1Vectron SAW Products, Apr 2015 Property of Vectron International

Surface Acoustic Wave Devices -

Challenges for Technology

Development

Richard Gruenwald

Vectron International

April 20th 2015

2Vectron SAW Products, Apr 2015 Property of Vectron International

Agenda

� SAW Functionality and Design Principles

� Challenges and Solutions:

� Miniaturization

� RF coexistence situations

� Power Handling

4Vectron SAW Products, Apr 2015 Property of Vectron International

Motivation

� Why Micro-Acoustic Filters (convert EM ���� acoustic ���� EM)?

� ����(��) ≈ ������(��)

� Size advantage over EM-filters (e.g. Microstrip, Cavity, ...)

� Smaller size results in high power densities

� Established high-volume filter solution for � ≈ 30…3000 MHz

�� ≈ ��

17mm

1.1mm

5Vectron SAW Products, Apr 2015 Property of Vectron International 5

92 112 132 152 172 192 212 232 252 272 292-70

-60

-50

-40

-30

-20

-10

0

frequency in MHz

ma

gn

itu

de

in

dB

731.5 761.5 791.5 821.5 851.5 881.5 911.5 941.5 971.5 1001.5 1031.5-60

-54

-48

-42

-36

-30

-24

-18

-12

-6

0

frequency in MHz

ma

gn

itu

de

in

dB

Key Applications:

A. Transceivers:

� Filtering („isolation“) of receive signal in RF (frontend and interstage) and IF

� Suppression of spurious signals in transmit path

� Separation of receive and transmit signal at antenna port - duplexer

B. Oscillators:

� Signal generation (VCSO) – 1- or 2-port SAW resonator

� Output (clean-up) filtering

1140 1150 1160 1170 1180 1190 1200 1210 1220 1230 1240-70

-60

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-20

-10

0

Frequency in MHz

Insertion m

agnitude (S21) in dB

BLUE: average

+30 degC

RED: average

+90 degC

Rx IS LNA Rx Frontend

1745.5 1746 1746.5 1747 1747.5 1748 1748.5 1749 1749.5 1750 1750.50

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

Frequency / MHz

Conductance / S

9 608.8 1208.6 1808.4 2408.2 3008 3607.8 4207.6 4807.4 5407.2 6007-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

frequency in MHz

ma

gn

itu

de

in

dB

insertion loss: -2.62 dB

IF

PATx IS

IF

Rx BB

Tx BB

DPX

Osc Out

VSWR

PD PD

SAW Applications

7Vectron SAW Products, Apr 2015 Property of Vectron International 7

Surface Acoustic Waves:

• Filters

• Resonators

How do SAW/BAW devices work?

Bulk Acoustic Waves:

• Crystals

• Monolithic Crystal Filters

Piezo-Electric Effect: electrical energy ⇔mechanical (acoustic) energy

Quartz (SiO2) LiTaO3 LiNbO3 La3Ga5SiO14

Achievable bandwidth / coupling coefficient k²

- - + ++ ++high

temperature stability

Temperature sensitivity + - - -

Manufacturing sensitivity + - - -

9Vectron SAW Products, Apr 2015 Property of Vectron International 9

IN OUT

“=”

Electro-acoustic

transfer function

“•”

Acousto-electric

transfer function

How Does a SAW Filter Work?

h(t)

t-T T

h(t)

t

∫∞

∞−

−= dtethH tjωω )()(

“*”

10Vectron SAW Products, Apr 2015 Property of Vectron International 10

695 700 705 710 715 720 725 730 735 740 745

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-10

0

Frequency in MHz

Transversal SAW Filter

FIR Filter

CH1 S21 LOG 7 dB/ REF -24.48 dB

CENTER 150 . 000 000 MHz SPAN 100 . 000 000 MHz

TFS150AL sample 12/2009

Cor

Hld

4 Dec 2009 08:36:33

1

2

3 4

1 : 0. 0000 dB 0. 000 000 MHz

BW:

cent :

1_ loss

CH1 PASS

� Performance

� FIR Filter approach

� Lowest Shape factor:

BWstopband / BWpassband ≥≥≥≥ 1.03

� Typically matching network required

� Insertion attenuation:

IA ≈ 12dBD35dB

� Strong correlation between shape factor and size (>10³ wavelengths)

IN OUT

REF -24.48 dB

11Vectron SAW Products, Apr 2015 Property of Vectron International 11

Pulse Compression Filter

o SAW Modules (with Integrated Matching)

o Matched Pairs of

a) Expansion Filter �� �

b) Compression Filter �� �

o Analogue pulse compression (typ. radar application)

o Limitations apply for

o ττττ · B > 100

o ττττ > 10 µs

96 97 98 99 100 101 102 103 104

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0

Frequency (MHz)

Magnitu

de (dB)

(Amplitude response)

ILoss = -31.9 dB

Expander HA(f)

∫ −⋅=τ

τττ dthhth BAcorr )()()(

x

96 97 98 99 100 101 102 103 104

-60

-50

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-30

-20

-10

0

Frequency (MHz)

Magnitude (dB)

(Amplitude response)

ILoss = -31.3 dB

Compressor HB(f)

0 5 10 15 20 25-80

-70

-60

-50

-40

-30

-20

-10

0

10

Time (us)

Magnitude (dB)

ILoss = -23.6 dB-1.0 dB bw = 0.1450 us-3.0 dB bw = 0.2496 us-6.0 dB bw = 0.3476 us-20.0 dB bw = 0.5803 us-30.0 dB bw = 0.6582 us-40.0 dB bw = 12.2644 us

Convolution hcorr(t)

12Vectron SAW Products, Apr 2015 Property of Vectron International

� Power-sensitive devices require low-loss

components

� Constructive use of SAW reflections to trap

acoustic energy in SAW resonator

� Electrical and/or acoustic coupling between

resonant circuits forms filter passband

� Low-loss performance:

IL ≈≈≈≈ 1…5 dB

� Relative bandwidth constrained by material

properties (electro-acoustic coupling ��):

BWrel ≈ 0.05…8%

Loss Reduction

πϕλ

22

. =∆⇔=∆ reflx

λ0

πϕλ

=∆⇔=∆ .4

reflx

λ0

731 .5 761.5 791.5 821 .5 851 .5 881.5 911.5 941 .5 971.5 1001.5 1031.5-60

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-18

-12

-6

0

frequ en cy in MH z

ma

gn

itu

de

in

dB

13Vectron SAW Products, Apr 2015 Property of Vectron International

Bandpass Filter:

� Resonance:

� Anti-resonance:

� Pole-zero distance:

Bandstop / Notch SAW Filter:

� Inversion of series and shunt admittances

� Smaller bandwidth than bandpass filter

Impedance Element Filter:

Resonator SAW Filter

Ys1

Yp1

Ys2 Ys.. YsN

YpNYp..

Ls

Rs

Cp Cs

( )ss

rresCL

fZfπ21

0 ==→

( )pss

pS

aresCCL

CCfYf

π20

+==→

2111

2

1k

C

Cf

LCLCC

CCffPZD

p

sr

ssssp

sp

ra ∝

−+=

−

+=−=

π

14Vectron SAW Products, Apr 2015 Property of Vectron International

Merging Transduction and Reflection

IIR Filter

Acoustic

reflections

Excitation

� Additional degrees of freedom for signal shaping � weighting of excitation and reflection

λ λ

⇒ Unidirectional performance: Loss reduction!

16Vectron SAW Products, Apr 2015 Property of Vectron International

Wideband SAW Structures

Slanted Finger IDT (SFIT) Filter:

� Parallel Connection of multiple narrow-band

channels

� Insertion attenuation ≈≈≈≈ 6 ... 20dB

� Fractional bandwidth ≈≈≈≈ 2% ... 60%

� Challenging 2.5-D design procedure

17Vectron SAW Products, Apr 2015 Property of Vectron International 17

Package Technology RF Filters

Migration to FlipChip Technology:

� Reduced space for package/chip inter-connects

⇒ Reduced electro-magnetic influence of inter-

connects

⇒ Increased chip space for SAW performance

� Performance advantages:

� Reduced insertion attenuation

� Improved skirt steepness

� Reduced ‘fly back’ in GHz frequency range

� Hermetic package solution

� High reliability stud-bump solution

1880 1900 1920 1940 1960 1980 2000 2020 2040 2060-50

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-10

-5

0|S21|,TFS1960F (blue) vs. TFS1960 (green)

Frequency in MHz

|S21| in dB

0 1000 2000 3000 4000 5000 6000-80

-70

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-30

-20

-10

0

Frequency in MHz

|S21| in dB

Wire-bonded 3x3mm²

Flip-chip 2.5x2mm²

Same size

3x3mm²2.5x2mm²:

-44% BGA - WLP2x1.6mm²:

-40%

prototypeavailable

19Vectron SAW Products, Apr 2015 Property of Vectron International

Motivation for Technology Development

e.g. LTE Frequency Bands

Requirements towards

a) Reduced transition band:

�f � ����� � ��� !� � ���"#$b) Increased fractional bandwidth:

���%&∝�²

0

5

10

15

20

25

30

35

40

45

600 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000

LTE

Ba

nd

frequency / MHz

Frequency

S21/ dB

∆∆∆∆f

∆∆∆∆ftyp

21Vectron SAW Products, Apr 2015 Property of Vectron International

LiTaO3 / LiNbO3 + Al / Cu + 0.2λλλλ0 SiO2

LiTaO3 / LiNbO3 + Al / Cu

� High-performance filter / duplexer applications

require minimum transition bandwidth ∆∆∆∆f

� Temperature compensation required to ensure

temperature-stable performance

� Achieved by deposition of optimized SiO2-

overcoat (opposite expansion to piezo substrate)

� Mandatory for challenging bands and co-

existence RF environments

New Technologies

Temperature Compensation

Frequency

S21/ dB

∆∆∆∆f

Frequency

S21/ dB

Tem

p.

+ p

rod

. m

arg

in

Gu

ara

nte

ed

sp

ec

22Vectron SAW Products, Apr 2015 Property of Vectron International

Frequency

S21/ dB

∆∆∆∆f

Frequency

S21/ dB

� High-performance filter / duplexer applications require reduced / minimum transition

bandwidth ∆∆∆∆f

� Wafer-level area-selective ion-beam trimming to achieve 55...80% reduced process

variations over one product

Tem

p.

+ p

rod

. m

arg

in

Gu

ara

nte

ed

sp

ec

New Technologies

Low-Tolerance Wafer Process

23Vectron SAW Products, Apr 2015 Property of Vectron International 23

Why High Power?

System level:

• Design of receiver chain with low-noise

amplifiers (LNA) and filters

⇒ Improved signal-to-noise ratio

⇒ Improved receiver sensitivity

⇒ Reduced bit-error-rate

� High power critical for SAW devices:

Low phase velocity ����(��) ≈ ������(��)⇔⇔⇔⇔

Small structures

⇔⇔⇔⇔High power densities

820 840 860 880 900 920 940-30

-25

-20

-15

-10

-5

0

5

10

15

20881D\power\17dBm\881D_power#. - device 1

frequency / MHz

power / dBm

820 840 860 880 900 920 940-30

-25

-20

-15

-10

-5

0

5

10

15

20881D\power\17dBm\881D_power#. - device 1

frequency / MHz

power / dBm

24Vectron SAW Products, Apr 2015 Property of Vectron International 24

Ref = -15...-30dB

SAW Propagation Effects

SAW Device Functionality:

� Conversion between electric and mechanical energy

� Propagation and reflection of SAW within structure

� Amplitude of SAW (10-11...10-12 m range) depends on applied RF

power level and causes stress phenomena

� Resonant – i.e. low-loss – SAW filters face more challenging stress

patterns than transversal (FIR) design techniques

� Narrow-band devices are more critical than wider bandwidth

solutions

100 200 300 400 500 600 700 800 900 1000 1100 1200-100

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0

frequency in MHz

ma

gn

itu

de

in

dB

IN OUT

IN

OUT

25Vectron SAW Products, Apr 2015 Property of Vectron International 25

High-Power Damage Modes

820 840 860 880 900 920 940

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0

frequency [MHz]

magnitude [dB]

Damage progress:

� Acousto-migration causes extrusions and voids

� Damage of metallization system causes (typ.)

increased insertion attenuation and reduced

bandwidth� Ultimately: Contact between extrusions ����

catastrophic short-circuit

26Vectron SAW Products, Apr 2015 Property of Vectron International 26

Power Handling Capabilities - SAW

� High power exposure � micro-acoustic stress � material deformation

� Extrusions and voids in fingers deteriorate performance (ultimately total failure)

� Lifetime and acceptable power level depends on

multiple factors:

� Power density (abs. power, fc, size of acoustic

elements)

� Duty cycle / modulation scheme (e.g. CW

exposure vs. LTE-spectrum)

� In-band (electric ↔ acoustic) / out of band

exposure (“IDT = capacitance”)731.5 761.5 791.5 821.5 851.5 881.5 911.5 941.5 971.5 1001.5 1031.5

-60

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0

frequency in MHz

mag

nit

ud

e in

dB

up

-lin

k

do

wn

-lin

k

27Vectron SAW Products, Apr 2015 Property of Vectron International

Accelerated Lifetime Testing:

� Repeated power exposure and measurement

/evaluation of device at

� maximum operating temperature

� worst-case frequency position

� Pre-defined performance degradation defines time-to-failure (e.g. �()/��� � −�. �%)

� Test is repeated for multiple devices and power

levels (optionally temperatures)

SAW Filter Lifetime Model

820 840 860 880 900 920 940

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-5

0

frequency [MHz]

magnitude [dB]

0 10 20 30 40 50 60 70

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

∆ IL > -0.5dB: N = 716; 102.795h

time / h

∆ B-15dB / %

14 16 18 20 22 24 26 28 30

100

101

102

103

104

105

power / dBm

time to failure / h

TFS820A-std: P(15yr, T~P-3

) = 15.5dBmTFS820A-std

TFS820A-std corr.

TFS820A-std lifetime

TFS820A-std lifetime corr.

28Vectron SAW Products, Apr 2015 Property of Vectron International

ϑkW

N

in ePCTTF0

⋅⋅= −

Eyring lifetime model:

C - constant (design, material, D)

Pin - power at filter input

N - acceleration exponent (typically N = 3)

W0 - activation energy

k - Boltzmann’s constant

ϑϑϑϑ - ambient temperature

���� Rules of thumb (N = 3):

∆ϑ∆ϑ∆ϑ∆ϑ = +10K ⇔⇔⇔⇔ -50% TTF

∆ϑ∆ϑ∆ϑ∆ϑ = +10K ⇔⇔⇔⇔ Pin - 1dB

∆∆∆∆P = +1dB ⇔⇔⇔⇔ -50% TTF

Power durability specifications consider (default):• Exposure (continuous wave) over 15 years

• Specified power applied at

• maximum operating temperature• worst-case frequency position

Frequency-dependence of power durability:

• ‘Constant’ max. power density (W/mm²)

• E.g. comparable design: Pmax,1GHz = Pmax,2GHz + 6dB

SAW Filter Lifetime Model II

2

1

0max

0

1~

=⇔

f

f

P

PAP

f

f

IDT

10 15 20 25 30

10-1

100

101

102

103

104

105

power / dBm

time to failure / h

TFS820A-std

TFS820A-std corr.

TFS820A-std lifetime corr.

-30°C

0°C

30°C

60°C

120°C

29Vectron SAW Products, Apr 2015 Property of Vectron International 29

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

100 1000

po

we

r d

ura

bilit

y /

dB

m

center frequency / MHz

Impedance Element Filter

LCRF

Quartz resonator / -filter

Loss-reduced IF filter

-20

-15

-10

-5

0

5

10

15

20

25

30

35

40

100 1000

po

we

r d

ura

bilit

y /

dB

m

center frequency / MHz

Impedance Element Filter

LCRF

Quartz resonator / -filter

Loss-reduced IF filter

Analysis of overstress risk

1745.5 1746 1746.5 1747 1747.5 1748 1748.5 1749 1749.5 1750 1750.50

0.005

0.01

0.015

0.02

0.025

0.03

0.035

0.04

0.045

Frequency / MHz

Conductance / S

1050 1100 1150 1200 1250 1300 1350 1400-100

-90

-80

-70

-60

-50

-40

-30

-20

-10

0

frequency in MHz

magnitude in dB

731.5 761.5 791.5 821.5 851.5 881.5 911.5 941.5 971.5 1001.5 1031.5-60

-54

-48

-42

-36

-30

-24

-18

-12

-6

0

frequency in MHz

mag

nit

ud

e in

dB

92 112 132 152 172 192 212 232 252 272 292-70

-60

-50

-40

-30

-20

-10

0

frequency in MHz

ma

gn

itu

de

in

dB

IL ≈≈≈≈5...15dB

High-power material system

30Vectron SAW Products, Apr 2015 Property of Vectron International

ϑkW

N

in ePCTTF0

⋅⋅= −

SAW Filter Lifetime - Limitations

Limits of accelerated test (e.g. 820MHz filter):

+ Test at 35dBm (3.2W)

>10³ h test time required

― Test at 36dBm (4.0W)Breakdown in <<1s ���� overstress

� Test at worst-case frequencies

(electric and acoustic fields)

15 20 25 30 35

10-2

10-1

100

101

102

103

104

105

left, -20dB corr meas

power / dBm

time to failure / h

TFS820A-std: P(15yr, T~P-3

) = 15.3dBm

TFS820-HP: P(15yr, T~P-3

) = 32.3dBm

TFS820A-std

TFS820A-std corr.

TFS820A-std lifetime

TFS820A-std lifetime corr.

TFS820-HP

TFS820-HP corr.

TFS820-HP lifetime

TFS820-HP lifetime corr.

34Vectron SAW Products, Apr 2015 Property of Vectron International

Technological Solution:

Improved power density handling though optimized metallization system

Significantly improved stability against grain boundary diffusion effects!

Standard system:<1h @ 30dBm (~30W/mm²) optimized system:

190h @ 34dBm (~80W/mm²)

Substrate

Adhesion layer

Aluminium layerDoped aluminum layer

Improved Power Durability - Technology

Standard technology:

140h @ 27dBm

high power technology:

250h @ 35dBm

35Vectron SAW Products, Apr 2015 Property of Vectron International

Summary:

� Typ. 10...17 dB power handling improvement for all SAW designs

� Power density capabilities close to breakdown limit

� ‚Identical‘ performance between standard and high-power system

� Technology fully qualified and in production

� Employed for

� New high-power designs

� High-power versions of existing products

850 860 870 880 890 900 910 920-100

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0

frequency [MHz]

magnitude [dB]

TFS820A-std.TiAl

TFS820A-HP

15 20 25 30 35

10-1

100

101

102

103

104

105

power / dBm

time to failure / h

TFS820A-std: P(15yr, T~P-3

) = 15.5dBm

TFS820-HP: P(15yr, T~P-3

) = 31.9dBm

TFS820A-std

TFS820A-std corr.

TFS820A-std lifetime

TFS820A-std lifetime corr.

TFS820-HP

TFS820-HP corr.

TFS820-HP lifetime

TFS820-HP lifetime corr.

High Power Process

40Vectron SAW Products, Apr 2015 Property of Vectron International