Phosphorus, a crucial nutrient for organism development in the ecosystem, poses a significant environmental challenge due to the excessive discharge of phosphates into water, leading to widespread algae proliferation and degradation of water quality. Therefore, it is essential to develop a real-time monitoring method for determining phosphorus concentration in water. In this study, we functionalized the electrode with lanthanide-based receptors and utilized a portable potentiostat with amperometric measurement to investigate phosphate sensing within a real-time monitoring platform. This study provides a basis for portable electronics in phosphate monitoring in environmental sensing.
Organic retinomorphic sensors are particularly effective for motion detection, offering the advantage of in-sensor processing that can remove repetitive static backgrounds. In this study, we investigate the important impact of high-k dielectrics in promoting charge accumulation to increase the intrinsic photo-response of photo-sensitive capacitors within this promising framework. We demonstrate a retinomorphic sensor array to detect the motion of a sample moving at different speeds and directions. These proof-of-concept results represent a promising advance toward scalable integration of organic retinomorphic arrays to meet the growing demand for more efficient motion tracking systems.
Understanding the influence of environmental changes on marine life is important to ecological sustainability and aqua-culture. Existing sensors are limited by size and costs that preclude widespread non-intrusive monitoring. This work reports on various organic electrochemical transistors (OECTs) to track dissolved oxygen concentration and nutrient runoff in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents. We present the dual-gate configuration that extended the device stability window by preventing undesirable reactions at the OECT channel. Specifically, the sensor achieved a detection limit of 0.5 ppm dissolved oxygen concentration in seawater. We engineer a system to monitor the correlation of oyster movement with dissolved oxygen in its environment, and it offers a new design to realize compact, highly sensitive, economical in-situ sensors for harsh marine environments.
In this presentation, we discuss point-of-use applications for motor skills characterization. There is no objective metric for evaluating motor skill training progress, and current assessments rely on qualitative surveys. We have fabricated an instrumented glove with pressure and motion sensors for motor characterization. This glove is useful for characterizing motor skills of people suffering from hypertonicity, a neuromuscular disorder that causes muscle stiffness/resistance and jerky movement. Analyses of force versus velocity show movement-dependent muscle resistance in a patient with hypertonicity. Through the flexible sensor systems, the shift from subjective scores to objective measurement will promote better diagnosis and dramatically improve the accuracy in tracking patient response to therapy.
Organic infrared photodetectors with improved detectivity would enable low-cost spectroscopic analysis and other imaging applications. However, organic infrared materials are challenged by inefficient transduction due to increasing recombination with lower bandgaps. Here we report the approach of phototransistor structures to increase signal gain for materials responsive from 1100 to 1800 nm with a peak absorption of 1550 nm. The device is consisted of a bilayer transistor channel that decouples charge photogeneration and transport, enabling charge injection for signal gain. The frequency and light dependence of the phototransistor characteristics are analyzed to understand the change in photoconductive gain under different working conditions. Lastly, we will also compare the phototransistor performance to a metal-insulator-semiconductor capacitive detector, to evaluate the potentials and tradeoff for these alternative structures for infrared detection.
This talk will present the designs of polymeric upconversion imagers that combine photo-sensing and display in a compact structure, to enable infrared visualization to 1300 nm. The organic photodetectors are further improved by incorporating a new heterojunction interlayer to trigger trap-assisted photomultiplication. The interlayer served to suppress the dark current and enhance the photoresponse. The large active area of 2 square cm enabled demonstrations such as object inspection, imaging through smog, and concurrent recording of blood vessel location and blood flow pulses.
With our marine ecosystems under threat from climate change, there is an urgent need to continuously monitor marine conditions. One key indicator is the dissolved oxygen level, but existing sensors are limited by size and costs that preclude widespread non-intrusive monitoring. This work reports a new dual-gate design based on organic electrochemical transistors (OECTs) to track dissolved oxygen concentration in seawater, a highly challenging matrix owing to its high ionic strength and multitude of chemical interferents. We present the novel operating principle, by deriving the channel conductance with respect to potentials on the two gates. The sensor achieved a detection limit of 0.5 ppm dissolved oxygen concentration in seawater. The device demonstrated reliable operation over five days and was capable of monitoring oxygenation changes arising from the photosynthesis cycles of saltwater macro-algae.
Filtering capacitors are essential components in electronic circuits for converting high frequency alternating current (AC) into direct current (DC) with minimal energy dissipation. Yet the bulkiness and rigid configuration of traditional filtering capacitors (e.g. Aluminum electrolyte capacitors) impose size restrictions. Supercapacitor offers the potential of high capacitance density to function as miniaturized filtering capacitors. However, the charging/discharging speed of supercapacitors tend to be slow below 100 Hz and limit their use in ac filtering. To understand the mechanisms of the charging/discharging process in electrode materials, this study measures electrochromic properties of the conducting polymer PEDOT, one of the most widely used electrode materials in organic supercapacitors. The contributions of redox reactions and electrical double layer to the total capacitance were quantified. We found that redox reactions were active and dominant when the switching frequency was higher than 100 Hz. The rate of redox reactions for PEDOT changes with different applied potential due to the changing conductivity of PEDOT . The main bottleneck to fast kinetics were due to the interfacial impedance between the Faradaic materials and the current collector electrode. These results will guide future optimization of the materials and morphology design for filtering capacitor electrode.
Low-cost sensors for in situ monitoring of ocean conditions will provide critical information to understand how nutrients and oxygen levels correlate to fish kills and aquaculture issues. The compatibility of organic electrochemical transistors (OECTs) with aqueous environments makes them promising sensor components in an ocean sensing platform. Our OECTs is based on PEDOT as channel and carbon as electrodes. Here we design the sensor for detecting dissolved oxygen (DO) and explain the challenges in balancing the oxygen reduction reaction with the doping/dedeoping process in OECTs. We will show the device sensitivity and stability with respect to DO concentration under simulated marine environment.
Low-cost, compact sensor systems for in-situ monitoring of marine conditions will provide critical information to understand how pollution and oxygen levels correlate to fish kills and aquaculture issues. The compatibility of organic electrochemical transistors (OECTs) with aqueous environments makes them promising sensor components in an ocean-sensing platform. This presentation will discuss the development of dissolved oxygen (DO) sensors, which has a detection limit to 3 ppm as required in marine studies. The challenges in balancing the oxygen reduction reaction with the doping/dedeoping process in OECTs will be shown and mitigated by using multiple voltage rails. The DO sensor will be used in conjunction with pH ion-selective transistors, to provide multi-modal measurements that assess how these parameters correlate to water quality. We will show the device sensitivity and stability under simulated marine environment.
Shortwave Infrared (SWIR) light imaging is critical in a variety of applications ranging from medical diagnosis, industrial inspection and safety monitoring, etc. due to their information-rich merits. This report presents an organic up-conversion imager for SWIR light imaging. The imager integrates an organic SWIR photodiode (OPD) and an organic light emitting diode (OLED) to convert invisible SWIR image directly into visible image without sophisticated data acquisition and processing electronics. Our imager is capable of imaging light signal with wavelength up to 1400 nm, due to the sensitivity of the novel OPD. The design guidelines for attaining highly sensitive and low voltage up-conversion imagers are revealed by studying the photo responsivity and current-voltage characteristics of the SWIR PD and OLED. The results show that the elimination of deep trap states in the SWIR PD favors the photo sensitivity and reduces the operating voltage of the up-conversion imager.
A Printed pressure sensor is demonstrated to measure dynamic pressure of the blood flow in an artificial blood vessel construct. The sensor is an oscillator with printed inductor and compressible porous PDMS capacitor which responds to the changing pressure. The variable capacitance of capacitor modulates the resonance frequency of the LC oscillator. Outside the vessel a readout coil connected to a network analyzer measures the resonance frequency of the LC oscillator, which changes with the applied pressure in the liquid environment. The inductor coils in the sensor circuit and outer readout coil are optimized for higher wireless response by increasing the trace conductivity and geometric designs. Also the porous PDMS capacitor is tuned by pore size and concentration to increase the reliability and sensitivity under changing pressure. The sensor responded to dynamic liquid pressure in the range of 30~170 mmHg within 50 msec, and the current measurement setup followed pulse frequency up to 144 beats per minute. The application of this sensor can be extended to monitoring fluid pressure in other structures, such as in microfluidic chips and environmental monitoring devices.
Short wavelength infrared (SWIR) sensors are important to applications in environmental monitoring, medical diagnosis and optical communications, but there are only a few organic semiconductors that show optoelectronic response in the SWIR region. Recently we demonstrated a family of novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the bulk heterojunction photodiodes based on these polymers show detectivity up to 1E11 Jones at a wavelength of 1.37 micron, with absorption edge extending out to 1.7 micron. A SWIR photodiode was incorporated into the etalon-array reconstructive spectroscopy system to demonstrate its imaging capabilities.
As the initial performance is very promising, we proceed to investigate the stability of the encapsulated devices and to infer the degradation mechanisms. The performance of photodiodes were monitored by IV measurement, external quantum efficiency (EQE) and electrochemical impedance spectroscopy. The IV measurement and electrochemical impedance spectroscopy were conducted both in the dark and under illumination, to track over several weeks the change in charge generation and recombination processes under the short circuit and open circuit conditions. The characteristics from band-to-band absorption and from absorption in charge-transfer states were compared to quantify the lifetime and recombination losses of photogenerated carriers in these devices.
KEYWORDS: Short wave infrared radiation, Infrared radiation, Infrared photography, Chemical analysis, Polymers, Transistors, Electronics, Infrared detectors, Signal to noise ratio, Analytical research
Low-cost infrared photo-transistors with improved detectivity (i.e. higher signal-to-noise ratio) could find further use in spectral analysis, which is important for chemical identifications, as well as other applications from environmental monitoring to optical communications. Accordingly, the main goal of this research is to advance printed, flexible photo-transistors by using a family of novel donor-acceptor polymers with narrow bandgap that are responsive in the short wavelength infrared (SWIR) region. In particular, the transistors show optical response extending out to a wavelength of 1.8 micrometer. The external quantum efficiency and the rectification ratio are used to characterize the performance of devices with different polymer layer thickness, in order to optimize detectivity. The individual transistors could further be exploited for the fabrication of integrated arrays for bio-medical and/ or robotic applications. It paves the way to large-area, conformal designs that are currently not achievable with conventional inorganic SWIR materials.
Wireless sensing has broad applications in a wide variety of fields such as infrastructure monitoring, chemistry, environmental engineering and cold supply chain management. Further development of sensing systems will focus on achieving light weight, flexibility, low power consumption and low cost. Fully printed electronics provide excellent flexibility and customizability, as well as the potential for low cost and large area applications, but lack solutions for high-density, high-performance circuitry. Conventional electronics mounted on flexible printed circuit boards provide high performance but are not digitally fabricated or readily customizable. Incorporation of small silicon dies or packaged chips into a printed platform enables high performance without compromising flexibility or cost.
At PARC, we combine high functionality c-Si CMOS and digitally printed components and interconnects to create an integrated platform that can read and process multiple discrete sensors. Our approach facilitates customization to a wide variety of sensors and user interfaces suitable for a broad range of applications including remote monitoring of health, structures and environment. This talk will describe several examples of printed wireless sensing systems. The technologies required for these sensor systems are a mix of novel sensors, printing processes, conventional microchips, flexible substrates and energy harvesting power solutions.
Photosensors responsive to the short wavelength infrared (SWIR) spectra are used in a variety of applications including environmental monitoring, medical diagnosis and optical communications. However, most organic semiconductors do not absorb in the SWIR region. Here we show novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the polymers are processed into photodiodes with structure of ITO/PEDOT:PSS/Bulk Heterojunction (BHJ)/Al. The performance of devices with different polymer structures are compared through metrics including detectivity, quantum efficiency, response time and rectification ratio, to determine the mechanisms of charge recombination loss in charge transfer states and charge transport process. We also use different solution-processed interfacial functional layers (e.g. ZnO, MoO3, TiO2) as electrode interface structures. The results provide guideline for selecting suitable polymers and design of device structures, to enable high performance SWIR photosensor via scalable solution-processed fabrication.
In electronic systems, components often require different supply voltage for operation. In order to meet this requirement and to optimize power consumption for flexible electronics, we demonstrate a pulsed voltage multiplier that boosts the voltage at specific circuit nodes above the supply voltage. A five-stage pulsed voltage multiplier is shown to provide an output voltage up to 18 V from a supply voltage of 10 V, with minimum 10 ms pulse rise time for a 70 pF load.
A key requirement for the pulsed voltage multiplier circuit is low device leakage to boost the output voltage level. To minimize leakage, the composition of the organic semiconducting layer is modified by blending an insulating polymer with the small molecule semiconductor. This modification allows control over the transistor turn-on voltage, which enables low leakage current required for operation of the circuits. The printed multiplier allows a single power source to deliver multiple voltage levels and enables integration of lower voltage logic with components that require higher operating voltage, for example, in the case of recording data into memory cells in sensor tags.
With the recent improvements in printed devices, it is now possible to build integrated circuit systems out of printed devices. The combination of sensor, logic, and rewritable memory will greatly enhance the functionalities of printed electronics. We have demonstrated integrated sensor tags based on organic complementary circuits patterned by inkjet printing. One example is a temperature threshold sensor tag, wherein if the thermistor temperature exceeds a pre-set threshold, the control circuit generates a pulse to write into a nonvolatile ferroelectric memory cell. The trigger temperature is set by adjusting the bias voltage across the thermistor bridge to match the trigger voltage of the printed threshold circuit, and the threshold temperatures has been tuned between 8 °C and 45 °C with a bias voltage below 30V.
Two types of printable conductor and a bilayer gate dielectric are evaluated for use in all-additive, inkjetprinted
complementary OTFTs. The Ag nanoparticle ink based on nonpolar alkyl amine surfactant or stabilizer enables
good charge injection into p-channel devices, but this ink also leaves residual stabilizer that modifies the transistor backchannel
and shifts the turn-on voltage to negative values. The Ag ink based on polar solvent requires dopant
modification to improve charge injection to p-channel devices, but this ink allows the OTFT turn-on voltage to be close
to 0 V. The reverse trend is observed for n-channel OTFTs. For gate insulator, a bilayer dielectric is demonstrated that
combines the advantages of two types of insulator materials, in which a fluoropolymer reduces dipolar disorder at the
semiconductor-dielectric interface, while a high-k PVDF terpolymer dielectric facilitates high gate capacitance. The
dielectric is incorporated into an inverter and a three-stage ring oscillator, and the resulting circuits were demonstrated to
operate at a supply voltage as low as 2 V, with bias stress levels comparable to circuits with other types of dielectrics.
The combination of organic semiconductors and emerging
solution-dispersible metal and metal oxide nanoparticles
and nanowires enables the fabrication of electronic devices that are fully built from solution. This establishes a new
device-processing platform that, in turn allows integration of functionality in systems not feasible in any
conventional semiconductor technology. Examples of novel applications and systems enabled by this include:
large-area, ultra light and flexible power harvesting,
logic-integrated sensing and memory technologies. In this
paper we discuss the use of organic Thin Film Transistors (TFTs) based on printed solution-processed materials for
displays and memory applications. Polarizable solution-processed dielectrics and polymer semiconductors were
integrated in the fabrication of non-volatile analog memory arrays. The stability of memory TFTs over 7 days was
studied and characterized, and a stable process to achieve all printed TFTs is presented.
In this paper we report on the use of two solution-processable polymeric and molecular n-channel semiconductors for the
fabrication of transistors and CMOS inverters by gravure printing and inkjet printing. Furthermore, the injket-printed
TFT/invertor stability characteristics are analyzed and discussed.
Methods used to deposit and integrate solution-processed materials to fabricate thin film
transistors by ink-jet printing are presented. We demonstrate successful integration of a complete
additive process with the fabrication of simple prototype TFT backplanes on glass and on flexible
plastic substrates, and we discuss the factors that make the process possible. Surface energy control
of the gate dielectric layer allows printing of the metal
source-drain contacts with gaps as small as
10 um as well as the polymer semiconductor whose electronic properties are very sensitive to
surface energy. Silver nanoparticles are used as gate and data metals, and a polythiophene
derivative (PQT-12) is used as the semiconducting layer, and the gate dielectric is a polymer. The
maximum processing temperature used is 150°C, making the process compatible with flexible
substrates. The ION/IOFF ratio is 105-106, and TFT mobilities of 0.05 cm2/Vs were obtained. The electrical stability of the
all-printed transistors was compared to conventional fabrication methods and it is shown to be acceptable for array operation. Here we discuss the yield of the printing process and show arrays that are integrated with E-ink media to form flexible paper-like displays.
A prototype of mechanically flexible photosensor arrays using organic bulk heterojunction photodiodes has been developed on plastic substrates. The integration of a 4 μm thick sensor layer onto a flexible amorphous silicon thin-film transistor backplane gave an image sensor array with 35% external quantum efficiency and noise equivalent power of 30 pW/cm2 at reverse bias voltage of -4 V. Sensor properties such as sensitivity and spatial resolution are determined and compared to those of amorphous silicon photodiodes.
We present an electric force microscope and transport study of the degradation of the contact between Au and TPD, a triarylamine widely employed as a hole transporting layer in light emitting diodes. TPD was dispersed into a polystyrene (PS) binder and spin casted onto a quartz substrate with coplanar gold electrodes. Electric force microscopy was used to map the electrostatic potential drop in the device channel while a voltage was applied and the current was measured. Two contact degradation mechanisms were observed. When the TPD-PS film was allowed to age in high vacuum, the TPD crystallized out of solution. We show that the observed loss of current is the result of both a decrease in bulk mobility and a decrease in injection efficiency. The operating temperature of a freshly prepared device was then varied from 296 K to 330 K to simulate heating that might occur during light emitting diode operation. While the current increased in an apparently smooth way as the temperature was raised, electric force microscopy revealed that the underlying injection efficiency had undergone a dramatic change. Above a temperature of 330 K, running current through the device led to a dramatic decrease in injection efficiency which we found was associated with the creation of a dipole layer at the injecting contact. Upon decreasing temperature, we found that a measurable charge remained in the device channel when the applied voltage was switched to zero. The decay of the associated electrostatic potential, which appears to be governed primarily by charge-charge repulsion and not diffusion, provides an estimate the zero-field mobility of the holes in the film.
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