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RF MEMS CircuitsApplications of MEMS switch and tunable capacitor
Dr. Jeffrey DeNatale,Manager, MEMS DepartmentElectronics [email protected]
Panamerican Advanced Studies InstituteMicroElectroMechanical SystemsJune 21-30, 2004
Chart 2
Outline
• Motivation for RF MEMS circuits
• MEMS Tunable Filters
– Switch based
– Tunable capacitor based
• MEMS Phase Shifters
• Low-Loss Switching Networks
• Reconfigurable MMIC Circuits
• Summary / Acknowledgements
Chart 3
MEMS for RF Communications
• MEMS is key enabling technology addressing pervasive trends in communications and radar systems:
– tunability / agility / modularity / reconfigurability
– increased functionality (component, system)
• Substantial performance improvements:
– Insertion loss, isolation, linearity, power consumption, bandwidth, size, integration
Range of device concepts under development• RF Switches / Relays• Tunable Capacitors• Micromachined inductors• Micromechanical resonators
⇒ Building Blocks for High-Performance Miniaturized RF Subsystems
Range of device concepts under development• RF Switches / Relays• Tunable Capacitors• Micromachined inductors• Micromechanical resonators
⇒ Building Blocks for High-Performance Miniaturized RF Subsystems
X-Band Phase Shifter
80 90 100 110 120 130 140 150 160 170 180-80
-70
-60
-50
-40
-30
-20
-10
0
Frequency (MHz)
S2
1,
dB
Low band Mid band High Band
80 90 100 110 120 130 140 150 160 170 180-80
-70
-60
-50
-40
-30
-20
-10
0
Frequency (MHz)
S2
1,
dB
Low band Mid band High Band
Multi-band (X, Ku) amplifier
2-Pole MEMS Switched Filter
SP4T Routing Network
Leverage small mechanical motions for large RF property excursionsLeverage small mechanical motions for large RF property excursions
Chart 4
RSC MEMS RF Switch
Key Elements of RSC MEMS RF Switch• Low-temperature processing (circuit compatible)• Broadband (DC- mmWave)• Electrostatic drive for low power consumption• Low insertion loss (<0.1dB)• High isolation (<-40dB @ 10GHz)• High linearity (IP3> +80dBm)
Key Elements of RSC MEMS RF Switch• Low-temperature processing (circuit compatible)• Broadband (DC- mmWave)• Electrostatic drive for low power consumption• Low insertion loss (<0.1dB)• High isolation (<-40dB @ 10GHz)• High linearity (IP3> +80dBm)
Insertion Loss Isolation
0 20 40 60Frequency (GHz)
-0.6
-0.4
-0.2
0.0
Swi t
chin
sert
ion
loss
(dB
)
Switched Line(as measured)
Switch Only(extracted)
0 20 40 60
Frequency (GHz)
-60.0
-40.0
-20.0
0.0
Off
-sw
itch
isol
atio
n (
dB
)
Select circuits / applications to exploit
MEMS advantages
Select circuits / applications to exploit
MEMS advantages
Chart 5
MEMS RF Switch Step-Tuned Filter Demobenchmark MEMS switch vs. PIN diode
VHF Filter Circuit– VHF Step-tuned Bandpass Filter 116-152 MHz
– dual MEMS switch replaces 2 PIN dual diodes
– increased dynamic range, reduced parts count
Filter Specifications (2-Pole VHF Filter)
– Center Freq. Tuning Range: 116-151.975 MHz
– Selectivity (fo ±±8 MHz) ≥≥ 13.4 dB rejection
– Tune time: < 75 microseconds
– 2-pole midband loss < 4.5 dB
– 2-pole 1 dB compression pt. > +20 dBm
MTO MEMS
DARPADARPA
Derived Component Requirements - RF Switch (Packaged)
Max Rs (on): 1.8 Ohm (0.5 GHz)Max Cs (off): 0.5 pF (0.5 GHz)Min. 3rd Order IP: 50 dBmIRF, VRF (survive): 0.2 A, 10.4 V rmsIRF, VRF (op): 0.03 A, 2.1 V rmsSw Time: 15 usec max.
2-Pole Sub-section
6-Pole Filter
Switch Drivers
Chart 6
VHF 2-Pole MEMS Switched Filter Prototype
2-Pole MEMS Switched Filter Prototype
Packaged MEMS Switches (8X)
Future: IntegratedMonolithic Switches + Capacitors
Packaged circuit with 16 switched capacitors, in one monolithic die
Step-Tunable Filter withMEMS Switches + Discrete Capacitors
• 500x Improvement in Linearity• 42% Parts Count Reduction (123 vs 71 for 2 pole)• Static Power Reduced from 0.5W to near-zero (2 pole)
Chart 7
VHF 2-Pole MEMS Switched Filter Test Data
60 70 80 90 100 110 120 130 140 150 160 170 180 19050 200
-70
-60
-50
-40
-30
-20
-10
-80
0
Inse
rtio
n G
ain
(d
B)
Frequency (MHz)
Demonstrate Step-Tuning with good filter characteristics over full band
Demonstrate Step-Tuning with good filter characteristics over full band
Chart 8
VHF 2-Pole MEMS Switched Filter Intermodulationkey parameter for cosite mitigation
3rd Order In-Band IM Distortion - 112.05 MHz Fc
Output Tone Level+20 dBm
IMR3 = -71.5 dBc
IP3o = +55.75 dBm
Chart 9
RSC MEMS Tunable Capacitor (Varactor)
5 µm
30 µm
100 µmSEM micrographs showing the high aspect ratio feature of the MEMS tunable cap.
Tuning range: >8:1Base capacitance: 1.5 - 2pFElectrical Q: 30-150Max tuning voltage: 6-40VMechanical Resonance : 0.4 - 2kHz typElectrical self-resonance: 6GHz
Tuning range: >8:1Base capacitance: 1.5 - 2pFElectrical Q: 30-150Max tuning voltage: 6-40VMechanical Resonance : 0.4 - 2kHz typElectrical self-resonance: 6GHz
Capacitor Tuning Range
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7 8 9
Voltage (V)
Cap
acita
nce
(pF)
8.4X
Tuning range >8.4XTuning range >8.4X
Chart 10
Voltage Tunable Filter Demonstrationbenchmark MEMS vs. semiconductor varactor
UHF Filter Circuit– UHF Voltage-tuned Bandpass Filter 225-400 MHz
– MEMS variable capacitor replaces varactor diode array
– increased dynamic range, drastically reduced parts count
Filter Specifications (2-Pole UHF Filter)– Center Freq.Tuning Range: 225-399.975 MHz
– Selectivity (fo ±±13 MHz) ≥≥ 10.75 dB rejection
– Tune time: < 27 microseconds
– 2-pole midband loss < 5.5 dB
MTO MEMS
DARPADARPA
Derived Component Requirements -Variable Capacitor (Packaged)
– Cap. Range: 2.5 - 10 pF (4:1)
– Tune V Range: 1-6 VDC
– Max Rs: 1.0 Ohm @ 10 pF
– IRF, VRF (op): 0.18 A, 21 V rms
– Tune Time: 10 usec max.
16-diode series-parallel array for high IP (1 array per pole)
16-diode series-parallel array for high IP (1 array per pole)
Chart 11
UHF 2-Pole MEMS Capacitor Filter Schematic
MEMS Capacitor Filter Schematic
MEMS Filter, 2 tunable capacitors
• Dramatic (90%) parts count reduction validated for MEMS circuit
• Slightly improved IP3 (+30 to +37dBm)
• Dramatic (90%) parts count reduction validated for MEMS circuit
• Slightly improved IP3 (+30 to +37dBm)
Existing Varactor Version16-diode series-parallel arrays
Chart 12
UHF 2-Pole MEMS Capacitor Filter Test Data
-80
-75
-70
-65
-60
-55
-50
-45
-40
-35
-30
-25
-20
-15
-10
-5
0
150.0 200.0 250.0 300.0 350.0 400.0 450.0
Frequency (MHz)
Ins
ert
ion
Ga
in (
dB
)
228 MHz Fo
312.5 MHz Fo
398 MHz Fo
Nearly full octave tuning achievedNearly full octave tuning achieved
Chart 13
Tunable Capacitor Improvements Required Results from tunable capacitor filter demo
• Initial filter insertion validated utility of MEMS tunable capacitor in filter tuning circuit, but issues noted:
– Device Q: series resistance ~1ΩΩ (solution: improvedmetalization, device design)
– Tuning speed, Vibration Immunity: (solution: stiff flexures, reduced mass, package environment)
– Mechanical Ringing: settling time ~4msec (solution: package environment)
– Maximum capacitance value: ~12pF (solution:thicker device layer, package environment - up to 25pF demonstrated)
Tunable Capacitor Response Time
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
-0.0005 0.0005 0.0015 0.0025 0.0035 0.0045 0.0055 0.0065 0.0075 0.0085
Time (seconds)
Rel
ativ
e C
apac
itan
ce (
Arb
)
Filtered Response
0
0.2
0.4
0.6
0.8
1
1.2
-0.0005 0.0015 0.0035 0.0055 0.0075 0.0095
Time (sec)
Fil
tere
d O
utp
ut
AirDamping
NearCriticalDamping
Tunable Capacitor with 80µµm deep combs
Filtered response to step input
Effect of damping on device response time
Chart 14
MEMS TTD Phase Shifter DevelopmentKey Component for Steerable Phased Arrays
Switchable Delay Line• MEMS Switch can enable significant advances in reconfigurable electronics
• Low insertion loss compatible with multi-switch implementation
• High isolation reduces resonant effects of off-state leakage
• Metal-Metal contacts enable broad bandimplementation
• Compatible with MMIC processing
Exploit low-loss, broadband characteristics for multi-bit True
Time Delay (TTD) Circuit
Exploit low-loss, broadband characteristics for multi-bit True
Time Delay (TTD) Circuit
Steering of main lobe at
φ = cos-1(-δ/d)
Powerdivider
Phaseshifter
Antenna
δ δ2 δ30
γ
φd
Chart 15
MEMS-Based Phase Shifter Circuits
• RSC has demonstrated broad portfolio of MEMS-based phase shifter circuits
• Exploit low-loss, broadband nature of RSC MEMS switch
• Novel circuits demonstrated for low loss, compact size, broad bandwidth
3-Bit Ka-Band (2.2dB avg)
6-Bit Broad Band
4-Bit Broad Band (2.4dB avg)
2-Bit X-Band(1dB avg)
2-Bit Low LossX-Band (.56 dB avg)
4-Bit Low LossX-Band (1.2 dB avg)
Miniature 2-bit, 4-bit X-Band (0.7dB 9.5GHz
Chart 16
4-Bit Broadband TTD Phase Shifter Circuitexploit broadband nature of RSC switch
• 4-Bit TTD circuits implemented (16 MEMS switches per circuit)
• 2.2 to 2.6 dB insertion loss at 10GHz
• Mismatch loss below 15 dB at all frequencies
• group delay ripple <5ps up to 30GHz
• 5.8psec gap among different states
• 4-Bit TTD circuits implemented (16 MEMS switches per circuit)
• 2.2 to 2.6 dB insertion loss at 10GHz
• Mismatch loss below 15 dB at all frequencies
• group delay ripple <5ps up to 30GHz
• 5.8psec gap among different states 0 10 20 30 40
Frequency (GHz)
-40
0
40
80
120
160
200
80
120
160
200
240
280
320
Gro
up
del
ay
(pse
c)
Type A
Type B
0 4 8 12 16
Switch position
0
20
40
60
80
100
Ad
ded
gro
up
del
ay (
pse
c)
-5
-4
-3
-2
-1
0
Insertion
loss (dB
)
Chart 17
Low-Loss SP4T-Based Phase Shifters (RSC/UofM)
• Address major elements of loss budget:
–Conductor loss, switch loss, long reference path
• Low-loss X-band TTD phase shifter developed
–“star” SP4T switch network, 8-mil GaAs µµstrip process
–Compact circuit, short reference line
• Excellent performance characteristics:
–-0.6dB avg insertion loss 8-12 GHz
–-23dB return loss 8-12GHz
–Wide operational bandwidth (RL<-14 dB DC-14 GHz)
• Low phase error ( ± 2 deg @10 GHz)
Chart 18
Extension to 4-Bit Phase Shifter Circuit
Phase at 10GHz
-400
-350
-300
-250
-200
-150
-100
-50
0
0 5 10 15
State
Ph
ase
Sh
ift
[deg
]
• Phase Accuracy = ± 2 deg (10 GHz)
• Average Insertion Loss = -1.1 dB (10 GHz)
• Return loss < -14 dB DC-14 GHz
Chart 19
Miniature (Mini-MEMS) Phase Shifters: UoM/RSC
• Phase Accuracy = ± 3 deg (9.5 GHz)
• Average Insertion Loss = -0.7 dB (9.5 GHz)
• Return loss < -14 dB DC-14 GHz
• Area = 4.9 mm2 (1.95x2.49mm)
• 4-bit Design: 7 mm2 (not shown)
• CLC phase shift networks with discrete capacitors, transmission-line inductors
• Compact 1x2 MEMS metal-contact switch designs
• RSC low-loss 8-mil GaAs microstrip process
Chart 20
Measured 4-bit X-band Phase ShiftersSize Comparison
Raytheon
RSC SP4TUoM/RSC
* S11 < -14 dB. Stricter definition of bandwidth.
DC-14 GHz*DC-18 GHz*DC-40 GHz*7-10 GHz (S11 <-10 dB) BandwidthLinearLinearLinearLinearPhase
1.45 dB/10 GHz1.2 dB/10 GHz2.1 dB (1.6 dB)/10 dB1.4 dBAverage
Loss
200 µm200 µm75 µm (200 µm)500µmThicknessGaAs or SiGaAs or SiGaAs or SiSiliconSubstrate
7 mm217 mm230 mm280 mm2 (Si, coupler area only)Size
MiniatureUoM/RSC
Chart 21
Capacitive Switch: Ka-Band Phase ShiftersRaytheon membrane switch circuit
• Loss 0.65-0.75 dB/bit
Courtesy Rebeiz, UofM
Chart 22
Low Loss SP4T MEMS Switch Networks
• Low-loss switch network ideal for signal routing, component selection circuits
– Tunable filters
– Band-select operation
– Reconfigurable I/O
• 8-mil GaAs µµstrip process, compact switch geometry for low loss
-80
-70
-60
-50
-40
-30
-20
-10
0
0 0.5 1 1.5 2 2.5 3 3.5
Data FIL01L1 F24D1A
Isolation AIsolation BIsolation CIsolation D
Iso
latio
n (
dB
)Frequency (GHz)
Insertion Loss < -0.1dBIsolation > -45dB
Insertion Loss < -0.1dBIsolation > -45dB
-0.5
-0.4
-0.3
-0.2
-0.1
0
0 0.5 1 1.5 2 2.5 3 3.5
Data FIL01L1 F24D1A
Insertion AInsertion BInsertion CInsertion D
Inse
rtio
n L
oss
(d
B)
Frequency (GHz)
Chart 23
MEMS/MMIC Integration
RSC MEMS switch compatible with monolithic MMIC integrationRSC MEMS switch compatible with monolithic MMIC integration
Switchable Gain Amplifier
MEM relay allows reconfiguration of electronic circuit
Low “on” insertion lossGood “off” isolation
Multi-band (X, Ku) amplifier with MEMS
Efficiency-Optimized X-Band PA
-90-80-70-60-50-40-30-20-10
0102030
0 2 4 6 8 10 12 14 16 18 20 22
GHz
para
met
er d
B
Input Output
80-µµm
640-µµm
Chart 24
Summary and Conclusions
• MEMS RF switch highly attractive for tunable filter, phase shifter circuits:
– low loss, high isolation, high linearity, wide band, low power, integration compatible
• MEMS tunable capacitor enables wide tuning range operation for low-frequency applications
– Present efforts targeting improved tuning speed, damping, Q
• MEMS SP4T, DPDT switch elements provide ultra-low loss switching networks
• Integration compatibility of MEMS switch enables reconfigurable / agile / adaptable electronics
06/24/2004 Chart 25
Acknowledgements
Supporters and Collaborators:
• DARPA
• Air Force Research Lab
• NASA
• Rockwell Collins
• Lockheed Martin
• Jet Propulsion Lab
• The Aerospace Corp
• University of Michigan
• UC Santa Barbara
THE AEROSPACETHE AEROSPACECORPORATIONCORPORATION
• RSC RF MEMS Team
–Switch: Rob Mihailovich, JudyStuder
–Tunable Cap: Rob Borwick, PhilStupar, Kathleen Garrett
• Collaboration with University of Michigan (Prof. Gabriel Rebeiz and G.L. Tan) gratefully acknowledged
• RSC RF MEMS Team
–Switch: Rob Mihailovich, JudyStuder
–Tunable Cap: Rob Borwick, PhilStupar, Kathleen Garrett
• Collaboration with University of Michigan (Prof. Gabriel Rebeiz and G.L. Tan) gratefully acknowledged