Nanotubes reduce heat in electronics
THE CHIPS inside an electronic device give off heat as a byproduct of power consumption when the object is on or being used.
To reduce high temperatures, heat sinks — finned devices made of conductive metal such as aluminium or copper — are attached to the back of the chips to `pull' thermal energy away from the microprocessor and transfer it into the surrounding air.
Fans or fluids are sometimes used to improve the cooling process, but they increase the device weight, size, and bulk. As the electronics industry continues to churn out smaller and slimmer portable devices, manufacturers have been challenged to find new ways to combat the persistent problem of thermal management.
New research published in the March 19 issue of Applied Physics Letters suggests that carbon nanotubes may soon be integrated into ever-shrinking cell phones, digital audio players, and personal digital assistants to help ensure the equipment does not overheat, malfunction, or fail.
As good as copper
"As devices continue to decrease in dimension, there is a growing need for miniature on-chip thermal management applications," said Robert Vajtai, a researcher with the Rensselaer Nanotechnology Center and corresponding author on the paper.
When reduced to sub-millimetre sizes, the integrity of materials typically used for cooling structures breaks down. Silicon becomes very brittle and easily shatters, while metallic structures become bendable and weak.
Using microfin structures made of aligned multiwalled carbon nanotube arrays mounted to the back of silicon chips, researchers from Rensselaer Polytechnic Institute and the University of Oulu in Finland have proven that nanotubes can dissipate chip heat as effectively as copper.
Copper is the best known, but most costly, material for thermal management applications.
And the nanotubes are more flexible, resilient, and 10 times lighter than any other cooling material available, according to a Rensselaer Polytechnic Institute press release.
Carbon nanotubes, however, maintain their impressive combination of high strength, low weight, and excellent conductivity, and the carbon nanotube coolers can be manufactured very cost effectively, Vajtai said.
The researchers have developed a simple and scalable assembly, using an innovative processing and transfer technique to integrate the nanotube structures on the chip.
Laser used
Thick films consisting of 1.2 millimetre long multi-walled carbon nanotubes were grown and detached from silicon/silicon oxide templates, and a laser was used to carve out freestanding 10x10 fin array blocks.
The bottom of the nanotube cooler blocks were then soldered onto the backside of a thermometer test chip that was mounted on a silicon substrate.
This technique employs conventional manufacturing methods, providing an easy protocol to transfer and integrate nanotube arrays onto the silicon platforms currently used in electric circuits consisting of miniaturized components, according to the researchers. — Our Bureau
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