Mechanical Pressure Converted to Light Signals

A new sensor device uses thousands of nanometer-scale wires to convert mechanical pressure into light signals that can be captured and processed optically.

Developed at the Georgia Institute of Technology (Georgia Tech), the sensor could be used in biological imaging and microelectromechanical systems. With the potential to provide an artificial sense of touch with sensitivity comparable to that of human skin, the device may provide a new approach for human-machine interfaces.

Georgia Institute of Technology researchers, led by professor Zhong Lin Wang, have developed a sensor device that converts mechanical pressure — from a signature or a fingerprint — directly into light signals that can be captured and processed optically. Courtesy of Georgia Tech, photo by Gary Meek.

"You can write with your pen, and the sensor will optically detect what you write at high resolution and with a very fast response rate," said Regents’ professor and Hightower Chair at Georgia Tech, Zhong Lin Wang. "This is a new principle for imaging force that uses parallel detection and avoids many of the complications of existing pressure sensors."

Individual zinc oxide nanowires operate as tiny LEDs in the device, providing detailed information when placed under strain from mechanical pressure. Known as piezophototronics, the technology provides a new way to capture information about pressure applied at very high resolution, up to 6300 dots per inch.

Nanowires are compressed along their axial direction when pressure is applied to the device, creating a negative piezo potential, while uncompressed nanowires have no potential. Differences in the amount of pressure applied translate to differences in light emitted from the root, where the nanowires contact gallium nitride film.

This schematic shows a device for imaging pressure distribution by the piezophototronic effect. The illustration shows a nanowire-LED based pressure sensor array before (a) and after (b) applying a compressive strain. A convex character pattern, such as "ABC," molded on a sapphire substrate, is used to apply the pressure pattern on the top of the indium-tin oxide (ITO) electrode. Courtesy of Zhong Lin Wang.

The ability to see all of the emitters simultaneously allows the device to provide a quick response. "You can read a million pixels in a microsecond," Wang said. "When the light emission is created, it can be detected immediately with the optical fiber."

To fabricate the device, a low-temperature chemical growth technique creates a patterned array of zinc oxide nanowires on a gallium nitride thin-film substrate. The interfaces between the nanowires and the gallium nitride film form the bottom surfaces of the nanowires. After the space between nanowires is infiltrated with a PMMA thermoplastic, oxygen plasma is used to etch away the PMMA enough to expose the tops of the zinc oxide nanowires.

A nickel-gold electrode forms ohmic contact with the bottom gallium-nitride film, and a transparent indium-tin oxide film is deposited on top of the array to function as a common electrode.

The research was published this week in Nature Photonics.

For more information, visit: www.gatech.edu