Electrical contacts to CRT Bi-2212 superconductors: Preparation, characterization and analysis

The application of bulk high-temperature superconductors (HTSs) in power engineering systems requires the development of reliable contact preparation technology and a thorough understanding of the current transfer and voltage characteristics of the HTS-normal metal interface. This article describes a technique for preparing in situ Au electrical contacts to Bi2Sr2CaCu2O8+delta (Bi-2212) bulk superconductors and a method for measuring the spatial dependence of voltage and current in a contact. Currents of approximately 70 A (the I-c of the sample) transfer from the contact metal to Bi-2212 over a surface area of 0.15 cm(2). An expression for the spatial dependence of voltage and current in a contact is derived and discussed in the context of semiconducting devices, LTSs and HTSs. The surface resistivity of the Au-Bi-2212 interface is measured at 0.25 mu Omega cm(2) and it is demonstrated that an anisotropic critical current density significantly increases the apparent surface resistivity by as much as a factor of 10 in the region where current first transfers to the HTS. Modified expressions for the spatial dependence of voltage and current in contacts are given which account for surface and flux flow resistive components.