Effect of ${\hbox{SiO}}_{2}$ and/or ${\hbox{SiN}}_{x}$ Passivation Layer on Thermal Stability of Self-Aligned Coplanar Amorphous Indium–Gallium–Zinc–Oxide Thin-Film Transistors

We report the post-annealing effect on the performance of amorphous indium-gallium-zinc-oxide (a-IGZO) thin-film transistors (TFTs) with self-aligned coplanar structure. The a-IZGO layer was passivated with SiO
₂
or SiN
_x
by plasma enhanced chemical vapor deposition (PECVD). The field-effect mobility of a-IGZO TFT with SiN
_x
is almost unchanged by extending the post-annealing time at 250 °C, but that of SiO
₂
passivated TFT significantly degrades by increasing annealing time. It is found that the resistivity of the a-IGZO under SiN
_x
is low enough and thus can be good conduction path, leading to the high performance TFT. It is also found that the interface trap density (N
_it
) between a-IGZO TFT with SiN
_x
passivation decreases from 3.0×10
¹¹
to 1.54×10
¹¹
cm
^-2
eV
^-1
, and the stability of the a-IGZO TFT with SiN
_x
passivation is significantly improved by long post-annealing.