While most electronics research has its twists and turns, a project currently
under way at the Georgia Institute of Technology offers more than its share
of new angles. That's because the research is entirely focused on bending things.
Georgia Tech researchers are investigating how simple bends made in nanowires,
using a kind of molecular origami, can lead to a completely new class of electronic
parts. "We're utilizing the coupling of piezoelectric and semiconducting properties
to fabricate novel electronic components," says Zhong Lin Wang, a professor
at Georgia Tech's School of Materials Science and Engineering (Fig.
1).
Wang's research explores the relationship between the mechanical and coupled
behavior of piezoelectric nanomaterials. By bending zinc-oxide nanowires and
slightly wider nanobelts, Wang's team has created a series of microscopic field-effect
transistors, diodes, sensors, and even current-producing nanogenerators. The
new devices support a variety of applications.
In a nano-piezotronic transistor, bending a one-dimensional zinc-oxide nanostructure
alters the distribution of electrical charges, allowing control over the current
flowing through the device. Piezotronic sensors, which can measure changes in
the current flowing through them, can be used to detect forces in the nano-
or even pico-Newton range. On the other hand, an electrical connection made
to one side of a bent zinc-oxide nanostructure creates a piezotronic diode that
limits current flow to a single direction.
The new technology, which Wang has dubbed "nano-piezotronics," takes advantage
of a basic property offered by nanowires and nanobelts made out of piezoelectric
materials—bending the structures creates a charge separation that's positive
on one side and negative on the other. The same principle can also be used to
build nanogenerators that create measurable electrical currents when an array
of zinc-oxide nanowires is bent and then released.
Wang sees great potential for his technology in many applications, including
biomedical devices. "Self-powered nanodevices will find key applications in
real-time monitoring of blood pressure and blood sugar level, in-vivo detection
of cancer cells, and wireless measurements of fluid pressure in the brain,"
he says (Fig. 2).
Business and consumer electronics also stand to benefit from nano-piezotronic
technology. "For personal electronics, it offers the possibility of charging
a battery using the energy harvested from human walking, arm swing, stretching
legs, sound/ultrasound waves, wind and air flow, mechanical vibration, and even
thermal noises," Wang says.
Wang points out that nano-piezotronic devices offer a number of inherent benefits
that are unmatched by conventional technologies. Zinc-oxide nanostructures can,
for instance, tolerate large amounts of deformation without damage, allowing
their use in flexible electronics like foldable power sources. Zinc-oxide materials
are also biocompatible, enabling their use in the body without toxic effects,
while nanogenerators' flexible polymer substrates permit implanted devices to
conform to internal structures inside the body.
Perhaps most interesting is that the technology may encourage people to start
thinking about power sources and generation in an almost Zen-like way. "The
nanogenerator will... be used to harvest and recycle energy wasted in our daily
life," Wang says, "such as energy created by pressure change in a tire, mechanical
vibration of a moving car, and vibration of a tent surface."
