Nanotubes, Circuits Integrated

Researchers at UC Berkeley, in collaboration with scientists at Stanford University, have become the first in the world to grow carbon nanotubes on top of a silicon integrated circuit.

UC Berkeley electrical engineering and computer sciences (EECS) graduate student Yu-Chih Tseng along with Stanford graduate student Ali Javey Stanford, first documented this breakthrough in the January 2004 issue of Nano Letters, an accomplishment which may herald an important advancement in the emerging field of nanotechnology.

The research team led by UC Berkeley EECS professor Jeffrey Bokor and Stanford professor Hongjie Dai, started with a silicon integrated circuit and then deposited iron catalyst particles, embedded a silicon dioxide matrix.

Methane gas and other hydrocarbons were then allowed to pass over the integrated circuit in a reaction chamber. Nanotubes then began to "grow" on top of the integrated circuit.

This breakthrough has further opened the door for future developments on the nanoscale.

The term nanotechnology generally refers to the creation of mechanical or electrical structures on the scale of less than 1,000 nanometers. A carbon nanotube is thousands of times smaller than a human hair and looks like rolled-up chicken wire.

For electrical engineers, carbon nanotubes provide the building block for transistors. Such transistors could in the future be used to build extremely small electronic devices.

Computer memory would be able to take advantage of the nanotubes' extraordinarily small size as well. This would allow for extremely dense memory chips.

The direct incorporation of the nanotube on integrated circuits is especially important for the development of tiny chemical detectors. Such devices could identify the presence of extremely minute samples of toxic chemicals.

"Lots of work remains to be done before practical integrated circuits made from nanotubes can be realized," said Tseng. "The process of growing these tubes is not very mature. By integrating carbon nanotubes with conventional silicon circuitry, we bring carbon nanotubes-based devices closer to commercial applications."

Next on the agenda for the research team is the expansion of the technology to another type of integrated circuit. The research team will also work on refining the current growth process.

The growth of the nanotubes took place at Stanford University, while the fabrication and the design of the circuit occurred here at Cal.

Also collaborating on this project were graduate students Qian Wang at Stanford and Peiqi Xuan and Ryan Malloy at Berkeley.

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