It’s wafer-thin and transparent even under a microscope. And yet graphene is more stable than diamond. It also conducts heat and electricity, making it perfect for electronic components. | Photo: Imec

Two physicists take a dark, shiny piece of graphite – the same substance we find in a pencil lead – and use a strip of adhesive tape to peel several layers of carbon atoms from it. Then they repeat the procedure until only a transparent layer of atoms can be seen under the microscope, forming a two-dimensional, honeycomb pattern. This is graphene. It’s wafer-thin, more durable than diamond, and it conducts both electricity and heat. In other words, it’s an ideal material for electronic components.

The electrons in this unique lattice structure are extremely mobile, according to Oliver Gröning of the Swiss Federal Laboratories for Materials Science and Technology (Empa) in Dübendorf. What’s more, graphene is versatile. Depending on its structure on the nanoscale, you can alter and control its electrical, optical and magnetic properties. “You can create everything from it that you need in electronics: a conductor, an insulator or a semiconductor”, says Gröning. “This effectively makes graphene the stem cell of electronics”.

His research team at Empa is working with graphene nanoribbons in different shapes. They are manufacturing them synthetically and can control their geometry at the atomic level. This has enabled them to create a transistor, which is a key component of modern electronics. And it has a ‘band gap’ that graphene doesn’t actually possess. The band gap is the energy threshold that determines whether or not current can flow through a transistor. “We can now even adjust this band gap specifically in our graphene transistor, thereby making it sensitive to certain voltage ranges or special optical wavelengths”.

It’s still ‘advantage silicon’

Silicon nevertheless still remains the gold standard in chip electronics. Compared to graphene, says Gröning, the silicon industry has a head start of decades in processing technologies. It’s not only about the components themselves, but also about ensuring that the manufacturing processes can impart the same properties to a chip in production that it had under laboratory conditions. “There’s a ‘Valley of Death’”, says Gröning, referring to the phase when clarity emerges on whether an idea can make the leap from the lab to industrial production. To get that far requires immense development work, major infrastructure and significant financial resources.

But miniaturisation and increasing clock speeds will soon bring classical silicon chips to the boundaries of the possible. Gröning thinks it’s likely that individual, highly specialised graphene components might initially be integrated in existing circuits. Alberto Morpurgo, who is based at the University of Geneva, also believes that “graphene could help to solve some of silicon’s problems – such as by efficiently dissipating heat from high-performance chips and thus allowing higher clock speeds”.

Morpurgo’s group, for example, is investigating applications in so-called ‘spintronics’. This is where the spin of an electron is manipulated specifically and used as logical memory, with its states corresponding to 0 and 1. It can enable components to be switched quickly, and lends itself to significant miniaturisation. “But we’re still at the beginning here”, says Morpurgo, who was also involved in the EU’s ‘Graphene’ flagship.

A new paradigm

Applications such as infrared sensors are also possible. In this regard, Morpurgo mentions a project run by a Spanish startup to develop an infrared camera using graphene. “It could help cars to see through fog. While water droplets absorb a lot of visible light, they can’t do the same with deep infrared”. The startup’s prototypes use a silicon chip with a matrix of contacts and a layer of graphene semiconductor nanostructures on top of them. These absorb infrared light and pass electrons on to the graphene. Every one of the contacts functions like a pixel in a camera.

Morpurgo expects two-dimensional materials to become increasingly important in electronics in general. Besides graphene, these could include hexagonal boron nitride, for example, or hybrid systems made from both materials. “Graphene has opened up a new field of research”, says Morpurgo. “Something that used to seem unique is now part of a larger territory. Graphene has created a new paradigm”.

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