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  • 1
    Electronic Resource
    Electronic Resource
    New cryoelectronic detector concept based on two-dimensional heat diffusion (1993)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 73 (1993), S. 2659-2666 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting Nb/AlOx/Nb tunnel junctions have been fabricated on Si membrane windows of only 1.2 μm thickness acting as substrates. The membrane windows with areas between (600 μm)2 and (1200 μm)2 remained undamaged after the different fabrications steps. The tunnel junctions positioned on the membranes and the bulk silicon substrate have very similar current-voltage characteristics. Using low-temperature scanning electron microscopy the two-dimensional heat diffusion process has been imaged in the detector geometry. This two-dimensional heat diffusion leads to a new cryoelectronic radiation detector concept combining high energy and spatial resolution with a large effective detector area. Applications of this detector concept include soft-x-ray spectroscopy and the nuclear β decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.353061
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  • 2
    Electronic Resource
    Electronic Resource
    The interfaces of NbN-MgO-NbN tunnel junctions (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 584-591 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The chemical composition of the surfaces and interfaces of NbN-MgO-NbN trilayers has been studied by x-ray photoelectron spectroscopy during the fabrication of the trilayer without breaking the vacuum. The NbN and MgO layers were prepared by rf magnetron sputtering. The results of the chemical analysis have been correlated to the electrical characteristics of the completed NbN-MgO-NbN tunnel junctions. During the deposition of the MgO barrier layer the presence of a high amount of energetic oxygen ions and atoms in the sputtering plasma results in a strong plasma oxidation of the NbN base electrode and, hence, in mixed Nb2O5-MgO barriers. The oxygen ions and atoms are generated by the dissociation of the target material and the water of the background pressure. Their amount was found to increase with increasing argon pressure during the MgO sputtering process. Also, adsorption layers of hydroxides on the MgO-target result in the formation of an uncontrollable amount of niobium oxide components at the interface between the NbN base electrode and the MgO barrier. The current-voltage characteristics of tunnel junctions with such barriers show large subgap leakage currents. Pure MgO barriers can be prepared by reducing the oxygen bombardment of the NbN films during the MgO deposition. Pure MgO barriers are oxygen deficient and easily adsorb hydroxides. These hydroxides react with the first layers of the NbN top electrode to NbO2 and NbO thereby reducing and broadening the sumgap value of the tunnel junctions. Tunnel junctions with pure MgO barriers of a nominal thickness of less than 2 nm usually have current-voltage characteristics indicative for microshorts. A special annealing procedure of the NbN-MgO bilayers prior to the deposition of the top electrode desorbs the hydroxides, transforms Mg(OH)2 to MgO without forming metallic magnesium and prevents the formation of intermediate layers of niobium suboxides and metallic shorts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351836
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  • 3
    Electronic Resource
    Electronic Resource
    Ultraviolet light assisted oxygenation process for submicron YBa2Cu3O7−δ thin film devices (2002)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 91 (2002), S. 5411-5418 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial YBa2Cu3O7−δ thin films with thickness between 20 and 30 nm and width down to ∼100 nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to 4×107 A cm−2 for the nanobridges and 5×103–2×105 A cm−2 for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to 2.3×10−3 μm2 showed superconductivity. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1459599
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  • 4
    Electronic Resource
    Electronic Resource
    Spatially resolved analysis of high-Tc grain boundary Josephson junctions and arrays (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 8005-8015 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using Low Temperature Scanning Electron Microscopy (LTSEM) we have studied the spread of the critical current values in one- and two-dimensional arrays of high-Tc grain boundary Josephson junctions (GBJs). For series arrays the critical current values and the magnetic field dependences of all GBJs within the array could be imaged by LTSEM. Our measurements showed that part of the spread of the critical current values derived from measurements of the current-voltage characteristics is caused by variations of the local magnetic field at the junction position. For bicrystal GBJs a Gaussian distribution of the critical current values with a spread as small as ±20% was found. For the investigated step-edge and biepitaxial GBJs the spread of the critical current values was considerably larger. The LTSEM technique also was used to study the spatial homogeneity of the critical current density of the different types of YBa2Cu3O7−δ grain boundary Josephson junctions with a spatial resolution of 1μm. Whereas the critical current density of bicrystal GBJs showed only small variations on this length scale, strong inhomogeneities were found for step-edge and biepitaxial GBJs. © 1994 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357918
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  • 5
    Electronic Resource
    Electronic Resource
    Surface impedance of YBa2Cu3O7−x thin film grain boundary Josephson junctions: Evaluation of the IcRn product (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4581-4587 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The temperature and the dc magnetic field dependence of the effective surface impedance Zs of epitaxial YBa2Cu3O7−x thin films on [001] tilt SrTiO3 bicrystals with tilt angles of 36.8° and 24° have been investigated at 87 GHz. The effects of the grain boundaries become increasingly important with decreasing characteristic voltage IcRn and increasing unit areal normal resistance RnA. The boundaries can consistently be described with a resistively shunted Josephson transmission line model taking into account the effect of finite film thickness. Thermal or magnetic loading of the junction leads to additional losses, whereas the effective microwave penetration depth exhibits a specific extremal behavior. From the magnetic response of Zs at 4.2 K, the junction lower critical fields as well as the values of IcRn and RnA can be deduced. The data agree well with dc transport measurements.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355953
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  • 6
    Electronic Resource
    Electronic Resource
    Magnetic-field-effect three-terminal device based on YBa2Cu3O7−δ grain boundary junctions (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1843-1845 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Three-terminal YBa2Cu3O7−δ thin film devices based on a parallel array of grain boundary Josephson junctions were fabricated. The multiloop superconducting device is controlled by the magnetic field generated by a current Ictrl, which modulates the critical current Ic through the Josephson junction array. For these devices a current gain ranging between 2 at 77 K and 5 at 30 K was obtained. The spatial homogeneity of the device properties was studied by low-temperature scanning electron microscopy and by the determination of the supercurrent correlation function. Comparing the measured and the theoretically expected supercurrent correlation function shows that the device characteristics agree well with those expected from the device geometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356326
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  • 7
    Electronic Resource
    Electronic Resource
    Critical current density of strained multilayer thin films of Nd1.83Ce0.17CuOx/YBa2Cu3O7−δ (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 203-205 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The superconducting transport properties of strained multilayer thin films of YBa2Cu3O7−δ/ Nd1.83Ce0.17CuOx, grown heteroepitaxially by laser ablation deposition, are reported. For individual layer thicknesses below a critical layer thickness of about 250 A(ring), coherency strain removes the orthorhombic distortion in the YBa2Cu3O7−δ layers and makes them twin-free. Zero-field critical current densities as high as 1.1×107 A/cm2 at 77 K have been measured for the YBa2Cu3O7−δ layers. Flux pinning energies at zero temperature and zero magnetic field in the range of 80–140 meV have been found.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104216
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  • 8
    Electronic Resource
    Electronic Resource
    Low noise YBa2Cu3O7−δ grain boundary junction dc SQUIDs (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 727-729 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have fabricated YBa2Cu3O7−δ grain boundary junction dc superconducting quantum interference devices (SQUIDs) with a square washer geometry design. The SQUIDs were formed in c-axis oriented epitaxial films with a single grain boundary of predetermined nature. These SQUIDs show perfectly periodic voltage-flux characteristics without hysteresis from 4.2 to 87 K. At 77 K intrinsic energy sensitivities of 1.5×10−30 and 3.0×10−30 J/Hz at 10 kHz were obtained for 60 and 110 pH SQUIDs, respectively. The intrinsic energy sensitivity limited by 1/f noise at 10 Hz was 1.2×10−28 and 5.5×10−28 J/Hz. The SQUID voltage noise was found to be almost identical to the voltage noise from one of its junctions. The flux focusing effect of the washer geometry was also measured.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103600
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  • 9
    Electronic Resource
    Electronic Resource
    Superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 63 (1993), S. 996-998 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have performed a detailed study of the superconducting transport properties of Bi2Sr2CaCu2O8+x bicrystal grain boundary junctions (GBJs). The GBJs were fabricated by the deposition of c-axis oriented epitaxial Bi2Sr2CaCu2O8+x films on SrTiO3 bicrystal substrates. The measured resistive transition R(T), the current-voltage characteristics (IVCs), the temperature dependence of the critical current density Jc(T), and the magnetic field dependence of the critical current Ic(B) of the Bi2Sr2CaCu2O8+x GBJs are similar to those observed for YBa2Cu3O7−δ GBJs. However, for the same misorientation angle the magnitude of Jc is almost an order of magnitude smaller for the BSCCO-GBJs. The R(T) dependencies and the IVCs of the BSCCO-GBJs are close to the prediction of the resistively shunted junction (RSJ) model. The Ic(B) dependencies are close to those of large Josephson junctions with overlap geometry. Our results show that BSCCO-GBJs may be useful for cryoelectronic applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109818
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  • 10
    Electronic Resource
    Electronic Resource
    Spatially resolved electrical characterization of a YBa2Cu3O7−δ flux transformer (1993)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 62 (1993), S. 2871-2873 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the spatially resolved transport properties of a three-layer YBa2Cu3O7−δ flux transformer using low-temperature scanning electron microscopy. The seven-turn spiral coil is fabricated using a crossover technology with SrTiO3 as an insulator. The different layers were patterned with shadow masks or optical lithography. We show that the insulating SrTiO3 film has no shorts and that the overlaying YBa2Cu3O7−δ spiral reveals a reduced zero resistance critical temperature at the steps and edges of the insulator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.109185
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