High-quality indium–gallium–zinc oxide films synthesized by atomic layer deposition using a single cocktail precursor based on a liquid-delivery system and their application in transistors and inverters

Abstract

High-quality indium–gallium–zinc oxide (IGZO) films synthesized by atomic layer deposition (ALD) using a single cocktail precursor based on a liquid-delivery system are demonstrated for the first time. A bottom-gate-top-contact thin-film transistor (TFT) consisting of an ALD-derived IGZO channel exhibited outstanding device performance, including a high linear field-effect mobility (∼20 cm² V⁻¹ s⁻¹), a substantial on/off ratio (∼5 × 10⁹), and a low subthreshold swing (∼0.07 V dec⁻¹) at an operating voltage of 5 V. High reliability and reproducibility of the proposed ALD-based IGZO TFT are confirmed from the statistics of device key parameters. The operational stability of the IGZO TFT subjected to electrical bias stresses for 20 000s is investigated, which is attributed to the oxygen-related defect states of the ALD-derived IGZO film and the field-induced interaction with oxygen on the surface. In addition, full recovery of V_th without additional processes was achieved, indicating that the instability mechanism can be explained by shallow charge trapping at the interface. A simple and effective method of oxygen annealing is induced to improve the operational stability of the IGZO TFT by suppressing the oxygen-related shallow trap states. Finally, an enhancement-load-type n-channel metal-oxide semiconductor inverter consisting of two IGZO TFTs proposed in this study is developed.