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Researchers in Switzerland demonstrated an approach that may have gone some way to addressing the sweltering heat and worrying carbon emissions from large computer systems: by integrating liquid cooling into microprocessor fabrication.

Professor Elison Matioli of the Swiss university EPFL and his team have demonstrated performance 50 times greater than conventional approaches to cooling, according to a paper published in Nature this week, potentially saving money, energy and emissions.

[1]Youtube Video

Cooling microelectronics with liquid is not new, and has the advantage of transferring heat to a medium more rapidily than air cooling, reducing the likelihood of processor hot-spots.

But in power electronics, liquid cooling has so far had its limitations. Some techniques rely on a thermal interface material to protect the processor and transfer heat to the liquid coolant, but their efficiency is limited by the interfaces between the material layers and the processor die and cold plate, according the paper.

Other techniques bring the coolant directly to the chip with jet cooling via nozzles in microchannels. Although this cools efficiently and works without altering processor design, the fluids involved can be expensive.

Meanwhile, another approach is to pump liquid through straight, parallel microchannels etched directly into the semiconductor, turning the back of the chip into a heat sink. The performance is great, but the cost is extra manufacturing processes to make the chip die, and they require high powered pumps which consume energy, kind of defeating the object. Embedded manifold microchannels, while separating the coolant flow into multiple parallel sections, also increase the complexity and cost of constructing the devices.

Matioli's lab team, including first author PhD student Remco van Erp, developed a technique in which liquid cooling channels are integrated and co-fabricated with a chip in a single die, so called "monolithically integrated manifold microchannels".

Studies of the performances of power chips built using the technique show that heat fluxes of more than 1.7 kilowatts per square centimetre can be extracted while consuming just 0.57 watts of pumping power per square cm, more than 50 times the performance of comparable conventional approaches, the authors claimed.

The technique promises to greatly improve the efficiency of data centres. In the US alone, DCs use 24 terawatt-hours of electricity and 100 billion litres of water for cooling per year – about the same as a city of the size of Philadelphia.

But to prove effective in combatting mounting data centre electricity consumption and carbon emissions, the structural integrity of the dies produced with it need to prove stable in the long term. Meanwhile, one adhesive it uses has a maximum operating temperature of 120˚C and would not withstand the 250˚C heat of reflow soldering used to attach thousands of tiny electrical components to circuit boards.

Still, if these hurdles can be overcome, the techniques show great potential.

“The proposed cooling technology should enable further miniaturisation of electronics, potentially extending Moore’s law and greatly reducing the energy consumption in cooling of electronics. Furthermore, by removing the need for large external heat sinks, this approach should enable the realization of very compact power converters integrated on a single chip,” [2]the researchers said.

The paper, "Co-designing electronics with microfluidics for more sustainable cooling", was published earlier this week. ®

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[1] https://www.youtube.com/watch?v=dvez_iOLnIA&feature=youtu.be&ab_channel=NPGPress

[2] https://www.nature.com/articles/s41586-020-2666-1

[3] https://whitepapers.theregister.com/