handbook of modern sensors

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18 Sensor Materials and Technologies Methods of sensor fabrication are numerous and specific for each particular design. They comprise processing of semiconductors, optical components, metals, ceramics, and plastics. Here, we briefly describe some materials and the most often used techniques. 18.1 Materials 18.1.1 Silicon as a Sensing Material Silicon is present in the Sun and stars and is a principle component of a class of meteorites known as aerolites. Silicon is the second most abundant material on Earth, being exceeded only by oxygen; it makes up to 25.7% of the Earth’s crust, by weight. Silicon is not found free in nature, but occurs chiefly as the oxide and as silicates. Some oxides are sand, quartz, rock crystal, amethyst, clay, mica, and so forth. Silicon is prepared by heating silica and carbon in an electric furnace, using carbon electrodes. There are also several other methods for preparing the element. Crystalline silicon has a metallic luster and grayish color 1 . The Czochralski process is commonly used to produce single crystals of silicon used for the solid-state semiconductors and micromachined sensors. Silicon is a relatively inert element, but it is attacked by halogens and dilute alkali. Most acids, except hydrofluoric, do not affect it. Elemental silicon transmits infrared radiation and is commonly used as windows in far-infrared sensors. Silicon’s atomic weight is 28.0855, and its atomic number is 14. Its melting point is 1410 ◦ C and the boiling point is 23 ◦ C. The specific gravity at 25 ◦ C is 2.33 and its valence is 4. Properties of silicon are well studied and its applications to sensor designs have been extensively researched worldwide. The material is inexpensive and can now be produced and processed controllably to unparalleled standards of purity and perfection. Silicon exhibits a number of physical effects which are quite useful for sensor applications (see Table 18.1). 1 Silicon should not be confused with silicone, which is made by hydrolyzing silicon organic chloride, such as dimethyl silicon chloride. Silicones are used as insulators, lubricants, and for the production of silicone rubber.
534 18 Sensor Materials and Technologies Table 18.1. Stimuli of Silicon-Based Sensors Stimuli Effects Radiant Photovoltaic effect, photoelectric effect, photoconductivity, photo-magneto-electric effect Mechanical Piezoresistivity, lateral photoelectric effect, lateral photovoltaic effect Thermal Seebeck effect, temperature dependence of conductivity and junction, Nernst effect Magnetic Hall effect, magnetoresistance, Suhi effect Chemical Ion sensitivity Source: Ref. [1]. Unfortunately, silicon does not posses the piezoelectric effect. Most effects of silicon such as the Hall effect, the Seebeck effect, piezoresistance, and so forth are quite large; however, a major problem with silicon is that its responses to many stimuli show substantial temperature sensitivity. For instance: strain, light, and magnetic field responses are temperature dependent. When silicon does not display the proper effect, it is possible to deposit layers of materials with the desired sensitivity on top of the silicon substrate. For instance, sputtering of ZnO thin films is used to form piezoelectric transducers which are useful for the fabrication of SAW (surface acoustic waves) devices and accelerometers. In the later case, the strain at the support end of the an etched micromechanical cantilever is detected by a ZnO overlay. Silicon itself exhibits very useful mechanical properties which currently are widely used to fabricate such devices as pressure transducers, temperature sensors, force and tactile detectors by employing the MEMS technologies. Thin film and photolithographic fabrication procedures make it possible to realize a great variety of extremely small, high-precision mechanical structures using the same processes that have been developed for electronic circuits. High-volume batch-fabrication techniques can be utilized in the manufacture of complex, miniaturized mechanical components which may not be possible with other methods. Table A.14 in the Appendix presents a comparative list of mechanical characteristics of silicon and other popular crystalline materials. Although single-crystal silicon (SCS) is a brittle material, yielding catastrophically (not unlike most oxide-based glasses) rather than deforming plastically (like most metals), it certainly is not as fragile as is often believed. Young’s modulus of silicon (1.9 × 10 12 dyn/cm or 27 × 10 6 psi), for example, has a value of that approaching stainless steel and is well above that of quartz and of most glasses. The misconception that silicon is extremely fragile is based on the fact that it is often obtained in thin slices (5–13-cm-diameter wafers) which are only 250–500 µm thick. Even stainless steel at these dimensions is very easy to deform inelastically. As mentioned earlier, many of the structural and mechanical disadvantages of SCS can be alleviated by the deposition of thin films. Sputtered quartz, for example, is utilized routinely by industry to passivate integrated circuit chips against airborne impurities and mild atmospheric corrosion effects. Another example is a deposition of silicon nitrate (TableA.14) which has a hardness second only to diamond.Anisotropic
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HANDBOOK OF MODERN SENSORS PHYSICS,
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HANDBOOK OF MODERN SENSORS PHYSICS,
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To the memory of my father
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Preface Seven years have passed sin
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Contents Preface ..................
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Contents XI 4.5 Lenses ............
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Contents XIII 7.7.1 Micropower Impu
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Contents XV 15 Radiation Detectors
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Contents XVII Table A.9 Physical Pr
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1 Data Acquisition “It’s as lar
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1.1 Sensors, Signals, and Systems 3
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1.1 Sensors, Signals, and Systems 5
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1.2 Sensor Classification 7 oscillo
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1.3 Units of Measurements 9 Table 1
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Table 1.7. SI Basic Units Reference
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2 Sensor Characteristics “O, what
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2.2 Span (Full-Scale Input) 15 Fig.
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2.4 Accuracy 17 2.4 Accuracy Avery
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2.6 Calibration Error 19 To compute
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2.8 Nonlinearity 21 Fig. 2.4. Trans
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2.12 Resolution 23 (A) (B) Fig. 2.7
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2.16 Dynamic Characteristics 25 2.1
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2.16 Dynamic Characteristics 27 Sub
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2.17 Environmental Factors 29 2.17
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2.18 Reliability 31 guide. For inst
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2.20 Uncertainty 33 • Thermal sho
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Table 2.2. Uncertainty Budget for T
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3 Physical Principles of Sensing
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3.1 Electric Charges, Fields, and P
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3.2 Capacitance 45 The capacitor ma
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3.2 Capacitance 47 (A) (B) Fig. 3.6
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3.2 Capacitance 49 h 0 (A) (B) Fig.
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3.3 Magnetism 51 N S S N (A) (B) Fi
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3.3 Magnetism 53 electric charge ca
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3.3 Magnetism 55 3.3.3 Toroid Anoth
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3.4 Induction 57 • Changing the o
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3.5 Resistance 59 Fig. 3.16. Voltag
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3.5 Resistance 61 For pure resistan
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3.5 Resistance 63 resistor) and the
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3.5 Resistance 65 Fig. 3.19. Strain
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3.6 Piezoelectric Effect 67 (A) (B)
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3.6 Piezoelectric Effect 69 Another
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3.6 Piezoelectric Effect 71 Another
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3.6 Piezoelectric Effect 73 absorpt
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3.6 Piezoelectric Effect 75 that en
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3.7 Pyroelectric Effect 77 circuit
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3.7 Pyroelectric Effect 79 through
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3.7 Pyroelectric Effect 81 Fig. 3.2
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3.8 Hall Effect 83 Fig. 3.30. Hall
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Table 3.2. Typical Characteristics
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3.9 Seebeck and Peltier Effects 87
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3.10 Sound Waves 93 If we consider
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3.11 Temperature and Thermal Proper
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3.11 Temperature and Thermal Proper
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3.12 Heat Transfer 99 to about 35
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3.12 Heat Transfer 101 (A) (B) Fig.
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3.12 Heat Transfer 103 Fig. 3.41. S
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3.12 Heat Transfer 105 Fig. 3.42. S
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3.12 Heat Transfer 107 Fig. 3.44. W
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3.12 Heat Transfer 109 (A) (B) Fig.
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3.13 Light 111 [38] whose emissivit
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3.14 Dynamic Models of Sensor Eleme
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References 119 specified and three
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References 121 34. Thomson, W. On t
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124 4 Optical Components of Sensors
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150 Optical Components of Sensors 1
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5 Interface Electronic Circuits 5.1
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5.1 Input Characteristics of Interf
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5.1 Input Characteristics of Interf
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5.2 Amplifiers 157 (A) (B) Fig. 5.5
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5.2 Amplifiers 159 Fig. 5.7. Voltag
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5.2 Amplifiers 161 (A) (B) Fig. 5.9
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5.2 Amplifiers 163 Fig. 5.11. An eq
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5.3 Excitation Circuits 165 5.3.1 C
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5.3 Excitation Circuits 167 (A) (B)
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5.3 Excitation Circuits 169 Fig. 5.
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5.3 Excitation Circuits 171 atures.
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5.3 Excitation Circuits 173 (A) (B)
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5.4 Analog-to-Digital Converters 17
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Table 5.2. Binary Bit Weights and R
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5.5 Direct Digitization and Process
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5.5 Direct Digitization and Process
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5.6 Ratiometric Circuits 191 (A) (B
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5.7 Bridge Circuits 193 determine t
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5.7 Bridge Circuits 195 Fig. 5.38.
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5.7 Bridge Circuits 197 Fig. 5.39.
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It can be solved for the temperatur
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5.8 Data Transmission 201 (A) (B) (
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5.8 Data Transmission 203 wire meth
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5.9 Noise in Sensors and Circuits 2
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5.10 Batteries for Low Power Sensor
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References 225 nickel-metal hydrate
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6 Occupancy and Motion Detectors Se
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6.2 Microwave Motion Detectors 229
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6.2 Microwave Motion Detectors 231
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6.3 Capacitive Occupancy Detectors
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6.3 Capacitive Occupancy Detectors
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6.4 Triboelectric Detectors 237 6.4
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6.5 Optoelectronic Motion Detectors
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and the facet pitch is 6.5 Optoelec
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References 251 Fig. 6.17. Calculate
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7 Position, Displacement, and Level
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7.1 Potentiometric Sensors 255 (A)
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7.2 Gravitational Sensors 257 (A) (
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7.3 Capacitive Sensors 259 (A) (B)
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7.3 Capacitive Sensors 261 Fig. 7.7
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7.4 Inductive and Magnetic Sensors
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7.5 Optical Sensors 275 Therefore,
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7.5 Optical Sensors 277 (A) (B) (C)
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7.5 Optical Sensors 279 (A) (B) Fig
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7.5 Optical Sensors 281 Fig. 7.32.
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7.5 Optical Sensors 283 (A) (B) (C)
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7.5 Optical Sensors 285 is proporti
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7.6 Ultrasonic Sensors 287 (A) (B)
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7.7 Radar Sensors 289 (A) (B) Fig.
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7.7 Radar Sensors 291 (A) (B) Fig.
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7.8 Thickness and Level Sensors 293
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References 299 8. Dakin, J. P., Wad
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8 Velocity and Acceleration Acceler
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8.1 Accelerometer Characteristics 3
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8.2 Capacitive Accelerometers 305 a
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8.3 Piezoresistive Accelerometers 3
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8.5 Thermal Accelerometers 309 Fig.
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8.5 Thermal Accelerometers 311 forc
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8.6 Gyroscopes 313 8.6 Gyroscopes N
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8.6 Gyroscopes 315 (A) (B) Fig. 8.1
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8.6 Gyroscopes 317 Products Company
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8.7 Piezoelectric Cables 319 (A) (B
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References 321 (A) (B) Fig. 8.16.Ap
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9 Force, Strain, and Tactile Sensor
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9.1 Strain Gauges 325 (A) (B) Fig.
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9.2 Tactile Sensors 327 9.2 Tactile
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9.2 Tactile Sensors 329 (A) (B) Fig
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9.2 Tactile Sensors 331 Fig. 9.7. P
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9.2 Tactile Sensors 333 Fig. 9.9. T
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9.3 Piezoelectric Force Sensors 335
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References 337 14. Karrer, E. and L
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10 Pressure Sensors “To learn som
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10.3 Mercury Pressure Sensor 341 1
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10.4 Bellows, Membranes, and Thin P
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10.5 Piezoresistive Sensors 345 Fig
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10.5 Piezoresistive Sensors 347 bri
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10.6 Capacitive Sensors 349 (A) (B)
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10.7 VRP Sensors 351 (A) (B) Fig. 1
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10.8 Optoelectronic Sensors 353 Fig
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10.9 Vacuum Sensors 355 (A) (B) Fig
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References 357 (A) (B) (C) Fig. 10.
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11 Flow Sensors It’s a simple tas
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11.2 Pressure Gradient Technique 36
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11.3 Thermal Transport Sensors 363
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11.3 Thermal Transport Sensors 365
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11.4 Ultrasonic Sensors 367 A senso
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11.4 Ultrasonic Sensors 369 Fig. 11
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induced in the liquid. The magnitud
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11.6 Microflow Sensors 373 (A) (B)
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11.7 Breeze Sensor 375 (A) (B) Fig.
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11.9 Drag Force Flow Sensors 377 Wi
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References 379 11. Philip-Chandy, R
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12 Acoustic Sensors “Your ears wi
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12.3 Fiber-Optic Microphone 383 (A)
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12.4 Piezoelectric Microphones 385
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12.5 Electret Microphones 387 Fig.
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12.6 Solid-State Acoustic Detectors
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References 391 References 1. Hohm,
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13 Humidity and Moisture Sensors 13
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13.1 Concept of Humidity 395 Table
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13.2 Capacitive Sensors 397 Fig. 13
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13.3 Electrical Conductivity Sensor
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13.4 Thermal Conductivity Sensor 40
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13.6 Oscillating Hygrometer 403 chi
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References 405 9. Jachowicz, R. S.
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14 Light Detectors “There is noth
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14.1 Introduction 409 Table 14.1. B
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14.2 Photodiodes 411 Maximum revers
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14.2 Photodiodes 413 when i = 0), w
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14.2 Photodiodes 415 (A) (B) (C) Fi
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14.2 Photodiodes 417 Fig. 14.9. Res
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14.3 Phototransistor 419 Fig. 14.12
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14.4 Photoresistors 421 (A) (B) Fig
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14.5 Cooled Detectors 423 (A) (B) F
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14.6 Thermal Detectors 425 Table 14
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14.6 Thermal Detectors 427 Fig. 14.
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Table 14.3. Typical Specifications
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14.6 Thermal Detectors 431 A dual e
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14.6 Thermal Detectors 433 Fig. 14.
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14.6 Thermal Detectors 435 (A) (B)
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14.6 Thermal Detectors 437 Section
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14.7 Gas Flame Detectors 439 P = V
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References 441 housing assures wide
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15 Radiation Detectors Figure 3.41
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15.1 Scintillating Detectors 445 Fi
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15.2 Ionization Detectors 447 emitt
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15.2 Ionization Detectors 449 Fig.
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15.2 Ionization Detectors 451 parti
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15.2 Ionization Detectors 453 There
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References 455 the pure intrinsic t
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16 Temperature Sensors When a scien
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16 Temperature Sensors 459 from whi
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16.1 Thermoresistive Sensors 461 2.
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16.1 Thermoresistive Sensors 463 Ta
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16.1 Thermoresistive Sensors 465 Fi
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16.1 Thermoresistive Sensors 467 pr
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16.1 Thermoresistive Sensors 475 (m
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16.2 Thermoelectric Contact Sensors
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Page 518 and 519: 17 Chemical Sensors 1 Chemical sens
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Page 536 and 537: 17.5 Complex Sensors 517 frequency
Page 538 and 539: Table 17.1. SAW Chemical Sensors 17
Page 540 and 541: 17.6 Chemical Sensors Versus Instru
Page 550 and 551: References 531 13. LaCourse, W.R. P
Page 554 and 555: 18.1 Materials 535 etching is a key
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Page 558 and 559: 18.1 Materials 539 The following is
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Page 562 and 563: 18.2 Surface Processing 543 sensor
Page 564 and 565: 18.2 Surface Processing 545 On a co
Page 566 and 567: 18.3 Nano-Technology 547 6000-Å la
Page 568 and 569: 18.3 Nano-Technology 549 exposed to
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Page 572 and 573: 18.3 Nano-Technology 553 (A) (B) Fi
Page 574 and 575: References 555 Fig. 18.17. Bonding
Page 576 and 577: Appendix Table A.1. Chemical Symbol
Page 578 and 579: Table A.4. SI Conversion Multiples
Page 580 and 581: Table A.4 Continued Light cd/in. 2
Page 582 and 583: Table A.4 Continued Cup 2.36588 ×
Page 584 and 585: Appendix 565 Table A.7. Some Materi
Page 586 and 587: Appendix 567 Table A.11. Thermoelec
Page 588 and 589: Table A.14. Mechanical Properties o
Page 590 and 591: Appendix 571 Table A.18. Typical Em
Page 592 and 593: Table A.20. Characteristics of C-Zn
Page 594 and 595: Table A.23 Continued Manufacturer P
Page 596 and 597: Table A.25. Properties of Glasses S
Page 598 and 599: Index α-particles, 443 A/D, 175, 1
Page 600 and 601: Index 581 Coulomb’s law, 40 cross
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Index 583 H 2 O, 108 Hall, 82 Hall
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Index 585 occupancy sensors, 227 od
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Index 587 SAW, 75, 388, 404, 496, 5
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Index 589 velocity sensor, 302 vert
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