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Flexible Display

Technologies For Flexible Displays

AMOLEDs

FlexUp technology

Passivation and encapsulation of flexible AMOLEDs

Applications of flexible AMOLED displays

i2r E-paper

Production of i2R E-paper

Applications of i2r E-paper

Conclusion

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EVOLUTION OF ELECTRONIC DISPLAY

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FLEXIBLE DISPLAY

Flexible displays are essentially very thin display screens that can be printed onto flexible material and then attached to other surfaces or produced in a variety of shapes.

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Flat – made on plastic or other non-glass substrates for the purpose of lightness

Conformable – bent once in application

Bendable/Foldable – intended to be bent or flexed repeatedly during use

Rollable – intended to be rolled and unrolled during use

FLEXIBLE DISPLAY MARKET

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Global market revenue for flexible display panels will reach US$339 million in 2013, rising at a compound annual growth rate (CAGR) of 83.5% from US$5 million in 2006.

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Tech.AM-LCD

(Liquid Crystal Display)

AM-EPD(Electrophoretic Display)

AM-OLED(Organic Light Emitting

Diode)

Structure

Prototype

Flexibility Poor Good Excellent

Performance(Video rate)

Excellent Poor Excellent

AUO/ITRI, 2009 ITRI, 2010ITRI, 2007

TECHNOLOGIES FOR FLEXIBLE DISPLAYS

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OLED front panel and TFT backplane

RGB OLED Pixels

• Full layers of cathode, anode, organic molecules

Thin Film Transistor matrix (TFT) on top of anode

• Full layers of cathode, anode,organic molecules

• The TFT matrix backplane isused to drive OLED pixels

• Made of tungsten.

Cathode

• Made of organic plastic molecules.

Emissive Layer

• Made of organic plastic molecules.

Conductive Layer

• Made of transparent graphite particles, ITO etc.

Anode

• Made of glass/plastic foil.

Substrate

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WORKING OF OLED• Voltage is applied across the AMOLED such that the anode is positive with

respect to the cathode.• Electrons from cathode flows into LUMO of the organic layer.• Holes from anode are flows into HUMO of the organic layer through

Conductive layer.• They recombine in emissive layer forming an exciton.• Decay of exciton results in release of energy as radiation whose frequency is in

visible region.• This frequency depends on energy difference between HOMO and LUMO.

Transparent substrate

Anode(ITO)

Conductive layer

Emissive layer Cathode

LUMOLUMO

HOMOHOMO

eˉeˉ

h+h+h+

Light

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Data Line

Data Storage Capacitor

Power Transistor T2

Write Transistor T1

Data Line (applies voltage to power transistor gate)

Row Scan Line

Power Line(Vdd = 13 volts)

OLED

Common Cathode

ACTIVE MATRIX TFT BACK PANEL

ADVANDAGES OF AMOLEDs

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Thinner, lighter and more flexible

Do not require backlighting

Brighter than LEDs because the organic layers

Do not require glass for support

Easier to produce and can be made to large sizes using roll to roll technology

Can enable a greater artificial contrast ratio

Better viewing angle compared to LCDs.

Requires a low amount of energy consumption

Faster refresh rate

FLEXUP : FLEXIBLE UNIVERSAL PLANE

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• FlexUP used integrate flexible Si based transistor array on a flexible

transparent polyimide substrate.

• Utilizes the existing glass line production facility.

• FlexUP enables a high temperature process with high accuracy.

• Also increases the efficiency of de-bonding procedure that separates the

flexible substrate from production carrier.

• Increase mobility of display panels by reducing weight and increasing

rigidness.

• Reduce overall production cost by utilizing current display fabrication

facility.

FLEXUP ON AMOLED

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1. Coating a debonding layer a directly ontothe glass carrier.

2. Coating a PI solution on debonding layer.

3. Debounding layer helps in residue-freedebonding of the PI substrate from glasscarrier

4. Followed by fabricating TFT devices andOLED layer on PI layer.

5. The final residue-free de-bonding of thesubstrate from the glass carrier.

LAMINATION V/S FLEXUP

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PI Solution

PI film

Substrate Holder (Glass)

Slot Die

Coater

•Good alignment

•No residual

•High process temp.

Lamination FlexUP

PASSIVATION AND ENCAPSULATION OF FLEXIBLE AMOLED DISPLAYS

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• Top most flexible cover is made of ultra thin flexible glass. • A soft BL will offset the stress during bending .• Passivation structure includes an inorganic multi layer and BL.• Inorganic multi layer serves as a primary barrier against moisture and oxygen

infiltration. • AIL together with BL between the passivation layer and the OLED layer,

effectively improves flexibility.

PIBarrier

Flexible glass

OLEDAIL

Multi LayerBL

Multi layerAdhesive

TFT BACKPLANE TECHNOLOGIES FOR FLEXUP

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• Low-temperature poly-Si TFTs and IGZO TFTs are excellent semiconductorsfor OLED driving.

• a-IGZO TFTs are excellent for flexible display, improves the pixel apertureratio and also reduce cost.

• The Back Channel Etching type a-IGZO TFTs were fabricated on a FlexUPsubstrate by using a four-mask process with a process temperature lessthan 300°C.

• The a-IGZO TFT backplane was bent at a 25 mm radius up to 10000 times,with the leakage current maintained below 10–11A.

• Flexible transparent a-IGZO TFTs have the advantages of good electricalcharacteristics and low process temperature.

BENDING PERFORMANCE OF A BCE-TYPE AMORPHOUS-IGZO TFT

APPLICATIONS OF FLEXIBLE AMOLED DISPLAYS

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• Rollable and foldable electronic gadgets.

• Wearable devices.

ELECTRONIC PAPER : i2R E-PAPER

• Display technology designed to mimic the appearance of ordinary paper.

• It provides a rewritable, reusable and environmentally friendly print medium - an "electronic paper" - to reduce traditional paper consumption.

• Capable of holding text and images indefinitely without drawing energy, while allowing the image to be changed later

Key features :Wide viewing angleReflects light like ordinary paper Image retain without powerExtremely thin Low manufacturing cost

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STRUCTURE

• Substrate: Made of PET

• ITO layer : Transparent and conducting

• ChLC layer : Made of encapsulated Cholesteric Liquid Crystals and gelatinto reflect a certain wavelength of incident light.

• Nano-Pigment (NP) layer : Light absorption layer to improve contrast,also reflects a certain wavelength of incident light.

• Conducting layer : Made of Aluminum.

• Protection layer : Prevent user damage, composed of polymer and silica.

Substrate Patterned ITO

ChLC

NP layer

Conducting layer

~~ ~~

Protection Layer

WORKING• ChLCD was selected because of its bistability and multi-color possibilities.

• Bistability feature represents two stable states.

1. Planar state

2. Focal conic state

• Voltage applied between ITO and conducting layers switch ChLC states.

• These stable states can be maintained without power consumption

• Voltage is required only during switching of states.

• ChLC and NP layer reflect a certain wavelength of incident light.

• ChLCD shows images by reflecting ambient light.

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E-PAPER PRINTING

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• E-paper can be addressed by applying a bias voltage of 100 V between ITOand conducting layers to change state of ChLC.

• Segmented driving of conducting layer can form different patterns byselective turning on and off of pixels.

• Also addressed by using thermal printer with roller inside, e-paper is rolledthrough thermal printhead and heat generated will switch state.

• Simultaneous application of voltage during thermal printing process canimprove contrast ratio to more than 10:1.

• The thermal writing head only requires temperature of 86°C and 37Wpower for writing.

Thermal Printhead

Platen Roller

Spool

Thermal addressing system

Al electrode

Platen Roller

ChLCD

R2R MANUFACTURING OF i2R E-PAPER

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ITO Laser Patterning

Slot Die Coating of ChLC & Absorption Layer

Forming conducting Layer

Forming Protection Layer

Cutting

Applications

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3m long 24cm wide 300 dpi thermal printed e-paper

• E-cards with fine pictures

• E-tags showing detailedinformation

• E-badges with visitor data

• E-tickets similar to printed papertickets.

• Paper usage could be reduced bymore than 40 million pieces/year.

CONCLUSION

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• We reported a novel technology, the FlexUP, to fabricate AMOLEDdisplays on current glass carrier production line.

• By inserting a release layer, displays and electronic devices are easilyfabricated on substrates and thereafter debonded.

• Presented barrier encapsulation technologies for protecting flexibleAMOLEDs from stress, oxygen and moisture infusion.

• Also attained flexible cheap and rewritable e-paper technology usingR2R production technology.

THANK YOU

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