Materials issues related to the fabrication of HTS SQUIDs

A number of materials related problems have hindered the development of a reproducible process for the fabrication of high-quality SQUIDs and magnetometers. In this paper we discuss the use of GdBa/sub 2/Cu/sub 3/O/sub 7/ and YBa/sub 2/Cu/sub 3/O/sub 7/ thin films for the fabrication of step-edge and bicrystal magnetometers and how materials selection can influence issues such as reproducibility, yield and noise performance. Magnetometers with noise performance as low as 63 fT//spl radic/Hz have been made with variations in junction parameters (I/sub c/ and R/sub n/) that are as low as 25% on-chip and 57% from chip-to-chip.