The Future of RF Microelectromechanical Systems (MEMS)

C. T.-C. Nguyen, “Towards MEMS-Based Receivers,” BWRC Winter Retreat, 1/(8-9)/06

The Future of RF Microelectromechanical

Systems (MEMS)

Clark T.-C. Nguyen

Dept. of Electrical Engineering & Computer SciencesUniversity of California

Berkeley, California 94720E-mail: [email protected]

BEARS’07Feb.15, 2007


Outline

• Motivation: Miniaturization of Transceiversneed for high-Q

• Micromechanical Resonatorsclamped-clamped beamsmicromechanical disks

• Micromechanical Circuitsmicromechanical filtersarraying techniques

• Towards RF Channel-Selection

• Conclusions


Wireless Phone

Motivation: Miniaturization of RF Front-Ends

26-MHz Xstal Oscillator

26-MHz Xstal Oscillator

DiplexerDiplexer

925-960MHz RF SAW Filter




897.517.5MHz RF SAW Filter

897.517.5MHz 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

Problem: high-Q passives pose a bottleneck against miniaturizationProblem: high-Q passives pose a bottleneck against miniaturization

90o

0o

A/D

A/D

RF PLL

Diplexer

From TX

RF BPF

Mixer I

Mixer Q

LPF

LPF

RXRF LO

Xstal Osc

I

Q

AGC

AGC

LNA

Antenna


Multi-Band Wireless Handsets

Duplexer

90o

0o

A/D

A/D

RXRF ChannelSelect PLL

I

Q

LPF

LPF

RXRF LO

I

QAGC

AGC

LNA

Duplexer RF BPF

LNA

From TX

LNA

LNA

RF BPF

RF BPF

RF BPF

WCDMAWCDMA

CDMA-2000CDMA-2000

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 Xstal Osc

Antenna

• The number of off-chip high-Q passives increases dramatically

• Need: on-chip high-Q passives


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 Q Tanks

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


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 200m for 1.6 GHz link 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


Vibrating RF MEMS


Basic Concept: Scaling Guitar Strings

Guitar String

Guitar

Vibrating “A”String (110 Hz)


High Q

110 Hz Freq.

Vib

. A

mp

litu

de

Low Q

r

ro m

kf

21

Freq. Equation:

Freq.

Stiffness

Mass

fo=8.5MHzQvac =8,000

Qair ~50

Mechanical Resonator

Performance:Lr=40.8m

mr ~ 10-13 kgWr=8m, hr=2md=1000Å, VP=5VPress.=70mTorr

[Bannon et al JSSC’00]

C. T.-C. Nguyen, “Towards MEMS-Based Receivers,” BWRC Winter Retreat, 1/(8-9)/06• Fabrication steps compatible with planar IC processing

Surface Micromachining


• 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]


Basic Concept: Scaling Guitar Strings

Guitar String

Guitar



High Q

110 Hz Freq.

Vib

. A

mp

litu

de

Low Q

r

ro m

kf

21

Freq. Equation:

Freq.

Stiffness

Mass

fo=8.5MHzQvac =8,000

Qair ~50

Mechanical Resonator

Performance:Lr=40.8m

mr ~ 10-13 kgWr=8m, hr=2md=1000Å, VP=5VPress.=70mTorr

[Bannon et al JSSC’00]


Radial-Contour Mode Disk Resonator

VP

vi

Input Electrode

Output Electrode

io

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

R

E

m

kf

r

ro

1

2

1

Frequency:

R

VP

C(t)

dt

dCVi Po

Note: If VP = 0V device off

Note: If VP = 0V device off


-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

Mechanical 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 m diameter disk

PolysiliconElectrode R

Polysilicon Stem(Impedance Mismatched

to Diamond Disk)

GroundPlane

CVD DiamondMechanical Disk

Resonator Frequency [MHz]

Mix

ed

Am

plit

ud

e [

dB

]

Design/Performance:R=10m, t=2.2m, d=800Å, VP=7V

fo=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)


Commercialization of MEMS Timekeepers

High-Q, low drift, make possible a very stable, low

power timekeeper

High-Q, low drift, make possible a very stable, low

power timekeeper$3.5 Billion

Market

‘s pure silicon high-Q vibrating mechanical resonator oscillator

Discera TCMO

Smaller size Lower cost Lower power

consumption

Smaller size Lower cost Lower power

consumption

Package Package CapCap

ASICASICMechanical Mechanical

Resonator DieResonator Die


OutputOutput

Custom IC fabricated via TSMC 0.35m process

Custom IC fabricated via TSMC 0.35m 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]

Ph

ase

No

ise

[d

Bc/

Hz]

9-Wine-Glass Disk ArrayQQ = 118,900 = 118,900 , Rx = 2.56 k9-Wine-Glass Disk ArrayQQ = 118,900 = 118,900 , Rx = 2.56 k

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!


Integrated Micromechanical Circuits


Micromechanical Filter Design Basics

RQ

vo

vi

RQ

VP

xovi

o

xovi

o

vovi

o

vovi

o

Disk Resonator

Coupling Beam

Bridging Beam

Termination Resistor

Loss Pole

Loss Pole


-60

-50

-40

-30

-20

-10

0

8.7 8.9 9.1 9.3Frequency [MHz]

Tra

nsm

issi

on

[d

B]

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



Design:Lr=40m

Wr=6.5m hr=2m

Lc=3.5mLb=1.6m VP=10.47VP=-5dBm

RQi=RQo=12k

[S.-S. Li, Nguyen, FCS’05]

3CC 3/4 Bridged Mechanical Filter

[Li, et al., UFFCS’04]


Micromechanical Filter Circuit

1/krmr cr1/krmr cr

1/krmr cr-1/ks -1/ks

1/ks

-1/ks -1/ks

1/ks

1/kb 1/kb

-1/kb

Co Co

1:e e:1

1:c 1:cc:1 c:1

1:b b:1

/4

/4

/4Input

Outputvi

RQ

RQ

vo

VP

Bridging Beam

Coupling Beam

Resonator

vovi


vovi

Micromechanical Filter Circuit

1/krmr cr1/krmr cr

1/krmr cr-1/ks -1/ks

1/ks

-1/ks -1/ks

1/ks

1/kb 1/kb

-1/kb

Co Co

1:e e:1

1:c 1:cc:1 c:1

1:b b:1

/4

/4

/4Input

Outputvi

RQ

RQ

vo

VP

Bridging Beam

Coupling Beam

Resonator

All circuit element values determined

by CAD layout

All circuit element values determined

by CAD layout

Amenable to automated circuit

generation

Amenable to automated circuit

generation


-60

-50

-40

-30

-20

-10

0

8.7 8.9 9.1 9.3Frequency [MHz]

Tra

nsm

issi

on

[d

B]

Pin=-20dBm

In Out

VP

Sharper roll-off

Sharper roll-off

Loss PoleLoss Pole





Design:Lr=40m

Wr=6.5m hr=2m

Lc=3.5mLb=1.6m VP=10.47VP=-5dBm

RQi=RQo=12k

[S.-S. Li, Nguyen, FCS’05]

3CC 3/4 Bridged Mechanical Filter

[Li, et al., UFFCS’04]


Square-Plate Micromechanical

Resonator

Coupling Beam

h

Ws

gap, do

Lr

50-Terminated 68-MHz Coupled-Array Mechanical

Filter

-21

-18

-15

-12

-9

-6

-3

0

67.60 67.80 68.00 68.20 68.40 68.60

Frequency [MHz]

Tran

smis

sion

[dB

]

Use square-plate mechanical

resonator arrays

Use square-plate mechanical

resonator arrays

Lower end resonator impedance & raise

power handling

Lower end resonator impedance & raise

power handling

50 termination w/ L-network

50 termination w/ L-network

Lr = 16mh = 2.2mdo = 90nm

Lr = 16mh = 2.2mdo = 90nm

RQ = 12kRterm = 50

RQ = 12kRterm = 50

fo=68MHzBW=190kHzPBW=0.28%I.L.<2.7dB

fo=68MHzBW=190kHzPBW=0.28%I.L.<2.7dB

[Demirci, Nguyen 2005]


RF Channel-Selection


Motivation: Need for High Q

Antenna

Demodulation Electronics

The higher the Q of the Pre-

Select Filter the simpler the demodulation

electronics



electronics

Pre-SelectFilter in the GHz Range

Presently use resonators

with Q’s ~ 400


with Q’s ~ 400

Wireless Phone

Rec

eive

dP

ower

FrequencyRF

DesiredSignal


Motivation: Need for Q’s > 10,000

Antenna




electronics



electronics



with Q’s ~ 400


with Q’s ~ 400

Wireless Phone

Rec

eive

dP

ower

FrequencyRF

DesiredSignal

If can have resonator

Q’s > 10,000


Q’s > 10,000



Antenna




electronics



electronics



with Q’s ~ 400


with Q’s ~ 400


Q’s > 10,000


Q’s > 10,000

Wireless Phone

Non-Coherent FSK Detector?(Simple, Low Frequency, Low Power)

Front-End RF Channel Selection

Front-End RF Channel Selection

Rec

eive

dP

ower

FrequencyRF

DesiredSignal

Substantial Savings in Cost and Battery PowerSubstantial Savings in

Cost and Battery Power



Antenna




electronics



electronics



with Q’s ~ 400


with Q’s ~ 400


Q’s > 10,000


Q’s > 10,000

Wireless Phone

Direct-Sampling A/D Converter Software-Defined Radio

Maximum Flexibility one circuit satisfies all

comm. standards

Maximum Flexibility one circuit satisfies all

comm. standardsFront-End RF

Channel SelectionFront-End RF

Channel Selection

Rec

eive

dP

ower

FrequencyRF

DesiredSignal


RF Channel-Select Filter Bank

Bank of UHF mechanical

filters

Bank of UHF mechanical

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 decoder

Tra

nsm

iss

ion

Freq.

Tra

nsm

iss

ion

Freq.

Tra

nsm

iss

ion

Freq.

1 2 n3 4 5 6 7RF Channels

Remove all interferers!

Remove all interferers!


Conclusions

• Vibrating RF MEMS have achievedVibrating RF MEMS have achievedQ’s >10,000 at GHz frequencies in sizes less than 20 m in

diameter and w/o the need for vacuum encapsulationTCf’s < -0.24 ppm/oC (better than quartz)aging at least on par with quartzcircuit-amenable characteristics VLSI potential

• 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 passivesmechanical radio front-ends …

• In ResearchIn Research: Time to turn our focus towards mechanical circuit : Time to turn our focus towards mechanical circuit design and mechanical integrationdesign and mechanical integrationmaximize, rather than minimize, use of high-Q componentse.g., RF channelizer paradigm-shift in wireless designeven deeper frequency computation

• What’s possible with an unlimited supply of high-What’s possible with an unlimited supply of high-QQ passives? passives?

The Future of RF Microelectromechanical Systems (MEMS)

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