ELECTRICAL CHARACTERISTICS AND PHOTOLYTIC TUNING OF POLY(3-HEXYLTHIOPHENE) THIN-FILM METAL-INSULATOR-SEMICONDUCTOR FIELD-EFFECT TRANSISTORS(MISFETS)

In this paper, we present results on the electrical characteristics of both thick and thin film Polymer metal-insulator-semiconductor field- effect transistors (MISFETs) based on poly(3-hexylthiophene) semicondu cting substrate. These MISFETs were fabricated in eight steps using co nventional semiconductor processing technology.The MISFETs had excelle nt current-voltage characteristics and showed little degradation with time. Electrical parameters of threshold voltage, mobility, and transc onductance were -1 V. 10(-4)-10(-5) cm2 V-1 s-1. and 10(-9) S, respect ively. These values are typical of pi-conjugated polymer-based MISFETs . Electrical transport in MISFETs were by both bulk (or resistive) and FET-like mechanisms in the thick film transistors. The resistive curr ent component and the electrical characteristics were found to be tuna ble by photolytic degradation of the semiconducting polymer. In this p rocess. the semiconducting pi-conjugated regions were spatially conver ted to insulating regions by novel photo-oxidative chemistry. We were also successful in modelling the MISFETs as an intrinsic FET with para sitic source and drain resistances in series with it and a varistor (f or the bulk current component) in parallel with the intrinsic FET. Usi ng this circuit model. we obtained very good agreements between SPICE simulations and the experimental results.