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IEEE Microwave and Guided Wave Letters

Experimental results of SIS mixers with distributed junction arrays

Sheng‐Cai Shi, Takashi Noguchi, Junji Inatani, Yoshihisa Irimajiri, Tatsunari Saito

Published Jan 1, 1998• 23 citations
Publisher

Abstract

The heterodyne mixing performance of three respective distributed junction arrays, i.e., a number of superconductor-insulator-superconductor (SIS) junctions distributed along a thin-film transmission line involving two, five, and ten junctions are measured and compared to their Fourier transform spectroscopy (FTS) detection responses. It has been found that distributed junction arrays have a rather large bandwidth in comparison to conventional SIS junction devices, while still keeping a quantum-limited noise performance. Detailed experimental results are presented.

DOI
10.1109/75.736252

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The heterodyne mixing performance of three respective distributed junction arrays, i.e., a number of superconductor-insulator-superconductor (SIS) junctions distributed along a thin-film transmission line involving two, five, and ten junctions are measured and compared to their Fourier transform spectroscopy (FTS) detection responses. It has been found that distributed junction arrays have a rather large bandwidth in comparison to conventional SIS junction devices, while still keeping a quantum-limited noise performance. Detailed experimental results are presented.
Heterodyne mixing performance of a waveguide SIS mixer with inhomogeneous distributed junction (DJ) array composed of 3 SIS junctions is experimentally investigated at 375-500 GHz. Quantum-limited noise temperature of 3-DJ mixer is demonstrated. Besides its low noise temperature, the mixer conversion gain of 3-DJ mixer is found to be more uniform over RF band than that of a PCTJ (parallel-connected twin junctions) mixer. The FTS (Fourier transform spectrum) response indicates a broad RF bandwidth of the 3-DJ mixer that is limited by the bandwidth of waveguide probe instead of mixer's tuning circuit.
Heterodyne mixers based on superconducting SIS (superconductor-insulator-superconductor) tunnel junctions have been demonstrated to be the most sensitive coherent detectors at millimeter and submillimeter wavelengths. In fact, conventional superconducting SIS mixers with Nb/AlOx/Nb junction and Nb/SiO2/Nb tuning circuit have shown good performances with the noise temperature reaching as low as three times the quantum limit below 0.7THz, which is the gap frequency of Nb-based SIS junctions. However, due to the large loss in Nb thin-film superconducting microstrip lines, the noise performance of Nb SIS mixers deteriorates significantly above 0.7THz. With a gap frequency double that of Nb-based SIS junctions, NbN-based SIS junctions are of particular interest for the development of heterodyne mixers in the terahertz region. Considering the bandwidth and output power of local-oscillator (LO) signal sources are quite limited around 1THz, we firstly develop a waveguide NbN-based SIS mixer at 0.5THz. Three types of SIS junctions, i.e., long junction, parallel-connected tunnel junction (PCTJ) and distributed junction array (DJ) are investigated. They are all comprised of NbN-AlN-NbN tri-layer fabricated on an MgO substrate and have the same current density (Jc) of 10kA/cm2. In this paper, we describe their design, fabrication and preliminary experimental results.
Heterodyne mixing performance of a waveguide SIS mixer with inhomogeneous distributed junction (DJ) array composed of 3 SIS junctions is experimentally investigated at 375-500 GHz. Quantum-limited noise temperature of 3-DJ mixer is demonstrated. Besides its low noise temperature, the mixer conversion gain of 3-DJ mixer is found to be more uniform over RF band than that of a PCTJ (parallel-connected twin junctions) mixer. The FTS (Fourier transform spectrum) response indicates a broad RF bandwidth of the 3-DJ mixer that is limited by the bandwidth of waveguide probe instead of mixer's tuning circuit.
A Superconductor-Insulator-Superconductor (SIS) mixer using parallel array of N junctions have been studied. It has been shown by theoretical analysis that the performance of this type of device is excellent and that nearly quantum-limited performance of the mixer can be obtained. It has been demonstrated that the double sideband (DSB) noise temperature of a receiver employing parallel array of twin junctions, which is the most simplest case in the parallel array of N junctions, was approximately 3 to 5 times as large as the quantum limited photon noise up to the gap frequency of Nb (approximately 700 GHz). It has been also shown that the bandwidth performance of parallel junction arrays can be improved significantly with a large number of SIS junctions even if SIS junctions with a relatively low current density or a large (omega) RNCJ product are adopted in the arrays.
This paper presents the direct-detection responses of a 500-GHz and a 660-GHz waveguide superconducting SIS (superconductor-insulator-superconductor) mixer measured with a Fourier transform spectrometer (FTS). The two superconducting SIS mixers adopt the same type of junction tuning circuit (i.e., parallel connected twin SIS junctions), but are of different designs for the junction feed point where RF signals are coupled and then transmitted to the SIS junction tuning circuit and have different mixer design criteria. The experimental results are discussed in detail.
Experiments on the performance of superconductor-insulator-superconductor (SIS) tunnel junctions as heterodyne mixers at 40 GHz are reported. The techniques developed for the fabrication of multi-junction SIS series arrays differ from, and are considerably simpler than, other methods described in the literature. Results are reported on mixer noise temperature, conversion loss, saturation, local oscillator power levels and mixer dynamic range. Factors affecting the mixer's conversion performance are identified and comparisons are made with other reported results. It is concluded that mixer performance in the present experiments is limited by imperfect impedance matching at the signal frequency, due to relatively large values of parasitic capacitance in the junctions. Future work is aimed at both reducing the junction capacitance and redesigning the mixer mount to give improved r.f. matching.