Armand J. Panson

High Tc superconductor/noble‐metal contacts with surface resistivities in the 10−10 Ω cm2 range

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...

Method for making low‐resistivity contacts to high Tc superconductors

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 a...

Chemical vapor deposition of YBa2Cu3O7 using metalorganic chelate precursors

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 (1102) Al2O3 showed zero resistance at 65 K.

Chemical vapor deposition of YBa/sub 2/Cu/sub 3/O/sub 7/ using metalorganic chelate precursors

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 (1102) Al2O3 showed zero resistance at 65 K.

The MnTeMnSe system

Abstract The solid solution region for the pseudo-binary MnTeMnSe system has been determined over the entire composition range. An X-ray lattice parameter study was made and the results were employed to determine phase boundaries between 500 and 650°C. Above 650°C phase boundaries were determined by dilatometer measurements.

A study of substituted MnTe

Abstract The system LiξMn1−ξTe and NaξMn1−ξTe were prepared and were found to be single-phase NiAs structures over the concentration ranges 0 ≤ x ≤ 0.09 for the lithium compounds and 0 ≤ x ≤ 0.01 for the sodium compounds. Selenium was also incorporated into the lattice of MnTe with lithium and also sodium to form compounds of the type LiξMn1−xTe1−ySey. Selenium concentrations between 0 ≤ y ≤ 0.15 had little effect on the solubility of lithium or sodium in MnTe. The position of the phase boundaries was determined by Seebeck coefficient measurements. Lattice parameter studies were also made to determine phase limits for LiξMn1−ξTe and Li0.04Mn0.96Te1−ySey.

Monitored Beam X Ray Absorption Spectrometer

A monitored beam x ray absorption spectrometer arrangement is described. With this geometry inaccuracies in determining absorption coefficients due to fluctuating source intensity are eliminated. In the spectrometer the incident x ray beam passes first through a monitor counter and then through the absorber specimen to a detector counter. The arrangement was tested experimentally using two commercial mica side‐window proportional counters.

Effect of Oxygen Annealing on Low-Resistivity Contactsfor High-Tc Superconductors

A method for making low resistivity contacts to high-T c superconductors has been developed, consisting of depositing noble metal contact pads (silver or gold) on a clean superconductor surface at low temperatures ( 2 at 76 K are obtained, about six orders of magnitude less than for indium-solder contacts. Before annealing, the contact resistivities are still very low, in the 10 -6 to 10 -5 Ω-cm range at 76 K, which would be useful when contacts with low fabrication temperatures are required. The voltage-current characteristics of the contacts are strongly nonlinear after annealing, having a superconducting transition character. This is ascribed to the critical current of the superconducting material being exceeded at the contact interface. External connections to the contact pads have been made using both solder and thermosonic wire-bonding techniques.