Table Of ContentHandbook of Humidity Measurement
Methods, Materials and Technologies
Volume 2: Electronic and Electrical Humidity Sensors
Handbook of Humidity Measurement: Methods, Materials
and Technologies, 3-Volume Set
(ISBN: 978-1-138-29787-6)
Handbook of Humidity Measurement,
Volume 1: Spectroscopic Methods of Humidity Measurement
(ISBN: 978-1-138-30021-7)
Handbook of Humidity Measurement,
Volume 2: Electronic and Electrical Humidity Sensors
(ISBN: 978-1-138-30022-4)
Handbook of Humidity Measurement,
Volume 3: Sensing Materials and Technologies
(ISBN: 978-1-138-48287-6)
Handbook of Humidity Measurement
Methods, Materials and Technologies
Volume 2: Electronic and Electrical Humidity Sensors
Ghenadii Korotcenkov
CRC Press
Taylor & Francis Group
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Contents
Preface .....................................................................................................................................................................xiii
Acknowledgments .....................................................................................................................................................xv
Author .....................................................................................................................................................................xvii
Section i introduction in Humidity Sensors
Chapter 1 Introduction to Electronic and Electrical Humidity Sensors ...............................................................3
1.1 Introduction ..............................................................................................................................3
1.2 Classification of Humidity Sensors ..........................................................................................5
1.3 Materials Acceptable for Application in Humidity Sensors .....................................................7
1.4 Requirements for Humidity Sensors ......................................................................................10
1.5 Purpose and Content of Book ................................................................................................11
References ..........................................................................................................................................12
Section ii conventional Methods and Brief History
of Humidity Measurements
Chapter 2 Gravimetric Method of Humidity Measurement ...............................................................................17
2.1 History of Gravimetric-Based Hygrometers ..........................................................................17
2.2 Gravimetric Measurement of Air Humidity...........................................................................18
References ..........................................................................................................................................21
Chapter 3 Mechanical (Hair) Hygrometer ..........................................................................................................23
3.1 History of Hair Hygrometers .................................................................................................23
3.2 Features of Humidity Control Using Hair Hygrometers ........................................................25
3.3 Other Types of Mechanical Hygrometers ..............................................................................26
3.4 Hygrographs and Hygrothermographs ...................................................................................27
3.5 Electronic Expansion Hygrometer .........................................................................................28
References ..........................................................................................................................................28
Chapter 4 Psychrometer......................................................................................................................................31
4.1 History ....................................................................................................................................31
4.2 Principles of Operation ..........................................................................................................31
4.3 Realization .............................................................................................................................33
4.4 Accuracy of Measurements ....................................................................................................36
4.5 Advantages and Limitations ...................................................................................................38
References ..........................................................................................................................................40
Chapter 5 Chilled-Mirror Hygrometer or Mirror-Based Dew-Point Sensors .....................................................41
5.1 Condensation Methods of Humidity Measurement ................................................................41
5.2 Chilled-Mirror Hygrometers ..................................................................................................42
v
vi Contents
5.3 Surface Conductive Dew-Point Hygrometer ..........................................................................46
5.4 Dew-Point Hygrometers and Their Performances .................................................................47
References ..........................................................................................................................................48
Chapter 6 Heated Salt-Solution Method for Humidity Measurement ................................................................51
6.1 The Dunmore Cell..................................................................................................................51
6.2 Limitations of LiCl-Based Humidity Sensors ........................................................................52
6.3 Planar LiCl-Based Humidity Sensors ....................................................................................53
References ..........................................................................................................................................55
Chapter 7 Electrolytic or Coulometric Hygrometers ..........................................................................................57
7.1 P O -Based Coulometric Hygrometers ..................................................................................57
2 5
7.1.1 Principles of Operation ............................................................................................57
7.1.2 Sensor Configuration ...............................................................................................57
7.1.3 Advantages and Limitations.....................................................................................58
7.1.4 Modern P O -Based Humidity Sensors ...................................................................61
2 5
7.2 Pope Cell ................................................................................................................................62
7.2.1 Advantages and Limitations of Pope Cell ................................................................63
7.3 Other Possible Coulometric Methods of Humidity Measurement .........................................63
References ..........................................................................................................................................63
Chapter 8 Humidity Measurement Based on Karl Fischer Titration ..................................................................65
8.1 KF Titration ............................................................................................................................65
8.2 Principles of KF Titration Method .........................................................................................65
8.3 Advantages and Limitations ...................................................................................................67
References ..........................................................................................................................................69
Chapter 9 Other Conventional Methods of Humidity Measurement ..................................................................71
9.1 Chemical Method ...................................................................................................................71
9.1.1 Calcium Carbide Method .........................................................................................71
9.2 Constant-Pressure Hygrometer ...............................................................................................71
9.3 Constant-Volume Hygrometer ................................................................................................71
9.4 Pneumatic Bridge Method of Humidity Measurement ..........................................................72
9.5 Diffusion Hygrometer ............................................................................................................72
9.6 Cloud or Fog Chamber Hygrometer .......................................................................................73
9.7 Mass Spectrometric Measurement of Air Humidity ..............................................................73
References ..........................................................................................................................................74
Section iii electronic and electrical Humidity Sensors and Basic
Principles of their operation
Chapter 10 Capacitance-Based Humidity Sensors ...............................................................................................79
10.1 Basic Principles of Operation .................................................................................................79
10.1.1 Humidity Sensors of Permittivity-Type ....................................................................79
10.1.1.1 Parallel Plate Structure ............................................................................81
10.1.1.2 Planar Capacitive Sensors with IDE ........................................................83
10.1.2 Requirements for Materials Suitable for Use in Capacitive Humidity Sensors .......85
Contents vii
10.2 Polymer-Based Capacitance Humidity Sensors .....................................................................86
10.2.1 Mechanisms of Water Interaction with Polymers ....................................................86
10.2.2 Implementation of Polymer Humidity Sensors ........................................................87
10.3 Metal Oxide–Based Capacitive Humidity Sensors ................................................................93
10.3.1 Metal Oxides in Humidity Sensors ..........................................................................93
10.3.2 Mechanisms of Water Interaction with Metal Oxides .............................................94
10.3.3 Al O -Based Humidity Sensors ...............................................................................96
2 3
10.3.4 Other Metal Oxide-Based Humidity Sensors ........................................................100
10.4 Summary ..............................................................................................................................103
References ........................................................................................................................................105
Chapter 11 Resistive Humidity Sensors .............................................................................................................113
11.1 General Consideration ..........................................................................................................113
11.2 Polymer-Based Resistive Humidity Sensors ........................................................................114
11.2.1 Introduction ............................................................................................................114
11.2.2 Semiconductor or Conductive Polymers ................................................................115
11.2.3 Polymers Containing Inorganic Salts .....................................................................117
11.2.4 Polyelectrolyte-Based Humidity-Sensitive Materials .............................................119
11.2.5 Nanocomposite-Based Humidity Sensors ..............................................................126
11.2.6 Summary ................................................................................................................131
11.3 Metal Oxide–Based Resistive Humidity Sensors .................................................................133
11.3.1 Mechanisms of Conductivity in Metal Oxides in Humid Air ................................133
11.3.1.1 Grotthuss-Type Transport of Protons .....................................................133
11.3.1.2 Conductivity in Heated Semiconducting Metal Oxides ........................135
11.3.1.3 Conductivity in Metal Oxides Doped with Alkali Ions .........................135
11.3.2 Metal Oxides in Resistive Humidity Sensors .........................................................136
11.3.3 Examples of Realization ........................................................................................137
11.3.3.1 General Consideration ...........................................................................137
11.3.3.2 RT Humidity Sensors ............................................................................138
11.3.4 Mechanism of Sensor Response and the Role of Structural Factor in the
Sensor Performance ...............................................................................................142
11.3.5 The Role of Alkaline Ions in Sensing Effect Observed in Metal
Oxide-Based Humidity Sensors .............................................................................145
11.3.6 Heated Sensors with Semiconducting and Ionic Metal Oxides .............................148
11.3.7 Summary ................................................................................................................150
11.4 Other Materials Acceptable for Application in Resistive Humidity Sensors .......................150
References ........................................................................................................................................151
Chapter 12 Gravimetric Humidity Sensors ........................................................................................................161
12.1 Introduction ..........................................................................................................................161
12.2 QCM-Based Sensors ............................................................................................................162
12.2.1 General Consideration ............................................................................................162
12.2.2 FBAR Sensors ........................................................................................................164
12.2.3 SMR Structures ......................................................................................................166
12.3 Surface Acoustic Wave Sensors ...........................................................................................167
12.3.1 Propagation Modes of the Acoustic Wave .............................................................168
12.3.2 SAW Oscillator as Sensing Element ......................................................................170
12.4 Advantages and Shortcomings of Acoustic Mass-Sensitive Sensors ...................................171
viii Contents
12.5 Sensing Layers in Gravimetric Humidity Sensors ...............................................................173
12.5.1 General Requirements ............................................................................................173
12.5.2 Humidity-Sensitive Materials Used in Gravimetric Humidity Sensors .................175
12.5.2.1 Polymers ................................................................................................175
12.5.2.2 Metal Oxides .........................................................................................176
12.5.2.3 Other Materials ......................................................................................177
12.6 Acoustic Humidity Sensors’ Performance ...........................................................................177
12.6.1 QCM Humidity Sensors .........................................................................................177
12.6.1.1 Conventional QCM Humidity Sensors ..................................................177
12.6.1.2 FBAR Humidity Sensors .......................................................................181
12.6.2 SAW-Based Humidity Sensors ...............................................................................183
12.6.2.1 General Consideration ...........................................................................183
12.6.2.2 Polymer SAW-Based Humidity Sensors ................................................187
12.6.2.3 SAW Humidity Sensors Based on Inorganic Humidity-Sensitive
Materials ................................................................................................190
12.6.2.4 Stability of SAW Humidity Sensors ......................................................193
12.6.2.5 New Approaches to Development of SAW-Based Humidity
Sensors ...........................................................................................194
12.6.3 Dew-Point Hygrometers .........................................................................................194
12.7 Summary ..............................................................................................................................197
References ........................................................................................................................................199
Chapter 13 Cantilever- and Membrane-Based Humidity Sensors ......................................................................205
13.1 General Consideration ..........................................................................................................205
13.1.1 Membrane-Based Sensors ......................................................................................205
13.1.2 Microcantilevers.....................................................................................................205
13.2 Sorption-Induced Effects and Their Influence on Cantilever Operation ..............................207
13.2.1 Sorption Models .....................................................................................................207
13.2.2 Microcantilevers and Their Modes of Operation ...................................................209
13.2.2.1 Static Mode ............................................................................................209
13.2.2.2 Dynamic Mode ......................................................................................209
13.3 Microcantilever Deflection Detection Methods ...................................................................211
13.3.1 Optical Methods .....................................................................................................211
13.3.2 Capacitive Method .................................................................................................212
13.3.3 Piezoelectric Method .............................................................................................212
13.3.4 Interferometry Method ...........................................................................................212
13.3.5 Optical Diffraction Grating Method ......................................................................213
13.3.6 CCD Detection Method .........................................................................................213
13.3.7 Hard-Contact/Tunneling ........................................................................................213
13.3.8 Piezoresistive Method ............................................................................................213
13.4 Resonant Operating Mode ...................................................................................................215
13.4.1 Mechanical Properties of Microcantilevers ...........................................................215
13.4.2 Mass Resolution Limitations ..................................................................................216
13.5 Humidity-Sensitive Materials ...............................................................................................216
13.5.1 Polyimide ...............................................................................................................216
13.5.2 Other Humidity-Sensitive Polymers.......................................................................218
13.6 Humidity Sensor Implementation ........................................................................................218
13.6.1 Functionalization Methods .....................................................................................218
13.6.2 Capacitive Humidity Sensors .................................................................................221
Contents ix
13.6.3 Piezoresistive Humidity Sensors ............................................................................224
13.6.3.1 Piezoresistors .........................................................................................224
13.6.3.2 Sensor Performance ...............................................................................227
13.7 Microresonator-Based Humidity Sensors .............................................................................233
13.8 Summary ..............................................................................................................................235
References ........................................................................................................................................236
Chapter 14 Thermal Conductivity-Based Hygrometers .....................................................................................243
14.1 Principle of Operation ..........................................................................................................243
14.2 Approaches to the Design of Thermal Conductivity-Based Hygrometers ...........................244
14.3 Micromachined Humidity Sensors.......................................................................................247
14.4 Summary ..............................................................................................................................250
References ........................................................................................................................................251
Chapter 15 Field Ionization Humidity Sensors ..................................................................................................253
15.1 Principles of Operation: Corona Discharge..........................................................................253
15.2 Gas Ionization Sensors Based on 1D Structures ..................................................................253
15.3 Summary ..............................................................................................................................256
References ........................................................................................................................................256
Chapter 16 Humidity Sensors Based on Thin-Film and Field-Effect Transistors ..............................................257
16.1 Thin-Film and Field-Effect Transistors ................................................................................257
16.2 Humidity-Sensing Characteristics of Organic-Based Transistors ........................................259
16.2.1 TFT-Based Sensors ................................................................................................259
16.2.2 MISFET-Based Sensors .........................................................................................267
16.3 Other Materials in TFT and FET-Based Humidity Sensors ................................................267
16.3.1 MISFET-Based Sensors .........................................................................................268
16.3.2 GasFET or FET with Air Gap ...............................................................................269
16.3.3 TFT-Based Sensors ................................................................................................275
16.4 Summary ..............................................................................................................................277
References ........................................................................................................................................278
Chapter 17 Hetero-Junction-Based Humidity Sensors .......................................................................................283
17.1 Schottky Barrier-Based Humidity Sensors ..........................................................................283
17.1.1 Principles of Operation ..........................................................................................283
17.1.2 Sensor Performance ...............................................................................................283
17.2 p–n Hetero-Contact-Type Humidity Sensors .......................................................................286
17.3 Summary ..............................................................................................................................289
References ........................................................................................................................................289
Chapter 18 Kelvin Probe as a Humidity Sensor .................................................................................................291
18.1 Work Function ......................................................................................................................291
18.2 Kelvin Probe.........................................................................................................................291
18.3 Sensor Performance .............................................................................................................293
18.4 Summary ..............................................................................................................................296
References ........................................................................................................................................297
