Thin film technology for high and low Tc SQUIDs

Abstract

The author reviews recent advances in thin-film technology for low-temperature and high-temperature SQUIDs (superconducting quantum interference devices) and their associated coupling structures. For years, nearly quantum limited operation of low-Tc SQUIDs has been available in laboratory demonstrations, but only recently have practical devices that harness this sensitivity for useful measurements been put into operation. Until now this has mostly been done by configuring experiments that can be well coupled to the small inductance of nearly quantum limited SQUIDs. As an example, a SQUID operating at 290 mK has been coupled to a pickup coil in a microsusceptometer configuration so as to achieve an equivalent spin sensitivity of approximately 3 × 103 spins/√Hz. It is suggested that future progress in lithography and the concomitant processes of fine feature reproduction will allow one to shrink the size of coupling structures and thereby extend the range of SQUID applications that can take advantage of the improved sensitivity available in low-inductance SQUIDs.