A chip that uses copper rather than aluminum in the top metalization layers, which interconnect all transistors and components together. Copper provides better performance, because it has less resistance than aluminum. Resistance increases as the lines (tracks) get smaller. In order to accommodate ever-decreasing die sizes, materials with inherent less resistance are required. Copper might have been used earlier, but it diffused into the silicon until IBM discovered a way to prevent that from happening. IBM delivered the first copper-based microprocessors in 1998. See metalization layer.