Nitric oxide plasma treatment effect on SiO₂ gate insulator for the stability improvement of InGaZnO thin-film transistors

The performance of amorphous indium-gallium-zinc oxide (a-IGZO) thin-film transistors (TFTs) is significantly affected by intrinsic defects such as oxygen vacancies (V_o) and dangling bonds. These defects typically exist both in the bulk of gate dielectric and at the channel/gate insulator interface, especially when the silicon dioxide (SiO₂), commonly used as a gate insulator, is deposited by plasma-enhanced chemical vapor deposition (PECVD) at low temperature. In this study, we investigate the electrical properties and reliability of a-IGZO TFTs by incorporating nitric oxide (NO) plasma-treated SiO₂ as the gate insulator. The interface of the a-IGZO/SiO₂ structure was observed by cross-sectional transmission electron microscopy (TEM). In addition, electrical characterization of the NO plasma treated TFT device exhibited an on/off ratio (I_on/I_off) of 3.6 × 10⁶, a mobility (μ_eff) of 9.62 cm²/V·s, subthreshold swing (SS) of 0.862 V/dec, and interface trap density (D_it) of 2.9 × 10¹² cm²·eV. Furthermore, a positive bias stress (PBS) test showed V_th shift of 8.9 V for the w/o plasma device, compared to 4.7 V for the with plasma device. These results demonstrate that NO plasma treatment effectively reduces oxygen-related defect in the a-IGZO channel layer and improves interfacial properties at the gate insulator/channel, thereby enhancing both performance and stability of the TFT.