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Thursday, Feb 12, 2009
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New material for nano-devices

It could be moulded like plastic to create features at nano-scale

Bulk metallic glasses are like slow-flowing liquid
Process could replace steps in chip production

New Haven: Yale University engineers have created a process that may revolutionise the manufacture of nano-devices from computer memory to biomedical sensors by exploiting a novel type of metal. The material can be moulded like plastic to create features at the nano-scale and yet it is more durable and stronger than silicon or steel. The work is reported in the February 12 issue of Nature.

The search for a cost-effective and manageable process for higher-density computer chip production on a nano-scale has been a challenge. One solution is making nano-scale devices by simple stamping or moulding, similar to the method used to fabricate CDs or DVDs. This, however, requires stamps or master moulds with nano-scale features.

While silicon-based moulds produce relatively fine detail, they are not very durable. Metals are stronger, but the grain size of their internal structure does not allow nano-scale details to be imprinted on their surfaces.

Unlike most metals, “amorphous metals,” known as bulk metallic glasses (BMGs), do not form crystal structures when they are cooled rapidly after heating. Although they seem solid, they are more like a very slow-flowing liquid that has no structure beyond the atomic level. This property makes them ideal to mould fine details, said senior author Jan Schroers of the Yale School of Engineering & Applied Science.

Researchers have been exploring the use of BMGs for about a decade, according to Dr. Schroers. “We have finally been able to harness their unusual properties to transform both the process of making moulds and producing imprints.”

“This process has the potential to replace several lithographic steps in the production of computer chips,” Dr. Schroers says. BMGs have the pliability of plastics at moderately elevated temperatures, but are stronger and more resilient than steel or metals at normal working temperatures. “We now can make template moulds that are far more reliable and lasting than ones made of silicon and are not limited in their detail by the grain size that most metals impose.”

To actually get detail at the nano-scale the researchers had to overcome an issue faced in any moulding process — how to get the material to cover the finest detail, and then how to separate the material intact from the mould. Surfaces of liquid metals exhibit high surface tension and capillary effects that can interfere in the moulding.

Post-doctoral fellow Golden Kumar found that by altering the mould-BMG combination they could create surfaces so that the atoms take advantage of their favourable interaction with the mould — to fill the mould and then release the product.

The team reports nano-patterning of details as small as 13 nanometres, one ten-thousandth the thickness of a hair. — Courtesy: Yale University Science News

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