AMBARISH PAUL, PhD, is currently working on bendable sensors for healthcare management at the University of Glasgow, UK. He has authored research articles in reputed IEEE journals in the fields of microfabrication and chemical-based pressure sensors. MITRADIP BHATTACHARJEE, PhD, is an Assistant Professor with the Department of Electrical Engineering and Computer Science at the Indian Institute of Science Education and Research (IISER) Bhopal, India. RAVINDER DAHIYA, PhD, is a Professor in the Department of Electrical and Computer Engineering at Northeastern University, Boston, USA. His group (Bendable Electronics and Sustainable Technologies) conducts research in flexible printed electronics, electronic skin, and their applications in robotics, wearables, and interactive systems.

• About the Authors xvPreface xvii1 Introduction 11.1 Overview 11.1.1 Growth in Solid-State Sensor Market 21.1.2 Solid-State Sensors: A Recipe for Smart Sensing Systems 51.2 Evolution of Solid-State Sensors 61.2.1 Origin and Early Developments in Detection Devices 61.2.2 Solid-State Electronics: Post Transistor Era 91.2.3 Emergence of New Technologies 121.2.3.1 Thin-Film Technology 141.2.3.2 Advancements in Micro- and Nanofabrication 141.2.3.3 Emergence of Nanotechnology 161.2.3.4 Printed Electronics on Flexible Substrates 171.2.3.5 Smart Devices with Artificial Intelligence 201.2.3.6 IoT-Enabled Sensors 211.2.4 Paradigm Shift in Solid-State Sensor Research 221.2.4.1 Organic Devices 231.2.4.2 Wearable Devices 241.2.4.3 Implantable Sensors 251.3 Outline 27References 282 Classification and Terminology 352.1 Sensor Components 352.2 Classification of Solid-State Sensors 362.3 Sensor Terminology 402.3.1 Accuracy 402.3.2 Precision 412.3.3 Calibration Curve 412.3.4 Sensitivity 412.3.5 Threshold/Minimum Detectable Limit 422.3.6 Null Offset 422.3.7 Dynamic Range 422.3.8 Nonlinearity 422.3.9 Hysteresis 432.3.10 Selectivity 432.3.11 Repeatability 432.3.12 Reproducibility 432.3.13 Resolution 432.3.14 Stability 432.3.15 Noise 442.3.16 Response and Recovery Time 442.3.17 Drift 452.4 Conclusion 45References 453 Fabrication Technologies 473.1 Introduction 473.2 Deposition 483.2.1 Physical Vapor Deposition 493.2.1.1 Thermal Evaporation 503.2.1.2 Sputter Deposition 523.2.1.3 Electron-Beam PVD 553.2.1.4 Laser Ablation 583.2.2 Electroplating 593.2.3 Thermal Oxidation 613.2.4 Chemical Vapor Deposition 623.2.4.1 Atmospheric Pressure Chemical Vapor Deposition 623.2.4.2 Low-Pressure Chemical Vapor Deposition 633.2.4.3 Plasma-Enhanced Chemical Vapor Deposition 633.3 Exposure-Based Lithography Techniques 643.3.1 UV Lithography 653.3.1.1 Exposure Tool 653.3.1.2 Mask 663.3.1.3 Photoresist 673.3.2 Electron-Beam Lithography 683.3.3 X-Ray Lithography 713.3.4 Ion-Beam Lithography 713.4 Soft Lithography Techniques 723.4.1 Particle Replication in Nonwetting Templates 743.4.2 Microcontact Printing 753.4.3 Microfluidic Patterning 773.4.4 Laminar Flow Patterning 793.4.5 Step and Flash Imprint Lithography 803.4.6 Hydrogel Template 823.5 Etching 833.5.1 Wet Etching 853.5.2 Dry Etching 893.6 Doping 903.6.1 Diffusion 923.6.2 Ion Implantation 943.7 Solution Processed Methods 953.7.1 Inkjet Printing 953.7.2 Drop Dispensing 983.7.3 Spray Deposition 1003.7.4 Screen Printing 1013.7.5 Tape Casting 1033.8 Conclusions 105References 1064 Piezoelectric Sensors 1134.1 Overview 1134.2 Theory of Piezoelectricity 1154.2.1 Direct Piezoelectric Effect 1154.2.2 Poling 1164.2.3 Static Piezoelectricity 1184.2.4 Anisotropic Crystals 1184.3 Basic Mathematical Formulation 1194.3.1 Contribution of Piezoelectric Effect to Elastic constant C 1204.3.2 Contribution of Piezoelectric Effect to Dielectric Constant ε 1214.4 Constitutive Equations 1224.4.1 Piezoelectric 1224.4.2 Sensor Equations for Electrical Circuits 1244.4.3 Piezoelectric Constants for a Material 1264.4.3.1 Piezoelectric Strain Constant d 1274.4.3.2 Piezoelectric Voltage Coefficient g 1274.4.3.3 Piezoelectric Coupling Coefficients k 1284.4.3.4 Mechanical Quality Factor QM 1284.4.3.5 Acoustic Impedance 1294.4.3.6 Aging Rate 1294.4.3.7 Dielectric Constants KTij 1294.5 Piezoelectric Materials 1304.5.1 Natural Piezoelectric Materials 1314.5.1.1 Piezoelectric Single Crystals 1314.5.1.2 Organic Materials 1334.5.1.3 Biopiezoelectric Materials 1384.5.2 Man-made/Synthetic Piezoelectric Material 1414.5.2.1 Polymers 1414.5.2.2 Ceramics 1434.5.2.3 Piezoelectric Composites 1464.5.2.4 Thin Film 1504.5.2.5 Choice of Piezoelectric Material for Desired Applications 1514.6 Uses of Piezoelectric Materials 1514.6.1 Piezoelectric Transducer 1524.6.2 Piezoelectric Actuator 1534.6.3 Piezoelectric Generator 1554.7 Piezoelectric Transducers as Sensors 1574.7.1 Pressure Sensor 1574.7.2 Accelerometer 1584.7.3 Acoustic Sensor 1594.8 Design of Piezoelectric Devices 1634.8.1 Orientation of Piezo Crystals 1634.8.2 Piezo Stacks 1644.8.3 Bimorph Architecture 1664.9 Application of Piezoelectric Sensors 1674.9.1 Industrial Applications 1674.9.1.1 Engine Knock Sensors 1674.9.1.2 Tactile Sensors 1684.9.1.3 Piezoelectric Motors 1694.9.1.4 Sonar 1714.9.2 Consumer Electronics 1724.9.2.1 Piezoelectric Igniters 1724.9.2.2 Drop on Demand Piezoelectric Printers 1724.9.2.3 Speakers 1734.9.2.4 Other Daily Use Products 1734.9.3 Medical Applications 1744.9.3.1 Ultrasound Imaging 1744.9.3.2 Surgery and Ultrasound Procedures 1754.9.3.3 Wound and Bone Fracture Healing 1754.9.4 Defense Applications 1764.9.4.1 Micro Robotics 1764.9.4.2 Laser-Guided Bullets and Missiles 1784.9.5 Musical Applications 1794.9.5.1 Piezoelectric Pickups for Instruments 1794.9.5.2 Microphones and Ear Pieces 1794.9.6 Other Applications 1804.9.6.1 Energy Harvesters 1804.9.6.2 Sports-Tennis Racquets 1844.10 Conclusions 184References 1885 Capacitive Sensors 1935.1 Overview 1935.1.1 A Capacitor 1945.1.2 Capacitance of a Capacitor 1955.2 Sensor Construction 1965.2.1 Overlapping Electrode Area A 1965.2.2 Dielectric Thickness d 1975.2.3 Dielectric Material 1995.2.4 Parallel Fingers and Fringing Fields 2015.3 Sensor Architecture 2035.3.1 Mixed Dielectrics 2035.3.2 Multielectrode Capacitor 2075.3.3 Geometry 2095.4 Classifications of Capacitive Sensors 2115.4.1 Displacement Capacitive Sensor 2115.4.2 Overlapping Area Variation Based Capacitive Sensor 2135.4.3 Effective Dielectric Permittivity Variation Based Capacitive Sensor 2145.4.4 Fringing Field Capacitive Sensor 2185.5 Flexible Capacitive Sensors 2195.6 Applications 2215.6.1 Motion Detection 2215.6.1.1 Displacement Motion (z-Direction) 2215.6.1.2 Shear Motion (x Direction) 2215.6.1.3 Tilt Sensor 2215.6.1.4 Rotary Motion Sensor 2225.6.1.5 Finger Position (2D, x–y Direction) 2225.6.2 Pressure 2225.6.3 Liquid Level 2235.6.4 Spacing 2235.6.5 Scanned Multiplate Sensor 2235.6.6 Thickness Measurement 2235.6.7 Ice Detector 2235.6.8 Shaft Angle or Linear Position 2235.6.9 Lamp Dimmer Switch 2235.6.10 Key Switch 2235.6.11 Limit Switch 2245.6.12 Accelerometers 2245.6.13 Soil Moisture Measurement 2245.7 Prospects and Limitations 2245.7.1 Prospects 2245.7.2 Limitations 224References 2266 Chemical Sensors 2336.1 Introduction 2336.1.1 Overview 2336.1.2 Global Limelight 2376.1.3 Evolution of Chemical Sensors 2376.1.4 Requirements for Chemical Sensors 2406.1.4.1 Selectivity 2406.1.4.2 Stability 2406.1.4.3 Sensitivity 2416.1.4.4 Response Time 2416.1.4.5 Limit of Detection 2416.2 Materials for Chemical Sensing 2416.2.1 Metal Oxides 2416.2.1.1 Types of Metal Oxides 2426.2.1.2 Chemical Sensing Mechanism 2436.2.1.3 Metal Oxide Nanoparticles and Films as Sensor Materials 2446.2.2 Honeycomb Structured Materials 2456.2.2.1 Graphene 2466.2.2.2 Carbon Nanotubes 2486.2.2.3 Other 2D Materials 2506.2.3 Biopolymers 2516.2.3.1 On the Basis of Type 2526.2.3.2 On the Basis of Origin 2556.2.3.3 On the Basis of Monomeric Units 2616.2.4 Functionalization 2656.2.4.1 Covalent Functionalization 2666.2.4.2 Noncovalent Functionalization 2686.2.5 Biocomposites 2706.3 Architectures in Chemical Sensors 2726.3.1 Chemiresistors 2726.3.2 ChemFET 2756.4 Applications 2776.4.1 Gas Sensors 2776.4.2 Environmental Sensors 2786.4.2.1 Pollutants/Aerosols Sensors 2796.4.2.2 Water Quality Monitoring Sensors 2816.4.2.3 Humidity Detectors 2826.4.2.4 UV Radiation Exposure Monitoring 2836.4.3 Biomolecule Sensors 2846.4.4 Food Quality Monitoring 2846.4.4.1 Relative Humidity Monitoring 2846.4.4.2 Gas Monitoring 2856.4.4.3 Temperature Monitoring 2856.4.4.4 Presence of Toxic Metals 2866.4.5 Water Quality Management in Public Pools 2866.4.6 Health Monitoring 2876.4.7 Defense and Security 2886.5 Conclusions 290References 2937 Optical Sensors 3097.1 Introduction 3097.2 Classifications of Optical Properties 3117.2.1 Absorbance 3117.2.2 Reflectance 3127.2.3 Light Scattering 3127.2.4 Luminescence 3147.2.5 Fluorescence 3147.2.6 Circular Dichroism 3157.2.7 Z-Scan Technique 3177.2.8 Förster Resonance Energy Transfer 3177.3 Materials for Optical Sensing 3197.3.1 Metal Oxide Materials 3197.3.2 Polymer Materials 3197.3.3 Carbon Materials 3207.4 Optical Techniques for Sensing 3207.4.1 SPR-Based Detection 3217.4.2 Nanostructure Aggregation-Mediated Detection 3237.4.3 Micro/Nanofiber-Based Detection 3237.4.4 Colorimetric Sensing 3247.4.5 Spectroscopy Techniques Associated with Sensing 3257.4.5.1 Raman Spectroscopy 3267.4.5.2 Luminescence Spectroscopy 3267.4.5.3 Absorption Spectroscopy 3267.5 Fabrication Technique of Optical Sensors 3277.5.1 Solution Process 3277.5.2 Inkjet Printing 3287.5.3 Screen Printing 3287.6 Applications of Optical Sensing 3287.6.1 Environment Monitoring and Gas Sensing 3287.6.2 Health Monitoring 3327.6.3 Fingerprint Detection 3327.6.4 Defense and Security 3337.6.5 Motion Detection 3347.6.6 Water Quality Monitoring 3347.6.7 e-Waste and Detection of Toxic Materials 3357.6.8 Detection of Microorganisms 3377.7 Prospects and Limitations 337References 3398 Magnetic Sensors 3418.1 Introduction 3418.2 Materials’ Magnetic Properties 3428.2.1 Diamagnetism 3438.2.2 Paramagnetism 3438.2.3 Ferromagnetism and Antiferromagnetism 3448.3 Nanomagnetism 3478.3.1 Magnetic Anisotropy 3478.3.2 Interlayer Exchange Coupling 3478.3.3 Exchange Bias 3478.3.4 Spin-Polarized Transport 3478.4 Magnetic Sensing Techniques 3498.4.1 Hall Effect Sensors 3498.4.2 Magnetoresistive Sensors 3548.4.2.1 Ordinary Magnetoresistance 3548.4.2.2 Anisotropic Magnetoresistance 3568.4.2.3 Giant Magnetoresistance 3578.4.2.4 Tunnel Magnetoresistance 3588.4.2.5 Colossal Magnetoresistance 3608.5 Fabrication and Characterization Technologies 3608.5.1 Conventional Fabrication 3618.5.2 Solution Process 3618.5.3 Printing Technologies 3618.6 Magnetic Sensor Applications 3618.6.1 Biosensors 3618.6.2 Magnetic Storage and Read Heads 3628.6.3 Current Sensing 3628.6.4 Position and Angle Sensors 3648.7 Prospects and Limitations 365References 3659 Interface Circuits 3699.1 Introduction 3699.1.1 Functions of Interface 3699.1.2 Types of Sensor Interfacing Circuits 3709.1.3 Battery 3729.1.4 Battery Characteristics in System Analysis 3739.1.5 Applications of an I/O Interface Device 3769.1.6 Importance of Input Impedance 3779.2 Amplifier Circuits 3789.2.1 Ideal Operational Amplifier (Op-amp) 3789.2.2 Inverting and Noninverting Op-amps 3799.2.3 Voltage Follower 3809.2.4 Instrumentation Amplifier 3819.2.5 Charge Amplifiers 3829.2.6 Applications of Amplifiers 3829.3 Excitation Circuits 3839.3.1 Current Generators 3839.3.2 Voltage Reference 3839.3.3 Oscillators 3859.3.4 Drivers 3869.4 Analog-to-Digital Converters 3869.4.1 Basic Concepts of ADC 3869.4.2 V/F Converter 3879.4.3 Dual-Slope Converter 3899.4.4 Successive Approximation Converter 3909.4.5 Resolution Extension 3919.5 Noise in Sensors and Circuits 3919.5.1 Inherent Noise 3929.5.2 Electric Shielding 3939.5.3 Bypass Capacitor 3949.5.4 Magnetic Shielding 3949.5.5 Ground Planes 3959.5.6 Ground Loops and Ground Isolation 3969.6 Batteries for Low-Power Sensors and Wireless Systems 3989.6.1 Primary Cells 4009.6.2 Secondary Cells 4019.6.3 Energy Harvesting for WSN 401References 403Index 409