Human life is a process of symbiosis and struggle with various types of bacteria for a long time. For example, probiotics can promote the balance of the flora in the body, so that the body is healthier, and harmful bacteria will cause many diseases. For example, air conditioners, humidifiers, bathrooms, kitchens, etc. where there is water, only a little slack, these places will easily breed bacteria.
First, the future of light "deep ultraviolet rays"
A new generation of cutting-edge technology, "deep-UV LEDs", emits light that is bactericidal and invisible to the naked eye. This bactericidal light is called deep ultraviolet light. The main development in the field of LEDs is to release "UV-C", a type of light of 100 to 280 nm (nano, nanometer is 1 part per billion).
The power of deep ultraviolet light has long been confirmed. Deep ultraviolet light can directly act on the basis of life - DNA, which fundamentally breaks down bacterial reproduction. Studies have shown that deep ultraviolet light with a wavelength of 260 nm is particularly susceptible to absorption by DNA. Has the effect of eliminating DNA genetic information.
a, sterilization efficiency and wavelength b, DNA damage
Figure 1. Principle of ultraviolet sterilization (Nikkiso Giken Co., Ltd)
Second, the development of deep ultraviolet rays
The development technology of deep ultraviolet rays is mainly in the United States, Japan, South Korea and other countries. In 2014, Akasaka and Amano were awarded the Nobel Prize in Physics for developing blue LEDs. With the Nobel technology source, Japan is currently at the forefront of deep UV development. The United States is a leader in deep ultraviolet research. The representative company is SETI in the United States. However, in recent years, Japan has surpassed Japan. NIKKISO has started mass production of 255-350 nm from spring 2015. Deep ultraviolet LED.
Korean manufacturers Seoul Semiconductor and LG Innotek are also developing UV LEDs. At the same time, the Japan Information and Communication Research Institute (NICT) announced that the newly developed deep-UV LED with a wavelength of 265 nm has achieved continuous illumination with an output power of up to 90 mW/cm2, which is sufficient for practical use. In order to capture the growth market, the goal of cost-effectiveness is achieved by improving luminous efficiency, mass production technology, and global technology development competition. The first ones were three Japanese companies: Nikkiso, Asahi Kasei and Tokuyama.
Figure 2. Schematic diagram of UVCLED package product
The shorter the wavelength of the ultraviolet LED chip, the greater the technical difficulty. In the field of deep ultraviolet LED chips, there are also excellent enterprises represented by Qingdao Jiesheng. In addition, the midstream packaging companies represented by Hongli Zhihui and Guoxing Optoelectronics all plan to launch their own deep ultraviolet LED products.
Third, there are problems in the development of deep ultraviolet LED
The UV-LED single chip has a small area and is easy to design flexibly; however, the radiant power of a single chip is also low, and it is difficult to meet the requirements of high radiant power density in many applications, which is currently difficult to replace in many fields. One of the important reasons for UV discharge lamps.
Table 1, mercury mercury lamp and UVC LED comparison
3.1 Improve chip luminous efficiency
1) High quality AlN crystal layer
The first thing that needs to be solved is the high quality AlN module in each band of the UVC LED chip. When a blue LED is fabricated, a crystal layer of indium gallium nitride is stacked on the sapphire substrate. Producing high-quality crystal layers is the focus of mass production and performance stabilization, but indium gallium nitride is not easily crystallized on sapphire.
To this end, people have come up with a method of first setting a gallium nitride "buffer layer" on sapphire and then superposing an indium gallium nitride layer on it. However, the luminescent material of the deep ultraviolet LED is different from the blue LED, and aluminum gallium nitride is used, and gallium nitride has a property of easily absorbing ultraviolet rays, so the material of the buffer layer needs to be changed to aluminum nitride. With the advancement of crystal growth technology, high IQE (internal quantum efficiency) single crystal AlN is gradually maturing.
Figure 3. Substrate for high quality deep ultraviolet chips
2) Research on AlGaN doping technology
First, the characteristics of n-AlGaN composed of high Al are studied. The effects on activation energy, changes in ohmic resistance, and Schott characteristics were investigated under different Al content conditions.
Figure 4. High Al composition of n-AlGaN parameters
Secondly, the properties of P-AlGaN composed of high Al are studied. Studies have shown that when Al composition is 70%, the activation energy of Mg in AlGaN will reach 320meV, so the new doping technology is the key factor determining whether UVC LED chips can achieve high output power.
Figure 5. High Al composition of P-AlGaN parameters
3) UV LED light extraction efficiency improvement technology
The AlN substrate has a problem of a large refractive index and a very low light extraction efficiency, and therefore it is necessary to improve the light extraction efficiency of the chip. Therefore, it is proposed that the surface of the AlN substrate forms a two-dimensional structure of substantially the same size and wavelength.
Figure 6. Schematic diagram of photonic crystal structure
The sub-crystal structure has a light extraction efficiency of 140% without the surface processing, and a combination of nanostructures having a smaller size than the wavelength. The light extraction efficiency reached 196% when this surface processing was not performed.
3.2 heat and UV resistant packaging
Because the deep ultraviolet photon energy is very large, if it is encapsulated by white light, it is encapsulated by optical resin. Under long-term high-energy ultraviolet irradiation, the optical resin is easily yellowed, which leads to
UVC LED life is greatly reduced.
Metal glass hermetic glass ceramic gas-sealed glass ceramic bonding package glass ceramic bonding package
Table 2, several UVC LED packaging methods
Therefore, the current packaging of UVC LEDs is inconsistently oriented with inorganic metal or ceramic or glass packages. Packaging UVC LEDs with inorganic materials avoids shortened lifetimes due to organic materials. With the CMH technology platform, Hongli realizes the full inorganic packaging of UVLED, and at the same time proposes a hermetic package of protective gas or vacuum to provide a relatively stable working environment for UVC LED chips. Provides a deep UV, cost effective package for UVC LED packages. (CMH is C=ceramic ceramic, M=Metal metal, H=Glass glass)
Figure 7. Schematic diagram of the CMH package UVC LED
Ts=75°C IF=700mA Ta=25°C RH<50%
Ts=75°C IF=700mA Ta=25°C RH<50%
Fourth, the conclusion
Although the application market of deep ultraviolet is huge, the power and stability of the chip have been greatly improved, but the packaging technology of UVC LED is slightly backward, so it is very urgent to find a stable and reliable packaging method. Due to the limitation of organic materials, the thinking of DNA in blue-encapsulation mode needs to be broken. Seeking an inorganic, airtight and relatively high-priced packaging method is one of the constraints to achieve large-scale promotion of UVC LED.
Hongli hopes to encapsulate UV LEDs with the help of CMH technology platform, and strive to improve the stability of UV LEDs. With the help of the CMH platform to help the UV LED SMD reliable packaging, the deep ultraviolet UV LED can be protected or vacuum packaged to achieve stable and reliable packaging, thereby improving its service life. At the same time, with the help of the CMH platform, the application of UV LED in the harsh environment (such as high humidity, underwater, etc.) is expanded.
Editor: Yingzi
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