After the outbreak of the COVID-19, the UVC LED market showed explosive growth in the first half of 2020. In particular, the chip market is in full swing, which was once in short supply. With the gradual control of the epidemic, the development of the UVC LED market has returned to rationality.
How to choose the right UVC chip and what to pay attention to in the purchase process have become the part that packaging companies and even consumers pay great attention to.
Next, we will analyze them from different parts, the current mainstream chip structure, the main problems of the current UVC LED, and the key indicators of the chip.
Main UV LED Chip Structure:
There are three main types of chips:normal chip, flip-chip and vertical.
At present, the difficulties of UVC LED chips are low yield, low external quantum efficiency, and poor reliability, resulting in high costs. Among them, since the P-GaN on the P-type layer on the front light-emitting surface of the positive chip will absorb deep ultraviolet rays, the light efficiency will be affected. Therefore, the current main chip is a flip-chip structure.
UV LED Chip Structure
The vertical structure is produced on the basis of the normal chip structure. This kind of chip is a traditional sapphire substrate chip that is inverted and bonded to a silicon substrate or metal substrate with good thermal conductivity and then peels off the sapphire substrate by laser. This structure is currently the mainstream chip structure of high power in UVA-LED (365nm-395nm), and the medium and small power of UVA-LED is still dominated by horizontal structure.
However, although the flip-chip is the mainstream in the current 310nm and below, it does not mean that it is the best structure. Based on the vertical structure with the better current expansion, less light absorption, and better heat dissipation, it will have the opportunity to become the mainstream of high-power UVC-LED, provided that an economical and simple method to peel off the sapphire substrate is found.
UVC Flip Chip
UVC Vertical Chip
After the aluminum nitride with high aluminum composition grows on the sapphire, the sapphire is peeled off with a laser. However, the damage to the epitaxial layer of the laser is very large, and the leakage of the epitaxial layer after the laser is peeled off is relatively large. In the peeling process, the wavelength of the conventional semiconductor laser is not enough, and there is no way to break the chemical bond.
Main technical route
There is a chance (find a way to strip the substrate)
The Main Problems of Current UVC Chips
At present, the main problems at the UVC LED chip side are that the growth of aluminum nitride materials is difficult, and the conversion efficiency is low due to severe pre-reaction – high heat, low crystal quality – low yield.
According to the principle of energy conservation, the electric energy is not converted into the light is presented in the form of heat energy, and the service life of the LED chip is inversely proportional to the temperature. Due to the low luminous efficiency of the UV LED chip, it brings a high amount of heat, which requires extremely high heat dissipation. According to the existing heat dissipation methods, it is difficult to achieve effective heat dissipation of high-power UVB/UVC-LED chips. Even in the multi-chip integrated UVC-LED light sources, some need to install fans for heat dissipation, thereby increasing the cost again.
The photoelectric conversion efficiency of UVC LED is low, and it is difficult to achieve a qualitative leap in a short period of time. At this stage, the industry generally achieves the improvement of power by adjusting materials and MQW. However, due to a large number of surface defects on the epitaxial wafer, the small size (low power) can avoid defects during the dicing stage, while the large size is more difficult to avoid, resulting in a lower yield of large size (high power) chips.
What parameters to look for when purchasing a UVC chip?
When purchasing UVC LED chips, in addition to looking at the chip structure, and evaluating the heat dissipation and yield, you can also consider the wavelength, optical power, electro-optical conversion efficiency, and lifespan according to the needs of the scene.
The wavelength range of UVC LED is between 200-280nm, of which the wavelength of about 265nm has the highest sterilization efficiency.
The relationship between wavelength and sterilization rate is shown in the following figure:
The relationship between wavelength and sterilization rate
For the current UVC LED chips, the shorter the wavelength, the higher the manufacturing cost and the lower the corresponding luminous efficiency. Therefore, considering the wavelength, luminous efficiency, and cost, most manufacturers will choose the wavelength range of 260-280nm. The typical wavelength range is 265nm, 275nm, and 280nm.
Currently, available UVC LED chip sizes on the market are 1020mil, 2020mil, 3030mil, 4545mil, etc. The larger the size, the greater the theoretically corresponding optical power, ranging from 2mW-60mW. The choice of optical power mainly depends on the application scenario, which depends on the size of the product, the radiation dose and irradiation time required by the product, etc. The formula for UV sterilization is: UV irradiation dose (mJ/c㎡) = irradiation time (s) × UVC output intensity (mW/c㎡)
IQE,EQE and WPE
Internal Quantum Efficiency – IQE: The ratio of the number of photons produced in a PN junction to the total number of recombination carriers; where very few photons are produced, most of the recombination produces heat.
External Quantum Efficiency – EQE: The ratio of the number of photons emitted by the LED chip to the total number of photons generated by the PN junction; affected by the refractive index of the material, chip structure, and packaging structure, the conversion efficiency is only about 20%.
Wall-Plug Efficiency – WPE: The ratio of the optical power of the LED to the input electrical power. WPE is an important indicator commonly used to evaluate luminous efficiency. Therefore, when purchasing chips, the above key conversion efficiencies need to be considered.
At present, the IQE of UVC LEDs on the market is generally around 50%-80%, the mainstream level of WPE is about 2-3%, and some manufacturers can reach 4-5%.
UVC LEDs work for a long time and will cause light decay and aging. Especially for high-power UVC LEDs, the problem of light decay is more serious. When measuring the lifetime of UVC LEDs, the lifetime of LEDs is generally specified by the percentage of light attenuation of UVC LEDs.
Due to the sterilization formula: UV irradiation dose (mJ/c㎡) = irradiation time (s) × UVC output intensity (mW/c㎡), when the irradiation dose is constant, the output power of the light source is inversely proportional to the irradiation time.
For the selection of light source life, the industry currently has two technical routes:
1. Low power route:
It takes a long time to irradiate to reach the corresponding UV dose, the light decay is relatively low, and the lifespan is relatively long, which is suitable for routine disinfection scenarios. The disinfection of traditional mercury lamps is the use plan. The market batch mercury lamps have an ultraviolet output power of several hundred mW, and their life spans range from thousands to tens of thousands. In the future, UVC LEDs will replace mercury lamps, which is an important technical route.
2. Instantaneous high-power UV power output route:
The sterilization dose can be achieved by irradiation in a very short period of time. For example, in the pulse xenon lamp that is currently used, the instantaneous ultraviolet output power can range from several W to several hundreds of W. For UVC LEDs, this technical route needs to increase the saturation current value and pass in a pulsed high current of several A or even greater in an instant. As a result, high-power ultraviolet power output can be obtained, which can replace the pulsed xenon lamp disinfection market in the future.
Of course, in addition to comprehensive comparison and selection from the above aspects, the final step is to measure the chip. After comparing the degree of matching between the test results and the requirements, more correct judgments and choices can be made.
Mainstream Manufacturers and Chip Specifications
At present, the main suppliers of UVC LED chips are Yuanrong·Jason, Zhongke Lu’an, PhotonWave, Sanan Optoelectronics, and Photon Technology. The main typical application wavelengths are 265nm, 275nm, and 280nm, of which the first two wavelengths are the main types.
Typical chip specifications and current ratings are:
At present, in the UVC-LED market, more than 90% of the chips are shipped in specifications of 10*20mil. And the application of 20*20m has an obvious upward trend, and small medium-power devices dominate this market. Lots of companies currently mainly promote 10*18mil 3.0mW@20mA and 20*20mil 15mW@100mA chips. The terminal products can basically cover disinfection boxes, air conditioners, humidifiers, air purifiers, static water dispensers, etc. Such as LG Electronics, Gree, Haier, Xiaomi, Midea, Bishuiyuan, and other related products have successively produced UVC LED sterilization products.
In addition, the trend also clearly points to medium and high-power applications, such as the LG Huissen ThinQ air conditioner, and the cooperation between Zhongke Lu’an and CRRC Group to allow UVC LED products to enter the rail transit disinfection system.
With the improvement of chip technology and the gradual maturity of the production process, the market trend will move towards larger power sizes, opening up the high-power application market.
UVC is the first choice for sterilization
The industry usually divides ultraviolet rays into three categories: A, B, and C, namely near-ultraviolet (UVA), far-ultraviolet (UVB), and ultra-short ultraviolet/deep ultraviolet (UVC). Among three of them, UVC has the greatest energy and is extremely destructive to microorganisms.
Compared with UVB and UVA, UVC is the first choice for healthy light sources; compared with chemical sterilization, UVC has the advantage of high sterilization efficiency and no other chemical pollutants.
It can produce melanin, brown spots, dry and wrinkled skin, and cause skin cancer
It can lead to the appearance of sunburn (erythema) because it blocks the synthesis of deoxyribonucleic acid (DNA), ribonucleic acid (RNA) and proteins, and is considered to be the main cause of skin cancer.
It has strong penetrating power, close to X and Y rays, and has a great impact on human beings, which can affect white blood cells and cause cancer. But most of it is absorbed by the ozone layer, carbon dioxide or clouds in the atmosphere, and only a small amount reaches the ground.
China has a complete UVC semiconductor industry chain, and UVC semiconductors have higher requirements for chip, packaging technology, and material performance. At present, Chip technology is the main bottleneck and core competitiveness of deep ultraviolet semiconductor technology, and the investment of leading manufacturers in the industry and leading enterprises in the ultraviolet LED segment continues to increase.
For now, there are two main ways to obtain UVC for sterilization and disinfection: traditional mercury lamps and ultraviolet LEDs. Compared with the traditional mercury lamps, UVC semiconductors have obvious advantages: miniaturization, non-toxicity, and convenient use.
In addition, the improvement direction of the UVC semiconductor process is clear, and technical problems are constantly breaking through the market.
In this context, traditional UV mercury lamp disinfection and sterilization products will be replaced by UV LEDs quickly.
According to the report of Yole, the UV LED market is mainly driven by UV curing applications. However, the recent influx of Taiwanese and mainland manufacturers into the UVA LED industry has created strong price pressures, which limit the growth of the UVA LED market size.
In the face of the COVID-19, various companies have actively developed and launched UVC disinfection products, and the UVC LED chip industry has also attracted more attention.