High Performance Organic Transistors for Organic Electronic Applications

Abstract

Thin-film transistor (TFT) devices using organic semiconducting materials have attracted widespread attentions due to their low cost, flexible form factor, and easy fabrication. However, organic materials’ poor performance as compared to inorganic semiconductor such as silicon limits their applications. Specially, high-frequency operation in organic transistors has never been achieved with organic semiconducting material. One very attractive application for organic electronics is low-cost and flexible Radio Frequency Identification Tag (RFID), which requires relatively high frequency operation. Because of low mobility and high operating bias voltage, the current organic TFT is not appropriate for the most of applications including RFID.

The objective of this research is to develop the high performance organic transistor structures which are suitable for organic electronic applications. In designing, two major performance metrics of devices are focused to be improved, which are the on-current level with high on-off ratio and the cutoff frequency of the transistors. They are determined mainly by the carrier mobility, the injection of carrier at the metal/semiconductor boundary, and the passive parasitic components introduced by device geometry. In this study, three new structures are investigated, namely dual-organic layer Metal-Semiconductor Field-Effect Transistor (MESFET), depletion mode organic Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET), and organic Heterojunction Bipolar Transistor (HBT). Each of these devices is optimized to enhance the performance of the devices based on comprehensive theoretical modeling, and validated by simulation using TCAD. The devices with channel length of longer than 4 µm exhibit a few µA of on-current and ~10 MHz cutoff frequency. The results obtained in this work show those novel transistor structures can overcome the weakness of conventional organic TFTs and have great potential in realizing organic circuit applications in the future.