Home > Press > Device for capturing signatures uses tiny LEDs created with piezo-phototronic effect: Your signature in lights
This schematic shows a device for imaging pressure distribution by the piezo-phototronic 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.
Credit: Courtesy of Zhong Lin Wang |
Abstract:
Researchers at the Georgia Institute of Technology want to put your signature up in lights - tiny lights, that is. Using thousands of nanometer-scale wires, the researchers 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.
The sensor device could provide an artificial sense of touch, offering sensitivity comparable to that of the human skin. Beyond collecting signatures and fingerprints, the technique could also be used in biological imaging and micro-electromechanical (MEMS) systems. Ultimately, it could provide a new approach for human-machine interfaces.
"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 Zhong Lin Wang, Regents' professor and Hightower Chair in the School of Materials Science and Engineering at Georgia Tech. "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 (ZnO) nanowires that are part of the device operate as tiny light emitting diodes (LEDS) when placed under strain from the mechanical pressure, allowing the device to provide detailed information about the amount of pressure being applied. Known as piezo-phototronics, the technology - first described by Wang in 2009 - provides a new way to capture information about pressure applied at very high resolution: up to 6,300 dots per inch.
The research was scheduled to be reported August 11 in the journal Nature Photonics. It was sponsored by the U.S. Department of Energy's Office of Basic Energy Sciences, the National Science Foundation, and the Knowledge Innovation Program of the Chinese Academy of Sciences.
Piezoelectric materials generate a charge polarization when they are placed under strain. The piezo-phototronic devices rely on that physical principle to tune and control the charge transport and recombination by the polarization charges present at the ends of individual nanowires. Grown atop a gallium nitride (GaN) film, the nanowires create pixeled light emitters whose output varies with the pressure, creating an electroluminescent signal that can be integrated with on-chip photonics for data transmission, processing and recording.
"When you have a zinc oxide nanowire under strain, you create a piezoelectric charge at both ends which forms a piezoelectric potential," Wang explained. "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 efficiency increase in the LED is proportional to the strain created. Differences in the amount of strain applied translate to differences in light emitted from the root where the nanowires contact the gallium nitride film.
To fabricate the devices, a low-temperature chemical growth technique is used to create a patterned array of zinc oxide nanowires on a gallium nitride thin film substrate with the c-axis pointing upward. The interfaces between the nanowires and the gallium nitride film form the bottom surfaces of the nanowires. After infiltrating the space between nanowires 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 is then used to form ohmic contact with the bottom gallium-nitride film, and a transparent indium-tin oxide (ITO) film is deposited on the top of the array to serve as a common electrode.
When pressure is applied to the device through handwriting, nanowires are compressed along their axial directions, creating a negative piezo-potential, while uncompressed nanowires have no potential.
The researchers have pressed letters into the top of the device, which produces a corresponding light output from the bottom of the device. This output - which can all be read at the same time - can be processed and transmitted.
The ability to see all of the emitters simultaneously allows the device to provide a quick response. "The response time is fast, and you can read a million pixels in a microsecond," said Wang. "When the light emission is created, it can be detected immediately with the optical fiber."
The nanowires stop emitting light when the pressure is relieved. Switching from one mode to the other takes 90 milliseconds or less, Wang said.
The researchers studied the stability and reproducibility of the sensor array by examining the light emitting intensity of the individual pixels under strain for 25 repetitive on-off cycles. They found that the output fluctuation was approximately five percent, much smaller than the overall level of the signal. The robustness of more than 20,000 pixels was studied.
A spatial resolution of 2.7 microns was recorded from the device samples tested so far. Wang believes the resolution could be improved by reducing the diameter of the nanowires - allowing more nanowires to be grown - and by using a high-temperature fabrication process.
In addition to Wang, the research team also included Caofeng Pan, Lin Dong, Guang Zhu, Simiao Niu, Ruomeng Yo, Qing Yang and Ying Liu, all associated with Georgia Tech. In addition, Pan is associated with the Beijing Institute of Nanoenergy and Nanosystems in the Chinese Academy of Sciences.
This research was supported by the U.S. Department of Energy (DOE), Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-FG02-07ER46394; the National Science Foundation (NSF) under award CMMI-040367; and by the Knowledge Innovation program of the Chinese Academy of Sciences under KJCX2-YW-M13. The opinions and conclusions expressed are those of the authors and do not necessarily represent the official views of the DOE or NSF.
####
For more information, please click here
Contacts:
John Toon
404-894-6986
Copyright © Georgia Institute of Technology
If you have a comment, please Contact us.Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
Related News Press |
News and information
Simulating magnetization in a Heisenberg quantum spin chain April 5th, 2024
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Good as gold - improving infectious disease testing with gold nanoparticles April 5th, 2024
Law enforcement/Anti-Counterfeiting/Security/Loss prevention
With VECSELs towards the quantum internet Fraunhofer: IAF achieves record output power with VECSEL for quantum frequency converters April 5th, 2024
Researchers’ approach may protect quantum computers from attacks March 8th, 2024
Display technology/LEDs/SS Lighting/OLEDs
Utilizing palladium for addressing contact issues of buried oxide thin film transistors April 5th, 2024
Light guide plate based on perovskite nanocomposites November 3rd, 2023
Imaging
Nanoscale CL thermometry with lanthanide-doped heavy-metal oxide in TEM March 8th, 2024
The USTC realizes In situ electron paramagnetic resonance spectroscopy using single nanodiamond sensors November 3rd, 2023
Govt.-Legislation/Regulation/Funding/Policy
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Chemical reactions can scramble quantum information as well as black holes April 5th, 2024
MEMS
Sensors
Discoveries
Chemical reactions can scramble quantum information as well as black holes April 5th, 2024
New micromaterial releases nanoparticles that selectively destroy cancer cells April 5th, 2024
Utilizing palladium for addressing contact issues of buried oxide thin film transistors April 5th, 2024
Announcements
NRL charters Navy’s quantum inertial navigation path to reduce drift April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Interviews/Book Reviews/Essays/Reports/Podcasts/Journals/White papers/Posters
Simulating magnetization in a Heisenberg quantum spin chain April 5th, 2024
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Research partnerships
Discovery points path to flash-like memory for storing qubits: Rice find could hasten development of nonvolatile quantum memory April 5th, 2024
Researchers’ approach may protect quantum computers from attacks March 8th, 2024
'Sudden death' of quantum fluctuations defies current theories of superconductivity: Study challenges the conventional wisdom of superconducting quantum transitions January 12th, 2024
The latest news from around the world, FREE | ||
Premium Products | ||
Only the news you want to read!
Learn More |
||
Full-service, expert consulting
Learn More |
||