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‘ 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
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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
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I. Introduction
• What is Liquid Crystal ?
• Structure of L/C
• Alignment of L/C
• TN & STN Modes
• Normally White and Black Modes
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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
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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
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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
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Intermolecular Attraction: Long Axis > Short Axis
n
n
n
n
move
Nematic
Figure 4. Types of liquid crystal phases
n
Chiral Dopant
n
Cholesteric
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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)
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Alignment of Liquid Crystal
Interaction: L/C Molecule & Substrate
L/C Molecule
Alignment Layer
Glass Substrate
Figure 6. Liquid crystal alignment layer
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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
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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
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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.
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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
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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
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II. Liquid Crystal Displays
• Passive and Active Matrix LCD’s
• Kinds of AMLCD’s
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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)
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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)