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10 August, 2021 - 21:05 By Tony Quested

Breakthrough promises brighter, sharper, more vivid displays for smart devices

University of Cambridge spin-out Porotech is set to transform next-generation display technology – heralding a new era of brighter, sharper, more vivid microdisplays for even the smallest devices.

It’s all thanks to the company’s revolutionary micro-LED production technique using a new class of semiconductor material that is redefining what is possible. It offers performance improvements that are suitable for mass production yet can be customised for individual needs.

Micro-LED is the next major leap forward for displays on products such as smartphones and smartwatches, as well as virtual reality (VR) and augmented reality (AR) headsets. 

It is particularly useful in outdoor settings, where sunlight can often make existing displays difficult to see clearly. But the performance of current micro-LED technologies deteriorates as the device size decreases.

Porotech has created a new class of porous gallium nitride (GaN) semiconductor material – basically GaN with tiny holes in it that are a few tens of nanometres across. It’s an entirely new engineered GaN material platform to build semiconductor devices on – and it offers performance improvements that are crucial for the next generation of microdisplay devices.

Despite only spinning out in January last year, Porotech has been generating revenue for 12 months, with a string of repeat orders – and is working with some of the biggest global names in display technology. 

In November 2020, the company launched the world’s first commercial native red indium gallium nitride (InGaN) LED epiwafer for micro-LED applications.

Porotech’s next step is to expand its novel approach to integrate InGaN-based red, green and blue (RGB) micro-LEDs for full-colour microdisplays – and ultimately create ‘smart’ pixels that can be controlled independently for unrivalled responsiveness and accuracy for things like AR gestures.

Currently, technologies being tested for smart pixels are largely based on aluminum indium gallium phosphide (AllnGaP) material and quantum dot colour conversion (QDCC). 

But AllnGaP struggles at the small pixel sizes required by AR – and QDCC suffers from uniformity and stability issues. In addition, both approaches require a mixture of different material.

Porotech’s novel approach enables all three primary colours to be made with the same GaN material and integrated on a single wafer, with no need for special structuring. The company also plans to develop its own supply chain ecosystem to help it develop and produce products more quickly.

CEO and co-founder Dr Tongtong Zhu said: “We are already seeing high levels of demand for our standard and customised porous GaN substrates and micro-LED epiwafers, which we can provide on sapphire and silicon platforms ranging from 100mm (4”) to 300mm (12”). 

“Smart pixels will be our next development – monolithically generated and integrating native self-emissive RGB micro-LEDs on a single wafer to give smaller, lighter, thinner displays that use less energy and offer the greater accuracy required for things like AR gestures.”

In June this year, Porotech announced that it had raised £3 million to fund the next stage of development of its novel production technique. The funding round was led by Speedinvest, with participation from previous investors IQ Capital, Cambridge Enterprise, Martlet and Cambridge Angels.

Rick Hao, Principal at Speedinvest, said: “The revolutionary technology developed by Porotech is set to transform the electronics industry as demand grows for smaller, lighter, sharper displays that are more accurate and environmentally friendly than ever before.

“This new type of porous GaN semiconductor material fits within existing industry processes and is robust and flexible enough to be tailored to different applications. Porotech has demonstrated that it has both the product and the commercial capability to become a key player in next-generation display technology.”

Micro-LED displays using GaN-based material technology are widely seen as the only technology that can deliver displays bright and efficient enough to meet the requirements of AR. But, until now, achieving the necessary high-efficiency, ultra-fine-pitch red pixels has proved a challenge.

“Integration of AlInGaP red and indium InGaN green and blue LED displays in a module with micron-scale pixels is extremely challenging as high surface recombination velocities in AllnGaP devices make this material unsuitable for efficient micro-LEDs,” said Dr Zhu. 

“Our breakthrough extends the emission range of InGaN LEDs to meet the performance needs of the red display, whilst delivering the ability to scale wafer size required by micro-LED semiconductor display technology.”

GaN is a material poised to make an impact across electronics and optoelectronics – from efficient power transistors and lasers to quantum devices, sensors and solar cells – and the introduction of porous architectures can extend its capability in all these realms. 

Porotech’s proprietary technology is robust but also flexible enough to be tailored to the needs of different applications. Its native red InGaN micro-LEDs have a wavelength of 640 nm at 10 A/cm2, and improved performance over conventional AlInGaP and colour-converted red at very small pixels and pitches.

The Porotech team creates the nanoscale porosity in GaN wafers using electrochemical etching. The etch is conductivity selective and responds differently to the material, depending on its doping density. Porosity is created in doped layers while undoped layers are left undamaged, allowing complex 3D nanostructures to be created. 

The etchant flows to and from the doped layers via the many nanometre-scale channel-like defects that exist within any GaN wafer.

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