ZnO thin-film transistor grown by rf sputtering using carbon dioxide and substrate bias modulation

Abstract

ZnO thin-film transistor (TFT) grown by rf magnetron sputtering in Ar/Oatmosphere shows inferior turn-off characteristics compared to ZnO TFT grown by other methods. We thought that reactions between Zn and Omight produce defects responsible for the poor turn-off behavior. In order to solve this problem, we studied sputtering growth in Ar/COatmosphere at 450°C. During sputtering growth, we modulated substrate dc bias to control ion supply to the substrate. After growth ZnO was annealed in COand Ogas. With these methods, our bottom-gate ZnO thin-film transistor showed 4.7 cm2/Vsec mobility, 4 × 10 6 on/off ratio, and -2 V threshold voltage.