Frequency-dependent complex conductivity of an organic thin-film transistor

TL;DR

This study investigates the frequency-dependent complex conductivity of pentacene thin-film transistors by measuring impedance over a range of frequencies and modeling the device as a distributed RC network, revealing significant frequency effects.

Contribution

It introduces a method to extract the complex sheet conductivity of organic TFTs from impedance measurements using an RC transmission line model, highlighting frequency-dependent behavior.

Findings

Complex conductivity increases with frequency.

At high frequencies, sigma' and sigma'' become comparable.

On/off ratio decreases at higher frequencies.

Abstract

We measure the complex impedance between source/drain electrodes and the gate electrode of a pentacene thin-film transistor (TFT) at frequencies 50 Hz < omega/2pi < 20 kHz. Modeling the TFT as a distributed RC network (RC transmission line), we find that the data cannot be explained by a model including only a real, frequency-independent sheet conductivity. Instead, we use the RC transmission line model to extract the frequency-dependent complex sheet conductivity sigma(omega) = sigma'(omega) + jsigma"(omega) of the pentacene film. At high frequencies, sigma(omega) increases with frequency, sigma'(omega) and sigma"(omega) become similar in magnitude, and the on/off ratio is significantly reduced.