IBM researchers use DNA to assemble nano-switching devices on a semiconductor chip

Traditionally, lithogrpahy technology is used to create switching FETs of size measuring around 100nm - 200nm. This technology is hitting wall with tough challenges to print nm measuring shapes (<22nm) on semiconductor wafer. Now to make the semiconductor chips below 22nm, engineers and scientists are looking for some new technologies (more at life-sciences and biotechnology) to assemble nano measuring switching elements like nano-tubes or wires. The most nearest practical solution is the way the body cells or its constituents stay one-next to the other and how they are grown. IBM researchers have attempted pairing nanotubes or such elements with DNA nanostructures. This concept still uses lithography technique but aims to solve some of the challenges faced by traditional semiconductor manufacturing.

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.

IBM has used DNA molecules as scaffolding to deposit and self-assemble carbon nanotubes into precise patterns by sticking to the DNA molecules. The positioned DNA nanostructures can serve as scaffolds, or miniature circuit boards. Either electron beam or optical lithography was 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.

"The cost involved in shrinking features to improve performance is a limiting factor in keeping pace with Moore's Law and a concern across the semiconductor industry," said Spike Narayan, manager, Science & Technology, IBM Research - Almaden. "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 chip-making process."

The techniques for preparing DNA origami, 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 paper on this work, "Placement and orientation of DNA nanostructures on lithographically patterned surfaces," by scientists at IBM Research and the California Institute of Technology will be published in the September issue of Nature Nanotechnology and is currently available at: http://www.nature.com/nnano/journal/vaop/ncurrent/abs/nnano.2009.220.html