Is it possible to fabricate a relaxation oscillation SQUID, using high temperature superconductors and grain boundary junctions?

We discuss whether it would be possible to fabricate Relaxation Oscillation SQUIDs (ROSs) using high temperature superconductors (HTSs). This would require HTS junctions with significant hysteresis at high temperatures and we have attempted to induce this using external capacitive shunts. We achieved McCumber parameter values as large as /spl beta//sub c/=4.5 at 40 K and were able to maintain /spl beta//sub c/>1 to 72 K. However we found that small junction resistances, thermal noise associated with high temperature operation and transmission line resonances in the shunt capacitor limit the value of /spl beta//sub c/. Using the parameters we obtained, we have simulated the performance of a ROS at 60 K and found that voltage pulses were generated. However, the small time averaged voltage across the ROS, would make it impossible to construct a working D-ROS. Despite this, it may be possible to detect the pulses and use them to construct a digital SQUID.