Jan. 25, 2007 -- A team of UCLA and California Institute of Technology chemists reported in the Jan. 25 issue of the journal Nature the successful demonstration of a large-scale, "ultra-dense" memory device that stores information using reconfigurable molecular switches. This research represents an important step toward the creation of molecular computers that are much smaller and could be more powerful than today's silicon-based computers.
The 160-kilobit memory device uses interlocked molecules manufactured in the UCLA laboratory of J. Fraser Stoddart, director of the California NanoSystems Institute (CNSI), who holds UCLA's Fred Kavli Chair in Nanosystems Sciences.
The research published in Nature describes the fabrication and operation of a memory device. The memory is based on a series of perpendicular, crossing nanowires, similar to a tic-tac-toe board, with 400 bottom wires and another 400 crossing top wires. Sitting at each crossing of the tic-tac-toe structure and serving as the storage element are approximately 300 bistable rotaxane molecules. These molecules may be switched between two different states, and each junction of a crossbar can be addressed individually by controlling the voltages applied to the appropriate top and bottom crossing wires, forming a bit at each nanowire crossing.
The 160-kilobit molecular memory was fabricated at a density of 100,000,000,000 (1011) bits per square centimeter - "a density predicted for commercial memory devices in approximately 2020," Stoddart said.
"For this commercial dream to be realized, many fundamental challenges of nano-fabrication must be solved first," Stoddart said in a prepared statement. "The use of bistable molecules as the unit of information storage promises scalability to this density and beyond. However, there remain many questions as to how these memory devices will work over a prolonged period of time. This research is an initial step toward answering some of those questions."
"Using molecular components for memory or computation or to replace other electronic components holds tremendous promise," Stoddart said. "This research is the best example - indeed one of the only examples - of building large molecular memory in a chip at an extremely high density, testing it and working in an architecture that is practical, where it is obvious how information can be written and read."
"We have shown that if a wire is broken or misaligned, the unaffected bits still function effectively; thus, this architecture is a great example of 'defect tolerance,' which is a fundamental issue in both nanoscience and in solving problems of the semiconductor industry. This research is the culmination of a long-standing dream that these bistable rotaxane molecules could be used for information storage," said Stoddart, whose areas of expertise include nanoelectronics, mechanically interlocked molecules, molecular machines, molecular nanotechnology, self-assembly processes and molecular recognition, among many other fields of chemistry.
"Our goal here was not to demonstrate a robust technology; the memory circuit we have reported on is hardly that," said James R. Heath in the announced release. Heath is Caltech's Elizabeth W. Gilloon Professor of Chemistry and a co-author of the Nature paper. "Instead, our goal was to demonstrate that large-scale, working electronic circuits could be constructed at a density that is well-beyond - 10 to 15 years - where many of the most optimistic projections say is possible."
Caltech chemists and chemical engineers, led by Heath, are the world leaders at making nanowires, according to Stoddart. "Nobody can equal them in terms of the precision with which they carry this research out," he said. The memory device's top and bottom nanowires, each 16 nanometers wide, were fabricated using a method developed by Heath's group.
Stoddart's research team is widely considered the world's leader in making molecular switches, an area in which Stoddart and his colleagues have conducted 25 years of research that has laid the foundation for this current work. Stoddart's group designs and manufactures intricate interlocked molecules in which the relative motions of the interlocked components can be switched in controlled ways.
While this research could affect the computer industry dramatically, it also may have a significant impact on very different uses of information technologies as well, said Heath and Stoddart, whose research is funded primarily by the Defense Advanced Research Projects Agency, the central research and development organization for the U.S. Department of Defense, with additional funding by the National Science Foundation.
"Molecular switches will lead to other new technologies beyond molecular electronic computers." Stoddart said. "It is too soon to say precisely which ones will be the first to benefit, but they could include areas such as health care, alternative energy and homeland security."