Flexible ‘off the shelf’ white LEDs to be used in wearable displays and non-flat surfaces

Developed by researchers at the National Chiao Tung University, Taiwan, a highly flexible yellow-tinged white-light LED combines off-the-shelf components with design for 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 built from pre-existing technologies, allowing others to easily replicate it. Made from 81 blue LED chips, measuring 1.125 mm x 1.125 mm, mounted onto copper foil covered by a polyimide substrate, the device is very flexible. In order to provide a warm white-yellow light, the researchers added a layer of yellow phosphor film coated in polydimethylsiloxane (PDMS), which is a silicone-based substance known for its stability, transparency, and elasticity.

“Compared to organic LED, this design of flexible LED is 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 Lin Chien-Chung, an associate professor at the College of Photonics, National Chiao Tung University, Taiwan.

The thickness of the silicone between the film and the LED chips determines how much light is dispersed and reflected; if the platform is too thin, the individual point sources of light are clearly eminent, but if the thickness is just right, it provides a uniform sheet of light.

To test its durability, the device was ran for a standard 1,000 hours, finding that the LED light’s emission decayed by only five percent, and its potential use for wearables was demonstrated through bending tests, holding a power output curvature with a 1.5-cm radius and exhibiting a light efficiency of 120 lumens per watt.

“Because the components are all available by current technology, the combined reliability is 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.”

Published in the journal, Optics Express , the paper can be found here, and while no release date is confirmed, the device is expected to make it to the market sooner rather than later.

Source: Gizmag