Process Issues and Components for HTS Digital Integrated Circuit Fabrication

An etch-back planarization technique has been developed to planarize SrTiO3 insulating layers, which may be used in a YBCO IC process. Films of YBCO have been deposited on the planarized SrTiO3 surface. Structural and electrical characterization of these films suggests that the planarized surface can support the growth of epitaxial, c-axis oriented YBCO films. Experiments to evaluate and compare coupling efficiency in YBCO and Nb thin film Transformers are also described. Easy flux penetration in YBCO films may reduce the efficiency of transformer coupling below that found for Nb Transformers. The current coupling for Nb Transformers, as extracted from the SQUID threshold curves, was found to be high (M/L ∼ 0.93). The coupling in YBCO Transformers, as measured from the voltage modulation of bicrystal grain boundary junction SQUIDs, was found to be much lower (MIL ~ 0.75).