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Presentation by: MD ERFAN (33108908)

Masters in Electrical Communication Engineering

RF MEMS BASIC

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Outline

• What are the MEMS? • Function of MEMS• Motivation• RF MEMS• MEMS characterization• Market Potential And Applications• RF MEMS Components• Recent RF MEMS development• RF MEMS Limitations• RF MEMS Challenges• Summary• References

RF MEMS BASIC

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What are the Mems?

1) MEMS refer to miniature mechatronicsystems

2) Fabricated using VLSItechnology

3) Techniques and processes to design andcreate miniature systems Miniature embedded system.[3]

Micro electro mechanical Systems (MEMS) have been developed since the 1970sfor pressure and temperature sensors, accelerometers and other sensor devices

The one main criterion of MEMS: Sort of mechanical functionality whether or not these elements can move. [2]

[2]

RF MEMS BASIC

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Function of MEMS

1. Converts physical stimuli, events and parameters to Electrical, Mechanical, and optical signals and vice versa

2. Performs actuation, sensing and other functions

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MEMS benefits:

Micro size sensors and actuators: Integration withelectronics on single chip (system or lab on chip)

Decreased cost of production: bulk processing

Many new features and products previouslyunthought can be possible

Combination of MEMS with other branches:Example optical MEMS, Bio-MEMS Æ futuristicdevices

Motivation

[3]

RF MEMS BASIC

6Microwave Couplers

MEMS Fabrication Process

[4]

Silicon-On-Insulator wafers.

This type of wafer consists of a three layers:

1. Silicon substrate layer (~400 mm)2. Silicon dioxide buried layer (~1 mm)3. Silicon device layer (~50 mm)

Five steps:

1) Photo resist spinning and mask contact photolithography

2. Photo resist development

3. Anisotropic DRIE etching

4. Resist removal

5. Isotropic vapour HF etching

7Microwave Couplers

Mostly used material is silicon

Other materials

ƒ 1) Polycrystalline silicon (poly silicon)„ 2) Silicon dioxide (SiO2)„ 3) Silicon nitride (Si3N4)„ 4) Aluminum (thin film)„ 5) Gold (thin film)„ 7) Many more including polymers now a days„ 8) Doping of silicon [3]

MEMS Materials

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Micro-electromechanical systems with electronic components comprising moving sub-millimeter-sized parts that provide radio frequency functionality.

RF MEMS

• Micro system for radio and millimeter wave applications

• Micro switches

•Micro-machined inductors• •capacitors

•Antennas

•Resonators

•filters

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MEMS characterization

Technologies for MEMS characterization:

• Scanning Probe Microscopy (SPM)„ • Atomic Force Microscopy (AFM)„ • Scanning Tunneling microscopy (STM)„ • Magnetic Force Microscopy (MFM)„ •Scanning Electron Microscope (SEM)„•Laser Doppler Vibro meter„ •Electronic Speckle Interference Pattern technology(ESPI)

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Market Potential And Applications

[5]

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Market Potential And Applications

[6]

Cell phones dominate the growthled by the successes of Apple's iPhoneand other smart phones

Apple's iPad will propel the MEMSchip market to over $3 billion by 2014

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RF MEMS Components

Switching networks are used in virtually every communication system for filter or amplifier selection.

Fig: Schematic diagram of the RF MEMS switch at (a) on-state and (b) off-state. [ 7] 

One of the proposed RF MEMS switch that exploits in-plane, bi-stable, electromagnetic actuators• It is similar to a typical coplanar waveguide•Impedance mismatch, RF signal is reflected , off-state. Fig(b)•, the actuators, original positions, on state Figure(a)

The switch consumes no standing power due to bi-stability of the actuatorsThe switch operates at very low voltageFabrication process is much simpler than that of the conventional devices Since the actuators do not face the signal line, they are less susceptible to high power RF signal

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RF MEMS Component (Ohmic switch)

• G voltage 40 to 120 V depends on design• Operate up to 60Ghz• operated under 200 µN• At 10 GHz: Insertion loss of 0.27 dBisolation of 12 dB for an 8 contact switch• on resistance is less than 1 Ω

SEM image of Ohmic switch by Radant[8]

• Electro statically actuated MEMS micro switch for both DC and RF applications•The micro switch is a 3-terminal device•The beam is deflected by applying a voltage between the G and S

Schematic representation of the ohmic switch

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Components Capacitive switch

[9]

That employ the movement of a mechanical component to place a variable capacitance in the path of a radio-frequency transmission line so either block transmit RF signal

Applications :1)Telecommunications, 2)Aerospace and defense3) Automotive and 4)low-voltage capacitive shunt micro switch5)Cmos compatible

•Switch consists of a metallic electrode

•Voltage is applied between the suspended electrode

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Advantages and Application of RF MEMS Switches

Advantages of MEMS switches over pin diode and FET switch:

Very low Power ConsumptionVery High IsolationVery Low Insertion LossHigh LinearityBetter stability with temperatureMultiple frequency rangeMiniaturization (<100um²)Potential for Low Cost

Applications :Cellular phonesTransmittersReceiversAntennas and transmission linesPhase shiftersLow frequency applications:Automatic test equipmentIndustrial and medical instrumentations

RF MEMS BASIC

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[10]

Passive Components Tunable Inductor

Very flexible analog integrated circuits can be implemented by Tunable Inductor

Proposed structure of a variable inductor.

Structure of an improved heat expansion actuator.

When current flows and heat is generated in the lower metal, the tip portion goes up.

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Components (Tunable Capacitor)

Top plate : Electroplating nickel (20um)covered by a gold layer(2um) thickness

Bottom plate :Poly silicon covered by anitride layer of 0.35um thickness

[11]

Two dimensional RF MEMS capacitor structure configuration

• It consists of two parallel plates

• Four T shaped beams

• Air is between the top plate and bottom plate

•Two plates are flexible

•300% capacitance increase

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Mems resonator

[12]

•A fixed micro disk is sandwiched between two suspended deformable waveguides •The device is fabricated on a silicon-on-insulator (SOI) wafer

•The radius of the micro disk is 10 m and initial gap spacing is 1.4 micro meter.•To avoid the pull-in instability in gap-closing actuators, the actuator spacing is designed to be three times larger than the disk-waveguide spacing•Using this design, the coupling gap can be continuously reduced until physical contact without experiencing instability

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[13]

Single-stage phase shifter

•High-resistivity mono crystalline-silicon block

Functional drawing of a single-stage dielectric-block phase shifter with actuation contact points for electrostatic actuation and its cross-sections

The relative phase shift is achieved by vertically pulling the mono crystalline-silicon block down above the CPW by electrostatic actuation.

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Linear-coded phase shifters

[13]

•Multi-stage linear-coded phase shifter with total phase-shift of 360° (left), and its phase resolution of 45°

•A multi-stage linear-coded phase shifter with 45° phase-shift steps can be achieved by placing seven single 45° stages in series.

•The distance between each stage is 10 µm

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Today's smart phones antennas have gotten smaller hey are being asked to cover lower-frequency bands that would normally require larger antenna form factors.

professor Gabriel Rebeiz, holding a dual-band frequency tunable antenna

[14]

Recent RF MEMS development

•Incorporating RF MEMS into smart phone antennas yields "tunable" antennas

• It work efficiently across one or two frequency bands at a time

RF MEMS serves:

•low-loss switched variable capacitor

• Capable of changing the antenna's resonant frequency

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Metal contact RF MEMS switches

•These metal switches the width of a human hair Insertion loss: <0.3db at 3Ghz. Ultra-high linearity• 50um x 50um which directly impacts cost.•Used in 4G phones to provide muchfaster speeds.

Metal Switch

Metal-contact and capacitive switches could turn out to be extremely important for tunable RF front ends of next-generation communication systems

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Relatively low switching speed&

Lifetime reliability

Switching speed :

• Most electrostatic MEMS switches is 2-40 μs•Thermal/magnetic switches are 200-3, 000 μs

Lifetime :•Mature MEMS switches is 0.1-40 Billion cycles

•Many systems require switches with 20-200 Billion cycles

RF MEMS Limitations

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RF MEMS Limitations

Temperature changes

•Problems in metal packaging

• coefficient of expansion of metals> 10 times of silicon

• special isolation techniquesrequired to prevent packageexpansion

[16]

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Humidity effects

•Humidity can be considered a serious issue for MEMS structure.

•Surface micro machined devices are extremely hydrophilic for reasons related to processing and, for this reason, the surfaces in a humidity atmosphere will experience both condensation

• Which will create bending moment in structures, and capillarity forces.

• Which will create stronger adhesive bonds than Vander Waals forces alone.

[16]

RF MEMS Limitations

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Vibrations and shocks:

[16]

•Vibration is a large reliability concern in MEMS.

• Due to the sensitivity and fragile nature of many MEMS

•External vibrations can have disastrous implications.

•External vibration can cause failure.

•Long-term vibration will also contribute to fatigue.

•For space applications, vibration considerations are important, because devices are subjected to large vibrations in the launch process

Fig: Crack in single crystal silicon support beams caused by vibrations from a launch test

RF MEMS Limitations

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RF MEMS Challenges

Solution of several challenges:

EnvironmentModeling reliabilityIntegration

Most important for commercialization

packaging

[17]

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summary

•RF MEMS is a promising Technology

• A lot of applications

• Better performance than convention RF components

• Packaging is a challenging factor

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References

1) RF MEMS: Theory, Design, and Technology.Gabriel M. Rebeiz2)http://fadikhalil.perso.sfr.fr/MEMS.html3) MEMS Motivation, Prasanna S. Gandhi4) http://www.utwente.nl/ctw/wa/web_dev/old/research/mechatronics/clemps/MoreInfo/20101117MemsFabrication/5) http://m.wangchao.net.cn/baike/scdetail_2662517.html6) http://1.bp.blogspot.com/_o74ruxv2td0/TGmZYIApieI/AAAAAAAACu0/pRBY0eLSa8A/s1600/rcjMEMSmarket2.jpg7) http://www.ece.lsu.edu/dyhah/RF_switch.html8) http://www.radantmems.com/radantmems.data/Library/MTT_2003summary022403.pdf9) http://www.tyndall.ie/content/rf-mems-capacitive-switch10)http://www.el.gunma-u.ac.jp/~kobaweb/news/pdf/AVLSIWS2005.pdf11)http://www.ime.pku.edu.cn/mems/faculty/zhanghx/Achievements/en/Publications/2009-5-Tunable%20RF%20MEMS%20capacitor%20for%20wireless%20communication.pdf12)http://nanophotonics.eecs.berkeley.edu/pdf/Lee%20-%20MEMS-Actuated%20Microdisk%20Resonators.pdf13)http://www.diva-portal.org/smash/get/diva2:516789/FULLTEXT01.pdf14)http://www.jacobsschool.ucsd.edu/news/news_releases/release.sfe?id=146415) http://www.gereports.com/post/79899413936/mems-at-work-tiny-switches-could-support16) http://paduaresearch.cab.unipd.it/3605/1/Tesi_dottorato_Enrico_Autizi.pdf17) http://www.iject.org/vol2issue2/tpsingh.pdf

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