Low voltage operation of IGZO thin film transistors enabled by ultrathin Al_2O_3 gate dielectric

摘要

An ultrathin, 5 nm, Al_2O_3 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 Al_2O_3 layer showed a low surface roughness of 0.15nm, a low leakage current, and a high breakdown voltage of 6 V. 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 1 V but also exhibit desirable properties including a low threshold voltage of 0.3 V, a small subthreshold swing of 100mV/decade, and a high on/off current ratio of 1.2 x 107. 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 Al_2O_3 layer has also been analyzed, indicating the Fowler-Nordheim tunneling mechanism.