Currently, these microscopic elements are connected by metal wires, which are made by filling tiny trenches in the surface of the chip with aluminum or aluminum alloys. Unfortunately, aluminum won't meet the requirements for the more densely populated chips of the future, so researchers are hunting for another suitable material.
Copper is a likely candidate for several reasons.
To begin with, it's more conductive than aluminum, allowing finer wires with lower resistive losses. Unfortunately, copper readily diffuses into silicon and causes deep-level chip defects. Nonetheless, scientists at Lawrence Berkeley National Laboratory, led by researcher Othon Monteiro, have devised a way to inlay copper wires to replace the aluminum wires. This method, known as ion-assisted trench filling, promises to open the door to ever more densely packed chips. Also needed, he says, is a material that is compatible with materials of lower dielectric constants, which have been introduced by chip manufacturers to improve insulation and reduce circuit delays.