Low Voltage Oxide-based Thin Film Transistors Gated By Chitosan

Thin film transistors have attracted much attention due to their promisingapplication in many fields such as smart card, portable equipment, sensors and activematrix display drive array. Recently, there has been significant interest in developingnew kinds of solution-processed organic materials that can serve as gate insulators inthin-film transistors （TFTs）. The use of solution-processed polymers have attractedconsiderable attention due to the low-cost, large-area, nice film-forming,mechanically flexible and good compatibility characteristics. However, one of the keyproblems with existing organic TFTs is their large operating voltage, which oftenexceeds20V. To reduce the operation voltage, solution-processed polymer electrolytesand ionic liquids were proposed to be used as the gate dielectric due to their largecapacitance. Several effords have been made for developing such high-capacitancesolution-processed organic dielectrics, but the reported organic dielectrics forlow-voltage operation are still very limited, and the investigation of new organicdielectric with large capacitance is desirable for low-voltage TFT application.In this study, chitosan is found to be a new kind of solution-processed compatibleorganic polymer dielectric materials because of its low-cost and widely existingfeatures compared with others. Chitosan is a linear β-1,4-linked polysaccharie that isobtained by the partial deacetylation of chitin. As the polymer solid-state electrolytes,chitosan can format electric double layers along the two interfaces in contact with theelectrolyte, exhibiting a high capacitance, as large as8.06μF/cm². Thin filmtransistors with such an electric-double-layer capacitor exhibit a low operationvoltage and a high output current. In this paper, we report the thin film transistorsdevice gated by such solution-processed chitosan with different channel materials atroom temperature, and confirm the possibility for achieve low voltage thin filmtransistors by testing the characteristics of the thin film and the device.The first channel material was Indium-Zinc-Oxide （IZO）. The device used ITOglass substrate and also as common bottom gate. These transisitors exhibit a goodperformance, such as a good field-effect mobility of1.24cm²V^-1s^-1, a smallsubthreshold swing of0.3V/dec, a large on-off current ratio of106, and a lowoperation voltage of2V.The second channel material was Indium-Tin-Oxide （ITO）. These transisitors exhibit a good performance, such as a good field-effect mobility of3.89cm²V^-1s^{-1, asmall subthreshold} swing of0.23V/dec, a large on-off current ratio of10⁶, and a lowoperation voltage of1.5V.The solution-processed chitosan-based TFTs may have many potentialapplications for large-area, mechanically flexible, lightweight, and inexpensiveelecronic logic circuits.