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  • 1
    Electronic Resource
    Electronic Resource
    Growth and properties of YBa2Cu3O7−x/(SrTiO3/PrGaO3)/YBa2Cu3O7−x trilayers: Optimization of the insulation (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 827-834 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: YBa2Cu3O7−x/insulator/YBa2Cu3O7−x trilayers with a single PrGaO3 (PGO) layer or a SrTiO3 (STO)/PGO multilayer as the insulator were prepared by laser deposition. The PGO layers contained pinholes extending down to the bottom layer, causing superconducting microshorts. The pinholes were eliminated by introducing thin STO films, both as buffer layers and in the PGO itself. Insulation resistivity values of 2×109 Ω cm were measured at 77 K for areas up to 1500 μm2 in these trilayers. For larger areas the insulation decreased by orders of magnitude. This was caused by local disruption of the insulator layer, possibly induced by contaminations or defects in the substrate. The particles observed on the bottom layer were in general continuously covered by the multilayer insulator, and did not affect the insulation. The high-quality insulator layer was found to limit the oxidation of the bottom layer, due to a slower rate of oxygen diffusion. The structure of the STO/PGO layers depended on the thickness of the individual films. Voids started to form in the PGO above a critical thickness of 40 nm. The voids lowered the dielectric constant of the insulator, and a value of 18.5±4.5 was measured at room temperature for a STO/PGO multilayer insulator. The voids could be eliminated by decreasing the thickness of the individual PGO films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356436
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  • 2
    Electronic Resource
    Electronic Resource
    Bicrystal junctions and superconducting quantum interference devices in YBa2Cu3O7 thin films (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 7972-7977 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson junctions and superconducting quantum interference devices (SQUIDs) were made by depositing thin films of YBa2Cu3O7 on bicrystal substrates of Y-ZrO2 and SrTiO3. The critical current density of the junctions at 77 K could be adjusted from 100 to 106 A/cm2 by selecting bicrystals with misorientation angles θ from 45° to 0°. Current-voltage curves from junctions with θ(approximately-greater-than)22° followed the resistively shunted junction model with noise rounding close to the transition temperature. The response of the critical current to magnetic fields was Fraunhofer-like and the width (w) dependence was 1/w2 due to flux focusing effects. Shapiro steps under microwave radiation were observed. SQUIDs based on these junctions had energy resolutions at 77 K down to 8.6×10−30 J/Hz and a 10 Hz flux noise level down to 1.5×10−9 Φ20/Hz at 85 K. A SQUID of the Ketchen design with a flux focusing washer had a magnetic field sensitivity of 15 pT/(square root of)Hz at 77 K. The temperature dependence of the voltage modulation depth close to TC was examined and found to be in agreement with theory [K. Enpuku, Y. Shimomura, and T. Kisu, J. Appl. Phys. 73, 7929 (1993)].
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356559
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  • 3
    Electronic Resource
    Electronic Resource
    Reduction of 1/f noise in high-Tc dc superconducting quantum interference devices cooled in an ambient magnetic field (1996)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 69 (1996), S. 4099-4101 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The spectral density SΦ(f ) of the low-frequency 1/f noise of high transition temperature dc superconducting quantum interference devices (SQUIDs) with narrow linewidths was independent of B0, the magnetic field in which they were cooled, up to a threshold value, about 33 μT in the best case. Above this threshold, which is associated with the entry of flux vortices into the film, the noise increased rapidly. By contrast, for large square washer SQUIDs, SΦ(f ) scaled linearly with B0. Estimates indicate that the 1/f flux noise produced by the pickup loop of a directly coupled magnetometer is negligible. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.117831
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  • 4
    Electronic Resource
    Electronic Resource
    100 GHz oscillations on monolithic high Tc chip (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 896-898 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have coupled 80–180 GHz oscillations from a HTc Josephson junction onto an on-chip YBa2Cu3O7/SiO/Au microstrip resonator. Efficient coupling was achieved at the resonance frequencies and both resonance frequency and Q value could be measured from the I-V curve. The use of a superconductor in the microstrip gave negligible dispersion (〈4%) from 80 to 180 GHz, whereas the attenuation of 4–8 dB/nm originated mainly from the normal metal groundplane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.108559
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  • 5
    Electronic Resource
    Electronic Resource
    Effects of substrate temperature on the microstructure of YBa2Cu3O7−δ films grown on (001) Y-ZrO2 substrates (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 723-725 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-quality YBa2Cu3O7−δ films grown on (001) single-crystal Y-ZrO2 substrates by pulsed laser deposition have been studied as a function of substrate temperature using transmission electron microscopy. A transition from epitaxial films to c-axis oriented polycrystalline films was observed at 740 °C. An intermediate, polycrystalline, BaZrO3 layer was formed from a reaction between the film and the substrate. A dominant orientation relationship of [001]YBCO//[001]int. layer//[001]YSZ and [110]YBCO//[110]int. layer//[100]YSZ was observed. The formation of grain boundaries in the films resulted in an increased microwave surface resistance and a decreased critical-current density. The superconducting transition temperature remained fairly constant at about 90 K.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107779
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  • 6
    Electronic Resource
    Electronic Resource
    Influence of inductance induced noise in an YBa2Cu3O7 dc-SQUID at high operation temperatures (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 2445-2447 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The voltage modulation depth of a high Tc dc-SQUID was measured at temperatures close to Tc and compared to a model by Enpuku et al. where the flux noise from the SQUID inductance is taken into account. The device was an YBa2Cu3O7 dc-SQUID made on a bicrystal substrate of SrTiO3. The design was of the Ketchen square-washer type with an inductance of 67 pH. Measurements were made in a temperature interval from 75 to 87 K, where the voltage modulation depth changed from 4.5 to 1.4 μV in close agreement with the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111594
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  • 7
    Electronic Resource
    Electronic Resource
    Flux-flow transistors based on long YBa2Cu3O7−δ bicrystal grain boundary junctions (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1153-1155 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Josephson flux-flow transistors were made from long YBa2Cu3O7−δ bicrystal grain boundary junctions. A normal metal loop, separated from the junction by an SiO layer, was used as the current control line. The line modulated the critical current, Ic , which for temperatures ≤60 K showed the typical dependence for a long junction, while at higher temperatures the regular small junction modulation was seen. Current gain larger than unity was obtained below 70 K. The current gain increased with the junction length, and varied roughly like (square root of)Ic when decreasing the temperature. A transresistance larger than 5 Ω was obtained at 15 K. Better performance is expected from junctions with higher current densities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110836
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  • 8
    Electronic Resource
    Electronic Resource
    Low 1/f noise in YBa2Cu3O7 dc SQUIDs on (Y)ZrO2 bicrystal substrates (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 861-863 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report low noise operation of YBa2Cu3O7 SQUIDs superconducting quantum interference devices using Josephson junctions grown on bicrystal substrates of (Y)ZrO2. Energy sensitivities measured at 10 Hz (Sε=4.5×10−29 J/Hz) were to our knowledge lower than previously reported for a YBa2Cu3O7 SQUID with practical loop size (∼40 μm). The 1/f part of the voltage noise reached a maximum at 85 K where the noise spectrum was essentially white. The 1/f noise increased both at lower temperatures due to increased critical current fluctuations (∼Ibias2.2) and at higher temperatures, where the flux noise from the film produces a peak below Tc(=89 K).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107769
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  • 9
    Electronic Resource
    Electronic Resource
    Elimination of pinholes in epitaxial thin film YBa2Cu3O7−x/SrTiO3/PrGaO3 multilayers (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 1567-1569 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Pinholes have been eliminated in trilayers of YBa2Cu3O7−x(YBCO)/PrGaO3(PGO)/YBCO by introducing 13-nm-thick SrTiO3(STO) films in the intermediate PGO film. The STO continuously covers the bottom YBCO layer and promotes a uniform growth of the subsequent PGO films. The individual PGO films are of high quality up to a thickness of about 40 nm where voids start to appear in the films. The voids disrupt the continuity of the subsequent STO and PGO layers. The technique of introducing thin layers that establish the growth of pinhole-free films can be used for other similar multilayer systems that suffer from pinholes between individual films.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.110751
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  • 10
    Electronic Resource
    Electronic Resource
    Laser-deposited PrGaO3 films on SrTiO3 substrates and in YBa2Cu3O7/PrGaO3/YBa2Cu3O7 trilayers (1992)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 61 (1992), S. 486-488 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: PrGaO3 films were successfully grown by laser deposition at temperatures between 730 and 785 °C. The minimum full width at half maximum value of the (004) x-ray diffraction peak was 0.14°, for films deposited on SrTiO3 substrates at 760 °C. The optimum temperature for deposition of PrGaO3 in YBa2Cu3O7/PrGaO3/YBa2Cu3O7 trilayers was found to be 760 °C. Three distinct layers were observed , and the PrGaO3 exhibited two orientations with respect to the c-axis oriented bottom layer; either the [001] or the [110] direction parallel to the YBa2Cu3O7 c axis. Two orthogonal in-plane orientations were observed for each of these cases. The highest resistivity (at 100 K) of the PrGaO3 layer was 105 Ω cm. Considerable interaction occurred between the PrGaO3 and the YBa2Cu3O7 bottom layer at 785 °C, where the two bottom layers deteriorated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.107865
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