Strategic Thinking on China's LED R&D and Industrial Development

Author: Luo Yi Han Yanjun Li Hongtao Wang Lai Meng Yanlong

Tsinghua National Laboratory for Information Science and Technology (Financing) 2. State Key Laboratory of Integrated Optoelectronics 3. Department of Electronic Engineering, Tsinghua University

   In recent years, China's LED industry has developed rapidly. At present, there are hundreds of thousands of people engaged in the industry, nearly 100 research institutes and thousands of enterprises. From the perspective of the global LED industry competition, the automation level of LED packaging enterprises in mainland China has improved rapidly. The lighting application industry, which is mainly based on road lighting, has made breakthroughs. LED packaging and application have global scale and industrialization technologies. On the other hand, the capacity and technical level of LED epitaxy and chip companies in mainland China have improved, and the upstream industry has maintained a good momentum of development. However, in general, the competitiveness in the world is relatively weak. In this context, the Ministry of Science and Technology launched the “Ten Cities and Ten Thousand Miles” program in a timely manner, which greatly promoted the enthusiasm of the domestic government, industry, and students for the development of semiconductor lighting. On this occasion, we will put forward the ideas on LED R&D and industrial development in mainland China based on research in recent years, for reference and correction by colleagues in the industry.

I. Future industrial development characteristics: technology and market grow together

The output luminous flux of an actual lighting fixture is usually in the range of thousands to tens of thousands of lumens. Currently, the luminous flux of a single high-end power white LED is only about 100 lumens. Therefore, a semiconductor lighting fixture usually consists of tens to hundreds of cluster white LEDs. In terms of current LED performance, the use of low-voltage, constant-current-driven cluster LEDs has caused semiconductor lighting fixtures to address the dissipating of large amounts of heat and power management issues caused by the conversion of AC mains to low-voltage constant current. In addition, the small light-pass and high-brightness luminescence characteristics of the conventional packaged power LEDs cause very severe glare. Therefore, semiconductor lighting technology is not limited to chip fabrication and packaging technology, but a system-level technology that includes optical design, heat and power management.

From LED epitaxial wafers to final lighting fixtures, a series of industrial chain links such as material epitaxy → chip fabrication → die encapsulation → luminaire design and assembly are required. On the one hand, from epitaxial wafers to final lighting and display applications, all aspects of the industry chain can form independent products with their own technical barriers and research and development needs; on the other hand, the quality of the terminal application products will be affected by each link. influences. For example, the core component of semiconductor lighting is an LED chip, but the luminous efficiency of the LED chip reaches 100 lm/W, which is not equal to the efficiency of the semiconductor lighting fixture. It also reaches 100 lm/W; more importantly, the semiconductor lighting product needs to be obtained. Market recognition, including the comprehensive performance of luminaire efficiency, reliability, human eye comfort, etc., must have significant advantages over traditional lighting products. In other words, even if the efficiency of a semiconductor lighting fixture reaches 100 lm/W, it does not mean that it will be accepted by the market. There are still many scientific problems in semiconductor lighting itself, such as lighting effects and quality including color rendering. Color consistency, human eye comfort, etc.

Only when the development of technology makes semiconductor lighting fixtures have advantages over traditional light sources in terms of efficiency, lighting quality, and design novelty, semiconductor lighting is likely to enter and continue to open up the market. On the other hand, the expansion of the market will lead to an increase in production and an increase in industry R&D investment, accelerating technological progress, resulting in improved performance and a gradual decline in cost and price. The above two processes alternated and reciprocated, eventually leading to the rapid development of the semiconductor lighting industry.

Second, the future market concentration areas: semiconductor lighting and LED display

The semiconductor lighting industry mainly includes the upstream, middle and downstream industries for outdoor general lighting and indoor general lighting; the LED display industry mainly includes the LED backlight and the upper, middle and lower reaches of the LED display field. On the technical level, the upstream, middle and downstream industrial technologies are material extension and chip fabrication, packaging, module and luminaire manufacturing technologies. The upstream and midstream industry technologies of semiconductor lighting and LED display products are basically the same, and the difference lies mainly in downstream technologies.

1. The biggest part of the future semiconductor lighting market will be general lighting

General lighting includes two categories: indoor lighting and outdoor lighting. Both types of applications require high luminous efficiency, long life, and environmental protection. The main difference is the lighting effect and quality of the indoor lighting source (including color rendering, color consistency, light source emission and uniformity, Human eye comfort, etc.) have higher requirements, and the consumer groups they face are more sensitive to the price of lamps. On the other hand, the advantages of the luminous efficiency of the blue chip need to be further improved and limited by the packaging technology of the white LED. Most of the current semiconductor lighting fixtures are high color temperature and cool white light, and the consistency of the color product is not as good as that of the conventional lighting. The intention is that semiconductor lighting fixtures are currently in large-scale applications in outdoor lighting, and have just begun to take off in indoor lighting. Therefore, limited by cost and lighting quality, semiconductor lighting will be the first to be applied in large-scale outdoor lighting, and then gradually enter the field of indoor lighting with the continuous development of technology.

A typical application of outdoor lighting is street lighting, which is an important part of urban lighting, and its power consumption accounts for a large part of the total lighting power. The traditional street lamp adopts high-pressure sodium lamp, and the high luminous efficiency of high-pressure sodium lamp has a low color rendering index, which makes the color distortion of the irradiated object very obvious; the color rendering of high color rendering high-pressure sodium lamp is improved, but its luminous efficiency and life span are all Loss; limited by its short life, it is necessary to carry out expensive high-altitude maintenance operations frequently. Generally, the high-pressure sodium lamp has poor light distribution performance, that is to say, the uniformity of road illumination is not good enough, and in order to meet the uniformity requirements of road illumination, the high-pressure sodium lamp street lamp generally adopts a rated power much larger than the illumination requirement under the lamp post. As a result, energy is wasted. Therefore, the development of new high-efficiency, energy-saving, long-life, good color rendering index and environmentally friendly street lamps is of great significance for urban lighting energy conservation. The huge market demand in the field of outdoor lighting has promoted the continuous improvement of the technical level of lamps such as power LED street lamps, the cost has been declining, and new products have emerged.

On the other hand, the most commonly used products for indoor lighting are incandescent and fluorescent lamps. Incandescent lamps have extremely low luminous efficiency, only a few lumens per watt, while fluorescent lamps contain harmful substances such as mercury, which is not conducive to environmental protection. Therefore, indoor lighting has a stronger demand for efficient and environmentally friendly lighting products. Although the current white LED devices have surpassed incandescent lamps and fluorescent lamps in terms of luminous efficiency and environmental protection, the lighting effects and quality of the lamps formed by them have not rapidly formed the advantages of traditional illumination sources, and their applications in indoor lighting. just began. However, the huge market demand for indoor lighting is bound to drive the rapid development of packaging and system-level application technologies for indoor lighting applications.

2. LED display industry has huge market potential

The LED display industry includes LED displays and LED backlights. Needless to say, LED displays have an absolute advantage in the field of outdoor displays. For indoor display, there are currently many options, including PDP, TFT-LCD, full color LED display. However, in contrast, PDPs and LCDs are difficult to achieve oversized display, and the overall efficiency is low, and the power consumption is large; while the LED indoor display can provide high-quality display on the one hand and easy to achieve oversized size, on the other hand, it is beneficial. Energy saving and environmental protection. It is generally believed that LED displays are already mature industrial technologies. However, in the field of indoor large screen display, it is necessary to give full play to the advantages of high display quality, large size, energy saving, and environmental protection of the LED display. The ordinary large pixel spacing LED display is far from meeting the application requirements. We believe that on the basis of a number of key technological breakthroughs, as large as stadiums, exhibition halls, large venues, small 46 to small and medium-sized auditoriums, conference rooms and even home places, will be the stage for LED display to display its strengths.

On the other hand, compared with CCFL (Cold Cathode Fluorescent Lamp), LED backlight has the advantages of energy saving, environmental protection, more perfect moving image, wider color gamut, etc., and will be used in notebook computers, LCD-TV and other applications.

Third, the future breakthrough areas: LED packaging and applications, such as the middle and downstream industries

We conducted systematic research and in-depth analysis of international and domestic related patents in the GaN-based LED industry, focusing on the selection of well-known companies and core patents in the field for statistics, and the patent database (esp@cenet) produced by the European Patent Office. , Derwent Innovations Index (DII) and related patent searches in the Patent Search Database of the State Intellectual Property Office of China, for the United States (US), Japan (JP), Europe (EP), and China (CN) More than 3,000 patents were counted and analyzed.

It can be seen that most of the patents in the LED industry are concentrated in the upstream link, and the patents in the middle and downstream parts are relatively small. This result is also related to the development of LED technology. Since the development of GaN-based LEDs by Shuji Nakamura in the early 1990s, a large amount of research work has been devoted to material epitaxy and chip fabrication, and the performance of GaN-based LEDs has been improved from various details. In this process, upstream industry technology has developed rapidly, and a large number of patented technologies have emerged, many of which are core technologies, while the development of middle and downstream products is relatively lagging behind. This has formed the current state of the patent technology "up and down".

However, to this day, the performance of GaN-based LEDs, although still far from the theoretical limit, has basically met the needs of lighting. With the gradual maturity of upstream technology and the gradual growth of the downstream market, LED packaging and application problems have gradually emerged. From the product point of view, whether it is a semiconductor lighting fixture or an LED display module, it is not simply a combination of LED devices. The packaging and application aspects include a series of major scientific and technical issues such as drive circuit, heat dissipation and optical design, and the solution of these problems means the creation of patented technology.

On the other hand, the patent scope of the middle and downstream industries is more extensive than that of the upstream industry. The patented technology of the upstream industry is basically related to semiconductor materials, chip preparation processes, etc., while the middle and downstream industries are more directly oriented to the market, and their product design is closely related to the use of the product, the use environment and the use requirements. It is easier to give birth to new patents.

As can be seen from the above analysis, the number of existing patents in the middle and downstream technologies is relatively small, and the number of patents that can be excavated is very large. The patent barriers of large foreign companies in this field have not yet been constructed as strong as the upstream field. Therefore, in the next few years, major companies may be competing for patents in LED packaging and application technology, and patents in application are more important. It can be seen from Figure 1 that in the patents applied for in mainland China, the proportion of downstream industries is larger than that of upstream industries. This also reflects that some enterprises in mainland China have already possessed certain strength in downstream technology. In the middle and downstream technology, it has greater advantages than upstream technology. Therefore, the middle and downstream industries such as LED packaging and applications are the most difficult breakthroughs in mainland China.

Fourth, the future development trend of the upstream sector: selective breakthrough, development of independent extension and chip technology

At present, many domestic research institutions have carried out a lot of research work on many aspects of material extension and chip production. On the other hand, although the capacity and technology level of LED epitaxy and chip companies in China have been improved recently, on the whole, many upstream enterprises have not yet formed a technical route with independent intellectual property rights, and some enterprises have developed future technologies. The direction is still quite confused.

We believe that the main problem facing the LED industry in China in the upstream field is that most of the chip's luminous efficiency is not high enough, and the reliability of the device needs to be improved. It is recommended to focus on resources and select key breakthroughs in some directions that have been clearly seen to improve the level of upstream industries in China. At present, the domestic upstream field should focus on improving the internal and external quantum efficiency. Based on an in-depth understanding of the physical properties of GaN-based materials, research and development of material epitaxy and chip fabrication techniques to improve crystal quality, reduce dislocation density, and optimize quantum well structure. Control stress and improve light extraction efficiency, and form independent intellectual property rights on core technologies as soon as possible.

In addition, the lack of localized high-level talents in the field of LED material epitaxy and chip industry in mainland China is one of the key issues that restrict the healthy development of upstream industries. Many high-level talents in China's LED epitaxial and chip companies are recruited by overseas returnees or hired from Taiwan. Their participation has undoubtedly promoted the technological advancement of the domestic upstream industry to a certain extent, but for the long-term healthy development of the industry, it will create a localized high as soon as possible. A level talent team is very necessary.

It is recommended to establish a multi-level talent support system, establish an enterprise-centered, innovative talent training mechanism based on universities and research institutions, and jointly cultivate optical and physical, through joint construction of postdoctoral mobile stations and joint masters of engineering. Innovative talents in the fields of electronics, microelectronics, materials, etc. (Source: "Semiconductor Lighting")

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