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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