Carbon nanotube transistors pave way to improved electronics

University of Wisconsin-Madison materials engineers have made an advance toward creating higher-performance electronics with improved battery life – and the ability to flex and stretch.

Led by materials science Associate Professor Michael Arnold and Professor Padma Gopalan, the team has reported the highest-performing carbon nanotube transistors ever demonstrated. In addition to paving the way for improved consumer electronics, this technology could also have specific uses in industrial and military applications.

In a paper published in ACS Nano, Arnold, Gopalan and their students reported transistors with an on-off ratio claimed to be 1,000 times better and a conductance that is 100 times better than previous carbon nanotube transistors.

‘Carbon nanotubes are very strong and very flexible, so they could also be used to make flexible displays and electronics that can stretch and bend, allowing you to integrate electronics into new places like clothing,’ Arnold said in a statement. ‘The advance enables new types of electronics that aren’t possible with the more brittle materials manufacturers are currently using.’

Carbon nanotubes are single atomic sheets of carbon rolled up into a tube. As some of the best electrical conductors ever discovered, carbon nanotubes have long been recognised as a promising material for next-generation transistors.

According to the University, researchers have struggled to isolate purely semiconducting carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and short the device. Researchers have also struggled to control the placement and alignment of nanotubes. Until now, these two challenges have limited the development of high-performance carbon nanotube transistors.

Building on more than two decades of carbon nanotube research in the field, the UW-Madison team drew on technologies that use polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.

Previous techniques to align the nanotubes resulted in less-than-desirable packing density. However, the UW-Madison researchers pioneered a new technique – floating evaporative self-assembly, or FESA – that they described earlier in 2014 in Langmuir. In that technique, researchers exploited a self-assembly phenomenon triggered by rapidly evaporating a carbon nanotube solution.

The team’s most recent advance also brings the field closer to realising carbon nanotube transistors as a feasible replacement for silicon transistors in computer chips and in high-frequency communication devices, which are approaching their physical scaling and performance limits.

‘This is not an incremental improvement in performance,’ Arnold said. ‘With these results, we’ve really made a leap in carbon nanotube transistors. Our carbon nanotube transistors are an order of magnitude better in conductance than the best thin film transistor technologies currently being used commercially while still switching on and off like a transistor is supposed to function.’

The researchers have patented their technology through the Wisconsin Alumni Research Foundation and have begun working with companies to accelerate the technology transfer to industry.