1

A REPORT

ON

Design of RF MEMS Ohmic switch for

Communication Applications

BY

SARJAK SHAH 2010AAA4091H SAKINA UNTHALAWALA 2010A3PS220H

AT

CEERI, PILANI

A PRACTICE SCHOOL-1 STATION OF

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI

June 2012

2

A REPORT

ON

Design of RF MEMS Ohmic switch for

Communication Applications

BY

SARJAK SHAH 2010AAA4091H B.E. Electronics and Communication & B.E. Mechanical Engineering SAKINA UNTHALAWALA 2010A3PS220H B.E. Electrical and Electronics

Prepared in partial fulfillment of the

Practice School-I Course No.

BITS C221/BITS C231/BITS C241/BITS GC221/BITS GC231

AT

CEERI, PILANI

A PRACTICE SCHOOL-I STATION OF

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE, PILANI

June 2012

3

BIRLA INSTITUTE OF TECHNOLOGY AND SCIENCE PILANI (RAJASTHAN)

Practice School Division

Station: Central Electronics Engineering Research Institute Centre: Pilani Duration: From: 21st May 2012 Till: 13th July, 2012 Date of Submission: 15th June, 2012 Title of Project: Design of RF MEMS Ohmic switch for Communication Applications 2010AAA4091H SARJAK SHAH B.E. Electronics and Communication & B.E. Mechanical Engineering 2010A3PS220H SAKINA UNTHALAWALA B.E. Electrical and Electronics

Name of Expert: Dr.K. J. Rangra Designation: Scientist F

Name of PS Faculty: Mr. Mahesh Angira

Key Words: RF switches, MEMS, actuation

Project Areas: Electrostatics, Mechanics of Solids, CAD softwares, Semiconductor devices.

Abstract: MEMS (Micro Electro Mechanical Systems) is a concept that came out only in the

last decade and the innovation in the field is accelerating. So is the case with RF MEMS

(Radio Frequency MEMS) switches. The study of RF MEMS switches is inspired by their

superior performance over the contemporary electro-mechanical relays and other solid

state devices (FETs and PIN diodes).

Many applications in today’s world demand the use of micro-devices for their usage. For

example, a mobile phone nowadays has multiple transmitters and receivers in the same

device and packaging them is a challenge. Global Positioning System (GPS), Bluetooth,

Home RF, wireless LAN systems are just a few of the RF module candidates awaiting

integration into mobile phones. RF MEMS has a great importance in terms of its application

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in wireless communication. RF MEMS presently has some reliability issues which are

discussed in the following topics, when solved, RF MEMS will find a place in the satellite

communication at a huge scale.

The present report starts with what is MEMS, then going to RF MEMS switches, advantages

of RF switches, their limitations and their reliability issues, types of RF switches,

specifications and design considerations.

Signatures of the Students Signature of the PS Faculty

Date: Date:

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CONTENTS

Certificate 6 Acknowledgements 7 About CEERI and Orientation 8 About SNG-SEM: MEMS 15 RF MEMS Switch 16 Advantages of RF MEMS switches 17 Limitations of RF MEMS switches 18 Types of RF switches and basic configurations 19 Specifications used to design an RF MEMS switch 20 Design considerations of RF MEMS switch 21 Conclusions and future work 22 References 23

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CERTIFICATE

This is to certify that this project report is being submitted by Mr. Sarjak Shah and Ms. Sakina Unthalawala in partial fulfillment of the Practice School I course which embodies work carried out by them under my supervision at CEERI (Central Electronics Engineering Research Institute) Pilani during the period 21st May, 2012 to 13th July, 2012. Dr. K. J. Rangra Sensors and Nanotechnology Group CEERI, Pilani

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ACKNOWLEDGEMENTS

We would like to thank the Practice School Division of BITS Pilani for providing us an

opportunity through the Practice School Program to become a part of professional

organization and provide an opportunity to all students to interact with the professional

world.

We are grateful to Dr. Chandra Shekhar, Director of Central Electronics Engineering

Research Institute, Pilani, without whom we would never have had an opportunity to work

at CEERI, Pilani.

We extend our sincere thanks to Dr. K. J. Rangra, Scientist F, Sensors and Nanotechnology

Group, RF MEMS Division for his constant support and guidance.

We would also express our sincere gratitude towards Mr. Akshdeep Sharma, Ms. K.

Maninder and Mr. Deepak Bansal for their expert guidance which made this work possible.

Our acknowledgements also extend to Mr. Mahesh Angira, P.S. faculty (BITS Pilani) for the

pains he took in allotting our departments and scheduling our P.S. program.

We would strive to accomplish our goals by the end of the Practice School I programme.

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ABOUT CEERI

Birla Institute of Technology and Science, Pilani organises its Practice School-I programme

BITS C221 for its students who have passed out the second year of their respective degrees.

The PS-I programme is meant to give the students a much needed exposure to the

professional world be it industries, research institutes or social service organisations. It

acquaints the students with the complexity, discipline and professionalism of work areas.

Central Electronics Engineering Research Institute (CEERI),Pilani (Rajasthan) was founded

on September21,1953 by the then prime minister Pt. Jawaharlal Nehru for pioneering

scientific and technological advancement in the ever-growing field of electronics. The work

of research and development started in the year 1958. Since then, under the Council of

Scientific and Industrial Research (CSIR), CEERI is carving a niche in the field of R&D in

electronics with its innovation for the benefit of society. CEERI is a premier research

institute currently working on three major areas of research and scientific application:

1. Electronic Systems

2. Microwave Tubes

3. Semiconductor devices

The mandate of CEERI recognizes and clearly states the vision and objectives for which this

institute was established, is currently working on and will pursue in the future:

1. Research and Development in the field of electronic devices and systems.

2. Efforts for the absorption, upgradation and diversification of technology in industry.

3. To assist in design, fabrication and testing of technology for industry and users.

4. Provide services for specific needs in product development, quality and precision.

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The three thrust areas are further diversified into various groups:

1. Microwave tubes- Communication tubes and Industrial tubes

2. Electronic systems-Digital Systems Group and Agri-electronics Group

3. Semiconductor devices-IC Design, Sensors and Nanotechnology, Power devices,

Hybrid microcircuits and Optoelectronics

Currently the director of CEERI, Pilani is Dr. Chandra Shekhar who has to his credentials

numerous achievements including the design of Motorola 68010- our country’s first general

purpose microprocessor chip. He has been a proud recipient of the CEERI Foundation

Reward for designing of Application Specific Integrated Circuit (ASIC).

ORIENTATION

The PS-I programme for the academic year 2012-2013 started on May21, 2012. The first

two days at Central Electronics Engineering Research Institute, Pilani went in orientation

whereby the students visited the various departments to have a close look on the research

work going on there.

On the first day, the students were made to visit the departments under semiconductor

devices.

The first scientist whom the students met was Dr. Ajay Agarwal from the MEMS and

Microsensors group. He and his team are currently working on MEMS and their

applications and integration in various control systems. MEMS is an acronym for Micro

Electro Mechanical Systems. MEMS are basically small scale moving mechanical elements

that move from the order of microns to maximum of a millimeter when provided an

electrostatic actuation. This field encompasses sophisticated and beautiful integration of

mechanical and electrical domains and has received focus in recent years as a growing field

of research and application in semiconductor devices. MEMS are basically active devices

used along with passive devices like resistors, inductors and capacitors to design complete

control circuits. In this field, CEERI is currently working on sensors like pressure sensors and

biosensors, gyroscope, accelerometers, micromirrors and silicon nanogap based devices.

The next scientist was Dr.Raheja from the Digital System Design group. He and his team

are currently striving to find out optimum solutions for real-life processing problems in

industries. Some of these outstanding projects include applying image processing in finding

out the size of spherical objects in real-time processing. In iron and steel industry, when

steel balls are crushed to optimum size, the correct size has to be ensured inside the

crusher only otherwise the same step has to be repeated again and again. The project tries

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to identify the size of steel balls within the crusher, compare it with the standard size and

reject those that do not meet the constraints.

Another project is based on human machine interface whereby they are trying to develop a

robot which can show hand gestures exactly like a human. Such a machine can be used to

perform surgeries in future bringing a revolution in the medical and surgical field. This

project is the current focus of the research team.

The third project is meant for detecting fracture of civil structures. All the civil structures, as

we know are prone to damage and failure. The project aims at determining the vulnerability

of civil structures to natural disasters by determining certain criteria and comparing it with

the optimal values thereby drawing a conclusion about the life of that structure.

In a nutshell, Dr. Raheja’s team is working on developing technologies that will assist in

industrial services and also benefit the society as a whole.

The third department that the students came across was Scanning Electron Microscope

(SEM) headed by a very dynamic scientist Dr. Kamal Jit Rangra. SEM is a separate unit

functioning under Sensors and Nanotechnology Group headed by Dr. Jamil Akhtar. Dr.

Rangra and his team are working on state of the art devices like Radio Frequency Micro

Electro Mechanical Systems (RF MEMS) Switches and Digital Mirror Devices (DMDs). Dr.

Rangra briefed the students about the basic concept of MEMS and how over the years it

has become a growing area of interest in research among scientists and technocrats all over

the world. MEMS can be any distinguishable moving element or even vibrations that can

detect any change in the physical surroundings and respond accordingly. He gave the

students an overview of the various elements involved in the design of a RF MEMS switch

particularly cantilever-based DC contact switches. RF MEMS switches are generally used in

the working of electromagnetic relays that operate in the RF frequency domain. DC contact

switches are basically used in wireless communication applications particularly as SPNT

switches in mobile communication for the transmission and receiving of data. Capacitive

switches are another kind of RF MEMS Switches used more specifically in satellite

communication. Students were also told about the similarities in Integrated Circuit (IC) and

MEMS fabrication process. The fabrication of both techniques involves processes like

etching (removal of a metal layer) and lithography (projection of 3-D design onto 2-D silicon

wafer). The students were also told difference between sensors and actuators. Sensors

interact with physical environment and convert the response to electrical signals.

Actuators, on the other hand convert it back to mechanical domain which is realized as an

output.

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The second project being undertaken by the SEM department is on DMDs. Digital Mirror

Device as Dr. Rangra said, is a kind of see-saw structure that works on the principle of

selectivity. DMDs consist of mirrors arranged as an array in which each mirror acts as a

pixel. The issue that they are facing in this project is addressing each mirror in the array for

changing its orientation independently of the other mirrors. DMDs are basically used for

two purposes:

1. As a slit to select one object from the field of view.

2. As an array of mirrors that can be used to accomplish multiobject spectroscopy.

In a nutshell, Dr. Rangra acquainted the students with the current progress in the

sophisticated instrument designs in MEMS field and also threw light on the future prospects

of this technology.

Next, the students got a chance to meet Dr. P.K. Khanna from the Hybrid Microcircuits

group which is a separate unit under Semiconductor Devices department at CEERI. The

department works on fabrication of electric circuits that can meet the stringent

temperature and pressure conditions encountered in aircrafts, submarines and satellites.

Currently, the department is working on Total Integration Technology (TIT) using Low

Temperature Cofired Ceramic (LTCC) whereby passive components are fabricated in layers

of ceramic and active components are later added in between the layers to make the

complete signal conditioning circuit. CEERI designs such circuits with the given

specifications which are then send to laboratories in Belgium for packaging and the final

product is then supplied to three Indian industries. The department of hybrid microcircuits

has achieved space qualification after designing signal conditioning circuits for the INSAT

satellites. The other activities of this group are:

1. Thick-film hybrid micro-circuit (HMC) fabrication for specific applications. 2. Bonding and packaging of fine-pitch devices and components. 3. High temperature stable interconnections based on isothermal solidification. 4. Smart materials based on phase transformation and domain polarization.

Students then visited Dr. Mandal from the IC Design group. Dr. Mandal is currently working

on a very amazing or rather say astounding project on smart cameras and developing a

unique machine that can identify human emotions and facial expressions. This machine, he

said would prove to be very beneficial in the field of telemedicine where the doctor is not

able to attend the patient personally. Smart cameras that CEERI IS working upon, will be

able to detect human expressions with reliable accuracy.

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Broadly speaking, the team is working on following ideas:

1. Immersive experience under National Programme on Perception Engineering.

2. Smart cameras

3. Pain analysis as a part of Supra Institutional Project.

4. Brain Modelling

The last department visited on first day of orientation was Optoelectronics headed by Dr.

Dhanvantri. The department comes under semiconductor devices. The current field of

research in this department is Metal Semiconductor Field Effect Transistor (MESFETs). The

lithography technique used for fabrication is Chemical Vapour Deposition (CVD). The

department is currently working on following projects:

1. Gallium Nitride based Devices 2. Gallium Arsenide based Devices 3. Silica-on-Silicon based Planar Lightwave Circuits

On May 22, 2012 the students visited a few more departments of CEERI.

The orientation programme on second day started with the students visiting the Plasma

Physics Laboratory where they interacted with Dr. U.N. Pal. Dr. Pal told the students about

the concept of plasma, how it is generated and how it can be used as a potential energy

source for future. He called plasma as the energy for 21st century. Dr. Pal told that plasma

has been identified as the fourth state of matter. Plasma is conceptually a cluster of ionized

materials be it electrons or ionized gas that behave like a crowd with an identity and

distinguishable properties. Plasma exists everywhere from vacuum to the wide space in our

universe. Plasma laboratory of CEERI is functional under the high power Microwave Tubes

department of CEERI. Currently there are four projects going on under this department of

plasma physics:

1. High power switches that work on high voltages for use in radar applications.

2. Development of UV sources for changing the surface properties of material

particularly a Mercury (Hg) free eco-friendly RO system.

3. Calibration of spectrometers using DC Glow Discharge for measurement of

wavelengths involved in spectroscopy.

4. Plasma assisted micro applications that are used in communication domain to

accommodate more signals.

Some of the hi-tech instruments used in the laboratory were also shown to the students

which included DC Glow Discharge, Plasma Cathode Electron Gun and Vacuum Ultra Violet

(VUV) Spectrometer.

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The next department visited was Cathode Ray Tubes department where the students were

told details about electron emission. There are basically three kinds of emission processes:

High field emission through tunneling effect

Photoemission through photons

Thermal emission through thermionic cathodes

Here arises the concept of OJ electrons. OJ electrons are those electrons which are knocked

off from their respective orbits as a result of the energy gained in transition from one

atomic level to another. The device used in this laboratory for cathode characterization is a

long-life dispenser that has better accuracy than the Scanning Electron Microscope.

Cathode characterization is done in order to identify the surface contaminants. The

instrument obtains a spectrum of the surface material through an analyser. Since different

elements give peaks at different wavelengths the surface contaminant can be identified.

The department visited next was that of Travelling Wave Tubes and Klystron. Klystron is

basically a microwave amplifier. The instrument consists of three sections: Electron gun,

Radio Frequency (RF) section and the Collector for spent electron beam. The spent electron

beam can be used again for the entire process. It is collected through the window at the top

of Klystron device.

Next, the students saw the Brazing Workshop where equipments with precise dimensions

are made in a furnace using Hydrogen (H2) gas. Special care is taken to prevent any leakage

in the furnace which may otherwise blast. H2 is used because it is a reducing agent and

provides uniformity in the process of brazing. To prevent any leakage, N2 gas is also

supplied as it is an inert gas.

Gyrotron was the next department visited by the BITS students. Here, the students were

told how microwave tubes can be used as oscillators and amplifiers and the application of

TWT in transponders of satellites. Throughout the world, scientists are working in

developing a fusion reactor that will perform the same reaction as it happens on the

surface of the sun. The immense energy produced can be efficiently used to meet the

energy needs globally. Such a reactor will need heavy amounts of power supply in order to

initiate the fusion reaction. CEERI is working on developing 200 kW Gyrotron to meet this

need of power supply.

Dr. Pramod from Reconfigurable Computing Systems was the next person to orient the

students. He told the students about the use of Field Programmable Gate Arrays (FPGA) for

designing reconfigurable computing systems. IC functionality cannot be changed but such is

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not the case with FPGA where different operations can be done for different time domains

in the same chip.

The objectives of digital systems group are:

1. Wireless Sensor Networks - Institutional Supra Project 2. Image Processing based Smart System for Human Gesture Identification – Institutional Supra Project. 3. Sensor characterization and development of intelligent measurement systems – Institutional Supra Project. 4. Development of system level reconfiguration techniques for smart reconfigurable computing system- Institutional Supra Project. 5. Development of impact analysis and pulsation behavior monitoring subsystems for Iron ore processing - Network Project. 6. Development of image processing techniques to measure the pellet size distribution -Network Project. 7. Development of comprehensive technology for disaster prevention and management for Jharia coalfields - Network Project. 8. Modular Re-configurable Micro Manufacturing Systems (MRMMS) for Multi Material Desktop Manufacturing Capabilities - Network Project. 9. Cartographic Generalization of Map objects - Sponsored Project. 10. Development of an E-tongue system based on voltammetry - Sponsored Project. 11. Design and development of System level reconfiguration techniques for Reconfigurable

Computing systems- Sponsored Project.

The next department was Agri-electronics where Mr. V. Saikrishna told the students about the achievements of the department and the current projects being undertaken. CEERI is involved in the design and development of state-of-art technologies for agro-based industries of India for more than two decades. Some of the technologies developed (know-how) are transferred to the industry and absorbed in their processes. Industry and the Government recognized the scientific efforts and work of AEG CEERI team by bestowing honors such as NRDC award, CSIR technology shield, FICCI award, ELCINA award, Sugar Technology Mission award etc. Notable areas where CEERI contributed extensively in agro based applications are technology development and value addition for Sugar, Tea, Energy and food storage industries in improving the product quality and sustainability, energy saving. The last department visited by the students was IC Design Group where the students met Dr. Bose. He informed the students about various hardware languages like Verilog and VHDL and simulation software like PSPICE and MATLAB. He gave the students a brief idea on incorporating various logics on a single chip through behavioral design and squeezing approach.

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ABOUT SNG-SEM

MEMS Micro-electro-mechanical-systems, is also known as the miniature engineering, is a multi disciplinary approach for fabricating systems with dimensions in microns or less. MEMS as the name suggests, ‘Micro’ means the micro dimensional scale, ‘electro’ means electricity or electronics, ‘mechanical’ means some form of moving or rotating or tilting part. These fields contribute to the making of MEMS systems. The concept of MEMS has evolved rapidly in the past two decades. It has incorporated nanolevel changes in physical quantities like optical, magnetic, piezo, thermal and pressure. The origin of MEMS is traced to R P Feyman's hypothesis on miniaturization of devices and systems to the extent till physical laws and material properties impose no limit. MEMS and ICs are similar in terms of fabrication methods and mechanisms (etching and lithography), but the major difference between them is how they work. In ICs the moving thing are the electrons which make the switch work whereas in MEMS switches, there is a mechanical part like a cantilever or a beam which actually moves, rotates or tilts to make the switch work and perform desired action. Any MEMS device has two principal components: sensing and/or actuation component and a signal transduction unit. So any MEMS device transmits signals based on the sensing done or actuates a component based on the signal it receives. The application of MEMS in radio frequency is more recent than other regimes. It is called RF MEMS (Radio Frequency MEMS). At present, RF MEMS devices such as switches or relays, tunable capacitors or varactors, high Q inductors, resonators and filters, which constitute the `fundamental building blocks' of radio frequency applications, are the most vigorously pursued MEMS devices by academic and industrial research communities.

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RF MEMS SWITCH

The basic device of RF MEMS, the switch is one of the first and most studied device in this

field. The basic functioning of the RF switch resembles an electromechanical relay, but at a

size of microns, which is commensurable to semiconductor switches. The moving beam or

cantilever has a length equal to 100 microns and a thickness of 1-5 microns. The material

used depends on switch configurations and available fabrication technologies. The

actuation mechanism may be anything from electrostatic to electromagnetic, electro-

thermal or piezoelectric. In most cases, we use electrostatic due to very low power

consumption and easy integration with the existing fabrication technologies. Other devices

used in the same domain are PIN diodes, GaAs FETs and the conventional electro-

mechanical relays. The comparison among them is shown in the table below.

As seen in the table above, RF MEMS switches offer lower capacitance and lower contact

resistance as compared to the FET or PIN diodes, which results in better performance of RF

MEMS switch.

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ADVANTAGES OF RF MEMS SWITCHES

1. Near Zero Power Consumption: The electrostatic actuation requires almost 30-80 V,

but does not pass any current. So the power consumption is almost zero, which is an

excellent characteristic of RF MEMS switch. On the other hand, thermal or magnetic

switches consume a lot of current.

2. Very high isolation: RF MEMS switches are fabricated with air gaps and therefore

have a very low capacitance resulting in excellent isolation at even high frequencies

of the order of 100 GHz.

3. Very low insertion loss: RF MEMS metal contact and capacitive switches have an

insertion loss of 0.1 db even at 100 GHz.

4. Linearity and Inter-modulation products: MEMS switches are extremely linear

devices, and therefore result in low inter-modulation products in switching and

tuning operations. Their performance is far better than PIN diode or FETs.

5. Potential for low cost: RF MEMS are fabricated on quartz or silicon, which are not

costly materials, but the packaging cost is high due to which the net cost of RF

switches increases.

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LIMITATIONS OF RF MEMS SWITCHES

There are mainly two limitations of RF MEMS switches:

1. Device Packaging: RF MEMS switch packaging is crucial not only for proper device functioning, but also for the fast dissemination of the technology. The operational characteristics of the devices are severely affected by the presence of water vapors, oxygen, hydrocarbons and other contaminants.

2. Power Handling and Reliability: The number of on-of cycles of a MEMS device is considered to be one of the major reliability criteria. As shown in the Table above devices have been reported with life time up to a few billions cycles, under low power conditions (0.5-5mW). The failure mechanisms depend on the RF Power used and can be due to thermal stress, dielectric break down, self-actuation or critical current density issues. Dielectric charging, pitting, hardening, dielectric formation typically undermine the reliability of devices.

Talking about reliability issues in detail, we have five cases for ohmic and capacitive switches.

1. Contamination: contact resistance increases due to organic deposits, absorbed

hydrocarbon layers and contamination around the contact area. Can be avoided by

proper material selection.

2. Stiction: Arises when the surface interaction energy at a contact point is greater than

the restoring force which tends to bring the switch into the equilibrium/open

position. In such a case the RF MEMS switch will stick in the closed position. At high

current conditions, stiction will generally be generated by hot-welding. Can be

avoided by using stiff elements.

3. Wear: The contact may be damaged by a large impact force which can be much

greater than the high static contact force needed for low contact resistance.

4. Cycling mode: In cold switching contact damage, pitting, and hardening of the metal

occur since the same point is repeatedly hit during cycling. In the long term the

contact area is reduced, increasing the contact resistance. In hot switching, metal

arcs are produced at contact melting the asperities thereby increasing the area.

5. Dielectric charging: This reliability issue is applicable only for capacitive switches. The theory of dielectric charging involves the concept of charges tunneling into the dielectric and becoming trapped. In an effort to maximize the on-capacitance of a MEMS capacitive switch, the dielectric is typically made quite thin, usually less than 3000 A0.

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TYPES OF RF SWITCHES AND BASIC CONFIGURATIONS RF switches can be distinguished into 2 main categories: Capacitive and Ohmic.

Capacitive switches: As seen from the figure there is a thin layer of dielectric which

separates two conducting electrodes. There is no direct metal to metal contact. The capacitive switch is mainly used in a shunt switch configuration where RF signal is shorted to ground by a variable capacitor.

Bandwidth is limited by the capacitance ratio between the ON and OFF states and generally the RF signal range for capacitive RFMEMS switches is 4GHz-120 GHz

Ohmic switches: The Basic structure has a conductive beam suspended over a break in

the transmission line. Ohmic switch can be of two types, broadside and inline switch.

The signal range for ohmic switches is DC to 40 GHz, with the upper limit to be set by the parasitic capacitance which is formed between the metallic contacts.

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SPECIFICATIONS USED TO DESIGN AN RF MEMS SWITCH

1. Insertion loss ( S11 ) : The loss of signal power while passing from a switch in ON state

2. Isolation ( S21 ) : Isolation is defined as the magnitude of a signal that gets coupled

across an open circuit.

3. Impedance matching: The switching device should be matched at both input and output sides, for both ON and OFF state of the switch, to minimize its influence on the performance of the rest of the system.

4. Transition time: The time required for the output RF signal to rise from 10% to 90% of its maximum value.

5. Switching speed: The time is measured from 50% on the control voltage to 90% of the RF envelop when the switch is turned on.

6. Power handling: It is a measure of how efficiently the RF signal is passing through a switch.

7. Bandwidth: Range of frequencies in which the switch will work. a. Ohmic switch : DC to 40 GHz b. Capacitive switch : 4 to 120 GHz

8. Actuation voltage: The minimum voltage required for actuation of the

switch/cantilever/beam.

9. Lifetime: Electromechanical switches involve moving parts so it becomes important to consider lifetime (usually mentioned in terms of number of cycles).

10. Resonant frequency: The moving parts have resonant frequencies that can be modelled in terms of effective spring constants and resonating mass. At this frequency PE and KE resonate.

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DESIGN CONSIDERATIONS OF RF MEMS SWITCH

1. Mechanical modelling: Getting a relation between the distance, force and material properties, basically young’s modulus and beam geometry.

2. Electrostatic modelling: Getting a relation between the electrostatic force and activation voltage.

3. Contact area modelling: Getting a relation between contact force with actuation voltage and beam geometry.

4. Fringing capacitance: The capacitance relations we use are based on the assumption that the beam dimensions are very large than the gap between plates. But in this case the gap is comparable to the beam dimensions. So the effect of fringing capacitance has to be taken care of.

5. Perforation: To avoid the squeeze film damping and viscous effects of the air film between the beam and the contact at the bottom, we use holes in the cantilever so that air gets a way to go out and not disturb the pull down of the cantilever.

6. Self actuation: Self actuation is another failure phenomenon which degrades the RF

MEMS switch operation under hot mode cycling. When an RF signal is applied to the

RF MEMS switch, with frequency much higher than its resonant frequency, an

equivalent DC voltage will unavoidably be applied to the switch. For high-power RF

signals this DC voltage may generate large actuation force which can excite the

switch and finally close it.

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CONCLUSIONS AND FUTURE WORK

The following objectives have been met in the first two weeks:

1. Study of the basics of electric switches.

2. Study of the modelling and working of RF MEMS switches.

3. Study of research and review papers on the configuration of capacitive and DC

contact switches from the current literature.

In the coming weeks, we intend to:

1. Select a particular switch configuration of ohmic contact switches and analyze the

pros and cons of its design.

2. Simulation of the improved design on CAD softwares like ANSYS, COMSOL, HFSS and

COVENTORWARE.

3. Develop a 3-D model of asperities on the contact surface of a real specimen surface

using COMSOL or ANSYS.

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REFERENCES

1. K. J. Rangra, “Electrostatic Low Actuation Voltage RF MEMS Switches for Telecommunications”, PhD Thesis, University of Trento, Italy 2005.

2. G. M. Rabeiz, “RF MEMS switches and Switch Circuits”, IEEE Microwave magazine, December 2001.

3. G. M. Rebeiz, “RF MEMS Theory, Design and Technology”, Wiley Publications, Canada, 2003.

4. Michail N. Spasos, “RF MEMS switch for reconfigurable antennas”, PhD thesis, School of Engineering and Design, Brunel University, July 2011.

5. Soumendhu Sinha, “RF MEMS redundancy switch design for switch matrix applications”, PS II Report, BITS Pilani, December 2011.

6. CSIR-CEERI website: www.ceeri.ernet.in