Old Idea Inspires Breakthrough Device on a Very Small Scale

Scientists have announced a breakthrough that found its inspiration in Thomas Jefferson’s invention that created multiple copies of a signature with a single signing. A modern version of that could lead to the production of ultra-powerful microprocessors and better medical diagnostic methods.

This new rendering device could improve photolithography--a key semiconductor-production method that uses light to etch circuitry pathways on photosensitive materials--according to Chad A. Mirkin, a professor of chemistry at Northwestern University in Evanston, Ill., coauthor of an article describing the research that appeared last week in the journal Science.

After decades of refining photolithography to create smaller and smaller circuits, engineers now face huge challenges. The most advanced current photolithography equipment can create circuits about 130 nanometers wide (a nanometer, one-billionth of a meter, is about one-twenty-thousandth the thickness of a human hair). Many engineers fear that the technology will soon reach its practical limits, and so stall the drive toward more powerful microprocessors.

But Mirkin’s “dip-pen nanoplotter” suggests a way to create circuits several orders of magnitude smaller and more powerful than today’s, he said. The device uses nanotechnology--a technique that involves construction of structures one atom or one molecule at a time.

By dipping the nanoplotter pen tips into wells of organic molecules, Mirkin’s research team drew eight identical structures with lines 15 nanometers wide. Mirkin predicts that it will eventually be possible to draw structures down to the one-nanometer scale--about half the diameter of a strand of DNA, the genetic blueprint.

Even with this research, though, today’s semiconductor manufacturing methods will not be replaced any time soon. Photolithography is much faster and more efficient than nanoplotters may ever be for industrial-scale production.

“But can it be fast enough to be useful? The answer is yes,” Mirkin said.

He believes that the technology can be used for practical applications as it is expanded to hundreds, and ultimately thousands of pens within the next few years. The pens would be operated simultaneously by a conventional atomic force microscope, standard equipment in modern chemistry labs.

“This provides a cheap way of patterning materials on very small length scales,” particularly biological materials, said Robert Hamers, professor of chemistry at the University of Wisconsin at Madison.

Other experts agreed.

“Writing with these molecules is important and unique,” said Calvin Quate, a nanotechnology expert at Stanford University.

For example, the technique might be used to create connecting wiring between banks of molecular-scale microcircuits created in other research labs using different methods.

Or the nanoplotters could create a master circuitry template at a scale impossible to achieve using photolithography. That template could then be used to “stamp out” multiple copies in mass production.

But the greater significance of the work may be in the ability of the plotter to successfully contain other molecules for chemical and biological testing. “That’s going to open up a new frontier” if the nanoplotter can be scaled up and operated much more rapidly, Quate said. Scientists could rapidly test for chemical interactions, identify disease organisms and test their sensitivity to drugs or other chemicals--potentially leading to new treatments or diagnostic tools.

“Gene chips” created using photolithography and other methods currently operate in this fashion, providing up to thousands of separate DNA test areas in a grid array. But a nano-scale chip could produce many more test areas on much smaller space--suggesting unprecedented speed and precision in examining chemical or biological interactions at a far lower cost than today’s methods.

If patterns can eventually be plotted down to 5 to 10 nanometers, the method could be used to rapidly pinpoint genetically linked abnormalities and design and test synthetic antibodies, Mirkin said. Antibodies provide the biological basis for disease immunity.

Major technical challenges--increasing the plotter’s speed and scaling it up to accommodate thousands of pens, among others--will have to be overcome to achieve this.

Hamers, who is conducting research on gene chips, doubts that the nanoplotter will ever become a significant tool for industrial-scale production.

“But it’s going to have big implications for what those of us in the laboratory can do,” he said. “Whether it will be used in production may be irrelevant, because the crucial step now is in the hands of the individual investigators.”