Aqueous Inorganic Inks for Low-Temperature Fabrication of ZnO TFTs

A simple, low-cost, and nontoxic aqueous ink chemistry is described for digital printing of ZnO films. Selective design through controlled precipitation, purification, and dissolution affords an aqueous Zn(OH) x (NH3) y (2−x)+ solution that is stable in storage, yet promptly decomposes at temperatures below 150 °C to form wurtzite ZnO. Dense, high-quality, polycrystalline ZnO films are deposited by ink-jet printing and spin-coating, and film structure is elucidated via X-ray diffraction and electron microscopy. Semiconductor film functionality and quality are examined through integration in bottom-gate thin-film transistors. Enhancement-mode TFTs with ink-jet printed ZnO channels annealed at 300 °C are found to exhibit strong field effect and excellent current saturation in tandem with incremental mobilities from 4−6 cm2 V−1 s−1. Spin-coated ZnO semiconductors processed at 150 °C are integrated with solution-deposited aluminum oxide phosphate dielectrics in functional transistors, demonstrating both high performance, i.e., mobilities up to 1.8 cm2 V−1 s−1, and the potential for low-temperature solution processing of all-oxide electronics.