IBM scientists have developed a transistor technology that could enable the production of a new class of smaller, faster and lower power ICs.
The researchers have built the world’s first array of transistors out of carbon nanotubes – cylinders of carbon atoms that measure as small as 10 atoms across and are 500 times smaller than today’s silicon-based transistors.
‘This is a major step forward in our pursuit to build molecular-scale electronic devices,’ said Phaedon Avouris, lead researcher and manager of IBM’s Nanoscale Science Research Department. ‘Our studies prove that carbon nanotubes can compete with silicon in terms of performance, and since they may allow transistors to be made much smaller, they are promising candidates for a future nanoelectronic technology. The new (batch fabrication) process (we have developed) gives us a practical way of making nanotube transistors, which is essential for future mass production.’
Depending on their size and shape, the electronic properties of carbon nanotubes can be metallic or semiconducting. The problem scientists had faced in using carbon nanotubes as transistors was that all synthetic methods of production yield a mixture of metallic and semiconducting nanotubes which stick together to form ropes or bundles.
This compromises their usefulness because only semiconducting nanotubes can be used as transistors and when they are stuck together, the metallic nanotubes ‘overpower’ the semiconducting nanotubes.
Beyond manipulating them individually, a slow and tedious process, there has been no practical way to separate the metallic and semiconducting nanotubes — a roadblock in using carbon nanotubes to build transistors.
The IBM team overcame this problem with ‘constructive destruction’, a technique that allows the scientists to produce only semiconducting carbon nanotubes where desired and with the electrical properties required to build computer chips.
The basic premise of ‘constructive destruction’ is that in order to construct a dense-array of semiconducting nanotubes, the metallic nanotubes must be destroyed.
This is accomplished with an electric shockwave that destroys the metallic nanotubes, leaving only the semiconducting nanotubes needed to build transistors.
IBM scientists have also shown how electrical breakdown can be used to remove individual carbon shells of a multi-walled nanotube one-by-one, allowing the scientists to fabricate carbon nanotubes with precise electrical properties.
In parallel studies of carbon nanotubes, IBM researchers have been working to improve the electrical characteristics of individual nanotube transistors. The unpublished data from these studies show that if the carbon nanotubes are scaled up to the size of today’s silicon-based transistors, the performance would be the same.
This proves that the smaller carbon nanotube transistors should allow for Moore’s Law to continue on its path when silicon devices cannot be made any smaller.