Moving cooling directly to the chip for denser, longer-life electronics

October 15, 2015

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 advantage in computing throughput. (credit: Rob Felt/Georgia Tech)

Using microfluidic passages cut directly into the backsides of production field-programmable gate array (FPGA) devices, Georgia Institute of Technology researchers have put liquid cooling where it’s needed the most: a few hundred microns away 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 on top of the integrated circuits.

Working with popular 28-nanometer FPGA devices made by Altera Corp., the researchers demonstrated a monolithically-cooled chip that can operate at temperatures more than 60 percent below those of similar air-cooled chips.

The lower temperatures can also 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.

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 CMOS chip.

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.

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 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.

The research team chose FPGAs for their test because they provide a platform to test different circuit designs, and because FPGAs are common in many market segments, including defense. However, the same technology could also be used to cool CPUs, GPUs and other devices such as power amplifiers, according to the researchers.

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 also allow more compact packaging of electronic devices.

The cooling research was funded by DARPA’s Microsystems Technology Office, through the ICECOOL program.


Abstract of Embedded Cooling Technologies For Densely Integrated Electronic Systems

In modern integrated systems, interconnect and thermal management technologies have become two major limitations to system performance.  In this paper we present a number of technologies to address these challenges.  First, low-loss polymer-embedded vias are demonstrated in thick wafers compatible with microfluidics.  Next, fluidic I/Os for delivery of fluid to microfluidic heat sinks are demonstrated in assembled 2.5D and 3D stacks.  Next, thermal coupling between dice in 2.5D and 3D systems is explored.  Lastly, the utility of microfluidic cooling is demonstrated through an FPGA, built in a 28nm process, with a monolithically integrated microfluidic heat sink.