Abstract <p>A new thin-film transistor (TFT) structure based on hydrogenated amorphous silicon-germanium (a-SiGe:H) is proposed and analyzed, incorporating a double-layer gate dielectric. Silvaco TCAD simulations are employed to evaluate the electrical performance of a conventional single-layer silicon dioxide (SiO₂) dielectric compared to a novel bi-layer configuration combining hafnium dioxide (HfO₂) and SiO₂. The bi-layer design leverages the high permittivity of HfO₂ to enhance gate control while maintaining excellent interface quality through the inclusion of a thin interfacial SiO₂ layer. This structure effectively addresses common limitations of high-κ dielectrics, such as interface traps and gate leakage. Simulation results demonstrate that the proposed bi-layer dielectric significantly improves device characteristics, reducing the threshold voltage from 0.458 to 0.130 V, increasing the ON-state current from 1.85 × 10⁻⁷ to 3.24 × 10⁻⁵ A, and enhancing the ON/OFF current ratio from 1.71 × 10⁵ to 4.68 × 10⁶, with only a modest increase in subthreshold swing. Electric field and energy band analyses further confirm improved electrostatic control and reduced leakage current. These findings underscore the potential of the HfO₂/SiO₂ bi-layer dielectric structure for advancing the performance and scalability of a-SiGe:H TFTs in future electronic applications.</p>