What is electromigration (EM) and why is it something we should care about?
Here’s the definition of electromigration from Wikipedia: “Electromigration is the transport of material caused by the gradual movement of the ions in a conductor due to the momentum transfer between conducting electrons and diffusing metal atoms.”
Put simply, when the current density gets too high for a given wire width, you get problems. These problems manifest themselves in two ways, either a void in the metal wire that creates an open circuit or a hillock that creates a short to another wire. Either way your chip fails. Electromigration is made worse by temperature and mechanical stresses.
Electromigration in the FinFET process is now a first-order effect and has a huge impact on the Mean Time To Failure (MTTF) of a metal wire. So, as you can imagine, to ensure you have a robust design that will last, great care has to be taken when choosing wire widths for interconnect and power grids.