Performance Optimization of Atomic Layer Deposited ZnO Thin-Film Transistors by Vacuum Annealing

Mengfei Wang,Dan Zhan,Xin Wang,Qianlan Hu,Yanqing Wu,Xuefei Li,Chengru Gu

doi:10.1109/led.2021.3068992

Abstract

In this letter, high-performance zinc oxide thin-film transistors (ZnO TFTs) have been fabricated on Si substrate by atomic layer deposition (ALD) at 190 °C. The field-effect mobility ( μ FE ) can be improved from 18.5 cm 2 / V·s to a record high 43.2 cm 2 / V·s while maintaining a large I on /I off ratio of 5 × 10 9 after rapid thermal annealing (RTA) under vacuum at 350 °C. The excellent performance can be attributed to the improvement in the ZnO channel and the interface. The oxygen vacancy ratio in ZnO increases from 36.2% to 40.0%. The interface trap density ( N it ) between silicon oxide (SiO 2 ) and ZnO decreases from 5.1 × 10 11 eV -1 cm -2 to 1.4 × 10 11 eV -1 cm -2 . Furthermore, the oxide trap density ( N ot ) of the SiO 2 dielectric reduces from 3.7 × 10 19 eV -1 cm -3 to 1.1 × 10 19 eV -1 cm -3 . Finally, we systematically study the electrical performance of the annealed ZnO device at measurement temperature from room temperature of 20 °C to a much higher temperature of 180 °C without device failure.

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