Scientists grow nanowires reliably enough to create circuits
Gaithersburg (MD) - Researchers at the National Institute of Standards and Technology (NIST) have developed a reliable way to create nanowires just a few nanometers in diameter. Previous efforts in growing nanowires commercially at this scale have met with significant limitations, especially when attempting to grow in a desired direction. But now, NIST researchers believe they have found one solution which has been shown to accurately connect nanoscopic circuits.
The researchers began with a sapphire substrate material. It served as the base for growing nanowires using commercial lithography techniques. Previous attempts have attempted to grow nanowires vertically, like blades of grass. This process involved growing, mowing, moving and affixing the nanowires to the final substrate material. In this process it was not known in advance what the layout of the nanowires would be as they were deposited by a liquid. Luck and hope played a big factor in finding portions of the substrate with orientations suitable for use in a circuit. This non-viable approach used previously has now found an amazingly simple alternative.
In the same way ants can be made to follow an odd-shaped chemical trail left across a tabletop, the researchers have discovered that if they deposit tiny drops of gold in lines along the desired pathways, then nanowires will follow those lines when grown in a high heat environment. Zinc oxide was chosen as the semiconductor material as there are minor differences between it and sapphire. These differences cause the nanowires to naturally form into very small, discrete lines however, making it a most desirable relationship. In addition, the pathways grow in a particular direction. They follow the bread crumb trail of gold left by the previous process, making it easy to add electrical contacts and other features because the growth pattern for encroachment upon those features can be determined.
In the laboratory researchers have developed a 600-circuit transistor assembly similar to those used in digital memory chips. There have been some initial observations which indicate this process can be refined even further for mass production, resulting in methods of production suitable for industrial-scale manufacturing of even very complex circuits.
Successful results in this area have been the result of cumulative efforts in several disciplines. These have included glowing(sic) nanowires, ultraviolet LEDs, individual nanowire growth and released research into substrates, materials and process technologies. Research will continue in this area and the real question remaining is when will this actually become beneficial? The world of the ultra-small is still just outside of our reach. It may be 10 to 20 years before this kind of technology truly reaches us in anything commercial.