STUDIES ON YBCO AND BSCCO THICK-FILM RF-SQUIDS AT LIQUID-NITROGEN TEMPERATURES

RF-SQUID behaviour in YBCO and BSCCO thick films has been studied by patterning a hole interrupted with a microbridge type of structure on the films. YBCO film used for the rf-SQUID fabrication had mixed orientation with T(c)(R = O) of 91 K, whereas BSCCO film had predominantly c-axis oriented high-T(c) 2223 phase with T(c)(R = O) of 104 K. Voltage-flux (V-PHI) modulations in YBCO rf-SQUID have been observed up to 85.1 K, whereas, in BSCCO rf-SQUID, the modulations were present up to 98 K. Both the SQUIDs have been operated successfully in flux-locked-loop mode at 77 K. Both YBCO and BSCCO rf-SQUIDs showed single periodicity in V-PHI modulations corresponding to the area of the SQUID loop. Flux noise density, square-root S(PHI) almost-equal-to 5 x 10(-4) PHI(o)/square-root Hz for BSCCO rf-SQUID is found to be less than YBCO rf-SQUID (1 X 10(-3) PHI(o)/square-root Hz) at 77 K in the white noise region (f > 1 Hz). As compared to YBCO rf-SQUID, BSCCO rf-SQUID has been found to be more stable even after several thermal cycling.