A chip made with carbon nanotubes, not silicon, marks a computing milestone

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Inside a new microprocessor, the transistors — tiny electronic switches that collectively perform computations — are made with carbon nanotubes, rather than silicon. By devising techniques to overcome the nanoscale defects that often undermine individual nanotube transistors (SN: 7/19/17), researchers have created the first computer chip that uses thousands of these switches to run programs.

The prototype, described in the Aug. 29 Nature, is not yet as speedy or as small as commercial silicon devices. But carbon nanotube computer chips may ultimately give rise to a new generation of faster, more energy-efficient electronics.

This is “a very important milestone in the development of this technology,” says Qing Cao, a materials scientist at the University of Illinois at Urbana-Champaign not involved in the work.
The heart of every transistor is a semiconductor component, traditionally made of silicon, which can act either like an electrical conductor or an insulator. A transistor’s “on” and “off” states, where current is flowing through the semiconductor or not, encode the 1s and 0s of computer data (SN: 4/2/13). By building leaner, meaner silicon transistors, “we used to get exponential gains in computing every single year,” says Max Shulaker, an electrical engineer at MIT. But “now performance gains have started to level off,” he says. Silicon transistors can’t get much smaller and more efficient than they already are.

Because carbon nanotubes are almost atomically thin and ferry electricity so well, they make better semiconductors than silicon. In principle, carbon nanotube processors could run three times faster while consuming about one-third of the energy of their silicon predecessors, Shulaker says. But until now, carbon nanotubes have proved too finicky to construct complex computing systems.

One issue is that, when a network of carbon nanotubes is deposited onto a computer chip wafer, the tubes tend to bunch together in lumps that prevent the transistor from working. It’s “like trying to build a brick patio, with a giant boulder in the middle of it,” Shulaker says. His team solved that problem by spreading nanotubes on a chip, then using vibrations to gently shake unwanted bundles off the layer of nanotubes.
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