In the study, we fabricated a-IGZO thin film transistors (TFTs) with SiO2 and dual gate insulator SiO2/Al2O3, the thicknesses of SiO2/Al2O3 were 200/0 nm, 180/20 nm, 170/30 nm and 160/40 nm, respectively. The devices were annealing at 300℃ for one hour. After annealing, the results show that TFT with 170/30 nm SiO2/Al2O3 dual gate insulator display the best electrical performance compared to single SiO2 gate insulator based. The measured result show that saturation current, leakage current, insulator surface roughness, saturation mobility, threshold voltage, subthreshold swing (SS), Ion/Ioff ratio and the maximum density of surface states at the channel–insulator interface values obtained were 81.2 μA, 5.42x10-11 A/cm2, 2.95 nm, 7.86 cm2/V.s, 2.65 V, 0.19 V/dec, 4.31×1011 and 8.59×1011cm-2 respectively. We test device bias stability, the 170/30 nm SiO2/Al2O3 bilayer gate insulator device shows a substantially smaller threshold voltage shift of 0.98 V and -0.69 V after a 10 and -10 V gate voltage is applied for 1000s, and hysteresis ΔVTH shift 0.06 V. In addition, we measure the photo responsivity of IGZO TFT, the responsivity was 200 (A/W) with the illumination of 300 nm wavelength. Showing that IGZO has photosensitive properties and has the potential to be made into phototransistors.
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