In the last decade there’s been a move away from raw CPU speed as an indicator of performance. Back when single cores were the norm it was an easy way to judge which CPU would be faster than the other in a general sense however the switch to multiple cores threw this into question. Partly this comes from architecture decisions and software’s ability to make use of multiple cores but it also came hand in hand with a stalling CPU speeds. This is mostly a limitation of current technology as faster switching meant more heat, something most processors could not handle more of. This could be set to change however as research out IBM’s Thomas J. Watson Research Center proposes a new way of constructing transistors that overcomes that limitation.
Current day processors, whether they be the monsters powering servers or the small ones ticking away in your smartwatch, are all constructed through a process called photolithography. In this process a silicon wafer is covered in a photosensitive chemical and then exposed to light through a mask. This is what imprints the CPU pattern onto the blank silicon substrate, creating all the circuitry of a CPU. This process is what allows us to pack billions upon billions of transistors into a space little bigger than your thumbnail. However it has its limitations related to things like the wavelength of light used (higher frequencies are needed for smaller features) and the purity of the substrate. IBM’s research takes a very different approach by instead using carbon nanotubes as the transistor material and creating features by aligning and placing them rather than etching them in.
Essentially what IBM does is take a heap of carbon nanotubes, which in their native form are a large unordered mess, and then aligns them on top of a silicon wafer. When the nanotubes are placed correctly, like they are in the picture shown above, they form a transistor. Additionally the researchers have devised a method to attach electrical connectors onto these newly formed transistors in such a way that their electrical resistance is independent of their width. What this means is that the traditional limitation of increasing heat with increased frequency is now decoupled, allowing them to greatly reduce the size of the connectors potentially allowing for a boost in CPU frequency.
The main issue such technology faces is that it is radically different from the way we currently manufacture CPUs today. There’s a lot of investment in current lithography based fabs and this method likely can’t make use of that investment. So the challenge these researchers face is creating a scalable method with which they can produce chips based on this technology, hopefully in a way that can be adapted for use in current fabs. This is why you’re not likely to see processors based on this technology for some time, probably not for another 5 years at least according to the researchers.
What it does show though is that there is potential for Moore’s Law to continue for a long time into the future. It seems whenever we brush up against a fundamental limitation, one that has plagued us for decades, new research rears its head to show that it can be tackled. There’s every chance that carbon nanotubes won’t become the new transistor material of choice but insights like these are what will keep Moore’s Law trucking along.