Carbon Nanotube Transistors Outperform Silicon

Material engineers at the University of Wisconsin–Madison have created carbon nanotube transistors that outperform state-of-the-art silicon transistors. A team led by Michael Arnold and Padma Gopalan, UW–Madison professors of materials science and engineering developed the carbon nanotube transistors. The transistor achieved a current, which is 1.9 times higher than silicon transistors. The researchers reported their advance in a paper in the journal Science Advances.

The group compared the performance of their carbon nanotube transistor with that of a silicon transistor of the same size, geometry, and leakage current. The new transistors are particularly promising for wireless communications technologies that require high current to flow across a relatively small area; the researchers said.

Carbon nanotubes have long been recognized as a promising material for next-generation transistors because they are among the best electrical conductors known.

According to extrapolations from single nanotube measurements, carbon nanotube transistors should be able to perform five times faster or consume just one-fifth of the energy of silicon transistors. The nanotube’s ultra-small form factor allows a rapid current signal change, which could lead to significant gains in wireless device communication bandwidth.

Method for Fabricating Carbon Nanotube Transistors

Isolating pure nanotubes has been a struggle for scientists. However, the UW–Madison team was able to employ polymers to selectively sort out the semiconducting nanotubes and achieve a solution of ultra-high-purity carbon nanotubes.

In nanotube fabrication, their alignment and placement are also difficult to control.  So, the group used a technique that they developed and first announced back in 2014 to overcome this challenge called “floating evaporative self-assembly.” They  then “baked” the nanotube arrays in a vacuum oven to remove the insulating layer to form the electrical contacts. The group also employed a treatment that they devised, which removes residues from the nanotubes after processing them in a solution.

They patented the technology through the Wisconsin Alumni Research Foundation. Funding from the National Science Foundation, the Army Research Office and the Air Force supported the work.

Work Cited

Brady, G. J. ,  Way, A. J., Safron, N. S.,  Evensen, H. T., Gopalan, P., and Arnold, M. S. “Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs” Science Advances  02 Sep 2016: Vol. 2. no. 9, e1601240 DOI: 10.1126/sciadv.1601240