One of the most significant problems facing modern CPUs is the efficient transmission of heat between the CPU cores themselves and the heatsinks that cool them. The problem is twofold: Conventional thermal interface materials (TIMs) are terrible at conducting heat, while processors are terrible at spreading heat laterally (across the surface of the chip). The first problem means that a great deal of thermal energy gets “stuck” at the top of the CPU core, while the latter creates hot spots on the die. Now, a new approach to cooling via the use of carbon nanotubes could aggressively improve the first half of the problem (We discussed possible solutions to the second problem in an article last year).

Carbon nanotubes have long been known to have amazing thermal conductivity, but bonding them to thermal interfaces has been problematic. A new paper published in Nature claims to have solved this problem by using organic compounds to form strong covalent bonds between the carbon nanotubes themselves and the metal layer at the top of a chip. Once formed, this thermal interface material can conduct heat 6x more effectively off the top of a chip. Even better, the bonding technique can work with aluminum, silicon, gold, and copper. Old methods of bonding carbon nanotubes to cooling surfaces added roughly 40 microns of material on each side of the CNT layer; this new approach adds just seven microns of additional material. (Research paper: doi:10.1038/ncomms4082 – “Enhanced thermal transport at covalently functionalized carbon nanotube array interfaces”.)

The Lawrence Berkeley National Lab (Berkeley Lab) team is working on a method that would ensure more of the nanotubes come into contact with the actual metal layer, but the six-fold improvement is already extraordinary. As for how important the advance is, consider the fact that scientists are experimenting with TIMs made of wax to allow for high-speed burst computing, precisely because metal caps, paste, and solder layers are such an inefficient way of dealing with the problem. The one downside, as with many of the cooling methods we considered last year, is that there would be no way for the end-user to service this kind of layer. Intel could theoretically deploy a nanotube layer in between the CPU and its heat spreader, but you’d also need to connect a layer of material between the heat spreader and the actual heat sink in order to see lasting benefits.

Those benefits, however, could be significant. Moving heat more efficiently into the heatsink would reduce CPU core temps and allow for higher frequency operation or longer periods at Turbo Boost clocks as opposed to being stuck at base clock. As it becomes more difficult to push CPU advances through silicon technology improvements, ancillary methods of improving the thermal conductivity of the entire system will become increasingly important.