Asymmetric ferroelectricity and conduction of anomalous leakage current were observed in heteroepitaxial BaTiO3 thin films grown by rf magnetron sputtering at 600° C on three different electrode/substrate combinations: SrRuO3/SrTiO3, Pt/MgO and Nb doped SrTiO3. The voltage shift of hysteresis loops of the capacitance was a linear function of the thickness of the BaTiO3 films and became as large as 10 V in the film with a thickness of 410 nm. The asymmetry did not disappear even after a heat treatment carried out at 800° C in air. On the other hand, a steep increase in the leakage current was observed in the heteroepitaxial films when a positive voltage was applied. The origin of both the asymmetric hysteresis and the anomalous conduction is discussed in terms of asymmetric crystal structure caused by misfit dislocations introduced in heteroepitaxial growth.

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Ferroelectric properties were investigated using SrRuO3/(Ba x , Sr1-x )TiO3(BSTO)/SrRuO3 all-perovskite heteroepitaxial capacitors on strontium titanate substrates. The dielectric film had a composition with a Ba content of x=0 to 1, i.e., the whole composition of the SrTiO3–BaTiO3 solid-solution system. The c-axis of the BSTO film was elongated depending on the Ba content, and reached 0.441 nm at the BaTiO3 composition, which was 8.6% larger than the bulk c-axis. A peak relative dielectric constant of 870 and maximum remanent polarization (2P r) of 58 µC/cm2 were obtained depending on the Ba content at a dielectric thickness of 20 nm. These are the highest storage capacitance capacitor and the thinnest ferroelectric capacitor reported so far. Possibilities for deep submicron ferroelectric and dielectric memory applications are also discussed.

Crystal structure and magnetic properties in epitaxially grown Sr1−xBaxRuO3 on SrTiO3 substrates were determined. Epitaxial Sr1−xBaxRuO3 exhibits a simple perovskite structure in the whole region of the Ba/Sr ratio, in contrast to the complex hexagonal layered perovskite of Ba-rich bulk Sr1−xBaxRuO3, which has plane-sharing oxygen octahedra. Tetragonal deformation was enhanced from pseudocubic in SrRuO3 to a highly distorted tetragonal lattice in BaRuO3. Electronic properties such as conductivity and magnetization were examined. A metal–insulator transition was not observed in this system, and metallic conductivity was maintained in the whole region of Ba concentration. Ferromagnetic ordering at 160 K seen in bulk SrRuO3 was observed to be suppressed in the Sr1−xBaxRuO3 films with increasing tetragonal deformation and Curie temperatures decreased to 50 K in BaRuO3.

Heteroepitaxial Ba0.6Sr0.4TiO3 thin films with thicknesses from 26 nm to 97 nm were grown on SrRuO3 bottom electrode films on SrTiO3 single crystal substrates. Although the films have a paraelectric composition, ferroelectric hysteresis was observed in displacement versus electric field (D–E) loops. The ferroelectricity is considered to be developed as a result of bi-axial stress, caused by lattice mismatch between the dielectric films and the bottom electrodes. The maximum difference in the displacement was over 0.4 C/m2, even when the thickness of the film was reduced to 26 nm. The hysteresis loops showed an asymmetric characteristic at a polarity of applied voltage. The asymmetry was discussed in terms of an asymmetrical deformation of the crystal structure, which is probably introduced during the heteroepitaxial growth.