Tongtong Zhu is an experienced researcher in III-nitride semiconductor materials but since 2018 he has been the co-founder and CEO of UK startup Poro Technologies Ltd., with big plans in the field of microLED displays.
Porotech was founded in April 2018 by Tongtong Zhu, CEO, and Yingjun Liu, CTO and Professor Rachel Oliver, chief scientific officer, to develop and commercialize work done at the University of Cambridge.
The company, headquartered in Cambridge, trades as Porotech and has capabilities in making porous gallium nitride which it has been applying to light emitting diode (LED) arrays. We took up an opportunity to quiz Zhu about the company’s technology and advantage over its competition?
Zhu answered directly: “Our biggest advantage is in the limitations of GaN. It is a compound semiconductor material with a wide band gap but because of the alloy nature there are always limitations: wafer bow; lattice mismatch, crystal dislocations. The difference is in how you deal with those issues.”
Zhu claims the addition of a porous buffer zone can support enhanced performance in many areas: optical, mechanical, thermal, electrical and even in the piezoelectric effect. Zhu confirmed that the porosity is created using wet chemistry at room temperature. He added that the porosity can be created within the interior of the material without effecting the immediate surface and sub-surface mechanical integrity. After the porosity is introduced it is still possible to grow standard material on the surface and define P-N junctions, he said.
The company offers natively emissive red, yellow, green, and blue diodes. And has a display with what it calls ‘Dynamic Pixel Tuning’ technology. Zhu commented that a mixed signaling modulation technique is applied to control the wavelength of the pixels.
For now, the company’s work is done on either 4-inch diameter sapphire or 8-inch diameter silicon wafers. The advantage of the later, GaN-on-silicon, is that it opens up the possibility of integrating CMOS active-matrix drivers, said Zhu. “A great advantage for us is to bring GaN and silicon together.”
MicroLED is one of the most recently developed display technologies theoretically offering better contrast, response times and energy efficiency than established technologies such as LCD and OLED. LCD and OLED, which are already in mass production, have the price advantage, for now.
MicroLED can be made flexible and transparent so it is expected that microLEDs could become established in new applications, such as artificial reality glasses and virtual reality headsets. In addition, there have already been demonstrations of large cinema-style displays screens made of tessellated microLED modules.
Zhu said the porous buffer confers the advantage of reducing the number of crystal dislocations in material grown on the surface. This allows greater control of InGaN, GaN quantum wells used to make light emitting diodes. In effect the porosity can compensate for crystal lattice strain that would promote the formation of lattice defects that act as electron traps and reduce conversion efficiency. This, in turn, has been leveraged into the ability to produce RGB LEDs on a single substrate and without stacking. “From a single-pixel you can get three colours, without stacking,” said Zhu.
This is an important point of difference from other GaN-on-silicon microLED vendors who may have to stack different layers to get multiple colors rather than put RGB side-by-side. This is an inherently more costly and less efficient process.
“We are agnostic about the display format; TV, signage, HDTV, PC down to smart glasses. “Big-screen TV, we are working on that: mass production test by the end of 2022.” Zhu would not name the company Porotech is working with but indicated it was an already-established Asian consumer electronics supplier.”
Meanwhile Porotech has been out and about, attending conferences and winning awards for its monolithic integration capability which offers a pathway to microLED displays.
There is a 1960 by 1080p display in a 0.7-inch diagonal format that was shown at the SID event with a pixel density of 3,000 pixels per inch.
The success achieved has persuaded Zhu to make Porotech into a product company. “We are a display component company; a product company. We won’t make every part of the component. So rather than being fabless, we are a virtual IDM.”
The company has already gone public on two partnerships; one upstream and one downstream. The first is with wafer supplier IQE plc (see IQE, Porotech partner up on GaN microLED displays) and the second with Chinese company Jade Bird Display (see Porotech in key porous GaN microLED partnership).
“We will work with as many partners as possible but will be a business-to-business company. We will not try to sell goggles and glasses,” said Zhu.
Zhu explained that the microLED array manufacturing can be done for Porotech by foundry suppliers but that the critical step of introducing the porous buffer zone into wafers is done in-house in Cambridge. “We are expanding in Cambridge,” said Zhu. “The pilot plant is in Cambridge and capable of 300 wafers per week moving up to 1,000 wafers per week.
Notwithstanding the success with the large-screen TV maker, it is hard for Zhu to predict when products will emerge based on Porotech technology, but it feels like it could be in 2023. “We are trying to align our internal roadmap with key customer objectives. For example, the introduction of AR products is not something we can decide,” he said.
But one thing Zhu is sure of is that he intends Porotech to be a global company. Besides its Cambridge base it already has offices in Hsinchu, Taiwan and in Chandler, Arizona. The fact that much of the displays industry is located in South Korea and southeast Asia does mean Zhu may have to consider where the headquarters needs to be during various phases of the company’s development.
For now much of the work is focused in R&D and Cambridge is the right place to be, Zhu said.
And that R&D could continue to develop. Zhu said that applying porous technology to GaN could also bring advantages for power electronics, for RF circuits, for quantum crypto, single-photon nanolasers, and for on-chip optical communications. This is a broad range of activities.
However, to achieve commercial success it is necessary for a company to focus, said Zhu. “We are focused on the microLED opportunity for now.”
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