Dual-Pigment Electrophoretic Displays for Reading Textbooks

In recent years, electronic paper has been hugely successful in augmenting traditional paper in the area of "leisure reading." Now its developers are aiming at academic textbooks.

by Sriram K. Peruvemba

THE BENEFITS of today's eReaders are well-known. They are easy on the eye, providing a reading experience similar to that of paper. They can be read in bright sunlight, making it possible to read an "e-Bestseller" on the beach. They can store thousands of books, enabling a reader to carry a year's worth of reading or more in a purse or briefcase. At the same time, they offer instant gratification in the form of downloadable reading matter that is available 24/7.

Many of these qualities make eReaders especially suitable as e-Textbooks (Fig. 1). Electronic-textbook content, as a percentage of total textbooks sold in North America, is growing rapidly. While the overall textbook market is fairly flat, e-Textbook content is exhibiting double-digit growth rates according to various industry surveys. Xplana's research1 estimates that digital textbook content will comprise almost 50% of the entire Higher and Career Education market by 2017. The content is currently consumed via dedicated eReaders and multipurpose devices such as laptops and tablets.



Fig. 1: eReaders are being used in an increasing number of schools and universities to display textbook content. Image courtesy E Ink.


The Most Successful Information Display to Date

Information display to most of us in the industry means an electronic display. To many of us it means specifically a liquid-crystal display (LCD), since that technology comprises over 90% of the roughly $100 billion electronic-display industry. And we would be wrong. The most widely used information display is printed paper – yes, the kind you get by chopping down trees.

Human beings love printed paper, and the publishing industry alone is four times as large as the entire electronic-display industry. Printed paper is a 500-year-old technology that is used everywhere. It's proven, rugged, and inexpensive relative to its competition; it just works. This information display is very readable, but its contents cannot be changed.

The $100 billion electronic-display industry comprises technologies including LCD, CRT (yes there are still some CRTs around), plasma, vacuum fluorescent, electroluminescent, LED, organic EL/OLED, electro-phoretic, electrochromic, and emerging technologies such as MEMS, electrowetting, electrofluidic, laser, nanocrystal/quantum dot, and others still in the lab, together with projection displays and electro-mechanical displays. All offer one major advantage over printed paper – their content is changeable.

With the ability to change content, as well as other advantages to be discussed later, electronic displays have been gradually displacing printed paper in applications ranging from large signage to small phone books. However, printed paper, a tough competitor, continues to hold its own in performance and cost. This is why we still have printed-paper signs indoors and out – and in the author's town the printed phonebook is still delivered. Printed paper continues to hold more than a 90% share of the publishing world.

Rock, Paper, e-Paper

One of the strongest bastions of printed paper is in the area of reading media – books, magazines, and newspapers. Until recently, electronic displays could not come close to providing the reading pleasure offered by printed paper. However, this category is where electronic paper was first able to compete, in the form of widely popular eReaders. The first technology for eReaders that went from "emerging" status to mainstream was electrophoretic technology. Other display technologies labeled as e-paper that are also aiming to displace printed paper in reading applications include MEMS, electrowetting, and variations of conventional LCD technologies, including cholesteric, transflective, polymer-dispersed liquid crystals, and others.

What Is Reading?

It may sound odd that printed paper reigns supreme when it comes to "reading." How can this be true when most of us spend the entire day in front of our laptops, watch TV for hours, converse on mobile phones until the battery drains, and sit through innumerable slide presentations shown via electronic projectors on a screen? Surely, the hours spent in front of electronic displays add up to far more than those spent reading from printed paper. And this may be true when it comes to consuming information, but "reading" is something else.

Reading is the process of recognizing text or words and converting an image of a word into audio, either aloud or silently. Once this image is converted, reading leads to comprehension, fluency, deeper understanding, acquisition of knowledge, improvement of vocabulary, and enjoyment. There is more than one form of reading, and there is much ongoing research about the different forms, as well as research about our reading habits with both electronic media and conventional printed paper.a For the sake of simplicity, reading can be divided into two broad categories: short-form and long-form reading.

Short-form reading involves reading a letter, a note, a brochure, headlines, billboards, or menus. With short-form reading, we are skimming, trying to gather a lot of information quickly, and this type of reading has become even more important in the last decade. With printed paper's inability to provide vast and up-to-date content instantaneously, electronic displays have made great inroads and are increasingly preferred for short-form reading. We read e-mails on our laptop LCD, track sports scores on our plasma TV, read a text message on an OLED screen of our mobile phone, and browse the Internet on our fringe-field-switching (FFS) LCD tablet.

Long-form reading refers to an entire novel, a physics textbook, a company's annual report, a religious text, or a lengthy book prescribed by your CEO that you are obligated to read. With long-form reading, one reads more than a few minutes at a time. One may read many pages or spend many minutes per page going through a chart or table. One attempts to gain a deeper understanding of the subject, is immersed in the subject, or is "lost" in the book. More than 90% of all long-form reading is still performed on printed paper. Only 4 years ago, nearly 100% of long-form reading was via printed paper, but e-paper, in particular dual-pigment electrophoretic-based e-paper, has now taken significant share. Use of electrophoretic displays in eReaders for long-form reading has been tripling in volume since 2006. In that year, there were roughly 100,000 dual-pigment electrophoretic displays shipped to eReader applications. That number is projected to exceed 25 million units in 2011.

Electrophoretic Basics

Electrophoretic displays are based on the principle of electrophoresis, which explains the motion of charged particles in a fluid under the influence of an electric field. The principal component of a dual-pigment electro-phoretic display is a microcapsule with a diameter about the size of a human hair, and each display contains millions of micro-capsules. Each microcapsule contains a mixture of very tiny, positively charged black particles and negatively charged white particles suspended in a fluid. When a positive or negative electric field is applied, corresponding particles move to the top of the micro-capsule where they become visible to the user. This makes the surface appear white or black at that spot.

To form a dual-pigment electrophoretic display, the microcapsules are suspended in a liquid "carrier medium," which allows them to be coated onto a sheet of plastic film that is laminated to a layer of circuitry. The circuitry forms a pattern of pixels that can then be controlled by a display driver. The final laminate can be applied onto virtually any surface, including glass, plastic, fabric, or even paper. Figure 2 shows a large-scale example of dual-pigment display film.



Fig. 2: E Ink's dual-pigment electrophoretic display is made in a roll-to-roll processing plant in Massachusetts. In this picture, the latest generation of E Ink's display film, Pearl, is unrolled alongside the Charles River near Boston. Source: E Ink.


Where eReaders Excel

Dual-pigment electrophoretic displays look like printed paper – and are as pleasant to read as printed paper – because they utilize the same pigments used in the printed-paper industry. With resolutions up to 300 dpi, they render a smooth image with gray tones that mimic the book or newspaper reading experience. They are reflective and therefore sunlight readable and do not cause eyestrainb and/or battery-weight strain, as is commonly associated with displays used in computer monitors and laptops. Because they lack a backlight and require no power to maintain an image on-screen (using a small amount of power only when changing the image), they are low-power devices that can perform for approximately 2 months on a single battery charge (Fig. 3).



Fig. 3: The Nook dual-pigment eReader by Barnes & Noble can be read for 2 months on a single battery charge. Photo courtesy Barnes & Noble.


Better Textbooks

As mentioned earlier, many of the eReader's qualities make these devices especially suitable as textbooks. These qualities include:

Interactivity: An eReader can help the interaction between teacher and student move beyond the classroom. A teacher can easily tell what areas of the subject matter pose greater challenges to the students based on interaction between the students' e-Textbook device and the teacher's e-Textbook. The teacher can then focus on those specific areas. Tests can be graded almost instantly. While researching, students can search the e-Textbook to locate remembered passages that support an argument for a paper (a process that can be laborious with a conventional textbook).

Cost Savings for Students: The cost-saving potential for electronic content is tremendous. In the near term, students can borrow books via their eReader devices,2 as libraries have already begun lending electronic textbooks. In the long run, the publishing industry will benefit due to the cost savings from not having to print on paper. Today, all books are created in electronic form and then printed on dead trees (the true cost of printed paper is very high; see the YFY Group disclosure below). In the future, the printing step can be eliminated.

Viewing Angle and Glare: Just like printed paper and unlike many other display technologies, dual-pigment electrophoretic displays have a very wide, almost 180° viewing angle. That makes it easy for students using an e-Textbook application to share information from the same device. Most of the e-paper displays used in eReaders today have an anti-glare, anti-fingerprint/anti-smudge coating that reduces glare and makes the display look clean compared to a glossy tablet device with a lot of fingerprints.

Controllable Font Size: Changing font size to match individual needs, and especially increasing the font size while reading on e-paper, has been shown to be very beneficial for people with less-than-perfect eyesight. Increased font sizes reduce "crowding" of words, leading to better reading rates for the typical reader. This is even more beneficial for the dyslexic reader, as concluded by William DeLamater in an EReadia article dated April 29, 2010.3

Less Distraction: Single-purpose eReader devices can be configured so they do not support non-school video or web browsing, therefore reducing distractions for younger students. The content is typically teacher-selected, allows for interaction with the teacher's e-Textbook device, and enables note-taking and annotation. The risk of accidentally downloading viruses onto the device is minimized.

Library in Every Backpack: Today's school backpacks filled with printed books can weigh about a quarter of a student's body weight, causing back pain. According to the American Chiropractic Association, young children are experiencing back pain sooner than previous generations and overweight backpacks are a contributing factor.4 e-paper-based devices replacing textbooks allow students to carry all of their textbooks, most of their reference materials, all of their notes, and all of the instructions from the teacher, in their backpacks. A typical device can carry a few thousand books, about the size of a small library for about the weight of one book (Fig. 4). (In a lighter vein, The New York Times, quoting Dr. J. Kubiatowicz, says that thousands of eBooks actually have some weight, about one atogram or 10–18 grams, but unmeasurable by the most sensitive scale.5



Fig. 4: This Jetbook eReader from Ectaco displays a page from a biology textbook. Like all eReaders, this device can hold the contents of the stack of books behind it and much more. Image courtesy Ectaco.


The Future of e-Textbooks

In the relatively near future, electronic-textbook devices will continue to evolve, more content will be available via these devices, the cost of content will reduce drastically, and there will also be greater access to content. Recently introduced flexible electro-phoretic displays allow designers to envision products that can take the everyday rough-and-tumble experienced by pulp-based books and newspapers. These displays are extremely thin and will not easily dent; there is also no polar-izer to scratch or glass to shatter. Designers do not have to "cushion" the display like they would with a glass-based display. Such a display can sustain bumps and vibration and withstand drop tests easily. It might finally be "student proof."

Future e-paper displays will show animated content, stimulate faster interaction with the teacher, enable quicker feedback on tests, eliminate library late fees, and stop the problem of out-of-stock books – all of which gives students more time to learn. An e-Textbook device is interactive, intuitive, able to convert text to voice, and provides a ubiquitous learning medium. The greatest barriers to the adoption of e-Textbook applications appear to be non-hardware related and include cost of content, access to content, and availability of content.

Printed paper is the toughest of all display competitors because everyone loves it. But consider that if one person decides to change his or her behavior by reading all of their books, magazines, and newspapers on an eReader, that one person alone can save at least 20 trees in the next 2 years. And in the field of education, electronic displays, especially flexible ones, can make for a better textbook. We are talking about putting an entire library in a child's backpack. Our children are already researching primarily on the Internet and are less and less dependent on the traditional library. Imagine the Boston Public Library open to students in Baghdad, Bangalore, Beijing, and Budapest with no books lost, no additional printing or transportation costs, no late fees, and no out-of-stock books. This is not an evolution but a revolution in education and it has already started, though without much fanfare.

What does this mean to the electronic-display industry? It is a multi-billion dollar market opportunity that could compare with smart phones and TVs in volume. Its target audience (students) demands display ruggedness along the same lines as the military. And it is an opportunity for a huge ecosystem surrounding the display to develop and deliver a smart electronic device – a better textbook.


aBenjamin Paletsky, Product Marketing Manager, E Ink Holdings, for sharing his insight on this subject.

bSteve Battista, Jen Barlow, and Ana Lopes for their inputs.


1W. E. Lamater, M. Ed., "How Larger Font Size Impacts Reading and the Implications for Educational Use of Digital Text Readers,"eReadia (2010).

2C. C. Ray, "The Weight of Memory," The New York Times (Oct. 24, 2011).

3R. Reynolds, Xplana Whitepaper (2011).

4"Back to School with Rentable Textbooks," Information Display 27, No. 9, 3 (Industry News) (September 2011).



E Ink's parent company, the YFY Group, has a large paper and pulp business. •


Sriram K. Peruvemba is Chief Marketing Officer for E Ink Holdings. With 25 years of experience in the electronics industry, he leads worldwide marketing for e-paper and LCD products at E Ink. He can be reached at speruvemba@eink.com.