Fabrication of high quality YBa/sub 2/Cu/sub 3/O/sub y/ thin films using pulsed laser deposition

High quality YBa/sub 2/Cu/sub 3/O/sub y/ (YBCO) thin films for directly coupled DC-SQUIDs were fabricated by pulsed laser deposition. Several critical parameters have been optimized through systematic studies. The best quality YBCO thin films on MgO and on LaAlO/sub 3/ substrates were made under the O/sub 2/ pressure of 400/spl sim/500 mTorr at the substrate temperature of 780/spl sim/800/spl deg/C and target to substrate distance of 50/spl sim/60 mm. Films showing a T/sub c/ above 91 K and J/sub c/ above 2/spl times/10/sup 6/ A/cm/sup 2/ at 77 K were routinely obtained. Extensive AFM and x-ray diffraction studies have been conducted for morphological and structural analyses. The directly coupled DC-SQUIDs were fabricated from the YBCO thin films deposited on SrTiO/sup 3/ bicrystals under the optimized conditions. Measurement of 2I/sub c/ and swing voltage gives values of 420 /spl mu/A and 30 /spl mu/V at 77 K, respectively.