Role of Invisible Oxygen in the Trilayer Laminates of Ultrathin a‑IGZO/SiOx/a-IGZO Films

In this study, ultrathin multilayered films of IGZO/SiOx/a-IGZO were fabricated via radio frequency (RF) magnetron cosputtering, with the SiOx layer thickness systematically varied between 1 and 7 nm while maintaining a constant a-IGZO layer thickness. The effect of the SiOx thickness on the electrical properties of the films was thoroughly investigated. A significant deterioration in electrical performance was observed for SiOx layers up to 3 nm; however, an improvement was noted as the SiOx thickness increased to 7 nm. X-ray photoelectron spectroscopy (XPS) analysis revealed that the oxygen structure and chemical composition within the multilayers remained unchanged. However, it confirmed that the ultrathin 2 nm thick SiOx (x ∼ 1.5) layer exhibited nonstoichiometric configurations. The contribution of Fowler–Nordheim (FN) tunneling was observed in multilayer films with varying thicknesses of SiOx. The presence of oxygen was found to play a critical role in modulating electron trap states within the SiOx layer, thereby mitigating the reduction in the charge carrier concentration in the films. By optimizing oxygen flow during deposition, we successfully eliminated the charge carrier drop in a-IGZO20 nm/SiOx(2 nm)/a-IGZO10 nm and a-IGZO20 nm/SiOx(3 nm)/a-IGZO10 nm films. Notably, the ultrathin SiOx layers in the a-IGZO/SiOx/a-IGZO films functioned as highly effective carrier suppressor layers, presenting a promising alternative to conventional doping approaches for controlling electrical performance.