RF MEMS CircuitsApplications of MEMS switch and tunable capacitor

Dr. Jeffrey DeNatale,Manager, MEMS DepartmentElectronics Divisionjdenatale@rwsc.com805-373-4439

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