Improved Negative Bias Stability of Sol–Gel-Processed SnO₂ Thin-Film Transistors with Vertically Controlled Carrier Concentrations

Abstract

This study investigates the performance of SnO2 thin-film transistors (TFTs) fabricated with vertically controlled carrier concentrations using a sol–gel method. In the proposed fabrication method, thin Al layers are deposited on SnO2 surfaces to control carrier concentrations. The deposited Al layers are converted into Al2O3 islands on the SnO2 surfaces, functioning as Al3+ dopant sources after an additional annealing process. Using this process, an oxygen-vacancy-less surface regime inside SnO2 semiconductors is successfully formed. It is demonstrated that this morphology significantly reduces bias stress instability by inhibiting trap and de-trap events at the surface of the back channel of TFTs. The fabricated SnO2 TFTs with oxygen-vacancy (VO)-less surfaces demonstrate a field-effect mobility of 8.49 cm2/Vs and a threshold voltage shift of only −3.84 V during negative bias tests. However, compared to other existing bias stress stable metal-oxide semiconductors, the proposed SnO2 TFTs exhibit only a 3.2% loss in field-effect mobility, alongside improved negative bias stability.