An essential need for all superconductor devices is to make ohmic, low resistivity contacts with normal conductors. Contacts made with indium solder, silver paint or epoxy, direct wire bonds, and pressure contacts have contact surface resistivities typically in the range 10-2-10 0-cm2, several orders of magnitude too high for many practical applications and critical current measurements. Contact resistivity levels on the order of 10-4-10-5 12-cm2 or lower are needed for critical current measurements to keep contact heating from becoming a problem (unless pulsed-current methods and sample necking techniques are used). For thin-film package inter-connects, contact resistivities in the 10-8 12-cm2 range are needed and finally, for on-chip interconnects, resistivities in the 10-10 Ω-cm2 range are required.
|