Ferroelectric Properties in Heteroepitaxial Ba0.6Sr0.4TiO3 Thin Films on SrRuO3/SrTiO3 Substrates

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.