Rolling toward a Revolution?
Polymer Vision plans to launch the Readius, the first commercial application to feature a rollable flexible display, to be released in early 2009. Will it be the "killer app" for rollable flexible displays?
by Michael Morgenthal
"We're trying to break the rules." That is how Michael McCreary, Vice President of Research and Advanced Development at E Ink Corp., describes the Polymer Vision Readius, which will be the first rollable flexible-display device to enter the marketplace when it launches in 2009. Polymer Vision has partnered with E Ink in the development of the Readius, which will initially serve as an e-reader device, but one that clearly will be unlike any that has preceded it.
Certainly, attendees at Display Week 2008 can testify to the ground-breaking nature of the Readius. Polymer Vision showcased various prototypes of its rollable flexible display there, and it quickly became one of the most talked about demonstrations at Display Week. Audible gasps were heard as the electrophoretic screen unspooled from its case, reaching a diagonal width of nearly 5 in. The image on the screen refreshed several times, and then the screen disappeared back into its packaging.
But wowing display enthusiasts with prototypes is one matter; ramping up for commercial production on a product that "is trying to break the rules" and then winning over consumers represents a entirely different set of challenges.
Officials from Polymer Vision and E Ink allowed ID a look at how the Readius has evolved, what their hopes are for the product, and what they think it represents in terms of flexible-display development.
Polymer Vision believes that the Readius will distinguish itself from all other current e-reader products in the marketplace, such as the Amazon Kindle, because none of those are truly portable in the modern sense. Edzer Huitema, CTO of Polymer Vision, compares those devices moreso to tablet or notebook PCs because they are too big to fit into a consumer's pocket.
"Our aim for this product is to be the first ones to make a real mobile product for e-reading," Huitema said. "(The Readius) has mobile-phone size and weight – not smart-phone weight but typical mobile-phone weight (115 g) and still has a large display (5 in.)."
The device is 115 mm long and 21 mm thick at all times, but expands from 57 mm wide when the screen is closed to 160 mm when it is open (Fig. 1). The active-matrix backplane, developed and manufactured by Polymer Vision, has a performance level comparable to that of a-Si backplanes, Huitema stated (the on/off ratio is a little higher than that for a-Si backplanes, but the drive voltages are similar). The resolution is QVGA (320 x 240), which is lower than most e-readers currently on the market. This decision was made as a compromise between technological capability and market demands.
"We didn't want to make the display too complex from a manufacturing perspective, while also trying to make a display that is acceptable from a market perspective," Huitema disclosed. "At Display Week, we showed a display that is 900 x 550 with a 254-ppi resolution. Our technology now is so far developed that we can do that (build it in our R&D line). For production, we said we would first make a QVGA 5-in. display. Technology-wise, we can go larger – it's more a limitation of our equipment set."
E Ink used its Vizplex™ electrophoretic imaging film to develop the frontplane. The entire display weighs just 5.6 g and is only about 100 μm thick, about 10 times thinner than glass displays of similar size and about five times thinner than current plastic displays.
Developing such a thin display was critical for several reasons. The first of which is display performance. When pieces of plastic are rolled up, they tend to spring apart, and it is hard to keep them aligned, which is critical for in the performance of any display. As the display rolls up, tremendous strain is placed on the outer and inner layers, McCreary explained, but there is a "neutral plane" in the middle where strain is minimal, but increases with the thickness of the stack. This can result in separation of layers, cracking, or crinkling, any of which could drastically reduce the display's performance.
"Normally, we have a protective sheet that goes on top of the displays that is several hundred microns thick, and the electronic-ink sheet that is laminated to the transistor backplanes is also several hundred microns," McCreary detailed. "We developed new types of materials that could collapse a 100-μm-thick display down to 60–70 μm. Everything is integrated under one sheet, and the actual plastic substrates we use are about the thickness of a piece of Saran Wrap – they are that floppy and really really thin."
While McCreary would not elaborate on how this was accomplished other than to say that E Ink modified the polymers and process flow it normally employs, he did state that working with such thin layers of plastic was obviously a tremendous challenge, as was getting all the multiple layers required for the display in a protective sheet – including UV absorbers to eliminate glare and humidity barriers – that could then be coated with the ink for the display.
"We did tests where we rolled (the display) 25,000 times, and afterwards, we would not accept degradation in image quality," Huitema added. "There were tests at high temperature, low temperature, rolled-up storage — all kinds of tests on the mechanical side. In the end, it really comes down to having good adhesion between the layers as well. All layers really need to stick very well to each other and that is the only way you can get a rollable system that you can roll multiple times."
The thickness was also critical in order to keep the Readius at a comfortable size – the device could not be too thick when the display was rolled up.
"In general, the rule of thumb (with plastic displays) is that you can roll (the display) to a radius that is 50 times its thickness," Huitema explained. "In 2003, we set a spec for ourselves in that we wanted to be able to roll the display 10,000 times at a radius of 7.5 mm. At that time, we were not close to that. But we knew that if you go below those specs, it would be very hard to make any product because either the device becomes too thick or it has a serious reliability problem because you cannot roll it enough."
Polymer Vision has been pleasantly surprised by recent improvements in shelf lifetime, Huitema added. Lifetime has been an issue throughout the plastic electronics field, but lifetime for the Readius currently exceeds 5 years.
Manufacturing: From R&D to Pilot Production
In 2004, Polymer Vision started a "pre-pilot" line in the Netherlands to develop rollable displays for research and development. There, the company made 50–100 displays per week in, week out, and then subjected them to all manner of torture tests in order to eliminate defects, which come from what Huitema colorfully describes as a "big burrito" of sources. Gradually, the company eliminated the defect sources until it reached a point where only particle-related defects remained.
"We replaced a number of processing steps used in the a-Si world – which are performed at high temperature – by spin-coating or spray-coating steps, all of which are done at room temperature," he said. "This is really important because our plastic substrates are so thin that firstly you do not want to melt them and, secondly, you do not want to deform them.
"If you go to high temperature, the plastic will deform. We need to align five masks on top of each other, as in all typical displays, within 1 μm per sheet; thus a total of 5 μm. So we really need to have only very small deformations in the plastic during the processing steps. That is key for all other technologies on plastic, to get that right."
In February 2007, the company partnered with British manufacturing concern Innos to launch its pilot line at a factory in Southampton, U.K. A carbon copy of the R&D line from Holland was installed in the U.K. and within two months the first displays were being produced there.
Huitema would not discuss yields other than to say that they plan to scale up to mass-production levels in the coming years.
(a) (b) (c)
Fig. 1: (a) When the display is closed, the Readius measures 115 mm long, 21 mm thick, and 57 mm wide. (b) The display is only about 100 μm thick, about 10 times thinner than glass displays of similar size and about 5 times thinner than current plastic displays. This allows it to bend easily as well as to roll and unroll frequently without any degradation to image quality. (c) When fully extended, the display measures about 5 in. on the diagonal and extends the device to a width of 160 mm.
Flexible Displays' Killer App?
Huitema is buoyed by the success of e-reader devices such as the Kindle (Amazon does not release sales figures for the device, but speculation online and in the media has centered around 500,000 devices shipped in 2008), but he is quick to add that he does not see the Readius as direct competition for the Kindle and other current e-readers.
"We will probably attract a different set of customers," he explained. "The reason I say that is that we are a portable solution for e-reading. The Kindle is a rigid-based e-reader tightly connected to a proprietary library, while we are more like an open platform that targets mobility. So it will attract a different set of consumers, and in that way make the market bigger. I don't think there will be a lot of consumers where we are competing."
Polymer Vision already has a section of its Web site called Content World, where both free and paid content such as eBooks and RSS feeds will be available.
"You can choose your content from whatever source you wish, be it via Content World, another Web site, or from your own PC," the Web site states. In addition, the Readius will come complete with a 3.5G cellular-phone platform, although there is no specific speaker or earpiece on the device – a headset will be necessary to use the phone.
Pricing for both the device itself and its content has yet to be made public; in fact, Polymer Vision has been quiet about which retail and service-provider partners will carry the Readius. However, in 2007, the company did announce a deal with Italian mobile provider Telecom Italia to distribute the device in Italy.
Huitema stressed that the e-reading platform will be the main application for the Readius "for a while," but other uses are definitely being explored, including full-color and video. At Display Week 2008, Polymer Vision showed a full-color prototype of the Readius that generated a tremendous amount of buzz.
"We have solved the problem of aligning a flexible color filter with a flexible display. It is a difficult problem to solve because they both expand and shrink during the processing, and aligning them at the end on top of each other is almost impossible," he explained. "We are now in the process of tuning color performance, whiteness, and the color-filter process, but we are already quite far along in making the complete stack to a level that we can put it into production. I would say in general it will be ready within 2 years."
So, this is how the Readius differentiates itself from current e-readers. But will it succeed and live up to its billing – that of a killer app for flexible displays?
"For rollable displays, we see this as a killer app, and the reason is very simple," Huitema proclaimed. "At this moment, data-centric devices are becoming more and more dominant in the mobile space. Smart phones are gaining increasing market share in the mobile space and they are more and more data-centric. Data revenues are rapidly increasing, and voice revenues are shrinking a little bit per user. So data is becoming important."
He added that while typical smart phones have about 30% of their area covered by a display and the iPhone's display occupies almost the entire device, the Readius will allow users to go beyond 100% of the device's size for the display.
"That is without adding any weight," he added. "People don't want to have a larger device, but want to have a larger display because we have high-speed networks."
David Barnes, Vice President of Strategic Analysis for a market-research firm, likened the Readius' potential impact to that of the iPhone.
"I hesitate to forecast (the potential of the Readius) because in my mind, it is a category creator (not a category changer)," Barnes said. "You look at something like the iPhone. We had touch technology around for more than a decade, and no one was really that excited about it until Apple managed to package it with the right kind of hardware and software, and suddenly everyone wants it."
"Even though people say they may read a book or read e-mail on a cell phone, frankly the only way to have a big screen in a small pocketable device is to have it be able to be folded up or rolled up – I can't think of another good way of doing it, where the screen is bigger than the actual device you are sticking in your pocket," McCreary concluded. "It's ground-breaking. It's a major technical and capability milestone in the growth of non-glass displays. I do think it's the first concept, not the last. It's just the beginning." •