Display breakthrough for AR tech boost

Cambridge spinout Porotech has made a breakthrough in its microdisplay technology that it says could be a boon for AR screen technology.

The advance is based around red indium gallium nitride (InGaN). Microdisplays such as those found in AR glasses have, until now, only been able to work with green and blue GaN-based light-emitting devices. Red emission has relied on aluminium indium gallium phosphide (AlInGaP), which struggles at the small pixel sizes required by AR can also be tricky to combine with the green and blue elements in order to achieve full colour.

According to Porotech, its breakthrough means all three light-emitting elements can be produced using a single toolchain, removing the complexities of mixing devices based on different material structures. The microdisplay has an active area of 0.55 inches diagonally and a resolution of 960×540.

“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 Dr 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 more easily scaled down than traditional LCD or organic semiconductor displays – allowing for smaller, lighter, brighter and reliable high-resolution displays to be made.”

A key challenge has been the need to combine light-emitting devices based on different material structures. One solution has been the use of prisms – but this is a relatively large and bulky approach. Stacking emitting layers on top of each other is another option. However, this results in the light emitted by each colour coming from a different depth in the display, which complicates the design of the optics. Combining LEDs from different materials onto one panel horizontally is an alternative approach, but this requires very high precision in placing each individual LED element and other optical components.

“Porotech’s new class of porous GaN semiconductor material is now redefining what is possible – enabling the creation of efficient and bright native red InGaN micro-LEDs and microdisplays,” said Dr Zhu.

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