Flexible Flat Panel Displays

Darran R. Cairns, PhD, is a member of the Faculty in the School of Science & Engineering at University of Missouri - Kansas City, USA. His research interests include solution-based processing of composite materials including sol-gel materials, nano-composite materials, and liquid crystalline materials and composites. Dirk J. Broer, is a Polymer Chemist specialized in polymer structuring and self-organizing polymer networks. This entails the development of polymers with new functionalities and integrating them into devices to meet industrial and societal challenges in the fields of sustainable energy, water-management, healthcare and personal comfort. Gregory P. Crawford, PhD, is President of Miami University, USA, and Professor of Physics. His research interests include liquid crystal and polymer materials for display and biotechnology applications. He is the editor of the first edition of Flexible Flat Panel Displays (2005).

Series Editor’s Foreword xv

List of Contributors xvii

1 Introduction 1
Darran R. Cairns, Gregory P. Crawford, and Dirk J. Broer

1.1 Toward Flexible Mobile Devices 1

1.2 Flexible Display Layers 2

1.3 Other Flexible Displays and Manufacturing 2

2 Engineered Films for Display Technology 5
W.A. MacDonald

2.1 Introduction 5

2.2 Factors Influencing Film Choice 5

2.2.1 Application Area 5

2.2.2 Physical Form/Manufacturing Process 6

2.2.3 Film Property Set 7

2.2.3.1 Polymer Type 7

2.2.3.2 Optical Clarity 9

2.2.3.3 Birefringence 10

2.2.3.4 The Effect of Thermal Stress on Dimensional Reproducibility 10

2.2.3.5 Low-bloom Films 11

2.2.3.6 Solvent and Moisture Resistance 12

2.2.3.7 The Effect of Mechanical Stress on Dimensional Reproducibility 16

2.2.3.8 Surface Quality 18

2.3 Summary of Key Properties of Base Substrates 19

2.4 Planarizing Coatings 21

2.5 Examples of Film in Use 23

2.6 Concluding Remarks 24

Acknowledgments 25

3 Liquid Crystal Optical Coatings for Flexible Displays 27
Owain Parri, Johan Lub, and Dirk J. Broer

3.1 Introduction 27

3.2 LCN Technology 27

3.3 Thin-film Polarizers 29

3.3.1 Smectic Polarizers 29

3.3.2 Cholesteric Polarizers 32

3.4 Thin-film Retarders 34

3.4.1 Reactive Mesogen Retarders 35

3.4.2 Chromonic Liquid Crystal-based Retarders 37

3.4.3 Liquid Crystal Alignment and Patterned Retarders 37

3.5 Color Filters 41

3.6 Conclusion 43

4 Large Area Flexible Organic Field-effect Transistor Fabrication 47
Zachary A. Lamport, Marco Roberto Cavallari, and Ioannis Kymissis

4.1 Introduction 47

4.2 Substrates 48

4.3 Photolithography 49

4.4 Printing for Roll-to-roll Fabrication 52

4.4.1 Inkjet Printing 52

4.4.2 Gravure and Flexographic Printing 55

4.4.3 Screen Printing 56

4.4.4 Aerosol Jet Printing 56

4.4.5 Contact Printing 58

4.4.6 Meniscus Dragging 60

4.5 Conclusions 62

5 Metallic Nanowires, Promising Building Nanoblocks for Flexible Transparent Electrodes 67
Jean-Pierre Simonato

5.1 Introduction 67

5.2 TEs Based on Metallic Nanowires 68

5.2.1 Metallic Nanowires, New Building Nanoblocks 68

5.2.2 Random Network Fabrication 69

5.2.3 Optical Characterization 70

5.2.4 Electrical Characterization 71

5.2.5 Mechanical Aspect 73

5.3 Application to Flexible Displays 73

5.3.1 Touch Screens 73

5.3.2 Light-emitting Diodes Displays 74

5.3.3 Electrochromic Flexible Displays 76

5.3.4 Other Displays 77

5.4 Conclusions 78

6 Optically Clear Adhesives for Display Assembly 85
Albert I. Everaerts

6.1 Introduction 85

6.2 OCA Definition and General Performance Specifications 86

6.3 Application Examples and Challenges 89

6.3.1 Outgassing Tolerant Adhesives 90

6.3.2 Anti-whitening Adhesives 91

6.3.3 Non-corrosive OCAs 92

6.3.4 Compliant OCAs for High Ink-step Coverage and Mura-free Assembly of LCD Panels 94

6.3.5 Reworkable OCAs 102

6.3.6 Barrier Adhesives 103

6.4 Summary and Remaining Challenges 104

7 Self-healing Polymer Substrates 107
Progyateg Chakma, Zachary A. Digby, and Dominik Konkolewicz

7.1 Introduction 107

7.2 General Classes of Self-healing Polymers 108

7.2.1 Types of Dynamic Bonds in Self-healing Polymers 109

7.2.2 Supramolecularly Crosslinked Self-healing Polymers 109

7.2.2.1 Hydrogen Bonding 110

7.2.2.2 π–π Stacking 110

7.2.2.3 Ionic Interactions 111

7.2.3 Dynamic-covalently Crosslinked Self-healing Polymers 111

7.2.3.1 Cycloaddition Reactions 111

7.2.3.2 Disulfides-based Reversible Reactions 112

7.2.3.3 Acylhydrazones 113

7.2.3.4 Boronate Esters 113

7.3 Special Considerations for Flexible Self-healing Polymers 114

7.4 Incorporation of Electrically Conductive Components 115

7.4.1 Metallic Conductors 115

7.4.2 Conductive Polymers 116

7.4.3 Carbon Materials 118

7.4.4 Polymerized Ionic Liquids 119

7.5 Additional Possibilities Enabled by Three-dimensional Printing 119

7.6 Concluding Remarks 121

8 Flexible Glass Substrates 129
Armin Plichta, Andreas Habeck, Silke Knoche, Anke Kruse, Andreas Weber, and Norbert Hildebrand

8.1 Introduction 129

8.2 Display Glass Properties 129

8.2.1 Overview of Display Glass Types 129

8.2.2 Glass Properties 130

8.2.2.1 Optical Properties 130

8.2.2.2 Chemical Properties 130

8.2.2.3 Thermal Properties 131

8.2.2.4 Surface Properties 132

8.2.2.5 Permeability 133

8.3 Manufacturing of Thin “Flexible’’ Glass 134

8.3.1 Float and Downdraw Technology for Special Glass 134

8.3.2 Limits 135

8.3.2.1 Thickness Limits for Production 135

8.3.2.2 Surface Quality Limits for Production 136

8.4 Mechanical Properties 137

8.4.1 Thin Glass and Glass/Plastic Substrates 137

8.4.2 Mechanical Test Methods for Flexible Glasses 137

8.5 Improvement in Mechanical Properties of Glass 140

8.5.1 Reinforcement of Glass Substrates 140

8.5.1.1 Principal Methods of Reinforcement 141

8.5.1.2 Materials for Reinforcement Coatings 141

8.6 Processing of Flexible Glass 142

8.6.1 Cleaning 143

8.6.2 Separation 143

8.7 Current Thin Glass Substrate Applications and Trends 144

8.7.1 Displays 145

8.7.2 Touch Panels 145

8.7.3 Sensors 145

8.7.4 Wafer-level Chip Size Packaging 146

9 Toward a Foldable Organic Light-emitting Diode Display 149
Meng-Ting Lee, Chi-Shun Chan, Yi-Hong Chen, Chun-Yu Lin, Annie Tzuyu Huang, Jonathan HT Tao, and Chih-Hung Wu

9.1 Panel Stack-up Comparison: Glass-based and Plastic-based Organic Light-emitting Diode 149

9.1.1 Technology for Improving Contrast Ratio of OLED Display 151

9.2 CF–OLED for Achieving Foldable OLED Display 153

9.2.1 Mechanism of the AR coating in CF–OLED 154

9.2.2 Optical Performance of CF–OLED 155

9.3 Mechanical Performance of CF–OLED 157

9.3.1 Bi-directional Folding Performance and Minimum Folding Radius of SPS Cf–oled 159

9.4 Touch Panel Technology of CF–OLED 160

9.5 Foldable Application 162

9.5.1 Foldable Technology Summary 162

9.5.1.1 Polymer Substrates and Related Debonding Technology 162

9.5.1.2 Alternative TFT Types to LTPS 162

9.5.1.3 Encapsulation Systems to Protect Devices against Moisture 163

9.5.2 Novel and Next-generation Display Technologies 163

10 Flexible Reflective Display Based on Cholesteric Liquid Crystals 167
Deng-Ke Yang, J. W. Shiu, M. H. Yang, and Janglin Che

10.1 Introduction to Cholesteric Liquid Crystal 167

10.2 Reflection of CLC 169

10.3 Bistable CLC Reflective Display 171

10.4 Color Design of Reflective Bistable CLC Display 173

10.4.1 Mono-color Display 173

10.4.2 Full-color Display 173

10.5 Transitions between Cholesteric States 175

10.5.1 Transition from Planar State to Focal Conic State 175

10.5.2 Transition from Focal Conic State to Homeotropic State 177

10.5.3 Transition from Homotropic State to Focal Conic State 177

10.5.4 Transition from Homeotropic State to Transient Planar State 178

10.5.5 Transition from Transient Planar State to Planar State 179

10.6 Driving Schemes 181

10.6.1 Response to Voltage Pulse 181

10.6.2 Conventional Driving Scheme 183

10.6.3 Dynamic Driving Scheme 183

10.6.4 Thermal Driving Scheme 185

10.6.5 Flow Driving Scheme 186

10.7 Flexible Bistable CLC Reflective Display 187

10.8 Bistable Encapsulated CLC Reflective Display 188

10.9 Production of Flexible CLC Reflective Displays 189

10.9.1 Color e-Book with Single-layered Structure 191

10.9.2 Roll-to Roll E-paper and Applications 195

10.10 Conclusion 202

11 Electronic Paper 207
Guofu Zhou, Alex Henzen, and Dong Yuan

11.1 Introduction 207

11.2 Electrophoretic Display 210

11.2.1 Development History and Working Principle 210

11.2.2 Materials 212

11.2.2.1 Colored Particles/Pigments 212

11.2.2.2 Capsule Shell Materials 213

11.2.2.3 Suspending Medium (Mobile Phase) 213

11.2.2.4 Charge Control Agents 213

11.2.2.5 Stabilizers 213

11.2.3 Device Fabrication 214

11.2.4 Flexible EPD 215

11.3 Electrowetting Displays 216

11.3.1 Development History and Working Principle 216

11.3.2 Materials 218

11.3.2.1 Absorbing (Dyed) Hydrophobic Liquid 218

11.3.3 Device Fabrication 220

11.3.4 Flexible EWD 221

11.4 Other E-paper Display Technologies and Feasibility of Flexibility 222

11.4.1 Pcd 222

11.4.2 Lpd 223

11.5 Cholesteric (Chiral Nematic) LCDs 224

11.6 Electrochromic Displays 224

11.7 MEMS Displays 226

12 Encapsulation of Flexible Displays: Background, Status, and Perspective 229
Lorenza Moro and Robert Jan Visser

12.1 Introduction 229

12.2 Background 230

12.3 Multilayer TFE Technology 234

12.3.1 Multilayer Approach 234

12.3.2 Inorganic Layer Deposition Techniques 237

12.3.3 Organic Layer Deposition Techniques 238

12.4 Current Technology Implementation 242

12.5 Future Developments 246

12.6 Conclusions 249

Acknowledgments 250

13 Flexible Battery Fundamentals 255
Nicholas Winch, Darran R. Cairns, and Konstantinos A. Sierros

13.1 Introduction 255

13.2 Structural and Materials Aspects 256

13.2.1 Shape 257

13.2.2 One-dimensional Batteries 257

13.2.3 Two-dimensional Planar Batteries 258

13.2.4 Solid versus Liquid Electrolyte 259

13.2.5 Carbon Additives 259

13.3 Examples of Flexible Batteries 260

13.4 Future Perspectives 266

14 Flexible and Large-area X-ray Detectors 271
Gerwin Gelinck

14.1 Introduction 271

14.2 Direct and Indirect Detectors 272

14.3 Thin-film Photodiode Sensors for Indirect-conversion Detectors 273

14.3.1 Performance Parameters 273

14.3.2 Photodiode Materials on Plastic Substrates 275

14.3.2.1 Amorphous Silicon 275

14.3.2.2 Organic Semiconductor Materials 275

14.4 TFT Array 277

14.4.1 Pixel Architecture and Transistor Requirements 277

14.4.2 Flexible Transistor Arrays 278

14.5 Medical-grade Detector 282

14.6 Summary and Outlook 283

15 Interacting with Flexible Displays 287
Darran R. Cairns and Anthony S. Weiss

15.1 Introduction 287

15.2 Touch Technologies in Non-Flexible Displays 287

15.2.1 Resistive Touch Sensors 287

15.2.2 4-Wire Resistive 288

15.2.3 5-Wire Resistive 289

15.2.4 Capacitive Sensing 290

15.2.5 Surface Capacitive 291

15.2.6 Projected Capacitive 291

15.2.7 Infrared Sensing 293

15.2.8 Surface Acoustic Wave 293

15.2.9 Bending Wave Technologies 294

15.3 Touch Technologies in Flexible Displays 294

15.4 Summary 299

16 Mechanical Durability of Inorganic Films on Flexible Substrates 301
Yves Leterrier

16.1 Introduction 301

16.2 Flexible Display Materials 302

16.2.1 Property Contrast between Coating and Substrate Materials 302

16.2.2 Determination of Mechanical Properties of Inorganic Coatings 302

16.3 Stress and Strain Analyses 304

16.3.1 Intrinsic, Thermal, and Hygroscopic Stresses and Strains 304

16.3.2 Strain Analysis of Multilayer Films under Bending 307

16.3.3 Critical Radius of Curvature 308

16.4 Failure Mechanics of Brittle Films 309

16.4.1 Damage Phenomenology under Tensile and Compressive Loading 309

16.4.2 Experimental Methods 310

16.4.3 Fracture Mechanics Analysis 311

16.4.4 Role of Internal Stresses 312

16.4.5 Influence of Film Thickness on Critical Strain 312

16.5 Durability Influences 313

16.5.1 Influence of Temperature 313

16.5.2 Fatigue 314

16.5.3 Corrosion 315

16.6 Toward Robust Layers 317

16.7 Final Remarks 317

Acknowledgments 318

Nomenclature 318

17 Roll-to-roll Production Challenges for Large-area Printed Electronics 325
Dr. Grzegorz Andrzej Potoczny

17.1 Introduction 325

17.2 Infrastructure 327

17.3 Equipment 328

17.4 Materials 329

17.5 Processing 331

17.6 Summary 334

18 Direct Ink Writing of Touch Sensors and Displays: Current Developments and Future Perspectives 337
Konstantinos A. Sierros and Darran R. Cairns

18.1 Introduction 337

18.2 DIW and Ink Development 338

18.3 Applications of DIW for Displays and Touch Sensors 343

18.4 Future Challenges and Opportunities 347

19 Flexible Displays for Medical Applications 351
Uwadiae Obahiagbon, Karen S. Anderson, and Jennifer M. Blain Christen

19.1 Introduction 351

19.1.1 Flexible Displays in Medicine 351

19.1.2 A Brief Historical Perspective 351

19.1.3 Application of Flexible Displays for Biochemical Analysis 352

19.1.4 OLEDs and Organic Photodiodes as Optical Excitation Sources and Detectors 352

19.1.5 Device Integration 354

19.1.6 Fluorescence, Photoluminescence Intensity, and Decay-time Sensing 355

19.2 Flexible OLEDs for Oxygen Sensors 356

19.3 Glucose Sensing Using Flexible Display Technology 358

19.4 POC Disease Diagnosis and Pathogen Detection Using Flexible Display Optoelectronics 359

19.5 Flexible Display Technology for Multi-analyte Sensor Array Platforms 364

19.5.1 Integrated LOC and Flexible Display Devices 364

19.5.2 Multiplexed Sensor Platforms 364

19.6 Medical Diagnostic Displays 366

19.7 Wearable Health Monitoring Devices Based on Flexible Displays 366

19.7.1 Monitoring Vital Signs Using Flexible Display Technology 367

19.7.2 Flexible Display Technology for Phototherapy 369

19.7.3 Smart Clothing Using Flexible Display Technology 370

19.8 Competing Technologies, Challenges, and Future Trends 371

19.9 Conclusion 372

Acknowledgment 373

Conflicts of Interest 373

Index 379