'Intrachip' Micro-Cooling System for High-Performance Radar, Supercomputers

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Purdue doctoral student Kevin Drummond led much of the research. (Purdue University photo/ Jared Pike)  

Much of the integration and testing of the system was performed by Purdue doctoral student Kevin Drummond. Key to fabrication of the devices used in the demonstration were teams led by co-investigators David Janes, a professor of electrical and computer engineering, and Dimitrios Peroulis, a professor of electrical and computer engineering and Deputy Director of the Birck Nanotechnology Center in Purdue’s Discovery Park.

The team has presented preliminary findings in several conference papers during the course of the project. The researchers received a best paper award last year in the emerging technologies category at the IEEE-ITherm conference, and additional papers will be published, Garimella said.

The system uses a commercial refrigerant called HFE-7100, a dielectric, or electrically insulating fluid, meaning it won’t cause short circuits in the electronics. As the fluid circulates over the heat source, it boils inside the microchannels.

“Allowing the liquid to boil dramatically increases how much heat can be removed, compared to simply heating a liquid to below its boiling point,” he said.

The team created an elaborate testing apparatus that simulates the heat generated by real devices. An array of heaters and temperature sensors allow the researchers to test the system under a range of conditions, including the effects of hot spots. The testing system was fabricated at the Birck Nanotechnology Center.

The new approach improves efficiency by eliminating the need to attach cooling devices to chips.

 “Any time you are attaching heat sinks to the chip there are a lot of resistances and inefficiencies associated with that interface,” Garimella said.

This interfacial, or "parasitic," thermal resistance limits the performance of heat sinks.

"We are going to a technology that eliminates those interfaces because the cooling is occurring inside the chips," Weibel said.

Using ultra-small channels allows for high performance.

"It's been known for a long time that the smaller the channel the higher the heat-transfer performance," Drummond said. "We are going down to 15 or 10 microns in channel width, which is about 10 times smaller than what is typical for microchannel cooling technologies."

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