Vertical‐ and lateral‐type organic FET using pentacene evaporated films

Organic semiconductor transistors are expected for flexible displays, information tags, and the like. However, organic transistors have some disadvantages of current density and speed of operation, because of their high resistivity and low carrier mobility. To improve their performance, it is valuable to analyze the mechanism of operation. We have compared characteristics of lateral‐ and vertical‐type transistors using pentacene evaporated films. The pentacene lateral‐type FET characteristics showed large variation due to fabrication parameters such as deposition rate, substrate temperature, and film thickness. It was found that evaporated pentacene thin films have large grain gaps, which disturb carrier flow along the channel formed pentacene film/SiO2 interface direction and make FET characteristics unstable. It is assumed that pentacene films are not suitable lateral‐type transistors. Accordingly, we have fabricated vertical‐type organic static induction transistors (SITs) using pentacene evaporated films. The pentacene SITs show high‐speed operation (cutoff frequency of 7.5 kHz) at relatively low voltages. Further optimization of SIT structure will improve the device performance.