Present status and future of DC SQUIDs made from high-T_c superconductors

Superconducting Quantum Interference Devices (SQUIDs) that operate at 77 K have now been fabricated by many groups from high temperature superconductors. We will examine the performance of high-Tc SQUIDs, including the issues of the periodicity and hysteresis of the response, the magnitude of the noise in the SQUIDs, and the manufacturability of the devices. The nature of the junctions forming the SQUIDs, which have been naturally occurring grain boundaries in all but a few of the reported devices, and the physical mechanisms responsible for the noise sources will be reviewed. The possible applications of these and future high-Tc SQUIDs will also be examined. © 1991.