There is no doubt that the world needs high-brightness light-emitting diodes (HB LEDs), not only high-brightness white LEDs (HB WLEDs), but also high-brightness LEDs of various colors, and the future is more active and demanding. Brightness LED (UHD LED).
Replacing the original EL backlight and CCFL backlight of the handheld device with LED backlight not only makes the circuit design simpler and easier, but also has higher resistance to external forces. Replacing the original CCFL backlight of LCD TVs with LED backlights is not only more environmentally friendly, but also displays more vivid and beautiful. LED lighting instead of white light, halogen light and other lighting, not only more bright and energy-saving, the use is also longer, and the lighting response is faster, can reduce the rear car collision rate when used in the vehicle lights. Therefore, LEDs can only be used in the state of the electronic device in the past, to become the backlight of the liquid crystal display, and then extended to electronic lighting and public display, such as car lights, traffic lights, information billboards, large video walls, and even It is the illumination inside the projector, etc., and its application continues to extend. More importantly, the brightness efficiency of LEDs is doubled every 24 months, just like Moore's Law. In the past, white LEDs could only be used to replace incandescent and halogen lamps that consume too much power. The luminous efficiency is in the range of 10 to 30 lm/W. However, after the white LED breaks through 60 lm/W or even 100 lm/W, even fluorescent lamps and high-pressure gas discharge lamps are beginning to feel threatened.
Although LEDs continue to enhance brightness and luminous efficiency, in addition to the core patented technologies such as phosphor and light mixing, packaging will be an increasingly challenging challenge and a double challenge. On the one hand, packaging must allow LEDs. It has the highest light extraction rate and the highest luminous flux, which minimizes the light loss, and also pays attention to the divergence angle of the light, the light uniformity, and the compatibility with the light guide plate. On the other hand, the package must have the best heat dissipation of the LED, especially HB (high brightness) almost means HP (high power, high power), the current value of the incoming and outgoing LEDs continues to increase, if not good heat dissipation, Not only will the brightness of the LED be reduced, but the life of the LED will also be shortened. Therefore, the continuous pursuit of high-brightness LEDs, if the package technology used does not have the corresponding enhancement, then the high-brightness performance will be discounted. Therefore, this article will discuss more about the packaging technology of HB LEDs, including the discussion of optical communication. Also includes discussion on thermal conductivity.
Bare layer: "quantum well, multi-quantum well" enhances "light conversion efficiency"
Although this article is mainly about the enhancement of the luminous flux of the LED package, it is necessary to first explain the bare part of the deeper core. After all, the improvement of the bare crystal structure can also greatly increase the luminous flux. The first is to enhance the efficiency of light conversion, which is also the most fundamental source. Only 15% to 2% of the electricity used per watt of LED is converted into light energy, and the rest are converted into heat energy and dissipated (waste heat). The key to improving this conversion efficiency is on the pn junction. The pn junction is the main illuminating heating position of the LED. The structural design change through the pn junction can improve the conversion efficiency. At present, quantum wells (Qumbo) are built on the pn junction to increase the proportion of electricity converted into light energy. Further, efforts will be made to more chiseling, that is, multiple quantum wells. (Multiple Quantum Well; MQW) technology.
"Refueling and remodeling, light and light folding" to raise the "lighting efficiency"
If the light conversion efficiency is difficult to re-require, further steps must be taken from the level of light extraction efficiency. There are quite a few different methods at this level. Different materials are different according to different materials. Currently, the two compounds commonly used for HB LEDs are AlGaInP and GaN/ InGaN, the former is used to produce high-brightness orange, orange, yellow, and green light, while the latter is used to produce green, emerald, and blue light, and to produce near-ultraviolet, blue-green, and blue light using InGaN. The method includes changing the physical geometry (transverse to vertical), changing the material of the substrate, adding a new material layer, changing the bonding mode of the material layer, and different surface treatment of the material. However, no matter how it changes, it basically does not deviate from two principles: First, reduce the shadow and increase the light transmittance. Second, strengthen the utilization of light refraction and reflection. For example, in the past, AlGaInP LEDs used GaAs as the substrate. However, GaAs on the black surface occludes half of the light emitted from the pn junction, causing waste of light energy. Therefore, a transparent GaP material is used as the substrate. Another example is Nichia, which uses a p-type electrode to form a mesh pattern to increase the transparency of the p-pole, reduce light obstruction, and increase light transmission. As for the increase of the fold reflection, a layer of DBR (Distributed Bragg Reflector) reflective layer is added to the structure of the AlGaInP, and the other side of the light source is folded to the same side. In GaN, the substrate material is replaced with sapphire (aluminum oxide) to increase the reflection, and the surface of the substrate is designed to be embossed, thereby increasing the scattering angle after light reflection, thereby increasing the light extraction rate. Or use a substrate of SiC material such as OSRAM in Germany, and design the substrate as a bevel, which also helps to increase the reflection, or add a silver, aluminum metal mirror layer.