| Summary: | This study investigates the effect of gate insulators on thin-film transistors (TFTs) using an amorphous InGaZnO<sub>4</sub> (a-IGZO) channel layer. TFTs with single-layer Ta<sub>2</sub>O<sub>5</sub> and dual-layer Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> gate insulators were fabricated on a glass substrate. An evaluation of the insulating film using the MIM (Metal-Insulator-Metal) structure confirmed its electrical characteristics. Microscopic imaging showed that the dual-layer Ta<sub>2</sub>O<sub>5</sub>/SiO<sub>2</sub> dielectric significantly improved surface characteristics. A reduction in the leakage current, better on/off ratios, and a decreased subthreshold swing (SS) compared to a single-layer Ta<sub>2</sub>O<sub>5</sub> dielectric were reported. The dual-layer insulator composed of SiO<sub>2</sub>/Ta<sub>2</sub>O<sub>5</sub> was highly effective in improving device characteristics.
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