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Microwave and Optical Technology Letters

Broadband twin‐junction tuning circuit for submillimeter SIS mixers

Victor Y. Belitsky, Stellan Jacobsson, Lyudmila V. Filippenko, E. Kollberg

Published Oct 5, 1995• 19 citations
Publisher

Abstract

Abstract A 400–550‐GHz fixed tuned quasioptical Nb/AlOx/Nb SIS heterodyne receiver has been built, and its performance has been evaluated. The receiver, operated at 3.5 K, showed noise temperatures ≤ 300‐K DSB within the tuning range of the available LO source (440–520 GHz). The SIS junction capacitance was tuned out by a novel twin‐junction circuit, which offered 130‐GHz fixed tuned bandwidth at 480 GHz. Large‐area SIS junctions (3.5 μm2, ωRnC ≈︁ 7.5 at 500 GHz), patterned by optical lithography, were used. © 1995 John Wiley & Sons, Inc.

DOI
10.1002/mop.4650100203

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The capacitance of superconducting tunnel junctions can seriously degrade the performance of quasiparticle (SIS) mixers operating in the submillimeter band, so it is essential to provide a circuit for tuning out this capacitance at the operating frequency. In this article, we present two new tuning circuits for SIS mixers which use a pair of SIS junctions connected by an inductance. Compared to previously proposed tuning circuits, ours have a broader bandwidth, are easier to scale to higher frequencies, and may be easier to fabricate. We have constructed quasi-optical mixers which employ these tuning circuits, using Nb/Al-Oxide/Nb SIS junctions defined by optical lithography. The performance of these devices is excellent, giving receiver noise temperatures of 113 K (DSB) at 490 GHz and 230 K DSB at 612 GHz. In addition to demonstrating the effectiveness of our tuning circuit, these results show that quasi-optical mixers can be competitive with or superior to waveguide mixers at submillimeter wavelengths. The mixers continue to perform well at frequencies up to 672 GHz, which is about 95% of the Nb gap frequency.>

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IEEE Transactions on Magnetics•Mar 1, 1989•32 citations
Abstract A 400–550‐GHz fixed tuned quasioptical Nb/AlOx/Nb SIS heterodyne receiver has been built, and its performance has been evaluated. The receiver, operated at 3.5 K, showed noise temperatures ≤ 300‐K DSB within the tuning range of the available LO source (440–520 GHz). The SIS junction capacitance was tuned out by a novel twin‐junction circuit, which offered 130‐GHz fixed tuned bandwidth at 480 GHz. Large‐area SIS junctions (3.5 μm2, ωRnC ≈︁ 7.5 at 500 GHz), patterned by optical lithography, were used. © 1995 John Wiley & Sons, Inc.
A quasi optical SIS mixer for the frequency band 400-550 GHz has been designed and successfully testedin a laboratory receiver setup. The intrinsic SIS junction capacitance was tuned out by a novel pair (twin) SISjunction compensation circuit. The 4µm2 area Nb-A10x-Nb junctions, with (oRnC product as high as 7.4 at500 GHz, were patterned by optical lithography and integrated with a equiangular spiral antenna to give broad- band SIS mixer operation. The receiver demonstrated flat response within the tuning range of the available LOsource (440 - 520 GHz) with DSB noise temperatures below 300 K over the entire band and with the best re- ceiver noise temperature below 250 K DSB at 453 GHz (measured at 3.5 K physical temperature). No mechani- cal tuning was employed in the SIS mixer. These noise temperatures include all losses and was measured atan IF center frequency of 1.5 GHz.
We report on low-noise heterodyne mixing with NbN/A1N/NbN tunnel junctions in the submillimeter-wave region for the first time. The receiver consists of the quasi-optical NbN SIS mixer with an integrated tuning circuit in which a radial short stub tuner is incorporated to resonate out the junction capacitance for RF matching and a balanced IF circuit for broadband IF matching. The prepared NbN SIS junction has a current density of 20 kA/cm 2 and is about 1 I1111 in diameter, supplying a small coC JRN product (o)CJRN = 3 at 300 GHz). The junctions showed good dc I-V characteristics, excellent submillimeter-wave responses and sensitive heterodyne mixing responses. From 254 to 350 GHz the average receiver noise temperature measured using by the standard Y-factor method was about 250 K (DSB) at 5 K. The lowest receiver noise temperature, 200 K (DSB), was obtained at around 303 GHz. Comparing NbN/A1N/NbN and Nb/A10x/Nb tunnel junction performance with the same tuning circuit showed that the frequency dependence of the receiver noise temperature agreed well in the two receivers. These results suggest that our well-controlled NbN SIS junctions can be used for terahertz mixer elements instead of Nb SIS junctions.
We report on the development of low-noise quasi-optical SIS mixers for the frequency range 400-850 GHz. The mixers utilize twin-slot antennas, two-junction tuning circuits, and Nb-trilayer junctions. Fourier-transform spectrometry has been used to verify that the frequency response of the devices is well predicted by computer simulations. The 400-850 GHz frequency band can be covered with four separate fixed-tuned mixers. We measure uncorrected double-sideband receiver noise temperatures around 5h/spl nu//k/sub B/ to 700 GHz, and better than 540 K at 808 GHz. These results are among the best reported to date for broadband heterodyne receivers.
The capacitance of superconducting tunnel junctions can seriously degrade the performance of quasiparticle (SIS) mixers operating in the submillimeter band, so it is essential to provide a circuit for tuning out this capacitance at the operating frequency. In this article, we present two new tuning circuits for SIS mixers which use a pair of SIS junctions connected by an inductance. Compared to previously proposed tuning circuits, ours have a broader bandwidth, are easier to scale to higher frequencies, and may be easier to fabricate. We have constructed quasi-optical mixers which employ these tuning circuits, using Nb/Al-Oxide/Nb SIS junctions defined by optical lithography. The performance of these devices is excellent, giving receiver noise temperatures of 113 K (DSB) at 490 GHz and 230 K DSB at 612 GHz. In addition to demonstrating the effectiveness of our tuning circuit, these results show that quasi-optical mixers can be competitive with or superior to waveguide mixers at submillimeter wavelengths. The mixers continue to perform well at frequencies up to 672 GHz, which is about 95% of the Nb gap frequency.>
A heterodyne receiver using an SIS (superconductor-insulator-superconductor) waveguide mixer with two mechanical tuners has been built and characterized over the frequency range of 460 GHz to 630 GHz. This receiver is designed for radioastronomy applications. The mixer uses high-current-density, 0.25- mu m/sup 2/, Nb/AlO/sub x//Nb SIS tunnel junctions with integrated superconductive RF circuits to tune the junction capacitance. A DSB (double sideband) receiver noise temperature as low as 200+or-17 K has been obtained at 540 GHz. In addition, negative differential resistance has been observed in the DC I-V (current-voltage) curve at 487-491 GHz.>
The authors have tested the performance of planar SIS (superconductor-insulator-superconductor) mixers with log-periodic antennas at near millimeter and submillimeter wave frequencies from 90 to 360 GHz. The large omega R/sub N/C product ( approximately 10 at 90 GHz) of the Nb/NbO/sub x//Pb-In-Au junctions requires an integrated inductive tuning element to resonate the junction capacitance at the operating frequencies. Two types of integrated tuning element were used which were designed with the aid of measurements using a Fourier transform spectrometer. Preliminary results indicate that the tuning elements can give very good mixer performance up to at least 200 GHz. An inductive wire in parallel with a 5-junction array gives a minimum mixer noise temperature of 115 K (DSB) at 90 GHz with a FWHM (full width at half maximum) bandwidth of 8 GHz. An open-ended microstrip stub in parallel with a single junction gives minimum mixer noise temperatures at 150 and 200 K (DSB) near 90 and 180 GHz with FWHM bandwidths of 4 and 3 GHz, respectively. The relatively high mixer noise temperatures compared to those of waveguide SIS mixers in a similar frequency range are attributed mainly to the losses in the optical system.>