CLEARink Brings New Wrinkle to Electrophoretic Displays

Terry Gou finally pulled the trigger yesterday and finalized Hon Hai’s purchase of 66% of Sharp, but only after $2 billion was knocked off the price to cover previously unannounced potential liabilities. The new company will command 21% of global TFT-LCD manufacturing in 2016, according to IHS – more than LGD, Samsung Display, or BOE. But everybody’s writing about that.

So why don’t we talk about something you will see only in Display Daily, at least for a while? Recently, the electrophoretic displays landscape – dominated by E Ink – has been predictable. E Ink’s top-of-the line Carta display film for eReaders and similar applications offers 300 dpi, 44% reflectance, and L* (white state) of 74 minimum and L* (dark state) of 19 maximum for a minimum contrast ratio of 15:1. The black-and-white image update time is 120 ms at the film’s 15-volt switching voltage. I do a lot of my leisure reading on a Kindle Voyage eReader with Carta, and it is a nearly perfect display for this application.

However, it is not a general-purpose display. The current approach to full color is to use a matrix filter over the display film, which makes for a rather dark image. And, as always, the image update time is too slow for high-quality full-screen video. These are the issues that stimulated significant work a few years ago on reflective technologies that could offer color and video rate. One of those technologies was the Mirasol interferometric approach, which Qualcomm heroically tried to develop into a viable commercial technology. It finally gave up and in 2014 sold its Taiwan fab to TSMC, which planned to convert it into a packaging plant. (There are reports that Apple is now operating a former Mirasol development lab in Taiwan, but no solid information about what Apple might be doing there.)

The other leading reflective video-rate color technology of the time was the Liquavista electrowetting technology, originally devoloped at Philips and temporarily owned by Samsung. Several years ago, the Liquavista team disappeared into the corporate bowels of Amazon, although the team is still based in the Netherlands. For a long time it was hard to obtain any information about the Liquavista effort, but now there is actually a rather detailed website ( with an “Amazon Liquavista” logo. An industry source tells me the Liquavista team has been expanded to 100 people.

Don’t worry. I really will get to the content the title of this column promises, but I want to remind you that the vision of a full-color, video-rate display is neither new nor dead. And the growth of personal and wearable electronics makes the development of such displays more and more desirable as time goes on.

So, back to electrophoretics. An electrophoretic displays is based on the motion of charged particles through a medium when an electrical field is applied. The medium can be a gas, but today is always a liquid in commercial displays. The E Ink approach is to use black and white particles, one color carrying a positive charge and the other color carrying a negative charge. When a field is applied across a pixel, black particles are attracted to the front of the display with white particles to the back, so that pixel appears black, and vice versa. At a lower net voltage, the black and white particles can have intermediate positions in the cell for several levels of gray scale. (A lot of development went into that.)

An alternative approach was championed by SiPix, a company E Ink eventually bought. In this approach, a single color and charge of particle was contained in a colored medium. When the particles are attracted to the front of a pixel, the user sees that color. When the particle is attracted to the rear of the pixel area, the user sees the color of the medium.

For both approaches, many devils were in the details. We’ll skip them.

Now, I have learned of another electrophoretic approach from a four-year-old University of British Columbia (UBC) spin-out called CLEARink. CLEARink uses a plate with micro-wells to hold the medium, much as SiPix did, rather than microspheres as E Ink does. (Those are two of the details we agreed to skip.) The single color and charge of particle (CLEARink calls its particles “ink”) are moved between a charged backplane and front plate when a field is applied. No surprises yet.

The front plate is a film with hemispherical reflectors on its bottom face that operate via total internal reflection (TIR). When the ink is attracted to a pixel area on the reflector film, it frustrates the TIR and the pixel is black (or whatever color the ink is). Otherwise the pixel is white (or whatever color the ambient light is). Significantly, an ink particle only needs to be moved by half a micron to switch between TIR and frustrated TIR, which allows 30Hz operation at low power, according to a paper delivered by Merck at SID Display Week 2015 (Paper 23.1). Merck is producing the ink and medium for CLEARink.

Table and figure from M. Goulding et al., “Colloidal Dispersion Materials for Electrophoretic Displays and Beyond,” SID 2015 Digest, pp. 326-329 (Society for Information Display, 2015)The current reflector structure is intended for maximum reflectivity over a rather narrow viewing angle, but that can obviously be tailored for each application. CLEARink maintains that the reflectivity is so good it is possible to apply a color matrix filter and still have an agreeably bright display.

CLEARink is less than four years old, but the technology is based on a decade of R&D done at UBC. Last Tuesday, the company announced the close of its latest funding round, which netted approximately $7 million. The company intends to close on up to additional $6 million in the next four months. CLEARink believes it has a solid patent portfolio for its technologies.

In its press release, the company said, “CLEARink’s lead customer intends to launch their first ESL product in mass production, at the end of 2016.”

I’ll be meeting with CLEARink’s CEO during Display Week. This is interesting. There’s always a new wrinkle.

Ken Werner is Principal of Nutmeg Consultants, specializing in the display industry, manufacturing, technology, and applications, including mobile devices and television. He consults for attorneys, investment analysts, and companies re-positioning themselves within the display industry or using displays in their products. You can reach him at [email protected].