by the position of the phases relative to the electrodes. Vertical segregation is shown to reduce leakage current and enhance charge injection and recombination in light emitting diodes resulting in highly luminescent devices. In addition, film composition and morphology analysis together with device characteristics show that the environmental stability of bottom gate polymer-based TFTs is greatly enhanced by a self-encapsulation method achieved with the use of a semiconductor/insulator polymer blend.

   @article{doi10.1080/15321790500471251, author = {Claudia Arias, Ana}, title = {Vertically Segregated Polymer Blends: Their Use in Organic Electronics}, journal = {Journal of Macromolecular Science, Part C: Polymer Reviews}, volume = {46}, number = {1}, pages = {103-125}, year = {2006}, doi = {10.1080/15321790500471251}, url = {http://www.tandfonline.com/doi/abs/10.1080/15321790500471251}, eprint = {http://www.tandfonline.com/doi/pdf/10.1080/15321790500471251} }
2. Jet printing flexible displays R.A. Street, W.S. Wong, S.E. Ready, M.L. Chabinyc, A.C. Arias, S. Limb, A. Salleo, and R. Lujan Materials Today, 2006 9, 4. [Abstract] [Bibtex]

   Jet printing is an interesting patterning technique for electronic devices because it requires no physical mask, has digital control of ejection, and provides good layer-to-layer registration. It also has the potential to reduce display manufacturing costs and enable roll-to-roll processing. The technique is illustrated with examples of prototype printed displays using amorphous silicon and polymer semiconductors.

   @article{Street200632, title = {Jet printing flexible displays}, journal = {Materials Today}, volume = {9}, number = {4}, pages = {32 - 37}, year = {2006}, note = {}, issn = {1369-7021}, url = {http://www.sciencedirect.com/science/article/pii/S1369702106714456}, author = {Street, R.A. and Wong, W.S. and Ready, S.E. and Chabinyc, M.L. and Arias, A.C. and Limb, S. and Salleo, A. and Lujan, R.} }

3. The Road Towards Large-Area Electronics Without Vacuum Tools Jurgen Daniel, Ana Claudia Arias, Brent Krusor, Rene Lujan, and Robert Street Meeting Abstracts, 2006 MA2006-02, 33. [Abstract] [Bibtex]

   Abstract not Available.

   @article{Daniel30062006, author = {Daniel, Jurgen and Arias, Ana Claudia and Krusor, Brent and Lujan, Rene and Street, Robert}, title = {The Road Towards Large-Area Electronics Without Vacuum Tools}, volume = {MA2006-02}, number = {33}, pages = {1579}, year = {2006}, url = {http://ma.ecsdl.org/content/MA2006-02/33/1579.abstract}, eprint = {http://ma.ecsdl.org/content/MA2006-02/33/1579.full.pdf+html}, journal = {Meeting Abstracts} }

4. Thin-film Transistor Fabrication by Digital Lithography 2006 [Abstract] [Bibtex]

   This chapter contains sections titled: * Introduction * Jet-printed Patterning for Thin-film Transistor Processing * Introduction * Jet-printed Phase-change Etch Masks * Digital Lithography * Digital Lithography for TFT Device Fabrication * Thin-film Transistor Device Structures * Amorphous Silicon TFTs * Polymeric TFTs by Digital Lithography * Thin-film Transistor Device Characteristics * a-Si:H TFTs * Printed Polymeric TFTs * TFTs on Flexible Substrates * Introduction * TFT Pixel Design Considerations * Digital Lithography for Flexible Backplanes * Display Applications with Print-patterned Backplanes * Conclusions * Acknowledgments * References

   @inbook{wong2006, title = {Thin-film Transistor Fabrication by Digital Lithography}, author = {}, publisher = {Wiley-VCH Verlag GmbH & Co. KGaA}, isbn = {9783527608751}, url = {http://dx.doi.org/10.1002/3527608753.ch11}, doi = {10.1002/3527608753.ch11}, pages = {271--293}, keywords = {organic electronics, manufacturing, thin-film transistor (TFT) fabrication, digital lithography, jet-printed patterning, TFTs on flexible substrates, display applications, print-patterned backplanes}, booktitle = {Organic Electronics}, year = {2006} }

2005

1. 54.1: Flexible Electrophoretic Displays with Jet-Printed Active-Matrix Backplanes J. H. Daniel, A. C. Arias, W. S. Wong, R. Lujan, B. S. Krusor, R. B. Apte, M. L. Chabinyc, A. Salleo, R. A. Street, N. Chopra, G. Iftime, and P. M. Kazmaier SID Symposium Digest of Technical Papers, 2005 36, 1. [Abstract] [Bibtex]

   We report on the integration of electrophoretic media with flexible backplanes. The active-matrix backplanes are based on amorphous-silicon or on organic-semiconductor technology. Conventional photolithography was fully replaced by jet-printing. Flexible electrophoretic media is fabricated by photolithography and by molding of micro-cell structures. Various aspects will be addressed, concerning the media, the backplanes and the integration.

   @article{SDTPSDTP4718, author = {Daniel, J. H. and Arias, A. C. and Wong, W. S. and Lujan, R. and Krusor, B. S. and Apte, R. B. and Chabinyc, M. L. and Salleo, A. and Street, R. A. and Chopra, N. and Iftime, G. and Kazmaier, P. M.}, title = {54.1: Flexible Electrophoretic Displays with Jet-Printed Active-Matrix Backplanes}, journal = {SID Symposium Digest of Technical Papers}, volume = {36}, number = {1}, publisher = {Blackwell Publishing Ltd}, issn = {2168-0159}, url = {http://dx.doi.org/10.1889/1.2720336}, doi = {10.1889/1.2720336}, pages = {1630--1633}, year = {2005} }
2. Printing Methods and Materials for Large-Area Electronic Devices M.L. Chabinyc, W.S. Wong, A.C. Arias, S. Ready, R.A. Lujan, J.H. Daniel, B. Krusor, R.B. Apte, A. Salleo, and R.A. Street Proceedings of the IEEE, 2005 93, 8. [Bibtex]

   @article{1468606, author = {Chabinyc, M.L. and Wong, W.S. and Arias, A.C. and Ready, S. and Lujan, R.A. and Daniel, J.H. and Krusor, B. and Apte, R.B. and Salleo, A. and Street, R.A.}, journal = {Proceedings of the IEEE}, title = {Printing Methods and Materials for Large-Area Electronic Devices}, year = {2005}, month = aug, volume = {93}, number = {8}, pages = {1491 -1499}, keywords = {active matrix thin film transistor fabrication;digital lithography;digital printing methods;electrophoretic media;inkjet printing;large area electronic devices;digital printing;lithography;polymers;printed circuits;resists;thin film transistors;}, doi = {10.1109/JPROC.2005.851492}, issn = {0018-9219} }
3. Printed Organic Electronics 2005 [Abstract] [Bibtex]

   This chapter contains sections titled: * Introduction * System Requirements * Transistor Requirements * Organic Semiconductors * Digital Lithography * Prospects * Acknowledgements * References

   @inbook{apte2005, title = {Printed Organic Electronics}, author = {}, publisher = {John Wiley & Sons, Ltd}, isbn = {9780470870501}, url = {http://dx.doi.org/10.1002/0470870508.ch12}, doi = {10.1002/0470870508.ch12}, pages = {219--243}, keywords = {organic thin film transistors (OTFTs), poly(dialkylquaterthiophene) (PQT), organic light-emitting diodes (OLEDs), printed organic electronics, contact resistance, bias stress, OTFTs}, booktitle = {Flexible Flat Panel Displays}, year = {2005} }

2004

1. All jet-printed polymer thin-film transistor active-matrix backplanes A. C. Arias, S. E. Ready, R. Lujan, W. S. Wong, K. E. Paul, A. Salleo, M. L. Chabinyc, R. Apte, Robert A. Street, Y. Wu, P. Liu, and B. Ong Applied Physics Letters, 2004 85, 15. [Bibtex]

   @article{arias3304, author = {Arias, A. C. and Ready, S. E. and Lujan, R. and Wong, W. S. and Paul, K. E. and Salleo, A. and Chabinyc, M. L. and Apte, R. and Street, Robert A. and Wu, Y. and Liu, P. and Ong, B.}, collaboration = {}, title = {All jet-printed polymer thin-film transistor active-matrix backplanes}, publisher = {AIP}, year = {2004}, journal = {Applied Physics Letters}, volume = {85}, number = {15}, pages = {3304-3306}, keywords = {polymer films; flat panel displays; organic semiconductors; thin film transistors; carrier mobility; polymer structure}, url = {http://link.aip.org/link/?APL/85/3304/1}, doi = {10.1063/1.1801673} }
2. Self-Organized Photonic Structures in Polymer Light-Emitting Diodes G. Fichet, N. Corcoran, P._K._H. Ho, A._C. Arias, J._D. MacKenzie, W._T._S. Huck, and R._H. Friend Advanced Materials, 2004 16, 21. [Bibtex]

   @article{ADMAADMA200400316, author = {Fichet, G. and Corcoran, N. and Ho, P._K._H. and Arias, A._C. and MacKenzie, J._D. and Huck, W._T._S. and Friend, R._H.}, title = {Self-Organized Photonic Structures in Polymer Light-Emitting Diodes}, journal = {Advanced Materials}, volume = {16}, number = {21}, publisher = {WILEY-VCH Verlag}, issn = {1521-4095}, url = {http://dx.doi.org/10.1002/adma.200400316}, doi = {10.1002/adma.200400316}, pages = {1908--1912}, keywords = {Light emitting diodes, organic, Photonic crystals, Thin films, polymers}, year = {2004} }
3. Highly-efficient broadband waveguide outcoupling in light-emitting diodes with self-organized polymer blends N. Corcoran, P. K. H. Ho, A. C. Arias, J. D. Mackenzie, R. H. Friend, G. Fichet, and W. T. S. Huck Applied Physics Letters, 2004 85, 14. [Bibtex]

   @article{corcoran2965, author = {Corcoran, N. and Ho, P. K. H. and Arias, A. C. and Mackenzie, J. D. and Friend, R. H. and Fichet, G. and Huck, W. T. S.}, collaboration = {}, title = {Highly-efficient broadband waveguide outcoupling in light-emitting diodes with self-organized polymer blends}, publisher = {AIP}, year = {2004}, journal = {Applied Physics Letters}, volume = {85}, number = {14}, pages = {2965-2967}, keywords = {polymer blends; organic light emitting diodes; optical waveguides; diffraction gratings; phase separation; organic semiconductors; polymer films; surface chemistry}, url = {http://link.aip.org/link/?APL/85/2965/1}, doi = {10.1063/1.1801680} }

2003

1. Photovoltaic devices based on photo induced charge transfer in polythiophene: CN-PPV blends L. S. Roman, A. C. Arias, M. Theander, M. R. Andersson, and O. InganÃ\textcurrencys Brazilian Journal of Physics, 2003 33, [Bibtex]

   @article{ROMAN2003, title = {{Photovoltaic devices based on photo induced charge transfer in polythiophene: CN-PPV blends}}, journal = {{Brazilian Journal of Physics}}, author = {Roman, L. S. and Arias, A. C. and Theander, M. and Andersson, M. R. and Ingan\~A\textcurrencys, O.}, issn = {0103-9733}, language = {en}, url = {http://www.scielo.br/scielo.php?script=sci_arttext&pid=S0103-97332003000200041&nrm=iso}, volume = {33}, year = {2003}, month = jun, pages = {376 - 381}, publisher = {scielo}, crossref = {10.1590/S0103-97332003000200041} }

2. 34.1: Active Matrix Displays Made with Printed Polymer Thin Film Transistors H. Sirringhaus, S. E. Burns, C. Kuhn, K. Jacobs, J. D. MacKenzie, M. Etchells, K. Chalmers, P. Devine, N. Murton, N. Stone, D. Wilson, P. Cain, T. Brown, A. C. Asais, J. Mills, and R. H. Friend SID Symposium Digest of Technical Papers, 2003 34, 1. [Abstract] [Bibtex]

   We present a process for active matrix flat panel display manufacture by printing polymer thin film transistors. In this process, transistors are fabricated using soluble semi-conducting and conducting materials. Accurate definition of the transistor channel and other circuit components is achieved by direct inkjet printing combined with surface energy patterning. We have used this process to create a 4,800 pixel, 50 dpi, active matrix display. This process is in principle environmentally friendly, low temperature, compatible with flexible substrates, cost effective and advantageous for short run length and large display sizes.

   @article{SDTPSDTP4233, author = {Sirringhaus, H. and Burns, S. E. and Kuhn, C. and Jacobs, K. and MacKenzie, J. D. and Etchells, M. and Chalmers, K. and Devine, P. and Murton, N. and Stone, N. and Wilson, D. and Cain, P. and Brown, T. and Asais, A. C. and Mills, J. and Friend, R. H.}, title = {34.1: Active Matrix Displays Made with Printed Polymer Thin Film Transistors}, journal = {SID Symposium Digest of Technical Papers}, volume = {34}, number = {1}, publisher = {Blackwell Publishing Ltd}, issn = {2168-0159}, url = {http://dx.doi.org/10.1889/1.1832476}, doi = {10.1889/1.1832476}, pages = {1084--1087}, year = {2003} }
3. Polyfluorenes as organic semiconductors for polymeric field effect transistors David J. Brennan, Paul H. Townsend III, Dean M. Welsh, Mitchell G. Dibbs, Jeff M. Shaw, Jessica L. Miklovich, Robyn B. Boeke, Ana Claudia Arias, Lisa Creswell, J. D. MacKenzie, Catherine Ramsdale, Anoop Menon, and Henning Sirringhaus , 2003 , . [Bibtex]

   @article{doi10.1117/12.505749, author = {Brennan, David J. and Townsend III, Paul H. and Welsh, Dean M. and Dibbs, Mitchell G. and Shaw, Jeff M. and Miklovich, Jessica L. and Boeke, Robyn B. and Arias, Ana Claudia and Creswell, Lisa and MacKenzie, J. D. and Ramsdale, Catherine and Menon, Anoop and Sirringhaus, Henning}, title = {Polyfluorenes as organic semiconductors for polymeric field effect transistors}, volume = {}, number = {}, pages = {1-6}, year = {2003}, doi = {10.1117/12.505749}, url = { + http://dx.doi.org/10.1117/12.505749}, eprint = {} }
4. Increased efficiency in vertically segregated thin-film conjugated polymer blends for light-emitting diodes N. Corcoran, A. C. Arias, J. S. Kim, J. D. MacKenzie, and R. H. Friend Applied Physics Letters, 2003 82, 2. [Bibtex]

   @article{corcoran299, author = {Corcoran, N. and Arias, A. C. and Kim, J. S. and MacKenzie, J. D. and Friend, R. H.}, collaboration = {}, title = {Increased efficiency in vertically segregated thin-film conjugated polymer blends for light-emitting diodes}, publisher = {AIP}, year = {2003}, journal = {Applied Physics Letters}, volume = {82}, number = {2}, pages = {299-301}, keywords = {segregation; conducting polymers; organic semiconductors; polymer blends; light emitting diodes; semiconductor device measurement; polymer films}, url = {http://link.aip.org/link/?APL/82/299/1}, doi = {10.1063/1.1537049} }

2002

1. Efficient light harvesting in a photovoltaic diode composed of a semiconductor conjugated copolymer blend David M. Russell, Ana C. Arias, Richard H. Friend, Carlos Silva, Christophe Ego, Andrew C. Grimsdale, and Klaus Mullen Applied Physics Letters, 2002 80, 12. [Bibtex]

   @article{russell2204, author = {Russell, David M. and Arias, Ana C. and Friend, Richard H. and Silva, Carlos and Ego, Christophe and Grimsdale, Andrew C. and Mullen, Klaus}, collaboration = {}, title = {Efficient light harvesting in a photovoltaic diode composed of a semiconductor conjugated copolymer blend}, publisher = {AIP}, year = {2002}, journal = {Applied Physics Letters}, volume = {80}, number = {12}, pages = {2204-2206}, keywords = {conducting polymers; organic semiconductors; polymer blends; dyes; photovoltaic effects; polarons; radiative lifetimes; photodiodes}, url = {http://link.aip.org/link/?APL/80/2204/1}, doi = {10.1063/1.1464226} }
2. The origin of the open-circuit voltage in polyfluorene-based photovoltaic devices C. M. Ramsdale, J. A. Barker, A. C. Arias, J. D. MacKenzie, R. H. Friend, and N. C. Greenham Journal of Applied Physics, 2002 92, 8. [Bibtex]

   @article{ramsdale4266, author = {Ramsdale, C. M. and Barker, J. A. and Arias, A. C. and MacKenzie, J. D. and Friend, R. H. and Greenham, N. C.}, collaboration = {}, title = {The origin of the open-circuit voltage in polyfluorene-based photovoltaic devices}, publisher = {AIP}, year = {2002}, journal = {Journal of Applied Physics}, volume = {92}, number = {8}, pages = {4266-4270}, keywords = {polymer films; photoelectric devices; work function}, url = {http://link.aip.org/link/?JAP/92/4266/1}, doi = {10.1063/1.1506385} }
3. Charge Generation Kinetics and Transport Mechanisms in Blended Polyfluorene Photovoltaic Devices Henry J. Snaith, Ana C. Arias, Arne C. Morteani, Carlos Silva, and Richard H. Friend Nano Letters, 2002 2, 12. [Bibtex]

   @article{doi10.1021/nl0257418, author = {Snaith, Henry J. and Arias, Ana C. and Morteani, Arne C. and Silva, Carlos and Friend, Richard H.}, title = {Charge Generation Kinetics and Transport Mechanisms in Blended Polyfluorene Photovoltaic Devices}, journal = {Nano Letters}, volume = {2}, number = {12}, pages = {1353-1357}, year = {2002}, doi = {10.1021/nl0257418}, url = {http://pubs.acs.org/doi/abs/10.1021/nl0257418}, eprint = {http://pubs.acs.org/doi/pdf/10.1021/nl0257418} }
4. 43.1: Invited Paper: Inkjet Printed Polymer Thin Film Transistors for Active-Matrix Display Applications S. Burns, C. Kuhn, N. Stone, D. Wilson, A. C. Arias, T. Brown, P. Cain, P. Devine, K. Jacobs, N. Murton, J. D. MacKenzie, J. Mills, and H. Sirringhaus SID Symposium Digest of Technical Papers, 2002 33, 1. [Abstract] [Bibtex]

   We have recently demonstrated fabrication of polymer thin film transistor (TFT) circuits by a combination of solution self-assembly and direct inkjet printing. Control over the morphology of the polymer semiconductor and uniaxial alignment of polymer chains parallel to the direction of current flow in the device is obtained by making use of polymer self-organisation. Accurate definition of the transistor channel and other circuit components is achieved by direct inkjet printing combined with surface energy patterning. Here we discuss the application of this novel manufacturing process for polymer TFTs to active matrix displays. We will focus on advantages and disadvantages of polymer TFT technology compared with conventional thin film silicon devices.

   @article{SDTPSDTP3922, author = {Burns, S. and Kuhn, C. and Stone, N. and Wilson, D. and Arias, A. C. and Brown, T. and Cain, P. and Devine, P. and Jacobs, K. and Murton, N. and MacKenzie, J. D. and Mills, J. and Sirringhaus, H.}, title = {43.1: Invited Paper: Inkjet Printed Polymer Thin Film Transistors for Active-Matrix Display Applications}, journal = {SID Symposium Digest of Technical Papers}, volume = {33}, number = {1}, publisher = {Blackwell Publishing Ltd}, issn = {2168-0159}, url = {http://dx.doi.org/10.1889/1.1830158}, doi = {10.1889/1.1830158}, pages = {1193--1195}, year = {2002} }
5. Vertically segregated polymer-blend photovoltaic thin-film structures through surface-mediated solution processing A. C. Arias, N. Corcoran, M. Banach, R. H. Friend, J. D. MacKenzie, and W. T. S. Huck Applied Physics Letters, 2002 80, 10. [Bibtex]

   @article{arias1695, author = {Arias, A. C. and Corcoran, N. and Banach, M. and Friend, R. H. and MacKenzie, J. D. and Huck, W. T. S.}, collaboration = {}, title = {Vertically segregated polymer-blend photovoltaic thin-film structures through surface-mediated solution processing}, publisher = {AIP}, year = {2002}, journal = {Applied Physics Letters}, volume = {80}, number = {10}, pages = {1695-1697}, keywords = {polymer blends; polymer films; liquid phase deposited coatings; semiconductor thin films; organic semiconductors; surface treatment; evaporation; surface segregation; photoelectric devices; surface energy; self-assembly; monolayers; semiconductor growth}, url = {http://link.aip.org/link/?APL/80/1695/1}, doi = {10.1063/1.1456550} }
6. Exciton and polaron dynamics in a step-ladder polymeric semiconductor: the influence of interchain order Carlos Silva, David M Russell, Anoop S Dhoot, Laura M Herz, Clement Daniel, Neil C Greenham, Ana C Arias, Sepas Setayesh, Klaus Mullen, and Richard H Friend Journal of Physics: Condensed Matter, 2002 14, 42. [Bibtex]

   @article{0953-8984-14-42-302, author = {Silva, Carlos and Russell, David M and Dhoot, Anoop S and Herz, Laura M and Daniel, Clement and Greenham, Neil C and Arias, Ana C and Setayesh, Sepas and Mullen, Klaus and Friend, Richard H}, title = {Exciton and polaron dynamics in a step-ladder polymeric semiconductor: the influence of interchain order}, journal = {Journal of Physics: Condensed Matter}, volume = {14}, number = {42}, pages = {9803}, url = {http://stacks.iop.org/0953-8984/14/i=42/a=302}, year = {2002} }

7. Phase separation in polyfluorene blends investigated with complementary scanning probe microscopies R. G. Milner, A. C. Arias, R. Stevenson, J. D. Mackenzie, D. Richards, R. H. Friend, D.-J. Kang, and M. Blamire Materials Science and Technology, 2002 18, 7. [Bibtex]

   @article{Milner2002-07-01T00:00:00:0267-0836:759, author = {Milner, R. G. and Arias, A. C. and Stevenson, R. and Mackenzie, J. D. and Richards, D. and Friend, R. H. and Kang, D.-J. and Blamire, M.}, title = {Phase separation in polyfluorene blends investigated with complementary scanning probe microscopies}, journal = {Materials Science and Technology}, volume = {18}, number = {7}, year = {2002}, pages = {759-762}, url = {http://www.ingentaconnect.com/content/maney/mst/2002/00000018/00000007/art00012}, doi = {doi:10.1179/026708302225003910} }
8. ESEM imaging of polyfluorene blend cross-sections for organic devices C.M Ramsdale, I.C Bache, J.D MacKenzie, D.S Thomas, A.C Arias, A.M Donald, R.H Friend, and N.C Greenham Physica E: Low-dimensional Systems and Nanostructures, 2002 14, 1-2. [Abstract] [Bibtex]

   We report the use of environmental scanning electron microscopy (ESEM) to determine the phase separation in the cross-section of a 200 nm thick polyfluorene blend film, of the type used in polymer photovoltaic devices and LEDs. The micron and sub-micron surface phases are found to penetrate through the film to the underlying substrate, whilst smaller surface features do not necessarily propagate through the film. The observed cross-sectional structure helps to explain the optoelectronic response of these blends and shows that ESEM is an effective tool in the characterisation of polymer blend cross-sections.

   @article{Ramsdale2002268, title = {ESEM imaging of polyfluorene blend cross-sections for organic devices}, journal = {Physica E: Low-dimensional Systems and Nanostructures}, volume = {14}, number = {1-2}, pages = {268 - 271}, year = {2002}, note = {}, issn = {1386-9477}, url = {http://www.sciencedirect.com/science/article/pii/S1386947702003922}, author = {Ramsdale, C.M and Bache, I.C and MacKenzie, J.D and Thomas, D.S and Arias, A.C and Donald, A.M and Friend, R.H and Greenham, N.C}, keywords = {Solar cells} }

2001

1. Raman microscopy determination of phase composition in polyfluorene composites R. Stevenson, A. C. Arias, C. Ramsdale, J. D. MacKenzie, and D. Richards Applied Physics Letters, 2001 79, 14. [Bibtex]

   @article{stevenson:2178, author = {Stevenson, R. and Arias, A. C. and Ramsdale, C. and MacKenzie, J. D. and Richards, D.}, collaboration = {}, title = {Raman microscopy determination of phase composition in polyfluorene composites}, publisher = {AIP}, year = {2001}, journal = {Applied Physics Letters}, volume = {79}, number = {14}, pages = {2178-2180}, keywords = {polymer blends; Raman spectra; optical microscopy; phase separation; excitons; optical polymers}, url = {http://link.aip.org/link/?APL/79/2178/1}, doi = {10.1063/1.1407863} }
2. Efficient exciton dissociation via two-step photoexcitation in polymeric semiconductors Carlos Silva, Anoop S. Dhoot, David M. Russell, Mark A. Stevens, Ana C. Arias, J. Devin MacKenzie, Neil C. Greenham, Richard H. Friend, Sepas Setayesh, and Klaus Müllen Phys. Rev. B, 2001 64, [Bibtex]

   @article{PhysRevB.64.125211, title = {Efficient exciton dissociation via two-step photoexcitation in polymeric semiconductors}, author = {Silva, Carlos and Dhoot, Anoop S. and Russell, David M. and Stevens, Mark A. and Arias, Ana C. and MacKenzie, J. Devin and Greenham, Neil C. and Friend, Richard H. and Setayesh, Sepas and M\"ullen, Klaus}, journal = {Phys. Rev. B}, volume = {64}, issue = {12}, pages = {125211}, numpages = {7}, year = {2001}, month = sep, doi = {10.1103/PhysRevB.64.125211}, url = {http://link.aps.org/doi/10.1103/PhysRevB.64.125211}, publisher = {American Physical Society} }
3. Fluorescence scanning near-field optical microscopy of polyfluorene composites R. Stevenson, R. G. Milner, D. Richards, A. C. Arias, J. D. Mackenzie, J. J. M. Halls, R. H. Friend, D.-J. Kang, and M. Blamire Journal of Microscopy, 2001 202, 2. [Bibtex]

   @article{JMIJMI871, author = {Stevenson, R. and Milner, R. G. and Richards, D. and Arias, A. C. and Mackenzie, J. D. and Halls, J. J. M. and Friend, R. H. and Kang, D.-J. and Blamire, M.}, title = {Fluorescence scanning near-field optical microscopy of polyfluorene composites}, journal = {Journal of Microscopy}, volume = {202}, number = {2}, publisher = {Blackwell Science Ltd}, issn = {1365-2818}, url = {http://dx.doi.org/10.1046/j.1365-2818.2001.00871.x}, doi = {10.1046/j.1365-2818.2001.00871.x}, pages = {433--438}, keywords = {charge transfer, conjugated polymers, morphology, nanostructures, phase separation, photovoltaic devices, SNOM}, year = {2001} }
4. Photovoltaic Performance and Morphology of Polyfluorene Blends:_ A Combined Microscopic and Photovoltaic Investigation A. C. Arias, J. D. MacKenzie, R. Stevenson, J. J. M. Halls, M. Inbasekaran, E. P. Woo, D. Richards, and R. H. Friend Macromolecules, 2001 34, 17. [Bibtex]

   @article{doi10.1021/ma010240e, author = {Arias, A. C. and MacKenzie, J. D. and Stevenson, R. and Halls, J. J. M. and Inbasekaran, M. and Woo, E. P. and Richards, D. and Friend, R. H.}, title = {Photovoltaic Performance and Morphology of Polyfluorene Blends:_ A Combined Microscopic and Photovoltaic Investigation}, journal = {Macromolecules}, volume = {34}, number = {17}, pages = {6005-6013}, year = {2001}, doi = {10.1021/ma010240e}, url = {http://pubs.acs.org/doi/abs/10.1021/ma010240e}, eprint = {http://pubs.acs.org/doi/pdf/10.1021/ma010240e} }

2000

1. The use of tin oxide thin films as a transparent electrode in PPV based light-emitting diodes A.C Arias, L.S Roman, T Kugler, R Toniolo, M.S Meruvia, and I.A Hummelgen Thin Solid Films, 2000 371, 1-2. [Bibtex]

   @article{Arias2000201, title = {The use of tin oxide thin films as a transparent electrode in PPV based light-emitting diodes}, journal = {Thin Solid Films}, volume = {371}, number = {1-2}, pages = {201 - 206}, year = {2000}, note = {}, issn = {0040-6090}, url = {http://www.sciencedirect.com/science/article/pii/S0040609000009676}, author = {Arias, A.C and Roman, L.S and Kugler, T and Toniolo, R and Meruvia, M.S and Hummelgen, I.A} }

2. Photodiodes Based on Polyfluorene Composites: Influence of Morphology J. J. M. Halls, A. C. Arias, J. D. MacKenzie, W. Wu, M. Inbasekaran, E. P. Woo, and R. H. Friend Advanced Materials, 2000 12, 7. [Bibtex]

   @article{ADMAADMA498, author = {Halls, J. J. M. and Arias, A. C. and MacKenzie, J. D. and Wu, W. and Inbasekaran, M. and Woo, E. P. and Friend, R. H.}, title = {Photodiodes Based on Polyfluorene Composites: Influence of Morphology}, journal = {Advanced Materials}, volume = {12}, number = {7}, publisher = {WILEY-VCH Verlag GmbH}, issn = {1521-4095}, pages = {498--502}, keywords = {Composite materials, Conjugated polymers, Photodiodes, Photovoltaic cells, Polyfluorenes, Semiconductors}, year = {2000} }

1999

1. Organic photodiodes using polymeric anodes AC Arias, M Granström, K Petritsch, and RH Friend Synthetic metals, 1999 102, 1-3. [Bibtex]

   @article{arias1999organic, title = {Organic photodiodes using polymeric anodes}, author = {Arias, AC and Granstr{\"o}m, M and Petritsch, K and Friend, RH}, journal = {Synthetic metals}, volume = {102}, number = {1-3}, pages = {953--954}, year = {1999}, publisher = {Elsevier} }

2. Doped conducting-polymer\char21semiconducting-polymer interfaces: Their use in organic photovoltaic devices A. C. Arias, M. Granström, D. S. Thomas, K. Petritsch, and R. H. Friend Phys. Rev. B, 1999 60, [Bibtex]

   @article{PhysRevB.60.1854, title = {Doped conducting-polymer\char21{}semiconducting-polymer interfaces: Their use in organic photovoltaic devices}, author = {Arias, A. C. and Granstr\"om, M. and Thomas, D. S. and Petritsch, K. and Friend, R. H.}, journal = {Phys. Rev. B}, volume = {60}, issue = {3}, pages = {1854--1860}, year = {1999}, month = jul, doi = {10.1103/PhysRevB.60.1854}, url = {http://link.aps.org/doi/10.1103/PhysRevB.60.1854}, publisher = {American Physical Society} }
3. High efficiency polymer photodiodes Magnus Granström, Klaus Petritsch, Ana Claudia Arias, and Richard H Friend Synthetic metals, 1999 102, 1-3. [Bibtex]

   @article{granstrom1999high, title = {High efficiency polymer photodiodes}, author = {Granstr{\"o}m, Magnus and Petritsch, Klaus and Arias, Ana Claudia and Friend, Richard H}, journal = {Synthetic metals}, volume = {102}, number = {1-3}, pages = {957--958}, year = {1999}, publisher = {Elsevier} }

1998

1. Laminated fabrication of polymeric photovoltaic diodes M. Granstrom, K. Petritsch, A. C. Arias, A. Lux, M. R. Andersson, and R. H. Friend Nature, 1998 395, 6699. [Bibtex]

   @article{Granstrom1998, author = {Granstrom, M. and Petritsch, K. and Arias, A. C. and Lux, A. and Andersson, M. R. and Friend, R. H.}, title = {Laminated fabrication of polymeric photovoltaic diodes}, journal = {Nature}, volume = {395}, number = {6699}, url = {http://dx.doi.org/10.1038/26183}, doi = {10.1038/26183}, pages = {257-260}, year = {1998} }
2. Tin Oxide as a Cathode in Organic Light-Emitting Diodes Ana C. Arias, Joaquim R. Lima, and Ivo A. Hummelgen Advanced Materials, 1998 10, 5. [Bibtex]

   @article{ADMAADMA392, author = {Arias, Ana C. and de Lima, Joaquim R. and Hummelgen, Ivo A.}, title = {Tin Oxide as a Cathode in Organic Light-Emitting Diodes}, journal = {Advanced Materials}, volume = {10}, number = {5}, publisher = {WILEY-VCH Verlag GmbH}, issn = {1521-4095}, pages = {392--394}, year = {1998} }

Last modified: 2024-02-29