Effect of the residual stress induced by external stress application on dielectric properties of epitaxial lead titanate film

Relationships among in-plane residual stress and some dielectric properties (remanent polarization, coercive field, dielectric permittivity, etc.) were investigated on ferroelectric thin films. Epitaxial PbTiO₃ thin films were deposited on Pt/(100)SrTiO₃ substrate by MOCVD. Residual stresses of the films were determined by a modified sin2Ψ method. The external stress in this study could be varied from +2.0 GPa up to +6.0 GPa. We first observed the change of the dielectric properties together with the tensile stress application in actual experiments; decrease of the remanent polarization from 11 μC·cm^-2 down to 3 μC·cm^-2 and of the coercive field from 115 kV·cm^-1 down to 95 kV·cm^-1. The Curie temperature of the film was decreased from 450°C to 437°C with increasing the residual stress, while the dielectric permittivity at room temperature was measured to be approximately 210, irrespectively of the residual stress. Further, the tensile stress caused deformation of PbTiO₃ crystal lattice, which was described as the decrease of the c/a ratio. We conclude that the residual stress varied the dielectric properties by deforming: the crystal lattice.