Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Journal of Applied Physics

Fabrication of niobium superconductor–insulator–superconductor junctions with a magnetic tunneling barrier NiOx for millimeter and submillimeter mixer applications

Kazuyuki Seko, Yoshiko Ichikawa, Ryo Terajima, Joe Sakai, Syozo Imai

Published Sep 1, 2002• 3 citations
Publisher

Abstract

A thin-film superconductor-insulator-superconductor junction with a magnetic barrier, NiOx, and superconducting electrode, Nb, was fabricated. It is shown that the Josephson current was strongly suppressed without external magnetic field. The tunneling barrier was formed by plasma oxidation and or thermal oxidation. The junction with thermal oxidation showed low specific resistance and current–voltage characteristics with a clear energy gap structure. It is shown that this junction has the potential for quasiparticle mixer working at higher submillimeter wave frequency region above ∼700 GHz, especially suited for making an imaging array.

DOI
10.1063/1.1500415

Related papers

Low-noise submillimeter-wave NbTiN superconducting tunnel junction mixers

Jonathan H. Kawamura, Jian Chen, David Miller +5 more

We have developed a low-noise 850 GHz superconductor–insulator–superconductor quasiparticle mixer with NbTiN thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. The mixer uses a quasioptical configuration with a planar twin-slot antenna feeding a two-junction tuning circuit. At 798 GHz, we measured an uncorrected double-sideband receiver noise temperature of TRX=260 K at 4.2 K bath temperature. This mixer outperforms current Nb SIS mixers by a factor of nearly 2 near 800 GHz. The high-gap frequency and low loss at 800 GHz make NbTiN an attractive material with which to fabricate tuning circuits for SIS mixers. NbTiN mixers can potentially operate up to the gap frequency, 2Δ/h∼1.2 THz.

Applied Physics Letters•Dec 20, 1999•81 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

Fabrication of Nb/Al-N/sub x//NbTiN junctions for SIS mixer applications

B. Bumble, Henry George LeDuc, Jeff A. Stern +1 more

We discuss fabrication and characteristics of superconductor-insulator-superconductor (SIS) junctions which typically exhibit a 3.5 mV sum-gap voltage. Junctions have a sub-gap to normal state resistance ratio of R/sub SG//R/sub N/=27 for resistance-area products down to R/sub N/A=8 /spl Omega/ /spl mu/m/sup 2/ and high quality junctions have been produced with RNA products as low as 4 /spl Omega/ /spl mu/m/sup 2/. The device structure incorporates a Nb base electrode, a tunnel barrier formed by plasma nitridation of a thin Al proximity layer, and a NbTiN counter-electrode. Results for all Nb junctions with high current density aluminum-nitride barriers are also shown. Nitridation of the aluminum layer is investigated by control of the dc floating potential on a separate rf driven electrode in the vacuum process chamber. Devices are integrated to a mixer antenna structure incorporating NbTiN as a ground plane. The wire circuit layer can be either normal metal or NbTiN. Annealing results show improved I-V characteristics with increased RNA products. Recent receiver measurements employing these junctions exhibit low noise performance up to 900 GHz.

IEEE Transactions on Applied Superconductivity•Mar 1, 2001•53 citations

Low barrier ZrO x -based Josephson junctions

Jae‐Hong Choi, Maciej Olszewski, Luojia Zhang +8 more

The Josephson junction is a crucial element in superconducting devices, and niobium is a promising candidate for the superconducting material due to its large energy gap relative to aluminum. AlOx has long been regarded as the highest quality oxide tunnel barrier and is often used in niobium-based junctions. Here, we propose ZrOx as an alternative tunnel barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has excellent oxygen retention properties and experimentally verify that there is no significant oxygen diffusion leading to NbOx formation in the adjacent Nb electrode. We develop a top–down, subtractive fabrication process for Nb/Zr–ZrOx/Nb Josephson junctions, which enables scalability and large-scale production of superconducting electronics. Using cross-sectional scanning transmission electron microscopy, we experimentally find that depending on the Zr thickness, ZrOx tunnel barriers can be fully crystalline with chemically abrupt interfaces with niobium. Further analysis using electron energy loss spectroscopy reveals that ZrOx corresponds to tetragonal ZrO2. Room temperature characterization of fabricated junctions using Simmons’ model shows that ZrO2 exhibits a low tunnel barrier height, which is promising in merged-element transmon applications. Low temperature transport measurements reveal sub-gap structure, while the low-voltage sub-gap resistance remains in the megaohm range.

arXiv:2508.11593•APL Materials•Nov 1, 2025•4 citations

Pushing the operating range of SIS mixers into the THz regime

T. M. Klapwijk, Pieter Dieleman, M. W. M. de Graauw

In recent years, responding to the need of the astronomical community, superconductor - insulator - superconductor (SIS) mixers have been developed to operate at THz frequencies. Best results are obtained by using niobium-based tunnel junctions with well-matched low-loss normal metal striplines, which are found to be less lossy than niobium striplines operated above the gap frequency of niobium (700 GHz). Niobium nitride tunnel junctions with a magnesium oxide tunnel barrier, although having reasonable-quality current - voltage characteristics, have been found to be unsuitable owing to excess shot noise resulting from pinholes in the barrier.

Superconductor Science and Technology•Dec 1, 1997•5 citations

Fabrication and dc characteristics of small-area tantalum and niobium superconducting tunnel junctions

Dean W. Face, D. E. Prober

We discuss the fabrication and dc electrical characteristics of small-area (1–6 μm2) superconducting tunnel junctions with Ta or Nb base electrodes and Pb or Pb0.9Bi0.1 counterelectrodes. These junctions have very small subgap leakage currents, a ‘‘sharp’’ current rise at the sum-gap voltage, and show strong quantum effects when used as microwave mixers. The use of a low-energy (∼150 eV) ion cleaning process and a novel step-defined fabrication process that eliminates photoresist processing after base electrode deposition are discussed. Tunnel barriers formed by dc glow discharge oxidation were the most successful. Tunnel barrier formation by thermal oxidation and ion-beam oxidation is also discussed. An oxidized Ta overlayer (∼7 nm thick) was found to improve the characteristics of Nb-based junctions. The electrical characteristics of junctions with different electrode and barrier materials are presented and discussed in terms of the physical mechanisms that lead to excess subgap current and to a width of the current rise at the sum-gap voltage.

Journal of Applied Physics•Oct 15, 1987•12 citations
A thin-film superconductor-insulator-superconductor junction with a magnetic barrier, NiOx, and superconducting electrode, Nb, was fabricated. It is shown that the Josephson current was strongly suppressed without external magnetic field. The tunneling barrier was formed by plasma oxidation and or thermal oxidation. The junction with thermal oxidation showed low specific resistance and current–voltage characteristics with a clear energy gap structure. It is shown that this junction has the potential for quasiparticle mixer working at higher submillimeter wave frequency region above ∼700 GHz, especially suited for making an imaging array.
We have developed a low-noise 850 GHz superconductor–insulator–superconductor quasiparticle mixer with NbTiN thin-film microstrip tuning circuits and hybrid Nb/AlN/NbTiN tunnel junctions. The mixer uses a quasioptical configuration with a planar twin-slot antenna feeding a two-junction tuning circuit. At 798 GHz, we measured an uncorrected double-sideband receiver noise temperature of TRX=260 K at 4.2 K bath temperature. This mixer outperforms current Nb SIS mixers by a factor of nearly 2 near 800 GHz. The high-gap frequency and low loss at 800 GHz make NbTiN an attractive material with which to fabricate tuning circuits for SIS mixers. NbTiN mixers can potentially operate up to the gap frequency, 2Δ/h∼1.2 THz.
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.
We discuss fabrication and characteristics of superconductor-insulator-superconductor (SIS) junctions which typically exhibit a 3.5 mV sum-gap voltage. Junctions have a sub-gap to normal state resistance ratio of R/sub SG//R/sub N/=27 for resistance-area products down to R/sub N/A=8 /spl Omega/ /spl mu/m/sup 2/ and high quality junctions have been produced with RNA products as low as 4 /spl Omega/ /spl mu/m/sup 2/. The device structure incorporates a Nb base electrode, a tunnel barrier formed by plasma nitridation of a thin Al proximity layer, and a NbTiN counter-electrode. Results for all Nb junctions with high current density aluminum-nitride barriers are also shown. Nitridation of the aluminum layer is investigated by control of the dc floating potential on a separate rf driven electrode in the vacuum process chamber. Devices are integrated to a mixer antenna structure incorporating NbTiN as a ground plane. The wire circuit layer can be either normal metal or NbTiN. Annealing results show improved I-V characteristics with increased RNA products. Recent receiver measurements employing these junctions exhibit low noise performance up to 900 GHz.
The Josephson junction is a crucial element in superconducting devices, and niobium is a promising candidate for the superconducting material due to its large energy gap relative to aluminum. AlOx has long been regarded as the highest quality oxide tunnel barrier and is often used in niobium-based junctions. Here, we propose ZrOx as an alternative tunnel barrier material for Nb electrodes. We theoretically estimate that zirconium oxide has excellent oxygen retention properties and experimentally verify that there is no significant oxygen diffusion leading to NbOx formation in the adjacent Nb electrode. We develop a top–down, subtractive fabrication process for Nb/Zr–ZrOx/Nb Josephson junctions, which enables scalability and large-scale production of superconducting electronics. Using cross-sectional scanning transmission electron microscopy, we experimentally find that depending on the Zr thickness, ZrOx tunnel barriers can be fully crystalline with chemically abrupt interfaces with niobium. Further analysis using electron energy loss spectroscopy reveals that ZrOx corresponds to tetragonal ZrO2. Room temperature characterization of fabricated junctions using Simmons’ model shows that ZrO2 exhibits a low tunnel barrier height, which is promising in merged-element transmon applications. Low temperature transport measurements reveal sub-gap structure, while the low-voltage sub-gap resistance remains in the megaohm range.
In recent years, responding to the need of the astronomical community, superconductor - insulator - superconductor (SIS) mixers have been developed to operate at THz frequencies. Best results are obtained by using niobium-based tunnel junctions with well-matched low-loss normal metal striplines, which are found to be less lossy than niobium striplines operated above the gap frequency of niobium (700 GHz). Niobium nitride tunnel junctions with a magnesium oxide tunnel barrier, although having reasonable-quality current - voltage characteristics, have been found to be unsuitable owing to excess shot noise resulting from pinholes in the barrier.
We discuss the fabrication and dc electrical characteristics of small-area (1–6 μm2) superconducting tunnel junctions with Ta or Nb base electrodes and Pb or Pb0.9Bi0.1 counterelectrodes. These junctions have very small subgap leakage currents, a ‘‘sharp’’ current rise at the sum-gap voltage, and show strong quantum effects when used as microwave mixers. The use of a low-energy (∼150 eV) ion cleaning process and a novel step-defined fabrication process that eliminates photoresist processing after base electrode deposition are discussed. Tunnel barriers formed by dc glow discharge oxidation were the most successful. Tunnel barrier formation by thermal oxidation and ion-beam oxidation is also discussed. An oxidized Ta overlayer (∼7 nm thick) was found to improve the characteristics of Nb-based junctions. The electrical characteristics of junctions with different electrode and barrier materials are presented and discussed in terms of the physical mechanisms that lead to excess subgap current and to a width of the current rise at the sum-gap voltage.