Low voltage operation of IGZO thin film transistors enabled by ultrathin Al2O3 gate dielectric

An ultrathin, 5 nm, Al2O3 film grown by atomic-layer deposition was used as a gate dielectric for amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs). The Al2O3 layer showed a low surface roughness of 0.15 nm, a low leakage current, and a high breakdown voltage of 6V. In particular, a very high gate capacitance of 720 nF/cm(2) was achieved, making it possible for the a-IGZO TFTs to not only operate at a low voltage of 1V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100 mV/decade, and a high on/off current ratio of 1.2 x 10(7). Furthermore, even under an ultralow operation voltage of 0.6 V, well-behaved transistor characteristics were still observed with an on/off ratio as high as 3 x 10(6). The electron transport through the Al2O3 layer has also been analyzed, indicating the Fowler-Nordheim tunneling mechanism. (C) 2018 Author(s).