Multilayer edge SNS SQUIDs for digital circuits

Abstract

We have fabricated and characterized direct-injection High Temperature Superconducting (HTS) SQUIDs using a six-epitaxial-layer process which integrates edge geometry superconductor-normal-superconductor (SNS) junctions with an HTS ground plane. The period of the SQUID threshold curves was used to infer microstrip inductances of approximately 1 pH//spl square/ at 65 K. Total SQUID inductances as low as /spl ap/5 pH were inferred from the measured critical current modulation depth. A novel junction geometry was used in some devices to reduce the parasitic inductances of the junction leads by approximately 1 pH. Maintaining such low inductances is particularly important for Single Flux Quantum digital circuits.