Sol-gel processed high-k aluminum oxide dielectric films for fully solution-processed low-voltage thin-film transistors

High-k oxide dielectric films have attracted intense interest for thin-film transistors (TFTs). However, high-quality oxide dielectrics were traditionally prepared by vacuum routes. Here, amorphous high-k alumina (Al2O3) thin films were prepared by the simple sol-gel spin-coating and post-annealing process. The microstructure and dielectric properties of Al2O3 dielectric films were systematically investigated. All the Al2O3 thin films annealed at 300-600 °C are in amorphous state with ultrasmooth surface (RMS ~ 0.2 nm) and high transparency (above 95%) in the visible range. The leakage current of Al2O3 films gradually decreases with the increase of annealing temperature. Al2O3 thin films annealed at 600 °C showed the low leakage current density down to 3.9 × 10−7 A/cm2 at 3 MV/cm. With the increase of annealing temperature, the capacitance first decreases then increases to 101.1 nF/cm2 (at 600 °C). The obtained k values of Al2O3 films are up to 8.2. The achieved dielectric properties of Al2O3 thin films are highly comparable with that by vapor and solution methods. Moreover, the fully solution-processed InZnO TFTs with Al2O3 dielectric layer exhibit high mobility of 7.23 cm2 V−1 s−1 at the low operating voltage of 3 V, which is much superior to that on SiO2 dielectrics with mobility of 1.22 cm2/V−1 s−1 at the operating voltage of 40 V. These results demonstrate that solution-processed Al2O3 thin films are promising for low-power and high-performance oxide devices.