Effect of hydrochloric acid addition on dielectric properties of solution-processed aluminum titanium oxide thin film annealed at low temperature

This study investigated the effect of hydrochloric acid (HCl) addition on the dielectric properties of solution-processed aluminum titanium oxide (ATO) applied to thin-film transistors (TFTs) as a gate insulator layer. The formation of the solution-processed ATO film can be accelerated by adding HCl to the precursor solution because of the hydrolysis catalyst effect of HCl. The solution-processed ATO film exhibits higher crystallinity as the amount of HCl added increases. Furthermore, the addition of HCl suppresses the formation of oxygen vacancies, which can act as defect states in the ATO film. Consequently, the optimized ATO film annealed at 450 ℃ exhibited minimum leakage current density level of 5.14×10⁻⁹ A/cm² at 0.33 MV/cm and dielectric constant of 13.9 when HCl of 2 ml was added to the precursor solution. These results are comparable with the dielectric properties of the ATO film annealed at 750 ℃ without HCl addition, because HCl addition catalyses hydrolysis and enhances the formation of metal-oxide bonding. Solution-processed amorphous indium-gallium-zinc oxide (IGZO) TFTs using the optimized ATO/AlO_x film as gate insulator displayed excellent electrical properties such as threshold voltage of 0.17 V, field-effect mobility of 2.59 cm²/V∙s, subthreshold swing of 0.22 V/dec, and on/off ratio of 4.54×10⁵. In addition, the IGZO TFT with the ATO gate insulator exhibited superior current driving capability compared to that of silicon dioxide (SiO₂). These results indicate that solution-processed ATO films with HCl addition could be promising candidates for gate insulator layers in achieving low power consumption, high performance, and low cost TFTs.