DEVELOPMENT OF MATERIALS FOR HIGH-TEMPERATURE SUPERCONDUCTOR JOSEPHSON-JUNCTIONS

We have conducted a systematic optimization of deposition parameters for fabrication of multilayered oxide films to be used in the development of high temperature superconducting YBa2Cu3O7-x Superconducting Normal Superconducting junctions. These films were deposited onto <100> MgO substrates by off-axis sputtering using a custom fabricated multi-gun planar magnetron system. Each layer and the various combinations of materials were optimized for: epitaxial lattice match, crystal quality, film uniformity, electrical properties, and surface microstructure. In addition to the standard procedures commonly used to sputter deposit epitaxial oxide films, a variety of unique insitu and exsitu procedures were used to produce high quality multilayer devices, including: using a film nucleation temperature lower than the final film growth temperature, establishing the optimum substrate to target relationship, and timing of the oxygen anneal. Using a lower nucleation temperature when depositing the YBa2Cu3O7-x allowed us to dramatically improve the crystallinity and orientation of the superconductor on both unprocessed and ion-milled substrates. Completed multilayer devices consistently exhibited resistively shunted Josephson junction behavior in patterned bridges and SQUID's.