Flexible Electronics, Volume 1 · Mechanical Background, Materials and Manufacturing by Khanna, Vinod Kumar -- Read -- Imperial Library of Trantor

Index

Cover Title Copyright Contents Preface Acknowledgements About the book Author biography Abbreviations, acronyms, chemical symbols and formulae Mathematical symbols and general notation 1 The flexible electronics paradigm

1.1 Introduction 1.2 Traditional versus flexible electronics 1.3 Three-pronged approach to flexible electronics 1.4 Defining flexible electronics 1.5 Broad scope of flexible electronics 1.6 Organization of the book 1.7 Discussion and conclusions Review exercises References

Part I Mechanical background

2 Mechanical bending of a circuit

2.1 Introduction 2.2 Bending-mode deformation 2.3 Curvature and radius of curvature 2.4 Neutral axis

2.4.1 First moment of area or first moment of inertia 2.4.2 Centroid 2.4.3 Moment of area about the centroidal axis 2.4.4 Proving that neutral axis is located on the centroid for a beam of uniform composition 2.4.5 Position of the neutral axis and strain at the top surface of a film–substrate structure with equal Young’s moduli of film and substrate 2.4.6 Shift in the position of the neutral axis of a film–substrate structure for a compliant substrate

2.5 Critical strain and critical radius of curvature 2.6 εCritical and ρCritical as characteristic parameters defining flexible, compliant and stretchable electronics 2.7 Discussion and conclusions Review exercises References

3 Stresses and strains in the hard-film–soft-substrate structure

3.1 Introduction 3.2 Stresses in thin films 3.3 Built-in residual stress

3.3.1 Examples of built-in residual stress 3.3.2 Causes of residual stress creation 3.3.3 Effects of residual stress 3.3.4 Residual stress control 3.3.5 Measurement methods for built-in residual stress

3.4 Tensile versus compressive built-in stress in a film-on-foil structure in flexible electronics 3.5 Thermal coefficient mismatch stress

3.5.1 Effect of difference in CTE between film and substrate for a thin film deposited on a thick and hard substrate 3.5.2 Effect of difference in CTE between film and substrate for a thin film deposited on a thin and supple substrate 3.5.3 Reaching the crux of the problem

3.6 Mechanical stress and strain at different stages in a film-on-foil structure 3.7 Modeling the film-on-foil structure

3.7.1 Strain equations 3.7.2 Stress equations 3.7.3 Force and moment balance equations 3.7.4 Flattened film-on-foil structure 3.7.5 Temperature dependence equations 3.7.6 Built-in strain εbi and built-in stress σbi

3.8 Applications of the model

3.8.1 Strain in the substrate εs(Td) and the film εf(Td) at the deposition temperature (Td) 3.8.2 Strain in the substrate εs(Tr) and the film εf(Tr) at room temperature (Tr)

3.9 Discussion and conclusions Review exercises References

4 Curvature and overlay alignment of the hard-film–soft-substrate structure

4.1 Introduction 4.2 Classical theory of curvature produced by thin film deposition

4.2.1 Stoney’s equation relating stress in the film with curvature induced in the substrate by film 4.2.2 Mode of deformation of a substrate by film stress 4.2.3 Timoshenko’s model of a film–substrate bilayer

4.3 Evolution of spherical shape from the dominance of the substrate effect 4.4 Radius of curvature of cylindrical roll contour for a compliant substrate 4.5 Discussion and conclusions Review exercises References

5 Providing stretchability by controlled buckling of films

5.1 Introduction 5.2 Spontaneously produced ordered structures 5.3 Using ordered structures in stretchable electronics 5.4 Process of formation of activated/inactivated sites 5.5 The buckling profile 5.6 Approach and assumptions in the formulation of buckling geometry model 5.7 Bending energy Ub in thin film 5.8 Membrane strain (ε11)

5.8.1 One-dimensional point strain 5.8.2 Strain of the beam due to rotation of the element 5.8.3 Total strain of the beam

5.9 In-plane displacement u1 5.10 Modifying the strain equation 5.11 Membrane energy in the thin film (Um) 5.12 Substrate energy (Us) 5.13 Total energy (U) 5.14 Amplitude and critical strain 5.15 Independence of amplitude from thin film properties 5.16 Maximum strain 5.17 Environmental protection of buckled thin film in a practical application 5.18 Substrate effects 5.19 Discussion and conclusions Review exercises References

6 Bending brittle films

6.1 Introduction 6.2 Failure by cracking, slipping and delamination 6.3 Surface strain, interfacial shear stress and interfacial normal (or peeling) stress 6.4 Applying self-equilibrium beam theory for trilayer electronic assemblies 6.5 Analyzing a structure with a slipping crack on the interface between Si thin film and PET substrate 6.6 Fracture toughness and delamination toughness of brittle thin films on compliant substrates by controlled buckling experiments 6.7 Building self-healing capabilities in circuits 6.8 Discussion and conclusions Review exercises References

7 Deformation and cycling of ductile films

7.1 Introduction 7.2 In situ fragmentation testing of copper films 7.3 Cyclic bending of copper films 7.4 Discussion and conclusions Review exercises References

8 Straining permeation barriers

8.1 Introduction 8.2 The electromechanical two-point bending equipment

8.2.1 Dynamic and static loading of the barrier layer 8.2.2 Advantages of the two-point bending method

8.3 The ΔR/R0 ratio–strain curve for the film 8.4 Internal compressive strain in the film 8.5 Controlling internal compressive strain in a film 8.6 Inorganic–organic multilayer permeation barrier 8.7 Failure mechanisms of inorganic/organic coatings 8.8 Discussion and conclusions Review exercises References

Part II Materials

9 Inorganic materials

9.1 What are inorganic materials? 9.2 Amorphous silicon films 9.3 Hydrogen-terminated amorphous silicon (a-Si:H) films 9.4 Nanocrystalline (nc), microcrystalline (μc) and polycrystalline (pc) silicon films 9.5 Solution-processed a-Si and pc-Si films 9.6 Transparent oxides 9.7 Zinc oxide-based binary and ternary oxides 9.8 High dielectric constant materials 9.9 Discussion and conclusions Review exercises References

10 Organic materials

10.1 What are organic materials? 10.2 Mechanisms of electrical behavior of organic compounds

10.2.1 Hybridization of atomic orbitals 10.2.2 Bonding and antibonding molecular orbitals 10.2.3 sp, sp2 and sp3 hybridizations 10.2.4 sp hybridization 10.2.5 sp2 hybridization 10.2.6 sp3 hybridization 10.2.7 Conjugated systems and delocalization of electrons 10.2.8 Organic semiconductors and insulators 10.2.9 Conductive polymers

10.3 Dielectric materials

10.3.1 Polyimide (PI) 10.3.2 Polyethylene terephthalate (PET) 10.3.3 Polyethylene napthalate (PEN) 10.3.4 Polyethersulfone (PES) 10.3.5 Polycarbonate (PC) 10.3.6 Poly(methyl methacrylate) (PMMA) 10.3.7 Polypropylene (PP) 10.3.8 Polydimethylsiloxane (PDMS) 10.3.9 Polytetrafluoroethylene (PTFE) 10.3.10 Polyvinylalcohol (PVA or PVOH) 10.3.11 Parylene C 10.3.12 CYTOPTM

10.4 Semiconducting materials

10.4.1 Pentacene 10.4.2 Rubrene 10.4.3 Tetracene 10.4.4 Poly(3,4-ethylenedioxythiophene)–poly(styrenesulfonate) (PEDOT: PSS) 10.4.5 Poly(3-hexylthiophene-2,5-diyl) (P3HT) 10.4.6 Poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) 10.4.7 Copper(ii) phthalocyanine 10.4.8 7,7,8,8-Tetracyanoquinodimethane (TCNQ) 10.4.9 Fullerene 10.4.10 Copper hexadecafluorophthalocyanine (F16CuPc) 10.4.11 2,9-Bis[(4-methoxyphenyl)methyl]anthra[2,1,9-def:6,5,10-d′e′f′]diisoquinoline-1,3,8,10(2H,9H)tetrone

10.5 Organic conductors

10.5.1 Polyaniline (PANI) and polyaniline (emeraldine salt) 10.5.2 Polypyrrole (Ppy) and polypyrrole (Ppy) doped with sulfonic acid 10.5.3 Polyacetylene (PAc) 10.5.4 Iodine-doped poly(3-hexylthiophene-2,5-diyl) (P3HT)

10.6 Discussion and conclusions Review exercises References

11 Nanomaterials: CNTs, nanowires, graphene and 2D materials

11.1 What is a nanomaterial? 11.2 Two approaches to nanomaterial film growth/deposition on flexible substrates 11.3 Direct CNT growth on PI 11.4 Direct Si NW growth on PI 11.5 Direct graphene pattern growth on flexible glass substrate 11.6 Direct low-temperature synthesis of MoS2 on PI substrate 11.7 CNT film transfer to any substrate

11.7.1 CNT synthesis 11.7.2 V-SWCNT film transfer

11.8 Microwave-assisted V-CNT array patterning on PC substrate

11.8.1 Growth of V-CNT arrays 11.8.2 Transfer of V-CNT arrays to PC

11.9 Transfer printing of silicon NWs to PDMS

11.9.1 Nanowire growth on the donor substrate 11.9.2 P-type Si NW growth parameters 11.9.3 Intrinsic-Si NW growth parameters 11.9.4 Surface preparation of acceptor substrate 11.9.5 Contact printing of NWs from donor substrate to acceptor substrate 11.9.6 Deposition of two contact pads 11.9.7 Re-transfer of NW devices to PDMS

11.10 PMMA-mediated graphene transfer to non-specific substrates

11.10.1 Formation of Ni grains 11.10.2 Graphene synthesis 11.10.3 Release of graphene film

11.11 Graphene transfer to PET substrate via hot-press lamination (HPL) and ultraviolet adhesive (UVA)

11.11.1 Graphene growth 11.11.2 HPL transfer method 11.11.3 Room temperature UVA-based transfer method 11.11.4 Mechanical robustness of transferred graphene

11.12 Transfer of MoS2 devices to PI foil 11.13 Discussion and conclusions Review exercises References

Part III Manufacturing equipment and machines

12 Printing techniques

12.1 What is printing? 12.2 Classification of printing technologies (I): subtractive versus additive 12.3 Classification of printing technologies (II): contact versus non-contact 12.4 Gravure printing 12.5 Gravure offset printing 12.6 Flexographic printing 12.7 Lithographic printing 12.8 Offset lithographic printing 12.9 Screen printing

12.9.1 Stencil and screen 12.9.2 Squeegee 12.9.3 Flatbed screen printing machine 12.9.4 Rotary-bed screen printing machine

12.10 Inkjet printing

12.10.1 Valvejet printing 12.10.2 Thermal bubble or bubble inkjet printing 12.10.3 Piezoelectric inkjet printing 12.10.4 Electrostatically-actuated inkjet printing

12.11 Electrohydrodynamic printing 12.12 Pyroelectrodynamic printing 12.13 Dielectrophoretic printing 12.14 Surface acoustic wave (SAW) printing 12.15 Discussion and conclusions Review exercises References

13 Vacuum deposition

13.1 What is vacuum deposition? 13.2 Vacuum evaporation

13.2.1 Thermal evaporation 13.2.2 Electron-beam (e-beam) evaporation

13.3 Sputtering

13.3.1 DC diode sputtering 13.3.2 Magnetron sputtering 13.3.3 RF reactive sputtering for insulating film deposition 13.3.4 RF sputtering of a compound target for insulating film deposition 13.3.5 Pulsed DC sputtering 13.3.6 Co-sputtering

13.4 Molecular beam epitaxy (MBE) 13.5 Organic molecular beam deposition (OMBD)

13.5.1 The OMBD process 13.5.2 Film growth rates 13.5.3 Substrate temperature effects 13.5.4 Film purity 13.5.5 Binding forces and structural defects 13.5.6 Epitaxial growth 13.5.7 Epitaxy and quasi-epitaxy

13.6 Organic vapor phase deposition (OVPD) 13.7 Chemical vapor deposition (CVD)

13.7.1 Thermal CVD 13.7.2 Construction of CVD system 13.7.3 Plasma-enhanced chemical vapor deposition (PECVD) 13.7.4 Common PECVD chemistries 13.7.5 Metal organic chemical vapor deposition (MOCVD) 13.7.6 Metal organic vapor phase epitaxy (MOVPE) 13.7.7 Thermal atomic layer deposition (ALD) 13.7.8 Plasma-enhanced ALD versus conventional thermal ALD

13.8 Discussion and conclusions Review exercises References

14 Silicon microelectronics/MEMS processes

14.1 Introduction 14.2 Thermal oxidation of silicon 14.3 Thermal diffusion of impurities into silicon

14.3.1 Diffusion of P-type impurity in silicon 14.3.2 Diffusion of N-type impurity in silicon 14.3.3 Diffusion of P- and N-type impurities in silicon using spin-on dopants 14.3.4 Mathematics of diffusion 14.3.5 Predeposition and drive-in diffusion 14.3.6 Predeposition equations 14.3.7 Drive-in equations

14.4 Ion implantation

14.4.1 Ion implantation system 14.4.2 Post-implantation annealing 14.4.3 Advantages of ion implantation

14.5 Photolithography (deep UV or optical lithography) and etching

14.5.1 Positive and negative photoresists 14.5.2 Substrate preparation and cleaning before photolithography 14.5.3 Photoresist coating 14.5.4 Soft baking of the photoresist 14.5.5 Alignment and UV exposure of the photoresist through a mask 14.5.6 Developing the photoresist 14.5.7 Hard baking of the photoresist 14.5.8 Wet and dry etching 14.5.9 Reactive ion etching 14.5.10 Uses of oxygen plasma 14.5.11 Deep reactive ion etching (DRIE), BOSCH process

14.6 Electron-beam (e-beam) lithography 14.7 Discussion and conclusions Review exercises References

15 Packaging

15.1 Electronic packaging or encapsulation 15.2 Ultra-thin chip-in flex technology

15.2.1 Silicon wafer thinning methods 15.2.2 Main considerations in wafer thinning 15.2.3 Generic wafer thinning process and die singulation 15.2.4 Flip-chip bonding

15.3 Flip-chip assembly of ultra-thin silicon chips on flexible substrates

15.3.1 SRAM 3D memory module < 150 μm thick 15.3.2 Ultra-thin IC chip < 20 μm packaging 15.3.3 Ultra-thin assembly < 80 μm

15.4 High-yield manufacturing process for flip-chip assembly of 25 μm thick silicon dies on polyimide substrates 15.5 Laser-enabled advanced packaging (LEAP)

15.5.1 Gold stud bump formation 15.5.2 Wafer dicing 15.5.3 Preparing the flexible substrate 15.5.4 Laser-induced forward transfer (LIFT) method

15.6 Thermo-mechanical selective laser-assisted die transfer (tmSLADT) method 15.7 Discussion and conclusions Review exercises References

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