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A heteroepitaxial BaTiO3 film with a thickness of 65 nm was prepared on SrRuO3/Pt/TiAlN/Si. The Ti0.91Al0.09N film was grown on Si substrate by DC sputtering in Ar/N2 ambient at 700°C. The BaTiO3, SrRuO3 and Pt films were deposited by radio-frequency magnetron sputtering at substrate temperatures ranging from 450°C to 600°C. The BaTiO3 film has a c-axis 1.6% longer (0.410 nm) than that of bulk, due to lattice misfit between SrRuO3 and BiTiO3. When positive and negative voltage pulses with an amplitude of 5 V were applied, a switching charge density, Q sw, of 40 μC/cm2 was obtained. No fatigue was observed after 1011 cycles of polarization switching even when an amplitude of 7 V was applied. Remanence of polarization for 4 hours was confirmed in a retention test. These results indicate that the heteroepitaxial BaTiO3 film capacitors on Si substrates can be used for ferroelectric nonvolatile memory applications.

Modification of ferroelectricity in heteroepitaxial Ba x Sr1-x TiO3(BST) films by making use of lattice misfit was investigated. Theoretical calculation suggested that application of two-dimensional compressive stress of 3 GPa to the ferroelectric crystal would result in Curie temperature increase by 270°C. This theoretical prediction was experimentally confirmed. Heteroepitaxial Ba0.6Sr0.4TiO3 films grown on SrRuO3/SrTiO3 substrates exhibited ferroelectric hysteresis at 200°C, even though the inherent Curie temperature is known to be 0°C. The possibility of heteroepitaxial BST films for ferroelectric non-volatile memory applications and their advantages were pointed out.