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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Tunable THz source using superconducting tunnel junctions

Faouzi M. Boussaha, A. Féret, Christine Chaumont, L. Loukitch, T. Vacelet

Published Sep 24, 2013• 0 citations
Publisher

Abstract

We report on tunable submillimeter-wave radiation sources based on micrometer-sized superconducting tunnel junction arrays optimized within a bandwidth of 350-520 GHz. The arrays consist of 10, 20 and 40 Superconductor-Insulator- Superconductor (SIS) parallel-connected Nb/AlOx/Nb junctions embedded in superconducting microstrip lines. A SIS twin-junction is integrated along with each array to detect output signals. The pumped detector’s I-V characteristic exhibits clearly photon-assisted quasiparticule steps when the arrays are biased upon corresponding Josephson resonances ranging from 370 to 520 GHz.

DOI
10.1117/12.2026955

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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE•Nov 29, 2007•1 citation
We report on tunable submillimeter-wave radiation sources based on micrometer-sized superconducting tunnel junction arrays optimized within a bandwidth of 350-520 GHz. The arrays consist of 10, 20 and 40 Superconductor-Insulator- Superconductor (SIS) parallel-connected Nb/AlOx/Nb junctions embedded in superconducting microstrip lines. A SIS twin-junction is integrated along with each array to detect output signals. The pumped detector’s I-V characteristic exhibits clearly photon-assisted quasiparticule steps when the arrays are biased upon corresponding Josephson resonances ranging from 370 to 520 GHz.
We developed submillimeter superconducting oscillators using Josephson effects in the Nb-based superconductor-insulator-superconductor (SIS) parallel array. The radiation emitted from the array is detected using integrated SIS twin junctions. Despite the small junction number (N = 21), the (I-V ) characteristics of the detector clearly exhibit photon-assisted quasiparticle steps when the array is biased upon its Josephson resonances, ranging from 370 to 500 GHz. The array has a moderate current density (Jc≈= 6 kA/cm2) but provides an output power around 0.28 μW, which would be sufficient in achieving sensitive heterodyne reception. The impedance array can be matched easier to microwave circuits than the usual long Josephson junctions. Furthermore, the parallel array approach can be also extended up to about 1.4 THz using Nb-based SIS junctions.
We report on the first direct detection of submillimeter waves emitted by small parallel tunnel junction arrays. The arrays made up of 10 and 20 Nb/Al-AlOx/Nb junctions of 6 μm2is integrated and coupled in RF to Nb/Al-AlOx/Nb twin junction-based detector by a microstrip/slotline transition. The detector's I-V curve exhibits clearly photonassisted steps when the array is biased on the corresponding Josephson resonance at 390 and 480 GHz. These results are of particular significance in the light of previous work done on this type of devices. The arrays are specially suited for applications such as clock for RSFQ electronics or as local oscillator for THz superconducting integrated receivers.
We report heterodyne measurements of Josephson microwave radiation emitted by a parallel array of small superconductor-insulator-superconductor (SIS) junctions at submillimeter-wave frequencies. The array consists of five Nb/Al–AlOx/Nb junctions nonevenly distributed in a niobium superconducting stripline, and is optimized for rf coupling in the 450–640 GHz range. We observed Fiske-like resonant steps in its I-V curve in the presence of magnetic field. The device was placed in a waveguide mount, and its radiation was quasioptically coupled out of the cryostat, to a SIS-mixer spectrometer in the same frequency range, with a 4–8 GHz band for spectral analysis. We detected a coherent signal in the spectra when the array was biased on the first and third steps, respectively, at the first harmonic frequency of 242 GHz and at the fundamental frequency of 493 GHz, both being the Josephson frequencies associated with their dc voltages. This strongly suggests that this type of parallel arrays optimized for wideband rf coupling, though strongly discretized, hosts dynamic fluxon regimes similar to long Josephson junctions, which could find applications in superconducting digital electronics or integrated heterodyne submillimeter-wave receivers.
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.
Submillimeter-wave direct detectors employing niobium-based superconducting tunnel junctions(STJs) match the request of broadband spectral response and high sensitivity,and having capability of large format arrays. We aim to realize the fractional bandwidth of 10 percent(60 GHz) at 650 GHz.The broadband coupling was designed using 2 distributed junction(DJ) arrays,which were composed of six STJs connected in parallel by a superconducting microstrip line.By analyze the DJ arrays,we found N-resonance combination needs to connect N-set of twin-junctions with short inductances through(N—1)-long inductances,alternatively.And we got the experiment result at 4.2 K that the center frequency of the STJ is 655 GHz,bandwidth about 50GHz,and the sensitivity is 1A/ W.
Superconducting tunnel junctions, which are also known as superconductor-insulator-superconductor (SIS) junctions, are widely used in coherent detection (heterodyne mixing) of electromagnetic radiation at millimeter and submillimeter wavelengths to achieve high spectral resolution (Δν/ν<10-6). With extremely low dark current and high quantum efficiency, superconducting tunnel junctions are also promising for THz photon detection. Besides the merit of high detection sensitivity, THz photon detectors with superconducting tunnel junctions can be operated at relatively high temperatures (above 0.3 K) and don't need rather complicated filtering systems by simply incorporating a superconducting resonant circuit with superconducting tunnel junctions. This paper mainly investigates the characteristics of THz photon detectors with Nb and NbN-based superconducting tunnel junctions. The MAR effect and associated shot noise are addressed. Some analytical and preliminary experimental results are presented.