Thin-film transistors based on ZnO fabricated by using radio-frequency magnetron sputtering

We report on enhancement-mode thin-film transistors (TFTs) using ZnO as an active channel layer deposited by radio-frequency (rf) magnetron sputtering at 350°C. The TFT structure consisted of ZnO as a channel, SiN _x as a gate insulator, and indium tin oxide (ITO) as a gate, which were deposited onto a Corning glass substrate. Atomic force microscopic images showed an atomically flat morphology of ZnO channel layer with a root-mean-square roughness of 0.7 nm. The X-ray diffraction pattern revealed a dense columnar structure of closely packed ZnO nano grains along the c-axis. The transfer characteristics of a typical ZnO TFT exhibited a field effect mobility of 1.698 cm ²/V·S, a drain current on/off ratio of 10 ⁵, a low off-current value on the order of 10 ^-10 A, and a threshold voltage of 2.5 V.