An analytical model for short-channel organic thin-film transistors

Abstract

An analytical model that describes the operation of α-hexathienylene (α-6T) thin-film-transistors (TFTs) is presented. The current-voltage characteristics of TFTs with channel lengths ranging from 1.5 to 25 μm have been calculated after modifying the equations that describe the characteristics of conventional enhancement mode p-channel metal-oxide-semiconductor field-effect-transistors. The calculated current-voltage characteristics are compared with the experimental data. The model takes into account the non-inversion-mode operation of α-6T TFTs as well as short channel effects such as series parasitic resistance, channel length shortening, apparent threshold voltage, and apparent field-effect mobility. Furthermore, the field-effect mobility is observed to depend on longitudinal electric fields which are higher than 105 V/cm, and this effect is also included in the model. The highest field-effect mobility measured is 0.03 cm2/V s. From an analysis of measured data, the carrier mobility of field-induced positive carriers in α-6T is estimated to be at least as high as 0.08 cm2/V s.