According to LEDinside’s latest findings, micro-LEDs will enter mass production by 2018. To understand micro-LED technology comprehensively, and tap into its market potential, LEDinside has organized its history, current situation, theory, manufacturing process, and related manufacturers.
The history of micro-LEDs can be traced back to the development of TFT-LCD display backlight module applications, when in the 1990s TFT-LCD developments emerged. Due to the LEDs features in high color saturation, energy efficiency, and in thinness, some manufacturers used the LED as a backlight source. Yet, overtly high costs and poor thermal dissipation, low photoelectric conversion efficiency and other factors, it was not widely applied in TFT-LCD products.
It was not until the year 2000 that white LED chip technology matured, where blue LEDs coated in phosphor powder were excited by electricity to emit white light. By 2008, white LED backlight modules underwent exponential growth, completely replacing CCFL in a short time frame. Leading application sectors included smartphones, tablets, notebooks, table top monitors and TVs.
However, TFT-LCDs are limited by its none-self luminous properties and theory, which caused open cell transmission rate to fall below 7%, causing low photoelectric conversion efficiency in TFT-LCDs. Moreover, white LEDs color saturation performance is much lower than RGB LEDs, hence most TFT-LCD products only have 72% NTSC. Additionally, in outdoor environments a major flaw of TFT-LCDs is its brightness failed to reach above 1,000 nits, causing low image quality and color recognition. Other solutions and developments include using RGB LED as a self-luminous pixel micro LED display.
As LEDs mature and evolve, micro-LED display has appeared in a completely new form as of 2010.
From its development history, Sony launched its 55-inch “Crystal LED Display” in 2012, a new micro LED display technology utilizing Full HD Resolution. The display uses about 6.22 million micro LEDs (formula: 1920 x 1080 x 3) for high resolution displays, the contrast ratio can reach 1 million to one, and color saturation of 140% NTSC. The display also does not have reaction time and lifetime issues, but because it uses a single micro LED embedded in the display, there are still a lot of costs and technology barriers to overcome before the product can be commercialized and mass produced.
Although, in theory micro-LEDs can be applied in displays of various sizes, the manufacturing process and yield rates have a negative correlation with display resolution demands. Hence, the products are being introduced into small display applications first, such as wearable devices because of its small size, higher yield rates and high brightness in outdoor environments compared to OLEDs. Additionally, it has low energy consumption.
The average LED chip including substrates and epi-wafer layers measures about 100 to 500 microns (μm), while advanced micro-LED display research is now focused on removing the 4 to 5μm thick LED surface by mechanical or chemical process to transfer the chip onto an IC board.
Micro LED displays combine TFT-LCD and LED technology features, and is a more mature technology in terms of material, manufacturing process, and equipment development than OLED technology. Additionally, micro LEDs product specs are much more advanced than TFT-LCD or OLED, and covers wider applications including flexibility, transparent displays, and is a more feasible next generation display technology.
Starting from 2010, manufacturers have been aggressively developing micro-LED display technology through integration and R&D. Yet, micro LED displays do not have a standardized micro-LED structure, and manufacturers are competing in the fronts of mass production, driver IC design, and aggressively deploying their patent strategies.
As of 2016, manufacturers leading in micro-LED patent applications include Apple affiliated Luxvue, Mikro Mesa, Sony, Leti and others. There are also many companies and research centers that are investing in related technology developments.