Development trend and high efficiency technology o

2022-10-24
  • Detail

The development trend of high brightness LED manufacturing process and high efficiency technology

with the continuous improvement of LED performance, the application market has also expanded rapidly. The hidden reason is that the high brightness LED using Gan and allngap luminescent materials has excellent characteristics such as long life, power saving, shock resistance, low voltage drive, and surpasses bulbs and halogens, and the LED with high luminescent efficiency has been developed in recent years. Therefore, In the future, the development of high brightness LED market will grow more rapidly and widely

among them, white LED is the most obvious one. In the late 1990s, it was more expected by the market under the background of environmental protection and energy conservation, and it also stimulated the industry to rapidly develop related technologies. At present, the main applications of white LED include LCD backlighting and vehicle interior lighting. These markets alone have accounted for about 25% of the overall led sales

on the other hand, the lighting application is in its infancy. The lighting of general buildings often accounts for 20% of the total electricity consumption. In Japan, it has exceeded 100billion kwh per year in the 1990s. Therefore, there are great expectations for a new generation of energy-saving light sources, but unfortunately, so far, white LED can only be used in a relatively small range. Because small white LEDs like 5mm can't get the amount of light required by the environment with just one light bulb or fluorescent lamp. Therefore, if we hope that led can step into building lighting, we need greater breakthroughs in the overall technology

basic structure of high brightness white LED

white LED basically has two ways. One is multi chip type, and the other is single chip type. The former is to package the red, green and blue LEDs together and make them glow at the same time to produce white light. The latter is to use blue, purple and ultraviolet LEDs as light sources and use fluorescent powder to emit white light. In the former way, the characteristics of various LEDs must be combined, and the driving circuit is relatively complex. In the latter single-chip type, there is only one kind of LED, so the circuit design is relatively easy. Single chip type is further divided into two categories, one is blue LED as the light source, and the other is near ultraviolet and ultraviolet light. At present, most white LEDs on the market are blue LEDs combined with YAG phosphors

in the past, only blue LEDs used Gan as the substrate material, but now from the green field to the near ultraviolet LED, they also began to use Gan compounds as the material. And with the expansion of white LED applications, the market expectations for its efficiency are also gradually increasing. From a simple point of view, the pursuit of high efficiency has always been expected by the market and operators. But on the other hand, color rendering will also be an important performance index. If it is only used for display, the luminous color of white may be enough, but from the perspective of lighting, in order to achieve higher efficiency, how to achieve a color close to natural light is very necessary

gan is becoming more and more popular as the base material of high brightness LED.

in the early stage of technological development, only 23 manufacturers in the world developed and produced ganled, but so far, the number of manufacturers has been close to 10 enterprises, so there is also fierce competition in the market. Compared with the initial stage, although the brightness has been improved by leaps and bounds today, the technology is about to face a more difficult threshold, so now both academia and business circles are focusing on technology and research and development. In terms of the current overall research and development direction of ganled, it can be roughly divided into the development directions of high current, short wavelength, high efficiency and so on

so far, the number of ganled producers has been close to 10

how to make LEDs support greater current

in recent years, the industry has been very active in the research and development of LEDs that can achieve considerable brightness with only one LED. Therefore, the technology in this regard also focuses on how to make LEDs support greater current. Generally, 30U ㎡ LED can drive 30mA current at most, but this result is still far from meeting the market expectations, so the goal is to conduct more than 10 times the current into the LED components. Therefore, when the area size of LED can be expanded to 1m ㎡, the next work is how to make the current value reach 350500ma. Because the driving voltage is more than 3V, 1W of power can flow into the chip area of 1m ㎡

in terms of luminescence and color rendering, although such a large power is input into ganled, three quarters of the input power cannot be converted into light to form heat, so the LED will overheat, which will also directly affect the color rendering results of LED. Because the basic characteristic of LED components is that if the temperature rises, the luminous efficiency will decline and cause color rendering deviation, so how to effectively release the exothermic technology that generates a lot of heat has become the key. Therefore, installing led on materials with high heat conductivity and large heat capacity has become a very important problem. At present, most of them use valuable metals or ceramics

high brightness LED process development trend and high efficiency technology

short wavelength brings high-energy quantification of excitation light to improve the luminous efficiency of phosphors

ganled, which started with blue light, has successfully developed high brightness green LED. Although there is also a long wavelength research and development trend at the beginning, the crystallization deterioration caused by the increase of the mixed crystal ratio of inn has been gradually abandoned by the industry. On the other hand, research and development for new applications such as laser substitutes have also begun to be considered, so the industry is actively developing short wavelength research and development. Recently, laboratories in some universities in Japan have successfully developed 250nm LEDs, but the practicality still needs to be considered, because the acceptance of the human eye for the wavelength is about 380nm, so if the wavelength is shorter than 380nm, it is impossible to produce LEDs in the viewable range, or it will produce low output

in order to avoid the above problems, the following solutions are mostly adopted at present:

1 Change the structure of the light-emitting layer: instead of using GaInN structure on the chip of visual field led, AlGaN or AlGaInN with larger eg is used

2. Avoid light absorption loss: if there is a GaN or gainm layer in the chip structure of LED, it will not be able to emit light because of its own light absorption. Therefore, using AlGaN layer as the basis to form all structural layers will have better results, or using Gan as an important n-type bottom layer

3. Reducing crystal defects: the density of crystal defects in short wavelength LEDs will have a great impact on light output and life

if the above three topics can be successfully solved, it is believed that the practical distance of using LED as general lighting can be greatly shortened. At present, the efficiency of Gan white LED can exceed that of white heat bulb and halogen lamp (1525lm/w). However, in order to surpass fluorescent lamp with overwhelming light output (above 5080lm/w), it is necessary to greatly improve the efficiency and increase the amount of light by leaps and bounds. In order to achieve the same light source characteristics as fluorescent lamps, the white photochemical technology formed by the color mixing of fluorescent powder has become a key factor. If we make full use of the efficiency of LED and realize short wavelength, we believe that the luminous efficiency of phosphor will also rise significantly by using the high-energy quantization of excitation light

if we make full use of the efficiency of LEDs and can achieve short wavelength, we believe that the luminous efficiency of phosphors will also rise significantly by using the high-energy quantization of excitation light

the key is to obtain uniform quality on the long crystal plane.

the so-called internal luminous efficiency refers to the proportion of electrons converted into internal light. It can be said to be the luminous efficiency of the central part of the LED. But often because of crystal defects, the luminous efficiency of LED is seriously affected. When Gan is long crystal, because of the difference in lattice number and thermal expansion coefficient between sapphire substrate used on the substrate and GaN single crystal, very high-density migration defects appear in the long crystal direction

generally speaking, the density produced is more than 109C ㎡, which will become fatal if it appears in short wavelength LEDs and laser diodes

in order to reduce this transposition density, there are roughly two methods, one is to prevent the transposition from penetrating into the growth direction, and the other is to suppress the transposition phenomenon. The experimental method is also relatively simple. In the aspect of not allowing the transposition to penetrate into the growth direction, the substrate processed by patterning can be used. When it is vertically grown, it can be grown in the horizontal direction, the growth edge of the defect will be bent towards the horizontal direction, and the vertical direction will achieve the penetration result, so as to reduce the transposition phenomenon. Although this approach can probably achieve a low transposition of less than 107c ㎡, the key to the actual mass production is to obtain uniform quality on the long crystal surface. The latter method is to use the group III nitride substrate with low crystal defect density or the group III nitride with low defect on the substrate that has been formed

it turns out that there is no single crystal bulk in group III nitrides. When using sapphire substrate for hetero epitaxial generation, the root of high density of transposition is the use of this heterogeneous substrate. Of course, using bulk substrate is the best solution. Therefore, the R & D and mass production of various production methods are under active development, and some have begun to enter the stage of sales. On the other hand, compared with the ultimate substrate bulk substrate, the template substrate can realize its similar functions. At present, several manufacturers have begun to produce in small quantities. Although these are not as expensive as bulk substrates, the cost is not low, because considering the high cost and efficiency, they can only be used in lasers, electronic equipment, UVLED, etc

although there are many crystal defects, why can GaN LED components achieve high brightness and the chip will not deteriorate rapidly? These structural phenomena are still being studied by engineers and scholars, but there is no complete theory. Therefore, in order to maximize the material and give full play to the limit of Gan, it is necessary to determine the ideal layer composition and structure design of the light-emitting structure

if you can't achieve a good long crystal, everything is in vain

crystal generation is a key technology for LED component manufacturing, and it is also the key to efficient research and development. No matter how good the structural layer design is, if it cannot achieve good long crystals, everything will be in vain. At the initial stage, the mass-produced ganled is a face-up element. The contact electrode on the p side adopts a transparent thin film electrode, through which light is emitted, and the material uses an Au alloy electrode. Although it has the characteristics of light transmission, the actual light transmission can not meet the needs of practical applications, because a considerable amount of light cannot be emitted through the light coefficient or reflection of the electrode, The luminous efficiency has been unable to be improved after being exposed to a large number of entrepreneurial projects. Therefore, the R & D personnel later considered that because the reflectivity of the face up LED element is very high, it is necessary to use a material with high stability as the electrode to emit light from the side of the sapphire substrate to improve the luminous flux

it is necessary for ordinary LED chips to be fixed through organic materials. The composite materials often obtained reflect high electromagnetic shielding performance. With the heat of this packaging material, the quality of light will be degraded,

Copyright © 2011 JIN SHI