A simple shift register circuit for depletion-mode oxide TFTs

Abstract

We report the simplest shift register circuit compatible with metal-oxide thin-film transistors (TFTs). Since the oxide TFT often exhibits depletion-mode characteristic, it is impossible to guarantee stable operation of the shift register when we resort to conventional circuit scheme. In order to resolve this problem, we employed two different low-voltage levels for the clock signals. As a result, we could turn off the depletion-mode oxide TFTs completely with sufficient voltage margin. According to the simulation results, the new shift register composed of only 6 TFTs operates properly over the threshold voltage (V-T) range of -5-+9 V. The fabricated circuit also worked successfully even though V-T of the TFTs ranged from -5 V to -3 V. (C) 2012 Elsevier Ltd. All rights reserved.