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Technical Insight

Magazine Feature
This article was originally featured in the edition:
Volume 30 Issue 5

Nanowires eye augmented-reality displays


The mass market seeks augmented-reality displays small enough to embed in a pair of sleek, lightweight eyeglass frames.


When Apple shipped its first Vision Pro headsets this February, it joined a battle with Meta and other manufacturers for a share of the emerging global market for virtual reality (VR), augmented reality (AR), and mixed reality (MR) applications. But the Vision Pro’s large form factor and its hefty price tag raised as many questions as Apple answered in its presentation on the future of a new age of ‘spatial computing’.

Initial reviews noted that, like the popular Meta Quest headsets, the Vision Pro is large, bulky, and generally too heavy for all-day use. And while it offers spectacular immersive video and audio experiences, this comes at a hefty price. Retailing at $3,499, the Vision Pro is four-to-five times as expensive as its competitors.

Unfortunately, all of these rivals, which are capable of demonstrating the exciting possibilities of AR, MR, and VR applications, are held back by several issues. Today they are not small enough, are limited in efficiency, not easy to manufacture, and lack the affordability that would see many consumers make them a constant companion. The mass market wants to go beyond those headsets that resemble oversized ski goggles for immersive VR and MR applications, and move to AR displays that are small enough to embed in a pair of sleek, lightweight eyeglass frames that one can comfortably wear all day.

Delivering AR displays that are this small and efficient is far from easy. It demands advances in a range of technologies, starting first and foremost with a reduction in the size of the display. The bulk required for smart AR features to be added to a normal pair of glasses is determined largely by the display size, which governs the size of the waveguides, battery, mechanical parts, and other optical components necessary to deliver satisfying AR images. Today’s displays that are suitable for AR are still far too large to integrate with normal-sized eyeglasses. And because weight is largely determined by the size of the battery required, displays with greater efficiency are needed to ensure smaller power sources. Therefore, today’s displays that are based on microOLED and microLED emitters, small as they are, will need to be even smaller and far more efficient.

‘Bottom-up’ fabrication
One promising approach to realising these much-needed size and efficiency breakthroughs is to turn to nanowire-based LEDs. It is possible to integrate these submicron-scale emitters into displays that are small enough for a standard pair of eyeglasses (see Figure 1).

Figure 1. A single submicron-scale nanowire can be a complete LED (left). However, in most cases tens to hundreds of nanowires will make up a single sub-pixel of a full colour display (left-centre). LEDs can then be integrated on an red-green-blue display (right-centre) that’s small enough to fit unobtrusively into a standard pair of eyeglass frames (right).

Many of the early developers of this revolutionary technology are growing GaN nanowires on silicon or sapphire substrates with a core-shell architecture featuring a p-GaN shell and an n-GaN core. It is hard to overstate the potential benefits of these efficient nanowire LEDs. Individual microscopic nanowire LEDs, bundled and working in concert on a standard semiconductor substrate, have the potential to combine an extremely high efficiency at higher brightness with much lower costs and longer lifetimes than today’s LEDs and microLEDs. Allied to this, there is the use of simpler fabrication processes, offering the potential to scale-up mass production while minimising defects and delivering higher yields.

However, current nanowire LEDs and microOLEDs have yet to fulfil their promise. They are failing to deliver the brightness and efficiency that’s required to meet the demanding requirements of future AR displays. What’s more, they do not yet emit red or green light, and they require either filters or a layer of quantum dots to convert the blue emission to the red and green to create colour displays – and this adds to device manufacturing complexity and cost. On top of all these concerns, when the quantum dot down-conversion approach is scaled to a 1 µm pixel size, an efficiency loss results, undermining the advantages of the microLED.