Researchers at IBM and the California Institute of Technology say they have a possible solution to key problems looming for post-22nm node semiconductor manufacturing: a combination of lithographic patterning and self-assembly that arranges DNA structures on surfaces compatible with current manufacturing equipment.

DNA origami, they explain, involves folding a long single strand of viral DNA using shorter, synthetic "staple" strands, which researchers claim display 6nm-resolution patterns, and could "in principle" be used to arrange carbon nanotubes, silicon nanowires, or quantum dots. Making the starting structures, though, depends on an "uncontrolled deposition," which "results in random arrangements" whose properties are difficult to measure, and to integrate with microcircuitry.

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High concentrations of triangular DNA origami binding to wide lines on a lithographically patterned surface. Inset shows individual origami structures at high resolution. (Source: IBM)

The researchers' approach, detailed in the September issue of Nature Nanotechnology, is to use e-beam lithography and dry oxidative etch to create DNA origami-shaped binding sites on certain materials, such as SiO2 and "diamond-like" carbon. Caltech's techniques for preparing the DNA origami structure cause single DNA molecules to self-assemble via a reaction between the long viral DNA strand and shorter synthetic oligonucleotide strands, which fold the viral DNA strand into 2D shapes; these can be modified to be attached by nanoscale components. They tout the ability to create squares, triangles, and stars with 100-150nm dimensions on an edge, and thickness as wide as a DNA double helix. Processing work at IBM used either e-beam or optical lithography to create arrays of the "binding sites" to match those of individual origami structures; key was discovering template material and optimal deposition conditions so that the origami structures bound only to patterns of "stick patches."

In their journal paper, they claim the DNA origami bind with high selectivity and good orientation—70%-95% aligned with angular dispersion as low as ±10° (on diamond-like carbon) or ±20° (on SiO2).

Essentially, the researchers explain, the DNA molecules act as "scaffolding," onto which deposited carbon nanotubes would be stuck and self-assembled, at smaller dimensions than conventional semiconductor manufacturing capabilities. "The combination of this directed self-assembly with today's fabrication technology eventually could lead to substantial savings in the most expensive and challenging part of the chipmaking process," said Spike Narayan, manager of science & technology at IBM's Almaden (CA) research center, in a statement. — J.M.

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