Overview of the Development
On October 9, reports from Chinese Optics, Light: Science & Applications, and other sources announced that Professor Pan Anlian and Professor Li Dong from Hunan University, in collaboration with Innovision and LatticePower, successfully developed IC-level GaN-based Micro LED wafer manufacturing technology. This technology encompasses processes for producing large-sized, high-quality silicon-based Micro LED epitaxial wafers, non-aligned bonding integration techniques, and atomic-level sidewall passivation techniques, achieving the highest reported brightness for green Micro LED micro-display modules on GaN epitaxial wafers with silicon substrates.
Research Publication
The relevant research results were published in Light: Science & Applications under the title “Ultra-high Brightness Micro-LEDs with Wafer-Scale Uniform GaN-on-Silicon Epitaxial Layers.”
Key Findings and Innovations
In Figure 1a, a real photograph of the 4-inch silicon substrate GaN-based Micro LED epitaxial wafer is presented along with its structural schematic. The research team explored a method called “Ga atomic surfactant-assisted growth,” successfully cultivating a high-quality AlN buffer layer at a moderate temperature of 1100°C. This resulted in a low dislocation density (approximately 5.25×10⁸ cm⁻²), low warping (16.7 μm), and excellent wavelength uniformity (with a standard deviation of 0.939 nm) for the green Micro LED epitaxial structure (as shown in Figures 1b – 1d). Currently, this technology has been successfully extended to 6, 8, and 12-inch silicon substrate GaN wafers.
Sidewall Repair and Roughening Techniques
Leveraging the high-quality silicon substrate GaN-based green epitaxial materials, the research team successfully developed a wet repair and roughening technique for Micro LED sidewalls. Utilizing the anisotropic etching rates of polar and non-polar GaN surfaces in alkaline solutions, they effectively removed etching damage from the Micro LED sidewalls. By combining this with atomic-level sidewall passivation, the non-radiative recombination rate on the sidewalls was significantly reduced. This technique also achieved sub-micrometer level roughening of the light-emitting surface, effectively enhancing the light extraction efficiency of the Micro LEDs. As shown in Figure 2, the results clearly indicate that the wet repair and roughening techniques greatly improved the brightness of the Micro LEDs, with a micro-display array of Micro LEDs having a pixel size of 5 μm achieving a maximum luminous brightness of 10 million nits.
Vertical Non-Aligned Bonding Integration
The research team further developed a vertical non-aligned bonding integration technology, successfully constructing independently addressable Micro LED display chips that are closely integrated with silicon-based CMOS. The 0.39-inch display features excellent brightness uniformity, with a standard deviation of only 720 cd/m² (2.2%), and a pixel density of up to 3400 PPI, achieving high-definition display for images and videos.
Conclusion
This research work, based on high-quality silicon substrate GaN-based Micro LED epitaxial materials, has developed IC-level Micro LED wafer processing technologies, including wet treatment techniques, atomic-level passivation techniques, and vertical non-aligned bonding techniques. This has successfully produced ultra-high-brightness Micro LED micro-display matrices and Micro LED micro-displays integrated with silicon-based CMOS, providing significant support for the large-scale manufacturing and application of high-brightness GaN-based Micro LED micro-displays.
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