ZrO2 insulator modified by a thin Al2O3 film to enhance the performance of InGaZnO thin-film transistor

• The ZrO2–Al2O3 gate insulator was fabricated by ALD.
• A thin Al2O3 layer was used to modify ZrO2.
• The performance of TFT was enhanced by employing ZrO2–Al2O3 gate insulator.

A high-performance InGaZnO (IGZO) thin-film transistor (TFT) with ZrO2–Al2O3 bilayer gate insulator is fabricated. Compared to IGZO-TFT with ZrO2 single gate insulator, its electrical characteristics are significantly improved, specifically, enhancement of Ion/Ioff ratios by one order of magnitude, increase of the field-effect mobility (from 9.8 to 14 cm2/Vs), reduction of the subthreshold swing from 0.46 to 0.33 V/dec, the maximum density of surface states at the channel-insulator interface decreased from 4.3 × 1012 to 2.5 × 1012 cm−2. The performance enhancements are attributed to the suppression of leakage current, smoother surface morphology, and suppression of charge trapping by using Al2O3 films to modify the high-k ZrO2 dielectric.