MicroLEDs, AR/VR Displays, and Micro-Optics: Innovations, Start-Ups, Market Trends

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MicroLED technology has the potential to revolutionize augmented reality (AR) glasses by offering high-performance displays, but its success depends on aligning with the needs of AR developers and the markets they serve. In this talk, I will share insights from an AR system developer’s perspective, focusing on the role of MicroLED in various AR use cases across industries. We will discuss: Optical layouts and system architectures in AR glasses, Critical microdisplay requirements: resolution, brightness, efficiency, size, and power consumption, How MicroLED can be best implemented to address the unique challenges of AR systems,Key factors that MicroLED companies should consider to deliver added value for AR developers and differentiate themselves from alternative display technologies.By understanding the expectations and constraints of AR system development, MicroLED technology providers can better position their solutions to drive adoption, attract AR developers, and unlock opportunities across diverse markets, from consumer electronics to medical, defense, and industrial applications.

The next-generation displays built on nitride-micro-LEDs aim to provide high brightness and resolution covering a large display area. They therefore require driving transistors in their active-matrix arrays capable of delivering a high current density within a limited footprint and can be fabricated cost-effectively over a large-area substrate. We show that ordered defect compound semiconductor CuIn 5 Se 8 , which forms regular defect complexes with defect-pair compensation, can simultaneously achieve high performance and scalable solution processability. After printing from their molecular precursors which decompose after a low temperature (370 o C) annealing, the uniform thin films of CuIn 5 Se 8 can be incorporated as the semiconductor channel of thin-film transistors, exhibiting defect-tolerant, band-like electron transport supplying an output current above 35 microamperes per micrometer, with a large on/off ratio greater than 10 6 , a small subthreshold swing of 189 ± 21 millivolts per decade, and a high field-effect mobility of 58 ± 10 square centimeters per volt per second, with excellent device uniformity and stability, superior to devices built on its less defective parent compound CuInSe 2 , analogous binary compound In 2 Se 3 , and other solution-deposited semiconductors. CuIn 5 Se 8 transistors can be monolithically integrated with carbon nanotube transistors to form high-speed and low-voltage three-dimensional complementary logic circuits with a short stage delay of 75 ns under a low supply voltage of 6 V. They can also be fabricated directly on top of GaN micro- LED arrays under a low thermal budget. Their high performance allows them to drive these micro-LEDs to a high current density above 200 amperes per square centimeter and realize high-resolution active-matrix displays with pixels per inch greater than 500.

Micro-LED is known as the best display technology for the next generation displays, however real commercialization has been repeatedly delayed due to lack of advanced process technologies. Besides the mass transfer, RGB integration and enhancing efficiency of the small LED die appears more critical to be resolved. The biggest hurdle for RGB integration is making small red LED die having comparable efficiency to the blue and green. AlGaInP native red, quantum dot, and InGaN reds have been widely attempted. While AlGaInP red appears to be a strong contender, however, fatal disadvantage is an outrageously low efficiency due to sidewall defects formed by mesa dry etching, thus, defect-free mesa etching technology has been highly sought. Recently, we have achieved a crucial breakthrough in developing mesa etching of the AlGaInP native red micro-LED by “defect-free” wet chemical etching. In the past most of the efforts have been focused on the post dry etching recovery, However, they are helpful for partial recovery only. More importantly, they are not effective for the small die because sidewall defect penetration depth is close to or excess of the micro-LED die. According to our cathodoluminescence results, the sidewall defect penetration depth of the dry etched micro-LED is more than 7 m, while it is less than 0.2 m for the wet etched micro-LED. Thus, effective mesa area of the dry etched red micro-LED is only 28% of the wet etched, which implies that almost no or negligible number of defects exist in the wet etched red micro-LED. Further, our wet etching is capable to etch thicker than 6 m AlGaInP epi layers with etch rate similar to dry etching. In particular, it is one-step etching for any combination of binary, trinary, and quaternary compound semiconductor alloys without need for multiple photo-lithography processes. The chip sidewall is highly vertical and anisotropic; thus, no undercuts are observed after mesa etching. Both defect-free etching and promising etch profile results indicate that our wet etching technology is ready to apply for mass production process for mesa etching of the phosphide-base native red micro-LEDs.