Flexible electronic displays

M. S. Ramaiah Institute of Technology 1
Flexible Electronic Displays
Sindhu A
USN No:1MS09TE054
B.E- Telecommunication Engg
Guide :
Mrs Parimala P
Asst. Professor
MSRIT, Bangalore

Acknowledgements
I express immense gratitude towards the Head of
the Department of Telecommunication Engineering,
Dr K Natarajan for continued support.
I would also like to thank, Mrs. Parimala P,
Mr.Venu K N and Mr.Satish Tunga for their appropriate
guidance.
2
M. S. Ramaiah Institute of Technology,

Aim of the Project
• To understand the various flexible
electronic display technologies.

Outline
• Introduction and Scope
• What makes flexible electronic displays attractive ?
• Based on Reflectivity or Emissivity
• Properties
• Different types of display technologies
• Flexible electronic displays have two plans
• Flexible Electronic displays based on Reflectivity-Gyricon
• Electrophoretic Ink
• Self-Emissive based flexible displays -->FOLED
• How OLED technology works?
• Small molecule OLED vs Polymer OLED
• OLED ACTIVE AND PASSIVE DISPLAYS
• Advantages and Disadvantages FOLED
• Wide variety of applications..
• Challenges and Conclusion
• References M. S. Ramaiah Institute of Technology 4

Introduction
• A flexible display is a display which is flexible in nature;
differentiable from the more prevalent traditional flat
screen displays used in most electronics devices.
• It Enables a New Intuitive User Interface,
suitable for simple operations in application software and
opens up new possibilities for flexible displays to be used as
user-interface devices.
Scope
• Offers a more natural way to interact with our gadgets.

What makes flexible electronic displays
attractive ?
• Rugged
• light weight
• unconventional form factors
• very thin
• non-brittle
• the ability to curve, flex, conform, roll,
and fold
• portability
• Low power M. S. Ramaiah Institute of Technology 6

Based on either
– Reflectivity or Emissivity
there are 2 forms of displays
Flexible E-Paper based displays and
Flexible OLED based displays
As Both of these technologies work on different principles,
they exhibit different properties and various different types of display
technologies.

Properties
• Similarities
• Differences
Reflective based—E-Paper Technology Emissive based–Flexible OLED Technology
Comfortable to Eyes, as screens reflect light
like real paper.
They emit light
This relies on reflected ambient light(can be
read in direct sunlight without the images
appearing to fade)
Each individual light generating pixel
generates light when an electric charge is
applied
Holds static image and text indefinitely
without using electricity
Both forms can show images while being bent without
suffering from distortion or blank spots
Both the technologies do not rely on back light

• Based on Reflectivity
– Flexible Electronic Paper based
• Gyricon
• Electrophoretic
• Cholesteric based bi-stable display
• Electrowetting
• Electrochromic
• Self-Emissivity Based
– Flexible OLED (Organic Light Emitting Diode)
based
Different types of display technologies

The flexible electronic displays have two plans
 The back plane – It is made up of organic thin film transistor arrays
which provide voltage needed by the, E-Paper or the FOLED (Flexible
Organic Light Emitting Diode) based front plane.
 The front plane – It is the part where visible images will be displayed.
Back Plane construction
Flexible Printed Organic back planes
A piece of
Flexible
Plastic
Substrate
Coated
with
OTFT
material
To produce
Backplane
and a display
that can be
handled like a
paper

Flexible Electronic displays based on
Reflectivity-- Gyricon
 Nicholas K. Sheridon invented Gyricon at
Xerox Palo Alto Research Center (Xerox PARC),
In the 1970s
 A new display technology
 eventually became the basis of the e-paper.
 designed to mimic the appearance of ordinary ink on
paper, as they reflect light.
 Theoretically making it more comfortable to read,
and giving the surface a wider viewing angle
compared to conventional displays.

each bead is a dipole
spheres are embedded in a transparent silicone sheet,
suspended in a bubble of oil so that they can rotate freely.
polarity of the applied voltage by the backplane to each pair of electrodes determines
whether white or black face is up.
Thus giving the pixel a white or black appearance in the front-plane.
bi-chromal front-plane had a number of limitations, including relatively low brightness and
resolution and a lack of color.
used only in message boards
Polyethylene
spheres, 75 to
106
micrometers
-ve Charged
white plastic
+ ve
charged
Black
Plastic

Electrophoretic Ink- Rearranging charged pigment
particles using an applied electric field
• Developed by the E Ink Corporation
Millions of
Microcapsules,
100
micrometers in
diameter
(size of a
human hair)
Each capsule contains
- Oily solution (black dye)
-numerous suspended
titanium dioxide particles
Titanium particles
–vely charged and
naturally white

• The brightness and resolution of electrophoretic-based e-ink
is better than that of gyricon-based e-ink, but both are
monochromatic in nature.
• To create color, E Ink joined hands with the Japanese
company Toppan Printing, which produces color filter
Using
Microcapsule
Allowed the display to be used
on flexible plastic sheets instead
of glass

Generations of E-ink
E Ink Vizplex -internal name of E Ink's current line of display technologies
E Ink Pearl- is the second generation of E Ink Vizplex displays, a higher
contrast screen
E Ink Triton - third generation of E Ink Vizplex displays: a colour display that is
easy to read in high light. The Triton is able to display 16 shades of gray,
and 4096 colours.
Drawback of electrophoretic e-ink is
– Low Refresh rate  causing Ghost of the images.
– drawing a new text or image is too slow and creates a flicker effect.

• Cholesteric based bi-stable display
– Possess a helical structure
The planer texture
» They reflect circularly polarized light
The focal conic texture
» Scatter light in forward direction
Switched from planar to focal conic texture by Low Voltage
Focal conic texture to planar by high voltage
Used in price labels,e-books.
• Electrowetting
– Modification of the wetting properties of a surface(typically hydrophobic)
with applied electric field
• Electrochromic
– Reversibly changing color when a burst of charge is applied
Are other technologies used to increase resolution.

Self-Emissive based flexible displays
-FOLED
A flexible organic light emitting diode (FOLED) is a type of organic light-emitting
diode (OLED) incorporating a flexible plastic substrate on which the electroluminescent
organic semiconductor is deposited. This enables the device to be bent or rolled while
still operating. The organic semiconductor is situated between two electrodes. Generally,
at least one of these electrodes is transparent. An OLED display works without
a backlight

How OLED technology works?
Substrate (clear plastic, glass, foil) -
The substrate supports the OLED.
(polyethylene terephthalate (PET))
Anode (transparent) – positively
charged wrt to cathode, provides
"holes“ when a current flows through
the device.(Indium Tin Oxide)
Cathode (may not be transparent) -
The cathode injects electrons when
a current flows through the device.
(Barium or Calcium)
Conducting layer-made of organic
plastic molecules that transport
"holes" from the anode.(polyaniline)
Emissive layer-made of organic
plastic molecules (different from the
conducting layer) that transport
electrons from the cathode; this is
where light is made.(polyfluorene.)

OLED light is created
through a process called
electrophosphorescence
•The color of the light
depends on the type of
organic molecule in the
emissive layer.
•Manufacturers place several
types of organic films on the
same OLED to make color
displays.
•The intensity or brightness
of the light depends on the
amount of electrical current
applied: the more current,
the brighter the light.

Small molecule OLED vs Polymer OLED
• Although small molecules emit bright light, deposition onto
the substrates is by thermal evaporation process in vaccum.
• This is an expensive manufacturing process called vacuum
deposition.
 For depositing thin films of Polymers-Vacuum deposition is
not a suitable method.
 However, polymers can be processed in solution, and spin
coating is a common method of depositing thin polymer films.
 This method is more suited to forming large-area films than
thermal evaporation.
 No vacuum is required, and the emissive materials can also be
applied on the substrate by a technique derived from
commercial inkjet printing.M. S. Ramaiah Institute of Technology 20

OLED ACTIVE AND PASSIVE DISPLAYS

Advantages and Disadvantages
FOLED
•Advantages
•Thinner(hence brighter), lighter ,flexible(used
plastic instead of glass)
•Backlight not required hence consume less
power
•easier to produce and can be made to larger
sizes. As they are essentially plastics, they can
be made into large, thin sheets. It is much
more difficult to grow and lay down so many
liquid crystals.
•Large field of view about 170 degrees
•Low heat generation
•Low Power requirement
•Contrast Ratio Over 1,000,000:1
Disadvantages
Lifetime -Red and green OLED films have
longer lifetimes (46,000 to 230,000 hours),
blue organics currently have much shorter
lifetimes (up to around 14,000 hours
residual stress from the deposition of layers
onto a flexible substrate
thermal stresses due to the different
coefficient of thermal expansion of materials in
the device,in addition to the external stress
from the bending of the device.
•Manufacturing - Manufacturing processes are
expensive right now.
•Water - Water can easily damage OLEDs.

Its wide variety of applications..
1. Smart Cards, Electronic Paper
2. Mobile communications
3. Personal computers/
portable displays/E-Readers
4. Large area displays
5. Wearable Electronics
6. Automotive Applications
7.Non-display Applications (toys, plastic arts etc.)
8. Electronic billboards

Challenges
• Encapsulation is challenge for flexible OLED devices.
• Integration of components
Conclusion
• Flexible electronic displays have the
opportunity to revolutionize an Industry.
• Effort to understand the failure limits and
mechanisms have been gaining momentum.

References
• Development of a Flexible Electronic Display Using Photographic Technology by Stanley W. Stephenson,
David M. Johnson, John I. Kilburn, Xiang-Dong Mi, Charles M. Rankin, Robert G. Capurso
• Flexible Electronics: The Next Ubiquitous Platform by
By Arokia Nathan, Fellow IEEE, Arman Ahnood, Matthew T. Cole, Sungsik Lee, Member IEEE, Yuji Suzuki,
Pritesh Hiralal, Francesco Bonaccorso,Tawfique Hasan, Luis Garcia-Gancedo, Andriy Dyadyusha, Samiul
Haque,Piers Andrew, Stephan Hofmann, James Moultrie, Daping Chu, Andrew J. Flewitt,Andrea C.
Ferrari, Michael J. Kelly, John Robertson, Fellow IEEE,Gehan A. J. Amaratunga, and William I. Milne
• Invited Paper: Ultra-thin and Flexible LSI Driver Mounted Electronic
Paper Display using Quick-Response Liquid-Powder Technology Ryo Sakurai, Reiji Hattori+, Michihiro
Asakawa+, Takuro Nakashima+, Itsuo Tanuma,Akihiko Yokoo, Norio Nihei, and Yoshitomo Masuda
• Distinguished Paper: Ultra Thin and Flexible Paper-Like Display using QR-LPD Technology Reiji Hattori,
Shuhei Yamada
• IBM Research Report Unraveling Flexible OLED Displays for Wearable Computing Chandra
Narayanaswami, M. T. Raghunath
• Flexible and Roll-able Displays/Electronic Paper A Brief Technology OverviewRong-Chang (R.C.) Liang
• Flexible display enabling technology Sigurd Wagnera, Stephen J. Fonashb, Thomas N. Jacksonb, James C.
Sturma aPrinceton University, bPennsylvania State University
• Resources from How Stuff Works.
• Resources From Wikipedia. M. S. Ramaiah Institute of Technology 26

Thank You

Flexible electronic displays

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