Electrical properties of ZnO-based bottom-gate thin film transistors 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 300 deg. C. The TFT structure consisted of ZnO as a channel, SiNx as a gate insulator and indium tin oxide (ITO) as a gate which were deposited onto a Corning glass substrate. X-ray diffraction pattern revealed that 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 31 cm2/V s, a drain current on/off ratio of 104, the low off-current value in the order of 10-10 A, and a threshold voltage of 1.7 V. The transparent ZnO TFT exhibited n-channel enhancement mode behavior.