Ken-ya HashimotoChiba University

k.hashimoto@ieee.orghttp://www.em.eng.chiba-u.jp/~ken

Part 1: What is SAW Device?

Introduction to Surface Acoustic Wave (SAW) Devices

•SAW Transversal Filter•SAW Unidirectional IDT Filters•SAW Resonator Filters•SAW Wireless Tags and Sensors

Contents

•SAW Transversal Filter•••SAW Unidirectional IDT FiltersSAW Unidirectional IDT FiltersSAW Unidirectional IDT Filters•••SAW Resonator FiltersSAW Resonator FiltersSAW Resonator Filters•••SAW Wireless Tags and SensorsSAW Wireless Tags and SensorsSAW Wireless Tags and Sensors

Contents

Surface Acoustic WaveSurface Acoustic Wave

Bulk Acoustic Wave (BAW):•Longitudinal Wave (Primary Wave)

•Transverse Wave (Share Wave, Secondary Wave)

Surface Acoustic Wave (SAW):

(Rayleigh SAW)Propagation of

Seismological Waves

Surface Acoustic Wave (SAW) Device

Vout

Vin

Piezoelectric substrate

Interdigital Transducers (IDT)

SAW

• Mass Production by Photolithography• Low loss, Miniature & Low price• Operation inVHF-UHF ranges

Line width λ/4=0.5μm (f=2GHz)

Impulse Response

• Independent Control of Amplitude and Phase Responses

SAW Transversal FiltersSAW Transversal Filters

Impulse Response Frequency Response

t f

t

t

∫+∞

∞−

−= dtjftthfH )2exp()()( π∫+∞

∞−

+= dfjftfHth )2exp()()( π

f

f

Why Acoustic Wave Devices?Why Acoustic Wave Devices?

• Temperature Stability

]1)/[exp(0 −= kTqVII

cf. For Si, 3000ppm/oC

ppm100(1.9GHz) Freq.Center GSM1900

(200kHz)Bandwidth GSM≅

ppm 10day 1sec. 1

≅For watch,

Trade-Off Between Temp. Stability & Bandwidth

T driftω

(a) Wider Transition Bandwidth

(b) Narrower Transition Bandwidth

T driftω

Efficient Use of Frequency Resources ⇔ Narrow Transition Bandwidth (Or Improve Production Yield)

-45-40-35-30-25-20-15-10

-505

-0.2 -0.1 0 0.1 0.2 -1

-0.8-0.6-0.4-0.2

00.20.40.60.81

Tran

sfer

func

tion

in d

B

Relative Frequency

Tran

sfer

func

tion

in d

B

Fourier-Transform-Based DesignFourier-Transform-Based Design

Ripple due to truncation [Gibb’s Phenomenon]

t

w(t)t

thd(t)w(t)

hd(t)

Influence of TruncationInfluence of Truncation

∫+∞

∞−

−= ξξξ dfWHfH dw )()()(

Convolution Relation

Window FunctionsWindow Functions

t f

t f

Hamming:w(t)=0.54+0.46cos(2πt/T)

Blackmann:w(t)=0.42+0.5cos(2πt/T) +0.08cos(4πt/T)

Blackmann-Harris:w(t)=0.35875+0.48829cos(2πt/T)+0.14128cos(4πt/T)+0.01168cos(6πt/T)

0

0.2

0.4

0.6

0.8

1

-1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1

Wei

ght

Relative Position

HammingBlackmann

Blackmann-Harris

-120

-100

-80

-60

-40

-20

0

0 2 4 6 8 10

rectangularHammingBlackmann

Blackmann-Harris

Relative frequency

Am

plitu

de in

dB

Frequency Response of Window Functions with same T

Frequency Response of Window Functions with same T

-70-65-60-55-50-45-40-35-30-25-20-15-10-505

-0.2 -0.1 0 0.1 0.2

-0.8-0.6-0.4-0.2

00.20.40.60.81

-1

Tran

sfer

func

tion

in d

B

Relative frequency

Tran

sfer

func

tion

in d

B

Design by Fourier Transform + Window Function

Design by Fourier Transform + Window Function

454137 49 53

10 dB/div

FREQUENCY (MHz)43.7541.7539.75 45.7547.75

1 dB/div

50ns/div

FREQUENCY (MHz)

SAW Transversal Filter for CATV

Ref. 15dB

8070605040302010

0

67.5 68 68.5 69 69.5 70 70.5 71 71.5 72 72.5

Inse

rtion

loss

in d

B

Frequency in MHz

ExperimentSimulation

SAW IF Filter for IS-95SAW IF Filter for IS-95

Effects of Diffraction(2D SAW Propagation)

Courtesy of Fujitsu Labs.

(a) For Wide Aperture (b) Narrow Aperture

For Weighted IDT

Variation with Aperture Size

DAT

CD player Amp.

E

SR

SLR

Power source Load

E

SR

SLR

Power source Load

?

Low Frequency Design

High Frequency DesignHigh Zin and Low Zout for Minimum Interference

RL=RS for Maximum Power Transfer

How about for this case?

Triple Transit Echo (TTE)Triple Transit Echo (TTE)Interdigital Transducers (IDT)

• Mechanical Reflection + Electrical Regeneration ⇒Mutual-Connection Dependent

• Trade-Off: TTE ⇔ Insertion Loss• Intrinsic for Bidirectional IDTs

504540353025201510

50

-0.2 -0.1 0 0.1 0.2

Inse

rtion

loss

in d

B

Relative FrequencyS21 S21

0

Influence of TTEInfluence of TTE

Bragg ReflectionBragg Reflection

p

Bragg Condition

p=nλ/2

Double-Electrode IDT

Single-Electrode IDT

absorber absorber

Guard electrode

Transversal SAW FilterTransversal SAW Filter

·Absorbers for Suppression of Reflection at Substrate Edges

·Dummy Electrode for Suppression of Reflection and Charge Concentration at Edges

·Guard Electrode for Suppression of EM Feedthrough

•••SAW Transversal FilterSAW Transversal FilterSAW Transversal Filter•SAW Unidirectional IDT Filters•••SAW Resonator FiltersSAW Resonator FiltersSAW Resonator Filters•••SAW Wireless Tags and SensorsSAW Wireless Tags and SensorsSAW Wireless Tags and Sensors

Contents

PLL/VCO

DuplexerIF-BPFRF-BPF

AntennaLNA

PA

φ

φ

PLL/VCO

A/D

D/A

A/D

D/A I

Q

I

Q

PLL/VCO

IF-BPFRF-BPF

Heterodyne Transceiver

Red：SAW Devices

Single Phase Unidirectional Transducer (SPUDTs)

Single Phase Unidirectional Transducer (SPUDTs)

(b) Inlayed Reflector(Complex but Wideband)

(a) Combination with Reflector(Simple but Narrowband)

• TTE Suppression• Low Loss• Frequency Response

⇒ Weighting for Excitation Profile

• Reflection Bandwidth < IDT Bandwidth ⇒Reflector Weighting

Independent Weighting to both Excitation and Reflection

ΔpI

CtCrCtCr

For +X Direction, πβ m22 =Γ∠+Δ−πβ )12()(2 +=Γ∠+Δ−− npI

X

For -X Direction

Unidirectional Cond. 8/ ,2/ λπ ±=Δ±=Γ∠

Unidirectional ConditionUnidirectional Condition

Ct: Excitation Center

Cr: Reflection Center

(d) With Excit. & Ref.

(b) With Excit., Ref.-Less

(c) Excit.-Less, With Ref.

(a) Excit.-Less, Ref.-Less

For Independent Weighting to Excitation and ReflectionFor Independent Weighting to Excitation and Reflection

EWC(Electrode-Width-Control)/SPUDT

Scat

terin

g C

oeff

icie

nt (d

B)

-40-35-30-25-20-15-10-50

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.2Relative Frequency

ψ=90o

ψ=0oLT=50pI

LI=20pI

κpI=0.02π

Filter Response with Reduced TTE

Low Loss and Suppressed TTE

Resonant SPUDT (R-SPUDTs)Resonant SPUDT (R-SPUDTs)

Reversed Reflection WeightingDirect Pulse

Multiple Echoes

Extension of Impulse Response

With Reflection

ω

Without Reflection

• Skirt Characteristics are Defined by Impulse Response Length

• Out-of-Band Characteristics are Defined by Excitation Profile

-60

-50

-40

-30

-20

-10

0

0.8 0.85 0.9 0.95 1 1.05 1.1 1.15 1.220

30

40

50

60

70

80

Relative Frequency

Scat

terin

g C

oeff

icie

nt (d

B)

τ

Gro

up D

elay

τ/τ

p

|S21|LT=0LI=34pI κpI|max=0.1π

Designed Example

Sharp Passband Shape + Flat Group Delay

-1-0.8-0.6-0.4-0.2

00.20.40.60.8

1

2 4 6 8 10 12 14 16 18 20

Excitation

ReflectionForward

Relative Position

Wei

ghtin

g Fu

nctio

n

Optimized weighted function

Courtesy of EPCOS AG

Weak Resonant SPUDT FilterWeak Resonant SPUDT Filter

Courtesy of EPCOS AG

Strong Resonant SPUDT FilterStrong Resonant SPUDT Filter

•••SAW Transversal FilterSAW Transversal FilterSAW Transversal Filter•••SAW Unidirectional IDT FiltersSAW Unidirectional IDT FiltersSAW Unidirectional IDT Filters•SAW Resonator Filters•••SAW Wireless Tags and SensorsSAW Wireless Tags and SensorsSAW Wireless Tags and Sensors

Contents

DuplexerRF-BPF

AntennaLNA

PA

φ

φ

PLL/VCO

A/D

D/A

A/D

D/A I

Q

I

Q

PLL/VCO

RF-BPF

Homodyne Transceiver

• Circuit Simplification ⇒ Reducing Component Number• No Image Signal ⇒ Relaxing Specs to RF Filters

(a) 1-Port Resonator

(b) 2-Port Resonator Filter

SAW Resonator

Piezoelectric Material

+

-

C0 η

Mk-1

V F

i v

C0

Lm

Rm

Cm

Analogies between V⇔F and I⇔v reduce toM⇔L, h⇔ R, k ⇔ 1/C

(a) Electric + Mechanical Circuit

Application of Electric Field to Piezoelectric Material,

(b) Electrical Equiv. Circuit

∫ ∝=++ VFvdtkvdtdvM η

(a) Electrical Equiv. Circuit (b) Equiv. Mechanical Circuit

•Resonance Frequency ωr=1/ CmLm•Anti-Resonance Frequency ωa=1/ Lm(Cm

-1+C0-1)-1

•Resonance Q (Steepness of Resonance) Q=ωrLm/Rm

•Capacitance Ratio (Weakness of Piezoelectricity)γ=C0/Cm=[(ωa/ωr)2-1]-1

⇒ Determine Insertion Loss and Skirt Characteristics

⇒ Determine Insertion Loss and Bandwidth

k η

M

F

k0C0

Lm

Rm

Cm

-0.6-0.4-0.20

0.20.40.60.81

0.96 0.98 1 1.02 1.04

Adm

ittan

ce [S

]

Frequency [GHz]

fr fa

•Resonance Frequency ωr=1/ CmLm•Anti-Resonance Frequency ωa=1/ Lm(Cm

-1+C0-1)-1

Transverse ModeTransverse Mode

Frequency

Adm

ittan

ce

ω r ω a

B

GIn-harmonic Resonance

Ladder-Type SAW FilterLadder-Type SAW Filter

Topology

• Low Loss• High Power Durability• Moderate Out-of-Band Rejection

ωr ωa

ω

Inse

rtion

Los

s (dB

)

Frequency ωInse

rtion

Los

s (dB

)

Frequency

ωr ωa

Parallel-ConnectionSeries-Connection

YsYp

Ys

Yp Yp

ω

Inse

rtion

Los

s (dB

)

Frequency

sp

p s

ωr

ωa=ωr

ωa

π-Connection

Null Generation

at Both Sides

Performance of Ladder-Type SAW FilterPerformance of Ladder-Type SAW Filter

W-CDMA-Rx

-50-45-40-35-30-25-20-15-10-50

1900 2000 2100 2200 2300 2400-5

-4

-3

-2

-1

0

Tx Rx

Frequency (MHz)

Fujitsu FAR-F6CP-2G1400-L21M

Scat

terin

g Pa

ram

eter

S21

(dB

)

Scat

terin

g Pa

ram

eter

S21

(dB

)

λ/4

λ/4

TX-port

RX-port

Antenna-port

SAW filter, TX

SAW filter, RXstrip line

strip line

F re q u e n c y [M H z]

Att

enua

tion

[dB]

0

-2 0

-4 0

-6 018 0 0 19 0 0 20 0 0

T x ba n d Rx ban d

F re q u e n c y [M H z]

Att

enua

tion

[dB]

0

-2 0

-4 0

-6 018 0 0 19 0 0 20 0 0

T x ba n d Rx ban d

Antenna Duplexer for US PCS

Rx Band

Tx Band

Courtesy of Fujitsu Labs.

J.Tsutsumi, et al., Proc. IEEE Ultrason. Symp. (2004) pp. 954-958

Fujitsu Labs.

Bonding with Small Thermal Expansion Coef.

Temperature Compensation (1)

Temperature Compensation (2)

M.Kadota, et al., Proc. IEEE Ultrason. Symp. (2004) pp. 1970-1975 Murata MFG

Depositing SiO2 with Negative Temp. Coef.

• Good Out-of-Band Rejection

• Balun Function• Transformer Function• Low Loss• Lower Power Durability

Symmetrical & Anti-

symmetricalResonances

Double Mode SAW (DMS) Filter

arsω ωr

ω

Inse

rtio

n lo

ss (d

B)

Frequency

Electrically Isolated I/O

Structure of PitchPitch--Modulated IDT & ReflectorModulated IDT & ReflectorConventional Structure PitchPitch--Modulated StructureModulated Structure

IDT IDTREFECTOR

ModulatedModulated

ModulatedModulatedGap ControlledGap Controlled

Presented at IEEE 2004 UFFC Conf.

-8-7-6-5-4-3-2-10

800 850 900 950 1000 1050-80-70-60-50-40-30-20-10

0

Frequency [MHz]

Scat

terin

g pa

ram

eter

. S21

[dB

]

Scat

terin

g pa

ram

eter

. S21

[dB

]

DMS Filter with Modulated StructureDMS Filter with Modulated Structure

Fujitsu FAR-F5EB-942M50-B28E

Integrated RF Circuit Integrated RF Circuit

Current Antenna and RF Stage are Unbalanced

(a) Balanced I/O

(b) Unbalanced I/O

+

-

+-

Front-endBPF LNA

Inter-stageBPF IF-BPFMixer

Front-endBPF LNA IF-BPFMixer

Balun IF-Amp

IF-Amp

Discrete SAW Filter & Balun

Inter-stageBPF

SAW Filter with Balun Function

Vout+

Vout-

Vin

DMS Filter (Ideally No Common Signal)

Acoustically Coupled but Electrically Isolated

Common Signal Generation by Parasitics

Vout+

Vout-

Vin

Vin

Vout+Vout-

Z-conversion by DMS Filter

•••SAW Transversal FilterSAW Transversal FilterSAW Transversal Filter•••SAW Unidirectional IDT FiltersSAW Unidirectional IDT FiltersSAW Unidirectional IDT Filters•••SAW Resonator FiltersSAW Resonator FiltersSAW Resonator Filters•SAW Wireless Tags and Sensors

Contents

AT-cut Quartz

Quartz Micro-Balance (QMB)Quartz Micro-Balance (QMB)

• Temperature Stability• Phase (or Frequency) Output ⇒ High Resolution• Low Price

Mass Loading

Sensor Applications: Physical (Film Thickness, Pressure), Chemical(Gas, Liquid), Bio

Vout

Vin

Piezo-Substrate

IDT

SAW

• High f (Δ f =−K f02Δm) ⇒ High Sensitivity

• Moderate Temperature Stability• Surface Protection (Packaging) ?

SAW SensorSAW Sensor

Area 1 mm2 & f0=1 GHz give K f0 ~ 107 / kg⇒ 1 ppm of f deviation=Resolution 0.1 pg.

SAW Sensor Configuration

Frequency Detection

Phase Detection

Δφ~ Δm

Δf ~ Δm

SAW Chemical Sensor

• Sensitive Layer: A calixarene (10 nm)• Object: tetrachloroethene• f0: 434 MHz

Time [min]Freq

uenc

y D

evia

tion

[Hz]

0

-200

-400

-6000 10 20 30

Con

tent

[ppm

]

0

20

40

60

Pattern Recognisition with Sensor Array

Sensor : Sensitive FilmA Calix[4]resorcinearene 1B Calix[4]resorcinearene 2C Cyclodextrine-functiona-

lized polymer 1D Cyclodextrine-functiona-

lized polymer 2

C DA B

Sensor Array

p-xylenem-xylene

humidity

What is SAW ID-TAG?

Antenna

Transceiver

• Large Group Delay (Separation with Environmental Echoes)

• Wireless, Batteryless

Separation of SAW Signal in Time Domain

Excited Signal

Environmental Echo

Sensor Echo

RF Response

time

Which Frequency?

•5.2 GHz (ISM Band)Wideband (100MHz), Short Accessible Distance (<1m), Hard to Realize SAW Devices

•2.45 GHz (ISM Band) Wideband(22MHz), Short Accessible Distance (2-3m), Price of SAW Devices?

•433.92 MHz (RKE Band) Narrowband(1.7MHz), Long Accessible Distance (>10m), Low SAW Device Cost

SAW ID Tag with 5 reflectors in one track (f0 = 2.45 GHz) using pulse position coding

2nd reflector

Possible coding positionof 1st reflector

1st reflecor

AntennaPossible coding positionof 2nd reflector

Tag by

Pulse position coding schema

OIS - W

Baumer Ident (2.45 GHz ISM)

Brake temperature of a train entering a station

60,00

70,00

80,00

90,00

100,00

Time

Tem

pera

ture

°C

reader antenna

Brake (with attached SAW temperature transponder, not seen)

The dynamic range of monitoringthe torque with SAW can be up to several tenths of kHz

SAW Torque Sensor

strain in ‰

phas

e di

ffere

nce

in d

eg.

0

50

100

150

200

150

0 0.05 0.10 0.15 0.20

SAWsensors

rotatingshaft

Tx antennas

Rx antennas

measurement set-up

SAW pressure sensor

diaphragm

adhesive

cover-plateclosed cavity withreference-pressure

antenna

1.001.201.401.601.802.002.202.402.602.803.00

14:30

:5514

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14:31

:0414

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14:31

:1314

:31:18

14:31

:2214

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pressure[Bar]

time

Two Track Railway Crossing

Adjacent Water Channel