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A quantum-limited submillimeter mixer with an inhomogeneous distributed SIS junction array

Wenlei Shan, Sheng‐Cai Shi, Yutaro Sekímoto, Takashi Noguchi

Published Jan 1, 2007• 0 citations
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Abstract

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.

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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 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.
The study of submillimeter-wave radiation in astronomy and atmospheric sciences requires increasingly performant receivers, in particular allowing extended spectral line surveys. To this end, we are developing a quantum-noise limited heterodyne receiver based on SIS junction parallel arrays with broad (larger than 30%) fixed tuned bandwidth. Simulations show that networks of junctions (N>2) of micronic size, embedded in a superconducting inicrostrip line, can provide a bandwidth in excess of the ultimate limit for a single or even twin junction device. These circuits can be viewed as passband filters which have been optimized by varying the spacings between junctions. The results of simulations are confirmed by the first heterodyne measurements in the 480-650GHz bandwidth, and by preliminary FTS measurements beyond. The influence of the Josephson effect in these devices is also investigated.
This paper presents design and performance data for a 100-GHz waveguide superconductor-insulator-superconductor (SIS) mixer, which is incorporated with a twin-junction device (i.e., two identical junctions connected in parallel through a tuning inductance) and a fixed-tuned broad-band waveguide mixer mount. The 100-GHz mixer is actually developed as a prototype of the 500-GHz one. The constructed 100-GHz SIS receiver results in an overall receiver noise temperature (DSB) of less than 40 K over the frequency range from 80-120 GHz, with a minimum value of just 20 K that is four times as large as the quantum limit (i.e., 4/spl planck//spl omega//k). Such a performance is comparable or even superior to those of the best mechanically tunable waveguide SIS receivers at the same frequency band. In addition, some interesting mixing behaviors related to this two-junction device are described in detail.
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.
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.