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Technologies For Flexible Displays
Passivation and encapsulation of flexible AMOLEDs
Applications of flexible AMOLED displays
Production of i2R E-paper
Applications of i2r E-paper
EVOLUTION OF ELECTRONIC 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
Flat – made on plastic or other non-glass substrates for the purpose of
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
12/29/2014 Footer Text 5
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
(Liquid Crystal Display)
(Organic Light Emitting
Flexibility Poor Good Excellent
Excellent Poor Excellent
AUO/ITRI, 2009 ITRI, 2010ITRI, 2007
TECHNOLOGIES FOR FLEXIBLE DISPLAYS
OLED front panel and TFT
RGB OLED Pixels
• Full layers of cathode, anode,
Thin Film Transistor matrix
(TFT) on top of anode
• Full layers of cathode, anode,
• The TFT matrix backplane is
used to drive OLED pixels
• Made of tungsten.
• Made of organic plastic molecules.
• Made of organic plastic molecules.
• Made of transparent graphite particles, ITO
• Made of glass/plastic foil.
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
• They recombine in emissive layer forming an exciton.
• Decay of exciton results in release of energy as radiation whose frequency is in
• This frequency depends on energy difference between HOMO and LUMO.
Emissive layer Cathode
Data Storage Capacitor
Power Transistor T2
Write Transistor T1
Data Line (applies voltage to power transistor gate)
Row Scan Line
(Vdd = 13 volts)
ACTIVE MATRIX TFT BACK PANEL
ADVANDAGES OF AMOLEDs
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
• 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
• Reduce overall production cost by utilizing current display fabrication
FLEXUP ON AMOLED
1. Coating a debonding layer a directly onto
the glass carrier.
2. Coating a PI solution on debonding layer.
3. Debounding layer helps in residue-free
debonding of the PI substrate from glass
4. Followed by fabricating TFT devices and
OLED layer on PI layer.
5. The final residue-free de-bonding of the
substrate from the glass carrier.
LAMINATION V/S FLEXUP
Substrate Holder (Glass)
•High process temp.
PASSIVATION AND ENCAPSULATION OF
FLEXIBLE AMOLED DISPLAYS
• 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
• AIL together with BL between the passivation layer and the OLED layer,
effectively improves flexibility.
TFT BACKPLANE TECHNOLOGIES FOR FLEXUP
• Low-temperature poly-Si TFTs and IGZO TFTs are excellent semiconductors
for OLED driving.
• a-IGZO TFTs are excellent for flexible display, improves the pixel aperture
ratio and also reduce cost.
• The Back Channel Etching type a-IGZO TFTs were fabricated on a FlexUP
substrate by using a four-mask process with a process temperature less
• 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 electrical
characteristics and low process temperature.
BENDING PERFORMANCE OF A BCE-TYPE
APPLICATIONS OF FLEXIBLE AMOLED DISPLAYS
• Rollable and foldable electronic
• Wearable devices.
ELECTRONIC PAPER : i2R E-PAPER
• Display technology designed to mimic the appearance of ordinary
• It provides a rewritable, reusable and environmentally friendly
print medium - an "electronic paper" - to reduce traditional paper
• Capable of holding text and images indefinitely without drawing
energy, while allowing the image to be changed later
Key features :
Wide viewing angle
Reflects light like ordinary paper
Image retain without power
Low manufacturing cost
• Substrate: Made of PET
• ITO layer : Transparent and conducting
• ChLC layer : Made of encapsulated Cholesteric Liquid Crystals and gelatin
to 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
• 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.
• E-paper can be addressed by applying a bias voltage of 100 V between ITO
and conducting layers to change state of ChLC.
• Segmented driving of conducting layer can form different patterns by
selective turning on and off of pixels.
• Also addressed by using thermal printer with roller inside, e-paper is rolled
through thermal printhead and heat generated will switch state.
• Simultaneous application of voltage during thermal printing process can
improve contrast ratio to more than 10:1.
• The thermal writing head only requires temperature of 86°C and 37W
power for writing.
Thermal addressing system
R2R MANUFACTURING OF i2R E-PAPER
Slot Die Coating of
3m long 24cm wide 300 dpi thermal printed e-paper
• E-cards with fine pictures
• E-tags showing detailed
• E-badges with visitor data
• E-tickets similar to printed paper
• Paper usage could be reduced by
more than 40 million pieces/year.
• We reported a novel technology, the FlexUP, to fabricate AMOLED
displays on current glass carrier production line.
• By inserting a release layer, displays and electronic devices are easily
fabricated on substrates and thereafter debonded.
• Presented barrier encapsulation technologies for protecting flexible
AMOLEDs from stress, oxygen and moisture infusion.
• Also attained flexible cheap and rewritable e-paper technology using
R2R production technology.