JPH10215144A - Surface acoustic wave resonator and surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave(SAW) resonator of low loss and a SAW device using it by suppressing the adverse effects of spuriousness. SOLUTION: By setting a distance d1 between an interdigital transducer(IDT) 14 and a reflector 151 on a left side and the distance dr between the IDT 14 and the reflector 15r on a right side to different values, frequency bands generated by the spuriousness of the left side reflector 151 and the spuriousness of the right side reflector 15r are made different and the two pieces of the independent spuriousness are attained without adding the levels of the spuriousness. Thus, conventional one piece of the spuriousness is dispersed to the two pieces of the spuriousness of a size about the half of it for instance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave resonator and a surface acoustic wave device such as a resonator type surface acoustic wave filter formed using the same, and more particularly, to a configuration of the resonator type surface acoustic wave filter or the like. The present invention relates to an indispensable design method for spurious suppression of a surface acoustic wave resonator.

[0002]

2. Description of the Related Art Generally, a surface acoustic wave device is an interdigitated transducer (Interdigit) for exciting a surface acoustic wave (hereinafter, referred to as "SAW").
al Transducer (hereinafter, referred to as “IDT”), and by processing this IDT, a SAW device can have various characteristics and functions. Conventionally, SAW devices are often mainly referred to as SAW filters, and among these SAW filters, multi-electrode SAW filters have been mainly used. In recent years, research and development of a resonator type SAW filter in addition to a multi-electrode type SAW filter have been actively conducted, and the term “SAW filter” does not necessarily mean a multi-electrode type SAW filter.

FIG. 2 is a plan view of a conventional general SAW resonator. This SAW resonator has a piezoelectric substrate 1. On the piezoelectric substrate 1, an input terminal 2 and an output terminal 3
And an IDT 4 for SAW excitation having a plurality of electrode fingers made of an aluminum thin film or the like, and a plurality of electrode fingers made of an aluminum thin film or the like acoustically reflected to return the SAW leaked from the left and right sides of the IDT 4 to the IDT 4. A left reflector ₅₁ and a right reflector _5r and a ground bonding pad 6 are formed. Since the input side and the output side of this SAW resonator are symmetrically structured,
The input terminal 2 may be an output terminal and the output terminal 3 may be an input terminal. Usually, the pitch between the electrode fingers of the adjacent IDT 4 and the electrode fingers of the reflectors 5 _l and 5 _r (that is, two adjacent electrode fingers).
The electrode finger center distance is designed to be half the wavelength of the excitation SAW, similarly to the pitch of the electrode fingers of the IDT 4. On the other hand, since the bonding pad 6 has the same thickness as the IDT 4, if the thickness of the IDT 4 is 4000 ° or more, it is possible to perform bonding without providing a gold bonding pad thereon. Reflectors 5 _l and 5 _r are ID
Since the reflectors 5 _l and 5 _r are formed at the same time as T4, the material (Al) and the film thickness of the reflectors 5 _l and 5 _r are the same as those of the IDT 4. Similarly, the IDT 4 has some variations depending on the purpose of use.

[0004]

However, the conventional SAW resonator and the SAW device using the same have the following problems, which have been difficult to solve. The characteristics of the SAW resonator greatly differ depending on whether the reflectors 5 _l and 5 _r are not provided. That is, the reflectors 5 _l and 5
If there is no _r , the SAW leaked from the left and right of IDT4
Becomes a loss as it is, and the transmission loss of the SAW resonator increases. Conversely, if there are reflectors 5 _l and 5 _r , the ID
Most of the energy of the SAW leaked to the left and right of T4 is reflected by the reflectors 5 _l and 5 _r and returns to the IDT 4, so that the transmission loss is low. It narrows the range of use. FIG.
(A), (b) is a diagram for explaining a conventional problem, is a characteristic diagram of a SAW resonator having no reflectors 5 _l , 5 _r , FIG. (B) is an insertion loss characteristic diagram. Each characteristic also shows a schematic diagram of the measurement circuit. The impedance characteristics of FIG. 3A and the insertion loss characteristics in the through state of FIG. 3B behave the same as the impedance characteristics and insertion loss characteristics of a general LC resonator, but the reflectors 5 _l and 5 _r Because there is no
The energy of the SAW leaking to the left and right of the DT4 becomes a loss, which increases the transmission loss.

FIGS. 4A and 4B are diagrams for explaining a conventional problem, and are characteristic diagrams of a SAW resonator having reflectors 5 _l and 5 _r , and FIG. The characteristic diagram and the diagram (b) are the insertion loss characteristic diagrams. FIG.
7a in the impedance characteristic of (a) is a spur of the impedance characteristic, and 7b in the insertion loss characteristic of FIG. (B) is a spurious appearing in the insertion loss characteristic. Since there are reflectors 5 _l and 5 _r , FIG.
The transmission loss in the through state shown in (b) is greatly improved as compared with FIG. 3 (b), but spurious 7b occurs in a higher frequency range than the center frequency. On the other hand, when a resonator type SAW filter, which is one of the SAW devices, is configured using a SAW resonator, the presence of spurious components 7a and 7b is generally not preferable. That is, if the spurious components 7a and 7b exist in the frequency band to be used, a ripple or an absorption band occurs in the insertion loss characteristic, which may have a serious adverse effect on the filter characteristic. Conventionally, to suppress this, SAW
There are methods of increasing the film thickness of the IDT 4 of the resonator and the reflectors 5 _l and 5 _r and changing the material to a heavy metal such as Au.
Not only the adverse effect of b but also the problem of adjustment of the center frequency, the problem of transmission loss, etc. are added, so that a technically satisfactory one cannot be obtained. The present invention solves the problems of the prior art and provides a low-loss SAW resonator and a SAW device using the same by suppressing the adverse effect of spurious by devising the design of the reflector and the IDT. The purpose is to:

[0006]

FIG. 5 is an enlarged view of the vicinity of an IDT and a reflector of a SAW resonator for explaining the principle of the present invention. The SAW resonator according to the present invention includes an IDT 14 having a plurality of electrode fingers, and a reflector 15 having a plurality of electrode fingers is provided on both sides of the IDT 14. Usually, the pitch of the IDT 14 and the distance d between the center of the adjacent reflector 15 and the center of the electrode fingers of the IDT 14 are determined by the excitation S
It is designed to be equal to a half wavelength (= λ / 2) of the wavelength λ of the AW. In this case, spurs occur in a certain frequency band, but if the value of the distance d is changed, the frequency band in which the spurious occurs changes accordingly, and each time the distance d increases or decreases by half a wavelength, the spurious returns to the original frequency band. . It has been confirmed theoretically and experimentally that when the distance d is increased from λ / 2, the spurious moves to the lower frequency range, and the distance d
When the amount of increase reaches λ / 2, the spurious returns to the original position. Therefore, it can be said that the value of the distance d is an important factor that determines the frequency band in which spurious occurs. Hereinafter, it is assumed that the following conditions are always satisfied unless otherwise specified. λ / 2 ≦ d <λ On the other hand, one of the left and right reflectors of the SAW resonator (1
Even if only 5) is left, spurious is generated in the conventional frequency band, but the level is found, for example, that the size of the loop in the impedance characteristic is half that of the conventional spurious loop. Therefore, it can be said that spurs generated by reflections of the left and right reflectors are completely independent.

According to the first aspect of the present invention, based on the above principle, the SAW resonator has a SAW resonator.
And a left reflector that is disposed on the left side of the IDT at a distance d _l (where λ / 2 ≦ d _l <λ, λ is a SAW wavelength) and reflects the SAW to the IDT side. , A distance d _r (where λ / 2 ≦ d _{r) on} the right side of the IDT.
<Λ) and a right reflector for reflecting the SAW to the IDT side are formed on the piezoelectric substrate. Then, setting the distance d _l and d _r, a different value may be dispersed in two spurious spurious generated suppressed low predetermined frequency band at and their levels by the reflective action of the left and right reflectors doing. By adopting such a configuration, when a high-frequency signal is input to the input side of the IDT, a high-frequency voltage is generated in the IDT,
The surface of the piezoelectric substrate below the electrode finger is distorted, and a SAW having the same frequency as the input high-frequency signal is excited. Excited S
The AW propagates to the left and right of the IDT and goes to the outside of the IDT, but when reaching the left and right reflectors, reflection occurs there, and the SAW reflected from both sides of the IDT goes to the center of the IDT. . As a result, a SAW standing wave is generated in a region between the two reflectors, and a high-frequency signal is output from the output side of the IDT. At this time, since there is a reflected wave from the reflector, spurious is generated. However, in the invention of claim 1, the distance between the IDT and the left and right reflectors sandwiching the exciting the SAW d _l, since the set of d _r to a different value, the conventional one spur For example, it is distributed to two spurious components having a size about half that of this.

According to a second aspect of the present invention, in the SAW resonator, the IDT for exciting the SAW is divided into a plurality of stages and distances d _lm (where λ / 2 ≦ d
_lm <λ, where λ is the SAW wavelength, m is the number of division stages and m is a positive integer), and the left reflector reflects the SAW to the IDT side; To the distance d _rn (where λ / 2 ≦ d _rn <λ, n
Is the number of division stages and is a positive integer)
The right reflector for reflecting the AW to the IDT side is formed on the piezoelectric substrate. Then, the distances d _lm and d _rn
Are set to different values that can disperse the spurious generated by the reflection action of the left and right reflectors into m + n spurs in a predetermined frequency band and at a low level. By adopting such a configuration, when a high-frequency signal is input to the input side of the IDT, the surface of the piezoelectric substrate under the IDT is distorted, and a SAW having the same frequency as the input high-frequency signal is excited. Excited S
The AW is reflected by the left and right reflectors, a SAW standing wave is generated in a region between the two reflectors, and a high-frequency signal is output from the output side of the IDT. At this time, since there are reflected waves from the left and right reflectors, spurious is generated. However, in the invention of claim 2, each of the left and right reflectors is divided into a plurality of stages as necessary, and the distances d _lm and d _rn between each stage and the IDT are set to various values. Is distributed to a small number of spurious components corresponding to the number of divided stages of the left and right reflectors.

According to a third aspect of the present invention, a SAW device such as a filter is configured using the SAW resonator according to the first or second aspect. In the SAW device having such a configuration, when an input signal is input, a predetermined band of the input signal is filtered and output. At this time, spurious components generated in the SAW resonator constituting the SAW device are dispersed into two or more weak spurious components, and these spurious components are led to unnecessary frequency bands.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment (1) The configuration, (2) operation, and (3) advantages of a SAW resonator according to a first embodiment of the present invention will be described. (1) Configuration FIG. 1 is a plan view of a SAW resonator according to a first embodiment of the present invention. This SAW resonator has a piezoelectric substrate 11, as in the conventional FIG. 2, and on this piezoelectric substrate 11, an input terminal 12, an output terminal 13, an excitation IDT 14 having a plurality of electrode fingers, and a SAW and reflectors 15 _l and right reflectors 15 _r of the left having a plurality of electrode fingers for reflecting the IDT 14, are formed and the bonding pad 16 of the ground. The input terminal 12 and the output terminal 13
Although connected to the DT 14, the input terminal 12 may be an output terminal and the output terminal 13 may be an input terminal due to its structure. I
DT14, left reflectors 15 _l, and right reflectors 15
_r is surrounded by a bonding pad 16, and the IDT 14, the reflectors 15 _l and 15 _r, and the bonding pad 16 are formed of a thin film of, for example, Al having a thickness of 4000 ° or more. The configuration of the SWA resonator of this embodiment is basically the same as the conventional one, but differs from the conventional one in that the distance d between the left reflector 15 _l and the IDT 14 is d.
_l and the distance d _r between the right reflector 15 _r and the IDT 14 are set to different values. As described above, the spurs generated by the reflections of the reflectors 15 _l and 15 _r are independent of each other.
Let _l be λ / 2 + λ / 8 and set the right-hand distance _dr to the same distance as in the prior art.

(2) Operation For example, when a high frequency signal of several MHz or more is input to the input terminal 12 (or the output terminal 13), the input terminal 12
A high frequency voltage is applied to the electrode fingers of the IDT 14 that are electrically connected to the IDT 14. When a high-frequency voltage is applied, the adjacent output terminals 13
(Or input terminal 12) IDT 14 electrically connected to
Although a high-frequency voltage is inductively generated in the electrode fingers of the above, a phase difference is caused, so that a potential difference occurs between the input terminal 12 and the output terminal 13. As a result, the surface of the piezoelectric substrate 11 below the electrode finger of the IDT 14 is distorted, and a SAW having the same frequency as the input high-frequency signal is excited. Excited SA
W propagates to the left and right of the IDT 14 and goes to the outside of the IDT 14, but when it reaches the left and right reflectors 15 _l and 15 _r , reflection occurs here, and the SAW reflected from both sides of the IDT 14 becomes To the center of As a result, SA in the region between the two reflectors 15 _l and 15 _r
A standing wave of W is generated, and the coupling between the electrode finger on the input terminal 12 side and the electrode finger on the output terminal 13 side is further strengthened.
3 outputs a high-frequency signal in a certain band. here,
Since there are reflected waves from the reflectors 15 _l and 15 _r , spurious generation is inevitable, but there are the following advantages.

(3) Advantages For example, if the distances d _l and _dr are equal, the left reflector 1
Since the spur of 5 _{l and} the spur of the right reflector 15 _r occur in the same frequency band, their levels are added to one large spur. However, since the left side of the distance d _l and the right distance d _r is different in this embodiment,
The frequency band in which the spurious of the left reflector 15 _{l and} the spurious of the right reflector 15 _r occur is different.
The levels are not added and become two independent spurs. This state is shown in FIGS. 6 (a) and 6 (b). FIG.
(A), (b) is a characteristic diagram of the SAW resonator of FIG.
FIG. 7A is an impedance characteristic diagram, and FIG. 7B is an insertion loss characteristic diagram. 17 _al and 17 _{ar in} FIG.
Is a spurious appearing in the impedance characteristic.
Also, 17 _bl and 17 _br in FIG. 6B are spurious components appearing in the insertion loss characteristics. Reflector 15 as in FIG.
One large spurious conventionally generated in the arrangement of _l and 15 _r is distributed to two small spurious 17 _al , 17 _ar , 17 _bl and 17 _br as shown in FIGS. 6 (a) and 6 (b). . By properly adjusting the distances d _l and _dr as described above, the frequency band in which the spurious components 17 _al , 17 _ar , 17 _bl , and 17 _br occur can be derived to unnecessary frequency bands. 17 _al , 17 _ar , 1
The levels of 7 _bl and 17 _br can be kept low.

Second Embodiment The (1) configuration, (2) operation, and (3) advantages of a SAW resonator according to a second embodiment of the present invention will be described. (1) Configuration FIG. 7 is a plan view of a SAW resonator according to a second embodiment of the present invention. Elements common to those in FIG. 1 according to the first embodiment are denoted by the same reference numerals. Have been. The SAW resonator according to the second embodiment is basically the same as the first embodiment. However, the first embodiment is further developed by adding a reflector 15 _l on the left side of the IDT 14 in FIG. Split (for example,
Two equally divided reflectors 15 _l1 , 15 _l2 )
The reflector 15 _r on the right side is divided (for example, two reflectors 15 _r1 and 15 _r2 divided into two equal parts), and the distance between each part and the IDT 14 is set to a different value as follows. The distance between the left half of the reflectors 15 _l1 , 15 _l2 and the IDT 14 is d _l1 , d _l2 , and the right half of the reflector 1
The 5 _r1, 15 the distance between _r2 and IDT14 and d _r1, d _r2. Then, for example, when the distance d _l1 is λ / 2 + (2/8) λ,
The distance _{d l2 λ / 2 + (3/8} ) λ, is set respectively the distance d _r1 conventional same lambda / 2, and the distance d _r2 in λ / 2 + λ / 8.

(2) Operation The operation principle of the SAW resonator according to the present embodiment is substantially the same as the operation principle according to the first embodiment, so that the description will be simplified. When a high-frequency signal is input to the input terminal 12, the SAW is excited by the IDT 14, and the excited SAW propagates to the left and right of the IDT 14, and the distances d _l1 , d _l2,.
d _r1, d _r2 is different four reflectors 15 _l1, 15 _l2, 1
The light is reflected by 5 _r1 and 15 _r2 and returns to the IDT 14. As a result, a standing wave is generated similarly to the SAW resonator having the conventional reflector, and a signal in the pass band is strongly output from the output terminal 13. Since there are reflectors 15 _l1 , 15 _l2 , 15 _r1 and 15 _r2, there is almost no leakage SAW energy, and the output signal level is the same as that of the conventional one, but has the following advantages.

(3) Advantage In this embodiment, the SAW leaked from both sides of the IDT 14
The energy is calculated for each reflector 15 _l1 , 15 _l2 , 1
The light is reflected by 5 _r1 , 15 _r2 and returns to the IDT 14, and the respective reflectors 15 _l1 , 15 _l2 , 15 _r1 , 15 _r2 and the IDT 14 are reflected.
Since the distances _d.sub.11 , _d.sub.l2 , _d.sub.r1 , and _d.sub.r2 are different from each other, 4
Two reflected waves occur. ID of leaked SAW energy
Returning to T14, the loss of S
The AW resonator is the same as the conventional SAW resonator.
Also, since each reflected wave generates one spurious,
There are four spurious characteristics in the characteristics of the SAW resonator of the present embodiment. 8A and 8B show characteristic diagrams of the SAW resonator shown in FIG. 7, wherein FIG. 8A is an impedance characteristic diagram, and FIG. 8B is an insertion loss characteristic diagram. FIG.
(A) in _{18 al1, 18 al2, 18 ar1} , 18
_ar2 is a spurious due to the impedance characteristics of the reflectors 15 _l1 , 15 _l2 , 15 _r1 and 15 _r2 . FIG.
18 _bl1 , 18 _bl2 , 18 _br1 , 18 in (b)
_br2 is the spurious of the insertion loss characteristic due to the reflectors 15 _l1 , 15 _l2 , 15 _r1 and 15 _r2 . The frequency band of the spurious 18 _ar1 or 18 _br1 by the reflector 15 _r1 is the frequency band of the spurious of the conventional SAW resonator, and the spurious 18 _ar2 , 1 by the reflectors 15 _r2 , 15 _l1 , and 15 _l2.
8 _al1 , 18 _al2 or 18 _br2 , 18 _bl1 , 18 _bl2
Move to a lower frequency band than the conventional spurious frequency band. Thus, the reflectors 15 _l1 , 15 _l2 , 15
_{When r1} and 15 _r2 are divided, spurious 18 _al1 and 18
_al2 , 18 _ar1 , 18 _ar2 , 18 _bl1 , 18 _bl2 , 18
_br1 and 18 _br2 are also dispersed, the number of which is
The number is the same as that of 5 _l1 , 15 _l2 , 15 _r1 , and 15 _r2 , but the size is reduced accordingly.

Third Embodiment A conventional SAW resonator and the SAW resonator of the above embodiment are:
Similar to a crystal resonator or a ceramic resonator, it can be represented by a lumped constant equivalent circuit diagram as shown in FIG. This equivalent circuit includes an inductor L and a capacitor c connected in series.
₁ and a resistor r, and a capacitor C ₀ connected in parallel with the resistor r.
It is composed of Such a SAW resonator has a resonance frequency and an anti-resonance frequency.
Since the theory of configuring a bandpass filter as a W device has been known for a long time, a detailed description thereof will be omitted, but the configuration of the bandpass filter using the SAW resonator of FIG. An example is shown in FIG. FIG. 10 is a configuration diagram of a four-stage ladder filter according to the third embodiment of the present invention. The four-stage ladder filter is the SAW of FIG.
And two series arm resonators 2
2, and three parallel arm resonators 21, 23, 25. FIGS. 11A and 11B show a conventional SAW.
10A and 10B show characteristic diagrams of a ladder-type filter constituted by using a resonator and the ladder-type filter of FIG. 10, and FIG. 10A shows an insertion loss characteristic diagram of a ladder-type filter constituted by using a conventional SAW resonator; 10 (b) is an insertion loss characteristic diagram of the ladder type filter of FIG.

Conventionally, when a ladder filter is formed using a SAW resonator, it is necessary to adjust the resonance frequency of the series arm resonator and the anti-resonance frequency of the parallel arm resonator so as to match as much as possible. For example, if such a condition is satisfied, the insertion loss characteristic of the ladder filter becomes a characteristic as shown in FIG. In FIG. 11A, 31 indicates a pass band, and 32 indicates spurious. In the conventional ladder-type filter, the frequency band having a low insertion loss is the pass band 31, and the other band is the forbidden band. Further, when a ladder filter is formed using a SAW resonator having a conventional reflector, spurious components 32 are also generated. As is clear from FIG. 11A, since the series arm SAW resonator has one large spurious, the ladder filter also has one large spurious. On the other hand, if a ladder-type filter as shown in FIG. 10 is formed by using the SAW resonator of the first embodiment, the insertion loss characteristic of FIG.
1 (b) is obtained. In this ladder-type filter, since the series arm resonators 22 and 24 have two small spurious components, the ladder-type filter also includes two small spurious components 41 (here, the two spurious components are combined into one name). Will have. By using such a SAW resonator of the first embodiment, one spurious component 32 having a strong adverse effect of a ladder filter formed of a conventional SAW resonator can be replaced with two spurious components 4 having a weak adverse effect.
1 and by adjusting the arrangement of the reflectors 15 _l , 15 _r , each spurious can be led to an unnecessary frequency band.

Fourth Embodiment In a fourth embodiment of the present invention, a ladder filter as shown in FIG. 10 is formed by using the SAW resonator shown in FIG. 7 showing the second embodiment. FIG. 12 is an insertion loss characteristic diagram of a ladder-type filter according to the fourth embodiment of the present invention, which is configured using the SAW resonator shown in FIG. 7 showing the second embodiment.
As shown in FIG. 12, the series arm resonator (22, 2 in FIG. 10)
4) have four small spurious components, the ladder-type filter of this embodiment also has four small spurious components 51 (here, the four spurious components are combined into one name). Further, the size of each spurious component 51 is 1/4 of that of the ladder filter using the conventional SAW resonator, and the size of the ladder filter of the third embodiment using the SAW resonator of the first embodiment is further reduced. 1/2
become. Thus, when the spurious 51 is dispersed,
The adverse effect of the spurious is further reduced, and the filter characteristics are further improved.

Note that the present invention is not limited to the above embodiment, and various modifications are possible. For example, in the above embodiment, the distances d _l and dr between the left and right reflectors 15 _l and 15 _r and the IDT 14 are set to different values, or the left and right reflectors 1 _l and 15 _r are different.
5 _l1 , 15 _l2 , 15 _r1 , 15 _r2 are each divided into two equal parts,
The obtained four reflectors 15 _l1 , 15 _l2 , 15 _r1 , 15 _r2
From the IDT 14 are distances d _l1 , d _l2 ,
Although they are arranged at _dr1 and _dr2 , the way of dividing and arranging these reflectors is not limited to the illustrated one, and various modifications are possible. Further, the SAW device configured using these SAW resonators is not limited to the four-stage ladder filter as shown in FIG. 10, but may be a device having another configuration.

[0020]

As has been detailed description, according to the present invention, According to the present invention, since the set IDT and different values the distance d _l and d _r of the reflector of the left and right sandwiching the exciting the SAW The spurious of the left reflector and the frequency of the spurious of the right reflector are different from each other, so that one conventional spurious can be dispersed into two spurs, for example, about half as large as this. Therefore, it is possible to derive a frequency band in which spurious is generated into an unnecessary frequency band, and it is possible to keep the level of spurious low. According to the second aspect of the invention, each of the left and right reflectors is divided into a plurality of stages as necessary, and the distances d _lm and d _rn between each stage and the IDT are set to various values. Can be dispersed into a small number of spurious components corresponding to the number of divisions of the left and right reflectors. Therefore, it is possible to derive a frequency band in which spurious is generated into an unnecessary frequency band, and it is possible to keep the level of spurious low. According to the invention of claim 3, claim 1
Alternatively, since a SAW device such as a filter is configured by using the two SAW resonators, spurious components are dispersed, adverse effects of spurious components are reduced, and filter characteristics and the like can be improved.

[Brief description of the drawings]

FIG. 1 is a plan view of a SAW resonator according to a first embodiment of the present invention.

FIG. 2 is a plan view of a conventional SAW resonator.

FIG. 3 is a characteristic diagram of a SAW resonator having no reflector.

FIG. 4 is a characteristic diagram of a SAW resonator having a reflector.

FIG. 5 is an enlarged view of the vicinity of an IDT and a reflector of a SAW resonator for explaining the principle of the present invention.

FIG. 6 is a characteristic diagram of the SAW resonator of FIG.

FIG. 7 is a plan view of a SAW resonator according to a second embodiment of the present invention.

FIG. 8 is a characteristic diagram of the SAW resonator shown in FIG. 7;

FIG. 9 is a lumped constant equivalent circuit diagram of a SAW resonator.

FIG. 10 is a configuration diagram of a four-stage ladder filter showing a third embodiment of the present invention.

FIG. 11 is a characteristic diagram of the conventional and ladder-type filters of FIG. 10;

FIG. 12 is an insertion loss characteristic diagram of a ladder filter according to a fourth embodiment of the present invention configured using the SAW resonator of FIG. 7;

[Explanation of symbols]

_{DESCRIPTION OF SYMBOLS} 11 Piezoelectric substrate 12 Input terminal 13 Output terminal 14 IDT 15 Reflector 15 _l , 15 _l1 , 15 _l2 Left reflector 15 _r , 15 _r1 , 15 _r2 Right reflector 21, 23, 25 Parallel arm resonator 22, 24 Series arm Resonator

Claims (3)

[Claims] An interdigital transducer for exciting a surface acoustic wave, and a distance d _l (where λ / 2)
≦ d _l <λ, λ is disposed surface acoustic wavelength) separated by a left reflector for reflecting the surface acoustic wave to said transducer side, the right a distance d _r of the transducer (However, lambda / 2
≦ d _r <λ), and a right reflector for reflecting the surface acoustic wave to the transducer side is formed on a piezoelectric substrate, and the distances d _l and _dr are defined by the left and right sides. A surface acoustic wave resonator characterized in that the spurious generated by the reflecting action of the reflector is set to a different value that can be dispersed in two spurious components whose level is kept low in a predetermined frequency band. 2. An interdigital transducer that excites a surface acoustic wave, and a distance d _lm (where λ / 2 ≦ d _lm <λ, where λ is a surface acoustic wave wavelength, m is the number of division stages and is arranged as a positive integer. A left reflector for reflecting the surface acoustic wave to the transducer side, a plurality of stages and a distance d _rn (provided on the right side of the transducer, respectively) , Λ / 2 ≦ d _rn <λ, where n is the number of division stages and n is a positive integer), and a right-side reflector that reflects the surface acoustic wave to the transducer side includes:
All of the distances d _lm and d _rn formed on the piezoelectric substrate are converted into m + n spurs in a predetermined frequency band and the level of the spurious generated by the reflection action of the left and right reflectors is reduced. A surface acoustic wave resonator characterized by being set to different values that can be dispersed. 3. A surface acoustic wave device comprising the surface acoustic wave resonator according to claim 1.