Effect of UV-ozone treatment on the bias-stress stability of indium-zinc-oxide thin-film transistors fabricated by using a sol-gel process

Thin film transistors (TFTs) with indium-zinc-oxide (IZO) channel layers were fabricated by using a solution process. The channel and the SiO2 insulator layers were exposed to ultraviolet (UV)-ozone to investigate the effect of UV-ozone treatment. The enhancement of the subthreshold slope of the UV-ozone-treated TFTs was dominantly attributed to a decrease in the defect density and an increase in the adhesion due to the ozone treatment on the SiO2 insulator layer. The positive-bias temperature stress results for the UV-ozone-treated IZO thin film showed that the threshold voltage shift and the subthreshold slope variation of the TFTs with an UV-ozone-treated IZO thin film were smaller than those with an as-deposited IZO thin film, indicative of an enhancement in the bias-stress stability. X-ray photoelectron spectroscopy spectra showed that the number of the oxygen vacancies and the number of trap sites for the as-deposited IZO film were larger than those of the UV-ozone- treated IZO film.