Effect of SiO₂ and/or 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 SiO₂ 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× 10¹¹cm^-2 eV^-1, and the stability of the a-IGZO TFT with SiN_x passivation is significantly improved by long post-annealing.