Saturday, October 19

UCLA engineers recycle old method in new application to cool powerful transistors


A team of UCLA engineers have taken an old spray-cooling method
and applied it to silicon-based transistors. The result is a new
method to cool down powerful transistors like those found in
electric cars, aircraft, radar stations and personal computers.

Transistors work by amplifying electric current in various types
of electronic devices, from household items like microwaves and
computers to industrial-sized motors and power plants.

The more electrical power needed to run a device, the greater
the chance that the transistors in it will overheat. Once
transistors reach a certain temperature threshold, their efficiency
drops and can even result in failure. In devices like large
machinery or vehicles, which are often cooled by fans, the danger
of overheating is a potentially serious and costly problem.

“Air cooling won’t do (the job),” said Vijay
K. Dhir, interim dean of the Henry Samueli School of Engineering
and Applied Science.

This is where Dhir and Elliott Brown, professor of electrical
engineering step in.

Brown and Dhir’s research team discovered that they could
prevent overheating and increase transistor performance by 34
percent by simply coating the transistor surface with a dielectric
substance and spraying the surface of the chip with tiny jets of
water.

The cooling system uses a traditional water pump attached to a
tiny nozzle near the hot transistor. The nozzle can be machined
microscopically small using micro-electronic machining technology.
This allows each stream to be so small that it evaporates
immediately after landing on the surface of the chip.

Aside from a layer of protective material to protect the chip
from the harmful effects of water (causing a short), the underlying
transistor is untouched by the spray-cooling method.

After evaporating, the steam condenses back into water, trickles
through the system back into the pump, and the process repeats
itself.

This cooling system allows transistors to be driven harder,
which results in more power from these chips. The cooling system
will also allow transistors to be more effective in harsh
temperature environments where they might not normally prove to be
effective.

In fact, the cooling system is so effective that when driving an
amplifier hard over a long period of time, the cooled transistor
outperformed other parts of the amplifier, revealing other parts of
the system as the weakest link, Brown explained.

In order for the system’s performance to increase by more
than 34 percent, the other components must first be improved to
match the quality of the spray-cooled transistor, according to
Brown.

In the future, Dhir explains, “The speed of chips will be
limited by cooling.”

While Dhir admits the process is more expensive than traditional
cooling methods like powered fans, he is convinced spray-cooling is
worth the extra cost ““ particularly to companies dealing with
telecommunications systems, gasoline and electric cars, satellites,
high-power lighting and alternative energy sources like wind and
solar power stations.

While the immediate benefits for the spray-cooling method will
lie largely with heavy machinery and other power electronics, Brown
claims that the microprocessor chip in high-performance desktop PCs
can also be spray-cooled.

Matteo Fabbri, an engineering graduate student who tested
variations of the design for Dhir and Brown, agrees that
applications for personal computers are not too far off.

“Already the heat sinks for processors like the Pentium 4
are huge and also require fans,” Fabbri said. “Based on
present computer limitations, personal computers will need a more
advanced cooling solution than fans or heat sinks if their
speed and power continues to increase.”

Brown and Dhir’s findings were presented in June in San
Diego at the Eighth Intersociety Conference on Thermal and
Thermomechanical Phenomena in Electronic Systems.

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