Flexible vertical-channel thin-film transistors using In-Ga-Zn-O active channel and polyimide spacer on poly(ethylene naphthalate) substrate

A flexible vertical-channel thin-film transistor (VTFT) with a channel length of 400 nm was fabricated on a poly (ethylene naphthalate) substrate. The vertical gate-stack composed of gate electrode/gate insulator/active channel was prepared by a conformal atomic layer deposition and a dry etching process of an organic polyimide spacer. The transfer characteristics of the fabricated flexible VTFT were well confirmed after the postannealing process at 200 degrees C, in which the on/off ratio was obtained to be 1.8 x 10(2). The threshold voltage shifts were estimated to be +6.1 and -4.5 V under the positive and negative bias-stress conditions for 10(4) s, respectively. The device characteristics showed no remarkable degradation when delaminating from the carrier glass substrate. Furthermore, there were no marked changes in transfer curves even when the device was bent with a radius of curvature of 10mm. A suitable choice of spacer material, optimization of the dry etching process, and employment of ultra-thin flexible film substrate were suggested to appropriate solutions for enhancing the device performance of the proposed flexible VTFTs. Published by the AVS.