Coating Wires in Graphene Offers a Way Beyond the 'Copper Bottleneck'

A simple coating allows for much smaller, much faster data transmission.

by Michael Byrne
Jun 20 2015, 10:00am

Image: Oak Ridge NL

A simple and relatively cheap graphene upgrade has the potential to boost the speeds of future computer processors beyond current limits, according to research presented this week at the Symposia of VLSI Technology and Circuits in Kyoto by a group of Stanford engineers. It all comes down to the regular old copper wiring—albeit very, very small copper wiring—tasked with connecting the millions of transistors powering a typical computer chip.

More specifically, the advance has to do with the "glue" that binds together conductive copper and the surrounding silicon foundation of a circuit. This material acts as a sheath or protective coating that also keeps the copper from "migrating" into the transistors of the chip. (Unlike the colorful household the wires you're probably imagining, this is all happening at the atomic level with the "wires" etched onto the substrate of a chip.) Nowadays, this barrier is typically a compound called tantalum nitride, which does the job just fine, but also has a lower limit of thinness and this limit more or less enforces a lower limit on the size of the chip itself.

The Stanford group found that, first, by using graphene—you know, the super-strong and super-conductive wonder-material of future electronics—as a coating instead of tantalum nitride, they could use much less of it, allowing a thickness of about one-eighth that of the current minimum. That's a pretty big potential reduction in scale, but perhaps even more significant is graphene's ability to boost the transmission speeds of the copper wiring.

And this is kind of strange thing about the wiring of computer processors. The coating isn't there strictly as a barrier, but also functions as a conductor itself. So, it's like a wire that's wrapped in another wire that also happens to function as a protective layer. Graphene is, of course, an excellent conductor as a single-atom-thick two-dimensional material—as a coating, it allows electrons to bounce freely along the exterior of the wire as it contains the copper atoms of the wire itself. More electrons moving at faster speeds means faster computing.

"Even when the wire width is scaled to 10 nm, the effective resistivity of the [copper] interconnect is maintained near the intrinsic value of [copper] using a single layer graphene barrier," the Stanford group, led by nanoengineering professor Philip Wong, write.

How much faster? Given current chips, swapping in a graphene coating would offer a nominal to decent speed-up of between 4 and 18 percent. In future chips, however, featuring smaller and smaller transistors and smaller and smaller wires, graphene coatings could boost performance by up to 30 percent, according to the Stanford group. This could be realized within two generations of chips.

"Graphene has been promised to benefit the electronics industry for a long time, and using it as a copper barrier is perhaps the first realization of this promise," Wong offered in a seperate Stanford statement.