Effect of gate insulator thickness on device performance of InGaZnO thin-film transistors

Top-contact thin-film transistors (TFTs) are fabricated in this work using atomic layer deposition (ALD) Al2O3 as the gate insulator and radio frequency sputtering InGaZnO (IGZO) as the channel layer so as to investigate the effect of Al2O3 thickness on the performance of IGZO-TFTs. The results show that TFT with 100-nm-thick Al2O3 (100 nm-Al2O3-TFT) exhibits the best electrical performance; specifically, field-effect mobility of 5 cm2/Vs, threshold voltage of 0.95 V, Ion/Ioff ratio of 1.1×107 and sub-threshold swing of 0.3 V/dec. The 100 nm-Al2O3-TFT also shows a substantially smaller threshold voltage shift of 1.1 V after a 10 V gate voltage is applied for 1 h, while the values for TFTs with an Al2O3 thickness of 220 and 280 nm are 1.84 and 2 V, respectively. The best performance of 100 nm-Al2O3-TFT can be attributed to the larger capacitance and the smaller amount of total trap centers possessed by a thinner insulator compared to the thicker ones.