FOCUSED ION-BEAM HIGH-TC SUPERCONDUCTING SQUIDS

Light-ion implantation controllably reduces the critical currents in high temperature superconducting (HTS) thin film materials. Reported here is the behavior of HTS thin films patterned into microbridge d.c. and r.f. SQUID structures and irradiated with a rastered high energy focused ion beam 70 nanometers in diameter. D.C. SQUIDs have demonstrated 51% modulation of the critical current with an applied magnetic field at 46K. 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 4K and disappear at temperatures above liquid helium. The I(c)R(n) product of the microbridges are 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.