liquid crystal displays · 2014-04-08 · liquid crystal displays-a technological revolution avtar...
TRANSCRIPT
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Liquid Crystal Displays-a Technological Revolution
Avtar S Matharu
EY/IeMRC
Innovative Electronics Manufacturing Seminar
26th June 2007
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1. IntroductionLCDs everywhere, market dominance, TN Display type, definitions, economic factors.
2.Cell assemblyBacklighting: clarity, luminance.
3.ManufacturingMinimising costs, panel size, filling, thinning.
[4.See examples of liquid crystals: both display and non-display]
‘A Technological Revolution’Contents
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‘A Technological Revolution’LCDs - everywhere
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‘A Technological Revolution’- market penetration
Data source: Norman Bardsley, DisplaySearch
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Benefits:
Flat panel
Lightweight
Low power
Do not emit harmful radiation
LC requirements (problems)
Wide operating range, -40oC to +50oC
chemical, physical and electro-chemical stability
Wide viewing angle, contrast, brightness
Low viscosity
versus
‘A Technological Revolution’LCDs versus CRTs
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‘A Technological Revolution’- Not just LCDs
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‘A Technological Revolution’-what are liquid crystals?
A FOURTH STATE!“Liquid crystals are materials that exhibit an intermediate state of matter that exists between the crystalline and isotropic liquid states”
Conventional wisdom – 3 states
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Front glass substrateITO layerAlignment layer
Nematic Liquid crystal
ITO layerRear glass substrate
Alignment layer
Rear polariser
Backlight
Front polariser
‘A Technological Revolution’Twisted Nematic Display
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ON STATE (DARK)
0 V
OFF STATE (BRIGHT)
V
‘A Technological Revolution’Twisted Nematic Display
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In-Plane Switching
(IPS)
Vertically-Aligned Nematic
(VAN)
‘A Technological Revolution’New - IPS and VAN
http://www.ips-alpha.co.jp/en/technology/ips.html
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Diffuser
DBEFBEF
BEF
Diffuser
PolarizerImage LayerPolarizer
‘A Technological Revolution’Display Construction
Reflector
Light guide plane
LIGHT SOURCE
COLLIMATION
LC CELL
ANTIGLARE
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CLARITY POWER PORTABILITY
COST
‘cut-throat business’
‘A Technological Revolution’Economic considerations
MATERIALS MACHINERY PROCESS TIME
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Clear Plastic lightguide
LCD cell
Point sources emitting sideways into light guide
Line sources
LCD cell
Reflective surface
‘A Technological Revolution’Backlighting types
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Total Internal Reflection
Dots for extracting light from light guide
Light Guide
Cold Cathode fluorescent lamp (CCFL) White reflector
LightguideCCFT Lamp
ESR3M Enhanced Specular Reflector is a 98.5%, non-metallic specular (mirror-like) reflector
‘A Technological Revolution’Backlighting - collimation
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Diffuselyrecycled
Total Internal Reflection
Refraction - Usable refracted rays are increased 40% – 70%
Low percentage lost
Re-enternext prism
Diffuse Illumination
70°
BEF
‘A Technological Revolution’Brightness Enhancement Films
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‘A Technological Revolution’Backlighting - integrated
http://www.cmo.com.
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100% of light
Backlight
Display with active pixel areas
< 100% of light available passes through pixel areas
‘A Technological Revolution’Backlighting losses
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Actual size of pixel to pixel gap
Actual size of active pixel area (overlap of upper and lower electrodes)
Aperture% = active pixel area / actual pixel area
Aperture of typical (pixellated) passive LCD = 90 - 95%
Aperture of typical AM TFT LCD ~ 35 -65%
‘A Technological Revolution’Backlighting losses
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Commercial grade ~ < 48% transmission
Extended grade ~ < 40-45% transmission
‘A Technological Revolution’Polariser losses
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‘A Technological Revolution’Colour Filter losses
0%LBL
100% LBL
33% LBL
33% LBL
33% LBL
Monoch
rome d
isplay
White
= 100%
LBL
Colour d
isplay
White
= 33%
LBL
LBLLBL
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Mother glass preparation
• Glass substrates coated with Indium Tin Oxide (ITO). Resistivity in the range of 10 – 125 Ohm sq.
• Substrate thickness ranges from 0.3 to1.1 mm.
• Soda lime or Borosilicate
Mother glass Preparation
‘A Technological Revolution’Putting it together
Generation 1 = 320 x 400Gen 2 = 370 x 470Gen 2.5 = 400 x 500Gen 3 = 550 x 650Gen 3.25 = 620 x 750Gen 3.5 = 650 x 830Gen 4 = 730 x 920Gen 5 = 1100 x 1250Gen 6 (2003) = 1500 x 1800Gen 7 (2004) = 1800 x 2100
Gen 8 (2006) = 2160 x 2460(0.7 mm thick!!)
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Pre-cleaning
• Use detergent and ultrasonic baths to remove oil and particles on the substrate surface
Mother glass Preparation
Pre-Cleaning
Glass
Glass
ITO
ITO
‘A Technological Revolution’Putting it together
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ITO Patterning• Photo-resist coating• Coat a photo-resist layer on the
substrate surface• Thickness of PR at ~1.2 um• Offset printer spin-coat
techniques used
Mother glass Preparation
Pre-Cleaning
Photo-resist Coating
Glass
Glass
ITO
ITO
PR
PR
‘A Technological Revolution’Putting it together
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ITO Patterning• Photolithography• The UV exposure time
depends on the resolution, usually at around 10 to 20 sec.
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure/developmentUV light
Chrome Mask
PR ITO Glass
‘A Technological Revolution’Putting it together
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ITO Etching• Etch the ITO pattern by using
strong acid• Control bath temperature to
control the etching rate• The etching time depends on
the ITO layer thickness
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure
Developing
ITO Etching
‘A Technological Revolution’Putting it together
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• Polyimide alignment layer• PI offset printed coating or
spin coated• Coat the patterned or coated PI
layer on the mother glass • Cure under high temperature for
around 3 hours
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure
Developing
Mother glass Preparing
ITO Etching
Final cleaning PI offset coating
PI layer
‘A Technological Revolution’Putting it together
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Spin coating Offset lithographic printing
No tooling = cheap process Tooling required
more expensive process
‘A Technological Revolution’Maximising yield - coatings
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‘A Technological Revolution’Maximising yield - coatings
http://www.cmo.com.
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Buffing (Rubbing)
• Determine the buffing direction of display which determines the LC twist angle
• Rub the PI layer using Wool, Nylon or Rayon
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure
Developing
Mother glass Preparing
ITO Etching
Final cleaning PI offset coating
Buffing
‘A Technological Revolution’Putting it together
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Perimeter seal, conductive dot screen printing, spacer filling
‘A Technological Revolution’Putting it together
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure
Developing
ITO Etching
Final cleaning PI offset coating
Buffing
Main seal screen printing
Spacer spraying
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GlassMetalDielectric
Epoxy seal
GlassMetalDielectric
Epoxy seal
Spin process Off set litho print process
Epoxy seal rests on dielectric = low strength, poor reliability, low lifetime
but CHEAP
Epoxy seal on glass or metal = high strength, good reliability, long lifetime
but MORE EXPENSIVE
‘A Technological Revolution’Maximising yield - sealants
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‘A Technological Revolution’Putting it together
Sealed
Plastic Bag
Mother glass Preparing
Pre-Cleaning
Photo Resist Coating
UV Exposure
Developing
ITO Etching
Final cleaning PI offset coating
Buffing
Main seal screen printing
Spacer spraying
Coupling
Vacuum pack
Coupling and Vac pack
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http://www.cmo.com.30 inch Panel 5 DAYS!
30 inch Panel 5 MINS!
‘A Technological Revolution’Maximising yield - filling
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x4 rows
x5 rows
25% moreper panel
‘A Technological Revolution’Maximising yield - glass
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‘A Technological Revolution’Maximising yield - Electronics
Wire on Array and Chip on Glass Technology
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‘A Technological Revolution’Maximising yield
Glass weight
Spacer Technology
Rubbing direction and alignment layers
Backlight optimisation
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Chris Williams, Logystyx UK, for the use of slides on LCD manufacturing and backlighting
Rob Bennett, 3M Optical Systems, for the use of slides on backlighting, BEFS.
‘A Technological Revolution’Acknowledgements