Gate insulator (GI) materials in top gate structured InGaZnO thin‐film transistor (TFT) with copper gate electrode are examined for the application to the large area display. To overcome the problems with hydrogen diffusion, which can influence the number of carriers in oxide semiconductor and to gain large trans‐conductance coefficient, a double‐layered GI of 30 nm Al2O3/120 nm SiNxis adopted. The TFT showed field‐effect mobility, Von, SS, and hysteresis of 12.8 cm2 V−1 s−1, −0.7 V, 0.17 V decade−1, and almost 0 V, respectively, and the ΔVon under the positive bias stress of 20 V and negative bias stress of −20 V at 60 C for 10 000 s are +0.1 and −0.4 V, respectively.

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