SAMSUNG TFT fundamentals Service Manual

‘ 01 SHORT COURSE =====

(S-2)

Fundamentals of Active -Matrix

Liquid-Crystal Displays

(Sunday, June 3, 2001)

Sang Soo Kim, Ph.D.
Vice President, AMLCD Div.
Semiconductor Business
Samsung Electronics Co., Ltd.
Kyunggi-Do, Korea

Fundamentals of Active -Matrix

Liquid-Crystal Displays

I. Introduction

II. Liquid Crystal Displays
III. Structure of Color TFT -LCDs
IV. Basic Operation Principles &

Design of Color TFT-LCDs
V. Color TFT-LCD Fabrication Process
VI. Summary and Projections

I. Introduction

• What is Liquid Crystal ?

• Structure of L/C

• Alignment of L/C

• TN & STN Modes

• Normally White and Black Modes

What is Liquid Crystal ?

Flexible Part Rigid Part

C

N

H

Terminal Group

H H
C C

H H

Alkyl Chain

...

H H
C C

H H

Alkyl group Biphenyl group Terminal Group

F

F

F

F

C C
H N

C C C

Fluorine

C

N

N

Cyano Group

Figure 1. The structure of a L/C

Phases of L/C vs. Temperature

* Operating Temperature Range for Display Application

Solid

Crystalline

(Melting Point)

Smectic Phase Nematic Phase

Liquid Crystalline

Tm

(Clearing Point)

Figure 2. Phases of a Liquid Crystal

Tc

Liquid

Isotrope

Temperature

Structure of Liquid Crystal

Birefringence: ∆n = -n

e

n

o

Dielectric Anisotropy: ∆ε = -εe εo

n

o

εo

n

e

εe

D(Director)

p-type (∆ n >0) n-type (∆ n <0)

ne > no ne < no

D

D

E

C

N

Figure 3. Anisotropy of a L/C

E

C O

O

F

F

OC2H

5

Intermolecular Attraction: Long Axis > Short Axis

n

n

n

n

move

Nematic

Figure 4. Types of liquid crystal phases

n

Chiral Dopant

n

Cholesteric

Intermolecular Attraction: Short Axis > Long Axis

Perpendicular to the layer

n

Tilted to the layer

n

move

Smetic A

(SmA)

Figure 5. Types of Liquid Crystal Phases

Smetic C

(SmC)

Alignment of Liquid Crystal

Interaction: L/C Molecule & Substrate

L/C Molecule

Alignment Layer

Glass Substrate

Figure 6. Liquid crystal alignment layer

TN and STN Modes

Mauguin’s Condition for TN: ∆n? p = ∆ n? d x 2π/Θ > λ

Retardation for TN: ∆ n? d = 0.3~0.5µm

D~ 5µm

Φ = 90°

TN Mode

180°< Φ < 270°

STN Mode

Figure 7. Orientation of L/C molecules in TN and STN cells

2

/

Design of TN Cell

Gooch -Tarry’s Law:

Normal Black Mode

(1st min.)

d~ 5µm

T = sin

T






π



2 2 2





1 1

2

u u

+








/

( )




+

∆

w u =

ith

λ

1st Minimum (∆n d ~ 0.48µm)

2nd Minimum (∆n d ~ 1.47µm)

3rd minimum

n d

⋅

u

3 15 35

∆n=0.09~0.10 5µm 14.7µm

Figure 8. Design of TN cell

NW-Mode

V-T Characteristics

Transmittance(%)

100

90% Trans.

STN

50

TN

TN-Mode

(V10/V

~ 1.6)

90

Vth

STN-Mode

(V10/V

Figure 9. V-T curves for TN and STN cells in NW mode

~ 1.06)

90

0

1.0 2.0 3.0 4.00

L/C Voltage (V)

Vsat

10% Trans.

NW Mode TN Cell

Normal White (NW) Mode:

• Higher C/R, True Black

• Less Cell Gap Dependent

Cross Nicols

Optical

Rotation

Light On

0 volt 5 volt

Polarizer(2)

L/C

Polarizer(1)

E

Light Off

No

Optical

Rotation

BacklightBacklight

Figure 10. Normally white mode TN cell

NB Mode TN Cell

Light Off

0 volt 5 volt

Light On

Polarizer(2)

L/C

E

Polarizer(1)

BacklightBacklight

Figure 11. Normally black mode TN cell

II. Liquid Crystal Displays

• Passive and Active Matrix LCD’s

• Kinds of AMLCD’s

Liquid Crystal Operating Modes

• TN (Twisted Nematic)

• STN(Super TN)

• DSTN(Double STN)

• FLC(Ferroelectric LC)

• GH(Guest-Host)

• DS(Dynamic Scattering)

• PDLC(Polymer Dispersed LC)

• VA(Vertical Alignment)

• IPS(In-plane Switching)

Segment & Dot- Matrix Driving

Segment Display

(7-segment)

Figure 12. Example of rendering an L/C image using direct driving

Dot-Matrix Display

(5x7 matrix)