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Global Symposium on Millimeter-Waves

Development of a 0.85 THz Nb-AlN-NbN superconductor-insulator-superconductor mixer

Ming Yao, Jing Li, Dong Liu, Shaoliang Li, Sheng‐Cai Shi, Pavel Dmitriev, M. Yu. Fominsky, Valery Koshlets

Published May 1, 2017• 2 citations
Publisher

Abstract

China is planning to build a 5-m THz telescope named DATE5 at Dome A in Antarctica. The telescope will operate in 0.85 THz and 1.5 THz frequency bands. A waveguide superconductor-insulator-superconductor (SIS) mixer is developed for the 0.85 THz frequency band by utilizing parallel-connected tunnel junctions (PCTJ) with Nb/AlN/NbN trilayer and NbTiN/SiO2/Al microstrip tuning circuit on quartz substrate. Its frequency response is measured by a Fourier-transform spectrometer (FTS), showing an FWHM frequency coverage of 762-925 GHz. The measured uncorrected double sideband (DSB) receiver noise temperature is approximately equal to 450 K at 840 GHz. With the vacuum window and beamsplitter losses corrected, the receiver noise temperature is less than five times the quantum-limited noise. Detailed mixer design and measurement results will be presented.

DOI
10.1109/gsmm.2017.7970320

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China is planning to build a 5-m THz telescope named DATE5 at Dome A in Antarctica. The telescope will operate in 0.85 THz and 1.5 THz frequency bands. A waveguide superconductor-insulator-superconductor (SIS) mixer is developed for the 0.85 THz frequency band by utilizing parallel-connected tunnel junctions (PCTJ) with Nb/AlN/NbN trilayer and NbTiN/SiO2/Al microstrip tuning circuit on quartz substrate. Its frequency response is measured by a Fourier-transform spectrometer (FTS), showing an FWHM frequency coverage of 762-925 GHz. The measured uncorrected double sideband (DSB) receiver noise temperature is approximately equal to 450 K at 840 GHz. With the vacuum window and beamsplitter losses corrected, the receiver noise temperature is less than five times the quantum-limited noise. Detailed mixer design and measurement results will be presented.
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.
We have successfully demonstrated a low-noise 0.78–0.95-THz waveguide mixer based on Nb/AlO x /Nb superconductor–insulator–superconductor (SIS) junctions integrated with an NbTiN/SiO 2 /Al superconducting inverted microstrip. The mixer employs a twin-junction tuning circuit and an impedance transformer which are designed to achieve both low noise and wideband operation. Corrected for optical input losses in front of the mixer, the double-sideband (DSB) noise temperature is below 120 K (<3 hf / k B ) around the local oscillator (LO) frequency of 0.88 THz and at an operating temperature of 2 K. The results represent state-of-the-art performance for mixers in the terahertz frequency range.
Superconductor–insulator–superconductor (SIS) mixers remain the choice of heterodyne mixers for single-dish telescopes and interferometers at millimeter and submillimeter wavelengths. Compared with conventional Nb/AlOx/Nb superconducting tunnel junctions, Nb/AlN/NbN ones have larger gap voltage and may reach critical-current density beyond 10kA/cm2, which are both of particularly interest in developing broadband SIS mixers. Here we report on the design and measurement of an SIS mixer based on Nb/AlN/NbN parallel connected twin junctions (PCTJ) incorporating NbTiN/SiO2/Al microstrip circuit. The junctions have a gap voltage of 3.18mV and a critical-current density of 15kA/cm2. The measured receiver noise temperature reach 5hν/kB among 200-260GHz band, and the mixer’s fractional bandwidth is about 40% centered at 230GHz.
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.
A total of 73 dual polarization superconductor-insulator-superconductor (SIS) receivers for the Atacama Large Millimeter/submillimeter Array (ALMA) have been successfully produced to observe astronomical signals in the 787-950 GHz frequency band. The receivers use two double sideband (DSB) waveguide mixers with Nb/AlOx/Nb tunnel junctions and NbTiN/SiO2/Al microstrip tuning circuits on quartz substrate. The best achieved DSB receiver noise temperature is 125 K, corresponding to about 3 hf/kBfor 4 K operation.
This paper mainly reports the development of a 0.5-THz waveguide SIS (superconductor – insulator – superconductor) mixer, which adopts twin NbN-based SIS junctions (NbN/AlN/NbN) connected in parallel. The 0.5-THz waveguide NbN SIS mixer is designed incorporating with a 51-μm thick MgO substrate and a waveguide mixer mount with no back-short cavity. Detailed simulation results, junction fabrication process and junction I-V characteristics are described. Preliminary FTS (Fourier Transform Spectrometer) measurement results will also be discussed.