A suitable solution when power-hungry devices cannot be used
DEBBIE SNIDERMAN, CEO
Ultra-low-power displays, such as e-paper displays with E Ink, are used in many
applications in which a power-hungry backlit LCD isn’t suitable. With a 180° viewing angle and excellent
readability indoors and outdoors, electrophoretic displays are like viewing
printed ink on paper. Displays using E Ink are the only ones that have
high reflectivity and contrast, a wide viewing angle, and are ultra-low-power.
Why e-paper displays are important now
Lee, CTO and President of Pervasive Displays (PDi), the Taiwan-based display design
house specializing in ultra-low-power e-paper displays primarily for retail
electronic shelf labels (ESLs), says that they are much more than beautiful
shelf labels display up-to-date information, such as stock levels and product
information, in real time, integrate with customer referral programs to show
star ratings and product rankings, and can last up to five years on one battery
charge. They’re also important in stores that have thousands of products that
would be impossible to connect with wires.
in Westminster Abbey supplied by Casala use simple, energy-free e-paper
displays from Pervasive Displays that don’t require batteries.
McCreary, Chief Technology Officer at E Ink Corp., says that new products are often
introduced using these types of displays, from shelf signage to
point-of-purchase displays to package-tracking labels. The package-tracking
labels offer the ability to display multiple messages at different stages of a
shipment’s journey and even change a parcel’s destination while en route, a key
feature for last minute re-routing, just-in-time deliveries, or inventory
adjustments. And the age of IoT is coming, when most devices are battery-driven
and users demand long battery lives.
How they work
Ink’s displays are very different from conventional OLED and LCD displays,
which need a backlight to display an image. All have backplanes to drive them,
but that’s where the similarities end. E Ink displays use black-and-white or
colored particles that are charged and suspended in a clear liquid that is
encapsulated in either sealed microcups or microcapsules and coated onto a
clear film. This film is sandwiched between a back electrode and an unpatterned
transparent front electrode.
42-in. E Ink display provides digital signage solutions across industries like
public information, retail, and transportation.
simplest form contains black particles, which are charged positively, and white
particles, which are charged negatively. When an electric field is put across
the sandwich, positive on the front and negative on the back, white particles
migrate toward the front and black particles migrate toward the back. The white
particles are reflective, so they hide what’s behind them, and when all white
particles are at the front, the display looks like a black sheet of paper.
small 2-, 2.5-, or 3-in. bi-stable e-paper displays are mostly used for labels
and are programmed by remote control. E Ink of Boston supplies the
microcapsules of ink used in their display modules, which contain one or two
TFTs, an ink layer, a protective sheet, driver electronics, and a connector.
Ink displays are considered bi-stable in that power is needed only to change
the image, not to maintain it. Images will remain “on all the time” for up to 10
years without power for a shelf label, and, in most cases, Lee says that e-paper
customers use batteries or a solar cell to drive the display. “A watch only
needs very little power to move the minute hand every minute. Most electronic
readers only need to be charged every few months,” McCreary says.
E Ink’s Spectra technology, electronic shelf labels allow retailers to have the
most up-to-date prices in less than a minute.
displays using E Ink technology look like paper, but in dark lighting
conditions, visibility is also different. “OLED and LCD displays use
backlighting that has to make it through the TFT backplane before it is seen.
Only a small percentage is transparent, so a lot of light is thrown away. E Ink
displays utilize front-lighting in dark areas, where virtually all of the light
reflects back into the eyes, so they are more than a factor of 10 times more efficient.
Even using front-lighting, E Ink e-readers only need to be charged once a
month,” McCreary says.
Ink displays also have Lambertian reflections, which scatter light in all
directions similar to printed ink on paper, so they have much wider viewing
angles than LCDs. This is important for viewing shelf labels in a store that
need to be viewed while walking down the aisle before standing in front of it
and from customers of all heights. Resolutions are about 200 to 300 pixels per
inch, and these screens are widely used today.
Group’s PhutureMed smart packaging uses an E Ink display to allow for stricter
medication adherence and safer travel for medicine.
flexible front plane used for viewing the E Ink display is also different. It
is made from plastic substrates with transparent conductors to create the field
and view the ink particles through. “We coat ink on the encapsulated material a
mile at a time in our manufacturing facility, roll it up, and ship it to backplane
manufacturers that can be located anywhere in the world. They cut it out, like
a sticker, and laminate it to their transistor backplanes to complete the
displays. Because the front plane is unpatterned, it can be cut and there is no
critical alignment step to display assembly,” McCreary says.
color displays, substituting black particles for a color, still use plus/minus
charging. This new film, E Ink Prism, is used in architectural applications
like color-changing walls and on furniture. E Ink Spectra, created for
shelf-label applications, is a three-particle system currently available in
black-and-white plus red or yellow, with more colors to come in the future.
to Lee, three-color displays are the biggest innovation that has arisen in
e-paper displays. “It took about five years to perfect three-color displays
with red,” Lee says. “And we are demo’ing black/white/yellow displays now.”
Ink’s Advanced Color ePaper (ACeP) offers a high-quality, full-color reflective
three particles inside — black, white, and red or yellow — things are different.
“By controlling the charges, sizes, and waveforms of not only plus/minus
voltage but time and length of pulses, as well as the liquid inside the
capsule, we can control all three pigments independently to have all red,
white, or black in front and look as good as black and white. This requires
slightly longer waveforms, so it takes a few seconds to update rather than the
fraction of a second needed for black and white, but that is OK for shelf
labels,” McCreary explains.
displays are also shipping with new driver support for integrated development
platforms like the Energia LaunchPad family that supports Texas Instruments processors,
WireIE, and Arduino. PDi also has new, very small boards to link displays
suitcases feature E Ink displays for luggage tags to reduce the risk of losing
luggage while traveling and to speed check-in.
Ink is expanding the temperature range of the displays for freezers and
outdoors. Shelf labels inside a freezer are more convenient than constantly
opening and closing the door, and the newest materials are freezer-cold-compatible.
E Ink displays are moving toward higher temperatures as well to support outdoor
signage and architectural applications where temperatures may exceed 50°C.
backplanes are another new feature that opens up markets and products for
bendables, where weight and being unbreakable are important factors. “Wearables
can be thinner, lighter, on all the time, and laser-cut into any pattern
desired, like making a watchband from the same material as the watch. Notepad-sized
displays could be writeable and extremely lightweight and won’t break. From a design
standpoint, laptops don’t have to have rigid closed lids. Large architectural
signs that use thousands of macro-pixels could be safer because they are made
from lightweight plastic. Smart luggage tags are one of the worst environments
for needing unbreakables,” McCreary says.
ink is made up of millions of tiny microcapsules that contain positively
charged black particles and negatively charged white particles suspended in a
McCreary says that when considering displays using E
Ink technology, designers should think about these key technical parameters:
whether color or black-and-white is needed. If color is needed, will it be used
as a highlight or forecolor? Does the display need to be flexible? How
important is weight? Size? E Ink displays can be cut to any shape. Refresh
Response time is not as fast as that for an LCD and
is temperature-dependent. Black-and-white displays used in e-reader
applications can be updated at speeds that exceed 250 ms. But in three-particle
shelf labels, Lee says, it takes one to three seconds for the ink to update at
room temperature, and up to 90 seconds at –25°C. Response time needs to be
considered as part of the entire user experience, especially if integrating
into a touch panel in a freezer or cold environment. Lee also adds that most
design engineers are familiar with LCD interfaces, but they are different for
e-paper and need to be understood.
Wi-Fi CC3200 with Pervasive Displays e-paper screen.
“When looking for full-color video in a dark room,
use LCD or OLED displays. When designing a sign with a paper look that needs to
be updated but doesn’t burn power while it is on, like a list of doctors in a
hospital that may change office locations, that’s a perfect application for E Ink,”
“Energy use is also a higher-level consideration as
it becomes more important. Buildings, accents, and informational signs need to
comply with regulations controlling energy and greenhouse gas output. They are
turning to E Ink displays that don’t significantly increase the energy footprint
of a project,” McCreary says.
“Don’t just think
about the narrow sense of the specs needed to satisfy an application. Think
about the broader sense of the project managers and their higher-level goals.
In the case of a building, their commitment could be to energy use. In the case
of a wearable, it could be the overall user interaction and satisfaction. No
buttons need to be pushed or tapped to get a beautiful display of
on-all-the-time information. Specs should only be part of the consideration.”