Mar 28 2017
Eva Y. Andrei, Board of Governors professor of physics in the Department of Physics and Astronomy. Photo: Courtesy of Eva Y. Andrei
A powerful technique that will help to cool tiny chips has been discovered by Rutgers researchers using graphene. These tiny chips are vital components of electronic devices with billions of transistors apiece.
You can fit graphene, a very thin, two-dimensional material that can be miniaturized, to cool a hot spot that creates heating problems in your chip. This solution doesn’t have moving parts and it’s quite efficient for cooling.
Eva Y. Andrei, Professor, Rutgers
A Rutgers-led study that was recently featured in Proceedings of the National Academy of Sciences has explained that the shrinking of electronic components and the excessive heat produced by their increasing power has increased the requirement for chip-cooling solutions. The researchers used graphene mixed with boron nitride crystal substrate to demonstrate a cooling mechanism that is extremely powerful and efficient.
“We’ve achieved a power factor that is about two times higher than in previous thermoelectric coolers,” said Andrei, who works in the School of Arts and Sciences.
The power factor here refers to the efficiency of active cooling, which takes place when heat is carried away by an electrical current, as demonstrated in this study. Passive cooling refers to the natural diffusion of heat.
Graphene has a number of benefits. It is a one-atom-thick layer of graphite, which is the flaky stuff present inside a pencil. The thinnest flakes, graphene, comprises of carbon atoms positioned in a honeycomb lattice resembles a chicken wire, Andrei stated. Graphene conducts electricity in a much better manner than copper, quickly diffuses heat, and is 100 times stronger than steel.
Graphene is placed on devices developed from boron nitride, which is very flat and smooth like a skating rink, she said. Performance is hindered by silicon dioxide, the conventional base for chips, as it scatters electrons that are capable of carrying away heat.
Andrei further stated that another major issue is the increasing production of heat by billions of transistors in a smartphone chip or a tiny computer. The performance of transistors, electronic devices capable of controlling the flow of power and amplifying signals, is hindered by high temperatures and hence these devices need to be cooled.
The existing methods include small fans in computers, but these fans break down and are becoming less efficient, she stated. The bulky method of using water for cooling has complications and may even cause leaks that can fry computers.
In a refrigerator, you have compression that does the cooling and you circulate a liquid. But this involves moving parts and one method of cooling without moving parts is called thermoelectric cooling.
Eva Y. Andrei, Professor, Rutgers
Consider thermoelectric cooling in terms of the water in a bathtub. It the user turns on the cold water when in fact the tub has hot water, then too much time is taken up for the diffusion of the cold water below the faucet in the tub. Andrei explained that this is passive cooling as molecules slowly diffuse in bathwater and then become diluted.
However, if the water from the cold end is manually pushed by the user’s hands to the hot, then the cooling process, also referred to as active cooling or convection, will be a lot faster.
She stated that the same process takes place in smartphone and computer chips. A piece of wire, such as copper, can be connected to a hot chip and heat is then carried away in a passive manner, just like in a bathtub.
Imagine a piece of metal with cold and hot ends. The electrons and atoms of the metal zip around the hot end and turn out to be sluggish at the cold end, Andrei said. Her research group, in effect, applied voltage to the metal, in order to send a current from the hot end to the cold end.
Similar to the case of active cooling in the bathtub example, the electrons were spurred by the current in order to carry away the heat in a much more efficient manner than through passive cooling. Graphene is in fact considered to be superior in both its active and passive cooling capability. The blending of these two makes graphene an exceptional cooler.
The electronics industry is moving towards this kind of cooling. There’s a very big research push to incorporate these kinds of coolers. There is a good chance that the graphene cooler is going to win out. Other materials out there are much more expensive, they’re not as thin and they don’t have such a high power factor.
Eva Y. Andrei, Professor, Rutgers
The lead author of the study is Junxi Duan, a Rutgers physics post-doctoral fellow. Other authors include Xiaoming Wang, a Rutgers mechanical engineering post-doctoral fellow; Xinyuan Lai, a Rutgers physics undergraduate student; Guohong Li, a Rutgers physics research associate; Kenji Watanabe and Takashi Taniguchi of the National Institute for Materials Science in Tsukuba, Japan; Mona Zebarjadi, a former Rutgers mechanical engineering professor who is now at the University of Virginia; and Andrei. Zebarjadi conducted an earlier study on electronic cooling using thermoelectric devices.