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  • 1
    Electronic Resource
    Electronic Resource
    Thermal noise-limited sensitivity of the pulse-biased SQUID magnetometer (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1626-1630 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We numerically calculated and obtained an approximate expression for the thermal noise-limited sensitivity of the pulse-biased SQUID sensor used in the integrated magnetometer. We found that the sensitivity is inversely proportional to the bias frequency and inversely proportional to the critical current of the Josephson junction to the 4/3 power. The sensitivity is also proportional to the temperature to the 4/3 power, and is nearly independent of the bias pulse duration. The sensitivity expression is similar to that of the rf SQUID, however, the coefficient is more than one order of magnitude smaller. The best sensitivity has the same order of magnitude as that of the dc SQUID. The quantum limit is attained at a bias frequency of 0.9 GHz at 4.2 K with the typical junction parameters. This sensitivity is available for the SQUID magnetometer operated in the digital feedback loop.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342955
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  • 2
    Electronic Resource
    Electronic Resource
    A submicrometer Nb/AlOx/Nb Josephson junction (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1586-1588 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality, submicrometer Nb/AlOx /Nb Josephson junctions were fabricated. The junction area was defined by anodizing an upper Nb electrode using a thin SiO2 mask. By utilizing the anodized Nb as an etch stop during the reactive ion etching of the contact hole in an SiO2 insulator, we could make a junction smaller than the contact hole size. Using stress-free Nb for the junction electrodes was crucial in achieving good current-voltage characteristics. High-quality Nb/AlOx /Nb junctions as small as 0.7 μm square were produced. The quality parameter Vm was greater than 30 mV for a jc of 6800 A/cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341792
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  • 3
    Electronic Resource
    Electronic Resource
    Characterization of Nb/AlOx-Al/Nb Josephson junctions by anodization profiles (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 66 (1989), S. 2173-2180 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The thin tunneling barrier in a Nb/AlOx-Al/Nb Josephson junction was characterized by anodization profiles. Our studies focused on Nb/AlOx and Al/Nb interfaces in Nb/AlOx-Al/Nb junctions made by varying certain process parameters. The interface quality was checked by the anodization profiles and was greatly affected by film thickness, layer sequence, annealing treatment, and the existence of a thin oxide. By comparing the profiles with the junction characteristics measured at 4.2 K, we confirmed that the interface sharpness in the profiles is related to the junction quality. The anodization profile is a useful tool to diagnose the tunneling barrier interfaces in Nb/AlOx-Al/Nb Josephson junctions, especially at room temperature during fabrication.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.344314
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  • 4
    Electronic Resource
    Electronic Resource
    Plasma nitridation process for superconducting Nb wiring to improve their annealing stability (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 6958-6965 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We developed plasma nitridation for superconducting Nb wiring to improve their annealing stability. Plasma nitridation was observed to be very effective in increasing the critical currents and improve annealing stability. We analyzed the nitride layer formed on the surface of Nb film by plasma nitridation, and found that it prevented oxygen diffusion in Nb. Plasma nitridation is a currently feasible process to improve the reliability of Nb wiring in Josephson circuit.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349823
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  • 5
    Electronic Resource
    Electronic Resource
    Cross-sectional transmission electron microscopy observation of Nb/AlOx-Al/Nb Josephson junctions (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 645-647 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A study of microstructure of Nb/AlOx-Al/Nb Josephson junctions by cross-sectional transmission electron microscopy yielded much information regarding the junction barrier region. Both thick Nb and several-nanometer Al form polycrystalline films with columnar structures. Nb is oriented to the (110) plane, and Al is (111). The 200 nm lower Nb has a wavy surface with ∼5 nm smoothness, but its surface is planarized by several nanometers Al deposited on it. Thus AlOx with a smoothness under 1 nm can be formed on Al. The upper Nb has a good crystalline structure even just above the AlOx barrier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104556
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  • 6
    Electronic Resource
    Electronic Resource
    Annealing stability in superconducting Nb wiring with nitrogen plasma treatment (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 750-752 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We improved the annealing stability in superconducting Nb wiring used in Josephson circuits. Nb film was exposed to nitrogen plasma just after sputtering. We measured the critical current of the Nb wiring before and after annealing. Even before annealing, the critical current with nitrogen plasma treatment is 50% higher than that without treatment. The decrease in critical current after annealing is markedly suppressed. We confirmed using secondary-ion mass spectroscopy profiles that very little oxygen diffuses into Nb films treated using the nitrogen plasma.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104536
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  • 7
    Electronic Resource
    Electronic Resource
    Selective plasma oxidation of oxygen-deficient YBa2Cu3O7−x (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 7549-7555 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A selective plasma oxidation method was developed to make superconducting patterns in nonsuperconducting deoxygenated YBa2Cu3O7−x (YBCO) films. Superconductor- nonsuperconductor-superconductor junctions were fabricated in oxygen-deficient c-axis-oriented polycrystalline YBCO films by selective plasma oxidation using Au/BaF2 oxidation masks. These devices displayed SNS-like or SIN-like nonlinear current-voltage relationships, depending on the device size and oxidation time. The oxygen penetration depth beneath the oxidation mask was estimated to be about 2 μm for the polycrystalline films. Oxygen supplied to 300-nm-thick films for 5 min changes its phase, determined from x-ray diffraction patterns, from tetragonal to orthorhombic I having a critical temperature of about 85 K. X-ray diffraction and magnetic susceptibility measurement showed that the plasma oxidation can supply oxygen to a deoxygenated 0.7×0.5×0.05 mm YBCO single crystal, changing the entire crystal from tetragonal to the orthorhombic II phase whose critical temperature is about 50 K. Four-probe resistance measurement of the plasma oxidized single crystal showed that the phase of the surface of the sample became orthorhombic I with the critical temperature of 84 K by plasma oxidation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.354003
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  • 8
    Electronic Resource
    Electronic Resource
    Dielectric–base transistor using YBa2Cu3O7−x/NdGaO3/SrTiO3 heterostructures (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 5284-5286 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: This paper describes the fabrication and evaluation of dielectric-base transistors having high-Tc YBa2Cu3O7−x electrodes with NdGaO3 low-permittivity barriers on SrTiO3 high-permittivity substrates. The YBa2Cu3O7−x/NdGaO3/SrTiO3 heterostructures were made by laser ablation. Nb base electrodes were sputtered on the back of the SrTiO3 substrate. The device showed transistor characteristics with voltage and current gains exceeding unity at 4.2 K. The collector current density was about 10 A/cm2 at a collector voltage of 20 V, four orders of magnitude larger than that obtained for devices having no artificial barriers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350543
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  • 9
    Electronic Resource
    Electronic Resource
    Nb Josephson junction with a Hf/HfN double overlayer (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 2969-2972 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We fabricated a Nb Josephson junction with a Nb/HfOx-Hf/HfN/Nb structure. The junction showed an excellent current-voltage characteristics (Vm = 40 mV), and these characteristics were not degraded with annealing at temperatures up to 350 °C. Each layer in the Hf/HfN double overlayer plays an important role in the junction structure. The Hf layer acts as a layer for the tunneling barrier formation and as an effective etch stop for a reactive ion etching process in junction fabrication. The HfN layer greatly contributes to the annealing durability of the junction by acting as an effective stop for grain boundary diffusion between the Nb and Hf layers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351502
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  • 10
    Electronic Resource
    Electronic Resource
    Evaluation of AlOx barrier thickness in Nb Josephson junctions using anodization profiles (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2550-2552 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using anodization profiles, we have analyzed the thin AlOx-Al tunneling barrier in a Nb/AlOx-Al/Nb Josephson junction. We measured the voltage width at the AlOx-Al barrier in the profiles and found that it is closely related to the AlOx-Al thickness. We proposed a way to evaluate this thickness from the voltage width. The anodization profile is useful in diagnosing the 4.2 K critical current density of Josephson junctions even at room temperature.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101978
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