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IBM breakthrough could see carbon nanotubes powering IoT

Steve Rogerson
October 8, 2015
IBM Research has announced an engineering breakthrough that could accelerate carbon nanotubes replacing silicon transistors to power future computing technologies for mobile devices and the IoT.
Scientists have demonstrated a way to shrink transistor contacts without reducing performance of carbon nanotube devices, opening a pathway to faster, smaller and more powerful computer chips beyond the capabilities of traditional semiconductors. The results were reported in the October 2 issue of Science.
The breakthrough overcomes a major hurdle that silicon and any semiconductor transistor technologies face when scaling down. In any transistor, two things scale: the channel and its two contacts. As devices become smaller, increased contact resistance for carbon nanotubes has hindered performance gains until now. These results could overcome contact resistance challenges all the way to the 1.8nm node – four technology generations away.
Carbon nanotube chips could greatly improve the capabilities of high performance computers, enabling big data to be analysed faster, increasing the power and battery life of mobile devices and the IoT, and letting cloud data centres deliver services more efficiently and economically.
Silicon transistors have been made smaller year after year, but they are approaching a claimed point of physical limitation. With Moore's Law running out of steam, shrinking the size of the transistor – including the channels and contacts – without compromising performance has been a vexing problem troubling researchers for decades.
IBM has previously shown that carbon nanotube transistors can operate as switches at channel dimensions of less than 10nm, less than half the size of today’s leading silicon technology. The new contact approach overcomes the other major hurdle in incorporating carbon nanotubes into semiconductor devices, which could result in smaller chips with greater performance and lower power consumption.
Earlier this summer, IBM unveiled the first 7nm node silicon test chip, pushing the limits of silicon technologies. By advancing research of carbon nanotubes to replace traditional silicon devices, IBM is paving the way for a post-silicon future and delivering on its $3bn chip R&D investment announced in July 2014.
“These chip innovations are necessary to meet the emerging demands of cloud computing, internet of things and big data systems,” said Dario Gil, vice president of science and technology at IBM Research. “As silicon technology nears its physical limits, new materials, devices and circuit architectures must be ready to deliver the advanced technologies that will be required by the cognitive computing era. This breakthrough shows that computer chips made of carbon nanotubes will be able to power systems of the future sooner than the industry expected.”
Carbon nanotubes represent a new class of semiconductor materials that consist of single atomic sheets of carbon rolled up into a tube. The carbon nanotubes form the core of a transistor device whose superior electrical properties promise several generations of technology scaling beyond the physical limits of silicon.
Electrons in carbon transistors can move more easily than in silicon-based devices, and the ultra-thin body of carbon nanotubes provide additional advantages at the atomic scale. Inside a chip, contacts are the valves that control the flow of electrons from metal into the channels of a semiconductor. As transistors shrink in size, electrical resistance increases within the contacts, which impedes performance. Until now, decreasing the size of the contacts on a device caused a commensurate drop in performance – a challenge facing both silicon and carbon nanotube transistor technologies.
IBM researchers had to forego traditional contact schemes and invented a metallurgical process akin to microscopic welding that chemically binds the metal atoms to the carbon atoms at the ends of nanotubes. This end-bonded contact scheme allows the contacts to be shrunken down to below 10nm without deteriorating performance of the carbon nanotube devices.
“For any advanced transistor technology, the increase in contact resistance due to the decrease in the size of transistors becomes a major performance bottleneck,” Gil added. “Our novel approach is to make the contact from the end of the carbon nanotube, which we show does not degrade device performance. This brings us a step closer to the goal of a carbon nanotube technology within the decade.”