Design, fabrication, and performance of integrated miniature squid susceptometers

Abstract

Integrated, miniature, thin-film DC SQUID susceptometers have now been applied in the investigation of a number of interesting physical systems. The leverage of such susceptometers derives from their ability to measure with extreme sensitivity the magnetic properties of micron size samples at low temperatures. In this paper we first propose a figure of merit for miniature susceptometers and then go on to discuss hew this varies with scaling of dimensions, The range of applications for miniature susceptometers can be considerably broadened through improved magnetic, optical, and thermal isolation between the pickup loops and active SQUID elements. We review techniques for integrating such features into single chip structures, as well as modular designs where SQUID and pickup loops are on physically separate substrates and connected by low inductance wire bonds. Extension of this latter technique should make possible the incorporation of commercial SQUIDs as well as high Tc superconductors. Experimental results on some of the systems we have built and operated are also presented. © 1989 IEEE