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Video-capable colour ePaper in demand for Chinese school tablets

After Californian startup CLEARink Displays had closed a USD5 million in Series C funding, backed by a number of Asian display manufacturers, eeNews Europe caught up with the company's Vice President of Marketing, Sri Peruvemba.

 

CLEARink Displays' principle of operation.

 

CLEARink Displays claims it is the only company to be able to offer full colour e-paper capable of running video, with refresh rates over 30Hz. The technology which Peruvemba like to describes as ePaper 2.0, relies on a single-particle system. In the white state, the electrophoretic display's fluid-born black nanoparticles are positioned only nanometers away from the surface of a transparent film imprinted with micro-hemispherical cups. Those microcups then provide total internal reflection. When applying a positive charge, the negatively charged particles move up against the back of the film and absorb the light, creating a dark state. Full colour is added with an extra layer of colour filters.

According to Peruvemba, incumbent ePaper manufacturer E Ink fails to deliver video rates because it uses a slower two-particle system, with black and white particles having to interchange their positions on top of the substrate. The process is slower than the one-particle system CLEARink Displays uses, which has a much shorter distance to travel to the top film, explains Peruvemba who remembers demonstrating E Ink's animated ePaper almost ten years ago, as he was then the company's Marketing Chief Officer (he left E Ink in 2013).

"Since we are a small startup, we have to focus on the markets where E Ink is not strong, and video capability is our business driver", says Peruvemba, arguing that for e-Schoolbooks, animations just don't cut it, full colour video is what OEMs want.

 

"One of the investors in the company is currently manufacturing LCD-based e-Schoolbooks for China, but they want low-power video. Right now, they are buying LCDs and ePaper displays from E Ink, but they've pre-paid for three million of our display units to be shipped late 2018. If you have animations in school books, that helps, but they want to watch videos, they want children to have access to the best content" explained Peruvemba, noting that his company is currently trial manufacturing pilot units at a LCD factory in China.

"Following this, we will transition to production that might start mid next year and complete later in the year. This could also be on a line that is much bigger than the one on which we are building the trial samples now".

When asked if by refreshing the display so often, video rates would defeat the low-power benefits of bi-stable ePaper, Peruvemba claims that the voltage requirements of CLEARink's ePaper are significantly less than that for E Ink's ePaper, resulting in a video rate that draws less power than animated ePaper (in the 10 to 20 frames per second). Then again, if you compare this to backlit LCDs, the power savings are in the 80 to 90% range.

"Our consumption power is probably the same as that of the LCD driver electronics, without the backlight" says Peruvemba. However, curiously the primary need of these eSchoolbook manufacturers is not low-power, but sunlight readability, he says.

"There is a lot of debate in Asia about what causes the high incidence of myopia there among young people (reportedly, 90% of Chinese teenagers and young adults are short-sighted compared to 10 to 20% sixty years ago). This is not unique to China and the current belief is that kids spend too much time indoors. One possible prevention that is being experimented in various programs is to get the kids outdoors with their laptops, so they get more exposed to sunlight, or maybe so their eyes can also accommodate to distant objects. But they need a display that can be read even under bright sunlight".

Talking about display specifications, Peruvemba is cautious not to be too definitive, since the company only has lab prototypes which it says are not production representative.

"Our samples were optimized and the trial production of a few hundred units is happening right now in a LCD factory in China. That will result in units that we will use for characterization, testing etc. so we can create customer ready specifications (required for formal contracts). It is possible that we might have enough extra units that we can start sampling to customers and building kits that we can sell", explained Peruvemba.

So far, he says the lab samples exhibit a white state reflectance of 83% (compared to 43% with other ePaper technologies), and a contrast ratio of 1:20 (compared to 1:12). The company produced black & white samples at a resolution of 212dpi, which would yield a 106dpi resolution in colour, once RGBW filters are layered on top to create the colour pixels. Even with the colour filters overlaid, CLEARink says it still achieves a reflectance of roughly 40%, about twice that of colour ePaper.

"Our intent is to build displays at much higher resolution" Peruvemba told eeNews Europe. "Our resolution is determined by the TFT backplane, not by the microstructured film we place on top. In fact, the size of the reflective microcups can be varied. It is a few tens of micrometres in diameter but we can bring it down to single digit micrometres".

But high resolution on eSchoolbooks is a "nice-to-have", not a "must-have", and people do not want to pay a premium, argues Peruvemba. "I highly doubt they would want to pay for more than 300dpi" he says, emphasizing that a long list of companies approached CLEARink to invest in the startup.

The startup has established a joint development agreement with chemical company Merck who produces the ink. CLEARink plans to manufacture the ePaper via contract manufacturing in a fully depreciated LCD fab to address its target markets.

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