Chip designers have been in a furious race against Moore's Law -- the observation by Intel cofounder Gordon Moore that the number of transistors that can be placed on an integrated circuit doubles every two years -- with some experts suspecting the industry will soon be unable to maintain that rate of growth.
But research announced Thursday suggests chip designers still have a few tricks up their sleeves that may substantially advance Moore's Law. IBM  and the Berlin-based Fraunhofer Institute demonstrated a prototype design of a 3-D, water-cooled chipstack.
Rather than the traditional layout, in which chips and memory sit side-by-side on a piece of silicon, the 3-D design, stacks the components atop one another and cools the unit by piping water in between the layers.
'Breakthrough' Development
In a statement, IBM called the design "one of the most promising approaches to enhancing chip performance beyond its predicted limits." IBM has already applied the 3D design to the problem of increasing performance. The approach reduces the distance data needs to travel by 1,000 times and allows for 100 times more channels through which information can flow.
The problem with the approach has been overheating. The water-cooling approach may well take care of that issue, as well.
"As we package chips on top of each other to significantly speed a processor's capability to process data, we have found that conventional coolers attached to the back of a chip don't scale. In order to exploit the potential of high-performance 3-D chip stacking, we need interlayer cooling," Thomas Brunschwiler, project leader at IBM's Zurich Research Laboratory, said in a statement.
As Complex as Human Brain
Brunschwiler's team piped water between the chip layers through structures as thin as a human hair to remove heat at its source. "With classic backside cooling, the stacking of two or more high-power density logic layers would be impossible," said Bruno Michel, manager of the chip cooling research efforts at the IBM Zurich Lab.
According to IBM, the water-cooling system is a technological breakthrough as complex as the human brain. The water in the system has to flow through the layers without causing electrical shorts. The result is like the way that nerves and neurons are intermixed with blood vessels all within the same volume.
In these experiments, scientists piped water through a 1 by 1 cm test vehicle, consisting of a cooling layer between two dies or heat sources. The cooling layer measures only about 100 microns in height and is packed with 10,000 vertical interconnects per cm2.
The Future of Water Cooling
The team overcame key technical challenges in designing a system that maximizes the water flow through the layers, yet hermetically seals the interconnects to prevent water from causing electrical shorts. The complexity of such a system resembles that of a human brain, wherein millions of nerves and neurons for signal transmissions are intermixed but do not interfere with tens of thousands of blood vessels for cooling and energy supply, all within the same volume.
IBM worked with Fraunhofer to develop a sophisticated thin-film soldering technique to achieve the "quality, precision and robustness" need to ensure thermal and electrical contacts without shorts.
What's next for water-cooled chips? Brunschwiler and his team are now working to create cooling systems for smaller chip dimensions and more interconnects -- and investigating additional sophisticated structures for hotspot cooling.
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