By James Ellenbogen

In the not-too-distant future, computation will become a property of matter. Materials will be engineered on the nanometer scale, i.e., the molecular scale, to incorporate computation along with their other desirable structural properties. Computers might be incorporated in next-generation nanostructured materials in much the same way color is incorporated in the materials with which we now make clothing, appliances, motor vehicles, and aircraft. This vision is an extension of recent groundbreaking demonstrations of molecular-scale electronic devices.

For the past eight years, MITRE has been instrumental in developing designs and architectures for molecular-scale electronic computer circuits and devices. An example of MITRE’s work in nanometer-scale computing is a circuit, designed by MITRE in 1997, that adds two numbers. This device consists of a single molecule only 10 nanometers by 10 nanometers in size. (A nanometer, one billionth of a meter, spans only about 10 atomic diameters.)

In the future, “nanocomputers” could be so small that the circuitry for a simple computer might fit on a single conventional microelectronic transistor. A moderately capable electronic computer might fit on a surface with an area no bigger than that of a bacterium. A supercomputer integrated on the nanometer scale could fit easily on top of a grain of salt.

Three Factors for the Future

The implications of nanotechnology go beyond just the development of radically smaller, denser circuits. Working under the sponsorship of the MITRE Technology Program and the Defense Advanced Research Projects Agency (DARPA), MITRE’s Nanosystems Group also is investigating revolutionary new kinds of computer applications as well as new nanomanufacturing techniques. Consideration of three factors—design, manufacturing, and applications—is necessary to envision the implications of nanotechnology.

Benefits include new materials, complex micromachinery, advanced biomedical diagnostics and therapeutics, the design and deployment of much smaller but more capable aerospace systems, and the development of “smart,” self-repairing materials and systems. In addition, computers will at once become more pervasive yet less conspicuous and obtrusive, as they may be built seamlessly into the very fabric of everyday objects.

In this vein, the MITRE Nanosystems Group is prototyping radical new applications. One example, currently in design and fabrication, is a walking microrobot no bigger than a housefly. When completed, it will contain an entire network of on-board nanocomputers, each the approximate size of a grain of sand.

Tiny Wires, Tiny Switches, Big Potential

As different from today’s electronic computers as these new systems sound, keep in mind that they are founded upon actual experimental demonstrations of nanometer-scale electronic devices—switches and wires made from individual molecules or from only a very few. Each of these new devices is only about 2 or 3 nanometers long, but carries a current density orders of magnitude greater than ordinary copper wire. These experimental developments in nanotechnology are of great industrial importance, well beyond their scientific novelty. That is because these new molecular devices arrive at a crucial juncture, when it appears that the evolution of the present basis for electronic computing may be reaching an impasse.

The present information technology revolution is built upon a revolution in miniaturization that dates to the invention of the transistor more than 50 years ago and of the solid-state integrated circuit 10 years later. In 1965, Gordon Moore of Intel Corporation observed that each new chip, released within 18 to 24 months of the previous chip, contained roughly twice the capacity of its predecessor. But due to fundamental physical limits, the rate of electronic miniaturization may stall sometime in the next 10 or 15 years. The main reason is the very high cost and difficulty of fabricating from solids trillions of future nanometer-scale electrical components. Compounding these difficulties is that, unlike present micron-scale transistors, nanometer-scale switches seem likely to require new operating principles that depend much more on quantum mechanics (see “Quantum Information Science”).

The new quantum mechanical operating principles would require all the trillions of switches and wires on a next generation computer chip to be identical within one atomic diameter.

Therefore, to develop ever more densely integrated electronic computers, we find ourselves wishing for very uniform, naturally occurring nanometer-scale structures. Fortunately, there are such structures—they’re called molecules.

Breaking Moore’s Law

All molecules of a given type are exactly the same size within one atomic diameter. They can be made a “mole” at a time—that’s a trillion trillion molecules—for a few dollars. Molecules can even be designed to “self-assemble” quickly into larger structures where they are needed. Best of all, recent experiments have shown that individual molecules can be made into wires that conduct electricity and into switches that turn it on and off.

Now, if we can just find a way to build a computer from conductive molecular-scale electronic devices, then we can do more than perpetuate Moore’s Law. We can break it.

Make MITRE’s Molecular

Thus, the race to build the first ultra-densely integrated electronic computers is the race to find conductive molecules, then to figure out how to make them and assemble them into larger structures so that they will compute. Investigators at MITRE were among the first to appreciate and attempt to address this technological challenge.

From 1994 through 1997, MITRE produced a series of comprehensive, explanatory reports and review articles about nanometer-scale electronics. These papers have been influential in altering the perception of nanotechnology throughout the U.S. government and elsewhere in the world.

In 1997, MITRE was among the first to design computer circuits constructed from experimentally demonstrated molecular switches and wires. Work on these novel designs gave rise to an article published in the March 2000 issue of the Proceedings of the IEEE. “Architectures for Molecular Electronic Computers” reviewed recent experimental advances in testing and demonstrating molecular-scale electronic devices, then set forth a detailed, comprehensive strategy for integrating such devices to make molecular-scale computer circuits and systems. These MITRE-developed concepts also assisted officials at DARPA in forming its important Molecular Electronics (or “Moletronics”) R&D Program in 1997 and 1998.

Challenges to Come…Nanomanufacturing and Nanofingers

As a result of the progress in worldwide research in molecular-scale electronic computers, it seems likely that a functioning prototype of a molecular memory or a molecular processor will be demonstrated in the next 2 to 5 years. The prospects for this type of revolutionary advance have caught the attention of many major electronics corporations, including Hewlett-Packard, IBM, Lucent, Motorola, Siemens, and Hitachi. These companies now have active programs in molecular-scale electronics research and development.

One of the biggest technical challenges is how to arrange as many as a trillion molecular computing components in an area only a few millimeters square. To meet this challenge, MITRE’s Alex Wissner-Gross invented in 1998 a technique called nanometer-scale patterned granular motion, or “NanoPGM.” The goal of NanoPGM is to generate millions of “nanofingers,” finger-like structures each only a few nanometers long, that might someday perform precise, massively parallel manipulation of molecules and directed assembly of other nanometer-scale objects. A U.S. patent was issued for this process early in 2001. Over the past year, MITRE has mounted an experiment to test and demonstrate Wissner-Gross’s idea. Led by investigators David Goldhaber-Gordon and Johann Schleier-Smith, it has already produced some preliminary success.

Downloading Objects From the Internet

The evolution in manufacturing technologies required to make nanocomputers may be just as important as the design and prototyping of the computers themselves. Progress in this area may, in turn, result in techniques to fabricate a much wider range of material objects starting from their molecules and working up. These technologies would manipulate the most fundamental bits of matter much as we now manufacture, manipulate, and transmit bits of information in our computers and mass storage devices. Matter would become much like software.

Today’s information technology is actually a distributed manufacturing technology by which we now “download” information—letters, books, music, and videos—from the Internet by re-manufacturing them on our desktops. This may evolve to an even more flexible form in which factories or even isolated personnel in faraway locales, such as on ships at sea or even on the surface of other planets, can “download” such material goods as medicines, computers, and even spare parts for motor vehicles, aircraft, or spacecraft. Such innovations would certainly have a huge impact in the government and the commercial marketplace. MITRE is working on behalf of the American public toward both the nanocomputer technology and the nanomanufacturing technology to make this vision a reality.

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For more information, please contact James Ellenbogen using the employee directory.

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