Temperature-dependent transfer characteristics of low turn-on voltage InGaZnO metal-oxide devices with thin titanium oxide capping layers

This paper reports an InGaZnO thin-film transistor involving a wide bandgap gate dielectric of ZrO₂ and IGZO/TiO_x channel stack. According to our experimental results, the IGZO TFT with a thin TiO_x channel capping layer shows good device integrity of a low threshold voltage of 0.37 V, a small sub-threshold swing of 77 mV/decade, and a high mobility of 33 cm²/V·s under a low drive voltage of <2V. We also demonstrate that the significantly improved electrical property is mainly contributed by the enhanced channel electric field after TiO_x capping, associated with maximizing charge accumulated capability. The favorable high-temperature transfer characteristics are also obtained in IGZO/TiO_x TFT, indicating a weak Fermi-level pinning in IGZO/TiO_x channel structure. With the operating temperature increasing further, the thermal activated effect shall dominate IGZO channel property beyond percolation conduction.