Superconducting weak links created by electromigration

Electromigration is the displacement of ions in a metal resulting from the momentum transfer between conducting electrons and diffusing atoms. Although already investigated more than 100 years ago, it became a major problem only when the severe conditions necessary for operation of integrated circuits made it apparent in the late 1960s. In conventional wires such as those used for domestic applications, the current density is limited to about 10^4 A/cm2 due to Joule heating. Current densities exceeding this value will produce enough heat to melt the metal wire. In this case, electromigration is not a serious concern. In integrated circuits, however, current densities of 10^6 A/cm2 or even higher can circulate without burning the circuit. At these high current densities, electromigration becomes significant and an important cause of failure. The negative perception of electromigration has progressively changed during the last decades, as the scientific community first understood the physical mechanisms involved in the process and then learnt to master it. In this presentation, I will briefly review the historical evolution of the topic, discuss the physical mechanisms and some material aspects, propose a method to efficiently and safely control its rate, and show some recent applications to the study of superconducting circuitry.