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  • 1
    Digitale Medien
    Digitale Medien
    Performance limitations of niobium-based submillimeter-wave quasiparticle mixers operating near the gap frequency (1995)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 67 (1995), S. 424-426 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the noise temperature of heterodyne receivers employing Nb/AlOx/Nb tunnel junction mixers at frequencies ranging from 70% to 93% of the gap frequency of niobium (∼700 GHz). The sensitivity of the receiver is decreased by the overlap of the n=1 and n=2 photon steps of opposite sign. At bias voltages where these photon steps overlap, there is an increase in receiver noise up to 50%. Theoretical calculations using the Tucker theory agree well with the observed mixer performance. This overlap already affects the receiver operation for best performance at frequencies well below 700 GHz. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.114620
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  • 2
    Digitale Medien
    Digitale Medien
    Low-noise thin-film TlBaCaCuO dc SQUIDs operated at 77 K (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 951-953 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have made a series of single-level dc superconducting quantum interference devices (SQUIDs) from 4-μm-thick TlBaCaCuO films with large grain sizes and operated them in liquid nitrogen. Although device characteristics could not be precisely controlled, some devices had white-noise levels that approached thermally limited noise above ∼1000 Hz. In addition, devices with 5 and 80 pH loop inductances had 1/ f noise levels at 10 Hz of 2×10−29 and 5×10−29 J/Hz, respectively. The noise levels at these frequencies are comparable to commercial rf SQUIDs operating in liquid helium, but the hysteresis of the voltage-flux characteristic of the high Tc SQUIDs remains large.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100817
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  • 3
    Digitale Medien
    Digitale Medien
    Low-noise modular microsusceptometer using nearly quantum limited dc SQUIDs (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 2108-2110 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: A flexible combination of superconducting integrated circuits was used to construct a low-temperature magneto-optic microsusceptometer utilizing a dc superconducting quantum inteference device (SQUID) detector operating near the quantum limit (coupled energy sensitivity of 1.7(h-dash-bar)). Miniature pick-up loop assemblies on transparent substrates were joined by superconducting interchip connections to a thin-film dc SQUID, which is in turn read out by a second dc SQUID connected to room-temperature electronics. Measurements on an 8.5-μm-diam titanium dot evaporated directly into the pick-up loop demonstrate a spin sensitivity of ∼103 spins/(Hz)1/2 at T=290 mK.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100291
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  • 4
    Digitale Medien
    Digitale Medien
    Transient response of quasiparticle injected superconducting links (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 489-491 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have fabricated submicron injection-controlled NbN links with gain and measured their injection-triggered superconducting-to-normal transition to occur in 0.5–2.6 ns at 4 K, governed by condensate dynamics. The transient pulse shape displays a rising-edge kinetic-inductance spike and a strong dependence on the amplitude of the injected quasiparticle current similar to microbridges driven by supercritical currents. A modified dynamic effective-temperature model is used to interpret the transient time and the pulse shape.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.101861
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  • 5
    Digitale Medien
    Digitale Medien
    Noise and hysteresis in flux-locked TlBaCaCuO SQUIDs (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 2259-2261 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Measurements of TlBaCaCuO-based dc superconducting quantum interference devices (SQUIDs) performed using a practical feedback circuit gave a flat frequency response and an energy sensitivity of 6×10−30 J/Hz at 5 kHz and 77 K with an 80 pH SQUID. Flux-locked loop operation was demonstrated to be strongly effective in eliminating the magnetic field hysteresis of the SQUID. The SQUIDs were operated in the flux-locked loop at temperatures over 90 K and the 1/f noise was found to decrease with increasing temperature near 77 K.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.101141
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  • 6
    Digitale Medien
    Digitale Medien
    Reliable single-target sputtering process for high-temperature superconducting films and devices (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 444-446 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We report a simple, single-target magnetron sputtering process for films of high-temperature superconductors involving an off-axis sputtering geometry. The process lends itself both to film growth with high-temperature post-anneals and to low-temperature in situ film growth. The post-anneal process routinely yields YBa2Cu3O7−x films on SrTiO3 substrates that are fully superconducting at 86–89 K. Current densities at 77 K range from 104 to 8×105 A/cm2. A single-level superconducting quantum interference device (dc SQUID), made by photolithographically patterning a low current density film, has a flux noise level at 77 K of 3×10−4 Φ0/(Hz)1/2 at 20 Hz, dominated by low-frequency noise associated with flux motion in the film.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.100615
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  • 7
    Digitale Medien
    Digitale Medien
    Dispersion in Nb microstrip transmission lines at submillimeter wave frequencies (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 2712-2714 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: We have measured the effects of dispersion on the resonant mode frequencies of open-ended Nb-SiOx-Nb microstrip transmission lines over a frequency range from 50 to 800 GHz. Submicron Nb/Al-AlOx/Nb Josephson junctions were used as both voltage-controlled oscillators and detectors to sample the high order modes of the resonators. The resonator modes are equally spaced up to about 550 GHz where the mode spacing start to decrease gradually to a minimum above the gap frequency fg≈700 GHz and then increases. Results are in good agreement with the expected theoretical behavior based on the Mattis–Bardeen conductivity of the superconductor line.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.108069
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  • 8
    Digitale Medien
    Digitale Medien
    Low noise in a diffusion-cooled hot-electron mixer at 2.5 THz (1997)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 1567-1569 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The noise performance of a Nb hot-electron bolometer mixer at 2.5 THz has been investigated. The devices are fabricated from a 12-nm-thick Nb film, and have a 0.30 μm×0.15 μm in-plane size, thus exploiting diffusion as the electron cooling mechanism. The rf coupling was provided by a twin-slot planar antenna on an elliptical Si lens. The experimentally measured double sideband noise temperature of the receiver was as low as 2750±250 K with an estimated mixer noise temperature of (approximate)900 K. The mixer bandwidth derived from both noise bandwidth and IF impedance measurements was (approximate)1.4 GHz. These results demonstrate the low-noise operation of the diffusion-cooled bolometer mixer above 2 THz. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.119967
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  • 9
    Digitale Medien
    Digitale Medien
    Large bandwidth and low noise in a diffusion-cooled hot-electron bolometer mixer (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 1558-1560 
    Details
    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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  • 10
    Digitale Medien
    Digitale Medien
    Length scaling of bandwidth and noise in hot-electron superconducting mixers (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 68 (1996), S. 3344-3346 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Mixing experiments have been performed at frequencies from 4 to 20 GHz on Nb thin-film superconducting hot-electron bolometers varying in length from 0.08 to 3 μm. The intermediate frequency (IF) bandwidth is found to vary as L−2, with L the bridge length, for devices shorter than (square root of)12 Le−ph≈1 μm, with Le−ph the electron-phonon length. The shortest device has an IF bandwidth greater than 6 GHz, the largest reported for a low-Tc superconducting bolometric mixer. The conversion efficiencies range from −5 to −11 dB (single sideband, SSB). For short bridges, the mixer noise temperature is found to be as low as 100 K (double sideband, DSB), with little length dependence. The local oscillator power required is small, ≈10 nW. Such mixers are very promising for low-noise THz heterodyne receivers. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.116052
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