Betty A. Blankenship

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...

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.