IBM carbon nanotube discovery paves way for post-silicon future

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. A nanotube is an empty tube whose surfaces are created from just one layer of atomic carbon elements connected into hexagonal lattice models.

This means that the size of the semiconductor can decrease dramatically, while the substrate of carbon nanotubes makes the chip more energy efficient and is a soft and flexible material that could allow new device form factors.

Today’s chip transistors are made using the element silicon, taking advantage of the fact that under different circumstances it either conducts electricity or doesn’t. Electrons might opt to jump circuits instead of staying on track.

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 is saying it can now create that connection.

Above: A cross-section of a chip with IBM’s carbon nanotubes.

Nanotubes sip power the way a lizard lives off dew in the desert.

After decades of progress, the speeds of microprocessors stalled around the early 2000s at 3GHz to 5GHz, mainly because silicon is reaching its physical limits. When it comes to aligning nanotubes on the chip, though, a substantial amount of work remains to be done if the technology is to really displace silicon, says Arnold.

“When building silicon chips out of wafers, it’s akin to getting a piece of marble and sculpting it away to make a statue”, Han said. If nothing else, that explains its periodic announcements on nanotube advances.

The new research is jump-starting the move to a post-silicon future, and paying off on $3 billion in chip research and development investment IBM announced in 2014. On July 9, it said it had produced the first 7-nanometer functioning transistors, in partnership with GlobalFoundries and Samsung at the State University of New York Polytechnic Institute’s College of Nanoscale Science and Engineering in Albany. Each one is about 10 billionths of a meter wide – about 10,000 times thinner than a human hair. For purposes of comparison, 7 nanometers is slightly larger than one molecule of hemoglobin, estimated at 5 nanometers. “This strategy promises high-performance SWNT transistors enabling future ultimately scaled device technologies”. It was equivalent only to an Intel 4004 chip produced back in 1971, but was meant as a proof-of-concept device. IBM expects the end-bond configuration for nanotube transistors to efficiently scale all the way down to the 1.8-nanometer node. Each nanotube carries only about 15 microamps, but IBM plans to solve that problem by just using as many nanotube channels in parallel as required for the type of drive a transistor needs for a particular location in a design. Carbon nanotubes share this “semiconductor” nature that enables them to act as on-off switches that can process data. It has helped search engines to analyze a countless number of websites and allowed Facebook to identify our friends in images. See IBM Pledges Nanotube Transistor By 2020.].

IBM Research consists of 12 IBM labs around the world. Increased electrical resistance in a transistor results in performance reductions, meaning that, until now, smaller contacts would result in slower processors. As transistors shrink in size, electrical resistance increases within the contacts, which impedes performance.

To overcome the problem, IBM developed an entirely new metallurgical process that chemically binds metal atoms to the carbon atoms at the end of the nanotubes.