1

Examples of flat-panel liquid crystal displays

2

glass pixelated color filter + black mask Planarization layer (acrylate network) ITO electrode Polyimide orientation layer Liquid crystal Polyimide orientation layer ITO electrode pattern glass

polarizer

polarizer

Acrylic waveguide with scattering elements

glass pixelated color filter + black mask Planarization layer (acrylate network) ITO electrode Polyimide orientation layer Liquid crystal Polyimide orientation layer ITO electrode pattern glass

polarizer

polarizer

Acrylic waveguide with scattering elements

Display design

3

Display element Efficiency (%) individual cumulative

lamp reflector + in-coupling 80 80 backlight waveguide 70 56 diffuser + air gap 90 50 back polarizer 40 20display aperture 80 16 color filters 28 5effective area for color 33 2 front polar 95 1

Display element Efficiency (%) individual cumulative

lamp reflector + in-coupling 80 80 backlight waveguide 70 56 diffuser + air gap 90 50 back polarizer 40 20display aperture 80 16 color filters 28 5effective area for color 33 2 front polar 95 1

Light efficiency of flat-panel TN LCDs

4

Optical films for LCDs

5

Polymers in LCD displays

• Polarizers• Color Filters• Viewing angle compensation• Prism films• Multi-layer optical films• Specular reflectors• Liquid crystal alignment layers

6

Ceramics in LCD displays

• Display quality glass• Transparent conductive oxides• Spacers• Viewing angle compensation• Prism films• Multi-layer optical films• Specular reflectors

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Quenched-in misorientation of InO6 structural units leads to amorphous films

300

250

200

150

100

50

0co

un

ts

4035302520two theta (degrees)

{222}

{400}{211}

Bixbyite crystal structure: c-type rare earth sesquioxide

•Ia3 with 80 atom unit cell consisting of InO6 structural units

Indium oxide

8

Sputter Target Qualification

•Film purity

•Film properties

•Step coverage

•System throughput

•Uniformity of deposition

•Target integrity (& utilization)

•Process repeatability

Sputter Deposition Challenges

•Compositional analysis

•standard test conditions:•Sputter system•Power density•Voltage•Sputter gas•Film thickness

•Resistivity (film)

•Surface asperities (nodules)

•Sputter rate

Time dependence of...

Transparent Conducting Oxides

9

NS

NS

NS

DC Power supply

erosion center

substrate

target

sputtered atoms

incident ion

Target

Sequence of collisions results in ejection of target atom (sputtering)

sputtered atom

reflected ions and neutrals

secondary electrons

implanted ion

Magnetron Sputter Deposition

10

Crystalline and wt%SnO2 Indium Oxide

0.2 µm

Pure In2O3 In2O3:9.8 wt%SnO2

0.2 µm

Pure In2O3 In2O3:9.8 wt%SnO2

Crystallinity Wt% SnO2

11

• Erosion profile

•Surface profile

•Nodule formation

•Composition

•Toughness

Sputter target removed from service

Sputter target characterization

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TFT Foils

TFT Structure

• Flexible polyimide substrates• On surface minimum radius of curvature

depends on TFT strain to failure• Inside substrate minimum radius of curvature

depends on substrate

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By an external field • electrical field (e.g. 1 V/m) • magnetic field (e.g. 5 kG) • mechanical field (e.g. flow)

At an oriented surface • buffed substrate for planar alignment • surfactants for homeotropic alignment

form anisotropy anisotropic molecular properties

combined action of sterical and dispersive interfacial interactions

E

Liquid crystal alignment

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Rubbing directions and chiral dopants determines rotation direction

Twisted nematic displays

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rubbing

Tilt angle by selection of alignment material and rubbing

Rubbing direction in accordance with twist sense

90o twist by adding chiral dopant

Pretilt and chiral additives to prevent domain formation

Tilt, twist and rubbing directions

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N O

O

O

C14H19

CCH3

CH3

O N

O

O

N

O

O

O CCH3

CH3

O N

O

O C14H19

Alignment mechanism: • at nano grooves by excluded volume effects

of rod-like molecules at interface • at preferentially orientated chain segments

by anisotropic dispersive interactions with LC molecules

• apolar side/end groups provide pre-tilt control

n

Rubbing of polyimide provides liquid crystal orientation

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•Use polarized UV light to modify polymer surface in order to control liquid-crystal alignment

linearly polarized UV-light

*

Recent development: photo-alignment

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Problems with mechanical rubbing: • static electricity • dust formation • uniform rubbing of large surface area • uniform rubbing of irregular surface

Photo-alignment is a non-contact method that avoids these problems !

Why photoalignment ?

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• Orientation perpendicular to polarization direction • No or small pretilt

( )n

O

C O

C

C

( )n

O

C O

C

C

( )n

( )n

O

O

C O

C O

LP-UV

Photo-alignment using polyvinylcinnamates

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• Orientation parallel to polarization direction • Pretilt

O

O O

O

O

O O

O

LP-UV

Coumarin-based photoalignment (Rolic)

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• Multi-component mix for: • low melting temperature • high nematic to isotropic transition temperature • optimized optical anisotropy • small dispersion of refractive indices • low viscosity for fast response • small elastic constants • high dielectric anisotropy / low threshold voltage • low conductivity

LC mixtures for displays contain many components

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FC5H11

FC7H15

FC6H13

C3H7 OCF3

C5H11 OCF3

OCF3CH2CH2C3H7

OCF3CH2CH2C5H11

CH2CH2C3H7 F

F

C3H7

F

C3H7

C3H7

F

C5H11

C5H11

F

C5H11

12 w%

10 w%

10 w%

13 w%

12 w%

11 w%

9 w%

13 w%

3 w%

4 w%

3 w%

FC5H11

FC7H15

FC6H13

C3H7 OCF3

C5H11 OCF3

OCF3CH2CH2C3H7

OCF3CH2CH2C5H11

CH2CH2C3H7 F

F

C3H7

F

C3H7

C3H7

F

C5H11

C5H11

F

C5H11

12 w%

10 w%

10 w%

13 w%

12 w%

11 w%

9 w%

13 w%

3 w%

4 w%

3 w%

Example of LC mixture

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Column electrodes

Row electrodes

Active matrix LCD (TN)

Direct addressingPassive matrix LCD (STN) - row and column electrodes - LC responds to RMS voltage

switch at each pixel

Passive plate with counter electrode

Drive Schemes

24macroorganisch 6C275 / kernkeuze college 6C270 24-04-01 home

0

25

50

75

100

0 2 4 6

Applied voltage (VRMS)

Tra

nsm

issi

on (

%) TN cell

STN cell

TN STN for polars: (Super Twisted Nematic) 90o twist 180o-270o twist white off state colored on/off state black-on state compensation foil

for B/W for // polars: (poor) black off white on state

twist angle

Electro-optic response of TN and STN LCD’s

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active matrix:high end computer monitors, video ‘emissive’ by back light

passive matrix: simpler displays

??

passive matrix, bistable effect, reflective color: simpler displays, extremely low power consumption

paper-white reflective effects

• Polarizer-based LC effects • Twisted-nematic • In-plane switching of nematics • Vertically aligned nematics • Ferroelectric (SC*) • Supertwisted-nematic

• Polarizer-free LC effects • Polymer dispersed liquid crystals • LC gels • surface or polymer-stabilized cholesterics • guest-host LC’s

Other liquid crystal display effects

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h

E

transparent

scattering

Polymer stabilized liquid crystals

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• Schematic representation of different types of liquid crystal polymers • Network formation by photo-initiated polymerization • Formation of ordered networks by photopolymerization of liquid-crystalline

monomers • Example of photo-initiated polymerization in the liquid-crystalline state • Typical processing sequence • Reactive liquid crystals • Influence of functional moiety on mesomorphism of reactive liquid crystals • Refractive indices before and after polymerization • Order parameter of LC diacrylates before and after polymerization • Liquid crystalline networks for advanced optics • Three-dimensional polymer architectures • Combination of different alignment principles • Photopolymerization of a chiral monomer • Pitch of the helix can be freely chosen by blending chiral with nematic monomers • Reflection band of sample containing 62 % chiral diacrylate • Photo-induced diffusion in z-direction • Gradient in UV light by strong absorbing dye • Modulation of properties in z-direction • Cholesteric network with a pitch gradient

Polymeric liquid crystals and liquid crystal networks

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rod

rigid main chain

flexible main chain

disk

LC MAIN CHAIN POLYMERS

LC SIDE CHAIN POLYMERS

LC NETWORKS

Schematic representation of different types of liquid crystal polymers

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OO O

O

O

O

O

O

O

O

h

aligned LC monomer

Formation of LC networks by photopolymerization of LC monomers

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Iso-contrast lines

Grey scale inversion

Contrast and grey-scale inversion as function of viewing angle

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high contrastlow contrast

low V medium V high V

low low contrasthigh

dn >> 0dn = 0

Grey scale inversion • Contrast degradation

Viewing angle of TN-LCD’s

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towards towards homeotropic orientation homeotropic orientation at air interfaceat air interface

planar orientation planar orientation at rubbed substrateat rubbed substrate

with WVA

without WVA

Compensation foils to improve on viewing angle

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Tilted discotic networks to improve on viewing angle

O

O

C

C

O

H3C

OR

O CH3

OR

OO CC

OO

OR

H3C

RO

H3C

O

O

C

C

O

O

RO

CH3

CH3

RO

R = -C10H21 and/or

(CH2)11O C

O

CH CH2

Fuji film

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Reflecting polarizer, e.g. wide-band cholesteric film

Depolarizing or polarization converting reflector

100% polarized light instead of 50% by recycling principle

Non-absorbing polarizer improves on light-efficiency

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wideband cholesteric polarizer

Display partly provided with wide-band cholesteric polarizer

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monomer with steep temperature dependence

polymer with flat

temperature

dependence

300

400

500

600

700

800

20 40 60 80 100 120

Temperature (oC)

Ref

lect

ion

wav

elen

gth

(nm

) monomer

polymer 1

polymer 2

polymer 3

Cholesteric color filters: color generation without absorption improves LCD’s on light efficiency