Solid State Gas Sensing (eBook)

Preface 5
Contents 7
Contributors 12
Micro-Fabrication of Gas Sensors 15
1.1 Introduction 15
1.2 Gas Sensors and MEMS Miniaturization Techniques 17
1.2.1 Silicon as a Sensor Material 17
1.2.2 Thermal Sensors and Actuators 18
1.2.3 Thermal Microstructures 20
1.3 Specific Sensor Examples 25
1.3.1 Heat Conductivity Sensors 25
1.3.2 Metal-Oxide-Based Gas Sensors 29
1.3.3 Field-Effect Gas Sensors 33
1.3.4 Thermal Infrared Emitters 35
1.4 Gas-Sensing Microsystems 36
1.4.1 Low False-Alarm-Rate Fire Detection 37
1.4.2 Air Quality Monitoring and Leak Detection 41
1.5 Industrialization Issues 48
1.5.1 Initiating a System-Level Innovation 48
1.5.2 Building Added-Value Lines 48
1.5.3 Mastering the MEMS Challenge 50
1.5.4 Cooperation Across Technical and Economic Interfaces 51
1.5.5 Creating Higher Added Value 54
1.6 Conclusions and Outlook 54
References 55
Electrical-Based Gas Sensing 61
2.1 Introduction 61
2.2 Metal Oxide Semiconductor Surfaces 63
2.2.1 Geometric Structures 63
2.2.2 Electronic Structures 64
2.3 Electrical Properties of Metal Oxide Semiconductor Surfaces 64
2.3.1 Semiconductor Statistics 64
2.3.2 Surface States 66
2.3.3 Surface Space Charge Region 68
2.3.4 Surface Dipoles 71
2.4 Conduction Models of Metal Oxides Semiconductor 72
2.4.1 Polycrystalline Materials with Large Grains 74
2.4.2 Polycrystalline Materials with Small Grains 75
2.4.3 Mono-crystalline Materials 77
2.5 Adsorption over Metal Oxide Semiconductor Surfaces 79
2.5.1 Physical and Chemical Adsorption 79
2.5.2 Surface Reactions Towards Electrical Properties 81
2.5.3 Catalysts and Promoters 83
2.6 Deposition Techniques 84
2.6.1 Three-Dimensional Nanostructures 84
2.6.2 Two-Dimensional Nanostructures 85
2.6.3 One-Dimensional Materials 94
2.7 Conductometric Sensor Fabrication 98
2.7.1 Substrate and Heater 98
2.7.2 Electrical Contacts 102
2.7.3 Heating Treatments 103
2.7.4 Dopings, Catalysts and Filters 104
2.8 Transduction Principles and Related Novel Devices 106
2.8.1 DC Resistance 106
2.8.2 AC Impedance 108
2.8.3 Response Photoactivation 109
2.9 Conclusions and Outlook 113
References 113
Capacitive-Type Relative Humidity Sensor with Hydrophobic Polymer Films 122
3.1 Introduction 122
3.2 Fundamental Aspects 123
3.2.1 Sorption Isotherms of Polymers 123
3.2.2 Water Sorption Behavior of Polymers 124
3.2.3 Effects of the Sorbed Water on the Dielectric Properties 124
3.3 Characterization of Polymers 126
3.3.1 Sorption Isotherms 126
3.3.2 FT-IR Measurement 128
3.3.3 Solvatochromism 130
3.3.4 Capacitance Changes with Water Sorption 133
3.3.5 Cross-Linked Polymer 137
3.4 Humidity-Sensors-Based Hydrophobic Polymer Thin Films 143
3.4.1 Poly-Methylmethacrylate-Based Humidity Sensor 144
3.4.1.1 Initial Performances 144
3.4.1.2 Temperature Dependence 144
3.4.1.3 Long-Term Stability 145
3.4.2 Characteristics of Cross-Linked PMMA-Based Sensor 146
3.4.2.1 Initial Performances 146
3.4.2.2 Temperature Dependence 147
3.4.2.3 Durability against Acetone Vapor 147
3.4.2.4 Long-Term Stability 148
3.4.3 Polysulfone-based Sensor 149
3.4.3.1 Initial Performances 149
3.4.3.2 Long-Term Stability 150
3.4.4 Acetylene-Terminated Polyimide-based Sensor 151
3.4.4.1 Determination of Curing Condition 151
3.4.4.2 Initial Performances 154
3.4.4.3 Temperature Dependence 154
3.4.4.4 Other Sensing Characteristics 155
3.4.5 Cross-Lined Fluorinated Polyimide-Based Sensor 156
3.4.5.1 Sensor Fabrication 156
3.4.5.2 Initial Performances 156
3.4.5.3 Long-Term Stability 158
3.4.6 Improvements Using MEMS Technology 158
3.4.6.1 Sensor Preparation 159
3.4.6.2 Sensing Characteristics 160
References 162
FET Gas-Sensing Mechanism, Experimental and Theoretical Studies 165
4.1 Introduction 165
4.2 Brief Summary of the Detection Mechanism of FET Devices 166
4.3 UHV Studies of FET Surface Reactions 169
4.4 TEM and SEM Studies of the Nanostructure of FET Sensing Layers 172
4.5 Mass Spectrometry for Atmospheric Pressure Studies 173
4.6 The Scanning Light Pulse Technology 174
4.7 DRIFT Spectroscopy for In Situ Studies of Adsorbates 175
4.8 Atomistic Modelling of Chemical Reactions on FET Sensor Surfaces 180
4.9 Nanoparticles as Sensing Layers in FET Devices 183
4.10 Summary and Outlook 185
References 186
Solid-State Electrochemical Gas Sensing 192
5.1 Introduction 192
5.2 Mixed-Potential-Type Sensors 196
5.2.1 High-Temperature-Type NOx Sensors 196
5.2.2 Improvement in NO2 Sensitivity by Additives 200
5.2.3 Hydrocarbon (C3H6 or CH4) Sensors 202
5.2.4 Use of Nanostructured NiO-Based Materials 203
5.2.5 Nanosized Au Thin-Layer for Sensing Electrode 207
5.3 Amperometric Sensors 209
5.4 Impedancemetric Sensors 211
5.4.1 Sensing of Various Gases in ppm Level 211
5.4.2 Environmental Monitoring of C3H6 in ppb Level 212
5.5 Solid-State Reference Electrode 215
5.6 Conclusions and Future Prospective 216
References 217
Optical Gas Sensing 219
6.1 Introduction 219
6.2 Spectroscopic Detection Schemes 220
6.3 Ellipsometry 223
6.4 Surface Plasmon Resonance 226
6.5 Guided-Wave Configurations for Gas Sensing 231
6.5.1 Integrated Optical SPR Sensors 233
6.5.2 Fiber Optic SPR Sensors 233
6.5.3 Conventional and Microstructured Fibers for Gas Sensing 235
6.6 Conclusions 239
References 241
Thermometric Gas Sensing 247
7.1 Detection of Combustible Gases 247
7.1.3 Combustion 247
7.1.3 Thermal Considerations during Combustion 248
7.1.3 Catalysis 249
7.1.3 Explosive Mixtures 250
7.2 Catalytic Sensing 251
7.2.1 Pellistors 252
7.2.1.1 Safe Detection of Explosive Mixtures 254
7.2.1.2 Calibration of Pellistor Sensors 255
7.2.1.3 Reliability Issues 255
7.2.1.4 Limitations in Use of Pellistors 257
7.2.2 Microcalorimeters in Enzymatic Reactions 258
7.3 Thermal Conductivity Sensors 259
7.4 Calorimetric Sensors Measuring Adsorption/Desorption Enthalpy 261
7.5 MEMS and Silicon Components 261
7.5.1 Thermal Considerations 262
7.5.2 Temperature Readout 264
7.5.3 Integrated Calorimetric Sensors 266
7.6 Sensor Arrays and Electronic Noses 267
References 269
Acoustic Wave Gas and Vapor Sensors 271
8.1 Introduction 271
8.1.4 Acoustic Waves in Elastic Media 273
8.1.4 Advantages of Acoustic-Wave-Based Gas-Phase Sensors 276
8.2 Thickness Shear Mode (TSM)-Based Gas Sensors 277
8.2.1 Quartz Crystal Microbalance (QCM)-Based Gas Sensors 278
8.2.1.1 Gas and Vapor Sensitivity 279
8.2.1.2 QCM Gas Sensor Performance 282
8.2.2 Thin-Film Resonator (TFR)-Based Gas Sensors 286
8.2.2.1 TFBAR Structures 286
8.2.2.2 SMR Structures 286
8.2.2.3 Gas and Vapor Sensitivity 288
8.2.2.4 Advantages and Disadvantages of TFRs Over QCMs 288
8.2.2.5 TFR Gas Sensor Performance 289
8.3 Surface Acoustic Wave (SAW)-Based Gas Sensors 292
8.3.1 Conventional SAW Gas Sensors 295
8.3.2 Multi-Layered SAW Gas Sensors 296
8.3.3 Gas and Vapor Sensitivity 296
8.3.3.1 Mechanical Perturbations 297
8.3.3.2 Acoustoelectric Perturbations 298
8.3.4 SAW Device Gas Sensor Performance 301
8.4 Concluding Remarks 306
References 306
Cantilever-Based Gas Sensing 315
9.1 Introduction to Microcantilever-Based Sensing 315
9.1.5 Early Approaches to Mechanical Sensing 315
9.1.5 Cantilever Sensors 316
9.1.5 Deflection Measurement 317
9.1.3.1 Piezoresistive Readout 318
9.1.3.2 Piezoelectric Readout 318
9.1.3.3 Capacitive Readout 319
9.1.3.4 Beam-Deflection Optical Readout 319
9.2 Modes of Operation 320
9.2.1 Static Mode 320
9.2.2 Dynamic Mode 321
9.3 Functionalization 322
9.4 Example of an Optical Beam-Deflection Setup 323
9.4.1 General Description 323
9.4.2 Cantilever-Based Electronic Nose Application 324
9.5 Applications of Cantilever-Based Gas Sensors 326
9.5.1 Gas Sensing 326
9.5.2 Chemical Vapor Detection 328
9.5.3 Explosives Detection 329
9.5.4 Gas Pressure and Flow Sensing 331
9.6 Other Techniques 332
9.6.1 Metal Oxide Gas Sensors 332
9.6.2 Quartz Crystal Microbalance 333
9.6.3 Conducting Polymer Sensors 333
9.6.4 Surface Acoustic Waves 333
9.6.5 Field Effect Transistor Sensors Devices 334
References 335
Index 339