We have investigated the electrical performance of amorphous indium gallium zinc oxide (alpha-IGZO) thin-film transistors with various channel thicknesses. It is observed that when the a-IGZO thickness increases, the threshold voltage decreases as reported at other researches. The intrinsic field-effect mobility as high as 11.1 cm(2)/Vs and sub threshold slope as low as similar to 0.2 V/decade are independent on the thickness of a-IGZO channel, which indicate the excellent interface between a-IGZO and atomic layer deposited Al2O3 dielectric even for the case with alpha-IGZO thickness as thin as 10 nm. However, the source and drain series resistances increased with increasing of a-IGZO channel thickness, which results in the apparent field-effect mobility decreasing. The threshold voltage shift (Delta Vth) under negative bias stress (NBS) and negative bias illumination stress (NBIS) were investigated, also. The hump-effect in the sub threshold region under NBS and threshold voltage shift to negative position under NBIS were enhanced with decreasing of alpha-IGZO channel thickness, owing to the enhancement of vertical electrical field in channel. (C) 2014 Elsevier B.V. All rights reserved.