The little chill: tiny wind generator to cool microchip hot spots

Science News, Nov 11, 2006 by P. Weiss

Technologists cramming more and more transistors onto microchips face a common problem: too much heat. To make computers chill, manufacturers typically outfit hot chips with heat sinks, whose fins release heat into a stream of air.

Now, a team of university, and industrial engineers has created a prototype, microscale air pump that they say could be fabricated with the techniques used to mass-produce microelectronic components such as transistors. The pump would generate cooling breezes right where the heat is being created.

The new work shows for the first time that "the principle works at the scale and the rate needed," says electrical engineer Alexander V. Mamishev of the University of Washington in Seattle, who leads the group that came up with the device.

To make the pump, the researchers used a beam of high-energy ions to carve a slender needle jutting out from the edge of a piece of silicon. When mounted just above a pad of electrically conductive foam and energized with thousands of volts, the needle produces a powerful electric field that ionizes the surrounding air, says University of Washington team member Nels E. Jewell-Larsen.

Propelled by the electric field, ionized gas molecules rush toward the pad below. On their way, they run into gas molecules and push them along. The minuscule wind, which reaches about 25 kilometers per hour, cools the pad's surface, Jewell-Larsen says.

In recent tests of the prototype micropump mounted above a pad heated to roughly 50[degrees]C, the microwind cooled a fingerprint-size patch of the pad by as much as 25[degrees]C, Chi-Peng Hsu of the University of Washington reported on Tuesday in Chicago at a mechanical engineering conference.

The tests show that the pump's underlying principle, "which has been known for decades, can be applied at the chip level," comments thermal engineer David A. Rosato of the Canonsburg, Pa., company Ansys. Still, some further cooling mechanism must remove the heat picked up by the microwind and generated by the pump itself, he cautions.

Researchers at Purdue University in West Lafayette, Ind., have developed related technology also aimed at cooling chips by means of ion-propelled winds and have formed a company to commercialize the technology.

The high voltages employed by the Washington group may require precautions, such as isolating the microchip's sensitive electronic components from the pump. However, Mamishev notes that the power levels in the cooling devices don't pose a safety hazard.

Before the new cooling gadget begins serving on chips, it might show up between heat-sink fins, where air tends to stagnate, says Jewell-Larsen.

The Belmont, Mass.-based company Kronos Air Technologies plans to commercialize the Washington team's micropumps, he adds. The researchers have also been working with chip maker Intel Corp. on the technology. (Intel sponsors some of the educational programs of Science Service, the publisher of Science News.)