The Al2O3 gate insulator modified by SiO2 film to improve the performance of IGZO TFTs

• The Al2O3 gate insulator was fabricated by ALD.
• A SiO2 film is used to modify the Al2O3 gate insulator.
• The effect of SiO2 interlayer on performance of IGZO TFT is studied.
• The SiO2 interlayer improves the performance of IGZO TFT.

High-performance thin-film transistors (TFTs) using atomic layer deposited (ALD) Al2O3 as gate insulator and radio frequency (RF) sputtering In–Ga–Zn Oxide (IGZO) as channel layer were fabricated in this work. A SiO2 buffer layer was applied between IGZO and Al2O3 to prevent the picked-up defects when the samples were switched from ALD to RF sputtering. Contrasting to the TFTs without buffer layer, the SiO2 buffer layer improved the TFTs performances greatly, such as: the field effect mobility increases from 5.2 cm2/V s to 6.1 cm2/V s, the threshold voltage downshifts from 4.9 V to 1.7 V, the Ion/Ioff ratio increases from 2.8 × 107 to 9.6 × 107, the sub-threshold swing decreased from 0.76 V/dec to 0.6 V/dec. The maximum density of surface states at the channel–insulator interface decreased from 2.1 × 1012 cm−2 to 1.53 × 1012 cm−2.