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Liquid cooling cuts chip operating temperatures by 60 percent

08 October 2015

Georgia Tech researchers are putting liquid cooling right where it’s needed the most – a few hundred microns away from where the transistors are operating.

Liquid ports carry cooling water to specially designed passages etched into the backs of FPGA devices to provide more effective cooling (photo: Rob Felt/Georgia Tech)

Using microfluidic passages cut directly into the rear of production field-programmable gate array (FPGA) devices, Georgia Institute of Technology researchers have demonstrated a monolithically-cooled chip that can operate at temperatures more than 60 percent below those of similar air-cooled chips.

In addition to more processing power, the lower temperatures can mean longer device life and less current leakage. The cooling comes from simple de-ionized water flowing through microfluidic passages that replace the massive air-cooled heat sinks normally placed on the backs of chips.

“We believe we have eliminated one of the major barriers to building high-performance systems that are more compact and energy efficient,” says Gorgia Tech's Muhannad Bakir. “We have eliminated the heat sink atop the silicon die by moving liquid cooling just a few hundred microns away from the transistors. We believe that reliably integrating microfluidic cooling directly on the silicon will be a disruptive technology for a new generation of electronics.”

Liquid cooling has been used to address the heat challenges facing computing systems whose power needs have been increasing. However, existing liquid cooling technology removes heat using cold plates externally attached to fully packaged silicon chips – adding thermal resistance and reducing the heat-rejection efficiency.

To make their liquid cooling system, Bakir and graduate student Thomas Sarvey removed the heat sink and heat-spreading materials from the backs of stock Altera FPGA chips. They then etched cooling passages into the silicon, incorporating silicon cylinders approximately 100 microns in diameter to improve heat transmission into the liquid. A silicon layer was then placed over the flow passages, and ports were attached for the connection of water tubes.

In multiple tests a liquid-cooled FPGA was operated using a custom processor architecture provided by Altera. With a water inlet temperature of approximately 20 degrees Celsius and an inlet flow rate of 147ml/min, the liquid-cooled FPGA operated at a temperature of less than 24 degrees Celsius, compared to an air-cooled device that operated at 60 degrees Celsius.

In addition to improving overall cooling, the system could reduce hotspots in circuits by applying cooling much closer to the power source. Eliminating the heat sink could allow more compact packaging of electronic devices – but only if electrical connection issues are also addressed.

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