LIQUID COOLING MOVES ONTO THE CHIP
Water-based technique cuts operating temperatures by 60 percent
Liquid ports carry cooling water to specially designed passages etched into the backs of FPGA devices to provide more effective cooling. The liquid cooling provides a significant reduction in operating temperature. Photo by Rob Felt.
Using microfluidic passages cut directly into the backsides of production field-programmable gate array (FPGA) devices, Georgia Tech researchers are putting liquid cooling right where it’s needed most — a few hundred microns from where the transistors are operating.
Combined with connection technology that operates through structures in the cooling passages, the new technologies could allow development of denser and more powerful integrated electronic systems that would no longer require heat sinks or cooling fans atop chips. Working with FPGA devices made by Altera Corp., the researchers have demonstrated a monolithically cooled chip that can operate at temperatures more than 60 percent below those of similar air-cooled chips.
“We believe we have eliminated one of the major barriers to building high-performance systems that are more compact and energy efficient,” said Muhannad Bakir, an associate professor in the Georgia Tech School of Electrical and Computer Engineering. “We believe that reliably integrating microfluidic cooling directly on the silicon will be a disruptive technology for a new generation of electronics.”
Supported by the Defense Advanced Research Projects Agency (DARPA), the research is believed to be the first example of liquid cooling directly on an operating high-performance complementary metal oxide semiconductor (CMOS) chip. Details of the research were presented at the IEEE Custom Integrated Circuits Conference in San Jose, California.
To make their cooling system, Bakir and graduate student Thomas Sarvey removed the heat sink and heat-spreading materials from the backs of stock chips. They 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 connecting water tubes.
In tests with a water inlet temperature of approximately 20 degrees Celsius and an inlet flow rate of 147 milliliters per minute, 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. Microfabrication was done in facilities of the Georgia Tech Institute of Electronics and Nanotechnology.
— John Toon