Tech Smoothes Way to Cheaper Electronics

July 30, 2009 -- A new technique to produce ultra-smooth metal surfaces could secure a future of sensitive medical detectors, more efficient solar cells and faster computers, according to new research published today in the journal Science.

The key to this new technique is a five-minute epoxy that could actually be found at a local hardware store.

Scientists from the University of Minnesota created nano-scale structures on silicon templates that can be used over and over again, which should lower costs of manufacturing across a variety of technologies.

"Up to this point each device had to be hand-crafted one at a time, and because each device is different, they behave differently," said David Norris, one of the co-authors of the Science paper. "Our process allows you to turn out many identical devices that all act the same."

The scientists started with a single block of silicon. They then placed a mask over the block and treated the exposed area with potassium hydroxide to chemically etch various structures into the silicon. This process created a pattern in the silicon, which served as a template.

Other methods of etching patterns, such as electron beams, are available as well.

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The Minnesota scientists created bulls-eyes, pyramids and a handful of other patterns, although virtually any shape can be made.

With the mask removed, the scientists then deposited gold, silver or copper over the silicon template, which filled in the various pores.

So far, this is fairly standard procedure; the semiconductor industry and other sectors have been doing this for 15 years to create ultra-smooth flat surfaces to use with the technologies they manufacture. However, the technique used to remove the silicon on ultra-smooth, patterned surfaces is new.

Traditionally, companies and researchers dissolved the silicon template away. It's effective, but not efficient; for each device, a new silicon template has to be created.

The Minnesota scientists have figured out how a way to reuse these templates. Instead of destroying the silicon, they simply peel the metal off, revealing the ultra-smooth patterned surface underneath.

There are two ways to peel off these tiny structures. The first is to create a thin metal layer, 100-200 nanometers thick for silver, and then pour five minute epoxy over the metal. Once the epoxy hardens, the researchers simply peel the epoxy, and the metal underneath, off the silicon.

The other way to save the silicon is by adding more metal. When the metal layer becomes about one tenth of a millimeter thick it's strong enough to peel off.