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.
“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.