HIGH-TEMPERATURE OXIDE SUPERCONDUCTOR DOUBLE-HOLE RF-SQUID

A double-hole RF-SQUID made from sintered bulk YBCO has been developed. At both 77 K and 4.2 K devices can operate in lock mode and display typical flux modulation characteristics of the external field. At 77 K, the equivalent flux noise of the device is 2 x 10(-3) phi-0/ square-root Hz near the DC end, and it decreases to 5 x 10(-4) phi-0/ square-root Hz between 20 and 200 Hz. The characteristics of the device show similarities to those of the liquid helium conventional RF-SQUID. There is no detectable change in behavior of the device after it is stored in air or liquid nitrogen for more than two years and undergoing dozens of thermal cycles between 77 K and room temperature. Design and fabrication of the device, determination of critical current and its potential applications are discussed.