Outta my way – electrons coming through!
By Joel Mercier and Karen Chow
Ever been in a hurry to get to a meeting, but there were a bunch of people standing in your path? Even if you politely move through the crowd, the positions of those people change as you gently push your way through. And, if there’s a lot of you all trying to get to the same meeting, the positions of the coworkers in your way are going to change even more, as everyone attempts to get past them. Maybe some of them end up moving off to the side in little groups. Now imagine that the meeting goers are electrons, and your coworkers standing in the hallway are metal atoms. Congratulations! You’ve just defined electromigration (EM) and voltage (IR) drop in integrated circuit (IC) design.
EM is the movement of metal atoms in a metal wire caused by the flow of current through the wire. The electrons that make up the current are moving at some velocity, and thus have some magnitude of momentum. When these electrons collide with the metal atoms, some of their momentum transfers into the atoms, causing them to move. As the current density of a wire increases, so does the EM effect. At some critical point, this movement creates hills or divots in the metal that can either short the wire to another one, or create an open circuit on the wire. Bad news for circuit performance.
IR drop is similar to EM in that it is an effect that occurs in the interconnects. There is unintended (parasitic) resistance in all metal interconnects that impedes the free flow of electrons. This resistance will cause a drop in voltage over the length of the interconnect from the supply voltage to the block where it will be used. If the interconnect length is too long, the voltage may be too low when it arrives at the block, degrading performance or even causing chip failures.
EM and IR drop effects must be identified and analyzed during design verification to ensure circuit performance and reliability. The Calibre® xACT™ parasitic extraction and mPower™ power integrity analysis platforms offer design teams fast, accurate, easy to use parasitic extraction and EM/IR analysis for both digital and analog designs, from block level up to full-chip layouts. To better understand the causes of EM and IR drop, how to modify IC designs to minimize their impact, and how Calibre and mPower tools can help, download a copy of our technical paper, Analyzing EM/IR in IC design layouts to ensure reliability and performance.
