Chapter 175
High efficiency technology patents for micro UV-LED chips have been granted in Europe and the United States. The development of the micro LED display became active as Apple Inc. embarked on its own development as a display next to organic EL. The LED size of 100 μm or less is considered to be a micro LED, and to give a familiar example, the particle size of wheat flour is 5 μm to 130 μm. An LED chip that looks like powder to the naked eye is mounted on a circuit board with one red, one blue, and one green LED to form pixels. An image is drawn by emitting full color of these pixels. Micro LED displays outperform conventional displays in all performances such as high energy efficiency, high definition, high brightness, fast response, high contrast, long life and wide chromaticity display range. Since there is no merit in converting a large TV to a micro LED display, application development will proceed in the future for applications such as AR glasses, VR glasses, and flexible displays. It's like the transmissive glasses worn by actor Tom Cruise in the Hollywood movie "Mission Impossible," allowing you to enjoy full-color, high-definition footage. That way, you don't need a smartphone. Since the display is small, it consumes less power. Therefore, a large and heavy battery is no longer necessary, and there is no need to worry about charging. In addition, because it is an inorganic material, it has high durability and can be used in a car in summer or in a high temperature environment under the scorching sun. The merit of the micro UV chip is that in the method of arranging three-colors. Especially the red LED is a gallium P-based compound, the blue LED and the green LED are different materials from the InGaN-based compound, so the current and voltage to flow are different. When a red LED is made into a microchip, not only the luminous efficiency is lowered, but also the mechanical strength is insufficient and the red LED is easily cracked. Transferring a flour-sized LED onto a circuit board is called mass transfer, but it is difficult and time-consuming to solder such fine chips to the substrate for each color. Therefore, if the chip is made of one type of UV, mass transfer can be performed only once. Then, what about colors? For example, old CRT color TVs exposed electron beams to RGB phosphors. In addition, the plasma display, which lost to the liquid crystal display, also obtained full color by irradiating RGB phosphors with the ultraviolet rays obtained by electric discharge. Since the liquid crystal TV itself does not emit light, it has a backlight behind it and projects it like a shadow picture, but this does not provide a high contrast of self-luminous light like an organic EL. The micro UV-LED display obtains full color by emitting RGB phosphors with micro UV-LEDs. Therefore, although the contrast cannot be expected to be as high as that of LED TVs, the manufacturing process can be greatly simplified, and phosphor technology of fluorescent lamps and TVs having a history of more than half a century can be applied. The patent is expected to be granted in Asia before long, and Professor Tetsuya Goto and V Technology Co., Ltd. of the New Industry Creation Hatchery Center, Tohoku University will proactively use silicon single crystal CMOS pixel circuit chips on flexible substrates for LEDs. We are proceeding with epoch-making research and development to drive. The research results will be announced on December 2nd at the 28th International Display Workshop 2021.
Close to the fine particle size of wheat flour 12 µm x 24 µm micro UV-LED chips
Emission of RGB phosphor by 385nm UV-LED at a current density of 1µA / mm², emission area 20mm×24mm
Emission of RGB phosphor films by 385nm UV-LED
October 20th, 2021
Micro UV-LED patent established in Europe and America, accelerating development!
