Epitaxial Growth of BaTiO₃ Thin Films and Thier Internal Stresses

Effects of substrate pre-treatment and O 2 partial pressure on the epitaxial growth of sputter-deposited BaTiO 3 films on (100)MgO have been studied. When the film thickness is 20 nm, significant differences in the surface crystallinity and morphology of the films are produced by HCl etching of the substrate surface. In 200-nm-thick films, on the other hand, there is no significant difference in the crystallinity between films on etched and as-received substrates. Differences in surface structure with increasing film thickness are also observed. The lattice constant parallel to the film thickness of the 20-nm-thick films is smaller than the theoretical value, and in the 200-nm-thick films, the lattice constants both perpendicular and parallel to the growth direction are larger than those of the BaTiO 3 bulk material. The stress change can be well explained in terms of epitaxial restriction from the substrate and peening effect of O species during sputtering.