Fabrication and characterization of weak links anddc SQUIDs in the high-temperature superconductor yttrium barium copper oxide

Electron beam lithography and liftoff have been used to pattern sub-quarter-micron weak links in ;Microscopic examination of the bridge structures has revealed unexpected growth patterns of the YBCO material during post-deposition annealing. Faceting, which occurs in the corners of small (i.e. width ;These junctions have also been used to fabricate a dc SQUID which has 150 nm junctions, the smallest yet reported. In the case of the dc SQUID, its response to an applied magnetic field has been evaluated and the changes in this response as a function of temperature and applied bias current have been studied.;This SQUID not only functions at 77 K, but also has a greater voltage modulation at this temperature than typical grain boundary junction SQUIDS. At 77 K the voltage response to dc flux is sinusoidal and nonhysteretic, with maximum peak-to-peak amplitude of 5 ;Random telegraph noise was observed in this SQUID near 30-40 K and speculations as to the mechanisms responsible for this behavior are presented. Also, a possible explanation for the Josephson junction behavior of our sub-micron bridges is offered in light of recent results reported for other YBCO junctions.