Optimized hydrogen-supplying gate insulator for high-mobility indium oxide TFTs via atomic-level oxygen reactant engineering

Oxide thin-film transistors (TFTs) have garnered significant interest owing to their potential in advanced electronic applications. The performance of these devices can be positively or negatively modulated by hydrogen doping into oxide semiconductor, with atomic layer deposited gate insulators (GIs) serving as a key method. This study introduces a novel method of oxygen reactant engineering for the atomic layer deposition (ALD) of GI, specifically aimed at fabricating In₂O₃ TFTs using a super-cycle-deposited Al₂O₃ to effectively control the amount of hydrogen incorporation. Although In₂O₃ was selected as the channel layer for its exceptionally high mobility, it required further optimization due to its variable carrier concentration and numerous defects such as oxygen vacancies and interstitials. By alternately using H₂O and O₂ plasma as oxygen reactants in the deposition of Al₂O₃ GIs, we achieved precise modulation of hydrogen levels and simultaneously passivated the defects while managing the carrier concentration in In₂O₃. With appropriate hydrogen incorporation, the device exhibited a superior performance including a mobility of 148.1 cm²/Vs and a turn on voltage (V_on) of −0.85 V. The devices with either excessive or insufficient hydrogen demonstrated shifts in V_on and stability issues. Through various analyses, we confirmed that a specific level of hydrogen penetration passivated oxygen-related defects, while further hydrogen diffusion substantially increased the carrier concentration. This study reports the effectiveness of the oxygen reactant engineering in ALD for precise hydrogen control and optimization of electronic properties in oxide semiconductors for application in advanced TFTs.