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Universal Memory

NANOELECTRONICS Nanotubes make possible ultradense data storage.

Nantero CEO Greg Schmergel holds a circular wafer of silicon, about the size of a compact disc, sealed in an acrylic container. It’s a piece of hardware that stores 10 billion bits of ­digi­tal information, but what’s remarkable about it is the way it does it. Each bit is encoded not by the electric charge on a circuit element, as in conventional electronic ­memory, nor by the direction of a magnetic field, as in hard drives, but by the physical orientation of nanoscale structures. This technology could eventually allow vastly greater amounts of data to be stored on computers and mobile devices. Experts estimate that within 20 years, you may be able to fit the content of all the DVDs ever made on your laptop computer or store a digital file containing every conversation you have ever had on a handheld device.

Nantero’s approach is part of a broader effort to develop “universal memory” – next-generation memory systems that are ultradense and low power and could replace everything from the flash memory in digital cameras to hard drives. Nantero’s technology is based on research that the Woburn, MA, company’s chief sci­entist, Thomas Rueckes, did as a graduate student at Harvard University. Rueckes noted that no existing memory technologies seemed likely to prove adequate in the long run. Static and dynamic random-access memory (RAM), used in laptops and PCs, are fast but require too much space and power; flash memory is dense and nonvolatile – it doesn’t need power to hold data – but is too slow for computers. “We were thinking of a memory that combines all the advantages,” says Rueckes.

The solution: a memory each of whose cells is made of carbon nanotubes, each less than one-ten-thousandth the width of a human hair and suspended a few nanometers above an electrode. This default position, with no electric current flow between the nanotubes and the electrode, represents a digital 0. When a small voltage is applied to the cell, the nanotubes sag in the middle, touch the electrode, and complete a circuit – storing a digital 1. The nanotubes stay where they are even when the voltage is switched off. That could mean instant-on PCs and possibly the end of flash memory; the technology’s high storage density would also bring much larger memory capacities to mobile devices. Nantero claims that the ultimate refinement of the technology, where each nanotube encodes one bit, would enable storage of trillions of bits per square centimeter – thousands of times denser than what is possible today. (By comparison, a typi­cal DVD holds less than 50 billion bits total.) The company is not yet close to that limit, however; its prototypes store only about 100 million bits per square centimeter.

Nantero has partnered with chip makers such as Milpitas, CA-based LSI Logic to integrate its nanotube memory with sili­con circuitry. The memory sits on top of a layer of conventional transistors that read and write data, and the nanotubes are processed so that they don’t contaminate the accessing circuits. By late 2006, Schmergel predicts, Nantero’s partners should have produced samples of nanotube memory chips. Early applications may come in laptops and PDAs. Ultimately, however, the goal is to replace all memory and disk storage in all computers.

Suspending nanotubes is not the only way to build a universal memory. Other strategies include magnetic random-access memory, which Motorola and IBM and are pursuing, and molecular memory, where Hewlett-Packard is a research leader. But industry experts are watching Nantero’s progress with cautious optimism. “They have a very good approach, and it’s further along than any other,” says Ahmed Busnaina, professor of electrical engineering at Northeastern University and director of the National Science Foundation-funded Center for High-Rate Nanomanufacturing. If successful, this new kind of memory could put a world of data at your fingertips instantly, wherever you go.

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