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In the new year, Micro LED is still attracting attention. Some organizations predict that the market size of Micro LED is expected to reach 100 million yuan in 2019. The commercial application of Micro LED technology is called “micro-scale competition”, which shows that the implementation difficulty is still a bit large. New Year, I believe many manufacturers are also very concerned about the new development of Micro LED technology.
Flexible Micro LED implementation
At the 28th Fine Tech Japan Technical Symposium held in Messe, Japan (December 5-7), a theme by V·Technology Co., Ltd. (a large-scale enterprise that displays production equipment) was “Flexible Micro LED Implementation”. The presentation of the program. The main content of the presentation introduces the production process of the flexible Micro LED display independently developed by V·Technology (hereinafter referred to as V-Tech).
Colorization with UV Micro LEDs
V-Tech has developed a colorization scheme based on flexible UV Micro LEDs that utilizes a unique "sector" structure and fluorescent material to achieve a color display of the display. The flexible Micro LED display in this development uses a polyimide (PI) substrate on which the developer bonds the UV Micro LED chip and uses a 20um (height) * 7um (wide) sector sidewall structure. Encapsulating it, the package structure is filled with a phosphor coating to achieve color display.
The development of Micro LED technology began in Taiwan. When V-Tech first established its basic technology, it has already cooperated with Japanese companies and universities with core technologies. Nitride Semiconductors Co., Ltd. provided UV Micro LEDs for V-Tech. Photo Resist manufacturers provide materials such as photo-adhesives for Micro LED rearrangement technology. Northeastern University offers TFT and substrate technology. Guidance, Keio University and other guidance in the field of phosphor units and photoresist technology.
Since the luminous efficiency of red and green LEDs decreases as the chip size decreases, V-Tech chose the UV-LED solution. In theory, it is more appropriate to "excite" the phosphor with short-wavelength light. Considering the external quantum efficiency, the conversion efficiency of the phosphor, and the fluctuation of the emission wavelength, V-Tech finally chose ultraviolet light with a wavelength of 385 nm.
The UV Micro LED chip is a flip chip made of 4 sapphire wafers. The chip size is 17*49um, and in order to ensure electrical connection, the researchers deliberately made the size of the bond terminals larger. V-Tech said, "It is not the brightness that determines the size of the chip, but the size of the terminal that makes the electrical connection."
The UV Micro LED chip emits a wide dynamic range, which is said to guarantee illumination from 0.5uA to 10mA.
Unique area optional laser stripping technology - PSLLO
Stripping LEDs from sapphire wafers requires the LLO (Laser Lift Off) process, and V-Tech uses its unique "Partial Selective LLO (PSLLO)" process. A typical laser stripping technique selects a location on the back side of the sapphire wafer and illuminates the laser at the interface of the sapphire wafer and the LED chip film based on accuracy. However, PSLLO uses a unique "secret" for laser irradiation. The result is not to strip all of the Micro LEDs, but to weaken the adhesion of specific areas (in order to make them easier to strip), which is important for chip rearrangement in later processes.
The next step is to transfer the UV Micro LED chip on the sapphire wafer to the PI substrate. There are many bumps on the PI substrate that are electrically connected. The R&D personnel docks the bumps and the LED chips with high precision, and then bonds them by heating and pressing the adhesive coating. Finally, the sapphire wafer is removed. The transfer of the UV Micro LED chip from the wafer to the PI substrate is achieved. In this way, the transfer of the LED chip no longer requires a carrier tape.
During this period, if current is supplied, the chip that is electrically connected after heating and pressurization will emit light, so the transfer, packaging, and lighting inspection of the chip can be performed simultaneously with the process. The defective chip that was inspected will not be irradiated by the laser during the PSLLO process, and will not be transferred to the PI substrate. The sapphire wafer and the UV Micro LED chip are more adhesive than the adhesion strength of the coating, so the PSLLO process can selectively transfer chips from a specific area.
Use fan-shaped metal sidewalls to prevent color mixing
Next is a sector structure that forms a phosphor unit, which is the smallest display unit for color display. For example, a normal yellow light process, after the overall coating of the fluorescent coating, is exposed, developed and cleaned to form a pattern. However, the passage of UV light through the exposure will excite the phosphor unit next to it and cause color mixing. In order to avoid the occurrence of color mixing, V-Tech also designed a metal layer inside the phosphor unit. Since the phosphor unit is 20um thick and thick, the developer can use a pulsed laser after the metal layer is plated, thereby only "ablation" the metal coating at the bottom. After "cutting", the metal layer leaves only the sidewall portion of the phosphor unit.
After testing to evaluate the properties of life, persistence, luminescence and absorption of 20-30 phosphors (including quantum dots), V-Tech finally selected inorganic phosphors with a particle diameter of 1-3 um to fill the above phosphor units. Considering that a very thin phosphor coating does not absorb UV light and does not cause discoloration, the above-mentioned phosphor unit designed by V-Tech has a height of 20 μm.
V-Tech Flexible Micro LED Display New Process and Process Equipment
Already got an order for production equipment
V-Tech prototyped a flexible Micro LED display through the above series of process steps, and rolled it onto a 3 mm diameter round bar to confirm that it could emit light. Based on the results of this trial, V-Tech also started the development of production equipment.
As a future issue, V-Tech will develop high-speed maintenance equipment, reduce the cost of Micro LED chips, and develop flexible backplanes. V-Tech cannot produce substrates inside, and the company's solution is to cooperate with other manufacturers. In the future, will it only sell production equipment or produce displays at the same time? Their business model is not yet determined, according to V-Tech, they "hope to retain the opportunity to choose."
In November 2018, V-Tech announced that they had received orders for LLO equipment and LED transfer equipment for Micro LED production lines from large overseas customers. (Content from CINNO)
Samsung launches second-generation Micro LED TV
Recently, Samsung officially launched the second generation of Micro LED TV on the eve of CES 2019, and also introduced the 75-inch model The Window for home use, if you are full of suffocating, you can also choose 219-inch The Wall.
Although OLED is good, organic light-emitting screen materials always have life defect problems, but Samsung's future focus on Micro LED technology has no such concerns. Micro LED technology is to reduce the physical size of LED devices from millimeters to micrometers (usually below 100um) by micro-scale technology, which is 1% of the original LED. It is very exaggerated to say that it is smaller than a sand and wants different The size of the Micro LED screen requires a massive transfer technology to move the RGB tri-color Micro LEDs onto the substrate. Moreover, each pixel can be addressed and independently driven to achieve high-end display requirements of ultra-high pixel and ultra-high resolution, making Micro LED an unparalleled advantage in the display field.
OLEDs are only self-illuminating films made of current-driven organic materials, and the thickness is much less because backlights and liquid crystal modules are not required. But the Micro LED is more extreme, only need 4 layers of structure to complete the entire lighting module, the thickness is thinner, and can exceed the OLED in brightness, the power consumption is lower than the OLED, the screen time reaches the ns level, and the ordinary LCD Need ms level, OLED also μs.
Such excellent technology is currently only in the hands of several manufacturers, Samsung is one of the fastest, and it is no wonder that Samsung dares to continue to lead the display technology for more than a decade.
At this CES 2019, Samsung will exhibit the 75-inch Micro LED TV The Window, which means that the size is comparable to a window, which is very suitable for home use. Don't look at the 75-inch size. In fact, most people can accommodate this size TV, and the visual effect is better. At the same time, Samsung reduced its thickness from the first generation of 80mm to 30mm. However, Samsung has not announced its selling price and the date of its release. It is estimated that it is mainly based on sleek technology, regardless of commercial issues.
If your home is a big villa, then the TV size may be bigger, and a wall is not big enough? Samsung also released the larger-size Micro LED TV The Wall, which has reached an astonishing 219-inch size, which is even larger than the 146-inch CES 2018 release last year.
Samsung also mentioned that Micro LED TVs have very flexible sizes. What do you mean, what size you want, because Micro LED TVs can be seamlessly stitched together to make TVs change more.