List of contributors ....................................... xiv
Preface ................................................... xvii
List of abbreviations ....................................... xx
1 Introduction ................................................. 1
1.1 Introduction ............................................ 1
1.1.1 Defining terms ................................... 1
1.1.2 Enabling technology roadmap ...................... 2
1.2 Fabrication technologies ................................ 4
1.3 Electromechanical actuation ............................. 5
1.4 Generic RF MEMS components .............................. 8
1.4.1 Switches ......................................... 8
1.4.2 Variable capacitors ............................. 10
1.4.3 Antennas ........................................ 11
1.5 Circuits and subsystems ................................ 15
1.6 Conclusions ............................................ 18
References .................................................. 19
2 Electromechanical modelling of electrostatic actuators ...... 23
2.1 Introduction ........................................... 23
2.2 Energy methods and the equilibrium/momentum equation ... 24
2.3 Static equilibrium and stability ....................... 26
2.3.1 Actuators with one degree of freedom ............ 26
2.3.2 Actuators with several degrees of freedom ....... 27
2.3.3 Distributed systems ............................. 29
2.3.4 Numerical methods ............................... 30
2.4 Dynamic response of electrostatic actuators ............ 32
2.4.1 Dynamic pull-in of a one-DOF system ............. 32
2.4.2 Dynamic pull-in of the clamped-clamped beam
actuator ........................................ 35
2.4.3 Switching time of electrostatic actuators ....... 37
2.5 Conclusions ............................................ 38
References .................................................. 38
3 Switches and their fabrication technologies ................. 41
3.1 Introduction ........................................... 41
3.2 Substrate materials and fabrication technologies ....... 42
3.3 Actuation principles ................................... 43
3.3.1 Capacitive switches with electrostatic
actuation ....................................... 45
3.3.2 Ohmic switches with electrostatic actuation ..... 51
3.3.3 Switches with piezoelectric actuation ........... 55
3.3.4 Switches with electrothermal and
electromagnetic actuation ....................... 56
3.4 Switch building blocks ................................. 58
3.4.1 Metallisation ................................... 58
3.4.2 Capacitive switch dielectrics ................... 60
3.4.3 Ohmic switch contacts ........................... 61
3.4.4 Sacrificial layers .............................. 63
3.4.5 Moveable structures ............................. 65
References .................................................. 67
4 Niche switch technologies ................................... 73
4.1 Introduction ........................................... 73
4.2 Latching switches ...................................... 73
4.2.1 Magnetically actuated bistable switches ......... 74
4.2.2 Electrothermally actuated bistable switches ..... 75
4.2.3 Electrostatic bistable switch ................... 77
4.2.4 Mechanically latching switches .................. 79
4.3 Multiway switches ...................................... 83
4.3.1 SPDT switches ................................... 84
4.3.2 SP4T switches ................................... 88
4.3.3 SP6T switches ................................... 88
4.3.4 SP8T switches ................................... 88
4.3.5 SP9T switches and SP48T modules ................. 90
4.3.6 DPDT switches ................................... 92
4.3.7 Switch matrices ................................. 94
4.4 High-power switches .................................... 95
4.4.1 Additional hold electrodes ...................... 95
4.4.2 Beam cross section .............................. 95
4.4.3 Switching arrays ................................ 96
4.4.4 Contact force ................................... 97
4.4.5 Materials ....................................... 98
4.4.6 Non-beam architectures .......................... 98
4.4.7 Unconventional 3D power switch ................. 100
4.4.8 RF power measurements .......................... 102
References ................................................. 105
5 Reliability ................................................ 109
5.1 Introduction .......................................... 109
5.1.1 Terminology .................................... 110
5.1.2 Failure- and application-driven reliability
methodology .................................... 111
5.2 Failure mechanisms in RF MEMS ......................... 112
5.2.1 Creep/stress relaxation ........................ 112
5.2.2 Temperature- and stress-induced plastic
deformation .................................... 115
5.2.3 Temperature-induced elastic deformation ........ 117
5.2.4 Fatigue ........................................ 119
5.2.5 Stiction ....................................... 120
5.2.6 Electromigration ............................... 127
5.2.7 Self-actuation ................................. 127
5.2.8 Fly-catching effect ............................ 130
5.2.9 Outgassing and adsorption ...................... 130
5.2.10 Mechanical and acoustic coupling ............... 132
5.3 Conclusions ........................................... 132
5.4 Acknowledgments ....................................... 132
References ................................................. 133
6 Dielectric Charging ........................................ 140
6.1 Introduction .......................................... 140
6.2 Dielectric charging in MEMS ........................... 140
6.2.1 Capacitance-voltage characteristic ............. 141
6.2.2 Switch-ON and switch-OFF capacitance
transients ..................................... 146
6.2.3 Shift in pull-in and pull-out voltages ......... 151
6.2.4 Lifetime tests, material and environmental
effects ........................................ 159
6.2.5 Dielectric charging in MIM capacitors .......... 163
6.2.6 Kelvin probe force microscopy .................. 169
6.3 Dielectric polarisation ............................... 172
6.3.1 Dipolar polarisation ........................... 174
6.3.2 Space-charge polarisation ...................... 176
6.3.3 Interfacial polarisation ....................... 177
6.4 Charge injection mechanisms ........................... 178
6.4.1 Trap-assisted tunnelling ....................... 179
6.4.2 Poole-Frenkel process .......................... 180
6.4.3 Schottky injection ............................. 181
6.5 Conclusions ........................................... 181
References ................................................. 182
7 Stress and thermal characterisation ........................ 188
7.1 Introduction .......................................... 188
7.2 Theoretical background ................................ 188
7.2.1 Stress tensor .................................. 188
7.2.2 Strain tensor .................................. 190
7.2.3 Thermal transfer ............................... 192
7.2.4 Origin of stress and temperature ............... 193
7.3 Stress and temperature effects ........................ 194
7.3.1 Temperature dependence of resonance frequency
in BAW resonators .............................. 194
7.3.2 Thermoelastic deformations in tuneable
capacitors ..................................... 196
7.4 Stress and temperature measurement .................... 197
7.4.1 X-ray diffraction for stress determination ..... 198
7.4.2 Infrared thermography for temperature
determination .................................. 200
7.4.3 Other methods .................................. 203
7.5 Conclusions ........................................... 203
References ................................................. 203
8 High-power handling ........................................ 205
8.1 Introduction .......................................... 205
8.2 RF power handling related phenomena ................... 206
8.2.1 Electromigration ............................... 206
8.2.2 Self-biasing and RF latching ................... 208
8.2.3 Electromagnetic-induced
thermoelectromechanical effects ................ 214
8.3 Overview of power handling RF MEMS components ......... 224
8.3.1 Capacitive switches and varactors .............. 224
8.3.2 Ohmic contact switches ......................... 226
8.4 Conclusions ........................................... 227
References ................................................. 229
9 Packaging .................................................. 232
9.1 Introduction .......................................... 232
9.2 Zero-level packaging .................................. 233
9.2.1 Design considerations and performance .......... 235
9.2.2 Technologies and materials for the zero-level
package ........................................ 248
9.3 Package integration ................................... 258
9.3.1 Multiple MEMS in a single package .............. 258
9.3.2 Integrated RF MEMS ............................. 259
9.4 Conclusions ............................................ 264
References ................................................. 264
10 Impedance tuners and tuneable filters ...................... 271
10.1 Introduction .......................................... 271
10.2 Impedance tuners ...................................... 272
10.2.1 Stub-tuner design .............................. 272
10.2.2 Stub-based impedance tuners and matching
networks ....................................... 276
10.2.3 Distributed impedance tuners and matching
networks ....................................... 280
10.2.4 Discussion on impedance tuners and matching
networks ....................................... 285
10.3 Tuneable filters ...................................... 285
10.3.1 Tuning technologies for filters ................ 285
10.3.2 RF MEMS-based filters .......................... 287
10.4 Conclusions ........................................... 301
References ................................................. 301
11 Phase shifters and tuneable delay lines .................... 307
11.1 Introduction .......................................... 307
11.1.1 Definition and applications .................... 307
11.1.2 Technologies ................................... 308
11.1.3 Specifications ................................. 309
11.2 Reflection-type phase shifters ........................ 310
11.2.1 Theoretical analysis ........................... 310
11.2.2 Directional couplers ........................... 314
11.2.3 Analogue implementations ....................... 315
11.2.4 Digital implementations ........................ 316
11.2.5 Phase variation and bandwidth .................. 316
11.2.6 State of the art ............................... 317
11.3 Phase shifters based on LC networks ................... 317
11.3.1 Low/high-pass Networks ......................... 318
11.3.2 All-pass networks .............................. 319
11.3.3 State of the art ............................... 322
11.4 Loaded-line phase shifters ............................ 323
11.4.1 Theoretical analysis ........................... 323
11.4.2 Practical implementation and state of the
art ............................................ 326
11.5 Switched delay-line phase shifters .................... 327
11.5.1 Principle and design issues .................... 327
11.5.2 State of the art ............................... 328
11.6 Distributed loaded-line phase shifters ................ 329
11.6.1 Theoretical analysis ........................... 329
11.6.2 Practical implementation ....................... 331
11.6.3 State of the art ............................... 333
11.7 General issues ........................................ 333
11.7.1 Power handling ................................. 333
11.7.2 Noise and linearity ............................ 335
11.8 Conclusions ........................................... 336
References ................................................. 337
12 Reconfigurable architectures ............................... 343
12.1 Introduction .......................................... 343
12.2 Reconfigurable radios ................................. 344
12.2.1 General architectures .......................... 344
12.2.2 Handset front-ends ............................. 344
12.2.3 Base stations .................................. 347
12.2.4 Multiband and tracking receivers ............... 348
12.3 Reconfigurable antennas ............................... 348
12.3.1 Beam-steering antennas ......................... 348
12.3.2 Handset antennas ............................... 352
12.4 Measurement applications .............................. 353
12.4.1 Multifunctional RFOW probes .................... 353
12.5 Conclusions ........................................... 355
References ................................................. 356
13 Industry roadmap for RF MEMS ............................... 359
13.1 Introduction .......................................... 359
13.2 Roadmap of RF MEMS components ......................... 360
13.2.1 RF MEMS switches ............................... 360
13.2.2 Tuneable capacitors ............................ 365
13.2.3 Emerging RF MEMS and RF NEMS components ........ 369
13.3 Applications roadmap .................................. 371
13.3.1 RF MEMS for mobile and wireless systems ........ 371
13.3.2 RF MEMS for road transport applications ........ 386
13.3.3 RF MEMS for aeronautics ........................ 393
13.3.4 RF MEMS for satellites ......................... 395
13.4 Implementation of the roadmap ......................... 398
13.4.1 Modelling and design ........................... 398
13.4.2 Materials and processes ........................ 400
13.4.3 Heterogeneous integration, assembly and
packaging ...................................... 400
13.4.4 Testing, characterisation and reliability ...... 400
13.5 Conclusions ........................................... 401
References ................................................. 402
Author biographies ......................................... 404
Index ...................................................... 409
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