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Slide 1Lecture 76.976 Flat Panel Display Devices – Spring 2001
types of organic materials growth of organic materials organic light emitting devices OLED-based displays
Lecture 76.976 Flat Panel Display Devices
Emissive Displays – Organic Electroluminescence
Flexible OLED
Slide 2Lecture 76.976 Flat Panel Display Devices – Spring 2001
Organic Materials
Alq3
PPV
MOLECULAR MATERIALS
POLYMERS
Attractive due to:Attractive due to: Integrability with inorganic semiconductors Low cost (fabric dyes, biologically derived materials)
Large area bulk processing possible Tailor molecules for specific
electronic or optical properties Unusual properties not easily attainable with conventional materials
But problems exist:But problems exist: Stability Patterning Thickness control of polymers Low carrier mobilityn
Slide 3Lecture 76.976 Flat Panel Display Devices – Spring 2001
Scientific Interest in Organic Materials
1828 - Wöhler first synthesized ureawithout the assistance of a living organism
1950s - steady work on crystalline organics starts
1970s - organic photoconductors (xerography)
1980s - organic non-linear optical materials
1987 - Kodak group published the firstefficient organic light emitting device (OLED)
Since then, the field has dramatically expandedboth commercially and scientifically(OLEDs, transistors, solar cells, lasers, modulators, ... )
to date, about two million organic compounds have been madeto date, about two million organic compounds have been made- this constitutes nearly 90% of all known materials -- this constitutes nearly 90% of all known materials -
Slide 4Lecture 76.976 Flat Panel Display Devices – Spring 2001
VACUUMCHAMBER
TURBOPUMP
COLDTRAP
ROUGHINGPUMP
substrateholder
thicknessmonitor
shutter
GND
substrate
POWERSUPPLIES
sourceboats
Device Preparation and Growth
Glass substrates precoated with ITO- 94% transparent- 15 Ω/square
PrecleaningTergitol, TCEAcetone, 2-Propanol
Growth- 5 x 10-7 Torr- Room T
- 20 to 2000 Ålayer thickness
Slide 5Lecture 76.976 Flat Panel Display Devices – Spring 2001
OMBD II OMBD ISputtering
AnalysisChamber
Load Lock
Materials Growth Laboratory
III-V MBE
Load LockTransferChamber
Metale-Beam
Base Pressure 10-9 ~ 10-11 torr
PrincetonPrinceton University University
Slide 6Lecture 76.976 Flat Panel Display Devices – Spring 2001
Integrated MaterialsGrowth SystemEvaporative Deposition
molecular organics (amorphous and crystalline) metals
Sputtering
ITO ceramics
Wet N2 Glove Box
Load Lockwith Sample Storage
Ante Chamberand Oven
Laminar Flow Hood
Dry N2 Glove Box
Shadow Mask Storage
Probe Stationwith Cryostat
AFM
STM
Physical & Vapor Phase Dep.
molecular organics nano-dots ** solvated polymers ** colloids **
Slide 7Lecture 76.976 Flat Panel Display Devices – Spring 2001
Spin-on
Langmuir-Blodgett
Inkjet Printing
Dye Diffusion
Silkscreen
Other Growth Methods
glass substrate
ITO
doped polymer film
highly doped polymer film
glass substrate
DIFFUSIONSOURCE
SHADOW MASK
DEVICE
Slide 8Lecture 76.976 Flat Panel Display Devices – Spring 2001
Development of Organic LEDs
Conventional, Transparent, Inverted,Metal-Free, Flexible, Stacked
~ OLED, TOLED, OILED, MF-TOLED, FOLED, SOLED ~
Displays
Slide 9Lecture 76.976 Flat Panel Display Devices – Spring 2001
Personal Organizer,Personal Organizer,NotebookNotebook
Rugged, high resolution,full-color, video-rate
displays
Slide 10Lecture 76.976 Flat Panel Display Devices – Spring 2001
Multi-FunctionMulti-FunctionVideo WatchVideo Watch
Rugged, high resolution,full-color, video-rate
displays enable a multitudeof applications
AutomotiveAutomotiveDashboard displays,
external indicator lights,and road signs
Slide 11Lecture 76.976 Flat Panel Display Devices – Spring 2001
Active WallpaperActive WallpaperLarge area displays
Active ClothingActive ClothingLight, rugged, low voltage,
flexible displays
Slide 12Lecture 76.976 Flat Panel Display Devices – Spring 2001
Why do OLEDs Glow ?
+
electrons and holesform excitonsexcitons
(bound e--h+ pairs)
some excitons radiatesome excitons radiate
HOMO
LUMO
recombination region
ETLHTLE
_
V
+
-
GlassITO
Alq3
TPD
Mg:AgAg
400 500 600 700 800
Alq3 PLOLED EL
Wavelength [nm]
Alq3
AlN
O3
TPDN N
~1000 Å
~500 Å~500 Å
Slide 13Lecture 76.976 Flat Panel Display Devices – Spring 2001
Electroluminescence
Single Layer Device
Heterostructure Device
ITO
Al2.1 eV 2.4 eV
CN-PPV
PPV
hνννν
ITO
Ca
hνννν
PPV
EXCITONRECOMBINATION
CARRIERTRANSPORT
CARRIERINJECTION
Slide 14Lecture 76.976 Flat Panel Display Devices – Spring 2001
Exciton Recombination Zone
C. Adachi, et al.
Slide 15Lecture 76.976 Flat Panel Display Devices – Spring 2001
1 10
10-11
10-10
10-9
10-8
10-7
10-6
10-5
10-4
10-3
T=141KT=180KT=240KT=295K
Cur
rent
[A]
Voltage [V]
4 6 85
10
15
Tt = 1780 K
m
1/T [10-3/K]
HOMO
LUMO
trap level
moleculedistorts
E
Trap Limited Conduction in Organic Materials
charge trapping candominate conduction
free molecule
molecule distorts
∆∆∆∆ E
_
_
_
∆∆∆∆ E
Nt=3.1x1018cm-3,µµµµnNLUMO=4.8x1014/cm-V-s
J ∝ NLUMO µµµµnNtmd-2m-1Vm+1
m = Tt/T
Shen, Burrows, Bulovic, McCarty, Thompson, Forrest,Jpn. J. Appl. Phys. 35, L401 (1996).
´
Slide 16Lecture 76.976 Flat Panel Display Devices – Spring 2001
Progress in LED Efficiency
after Sheats et al., Science 273, 884 (1996).
Molecular
Solids
OLEDsPLEDs
Slide 17Lecture 76.976 Flat Panel Display Devices – Spring 2001
WE DEMONSTRATED WE DEMONSTRATED OLEDsOLEDs THAT ARE : THAT ARE :
Bright - 100,000 cd/m2 (30,000 ft-L)
Efficient - >30 lm/W
Scalable Emissive Area - from a few µµµµm to a few cm in size
Colors - fluorescent R,G,B and phosphorescent R,G
Low Voltage - 3 to 10 V
Low Cost Materials
Low Cost Substrates
Wide Viewing Angle - >160 deg
Reliability - 1,000,000 hrs (phosphorescent R half-life)
Why Make Organic LEDs
Slide 18Lecture 76.976 Flat Panel Display Devices – Spring 2001
Alq3 devices driven at 20 mA/cm2
Initial luminance for Alq3 is 510 cd/m2
for QA doped Alq3 devices is 1600 cd/m2
and for MQA doped Alq3 devices is 1400 cd/m2 (C.W. Tang)
QA/Alq
MQA/Alq
Alq
Hours of operation
Re
lati
ve lu
min
an
ce
[L
/L0]
1.0
0.9
0.8
0.7
0.6
0.51 10 100 1000 100005 50
OLED Stability
Slide 19Lecture 76.976 Flat Panel Display Devices – Spring 2001
Electroluminescence in Doped Organic Films
2.Excitons transfer to
luminescent dye
1.Excitons formed
from combinationof electrons and
holes
6.0 eV
a-NPD
2.6 eV
5.7eV
Alq3
2.7 eV electrons
exciton
trap states
low work functioncathode
transparent anode holes
host molecules(charge transport
material)
dopant molecule(luminescent dye)
Slide 20Lecture 76.976 Flat Panel Display Devices – Spring 2001
400 500 600 700 800
0.0
0.2
0.4
0.6
0.8
1.0
Nor
mal
ized
EL
Inte
nsity
Wavelength [nm]
Alq3
PtOEP:Alq3
DCM2:Alq3
PtN N
NN
AlN
O3
O
CNNC
N
αααα-NPDN N
Effect of Dopants on the OLED EL Spectrum
Slide 21Lecture 76.976 Flat Panel Display Devices – Spring 2001
Solid State Solvation EffectBulovic et al., Chem. Phys. Lett. 287, 455 (1998); 308, 317 (1999).´ AlqAlq33
DCM2 in AlqDCM2 in Alq33
low DCM2low DCM2 high DCM2high DCM2
500 600 700 8000.0
0.2
0.4
0.6
0.8
1.0 10%
5%
2%
1%
EL In
tens
ity [a
.u.]
Wavelength [nm]
Alq3
DCM2 inAlq3
EL Spectrum TuningEL Spectrum Tuning
Temporal ResponseTemporal Response
0.25 ns
0.50 ns
0.75 ns
1.00 ns 1.50 ns
2.00 ns
5.00 ns4
8
12
16
0
600 650 700 750
35 nm35 nmwavelength shift
10% DCM2in Alq3
10% DCM2in Alq3
Inte
nsity
[a.u
.]
host
dopant (chromophore)with DIPOLE MOMENT µµµµ
Slide 22Lecture 76.976 Flat Panel Display Devices – Spring 2001
Influence of µ0 and µ1on Chromatic Shift Direction
solvent
solute (chromophore)WITH DIPOLE MOMENT µµµµ
µ0 < µ1µ0 < µ1
SOLVENT POLARITY
S0
S1
groundstate
excitedstate
µ0 > µ1µ0 > µ1
SOLVENT POLARITY
S0
S1
∆∆∆∆E
Slide 23Lecture 76.976 Flat Panel Display Devices – Spring 2001
Solid State Solvation Effect (SSSE)
Eloc
R
dipolar hostwith moment µ
polarlumophore
µµµµ > > > > 0
µµµµ → → → → 0as R → large
self polarizationfor strongly dipolar lumophores
Slide 24Lecture 76.976 Flat Panel Display Devices – Spring 2001
500 600 700 800 900
0.0
0.2
0.4
0.6
0.8
1.01%
2%5%
10%20%
50%
Inte
nsity
[a.u
.]
Wavelength [nm]
0.0
0.2
0.4
0.6
0.8
1.0
Inte
nsity
[a.u
.] 1%2%
5%10%
20%100%
DCM2 in Alq3Alq3
DCM2 in Zrq4Zrq4
polar hostµµµµ ~ 5.5 D
non-polar host
Thin Film Photoluminescence
Slide 25Lecture 76.976 Flat Panel Display Devices – Spring 2001400 500 600 700
120 Å BCP80 Å BCP40 Å BCP
Wavelength [nm]
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength [nm]
400 500 600 700In
tens
ity [a
.u.]
0.6% 1.5%
3% 6%
0.0
0.2
0.4
0.6
0.8
1.0
Inte
nsity
[a.u
.]
changingDCM2 in α-NPDconcentration
(with 40A BCP)
changingBCP layerthickness
(with 0.6% DCM2) TPD
AgMg:Ag
ITO
glass
Alq3
BCP
NPD:DCM2
TuningEmission ofWhite OLEDs
Slide 26Lecture 76.976 Flat Panel Display Devices – Spring 2001
symmetry conserved
fast process ~10-9s
triplet to ground state transition is not permitted
slow process ~ 1s
Fluorescence
E
ground state(singlet)
singletexcitedstate
tripletexcitedstate
S1 T1
S0
FLUORESCENCEFLUORESCENCE
singlet excitonsinglet exciton
E
Phosphorescence
PHOSPHORESCENCEPHOSPHORESCENCE
triplet excitontriplet exciton
S1 T1
S0
Slide 27Lecture 76.976 Flat Panel Display Devices – Spring 2001
0 1 2 3 4 5 6 7 8 9 100.1
1
10
100
1,000
10,000
100,000
Lum
inan
ce [c
d/m
2 ]
Voltage [V]
0
5
10
15
20
25
30
Pow
er E
ffici
ency
[lm
/W]
10,000 cd/m2
Phosphorescent OLED Performance
N N
CBP
Ir3
NIr(ppy)36% Ir(ppy)3 in CBP OLED:
at 100 cd/m2 : 4.5 V, 19 lm/Wat 10,000 cd/m2 : 7.2 V, 8 lm/W
100 cd/m2
Slide 28Lecture 76.976 Flat Panel Display Devices – Spring 2001
Simulated Power Consumption(5 inch/320x240 pixels monochrome display)
33% pixels “on”
UDC, Inc.
0
100
200
300
400
500
600
700
800
Pow
er [m
W]
0 50 100 150 200Brightness [nits]
PM -
Fluor
esce
nt
PM - Phosphorescent
AM - Phosphorescent AM - Fluoresecent
AMLC
D
Slide 29Lecture 76.976 Flat Panel Display Devices – Spring 2001
Monochrome Passive-Matrix Polymer-LED Display
Cambridge Display Technologies, Ltd.
Slide 30Lecture 76.976 Flat Panel Display Devices – Spring 2001
Full-Color OLED Display
Kodak - Sanyo
Transparent Substrate:Glass, Plastic, Metal
Low Cost Potential
ITO Anode
Multi-Color Icons
Organic LED
Transparent Cathode
• Lower cost materials than LCDs• Fewer process steps than LCDs• Less capital cost than LCDs
Slide 32Lecture 76.976 Flat Panel Display Devices – Spring 2001
15” XGA Cost Comparison
0
50
100
150
200
250
300
350
400
AMLCD LTPS/OLED
US$
OtherLabor
Module MaterialCell MaterialArray Material
Equipment DepreciationBuilding Depreciation
Source: DisplaySearch
AT SAME YIELDS
Slide 33Lecture 76.976 Flat Panel Display Devices – Spring 2001
TECHNOLGY/ FEATURES
AMLCD PMLCD LED PDP FED OLED
Brightness Good Good VeryGood
Good Good VeryGood
Resolution High
High Low Medium High High
Voltage Low
Low High High High Low
Viewing Angle Medium
Poor Excellent Excellent Excellent Excellent
Contrast Ratio Good
Fair Good Poor-Good
Good Excellent
Response Time Good Poor Fast Very Fast Very Fast Very Fast
Power Efficiency Good Good Fair-Good
Medium VeryGood
VeryGood
Temp Range Poor Poor VeryGood
VeryGood
VeryGood
VeryGood
Form Factor Thin Thin Wide Wide Thin Very ThinConformable
Weight Light Light AboveAvg.
Heavy Light Light
Screen Size Small- Large
Small toMedium
Small toLarge
Large Medium Small toLarge
Primary Applications
Laptops, Desktop
SmallDisplay
Signs,Indicators
LargeScreen
Multiple MultipleNew/Existing
Cost Average Low High High Average BelowAverage
Technology Landscape
Slide 34Lecture 76.976 Flat Panel Display Devices – Spring 2001
Transparent OLEDs
Parthasarathy et al., Appl. Phys. Lett. 72, 2138 (1998).
-
V+
EL Light
500 Å500 Å ITO
ETLHTLITO
Glass
EL Light
50-100 Å50-100 Å Mg-Ag
Bulovic et al., Nature 380, 29 (1996).´
> 70% transparent
Alphanumeric TOLED Display Alphanumeric TOLED Display
TOLEDs MF-TOLEDs
Slide 38Lecture 76.976 Flat Panel Display Devices – Spring 2001
TOLED Applications
UDC, Inc.
Slide 39Lecture 76.976 Flat Panel Display Devices – Spring 2001
E1 E2
E4
E3
E5
Glass substrate
RedE1
E3E2
E4E5
R-G-B light
Stacked Organic LEDs (SOLEDs)
head-up, high resolution, true-color, high-contrast,brightly-emissive, flexible displays
Shen et al., Science 276, 2009 (1997).Gu et al., J. Appl. Phys. (1999).
0.0 0.2 0.4 0.6 0.80.0
0.2
0.4
0.6
0.8
y
x
YELLOWYELLOW
BLUEBLUE
REDRED
ORANGEORANGE
GREENGREEN
WHITEWHITE
PURPLEPURPLE
PINKPINK
400450
480
490
500
520
550560
540
580
600650
700
530
Microcavity EffectsMicrocavity EffectsBulovic et al.,Phys. Rev. B 58, 3730 (1998).
´
Glass
ITO
Mg:Ag Electrode
αααα - NPD
RADIATIONRADIATIONModesModes
WAVEGUIDEWAVEGUIDEModesModes
SurfaceSurfacePlasmonsPlasmons
MetalMetalLossesLosses
EDGEemission
SURFACEemission
Alq3
Θk
- EL Region -
Slide 40Lecture 76.976 Flat Panel Display Devices – Spring 2001
MATERIAL THICKNESS [Å] n
Mg:Ag 1000 ----
Ag 1000 ----
αααα-NPD 540 1.78
ITO 490 2.02
3% DCM2 in Alq3 330 1.72
Alq3 170 1.72
Alq’2OPh 390 1.66
αααα-NPD 250 1.77
CuPc 80 1.5+0.8i
Alq3 50 1.72Mg:Ag 80 ----
Alq3 540 1.72
αααα-NPD 445 1.77
ITO 1600 1.8
Glass ~1 mm 1.45
V4
V1
V2
V3
MIC
RO
CA
VIT
Y 1
MIC
RO
CA
VIT
Y 2
RE
DO
LE
DB
LU
EO
LE
DG
RE
EN
OL
ED
Example of a Stacked OLED Structure
Slide 41Lecture 76.976 Flat Panel Display Devices – Spring 2001
Up to 3 times the resolutionof conventional displays
Advantages of Stacked OLEDs
True-Color Pixels
Slide 43Lecture 76.976 Flat Panel Display Devices – Spring 2001
AMLCD
OLED backlight
TOLED stackRGB
~ 1mm
for for full-color displaysfull-color displays the backlight can consist of a the backlight can consist of astackstack of R,G, and B TOLED backlights of R,G, and B TOLED backlights
Organic LED Backlight Integrated with an AMLCD
Slide 44Lecture 76.976 Flat Panel Display Devices – Spring 2001
TOLED Stack
R - onG - offB - off
Principle of OLED Backlight Operation
R G Bsub-cycles
one display write cycle
ONOFF
ONOFF
ONOFF
R sub-cycle
time
ONOFF
Timing Diagram
AMLCD
B-TOLED
G-TOLED
R-TOLED
reflector
5 msResponse Times
OLED rise time ~ 1µµµµsLCD response time ~ 5 ms
AMLCD
Slide 45Lecture 76.976 Flat Panel Display Devices – Spring 2001
AMLCD
colorfilters
White Light TOLED Stack
pixel width(RED fill factor < 0.3)
R - onG - offB - off
pixel width(RED fill factor > 0.9)
White Backlight vs. TOLED R,G,B Stack
ADVANTAGES OF TOLED STACK BACKLIGHTSADVANTAGES OF TOLED STACK BACKLIGHTS
- AMLCD with no sub pixels - AMLCD with no sub pixels larger fill factorlarger fill factor- no color filters - no color filters more efficient use of backlight emitted light more efficient use of backlight emitted light
22 -- 4 %4 % 1010 -- 12 %12 %TRANSMITTANCETRANSMITTANCE
3 to 6 fold3 to 6 fold improvement in efficiency improvement in efficiency
Slide 46Lecture 76.976 Flat Panel Display Devices – Spring 2001
OLED backlight
AMLCD
anode cathode
computerinterface
Slide 48Lecture 76.976 Flat Panel Display Devices – Spring 2001
Flexible OLED (FOLED)
- Ultra lightweight- Thin form factor- Rugged- Impact resistant- Conformable
Manufacturing Paradigm Shift Web-Based Processing
Slide 49Lecture 76.976 Flat Panel Display Devices – Spring 2001
Low-Cost All-Polymer Integrated CircuitsDrury et al., Appl. Phys. Lett. 73, 108 (1998).
~ 3 mm
· 15 bit programmable code generator· 326 all-polymer transistors (2µµµµm x 1mm gates)
with vertical interconnections· µ µ µ µchannel = 3 x 10-4 cm2/Vs, 40-200 Hz bandwidth· 3” diameter polyimide substrate
LAYOUT
ID - VD RESPONSE
Slide 50Lecture 76.976 Flat Panel Display Devices – Spring 2001
FOLED-based Pixelated, Monochrome Display
Source: UDC, Inc.
Slide 51Lecture 76.976 Flat Panel Display Devices – Spring 2001
Transparent FOLED-based Pixel
Source: UDC, Inc.
Slide 52Lecture 76.976 Flat Panel Display Devices – Spring 2001
The PRESENT …
… and the nearby FUTURE …
… of ORGANIC DISPLAY TECHNOLOGY
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