Thin film Y-Ba-Cu-O/Ag composites for fluxonic devices

We have investigated thin film composites of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) with Ag for fluxonic device applications. YBCO/Ag composite films are produced by first depositing a layer of Ag onto a substrate and then heating the film to the YBCO deposition temperature of 680/spl deg/C or higher. YBCO is deposited by off-axis sputtering onto the Ag-coated substrate. The resulting YBCO/Ag film is a composite of YBCO with well-defined Ag regions several microns in size. Scanning electron micrograph images of the films' surfaces show a background of smooth YBCO grains dotted with Ag clusters. For a wide range of increasing Ag composition, the transition temperatures of the composite films on SrTiO/sub 3/ remain high, while the critical current densities have been reduced as much as 65 times. On MgO substrates, critical current density has been reduced by more than four orders of magnitude. Also on MgO, significant voltage response is seen in external magnetic fields of less than 1 mT. These measurements suggest that the films may be arrays of superconductor-normal-superconductor (SNS) junctions formed by weakly coupled YBCO grains with Ag in the grain boundaries. The field responsivity and low critical current densities of these composites make them potentially useful for fabrication of fluxonic devices.