Elastic wave device, elastic wave filter, demultiplexer, communication device

Abstract

Provided is an elastic wave device that is small but still increases the total electric capacity of an IDT electrode. An elastic wave device according to the present invention comprises a piezoelectric body and an IDT electrode that is on the piezoelectric body. The IDT electrode includes first electrode fingers that protrude from a first busbar, second electrode fingers that protrude from a second busbar, and a first electrode that is positioned between the first electrode fingers and the second electrode fingers in the arrangement direction of the first electrode fingers and the second electrode fingers.

Description

Acoustic wave devices, acoustic wave filters, duplexers, communication devices

[0001] The present disclosure relates to an acoustic wave device, and an acoustic wave filter, a duplexer, and a communication device that include the acoustic wave device.

[0002] Patent document 1 describes an elastic wave device that includes a thin-film piezoelectric element whose ends are supported by a support substrate, and electrode fingers formed in a position that includes a portion of the piezoelectric element that is not supported by the support substrate.

[0003] US Patent Application Publication No. 2022 / 0337225

[0004] An elastic wave device according to one aspect of the present disclosure includes a piezoelectric body and an IDT electrode on the piezoelectric body, the IDT electrode having a first bus bar, a second bus bar opposite the first bus bar, first electrode fingers electrically connected to the first bus bar and protruding from the first bus bar in a direction toward the second bus bar, second electrode fingers electrically connected to the second bus bar and protruding from the second bus bar in a direction toward the first bus bar, and a first electrode positioned between the first electrode fingers and the second electrode fingers in the arrangement direction of the first electrode fingers and the second electrode fingers.

[0005] FIG. 1 is a schematic plan view of an elastic wave device according to a first embodiment of the present disclosure. FIG. 2 is a schematic cross-sectional side view of the elastic wave device according to the first embodiment of the present disclosure. FIG. 3 is another schematic cross-sectional side view of the elastic wave device according to the first embodiment of the present disclosure. FIG. 4 is a schematic plan view of an elastic wave device according to a second embodiment of the present disclosure. FIG. 5 is a schematic plan view of an elastic wave device according to a fifth embodiment of the present disclosure. FIG. 6 is a schematic cross-sectional side view of an elastic wave device according to a sixth embodiment of the present disclosure. FIG. 7 is a schematic diagram of a communication device according to each embodiment of the present disclosure. FIG. 8 is an equivalent circuit diagram of a duplexer according to each embodiment of the present disclosure.

[0006] [Embodiment 1] Hereinafter, an embodiment according to the present disclosure will be described with reference to the drawings. The drawings used in the following description are schematic diagrams, and do not strictly represent the dimensional ratios of the components in the drawings.

[0007] <Overview of Acoustic Wave Device> An acoustic wave filter according to this embodiment includes at least one acoustic wave device as an acoustic wave resonator. For example, an acoustic wave filter may include a ladder filter in which multiple acoustic wave devices are connected in a ladder configuration. An acoustic wave filter according to this embodiment may include multiple acoustic wave devices arranged in parallel in a direction perpendicular to the arrangement direction of electrode fingers (described later) in each acoustic wave device.

[0008] An elastic wave device 1 according to this embodiment will be described in more detail below with reference to Fig. 1 to Fig. 3. Fig. 1 is a schematic plan view of the elastic wave device 1 according to this embodiment. Figs. 2 and 3 are schematic cross-sectional side views of the elastic wave device 1 according to this embodiment. In particular, Fig. 2 is a cross-sectional view taken along line II-II in Fig. 1, and Fig. 3 is a cross-sectional view taken along line III-III in Fig. 1.

[0009] In the schematic plan views of elastic wave devices in this specification, including FIG. 1 , an arrangement direction DD of first and second electrode fingers (described later) of the elastic wave device is defined as the up-down direction on the page. Furthermore, in the schematic cross-sectional side views of elastic wave devices in this specification, including FIG. 2 and FIG. 3 , the arrangement direction DD is defined as the left-right direction on the page. Furthermore, in the schematic plan views of elastic wave devices in this specification, including FIG. 1 , a protrusion direction PD of first and second electrode fingers (described later) of the elastic wave device is defined as the left-right direction on the page. Additionally, in the schematic cross-sectional side views of elastic wave devices in this specification, for simplicity of illustration, only the components in the cross section are shown, and components behind the cross section are not shown.

[0010] 1 to 3, an elastic wave device 1 according to this embodiment includes a piezoelectric body 2 and an IDT electrode 3 on the piezoelectric body 2. In the schematic cross-sectional side views of each elastic wave device in this specification, including FIGS. 2 and 3, the IDT electrode 3 is shown positioned above the piezoelectric body 2.

[0011] The piezoelectric body 2 is made of a piezoelectric material, and may be, for example, a lithium tantalate single crystal or lithium niobate. Hereinafter, lithium tantalate will also be referred to as LT. In the acoustic wave device 1, an acoustic wave propagating through the piezoelectric body 2 is excited by applying a voltage to a conductive layer including an IDT electrode 3, which will be described later. In this embodiment, the piezoelectric body 2 may have a constant thickness. In this specification, "constant thickness" does not necessarily mean that the thickness is strictly constant; rather, some variation is allowed within a range that does not significantly affect the characteristics of the acoustic wave propagating through the piezoelectric body 2.

[0012] <Acoustic Wave Device: IDT Electrode: Electrode Fingers> The IDT electrode 3 includes a pair of comb-tooth electrodes. In particular, in this embodiment, the IDT electrode 3 includes a pair of comb-tooth electrodes, a first comb-tooth electrode 10 and a second comb-tooth electrode 20, as shown in FIG. 1 . In this specification, the second comb-tooth electrode 20 is hatched in plan views of the acoustic wave device 1, including FIG. 1 , for improved visibility. The IDT electrode 3 is made of, for example, a metal material, and may be made of an alloy containing Al as a main component.

[0013] The first comb-tooth electrode 10 has a first bus bar 11, and the second comb-tooth electrode 20 has a second bus bar 21 facing the first bus bar 11. The first comb-tooth electrode 10 is electrically connected to the first bus bar 11 and has first electrode fingers 12 protruding from the first bus bar 11 in a direction toward the second bus bar 21. The second comb-tooth electrode 20 is electrically connected to the second bus bar 21 and has second electrode fingers 22 protruding from the second bus bar 21 in a direction toward the first bus bar 11.

[0014] In this embodiment, as shown in Figures 1 to 3, the IDT electrode 3 has a plurality of first electrode fingers 12 and a plurality of second electrode fingers 22, but is not limited to this and may have one or more first electrode fingers 12 and one or more second electrode fingers 22.

[0015] 1 , the first electrode fingers 12 and the second electrode fingers 22 protrude from the respective bus bars along a protruding direction PD that is parallel to the in-plane direction of the piezoelectric body 2. However, this embodiment is not limited to this, and the first electrode fingers 12 and the second electrode fingers 22 may protrude in different directions from each other as long as the characteristics of the elastic waves propagating through the piezoelectric body 2 are not significantly affected.

[0016] 1 , the first electrode fingers 12 and the second electrode fingers 22 are alternately arranged in an arrangement direction DD that is parallel to the in-plane direction of the piezoelectric body 2 and perpendicular to the protrusion direction PD. In this embodiment, all of the first electrode fingers 12 and second electrode fingers 22 are arranged in the arrangement direction DD, but this is not limited thereto, and it is sufficient that at least one pair of adjacent first electrode fingers 12 and second electrode fingers 22 are arranged in the arrangement direction DD. Furthermore, the distance between the first electrode fingers 12 and the second electrode fingers 22 in the arrangement direction DD may be designed appropriately depending on characteristics including the vibration mode and frequency of the elastic wave excited in the piezoelectric body 2.

[0017] The number of electrode fingers is not limited to the number shown in FIG. 1 and may be appropriately designed depending on the characteristics required of the acoustic wave device 1. Furthermore, the length of each electrode finger may be substantially constant as shown in FIG. 1 , or may be apodized, meaning that the lengths vary depending on the position in the arrangement direction DD. Some of the electrode fingers may be "thinned out" in part of the IDT electrode 3. In other words, the IDT electrode 3 may include a region where some of the electrode fingers are not formed.

[0018] <Acoustic Wave Device: IDT Electrode: Dummy Electrode> Furthermore, first comb-tooth electrode 10 is electrically connected to first bus bar 11 and has, as a first electrode, first dummy electrode 13 that protrudes in the same direction as protruding direction PD of first electrode fingers 12. Furthermore, second comb-tooth electrode 20 is electrically connected to second bus bar 21 and has, as a second electrode, second dummy electrode 23 that protrudes in the same direction as protruding direction PD of second electrode fingers 22. Second dummy electrode 23 is located closer to second bus bar 21 than first dummy electrode 13.

[0019] The first dummy electrode 13 and the second dummy electrode 23 are located between the first electrode finger 12 and the second electrode finger 22 in the arrangement direction DD. In particular, the first dummy electrode 13 and the second dummy electrode 23 are electrically continuous with the respective electrode fingers via the respective bus bars, but are discontinuous with the respective electrode fingers in the arrangement direction DD. For example, as shown in FIG. 1 , the first electrode finger 12 and the second electrode finger 22 are not located on a region 13E obtained by extending the first dummy electrode 13 in the protrusion direction PD.

[0020] With the above configuration, IDT electrode 3 has not only capacitance between first electrode finger 12 and second electrode finger 22, but also capacitance between first dummy electrode 13 and second electrode finger 22. Therefore, acoustic wave device 1 can further increase the capacitance without increasing the number of electrode fingers in IDT electrode 3. Therefore, acoustic wave device 1 can increase the total capacitance of IDT electrode 3 while being miniaturized, thereby reducing impedance. Furthermore, because IDT electrode 3 also has capacitance between second dummy electrode 23 and first electrode finger 12, acoustic wave device 1 can further increase the total capacitance of IDT electrode 3 and further reduce impedance.

[0021] 1 , because second dummy electrode 23 is located on region 13E, first dummy electrode 13 and second dummy electrode 23 overlap in protrusion direction PD, in other words, in the protrusion direction of at least one of first electrode fingers 12 and second electrode fingers 22. As a result, IDT electrode 3 has capacitance between first dummy electrode 13 and second dummy electrode 23, and therefore, the total capacitance of IDT electrode 3 in elastic wave device 1 is further increased and impedance is further reduced. In addition, because first dummy electrode 13 and second dummy electrode 23 overlap in arrangement direction DD, the overall size of IDT electrode 3 in arrangement direction DD is reduced, thereby further miniaturizing elastic wave device 1.

[0022] As described above, the first electrode fingers 12 and the first dummy electrodes 13 are electrically connected to the first bus bar 11, and therefore the first electrode fingers 12 and the first dummy electrodes 13 are electrically continuous via the first bus bar 11. On the other hand, the first dummy electrodes 13 are not electrically continuous with the second electrode fingers 22. Therefore, the potential difference between the first dummy electrodes 13 and the second electrode fingers 22 is more likely to increase compared to when the first dummy electrodes 13 are not electrically continuous with the first electrode fingers 12. Therefore, the electrical capacitance formed between the first dummy electrodes 13 and the second electrode fingers 22 is further increased.

[0023] In this embodiment, the IDT electrode 3 has a plurality of first electrode fingers 12 and a plurality of second electrode fingers 22, as well as a plurality of first dummy electrodes 13 and a plurality of second dummy electrodes 23. Therefore, in the arrangement direction DD, the plurality of first dummy electrodes 13 and the plurality of second dummy electrodes 23 are respectively positioned between the first electrode fingers 12 and the second electrode fingers 22. As a result, the IDT electrode 3 has electric capacitance between each dummy electrode and each electrode finger, thereby further increasing the total electric capacitance of the IDT electrode 3 in the acoustic wave device 1. However, this is not limited thereto, and the IDT electrode 3 may have one or more first dummy electrodes 13 and one or more second dummy electrodes 23.

[0024] In this embodiment, a distance D1 between the first bus bar 11 and a tip 22T of the second electrode finger 22 on the first bus bar 11 side is smaller than a distance D2 from the first bus bar 11 to a tip 13T of the first dummy electrode 13 on the second bus bar 21 side. Therefore, the first dummy electrode 13 overlaps with the second electrode finger 22 in the arrangement direction DD.

[0025] 2 shows a cross-sectional side view of the acoustic wave device 1 taken along a plane parallel to the array direction DD and passing through the first electrode fingers 12, the second electrode fingers 22, and the first dummy electrodes 13. The fact that the second electrode fingers 22 and the first dummy electrodes 13 are shown in FIG. 2 also makes it clear that the first dummy electrodes 13 overlap with the second electrode fingers 22 in the array direction DD.

[0026] With the above configuration, the distance between first dummy electrode 13 and second electrode finger 22 and the distance between second dummy electrode 23 and first electrode finger 12 are shortened, thereby increasing the capacitance between these electrodes. Therefore, in acoustic wave device 1, the total capacitance of IDT electrode 3 is further increased and the impedance is further reduced.

[0027] In particular, in the arrangement direction DD, the first dummy electrodes 13 overlap with the tips 22T of the second electrode fingers 22 on the side of the first bus bar 11. In addition, since the first dummy electrodes 13 are located on both sides of the second electrode fingers 22 in the arrangement direction DD, the two first dummy electrodes sandwich the tips 22T of the second electrode fingers 22 in the arrangement direction DD.

[0028] Elastic waves propagating through piezoelectric body 2 of elastic wave device 1 may be excited more efficiently closer to the center of each bus bar in projection direction PD. In this case, from the viewpoint of reducing the effect on the characteristics of elastic waves excited in elastic wave device 1, first dummy electrode 13 may be located closer to second bus bar 21 than to the center of piezoelectric body 2 in projection direction PD.

[0029] Therefore, in the arrangement direction DD, first dummy electrode 13 overlaps with tips 22T of second electrode fingers 22 that are located closer to each bus bar, thereby enabling IDT electrode 3 to reduce the effect of first dummy electrode 13 on the characteristics of elastic waves propagating through piezoelectric body 2. In particular, by sandwiching the tips of each electrode finger between dummy electrodes in the arrangement direction DD, elastic wave device 1 can more efficiently increase the capacitance of IDT electrode 3 while reducing the effect of first dummy electrode 13 on the characteristics of elastic waves propagating through piezoelectric body 2.

[0030] Furthermore, the distance D2 described above is smaller than the distance D3 from the first bus bar 11 to the tip 12T of the first electrode finger 12 on the side of the second bus bar 21. For the same reason as described above, with the above configuration, the IDT electrode 3 can reduce the influence that the first dummy electrode 13 has on the characteristics of the elastic wave propagating through the piezoelectric body 2.

[0031] Furthermore, in the arrangement direction DD, the second dummy electrodes 23 may overlap the first electrode fingers 12, and in particular, the second dummy electrodes 23 may overlap the tips of the first electrode fingers 12 on the side of the second bus bar 21. In addition, the distance from the second bus bar 21 to the tips of the second dummy electrodes 23 on the side of the first bus bar 11 may be shorter than the distance from the second bus bar 21 to the tips of the second electrode fingers 22 on the side of the first bus bar 11.

[0032] Focus is now placed on a certain first dummy electrode 13 among the multiple first dummy electrodes 13, and the first electrode finger 12 and the second electrode finger 22 adjacent to the certain first dummy electrode 13. Here, for the certain electrode of interest, in the arrangement direction DD, a distance D4 between a center 13C of the first dummy electrode 13 and a center 12C of the first electrode finger 12 is the same as a distance D5 between the center 13C and a center 22C of the second electrode finger 22. In this embodiment, the above-described distances D4 and D5 may be the same for any pair of the first dummy electrode 13 and the first electrode finger 12 and second electrode finger 22 adjacent to the certain first dummy electrode 13 in the arrangement direction DD. In this specification, the term "same distance" does not mean that the distances are strictly the same, but rather allows for some difference within a range that does not significantly affect the characteristics of the elastic waves propagating through the piezoelectric body 2.

[0033] The above configuration enables the IDT electrode 3 to be formed without increasing the complexity of the formation process. For example, when the IDT electrode 3 is formed by depositing a thin film of a metal material or the like and then etching the thin film according to a mask pattern, the above configuration can further simplify the mask pattern. Furthermore, the above configuration makes it easier to design the characteristics of the elastic waves propagating through the piezoelectric body 2 in the elastic wave device 1.

[0034] Additionally, the width W1 of the first electrode fingers 12 and the width W2 of the second electrode fingers 22 in the arrangement direction DD may be the same as the width W3 of the first dummy electrodes 13 in the arrangement direction DD. This allows the IDT electrodes 3 to be formed without increasing the complexity of the formation process, and also makes it easier to design the characteristics of the elastic waves propagating through the piezoelectric body 2 in the elastic wave device 1, for the same reasons as described above. In this specification, "the widths of the electrodes are the same" does not mean that the widths are strictly the same; rather, some difference is allowed within the range of, for example, manufacturing errors that may occur due to the method of forming the IDT electrodes 3 using the above-described formation method.

[0035] Furthermore, in the arrangement direction DD, the distance between the center of the second dummy electrode 23 and the center of the second electrode finger 22 may be the same as the distance between the center of the second dummy electrode 23 and the center of the second electrode finger 22. Furthermore, the width W1 and the width W2 may be the same as the width of the second dummy electrode 23 in the arrangement direction DD.

[0036] <Acoustic Wave Device: IDT Electrode: Supplementary Note> Acoustic wave device 1 may further include a pair of reflectors (not shown) located at both ends of the electrode fingers on piezoelectric body 2 in the arrangement direction DD. The reflectors may include multiple strip electrodes extending from a pair of opposing bus bars, and may be electrically floating or may be given a reference potential. The reflectors may be excited at a position overlapping with IDT electrode 3 in a plan view and may have the function of reflecting acoustic waves propagating toward the reflector in the arrangement direction DD back toward IDT electrode 3 in the arrangement direction DD.

[0037] The IDT electrode 3 may be covered with a protective film (not shown) formed at a position covering the top surface of the acoustic wave device 1. The protective film may be a thin film used to protect the conductors on the piezoelectric body 2, such as the IDT electrode 3, by, for example, reducing corrosion of the conductors on the piezoelectric body 2. The protective film may be formed of, for example, TEOS (tetraethoxysilane: Si(OC ２ H ５ ) ４ ), SiO ２ or Si ３ N ４The protective film may be formed by stacking multiple layers made of the above-mentioned materials. However, the material of the protective film is not limited to these. The protective film may have a thickness of approximately 130 Å. The protective film may have a thickness distribution within the surface of the acoustic wave device 1, or may be formed substantially uniformly.

[0038] <Acoustic Wave Device: Support Substrate> Returning to the description of the components of the elastic wave device 1, as shown in FIGS. 2 and 3 , the elastic wave device 1 further includes a support substrate 4 on the opposite side of the piezoelectric element 2 from the IDT electrode 3. In this embodiment, the effect of the support substrate 4 on the characteristics of the elastic waves propagating through the piezoelectric element 2 is sufficiently small. Therefore, the material and dimensions of the support substrate 4 may be designed appropriately. For example, the support substrate 4 may include an insulating material, such as a resin or ceramic. The thickness of the support substrate 4 is greater than the thickness of the piezoelectric element 2, for example. To further reduce the effect on the characteristics of the elastic waves due to temperature changes, the support substrate 4 may include a material with a linear expansion coefficient lower than that of the piezoelectric element 2.

[0039] <Acoustic Wave Device: Hollow Portion> As shown in Fig. 3 , the support substrate 4 has a recess 4R in a region that overlaps with a portion of the piezoelectric body 2 in a plan view. Therefore, the elastic wave device 1 has a hollow portion 5 between the piezoelectric body 2 and the support substrate 4. Here, in Fig. 1 , a region 5E that overlaps with the hollow portion 5 in a plan view of the elastic wave device 1 is indicated by a dotted line. As shown in Fig. 1 , the hollow portion 5 is located closer to the center than the peripheral edge of the piezoelectric body 2 in a plan view of the elastic wave device 1. Therefore, the piezoelectric body 2 is directly supported by the support substrate 4 at the peripheral edge in a plan view, as shown in Fig. 2 , but is not supported by the support substrate at the central side than the peripheral edge in a plan view, as shown in Fig. 3 .

[0040] A structure in which the piezoelectric body 2 has a portion that is not directly supported by the support substrate 4, such as the structure of the elastic wave device 1 according to this embodiment, is sometimes referred to as a membrane structure. The elastic wave device 1 having the membrane structure according to this embodiment efficiently excites A1 mode plate waves in the piezoelectric body 2.

[0041] In this preferred embodiment, first dummy electrodes 13 and second dummy electrodes 23 are not formed in region 5E that overlaps with hollow portion 5 in a plan view of elastic wave device 1. Therefore, as shown in FIG. 3 , in region 5E, first electrode fingers 12 face second electrode fingers 22 in arrangement direction DD.

[0042] On the other hand, the first dummy electrode 13 and the second dummy electrode 23 are located in a region overlapping with the periphery of the region 5E in a plan view, in other words, in a region where the piezoelectric body 2 is directly supported by the support substrate 4 in a plan view. Therefore, as shown in Fig. 2 , in the region overlapping with the periphery of the region 5E in a plan view, the first electrode fingers 12 and the second electrode fingers 22 face the first dummy electrode 13 and the second dummy electrode 23 in the arrangement direction DD.

[0043] In elastic wave device 1 having a membrane structure, elastic waves propagating through piezoelectric body 2 are excited more strongly in the portion of piezoelectric body 2 that is not supported by support substrate 4, in other words, in the portion located in region 5E. Therefore, by positioning first dummy electrode 13 and second dummy electrode 23 around region 5E in a plan view, IDT electrode 3 reduces the influence of first dummy electrode 13 and second dummy electrode 23 on the characteristics of elastic waves propagating through piezoelectric body 2.

[0044] <Additional Notes on Acoustic Wave Device> The piezoelectric body 2 may be supported by the support substrate 4 via an adhesive layer (not shown) located between the piezoelectric body 2 and the support substrate 4. The adhesive layer is a layer inserted to improve adhesion between the support substrate 4 and the piezoelectric body 2, and has a sufficiently small effect on the characteristics of the elastic waves propagating through the piezoelectric body 2. The laminate including the piezoelectric body 2 to the support substrate 4 including the adhesive layer is sometimes referred to as a fixed substrate.

[0045] [Embodiment 2] <Increasing the Width of the Dummy Electrode> Another embodiment of the present disclosure will be described below. For convenience of explanation, the same reference numerals will be used to designate components having the same functions as those described in the above embodiment, and the description thereof will not be repeated.

[0046] 4 is a schematic plan view of an elastic wave device 1A according to this preferred embodiment. The elastic wave device 1A according to this preferred embodiment may have the same configuration as the elastic wave device 1 according to the previous preferred embodiment, except that the IDT electrode 3 includes a first dummy electrode 14 instead of the first dummy electrode 13 and a second dummy electrode 24 instead of the second dummy electrode 23. The first dummy electrode 14 and the second dummy electrode 24 have the same configuration as the first dummy electrode 13 and the second dummy electrode 23, respectively, except for their widths in the array direction DD.

[0047] In particular, the width W4 of the first dummy electrode 14 in the arrangement direction DD is larger than at least one of the width W1 of the first electrode finger 12 and the width W2 of the second electrode finger 22 in the arrangement direction DD. This reduces the distance between the first dummy electrode 14 and the second electrode finger 22 in the arrangement direction DD, and increases the size of the portion of the first dummy electrode 14 that forms electrical capacitance with the second electrode finger 22. Therefore, the IDT electrode 3 according to this embodiment further increases the electrical capacitance formed between the first dummy electrode 14 and the second electrode finger 22. Furthermore, the width of the second dummy electrode 24 in the arrangement direction DD may be larger than at least one of the width W1 and the width W2.

[0048] 5 is a schematic plan view of an elastic wave device 1B according to a third embodiment. Elastic wave device 1B according to the third embodiment may have the same configuration as elastic wave device 1 described above, except that IDT electrode 3 includes first dummy electrode 15 instead of first dummy electrode 13 and second dummy electrode 25 instead of second dummy electrode 23.

[0049] Each first dummy electrode 15 is closer to the adjacent second electrode finger 22 than each of the above-described first dummy electrodes 13. Of the multiple first dummy electrodes 15, attention is focused on a certain first dummy electrode 15 and the first electrode finger 12 and second electrode finger 22 adjacent to that first dummy electrode 15. Here, for that electrode of interest, a distance D6 between a center 15C of the first dummy electrode 15 and a center 12C of the first electrode finger 12 is greater than a distance D7 between the center 15C and a center 22C of the second electrode finger 22 in the arrangement direction DD.

[0050] The above configuration reduces the distance between the first dummy electrodes 15 and the second electrode fingers 22 in the arrangement direction DD. Therefore, the IDT electrode 3 according to this embodiment further increases the electrical capacitance formed between the first dummy electrodes 15 and the second electrode fingers 22.

[0051] Furthermore, with the above configuration, the distance in the arrangement direction DD between adjacent electrodes among the first electrode fingers 12, the second electrode fingers 22, and the first dummy electrodes 13 varies depending on the position in the arrangement direction DD. Therefore, the frequency at which spurious components different from the main vibration intended to be excited by the elastic wave device 1B are excited among the elastic waves propagating through the piezoelectric body 2 can be varied depending on the position in the arrangement direction DD of the piezoelectric body 2. Therefore, the elastic wave device 1B reduces the overall intensity of spurious components that can be excited in the piezoelectric body 2, thereby improving the characteristics of the main vibration elastic wave propagating through the piezoelectric body 2.

[0052] In addition, the distance between the center of the second dummy electrode 25 and the center of the second electrode finger 22 in the arrangement direction DD may be greater than the distance between the center of the second dummy electrode 25 and the center of the first electrode finger 12 .

[0053] 6 is a schematic plan view of an elastic wave device 1C according to a fourth embodiment. The elastic wave device 1C according to the fourth embodiment may have the same configuration as the elastic wave device 1 described above, except that the IDT electrode 3 includes first dummy electrodes 15 instead of some of the first dummy electrodes 13 and second dummy electrodes 25 instead of some of the second dummy electrodes 23.

[0054] Therefore, in the arrangement direction DD, the distance between the center 13C of each first dummy electrode 13 and the center 12C of the first electrode finger 12 adjacent to the first dummy electrode 13 in the arrangement direction DD is the same as the above-mentioned distance D4. On the other hand, in the arrangement direction DD, the distance between the center 15C of each first dummy electrode 15 and the center 12C of the first electrode finger 12 adjacent to the first dummy electrode 15 in the arrangement direction DD is the same as the above-mentioned distance D6. As described above, the distance D6 is greater than the distance D4.

[0055] In other words, in this embodiment, between a first electrode finger and a first dummy electrode that are adjacent to each other in the arrangement direction DD, the distance between the centers of each electrode in the arrangement direction DD varies depending on the position on the piezoelectric body 2. In this embodiment, between a second electrode finger and a second dummy electrode that are adjacent to each other in the arrangement direction DD, the distance between the centers of each electrode in the arrangement direction DD may vary depending on the position on the piezoelectric body 2.

[0056] In this embodiment, it is sufficient that the distance between the centers of at least one pair of adjacent first electrode fingers and first dummy electrodes in the arrangement direction DD is different from the distance between at least another pair of electrodes. For example, the distance between the centers of at least two pairs of adjacent first electrode fingers and first dummy electrodes that are located at different positions may be the same in the arrangement direction DD.

[0057] The above configuration reduces the periodicity of the distance in arrangement direction DD between adjacent electrodes among first electrode fingers 12, second electrode fingers 22, first dummy electrodes 13, and first dummy electrodes 15. Therefore, elastic wave device 1C further reduces the overall intensity of spurious signals that can be excited in piezoelectric body 2, and ultimately further improves the characteristics of the main vibration elastic wave propagating through piezoelectric body 2.

[0058] In this embodiment, the distance in the arrangement direction DD between the center 13C of each first dummy electrode 13 and the center 22C of each second electrode finger 22 adjacent to the first dummy electrode 13 in the arrangement direction DD is the same as the distance D5 described above. Meanwhile, the distance in the arrangement direction DD between the center 15C of each first dummy electrode 15 and the center 22C of each second electrode finger 22 adjacent to the first dummy electrode 15 in the arrangement direction DD is the same as the distance D7 described above. As described above, the distance D7 is smaller than the distance D5. Therefore, the IDT electrode 3 according to this embodiment increases the capacitance formed between the first dummy electrode 15 and the second electrode finger 22 adjacent to each other in the arrangement direction DD.

[0059] 7 is a schematic plan view of an elastic wave device 1D according to a fifth embodiment. The elastic wave device 1D according to the fifth embodiment may have the same configuration as the elastic wave device 1 described above, except that the IDT electrode 3 includes a first floating island electrode 16 instead of the first dummy electrode 13 and a second floating island electrode 26 instead of the second dummy electrode 23.

[0060] Each of the first and second floating island electrodes 16 and 26 is located between the first bus bar 11 and the second bus bar 21, and in particular, is located on the piezoelectric body 2 at a distance from the first bus bar 11, the second bus bar 21, the first electrode fingers 12, and the second electrode fingers 22. Therefore, each of the first and second floating island electrodes 16 and 26 is electrically independent from other parts of the IDT electrode 3.

[0061] Therefore, each of the first floating island electrodes 16 and each of the second floating island electrodes 26 can have a potential different from that of the first electrode finger 12 and the second electrode finger 22. In particular, each of the first floating island electrodes 16 and each of the second floating island electrodes 26 can have a potential induced by an electric field generated from other parts of the IDT electrode 3.

[0062] Furthermore, in the arrangement direction DD, the first floating island electrode 16 overlaps with the second electrode finger 22, and the second floating island electrode 26 overlaps with the first electrode finger 12. Therefore, the first floating island electrode 16 forms an electric capacitance with the second electrode finger 22, and the second floating island electrode 26 forms an electric capacitance with the first electrode finger 12. Therefore, the acoustic wave device 1D increases the total electric capacitance of the IDT electrodes 3 and reduces the impedance while being miniaturized.

[0063] Sixth Embodiment <Acoustic Reflecting Film> Figure 8 is a schematic side cross-sectional view of an elastic wave device 1E according to this embodiment, particularly showing a cross-section of the elastic wave device 1E corresponding to the cross-section of the elastic wave device 1 shown in Figure 3. Unlike the previously described elastic wave device 1, the elastic wave device 1E according to this embodiment does not have a recess 4R in the support substrate 4, and therefore does not include a hollow portion 5. Furthermore, unlike the previously described elastic wave device 1, the elastic wave device 1E according to this embodiment includes an acoustic reflecting film 6 between the piezoelectric body 2 and the support substrate 4. Except for the above, the elastic wave device 1E according to this embodiment may have the same configuration as the previously described elastic wave device 1.

[0064] The acoustic reflection film 6 has the function of reducing leakage of elastic waves propagating through the piezoelectric body 2 by reflecting, back to the piezoelectric body 2, those that propagate toward the support substrate 4. Therefore, the elastic wave device 1E including the acoustic reflection film 6 efficiently excites bulk waves that can propagate three-dimensionally through the piezoelectric body 2. Compared to the elastic wave device 1 including the hollow portion 5, the elastic wave device 1E including the acoustic reflection film 6 increases the area that supports the piezoelectric body 2, thereby improving the strength of the piezoelectric body 2 and reducing damage to the piezoelectric body 2. The bulk waves are, for example, thickness shear waves.

[0065] The acoustic reflection film 6 may be a multilayer reflection film including alternately stacked first layers 7 and second layers 8. The material of the first layer 7 has a lower acoustic impedance than the material of the second layer 8. This increases the reflectivity of the acoustic wave at the interface between the first layer 7 and the second layer 8, thereby reducing leakage of the acoustic wave propagating through the piezoelectric body 2 to the support substrate 4 side.

[0066] For example, the first layer 7 may be made of silicon dioxide (SiO ２ The second layer 8 is mainly composed of hafnium oxide (HfO ２ The second layer 8 is mainly composed of tantalum pentoxide (Ta ２ O ５ ), zirconium dioxide (ZrO ２ ), titanium oxide (TiO ２ The main component of each of the first layer 7 and the second layer 8 refers to the material that is contained in the largest amount in each of the first layer 7 and the second layer 8.

[0067] The acoustic reflection film 6 may include at least one first layer 7 and at least one second layer 8. The total number of layers of the first layer 7 and the second layer 8 may be either an odd number or an even number.

[0068] For example, the acoustic reflection film 6 may include a total of three to twelve first layers 7 and second layers 8. However, the acoustic reflection film 6 may include only one layer of each of the first layer 7 and the second layer 8. Furthermore, an adhesive layer may be formed between each of the first layer 7 and the second layer 8, from the viewpoint of improving the adhesion between the layers of the acoustic reflection film 6 and reducing the diffusion of elastic waves in the acoustic reflection film 6.

[0069] 9 is a block diagram showing the main components of a communication device 40 according to each embodiment of the present disclosure. The communication device 40 performs wireless communication using radio waves. The duplexer 42 has a function of separating signals of a transmission frequency from signals of a reception frequency in the communication device 40.

[0070] In the communication device 40, a transmission information signal TIS containing information to be transmitted is modulated and frequency-upshifted by an RF-IC 44, in other words, converted into a high-frequency signal of a carrier frequency to become a transmission signal TS. Unwanted components outside the transmission passband of the transmission signal TS are removed by a bandpass filter 46, amplified by an amplifier 48, and input to a branching filter 42. The branching filter 42 removes unwanted components outside the transmission passband from the input transmission signal TS and outputs the signal to an antenna 50. The antenna 50 converts the input electrical signal, for example, the transmission signal TS, into a radio signal and transmits it.

[0071] In the communication device 40, a radio signal received by an antenna 50 is converted by the antenna 50 into an electrical signal, for example, a received signal RS, and input to a branching filter 42. The branching filter 42 removes unnecessary components outside the reception passband from the input received signal RS and outputs the signal to an amplifier 52. The output received signal RS is amplified by the amplifier 52, and unnecessary components outside the reception passband are removed by a bandpass filter 54. The received signal RS is then frequency-downshifted and demodulated by an RF-IC 44 to generate a received information signal RIS.

[0072] The transmit information signal TIS and the receive information signal RIS may be low-frequency signals, such as baseband signals, containing appropriate information, e.g., analog or digitized audio signals. The passband of the radio signals may comply with various standards, such as the Universal Mobile Telecommunications System (UMTS). The modulation method may be phase modulation, amplitude modulation, frequency modulation, or a combination of any two or more of these.

[0073] 10 is a circuit diagram showing a configuration of a duplexer 42 according to an embodiment of the present disclosure. The duplexer 42 is the duplexer 42 used in the communication device 40 in FIG.

[0074] 10 , the transmit filter 56 has series resonators S1 to S3 and parallel resonators P1 to P3. The duplexer 42 is mainly composed of an antenna terminal 58, a transmit terminal 60, a receive terminal 62, a transmit filter 56 arranged between the antenna terminal 58 and the transmit terminal 60, and a receive filter 64 arranged between the antenna terminal 58 and the receive terminal 62. A transmit signal TS from the amplifier 48 is input to the transmit terminal 60, and the transmit signal TS input to the transmit terminal 60 has unwanted components outside the transmit passband removed by the transmit filter 56 before being output to the antenna terminal 58. A receive signal RS from the antenna 50 is input to the antenna terminal 58, and the receive filter 64 has unwanted components outside the receive passband removed by the receive filter 64 before being output to the receive terminal 62.

[0075] The transmit filter 56 is configured, for example, by a ladder-type acoustic wave filter. Specifically, the transmit filter 56 has three series resonators S1, S2, and S3 connected in series between its input side and output side, and three parallel resonators P1, P2, and P3 provided between a series arm, which is a wiring for connecting the series resonators, and a reference potential portion G. In other words, the transmit filter 56 is a three-stage ladder-type filter. However, the number of stages of the ladder-type filter in the transmit filter 56 is arbitrary.

[0076] An inductor L is provided between the parallel resonators P1 to P3 and the reference potential section G. By setting the inductance of this inductor L to a predetermined value, an attenuation pole is formed outside the passband of the transmission signal, thereby increasing out-of-band attenuation. Each of the plurality of series resonators S1 to S3 and the plurality of parallel resonators P1 to P3 is made up of an acoustic wave resonator.

[0077] The receiving filter 64 includes, for example, a multimode acoustic wave filter 66 and an auxiliary resonator 68 connected in series to the input side of the filter. In this embodiment, the multimode includes a dual mode. The multimode acoustic wave filter 66 has a balanced-to-unbalanced conversion function, and the receiving filter 64 is connected to two receiving terminals 62 from which balanced signals are output. The receiving filter 64 is not limited to being configured using the multimode acoustic wave filter 66, but may also be configured using a ladder filter or a filter without a balanced-to-unbalanced conversion function.

[0078] An impedance matching circuit made up of an inductor or the like may be inserted between the connection point of the transmitting filter 56, the receiving filter 64 and the antenna terminal 58 and the ground potential portion G.

[0079] The above-described acoustic wave filter is an acoustic wave element that constitutes at least one of the ladder-type filter circuits, for example, the transmit filter 56 or the receive filter 64 in the branching filter 42 shown in Fig. 9 and Fig. 10. When either the transmit filter 56 or the receive filter 64 is the above-described acoustic wave filter, all or at least some of the acoustic wave resonators included in the filter are the acoustic wave devices according to the above-described embodiments.

[0080] By employing the duplexer 42 including such a transmission filter 56 or a reception filter 64, the communication device 40 can be made smaller and the filter characteristics of the communication device 40 can be improved.

[0081] <Summary> An elastic wave device according to aspect 1 of the present disclosure includes a piezoelectric body and an IDT electrode on the piezoelectric body, the IDT electrode including a first bus bar, a second bus bar opposite the first bus bar, first electrode fingers electrically connected to the first bus bar and protruding from the first bus bar in a direction toward the second bus bar, second electrode fingers electrically connected to the second bus bar and protruding from the second bus bar in a direction toward the first bus bar, and a first electrode positioned between the first electrode fingers and the second electrode fingers in the arrangement direction of the first electrode fingers and the second electrode fingers.

[0082] In an acoustic wave device according to a second aspect of the present disclosure, the first electrodes overlap the second electrode fingers in the arrangement direction in the first aspect.

[0083] In an elastic wave device according to a third aspect of the present disclosure, the first electrode overlaps with the tips of the second electrode fingers on the first bus bar side in the arrangement direction in the second aspect.

[0084] An elastic wave device according to a fourth aspect of the present disclosure is the elastic wave device of any one of the first to third aspects, wherein the first electrode is electrically connected to the first bus bar.

[0085] An elastic wave device according to aspect 5 of the present disclosure is the same as aspect 4 above, except that the distance from the first bus bar to the tip of the first electrode finger on the side of the second bus bar is shorter than the distance from the first bus bar to the tip of the first electrode finger on the side of the second bus bar.

[0086] According to a sixth aspect of the present disclosure, in the elastic wave device of any one of the first to third aspects, the first electrode is a floating island electrode that is electrically independent from other portions of the IDT electrode.

[0087] In an elastic wave device according to aspect 7 of the present disclosure, in the arrangement direction of any of aspects 1 to 6 above, the distance between the center of the first electrode and the center of the first electrode finger is greater than the distance between the center of the first electrode and the center of the second electrode finger.

[0088] In an elastic wave device according to aspect 8 of the present disclosure, in the arrangement direction of any of aspects 1 to 6 above, the distance between the center of the first electrode and the center of the first electrode finger is the same as the distance between the center of the first electrode and the center of the second electrode finger.

[0089] An elastic wave device according to a ninth aspect of the present disclosure is the elastic wave device according to any one of the first to eighth aspects, wherein the width of the first electrode is greater than the width of at least one of the first electrode fingers and the second electrode fingers in the arrangement direction.

[0090] An elastic wave device according to aspect 10 of the present disclosure is any one of aspects 1 to 9 above, wherein the IDT electrode is positioned closer to the second bus bar than the first electrode and has a second electrode positioned between the first electrode finger and the second electrode finger in the arrangement direction.

[0091] An elastic wave device according to an eleventh aspect of the present disclosure is based on the tenth aspect, wherein the first electrode and the second electrode overlap in a protruding direction of at least one of the first electrode fingers and the second electrode fingers.

[0092] An elastic wave device according to aspect 12 of the present disclosure is any one of aspects 1 to 11 above, wherein the IDT electrode has a plurality of the first electrodes, and in the arrangement direction, the plurality of first electrodes sandwich the tips of the second electrode fingers on the side of the first bus bar.

[0093] An elastic wave device according to aspect 13 of the present disclosure is any one of aspects 1 to 11 above, wherein the IDT electrode has a plurality of the first electrode fingers, a plurality of the second electrode fingers, and a plurality of the first electrodes, and in the arrangement direction, each of the first electrodes is positioned between the first electrode fingers and the second electrode fingers.

[0094] An elastic wave device according to aspect 14 of the present disclosure is, in the above-mentioned aspect 13, such that the distance between the center of the first electrode finger and the center of the first electrode between at least one pair of adjacent first electrode fingers and the first electrode in the arrangement direction is different from the distance between the center of the first electrode finger and the center of the first electrode between at least another pair of the first electrode fingers and the first electrode.

[0095] An elastic wave device according to aspect 15 of the present disclosure is any of aspects 1 to 14 above, and includes a support substrate located on the opposite side of the piezoelectric body from the IDT electrode, and a hollow portion located between the piezoelectric body and the support substrate, wherein in a region overlapping with the hollow portion in a planar view, the first electrode fingers face the second electrode fingers in the arrangement direction, and in a region overlapping with the periphery of the hollow portion in a planar view, the first electrode fingers and the second electrode fingers face the first electrodes in the arrangement direction.

[0096] An elastic wave device according to a sixteenth aspect of the present disclosure excites an A1 mode plate wave in the piezoelectric body of any one of the first to fifteenth aspects.

[0097] An elastic wave device according to a seventeenth aspect of the present disclosure excites bulk waves in the piezoelectric body according to any one of the first to fifteenth aspects.

[0098] An acoustic wave filter according to an eighteenth aspect of the present disclosure includes at least one acoustic wave device according to any one of the first to seventeenth aspects.

[0099] A duplexer according to aspect 19 of the present disclosure has an antenna terminal, a transmit filter that filters a transmit signal and outputs it to the antenna terminal, and a receive filter that filters a receive signal from the antenna terminal, and at least one of the transmit filter and the receive filter includes the elastic wave filter of aspect 18 described above.

[0100] A communication device according to aspect 20 of the present disclosure includes an antenna, a duplexer according to aspect 19 above in which the antenna terminal is connected to the antenna, and an IC connected to the transmit filter and the receive filter.

[0101] The invention according to the present disclosure has been described above based on the drawings and examples. However, the invention according to the present disclosure is not limited to the above-described embodiments. In other words, the invention according to the present disclosure can be modified in various ways within the scope of 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. In other words, it should be noted that a person skilled in the art can easily make various modifications or corrections based on the present disclosure. It should also be noted that these modifications or corrections are included in the scope of the present disclosure.

[0102] REFERENCE SIGNS LIST 1 Acoustic wave device 2 Piezoelectric body 3 IDT electrode 4 Support substrate 5 Hollow portion 6 Acoustic reflection film 11 First bus bar 12 First electrode finger 13 First dummy electrode 21 Second bus bar 22 Second electrode finger 23 Second dummy electrode 40 Communication device 42 Branching filter 44 RF-IC 56 Transmitting filter 64 Receiving filter

Claims

1. Piezoelectric material and The piezoelectric element comprises an IDT electrode, The IDT electrode is First bus bar and A second busbar opposite to the first busbar, A first electrode finger is electrically connected to the first busbar and protrudes in the direction toward the second busbar from the first busbar, A second electrode finger is electrically connected to the second busbar and protrudes in the direction toward the first busbar from the second busbar, In the alignment direction of the first electrode finger and the second electrode finger, the first electrode is located between the first electrode finger and the second electrode finger, An elastic wave apparatus having

2. The elastic wave apparatus according to claim 1, wherein in the aforementioned arrangement direction, the first electrode overlaps with the second electrode finger.

3. The elastic wave apparatus according to claim 2, wherein in the aforementioned arrangement direction, the first electrode overlaps with the tip of the second electrode finger on the side of the first busbar.

4. The elastic wave apparatus according to claim 1, wherein the first electrode is electrically connected to the first busbar.

5. The elastic wave apparatus according to claim 4, wherein the distance from the first busbar to the tip of the first electrode on the side of the second busbar is smaller than the distance from the first busbar to the tip of the first electrode finger on the side of the second busbar.

6. The elastic wave apparatus according to claim 1, wherein the first electrode is an island electrode electrically independent from the other parts of the IDT electrode.

7. The elastic wave apparatus according to claim 1, wherein, in the aforementioned arrangement direction, the distance between the center of the first electrode and the center of the first electrode finger is greater than the distance between the center of the first electrode and the center of the second electrode finger.

8. The elastic wave apparatus according to claim 1, wherein, in the aforementioned arrangement direction, the distance between the center of the first electrode and the center of the first electrode finger is the same as the distance between the center of the first electrode and the center of the second electrode finger.

9. The elastic wave apparatus according to claim 1, wherein in the aforementioned arrangement direction, the width of the first electrode is greater than the width of at least one of the first electrode finger and the second electrode finger.

10. The elastic wave apparatus according to claim 1, wherein the IDT electrode is located on the side of the second busbar than the first electrode, and has a second electrode located between the first electrode finger and the second electrode finger in the arrangement direction.

11. The elastic wave apparatus according to claim 10, wherein the first electrode and the second electrode overlap in the protruding direction of at least one of the first electrode finger and the second electrode finger.

12. The IDT electrode has a plurality of the first electrodes, The elastic wave apparatus according to claim 1, wherein, in the aforementioned arrangement direction, the plurality of first electrodes sandwich the tip of the second electrode finger on the side of the first busbar.

13. The IDT electrode has a plurality of first electrode fingers, a plurality of second electrode fingers, and a plurality of first electrodes. The elastic wave apparatus according to claim 1, wherein in the aforementioned arrangement direction, each of the first electrodes is located between the first electrode finger and the second electrode finger, respectively.

14. The elastic wave apparatus according to claim 13, wherein, in the arrangement direction, the distance between the center of one of the first electrode fingers and the center of the first electrode between at least one pair of adjacent first electrode fingers and the first electrode is different from the distance between the center of one of the first electrode fingers and the center of the first electrode between another at least one pair of first electrode fingers and the first electrode.

15. A support substrate located on the side opposite to the IDT electrode in the piezoelectric material, It comprises a hollow portion located between the piezoelectric element and the support substrate, In the region overlapping with the hollow portion in a plan view, the first electrode finger faces the second electrode finger in the direction of arrangement. The elastic wave apparatus according to claim 1, wherein in a region overlapping with the periphery of the hollow portion in a plan view, the first electrode finger and the second electrode finger face the first electrode in the direction of arrangement.

16. The elastic wave apparatus according to claim 1, wherein the piezoelectric material is excited to produce a plate wave in A1 mode.

17. The elastic wave apparatus according to claim 1, wherein a bulk wave is excited in the piezoelectric body.

18. An elastic wave filter comprising at least one elastic wave device according to any one of claims 1 to 17.

19. Antenna terminal and A transmission filter that filters the transmission signal and outputs it to the antenna terminal, A receiving filter that filters the received signal from the aforementioned antenna terminal, It has, A demultiplexer in which at least one of the transmitting filter and the receiving filter includes the elastic wave filter described in claim 18.

20. Antenna and, The demultiplexer according to claim 19, wherein the antenna terminal is connected to the antenna, ICs connected to the transmit filter and the receive filter, A communication device having [a certain feature].