SUBSTRATES FOR HIGH-T-C SUPERCONDUCTOR MICROWAVE INTEGRATED-CIRCUITS

This review paper presents a discussion on dielectric substrate materials suitable for the preparation of YBa2Cu3O7-x thin-film based microwave integrated circuits. The requirements on the properties of the substrate materials are specified. They cover the properties crucial both for the preparation of high-quality YBa2Cu3O7-x films and for the design of microwave elements. The former includes mainly the lattice match, the match of thermal expansivities, chemical stability, and absence of twinning. The latter includes the relative dielectric permittivity (epsilon) and the related tolerances, the microwave loss tangent, and the substrate area required for the accommodation of a microwave circuit. The properties of the currently available substrates suitable for YBCO film epitaxy are discussed in view of these requirements. The main attention is paid to the microwave properties. Current achievements and potential difficulties of the crystal growth technology in the preparation of the substrates are taken into account as well.