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.