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1

Digitale Medien

Accurate experimental and theoretical comparisons between superconductor-insulator-superconductor mixers showing weak and strong quantum effects (1988)

McGrath, W. R. ; Richards, P. L. ; Face, D. W. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 63 (1988), S. 2479-2491

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have made a systematic study of the gain and noise in superconductor-insulator-superconductor mixers employing Ta based, Nb based, and Pb-alloy based tunnel junctions. These junctions displayed both weak and strong quantum effects at a signal frequency of 33 GHz. The effects of energy gap sharpness and subgap current were investigated and are quantitatively related to mixer performance. Detailed comparisons are made of the mixing results with the predictions of a three-port model approximation to the Tucker theory. We have measured mixer performance with a novel test apparatus which is accurate enough to allow for the first quantitative tests of theoretical noise predictions. We find that the three-port model of the Tucker theory underestimates the mixer noise temperature by a factor of about 2 for all of our mixers. In addition, predicted values of available mixer gain are in reasonable agreement with experiment when quantum effects are weak. However, as quantum effects become strong, the predicted available gain diverges to infinity, which is in sharp contrast to the experimental results. Predictions of coupled gain do not always show such divergences.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.341026

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2

Digitale Medien

Fabrication and dc characteristics of small-area tantalum and niobium superconducting tunnel junctions (1987)

Face, D. W. ; Prober, D. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 62 (1987), S. 3257-3266

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: 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.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.339332

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3

Digitale Medien

Heterodyne mixing in diffusion-cooled superconducting aluminum hot-electron bolometers (2002)

Siddiqi, I. ; Verevkin, A. ; Prober, D. E.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 91 (2002), S. 4646-4654

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We present microwave (30 GHz) measurements on aluminum superconducting hot-electron bolometer (HEB) mixers. Aluminum HEB mixers have a lower superconducting transition temperature than niobium and niobium nitride devices, and are predicted to have improved sensitivity and require less local oscillator power. The devices studied consist of a narrow superconducting aluminum microbridge with contacts comprised of thick aluminum, titanium, and gold. A perpendicular magnetic field is used to suppress superconductivity in the contacts. The device length is much shorter than the electron–phonon inelastic length [L(very-much-less-than)(Dτe–ph)1/2] and thus the intermediate frequency (IF) bandwidth is set by the diffusion time of hot electrons from the microbridge into the contacts. We discuss limitations on the IF bandwidth in very short HEB mixers with fully normal contacts. Overall, the microwave heterodyne mixing results show good performance with a mixer noise temperature inferred from the conversion efficiency and output noise of TM≥4 K, double side band (DSB). Measurements at 618 GHz yield a conversion efficiency approximately 10 dB lower than observed at 30 GHz. Output saturation by background radiation is postulated to contribute significantly to this difference. A similar decrease in conversion efficiency in the microwave mixing measurements is observed when broadband noise is added to the rf input signal. We discuss the tradeoff between increased sensitivity and the occurrence of saturation effects in low transition temperature HEBs. © 2002 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1448865

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4

Digitale Medien

Improved energy resolution of x-ray single photon imaging spectrometers using superconducting tunnel junctions (2001)

Li, L. ; Frunzio, L. ; Wilson, C. ; [weitere]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 90 (2001), S. 3645-3647

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ISSN: 1089-7550

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We present measurements of the energy resolution of improved single-photon imaging x-ray spectrometers based on superconducting tunnel junctions. The devices have a Ta film absorber with an Al/AlOx/Al tunnel junction on each end. Recent device designs optimized for better quasiparticle cooling in the Al trap obtain an energy resolution of 13 eV full width at half maximum for a photon energy E=5.9 keV, an improvement of a factor of two over earlier devices. We also determined that the niobium contact used in previous devices degraded the energy resolution in the center section of the absorber. With a different contact configuration, we have eliminated this spatial broadening. © 2001 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.1391422

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5

Digitale Medien

Quantum-limited heterodyne detection of millimeter waves using superconducting tantalum tunnel junctions (1990)

Mears, C. A. ; Hu, Qing ; Richards, P. L. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 57 (1990), S. 2487-2489

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We have made accurate measurements of the noise and gain of heterodyne mixers employing small-area (1 μm2) Ta/Ta2O5/Pb0.9Bi0.1 superconductor-insulator-superconductor tunnel junctions. These junctions have very low subgap leakage current and an extremely sharp current rise at the sum gap. We have measured an added mixer noise of 0.61±0.31 quanta at 95.0 GHz, which is within 25% of the quantum limit of 0.5 quanta for a single-sideband mixer. Values of the imbedding admittances are deduced from the shapes of I-V curves pumped at the upper and lower sideband frequencies. Using these admittances, the mixer performance calculated from the quantum theory is in good agreement with the experiment.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.104111

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6

Digitale Medien

Noise mechanisms in superconducting tunnel-junction detectors (2000)

Segall, K. ; Wilson, C. ; Frunzio, L. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 76 (2000), S. 3998-4000

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We present a theory and measurements of noise mechanisms in superconducting tunnel-junction detectors used as single-photon spectrometers. These mechanisms result from incomplete cooling of the excited quasiparticles in the tunnel-junction electrode. Due to the incomplete cooling, only a fraction of the initially created charge is collected by tunneling. Additional effects include reduced dynamic resistance, voltage dependence of the integrated charge, and increased statistical broadening of the signal. We demonstrate these noise mechanisms in our device, and show that they explain the measured energy resolution of 25 eV at 5.9 keV. We also suggest ways to reduce their contribution in future devices. © 2000 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.126796

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7

Digitale Medien

Ferromagnetic artificial pinning centers in superconducting Nb0.36Ti0.64 wires (1996)

Rizzo, N. D. ; Wang, J. Q. ; Prober, D. E. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 69 (1996), S. 2285-2287

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We used ferromagnetic artificial pinning centers in superconducting NbTi wires to achieve a large critical current density (Jc) in a magnetic field. Four wires were fabricated that contained nanometer-sized arrays of Ni or Fe pins inside micron-sized filaments of Nb0.36Ti0.64 alloy. A ferromagnetic pin volume of only 2% Ni produced Jc's (e.g., 2500 A/mm2 at 5 T, 4.2 K) that were comparable to those of commercial wires that have a pin volume of ∼20% Ti. We conclude that ferromagnetic artificial pins are more effective than nonmagnetic pins for a given volume percent. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.117535

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8

Digitale Medien

Large bandwidth and low noise in a diffusion-cooled hot-electron bolometer mixer (1996)

Skalare, A. ; McGrath, W. R. ; Bumble, B. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 68 (1996), S. 1558-1560

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz. © 1996 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.115698

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9

Digitale Medien

Spectrum of thermal fluctuation noise in diffusion and phonon cooled hot-electron mixers (1998)

Burke, P. J. ; Schoelkopf, R. J. ; Prober, D. E.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 72 (1998), S. 1516-1518

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: A systematic study of the intermediate frequency noise bandwidth of Nb thin-film superconducting hot-electron bolometers is presented. We have measured the spectrum of the output noise as well as the conversion efficiency over a very broad intermediate frequency range (from 0.1 to 7.5 GHz) for devices varying in length from 0.08 μm to 3 μm. Local oscillator and rf signals from 8 to 40 GHz were used. For a device of a given length, the spectrum of the output noise and the conversion efficiency behave similarly for intermediate frequencies less than the gain bandwidth, in accordance with a simple thermal model for both the mixing and thermal fluctuation noise. For higher intermediate frequencies the conversion efficiency decreases; in contrast, the noise decreases but has a second contribution which dominates at higher frequency. The noise bandwidth is larger than the gain bandwidth, and the mixer noise is low, between 120 and 530 K (double side band). © 1998 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.121044

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10

Digitale Medien

Experimental quasiparticle dynamics in a superconducting, imaging x-ray spectrometer (1997)

Friedrich, S. ; Segall, K. ; Gaidis, M. C. ; [weitere]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 71 (1997), S. 3901-3903

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ISSN: 1077-3118

Quelle: AIP Digital Archive

Thema: Physik

Notizen: We present an experimental study of the time scales for various quasiparticle processes in a superconducting single photon spectrometer. Processes studied include quasiparticle recombination, diffusion, trapping, tunneling, and energy redistribution. Experiments were performed with a double junction, imaging x-ray detector whose charge output provides a measure of the photon energy. Time scales are extracted with a simple model and the values of several parameters, including the diffusion constant and recombination time, are found to differ from theoretical predictions. These results provide guidelines for performance analysis, device scaling, and future designs. © 1997 American Institute of Physics.

Materialart: Digitale Medien

URL: http://dx.doi.org/10.1063/1.120538

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