Light-emitting diodes (LEDs) have evolved into the mainstream of solid-state lighting technology and are widely used in lighting, display backlight, automotive lighting industry, etc., and advanced flexible LED technology has also attracted more and more people to invest in research and development. According to the latest issue of the international optical journal OpticsExpress, the research team of National Chiao Tung University has developed a highly efficient and flexible white LED chip, which is expected to be applied to large-area lighting, wearable devices and displays in the future.
More commonly known as flexible sheet-like light sources are organic light-emitting diodes (OLEDs). Lin Jianzhong, an associate professor at the National Chiao Tung University Optical System, said that the former is not only more efficient and has a longer life, but also has lower cost and very competitive performance compared to OLEDs.
The flexible White LED, published in OpticsExpress, is about 5x5cm in size. It uses a Polyimide (PI) flexible substrate covered with a layer of copper foil that passes through a photolithography process with oxygen plasma Etch the electrode pattern. The research team used flip-chip bonding technology, the 81 1.143x1.143mm blue LED chip size, with anisotropic conductive adhesive (anisotropicconductivefilm) adhesion to the substrate.
In order to generate white light, an additional layer of polydimethylsiloxane (PDMS) phosphor film containing a yellow phosphor "Y3Al5O12: Ce3 +" and a red phosphor "CaAlSiN3: Eu2 +" needs to be added to the LED chip. . PDMS non-toxic and non-flammable, with high transmittance, high stability and high flexibility and so on.
Flexible white LED chip structure
With flip-chip LED, PI substrate and PDMS phosphor film, the success of creating a thickness of about 6mm flexible white LED chip, can emit warm white or cool white light. At the color temperature of 3,000K and 5,000K, the maximum luminous efficiency of up to 81lm / W and 120lm / W, not only high luminous efficiency, the resulting light source distribution is uniform, the uniformity of 85%. As for the degree of flexibility, the radius of curvature can reach 15 mm.
Flux changes in flexing performance is not much impact, suitable for flexible displays and lighting
In addition, the flexible white LED to indoor temperature of 25 degrees Celsius, 1,000 hours of service life test, the measured results of 2.5% loss of luminous efficiency, estimated 10,000 hours will be depleted 22%. Although the service life is not as durable as the general LED lighting, it is expected to further break through the technology while continuing to enhance the overall performance of the flexible white LED. In the future, more applications will actually be imported.
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