The instability of amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) with different active layer thicknesses under temperature stress has been investigated through using the density-of-states (DOS). Interestingly, the a-IGZO TFT with 22 nm active layer thickness showed a better stability than the others, which was observed from the decrease of interfacial and semiconductor bulk trap densities. The DOS was calculated based on the experimentally-obtained activation energy (EA), which can explain the experimental observations. We developed the high-performance Al2O3 TFT with 22 nm IGZO channel layer (a high mobility of 7.4 cm(2)/V, a small threshold voltage of 2.8 V, a high I-on/I-off 1.8 x 10(7), and a small SS of 0.16 V/dec), which can be used as driving devices in the next-generation flat panel displays. (C) 2014 Elsevier B.V. All rights reserved.