PORTLAND, Ore. IBM Corp. researchers say they have harnessed DNA to position nanoscale components like carbon nanotubes and silicon nanowires into circuits 10 times smaller than can be achieved with current lithographic techniques.
The new technique was invented by professor Paul "W. K." Rothemund, a senior research associate at the California Institute of Technology (Caltech, Pasedena). It was perfected by a team of 10 IBM scientists led by Greg Wallraff, an IBM research scientist based in San Jose, Calif.
"The assembled DNA structures are relatively large--a hundred to 150 nanometers on an edge--but they are composed of strips of DNA that are only about 2 nanometers tall," said Wallraff. "Once we put these relatively large nanostructures down, then we can use them for component assembly of, for example, silicon nanowires, carbon nanotubes and quantum dots."
|IBM scientists are using DNA origami to build tiny circuit boards (triangles) which use self assembly for allignment on a substrate, here shown as confined to lines on a lithographically patterned surface.|
For their demonstration, IBM researchers used e-beam lithography to create triangular-shaped patches on a relatively large substrate, about 130 nanometers on an edge. The patches matched the size of DNA structures, each of which incorporated a pattern of hooks that could be customized to hold future nanoscale components of the circuit.
"In principle, we can use 130-nanometer lithography to get down to feature sizes that are much, much smaller," Wallraff claimed.
The DNA strands were customized by Caltech's Rothemund to create a pattern of chemical hooks to which nanoscale components will self-assemble into a circuit. The sticky patches created by IBM on the substrate then attracted the preassembled circuits, which automatically attached themselves in the correct orientation.
By self-assembling the circuits atop the DNA strands in a solution, it could eventually be possible to merely bath the substrate in the solution, prompting circuits to automatically attach themselves.
"In a single drop of water, we assembled more than 100 billion copies of the desired shape with a pattern on top to which components could be attached," said Rothemund. "The spacing between the components can be as small as 6 nanometers, giving you a resolution today that is about 10 times higher than the lithographic resolution we use today to make computer chips."
So far, the team has demonstrated alignment of circuit assemblies onto the sticky patches with an orientation accuracy of less than 10 degrees. Remaining technical hurdles include attaching the components to the hooks on DNA, interconnecting components on DNA strands and connecting pre-assembled circuits.
"Alignment, registration and overlay is extremely critical, so we are currently trying to understand what the tolerances are--how well we can position these and realign them if they get a little off," said Wallraff.
The remaining engineering hurdles will take at least five years to perfect into a process that could be commercialized, according to Rothemund.