Nanotubes Grown on “Computer Chip” Surface
MIT researchers have grown dense forests of crystalline carbon nanotubes on a metal surface at temperatures close to those characteristic of computer chip manufacturing. Unlike previous attempts to do the same thing, the researchers’ technique relies entirely on processes already common in the semiconductor industry. They also have shown that the crucial step in their procedure was to preheat the hydrocarbon gas from which the nanotubes form, before exposing the metal surface to it.
The transistors in computer chips are traditionally connected by tiny copper wires. However, as chip circuitry shrinks and the wires become thinner, their conductivity suffers and they become more likely to fail. A simple enough manufacturing process could enable carbon nanotubes to replace the vertical wires in chips, permitting denser packing of circuits.
In a vacuum chamber, researchers in the lab of MIT materials science professor Carl V. Thompson vaporized the metals tantalum and iron, which settled in layers on a silicon wafer. They then placed the coated wafer at one end of a quartz tube, which was inserted into a furnace. At the wafer’s end of the tube, the furnace temperature was 475 degrees C; but at the opposite end, the temperature varied.
The researchers pumped ethylene gas into the tube from the end opposite the wafer. When the temperature at that end approached 800 degrees, the ethylene decomposed, and the iron on the wafer catalyzed the formation of carbon nanotubes. The researchers are trying to determine whether different combinations of metals and hydrocarbon gases can lower the catalytic temperature even further and improve the quality of the nanotubes.
The research was sponsored by the MARCO Interconnect Focus Center and partially by. The paper, titled “Low Temperature Synthesis of Vertically Aligned Carbon Nanotubes with Electrical Contact to Metallic Substrates Enabled by Thermal Decomposition of the Carbon Feedstock,” Gilbert Nessim, Carl V. Thompson et al, was published in the August 31, 2009 issue of Nano Letters.