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1

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Chemical vapor deposition of YBa2Cu3O7 using metalorganic chelate precursors (1988)

Panson, A. J. ; Charles, R. G. ; Schmidt, D. N. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 53 (1988), S. 1756-1758

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Superconducting films of YBa2 Cu3 O7 were prepared using metalorganic chelate precursors at ambient pressure. Ba and Y were transported using fluoride-substituted β-diketonates, while a β-keto-imide chelate was used for Cu. Deposition at 500 °C on Al2 O3 and SrTiO3 substrates by reaction with O2 saturated with room temperature water vapor formed crystalline mixtures of BaF2 , YF3 , and CuO. Superconducting YBa2 Cu3 O7 formed after annealing in Ar/H2O at 835 °C followed by O2 at 900 and 400 °C with a slow cooling in O2 to below 200 °C. A 2.3 μm film on a (100) SrTiO3 substrate had an onset Tc of 90 K with zero resistance at 70 K. The film showed a mixture of c- and a-axis orientation. A similar film on (11¯02) Al2O3 showed zero resistance at 65 K.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.100475

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2

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High Tc superconductor/noble-metal contacts with surface resistivities in the 10−10 Ω cm2 range (1988)

Ekin, J. W. ; Larson, T. M. ; Bergren, N. F. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 52 (1988), S. 1819-1821

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: Contact surface resistivities (product of contact resistance and area) in the 10−10 Ω cm2 range have been obtained for both silver and gold contacts to high Tc superconductors. This is a reduction by about eight orders of magnitude from the contact resistivity of indium solder connections. The contact resistivity is low enough to be considered for both on-chip and package interconnect applications. The contacts were formed by sputter depositing either silver or gold at low temperatures (〈100 °C) on a clean surface of Y1 Ba2 Cu3 O7−δ (YBCO) and later annealing the contacts in oxygen. Annealing temperature characteristics show that for bulk-sintered YBCO samples there is a sharp decrease in contact resistivity after annealing silver/YBCO contacts in oxygen for 1 h at temperatures above ∼500 °C and gold/YBCO contacts for 1 h above ∼600 °C. Oxygen annealing for longer times (8 h) did not reduce the contact resistivity of silver contacts as much as annealing for 1 h. Auger microprobe analysis shows that indium/YBCO contacts contain a significant concentration of oxygen in the indium layer adjacent to the YBCO interface. Silver and gold contacts, on the other hand, contain almost no oxygen and have favorable interfacial chemistry with low oxygen affinity. Silver also acts as a "switchable'' passivation buffer, allowing oxygen to penetrate to the YBCO interface at elevated temperatures, but protecting the YBCO surface at room temperature.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.99725

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Method for making low-resistivity contacts to high Tc superconductors (1988)

Ekin, J. W. ; Panson, A. J. ; Blankenship, B. A.

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 52 (1988), S. 331-333

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: A method for making low-resistivity contacts to high Tc superconductors has been developed, which has achieved contact surface resistivities less than 10 μΩ cm2 at 76 K and does not require sample heating above ∼150 °C. This is an upper limit for the contact resistivity obtained at high current densities up to 102–103 A/cm2 across the contact interface. At lower measuring current densities the contact resistivities were lower and the voltage-current curve was nonlinear, having a superconducting transition character. On cooling from 295 to 76 K, the contact resistivity decreased several times, in contrast to indium solder contacts where the resistivity increased on cooling. The contacts showed consistently low resistivity and little degradation when exposed to dry air over a four-month period and when repeatedly cycled between room temperature and 76 K. The contacts are formed by sputter depositing a layer of a noble metal−silver and gold were used−on a clean superconductor surface to protect the surface and serve as a contact pad. External connections to the contact pads have been made using both solder and wire-bonding techniques.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.99455

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Josephson effect above 77 K in a YBaCuO break junction (1987)

Moreland, John ; Goodrich, L. F. ; Ekin, J. W. ; [et al.]

Woodbury, NY : American Institute of Physics (AIP)

Applied Physics Letters 51 (1987), S. 540-541

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ISSN: 1077-3118

Source: AIP Digital Archive

Topics: Physics

Notes: We have observed the Josephson effect in a YBaCuO break junction. Critical currents as high as 10 mA were measured at 4 K for break junctions with a point contact within the fracture of a sample. The junction was susceptible to microwave radiation showing Shapiro steps with the ratio of V/f of 2.04±0.05 μV/GHz compared to the pair tunneling value of h/2e=2.068 μV/GHz. These steps were clearly visible in the current-voltage characteristics at tempertures up to 85±5 K.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.98392

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Evidence for weak link and anisotropy limitations on the transport critical current in bulk polycrystalline Y1Ba2Cu3Ox (1987)

Ekin, J. W. ; Braginski, A. I. ; Panson, A. J. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 62 (1987), S. 4821-4828

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Measurements of the transport critical-current density (Jc), magnetization Jc, and magnetoresistance in a number of bulk sintered samples of Y1Ba2Cu3Ox from several different laboratories indicate that the transport Jc is limited by weak-link regions between high Jc regions. The weak-link Jc has a Josephson character, decreasing by two orders of magnitude as the magnetic field is increased from 0.1 to 10 mT at 77 K. An examination of the grain-boundary region in Y1Ba2Cu3Ox shows no observable impurities or second phases to the scale of the [001] lattice planes (∼12 A(ring)). The effect of intrinsic conduction anisotropy is discussed. A current-transfer model is proposed in which weak conduction along the c axis plays a role in limiting Jc at grain boundaries. Orienting the grains in the powder state during processing may result in enhanced transport Jc in bulk conductors.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.338985

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