INTRODUCTION
1.1: Motivation
The term “radio frequency” refers to frequency range from 0.1GHz to 300 GHz.
The MEMS technology had been predominantly used in radar for military and many
commercial purposes since the last forty years. Different frequency bands within the
spectrum have been intensively used for various applications. For example, the X-band,
(8-12 GHz) has been utilized for missile guidance; the Q-band (40-60 GHz) is the
operational spectrum for the military communication.
Starting from the military origin, their applications have been growing in the last
few decades in areas such as satellite communication, weather detection, wireless
communication and air traffic control systems. The immense success of personal
communication systems (mobile phones and wireless handheld devices), widens the RFMEMS technology for people.
Satellites and radio frequency (RF) systems are the main components of
communication network. The emergence of on-chip, discrete RF MEMS has attached the
attention of the wireless industry that is interested in smart phones, Bluetooth etc. By
using MEMS-based RF components, the performance can be increased by reducing
signal delay time and noise effects through the applications of on-chip components.
Basic RF-MEMS blocks of switches, inductors, varactors, and transmission lines
demonstrated imposing performances. Currently, many research and industry groups are
focusing on further improving the reliability, power-handling ability, RF-MEMS
packaging techniques, and extending RF-MEMS applications. The MEMS approach has
many attractive benefits such as less power consumption, lower signal attenuation, higher
isolation level and smaller estate requirement, compared to its semiconductor
counterparts.
The successes of these fundamental components give vast opportunities to design
and fabricate advanced and complex RF devices like phase shifters, tuners, and filters.
Due to high RF performance, low cost and low power consumption, RF-MEMS devices
allow system designers to explore new architectures and configuration which was not
possible with the traditional technology. Reliability and packaging, the two issues
1
discouraging RF-MEMS are on the threshold of solution and soon this technology will
make another revolution.
Table 1.1: Details the performance comparison between different technologies.
Sr. No.
Parameters
RF- MEMS
PIN
FET
1
Voltage (V)
20-80
± 3-5
3-5
2
Current (mA)
0
3-20
0
3
Power Consumption(mW)
0.05-0.1
5-100
0.05-0.1
4
Switching Time
1-300 μs
1-100 ns
1-100 ns
5
Isolation (1-40 GHz)
High
Medium
Low
6
Loss (1-100 GHz) (dB)
0.05-0.2
0.3-1.2
0.4-2.5
7
Size (mm2)
<0.05
0.1
1-5
Fabrication of RF-MEMS devices requires equipments, processes, and materials
similar to microelectronics. It is a positive factor for RF-MEMS mass production and
motivates to develop new RF-MEMS devices. Many RF-MEMS devices have been
successfully demonstrated on quartz, silicon, III-V compound and RF-grade glass
substrates for their wonderful RF characteristics. Integrating RF-MEMS devices into
current integrated circuits and the high material costs of the RF-MEMS substrates are big
challenges and hinder their beauty.
These outstanding advantages and promising applications of MEMS based RF
components become a driving motive force for many MEMS designers, including the
author of this thesis, to concentrate their research efforts on designing novel RF MEMS
devices, challenges, degradation mechanisms.
1.2: What is MEMS?
MEMS have numerous advantages as a manufacturing technology. Firstly, its vast
nature and diverse applications has resulted in unique range of devices and synergies.
Secondly, its batch fabrication techniques facilitate components and devices to be
manufactured with increased performance and reliability, and decreased physical size,
weight, and cost. Thirdly, MEMS provides the basis for the creation of products that
cannot be possible by the other methods. These factors make MEMS better technology
than ICs. However, there are many challenges and technological obstacles that need to be
overcome before MEMS can realize its vast potential.
2
MEMS are the abbreviation of micro- electro-mechanical system. In Europe, it is
called Microsystems. MEMS is a process technology used to make tiny integrated
devices or systems that combine mechanical and electronic components. MEMS
technology takes advantage of
mechanical and electrical properties of silicon. MEMS
technology is the integration of mechanical elements (actuators, sensors, gears, mirrors
etc.) with the necessary electronics components and circuit on the same silicon chip using
micro-fabrication processes. Figure 1.1 shows schematic of integration of mechanical and
electrical parts.
Figure 1.1: Schematic of MEMS showing integration of mechanical and electrical parts.
Microsensors sense environment by measuring mechanical, thermal, magnetic,
chemical or electromagnetic information. Microelectronics processes this information
and directs the microactuators to react and perform some tasks. These also consist of
microelectronics packaging, integrating antenna structures to command signals into
micro-electromechanical structures for needed sensing and actuating functions.
MEMS are integrated micro-devices that can sense, control, and actuate on the
micro scale and function to generate effects on the macro scale. MEMS components are
characterized by their small micro size (characteristically between 1 μm and 1 mm), low
cost, low power consumption, and integrity with electronics. Traditional MEMS are of
two kinds: MEMS actuators and MEMS sensors. MEMS actuator is a moving mechanism
activated by an electric signal.
1.3: Classification of MEMS Technology
Fabrication is the processing the material to form fundamental structures (cavities,
beams and membranes) are combined into devices: sensors to detect certain properties
(such as pressure) and actuators to perform certain jobs (such as moving a mirror). These
devices results in many applications in different fields, such as bio-medical, space,
3
communications and defense etc. Packaging of MEMS devices is done simultaneously
with fabrication as it is very important for creating healthy devices from the concerned
tiny and fragile components.
MEMS research technology can be broadly classified into four general technology
areas: fabrication, structures, devices and applications as shown in Figure 1.2.
FABRICATION
DEVICES
STRUCTURES
APPLICATIONS
BIO-MEDICAL
MATERIALS
CAVITY
SENSORS
PROCESSES
BEAMS
ACTUATORS
PACKAGING
MEMBRANES
PROCESSORS
COMM.
SPACE
AUTOMOTIVE
DEFENSE
INTEGRATED
SYSTEMS FOR
ACTIVE
CONTROL
ELECTRONICS
Figure 1.2: Classification of MEMS Technology
Many MEMS device failures are related to the operations related to the
fabrication process. Being miniature embedded systems, these devices are usually batch
fabricated using a process similar to that used in IC technology, using silicon wafers as
the material and etching techniques to create components. Both MEMS fabrication and
IC fabrication contribute to the same characteristics such as mass production, low cost,
complete assembling. But the MEMS fabrication is more complicated, as it involves
integration of mechanical and electronic parts on the same chip. They usually involve
complex, moving and fragile parts.
The manufacturing process flow chart is shown in Figure 1.3. The distinction
among the processes involved in the manufacturing of MEMS and ICs are mentioned in
the bold and the italics respectively here. In the design phase, complex CAD tools having
4
the ability to model complex 3D objects used for MEMS. The simultaneous modeling of
devices in many domains (electronic, mechanical etc.) and the ability to analyze interdomain effects is a challenge. The material deposition and material removal needs a
special notice for the mechanical parts. The process is repeated multiple times until the
required device is constructed. After etching away the sacrificial layer, moving parts can
be released.
Figure 1.3: Flow diagram showing distinction among different processes involved in
manufacturing of MEMS and ICs.
1.4: What is RF-MEMS?
The RF-MEMS acronym stands for radio frequency micro-electromechanical
system, and refers to components of which freestanding or moving sub-millimeter-sized
parts provide RF functionality. The term RF-MEMS actually denotes the design and
fabrication of MEMS for radio frequency integrated circuits. MEMS devices employed in
RF applications are called RF-MEMS. RF-MEMS devices, such as switches, tunable
capacitors, mechanical resonators and filters, contain movable and fragile parts that must
be encapsulated for reasons of safety like handling, wafer dicing or plastic moulding
operations and to make certain stable and reliable performance parameters.
5
MEMS technology is on the threshold of revolutionizing radio frequency and
microwave applications. RF-MEMS are not the traditional MEMS that operate at the
radio frequencies. In RF-MEMS, MEMS devices are used for actuation or to adjust
varactors, switches or inductors like other RF components. During the past few years,
RF-MEMS fabricated using semiconductor micro-fabrication technology has gained
significant interest for wireless communication applications owing to their small size,
integration capability and superior performance.
RF-MEMS is a fabrication technology employed to make very small integrated
devices or systems that combine mechanical and electrical components for employing
radio frequency functions. They are fabricated using integrated circuit batch processing
techniques and can range in size from a few micrometers to millimeters. These devices
(or systems) have the ability to sense, control, and actuate on the microscale and produce
tasks on the macroscale.
RF-MEMS are planned specially for electronics in radars, satellites, mobile
phones and other wireless communication and space applications such as radar, global
positioning systems (GPS) and steerable antennae. MEMS have greatly increased the
reliability, performance, and functionalities of these devices by decreasing their size and
cost all together. A miniaturized acoustic resonator is one-fifth the size of a traditional
component used in mobile phones and on-chip microphone has shown in the Figure 1.4.
Figure 1.4: (a)
An illustration of a miniaturized acoustic resonator and
(b) On-chip microphone may be used to build radios on a chip.
The interdisciplinary nature of RF-MEMS utilizes design, engineering and
manufacturing knowledge from a wide and diverse range of technical areas integrated
circuit fabrication technology, mechanical engineering, material science, electric
6
engineering, electronics engineering, optics, chemical engineering, instrumentation,
physics, thermal engineering, and packaging etc.
RF-MEMS has been identified as one of the most promising technologies for the
21st Century and has the prospective to revolutionize both industrial and consumer
products by combining microelectronics with micromachining technology. Its approaches
and microsystems have the prospective to considerably affect human beings lives and the
style of our living. Without any doubt, if we consider semiconductor micro-fabrication as
first micromachining revolution, then RF-MEMS must be the next revolution.
1.5: Classification of RF-MEMS
This technology includes circuit tuning elements such as switches, capacitors,
inductors, resonators, and filters. These ultra-miniature with low-loss and highly
integrative RF functions can and will ultimately substitute conventional RF elements and
facilitate a new generation of RF devices and systems. If RF-MEMS components go on
to substitute conventional components in contemporary wireless communication devices,
then such systems could become very small, and will require little battery power and may
even be of low expenditure.
RF-MEMS technology has reported many applications in communication, biomedical, space etc, due to its much better properties and performance. Novel
breakthroughs for personal communication systems have brought the signal frequency up
to millimeter and microwave range. The much precise fabrication MEMS technology
facilitates microlevel fine features, system integration capabilities, and provides the
unique performance in insertion loss, bandwidth for the microcomponents.
Surface
micromachined RF-MEMS switches exhibit better performance at larger frequencies as
compared to the traditional RF switching technology like GaAs based FET switches, and
PIN diodes.
RF-MEMS and microwave industry is reaping the benefits of MEMS technology.
The continuous advance in MEMS technology attracted researchers towards the
development of MEMS devices for RF applications. RF-MEMS devices have a wide
range of potential applications in wireless communication, navigation, sensor systems.
They could be used in switches, phase shifters, signal routings, impedance matching
7
networks, exciters, transmitters, filters, RF receivers. RF-MEMS devices can be grouped
as active devices and passive devices.

Active MEMS devices: switches, variable capacitors, and tuners.

Passive MEMS devices: bulk micro-machined transmission lines, filters, couplers,
antennas.
However, it is still premature for a classification of RF-MEMS devices, yet the
progress till date tends to put them into different classes depending on whether one takes
an RF or MEMS viewpoint. From the RF viewpoint, the MEMS devices are simply
grouped by the RF-circuit component they consists of, be it reactive elements, switches,
filters, or something else. From the MEMS viewpoint, these are put into three separate
classes based on where and how the MEMS actuation is carried out relative to the RF
circuit. The three classes are mentioned below:
1.5.1 RF Intrinsic:-These are the devices in which the MEMS structure is positioned inside the RF
circuit and has the dual roles of both the actuation and RF-circuit function. In this group,
one may regard as conventional cantilever and diaphragm type MEMS that can be
employed as electrostatic microswitch and comb-type capacitors. With the discovery of
electro-active polymers, multifunctional elegant polymers and micro-stereo lithography,
these RF-MEMS can be easily used with polymer based polymers. These are stable,
flexible, and lifelong. In addition, these can be integrated with the organic thin film
transistor. Shunt electrostatic microswitch, inductors and comb capacitors are the
examples that are put in the RF-intrinsic class.
1.5.2 RF Extrinsic:-These are the devices in which the MEMS structure is positioned outside the RF
circuit, but actuates or controls other devices (generally micromechanical ones) in the RF
circuit. One may regard as tunable micro-machined transmission line, waveguides, phase
shifters, and arrays as the important examples of this group. Micro-strip lines can be
fabricated easily by automated approaches and hence, these are extensively employed for
interconnecting very fast components and circuits.
8
1.5.3 RF Reactive:-In this group of RF-MEMS devices, the MEMS structure is positioned inside,
where it has role of RF function that is attached to the attenuation. The examples of this
class are capacitively coupled tunable filters and micromechanical resonators. These
devices facilitate the required RF functions in the associated circuit. Millimeter wave and
microwave planar filters on thin dielectric membrane exhibit low losses, and are suitable
for low price, compact, high performance millimeter wave one-chip integrated circuits.
A collection of these devices is shown in the RF-MEMS classification Figure 1.5.
The richest class is clearly the RF-intrinsic, which already boasts three promising
devices. Here, we have tunable capacitors and inductors that are expected to operate up to
at least a few GHz in frequency, and we have RF-embedded switches that operate well
from a few GHz up to at least 100 GHz.
Figure 1.5: Three different RF-MEMS device categories.
1.6: Design Methodology for RF-MEMS
Various concepts, specifications, physical conditions, fabrication methods and
packaging techniques must be considered earlier in mind while designing RF-MEMS
devices and components. For microwave and millimeter wave systems, the forces may
9
change the parameters of complete system. RF-MEMS design methodology can be
summarized with the flow chart given below in Figure 1.6.
While designing RF-MEMS devices and systems, their concept and required
specifications are considered and then detailed description of model of its structure is
given. Physical conditions and problem related constraints are applied to the model. After
that behavior of the model is analyzed. Then various components, parts and
microelectronics involved in the model are fabricated and packaged with suitable
materials and techniques. Then the packaged product of the RF-MEMS device is tested,
and inspected for its characteristics, performance, reliability and other mechanisms.
Various inspecting methods, tests, failure and degradation mechanisms of the specific
RF-MEMS device must be analyzed beforehand. In this way, the product becomes ready
for market.
Concept and Specifications
Model Description of the structure
Apply Stimuli and Physical
conditions
Analyze Model Behavior
Fabrication Techniques
Packaging Techniques
Testing and Inspection methods
Figure 1.6: Various common steps involved in methodology for designing RF-MEMS
devices and components.
Previous RF-MEMS designers relied on lengthy and expensive prototyping cycles
to achieve MEMS designs. Today accurate, easy-to-use, commercially available MEMS
design tools enable shorter time-to-market and lower design costs. The need for these
tools is driven by the nature of MEMS devices leading to multi-domain design aids that
10
can solve true coupled analysis. Successful RF-MEMS designs must take in to account
device layout, construction, packaging, modeling, integration, and simulation.
There are numerous RF-MEMS components which are either used directly for
replacement or integrated to form a microsystem along with other semiconductor devices.
The components can also go along with silicon technology or GaAs technology and the
MEMS components can be incorporated to give a system solution. The restrictions of the
usual RF integrated devices can be conquered by the flexibility and improved device
performance properties of RF-MEMS components, which finally propagate the device
level advantages to the system to achieve the unprecedented levels of performance. The
component level to circuit level and to system level growth of a characteristic
communication system using RF-MEMS devices is shown in Figure 1.7.
SYSTEM
(Phased Array Antenna, Switch Matrix, Cell Phone, GPS, Pagers)
CIRCUIT
(Phase Shifters, Transceivers, Filters, Oscillators)
DEVICE
(Switches, Inductors, Resonators, Varactors)
Figure 1.7: RF-MEMS Component level to system level.
1.7: Miniaturization
While creating successful MEMS, basic physics, operating principles scaling laws
etc. need to be fully understood at macro-level and micro-level. Things behave largely
different in the micro domain. The properties of materials are different at the nanoscale
(size in the 1-100 nanometers range) due to the main two reasons. Firstly, nanomaterials
have relatively larger surface area when compared to the same mass of the material
produced in a larger form. Secondly, quantum effects can begin to dominate the behavior
of matter at the nanoscale. These quantum effects change the optical, electrical, magnetic
properties of the materials.
In micro-domain, dominating size dependent quantum effects and increased
relative surface area can change the properties (like reactivity, strength, electronic,
11
mechanical, thermal and optical). As a particle decrease in size, a greater proportion of
atoms are at the surface compared to those inside. Thus, nano-particles have a much
greater surface area per unit mass compared with larger particles.
The relatively small and light in weight structures lead to devices having
relatively high resonating frequencies. These high resonating frequencies mean much
operating frequencies and bandwidth for sensors and actuators. Thermal time coefficients
such as the rates at which structures absorb and release heat are short for smaller and low
weight structures and devices. Miniaturization is not the key driving factor for RFMEMS like ICs in the sense that RF-MEMs devices interact with a particular feature of
environment like wireless communication etc.
(a)
(b)
Figure
1.8:
(a)
A
MEMS
silicon
motor
along
a
human
hair,
and
(b) Spider legs standing on gears of a micro-engine.
RF-MEMS is a diverse technology which is an amalgamation of all the faculty of
engineering and sciences. RF-MEMS is not only miniaturization; it is a manufacturing
technology employed to produce tiny integrated microsystems using IC batch fabrication
techniques. Similarly, miniaturization is not just about reducing existing devices; it is
12
about totally rethinking the structure of a microsystem. The micro-sized objects shown in
Figure 1.8 will also give an idea of miniaturization.
By miniaturization, we mean dimensions of the devices less than the thickness of
a human hair (~80000 nm wide). A nanometer is one thousand millionth of a meter
abbreviated as 10-9 m. It would take ten hydrogen atoms to make one nanometer. Forces
related to volume such as weight and inertia, tend to decrease significantly. Forces related
to the surface area such as friction, surface tension and electrostatics, tend to increase.
Increased surface areas (S) to volume (V) ratios at microscales have both considerable
advantages and disadvantages as shown in Figure 1.9.
Figure 1.9: Effect of miniaturization on surface area and volume.
Some of the important micro-scale issues are:

Material properties (Young’s modulus, Poisson’s ratio, grain structure) and
mechanical theory (residual stress, wear and fatigue etc.) may depend on size.

Capillary, electrostatic and atomic forces as well as stiction at a micro-level can
be significant because friction is more than inertia.

Heat dissipation is more than heat storage and hence, thermal transport properties
become an issue.

Mass transport properties are very significant. Tiny spaces for flow can be easily
getting blockages but can, on the contrary, control mass movement.

Integration with on-chip circuitry is complex and is device or domain dependent.

Packaging and testing of miniaturized device is not easy. Testing is not fast and is
costly compared with traditional IC devices. Packaging of RF-MEMS devices
plays a vital role as it is also application dependent.
13
Miniaturization is vital in integrating many components on a chip or in a package.
In this way, a tiny package can serve several functions. Miniaturization is enabled by
micro-fabrication processes. It is needed due to following points:

Miniaturization results in compact devices and systems.

Miniaturization makes the microsystems less costly due to the batch production
by the micro-fabrication processes. Many components and parts can be integrated
on a single chip and hence, cost per components reduces much.

Due to the miniaturization, mechanical components can be integrated with the
electronic components and hence, microsystems become simple and power
consumption is very much reduced.

Various conditions of processes can be easily controlled in miniaturized systems.
So, efficiency of microsystems increases compared to macro systems.

Miniaturization can lead to more rapid devices with increased thermal
management.

Materials requirement during the manufacturing processes reduces drastically and
hence it improves performance per cost.

Miniaturized systems and devices have improved reliability, selectivity,
sensitivity, and accuracy.
1.8: Applications of RF-MEMS
Now-a-days, RF-MEMS devices and components have become technologically
and economically competitive enough to enter the market. Miniaturized high frequency
circuits, with high system integration and low price for personal use, has become possible
with the advance of the RF-MEMS technology. The small size of MEMS has exciting
bio-medical applications. The medical devices can be made so small that they can be
injected into man’s bloodstream. They may selectively kill sick cells or germs without
damaging healthy body tissues. MEMS microsurgery devices can do surgery inside
human body without any cut on the skin. Hard disc drive read/write heads, inkjet printer
heads, accelerometers and pressure sensors are well known mass market applications.
14
Figure 1.10: Applications areas in 2004 and 2009.
RF-MEMS switch devices are typically in the sub-millimeter or hundreds of
micrometers in size. The scales of size make these devices attractive because they make it
possible to have switching solutions that can ideally take up 1 mm2 or less space. In
addition, the switches can be altered to create a variety of micro applications such as
delay lines and switched capacitor networks. In theory, up to 50 GHz signals RF-MEMS
technology can show better performance than high-speed semiconductors devices.
POTENTIAL APPLICATIONS OF RF MEMS
MASS APPLICATIONS
(MOBILES, GPS, RFID, WLAN, CONSUMER & IT)
TELECOM
INFRASTRUCTURE
BASE STATIONS
MICROWAVE COM
TEST
RF
INSTRUMENTATION
Mobile Phones
RF MEMS
AUTOMOTIVE
Airbag Sensors, ANTI-
HIGH VALUE
APPLICATIONS
MILTARY RADIO
DEFENSE
COMMUNICATION
SYSTEMS
MISSILES SATELLITES
COLLISION RADAR,
Aircraft Control
ROOF ANTENNA
Figure 1.11: Potential Applications of RF-MEMS devices.
RF-MEMS include several distinct types of devices, such as RF switches,
resonators, varactors (variable capacitors) and tuneable inductors. Applications of RFMEMS include wireless communications, radar, satellites, military radio, instrumentation
and test equipment. Compared to conventional RF components, RF-MEMS offer
15
significant benefits, like lower power consumption, lower insertion loss, and lower cost.
Application areas of RF-MEMS in 2004 and 2009 are presented in the Figure 1.10.
Table 1.2: Applications of MEMS and RF-MEMS.
Sr.
Automotive
Electronics
Medical
Communication
Space
No.
1
Defense
Internal
1
Inkjet Printer
Implanted
Fiber-Optic
Aircraft
Navigation
Heads
Pressure
Network Components
Control
Sensors
2
3
Sensors
Anti-Collision
2
Disk
Radar
Drive Muscle
Software
Defined Surveillance
Read & Write Stimulators
Radios,
Tunable &
Heads
Band-Pass Filters.
Watch
Projection
Blood
Projection Displays in Various
Control
Screens,
Pressure
Portable
Military
Accelerometer
Televisions
Sensors
Communications
Systems Like
Devices
RADAR etc.
Voltage Controlled
Missile
Oscillators (VCOs),
Communicati
Instrumentation
on
Fuel
4 & Vapor Earthquake
5
Close
Suspension
3
s
4
&
Prosthetics
Pressure
Sensors,
Test
Sensors
Equipments
Airbag
5
Avionics
Miniature
Splitters & Couplers; Data Storage
Sensors
Pressure
Analytical
Reconfigurable
& Embedded
Instruments
Antennas.
Sensors
& Brake Force Sensors
Sensors
6
7
8
Intelligent
6
Mass
Data Pacemaker
Tyres
Storage
s
Tunable Lasers
Air
7 Condition
Electronically
Drug
RF
Compressor
Scanned
Sensors
Arrays,
Ground
8
Displays
Sub- Delivery
Systems
in Micro-
Vehicle Roof Instrumentation
Surgery
Antenna
Mobile
Phones, Munitions
Relays
Switches,
And Satellite
Reference Communicati
Oscillators
Phase
Guidance
on Systems.
Shifters, IT
Impedance Tuners
Sector,
WLAN,
GPS.
The RF-MEMS technology has the potential of replacing many traditional RF
components used now in mobile, WLAN, IT, communication and satellite systems. The
16
potential applications of RF-MEMS devices are shown in Figure 1.11.
RF-MEMS
provide components with reduced power consumption, phase noise, losses, size, weight,
but wide bandwidth, higher linearity, better phase stability and high isolation. Wherever
the application needs such features, MEMS can offer solutions to substitute either
components or circuits or the subsystems using the components.
These days MEMS and RF-MEMS can be found in many different applications
across multiple markets. RF-MEMS experts believe market forces are enabling a second
wave of applications, limited to some selected but very large industries in which MEMS
components have clear advantages over traditional electronic components. In particular,
the telecommunications industry is ripe for MEMS technology. RF-MEMS are mainly
used in the fields such as automotive, electronics, space, defense, medical and
communications as mentioned in above Table 1.2.
RF-MEMS are applied in filters, reference oscillators, switches, switched
capacitors and varactors are applied in Software defined radios, reconfigurable antennas,
and tunable band-pass filters and electronically scanned sub-arrays, and phase shifters.
1.8.1: RF-MEMS in Mobile Phones
The need for multiband, multimode band switching at low insertion loss while
maintaining good linearity in mobile phones is driving the need for RF-MEMS switches.
New RF-MEMS switches have impact on 3G cellular phones. These newer 3G standards
provide a variety of services, including data and on-demand video. RF-MEMS
technology facilitate engineers in designing phones that meet the challenges of
integrating multiple bands and adding novel capabilities with long battery life, low cost
and decreasing the size of the mobile.
Figure 1.12: World RF-MEMS market for mobile phones.
17
Modern mobiles uses transmit/receive switch or a band switch, and/or duplexers
for interfacing the phone’s antenna with the chip. RF-MEMS technology can outdo the
performance of semiconductors devices. Many factors (like fabrication and packaging
approaches, stiction at the contact point, control voltages, reliability (switching life
cycles), switching speed, thermal constraint, and construction cost) restrict the feasibility
of RF-MEMS in mobile phones. But, RF-MEMS is a good alternative, as no other
solution is foreseen that can react to the challenges of the trend given by “More than
Moore's Law”. Figure 1.12 shows world RF-MEMS market sales for mobile phones from
2004 to 2009.
Table 1.3: Taxonomy of RF-MEMS devices as per the application domain.
Devices
Wireless
WLAN
very
very
large
large
----
----
large
large
Capacitors
----
large
large
Resonators
----
very
very
large
large
6
VCOs
----
----
7
MEMTENNA
----
----
Requirement
1
2
Switches
Phase shifters
MEMS
3
Inductors
GPS
Instrumentation
RFID
large
very large
large
----
----
----
----
----
----
large
very large
medium
----
very large
----
----
----
medium
very
large
Tunable
4
5
Radar
Missiles
very
very
large
large
very
very
large
large
----
----
very
very
large
large
very
large
Large
Large
very
large
Large
RF-MEMS may help engineers to design phones that meet the challenges of
integrating multiple bands while maintaining long battery life and reducing the size of the
handset. About 75% components in a mobile phone are passive elements (inductors or
variable capacitors). MEMS versions of these components promise to make phones more
18
reliable and power efficient. RF-MEMS can potentially provide a solid replacement for
existing solid-state switches.
Applications of MEMS in mobile phones:
• RF-MEMS passive and active devices provide better integration of passive devices for
RF module and for faster frequency selectivity.
• 3D accelerometers improve man-machine interface and silent mode activation.
• Silicon microphones enhance the manufacturability of microphones.
• Gyroscope for camera stabilization enables real digital imaging, and it also conserves
the GPS signal.
• Micro-fuel cells provide longer lifetime for the batteries.
• Chemical and Bio-chip: personal weather station and health care monitor.
1.9: Taxonomy of RF-MEMS Devices as per the Application Viewpoint
RF-MEMS include several distinct types of devices, such as RF-MEMS switches
and relays, tunable inductors, resonators, varactors (variable capacitors), antennas,
transceivers and phase shifters. Applications of RF-MEMS include all types of wireless
communications, radar, satellites, Missiles, instrumentation, WLAN, GPS, RFID and test
equipment. Compared to conventional RF components, RF-MEMS offer significant
benefits, like lower power consumption, lower insertion loss, and lower cost. Another
possible application of RF-MEMS is their implementation in transceivers in wireless
systems. Table 1.2 shows the taxonomy of RF-MEMS devices as per the application
viewpoint.
1.10: Summary
The term “RF-MEMS” encompasses several distinct types of devices, like RF
switches, resonators, varactors, inductors, and antennas. Applications of RF-MEMS
include all types of wireless communications, radar, satellites, military radio,
instrumentation and test equipment. Compared to conventional RF components, RF
MEMS offer significant benefits, including lower power consumption, lower insertion
loss, lower cost and smaller form factor. RF -MEMS have come to market more recently
than other types of MEMS, but the RF- MEMS market is now growing rapidly.
MEMS is a process technology used to make tiny integrated devices that combine
mechanical and electronic components. Current activities in MEMS research can be
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broadly described as falling into one of four general technology areas: fabrication,
structures, devices and applications. MEMS technology is on the verge of revolutionizing
radio frequency and microwave applications. The term RF-MEMS actually denotes the
design and fabrication of MEMS for radio frequency integrated circuits.
From the MEMS viewpoint, these are classified into three classes: RF-Intrinsic,
RF-extrinsic, and RF Reactive. RF-MEMS is not only miniaturization; it is a
manufacturing technology employed to produce tiny integrated micro-systems.
Miniaturization results in less costly, simple, more rapid, compact devices and systems,
with low power consumption, increased thermal management and efficiency, improved
performance per cost, improved reliability, selectivity, sensitivity, and accuracy. New
RF-MEMS switches have impact on 3G and 4G cellular phones.
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