阅读说明：本技术 纵向耦合谐振器型弹性波滤波器以及滤波器装置 (Longitudinally coupled resonator type elastic wave filter and filter device ) 是由 小笹茂生 照田千寻 于 2020-02-28 设计创作，主要内容包括：本发明提供一种能够在通带的低频侧附近的频带中抑制衰减量的偏差的纵向耦合谐振器型弹性波滤波器。本发明的纵向耦合谐振器型弹性波滤波器具备：压电性基板；多个IDT电极,设置在压电性基板上,并沿着弹性波传播方向配置；以及一对反射器,在压电性基板上设置在多个IDT电极的弹性波传播方向两侧。反射器(8B)具有相互对应的第1反射器汇流条(14)、第2反射器汇流条(16)和与第1反射器汇流条(14)以及第2反射器汇流条(16)中的至少一者连接的多个第1反射电极指(13)。反射器(8B)具有多个第1反射电极指(13)的长度在弹性波传播方向上变化的第1部分(9a)。(The invention provides a longitudinally coupled resonator type elastic wave filter capable of suppressing variation in attenuation amount in a frequency band near the low frequency side of a pass band. The longitudinally coupled resonator type elastic wave filter of the present invention includes: a piezoelectric substrate; a plurality of IDT electrodes provided on the piezoelectric substrate and arranged along the propagation direction of the elastic wave; and a pair of reflectors provided on the piezoelectric substrate on both sides of the plurality of IDT electrodes in the direction of propagation of the elastic wave. The reflector (8B) has a 1 st reflector bus bar (14), a 2 nd reflector bus bar (16) corresponding to each other, and a plurality of 1 st reflective electrode fingers (13) connected to at least one of the 1 st reflector bus bar (14) and the 2 nd reflector bus bar (16). The reflector (8B) has a 1 st portion (9a) in which the lengths of a plurality of 1 st reflective electrode fingers (13) vary in the elastic wave propagation direction.)

1. A longitudinally coupled resonator-type elastic wave filter is provided with:

a piezoelectric substrate;

a plurality of IDT electrodes provided on the piezoelectric substrate and arranged along an elastic wave propagation direction; and

a pair of reflectors provided on the piezoelectric substrate on both sides of the plurality of IDT electrodes in the direction of propagation of the elastic wave,

the reflector has:

a 1 st reflector bus bar and a 2 nd reflector bus bar which are opposed to each other; and

a plurality of reflective electrode fingers connected to at least one of the 1 st reflector bus bar and the 2 nd reflector bus bar,

the reflector has a 1 st portion in which lengths of the plurality of reflective electrode fingers vary in an elastic wave propagation direction.

2. The longitudinally coupled resonator-type elastic wave filter according to claim 1, wherein,

in the 1 st portion of the reflector, lengths of the plurality of reflection electrode fingers become shorter from the IDT electrode side toward an elastic wave propagation direction outer side.

3. The longitudinally coupled resonator-type elastic wave filter according to claim 1 or 2, wherein,

assuming that a virtual line formed by connecting the ends of the plurality of reflective electrode fingers connected to the 1 st reflector bus bar is a 1 st virtual line and a virtual line formed by connecting the ends of the plurality of reflective electrode fingers connected to the 2 nd reflector bus bar is a 2 nd virtual line, at this time, in the 1 st portion, at least one of the 1 st virtual line and the 2 nd virtual line is inclined with respect to an elastic wave propagation direction.

4. The longitudinally coupled resonator-type elastic wave filter as set forth in any one of claims 1 to 3,

the reflector has a 2 nd portion in which lengths of the plurality of reflective electrode fingers are fixed in an elastic wave propagation direction.

5. The longitudinally coupled resonator-type elastic wave filter according to claim 4, wherein,

in the reflector, the 2 nd portion is located closer to the plurality of IDT electrodes than the 1 st portion.

6. The longitudinally coupled resonator-type elastic wave filter as set forth in any one of claims 1 to 5,

the plurality of reflective electrode fingers of the reflector have:

a 1 st reflective electrode finger, one end of which is connected to the 1 st reflector bus bar and the other end of which is connected to the 2 nd reflector bus bar; and

and a 2 nd reflective electrode finger having one end connected to the 1 st reflector bus bar and the other end facing the 2 nd reflector bus bar with a gap therebetween.

7. The longitudinally coupled resonator-type elastic wave filter according to claim 6, wherein,

the plurality of reflective electrode fingers of the reflector have:

and a 3 rd reflective electrode finger having one end connected to the 2 nd reflector bus bar and the other end facing the 1 st reflector bus bar with a gap therebetween.

8. The longitudinally coupled resonator-type elastic wave filter as set forth in any one of claims 1 to 7,

the plurality of IDT electrodes each have:

a 1 st bus bar and a 2 nd bus bar facing each other;

a plurality of 1 st electrode fingers, one end of which is connected to the 1 st bus bar; and

a plurality of No. 2 electrode fingers, one end of which is connected with the No. 2 bus bar and is mutually staggered and inserted with the No. 1 electrode fingers,

the 1 st electrode finger and the 2 nd electrode finger are overlapped with each other in the elastic wave propagation direction and form an intersection region,

the intersection region has:

a central region located on a central side in a direction orthogonal to an elastic wave propagation direction;

a 1 st edge region disposed on the 1 st bus bar side of the central region; and

a 2 nd edge region disposed on the 2 nd bus bar side of the central region,

the plurality of IDT electrodes have:

a 1 st gap region between the 1 st edge region and the 1 st bus bar; and

a 2 nd gap region between the 2 nd edge region and the 2 nd bus bar,

in the 1 st edge region and the 2 nd edge region, low sound velocity regions having a sound velocity lower than that of the central region are formed, respectively.

9. The longitudinally coupled resonator-type elastic wave filter according to claim 8, wherein,

the 1 st bus bar and the 2 nd bus bar of the IDT electrode are respectively provided with an opening forming area provided with a plurality of openings along the propagation direction of the elastic wave,

in each of the opening forming regions, a high sound velocity region having a higher sound velocity than the central region is formed.

10. The longitudinally coupled resonator-type elastic wave filter according to claim 8 or 9, wherein,

the plurality of reflection electrode fingers in the 1 st section of the reflector overlap with the central region of the IDT electrode and do not overlap with the 1 st edge region and the 2 nd edge region as viewed from an elastic wave propagation direction.

11. The longitudinally coupled resonator-type elastic wave filter according to claim 9, wherein,

the plurality of reflection electrode fingers in the 1 st section of the reflector overlap with the central region of the IDT electrode as viewed from an elastic wave propagation direction,

at least the reflection electrode finger located closest to the IDT electrode in the 1 st section extends so as to overlap both the 1 st slot region and the 2 nd slot region, and any one of the reflection electrode fingers does not overlap the opening forming region when viewed in an elastic wave propagation direction.

12. The longitudinally coupled resonator-type elastic wave filter according to claim 9, wherein,

the 1 st bus bar and the 2 nd bus bar of the IDT electrode have outer bus bar regions located on outer sides of the opening forming regions in a direction orthogonal to an elastic wave propagation direction,

the plurality of reflection electrode fingers in the 1 st section of the reflector overlap with the central region of the IDT electrode as viewed from an elastic wave propagation direction,

at least the reflection electrode finger located closest to the IDT electrode in the 1 st section extends so as to overlap both the opening forming regions, and any one of the reflection electrode fingers does not overlap the outer bus bar region when viewed in the elastic wave propagation direction.

13. The longitudinally coupled resonator-type elastic wave filter according to claim 9, wherein,

the 1 st bus bar and the 2 nd bus bar of the IDT electrode have outer bus bar regions located on outer sides of the opening forming regions in a direction orthogonal to an elastic wave propagation direction,

in the 1 st portion of the reflector, at least the reflection electrode finger located closest to the IDT electrode overlaps the entire intersection region of the IDT electrode, and the reflection electrode finger extends so as to overlap both outer bus bar regions, as viewed in the elastic wave propagation direction.

14. The longitudinally coupled resonator-type elastic wave filter as set forth in any one of claims 1 to 13,

the piezoelectric substrate includes:

a layer of high acoustic velocity material; and

a piezoelectric layer disposed directly or indirectly on the layer of high acoustic velocity material,

the acoustic velocity of a bulk wave propagating through the high acoustic velocity material layer is higher than the acoustic velocity of an elastic wave propagating through the piezoelectric material layer.

15. The longitudinally coupled resonator-type elastic wave filter according to claim 14, wherein,

further provided with: a low acoustic velocity film disposed between the high acoustic velocity material layer and the piezoelectric layer,

the sound velocity of the bulk wave propagating through the low sound velocity film is lower than the sound velocity of the bulk wave propagating through the piezoelectric layer.

16. The longitudinally coupled resonator-type elastic wave filter according to claim 14 or 15, wherein,

the high acoustic velocity material layer is a high acoustic velocity support substrate.

17. The longitudinally coupled resonator-type elastic wave filter according to claim 15, wherein,

further comprises a support substrate, a plurality of support substrates,

the high acoustic velocity material layer is a high acoustic velocity membrane disposed between the support substrate and the low acoustic velocity membrane.

18. A filter device is provided with:

the longitudinally coupled resonator-type elastic wave filter as set forth in any one of claims 1 to 17; and

at least one resonator other than the longitudinally coupled resonator type elastic wave filter.

Technical Field

The present invention relates to a longitudinally coupled resonator type elastic wave filter and a filter device.

Background

Conventionally, longitudinally coupled resonator type elastic wave filters have been widely used as filters for mobile phones and the like. Patent document 1 listed below discloses an example of a longitudinally coupled resonator type elastic wave filter. In the longitudinally coupled resonator type elastic wave filter, a high acoustic velocity member, a low acoustic velocity film, and a piezoelectric film are laminated in this order. A plurality of IDT electrodes (InterDigital transducers) and reflectors are provided on the piezoelectric film. By providing the above laminated structure, the Q value is improved.

Prior art documents

Patent document

Patent document 1: international publication No. 2015/198904

Disclosure of Invention

Problems to be solved by the invention

When the IDT electrodes in the longitudinally coupled resonator type elastic wave filter are patterned, variations in the widths of the electrode fingers actually occur. Therefore, the attenuation amount varies particularly in a band near the low frequency side of the passband. Due to this, there is a concern that attenuation characteristics in the above frequency band deteriorate. Further, in the longitudinally coupled resonator type elastic wave filter having the above-described laminated structure, the variation in the width of the electrode fingers becomes particularly large due to the influence of the flatness of the piezoelectric film or the like. Therefore, even if the Q value can be increased, the variation in the attenuation amount in the band near the low frequency side of the passband becomes larger, and control becomes difficult.

An object of the present invention is to provide a longitudinally coupled resonator type elastic wave filter and a filter device capable of suppressing variation in attenuation in a frequency band near the low frequency side of the passband.

Means for solving the problems

The longitudinally coupled resonator type elastic wave filter according to the present invention includes: a piezoelectric substrate; a plurality of IDT electrodes provided on the piezoelectric substrate and arranged along an elastic wave propagation direction; and a pair of reflectors provided on the piezoelectric substrate on both sides of the plurality of IDT electrodes in an elastic wave propagation direction, the reflectors including: a 1 st reflector bus bar and a 2 nd reflector bus bar which are opposed to each other; and a plurality of reflective electrode fingers connected to at least one of the 1 st reflector bus bar and the 2 nd reflector bus bar, the reflector having a 1 st portion in which lengths of the plurality of reflective electrode fingers vary in an elastic wave propagation direction.

A filter device according to the present invention includes: a longitudinally coupled resonator type elastic wave filter constructed according to the present invention; and at least one or more resonators other than the longitudinally coupled resonator type elastic wave filter.

Effects of the invention

According to the longitudinally coupled resonator type elastic wave filter and the filter device according to the present invention, the Q value can be increased, and variation in the attenuation amount can be suppressed in the frequency band near the low frequency side of the passband.

Drawings

Fig. 1 is a circuit diagram of a filter device according to embodiment 1 of the present invention.

Fig. 2 is a schematic plan view showing the vicinity of the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1 of the present invention.

Fig. 3 is a plan view of the reflector of the 1 st longitudinally coupled resonator-type elastic wave filter according to embodiment 1 of the present invention.

Fig. 4 is a schematic front cross-sectional view of the vicinity of the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1 of the present invention.

Fig. 5 is a plan view of the vicinity of an IDT electrode in a 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1 of the present invention.

Fig. 6 is a plan view of the reflector and the vicinity of the IDT electrode in the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1 of the present invention.

Fig. 7 is a graph showing attenuation frequency characteristics of each filter device of the comparative example.

Fig. 8 is a diagram showing attenuation frequency characteristics of each filter device having the configuration of embodiment 1 of the present invention.

Fig. 9 is a plan view of a reflector of a 1 st longitudinally coupled resonator-type elastic wave filter according to a 1 st modification of embodiment 1 of the present invention.

Fig. 10 is a plan view of a reflector of a 1 st longitudinally coupled resonator-type elastic wave filter according to a 2 nd modification of embodiment 1 of the present invention.

Fig. 11 is a schematic front sectional view of the vicinity of a 1 st longitudinally coupled resonator type elastic wave filter in a filter device according to a 3 rd modification of embodiment 1 of the present invention.

Fig. 12 is a schematic front cross-sectional view of the vicinity of the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to the 4 th modification of embodiment 1 of the present invention.

Fig. 13 is a plan view of the vicinity of a reflector in the longitudinally coupled resonator-type elastic wave filter according to embodiment 2 of the present invention.

Fig. 14 is a plan view showing a vicinity of a portion corresponding to a reflector for explaining an example of a method of manufacturing a longitudinally coupled resonator type elastic wave filter according to embodiment 2 of the present invention.

Fig. 15 is a plan view showing a vicinity of a portion corresponding to a reflector for explaining an example of a method of manufacturing a longitudinally coupled resonator type elastic wave filter according to embodiment 2 of the present invention.

Fig. 16 is a plan view of the vicinity of a reflector in a longitudinally coupled resonator-type elastic wave filter according to modification 1 of embodiment 2 of the present invention.

Fig. 17 is a plan view of the vicinity of a reflector in a longitudinally coupled resonator-type elastic wave filter according to modification 2 of embodiment 2 of the present invention.

Fig. 18 is a plan view of the vicinity of a reflector in a longitudinally coupled resonator-type elastic wave filter according to modification 3 of embodiment 2 of the present invention.

Fig. 19 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 3 of the present invention.

Fig. 20 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 4 of the present invention.

Fig. 21 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 5 of the present invention.

Fig. 22 is a plan view showing a part of reflectors and IDT electrodes of a longitudinally coupled resonator type elastic wave filter of a comparative example.

Fig. 23 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 3 of the present invention.

Fig. 24 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 4 of the present invention.

Fig. 25 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 5 of the present invention.

Fig. 26 is a graph showing the return loss of the longitudinally coupled resonator-type elastic wave filter of the comparative example.

Detailed Description

The present invention will be made clear by the following description of specific embodiments of the present invention with reference to the accompanying drawings.

Note that the embodiments described in the present specification are exemplary, and partial replacement or combination of the structures may be performed between different embodiments.

Fig. 1 is a circuit diagram of a filter device according to embodiment 1 of the present invention. In addition, a portion of the reflector described later in fig. 1 is shown by a diagram in which two diagonal lines are added to a rectangle.

The filter device 10 has a 1 st signal terminal 17A and a 2 nd signal terminal 17B. Filter device 10 includes a 1 st longitudinally coupled resonator type elastic wave filter 1A and a 2 nd longitudinally coupled resonator type elastic wave filter 1B connected in parallel to each other between a 1 st signal terminal 17A and a 2 nd signal terminal 17B. Both of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B are longitudinally coupled resonator type elastic wave filters according to one embodiment of the present invention.

Filter device 10 has 1 st elastic wave resonator P1 connected between the ground potential and the connection point between 1 st longitudinally coupled resonator type elastic wave filter 1A and 2 nd longitudinally coupled resonator type elastic wave filter 1B and 1 st signal terminal 17A. Further, filter device 10 includes a 2 nd elastic wave resonator S1 connected between 1 st longitudinally coupled resonator type elastic wave filter 1A and 2 nd longitudinally coupled resonator type elastic wave filter 1B and 2 nd signal terminal 17B. The circuit configuration of the filter device 10 is not limited to the above-described circuit configuration, and at least one longitudinally coupled resonator type elastic wave filter according to the present invention and resonators other than the longitudinally coupled resonator type elastic wave filter may be provided.

The filter device 10 of the present embodiment is a bandpass filter, and the passband is a reception Band of Band3, and is 1805MHz to 1880 MHz. However, the pass band of the filter device 10 is not limited to the above pass band. Alternatively, the filter device according to the present invention may be a duplexer or a multiplexer.

Fig. 2 is a schematic plan view showing the vicinity of the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1. Fig. 2 shows a schematic diagram of a polygon with two diagonal lines added to the polygon, which shows IDT electrodes and reflectors described later. In fig. 2, the wiring connected to the 1 st longitudinally coupled resonator type elastic wave filter 1A is omitted.

The 1 st longitudinally coupled resonator type elastic wave filter 1A has a piezoelectric substrate 2, and IDT electrodes 3A, IDT, 3B, IDT, 3C, IDT, 3D and 3E provided on the piezoelectric substrate 2. An alternating voltage is applied to the IDT electrode, whereby an elastic wave is excited. In the present specification, the elastic wave propagation direction is defined as a 1 st direction x, and a direction orthogonal to the 1 st direction x is defined as a 2 nd direction y.

The IDT electrode 3A, IDT, the electrode 3B, IDT, the electrode 3C, IDT, the electrode 3D, and the IDT electrode 3E are arranged in this order along the 1 st direction x. A pair of reflectors 8A and 8B are provided on the piezoelectric substrate 2 on both sides of the plurality of IDT electrodes in the 1 st direction x. More specifically, reflector 8A is disposed adjacent to IDT electrode 3A, and reflector 8B is disposed adjacent to IDT electrode 3E. In this manner, the 1 st longitudinally coupled resonator type elastic wave filter 1A is a 5IDT longitudinally coupled resonator type elastic wave filter. However, the 1 st longitudinally coupled resonator type acoustic wave filter 1A is not limited to the 5IDT type, and may be, for example, a 3IDT type or a 7IDT type.

Fig. 3 is a plan view of the reflector of the 1 st longitudinally coupled resonator-type elastic wave filter in embodiment 1.

The reflector 8B includes a 1 st reflector bus bar 14 and a 2 nd reflector bus bar 16 opposed to each other, and a plurality of reflective electrode fingers. More specifically, the plurality of reflective electrode fingers of the present embodiment are the plurality of 1 st reflective electrode fingers 13 connected to both the 1 st reflector bus bar 14 and the 2 nd reflector bus bar 16. One end portions of the 1 st reflective electrode fingers 13 are connected to the 1 st reflector bus bar 14, and the other end portions are connected to the 2 nd reflector bus bar 16.

The reflector 8B has a 1 st portion 9a in which the lengths of a plurality of 1 st reflective electrode fingers 13 vary in the 1 st direction x. More specifically, in the 1 st part 9a, the 1 st reflective electrode finger 13 becomes shorter toward the 1 st direction x outer side. As such, the reflector 8B is a weighted reflector.

Here, a virtual line formed by connecting the ends of the plurality of reflective electrode fingers connected to the 1 st reflector bus bar 14 is referred to as a 1 st virtual line J. An imaginary line formed by connecting the end portions of the plurality of reflective electrode fingers connected to the 2 nd reflector bus bar 16 is set as a 2 nd imaginary line K. In the present embodiment, in the 1 st portion 9a, both the 1 st virtual line J and the 2 nd virtual line K are inclined with respect to the 1 st direction x. More specifically, the 1 st imaginary line J extends closer to the 2 nd reflector bus bar 16 toward the 1 st direction x-outer side. The 2 nd imaginary line K extends to be closer to the 1 st reflector bus bar 14 as it goes outward in the 1 st direction x. At least one of the 1 st virtual line J and the 2 nd virtual line K may be inclined with respect to the 1 st direction x.

The reflector 8B has a 2 nd portion 9B in which the lengths of a plurality of reflective electrode fingers are fixed in the 1 st direction x. In the 2 nd portion 9b, the 1 st imaginary line J and the 2 nd imaginary line K extend in parallel with the 1 st direction x. The 2 nd portion 9b is located closer to the IDT electrodes than the 1 st portion 9 a. The positional relationship between the 1 st part 9a and the 2 nd part 9b is not limited to the above positional relationship.

In the present embodiment, in the 2 nd portion 9b, a plurality of openings 14d are provided along the 1 st direction x in the 1 st reflector bus bar 14. The 2 nd reflector bus bar 16 is also provided with a plurality of openings 16d along the 1 st direction x. At least the 1 st reflective electrode finger 13 located on the side closest to the 2 nd portion 9b among the plurality of 1 st reflective electrode fingers 13 in the 1 st portion 9a overlaps the opening 14d and the opening 16d as viewed from the 1 st direction x. In addition, the reflective electrode fingers in the 1 st portion 9a may not overlap with the openings 14d and 16d when viewed from the 1 st direction x. Alternatively, the 1 st reflector bus bar 14 and the 2 nd reflector bus bar 16 may not have the openings 14d and 16 d. The reflector 8B may be formed of only the 1 st portion 9a without the 2 nd portion 9B.

The reflector 8A shown in fig. 2 also has the same structure as the reflector 8B. The reflector 8A is substantially line-symmetric to the reflector 8B with respect to a symmetry axis extending in the 2 nd direction y. More specifically, the reflector 8A includes a 1 st reflector bus bar and a 2 nd reflector bus bar facing each other, and a plurality of 1 st reflective electrode fingers connected to both the 1 st reflector bus bar and the 2 nd reflector bus bar. The reflector 8A has a 1 st portion in which the 1 st reflective electrode finger becomes shorter toward the outside of the 1 st direction x. As such, the reflector 8A is a weighted reflector.

Fig. 4 is a schematic front sectional view of the vicinity of the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1. In fig. 4, the IDT electrode and reflectors are shown by a schematic diagram in which two diagonal lines are added to a rectangle.

The piezoelectric substrate 2 of the present embodiment has a support substrate 4, a high acoustic velocity film 5 as a high acoustic velocity material layer provided on the support substrate 4, a low acoustic velocity film 6 provided on the high acoustic velocity film 5, and a piezoelectric layer 7 provided on the low acoustic velocity film 6. However, the piezoelectric substrate 2 may be a piezoelectric substrate including only the piezoelectric layer 7.

As a material of the piezoelectric layer 7, for example, a piezoelectric single crystal such as lithium tantalate or lithium niobate, or an appropriate piezoelectric ceramic can be used.

The low acoustic velocity membrane 6 is a relatively low acoustic velocity membrane. More specifically, the acoustic velocity of the bulk wave propagating through the low-acoustic-velocity membrane 6 is lower than the acoustic velocity of the bulk wave propagating through the piezoelectric layer 7. In the present embodiment, the low sound velocity membrane 6 is a silicon oxide membrane. SiO for silicon oxide_xTo indicate. x is any positive number. In the 1 st longitudinally coupled resonator type elastic wave filter 1A, the silicon oxide constituting the low acoustic velocity film 6 is SiO₂. The material of the low sound velocity membrane 6 is not limited to the above-described material, and for example, a material containing glass, silicon oxynitride, tantalum oxide, or a compound in which silicon oxide is added with fluorine, carbon, or boron as a main component can be used.

In the present embodiment, the high sound velocity material layer is the high sound velocity membrane 5. The layer of high acoustic velocity material is a layer of relatively high acoustic velocity. More specifically, the sound velocity of a bulk wave (bulk wave) propagating in the high-sound-velocity material layer is higher than the sound velocity of an elastic wave propagating in the piezoelectric layer 7. As the material of the high acoustic velocity film 5, for example, a medium containing alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesium oxide, a DLC (diamond-like carbon) film, diamond, or the like, which is a main component of the above-described material, can be used.

Examples of the material of the support substrate 4 include various ceramics such as alumina, lithium tantalate, lithium niobate, quartz, alumina, sapphire, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, forsterite, and the like, dielectrics such as diamond, glass, and the like, semiconductors such as silicon, gallium nitride, and the like, and resins.

Since the piezoelectric substrate 2 has a laminated structure in which the high sound velocity film 5, the low sound velocity film 6, and the piezoelectric layer 7 are laminated in this order, the Q value can be effectively increased, and the energy of the elastic wave can be effectively confined to the piezoelectric layer 7 side.

Here, the 1 st longitudinally coupled resonator type elastic wave filter 1A is an elastic wave device using a piston mode (piston mode). The structure of the IDT electrode of the present embodiment will be described in detail with reference to fig. 5 below, which shows one IDT electrode among a plurality of IDT electrodes.

Fig. 5 is a plan view of the vicinity of an IDT electrode in the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1. Fig. 6 is a plan view of the vicinity of the reflectors and IDT electrodes in the 1 st longitudinally coupled resonator type elastic wave filter of the filter device according to embodiment 1. In fig. 5, the IDT electrode and reflectors near the IDT electrode shown in fig. 5 are omitted. In fig. 5 and 6, the wiring connected to the longitudinally coupled resonator type elastic wave filter is omitted.

As shown in fig. 5, the IDT electrode 3E includes a 1 st bus bar 24 and a 2 nd bus bar 26 facing each other. The 1 st bus bar 24 is provided with a plurality of 1 st openings 24d along the 1 st direction x. The 2 nd bus bar 26 is also provided with a plurality of 2 nd openings 26d along the 1 st direction x. As shown in fig. 6, in the present embodiment, the 1 st opening 24d overlaps the opening 14d of the 1 st reflector bus bar 14 as viewed from the 1 st direction x. The 2 nd opening 26d overlaps with the opening 16d of the 2 nd reflector bus bar 16 when viewed from the 1 st direction x.

Returning to fig. 5, the IDT electrode 3E has a plurality of 1 st electrode fingers 25 each having one end connected to the 1 st bus bar 24. The other end of the 1 st electrode finger 25 faces the 2 nd bus bar 26 with a gap therebetween. The IDT electrode 3E has a plurality of 2 nd electrode fingers 27 each having one end connected to the 2 nd bus bar 26. The other end of the 2 nd electrode finger 27 faces the 1 st bus bar 24 with a gap therebetween. The plurality of 1 st electrode fingers 25 and the plurality of 2 nd electrode fingers 27 are interdigitated with each other.

In the IDT electrode 3E, a portion where the 1 st electrode finger 25 and the 2 nd electrode finger 27 overlap in the 1 st direction x is an intersection area a. The intersection region a has a central region B located on the central side in the 2 nd direction y.

The intersection region a has a 1 st edge region Ca disposed on the 1 st bus bar 24 side of the central region B and a 2 nd edge region Cb disposed on the 2 nd bus bar 26 side of the central region B. The IDT electrode 3E has a 1 st gap region Da between the 1 st edge region Ca and the 1 st bus bar 24 and a 2 nd gap region Db between the 2 nd edge region Cb and the 2 nd bus bar 26.

The 1 st bus bar 24 of the IDT electrode 3E has a 1 st inner bus bar region Ea located on the intersection region a side and a 1 st outer bus bar region Ga located outside the 1 st inner bus bar region Ea in the 2 nd direction y. The 1 st bus bar 24 has a portion located in the 1 st inner bus bar region Ea as the 1 st inner bus bar 24a, and a portion located in the 1 st outer bus bar region Ga as the 1 st outer bus bar 24 c. The 1 st bus bar 24 has a 1 st opening forming region Fa located between the 1 st inner bus bar region Ea and the 1 st outer bus bar region Ga and provided with the plurality of 1 st openings 24 d. The 1 st bus bar 24 includes a plurality of 1 st connecting electrodes 24b for connecting the 1 st inner bus bar portion 24a and the 1 st outer bus bar portion 24 c. The plurality of 1 st openings 24d are openings surrounded by the 1 st inner busbar portion 24a, the 1 st outer busbar portion 24c, and the plurality of 1 st connecting electrodes 24 b.

The plurality of 1 st connection electrodes 24b extend to be positioned on the extension lines of the plurality of 1 st electrode fingers 25. Here, the dimension of the electrode finger along the 1 st direction x is defined as a width. The width of the 1 st connection electrode 24b is the same as that of the 1 st electrode finger 25. The arrangement of the plurality of 1 st connecting electrodes 24b is not limited to the above arrangement, and may be extended so as to be positioned on the extension lines of the plurality of 2 nd electrode fingers 27, for example. The width of the 1 st connection electrode 24b may be different from the width of the 1 st electrode finger 25.

Similarly, the 2 nd bus bar 26 of the IDT electrode 3E includes a 2 nd inner bus bar region Eb, a 2 nd outer bus bar region Gb, and a 2 nd opening forming region Fb in which the plurality of 2 nd openings 26d are formed. A portion located in the 2 nd inner bus bar region Eb is the 2 nd inner bus bar portion 26a, and a portion located in the 2 nd outer bus bar region Gb is the 2 nd outer bus bar portion 26 c. The 2 nd bus bar 26 includes a plurality of 2 nd connecting electrodes 26b that connect the 2 nd inner bus bar portion 26a and the 2 nd outer bus bar portion 26 c. The plurality of 2 nd openings 26d are openings surrounded by the 2 nd inner busbar portion 26a, the 2 nd outer busbar portion 26c, and the plurality of 2 nd connecting electrodes 26 b.

The 1 st electrode finger 25 of the IDT electrode 3E has a 1 st width portion 25a having a width wider than that of a portion located in the center region B at a portion located in the 1 st edge region Ca. Similarly, the 2 nd electrode finger 27 has a 1 st width portion 27a at a portion located at the 1 st edge region Ca. Thus, the sound velocity in the 1 st edge region Ca is lower than the sound velocity in the center region B. As such, the 1 st low sound velocity region La having a lower average sound velocity than the sound velocity in the central region B is constituted from the 1 st edge region Ca to the 1 st inner bus bar region Ea.

The 1 st electrode finger 25 has a 2 nd wide portion 25B having a width wider than that of a portion located in the center region B in a portion located in the 2 nd edge region Cb. Similarly, the 2 nd electrode finger 27 has a 2 nd wide portion 27b in a portion located in the 2 nd edge region Cb. As such, the 2 nd low sound speed region Lb having an average sound speed lower than that in the central region B is configured from the 2 nd edge region Cb to the 2 nd inner bus bar region Eb.

In addition, at least one of the 1 st electrode finger 25 and the 2 nd electrode finger 27 may have the 1 st width portion 25a or the 1 st width portion 27 a. At least one of the 1 st electrode finger 25 and the 2 nd electrode finger 27 may have the 2 nd wide portion 25b or the 2 nd wide portion 27 b. Alternatively, the 1 st low sound velocity region La may be provided by providing the mass additional film in a portion of at least one of the 1 st electrode finger 25 and the 2 nd electrode finger 27, which is located in the 1 st edge region Ca. The same applies to the 2 nd edge region Cb. The 1 st and 2 nd low sound velocity regions La and Lb may be configured by providing the 1 st, 2 nd wide portions 25a, 27a, 25b, 27b, and the mass additional film.

Here, when the sound velocity in the central region B is set to V1 and the sound velocities in the 1 st and 2 nd low sound velocity regions La and Lb are set to V2, V2 < V1.

The plurality of 1 st connection electrodes 24b in the 1 st opening forming region Fa are located on the extension lines of the plurality of 1 st electrode fingers 25 and not located on the extension lines of the plurality of 2 nd electrode fingers 27. Thus, the sound velocity in the 1 st opening forming region Fa is higher than the sound velocity in the central region B. In this manner, the 1 st aperture forming region Fa constitutes the 1 st high sound velocity region Ha. Similarly, a 2 nd high sound velocity region Hb having a sound velocity higher than that in the central region B is formed in the 2 nd opening forming region Fb. Here, V1 < V3 is defined as V3 for the sound velocities in the 1 st high sound velocity region Ha and the 2 nd high sound velocity region Hb. In the present specification, the sound velocities compared in the center region B, the 1 st low sound velocity region La, the 2 nd low sound velocity region Lb, the 1 st high sound velocity region Ha, and the 2 nd high sound velocity region Hb are propagation velocities in the 1 st direction x of the elastic wave.

The relationship of the sound velocities in the respective regions is V2 < V1 < V3. The relationship between the sound velocities described above is shown in fig. 5. In the portion showing the relationship of the sound velocities in fig. 5, as indicated by the arrow V, the line showing the height of each sound velocity is located further to the left, and indicates that the sound velocity is higher.

The IDT electrode 3A, IDT, electrode 3B, IDT, electrode 3C and IDT electrode 3D shown in fig. 2 are also configured in the same manner as the IDT electrode 3E. However, the design parameters of the IDT electrodes may be different depending on the desired characteristics. In the 1 st longitudinally coupled resonator type elastic wave filter 1A, a central region B, a 1 st low sound velocity region La, and a 1 st high sound velocity region Ha are arranged in this order in the 2 nd direction y. Similarly, the central region B, the 2 nd low sound velocity region Lb, and the 2 nd high sound velocity region Hb are arranged in this order in the 2 nd direction y. By realizing such a sound velocity relationship, the 1 st longitudinally coupled resonator type elastic wave filter 1A utilizes the piston mode. This improves the Q value, blocks the energy of the elastic wave, and suppresses the stray waves caused by the high-order transverse mode. However, the longitudinally coupled resonator type elastic wave filter according to the present invention does not necessarily use the piston mode.

IDT electrode 3A, IDT electrode 3B, IDT electrode 3C, IDT electrode 3D, IDT electrode 3E, reflector 8A, and reflector 8B may include a laminated metal film in which a plurality of metal layers are laminated, or may include a single metal film. Each IDT electrode and each reflector can be formed by, for example, a separation method.

The 2 nd longitudinally coupled resonator type elastic wave filter 1B shown in fig. 1 is also configured in the same manner as the 1 st longitudinally coupled resonator type elastic wave filter 1A. However, the design parameters of each longitudinally coupled resonator-type elastic wave filter may be different depending on the desired filter characteristics. In the present embodiment, the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B are formed on the same piezoelectric substrate 2.

Similarly, 1 st elastic wave resonator P1 and 2 nd elastic wave resonator S1 are also formed on piezoelectric substrate 2 forming 1 st longitudinally coupled resonator type elastic wave filter 1A. Each of 1 st acoustic wave resonator P1 and 2 nd acoustic wave resonator S1 has an IDT electrode provided on piezoelectric substrate 2 and a pair of reflectors arranged on both sides of the IDT electrode in the 1 st direction x.

The present embodiment is characterized in that each reflector of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B has the 1 st portion in which the length of the plurality of reflective electrode fingers changes in the 1 st direction x. This can suppress variations in the attenuation amount in the band near the low-frequency side of the passband. This will be explained below by comparing the present embodiment with comparative examples.

30 filter devices having the structure of embodiment 1 and filter devices of comparative examples were produced. The comparative example is different from embodiment 1 in that the length of each of the plurality of reflecting electrode fingers is the same in each of the reflectors of the 1 st longitudinally coupled resonator type elastic wave filter and the 2 nd longitudinally coupled resonator type elastic wave filter.

The materials and thicknesses of the IDT electrodes and reflectors and the conditions of the piezoelectric substrate in embodiment 1 and comparative examples are as follows.

Material and thickness of piezoelectric layer: the material is LiTaO₃Thickness of 600nm

Material and thickness of the low acoustic velocity film: the material is SiO₂Thickness of 710nm

Material and thickness of the high acoustic velocity film: the material is SiN with a thickness of 200nm

Material of the support substrate: the material is Si

Material and thickness of each IDT electrode and each reflector: the material is Al, and the thickness is 156nm

The conditions of each resonator in embodiment 1 are shown in tables 1 to 3 below. The reflector A, IDT electrode A, IDT electrode B, IDT electrode C, IDT electrode D, IDT electrode E and reflector B in each table are reflectors and IDT electrodes arranged in this order along the 1 st direction x. For example, the reflector a corresponds to the reflector 8A in fig. 2, and the IDT electrode a corresponds to the IDT electrode 3A. Further, the duty ratio of the IDT electrode in each table indicates the duty ratio in the intersection region. The number of pairs of electrode fingers in the reflector is the sum of the number of pairs in section 1 and section 2. Further, λ denotes a wavelength defined by an electrode finger pitch of the IDT electrode. Here, the electrode finger pitch is a distance between the centers of the electrode fingers. The dimension of the intersection region along the 2 nd direction y is set as an intersection width.

[ Table 1]

[ Table 2]

[ Table 3]

The conditions of the resonators in the comparative examples are shown in tables 4 to 6 below.

[ Table 4]

[ Table 5]

[ Table 6]

The unit of the cross width and the wavelength in tables 1 to 6 is μm. The attenuation frequency characteristics of each filter device were measured.

Fig. 7 is a graph showing attenuation frequency characteristics of each filter device of the comparative example. Fig. 8 is a diagram showing attenuation frequency characteristics of each filter device having the configuration of embodiment 1.

As shown in fig. 7, in the comparative example, it is understood that a large variation occurs in the attenuation amount in the band near the low frequency side of the passband. In contrast, as shown in fig. 8, it is understood that in embodiment 1, the variation in the attenuation amount is small in the frequency band near the low frequency side of the passband.

Here, when a plurality of IDT electrodes are formed in the longitudinally coupled resonator type acoustic wave filter, the width of the electrode fingers actually varies due to the influence of the flatness of the piezoelectric substrate or the like. When a piezoelectric substrate including a high acoustic velocity material layer and a piezoelectric layer is used, the Q value can be increased, but the influence of variations in the width of the electrode fingers of the IDT electrode on the attenuation amount is also increased. Therefore, in the comparative example, even if the variation in the width of the electrode finger is small, a large variation occurs in the attenuation amount in the frequency band near the low frequency side of the pass band.

In contrast, in the filter device 10 of embodiment 1 shown in fig. 1, in addition to the piezoelectric substrate 2 including the high acoustic material layer and the piezoelectric layer 7, the reflectors of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B are weighted. More specifically, as shown in fig. 3, in the reflector 8B, the lengths of the plurality of 1 st reflective electrode fingers 13 vary in the 1 st direction x. Therefore, in the reflector 8B, the logarithm of the 1 st reflective electrode fingers 13 is substantially changed in the 2 nd direction y. In embodiment 1, the number of pairs of the 1 st reflective electrode fingers 13 increases from the outer side toward the inner side in the 2 nd direction y. The same applies to the reflectors of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B other than the reflector 8B. This makes it possible to disperse the response outside the passband and to smooth the attenuation characteristics in the frequency band near the low frequency side of the passband. This can reduce the influence of variations in the width of the electrode fingers of the IDT electrode on the attenuation amount. Therefore, the Q value can be increased, and variation in the attenuation amount can be suppressed in the band near the low frequency side of the passband. Further, even when the piezoelectric substrate is a piezoelectric substrate including only the piezoelectric layer 7, the influence of variations in the width of the electrode fingers of the IDT electrode or the like on the attenuation amount can be reduced. Therefore, even in this case, the variation in the attenuation amount can be suppressed in the band near the low frequency side of the passband.

As shown in fig. 3, the reflector 8B preferably has a 2 nd portion 9B in addition to the 1 st portion 9 a. More preferably, the 2 nd portion 9b is located closer to the IDT electrodes than the 1 st portion 9 a. This allows the elastic wave to be appropriately reflected toward the IDT electrodes without increasing the size of the reflector 8B. As shown in fig. 5 and 6, it is further preferable that the plurality of 1 st reflective electrode fingers 13 in the 2 nd portion 9b overlap at least a part of the 1 st slit region and the 2 nd slit region as viewed from the 1 st direction x. Still further preferably, the plurality of 1 st reflective electrode fingers 13 in the 2 nd portion 9b overlap with all of the 1 st slit region and the 2 nd slit region as viewed from the 1 st direction x. This allows the elastic wave to be more reliably and appropriately reflected toward the IDT electrodes by the reflector 8B. The same applies to the reflectors of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B other than the reflector 8B.

As shown in fig. 3, in embodiment 1, both the 1 st virtual line J and the 2 nd virtual line K are linear and inclined with respect to the 1 st direction x. The weighting method of each reflector is not limited to the above method. For example, in the 1 st modification shown in fig. 9, the 1 st imaginary line J1 is inclined with respect to the 1 st direction x and curved in the 1 st portion 39 a. In addition, the 1 st reflector bus bar 34 is also curved. On the other hand, the 2 nd imaginary line K1 and the 2 nd reflector bus bar 36 extend parallel to the 1 st direction x. Even in this case, as in embodiment 1, the Q value can be increased, and variations in the attenuation amount can be suppressed in the band near the low frequency side of the passband.

Fig. 10 is a plan view of a reflector of a 1 st longitudinally coupled resonator-type elastic wave filter according to modification 2 of embodiment 1.

This modification is different from embodiment 1 in that, when viewed from the 1 st direction x, all the 1 st reflective electrode fingers 13 in the 1 st portion 49a of the reflector do not overlap with the openings 14d and 16d in the 2 nd portion 9 b. In the present modification, the length of the 1 st reflective electrode finger 13 in the 1 st portion 49a is equal to or less than the length of the 1 st reflective electrode finger 13 in the 2 nd portion 9 b. All of the 1 st virtual line J2 and the 2 nd virtual line K2 overlap the 1 st reflective electrode finger 13 of the 2 nd segment 9b when viewed from the 1 st direction x.

The filter device of this modification also has a piezoelectric substrate similar to that of embodiment 1, and the reflectors of the 1 st longitudinally coupled resonator type elastic wave filter and the 2 nd longitudinally coupled resonator type elastic wave filter are weighted. Therefore, the Q value can be increased, and variation in the attenuation amount can be suppressed in the band near the low frequency side of the passband.

As shown in fig. 5, in embodiment 1, a plurality of 1 st openings 24d are formed in the 1 st bus bar 24 of the IDT electrode 3E. The 1 st high sound velocity region Ha is formed in the 1 st opening forming region Fa in the 1 st bus bar 24, and the 1 st low sound velocity region La is formed from the 1 st edge region Ca to the 1 st inner bus bar region Ea. Further, the opening portion may not be formed in the 1 st bus bar 24. In this case, the 1 st high sound velocity region Ha may be formed in the 1 st slot region Da, and the 1 st low sound velocity region La may be formed in the 1 st edge region Ca. Similarly, the opening may not be formed in the 2 nd bus bar 26. The 2 nd high sound velocity region Hb may be formed in the 2 nd gap region Db, and the 2 nd low sound velocity region Lb may be formed in the 2 nd edge region Cb. The same applies to the IDT electrodes of the 1 st longitudinally coupled resonator type elastic wave filter 1A and the 2 nd longitudinally coupled resonator type elastic wave filter 1B other than the IDT electrode 3E.

As shown in fig. 4, the piezoelectric substrate 2 according to embodiment 1 includes a laminate in which a support substrate 4, a high acoustic velocity film 5, a low acoustic velocity film 6, and a piezoelectric layer 7 are laminated in this order. The piezoelectric layer 7 is indirectly provided on the high sound velocity film 5 as the high sound velocity material layer via the low sound velocity film 6. However, the structure of the piezoelectric substrate 2 is not limited to the above structure. Hereinafter, a 3 rd modification and a 4 th modification of embodiment 1, in which only the structure of the piezoelectric substrate 2 is different from that of embodiment 1, will be described. In modification 3 and modification 4 as well, as in embodiment 1, the Q value can be increased, and variations in the attenuation can be suppressed in a frequency band near the low frequency side of the passband.

In the modification 3 shown in fig. 11, the high sound velocity material layer is a high sound velocity support substrate 54. The piezoelectric substrate 52A of the present modification includes a high acoustic velocity support substrate 54 and a piezoelectric layer 7 directly provided on the high acoustic velocity support substrate 54.

As a material of the high acoustic velocity support substrate 54, for example, a medium containing the above-described material as a main component, such as alumina, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesium oxide, a DLC film, or diamond, can be used.

The piezoelectric substrate 52B of modification 4 shown in fig. 12 includes a high sound velocity support substrate 54, a low sound velocity film 6 provided on the high sound velocity support substrate 54, and a piezoelectric layer 7 provided on the low sound velocity film 6.

Fig. 13 is a plan view of the vicinity of a reflector in the longitudinally coupled resonator-type elastic wave filter according to embodiment 2.

In the longitudinally coupled resonator type elastic wave filter of the present embodiment, the configuration of each reflector is different from that of the 1 st longitudinally coupled resonator type elastic wave filter 1A in embodiment 1. Except for the above-described points, the longitudinally coupled resonator-type elastic wave filter of the present embodiment has the same configuration as that of the 1 st longitudinally coupled resonator-type elastic wave filter 1A in embodiment 1.

As shown in fig. 13, in the 1 st portion 69a of the reflector 68B, the 1 st imaginary line J3 extends parallel to the 1 st direction x. On the other hand, the 2 nd imaginary line K3 is inclined with respect to the 1 st direction x. In addition, when the end portions of the plurality of reflective electrode fingers not connected to the 2 nd reflector bus bar 66 are set as the 3 rd virtual line, the 3 rd virtual line is also inclined with respect to the 1 st direction x in the 1 st portion 69 a. The 1 st reflector bus bar 64 and the 2 nd reflector bus bar 66 of the present embodiment do not have an opening portion.

The reflector 68B has a plurality of 2 nd reflective electrode fingers 65 and a plurality of 3 rd reflective electrode fingers 67 in addition to the 1 st reflective electrode finger 13. The plurality of 2 nd reflective electrode fingers 65 have a 1 st end portion 65a and a 2 nd end portion 65b, respectively. The 1 st end 65a is connected to the 1 st reflector bus bar 64, and the 2 nd end 65b is opposed to the 2 nd reflector bus bar 66 with a gap therebetween. Similarly, each of the 3 rd reflective electrode fingers 67 has a 3 rd end portion 67a and a 4 th end portion 67 b. The 3 rd end 67a is connected to the 2 nd reflector bus bar 66, and the 4 th end 67b faces the 1 st reflector bus bar 64 with a gap therebetween. The plurality of 2 nd reflective electrode fingers 65 and the plurality of 3 rd reflective electrode fingers 67 are interleaved with each other.

The reflector 68B of the present embodiment has one 1 st reflective electrode finger 13. The 1 st reflective electrode finger 13 is a reflective electrode finger positioned on the side closest to the IDT electrodes among the plurality of reflective electrode fingers. The number and position of the 1 st reflective electrode fingers 13 are not limited to the above.

One end portion of the 1 st reflective electrode finger 13, the 1 st end portion 65a of the 2 nd reflective electrode finger 65, and the 4 th end portion 67b of the 3 rd reflective electrode finger 67 in the 2 nd portion 69b overlap with the 1 st bus bar of the plurality of IDT electrodes as viewed from the 1 st direction x. Similarly, the other end portion of the 1 st reflective electrode finger 13, the 2 nd end portion 65b of the 2 nd reflective electrode finger 65, and the 3 rd end portion 67a of the 3 rd reflective electrode finger 67 in the 2 nd portion 69b overlap with the 2 nd bus bar of the plurality of IDT electrodes as viewed from the 1 st direction x. Thus, the 1 st reflective electrode finger 13, the plurality of 2 nd reflective electrode fingers 65, and the plurality of 3 rd reflective electrode fingers 67 in the 2 nd portion 69b overlap all of the 1 st slit region Da and the 2 nd slit region Db as viewed from the 1 st direction x. This makes it possible to more appropriately reflect the elastic wave toward the IDT electrodes. The positions of the 2 nd end portion 65b and the 4 th end portion 67b are not limited to the above-described positions.

The reflectors arranged so as to sandwich the IDT electrodes together with the reflector 68B also have the same configuration as the reflector 68B. The reflector is substantially line-symmetrical with the reflector 68B with respect to a symmetry axis extending in the 2 nd direction y.

The longitudinally coupled resonator type elastic wave filter of the present embodiment also has the same piezoelectric substrate as that of embodiment 1, and the reflectors are weighted. Therefore, the Q value can be increased, and variation in the attenuation amount can be suppressed in the band near the low frequency side of the passband.

However, the longitudinally coupled resonator type elastic wave filter according to the present embodiment can be formed by, for example, a lift-off method. The details thereof will be described below.

Fig. 14 is a plan view showing a portion corresponding to a reflector in the vicinity thereof for explaining an example of a method of manufacturing a longitudinally coupled resonator type elastic wave filter according to embodiment 2. Fig. 15 is a plan view showing a portion corresponding to a reflector in the vicinity thereof for explaining an example of a method of manufacturing a longitudinally coupled resonator type elastic wave filter according to embodiment 2.

As shown in fig. 14, a piezoelectric substrate 2 is prepared. Next, a resist layer is formed on the piezoelectric substrate 2. The resist layer can be formed by, for example, a printing method, a spin coating method, or the like. Next, the resist pattern 62 is formed by development after exposing the resist layer to light. At this time, the resist layer is connected in the vicinity of the 2 nd end portion of the 2 nd reflective electrode finger forming the reflector in the resist pattern 62 in a plan view. The resist layer is also connected in the vicinity of the portion of the resist pattern 62 where the 4 th end portion of the 3 rd reflective electrode finger of the reflector is formed. The same applies to a portion corresponding to another reflector in the resist pattern 62. Thus, it is possible to provide a region corresponding to a region between each reflector bus bar and each reflective electrode finger in addition to a region corresponding to a region between each reflective electrode finger. Therefore, a continuous wide region surrounded by the reflector bus bars and the reflective electrode fingers can be provided.

Next, as shown in fig. 15, a metal film 63 for forming each IDT electrode and each reflector is formed on the piezoelectric substrate 2 so as to cover the resist pattern 62. The metal film 63 can be formed by, for example, a vacuum deposition method, a sputtering method, or the like.

Next, the resist pattern 62 is stripped. At this time, as described above, the resist pattern 62 has portions where the resist layers are connected to each other in the portions corresponding to the reflectors. This makes it possible to provide a continuous wide region surrounded by the reflector bus bars and the reflective electrode fingers, and the resist stripping liquid can easily contact the resist. This makes it possible to more reliably and easily strip the resist pattern 62. Therefore, in this embodiment, resist residue is less likely to be generated.

Further, in the present embodiment, as shown in fig. 13, the 1 st reflective electrode finger 13 connected to both the 1 st reflector bus bar 64 and the 2 nd reflector bus bar 66 is provided. This allows all the reflective electrodes in the reflector 68B to be at the same potential, and thus, excitation of the elastic wave in the reflector 68B can be suppressed. The same applies to reflectors arranged so as to sandwich a plurality of IDT electrodes together with the reflector 68B. Therefore, ripples in the passband can be suppressed.

As described above, the number and position of the 1 st reflective electrode fingers 13 are not particularly limited. For example, in modification 1 shown in fig. 16, the 1 st reflective electrode finger 13 is a reflective electrode finger located near the center in the 1 st direction x among the plurality of reflective electrode fingers. In a 2 nd modification example of embodiment 2 shown in fig. 17, the 1 st reflecting electrode finger 13 is the reflecting electrode finger farthest from the IDT electrodes among the plurality of reflecting electrode fingers.

As shown in fig. 13, in the present embodiment, the plurality of 2 nd reflective electrode fingers 65 and the plurality of 3 rd reflective electrode fingers 67 are interleaved with each other, but the arrangement of the plurality of 2 nd reflective electrode fingers 65 and the plurality of 3 rd reflective electrode fingers 67 is not limited thereto. For example, in a modification 3 of embodiment 2 shown in fig. 18, in the 2 nd portion 79b, a plurality of 2 nd reflective electrode fingers 65 are arranged continuously in the 1 st direction x. Similarly, the plurality of 3 rd reflective electrode fingers 67 are continuously arranged in the 1 st direction x. In the 1 st portion 69a, the plurality of 2 nd reflective electrode fingers 65 and the plurality of 3 rd reflective electrode fingers 67 are interleaved with each other, as in the case of the 2 nd embodiment.

In addition, the reflector 68B may have the 1 st reflective electrode finger 13 and one of the 2 nd reflective electrode finger 65 and the 3 rd reflective electrode finger 67. However, reflector 68B preferably has 1 st reflective electrode finger 13 and both 2 nd reflective electrode finger 65 and3 rd reflective electrode finger 67. This improves the symmetry of the reflector 68B, and thus the filter characteristics are less likely to be deteriorated.

Hereinafter, as the positional relationship between the 1 st reflection electrode finger and the IDT electrode, the overlapping may be simply referred to as overlapping when viewed from the 1 st direction. As shown in fig. 5 and 6, in embodiment 1, at least the 1 st reflecting electrode finger 13 located on the side closest to the IDT electrode 3E in the 1 st portion 9a of the reflector 8B overlaps the entire intersection region a as viewed in the 1 st direction x. Further, the 1 st reflective electrode finger 13 extends so as to overlap both the 1 st opening formation region Fa and the 2 nd opening formation region Fb. On the other hand, none of the 1 st reflective electrode fingers 13 overlaps with the 1 st outer bus bar region Ga and the 2 nd outer bus bar region Gb of the IDT electrode 3E. Therefore, the weighted portion of the reflector 8B overlaps the central region B, the 1 st edge region Ca, the 1 st slit region Da, the 1 st inner bus bar region Ea, and the 1 st opening forming region Fa. Further, the weighted portion of the reflector 8B overlaps the 2 nd edge region Cb, the 2 nd slit region Db, the 2 nd inner bus bar region Eb, and the 2 nd opening forming region Fb. The same applies to the reflector 8A.

In longitudinally coupled resonator type elastic wave filters according to embodiments 3 to 5 described below, the arrangement of the weighted portion of the reflector is different from that of embodiment 1. The return loss of the longitudinally coupled resonator type elastic wave filters according to embodiments 3 to 5 is compared with that of the comparative example. In the comparative example, the weighting of the reflectors was not performed.

Fig. 19 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 3. Fig. 20 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 4. Fig. 21 is a plan view showing a part of the reflectors and IDT electrodes of the longitudinally coupled resonator type elastic wave filter according to embodiment 5. Fig. 22 is a plan view showing a part of reflectors and IDT electrodes of a longitudinally coupled resonator type elastic wave filter of a comparative example. In addition, the two-dot chain line in fig. 21 shows the positional relationship between the weighted portion of the reflector and the IDT electrode.

As shown in fig. 19, in the present embodiment, the arrangement of the weighted portion in reflector 88A is different from that of the 1 st longitudinally coupled resonator type elastic wave filter 1A of embodiment 1. The present embodiment is also different from the 1 st longitudinally coupled resonator type elastic wave filter 1A in that the 1 st reflector bus bar 84 and the 2 nd reflector bus bar 86 extend parallel to the 1 st direction x. In addition, in the 1 st part 89a of the reflector 88A, the 1 st imaginary line J4 and the 2 nd imaginary line K4 are inclined with respect to the 1 st direction x. The reflectors arranged with the plurality of IDT electrodes interposed therebetween together with the reflectors 88A are configured to be substantially line-symmetric with the reflectors 88A with respect to a symmetry axis extending in the 2 nd direction y. Except for the above-described points, the longitudinally coupled resonator-type elastic wave filter of embodiment 3 has the same configuration as that of the 1 st longitudinally coupled resonator-type elastic wave filter 1A.

In the present embodiment, the range in the 2 nd direction y of the weighted portion of the reflector 88A is wider than that in the 1 st embodiment.

More specifically, at least the 1 st reflecting electrode finger 13 located on the side closest to the IDT electrode 3A in the 1 st section 89a of the reflector 88A overlaps the entire intersection region a of the IDT electrode 3A as viewed from the 1 st direction x. Further, the 1 st reflective electrode finger 13 extends to overlap both the 1 st outer bus bar region Ga and the 2 nd outer bus bar region Gb. The plurality of 1 st reflective electrode fingers 13 become shorter toward the outside of the 1 st direction x. As such, reflector 88A is weighted. Therefore, the weighted portion of the reflector 88A overlaps the center region B, the 1 st edge region Ca, the 1 st slit region Da, the 1 st inner bus bar region Ea, the 1 st opening forming region Fa, and the 1 st outer bus bar region Ga. Further, the weighted portion of the reflector 88A overlaps the 2 nd edge region Cb, the 2 nd slit region Db, the 2 nd inner bus bar region Eb, the 2 nd opening forming region Fb, and the 2 nd outer bus bar region Gb.

In the present embodiment, the number of pairs of the 1 st reflective electrode fingers increases from the outer side toward the inner side in the 2 nd direction y, and therefore, the response outside the impedance band can be dispersed as in embodiment 1. This makes it possible to smooth the attenuation characteristics in a frequency band near the low-frequency side of the passband, and to suppress variations in the attenuation characteristics in this frequency band. In addition, since the longitudinally coupled resonator type elastic wave filter of the present embodiment has a piezoelectric substrate similar to the piezoelectric substrate 2 shown in fig. 4, the Q value can be increased. Similarly, in embodiments 4 and 5 described below, the Q value can be increased, and variations in the attenuation can be suppressed in a frequency band near the low frequency side of the passband.

As shown in fig. 20, in embodiment 4, the range in the 2 nd direction y of the weighted portion of the reflector 88C is narrower than that in embodiment 3.

More specifically, the plurality of 1 st reflection electrode fingers 13 in the 1 st portion 89C of the reflector 88C overlap the central region B of the IDT electrode 3A as viewed from the 1 st direction x. Further, at least the 1 st reflection electrode finger 13 located closest to the IDT electrode 3A in the 1 st section 89c extends so as to overlap both the 1 st slot region Da and the 2 nd slot region Db of the IDT electrode 3A. On the other hand, none of the 1 st reflective electrode fingers 13 overlaps with the 1 st opening forming region Fa and the 2 nd opening forming region Fb of the IDT electrode 3A. Thus, the weighted portion of the reflector 88C overlaps the center region B, the 1 st edge region Ca, the 1 st slit region Da, the 2 nd edge region Cb, and the 2 nd slit region Db as viewed from the 1 st direction x. On the other hand, the weighted portion of the reflector 88C does not overlap with the 1 st aperture forming region Fa and the 2 nd aperture forming region Fb.

As shown in fig. 21, in embodiment 5, the range in the 2 nd direction y of the weighted portion of the reflector 88E is narrower than that in embodiment 4.

More specifically, the plurality of 1 st reflection electrode fingers 13 in the 1 st portion 89E of the reflector 88E overlap the central region B of the IDT electrode 3A as viewed from the 1 st direction x. On the other hand, as shown by the two-dot chain line in fig. 21, none of the 1 st reflection electrode fingers 13 overlaps with the 1 st edge region Ca and the 2 nd edge region Cb of the IDT electrode 3A. Thus, the weighted portion of the reflector 88E overlaps the central region B and does not overlap the 1 st and 2 nd edge regions Ca and Cb as viewed from the 1 st direction x.

As shown in fig. 22, in the comparative example, the reflector 108A is not weighted.

Fig. 23 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 3. Fig. 24 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 4. Fig. 25 is a diagram showing the return loss of the longitudinally coupled resonator-type elastic wave filter according to embodiment 5. Fig. 26 is a graph showing the return loss of the longitudinally coupled resonator-type elastic wave filter of the comparative example.

As shown in fig. 23 to 26, in each longitudinally coupled resonator-type elastic wave filter, a ripple is generated in a frequency band indicated by a circle indicated by a one-dot chain line near the low frequency side of the pass band. Here, in the longitudinally coupled resonator type elastic wave filter in which the return loss is shown in fig. 23 to 25, the range in the 2 nd direction of the weighted portion in the reflector is gradually narrowed in the order of fig. 23, 24, and 25. As shown in fig. 23 to 25, it is understood that the narrower this range is, the smaller the ripple becomes in the frequency band near the low frequency side of the pass band.

On the other hand, as shown in fig. 26, the longitudinally coupled resonator type elastic wave filter of the comparative example has a larger ripple than the longitudinally coupled resonator type elastic wave filter of each embodiment. As described above, according to the present invention, not only the variation in the attenuation amount in the frequency band near the low frequency side of the pass band can be suppressed, but also the ripple can be suppressed. In embodiments 3 to 5, examples are shown in which the piezoelectric substrate 2 is a laminated substrate. However, the elastic wave device may have any one of the electrode structures of embodiments 3 to 5, and the piezoelectric substrate 2 may be a piezoelectric substrate including only a piezoelectric layer. Even in this case, the ripple can be suppressed. By using the longitudinally coupled resonator type elastic wave filter according to the present invention for a filter device, it is possible to suppress the influence of ripples on other filters connected in common.

Description of the reference numerals

1A, 1B: a 1 st longitudinally coupled resonator type elastic wave filter, a 2 nd longitudinally coupled resonator type elastic wave filter;

2: a piezoelectric substrate;

3A to 3E: IDT electrode

4: a support substrate;

5: a high acoustic velocity membrane;

6: a low acoustic velocity membrane;

7: a piezoelectric layer;

8A, 8B: a reflector;

9a, 9 b: part 1, part 2;

10: a filter means;

13: the 1 st reflective electrode finger;

14: 1 st reflector bus bar;

14 d: an opening part;

16: a 2 nd reflector bus bar;

16 d: an opening part;

17A, 17B: a 1 st signal terminal and a 2 nd signal terminal;

24: 1 st bus bar;

24 a: the 1 st inner busbar portion;

24 b: 1 st connecting electrode;

24 c: the 1 st outer busbar portion;

24 d: 1 st opening part;

25: the 1 st electrode finger;

25a, 25 b: a 1 st width part and a 2 nd width part;

26: a 2 nd bus bar;

26 a: the 2 nd inner busbar portion;

26 b: a 2 nd connecting electrode;

26 c: the 2 nd outer busbar portion;

26 d: a 2 nd opening part;

27: the 2 nd electrode finger;

27a, 27 b: a 1 st width part and a 2 nd width part;

34. 36: 1 st reflector bus bar, 2 nd reflector bus bar;

39 a: part 1;

44. 46: 1 st reflector bus bar, 2 nd reflector bus bar;

49 a: part 1;

52A, 52B: a piezoelectric substrate;

54: a high acoustic velocity support substrate;

62: a resist pattern;

63: a metal film;

64: 1 st reflector bus bar;

65: the 2 nd reflective electrode finger;

65a, 65 b: 1 st end and 2 nd end;

66: a 2 nd reflector bus bar;

67: a 3 rd reflective electrode finger;

67a, 67 b: the 3 rd end and the 4 th end;

68B: a reflector;

69a, 69 b: part 1, part 2;

79 b: part 2;

84: 1 st reflector bus bar;

86: a 2 nd reflector bus bar;

88A, 88C, 88E: a reflector;

89a, 89c, 89 e: part 1;

108A: a reflector;

a: a crossover region;

b: a central region;

ca. Cb: 1 st edge region, 2 nd edge region;

da. Db: a 1 st gap area and a 2 nd gap area;

ea. Eb: a 1 st inner bus bar region, a 2 nd inner bus bar region;

fa. Fb: a 1 st opening forming region and a 2 nd opening forming region;

ga. Gb: a 1 st outer bus bar region, a 2 nd outer bus bar region;

ha. Hb: a 1 st high sound velocity region and a 2 nd high sound velocity region;

la, Lb: a 1 st low sound velocity region and a 2 nd low sound velocity region;

p1: a 1 st elastic wave resonator;

s1: and 2 nd elastic wave resonator.