Hydrothermal and electrochemical growth of complex oxide thin films for electronic devices

Thin film growth of complex oxides including BaTiO3, SrTiO3, BaZrO3, SrZrO3, KTaO3, and KNbO3 were studied by the hydrothermal and the hydrothermal–electrochemical methods. Hydrothermal–electrochemical growth of ATiO3 (A = Ba, Sr) thin films was investigated at temperatures from 100 to 200 °C using a three-electrode cell. Current efficiency for the film growth was in the range from ca. 0.6 to 3.0%. Tracer experiments revealed that the ATiO3 film grows at the film/substrate interface. Thin films of AZrO3 (A = Ba, Sr) were also prepared on Zr metal substrates by the hydrothermal–electrochemical method. By applying a potential above ca. +2 V versus Ag/AgCl to the Zr substrates, AZrO3 thin films were formed uniformly. Thin films of KTaO3 and KNbO3 were prepared on Ta metal substrates by the hydrothermal method. Perovskite-type KTaO3 thin films were formed in 2.0 M KOH at 300 °C. Pyrochlore-type K2Ta2O6 thin films were formed at lower temperatures and lower KOH concentrations.