IBM looking to use DNA scaffolding for next gen chips

TechOnline India - August 17, 2009

Scientists at IBM Research and the California Institute of Technology are claiming a major breakthrough in packing more power and speed into ICs, while making them more energy efficient and less expensive to manufacture.

LONDON — Scientists at IBM Research and the California Institute of Technology are claiming a major breakthrough in packing more power and speed into ICs, while making them more energy efficient and less expensive to manufacture.

In a paper to be published in Nature Nanotechnology, they are suggesting that artificial DNA nanostructures and 'DNA origami', in which a long single strand of DNA is folded into a shape using shorter "staple strands", could be used to provide a template for the self-assembly of other materials into nanoelectronic or nano-optical devices on the surface of the chip.

The work is being done jointly between researchers at IBM's Almaden Research Center and those working at the California Institute of Technology.

As the researchers note, the costs of producing ever smaller and more powerful chips have soared, so semiconductor manufacturers have grown increasingly interested in alternative methods for constructing the microcircuits built on the surface of silicon or other semiconductors.

The industry, they note, is faced with the challenges of developing lithographic technology for feature sizes smaller than 22-nmm and exploring new classes of transistors that employ carbon nanotubes or silicon nanowires.

They say their approach of using DNA molecules as scaffolding -- where millions of carbon nanotubes could be deposited and self-assembled into precise patterns by sticking to the DNA molecules - may provide a way to reach sub-22 nm lithography.

The utility of their approach, they say 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 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."

However, the researchers caution the technique will need to be refined and tested. Narayan said that while the DNA origami could allow chipmakers to build frameworks that are far smaller than possible with conventional tools, the technique still needs perhaps ten years of experimentation and testing.

The researchers used electron-beam lithography and an etching process to create DNA origami-shaped "binding sites" on silicon and other materials used in making semiconductors.

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.

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. 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.

The paper will be published in the September issue of Nature Nanotechnology and is currently available here.

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