Low-temperature fabrication of solution-processed hafnium oxide gate insulator films using a thermally purified solution process

We proposed a simple method, a thermally purified solution (TPS) process, to lower the fabrication temperature of solution-processed hafnium oxide (HfO_x) gate insulator films. The TPS process is proceeded by transferring thermal energy to the HfO_x precursor solution 'BEFORE' film formation. The TPS process could induce chemical reactions including pre-hydrolysis by thermal energy in the HfO_x precursor solution. These chemical reactions reduce the required thermal energy for forming a solution-processed HfO_x film and improve the film quality. As a result, the HfO_x film fabricated via the TPS process has satisfactory dielectric characteristics: a breakdown electric field of ∼6 MV cm^-1, a leakage current density of ∼10^-9 A cm^-2, and a dielectric constant of 10.23 at low temperatures, i.e., below 200 °C. Solution-processed indium oxide (In₂O₃) thin film transistors with a HfO_x gate insulator fabricated via the TPS process exhibit a field effect mobility of 3.67 cm² V^-1 s^-1, an on/off current ratio of 9.8 × 10⁶, and a subthreshold swing of 0.18 V dec^-1.