Self-cooling observed in graphene electronics

Apr 03, 2011
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 for Advanced Science and Technology

With the first observation of thermoelectric effects at graphene contacts, University of Illinois researchers found that graphene transistors have a nanoscale cooling effect that reduces their temperature.

Led by mechanical science and engineering professor William King and electrical and computer engineering professor Eric Pop, the team will publish its findings in the April 3 advance online edition of the journal Nature Nanotechnology.

The speed and size of computer chips are limited by how much heat they dissipate. All electronics dissipate heat as a result of the in the current colliding with the device material, a phenomenon called resistive heating. This heating outweighs other smaller thermoelectric effects that can locally cool a device. Computers with silicon chips use fans or flowing water to cool the transistors, a process that consumes much of the energy required to power a device.

Future made out of – carbon sheets 1 atom thick – could be faster than silicon chips and operate at lower power. However, a thorough understanding of heat generation and distribution in graphene devices has eluded researchers because of the tiny dimensions involved.

The Illinois team used an atomic force microscope tip as a temperature probe to make the first nanometer-scale temperature measurements of a working graphene transistor. The measurements revealed surprising temperature phenomena at the points where the graphene transistor touches the metal connections. They found that thermoelectric cooling effects can be stronger at graphene contacts than resistive heating, actually lowering 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 , 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."

This self-cooling effect means that graphene-based electronics could require little or no cooling, begetting an even greater energy efficiency and increasing graphene's attractiveness 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 " said Pop, who is also affiliated with the Beckman Institute for Advanced Science, and the Micro and Nanotechnology Laboratory at the U. of I.

Next, the researchers plan to use the AFM temperature probe to study heating and cooling in carbon nanotubes and other nanomaterials.

Explore further: Tiny carbon nanotube pores make big impact

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User comments : 13

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kaasinees
1 / 5 (1) Apr 03, 2011
First we need to develop transistors that use graphene...
rgwalther
3 / 5 (4) Apr 03, 2011
We all know that carbon chose god because he plays with blocks
kaasinees
1 / 5 (1) Apr 03, 2011
The Illinois team used an atomic force microscope tip as a temperature probe to make the first nanometer-scale temperature measurements of a working graphene transistor.


How do they know the probe hasn't cooled the transistor?

Anyway graphene has very low resistence so its naturally that the transistors would develop less heat.
transient
4.4 / 5 (7) Apr 03, 2011
Quantum_Conundrum: >

The usual baloney from Quantum Con.
transient
4.2 / 5 (5) Apr 03, 2011
<>

The usual baloney from Quantum Con.
trekgeek1
5 / 5 (4) Apr 03, 2011
No wonder God chose Carbon as the primary building block of life.


No wonder why Carbon based life chose to create God.
Beard
not rated yet Apr 04, 2011
I'm not sure I understand; does this mean that the natural cooling effect will override the heat of processing? Or does it mean that graphene will be cooler than silicon but the heat produced by processing will still be substantial?
Mahal_Kita
5 / 5 (6) Apr 04, 2011
elcome to:

The website wholesale for many kinds of ...



Perhaps it's time to introduce a captcha tool?
Eikka
not rated yet Apr 04, 2011
Unless they also broke the laws of thermodynamics, I don't see how the transistors would work cooler as a circuit.

Because the thermoelectric effect invariably removes heat from one place and deposits it to another. It doesn't turn the heat back into work without having some other place that is even cooler to dump it into, which it doesn't in this case.

Perhaps, it may remove the heat from the transistor junction and deposit it somewhere else where the effects of it would be more easily tolerated, allowing the circuit to actually run much hotter without the negative effects of it. Like a fridge in a hot room keeping the beer cold but making the room hotter.
Eikka
not rated yet Apr 04, 2011
Because logically, if you allow the temperature of the circuit to rise while keeping the critical spots cool, then you get much more efficient heat flow out of it.

If you could let the CPU in your computer to heat up to 100 degrees C on the surface instead of the 50-ish it's probably running at right now, you would need half as large a heatsink to keep it running, or alternatively, you could use the same thing you have right now and put twice as many watts of heat through it. Double the number of transistors working.
rgwalther
not rated yet Apr 04, 2011
Physorg misspelled 'elk' tronics. This was the medieval version of 'Tron'. All the characters spoke liturgical Latin and rode phosphorescent Moose.
apaterson
not rated yet Apr 04, 2011
//Anyway graphene has very low resistence so its naturally that the transistors would develop less heat.//

Bulk graphene has no energy band gap between the valence and conduction bands, making it metallic in nature and a good conductor. Graphene used in transistors, however, is semiconducting and non-metallic. Bulk graphene made by chemical vapor deposition, liquid exfolitation, or micromechanical cleavage is patterned or etched by some process to make graphene nanoribbons on the order of 20 to 100 nanometers wide. Graphene nanoribbons below 100 nanometers in width no longer exhibit bulk electronic properties due to the lateral confinement of charges and decrease in the density of energy states. At these dimensions the band gap energy increases, making the graphene semiconducting. I would assume the researchers were working with semiconducting graphene nanoribbons, not bulk metallic graphene.
bluehigh
1 / 5 (1) Apr 10, 2011
As has been mentioned previously the band gap remains small and is not very useful for digital switching.(so far)
Graphene base transistors exist and are being developed for Analog applications.

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