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IEEE Transactions on Applied Superconductivity

An SIS mixer using two junctions connected in parallel

Takashi Noguchi, Sheng‐Cai Shi, Junji Inatani

Published Jun 1, 1995• 41 citations
Publisher

Abstract

We have fabricated a superconductor-insulator-superconductor (SIS) mixer using a couple of junctions connected in parallel through a stripline inductor. The junctions have significantly larger area, i.e. larger capacitance, and smaller normal resistance than conventional ones. In order to obtain a good impedance matching between the source and the junctions, an impedance transformer made of a superconducting stripline was integrated with the junctions. The capacitance of the junctions was tuned out by the inductor to obtain a broadband operation without mechanical tuning elements. It was shown that the double sideband noise temperature of the receiver employing this type of mixer device was less than 40 K over the bandwidth of 90-115 GHz. The lowest receiver noise temperature of /spl sim/20 K, which is only 4 times as large as the quantum limited photon noise of hv/k/sub B/, was obtained around 105 GHz.>

DOI
10.1109/77.403028

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The performance of a broadband SIS (superconductor-insulator-superconductor) receiver with no mechanical tuning elements was modeled and tested. The mixer mount had a broadband-waveguide-to-microstripline transition consisting of a four-step Chebyshev single-ridge transformer. The last step of the ridge connected the waveguide to a microstripline circuit. The on-chip circuit consisted of a microstripline that transmitted the RF and the local oscillator signals to the SIS mixer. Both the SIS element and the inductor had RF grounds provided by 90 degrees radial stubs. The inductor tuned out the junction capacitance to allow operation over the full frequency band. The SIS element can be a single junction or series array using Nb-AlO/sub x/-Nb trilayer tunnel junctions with areas as small as 0.5 mu m/sup 2/ and V/sub m/(2 mV)=39 mV. Preliminary results indicated a DSB receiver noise temperature of 65-80 K across the band measured at 4.4 K with an internal cryogenic RF hot/cold source and with T/sub if/=21 K. With another device, a mixer noise temperature of 35 K at 100 GHz was achieved, increasing to 45 K at 79.5 and 110 GHz. Coupled mixer gain of up to +3 dB and negative dynamic resistance on the first photon step were observed. The lowest noise temperature was obtained for an untuned single-junction mixer at 80 GHz: T/sub R/=41 K and T/sub M/=20 K were measured.

IEEE Transactions on Magnetics•Mar 1, 1991•11 citations
We have fabricated a superconductor-insulator-superconductor (SIS) mixer using a couple of junctions connected in parallel through a stripline inductor. The junctions have significantly larger area, i.e. larger capacitance, and smaller normal resistance than conventional ones. In order to obtain a good impedance matching between the source and the junctions, an impedance transformer made of a superconducting stripline was integrated with the junctions. The capacitance of the junctions was tuned out by the inductor to obtain a broadband operation without mechanical tuning elements. It was shown that the double sideband noise temperature of the receiver employing this type of mixer device was less than 40 K over the bandwidth of 90-115 GHz. The lowest receiver noise temperature of /spl sim/20 K, which is only 4 times as large as the quantum limited photon noise of hv/k/sub B/, was obtained around 105 GHz.>
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.
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.
A circuit that produces broadband impedance matching with low-current-density junctions at submillimeter wavelengths for tuning superconductor–insulator–superconductor (SIS) mixers is described; it consists of half-wavelength distributed SIS junctions connected alternately by half-wavelength microstrip lines. It is made of Nb and was designed for two practical source impedances using numerical calculation based on the Mattis–Bardeen theory of the anomalous skin effect at 660 GHz, assuming SIS junctions with a current density of 5 kA/cm 2 . An SIS mixer tuned using this circuit had a large fractional bandwidth of more than 18%, below -10 dB matching, even though the assumed ω C J R N product was about 16. Investigation of the mixer performance using Tucker's quantum theory of mixing showed that it has excellent broadband and low-noise characteristics compared with conventional mixers consisting of half- or full-wavelength distributed elements.
A fixed-tuned SIS(Superconductor-Insulator-Superconductor) mixer across 120∼180 GHz band has been developed. This mixer employs an SIS chip fabricated by Nobeyama radio observatory which consists of a series array of 6 Nb/Al-AlO/Nb junctions in a microstrip line on a fused quartz substrate. The SIS chip is placed at the center of the half-height waveguide mixer mount to have a good incoming signal coupling over the whole frequency band. No mechanical tuner was used in the SIS mixer and the RF signal and local oscillator power are injected to the mixer via a cooled cross-guide coupler. In order to prevent the IF signal loss, the If output impedance of the SIS mixer was matched to the 50 input impedance of the IF chain. Measured double sideband noise temperatures of a receiver using the SIS mixer are 32∼131 K over 120∼180 GHz band. The developed SIS mixer is now in use for radio astronomical observations on the TRAO 14 m radio telescope.
The possibility of overcoming the main drawbacks of the traditional series arrays by parallel connection of the SIS (superconductor-insulator-superconductor) junctions for DC and IF are demonstrated experimentally. The proposed mixing elements avoid the influence of the junction nonuniformity in the array, provide the optimal matching on both RF input and IF output, and tune out junction capacitance. Experimentally tested arrays contained up to eight high-quality Nb-AlO/sub x/-Nb junctions with R/sub n/=20-70 Omega at junction area 8/14 mu m/sup 2/. The best values of T/sub r/ (SSB) were measured to as low as 5 K on the mixer cold input flange in the 45-55-GHz bandwidth at an ambient temperature of 4.2 K. A mixer gain of up to 10 dB was obtained. The gain values were limited by bias stability at very high or even negative array output impedance. An experimental receiver noise temperature (SSB) of less than 20 K has been achieved.
The performance of a broadband SIS (superconductor-insulator-superconductor) receiver with no mechanical tuning elements was modeled and tested. The mixer mount had a broadband-waveguide-to-microstripline transition consisting of a four-step Chebyshev single-ridge transformer. The last step of the ridge connected the waveguide to a microstripline circuit. The on-chip circuit consisted of a microstripline that transmitted the RF and the local oscillator signals to the SIS mixer. Both the SIS element and the inductor had RF grounds provided by 90 degrees radial stubs. The inductor tuned out the junction capacitance to allow operation over the full frequency band. The SIS element can be a single junction or series array using Nb-AlO/sub x/-Nb trilayer tunnel junctions with areas as small as 0.5 mu m/sup 2/ and V/sub m/(2 mV)=39 mV. Preliminary results indicated a DSB receiver noise temperature of 65-80 K across the band measured at 4.4 K with an internal cryogenic RF hot/cold source and with T/sub if/=21 K. With another device, a mixer noise temperature of 35 K at 100 GHz was achieved, increasing to 45 K at 79.5 and 110 GHz. Coupled mixer gain of up to +3 dB and negative dynamic resistance on the first photon step were observed. The lowest noise temperature was obtained for an untuned single-junction mixer at 80 GHz: T/sub R/=41 K and T/sub M/=20 K were measured.