Fujifilm Corp. has developed an n-type organic semiconductor and exhibited an organic transistor made of this material at Advanced Surface Technology Exhibition & Conference (ASTEC 2007) being held from February 21-23, 2007 at Tokyo Big Sight. The latest semiconductor uses a phthalocyanine material and can be treated as a liquid in the production process of organic transistors. In addition, it can be coated by using a simple technique such as spin coating and printing. Since it is relatively stable to oxygen, vapor and light irradiation, the semiconductor is reportedly able to extend the device life of organic transistors in which it is used. The company says that it can ship samples of the latest material if in small quantities. There have been only few n-type materials suitable for coating unlike the p-type commonly seen. Fullerene-based materials are known as n-type organic semiconductors that can be coated, but "they hardly operate in the air where their deterioration is severe," says a Fujifilm demonstrator.
ASTEC 2007 is being held concurrently with International Nanotechnology Exhibition & Conference (nano tech 2007).
The organic transistor showcased is obtained by first forming a gate insulating film (SiO2) on a p-type Si substrate, and then forming the source and drain electrodes before applying and drying the n-type organic semiconductor. A threshold voltage of 17 V and on/off ratio (ratio of the current value when the transistor is turned on to the value when it is turned off) exceeding 102 were achieved. The carrier mobility is 8.1 x 10-5. The company reports that, when placed in vacuum or N2 atmosphere, no deterioration was observed after the transistor was left for several months. Its durability in the air is presently under evaluation and it showed no significant deterioration after 1 week, the company said.