Unveiling chemical and physical bulk defects in ultrathin indium oxide transistors with yttrium oxide capping via nanoscale channel thickness modulation

• Nanoscale thickness control clarifies bulk defect roles in ultrathin oxide TFTs. • Thickness-dependent defect properties systematically elucidated in ultrathin InO X. • Structural disorder and defect chemistry linked to bias stability in oxide TFTs. • Optimized 4.5-nm channel enables reliable, enhancement-mode oxide TFT operation. Ultrathin indium oxide (InO x ) semiconductors are promising candidates for overcoming the performance limits of oxide electronics. In this study, the chemical and physical bulk defects in ultrathin InO x are clarified to improve the positive bias stability of chemical-solution-deposited InO x thin-film transistors (TFTs) with a yttrium oxide (YO x ) capping layer (CL). By modulating channel thickness at the nanoscale, the underlying mechanisms of positive bias instability in ultrathin InO x TFTs are revealed through a combined analysis of film characteristics and computer-aided design simulation. A 2.0-nm-thick InO x channel exhibits pronounced structural disorder and retains abundant undesirable metal-hydroxide or silicon-oxygen species under the influence of the SiO 2 interfacial reaction. In contrast, a 4.5-nm-thick InO x channel shows high crystallinity with comparatively low densities of oxygen-related defects. A 7.0-nm-thick InO x bulk, however, displays increased disorder and a high oxygen vacancy defect density. As a result, unlike the 2.0- and 7.0-nm-thick InO x TFTs, the 4.5-nm-thick devices exhibit a small threshold voltage shift without degradation of the subthreshold swing under strong bias stress of 6.0 MV cm −1 . These findings demonstrate that nanoscale thickness optimization can simultaneously promote high crystallinity and suppress oxygen-related bulk defects, which enables TFTs with superior PBS reliability.