Scientists from the University of Wisconsin-Madison have engineered a carbon nanotube transistor that outperformed silicon transistors for the first time. (Photo : Stephanie Precourt)
University of Wisconsin-Madison materials engineers have created carbon nanotube transistors that outperform state-of-the-art silicon transistors, fulfilling the promise carbon nanotubes will replace silicon as the basic raw material for producing the microchips that basically power most electronic devices today.
It's the first time anyone has developed ultra-high-purity semiconductor carbon nanotubes with minuscule amounts of metallic impurities.
Led by Michael Arnold and Padma Gopalan, UW-Madison professors of materials science and engineering, the team's carbon nanotube transistors achieved current that's 1.9 times higher than silicon transistors.
The UW-Madison engineers used a solution process to deposit aligned arrays of carbon nanotubes onto one inch by one inch substrates. They used their scalable and rapid deposition process to coat the entire surface of this substrate with aligned carbon nanotubes in less than five minutes.
The team's breakthrough might pave the way for carbon nanotube transistors replacing silicon transistors.
Carbon nanotube transistors should be able to perform five times faster or use five times less energy than silicon transistors, according to extrapolations from single nanotube measurements. The nanotube's ultra-small dimension makes it possible to rapidly change a current signal traveling across it, which could lead to substantial gains in the bandwidth of wireless communications devices.
For decades, scientists have tried to harness the unique properties of carbon nanotubes to create high-performance electronics that are faster or consume less power, resulting in longer battery life, faster wireless communication and faster processing speeds for devices like smartphones and laptops.
"This achievement has been a dream of nanotechnology for the last 20 years," said Arnold.
"Making carbon nanotube transistors that are better than silicon transistors is a big milestone. This breakthrough in carbon nanotube transistor performance is a critical advance toward exploiting carbon nanotubes in logic, high-speed communications, and other semiconductor electronics technologies."
Because they're one of the best electrical conductors ever discovered, carbon nanotubes have long been recognized as a promising material for next-generation transistors.
But researchers have struggled to isolate purely carbon nanotubes, which are crucial, because metallic nanotube impurities act like copper wires and disrupt their semiconducting properties.
The UW-Madison team used polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes.
"We've identified specific conditions in which you can get rid of nearly all metallic nanotubes, where we have less than 0.01 percent metallic nanotubes," said Arnold.
A video of their breakthrough can be viewed here.
The researchers have patented their technology through the Wisconsin Alumni Research Foundation.
Additional authors on the paper include Harold Evensen, a University of Wisconsin-Platteville engineering physics professor, Gerald Brady, a UW-Madison materials science and engineering graduate student and lead author on the study and graduate student Austin Way and postdoctoral researcher Nathaniel Safron.
Funding from the National Science Foundation, the Army Research Office and the Air Force supported their work.
