ACOUSTIC WAVE DEVICE

An acoustic wave device includes an IDT electrode with an inclined IDT structure on a piezoelectric substrate. An intersection region, where a first electrode finger and a second electrode finger overlap each other when viewed in an acoustic wave propagation direction, includes a central region and first and second low acoustic velocity regions on both sides of the central region. The first and second low acoustic velocity regions have an asymmetric shape about a central axis extending in a length direction of the first and second electrode fingers.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an acoustic wave device including an inclined IDT electrode.

2. Description of the Related Art

International Publication No. 2015/098756 discloses an acoustic wave device having an inclined IDT electrode, and further having a structure for suppressing a transverse mode. In this acoustic wave device, in order to provide a low acoustic velocity region in an intersection region, an edge portion of an electrode finger is formed as a large-width portion, and is made wider than a width of the electrode finger in a central region.

SUMMARY OF THE INVENTION

In the acoustic wave device described in International Publication No. 2015/098756, since the large-width portion is provided in the low acoustic velocity region, the transverse mode can be suppressed. However, due to such an electrode structure, another ripple could be generated. In particular, in a case of an acoustic wave resonator, a ripple could appear near an upper end of a stop band.

Preferred embodiments of the present invention provide acoustic wave devices that are each capable of suppressing a ripple near an upper end of a stop band.

An acoustic wave device according to a preferred embodiment of the present invention includes a piezoelectric substrate, and an IDT electrode on the piezoelectric substrate, in which the IDT electrode includes a first busbar, a second busbar separated from the first busbar, a plurality of first electrode fingers including one end connected to the first busbar, a plurality of second electrode fingers including one end connected to the second busbar, a plurality of first dummy electrodes connected to the second busbar, tip ends of the first dummy electrodes facing tip ends of the first electrode fingers with a second gap interposed therebetween, and a plurality of second dummy electrodes connected to the first busbar, tip ends of the second dummy electrodes facing tip ends of the second electrode fingers with a first gap interposed therebetween, and when a first virtual line connecting the tip ends of the plurality of second electrode fingers is inclined with respect to an acoustic wave propagation direction that is a direction orthogonal to a direction in which the first and second electrode fingers extend, a distance between a tip end of a second electrode finger on one side, of a pair of second electrode fingers included in the second electrode fingers adjacent to any first electrode finger included in the first electrode fingers, and a base end of the first electrode finger is shorter than a distance between a tip end of the second electrode finger on an other side of the pair and the base end of the first electrode finger, and a direction toward a direction in which the distance is longer in the first virtual line is an inclination direction, at least one of, a projecting portion protruding toward the first electrode finger or the second electrode finger, in at least one of a side in the inclination direction at a tip end of the second electrode finger, a side opposite to the inclination direction at a tip end of a second dummy electrode included in the second dummy electrodes, a side opposite to the inclination direction of the first electrode finger positioned on an extension in the inclination direction from the tip end of the second dummy electrode, and a side in the inclination direction of the first electrode finger positioned on an extension in the inclination direction from the tip end of the second electrode finger, and a recessed portion provided in at least one of a side opposite to the inclination direction at the tip end of the second electrode finger, a side in the inclination direction at the tip end of the second dummy electrode, a side in the inclination direction of the first electrode finger positioned on the extension in the inclination direction from the tip end of the second dummy electrode, and a side opposite to the inclination direction of the first electrode finger positioned on the extension in the inclination direction from the tip end of the second electrode finger, is provided.

In another broad aspect of an acoustic wave device according to a preferred embodiment of the present invention includes a piezoelectric substrate, and an IDT electrode on the piezoelectric substrate, wherein the IDT electrode includes a first busbar, a second busbar separated from the first busbar, a plurality of first electrode fingers including one end connected to the first busbar, a plurality of second electrode fingers including one end connected to the second busbar, a plurality of first dummy electrodes connected to the second busbar, tip ends of the first dummy electrodes facing tip ends of the first electrode fingers with a second gap interposed therebetween, and a plurality of second dummy electrodes connected to the first busbar, tip ends of the second dummy electrodes facing tip ends of the second electrode fingers with a first gap interposed therebetween, a first virtual line connecting the tip ends of the plurality of second electrode fingers is inclined with respect to an acoustic wave propagation direction that is a direction orthogonal to a direction in which the first and second electrode fingers extend, a distance between a tip end of a second electrode finger on one side, of a pair of second electrode fingers included in the second electrode fingers adjacent to any first electrode finger included in the first electrode fingers, and a base end of the first electrode finger is shorter than a distance between a tip end of the second electrode finger on an other side of the pair and the base end of the first electrode finger, a side closer to the second electrode finger for which the distance is shorter, of sides of the first electrode finger, and a side closer to the second electrode finger for which the distance is shorter, of sides of a first dummy electrode included in the first dummy electrodes facing the first electrode finger, are each a first side, and a side opposite to the first side is a second side, a distance between a tip end of a first electrode finger on one side, of a pair of first electrode fingers included in the first electrode fingers adjacent to any second electrode finger included in the second electrode fingers, and a base end of the second electrode finger is shorter than a distance between a tip end of the first electrode finger on an other side of the pair and the base end of the second electrode finger, a side closer to the first electrode finger for which the distance is shorter, of sides of the second electrode finger, and a side closer to the first electrode finger for which the distance is shorter, of sides of a second dummy electrode included in the second dummy electrodes facing the second electrode finger, are each a second side, and a side opposite to the second side is a first side, a line connecting respective centers of first gaps, each of which being the first gap interposed between the tip ends, is a second virtual line, of a portion closer to the first gap of the second dummy electrode, a region closer to the first side is a first region and a region closer to the second side is a second region, of a portion closer to the first gap of the second electrode finger, a region closer to the first side is a fifth region and a region closer to the second side is a sixth region, and in the first electrode finger that is adjacent, in a portion closer to the first busbar with respect to the second virtual line, a region closer to the first side is a third region and a region closer to the second side is a fourth region, and in the first electrode finger, in a portion closer to the second busbar with respect to the second virtual line, a region closer to the first side is a seventh region and a region closer to the second side is an eighth region, and in the first region, the third region, the sixth region, and the eighth region, an angle defined by the first side or the second side in each region, and the first virtual line is an acute angle, and in the second region, the fourth region, the fifth region, and the seventh region, an angle defined by the first side or the second side positioned in each region, and the first virtual line is an obtuse angle, and at least one of a projecting portion provided in at least one region of the first region, the third region, the sixth region, and the eighth region, and a recessed portion provided in at least one region of the second region, the fourth region, the fifth region, and the seventh region is provided.

According to preferred embodiments of the present invention, it is possible to provide acoustic wave devices each capable of suppressing a ripple near an upper end of a stop band.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, specific preferred embodiments of the present invention will be described with reference to the accompanying drawings to clarify the present invention.

Preferred embodiments described in the present specification are merely examples, and partial replacement or combination of configurations is possible between different preferred embodiments.

FIG.1Ais a schematic plan view illustrating an electrode structure of an acoustic wave device according to a first preferred embodiment of the present invention andFIG.1Bis an enlarged view of a main portion thereof. Further,FIG.4is a front sectional view of the acoustic wave device according to the first preferred embodiment.

As illustrated inFIG.4, an acoustic wave device1includes a piezoelectric substrate2. An IDT electrode7and reflectors8and9are provided on the piezoelectric substrate2. As a result, a one-port-type acoustic wave resonator is provided.

The piezoelectric substrate2has a structure in which a support substrate3, a high acoustic velocity material layer4, a low acoustic velocity material layer5, and a piezoelectric film6are laminated in this order. The support substrate3is made of an appropriate semiconductor or dielectric material such as Si or alumina.

The piezoelectric film6is made of a piezoelectric single crystal such as LiTaO3. The high acoustic velocity material layer4is made of a high acoustic velocity material by which acoustic velocity of a bulk wave propagating therethrough is higher than acoustic velocity of an acoustic wave propagating through the piezoelectric film6. As such a high acoustic velocity material, various materials can be used such as aluminum oxide, silicon carbide, silicon nitride, silicon oxynitride, silicon, sapphire, lithium tantalate, lithium niobate, quartz, alumina, zirconia, cordierite, mullite, steatite, forsterite, magnesia, a diamond-like carbon (DLC) film or diamond, a medium including the above-described material as a main component, and a medium including a mixture of the above-described materials as a main component.

The low acoustic velocity material layer5is made of a low acoustic velocity material by which acoustic velocity of a bulk wave propagating therethrough is lower than acoustic velocity of a bulk wave propagating through the piezoelectric film6. As such a low acoustic velocity material, various materials can be used such as silicon oxide, glass, silicon oxynitride, tantalum oxide, a compound obtained by adding fluorine, carbon, boron, hydrogen, or a silanol group to silicon oxide, a medium including the above-described material as a main component, and the like.

Since the piezoelectric substrate2has a structure as described above, an acoustic wave excited in the piezoelectric film6can be effectively confined in the piezoelectric film6. Note that, the support substrate3may be a high acoustic velocity support substrate including a material similar to that of the high acoustic velocity material layer4. In this case, the piezoelectric substrate2need not have the high acoustic velocity material layer4. That is, the layer configuration of the piezoelectric substrate2may be a configuration in which a high acoustic velocity support substrate, a low acoustic velocity material layer, and a piezoelectric film are laminated in this order.

The IDT electrode7and the reflectors8and9are made of an appropriate metal or alloy. Alternatively, the IDT electrode7and the reflectors8and9may include a multilayer body including a plurality of metal films.

As illustrated inFIGS.1A and1B, the IDT electrode7has a so-called inclined structure. The IDT electrode7includes a first busbar11and a second busbar12. InFIGS.1A and1B, the first and second busbars11and12are inclined downward relative to a horizontal direction, while extending from a left side to a right side of the figure. The first busbar11and the second busbar12are parallel or substantially parallel to each other.

A plurality of first electrode fingers13is connected to the first busbar11. A plurality of second electrode fingers14is connected to the second busbar12. The plurality of first electrode fingers13and the plurality of second electrode fingers14are interdigitated with each other. On the other hand, a plurality of second dummy electrodes16is connected to the first busbar11. A plurality of first dummy electrodes15is connected to the second busbar12. Respective tip ends of the second dummy electrode16and the second electrode finger14face each other with a first gap G1interposed therebetween. Similarly, respective tip ends of the first electrode finger13and the first dummy electrode15face each other with a second gap G2interposed therebetween.

As illustrated inFIG.2, an acoustic wave propagation direction D is a direction orthogonal to a direction in which the first and second electrode fingers13and14extend. A first virtual line A is inclined with respect to the acoustic wave propagation direction D. The first virtual line A is a virtual straight line connecting tip ends of the plurality of second electrode fingers14. Note that, a virtual straight line connecting centers of the plurality of first gaps G1is a second virtual line B. Further, on a side of the second gap G2, a virtual line connecting tip ends of the plurality of first electrode fingers13is a third virtual line A1. A virtual line connecting centers of the plurality of second gaps G2is a fourth virtual line B1.

The first virtual line A and the third virtual line A1described above are inclined with respect to the acoustic wave propagation direction D.

As illustrated inFIG.1A, when viewed along the acoustic wave propagation direction D, a region in which the first electrode finger13and the second electrode finger14overlap each other is an intersection region K. The intersection region K has a central region C and first and second low acoustic velocity regions L1and L2provided on respective outer side portions of the central region C in a direction in which the first and second electrode fingers13and14extend. Here, a projecting portion17, which will be described later, is provided in each of the first and second low acoustic velocity regions L1and L2to achieve low acoustic velocity.

Note that, in the intersection region K, other regions may be further provided on respective outer side portions of the first and second low acoustic velocity regions L1and L2in the direction in which the first and second electrode fingers13and14extend.

In the acoustic wave device1, high acoustic velocity regions are further provided on the respective outer side portions of the first and second low acoustic velocity regions L1and L2to suppress a ripple caused by a transverse mode. Such structure for suppressing a transverse mode is similar to that in a case of the acoustic wave device described in International Publication No. 2015/098756.

As illustrated inFIG.1A, the reflectors8and9each have a structure in which both ends of a plurality of electrode fingers are short-circuited by respective busbars. In each of the reflectors8and9as well, the respective busbars on both sides are inclined similarly to the first and second busbars11and12.

The inclined IDT electrode described above is also disclosed in International Publication No. 2015/098756. In addition, in the acoustic wave device described in International Publication No. 2015/098756, a large-width portion is provided at a tip end of each of first and second electrode fingers in order to suppress a transverse mode. However, the inventor of the present application has discovered that a ripple appears near an upper end of a stop band due to the provision of such a large-width portion.

The acoustic wave device1is configured to be capable of suppressing the ripple near the upper end of the stop band. This is possible because the projecting portion17is provided at each of the first electrode finger13, the second electrode finger14, the first dummy electrode15, and the second dummy electrode16. This will be described in more detail.

As illustrated inFIG.1B, the first electrode finger13includes a first side13aand a second side13b,and the second electrode finger14includes a first side14aand a second side14b.Also, the first dummy electrode15includes a first side15aand a second side15b,and the second dummy electrode16includes a first side16aand a second side16b.

A direction in which the first busbar11is inclined downward relative to the horizontal direction inFIG.2is an inclination direction. As described above, the IDT electrode7has the inclined structure. Accordingly, a distance between a tip end of the second electrode finger14on one side, of the second electrode fingers14adjacent to any first electrode finger13, and a base end of the first electrode finger13is shorter than a distance between a tip end of the second electrode finger14on the other side and the base end. In the present preferred embodiment, a side closer to the second electrode finger14for which the distance is shorter, of sides of the first electrode finger13, is the first side13a.A side closer to the second electrode finger14for which the distance is shorter, of sides of the first dummy electrode15facing the first electrode finger13, is the first side15a.A side opposite to the first side13ais the second sides13band a side opposite to the first side15ais the second side15b.Similarly, a distance between a tip end of the first electrode finger13on one side, of the first electrode fingers13adjacent to any second electrode finger14, and a base end of the second electrode finger14is shorter than a distance between a tip end of the first electrode finger13on the other side and the base end. In the present preferred embodiment, a side closer to the first electrode finger13for which the distance is shorter, of sides of the second electrode finger14, is the second side14b.A side closer to the first electrode finger13for which the distance is shorter, of sides of the second dummy electrode16facing the second electrode finger14, is the second side16b.A side opposite to the second side14bis the first side14a,and a side opposite to the second side16bis the first side16a.

As illustrated inFIG.2, of a portion closer to the first gap G1of the second dummy electrodes16, a region closer to the first side16ais a first region R1and a region closer to the second side16bis a second region R2. Of the second electrode finger14facing the first gap G1, a region closer to the first side14ais a fifth region R5and a region closer to the second side14bis a sixth region R6. In the first electrode finger13adjacent in the inclination direction to the second dummy electrode16, in a portion on the side closer to the first busbar11with respect to the second virtual line B, a region closer to the first side13ais a third region R3and a region closer to second side13bis a fourth region R4, in the first electrode finger13, in a portion on the side closer to the second busbar12with respect to the second virtual line B, a region closer to the first side13ais a seventh region R7and a region closer to the second side13bis an eighth region R8.

In the first region R1and the third region R3, an angle F2defined by each of the first sides16aand13apositioned in the respective regions, and the first virtual line A is an acute angle. Similarly, in the sixth region R6and the eighth region R8, the angle F2defined by each of the second sides14band13bpositioned in the respective regions, and the first virtual line A is an acute angle.

On the other hand, in the second region R2and the fourth region R4, an angle F1defined by each of the second sides16band13band the first virtual line A is an obtuse angle. Similarly, in the fifth region R5and the seventh region R7, the angle F1defined by each of the first sides14aand13aand the first virtual line A is an obtuse angle.

Here, the angle defined by the first side or the second side and the first virtual line A in each of the first to eighth regions R1to R8refers to an intersection angle in a portion positioned in each of the first to eighth regions R1to R8. Further, the angle in each region refers to an intersection angle closer to the region, between a portion of the first side or the second side positioned in each region and the first virtual line A.

In a preferred embodiment of the present invention, at least one of, at least one projecting portion provided in at least one region of the first region R1, the third region R3, the sixth region R6, and the eighth region R8, and at least one recessed portion provided in at least one region of the second region R2, the fourth region R4, the fifth region R5and the seventh region R7, is provided. In other words, at least one of, a projecting portion protruding toward a first electrode finger or a second electrode finger, in at least one of a side in an inclination direction at a tip end of the second electrode finger, a side opposite to the inclination direction at a tip end of a second dummy electrode, a side opposite to the inclination direction of the first electrode finger positioned on an extension in the inclination direction from the tip end of the second dummy electrode, and a side in the inclination direction of the first electrode finger positioned on an extension in the inclination direction from the tip end of the second electrode finger, and a recessed portion provided in at least one of a side opposite to the inclination direction at the tip end of the second electrode finger, a side in the inclination direction at the tip end of the second dummy electrode, a side in the inclination direction of the first electrode finger positioned on the extension in the inclination direction from the tip end of the second dummy electrode, and a side opposite to the inclination direction of the first electrode finger positioned on the extension in the inclination direction from the tip end of the second electrode finger, is provided. As a result, the ripple near the upper end of the stop band can be suppressed.

In the present preferred embodiment, as illustrated inFIGS.1A and1B, the projecting portion17is provided as the recessed portion or projecting portion. More specifically, in the first side16aof the second dummy electrode16, the projecting portion17protruding to a side opposite to the first electrode finger13is provided in the first region R1. That is, the projecting portion17is provided in the first region R1. Similarly, the projecting portion17is provided also in the sixth region R6.

In the existing acoustic wave device, the large-width portion is provided at the tip end of the electrode finger. Thus, the ripple appeared near the upper end of the stop band.FIG.5is a diagram illustrating impedance-frequency characteristics of an acoustic wave resonator in the existing acoustic wave device andFIG.6is a diagram illustrating an enlarged portion thereof.

As is clear fromFIG.5, a large ripple appears near about 5780 MHz to about 5920 MHz higher than an anti-resonant frequency. The inventor of preferred embodiments of the present application has considered that this ripple is caused by the fact that the large-width portion is provided at the tip end of the electrode finger symmetrically about a center of the electrode finger. Thus, in a preferred embodiment of the present invention, as described above, the projecting portion and/or the recessed portion is provided in the first to eighth regions R1to R8, thus suppressing this ripple. This will be described in more detail below.

In the existing acoustic wave device, a low acoustic velocity region was formed by providing the large-width portion at the tip end of the electrode finger. A displacement distribution in this case will be described with reference toFIG.7.FIG.7is a schematic plan view illustrating an enlarged portion of an electrode structure of an existing acoustic wave device100. Here, a large-width portion102ais provided at a tip end of a second electrode finger102. Further, a tip end of a second dummy electrode104is also provided with a large-width portion104a.

The large-width portion102aand the large-width portion104aface each other with the first gap G1interposed therebetween. In this case, when a first electrode finger101connected to a first busbar becomes a hot side, since an IDT electrode includes an inclined structure, a region where displacement on a positive potential side is large is a region H2illustrated by hatching. On the other hand, a region where displacement on a negative potential side is large is a region H1or H3indicated by hatching.

As is apparent fromFIG.7, since the IDT electrode includes the inclined structure, the portion having the large displacement is inclined with respect to a direction in which the first and second electrode fingers101and102extend. That is, as further enlarged and illustrated inFIG.8, the region H2schematically illustrated is inclined with respect to a direction in which the second electrode finger102and the second dummy electrode104extend.

It is considered that, when the large-width portion102aor104ais provided symmetrically about a central axis passing in a length direction of the second electrode finger102or the second dummy electrode104, the above-described ripple appears due to shifting from the inclination angles of the respective regions H1to H3.

On the other hand, as illustrated inFIG.9, in the present preferred embodiment, for example, the projecting portion17is provided in each of the first region R1and the sixth region R6to adapt to the inclinations of the respective regions H1to H3. Accordingly, the ripple near the upper end of the stop band can be suppressed. This will be described based on a specific experimental example.

An acoustic wave device of Comparative Example 1 was configured based on the existing acoustic wave device described above, and an acoustic wave device of Example 1 was manufactured that was configured similarly to Comparative Example 1 except that the projecting portion17was provided instead of the large-width portion. Design parameters of the acoustic wave device of Example 1 were as follows.

A layer configuration of a piezoelectric substrate, materials of each layer, thicknesses of each layer: piezoelectric film/low acoustic velocity material layer/high acoustic velocity support substrate, LiTaO3/SiO2/Si, 0.350 μm/0.450 μm/250 μm.

A material of the IDT electrode7and the reflectors8and9: Al. A thickness=60 nm.

A wavelength λ determined by an electrode finger pitch of the IDT electrode7=0.7 μm.

The number of pairs of electrode fingers: a one pair model was configured to have an infinite period by a boundary condition.

An angle defined by the first virtual line A and the acoustic wave propagation direction D=5°.

A dimension of each of the first and second gaps G1and G2in a direction in which an electrode finger extends=0.28 μm.

An amount of protrusion of the projecting portion17from a first side or a second side=0.07 μm.

A dimension of the projecting portion17in the direction in which the electrode finger extends=0.2 μm.

FIG.10illustrates return loss characteristics of the acoustic wave device of each of Comparative Example 1 and Example 1. Note that, inFIG.10, a solid line shows a result of Example 1 and a broken line shows a result of Comparative Example 1.

As is clear fromFIG.10, in Comparative Example 1, a plurality of large ripples appears at positions from about 5780 MHz to about 5900 MHz higher than an anti-resonant frequency. These are the ripples near an upper end of a stop band. On the other hand, according to Example 1, such ripples can be effectively suppressed. Thus, according to Example 1, since the configuration was adopted in which the projecting portion17was provided such that a large-width portion of a tip end of each of the second electrode finger14and the second dummy electrode16was not symmetric, the ripples near the upper end of the stop band could be effectively suppressed.

Note that, as is clear from the regions H1to H3illustrated inFIG.9, instead of providing the projecting portion17, conversely, it is desirable to provide a recessed portion in the second region R2, the fifth region R5, the fourth region R4, and the seventh region R7. Thus, as in a modified example illustrated inFIG.3, it is preferable to further provide a recessed portion17A closer to the first side14aon a tip end side of the second electrode finger14, and the recessed portion17A closer to the second side16bin the second dummy electrode16as well. Note that, in the first preferred embodiment, the tip end of the electrode finger including the projecting portion17has a rectangular or substantially rectangular shape. On the other hand, as in the present modified example, a tip end of an electrode finger including the projecting portion17may have a parallelogram or substantially parallelogram shape.

However, in a preferred embodiment of the present invention, it is not necessary to provide the projecting portion17or the recessed portion17A in all of the first to eighth regions R1to R8. As described above, a projecting portion may be provided in at least one region of regions where a projecting portion is desirably provided, and a recessed portion may be provided in at least one region of regions where the recessed portion17A is desirably provided. In addition, it is sufficient that the projecting portion17or the recessed portion17A is provided in at least one region of the first to eighth regions R1to R8.

Further, the first to eighth regions R1to R8are illustrated for the side of the first gap G1, but similarly for a side of the second gap G2, it is sufficient that the first to eighth regions R1to R8are provided, and the projecting portion17or the recessed portion17A is provided. That is, as illustrated inFIG.2, the first to eighth regions R1to R8are defined based on the fourth virtual line B1connecting the centers of the second gaps G2and the third virtual line A1connecting the tip ends of the plurality of first electrode fingers13. At least one of the projecting portion17or the recessed portion17A described above is preferably provided in the first to eighth regions R1to R8. In other words, preferably, at least one of, a recessed portion provided in at least one of a side in an inclination direction at a tip end of a first electrode finger, a side opposite to the inclination direction at a tip end of a first dummy electrode, a side opposite to the inclination direction of a second electrode finger positioned on an extension opposite to the inclination direction from the tip end of the first dummy electrode, and a side in the inclination direction of the second electrode finger positioned on an extension opposite to the inclination direction from the tip end of the first electrode finger, and a projecting portion protruding toward the first electrode finger or the second electrode finger, in at least one of a side opposite to the inclination direction at the tip end of the first electrode finger, a side in the inclination direction at the tip end of the first dummy electrode, a side in the inclination direction of the second electrode finger positioned on the extension opposite to the inclination direction from the tip end of the first dummy electrode, and a side opposite to the inclination direction of the second electrode finger positioned on the extension opposite to the inclination direction from the tip end of the first electrode finger, is provided.

Note that, on the second gap G2side, in the first region R1, the third region R3, the sixth region R6, and the eighth region R8, an angle defined by the first side13aor14a,or the second side14bor15b,and the third virtual line A1is an acute angle, and in the second region R2, the fourth region R4, the fifth region R5, and the seventh region R7, an angle defined by the second side13bor14b,or the first side14aor15a,and the third virtual line A1is an obtuse angle. Thus, it is sufficient that, a projecting portion is provided in at least one of the first region R1, the third region R3, the sixth region R6, and the eighth region R8, and a recessed portion is provided in at least one region of the second region R2, the fourth region R4, the fifth region R5, and the seventh region R7.

Furthermore, preferably, as in the modified example illustrated inFIG.3, in the second region R2and the third region R3facing each other in an acoustic wave propagation direction, when the recessed portion17A is provided in the second region R2, the projecting portion17is preferably provided in the third region R3. As a result, a distance between the second dummy electrode16and the first electrode finger13along the acoustic wave propagation direction can be increased. Thus, surge resistance can be enhanced. Thus, a recessed portion and a projecting portion are preferably provided in at least one of a portion where the second region R2and the third region R3face each other and a portion where the sixth region R6and the seventh region R7face each other. To be more specific, the IDT electrode preferably has at least one of a configuration in which a recessed portion is provided in the second region R2and a projecting portion is provided in the third region R3, and a configuration in which a projecting portion is provided in the sixth region R6and a recessed portion is provided in the seventh region R7.

FIG.11is a front sectional view for describing an acoustic wave device according to a second preferred embodiment of the present invention. In an acoustic wave device31, a high acoustic velocity material layer4aalso defines and functions as a support substrate. That is, the high acoustic velocity material layer4ais a high acoustic velocity support substrate made of a high acoustic velocity material. In this case, the support substrate3illustrated inFIG.4can be omitted. Such a piezoelectric substrate2amay be used.

Furthermore, the low acoustic velocity material layer5may be omitted inFIG.4andFIG.11.

Further,FIG.12is a front sectional view for describing an acoustic wave device according to a third preferred embodiment of the present invention. In an acoustic wave device41, the piezoelectric substrate2is a single-plate piezoelectric substrate made of a piezoelectric single crystal such as LiNbO3. In a preferred embodiment of the present invention, the piezoelectric substrate2may be a single-plate piezoelectric substrate.