Electronic Design

Nanowires Get Bent Out Of Shape For New Technology

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."

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