Today, the white LED is still the existence of luminous uniformity is poor, the closed material life is not long, but can not play to the advantages of white LED applications are expected. Demand perspective, not only the general lighting purposes, with the extensive use of mobile phones, LCD TV, automotive, medical and other positive appearance, making the most appropriate development of stable white LED technology research also quite concerned.
■ to increase the amount of light emitted by raising the chip area
Expect to improve the luminous efficiency of white high power led, there are two directions, is to increase the area of the LED chip, that is, the current area of 1m square meters of small chips, light emitting area increased to more than 10m square meters in order to increase the amount of light-emitting or with several small chips packaged in the same module. Although the area of the LED chip to be large, able to take a much higher brightness, but a large area, just the opposite phenomenon can also occur in the application process and results. Therefore, in view of such problems, some LED manufacturers in accordance with the improvement of the electrode structure, and the structure in flip-chip, the chip surface to improve to achieve 50lm / W luminous efficiency.
Emitting layer is very close to the vicinity of the package, part of the white LED flip-chip package, for example, shed light emitting layer to the external, so the advantages of the electrode will not be obscured, but the drawback is that the generated heat is not easy to dissipate. Is not the chip surface to improve, coupled with the increase in chip area absolutely breath to enhance the brightness, when outward scattering of light from inside the chip, chip part of these improvements can not be a reflection, so will be on the light extraction some limits on the calculation, the best play of the light efficiency of LED chip size is about 7m square meters.
■ use of the package a number of small-area LED chip, the rapid increase in luminous efficiency
And compared to the large area LED Blue 150W chip, low power LED chips packaged into a module, so is able to quickly achieve high brightness requirements, for example, the Citizen will be 8 small LED package together, so that the luminous efficiency of the module reached 60lm / W, called the first of the industry.
However, this approach also led to some doubts, because the LED 400W package with a module, the module must be placed in some of the insulating material in order to avoid short circuit occurs between the LED chip, however, such a to will increase a lot of cost. The Citizen's explanation, in fact, the magnitude of the cost is fairly small, as compared to the overall cost ratio less than one percent of these insulating materials and can make use of existing materials do insulation applications, these insulating materials do not need to re-development, do not need to add new equipment to cope.
Citizen of the explanation is theoretically reasonable, but for less experienced operators, this is a challenge, because in terms of yield, R & D, production engineering needs to be overcome. Of course, there are other ways to achieve the goal to improve the luminous efficiency, many retailers have seen the LED 200W on sapphire substrate to produce structure uneven Tan, it may be possible to improve light output, so, gradually towards the wafer surface Texture Photonics crystal architecture. For example, Germany, OSRAM is out of this framework development of GaN Thin high-brightness LEDs, OSRAM is formed in the InGaN layer metal film and then stripped sapphire. In this way, the metal film will produce the effect of mapping to get more light out, and OSRAM information, such a structure can get 75% of the light extraction efficiency.