NEC scientists have figured out how to make the basic components of a carbon nanotube (CNT) transistor using a "stable fabrication technology".

CNTs are cylinders of carbon atoms just a few nanometres in diameter. The arrangement of the atoms is similar to that found in fullerenes - the near-spherical carbon structures also known as buckyballs. CNTs represent one of the materials chip designers hope to use when today's silicon techniques reach the end of their useful life thanks to ever-shrinking process technology.

CNTs are much better able to conduct electricity than silicon structures. In the lingo of transistor design, a CNT-based transistor should offer a higher 'transconductance' - a measure of the performance of a transistor - than silicon transistors. The higher the transconductance, the faster the transistor can switch on and off. That means higher clock frequencies can be supported, and that lower core voltages are necessary.

NEC's new process creates CNTs that will provide a transconductance more than ten times greater than today's silicon MOS (Metal Oxide Semiconductor) transistors. The company believes that the same technique can eventually be used to produce CNTs that offer 20 times the conductance of silicon transistors.

Don't expect chips based on CNTs any time soon, however. NEC's target is to produce a CNT transistor by 2010. First, it has to develop CNT control technology, work out how to control the CNT's electrical properties and build devices based on them. The fabrication process needs plenty of refinement too.

The NEC researchers were able to control the growth of the CNTs on a silicon substrate by placing minute quantities of a catalyst on top of the substrate, providing a level of control over the positioning of the CNT not possible using conventional fabrication techniques. They also developer a way of creating connections between electrodes and the CNT that have much lower resistance than has previously been possible. ®