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In this paper, we compared the structural and electrical properties of high- κ Gd2O3 and GdTiO3 gate dielectrics for an amorphous indium-gallium-zinc oxide ( α-IGZO) thin-film transistor (TFT) application. In comparison with the Gd2O3 dielectric, the α-IGZO TFT featuring the GdTiO3 dielectric exhibited better electrical characteristics in terms of a large field effect mobility of 26.9 cm2/Vs, a low threshold voltage of 0.04 V, a high ION/IOFF ratio of 1.2×108, and a low subthreshold swing of 200 mV/decade. We attribute these results to the incorporation of Ti into the Gd2O3 film, forming a smooth surface and thus reducing density of interface states at the oxide/channel interface. In addition, the stability of threshold voltage on high- κ Gd2O3 and GdTiO3 a-IGZO TFTs was studied under positive gate bias stress.