Unencapsulated Air-stable Organic Field Effect Transistor by All Solution Processes for Low Power Vapor Sensing

Abstract

With its excellent mechanical flexibility, low-cost and low-temperature processing, the solution processed organic field-effect transistor (OFET) is a promising platform technology for developing ubiquitous sensor applications in digital health, environment monitoring and Internet of Things. However, a contradiction between achieving low voltage operation and having stable performance severely hinder the technology to become commercially viable. This work shows that, by reducing the sub-gap density of states (DOS) at the channel for low operation voltage and using a proper low-k non-polar polymer dielectric layer, such an issue can be addressed. Stable electrical properties after either being placed for weeks or continuously prolonged bias stressing for hours in ambient air are achieved for all solution processed unencapsulated OFETs with the channel being exposed to the ambient air for analyte detection. The fabricated device presents a steep subthreshold swing less than 100 mV/decade, and an ON/OFF ratio of 106 at a voltage swing of 3 V. The low voltage and stable operation allows the sensor made of the OFET to be incorporated into a battery-powered electronic system for continuously reliable sensing of ammonia vapor in ambient air with very small power consumption of about 50 nW.

Current Status and Opportunities of Organic Thin-Film Transistor Technologies

“…Recently, several studies have shown that it is feasible to reduce the subgap density of states (DOS) at the channel through solution processed OSCs for realizing low-voltage OTFTs with small gate dielectric capacitance [74], [110]. Therefore, a relatively thick low-k polymer dielectric can be applied, which can help to achieve excellent stability and also has wide material choices [71], [72], [83], [86], [87]. Such a low-voltage OTFT can be fabricated by inkjet printing all layers including electrodes, gate dielectric, OSC, and encapsulation layers, proving the most economic manufacturing approach [111].…”

“…However, from an industry perspective, to achieve a commercially competitive OTFT technology, solution processable polymer dielectrics are preferable, because of their potential for low-cost manufacturing and excellent mechanical flexibility, though some vacuum deposited organic dielectrics have also been studied to provide high-insulation properties [66], [67]. Various solution processable polymer dielectrics (e.g., CYTOP [40], polystyrene [68], BCB [69], polyimide (PI) [70], PVC [71], poly (methyl methacrylate) (PMMA) [40], SU8 [72], polyvinylphenol (PVP) [73], and poly(vinyl alcohol) (PVA) [74]) have thus been extensively studied as summarized in Table I. However, most polymeric dielectrics have relatively low k. As a result, with a thick dielectric layer required to eliminate gate leakage and be compatible for large area solution-based processing, the reported OTFTs often require an operation voltage of a few tens of volts or even above 100 V.…”

“…With a fixed silicon chip design and additive printing of the OTFTbased front end for the custom design, this hybrid integration would provide a low cost and versatile solution to "smart tag" systems. For this integration, with the fully-printable low voltage and stable OTFT, sensor tags were made to be operated in a low-voltage (3.3 V) battery powered electronic system for long term and repeatable ammonia and pH sensing, respectively [24], [71].…”

Experimental and Computational Analyses of Temperature Distributions in Slope-Type Thin-Film Thermoelectric Generators at Different Slope Angles and Evaluation of Their Thermoelectric Performance

“…This P max was insufficient to drive the various sensors. For example, sensors for ammonia vapor in ambient air require an electrical power of approximately 50 nW [43]. The comparison of the experimental and theoretical results shows a similar trend for the slope angle's dependence of P max .…”

Fast Development of Self‐Assembled, Highly Oriented Polymer Thin Film and Observation of Dual Sensing Behavior of Thin Film Transistor for Ammonia Vapor

“…In recent years, rapid industrial development has created a global concern due to severe air pollution and the tremendous effect on our daily life due to the polluted environment. Environmental care, particularly air quality monitoring to a safe limit has become a necessity for surveilling the quality of our daily life, particularly in the industrial environment and fertilizer industry, where ammonia release is very common . Therefore, the ammonia gas sensor has emerged as one of the most promising devices to monitor the food quality and to ensure the safety of the industrial working environment because of its severe complications and adverse impacts on the entire living organism …”