Advanced RF MEMS CAMBRIDGE UNIVERSITY PRESS. Edited by STEPAN LUCYSZYN. Imperial College London

Transcription

1 Advanced RF MEMS Edited by STEPAN LUCYSZYN Imperial College London n CAMBRIDGE UNIVERSITY PRESS

2 Contents List of contributors Preface List of abbreviations page xiv xvii xx Introduction Introduction Defining terms Enabling technology roadmap Fabrication technologies Electromechanical actuation Generic RF MEMS components Switches Variable capacitors Antennas Circuits and subsystems Conclusions 18 References 19 Electromechanical modelling of electrostatic actuators Introduction Energy methods and the equilibrium/momentum equation Static equilibrium and stability Actuators with one degree of freedom Actuators with several degrees of freedom Distributed systems Numerical methods Dynamic response of electrostatic actuators Dynamic pull-in of a one-dof system Dynamic pull-in of the clamped-clamped beam actuator Switching time of electrostatic actuators Conclusions 38 References 38

3 viii Contents Switches and their fabrication technologies ; Introduction Substrate materials and fabrication technologies Actuation principles Capacitive switches with electrostatic actuation Ohmic switches with electrostatic actuation Switches with piezoelectric actuation Switches with electrothermal and electromagnetic actuation Switch building blocks Metallisation Capacitive switch dielectrics Ohmic switch contacts Sacrificial layers Moveable structures References Niche switch technologies Introduction Latching switches Magnetically actuated bistable switches Electrothermally actuated bistable switches Electrostatic bistable switch Mechanically latching switches Multiway switches SPDT switches SP4T switches SP6T switches SP8T switches SP9T switches and SP48T modules DPDT switches Switch matrices High-power switches Additional hold electrodes Beam cross section Switching arrays Contact force Materials Non-beam architectures Unconventional 3D power switch RF power measurements References

4 Contents Reliability Introduction Terminology Failure- and application-driven reliability methodology Failure mechanisms in RF MEMS Creep/stress relaxation Temperature- and stress-induced plastic deformation Temperature-induced elastic deformation Fatigue Suction Introduction Microwelding Dielectric charging Electromigration Self-actuation Lorentz forces Self-Biasing due to RF power Self-actuation due to drop or shock Fly-catching effect Outgassing and adsorption Mechanical and acoustic coupling Conclusions Acknowledgments 132 References 133 Dielectric Charging Introduction Dielectric charging in MEMS Capacitance-voltage characteristic Switch-ON and switch-off capacitance transients Shift in pull-in and pull-out voltages Lifetime tests, material and environmental effects Dielectric charging in MIM capacitors Kelvin probe force microscopy Dielectric polarisation Dipolar polarisation Space-charge polarisation Interfacial polarisation Charge injection mechanisms Trap-assisted tunnelling Poole-Frenkel process Schottky injection Conclusions 181 References 182

5 x Contents Stress and thermal characterisation Introduction Theoretical background Stress tensor Strain tensor Thermal transfer Origin of stress and temperature Stress and temperature effects Temperature dependence of resonance frequency in BAW resonators Thermoelastic deformations in tuneable capacitors Stress and temperature measurement X-ray diffraction for stress determination Infrared thermography for temperature determination Other methods Conclusions 203 References 203 High-power handling Introduction RF power handling related phenomena Electromigration Self-biasing and RF latching Electromagnetic-induced thermoelectromechanical effects Experimental investigation of self-heating due to RF power Numerical investigation of self-heating due to RF power Overview of power handling RF MEMS components Capacitive switches and varactors Ohmic contact switches Conclusions 227 References 229 Packaging Introduction Zero-level packaging Design considerations and performance Technologies and materials for the zero-level package Thin-film encapsulation Chip capping Package integration Multiple MEMS in a single package 258

6 Contents xi Integrated RF MEMS System-on-chip versus system-in-package RF MEMS planar system-in-package RF MEMS 3D system-in-package Conclusions 264 References Impedance tuners and tuneable filters Introduction Impedance tuners Stub-tuner design Stub topologies Tuning methods Stub-based impedance tuners and matching networks Distributed impedance tuners and matching networks Slug tuners DMTL tuners DGS-based tuners Other switchable tuner architectures Discussion on impedance tuners and matching networks Tuneable filters Tuning technologies for filters RF MEMS-based filters Reconfigurable filter design basics Analogue versus digital tuning Discussion on future challenges for filter designers Conclusions 301 References Phase shifters and tuneable delay lines Introduction Definition and applications Technologies Specifications Reflection-type phase shifters Theoretical analysis Capacitive load Series LC load Directional couplers Analogue implementations Digital implementations Phase variation and bandwidth State of the art Phase shifters based on LC networks 317

7 xii Contents Low/high-pass Networks All-pass networks State of the art Loaded-line phase shifters Theoretical analysis Practical implementation and state of the art Switched delay-line phase shifters Principle and design issues State of the art Distributed loaded-line phase shifters Theoretical analysis Practical implementation State of the art General issues Power handling Noise and linearity Conclusions 336 References Reconfigurable architectures Introduction Reconfigurable radios General architectures Handset front-ends Base stations Multiband and tracking receivers Reconfigurable antennas Beam-steering antennas Phased-array antennas Reflectarray antennas Lenses, grids and frequency-selective surfaces Switched-diversity antenna arrays Handset antennas Measurement applications Multifunctional RFOW probes Conclusions 355 References Industry roadmap for RF MEMS Introduction Roadmap of RF MEMS components RF MEMS switches Current state of the art and potential improvements RF MEMS switches versus alternative technologies 361

8 Contents xiii Switch applications roadmap Tuneable capacitors Current state of the art and potential for improvements Alternative technologies Capacitor applications roadmap Emerging RF MEMS and RF NEMS components Tuneable inductors CNT-based RF NEMS Applications roadmap RF MEMS for mobile and wireless systems Mobile handsets Base stations Wireless interconnections RF MEMS for road transport applications Automotive radar Roofantennas RF MEMS for aeronautics RF MEMS for satellites Potential applications of RF MEMS in satellites Roadmap ofrf MEMS for satellites Implementation of the roadmap Modelling and design Materials and processes Heterogeneous integration, assembly and packaging Testing, characterisation and reliability Conclusions 401 References 402 Author biographies 404 Index 409