This image from a scanning electron microscope shows a tiny mechanical device, an electrostatically actuated nanoresonator, that might ease congestion over the airwaves to improve the performance of cell phones and other portable devices. Credit: Purdue University
have learned how to mass produce tiny mechanical devices that could
help cell phone users avoid the nuisance of dropped calls and slow
downloads. The devices are designed to ease congestion over the airwaves
to improve the performance of cell phones and other portable devices.
is not enough radio spectrum to account for everybody’s handheld
portable device,” said Jeffrey Rhoads, an associate professor of
mechanical engineering at Purdue University.
overcrowding results in dropped calls, busy signals, degraded call
quality and slower downloads. To counter the problem, industry is trying
to build systems that operate with more sharply defined channels so
that more of them can fit within the available bandwidth.
do that you need more precise filters for cell phones and other radio
devices, systems that reject noise and allow signals only near a given
frequency to pass,” said Saeed Mohammadi, an associate professor of
electrical and computer engineering who is working with Rhoads, doctoral
student Hossein Pajouhi and other researchers.
Purdue team has created devices called nanoelectromechanical
resonators, which contain a tiny beam of silicon that vibrates when
voltage is applied. Researchers have shown that the new devices are
produced with a nearly 100 percent yield, meaning nearly all of the
devices created on silicon wafers were found to function properly.
are not inventing a new technology, we are making them using a process
that’s amenable to large-scale fabrication, which overcomes one of the
biggest obstacles to the widespread commercial use of these devices,”
Findings are detailed in a research paper appearing online in the journal IEEE Transactions on Nanotechnology. The paper was written by doctoral students Lin Yu and Pajouhi, Rhoads, Mohammadi, and graduate student Molly Nelis.
addition to their use as future cell phone filters, such nanoresonators
also could be used for advanced chemical and biological sensors in
medical and homeland-defense applications and possibly as components in
computers and electronics.
devices are created using silicon-on-insulator, or SOI, fabrication –
the same method used by industry to manufacture other electronic
devices. The resonators can be readily integrated into electronic
circuits and systems because SOI is compatible with complementary
metal–oxide–semiconductor technology, or CMOS, another mainstay of
electronics manufacturing used to manufacture computer chips.
The resonators are in a class of devices called nanoelectromechanical systems, or NEMS.
new device is said to be “highly tunable,” which means it could enable
researchers to overcome manufacturing inconsistencies that are common in
of manufacturing differences, no two nanoscale devices perform the same
rolling off of the assembly line,” Rhoads said. “You must be able to
tune them after processing, which we can do with these devices.”
heart of the device is a silicon beam attached at two ends. The beam,
which vibrates in the center like a jump rope, is about two microns long
and 130 nanometers wide, or about 1,000 times thinner than a human
hair. Applying alternating current to the beam causes it to selectively
vibrate side-to-side or up and down and also allows the beam to be
finely adjusted, or tuned.
nanoresonators were shown to control their vibration frequencies better
than other resonators. The devices might replace electronic parts to
achieve higher performance and lower power consumption.
vivid example is a tunable filter,” Mohammadi said. “It is very
difficult to make a good tunable filter with transistors, inductors and
other electronic components, but a simple nanomechanical resonator can
do the job with much better performance and at a fraction of the power.”
Not only are they more efficient than their electronic counterparts, he said, but they also are more compact.
the devices are tiny and the fabrication has almost a 100% yield, we can pack millions of these devices in a small chip if we need
to,” Mohammadi said. “It’s too early to know exactly how these will find
application in computing, but since we can make these tiny mechanical
devices as easily as transistors, we should be able to mix and match
them with each other and also with transistors in order to achieve
specific functions. Not only can you put them side-by-side with standard
computer and electronic chips, but they tend to work with near 100% reliability.”
The new resonators could provide higher performance than previous MEMS, or microelectromechanical systems.
sensing application, the design enables researchers to precisely
measure the frequency of the vibrating beam, which changes when a
particle lands on it. Analyzing this frequency change allows researchers
to measure minute masses. Similar sensors are now used to research
fundamental scientific questions. However, recent advances may allow for
reliable sensing with portable devices, opening up a range of potential
applications, Rhoads said.
sensors have promise in detecting and measuring constituents such as
certain proteins or DNA for biological testing in liquids, gases and the
air, and the NEMS might find applications in breath analyzers,
industrial and food processing, national security and defense, and food
and water quality monitoring.
smaller your system, the smaller the mass you can measure,” Rhoads
said. “Most of the field-deployable sensors we’ve seen in the past have
been based on microscale technologies, so this would be hundreds or
thousands of times smaller, meaning we should eventually be able to
measure things that much smaller.”
work is based at the Dynamic Analysis of Micro- and Nanosystems
Laboratory at the Birck Nanotechnology Center in Purdue’s Discovery
Park. Other faculty members and graduate students also use the
The researchers have filed a patent application for the concept. The research is funded by the National Science Foundation.
Tunable, Dual-Gate, Silicon-on-Insulator (SOI) Nanoelectromechanical Resonators
Source: Purdue University