IBM has revealed that graphene can't yet fully replace silicon inside CPUs, as a graphene transistor can't actually be completely switched off.
In an interview for a forthcoming Custom PC
feature about chip-building materials, Yu-Ming Lin from IBM Research - Nanometer Scale Science and Technology told us that 'graphene as it is will not replace the role of silicon in the digital computing regime.'
Last year, IBM demonstrated a graphene transistor running at 100GHz
, claiming that the technology could be used to manufacture 'zippy computer chips'
in the years to come. The story, along with news that researchers at the UCLU had produced a graphene transistor with a cut-off frequency of 300GHz
, prompted all sorts of predictions of silicon marching towards its demise, making way for a graphene-based future with 1THz (one terahertz, or 1,000GHz) CPUs.
However, Lin says that 'there is an important distinction between the graphene transistors that we demonstrated, and the transistors used in a CPU. Unlike silicon, 'graphene does not have an energy gap, and therefore, graphene cannot be “switched off," resulting in a small on/off ratio.'
However, he also pointed out that graphene 'may complement silicon in the form of a hybrid circuit to enrich the functionality of computer chips.'
He gives the example of RF circuits, which aren't dependent on a large on/off ratio.
Graphene is a two-dimensional atomic-scale material, made from a hexagonal lattice of carbon atoms and their bonds. A single graphene sheet measures just one atom-thick, potentially paving the way for the smallest transistors physically possible.
'In principle, there's no limit to the size of a graphene transistor,'
says Lin. 'Compared to silicon, graphene is more robust in terms of device scaling, because it has the thickness of a single layer of atoms, while it's known that the quality of silicon will suffer significantly once it's thinned down.'
Graphene also offers much higher potential clock speeds over comparable silicon transistors. 'Graphene transistors can achieve a higher clock speed than those made of silicon with the same gate length,'
explains Lin, 'because the electrons in graphene can move at a higher speed than those in silicon.'
Intel's director of components research, Mike Mayberry, concurred. 'Graphene is still very much in the research phase,'
Mayberry told us, but 'researchers are predicting a number of interesting properties for it and now experimentalists are trying to confirm them.'
Mayberry also added that 'silicon’s properties make it a nearly ideal material. The industry has so much experience with it that there are no plans to move away from silicon as the substrate for chips.'
Basically, graphene has lots of potential advantages over silicon, but it's not going to replace it as the main material for building CPUs, at least not in its current research state.
Look out for a full feature on the future of silicon and chip-building materials in Issue 91 of Custom PC
magazine, on sale from 17 Feb and online at Zinio