The Role of Germanium Incorporation in Enhancing the Stability of Indium Zinc Oxide Thin-Film Transistors Under Water Vapor Exposure and Thermal Stress

This work demonstrates the potential of indium germanium zinc oxide (InGeZnO) as a promising oxide semiconductor offering an improved trade-off between mobility and stability under water exposure and thermal stress. The effect of Ge incorporation in enhancing the stability of indium zinc oxide (InZnO) thin-film transistors (TFTs) is systematically investigated through negative bias stress (NBS) and negative bias temperature stress (NBTS) measurements after different durations of deionized-water immersion. The results show that InGeZnO exhibits smaller threshold voltage (VTH) shift magnitudes and reduced subthreshold swing (SS) degradation after prolonged immersion, as well as an attenuated difference between the SS changes induced by NBS and NBTS, compared with InZnO. These electrical trends suggest that water exposure disrupts the metal–oxygen (M–O) coordination structure and increases oxygen vacancies in the exposed back channel, whereas Ge–O bonding stabilizes the M–O network and limits the evolution of these defects under gate bias and thermal stress. X-ray photoelectron spectroscopy (XPS) analysis provides further support for the proposed mechanism. Collectively, the results position Ge doping as a promising strategy for balancing high mobility with robust stability against water vapor exposure and thermal stress in oxide TFTs.