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A
group of researchers at the University of California, Riverside Bourns
College of Engineering have developed a technique to keep cool a
semiconductor material used in everything from traffic lights to
electric cars.
Gallium
nitride (GaN), a semiconductor material found in bright lights since
the 1990s, is used in wireless applications due to its high efficiency
and high voltage operation. However, the applications and market share
of GaN electronics is limited because it is difficult to remove heat
from them.
That
could change due to a technique developed by the Nano-Device Laboratory
research group led by Alexander Balandin, professor of electrical
engineering and founding chair of Materials Science and Engineering
program.
The
research group demonstrated that hot spots in GaN transistors can be
lowered by as much 20 C through the introduction of alternative
heat-escaping channels implemented with graphene multilayers, which are
excellent heat conductors. The temperature reduction translates to an
increase in the lifetime of the device by a factor of 10.
“This represents a transformative change in thermal management,” Balandin said.
The
new approach to thermal management of power electronics with graphene
was outlined in a paper “Graphene quilts for thermal management of
high-power GaN transistors” that was published May 8 in Nature
Communications.
GaN
transistors have been offered commercially since 2006. The problem with
them, like all high power operating devices, is significant amount of
dissipated heat, which has to be fast and efficiently removed. Various
thermal management solutions such as flip-chip bonding or composite
substrates have been attempted. However, applications have still been
limited because of increases in temperature due to dissipated heat.
The
breakthrough in thermal management of GaN power transistors was
achieved by Balandin and three of his electrical engineering graduate
students: Guanxiong Liu, Zhong Yan, both Ph.D. candidates, and Javed
Khan, who earned his Ph.D. and started working at Intel Corporation this
year.
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Balandin—recipient
of IEEE Nanotechnology Pioneer Award for 2011—has previously discovered
that graphene is an excellent heat conductor. Few-layer graphene films
preserve their excellent thermal properties even when their thickness is
only a few nanometers, which is unlike metal or semiconductor films.
The latter makes them excellent candidates for applications as the
lateral heat spreaders and interconnects.
The
Balandin group researchers designed and built graphene-graphite
“quilts” on top of GaN transistors. The graphene-graphite quilts’
function was to remove and spread the heat from the hot spots—the
opposite of what you expect from the conventional quilts.
Using
micro-Raman spectroscopic thermometry the researchers demonstrated that
temperature of the hot spots can be lowered by as much 20 C in
transistors operating at the large power levels.
The
computer simulations performed by the group suggested that graphene
quilts can perform even better in GaN devices on more thermally
resistive substrates.
The
Balandin group is also known in graphene community for their
investigation of low-frequency noise in graphene transistors,
development of the first large-area method for quality control of
graphene and demonstration of the first selective gas sensor implemented
with pristine graphene.
The
work on thermal management of GaN transistors with graphene quilts was
supported by the Office of Naval Research. Balandin’s research of the
thermal properties of graphene was funded by the Semiconductor Research
Corporation and the Defense Advanced Research Project Agency.
Graphene quilts for thermal management of high-power GaN transistors
