Surface acoustic wave (SAW) resonators - Part 2: Guide to the use

IEC 61019-2:2005 gives practical guidance to the use of surface acoustic wave (SAW) resonators which are used in telecommunications, radio equipments and consumer products. It is to be used in conjunction with IEC 61019-1. The features of SAW resonators are small size, light weight, adjustment-free and high stability,operating frequencies extend to the VHF and UHF ranges. 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 LiNbO3 (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).

Résonateurs à ondes acoustiques de surface (OAS) - Partie 2: Guide d'emploi

L'IEC 61019-2:2005 donne un guide pratique des résonateurs à OAS utilisés dans les télécommunications, dans les équipements de radio et les produits de consommation. Il doit être utilisé dans la conjonction avec IEC 61019-1. Les résonateurs à OAS sont caractérisés par leurs petites dimensions, leur faible poids, l'absence de réglage et leur fiabilité élevée. Les principales modifications par rapport à l'édition antérieure sont indiquées ci-dessous:
- à la fin de 5.1, le réflecteur de bord a été ajouté. L'ouvrage de référence qui s'y rapporte a été inséré dans la bibliographie;
- dans le Tableau 1, les propriétés de propagation du LiNbO3 (64° Y) ont été ajoutées;
- dans le Tableau 3, les numéros des articles et des paragraphes ont été corrigés pour correspondre à la CEI 61019-1 (2004) qui remplace la CEI 61019-1-1 (1990) et la CEI 61019-1-2 (1993).

General Information

Status
Published
Publication Date
11-May-2005
Current Stage
PPUB - Publication issued
Start Date
12-May-2005
Completion Date
12-May-2005
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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
IEC 61019-2:2005-05(EN-FR)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
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

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 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

---------------------- Page: 4 ----------------------
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

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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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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of

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).
---------------------- Page: 5 ----------------------
– 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.
---------------------- Page: 6 ----------------------
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.
---------------------- Page: 7 ----------------------
– 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.
---------------------- Page: 8 ----------------------
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).
eff
Grating reflector Grating reflector
d = λ /2
IDT
IEC 694/05
Figure 1 – One-port SAW resonator configuration
eff
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.

---------------------- Page: 9 ----------------------
– 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

determined by
f ≈ v /(2d) = v /λ
r s s 0
where
v is the SAW propagation velocity;
d is the distance between electrode centres;
λ is the SAW wavelength at the stop band centre frequency.
IDT
Grating reflector Grating reflector
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.
---------------------- Page: 10 ----------------------
61019-2  IEC:2005 – 9 –
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:

|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.
---------------------- Page: 11 ----------------------
– 10 – 61019-2  IEC:2005
1,0
N × ε = 2
0,5
0,0
–4 –2 0 2 4
(f – f )
Frequency
× ε/π
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

be larger. Increasing reflector element number N is the easiest way to obtain a higher

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

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

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

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|
---------------------- Page: 12 ----------------------
61019-2  IEC:2005 – 11 –
Spurious
resonance
Frequency Frequency
of maximum of minimum
admittance (f ) admittance (f )
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
IEC 702/05
is the motional (series) resonance frequency;
f =
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
---------------------- Page: 13 ----------------------
– 12 – 61019-2  IEC:2005
≈ M
Resonance frequency
of zero susceptance (f )
Anti-resonance frequency
of zero susceptance (f )
Frequency
IEC 703/05
Figure 8 – Frequency response for series equivalent resistance (R ),
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)
---------------------- Page: 14 ----------------------
61019-2  IEC:2005 – 13 –
Minimum insertion
attenuation
Spurious
response
rejection
Centre frequency (f )
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.
L R
1 1 1:φ
C C
IN OUT
IEC 705/05
Key
L motional inductance C input capacitance
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
---------------------- Page: 15 ----------------------
– 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 ;
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;
ε is the relative permittivity of a piezoelectric substrate;
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 OU
...

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