IBM tries to tackle nanotube chip cooling

IBM researchers on Monday said they are looking at ways to improve heat management in carbon nanotube transistors to prevent them from self-destructing.

The researchers have found ways to measure the temperatures of tiny carbon nanotubes, which was not previously possible, said Phaedon Avouris, IBM fellow and manager, nanoscale science and technology, at IBM Research.

Today's laptops and desktops use silicon chips that are being scaled down to smaller sizes to make them faster and more power efficient. To that end, more transistors are being bundled into chips, and the smaller a transistor, the better it performs. To create smaller transistors, chip developers are exploring the use of carbon nanotubes. Carbon nanotubes are cylinders made out of carbon atoms, with a diameter of 1 to 2 nanometers.

But carbon nanotubes need to be understood before being implemented, and heat dissipation is one of their limitations, Avouris said. Too many carbon nanotubes bunched together are difficult to cool by just blowing air through the circuits, he said. Excess heat lowers performance and eventually could cause the nanotubes to self-destruct.

"The first step is we want to understand how electrons flow through this material, as it is completely different from the way electrons flow through silicon," Avouris said. Carbon nanotubes based on materials such as graphene have unusual heating and dissipation mechanisms that could have wider implications for nanotechnology.

Heat is generated in carbon nanotubes by how quickly atoms vibrate. The faster the atoms vibrate, the more heat they generate, which is then dissipated to the substrate, which is the material that holds the nanotube in place. The scientists likened understanding the heating and dissipation of nanotubes to understanding heat dissipation in conventional silicon chips.

"That's what you care about in a computer. Not only how the individual devices heat up, but how the whole computer heats up. You take your laptop, put it on your lap, you eventually start burning your legs. That's the transfer of heat from the individual devices to the substrate of the computer, then to the chassis... on to your leg," Avouris said.

However, silicon and the newer carbon nanotubes work differently, so the researchers have to take a step back and understand the science of this new material, the researchers said.

The researchers examined efficient ways to transfer heat from the nanotubes to the substrate with the help of another carbon material that sits in between.

The findings are of fundamental scientific importance and crucial in the creation of thermal management systems that will regulate heat of future carbon nanotube-based devices, Avouris said.

This is initial research into understanding heat and cooling on carbon nanotubes, Avouris said. Many more steps are required in the research before any such devices could be commercially produced, but this is an extremely important step, he said.

"The understanding of how heat flows through specific nanotube devices will have important implications on the operation and integration of future carbon-based devices," Avouris said.

The researchers published their findings in a recent issue of Nature Nanotechnology.

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