Top-Gated Indium–Zinc–Oxide Thin-Film Transistors With In Situ Al2O3/HfO2 Gate Oxide

We report on top-gated indium-zinc-oxide (IZO) thin-film transistors (TFTs) with a 3-nm layer of aluminum between the IZO active layer and high-k HfO₂ gate insulator. A series of anneals at 300°C was used to convert the Al metal into Al₂O₃, resulting in high-performance top-gated TFTs. The 8-h-annealed TFT with Al layer has a threshold voltage |V_T| <; 0.5 V, an ON/OFF ratio of 1 × 10⁷, a subthreshold slope (SS) of 0.14 V/decade, and a saturation mobility μs ~115 cm^2/V · s in devices with L_G = 50μm gate length. For smaller devices with L_G = 5 μm, the threshold voltage and SS are similar, but the ON/OFF ratio and mobility are lower. Cross-sectional TEM images and C-V_G characteristics with little hysteresis confirm that the thin Al layer, converted in situ into Al₂O₃, can protect the IZO channel during processing and produce a good high-k gate-stack.