Origin of Threshold Voltage Instabilities in Indium Oxide Transistors

Oxide semiconductors have gained substantial interest for their low-temperature processability, allowing for their integration as functional add-on device layers for advanced monolithic 3D integrated circuits (ICs). However, reliability issues, particularly under thermal, environmental, and electrical stresses, remain critical issues and require immediate solutions. This study investigates the instability of ultrathin In₂O₃ transistors, revealing that threshold voltage (VT) drifts arise from interactions between surface-adsorbed oxygen and the In₂O₃ channels. We show that the oxygen in the ambient atmosphere attached to the In₂O₃ surface plays a crucial role in modulating In₂O₃ conductivity, thereby governing VT. External perturbations such as ultraviolet (UV)/X-ray illumination, thermal annealing, and bias stress could alter this interaction of surface oxygen with ultrathin In₂O₃, leading to a VT drift. Importantly, we propose a unified kinetic model that provides a generic physical description of VT instabilities induced by these commonly observed factors. By characterizing time-dependent VT instability, the model demonstrates that recovery dynamics exhibit identical behavior across all tested perturbations, indicating that the recovery process is independent of the initial stimulus. This study uncovers the surface oxygen as a critical factor affecting In₂O₃ transistor reliability, offering insights for designing oxide-based devices for advanced electronic and optoelectronic devices.