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Why Future Microprocessors May Ditch Silicon for Carbon

For the first time a carbon nanotube transistor significantly outperformed a silicon transistor, paving the way for faster phones and computers.

by Daniel Oberhaus
Sep 3 2016, 5:00pm

Image: Stephanie Precourt/UW-Madison.

Researchers at the University of Wisconsin, Madison have finally created what nanotechnologists have only been able to dream of for decades: a carbon nanotube transistor which is almost two times faster than its silicon counterparts. According to the researchers, these carbon nanotube transistors will likely lead to phones and computers which have longer battery life and significantly faster processing power than those running on silicon chips today.

"Making carbon nanotube transistors that are better than silicon transistors is a big milestone," said Michael Arnold, an associate professor of materials science and engineering at the University of Wisconsin. "This achievement has been a dream of nanotechnology for the last 20 years."

It has long been known that carbon nanotubes—essentially straws made out of carbon that are only one atom thick—have a number of amazing properties, such as being over 100 times stronger than steel while still being able to stretch. Carbon nanotubes are also one of the most conductive materials ever discovered, which makes them ideal for applications where a lot of electrical current is moving across a small area such as in the transistors (electrical switches) that make up a computer's central processing unit.

Despite the obvious potential in carbon nanotube-based technologies, developing them has been slow going. The problem has been the inability to isolate pure carbon nanotubes—most that were being produced had small metallic impurities which negatively affected their semiconducting ability.

Yet thanks to a new carbon nanotube production technique developed by the University of Wisconsin researchers back in 2014 called floating evaporative self-assembly, they were able to develop ultra-pure carbon nanotubes that could be integrated into a transistor. This technique works by leveraging the self-assembling properties of carbon nanotubes in a polymer solution, which also allows the researchers to manipulate the proper spacing of the ultrapure nanotubes on a wafer.

The end result are nanotubes with less than .01 percent metallic impurities integrated on a transistor that was able to achieve a current that was 1.9 times higher than the most state-of-the-art silicon transistors in use today.

This is just the tip of the iceberg, however: based on what is known about carbon nanotubes today, the researchers estimate that future transistors which make use of this nanotechnology should be able perform five times faster and use five times less energy than their silicon equivalents.

"There has been a lot of hype about carbon nanotubes that hasn't been realized, and that has kind of soured many people's outlook," said Arnold. "But we think the hype is deserved. It has just taken decades of work for the materials science to catch up and allow us to effectively harness these materials."

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