EVERY page of every book is a wonder. Each sheet of paper glows white with
reflected light, every letter and dot stands out clearly against the background.
Nothing else has the look or feel of paper, nothing is as versatile, nothing is
simpler.
Or is it? A remarkable new medium could spell the end for old-fashioned
paper. In the US, two groups of researchers鈥攐ne in California, the other
on the East Coast鈥攈ave created electronic versions of paper and ink. Like
today鈥檚 LCD screens, they display images generated by a computer, but they are
as thin, flexible, portable and crisply readable as paper. Stack these
electronic pages together, flick a switch and you can have any book you want:
Hamlet, the latest John Grisham or the proceedings from the conference
you attended last week. As with any other book, the print and pictures will
remain in place for years without drawing electrical power. The one big
difference is that when you want something else to read, the old text vanishes
and the new replaces it.
From newspapers and magazines to fax machines and advertising hoardings, the
possibilities for electronic paper are endless. Already, posters made from
electronic paper are hanging in a store near Boston. Within a couple of years,
the inventors expect, they will have spread to supermarkets, airports and other
public places. By 2006, the researchers predict that they will have mastered the
subtleties of colour, and electronic paper will begin to replace the displays on
pagers, machinery, calculators, digital clocks and even computer screens. Twenty
years from now your groaning bookshelves could be replaced by a single
electronic book.
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Electronic paper and ink combine the advantages of traditional paper and
computer screens, explains Nicholas Sheridon at the Xerox Palo Alto Research
Center (PARC) in California, who has been actively working on the new display
medium since 1992. But the idea goes back much further, to the pioneering days
of desktop computing. 鈥淚n the mid-1970s, a lot of us at Xerox PARC were working
with Alto machines,鈥� he recalls. 鈥淭he first thing we would do after turning on
the machine was to pull the window blinds and turn out the lights because the
screen was so hard to read. I began to think about more readable ways to display
information from a computer.鈥�
His yardstick was ordinary white paper. 鈥淚t鈥檚 very bright and readable from
almost any angle,鈥� he notes. 鈥淏ut manufacturing paper creates large volumes of
polluted water and waste pulp, and disposing of used paper is still an enormous
solid-waste problem.鈥� Similar problems and costs come with the ink, toner and
other chemicals needed to print on paper.
Computer screens do not have these problems, but their comparatively low
contrast makes them harder on the eyes than ordinary paper. What鈥檚 more, keeping
an image on a screen requires a steady flow of electrical power and the ongoing
services of a computer, two encumbrances that ordinary paper works perfectly
well without.
A piece of electronic paper gives you the best of both worlds. It is highly
readable and portable, and can be reused millions of times, just as a single
computer screen can display an endless series of images. Working separately from
the Xerox group, a team at MIT鈥檚 Media Lab led by physicist Joe Jacobson has
developed its own version of electronic paper. It can hold an image
indefinitely, or erase an existing image and replace it with a new one. The team
has already written text onto samples more than 100 million times without any
loss of quality.
To develop and market Jacobson鈥檚 electronic paper, a group that includes two
of Jacobson鈥檚 former students, Barrett Comiskey and J. D. Albert, has formed a
Boston-based company called E Ink. The company has already raised more than
$15 million to finance its technology.
The key component of Jacobson鈥檚 electronic paper is the 鈥渋nk鈥濃�攖iny
black-and-white particles locked inside minuscule capsules. To create it, the
researchers grind titanium dioxide鈥攖he white pigment in paints鈥攊nto
granules about a micrometre across. The surface of each granule is given a
slight negative charge and they are dispersed in an oily solution containing a
black dye.
To form the microcapsules, this solution is stirred into water, where the oil
forms beads containing the black dye and white particles. The E Ink scientists
then add a water-based polymer to the solution which turns the beads into tough,
transparent capsules about 40 micrometres across, each with white titanium
dioxide particles and black dye trapped inside.
To make the electronic paper, these microcapsules are dispersed into a liquid
polymer which is painted onto a layer of indium tin oxide, a transparent
conducting material that is commonly used in the manufacture of computer and
calculator displays. The indium tin oxide layer is patterned to form an array of
transparent electrodes: this will form the top surface of the electronic paper.
A conducting material is also printed onto the opposite side of the microcapsule
layer to form a matching pattern of electrodes, and the whole sheet is laminated
with a protective layer of plastic. The resulting sheet of electronic paper is
about 80 micrometres thick鈥攖wice the thickness of a sheet of ordinary
paper.
Making a mark
The network of electrodes creates a regular array of pixels. A series of
fine, hair-like wires links the electrodes to the display circuitry: this is the
same technology used in conventional electronic displays such as digital clocks
and computer screens. To switch the ink on or off, the display circuits apply a
voltage across a pair of electrodes. Making the upper electrode negative repels
the negatively charge titanium dioxide particles, forcing them to dive beneath
the dye to the bottom of the microcapsules and so turns the surface of the paper
black. If the voltage is reversed, the white titanium dioxide particles are
attracted to the top and the black mark disappears
(see Diagram).
Unlike conventional electronic displays that use liquid crystals, a current
of just a few nanoamps is enough to switch the colour of the ink. E Ink鈥檚
electronic paper can even produce images with a resolution as fine as 600 dots
per inch鈥攃omparable to a laser printer鈥攚hich can be read from any
angle, even in direct sunlight.
E Ink is already testing a commercial version. Last month, the company hung a
sign in a department store near Boston. It is a robust 2 millimetres thick, with
an area of just over 2 square metres, and displays a series of messages that
change every ten seconds or so. The display is controlled by a computer in the
store鈥檚 main office. Within a few months, 10 stores around the US will also be
testing the signs, and E Ink plans to produce commercial versions within a
year.
鈥淪igns are always a headache for retailers,鈥� says Lisa Merriam, E Ink鈥檚
marketing director. 鈥淒id my signs arrive? Did they get put up? Are they spelt
right? The point of this technology is to give retailers control from a central
location.鈥� With electronic posters, the retailer can turn signs on or off,
change the text, make all signs uniform throughout a store or give each one a
unique message in a few seconds.
E Ink has not priced its electronic posters yet. But Merriam is confident
that a simple sign a metre square would cost no more than a few hundred dollars.
鈥淭he cost of designing, printing, shipping and hanging a two-colour paper sign
of the same size is about $70,鈥� she notes. 鈥淚f a store changes its signs
weekly, over a year that would cost $3500. When we鈥檙e in full production,
the cost of one of our signs, including the software, controllers and other
support systems, will be well under $1000.鈥�
Jacobson estimates that a sheet of electronic paper the size of a standard
letter would cost less than $10 to make. The price will be low partly
because electronic paper can be made using existing techniques. 鈥淥ne of the nice
things about the technology is that we can use standard industrial processes and
materials,鈥� says Paul Drzaic, E Ink鈥檚 director of display technology. 鈥淚n fact,鈥�
adds Jacobson, 鈥渢he very first prototype we made, back in 1996, was on a sheet
of real paper.鈥�
Xerox鈥檚 version of electronic paper is slightly different. Instead of
microcapsules filled with pigment, Sheridon and his team use tiny polyethylene
spheres between 20 and 100 micrometres across.
The spheres are made from black plastic with a slight negative charge and
white plastic with a slight positive charge. Molten black plastic is sprayed
onto one side of a large disc that is spinning at about 45 revolutions per
minute while the white plastic is sprayed onto the other side. The two liquids
run across the disc and meet at the edge, where they join to form tiny droplets
that are black on one hemisphere and white on the other.
The freshly formed spheres fly from the edge of the spinning disc, cool, and
are collected in a tray. After being sorted by size, the two-tone balls are
mixed with a transparent silicone, which when heated forms a tough rubber sheet
with the two-coloured spheres embedded inside.
Floating in oil
Encased in the rubber, the spheres cannot move. But when the sheet is soaked
in a silicone oil the rubber absorbs the oil and swells. This leaves each sphere
suspended in a bubble of oil, in which it can spin freely. Add a grid of
electrodes to the top and bottom of the sheet, apply a voltage, and the polar
spheres will align either black or white side up, depending on the direction of
the applied voltage.
Sheridon and his team have already made square tiles of electronic paper 30
centimetres across containing an embedded processor that allows them to display
a different image every second. But there鈥檚 still room for improvement. With
their protective plastic skin, the sheets of cured rubber are noticeably stiffer
than paper. The Xerox researchers have also discovered that it is difficult to
control the size of their polyethylene spheres. Most are 80 or 90 micrometres
across, producing electronic paper with a resolution of about 110 dots per inch.
Reducing the spheres鈥� diameter would boost resolution, but this requires more
complex manufacturing equipment.
The spheres are also packed randomly into the rubber. Finding a way to
disperse them uniformly should sharpen resolution to almost 300 dots per inch.
鈥淎t resolutions of 110 dots per inch, applications such as signs in airports and
stores are possible,鈥� Sheridon says. 鈥淲e鈥檝e worked with 50-micrometre spheres to
yield 200 dots per inch, fine enough for fax resolution. At 300 dots per inch,
it becomes virtually indistinguishable from regular print on paper.鈥�
However electronic paper is made, downloading the information needed to
create images is pretty straightforward. The pages can be connected to a
computer with a standard cable, or built-in receivers can pick up data from
infrared beams or radio signals. But researchers at MIT and Xerox are also
experimenting with more unusual technologies. Each group has developed its own
version of a 鈥渕agic wand鈥�.
The wand, which is about the size of a pencil, is loaded with memory chips
and its flat belly is studded with electrical contacts. As you wave the wand
across the surface of a piece of electronic paper, the electrical contacts
translate the data held in the wand鈥檚 memory into instructions to the pixels in
the paper. Fill the wand with data from a computer and you can download the data
into a sheet of electronic paper with a stroke across the page, making the wand
an easy way to transport information. For example, you could download a
presentation into a wand, tuck it in a pocket and head off for a meeting.
Other ideas are also being explored. Connect a sheet of electronic paper to a
telephone line and it could be used as a kind of fax machine. Jacobson foresees
sheets of electronic paper attached to the sides of machines in factories,
offices, labs or kitchens, to display instruction manuals or recipes. And a
sheaf of electronic paper could serve as an everlasting daily newspaper,
recharging itself with fresh news overnight ready for the morning.
And then there鈥檚 the electronic book. If an average 250-page novel takes up 1
megabyte of storage space, existing technology would allow up to 100 books to be
squeezed into tiny chips embedded in an electronic book鈥檚 spine or covers.
Memory chips are getting ever smaller, and in future minuscule magnetoresistive
drives may be able to store up to 35 000 books鈥攎ore than almost anyone can
read in a lifetime. E Ink鈥檚 electronic paper can even change the image on a page
as often as 20 times a second, raising the possibility of a book that can
display video clips too.
So how far off is the ultimate book? 鈥淭he scientific issues are solved,鈥�
Jacobson declares. All that remains is for cost-efficient manufacturing
technologies to be perfected. 鈥淭he question is not technology-driven,鈥� he adds.
鈥淚t鈥檚 whether people are ready for an entirely new way to store and display
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