IS THERE anything carbon nanotubes can鈥檛 do? Using them to make transistors about half the size of the silicon ones available today suggests they might help maintain the continual growth of computing power that we have come to rely on.
There are fears that this growth is threatened as engineers run out of ways to shrink silicon transistors and cram more power into chips. Finding new ways to make smaller transistors has become a priority (麻豆传媒, 6 December 2008, p 35).
But while carbon nanotubes had been considered a potential saviour, making transistors with them has proved to be difficult.
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Performance in such transistors is limited by an effect that creates an electrical barrier at each point a nanotube joins any metal, impeding current flow. This seemed a deal-breaker because a nanotube in a transistor must connect to two metal electrodes, with a third 鈥済ate鈥� electrode placed nearby. Using fatter nanotubes reduced the size of the electrical barriers, but goes against the computer scientists鈥� goal of constantly making things smaller.
Now and colleagues at IBM鈥檚 Watson Research Center in Yorktown Heights, New York state, have found a way to use thinner tubes to build a competitive nanotube transistor.
鈥淭hat success is largely due to its geometry,鈥� says Franklin. His team placed the gate electrode, which controls the transistor, below the nanotube instead of in its usual position above it. This makes it possible to position the two closer together, and increases the gate鈥檚 influence on electrons inside the nanotube, enabling them to punch through the electronic barriers.
Moving the nanotube and gate electrode closer together also makes it possible to shrink the device鈥檚 length down to 15 nanometres. 鈥淭hat鈥檚 about half the length of the best silicon technology on the market today,鈥� says Franklin.
鈥淭he carbon nanotube transistor is half the length of the silicon alternatives on the market today鈥�
The work was presented at the International Electron Devices Meeting in Baltimore, Maryland, last month.
鈥淭his is great work that helps shed light on the scaling of carbon nanotube transistors,鈥� says at Arizona State University in Tempe, who was not involved with the study.
But Cao adds that nanotubes are still not ready for commercialisation. For example, physically manipulating them to build devices is tricky.
Franklin agrees. It鈥檚 difficult to predict whether nanotubes can yet compete with silicon, he says.
