FABRICATION OF YBCO STEP-EDGE JOSEPHSON-JUNCTIONS BY INVERTED CYLINDRICAL MAGNETRON SPUTTERING TECHNIQUE

The Inverted Cylindrical Magnetron Sputtering (ICMS) technique has been used to fabricate YBCO step-edge junction dc SQUIDs. Steps are obtained by standard ion milling procedure on LaAlO3 (100) substrates using Nb-masks patterned by reactive ion etching. Thin films are then deposited under different conditions (both step and deposition angles) and patterned by standard lithography and wet chemical etching. An analysis of junction properties in terms of step height and film thickness has been carried out. Measurements on current vs voltage, maximum dc Josephson current vs magnetic field and SQUID voltage response measurements have been performed. Their temperature dependences have been also considered. Operating temperature as high as 77 K 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(o) and a good periodicity of the V-phi modulation up to 20 Phi(o) without any sign of hysteresis.