Effect of sintering time at low temperature on the properties of IGZO TFTs fabricated by using the sol-gel process

We explored the application of the sol-gel process technique to the fabrication of InGaZnO (IGZO) thin film transistors (TFTs). We fabricated IGZO TFTs by using the sol-gel method and evaluated the effect of the sintering time on the electrical properties of the IGZO system with an atomic ratio of In:Ga:Zn = 2:1:1. In the process, IGZO precursor solutions were prepared by mixing In nitrate, Ga nitrate, and Zn acetate and were then deposited on a p-type Si-wafer covered with a thermallygrown SiO₂ layer by spin-coating. The sintering process was performed for 3 h, 6 h or 12 h at 300 °C in the ambient atmosphere. The source/drain electrodes of the TFT devices were fabricated using Al thermal evaporation. For all of the samples, a low off current (~10^-11 A) and on-to-off current ratio (~5 × 10⁴) were obtained in their transfer curves. The saturation mobility increased with increasing sintering time: for the samples sintered for 3 h, 6 h and 12 h, the saturation mobilities were calculated to be 0.825 cm²/Vs, 1.65 cm²/Vs, and 2.06 cm²/Vs, respectively. Based on the XPS and TEM analyses, the enhancement of the mobility was attributed to the increase in the number of oxygen vacancies and the nanocrystalline structure in the amorphous matrix with increasing sintering time. These results demonstrate for the potential application of sol-gel processed IGZO devices on flexible polymer substrates.