Researchers Create Highly Flexible, Efficient White LEDs
August 21, 2015 | OSAEstimated reading time: 2 minutes
Researchers from National Chiao Tung University, Taiwan have created highly flexible, efficient white LEDs with potential use in wearable displays and non-flat surfaces, such as curved and flexible television screens. While the design itself is new, the LED was completely fabricated from pre-existing technologies, allowing others to easily replicate and build on the platform.
"Compared to organic light-emitting diodes, this design of flexible LEDs can be very attractive, due to the low cost, prolonged lifetime and high efficiency. In addition, all of the technologies associated with this design are currently available," said Chien-Chung Lin, associate professor, College of Photonics, National Chiao Tung University, Taiwan.
A paper by Lin, Professor Hao-Chung Kuo, and their research team appears this week in Optics Express, a journal published by The Optical Society (OSA). This is their first flexible LED device, while their previous work had involved conventional gallium-nitride LEDs.
The researchers’ off-the-shelf LED device gets its flexibility from its two primary materials, polyimide and polydimethylsiloxane. To construct it, Lin and his colleagues first covered a polyimide substrate with copper foil shielding tape. In a process known as flip-chip bonding, which reduces thermal resistance and results in higher heat dissipation than traditional wire bonding, they mounted 81 Blue LED chips, measuring 1.125 mm x 1.125 mm, to the foil in an upside down position.
To provide a warm white-yellow light, the researchers then added another layer consisting of a yellow phosphor film that had been mixed and spin-coated in polydimethylsiloxane, or PDMS, a widely used silicone-based organic polymer. It was chosen for its high degree of transparency, stability, and flexibility. The final film measured five centimeters by five centimeters, but there is no reasonable limitation to the size of the film.
The researchers ran the device for a standard 1,000 hours, to test its durability, finding that its emission decayed by only 5%. Its potential for use in wearables was demonstrated when subjected to bending tests. It held its power output when bent to a curvature with a 1.5-cm radius. It also exhibited a light efficiency of 120 lumens per watt.
"Because the components are all available by current technology, the combined reliability can be very good," Lin said. "Most of the novel processes or materials require a lengthy procedure to verify their reliability, but our design uses only available parts to avoid this issue."
Future work for Lin and his colleagues includes reducing the LED device's thickness, as well as increasing its functional lifetime and energy efficiency.
About Optics Express
Optics Express reports on new developments in all fields of optical science and technology every two weeks. The journal provides rapid publication of original, peer-reviewed papers. It is published by The Optical Society and edited by Andrew M. Weiner of Purdue University.
About The Optical Society
Founded in 1916, The Optical Society (OSA) is the leading professional organization for scientists, engineers, students and entrepreneurs who fuel discoveries, shape real-life applications and accelerate achievements in the science of light. Through world-renowned publications, meetings and membership initiatives, OSA provides quality research, inspired interactions and dedicated resources for its extensive global network of optics and photonics experts. OSA is a founding partner of the National Photonics Initiative and the 2015 International Year of Light.
Suggested Items
Trouble in Your Tank: Supporting IC Substrates and Advanced Packaging, Part 5
03/19/2024 | Michael Carano -- Column: Trouble in Your TankDirect metallization systems based on conductive graphite or carbon dispersion are quickly gaining acceptance worldwide. Indeed, the environmental and productivity gains one can achieve with these processes are outstanding. In today’s highly competitive and litigious environment, direct metallization reduces costs associated with compliance, waste treatment, and legal issues related to chemical exposure. What makes these processes leaders in the direct metallization space?
AT&S Shines with Purest Copper on World Recycling Day
03/18/2024 | AT&SThe Styrian microelectronics specialist AT&S is taking World Recycling Day as an opportunity to review the progress that has been made in recent months at its sites around the world in terms of the efficient use of resources:
Matrix to Exhibit at IPC APEX EXPO 2024 in Anaheim, CA
03/05/2024 | MatrixMatrix will be exhibiting at IPC APEX EXPO 2024, to be held on April 9-12, 2024, at the Anaheim Convention Center, Anaheim, CA.
The Chemical Connection: Getting to Know Your Vendor
02/16/2024 | Don Ball -- Column: The Chemical ConnectionAfter working for a capital equipment supplier for almost 50 years, I’ve found that the most important part of getting to know your vendor is good communication among all parties. While contact between fabricators of a constantly changing product line and the designers of those products may occur daily or weekly, conversations between you and your equipment supplier may be years apart. That lengthy gap often means that previous contacts may have been promoted, retired, or moved on to other opportunities. You may have also migrated to a new supplier with whom you have little or no history. In either case, you will be interacting with someone you are unfamiliar with (as they are with you). Therefore, it is essential for both sides to communicate clearly so expectations will align.
EIPC Winter Conference 2024, Day 2: A Closer Look at Global Trends
02/14/2024 | Pete Starkey, I-Connect007The opening session of the second day’s conference proceedings focused on global PCB trends and was introduced and moderated by Dr. Michele Stampanoni, vice president of strategic sales and business development at Cicor Group in Switzerland. He opened the session with Dr. Hayao Nakahara’s knowledgeable and enlightening video presentation on the IC substrates industry.