High-Mobility IZO Thin-Film Transistors Enabled by Precise Hydrogen Control Using a SiO ₂ –Al ₂ O ₃ Supercycle via Plasma-Enhanced Atomic Layer Deposition

A precise strategy to control hydrogen incorporation is essential for achieving high-performance oxide thin-film transistors (TFTs) as hydrogen plays a key role in tuning carrier concentration and passivating defect states. In this study, we report a top-gate oxide thin-film transistor structure that utilizes a plasma-enhanced atomic layer deposition (PEALD) supercycled SiO₂-Al₂O₃ gate insulator (GI), enabling precise hydrogen control through a tunable layering sequence. Hydrogen incorporation into the active channel is modulated with precise control by varying the number of hydrogen-rich SiO₂ subcycles. Comprehensive analyses reveal that moderate hydrogen incorporation effectively passivates oxygen-related defects while introducing shallow donor states, enhancing mobility, and suppressing charge trapping. The optimized device with ten cycles of H-rich SiO₂ exhibits a high field-effect mobility of 47.4 cm²/V·s, a turn-on voltage (<i>V</i>_on) of -0.46 V, a subthreshold swing of 71.3 mV/dec and negligible hysteresis, an on/off current ratio of ∼10⁷, and superior bias stability under positive and negative stress conditions. In contrast, excess hydrogen from 15 cycles leads to the loss of switching behavior caused by the intermixing of GI layers, resulting in uncontrolled hydrogen diffusion and excessive carrier generation. These results demonstrate that the PEALD supercycle process offers a reliable strategy for hydrogen modulation in oxide semiconductors, enabling an optimized trade-off between mobility and stability in high-performance TFTs.