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

초록

Ultrathin indium oxide (InOx) semiconductors are promising candidates for overcoming the performance limits of oxide electronics. In this study, the chemical and physical bulk defects in ultrathin InOx are clarified to improve the positive bias stability of chemical-solution-deposited InOx thin-film transistors (TFTs) with a yttrium oxide (YOx) capping layer (CL). By modulating channel thickness at the nanoscale, the underlying mechanisms of positive bias instability in ultrathin InOx TFTs are revealed through a combined analysis of film characteristics and computer-aided design simulation. A 2.0-nm-thick InOx channel exhibits pronounced structural disorder and retains abundant undesirable metal-hydroxide or silicon-oxygen species under the influence of the SiO2 interfacial reaction. In contrast, a 4.5-nm-thick InOx channel shows high crystallinity with comparatively low densities of oxygen-related defects. A 7.0-nm-thick InOx bulk, however, displays increased disorder and a high oxygen vacancy defect density. As a result, unlike the 2.0- and 7.0-nm-thick InOx 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.

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