We’ve covered the field of piezoelectronics on and off for the past couple of years, in which certain materials produce electricity when you apply pressure to them. Well, here’s yet another twist: piezo-phototronics. A research team at the Georgia Institute of Technology has developed an LED sensor that produces a high resolution image when you press on it, and it doesn’t require an outside source of electricity. Aside from providing some competition for Lite Brite, the new sensor could develop into a game-changing interface between us and our electronic devices.
The New Georgia Tech LED Sensor
To recap just a bit, the piezoelectric effect occurs when certain materials are placed under strain, for example when you step on them. The effect can also occur when materials are vibrated, as in the piezoelectric “micro-machine” under development at Europe’s Holst Centre.
Conventional piezoelectric devices are typically made with lead, so one of the challenges of the field today is to find safer piezoelectric materials that generate an electric charge efficiently.
The new Georgia Tech LED sensor is based on zinc oxide nanowires grown on a gallium nitride film, which function like LEDs when pressure is applied (hence the term piezo-phototronics).
Researcher Zhong Lin Wang explains:
This is a new principle for imaging force that uses parallel detection and avoids many of the complications of existing pressure sensors…When you have a zinc oxide nanowire under strain, you create a piezoelectric charge at both ends which forms a piezoelectric potential. The presence of the potential distorts the band structure in the wire, causing electrons to remain in the p-n junction longer and enhancing the efficiency of the LED.
The field of nanowires produce an image in pixels. Think of the popular children’s toy Lite Brite on a nanoscale and you’re on the right track, only among other differences the new device has a resolution of up to 6,300 dots per inch.
When written on or otherwise pressed upon, the nanowires under pressure instantly react to produce light. They also “switch off” as soon as pressure is released. According to Wang, the nanowires take 90 milliseconds or less to switch back and forth. The result is that the image is readable in real time from the bottom of the device, and it can be processed and transmitted instantly.
An Energy Efficient Sensor Twofer
Since the new sensor uses human power to light up, it already has one form of energy conservation under its belt, and the research team has also been mindful of the process that would eventually be used to fabricate the device on a commercial scale.
As described by Georgia Tech writer John Toon, the zinc oxide nanowires were grown on the gallium nitride film using a chemical growth technique, which does not require extreme heat.
With the bottoms of the nanowires at the film, the spaces in between were filled with a transparent thermoplastic known as “acrylic glass.” Oxygen plasma was used to remove excess thermoplastic from the top, exposing the tips of the nanowires.
A nickel-gold electrode finishes off the bottom contact, and a thin film of indium-tin oxide serves as the common electrode on top.
Hey, We Built This Amazing Piezo-Phototronic Thingy!
If it proves commercially viable, the new sensor could have practically limitless application in the private sector. Aside from offering a new platform for interacting with consumer electronics, it could be used to develop artificial touch mechanisms as well as security and identification systems based on fingerprints and handwriting.
The “makers” of the future stand to enrich themselves upon this new technology, but in all fairness they should make room for a global group hug. This taxpayer-supported research has been funded by the U.S. Department of Energy and the National Science Foundation along with the Chinese Academy of Sciences.
As for the field of piezoelectronics in general, the applications are just beginning. A couple of early examples of relatively large-scale energy generating potential are the piezoelectric dance floor in Rotterdam and the piezoelectric train stations in Tokyo.
Researchers at Israel’s Technion have also embedded piezoelectric crystals in a highway to generate electricity from passing traffic.
On a smaller scale, another research team at Georgia Tech has developed a lithium-ion battery that charges when you apply pressure, and a U.K. team is working on piezoelectric fiber that could be embedded in clothing.
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