Amorphous InGaZnO (a-IGZO) thin film transistors (TFTs) with double-layer gate dielectric were fabricated at low temperature and characterized. A stacked 150 nm-thick SiO2/50 nm-thick HfO2 dielectric layer was employed to improve the capacitance and leakage characteristics of the gate oxide. The SiO2/HfO2 showed a higher capacitance of 35 nF/cm(2) and a lower leakage current density of 4.6 nA/cm(2) than 200 nm-thick SiO2. The obtained saturation mobility (mu(sat)), threshold voltage (V-th), and subthreshold swing (S) of the fabricated TFTs were 18.8 cm(2) V-1 s(-1), 0.88 V. and 0.48 V/decade, respectively. Furthermore, it was found that oxygen pressure during the IGZO channel layer deposition had a great influence on the performance of the TFTs. (C) 2012 Elsevier Ltd. All rights reserved.