The Propolys project, carried out at CEA-Leti from 2021 to 2025 with Carnot funding, has validated several core technology building blocks needed for full-color micro-LED displays, a key enabler for future augmented reality glasses and headsets.

Micro-displays for AR are extremely small, measuring barely a centimeter across, yet they must pack in millions of micro-LEDs, each only a few micrometers in size. GaN-based micro-LEDs are especially attractive because they can deliver much higher brightness than OLEDs, which is crucial for keeping overlaid information visible in bright ambient light.

To move beyond today’s approach of assembling multiple monochrome displays, Propolys explored a monolithic strategy: sequentially growing the structures for the three colors on the same substrate. The work drew on an unusually broad mix of CEA-Leti expertise, involving about 20 researchers from four laboratories across the Optics and Photonics Department and the Technology Platforms Department. That combination allowed the teams to iteratively refine both epitaxy and component manufacturing.

After four years, the project achieved blue, green and red emitters on a 200 mm GaN-on-silicon substrate. The teams also demonstrated multiple successive epitaxial growth sequences on the same substrate, including blue and green emitters placed side by side with a 5 µm pixel pitch. Crucially, they also developed an integration process compatible with micro-display fabrication.

This monolithic integration is a significant step toward industrialization in a market seen as highly promising but intensely competitive. A complete RGB display still requires further advances, but the know-how generated by Propolys now provides a strong base for future full-color micro-LED development and potential industrial partnerships.

​​The Propolys project, conducted at CEA-Leti between 2021 and 2025, successfully validated several key technology building blocks for the development of full-color micro-LED displays. Supported by Carnotfunding, the project will contribute to future augmented reality applications.

At the heart of augmented reality glasses and headsets are micro-displays measuring barely a centimeter across. These tiny displays can integrate millions of micro-LEDs, light sources only a few micrometers in size.

In particular, gallium nitride (GaN)-based micro-LEDs offer significantly higher brightness than current OLED technologies. This is essential for displaying information overlaid on glasses, even in bright ambient environments.

The Propolys teams therefore decided to explore an innovative approach: sequentially growing the structures emitting the three colors on the same substrate, rather than assembling several monochrome displays, as is currently done.

This strategy was made possible by combining a wide range of CEA-Leti expertise.

The project brought together around twenty researchers from four laboratories of the Optics and Photonics Department and the Technology Platforms Department.

This rare combination of complementary expertise enabled the teams to continuously fine-tune both the epitaxy and component manufacturing processes.

The results are particularly encouraging.

After four years of research, the teams successfully obtained blue, green and red emitters on a 200 mm GaN-on-silicon substrate. They also demonstrated several successive epitaxial growth sequences on the same substrate, producing blue and green emitters side by side with a 5 µm pixel pitch.

Most importantly, they developed an integration process compatible with the fabrication of a micro-display.

This monolithic integration approach represents a key step toward future industrial developments in a market that is both highly promising and highly competitive.

However, developing a complete RGB display will require further progress.

The knowledge and expertise acquired through Propolys now provide a strong foundation for further development of full-color micro-LED displays and for establishing future industrial partnerships.