Dielectric spectroscopy of perovskite-type artificial superlattice in micro to millimeter wave region

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Artificial superlattices made by a thin film technology of atomic level have potential to show excellent and new properties due to the man made structures. In this study, we have developed a technology to measure dielectric properties of the perovskite type artificial superlattices from kHz to few GHz in order to find unique properties of the superlattices in micro and millimeter wave regions. At first, a system which enables us to measure dielectric properties up to 110MHz was developed and the properties of BaTiO_3/SrTiO_3 superlattices were measured. The dielectric permittivity of the superlattices was determined using electromagnetic field analysis of admittance data obtained using interdigital electrodes on the films. It was found that the superlattice with the period of 10 unit cells showed high permittivity of 33,000 up to 110 MHz. The dielectric properties of SrZrO_3/SrTiO_3 superlattices were also measured and it was found that the superlattice with the period of 10 unit cells showed ferroelectricity in spite of the paraelectric/paraelectric combination of the materials. Furthermore, a new measuring method of dielectric properties in micro wave region was proposed. In this method, fine planer electrodes were employed to measure admittance of the specimen. The dielectric permittivity of [(SrZrO_3)_<10>/(SrTiO_3)_<10>]_4 superlattice was above 8,000 below 100 MHz and it decreased around 4,000 at 3 GHz.