Vibration Device

Abstract

To provide a vibration device capable of suppressing the unnecessary vibration generation in a diaphragm.SOLUTION: A vibration device 1 comprises: a piezoelectric element 3 having an element 11 having main surfaces 11a and 11b which face each other, electrode layers 21, 22, 23, and 24 arranged in the element 11, and external electrodes 13 and 15 connected to the electrode layers 21, 22, 23, and 24; a diaphragm 5 having main surfaces 5a and 5b which face each other, and in which the piezoelectric element 3 is arranged; and a bonding member 7 which is at least arranged between the main surface 11b of the piezoelectric element 3 and the main surface 5a of the diaphragm 5, and bonds the piezoelectric element 3 and the diaphragm 5. A part of the main surface 11b of the piezoelectric element 3 is not bonded to the main surface 5a of the diaphragm 5.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a vibration device. [Background technology]

[0002] The vibration device includes a piezoelectric element and a vibration plate on which the piezoelectric element is arranged (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-70100 Summary of the Invention [Problem to be solved by the invention]

[0004] In a vibration device, a piezoelectric element and a vibration plate are bonded (adhered). In a conventional vibration device, the entire main surface of the piezoelectric element and the main surface of the vibration plate are bonded with a bonding material to transmit the vibration (displacement) of the piezoelectric element to the vibration plate. While the vibration plate amplifies the vibration of the piezoelectric element, it may also generate unnecessary vibrations (distortion, noise, etc.) due to its configuration that amplifies the vibration by bending. In this case, the vibration device cannot produce vibrations corresponding to the frequency input to the piezoelectric element, so there is a risk that the desired vibrations may not be obtained.

[0005] An object of one aspect of the present invention is to provide a vibration device capable of suppressing the generation of unnecessary vibrations in a diaphragm. [Means for solving the problem]

[0006] A vibration device according to one aspect of the present invention comprises a base body having first and second main surfaces facing each other, a piezoelectric element having an internal electrode disposed within the base body and an external electrode connected to the internal electrode, a vibration plate having third and fourth main surfaces facing each other and on which the piezoelectric element is disposed, and a bonding member disposed at least between the second main surface of the piezoelectric element and the third main surface of the vibration plate, bonding the piezoelectric element to the vibration plate, wherein a portion of the second main surface of the piezoelectric element is not bonded to the third main surface of the vibration plate.

[0007] In a vibration device according to one aspect of the present invention, a part of the second main surface of the piezoelectric element is not bonded to the third main surface of the vibration plate. As a result, in the vibration device, the piezoelectric element is less likely to be constrained by the vibration plate, and therefore it is possible to suppress the generation of unnecessary vibrations in the vibration plate. As a result, in the vibration device, it is possible to produce vibrations according to the frequency input to the piezoelectric element, thereby making it possible to obtain the desired vibrations.

[0008] In one embodiment, the vibration plate has an opening formed through the third main surface and the fourth main surface, and the piezoelectric element is disposed at a position where the second main surface faces the opening. In this configuration, a configuration can be realized in which a part of the second main surface of the piezoelectric element and the third main surface of the vibration plate are not joined.

[0009] In one embodiment, the vibration plate has an opening formed in a concave shape so as to open to the third main surface, and the piezoelectric element is disposed at a position where the second main surface faces the opening. In this configuration, a configuration can be realized in which a part of the second main surface of the piezoelectric element and the third main surface of the vibration plate are not joined.

[0010] In one embodiment, the opening may have a shape similar to the shapes of the first and second main surfaces of the element body when viewed from the opposing direction of the third and fourth main surfaces. In this configuration, by matching the opening to the shape of the element body, the bonding surface (at least the inner peripheral surface) between the piezoelectric element and the diaphragm can be easily formed to conform to the shape of the element body. This makes it easy to bond (attach) the piezoelectric element to the diaphragm, and reduces individual variations. Furthermore, in this configuration, when the vibration of the piezoelectric element is transmitted to the diaphragm via the bonding surface, it is possible to make it difficult for unnecessary vibrations (distortion) to occur between the vibration of the piezoelectric element (spreading vibration) and the vibration of the diaphragm.

[0011] In one embodiment, the element has four side surfaces connecting the first and second main surfaces, and the end of the internal electrode of the piezoelectric element on the side surface may be located between the side surface and the edge of the opening. With this configuration, it is possible to suppress the occurrence of cracks due to the end of the internal electrode.

[0012] In one embodiment, the bonding member may have a first portion disposed across the side surface of the element body and the third main surface of the diaphragm, a second portion disposed across the second main surface of the element body and the side surface of the opening, and a third portion disposed between the second main surface of the element body and the third main surface of the diaphragm. In this configuration, the piezoelectric element and the diaphragm are bonded by the first portion, the second portion, and the third portion, so that the piezoelectric element can be more reliably bonded to the diaphragm. In addition, in this configuration, contact between the corners of the piezoelectric element and the diaphragm and contact between the piezoelectric element and the edge of the opening of the diaphragm during vibration can be suppressed, so that damage such as cracks can be suppressed in the piezoelectric element.

[0013] In one embodiment, a space may be formed between a part of the second main surface of the piezoelectric element and the third main surface of the vibration plate. In this configuration, a configuration in which the part of the second main surface of the piezoelectric element and the third main surface of the vibration plate are not joined can be realized.

[0014] In one embodiment, the region where the external electrode is arranged, as viewed from the opposing direction of the first and second principal surfaces of the piezoelectric element, may not be joined to the third principal surface of the diaphragm. In this configuration, the connection portion between the external electrode and the wiring member does not contact the diaphragm, so that the generation of unnecessary vibrations in the diaphragm can be further suppressed. In addition, since the structure makes it easy to attach the wiring member to the external electrode, mass productivity is improved and the characteristic variation between individual units can be suppressed.

[0015] In one embodiment, the piezoelectric element may be a unimorph type. In the case where the piezoelectric element is a unimorph type, in a configuration in which a part of the second main surface of the piezoelectric element is not joined to the third main surface of the vibration plate, the constraint component that the piezoelectric element receives from the vibration plate is unlikely to be biased to one side. This allows uniform displacement to be generated in the piezoelectric element. As a result, it is possible to produce vibrations according to the frequency input to the piezoelectric element, making it possible to obtain the desired vibrations.

[0016] In one embodiment, the piezoelectric element may be of the bimorph type. Effect of the Invention

[0017] According to one aspect of the present invention, it is possible to suppress the generation of unnecessary vibrations in the diaphragm. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a perspective view showing a vibration device according to an embodiment. [Diagram 2] FIG. 2 is an exploded perspective view of the vibration device. [Diagram 3] FIG. 3 is a plan view of the vibration device. [Figure 4] FIG. 4 is a diagram showing a cross-sectional configuration taken along line IV-IV in FIG. [Diagram 5] FIG. 5 is an exploded perspective view of the piezoelectric element. [Figure 6] FIG. 6 is a graph showing the measurement results of sound pressure versus frequency. [Figure 7]FIG. 7 is a graph showing the results of measuring total harmonic distortion versus frequency. [Figure 8] FIG. 8 is a diagram showing a cross-sectional configuration of a vibration device according to another embodiment. [Figure 9] FIG. 9 is a diagram showing a cross-sectional configuration of a vibration device according to another embodiment. [Figure 10] FIG. 10 is a diagram showing a cross-sectional configuration of a vibration device according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same or corresponding elements are designated by the same reference numerals, and duplicated explanations will be omitted.

[0020] FIG. 1 is a perspective view showing a vibration device according to an embodiment. FIG. 2 is an exploded perspective view of the vibration device. FIG. 3 is a plan view of the vibration device. As shown in FIGS. 1, 2, and 3, the vibration device 1 includes a piezoelectric element 3 and a diaphragm 5. The vibration device 1 is an acoustic device used, for example, as a speaker or a buzzer. In the vibration device 1, a wiring member 50 is connected to the piezoelectric element 3. The wiring member 50 is, for example, a flexible printed circuit board (FPC) or a flexible flat cable (FFC). The wiring member 50 is electrically connected to external electrodes 13, 15 described later.

[0021] The piezoelectric element 3 has an element body 11 and a plurality of external electrodes 13, 15. In this embodiment, the piezoelectric element 3 has a pair of external electrodes 13, 15. The piezoelectric element 3 is of a unimorph type.

[0022] The element body 11 has a rectangular parallelepiped shape. The element body 11 has a pair of main surfaces (first main surface, second main surface) 11a, 11b facing each other, a pair of side surfaces 11c facing each other, and a pair of side surfaces 11e facing each other. The rectangular parallelepiped shape includes, for example, a rectangular parallelepiped shape with chamfered corners and ridges, and a rectangular parallelepiped shape with rounded corners and ridges. The facing direction in which the pair of main surfaces 11a, 11b face each other is the first direction D1. The first direction D1 is also a direction perpendicular to each of the main surfaces 11a, 11b. The facing direction in which the pair of side surfaces 11c face each other is the second direction D2. The second direction D2 is also a direction perpendicular to each of the side surfaces 11c. The facing direction in which the pair of side surfaces 11e face each other is the third direction D3. The third direction D3 is also a direction perpendicular to each of the side surfaces 11e.

[0023] Each of the principal surfaces 11a, 11b has a rectangular shape. Each of the principal surfaces 11a, 11b has a rectangular shape having a pair of long sides and a pair of short sides. That is, the piezoelectric element 3 (element body 11) has a rectangular shape having a pair of long sides and a pair of short sides in a plan view. The rectangular shape includes, for example, a shape in which each corner is chamfered and a shape in which each corner is rounded. In this embodiment, the long side direction of the principal surfaces 11a, 11b coincides with the third direction D3. The short side direction of the principal surfaces 11a, 11b coincides with the second direction D2.

[0024] The pair of side surfaces 11c extend in the first direction D1 so as to connect the pair of main surfaces 11a, 11b. The pair of side surfaces 11c also extend in the third direction D3. The pair of side surfaces 11e extend in the first direction D1 so as to connect the pair of main surfaces 11a, 11b. The pair of side surfaces 11e also extend in the second direction D2. The length of the element body 11 in the second direction D2 is, for example, 10 mm. The length of the element body 11 in the third direction D3 is, for example, 20 mm. The length (thickness) of the element body 11 in the first direction D1 is, for example, 0.5 mm. Each of the main surfaces 11a, 11b and each of the side surfaces 11c, 11e may be indirectly adjacent to each other. In this case, a ridge portion is located between each of the main surfaces 11a, 11b and each of the side surfaces 11c, 11e.

[0025] As shown in FIG. 4 and FIG. 5, the element body 11 is configured by stacking a plurality of piezoelectric layers 17a, 17b, 17c, 17d, and 17e in a first direction D1. The element body 11 has a plurality of stacked piezoelectric layers 17a, 17b, 17c, 17d, and 17e. In this embodiment, the element body 11 has five piezoelectric layers 17a, 17b, 17c, 17d, and 17e. In the element body 11, the direction in which the plurality of piezoelectric layers 17a, 17b, 17c, 17d, and 17e are stacked coincides with the first direction D1. The piezoelectric layer 17a has a main surface 11a. The piezoelectric layer 17e has a main surface 11b. The piezoelectric layers 17b, 17c, and 17d are located between the piezoelectric layer 17a and the piezoelectric layer 17e.

[0026] Each of the piezoelectric layers 17a, 17b, 17c, 17d, and 17e is made of a piezoelectric ceramic material. That is, the element body 11 is made of a piezoelectric ceramic material. Examples of the piezoelectric ceramic material include PZT [Pb(Zr,Ti)O3], PT (PbTiO3), PLZT [(Pb,La)(Zr,Ti)O3], PZN [Pb(Zn,Nb)O3], and barium titanate (BaTiO3). Each of the piezoelectric layers 17a, 17b, 17c, 17d, and 17e is made of a sintered ceramic green sheet containing the above-mentioned piezoelectric ceramic material. In the actual element body 11, each of the piezoelectric layers 17a, 17b, 17c, 17d, and 17e is integrated to such an extent that the boundaries between the piezoelectric layers 17a, 17b, 17c, 17d, and 17e are not recognizable.

[0027] The length (thickness) of each of the piezoelectric layers 17a, 17b, 17c, 17d, and 17e in the first direction D1 is, for example, 40 μm. The piezoelectric layer 17a has a transparency such that an electrode layer 21, which will be described later, can be seen through the piezoelectric layer 17a from the main surface 11a side. The other piezoelectric layers 17b, 17c, 17d, and 17e have the same transparency as the piezoelectric layer 17a.

[0028] The piezoelectric element 3 includes a plurality of electrode layers 21, 22, 23, 24 arranged in the base body 11. In this embodiment, the piezoelectric element 3 includes four electrode layers 21, 22, 23, 24. Each of the electrode layers 21, 22, 23, 24 is an internal electrode. Each of the electrode layers 21, 22, 23, 24 is made of a conductive material. For example, Ag, Pd, or an Ag-Pd alloy is used as the conductive material. Each of the electrode layers 21, 22, 23, 24 is formed as a sintered body of a conductive paste containing the conductive material.

[0029] The electrode layers 21, 22, 23, and 24 are disposed at different positions (layers) in the first direction D1. The main surface 11a and the electrode layer 21 face each other with a gap in the first direction D1. The electrode layer 21 and the electrode layer 22 face each other with a gap in the first direction D1. The electrode layer 22 and the electrode layer 23 face each other with a gap in the first direction D1. The electrode layer 23 and the electrode layer 24 face each other with a gap in the first direction D1. The electrode layer 24 and the main surface 11b face each other with a gap in the first direction D1.

[0030] The electrode layer 21 is located between the piezoelectric layer 17a and the piezoelectric layer 17b. The electrode layer 22 is located between the piezoelectric layer 17b and the piezoelectric layer 17c. The electrode layer 23 is located between the piezoelectric layer 17c and the piezoelectric layer 17d. The electrode layer 24 is located between the piezoelectric layer 17d and the piezoelectric layer 17e. The electrode layers 21, 22, 23, and 24 are not exposed on the surface of the element body 11. That is, the electrode layers 21, 22, 23, and 24 are provided at a distance from the side surface 11c and the side surface 11e, and are not exposed at the side surface 11c and the side surface 11e. The electrode layers 21, 22, 23, and 24 are located at a distance from all edges (four sides) of the main surfaces 11a and 11b when viewed from the first direction D1.

[0031] Each of the electrode layers 21, 22, 23, 24 has a rectangular shape when viewed from the first direction D1. Each of the electrode layers 21, 22, 23, 24 has a rectangular shape having a pair of long sides and a pair of short sides when viewed from the first direction D1 (in a plan view). In this embodiment, the long side direction of each of the electrode layers 21, 22, 23, 24 coincides with the third direction D3. The short side direction of each of the electrode layers 21, 22, 23, 24 coincides with the second direction D2. When viewed from the first direction D1, the outer edges of the electrode layers 21, 22, 23, 24 have the same shape and coincide with each other.

[0032] When viewed from the first direction D1, the four corners of each of the electrode layers 21, 22, 23, and 24 are rounded and have a so-called R-shape. Here, a rounded corner does not mean a corner formed by the intersection of two straight lines, but a curved corner formed by connecting the ends of two straight lines with a curve.

[0033] Each of the external electrodes 13, 15 is disposed on the main surface 11a. The external electrodes 13 and 15 are aligned in the third direction D3. The external electrodes 13 and 15 are adjacent to each other in the third direction D3. When viewed from the first direction D1, each of the external electrodes 13, 15 is spaced apart from all edges (four sides) of the main surface 11a. When viewed from the first direction D1, each of the external electrodes 13, 15 has a rectangular shape. The rectangular shape includes, for example, a shape in which each corner is chamfered and a shape in which each corner is rounded.

[0034] The pair of external electrodes 13, 15 have the same shape as each other when viewed from the first direction D1. When viewed from the first direction D1, the short side direction of each external electrode 13, 15 coincides with the second direction D2, and the long side direction of each external electrode 13, 15 coincides with the third direction D3. Each external electrode 13, 15 is made of a conductive material. For example, Ag, Pd, or an Ag-Pd alloy is used as the conductive material. Each external electrode 13, 15 is configured as a sintered body of a conductive paste containing the conductive material.

[0035] The external electrode 13 is electrically connected to the connection conductor 25 through the via conductor 31. The connection conductor 25 is located in the same layer as the electrode layer 21. The connection conductor 25 is located inside the electrode layer 21. An opening is formed in the electrode layer 21 at a position corresponding to the external electrode 13 when viewed from the first direction D1. The connection conductor 25 is located in the opening formed in the electrode layer 21. When viewed from the first direction D1, the entire edge of the connection conductor 25 is surrounded by the electrode layer 21.

[0036] The connection conductor 25 is located between the piezoelectric layer 17a and the piezoelectric layer 17b. The electrode layer 21 and the connection conductor 25 are spaced apart from each other. The connection conductor 25 faces the external electrode 13 in the first direction D1. The via conductor 31 is connected to the external electrode 13 and is also connected to the connection conductor 25. The connection conductor 25 is electrically connected to the electrode layer 22 through the via conductor 32. The connection conductor 25 faces the electrode layer 22 in the first direction D1. The via conductor 32 is connected to the connection conductor 25 and is also connected to the electrode layer 22.

[0037] The electrode layer 22 is electrically connected to the connection conductor 26 through the via conductor 32. The connection conductor 26 is located in the same layer as the electrode layer 23. The connection conductor 26 is located inside the electrode layer 23. An opening is formed in the electrode layer 23 at a position corresponding to the external electrode 13 (connection conductor 25) when viewed from the first direction D1. The connection conductor 26 is located in the opening formed in the electrode layer 23. When viewed from the first direction D1, the entire edge of the connection conductor 26 is surrounded by the electrode layer 23.

[0038] The connection conductor 26 is located between the piezoelectric layer 17c and the piezoelectric layer 17d. The electrode layer 23 and the connection conductor 26 are spaced apart from each other. The connection conductor 26 faces the electrode layer 22 in the first direction D1. The via conductor 33 is connected to the electrode layer 22 and is also connected to the connection conductor 26. The connection conductor 26 is electrically connected to the electrode layer 24 through the via conductor 34. The connection conductor 26 faces the electrode layer 24 in the first direction D1. The via conductor 34 is connected to the connection conductor 26 and is also connected to the electrode layer 24.

[0039] The external electrode 15 is electrically connected to the electrode layer 21 through the via conductor 35. The electrode layer 21 faces the external electrode 15 in the first direction D1. The via conductor 35 is connected to the external electrode 15 and also to the electrode layer 21.

[0040] The electrode layer 21 is electrically connected to the connection conductor 27 through the via conductor 36. The connection conductor 27 is located in the same layer as the electrode layer 22. The connection conductor 27 is located inside the electrode layer 22. An opening is formed in the electrode layer 22 at a position corresponding to the external electrode 15 when viewed from the first direction D1. The connection conductor 27 is located within the opening formed in the electrode layer 22. When viewed from the first direction D1, the entire edge of the connection conductor 27 is surrounded by the electrode layer 22.

[0041] The connection conductor 27 is located between the piezoelectric layer 17b and the piezoelectric layer 17c. The electrode layer 22 and the connection conductor 27 are spaced apart from each other. The connection conductor 27 faces the electrode layer 21 in the first direction D1. The via conductor 36 is connected to the electrode layer 21 and is also connected to the connection conductor 27. The connection conductor 27 is electrically connected to the electrode layer 23 through the via conductor 37. The connection conductor 27 faces the electrode layer 23 in the first direction D1. The via conductor 37 is connected to the connection conductor 27 and is also connected to the electrode layer 23.

[0042] The electrode layer 23 is electrically connected to the connection conductor 28 through the via conductor 38. The connection conductor 28 is located in the same layer as the electrode layer 24. The connection conductor 28 is located inside the electrode layer 24. An opening is formed in the electrode layer 24 at a position corresponding to the external electrode 15 when viewed from the first direction D1. The connection conductor 28 is located inside the opening formed in the electrode layer 24. When viewed from the first direction D1, the entire edge of the connection conductor 28 is surrounded by the electrode layer 24.

[0043] The connecting conductor 28 is located between the piezoelectric layer 17d and the piezoelectric layer 17e. The electrode layer 24 and the connecting conductor 28 are spaced apart from each other. The connecting conductor 28 faces the electrode layer 23 in the first direction D1. The via conductor 38 is connected to the electrode layer 23 and also to the connecting conductor 28.

[0044] The external electrode 13 is electrically connected to the via conductor 31, the connecting conductor 25, the via conductor 32, the electrode layer 22, the via conductor 33, the connecting conductor 26, the via conductor 34, and the electrode layer 24. The external electrode 15 is electrically connected to the via conductor 35, the electrode layer 21, the via conductor 36, the connecting conductor 27, the via conductor 37, the electrode layer 23, the via conductor 38, and the connecting conductor 28.

[0045] The connection conductors 25, 26, 27, 28 and the via conductors 31, 32, 33, 34, 35, 36, 37, 38 are made of a conductive material. For example, Ag, Pd, or an Ag-Pd alloy is used as the conductive material. The connection conductors 25, 26, 27, 28 and the via conductors 31, 32, 33, 34, 35, 36, 37, 38 are formed as a sintered body of a conductive paste containing the conductive material. The connection conductors 25, 26, 27, 28 have a rectangular shape when viewed from the first direction D1. The via conductors 31, 32, 33, 34, 35, 36, 37, 38 are formed by sintering a conductive paste filled in a through hole formed in a ceramic green sheet for forming the corresponding piezoelectric layer 17a, 17b, 17c, 17d.

[0046] On the main surface 11b of the element body 11, a conductor electrically connected to the electrode layers 21, 23 and a conductor electrically connected to the electrode layers 22, 24 are not arranged. In this embodiment, when the main surface 11b is viewed from the first direction D1, the entire main surface 11b is exposed. On each of the side surfaces 11c, 11e of the element body 11, a conductor electrically connected to the electrode layers 21, 23 and a conductor electrically connected to the electrode layers 22, 24 are not arranged. In this embodiment, when each of the side surfaces 11c is viewed from the second direction D2, the entire side surface 11c is exposed. When each of the side surfaces 11e is viewed from the third direction D3, the entire side surface 11e is exposed.

[0047] A region in piezoelectric layer 17b sandwiched between electrode layers 21 and 22, a region in piezoelectric layer 17c sandwiched between electrode layers 22 and 23, and a region in piezoelectric layer 17d sandwiched between electrode layers 23 and 24 constitute piezoelectrically active regions. That is, in element body 11, active regions are formed between electrode layers 21 and 22, between electrode layers 22 and 23, and between electrode layers 23 and 24. When viewed from first direction D1, the outer edges of electrode layers 21, 22, 23, and 24 form boundaries between active regions and piezoelectrically inactive inactive regions.

[0048] In this embodiment, the active region is positioned so as to surround the multiple external electrodes 13, 15 as viewed from the first direction D1. In other words, as viewed from the first direction D1, the region in which the external electrodes 13, 15 are arranged is an inactive region. As viewed from the first direction D1, the element body 11 includes an active region in a region located between the external electrodes 13 and 15. As viewed from the first direction D1, the element body 11 also includes an active region outside the region in which the external electrodes 13 and 15 are located.

[0049] As shown in FIG. 1, FIG. 2, or FIG. 4, the diaphragm 5 has main surfaces (third main surface, fourth main surface) 5a, 5b facing each other. In this embodiment, the diaphragm 5 is a plate-shaped member. The diaphragm 5 is made of, for example, a metal. The diaphragm 5 is made of, for example, a Ni-Fe alloy, glass, resin, or stainless steel. Each of the main surfaces 5a, 5b has a pair of long sides and a pair of short sides. Each of the main surfaces 5a, 5b has a rectangular shape having a pair of long sides and a pair of short sides. That is, the diaphragm 5 has a rectangular shape having a pair of long sides and a pair of short sides in a plan view. In this embodiment, the long side direction of the main surfaces 5a, 5b coincides with the third direction D3. The short side direction of the main surfaces 5a, 5b coincides with the second direction D2. The length (thickness) of the diaphragm 5 in the first direction D1 is, for example, 1.0 mm.

[0050] The vibration plate 5 has an opening 5h. The opening 5h is formed penetrating the main surface 5a and the main surface 5b of the vibration plate 5. The center of the opening 5h is located at the center of the vibration plate 5. The opening 5h has a rectangular shape. That is, the opening 5h has a shape similar to the outer shape of the main surfaces 11a, 11b of the body 11 of the piezoelectric element 3 in a plan view. In this embodiment, the area of ​​the opening 5h is smaller than the area of ​​the main surfaces 11a, 11b of the body 11 of the piezoelectric element 3. The area of ​​the opening 5h is equal to or larger than the area that can include the inactive region in which the external electrodes 13, 15 of the piezoelectric element 3 are arranged.

[0051] As shown in FIG. 2 and FIG. 4, the bonding member 7 bonds the piezoelectric element 3 and the vibration plate 5. The bonding member 7 has a rectangular frame shape. The outer shape of the bonding member 7 has the same dimensions as the outer shape of the main surface 11b of the piezoelectric element 3. The length (thickness) of the bonding member 7 in the first direction D1 is, for example, 0.2 mm. The main surface 11b of the element 11 and the main surface 5a of the vibration plate 5 face each other via the bonding member 7. The bonding member 7 is located between the main surface 11b and the main surface 5a. The bonding member 7 is disposed along the outer edge of the main surface 11b of the piezoelectric element 3. The main surface 11b and the main surface 5a are bonded by the bonding member 7. The bonding member 7 is, for example, a double-sided tape. In a state where the piezoelectric element 3 is bonded to the vibration plate 5, the first direction D1 is the same as the direction in which the main surface 5a and the main surface 5b face each other.

[0052] As shown in FIG. 4, in the vibration device 1, a part of the main surface 11b of the piezoelectric element 3 and the main surface 5a of the vibration plate 5 are not bonded. The piezoelectric element 3 is disposed at a position where the main surface 11b faces the opening 5h. The piezoelectric element 3 covers the opening 5h of the vibration plate 5. In this embodiment, a region including a central portion of the main surface 11b of the piezoelectric element 3 is disposed at a position facing the opening 5h. That is, as viewed from the first direction D1, a region including a central portion of the main surface 11b of the piezoelectric element 3 is located within the region formed by the opening 5h. As viewed from the first direction D1, a region where the external electrodes 13, 15 of the piezoelectric element 3 are arranged is not bonded to the main surface 5a of the vibration plate 5. That is, as viewed from the first direction D1, an inactive region of the piezoelectric element 3 is located within the region formed by the opening 5h. In the first direction D1, a space is formed below the main surface 11b of the piezoelectric element 3.

[0053] The end of each electrode layer 21, 22, 23, 24 of the piezoelectric element 3 on the side of the side surface 11e is located between the side surface 11e and the edge of the opening 5h. Similarly, the end of each electrode layer 21, 22, 23, 24 of the piezoelectric element 3 on the side of the side surface 11c is located between the side surface 11c and the edge of the opening 5h. That is, when viewed from the first direction D1, the end of each electrode layer 21, 22, 23, 24 of the piezoelectric element is disposed at a position overlapping with the vibration plate 5. In other words, when viewed from the first direction D1, the end of each electrode layer 21, 22, 23, 24 of the piezoelectric element is disposed at a position not overlapping with the opening 5h of the vibration plate 5.

[0054] As described above, in the vibration device 1 according to this embodiment, a part of the main surface 11b of the piezoelectric element 3 is not joined to the main surface 5a of the vibration plate 5. As a result, in the vibration device 1, the piezoelectric element 3 is less likely to be constrained by the vibration plate 5, and therefore it is possible to suppress the generation of unnecessary vibrations in the vibration plate 5. As a result, in the vibration device 1, it is possible to produce vibrations according to the frequency input to the piezoelectric element 3, and therefore it is possible to obtain the desired vibrations.

[0055] Fig. 6 is a graph showing the measurement results of sound pressure versus frequency. In Fig. 6, the horizontal axis indicates frequency (Hz) and the vertical axis indicates sound pressure (SPL: sound pressure level) (dB). In Fig. 6, the measurement results of the vibration device 1 according to this embodiment are shown by a solid line, and the measurement results of the vibration device according to the comparative example are shown by a dashed line. In the vibration device according to the comparative example, the piezoelectric element is bonded to a vibration plate that does not have an opening. That is, in the vibration device according to the comparative example, the entire main surface of the piezoelectric element is bonded to the vibration plate.

[0056] The measurement was performed under the following conditions. In a device configuration in which a resistor (for example, 4.7 [Ω]) and an amplifier were connected to the vibration device 1, the input voltage was 12 [Vpp] and the input frequency was 100 to 20000 [Hz]. The sound emitted from the vibration device 1 was collected by a microphone and measured by a measuring device. The distance between the vibration device 1 and the microphone was 10 cm. As shown in FIG. 6, there is no significant difference in sound pressure between the vibration device 1 according to this embodiment and the vibration device according to the comparative example. That is, it was confirmed that even in a structure in which an opening 5h is provided in the vibration plate 5 and a part of the main surface 11b of the piezoelectric element 3 is not joined to the main surface 5a of the vibration plate 5, a sound pressure equivalent to that of the vibration device according to the comparative example can be obtained.

[0057] FIG. 7 is a graph showing the measurement results of total harmonic distortion versus frequency. In FIG. 7, the horizontal axis indicates frequency (Hz) and the vertical axis indicates total harmonic distortion (THD) (%). In FIG. 7, the measurement results of the vibration device 1 according to the present embodiment are shown by a solid line, and the measurement results of the vibration device according to the comparative example are shown by a dashed line. As shown in FIG. 7, the vibration device 1 according to the present embodiment has a smaller total harmonic distortion (distortion rate) than the vibration device according to the comparative example. That is, the vibration device 1 suppresses the generation of distortion compared to the vibration device according to the comparative example. Therefore, the vibration device 1 can suppress the generation of unnecessary vibrations in the diaphragm 5.

[0058] In the vibration device 1 according to this embodiment, the vibration plate 5 has an opening 5h formed penetrating the main surface 5a and the main surface 5b. The piezoelectric element 3 is disposed at a position where the main surface 11b faces the opening 5h. In this configuration, a configuration can be realized in which a part of the main surface 11b of the piezoelectric element 3 and the main surface 5a of the vibration plate 5 are not joined.

[0059] In the vibration device 1 according to this embodiment, the opening 5h of the vibration plate 5 has a shape similar to the shape of the main surfaces 11a, 11b of the element body 11 when viewed from the first direction D1. In this configuration, by matching the opening 5h to the shape of the element body 11, the bonding surface (at least the inner peripheral surface) between the piezoelectric element 3 and the vibration plate 5 can be easily formed to conform to the shape of the element body 11. This makes it easy to bond (attach) the piezoelectric element 3 and the vibration plate 5, and reduces individual variations. Furthermore, in the vibration device 1, when the vibration of the piezoelectric element 3 is transmitted to the vibration plate 5 via the bonding surface, it is possible to make it difficult for unnecessary vibration (distortion) to occur between the vibration (spreading vibration) of the piezoelectric element 3 and the vibration of the vibration plate 5.

[0060] In the vibration device 1 according to this embodiment, the ends of the electrode layers 21, 22, 23, and 24 of the piezoelectric element 3 on the side surfaces 11c and 11e are located between the side surfaces 11c and 11e and the edge of the opening 5h. With this configuration, the occurrence of cracks due to the ends of the electrode layers 21, 22, 23, and 24 can be suppressed.

[0061] In the vibration device 1 according to this embodiment, when viewed from the first direction D1, the region in which the external electrodes 13, 15 of the piezoelectric element 3 are arranged is not joined to the main surface 5b of the vibration plate 5. In this configuration, the connection portions between the external electrodes 13, 15 and the wiring member 50 do not contact the vibration plate 5, so that the generation of unnecessary vibrations in the vibration plate 5 can be further suppressed. In addition, since the structure makes it easy to attach the wiring member 50 to the external electrodes 13, 15, mass productivity is improved and characteristic variations between individual units can be suppressed.

[0062] In the vibration device 1 according to this embodiment, the piezoelectric element 3 may be of a unimorph type. In the case where the piezoelectric element 3 is of a unimorph type, in a configuration in which a part of the main surface 11b of the piezoelectric element 3 and the main surface 5a of the vibration plate 5 are not joined, the constraint component that the piezoelectric element 3 receives from the vibration plate 5 is unlikely to be biased to one side. This allows uniform displacement to occur in the piezoelectric element 3. As a result, it is possible to produce vibration according to the frequency input to the piezoelectric element 3, making it possible to obtain the desired vibration.

[0063] In the vibration device 1 according to this embodiment, the bonding member 7 is a double-sided tape. The bonding member 7 has a frame shape and is disposed along the edge of the main surface 11b of the piezoelectric element 3. With this configuration, the piezoelectric element 3 and the vibration plate 5 are bonded together, while the piezoelectric element 3 is prevented from being restrained by the vibration plate 5.

[0064] Although the embodiment of the present invention has been described above, the present invention is not necessarily limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention.

[0065] In the above embodiment, the piezoelectric element 3 is of a unimorph type. However, the piezoelectric element 3 may be of a bimorph type.

[0066] In the above embodiment, an example of the bonding member 7 being a double-sided tape has been described. However, the bonding member is not limited to a double-sided tape. As shown in FIG. 8, in the vibration device 1A, the bonding member 40 may be an adhesive. The bonding member 40 is made of a resin (for example, an epoxy resin or an acrylic resin). The bonding member 40 has a first portion 40a, a second portion 40b, and a third portion 40c. The first portion 40a is disposed across the side surface 11e of the element body 11 and the main surface 5a of the vibration plate 5. The second portion 40b is disposed across the main surface 11b of the element body 11 and the side surface of the opening 5h. The third portion 40c is disposed between the main surface 11b of the element body 11 and the main surface 5a of the vibration plate 5. The bonding member 40 is disposed around the entire circumference of the piezoelectric element 3. In this configuration, the piezoelectric element 3 and the vibration plate 5 are bonded by the first portion 40a, the second portion 40b, and the third portion 40c, so that the piezoelectric element 3 can be more reliably bonded to the vibration plate 5. In addition, with this configuration, contact between the corners of the piezoelectric element 3 and the vibration plate 5, and contact between the piezoelectric element 3 and the edges of the opening 5h of the vibration plate 5 during vibration can be suppressed, thereby suppressing damage such as cracks in the piezoelectric element 3.

[0067] In the above embodiment, the vibration plate 5 has an opening 5h penetrating therethrough. However, the shape of the vibration plate is not limited to this. As shown in FIG. 9, the vibration device 1B has a vibration plate 5A. The vibration plate 5A has an opening 5Ah. The opening 5Ah is formed in a concave shape so as to open to the main surface 5a of the vibration plate 5A. The center of the opening 5Ah is located at the center of the vibration plate 5A. The opening 5Ah has a rectangular shape. That is, the opening 5Ah has a shape similar to the outer shape of the main surfaces 11a, 11b of the base body 11 of the piezoelectric element 3 in a plan view. The area of ​​the opening 5Ah is smaller than the area of ​​the main surfaces 11a, 11b of the base body 11 of the piezoelectric element 3. Even in this configuration, the piezoelectric element 3 is unlikely to be restrained by the vibration plate 5A, so that the generation of unnecessary vibrations in the vibration plate 5A can be suppressed. As a result, in the vibration device 1A, it is possible to produce vibrations according to the frequency input to the piezoelectric element 3, so that it is possible to obtain the desired vibrations.

[0068] As shown in FIG. 10, the vibration device 1C has a piezoelectric element 3, a vibration plate 5B, and a bonding member 7B. The vibration plate 5B is a flat plate and has no opening. The vibration plate 5B has a flat main surface 5Ba and a main surface 5Bb over the entire surface. The length (thickness) of the bonding member 7B in the first direction D1 is, for example, 0.5 mm. The bonding member 7B separates the piezoelectric element 3 and the vibration plate 5B. This forms a space between a part of the main surface 11b of the piezoelectric element 3 and the main surface 5Ba of the vibration plate 5B. Even in this configuration, the piezoelectric element 3 is unlikely to be restrained by the vibration plate 5B, so that it is possible to suppress the generation of unnecessary vibrations in the vibration plate 5B. As a result, in the vibration device 1B, it is possible to generate vibrations according to the frequency input to the piezoelectric element 3, so that it is possible to obtain the desired vibrations.

[0069] In the above embodiment, an example has been described in which the opening 5h of the diaphragm 5 has a shape similar to the shape of the main surfaces 11a, 11b of the element body 11. However, the shape of the opening 5h is not limited to this, and may be, for example, a polygonal shape, a circular shape, or the like.

[0070] In the above embodiment, an example has been described in which the area of ​​the opening 5h of the diaphragm 5 is smaller than the area of ​​the main surfaces 11a, 11b of the body 11 of the piezoelectric element 3. However, the opening 5h may be larger than the area of ​​the main surfaces 11a, 11b of the body 11 of the piezoelectric element 3.

[0071] In the above embodiment, the joining member 7 has a frame shape. However, the joining members may be arranged in pairs facing each other. For example, the joining members may be arranged in pairs facing each other in the third direction D3 along the side surface 11e of the element body 11.

[0072] In the present invention, the opening 5h of the diaphragm 5 is a hole, and forms a closed space when the diaphragm 5 is viewed from the opposing direction of the main surfaces 5a, 5b (first direction D1). The opening 5h of the diaphragm 5 is defined by the inner surface of the diaphragm 5. That is, the opening 5h of the diaphragm 5 is not formed by cutting out the diaphragm 5 (when the diaphragm 5 is viewed from the opposing direction of the main surfaces 5a, 5b (first direction D1), a part of the opening 5h is not opened). In a configuration in which the opening of the plate-like member is formed by a cutout and the piezoelectric element is disposed on the plate-like member so as to straddle the opening, when the vibration of the piezoelectric element is transmitted to the plate-like member, each of the joints between the piezoelectric element and the plate-like member vibrates. This causes unnecessary vibrations in the plate-like member, and sound pressure cannot be obtained. [Explanation of symbols]

[0073] 1,1A,1B,1C...vibration device, 3...piezoelectric element, 5,5A,5B...diaphragm, 5h,5Ah...opening, 7,7B,40...joining member, 11...element body, 11c,11e...side surface, 13...external electrode, 15...external electrode, 40a...first part, 40b...second part, 40c...third part.

Claims

1. a piezoelectric element including an element body having a first principal surface and a second principal surface opposed to each other, an internal electrode disposed within the element body, and an external electrode connected to the internal electrode; a vibration plate having a third principal surface and a fourth principal surface opposed to each other, the vibration plate having the piezoelectric element disposed thereon; a bonding member disposed at least between the second main surface of the piezoelectric element and the third main surface of the vibration plate, bonding the piezoelectric element and the vibration plate; a part of the second main surface of the piezoelectric element and the third main surface of the vibration plate are not joined together, the diaphragm has an opening formed through the third main surface and the fourth main surface, the piezoelectric element is disposed at a position where the second main surface faces the opening, A vibration device, wherein the opening has a shape similar to the shapes of the first main surface and the second main surface of the base body when viewed from the opposing direction of the third main surface and the fourth main surface.

2. a piezoelectric element including an element body having a first principal surface and a second principal surface opposed to each other, an internal electrode disposed within the element body, and an external electrode connected to the internal electrode; a vibration plate having a third principal surface and a fourth principal surface opposed to each other, the vibration plate having the piezoelectric element disposed thereon; a bonding member disposed at least between the second main surface of the piezoelectric element and the third main surface of the vibration plate, bonding the piezoelectric element and the vibration plate; a part of the second main surface of the piezoelectric element and the third main surface of the vibration plate are not joined together, the diaphragm has an opening formed in a concave shape so as to open to the third main surface, the piezoelectric element is disposed at a position where the second main surface faces the opening, A vibration device, wherein the opening has a shape similar to the shapes of the first main surface and the second main surface of the base body when viewed from the opposing direction of the third main surface and the fourth main surface.

3. the element body has four side surfaces connecting the first main surface and the second main surface, The vibration device according to claim 1 , wherein an end portion of the internal electrode of the piezoelectric element on the side surface side is located between the side surface and an edge of the opening.

4. The vibration device described in claim 3, wherein the joining member has a first portion arranged across the side surface of the base body and the third main surface of the vibration plate, a second portion arranged across the second main surface of the base body and a side surface of the opening, and a third portion arranged between the second main surface of the base body and the third main surface of the vibration plate.

5. A vibration device as described in any one of claims 1 to 4, wherein, when viewed from the opposing direction of the first main surface and the second main surface of the piezoelectric element, the area in which the external electrode is arranged is not joined to the third main surface of the vibration plate.

6. The vibration device according to any one of claims 1 to 5, wherein the piezoelectric element is of a unimorph type.

7. The vibration device according to claim 1 , wherein the piezoelectric element is of a bimorph type.

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