Carbon nanotubes as transistors

Since the discovery of Carbon nanotubes made in 1991 scientists have tried to harness the unique properties of carbon nanotubes.  Some of them are calling it the material of 21. Century because of its extraordinary mechanical, electrical and thermal characteristics. The idea was to create high performance electronics that is faster and consume less power. Of course there was a number of challenges along the way and so far the silicon and gallium arsenide semiconductors outperformed carbon nanotube transistor. Just F.Y.I. the silicon and gallium arsenide semiconductors are used in computer chips.

The team from University of Wisconsin-Madison materials created carbon nanotube transistor that outperform conventional, latest silicon transistors. The team led by Michael Arnold and Padma Gopalan achieved current in carbon nanotube transistor that is 1.9 times higher than silicon transistors. Their discovery was published in journal Science Advances on September 2^nd 2016.

Carbon nanotube transistor should replace silicon transistors and continue delivering the performance gains in computer industry. Carbon nanotube transistors should be able to perform five times faster or use five times less energy than silicon transistors according to research done so far.

The problem in creating this type of transistor was to isolate purely carbon nanotubes and they are crucial because metallic impurities act like copper wires and disrupt semiconducting properties. The research team used polymers to selectively sort out the semiconducting nanotubes and in this way they got carbon nanotubes with ultra-high-purity. To be more specific with this method the team have created carbon nanotubes with 0.01 % metallic impurities.

The other challenge in this research was placement and alignment of the nanotubes and that was very difficult to control. In order to make transistor CNT-s or carbon nanotubes have to be aligned in right order with just the right spacing when assembled on wafer. Of course the same team found the method to do so in 2014 called floating evaporative self-assembly.

Since they’ve used the polymer to isolate nanotubes this polymer acted as insulating layer between the nanotubes and the electrodes. To remove the polymer from CNT they’ve baked the nanotube arrays using vacuum oven to remove them. The result was excellent electrical contacts to nanotubes.

To validate extraordinary performance they benchmarked it against a silicon transistor of same size. So it’s finally here the point where researchers can exploit the nanotubes and nanostructures in general to attain performance gains in actual technology.

For more information about this cool new technology check out the Science Advances, DOI: 10.1126/sciadv.1601240