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.

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Thermal cross-linking the bi-functional polymer thin-films at low temperature for gate dielectric application in solution processed organic field-effect transistors.

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A facile method for realizing both inkjet printed electrodes with improved resolution and patterned semiconductor islands was developed to fabricate all solution processed low-voltage organic thin film transistors (OTFTs). By reducing the surface wettability of the polymer gate dielectric layer through coating of a self-assembled monolayer (SAM), fine and narrow inkjet printed source/drain electrodes (a line width of about 35 mm) and short channels (about 15 mm) were formed with very good yield and uniformity using an inkjet printer with a 10 pL drop volume print head and limited registration accuracy.The coated SAM layer was then selectively removed by ultraviolet ozone treatment to create patterned wettable and less wettable regions to form self-assembled organic semiconductor islands. The fabricated low voltage OTFTs present a high quality semiconductor/dielectric interface and good device performance.