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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.