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Bandwidth of Nb/AlN/Nb SIS Mixers Suitable for Frequencies around 700 GHz

C. F. J. Lodewijk, Elfi van Zeijl, T. Zijlstra, Denis Loudkov, Fausto Patricio Mena, A. M. Baryshev, T. M. Klapwijk

Published Apr 1, 2008• 5 citations
OpenAlex

Abstract

Abstract — We have developed a new fabrication process for AlN barriers with excellent reproducibility and control compared to previous work, enabling the use of these barriers in SIS mixers. We report results with niobium-aluminum nitride-niobium superconductor-isolator-superconductor (SIS) mixers for 700 GHz, demonstrating a wide bandwidth behavior with Fourier Transform Spectrometer (FTS) measurements. These measurements have been performed in air and reveal that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. We also present noise temperature measurements of AlN SIS mixers that complement the FTS results. I.

Related papers

Bandwidth Limitations of Nb/AlN/Nb SIS Mixers Around 700 GHz

C. F. J. Lodewijk, T. Zijlstra, Shaojiang Zhu +3 more

We study, using niobium-technology, the bandwidth of SIS mixers operating at frequencies close to the energy-gap frequency. Microstriplines of niobium-silicon dioxide-niobium have different properties for the top and bottom superconductor, which we find to depend on the used fabrication process. Replacing the AlOxtunnel barrier by AlN, the bandwidth increases by 53%. The measurements, using a Fourier Transform Spectrometer (FTS) and performed in ambient air, demonstrate that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. Excellent noise temperatures are found over a full band of 600 to 720 GHz.

IEEE Transactions on Applied Superconductivity•Jun 1, 2009•10 citations

High-Gap Nb-AlN-NbN SIS Junctions for Frequency Band 790–950 GHz

Andrey V. Khudchenko, Andrey M. Baryshev, Kirill I. Rudakov +4 more

We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm2, providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.

IEEE Transactions on Terahertz Science and Technology•Dec 24, 2015•49 citations

Very high-current-density Nb/AlN/Nb tunnel junctions for low-noise submillimeter mixers

Jonathan H. Kawamura, David Miller, Jian Chen +4 more

We have fabricated and tested submillimeter-wave superconductor–insulator–superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (Jc≈30 kA cm−2). The junctions have low-resistance-area products (RNA≈5.6 Ω μm2), good subgap-to-normal resistance ratios Rsg/RN≈10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that ωRNC=1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of TRX=110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits.

Applied Physics Letters•Apr 10, 2000•55 citations

THz SIS mixers with normal-metal Al tuning circuits

M. Bin, Michael C. Gaidis, Jonas Stasys Zmuidzinas +2 more

Nb-based superconductor - insulator - superconductor (SIS) mixers with Nb tuning circuits have demonstrated good results up to the Nb gap frequency. Above the gap frequency the performance is expected to degrade quickly because RF loss in Nb becomes significant. In this paper we present the results of an effort to extend Nb-based SIS mixers to THz frequencies by employing lower-loss normal-metal Al wiring and tuning structures. The SIS mixer has two Nb/Al-oxide/Nb junctions connected by an Al microstrip inductor. The direct detection response of the device was measured by a Fourier transform spectrometer. A double-side-band receiver noise temperature of 840 K was obtained at 1042 GHz when the device was operated at 2.5 K.

Superconductor Science and Technology•Apr 1, 1996•5 citations

Fabrication of aluminum nitride barrier SIS mixer devices using nitrogen plasma diluted by noble gases

Akira Endo, Hisato Inoue, Shin’ichiro Asayama +3 more

Nb/Al–AlN x /Nb SIS junctions have been fabricated by various RF plasma nitridation techniques. The reproducibility of the R N A product from batch to batch was improved by diluting the N 2 plasma with He or Ar. For the He+N 2 process, a power-law relation between the R N A product and the nitridation time was found to hold along 10 0 -10 6 Ω μm 2 , which implies that the thickness of the barrier grows logarithmically during the time it is exposed to the plasma. By applying a pulse-time-modulated RF power, we were able to slow down the nitridation significantly. Finally, we present the results of preliminary RF measurements. The Nb/Al–AlN x /Nb SIS mixers were tested at around 150GHz and 350GHz, and showed noise performances comparable to those of Nb/Al–AlO x /Nb SIS mixers.

Journal of Physics Conference Series•Feb 1, 2008•2 citations

Modeling and optimization of Nb tuning circuits for Nb/AlOx/Nb SIS mixers in the 600-720 GHz range

Omid Noroozian

This thesis describes the development, modeling, and optimization of Nb superconducting microstrip tuning circuits for Superconductor-Insulator-Superconductor mixers. The ultimate goal is to extend the quantum limited noise performance of Nb/AlOx/Nb SIS mixers to above the Nb gap frequency (680 GHz). The mixers are intended to be used in the Atacama Large Millimeter Array (ALMA) band 9 frequency range (600-720 GHz). The behavior of Nb microstrip tuning circuits especially above the gap frequency is modeled using the complex conductivity given by the Mattis-Bardeen theory of the anomalous skin effect [72]. A computer code utilizing two-port network theory is utilized to predict and optimize the RF coupling efficiency and bandwidth of the tuning circuits and embedding impedances. The effect of material and geometrical variations on the coupling has been evaluated. The installment of the devices in the waveguide has been found to be a crucial factor explaining the observed scattering in measurement results for nominally identical devices. Despite parameter variations, modeling of the RF coupling efficiency proved to be successful within the limitations set by scattering of the measured results. Using this model, the tuning circuit geometry has been optimized for bandwidth and maximum coupling efficiency. During the work several SIS devices have been fabricated and Fourier transform spectroscopy measurements have been made for RF coupling evaluation. Finally, using simulations, it has been found that application of Nb/AlN/Nb junctions would increase the bandwidth to an extent which should dramatically decrease the sensitivity to parameter variations.

•Aug 15, 2006•0 citations
Abstract — We have developed a new fabrication process for AlN barriers with excellent reproducibility and control compared to previous work, enabling the use of these barriers in SIS mixers. We report results with niobium-aluminum nitride-niobium superconductor-isolator-superconductor (SIS) mixers for 700 GHz, demonstrating a wide bandwidth behavior with Fourier Transform Spectrometer (FTS) measurements. These measurements have been performed in air and reveal that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. We also present noise temperature measurements of AlN SIS mixers that complement the FTS results. I.
We study, using niobium-technology, the bandwidth of SIS mixers operating at frequencies close to the energy-gap frequency. Microstriplines of niobium-silicon dioxide-niobium have different properties for the top and bottom superconductor, which we find to depend on the used fabrication process. Replacing the AlOxtunnel barrier by AlN, the bandwidth increases by 53%. The measurements, using a Fourier Transform Spectrometer (FTS) and performed in ambient air, demonstrate that the bandwidth is no longer limited by the tuning circuit but by the atmospheric absorption of radiation. Excellent noise temperatures are found over a full band of 600 to 720 GHz.
We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm2, providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.
We have fabricated and tested submillimeter-wave superconductor–insulator–superconductor (SIS) mixers using very high-current-density Nb/AlN/Nb tunnel junctions (Jc≈30 kA cm−2). The junctions have low-resistance-area products (RNA≈5.6 Ω μm2), good subgap-to-normal resistance ratios Rsg/RN≈10, and good run-to-run reproducibility. From Fourier transform spectrometer measurements, we infer that ωRNC=1 at 270 GHz. This is a factor of 2.5 improvement over what is generally available with Nb/AlOx/Nb junctions suitable for low-noise mixers. The AlN-barrier junctions are indeed capable of low-noise operation: we measure an uncorrected double-sideband receiver noise temperature of TRX=110 K at 533 GHz for an unoptimized device. In addition to providing wider bandwidth operation at lower frequencies, the AlN-barrier junctions will considerably improve the performance of THz SIS mixers by reducing rf loss in the tuning circuits.
Nb-based superconductor - insulator - superconductor (SIS) mixers with Nb tuning circuits have demonstrated good results up to the Nb gap frequency. Above the gap frequency the performance is expected to degrade quickly because RF loss in Nb becomes significant. In this paper we present the results of an effort to extend Nb-based SIS mixers to THz frequencies by employing lower-loss normal-metal Al wiring and tuning structures. The SIS mixer has two Nb/Al-oxide/Nb junctions connected by an Al microstrip inductor. The direct detection response of the device was measured by a Fourier transform spectrometer. A double-side-band receiver noise temperature of 840 K was obtained at 1042 GHz when the device was operated at 2.5 K.
Nb/Al–AlN x /Nb SIS junctions have been fabricated by various RF plasma nitridation techniques. The reproducibility of the R N A product from batch to batch was improved by diluting the N 2 plasma with He or Ar. For the He+N 2 process, a power-law relation between the R N A product and the nitridation time was found to hold along 10 0 -10 6 Ω μm 2 , which implies that the thickness of the barrier grows logarithmically during the time it is exposed to the plasma. By applying a pulse-time-modulated RF power, we were able to slow down the nitridation significantly. Finally, we present the results of preliminary RF measurements. The Nb/Al–AlN x /Nb SIS mixers were tested at around 150GHz and 350GHz, and showed noise performances comparable to those of Nb/Al–AlO x /Nb SIS mixers.
This thesis describes the development, modeling, and optimization of Nb superconducting microstrip tuning circuits for Superconductor-Insulator-Superconductor mixers. The ultimate goal is to extend the quantum limited noise performance of Nb/AlOx/Nb SIS mixers to above the Nb gap frequency (680 GHz). The mixers are intended to be used in the Atacama Large Millimeter Array (ALMA) band 9 frequency range (600-720 GHz). The behavior of Nb microstrip tuning circuits especially above the gap frequency is modeled using the complex conductivity given by the Mattis-Bardeen theory of the anomalous skin effect [72]. A computer code utilizing two-port network theory is utilized to predict and optimize the RF coupling efficiency and bandwidth of the tuning circuits and embedding impedances. The effect of material and geometrical variations on the coupling has been evaluated. The installment of the devices in the waveguide has been found to be a crucial factor explaining the observed scattering in measurement results for nominally identical devices. Despite parameter variations, modeling of the RF coupling efficiency proved to be successful within the limitations set by scattering of the measured results. Using this model, the tuning circuit geometry has been optimized for bandwidth and maximum coupling efficiency. During the work several SIS devices have been fabricated and Fourier transform spectroscopy measurements have been made for RF coupling evaluation. Finally, using simulations, it has been found that application of Nb/AlN/Nb junctions would increase the bandwidth to an extent which should dramatically decrease the sensitivity to parameter variations.