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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’ study is described in detail in the paper, “High-resolution electroluminescent imaging of pressure distribution using a piezoelectric nanowire LED array,” by Caofeng Pan et al in Nature Photonics (2013), published online on 11th August 2013. DOI:10.1038/nphoton.2013.191
This research 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.
Latest GaN transistor developments to be
presented at summit Characterisations and performance of D-Mode GaN HEMT transistor used in a cascode configuration revealed
A team of experts on gallium nitride technologies from GaN Systems Inc, a developer of gallium nitride power switching semiconductors, is presenting a major conference paper at the 224th ECS Electrochemical Energy Summit (San Francisco, California October 27 – November 1).
Schematic showing 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.
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,” says Wang. “When the light emission is created, it can be detected immediately with the optical fibre.”
The nanowires stop emitting light when the pressure is relieved. Switching from one mode to the other takes 90 milliseconds or less, Wang says.
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 5 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 µm 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.
August/September 2013
www.compoundsemiconductor.net 173
“Characterisations and performance of D-Mode GaN HEMT transistor used in a cascode configuration” authored by Tom MacElwee, John Roberts, Hughes Lafontaine, I. Scott, Greg Klowak, and Lyubov Yushyna will be presented during the GaN and SiC Power Technologies symposium.
GaN Systems has developed proprietary gallium nitride high power transistors for clean technology power conversion applications, enabling superior switching efficiencies over current silicon based solutions. These devices offer substantial benefits to switching power supply designs, inverters, hybrid and electric vehicles, battery management and power factor correction.
The paper reports on D-mode HEMT device performance when configured in cascode mode, including basic parameters of the device and its integration into a PQFN package. A detailed discussion demonstrates the 500V 3.3A switching characteristics of the cascode and proves excellent switching performance with measured voltage slew rates as large as 70 V/ns.
The GaN D-mode HEMT device developed in the work covered by the paper was fabricated using a conventional RF GaN process flow on 3” 4H SI-SiC starting substrate. The SiC substrate should allow for excellent thermal performance and high voltage operation of the switching device due to the semi- insulating nature of the SiC substrate.
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