According to the Cambridge University spin-out, it has only been possible until now to produce blue and green microdisplays using GaN-based light-emitting devices. Red emission has relied on devices based on aluminum indium gallium phosphide (AlInGaP), which has difficulties at the small pixel sizes required by AR, meaning there is an efficiency drop as the device size decreases. Furthermore, to produce a full-colour display, the light from different panels has had to be combined.
In Porotech’s breakthrough 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 960x540.
Porotech raises £3m for microdisplay development
"AR technology is set to be a game changer and micro-LEDs are particularly vital for the advancement of AR interfaces," Porotech CEO and co-founder Dr Tongtong Zhu said in a statement. "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."
According to Porotech, the problem so far 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 but this results in the light emitted by each colour coming from a different depth in the display, which complicates the design of the optics and requires very high precision in the pitch of the LEDs in each display, as well as the alignment of the various layers in the structure. 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."
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