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Performance limitations of NbN SIS junctions with Al striplines at 600 - 850 Gliz

Pieter Dieleman, T. M. Klapwijk, Herman van de Stadt, Matthias Schicke, B. Plathner, K. H. Gundlach

Published Jan 1, 1997• 0 citations
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Abstract

We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shotn.oise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q >> e. Using this charge enhancement mechanism we explain the junction shotnoise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. Measured double side band noise temperatures are 1450 K and 3300 K at 600 and 850 GHz respectively. Main limitations to the receiver sensitivity are the loss in the aluminum circuit and the subgap current induced shotnoise.

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Shot noise in NbN SIS junctions suitable for THz radiation detection

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We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shot noise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q much greater than e. Using this charge enhancement mechanism we explain the junction shot noise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. The measured double side band noise temperatures are 1450 K at 600 GHz and 2800 K at 950 GHz.

•Jan 1, 1997•1 citation

Analysis of Nb superconductor-insulator-superconductor tunnel junctions with Al striplines for THz radiation detection

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We study the gain and noise of a receiver consisting of a niobium junction embedded in an aluminum impedance matching circuit. The junction is operated in a waveguide mount with an adjustable backshort. The uncorrected double side band noise temperatures are 940 K to 1388 K for 820 to 980 GHz respectively. The total optical loss is obtained from the losses of the individual components, the losses in the stripline are calculated using the Reuter-Sondheimer equation in the extreme anomalous limit. The embedding impedance follows from the pumped curves and the Tucker equations which are also used to determine the noise and gain of the junction. The main limitation to the receiver sensitivity is shown to be the loss in the aluminum circuit.

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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
We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shotn.oise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q >> e. Using this charge enhancement mechanism we explain the junction shotnoise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. Measured double side band noise temperatures are 1450 K and 3300 K at 600 and 850 GHz respectively. Main limitations to the receiver sensitivity are the loss in the aluminum circuit and the subgap current induced shotnoise.
We study the behavior of NbN SIS junctions as radiation detectors with emphasis on the shot noise generated at voltages below the gap voltage. The intrinsically large subgap current of NbN junctions is carried by pinholes with a conduction attributed to multiple Andreev reflection, leading to transported charges q much greater than e. Using this charge enhancement mechanism we explain the junction shot noise characteristics in the unpumped case as well as in the pumped case. The measured mixer noise temperature in the pumped case is more than twice that calculated with standard Tucker theory. The measured double side band noise temperatures are 1450 K at 600 GHz and 2800 K at 950 GHz.
We study the gain and noise of a receiver consisting of a niobium junction embedded in an aluminum impedance matching circuit. The junction is operated in a waveguide mount with an adjustable backshort. The uncorrected double side band noise temperatures are 940 K to 1388 K for 820 to 980 GHz respectively. The total optical loss is obtained from the losses of the individual components, the losses in the stripline are calculated using the Reuter-Sondheimer equation in the extreme anomalous limit. The embedding impedance follows from the pumped curves and the Tucker equations which are also used to determine the noise and gain of the junction. The main limitation to the receiver sensitivity is shown to be the loss in the aluminum circuit.
With sensitivity approaching the quantum limit, superconductor-insulator-superconductor (SIS) mixers play an important role in radio astronomy and atmospheric science at millimeter and submillimeter wavelengths. As one of the intrinsic noise sources in superconducting tunneling junctions, shot noise is still not well understood, particularly for those of relatively high energy gap (e.g., NbN/AlN/NbN). In this paper, we mainly study the multiple Andreev reflection (MAR) enhanced shot noise of two different NbN SIS junctions (i.e., junction array and long junction) as well as their temperature dependence. Barrier strength Z is taken into consideration for theoretical analysis of effective charge of the MAR effect based on the Blonder-Tinkham-Klapwijk (BTK) theory with the Andreev clusters method. It has been found that the effective charge of the MAR effect is inversely proportional to temperature, the barrier strength Z and transparency T are proportional to temperature. Detailed measurement results and analysis will be presented.
We have theoretically and experimentally investigated submillimeter-wave receiver performances employing NbN/ALN/NbN tunnel junctions with high current density and high energy. gap. The receiver noise based on parameters for our typical NbN SIS junction were analyzed using Tucker's quantum theory of mixing, which showed that DSB receiver noise temperatures of below 3hv/K B can be achieved by using the NbN SIS junctions for frequencies up to 2 THz. An experimental receiver has been designed and tested for the 1 THz band. The mixer consists of a MgO hyperhemispherical lens with anti-reflection cap, a NbN twin-slot antenna, and NbN tuning circuits. The prepared NbN/A1N/NbN junction size was about 0.5 !mut), and the current density was about 30 kA/cm 2 (o)CJRN = 11 at 1 THz). Although the junctions showed good dc I-V characteristics with a small sub-gap leakage current, the receiver noise temperature measured by the standard Y-factor method was about 2700 K(DSB) at 761 GHz, which is much larger than the theoretical prediction. The relative high noise performance may be caused by the large RF losses in the tuning circuit of polycristalline NbN on the SiO.
The electrical and shot-noise characteristics of high-current-density niobium superconductor–insulator–superconductor (SIS) tunnel junctions suitable for heterodyne detection of THz radiation are studied. It is found that a significant part of the current at voltages V<2Δ/e is carried via barrier defects (pinholes). Due to the transport mechanism in these pinholes, the shot noise is considerably increased. The data presented clarify an often-observed discrepancy between measured and expected heterodyne mixer noise temperatures and predict a 25% increase in the receiver noise temperature of Nb SIS heterodyne detectors at 1 THz.
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.