High-Mobility a-InZnO Thin-Film Transistors Incorporating an Oxygen-Related Defect Control Layer for Improved Illumination Stability and Environmental Reliability

Abstract The introduction of an appropriate passivation layer is considered a viable strategy for improving the long-term stability and electrical performance of thin-film transistors (TFTs). In this study, an additional layer deposition strategy involving the deposition of a single-layer oxygen-related defect control layer on amorphous indium zinc oxide (a-IZO) thin-film transistors is developed. This approach improves the electrical characteristics and negative-bias illumination stress (NBIS) stability of the channel layer. The oxygen-related defect control layer is a hafnium oxynitride (HfON) layer. It functions as an insulating material with a relatively high dielectric constant, high film density, and low surface energy, serving as a protective barrier against environmental degradation such as exposure to ambient air and moisture. In addition, it contributes to the improvement of NBIS-induced stability by passivating the defect sites in a-IZO during the activation annealing process. Furthermore, the number of carriers in the channel layer increased because of the formation of oxygen vacancies in the a-IZO front channel through the oxygen adsorption of the oxygen-related defect control layer, resulting in the fabrication of thin films with better electrical properties. This resulted in field-effect mobility improving from 37.53 to 66.43 cm2/(V s), the on/off current ratio was enhanced from 1.93 × 109 to 5.77 × 1011, and the threshold voltage shift under NBIS at green light (532 nm) flux density of 1 mW/cm2 for 10,000 s decreased from 15.25 to 2.64 V.