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Softwaretechnik-Trends

NbN Mixers and Tuning Circuits for 630 GHz Design and Preliminary Measurements

Morvan C. Salez, Pascal Febvre, William R. McGrath, Jeff A. Stern, Henry George LeDuc

Published Mar 1, 1995• 1 citation
OpenAlex

Abstract

At frequencies above the gap frequency of niobium (710 GHz), the performance of Nb/A10x/Nb SIS mixers degrades and the losses in the niobium films of the superconductive Nb/SiO/Nb microstrip circuits used to provide a good RF impedance match severely limit the performance. Therefore, we are investigating the properties of NbN mixers, and in particular of NbN/SiO/NbN microstrip circuits integrated with submicron IlbN/Mg0/NbN tunnel junctions. The very large penetration depth of NbN (3000-4000 A) makes the circuit design difficult and also puts critical constraints on alignment during fabrication. We present here the design of several rf tuning circuits for 630 GHz including novel symmetric designs which ease the alignment tolerances. In addition, a new approach for determining experimentally the penetration depth in the NbN films is presented.

Related papers

Fabrication and DC-Characterization of NbTiN Based SIS Mixers for Use Between 600 and 1200 GHz

Jeff A. Stern, B. Bumble, Henry George LeDuc +2 more

SIS mixers incorporating two-junction, NbTiN tuning-circuits have been designed and fabricated using two different types of tunnel-junctions. The first type of tunnel junction-NbTiN/MgO/NbTiN--has the advantage of a large gap voltage (5 mV), but has a relatively soft I-V characteristic and high specific capacitance as compared to Nb/Al-Ox/Nb tunnel-junctions. The second type of junction--Nb/Al-AlNx/NbTiN, is a hybrid structure, which has many of the advantages of Nb junctions, with a slightly larger energy gap voltage (3.5 mV) and more robust thermal properties. A detailed description of the deposition techniques used in making the AlNx devices will be given in a separate paper. In this paper, we discuss the deposition of high-quality NbTiN films, and the trade-off between stress and quality in these films. We also discuss the deposition details for the NbTiN/MgO/NbTiN junctions. We measured the magnetic-penetration-depth of our NbTiN films with SQUID circuits. Using long resonators coupled to Josephson junctions, we measured propagation velocities for our microstrip-line circuits; this measurement gave us an independent estimate of the NbTiN magnetic-penetration-depth and a qualitative measure of RF-losses in the microstrip-lines.

Softwaretechnik-Trends•Mar 1, 1998•27 citations

Low-noise waveguide SIS mixer with NbN/AlN/NbN tunnel junctions tuned by an NbN/MgO/NbTiN microstrip circuit

Masanori Takeda, Wenlei Shan, Takafumi Kojima +4 more

The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.

Superconductor Science and Technology•Jun 10, 2009•10 citations

0.5-THz waveguide SIS mixers with NbN/AlN/NbN technology

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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.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 29, 2007•3 citations

Development of SIS mixers for 1 THz

Jonas Stasys Zmuidzinas, J. Kooi, Jonathan H. Kawamura +4 more

SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4(Delta) /h). However, the performance degrades rapidly above the gap frequency of niobium (2(Delta) /h approximately equals 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Jul 31, 1998•27 citations

SIS and bolometer mixers for terahertz frequencies

K. H. Gundlach, Matthias Schicke

The need for extremely sensitive heterodyne receivers in the astronomical community has created strong efforts to develop appropriate frequency mixers. Nb/Al-Al x O y -Nb tunnel junctions with Nb matching circuits lead to best results up to approximately 700 GHz, the energy-gap frequency of Nb. For higher frequencies the Nb in the matching circuit becomes lossy and is replaced beyond 800 GHz by Al (which operates in the normal conducting state). The gap frequency of NbN is as high as 1.2 THz, but NbN technology is not yet mature. Practical films still have substantial radio frequency losses and the barrier of NbN tunnel junctions is too leaky. More recently, NbTiN, for which the gap frequency is also about 1.2 THz, was found to have very low losses, and is therefore a good choice for tuning circuits. New interesting tunnel junctions for mixers around 1 THz are NbTiN-MgO-NbTiN and Nb/Al-AlN x -NbTiN. Excellent performance from about 1 THz up to several terahertz can be expected from hot-electron transition-edge bolometer mixers. They consist of NbN or Nb microbridges, they do not need matching circuits and their frequency limit is not determined by the gap frequency.

Superconductor Science and Technology•Nov 23, 2000•20 citations

0.5-THz waveguide SIS mixers with NbN/AlN/NbN technology - art. no. 684013

Jing Li, Takeda Masanon, Zhen Wang

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/AIO(x)/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.

•Jan 1, 2008•0 citations
At frequencies above the gap frequency of niobium (710 GHz), the performance of Nb/A10x/Nb SIS mixers degrades and the losses in the niobium films of the superconductive Nb/SiO/Nb microstrip circuits used to provide a good RF impedance match severely limit the performance. Therefore, we are investigating the properties of NbN mixers, and in particular of NbN/SiO/NbN microstrip circuits integrated with submicron IlbN/Mg0/NbN tunnel junctions. The very large penetration depth of NbN (3000-4000 A) makes the circuit design difficult and also puts critical constraints on alignment during fabrication. We present here the design of several rf tuning circuits for 630 GHz including novel symmetric designs which ease the alignment tolerances. In addition, a new approach for determining experimentally the penetration depth in the NbN films is presented.
SIS mixers incorporating two-junction, NbTiN tuning-circuits have been designed and fabricated using two different types of tunnel-junctions. The first type of tunnel junction-NbTiN/MgO/NbTiN--has the advantage of a large gap voltage (5 mV), but has a relatively soft I-V characteristic and high specific capacitance as compared to Nb/Al-Ox/Nb tunnel-junctions. The second type of junction--Nb/Al-AlNx/NbTiN, is a hybrid structure, which has many of the advantages of Nb junctions, with a slightly larger energy gap voltage (3.5 mV) and more robust thermal properties. A detailed description of the deposition techniques used in making the AlNx devices will be given in a separate paper. In this paper, we discuss the deposition of high-quality NbTiN films, and the trade-off between stress and quality in these films. We also discuss the deposition details for the NbTiN/MgO/NbTiN junctions. We measured the magnetic-penetration-depth of our NbTiN films with SQUID circuits. Using long resonators coupled to Josephson junctions, we measured propagation velocities for our microstrip-line circuits; this measurement gave us an independent estimate of the NbTiN magnetic-penetration-depth and a qualitative measure of RF-losses in the microstrip-lines.
The low-noise performance of a waveguide SIS mixer with NbN/AlN/NbN tunnel junctions and an NbN/MgO/NbTiN tuning circuit on an MgO substrate was demonstrated at frequencies above the gap frequency of Nb. To design the mixer, the complex refractive index of the MgO substrate was measured by using a THz time-domain spectrometer. The superconductive properties of NbTiN films on MgO were examined in detail. An uncorrected receiver noise temperature of 262 K (DSB) at 820 GHz was achieved in an IF bandwidth of 4-12 GHz at a bath temperature of 4.2 K. By comparing the measured and calculated conversion gains, the loss in the NbN/MgO/NbTiN tuning circuit was estimated to be 0.98 dB at 810 GHz.
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.
SIS heterodyne mixer technology based on niobium tunnel junctions has now been pushed to frequencies over 1 THz, clearly demonstrating that the SIS junctions are capable of mixing at frequencies up to twice the energy gap frequency (4(Delta) /h). However, the performance degrades rapidly above the gap frequency of niobium (2(Delta) /h approximately equals 700 GHz) due to substantial ohmic losses in the on-chip tuning circuit. To solve this problem, the tuning circuit should be fabricated using a superconducting film with a larger energy gap, such as NbN; unfortunately, NbN films often have a substantial excess surface resistance in the submillimeter band. In contrast, the SIS mixer measurements we present in this paper indicate that the losses for NbTiN thin films can be quite low.
The need for extremely sensitive heterodyne receivers in the astronomical community has created strong efforts to develop appropriate frequency mixers. Nb/Al-Al x O y -Nb tunnel junctions with Nb matching circuits lead to best results up to approximately 700 GHz, the energy-gap frequency of Nb. For higher frequencies the Nb in the matching circuit becomes lossy and is replaced beyond 800 GHz by Al (which operates in the normal conducting state). The gap frequency of NbN is as high as 1.2 THz, but NbN technology is not yet mature. Practical films still have substantial radio frequency losses and the barrier of NbN tunnel junctions is too leaky. More recently, NbTiN, for which the gap frequency is also about 1.2 THz, was found to have very low losses, and is therefore a good choice for tuning circuits. New interesting tunnel junctions for mixers around 1 THz are NbTiN-MgO-NbTiN and Nb/Al-AlN x -NbTiN. Excellent performance from about 1 THz up to several terahertz can be expected from hot-electron transition-edge bolometer mixers. They consist of NbN or Nb microbridges, they do not need matching circuits and their frequency limit is not determined by the gap frequency.
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/AIO(x)/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.