Home > Press > Nanotubes act as 'thermal velcro'
Nanotubes act as 'thermal velcro' to reduce computer-chip heating
West Lafayette, IN | Posted on May 01, 2006
Engineers have created carpets made of tiny
cylinders called carbon nanotubes to enhance the flow of heat at a
critical point where computer chips connect to cooling devices called
heat sinks, promising to help keep future chips from overheating.
Researchers are trying to develop new types of "thermal interface
materials" that conduct heat more efficiently than conventional
materials, improving overall performance and helping to meet cooling
needs of future chips that will produce more heat than current
microprocessors. The materials, which are sandwiched between silicon
chips and the metal heat sinks, fill gaps and irregularities between
the chip and metal surfaces to enhance heat flow between the two.
Purdue University researchers have made several new thermal interface
materials with carbon nanotubes, including a Velcro-like nanocarpet.
"The bottom line is the performance that we see with nanotubes is
significantly better than comparable state-of-the-art commercial
materials," said Timothy Fisher, an associate professor of mechanical
engineering who is leading the research. "Carbon nanotubes have
excellent heat-conduction properties, and our ability to fabricate
them in a controlled manner has been instrumental in realizing this
application."
Recent findings have shown that the nanotube-based interfaces can
conduct several times more heat than conventional thermal interface
materials at the same temperatures. The nanocarpet, called a "carbon
nanotube array thermal interface," can be attached to both the chip
and heat sink surfaces.
"We say it's like Velcro because it creates an interwoven mesh of
fibers when both sides of the interface are coated with nanotubes,"
Fisher said. "We don't mean that it creates a strong mechanical bond,
but the two pieces come together in such a way that they facilitate
heat flow, becoming the thermal equivalent of Velcro. In some cases,
using a combination of nanotube material and traditional interface
materials also shows a strong synergistic effect."
Findings related to the combination of carbon nanotubes and
traditional interface materials are detailed in a paper appearing in
the May issue of the International Journal of Heat and Mass Transfer.
The paper was written by mechanical engineering doctoral student Jun
Xu and Fisher.
Heat is generated at various points within the intricate circuitry of
computer chips and at locations where chips connect to other parts.
As heat flows through conventional thermal interface materials, the
temperature rises about 15 degrees Celsius, whereas the nanotube
array material causes a rise of about 5 degrees or less.
It will be necessary to find more efficient thermal interface
materials in the future because as computer chips become increasingly
more compact, more circuitry will be patterned onto a smaller area,
producing additional heat. Excess heat reduces the performance of
computer chips and can ultimately destroy the delicate circuits.
The nanotubes range in diameter from less than one nanometer to about
100 nanometers. A nanometer is a billionth of a meter, or about the
distance of 10 atoms strung together.
The nanotube carpets also might have military and other commercial
applications for cooling "power electronics," which are systems that
control and convert the flow of electrical power so that it can be
used for various purposes on an aircraft, ship or vehicle.
The research has been funded by Purdue's Cooling Technologies
Research Center, supported by the National Science Foundation,
industry and Purdue to help corporations develop miniature cooling
technologies for a wide range of applications, from electronics and
computers to telecommunications and advanced aircraft. Applications
in power electronics are being supported by the Air Force Research
Laboratory in association with the Birck Nanotechnology Center at
Purdue's Discovery Park.
The technology is ready for commercialization and is being pursued by
several corporate members of the cooling research center, including
Nanoconduction Inc., a startup company in Sunnyvale, Calif., which is
a new member of the cooling center.
####
Writer: Emil Venere, (765) 494-4709, venere@purdue.edu
Source Timothy Fisher, (765) 494-5627, tsfisher@purdue.edu
Related Web site:
Timothy Fisher: tools.ecn.purdue.edu/ME/Fac_Staff/fisher.whtml
Note to Journalists: An electronic copy of the research paper is available from Emil Venere, (765) 494-4709, venere@purdue.edu
ABSTRACT
Enhancement of thermal interface materials with carbon
Jun Xu, Timothy S. Fisher
This paper describes an experimental study of thermal contact
conductance enhancement enabled by carbon nanotube (CNT) arrays
synthesized directly on silicon wafers using plasma-enhanced chemical
vapor deposition. Testing based on the one-dimensional reference bar
method occurred in a high-vacuum environment with radiation
shielding, and temperature measurements were made with an infrared
camera. Results from other thermal interface materials are presented,
as well as combinations of these materials with CNT arrays. Dry CNT
arrays produce a minimum thermal interface resistance of 19.8 mm2 K/ W, while the combination of a CNT array and a phase change material
produces a minimum resistance of 5.2 mm2 K/W.Text of abstract, with
leading set at 14 points, so it doesn't take as much room.
Contact:
Purdue University
News Service
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West Lafayette, IN 47907-2016
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fax: (765) 494-0401
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