Large Area and Flexible Electronics

List of Contributors XV

Overview XXIII

Part I: Materials 1

1 Polymeric and Small-Molecule Semiconductors for Organic Field-Effect Transistors 3
Hakan Usta and Antonio Facchetti

1.1 Introduction 3

1.2 Organic Semiconductor Structural Design 3

1.3 Thin-Film Transistor Applications 6

1.4 p-Channel Semiconductors 8

1.4.1 Polymers 8

1.4.2 Small Molecules 26

1.5 n-Channel Semiconductors 37

1.5.1 Polymers 37

1.5.2 Small Molecules 51

1.6 Ambipolar Semiconductors 68

1.6.1 Polymers 69

1.6.2 Small Molecules 77

1.7 Conclusions 85

References 85

2 Metal-Oxide Thin-Film Transistors for Flexible Electronics 101
Yong-Hoon Kimand Sung Kyu Park

2.1 Introduction 101

2.2 Metal-Oxide TFTs 102

2.2.1 Advantages and Applications 102

2.2.2 Vacuum Deposition 102

2.2.3 Solution Processing 103

2.3 Solution-Processed MOThin Films 103

2.3.1 Nanoparticle-Based Process 103

2.3.2 Sol–Gel-Based Process 104

2.3.3 Hybrid Type 105

2.4 Low-Temperature-Processed MO TFTs for Flexible Electronics 105

2.4.1 Low-Temperature-Processed MO TFTs 106

2.4.1.1 Annealing Environment 106

2.4.1.2 Ink Formulation 106

2.4.1.3 Alternate Annealing Process 107

2.4.2 Photochemical Activation of Oxide Semiconductors 107

2.5 Summary 114

References 115

3 Carbon Nanotube Thin-Film Transistors 117
Taishi Takenobu

3.1 Introduction 117

3.2 Individual SWCNTs and SWCNT Thin Films 118

3.3 Chemical Vapor Deposition Growth of SWCNT TFTs 118

3.4 Solution-Based Methods for SWCNT TFTs 120

3.5 Inkjet Printing of Flexible SWCNT TFTs 120

3.6 Fabrication Schemes for High-Performance Inkjet-Printed SWCNT TFTs 122

3.7 Inkjet Printing of SWCNT CMOS Inverters 124

3.8 Inkjet Printing of Aligned SWCNT Films 128

3.9 Conclusion 129

References 129

4 Organic Single-Crystalline Semiconductors for Flexible Electronics Applications 133
Marcos A. Reyes-Martinez, Nicholas S. Colella, and Alejandro L. Briseno

4.1 Introduction 133

4.2 Electronic and Structural Properties of Single Crystals 134

4.2.1 Intrinsic Transport Properties 135

4.2.2 Crystal Dimensionality 136

4.3 Crystallization Techniques 138

4.3.1 Growth from Vapor Phase 138

4.3.2 Growth from Solution 138

4.4 Single-Crystal Flexible Electronic Devices 139

4.4.1 Fundamental Mechanics for Flexible Electronics 139

4.4.2 Mechanical Versatility of Organic Single Crystals 141

4.4.3 Importance of Mechanical Properties Knowledge 142

4.4.4 The Elastic Constants of Rubrene Single Crystals 144

4.5 Strategies for Flexible Organic Single-Crystal Device Fabrication 149

4.5.1 Discrete Ultrathin Single-Crystal Transistor 150

4.5.2 Transistor Arrays Based on Micropatterned Single Crystals 150

4.5.3 Flexible Single-Crystal Nanowire Devices 156

4.6 Conclusions 158

Acknowledgments 159

References 159

5 Solution-Processable Quantum Dots 163
Hongbo Li, Vladimir Lesnyak, and Liberato Manna

5.1 Introduction 163

5.2 Optimization of the Colloidal Synthesis of Quantum Dots by Selection of Suitable Solvents, Ligands, and Precursors 164

5.3 Large-Scale Synthesis of Quantum Dots 166

5.4 Surface Chemistry of Quantum Dots 169

5.5 Post-Synthetic Chemical Modification of Nanocrystals 174

5.6 Conclusions and Outlook 179

References 179

6 Inorganic Semiconductor Nanomaterials for Flexible Electronics 187
Houk Jang,Wonho Lee,Min-Soo Kim, and Jong-Hyun Ahn

6.1 Introduction 187

6.2 Characteristics and Synthesis of Inorganic Semiconducting NMs 188

6.2.1 Characteristics of Inorganic NMs 188

6.2.1.1 Mechanical Properties of Inorganic NMs in Bending and Stretching 188

6.2.1.2 Optoelectrical Properties 191

6.2.2 Fabrication of Inorganic NMs for Flexible Electronics 193

6.2.2.1 Selective Etching 193

6.2.2.2 Anisotropic Etching 194

6.2.2.3 Mass Production of Inorganic NMs 195

6.2.2.4 Transfer Process 197

6.3 Applications in Flexible Electronics 198

6.3.1 Flexible Electronics 198

6.3.1.1 Flexible Solar Cell 198

6.3.1.2 Flexible Memory 201

6.3.1.3 Flexible High-Frequency Transistor 202

6.3.1.4 Foldable Transistor Using Ultrathin Si NMs 203

6.3.2 Conformal Device 205

6.3.2.1 Conformal Biomonitoring System 206

6.3.3 Stretchable Electronics 207

6.3.3.1 Stretchable Logic Circuit 207

6.3.3.2 Stretchable Light-Emitting Diode 211

6.3.3.3 Photodetector 211

6.3.4 Utilizing Deformation of NMs 215

6.3.4.1 Nanogenerator and Actuator 217

6.3.4.2 RF Device Using Strained NMs 218

6.3.5 Transparent Transistor 219

6.4 Concluding Remarks 221

References 221

7 Dielectric Materials for Large-Area and Flexible Electronics 225
Sungjun Park, Sujin Sung,Won-June Lee, andMyung-Han Yoon

7.1 Introduction 225

7.2 General Polymer Dielectrics 226

7.3 Cross-Linked Polymer Dielectrics 227

7.4 High-k Polymer Dielectrics 228

7.5 Electrolyte Gate Dielectrics 230

7.6 Self-Assembled Molecular Layer Dielectrics 234

7.7 Hybrid Dielectrics 237

7.7.1 Organic–Inorganic Laminated Bilayers/Multilayers 237

7.7.2 Organic Polymeric/Inorganic Nanoparticle and Nanocomposites 238

7.7.3 Hybrid Dielectrics Based on Organosiloxane and Organozirconia 240

7.8 Sol–Gel High-k Inorganic Dielectrics 243

7.9 Summary and Outlook 246

References 247

8 Electrolyte-Gating Organic Thin Film Transistors 253
Moon Sung Kang, Jeong Ho Cho, and Se Hyun Kim

8.1 Introduction 253

8.2 Electrolyte-Gated OTFT OperationMechanisms 255

8.3 Electrolyte Materials 257

8.4 OTFTs Gated with Electrolyte Dielectrics 260

8.5 Circuits Based on Electrolyte-Gated OTFTs 263

8.6 Conclusions 267

References 267

9 Vapor Barrier Films for Flexible Electronics 275
Seok-Ju Kang, Chuan Liu, and Yong-Young Noh

9.1 Introduction 275

9.2 Thin-Film Permeation Barrier Layers 277

9.3 Permeation through Inorganic Thin Films 280

9.4 Time-Resolved Measurements on Barrier Layers 283

9.5 Mechanical Limitations of Inorganic Films 284

9.6 Mechanics of Films on Flexible Substrates 284

9.7 Summary 286

References 287

10 Latest Advances in Substrates for Flexible Electronics 291
William A. MacDonald

10.1 Introduction 291

10.2 Factors Influencing Film Choice 292

10.2.1 Application Area 292

10.2.2 Physical Form/Manufacturing Process 292

10.3 Film Property Set 293

10.3.1 Polymer Type 293

10.3.2 Optical Clarity 295

10.3.3 Birefringence 296

10.3.4 The Effect of Thermal Stress on Dimensional Reproducibility 296

10.3.5 Cyclic Oligomers 298

10.3.6 Solvent and Moisture Resistance 299

10.3.7 The Effect of Mechanical Stress on Dimensional Reproducibility 302

10.3.8 Surface Quality 303

10.3.8.1 Inherent Surface Smoothness 303

10.3.8.2 Surface Cleanliness 305

10.4 Summary of Key Properties of Base Substrates 306

10.5 Planarizing Coatings 308

10.6 Examples of Film in Use 310

10.7 Concluding Remarks 312

Acknowledgments 312

References 312

Part II: Devices and Applications 315

11 Inkjet Printing Process for Large Area Electronics 317
Sungjune Jung, Steve D. Hoath, Graham D. Martin, and Ian M. Hutchings

11.1 Introduction 317

11.2 Dynamics of Jet Formation 318

11.3 Ink Rheology: Non-Newtonian Liquids 322

11.4 Dynamics of Drop Impact and Spreading 327

11.5 Applications of Inkjet Printing for Large-Area Electronics 333

11.5.1 Light-Emitting Diodes 333

11.5.2 Thin-Film Transistors 335

11.5.3 Solar Cells 339

11.6 Summary 340

References 341

12 Inkjet-Printed Electronic Circuits Based on Organic Semiconductors 345
Kang-Jun Baeg and Yong-Young Noh

12.1 Printed Organic Electronics 345

12.1.1 Printed Electronic Devices 345

12.1.2 Inkjet Printing Technology 347

12.2 CMOS Technology 349

12.2.1 CMOS Inverters 350

12.2.2 Ring Oscillators 353

12.3 High-Speed Organic CMOS Circuits 355

12.3.1 High-Mobility Printable Semiconductors 356

12.3.2 Downscaling of Channel Length 358

12.3.3 Reducing Contact Resistance 359

12.3.4 Reducing Parasitic Overlap Capacitance 359

12.4 Conclusions 361

References 362

13 Large-Area, Printed Organic Circuits for Ambient Electronics 365
Tsuyoshi Sekitani, Tomoyuki Yokota, and Takao Someya

13.1 Introduction 365

13.2 Manufacturing Process and Electrical Characteristics 366

13.2.1 Materials and Methods 366

13.2.2 Organic Transistors Manufactured Using Printing Technologies 366

13.2.2.1 Manufacturing Process for DNTT Transistors 369

13.2.2.2 Electrical Performance of DNTT Transistors 369

13.2.2.3 Manufacturing Process for All-Printed Transistors 369

13.2.2.4 Electrical Performance of All-Printed Transistors 369

13.2.3 Mechanical Characteristics 370

13.2.4 Inverter Circuits and Ring Oscillator Using Printed Transistors 371

13.2.5 Printed Organic Floating-Gate Transistors 371

13.2.5.1 Manufacturing Process 373

13.2.5.2 Electrical Performance 373

13.3 Demonstration 376

13.3.1 Organic Active-Matrix LED Pixel Circuits 376

13.3.2 Large-Area Flexible Pressure Sensor Sheet 376

13.3.3 Intelligent Sensor Catheter for Medical Diagnosis 378

13.4 Future Prospects 378

Acknowledgments 378

References 379

14 Polymer and Organic Nonvolatile Memory Devices 381
Seung-Hoon Lee, Yong Xu, and Yong-Young Noh

14.1 Introduction 381

14.2 Resistive Switching Memories 384

14.2.1 Fundamentals of Resistive Switching Principles 384

14.2.2 Mechanisms of Resistive Switching 386

14.2.2.1 Filamentary Conduction 386

14.2.2.2 Space Charge and Traps 387

14.2.2.3 Charge Transfer 388

14.2.2.4 Ionic Conduction 388

14.2.3 The Role of π-Conjugated Material in Switching Process 388

14.2.4 Recent Flexible RRAM Based on Organic–Inorganic Bistable Materials 389

14.3 Charge Storage in Transistor Gate Dielectric 390

14.3.1 Operation of Charge-Storage OFET Memory Devices 391

14.3.2 Charge Storage in Polymer Electrets 392

14.3.3 Nanoparticle-Embedded Gate Dielectrics 394

14.4 Polymer Ferroelectric Devices 396

14.4.1 Materials 399

14.4.2 Principles of Memory Operation 401

14.4.2.1 Capacitor 402

14.4.2.2 Field-Effect Transistor 402

14.5 Conclusions 407

References 407

15 Flexible Displays 411
Chung-kun Song and Gi-Seong Ryu

15.1 Introduction 411

15.2 Flexible Substrates 412

15.2.1 Thermal Stability 413

15.2.2 Optical Transparency 414

15.2.3 Permeation of Oxygen and Moisture 414

15.2.4 Chemical Resistance 415

15.2.5 Surface Roughness 415

15.3 Display Mode 415

15.4 Thin-Film Transistor 418

15.4.1 a-Si TFT 419

15.4.2 LTPS TFT 420

15.4.3 Oxide TFT 420

15.4.4 OTFT 422

15.5 AMOLED Panel with Printing Technology 426

15.5.1 Design and Fabrication of OTFT Backplane 426

15.5.2 Screen Printing of the Gate Electrodes and Scan Bus Lines 428

15.5.3 Inkjet Printing of TIPS-Pentacene for OTFTs 431

15.6 Fabrication of the OLED and AMOLED Panel 433

15.7 Future Prospects 435

References 435

16 Flexible Organic Solar Cells for Scalable, Low-Cost Photovoltaic Energy Conversion 439
Seunghyup Yoo, Jongjin Lee, Donggeon Han, and Hoyeon Kim

16.1 Overview of Organic Photovoltaic (OPV) Cells 439

16.1.1 Motivation for OPV Cells 439

16.1.2 Fundamentals of OPV Technologies 441

16.1.2.1 General Operation of PV Cells 441

16.1.2.2 Working Principle of OPV Cells 442

16.1.2.3 Major Components and Various Configuration of OPV Cells 444

16.2 Efforts toward Realization of Flexible OSCs 449

16.2.1 Overview 449

16.2.2 Transparent Electrodes (TEs) for Flexible OSCs 449

16.2.2.1 Metal Grids Combined with Other Transparent Electrodes 450

16.2.2.2 Other Flexible Transparent Electrodes 451

16.2.3 Encapsulation Issues 454

16.3 Flexible OSCs for High-Throughput Production: A Printing-Based Approach to Low-Cost Solar Energy Conversion 455

16.3.1 Printing Technology Overview 455

16.3.2 Review of Printing Technologies Used for OSCs 456

16.3.2.1 Screen Printing 456

16.3.2.2 Droplet Coating and Printing 456

16.3.2.3 Blade/Knife Edge Coating and Slot-Die Printing 458

16.3.2.4 Gravure Printing 460

16.3.2.5 Other Coating/Printing Methods 460

16.3.3 Issues in Module Fabrication 462

16.4 Summary and Outlook 463

References 463

17 Flexible Inorganic Photovoltaics 469
Zhuoying Chen

17.1 Introduction 469

17.2 Thin Crystalline Solar Cells Transferred onto Flexible Substrates 470

17.3 Thin-Film Solar Cells Grown Directly onto Flexible Substrates by Vapor Deposition 472

17.4 Solution-ProcessedThin-Film Solar Cells Deposited Directly onto Flexible Substrates 477

17.5 Summary 480

References 480

18 Scalable and Flexible Bioelectronics and Its Applications to Medicine 485
Salvatore Iannotta, Pasquale D’Angelo, Agostino Romeo, and Giuseppe Tarabella

18.1 Biosensing and Bioelectronics: A Fast Growing Field and a Challenging Research Area 485

18.2 Inorganic and Silicon-Based Flexible Electronics for Biosensing Devices 490

18.2.1 Inorganic Semiconductors for Flexible Electronics: From Hybrids and Inorganic Semiconducting Composites to Silicon 491

18.2.2 Bioapplications: From Cell–Silicon Junctions Toward Neuroprosthesis and Neuromedicine 496

18.3 EGOFETs for Flexible Biosensing 507

18.3.1 EGOFET: Architecture,Working Principle, and Materials 508

18.3.2 Biochemical Sensing 512

18.3.3 Interfacing with Neural Tissue 517

18.3.4 Opportunities and Challenges 519

18.4 OECTs for Biosensing and Biomonitoring 520

18.4.1 OECT Architecture andWorking Principle 520

18.4.2 The Applications of OECT as a Biological Sensor 522

18.4.2.1 Drug Nanocarriers for Drug Delivery 522

18.4.2.2 Dopamine and Eumelanin Sensing 523

18.4.2.3 Sensing Cell and Bacterial Activity 526

18.4.2.4 DNA 528

18.4.2.5 Biosensing Toward e-Textile Applications 529

18.4.3 Organic Electronic Ion Pumps (OEIPs) 529

18.5 Conclusions and Outlook 531

References 533

Index 541