Fabrication and Testing of Superconducting Tunnel Junctions for AN SIS Mixer Operating at 265-280 GHZ.

G. Pance, Noshir Dubash, Michael J. Wengler

We have designed and tested a quasioptical superconducting tunnel junction (SIS) mixer with integrated tuning elements. Devices were fabricated by the Consortium for Superconducting Electronics. The designs consist of a self- complementary log-periodic antenna, superconductor-insulator- superconductor (SIS) tunnel junction, and the broadband superconducting tuning circuit. The tuning circuit is placed between the SIS junction and the center of the antenna. Tuning circuits are designed for 98 GHz and 492 GHz. Self induced resonant steps are observed in I-V curves. We performed noise temperature measurements between 89 GHz and 104.4 GHz and report the results.

Cornelia E. Honingh

史生才

Phichet Kittara, Paul Grimes, G. Yassin +3 more

We report the successful operation of a superconductor-insulator-superconductor (SIS) finline mixer operating near the superconducting energy gap of Nb. The mixer employs a new type of Pickett-Potter horn-reflector (PPHR) antenna, which exhibits low sidelobes and low cross-polarization levels, and yet is easy to fabricate. The SIS tunnel junction and all of the integrated superconducting tuning circuits are fabricated from Nb using planar-circuit technology. The mixer employs an antipodal finline section, deposited on one side of a quartz substrate, which transforms the high impedance of the waveguide (/spl ap/300 /spl Omega/) to the low impedance of the microstrip line (/spl ap/20 /spl Omega/). The Nb/Al-oxide/Nb tunnel junction is fabricated at the same time as the finline circuit. In this paper, we describe the design and testing of the mixer, and pay particular attention to the electromagnetic design of the PPHR antenna. We investigate the noise temperature and gain of the mixer over 642-714 GHz, and analyze the experimental results using rigorous theories that were developed specifically for the purpose. Our investigation demonstrates that finline mixers have good performance both below and above the superconducting energy gap.

J. A. Stern, B. D. Hunt, Henry George LeDuc +4 more

The authors report on the fabrication and testing of all-refractory NbN/MgO/NbN SIS (superconductor-insulator-superconductor) tunnel junctions for use as high-frequency mixers. Progress in the development of techniques for the fabrication of submicron-area tunnel junctions is described. Junction structures which have been investigated include mesa, crossline, and edge geometries. Using reactive sputtering techniques, NbN tunnel junctions with critical currents in excess of 10/sup 4/ A/cm/sup 2/ have been fabricated with V/sub m/ values as high as 65 mV and areas down to 0.1 mu m/sup 2/. Specific capacitance measurements on NbN/MgO/NbN mesa-type tunnel junctions give values in the range 60-90 fF/ mu m/sup 2/. These SIS tunnel junctions have been integrated with antennas and coupling structures for mixer tests in a waveguide receiver at 207 GHz. Preliminary mixer results are reported.>

Zhenfeng Xi