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C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
MEMS Technologies and Devices for Single-Chip RF
Front-Ends
Clark T.-C. Nguyen
Dept. of Electrical Engineering & Computer ScienceUniversity of Michigan
Ann Arbor, Michigan 48105-2122
CICMT’06April 25, 2006
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Outline
• Motivation: Miniaturization of Transceiversneed for high-Qmerged transistor/MEMS process
• High-Q Vibrating Micromechanical Resonatorsclamped-clamped beamsmicromechanical disksmicromechanical circuits
• Low-loss Micromechanical Switches• Tunable C’s and L’s• Conclusions
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Wireless Phone
Motivation: Miniaturization of RF Front-Ends
26-MHz XstalOscillator
26-MHz XstalOscillator
DiplexerDiplexer
925-960MHz RF SAW Filter925-960MHz
RF SAW Filter
1805-1880MHz RF SAW Filter
1805-1880MHz RF SAW Filter
897.5±17.5MHz RF SAW Filter
897.5±17.5MHz RF SAW Filter
RF Power Amplifier
RF Power Amplifier
Dual-Band Zero-IF Transistor Chip
Dual-Band Zero-IF Transistor Chip
3420-3840MHz VCO
3420-3840MHz VCO
90o0o
A/D
A/D
RF PLL
Diplexer
From TX
RF BPF
Mixer I
Mixer Q
LPF
LPF
RXRF LO
XstalOsc
I
Q
AGC
AGC
LNA
Antenna
Problem: high-Q passives pose a bottleneck against miniaturizationProblem: high-Q passives pose a bottleneck against miniaturization
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Multi-Band Wireless Handsets
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
RF BPF
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
RF BPF
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
• The number of off-chip high-Qpassives increases dramatically
• Need: on-chip high-Q passives
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06• Fabrication steps compatible with planar IC processing
Surface Micromachining
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
• Completely monolithic, low phase noise, high-Q oscillator (effectively, an integrated crystal oscillator)
• To allow the use of >600oC processing temperatures, tungsten (instead of aluminum) is used for metallization
OscilloscopeOutput
Waveform
Single-Chip MEMS/Transistor Integration
[Nguyen, Howe 1993][Nguyen, Howe JSSC’99]
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
MEMSMEMSTechnologyTechnology
Single-Chip Integration
26-MHz XstalOscillator
26-MHz XstalOscillator
DiplexerDiplexer
925-960MHz RF SAW Filter925-960MHz
RF SAW Filter
1805-1880MHz RF SAW Filter
1805-1880MHz RF SAW Filter
897.5±17.5MHz RF SAW Filter
897.5±17.5MHz RF SAW Filter
RF Power Amplifier
RF Power Amplifier
Dual-Band Zero-IF Transistor Chip
Dual-Band Zero-IF Transistor Chip
3420-3840MHz VCO
3420-3840MHz VCO
Single-ChipTransceiver
Wrist-watch-sized multi-band wireless device might be possible!
Wrist-watch-sized multi-band wireless device might be possible!
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
All High-Q Passives on a Single Chip
WCDMARF Filters
(2110-2170 MHz)
CDMA-2000RF Filters
(1850-1990 MHz)
DCS 1800 RF Filter(1805-1880 MHz)
PCS 1900 RF Filter(1930-1990 MHz)
GSM 900 RF Filter(935-960 MHz)
CDMA RF Filters(869-894 MHz)
0.25 mm
0.5 mm
Low Freq. Reference Oscillator Ultra-High
Q Tank
Optional RF Oscillator
Ultra-High QTanks
Vibrating Resonator62-MHz, Q~161,000
Vibrating Resonator62-MHz, Q~161,000
Vibrating Resonator1.5-GHz, Q~12,000
Vibrating Resonator1.5-GHz, Q~12,000
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Thin-Film Bulk Acoustic Resonator (FBAR)
• Piezoelectric membrane sandwiched by metal electrodesextensional mode vibration: 1.8 to 7 GHz, Q ~500-1,500dimensions on the order of 200μm for 1.6 GHzlink individual FBAR’s together in ladders to make filters
Agilent FBAR
• Limitations:Q ~ 500-1,500, TCf ~ 18-35 ppm/oCdifficult to achieve several different freqs. on a single-chip
h
freq ~ thicknessfreq ~ thickness
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Vibrating RF MEMS
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Basic Concept: Scaling Guitar StringsGuitar String
Guitar
Vibrating “A”String (110 Hz)Vibrating “A”
String (110 Hz)
High Q
110 Hz Freq.
Vib.
Am
plitu
de
Low Q
r
ro m
kfπ21
=
Freq. Equation:
Freq.
Stiffness
Mass
fo=8.5MHzQvac =8,000
Qair ~50
μMechanical Resonator
Performance:Lr=40.8μm
mr ~ 10-13 kgWr=8μm, hr=2μmd=1000Å, VP=5VPress.=70mTorr
[Bannon et al JSSC’00]
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
-100-98-96-94-92-90-88-86-84
1507.4 1507.6 1507.8 1508 1508.2
1.51-GHz, Q=11,555 Nanocrystalline Diamond Disk μMechanical Resonator
• Impedance-mismatched stem for reduced anchor dissipation
• Operated in the 2nd radial-contour mode• Q ~11,555 (vacuum); Q ~10,100 (air)• Below: 20 μm diameter disk
PolysiliconElectrode R
Polysilicon Stem(Impedance Mismatched
to Diamond Disk)
GroundPlane
CVD DiamondμMechanical Disk
Resonator Frequency [MHz]
Mix
ed A
mpl
itude
[dB
]
Design/Performance:R=10μm, t=2.2μm, d=800Å, VP=7Vfo=1.51 GHz (2nd mode), Q=11,555
fo = 1.51 GHzQ = 11,555 (vac)Q = 10,100 (air)
[Wang, Butler, Nguyen MEMS’04]
Q = 10,100 (air)
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Radial-Contour Mode Disk Resonator
VP
vi
Input Electrode
Output Electrode
io ωωο
ivoi
Q ~10,000Disk
Supporting Stem
Smaller mass higher freq. range and lower series Rx
Smaller mass higher freq. range and lower series Rx(e.g., mr = 10-13 kg)(e.g., mr = 10-13 kg)
Young’s Modulus
Density
Mass
Stiffness
RE
mkf
r
ro
121
⋅∝=ρπ
Frequency:
R
VP
C(t)
dtdCVi Po =
Note: If VP = 0V device off
Note: If VP = 0V device off
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
RF BPF
RF BPF
RF BPF
Multi-Band Wireless Handsets
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
Capacitively transduced
micromechanical resonators switch
themselves
Capacitively transduced
micromechanical resonators switch
themselves
No need for switches!
No need for switches!
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
-100-98-96-94-92-90-88-86-84
1507.4 1507.6 1507.8 1508 1508.2
1.51-GHz, Q=11,555 Nanocrystalline Diamond Disk μMechanical Resonator
• Impedance-mismatched stem for reduced anchor dissipation• Operated in the 2nd radial-contour mode• Q ~11,555 (vacuum); Q ~10,100 (air)• Below: 20 μm diameter disk
PolysiliconElectrode R
Polysilicon Stem(Impedance Mismatched
to Diamond Disk)
GroundPlane
CVD DiamondμMechanical Disk
Resonator Frequency [MHz]
Mix
ed A
mpl
itude
[dB
]
Design/Performance:R=10μm, t=2.2μm, d=800Å, VP=7Vfo=1.51 GHz (2nd mode), Q=11,555
fo = 1.51 GHzQ = 11,555 (vac)Q = 10,100 (air)
[Wang, Butler, Nguyen MEMS’04]
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Integrated Micromechanical Circuits
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Micromechanical Filter Design Basics
RQ
vo
vi
RQ
VP
ω
xovi
ωo ω
xovi
ωo ω
vovi
ωo ω
vovi
ωo
Disk Resonator
Coupling Beam
Bridging Beam
Termination Resistor
Loss Pole
Loss Pole
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
-60
-50
-40
-30
-20
-10
0
8.7 8.9 9.1 9.3Frequency [MHz]
Tran
smis
sion
[dB
]
Pin=-20dBm
In Out
VP
Sharper roll-off
Sharper roll-off
Loss PoleLoss Pole
Performance:fo=9MHz, BW=20kHz, PBW=0.2%
I.L.=2.79dB, Stop. Rej.=51dB20dB S.F.=1.95, 40dB S.F.=6.45
Performance:fo=9MHz, BW=20kHz, PBW=0.2%
I.L.=2.79dB, Stop. Rej.=51dB20dB S.F.=1.95, 40dB S.F.=6.45
Design:Lr=40μm
Wr=6.5μm hr=2μm
Lc=3.5μmLb=1.6μm VP=10.47VP=-5dBm
RQi=RQo=12kΩ
[S.-S. Li, Nguyen, FCS’05]
3CC 3λ/4 Bridged μMechanical Filter
[Li, et al., UFFCS’04]
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Design:Disk Radius, R =17μm
Thickness, h =2μmNitride Gap, d =3.5μmArray Coupling Beam Length, La =26.9μm
Filter Coupling Beam Length, Lc =40.4μm
VP=4V RQi=RQo=13kΩ
Disk Array Composite μMechanical Filter
-25
-20
-15
-10
-5
0
155.2 155.4 155.6 155.8 156.0 156.2 156.4
Tran
smis
sion
[dB
]
Frequency [MHz]
[S.-S. Li, Nguyen, 2006]
Filter Extensional-Mode 3λ/4 Coupling Beam
Filter Extensional-Mode 3λ/4 Coupling Beam
λ/2 Array Couplerλ/2 Array Coupler
Performance:fo=155.9MHzBW=201kHzPBW=0.13%
I.L.=2dB
Performance:fo=155.9MHzBW=201kHzPBW=0.13%
I.L.=2dB
Disk array “composite”end resonator reduces
impedance & suppresses spurious modes
Disk array “composite”end resonator reduces
impedance & suppresses spurious modes
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Low Loss Switch Needs
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
RF BPF
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
RF BPF
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
For lowest on-chip loss, replace with RF MEMS switch
For lowest on-chip loss, replace with RF MEMS switch
Low loss switch
Low loss switch
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Micromechanical Switch
[C. Goldsmith, 1995]
• Operate the micromechanical beam in an up/down binary fashion
• Performance: I.L.~0.1dB, IIP3 ~ 66dBm (extremely linear)• Issues: switching voltage ~ 50V, switching time: 1-5μs
Electrode
OutputInput
Dielectric
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
RF MEMS Switch (Radant)
• Metal cantilever DC switch3-terminal devicePt contact interfacehigh R silicon substrateelectrostatic actuation
Vactuate ~ 90V• Package: wafer-to-wafer
glass frit bonded caplow costenv. protection
100 μm
Drain
Gate
Beam
Source
Contact Detail
Packaged Device
• Reliability (gov’t tested):>1 T mechanical cycles>700 B cycles 100mW RF cold switch
• Reliability (Radant tested):>2.5 B cycles 2W RF cold switched>100 B cycles 0.5W RF cold switched
[Radant]
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Medium Q Inductor & Capacitor Needs
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
RF BPF
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
RF BPF
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
Tunable MEMS C’s and
μmachined L’s have higher Q
Tunable MEMS C’s and
μmachined L’s have higher Q
GSM VCO attainable by on-chip L and switched C’s
GSM VCO attainable by on-chip L and switched C’s
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
• Micromachined, movable, aluminum plate-to-plate capacitors• Tuning range exceeding that of on-chip diode capacitors and
on par with off-chip varactor diode capacitors
• Challenges: microphonics, tuning range truncated by pull-in
Voltage-Tunable High-Q Capacitor
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Suspended, Stacked Spiral Inductor
• Strategies for maximizing Q:15μm-thick, electroplated Cu windings reduces series Rsuspended above the substrate reduces substrate loss
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
• Molybdenum-chromium metal solenoids perpendicular to the plane of the substrate
reduced substrate loss high Q• Assembled out-of-plane via curling
stresses, then locked into place• Record Q’s: ~70 on glass, ~40 on
20Ω-cm silicon (85 w/ Cu underside)
LockingMechanism
SolenoidInductor
Stress CurledMetal
Design/Performance:D=600μm, t=1μm
On Glass Substrate:L = 8nH, Q = 70 @ 1GHz
On 20Ω-cm Silicon:L = 6 nH, Q = 40 @ 1GHz(Q ~ 85 w/ Cu underside)
Design/Performance:D=600μm, t=1μm
On Glass Substrate:L = 8nH, Q = 70 @ 1GHz
On 20Ω-cm Silicon:L = 6 nH, Q = 40 @ 1GHz(Q ~ 85 w/ Cu underside)
D
[Chua, Hilton Head’02][PARC]
Out-of-Plane Micromachined Inductor
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Reference Oscillator Needs
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
RF BPF
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
RF BPF
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
Replace with vibrating
μmechanicalresonator
Replace with vibrating
μmechanicalresonator
Today, use quartz crystal
to attain Q>10,000
Today, use quartz crystal
to attain Q>10,000
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
OutputOutputCustom IC fabricated via TSMC 0.35μm process
Custom IC fabricated via TSMC 0.35μm process
InputInput
GSM-Compliant Oscillator
[Y.-W. Lin, Nguyen, IEDM’05]
-160
-140
-120
-100
-80
-60
-40
-20
1.E+01 1.E+02 1.E+03 1.E+04 1.E+05
Offset Frequency [Hz]
Phas
e N
oise
[dB
c/H
z]
9-Wine-Glass Disk ArrayQ = 118,900 , Rx = 2.56 kΩ9-Wine-Glass Disk ArrayQQ = 118,900 = 118,900 , Rx = 2.56 kΩ
9-WG Disk Array @ 62 MHz9-WG Disk Array @ 62 MHz
Single WG Disk @ 62 MHzSingle WG Disk @ 62 MHz
Down to 13 MHz
Down to 13 MHz
GSM specGSM spec
Satisfies Global System for Mobile Communications (GSM)
phase noise specifications!
Satisfies Global System for Mobile Communications (GSM)
phase noise specifications!
All made possible by mechanical circuit design!
All made possible by mechanical circuit design!
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Multi-Band Wireless Handsets
Duplexer
90o0o
A/D
A/D
RXRF ChannelSelect PLL
I
Q
LPF
LPF
RXRF LO
I
QAGC
AGC
LNA
Duplexer RF BPF
LNAFrom TX
LNA
LNA
RF BPF
RF BPF
RF BPF
WCDMAWCDMA
CDMACDMA--20002000
DCS 1800DCS 1800
PCS 1900PCS 1900
LNA
RF BPF
Duplexer
LNA RF BPF
GSM 900GSM 900
CDMACDMA
From TX
From TX90o
0o
I
Q
Tank
÷ (N+1)/N XstalOsc
Antenna
• The number of off-chip high-Qpassives increases dramatically
• Need: on-chip high-Q passives
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
RF Channel-Select Filter Bank
Bank of UHF μmechanical
filters
Bank of UHF μmechanical
filters
Switch filters on/off via
application and removal of dc-bias VP, controlled by
a decoder
Switch filters on/off via
application and removal of dc-bias VP, controlled by
a decoderTr
ansm
issi
on
Freq.
Tran
smis
sion
Freq.
Tran
smis
sion
Freq.
1 2 n3 4 5 6 7RF Channels
Removes all interferers!
Removes all interferers!
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Conclusions
• Integrated micromechanical technologies possess high-Q and low loss characteristics capable of greatly enhancing the performance of wireless communications
•• Probable evolution of products based on vibrating RF MEMS:Probable evolution of products based on vibrating RF MEMS:timing devices using micromechanical resonatorscommunication-grade frequency synthesizerssingle-chip of all needed high-Q passivessingle-chip radio (cognitive radio)mechanical radio front-ends …
•• In ResearchIn Research: Time to turn our focus towards mechanical : Time to turn our focus towards mechanical circuit design and mechanical integrationcircuit design and mechanical integration
maximize, rather than minimize, use of high-Q componentse.g., RF channelizer paradigm-shift in wireless designeven deeper frequency computation using VLSI micromechanics
•• Beginnings of a revolution reminiscent of the IC revolution?Beginnings of a revolution reminiscent of the IC revolution?
C. T.-C. Nguyen, “MEMS Technologies and Devices for Single-Chip RF Front-Ends,” CICMT’06, 4/25/06
Acknowledgment
Much of the work presented (of mine and others) was supported by funding from
DARPA.