Monday, 29 July 2013

Researchers discover novel material for cooling of electronic devices

Researchers discover novel
material for cooling of electronic
devices
This is a schematic of thermal
management in electronics: Local
temperature increases occur as a
result of current flow in active
regions of devices and can lead to
degradation of device performance.
Materials with high thermal
conductivities are used in heat
spreading and sinking to conduct
heat from the hot regions. Credit: US
Naval Research Laboratory
A team of theoretical physicists at
the U.S. Naval Research Laboratory
(NRL) and Boston College has
identified cubic boron arsenide as a
material with an extraordinarily high
thermal conductivity and the
potential to transfer heat more
effectively from electronic devices
than diamond, the best-known
thermal conductor to date.
As microelectronic devices become
smaller, faster and more powerful,
thermal management is becoming a
critical challenge. This work provides
new insight into the nature of
thermal transport at a quantitative
level and predicts a new material,
with ultra-high thermal conductivity,
of potential interest for passive
cooling applications.
Calculating the thermal conductivity
of cubic III-V boron compounds
using a predictive first principles
approach, the team has found boron
arsenide (BAs) to have a remarkable
room temperature thermal
conductivity, greater than 2,000 Watts
per meter per degree Kelvin (>2000
Wm-1 K -1 ). This is comparable to
those in diamond and graphite, which
are the highest bulk values known.
Unlike metals, where the electrons
carry the heat, diamond and boron
arsenide are electrical insulators. For
the latter type of materials heat is
carried by vibrational waves
(phonons) of the constituent atoms,
and intrinsic resistance to heat flow
results from these waves scattering
from one another. Diamond is of
interest for cooling applications but it
is scarce and its synthetic fabrication
suffers from slow growth rates, high
costs and low quality. However, little
progress has been made to date in
identifying new high thermally
conductive materials .
Historically, fully microscopic,
parameter-free computational
materials techniques have been more
advanced for electronic properties
than for thermal transport.
"In the last few years with
contributions from the NRL team, 'ab
initio' quantitative techniques have
been developed for thermal
transport," said Dr. Thomas L.
Reinecke, physicist, Electronics
Science and Technology Division.
"These techniques open the way to a
fuller understanding of the key
physical features in thermal transport
and to the ability to predict
accurately the thermal conductivity of
new materials."
These surprising findings for boron
arsenide result from an unusual
interplay of certain of its vibrational
properties that lie outside of the
guidelines commonly used to
estimate the thermal conductivity of
electrical insulators. These features
cause scatterings between vibrational
waves to be far less likely than is
typical in a certain range of
frequencies, which in turn allows
large amounts heat to be conducted
in this frequency range. "If these
exciting results are verified by
experiment, it will open new
opportunities for passive cooling
applications with boron arsenide, and
it would demonstrate the important
role that such theoretical work can
play in providing guidance to identify
new high thermal conductivity
materials," Reinecke says.
Thermal conductivity calculations
from this group are in good
agreement with available
experimental results for a wide range
of materials. The team consisted of
Drs. Lucas Lindsay and Tom Reinecke
at NRL and Dr. David Broido at
Boston College.
This research, supported in part by
the Office of Naval Research (ONR)
and the Defense Advanced Research
Projects Agency (DAPRA), gives
important new insight into the
physics of thermal transport in
materials, and it illustrates the power
of modern computational techniques
in making quantitative predictions for
materials whose properties have yet
to be measured.
Provided by Naval Research
Laboratory

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