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) 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 Vanfl eteren

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

About the Author

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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About the Author