The N-type organic field effect nonvolatile photo memory transistors based on modified polymeric electrets
Yu-Fu Wang1, Chin-Yang Lin1, Min-Ruei Tsai2, Horng-Long Cheng1, Wei-Yang Chou1*
1Department of Photonics, National Cheng Kung University, Tainan, Taiwan
2Polyimide Department, Daxin Materials Corporation, Taichung, Taiwan
* presenting author:Yu-Fu Wang,
In the past few decades, organic field-effect transistor-based memories have become high anticipation in organic electronics because of their unique advantages, such as solubility processing, excellent compatibility with integrated circuits, flexibility, and non-destructive reading out of digital signals. Based on review reports, the polymeric dielectric with charge storage ability was often used as a charge trapping layer in OFET-based memories. To achieve significant trapping effect in memory device, we propose a new polyimide electret with a quasi-permanent electrostatic polarization on side chain moiety, which provides a localized distribution of charge trap states. An apparent shift of transfer curve was observed for the polyimide-based memory device when programming and erasing processes were conducted on it. Unfortunately, the window of memory was limited by the relatively low concentration of minority carrier in n-type semiconductors (holes) to erase the trapped electrons. When the light illumination was performed at erasing state simultaneously, the memory window can be extremely extended for ten times larger than that of unexposed device. This result can be attributed to large shift of threshold voltage toward both negative and positive voltages, indicating that a behavior of am-bipolar charge storage occurs in our memory device. Owing to the generation of quasi-permanent dipoles on the polar groups of PI under a gate bias pulse, the photo-induced electron/hole pairs within organic semiconductor can be efficiently dissociated by gate field and dipole-induced field and then the trapped electrons were erased by photo-induced holes. The ratio of ON/OFF state current for PI-memory device can be maintained over three orders for 103s, showing that the behavior of long-lifetime charge traps can be applied in nonvolatile memory device.
Consequently, the superior n-operating memory transistor with an extra-high memory window and a field-effect carrier mobility of 0.14 cm2/Vs was successfully fabricated. The memory device has great potential to apply in photo memories and sensors due to its high sensitivity under light illumination.

Keywords: organic transistor, photo memory, n-type semiconductor, polyimide