Graphene gets noise treatment

IBM researchers have stumbled across a possible solution to one of the biggest obstacles to the use of graphene as a substitute for silicon in future electronic devices. They have developed a way to suppress the noise that would otherwise render nanoscale graphene transistors useless.

Scientists around the world are exploring the use of graphene as a much smaller replacement for today’s silicon transistors. Graphene is a two-dimensional honeycomb lattice of carbon atoms, with a molecular structure that resembles chicken-wire but which has very high conductivity thanks to the unusual arrangement of electron orbitals in the lattice. One problem in using these nano-devices is the inverse relationship between the size of the device and the amount of uncontrolled electrical noise that is generated: as they are made smaller and smaller, the noise grows larger and larger. This trend is known as Hooge’s rule, and occurs in traditional silicon based devices as well as in graphene nano-ribbons and carbon nanotube based devices.

“The effect of noise from Hooge’s rule is exaggerated at the nanoscale because the dimensions are approaching the nearly smallest limits, down to only a handful of atoms, and the noise that is created can overwhelm the electrical signal that needs to be achieved to be useful,” said IBM researcher Phaedon Avouris, who leads IBM’s exploration into carbon nanotubes and graphene. “To quote the famous physicist Rolf Landauer, at the nanoscale ‘the noise is your signal’ in other words, you cannot produce any useful electronic device at the nanoscale if the noise is comparable to the signal you are trying to switch on and off.”

Now, IBM scientists have found that the noise in graphene-based semiconductor devices can, in fact, be suppressed and report the results today (March 6) in the journal Nano Letters.

In their experiments, the IBM Researchers first used a single layer, or sheet, of graphene to build a transistor and noted that the device does in fact follow Hooge’s Rule: as they are made smaller and smaller, there is an increase in the noise that is created. However, when the IBM researchers built the same device with two sheets of graphene instead of one -- one stacked on top of the other -- they noted that the noise generated was much lower: weak enough for bilayer graphene ribbons to be candidates future semiconductor devices. The noise reductions comes from strong electronic coupling between the two graphene layers that counteracts the influence of the noise sources: the system acts as a noise insulator. However, the researchers said more work is needed to understand why the interactions have this effect.

Image: Schematic of the dual-layer structure used by IBM's research team

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