YBCO STEP-EDGE SQUIDS BY MAGNETRON SPUTTERING TECHNIQUE

YBCO step-edge junction d.c. SQUIDs have been realized by using the Inverted Cylindrical Magnetron Sputtering (ICMS) technique. This last represents a novel technology for high-T-c Josephson junctions (HTSC). Steps are obtained by standard ion milling procedure on LaAlO3 (100) substrates using Nb-masks patterned by reactive ion etching. Measurements of current vs. voltage, maximum d.c. Josephson current vs. magnetic field and SQUID voltage response measurements have been performed, also as a function of the temperature. Operating temperature as high as 77K has been achieved. At 4.2 K the SQUIDs show a maximum voltage to flux transfer function (partial derivative V/partial derivative phi)(max) = 870 mu V/Phi(0) and a good periodicity of the V-phi modulation up to 20 Phi(0) without any sign of hysteresis. The ratio between the step height (h) and the film thickness (d) seems to play a fundamental role in determining Josephson properties of the bridges, these conditions being more severe with respect to most of the data available in literature.