Beyond silicon: How graphene can help reinvigorate Moore’s Law

How using graphene could allow for smaller and faster electronic devices and extend Moore's Law yet further.

When Intel co-founder Gordon Moore made the observation that came to be known as Moore's Law, he projected that transistor density would continue doubling in density every two years... for another ten years.

Since then, transistor density has increased by 600,000 times, according to IEEE, with modern technology packing close to a whopping 200 million transistors into 1 square millimeter. High-end desktop processors peak at 64 multithreaded cores and include more memory than entire personal computers had 15 years ago. 

It's getting harder though. The smaller the transistor the easier it is for electrons to tunnel through them, and higher density also packs more heat into a smaller area, which is another challenge. In the Pentium4 era process engineers used new strategies such as changing the doping material, Silicon on Insulator, and strained silicon. As the artefact sizes dipped down into the nanometer scales, engineers started using Field Effect Transistors (FETs), using electrical fields to help block that leakage current. And, as shrinking continued, they started making the transistors three dimensional – hence the FinFET.

Because of these more complex transistor designs, the transistor counts are not increasing as much as they used to with new process nodes, so the engineers have also been working on new ways to put more gates in the same area by building upward. This is not only difficult to do engineering wise, but also hampers heat dissipation. AMD's 3D VCache models reflect this with their lower peak clock speeds, because the extra layer of silicon impedes heat transfer out of the CPU itself.

Now, as semiconductor manufacturers are reaching below the 5nm threshold, they are working on even more exotic transistor designs, such as vertical transistor designs called FTFETs (Vertical-Transport Nanosheet Field Effect Transistor). These allow for denser packing, but they are more complex to manufacture and, like 3D stacked gates, harder to cool than current designs. 

These vertical transistor designs hold out the promise for keeping Moore's Law alive yet again, but what happens when the transistors reach the point where they are just atoms across?

To solve this, researchers have been trying new materials, and one that holds some promise is graphene, a carbon crystal. Graphene has made a mark in battery technology because it's more stable than lithium ion and lithium polymer, has higher charge density, and is based on carbon rather than lithium. Because it conducts heat so well, graphene is also a good candidate as it doesn’t heat up as much, allowing for electrons to move at higher speeds.

What graphene does not have is a band gap, meaning that while great for wires it does not work for gates.

Working with Tianjin University in China, though, researchers at Georgia Tech have made a breakthrough in this department by growing graphene on doped silicon carbide wafers, introducing impurities into the graphene that give it a usable band gap, enabling the researchers to create graphene transistors the size of a carbon atom.

These switches can reach into the teraHertz range and run cooler than silicon transistors, potentially breathing new life into the aging Moore's Law.

Here’s a great video overview of all this from vlogger Anastasi in Tech.

GA Tech research article: Researchers Create First Functional Semiconductor Made From Graphene | Research