Frequency Dependences of Displacement Current and Channel Current in Pentacene Thin-Film Transistors

Abstract

We demonstrate the gate voltage (VGS) frequency dependences of displacement current (Idis) and channel current (IDS), which were simultaneously measured under the application of a triangular wave of VGS and a constant drain voltage in top-contact pentacene organic thin-film transistors (OTFTs). Carrier injection and carrier transport properties, such as field-effect mobility, threshold voltage, and carrier injection voltages at the source and drain electrodes, were evaluated; they showed no frequency dependences at frequencies between 1 and 50 kHz. From the source current -VGS and drain current -VGS characteristics, a charge sheet at the interface of the pentacene thin-film and gate dielectric was found to form below the source and drain electrodes in this frequency range. For the practical use of OTFTs, a simultaneous measurement system for Idis and IDS is a simple and powerful technique for evaluating both carrier injection and carrier transport properties under OTFT operations.