Focused ion beam high T/sub c/ superconducting SQUIDs

The behavior of HTS thin films patterned into microbridge DC and RF SQUID structures and irradiated with a rastered high-energy focused ion beam 70 mm in diameter is discussed. DC SQUIDs have demonstrated 51% modulation of the critical current with an applied magnetic field at 46 K. All devices with appropriate critical currents exhibited Shapiro steps when exposed to microwave irradiation. Multiple interference patterns, probably from weak links within each microbridge segment, are seen at 4 K and disappear at temperatures above liquid helium. The I/sub c/R/sub n/ product of the microbridges is typically a few millivolts, and the temperature dependence of the device resistance is consistent with electrical conduction through metallic filaments. The process demonstrates an acceptable yield and reliability for a variety of microelectronics applications.