SIS Junction Technology Development for Wideband 2SB Receivers

Principal Investigator: Victor Belitsky

Institute: Group for Advanced Receiver Development, Sweden

Abstract:

This proposal addresses suggested in the “ALMA 2030 Roadmap” document call for “Larger bandwidths and better receiver sensitivity”. The reasons and justification for a wider IF band and improved noise performance are well signified in the “ALMA 2030” document. In order to reach these goals and keep possibilities open for future ALMA upgrades, we propose to work on superconductor-insulator-superconductor (SIS) junction technology to obtain stable process that would allow us to fabricate Nb-AlN-Nb tunnel junctions for SIS mixer applications in addition to stable processing of Nb-AlxOy-Nb SIS junctions already existing at GARD. Our work is based on significant heritage, experienced staff and complemented by availability of the Chalmers Clean Room facility and dedicated sputter equipment. Once technology is available, GARD would be ready to offer it as “foundry” service to the instrumentation groups in Europe involved in the ALMA Upgrade studies and projects, e.g., the 2SB Band 9 upgrade where use of SIS junctions with AlN tunnel barrier is critical.

The suggested work would bring benefits for both widening the IF and RF bands of 2SB (sideband separation) SIS mixers by reducing the specific capacitance of the SIS junctions with the given critical current density as compared to the Nb-AlxOy-Nb SIS junctions. With higher current density achievable with the use of the Nb-AlN-Nb SIS tunnel junctions, it will be easier to accomplish broad band RF design without compromising the IF performance.