Preparation of epitaxial ABO₃ perovskite-type oxide thin films on a (100)MgAl₂O₄/Si substrate

Epitaxial thin films of ABO₃ perovskite-type oxides, including PbTiO₃, (Pb_0.90La_0.10) (Zr _0.65Ti_0.35)_0.975O₃,BaTiO ₃, and SrTiO₃, have been successfully obtained by rf magnetron sputtering on (100)Si substrate with an intermediate epitaxial layer of MgAl₂O₄. Only PbTiO₃ grew in the tetragonal crystal structure and other materials grew in the cubic structure. The unit axis direction of the perovskite-type oxide films was coincident with that of the underlying MgAl₂O₄ films. The tetragonal PbTiO₃ films were a mixture of c and a domain. The preferred orientation of the tetragonal PbTiO₃ film, that is c to a domain volume ratio, could be controlled by the conditions of sample cooling after the deposition. Highly c-axis oriented films, which consisted of more than 90% c domains, were produced by cooling the sample at a high cooling rate, typically 30°C/min, and by maintaining an rf plasma during cooling. The mechanism of the preferred orientation of PbTiO₃ film has been explained by a balance of compressive stress due to a self-bias effect and tensile stress due to the lattice mismatch and due to the lattice anisotropy of tetragonal PbTiO ₃.