China-based Hongshi Intelligent Technology Co. is developing microLED-based headlights and puddle lights to compete with DLP-based and alternative LED-based solutions. In a presentation given at the Vehicle Displays and Interfaces conference, the company described a 3-panel X-cube full-color solution, a 0.61-inch green/white microLED, a 0.12-inch green microLED, along with a novel approach to a full-color monolithic microLED.
Adaptive headlights that feature controllable pixels offer many benefits for drivers. ams Osram introduced the first LED-based headlight in 2017 and recently introduced their second-generation product, the EVIYOS II. This increased the number of addressable LEDs from 1024 to 25,600 (320×80) using microLEDs with a 40-micron pixel pitch.
Texas Instruments launched DLP projection solutions in 2018 and offer a range of options today. These systems are large and power hungry, which is why microLED-based options are attractive at this time.
Hongshi described their 0.61-inch device which is targeted for Adaptive Dynamic Beam (ADB) or smart headlight applications. The specifications for the 0.61-inch device integrated into a headlamp package are shown below. It can be operated in green-only or white modes. Note that the lumen output is shown, not the luminance of the microLEDs in the table below. However, in the presentation, speaker Yi Liu noted that the engine can achieve 8 million nits in green. He noted that their microLED ADB solution is 50% smaller and offers 80% less power consumption than a DLP ADB product.
Hongshi also has a 3-panel color solution using 0.12-inch displays that appears to be similar to the micro-projector offered by Jade Bird Display. That means 3 panels with an X-cube combiner and a small projection lens. This was not demonstrated in Detroit but was shown at the CIOE show in Shanghai. Resolution is 640×480 with a 0.35 cc volume, 2.5 million nits of brightness and field of view of 30-degrees. They plan to shrink the discrete microLED chips in this product to 0.1” or even 0.08-inch diagonal and increase the resolution to 800×600.
Interestingly, Liu said that their red-only panel uses quantum dot conversion and has achieved a record output of 2 million nits for devices less than 4 microns in size, the same as the native blue microLED. Placing quantum dots directly on the LED has remained a challenge due to the high flux loading which can rapidly degrade the quantum dots. Pacific Light Technologies was developing this technology and was later acquired by ams Osram. But that operation has now been shut down. While 2 million nits is impressive, Liu did not specify the lifetime, so it may not be commercially viable yet.
Hongshi has also developed a 0.12-inch green monochrome device that can be used for exterior courtesy lights or AR glasses. This display offers a resolution of 640 x 480 using 3.75 x 3.75-micron microLEDs. Luminance is specified as 8 million nits, but at 3 million nits, the power consumption is a modest 100 mW.
Hongshi fabricates their monolithic full-color microLEDs using what they call a “Hybrid Stack Structure.” This starts with a wafer-to-wafer bonding of the 8-inch CMOS wafer to an 8-inch GaN-on-silicon substrate that has a green epi layer. This green epi layer is processed to define green sub-pixels. A second 8-inch GaN-on-Silicon wafer with a blue epi layer is then bonded to the pixelated green wafer. Again, sub-pixels are fabricated (one for blue and two smaller ones for red) with red sub-pixels getting red quantum dots. A full-color pixel is thus composed of a large green, medium blue and two small red sub-pixels. Microlenses are added above each sub-pixel to increase collection efficiency and provide a collimated beam. The wafer is then diced and packaged into individual microdisplays.
Liu described the process but did not reveal any performance data, so still early days.
