OLED-type microdisplays, used in camera viewfinders and virtual-reality systems, measure just several square millimeters. One of the main complaints about the displays is their low luminosity, a problem especially for augmented reality systems. “This is because the microdisplay generates images that are going to be superimposed on the real environment by way of an optical system. Because the real environment is well-lit, the microdisplay has to offer particularly good luminosity to be effective,” explained a Leti researcher.
Gallium nitride (GaN) LEDs, already widely used in lighting and known for their excellent yields, were the ideal candidates for more luminous microdisplays. To make them work, Leti researchers first had to make them much, much smaller and find a way to reproduce hundreds of thousands of the microsources on a very small surface while maintaining the ability to power them individually.
Leti leveraged know-how in assembly technologies to couple a GaN micro-LED network with a power circuit. The resulting prototype, presented at the TechConnect trade show, boasts more than 70,000 LEDs with a 10-micron pitch (the density of a traditional microdisplay) and is 1,000 times more luminous than current microdisplays. A second prototype, this one with 500,000 LEDs, is currently being built. This new prototype will be able to display HD video. In addition to augmented-reality glasses, the technology could also find its way into head-up displays for cars and planes and pico-projectors.