Enhancement Mode Flexible SnO2 Thin Film Transistors Via a UV/Ozone-Assisted Sol-Gel Approach

The effect of ultraviolet/Ozone (UV/O₃)-assisted annealing process on the structural, chemical, and electrical properties of sol-gel-processed SnO₂ films is investigated in this study. Via the UV/O₃-assisted annealing processes, mixed-phase SnO₂ films composed of amorphous SnO₂ and polycrystalline SnO were obtained. Furthermore, the XPS spectra indicate an increase in the SnO₂/SnO ratio and a substantial decrease in the number of -OH groups (serving as trap sites). This results in an increase in the conductivity and field-effect mobility of the films. The field-effect mobility of the UV/Ozone-assisted 300 °C-annealed SnO₂ thin film transistor (TFT) increases considerably (by ~500×), yielding a device with a field-effect mobility of 3.09 cm²/Vs. In addition, flexible SnO₂ TFTs with Al₂O₃ insulator and Au gate on Polyimide substrate fabricated via gate electrode engineering shows a decreased conduction bandgap offset, compared to the SnO₂ TFTs on SiO₂, and enhancement mode operation properties (normally off at zero gate voltage) with a field-effect mobility of 1.87 cm²/Vs.