Introduction to display technologiesIntroduction to display technologies

Jean-Michel LechevallierJean-Michel Lechevallier

SummarySummary

1. Introduction to LCD.1. Introduction to LCD. History.History. How it works.How it works. Optical modes.Optical modes. CCFL, EL, Led. CCFL, EL, Led. Lightguides.Lightguides. Optical films.Optical films. LED and their chromatic characteristics.LED and their chromatic characteristics.

2. Bistable LCD.2. Bistable LCD.

SummarySummary

3. LCD module architecture.3. LCD module architecture. LCD - driver connection.LCD - driver connection. Complete architecture of a module. Complete architecture of a module.

4. Color LCD.4. Color LCD. 4.1. Passive matrix.4.1. Passive matrix.

Color cell (Transmissive, Reflective, Transflective).Color cell (Transmissive, Reflective, Transflective). Optical modes comparisonOptical modes comparison Grey scale generation (FRC, PWM).Grey scale generation (FRC, PWM).

4.2. Active matrix.4.2. Active matrix. Introduction to TFT.Introduction to TFT. LTPSLTPS System on module.System on module.

SummarySummary

5. Other technologies.5. Other technologies.

5.1. Field sequential5.1. Field sequential

5.2. OLED5.2. OLED

5.3. Others.5.3. Others.

6. Display technical characteristics.6. Display technical characteristics.

6.1. Main characteristics.6.1. Main characteristics.

6.2. Measurement methods.6.2. Measurement methods.

7. Comparison.7. Comparison.

CSTN, TFT, OLED.CSTN, TFT, OLED.

 

1. Introduction to LCD.1. Introduction to LCD.

History.History.

1888 : discovery of liquid crystal phase by an Austrian botanist, Dr Rheinitzer

1968 : first liquid crystal display built by RCA

years 1970 : developement of first LCD for mass production in Japan.

 

1. Introduction to LCD.1. Introduction to LCD.

How it works (1/3).How it works (1/3).

 

1. Introduction to LCD.1. Introduction to LCD.

How it works (2/3).How it works (2/3).

TN, STN, DSTN, FSTN technologies.TN, STN, DSTN, FSTN technologies.

 

1. Introduction to LCD.1. Introduction to LCD.

How it works (3/3).How it works (3/3).

Alignment layers.Alignment layers.

 

1. Introduction to LCD.1. Introduction to LCD.

Optical modes.Optical modes.

ReflectiveReflectiveReflectiveReflectiveTransmissiveTransmissiveTransmissiveTransmissive TransflectiveTransflectiveTransflectiveTransflective

Backlight ONBacklight ONBacklight ONBacklight ON Backlight ONBacklight ONBacklight ONBacklight ONBacklight OFFBacklight OFFBacklight OFFBacklight OFFFrontlight ONFrontlight ONFrontlight ONFrontlight ONFrontlight OFFFrontlight OFFFrontlight OFFFrontlight OFF

= LCD panel= LCD panel= LCD panel= LCD panel = backlight or frontlight= backlight or frontlight= backlight or frontlight= backlight or frontlight

 

1. Introduction to LCD.1. Introduction to LCD.

sources : CCFL, EL, Led. sources : CCFL, EL, Led.

Lightguides : Lightguides : FrontlightFrontlight BacklightBacklight

 

1. Introduction to LCD.1. Introduction to LCD.

Optical filmsOptical films main supplier : 3M main supplier : 3M

2 technologies:

- microreplication :adjustment of the light reflection angles => ex. : BEF, xBEF

- multi layer :light filtering => ex. : DBEF

 

LED and chromatic characteristics.LED and chromatic characteristics.Coordonnées chromatiques

0,19

0,2

0,21

0,22

0,23

0,24

0,25

0,26

0,27

0,28

0,29

0,3

0,31

0,32

0,33

0,34

0,35

0,36

0,37

0,38

0,39

0,4

0,41

0,42

0,43

0,44

0,45

0,24 0,25 0,26 0,27 0,28 0,29 0,3 0,31 0,32 0,33 0,34 0,35 0,36 0,37 0,38 Cx

Cy

a0

b1

b2

c0

Rangs Nichia

LE

D a

nd t

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chro

mat

ic c

hara

cter

istic

s.LE

D a

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1. I

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to

LC

D.

1. I

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LC

D.

 

2. Bistable LCD.2. Bistable LCD.

Bistable LCD - BiNem technology from NemopticBistable LCD - BiNem technology from Nemoptic

 

3. LCD module architecture.3. LCD module architecture.

LCD - driver connection.LCD - driver connection.

COBCOB : Chip On Board, : Chip On Board,

TABTAB : Tape Automated Bonding (TCP : Tab Carrier Package), : Tape Automated Bonding (TCP : Tab Carrier Package),

COFCOF : Chip On Foil - Flex, : Chip On Foil - Flex,

COGCOG : Chip On Glass. : Chip On Glass.

 

3. LCD module architecture.3. LCD module architecture.

Complete architecture of a module. Complete architecture of a module. TAB

COG

Driver

Driver

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Color cellColor cell

Transmissive display

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Color cellColor cell

Reflective display

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Color cellColor cell

Transflective displaysolution 1 : with a transflective sheet

The display reflectivity is adjusted by changing the reflectivity (transmissivity) of the transflector.

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Color cellColor cell

Transflective displaysolution 2 : reflective surface on color filters

Reflective areaReflective area

Transmissive areaTransmissive area

surfacetotale

surfacevetransmissiRatioOpen

..

....

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Optical modes comparisonOptical modes comparison

Transmissive Reflective Transflective

Indoorreadability

+++ + ++

Outdoorreadability

+ +++ ++

contrast +++ + ++

Colorgamut

(saturation)+++ + ++

 

4. Color LCD4. Color LCD4.1. Passive matrix4.1. Passive matrix

Grey scale generatorGrey scale generator

FRC = Frame Rate ControlFRC = Frame Rate Control

alternatively light on and off pixels alternatively light on and off pixels during several frames => the average during several frames => the average

light creates the grey level.light creates the grey level.

Advantages:Advantages:lower power consumptionlower power consumption

better contrastbetter contrastless flickeringless flickering

Disadvantage :Disadvantage :jitteringjittering

PWM = Pulse Width ModulationPWM = Pulse Width Modulation

Advantage:Advantage:No jitteringNo jittering

Disadvantage:Disadvantage:higher power consumptionhigher power consumption

ONON OFFOFF OFFOFFONON OFFOFFONONOFFOFF TframeTframe

tHtH

Duty cycle=tH/TframeDuty cycle=tH/Tframe

ExampleExampleGL=3/7GL=3/7

ExampleExampleGL=3/7GL=3/7

Frames 1 2 3 4 5 6 7Frames 1 2 3 4 5 6 7Frames 1 2 3 4 5 6 7Frames 1 2 3 4 5 6 7

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

Introduction to TFT Introduction to TFT

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

Introduction to TFTIntroduction to TFT

TFT cell structure TFT cell structure

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

Advantages of TFT Advantages of TFT compared to CSTNcompared to CSTN

contrastcontrast

color saturationcolor saturation

response timeresponse time

viewing anglesviewing angles

Disadvantages of TFT Disadvantages of TFT compared to CSTNcompared to CSTN

power consumptionpower consumption

costcost

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

TFT LTPS (Low temperature Poly Silicon) TFT LTPS (Low temperature Poly Silicon)

LTPS : electron mobility increased compared to amorphous TFT technology :

electron mobility

p-SI TFT = 200cm²/V.S

a-Si TFT = 0.5cm²/V.S

=> enable to reduce transistor size and embed more electronic functions on the glass substrate.

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

Advantages and disadvantages of LTPSAdvantages and disadvantages of LTPS

Advantages:

higher electron mobility

higher aperture ratio => enable to increase the resolution

Disadvantages :

production yield

cost

 

4. Color LCD4. Color LCD4.2. Active matrix4.2. Active matrix

System On Module System On Module

Display areaSensor

MemoriesInterface

Controller Driver,DAC

Embedded functions :

- driver / controller- memories- peripheral audio functions- scanner- finger print recognition- etc.

 

5. Other technologies.5. Other technologies.5.1. Field sequential5.1. Field sequential

IntroductionIntroduction

 

5. Other technologies.5. Other technologies.5.1. Field sequential5.1. Field sequential

Advantages:

up to 85% of NTSC color gamut

High resolution (1dot/pixel)

Disadvantages:

the display is black and white in reflective mode

dedicated controller

specific LC cells (very fast response time)

a sorting of tricolor LED is necessary to reduce color variations

Necessary to adjust the color balance

Advantages / DisadvantagesAdvantages / Disadvantages

 

5. Other technologies.5. Other technologies.5.2. OLED.5.2. OLED.

IntroductionIntroduction

Anode (ITO)

Glass Substrate

Cathode (AL:Li)

+

－

Hole

Electron

Hole Injection Layer

Emission Layers

Light

－－－－－－－－－－

+ + + + + + + + + + +

CurrentLight

 

5. Other technologies.5. Other technologies.5.2. OLED.5.2. OLED.

Advantages / DisadvantagesAdvantages / Disadvantages

Advantages

contrast

viewing angles

very thin module (no backlight)

response time (1µs)

color saturation

Disadvantages

lifetime (especially for blue)

Brightness is a bit low

power consumption

emissive technology

 

5. Other technologies.5. Other technologies.5.3. Others.5.3. Others.

 

6. Display technical characteristics6. Display technical characteristics6.1. Characteristics6.1. Characteristics

Contrast (transmissive and reflective)

Transmittance (%)

Reflectance (%)

Response time (ms)

Viewing angles (transmissive and reflective) (degrees)

Chromatic co-ordinates (transmissive and reflective) (defined in CIE 1931 diagram)

Color gamut (surface or % of NTSC triangle)

Open ratio (%)

Aperture ratio (%)

Brightness (cd/m²)

Backlight uniformity (%)

Power consumption (mW)

 

6. Display technical characteristics 6. Display technical characteristics 6.2. Measurement methods6.2. Measurement methods

2 methods for measurements in reflective mode (contrast, reflectivity, …) 2 methods for measurements in reflective mode (contrast, reflectivity, …)

Specular diffuse

Use a sphere to diffuse the light in every direction => this method is the

most representative of normal lighting condition.

Use a point light source.

 

7. Comparison7. Comparison

CSTN TFT AM OLED Thickness 2.7mm with backlight 2.7mm with backlight 1.7 Brightness TF : 70cd/m²

TM : 170cd/m² TF : 100cd/m² TM : 250cd/m²

150 to 200 cd/m²

Response time 150 à 300ms 30ms 1µs NTSC ratio TF : 15%

TM : 35% TF : 40%

TM : 60% (up to) 65%

(50% for PM OLED) Contrast TF : 20

TM : 30 TF : 70

TM : 300 500

Viewing angles 60 à 90 degres 60 à 160 degres 180 degres Power consumption (all on) based on 96*64 display

BL off : 2mW BL on : 180mW

BL off : 3~4mW BL on : 180mW

200mW

Lifetime (defined at half brightness)

>30K hrs >30K hrs <5 to 10 K hrs (with color deviation)

 

7. Comparison7. ComparisonColor gamutColor gamut

 

FINFIN