Precision Carbon Nanotube Layout
Brian Dance, Contributing Editor -- Semiconductor International, 12/1/2001
Researchers in the engineering department at the University of Cambridge (Cambridge, UK) have developed a technique for depositing carbon nanotubes with high precision onto a silicon substrate.
They first deposit a thin layer of nickel onto the substrate and etch a pattern in it by standard e-beam lithography. Annealing at 700° C causes the nickel to form into nanoscale globules. A plasma chemical vapor deposition process is then used to deposit nanotubes onto the nickel.
The plasma deposition of carbon nanotubes previously resulted in the deposition of amorphous carbon on the substrate surface that can cause unwanted field emission and other processing problems. The researchers have solved this problem by controlling the ratio of the deposition gas (acetylene) to the etching gas (ammonia). Control of the temperature and the timing fixes the length of the nanotubes at ~5 µm. The spacing between the tubes is ~10 µm.
This is the first time carbon nanotubes have been grown on a silicon substrate in a controlled manner with the required size and location, said Gehan Amaratunga, professor of electrical and electronic engineering. He added that the technique is compatible with current silicon microelectronics technology and has both time and cost implications.
For additional information on materials science, go to www.semiconductor.net/materials.
