Carbon nanotube transistors finally surpass silicon

Article By : University of Wisconsin-Madison

The new transistors are promising for wireless communications technologies that require a lot of current flowing across a relatively small area.

For the first time in history, materials engineers at the University of Wisconsin-Madison have created nanotube transistors that outshine state-of-the-art silicon transistors.

Scientists have tried for decades 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. But a number of challenges have impeded the development of high-performance transistors made of carbon nanotubes, tiny cylinders made of carbon just one atom thick. Consequently, their performance has lagged far behind semiconductors such as silicon and gallium arsenide used in computer chips and personal electronics.

The UW-Madison team, led by materials science and engineering professors Michael Arnold and Padma Gopalan, developed carbon nanotube transistors with current that’s 1.9 times higher than silicon transistors. The researchers reported their advance in a paper published in the journal Science Advances.

“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.”

This advance could pave the way for carbon nanotube transistors to replace silicon transistors and continue delivering the performance gains the computer industry relies on and that consumers' demand. The new transistors are particularly promising for wireless communications technologies that require a lot of current flowing across a relatively small area.

As some of the best electrical conductors ever discovered, carbon nanotubes have long been recognised 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—like a short in an electronic device.
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% metallic nanotubes,” said Arnold.

The researchers also developed a treatment that removes residues from the nanotubes after they're processed in solution.

“In our research, we’ve shown that we can simultaneously overcome all of these challenges of working with nanotubes, and that has allowed us to create these ground-breaking carbon nanotube transistors that surpass silicon and gallium arsenide transistors,” said Arnold.

The researchers are continuing to work on adapting their device to match the geometry used in silicon transistors, which get smaller with each new generation. Work is also underway to develop high-performance radio frequency amplifiers that may be able to boost a cell phone signal. While the researchers have already scaled their alignment and deposition process to 1in x 1in wafers, they’re working on scaling the process up for commercial production.

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