Patent Publication Number: US-2020304092-A1

Title: Acoustic wave device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority to Japanese Patent Application No. 2017-242526 filed on Dec. 19, 2017 and is a Continuation Application of PCT Application No. PCT/JP2018/039061 filed on Oct. 19, 2018. The entire contents of each application are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to an acoustic wave device and, more specifically, to an acoustic wave device including an interdigital transducer electrode. 
     2. Description of the Related Art 
     As an acoustic wave device, there is known an acoustic wave device that includes a piezoelectric substrate (piezoelectric body portion) and an interdigital transducer electrode provided on or above the piezoelectric substrate and in which wide portions are provided in part of electrode fingers of the interdigital transducer electrode (see, for example, International Publication No. 2014/192756). In an example of the acoustic wave device described in International Publication No. 2014/192756, a reflector is formed on each side of the interdigital transducer electrode in a propagation direction of surface acoustic waves on the piezoelectric substrate. The interdigital transducer electrode and the reflectors include a metal material. The acoustic wave device described in International Publication No. 2014/192756 has such characteristics that the acoustic wave device has a structure of suppressing a transverse-mode ripple by forming a piston mode in the interdigital transducer electrode. 
     In the acoustic wave device described in International Publication No. 2014/192756, the interdigital transducer electrode includes a first busbar, a second busbar disposed apart from the first busbar, a plurality of first electrode fingers of which proximal ends are electrically connected to the first busbar and distal ends are have a greater width toward the second busbar, and a plurality of second electrode fingers of which proximal ends are connected to the second busbar and distal ends are have a greater width toward the first busbar. In the above-described acoustic wave device, wide portions are provided in both of the first electrode fingers and the second electrode fingers. 
     The first busbar includes a plurality of opening portions separately disposed along a length direction of the first busbar. The first busbar includes an inner busbar portion located closer to the first electrode fingers than the plurality of opening portions and having a greater width in the length direction of the first busbar, a center busbar portion in which the plurality of opening portions is provided, and an outer busbar portion located across the center busbar portion from the inner busbar portion. 
     The second busbar includes a plurality of opening portions separately disposed along a length direction of the second busbar. The second busbar includes an inner busbar portion located closer to the second electrode fingers than the plurality of opening portions and having a greater width in the length direction of the second busbar, a center busbar portion in which the plurality of opening portions is provided, and an outer busbar portion located across the center busbar portion from the inner busbar portion. 
     In the acoustic wave device in which the wide portions are provided in a portion of the electrode fingers of the interdigital transducer electrode, for example, the outer busbar portions are located adjacent to metal material portions such as reflectors different in potential in end regions of the interdigital transducer electrode in the length directions of the first busbar and second busbar, so a surge breakdown sometimes occurs in the outer busbar portions because of electrostatic discharge (ESD). 
     SUMMARY OF THE INVENTION 
     Preferred embodiments of the present invention provide acoustic wave devices that are each able to significantly improve ESD tolerance while significantly reducing or preventing interference with a piston mode. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, an interdigital transducer electrode, and a reflector. The second terminal has a lower potential than the first terminal. The interdigital transducer electrode is provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. The reflector is provided on or above the piezoelectric body portion and electrically connected to the second terminal. The interdigital transducer electrode includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The first busbar is electrically connected to the first terminal. The second busbar is opposed to the first busbar in a first direction and electrically connected to the second terminal. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. In the interdigital transducer electrode, where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger located at one end in the second direction is a first end electrode finger and the electrode finger located at another end is a second end electrode finger, the first end electrode finger is located between the reflector and the second end electrode finger in the second direction. The outer busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, is located on an inner side in the second direction relative to a center portion, in the first direction, of the first end electrode finger. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, a plurality of interdigital transducer electrodes, and two reflectors. The second terminal has a lower potential than the first terminal. The plurality of interdigital transducer electrodes are provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. The two reflectors are provided on or above the piezoelectric body portion and reflect acoustic waves excited by the plurality of interdigital transducer electrodes. Each of the plurality of interdigital transducer electrodes includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The second busbar is opposed to the first busbar in a first direction. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. The plurality of interdigital transducer electrodes are provided in the second direction. The two reflectors each are located across the interdigital transducer electrode at any one of both sides of the plurality of interdigital transducer electrodes provided in the second direction from the interdigital transducer electrode adjacent to the interdigital transducer electrode at the any one of both sides. In the interdigital transducer electrode adjacent to one of the two reflectors, of the plurality of interdigital transducer electrodes, where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger located at one end in the second direction is a first end electrode finger and the electrode finger located at another end is a second end electrode finger, the first end electrode finger is located between the one of the two reflectors and the second end electrode finger in the second direction. In the interdigital transducer electrode adjacent to the one of the two reflectors, the outer busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, is located on an inner side in the second direction relative to a center portion, in the first direction, of the first end electrode finger. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, an interdigital transducer electrode, and a reflector. The second terminal has a lower potential than the first terminal. The interdigital transducer electrode is provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. The reflector is provided on or above the piezoelectric body portion and electrically connected to the second terminal. The interdigital transducer electrode includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The first busbar is electrically connected to the first terminal. The second busbar is opposed to the first busbar in a first direction and electrically connected to the second terminal. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. In the interdigital transducer electrode, where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger located at one end in the second direction is a first end electrode finger and the electrode finger located at another end is a second end electrode finger, the first end electrode finger is located between the reflector and the second end electrode finger in the second direction. The outer busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, is located on an inner side in the second direction relative to the inner busbar portion of the busbar not connected to the first end electrode finger. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, a plurality of interdigital transducer electrodes, and two reflectors. The second terminal has a lower potential than the first terminal. The plurality of interdigital transducer electrodes are provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. The two reflectors are provided on or above the piezoelectric body portion and reflect acoustic waves excited by the plurality of interdigital transducer electrodes. Each of the plurality of interdigital transducer electrodes includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The second busbar is opposed to the first busbar in a first direction. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. The plurality of interdigital transducer electrodes are provided in the second direction. The two reflectors each are located across the interdigital transducer electrode at any one of both sides of the plurality of interdigital transducer electrodes provided in the second direction from the interdigital transducer electrode adjacent to the interdigital transducer electrode at the any one of both sides. In the interdigital transducer electrode adjacent to one of the two reflectors, of the plurality of interdigital transducer electrodes, where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger located at one end in the second direction is a first end electrode finger and the electrode finger located at another end is a second end electrode finger, the first end electrode finger is located between the one of the two reflectors and the second end electrode finger in the second direction. In the interdigital transducer electrode adjacent to the one of the two reflectors, the outer busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, is located on an inner side in the second direction relative to the inner busbar portion of the busbar not connected to the first end electrode finger. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, and a plurality of interdigital transducer electrodes. The second terminal has a lower potential than the first terminal. The plurality of interdigital transducer electrodes is provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. Each of the plurality of interdigital transducer electrodes includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The second busbar is opposed to the first busbar in a first direction. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. Where, of the plurality of interdigital transducer electrodes, one of the two interdigital transducer electrodes adjacent to each other in the second direction is a first interdigital transducer electrode and another one of the two interdigital transducer electrodes is a second interdigital transducer electrode, a distance between the outer busbar portion not connected to, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger closest to the second interdigital transducer electrode in the first interdigital transducer electrode and the outer busbar portion not connected to, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger closest to the first interdigital transducer electrode in the second interdigital transducer electrode is greater than a distance between a center portion of the electrode finger closest to the second interdigital transducer electrode in the first interdigital transducer electrode and a center portion of the electrode finger closest to the first interdigital transducer electrode in the second interdigital transducer electrode. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, and a plurality of interdigital transducer electrodes. The second terminal has a lower potential than the first terminal. The plurality of interdigital transducer electrodes are provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. Each of the plurality of interdigital transducer electrodes includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The second busbar is opposed to the first busbar in a first direction. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. Where, of the plurality of interdigital transducer electrodes, one of the two interdigital transducer electrodes adjacent to each other in the second direction is a first interdigital transducer electrode and another one of the two interdigital transducer electrodes is a second interdigital transducer electrode, and where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers of the first interdigital transducer electrode, the electrode finger located at an end closer to the second interdigital transducer electrode in the second direction is a first end electrode finger of the first interdigital transducer electrode and the electrode finger located at an end away from the second interdigital transducer electrode is a second end electrode finger of the first interdigital transducer electrode, and, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers of the second interdigital transducer electrode, the electrode finger located at an end closer to the first interdigital transducer electrode in the second direction is a first end electrode finger of the second interdigital transducer electrode and the electrode finger located at an end away from the first interdigital transducer electrode is a second end electrode finger of the second interdigital transducer electrode, the first end electrode finger of the first interdigital transducer electrode is connected to the first terminal, and the first end electrode finger of the second interdigital transducer electrode is connected to the second terminal. In each of the first interdigital transducer electrode and the second interdigital transducer electrode, the outer busbar portion electrically connected to one of the first terminal and the second terminal, different from the terminal to which the first end electrode finger is connected, is located on an inner side in the second direction relative to the inner busbar portion electrically connected to the one of the first terminal and the second terminal, different from the terminal to which the first end electrode finger is connected. 
     An acoustic wave device according to a preferred embodiment of the present invention includes a first terminal, a second terminal, a piezoelectric body portion, and a plurality of interdigital transducer electrodes. The second terminal has a lower potential than the first terminal. The plurality of interdigital transducer electrodes are provided on or above the piezoelectric body portion and electrically connected to the first terminal and the second terminal. Each of the plurality of interdigital transducer electrodes includes a first busbar, a second busbar, a plurality of first electrode fingers, and a plurality of second electrode fingers. The second busbar is opposed to the first busbar in a first direction. The plurality of first electrode fingers are connected to the first busbar and have a greater width from the first busbar toward the second busbar in the first direction. The plurality of second electrode fingers are connected to the second busbar and have a greater width from the second busbar toward the first busbar in the first direction. The plurality of first electrode fingers and the plurality of second electrode fingers are spaced apart from each other in a second direction perpendicular or substantially perpendicular to the first direction. At least one electrode finger of the plurality of first electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger, and at least one electrode finger of the plurality of second electrode fingers includes a wide portion having a greater width in the second direction than a center portion, in the first direction, of the at least one electrode finger. Each of the first busbar and the second busbar includes an opening portion, an inner busbar portion, an outer busbar portion, and a coupling portion. The inner busbar portion is located closer to the plurality of first electrode fingers and the plurality of second electrode fingers than the opening portion in the first direction. The outer busbar portion is located across the opening portion from the inner busbar portion in the first direction. The coupling portion couples the inner busbar portion and the outer busbar portion in the first direction. In at least one interdigital transducer electrode of the plurality of interdigital transducer electrodes, where, of a group of electrode fingers including the plurality of first electrode fingers and the plurality of second electrode fingers, the electrode finger located at one end in the second direction is a first end electrode finger and the electrode finger located at another end is a second end electrode finger, the first end electrode finger is located closer to the interdigital transducer electrode adjacent to the at least one interdigital transducer electrode in the second direction. In the at least one interdigital transducer electrode, the outer busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, is located on an inner side in the second direction relative to the inner busbar portion of one of the first busbar and the second busbar, not connected to the first end electrode finger, at least at a side closer to the adjacent interdigital transducer electrode. 
     Acoustic wave devices according to preferred embodiments of the present invention are each able to significantly improve ESD tolerance while significantly reducing or preventing interference with a piston mode. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a plan view of an acoustic wave device according to a first preferred embodiment of the present invention. 
         FIG. 2A  is a plan view of a portion of the acoustic wave device according to the first preferred embodiment of the present invention.  FIG. 2B  relates to the above acoustic wave device and is a cross-sectional view taken along the line A-A in  FIG. 2A . 
         FIG. 3  is an enlarged view of a main portion of the above acoustic wave device. 
         FIG. 4  is a view showing a velocity distribution, in a first direction, of an acoustic velocity of acoustic waves that propagate in an acoustic wave propagation direction (second direction) in the above acoustic wave device. 
         FIG. 5  is a view showing an electric charge distribution in the above acoustic wave device. 
         FIG. 6  is an enlarged view of a main portion of an acoustic wave device according to a first modification of the first preferred embodiment of the present invention. 
         FIG. 7  is a plan view of an acoustic wave device according to a second preferred embodiment of the present invention. 
         FIG. 8  is a plan view of a portion of the acoustic wave device according to the second preferred embodiment of the present invention. 
         FIG. 9  relates to the above acoustic wave device and is a cross-sectional view taken along the line A-A in  FIG. 8 . 
         FIG. 10  is an enlarged view of a main portion of the above acoustic wave device. 
         FIG. 11  is a view showing an electric charge distribution in the above acoustic wave device. 
         FIG. 12  is an enlarged view of a main portion of an acoustic wave device according to a first modification of the second preferred embodiment of the present invention. 
         FIG. 13  is a plan view of a portion of an acoustic wave device according to a second modification of the second preferred embodiment of the present invention. 
         FIG. 14  is an enlarged view of a main portion of the above acoustic wave device. 
         FIG. 15  is an enlarged view of a main portion of an acoustic wave device according to a third modification of the second preferred embodiment of the present invention. 
         FIG. 16  is a cross-sectional view of an acoustic wave device according to a fourth modification of the second preferred embodiment of the present invention. 
         FIG. 17  is a cross-sectional view of an acoustic wave device according to a fifth modification of the second preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, acoustic wave devices according to preferred embodiments will be described with reference to the drawings. 
       FIG. 1  to  FIG. 17  that will be used in the following preferred embodiments, and the like, all are representative diagrams, and the ratios of the sizes and thicknesses of components in the drawings do not always reflect actual scale ratios. 
     First Preferred Embodiment 
     (1.1) Overall Configuration of Acoustic Wave Device 
     Hereinafter, an acoustic wave device  1  according to a first preferred embodiment of the present invention will be described with reference to the drawings. 
     As shown in  FIG. 1 ,  FIG. 2A ,  FIG. 2B ,  FIG. 3 , and  FIG. 4 , the acoustic wave device  1  according to the first preferred embodiment includes a first terminal (for example, a signal terminal)  11 , second terminals (for example, ground terminals)  12 , a piezoelectric body portion  24 , an interdigital transducer (IDT) electrode  3 , and reflectors  8 . Each second terminal  12  has a lower potential than the first terminal  11 . Therefore, the first terminal  11  has a higher potential than each second terminal  12 . The first terminal  11  and the second terminals  12  are provided on or above the piezoelectric body portion  24 . Here, the state “provided on or above the piezoelectric body portion  24 ” includes the case of being directly provided on the piezoelectric body portion  24  and the case of being indirectly provided on the piezoelectric body portion  24 . The acoustic wave device  1  includes the plurality of (for example, three) second terminals  12 . However, the acoustic wave device  1  only needs to include at least one second terminal  12 . The piezoelectric body portion  24  I made of a piezoelectric material. The interdigital transducer electrode  3  and the reflectors  8  are provided on or above the piezoelectric body portion  24 . Here, the state “provided on or above the piezoelectric body portion  24 ” includes the case of being directly provided on the piezoelectric body portion  24  and the case of being indirectly provided on the piezoelectric body portion  24 . The acoustic wave device  1  according to the first preferred embodiment is a single-port surface acoustic wave resonator. The acoustic wave device  1  includes the two reflectors  8 . 
     The acoustic wave device  1  according to the first preferred embodiment further includes a first wiring layer  13  electrically connecting the interdigital transducer electrode  3  and the first terminal  11  and a second wiring layer  14  electrically connecting the interdigital transducer electrode  3  and the second terminals  12 . In  FIG. 1 , for the sake of convenience of description, the label “H” is assigned to the first terminal  11  and portions (high potential portions) electrically connected to the first terminal  11  in the interdigital transducer electrode  3 , and the label “E” is assigned to the second terminals  12  and portions (low potential portions) electrically connected to the second terminals  12  in the interdigital transducer electrode  3 . The high potential portions are different in potential from the low potential portions. The high potential portions are portions higher in potential than the low potential portions. The labels “H”, “E” are not signs and are not actually present. In  FIG. 1  and  FIG. 2A , dot hatching is applied to the interdigital transducer electrode  3  and the reflectors  8 . These hatchings do not represent cross sections and are provided to clearly show the relationship among the interdigital transducer electrode  3 , the reflectors  8 , and the piezoelectric body portion  24 . In  FIG. 1 , dot hatching is applied to the first terminal  11 , the second terminals  12 , the first wiring layer  13 , and the second wiring layer  14 . These hatchings do not represent cross sections and are provided to clearly show the relationship among the first terminal  11 , the second terminals  12 , the first wiring layer  13  and the second wiring layer  14 , and the piezoelectric body portion  24 . 
     In the acoustic wave device  1  according to the first preferred embodiment, the piezoelectric body portion  24  is a piezoelectric film, and the above-described interdigital transducer electrode  3  is provided on or above a multilayer board including the piezoelectric body portion  24 . The multilayer board  2  is a piezoelectric substrate at least partially having piezoelectricity. 
     (1.2) Components of Acoustic Wave Device 
     Next, the components of the acoustic wave device  1  will be described with reference to the drawings. 
     (1.2.1) Multilayer Board 
     As shown in  FIG. 2B , the multilayer board  2  includes a high acoustic velocity support substrate  21 , a low acoustic velocity film  23  directly laminated on the high acoustic velocity support substrate  21  and through which bulk waves propagate at a lower acoustic velocity than acoustic waves that propagate through the piezoelectric body portion  24 , and the piezoelectric body portion  24  directly laminated on the low acoustic velocity film  23 . In the high acoustic velocity support substrate  21 , bulk waves propagate at a higher acoustic velocity than acoustic waves that propagate through the piezoelectric body portion  24 . The low acoustic velocity film  23  is provided on or above the high acoustic velocity support substrate  21 . Here, the state “provided on or above the low acoustic velocity film  23 ” includes the case of being directly provided on the low acoustic velocity film  23  and the case of being indirectly provided on the low acoustic velocity film  23 . The piezoelectric body portion  24  is indirectly laminated on the high acoustic velocity support substrate  21 . Accordingly, since the low acoustic velocity film  23  is located between the high acoustic velocity support substrate  21  and the piezoelectric body portion  24  in the acoustic wave device  1 , the acoustic velocity of acoustic waves decreases. The energy of acoustic waves substantially concentrates in a low acoustic velocity medium. Therefore, with the acoustic wave device  1 , the effect of enclosing acoustic wave energy into the piezoelectric body portion  24  and the interdigital transducer electrode  3  in which acoustic waves are excited is significantly improved. Therefore, with the acoustic wave device  1 , a loss is reduced, and the quality factor is increased, in comparison with the case where no low acoustic velocity film  23  is provided. 
     The piezoelectric body portion  24   i  is preferably made of, for example, lithium tantalate (LiTaO 3 ), lithium niobate (LiNbO 3 ), zinc oxide (ZnO), aluminum nitride (AlN), or lead zirconate titanate (PZT). 
     The high acoustic velocity support substrate  21  supports a multilayer body including the low acoustic velocity film  23  and the piezoelectric body portion  24 . Here, the high acoustic velocity support substrate  21  includes a first main surface  211  and a second main surface  212  that are on opposite sides in the thickness direction. The first main surface  211  and the second main surface  212  are provided back to back to each other. The plan-view shape of the high acoustic velocity support substrate  21  (the outer peripheral shape of the high acoustic velocity support substrate  21  when viewed in the thickness direction) is a square or substantially square shape, for example. However, the shape is not limited to a square or substantially square shape and may be, for example, a rectangular or substantially rectangular shape. The thickness of the high acoustic velocity support substrate  21  is preferably, for example, about 120 μm. The material of the high acoustic velocity support substrate  21  is preferably, for example, silicon. The high acoustic velocity support substrate  21  is not limited to silicon and may include any one of piezoelectric bodies, for example, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, sapphire, lithium tantalate, lithium niobate, and quartz crystal, various ceramics, for example, alumina, zirconia, cordierite, mullite, steatite, and forsterite, magnesia diamond, a material including any one of the above materials as a main ingredient, and a material including a mixture of some of the above materials as a main ingredient. 
     The low acoustic velocity film  23  is preferably made of, for example, any one of silicon oxide, glass, silicon oxynitride, tantalum oxide, a chemical compound provided by adding fluorine, carbon, or boron to silicon oxide, and a material including any one of the above materials as a main ingredient. 
     When the low acoustic velocity film  23  is silicon oxide, temperature characteristics are significantly improved. The elastic constant of lithium tantalate has negative temperature characteristics, and the elastic constant of silicon oxide has positive temperature characteristics. Therefore, with the acoustic wave device  1 , the absolute value of temperature coefficient of frequency (TCF) is reduced. In addition, the specific acoustic impedance of silicon oxide is less than the specific acoustic impedance of lithium tantalate. Therefore, with the acoustic wave device  1 , both an increase in electromechanical coupling coefficient, that is, an expansion of fractional band width and a significant improvement in temperature coefficient of frequency are provided. 
     The thickness of the piezoelectric body portion  24  is preferably less than or equal to about 3.5λ, for example, when the wave length of acoustic waves, which is determined by the electrode finger pitch of the interdigital transducer electrode  3 , is λ. This is because the quality factor increases. In the acoustic wave device  1 , when the thickness of the piezoelectric body portion  24  is less than or equal to about 2.5λ, for example, the temperature coefficient of frequency significantly improves. In addition, in the acoustic wave device  1 , when the thickness of the piezoelectric body portion  24  is less than or equal to about 1.5λ substantially, adjustment of acoustic velocity becomes easy. The thickness of the piezoelectric body portion  24  is preferably, for example, about 600 nm. 
     The thickness of the low acoustic velocity film  23  is preferably less than or equal to about 2.0λ, for example, when the wave length of acoustic waves, which is determined by the electrode finger pitch of the interdigital transducer electrode  3 , is λ. In the acoustic wave device  1 , when the thickness of the low acoustic velocity film  23  is less than or equal to about 2.0λ, for example, membrane stress is reduced. As a result, warpage of wafer that is the source of the high acoustic velocity support substrate  21  during manufacturing is reduced, and an efficacy percentage is able to be significantly increased and characteristics are able to be stabilized. The thickness of the low acoustic velocity film  23  is, for example, about 600 nm. 
     (1.2.2) Reflector 
     The two reflectors  8  are provided on or above one main surface  241  of the piezoelectric body portion  24 . Here, the two reflectors  8  are provided one by one on both sides of the interdigital transducer electrode  3  in the second direction D 2 . 
     Each of the two reflectors  8  reflects acoustic waves. Each of the two reflectors  8  is a grating-type reflector. Each of the two reflectors  8  include a plurality of electrode fingers  9 . One ends of the plurality of electrode fingers  9  in the first direction D 1  are short-circuited, and the other ends are also short-circuited. In  FIG. 1 ,  FIG. 2A ,  FIG. 2B , and the like, each of the two reflectors  8  is drawn with the number of the electrode fingers  9  reduced to facilitate visualization. The reflectors  8  each may be made of an appropriate metal material, for example, aluminum (Al), copper (Cu), platinum (Pt), gold (Au), silver (Ag), titanium (Ti), nickel (Ni), chromium (Cr), molybdenum (Mo), tungsten (W), and an alloy including any one of these metals as a main ingredient. Alternatively, the reflectors  8  each may include a structure in which a plurality of metal films including any one of these metals or alloys is laminated. The thickness of each reflector  8  is preferably, for example, about 150 nm. 
     (1.2.3) Interdigital Transducer Electrode 
     The interdigital transducer electrode  3  may include an appropriate metal material, for example, aluminum, copper, platinum, gold, silver, titanium, nickel, chromium, molybdenum, tungsten, and an alloy including any one of these metals as a main ingredient. Alternatively, the interdigital transducer electrode  3  may include a structure in which a plurality of metal films including any one of these metals or alloys is laminated. The thickness of the interdigital transducer electrode  3  is preferably, for example, about 150 nm. 
     As shown in  FIG. 1  and  FIG. 2A , the interdigital transducer electrode  3  includes a first busbar  4 , a second busbar  5 , a plurality of first electrode fingers  6 , and a plurality of second electrode fingers  7 . 
     In the interdigital transducer electrode  3 , the first busbar  4  and the second busbar  5  are opposed to each other in a first direction D 1  perpendicular or substantially perpendicular to the thickness direction (up-down direction in  FIG. 2B ) of the piezoelectric body portion  24 . In other words, the second busbar  5  is opposed to the first busbar  4  in the first direction D 1 . 
     The first busbar  4  and the second busbar  5  each have a long shape having a second direction D 2  perpendicular or substantially perpendicular to the first direction D 1  as a longitudinal direction. In  FIG. 1 ,  FIG. 2A ,  FIG. 4 , and the like, the first busbar  4  and the second busbar  5  do not look like a long shape. This is because each of the number of the first electrode fingers  6  and the number of the second electrode fingers  7  is reduced to facilitate visualization. The second direction D 2  is a direction along a propagation direction of acoustic waves. The second direction D 2  is also perpendicular or substantially perpendicular to the thickness direction of the piezoelectric body portion  24 . 
     The plurality of first electrode fingers  6  are connected to the first busbar  4  and have a greater width from the first busbar  4  toward the second busbar  5  in the first direction D 1 . Here, the plurality of first electrode fingers  6  have greater widths from the first busbar  4  along a direction perpendicular or substantially perpendicular to the longitudinal direction of the first busbar  4 . In other words, the plurality of first electrode fingers  6  have greater widths along a direction perpendicular or substantially perpendicular to the propagation direction of acoustic waves. In the interdigital transducer electrode  3 , the plurality of first electrode fingers  6  is spaced apart from the second busbar  5 , and a gap  31  is provided between the first electrode fingers  6  and the second busbar  5  that are opposed to each other in the first direction D 1 . When the wave length of the above-described acoustic waves is λ, the length of the gap  31  in the first direction D 1  is preferably, for example, less than or equal to about 0.5λ. 
     In the example of  FIG. 1  and  FIG. 2A , the plurality of first electrode fingers  6  each have the same or substantially the same length. A distal end portion  61  of each of the plurality of first electrode fingers  6  includes a wide portion  62  having a greater width in the second direction D 2  than a center portion  60 , in the first direction D 1 , of the first electrode finger  6 . Each of the plurality of first electrode fingers  6  includes a wide portion  64  (see  FIG. 2A ) in addition to the wide portion  62 . The wide portion  64  is located between the center portion  60  and a proximal end portion  63  (see  FIG. 2A ), opposite from the distal end portion  61 , of the first electrode finger  6 . The wide portion  64  has a greater width in the second direction D 2  than the center portion  60 , in the first direction D 1 , of the first electrode finger  6 . The wide portion  64  is located away from the first busbar  4  in the first direction D 1 . In each of the plurality of first electrode fingers  6 , a portion between the wide portion  62  and the wide portion  64  in the first direction D 1  is the center portion  60 . In each of the plurality of first electrode fingers  6 , the center portion  60  is longer in the first direction D 1  than each of the wide portions  62 ,  64 . 
     In the example of  FIG. 1  and  FIG. 2A , the center portion  60  of each of the plurality of first electrode fingers  6  has the same or substantially the same width. The wide portion  62  at the distal end portion  61  of each of the plurality of first electrode fingers  6  has the same or substantially the same width. The wide portion  64 , closer to the proximal end portion  63 , of each of the plurality of first electrode fingers  6  has the same or substantially the same width. The width of the wide portion  62  at the distal end portion  61  and the width of the wide portion  64  closer to the proximal end portion  63  are the same or substantially the same in each of the plurality of first electrode fingers  6 . Each of the plurality of first electrode fingers  6  has a line-symmetric shape with respect to a center line  6 X (see  FIG. 3 ) along the first direction D 1 . The shape of each of the wide portions  62 ,  64  is a rectangular or substantially rectangular shape, for example. However, the shape is not limited thereto and may be, for example, a hexagonal or substantially hexagonal shape, a circular or substantially circular shape, or the like. 
     The plurality of second electrode fingers  7  are connected to the second busbar  5  and have a greater width from the second busbar  5  toward the first busbar  4  in the first direction D 1 . Here, the plurality of second electrode fingers  7  have greater widths from the second busbar  5  along a direction perpendicular or substantially perpendicular to the longitudinal direction of the second busbar  5 . In other words, the plurality of second electrode fingers  7  have greater widths along a direction perpendicular or substantially perpendicular to the propagation direction of acoustic waves. In the interdigital transducer electrode  3 , the plurality of second electrode fingers  7  are spaced apart from the first busbar  4 , and a gap  32  is provided between the second electrode fingers  7  and the first busbar  4  that are opposed to each other in the first direction D 1 . When the wave length of the above-described acoustic waves is λ, the length of the gap  32  in the first direction D 1  is preferably, for example, less than or substantially equal to about 0.5λ. 
     In the example of  FIG. 1  and  FIG. 2A , the plurality of second electrode fingers  7  each have the same or substantially the same length. A distal end portion  71  of each of the plurality of second electrode fingers  7  includes a wide portion  72  having a greater width in the second direction D 2  than a center portion  70 , in the first direction D 1 , of the second electrode finger  7 . Each of the plurality of second electrode fingers  7  includes a wide portion  74  (see  FIG. 2A ) in addition to the wide portion  72 . The wide portion  74  is located between the center portion  70  and a proximal end portion  73  (see  FIG. 2A ), opposite from the distal end portion  71 , of the second electrode finger  7 . The wide portion  74  has a greater width in the second direction D 2  than the center portion  70 , in the first direction D 1 , of the second electrode finger  7 . The wide portion  74  is located away from the second busbar  5  in the first direction D 1 . In each of the plurality of second electrode fingers  7 , a portion between the wide portion  72  and the wide portion  74  in the first direction D 1  is the center portion  70 . In each of the plurality of second electrode fingers  7 , the center portion  70  is longer than each of the wide portions  72 ,  74  in the first direction D 1 . 
     In the example of  FIG. 1  and  FIG. 2A , the center portion  70  of each of the plurality of second electrode fingers  7  has the same or substantially the same width. The wide portion  72  at the distal end portion  71  of each of the plurality of second electrode fingers  7  has the same or substantially the same width. The wide portion  74 , closer to the proximal end portion  73 , of each of the plurality of second electrode fingers  7  has the same or substantially the same width. The width of the wide portion  72  at the distal end portion  71  and the width of the wide portion  74  closer to the proximal end portion  73  are the same or substantially the same in each of the plurality of second electrode fingers  7 . Each of the plurality of second electrode fingers  7  has a line-symmetric shape with respect to a center line  7 X (see  FIG. 3 ) along the first direction D 1 . The shape of each of the wide portions  72 ,  74  is a rectangular or substantially rectangular shape; however, the shape is not limited thereto and may be, for example, a hexagonal or substantially hexagonal shape, a circular or substantially circular shape, or the like. 
     In the interdigital transducer electrode  3 , the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1 . Therefore, the first electrode finger  6  and the second electrode finger  7  adjacent to each other in the second direction D 2  are spaced apart from each other. 
     In the interdigital transducer electrode  3 , the wide portions  62  of the distal end portions  61  of the plurality of first electrode fingers  6  and the wide portions  74 , closer to the proximal end portions  73 , of the second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2 . In addition, in the interdigital transducer electrode  3 , the wide portions  64 , closer to the proximal end portions  63 , of the plurality of first electrode fingers  6  and the wide portions  72  of the distal end portions  71  of the second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2 . The electrode finger pitch of the interdigital transducer electrode  3  is about twice the distance between sides respectively corresponding to the center portion  60  of the first electrode finger  6  and the center portion  70  of the second electrode finger  7 , adjacent to each other. The electrode finger pitch of the interdigital transducer electrode  3  is the same or substantially the same value when defined by the distance between the center lines  6 X (see  FIG. 3 ) of the adjacent two first electrode fingers  6  in the second direction D 2  of the plurality of first electrode fingers  6 . In addition, the electrode finger pitch of the interdigital transducer electrode  3  is the same or substantially the same value when defined by the distance between the center lines  7 X (see  FIG. 3 ) of the adjacent two second electrode fingers  7  in the second direction D 2  of the plurality of second electrode fingers  7 . A group of electrode fingers includes the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1  and may also include the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  not provided alternately and spaced apart from each other. For example, a region in which the first electrode finger  6  and the second electrode finger  7  are provided one by one and spaced apart from each other and a region in which the two first electrode fingers  6  or the two second electrode fingers  7  are provided in the second direction D 2  may be mixed. 
     The first busbar  4  includes opening portions  40 , an inner busbar portion  42 , an outer busbar portion  41 , and coupling portions  43 . The inner busbar portion  42  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions  40  in the first direction D 1 . The outer busbar portion  41  is located across the opening portions  40  from the inner busbar portion  42  in the first direction D 1 . In other words, the outer busbar portion  41  is located away in the first direction D 1  from a side where the plurality of first electrode fingers  6  is present. The coupling portions  43  couple the inner busbar portion  42  and the outer busbar portion  41  in the first direction D 1 . The coupling portions  43  are located on both sides of each opening portion  40  in the second direction D 2 . In the example of  FIG. 1 , each coupling portion  43  has the same or substantially the same width as the center portion of the first electrode finger  6  and is located along an extension from the first electrode finger  6 . However, the dimensions of each coupling portion  43  and the locations of the coupling portions  43  are not limited thereto. 
     The opening shape of each opening portion  40  is rectangular or substantially rectangular, for example. However, the opening shape is not limited thereto. When the wave length of the above-described acoustic waves is λ, the width of the inner busbar portion  42  in the first direction D 1  is preferably, for example, less than or substantially equal to about 0.5λ. The length of each coupling portion  43  in the first direction D 1  is preferably, for example, about 2.0λ. 
     The first busbar  4  includes the plurality of opening portions  40 . However, to facilitate visualization, the number of the first electrode fingers  6  is reduced in  FIG. 1  and  FIG. 2A , such that only one opening portion  40  is shown in  FIG. 1  and  FIG. 2A . The plurality of opening portions  40  are, for example, located at equal or substantially equal intervals in the second direction D 2 . In the example of  FIG. 1  and  FIG. 2A , the opening width of each opening portion  40  in the second direction D 2  is, for example, the same or substantially the same as the distance between the center portions  60  of the adjacent two first electrode fingers  6  in the second direction D 2 . Although only one opening portion  40  is shown in  FIG. 1  and  FIG. 2A  as described above, the distance between the two adjacent opening portions  40  in the second direction D 2  is, for example, the same or substantially the same as the width of the center portion  60  of the first electrode finger  6  in the second direction D 2 . 
     The second busbar  5  includes opening portions  50 , an inner busbar portion  52 , an outer busbar portion  51 , and coupling portions  53 . The inner busbar portion  52  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions  50  in the first direction D 1 . The outer busbar portion  51  is located across the opening portions  50  from the inner busbar portion  52  in the first direction D 1 . In other words, the outer busbar portion  51  is located away in the first direction D 1  from a side where the plurality of second electrode fingers  7  is present. The coupling portions  53  couple the inner busbar portion  52  and the outer busbar portion  51  in the first direction D 1 . The coupling portions  53  are located on both sides of each opening portion  50  in the second direction D 2 . In the example of  FIG. 1  and  FIG. 2A , each coupling portion  53  has the same or substantially the same width as the center portion  70  of the second electrode finger  7  and is located along an extension from the second electrode finger  7 . However, the dimensions of each coupling portion  53  and the locations of the coupling portions  53  are not limited thereto. 
     The opening shape of each opening portion  50  is rectangular or substantially rectangular, for example. However, the opening shape is not limited thereto. When the wave length of the above-described acoustic waves is λ, the width of the inner busbar portion  52  in the first direction D 1  is preferably, for example, less than or equal to about 0.5λ. The length of each coupling portion  53  in the first direction D 1  is preferably, for example, about 2.0λ. 
     The acoustic wave device  1  according to the first preferred embodiment includes a structure that significantly reduces or prevents a transverse-mode ripple by providing a piston mode in the interdigital transducer electrode  3 . This point will be described with reference to  FIG. 4 . 
     As shown at the left side of  FIG. 4 , the acoustic wave device  1  includes  11  regions A 1  to A 11  in the first direction D 1  in plan view taken in the thickness direction of the acoustic wave device  1 . The  11  regions A 1  to A 11  respectively include different portions in each of the piezoelectric body portion  24  and the interdigital transducer electrode  3 .  FIG. 4  shows the velocity (acoustic velocity) of acoustic waves that propagate through the  11  regions A 1  to A 11  at the right side. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the region A 6  located in the center in the first direction D 1  is a center region. The center region includes the center portions  60  of the plurality of first electrode fingers  6  and the center portions  70  of the plurality of second electrode fingers  7 . In short, the center region is a region in which the center portions  60  of the plurality of first electrode fingers  6  and the center portions  70  of the plurality of second electrode fingers  7  overlap in the second direction D 2 . In the center region, a value (duty ratio) determined by dividing the electrode finger width (the width of each of the center portion  60  of the first electrode finger  6  and the center portion  70  of the second electrode finger) by a value half the above-described electrode finger pitch is preferably, for example, about 0.5. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the regions A 1 , A 11  respectively located at both ends in the first direction D 1  are outer busbar regions. The region A 1  includes the outer busbar portion  41  of the first busbar  4 . The region A 11  includes the outer busbar portion  51  of the second busbar  5 . The acoustic velocity of acoustic waves in the outer busbar regions is lower than the acoustic velocity in the center region. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the regions A 2 , A 10  respectively located at the second from both ends in the first direction D 1  are coupling regions. The region A 2  includes the plurality of coupling portions  43  and plurality of opening portions  40  of the first busbar  4 . The region A 10  includes the plurality of coupling portions  53  and plurality of opening portions  50  of the second busbar  5 . The acoustic velocity of acoustic waves in the coupling regions is higher than the acoustic velocity in the outer busbar regions or the acoustic velocity in the center region. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the regions A 3 , A 9  respectively located at the third from both ends in the first direction D 1  are inner busbar regions. The region A 3  includes the inner busbar portion  42  of the first busbar  4 . The region A 9  includes the inner busbar portion  52  of the second busbar  5 . The acoustic velocity of acoustic waves in the inner busbar regions is lower than the acoustic velocity in the center region. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the regions A 4 , A 8  respectively located at the fourth from both ends in the first direction D 1  are gap regions. The region A 4  includes the proximal end portions  63  of the plurality of first electrode fingers  6  and the plurality of gaps  32 . The region A 8  includes the proximal end portions  73  of the plurality of second electrode fingers  7  and the plurality of gaps  31 . The acoustic velocity of acoustic waves in the gap regions is higher than the acoustic velocity in the inner busbar regions or the acoustic velocity in the center region. 
     In the acoustic wave device  1 , of the above-described  11  regions A 1  to A 11 , the regions A 5 , A 7  respectively located at the fifth from both ends in the first direction D 1  are wide regions. The region A 5  includes the wide portions  64  of the plurality of first electrode fingers  6  and the wide portions  72  of the plurality of second electrode fingers  7 . The region A 7  includes the wide portions  62  of the plurality of first electrode fingers  6  and the wide portions  74  of the plurality of second electrode fingers  7 . The acoustic velocity of acoustic waves in the wide regions is lower than the acoustic velocity in the center region. 
     In the acoustic wave device  1 , since the interdigital transducer electrode  3  is provided as described above, the low acoustic velocity regions (the regions A 5 , A 3  and the regions A 7 , A 9 ) are present on the outer side of the center region (the region A 6 ), and the high acoustic velocity regions A 2 , A 10  are present on the outer side of the low acoustic velocity regions. Therefore, the acoustic wave device  1  is able to provide a piston mode, so a transverse-mode ripple is significantly reduced or prevented. 
     (1.3) Potentials of Interdigital Transducer Electrode and Reflectors 
       FIG. 5  shows an electric charge distribution in the surface (including the surface of the interdigital transducer electrode  3  and the one main surface  241  of the piezoelectric body portion  24 ) of the acoustic wave device  1  according to the first preferred embodiment. A precondition for the electric charge distribution shown in  FIG. 5  includes a condition that an excitation phenomenon of surface acoustic waves is occurring in the region associated with the interdigital transducer electrode  3 , a condition that each reflector  8  is electrically short-circuited (short-circuited grating), and a condition that no excitation phenomenon of surface acoustic waves is occurring in the regions associated with the reflectors  8  (since the reflectors  8  are electrically short-circuited, a driving voltage that causes a piezoelectric effect is zero). Here, the principle that the electric charge distribution shown in  FIG. 5  occurs is as follows. An edge effect (also referred to as cut-edge effect) occurs in a boundary region between a region where excitation of surface acoustic waves is occurring and a region where no excitation is occurring. Because of the edge effect, the amount of electric charge in a boundary region locally increases as compared to the amount of electric charge in regions around the boundary region. Therefore, in the acoustic wave device  1 , the electric charge distribution as shown in  FIG. 5  occurs. 
     As is apparent from  FIG. 5 , in the acoustic wave device  1 , in the second direction D 2  in which a group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  is provided, the amount of electric charge at each end of the interdigital transducer electrode  3  is greater than the amount of electric charge in the center of the interdigital transducer electrode  3 . In the direction along the second direction D 2 , the amount of electric charge at an end, closer to the interdigital transducer electrode  3 , of each reflector  8  is greater than the amount of electric charge at an end away from the interdigital transducer electrode  3 . Accordingly, in the acoustic wave device  1 , for example, the density of electric lines of force tends to increase between the outer busbar portion  41  having a relatively higher potential between the two outer busbar portions  41 ,  51  and the reflector  8  adjacent to the outer busbar portion  41 . 
     Hereinafter, for the above-described group of electrode fingers, the second electrode finger  7  located at the left-side end in  FIG. 1  and  FIG. 2A  in the second direction D 2  may be referred to as second electrode finger  7 L, and the second electrode finger located at the right-side end in  FIG. 1  and  FIG. 2A  may be referred to as second electrode finger  7 R. 
     In the interdigital transducer electrode  3 , of the inner busbar portion  42  of the first busbar  4  and the inner busbar portion  52  of the second busbar  5 , the inner busbar portion  42  of the first busbar  4  is close to the second electrode fingers  7 L,  7 R. The outer busbar portion  41  different in potential from the second electrode fingers  7 L,  7 R is located on an inner side in the second direction D 2  relative to the center portion  70 , in the first direction D 1 , of the second electrode finger  7 L located at one end and the center portion  70 , in the first direction D 1 , of the second electrode finger  7 R located at the other end of the above-described group of electrode fingers. 
     In  FIG. 3 , for the sake of convenience of description, in the interdigital transducer electrode  3 , the label “H” is assigned to the portion (high potential portion) electrically connected to the first terminal  11 , and the label “E” is assigned to the portion (low potential portion) electrically connected to the second terminals  12 . The high potential portion is different in potential from the low potential portion. The high potential portion is a portion higher in potential than the low potential portion. The labels “H”, “E” are not signs and are not actually present.  FIG. 3  is an enlarged view including the second electrode finger  7  located at the left-side end in  FIG. 1  and  FIG. 2A  and the inner busbar portion  42  close to this second electrode finger  7 . In  FIG. 1  and  FIG. 2A , the high potential portions (first conductive portions including the first busbar  4  and the plurality of first electrode fingers  6 ) to which the label “H” is assigned are different in potential from low potential portions (second conductive portions including the second busbar  5  and the plurality of second electrode fingers  7 ) to which the label “E” is assigned. 
     (1.4) Advantageous Effects 
     The acoustic wave device  1  according to the first preferred embodiment includes the first terminal  11 , the second terminals  12 , the piezoelectric body portion  24 , the interdigital transducer electrode  3 , and the reflectors  8 . Each second terminal has a lower potential than the first terminal  11 . The interdigital transducer electrode  3  is provided on or above the piezoelectric body portion  24 , and electrically connected to the first terminal  11  and the second terminals  12 . The reflectors  8  are provided on or above the piezoelectric body portion  24  and electrically connected to the second terminals  12 . The interdigital transducer electrode  3  includes the first busbar  4 , the second busbar  5 , the plurality of first electrode fingers  6 , and the plurality of second electrode fingers  7 . The first busbar  4  is electrically connected to the first terminal  11 . The second busbar  5  is opposed to the first busbar  4  in the first direction D 1  and electrically connected to the second terminals  12 . The plurality of first electrode fingers  6  are connected to the first busbar  4  and have a greater width from the first busbar  4  toward the second busbar  5  in the first direction D 1 . The plurality of second electrode fingers  7  are connected to the second busbar  5  and have a greater width from the second busbar  5  toward the first busbar  4  in the first direction D 1 . The plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1 . At least one electrode finger (first electrode finger  6 ) of the plurality of first electrode fingers  6  includes the wide portion  62  having a greater width in the second direction D 2  than the center portion  60 , in the first direction D 1 , of the at least one electrode finger (first electrode finger  6 ). At least one electrode finger (second electrode finger  7 ) of the plurality of second electrode fingers  7  includes the wide portion  72  having a greater width in the second direction D 2  than the center portion  70 , in the first direction D 1 , of the at least one electrode finger (second electrode finger  7 ). The first busbar  4  includes the opening portions  40 , the inner busbar portion  42 , the outer busbar portion  41 , and the coupling portions  43 . The second busbar  5  includes the opening portions  50 , the inner busbar portion  52 , the outer busbar portion  51 , and the coupling portions  53 . The inner busbar portion  42  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions in the first direction D 1 . The inner busbar portion  52  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions  50  in the first direction D 1 . The outer busbar portion  41  is located across the opening portions  40  from the inner busbar portion  42  in the first direction D 1 . The outer busbar portion  51  is located across the opening portions  50  from the inner busbar portion  52  in the first direction D 1 . The coupling portions  43  couple the inner busbar portion  42  and the outer busbar portion  41  in the first direction D 1 . The coupling portions  53  couple the inner busbar portion  52  and the outer busbar portion  51  in the first direction D 1 . In the interdigital transducer electrode  3 , where, of the group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7 , the electrode finger (the second end electrode finger  7 L or the second end electrode finger  7 R) located at one end in the second direction D 2  is a first end electrode finger and the electrode finger (the second end electrode finger  7 R or the second end electrode finger  7 L) located at the other end is a second end electrode finger, the first end electrode finger is located between the reflector  8  and the second end electrode finger in the second direction D 2 . 
     The outer busbar portion (outer busbar portion  41 ) of one (first busbar  4 ) of the first busbar  4  and the second busbar  5 , not connected to the first end electrode finger, is located on an inner side in the second direction D 2  relative to the center portion (center portion  70 ), in the first direction D 1 , of the first end electrode finger. 
     Thus, with the acoustic wave device  1  according to the first preferred embodiment, the interdigital transducer electrode  3  includes the above-described features, such that interference with a piston mode is significantly reduced or prevented. In addition, with the acoustic wave device  1  according to the first preferred embodiment, for the outer busbar portion  41  not connected to the second electrode fingers  7 L,  7 R, surge breakdown due to ESD between the outer busbar portion  41  and the reflectors  8  is less likely to occur, so significant improvement in ESD tolerance is provided. Thus, with the acoustic wave device  1  according to the first preferred embodiment, ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     The acoustic wave device  1  according to the first preferred embodiment includes the two reflectors  8 . The reflectors are provided one by one on both sides of the interdigital transducer electrode  3  in the second direction D 2 . In the acoustic wave device  1  according to the first preferred embodiment, the outer busbar portion  41  of the first busbar  4  not connected to the second electrode fingers  7 L,  7 R is located on an inner side in the second direction D 2  relative to the wide portions  72  of the second electrode finger  7 L and the wide portion  72  of the second electrode finger  7 R. Thus, with the acoustic wave device  1 , surge breakdown is less likely to occur and ESD tolerance significantly improves as compared to when the wide portion  72  of the second electrode finger  7 L and the outer busbar portion  41  overlap in the first direction D 1 . 
     In the acoustic wave device  1 , the outer busbar portion  41  is located on an inner side in the second direction D 2  relative to the second electrode finger  7 L and the second electrode finger  7 R and does not overlap the second electrode finger  7 L or the second electrode finger  7 R in the first direction D 1 . Thus, with the acoustic wave device  1 , the shortest distance between the outer busbar portion  41  and each reflector  8  is have a greater width, so ESD tolerance is further improved. 
     In the acoustic wave device  1 , one (left in the second direction D 2 ) side  42 L, along the first direction D 1 , of the inner busbar portion  42  of the first busbar  4  not connected to the second electrode fingers  7 L,  7 R and a (left) side  72 LL, away from the second electrode finger  7 R, of the wide portion  72  of the second electrode finger  7 L are aligned in a straight line or substantially in a straight line, and the other (right in the second direction D 2 ) side  42 R, along the first direction D 1 , of the inner busbar portion  42  and a (right) side  72 RR, away from the second electrode finger  7 L, of the wide portion  72  of the second electrode finger  7 R are aligned in a straight line or substantially in a straight line. Thus, with the acoustic wave device  1 , ESD tolerance is significantly improved by changing only the shape of the outer busbar portion  41  without changing the shape of the inner busbar portion  42 , so ESD tolerance is further improved while interference with a piston mode is significantly reduced or prevented. 
     In the interdigital transducer electrode  3 , of the group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7 , the outer busbar portion  41  of the first busbar  4  not connected to the second electrode finger  7 L located at one end in the second direction D 2  or the second electrode finger  7 R located at the other end is located on an inner side in the second direction D 2  relative to the inner busbar portion  42  close to the second electrode fingers  7 L,  7 R respectively located at both ends in the second direction D 2 . 
     Thus, with the acoustic wave device  1  according to the first preferred embodiment, the outer busbar portion  41  of the first busbar  4  not connected to the second electrode finger  7 L or the second electrode finger  7 R is able to significantly reduce or prevent surge breakdown due to ESD. Thus, with the acoustic wave device  1  according to the first preferred embodiment, ESD tolerance is significantly improved. 
     (1.5) First Modification of First Embodiment 
     In an acoustic wave device  1   a  according to a first modification of the first preferred embodiment shown in  FIG. 5 , the left side of the outer busbar portion  41  and the right side of the wide portion  72  of the second electrode finger  7 L are aligned in a straight line or substantially in a straight line. In addition, the right side of the outer busbar portion  41  and the left side of the wide portion  72  of the second electrode finger  7 R (see  FIG. 2A ) are aligned in a straight line or substantially in a straight line. Other features of the acoustic wave device  1   a  according to the first modification are the same as or similar to those of the acoustic wave device  1  according to the first preferred embodiment, so the drawings and description thereof are omitted. 
     With the acoustic wave device  1   a  according to the first modification, the length of the outer busbar portion  41  in the second direction D 2  is increased as compared to the acoustic wave device  1  according to the first preferred embodiment, such that interference with a piston mode is further reduced or prevented. 
     (1.6) Other Modifications of First Embodiment 
     The number of the plurality of first electrode fingers  6  and the number of the plurality of second electrode fingers  7  in the interdigital transducer electrode  3  are not limited. Here, in the interdigital transducer electrode  3 , the electrode fingers respectively located at both ends in the second direction D 2  of the group of electrode fingers are not limited to the second electrode fingers  7 . For example, of the group of electrode fingers, the electrode finger located at one end in the second direction D 2  may be the second electrode finger  7 , and the electrode finger located at the other end may be the first electrode finger  6 . Accordingly, the inner busbar portion  42  of the first busbar  4  is close to the second electrode finger  7  located at one end, and the inner busbar portion  52  of the second busbar  5  is close to the first electrode finger  6  located at the other end. Of the group of electrode fingers, the electrode fingers respectively located at one end and the other end in the second direction D 2  may be the first electrode fingers  6 . Accordingly, the inner busbar portion  52  of the second busbar  5  is close to the first electrode fingers  6  respectively located at one end and the other end. The group of electrode fingers only needs to include the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1 . For example, in an acoustic wave device of one modification, a region in which the first electrode finger  6  and the second electrode finger  7  are provided one by one and spaced apart from each other and a region in which the two first electrode fingers  6  or the two second electrode fingers  7  are provided in the second direction D 2  may be mixed. With the acoustic wave device of any one of these modifications as well, the outer busbar portion not connected to at least one electrode finger of the two electrode fingers respectively located one by one at one end and the other end in the second direction D 2  of the group of electrode fingers is located on an inner side in the second direction D 2  relative to the center portion, in the first direction D 1 , of the at least one electrode finger, ESD tolerance is significantly improved. At least one first electrode finger  6  of the plurality of first electrode fingers  6  in the interdigital transducer electrode  3  only needs to include the wide portion  62 , and at least one second electrode finger  7  of the plurality of second electrode fingers  7  in the interdigital transducer electrode  3  only needs to include the wide portion  72 . 
     In the interdigital transducer electrode  3 , of the group of electrode fingers, at least one electrode finger may have three or more wide portions. 
     The acoustic wave device  1  may further include an electrically conductive first bump provided on or above the first terminal  11  and an electrically conductive second bump provided on or above each of the second terminals  12 . The number of the second terminals  12  is not limited to a multiple number and may be, for example, one. 
     Second Preferred Embodiment 
     (2.1) Overall Configuration of Acoustic Wave Device 
     Hereinafter, an acoustic wave device  1   b  according to a second preferred embodiment of the present invention will be described with reference to the drawings. 
     The acoustic wave device  1   b  according to the second preferred embodiment is a longitudinally coupled resonator filter, and, as shown in  FIG. 7  to  FIG. 10 , includes the first terminals (for example, signal terminals)  11 , the second terminals (for example, ground terminals)  12 , the piezoelectric body portion  24 , and a plurality of the interdigital transducer electrodes  3 . The piezoelectric body portion  24  is made of a piezoelectric material. The plurality of interdigital transducer electrodes  3  is provided on or above the piezoelectric body portion  24 . The acoustic wave device  1   b  according to the second preferred embodiment further includes the two reflectors  8 . In  FIG. 7  and  FIG. 8 , dot hatching is applied to the plurality of interdigital transducer electrodes  3  and the reflectors  8 . These hatchings do not represent cross sections and are provided to clearly show the relationship among the plurality of interdigital transducer electrodes  3 , the reflectors  8 , and the piezoelectric body portion  24 . As for the acoustic wave device  1   b  according to the second preferred embodiment, like reference numerals denote similar components to those of the acoustic wave device  1  (see  FIG. 1  to  FIG. 4 ) according to the first preferred embodiment, and the description thereof may be omitted. 
     (2.2) Components of Acoustic Wave Device 
     Next, the components of the acoustic wave device  1   b  will be described with reference to the drawings. 
     (2.2.1) Multilayer Board 
     In the acoustic wave device  1   b  according to the second preferred embodiment, the piezoelectric body portion  24  is a piezoelectric film, and the plurality of interdigital transducer electrodes  3  is provided on or above a multilayer board  2   b  including the piezoelectric body portion  24 . The plan-view shape (the outer peripheral shape of the high acoustic velocity support substrate  21  when viewed in the thickness direction) of the high acoustic velocity support substrate  21  (see  FIG. 9 ) in the multilayer board  2   b  is a rectangular or substantially rectangular shape, for example. However, the shape is not limited to a rectangular or substantially rectangular shape and may be, for example, a square or substantially square shape. 
     (2.2.2) Reflector 
     The two reflectors  8  are provided on or above the piezoelectric body portion  24 . Here, the two reflectors  8  each are provided one by one across the interdigital transducer electrode  3  at any one of both sides of the three interdigital transducer electrodes  3  in the second direction D 2  from the center interdigital transducer electrode  3 . Hereinafter, for the sake of convenience of description, when the three interdigital transducer electrodes  3  are distinguished from one another, of the plurality of interdigital transducer electrodes  3 , one of the adjacent two interdigital transducer electrodes  3  in the second direction D 2  may be referred to as first interdigital transducer electrode  3 A and the other may be referred to as second interdigital transducer electrode  3 B. In the example of  FIG. 7  and  FIG. 8 , of the three interdigital transducer electrodes  3 , the center interdigital transducer electrode  3  is referred to as first interdigital transducer electrode  3 A, and the interdigital transducer electrodes  3  at both ends are referred to as second interdigital transducer electrodes  3 B. 
     (2.2.3) Interdigital Transducer Electrode 
     In the acoustic wave device  1   b  according to the second preferred embodiment, the three interdigital transducer electrodes  3  are provided in the second direction D 2 . Each of the three interdigital transducer electrodes  3  includes the first busbar  4 , the second busbar  5 , the plurality of first electrode fingers  6 , and the plurality of second electrode fingers  7 . 
     The first busbar  4  includes the opening portions  40 , the inner busbar portion  42 , the outer busbar portion  41 , and the coupling portions  43 . The second busbar  5  includes the opening portions  50 , the inner busbar portion  52 , the outer busbar portion  51 , and the coupling portions  53 . In the interdigital transducer electrode  3 , the wide portions  62  of the distal end portions  61  of the plurality of first electrode fingers  6  and the wide portions  74 , closer to the proximal end portions  73 , of the second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2 . In addition, in the interdigital transducer electrode  3 , the wide portions  64 , closer to the proximal end portions  63 , of the plurality of first electrode fingers  6  and the wide portions  72  of the distal end portions  71  of the second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2 . 
     (2.3) Potential of Interdigital Transducer Electrode 
     In  FIG. 7  and  FIG. 8 , for the sake of convenience of description, the label “H” is assigned to portions (high potential portions) electrically connected to the first terminals (signal terminals)  11  in the interdigital transducer electrodes  3 , and the label “E” is assigned to portions (low potential portions) electrically connected to the second terminals (ground terminals)  12  in the interdigital transducer electrodes  3  and the reflectors  8 . The high potential portions are different in potential from the low potential portions. The high potential portions are portions higher in potential than the low potential portions. The labels “H”, “E” are not signs and are not actually present. 
     The acoustic wave device  1   b  includes the two first terminals  11  and the two second terminals  12 . When the two first terminals  11  are distinguished from each other, one is referred to as first terminal  11 A, and the other is referred to as first terminal  11 B. When the two second terminals  12  are distinguished from each other, one is referred to as second terminal  12 A, and the other is referred to as second terminal  12 B. 
     The first busbar  4  of the first interdigital transducer electrode  3 A is electrically connected to the first terminal  11 A. The acoustic wave device  1   b  includes the first wiring layer  13  ( 13 A) that electrically connects the first terminal  11 A and the first busbar  4  of the first interdigital transducer electrode  3 A. The second busbar  5  of the first interdigital transducer electrode  3 A is electrically connected to the second terminal  12 A and the second terminal  12 B. The acoustic wave device  1   b  includes the second wiring layer  14  ( 14 A) that electrically connects the second terminal  12 A, the second terminal  12 B, and the second busbar  5  of the first interdigital transducer electrode  3 A. In the first interdigital transducer electrode  3 A, the second busbar  5  has a lower potential than the first busbar  4 . 
     The first busbar  4  of each second interdigital transducer electrode  3 B is electrically connected to the second terminal  12 B. The acoustic wave device  1   b  includes the second wiring layer  14  ( 14 B) that electrically connects the second terminal  12 B and the first busbar  4  of each second interdigital transducer electrode  3 B. The second busbar  5  of each second interdigital transducer electrode  3 B is electrically connected to the first terminal  11 B. The acoustic wave device  1   b  includes the first wiring layer  13  ( 13 B) that electrically connects the first terminal  11 B and the second busbar  5  of each second interdigital transducer electrode  3 B. In each second interdigital transducer electrode  3 B, the first busbar  4  has a lower potential than the second busbar  5 . 
     Each reflector  8  is electrically connected to the second terminal  12 A and the second terminal  12 B. Each reflector  8  has a lower potential than the second busbar  5  of each second interdigital transducer electrode  3 B. 
     The acoustic wave device  1   b  includes an electrically insulating layer  15  that electrically insulates the first wiring layer  13  ( 13 A) and the second wiring layer  14  ( 14 B) from each other. The electrically insulating layer  15  is provided on or above the piezoelectric body portion  24  and partially interposed between the first wiring layer  13  ( 13 A) and the second wiring layer ( 14 B). The acoustic wave device  1   b  includes an electrically insulating layer  16  that electrically insulates the first wiring layer  13  ( 13 B) and the second wiring layer  14  ( 14 A) from each other. The electrically insulating layer  16  is provided on or above the piezoelectric body portion  24  and partially interposed between the first wiring layer  13  ( 13 B) and the second wiring layer ( 14 A). 
     The acoustic wave device  1   b  may further include an electrically conductive first bump provided on or above each of the first terminals  11  and an electrically conductive second bump provided on or above each of the second terminals  12 . The number of the first terminals  11  and the number of the second terminals each are not limited to a multiple number and may be, for example, one. 
       FIG. 10  is an enlarged view including the first electrode finger  6  located at the left-side end of the center first interdigital transducer electrode  3 A in  FIG. 7  and  FIG. 8  and the first electrode finger  6  located at the right-side end of the left-side second interdigital transducer electrode  3 B in  FIG. 7  and  FIG. 8 . In  FIG. 7 ,  FIG. 8 , and  FIG. 10 , the high potential portions to which the label “H” is assigned are different in potential from the low potential portions to which the label “E” is assigned. For example, in  FIG. 10 , the first electrode finger  6  located at the left-side end of the first interdigital transducer electrode  3 A and the first electrode finger  6  located at the right-side end of the second interdigital transducer electrode  3 B are different in potential. In  FIG. 10 , the first electrode finger  6  located at the left-side end of the first interdigital transducer electrode  3 A and the second busbar  5  of the first interdigital transducer electrode  3 A, close to this first electrode finger  6 , are different in potential. In  FIG. 10 , the first electrode finger  6  located at the right-side end of the second interdigital transducer electrode  3 B and the second busbar  5  of the second interdigital transducer electrode  3 B, close to this first electrode finger  6 , are different in potential. The second busbar  5  of the first interdigital transducer electrode  3 A and the second busbar  5  of the second interdigital transducer electrode  3 B are different in potential. 
       FIG. 11  shows an electric charge distribution in the surface (including the surfaces of the three interdigital transducer electrodes  3  and the one main surface  241  of the piezoelectric body portion  24 ) of the acoustic wave device  1   b  according to the second preferred embodiment. A precondition for the electric charge distribution shown in  FIG. 11  includes a condition that an excitation phenomenon of surface acoustic waves is occurring in the region associated with the first interdigital transducer electrode  3 A and each region associated with the second interdigital transducer electrode  3 B, a condition that the region associated with the first interdigital transducer electrode  3 A and each region associated with the second interdigital transducer electrode  3 B are respectively connected to different electrical terminals (the first terminal  11 A and the first terminal  11 B), a condition that each reflector  8  is electrically short-circuited (short-circuited grating), and a condition that no excitation phenomenon of surface acoustic waves is occurring in the regions associated with the reflectors  8  (since the reflectors  8  are electrically short-circuited, a driving voltage that causes a piezoelectric effect is zero). Here, the principle that the electric charge distribution shown in  FIG. 11  occurs is as follows. An edge effect (also referred to as cut-edge effect) occurs in a boundary region between a region where excitation of surface acoustic waves is occurring and a region where no excitation is occurring. An edge effect also occurs in a boundary region between two regions in which the states of excitation of surface acoustic waves are different from each other. Because of the edge effect, the amount of electric charge in a boundary region locally increases as compared to the amount of electric charge in regions around the boundary region. An edge effect, in principle, may occur in applicable various boundary regions when the states of excitation of surface acoustic waves are different from each other. However, in the case of the acoustic wave device  1   b  (longitudinally coupled resonator-type filter) according to the second preferred embodiment, as shown in  FIG. 11 , the amount of electric charge mostly locally concentrates in the boundary region between the region associated with the first interdigital transducer electrode  3 A and each region associated with the second interdigital transducer electrode  3 B and in the boundary region between each region associated with the second interdigital transducer electrode  3 B and the region associated with the reflector  8 . Therefore, in the acoustic wave device  1   b  according to the second preferred embodiment, the electric charge distribution as shown in  FIG. 11  occurs. 
     As is apparent from  FIG. 11 , in the acoustic wave device  1   b,  in the second direction D 2  in which a group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  is provided, the amount of electric charge at each end of the interdigital transducer electrode  3  is greater than the amount of electric charge in the center of the interdigital transducer electrode  3 . Accordingly, in the acoustic wave device  1   b,  for example, the density of electric lines of force tends to increase between the outer busbar portions  51  of the adjacent interdigital transducer electrodes  3 . In the direction along the second direction D 2 , the amount of electric charge at an end, closer to the interdigital transducer electrode  3 , of each reflector  8  is greater than the amount of electric charge at an end away from the interdigital transducer electrode  3 . Accordingly, in the acoustic wave device  1   b,  for example, the density of electric lines of force tends to increase between the outer busbar portion  41  having a relatively higher potential between the two outer busbar portions  41 ,  51  and the reflector  8  adjacent to the outer busbar portion  41 . 
     (2.4) Advantageous Effects 
     The acoustic wave device  1   b  according to the second preferred embodiment includes the first terminals  11 , the second terminals  12 , the piezoelectric body portion  24 , and the plurality of interdigital transducer electrodes  3 . Each second terminal  12  has a lower potential than each first terminal  11 . The plurality of interdigital transducer electrodes  3  are provided on or above the piezoelectric body portion  24  and electrically connected to the first terminals  11  and the second terminals  12 . Each of the plurality of interdigital transducer electrodes  3  includes the first busbar  4 , the second busbar  5 , the plurality of first electrode fingers  6 , and the plurality of second electrode fingers  7 . The second busbar  5  is opposed to the first busbar  4  in the first direction D 1 . The plurality of first electrode fingers  6  are connected to the first busbar  4  and have a greater width from the first busbar  4  toward the second busbar  5  in the first direction D 1 . The plurality of second electrode fingers  7  are connected to the second busbar  5  and have a greater width from the second busbar  5  toward the first busbar  4  in the first direction D 1 . The plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  are provided alternately one by one and spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1 . Each of the plurality of first electrode fingers  6  includes the wide portion  62  having a greater width in the second direction D 2  than the center portion  60  in the first direction D 1 . Each of the plurality of second electrode fingers  7  includes the wide portion  72  having a greater width in the second direction D 2  than the center portion  70  in the first direction D 1 . The first busbar  4  includes the opening portions  40 , the inner busbar portion  42 , the outer busbar portion  41 , and the coupling portions  43 . The second busbar  5  includes the opening portions  50 , the inner busbar portion  52 , the outer busbar portion  51 , and the coupling portions  53 . The inner busbar portion  42  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions  40  in the first direction D 1 . The inner busbar portion  52  is located closer to the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  than the opening portions  50  in the first direction D 1 . The outer busbar portion  41  is located across the opening portions  40  from the inner busbar portion  42  in the first direction D 1 . The outer busbar portion  51  is located across the opening portions  50  from the inner busbar portion  52  in the first direction D 1 . The coupling portions  43  couple the inner busbar portion  42  and the outer busbar portion  41  in the first direction D 1 . The coupling portions  53  couple the inner busbar portion  52  and the outer busbar portion  51  in the first direction Dl. Where, of the plurality of interdigital transducer electrodes  3 , one of the adjacent two interdigital transducer electrodes  3  in the second direction D 2  is the first interdigital transducer electrode  3 A and the other one is the second interdigital transducer electrode  3 B, the distance between the outer busbar portion  51  not connected to, of the group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7 , the first electrode finger  6  closest to the second interdigital transducer electrode  3 B in the first interdigital transducer electrode  3 A and the outer busbar portion  51  not connected to, of the group of electrode fingers including the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7 , the first electrode finger  6  closest to the first interdigital transducer electrode  3 A in the second interdigital transducer electrode  3 B is greater than the distance between the center portion  60  of the first electrode finger  6  closest to the second interdigital transducer electrode  3 B in the first interdigital transducer electrode  3 A and the center portion  60  of the first electrode finger closest to the first interdigital transducer electrode  3 A in the second interdigital transducer electrode  3 B. 
     Thus, with the acoustic wave device  1   b  according to the second preferred embodiment, surge breakdown due to ESD between the outer busbar portion  51  of the first interdigital transducer electrode  3 A and the outer busbar portion  51  of the second interdigital transducer electrode  3 B is significantly reduced or prevented, such that ESD tolerance is significantly improved. 
     In the acoustic wave device  1   b  according to the second preferred embodiment, for the first interdigital transducer electrode  3 A, the outer busbar portion  51  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52 . Thus, with the acoustic wave device  1   b,  in comparison with the case where the outer busbar portion  51  of the first interdigital transducer electrode  3 A, as well as the inner busbar portion  52 , overlaps in the first direction D 1  each of the first electrode fingers  6  respectively located one by one at one end and the other end in the second direction D 2  of the group of electrode fingers, surge breakdown is less likely to occur, such that ESD tolerance significantly improves. In the acoustic wave device  1   b  according to the second preferred embodiment, for the second interdigital transducer electrode  3 B, the outer busbar portion  51  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52 . Thus, with the acoustic wave device  1   b,  in comparison with the case where the outer busbar portion  51  of the second interdigital transducer electrode  3 B, as well as the inner busbar portion  52 , overlaps in the first direction D 1  each of the first electrode fingers  6  respectively located one by one at one end and the other end in the second direction D 2  of the group of electrode fingers, surge breakdown is less likely to occur, so ESD tolerance significantly improves. 
     In each of the first interdigital transducer electrode  3 A and the second interdigital transducer electrode  3 B of the acoustic wave device  1   b  according to the second preferred embodiment, the outer busbar portion  51  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52 . In the acoustic wave device  1   b,  from the viewpoint of significantly reducing or preventing a transverse-mode ripple by providing a piston mode, of a state where the inner busbar portion  52  overlaps in the first direction D 1  each of the first electrode fingers  6  located one by one at one end and the other end in the second direction D 2  of the group of electrode fingers and a state where the outer busbar portion  51  overlaps in the first direction D 1  each of the first electrode fingers  6  respectively located at both ends in the second direction D 2  of the group of electrode fingers, the former one is more important. Thus, with the acoustic wave device  1   b  according to the second preferred embodiment, ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. With the acoustic wave device  1   b,  of the inner busbar portion  52  and the outer busbar portion  51 , only the inner busbar portion  52  overlaps in the first direction D 1  each of the first electrode fingers  6  located one by one at one end and the other end in the second direction D 2  of the group of electrode fingers, so ESD tolerance is further improved while interference with a piston mode is significantly reduced or prevented. 
     (2.5) First Modification of Second Embodiment 
     An acoustic wave device  1   c  according to a first modification of the second preferred embodiment shown in  FIG. 12  differs from the acoustic wave device  1   b  according to the second preferred embodiment in that the length of the outer busbar portion  51  in each of the plurality of interdigital transducer electrodes  3  is greater than that in the acoustic wave device  1   b  according to the second preferred embodiment. The other features of the acoustic wave device  1   c  according to the first modification are the same as or similar to that of the acoustic wave device  1   b  according to the second preferred embodiment, so the drawings and description thereof are omitted. 
     In the acoustic wave device  1   c  according to the first modification, the distance between the inner busbar portions  52  of the adjacent two interdigital transducer electrodes  3  is the same or substantially the same as the distance between sides close to each other in the adjacent wide portions  62  in the adjacent two interdigital transducer electrodes  3 . In the acoustic wave device  1   c  according to the first modification, the distance between the outer busbar portions  51  of the adjacent two interdigital transducer electrodes  3  is the same or substantially the same as the distance between sides opposite from the sides adjacent to or in a vicinity of each other in the adjacent wide portions  62  in the adjacent two interdigital transducer electrodes  3 . 
     In the acoustic wave device  1   c,  a side, closer to the second interdigital transducer electrode  3 B, of the outer busbar portion  51  of the first interdigital transducer electrode  3 A and a side, closer to the second electrode finger  7 , of the wide portion  62  of the first electrode finger  6  closest to the second interdigital transducer electrode  3 B of the above-described group of electrode fingers of the first interdigital transducer electrode  3 A are aligned in a straight line or substantially in a straight line. In the acoustic wave device  1   c,  a side, closer to the first interdigital transducer electrode  3 A, of the outer busbar portion  51  of the second interdigital transducer electrode  3 B and a side, closer to the second electrode finger  7 , of the wide portion  62  of the first electrode finger  6  closest to the first interdigital transducer electrode  3 A of the above-described group of electrode fingers of the second interdigital transducer electrode  3 B are aligned in a straight line or substantially in a straight line. 
     With the acoustic wave device  1   c  according to the first modification, the length of the outer busbar portion  51  is increased as compared to the acoustic wave device  1   b  according to the second preferred embodiment, such that interference with a piston mode is significantly reduced or prevented. 
     (2.6) Second Modification of Second Embodiment 
     As shown in  FIG. 13  and  FIG. 14 , an acoustic wave device  1   d  according to a second modification of the second preferred embodiment differs from the acoustic wave device  1   b  (see  FIG. 7  to  FIG. 11 ) according to the second preferred embodiment in that, in only the left-side second interdigital transducer electrode  3 B of the three interdigital transducer electrodes  3 , the outer busbar portion  51  of the second busbar  5  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52  at a side closer to the first interdigital transducer electrode  3 A. The other features of the acoustic wave device  1   d  according to the second modification are the same as or similar to that of the acoustic wave device  1   b  according to the second preferred embodiment, so the drawings and description thereof are omitted. 
     In the acoustic wave device  1   d  according to the second modification, in each of the center first interdigital transducer electrode  3 A and the right-side second interdigital transducer electrode  3 B of the three interdigital transducer electrodes  3 , the outer busbar portion  51  of the second busbar  5  overlaps the inner busbar portion  52  in the first direction D 1  over the entire or substantially the entire length. Here, the length of the outer busbar portion  51  is the same or substantially the same as the length of the inner busbar portion  52 . In the outer busbar portion and the inner busbar portion  52 , left sides in the second direction D 2  are aligned in a straight line or substantially in a straight line, and right sides are aligned in a straight line or substantially in a straight line. 
     With the acoustic wave device  1   d  according to the second modification, interference with a piston mode is significantly reduced or prevented as compared to the acoustic wave device  1   b  according to the second preferred embodiment. In the acoustic wave device  1   d  according to the second modification, for the second interdigital transducer electrode  3 B, the outer busbar portion  51  of the second busbar  5  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52  at a side closer to the first interdigital transducer electrode  3 A. Thus, with the acoustic wave device  1   d  according to the second modification, surge breakdown due to ESD between the outer busbar portion  51  of the second interdigital transducer electrode  3 B and the outer busbar portion  51  of the first interdigital transducer electrode  3 A is significantly reduced or prevented, such that ESD tolerance is significantly improved. 
     (2.7) Third Modification of Second Embodiment 
     An acoustic wave device  1   e  according to a third modification of the second preferred embodiment shown in  FIG. 15  differs from the acoustic wave device  1   d  in that the length of the outer busbar portion  51  of the left-side second interdigital transducer electrode  3 B is greater than that in the acoustic wave device  1   d  according to the second modification of the second preferred embodiment. The other features of the acoustic wave device  1   e  according to the third modification are the same as or similar to that of the acoustic wave device  1   d  according to the second modification of the second preferred embodiment, so the drawings and description thereof are omitted. 
     In the acoustic wave device  1   e,  a side, closer to the first interdigital transducer electrode  3 A, of the outer busbar portion  51  of the left-side second interdigital transducer electrode  3 B and a side, closer to the second electrode finger  7 , of the wide portion  62  of the first electrode finger  6  closest to the first interdigital transducer electrode  3 A of the above-described group of electrode fingers of the left-side second interdigital transducer electrode  3 B are aligned in a straight line or substantially in a straight line in the first direction D 1 . 
     With the acoustic wave device  1   e  according to the third modification, the length of the outer busbar portion  51  of the left-side second interdigital transducer electrode  3 B is increased as compared to the acoustic wave device  1   d  according to the second modification, such that interference with a piston mode is significantly reduced or prevented. 
     (2.8) Fourth Modification of Second Embodiment 
     As shown in  FIG. 16 , in an acoustic wave device  1   f  according to a fourth modification of the second preferred embodiment, a multilayer board  2   f  includes a high acoustic velocity film  22 , the low acoustic velocity film  23 , and the piezoelectric body portion  24 . The high acoustic velocity film  22  is provided on or above the support substrate  20 . Here, the state “provided on or above the support substrate  20 ” includes the case of being directly provided on the support substrate  20  and the case of being indirectly provided on the support substrate  20 . In the high acoustic velocity film  22 , bulk waves propagate at a higher acoustic velocity than acoustic waves that propagate through the piezoelectric body portion (piezoelectric film)  24 . The low acoustic velocity film  23  is provided on or above the high acoustic velocity film  22 . Here, the state “provided on or above the high acoustic velocity film  22 ” includes the case of being directly provided on the high acoustic velocity film  22  and the case of being indirectly provided on the high acoustic velocity film  22 . In the low acoustic velocity film  23 , bulk waves propagate at a lower acoustic velocity than acoustic waves that propagate through the piezoelectric body portion  24 . The piezoelectric body portion  24  is provided on or above the low acoustic velocity film  23 . Here, the state “provided on or above the low acoustic velocity film  23 ” includes the case of being directly provided on the low acoustic velocity film  23  and the case of being indirectly provided on the low acoustic velocity film  23 . As for the acoustic wave device  1   f  according to the fourth modification, like reference numerals denote similar components to those of the acoustic wave device  1   b  (see  FIG. 7  to  FIG. 11 ) according to the second preferred embodiment, and the description thereof is omitted. 
     The support substrate  20  may include a piezoelectric body, for example, sapphire, lithium tantalate, lithium niobate, and quartz crystal, various ceramics, for example, alumina, magnesia, silicon nitride, aluminum nitride, silicon carbide, zirconia, cordierite, mullite, steatite, and forsterite, a dielectric, for example, glass, or a semiconductor, for example, silicon and gallium nitride, a resin substrate, or the like. 
     In the acoustic wave device  1   f  according to the fourth modification, the high acoustic velocity film  22  significantly reduces or prevents acoustic waves from leaking to the structure below the high acoustic velocity film  22 . 
     In the acoustic wave device  1   f  according to the fourth modification, the energy of acoustic waves in a specific mode that provides the characteristics of a filter or resonator is distributed all over the piezoelectric body portion  24  and the low acoustic velocity film  23 , the energy is also distributed to a portion, closer to the low acoustic velocity film  23 , of the high acoustic velocity film  22 , and the energy is not distributed to the high acoustic velocity support substrate  21 . Enclosing acoustic waves with the high acoustic velocity film  22  is similar to the case of enclosing surface acoustic waves of a Love wave type that is non-leaking SH (shear horizontal) waves and is, for example, described in Document “Introduction to surface acoustic wave device simulation technology”, Kenya HASHIMOTO, published by 
     Realize Inc., p.26 to p.28. The above-described structure that encloses acoustic waves differs from a structure that encloses acoustic waves with Bragg reflector with an acoustic multilayer film. 
     The high acoustic velocity film  22  is preferably made of any one of piezoelectric bodies, for example, diamond-like carbon, aluminum nitride, aluminum oxide, silicon carbide, silicon nitride, silicon, sapphire, lithium tantalate, lithium niobate, and quartz crystal, various ceramics, for example, alumina, zirconia, cordierite, mullite, steatite, and forsterite, magnesia diamond, a material including any one of the above materials as a main ingredient, and a material including a mixture of some of the above materials as a main ingredient. 
     For the thickness of the high acoustic velocity film  22 , since the high acoustic velocity film  22  encloses acoustic waves in the piezoelectric body portion  24  and the low acoustic velocity film  23 , the thickness of the high acoustic velocity film  22  is preferably thicker than the low acoustic velocity film  23 , for example. 
     With the acoustic wave device  1   f  according to the fourth modification, as well as the acoustic wave device  1   b  (see  FIG. 7  to  FIG. 11 ) according to the second preferred embodiment, surge breakdown due to ESD between the outer busbar portion  51  of the first interdigital transducer electrode  3 A and the outer busbar portion  51  of the second interdigital transducer electrode  3 B is significantly reduced or prevented, so ESD tolerance is significantly improved. 
     (2.9) Fifth Modification of Second Embodiment 
     As shown in  FIG. 17 , in an acoustic wave device  1   g  according to a fifth modification of the second preferred embodiment, a piezoelectric body portion  24   g  includes a piezoelectric substrate, and the high acoustic velocity support substrate  21  and the low acoustic velocity film  23  in the acoustic wave device  1   b  according to the second preferred embodiment are not provided. As for the acoustic wave device  1   g  according to the fifth modification, like reference numerals denote the same or similar components to those of the acoustic wave device  1   b  (see  FIG. 7  to  FIG. 11 ) according to the second preferred embodiment, and the description thereof is omitted. 
     In the acoustic wave device  1   g,  the piezoelectric substrate that defines the piezoelectric body portion  24   g  is preferably a 128-degree Y-X lithium niobate (LiNbO 3 ) substrate, for example. The piezoelectric substrate is preferably made of, for example, a substrate including a 50-degree Y-cut X-propagation lithium tantalate (LiTaO 3 ) piezoelectric monocrystal or piezoelectric ceramics (lithium tantalate monocrystal or ceramics cut along a plane having an axis rotated by about 50 degrees from the Y-axis about the X-axis as the direction of the normal, and through which acoustic waves propagate in the X-axis direction). Although not shown in  FIG. 17 , the acoustic wave device  1   g  includes a silicon oxide (SiO 2 ) film that covers the plurality of (three) interdigital transducer electrodes  3 , the two reflectors  8 , and a region not covered with the plurality of (three) interdigital transducer electrodes  3  and the two reflectors  8  on one main surface  241   g  of the piezoelectric body portion  24   g.  In the acoustic wave device  1   g,  the surface shape of the silicon oxide film has recesses and protrusions corresponding to the shapes of the three interdigital transducer electrodes  3  and two reflectors  8 . 
     With the acoustic wave device  1   g  according to the fifth modification, as well as the acoustic wave device  1   b  (see  FIG. 7  to  FIG. 11 ) according to the second preferred embodiment, surge breakdown due to ESD between the outer busbar portion  51  of the first interdigital transducer electrode  3 A and the outer busbar portion  51  of the second interdigital transducer electrode  3 B is significantly reduced or prevented, so ESD tolerance is significantly improved. 
     (2.10) Other Modifications of Second Embodiment 
     The number of the plurality of first electrode fingers  6  and the number of the plurality of second electrode fingers  7  in each of the plurality of interdigital transducer electrodes  3  are not limited. Here, in the first interdigital transducer electrode  3 A, the first end electrode finger and the second end electrode finger respectively located at one end and the other end in the second direction D 2  of the group of electrode fingers are not limited to the first electrode fingers  6 . For example, one of the first end electrode finger and the second end electrode finger may be the first electrode finger  6 , and the other may be the second electrode finger  7 . Accordingly, the inner busbar portion  52  of the second busbar  5  is close to the first electrode finger  6  that is the first end electrode finger, and the inner busbar portion  42  of the first busbar  4  is close to the second electrode finger  7  that is the second end electrode finger. Each of the first end electrode finger and the second end electrode finger may be the second electrode finger  7 . Accordingly, the inner busbar portion  42  of the first busbar  4  is close to the second electrode fingers  7  that are respectively the first end electrode finger and the second end electrode finger. The group of electrode fingers only needs to include the plurality of first electrode fingers  6  and the plurality of second electrode fingers  7  spaced apart from each other in the second direction D 2  perpendicular or substantially perpendicular to the first direction D 1 . For example, in an acoustic wave device of one modification, a region in which the first electrode finger  6  and the second electrode finger  7  are provided one by one and spaced apart from each other and a region in which the two first electrode fingers  6  or the two second electrode fingers  7  are provided in the second direction D 2  may be mixed. In the acoustic wave device  1 d according to the second modification, for the left-side second interdigital transducer electrode  3 B in  FIG. 13  of the two second interdigital transducer electrodes  3 B, the outer busbar portion  51  of the second busbar  5  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52  at a side closer to the first interdigital transducer electrode  3 A. However, the features are not limited thereto. For example, for the right-side second interdigital transducer electrode  3 B in  FIG. 13 , the outer busbar portion  51  of the second busbar  5  may be located on an inner side in the second direction D 2  relative to the inner busbar portion  52  at a side closer to the first interdigital transducer electrode  3 A. For the first interdigital transducer electrode  3 A, the outer busbar portion  51  of the second busbar  5  may be located on an inner side in the second direction D 2  relative to the inner busbar portion  52  at a side closer to at least one of the two second interdigital transducer electrodes  3 B. With the acoustic wave device of any one of these as well, the outer busbar portion  51  is located on an inner side in the second direction D 2  relative to the inner busbar portion  52 , so ESD tolerance is significantly improved. At least one first electrode finger  6  of the plurality of first electrode fingers  6  in each interdigital transducer electrode  3  only needs to include the wide portion  62 , and at least one second electrode finger  7  of the plurality of second electrode fingers  7  in each interdigital transducer electrode  3  only needs to include have the wide portion  72 . 
     The above-described first and second preferred embodiments, and the like, are each merely one of various preferred embodiments of the present invention. The above-described preferred embodiments each may be modified into various forms according to design, or the like, as long as the object of the present invention is provided. 
     For example, in the acoustic wave devices  1 ,  1   a,    1   b,    1   c,    1   d,    1   e,    1   f,    1   g,  the interdigital transducer electrode(s)  3  is/are directly provided on one main surface  214  of the piezoelectric body portion  24  or one main surface  241   g  of the piezoelectric body portion  24   g.  However, the present invention is not limited thereto. The interdigital transducer electrode(s)  3  may be indirectly provided on one main surface  214  of the piezoelectric body portion  24  or one main surface  241   g  of the piezoelectric body portion  24   g.  For example, in the acoustic wave devices  1 ,  1   a,    1   b,    1   c,    1   d,    1   e,    1   f,    1   g,  the interdigital transducer electrode(s)  3  may be provided on one main surface  241  of the piezoelectric body portion  24  or one main surface  241   g  of the piezoelectric body portion  24   g  via a dielectric film. 
     In the acoustic wave devices  1 ,  1   a,    1   b,    1   c,    1   d,    1   e,  the multilayer board  2  or multilayer board  2   b  may include a film interposed between the low acoustic velocity film  23  and the high acoustic velocity support substrate  21 . In the acoustic wave device  1   f,  the multilayer board  2   f  may include at least one of a film interposed between the high acoustic velocity film  22  and the support substrate  20  and a film interposed between the low acoustic velocity film  23  and the piezoelectric body portion  24 . In the acoustic wave devices  1 ,  1   a,    1   b,    1   c,    1   d,    1   e,  the multilayer board  2  or multilayer board  2   b  may include an acoustic impedance layer instead of the low acoustic velocity film  23  between the piezoelectric body portion  24  and the high acoustic velocity support substrate  21 . The acoustic impedance layer significantly reduces or prevents leakage of acoustic waves excited by the interdigital transducer electrode  3  into the high acoustic velocity support substrate  21 . The acoustic impedance layer has a multilayer structure in which at least one high acoustic impedance layer having a relatively high acoustic impedance and at least one low acoustic impedance layer having a relatively low acoustic impedance are laminated in the thickness direction of the high acoustic velocity support substrate  21 . In the above-described multilayer structure, a plurality of the high acoustic impedance layers may be provided, and a plurality of the low acoustic impedance layers may be provided. Accordingly, the above-described multilayer structure is a structure in which the plurality of high acoustic impedance layers and the plurality of low acoustic impedance layers are alternately laminated one by one in the thickness direction of the high acoustic velocity support substrate  21 . 
     The high acoustic impedance layer is preferably made of, for example, platinum, tungsten, aluminum nitride, lithium tantalate, sapphire, lithium niobate, silicon nitride, or zinc oxide. 
     The low acoustic impedance layer is preferably made of, for example, silicon oxide, aluminum, or titanium. 
     The structure including the plurality of interdigital transducer electrodes  3  is not limited to the longitudinally coupled resonator filter and may be, for example, transversely coupled resonator-type filter, a ladder filter, or the like. 
     From the above-described preferred embodiments, and the like, the following features are provided. 
     An acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), an interdigital transducer electrode ( 3 ), and a reflector ( 8 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The interdigital transducer electrode ( 3 ) is provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). The reflector ( 8 ) is provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the second terminal ( 12 ). The interdigital transducer electrode ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The first busbar ( 4 ) is electrically connected to the first terminal ( 11 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in a first direction (D 1 ) and electrically connected to the second terminal ( 12 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). In the interdigital transducer electrode ( 3 ), where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) located at one end in the second direction (D 2 ) is a first end electrode finger and the electrode finger (the second electrode finger  7 R or the second electrode finger  7 L) located at the other end is a second end electrode finger, the first end electrode finger is located between the reflector ( 8 ) and the second end electrode finger in the second direction (D 2 ). The outer busbar portion ( 41 ) of one (first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R), is located on an inner side in the second direction (D 2 ) relative to the center portion ( 70 ), in the first direction (D 1 ), of the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R). 
     With the above-described acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes the two reflectors ( 8 ). The two reflectors ( 8 ) are provided one by one on both sides of the interdigital transducer electrode ( 3 ) in the second direction (D 2 ). The outer busbar portion ( 41 ) of one (first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), is located on an inner side in the second direction (D 2 ) relative to the wide portion ( 72 ) of the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) and the wide portion ( 72 ) of the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L). 
     With the above-described acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), surge breakdown is less likely to occur, and ESD tolerance significantly improves as compared to when the outer busbar portion ( 41 ) of one (first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), overlaps in the first direction (D 1 ) the wide portion ( 72 ) of the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) and the wide portion ( 72 ) of the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L). 
     An acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes the two reflectors ( 8 ). The two reflectors ( 8 ) are provided one by one on both sides of the interdigital transducer electrode ( 3 ) in the second direction (D 2 ). The outer busbar portion ( 41 ) of one (the first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), is located on an inner side in the second direction (D 2 ) relative to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) and the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L) and does not overlap in the first direction (D 1 ) each of the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) and the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L). 
     With the above-described acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved. 
     In an acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention, one side (the side  42 L or the side  42 R), along the first direction (D 1 ), of the inner busbar portion ( 42 ) of one (the first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), and a side (the side  72 LL or the side  72 RR), away from the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), of the wide portion ( 72 ) of the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) are aligned in a straight line or substantially in a straight line. 
     With the above-described acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved by changing only the shape of the outer busbar portion ( 41 ) of one (the first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), without changing the shape of the inner busbar portion ( 42 ) of the busbar (the first busbar  4 ) not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) or the second end electrode finger (the second electrode finger  7 R or the second electrode finger  7 L), so ESD tolerance is further improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), a plurality of interdigital transducer electrodes ( 3 ), and two reflectors ( 8 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The plurality of interdigital transducer electrodes ( 3 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). The two reflectors ( 8 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and reflect acoustic waves excited by the plurality of interdigital transducer electrodes ( 3 ). Each of the plurality of interdigital transducer electrodes ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). The plurality of interdigital transducer electrodes ( 3 ) are provided in the second direction (D 2 ). The two reflectors ( 8 ) each are located across the interdigital transducer electrode ( 3 ) at any one of both sides of the plurality of interdigital transducer electrodes ( 3 ) provided in the second direction (D 2 ) from the interdigital transducer electrode ( 3 ) adjacent to the interdigital transducer electrode ( 3 ) at the any one of both sides. In the interdigital transducer electrode ( 3 ) adjacent to one of the two reflectors ( 8 ) of the plurality of interdigital transducer electrodes ( 3 ), where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger (the first end electrode finger  6 ) located at one end in the second direction (D 2 ) is a first end electrode finger and the electrode finger (the first electrode finger  6 ) located at the other end is a second end electrode finger, the first end electrode finger is located between the one of the two reflectors ( 8 ) and the second end electrode finger in the second direction (D 2 ). In the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), the outer busbar portion ( 51 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ), is located on an inner side in the second direction (D 2 ) relative to a center portion ( 60 ), in the first direction (D 1 ), of the first end electrode finger (the first electrode finger  6 ). 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     In an acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention, in the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), the outer busbar portion (the outer busbar portion  51 ) of one (second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), is located on an inner side in the second direction (D 2 ) relative to the wide portion ( 62 ) of the first end electrode finger (the first electrode finger  6 ) and the wide portion ( 62 ) of the second end electrode finger (the first electrode finger  6 ). 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   e;    1   f;    1   g ), surge breakdown is less likely to occur, and ESD tolerance significantly improves as compared to when, in the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), the outer busbar portion ( 51 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), overlaps in the first direction (D 1 ) the wide portion ( 62 ) of the first end electrode finger (the first electrode finger  6 ) and the wide portion ( 62 ) of the second end electrode finger (the first electrode finger  6 ). 
     In an acoustic wave device ( 1   b;    1   c;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention, in the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), the outer busbar portion ( 51 ) of one (second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), is located on an inner side in the second direction (D 2 ) and does not overlap in the first direction (D 1 ) the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ). 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved. 
     In an acoustic wave device according to a preferred embodiment of the present invention, in the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), a side, closer to the one of the reflectors ( 8 ), of the inner busbar portion (the inner busbar portion  52 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), and a side, closer to the one of the reflectors ( 8 ), of the wide portion ( 62 ) of the first end electrode finger (the first electrode finger  6 ) are aligned in a straight line or substantially in a straight line. 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved by changing only the shape of the outer busbar portion ( 51 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), without changing the shape of the inner busbar portion ( 52 ) of the one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ) or the second end electrode finger (the first electrode finger  6 ), so ESD tolerance is further improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), an interdigital transducer electrode ( 3 ), and a reflector ( 8 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The interdigital transducer electrode ( 3 ) is provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). The reflector ( 8 ) is provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the second terminal ( 12 ). The interdigital transducer electrode ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The first busbar ( 4 ) is electrically connected to the first terminal ( 11 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in a first direction (D 1 ) and electrically connected to the second terminal ( 12 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). In the interdigital transducer electrode ( 3 ), where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger (the second electrode finger  7 L or the second electrode finger  7 R) located at one end in the second direction (D 2 ) is a first end electrode finger and the electrode finger (the second electrode finger  7 R or the second electrode finger  7 L) located at the other end is a second end electrode finger, the first end electrode finger is located between the reflector ( 8 ) and the second end electrode finger in the second direction (D 2 ). The outer busbar portion ( 41 ) of one (first busbar  4 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R), is located on an inner side in the second direction (D 2 ) relative to the inner busbar portion ( 42 ) of the busbar (the first busbar  4 ) not connected to the first end electrode finger (the second electrode finger  7 L or the second electrode finger  7 R). 
     With the above-described acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), a plurality of interdigital transducer electrodes ( 3 ), and two reflectors ( 8 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The plurality of interdigital transducer electrodes ( 3 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). The two reflectors ( 8 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and reflect acoustic waves excited by the plurality of interdigital transducer electrodes ( 3 ). Each of the plurality of interdigital transducer electrodes ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). The plurality of interdigital transducer electrodes ( 3 ) is provided in the second direction (D 2 ). The two reflectors ( 8 ) each are located across the interdigital transducer electrode ( 3 ) at any one of both sides of the plurality of interdigital transducer electrodes ( 3 ) provided in the second direction (D 2 ) from the interdigital transducer electrode ( 3 ) adjacent to the interdigital transducer electrode ( 3 ) at the any one of both sides. In the interdigital transducer electrode ( 3 ) adjacent to one of the two reflectors ( 8 ) of the plurality of interdigital transducer electrodes ( 3 ), where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger (the first end electrode finger  6 ) located at one end in the second direction (D 2 ) is a first end electrode finger and the electrode finger (the first electrode finger  6 ) located at another end is a second end electrode finger, the first end electrode finger (the first electrode finger  6 ) is located between the one of the reflectors ( 8 ) and the second end electrode finger (the first electrode finger  6 ) in the second direction (D 2 ). In the interdigital transducer electrode ( 3 ) adjacent to the one of the reflectors ( 8 ), the outer busbar portion ( 51 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger (the first electrode finger  6 ), is located on an inner side in the second direction (D 2 ) relative to the inner busbar portion ( 52 ) of the busbar (the second busbar) not connected to the first end electrode finger (the first electrode finger  6 ). 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to the tenth aspect, ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), and a plurality of interdigital transducer electrodes ( 3 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The plurality of interdigital transducer electrodes ( 3 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). Each of the plurality of interdigital transducer electrodes ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). Where, of the plurality of interdigital transducer electrodes ( 3 ), one of the adjacent two interdigital transducer electrodes ( 3 ) in the second direction (D 2 ) is a first interdigital transducer electrode ( 3 A) and another one is a second interdigital transducer electrode ( 3 B), a distance between the outer busbar portion ( 51 ) not connected to, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger closest to the second interdigital transducer electrode ( 3 B) in the first interdigital transducer electrode ( 3 A) and the outer busbar portion ( 51 ) not connected to, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger closest to the first interdigital transducer electrode ( 3 A) in the second interdigital transducer electrode ( 3 B) is greater than a distance between a center portion ( 60 ) of the electrode finger (the first electrode finger  6 ) closest to the second interdigital transducer electrode ( 3 B) in the first interdigital transducer electrode ( 3 A) and a center portion ( 60 ) of the electrode finger (the first electrode finger  6 ) closest to the first interdigital transducer electrode ( 3 A) in the second interdigital transducer electrode ( 3 B). 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to the eleventh aspect, ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1   b;    1   c;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 12 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), and a plurality of interdigital transducer electrodes ( 3 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The plurality of interdigital transducer electrodes ( 3 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). Each of the plurality of interdigital transducer electrodes ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). Where, of the plurality of interdigital transducer electrodes ( 3 ), one of the adjacent two interdigital transducer electrodes ( 3 ) in the second direction (D 2 ) is a first interdigital transducer electrode ( 3 A) and another is a second interdigital transducer electrode ( 3 B), and where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) of the first interdigital transducer electrode ( 3 A), the electrode finger (the first end electrode finger  6 ) located at an end closer to the second interdigital transducer electrode ( 3 B) in the second direction (D 2 ) is a first end electrode finger of the first interdigital transducer electrode ( 3 A), the electrode finger (the first electrode finger  6 ) located at an end away from the second interdigital transducer electrode ( 3 B) is a second end electrode finger of the first interdigital transducer electrode ( 3 A), and, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) of the second interdigital transducer electrode ( 3 B), the electrode finger (the first electrode finger  6 ) located at an end closer to the first interdigital transducer electrode ( 3 A) in the second direction (D 2 ) is a first end electrode finger of the second interdigital transducer electrode ( 3 B) and the electrode finger (the first electrode finger  6 ) located at an end away from the first interdigital transducer electrode ( 3 A) is a second end electrode finger of the second interdigital transducer electrode ( 3 B), the first end electrode finger of the first interdigital transducer electrode ( 3 A) is connected to the first terminal ( 11 ), and the first end electrode finger of the second interdigital transducer electrode ( 3 B) is connected to the second terminal ( 12 ). In each of the first interdigital transducer electrode ( 3 A) and the second interdigital transducer electrode ( 3 B), the outer busbar portion ( 51 ) electrically connected to one of the first terminal ( 11 ) and the second terminal ( 12 ), different from the terminal to which the first end electrode finger is connected, is located on an inner side in the second direction (D 2 ) relative to the inner busbar portion ( 52 ) electrically connected to the one of the first terminal ( 11 ) and the second terminal ( 12 ), different from the terminal to which the first end electrode finger is connected. 
     With the above-described acoustic wave device ( 1   b;    1   c;    1   f;    1   g ), ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     An acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention includes a first terminal ( 11 ), a second terminal ( 12 ), a piezoelectric body portion ( 24 ;  24   g ), and a plurality of interdigital transducer electrodes ( 3 ). The second terminal ( 12 ) has a lower potential than the first terminal ( 11 ). The plurality of interdigital transducer electrodes ( 3 ) are provided on or above the piezoelectric body portion ( 24 ;  24   g ) and electrically connected to the first terminal ( 11 ) and the second terminal ( 12 ). Each of the plurality of interdigital transducer electrodes ( 3 ) includes a first busbar ( 4 ), a second busbar ( 5 ), a plurality of first electrode fingers ( 6 ), and a plurality of second electrode fingers ( 7 ). The second busbar ( 5 ) is opposed to the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) are connected to the first busbar ( 4 ) and have a greater width from the first busbar ( 4 ) toward the second busbar ( 5 ) in the first direction (D 1 ). The plurality of second electrode fingers ( 7 ) are connected to the second busbar ( 5 ) and have a greater width from the second busbar ( 5 ) toward the first busbar ( 4 ) in the first direction (D 1 ). The plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) are spaced apart from each other in a second direction (D 2 ) perpendicular or substantially perpendicular to the first direction (D 1 ). At least one electrode finger of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ) having a greater width in the second direction (D 2 ) than a center portion ( 60 ), in the first direction (D 1 ), of the at least one electrode finger. At least one electrode finger of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ) having a greater width in the second direction (D 2 ) than a center portion ( 70 ), in the first direction (D 1 ), of the at least one electrode finger. Each of the first busbar ( 4 ) and the second busbar ( 5 ) includes an opening portion ( 40 ,  50 ), an inner busbar portion ( 42 ,  52 ), an outer busbar portion ( 41 ,  51 ), and a coupling portion ( 43 ,  53 ). The inner busbar portion ( 42 ,  52 ) is located closer to the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ) than the opening portion ( 40 ,  50 ) in the first direction (D 1 ). The outer busbar portion ( 41 ,  51 ) is located across the opening portion ( 40 ,  50 ) from the inner busbar portion ( 42 ,  52 ) in the first direction (D 1 ). The coupling portion ( 43 ,  53 ) couples the inner busbar portion ( 42 ,  52 ) and the outer busbar portion ( 41 ,  51 ) in the first direction (D 1 ). In at least one of the plurality of interdigital transducer electrodes ( 3 ), where, of a group of electrode fingers including the plurality of first electrode fingers ( 6 ) and the plurality of second electrode fingers ( 7 ), the electrode finger (the first electrode finger  6 ) located at one end in the second direction (D 2 ) is a first end electrode finger and the electrode finger (the first electrode finger  6 ) located at another end is a second end electrode finger, the first end electrode finger is located closer to the interdigital transducer electrode ( 3 ) adjacent to the at least one interdigital transducer electrode ( 3 ) in the second direction (D 2 ). In the at least one interdigital transducer electrode ( 3 ), the outer busbar portion ( 51 ) of one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger, is located on an inner side in the second direction (D 2 ) relative to the inner busbar portion ( 52 ) of the one (the second busbar  5 ) of the first busbar ( 4 ) and the second busbar ( 5 ), not connected to the first end electrode finger, at least at a side closer to the adjacent interdigital transducer electrode ( 3 ). 
     With the above described acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ), ESD tolerance is significantly improved while interference with a piston mode is significantly reduced or prevented. 
     In an acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention, the plurality of interdigital transducer electrodes ( 3 ) are provided in the second direction (D 2 ), and the acoustic wave device further includes two reflectors ( 8 ). The two reflectors ( 8 ) each are provided across the interdigital transducer electrode ( 3 ) at any one of both sides of the plurality of interdigital transducer electrodes ( 3 ) provided in the second direction (D 2 ) one by one on or above the piezoelectric body portion ( 24 ) from the interdigital transducer electrode ( 3 ) adjacent to the interdigital transducer electrode ( 3 ) at the any one of both sides. The two reflectors ( 8 ) are reflect acoustic waves excited by the plurality of interdigital transducer electrodes ( 3 ). 
     The above-described acoustic wave device ( 1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) is able to provide a longitudinally coupled resonator filter. 
     In an acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f ) according to a preferred embodiment of the present invention, a distal end portion ( 61 ) of at least one of the plurality of first electrode fingers ( 6 ) includes a wide portion ( 62 ), and a distal end portion ( 71 ) of at least one of the plurality of second electrode fingers ( 7 ) includes a wide portion ( 72 ). 
     In an acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) according to a preferred embodiment of the present invention, the acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ) includes a plurality of regions (A 1  to A 11 ) different from each other in the first direction (D 1 ) in plan view taken in a thickness direction of the acoustic wave device ( 1 ;  1   a;    1   b;    1   c;    1   d;    1   e;    1   f;    1   g ). The plurality of regions (A 1  to A 11 ) include a center region (the region A 6 ), two outer busbar regions (the regions A 1 , A 11 ), two inner busbar regions (the regions A 3 , A 9 ), two coupling regions (the regions A 2 , A 10 ), two gap regions (the regions A 4 , A 8 ), and two wide regions (A 7 , A 5 ). The center region (the region A 6 ) is located in a center in the first direction (D 1 ) and includes center portions ( 60 ) of the plurality of first electrode fingers ( 6 ) and center portions ( 70 ) of the plurality of second electrode fingers ( 7 ). The two outer busbar regions (the regions A 1 , A 11 ) respectively include the outer busbar portion ( 41 ) of the first busbar ( 4 ) and the outer busbar portion ( 51 ) of the second busbar ( 5 ). The two inner busbar regions (the regions A 3 , A 9 ) respectively include the inner busbar portion ( 42 ) of the first busbar ( 4 ) and the inner busbar portion ( 52 ) of the second busbar ( 5 ). The two coupling regions (the regions A 2 , A 10 ) respectively include the coupling portion ( 43 ) and opening portion ( 40 ) of the first busbar ( 4 ) and the coupling portion ( 53 ) and opening portion ( 50 ) of the second busbar ( 5 ). The two gap regions (the regions A 4 , A 8 ) respectively include a gap ( 31 ) between the plurality of first electrode fingers ( 6 ) and the second busbar ( 5 ) and a gap ( 32 ) between the plurality of second electrode fingers ( 7 ) and the first busbar ( 4 ). The two wide regions (A 7 , A 5 ) respectively include the wide portion ( 62 ) of at least one electrode finger (the first electrode finger  6 ) of the plurality of first electrode fingers ( 6 ) and the wide portion ( 72 ) of at least one electrode finger (the second electrode finger  7 ) of the plurality of second electrode fingers ( 7 ). An acoustic velocity of acoustic waves in the two outer busbar regions (the regions A 1 , A 11 ) is lower than the acoustic velocity in the center region (the region A 6 ). An acoustic velocity of acoustic waves in the two inner busbar regions (the regions A 3 , A 9 ) is lower than the acoustic velocity in the center region (the region A 6 ). An acoustic velocity of acoustic waves in the two coupling regions (the regions A 2 , A 10 ) is higher than the acoustic velocity in the two outer busbar regions (the regions A 1 , A 11 ) or the acoustic velocity in the center region (the region A 6 ). An acoustic velocity of acoustic waves in the two gap regions (the regions A 4 , A 8 ) is higher than the acoustic velocity in the two inner busbar regions (the regions A 3 , A 9 ) or the acoustic velocity in the center region (the region A 6 ). An acoustic velocity of acoustic waves in the two wide regions (A 7 , A 5 ) is lower than the acoustic velocity in the center region (the region A 6 ).