MicroLED displays, the technology of tomorrow, and ArrayFIX, the particle-arrayed ACF that can support their adoption

MicroLED displays: innovative display technology

As of 2024, electronics manufacturers all over the world are focusing on a new technology called microLED as the next generation of display technology. While it has been the subject of research for many years, it is finally seeing practical application for various purposes and its use is expected to spread rapidly.

LEDs, or light-emitting diodes, have seen rapid global adoption as the fourth generation of lighting (after the candle, incandescent bulb, and fluorescent lamp) since the development of the white LED in 1996. Due to advantages such as high luminous efficiency, low power consumption, and long lifespan, they are now seeing widespread use as replacements for conventional incandescent and fluorescent lighting. The microLED is a type of LED where the size of an individual LED chip is extremely small, measuring less than a tenth of a millimeter on a side.  While a common LED chip measures 1 mm or more on each side, a smaller version known as the miniLED is around 100 to 200 micrometers. The microLED is even smaller, measuring less than 100 micrometers.

This article focuses on the microLED display, which consists of microLEDs smaller than 100 micrometers arrayed on a flat panel to form a display. Its high brightness and image quality have raised expectations for applications in large-scale displays such as signage and televisions as well as wearable devices. Many major electronics manufacturers have been engaged in development efforts, and some pioneering companies have already commercialized outdoor displays. MicroLED displays have been installed in places such as a direct sales stores of PC manufacturers in North America.

To create color images with microLEDs, the three primary colors—red, green, and blue—are generated with LED chips and combined to form one pixel. MicroLED displays can show accurate color by precisely controlling the brightness of individual LEDs and produce images by controlling each pixel across the entire display. The principle is the same as the way athletes are shown on the large screens in sports arenas. But with microLED displays, each individual light source is far smaller than those on an arena’s screen, allowing the viewer to enjoy far more detailed images from up close.

MicroLED’s advantages over LCD and OLED

LED elements emit their own light, allowing them to produce higher brightness and higher-contrast images than conventional LCD displays. LCD displays produce pixels by shining a white backlight from behind the liquid crystals and applying color with a color filter. As a result, they were fundamentally limited by the power to image conversion efficiency. In addition, they take advantage of the liquid crystal molecules’ properties to adjust the amount of light that passes through. But because they cannot completely block light from the backlight, it was difficult to produce true blacks or high contrast between light and dark. Another issue was motion blur and difficulty in tracking footage with rapid motion or sports footage, as liquid crystal molecules take time to respond to control signal changes. To address this problem, LCD displays employ frame-doubling technology that shows an additional frame generated by the graphic engine between each frame of footage. However, this is not a fundamental solution to the  motion blur issue.

An LED display, on the other hand, can instantly turn each pixel on or off. This makes it more responsive than an LCD display. And because it can control the brightness of each pixel, there is no problem with unwanted light passing through. In addition, the lack of a backlight improves its power efficiency. Hopes are high for LED display use in wearable devices and AR smart glasses because of long battery life due to low power consumption and the ability to show detailed images in sunlit outdoor areas due to high brightness. And with no need for parts such as backlighting, polarizers, or diffusers, LED displays can be made thinner than LCD.

Source: https://www.ite.or.jp/contents/keywords/1909keyword.pdf

There is another display technology called organic LED or OLED, but microLED displays have advantages over OLED as well. OLED displays use organic compounds to emit light, making them susceptible to degradation over time due to oxygen and light. They are said to have issues with long-term durability as a result. The LED chips in MicroLED displays, on the other hand, are made of inorganic materials. This gives them higher durability and avoids the issues with image burn-in and image quality degradation seen in OLED displays.

To address burn-in and image quality degradation, OLED displays lower image brightness. Because these are less of an issue for microLED, it is possible to deliver better image quality than OLED.

Challenges for practical application of microLED displays

MicroLED displays enjoy many advantages in their structure and the way they work, making them seem like the ideal display technology. But various challenges stand in the way of widespread use, and as of 2024 they have very little presence in the global market. To achieve widespread adoption, the challenge of cost must be overcome. The reason for this high cost lies in structural issues.

• Cost
  When a major South Korean electronics manufacturer began selling televisions with microLED displays in 2022, they were extremely expensive with 89-inch models priced at approximately 80,000 USD and 110-inch models at approximately 150,000 USD. Even as of September 2024, microLED TV prices remain extremely high, well outside the price range of the average consumer. The following manufacturing challenges play a large role in these high prices.
• Manufacturing challenges
  To manufacture microLED displays, it is necessary to place the microLED elements that constitute pixels on the circuit board in a dense array without any gaps. More than 8 million pixels are necessary to make one of the 4K displays that are already widespread. To match that by lining up red, green, and blue LEDs for each pixel, it would be necessary to precisely arrange and connect 24 million microLEDs. In the case of an 8K display, approximately 100 million are needed.
  
  As of 2024, a process called “pick and place” is the primary way to arrange microLEDs on a display. Each individual LED chip is picked up, moved to its position on the circuit board, and connected. The issue is that this takes an extremely long time due to the large number of chips. About 10 years ago, when the development of microLED displays began, it was said that manufacturing a single display could take several months.. The cost of the LED chips is another issue. If each LED chip were to cost 1 JPY, the microLEDs needed to make a 4K TV display would cost 24 million JPY.

To take on these challenges, various manufacturers are working to develop technologies such as the formation of multiple LEDs on a wafer and the mass transfer of LED chips. But even with mass transfer technology, it seems to take about 5 days to manufacture a single 4K display. And in addition to arranging microLEDs in an extremely small space, it is also necessary to establish a stable manufacturing process with a low defect rate.

Despite these challenges, hopes are high for microLED displays to become the next generation of displays and the competition to develop new technologies is sure to continue. Corporate acquisition and business partnership activity to acquire technology is also high, driven by high expectations for new products. For example, there is much talk of a major North American IT company’s acquisition of a startup with many relevant technologies. There will no doubt be more opportunities to see microLED displays showing beautiful images in big-box electronics retailers and on large outdoor screens.

ArrayFIX’s potential to support microLED display production

As rapid technology development continues, Dexerials can potentially provide a range of solutions for innovative microLED displays. One primary example is optical films such as anti-reflection films manufactured with our own sputtering technology. They are already widely used in conventional LCD and OLED displays. Another example is optical elastic resin (SVR), a type of optical transparent resin. In addition, many of our Anisotropic Conductive Film (ACF) models are used in LCD and OLED displays for the electrical connection between the FPC from the display and the circuit board. We expect that our ACFs will become similarly indispensable for microLED displays.

In addition to FPC connections, our particle-arrayed ACF ArrayFIX can make significant contributions in mounting microLED chips on the circuit board. As discussed above, it is necessary to use microscopic LED chips to create a microLED display. But the smaller the LED chip, the smaller the area of the LED chip’s connection terminal and the more difficult the connection becomes. Dexerials’ ArrayFIX continues to evolve to adapt to the shrinking connection area. We are currently working to reduce conductive particle diameter even further and develop products with denser particle arrays.

For these reasons, we look forward to seeing ArrayFIX used in microLED displays. The arrayed particles provide a stable number of conductive particles, enabling low-resistance connectivity despite a small area. In addition, the fact that particles do not move after connection maintains insulation despite narrow electrode spacing to prevent short circuits.

Another major advantage is that when using ArrayFIX to mount microLED chips, there is no need for the Au/Sn bump formation preprocessing on electrode terminals that is required before solder bonding. While solder bonding requires heating to around 240°C in a reflow oven, ArrayFIX allows mounting at a low temperature of about 140°C. This adds the advantage of reduced heat damage to the LED chips.

In January 2023, Dexerials, in collaboration with Shin-Etsu Chemical Co., Ltd., developed innovative process technologies for microLED displays based on this ArrayFIX technology. These process technologies enable precise mounting of LED chips by using lasers to transfer ArrayFIX onto locations where microLED chips will be mounted. This can reduce connection defects during microLED display manufacturing and significantly boost production.

Dexerials will continue to  drive cutting-edge technological innovations for the next generation of displays to deliver more convenient and immersive visual experiences to our customers.