In the rapidly evolving world of technology, Micro LED micro-display chips have emerged as a critical enabler across various cutting-edge fields. By 2024, Micro LED is projected to capture 18% of the AR device market. By 2030, the AR device market is expected to reach 25.5 million units, with Micro LED’s market share anticipated to grow to 44%, showcasing its vast market potential.
Moreover, as the technology matures, Micro LED’s unique advantages—ultra-compact size, ultra-high brightness, and ultra-low power consumption—are gradually displacing DLP optical engines, driving advancements in products like micro projectors, digital car lights, 3D printers, and automotive HUDs.
In this technological race, Yancheng Hongshi Intelligent Technology Co. Ltd. (hereinafter referred to as Hongshi Intelligent) has made significant breakthroughs in silicon-based Micro LED micro-display chips, positioning itself as a focal point in the industry. This article delves into Hongshi Intelligent’s recent achievements in Micro LED technology.
I. Enhanced Light Efficiency: Breaking Industry Bottlenecks
AR glasses have long been a pioneer in Micro LED applications. By 2024, 11 AR glasses manufacturers are expected to adopt Micro LED optical engines as their imaging source.
However, constrained by the low coupling efficiency of diffractive waveguides, the eye-view brightness must reach 1000 Nits, necessitating Micro LED chips to deliver over 2.5 million Nits. Given that Micro LED chips typically have a single pixel size of less than 10μm, enhancing light efficiency involves multi-dimensional technical optimizations.
1. Size Effect and Peel-off Damage
Traditionally, Micro LED manufacturing relied on sapphire epitaxial wafers, limited to 4-inch and 6-inch sizes. In contrast, silicon-based epitaxial wafers can scale up to 8-inch and 12-inch sizes, offering better performance and cost-effectiveness for micro-display chip manufacturing, albeit with greater technical challenges.
Sapphire substrate peel-off is a damaging process that can harm the chip’s epitaxial layer during laser lift-off, hindering light efficiency improvements. Hongshi Intelligent focuses on silicon-based substrate Micro LED manufacturing, which employs a non-destructive peel-off process, preserving the epitaxial layer and laying a solid foundation for enhanced light efficiency.
In simpler terms, the size effect significantly impacts the external quantum efficiency (EQE) of epitaxial wafers, which in turn affects the chip’s overall performance. At the Micro LED scale, the behavior of electrons and photons changes dramatically. For context, a human hair is about 50-70μm in diameter, while a Micro LED chip’s single pixel is much finer.
The correlation between EQE and the size effect is determined by current density. Typically, epitaxial wafer manufacturers test EQE for sizes above 40μm, leaving a gap for smaller sizes, which are crucial for AR glasses. Hongshi Intelligent’s Polaris A6 (single green) Micro LED achieves over 10% EQE at a 3.75μm pixel pitch, and 10%-15% EQE for blue Micro LEDs, demonstrating superior performance in small-scale applications.
2. Sidewall Effect Suppression
As Micro LED chip sizes shrink, the sidewall area ratio increases significantly. For instance, when the chip size reduces to 15μm, the sidewall emission ratio increases by 184%, often causing sidewall damage during etching.
Defects at the sidewalls exacerbate the quantum-confined Stark effect (QCSE), leading to non-radiative recombination (SRH), where electrons and holes recombine to release energy as heat rather than light, reducing light efficiency. Additionally, inclined sidewalls increase the exposure area of the multiple quantum well (MQW) layer, introducing more defects and enhancing charge coupling at the sidewalls, further diminishing light efficiency.
To address this, Hongshi Intelligent employs three methods for sidewall repair:
- Atomic Layer Deposition (ALD): Precisely controls film growth at the atomic scale, stabilizing dangling bonds and reducing non-radiative recombination.
- Coating: Applies suitable films to the sidewalls, neutralizing dangling bonds through chemical reactions or physical adsorption.
- Wet Processing: Uses specific chemical solutions to react with sidewall ions, converting dangling bonds into stable chemical bonds, thereby enhancing Micro LED chip performance.
3. Cavity Structure Optimization
Optimizing the cavity structure improves light generation, transmission, and extraction. A well-designed cavity enhances internal electric field distribution, promoting more efficient electron-hole recombination.
For example, precise control of cavity dimensions increases the probability of electron-hole recombination, boosting photon generation efficiency. Using high-reflectivity materials for cavity walls minimizes light absorption and scattering during transmission.
Hongshi Intelligent’s optimized cavity designs significantly reduce light loss, enhancing light utilization within the cavity and improving light extraction efficiency. For instance, using microlens arrays can increase light extraction efficiency by 40%.
4. Optical Reflector Selection
The optical reflector plays a crucial role in light reflection, absorption, and scattering, directly impacting the efficiency of converting electrical energy into emitted light.
By placing optical reflectors at the chip’s bottom or sides, light that would otherwise be lost is redirected towards the front, increasing light extraction efficiency. Hongshi Intelligent’s optimized optical reflectors can improve light extraction efficiency by 30%-50%.
Despite Micro LED’s potential for ultra-high brightness (millions to tens of millions of Nits), not all pixels emit light simultaneously. Typically, only 10%-15% of pixels are active at any given time, leading to the industry’s use of APL 10% for measurements. Hongshi Intelligent has achieved an average light efficiency of 3 million Nits (at 100mW power) for 0.12 single green Micro LED micro-display chips, marking a global milestone in 8-inch silicon-based micro-display chip production.
II. Uniformity Leadership: Achieving Superior Display Quality
Uniformity is a critical metric for Micro LED micro-display chips. Since the projection size is often over 10,000 times the chip size, any non-uniformity is magnified in the display.
Key technical factors affecting uniformity include film thickness uniformity and etching consistency. Hongshi Intelligent has achieved a 98% uniformity rate, surpassing the industry’s leading standard of 90% and the average of 80%.
Improving uniformity is a gradual process. Hongshi Intelligent has progressed from 60% to over 90% through stable 8-inch wafer processes and advanced Demura correction technology, solidifying its leadership in Micro LED uniformity.
III. Screen Defect Control and Optical Coupling Optimization
Micro LED chip screen defects are subject to stringent industry standards: zero bright spots, no more than one continuous dark spot, and fewer than 100 individual dark spots. Hongshi Intelligent has achieved zero bright spots, no continuous dark spots, and fewer than 30 individual dark spots, setting an industry benchmark.
In optical coupling, controlling the beam divergence angle is crucial. Traditional LEDs exhibit a Lambertian radiation pattern with a ±60° emission angle, limiting waveguide coupling efficiency. Hongshi Intelligent employs wafer-level micro-nano processing to create microlens arrays on Micro LED surfaces, compressing the emission angle to ±25°-30°, enhancing axial light intensity by 2.8 times and meeting the stringent directional requirements of high-density integrated waveguide systems.
IV. Production Efficiency, Yield, and Cost Advantages: Building Comprehensive Competitiveness
Micro LED micro-display chip manufacturing involves eight major processes and over 200 sub-processes, including epitaxial growth, bonding and peel-off, photolithography, etching, coating, electrode fabrication, chip dicing, packaging, testing, and sorting. The precision required at such a microscopic scale makes the process highly challenging.
Gallium nitride (GaN), a key material in Micro LED manufacturing, is also used in GaN radar for aerospace applications. However, Micro LED’s tiny size (4μm×4μm) presents greater challenges in achieving uniformity and consistency compared to GaN radar’s larger emitters (100μm×100μm).
Hongshi Intelligent excels in nanoscale film thickness uniformity control (±3%), plasma etching anisotropy deviation (<5°), and particle contamination control (0.1 particles/cm²), ensuring high product quality. The 8-inch silicon substrate offers significant cost advantages, with production costs being 1/6 of those for 4-inch substrates, and a 4.8-fold increase in single-wafer productivity.
By expanding the critical process window to over 85% of theoretical values, Hongshi Intelligent has achieved a 2.3-fold improvement in process uniformity, a 4.8-fold increase in single-wafer productivity, and a 50% reduction in overall manufacturing costs, delivering high-quality, cost-effective products to customers.
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