A HIGH TRANSITION TEMPERATURE SUPERCONDUCTING INTEGRATED CIRCUIT (DC SQUID, INPUT COIL, PLANAR COUPLING, MICROBRIDGE).

摘要

This thesis describes the design and fabrication of the first superconducting integrated circuit capable of operating at over 10 K. The primary component of the circuit is a dc SQUID (Superconducting QUantum Interference Device) which is extremely sensitive to magnetic fields. The dc SQUID consists of two superconductor-normal metal-superconductor (SNS) Josephson microbridges which are fabricated using a novel step-edge process which permits the use of high transition temperature superconductors. By utilizing electron-beam lithography in conjunction with ion-beam etching, very small microbridges can be produced. Such microbridges lead to high performance dc SQUIDs with products of the critical current and normal resistance reaching 1 mV at 4.2 K. These SQUIDs have been extensively characterized, and exhibit excellent electrical characteristics over a wide temperature range.; In order to couple electrical signals into the SQUID in a practical fashion, a planar input coil was integrated for efficient coupling. A process was developed to incorporate the technologically important high transition temperature superconducting materials, Nb-Sn and Nb-Ge, using integrated circuit techniques. The primary obstacles were presented by the metallurgical idiosyncrasies of the various materials, such as the need to deposit the superconductors at elevated temperatures, 800-900(DEGREES)C, in order to achieve a high transition temperature. Consequently, the fabrication process had to allow for these elevated deposition temperatures.; The completed circuits operated successfully over a wide temperature range, from 4.2 K to 14 K. Limitations were encountered in the form of an excess inductance. The origins of such an inductance have important and wide-ranging ramifications for superconducting devices employing the high transition temperature materials.