DC SQUIDS BASED ON YBCO STEP-EDGE JUNCTIONS

We describe the fabrication and testing of dc SQUIDs (Superconducting QUantum Interference Devices) obtained by photolithographic patterning of YBa2Cu3O7-x thin films deposited both on SrTiO3 and MgO substrates. The Josephson junctions in the superconducting loop are of the ''step-edge'' type, where the weak link is obtained through the growth of grains with different orientations across suitably prepared steps previously etched on the substrate surface. The I - V characteristics of the devices tested show multiple branches and instabilities having a weak dependence on the external magnetic field, probably due to formation of junction clusters on the substrate step. The SQUID devices showed quantum interference behavior and an easily detectable voltage modulation with the applied magnetic field at a temperature of 77 K.