Effects of Solution Temperature on Solution-Processed High-Performance Metal Oxide Thin-Film Transistors

Herein, we report a novel and easy strategy for fabricating solution-processed metal oxide thin-film transistors by controlling the dielectric constant of H2O through manipulation of the metal precursor solution temperature. As a result, indium zinc oxide (IZO) thin-film transistors (TFTs) fabricated from IZO solution at 4 °C can be operated after annealing at low temperatures (∼250 °C). In contrast, IZO TFTs fabricated from IZO solutions at 25 and 60 °C must be annealed at 275 and 300 °C, respectively. We also found that IZO TFTs fabricated from the IZO precursor solution at 4 °C had the highest mobility of 12.65 cm2/(V s), whereas the IZO TFTs fabricated from IZO precursor solutions at 25 and 60 °C had field-effect mobility of 5.39 and 4.51 cm2/(V s), respectively, after annealing at 350 °C. When the IZO precursor solution is at 4 °C, metal cations such as indium (In3+) and zinc ions (Zn2+) can be fully surrounded by H2O molecules, because of the higher dielectric constant of H2O at lower temperatures. These chemical complexes in the IZO precursor solution at 4 °C are advantageous for thermal hydrolysis and condensation reactions yielding a metal oxide lattice, because of their high potential energies. The IZO TFTs fabricated from the IZO precursor solution at 4 °C had the highest mobility because of the formation of many metal-oxygen-metal (M-O-M) bonds under these conditions. In these bonds, the ns-orbitals of the metal cations overlap each other and form electron conduction pathways. Thus, the formation of a high proportion of M-O-M bonds in the IZO thin films is advantageous for electron conduction, because oxide lattices allow electrons to travel easily through the IZO.