1 of the first preferred embodiment, even when the number of pairs of the electrodes 3 and the electrodes 4 is reduced to achieve a reduction in size, a fall of the Q-value is less likely to occur. This is because the resonator does not need reflectors to be disposed on both sides and a propagation loss is small. The reason why the reflectors are not needed is because the bulk wave in the thickness shear mode is utilized.

FIG. 3A is a schematic sectional view to explain a Lamb wave propagating in a piezoelectric layer of a comparative example. FIG. 3B is a schematic sectional view to explain the bulk wave in the thickness shear mode propagating in the piezoelectric layer of the first preferred embodiment. FIG. 4 is a schematic sectional view to explain an amplitude direction of the bulk wave in the thickness shear mode propagating in the piezoelectric layer of the first preferred embodiment.

FIG. 3A represents the acoustic wave device disclosed in Japanese Unexamined Patent Application Publication No. 2012-257019 in which the Lamb wave propagates in the piezoelectric layer. As illustrated in FIG. 3A, the wave propagates in a piezoelectric layer 201 as denoted by an arrow. The piezoelectric layer 201 includes a first principal surface 201a and a second principal surface 201b, and a thickness direction connecting the first principal surface 201a and the second principal surface 201b is a Z-direction. An X-direction is a direction in which electrode fingers of IDT (interdigital transducer) electrodes are arranged side by side. As seen from FIG. 3A, the Lamb wave propagates in the X-direction as illustrated. Because the Lamb wave is a plate wave, the piezoelectric layer 201 vibrates in its entirety while the wave propagates in the X-direction. Therefore, resonance characteristics are obtained with reflectors on both sides. Accordingly, a propagation loss of the wave is generated, and the Q-value falls in the case of trying to achieve a reduction in size, namely in the case of reducing the number of pairs of the electrode fingers.

In contrast, in the acoustic wave device of the first preferred embodiment, as illustrated in FIG. 3B, because a vibration displacement occurs in a direction of thickness shear, a wave propagates substantially in a direction connecting the first principal surface 2a and the second principal surface 2b of the piezoelectric layer 2, namely in the Z-direction, and causes resonance. In other words, a component of the wave in the X-direction is much smaller than a component of the wave in the Z-direction. Moreover, since resonance characteristics are obtained with the propagation of the wave in the Z-direction, reflectors are not required. Thus, a propagation loss attributable to the propagation including reflections at the reflectors does not generate. Consequently, a fall of the Q-value is less likely to occur even when the number of electrode pairs each including the electrode 3 and the electrode 4 is reduced to realize a reduction in size.

The amplitude direction of the bulk wave in the thickness shear mode is reversed, as illustrated in FIG. 4, between a first region 451 included in the excitation region C (see FIG. 1B) of the piezoelectric layer 2 and a second region 452 included in the excitation region C. FIG. 4 schematically illustrates the bulk wave when a voltage with a higher potential at the electrode 4 than at the electrode 3 is applied between the electrode 3 and the electrode 4. The first region 451 is a portion of the excitation region C between a virtual plane VP1 extending perpendicular or substantially perpendicular to the thickness direction of the piezoelectric layer 2 and dividing the piezoelectric layer 2 into two portions and the first principal surface 2a. The second region 452 is a portion of the excitation region C between the virtual plane VP1 and the second principal surface 2b.

The acoustic wave device 1 includes at least one pair of electrodes defined by the electrode 3 and the electrode 4. In the acoustic wave device 1, however, since the wave does not propagate in the X-direction, the number of the electrode pairs each defined by the electrode 3 and the electrode 4 is not always required to be multiple. In other words, it is just necessary to provide at least one pair of electrodes.

In an example, the electrode 3 is an electrode connected to a hot potential, and the electrode 4 is an electrode connected to a ground potential. Conversely, the electrode 3 may be connected to the ground potential, and the electrode 4 may be connected to the hot potential. In the first preferred embodiment, each electrode included in at least one pair of the electrodes is the electrode connected to the hot potential or the electrode connected to the ground potential as described above, and a floating electrode is not disposed.

FIG. 5 is an explanatory view indicating an example of the resonance characteristics of the acoustic wave device of the first preferred embodiment. Design parameters of the acoustic wave device 1 with which the resonance characteristics indicated in FIG. 5 are obtained are as follows.

- Piezoelectric layer 2: LiNbO₃with Euler angles (0°, 0°,) 90°
- Thickness of the piezoelectric layer 2: about 400 nm Length of the excitation region C (see FIG. 1B): about 40 μm
- Number of pairs of electrodes including the electrodes 3 and the electrodes 4: 21 pairs
- Center-to-center distance (pitch) between the electrode 3 and the electrode 4: about 3 μm
- Width of the electrodes 3 and the electrodes 4: about 500 nm
- d/p: about 0.133
- Intermediate layer 7: silicon oxide film with thickness of about 1 μm
- Support member 8: Si

The excitation region C (see FIG. 1B) is a region where the electrode 3 and the electrode 4 overlap with each other when viewed in the X-direction perpendicular or substantially perpendicular to the lengthwise direction of the electrode 3 and the electrode 4. The length of the excitation region C is a dimension of the excitation region C along the lengthwise direction of the electrode 3 and the electrode 4.

In the first preferred embodiment, the electrode-to-electrode distances between the electrodes in pairs each defined by the electrode 3 and the electrode 4 are set to be equal or substantially equal in all the pairs. In other words, the electrodes 3 and the electrodes 4 are arranged at the same or substantially the same pitch.

As is apparent from FIG. 5, good resonance characteristics with a fractional band width of about 12.5% is obtained even though no reflectors are disposed.

Assuming that the thickness of the piezoelectric layer 2 is denoted by d and the center-to-center distance between the electrodes including the electrode 3 and the electrode 4 is denoted by p, d/p is set to be, for example, about 0.5 or less and more preferably about 0.24 or less in the first preferred embodiment. The reason is described below with reference to FIG. 6.

Multiple acoustic wave devices were fabricated in a similar manner to the acoustic wave device with the resonance characteristics indicated in FIG. 5 except for changing d/2p. FIG. 6 is an explanatory view indicating a relationship between d/2p and the fractional band width in operation as a resonator on an assumption that, in the acoustic wave device of the first preferred embodiment, the center-to-center distance between the adjacent electrodes or an average value of the center-to-center distances therebetween is denoted by p and an average thickness of the piezoelectric layer is d.

As indicated in FIG. 6, if d/2p exceeds about 0.25, namely in the case of d/p > about 0.5, the fractional band width is less than about 5% regardless of adjustment of d/p. On the other hand, in the case of d/2p ≤about 0.25, namely d/p ≤about 0.5, the fractional band width can be increased to about 5% or more by changing d/p in the above-mentioned range, and thus a resonator with a higher coupling coefficient can be provided. Furthermore, when d/2p is about 0.12 or less, namely when d/p is about 0.24 or less, the fractional band width can be increased to about 7% or more. In addition, by adjusting d/p in the above-mentioned range, a resonator with an even wider fractional band width can be obtained, and a resonator with an even higher coupling coefficient can be achieved. Thus, it is understood that a resonator utilizing the bulk wave in the thickness shear mode and having a high coupling coefficient can be provided by setting d/p to be about 0.5 or less.

The at least one pair of electrodes may be one pair of electrodes. In the case of one pair of electrodes, the above-mentioned parameter p is defined as the center-to-center distance between the electrode 3 and the electrode 4 adjacent to each other. In the case of 1.5 or more pairs of electrodes, p may be defined as an average value of the center-to-center distances between adjacent twos among the electrode(s) 3 and the electrode(s) 4.

Regarding the thickness d of the piezoelectric layer, when the piezoelectric layer 2 has a variation in thickness, an average thickness value may be used in a similar manner.

FIG. 7 is a plan view illustrating an example in which one pair of electrodes are disposed in the acoustic wave device of the first preferred embodiment. In an acoustic wave device 31, one pair of electrodes including the electrode 3 and the electrode 1 are disposed on the first principal surface 2a of the piezoelectric layer 2. K in FIG. 7 denotes an intersecting width. As described above, in acoustic wave devices according to preferred embodiments of the present invention, the number of pairs of electrodes may be one. In that case as well, when d/p is about 0.5 or less, the bulk wave in the thickness shear mode can be effectively excited.

FIG. 8 represents a first modification of the first preferred embodiment and is a sectional view taken along the cross-section denoted by the line II-II in FIG. 1A. As illustrated in FIG. 8, in an acoustic wave device 41, an acoustic multilayer film 42 is laminated on the second principal surface 2b of the piezoelectric layer 2. The acoustic multilayer film 42 has a multilayer structure including low acoustic impedance layers 42a, 42c, and 42e each having relatively low acoustic impedance and high acoustic impedance layers 42b and 42d each having relatively high acoustic impedance. With the acoustic multilayer film 42, a bulk wave in a thickness shear primary mode can be enclosed within the piezoelectric layer 2 without using the cavity 9 in the acoustic wave device 1. In the acoustic wave device 41 as well, resonance characteristics based on the bulk wave in the thickness shear primary mode can be obtained by setting d/p to be about 0.5 or less. In the acoustic multilayer film 42, the number of the low acoustic impedance layers 42a, 42c, and 42e to be laminated and the number of the high acoustic impedance layers 42b and 42d to be laminated are not limited to particular values. It is only required that at least one of the high acoustic impedance layers 42b and 42d is disposed on a side farther away from the piezoelectric layer 2 than the low acoustic impedance layers 42a, 42c, and 42e.

The low acoustic impedance layers 42a, 42c, and 42e and the high acoustic impedance layers 42b and 42d can be made of any suitable materials as long as the above-described relationship with regards to the acoustic impedance is satisfied. For example, silicon oxide or silicon oxynitride can be used as the material of the low acoustic impedance layers 42a, 42c, and 42e. For example, alumina, silicon nitride, or a metal can be used as the material of the high acoustic impedance layers 42b and 42d.

In the acoustic wave device 1, preferably, assuming the excitation region C to be a region where any adjacent two among the electrode 3 and the electrode 4 overlap with each other when viewed in the opposing direction of the electrode 3 and the electrode 4, a metallization ratio MR of those two adjacent electrodes 3 and 4 to the excitation region C satisfies MR ≤1.75 (d/p)+0.075. In such a case, spurious modes can be effectively reduced. The above point will be described below with reference to FIGS. 9 and 10.

FIG. 9 is a reference view indicating an example of the resonance characteristics of the acoustic wave device of the first preferred embodiment. Spurious wave denoted by an arrow B appears between a resonant frequency and an anti-resonant frequency. The indicated example is obtained on condition of d/p=0.08 and LiNbO₃having the Euler angles (0°, 0°,) 90°. Moreover, the metallization ratio MR is set to MR=0.35.

The metallization ratio MR is described with reference to FIG. 1B. It is assumed, looking at one pair of the electrode 3 and the electrode 4 in the electrode structure of FIG. 1B, that only the one pair of the electrode 3 and the electrode 4 are provided. In this case, a portion surrounded by a one-dot-chain line is the excitation region C. More specifically, the excitation region C is a region of the electrode 3 where the electrode 3 overlaps with the electrode 4 when the electrode 3 and the electrode 4 are viewed in the direction perpendicular or substantially perpendicular to the lengthwise direction of the electrode 3 and the electrode 4, namely in the opposing direction of both the electrodes, a region of the electrode 4 where the electrode 4 overlaps with the electrode 3, and a region between the electrode 3 and the electrode 4 where the electrode 3 and the electrode 4 overlap with each other. The metallization ratio MR is a ratio of an area of both of the electrode 3 and the electrode 4 within the excitation region C to an area of the excitation region C. In other words, the metallization ratio MR is a ratio of an area of metallized portions to the area of the excitation region C.

When multiple pairs of the electrodes 3 and the electrodes 4 are disposed, a proportion of the metallized portions included in the excitation regions C with respect to a total area of the excitation regions C may be used as the MR.

FIG. 10 is an explanatory view indicating a relationship between the fractional band width and a magnitude of spurious modes, namely a phase rotation amount of spurious impedance normalized on the basis of 180 degrees, when many acoustic wave resonators are included in the acoustic wave device of the first preferred embodiment. Here, the fractional band width is adjusted by variously changing the film thickness of the piezoelectric layer 2 and the dimensions of the electrode 3 and the electrode 4. While FIG. 10 indicates a result in an example of using the piezoelectric layer 2 made of Z cut LiNbO₃, a similar tendency is also obtained in the case of using the piezoelectric layer 2 with other cut-angles.

In a region surrounded by an ellipse J in FIG. 10, the spurious wave is as large as about 1.0. As is apparent from FIG. 10, when the fractional band width exceeds about 0.17, namely about 17%, large spurious modes with a spurious level of 1 or more appears in a pass band even when the parameters for the fractional band width are changed. In other words, as in the resonance characteristics indicated in FIG. 9, the large spurious modes denoted by the arrow B appears in the band. Accordingly, the fractional band width is preferably set to be about 17% or less. In that case, the spurious modes can be reduced by adjusting the film thickness of the piezoelectric layer 2 and the dimensions of the electrode 3 and the electrode 4.

FIG. 11 is an explanatory view indicating relationships among d/2p, the metallization ratio MR, and the fractional band width. In accordance with the acoustic wave device 1 of the first preferred embodiment, various types of acoustic wave devices 1 with d/2p and MR set to different values were fabricated, and fractional band widths were measured. A portion denoted by hatching on a right side of a dashed line D in FIG. 11 represents a region where the fractional band width is about 17% or less. A boundary between the hatched region and a not-hatched region is expressed by MR=3.5 (d/2p)+0.075. In a different form, the boundary is expressed by MR=1.75 (d/p)+0.075. Thus, MR≤1.75 (d/p)+0.075 is preferably satisfied. In this case, the fractional band width can be easily made about 17% or less. It is more preferable to utilize a region on a right side of a one-dot-chain line D1, in FIG. 11, which is expressed by MR=3.5 (d/2p)+0.05. Stated another way, when MR≤1.75 (d/p)+0.05 is satisfied, the fractional band width can be reliably made about 17% or less.

FIG. 12 is an explanatory view indicating a map of the fractional band width with respect to Euler angles (0°, 0, 4) of LiNbO₃when d/p is assumed to be as close as possible to 0. Portions denoted by hatching in FIG. 12 represent regions where the fractional band width of at least about 5% or more is obtained. Extents of those regions are approximately defined by the following expressions (1), (2), and (3).

(0°±10°, 0° to 20°, arbitrary ψ) (1)

(0°±10°,20°to 80°,0°to 60°(1−(θ−50)²/900)^1/2) or(0°±10°,20°to 80°,[180°−60°(1−(θ−50)²/900)^1/2]to 180° (2)

(0°±10°, [180°−30° (1−(ψ−90)²/8100)^1/2] to 180°, arbitrary ψ) (3)

Thus, the Euler angles preferably fall within an Euler angle range defined by the above-described expression (1), (2), or (3) for the reason that the fractional band width can be sufficiently widened in such a case.

As described above, the bulk wave in the thickness shear mode is utilized in the acoustic wave devices 1, 31, and 41. Furthermore, in the acoustic wave devices 1, 31, and 41, the first electrode 3 and the second electrode 4 are adjacent electrodes, and d/p is set to be about 0.5 or less on the assumption that the thickness of the piezoelectric layer is denoted by d and the center-to-center distance between the first electrode 3 and the second electrode 4 is denoted by p. With that feature, the Q-value can be increased in spite of a reduction in size of the acoustic wave devices.

In the acoustic wave devices 1, 31, and 41, the piezoelectric layer 2 is made of lithium niobate or lithium tantalate, for example. The first electrode 3 and the second electrode 4 are disposed on the first principal surface 2a or the second principal surface 2b of the piezoelectric layer 2 to be positioned opposite to each other in the direction intersecting the thickness direction of the piezoelectric layer 2. A protective film preferably covers the first electrode 3 and the second electrode 4.

A configuration of the acoustic wave device 1 including multiple piezoelectric layers (chips) will be described below. FIG. 13 is an explanatory view to explain an example of the acoustic wave device of the first preferred embodiment. FIG. 14 is a plan view illustrating a portion of a first chip included in the acoustic wave device of the first preferred embodiment. FIG. 15 is a plan view illustrating a portion of a second chip included in the acoustic wave device of the first preferred embodiment.

As illustrated in FIG. 13, the acoustic wave device 1 includes a first chip 61, a second chip 62, a third chip 63, and connection wirings 71 and 72. The first chip 61, the second chip 62, and the third chip 63 are connected in parallel through the connection wirings 71 and 72. Stated another way, a first acoustic wave resonator 51, a second acoustic wave resonator 52, and a third acoustic wave resonator 53 included in the individual chips are connected in parallel through the connection wirings 71 and 72. The wording “multiple chips (acoustic wave resonators) are connected in parallel” indicates a configuration in which respective input sides of the first acoustic wave resonator 51, the second acoustic wave resonator 52, and the third acoustic wave resonator 53 included in the chips are connected in parallel through a common wiring (for example, the connection wiring 71) and respective output sides thereof are connected in parallel through a common wiring (for example, the connection wiring 72).

As illustrated in FIGS. 13 and 14, the first chip 61 includes a first piezoelectric layer 21 and at least one pair of a first electrode 3A and a second electrode 4A disposed on a first principal surface 21a of the first piezoelectric layer 21. The first piezoelectric layer 21 and the pair of the first electrode 3A and the second electrode 4A define the first acoustic wave resonator 51. The first acoustic wave resonator 51 further includes a first busbar 5A and a second busbar 6A (see FIG. 14). The first electrode 3A, the second electrode 4A, the first busbar 5A, and the second busbar 6A are structured in the same or substantially the same configuration as the above-described one illustrated in FIG. 1B, and repetitive description is omitted.

As illustrated in FIG. 13, two first acoustic wave resonators 51 are disposed on one first chip 61. A direction (X-direction) perpendicular or substantially perpendicular to a lengthwise direction of the first electrode 3A and the second electrode 4A included in each first acoustic wave resonator 51 is along an outline 21e (long side) of the first piezoelectric layer 21. Directions perpendicular or substantially perpendicular to the lengthwise directions of the first electrodes 3A and the second electrodes 4A in the two first acoustic wave resonators 51 are parallel or substantially parallel to each other. The two first acoustic wave resonators 51 are arranged side by side in the lengthwise direction of the first electrode 3A and the second electrode 4A.

In FIGS. 13 and 14, crystal orientations CX1 and CY1 of the first piezoelectric layer 21 in the first chip 61 are schematically denoted by arrows. The crystal orientation CX1 of the first piezoelectric layer 21 is set along the outline 21e of the first piezoelectric layer 21. In other words, the crystal orientation CX1 of the first piezoelectric layer 21 is set along the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the first electrode 3A and the second electrode 4A. Moreover, the crystal orientation CY1 of the first piezoelectric layer 21 is set to be perpendicular or substantially perpendicular to the crystal orientation CX1, namely along the lengthwise direction of the first electrode 3A and the second electrode 4A. When the first piezoelectric layer 21 is made of, for example, lithium niobate (LiNbO₃) or lithium tantalate (LiTaO₃), the crystal orientations CX1 and CY1 correspond to an X-axis and a Y-axis, respectively.

As illustrated in FIGS. 13 and 15, the second chip 62 includes a second piezoelectric layer 22 and at least one pair of a third electrode 3B and a fourth electrode 4B disposed on a first principal surface 22a of the second piezoelectric layer 22. The second piezoelectric layer 22 and the pair of the third electrode 3B and the fourth electrode 4B define the second acoustic wave resonator 52. The second acoustic wave resonator 52 further includes a third busbar 5B and a fourth busbar 6B (see FIG. 15). The third electrode 3B, the fourth electrode 4B, the third busbar 5B, and the fourth busbar 6B are structured in the same or substantially the same configuration as the above-described one illustrated in FIG. 1B, and repetitive description is omitted.

Two second acoustic wave resonators 52 are disposed on one second chip 62. A direction (X-direction) perpendicular or substantially perpendicular to a lengthwise direction of the third electrode 3B and the fourth electrode 4B included in each second acoustic wave resonator 52 is along an outline 22e (long side) of the second piezoelectric layer 22. Directions perpendicular or substantially perpendicular to the lengthwise directions of the third electrodes 3B and the fourth electrodes 4B in the two second acoustic wave resonators 52 are parallel or substantially parallel to each other. The two second acoustic wave resonators 52 are arranged side by side in the lengthwise direction of the third electrode 3B and the fourth electrode 4B.

In FIGS. 13 and 15, crystal orientations CX2 and CY2 of the second piezoelectric layer 22 in the second chip 62 are schematically denoted by arrows. The crystal orientation CX2 of the second piezoelectric layer 22 is set to be inclined relative to the outline 22e of the second piezoelectric layer 22. In other words, the crystal orientation CX2 of the second piezoelectric layer 22 is inclined at an angle ¢ relative to the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the third electrode 3B and the fourth electrode 4B. Moreover, the crystal orientation CY2 of the second piezoelectric layer 22 is set to be perpendicular or substantially perpendicular to the crystal orientation CX2 and to be inclined at the angle ϕ relative to the lengthwise direction of the third electrode 3B and the fourth electrode 4B.

As illustrated in FIG. 13, the third chip 63 includes a third piezoelectric layer 23 and at least one pair of a fifth electrode 3C and a sixth electrode 4C disposed on a first principal surface 23a of the third piezoelectric layer 23. The third piezoelectric layer 23 and the pair of the fifth electrode 3C and the sixth electrode 4C define the third acoustic wave resonator 53. Although not illustrated, the third acoustic wave resonator 53 further includes a fifth busbar and a sixth busbar. The fifth electrode 3C, the sixth electrode 4C, the fifth busbar, and the sixth busbar are structured in the same or substantially the same configuration as the above-described one in the first acoustic wave resonator 51 and the second acoustic wave resonator 52 illustrated in FIGS. 14 and 15.

Two third acoustic wave resonators 53 are disposed on one third chip 63. A direction (X-direction) perpendicular or substantially perpendicular to a lengthwise direction of the fifth electrode 3C and the sixth electrode 4C included in each third acoustic wave resonator 53 is along an outline 23e (long side) of the third piezoelectric layer 23. Directions perpendicular or substantially perpendicular to the lengthwise directions of the fifth electrodes 3C and the sixth electrodes 4C in the two third acoustic wave resonators 53 are parallel or substantially parallel to each other. The two third acoustic wave resonators 53 are arranged side by side in the lengthwise direction of the fifth electrode 3C and the sixth electrode 4C.

In FIG. 13, crystal orientations CX3 and CY3 of the third piezoelectric layer 23 in the third chip 63 are schematically denoted by arrows. The crystal orientation CX3 of the third piezoelectric layer 23 is set to be perpendicular or substantially perpendicular to the outline 23e (long side) of the third piezoelectric layer 23. In other words, the crystal orientation CX3 of the third piezoelectric layer 23 is set along the lengthwise direction of the fifth electrode 3C and the sixth electrode 4C. Moreover, the crystal orientation CY3 of the third piezoelectric layer 23 is set to be perpendicular or substantially perpendicular to the crystal orientation CX3, namely along the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the fifth electrode 3C and the sixth electrode 4C.

As described above, in the acoustic wave device 1, an angle (for example, about) 0° between the crystal orientation CX1 of the first piezoelectric layer 21 and the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the pair of the first electrode 3A and the second electrode 4A is different from an angle (for example, about) 40° between the crystal orientation CX2 of the second piezoelectric layer 22 and the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the pair of the third electrode 3B and the fourth electrode 4B. Moreover, the angle (for example, about) 0° between the crystal orientation CX1 of the first piezoelectric layer 21 and the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the pair of the first electrode 3A and the second electrode 4A is different from an angle (for example, about) 90° between the crystal orientation CX3 of the third piezoelectric layer 23 and the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the pair of the fifth electrode 3C and the sixth electrode 4C.

With the configuration described above, in the acoustic wave device 1, strengths and frequencies of spurious modes generated in the individual chips can be made different from one another and can be dispersed. Accordingly, in comparison with the case in which the first chip 61, the second chip 62, and the third chip 63 are structured in the same configuration, the strength of spurious modes can be reduced or prevented overall without deteriorating the resonance characteristics of a main mode. As a result, the acoustic wave device 1 can be suitably applied to the case of structuring a bandpass filter by using the first acoustic wave resonator 51, the second acoustic wave resonator 52, and the third acoustic wave resonator 53. In such a case, since the spurious modes are reduced, deterioration of filter characteristics can be reduced or prevented.

In FIG. 13, two acoustic wave resonators are disposed in each of the first chip 61, the second chip 62, and the third chip 63. However, the present invention is not limited to that case, and one or three or more acoustic wave resonators may be disposed in each chip. When multiple acoustic wave resonators are disposed in each chip, the acoustic wave resonators in each chip may be connected in parallel or in series. The number and connection configuration of the acoustic wave resonators in each chip can be changed as appropriate depending on the filter characteristics demanded for the acoustic wave device 1. While the acoustic wave device 1 includes three chips, namely the first chip 61, the second chip 62, and the third chip 63, the present invention is not limited to that case, and the acoustic wave device 1 is just required to include at least two chips.

FIG. 16 is an explanatory view to explain an example of an acoustic wave device according to a second modification of the first preferred embodiment. As illustrated in FIG. 16, an acoustic wave device 1A according to the second modification is structured such that, in two first acoustic wave resonators 51a and 51b included in a first chip 61A, directions (X-direction) perpendicular or substantially perpendicular to the lengthwise directions of the first electrodes 3A and the second electrodes 4A in the first acoustic wave resonators 51a and 51b are along the outline 21e of the first piezoelectric layer 21. Here, the wording “along the outline 21e of the first piezoelectric layer 21” indicates that an angle between an extension direction of any side of the first piezoelectric layer 21, the side defining the outline 21e, and the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the first electrode 3A and the second electrode 4A in the first acoustic wave resonator 51 is within about 0°+10°.

In the second modification illustrated in FIG. 16, for example, looking at one first acoustic wave resonator 51a in the first chip 61A, one second acoustic wave resonator 52a in the second chip 62A, and both third acoustic wave resonators 53a and 53b in the third chip 63A, an angle between a direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of each of the electrodes in those resonators and an extension direction of a long side defining each of respective outlines 21e, 22e, and 23e of the individual chips is about 0°.

Furthermore, for example, in the other first acoustic wave resonator 51b in the first chip 61A and the other second acoustic wave resonator 52b in the second chip 62A, an angle between a direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of each of the electrodes in those resonators and the extension direction of the long side defining each of the outlines 21e and 22e of the individual chips is about +5° or about −5°.

Thus, in the configuration of the first chip 61A, the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the first electrode 3A and the second electrode 4A included in each of the first acoustic wave resonators 51a and 51b is not limited to being parallel or substantially parallel to the outline 21e and may be set along the outline 21e at a predetermined angle therebetween. Moreover, the direction (X-direction) perpendicular or substantially perpendicular to the lengthwise direction of the first electrode 3A and the second electrode