Self-aligned top-gate amorphous indium-gallium-zinc oxide (a-IGZO) thin film transistors (TFTs) utilizing SiO2/Al2O3 stack thin films as gate dielectric are developed in this paper. Due to high quality of the high-k Al2O3 and good interface between active layer and gate dielectric, the resulting a-IGZO TFT exhibits good electrical performance including field-effect mobility of 9 cm(2)/Vs, threshold voltage of 2.2 V, subthreshold swing of 0.2 V/decade, and on/off current ratio of 1 x 10(7). With scaling down of the channel length, good characteristics are also obtained with a small shift of the threshold voltage and no degradation of subthreshold swing. (C) 2013 Elsevier B. V. All rights reserved.