Low temperature synthesis of Y-Ba-Cu oxide films and preparation of DC-SQUIDs

The authors have synthesized superconducting Y-Ba-Cu oxide thin films by RF sputtering at a relatively low substrate temperature (about 650°C). Films of 300-700 nm thickness have Tc of 60-72 K without annealing after the deposition. A preferential orientation with a c -axis perpendicular to the surface was observed. DC SQUIDs (superconducting quantum interference devices) having two parallel microbridges with constriction of submicrometer to 40-μm width were fabricated from the oxide films by chemical etching. The microbridges with greater than 2-μm-width did not operate as Josephson devices. The characteristics of these SQUIDs suggested vortex flow. Periodic modulation of the voltage with magnetic flux was observed in a SQUID having submicrometer microbridges. Telegraph-like noise of the voltage which exhibits switching between two or more discrete levels was observed in all of the SQUIDs irrespective of the width of the microbridges. This noise was also observed in a single microbridge, and its effective switching rate increased exponentially with the increase of temperature above 15 K