Since 2018, Plessey has been at the forefront of the display technology industry. Utilising its proprietary GaN-on-Silicon platform with its monolithic process, Plessey’s microLEDs allow the next generation of wearable devices and optical instruments: from AR glasses to personal information displays to be brought to life.
The biggest asset within Plessey is its employees. The combination of extensive skill sets, knowledge and expertise is critical to Plessey’s continued success and ground-breaking technology developments. In 2019, Plessey saw a 20% increase in headcount and will continue to see significant headcount increases during 2020, in line with exciting growth plans.
Plessey’s monolithic GaN-on-Si technology is IP protected and one of a kind. Upgrading to full-field emissive microLED displays from illuminators allows Plessey to target the display market and compete with incumbent LCD and OLED technologies.
The silicon substrates’ thermal conductivity means heat can be dissipated from the system much more quickly compared to the widely used sapphire substrate. As a result, GaN-on-Si LEDs are more reliable and reduce both the cost of heatsinking and the space this takes up.
This also results in greater lumen output, increased energy efficiency, higher resolution and better contrast. It’s also more cost-effective to produce than competing LED technologies. Plessey processes 150mm and 200mm wafers but the technique can easily be scaled to 300mm and larger, improving cost and yield. GaN-on-sapphire currently uses 50mm and 100mm wafers.
Displays require microLEDs to interface to a backplane, and while bonding individual LEDs to a backplane has been shown to be technically viable, it is questionable whether it is commercially viable to scale it down to smaller displays. By contrast, Plessey’s monolithic solution enables all the microLEDs to be bonded to an active matrix backplane in a single, wafer-level process, which increases pixel performance and improves manufacturability. This approach can only be achieved using GaN-on-Silicon as sapphire substrates are not flat enough to allow for accurate wafer-level bonding between the microLED arrays and the CMOS backplane.
Full RGB Native Pixels
To create a bright enough full-colour microLED display for a variety of applications, Plessey needed a native Green and Red as colour converted Blue to Green/Red had a lot of losses and we knew performance quality could be dramatically improved.
To do this, we used our proprietary GaN-on-Si technology and engineered the early layers in the manufacturing process, to alter natural emission from 450 nanometres (Blue) to 530 nanometres (Green) and 630 nanometres (Red). Native Green was achieved in March 2019 and native Red in December 2019.
With a total input power of 250 mW, Plessey’s native Green segments can emit 2 million nits of brightness.
Plessey’s native Red LEDs have a wavelength of 630 nm at 10 A/cm2, full width at half maximum of 50 nm, a hot/cold factor over 90% and higher efficiencies over conventional AlInGaP or colour converted Red, at ultra-fine pixel pitches.
In October 2019, Plessey also announced the ground-breaking ability to grow native Blue and Green on the same silicon wafer.
In May 2019, Plessey achieved the world’s first monolithic GaN-on-Si wafer to CMOS backplane wafer bonding, which was a massive breakthrough for not only the company but the industry. This creates a full HD active-matrix allowing each of the two million pixels to be addressed creating a video when connected to an image source.
In January 2020, Plessey has further optimised their processes to achieve a successful wafer to wafer bond of a monochrome native Green 1080p microLED display (0.26” diagonal) to a 3-micron pixel-pitch backplane from Compound Photonics, creating over two million individual electrical bonds.
In January 2020, Plessey will target more specialised applications with direct-drive displays, featuring high resolution, symbolic content. The fully emissive direct drive display segments are driven directly from an external source. No intelligent backplane is required, therefore cutting out a more complex bonding process, as required by our active-matrix technology offering.
The direct-drive displays have pixel capability down to 10-micron, allowing for ultra-fine, ultra-high-resolution detail. Also due to the small form factor of the direct drive display, it can be easily integrated into smart glasses and head-mounted displays from swimming/ski/scuba-diving goggles to cycling glasses, range finders and motorcycle helmets.
To achieve these key milestones, Plessey invested over £5million in production-grade equipment including a GEMINI® production wafer bonding system from EVG and an AIXTRON G5+ C metalorganic chemical vapour deposition reactor.
Smartphones and smartwatches might typically offer 400ppi pixels per inch (PPI) displays, based on an 80-micron pixel pitch. But moving to AR applications means the pixel pitch needs to be reduced to 40-micron, or even as low as 10-micron. It is beyond the ability of pick-and-place machinery to place pixels with any kind of accuracy at this scale. Plessey’s IP protected technology can help to significantly reduce the pixel pitch and allow pixel capabilities down to 1-micron. Our current microLED emissive display demonstration has a pixel pitch of 2.5-micron which already exceeds the needs of the typical AR application and we are continually striving to develop our microLEDs further.
As microLED is the first new display technology to be commercialized in over a decade, consumer electronics and television manufacturers such as Samsung, LG, Apple etc. are all looking to create a product including the hot-new piece of tech that could dramatically improve their products.
Plessey’s microLEDs are still a developing technology, however, Vuzix, one of the world’s leading developers of smart glasses and video wearable devices, announced in June 2018 and reconfirmed in June 2019, it will be using Plessey’s microLED technology in the development of its next-generation AR glasses.
In 2020, we will continue our commitment to provide ‘world firsts’ and ‘technology breakthroughs’ for the microLED display market and for the wider display industry.
To support these achievements, Plessey has formed an influential advisory board including former VP of Macintosh Hardware Systems Engineering at Apple, Dr Edward H. Frank. It is also essential to note that, Plessey has several active R&D partnerships, many confidential, but do include some key players within the consumer electronics industry. Announced already include, Vuzix and Compound Photonics.