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

This study investigates the performance of SnO 2 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 SnO 2 surfaces to control carrier concentrations. The deposited Al layers are converted into Al 2 O 3 islands on the SnO 2 surfaces, functioning as Al 3+ dopant sources after an additional annealing process. Using this process, an oxygen-vacancy-less surface regime inside SnO 2 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 SnO 2 TFTs with oxygen-vacancy (VO)-less surfaces demonstrate a field-effect mobility of 8.49 cm 2 /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 SnO 2 TFTs exhibit only a 3.2% loss in field-effect mobility, alongside improved negative bias stability.