Silicon Sensors S. MIDDELHOEK S.A. AUDET Department of Electrical Engineering Delft University of Technology Delft, The Netherlands ACADEMIC PRESS Harcourt Brace Jovanovich, Publishers London San Diego New York Berkeley Boston Sydney Tokyo Toronto
Contents Preface v 1 Introduction 1.1 Information and information-processing systems 1 1.2 Measurement and control systems 3 1.3 Transducers 6 1.3.1 Form of signal-carrying energy 6 1.3.2 Signal conversion in transducers 8 1.3.3 Terminology in the transducer field 11 1.3.4 Self-generating and modulating transducers 15 1.3.5 Two- and three-dimensional representation of input and output transducers 18 1.3.6 Signal conversion inside modifiers 22 1.4 Transducer technologies 24 1.4.1 Introduction 24 1.4.2 Non-silicon generic technologies 27 1.4.3 Silicon 29 1.5 Future outlook on measurement and control systems 31 1.5.1 Traditional products 31 1.5.2 Present innovative markets 32 1.5.3 Future innovative markets 33 References 34 2 Silicon Sensors for Radiant Signals 35 2.1 Introduction 35 2.1.1 Electromagnetic radiation 35 VII
viii Contents 2.1.2 Nuclear-particle radiation 36 2.2 Basic physical principles 39 2.2.1 Characterization of electromagnetic and nuclear-particle energy and their interactions with substances 39 2.2.2 Interactions of electromagnetic radiation with silicon 45 2.2.3 Interactions of nuclear particles with silicon 72 2.3 Applications for visible light 73 2.3.1 Photoconductors 73 2.3.2 Photodiodes 74 2.3.3 Avalanche photodiodes 77 2.3.4 P-I-N photodiodes 79 2.3.5 Quadrant photodiodes 80 2.3.6 Position-sensitive detectors 81 2.3.7 One- and two-dimensional photodiode arrays 85 2.3.8 Phototransistors 88 2.3.9 Charge-transfer devices 89 2.4 Applications for nuclear-particle radiation 92 2.4.1 Nuclear-particle radiation detectors 92 2.4.2 Silicon microstrip detector 94 2.4.3 Silicon drift chamber 96 2.5 Applications for x- and gamma-rays 97 References 98 3 Silicon Sensors for Mechanical Signals 105 3.1 Introduction 105 3.2 Basic physical principles 106 3.2.1 The piezoresistive effect 106 3.2.2 Other stress-sensitive silicon devices 125 3.2.3 Piezoelectricity 128 3.2.4 Capacitive pressure sensors 132 3.2.5 Mechanics of cantilevers and diaphragms 133 3.2.6 Surface acoustic wave transducers 140 3.3 Applications 143 3.3.1 Silicon strain gauges 143 3.3.2 Diffused diaphragm pressure sensors 144 3.3.3 Accclcrometers 147 3.3.4 Silicon tactile sensors for robot applications 148 References 149
Contents ix 4 Silicon Sensors for Thermal Signais 153 4.1 Introduction 153 4.2 Basic physical principles 154 4.2.1 Thermoelectric effects 154 4.2.2 Thermoresistors 174 4.2.3 Silicon diodes and transistors as thermal sensors 184 4.3 Applications of silicon thermal sensors 189 4.3.1 Flow sensors 189 4.3.2 Vacuum sensors 191 4.3.3 Infrared sensors 193 4.3.4 Integrated PTAT temperature sensors 195 References 197 5 Silicon Sensors for Magnetic Signals 201 5.1 Introduction 201 5.2 Basic physical principles 202 5.2.1 Hall effect and magnetoresistivity 202 5.2.2 Silicon Hall plates 215 5.2.3 Magnctodiodcs 225 5.2.4 Magnetotransistors 227 5.2.5 Carrier-domain magnetic-field sensors 235 5.3 Applications of magnetic-field sensors 238 5.3.1 Magnetic-field measurements 238 5.3.2 Proximity and angle detectors 241 5.3.3 Hall multipliers 244 References 245 6 Silicon Sensors for Chemical Signals 249 6.1 Introduction 249 6.2 Basic physical principles 252 6.2.1 Chemo-resistors and chemo-capacitors 252 6.2.2 Chemdiodes 256 6.2.3 MOSFET-based chemical sensors 259
x Contents 6.2.4 Humidity sensors 271 6.2.5 Integrated oxygen sensors 278 6.3 Applications 280 6.3.1 Biosensors 281 6.3.2 Silicon-wafer gas Chromatograph 283 References 284 7 Sensor Technology 287 7.1 Silicon-planar technology 287 7.1.1 Introduction 287 7.1.2 Device technologies 289 7.1.3 Basic silicon planar processing steps 292 7.1.4 Special requirements for silicon-sensor processing 306 7.2 Compatible technologies 311 7.2.1 Thin-film deposition 311 7.2.2 ZnO thin-film deposition 313 7.2.3 Thick-film deposition 314 7.2.4 Magnetic-film deposition 315 7.3 Micromachining technologies 316 7.3.1 Introduction 316 7.3.2 Etching solutions and gases 316 7.3.3 Etching procedures and techniques 318 7.3.4 Micromachined structures 320 7.3.5 Devices fabricated with micromachining technologies 322 References 322 8 Sensor Interfaces, Smart Sensors and Bus Systems 331 8.1 Introduction 331 8.2 Signal conditioning 334 8.2.1 Noise 334 8.2.2 Offset 336 8.2.3 Cross-sensitivities 339 8.2.4 Bridge circuits 342 8.3 Signal converters 343 8.3.1 Amplitude analog signals 344 8.3.2 Time analog signals 344 8.3.3 Binary encoded signals 352
Contents xi 8.4 Digital signal processing 352 8.4.1 Advantages and disadvantages of integrated smart sensors 353 8.4.2 Circuit partitioning 355 8.4.3 Multi-sensor arrays 355 8.4.4 Bus systems 358 References 359 Appendices 361 A Physical and chemical effects in solid-state materials 361 В Sensor characteristics 365 Subject Index 369