Shake it, baby—at one gigahertz

Nanoscientists have achieved a milestone in their burgeoning field by creating a device that vibrates a billion times per second, or at one gigahertz (1 GHz). This feat further increases the likelihood that tiny mechanical devices working at the quantum level can someday supplement electronic devices for new products.

Reporting in the January 30 issue of Nature, Caltech professor of physics, applied physics, and bioengineering Michael Roukes; graduate student in physics Xue-Ming (Henry) Huang; and engineering professors Chris Zorman and Mehran Mehrengany of Case Western Reserve University demonstrate that the tiny mechanism operates at microwave frequencies. A prototype, the device is not developed enough to be integrated into a commercial application. Nevertheless, it demonstrates progress in the quest to turn nanotechnology into a reality—that is, to make useful devices whose dimensions are less than a millionth of a meter.

This latest effort in the field of NEMS, or nanoelectromechanical systems, is part of a larger emerging effort to produce mechanical devices for sensitive force detection and high-frequency signal processing. According to Roukes, the technology could also have implications for enhancing biological imaging and, ultimately, for observing individual molecules with improved magnetic resonance spectroscopy, as well as for a new form of mass spectrometry that may permit single molecules to be “fingerprinted” by their mass.

“When we think of microelectronics today, we think about moving charges around on chips,” says Roukes. “We can do this at high rates of speed, but in this electronic age our mindset has been somewhat tyrannized in that we typically think of electronic devices as involving only the movement of charge.

“But since 1992, we’ve been trying to push mechanical devices to ever-smaller dimensions, because as you make things smaller, there’s less inertia in getting them to move. So the time scales for inducing mechanical response go way down.”

Though some home computers these days have speeds of one gigahertz or more, the quest to construct a mechanical device that can operate at such speeds has required multiple breakthroughs in manufacturing technology. In the case of the Roukes group, using silicon carbide epilayers to precisely control layer thickness and a balanced high-frequency technique for sensing motion have been crucial to success. Both advances were pioneered in the Roukes lab.

Grown on silicon wafers, the films used in the work are prepared in such a way as to produce two nearly identical beams, each 1.1 microns long, 120 nanometers wide, and 75 nanometers thick.

When driven by a microwave-frequency electric current while exposed to a strong magnetic field, the beams mechanically vibrate at slightly more than one gigahertz.

Future work will include improving the nanodevices to better link their mechanical function to real-world applications, Roukes says. The issue of communicating information, or measurements, from the nanoworld to the scale of the everyday world we live in is not trivial. As devices become smaller, it becomes increasingly difficult to recognize the very small displacements that occur at much shorter time scales.

Such progress in NEMS might eventually lead to improvements in magnetic resonance imaging, to the extent of being able to image individual macromolecules; to novel forms of mass spectrom-
etry that can sense individual biomol-ecules in fluids; or to quantum computing, through solid-state manifestations of the quantum bit.
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