JP2007306493A - Surface acoustic wave filter apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave filter apparatus of a transversal type capable of promoting downsizing without incurring deterioration in the filter characteristic. <P>SOLUTION: The surface acoustic wave filter apparatus 1 is provided with: an input side IDT 3 and an output side IDT 4 each comprising a tilt type IDT electrode which are located on a first principal side 2c of a piezoelectric substrate 2 and apart from each other in a surface acoustic wave propagation direction; a first sound absorbent member 7 located to a region at a side of a first end face 2a at the outside of the input side IDT 3 in the surface acoustic wave propagation direction; and a second sound absorbent member 8 located to a region at a side of a second end face 2b at the outside of the output side IDT 4 in the surface acoustic wave propagation direction, wherein the first and second sound absorbent members 7, 8 are respectively provided to reach parts of the input side IDT 3 and the output side IDT 4 from outside ends of the input side IDT 3 and the output side IDT 4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a transversal surface acoustic wave filter device, and more particularly to a surface acoustic wave filter device in which a sound absorbing material is provided on a piezoelectric substrate and is configured using an inclined IDT. .

  Conventionally, as a transversal surface acoustic wave filter device, an interdigital electrode (IDT electrode) is configured such that the electrode finger pitch is different between one side and the other side in a direction orthogonal to the surface wave propagation direction. A surface acoustic wave filter device using a type, that is, a slant type IDT electrode has been proposed.

  For example, Patent Document 1 below discloses a transversal surface acoustic wave filter device 101 shown in FIG. In the transversal surface acoustic wave filter device 101, an input-side IDT electrode 103 and an output-side IDT electrode 104 are arranged on a piezoelectric substrate 102 with a predetermined distance in the surface acoustic wave propagation direction. As shown in the figure, the IDT electrodes 103 and 104 are composed of tilted IDT electrodes in which the electrode finger pitch changes in a direction orthogonal to the surface wave propagation direction.

  Since the input-side IDT electrodes 103 and 104 are formed of inclined IDT electrodes, the input-side IDT electrode 103 and the output are provided on one side and the other side in the direction orthogonal to the surface acoustic wave propagation direction in the surface acoustic wave propagation path. The pitch of the electrode fingers of the side IDT electrode 104 is different. Therefore, the frequency response of each track is continuously changed, and it is said that a surface acoustic wave filter device advantageous for widening the band can be provided.

On the other hand, a shield electrode 105 is disposed between the input-side IDT electrodes 103 and 104. A sound absorbing material 106 is disposed in a portion opposite to the surface wave propagation portion of the input-side IDT electrode 103, that is, in an outer region, and is a region opposite to the surface wave propagation portion of the output-side IDT electrode 104. The sound-absorbing material 107 is disposed on the side. The sound absorbing materials 106 and 107 are made of a sound absorbing material such as a material having rubber elasticity. By providing the sound absorbing materials 106 and 107, surface waves leaking from the IDT electrodes 103 and 104 to the outside in the surface wave propagation direction are absorbed, and deterioration of characteristics due to reflected waves can be prevented.
JP-A-6-90132

  As described above, in the surface acoustic wave filter device 101 using the tilted IDT electrode, since the frequency characteristics of each track are continuously changed, a broadband filter characteristic can be easily obtained.

  On the other hand, the surface acoustic wave filter device 101 is strongly required to be miniaturized in the same manner as other electronic components. In order to promote downsizing, it is desirable to reduce the dimension along the surface wave propagation direction in the region where the sound absorbing materials 106 and 107 are applied. However, if the dimensions of the sound absorbing materials 106 and 107 along the surface wave propagation direction are reduced, the sound absorbing effect becomes insufficient. For this reason, the influence of the leakage wave reflected on the end face of the piezoelectric substrate 102 cannot be ignored, and ripples or the like are generated in the pass band or in the vicinity of the pass band, which may deteriorate the filter characteristics.

  An object of the present invention is a transversal surface acoustic wave filter device using an inclined IDT electrode in view of the above-described state of the prior art, and further miniaturization is achieved without causing deterioration of characteristics. It is an object of the present invention to provide a surface acoustic wave filter device which can be used.

  According to the present invention, on the first main surface of the piezoelectric substrate, the piezoelectric substrate having the first and second end surfaces facing each other and the first and second main surfaces facing each other, The input side IDT disposed on the first end surface side, the output side IDT disposed on the second end surface side, and the first of the piezoelectric substrates are provided to be separated in a direction connecting the second end surfaces. On the first principal surface of the piezoelectric substrate, and on the first principal surface of the piezoelectric substrate, the output is provided on the first principal surface of the piezoelectric substrate. A second sound absorbing material provided in a region on the second end face side which is a region outside the surface wave propagation direction of the side IDT, and the input side IDT and the output side IDT are perpendicular to the surface acoustic wave propagation direction. Electrode finger pitch on the first end side in the direction, and the second end side opposite to the first end side In the transversal surface acoustic wave filter device, which is an inclined IDT having a different electrode finger pitch, the first and second sound absorbing materials are respectively propagated by the surface acoustic wave propagation of the input side IDT and the output side IDT. A surface acoustic wave filter device is provided that is provided so as to extend from a direction outer side end part to the input side IDT and a part of the output side IDT.

  In a specific aspect of the surface acoustic wave filter device according to the present invention, a region where the first sound absorbing material covers a part of the input side IDT is an outer end portion in the surface wave propagation direction of the input side IDT. In the vicinity, the first sound absorbing material covers the first end on the side where the electrode finger pitch is relatively wide and does not reach the second end where the electrode finger pitch is relatively narrow. The second sound absorbing material covers the input side IDT, the second sound absorbing material covers the first end portion side where the electrode finger pitch of the output side IDT is relatively wide, and the electrode finger pitch is relatively narrow. A part of the output IDT is covered so as not to reach the end of the output side. In this case, the input side IDT and the output side are arranged so that the first and second sound absorbing materials do not reach the second end portion side where the electrode finger pitch is relatively narrow in the input side IDT and the output side IDT. Since part of the IDT is covered, not only can the downsizing be promoted, but also the filter characteristics are likely to be affected, that is, the second end side where the electrode finger pitch is relatively narrow is made of a sound absorbing material. Since it is not covered, the characteristic deterioration is less likely to occur.

  In the present invention, preferably, a dielectric film provided on the piezoelectric substrate is further provided so as to cover the input-side IDT and the output-side IDT. In this case, by applying the dielectric film, a frequency temperature coefficient is provided. It is possible to improve the temperature characteristics such as, and to protect the portion where the IDT is formed.

  In another specific aspect of the surface acoustic wave filter device according to the present invention, the dielectric film is formed with first and second notches, and the first and second notches are formed on the input-side IDT. The first and second sound absorbing materials are disposed in the first and second cutouts, and reach the region outside the portion in which the output IDT is provided in the surface wave propagation direction. Therefore, the first and second sound absorbing materials and the piezoelectric substrate are in direct contact with each other in the first and second cutouts of the dielectric film. In this case, since the first and second sound absorbing materials are in direct contact with the piezoelectric substrate, the damping effect and sound absorbing effect by the first and second sound absorbing materials are further enhanced.

  In the surface acoustic wave filter device according to the present invention, it is preferable that the first and second sound absorbing materials have a surface acoustic wave attenuation effect of 0.8 dB / λ to 1.6 dB / λ (where λ is a surface of an elastic surface). (Wave wavelength). In this case, unnecessary reflected waves can be effectively attenuated by the first and second sound absorbing materials, and thereby the deterioration of the characteristics of the surface acoustic wave filter device can be more effectively suppressed. it can.

  In still another specific aspect of the surface acoustic wave filter device according to the present invention, the first and second sound absorbing materials are second on the side where the electrode finger pitch between the input side IDT and the output side IDT is relatively narrow. It is provided so that it may reach the edge part. Thus, the first and second sound absorbing materials may be provided so as to reach the second end portion on the side where the electrode finger pitch of the input side IDT and the output side IDT is relatively narrow.

  In still another specific aspect of the surface acoustic wave filter device according to the present invention, the input-side IDT and the output-side IDT are configured by regular inclined IDTs. In other words, since it is not necessary to perform intersection width weighting or the like, the IDT design can be simplified.

  In the surface acoustic wave filter device according to the present invention, in the transversal surface acoustic wave filter device having an input side IDT and an output side IDT configured by an inclined IDT, the first and second sound absorbing materials are: Since the input side IDT and the output side IDT are provided so as to cover a part of the input side IDT and the output side IDT from the outer end portions in the surface acoustic wave propagation direction, the surface acoustic waves of the first and second sound absorbing materials are provided. By setting the dimension along the propagation direction to a certain size, it is possible to suppress deterioration of characteristics due to reflected waves. Further, the surface acoustic wave filter device can be reduced in size.

  That is, since the first and second sound absorbing materials are provided so as to extend from the outer end portions in the surface acoustic wave propagation direction of the input side IDT and the output side IDT to a part of the inside, the surface acoustic wave propagation of the sound absorbing material. The dimension along the direction can be made large enough to obtain a sound absorption effect. Even in that case, since a part of the sound absorbing material covers a part of the input side IDT and the output side IDT, the dimension along the surface wave propagation direction of the piezoelectric substrate can be reduced, and the size can be reduced. It is possible to proceed.

  Therefore, according to the present invention, it is possible to reduce the size of the transversal surface acoustic wave filter device using the inclined IDT electrode without causing deterioration of characteristics.

  Hereinafter, the present invention will be clarified by describing specific embodiments of the present invention with reference to the drawings.

  FIG. 1A is a plan view of a surface acoustic wave filter device according to an embodiment of the present invention, and FIGS. 1B and 1C show an input side IDT and an output side IDT of the surface acoustic wave filter device. It is each schematic top view shown.

  The surface acoustic wave filter device 1 has a rectangular piezoelectric substrate 2. The piezoelectric substrate 2 has first and second end surfaces 2a and 2b facing each other, 2c as a first main surface, and a lower surface as a second main surface.

The piezoelectric substrate 2 can be formed of, for example, a piezoelectric single crystal such as LiTaO ₃ or a piezoelectric ceramic such as PZT.

In the present embodiment, the piezoelectric substrate 2 is made of LiTaO _{3 that} propagates in a Y-cut 112 ° X direction, and has a negative frequency temperature coefficient TCF.

  On the upper surface 2 c of the piezoelectric substrate 2, the input side IDT 3 and the output side IDT 4 are arranged at a predetermined distance in the surface acoustic wave propagation direction. IDT3 and IDT4 are both inclined IDT electrodes. That is, as shown in FIG. 1B, the input-side IDT 3 is provided with a plurality of electrode fingers 3a and 3b inclined from a direction orthogonal to the surface acoustic wave propagation direction. One end of the plurality of electrode fingers 3a is connected to a bus bar 3c connected to one potential. The electrode finger 3a is composed of a split-type electrode finger in which two electrode fingers are a set. One end of the plurality of electrode fingers 3b is connected to a bus bar 3d connected to the other potential. The electrode finger 3b is also a split electrode finger in which two electrode fingers are made into one set.

  In the present invention, in the tilted IDT electrode, the electrode finger does not need to be a split type, and may be constituted by a single electrode composed of one electrode finger.

  When an AC signal is applied to the input side IDT 3, surface waves are excited in a region where a plurality of electrode fingers 3 a and a plurality of electrode fingers 3 b overlap in the surface wave propagation direction, that is, a crossing region. In this case, as shown in the drawing, the plurality of electrode fingers 3a and 3b are inclined from the direction orthogonal to the surface wave propagation direction, so the electrode finger pitch on the first end 3e side on one side of the intersecting region. And the electrode finger pitch on the other second end 3f side is different. That is, in the crossing region, the first end 3e on one side in the direction perpendicular to the surface acoustic wave propagation direction, that is, the second end 3f side on the bus bar 3c side, from the electrode finger pitch on the bus bar 3d side end. The electrode finger pitch changes so that the electrode finger pitch becomes smaller as it goes to.

  Also on the output side IDT 4, the plurality of electrode fingers 4 a and 4 b are inclined with respect to a direction orthogonal to the surface wave propagation direction, and are similarly inclined IDT electrodes.

  In the present embodiment, the input side IDT 3 and the output side IDT 4 are made of Al. However, it may be formed of a metal or alloy other than Al, and the input-side IDT 3 and the output-side IDT 4 may be configured by a laminated film in which a plurality of metal films are laminated.

  A shield electrode 5 is formed between the input side IDT 3 and the output side IDT 4. The shield electrode 5 is extended in a direction orthogonal to the surface wave propagation direction in the surface wave propagation path between the IDTs 3 and 4. That is, the shield electrode 5 is formed so as to cross the surface wave propagation path. The shield electrode 5 is not necessarily provided. In the present embodiment, the shield electrode 5 is made of Al, like the input side IDTs 3 and 4.

  By forming the shield electrode 5 from the same material as the input side IDT 3 and the output side IDT 4, the manufacturing process can be simplified. But the shield electrode 5 may be comprised with the material different from input side IDT3 and output side IDT4.

  In the present embodiment, similarly to the conventional surface acoustic wave filter device 101, since the input side IDT3 and the output side IDT4 are formed of inclined IDT electrodes, the frequency response of each track is continuously changed, and a wideband frequency is obtained. Characteristics can be obtained.

In addition, since LiTaO ₃ has a negative frequency temperature coefficient TCF as described above, in this embodiment, the dielectric film 6 made of SiO ₂ having the positive frequency temperature coefficient TCF is used as the IDTs 3 and 4 and the surface wave propagation. It is formed to cover the road. Therefore, a change in filter characteristics due to a temperature change is suppressed.

  The dielectric film 6 has first and second notches 6a and 6b.

  In the present embodiment, the first and second sound absorbing materials 7 and 8 are formed in the region including the notches 6a and 6b. In the present embodiment, the first and second sound absorbing materials 7 and 8 are made of a photosensitive polyimide resin. That is, after the notches 6a and 6b are formed, a photosensitive polyimide resin is applied to the entire surface, and then the first and second sound absorbing materials made of the photosensitive polyimide resin including the notches 6a and 6b by photolithography. 7,8 are provided. Therefore, as shown in FIG. 2, the first sound absorbing material 7 is provided including the notch 6 a, and therefore there is a portion that is in direct contact with the upper surface 2 c of the piezoelectric substrate 2. Since the second sound absorbing material 8 is also formed including the notch 6b, there is a portion that is in direct contact with the upper surface 2c of the piezoelectric substrate 2.

  That is, the first and second sound absorbing materials 7 and 8 are made of photosensitive polyimide resin, absorb sound from the surface waves leaking outward from the input side IDT 3 and the output side IDT 4 in the surface wave propagation direction, and from the end faces 2a and 2b. It is provided to reduce the influence of the reflected wave. In this case, the first and second sound absorbing materials 7 and 8 not only have a sound absorbing action due to the properties of the materials themselves, but the first and second sound absorbing materials 7 and 8 are directly on the upper surface of the piezoelectric substrate 2. Since the added portion is included, the damping effect by the sound absorbing materials 7 and 8 can be sufficiently obtained, and thereby, the influence of the reflected wave can be more effectively suppressed.

  Therefore, in this embodiment, even when the dimension A along the surface acoustic wave propagation direction of the first and second sound absorbing materials 7 and 8 is reduced, a sufficient sound absorbing effect can be obtained and the characteristics are deteriorated. It is hard to produce.

  In addition, in the present embodiment, the first and second sound absorbing effects 7 and 8 are part of the input side IDT 3 and the output side IDT 4 so as to reach the inside from the outer end portions in the surface wave propagation direction of the IDTs 3 and 4. It is provided so as to cover. That is, the inner ends of the first and second sound absorbing materials 7 and 8 are inside the surface wave propagation direction outer end of the input side IDT 3, and the inner ends of the second sound absorbing material 8 are The output side IDT 4 is located on the inner side of the outer end portion in the surface wave propagation direction. Therefore, when the dimension along the surface wave propagation direction of the first and second sound absorbing materials 7 and 8 is constant, compared to the configuration in which the sound absorbing material is provided outside the outer end portion in the surface wave propagation direction of the IDTs 3 and 4. Thus, the dimension along the surface wave propagation direction of the surface acoustic wave filter device 1 can be reduced. That is, the surface acoustic wave filter device 1 can be downsized.

  Therefore, according to the present embodiment, it is possible to reduce the size of the transversal surface acoustic wave filter device 1 without causing deterioration of characteristics.

  In particular, in the present embodiment, the first and second sound absorbing materials 7 and 8 are located on the inner side with respect to the outer ends in the surface wave propagation direction of the input side IDT 3 and the output side IDT 4, as shown in FIG. The second end portions 3f and 4f are not reached. That is, it covers the first end 3e on the one side in the direction perpendicular to the surface wave propagation direction of the input side IDT 3 and has a relatively large electrode finger pitch, but the second side on the opposite side. The end 3f is not covered with the sound absorbing material 7. Similarly, in the output side IDT 4, the first end 4 e is covered with the second sound absorbing material 8 in the direction orthogonal to the surface wave propagation direction, but the electrode finger pitch on the side where the electrode finger pitch is relatively small. The second end 4 f is not covered with the second sound absorbing material 8.

  Since the electrode finger pitch is relatively small on the second end portions 3f and 4f side, characteristics are likely to fluctuate due to the damping effect when covered with the sound absorbing materials 7 and 8. On the other hand, in this embodiment, since the 2nd edge part 3f, 4f side is not covered with the sound-absorbing materials 7 and 8, degradation of a characteristic can be suppressed further, advancing size reduction.

  However, in the present invention, the first and second sound absorbing materials 7 and 8 may be provided so as to cover the second end portions 3f and 4f. In that case, the damping effect is increased and the characteristics may be deteriorated, but further miniaturization can be achieved.

  According to the present embodiment, the fact that the size reduction can be promoted without causing deterioration of the filter characteristics will be described using a specific experimental example.

As the surface acoustic wave filter device 1 of the above embodiment, the IDTs 3 and 4 and the shield electrode 5 are formed on the piezoelectric substrate with Al having a thickness of 260 nm, and the dielectric film 6 is a SiO ₂ film having a thickness of 1.1 μm. Formed. Note that the input side IDT 3 and the output side IDT 4 have the following specifications.

Crossing width: 630 μm
Number of electrode fingers: 117.5 pairs for input side IDT3, 89.5 pairs for output side IDT4 Weighting: Normal IDT without electrode pitch The electrode finger pitch of IDTs 3 and 4 is relatively small The pitch at the end on the side is 12.43 μm, the electrode finger pitch at the end on the relatively large electrode finger pitch is 13.20 μm, the wavelength based on the electrode finger pitch at the center is 12.82 μm, and the center frequency is 259. A surface acoustic wave filter device 1 of .861 MHz was produced.

  In addition, about the 1st, 2nd sound-absorbing materials 7 and 8, photosensitive polyimide resin was formed by the photolithographic method so that it might become thickness of 13 micrometers.

  In addition, the said 1st, 2nd sound-absorbing materials 7 and 8 may be formed by the screen printing method other than the method of providing by the photolithography method.

In this case, the SiO ₂ film was first formed so as to cover the entire upper surface of the piezoelectric substrate 2 and then etched using an etchant or the like to remove a part thereof. That is, in FIG. 1 (a), the SiO ₂ film in the portion of the dimension C (20 μm) from the end face 2a was removed by etching. At the same time, the SiO ₂ film of the dimension D was etched so that the notch 6a was formed. Etching was similarly performed on the side where the notch 6b was provided. And the 1st, 2nd sound-absorbing material 7 and 8 was provided so that the area | region which reaches in the notches 6a and 6b and the edge of the said end surfaces 2a and 2b and the upper surface 2c may be included. In this case, the dimension D was variously changed. However, the dimension A along the surface wave propagation direction of the sound absorbing materials 7 and 8 was constant at 240 μm. FIG. 3 shows the relationship between the dimension D of the various surface acoustic wave filter devices 1 thus obtained and the ripples in the passband.

  As is clear from FIG. 3, the damping effect increases as the dimension D increases despite the fact that the dimension A along the surface wave propagation direction of the region damped by the sound absorbing materials 7 and 8 is the same. It can be seen that the in-band ripple is reduced. In particular, it is understood that the dimension D is preferably 100 μm, that is, about 8λ or more, in order to make the ripple in the passband 1.5 dB or less.

  The upper limit of the dimension D is, of course, the distance between the outer end of the input side IDT 3 in the surface wave propagation direction and the end surface 2a.

  Next, various types of surface acoustic wave filter devices were manufactured by changing the dimension A corresponding to the above-described damping width, except that the dimension D in FIG. The filter characteristics of these surface acoustic wave filter devices were measured, and the ripple in the passband was evaluated. The results are shown in FIG.

  In FIG. 4, the result of both the case where the said 1st, 2nd sound-absorbing materials 7 and 8 are formed with a polyimide resin and a urethane resin is shown. In the polyimide resin, the surface wave attenuation effect is 0.8 dB / λ, and in the urethane resin, 1.6 dB / λ. The sound absorbing material made of urethane resin was made to have a thickness of 15 μm by screen printing. In FIG. 4, the result when the symbol “◯” is polyimide resin and the symbol “Δ” urethane resin is shown.

  As apparent from FIG. 4, even when the first and second sound absorbing materials 7 and 8 are formed using any resin, the ripple in the passband decreases as the dimension A increases. I understand that In the surface acoustic wave filter device 1, the distance from the end surface 2a to the outer end of the input-side IDT 3 in the surface wave propagation direction is about 200 μm. Therefore, when the dimension A is 200 μm or more, it corresponds to the above embodiment, and as can be seen from FIG. 4, it can be seen that the ripple in the passband can be made sufficiently small.

  As described above, when the sound absorbing materials 7 and 8 cover a part of the input side IDT 3 and the output side IDT 4, the end portions on the side where the frequency characteristics, particularly the electrode finger pitch is relatively large, are covered with the sound absorbing material. Therefore, there is a concern about the deterioration of the frequency characteristics on the low frequency side. Therefore, the ratio of the 3 dB bandwidth and the 18 dB bandwidth when the dimension A was changed was obtained. The 3 dB bandwidth is a width of a band with an attenuation of 3 dB in the pass band, and 18 dB is a bandwidth with an attenuation of 18 dB. As the 3 dB bandwidth / 18 dB bandwidth ratio decreases, the steepness of the filter characteristics deteriorates. The results are shown in FIG.

  As is apparent from FIG. 5, even when the dimension A is 200 μm or more, that is, as in the above embodiment, the first and second sound absorbing materials 7 and 8 are input side IDT3 and output side IDT4. It can be seen that the steepness of the filter characteristics hardly changes even when a part of the filter is covered.

  When the dimension A is 250 μm or more, the first sound absorbing material 7 covers the second end 3f on the side where the electrode finger pitch of the input side IDT 3 is narrow. Therefore, preferably, as in the above embodiment, the first and second sound absorbing materials 7 and 8 are not more than 250 μm, that is, the first and second sound absorbing materials 7 and 8 do not cover the portions indicated by the second end portions 3f and 4f. It is desirable to form the second sound absorbing materials 7 and 8.

  In this way, by using a sound absorbing material having an attenuation effect in the range of 0.8 to 1.6 dB / λ, as is apparent from FIG. 4 and FIG. I know you get.

  In the above embodiment, the width dimension of the notches 6a and 6b is substantially the same as the width dimension of the input side IDT3 and the outlet side IDT4, but may be smaller than this. Further, the dimension C may be increased in the same manner as the dimension D and may be cut out linearly.

The top view of the surface acoustic wave filter apparatus which concerns on one Embodiment of this invention, (b) And (c) is a top view which shows the input side IDT and the output side IDT. The partial distance front sectional view which shows the principal part of the surface acoustic wave filter apparatus of embodiment shown in FIG. In the surface acoustic wave filter device of this embodiment, the dimension D of FIG. 1, that is, the dimension between the end face 2a and the end of the dielectric film made of SiO ₂ is changed, and the dimension A of the first sound absorbing material is 240 μm. The figure which shows the relationship between the dimension C at the time of being constant, and the ripple in a passband. In the surface acoustic wave filter apparatus of embodiment shown in FIG. 1, the figure which shows the change of the ripple in a passband at the time of changing the dimension A in FIG. The surface acoustic wave filter apparatus of embodiment shown in FIG. 1 is a figure which shows the change of 3 dB bandwidth / 18 dB bandwidth when the dimension A of FIG. The top view for demonstrating an example of the conventional surface acoustic wave filter apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Surface acoustic wave filter apparatus 2 ... Piezoelectric substrate 2a, 2b ... 1st, 2nd end surface 2c ... Upper surface (1st main surface)
3. Input side IDT
3a, 3b ... electrode fingers 3c, 3d ... bus bar 4 ... output side IDT
4a, 4b ... electrode finger 5 ... shield electrode 6 ... dielectric film 6a, 6b ... first and second distances 7, 8 ... first and second sound absorbing materials

Claims (7)

A piezoelectric substrate having first and second end faces facing each other and first and second main faces facing each other;
On the first main surface of the piezoelectric substrate, the input side IDT disposed on the first end surface side and the second end surface side are provided in a direction connecting the first and second end surfaces. An output-side IDT arranged in
On the first main surface of the piezoelectric substrate, a first sound absorbing material provided in a region on the first end surface side outside the surface acoustic wave propagation direction of the input side IDT;
A second sound-absorbing material provided on a region on the second end surface side, which is a region outside the output-side IDT in the surface wave propagation direction, on the first main surface of the piezoelectric substrate;
The input-side IDT and the output-side IDT are electrode finger pitches on the first end side in a direction perpendicular to the surface acoustic wave propagation direction, and electrodes on the second end side opposite to the first end part. In a transversal surface acoustic wave filter device that is an inclined IDT having a different finger pitch,
The first and second sound absorbing materials are respectively provided so as to reach a part of the input-side IDT and the output-side IDT from the outer ends of the input-side IDT and the output-side IDT in the surface acoustic wave propagation direction. A surface acoustic wave filter device. The region where the first sound-absorbing material covers a part of the input-side IDT is in the vicinity of the outer end portion in the surface wave propagation direction of the input-side IDT. The first sound-absorbing material covers the input-side IDT so that the electrode finger pitch does not reach the second end having a relatively narrow electrode finger pitch,
The second sound absorbing material covers the first end portion side where the electrode finger pitch of the output side IDT is relatively wide and does not reach the second end portion where the electrode finger pitch is relatively narrow. The surface acoustic wave filter device according to claim 1, wherein a part of the output-side IDT is covered.   The surface acoustic wave filter device according to claim 1, further comprising a dielectric film provided on the piezoelectric substrate so as to cover the input-side IDT and the output-side IDT.   First and second cutouts are formed in the dielectric film, and the first and second cutouts are on the outer side in the surface wave propagation direction than the portion where the input side IDT and the output side IDT are provided. And the first and second sound absorbing materials are disposed in the first and second cutouts, whereby the first and first cutouts of the dielectric film The surface acoustic wave filter device according to claim 1, wherein two sound-absorbing materials and the piezoelectric substrate are in direct contact with each other.   The first and second sound absorbing materials are made of a resin having a surface acoustic wave attenuation effect in a range of 0.8 dB / λ to 1.6 dB / λ (where λ is the wavelength of the surface acoustic wave). The surface acoustic wave filter device according to any one of claims 1 to 4.   The said 1st, 2nd sound-absorbing material is provided so that the electrode finger pitch of the said input side IDT and the output side IDT may reach the 2nd edge part of the side with a relatively narrowness. The surface acoustic wave filter device according to claim 1. The surface acoustic wave filter device according to any one of claims 1 to 6, wherein the input-side IDT and the output-side IDT are regular inclined IDTs.

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