MicroLED Technology Shift Signifies a Transformative Moment in Displays

Abstract

THE USE OF MICROLEDS (TINY LIGHT-EMITTING DIODES of gallium nitride) as subpixels represents a significant advancement in display technology, offering improved luminance, energy efficiency, and color quality. This innovation unlocks new opportunities in high dynamic range in direct-view displays, while also enabling high brightness and wider viewing angle near-eye displays for augmented and mixed reality (AR/MR) applications. However, to fully realize this potential, several critical challenges must be addressed, particularly in the realms of pixel yield during die-transfer and laser-assisted or anisotropic conductive film (ACF) bonding, optical efficiency, and manufacturing costs.

The traditional fabrication methods for microLED displays involve the use of red, green, and blue (RGB) GaN LED dice epitaxially grown on sapphire (or silicon) wafers. It is worth noting that AlGaInP red dice grown on gallium arsenide (or silicon or germanium) substrates may be substituted. In these conventional approaches, arrays of dice are created on each wafer and subsequently transferred to a backplane through a series of complex steps involving multiple interposers. This intricate transfer process can lead to yield loss, necessitating the implementation of die repair measures or redundancy in the form of two sets of RGB dice, both of which contribute to higher manufacturing costs. Furthermore, as the die-size decreases to achieve cost efficiency, microLED efficiency tends to decline based on increased carrier loss at the sidewalls, ultimately limiting overall pixel efficiency.

Current display technologies predominantly use backplanes with thin-film transistors (TFT) on glass substrates, optimized for high-yield production in display fabrication facilities that handle large substrates. Transitioning these TFT production lines to accommodate high-resolution microLED backplanes required for AR/MR displays presents significant engineering hurdles that may not be financially sustainable. For instance, manufacturing AR/MR displays at 5,000 ppi entails producing millions of subpixels in a small area—a monumental engineering feat. A more viable solution for AR/MR displays may lie in using silicon complementary metal-oxide semiconductor (CMOS) backplanes. Some companies have already demonstrated silicon CMOS backplanes capable of achieving 3,000-ppi resolutions. The ongoing development of high-yield CMOS backplanes at larger sizes with resolutions exceeding 5,000 ppi is still in its nascent stages, but this holds promise for future advancements.

To foster a sustainable business model, it is essential to develop microLED display technology applicable to both direct-view and near-eye applications using processes and tools adaptable for both TFT on glass and silicon CMOS backplanes. The advancements in microLED display manufacturing are highlighted in this issue, which includes three articles focused on critical aspects of microLED manufacturing technology. Additionally, a fourth article discusses scaling OLED technology, showcasing the ongoing innovations in display manufacturing.

In the article “Laser-Assisted Bonding for MicroLED Modules in Head-Up Display Applications,” Wenya Tian et al. discuss a 3.8-inch, 1,280 × 1,024 ultrahigh-resolution, ultrahigh-brightness head-up display module that achieves a lighting yield exceeding 99.9 percent. The laser-assisted eutectic bonding used in assembling this display is shown to have improved photoelectric efficiency by 51.3 percent.

In the next article, “Enabling Next-Generation MicroLED Displays Through ACF-Based Bonding Solutions,” Hiroki Ozeki et al. describe the use of a novel particle-arrayed ACF specifically designed for microLED display applications. The methods used in this approach enable reliable, low-temperature bonding on ultra-small pads, addressing key manufacturing challenges in next-generation display technologies.

In the third article, “Novel Package Design Enhances Optical Efficiency of MicroLED Displays,” Naiwei Liu et al. used a high-refractive-index transparent resist to significantly enhance the light extraction efficiency of microLEDs. Additionally, a high-reflectivity white resin material combined with lens microstructures is adopted to converge the light from a wide viewing angle, increasing the brightness at the 0-degree viewing angle by approximately 53 percent.

In the final article, “Revolutionary MAX OLED Solution for Next-Generation OLED Displays,” Yu-Hsin Lin et al. addressed critical limitations of traditional RGB OLED patterning processes. It was shown that MAX OLED significantly improved aperture ratio, brightness, resolution, and display longevity. The precise angle-controlled deposition and pixelated encapsulation techniques protect sensitive OLED materials.

This shift toward microLED technology signifies a transformative moment in the future of displays, while advances in OLED display manufacturing continue to evolve with the potential to redefine performance standards across a variety of applications.