INTRODUCTION1.1: 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 RF-

MEMS 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

FABRICATION STRUCTURES DEVICES APPLICATIONS

MATERIALS

PROCESSES

PACKAGING

CAVITY

BEAMS

MEMBRANES

SENSORS

ACTUATORS

PROCESSORS AUTOMOTIVE

DEFENSE

BIO-MEDICAL

COMM.

SPACE

ELECTRONICS

INTEGRATED SYSTEMS FOR ACTIVE CONTROL

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.

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 inter-

domain 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, bio-

medical, 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

Concept and Specifications

Testing and Inspection methods

Model Description of the structure

Apply Stimuli and Physical conditions

Analyze Model Behavior

Fabrication Techniques

Packaging Techniques

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.

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

SYSTEM(Phased Array Antenna, Switch Matrix, Cell Phone, GPS, Pagers)

CIRCUIT(Phase Shifters, Transceivers, Filters, Oscillators)

DEVICE(Switches, Inductors, Resonators, Varactors)

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.

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 RF-

MEMS 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

RF MEMS

AUTOMOTIVE Airbag Sensors, ANTI-COLLISION RADAR, ROOF ANTENNA

TELECOM INFRASTRUCTUREBASE STATIONS MICROWAVE COM TEST RF INSTRUMENTATION Mobile Phones

POTENTIAL APPLICATIONS OF RF MEMS MASS APPLICATIONS (MOBILES, GPS, RFID, WLAN, CONSUMER & IT)

HIGH VALUE APPLICATIONS MILTARY RADIO DEFENSE COMMUNICATION SYSTEMS MISSILES SATELLITES Aircraft Control

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.

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 RF-

MEMS 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.

No.

Automotive Electronics Medical Communication Space &

Defense

1

1

Internal

Navigation

Sensors

Inkjet Printer

Heads

Implanted

Pressure

Sensors

Fiber-Optic

Network Components

Aircraft

Control

2

2

Anti-Collision

Radar

Disk Drive

Read & Write

Heads

Muscle

Stimulators

Software Defined

Radios, Tunable

Band-Pass Filters.

Surveillance

& Close

Watch

3

3

Suspension

Control

Accelerometer

s

Projection

Screens,

Televisions

Blood

Pressure

Sensors

Projection Displays in

Portable

Communications

Devices

Various

Military

Systems Like

RADAR etc.

4

4

Fuel & Vapor

Pressure

Sensors

Earthquake

Sensors, Test

Equipments

Prosthetics Voltage Controlled

Oscillators (VCOs),

Instrumentation

Missile

Communicati

on

5

5

Airbag

Sensors

& Brake Force

Sensors

Avionics

Pressure

Sensors

Miniature

Analytical

Instruments

Splitters & Couplers;

Reconfigurable

Antennas.

Data Storage

& Embedded

Sensors

6

6

Intelligent

Tyres

Mass Data

Storage

Pacemaker

s

Mobile Phones,

Tunable Lasers

Munitions

Guidance

7

7

Air Condition

Compressor

Sensors

Electronically

Scanned Sub-

Arrays,

Drug

Delivery

Systems

RF Relays And

Switches, Reference

Oscillators

Satellite

Communicati

on Systems.

8

8

Ground

Vehicle Roof

Antenna

Displays in

Instrumentation

Micro-

Surgery

Phase Shifters,

Impedance Tuners

IT 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

RequirementWireless WLAN GPS Instrumentation RFID Radar Missiles

1 Switchesvery

large

very

largelarge very large large

very

large

very

large

2 Phase shifters---- ---- ---- ---- ----

very

large

very

large

3MEMS

Inductors large largevery

large---- ---- ---- ----

4Tunable

Capacitors ---- large large ---- largevery

large

very

large

5 Resonators ----very

large

very

largevery large medium

very

largeLarge

6 VCOs ---- ---- ---- very large ---- Large

7 MEMTENNA ---- ---- ---- ---- mediumvery

largeLarge

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

19

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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