Temperature dependence of dielectric permittivity of Perovskite-type artificial superlattices

Perovskite-type BaTiO₃/SrTiO₃ (BTO/STO) artificial superlattices were fabricated on STO substrates by molecular beam epitaxy method. The XRD profiles and the RHEED oscillations during the growth of superlattices indicated that crystalline orientation toward (001) direction and two dimensional layer-by-layer growth were achieved. The capacitance and complex admittance of superlattices were measured up to 145degC and up to the frequency of 100 MHz with the micro-planer interdigital electrodes. Dielectric permittivity of superlattices was evaluated from the complex admittance with an electromagnetic field analysis as a function of temperature. The relative permittivity of [BTO₁₀/STO₁₀]₄ superlattices was about 20,000 at room temperature and increased with increasing temperature. It was found that the BTO/STO superlattices did not show a peak in the dielectric permittivity vs. temperature curve, which was different from the behavior of BTO-STO bulk ceramics and thin films. This result strongly supported that the high permittivity of the superlattices was caused by a temperature stable anisotropic strains induced in the superlattices.