Investigation on the electrical characteristics of a pentacene thin-film transistor and its reliability under positive drain bias stress

Abstract

This study systematically investigates the effects of pentacene deposition rates and channel lengths on the electrical characteristics of pentacene-based organic thin-film transistors (OTFTs), and the performance degradation of OTFTs under the positive drain bias stress. With a slower deposition rate of the pentacene channel layer, the larger grain size is formed, and it improves the performance of pentacene-based OTFTs. As the channel length decreases, the threshold voltage (VTH) shifts toward the positive direction and the field-effect mobility (µFE) decreases, which are due to the drain-induced barrier lowering effect and the lower mobility in the active channel near the region of source/drain electrodes, respectively. In addition, we also propose a mechanism to present the channel length dependence on the field-effect mobility. Results also show that the pentacene-based OTFTs, which are under positive drain bias stress, exhibit greater performance degradation than those under negative drain bias stress. The greater performance degradation, the decreasing ION and the larger VTH shift are due to the greater trap state density (Ntrap) created in the bulk channel by the large lateral electrical field and the carriers injected into the gate insulator by the large vertical electrical field, respectively.