Lockheed Martin39s liquid cooling system was designed to be a slight 250 microm thick 5 mm long and 25 mm wide One of the major problems with conventional heat sinks is that they have to be enlarged as microchips get more powerful and susceptible to heat buildup Image courtesy of Lockheed Martin

Lockheed Martin's liquid cooling system was designed to be a slight 250 µm thick, 5 mm long, and 2.5 mm wide. One of the major problems with conventional heat sinks is that they have to be enlarged as microchips get more powerful and susceptible to heat build-up. (Image courtesy of Lockheed Martin).

Liquid Cooling System Boosts Amplifier RF Output

An engineering team at Lockheed Martin has built an experimental cooling system that sprays tiny drops of water on the bottom of microchips, dissipating heat that can hurt chip performance. In laboratory tests, the cold plate helped boost the RF output of power amplifiers six times higher than chips cooled with traditional heat sinks.

The new technology was designed to remove heat from the thousands of microchips contained in anything from radars to high-performance computers and data centers. Though the cold plate was designed to be general purpose, Lockheed Martin has targeted the project at gallium-nitride (GaN) power amplifiers, which are widely used in electronic warfare and other military systems. Lower operating temperatures make these systems not only more powerful, but also vastly more efficient.

“Right now, we’re limited in the power we can put into microchips,” said John Ditri, the project’s principal investigator, in a statement. “If you can manage the heat, you can use fewer chips and that means using less material, which results in cost savings as well as reduced system size and weight. If you manage the heat and use the same number of chips, you’ll get even greater performance.”

Lockheed Martin said that in recent demonstrations, its liquid cooling system had vastly improved the thermal resistance of GaN monolithic microwave integrated circuits (MMICs). The company measured resistance four times higher than chips cooled with conventional, dry heat sinks. The cold plate dissipated 1,000 watts per square centimeter heat flex on the die. And in several local hot spots, it removed around 30,000 watts per square centimeter.

As computer processors and wireless amplifiers have grown more powerful, the microchips inside them have become smaller and more susceptible to heat build-up. That heat can impact chip performance and even raise the risk of failure. When your personal computer begins to overheat, for instance, you normally hear the fan underneath start whirring and can notice a slight dip in the time it takes to load apps.

The most common way to remove heat from electronics is using fans or materials like copper that divert heat from the chip. The problem is that these heat sinks get larger as processors become more powerful, adding size and weight to the system.

But liquid cooling systems are positioned closer to the chip than these more conventional heat sinks. Though these systems have long held promise, engineers have struggled to integrate practical designs into products. Lockheed Martin's cold plate was designed with that problem in mind. It measures only 250 µm thick, 5 mm long, and 2.5 mm wide.

The cold plate was developed as part of the Interchip/Intrachip Enhanced Cooling (ICECool) program run by the Defense Advanced Research Projects Agency , or DARPA. The program aims to bring liquid cooling right up against the chip, sending water through channels or pores etched into chip.

For Lockheed Martin, the long-term goal is “to see the ICECool program transition to something that will help the warfighter," said Denise Luppa, a program manager at Lockheed Martin who worked on the cold plate. "I think we’re getting close to that.”

Going forward, Lockheed Martin is trying to develop an antenna prototype using the new cooling system. While early trials have focused on GaN semiconductors, the cold plate could also be used with gallium-arsenide and GaN-on-diamond wafers.

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