Study & Analysis of Shunt Rf Mems Capacitive

7/30/2019 Study & Analysis of Shunt Rf Mems Capacitive

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NATIONAL INSTITUTE OF TECHNOLOGY SILCH

STUDY, DESIGN & ANALYSIS OF SHU

MEMS CAPACITIVE SWITCHES AND SW

CAPACITORS

JOHNSON TAYE

SCHOLAR: 11-24-104

M.TECH 3

RD

SEMESTER

PROJECT GUIDE

MR. KOUSHIK GUHA

ASST. PROFESSOR


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INTRODUCTION

Developed since 1970s. Four distinct areas

1. RF MEMS switches, varactors, and inducto

2. Micromachined transmission lines, high-Q

resonators, filters, and antennas (suitable forGHz).

3. FBAR (thin film bulk acoustic resonators) a

4. RF micromechanical resonators and filters mechanical vibrations of extremely small beams to ac

resonance at 0.01200 MHz in vacuum).


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RF MEMS SWITCHES

Essentially, miniature devices that use a mmovement to achieve a short circuit orcircuit in a transmission line.

Dr. Larry Larson developed the first MEMS

1990-1991 under the support of DARPA. Conventional switching devices: FET

diodes

High Insertion loss, low isolation

MEMS switches: low insertion loss, high is


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COMPARISON

PARAMETERS RF MEMS PIN DIODE FETVoltage (V) 2080 35 35

Current (mA) 0 320 0

Power consumption(mW) 0.050.1 5100 0.050.

Switching time 1300 ms 1100 ns 1100 n

Cup (series) (fF) 16 4080 70140

Rs (series) () 0.52 24 46

Capacitance ratio 40500 10 n/a

Cut-off frequency (THz) 20-80 THz 41000 0.5-2

Isolation (110 GHz) Very High High Medium

Isolation (1040 GHz) Very High Medium Low

Isolation (60100 GHz) High Medium None

Loss (1

100 GHz) (dB) 0.05-0.2 0.3-1.2 0.4-2.5

S S C


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RF MEMS SWITCH

CONFIGURATIONS

Two distinct parts:Mechanical(actuation) section

Electrostatic, magnetostatic, piezoelectric an

Electrical section

Series or Shunt

Metal-to-metal(DC) contact or Capacitive co

ELECTROSTATIC SHUNT CAPACITIVE

CONTACT

MEMS SHUNT CAPACITIVE


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MEMS SHUNT CAPACITIVE

SWITCHES

Why?? High Frequency::10-200 GHz

large contact area

100500 mW of RF power

Easier to fabricate than series

switches

Figure:Illustration of typicalMEMS shunt switch:: its crosssection, plan view and

equivalent circuit(copyrightIEEE)


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PERFORMANCE METRICS1.

Spring constant(k)2. Capacitance

Up-state

Down-state

Capacitance ratio, Cd/Cup

3. Pull-in voltage(Vp)

4. Switching time5. Mechanical resonant frequency

6. S-parameters(S11,S21) Insertion loss

Isolation

Return loss


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PARAMETERS(Spring cons

E= Youngs modulus of the beam material

t= thickness of the beam

w=width of the beam Lm=length of the beam

=residual tensile stress in the membrane

=poisons ratio for the membrane material


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PARAMETERS(Capacitance

Up-state

Down-state

Capacitance ratio

r = dielectric constan

td= dielectric thicknes

W= t-line width

G= bridge height

o=permittivity of free

8.854X10^-12 F/m


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PARAMETERS(S-Paramete

Reflection coefficient, S11

S11= Vi-/Vi+

Transmission Coefficient, S21

S21= Vo/Vi+Insertion loss(Switch ON state): (ideally zero)

IL= -20log10|S21| dB

Isolation(Switch OFF state): (ideally infinite)

Isolation= 1/|S21|


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PARAMETERS(Pull-In volta

Actuation voltage Beam snaps down

Independent of w


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WORKING PRINCIPLE DC voltage Bias b/w t-line and

beam.

Electrostatic force develops.

Mechanical restoration force.

Electrostatic force exceedsmechanical force at g=(2/3)go for

Vp. Beam unstable & snaps down,

providing a high capacitance pathfor RF signal to ground.

Electrostatic force=Mechanicalforce,

Fig1:RF

Transmission

F

Fig2:Voltage Biasing


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n e emeMethod)

L=280m t=1m

w=100m

W=100m td=0.15m

go=2m

l

WFig1:Standard Shunt

Capacitive SwitchFig2:To

CPW

Grounds

Center

conductorDielectric


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RESULTS

Pull-in Voltage, Vp=15.5 V

VOLTAGE vs


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RESULTSCONTACT ANALYSIS

Voltage


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RESULTS

UP-STATE DOWN-STATE


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PULL-DOWN AT ACTUATION VOLTAGE


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VARIOUS DESIGNS

1.With Holes 3.

st

2.Flexure

Beam


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SIMULATION RESULTS

PULL-IN VOLTAGES


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SUMMARYPull-in Voltages(Volts)Residual Stress= 0 MPa

Dimensions ThicknessLength 0.8um 1um280um 11.875 V 15.5 V280um_Holes 11.625 V 15.37 V280um_Flexures 7.5V 9.25280um_Stripes 15.9375 V250um 14.375 V 19 V250um_Flexures 9.375 V250um_Stripes 14 V 17.25 V230um 16.875 V 21.75 V230um_Flexures 12.1875 V230um_Stripes 20.63 V


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SCOPE OF WORK

S-parameters(insertion loss, isolation, loss).

More structures with different membran

materials.

Switched capacitors

Reduce dimensions to reduce capacitanc

Integrate energy harvesting device to s


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REFERENCES[1] G. M. Rebeiz, RF MEMS-Theory, Design and Technology, John Wiley & Sons. I

[2] Gabriel M. Rebeiz, RF MEMS Switches: Status of the Technology, In 12Conference on Solid State Sensors, Actuators and Microsystems, Boston, June 8-12

[3] Rebeiz, G.M. and J.B. Muldavin, 2001. RF-MEMS switches and switch circuits. IMagaz., 2: 59-71. DOI: 10.1109/6668.969936.

[4] Coventorware. ver. 2010, Coventor Inc., Cary, NC, 2010.

[5] J. B. Muldavin and G. M. Rebeiz, High isolation MEMS shunt switchesPart 1:Trans. Microwave Theory Tech., vol. 48, pp. 10451052, June 1999.

[6] S. P. Pacheco, L. P. B. Katehi, and C. T .C. Nguyen, "Design of Low Actuation VoSwitch", IEEE MTT-S Digest 2000. TU3B-4.

[7] D. Mercier, K. Van Caekenberghe, and G. M. Rebeiz, Miniature RF MEMS switchin IEEE MTT-S Int. Microw. Symp. Dig., Jun. 2005, vol. 1, pp. 1217.

[8] B. Lakshminarayanan, D. Mercier, and G. M. Rebeiz, "High Reliability MiniaSwitched capacitors, " IEEE Trans. Microwave Theory and Tech., vol. 56, no. 4, p

2008.


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THANK YOU!!

National Institute of Technology Silchar, Assam-788010

Study & Analysis of Shunt Rf Mems Capacitive

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