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Journal of Applied Physics

Superconductor-insulator-superconductor mixing with arrays at millimeter-wave frequencies

S. Rudner, M. J. Feldman, E. Kollberg, T. Claeson

Published Oct 1, 1981• 50 citations
Publisher

Abstract

We report high-frequency mixing at 75 GHz using superconductor-insulator-superconductor (SIS) tunnel junction arrays of various length and composition. Short (6-junction) arrays, both of Pb (In) and of Pb, and long (36-junction) arrays of Pb are used. The array geometry and antenna coupling can be scaled to 300 GHz with existing technology. Comparing the experiments to each other and to theory provides criteria for SIS mixer design. The measured single side band (SSB) conversion loss is as good as 2.0±0.9 dB. This is marginally the best published conversion result for any resistive mixer without image rejection, and quantitatively agrees with the quantum theory of mixing. We examine Josephson effect noise in this device and give a rough upper frequency limit for single-junction SIS mixers. Conversion maxima are also noted close to the half-gap singularity present in Pb (In) junctions.

DOI
10.1063/1.328580

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European Microwave Conference (EuMC)•Oct 1, 1984•3 citations
We report high-frequency mixing at 75 GHz using superconductor-insulator-superconductor (SIS) tunnel junction arrays of various length and composition. Short (6-junction) arrays, both of Pb (In) and of Pb, and long (36-junction) arrays of Pb are used. The array geometry and antenna coupling can be scaled to 300 GHz with existing technology. Comparing the experiments to each other and to theory provides criteria for SIS mixer design. The measured single side band (SSB) conversion loss is as good as 2.0±0.9 dB. This is marginally the best published conversion result for any resistive mixer without image rejection, and quantitatively agrees with the quantum theory of mixing. We examine Josephson effect noise in this device and give a rough upper frequency limit for single-junction SIS mixers. Conversion maxima are also noted close to the half-gap singularity present in Pb (In) junctions.
We have investigated high-frequency limits of superconducting quasiparticle mixers from experiments on Al/Al-oxide-In/Al (or Ag) tunnel junctions, and from calculations based on Tucker’s quantum theory of mixing (QTM). The small superconducting energy gap of Al enabled us to study mixer performance at around the junction gap frequency, fg =(Δ1+Δ2)/h≊87 GHz, of superconductor-insulator-superconductor (SIS) mixers, and at twice the junction gap frequency for S-I-normal metal (SIN) mixers ( fg =Δ1/h) with available millimeter wave sources. Because of the low transition temperature of Al (Tc ≊1.3 K), a dilution refrigerator was used for providing temperatures below 1 K. The best mixer conversion efficiency was obtained for a low-resistance (∼34 Ω) six-junction array SIS mixer operated at f/fg ≊1 (in this case 73 GHz). The coupled single sideband conversion gain (with no image rejection) was −13.8 dB and the available conversion gain was estimated to −8.4 dB. Complicating nonequilibrium phenomena made it difficult to compare the performance of these relatively high-current-density mixers to the QTM. However, good agreement between calculated and corresponding measured conversion efficiencies and dynamic resistance values was obtained for the low-current-density mixers. Noise due to switching between rf-induced Josephson steps and interference from Josephson mixing could be quenched by a magnetic field. Several high-frequency limits are considered in this paper (such as Josephson switching noise, nonequilibrium phenomena, pair breaking, and energy gap limitations). Our results indicate that submillimeter wave SIS mixer receivers are likely to perform well, at least up to their gap frequencies, i.e., the THz region for large gap superconductors. Our QTM calculations showed that conversion gain larger than unity should be possible up to twice the gap frequency. Above this frequency the conversion loss will increase rapidly.
The authors present two different designs of integrated tuning elements for superconducting tunnel junction mixers. The structures consist of a self-complementary log-periodic antenna, superconductor-insulator-superconductor (SIS) tunnel junction, and a broadband superconducting tuning circuit placed between the center of the antenna and the SIS junction. The designs allow good coupling to relatively large-area (7 mu m/sup 2/) junctions. The best design has a 3-dB bandwidth of 102 GHz at the central frequency of 98 GHz, and 75 GHz at the central frequency of 492 GHz. Microwave scale-model measurements show excellent agreement with simulation results. Devices are being fabricated in niobium technology.>
We propose a low-noise and low-power-consumption microwave amplifier using superconductor-insulator-superconductor (SIS) mixers as quasi-particle frequency up- and down-converters pumped by a Josephson array oscillator in the millimeter-wave band. A proof-of-concept study of an amplifier with two W-band waveguide mixers using Nb/Al-AlOx/Nb junctions in a cascade connection demonstrated an average gain of 6 dB and a noise temperature of 12 K from nearly DC to 5 GHz. We also designed and fabricated a Josephson array oscillator at 100 GHz, which consisted of 31 overdamped Josephson junctions placed at each half-wavelength in an Nb microstrip line. The estimated output power of the oscillator was 0.2 μW at 100 GHz, which can be increased by increasing the number of the oscillator junctions. These results suggest that the proposed SIS mixer-based amplifier is suitable for on-chip integrated circuits to be implemented in large-scale multipixel SIS receivers and quantum computers.
The superconductor-insulator-superconductor (SIS) tunnel junction is an attractive candidate for millimeter wave mixers offering conversion gain and quantum limited noise.1SIS mixers have been operated at 36 GHz with a single sideband noise temperature of 3.7K which is within a factor of 2 of quantum limited performance.2These results were obtained with devices fabricated from lead alloy technology. While this technology is very useful for the demonstration of quantum limited noise an all refractory junction technology would be desirable as it would have the advantages of being mechanically rugged, cycle well between room temperature and 4K be resistant to radiation damage and have enhanced high frequency response.