Stop Press! Electronic paper is here

For the last 25 years people have talked about the idea of replacing paper with a material that looked like printed paper, felt like paper, was flexible, viewable in bright light and yet unlike paper could be written on and erased electronically.

The cost and environmental advantages of being able to reuse the same piece of paper thousands of times is obvious, as is the potential for new applications in information display.

Applications for the technology include digital, low-power portable displays, wearable displays, signs and posters of all sorts.

The need for a new display technology is widely recognised. There is a huge volume of information such as newspapers and magazines that is not accessible to people on the move, except in paper format, simply because they do not have a suitable device to display it. Light weight flexible — perhaps even roll-up — screens, would be one way to solve the problem.

Indeed whilst advances in data processing and storage have given us devices such as the iPod and the portable games console, display technology has not advanced considerably over the last decade and displays are still generally heavy, power hungry and expensive.

E-paper technologies are about to change this situation, offering designers and users a number of advantages. For example they use less power and are both lighter and more robust than the glass-based screens currently used in laptops as they are made of plastic. They are also much cheaper to manufacture, can be made in much larger panels, and perhaps most importantly, offer a far higher quality display and better reading experience than conventional displays.

For years, research laboratories, big companies and start-ups have been working hard to turn the idea of e-paper into a reality, talks were given, articles written, concept models built, but until recently very few practical solutions to the problem had emerged. This has led many to dismiss flexible electronic paper displays as a technology that was all promise but no product. Now prototypes have finally arrived from two companies, Philips Polymer Vision of the Netherlands and Plastic Logic of the UK.

"We shall be shipping fully functional high quality engineering samples to customers interested in incorporating flexible screen technology into their products in the fourth quarter of 2005," says Hans Driessen of Philips Polymer Vision.

Plastic Logic claims it too will begin shipping fully functional 800 pixel × 600 pixel A5 flexible displays to their applications development partners in late 2005.

Although it seems that much of the technology required to build flexible paper thin displays is now in place, that isn't the whole story. The bigger issues are whether consumers are ready for flexible electronic displays, and the impact they will have on paper.

According to most of the companies involved, the first commercial products using e-paper displays should appear in mid-to-late 2006. Initially these will niche market products, such as Philips proposed GPS unit with roll-up map display, the animated point-of-sale displays being developed by NeoLux in Korea, or the signs under development by Vossloh of Germany. It will, most agree, be 2007-8 before we start to see the arrival of e-publication readers with A4 digital paper displays.

According to a report on e-paper displays due to be published at the end of July by the consultancy DigitalPublishingNews.net flexible displays will in 2010 account for about 40 percent of the annual global production of 3.5 million square metres of flat panel displays. The total global market for such flexible displays is expected to be worth about $7.8bn (£4.4bn), split almost equally between organic electronics/electrophoretic displays and a new generation of flexible LCD displays currently under development by companies like HP and Philips.

The largest proportion of this market will initially go to signage products, with e-readers only starting to take off after about 2008. The report also predicts that commercial A4 size e-readers using digital paper will be on sale in 2010 at around $100 and will support a range of PDA-type functions.

Compared to the size of the paper and printer market, the size of the e-paper display market in 2010 is small, and certainly the makers of printers and the suppliers of printing-related products, like Xerox and HP, will not be losing too much sleep at this stage.

However, it is interesting to note that both HP and Xerox have e-paper development projects under way in their research labs. These are second-generation e-paper displays supporting full colour and video speed refresh. This indicates that these companies at least are taking the emergence of e–paper seriously and will be ready to jump into the market when they start to see it impacting on the market for their traditional paper based print products.

The one group of businesses who do not seem to be taking this technological development seriously are the publishers. Although a few publishers, primarily newspaper companies, have looked at the technology it would seem that even fewer are actively developing strategies for using a technology that could well overtake paper as the primary 'print' medium within the next two decades.

A prediction that is backed by Lynne Brindley, the British Library's chief executive, is that the switch from print to digital will be mainly complete by 2020, with only 10 percent of new material remaining as traditional print only.

Of course people will continue using paper for a long time, just as people still use velum, but increasingly paper documents, whether books, magazines, newspapers or the myriad other pieces of paper that we print out or photocopy will be replaced by e-paper displays that will offer a reading experience that is virtually indistinguishable from using paper. E-paper will, however, have environmental benefits and above all will be seamlessly integrated into the digital world.

But just how practical is the technology behind e-paper? Read on for a more detailed look at how this new technology actually works.

What is e-paper technology?
The reason it has taken so long to create a commercially practical electronic paper is that two entirely new technologies are required. The first is the electronic ink that will create the actual 'print' display on the e-paper page, and the second is the flexible electronics required to generate the pattern of text and images on the page of electronic ink.

The development of both technologies has proved to be a lot more complex than was initially conceived. Most flat panel displays, such as LCDs, consist of two main elements: a backplane that controls which pixels on the display turn on and off, and a frontplane that either emits light, or acts as a shutter controlling the light coming from another source at the pixel locations determined by the backplane.

On most modern flat panel displays the backplane has an electronic 'switch' under each pixel, so that the pixel can be turned on and off without affecting its neighbours; this is referred to as an active matrix display. Older displays did not have this 'switch', just a matrix of connections, and are known as passive matrix displays. TThey have the disadvantage that the length of the conductor that links the driving circuit and the pixel delays and distorts the precise signal needed to generate a sharp, rapidly refreshed picture and are thus too slow and smeary for modern applications.

The usual way of fabricating the transistors used to construct the backplane switches is to deposit a thin layer of silicon onto a glass substrate and then use conventional semiconductor manufacturing techniques to create the transistors and associated circuitry. The trouble is that these manufacturing processes require very high temperatures and this makes such backplanes not only expensive to manufacture but also precludes the use of a substrate made of a material such as plastic, since this would melt during processing.

The solution is to use a semiconductor other than silicon to fabricate the transistors, one that can be formed into the appropriate circuitry at room temperature. The newly developed technology of organic semiconductors fits the bill perfectly, and is the solution that has been adopted by Philips Polymer Vision and Plastic Logic.

Both these companies have developed organic electronic materials that are soluble, and can thus be used at room temperature allowing the circuitry to be mounted upon a flexible plastic substrate. Another advantage of organic semiconductors is that the circuitry can be created using conventional screen printing and ink jet technologies, this makes manufacturing such displays a lot cheaper since they do not require such an enormous investment in capital equipment.

A modern LCD plant producing 2m × 2m substrates for the LCD TV market costs upwards of $4bn, whereas an organic electronics display plant will cost $10 or $20m. This means that when they are in volume production, in about 2010, the cost of an A4 150dpi flexible organic electronic display is very likely to be a lot cheaper than a comparable LCD display.

"With the expectation that the materials and processes used in the manufacture of flexible displays will advance in the next five years, there is the possibility for a new paradigm in display manufacturing that could produce low-cost, high-volume flexible display products. Assuming current display component pricing trends continue on their downward trend, this could signal the potential for highly rugged displays that are one third the cost of today's fragile, glass-based displays," says Darren Bischoff, senior marketing Manager of E Ink.

Developing the technology for the frontplane of a flexible display brings new and different challenges. In a conventional LCD display the frontplane is also made of a rigid piece of glass in order to ensure that the cell gap between it and the backplane are precisely maintained as even slight variations in this gap will produce image distortions. Maintaining such a precise gap in a rollable or bendable display is extremely difficult, although researchers at both Philips and HP are working on the problem and have demonstrated prototype solutions.

For flexible high-resolution displays the best alternative to a liquid crystal frontplane is what is known as an electrophoretic frontplane. Besides being flexible, this frontplane technology also has the advantage that it uses reflected light, as opposed to conventional transmitted light or emitted light displays, which are used in LCD and CRT displays respectively. In this respect electrophoretic displays are much closer to paper in readability since they are viewable in ambient light, have a wide viewing angle, and a high contrast ratio.

A typical example is the technology developed by E Ink: tiny white and black pigment particles are given opposite electrical charges and are then encapsulated in microcapsules, each smaller than the diameter of a human hair. When an electric field is applied to a microcapsule, the pigment particles within it move, turning one side of the capsule white and the other black. These microcapsules are suspended in a flexible carrier medium to form the frontplane that can then be bonded to the backplane.

E Ink, a spin-out from MIT Media Lab, has been working on development of their frontplane technology since 1997, and last year it saw its first commercial application, the Sony LIBRIe e-book reader. While this is not a flexible-screen device, as it uses a rigid backplane like a conventional LCD, the device has been much acclaimed for its high-resolution, high-contrast display.

The big drawbacks with the current generation of electrophoretic displays are firstly that they have slow refresh times, since the pigment particles take time to move, and secondly that they are monochrome. According to Darren Bischoff of E Ink "these problems have already been solved in our labs and we will be demonstrating a colour display in late 2005. Refresh times are also being improved and or commercial product will be 50 percent faster next year, in the lab we have recently demonstrated display refresh rates at video speed."

Bishoff agrees that full colour, fully flexible displays that can switch fast enough to show video are still some way off, however, he emphasizes that flexible monochrome displays are here right now.

Plastic Logic, which entered into a cooperation agreement with E Ink in December 2004, is already producing A5 displays using flexible organic electronic backplanes and E Ink frontplanes from a pilot manufacturing plant. They will be shipping engineering samples to companies interested in using the technology in their products within the next few months.

Plastic Logic are now installing new equipment at their plant that will allow them to build 150dpi resolution A4 displays, according to company spokesman. "Our partners are already designing products around our displays and we expect to be conducting field trials of a 100dpi e-reader in mid 2006."