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IBM Research announced a major engineering breakthrough that could accelerate carbon nanotubes, replacing silicon transistors to power future computing technologies.
IBM scientists demonstrated a new way to shrink transistor contacts without reducing performance of carbon nanotube devices, opening a pathway to dramatically faster, smaller and more powerful computer chips beyond the capabilities of traditional semiconductors. The results will be reported in the October 2 issue of Science magazine.
In an interview with eWEEK, Shu-Jen Han, manager of the Nanoscale Science & Technology Group at IBM Research, said IBM’s 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. “When we talk about the transistor scaling there are two parts,” Han said. “Most people focus on the transistor channel length — channel length scaling. But when you look at a transistor there is the channel but also contacts. Our breakthrough is on the 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 1.8 nanometer node – four technology generations away.
Carbon nanotube chips could greatly improve the capabilities of high performance computers, enabling faster analysis of big data, increased power and battery life of mobile devices and the Internet of things, and allowing cloud data centers to deliver services more efficiently and economically.
IBM’s breakthrough will help enable “anything related to computation – from high performance computing to lower power computation like mobile phones,” Han said. “Our goal is to try to push carbon nanotube technology beyond silicon, so there are many challenges that we have to solve and one of the biggest ones is the contacts. We tackled that with this work. But our ultimate goal is to try to replace silicon and continue to push Moore’s Law.”
Han added that IBM’s breakthrough brings the company a step closer to the goal of a carbon nanotube technology within the decade.
Silicon transistors, tiny switches that carry information on a chip, have been made smaller year after year, but they are approaching a 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 challenge troubling researchers for decades.
IBM has previously shown that carbon nanotube transistors can operate as effective switches at channel dimensions of less than ten nanometers – the equivalent to 10,000 times thinner than a strand of human hair and less than half the size of today’s leading silicon technology. IBM’s 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.
IBM Makes Carbon Nanotube Breakthrough
Over the summer, IBM unveiled the first seven nanometer node silicon test chip, pushing the limits of silicon technologies and ensuring further innovations for IBM Systems and the IT industry. 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 $3 billion 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 & Technology at IBM Research, in a statement. “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.
“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 said. “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.”
Electrons in carbon transistors can move more easily than in silicon-based devices, and the ultra-thin body of carbon nanotubes provides 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 10 nanometers without deteriorating performance of the carbon nanotube devices.
“This IBM end-cap success paves the way for commercial nanotube structure chips using time-proven silicon photolithography techniques for manufacturing at scale,” Richard Doherty, research director at The Envisioneering Group, told eWEEK. “Succeeding with these welded end caps at nine nanometers gives courage and confidence to the industry to there being an alternative semiconductor path for silicon getting more and more inefficient as we push the limits of silicon under Moore’s Law. The goal is production within a decade, I am sure they want to achieve this faster than that if possible.”