Yukun Huang

Low-Voltage pH Sensor Tag Based on All Solution Processed Organic Field-Effect Transistor

By reducing the sub-gap density of states at the channel, an all solution processed low-voltage organic field-effect transistor (OFET) was realized on a micrometer-thick SU8 gate dielectric layer. The device exhibits excellent operational stability under continuous bias stress. An integrated pH sensor tag was fabricated based on this low-voltage OFET, using an extended gate OFET for sensing and the other OFET as the load to convert the current signal to a voltage output for easy design of the subsequent readout circuit. With the low-voltage operation behavior and excellent operational stability of the OFET, the sensor tag was demonstrated to be operated in a 3.3 V battery powered electronic system for reliable pH sensing.

Bias Stress Stability Improvement in Solution-Processed Low-Voltage Organic Field-Effect Transistors Using Relaxor Ferroelectric Polymer Gate Dielectric

Low-voltage organic-field effect transi-stors (OFETs) using relaxor ferroelectric polymer poly (vinylidene fluoridetrifluoroethylene-chlorofloroethylene) P (VDF-TrFE-CFE)) were fabricated. The measured hysteresis loop and the threshold voltage shift under negative bias stress (NBS) are opposite to that of the reference device using low-

Silver nanowire/polymer composite soft conductive film fabricated by large-area compatible coating for flexible pressure sensor array

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Stable Thin-Film Reference Electrode on Plastic Substrate for All-Solid-State Ion-Sensitive Field-Effect Transistor Sensing System

CYTOP gate dielectric layer, in which the hysteresis and NBS-induced instabilities are explained by gate bias-induced charge trapping. The anomalous behaviors in the P (VDF-TrFE-CFE) OFETs are attributed to the stress-induced remnant polarization in P (VDF-TrFE-CFE), which induces additional mobile charges into the channel. By adding a thin CYTOP layer between the P (VDF-TrFE-CFE) layer and the semiconductor layer, the two effects of charge trapping and remnant polarization under gate bias are found to be neutralized with each other, resulting in low-voltage OFETs of negligible hysteresis and excellent NBS stability.

A Facile Photo Cross-linking Method for Polymer Gate Dielectrics and Their Applications in Fully Solution Processed Low Voltage Organic Field-effect Transistors on Plastic Substrate

Soft conductive films composed of a silver nanowire (AgNW) network, a neutral-pH PEDOT:PSS over-coating layer and a polydimethylsiloxane (PDMS) elastomer substrate are fabricated by large area compatible coating processes. The neutral-pH PEDOT:PSS layer is shown to be able to significantly improve the conductivity, stretchability and air stability of the conductive films. The soft conductive films are patterned using a simple maskless patterning approach to fabricate an 8 × 8 flexible pressure sensor array. It is shown that such soft conductive films can help to improve the sensitivity and reduce the signal crosstalk over the pressure sensor array.

Flexible-Blade Coating of Small Molecule Organic Semiconductor for Low Voltage Organic Field Effect Transistor

Solid-state thin-film reference electrodes (REs) were fabricated on plastic substrate based on a titanium/gold/silver/silver chloride (Ti/Au/Ag/AgCl) multi-layer metal structure for ion-sensitive field-effect-transistor (ISFET)-based sensing systems. A porous structure polyvinyl butyral membrane was formed on top to maintain a constant concentration of chloride as well as acting as a bridge between the electrolyte inside the membrane and the test solution. Excellent measurement stability was achieved with the fabricated RE, with a small drift rate of the open circuit potential less than 1.7 mV per hour. An all-solid-state ISFET sensing system was thus able to be built using the RE for pH measurement, showing excellent reproducibility. The system was finally applied for measuring different beverages, and the measurement results agreed well with those obtained with a commercial pH meter.

Improved bias stress stability for low-voltage polymer OTFTs with low-k/high-k bilayer gate dielectric

A simple and effective photochemical method was developed for cross-linking of polymer gate dielectrics. Laborious synthetic processes for functionalizing polymer dielectrics with photo-cross-linkable groups were avoided. The photo-cross-linker, BBP-4, was added into host polymers by simple solution blending process, which was capable of abstracting hydrogen atoms from polymers containing active C―H groups upon exposure to ultraviolet (UV) radiation. The cross-linking can be completed with a relatively long wavelength UV light (365 nm). The approach has been applied to methacrylate and styrenic polymers such as commercial poly(methylmethacrylate) (PMMA), poly(iso-butylmethacrylate) (PiBMA) and poly(4-methylstyrene) (PMS). The cross-linked networks enhanced dielectric properties and solvent resistance of the thin films. The bottom-gate organic field-effect transistors (OFETs) through all solution processes on plastic substrate were fabricated. The OFET devices showed low voltage operation and steep subthreshold swing at relatively small gate dielectric capacitance.

Subthreshold-Operated Low-Voltage Organic Field-Effect Transistor for Ion-Sensing System of High Transduction Sensitivity

A flexible-blade coating (FBC) approach, using a simple thin and flexible steel sheet as the meniscus guide, is developed to deposit the blended small molecule organic semiconductor (OSC) solution on substrate surface with pre-fabricated electrode patterns. During coating, the bottom edge of the used flexible steel film touches the substrate surface, but can bend up adapting to the surface morphology variation without causing any damages to the bottom electrodes. With this approach, little amount of very dilute ink solution can be used to coat the channel film, resulting in the greatest material saving among all reported methods. It is shown that, by using the FBC at a moving speed of 12 mm/s to deposit the OSC layer, all solution processed low-voltage organic field effect transistor composed of another polymer gate dielectric layer and inkjet printed metal electrodes were achieved over relatively large area with high performance and good uniformity.

Improved Sensitivity of Inkjet-Printed PEDOT:PSS Ammonia Sensor With Nonideal Morphology

Low-voltage solution-processed organic thin-film transistors (OTFTs) were developed using a large permittivity (high-k) polymer P(VDF-TrFE-CFE). It was shown that by inserting a thin, low-polar dielectric layer (CYTOP) between the high-k one and the channel, the bias stability was much improved due to screening of the dipole field from high-k dielectric.