Scientists at IBM Research and the California Institute of Technology has made an advancement that could be a major breakthrough in enabling the semiconductor industry to pack more power and speed into tiny computer chips, while making them more energy efficient and less expensive to manufacture. IBM Researchers and collaborator Paul W.K. Rothemund, of the California Institute of Technology, have combined lithographic patterning with self assembly — a method to arrange DNA origami structures on surfaces compatible with today’s semiconductor manufacturing equipment.
By using DNA molecules as scaffolding, millions of carbon nanotubes could be deposited and self-assembled into precise patterns by sticking to the DNA molecules. IBM’s approach may provide a way to reach sub-22 nm lithography. The utility of this approach lies in the fact that the positioned DNA nanostructures can serve as scaffolds, or miniature circuit boards, for the precise assembly of components — such as carbon nanotubes, nanowires and nanoparticles — at dimensions significantly smaller than possible with conventional semiconductor fabrication techniques. This opens up the possibility of creating functional devices that can be integrated into larger structures, as well as enabling studies of arrays of nanostructures with known coordinates.
The techniques for preparing DNA origami, which was developed at Caltech, cause single DNA molecules to self assemble in solution via a reaction between a long single strand of viral DNA and a mixture of different short synthetic oligonucleotide strands. These short segments act as staples — effectively folding the viral DNA into the desired 2D shape through complementary base pair binding. The short staples can be modified to provide attachment sites for nanoscale components at resolutions (separation between sites) as small as 6 nanometers (nm). In this way, DNA nanostructures such as squares, triangles and stars can be prepared with dimensions of 100 – 150 nm on an edge and a thickness of the width of the DNA double helix.
The lithographic templates were fabricated at IBM using traditional semiconductor techniques to etch out patterns. This is the same technology used to make the chips found in today’s computers. Either electron beam or optical lithography were used to create arrays of binding sites of the proper size and shape to match those of individual origami structures. Key to the process were the discovery of the template material and deposition conditions to afford high selectivity so that origami binds only to the patterns of “sticky patches” and nowhere else.