What do electronic signatures, fingerprint scans and touch-sensitive robot skin have in common? All three technologies may soon be advancing, thanks to a new system that turns an array of zinc oxide nanowires into tiny LEDs. Each wire illuminates in response to externally-applied mechanical pressure. By analyzing the resulting mosaic of miniscule points of light, a computer is able to produce a high-resolution map of the pressure-applying surface.

The “piezo-phototronic LED” technology has been in development since 2009, and was created by a team from the Georgia Institute of Technology led by Prof. Zhong Lin Wang.

The nanowires are grown on a gallium nitride film, with the light emanating from the “root” where each wire meets with that substrate. When any of those wires are subjected to strain (such as through pressure exerted by a stylus, or fingerprint ridges), a piezolelectric charge develops – the higher the amount of strain, the larger the charge and the brighter the light.

When the subsequent electroluminescent signal is processed, both the shape and the pressure gradient of the surface touching the wires can be ascertained.

According to Wang, the piezo-phototronic LED arrays respond to pressure within milliseconds, plus they shut back off within milliseconds of the pressure being removed. They currently offer a resolution of up to 6,300 dots per inch, although he believes that this figure could be boosted by making the wires smaller.

A paper on the research was published yesterday in the journal Nature Photonics.

Source: Georgia Tech

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