Low-voltage-drive and high output current ZnO thin-film transistors with sputtering SiO2 as gate insulator

Low-voltage-drive ZnO thin-film transistors (TFTs) with room-temperature radio frequency magnetron sputtering SiO2 as the gate insulator were fabricated successfully on the glass substrate. The ZnO-TFT operates in the enhancement mode with a threshold voltage of 4.2 V, a field effect mobility of 11.2 cm2/V s, an on/off ratio of 3.1 × 106 and a subthreshold swing of 0.61 V/dec. The drain current can reach to 1 mA while the gate voltage is only of 12 V and drain voltage of 8 V. The C–V characteristics of a MOS capacitor with the structure of ITO/SiO2/ZnO/Al was investigated. The carrier concentration ND in the ZnO active layer was determined, the calculated ND is 1.81 × 1016 cm−3, which is the typical value of undoped ZnO film used as the channel layer for ZnO-TFT devices. The experiment results show that SiO2 film is a promising insulator for the low voltage and high drive capability oxide TFTs.