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  • 1995-1999  (6)
  • 1990-1994  (3)
  • 1
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.114620
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108069
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.119967
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.115698
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  • 5
    Electronic Resource
    Electronic Resource
    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
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.116052
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  • 6
    Electronic Resource
    Electronic Resource
    A low-noise SIS receiver measured from 480 GHz to 650 GHz using Nb junctions with integrated RF tuning circuits (1994)
    Springer
    International journal of infrared and millimeter waves 15 (1994), S. 943-965 
    Details
    ISSN: 1572-9559
    Keywords: superconductors ; SIS junctions ; SIS mixers ; SIS receivers ; integrated tuning circuits
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A heterodyne receiver using an SIS waveguide mixer with two mechanical tuners has been characterized from 480 GHz to 650 GHz. The mixer uses either a single 0.5 × 0.5 µm2 Nb/AlOx/Nb SIS tunnel junction or a series array of two 1 µm2 Nb tunnel junctions. These junctions have a high current density, in the range 8 – 13 kA/cm2. Superconductive RF circuits are employed to tune the junction capacitance. DSB receiver noise temperatures as low as 200 ± 17 K at 540 GHz, 271 K ± 22 K at 572 GHz and 362 ± 33 K at 626 GHz have been obtained with the single SIS junctions. The series arrays gave DSB receiver noise temperatures as low as 328 ± 26 K at 490 GHz and 336 ± 25 K at 545 GHz. A comparison of the performances of series arrays and single junctions is presented. In addition, negative differential resistance has been observed in the DC I–V curve near 490, 545 and 570 GHz. Correlations between the frequencies for minimum noise temperature, negative differential resistance, and tuning circuit resonances are found. A detailed model to calculate the properties of the tuning circuits is discussed, and the junction capacitance as well as the London penetration depth of niobium are determined by fitting the model to the measured circuit resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02096128
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  • 7
    Electronic Resource
    Electronic Resource
    180–425 GHz low noise SIS waveguide receivers employing tuned Nb/AIO x /Nb tunnel junctions (1994)
    Springer
    International journal of infrared and millimeter waves 15 (1994), S. 783-805 
    Details
    ISSN: 1572-9559
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report recent results on a 20% reduced height 270–425 GHz SIS waveguide receiver employing a 0.49 µm2 Nb/AlO x /Nb tunnel junction. A 50% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner reduced height waveguide mixer block. The junction uses an “end-loaded” tuning stub with two quarter-wave transformer sections. We demonstrate that the receiver can be tuned to give 0–2 dB of conversion gain and 50–80% quantum efficiency over parts of it's operating range. The measured instantaneous bandwidth of the receiver is ≈ 25 GHz which ensures virtually perfect double sideband mixer response. Best noise temperatures are typically obtained with a mixer conversion loss of 0.5 to 1.5 dB giving uncorrected receiver and mixer noise temperatures of 50K and 42K respectively at 300 and 400 GHz. The measured double sideband receiver noise temperature is less than 100K from 270 GHz to 425 GHz with a best value of 48K at 376 GHz, within a factor of five of the quantum limit. The 270–425 GHz receiver has a full 1 GHz IF passband and has been successfully installed at the Caltech Submillimeter Observatory in Hawaii. Preliminary tests of a similar junction design in a full height 230 GHz mixer block indicate large conversion gain and receiver noise temperatures below 50K DSB from 200–300 GHz. Best operation is again achieved with the mixer tuned for 0.5–1.5 dB conversion loss which at 258 GHz resulted in receiver and mixer noise temperature of 34K and 27K respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02096576
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    Paper (German National Licenses)
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  • 8
    Electronic Resource
    Electronic Resource
    230 and 492 GHz low noise sis waveguide receivers employing tuned Nb/AlOx/Nb tunnel junctions (1995)
    Springer
    International journal of infrared and millimeter waves 16 (1995), S. 2049-2068 
    Details
    ISSN: 1572-9559
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report results on two full height waveguide receivers that cover the 200–290 GHz and 380–510 GHz atmospheric windows. The receivers are part of the facility instrumentation at the Caltech Submillimeter Observatory on Mauna Kea in Hawaii. We have measured receiver noise temperatures in the range of 20K–35K DSB in the 200–290 GHz band, and 65–90K DSB in the 390–510 GHz atmospheric band. In both instances low mixer noise temperatures and very high quantum efficiency have been achieved. Conversion gain (3 dB) is possible with the 230 GHz receiver, however lowest noise and most stable operation is achieved with unity conversion gain. A 40% operating bandwidth is achieved by using a RF compensated junction mounted in a two-tuner full height waveguide mixer block. The tuned Nb/AlO x /Nb tunnel junctions incorporate an “end-loaded” tuning stub with two quarter-wave transformer sections to tune out the large junction capacitance. Both 230 and 492 GHz SIS junctions are 0.49µm2 in size and have current densities of 8 and 10 kA/cm2 respectively. Fourier Transform Spectrometer (FTS) measurements of the 230 and 492 GHz tuned junctions show good agreement with the measured heterodyne waveguide response.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02073409
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  • 9
    Electronic Resource
    Electronic Resource
    Low-Loss NbTiN Films for THz SIS Mixer Tuning Circuits (1998)
    Springer
    International journal of infrared and millimeter waves 19 (1998), S. 373-383 
    Details
    ISSN: 1572-9559
    Keywords: NbTiN superconducting films ; SIS junctions ; Niobium bandgap
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent results at 1 THz using normal-metal tuning circuits have shown that SIS mixers can work well up to twice the gap frequency of the junction material (niobium). However, the performance at 1 THz is limited by the substantial loss in the normal metal films. For better performance superconducting films with a higher gap frequency than niobium and with low RF loss are needed. Niobium nitride has long been considered a good candidate material, but typical NbN films suffer from high RF loss. To circumvent this problem we are currently investigating the RF loss in NbTiN films, a 15K Tc compound superconductor, by incorporating them into quasi-optical slot antenna SIS devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1022595223782
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