IEC 61019-2:2005

IEC 61019-2 ®
Edition 2.0 2005-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Surface acoustic wave (SAW) resonators –
Part 2: Guide to the use
Résonateurs à ondes acoustiques de surface (OAS) –
Partie 2: Guide d’emploi
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IEC 61019-2 ®
Edition 2.0 2005-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Surface acoustic wave (SAW) resonators –

Part 2: Guide to the use
Résonateurs à ondes acoustiques de surface (OAS) –

Partie 2: Guide d’emploi
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX U
ICS 31.140 ISBN 978-2-8322-1340-7

– 2 – 61019-2  IEC:2005
CONTENTS
FOREWORD . 3
INTRODUCTION . 5

1 Scope . 6
2 Normative references . 6
3 Technical considerations . 6
4 Fundamentals of SAW resonators. 7
4.1 Basic structure . 7
4.2 Principle of operation . 7
5 SAW resonator characteristics . 8
5.1 Reflector characteristics . 8
5.2 SAW resonator characteristics. 10
5.3 Spurious modes . 14
5.4 Substrate materials and their characteristics . 15
5.5 Available characteristics . 17
6 Application guide . 19
6.1 Oscillator circuits and oscillation condition . 19
6.2 Practical remarks for oscillator applications . 21
7 Checklist of SAW resonator parameters for drawing up specifications . 22

Bibliography . 25

61019-2  IEC:2005 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
SURFACE ACOUSTIC WAVE (SAW) RESONATORS –

Part 2: Guide to the use
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61019-2 has been prepared by IEC technical committee 49:
Piezoelectric and dielectric devices for frequency control and selection.
This second edition cancels and replaces the first edition published in 1995. This edition
constitutes a technical revision.
The main changes with respect to the previous editon are listed below:
• at the end of 5.1, the edge reflector has been added. Its reference literature has been
inserted in the bibliography;
• in Table 1, the propagation properties of LiNbO (64° Y) have been added;
• in Table 3, the clause and subclause numbers have been corrected in order to be
consistent with IEC 61019-1 (2004) which has replaced IEC 61019-1-1 (1990) and
IEC 61019-1-2 (1993).
– 4 – 61019-2  IEC:2005
This bilingual version (2014-02) corresponds to the monolingual English version, published in
2005-05.
The text of this standard is based on the following documents:
FDIS Report on voting
49/714/FDIS 49/723/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
The French version of this standard has not been voted upon.
IEC 61019 consists of the following parts, under the general title Surface acoustic wave
(SAW) resonators
Part 1: Generic information
Part 2: Guide to the use
Part 3: Standard outlines and lead connections
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
61019-2  IEC:2005 – 5 –
INTRODUCTION
This part of IEC 61019 gives practical guidance to the use of SAW resonators which are used
in telecommunications, radio equipments and consumer products. IEC 61019-1 can be referred
to for general information, standard values and test conditions.
The features of these SAW resonators are small size, light weight, adjustment-free and high
stability. In addition, the operating frequency of SAW resonators extends to the VHF and UHF
ranges.
This part has been compiled in response to a generally expressed desire on the part of both
users and manufacturers for a guide to the use of SAW resonators, so that the resonators
may be used to their best advantage. To this end, general and fundamental characteristics
have been explained in this guide.

– 6 – 61019-2  IEC:2005
SURFACE ACOUSTIC WAVE (SAW) RESONATORS –

Part 2: Guide to the use
1 Scope
SAW resonators are now widely used in a variety of applications: VCR RF-converters, CATV
local oscillators, measuring equipment, remote control and so on. While SAW resonators are
also applied to narrow bandwidth filters, the scope of this part of IEC 61019 is limited to SAW
resonators for oscillator applications
It is not the aim of this guide to explain theory, nor to attempt to cover all the eventualities
which may arise in practical circumstances. This guide draws attention to some of the more
fundamental questions, which should be considered by the user before he places an order for
a SAW resonator for a new application. Such a procedure will be the user's insurance against
unsatisfactory performance.
Standard specifications, such as those of the IEC of which this guide forms a part, and
national specifications or detail specifications issued by manufacturers, will define the
available combinations of resonance frequency, quality factor, motional resistance, parallel
capacitance, etc. These specifications are compiled to include a wide range of SAW
resonators with standardized performances. It cannot be over-emphasized that the user
should, wherever possible, select his SAW resonators from these specifications, when
available, even if it may lead to making small modifications to his circuit to enable the use of
standard resonators. This applies particularly to the selection of the nominal frequency.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 61019-1:2004, Surface acoustic wave (SAW) resonators – Part 1: Generic specification
IEC 61019-3:1991, Surface acoustic wave (SAW) resonators – Part 3: Standard outlines and
lead connections
3 Technical considerations
It is of prime interest to a user that the resonator characteristics should satisfy particular
specifications. The selection of oscillating circuits and SAW resonators to meet such
specifications should be a matter of agreement between user and manufacturer.
Resonator characteristics are usually expressed in terms of resonance frequency, motional
resistance, quality factor and parallel capacitance (for the one-port type) and centre
frequency, insertion attenuation, loaded and unloaded quality factor, input capacitance and
output capacitance (for the two-port type). A standard method for measuring resonator
characteristics is described in 8.5 and 8.6 of IEC 61019-1. The specifications are to be
satisfied between the lowest and highest temperatures of the specified operating temperature
range and before and after environmental tests.

61019-2  IEC:2005 – 7 –
4 Fundamentals of SAW resonators
4.1 Basic structure
SAW resonators consist of interdigital transducers (IDT) and of grating reflectors, which are
placed on the surface of a piezoelectric substrate. In most cases, the grating reflectors are
made of thin metal (such as Al, Au) film while, in some cases, they are constructed with
periodic grooves. The die is bonded by an adhesive agent into a sealed enclosure, and the
IDT is electrically connected to the terminals with bonding wires. There are two SAW
resonator configurations. One is a one-port SAW resonator. The other is a two-port SAW
resonator. The former has a single IDT between two reflectors, as shown in Figure 1. The
latter has two IDTs between two reflectors, as shown in Figure 2. In the figures,  is the
eff
resonator cavity length, as described in 5.2 c).

l
eff
S
Grating reflector Grating reflector
d = λ /2
IDT
IEC  694/05
Figure 1 – One-port SAW resonator configuration
l
eff
S
Grating reflector Grating reflector
IDT
d = λ /2
IEC  695/05
Figure 2 – Two-port SAW resonator configuration
4.2 Principle of operation
The resonance phenomenon for SAW resonators is achieved by confining the SAW vibration
energy within grating reflectors. The SAW, excited by an alternating electrical field between
IDT electrode fingers, propagates outside the IDT to be reflected by grating reflectors.

– 8 – 61019-2  IEC:2005
The grating reflectors feed the perturbation to the SAW, owing to the discontinuity in electrical
or mechanical impedance. When the SAW is incident on such grating reflectors, the incident
wave is gradually converted into a reflected wave. Although the amount of perturbation per
unit reflective element may be very small, a large number of such elements, arranged
periodically, reflect the SAW in phase, and maximize coherent reflection.
These grating configurations can form effective reflecting boundary, creating a standing wave
between the reflectors and make resonance with a very high Q. Figure 3 shows the
displacement distribution for this standing wave for a one-port SAW resonator. As shown in
the figure, the SAW energy is maximum near the centre of the IDT, and gradually decays
towards the edges of the grating reflectors. The resonance frequency, f , is approximately
r
determined by
f ≈ v /(2d) = v /λ
r s s 0
where
v is the SAW propagation velocity;
s
d is the distance between electrode centres;
λ is the SAW wavelength at the stop band centre frequency.
IDT
Grating reflector Grating reflector
d
Substrate
SAW energy
distribution
IEC  696/05
Figure 3 – Standing wave pattern and SAW energy distribution
5 SAW resonator characteristics
5.1 Reflector characteristics
The reflector for SAW resonators consists of a periodically arranged array of reflective
elements, called a grating reflector. As cross-sections show in Figure 4, possible array
elements are:
a) metal strips or dielectric ridges;
b) grooves;
c) ion-implanted or metal-diffused strips.
For example, an aluminum strip on ST-cut quartz, whose thickness h is 1 % of wave length
λ(h/λ ) and whose width w is half the spatial period (w = d/2 = λ /4), has a small reflection
0 0
coefficient ε of approximately 0,5 %. A groove with 1 % depth has almost the same ε. This
periodic perturbation causes efficient reflection of SAW energy, if its wavelength equals twice
its periodicity.
61019-2  IEC:2005 – 9 –
h
d
IEC  697/05
4a – Metal strips or dielectric ridges

IEC  698/05
4b – Grooves
IEC  699/05
4c – Ion-implanted or metal diffused strips
Figure 4 – Grating reflector configurations
A grating reflector without loss with a finite number of array elements has a frequency range
of nearly total reflection called the stop band. The fractional stop bandwidth to centre
frequency is 2ε/π, where ε is the reflection coefficient for one element. Figure 5 indicates the
frequency dependency on the total reflectivity |Γ| for the grating reflector with a finite number
N of array elements. Theoretically, the reflectivity maximum value is derived as:
R
|Γ| = tanh(N × ε)
max R
at the centre frequency f of the stop band. A greater reflectivity makes SAW resonator Q
value higher, due to decreasing the leakage of SAW energy stored in the cavity between two
grating reflectors.
– 10 – 61019-2  IEC:2005
1,0
N × ε = 2
R
0,5
0,0
–4 –2 0 2 4
(f – f )
Frequency
× ε/π
f
IEC  700/05
Figure 5 – Reflectivity response for grating reflection
For obtaining a greater reflectivity, it is clear, from the preceding equation, that N × ε should
R
be larger. Increasing reflector element number N is the easiest way to obtain a higher
R
reflectivity. However, in practice, a greater element number, i.e. longer reflector size, requires
a larger SAW chip size and means an expensive SAW resonator. Generally, N × ε = 4 is
R
adequate for practical SAW resonators.
For obtaining greater reflectivity, increasing the reflection from one element is also effective.
To accomplish this, strips should be thicker or grooves should be deeper. For the most part,
ε is proportional to the thickness or the depth h/λ . Thicker strips or deeper grooves require
less element number N for the same reflection coefficient and realize greater stop
R
bandwidth. However, a reflector with a large h/λ has the following disadvantages:
a) the mode conversion loss from SAW to bulk wave tends to increase, which may degrade
the quality factor;
b) stopband centre frequency deviation from the frequency v /(2d) increases, because the
s
centre frequency is a function of the square of h/λ . This may cause mass production
difficulties.
For a substrate material supporting shear wave, reflection at the edge of a substrate can be
utilized as a substitute for a grating reflector. This gives the advantage of size reduction
corresponding to the size of array elements.
5.2 SAW resonator characteristics
a) One-port SAW resonators
A one-port SAW resonator has the transmission characteristics shown in Figure 6.
Reflection coefficient  |Γ|
61019-2  IEC:2005 – 11 –
Spurious
resonance
Frequency Frequency
of maximum of minimum
admittance (f ) admittance (f )
m
n
Frequency  MHz
IEC  701/05
Figure 6 – Typical frequency characteristics for a one-port SAW resonator,
inserted into a transmission line in series
The equivalent circuit in Figure 7 represents this one-port SAW resonator resonance.
Comparing SAW resonators made from different piezoelectric materials, the figure of merit
M = Q/r derived from the equivalent circuit can be used. For example, SAW resonators on
a quartz substrate have a high Q factor and a large r, while the values on X-cut LiTaO
are both smaller. Both resonators have similar figure of merit values. Considering only Q
or the capacitance ratio r is insufficient for comparison purposes.
The equivalent circuit in Figure 7 can be replaced by a reactance with a series resistance:
R (f) + jX (f), where X and R are an equivalent series reactance and an equivalent series
e e e e
resistance, respectively. The frequency dependencies for these values are shown in
Figure 8, where the value X /R reaches the maximum at the arithmetic mean of
e e
resonance and anti-resonance frequencies of zero susceptance.

L R
1 C
C
IEC  702/05
is the motional (series) resonance frequency;
f =
s
2π L × C
1 1
Q = 2πf × L /R is the quality factor;
s 1 1
r = C /C is the capacitance ratio;
0 1
M = Q/r is the figure of merit;
L , C , R are the motional inductance, motional capacitance and motional resistance respectively;
1 1 1
C is the static capacitance.
Figure 7 – Equivalent circuit for a one-port resonator
Attenuation  dB
– 12 – 61019-2  IEC:2005
X
e
≈ M
R
e
R
e
Resonance frequency
of zero susceptance (f )
r
X
e
Anti-resonance frequency
of zero susceptance (f )
a
X
e
Frequency
IEC  703/05
Figure 8 – Frequency response for series equivalent resistance (R ),
e
reactance (X ) and X /R
e e e
The maximum value can be derived from the equivalent circuit as:
(X /R ) ≈ (Q/r) /4
e e max
In order to achieve oscillation more easily, resonators should show high Q reactance.
Consequently, the figure of merit is adequate to compare SAW resonators.
Resonator impedance is inversely proportional to the aperture design. However, an over-
narrow aperture resonator tends to increase r, due to the stray capacitance, and to
degrade Q, due to the diffraction loss. On the other hand, an over-wide aperture resonator
has a relatively low Q, due to electrode resistance.
b) Two-port SAW resonators
Two-port resonator transmission characteristics are shown in Figure 9.
(arbitrary unit)
61019-2  IEC:2005 – 13 –
Minimum insertion
attenuation
Spurious
response
rejection
Centre frequency (f )
c
Frequency  MHz
IEC  704/05
Figure 9 – Insertion attenuation and spurious response characteristics
for a two-port resonator
An equivalent circuit for a two-port SAW resonator, in the vicinity of the centre frequency,
is shown in Figure 10. It is constructed with a motional arm with motional inductance (L ),
capacitance (C ), and resistance (R ) in series, two parallel capacitances (C and C )
1 1 IN OUT
shunting the input and output ports and an ideal transformer. The turns ratio φ for the ideal
transformer is derived from the input and output transducer structures. When both
structures are the same, the φ value is unity; a 0° phase shift type is expressed as φ = 1
and a 180° type is expressed as φ = –1. Two-port SAW resonators, with different input
and output impedances, have a |φ| value, which is not equal to unity.

C
L R
1 1 1:φ
C C
IN OUT
IEC  705/05
Key
L motional inductance C input capacitance
IN
C motional capacitance C output capacitance
OUT
R motional resistance φ  turns ratio
Figure 10 – Equivalent circuit for a two-port resonator
For two-port resonators, there is no evident index as figure of merit as for one-port
resonators. Easy-to-oscillate resonators are devices with low loss in the specific circuit
and with the appropriate phase transition of 0° or 180°. Small motional resistance R is
essential for low loss. A lower impedance resonator (larger C and C ) has lower loss,
IN OUT
in most cases.
Attenuation  dB
– 14 – 61019-2  IEC:2005
c) Equivalent circuit parameters
Equivalent circuit parameters for a one-port SAW resonator can be represented as follows,
when SAW reflection at IDT fingers is neglected:

l /λ
eff 0
L = × R
1 a
4 f Γ
1− Γ
R = × R
1 a
2 Γ
C =
(2πf ) L
0 1
C = N × w(1+ ε )× ε
0 r 0
where
R = is the IDT radiation resistance at f ;
a
8k f NC
s 0 0
f = v /(2d);
0 s
N is the IDT finger pair number;
w is the aperture;
k is the SAW coupling coefficient;
s
ε is the relative permittivity of a piezoelectric substrate;
r
ε is the permittivity of vacuum;
Γ is the reflection coefficient of a reflector;
λ is the SAW wavelength at the centre frequency;
l is the resonator cavity length shown in Figures 1 and 2 (l ≈ S + λ /(2ε)), where S
eff eff 0
is a separation of grating reflectors.
For two-port SAW resonators, C shall be replaced by C or C respectively. Other
0 IN OUT
equations are the same as the above equations.
5.3 Spurious modes
SAW resonators have many kinds of spurious modes. One is higher-order SAW resonance
modes, called longitudinal and transverse modes. Other types of SAW modes, such as leaky
SAW, SSBW, Love waves, may be excited by the IDT. Another mode is bulk wave modes.
Figures 6 and 9 show the typical spurious characteristics for one-port and two-port
resonators, respectively. These spurious modes can be reduced by applying several
techniques to the resonators.
When used in an oscillator circuit, these spurious modes rarely cause problems. However,
should there be spurious responses near the main mode or responses with relatively large
amplitude, oscillation problems at those spurious frequencies could occur.
These spurious responses could result in anomalous frequency-temperature, resistance-
temperature and frequency pulling characteristics. Even very small perturbations of this type
can have very deleterious effects for VCO (voltage controlled oscillator) applications. It is
more difficult to eliminate these spurious responses from the resonators. However, these
resonators seldom give trouble, because the spurious resonance resistance is in general
larger than that for the main mode. Manufacturers' standard products involve design
measures which minimize these effects when coupled with reasonable oscillator design.

61019-2  IEC:2005 – 15 –
In any application, where there are spurious responses, it should be considered that there is a
possibility of the oscillator starting at the spurious responses. In a frequency range around the
main response, one of the following ratios can be specified:
spurious resonance motional resistance
for a one-port resonator
main resonance motional resistance
spurious resonance response level
for a two-port resonator
main resonance response level
For two-port resonators, only spurious resonances which fulfil the phase condition of the
oscillator feedback loop have to be considered.
5.4 Substrate materials and their characteristics
Various kinds of piezoelectric substrates are available for use in SAW resonators.
Piezoelectric substrates for SAW resonators are selected, in consideration of the following
items:
1) propagation velocity (v );
s
2) coupling coefficient (k );
s
3) temperature coefficient of frequency (TCF);
4) relative permittivity (ε );
r
5) material propagation loss;
6) reproducibility and reliability;
7) price.
Items 1) to 5) are constants concerned mainly with materials. Items 6) and 7) are conditions
depending on both materials and substrate fabrication techniques. Several kinds of substrates
have been developed and put into practical use.
Ideally, a high coupling coefficient and a zero temperature coefficient are desired. At present,
this is not possible. Thus, a design trade-off is required. It is necessary to select a substrate
according to the required specifications. Relationships between material constants and
resonator characteristics are descried below.
a) Propagation velocity
The propagation velocity v (m/s) is an important factor, which determines the frequency
s
range. Resonance frequency f (MHz) is given approximately by:
r
f = v /(2d)
r s
where d (µm) is the spatial period of the grating. For a specified resonance frequency,
slower velocities require a shorter finger period and, consequently, a smaller chip
size. Faster velocity is desirable for high frequency resonators, in order to make the
IDT fabrication easier. Propagation velocity for a practical substrate is usually in the
2 000 m/s to 5 000 m/s range.
b) Coupling coefficient
SAW coupling coefficient k is the transformation ratio between the electric energy and
s
the mechanical (SAW) energy. The coupling coefficient is the principal factor that
determines capacitance ratio r. When the coupling coefficient of the substrate is large
enough, it is easy to design a low capacitance ratio SAW resonator. An achievable
minimum capacitance ratio is represented as:
2 2
r ≈ π /(8k )
min s
– 16 – 61019-2  IEC:2005
c) Temperature coefficient
This characteristic is determined mainly by the piezoelectric material and crystal
orientations. Rotated Y-cut (around ST-cut) quartz and Li B O materials have parabolic
2 4 7
frequency-temperature characteristics, but with other piezoelectric materials they are
nearly linear. Figure 11 shows frequency-temperature characteristics for various common
substrate materials.
36° Y – X
LiTaO
X–112° Y
LiTaO
200 3
128° Y – X
LiNbO
ST quartz
–100
45° Y – Z
–200
Li B O
2 4 7
–300
–40 –20 0 20 40 60 80 100
T  °C
IEC  706/05
Figure 11 – Frequency-temperature characteristics for various common materials
and their angles of cut
Typically the frequency-temperature dependence is:
∆f
= a × (T – T ) + b × (T – T )
0 0
f
where
∆f
is the fractional frequency change;
f
T is the turnover temperature;
T is the operating temperature;
a is the first order temperature coefficient;
b is the second order temperature coefficient.
Typical temperature coefficient values are listed in Table 1.
d) Relative permittivity
The piezoelectric material permittivity is a second-order symmetric tensor. The static
capacitance for the IDT, C , directly depends on the substrate permittivity.
–6
∆f/f (10 )
61019-2  IEC:2005 – 17 –
e) Material propagation loss
The quality factor for the SAW resonator is a function of its various losses. The Q value
depends on: material propagation loss (viscous damping and air loading), surface
propagation loss (imperfect surface finish), bulk mode conversion loss, diffraction and
other leakage losses from sides of reflectors and ohmic and frictional losses of electrodes.
The material propagation loss determines the maximum Q limit, which is called material
quality factor Q .
m
f) Typical single-crystal materials
Properties of single-crystal substrates are governed by the angle of cut and the SAW
propagation direction, because of the crystal anisotropy. Single crystals have advantages
concerning reproducibility, reliability, and low propagation loss.
However, it is still difficult to obtain a material which satisfies both large coupling
coefficient and small temperature coefficient, simultaneously.
Typical crystals and their angles of cut recommended for SAW resonators are listed in
Table 1 with their material constants.
Table 1 – Properties of single-crystal substrate materials
Temperature
Relative
Coupling
Angle of Propagation Velocity
coefficient
Material coefficient permittivity
cut direction V
s
k ε
s a b r
–6 –9 2
Degrees Degrees m/s % 10 /K 10 /K
ST-quartz 42,75° Y X 3 157 0,16 0 –34 4,5
rd
LST-quartz –75° Y X 3 960 0,11 0 3 order 4,5
LiNbO Y Z 3 488 4,82 –94 – 36,7
LiNbO 128° Y X 4 000 5,56 –74 – 39,1
LiNbO 64° Y X 4 742 11,3 –79 – 58,4
LiTaO X 112°Y 3 295 0,64 –18 – 44,0
LiTaO 36° Y X 4 178 4,8 –33 – 51,1
Li B O 45° Y Z 3 401 1 0 –270 9,6
2 4 7
5.5 Available characteristics
a) Frequency range
The upper-limit frequency for SAW resonators is determined by fine pattern fabrication
pitch is d (µm), the frequency is v /(2d) (MHz), where v (m/s) means SAW velocity. The
s s
lower-limit frequency depends on chip size restriction. Available substrate wafer size and
package dimensions are finite. In practice, demanded resonator cost also confines the
allowable chip size. The typical frequency range for SAW resonators is from approximately
60 MHz to several GHz. However, this limitation is never strict.
b) Quality factor
The maximum possible quality factor for ideally designed and processed SAW resonator is
limited to Q described in 5.4 e). Q depends on frequency and is approximately
m m
expressed as Q = 10 /f for typical substrate materials, where f is the frequency in
m
at several frequencies. However,
megahertz. SAW resonators are reported to achieve Q
m
mass-produced SAW resonators using ST-cut quartz typically exhibit to have Q = 15 000
～ 20 000 at 100 MHz and Q = 10 000 at 600 MHz.

– 18 – 61019-2  IEC:2005
c) Temperature coefficient of frequency
Temperature-frequency characteristics of resonance frequency for SAW resonators are
closely connected with the substrate material. However, mechanical stress to the
substrate (such as adhesive agent), IDT and grating reflectors slightly affect the
temperature dependency of the substrate itself.
Temperature-frequency characteristics for the quartz and Li B O resonators have
2 4 7
parabolic dependency. The temperature, where the parabolic curve locates its top
position, is called turn-over temperature. It can be chosen by selecting an appropriate
cut angle of the substrate. Generally, it is within the –20 °C to 75 °C range, and
controlled within ±10 °C of a particular temperature.
SAW resonators with other materials provide a linear temperature-frequency relation.
The temperature coefficient is also affected by the adhesive agent, IDT and grating
reflectors, but is negligible compared with the material itself.
d) Long-term stability
Characteristic changes caused by ageing or long-term stability for SAW resonators are
shown in resonance frequency changes and in quality factor degradation. These changes
are influenced by
– contamination on the resonator chip surface;
– mechanical stress, for example by differences in thermal expansion between the
resonator substrate and the package;
– too high drive level.
In the first two cases the cause exists in the SAW resonator device itself, and there may
be many occasions where they arise. It is well-known that some of them occur during the
manufacturing process. Examples are the bare-chip manufacturing process, the chip-
bonding process using adhesive agent, the package sealing process and others.
In the third case, the characteristic changes occur in the over-excited condition and
depend on oscillator circuit design. Excessive drive level damages electrodes in the SAW
resonator and shortens its life. This is described in 5.5 e). Usually, with care applied to the
drive level limitation, long-term stability is several parts per million/year or less.
e) Power durability
The excessive repeated mechanical stress may induce electrode deterioration, such as
voids and hillocks. This brings about resonance frequency shifts and quality factor
degradation. To make a resonator work for a long enough period in most applications, the
drive level shall be less than several milliwatts.
To improve high-power withstanding durability, doping a small amount of copper or
titanium to the aluminium electrodes is used. Epitaxially-grown aluminium electrodes on
quartz are also used. They are all designed to be effective to control the grain boundary in
deposited, aluminium thin film. This limitation level depends on frequency, ambient
temperatures, electrode constitutions and device design.
f) Short-term stability for SAW oscillator
Short-term stability is the spectrum purity of the oscillator and is defined as SSB (single
side-band) noise, residual FM noise or C/N (carrier to noise ratio) for the oscillation signal.
The performance depends on the quality factor of the SAW resonator and handling power
level in an oscillation loop. In general, SAW oscillators can achieve higher, short-term
stabilities compared with LC oscillators and dielectric resonator oscillators.
g) Availability
Typical properties of the available one-port SAW resonators for the various materials are
shown in Table 2. For the two-port resonators, the quality factor is almost the same as for
one-port resonators.
61019-2  IEC:2005 – 19 –
Table 2 – Typical properties of available one-port SAW resonators
up to about 600 MHz
Substrate materials ST-cut quartz X-112° Y 36° Y-X
LiTaO LiTaO
3 3
Quality factor Q 12 000 – 24 000 12 000 – 17 000 600
Capacitance ratio r 1 200 – 1 600 800 14
Figure of merit M = Q/r 9 – 17 18 40
–6 2 –6 –6
TCF –0,034 × 10 /K –18 × 10 /K –33 × 10 /K
6 Application guide
6.1 Oscillator circuits and oscillation condition
Oscillators using SAW resonators provide stable oscillation in VHF and UHF frequency ranges
without frequency multiplexing, and have good spectrum purity (i.e. short-term stability).
One-port SAW resonators are very similar to crystal resonators, from the electrical viewpoint,
in spite of differences in mechanical vibration modes and frequency ranges used.
Consequently, oscillators are constructed with the same type of crystal oscillator circuits.
On the other hand, two-port SAW resonators are electrically treated as narrow bandwidth
filters. Oscillators are constructed with feedback amplifiers.
Figure 12a presents a typical one-port SAW resonator oscillator in the 100 MHz frequency
range. This can be reduced to that shown in Figure 12b, considering the r.f. signal alone. The
oscillation occurs in the frequency range, where the resonator is inductive.
In order to analyze the oscillation condition, the oscillator circuit is modelled by the equivalent
circuit, consisting of a resonator element side and an active element side, as shown in Figure
12c.
The resonator on the left-hand side can be re-written into the lumped element equivalent
circuit, which is a reactance X (f) in series with a resistance R (f). The active element side
e e
can be replaced by a negative resistance R with a load capacitive reactance
L
X (= 1/(2πf × C )).
L L
Oscillation occurs at the frequency f where the following equations are satisfied:
OSC
X ( f ) = X

e L

R ( f ) = R
 e L
– 20 – 61019-2  IEC:2005
0,01 µF
Out
C
2SC387
510 Ω
0,01 µF
7,5 kΩ
C 16 kΩ 1 kΩ
V
cc
+9 V
0,01 µF
47 µF
IEC  707/05
a) – Oscillator circuit
a
a
R –R
e L
C
C
b
–jX
jX L
e
C
B
b
IEC  708/05
IEC  709/05
b) – RF circuit of the oscillator c) – Equivalent circuit
Figure 12 – 100 MHz one-port SAW resonator oscillator
The oscillation frequency can be approximately determined by the following equation:
 
C
 
f = f × 1+
OSC r
 
2r(C + C )
 0 L 
where
f is the resonance frequency;
r
/C ) of the resonator;
r is the capacitance ratio (C
0 1
This means that the oscillation frequency can be changed slightly by varying the load
reactance.
Figure 13a presents a typical two-port SAW resonator oscillator, for the 600 MHz frequency
range. This can be simplified as shown Figure 13b, where an active element works as a
feedback amplifier. The feedback amplifier shall be designed to satisfy the following
conditions:
I
...