High-T_c superconducting quantum interference devices: Status and perspectives

In this paper, an overview of the current status of high- Tc superconducting quantum interference devices (SQUIDs), from device engineering to biomagnetic applications, is given. The authors offer a description of the current status of SQUID sensors, challenges encountered, and the solution of fabricating SQUID sensors with low flux noises. The current challenge that we face is to fabricate high- Tc SQUIDs that are not only more reproducible than the current technology but also capable of providing a high Ic Rn product and fabricating SQUID with high yield. Improvement of flux noises and fabrication yield in the integrated multichoices directly coupled SQUID magnetometer or gradiometer with series SQUID array are presented. High- Tc SQUID magnetometers exhibiting magnetic field sensitivity of ∼30-50 fT Hz12 or better at 100 Hz was demonstrated by incorporating serial SQUID into the pickup loop of the magnetometers. New technologies currently being developed and applications for high- Tc SQUIDs are addressed.