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Efficient Red Micro-LEDs with Pixel Size < 5 Microns for Next-Generation Displays and Visible Light Communication Systems

Description:

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): FutureG, Integrated Sensing and Cyber, Microelectronics, Integrated Network Systems-of-Systems, Advanced Materials, Human-Machine Interfaces

 

OBJECTIVE: Develop and demonstrate new micro-LED architectures which will lead to red micro-LEDs with high external quantum efficiency (>2%) when the pixel size is less than 5 microns.

 

DESCRIPTION: Due to their fast response, lightweight, low power consumption, and high efficiency, micro-LEDs have received considerable attention in the development of next-generation displays and visible light communication systems for strategic and tactical battlefield applications for dismounted soldiers, as well as command and control systems. Virtual Reality (VR) and Augmented Reality (AR) systems must have a high number of PPI (at least 4,000) since they emphasize the importance of small areas and high resolutions for battlefield visualization. In order to achieve the required miniaturization and high-resolution design, each micro-LED must be less than 5 microns in size.

 

In spite of the reduction in LED chip size to below 10 microns, GaN-based blue and green micro-LEDs retain high performance in terms of external quantum efficiency (EQE). Most red micro- LEDs, however, suffer from significant size-dependent efficiency droop as a result of serious surface recombination at the edges of the device. Existing red micro-LEDs shows EQE as low as 0.1% when their size is less than 5 microns which represents a significant challenge for next-generation high-resolution AR/VR systems.

 

Many approaches, such as those based on InGaN-quantum wells, quantum dots enhanced structures, etc. have been proposed in the literature to address this problem with some success. However, many of these approaches are for chips with larger dimensions than what is required in this solicitation. In spite of this, they indicate that there are potential paths towards realizing high efficient red micro-LEDs. As part of addressing this technology gap, innovations in material development and novel fabrication technologies as well as significant improvements in existing materials and processes will be necessary to minimize, if not eliminate, sidewall damage and degradation of electrical injection. Several strain engineering methodologies have also been reported in the literature, especially those relating to the fabrication of multiple quantum well structures.  In order to achieve EQE greater than 2% for red micro-LEDs with a size between 2 and 5 microns, the Army is seeking solutions. A new LED architecture should be compatible with RGB full color integration and be capable of accommodating large arrays. It should be noted that we are not looking for traditional technical approaches such as sidewall passivation using ALD or micro-LED pyramids.

 

PHASE I: Develop a proof-of-concept solution for red micro-LEDs with pixel sizes of 2-5 microns and EQEs exceeding 2%. A detailed micro-LED architecture design and theoretical/numerical estimations of the EQE based on the pixel size must be included in the solution. Ensure that all aspects of device fabrication are considered, including a preliminary assessment of long-term environmental stability and justify the approach's feasibility and practicality. Phase I is designed to assess the technical merit, feasibility, and commercial potential of a proposed effort, and to evaluate the performance prior to providing further support in Phase II. The deliverables should include a comprehensive final report, a presentation of the concept design, models, modeling data and results, model validation data, an optional demonstration of the proof of technology, and plans for the continuation of Phase II work.

 

PHASE II: Using the results of Phase I, develop and demonstrate a prototype red micro-LED device that meets all the requirements stated above. The prototypes should be fabricated by using standard cleanroom processes and be capable of integrating with the existing standard LED drivers for displays. In addition, they should demonstrate the modularity of the system and prove the feasibility of large arrays during operational demonstrations. Conduct accelerated aging tests to determine the lifetime reliability and performance characteristics of the devices in both storage and operation. Deliverables must also include a detailed final report comprising a comprehensive assemblage of design documents, fabrication methods, experimental protocols, and prototype testing data and results. In addition, a full-scale prototype system with associated documentation must also be delivered to the government point of contact for independent testing and evaluation at a government laboratory.

 

PHASE III DUAL USE APPLICATIONS: Based on the prototypes developed in Phase II, continuing development must lead to productization of miniaturized red micro-LEDs for optical systems. Conduct testing on variety of military platforms and develop a process for a large-scale production to support potential transition partners including Army, and other DoD agencies. Despite the fact that this technology is aimed at military and strategic applications, many other optical circuit applications, including in telecom industry hardware, can also be benefited by miniaturized red micro-LEDs. The sources that can operate over a very wide range of environmental conditions are likely to bring value to many existing commercial applications. Also, technology meeting the needs of this topic could be leveraged to bring AR/VR systems toward a price point that could make them more attractive to the commercial markets.

 

REFERENCES:

  1. "Laser Lift-off Mechanism and Optical-electric Characteristics of Red Micro-LED Devices," Opt. Express, 31, pp. 7887-7899 (2023).;
  2. "An Ultrahigh Efficiency Excitonic Micro-LED," Nano Lett. 23, PP. 1680–1687 (2023).;
  3. "InGaN-based Red Light-emitting Diodes: From Traditional to Micro-LEDs,"  Jpn. J. Appl. Phys. 61 SA0809 (2022).;
  4. "2000 PPI Silicon-based AlGaInP Red Micro-LED Arrays Fabricated via Wafer Bonding and Epilayer Lift-off," Optics Express, 29, pp. 20217-20228 (2021).;
  5. "Fabrication and Study on Red Light Micro-LED Displays," IEEE J. Electron Devices Soc., 6, pp. 1064-1069 (2018).;
  6. "Enhanced Efficiency InGaN/GaN Multiple Quantum Well Structures via Strain Engineering and Ultrathin Subwells Formed by V-Pit Sidewalls," ACS Appl. Opt. Mater. 2, pp. 220-229 (2024).;
  7. "The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs,"  Micromachines, 14, (2023).;
  8. "Improvement of 0ptical Properties of InGaN-based Red  Multiple Quantum Wells," Optics Express, 31, pp. 18567-18575 (2023).

 

KEYWORDS: Micro-LEDs, Full-color display, Display devices, RGB displays, Light emitting diodes, Optoelectronic devices, Virtual reality, Augmented reality, External quantum efficiency

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