As microprocessors have grown in size and complexity, it’s become increasingly difficult to increase performance without skyrocketing power consumption and heat. Intel’s CPU clock speeds have remained mostly flat for years, while AMD’s FX-9590 and its R9 Nano GPU both illustrate dramatic power consumption differences as clock speeds change. One of the principle barriers to increasing CPU clocks is that it’s extremely difficult to move heat out of the chip. New research into microfluidic cooling could help solve this problem, at least in some cases.
Microfluidic cooling has existed for years; we covered IBM’s Aquasar cooling system back in 2012, which uses microfluidic channels — tiny microchannels etched into a metal block — to cool the SuperMUC supercomputer. Now, a new research paper on the topic has described a method of cooling modern FPGAs by etching cooling channels directly into the silicon itself. Previous systems, like Aquasar, still relied on a metal transfer plate between the coolant flow and the CPU itself.
Here’s why that’s so significant. Modern microprocessors generate tremendous amounts of heat, but they don’t generate it evenly across the entire die. If you’re performing floating-point calculations using AVX2, it’ll be the FPU that heats up. If you’re performing integer calculations, or thrashing the cache subsystems, it generates more heat in the ALUs and L2/L3 caches, respectively. This creates localized hot spots on the die, and CPUs aren’t very good at spreading that heat out across the entire surface area of the chip. This is why Intel specifies lower turbo clocks if you’re performing AVX2-heavy calculations.
By etching channels directly on top of a 28nm Altera FPGA, the research team was able to bring cooling much closer to the CPU cores and eliminate the intervening gap that makes water-cooling less effective then it would otherwise be. According to the Georgia Institute of Technology, the research team focused on 28nm Altera FPGAs. After removing their existing heatsink and thermal paste, the group etched 100 micron silicon cylinders into the die, creating cooling passages. The entire system was then sealed using silicon and connected to water tubes.
“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 and ON Semiconductor Junior Professor in the Georgia Tech School of Electrical and Computer Engineering. “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.”