Oxygen vacancy defect engineering in IGZO thin film by sequential ultraviolet ozone and forming gas annealing

Indium gallium zinc oxide (IGZO) thin film is a promising material for advanced electronics. However, the properties of IGZO and electrical characteristics of IGZO thin film transistors (TFTs) are strongly affected by oxygen vacancy (V o ) states. Herein, we investigate the effects of a sequential ultraviolet ozone (UVO) and forming gas annealing (FGA) treatment on oxygen vacancy control. With this two-step treatment on IGZO, which combines 3 min of ultraviolet ozone (UVO) with hydrogen passivation via forming gas annealing (FGA) at 350 °C for 1 h, the optical band gap of IGZO is improved from 3.62 eV to 3.74 eV and the roughness of IGZO decreased from 4.9 nm to 2.3 nm. Correspondingly, the threshold voltage (V TH ) for different dimensions IGZO TFTs is modulated from −27.92 V to around 0.71 V, and the drain current (I DS ) is reduced from 36.9 μA to near 0.55 μA. According to depth profiled X-ray photoelectron spectroscopy (XPS) characterization, these changes are mainly due to a reduction of oxygen vacancy (V o ) proportion from 35.50% to 24.89% in IGZO. The oxygen vacancies are effectively controlled through a combined response of reactive oxygen radicals during the UVO process and hydrogen passivation in the FGA process, reducing the carrier concentration and the conductivity of IGZO, tuning the key electrical characteristics IGZO TFTs for low-power operation. These results demonstrate that sequential UVO/FGA enables practical oxygen-vacancy control that governs band alignment, carrier transport, and oxide-device electrical characteristics, offering both fundamental understanding and process guidance for electronic optimization.