Water-Mediated Photochemical Treatments for Low-Temperature Passivation of Metal-Oxide Thin-Film Transistors

The low-temperature electrical passivation of an amorphous oxide semiconductor (AOS) thin-film transistor (TFT) is achieved by a deep ultraviolet (DUV) light irradiation–water treatment–DUV irradiation (DWD) method. The water treatment of the first DUV-annealed amorphous indium–gallium–zinc–oxide (a-IGZO) thin film is likely to induce the preferred adsorption of water molecules at the oxygen vacancies and leads to subsequent hydroxide formation in the bulk a-IGZO films. Although the water treatment initially degraded the electrical performance of the a-IGZO TFTs, the second DUV irradiation on the water-treated devices may enable a more complete metal–oxygen–metal lattice formation while maintaining low oxygen vacancies in the oxide films. Overall, the stable and dense metal–oxygen–metal (M-O-M) network formation could be easily achieved at low temperatures (below 150 °C). The successful passivation of structural imperfections in the a-IGZO TFTs, such as hydroxyl group (OH−) and oxygen vacancies, mainly results in the enhanced electrical performances of the DWD-processed a-IGZO TFTs (on/off current ratio of 8.65 × 109, subthreshold slope of 0.16 V/decade, an average mobility of >6.94 cm2 V–1 s–1, and a bias stability of ΔV TH < 2.5 V), which show more than a 30% improvement over the simple DUV-treated a-IGZO TFTs.