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 Tc(R=0) of 91K, whereas BSCCO film had predominantly c-axis oriented high-Tc 2223 phase with Tc(R=0) of 104K. Voltage-flux (V=Φ) modulations in YBCO rf-SQUID have been observed up to 85.1K, whereas, in BSCCO rf-SQUID, the modulations were present up to 98K. Both the SQUIDS have been operated successfully in flux-locked-loop mode at 77K. Both YBCO and BSCCO rf-SQUIDs showed single periodicity in V-Φ modulations corresponding to the area of the SQUID loop. Flux noise density, √S sub(Φ) ∼ 5 x 10-4 Φ0/√Hz for BSCCO rf-SQUID is found to be less than YBCO rf-SQUID (1 X 10-3Φ0/√Hz) at 77K in the white noise region (f> 1Hz). As compared to YBCO rf-SQUID, BSCCO rf-SQUID has been found to be more stable even after several thermal cycling. (author). 13 refs., 18 figs., 1 tab