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OLED TechnologyOLED TechnologyDavid Hsieh
Contents•• OLED Development StatusOLED Development Status
Key MilestoneKey MilestoneResolution vs. SizeResolution vs. SizeAM and PM Development DisplayAM and PM Development Display
•• Materials Status : Polymer vs. Small MoleculeMaterials Status : Polymer vs. Small MoleculeEfficiency ProgressEfficiency ProgressLifetime ProgressLifetime Progress
•• Tech. Status of OLED Color patterningTech. Status of OLED Color patterning
•• Pending Issues in OLEDPending Issues in OLEDOutOut--coupling Efficiencycoupling EfficiencyLifetime Differential AgingLifetime Differential AgingLTPS NonLTPS Non--Uniformity for AMOLEDUniformity for AMOLED
•• ConclusionConclusion
OLED Development StatusKey Milestone of OLED Development
1995 1999 2000 2002
Pioneer, PM-95
Pioneer, PM, 4 Area Color-99
5.7”PM-OELDIdemistu-97
Motorola Cellular Phone -00
CDT-Seiko Epson2.5” AMPLED-00
Sanyo-Kodak2.4” AMOLED-99
Sony 13” SVGA AMOLED -01
Samsung 15” XGA AMOLED -01
Kodak Digital Camera-03
Chi-Mei & IBM 20” WXGA a-SiAMOLED -03
OLED Development StatusPM Commercialized Displays
PM Mobile Phone (Small Molecule)
Motorolla(Pioneer)
Samsung(SNMD)
LG(Pioneer)
OLED Development StatusSamsung NEC Mobile Display (SNMD)PM OLED Products☞ Current Product
1.1” 94 × 64 Dots, 256 ColorAnycall (SEC) Sub Display Mass Production from 2002. July
☞ Next Product
96×64+IconArea color
96×9665k color
96×64+Icon256 color
Type 1 Type 2 Type 3
Mobile Mono
PM OLED
Mobile Full ColorPM OLED
Mobile S/M *
AM OLED
FlexiblePolymer
AM OLED
Large S/M * , Polymer
AM OLED
* S/M : Small Molecule
Now & Near-term• Cell phones (sub display)• Auto displays• audio, meters, appliances
Next StepNext Step•• Cell phones (main display)Cell phones (main display)•• PDAsPDAs•• Small video (DVC,DSC)Small video (DVC,DSC)
Final & Long Term• Mobile Applications (Flexible)• Monitors• TVs
~ 2001 ~ 2003 ~ 2004 ~ 2007 ~ 2009
Applications of OLED
Glass Clean & Bake
AZ5214 Bus Metal PR Coat
& Bake
Bus Metal PR Thickness ( 1.7 µm )
Bus Resist Expose (Mask
# 1)
Bus Resist Develop
Bus CD & Inspect
Bus Etch and Inspect
Bus PR Strip, Inspect & CD
Dehydration Bake
ITO PR Coat and Bake
ITO PR Thickness ( 1.7 µm )
ITO Resist Expose
(Mask # 2)
ITO Resist Develop
ITO CD and Inspect
ITO Etch and Inspect
ITO PR Strip, Inspect & CD
Dehydration Bake
AZ5206-E Base PR Coat and
Bake
Base PR Thickness ( 0.6 µm )
Base Resist Expose (Mask
# 3)
Base Resist Develop
Base CD and Inspect
Base Cure-Hot Plate
AZ5214 Pillar PR Coat &
Bake
Pillar PR Thickness
(1.7 – 3.7 µm )
Pillar PR Expose
(Mask # 4)
Pillar PR Post Exposure Bake
Passive Matrix Displays: Process Flow
Continue
380x470 glass\ITO\Cr panels start
Continue Pillar PR Flood Exposure
Pillar PR Develop
Pillar CD and Inspect
Oven Hard Bake
Dehydration Bake
O2/CFx Pretreatment
Hole Transport Layer (8 min)
Green Emission Layer (3 min)
Electron Transport
Layer(2 mins)
Electron Injection Layer (0.83 min)
Cathode (0.83 mins)
Encapsulation Cover Clean
Desiccant Dispense
Seal Epoxy Dispense Lamination UV Cure Post Cure Bake Scribe & Break
to final size.
Probe Test: O/S, Log Jrb, Lum,
CIEAssembly Final Test
Sample: Aging/Fade
TestOutgoing QC
Ship
Passive Matrix Displays: Process Flow (continued)
Process Specifications: Materials
Substrates: Glass\ITO\Mo-Ta• Glass: 380 x 470, 0.7 ± 0.03 mm, no visible defects under 10 K lux• ITO: 20-30 Ohms/square, 750 ± 75 Å, 85% Transmission at 400 to 760 nm, . .Roughness < 50 Å, Max. Peak Height 200 Å.• Bus Metal: < 0.3 Ohms/square, 5000 ± 500 Å.
Resist•Photoresist for Pillars (Cathode Isolation) and Base (Cathode Insulation) needs to be morphologically stable upon baking. Layer thickness should be controllable to 0.5 (base) and 1.5 - 4 µm (pillars).
Thin Films• Organics: Purity > 95% (zone sublimed/purified) • Metals: Purity > 90%
Encapsulation• Epoxy Seal: + 0.5 Water absorption when boiled for two hrs, less than 5.0 g/m2
water permeability for 24 hrs, 40 µg/g outgas trapping 120 0C x 15 mins.
Process Specifications: Photo
Facility: Class 100 Clean Room
ITO: The minimum gap between ITO conductors shall be 12.5 µm, the minimum . leakage resistance between neighboring ITO lines shall be 1 Mohm.
Base:• Thickness: 0.5 to 0.6 µm• 12 (VGA) to 4 µm (mono)• Spin Speed ~ 3000 RPM• Soft Bake ~ 90 0C / 90 secs• Hard Bake ~ 250 0C / 200 secs
Pillar: • Thickness ~ 4 µm• 8 (VGA) to 12 µm (mono)• Spin Speed ~ 3000 RPM• Retrograde Angle ~ 45 / 70 0C• Minimum linewidth at 45 / 70 0C ~ 12 / 8 µm• UV Cure ~ ~ 90 mJ/cm2, 200 to 400 nm / 90 secs @ 110 0C
Process Specifications: Thin Films
Vacuum Levels:•Buffer Chamber 1E-6 Torr•Organic Chamber(s) 5E-7 Torr•Electrode 6E-6 Torr
Deposition Rates/Temperatures: •Organics 2 - 4 Å/sec / 270 - 500 0C•Dopants 0.05 - 0.1 Å/sec / 270 - 500 0C•Electrode 0.1 & 20 Å/sec / 500 - 1000 0C
Thickness Uniformity:•Organics > 100 ± 10%•Electrode > 100 ± 20%
Device Structures:•ITO \ HI \ HTL \ Host: Dopant \ ETL \ EIL \ Cathode, where
• HI : IDE406 or CuPC• HTL : IDE320 or HT2• Green/Red Host: AlQ3, Blue Hosts: KBH or IDE120• Dopants: KBD, or IDE102 (B), C545T (G), DCJTB or P1 (R)• ETL: AlQ3• EIL : LiF or Al:Li, 0.5 to 20 nm• Cathode: Al, 70 to 150 nm
Pillar Process
OLED Materials StatusEfficiency Status of Small Molecule
5~6 @ 300 cd/m20.60, 0.38Red
20~22@ 600 cd/m20.27, 0.63Green5~6 @ 300 cd/m20.65, 0.35
14~15 @ 300 cd/m20.61, 0.38RedPh.
OLED
5~6 @ 200 cd/m20.14, 0.14Blue12~13 @ 600 cd/m20.30, 0.65Green
2~3 @ 300 cd/m20.64, 0.36Fl.OLED
Materials Efficiency [cd/A]Color Index
Blue(0.16, 0.32)
Green(0.30, 0.63)
NTSCsRGB
Red 1 (0.61, 0.38)
Red 2 (0.65, 0.35)
Condition : <1000cd/mCondition : <1000cd/m22 @ 4.5~5.5V@ 4.5~5.5V
OLED Materials StatusLifetime Progress
~10,000 @800 cd/m20.61, 0.36Red
~10,000 @400 cd/m20.14, 0.14Blue
~10,000 @800 cd/m20.65, 0.34Phosphorescence
~10,000 @600 cd/m20.27, 0.63Green--Blue
Fluorescence
Materials
~10,000 @500 cd/m20.63, 0.38Red
Lifetime(t ½, D/C Constant Current)
Color Coordinates (x,y)
~10,000 @500 cd/m20.30, 0.65Green
Required RGB Brightness for White 100 cd/m2 AM OLED Driving (Aperture Ratio 40%)- Red : ~600 cd/m2, Green : ~800 cd/m2, Blue : ~400 cd/m2
Tech. Status of OLED Color Patterning Color Patterning Ways of Small Molecule
B G R
Blue EL+
Color Changing Material Blue,Green, Red EL
Emitting Layer
ColorTechnology
Company Main Stream
Advantages
Challenges
High Efficiency,Good Color
High Resolution,Substrate Size
White EL+
C/F
B G R
Simple Process,High Resolution
Top Emission,Color Purity, Low Efficiency
B G R
Idemitsu Kosan TDK, Sanyo
Simple Process,Relatively High Efficiency
Top Emission,Low Efficiency, CCM Cost
Tech. Status of OLED Color Patterning
Current Status of Thermal EvaporationMax. Handling Glass Size : 400x400mm available (Max. 17 inch Display),
600x720 under DevelopmentResolution : about 120ppi
New TechnologiesExtension of Current Tech. : Linear Source, Moving or Multi-Source TechnologyNew Approach : OVPD, DSP
Uniformity may not be a serious IssueMain Challenge Technology : Shadow Mask Tech.
with Bigger Size Glass Handling (Development of New Shadow Mask Tech.)
Tech. Status of OLED Color Patterning Ink- jet Printing Technology
Advantages : Simple Process, Small Usage of MaterialChallenges :
Performance Degradation after Printing (Ink Formulation Issues)Repeatability of Ink-Jet Printing (Blocking of Head, Volume Variation),Non-Uniformity of LEP Film (Non Homogeneous Edges in Pixels )
ITO
WT
PassivationTR Units
Glass Substrate
Bank
Insulator Layer
Subpixel
Bank Channel
Wall layer defines pixel area
Substrate : Top View
Laser Induced Thermal Imaging Technology (LITI)Advantages : High Resolution, Multi-Layer Stacking Capability,
Possible Small Molecule & Polymer Hybrid OLEDChallenges :
Performance Degradation after Printing (Blending Issues)Uniform Film Roll Coating Sensitive Process to Particle Contamination
LTHCPlastic Film
EML LAYER
HTLITO
LASER BeamLASER Beam
Tech. Status of OLED Color Patterning
Tech. Status of OLED Color Patterning LITI Hybrid OLED
LITI Hybrid 2.2“ AMOLED
CathodeETL EML HTL HILITO
EML patterning
Donor Film EML
Polymer, Spin- coatable SM
Evaporated SM
Spin coating or Evaporation on film
Comparison of Aperture Ratio for Various Color Patterning Tech.
Possible High Aperture Ratio in AMOLED,But It Depends on Color Patterning Methods!
70~80%~60%40~50%Aperture Ratio(Top Emission)
± 2.5㎛± 15㎛± 20㎛Patterning Accuracy
>200ppi~150ppi~130ppiResolution
Polymer (LEP)
Ink-JetPrinting
Small Molecule (SM)
Evaporation(Precision Shadow Mask)
Polymer (LEP)Hybrid (Polymer/SM)Materials
LITIItems
Tech. Status of OLED Color Patterning
Pending Issues in OLED
Glass ITO EML ETL Cathode
Optical Out-Coupling Efficiency Improvement(Loss of Optical Output due to Optical Guiding Effect)(Loss of Optical Output due to Optical Guiding Effect)
Eliminate Internal ReflectionEliminate Internal Reflection
Approaches1D/2D Grating Shaped Glass or High Index Glass(n=1.85, Schott SFL57): ~50% upAerogel/Sol-gel Tech.: ~60% upOrdered Micro-lens Array: ~50% up
1D/2D Grating
Aerogel/sol-gel Micro-lens Array
Shaped Glass
Out-Coupling Efficiency Improvement
0
30
6090
120
150
180
Blue-Nano 1 Blue-Nano 2Blue-Nano 3 Blue-Nano 4Blue-Ref.
50 100 150 200 250250 200 150 100 50
L (Cd)
External Q.E. ImprovementExternal Q.E. ImprovementBest Results: Best Results: Up to 70%(Green) Improvement at the Front LightUp to 70%(Green) Improvement at the Front Light
Pending Issues in OLEDPhotonic Crystal Results
Normal PhotonicNormal Photonic Crystal Crystal Test Coupon Test Coupon Test CouponTest Coupon
G: 78 cd/m2 @100mA G: 134 cd/m2 @100mA
Photonic Crystal Results (Test Coupon)
Pending Issues in OLED
Pending Issues in OLEDLifetime Differential Aging ProblemDifferential Aging Problem
Image Burning Image Burning Improvement of OLED LifetimeImprovement of OLED LifetimeDevelopment of Avoiding Driving Tech.Development of Avoiding Driving Tech.
White Balance Shift : Yellowish ProblemWhite Balance Shift : Yellowish ProblemRequired the Same Lifetime of RGBRequired the Same Lifetime of RGB
Image
Pending Issues in OLEDLTPS non-Uniformity Issues
Vth Variation
Ids
Vgs
ELA NonELA Non--uniformity uniformity Improvement of ELA Beam UniformityImprovement of ELA Beam UniformityCompensation Pixel CircuitCompensation Pixel CircuitNonNon--ELA Crystallization is under the DevelopmentELA Crystallization is under the Development
ELA non-Uniformity (2TR)
Voltage or Current Compensation Pixel Circuit
Aperture Ratio IssuesAperture Ratio IssuesAperture Ratio of AM OLED
Top Emission Provides Higher Top Emission Provides Higher Aperture Ratio
50 100 150 2000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8 2TR bottom emitting 4TR bottom emitting 4TR top emitting
Ape
rture
Rat
io
Resolution (ppi)
Low Aperture Ratio Decreases the OLED Lifetime So Much.
Pending Issues in OLED
Top Emission Scheme is the Best Solution, But it Requires a Clear Encap.
Tech.
1st Generation Deposition Equipment
Pretreatment
HIL
HTL
EML/ETLCathode
CathodeEML/ ETL
Zelda
NEW ZELDA
Inverter HTL/ HTLModule
EML/ ETLModule
CathodeModule
2nd Generation Deposition Equipment
Encapsulation • Basic design concept 1. Sheet to sheet process (same as LCD?)2. Isolate device from humidity and oxygen 3. Absorb the humidity into the cell• Key considerations 1. Inner pressure release – mechanical & dispenser2. Capability of desiccant - How long can it works?3. Mechanism – Physical absorption or Chemical
reaction.4. Minimize the humidity and oxygen penetrates –seal
material and cell gap control5. Dry and oxygen free environment
UV
Pressure
Alignment CCD
Quartz Plate
Press Plate
Mechanical Design of Encapsulation
Substrate
x
yθ
Testing• Basic design concept 1. To differentiate good and defective ones before IC
bonding2. To make sure brightness lifetime(to extend not to
shorten)3. To make sure no defect found after sell to customers• Key considerations 1. Simulated driving single input when test to make
sure correct inspection. 2. Burn-in process design to make the device
brightness decay rate smoother – high temperature needed
3. Reliability test under high temperature and high humidity to simulate the failure mode.
Burn-in ProcessLight On Test
Testing Process
Area Color Series Full color series High color seriesMonochrome
96x3x64 ( A )262k Full color
COFSub display
96x392-AC COG
Sub display
80x48Mono TABSub display
42x3x644K full color
COGSub display
80x484 Area color
TAB Sub display
96x16Mono COGSub display
96x3x64 (A )256 Full color
TABSub display
developing
Done
Planning
96x3x6465k Full color
TABSub display
Sub-Display for Mobile Phone in RiTdisplay
ConclusionOLED Manufacturing is Being Matured for Small Size Mobile Application.
Long Life OLED Performance is very Essential to Meet Lifetime Requirements of Various Application.
Image Burning & White Balance Shift
LTPS non-Uniformity is Still a Problem for AM OLED Design.Low Aperture RatioRequired Vth Compensation Driving Scheme
Significant Improvement of OLED Technologies is Progressing. Phosphorescent OLED, OLED Material ImprovementOptical Out-coupling Improvement, Top Emission OLED
Shadow Mask Color Patterning is Seen as a Key Bottle Neck. Required a New Color Patterning Tech. such as LITI
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