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C. T.-C. Nguyen

RF MEMS for Wireless Communications

iMEMS’01 Short Course



Instructor: Clark T.-C. Nguyen

Center for Integrated Wireless MicrosystemsDept. of Electrical Engineering and Computer Science

University of MichiganAnn Arbor, Michigan 48109-2122

http://www.eecs.umich.edu/~ctnguyen

C. T.-C. Nguyen



Outline• Miniaturization of Transceivers

the need for high-Q• Receiver Design and Operation• Oscillator Fundamentals and Needs• Medium-Q Tunable μMech. Capacitors• Medium-Q Micromachined Inductors• High-Q Micromechanical Resonators• High-Q Micromechanical Filters• Micromechanical Mixer-Filters• Micromechanical Switches• Integration Technologies• Power Savings Via High-Q MEMS• Conclusions

C. T.-C. Nguyen



Frequency Division Multiplexed Communications

• Information is transmitted in specific frequency channels within specific bands

TransmittedPower

Frequency

GSM Band DCS1800 BandAdj. BandBand

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TransmittedPower

Frequency


Filter

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TransmittedPower

Frequency


Filter

• Need: high frequency selectivity

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Quality Factor (or Q)• Measure of the frequency

selectivity of a tuned circuit• Definition:

• Example: series LCR circuit

• Example: parallel LCR circuit

dB3CyclePer Lost EnergyCyclePer Energy Total

BWfQ o==

( )( ) CRR

LZZQ

o

o

ωω 1

ReIm

===

( )( ) LGG

CYYQ

o

o

ωω 1

ReIm

===

C. T.-C. Nguyen



Need for High-Q: Selective Low-Loss Filters

• In resonator-based filters: high tank Q ⇔ low insertion loss

• At right: a 0.3% bandwidth filter @ 70 MHz (simulated)

heavy insertion loss for resonator Q < 5,000

C. T.-C. Nguyen



Attaining High-Q• Problem: IC’s cannot achieve Q’s in the thousands

transistors consume too much power to get Qon-chip spiral inductors Q’s no higher than ~10off-chip inductors Q’s in the range of 100’s

• Observation: vibrating mechanical resonances Q > 1,000• Example: quartz crystal resonators (e.g., in wristwatches)

extremely high Q’s ~ 10,000 or higher (Q ~ 106 possible)mechanically vibrates at a distinct frequency in a thickness-shear mode

C. T.-C. Nguyen



Miniaturization of Transceivers

• High-Q functionality required by oscillators and filters cannot be realized using standard IC components use off-chip mechanical components

• SAW, ceramic, and crystal resonators pose bottlenecks against ultimate miniaturization

C. T.-C. Nguyen



So Many Passive Components!• The total area on a printed circuit board for a

wireless phone is often dominated by passive components passives pose a bottleneck on the ultimate miniaturization of transceivers

TransistorChips

TransistorChips

QuartzCrystalQuartzCrystal

IF Filter(SAW)

IF Filter(SAW)

InductorsCapacitorsResistors

InductorsCapacitorsResistors

IF Filter(SAW)

IF Filter(SAW)

RF Filter(ceramic)RF Filter(ceramic)

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Surface Micromachining

• Fabrication steps compatible with planar IC processing

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Post-CMOS Circuits+μMechanics Integration• Completely monolithic, low phase noise, high-Q oscillator

(effectively, an integrated crystal oscillator) [Nguyen, Howe]

• To allow the use of >600oC processing temperatures, tungsten (instead of aluminum) is used for metallization

OscilloscopeOutput

Waveform

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Micromechanical Resonator Oscillator Video

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Target Application: Integrated Transceivers

• Off-chip high-Q mechanical components present bottlenecks to miniaturization replace them with μmechanical versions

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• A large number of off-chip high-Q components replaceable with μmachined versions; e.g., using μmachined resonators, switches, capacitors, and inductors

[Bannon, Clark,Nguyen 1996]

[Young, Boser 1996]

[J.-B. Yoon, et al. 1999]

[Wang, Yu, Nguyen 1999]

[Yao 1997]

MEMS-Replaceable Transceiver Components

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Receiver Architectures• Super-Heterodyne:

most widely used architecture for the majority of communication standardsadv.: best performanceproblem: requires many off-chip passive components

• Homodyne: (or zero-IF)mix received signal directly from RF to basebandadv.: removes at least one off-chip passive filter (IF filter); also, relaxes image-reject filter requirementsproblem: dc-offset variation, need for higher dynamic range poorer performance than super-heterodyne

• Wideband IF:uses image-reject mixers, no IF filteradv.: removes IF filter; relaxes image-reject filter req.problem: need image-reject mixers, need higher dynamic range higher power consumption

C. T.-C. Nguyen



Wireless Receiver Operation

TransmittedPower

FrequencyωRFωLOωIF

RF Pre-Select Filter~945 MHz, Qres ~500RF Pre-Select Filter~945 MHz, Qres ~500

DesiredSignal

ωimage

RF Image-Reject Filter~945 MHz, Qres ~1,000


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• Question: why not select the channel right at RF?

insufficient Qbut it would be preferred

TransmittedPower


RF Pre-Select Filter~945 MHz, Qres ~500RF Pre-Select Filter~945 MHz, Qres ~500 RF Pre-Select Filter

~945 MHz, Qres ~500RF Pre-Select Filter~945 MHz, Qres ~500

DesiredSignal

ωimage

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TransmittedPower


Local Oscillator Synthesizer~874 MHz

Local Oscillator Synthesizer~874 MHz

DesiredSignal

ωimage

No Image to Select

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TransmittedPower


DesiredSignal

IF Channel-Select Filter~71 MHz, Qres ~5,000


Signals Mixed Down to IF[Reason: easier (i.e., cheaper) to

select at low freq.]

ωimage

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TransmittedPower


DesiredSignal



Adjacent ChannelInterferers Removed

ωimage

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TransmittedPower


DesiredSignal

IQ Mixer~71 MHz

IQ Mixer~71 MHz

ωimage

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TransmittedPower


DesiredSignal

IQ Mixer~71 MHz

IQ Mixer~71 MHz

Signals translated in demodulation

process by IQ mixer

ωimage

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• Below: synthesizers indicated in yellow

• Need: oscillators with adequate frequency stability

Synthesizer Oscillators Within Transceivers

Down-ConvertingLocal Oscillator

Synthesizer~874 MHz


Synthesizer~874 MHz

Up-ConvertingLocal Oscillator

Synthesizer~831 MHz


Synthesizer~831 MHz

IQ Oscillator~71 MHz


C. T.-C. Nguyen



Communications Oscillator• Main Function: provide a stable output frequency• Difficulty: superposed noise degrades frequency stability

ωωο

ivoi

A

Frequency-SelectiveTank

SustainingAmplifier

ov

Ideal Sinusoid: ( ) ⎟⎠⎞⎜

⎝⎛= tofVotov π2sin

Real Sinusoid: ( ) ( ) ( )⎟⎠⎞⎜

⎝⎛⎟

⎠⎞⎜

⎝⎛ ++= ttoftVotov θπε 2sin

ωωο

ωωο=2π/TO

TO

Zero-Crossing Point

Higher QHigher QTighter SpectrumTighter Spectrum

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An Ideal Receiver

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Impact of Phase Noise on Receivers• Local oscillator phase noise can mask desired

information signals after mixing

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Plotting Phase Noise• Phase Noise = (1/2) x total output noise (other 1/2 is

amplitude noise, which can be removed by limiting)• Plot phase noise-to-carrier power ratio against offset

from the carrier on log scales

Carrier = { }oo ff

vCΔ

=2

{ } { }mo

mop ff

vfNΔ

=2

21

fo+fm

Plot RHS

opNC

1/f3 NoiseCaused By

Aliased 1/f Noise

1/f3 NoiseCaused By

Aliased 1/f Noise

1/f2 NoiseCaused By White Electronic Noise

1/f2 NoiseCaused By White Electronic Noise

White NoiseFrom Next Stage

White NoiseFrom Next Stage

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Phase Noise in Specific OscillatorsHigh-Q Oscillators

• Tank Q ~ tens of thousands• Example: crystal oscillator

• {fm=1kHz} = -140dBc/Hz• Adv.: extremely stable• Disadv.: large size; requires

off-chip component

Low- to Medium-Q Oscillators• Tank Q ~ less than 30• Example: LC or ring osc.

• {fm=600kHz} = -100dBc/Hz• Adv.: high frequency, large

tuning range (good VCO’s)• Disadv.: poor close-to-carrier

stabilityNeed: high-Q in small size

10MHz

800MHz

C. T.-C. Nguyen



• Below: synthesizers indicated in yellow

• Need: oscillators with adequate frequency stability

Synthesizer Oscillators Within Transceivers


Synthesizer~874 MHz


Synthesizer~874 MHz


Synthesizer~831 MHz


Synthesizer~831 MHz



C. T.-C. Nguyen



Today’s Local Oscillator Synthesizer

• Phase locking cleans up the VCO output spectrum

• Result: sufficiently stable, tunable oscillator

C. T.-C. Nguyen



Voltage-Controlled OscillatorsOff-Chip Implementation

• Off-chip inductor Q ~ 100’s• Tunable varactor diode

capacitor Q ~ 60

On-Chip Implementation

• Spiral (shown) or bond-wire inductor Q: 3 to 20

• Tunable reverse-biased diode capacitor high series R

• Problem: capacitor lacks Qand tuning range

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Voltage-Tunable High-Q Capacitor• Micromachined, movable, metal 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

Ground PlanePrevents Pull-Inof Suspensions

Ground PlanePrevents Pull-Inof Suspensions

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Governing Displacement Equations• Two forces at work

electrostatic force:

mechanical restoring force:

• Expression relating Va and dequate forces: Fa = Fm

222

21

21

dAV

xCV

xEF o

aaaε

=∂∂

=∂∂

=

( )ddkF om −=

( )dddAkV o

oa −= 22

ε

Plat

e H

eigh

t, d

Actuation Voltage, Va

do

(2/3)do

Va Fa d Fa(+) feedback instability

and ultimately pull-in

Pull-InVoltage, VPI

PlateOverlap

Area

( ) ( )a

oa Vd

AVC ε=

Initial GapSpacing, do

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Fabricated Voltage-Tunable High-Q Capacitor• Surface micromachined in sputtered aluminum

• Ctot = 2.2pF; 16% tuning range for ΔVtune=5.5V; Q=60• Challenge: contact and support line resistance degrades Q

C. T.-C. Nguyen



Enhancing the Tuning Range• Tuning range limited by pull-in caused by (+) feedback

in the force, charge, displacement sytemPull-In Voltage, VPI:

• Possible Solutions:use leveraged bending [Hung, Senturia JMEMS’99]alternative actuation methods (non-electrostatic)

electro-thermal actuators provide much wider tunng range; problem: power consumption [Harsh, Lee 1999]

use a series capacitor to add (-) feedback that counteracts the (+) feedback, making the system more stable [Seeger, Crary 1997]

AkdVV

o

oddaPI o ε278 3

32 == = Gap Spacing

Plate OverlapArea

SuspensionStiffness

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Va

Advantages:• Rigidly-anchored top and bottom plates

no need for long suspension beamslarger contacts lower Rs high Q

• Tuning range set by ratio of dielectric slab thickness to capacitive gap can be large

• No possibility for top to bottom plate shorting

Bottom Plate

MovableDielectric

F Va

Fixed Top PlateSpring

cf.

Tunable-Dielectric μMechanical Capacitor

Cross-Sectional View

Comb-TypeTop View

C. T.-C. Nguyen



Governing Equation for Tunable-Dielectric Micromechanical Capacitance

• Approximate formulation: (neglecting fringing fields)

C1

Cd

C2

C0

L

t0

td

x

kF

Vaεd εa

insensitive to vertical motion of the dielectric

:

( )( )

( )

) (if

00

000

210

add

da

a

ddda

daa

dtot

xtt

tLt

xtttt

L

seriesCseriesCCCC

εεε

εεεε

εεε

>>⎟⎟⎠

⎞⎜⎜⎝

⎛−

+=

⎥⎦

⎤⎢⎣

⎡−

+−+=

+=

(or metal slab)

d

a

ttx

−0

ε

C. T.-C. Nguyen



Expanded Equation for Tunable-Dielectric Micromechanical Capacitance

• In terms of applied voltage

• Again, neglecting fringing fields

L

t0

td

x

kF

Vaεd εa

( )

( )

( )

( ) ⎥⎦

⎤⎢⎣

⎡

−+=∴

−=−=

∂∂

∴

−−

=−=

=−

=∂∂

=

22

0

2

0

2

0

0

2

00

22

12

12 ,

12

,122

1

aaa

tot

aa

eq

aake

daaa

tote

Vakt

aLt

C

Vakt

axkxF

kxat

aVFFF

tta

ataVV

xCF

εε

ε

ε

ε

0

atL

0

ε

( )atLa

−10

ε

aLakt

aε)1(2 0 −

Ctot

Va

Cmax

Cmin

min

max

11

aCC

−=

=d− tt0

t0 (< )aεdε

C. T.-C. Nguyen



Bottom Plate

Top Electrode

Dielectric

To Anchor

Lateral Sprin

g

To anchor without any spring

L l

tl

wl

3μm

7μm

8μm

5μm

100μm

• Waffle-shaped top electrodesallow smaller travel distance for a given capacitance changeprovides etchant access paths during fabrication

• Flat bottom plateeliminates surface topography

( )

EtLw

n

VaLt

ak

ll

l

aa

×⎟⎟⎠

⎞⎜⎜⎝

⎛×=

−=

3

2

0

1

12ε

n=3 for the case above

Tunable-Dielectric Capacitor Design

C. T.-C. Nguyen



Tunable-Dielectric Capacitor Fabrication

PISi wafer

DielectricCr/Cu Seed

Plated Cu (5μm)Plated Ni (0.3μm)

PI

1st Sacrificial Al (0.2μm)PECVD SiNx (0.6μm)

PI

2nd Sacrificial Al (0.9μm)

(1)

(2)

(3) Bottom Cu

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(4)

(5)

PI

Thick Photoresist (10μm)

Plated Cu (7μm)

Cr/Cu Seed

Movable Dielectric (Anchor Not Shown)

All process temperatures < 200 ºCamenable to post-IC integration

Si wafer

Bottom Cu

Top CuCritical point drying for anti-stiction

Tunable-Dielectric Capacitor Fabrication

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Bent-Up PECVD SiNxLateral Spring Cu Bottom GND

Waffle-Shaped Cu Top Electrode

GSG Pads

Fabricated Tunable-Dielectric Capacitor

[Yoon et al, IEDM’00]

• Waffle-shaped top electrodesallow smaller travel distance for a given cap. changeprovides etchant access paths during fabrication

• Flat bottom plateeliminates surface topography 0 1 2 3 4 5 6

1.0

1.1

1.2

1.3

1.4

1.5

0

100

200

300

400

500

Frequency (GHz)

C(p

F)

Q-factor

(Line: measured, Symbol: modeled)

Q

C

Model0.4472Ω 0.05283nH

1.2047pF

0V BiasLateral Spring

(a)

RF Performance:C = 1.21pF @ 0VQ = 291 @ 1GHz

SRF = 19GHz7.7% tuning over 10V

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Spiral Inductor Deficiences

• Series Rs degrades Qsolns: increase L per unit length; use thicker metal

• Parasitic Co, Cox, Csub, and Rsub self-resonance, degrades Qsoln: isolate from substrate

C. T.-C. Nguyen



Three-Dimensional Coil Inductor• Electroplated copper winds achieved using maskless, 3-D,

direct-write laser lithography to pattern resist mold

C. T.-C. Nguyen



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



Self-Assembling Variable Inductors • Use interlayer stress to warp released inductors to

significantly elevate them above the substrate• Well-isolated from

substrate minimizes substrate currents and eddy current loss

• Hinged anchors reduce temperature dependence

• Challenge: microphonics

Design/Performance:(with 0.5μm Cr-Au turns

on 1 Ω-cm substrate)L = 1nH, Q =13 @ 7GHz

SRF = 15GHz

[Lubecke, Gammel 2000]

Hinges

C. T.-C. Nguyen



On-Chip Tunable High-Q LC Bandpass Filter

• Desired for implementing a tunable RF pre-select filter for multi-band reconfigurability; i.e., allowing a single phone to communicate in several standards, such as GSM, DCS1800, PCS, etc.

• Need: micro-scale inductors and tunable capacitors with Q’s >300 (topic for ongoing research)

Micromachined Inductor, Q ~300

Need: major Q increase

Micromachined Inductor, Q ~300

Need: major Q increase

Micromachined Tunable Capacitors

Q ~300

Micromachined Tunable Capacitors

Q ~300[Yao 1997]

C. T.-C. Nguyen



Components Realizable By Micromachined L and C Technology

• VCO Tank: for best on-chip performance• Tunable Bias/Matching Networks: save power in amplifiers• RF Multi-Band Pre-Select Filter: only if QL ~300 is possible

RF Pre-Select Filterfo~945MHz, BW~40MHz

Adv.: small size, tunableChallenge: QL~300

RF Pre-Select Filterfo~945MHz, BW~40MHz

Adv.: small size, tunableChallenge: QL~300

Bias/Matching Tanksfo~945MHz, 902MHzAdv.: lower power

Bias/Matching Tanksfo~945MHz, 902MHzAdv.: lower power

VCO Tanksfo~874MHz,71MHz, 831MHz

Adv.: lower power

VCO Tanksfo~874MHz,71MHz, 831MHz

Adv.: lower power

C. T.-C. Nguyen



Today’s Local Oscillator Synthesizer

• Phase locking cleans up the VCO output spectrum

• Result: sufficiently stable, tunable oscillator

C. T.-C. Nguyen



• Yellow: replaceable LC tanks (low- to medium-Q required)• Red: very high-Q tanks required (Q >1,000)

High-Q Transceiver Components

RF Pre-Select Filter~945 MHz, Qres ~500RF Pre-Select Filter~945 MHz, Qres ~500


RF Image-Reject Filter~945 MHz, Qres ~1,000 IF Channel-Select Filter

~71 MHz, Qres ~5,000IF Channel-Select Filter

~71 MHz, Qres ~5,000

High-Q ReferenceTank, Qres ~20,000




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Micromechanical Resonator History• Very first μmechanical resonators: Nathanson et al (1967)

metal structural materialresonant-beam serves as gate for NMOS transistorProblems: surface charge, high TCf, frequency drift, Q~90

• First polysilicon-based resonator combined with NMOS technology by Howe et al (1984)

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Vertically-Driven Micromechanical Resonator• To date, most used design to achieve VHF frequencies

• Smaller mass higher frequency range and lower series Rx

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Voltage-Controllable Center Frequency

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Micromechanical Resonator Equivalent Circuit

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Fabricated HF μMechanical Resonator• Surface-micromachined, POCl3-doped polycrystalline silicon

• Extracted Q = 8,000 (vacuum)• Freq. influenced by dc-bias

and anchor effects

C. T.-C. Nguyen



Off-Chip 10MHz Pierce Oscillator• Buffer stage added to the classic

Pierce to preserve 0o loop phase shift despite a large Rx ~ 2 kΩ

Vo: ~ 210 mV

TransconductanceStage

BufferStage

Oscilloscope Waveform

Fourier Spectrum

[Lee, Demirci,Nguyen,Trans’01]

Confidential: Not to be released without the expressed written permission of Prof. Clark T.-C. Nguyen and the NSF ERC on WIMS.

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Fabricated HF μMechanical Resonator• Surface-micromachined, POCl3-doped polycrystalline silicon

• Extracted Q = 8,000 (vacuum)• Freq. influenced by dc-bias

and anchor effects

C. T.-C. Nguyen



Desired Filter Characteristics

• Small shape factor generally preferred

C. T.-C. Nguyen



Micromechanical Circuits• A single mechanical beam can’t really do much on its own• But use many mechanical beams attached together in a

circuit, and attain a more complex, more useful function

InputForce

Fi

OutputDisplacement

xo

t

xo

t

Fi

Key Design Property: High Q

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Desired Filter Characteristics

• Small shape factor generally preferred

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Micromechanical Filter Circuit

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Ideal Spring-Coupled μMechanical Filter

ks12mr1

kr1

cr1

kr2

mr2

cr2

Symmetric Mode Anti-Symmetric Mode

BW ~ ks12

kr

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Micromechanical Filter Circuit

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Design Issue: Termination Resistance• Need to minimize

RQ for impedance matching want:

VP = largeAo = larged = small

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Small Electrode-to-Resonator Gaps

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HF Spring-Coupled Micromechanical Filter

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Attaining Better Performance• Use more resonators to attain higher order• Filter Order = 2 x (# of resonators)

• Higher Order sharper roll-off better stopband rejection

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High-Order μMechanical Filter

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Design Issue: Process Tolerances

• Process variations can lead to distortion in the filter passband

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Electrostatic Frequency Tuning• Use nonlinear parallel-plate transducers for electrostatic

frequency tuning

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μMechanical Filter Passband Correction

• Problems: too many interconnect leads, Δf small at VHF• Need: a permanent frequency trimming technique

[Wang,Nguyen,1997]

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Micromechanical Filter Video

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Capacitive Transducer

IFω ω

ElectricalSignal Input

MechanicalSignal Input

ωωIF

FilterResponse

ωo=ωIF

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ElectricalSignal Input

MechanicalSignal Input

ωRFωLO

ωRFωLOωIF

ω

ω

FilterResponse

Electromechanical Mixing

ωIF

ωo=ωIF

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Micromechanical Mixer-Filter

[Wong, Nguyen 1998]

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• Main Requirements:frequency extension for LPCVD deviceshigher Q for FBARs

Components Realizable By Vibrating MEMSIF Channel-Select Mixer-

Filter-Gain Stagefo~71MHz, BW~200kHz

Adv.: tiny, lower I.L., 0 W

IF Channel-Select Mixer-Filter-Gain Stage

fo~71MHz, BW~200kHzAdv.: tiny, lower I.L., 0 W

RF Pre-Select Filterfo~945MHz BW~40MHz

Adv.: tiny, lower I.L.FBAR: now

LPCVD: freq. ext.

RF Pre-Select Filterfo~945MHz BW~40MHz


LPCVD: freq. ext.

RF Image-Rej. Filterfo~945MHzBW~25MHz


LPCVD: freq. ext.

RF Image-Rej. Filterfo~945MHzBW~25MHz


LPCVD: freq. ext.High-Q TankQ ~10,000Adv.: tiny

High-Q TankQ ~10,000Adv.: tiny

C. T.-C. Nguyen



Vibrating MEMS Research Issues:Frequency Extension

C. T.-C. Nguyen



Research Issue: Frequency Extension• To extend the frequency range

shrink beam dimensionsmust shrink gap d dimensions, as well

• Possible Problem: Q reduction with frequencymaterial and anchor loss mechanismssolution: defensive mechanical design, materials engineering

C. T.-C. Nguyen



Anchor Dissipation in Fixed-Fixed Beams

fo↑Q↓

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92 MHz Free-Free Beam μResonator• Free-free beam μmechanical resonator with non-intrusive

supports reduce anchor dissipation higher Q

~200 MHz SiC Resonator ( Caltech/Case Western Collaboration )

L,w,t ~ 3μm × 150nm × 259nm

magnetomotive readout( 50nm Al metallization )

192.0 192.5 193.0 193.5 194.0

0

200

400

600

800

1000

1200

Mag

neto

mot

ive

Resp

onse

(nV)

Frequency (MHz)

f0 ~ 193 MHzQ ~ 1230 (prelim.)

Initial devices are rather rough; future generations should yield v. significant improvements

M.L. Roukes, Condensed Matter Physics, Caltech DARPA MEMS/MTO PI Meeting - August 2000 90

C. T.-C. Nguyen



Research Issue: Frequency Extension• To extend the frequency range

shrink beam dimensionsmust shrink gap d dimensions, as well

• Possible Problem: Q reduction with frequencymaterial and anchor loss mechanismssolution: defensive mechanical design, materials engineering

• Possible Problem: size vs. power handling trade-offsmay limit the degree of size reduction allowablesolution: transducer design, other vibration modes

C. T.-C. Nguyen



156 MHz Radial Contour-Mode Disk μMechanical Resonator

• Below: Balanced radial-mode disk polysilicon μmechanicalresonator (34 μm diameter)

μmechanical DiskResonator

MetalElectrode

MetalElectrode

R

Anchor

Design/Performance:R=17μm, t=2μm

d=1,000Å, VP=35Vfo=156.23MHz, Q=9,400

[Clark, Hsu, Nguyen IEDM’00]

fo=156MHzQ=9,400

C. T.-C. Nguyen



Structural Polysilicon

μMechanical Disk Resonator Fabrication

Substrate

SiO2Groundplane and Electrode Polysilicon

AnchorGroundplane and Electrode Polysilicon

Si3N4

Sacrificial Oxide Spacer

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Substrate



Si3N4


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Substrate



Si3N4

Plated Metal Electrodes


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Substrate



Si3N4

Plated Metal Electrodes

Air Gap d = 1000 Å


C. T.-C. Nguyen



1000Å Lateral Electrode-to-Disk Gaps• Achieved via a fabrication process that combines

polysilicon surface micromachining, metal electroplating, and sidwall spacer technologies

μMechanicalDisk

Resonator

MetalElectrode

MetalElectrode

2 μm

1,000Å

[Clark, Hsu, Nguyen IEDM’00]

C. T.-C. Nguyen



Thin-Film Bulk Acoustic Resonator (FBAR)• Piezoelectric membrane sandwiched by metal electrodes

extensional mode vibration: 1.8 to 7 GHz, Q ~1,000dimensions on the order of 200μm for 1.6 GHz

• Link together in ladder networks to make filters

C. T.-C. Nguyen



Vibrating MEMS Research Issues:Temperature Stability

C. T.-C. Nguyen



Research Issue: Thermal Stability

• Need temperature compensation or control methods[Wang, Yu, Nguyen 2000]

C. T.-C. Nguyen



Geometric-Stress Temperature Compensation• Geometrically generate a stress vs. temperature function

that compensates Young’s modulus thermal variation

L1 ≠ L2

C. T.-C. Nguyen



Fabricated Temp.-Insensitive μResonator

Design/Performance:L1=39μm, L2=39μm, d =1038ÅW1=2.5μm, W2=20μm, t =2μm

VP=16V, fo=13.49MHz, Q=10,317

[Hsu, Clark,Nguyen IEDM’00]

C. T.-C. Nguyen



• Below: polysilicon structure, silicon substrate

• Less than 200 ppm fo variation over 80oC for L2/L1=60/40

Demonstration of Geometric-Stress Temperature Compensation

[Hsu, Clark, Nguyen 2000]

C. T.-C. Nguyen



Research Issue: Thermal Stability

• Need temperature compensation or control methods[Wang, Yu, Nguyen 2000]

C. T.-C. Nguyen



• Contamination fluctuations fo and Q fluctuations

• Factors influencing contamination-derived instabilitiescontaminant molecule size and weightpressure and temperature

• Need encapsulation for contamination protection

Research Issue: Contamination Sensitivity

• Typical μresonatormass: 10-13 kg

• Larger frequency fluctuations for micro-sized resonators than for more massive quartz crystals

C. T.-C. Nguyen



Planar Processed Vacuum Encapsulation• After surface micromachining, continue

depositing/patterning films to achieve a vacuum cap• Below: the permeable polysilicon method [Lebouitz 1999]

[Lebouitz, Pisano 1999]

C. T.-C. Nguyen



Research Issue: Vacuum Encapsulation• Below: localized heated bonding to seal a vacuum cap

over a released micromechanical resonator

Glass Cap

µHeaterand

AluminumSolder

Vanneal

Schematic of the BondingEncapsulation Procedure

Broken Glass Cap

Microcavity

2000

2250

2500

2750

3000

0 2 4 6 8 10 12Weeks

Q

40 weeks at 25 mTorr

[Cheng, Hsu, Lin, Nguyen, Najafi 2000]

C. T.-C. Nguyen





Κ

C. T.-C. Nguyen



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

C. T.-C. Nguyen



Phased Array Antenna

C. T.-C. Nguyen



Switchable Medium-Q Filters

• Need: very low loss switches to retain good Qtransistor switches not usable too much Rs

|v2/v1|

FrequencyLCtot determines fo

[Yao 1997]

C. T.-C. Nguyen



Micromechanical Switch Pros and ConsAdvantages:• Via use of metal material, the contact and spreading

resistance of ohmic FET or p-i-n diode switches are eliminated, significantly reducing resistive losses

• Extremely good linearity: IIP3 ~66dBm• Negligible DC power consumption (for electrostatic

actuation) switching energy ~10 nJProblems/Limitations:• Slow switching speed (τ~5μs) relative to FET switches

(τ~1ps) precludes use in high-speed applications, such as some transmit/receive switching schemes

• Large actuation voltage: Va ~ 50V• Reliability

actual contact between moving parts wear, weldingsoln.: use capacitive switch, if possiblehot switching can limit power handling

C. T.-C. Nguyen



Hot Switching• Phenomenon where excessive RF power can inadvertently

close an open switch

• AC voltage on the conductor is rectified in the electrical-to-mechanical conversion; DC force pulls down the beam

• Problem: switch can stay down even if RF power is lowered

tVv cc ωcos=RF Signal

xCv

xEF ca ∂

∂=

∂∂

= 2

21

txCV

xCV cc ω2cos

41

41 22

∂∂

+∂∂

=

Resulting Force:

Fa

DC Force

C. T.-C. Nguyen



Metrics and Design Issues• Cut-Off Frequency Figure of Merit:

frequency where the ratio of off-impedance to on-impedance degrades to unity

GaAs MESFET: fc = 280GHzGaAs p-i-n Diode: fc = 730GHzMetal Membrane Switch: fc > 9000GHz [Yao, Goldsmith 1999]

• On-off impedance ratio versus actuation voltage trade-offfor a large on-off impedance ratio (desired), must increase the electrode-to-beam gapfor a small actuation voltage (desired), must decrease the electrode-to-beam gap

• Hot switching versus actuation voltage trade-off

offonc CR

fπ2

1=

C. T.-C. Nguyen



Low-Voltage Micromechanical Switch

• Large actuation plates increase transducer capacitance• Thin switch conductor decreases “off” capacitance• Serpentine suspension springs decrease stiffness• (not shown) Upper actuation plates hold the structure

still in “off” states and prevent “hot switching”

C. T.-C. Nguyen



• Electroplated Ni material; problems with warping• With four meanders in the supporting springs: Vswitch= 9V

Fabricated Low-Voltage μMechanical Switch

[Pacheco,Katehi,

Nguyen 2000]

C. T.-C. Nguyen



Components Realizable Via Micromechanical Switch Technology

• RF Pre-Select Filter: if Q ~300 is possible, then this filter could satisfy multi-band requirements

• Antenna & Filter Switching: great performance; switch filters for multi-band reconfigurability

RF Pre-Select Filterfo~945MHzBW~40MHz

Adv.: low lossChallenge: Q ~300

RF Pre-Select Filterfo~945MHzBW~40MHz

Adv.: low lossChallenge: Q ~300

Antenna & Filter SwitchingAdv.: low loss, linearityChallenge: Reliability

Antenna & Filter SwitchingAdv.: low loss, linearityChallenge: Reliability Focus of Much

Research/Development

C. T.-C. Nguyen



• A large number of off-chip high-Q components replaceable with μmachined versions; e.g., using μmachined resonators, switches, capacitors, and inductors

MEMS-Replaceable Transceiver Components

C. T.-C. Nguyen



Miniaturization of Transceivers via MEMS


C. T.-C. Nguyen





Κ

C. T.-C. Nguyen



Merged Circuits/μMechanics Technologies (Process Philosophy)

• Mixed:problem: multiple passivation/protection steps ⇒ large number of masks requiredproblem: custom process for each product

• Pre-Circuits or Post-Circuits:adv.: modularity ⇒ flexibility ⇒ less development timeadv.: low pass./protection complexity ⇒ fewer masks

C. T.-C. Nguyen



Pre-Circuits Xsistor/μMechanics Integration• Problem: μstructural topography interferes with lithography

difficult to apply photoresist for submicron circuits

• Soln.: build μmechanics in a trench, then planarize before circuit processing [Smith et al, IEDM’95]

C. T.-C. Nguyen



Pre-Circuits Example: Sandia’s iMEMS• Used to demonstrate functional fully integrated oscillators• Issues:

lithography and etching may be difficult in trench may limit dimensions (not good for RF MEMS)μmechanical material must stand up to IC temperatures (>1000oC) problem for some switch metalsmight be contamination issues for foundry IC’s

[Smith et al, IEDM’95]

C. T.-C. Nguyen



Post-Circuits Xsistor/μMechanics Integration • Modular technology minimizes product updating effort

Module 1: circuit process (planar IC technology)Module 2: micromachining process (planar technology)

• Adv.: topography after circuit fabrication is much smaller• Problem: limited thermal budget

metal and junctions must withstand temperatures ~835oCtungsten metallization used with TiSi2 contact barriersin situ doped structural polySi; rapid thermal annealing

C. T.-C. Nguyen



Post-CMOS Circuits/μMechanics Integration• Completely monolithic, low phase noise, high-Q oscillator

(effectively, an integrated crystal oscillator) [Nguyen, Howe]

• To allow the use of >600oC processing temperatures, tungsten (instead of aluminum) is used for metallization

OscilloscopeOutput

Waveform

C. T.-C. Nguyen



Post-Circuits Xsistor/μMechanics Integration • Problem: tungsten is not an accepted primary interconnect

metal• Challenge: retain conventional metallization

minimize post-CMOS processing temperaturesexplore alternative structural materials (e.g., plated nickel, SiGe [Franke, Howe et al, MEMS’99])

C. T.-C. Nguyen



Post-Circuits Integration Using Bonding• Bonding technologies can potentially achieve true

modularity in post-CMOS integration, with the greatest flexibility in circuit and μmechanical technologies

• Avantages:modules completey separate; no compromises

virtually any circuit can be combined with virtually any MEMS process

no contamination or compatibility issues for integrated circuit foundriesany mechanical material can be used: polysilicon, aluminum, copper, CVD diamond, SiC

• Challenges: yield vs. bond area (which should be minimized to avoid excessive capacitance)

• Question: high volume production possible?

C. T.-C. Nguyen



Bonded-Platform Circuits/μMechanicsMerging Process (Bonding)

• Platform micromechanics and circuit wafer merged via compression bonding (completely modular)

Confidential: Not to be released without the expressed written permission of Prof. Clark T.-C. Nguyen and the NSF ERC on WIMS.

SupportingStruts Bend

C. T.-C. Nguyen



Miniaturization of Transceivers via MEMS


C. T.-C. Nguyen



MEMS-Based Receiver Architecture• Most Direct Approach: replace off-chip components (in

orange) with μmechanical versions (in green)

• Obvious Benefit: substantial size reduction

Replace with MEMSL1~0.3dBL1~0.3dB

L1~2dBL1~2dB

NF = 8.8dBNF = 8.8dB

NF = 2.8dBNF = 2.8dB

L3~6dBL3~6dB L5~12dBL5~12dB

L3~0.5dBL3~0.5dB L5~1dBL5~1dB

Antenna Diversity for

resilience against fading

Antenna Diversity for

resilience against fading

Higher Q

C. T.-C. Nguyen





Κ

C. T.-C. Nguyen



Power vs. Selectivity (or Q) Trade-Offs

ReceivedPower

Frequency

DesiredSignal

AntennaRF Pre-SelectFilter

(Res.Q ~500)

• Example: power consumption as a function of front-end selectivity

case: wideband front-end filtering

C. T.-C. Nguyen



ReceivedPower

Frequency

DesiredSignal

Antenna

Subsequent Electronics (e.g., LNA, mixer, ADC’s)

Out-of-BandInterferersRemoved

Power vs. Selectivity (or Q) Trade-Offs• Example: power consumption as a function of front-end

selectivitycase: wideband front-end filtering

RF Pre-SelectFilter

(Res.Q ~500)

• Problem: helpful, but does not go far enoughsubsequent electronics must still have more dynamic range than really necessary power wasted

C. T.-C. Nguyen



ReceivedPower

Frequency

DesiredSignal

Antenna


RF Pre-SelectFilter

(Res.Q ~500)


selectivitybetter approach: narrowband front-end filtering

C. T.-C. Nguyen



ReceivedPower

Frequency

DesiredSignal

Antenna


RF Channel-SelectFilter

(Q ~500)(Q ~10,000)



C. T.-C. Nguyen



ReceivedPower

Frequency

DesiredSignal

Antenna

Subsequent Electronics (e.g., LNA, mixer, ADC’s)• Result: substantial power savings in subsequent circuits

relaxed dynamic range requirementsrelaxed oscillator phase noise requirements

(Q ~10,000)

AllInterferersRemoved



RF Channel-SelectFilter

(Q ~500)

C. T.-C. Nguyen



ReceivedPower

Frequency

Antenna


Front-End Channel Selector

FilterOn

FilterOn

FilterOn

FilterOn

• Power Saving Strategy: select channels right up at RF• One Approach: Use a highly selective low-loss filter that

is tunable from channel to channel:

• Problem: high filter selectivity (i.e., high Q) often precludes tunability

C. T.-C. Nguyen



Voltage-Controllable Center Frequency

C. T.-C. Nguyen



ReceivedPower

Frequency

Antenna


FilterOn

FilterOn

FilterOn

FilterOn

• Solution: rather than cover the band by tuning, cover with a bank of switchable filters

• Problem: macroscopic high-Q filters are too big• Requirement: tiny filters μmechanical high-Q filters

present a good solution

Front-End Channel Selector

C. T.-C. Nguyen



MEMS vs. SAW Comparison

• MEMS offers the same or better high-Q frequency selectivity with orders of magnitude smaller size

C. T.-C. Nguyen



Micromechanical RF Pre-Selector• Use a massively parallel array of tunable, switchable filters

tiny size and zero dc power consumption ofμmechanical filters allows this

C. T.-C. Nguyen




the need for high-Q• Receiver Design and Operation• Oscillator Fundamentals and Needs• Medium-Q Tunable μMech. Capacitors• Medium-Q Micromachined Inductors• High-Q Micromechanical Resonators• High-Q Micromechanical Filters• Micromechanical Mixer-Filters• Micromechanical Switches• Integration Technologies• Power Savings Via High-Q MEMS• ConclusionsΚ

C. T.-C. Nguyen



Conclusions• Via enhanced selectivity on a massive scale,

micromechanical circuits using high-Q elements have the potential for shifting communication transceiver design paradigms, greatly enhancing their capabilities

• Advantages of Micromechanical Circuits:orders of magnitude smaller size than present mechanical resonator devicesbetter performance than other single-chip solutionspotentially large reduction in power consumptionalternative transceiver architectures that maximize the use of high-Q, frequency selective devices for improved performance… but there’s much more to it than just the above ...

C. T.-C. Nguyen



Transistor Signal Processors

• Signal Processor Block:

Sin

Tin

Sout

Tout

t

Sin

t

Sout

Key Design Property: High Gain

C. T.-C. Nguyen



Micromechanical Signal Processors

• Signal Processor Block:

Sin

Tin

Sout

Tout

Key Design Property: High Qt

Sin

t

Sout

C. T.-C. Nguyen



Micromechanical Signal Processors

μmechanical resonators can potentially implement a substantial portion of a receiver’s RF front end

C. T.-C. Nguyen



Conclusions• Compelling parallels between MEMS and integrated

transistor signal processor technologies:Before 1960: discrete transistor circuits wired on boards with limited functionalityAfter IC’s: VLSI CPU’s and memory circuits have revolutionized the way things are doneToday: discrete mechanical circuits coupled by welded wires with limited functionalityWith VLSI Micromechanical Signal Processors:

functions never before possible now realizable via a combination of transistor and mechanical circuits?a functional and system architectural revolution reminiscent of the IC revolution?

… potential for true revolution? …… but there is much work yet to be done …

C. T.-C. Nguyen



Selected Readings

C. T.-C. Nguyen



Overviews and MEMS-Based Architectures[1] C. T.-C. Nguyen, L. P.B. Katehi, and G. M. Rebeiz, “Micromachined

devices for wireless communications (invited),” Proc. IEEE, vol. 86, no. 8, pp. 1756-1768, Aug. 1998.

[2] C. T.-C. Nguyen, “Frequency-selective MEMS for miniaturized low-power communication devices (invited),” IEEE Trans. Microwave Theory Tech., vol. 47, no. 8, pp. 1486-1503, Aug. 1999.

[3] C. T.-C. Nguyen, “Micromechanical circuits for communication transceivers (invited),” Proceedings, 2000 Bipolar/BiCMOSCircuits and Technology Meeting (BCTM), Minneapolis, Minnesota, September 25-26, 2000, pp. 142-149.

[4] C. T.-C. Nguyen, “Micromechanical circuits for communications (invited),” Proceedings, 2000 Int. Conference on High Density Interconnect and Systems Packaging, Denver, Colorado, April 25-28, 2000, pp. 112-117.

[5] C. T.-C. Nguyen, “Vibrating RF MEMS for low power wireless communications (invited),” to be published in the Proceedings of the 2001 Int. MEMS Workshop, Singapore, July 4-6, 2001.

C. T.-C. Nguyen



Micromechanical Tunable Capacitors[1] D. J. Young and B. E. Boser, “A micromachined variable capacitor

for monolithic low-noise VCOs,” Technical Digest, 1996 Solid-State Sensor and Actuator Workshop, Hilton Head Island, South Carolina, June 3-6, 1996, pp. 86-89.

[2] J.-B. Yoon and C. T.-C. Nguyen, “A high-Q tunable micromechanical capacitor with movable dielectric for RF applications,” Technical Digest, IEEE Int. Electron Devices Meeting, San Francisco, California, Dec. 11-13, 2000, pp. 489-492.

[3] A. Dec and K. Suyama, “Micromachined electro-mechanically tunable capacitors and their applications to RF IC’s,” IEEE Trans. Microwave Theory Tech., vol. 46, pp. 2587-2596, Dec. 1998.

[4] A. Dec and K. Suyama, “A 1.9GHz CMOS VCO with micromachinedelectromechanically tunable capacitors,” IEEE J. Solid-State Circuits, vol. 35, pp. 1231-1237, Aug. 2000.

[5] Z. Feng, W. Zhang, B. Su, K. F. Harsh, K. C. Gupta, V. M. Bright, and Y. C. Lee, “Design and modeling of RF MEMS tunable capacitors using electro-thermal actuators,” 1999 IEEE MTT-S Int. Microwave Symposium, Baltimore, MD, June 8-11, 1999.

C. T.-C. Nguyen



Micromachined Inductors[1] D. J. Young, V. Malba, J.-J. Ou, A. F. Bernhardt, and B. E. Boser,

“Monolithic high-performance three-dimensional coil inductors for wireless communication applications,” Technical Digest, IEEE International Electron Devices Meeting, Washington, D. C., Dec. 8-11, 1997, pp. 67-70.

[2] J. A. Von Arx and K. Najafi, “On-chip coils with integrated cores for remote inductive powering of integrated microsystems,” Digest of Technical Papers, 1997 International Conference on Solid-State Sensors and Actuators (Transducers’97), Chicago, Illinois, June 16-19, 1997, pp. 999-1002.

[3] B. Ziaie, N. K. Kocaman, and K. Najafi, “A generic micromachined silicon platform for low-power, low-loww miniature transceivers,”Digest of Technical Papers, 1997 International Conference on Solid-State Sensors and Actuators (Transducers’97), Chicago, Illinois, June 16-19, 1997, pp. 257-260.

[4] M. G. Allen, “Micromachined intermediate and high frequency inductors,” 1997 IEEE International Symposium on Circuits and Systems, Hong Kong, June 9-12, 1997, pp. 2829-2832.

C. T.-C. Nguyen



Micromachined Inductors (cont.)[5] C. H. Ahn, Y. J. Kim, and M. G. Allen, “A fully integrated

micromachined toroidal inductor with nickel-iron magnetic core (the switched DC/DC boost converter application),” Digest of Technical Papers, the 7th International Conference on Solid-State Sensors and Actuators (Transducers’93), Yokohama, Japan, June 7-10, 1993, pp. 70-73.

[6] J. B. Yoon, et al., “Monolithic high-Q overhang inductors fabricated on silicon and glass substrates,” Tech. Digest, 1999 Int. Electron Devices Meeting, Washington, D. C., pp. 753-756.

C. T.-C. Nguyen



Vibrating μMechanical Resonators[1] H. Nathanson, W. E. Newell, R. A. Wickstrom, and J. R. Davis, Jr.,

“The resonant gate transistor,” IEEE Trans. Electron Devices, vol. ED-14, No. 3, pp. 117-133, March 1967

[2] R. T. Howe and R. S. Muller, “Resonant microbridge vapor sensor,” IEEE Trans. Electron Devices, ED-33, pp. 499-506, 1986.

[3] F. D. Bannon III, J. R. Clark, and C. T.-C. Nguyen, “High frequency micromechanical filters,” IEEE J. Solid-State Circuits, vol. 35, no. 4, pp. 512-526, April 2000.

[4] K. Wang and C. T.-C. Nguyen, “High-order medium frequency micromechanical electronic filters,” IEEE/ ASME J.Microelectromech. Syst., vol. 8, no. 4, pp. 534-557, Dec. 1999.

[5] W. C. Tang, T.-C. H. Nguyen, and R. T. Howe, “Laterally drivenpolysilicon resonant microstructures,” Sensors and Actuators, 20, 25-32, 1989.

[6] C. T.-C. Nguyen and R. T. Howe, “An integrated CMOS micromechanical resonator high-Q oscillator,” IEEE J. Solid-State Circuits, vol. 34, no. 4, pp. 440-445, April 1999.

C. T.-C. Nguyen



Vibrating μMechanical Resonators (cont.)[7] H. A. C. Tilmans, “Equivalent circuit representation of

electromechanical transducers: I. lumped-parameter systems,” J.Micromech. Microeng., 6, pp. 157-176 (1996).

[8] H. A. C. Tilmans and R. Legtenberg, “Electrostatically driven vacuum-encapsulated polysilicon resonators: Part II. Theory and performance,” Sensors and Actuators, vol. A45 (1994), pp. 67-84.

[9] M. L. Roukes, “Nanoelectromechanical systems,” Tech. Digest, 2000 Solid-State Sensor and Actuator Workshop, Hilton Head Island, South Carolina, June 4-8, 2000, pp. 367-376.

[10] J. R. Clark, W.-T. Hsu, and C. T.-C. Nguyen, “High-Q VHF micromechanical contour-mode disk resonators,” Technical Digest, IEEE Int. Electron Devices Meeting, San Francisco, California, Dec. 11-13, 2000, pp. 399-402.

[11] W.-T. Hsu, J. R. Clark, and C. T.-C. Nguyen, “Mechanically temperature compensated flexural-mode micromechanical resonators,” Technical Digest, IEEE Int. Electron Devices Meeting, San Francisco, California, Dec. 11-13, 2000, pp. 493-496.

C. T.-C. Nguyen



Vibrating μMechanical Resonators (cont.)[12] J. R. Vig and Y. Kim, “Noise in microelectromechanical system

resonators,” IEEE Trans. Utrason. Ferroelec. Freq. Contr., vol. 46, no. 6, pp. 1558-1565, Nov. 1999.

[13] R. Navid, J. R. Clark, M. Demirci, and C. T.-C. Nguyen, “Third-orderintermodulation distortion in capacitively-driven CC-beam micromechanical resonators,” Technical Digest, 14th Int. IEEE Micro Electro Mechanical Systems Conference, Interlaken, Switzerland, Jan. 21-25, 2001, pp. 228-231.

C. T.-C. Nguyen



Vibrating μMechanical Filters[1] F. D. Bannon III, J. R. Clark, and C. T.-C. Nguyen, “High frequency

micromechanical filters,” IEEE J. Solid-State Circuits, vol. 35, no. 4, pp. 512-526, April 2000.

[2] K. Wang and C. T.-C. Nguyen, “High-order medium frequency micromechanical electronic filters,” IEEE/ ASME J.Microelectromech. Syst., vol. 8, no. 4, pp. 534-557, Dec. 1999.

[3] J. R. Clark, A.-C. Wong, and C. T.-C. Nguyen, “Parallel-resonator HF Micromechanical Bandpass Filters,” Digest of Technical Papers, 1997 International Conference on Solid-State Sensors and Actuators, Chicago, Illinois, June 16-19, 1997, pp. 1161-1164.

[4] C. T.-C. Nguyen, A.-C. Wong, and H. Ding, “Tunable, switchable, high-Q VHF microelectromechanical bandpass filters,” Digest of Technical Papers, 1999 IEEE International Solid-State Circuits Conference, San Francisco, California, Feb. 15-17, 1999, pp. 78-79, 448.

[5] R. A. Johnson, Mechanical Filters in Electronics. New York: John Wiley & Sons, 1983.

C. T.-C. Nguyen



Vibrating μMechanical Mixer-Filters[1] A.-C. Wong, H. Ding, and C. T.-C. Nguyen, “Micromechanical

mixer+filters,” Technical Digest, IEEE International Electron Devices Meeting, San Francisco, California, Dec. 6-9, 1998, pp. 471-474.

C. T.-C. Nguyen



Micromechanical Switches[1] C. Goldsmith, J. Randall, S. Eshelman, T. H. Lin, D. Denniston, S.

Chen and B. Norvell, “Characteristics of micromachined switches at microwave frequencies,” IEEE MTT-S Digest, pp. 1141-1144, June, 1996.

[2] Z. Jamie Yao, S. Chen, S. Eshelman, D. Denniston, and C. Goldsmith, “Micromachined low-loss microwave switches,” J.Microelectromech. Syst., vol. 8, no. 2, pp. 129-134, June 1999.

[3] J. J. Yao and M. F. Chang, “A surface micromachined miniature switch for telecommunication applications with signal frequencies from DC up to 4 GHz,” Tech. Digest, Int. Solid-State Sensor and Actuator Conference (Transducers’95), Stockholm, Sweden, June 1995.

[4] S. Pacheco, C. T.-C. Nguyen, and L. P. B. Katehi, “Micromechanical electrostatic K-band switches,” Proceedings, IEEE MTT-S Int. Microwave Symposium, Baltimore, Maryland, June 7-12, 1998, pp. 1569-1572.

[5] S. Pacheco, L. P. B. Katehi, and C. T.-C. Nguyen, “Design of low actuation voltage RF MEMS switches,” Proceedings, IEEE MTT-S Int. Microwave Symposium, Boston, Massachusetts, June 11-16, 2000.

C. T.-C. Nguyen



Micromechanical Switches (cont.)[5] E. K. Chan, E. C. Kan, R. W. Dutton, and P. M. Pinsky, “Nonlinear

dynamic modeling of micromachined microwave switches,”Proceedings, IEEE MTT-S Int. Microwave Symposium, Denver, Colorado, June 1997, pp. 1511-1514.

C. T.-C. Nguyen



Circuit/μMechanics Integration Technologies[1] T. A. Core, W. K. Tsang, S. J. Sherman, “Fabrication technology for

an integrated surface-micromachined sensor,” Solid State Technology, pp. 39-47, Oct. 1993.

[2] J. H. Smith, S. Montague, J. J. Sniegowski, J. R. Murray, et al., “Embedded micromechanical devices for the monolithic integration of MEMS with CMOS,” Tech. Digest, IEEE Int. Electron Devices Meeting (IEDM), Washington, D.C., Dec. 10-13, 1995, pp. 609-612.

[3] J. M. Bustillo, G. K. Fedder, C. T.-C. Nguyen, and R. T. Howe, “Process technology for the modular integration of CMOS andpolysilicon microstructures,” Microsystem Technologies, 1 (1994),pp. 30-41.

[4] C. T.-C. Nguyen and R. T. Howe, “An integrated CMOS micromechanical resonator high-Q oscillator,” IEEE J. Solid-State Circuits, vol. 34, no. 4, pp. 440-445, April 1999.

[5] A. E. Franke, D. Bilic, D. T. Chang, P. T. Jones, T.-J. King, R. T.Howe, and G. C. Johnson, “Post-CMOS integration of germanium microstructures,” Technical Digest, 12th Int. IEEE MEMS Conf., Orlando, FA, Jan. 17-21, 1999, pp. 630-637.

C. T.-C. Nguyen



Circuit/μMechanics Integration Technologies[6] H. Baltes, O. Paul, and O. Brand, “Micromachined thermally based

CMOS microsensors,” Proc. IEEE, vol. 86, no. 8, pp. 1660-1678, Aug. 1998.

[7] G. K. Fedder, S. Santhanam, M. L. Reed, S. C. Eagle, D. F. Guillou, M. S.-C. Lu, and L. R. Carley, “Laminated high-aspect-ratio microstructures in a conventional CMOS process,” Sensors and Actuators, vol. A57, no. 2, pp. 103-110, March 1997.

[8] A.-C. Wong, Y. Xie, and C. T.-C. Nguyen, “A bonded-micro-platform technology for modular merging of RF MEMS and transistor circuits,” to be published in the Digest of Technical Papers, the 11th Int. Conf. on Solid-State Sensors & Actuators (Transducers’01), Munich, Germany, June 10-14, 2001 (4 pages).

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