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
${\hbox{ZrO}}_{2}$
and IGZO/
${\hbox{TiO}} _{x}$
channel stack. According to our experimental results, the IGZO TFT with a thin
${\hbox{TiO}} _{x}$
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
${\hbox{cm}}^{2} /{\hbox{V}}{\cdot}{\hbox{s}}$
under a low drive voltage of
$< {\hbox{2}}~{\hbox{V}}$
. We also demonstrate that the significantly improved electrical property is mainly contributed by the enhanced channel electric field after
${\hbox{TiO}} _{x}$
capping, associated with maximizing charge accumulated capability. The favorable high-temperature transfer characteristics are also obtained in IGZO/
${\hbox{TiO}} _{x}$
TFT, indicating a weak Fermi-level pinning in IGZO/
${\hbox{TiO}} _{x}$
channel structure. With the operating temperature increasing further, the thermal activated effect shall dominate IGZO channel property beyond percolation conduction.