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

This review paper presents a discussion on dielectric substrate materi als suitable for the preparation of YBa2Cu3O7-x thin-film based microw ave integrated circuits. The requirements on the properties of the sub strate materials are specified. They cover the properties crucial both for the preparation of high-quality YBa2Cu3O7-x films and for the des ign of microwave elements. The former includes mainly the lattice matc h, 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 circ uit. The properties of the currently available substrates suitable for YBCO film epitaxy are discussed in view of these requirements. The ma in attention is paid to the microwave properties. Current achievements and potential difficulties of the crystal growth technology in the pr eparation of the substrates are taken into account as well.