High-performance thin-film transistors (TFTs) using atomic layer deposited (ALD) Al 2 O 3 as gate insulator and radio frequency (RF) sputtering In–Ga–Zn Oxide (IGZO) as channel layer were fabricated in this work. A SiO 2 buffer layer was applied between IGZO and Al 2 O 3 to prevent the picked-up defects when the samples were switched from ALD to RF sputtering. Contrasting to the TFTs without buffer layer, the SiO 2 buffer layer improved the TFTs performances greatly, such as: the field effect mobility increases from 5.2cm 2 /Vs to 6.1 cm 2 /Vs, the threshold voltage downshifts from 4.9V to 1.7V, the I on /I off ratio increases from 2.8×10 7 to 9.6×10 7 , the sub-threshold swing decreased from 0.76V/dec to 0.6V/dec. The maximum density of surface states at the channel–insulator interface decreased from 2.1×10 12 cm − 2 to 1.53×10 12 cm −2 .