Fabrication and characterization of hybrid Nb-YBCO dc SQUIDs

This paper reports on the fabrication of hybrid low Tc/high Tc dc SQUIDs of two flavors. The first kind utilizes niobium tunnel junctions and a YBCO film strip as the most inductive portion of the SQUID loop. This configuration allows a direct measurement of the inductance of the YBCO microstrip from which the effective penetration depth can be calculated. The successful fabrication of these SQUIDs has required 1. superconducting Nb-to-YBCO contacts, 2. deposition and patterning of an SiO2 insulation layer over YBCO, and 3. selective patterning of niobium and SiO2 relative to YBCO. All these process steps are pertinent to the eventual use of YBCO thin films in electronic devices