Evaluation of Polyimide Gate Insulators of Pentacene Organic Thin Film Transistors

Abstract

Thin film organic transistors with Si/SiO₂ (300 nm)/pentacene (70 nm)/Au and Si/polyimide (320–690 nm)/pentacene (70 nm)/Au structures have been fabricated and their performances have been compared. The evaluated mobility of the holes of the SiO₂ transistor was 0.002 cm²/Vs, while those of the polyimide transistors were between 0.026–0.031 cm²/Vs. On the other hand, the threshold voltage of the SiO₂ transistor was −15 V, while the threshold voltages of the polyimide transistors were approximately +4 V independent of the polyimide thickness. This apparently strange behavior of the polyimide transistors might be attributed to some more negatively charged species accumulating at the polyimide/pentacene interface as the thickness of the polyimide film increases. The PI films had a significantly low level of the leakage current, and the estimated gate-drain leakage current of the corresponding transistor at the gate voltage of −100 V is estimated to be negligibly small compared with the source-drain current.

Keywords:

• gate insulator
• organic thin film transistor
• pentacene, polyimide

Acknowledgments

This work was supported by the Frontier Project of the Japan Ministry of Education, Culture, Sports, and Science and Technology.