LC Modesdisplay.donga.ac.kr/강의자료/2016학년도 1학기... · 2013. 5. 1. · LC Mode : Twist Nematic 1. TN Mode (5). Cell design – Film 보상(Black Pattern) ¾Black 상태LC

LC ModesLC Modes

이 기이 기 동

2006 07 192006. 07.19동아대학교, 전자공학과

C t tContents

1 Introduction1. Introduction

2. Liquid Crystal and Phase Retardation

3. Classification of LC Modes-. Twisted Nematic

-. Horizontal Switching

-. Vertical Switching

-. π cell

1. Introduction

DisplayDisplayDeviceDevice

LabLab FPD Application

Mobile OA TV

PJTPJT

TV 시장

LCDPJT

LCDLCD

PDPOLED

CRT-PJT

PDPOLED

10″ 20″ 30″ 40″ 50″ 60″(SIZE)

CRT-PJTFED

소형DISPLAY

N/B MONITOR

중/소형 TV대형 TV

PROJECT

출처 : J.H Kim


LabLab Principle of LCD

Light Source

LC P l

자극 분자배열변화 광학효과유발

LC Panel

전기장/자기장

Electro-Optic effect

LC Light Shutter

Image quality Moving picture, Viewing angle, Color shift출처 : J.H Kim


LabLab 주요 Display 특징비교

CRT평판 Display

기술격차는 미미해짐, 문제는 가격

CRTTFT-LCD PDP 유기EL

장점고화질

경량/박형

저소비전력박형

경량/박형

저소비전력장점저가격

저소비전력

고해상도대형크기

저소비전력

고선명/고속응답

단점부피

전자파동영상화질

가격

소비전력수명

단점 전자파

Size한계가격

소비전력

저효율/온도Size

크기(현수준) 10”~40” 2”~80” 32”~100” 40”이하

개발단계 성숙 양산/성장 양산/성장 연구개발

적용분야 모니터/TV모니터/HDTV

노트북 벽걸이TV 휴대폰/PDA적용분야 모니터/TV 노트북

휴대폰/PDA벽걸이TV 휴대폰/PDA

연구기술 평면/고정세

저가격화/대형화

응답속도개선

저가격화

고효율

기술개발(수명)양산성확보연구기술 평면/고정세 응답속도개선

광시야각확보

고효율

고해상도

양산성확보

대형화

출처 : J.H Kim


LabLab LCD Technology Trend

View AngleView AngleView AngleView AngleUniform in All directionsUniform in All directions

Response timeResponse timeResponse timeResponse timeMotion BlurMotion Blur Free Free Motion BlurMotion Blur Free Free LC + B/L + CircuitLC + B/L + Circuit

DataData

BacklightBacklight

LC + B/L + Circuit LC + B/L + Circuit

BrightnessBrightnessBrightnessBrightnessColor DepthColor DepthColor DepthColor Depth No dazzlingNo dazzling

White+White+

R G

More Natural More Natural /Peak Luminance/Peak Luminance8 bit 10 bit8 bit 10 bit

BW

■: TV2 80%0.8

1.0

② B/L Control

CRCRCRCRColor GamutColor GamutColor GamutColor Gamut

●: TV1 72%■: NTSC 100%

-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0.0

0.2

0.4

0.6

③ Data Stretch

② B/L Control① Histogram Analysis

CRCRCRCRStatic C/R → Dynamic C/RStatic C/R → Dynamic C/RAdaptive Dynamic Image ControlAdaptive Dynamic Image Control

More Natural More Natural Pigment Pigment

2. Liquid Crystal and Phase Retardation


LabLab2. Liquid Crystal and Phase Retardation

Liquid Crystals

Normal LiquidNormal Liquid

Liquid CrystalLiquid Crystal

SolidSolid



Li id C t l• Solid Anisotropic Liquid Isotropic• As T increases, order parameter decreases.

Liquid Crystals

Crystal: S=1; LC: S~0.6-0.8, Isotropic: S=0.

n

T

Crystal Nematic LC IsotropicRef. : S.T.Wu



Liquid Crystal Molecules and the Director

•• The local average direction of the molecular long axisThe local average direction of the molecular long axis

The moleculesThe molecules The directorThe director



The Director Field

•• There are elastic restoring forces that try to keep the director field uniformThere are elastic restoring forces that try to keep the director field uniform

ThisThisThisThis

will try to relaxwill try to relaxto thisto thisto thisto this



Director Configurations When Surfaces are Rubbed in Opposite Directions

No Field: High Field:



Director Configurations When Surfaces are Rubbed in Perpendicular Directions

No Field: Uniform twist High Field: No twist



• Intermediate Voltages

Director Configuration of a TN Cell• Intermediate Voltages

Near surface, directorin plane containingrub direction

Midplane directorMidplane directorin plane at 45 degreesto rub directions

Near surface, directorin plane containingrub directionrub direction



The Electrically Controllable Birefringence (ECB) Device

The ECB Cell

No Field: High Field: No Field: g



Light Propagation in Birefringent Materials

• Linearly polarized light traveling at right angles to the director:

v = c/ne

λe = λv/ne

v = c/no

λo = λv/no



d

Phase Retardation

d

d

φe = 2πd /λe

φo = 2πd/λo

− φ

Δφ = φ − φe o = 2 π d ( 1 / λ e− 1 / λ o) = 2 π d ( ne - n o ) / λ v

= 2 π d Δn / λ v

3. Classification of LC Modes

Twisted Nematic : TN-. Twisted Nematic : TN-. Horizontal Switching : IPS, FFS

i l S i hi A A AS-. Vertical Switching : MVA, PVA, ASV-. π cell (OCB)





LabLab3. LC Mode : Twist Nematic

1. TN Mode(1). TN Mode Cell 구성

Ref. : S.T.Wu



1. TN Mode(2). TN Mode 동작 animation

Ref. : S.T.Wu



입사한 직선편광은 액정 분자의 비틀림에 따라 편광방향이 90˚ 회전하기 때문에 직교하는

편광자를 통과하며 전압인가로 선광성이 손실되면서 빛은 차단됨

1. TN Mode

편광자를 통과하며, 전압인가로 선광성이 손실되면서 빛은 차단됨.



1. TN Mode(4). TN Mode – Electro optical effect

POLARIZER100

LC Configuration Electro-Optic Effect

AN

CE

(%)

60

80 R BG

GLASS

LC

TRA

NSM

ITTA

20

40

GLASS

T

0

VOLTAGE (V rms)0 1 2 3 4 5

POLARIZER

V=0 V~5Vrms

• Low operation voltage• Narrow view angle

Polarization rotation effect



1. TN Mode(5). Cell design - ∆nd

-. Normally White 최적 투과율 설정 Rule -. 파장대별 최적Δnd 및 실제 적용 상태 비교

최적Δnd

실제ΔndNormal TN

WV TN

( )effn dλΔ

λ

실제ΔndWV TN

Blue Green Red

point. maximumfirst ,32=

Δλnd Δnd 증가에 따른 시야각 감소.

White 영역에서 Yellowish 현상 증가.

λ×=Δ 866.0nd



1. TN Mode(5). Cell design – Color tracking

( )effn dλΔ

best Δnd condition

initial (Δnd)eff

λ

전압에 따른

finial (Δnd)effB G R

( )effn dλΔ

CCT

G64 G255

(∆nd)eff 증가

-. LC cell 휘도 효율 상승

-. White 색온도 감소G64 G255

전압에 따른 상관 색온도 변화



1. TN Mode(5). Cell design – ∆nd & Yellow shift (white state)

: Cell design 조건 - 파장 : 589nm 정면 관측: Cell design 조건 -. 파장 : 589nm-. 액정 spec.

ne = 1.5816no = 1.468

최적 Δnd

( )effn dλΔ

정면 관측

5

5.25

5.5

5.75

6최적 Δnd

case 1

case 1∆nd=410nm

5.46nmcase 2

effΓ

20 40 60 80

4.25

4.5

4.75

λ436nm 589nm 633nm

측면 관측θ

5

5.25

5.5

5.75

6

case 2∆nd=465nm

최적 Δnd

( )effn dλΔ

5.46nmΓ

20 40 60 80

4.25

4.5

4.75

5

λ

case 1

5.46nmcase 2

θ

effΓ

λ436nm 589nm 633nm

시야각 증가시 장파장 효율 증가로 Yellowish 현상 나타남.



1. TN Mode

: 좌우 시야각 대칭

(5). Cell design - 주시야각

: 좌우 시야각 대칭

하시야각 High Contrast Ratio

60φ=90

120

θ= 0CR = 50

3060 30 60 0

30150

180CR 50CR = 10

210

240 300CR = 5

330

270

주시야각 방향

“상꼬하대”



1. TN Mode(5). Cell design – 주시야각 : TN cell 근사 해석

좌 우 상 하

Cell design 조건

파장 589-. 파장 : 589nm-. cell gap : 3.52㎛

-. 액정 spec.1 5816 1 75

2

1 75

2effΓ

ne = 1.5816no = 1.468

-. 평균 director 각: 83˚ 0.5

0.75

1

1.25

1.5

1.75

0.5

0.75

1

1.25

1.5

1.75

θ: 83

1.5

1.75

2

20 40 60 80

0.25

1.5

1.75

2

20 40 60 80

0.25

effΓ

0.25

0.5

0.75

1

1.25

1.5

0.25

0.5

0.75

1

1.25

1.5

θ

액정 평균 director 각도에 따라서 정면 retardation 값의 변화가 크다.

20 40 60 8020 40 60 80



1

1. TN Mode(5). Cell design – gray inversion (하시야각) :TN cell 근사 해석

di t 83˚Γ

0.4

0.6

0.8

하

director : 83˚effΓ

0 8

1

20 40 60 80

0.2

θV1 V2 director : 78˚V3

effΓ

0.2

0.4

0.6

0.8

V1 V2 V3

V1>V2>V3

20 40 60 80

0.8

1

director 각 83˚ 78˚ 65˚θ

director : 65˚

with WV-A film

effΓ

0.2

0.4

0.6

θ

with WV A film

20 40 60 80

위 조건의 경우 시야각 20도 시점을 전후해서 Gray inversion이 발생한다.Mid gray 영역의 휘도는 시야각 증가에 따라 급격히 감소하는 형태를 가짐

θ



5

1. TN Mode(5). Cell design – gray inversion (상시야각) :TN cell 근사 해석

Γ

3.75

4

4.25

4.5

4.75

상

director : 5˚effΓ

4.75

5

20 40 60 80

3.25

3.5

θ

director : 10˚V1 V2 V3

effΓ

3.5

3.75

4

4.25

4.5

V1 V2 V3

V1>V2>V3

20 40 60 80

3.25

4.5

4.75

5

director : 15˚

θdirector 각 5˚ 10˚ 15˚

with WV A film

effΓ

3.25

3.5

3.75

4

4.25with WV-A film

20 40 60 80 θ

White 하부 계조 영역에서 시야각 증가시 inversion 현상 나타남.



1. TN Mode(5). Cell design – gray 통합 (좌우시야각) :TN cell 근사 해석

1.25

1.5

1.75

2

좌우

director : 83˚effΓ

20 40 60 80

0.25

0.5

0.75

1좌우

θ

1

1.25

1.5

1.75

2

20 40 60 80

V1 V2 director : 78˚

V1>V2>V3

V2 effΓ

20 40 60 80

0.25

0.5

0.75

2

θ

V1 V2 V3

계조 Black Low Gray

MidGray

Γ

0.75

1

1.25

1.5

1.75 director : 65˚director 각 83˚ 78˚ 65˚ effΓ

20 40 60 80

0.25

0.5

θ



1. TN Mode(5). Cell design – Film 보상 (Black Pattern)

Black 상태 LC director5

상시야각effΓ

Black 상태 LC director

1

2

3

4상시야각

4

520 40 60 80

1

4

5

좌시야각 우시야각

θ

effΓ

1

2

3

1

2

3

θ20 40 60 80

3

4

520 40 60 80

하시야각

θ

effΓ

20 40 60 80

1

2

θ

Black pattern에서 시야각에 따른 retardation의 변화가 다른 형태를 가진다.액정 director 방향을 고려한 film 설계가 요구된다.



1. TN Mode(5). Cell design – Film 보상 (Black Pattern)

Black 상태 LC director

Rleft > Rright Rleft ≈ Rright

By Matching tilt angle of TN LC and Discotic LC,

Enhance viewing angle characteristics of contrast and

color inversion.

( Irrelevant to Twist Angle of TN LC)



1. TN Mode(5). Cell design – Film 제조 (roll to roll 방식)

WV film – O modeWV film – O mode

TAC Film

연신 방향

PVA(absorption axis) TAC Film

PVA

TAC Film

TAC film

+TAC film

DLC layer

bbirubbing

편광판 제조 방식 (roll to roll)에 의해서 WV Film을 적용하는 TN의 경우 O mode 만이편광판 제조 방식 (roll to roll)에 의해서 WV Film을 적용하는 TN의 경우 O mode 만이적용되고 있다.



Image Quality Comparison between TN and WVTN





LabLab3. LC Mode : Horizontal Switching

2. IPS Mode

Off OnLight

Substrate

Light Light

Transmittance ⎟⎠⎞

⎜⎝⎛ Δ

⋅=λλπα dnT )(sin)2(sin

21 22



2. IPS Mode

Ref. : S.T.Wu



White 상태 Color Shift 현상

1) 위치별 Color Shift.Y ll Shif

2. IPS Mode

R bbi White

Blue Shift Yellow Shift

⎟⎠⎞

⎜⎝⎛ Δ

⋅=λλπα dnT )(sin)2(sin

21 22

⇒시야각에 따라서Δn(λ)d가 변하기 때문에

2) Yellow Shift

Rubbing White

Fig . 러빙방향에따른 Color Shift 위치

⇒시야각에 따라서Δn(λ)d가 변하기 때문에최대 투과 파장이 달라지게 된다.

Δnd

Angleg

⇒Maximum 투과 point 장파장으로 shift:Yellow Shift

3) Blue Shift

Δnd

4) Color Shift Free

Δnd Angle

⇒ Single domain에서 dual domain으로변경시 color shift 현상 개선됨.

Angle⇒Maximum 투과 point 단파장으로 shift

:Blue Shift

변경시 color shift 현상 개선됨.



2. IPS Mode



3. FFS Mode

z

IPS FFS

y

z

Glass

Light Light

Glass

LightAnalyzer

x

y

Electric Field

LC Molecule

Glass GlassGlassPolarizer

Field

w l

l’Cst

S.H. Lee etal,Asia Display ‘98

IPS FFS

Light Lightp y

Appl. Phys. Lett. ‘98

IPS FFSl/dl/w

Fi ld

>1<1 or 0<1 or 0

E EE>1

Field

Electrodes

Ey, EzEy

ITOMetals or ITO



IPS-Pro (FFS) Structure by Hitachi3. FFS Mode

(Reference SID’99, S. H. Lee, et. al.) * Ono etal., IDW’04 & SID ’05



IPS FFS

3. FFS Mode

Transmissioncurve

LCLC

Field

IPS FFSDriving Field Ey (low field density) Ey & Ezg y ( y) y

(high field density)Switching Principle Dielectric Torque only Dielectric Torque + Elastic Torque

LC director in white state -Twist deformation only -Twist/tilt deformation y-Φ(l) ~ constant -Φ(l) ~ not constant

=> Self-compensation



-Need a compensation film?

Uncompensated IPS and FFS cell : better viewing angle than other modes owing to the in-plane rotation of the LC director

However, to accomplish a perfect dark state comparable to the CRT, , p p p ,they must be compensated by one or more films in the dark state.

<Iso-luminance contour of conventional HS mode in dark state>



Light Leakage of O-type Crossed Polarizers at oblique incidence

2 44 sin 2 sin1 o

l kT T φ θ=

( )( )2 2 2 28 1 cos sin 1 sin sinleakageo o

T Tφ θ φ θ− −

※ The factor “T” accounts for the Fresnel transmission of light through the four interfaces of the two polarizers

Maximum light leakagein diagonal direction (Φ=45˚)

60

80

0 010.020.030.040.05

LeakageT IPS exhibits relatively low C/R indiagonal direction.We consider about the improvementof diagonal direction (Φ=45˚)

020

4060

80 0

20

40

600

0.01

020

4060

80Viewing angleθ

φ

of diagonal direction (Φ 45 )

Fig . Calculated transmission of light passing through a pair of crossed ideal polarizers

Crossed O-type polarizer



Proposed S-IPS cell. (The combination of uniaxial and biaxial films)

TAC( C Pl )

Bi i l fil (N 0 5)TAC(-C Plate)

PVATAC(-C Plate)

+C PlateTAC(-C Plate)

PVATAC(-C Plate)

PVATAC(-C Plate)

TAC( C Plate)A Plate

Horizontal switching Cell

Biaxial film (Nz=0.5)

A Plate


A Plate

TAC( C Plate)


TAC(-C Plate)PVA

TAC(-C Plate)PVA

TAC(-C Plate)

Fig . structure #2TAC(-C Plate)

PVATAC(-C Plate)

Fig structure #1

TAC(-C Plate)PVA

TAC(-C Plate)

Fig . general structure gFig . structure #1

Ref : Jo n Ho Lee et al SID 05 p642

g g

Ref. : Joun-Ho Lee, et. al., SID 05, p642



▣ Comparison of the iso-contrast contour between general homogeneousS-IPS LC cell and proposed splayed S-IPS LC cell

Characteristics on viewing angle has been much more improved by applyingthe proposed S-IPS cell







LabLab4. LC Mode : Vertical Switching

- Dark: Control of light leakage in oblique direction by Film Compensation- White: How to tilt down LC directors in 4 or 8 directions: MVA, PVA, ASV, etc.

related to Transmittance Vop Response time Image quality

MVA PVA ASV

related to Transmittance, Vop, Response time, Image quality

MVA by Fujitsu

PVA by SEC

ASV by Sharp

Appearance 1997 1998 2001

Initial LC alignment Slightly tilt 90o Almost 90o

Method to tilt P t i ( d

Patterned ITO + down the LC:

Control of Field Direction

Protrusion (wedge shape) + Patterned

ITO

Patterned ITOs on both substrates

Protrusion (nipple shape)

LC director in white state

Bend deformation in Four directions

(ECB)

Bend deformation in Four directions

(ECB)

Twist/Bend/SplayDeformation(Reverse TN)( ) ( ) ( )



4. VA Mode

Black State Grey State White State

255grey109grey 199grey0 gray



4. VA Mode

◈ Conventional Type

◈ Improved Type

Side View Top View*Asia Display’97

p ypProtrusion in CF

Common electrode

Leakage near protrusions

Cross-sectional View Top View of Pixel

Electric Field Pixel electrode



On StateOn State Off StateOff State

4. VA Mode

On StateOn State Off StateOff State

MM

Protrusion

VVAA

Slit

PP

Slit

PPVVAA

SlitSlit

-. Color filter 층의 resin층 삭제로 Black 특성은 MVA 대비 PVA 우수

반면 PVA의 경우 Black to White transition 응답특성에 문제 발생-. 반면 PVA의 경우 Black to White transition 응답특성에 문제 발생

새로운 구동법 개발을 통해서 개선 (DCC2)



4. VA Mode

Gamma shift

VAIPS

VA

VA Mode 구동 특성상 측면 시야각에서 gamma shift 현상 발생8 d i 구동 기술 도입: 8 domain 구동 기술 도입



4. VA Mode

:4 domain 8 domain

*IMID ’04



4. VA Mode

*S.S. Kim, SID ‘05





LabLab5. LC Mode : π - cell

5. π - cell

2축성 보상필름

편광판 Rubbing direction

V < Vth Vth < V

밴드 셀

( Bend Cell )

편광판

splay cell bend cell(off) bend cell(on)



(1) T-V curve

S l

5. π - cell

100

BendSplay

60

80

tace

40

Tra

nsm

it

0

20

0 1 2 3 4 5 6 7 8 9 100 1 2 3 4 5 6 7 8 9 10

Applied Voltage(V)

S l t B d h 전이과정이 필요(최소 1V 이상)Splay to Bend phase 전이과정이 필요(최소 1V 이상)



Fast response is possible as flow of the same direction appears in bend cell.

5. π - cell

flow

flowflow

Bend cellBend cell

Von VoffTN cellTN cell

Von Voff

When door are moved to the opposite di i i b i fl i

When force is applied to the same direction the door can be openeddirection, resistance by air flow increases. direction, the door can be opened more easily as there is little resistance due to air.



5. π - cell

Voltage OFF~

Voltage OFF(Splay)

~Lower Voltage(Bend)

P.J. Bos et el SID Digest p273 (1993)Higher Voltage(Bend)~



5. π - cell

Ref IDW’04

Major technologies used:

LTPS + High Aperture + CF on array + Ref. IDW’04, Toshiba Matsushita Display Technology. Co.,Ltd.Impulse driving method

Documents

LC Modesdisplay.donga.ac.kr/강의자료/2016학년도 1학기... · 2013. 5. 1. · LC Mode : Twist Nematic 1. TN Mode (5). Cell design – Film 보상(Black Pattern) ¾Black 상태LC