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Stretchable Electronics

Takao Someya (Editor)
ISBN: 978-3-527-32978-6
484 pages
January 2013
Stretchable Electronics (3527329781) cover image
On a daily basis, our requirements for technology become more innovative and creative and the field of electronics is helping to lead the
way to more advanced appliances. This book gathers and evaluates the materials, designs, models, and technologies that enable the fabrication of fully elastic electronic devices that can tolerate high strain. Written by some of the most outstanding scientists in the field, it lays down the undisputed knowledge on how to make electronics withstand stretching. This monograph provides a review of the specific applications that directly benefit from highly compliant electronics, including transistors, photonic devices, and sensors. In addition to stretchable devices, the topic of ultraflexible electronics is treated, highlighting its upcoming significance for the industrial-scale production of electronic goods for the consumer.

Divided into four parts covering:

* Theory
* Materials and Processes
* Circuit Boards
* Devices and Applications

An unprecedented overview of this thriving area of research that nobody in the field - or intending to enter it - can afford to miss.
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Preface XV

List of Contributors XVII

Part I Theory 1

1 Theory for Stretchable Interconnects 3
Jizhou Song and Shuodao Wang

1.1 Introduction 3

1.2 Mechanics of Stretchable Wavy Ribbons 5

1.2.1 Small-Deformation Analysis 5

1.2.2 Finite-Deformation Analysis 8

1.2.3 Ribbon Width Effect 12

1.3 Mechanics of Popup Structure 15

1.4 Mechanics of Interconnects in the Noncoplanar Mesh Design 19

1.4.1 Global Buckling of Interconnects 19

1.4.2 Adhesion Effect on Buckling of Interconnects 21

1.4.3 Large Deformation Effect on Buckling of Interconnects 24

1.5 Concluding Remarks 27

References 27

2 Mechanics of Twistable Electronics 31
Yewang Su, Jian Wu, Zhichao Fan, Keh-Chih Hwang, Yonggang Huang, and John A. Rogers

2.1 Introduction 31

2.2 Postbuckling Theory 31

2.3 Postbuckling of Interconnect under Twist 33

2.4 Symmetric Buckling Mode 34

2.5 Antisymmetric Buckling Mode 36

2.6 Discussion and Concluding Remarks 38

References 38

Part II Materials and Processes 41

3 Graphene for Stretchable Electronics 43
Chao Yan, Seoung-Ki Lee, Houk Jang, and Jong-Hyun Ahn

3.1 Introduction 43

3.2 Production of Graphene Films 44

3.2.1 Large-Area Graphene Synthesis by CVD 44

3.2.2 Exfoliation Methods 47

3.2.3 Epitaxial Growth Methods 48

3.3 Fabrication of Graphene Films on Substrates 50

3.3.1 Solution-Based Method 50

3.3.2 Transfer Printing 52

3.4 Applications in Flexible and Stretchable Electronics 54

3.4.1 Interconnect for Integrated Circuits 57

3.4.2 Flexible Electronics 60

3.4.2.1 Graphene Electrodes for Flexible FETs 60

3.4.2.2 Graphene Electrodes for Flexible OPVs 64

3.4.2.3 Graphene Electrodes for OLEDs 66

3.4.2.4 Graphene Film for Flexible Touch Screen Panels 70

3.4.3 Stretchable Electronics 71

3.5 Concluding Remarks 75

References 76

4 Stretchable Thin-Film Electronics 81
Stéphanie P. Lacour

4.1 Introduction 81

4.2 Silicone Rubber as a Substrate 82

4.2.1 Elastomers 82

4.2.2 Silicone Rubber – Polydimethylsiloxane (PDMS) 83

4.2.2.1 PDMS Surface Chemistry 83

4.2.2.2 PDMS Mechanical Properties 84

4.2.2.3 Dielectric Properties 85

4.2.2.4 Other Properties 86

4.2.3 Photosensitive Silicones 86

4.3 Mechanical Architecture 87

4.3.1 Preserving the Mechanical Integrity of Thin-Film Structures 88

4.3.1.1 Small Platforms (<500 μm Side) 89

4.3.1.2 Large Platforms (>500 μm Side) 90

4.3.2 Ensuring Smooth Strain Gradient across Interconnects 91

4.4 Stretchable Metallization 93

4.4.1 Morphology of Thin Gold Films on PDMS 94

4.4.2 Electromechanical Response 95

4.4.2.1 Uni-axial (1D) Stretching 96

4.4.2.2 Multi-axial (2D) Stretching 98

4.4.3 Printed Films on PDMS Substrate 99

4.5 Integrated Stretchable Thin-Film Devices 100

4.5.1 Soft Neural Electrode Arrays 100

4.5.2 Stretchable Capacitive Sensors 101

4.5.3 Stretchable Antennas 102

4.5.4 Stretchable Thin-Film Transistors 103

4.5.5 Stretchable Organic Lasers 105

4.6 Outlook 106

References 107

5 Stretchable Piezoelectric Nanoribbons for Biocompatible Energy Harvesting 111
Yi Qi, Thanh D. Nguyen, Prashant K. Purohit, and Michael C. McAlpine

5.1 Energy Harvesting and Piezoelectric Materials 111

5.1.1 Introduction to Biomechanical Energy Harvesting 111

5.1.2 Piezoelectric Materials and Lead Zirconate Titanate (PZT) 112

5.2 PZT Nanofabrication and Interfacing with Stretchable Substrates 116

5.2.1 Wafer-Scale PZT Nanowire Fabrication 116

5.2.2 Transfer Printing onto Stretchable Substrates 117

5.2.3 Stretchable Wavy and Buckled PZT Nanoribbons 120

5.3 Piezoelectric Characterization and Electrical Measurements 126

5.3.1 Piezoelectric Characterization 126

5.3.2 Electrical Measurements 130

5.4 Summary 133

References 134

Part III Circuit Boards 141

6 Modeling of Printed Circuit Board Inspired Stretchable Electronic Systems 143
Mario Gonzalez, Yung-Yu Hsu, and Jan Vanfleteren

6.1 Technology Development Considerations 143

6.2 Modeling and Simulation 145

6.2.1 Optimization of Metal Conductor Shape 146

6.2.1.1 Description of the Model 146

6.2.1.2 Material Properties 146

6.2.1.3 Stress/Strain Comparison of Different Conductor Shapes 147

6.2.1.4 Optimization of the Horseshoe Shape of Conductor 149

6.2.2 Influence of Substrate Stiffness on the Plastic Strain of the Conductor 151

6.2.3 Induced Mechanical Interaction on Multitracks 152

6.2.4 Polyimide-Supported Stretchable Interconnect 155

References 158

7 Materials for Stretchable Electronics Compliant with Printed Circuit Board Fabrication 161
Matthias Adler, Ruth Bieringer, Thomas Schauber, and Jürgen Günther

7.1 Introduction 161

7.1.1 Silicones 161

7.1.1.1 Fundamentals of Silicones 161

7.1.1.2 Silicone Elastomers 163

7.1.1.3 Durability 166

7.1.1.4 Processing 168

7.1.1.5 Fields of Application 170

7.1.2 Polyurethanes 171

7.1.2.1 Fundamentals of Polyurethanes 171

7.1.2.2 Properties of Polyurethanes 175

7.1.2.3 Thermoplastic Polyurethanes 176

7.1.2.4 Cast Polyurethanes 177

7.1.2.5 Commercial Raw Materials 179

7.1.2.6 Applications of Polyurethanes 181

7.1.2.7 Excursion Conductive Pastes (Developed during the STELLA Project) 182

References 184

Further Reading 185

8 Technologies and Processes Used in Printed Circuit Board Fabrication for the Realization of Stretchable Electronics 187
Frederick Bossuyt and Thomas Löher

8.1 Lamination Technology 187

8.1.1 Process Concept 187

8.1.2 Polyurethane Films 188

8.1.3 Printed Circuit Board Cu Foils 189

8.1.4 Lamination of Copper Foils to Polyurethane Films 189

8.1.5 Substrate Fabrication 190

8.1.6 Component Assembly and Interconnection 193

8.1.7 Encapsulation of Components 194

8.1.8 Outline Cutting of Circuits on the Fabrication Board and Release 195

8.1.9 Lamination to Textiles or Other Substrates 195

8.2 Molding Technology 196

8.2.1 General Introduction of the Process 196

8.2.2 Copper as Electrical Conductor 197

8.2.3 Polyimide as Mechanical Support 199

8.2.4 Lamination of Polyimide–Copper Sheet on Rigid Substrate Using a Temporary Adhesive 199

8.2.5 Copper Patterning 200

8.2.6 Solder Mask Application 200

8.2.7 Copper Finish Application 201

8.2.8 Assembly of Components 201

8.2.9 Encapsulation by Molding 202

8.2.10 Application to Textiles 203

References 205

9 Reliability and Application Scenarios of Stretchable Electronics Realized Using Printed Circuit Board Technologies 207
Jan Vanfleteren, Frederick Bossuyt, Thomas Löher, Yung-Yu Hsu, Mario Gonzalez, and Jürgen Günther

9.1 Application Considerations 207

9.2 Reliability 209

9.2.1 Results and Discussion of Single and Cyclic Elongation Tests 209

9.2.2 One-Time Stretch Tests 210

9.2.3 Cyclic Endurance Tests of Laminated and Molded Test Samples 211

9.2.3.1 Pure Copper Tracks 211

9.2.3.2 PDMS Encapsulated Parallel PI Supported Meander Tracks 212

9.2.4 Failure Analysis 214

9.2.4.1 In Situ Observation of the Deformation Behavior and Failure Mechanism of Encapsulated/Nonencapsulated Stretchable Interconnects 214

9.2.4.2 In Situ Electromechanical Measurement for One-Time-Stretching Reliability 216

9.2.4.3 Correlation between Numerical and Experimental Results 218

9.2.4.4 Fatigue Failure of Copper Meanders 219

9.2.4.5 Lifetime Prediction by FEM 221

9.2.5 Washability – An Introduction 222

9.3 Application Scenarios 223

9.3.1 Temperature Sensor 223

9.3.2 Wireless Power Circuit 224

9.3.3 Fitness Sensor 225

9.3.4 Pressure Senors in a Shoe Insole 226

9.3.5 Bandage Inlay for Compression Therapy 227

9.3.6 Baby Respiration Monitor Demonstrator 227

9.3.7 LED Matrix 229

9.3.8 RGB Led Matrix (SMI by Laser) 230

9.3.9 Thermoforming of Printed Conductors – Single Stretching 231

Reference 233

Further Reading 233

Part IV Devices and Applications 235

10 Stretchable Electronic and Optoelectronic Devices Using Single-Crystal Inorganic Semiconductor Materials 237
Dae-Hyeong Kim, Nanshu Lu, and John A. Rogers

10.1 Introduction 237

10.1.1 Materials Selection for High-Performance Stretchable Electronics 237

10.1.2 Monocrystalline Inorganic Semiconductors in Stretchable Designs 238

10.1.3 Bio-integrated Electronics 240

10.2 Stretchable Circuits 240

10.2.1 Wavy Electronic Devices and Circuits 240

10.2.2 Noncoplanar Electronic Devices and Circuits 242

10.2.3 Electronic Circuits with Serpentine Interconnects 244

10.2.4 Stretchable Electronic Devices on Unconventional Substrates 244

10.3 Application of Stretchable Designs to Microscale Inorganic Light Emitting Diodes (μ-ILEDs) 247

10.3.1 Stretchable μ-ILED Arrays 247

10.3.2 Lighting Devices on Substrates of Unconventional Materials and Shapes 249

10.4 Biomedical Applications of Stretchable Electronics and Optoelectronics 253

10.4.1 Encapsulation Strategy 253

10.4.2 Bio-applications of μ-ILEDs: Suture Threads and Proximity Sensors 253

10.4.3 Minimally Invasive Surgical Tools: Instrumented Balloon Catheters 256

10.4.4 Epidermal Electronic System (EES) 259

10.5 Stretchable Digital Imagers and Solar Modules 261

10.5.1 Hemispherical Electronic Eye Camera 261

10.5.2 Curvilinear Imagers and Stretchable Photovoltaic Modules with High Fill Factors 263

10.5.3 Hemispherical Electronic Eye Camera with Adjustable Zoom Magnification 264

10.6 Conclusions 265

References 267

11 Stretchable Organic Transistors 271
Tsuyoshi Sekitani and Takao Someya

11.1 Introduction 271

11.2 Perforated Organic Transistor Active Matrix for Large-Area, Stretchable Sensors 272

11.2.1 Simultaneous Sensing of Pressure and Temperature 274

11.3 Rubber-Like Stretchable Organic Transistor Active Matrix Using Elastic Conductors 275

11.3.1 Integration of Elastic Conductors with Printed Organic Transistors 276

11.3.1.1 Integration Process 276

11.3.2 Electrical and Mechanical Performances 278

11.4 Rubber-Like Organic Transistor Active Matrix Organic Light-Emitting Diode Display 280

11.5 Future Prospects 283

Acknowledgments 283

References 283

12 Power Supply, Generation, and Storage in Stretchable Electronics 287
Martin Kaltenbrunner and Siegfried Bauer

12.1 Introduction 287

12.2 Radio Frequency Power Supplies 287

12.3 Power Generation 289

12.3.1 Dielectric Elastomer Generators 290

12.3.2 Piezoelectric Energy Generation 292

12.3.3 Solar Cells 294

12.4 Power Storage 297

12.4.1 Supercapacitors 297

12.4.2 Batteries 299

12.5 Summary 301

Acknowledgments 301

References 301

13 Soft Actuators 305
Kinji Asaka

13.1 Introduction 305

13.2 Conducting Polymers 306

13.3 Ionic Polymer Metal Composites (IPMCs) 308

13.4 Nanocarbon Actuators 310

13.4.1 Carbon Nanotube (CNT) Actuators 310

13.4.2 CNT Actuators Based on Ionic-Liquid-Based Bucky-Gels 311

13.4.3 Materials of Bucky-Gel Actuators 313

13.4.4 Modeling of the Nanocarbon Actuators 315

13.5 Applications 319

13.6 Conclusion 319

References 320

14 Elastomer-Based Pressure and Strain Sensors 325
Benjamin C.K. Tee, Stefan C.B. Mannsfeld, and Zhenan Bao

14.1 Introduction 325

14.2 A Brief Elastomers Overview 326

14.3 Important Sensor Characteristics 327

14.3.1 Sensitivity 328

14.3.2 Hysteresis 329

14.3.3 Temporal Resolution 329

14.3.4 Sensitivity to Environmental Factors 330

14.3.5 Mechanical Durability 330

14.4 Elastomeric Force Sensors 330

14.4.1 Piezoresistive Sensors 331

14.4.1.1 Conductive Fillers in Elastomeric Composites 331

14.4.2 Elastomer as a Dielectric Material 335

14.4.2.1 Plain Elastomers 336

14.4.2.2 Foam 338

14.4.2.3 Microstructured Elastomers 339

14.4.3 Piezoelectric Films 341

14.4.4 Optical Pressure Sensors 342

14.5 Active Pressure/Strain Sensors Systems 343

14.6 Applications 348

14.7 Outlook 348

References 350

15 Conformable Active Devices 355
Robert A. Street and Ana Claudia Arias

15.1 Introduction 355

15.2 Printing Processes for Organic TFTs 356

15.2.1 Printing Considerations for Metals, Semiconductors, and Dielectrics 356

15.2.2 Printed Organic CMOS TFTs 359

15.2.3 Alternative Material Choices 360

15.2.4 Self-Assembly of TFTs from Solution 361

15.3 Sensing and Memory Devices Based on Piezoelectric Polymer 363

15.3.1 Pressure Sensor and Accelerometer 363

15.3.2 Chemical Sensors 364

15.3.3 Nonvolatile Printed Memory 365

15.3.4 Printed Memristor 366

15.3.5 Photodiodes and Other Devices 367

15.4 Electronic Circuits 368

15.4.1 All-Printed Organic TFT Display 369

15.4.2 Inverter, Ring Oscillator, and Shift Register 371

15.4.3 Self-Stabilized Amplifi er Circuits 372

15.5 Curved Conformal Devices by a Cut-and-Bend Approach 374

15.6 Summary 375

Acknowledgments 376

References 376

16 Stretchable Neural Interfaces 379
Woo Hyeun Kang, Wenzhe Cao, Sigurd Wagner, and Barclay Morrison, III

16.1 Introduction 379

16.2 Overview of MEAs 380

16.2.1 Advantages of Stretchable MEAs 381

16.3 Classes of SMEAs 382

16.3.1 Planar SMEAs 382

16.3.2 Cuff SMEAs 389

16.4 Common Limitations for All SMEAs 394

16.5 Future Directions in Stretchable Neural Interfaces 394

16.6 Conclusion 395

References 396

17 Bio-based Materials as Templates for Electronic Devices 401
Christian Müller and Olle Inganäs

17.1 Introduction 401

17.2 Polysaccharide-Based Templates 402

17.2.1 Cellulose: Paper Substrates 402

17.2.2 Cellulose: Nanofi ber Networks 403

17.2.3 Cellulose Fibers: Cotton, Lyocell, and Viscose 407

17.2.4 Vascular Bundles 407

17.2.5 Polysaccharide Hydrogels 408

17.3 Protein-Based Templates 409

17.3.1 Wool and Silk Fibers 409

17.3.2 Silk Fibroin Films 410

17.3.3 Protein Fibrils: Rhapidosomes, Microtubules, Actin Filaments, and Amyloid Fibrils 413

17.3.4 Collagen and Gelatin 415

17.4 DNA Templates 415

17.4.1 Intrinsic Electrical Properties of DNA 415

17.4.2 Decorated DNA 416

17.5 Virus Templates: Tobacco Mosaic Virus and M13 Bacteriophage 418

17.6 Summary 419

References 420

18 Organic Integrated Circuits for EMI Measurement 431
Makoto Takamiya, Koichi Ishida, Tsuyoshi Sekitani, Takao Someya, and Takayasu Sakurai

18.1 Introduction 431

18.2 Stretchable EMI Measurement Sheet 432

18.2.1 Overview of Stretchable EMI Measurement Sheet 432

18.2.2 2 V Organic CMOS Decoder 434

18.2.3 Stretchable Interconnects with CNTs 436

18.3 Silicon CMOS LSI for EMI Detection 437

18.4 Experimental Results and Discussion 440

18.4.1 Direct Silicon–Organic Circuit Interface 440

18.4.2 Comparison of Conventional and Proposed EMI Measurements 442

18.4.3 Calibration for EMI Measurement LSI 443

18.5 Conclusion 446

Acknowledgments 447

References 447

Index 449

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Takao Someya is Professor in the Department of Electrical and Electronic Engineering at the University of Tokyo, Japan. From 2001 to 2003, he worked at the Nanocenter of Columbia University, USA, and Bell Labs, Lucent Technologies, as a Visiting Scholar. His current research interests include organic transistors, flexible electronics, plastic integrated circuits, large-area sensors, and plastic actuators. Takao Someya has received a number of awards including the Japan Society for the Promotion of Science Prize, the first prize of the newly established German Innovation Award, the 2004 IEEE/ISSCC Sugano Award, and the 2009 IEEE Paul Rappaport Award.
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