Patent Publication Number: US-2022212230-A1

Title: Vibration device and electronic apparatus

Description:
TECHNICAL FIELD 
     The present disclosure relates to a vibration device and an electronic apparatus. 
     BACKGROUND ART 
     Known vibration devices include vibration plates and piezoelectric elements disposed on the vibration plates (for example, Patent Literature 1). Patent Literature 1 discloses a piezoelectric device including a disk and a sheet of piezoelectric material disposed on the disk. The piezoelectric device functions as a touch sensor, and detects pressing by a user&#39;s finger by bending vibration of the sheet of piezoelectric material. The piezoelectric device also functions as a tactile feedback element to impart a bending vibration to the sheet of piezoelectric material, thereby imparting a tactile vibration to the user&#39;s finger. 
     CITATION LIST 
     Patent Literature 
     
         
         Patent Literature 1: WO2013/167683 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     In the vibration device as described above, a wiring member may be disposed on the piezoelectric element, the wiring member may be electrically connected to an upper electrode of the piezoelectric element, and the wiring member may be electrically connected to a lower electrode of the piezoelectric element through the vibration plate. In this case, since there is a height difference between the vibration plate and the upper electrode, each of which is connected to the wiring member, the electrical connection of the wiring member may not be stable. 
     The present disclosure provides a vibration device and an electronic apparatus capable of stabilizing an electrical connection of a wiring member. 
     Solution to Problem 
     A vibration device according to an aspect of the present disclosure includes a vibration plate, a piezoelectric element, and a wiring member. The vibration plate has conductivity. The piezoelectric element is disposed on the vibration plate. The wiring member is disposed to oppose the vibration plate via the piezoelectric element. The piezoelectric element includes a piezoelectric element body, a first external electrode, and a second external electrode. The piezoelectric element body has a first main surface and a second main surface facing away from each other in an opposing direction of the vibration plate and the wiring member. The first external electrode is disposed on the first main surface and electrically connected to the vibration plate. The second external electrode is disposed on the second main surface and electrically connected to the wiring member. The vibration plate includes a first projection projecting toward the wiring member and electrically connected to the wiring member. 
     In the vibration device, the vibration plate includes a first projection, and the first projection projects toward the wiring member and is electrically connected to the wiring member. Therefore, a height difference between the vibration plate and the second external electrode of the piezoelectric element can be reduced as compared with the case where the vibration plate does not include the first projection. Therefore, the electrical connection of the wiring member can be stabilized. 
     The vibration plate may include a second projection projecting toward the wiring member to support the wiring member. In this case, the wiring member is supported by the second projection and stabilizes its posture. Therefore, the electrical connection of the wiring member can be further stabilized. 
     The vibration plate may have a third main surface opposing the piezoelectric element. The third main surface may include an opposing region opposing the piezoelectric element. A height of the first projection may be equal to a height of the second external electrode when a virtual plane including the opposing region is set as a reference surface. In this case, the electrical connection of the wiring member can be further stabilized. 
     A tip portion of the first projection may be a curved surface that is convex toward the wiring member. In this case, the connection strength between the first projection and the wiring member may be improved compared to a case where the tip portion of the first projection is pointed. 
     The wiring member may be adhered to the first projection by an adhesive. The adhesive may cover a side surface of the first projection. In this case, a connection between the first projection and the wiring member may be reinforced by the adhesive. 
     The first projection may be formed by bending the vibration plate. In this case, it is possible to suppress an increase in electrical resistance compared to a case where a separate member is attached to the vibration plate to configure the first projection. 
     A length of the first projection may be shorter than a distance between the first projection and the piezoelectric element when viewed from the opposing direction. In this case, a short circuit between the first projection and the piezoelectric element can be suppressed. 
     An electronic apparatus according to an aspect of the present disclosure includes the vibration device. 
     Since the electronic apparatus includes the vibration device, the electrical connection of the wiring member can be stabilized. 
     Advantageous Effects of Invention 
     According to an aspect of the present disclosure, a vibration device and an electronic apparatus capable of stabilizing electrical connection of a wiring member are provided. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a top view showing a vibration device according to a first embodiment. 
         FIG. 2  is a perspective view showing the piezoelectric element and the vibration plate in  FIG. 1 . 
         FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 . 
         FIG. 4  is a top view showing a vibration device according to a second embodiment. 
         FIG. 5( a )  is a cross-sectional view showing the vibration device according to a third embodiment.  FIG. 5( b )  is a cross-sectional view showing a vibration device according to a comparative example. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. In the description, the same reference numerals are used for the same elements or elements having the same functions with redundant description omitted. 
     First Embodiment 
       FIG. 1  is a top view showing a vibration device according to a first embodiment.  FIG. 2  is a perspective view showing the piezoelectric element and the vibration plate in  FIG. 1 .  FIG. 3  is a cross-sectional view taken along line III-III in  FIG. 1 . As shown in  FIGS. 1 to 3 , the vibration device  1  according to the first embodiment includes a vibration plate  10 , a piezoelectric element  20 , and a wiring member  30 . The piezoelectric element  20  is disposed on the vibration plate  10 . The wiring member  30  is disposed to oppose the vibration plate  10  via the piezoelectric element  20 . The piezoelectric element  20  is disposed between the vibration plate  10  and the wiring member  30 . Hereinafter, an opposing direction between the vibration plate  10  and the wiring member  30  is referred to as a first direction D 1 . 
     The vibration plate  10  is a plate member for amplifying the vibration of the piezoelectric element  20 . The vibration plate  10  has conductivity. The vibration plate  10  is made of, for example, metal. The vibration plate  10  is made of, for example, a Ni—Fe alloy, Ni, brass, or stainless steel. 
     The vibration plate  10  has main surfaces  10   a  and  10   b  facing away from each other. An opposing direction of the main surfaces  10   a  and  10   b  coincides with the first direction D 1 . The first direction D 1  is also a direction orthogonal to the main surfaces  10   a  and  10   b . The thickness of the vibration plate  10  (the length of the vibration plate  10  in the first direction D 1 ) is, for example, 50 μm or more and 300 μm or less. In the embodiment, the thickness of the vibration plate  10  is, for example, 120 μm. 
     The shape and area of the main surface  10   a  are substantially the same as those of the main surface  10   b . When viewed from the first direction D 1 , the outer edge of main surface  10   a  substantially coincides with the outer edge of main surface  10   b . The main surfaces  10   a  and  10   b  have, for example, a circular shape. In the embodiment, the main surfaces  10   a  and  10   b  have a perfect circular shape. The diameters of the main surfaces  10   a  and  10   b  are, for example, 8 mm or more and 30 mm or less. In the embodiment, the diameters of the main surfaces  10   a  and  10   b  are, for example, 15 mm. 
     The main surface  10   a  opposes the piezoelectric element  20  in the first direction D 1 . The main surface  10   a  has an opposing region R opposing the piezoelectric element  20  in the first direction D 1 . The opposing region R is a region overlapping the piezoelectric element  20  when viewed from the first direction D 1 . When viewed from the first direction D 1 , the outer edge of the opposing region R coincides with the outer edge of the piezoelectric element  20 . In the embodiment, the opposing region R has a circular shape. 
     The vibration plate  10  includes a projection  11  projecting toward the wiring member  30 . The projection  11  is a portion projecting toward the wiring member  30  from a reference surface described later. The projection  11  has, for example, a conical shape. The projection  11  is tapered toward a tip portion  11   a  of the projection  11 . The projection  11  has, for example, a circular shape when viewed from the first direction D 1 . In the embodiment, the projection  11  has a perfect circular shape when viewed from the first direction D 1 . The length L 1  of the projection  11  when viewed from the first direction D 1  is, for example, 0.05 mm or more and 0.25 mm or less. In the embodiment, the length L 1  is a diameter of the projection  11  when viewed from the first direction D 1 , and is, for example, 0.12 mm. 
     The projection  11  is provided apart from the piezoelectric element  20  when viewed from the first direction D 1 . When viewed from the first direction D 1 , the distance (shortest distance) L 2  between the outer edge of the projection  11  and the piezoelectric element  20  is, for example, 1 mm or more and 2 mm or less. In the embodiment, the distance L 2  is, for example, 1.5 mm. When viewed from the first direction D 1 , the length L 1  of the projection  11  is shorter than the distance L 2 . When viewed from the first direction D 1 , a distance (shortest distance) L 3  between the projection  11  and the outer edge of the main surface  10   a  of the vibration plate  10  is, for example, not less than 0.1 mm and not more than 1 mm. In the embodiment, the distance L 3  is, for example, 0.4 mm. 
     When viewed from the first direction D 1 , the projection  11  may have a shape other than a circular shape. In this case, the length L 1  may be defined as a length in which a straight line connecting the outer edge of the projection  11  and the piezoelectric element  20  at the shortest distance overlaps the projection  11  when viewed from the first direction D 1 . The length L 1  may be defined as a maximum length of a straight line connecting two points on the outer edge of the projection  11  when viewed from the first direction D 1 . 
     When a virtual plane including the opposing region R is set as a reference surface, a height H 1  of the projection  11  (the distance of the projection  11  in the first direction D 1 ) is, for example, 50 μm or more and 250 μm or less. In the embodiment, the height H 1  is, for example, 140 μm. 
     The surface of the projection  11  is constituted by a part of the main surface  10   a . The tip portion  11   a  is a curved surface that is convex toward the wiring member  30 . In the embodiment, the projection  11  is formed by bending the vibration plate  10 . That is, in the projection  11 , the main surfaces  10   a  and  10   b  are curved while being kept substantially parallel to each other. In projection  11 , it can be said that main surface  10   a  projects and main surface  10   b  is recessed. The projection  11  is formed by embossing the vibration plate  10 , for example. Specifically, the projection  11  is formed by pressing the vibration plate  10  from the main surface  10   b  side with a punch to plastically deform the vibration plate  10 . 
     The piezoelectric element  20  includes a piezoelectric element body  21 , an external electrode  22 , and an external electrode  23 . The piezoelectric element body  21  has a plate shape. The piezoelectric element body  21  has, for example, main surfaces  21   a  and  21   b  and a side surface  21   c . The main surfaces  21   a  and  21   b  face away from each other. The opposing direction of the main surfaces  21   a  and  21   b  coincides with the first direction D 1 . The first direction D 1  is also a direction orthogonal to the main surfaces  21   a  and  21   b.    
     Main surface  21   a  opposes main surface  10   a  in first direction D 1 . The main surface  21   b  opposes the wiring member  30  in the first direction D 1 . The side surface  21   c  extends in first direction D 1  in such a way as to connect main surface  21   a  and main surface  21   b . The main surfaces  21   a  and  21   b  and the side surface  21   c  are indirectly adjacent to each other via ridge portions. The thickness of the piezoelectric element body  21  (the length of the piezoelectric element body  21  in the first direction D 1 ) is, for example, 40 μm or more and 300 μm or less. In the embodiment, the thickness of the piezoelectric element body  21  is, for example, 140 μm. 
     The shape and area of the main surface  21   a  are substantially the same as those of the main surface  21   b . When viewed from the first direction D 1 , the outer edge of main surface  21   a  substantially coincides with the outer edge of main surface  21   b . The main surfaces  21   a  and  21   b  have, for example, circular shapes. In the embodiment, the main surfaces  21   a  and  21   b  have perfect circular shapes. The diameters of the main surfaces  21   a  and  21   b  are, for example, 5 mm or more and 20 mm or less. In the embodiment, the diameters of the main surfaces  21   a  and  21   b  are, for example, 10 mm. 
     The piezoelectric element body  21  is made of a piezoelectric material. In the embodiment, the piezoelectric element body  21  is made of a piezoelectric ceramic material. The piezoelectric ceramic material may be, for example, PZT [Pb (Zr, Ti) O3], PT (PbTiO 3 ), PLZT [(Pb, La) (Zr, Ti)O 3 ] or barium titanate (BaTiO 3 ). The piezoelectric element body  21  is formed of, for example, a sintered body of a ceramic green sheet containing the above-described piezoelectric ceramic material. 
     The external electrode  22  is disposed on the main surface  21   a . The external electrode  23  is disposed on the main surface  21   b . In the embodiment, the external electrode  22  covers the entire main surface  21   a . The external electrode  23  covers the entire main surface  21   b . The external electrodes  22  and  23  have circular shapes when viewed from the first direction D 1 . In the embodiment, the external electrodes  22  and  23  have perfect circular shapes. 
     The external electrodes  22  and  23  are made of conductive material. As the conductive material, for example, Ag, Pd, or an Ag—Pd alloy is used. The external electrodes  22  and  23  are formed as sintered bodies of a conductive paste containing the conductive material. In the embodiment, the piezoelectric element  20  does not include internal electrodes disposed inside the piezoelectric element body  21 . 
     The thicknesses of the external electrodes  22  and  23  (the lengths of the external electrodes  22  and  23  in the first direction D 1 ) are, for example, 3 μm or more and 20 μm or less. In the embodiment, the thicknesses of the external electrodes  22  and  23  are, for example, 7 μm, which are equivalent to each other. When a virtual plane including the opposing region R of the vibration plate  10  is defined as a reference plane, the height H 2  of the external electrode  23  (a surface of the external electrode  23  close to the wiring member  30 ) is equal to the height H 1  of the projection  11 . 
     The piezoelectric element  20  is adhered to the vibration plate  10 . The piezoelectric element  20  and the vibration plate  10  are connected via an adhesive  41 . The piezoelectric element  20  is connected to the vibration plate  10  so that the external electrode  22  opposes the main surface  10   a  of the vibration plate  10 . That is, the external electrode  22  and the main surface  10   a  of the vibration plate  10  oppose each other via the adhesive  41 . 
     The adhesive  41  is made of a conductive resin. Therefore, the external electrode  22  is electrically connected to the vibration plate  10  through the adhesive  41 . The conductive resin includes a resin (for example, thermosetting resin) and a conductive material (for example, metal powder). As the metal powder, for example, Ag powder is used. As the thermosetting resin, for example, a phenol resin, an acrylic resin, a silicone resin, an epoxy resin, or a polyimide resin is used. 
     The piezoelectric element  20  is located substantially at the center of the main surface  10   a  when viewed from the first direction D 1 . The substantial center of the main surface  10   a  includes not only the center position of the main surface  10   a  but also positions away from the center position of the main surface  10   a  due to manufacturing errors or tolerances. The substantial center of the main surface  10   a  also includes positions away from the center of the main surface  10   a  by a predetermined minute length. The predetermined length is, for example, 8% of the radius of the main surface  10   a.    
     When viewed from the first direction D 1 , the area of the piezoelectric element  20  is smaller than the area of the vibration plate  10 . When viewed from the first direction D 1 , the outer edge of the piezoelectric element  20  is located inside the outer edge of the vibration plate  10 . When viewed from the first direction D 1 , the distance (minimum distance) between the outer edge of the piezoelectric element  20  and the outer edge of the vibration plate  10  is, for example, 1 mm or more and 5 mm or less. 
     The wiring member  30  includes a base  31 , a conductive layer  32 , and a conductive layer  33 . The base  31  has, for example, a band shape and extends in a direction intersecting the first direction D 1 . Hereinafter, the direction in which the base  31  extends is referred to as a second direction D 2 . The base  31  has main surfaces  31   a  and  31   b  facing away from each other. The opposing direction of the main surfaces  31   a  and  31   b  coincides with the first direction D 1 . The wiring member  30  is disposed such that the main surface  31   b  opposes the vibration plate  10  and the piezoelectric element  20 . The base  31  is electrically insulating. The base  31  is, for example, a resin layer made of resin such as polyimide resin. 
     The thickness of the base  31  is, for example, 100 μm. The width of the base  31  (the length of the base  31  in a direction orthogonal to the first direction D 1  and the second direction D 2 ), for example, in the portions where the one end portions  32   a  and  33   a  of the conductive layers  32  and  33  and are provided is greater than those in the other portions. The maximum width of the base  31  is shorter than the diameter of the piezoelectric element  20  (the diameters of the main surfaces  21   a  and  21   b ). 
     Therefore, when viewed from the first direction D 1 , a portion of the piezoelectric element  20  and a portion of the vibration plate  10  are exposed from the wiring member  30 . The width of the base  31  is, for example, 10 mm or more and 35 mm or less. In the embodiment, the maximum value of the width of the base  31  is, for example, 20 mm, and the minimum value is, for example, 10 mm. 
     The conductive layers  32  and  33  are disposed on the main surface  31   b  of the base  31 . The conductive layers  32  and  33  are adhered to main surface  31   b  by an adhesive layer (not shown). The conductive layers  32  and  33  are made of, for example, Cu. The conductive layers  32  and  33  may have a configuration in which a Ni plating layer and an Au plating layer are provided in this order on a Cu layer, for example. The thicknesses of the conductive layers  32  and  33  are, for example, 20 μm. As long as the base  31  has the main surface  31   b  on which the conductive layers  32  and  33  are disposed, the shape thereof is not limited to the band shape. 
     The conductive layers  32  and  33  extend along the second direction D 2 . The one end portion  32   a  of the conductive layer  32  and the one end portion  33   a  of the conductive layer  33  are separated from each other in the second direction D 2 . The one end portions  32   a  and  33   a  have, for example, circular shapes when viewed from the first direction D 1 . The base  31  is formed in a circular shape along the outer edges of the one end portions  32   a  and  33   a  at the portions where the one end portions  32   a  and  33   a  are disposed. The other end (not shown) of the conductive layer  32  and the other end (not shown) of the conductive layer  33  are connected to a control unit (not shown) described later. 
     The one end portion  32   a  is disposed on the projection  11  of the vibration plate  10 . The one end portion  32   a  overlaps the entire projection  11  when viewed from the first direction D 1 . The one end portion  32   a  is adhered to the tip portion  11   a  of the projection  11  by an adhesive  42 . The one end portion  32   a  and the tip portion  11   a  are connected via the adhesive  42 . The wiring member  30  is connected to the vibration plate  10  such that one end portion  32   a  opposes the tip portion  11   a . That is, the one end portion  32   a  and the tip portion  11   a  oppose each other via the adhesive  42 . The adhesive  42  entirely covers the side surface  11   b  of the projection  11 . As indicated by gray hatching in  FIG. 1 , the adhesive  42  is disposed in a region where the one end portion  32   a  and the vibration plate  10  overlap each other when viewed from the first direction D 1  in the one end portion  32   a  and the vibration plate  10 . 
     The one end portion  33   a  of the conductive layer  33  is disposed on the external electrode  23 . The one end portion  33   a  overlaps substantially the center of the external electrode  23  when viewed from the first direction D 1 . The substantial center of the external electrode  23  includes not only the center position of the external electrode  23  but also positions away from the center position of the external electrode  23  due to manufacturing errors or tolerances. The substantial center of the external electrode  23  also includes a position away from the center of the external electrode  23  by a predetermined minute length. The predetermined length is, for example, 8% of the radius of the external electrode  23 . The one end portion  33   a  is adhered to the external electrode  23 . The one end portion  33   a  and the external electrode  23  are connected via an adhesive  43  (see  FIG. 5 ). That is, the one end portion  33   a  and the external electrode  23  oppose each other via the adhesive  43 . As shown by gray hatching in  FIG. 1 , the adhesive  43  is disposed between the entire one end portion  33   a  and the vibration plate  10 . 
     The adhesives  42  and  43  are made of conductive resin. Accordingly, the projection  11  is electrically connected to the conductive layer  32  of the wiring member  30  through the adhesive  42 . As described above, since the external electrode  22  is electrically connected to the vibration plate  10  through the adhesive  41 , the external electrode  22  is electrically connected to the conductive layer  32  of the wiring member  30  through the adhesive  41 ,  42 . The external electrode  23  is electrically connected to the conductive layer  33  of the wiring member  30  through the adhesive  43 . The adhesives  42  and  43  may be made of, for example, the same material as the adhesive  41  or may be made of different material. 
     The control unit is electrically connected to the piezoelectric element  20  by the wiring member  30 , and generally controls the vibration device  1 . The control unit includes, for example, a CPU (central processing unit), a ROM (read only memory), and a RAM (random access memory). In this case, the control unit loads a program stored in the ROM into the RAM and executes the program by the CPU to perform various processes. 
     For example, the vibration device  1  is used in such a manner that the outer edge portion of the vibration plate  10  is supported by a supporter and the piezoelectric element  20  can bend together with the vibration plate  10 . For example, a touch panel may be disposed on the wiring member  30 . When the fingertip of the user using the vibration device  1  contacts the touch panel and the piezoelectric element  20  is bent, the piezoelectric element  20  provides a detection signal to the controller. Upon receiving the detection signal, the control unit supplies a drive signal to the piezoelectric element  20  to drive the piezoelectric element  20 . The piezoelectric element  20  vibrates based on the drive signal. 
     Specifically, the controller applies AC voltages having different polarities to the external electrodes  22  and  23  through the conductive layers  32  and  33  of the wiring member  30  as the driving signal. As a result, an electric field is generated between the external electrode  22  and the external electrode  23 . A region sandwiched between the external electrode  22  and the external electrode  23  in the piezoelectric element body  21  becomes an active region, and displacement occurs in the active region. The piezoelectric element  20  repeats expansion and contraction according to the frequency of the AC voltage. 
     Since the vibration plate  10  and the piezoelectric element  20  are bonded to each other, the vibration plate  10  performs bending vibration integrally with the piezoelectric element  20  in response to repeated expansion and contraction of the piezoelectric element  20 . As a result, it is possible to provide a tactile sensation to the user. The tactile sensation is, for example, a click sensation. The click sensation is, for example, a pressing sensation or a touch sensation obtained when the push button switch is pressed. In the vibration device  1 , since the vibration from the piezoelectric element  20  and the vibration from the vibration plate  10  are transmitted to the wiring member  30  in such a way as to be shifted from each other, the vibration has a wide range. 
     As described above, in the vibration device  1 , the vibration plate  10  includes the projection  11 , and the projection  11  projects toward the wiring member  30  and is electrically connected to the wiring member  30 . Therefore, the height difference between the vibration plate  10  and the external electrode  23  can be reduced as compared with the case where the vibration plate  10  does not include the projection  11 . Therefore, the electrical connection of the wiring member  30  can be stabilized. In the vibration device  1 , the height H 1  of the projection  11  is equal to the height H 2  of the external electrode  23  when a virtual plane including the opposing region R is set as a reference surface. Therefore, the electrical connection of the wiring member  30  can be further stabilized. 
     The tip portion  11   a  of the projection  11  is a curved surface that is convex toward the wiring member  30 . Therefore, for example, the connection strength between the wiring member  30  and the vibration plate  10  can be improved compared to a case where the tip portion  11   a  of the projection  11  is pointed. 
     The wiring member  30  is adhered to the projection  11  by an adhesive  42 , and the adhesive  42  covers the side surface  11   b  of the projection  11 . Therefore, the connection between the projection  11  and the wiring member  30  can be reinforced by the adhesive  42 . 
     The projection  11  is formed by bending the vibration plate  10 . That is, since the vibration plate  10  and the projection  11  are formed of one member, it is possible to suppress an increase in electric resistance as compared with a case where another member other than the vibration plate is attached to the vibration plate to configure the projection. In addition, the projection  11  is not easily detached from the vibration plate  10 . That is, a reliability defect (e.g., separation) due to another member can be suppressed. 
     When viewed from the first direction D 1 , the length L 1  of the projection  11  is shorter than the distance L 2  between the projection  11  and the piezoelectric element  20 . Since the distance L 2  is long, a short circuit between the projection  11  and the piezoelectric element  20  can be suppressed. 
     Since the projection  11  exists, the vibration is transmitted to the user&#39;s finger not only from the piezoelectric element  20  but also from the projection  11 . Therefore, the tactile sensation can be stably provided to the user. 
     Second Embodiment 
       FIG. 4  is a top view showing a vibration device according to a second embodiment. As shown in  FIGS. 1 and 4 , the vibration device  1 A according to the second embodiment is different from the vibration device  1  in that a vibration plate  10 A and a wiring member  30 A are provided instead of the vibration plate  10  and the wiring member  30 . 
     The vibration plate  10 A is different from the vibration plate  10  in that it further includes projections  12  and  13 . The projections  12  and  13  project toward the wiring member  30 A and support the wiring member  30 . The projections  12  and  13  are disposed apart from the conductive layers  32  and  33  of the wiring member  30  and are connected to the base  31 . The projections  12  and  13  may or may not be adhered to the base  31  by an adhesive (not shown). As the adhesive in this case, a resin not containing a conductive material can be used. 
     The projections  12  and  13  have, for example, the same shapes as the projection  11 . The heights of the projections  12  and  13  are, for example, equal to the height H 1  of the projection  11  when a virtual plane including the opposing region R of the vibration plate  10  is set as a reference surface. The heights of the projections  12  and  13  may be higher than the height H 1  of the projection  11  by the thicknesses of the conductive layers  32  and  33 , for example. The projections  11 ,  12  and  13  are separated from each other. The projections  11 ,  12  and  13  are, for example, arranged at equal intervals around the piezoelectric element  20  so as to surround the piezoelectric element  20  when viewed from the first direction D 1 . 
     The wiring member  30 A is different from the wiring member  30  in that the width of the base  31  is greater than the diameter of the vibration plate  10  (the diameter of the main surface  10   a ). When viewed from the first direction D 1 , the piezoelectric element  20  and the vibration plate  10 A are disposed so as not to be exposed from the wiring member  30 A. In the embodiment, the base  31  has a constant width. 
     Also in the vibration device  1 A, since the vibration plate  10 A includes the projection  11 , the same effect as that of the vibration device  1  can be obtained. In the vibration device  1 A, the vibration plate  10 A further includes projections  12  and  13 , and the projections  12  and  13  support the wiring member  30 A. Therefore, the posture of the wiring member  30 A is stabilized. If the posture of the wiring member  30 A is inclined, the distance between the projection  11  and the wiring member  30 A is increased, and the electrical connection of the wiring member  30 A may not be stable. In contrast, in the vibration device  1 A, since the wiring member  30 A is supported by the projections  12  and  13  and stabilizes its posture, the electrical connection of the wiring member  30 A can be further stabilized. 
     Third Embodiment 
       FIG. 5( a )  is a cross-sectional view showing the vibration device according to a third embodiment, and  FIG. 5( b )  is a cross-sectional view showing a vibration device according to a comparative example. As shown in  FIG. 5( a ) , the vibration device  1 B according to the third embodiment is different from the vibration device  1  (see  FIG. 1 ) in that a plurality of vibration plates  10  and a plurality of piezoelectric elements  20  are provided and a wiring member  30 B is provided instead of the wiring member  30 . 
     The wiring member  30 B includes a plurality of conductive layers  32  and a plurality of conductive layers  33 . The plurality of conductive layers  32  and the plurality of conductive layers  33  are disposed on the main surface  31   b  of the single base  31 . In the vibration device  1 B, each piezoelectric element  20  is disposed on each vibration plate  10 . Each set of the vibration plate  10  and the piezoelectric element  20  is connected to the corresponding conductive layers  32  and  33 . A plurality of sets of the vibration plate  10  and the piezoelectric element  20  are arranged apart from each other. 
     As shown in  FIG. 5( a )  and  FIG. 5( b ) , a vibration device  100  according to the comparative example is different from the vibration device  1 B in that a plurality of vibration plates  110  are provided instead of the plurality of vibration plates  10 . The vibration plate  110  does not include the projection  11 . Therefore, there is a height difference between the vibration plate  110  and the external electrode  23 , each of which is connected to the wiring member  30 B. The amount of the adhesive  42  connecting the vibration plate  110  and the conductive layer  32  of the wiring member  30  needs to be appropriately set according to the height difference. If the amount of adhesive  42  varies, the posture of the wiring member  30 B may be inclined as shown in  FIG. 5( b ) . Accordingly, the connection between the vibration plate  110  and the wiring member  30 B is more likely to be unstable. In addition, when the user&#39;s finger presses the touch panel, it is difficult to uniformly apply the pressing force to each piezoelectric element  20 . 
     In contrast, in the vibration device  1 B, since each vibration plate  10  includes the projection  11 , the height difference between each vibration plate  10  and the external electrode  23  of each piezoelectric element  20  can be reduced. Therefore, the variation in the amount of the adhesive  42  hardly affects the posture of the wiring member  30 B. Therefore, the electrical connection between the wiring member  30 B and each vibration plate  10  can be stabilized. In addition, when the user&#39;s finger presses the touch panel, the pressing force is likely to be uniformly applied to each piezoelectric element  20 . Further, the tactile sensation provided to the user is stabilized. 
     The present invention is not necessarily limited to the above-described embodiments and modifications, and can be variously changed without departing from the scope of the invention. 
     For example, in the projections  11 ,  12  and  13 , the main surfaces  10   a  of the vibration plates  10  and  10 A may protrude and the main surfaces  10   b  may be flat surfaces. The projections  11 ,  12  and  13  may be formed by attaching another member other than the vibration plates  10  and  10 A to the vibration plates  10  and  10 A. The vibration plates  10  and  10 A may include one of the projections  12  and  13 , and may further include a projection for supporting the wiring member  30  in addition to the projections  12  and  13 . The projections  11 ,  12  and  13  may have not only conical shapes but also triangular pyramid shapes, pyramid shapes, or pillar shapes. 
     When viewed from the first direction D 1 , the vibration plates  10  and  10 A may have not only circular shapes but also rectangular shapes, for example. When viewed from the first direction D 1 , the piezoelectric element  20  may have not only a circular shape but also a rectangular shape, for example. The vibration device  1 B may include a vibration plate  10 A. In the vibration devices  1  and  1 A, the piezoelectric element  20  may be in a bent state in which the main surface  21   a  is on the outside of the curve and the main surface  21   b  is on the inside of the curve. In this case, the displacement amount of the piezoelectric element  20  can be increased (obtained) by the bending amount. At this time, since the vibration plates  10  and  10 A is bent in such a way that the main surface  10   b  is on the outer side of the curve and the main surface  10   a  is on the inside of the curve in correspondence with the piezoelectric element  20 , the wiring members  30  and  30 A and the projection  11  can be easily connected even when the height H 1  is lower than the height H 2 . 
     REFERENCE SIGNS LIST 
     
         
           1 ,  1 A,  1 B: vibration device,  10 ,  10 A: vibration plate,  10   a : main surface (third main surface),  11 : projection (first projection),  11   a : tip portion,  11   b : side surface,  12 ,  13 : projection (second projection),  20 : piezoelectric element,  21 : piezoelectric element body,  21   a : main surface (first main surface),  21   b : main surface (second main surface),  22 : external electrode (first external electrode),  23 : external electrode (second external electrode),  30 ,  30 A,  30 B: wiring member,  42 : adhesive, D 1 : first direction (opposing direction), R: opposing region.