V 3 Si-SiO x -Mo 3 Re 2 superconducting tunnel junctions

The possibility of obtaining sandwich-type Josephson junctions that can be operated at temperatures higher than 10 K is examined. A high-T c superconductor which can be deposited at substrate temperatures below room temperature is found, and the tunnel junctions are fabricated, therewith. Tunnel junctions are made by using the high-T c superconductors V 3 Si and Mo 3 Re 2 for the base electrode and counterelectrode, respectively. These films are prepared by a co-evaporation technique. Oxide-barrier formation is performed by oxidizing a Si thin film 2 to 3 nm thick which is deposited before exposing the V 3 Si film surface to air. The superconducting onset temperature of the V 3 Si thin film is 16 K. The Mo-Re thin film has a metastable A-15 type phase in the Re concentration range of 25 to 50 at.%. The T c of the Mo 3 Re 2 thin films deposited on the room temperature substrate is 10-11 K. However, the T c value decreases as the substrate temperature is lowered with a background gas pressure of about 10 -4 Pa. In fabricating the V 3 Si-SiO x -Mo 3 Re 2 junctions, the Mo 3 Re 2 thin film is deposited with the substrate at lower than room temperature. Superconducting characteristics are observed in the current-voltage curve of the junction.