26 June 2016

LED technology and application

Led components in the global market size of about $2005 in 5.74 billion, 50% in Japan, 20% in Taiwan. Application as well as various types of lighting, outdoor architecture and mobile phone back light applications, such as the industry is actively looking for a variety of new applications. This paper describes the basic principle of LED, the trend of the technology and market dynamics.

The LED industry trends

Light-emitting diode (LED is illuminated, using principle of optical radiation emitting light colors and materials have very close relationship. The development of LED technology, from the earliest days of red, green, all the way to the successful development of blue leds, only by integrating red, blue, green, or blue phosphor powder mixed with yellow phosphor, become white LED. The biggest benefits, successfully developed a white LED can be applied to multiple wavelength, make application extensive and profound.

1, the development of LED industry

Started as early as in 1907, people found that some of the semiconductor material made of a diode to the in light of the physical phenomena, but produce a red LED luminous efficiency is 1969 years. People developed the blue LED in 1994-1995, and has realized the real commercialization in 1998. From 2000 to 2002, researchers constantly pursue cost-effectiveness, the LED into the mobile phone back light market success. Today, LED has produced more than 30 years, various types of LED, the LED is used as the secondary
Fitted with development of products and LED products, such as white LED drive) is developing rapidly, new products are listed, and has developed into a new industry.

Einstein liked to tell about LED technology research and development path, the story, is to develop blue leds, silicon carbide (SiC) and gallium nitride (GaN) battle over the two branches. This also is many r&d team hard into the development of blue LED components, must be painful choice of two different roads.
Before, many large companies are global investment research and development of SiC, a Japanese company specializes in phosphor result - the Japanese and the chemical company (NichiaChemicalIndustriesLtd.) research and development personnel Mr Nakamura to fix two (ShujNakamura) in 1994 and 1995, the gallium nitride (GaN) a major breakthrough in the research, and has shocked global patent. The breakthrough of the research and development personnel, leading to the top executive of a consortium including Sony and Toshiba are to do for their wrong decision lead to backward technology and apologize. The Nakamura technology breakthrough, let the gallium nitride (GaN) camp quickly beyond formal SiC.

Originally do Nichia phosphor business due to the success of on the blue LED technology, make its annual turnover from the rapid development of about $100 million to $2003 in 900 million. And originally the patent of the company prepared to Nakamura bounty is 2 million yuan, the yen after a lawsuit, Nichia convicted should give the researcher RMB 200 million yen.

Ou lang company LED encapsulation trend

After blue light LED technology breakthrough, white LED launched a wide range of LED application, from the show, directives and mobile source, into the brewing - TV LCD back light, all sorts of door knocking by continual creative new opportunities.

2, LED technology

LED is the silicon (Si) in the 1950 s after semiconductor technology, from three to five family - V (III) the development of the compound semiconductor semiconductor devices. LED light-emitting principle is the use of electrons and holes in the semiconductor and emit photons, is different from the light bulb need to operate under the high temperature over 3000 degrees, also don't like to use high voltage excitation beam fluorescent lamp, LED and general electronic components are the same, only need to 2 to 4 v voltage, at room temperature can be normal action, therefore its life is longer than traditional light source.

Emitted from the LED color, mainly depends on the electron and hole energy release of the combination of high and low, which is decided by the energy gap of the semiconductor materials used. The wavelength of the same kind of material which is very nearly, so each of the LED light color is very pure, compared with the traditional light source is mixed with a variety of color, LED is a kind of digital light source.

LED chip size can be optional cut by purpose, common size is about 0.3 1.0 mm, compared with the traditional lamp or fluorescent lamp, the volume is relatively small. In order to use convenient, LED packaging, often use resin about 5 mm made of various shapes, strong shock resistance.

The basic structure of LED

LED the production process and production of silicon wafer are similar In IC, the first to use chemical III families of the ultra high purity elements In the periodic table - aluminum (Al), gallium (Ga), indium (In), and V elements, nitrogen (N), phosphorus (P), arsenic (As) As materials, under the high temperature reaction become compounds, through crystal growth technology, made from a single crystal rods, after cutting, grinding and polishing In chips, again As a substrate (substrate), use of epitaxial technology will grow luminescent material In the substrate, made of lei chip after semiconductor gold-plated and etching process, through the fine cut processed into LED grain.

It is important to note that in addition to all common visible light, LED and not visible light, such as "uv" and "infrared", such as TV remote control is a kind of infrared applications, its wavelength is about 900 nm, the ultraviolet light is because has the function of sterilization, so is widely used in medical use.

(1) improve the luminous intensity and luminous efficiency

As light applications, there are a few of the MCD luminous intensity can also, but made up of LED digital tube or character is brightness is not enough, to be used for outdoor signal or standard , according to its brightness is too low, cannot satisfy the requirement of use. So the LED the main development direction is to improve the luminous intensity (i.e., generally referring to improve brightness).

The evolution of the InGaAlP luminous efficiency and nGaNLED chip. For the InGaN blue leds, a, b for InGaN green leds

With the semiconductor material and the development of semiconductor technology, equipment, increasing the brightness of the leds, developed the high brightness and high brightness LED, and constantly create new records. Φ 5 standard package, a red glow, Angle difference of the LED, for example, different production date the luminous intensity of LED as shown in table 1.

Table 1 year of different production LED the luminous intensity of comparison

Can be seen from table 1, nearly 30 years LED the luminous intensity of raised about 8000 times. 1969-1987, LED the luminous intensity is very low, development is slow, but the brightness of LED 1994-2005 has a great development. Table 1 lists the luminescence intensity is not the highest. For example, AlInGaP technique adopted in GaAs substrate made of Φ 5, red light LED, in the small Angle of 4 °, 50 ma working current, its typical luminous intensity of 20000 MCD.

Based on GaAs substrate LED structure

LED another important performance index is eta, luminous efficiency with lm/W. Each year in the production of LED luminous efficiency as shown in table 2. Can be seen from table 2, which more than 30 years, LED luminous efficiency could be improved by more than 250 times. LED luminous efficiency increase slower in 1970-1990, 1990-2005, is to improve faster. For example, 1 W white light LEDXL7090WHT Cree company production, its luminous efficiency can reach 60 lm/W.

Table 2 year of different production LED luminous efficiency comparison

XL7090WHT is super high brightness, small size, encapsulation of white LED. XL7090WHT of luminous intensity big, the current 350 ma, the typical flux is 60 lm, typical flux during transient pulse current of 700 ma can reach 98 lm, which is generally 1 w white LED the luminous flux of 30 to 45 lm); XL7090WHT light-emitting efficiency is as high as 60 lm/W, wide Angle of 100 °. Package size is only 9 x 74.3 mm; Working temperature range is - 20 - to + 80 ℃.

Because XL7090WHT luminous intensity big, high luminous efficiency, so it is suitable for families, business or public places, DVD, notebook computers, the color of the television screen backlight; Advertising lights, street lamps and the  lamp; Automotive and transportation, both inside and outside lighting and digital camera flash light, etc.

Can be seen from table 1 and table 2, LED the luminous intensity and luminous efficiency mainly depends on the development of semiconductor materials and its processing technology. Early LED mainly by GaAs, GaP (ii) element semiconductor materials and GaAsP (three element semiconductor materials), with around 1994 AlInGaP (after four element semiconductor material), the luminous intensity and luminous efficiency is greatly improved. In addition, the technology used on the GaAs substrate with AlInGaP material production of red light, yellow light LED and InGaN in SiC substrate material production of green and blue leds, on the luminous intensity and luminous efficiency has great improvement.

(2) improve the LED power

We know, LED luminous intensity and forward current IF almost a linear relationship, which increase the forward current IF can increase the luminous intensity. But the LED has a maximum power dissipation PD value restrictions, PD = VF x IF for positive pressure drop (VF), IF ever the earth increases the IF and the PD exceeds the maximum, the LED will overheat and damage. In order to improve the luminous intensity, developed in power LED (generally a few hundred mW), the working current is increased to 70 ma. In recent years, in order to further improve the luminous intensity, developed the high power LED, its power is usually 1-10 w (some even greater than 10 w). Its working current is 350-700 ma, some can be more than 1 a.

To AmericanOptoPlusLED company production of 5 w WXX PU - 5 series, for example, in 700 ma electrical flow, its Tj junction temperature is 25 ℃, its typical luminous intensity as shown in table 3 (high power LED luminous flux in the luminous intensity).

Table 3 pu - 5 WXX series typical luminous intensity of LED

Can be seen from table 3, in addition to the blue LED the luminous intensity and luminous efficiency is low, other light color luminous intensity and luminous efficiency is quite high.
Early production of the LED is small power (tens to hundreds of mW), can now be made more than 10 w high power LED, on the power added more than 100 times.

Although small power LED with high power LED luminous efficiency is almost, but LUMILEDS company research has shown that high power white LED longer life than Φ 5 white LED. In addition, using a lot of small power white LED bulb also sent some reliability, bulb volume is bigger also. Made with 1 w white LED lamps and lanterns, for example, its size is 50.8 * 50.8 * 7.1 mm, and Φ 5 white LED is used to doing, the volume is much bigger. But the high power LED production time is not long, price is higher, so most of the LED lamp is made of small power LED.

3, white LED the coming of the era

White LED is LED came out the last one in the family, the birth of it is an important breakthrough in the production of LED, it will become a new lighting source.

White light is compound light, can use red, green, blue three primary colors (R, G, B) LED mixed into white light. Around 1995, the production of an integrated LED white light (or full color LED lights) by two high brightness blue leds, 15 of green light LED and five red leds. The large size, high purity of the white light is not white LED lamp, luminous efficiency is not high also. But the trichromatic lamp with single chip microcomputer to control the color change of issued QiSeGuang and white light the lamp, can be used for entertainment, increase the festive mood. In addition, the RGB RGBLED composed of three core pipe is often used in mobile phone color backlighting.

At the end of last century, which may be inspired by fluorescent lamp, people in high brightness blue LED tube core with a layer of fluorescent powder, white LED with blue light stimulate phosphor emit white light. Adopt different phosphors, a cold white light (color temperature is 4500-10000 k) and warm white (color temperature is 2850-3800 k) of white LED. Currently, most of the luminous efficiency of white LED has been more than 30 lm/W, some products have been more than 50 lm/W, it used for lighting to the LED bulbs to create a good condition.

In 2005, the industry development success without phosphor, Φ 5 transparent resin encapsulation of white LED. The white LED is sapphire (Al2O3) as substrate, the InGaN technology is made. When the IF of 20 ma, luminous intensity is 700-1200 MCD, which laid a foundation for the popularity of LED application.
White LED light bulbs

(1) TFT - LCD backlight

At present, CCFL is the most widely used in large size LCD products backlight technology. Although technically CCFL is quite mature, both in performance and stability of tried and tested. But in NB products, large size LCD TV products increasingly emphasize the colour of lightweight, higher performance and the even stronger trend of environmental protection features, gradually shows a strong application prospects. LED backlight technology advantage mainly displays in:

(A) long service life

In terms of light life, LED backlight technology will CCFL left behind. The service life of the ordinary CCFL back light general in 30000 hours, some top of CCFL backlight shining life but also in 60000 hours. Such life means for frequent users to use 2-3 years after the brightness of the LCD will decrease obviously, many LCD products in the use of a few years later will be yellow, screen brightness obvious dimmed, and had to replace the CCFL backlight of LCD module. The LED backlight is no such problem, at present the service life of white LED backlight has up to 100000 hours. Continuous use of 10 hours a day, can be used for 27 years in a row, even use 24 hours a day, this life is enough to use 5 years! And there is another promotion potential.

B, rich color expressive force

In color expressive force, LED backlight also is far better than the CCFL. Original CCFL backlight due to problems such as color purity, poor performance in terms of levels. This leads to the LCD in gray scale and color transition of CRT. And, more importantly, cold cathode fluorescent lamp color gamut is relatively narrow, will seriously affect the chromatographic displayed on the LCD display, led to almost all of the LCD display can achieve print AdobeRGB color gamut standard. According to the test, using CCFL backlight can only achieve 78% of the NTSC color area, a few recent panel makers using CCFL technology can achieve 92% NTSC, subsequent increase the space is not large, and the LED backlight is easily to get more than 100% of the NTSC color gamut. In terms of color expressive force and color order transition, LED backlight has significant advantages, its expressive than CCFL back light colors, color reproduction is good, but insufficient number of display color LCD technology have very good cover effect.

Compared with the efficiency of CCFL backlight of LED

C, smaller

Leds as LCD backlight what are the benefits? First of all, the volume of using LED backlight LCD will shrink further. LED back light source is formed by numerous grid of semiconductor, each "grid" has a LED semiconductor, so LED backlight source of complanation is implemented. The brightness of the light source not only has excellent uniformity of complanation, also does not need complex optical path design, so that the thickness of the LCD can do much more thin, at the same time also has higher reliability and stability. Thinner means laptop LCD panel has better mobility. SONY launched in October 2005, for example, 11.1 inches, using white LED TX series VAIO notebook computer, the thickness of only 4.5 mm LED backlit LCD screen, make NB weight drops to 1.26 kg, and the thickness of the screen also dropped to just 4.5 mm, a 16% drop in overall thickness more NB to 21 mm, brightness is increased by 30%, and due to the use of white LED also make the battery life improved.

For a backlight module factory, LED backlight module in structure, the main differences lies in the change of LGP. Using CCFL, due to the limited to CCFL diameter 1.8 mm, LGP light side must maintain a 2.0 mm or so, and become a wedge plate on both sides (oblique guide plate, guide plate thickness is differ), which makes the NB panel have no way to do a very thin. Use leds as back light source, the original thickness of LGP limit no longer exists, can let whole LGP even thickness and thinning, coupled with the thickness of the glass about from 0.5 mm to 0.5 mm, so it can satisfy the pursuit of NB for thin and short.
Development of NB with LED back light, the biggest bottleneck, still lies in how to make the guide plate thickness thinning. General guide plate thickness more than above 2 mm, and Sony which focuses on the use of light guide plate thickness of 0.6 mm, so the backlight manufacturers are actively developing guide plate is thinner.

D, brightness and white balance control

LED power control is easy, unlike the minimum brightness CCFL is a threshold. Therefore, the LED brightness adjustment range is big, no matter in the bright outdoor or indoor all black, users are easy to adjust the brightness of the display device to the most pleasing to the eye; LED backlight can adjust the white balance, while maintaining the overall contrast. When a user video source when switching between the computer and DVD player, can easily adjust the white balance between 9600 k and 6500 k, and will not sacrifice the brightness and contrast.

E and uniformity

Cold cathode fluorescent lamp belongs to the tubular light source, to the even distribution of light to every area of the panel will need to be fairly complex auxiliary components, the thickness of the screen is also difficult to control. And with the increase of the panel, you must use multiple light sources, this request from the CCFL light also must match. At the same time, CCFL back light energy use efficiency is low. In the process of light from a backlight to screen transmission, light energy loss is very serious, about 6% of light energy can be eventually real use. In order to achieve higher brightness and contrast, manufacturers must increase the output power of the light source or increase the number of the tubes, and this is the aftermath of the overall power consumption. For the desktop LCD monitor or LCD TV won't have much impact, but a great influence on the laptop LCD screen. Leds can provide continuous array light source for large size screens. LED is a kind of planar light source, is the most basic lighting units 3 to 5 mm on each side of the square after encapsulation, the auxiliary optical components can be done is very simple, very easy to combine together to established area in front of the light source, has the very good brightness uniformity.
In addition, LE using the 5-24 v low voltage power supply, very safe, the design of the power supply module is simple; LED light source produced no rays and there was no toxic substances such as mercury, is a green light source; Planar structure make leds have a solid internal structure, seismic performance is excellent.

LED backlight technology, like many new technologies have many attractive advantages, but LED to occupy the mainstream of the large size LCD back light, it is need to solve some technical problems, such as power consumption, cost, consistency, etc.

A, luminous efficiency

The mainstream of CCFL is still the highest luminous efficiency light source technology, by contrast, the LED luminous efficiency is lower. As a back light source of LED devices in the majority with white light type, at the start of white LED devices in luminous efficiency is not high, the screen brightness is generally low. In the current LED technology, for example, no matter who, screen manufacturers is the brightness of the LED components are different. The CCFL cold cathode fluorescent lamp luminous efficiency can reach 50-100 lm/W, and white LED devices in the beginning of 20 luminance lm/W is even lower. Now, however, the world has a large number of enterprises engaged in related research, technical progress in the field very quickly, the luminous efficiency of white LED rise by 60% a year, so far, the luminous efficiency of white LED devices through 50 lm/W, began to achieve the practical level. And the industry hope that before 2007, would improve the luminous efficiency of white LED to the high standards of 75 l m/W.

B, consistency,

With problems the consistency of white light LED as a back light, it is a disadvantage compared with CCFL. RGBLED back light will have a long period of time color wavelength will vary with temperature, produce different colors. This problem LED to the inconsistent color offset, color purity and inferior quality of the true "white", it is destined to LED in the beginning is not suitable for as the LCD back light. In order to eliminate this problem, the LED chip manufacturers to "partition" or decomposed into approximation color and brightness of the block. This process has certain help, but there are still insufficient, still existed in brightness and color deviation. Manufacturer's latest developed color correction circuits, and through the control of the primitive one by one, can be on the color and brightness deviation control in a reasonable range.
With high brightness light emitting LED lighting market size of the market

C, the cost is high

Cost is too high, the price is expensive, the same size of the back light source, LED is 4 times the price of CCFL. For the present price competitive market, some manufacturers. Only SONY to image quality at no cost. Of course, with the mature technology and the increase of the scale of production, the cost of the LED backlight will decline gradually.

Despite the advantages of LED, in a short period of time is difficult to popularize, such as LED back light system is higher than the cost of cold cathode fluorescent tube. The price of LED backlight module components is about five times of CCFL, screen size, the greater the higher the cost of using LED backlight technology. Toshiba U100 are using this kind of display technology, completely is that it only be applied Toshiba notebook the 20th anniversary of the establishment of souvenirs.

The good news is that the LED industry in a similar "Moore's law" in the microprocessor industry - Haitz's law, to agilent (leading companies in LED industry) scientists RolandHaitz named former technology. Its content is LED every 10 years will be the price of the original 1/10, performance is more than 20-fold. If this law can be consistently fulfilled, while with the increase of production capacity, the cost of the LED back light will decline rapidly. Predicts the next year or two of the LED backlight price can be down to about 2 times of CCFL backlight, only one step away from large-scale popularization.

(2) the home LED lighting

At present domestic lighting mainly incandescent lamp, fluorescent lamp, fluorescent lamp) and energy saving fluorescent bulbs. Light-emitting diodes (leds) compared with other light source characteristics are shown in table 5. White LED bulbs and fluorescent lamps, energy-saving fluorescent lamps, incandescent bulbs on the luminous efficiency and life expectancy is as shown in table 6.

Table 5 leds compared with other light source characteristics

The evolution of the human lighting technology

From table 6 shows that the luminous efficiency of white LED bulb than incandescent bulbs, but less than fluorescent lamps and energy saving fluorescent bulbs. The average life expectancy of white LED, more than 8 times the energy-saving fluorescent lamps, high 33 times more than incandescent bulbs.
Domestic lighting luminous efficiency and the comparison of the average life expectancy

Three kinds of lights on the energy saving and economic comparison

At present, the domestic has can produce 1-3 W white LED bulb composed of Φ 5 white LED (appearance is same as the incandescent light bulb, the spherical shell with transparent plastic, 60 mm diam., with E27 lamp holder screw lamp holder), its luminous efficiency eta more than 35 lm/W. 2-3 w white LED light bulb brightness and 25 w incandescent bulbs. In addition, the current will also be able to produce 12 W white LED fluorescent tube, its luminous flux over 500 lm, luminous efficiency of more than 40 lm/W. These two kinds of white LED lamp life are made of more than 50000 h. The two lights are made with ultra-high brightness Φ 5 small power white LED, the current price is higher, and not yet on the market.

LED as a city traffic lights and light

Made of white LED lighting energy saving, long life. In the use of electricity saving and efficiency, 3 w 5 w white LED light bulbs, energy saving fluorescent comparing with the results of 25 w incandescent bulbs are shown in table 7. Visible, from the aspects of energy saving, also use the 50000 h, electric incandescent lamp with 1250 degrees, and as long as 3 w white LED lamp, 250 KWH, 1000 KWH. If there are 100 million apple 3 w white LED lamp replacement for 25 w incandescent bulbs, is in the use of 50000 h time saves 100 billion KWH. In addition, to compare from the economic aspect, with a 3 w white LED lamps for 50000 h, the total cost is 209 yuan, if use 25 w incandescent bulbs will cost 688.4 yuan, 479.4 yuan.
Of course, since the invention of 150 years of history, because incandescent white LED bulb production only a few years. Currently on the market only white LED flashlight, white LED miner's lamp and so on a few products, household white LED bulb is not yet listed, and at present only in the production of small power bulbs, in terms of brightness is not as good as energy-saving fluorescent lights, and the price is high, ordinary families also hard to accept. If, however, considering the service life, efficiency and environmental protection and energy saving elements such as save electricity, LED lighting has its application value.
The LED car taillight

With the development of semiconductor materials and process technology, the increase of the production, the performance of the LED light will continue to increase, prices can also drop on continuously, and may in 3-5 years gradually entered innumberable families, became known as a power saving, the bright new choice.

(3) the flash

Digital cameras are gradually instead of using film camera, in the digital camera using high brightness white LED to replace the traditional xenon lamp. Using high brightness white LED for the flash is not only simple circuit, small size, power saving, and do not need to charge time. Mentioned earlier, for example, 1 w white LEDXL7090WHT, when it used as a flashlight, 700 ma when its pulse current typical flux is 98 lm.

The LED flashlight

5, the conclusion

LED components in the global market size of about $2005 in 5.5 billion, 50% in Japan, 20% in Taiwan. Now LED a large number of application in function, and the field is also LED the first to enter the market, such as outdoor display board, traffic number lamp and plane lighting, etc. Along with the high-end mobile phones using LED after the backlight source, LED and opened up a new application field. In the future, is the most promising application of LED in the 7-40 inch flat-panel display market, once LED successfully become a flat-panel display back light, its market value will grow significantly.

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