Report: Graphene electronics have self-cooling capabilities

Posted by Chris Nova

University of Illinois scientists have discovered that graphene transistors have a nanoscale cooling effect.

The phenomenon was discovered while observing thermoelectric effects at graphene contacts. The researchers observed that graphene transistors have a nanoscopic cooling effect that reduced their temperature.
    
The research was led by mechanical science and engineering professor William King and electrical and computer engineering professor Eric Pop. The Illini team will publish its results in the April 3 advance online edition of the academic journal Nature Nanotechnology.

Computer chips have size limitations because of the amount of heat they dissipate. All electronics dissipate heat because the electrons in the current collide with the device material, this is a scientific occurrence known as resistive heating.

This heating offsets other smaller thermoelectric effects that can cool an instrument. Computers that have silicon chips utilize fans or directed water to cool down the transistors; this is a process that eats up a lot of the energy required to power a device.
    
Computer chips in the future can be made out of graphene, which are carbon sheets 1 atom thick. In theory, they could be faster than silicon chips and require less power. Nonetheless, a detailed understanding of heat production and dispersal in graphene device has escaped scientists because of the miniscule measurements involved.

The team used an atomic force microscope (AFM) tip as temperature instrument to take the initial nanometer-scale temperature readings from a functioning graphene transistor.

The readings exposed unexpected temperature phenomena at the places where the graphene transistor meets the metal connections.

They established that thermoelectric cooling effects have the potential to be stronger at graphene contacts than resistive heating; this actually helps lower the temperature of the transistor.

"In silicon and most materials, the electronic heating is much larger than the self-cooling," King said. "However, we found that in these graphene transistors, there are regions where the thermoelectric cooling can be larger than the resistive heating, which allows these devices to cool themselves. This self-cooling has not previously been seen for graphene devices."

The self-cooling factor means that graphene-based electronics could need little to no cooling, leading to even better energy efficiency and bumping up graphene’s appeal as a silicon replacement.  
    
"Graphene electronics are still in their infancy; however, our measurements and simulations project that thermoelectric effects will become enhanced as graphene transistor technology and contacts improve," explained Pop, who is also affiliated with the Beckman Institute for Advanced Science, and the Micro and Nanotechnology Laboratory at the U. of I.
    
The researchers' next plan is to use the AFM temperature instrument to observe heating and cooling in carbon nanotubes and other nanomaterials.
    
King also has an affiliation with the department of materials science and engineering, the Frederick Seitz Materials Research Laboratory, the Beckman Institute, and the Micro and Nanotechnology Laboratory.
    
The Air Force Office of Scientific Research and the Office of Naval Research supported this work. Yes, we live in a world where the government/military has a hand in pretty much every cool scientific development. They throw down the money to develop tools for war, and eventually consumers see technological benefits.
    
Yay research!

Information provided by: University of Illinois at Urbana Champaign News Bureau.