University of Wisconsin–Madison materials engineers have created carbon nanotube transistors that, for the first time, outperform state-of-the-art silicon transistors. This breakthrough points the way to future high-performance nanotube electronics.
“This achievement has been a dream of nanotechnology for the last 20 years,” said Michael Arnold, who led the research team with Padma Gopalan. “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.”
Arnold and Gopalan are materials science and engineering professors at UW-Madison. The research results are reported in an article titled “Quasi-ballistic carbon nanotube array transistors with current density exceeding Si and GaAs,” published in Science Advances on September 2. The article is open access.
This advance indicates that carbon nanotube electronics could soon replace silicon electronics in the computer industry quest to keep pace with the Moore’s Law – the observation that the performance of computing components doubles approximately every two years. Moore’s Law holds since the 1960s, but there are indications that silicon electronics could be approaching its performance limits. According to the UW-Madison researchers, the new carbon nanotube transistors are particularly promising for wireless communications technologies that require a lot of current flowing across a relatively small area.
In fact, the nanotube’s ultra-small dimension permits rapidly varying the current that flows through, which could lead to substantial gains in the bandwidth of wireless communications devices. The nanotube transistors used in the UW study achieved a current 1.9 times higher than silicon transistors.
Nanotube Electronics Catching Up With Previous Hype
The enthusiasm for nanotechnology started with Eric Drexler’s cult book “Engines of Creation – The Coming Era of Nanotechnology,” published in 1986. While Engines of Creation was mostly focused on visionary dreams of unlimited power and abundance enabled by nanotechnology, Drexler’s last book, “Radical Abundance: How a Revolution in Nanotechnology Will Change Civilization,” published in 2013, is more focused on practical applications, which shows how the initially over-hyped sector is maturing.
Drexler explores in detail the concept, essentially equivalent to 3D nano-printing, of additive manufacturing at the nanoscale, or Atomically Precise Manufacturing (APM) – building precisely manufactured goods from the bottom up, one atom or molecule at the time.
Carbon nanotube electronics can be seen as a low-hanging fruit on the nanotechnology tree. Carbon nanotubes are extremely thin cilindrical nanostructures of carbon atoms (see the cover image above) with extraordinary thermal conductivity, mechanical, and electrical properties, which are finding applications as additives to advanced nano-engineered materials. Due to their high electrical conductivity, carbon nanotubes have long been considered as a promising material for next-generation transistors.
In theory, nanotube transistors should be able to perform five times faster or use five times less energy than silicon transistors. However, metallic impurities disrupt the semiconducting properties of nanotubes, and so far it has been difficult to manufacture nanotubes sufficiently pure for applications in electronics. Placement and alignment of the nanotubes have also been difficult to control.
The UW-Madison researchers used polymers to selectively sort out the semiconducting nanotubes, achieving a solution of ultra-high-purity semiconducting carbon nanotubes, with less than 0.01 percent metallic nanotubes, and found ways to remove residues from the nanotubes after they are processed in solution, precisely align the nanotubes, and ensure good electrical contacts with the metal electrodes of the transistor.
“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 groundbreaking carbon nanotube transistors that surpass silicon and gallium arsenide transistors,” said Arnold, adding that, while past hype about carbon nanotubes has promised too much and delivered too little, the hype is ultimately justified.
“It has just taken decades of work for the materials science to catch up and allow us to effectively harness these materials.”
In October, Hacked covered IBM’s announcement of a major engineering breakthrough that could open the way to replacing silicon transistors with carbon nanotubes in future electronics and computing technologies. According to IBM researchers, nanotube electronics could be operational sooner than expected, perhaps within the decade.
The prediction is supported by other recent advances. ZDNet notes that, earlier this year, Nantero announced the use of carbon nanotubes for storage that can be fabricated on DRAM, flash, and system production lines.
Images from University of Wisconsin-Madison and Shutterstock. Video from University of Wisconsin-Madison.