Top Ten Hot Issues in the Development of LED Application Technology

LED output value within the rapid growth of the general level of technological development at present, domestic and foreign LED industry technology development, what new changes and new features?

Looking at the global LED output value in 2013, Japan, South Korea, China's Taiwan, and China's mainland each account for about 20%. It should be said that the domestic LED output has grown rapidly. However, relatively speaking, while the domestic output value has grown rapidly, the development level of LED technology is relatively common. On the contrary, the output value of foreign LED lamps has grown in general and the technology has developed rapidly.

The main technical indicator of LED is luminous efficiency. According to reports, the LED packaging laboratory levels of several major companies in the world have exceeded 200 lm/w, among which Cree's laboratory level in the United States has reached 303 lm/w. We know that the industrialization goal of the US SSL program is to increase the luminous efficiency of LED to 250 lm/w, and to reduce the price to 0.5 US$/klm. The current industrialization level is 120 lm/w to 150 lm/w, and the price is about 3 U.S. dollars/klm.

As far as the level of LED lighting is concerned, the products of companies such as Cree and Philips have exceeded 200 lm/w, and OSRAM’s straight tube lamp products have reportedly reached 215 lm/w. However, the current domestic industrialization level is only 100lm/w~130lm/w, of course, the price level is relatively low.

Upstream of the industrial chain continues to break through The diversification of upstream and downstream LED packaging is the core technology of the LED industry chain. What are the new advances in core technologies?

Peng Wanhua, a well-known expert in the LED industry and deputy head of the Semiconductor Lighting Technical Standards Working Group of the Ministry of Industry and Information Technology, replied: Indeed, the upstream of the industrial chain is where LED's core technologies are located. Generally speaking, they include substrate, epitaxy and chips. Looking first at the substrate, the key issues in current research and development are lattice matching and thermal matching. Epitaxial growth of GaN on the substrate, mainly sapphire (α-Al2O3), SiC, Si three kinds of mainly, there are 2 inch, 4 inch, 6 inch wafer and 8 inch Si wafer. Some experts predict that 2015 will be a three-day period for sapphire, Si, and GaN homoepitaxial substrates. In 2016, it will be based on 6-inch wafers.

At the same time, in order to grow higher quality GaN crystals, reduce defects, dislocations, and further reduce costs, the industry is working on research and development of new substrates, such as 8-inch Si substrates, low-temperature growth GaN homogenous substrates, and semi-polar Sex and non-polar substrates, dielectric composite substrates, rare earth oxide REO composite substrates, β-Ga2O3 gallium oxide substrates, and the like.

Second is epitaxy, epitaxial growth of GaN, InGaAlP and many other layers on the substrate epitaxial, multi-quantum well structure to form a PN junction, the main goal is to improve the internal quantum efficiency. At present, the internal quantum efficiency has reached about 60%, and the ultimate goal is to reach more than 90%.

In order to improve the internal quantum efficiency and reduce the Droop effect, a number of new epitaxial technologies have also emerged, such as GaN homoepitaxy, 8-inch Si-based epitaxy, epitaxy on semi-polar nonpolar substrates, offset epitaxial growth, single Multi-color light (R, G, B) epitaxial wafers, epitaxy on a composite substrate, and the like.

The last is the chip. The main goal at present is to improve the external quantum efficiency, that is, the light extraction efficiency of the chip. Do not allow photons to be absorbed in multiple reflections in the crystal. Various surface treatment techniques are used on the bottom reflective surface and the light exit surface.

According to the light-emitting surface and size to distinguish, LED chips can be divided into a variety of different product forms, the most important three kinds, including dress, flip, vertical structure (including film structure). According to the power, the low power chip is generally less than 100mw, the medium power chip is generally several hundred mw, and the high power chip is generally more than 1w.

Of course, with the development of technology, other structural forms have emerged, such as a 6-side light-emitting chip structure, Cree's proprietary DA chip structure (GaN is grown on SiC substrate, and V-grooves are engraved on the SiC substrate. The highest level is on this structure form), single-chip multi-color light (R, G, B) combined into white light, high-voltage chips and so on.

How do you view the diversification of the LED package form?

Professor Peng Wanhua pointed out that the structure of LED packaging has reached more than 100 kinds, but whether Lamp, SMT, COB, PLCC, or high power package (CSP), modular packaging, etc., the principle of its technical development is important With the development of LED application products. Invariably, the basic content of LED packaging technology is to improve light extraction efficiency, improve light color quality, improve reliability and product cost-effectiveness (reducing costs).

If these package new structures and new technologies are summarized, then COB integrated package, LED wafer level package, COF integrated package, LED modular integrated package, flip chip package technology, and package-free chip technology belong to LED optical integrated packaging technology. . Other package structures also have their own characteristics, such as EMC packaging structure (embedded), EMC packaging technology (plastic bracket type), COG package (glass substrate), QFN packaging technology (small pitch pixel unit), 3D packaging technology, power frame Packaging technology.

Application focuses on the three major areas of technology focus on the ten hot industrial chain in all aspects of technological innovation, after all, or for application services, the current development of LED application technology focused on what hot?

Peng Wanhua pointed out that at present, the application of LED still focuses on three major aspects: the first is lighting, including indoor lighting, outdoor lighting, functional lighting, landscape lighting, stage lighting, but still replacing incandescent and energy-saving lamps. The main; followed by the display, including LED display, small-pitch display, backlight (IGZO using low-power LED), etc.; Finally, non-visual lighting, such as ecological agriculture, health care and so on. These have very good prospects for development.

Combined with the above applications, LED application technology development can be summarized into ten hot issues.

First, the total energy efficiency of LED light sources and lamps. Total energy efficiency = internal quantum efficiency × chip light extraction efficiency × package light efficiency × phosphor excitation efficiency × power efficiency × luminaire efficiency. At present, this value is even less than 30%, and our goal is to make it greater than 50%.

Second, the comfort of the light source. Including color temperature, brightness, color rendering, color tolerance (color temperature consistency and color drift), glare, no flicker, etc., but there is no unified standard.

Third, the reliability of LED light sources and lamps. Mainly the problem of life and stability, to ensure the reliability of products from all aspects to reach the service life of 20,000 to 30,000 hours.

Fourth, the LED light source is modular. The modularization of the LED light source system integrated packaging is the development direction of the semiconductor light source. The key to solve is the problem of the optical component interface and driving power supply.

Fifth, the safety of LED light source. To solve the problems of light bio-safety, ultra-brightness, and light flicker, especially the issue of strobe light.

Sixth, modern LED lighting. LED lighting sources and luminaires should be concise, beautiful and practical. Digital and intelligent technologies are used to make the LED lighting environment more comfortable and more in line with individual needs.

Seven, smart lighting. Combining communication, sensing, cloud computing, and the Internet of Things, LED lighting is effectively controlled to achieve multifunctional lighting and energy saving, and to improve the comfort of the lighting environment. This is also the main direction of development of LED applications.

Eighth, non-visual lighting applications. In this new area of ​​LED application, it was predicted that its market size is expected to exceed 100 billion yuan. Among them, ecological agriculture includes plant nursery, growth, livestock and poultry breeding, pest control, etc.; medical care includes treatment of certain diseases, improvement of sleep environment, health care functions, sterilization functions, disinfection, and purification of water.

Nine, is a small pitch display. At present, its pixel unit is about 1mm, and is developing P0.8mm~0.6mm products, which can be widely used in high-definition and 3D displays, such as projectors, command, scheduling, monitoring, large-screen televisions and so on.

Tenth, it is to reduce costs and increase cost performance. As mentioned earlier, the target price for LED products is 0.5 US$/klm, so new technologies, new processes, and new materials must be used in all aspects of the LED industry chain, including substrates, epitaxy, chips, packaging, and application design. , so that the cost will continue to decline and cost-effective. In this way, people can finally provide energy-saving, environmental protection, health, and comfortable LED lighting environment.