Effects of Substrate Bias on Microstructure of SnO2 Film and Thin-Film Transistor Performance

SnO2 exhibits low cost, high electron mobility and good optical transparency, making it a promising candidate for the active layer of indium-free oxide thin-film transistors (TFTs). However, its film qualities are highly sensitive to deposition conditions. In this work, SnO2 thin films and TFTs were fabricated by radio-frequency magnetron sputtering under different substrate biases (0 V, −70 V and −110 V) to investigate the effects of substrate bias on film structure, defect state, interface quality and device performance. With increasing substrate bias magnitude, the film crystallinity improved, the relative area fraction of the defect-related O 1s component decreased from 31% to 19%, while the surface roughness increased, continuously. At a substrate bias of −70 V, the device exhibited relatively optimal overall performance, with a linear mobility (μlin) of 3.7 cm2/Vs, a subthreshold swing (SS) of 0.61 V/dec, and a threshold-voltage shift (ΔVth) of 6.0 V after 3600 s of positive bias stress. These results indicate that an appropriate substrate bias can achieve a balance between crystalline quality and interface condition, thereby improving the performance of SnO2 TFTs.