Nanodevice breaks 1-GHz barrier

PASADENA, Calif.- 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). The accomplishment 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 the journal Nature, California
Institute of Technology professor of physics, applied physics, and
bioengineering Michael Roukes and his colleagues from Caltech and
Case Western Reserve University demonstrate that the tiny mechanism
operates at microwave frequencies. The device is a prototype and not
yet developed to the point that it is ready to be integrated into a
commercial application; nevertheless, it demonstrates the progress
being made 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, which is an acronym for
“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 new and improved
biological imaging and, ultimately, for observing individual
molecules through an improved approach to 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 mind-set 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 a good home computer these days can have a speed 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’s new
demonstration, the use of silicon carbide epilayers to control layer
thickness to atomic dimensions and a balanced high-frequency
technique for sensing motion that effectively transfers signals to
macroscale circuitry 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 that the end-products are two nearly-identical beams 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 everyday world we live in is by no means a trivial
matter. As devices become smaller, it becomes increasingly difficult
to recognize the very small displacements that occur at much shorter
time-scales.

Progress with the nanoelectromechanical system working at microwave
frequencies offer the potential for improving magnetic resonance
imaging to the extent that individual macromolecules could be imaged.
This would be especially important in furthering the understanding of
the relationship between, for example, the structure and function of
proteins. Also, the devices could be used in a novel form of mass
spectrometry, and for sensing individual biomolecules in fluids, and
perhaps for realizing solid-state manifestations of the quantum bit
that could be exploited for future devices such as quantum computers.

The coauthors of the paper are Xue-Ming (Henry) Huang, a graduate
student in physics at Caltech; and Chris Zorman and Mehran
Mehrengany, both engineering professors at Case Western Reserve
University.