A high-performance ZnO thin film transistor ZnO-TFT with SiO2/Ta2O5/SiO2 (STS) multilayer gate insulator is fabricated by sputtering at room temperature Compared to ZnO-TFTs with sputtering SiO2 gate insulator, its electrical characteristics are significantly improved, such as the field effect mobility enhanced from 11.2 to 52.4 cm(2)/V s, threshold voltage decreased from 4.2 to 2 V. and sub-threshold swing improved from 0 61 to 0.28 V/dec. The improvements are attributed to the high gate capacitance (from 50 to 150 nF/cm(2)) as well as nice surface morphology by using dielectric with high k Ta2O5 sandwiched by SiO2 layers. The capacitance-voltage characteristic of a metal-insulator-semiconductor capacitor with the structure of Indium Tin Oxide/STS/ZnO/Al was investigated and the trap charges at the interface or bulk is evaluated to be 2 24 x 10(12) CM-2. From the slope of C-2 versus gate voltage, the doping density N-D of ZnO is estimated to be 1.49 x 10(16) cm(-3). (C) 2010 Elsevier B V. All rights reserved.