Seeing Red: InGaN Microdisplay Sharpens AR Glasses

A microdisplay developed by University of Cambridge spinout Porotech is expected to accelerate the development and commercialization of augmented reality glasses. The company reports that the microdisplay is the first based on native red indium gallium nitride (InGaN). The display has an active area of 0.55 in. diagonally and a resolution of 960 × 540.

Previously it had only been possible to produce blue and green microdisplays with GaN-based LEDs; red emission is reliant on devices based on aluminum indium gallium phosphide (AlInGaP), which struggles to produce the small pixel sizes necessary for AR. Using those components, efficiency would drop drastically as the size of the device decreased. To produce a full-color display, the light from different panels had to be combined.

With the new technology, all three light-emitting elements can be produced using a single toolchain, and the complexities of mixing devices based on different material structures is removed.

“AR technology is set to be a game changer, and micro-LEDs are particularly vital for the advancement of AR interfaces,” said Porotech CEO and co-founder Tongtong Zhu. “In traditional liquid crystal displays (LCDs) the image is a result of both modulating and filtering the light from a white back-lighting module. As such, most of the light created by the panel is wasted by the very working principle of the display. In addition to this inefficiency, the various filtering diffusion and modulation stages of the LCD display impose limits on how lightweight the final display can be.

“Emissive display technologies, on the other hand, only produce the light that is required of them — allowing for the final devices to potentially achieve much higher efficiencies. Self-emitting displays based on inorganic semiconductors can also be produced in monolithic fashion, allowing them to be more easily scaled down than traditional LCD or organic semiconductor displays — allowing for smaller, lighter, brighter, and reliable high-resolution displays to be made.”

Porotech has developed a microdisplay based on native red indium gallium nitride (InGaN) — with an active area of 0.55 in. diagonally and a resolution of 960 × 540. The bright native red can push the maximum achievable wavelength to 640 nm and beyond — a first for microdisplay visualization, the company said. Courtesy of Porotech.

To this point, the need to combine light-emitting devices based on different material structures has been the barrier holding back the advance of the technology. One solution has been the use of prisms, though the approach is large and bulky. Another approach stacks emitting layers on top of one another, though the light emitted by each color comes from a different depth in the display, which complicates the design of the optics. Combining LEDs from different materials onto one panel horizontally is yet another approach, but it requires very high precision in placing each individual LED element and other optical components.

“This has been the missing piece of the puzzle,” Zhu said. “As well as reducing costs, the bright native red can push the maximum achievable wavelength to 640 nm and beyond — a first for microdisplay visualization. Our breakthrough is now set to accelerate the commercialization of AR glasses as well as heralding a new era of brighter, sharper, more vivid microdisplays for products such as smartphones and smartwatches.”