DIELECTRIC-PROPERTIES OF SINGLE-CRYSTALS OF AL2O3, LAALO3, NDGAO3, SRTIO3, AND MGO AT CRYOGENIC TEMPERATURES

A dielectric resonator technique has been used for measurements of the permittivity and dielectric loss tangent of single-crystal dielectric substrates in the temperature range 20-300 K at microwave frequencies . Application of superconducting films made it possible to determine d ielectric loss tangents of about 5 x 10(-7) at 20 K. Two permittivity tenser components for uniaxially anisotropic samples were measured. Ge nerally, single-crystal samples made of the same material by different manufacturers or by different processes have significantly different losses, although they have essentially the same permittivities. The pe rmittivity of one crystalline ferroelectric substrate, SrTiO3, strongl y depends on temperature. This temperature dependence can affect the p erformance of ferroelectric thin-film microwave devices, such as elect ronically tunable phase shifters, mixers, delay lines and filters.