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OLED Technology

David Hsieh

Contents

· OLED Development Status Key Milestone Resolution vs. Size AM and PM Development Display Materials Status : Polymer vs. Small Molecule Efficiency Progress Lifetime Progress Tech. Status of OLED Color patterning Pending Issues in OLED Out-coupling Efficiency Lifetime Differential Aging LTPS Non-Uniformity for AMOLED Conclusion

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OLED Development Status

Key Milestone of OLED Development

1995 1999 2000 2002

Pioneer, PM-95 Motorola Cellular Phone -00 Sony 13" SVGA AMOLED -01 Kodak Digital Camera-03

Pioneer, PM, 4 Area Color-99

CDT-Seiko Epson 2.5" AMPLED-00 5.7"PM-OELD Idemistu-97 Samsung 15" XGA AMOLED -01 Sanyo-Kodak 2.4" AMOLED-99 Chi-Mei & IBM 20" WXGA a-Si AMOLED -03

OLED Development Status

PM Commercialized Displays

PM Mobile Phone (Small Molecule)

Motorolla (Pioneer)

Samsung (SNMD)

LG (Pioneer)

OLED Development Status

Samsung NEC Mobile Display (SNMD) PM OLED Products

Current Product

1.1" 94 × 64 Dots, 256 Color Anycall (SEC) Sub Display Mass Production from 2002. July

Next Product

Type 1

96 64+Icon Area color

Type 2

96 64+Icon 256 color 96 96 65k color

Type 3

Applications of OLED

* S/M : Small Molecule

Next Step · Cell phones (main display) · PDAs · Small video (DVC,DSC) Mobile Mono PM OLED ~ 2001 Mobile Full Color PM OLED ~ 2003 Mobile S/M * AM OLED ~ 2004 Large S/M * , Polymer AM OLED ~ 2007 Flexible Polymer AM OLED ~ 2009

Now & Near-term · Cell phones (sub display) · Auto displays · audio, meters, appliances

Final & Long Term · Mobile Applications (Flexible) · Monitors · TVs

Passive Matrix Displays: Process Flow

380x470 glass\ITO\Cr panels start 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

Continue

Passive Matrix Displays: Process Flow (continued)

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, CIE

Assembly

Final Test

Sample: Aging/Fade Test

Outgoing QC

Ship

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: · · · · · Pillar: · · · · · · 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 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 Status

Efficiency Status of Small Molecule

Green (0.30, 0.63)

Materials Red Green Blue Ph. OLED

Color Index 0.60, 0.38 0.64, 0.36 0.30, 0.65 0.14, 0.14 0.61, 0.38 0.65, 0.35 0.27, 0.63

Efficiency [cd/A] 5~6 @ 300 cd/m2 2~3 @ 300 cd/m2 12~13 @ 600 cd/m2 5~6 @ 200 cd/m2 14~15 @ 300 cd/m2 5~6 @ 300 cd/m2 [email protected] 600 cd/m2

NTSC sRGB

Red 1 (0.61, 0.38) Red 2 (0.65, 0.35)

Fl. OLED

Red Green

Blue (0.16, 0.32)

Condition : <1000cd/m2 @ 4.5~5.5V

OLED Materials Status

Lifetime Progress

Materials Red Fluorescence Green Blue Red Phosphorescence Green Blue Color Coordinates (x,y) 0.63, 0.38 0.30, 0.65 0.14, 0.14 0.61, 0.36 0.65, 0.34 0.27, 0.63 Lifetime (t ½, D/C Constant Current) ~10,000 @500 cd/m2 ~10,000 @500 cd/m2 ~10,000 @400 cd/m2 ~10,000 @800 cd/m2 ~10,000 @800 cd/m2 ~10,000 @600 cd/m2 -

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

Emitting Layer

Color Technology B G R B G R B G R

Blue,Green, Red EL Company Advantages Challenges Main Stream High Efficiency, Good Color High Resolution, Substrate Size

White EL + C/F TDK, Sanyo Simple Process, High Resolution Top Emission, Color Purity, Low Efficiency

Blue EL + Color Changing Material Idemitsu Kosan Simple Process, Relatively High Efficiency Top Emission, Low Efficiency, CCM Cost

Tech. Status of OLED Color Patterning

Current Status of Thermal Evaporation

Max. Handling Glass Size : 400x400mm available (Max. 17 inch Display), 600x720 under Development Resolution : about 120ppi

New Technologies

Extension of Current Tech. : Linear Source, Moving or Multi-Source Technology New Approach : OVPD, DSP Uniformity may not be a serious Issue Main 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 Material Challenges : 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 )

Wall layer defines pixel area Bank

W T

Subpixel

ITO Passivation TR Units Glass Substrate

Insulator Layer

Bank Channel

Substrate : Top View

Tech. Status of OLED Color Patterning

Laser Induced Thermal Imaging Technology (LITI)

Advantages : High Resolution, Multi-Layer Stacking Capability, Possible Small Molecule & Polymer Hybrid OLED Challenges : Performance Degradation after Printing (Blending Issues) Uniform Film Roll Coating Sensitive Process to Particle Contamination

LASER Beam LASER Beam Plastic Film LTHC EML LAYER HTL ITO

Tech. Status of OLED Color Patterning

LITI Hybrid OLED

EML patterning

Cathode ETL EML HTL HIL ITO

Donor Film

EML

Spin coating or Evaporation on film

Polymer, Spin- coatable SM

Evaporated SM

LITI Hybrid 2.2" AMOLED

Tech. Status of OLED Color Patterning

Comparison of Aperture Ratio for Various Color Patterning Tech.

Possible High Aperture Ratio in AMOLED, But It Depends on Color Patterning Methods!

Items Materials Patterning Accuracy Resolution Aperture Ratio (Top Emission) Evaporation (Precision Shadow Mask) Small Molecule (SM) 20 ~130ppi 40~50% Ink-Jet Printing Polymer (LEP) 15 ~150ppi ~60% LITI Polymer (LEP) Hybrid (Polymer/SM) 2.5 >200ppi 70~80%

Pending Issues in OLED

Out-Coupling Efficiency Improvement

(Loss of Optical Output due to Optical Guiding Effect) Eliminate Internal Reflection

Optical Out-Coupling Efficiency Improvement

Glass ITO EML ETL Cathode

Approaches

1D/2D Grating Shaped Glass or High Index Glass (n=1.85, Schott SFL57): ~50% up Aerogel/Sol-gel Tech.: ~60% up Ordered Micro-lens Array: ~50% up

1D/2D Grating

Shaped Glass

Aerogel/sol-gel

Micro-lens Array

Pending Issues in OLED

Photonic Crystal Results

External Q.E. Improvement Best Results: Up to 70%(Green) Improvement at the Front Light

90 120 150 60 30

180

Blue-Nano 1 Blue-Nano 3 Blue-Ref. Blue-Nano 2 Blue-Nano 4

0

Pending Issues in OLED

Photonic Crystal Results (Test Coupon)

Normal Test Coupon G: 78 cd/m2 @100mA

Photonic Crystal Test Coupon G: 134 cd/m2 @100mA

Pending Issues in OLED

Lifetime Differential Aging Problem

Image Burning Improvement of OLED Lifetime Development of Avoiding Driving Tech. White Balance Shift : Yellowish Problem Required the Same Lifetime of RGB

Image

Pending Issues in OLED

LTPS non-Uniformity Issues

ELA Non-uniformity Improvement of ELA Beam Uniformity Compensation Pixel Circuit Non-ELA Crystallization is under the Development

Ids

Vgs Vth Variation ELA non-Uniformity (2TR) Voltage or Current Compensation Pixel Circuit

Pending Issues in OLED

Aperture Ratio Issues

Aperture Ratio of AM OLED Top Emission Provides Higher Aperture Ratio Low Aperture Ratio Decreases the OLED Lifetime So Much.

0.8 0.7 0.6

2TR bottom emitting 4TR bottom emitting 4TR top emitting

Aperture Ratio

0.5 0.4 0.3 0.2 0.1 0.0 50 100 150 200

Top Emission Scheme is the Best Solution, But it Requires a Clear Encap. Tech.

Resolution (ppi)

1st Generation Deposition Equipment Zelda

Pretreatment HTL EML/ ETL Cathode

HIL

EML/ETL

Cathode

2nd Generation Deposition Equipment

NEW ZELDA

Inverter

HTL/ HTL Module

EML/ ETL Module

Cathode Module

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 & dispenser 2. 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 control 5. Dry and oxygen free environment

Mechanical Design of Encapsulation

y x Pressure Alignment CCD Press Plate Substrate Quartz Plate

UV

Testing

· Basic design concept 1. To differentiate good and defective ones before IC bonding 2. 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.

Testing Process

Light On Test

Burn-in Process

Sub-Display for Mobile Phone in RiTdisplay

80x48

Mono TAB Sub display

80x48 4 Area color

TAB Sub display

96x3x64 (A )

96x3x64 ( A )

256 Full color

TAB Sub display

262k Full color

COF Sub display

96x3x64 96x16

Mono COG Sub display

96x39 2-AC COG

Sub display

42x3x64 4K full color

COG Sub display

65k Full color

TAB Sub display

Planning developing Done

Monochrome

Area Color Series

Full color series

High color series

Conclusion

OLED 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 Ratio Required Vth Compensation Driving Scheme Significant Improvement of OLED Technologies is Progressing. Phosphorescent OLED, OLED Material Improvement Optical 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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