article about the cooling device will appear in the
May issue of Electronics Cooling magazine. The article
was written by doctoral student Brian D. Iverson,
Garimella and former doctoral student Vishal Singhal,
who recently graduated and co-founded Thorrn Micro
Technologies Inc., in Redwood City, Calif.
in today's computers are cooled primarily with
an assembly containing conventional fans and "heat
sinks," or metal plates containing fins to dissipate
heat. But because chips a decade from now will likely
contain upwards of 100 times more transistors and
other devices, they will generate far more heat than
chips currently in use, Garimella said.
"Our goal is to develop advanced cooling systems
that are self-contained on chips and are capable
of handling the more extreme heating in future chips," said
Garimella, director of Purdue's Cooling
Technologies Research Center . The center, supported
by the National Science Foundation, industry and
Purdue, was formed to help corporations develop miniature
cooling technologies for a wide range of applications,
from electronics and computers to telecommunications
and advanced aircraft.
The prototype chip contains numerous water-filled
micro-channels, grooves about 100 microns wide, or
about the width of a human hair. The channels are
covered with a series of hundreds of electrodes,
electronic devices that receive varying voltage pulses
in such a way that a traveling electric field is
created in each channel. The traveling field creates
ions, or electrically charged atoms and molecules,
which are dragged along by the moving field.
"Say every sixth electrode receives the same voltage,
these varying voltages from one electrode to the
next produce a traveling electrical field that pulls
the ions forward, causing the water to flow and inducing
a cooling action," Garimella said. "Essentially,
you are pumping fluid forward."
This pumping action is created by a phenomenon called
electrohydrodynamics, which uses the interactions
of ions and electric fields to cause fluid to flow.
"Engineers have been using electrohydrodynamics
to move fluids with electric fields for a long time,
but it's unusual to be able to do this on the micro-scale
as we have demonstrated," Garimella said.
The researchers also have added a feature to boost
the force of the pumping action. A thin sheet of
piezoelectric material, which expands and contracts
in response to an electric current, was glued on
top of the cover of the liquid-filled channels.
"This material acts as a diaphragm that deforms
up and down when you give it a voltage, causing it
to push additional flow through the channels," Garimella
said. "We have developed mathematical models that
show this piezo action enhances the electrohydrodynamic
The diaphragm has enhanced the pumping action by
13 percent in the current prototype, but the modeling
indicates a possible enhancement of 100 percent or
greater, he said.
"Although electrohydrodynamics has generally not
been considered practical for pumping applications
due to the assumption that it requires a large amount
of energy and does not produce enough motive force
for thrust, the method has been shown to be far more
efficient for micro-cooling applications," Garimella
said. "We have shown that the power input required
is in the microwatts, but you can get milliwatts
of cooling. In other words, the cooling effect is
more than a thousand times greater than the energy
needed to drive the system. That's because all we
need to do is create enough of a flow to induce cooling."
However, several major challenges remain.
"One big challenge is further developing mathematical
models that are comprehensive and accurate because
this is a very complicated, dynamic system," Garimella
said. "You've got fluid flow on a micro-scale, you've
got electrohydrodynamic effects, electrical fields
and a moving diaphragm."
Other challenges include sealing the tiny channels
to prevent water leakage and designing the system
so that it could be manufactured under the same conditions
as semiconductor chips.
The work has been funded by the Indiana 21st Century
Research and Technology Fund. Garimella is a member
of the Birck Nanotechnology Center at Purdue's Discovery
Writer: Emil Venere, (765) 494-4709, firstname.lastname@example.org
Source: Suresh Garimella, (765) 494-5621, email@example.com
Purdue News Service: (765) 494-2096; firstname.lastname@example.org