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DECLARATION BY THE CANDIDATE
I declare that thesis entitled “A STUDY OF RADIO FREQUENCY MICRO-
ELECTRO MECHANICAL SYSTEMS” is my own work conducted under the
supervision of Dr. Raj Kishore Choudhary (Supervisor) at R. P. E. T. Group of
Institutions, Bastara, Karnal, approved by research Degree Committee. I have put in more
than 200 days of attendance with the supervisor at the centre.
I further declare that to the best of my knowledge the thesis does not contain any
part of any work which has been submitted for award of any degree either in this
University or any other university/ deemed university without proper citation.
Signature of Supervisor Signature of candidate
(with stamp)
Signature of the Head/Principal
(with stamp)
i
CERTIFICATE OF SUPERVISOR
This is to certify that work entitled “A STUDY OF RADIO FREQUENCY
MICRO-ELECTRO MECHANICAL SYSTEMS” is a piece of research work done by
Shri/ Smt. / Km. TEJINDER PAL SINGH under my supervision for the degree of
Doctor of Philosophy (Ph. D.) in PHYSICS of JJT University, Jhunjhunu, Rajasthan,
India that the candidate has put attendance of more than 200 days with me.
To the best of my knowledge and belief the thesis
I. Embodies the work of candidate himself / herself
II. Has duly been completed
III. Fulfills the requirement of ordinance related to Ph.D. degree of the University and
IV. Is up to the standard both in respect of content and language for being referred to
the examiner.
Signature of the Supervisor(with
stamp)
ii
ACKNOWLEDGEMENTS
Good luck is another name for tenacity of purpose. – Emerson
Eventually, this work reflects the combined efforts of many individuals over a
long period of time. I gratefully acknowledge my mentor and research advisor, Dr. R. K.
Choudhary. His support, knowledge, advice, patience and troubleshooting skills made my
research achievement possible.
My special thanks to Dr. D. D. Agrawal, Vice chanceller, J J T University,
Chudella, Jhunjhnu, Rajasthan; and to my Ph.D. co-ordinator, Dr. Satyavir for their help,
advice and patience.
I also would like to thank my friends and colleagues namely, Dr. Rajesh Saini,
Mr. Ravinder Madan, Mr. Surender Tanwar, Mr. Som Pal, and others. Their friendship
and support made my life more colorful and enjoyable. My colleagues provide their
invaluable contributions and encouragement. Without their continuous support, this work
would not have been possible.
My special gratitude is to Dr. Amit Goel, Dr. R.S.Chauhan, and Dr. Vinod Mehla
for their patience, their valuable suggestions, their encouragement and their serious
attitude towards research that has been a model for me.
Finally, I dedicate this work to my parents Smt. Bimla Devi and Sh. Dharam
Singh and to my brother Brijender Kahanwal. Their endless support and encouragement
made all of this possible. My father always wanted me to excel in my education and
achieve higher goals.
I express my deepest appreciation to my kids Mehak and Mayank because my
commitment to obtain this degree has been because of you and for you. But above all this
thesis is dedicated to my wife Usha for her infinite courage and for enduring all these
years with grace and patience. You always listened whenever I needed to vent,
encouraged me to keep trying, and provided excellent homemade goodies to enjoy while
working late at night.
iii
TABLE OF CONTENTS
Declaration by the Candidate ………………………………………………………… i
Certificate of Supervisor ……………………………………………………………... ii
Acknowledgements ………………………………………………………….…….... iii
Table of Contents ………………………………………………………….……....... iv
List of Figures ……………………………………………………………..…………. x
List of Tables …………………...……………………………………………….…… xv
Abstract ……………………………………………………………….…………….. xvi
CHAPTERS:
Chapter 1: INTRODUCTION 1
1.1 Motivation ..…………………………………………………....…….. 1
1.2 What is MEMS? .………………………………………...…………... 2
1.3 Classification of MEMS Technology? ……………………………… 3
1.4 What is RF-MEMS? ………………………………………………… 5
1.5 Classification of RF-MEMS ………………………………….……... 7
1.5.1 RF Intrinsic …..…………………………………….……...... 8
1.5.2 RF Extrinsic ….………………………………….…….....…. 8
1.5.3 RF Reactive …………………………………..…………..… 9
1.6 Design Methodology for RF-MEMS …….………………………..… 9
1.7 Miniaturization …….…………………………………….……...…… 11
1.8 Applications of RF-MEMS ………………………………………..... 14
1.8.1 RF-MEMS in Mobile Phones ………………………………. 17
1.9 Taxonomy of RF-MEMS Devices as per the Application Viewpoint.. 19
1.10 Summary …………………………………………………………….. 19
Chapter 2: LITERATURE REVIEW …………………………………………. 21
iv
2.1 Introduction ………………………………………………………….. 21
2.2 History of RF-MEMS ……………………………………………….. 22
2.3 RF-MEMS Switch …………………………………………………... 24
2.4 Tunable (Variable) Capacitors ………………………………………. 28
2.5 Film Bulk Acoustic Resonators (FBARs) …………………………... 31
2.6 High-Q Inductors ……………………………………………………. 34
2.7 Antenna ……………………………………………………………… 37
2.8 Phase Shifters ………………………………………………………... 40
2.9 Filters ………………………………………………………………... 42
2.10 Transmission Lines ………………………………………………….. 43
2.11 Summary …………………………………………………………….. 46
Chapter 3: MATERIALS AND FABRICATION TECHNOLOGY FOR RF-MEMS ……………………………………………………………….
47
3.1 Introduction ………………………………………………………….. 47
3.2 Materials used for MEMS Fabrication Process …………………....... 47
3.2.1 Single Crystal Silicon ………………………………………. 48
3.2.2 Gallium Arsenide …………………………………………... 50
3.2.3 Polycrystalline Silicon ……………………………………… 51
3.2.4 Silicon Dioxide ……………………………………………... 51
3.2.5 Silicon Carbide ……………………………………………... 52
3.2.6 Silicon Nitride ……………………………………………… 53
3.2.7 Other Materials ……………………………………………... 53
3.3 RF-MEMS Fabrication Techniques …………………………………. 55
3.3.1 Bulk Micromachining ……………………………………… 56
v
3.3.2 Surface Micromachining …………………………………… 58
3.3.3 Wafer-to-wafer Bonding …………………………………… 59
3.3.4 LIGA (High-Aspect-Ratio Micromachining ……………….. 60
3.3.5 Flip Chip Method …………………………………………... 62
3.4 Computer Aided Design …………………………………………….. 64
3.5 Summary …………………………………………………………….. 65
Chapter 4: RADIO FREQUENCY MICRO-ELECTRO-MECHANICAL SYSTEMS (RF-MEMS): A TECHNOLOGICAL ASPECT ……
67
4.1 Introduction ………………………………………………..………… 67
4.2 Comparison of Various Technologies …………………………….… 68
4.3 RF-MEMS Fabrication Technologies Outline …………..…………... 70
4.4 Actuation Mechanisms ………………….……………..……………. 71
4.5 RF-MEMS components and Circuits ………………………………... 73
4.5.1 Case Study of Switches ……….…………………………..... 74
4.5.2 Case Study of Variable Capacitors …………………………. 78
4.5.3 Case Study of Mechanical Resonators And Filters ………... 79
4.6 Promises and Challenges of RF-MEMS Technology …………......… 82
4.7 Summary ……..………...…………………………………...……….. 84
Chapter 5: PACKAGING ..……………………………………………………... 85
5.1 Introduction ……………………………...……………..……………. 85
5.2 Die Attach Materials ………………………...…...…..………...……. 86
5.3 Basic Elements of a Package ……..…………………..…...……….... 88
5.4 Various Levels of Packaging ……………………………...………… 88
5.4.1 Die Level Packaging …………………….....………………. 89
5.4.2 Device Level Packaging ……………..……..…...………….. 89
vi
5.4.3 System Level Packaging …………………….....…...……… 90
5.5 Fundamental Packaging Operations ……………………………...…. 90
5.5.1 Die Preparation ……………………………………………... 90
5.5.2 Die Attach …………………..……………………………… 91
5.5.3 Wire Bonding ………………...…………………………….. 91
5.5.4 Testing ……………………………………………………… 92
5.5.5 Hermetic Sealing …………………………………………… 92
5.5.6 Marking …………………………………………………….. 93
5.6 State-of-the-art Packaging of MEMS ……………………………….. 93
5.6.1 Single Chip Packaging ………………………...…………… 93
5.6.2 Wafer Level Packaging …………………..………………… 94
5.6.3 Multi Chip Modules …………………..……………………. 95
5.7 Types of MEMS Packages …………………………………………... 95
5.7.1 Metal Packages ……………………………………………... 95
5.7.2 Ceramic Packages ………………………………………….. 96
5.7.3 Thin-Film Multilayer Packages …………………………….. 98
5.7.4 Plastic Encapsulated Packages ……………………………... 99
5.7.5 MOEMS Packaging ………………………………………… 99
5.7.6 Flip-Chip Assembly Technology …………………………... 100
5.7.7 Wafer Level Capping Technology ……………………..…... 101
5.8 Summary …………………………………………………………….. 102
Chapter 6: VARIOUS PACKAGING CHALLENGES AND SOLUTIONS 104
6.1 Introduction …………………………..……………………………… 104
6.2 RF-MEMS Product Integration ……………....……………………... 105
6.3 Challenges in integration of RF-MEMS ……...…………………..…. 106
vii
6.3.1 Release and Stiction ………………………………………... 107
6.3.2 Wafer Dicing ……………………………………………….. 108
6.3.3 Die Handling ……………………………………………….. 109
6.3.4 Stress ……………………………………………………….. 109
6.3.5 Outgassing ………………………………………………….. 110
6.3.6 Testing ……………………………………………………… 110
6.4 Key Points for the Success of MEMS Packaging …………………… 111
6.5 Typical MEMS Design, and Manufacturing Process ……………….. 113
6.6 Overview of Packaging of MEMS …………………………………... 115
6.7 More Packaging Challenges ………………………………………… 116
6.8 Case study of RF-MEMS Switches …………………………………. 120
6.9 Challenges related to RF Performance ……………………………… 123
6.10 Industrial Challenges ………………………………………………... 125
6.11 Summary …………………………………………………………….. 126
Chapter 7: RF-MEMS DEVICES: PROBLEMS REGARDING RELIABILITY AND DEGRADATION MECHANISMS ……….
129
7.1 Introduction ………………………………………………………….. 129
7.2 Most General RF-MEMS Degradation Mechanisms ………………... 130
7.3 Reliability Classes of RF-MEMS …………………………...………. 132
7.4 Specific Reliability Problems of RF-MEMS Devices ………………. 134
7.4.1 Reliability Problems Related to fabrication ………………... 135
7.4.2 Reliability Problems of Contact Material …………………... 136
7.4.3 Reliability Problems Related to Dielectric Charging ………. 137
7.4.4 Reliability Problems Related to Electrical Characterization .. 137
7.4.5 Packaging Related Reliability Problems …………………… 138
viii
7.4.6 Reliability Problems Related to Radiation …………………. 139
7.5 Summary …………………………..………………………………… 141
Chapter 8: CURRENT STATUS OF RF MEMS DEVICES FOR WIRELESS COMMUNICATION SYSTEMS …………………...
143
8.1 Introduction ………………………………………………………….. 143
8.2 RF-MEMS Drawbacks and Novel Research Solutions ……………... 145
8.3 Novel RF-MEMS Switches …………………………………………. 147
8.4 Vibrating Micro-Mechanical Diamond Disc Resonator …………….. 151
8.5 RF-MEMS Variable Tunable Capacitor …………………………….. 152
8.6 RF-MEMS Tunable Inductors ………………………………………. 154
8.7 Summary …………………………………………………………….. 156
Chapter 9: RESULTS, DISCUSSIONS AND FORECAST OF RF-MEMS ... 158
9.1 Introduction ……………………………………………….. 158
9.2 Important Results and Discussion …………………………………… 158
9.2.1 Current Packaging Parameters, Challenges, and Solutions ….. 159
9.2.2 Reliability Classes, Problems and Degradation Mechanisms .. 161
9.3 RF-MEMS Market and Industry …………………………………….. 163
9.4 Market and Forecast of RF-MEMS …………………………………. 168
9.5 Summary …………………………………………………………….. 170
Chapter 10: CONCLUSION AND FUTURE WORKS ………………………... 171
10.1 Conclusion …………………………………………………………... 171
10.2 Future Works ………………………………………………………... 172
BIBLIOGRAPHY ………………………………………………….. 175
LIST OF RESEARCH PUBLICATIONS ………………………... 196
ix
LIST OF FIGURES
Figure
Pages
1.1: Schematic of MEMS showing integration of mechanical and electrical parts ………………………………………………………………………
3
1.2: Classification of MEMS Technology
……………………………………4
1.3: Flow diagram showing distinction among different processes involved in manufacturing of MEMS and ICs ………………………………………..
5
1.4: (a)An illustration of a miniaturized acoustic resonator
……………….6
1.4: (b)On-chip microphone may be used to build radios on a chip
……….6
1.5: Three different RF-MEMS device categories ……………………………
9
1.6: Various common steps involved in methodology for designing RF-MEMS devices and components …………………………………………
10
1.7: RF-MEMS Component level to system level ……………………………
11
1.8: (a) A MEMS silicon motor along a human hair ……………………….
12
1.8: (b) Spider legs standing on gears of a micro-engine …………………..
12
1.9: Effect of miniaturization on surface area and volume …………………...
13
1.10: Applications areas in 2004 and 2009 …………………………………….
15
1.11: Potential Applications of RF-MEMS devices ……………………………
15
x
1.12: World RF-MEMS market for mobile phones ……………………………
17
2.1: (a)Agilent film bulk acoustic resonator .
……………………………… 24
2.1: (b) University of Michigan micro-machined membrane filter …….…..
24
2.1: (c) SEM of Radant MEMS switch, and ………………………………..
24
2.1: (d) A two-pole 7-MHz filter based on micromechanical resonators …..
24
2.2:(a)
Schematic of the capacitive shunt switch using PZT/HFO2
dielectrics …………………………………………………………..
25
2.2:(b)
A micrograph of a capacitive coupling MEMS RF switch (from Raytheon/Texas Instruments (TI)) …………………………………
25
2.3:(a)
A top-view image of the three-plate gap-tuning variable capacitor developed by Dec and Suyama …………………………………….
29
2.3:(b)
A top-view image of the University of Colorado gap-tuning variable capacitor using an electro-thermal actuator ………………
29
2.4:(a)
Cross-sections of a membrane supported film bulk-acoustic resonator (FBAR) …………………………………………………..
32
2.4:(b)
Cross-sectional view of a solidly mounted bulk-acoustic resonator (SMR) ………………………………………………………………
32
2.5: (a) Three Dimensional Cu spiral inductors made on a glass substrate ...
35
2.5:(b)
Three Dimensional Berkeley Cu coil inductor with a low-loss alumina core ………………………………………………………..
35
2.6: (a) The photograph of the rectangular slot antenna loaded with MEMS capacitors
37
xi
…………………………………………………………...
2.6:(b)
The photograph of the patch antenna loaded with MEMS capacitors …………………………………………………………...
37
2.7: Schematic of the rectangular slot antenna loaded with six MEMS cantilever type capacitors ………………………………………………...
39
2.8: Micrograph of a DC to 40 GHz four-bit true time delay network on GaAs ……………………………………………………………………..
41
2.9: The Four-bit miniature X-band phase shifter developed by the Univ. of Michigan and Rockwell Scientific ……………………………………….
41
2.10: (a) A V-band two-bit phase shifter …………………………………….
42
2.10: (b) A 35 GHz, one-bit switched line phase shifter (180°bit) …………..
42
2.11: Design of a UHF five-pole filter (die size is 3.5 mm into 14 mm) ………
43
2.12: Various types of transmission lines ……………………………………...
44
2.13: Metalized single-crystal silicon transmission lines (50 μm in height) as a part of a 30 GHz stepped-impedance low pass filter …………………….
45
3.1: Various materials employed for fabrication of RF-MEMS devices ……..
48
3.2: (a) Crystal structure of silicon and …………………………………….
49
3.2: (b) Low crystallographic index planes of silicon ………………………
49
3.3: Energy band structure of silicon and gallium-arsenide …………………..
50
3.4: Cross-section representation of the Sandia MM/CMOS integrated MEMS technology
55
xii
……………………………………………………….
3.5: Different structures obtained by using bulk micromachining process …...
56
3.6: Bulk micromachining along crystallographic planes …………………….
57
3.7: Various processing steps involved in typical surface micromachining ….
58
3.8: Various steps involved in a typical LIGA process ……………………….
61
3.9: Various steps involved in a typical flip chip technique ………………….
63
4.1: Roadmap showing RF-MEMS technologies …………………………….
69
4.2: (a) Broadside MEMS-series switches with one electrode ……………..
75
4.2: (b) Broadside MEMS-series switches with two electrodes ……………
75
4.3: (a) Low-height high-spring-constant gold MEMS switch ……...……...
76
4.3: (b) Low spring-constant MEMS switch ………………………………..
76
4.4: Raytheon MEMS capacitive shunt switch: cross-section view and electrical CLR model …………………………………………………….
77
4.5: The University of Michigan capacitive membrane switch ………………
78
4.6: Electrostatically actuated bulk-micromachined silicon variable capacitor, designed and fabricated at Rockwell Science Center ……………………
79
4.7: A mechanical filter used in telephone systems by Rockwell International
80
4.8: A 70.95 MHz free–free torsional beam resonator ……………………….
81
xiii
5.1: Cost affecting elements in packaging ……………………………………
86
5.2: Elements of the package …………………………………………………
88
5.3: Four levels involved in the IC Packaging ………………………………..
89
5.4: Three levels of packaging ………………………………………………..
90
5.5: Circuit with its wire bonds ……………………………………………….
91
5.6: Single chip packaging ……………………………………………………
93
5.7: Wafer level packaging …………………………………………………...
94
5.8: Silicon wafer-level packaging of RF-MEMS ……………………………
94
5.9: A package of MCM-D/MEMS …………………………………………..
95
5.10: A cross-sectional view of a three-dimensional multilayered package for MEMS structures on silicon substrate …………………………………...
98
5.11: Flip-chip MEMS package ………………………………………………..
100
5.12: Cap wafer process flow …………………………………………………..
101
5.13: Cross-section of AuSn seal ………………………………………………
102
6.1: Beam-type structure being pulled down by the capillary forces …………
108
6.2: An illustration of dimples used for avoiding stiction …………………….
108
6.3: Block Diagram of MEMS Design, Fabrication and Packaging ………….
114
xiv
6.4: Percentage cost involved in different processes of MEMS ……………...
116
6.5: Diagram of a packaged RF-MEMS switch in an LCP enclosure ………..
121
6.6: Prototypes of the packaged RF-MEMS switch using LCP CAPPING 122
8.1: More than Moore’s Law …………………………………………………
144
8.2: Radio Frequency Micro-Mechanical Switches …………………………..
148
8.3: SEM picture of the fabricated MEMS shunt switch without top substrate.
150
8.4: SEM Photograph of the CVD Diamond Micromechanical Disk Resonator ………………………………………………………………...
152
8.5: A Schematic Diagram of MEMS Variable Capacitor ……………………
153
8.6: An SEM image of the MEMS Variable Capacitor ………………………
154
8.7: MEMS Tunable Inductor Chip …………………………………………..
155
9.1: Presentation of global RF-MEMS industries and main participants …….
164
9.2: The hype curve of new technologies for RF-MEMS …………………….
165
9.3: Approximate turnover for the RF-MEMS market by application ……….
167
9.4: Trend of market of RF-MEMS Switches and Variable capacitors ………
168
9.5: Prediction curve of growth of RF-MEMS market from 2009 to 2015 …..
169
9.6: Prediction curves of growth of emerging RF-MEMS market from 2009 to 2015 …………………………………………………………………...
169
xv
LIST OF TABLES
Table Pages
1.1: Details the performance comparison between different technologies …… 2
xvi
1.2: Applications of MEMS and RF-MEMS ………………………………….. 16
1.3: Taxonomy of RF-MEMS devices as per the application domain ………... 18
3.1: Well defined characteristics of Silicon …………………………………… 49
3.2: Fundamental characteristics of Gallium Arsenide ……………………….. 51
3.3: Remarkable characteristics of Silicon Dioxide …………………………... 52
3.4: Crucial characteristics of silicon nitride at room temperature …………… 53
4.1: Comparison of various technologies ……………………………………... 68
4.2: Roadmap of fabrication micromachining technologies for RF-MEMS ….. 71
5.1: Common materials used in packaging …………………………………… 87
6.1: Current packaging parameters, challenges, and solutions ………………... 106
7.1: General RF-MEMS degradation mechanisms ……………………………. 131
7.2: Classification of RF-MEMS Devices …………………………………….. 133
ABSTRACT
xvii
Radio Frequency Micro electro mechanical system (RF MEMS)
technology has shown its bright future in many different fields, especially in
electronics, communication, space and radio frequency (RF) systems. By using
MEMS technology, we can greatly shrink the cost and the footprint of RF
circuits since all the off-chip components such as inductors and capacitors can be
fabricated and integrated into a whole single chip at one time. Our research is
directed by the purpose of developing more powerful RF components, devices,
and architectures.
This thesis gives a study and literature survey on various radio frequency
microelectromechanical systems (RF-MEMS) and devices. This dissertation also
gives a critical report on various materials and fabrication processes used to
manufacture RF-MEMS devices. It documents the designs and models of novel
RF-MEMS devices such as RF-MEMS switches, variable capacitors, resonator,
high quality factor inductors etc. These novel RF-MEMS devices will help in
designing new wireless communication systems. This dissertation documents a
detailed and exhaustive survey of RF MEMS components, devices and systems to
increase the awareness and knowledge of this novel technology.
This dissertation documents a number of packages employed for MEMS
devices with their salient features. This thesis also describes a large number of
challenges and degradation/failure mechanisms related to packaging. Packaging is
a critical and vital issue for the RF performance of the RF-MEMS devices and
components. At the end, this thesis documents numerous reliability problems and
degradation mechanisms related to radiation, concerned to integration, involved
during designing, integrating and fabrication; and caused by contact material,
related to electrical characterization and concerned to dielectric charging.
xviii
