Toward ultraviolet solution processed ZrO_x/IZO transistors with top-gate and dual-gate operation: Selection of solvents, precursors, stabilizers, and additive elements

Low-temperature processed oxide thin-film transistors (TFTs) have been developed by the process of solution-processed metal oxide films using deep ultraviolet (UV) irradiation, although they still suffer from relatively poor electrical performance and severe electrical and chemical instability. This UV coating solution essentially involves chemical damage from acidic or basic precursor ligands; therefore, the top-gate and dual-gate TFTs suffer structurally inherent chemical damage, which limits the freedom of process design. An engineering concept solution using the four functional components of solvent, precursor, stabilizer, and additive was suggested for UV solution coating of high-k zirconium oxide (ZrO_x). Here the proposed solvent, stabilizer, precursor, and additive include polar-aprotic N,N-methylformamide, zirconium acetylacetonate, ethanolamine, and oleic acid for polar-aprotic solution, effective photolysis, complete precursor dissolution, and high densification, respectively. The ultrathin ZrO_x (15 nm) revealed a low leakage current density of <10⁻¹¹ mA/cm² at 1 MV/cm, good breakdown voltage, and a constant capacitance of approximately 260 nF/cm² at 1 MHz. Similar transfer characteristics of both the bottom and top gates, and a field-effect mobility of 24 cm²/V, without degradation of subthreshold swing and threshold voltage values in the dual-gate, were involved in the chemically durable process and the dense coating conditions of ZrO_x, regardless of the IZO and ZrO_x stacking sequence.