Evolution of the SAW Transducer
for Communication Systems
Donald C. Malocha
Electrical & Computer
Engineering Dept.
University of Central Florida
Orlando, Fl. 32816-2450
dcm@ece.engr.ucf.edu
Special thanks to the UFFC_S
and contributing members
who initiated, built and
maintain the UFFC_S Digital
Archive.
Presentation Approach
• In recognition of the 50th Anniversary of the
UFFC_S, the presentation will focus on the SAW
transducer evolution through the UFFC_S
publications.
If there are errors or
• The presentation highlights the development
inaccuracies
presentation,
through
the “eyes” of in
the the
UFFC,
not necessarily
crediting
citing theme
first publication,
inventor, etc.
pleaseor email
the correct
• There is a large body of contributions in other
citation(s).
Your
input
is
publications,
patents,
worldwide
symposiums,
non_English journals, etc., which makes it virtually
appreciated.
impossible
to site the first disclosure of ideas.
• Every
significant SAW transducer embodiment
dcm@ece.engr.ucf.edu
has eventually graced the pages of UFFC
publications.
•
Disclaimer: The material
presented does not
represent the views of the society fdhfdthftghffdhsdtewratseafowieejfcoiswejvcoiswejefoisiwifvnwomopskefoiwejkfoiwemfoimcwvwejfiowejriofjweoivmoiwejfiwjfiowejifojweiojfg9wer0iwekpvoewpo.
Any
sufficiently advance technology is
indistinguishable
from magic.
Arthur C. Clarke
SAW Transducer’s
Degrees of Freedom
• Transducer Parameter Degrees of Freedom
–
–
–
–
Amplitude
Phase
Delay
Frequency
• Device Infrastructure Degrees of Freedom
–
–
–
–
Material Choice
Thin Films on the Substrate
Spatial Diversity on the Substrate
Electrical Networks and Interface
Introduction
•
•
•
•
_
_
_
_
Transduction
Reflection
Re-Generation
Non-Linearity's
• This presentation addresses the first
three properties applicable to SAW
transducers
Transducer Embodiment Fundamentals
–basic bag of tricks
• Fundamental concepts
used in all transducers
–Electrodes
–Sampling
–Apodization
Multi- Electrode Transducers
Note: Floating Electrode
•
•
•
Split electrode transducer used to eliminate
reflections
Minimizes triple transit and self-resonance
3rd Harmonic Operation
“Reflection of a Surface Wave
from Three Types of ID
Transducer”, A. De Vries, R.
Miller and T. Wojcik, 1972 IUS,
pp. 353-358
“Applications of Double
Electrodes in SAW Device
Design”, T. Bristol, et.al.,
1972 IUS, pp. 377-380
Transducer Sampling- Harmonics
Note: Floating
Electrode
“Surface Acoustic
Wave Multielectrode
Transducers”, H. Engan,
UFFC_T, 1975, pp.
395-401
First Reference to a Balanced SAW
Transducer (Dual Track)
First introduced with regards to sampling
“Design of Interdigital Arrays for Acoustic Surface Wave
Filters, C. Atzani and L. Masotti, 1972 IUS, pp. 242-252
Space Harmonic Control
• Changing
electrode a/p can
control harmonics
“Space-Harmonic
Response of Surface
Wave Transducers”, R.D.
Weglein and G.R. Nudd,
1972 IUS, pp. 346-352.
Interdigitated IDT (IIDT)
Interleaved I/O transducers
Low loss structure
No weighting
“SAW Filters Employing Interdigitated Interdigital
Transducers, M. Lewis, 1982 IUS, pp.12-17.
Low Loss IIDT Antenna Duplexer
Weighted
transducer
structure
“Low Loss SAW Filter for Antenna Duplexer”, M. Hikita, T. Tabushi, H.
Kojima, A. Nakagoshi and Y. Kinoshita, IUS 1983, pp 77-82.
Q: How
doWeighting
we build arbitrary
filter
Tap
and Delay
•Apodization
responses?
Variable spatial profile,
maps ideal tap
weights into the
spatial profile
of the
transducer.
uniform amplitude
A: Use sampling theory and weight
the electrodes.
•Idealized
attenuated tap
weights and
electrodes
provide delay.
Uniform spatial profile,
variable amplitude
“Acoustic Surface Wave Filters”, R. Tancrell, 1969
IUS, pp. 48-64
FIR Filter to Apodized SAW Transducer
Relations between
transversal filter, impulse
response and SAW
transducer. The
transducer is a spatial
mapping of the time
domain response.
“Acoustic Surface Wave
Filters”, R. Tancrell, 1969 IUS,
pp. 48-64.
SAW Transducer Sampling
A SAW transducer
can use an arbitrary
sampling frequency
regardless of center
frequency, with a
uniform sampling rate,
subject to the Nyquist
criteria.
Not required to use
an integer number of
electrodes per
wavelength to obtain
a filter response.
“SAW Filter Sampling Technique”, Hunsinger &
Kansy, UFFC_T, 1975, pp. 270_273
Dual Passband Filters
“Multipassband Low Loss SAW Filters”, B. Potter & T.
Shoquist, 1977 IUS, pp., 736_739.
Apodized SAW Filter
RF @t=0
Main
SAW
TTE
SAW Apodization Analysis
Arbitrary SAW
Apodization Profile
SAW Conductance
SAW Apodization Loss
SAW Amplitude Beam Profile as a
Function of Frequency
XdB( f )
Am pn( f )
20
45
7
7.5 10
1 10
1.25 10
8
8
f
Wave Amp. vs Beam Position vs. Frequency
Normalized Beam Position (x/W a)
0.5
0.4
0.3
0.2
0.1
0
0.1
0.2
0.3
0.4
0.5
0.25
0
0.25
0.5
Relative SAW Amplitude
0.75
1
Center frequency (f0)
Amplitude
profile vs beam
0.95*f0
0.93*f0
position
@ 4 different
0.86*f0
frequencies
Ideal H(f) and Conductance: ACOS Fcn.
0
- Conductance vs frequency
10
dB
20
30
-Transfer function
40
50
0.75
0.8
0.85
Conductance
Frequency Response
0.9
0.95
1
1.05
Normalized Frequency (f/f0)
1.1
1.15
1.2
1.25
assumes a uniform
integrating transducer
Slant Centered Apodized IDT
Slanted transducers
2 wavelength gaps; in-line; dummy electrodes; split
electrode design
SAW transducer schematic; dummy
electrodes removed for clarity
“Low Shape Factor Design
Considerations”,P. Meyer, 1975
IUS, pp. 334_335
Acoustic Conductance vs
Apodization Technique
Each transducer has
the exact same
impulse response, but
the apodization
pattern affects the
electrical parameters
and can be a problem,
yielding a poor filter
response due to
electrical circuit
interactions.
Example Low Shape Factor
Slant-Apodized Transducer Filter
Phase Weighting
Approach a uniform beam profile
“Phase Weighting for Low Loss Filters”, M.
Hikita, Y. Kinoshita, and T. Tabuchi, 1980 IUS,
pp. 308-312.
Distance Weighting
•Each track is
approximately
a rect fcn.
•Uniform
magnitude of
beam profile
• Each track is uniform but differing bandwidth/group delay
• Sum of sampling functions
• Vary bandwidth by apodization profile
• Group delay varies with track
• Structure shown yields linear phase due to symmetry
“ Acoustic Surface Wave Filters Using New Distance
Weighting Technique”, K. Yamanouchi and T. Meguro, IUS
1980, pp. 313-316.
Weighting Techniques
• Q: How do we weight
both transducers to
obtain better filter
performance?
• A: Apply tap weighting to
the transducer without
using apodization
• Better filter shape factor
• Smaller device
Phase Weighting _ SAW Coded
Transducer
Input
Transducer
Coded
Transducer
-1 -1 1 -1 -1 1 1 -1
Data
Clock
Pulse
Generator
SAW Waveform
“Evaluation of Digitally
SAW Coded Transducer
Coded Acoustic Surface
Wave Matched Filters”, W.
Jones, C.S. Hartmann, and
Example of matched filter
L. Claiborne, UFFC-T, 1971,
response
pp.21-27
Block Weighting to a Desired Response
Phase, block, or
a modified
withdrawal
weighting
concept.
No apodization
but weighted IR.
Hamming
Function
Approximation
“Synthesis of Periodic Unapodized Surface Wave
Transducers”, T. Bristol, IUS 1972, pp. 377-380
Withdrawal Weighting
•Approximates apodization
pattern
•Works well for small
fractional bandwidths
•Allows weighting of in-line
transducers
•Actually removed electrodes
• “Weighting IDT SAW
Transducers by Selective
Withdrawal Weighting of
Electrodes” C.S. Hartmann,
1973, IUS, pp 423-426
Series Weighted IDT
Amplitude Weighted
- yields nearly
uniform spatial
beam profile
Uses a voltage
divider across
the aperture
“Series Weighting
of SAW
Transducers”, H.
Engan, 1974 IUS,
Combining
Series-Withdrawal Weighting
“Combining Series Section Weighting with Withdrawal Weighting
in Surface Acoustic Wave Transducers”, F. Sandy, UFFC_T, Vol.
26, No. 4, 1979, pp. 308-312
Tap Weight Enhancement
Analog tap
weight
control
rather than
just unity
taps
weights
“Tap Weight Enhancement for Broadband Filters” D.C.
Malocha, S. Datta, and B.J. Hunsinger, UFFC-T, 1978, pp.
51-54.
Capacitive Tap Weighted Network
•Uses thin film
capacitors fabricated in a
multi-level process
• a) a balance structure
• b) an unbalanced
structure
•Generates an analog
amplitude weighted
SAW-uniform spatial
beam profile
“CTW SAW Transducers”,
Malocha & Hunsinger, 1975,
IUS, pp. 411-413.
Spatial Diversity
Apodized, linear dispersive, and slanted
transducers. ( Chirp first discussed by R. Tancrell,
1969,1971)
“Acoustic Radiation Measurements and Calculations for
Three Surface Wave Filter Designs”, M. Daniel and J. de
Klerk, 1973 IUS, pp.449-455.
Non-Linear Phase Filter Using
Dispersive Transducers
Single dispersive
transducer filter
In-line doubly
dispersive
transducer filter
Slanted doubly
dispersive filter
SAW Slanted Dispersive Transducer
Slant provides
frequency/spatial diversity
and eliminated Fresnel
ripple in passband
“ Surface Acoustic Wave Slanted Correlators for Linear Pulse
Compressors”, B. Potter and C.S. Hartmann, IUS 1977, pp.
607-610.
Linear Phase Filter using
Dispersive Transducers
To 1st order,
flat passband
and linear
phase.
Linear Phase Slanted Transducer
• Transition band is determined by impulse response
length.
• Each strip is a relatively narrowband response but
the summation is a wideband response.
• Each strip’s group delay determines whether it is a
linear or non-linear phase filter.
“Wide-Band Linear Phase SAW Filter Design Using Slanted Transducer
Fingers” , C.K. Campbell, Y. Ye and J. Sferrazza Pappa, UFFC-T, 1982, pp.
224-228.
Slanted Transducer Energy Distribution
vs Frequency vs Beam Position
0.4
0.6
Band-edge
frequency
1.5
Normalized amplitude
Filter response is visualized as the sum of
multiple individual narrowband frequency
responses which are spatially separated
0.8
1
1.2
1.4
1.6
across the transducer aperture.
Normaliz ed Frequency
1
Mid-band
frequency
Center
frequency
Band-edge
frequency
0.5
0
0.5
0.5
0.4
0.3
0.2
0.1
0
0.1
Nor malized beam positio n
Cen ter freq u ency
P as s b and ed ge h ig h freq uen cy
P as s b and ed ge l ow fre qu ency
Mi d-ban d freq uen cy
Center of transducer beam
•Bandwidth is
determined by the upper
0.2
0.3
0.4
and lower
strip
band 0.5
edge frequencies.
1.
Example Slanted Transducer
Frequency Response
Normalized Magnitude (dB)
0
10
20
30
40
50
350
400
450
500
Frequency (MH z)
550
600
650
Wa
H( x f)  
( x)
2


 Sa2  ( f  f0( x) ) 
 2


A ( f) H( x f) d x

 Wa
( x) 
2


H t( f)  
2
Wa
Slanted Transducer Weighting
Across Passband
“Tapered Transducers- Design
and Applications”, L. Solie, 1998
IEEE IUS, pp.27-37.
Slanted Transducer Weighting
Technique
•Sidelobes are dependent on
weighting of electrodes.
Block weighting is a form
of capacitive weighting
but allows only discrete
amplitude steps.
“Tapered Transducers- Design
and Applications”, L. Solie, 1998
IEEE IUS, pp.27-37.
Multi-Phase Unidirectional SAW
Transducers
• Q: How do we eliminate bi-directional
loss?
• A: Change 3-port device into 2 port
device over bandwidth of interest
• UDT requires some non-symmetry in
transducer/electrical network
• Theoretically can have 0 dB loss
• TTE can be zero at center frequency
• Phasing network determines directivity
• Matching network determines electrical
reflection
Three Phase UDT
•Requires multi-level crossovers.
•Requires a 1 or 2 element 60o degree phase shift network
between ports.
•Requires 1 or 2 element matching network.
•Unidirectional fractional bandwidth up to approximately 20%.
“Wideband Unidirectional Interdigital Surface Wave
Transducers”, C.S. Hartmann, W. S. Jones and H. Vollers,
UFFC-T, 1972, pp378-381
3 Phase UDT Operation
•Analyzed as 3 collinear
transducers.
•Unit cell is 1 wavelength; no subharmonics. 1/3 wavelength
electrode period; strong 2nd harmonic
3 Phase UDT – Fo Vector Analysis
Simulation of forward
and reverse responses
Quadrature 3-Phase
Forward
response
Reverse
response
“Quadrature 3 Phase Unidirectional Transducer”, D.C.
Malocha, UFFC-T, Vol.26, no. 4, 1979, pp.
Apodized 3Phase UDT
Three Phase UDT Low Loss Filter Results
Wide Band
Filter
Response
Narrowband
Filter
Response
Group-Type UDT (GUDT)
•Single level fabrication
•Electrical phase shift network of
45o (1 or 2 elements) and
matching network (often 1
element) is used with the spatial
offset such that a SAW is
launched in one direction over a
determined bandwidth.
•Phasing always yields real input impedance; proper beam
width choice eliminates separate matching network.
“Low Insertion Loss Acoustic Surface Wave Filter Using
Group-Type Unidirectional Interdigital Filter Transducer”, IUS,
1975, K. Yamanouchi, F. Nyffeler and K. Shibayama, pp. 317321
Group-Type UDT
•GUDT uses
interleaved
transducers which
are spatially offset
from synchronism by
an integer number
plus one quarter
wavelength.
•Single level
metallization – no
crossovers.
+
I-Inphase
+
+
+
+
QQuadrature
I-Inphase
+
+
QQuadrature
+
Joining of transducers eliminates a
wavelength within each unit cell
composed of an I and Q port.
GUDT Simulated F/R Responses
GUDT 10units, 5pair/unit
0
The number of
electrodes in the
transducer sub-units is
determined from design
criteria. Sub-harmonics
are generated from I-Q
spacing.
dB
10
20
30
40
50
420
440
460
480
500
520
Frequenc y (MHz)
540
560
580
Forward response
Reverse response
Ideal response
f  fmin  fmin  df  fmax
0
HF ( f) HF ( f0)
Typical fractional
HR( f) HF ( f0)
bandwidth <15%.
Hdb ( f)
10
20
30
40
50
492
494
496
498
500
f
MHz
502
504
506
508
Single Phase UDT (SPUDT)
• Q: How can TTE be
reduced w/o multi-phase
UDT?
• A: Use internal transducer
mechanical reflections to
cancel regeneration
• Nearly eliminates TTE
• Requires 1 (or 2 matching)
elements
• Works like a UDT-lowers
insertion loss; theoretically
as low as 0dB
Original Single Phase UDT (SPUDT)
By matching the magnitudes
and opposing phases of the
acousto-mechanical reflection
and the reflected acoustoelectric wave the net reflected
wave from an acoustic port
can be minimized.
“A Triple Transit Suppression Technique”, K. Hanma and B.J
Hunsinger, 1976, IUS, pp. 328-331
SPUDT Schematic Concept
The transducer is
composed of a
transduction and
reflection structure. The
reflecting structure may
be incorporated into the
transducer structure or
can be superimposed
onto the transduction
structure. The reflector
can be made by mass
loading of metal, grooves,
or dielectric material.
SPUDT Macroscopic Reflection
The figure above illustrates schematically how a SPUDT
operates. The mechanical wave is equal in amplitude but 180o
out of phase with the regenerated wave. First order analysis
w/o cross coupling and first order reflection.
Figure: Abbott PhD Thesis1989
Single Phase UDT - Evolution
Multi-level
transducer with
a reflective
grating
“An Analysis of SAW Interdigital Transducers With Internal
Reflections and the Application to the Design of Single-Phase
Unidirectional Transducers”, C.S. Hartmann, P.V. Wright, R.J.
Kansy and E.M. Garber, IUS, 1982, pp. 40-45.
EWC -SPUDT Basic Unit Cells
Schematic example of
Electrode Width Controlled
SPUDT
A) Transduction and
reflector
B) Transduction and no
reflector
C) Reflector without
transduction
D) No transduction and no
reflector.
“Overview of Design Challenges for Single Phase
Unidirectional SAW Filters”, C.S. Hartmann and B.P. Abbott,
IUS 1989, pp. 79-89.
Distributed Acoustic Reflecting
Transducer (DART)
“Design of Low Loss SAW Filters Employing Distributed
Acoustic Reflection Transducers”, T. Kodama, H. Kawabata, Y.
Yasuhara and H. Sato, 1986 IUS, pp. 59-64.
Floating Electrode UDT (FEUDT)
Shorted or open electrode
configuration changes the
transduction/reflector
interaction and “selects”
forward/reverse directivity.
“ Low –Loss SAW Filter Using Internal
Reflection Type of New Single Phase
Unidirectional Transducer, K.
Yamanouchi and H. Furuyashiki, IUS
1984, pp. 68-71.
Example of SPUDT
Time/Frequency
Insertion loss ~ 5 dB
Main
SAW
TTE
Early Single Level SPUDT
•Transducer is comb structure with internal
series of reflectors
•Comb produces sub-harmonics
•Single level fabrication
“Low Loss SAW Devices Employing Single Stage Fabrication”, M.
Lewis, IUS 1983, pp.104-108,
Slanted SPUDT
Represents
a single
track of a
Slanted
SPUDT
Combining the SPUDT concept to slanted
transducers provided both a wideband
transduction and reflection mechanism.
“Improved Design of Single-Phase UDT for Low Loss SAW Filters,
C.B. Saw and C.K. Campbell, IUS 1987,pp. 169-172
SPUDT Slanted Transducer
Configuration
Each strip’s reflectors have a
narrowband response around the
strip’s center frequency
The electrical transduction and
mechanical reflections are
narrowband is each strip
The overall filter response is the sum
of narrowband responses, which is
wideband.
Conventional SPUDT: Mechanical
reflectors have only a narrowband
response around the filter center
frequency, SPUDT net effect is
narrowband
“Tapered Transducers- Design and
Applications”, L. Solie, 1998 IEEE IUS,
pp.27-37.
SPUDT Slanted Transducer Filter
“Tapered Transducers- Design and Applications”, L. Solie, 1998 IEEE IUS, pp.27-37.
Natural Single Phase Unidirectional
Transducer (NSPUDT)
•For some cuts of material, the
transducer/crystal cut combination is
“naturally unidirectional”.
•The effective center of transduction
can be within/near the electrode
region- this makes a spatial
asymmetry in the transducer with
respect to the transduction/reflection
centers.
•Quarter-wavelength electrodes are
used for the mechanical reflection.
•Problem: transducer only “looks” in
one direction.
“The Natural Single-Phase Unidirectional Transducer: A New Low-Loss SAW
Transducer”, P.V. Wright, IUS 1985, pp. 58-63.
Resonant SPUDT (RSPUDT)
“ A New Concept in SPUDT Design: the RSPUDT (Resonant SPUDT)”, P.
Ventura, M. Solal, P. Dufilie, J.M. Hode, and F., Roux. IUS 1994, pp. 1-6.
Waveguide SPUDT
“New SPUDT Cell Structure”, G. Martin, H. Schmidt, and B.
Wall, 2002 IUS, pp. 39-42.
Harmonic SPUDT (HSPUDT)
Slanted HSPUDT
“A New Type SPUDT for use in High Frequency around 2
GHz”, C_Y. Jian and S. Beaudin, 2002 IUS, pp. 279-282.
SAW Propagation Simulation
Don’t
Panic!!!
What
do you do when your
Diffraction
–
the
Designer’s
“Alibi”
filter doesn’t meet specs?!
Some Concluding Remarks
My
crystal
ball
is fuzzy,
so
I’ll refer
to
some
To
our
colleagues
who
developed
the
pasttrade
SAW!
You
now
have
seen
some
of
the
tricks
of
the
SAW
technology
is
mature
but
still
evolving.
unidentified
quotes of my
predecessors:
technology,
we
saluteinyou
!!! – CCDs will
•SAW devices have a limited future
filtering
take over signal processing applications (circa 1979)
•SAW RF filters with low insertion loss are merely laboratory
curiosities.
•SAW devices will have an estimated world wide market of
about $250,000 (circa 1985).
•SAW RF filters should be reduced in cost from $2.00 to less
than $.50 within 5 years. (circa 1994)
•SAW IF filters will be eliminated in all cellular radios by zeroIF by 2002.
•LGX is the material of the future, and always will be!!
•By the way, what is an effervescent wave ??
•We came, we SAW, we conquered !