IBM's hair-thin pipes carry water to cool hot chips

Keeping hot chip circuits cool is an ongoing battle. 

IBM today offered the latest weapon in that war: 3-D chip stacks that contain human hair-like pipes through which water can flow and cool the structure.  

IBM’s experimental 3-D chip stacks put chips and memory devices that usually sit side-by-side on a silicon wafer and stack them on top of one another. The idea is to shorten the distance information on a chip needs to travel by 1000 times, and allows for the addition of up to 100 times more channels for information to flow compared to 2-D chips, IBM said. 

IBM researchers in conjunction with the Fraunhofer Institute built a prototype 3-D chip and sent water into sealed cooling structures as thin as a human hair (50 microns) between the individual chip layers in order to remove heat.  

In experiments, scientists piped water through a 1 by 1 cm test package, consisting of a cooling layer between two wafers. The cooling layer measures only about 100 microns in height and is packed with 10,000 vertical interconnects per cm2. The team said it designed 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 said. 

By piping water through the individual layers in a chip stack, researchers achieved cooling performances of 180 Watts/cm2 per layer for a stack with an area of 4 cm2.  The fabrication of the individual layers was accomplished with existing fabrication methods, except those needed to etch or drill the holes for signal transmission from one layer to the next.

To insulate these "nerves," scientists left a silicon wall around each interconnect (also called through silicon vias) and added a fine layer of silicon oxide to insulate the electrical interconnects from the water. The structures had to be fabricated to an accuracy of 10 microns, 10 times more accurate than for interconnects in current chips.  

IBM isn’t the only organization looking to reduce the chip heat problem. 

NASA researchers last year  designed and built a Silicon Carbide (SiC) chip that  can operate in 600 degrees Celsius or 1,112 degrees Fahrenheit where conventional silicon-based electronics -- limited to about 350 C -- would fail. In the past, integrated circuit chips could not withstand more than a few hours of high temperatures before degrading or failing. This chip exceeded 1,700 hours of continuous operation at 500 degrees Celsius - a breakthrough that represents a 100-fold increase in what has previously been achieved, NASA said. 

Purdue researchers are showing off technology that promises to increase the cooling rate of computer chips by as much as 250%.  Purdue University researchers, in work funded by Intel are developing tiny "ionic wind engines” that when used in combination with a conventional computer fan, can enhance the fan's effectiveness by boosting airflow over the surface of a computer chip. IBM, AMD, Intel and others are scrambling to find new and improved ways to keep chips cool.

In another IBM example, Big Blue scientists have developed a glue-application technique used to assemble chips that will keep them running cooler, the company said.  Glues are used to bind the semiconductor packages, such as microprocessors and chipsets, with cooling elements that disperse the heat generated by today's powerful chips.

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