Enhanced switching characteristics in amorphous IGZO FETs via an HfO2-induced quasi-two-dimensional electron channel

Abstract

Enhancing the switching performance of amorphous oxide semiconductor-based transistors is critical for next-generation low-power electronics. In this study, we demonstrate enhanced switching characteristics in an InGaZnO (IGZO) transistor enabled by ultrathin (1 nm) HfO₂ passivation. A quasi-two-dimensional electron gas (2-DEG) channel spontaneously formed at the HfO₂/IGZO interface, despite the absence of an epitaxial crystalline film. X-ray photoelectron spectroscopy (XPS) depth profiling revealed controlled Hf ion diffusion into the IGZO channel during annealing, reconstruction of the interfacial band structure, and generation of a quantized electron channel. This emergent interfacial transport alters the switching behavior of the IGZO transistor, yielding reduced subthreshold swing by 62.08% and a narrow hysteresis window of 0.58 V for 1 nm HfO₂. The quasi-2-DEG of the HfO₂/IGZO junction induces on-current saturation at a low drain voltage (V_DS) owing to the strong carrier confinement, whereas a high V_DS suppresses scattering and enhances mobility. The low interface trap density in the HfO₂/IGZO transistor improved switching performance. Ultraviolet-visible spectrometry, ultraviolet photoelectron spectroscopy, and XPS valence band analyses experimentally validated quasi-2D channel formation at the HfO₂/IGZO interface. Our results reveal a scalable route for realizing quasi-2D transport in amorphous oxide heterostructures, establishing ultrathin HfO₂ passivation as a promising strategy for next-generation ultrafast and energy-efficient oxide transistors.