Flexible electronic displays

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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

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M. S. Ramaiah Institute of Technology 1

Flexible Electronic Displays

Sindhu AUSN No:1MS09TE054

B.E- Telecommunication Engg

Guide :

Mrs Parimala P Asst. ProfessorMSRIT, Bangalore

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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,

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Aim of the Project

• To understand the various flexible electronic display technologies.

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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

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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.

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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

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Based on either – Reflectivity or Emissivity there are 2 forms of displays

Flexible E-Paper based displays andFlexible OLED based displays

As Both of these technologies work on different principles,they exhibit different properties and various different types of display

technologies.

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Properties• Similarities

• Differences

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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

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• 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

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Different types of display technologies

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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

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A piece of Flexible Plastic Substrate

Coated with OTFT material

To produce Backplane and a display that can be handled like a paper

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Flexible Electronic displays based on Reflectivity-- Gyricon

Nicholas K. Sheridon invented Gyricon atXerox 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.

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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

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Polyethylene spheres, 75 to 106 micrometers

-ve Charged white plastic

+ ve charged Black Plastic

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Electrophoretic Ink- Rearranging charged pigment particles using an applied electric field

• Developed by the E Ink Corporation

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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

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• 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

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Generations of E-inkE Ink Vizplex -internal name of E Ink's current line of display technologiesE Ink Pearl- is the second generation of E Ink Vizplex displays, a higher

contrast screenE 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.

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• Cholesteric based bi-stable display– Possess a helical structure

The planer texture» They reflect circularly polarized lightThe focal conic texture» Scatter light in forward directionSwitched from planar to focal conic texture by Low VoltageFocal conic texture to planar by high voltageUsed 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.

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Self-Emissive based flexible displays-FOLED

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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

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How OLED technology works?

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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.)

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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.

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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.

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OLED ACTIVE AND PASSIVE DISPLAYS

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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

DisadvantagesLifetime -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 hoursresidual stress from the deposition of layers onto a flexible substratethermal 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.

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Its wide variety of applications..

1. Smart Cards, Electronic Paper2. Mobile communications3. Personal computers/

portable displays/E-Readers4. Large area displays5. Wearable Electronics6. Automotive Applications7.Non-display Applications (toys, plastic arts etc.) 8. Electronic billboards

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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.

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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 byBy 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 ElectronicPaper 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.

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Thank You

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