Organic Field Effect Transistors

This article begins with a brief overview of the structure, physical characteristics, and peculiarities of organic field effect transistors. The main differences from the silicon MOSFET are emphasized. The results of poly 3-hexylthiophene and cross-linked polyvinyl alcohol top gate-bottom contact transistors with different channel lengths fabricated by standard photolithography and plasma etching are described. Transistors showed good charge mobility, high ION/IOFF and excellent environmental stability. The Shockley model and the Transmission Line Method (TLM) were applied to characterize the transistors. Mobility was extracted by both methods and differences were discussed. The shorter the channel length and the higher the conductivity of the semiconductor, the greater the impact of contact resistance. In these cases, the use of TLM for parameters extraction becomes essential. The transistors were submitted to extended current-voltage measurements and drain current degradation was observed. Drain current as a function of the integral charge passing through the channel was investigated. The strong decrease in current was found to be related to reduced mobility of charge carriers. Reasons for this behavior are suggested.