FABRICATION OF THIN-FILM NB-(FINE NB WIRES)-NBN WEAK LINKS FOR SUPERCONDUCTING QUANTUM INTERFERENCE DEVICE APPLICATIONS

Thin film Nb-(fine Nb wires)-NbN dc-superconducting quantum interference devices (SQUIDs) with well-balanced critical current have been reproducibly fabricated by applying an electric field simultaneously to two insulating Nb/MgO/NbN edge-sandwiches (each junction area=0.2-mu-m2) in a superconducting loop, in liquid helium. Although the critical current of a dc-SQUID is not yet controlled sufficiently, this fabrication technique is well suited to use in short weak link dc-SQUIDs, thanks to the reproducibility of dc-SQUIDs with well-balanced critical current, the simplicity of fabrication processes, and the large device resistance.