Synthesis, Microstructure and Electrical Properties of Hydrothermally Prepared Ferroelectric BaTiO3 Thin Films

Thin films of polycrystalline, tetragonal BaTiO₃ on oxidized Ti metal substrates were synthesized at 240°C under hydrothermal conditions. Microstructure and electrical properties of the films generated over a four week period of synthesis formed the focus of this study. The films displayed a smooth and shiny surface with a relatively dense structure and no observable cracks. Film thickness reached 0.5 m after two weeks of synthesis and thereafter remained constant. Diameters of the grains on the film surface were in the range of 12 m. It is proposed that initial formation of the BaTiO₃ film occurs by reaction of Ba²⁺ with solubilized titanium oxide on the Ti metal surface followed at later stages by an in-situ growth via reaction of TiO_x with Ba²⁺ diffusing through the BaTiO₃ film. X-ray diffraction and Raman spectroscopy indicated that the BaTiO₃ films are tetragonal, and the films exhibited typical ferroelectric hysteresis loops at room temperature. However, no evidence of the dielectric anomaly (Curie transition) between 30 and 200°C was observed. Dielectric constant of the films at 1 kHz at room temperature was between 400–500. Both dielectric constant and tan exhibited low dispersion as a function of frequency at temperatures below 150°C, and the dispersion increased with temperature.