Flexible Electronics, Volume 3: Energy Devices and Applications

Preface
Acknowledgements
About the book
Author biography
Vinod Kumar Khanna
Abbreviations, acronyms, chemical symbols and formulae
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Mathematical symbols and general notation
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Chapter 1 Supercapacitors
1.1 Types of capacitors
1.1.1 Electrostatic capacitor
1.1.2 Electrolytic capacitor
1.1.3 Double layer capacitor
1.1.4 Pseudocapacitor
1.1.5 Supercapacitor or ultracapacitor
1.2 Graphene supercapacitor
1.2.1 Hummer’s method of preparation of graphitic oxide
1.2.2 Graphitic oxide to graphene oxide (GO)
1.2.3 Screen printing of GO onto woven cotton textile
1.2.4 Conversion of GO to reduced graphene oxide (rGO) by electrochemical method
1.2.5 Coating the rGO printed electrodes with electrolyte
1.2.6 Electrochemical characterization
1.3 Fiber supercapacitor
1.3.1 Electrodes
1.3.2 Advantages of ZnO NWs
1.3.3 Electrolyte
1.3.4 Hydrothermal growth of ZnO NWs on PMMA wire
1.3.5 Hydrothermal growth of ZnO NWs on Kevlar 129 fibers
1.3.6 Assembly of a fiber-based electrochemical capacitor
1.3.7 Characterization
1.3.8 Enhanced-capacitance structures
1.4 Two-ply yarn supercapacitor
1.4.1 Production of CNT yarn
1.4.2 CNT@PANI yarn formation by in situ PANI deposition
1.4.3 CNT@PANI@PVA yarn formation by PVA gel coating
1.4.4 Supercapacitor formation and characterization
1.4.5 Platinum filament-reinforced CNT yarn
1.5 Discussion and conclusions
Review exercises
References
Chapter 2 Batteries
2.1 Electrical battery
2.2 Lithium-ion microbattery
2.2.1 Basic lithium-ion battery
2.2.2 CBC 005 battery
2.2.3 Preparation of the PDMS handler substrate
2.2.4 Punching of the PDMS substrate into 8 mm diameter disks
2.2.5 Placement of the LIB die in inverted form on disks
2.2.6 Selective dry etching of the back side silicon of LIB die
2.2.7 Peeling off the thinned die
2.2.8 Electrochemical performance
2.3 Lithium-ion paper battery with free-standing CNT thin films as current collectors
2.3.1 Making free-standing CNT/LTO and CNT/LCO double layer films
2.3.2 Lamination process for battery fabrication
2.3.3 Rechargeable battery characteristics
2.4 Cable-type lithium-ion battery
2.4.1 Making the anode core
2.4.2 Separator winding
2.4.3 Cathode winding
2.4.4 Positive tab attachment
2.4.5 Packaging
2.4.6 Injection of the liquid organic electrolyte
2.4.7 Negative tab attachment
2.4.8 Electrochemical behavior
2.5 Out-of-plane deformable spiral-shaped lithium-ion battery
2.5.1 Solution casting of the electrolyte thin film
2.5.2 Assembly of battery components
2.5.3 Battery features
2.6 Safer lithium-ion battery with a solid-like electrolyte
2.6.1 Non-ideality of common battery electrolytes
2.6.2 PVDF–IL electrolyte film preparation
2.6.3 Making the anode and cathode
2.6.4 Battery assembly
2.6.5 Battery parameters
2.7 Zinc–silver oxide battery with enhanced mechanical designs
2.7.1 Basic zinc–silver oxide battery
2.7.2 Battery designs
2.7.3 Zinc anode
2.7.4 Silver oxide cathode
2.7.5 Polymer electrolyte of the cell
2.7.6 Assembly of battery components
2.7.7 Electrochemical–mechanical performance
2.8 Stencil printed Zn–Ag2O alkaline battery on PET substrate
2.8.1 Printing the bottom layer of silver current collector
2.8.2 Printing the zinc electrode
2.8.3 Printing the photopolymerizable poly(acrylic acid) (PAA) electrolyte
2.8.4 Printing the silver oxide electrode
2.8.5 Printing the silver flake/PEO layer
2.8.6 Dehydration, rehydration and encapsulation of the battery stack
2.8.7 Battery operations in flat and flexed conditions
2.9 Zn/MnO2 alkaline battery on mesh-embedded electrodes
2.9.1 Electrochemistry of Zn–MnO2 battery
2.9.2 Building flexibility in the battery
2.9.3 Printing the anode
2.9.4 Printing the cathode
2.9.5 Preparing the polymer gel electrolyte
2.9.6 Assembling the battery
2.9.7 Battery behavior in flat and bent conditions
2.10 Discussion and conclusions
Review exercises
References
Chapter 3 Energy harvesters
3.1 Introduction
3.2 Triboelectric generator by stacking PET and Kapton sheets
3.2.1 Triboelectric series of materials
3.2.2 PET/Kapton polymer TEG
3.2.3 Mechanism of power generation by TEG
3.3 Triboelectric nanogenerator (TENG) cloth with lithium-ion battery (LIB) belt
3.3.1 Making the Ni-cloth belt
3.3.2 Making the parylene-cloth belt
3.3.3 Weaving the TENG cloth
3.3.4 Contacting and separation (C–S) effects between Ni cloth and parylene cloth
3.3.5 The LIB belt battery
3.3.6 Charging and discharging of the unit
3.4 Piezoelectric PZT thin film nanogenerator (NG) on PET
3.4.1 PZT film deposition cycles
3.4.2 Laser lift-off of the PZT film and its transfer from sapphire to PET substrate
3.4.3 Interdigitated electrode pattern and contact pad formation, passivation and lead attachment
3.4.4 Poling of the PZT film
3.4.5 NG testing
3.5 MEMS cantilever-based bimorph piezoelectric energy harvester (B-PEH)
3.5.1 Fabrication of the energy harvester
3.5.2 Electrical characteristics of the energy harvester
3.6 Piezoelectric PMN–PT thin film energy harvester on PET
3.6.1 Growth of PMN–PT crystal ingot
3.6.2 Crystal finishing and PMN–PT poling
3.6.3 Exfoliation and transfer of the PMN–PT film from silicon to PET substrate
3.6.4 Bending effects and harvester operation
3.7 Arterial pulsewave energy harvester
3.7.1 Energy harvester fabrication
3.7.2 Characteristics of the energy harvester
3.8 Energy harvester for roadways
3.8.1 Horizontal and vertical stacking of harvester layers
3.8.2 Need of paralleling unit harvesters
3.8.3 Harvester module construction
3.8.4 Harvester testing
3.9 Thermal energy harvester
3.10 Discussion and conclusions
Review exercises
References
Chapter 4 Solar cells
4.1 Solar cell, module and panel
4.1.1 What is a solar cell?
4.1.2 Solar module
4.1.3 Solar panel
4.2 Homogeneous P–N junction solar cell
4.2.1 Construction
4.2.2 Operation
4.2.3 Generic P–I–N design of solar cell
4.3 Heterojunction solar cell
4.3.1 Reduction of surface recombination
4.3.2 Advantages
4.4 Solar cell performance indices
4.5 Ultrathin and lightweight organic solar cell on PET film (η = 4.2%)
4.5.1 Mounting the PET film on glass substrate to facilitate processing
4.5.2 PEDOT:PSS transparent electrode
4.5.3 P3HT:PCBM active layer
4.5.4 Ca/Ag metal electrode
4.5.5 Resilience to mechanical deformation and stretching
4.6 Amorphous silicon solar cell on a parylene template (η = 5.78%)
4.6.1 Conformal coating of parylene on glass plate
4.6.2 Thermal annealing and plasma treatments of parylene coating
4.6.3 Deposition of barrier films
4.6.4 Transparent conductive oxide (TCO) deposition
4.6.5 P–I–N structure formation
4.6.6 Back electrode deposition
4.6.7 Solar cell performance
4.7 Si thin-film/PEDOT:PSS heterojunction inorganic/organic solar cell (η = 10.15%)
4.7.1 Silicon thinning
4.7.2 Si-NS formation by MacEtch method
4.7.3 Rear side metallization
4.7.4 Heterojunction formation
4.7.5 Front side metallization
4.7.6 Properties of the solar cell
4.8 Monocrystalline silicon heterojunction solar cell on thin silicon substrate (η = 14.9%)
4.8.1 Kerfless wafering
4.8.2 Surface texturing and doping of both sides of thick N-type wafer
4.8.3 Top surface passivation with silicon nitride and opening contact windows
4.8.4 Deposition of seed metal layer and electroplating
4.8.5 Exfoliation of a thin (silicon + metal) layer
4.8.6 Texturing and passivation of the front surface of the wafer
4.8.7 P+ emitter formation on front surface
4.8.8 ITO sputtering and Ag paste screen printing
4.8.9 Measured cell parameters
4.9 CIGS solar cell on PI substrate (η = 18.7%)
4.9.1 About CIGS
4.9.2 Basic CIGS cell structure
4.9.3 Successive deposition of constituent layers
4.9.4 Cell performance indices
4.10 InAs/GaAs quantum dot (QD) solar cell on plastic film (η = 10.5%)
4.10.1 Inverse fabrication of solar cell as P-on-N on GaAs substrate
4.10.2 Transfer of solar cell to plastic film
4.10.3 Removal of GaAs substrate
4.10.4 Metallization and application of antireflection coating
4.10.5 Solar cell parameters
4.11 GaAs solar cell on PET substrate by low-pressure chemical welding (η = 13.2%)
4.11.1 Solar cell formation in inverted P-on-N configuration
4.11.2 Cold welding of the solar cell with PET substrate
4.11.3 Etching of the sacrificial AlAs layer
4.11.4 Metal grid formation for ohmic contact with N-layer
4.11.5 Electrical and bending tests
4.12 GaAs solar cell on flexible substrate using AuBe/Pt/Au as a P-ohmic contact (η = 22.08%)
4.12.1 Starting layer organization
4.12.2 Bonding of the structure with flexible substrate
4.12.3 Etching the AlAs layer
4.12.4 Etching the buffer layer, forming grid pattern and applying ARC
4.12.5 Solar cell parameters
4.13 GaAs single-junction solar cell (η = 27.6%) and GaAs tandem solar cell on flexible substrate (η > 30%)
4.13.1 Single-junction GaAs solar cell
4.13.2 Two-junction solar cell
4.14 High specific power InGaP/(In)GaAs tandem solar cell on PI tape by controlled spalling
4.14.1 Controlled spalling
4.14.2 Growth of solar cell layers
4.14.3 Spalling and subsequent processing
4.14.4 Tandem cell parameters
4.15 Discussion and conclusions
Review exercises
References
Chapter 5 Displays and light-emission devices
5.1 Introduction
5.1.1 Electronic display
5.1.2 Electronic light-emission device
5.2 Active matrix electronic ink display with amorphous silicon TFTs on stainless steel foil
5.2.1 The backplane
5.2.2 Lamination of electronic ink (e-ink) on the backplane
5.3 Active matrix electronic ink display using solution-processed pentacene TFTs on polyimide foil
5.3.1 TFT backplane and row shift registers
5.3.2 Frontplane of the display
5.3.3 Display performance
5.4 Photoluminescent plasma display using organic materials on PET substrate
5.4.1 Elementary structure of a plasma display
5.4.2 Flexible display process
5.4.3 Front plate process
5.4.4 Back plate process
5.4.5 Operation of the plasma display
5.5 Flexible OLED on PEN substrate with gas barrier film
5.5.1 Moisture and oxygen barrier
5.5.2 Multilayer anode
5.5.3 Remaining OLED layers
5.5.4 Properties of the structure
5.6 Monochrome AMOLED display on PEN foil
5.6.1 Foil-on-a-carrier process
5.6.2 Laminating the foil on a carrier and its surface planarization
5.6.3 Pentacene TFT backplane fabrication
5.6.4 OLED fabrication
5.6.5 Display parameters
5.7 Inkjet-printed TFT-driven OLED color display on PEN film
5.7.1 Principle of multiphoton OLED
5.7.2 Display chip fabrication
5.7.3 MPE OLED fabrication
5.7.4 Display performance
5.8 GaN LED on polyimide substrate by laser lift-off from sapphire substrate and thermal release tape-assisted transfer
5.8.1 Deposition of LED layers by MOCVD
5.8.2 Etching of holes and ohmic contact formation
5.8.3 Separation of islands
5.8.4 Passivation of LEDs
5.8.5 LLO process
5.8.6 LED parameters
5.9 GaN LED on PET substrate by LLO with PDMS stamp-aided transfer
5.9.1 Growth of the consecutive layers of LED
5.9.2 Ohmic contacts to N-GaN and P-GaN
5.9.3 Subdivision of stack into islands
5.9.4 PDMS stamp preparation
5.9.5 Transfer of LED stack from the PDMS stamp to the PET substrate
5.9.6 LED passivation
5.9.7 Comparison of the characteristics of PET-mounted LED with those of original sapphire-mounted LED
5.10 Pyramid-array based GaN LED on PET substrate by LLO and dual transfer processes
5.10.1 High-temperature deposition of layers of pyramidal-shaped LEDs by MVPE process
5.10.2 Fixation of LEDs on semi-solid PDMS
5.10.3 Removal of sapphire substrate and transfer of LEDs to PET substrate
5.10.4 Further steps of LED fabrication
5.10.5 Bending experiments
5.11 GaN LED by LLO and direct transfer to polyimide substrate
5.11.1 Deposition of LED layers
5.11.2 Formation of Ni/Ag/Ni ohmic contact cum reflector with P-GaN
5.11.3 Bonding metal deposition
5.11.4 Application of double-sided polyimide tape carrying a dummy sapphire substrate to the bonding metal
5.11.5 LLO at sapphire/N-GaN interface
5.11.6 Formation of individual chips and electrodes to P-GaN
5.11.7 Removal of dummy sapphire substrate
5.11.8 Comparing flexible LED with conventional LED
5.12 Discussion and conclusions
Review exercises
References
Chapter 6 CNT field emitters
6.1 Field emission
6.2 Field emission device with N-doped CNT/reduced graphene oxide film on polycarbonate substrate
6.2.1 Synthesis of graphite oxide from purified natural graphite by Hummer’s method
6.2.2 Deposition of graphene oxide film on SiO2/Si substrate
6.2.3 Creation of nanopatterned Fe catalyst array on graphene oxide film by block copolymer lithography
6.2.4 Catalytic PECVD of vertically aligned CNT arrays and thermal reduction of graphene oxide (GO)
6.2.5 Detachment of the N-doped CNTs/reduced graphene oxide film from SiO2/Si substrate and their transfer to flexible substrate
6.2.6 Field emission device construction
6.2.7 Field emission properties
6.3 Field emitter with double-walled CNT thin film on PET
6.3.1 Preparation of CNT suspension
6.3.2 Filtration transfer method
6.3.3 DWCNT emitter device
6.3.4 Effect of bending on resistance of the CNT emitter
6.3.5 Effect of bending on emission current
6.3.6 Field enhancement factor
6.3.7 Long-term emission stability
6.3.8 Flexible lamp feasibility
6.4 Transparent field emission device with spray-coated SWCNT thin film on arylite substrate
6.4.1 SWCNT dispersion preparation and its spray coating on arylite substrate
6.4.2 Field emission characterization
6.4.3 Transparency of the FED
6.5 MWCNTs-implanted Ni foil FED for x-ray production
6.5.1 Making MWCNT/PI paste
6.5.2 Forming MWCNT/PI film on a glass wafer
6.5.3 Partial etching of PI to obtain a flat surface
6.5.4 Nickel sputtering
6.5.5 Defining the active area of nickel substrate
6.5.6 Building up the thickness of nickel layer by electroplating
6.5.7 Removing the PI layer and the photoresist
6.5.8 Field emission experiments
6.6 Discussion and conclusions
Review exercises
References
Chapter 7 Sensors
7.1 What is a sensor?
7.2 Ultrathin silicon-based tactile sensor with spin-coated [P(VDF–TrFE)]
7.2.1 Properties of the ferroelectric polymer
7.2.2 Sensor fabrication with ferroelectric polymer
7.2.3 Poling of the piezoelectric material
7.2.4 Sensor performance
7.3 Tactile sensors using screen printed [P(VDF–TrFE)] and MWCNT/PDMS nanocomposite on polyimide/PET substrates
7.3.1 Piezoelectric tactile sensor using [P(VDF–TrFE)] polymer on polyimide substrate
7.3.2 Piezoresistive tactile sensor with MWCNT/PDMS nanocomposites on PET substrate
7.4 NH3 sensor with spray-deposited CNT thin film on polyimide substrate
7.4.1 Sensing mechanism
7.4.2 Basic construction and principle of the CNT sensor
7.4.3 Fabrication of the CNT sensor
7.4.4 Sensor characterization
7.5 CO2 sensor with CNT thin film transferred from Si substrate to polyimide substrate
7.5.1 Substrate preparation
7.5.2 Pretreatment of the substrate
7.5.3 Growth of CNTs
7.5.4 CNT transfer from Si substrate to PI substrate
7.5.5 Contact electrode deposition
7.5.6 Measurement of resistance of CNT film
7.6 NO2 sensor with LbL-SA MWCNTs on PET substrate
7.6.1 Preparation of negatively charged MWCNTs dispersion in aqueous medium
7.6.2 Preparation of negatively charged substrate
7.6.3 Deposition of two layers of PSSMA/PAH [poly(4-styrenesulfonic acid-co-maleic acid)/poly(allylamine hydrochloride)] film
7.6.4 Deposition of (MWCNTs/PAH)n multilayer film
7.6.5 Gas sensing behavior
7.6.6 Flexibility characteristics
7.7 NO2 sensor with LbL covalent bonding of graphene oxide on PET substrate and its in situ reduction to rGO
7.7.1 Fabrication of the rGO–CH/Au electrode
7.7.2 Sensor response
7.8 NO2 sensor with MWCNTs–WO3 NPs on PET substrate
7.8.1 Hydrothermal synthesis of WO3 NPs
7.8.2 Synthesis of MWCNTs–WO3 NPs hybrid
7.8.3 Gel casting of MWCNTs–WO3 NPs hybrid on gold electrodes on PET
7.8.4 Gas sensing properties
7.8.5 Selectivity
7.8.6 Mechanical flexibility tests
7.9 Discussion and conclusions
Review exercises
References
Chapter 8 Memories
8.1 Memory of a computer
8.2 Flexible charge trap-type memory (f-CTM) TFT on PEN substrate
8.2.1 CTM transistor background
8.2.2 Lamination of PEN substrate on carrier–glass substrate
8.2.3 Deposition of the organic/inorganic hybrid barrier layer
8.2.4 Source (S)/drain (D) electrodes
8.2.5 IGZO active channel layer
8.2.6 First aluminum oxide tunneling layer
8.2.7 Second Al2O3 tunneling layer, zinc oxide charge trapping layer and top Al2O3 protection layer
8.2.8 Al2O3 blocking layer
8.2.9 Gate electrode and source/drain pads
8.2.10 f-CTM TFT characteristics
8.2.11 On- and off-programming with the f-CTM TFT
8.3 Pentacene-based non-volatile memory (NVM) TFT on PES substrate
8.3.1 Deposition and patterning of aluminum gate electrodes
8.3.2 Spin casting and curing of P(VDF–TrFE) polymer
8.3.3 Thermal evaporation of pentacene
8.3.4 Thermal evaporation of source/drain gold pads
8.3.5 Properties of NVM TFT
8.4 Electrosprayed TiO2-based resistive memory device on PES substrate
8.4.1 Bottom silver electrode patterning
8.4.2 Electrospraying titanium dioxide
8.4.3 Top electrode patterning
8.4.4 Bipolar switching behavior
8.4.5 Cyclic endurance testing
8.4.6 Effect of bending radius on resistance
8.4.7 Multiple bending effect
8.5 PEALD TiO2 crossbar memory device on PES substrate for resistive random access memory (RRAM)
8.5.1 Glueing the PES substrate to a silicon wafer
8.5.2 Thermal evaporation of aluminum for first aluminum electrode formation
8.5.3 PEALD process for first TiO2 deposition
8.5.4 Thermal evaporation of aluminum for second aluminum electrode formation
8.5.5 Second TiO2 deposition
8.5.6 Thermal evaporation of aluminum for third aluminum electrode formation
8.5.7 Separation of silicon substrate from PES substrate carrying the device
8.5.8 Low- and high-resistance states
8.6 RRAM with one transistor–one memristor structure on PI substrate
8.6.1 Preparing the pattern of silicon islands weakly held by the BOX layer
8.6.2 Transferring the pattern of Si islands to a PDMS stamp
8.6.3 Transferring the Si islands to a flexible substrate
8.6.4 Isolating active regions of transistors and curing the PI precursor
8.6.5 Gate dielectric deposition
8.6.6 Source/drain contact window opening
8.6.7 Source/drain and gate metallization
8.6.8 Deposition of aluminum bottom electrodes at the drain regions
8.6.9 Amorphous titanium dioxide by PEALD
8.6.10 Deposition of aluminum top electrodes
8.6.11 Bit, source and word lines
8.6.12 Metal interlayer dielectric
8.6.13 NMOSFET characteristics
8.6.14 TiO2-based memristor characteristics
8.7 Write-once-read-many-times (WORM) memory polymeric device on polypyrrole substrate
8.7.1 Electrochemical polymerization of PPy substrate
8.7.2 Synthesis of P6FBEu polymer
8.7.3 Spin coating of P6FBEu polymer over PPy
8.7.4 Gold top electrodes
8.7.5 Electrical transition of device from off-state to on-state
8.8 Metal/insulator/metal capacitor on (100) silicon fabric
8.8.1 DRAM cell
8.8.2 Making the metal-oxide-semiconductor (MOS) capacitors on the silicon
8.8.3 Making the silicon fabric
8.8.4 Typical characteristics
8.9 Discussion and conclusions
Review exercises
References
Chapter 9 Antennas and RFID tags
9.1 RFID system preliminaries
9.2 Bendable Cu/Ti antenna on SU-8/PDMS substrate
9.2.1 SU-8/PDMS substrate features
9.2.2 Antenna design
9.2.3 Antenna fabrication
9.2.4 Effects of bending on the antenna
9.3 Stretchable Ag NW antenna on PDMS substrate
9.3.1 Growth of silver nanowires
9.3.2 Drop-casting the silver nanowires on silicon substrate and transferring them to PDMS
9.3.3 Making the PDMS substrate with the ground plane
9.3.4 Building the antenna
9.3.5 Resonance frequency of the antenna
9.4 Flexible and stretchable UHF RFID tag with Ag antenna on 3D printed NinjaFlex substrate
9.4.1 Features of the NinjaFlex substrate
9.4.2 Antenna fabrication
9.4.3 Connecting the RFID IC
9.4.4 Tag performance
9.5 Wearable e-textile UHF RFID tag for body-centric systems
9.5.1 Complications faced with antennas fixed on high conductivity objects
9.5.2 Electrically conducting textile as an antenna material
9.5.3 Slot patch antenna design
9.5.4 Radiator of the antenna
9.5.5 Ground plane of the antenna
9.5.6 The substrate
9.5.7 Fixing the radiator patches and the ground plane on the EPDM substrate
9.5.8 RFIC connection, and other connections
9.5.9 Comparing an e-textile antenna with Cu antenna
9.6 Flexible cum stretchable embroidered e-fiber RFID antenna for an automotive tire
9.6.1 Difficulties associated with an automotive tire-mounted antenna
9.6.2 Antenna construction to overcome the impediments
9.6.3 Comparison of threshold power of embroidered antenna with that of metal antenna
9.7 Flexible 13.56 MHz RFCPU on plastic film
9.7.1 First flexible RFCPU
9.7.2 Stress-peel-off-process (SPOP) for transferring the PolySi TFT-technology fabricated CPU to plastic
9.7.3 Testing of the CPU part
9.8 Flexible 915 MHz UHF RFCPU
9.8.1 Adding more features to RFCPU
9.8.2 Larger communication range
9.8.3 Two-phase clock scheme
9.8.4 Reduction of power consumption and increasing the memory capacity
9.8.5 Encryption function
9.8.6 Overall chip performance
9.9 Sensor interfacing with RFID tags on flexible foil
9.9.1 Compensating for the higher cost of RFIDs
9.9.2 Utilizing the analog response of RFID for sensing
9.9.3 Digital signal transfer and processing
9.9.4 UHF RFID tag for moisture sensing
9.9.5 Architectures of smart RFID tags
9.9.6 Implementation of RFID tags
9.9.7 Operation of RFID tags
9.9.8 RFID tag performance
9.10 Discussion and conclusions
Review exercises
References