J. Adam Fenster/University of Rochester

Wicked. A water drop applied to a laser-etched microchip quickly spreads uphill.

Toward Liquid-Cooled Computers

Tired of the dust bunnies sucked into your computer's air-intake grill? A new technique called superwicking might finally allow scientists to build liquid-cooled computers. Experts say the method could provide a better way to cool computer hardware and could help remove one of the biggest barriers to a new generation of high-powered microprocessors. And in the meantime, it could prove a boon to tiny fluid-based sensors.

Heat is an enemy of electronics. It cooks delicate components until they become brittle and prone to failure. And the more powerful a computer chip is, the more heat it generates. Until now, the only way to cool computer hardware has been with fans. But that technique generates problems of its own, including dust accumulation that can block air intakes and induce a figurative computer meltdown.

So optical physicists Chunlei Guo and Anatoliy Vorobyev of the University of Rochester in New York state, like others before them, attempted to find out whether silicon chips could be cooled by water or other fluids. One challenge is that the chips are often mounted vertically inside a computer, so the coolant might have to flow uphill. A year ago, they achieved an effect called superwicking—by which the texture of a material forces water to flow upward—on metal surfaces by etching them using extremely fast, quadrillionth of a second, high-energy laser pulses. So they decided to try the same technique in silicon chips.

The result, the researchers report today in Optics Express, is that the grooves, about 2 centimeters long and 100 microns wide, turned ordinary chips positively hydrophilic. The grooves attracted water molecules and wicked them straight up in defiance of gravity.

Guo adds that he and Vorobyev also conducted experiments with acetone and methanol and got the same results. That's good, he says, because the technology probably would be used in a closed-loop system such as in a conventional air conditioner, with an evaporator, condenser, and fluid running across the hot, grooved surface and carrying away heat. If so, it would require a volatile coolant that evaporates quickly.

The research "represents a benchmark contribution” to the development of liquid-cooled computers and will pave the way for new materials applications created by ultrafast lasers, says physicist Costas Fotakis, director of the Institute of Electronic Structure and Laser in Heraklion, Greece. He says the technology could produce "exciting developments in silicon-based, lab-on-a-chip applications" in which microcomputers are combined with sensing arrays.

Materials physicist J. Thomas "Tom" Dickinson of Washington State University in Pullman agrees that moving liquids through small channels is "indeed important for a number of microfluidic applications." The challenge, he says, will be in sorting out the many variables in the technology, such as the shape, depth, and number of channels, and the size of the fluid droplets. "Clearly, there are some very interesting experiments suggested," he says.

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