Electrically and environmentally stable nitric acid-assisted SnO₂ films for the active channel layer of thin-film transistors

Electrically and environmentally stable SnO₂ thin-film transistors (TFTs) were fabricated with nitric acid (HNO₃)-added liquid precursors using a low-temperature sol–gel process. The structural, chemical, optical, and electrical properties were investigated. The HNO₃-added precursors resulted in the formation of high-density and amorphous-phase SnO₂ films at 300 °C. The added HNO₃ boosted the oxidation and sol–gel processes, successfully producing SnO₂ films with SnON, fewer defects, and higher quality than pure SnO₂ films. The formation of the high-density, fewer defect and high quality SnO₂ with SnON resulted in significantly enhanced field-effect mobility. The HNO₃ precursor-based TFTs exhibited robustness to external continuous positive and negative biases while maintaining environmental stability by inhibiting the chemical reaction of H₂O absorption on the SnO₂ surface. Compared to the pure SnO₂-based TFTs, the SnO₂ TFTs fabricated with HNO₃-added liquid-phase precursors exhibited a twenty-fold higher field-effect mobility in the saturation regime of about 6.64 cm²/Vs, as well as good stability with negligible parameter variations and good environmental stability for up to two months. These findings are useful for forming electrically and environmentally stable metal oxide layers at relatively low temperatures for many metal oxide-based applications, such as TFTs, resistive random access memory and transparent electrodes for devices and solar cells.