A doctoral student in materials science and engineering who developed a method to manufacture brighter, more energy-efficient LEDs is the recipient of the 2013 Rensselaer Polytechnic Institute (RPI) Lemelson-Rensselaer Student Prize.
First presented in 2007, Ming Ma is the seventh recipient of the $30,000 prize, which is awarded to an RPI senior or graduate who has created or improved a product or process, applied a technology in a new way or otherwise demonstrated remarkable inventiveness. He is among three 2013 Lemelson-MIT Collegiate Student Prize winners announced this week.
“Invention is critical to the US economy. It is imperative we instill a passion for invention in today’s youth, while rewarding those who are inspiring role models,” said Joshua Schuler, executive director of the Lemelson-MIT Program. “This year’s Lemelson-MIT Collegiate Student Prize winners and finalists from the Massachusetts Institute of Technology, Rensselaer Polytechnic Institute and the University of Illinois at Urbana-Champaign prove that inventions and inventive ideas have the power to impact countless individuals and entire industries for the better.”
Ma’s patent-pending invention holds the promise of hastening the global adoption of LEDs and of reducing the overall cost and environmental impact of illuminating homes and businesses.
Conventional incandescent and fluorescent light sources are increasingly being replaced by more energy-efficient, longer-lived and environmentally friendlier LEDs, but LEDs still suffer from challenges related to brightness, efficiency and performance. With his project, “Graded-refractive-index (GRIN) Structures for Brighter and Smarter Light-Emitting Diodes,” Ma faced these problems head-on, tackling a fundamental, well-known technical shortcoming of LED materials: low light-extraction efficiency.
Currently, most unprocessed LEDs have a light-extraction efficiency — the percentage of produced light that actually escapes from the LED chip — of only 25 percent, which means 75 percent of light produced gets trapped within the device itself.
One resolution is to roughen the surface of LEDs to create nanoscale gaps and valleys that enable more light to escape. Surface roughening leads to brighter and more efficient light emission, but the roughening process creates random features on the LED’s surface that do not allow for complete control over other critical device properties, such as surface structure and refractive index.
Ma’s solution was to create an LED with well-structured features on the surface to minimize the amount of light reflected back into the device, thus boosting the amount of light emitted. He invented a process for creating LEDs with many tiny star-shaped pillars on the surface. Each pillar is made up of five nanolayers, specifically engineered to help “carry” the light out of the LED material and into the surrounding air.
The technology has demonstrated a light-extraction efficiency of 70 percent, meaning that 70 percent of light escapes and only 30 percent is trapped inside the device. In addition, GRIN LEDs also have controllable emission patterns and enable a more uniform illumination than today’s LEDs.
Overall, Ma’s innovation could lead to entirely new methods for manufacturing LEDs with increased light output, greater efficiency and more controllable properties than both surface-roughened LEDs and the LEDs currently available in the marketplace.
“The innovation of GRIN LEDs should not be underestimated — Ma’s invention is the first viable approach for high-efficiency LEDs with a controllable far-field emission pattern,” said E. Fred Schubert, the Wellfleet Senior Professor in the Future Chips Constellation at Rensselaer and a faculty member of the university’s Department of Electrical, Computer, and Systems Engineering and Department of Physics, Applied Physics, and Astronomy. “This is an important development for LED lighting, and it is already capturing the attention of industry.”
At RPI, Ma has been the first author on five research papers and has co-authored several studies. He is also a reviewer of Optics Letters and Optics Express.
Ma grew up in Jiangxi Province in southeast China and became interested in advanced materials as an undergraduate student at Fudan University in Shanghai, which inspired him to study LEDs as a graduate student at RPI. Upon completion of his doctoral degree later this year, he plans to continue researching materials and LEDs in academia or industry.
The Lemelson-Rensselaer Student Prize is funded through a partnership with the Lemelson-MIT Program, which has awarded the $30,000 Lemelson-MIT Student Prize to outstanding student inventors at MIT since 1995.
In 2008, the Lemelson-Rensselaer Student Prize also was awarded for LED innovation. Martin Schubert, then a doctoral student in electrical, computer and systems engineering, developed the first polarized LED, an innovation that could vastly improve LCD screens, conserve energy, and usher in the next generation of ultraefficient LEDs. (See: Student Awarded for New LED)