Elastic wave filter, demultiplexer, and communication device

Abstract

The present invention is to improve the frequency characteristics of elastic wave filters. This elastic wave filter comprises, as oblique resonators, series resonators and parallel resonators. In the series resonators: the duty of each of the dummy electrode fingers is greater than the duty of each of the electrode fingers in at least a portion of a first interlacing area where the electrode fingers in the series resonators interlace; and the duty of each of the electrode fingers at the root is greater than the duty of each of the electrode fingers in at least a portion of the first interlacing area. In the parallel resonators: the duty of each of the dummy electrode fingers is in a range of ± 0.08 relative to the duty of each of the electrode fingers in at least a portion of a second interlacing area where the electrode fingers in the parallel resonators interlace; and the duty of each of the electrode fingers at the root is in a range of ± 0.08 relative to the duty of each of the electrode fingers in at least a portion of the second interlacing area.

Description

Technical Field

[0001] One aspect of the present disclosure relates to an elastic wave filter element.

Background Art

[0002] The following Patent Document 1 discloses a configuration example of an elastic wave element.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

[0004] An elastic wave filter according to one aspect of the present disclosure includes at least one series resonator having a first IDT electrode and at least one parallel resonator having a second IDT electrode. The at least one series resonator and the one parallel resonator have a common piezoelectric film. The first IDT electrode includes a first bus bar and a second bus bar facing each other in a direction intersecting the propagation direction of the elastic wave propagating through the piezoelectric film, a plurality of first electrode fingers connected to the first bus bar, a plurality of second electrode fingers connected to the second bus bar and interposed between each of the plurality of first electrode fingers, a plurality of first dummy electrode fingers connected to the first bus bar and facing the tip of each of the plurality of second electrode fingers, and a plurality of second dummy electrode fingers connected to the second bus bar and facing the tip of each of the plurality of first electrode fingers. The direction connecting the tips of each of the plurality of first electrode fingers and the direction connecting the tips of each of the plurality of second electrode fingers are inclined with respect to the propagation direction. The second IDT electrode includes a third bus bar and a fourth bus bar facing each other in a direction intersecting the propagation direction, a plurality of third electrode fingers connected to the third bus bar, a plurality of fourth electrode fingers connected to the fourth bus bar and interposed between each of the plurality of third electrode fingers, a plurality of third dummy electrode fingers connected to the third bus bar and facing the tip of each of the plurality of fourth electrode fingers, and a plurality of fourth dummy electrode fingers connected to the fourth bus bar and facing the tip of each of the plurality of third electrode fingers. The direction connecting the tips of each of the plurality of third electrode fingers and the direction connecting the tips of each of the plurality of fourth electrode fingers are inclined with respect to the propagation direction. In the at least one series resonator, the duty of the first dummy electrode finger and the duty of the second dummy electrode finger are larger than the duty of the first electrode finger and the duty of the second electrode finger in at least a part of the first intersection region where the first electrode finger and the second electrode finger intersect. The duty at the root of the first electrode finger and the duty at the root of the second electrode finger are in at least a part of the first intersection region,Greater than the duty of the first electrode finger and the duty of the second electrode finger, in at least one of the at least one parallel resonator, the duty of the third dummy electrode finger and the duty of the fourth dummy electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second intersection region where the third electrode finger and the fourth electrode finger intersect, and the duty at the root of the third electrode finger and the duty at the root of the fourth electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second intersection region.

Brief Description of Drawings

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Figure 1

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Mode for Carrying Out the Invention

[0006] 〔Embodiment 1〕 The surface acoustic wave filter 100 of Embodiment 1 will be described below. For convenience of explanation, members having the same functions as the members described in Embodiment 1 will be given the same reference numerals in the following embodiments, and their descriptions will not be repeated. For the sake of brevity, descriptions of known technical matters will also be omitted as appropriate. Each configuration and each numerical value described in this specification are merely examples unless otherwise specified. Therefore, unless otherwise specified, the positional relationships of the respective members are not limited to the examples in the respective figures. Also, the respective members are not necessarily shown to scale.

[0007] (An example configuration of the surface acoustic wave filter 100) FIG. 1 is a diagram showing an example configuration of a surface acoustic wave filter 100. The surface acoustic wave filter 100 may have at least one series resonator 1S and at least one parallel resonator 1P as a plurality of surface acoustic wave elements (resonators). As shown in FIG. 1, the surface acoustic wave filter 100 may be a ladder-type filter in which the series resonator 1S and the parallel resonator 1P are arranged in a ladder shape.

[0008] The surface acoustic wave filter 100 in the example of FIG. 1 has three series resonators 1S and two parallel resonators 1P. In this specification, when distinguishing each of the three series resonators 1S, these are denoted as series resonators 1S-1 to 1S-3, respectively. Also, when distinguishing each of the two parallel resonators 1P, these are denoted as parallel resonators 1P-1 to 1P-2, respectively.

[0009] As shown in FIG. 1, the surface acoustic wave filter 100 may be connected to an input terminal Tin and an output terminal Tout. Hereinafter, for example, the input terminal Tin will be simply abbreviated as Tin as appropriate. The surface acoustic wave filter 100 may be configured as a frequency filter that filters an electrical signal input to Tin and outputs the filtered electrical signal to Tout.

[0010] The surface acoustic wave filter 100 may have a series wiring SL that connects a plurality of series resonators 1S, and a plurality of parallel wirings PL that connect each of the plurality of parallel resonators 1P. And the surface acoustic wave filter 100 may be connected to a plurality of ground terminals TGND corresponding to each of the plurality of PLs. In the example of FIG. 1, the surface acoustic wave filter 100 has two PLs. Therefore, the surface acoustic wave filter 100 is connected to two TGNDs. When distinguishing each of the two PLs, these are denoted as PL-1 to PL-2. Also, when distinguishing each of the two TGNDs, these are denoted as TGND-1 to TGND-2.

[0011] SL may be connected to Tin and Tout. Therefore, the series resonators 1S-1 to 1S-3 may each be connected to Tin and Tout via SL. In the example of FIG. 1, the series resonator 1S-1 is the series resonator closest to Tin. In contrast, the series resonator 1S-3 is the series resonator closest to Tout (in other words, the farthest from Tin).

[0012] In the example of FIG. 1, the parallel resonator 1P-1 is the parallel resonator closest to Tin. In contrast, the parallel resonator 1P-2 is the parallel resonator closest to Tout. PL-1 branches from SL between the series resonators 1S-1 and 1S-2 and is connected to TGND-1. PL-2 branches from SL between the series resonators 1S-2 and 1S-3 and is connected to TGND-2. In this way, the parallel resonators 1P-1 to 1P-2 may each be connected to TGND-1 to TGND-2 via PL-1 to PL-2. According to this configuration, unnecessary components included in the electrical signal can be filtered by letting them escape to TGND via the parallel resonator 1P.

[0013] (Another configuration example of the surface acoustic wave filter 100) The elastic wave filter 100 may be a frequency filter having at least one series resonator 1S and at least one parallel resonator 1P. Therefore, as is obvious to those skilled in the art, the elastic wave filter 100 may be, for example, a multi-mode type filter.

[0014] (One configuration example of the series resonator 1S) FIG. 2 is a plan view showing one configuration example of the series resonator 1S. The series resonator 1S is an example of a type 1 diagonal resonator described later. In Embodiment 1, as an example of the resonator, a SAW (Surface Acoustic Wave) element is shown. In the following description, for convenience, the orthogonal coordinate system (xyz coordinate system) shown in FIG. 1 is introduced. In the example of Embodiment 1, the x direction is the propagation direction of the elastic wave propagating through the piezoelectric film 2 of the series resonator 1S. On the other hand, the y direction is an example of a direction intersecting the x direction in the plan view.

[0015] FIG. 3 is a cross-sectional view taken along line III-III of FIG. 2. As shown in FIG. 3, in the example of Embodiment 1, the z direction is the thickness direction of each member of the series resonator 1S. In the following, with the positive direction of the z direction being upward, the term upper surface is used. Also, with the negative direction of the z direction being downward, the term lower surface is used.

[0016] As is obvious to those skilled in the art, the elastic wave according to one aspect of the present disclosure is not limited to SAW. The elastic wave may be any wave that can conceptually define the propagation direction. The elastic wave may be, for example, a BAW (Bulk Acoustic Wave). Therefore, as another example of the resonator according to one aspect of the present disclosure, a BAW element can also be cited. Therefore, the elastic wave filter according to one aspect of the present disclosure may be a SAW filter or, alternatively, a BAW filter.

[0017] The in-line resonator 1S may include (i) a piezoelectric film 2, (ii) a first IDT (Interdigital Transducer) electrode 3 located on the upper surface 2A of the piezoelectric film 2, (iii) a support substrate 98, and (iv) a low acoustic velocity film 8. The IDT electrode is also referred to as an excitation electrode. In the example of FIG. 2, the first IDT electrode 3 is located between two ports (terminals) P1 and P2. The ports P1 and P2 may be the input port and the output port of the first IDT electrode 3, respectively.

[0018] As shown in FIG. 2, the in-line resonator 1S may have a pair of reflectors 4A and 4B corresponding to the first IDT electrode 3. In this specification, each of the reflectors 4A and 4B is also generically referred to as a reflector 4. The reflector 4 may be positioned so as to sandwich the first IDT electrode 3 in the x direction.

[0019] The piezoelectric film 2 may be composed of a single crystal material having piezoelectricity. For example, the material of the piezoelectric film 2 may be lithium tantalate (LiTaO 3 : also referred to as LT) or lithium niobate (LiNbO 3 : also referred to as LN). As an example, the piezoelectric film 2 may be an LT film.

[0020] The support substrate 98 supports each part of the in-line resonator 1S. Therefore, as shown in FIG. 3, the support substrate 98 may be located on the lower surface 2B side of the piezoelectric film 2. The support substrate 98 may be configured such that the acoustic velocity of the elastic wave propagating through the support substrate 98 is higher than the acoustic velocity of the elastic wave propagating through the piezoelectric film 2. According to this configuration, the loss characteristics of the resonator can be improved. Therefore, the loss of the elastic wave filter 100 can be reduced. Examples of the material of the support substrate 98 include Si, sapphire, quartz, and AlN. As an example, the support substrate 98 may be a Si substrate.

[0021] The low acoustic velocity film 8 may be positioned between the piezoelectric film 2 and the support substrate 98. Therefore, as shown in FIG. 3, the low acoustic velocity film 8 may be positioned below the piezoelectric film 2 and above the support substrate 98. The piezoelectric film 2 and the support substrate 98 may be joined via the low acoustic velocity film 8. The low acoustic velocity film 8 only needs to be configured such that the acoustic velocity of the elastic wave propagating through the low acoustic velocity film 8 is slower than the acoustic velocity of the elastic wave propagating through the piezoelectric film 2. According to this configuration, the loss characteristics of the resonator can be improved. Therefore, the loss of the elastic wave filter 100 can be reduced. As an example of the material of the low acoustic velocity film 8, silicon oxide (SiO x ) can be mentioned. As an example, the low acoustic velocity film 8 may be a SiO 2 film.

[0022] As an example, in this specification, "low acoustic velocity" means the acoustic velocity of the bulk wave that is slower than the acoustic velocity of the bulk wave propagating through the piezoelectric film 2. Also, "high acoustic velocity" means the acoustic velocity of the bulk wave that is faster than the acoustic velocity of the bulk wave propagating through the piezoelectric film 2. The acoustic velocity of the bulk wave may be compared based on the acoustic velocity of any one of the longitudinal wave, the fast shear wave, and the slow shear wave.

[0023] As shown in FIG. 3, in this specification, the thickness of the first IDT electrode 3 is represented by s, the electrode finger pitch of the first IDT electrode 3 is represented by p1, the thickness of the piezoelectric film 2 is represented by Tp, and the thickness of the low acoustic velocity film 8 is represented by Ti, respectively. p1 is, for example, the pitch (repetition interval) in the x direction between the centers of the plurality of electrode fingers 32 (described later) of the first IDT electrode 3. As an example, p1 may be set equal to half the wavelength (λ / 2) of the elastic wave excited by the first IDT electrode 3. In this case, the wavelength λ of the elastic wave can be defined as twice the length of p1. That is, it can be defined as λ = 2 × p1.

[0024] The first IDT electrode 3 may have a first comb electrode 30a (the comb electrode on the port P1 side) and a second comb electrode 30b (the comb electrode on the port P2 side). In this specification, the first comb electrode 30a and the second comb electrode 30b are also collectively referred to as the comb electrode 30. In the following description, in the first IDT electrode 3, the suffix a is appropriately attached to each member corresponding to the first comb electrode, and the suffix b is appropriately attached to each member corresponding to the second comb electrode. For these members as well, the collective name corresponding to the comb electrode 30 is appropriately used.

[0025] The comb electrode 30 may have two bus bars 31 (a first bus bar 31a and a second bus bar 31b) facing each other in the y direction. The bus bar 31 may have a generally constant width and may be formed in a long shape extending linearly. However, the width of the bus bar 31 does not necessarily have to be constant.

[0026] In addition, the comb electrode 30 may have a plurality of electrode fingers 32 extending from one bus bar 31 (e.g., the first bus bar 31a) to the other bus bar 31 (e.g., the second bus bar 31b) side in the y direction. The first electrode fingers 32a and the second electrode fingers 32b may be alternately and repeatedly positioned on the upper surface 2A of the piezoelectric film 2 so as to have a generally constant interval in the x direction. As described above, the first electrode fingers 32a may be connected to the first bus bar 31a. The second electrode fingers 32b are connected to the second bus bar 31b and may be interposed between each of the plurality of first electrode fingers 32a.

[0027] In addition, the comb electrode 30 may have a plurality of dummy electrode fingers 35 extending from one bus bar 31 (e.g., the first bus bar 31a) to the other bus bar 31 (e.g., the second bus bar 31b) side in the y direction and facing the tips of the electrode fingers 32 extending from the other bus bar 31. The pitch of the dummy electrode fingers 35 may be set to a value equal to the pitch of the electrode fingers 32.

[0028] Therefore, the first dummy electrode finger 35a may be connected to the first bus bar 31a and may face the tip of each of the plurality of second electrode fingers 32b. For example, the first dummy electrode finger 35a may face the tip of each of the plurality of second electrode fingers 32b via a gap. Further, the second dummy electrode finger 35b may be connected to the second bus bar 31b and may face the tip of each of the plurality of first electrode fingers 32a. For example, the second dummy electrode finger 35b may face the tip of each of the plurality of first electrode fingers 32a via a gap.

[0029] As shown in FIG. 2, the direction connecting the tips of the plurality of first electrode fingers 32a may be inclined with respect to the x direction. In other words, the virtual line L1 connecting the tips of the plurality of first electrode fingers 32a may be inclined with respect to the x direction. Thus, the virtual line L1 may form a certain inclination angle A1 (first inclination angle) with respect to the x axis.

[0030] Also, the direction connecting the tips of the plurality of second electrode fingers 32b may be inclined with respect to the x direction. In other words, the virtual line L2 connecting the tips of the plurality of second electrode fingers 32b may be inclined with respect to the x direction. Thus, the virtual line L2 may form a certain inclination angle B1 (second inclination angle) with respect to the x axis.

[0031] The first inclination angle and the second inclination angle may be set equal to each other, or may be set different from each other. In FIG. 2, the case where the first inclination angle and the second inclination angle are equal is illustrated. In this specification, a resonator in which the first inclination angle and the second inclination angle are non-zero is referred to as an inclined resonator. Also, a resonator in which the third inclination angle and the fourth inclination angle described later are non-zero is also referred to as an inclined resonator. According to the inclined resonator, the transverse mode spurious (transverse mode ripple) generated in the resonator can be reduced (see Patent Document 1).

[0032] In this specification, the region where the first electrode finger 32a and the second electrode finger 32b intersect is referred to as the first intersection region. The shape of the first intersection region may be defined by (i) virtual lines L1 and L2 and (ii) the electrode fingers 32 located on the reflector 4 side. The shape of the first intersection region in the example of FIG. 2 is a parallelogram shape. Therefore, in FIG. 2, the IDT electrode 3 having a parallelogram outer shape is illustrated.

[0033] In this specification, the length of the electrode finger 32 in the x direction is referred to as the width of the electrode finger 32. Each width ws1 of the electrode fingers 32 (see FIG. 3) may be appropriately set according to, for example, the electrical characteristics required for the series resonator 1S. As an example, ws1 may be set according to p1 (the pitch of the electrode fingers 32). In this specification, the ratio of the width of the electrode finger to a certain electrode finger pitch, that is, ws1 / p1, is referred to as the Duty of the electrode finger. ws1 may be substantially constant. However, ws1 does not necessarily have to be constant throughout the y direction in one electrode finger 32. ws1 in the following description refers to, for example, the width of the electrode finger 32 at the center of the first intersection region.

[0034] As shown in FIG. 2, the width ws2 of the second dummy electrode finger 35b may be set to be larger than the width ws1 of the electrode finger 32 in at least a part of the first intersection region. Also, the width ws3 of the first dummy electrode finger 35a may be set to be larger than the width ws1 of the electrode finger 32 in at least a part of the first intersection region. In the example of FIG. 2, ws2 and ws3 are set to be equal to each other.

[0035] As described above, ws2 and ws3 may be set to be larger than the width ws1 of the electrode finger 32 (e.g., the width of the first electrode finger and the width of the second electrode finger) in at least a part of the first intersection region. According to this configuration, the transverse mode spurious in the series resonator 1S can be further reduced. As an example, ws2 and ws3 may be set to be larger than the average value of the widths w1 of the plurality of electrode fingers 32 in the intersection region.

[0036] In the example of FIG. 2, a region on the side of the first bus bar 31a with respect to the virtual line L3 connecting the tips of the plurality of first dummy electrode fingers 35a is referred to as the first dummy region. And a region on the side of the second bus bar 31b with respect to the virtual line L4 connecting the tips of the plurality of second dummy electrode fingers 35b is referred to as the second dummy region. As shown in FIG. 2, the width of the first electrode finger 32a (the base portion of the first electrode finger 32a) located on the side of the first dummy electrode finger may be set to be larger than ws1. The width of the second electrode finger 32b (the base portion of the second electrode finger 32b) located on the side of the second dummy electrode finger may also be set to be larger than ws1. In the example of FIG. 2, the width of the base portion of each electrode finger 32 is set to a value equal to ws2. Thus, the base portion of the electrode finger 32 may be formed wider than other portions of the electrode finger. According to this configuration, the horizontal mode ripple in the series resonator 1S can be effectively reduced (see Patent Document 1).

[0037] In the following description, for convenience, the Duty of the first dummy electrode finger 35a and the Duty of the second dummy electrode finger 35b are referred to as Dutyd1 and Dutyd2, respectively. Also, the Duty of the first electrode finger 32a and the Duty of the second electrode finger 32b are referred to as Duty1 and Duty2, respectively.

[0038] As is clear from the above descriptions regarding the relationship among ws1 to ws3, Dutyd1 and Dutyd2 may be set to be larger than Duty1 and Duty2 in at least a part of the first intersection region. According to this configuration, the horizontal mode spurious in the series resonator 1S can be further reduced.

[0039] As an example, Dutyd1 and Dutyd2 may be set to be 0.08 or more larger than Duty1 and Duty2 in at least a part of the first intersection region. More specifically, Dutyd1 and Dutyd2 may be within a range of +0.08 or more and +0.16 or less with respect to Duty1 and Duty2 in at least a part of the first intersection region.

[0040] Dutyd1 and Dutyd2 may be set larger than Duty1 and Duty2 at the center of the first intersection region. Dutyd1 and Dutyd2 may be set larger than Duty1 and Duty2 in the entire region of the first intersection region. According to this configuration, the transverse mode spurious in the series resonator 1S can be further reduced.

[0041] In addition, Duty1 at the root of the first electrode finger 32a and Duty2 at the root of the second electrode finger 32b may be set larger than Duty1 and Duty2 of the second electrode finger in at least a part of the first intersection region. According to this configuration, the transverse mode spurious in the series resonator 1S can be further reduced.

[0042] As an example, Duty1 at the root of the first electrode finger 32a and Duty2 at the root of the second electrode finger 32b may be set 0.08 or more larger than Duty1 and Duty2 in at least a part of the first intersection region. For example, Duty1 at the root of the first electrode finger 32a and Duty2 at the root of the second electrode finger 32b may be in the range of +0.08 or more and +0.16 or less with respect to Duty1 and Duty2 in at least a part of the first intersection region.

[0043] Duty1 at the root of the first electrode finger 32a and Duty2 at the root of the second electrode finger 32b may be set larger than Duty1 and Duty2 at the center of the first intersection region. Duty1 at the root of the first electrode finger 32a and Duty2 at the root of the second electrode finger 32b may be set larger than Duty1 and Duty2 in the entire region of the first intersection region.

[0044] In this specification, an inclined resonator in which (i) the duty of each dummy electrode finger is larger than the duty of each electrode finger in at least a part of the intersection region (e.g., the first intersection region), and (ii) the duty at the base of each electrode finger is larger than the duty of each electrode finger in at least a part of the intersection region is referred to as a type 1 inclined resonator. An example of the frequency characteristics of the type 1 inclined resonator will be described later.

[0045] (One configuration example of the parallel resonator 1P) FIG. 4 is a plan view showing one configuration example of the parallel resonator 1P. The parallel resonator 1P is an example of a type 2 inclined resonator described later. FIG. 5 is a cross-sectional view taken along the line V-V of FIG. 4. As will be described later, the parallel resonator 1P may be located on the same chip as the series resonator 1S. Therefore, the parallel resonator 1P may have a common support substrate 98 with the series resonator 1S. For this reason, the parallel resonator 1P may have a common piezoelectric film 2 with the series resonator 1S. Further, the parallel resonator 1P may have a common low-velocity film 8 with the series resonator 1S.

[0046] The parallel resonator 1P may have a second IDT electrode 5 located on the upper surface 2A of the piezoelectric film 2. In the example of FIG. 4, the second IDT electrode 5 is located between two ports P3 and P4. The ports P3 and P4 may be the input port and the output port of the parallel resonator 1P, respectively. The parallel resonator 1P may have a pair of reflectors 7A and 7B corresponding to the second IDT electrode 5. In this specification, each of the reflectors 7A and 7B is also generically referred to as a reflector 7. The reflector 7 may be located so as to sandwich the second IDT electrode 5 in the x direction.

[0047] As shown in FIG. 5, in this specification, the electrode finger pitch of the second IDT electrode 5 is denoted as p2, and the width of the electrode finger 23 (described later) is denoted as wp1. In the example of FIG. 5, the second IDT electrode 5 has the same thickness (s) as the first IDT electrode 3. p2 is, for example, the pitch in the x direction between the centers of a plurality of electrode fingers 23. As an example, p2 may be set equal to half the wavelength (λ / 2) of the elastic wave excited by the second IDT electrode 5. In this case, the wavelength λ of the elastic wave can be defined as twice the length of p2. That is, λ can also be defined as λ = 2 × p2. The λ in this specification may be defined based on p1, or alternatively may be defined based on p2.

[0048] The second IDT electrode 5 may have a first comb electrode 13A (the comb electrode on the port P3 side) and a second comb electrode 13B (the comb electrode on the port P4 side). In this specification, the first comb electrode 13A and the second comb electrode 13B are also collectively referred to as the comb electrode 13. In the following description, in the second IDT electrode 5, the suffix A is appropriately attached to each member corresponding to the first comb electrode, and the suffix B is appropriately attached to each member corresponding to the second comb electrode. For these members as well, the general term corresponding to the comb electrode 13 is appropriately used.

[0049] The comb electrode 13 may have two bus bars 21 (a third bus bar 21A and a fourth bus bar 21B) facing each other in the y direction. The comb electrode 13 may have a plurality of electrode fingers 23 extending from one bus bar 21 (e.g., the third bus bar 21A) to the other bus bar 21 (e.g., the fourth bus bar 21B) side in the y direction. The third electrode finger 23A may be connected to the third bus bar 21A. The fourth electrode finger 23B is connected to the fourth bus bar 21B and may be interposed between each of the plurality of third electrode fingers 23A.

[0050] In addition, the comb teeth electrodes 30 may extend from one bus bar 21 (e.g., the third bus bar 21A) to the other bus bar 21 (e.g., the fourth bus bar 21B) in the y direction, and may have a plurality of dummy electrode fingers 25 facing the tips of the electrode fingers 23 extending from the other bus bar 31. The pitch of the dummy electrode fingers 25 may be set to a value equal to the pitch of the electrode fingers 23.

[0051] Therefore, the third dummy electrode finger 25A may be connected to the third bus bar 21A and may face the tip of each of the plurality of fourth electrode fingers 23B. For example, the third dummy electrode finger 25A may face the tip of each of the plurality of fourth electrode fingers 23B via a gap. Also, the fourth dummy electrode finger 25B may be connected to the fourth bus bar 21B and may face the tip of each of the plurality of third electrode fingers 23A. For example, the fourth dummy electrode finger 25B may face the tip of each of the plurality of third electrode fingers 23A via a gap.

[0052] As shown in FIG. 4, the direction connecting the tips of each of the plurality of third electrode fingers 23A may be inclined with respect to the x direction. In other words, the virtual line L5 connecting the tips of each of the plurality of third electrode fingers 23A may be inclined with respect to the x direction. Thus, the virtual line L5 may form a certain inclination angle A2 (third inclination angle) with respect to the x axis.

[0053] Also, the direction connecting the tips of each of the plurality of fourth electrode fingers 23B may be inclined with respect to the x direction. In other words, the virtual line L6 connecting the tips of each of the plurality of fourth electrode fingers 23B may be inclined with respect to the x direction. Thus, the virtual line L6 may form a certain inclination angle B2 (fourth inclination angle) with respect to the x axis.

[0054] The third inclination angle and the fourth inclination angle may be set equal to each other, or may be set to be different from each other. In FIG. 4, the case where the third inclination angle and the fourth inclination angle are equal is illustrated. As described above, the parallel resonator 1P in FIG. 4 is common to the series resonator 1S in FIG. 1 in that it is an inclined resonator.

[0055] In this specification, the region where the third electrode finger 23A and the fourth electrode finger 23B intersect is referred to as the second intersection region. The shape of the second intersection region may be defined by (i) the virtual lines L5 and L6, and (ii) the electrode fingers 23 located on the reflector 7 side. The above-mentioned wp1 may be substantially constant. However, wp1 does not necessarily have to be constant throughout the y direction in one electrode finger 23. In the following description, wp1 refers to, for example, the width of the electrode finger 23 at the center of the second intersection region.

[0056] As shown in FIG. 4, the width wp2 of the fourth dummy electrode finger 25B may be set to a value substantially equal to the width wp1 of the electrode finger 23 in at least a part of the second intersection region. Also, the width wp3 of the third dummy electrode finger 25A may be set to a value substantially equal to the width wp1 of the electrode finger 23 in at least a part of the second intersection region. In the example of FIG. 1, wp2 and wp3 are set to be equal to each other.

[0057] In the example of FIG. 4, the region on the third bus bar 21A side from the virtual line L7 connecting the tips of the plurality of third dummy electrode fingers 25A is referred to as the third dummy region. And the region on the fourth bus bar 21B side from the virtual line L8 connecting the tips of the plurality of fourth dummy electrode fingers 25B is referred to as the fourth dummy region. As shown in FIG. 4, the width of the third electrode finger 23A (the root portion of the third electrode finger 23A) located on the third dummy electrode finger side may be set to a value substantially equal to wp1. The width of the fourth electrode finger 23B (the root portion of the fourth electrode finger 23B) located on the fourth dummy electrode finger side may also be set to a value substantially equal to wp1. Thus, the root portion of each electrode finger 23 may have a width substantially equal to that other than the root portion of the electrode finger.

[0058] In the following description, for convenience, the Duty of the third dummy electrode finger 25A and the Duty of the fourth dummy electrode finger 25B are referred to as Dutyd3 and Dutyd4, respectively. Also, the Duty of the third electrode finger 23A and the Duty of the fourth electrode finger 23B are referred to as Duty3 and Duty4, respectively.

[0059] As is clear from the above descriptions of the relationships among wp1 to wp3, Dutyd3 and Dutyd4 may be set to be approximately equal to Duty3 and Duty4 in at least a part of the second intersection region.

[0060] As an example, in the second IDT electrode 5, "a certain Duty is approximately equal to another Duty" may mean that "the certain Duty is within the range of ±0.08 with respect to the other Duty". Therefore, Dutyd3 and Dutyd4 may be within the range of ±0.08 with respect to Duty3 and Duty4 in at least a part of the second intersection region.

[0061] For example, Dutyd3 and Dutyd4 may be set to be larger than Duty1 and Duty2 in the central part of the second intersection region. Dutyd3 and Dutyd4 may also be set to be larger than Duty3 and Duty4 in the entire region of the second intersection region.

[0062] In addition, Duty3 at the base of the third electrode finger 23A and Duty4 at the base of the fourth electrode finger 23B may be set to be approximately equal to Duty3 and Duty4 of the second electrode finger in at least a part of the second intersection region. For example, Duty3 at the base of the third electrode finger 23A and Duty4 at the base of the fourth electrode finger 23B may be set to be approximately equal to Duty3 and Duty4 in the central part of the second intersection region. Duty3 at the base of the third electrode finger 23A and Duty4 at the base of the fourth electrode finger 23B may also be set to be larger than Duty3 and Duty4 in the entire region of the second intersection region.

[0063] As is clear from the above description of the magnitudes of the Duties in the second IDT electrode 5, Duty3 at the base of the third electrode finger 23A and Duty4 at the base of the fourth electrode finger 23B may be within the range of ±0.08 with respect to Duty3 and Duty4 in at least a part of the second intersection region.

[0064] In this specification, a diagonal resonator in which (i) the duty of each dummy electrode finger is substantially equal to the duty of each electrode finger in at least a part of the intersection region (e.g., the second intersection region), and (ii) the duty at the base of each electrode finger is substantially equal to the duty of each electrode finger in at least a part of the intersection region is referred to as a type 2 diagonal resonator. An example of the frequency characteristics of the type 2 diagonal resonator will also be described later.

[0065] In the surface acoustic wave filter 100, at least one (e.g., one of the two parallel resonators 1P) of the at least one parallel resonator 1P may be a type 2 diagonal resonator. Therefore, for example, in the surface acoustic wave filter 100, all of the at least one parallel resonator 1P may be type 2 diagonal resonators.

[0066] (Another configuration example of the series resonator 1S and the parallel resonator 1P) FIG. 6 is a diagram showing another configuration example of the series resonator 1S and the parallel resonator 1P. In FIG. 6, (i) the reference numeral 6000A indicates a series resonator 1SV which is another configuration example of the series resonator 1S, and (ii) the reference numeral 6000B indicates a parallel resonator 1PV which is another configuration example of the parallel resonator 1P.

[0067] The series resonator 1SV and the parallel resonator 1PV may have a common high-velocity film 9. The high-velocity film 9 may be configured such that the sound velocity of the elastic wave propagating through the high-velocity film 9 is higher than the sound velocity of the elastic wave propagating through the piezoelectric film 2. As shown in FIG. 6, the high-velocity film 9 may be located between the piezoelectric film 2 and the low-velocity film 8. Therefore, for example, the high-velocity film 9 may be located below the piezoelectric film 2 and above the low-velocity film 8. By providing the high-velocity film 9, the loss characteristics of the resonator can be improved. Therefore, the loss of the surface acoustic wave filter 100 can be reduced.

[0068] Examples of the material of the high-velocity film 9 include, for example, Al 2 O 3 and the like. Therefore, the high-velocity film 9 is Al 2 O 3It may be a film. Note that the position of the high-speed film 9 is not limited to the example of FIG. 6. As another example, the high-speed film 9 may be located between the low-speed film 8 and the support substrate 98. Therefore, for example, the high-speed film 9 may be located below the low-speed film 8 and above the support substrate 98.

[0069] (Examples of the frequency characteristics of each diagonal resonator) FIG. 7 illustrates the frequency characteristics of each of the type 1 diagonal resonator and the type 2 diagonal resonator. In each graph of FIG. 7, the solid line indicates the characteristics of the type 1 diagonal resonator, and the dotted line indicates the characteristics of the type 2 diagonal resonator.

[0070] The design conditions of the type 1 diagonal resonator and the type 2 diagonal resonator in the example of FIG. 7 are · Tp (thickness of the LT film as a common dielectric film): 0.5 μm · Al 2 O 3 film (common high-speed film) thickness: 0.01 nm · Ti (thickness of the SiO 2 film as a common low-speed film): 0.3 μm · Resistivity of Si (common support substrate): 10 kΩ·cm · Electrode finger pitch of each IDT electrode: 1.17 μm · Configuration of each IDT electrode: Ti60 Å / AlCu1400 Å · Crossing width (width of the crossing region): 16λ · Number of electrode fingers in each IDT electrode: 400 · Duty of the electrode fingers in the crossing region of each IDT electrode: 0.5 · Tilt angle: -6° as follows. In the above design conditions, the first tilt angle to the fourth tilt angle are collectively referred to as the tilt angle. According to the design conditions, since p1 = p2 = 1.17 μm, λ = 1.17 μm × 2 = 2.34 μm. That is, Tp corresponds to 0.213λ. Thus, Tp may be less than or equal to λ. According to this configuration, as the piezoelectric film 2 is thinned, the loss characteristics of the resonator can be improved. Therefore, the loss of the elastic wave filter 100 can be reduced.

[0071] In the type 1 diagonal resonator in the example of FIG. 7, Duty1 = 0.5 and Duty2 = 0.5 are set in the entire area of the first crossing region. And in the type 1 diagonal resonator, the Duty at the base of the first electrode finger is set to 0.66, the Duty at the base of the second electrode finger is set to 0.66, and Dutyd1 = 0.66 and Dutyd2 = 0.66 are set. On the other hand, in the type 2 diagonal resonator in the example of FIG. 7, Duty3 = 0.5 and Duty4 = 0.5 are set in the entire area of the second crossing region. And in the type 2 diagonal resonator, the Duty at the base of the third electrode finger is set to 0.5, the Duty at the base of the fourth electrode finger is set to 0.5, and Dutyd3 = 0.5 and Dutyd4 = 0.5 are set.

[0072] The horizontal axis in each graph of FIG. 7 indicates the frequency (unit: MHz). In FIG. 7, the graph of reference numeral 7000A shows the impedance characteristics of each resonator. The vertical axis in the graph indicates the absolute value (magnitude) of the impedance (unit: Ohm). The graph of reference numeral 7000B shows the phase characteristics of the impedance of each diagonal resonator. The vertical axis in the graph indicates the phase of the impedance (unit: degree). In the following description, the phase of the impedance is simply abbreviated as "phase".

[0073] The main resonance frequency of a certain resonator is the frequency at which the absolute value of the impedance of the resonator takes the minimum value. The main resonance frequency is also the frequency at which the phase becomes 0° in the frequency band where the phase increases monotonically. The anti-resonance frequency of a certain resonator is the frequency at which the absolute value of the impedance of the resonator takes the maximum value. The anti-resonance frequency is also the frequency at which the phase becomes 0° in the frequency band where the phase decreases monotonically. In the example of FIG. 7, each diagonal resonator has substantially equal main resonance frequency and anti-resonance frequency. The passband of the elastic wave filter is defined by the main resonance frequency and anti-resonance frequency of each resonator included in the elastic wave filter.

[0074] FIG. 8 shows an enlarged view of regions REG1 to REG3 in the graph of reference numeral 7000B in FIG. 7. In FIG. 8, reference numeral 8000A is an enlarged view of region REG1. In the graph of reference numeral 8000A, the phase region near -90° in the first frequency band (1600 to 1660 MHz) is enlarged. The first frequency band is an example of a frequency band including the main resonance frequency of each diagonal resonator.

[0075] As shown in the graph of reference numeral 8000A, in the first frequency band, the phase of the type 1 diagonal resonator is smaller than the phase of the type 2 diagonal resonator. This indicates that according to the type 1 diagonal resonator, the transverse mode spurs generated in the low-frequency side stopband of the elastic wave filter can be reduced more effectively than the type 2 diagonal resonator.

[0076] Reference numeral 8000B is an enlarged view of region REG2. In the graph of reference numeral 8000B, the phase region near 90° in the second frequency band (1640 to 1700 MHz) is enlarged. The second frequency band is another example of a frequency band including the main resonance frequency of each diagonal resonator.

[0077] The maximum value of the phase (hereinafter referred to as MaxPhase) is one of the indexes indicating the performance of the resonator. The ideal value of the maximum value of MaxPhase is 90°. It is known that the higher MaxPhase is (that is, the closer MaxPhase is to 90°), the smaller the resonance loss in the resonator becomes.

[0078] As shown in the graph of reference numeral 8000B, in the second frequency band, the phase of the type 1 diagonal resonator is larger than the phase of the type 2 diagonal resonator. That is, the MaxPhase of the type 1 diagonal resonator is higher than the MaxPhase of the type 1 diagonal resonator. This indicates that according to the type 1 diagonal resonator, the resonance loss can be reduced more effectively than the type 2 diagonal resonator.

[0079] As shown in each graph of symbols 8000A and 8000B, according to the type 1 diagonal resonator, transverse mode spurs can be more effectively reduced, and as a result, resonance loss can be more effectively reduced. As can be understood from the above explanations, this effect is obtained by the configuration of the type 1 diagonal resonator (for convenience, referred to as the type 1 configuration), that is, "(i) the duty of each dummy electrode finger is larger than the duty of each electrode finger in at least a part of the intersection region, and (ii) the duty at the root of each electrode finger is larger than the duty of each electrode finger in at least a part of the intersection region."

[0080] Symbol 8000C is an enlarged view of region REG3. In the graph of symbol 8000C, the phase region near -90° in the third frequency band (1720 - 1820 MHz) is enlarged. The third frequency band is an example of a frequency band including the anti-resonance frequency of each diagonal resonator. As shown in the graph of symbol 8000C, in the third frequency band, the stop band spurs in the type 1 diagonal resonator are located on the lower frequency side than the stop band spurs in the type 2 diagonal resonator. Such a lowering of the stop band spurs is considered to be a side effect caused by the above type 1 configuration.

[0081] (Example of the relationship between the type of parallel resonator and the frequency filter of the surface acoustic wave filter) FIG. 9 is a diagram showing an example of the relationship between the type of parallel resonator and the frequency characteristics (more specifically, attenuation characteristics) of the surface acoustic wave filter. In the graph of symbol 9000A in FIG. 9, the frequency characteristics of the surface acoustic wave filter according to the embodiment (e.g., surface acoustic wave filter 100) and the surface acoustic wave filter according to the comparative example are illustrated respectively.

[0082] In the elastic wave filter according to the embodiment (hereinafter abbreviated as "embodiment"), the series resonator is a type 1 diagonal resonator, and the parallel resonator is a type 2 diagonal resonator. The design conditions of each diagonal resonator in the example of FIG. 9 are equivalent to those in the example of FIG. 7. On the other hand, in the elastic wave filter according to the comparative example (hereinafter abbreviated as "comparative example"), both the series resonator and the parallel resonator are type 1 diagonal resonators. Thus, the type of the parallel resonator is different between the embodiment and the comparative example.

[0083] The vertical axis in the graph of reference numeral 9000A in FIG. 9 indicates the attenuation amount (unit: dB). In this graph, the solid line indicates the characteristics of the embodiment, and the dotted line indicates the characteristics of the comparative example. The attenuation amount can also be referred to as the transmission amount. Therefore, the attenuation characteristic can also be referred to as the transmission characteristic. The band Bd1 in this graph is the pass band of the elastic wave filter, which is determined in advance according to the standard. The band Bd1 in the example of FIG. 9 is, for example, Band66Tx.

[0084] The graph of reference numeral 9000B in FIG. 9 shows the phase characteristics of one parallel resonator in each of the embodiment and the comparative example. Therefore, in this graph, the solid line indicates the phase characteristics of the type 2 diagonal resonator, and the dotted line indicates the phase characteristics of the type 1 diagonal resonator. The phase characteristics shown in this graph are equivalent to the phase characteristics shown in the graph of reference numeral 7000B in FIG. 7 described above. However, in the graph of reference numeral 9000B in FIG. 9, the range of the horizontal axis is made to coincide with the graph of reference numeral 9000A.

[0085] As described above, in the type 1 diagonal resonator, the stop band spurious is shifted to a lower frequency compared to the type 2 diagonal resonator. From this, in the comparative example, the stop band spurious of the type 1 diagonal resonator, which is the parallel resonator, is located within the pass band of the elastic wave filter. In the example of FIG. 9, the stop band spurious of the type 1 diagonal resonator is located within the band Bd1. Therefore, in the comparative example, the stop band spurious of the type 1 diagonal resonator, which is the parallel resonator, may have an adverse effect on the band pass characteristic of the frequency filter.

[0086] In contrast, in the embodiment, the stop-band spurious of the type 2 diagonal resonator, which is a parallel resonator, is located outside the pass-band of the elastic wave filter (more specifically, on the higher frequency side than the pass-band of the elastic wave filter). In the example of FIG. 9, the stop-band spurious of the type 2 diagonal resonator is located on the higher frequency side than band Bd1. Therefore, in the embodiment, the stop-band spurious of the type 2 diagonal resonator, which is a parallel resonator, does not have an adverse effect on the band-pass characteristics of the frequency filter.

[0087] From the above, in the elastic wave filter (e.g., elastic wave filter 100) according to one aspect of the present disclosure, at least one of the at least one parallel resonator may be a type 2 diagonal resonator. And the stop-band spurious of the type 2 diagonal resonator may be located on the higher frequency side than the pass-band of the elastic wave filter. According to this configuration, the band-pass characteristics of the elastic wave filter can be improved.

[0088] In the elastic wave filter according to one aspect of the present disclosure, all of the at least one parallel resonator may be type 2 diagonal resonators. According to this configuration, the band-pass characteristics of the elastic wave filter can be further improved.

[0089] In addition, in the elastic wave filter according to one aspect of the present disclosure, at least one series resonator may be a type 1 diagonal resonator. As described above, according to the type 1 diagonal resonator, the resonance loss can be more effectively reduced by more effectively reducing the transverse mode spurious. Therefore, by using the type 1 diagonal resonator as the series resonator, the loss characteristics of the elastic wave filter can also be improved.

[0090] As described above, in one aspect of the present disclosure, a type 1 diagonal resonator may be used as a series resonator, and a type 2 diagonal resonator may be used as a parallel resonator. In this way, by properly using different types of diagonal resonators for the series resonator and the parallel resonator, an elastic wave filter having good frequency characteristics (specifically, good band-pass characteristics and loss characteristics) can be realized. That is, the frequency characteristics of the elastic wave filter can be improved as compared with the prior art.

[0091] Further, in the elastic wave filter according to one aspect of the present disclosure, the stop band spurious of the type 2 diagonal resonator (parallel resonator) may be located on the higher frequency side than the stop band spurious of each of at least one type 1 diagonal resonator (series resonator). According to this configuration, the band-pass characteristics of the elastic wave filter can be further improved.

[0092] (Supplementary matters in Embodiment 1) (1) In this specification, the "position of the stop band spurious" may be understood to refer to, for example, "the value of the stop band spurious frequency of a certain resonator". And the stop band spurious frequency may be understood to mean, for example, the peak frequency of the stop band spurious.

[0093] Therefore, "the stop band spurious is located within the pass band of the elastic wave filter" means, for example, "the stop band spurious frequency of a certain resonator is equal to or greater than the lower limit value and equal to or less than the upper limit value of the frequency in the pass band". On the other hand, "the stop band spurious is located on the higher frequency side than the pass band of the elastic wave filter" means, for example, "the stop band spurious frequency of a certain resonator is higher than the upper limit value of the frequency in the pass band".

[0094] (2) As described above, in this specification, regarding the second IDT electrode, the technical matter that "Dutyd3 and Dutyd4 are substantially equal to Duty3 and Duty4 in at least a part of the second intersection region" is considered. The numerical range indicating "substantially equal" may be set, for example, as "a numerical range in which it is expected that the type 2 diagonal resonator does not adversely affect the band-pass characteristics of the frequency filter".

[0095] That is, the numerical range indicating "substantially equal" may be set from the viewpoint of the feasibility of the effect achieved by the type 2 diagonal resonator, which is to "improve the band-pass characteristics of the frequency filter". The example in Embodiment 1 of "within the range of ±0.08" is an example of a numerical range supported by the study of the inventors of the present application in terms of the feasibility of the effect.

[0096] However, the numerical range indicating "substantially equal" may be set according to another standard. For example, the numerical range may be set as "a numerical range in which each Duty can be regarded as substantially equal in terms of the manufacturing process of the second IDT electrode". Thus, the numerical range may be set from the viewpoint of the manufacturing process of the second IDT electrode.

[0097] As an example, from the viewpoint of the manufacturing process of the second IDT electrode, if the variation between each Duty is within the range of ±0.025, each Duty can be regarded as substantially equal. Therefore, in one aspect of the present disclosure, Dutyd3 and Dutyd4 may be within the range of ±0.025 with respect to Duty3 and Duty4 in at least a part of the second intersection region. ±0.025 is a numerical range narrower than ±0.08. Therefore, according to this configuration, the band-pass characteristics of the surface acoustic wave filter can be more effectively improved.

[0098] [Embodiment 2] FIG. 10 is a diagram showing a configuration example of the demultiplexer 101 in Embodiment 2. The demultiplexer is also referred to as a multiplexer. As shown in FIG. 10, the demultiplexer 101 may have a plurality of surface acoustic wave filters 100. In the example of FIG. 10, the demultiplexer 101 has four surface acoustic wave filters 100 (e.g., ladder type filters). The demultiplexer 101 in FIG. 10 is an example of a quadplexer. In the following description, the four surface acoustic wave filters 100 are referred to as a first filter 100A, a second filter 100B, a third filter 100C, and a fourth filter 100D, respectively.

[0099] As shown in FIG. 10, at least two of the plurality of surface acoustic wave filters may be connected to a common input terminal TCin. As an example, TCin may be an antenna terminal (see also Embodiment 3 described later). In the example of FIG. 10, the first filter 100A to the fourth filter 100D are connected to TCin. Thus, all of the plurality of surface acoustic wave filters may be connected to TCin.

[0100] TCin may be connected to TGND via a reactor 99. The first filter 100A to the fourth filter 100D may each be connected to an individual output terminal. As shown in FIG. 10, the first filter 100A to the fourth filter 100D may each be connected to output terminals Tout-1 to Tout-4.

[0101] The first filter 100A to the fourth filter 100D may be located on the same chip. In this case, between the first filter 100A to the fourth filter 100D, each resonator may have a common support substrate 98. Therefore, in each resonator, the thickness of the support substrate 98 may be common. In addition, each resonator may have a common piezoelectric film 2 and a low acoustic velocity film 8. Therefore, in each resonator, Tp and Ti may be common. Further, each resonator may be formed, for example, by a common film formation process. Therefore, in each resonator, s may be common.

[0102] 〔Embodiment 3〕 FIG. 11 is a diagram illustrating a schematic configuration of the communication device 151 in Embodiment 3. The communication device 151 is an application example of a surface acoustic wave filter according to an aspect of the present disclosure, and performs wireless communication using radio waves. The communication device 151 may include the above-described demultiplexer 101. The communication device 151 in the example of FIG. 11 may include one demultiplexer 101 as a transmission filter 109 and another demultiplexer 101 as a reception filter 111.

[0103] In the communication device 151, a transmission information signal TIS including information to be transmitted may be modulated and frequency-upconverted (converted into a high-frequency signal having a carrier frequency) by an RF-IC (Radio Frequency-Integrated Circuit) 153, and converted into a transmission signal TS. The band-pass filter 155 may remove unnecessary components other than the passband for transmission from the TS. Then, the TS after removing the unnecessary components may be amplified by the amplifier 157 and input to the transmission filter 109.

[0104] The transmission filter 109 may remove unnecessary components other than the passband for transmission from the input transmission signal TS. The transmission filter 109 may output the TS after removing the unnecessary components to the antenna 159 via an antenna terminal (e.g., the above-described TCin). The antenna 159 may convert the TS, which is an electrical signal input thereto, into radio waves as a wireless signal, and transmit the radio waves to the outside of the communication device 151.

[0105] Also, the antenna 159 may convert the received radio waves from the outside into a received signal RS, which is an electrical signal, and input the RS to the reception filter 111 via the antenna terminal. The reception filter 111 may remove unnecessary components other than the passband for reception from the input RS. The reception filter 111 may output the received signal RS after removing the unnecessary components to the amplifier 161. The output RS may be amplified by the amplifier 161. The band-pass filter 163 may remove unnecessary components other than the passband for reception from the amplified RS. The RS after removing the unnecessary components may be frequency-downconverted and demodulated by the RF-IC 153, and converted into a received information signal RIS.

[0106] The TIS and RIS may be low-frequency signals (baseband signals) containing appropriate information. For example, the TIS and RIS may be analog voice signals or digitalized voice signals. The passband of the radio signal may be set as appropriate and may conform to various known standards.

[0107] 〔Supplementary Notes〕 As described above, the invention according to the present disclosure has been described based on the various drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. That is, the invention according to the present disclosure can be variously modified within the scope shown in the present disclosure, and embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the invention according to the present disclosure. It should be noted that those skilled in the art can easily make various deformations or modifications based on the present disclosure. Also, note that these deformations or modifications are included in the scope of the present disclosure.

Explanation of Reference Numerals

[0108] 1S, 1SV Series Resonator (Type 1 Oblique Resonator) 1P, 1PV Parallel Resonator (Type 2 Oblique Resonator) 2 Piezoelectric Film 3 First IDT Electrode 5 Second IDT Electrode 8 Low-Speed Sound Film 9 High-Speed Sound Film 21A Third Bus Bar 21B Fourth Bus Bar 23A Third Electrode Finger 23B Fourth Electrode Finger 25A Third Dummy Electrode Finger 25B Fourth Dummy Electrode Finger 31a First Bus Bar 31b Second Bus Bar 32a First Electrode Finger 32b Second Electrode Finger 35a First Dummy Electrode Finger 35b Second Dummy Electrode Finger 98 Support substrate 100 SAW filter 100A to 100D First filter to fourth filter (SAW filter) 101 Demultiplexer 151 Communication device 159 Antenna TCin Common input terminal (antenna terminal)

Claims

1. At least one series resonator having a first IDT electrode, and At least one parallel resonator having a second IDT electrode, and the at least one series resonator and the one parallel resonator have a common piezoelectric film, The first IDT electrode includes A first bus bar and a second bus bar facing each other in a direction intersecting the propagation direction of the elastic wave propagating through the piezoelectric film, A plurality of first electrode fingers connected to the first bus bar, A plurality of second electrode fingers connected to the second bus bar and interposed between each of the plurality of first electrode fingers, A plurality of first dummy electrode fingers connected to the first bus bar and facing the tip of each of the plurality of second electrode fingers, A plurality of second dummy electrode fingers connected to the second bus bar and facing the tip of each of the plurality of first electrode fingers, and the directions connecting the tips of each of the plurality of first electrode fingers and the directions connecting the tips of each of the plurality of second electrode fingers are inclined with respect to the propagation direction, The second IDT electrode includes A third bus bar and a fourth bus bar facing each other in a direction intersecting the propagation direction, A plurality of third electrode fingers connected to the third bus bar, A plurality of fourth electrode fingers connected to the fourth bus bar and interposed between each of the plurality of third electrode fingers, A plurality of third dummy electrode fingers connected to the third bus bar and facing the tip of each of the plurality of fourth electrode fingers, A plurality of fourth dummy electrode fingers connected to the fourth bus bar and facing the tip of each of the plurality of third electrode fingers, and the directions connecting the tips of each of the plurality of third electrode fingers and the directions connecting the tips of each of the plurality of fourth electrode fingers are inclined with respect to the propagation direction, In the at least one series resonator, The duty of the first dummy electrode finger and the duty of the second dummy electrode finger are greater than the duty of the first electrode finger and the duty of the second electrode finger in at least a part of the first intersection region where the first electrode finger and the second electrode finger intersect. ​ ​ ​ The duty at the base of the first electrode finger and the duty at the base of the second electrode finger are greater than the duty of the first electrode finger and the duty of the second electrode finger in at least a part of the first crossing region. In at least one of the at least one parallel resonator, The duty of the third dummy electrode finger and the duty of the fourth dummy electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second crossing region where the third electrode finger and the fourth electrode finger cross each other. The duty at the base of the third electrode finger and the duty at the base of the fourth electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second crossing region, a surface acoustic wave filter.

2. In all of the at least one parallel resonator, The duty of the third dummy electrode finger and the duty of the fourth dummy electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second crossing region where the third electrode finger and the fourth electrode finger cross each other. The duty at the base of the third electrode finger and the duty at the base of the fourth electrode finger are within a range of ±0.08 with respect to the duty of the third electrode finger and the duty of the fourth electrode finger in at least a part of the second crossing region, the surface acoustic wave filter according to claim 1.

3. The stop band spurious of the at least one parallel resonator is located on the higher frequency side than the pass band of the surface acoustic wave filter, the surface acoustic wave filter according to claim 1.

4. The stop band spurious of the at least one parallel resonator is located on the higher frequency side than the stop band spurious of the series resonator having the lowest frequency among the stop band spurious of each of the at least one series resonator, the surface acoustic wave filter according to claim 1.

5. The duty of the first dummy electrode finger and the duty of the second dummy electrode finger are greater by 0.08 or more than the duty of the first electrode finger and the duty of the second electrode finger in at least a part of the first crossing region, the surface acoustic wave filter according to claim 1.

6. The duty of the first dummy electrode finger and the duty of the second dummy electrode finger are within a range of +0.08 or more and +0.16 or less with respect to the duty of the first electrode finger and the duty of the second electrode finger in at least a part of the first crossing region. The surface acoustic wave filter according to claim 5.

7. The duty of the first dummy electrode finger and the duty of the second dummy electrode finger are larger than the duty of the first electrode finger and the duty of the second electrode finger in the central portion of the first crossing region. The surface acoustic wave filter according to claim 1.

8. The duty of the first dummy electrode finger and the duty of the second dummy electrode finger are larger than the duty of the first electrode finger and the duty of the second electrode finger in the entire region within the first crossing region. The surface acoustic wave filter according to claim 7.

9. The at least one series resonator and the one parallel resonator have a common support substrate. When the wavelength λ of the surface acoustic wave is defined as a length twice the electrode finger pitch of the second IDT electrode. The thickness of the piezoelectric film is λ or less. The surface acoustic wave filter according to claim 1.

10. The support substrate has a sound velocity faster than the sound velocity of the surface acoustic wave. The surface acoustic wave filter according to claim 9.

11. The at least one series resonator and the one parallel resonator have a common low sound velocity film having a sound velocity slower than the sound velocity of the surface acoustic wave between the piezoelectric film and the support substrate. The surface acoustic wave filter according to claim 10.

12. The at least one series resonator and the one parallel resonator have a common high sound velocity film having a sound velocity faster than the sound velocity of the surface acoustic wave between the piezoelectric film and the low sound velocity film. The surface acoustic wave filter according to claim 11.

13. The piezoelectric film is an LT film. The surface acoustic wave filter according to claim 1.

14. The surface acoustic wave filter is a ladder type filter. The surface acoustic wave filter according to claim 1.

15. The surface acoustic wave filter is a multi-mode type filter. The surface acoustic wave filter according to claim 1.

16. Having a plurality of surface acoustic wave filters according to any one of claims 1 to 15. A demultiplexer in which at least two of the plurality of surface acoustic wave filters are connected to a common antenna terminal.

17. A communication device having the demultiplexer according to claim 16.

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