Multi-walled carbon nanotubes 70nm in diameter bridge two electrodes  (Source: Stanford University)
Stanford University researchers design the first GHz chip using carbon nanotubes

Carbon nanotubes are being used in all sorts of research thanks to their strength and much higher electron mobility. Scientists are looking to carbon nanotubes as a replacement for copper wire in circuits, seen to be a bottleneck in future chips.

The problem with using carbon nanotubes in circuits to date has been the difficulty in getting the nanotubes to align correctly on the chips for functional operation. A group of researchers at Stanford University believe they have solved the problem of alignment.

The researchers have developed the world’s first CMOS circuit using carbon nanotubes as an interconnect. The project, carried out in cooperation with Toshiba, fabricated a chip with 256 ring oscillators and 11,000 transistors that operates at 1GHz.

Researcher Philip Wong, professor of electrical engineering at Stanford told EETimes, “A lot of research labs are working toward using nanotubes to interconnect chips since they have higher electron mobility than copper, and can be grown much smaller. But ours is the first working digital chip to run at commercial speeds of 1 gigahertz.”

The problem of alignment with the carbon nanotubes was solved by the researchers by using a process that floated the carbon nanotubes in a solution over the chip. The solution suspended thousands of free-floating nanotubes over the chips surface.

An alternating current was the applied to the ring oscillators thereby attracting a floating nanotube to correct the gap built into the circuitry.  This nanotube clicked into place, completing the "last mile" of the interconnect. Once the nanotube was in place, the circuit was dried off.

The carbon nanotubes used by the researchers were multiwalled, five microns in length and 50 to 100 nanometers in diameter. The researchers say that future versions of the chip could use carbon nanotubes as small as 1nm in diameter.

Mass production of nanotubes themselves is still a daunting task in its own right. DailyTech reported in January 2008 that a group of scientists from South Korea had developed a new method for mass producing aligned carbon nanotubes.

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