SrTiO₃ films on platinized (0001) Al₂O₃: Characterization of texture and nonstoichiometry accommodation

Transmission electron microscopy and x-ray diffraction were used to study SrTiO₃ films grown on platinized (0001) Al₂O₃ substrates. The Pt films were epitaxial with an orientation relationship described by (111)_Pt‖(0001)_{Al₂O₃} and [110]_Pt‖[10^¯₁0]_{Al₂O₃}. SrTiO₃ films with two different Sr to Ti ratios, 1.02 and 1.4, were deposited by radio-frequency magnetron sputtering. In the film with a large amount of Sr excess, the grain sizes were smaller and a high density of planar defects was observed. The films were predominantly (111) textured, but a weaker (110) texture component was also found, independent of stoichiometry. While the (111) texture could be explained with the excellent lattice match with (111) Pt, the (110) textured grains had a large mismatch with the Pt electrode. We propose that the presence of the (110) oriented grains is due to nucleation at Pt surface defects. Planar defects in the films with a large amount of Sr excess served to accommodate the nonstoichiometry. Comparison with homoepitaxial SrTiO₃ films showed that the density of planar defects in the SrTiO₃ films on (111)Pt/Al₂O₃ is insufficient to accommodate all the excess Sr. The influence of the film microstructure on the dielectric properties is also discussed.