by Anton Shilov
10/31/2006 | 07:56 AM
International Business Machines has demonstrated several new technologies that the company hopes will help to cool down future microprocessors and other chip efficiently and without adding much to the cost.
Chips used in various electronics devices are becoming more and more complex in terms of transistor count as well as fast in terms of clock-speeds. Even though major chipmakers are utilizing various approaches to cut power consumption of microprocessors, one of the problems is power output density. Perhaps, 100W is not a lot, but what about removing them constantly from several square millimeters? IBM says it knows how to resolve the issue.
The vast majority of chips today use heat-sinks and airflow to remove heat from tiny pieces of silicon that contain millions of transistors. In order to improve the contact between chips and heat-sinks a special thermal paste is typically applied. This paste is kept as thin as possible in order to transport heat from chip to the cooling components efficiently. Yet, squeezing these pastes too thin between the cooling components and chip would damage or even crack the chip. However, if to put a special cap on the chip and then to apply the thermal grease, the contact may improve, while the chip will be saved from being crushed by heavy heat-spreader.
Using a micro-technology, IBM researchers have developed a chip cap with a network of tree-like branched channels on its surface. The pattern is designed such that when pressure is applied, the paste spreads much more evenly and the pressure remains uniform across the chip, allowing the right uniformity to be obtained with nearly two times less pressure, and a ten times better heat transport through the interface, IBM claims.
The company does not say when its chip caps be used in commercial applications, but explains that today’s high-performance chips already generate a power density of 100W per square centimeter, while tomorrow’s chips may attain even higher power densities, which would create surface temperatures close to that of the sun when not cooled (approximately 6000 degrees C). And while the chip caps may help to cool-down high-performance microprocessors in the next few years using conventional air or liquid coolers, IBM claims that in the long term different technologies should be applied.
Looking beyond the limits of air-cooling systems, IBM researchers are taking their concept of branched channel design even further and are developing a novel and promising approach for water-cooling. Called direct jet impingement, it squirts water onto the back of the chip and sucks it off again in a perfectly closed system using an array of up to 50 000 tiny nozzles and a complicated tree-like branched return architecture.
By developing a perfectly closed system, there is also no fear of coolant getting into the electronics on the chips. IBM said its team was able to enhance the cooling capabilities of the system by devising ways to apply it directly to the back of the chip and thereby avoiding the resistive thermal interfaces in between the cooling system and the silicon.
IBM has demonstrated cooling power densities of up to 370W per square centimeter with water as coolant. This is more than six times beyond the current limits of air-cooling techniques at about 75W per square centimeter, according to the researchers. Yet, the system uses much less energy for pumping than other cooling systems do.