Amorphous Indium-Zinc-Tin-Oxide thin-film transistors (a-IZTO TFT) using different types of high-k materials (like HfO2, ZrO2 and Al2O3) as gate dielectric are studied in this work. All gate dielectric films were deposited by physical vapor deposition (PVD) process for better composition control. Compared with the traditional SiO2 gate insulator, a high-k gate dielectric can reduce the operation voltage of TFT device significantly. The TFT device with ZrO2 gate insulator exhibits a small subthreshold swing of 0.126 V/decade, high field-effect mobility of similar to 40.7 cm(2)/Vs, low threshold voltage of -0.05 V, and large On/Off current ratio of similar to 1.01 x 10(7). The mechanisms for electrical improvements are also investigated. These results demonstrate the potential application of PVD-deposited ZrO2 thin film as a promising gate dielectric in oxide-based thin-film transistors.