Integrated thin-film dc SQUID sensors

This paper reviews the design of integrated thin-film dc SQUID sensors fabricated in planar technology. Included are both high performance devices with fully integrated input coils and more advanced devices that incorporate fully integrated pickup loop structures as well, such as gradiometers and miniature susceptometers and magnetometers. First the basic characterization of the dc SQUID is given. Operation and performance issues are discussed followed by a review of the status of planar coupling schemes. A brief discussion of packaging is given. Design considerations for planar gradiometers are presented. The configuration of a balanced coupled SQUID for gradiometer applications is detailed, and some key design concerns for gradiometer arrays are mentioned. The design and application of a miniature SQUID susceptometer is reviewed, and a brief description of several other miniature susceptometer and magnetometer designs is given.