Cooling electronic devices such as computers consumes a great deal of energy, typically in the form of air or water cooling. But what if the materials used in making the electronics cooled themselves during operation? Recent findings by William King and Eric Pop of the University of Illinois, Urbana-Champaign, published April 3rd in the online journal Nature Nanotechnology (DOI: 10.1038/nnano.2011.39), suggest that graphene components may be able to do just that.
Using a method they developed to measure the nanoscale temperature distribution with atomic force microscopy (AFM) tips, they were able to determine the temperature distribution in a working graphene field-effect transistor (FET) with a spatial resolution of about 10 nm and a thermal resolution of about 0.25°C. They used this data to construct temperature maps of the FET. “The first thing that was remarkable to me,” King said, “was that we could actually measure the temperature of a working FET where the device layer was just 1 atom thick.”
By feeding temperature data from these maps into a simulation program developed by Pop, they discovered that the temperature rise at a graphene/metal junction in the circuit differed depending on the direction of current flow through the device. In fact, they found a thermoelectric “nanoscale cooling” effect that accounted for about one-third of the temperature difference; the rest was due to resistive heating.
Additional simulations that looked at possible future improvements in graphene materials and metal contacts showed further promise for self-cooling electronics. “If graphene improves in the way that everyone thinks it will, the thermoelectric effect will grow in importance, and the resistive heating will shrink,” King said. “Projecting forward to carbon electronics of the future, the thermoelectric cooling effect will govern everything about the contacts.”
An atomic force microscope tip scans the surface of a graphene/metal contact to measure temperature with spatial resolution of about 10 nm and temperature resolution of about 250 mK. Color represents temperature data. Credit: Alex Jerez, Beckman Institute Imaging Technology Group
