Influence of active channel layer thickness on SnO₂ thin-film transistor performance

Sol-gel processed SnO₂ thin-film transistors (TFTs) were fabricated on SiO₂/p₊ Si substrates. The SnO₂ active channel layer was deposited by the sol-gel spin coating method. Precursor concentration influenced the film thickness and surface roughness. As the concentration of the precursor was increased, the deposited films were thicker and smoother. The device performance was influenced by the thickness and roughness of the SnO₂ active channel layer. Decreased precursor concentration resulted in a fabricated device with lower field-effect mobility, larger subthreshold swing (SS), and increased threshold voltage (V_th), originating from the lower free carrier concentration and increase in trap sites. The fabricated SnO₂ TFTs, with an optimized 0.030 M precursor, had a field-effect mobility of 9.38 cm²/Vs, an SS of 1.99, an I_on/I_off value of ~4.0 × 10⁷, and showed enhancement mode operation and positive V_th, equal to 9.83 V.