Enhancement Mode in ZnSnO Thin-Film Transistors with Ultrathin Al2O3 Contact Layer

ZnSnO-based thin-film transistor (TFT) is considered to be the most competitive candidate for next-generation displays and transparent electronics. However, ZnSnO TFTs usually work in depletion mode with a negative voltage. In this work, we designed a structure of ZnSnO/Al2O3 TFTs with ultrathin Al2O3 contact layers. As the thickness of tunnel layer increases, the threshold voltages of TFTs increase at first and then decrease. When the growth cycle of Al2O3 layer reaches 17 (with thickness of similar to 2 nm), the TFT has a positive threshold voltage of 2.3 V, as well as the best performances with an on-to-off current ratio of similar to 106, a saturation mobility of 23.5 cm2V- 1s- 1, and a small subthreshold swing of 0.57 V/decade. In this study, for the first time we propose an ultrathin contact method to modify the threshold voltage of amorphous oxide semiconductor (AOS) TFTs to get the enhancement mode without sacrificing mobility. It is expected that the method may open the door for practical applications of ZnSnO-based AOS TFTs.