Piezoelectric element

Abstract

To provide a piezoelectric element enabling the deviation thereof to be equalized.SOLUTION: A piezoelectric device 2 comprises: an element assembly 10 which includes main surfaces 10a and 10b opposite each other in a direction D1 and side surfaces 10c and 10d opposite each other in a direction D2; internal electrodes 15, 16, and 17 which are provided in the element assembly 10 and which are laminated in the direction D1; and external electrodes 11, 12, and 13 which have electrode portions 11c, 12c, and 13c provided on the side surface 10c, respectively, and electrode portions 11a, 12a, and 13a provided on the main surface 10a. The element assembly 10 includes active regions R11 and R12 which are piezoelectricity active and arranged between the plurality of internal electrodes 15, 16, and 17. The electrode portions 11a, 12a, and 13a include overlapping regions 11d, 12d, and 13d overlapped to the activation regions R11 and R12 in view of the direction D1. An area of each of the overlapping regions 11d, 12d, and 13d is 50% of each area of the electrode portions 11a, 12a, and 13a.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to piezoelectric elements. [Background technology]

[0002] Patent Document 1 describes a piezoelectric element comprising an element body, multiple internal electrodes, and multiple external electrodes. In this piezoelectric element, the element body has an active region and multiple inactive regions, with the inactive regions surrounding the periphery of the active region. This shifts the resonance point of the piezoelectric element to the low frequency side, allowing for high sound pressure to be obtained. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-121664 Summary of the Invention [Problem to be solved by the invention]

[0004] In the piezoelectric element, the displacement is greatest at the center of the element body, and when used in speakers, it is difficult to obtain uniform sound quality due to resonance at the center of the element body.

[0005] One aspect of the present disclosure provides a piezoelectric element capable of uniforming displacement. [Means for solving the problem]

[0006] A piezoelectric element according to one embodiment of the present disclosure comprises: an element body having a first main surface and a second main surface facing each other in a first direction, and a first side surface and a second side surface facing each other in a second direction perpendicular to the first direction and connecting the first main surface and the second main surface; a plurality of internal electrodes provided within the element body and stacked in the first direction; and a plurality of external electrodes each having a first electrode portion provided on the first side surface and connected to a corresponding internal electrode, and a second electrode portion provided on the first main surface and connected to the first electrode portion; the element body including a piezoelectrically active active region disposed between the plurality of internal electrodes; the second electrode portion including an overlapping region overlapping the active region when viewed from the first direction; and the area of ​​the overlapping region being 50% or more of the area of ​​the second electrode portion.

[0007] In the piezoelectric element, each of the plurality of external electrodes has a second electrode portion provided on the first main surface of the element body. The second electrode portion includes an overlapping region that overlaps with the active region of the element body. Because the area of ​​the overlapping region is at least half the area of ​​the second electrode portion, the active region is held down by the overlapping region of the second electrode portion, suppressing displacement of the center of the element body. This makes it possible to make the displacement uniform.

[0008] The length of the second electrode portion in the second direction may be 50% or more of the length of the first main surface in the second direction. In this case, displacement of the central portion of the element body is further suppressed, thereby making the displacement more uniform.

[0009] When viewed from the first direction, the active region may be spaced from the outer edge of the body. In this case, the active region is surrounded by the inactive region, and the resonance point of the piezoelectric element shifts to the lower frequency side. As a result, when the piezoelectric element is applied to an acoustic device, a sound pressure level high enough for practical use can be obtained.

[0010] The overlapping region may include a bonding region to be bonded to the wiring member. In this case, the bonding region is located on the active region. Since the wiring member displaces following the displacement of the active region, the bonding of the wiring member is less likely to come off than when the wiring member is not located on the active region.

[0011] The overlapping region may include an exposed region that is exposed from the wiring member, in which case displacement of the active region formed between the internal electrode disposed closest to the first main surface and the exposed region is less likely to be suppressed.

[0012] The overlapping region may be entirely covered with the wiring member, in which case corrosion of the overlapping region can be suppressed. [Effects of the Invention]

[0013] According to one aspect of the present invention, there is provided a piezoelectric element capable of uniforming displacement. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view showing a vibration device according to a first embodiment. [Figure 2] FIG. 2 is a plan view showing the piezoelectric element of FIG. [Figure 3] FIG. 3 is an exploded perspective view of the piezoelectric element of FIG. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV in FIG. [Figure 5] FIG. 5 is a cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is a cross-sectional view taken along line VI-VI in FIG. [Figure 7] FIG. 7 is a perspective view showing a vibration device including a piezoelectric element according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, the embodiments 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 redundant description will be omitted.

[0016] [First embodiment] A resonation device 1 according to a first embodiment shown in FIGS. 1 to 6 is an acoustic device used, for example, in a speaker. The resonation device 1 includes a piezoelectric element 2, a wiring member 3, and bonding members 4 and 5. The piezoelectric element 2 includes an element body 10 and external electrodes 11, 12, and 13 provided on the surface of the element body 10. In FIG. 2, the external electrodes 11, 12, and 13 are not shown. The piezoelectric element 2 is a multilayer piezoelectric element, and the element body 10 includes a plurality of stacked element layers 14. The element layers 14 are made of a piezoelectric material such as a piezoelectric ceramic material. The piezoelectric element 2 is, for example, a bimorph type.

[0017] The element body 10 has a rectangular, flat plate-like outer shape. The element body 10 has main surfaces 10a and 10b and four side surfaces 10c to 10f. The four side surfaces 10c to 10f connect the main surface 10a and the main surface 10b. The main surfaces 10a and 10b face each other in the stacking direction of the multiple element body layers 14. The side surfaces 10c and 10d face each other in the short side direction of the main surfaces 10a and 10b. The side surfaces 10e and 10f face each other in the long side direction of the main surfaces 10a and 10b. Hereinafter, the stacking direction of the multiple element body layers 14 is referred to as direction D1, the short side direction of the main surfaces 10a and 10b is referred to as direction D2, and the long side direction of the main surfaces 10a and 10b is referred to as direction D3.

[0018] The external electrodes 11, 12, and 13 are made of, for example, Ag or an Ag alloy. The external electrodes 11, 12, and 13 are arranged on the element body 10 at a distance from each other. The external electrodes 11, 12, and 13 are lined up in this order in the direction D3. The external electrode 11 is arranged closest to the side surface 10e. The external electrode 13 is arranged closest to the side surface 10f. The external electrode 12 is arranged between the external electrodes 11 and 13.

[0019] The width L1 of the external electrode 11 in the direction D3 is wider than the width L2 of the external electrode 12 in the direction D3 and the width L3 of the external electrode 13 in the direction D3. The width L2 is, for example, equal to the width L3. The separation distance L4 between the external electrodes 11 and 12 in the direction D3 is longer than the width L2. The separation distance L5 between the external electrodes 12 and 13 in the direction D3 is shorter than the width L2 and shorter than the width L3.

[0020] The external electrode 11 has electrode portions 11a, 11b, and 11c. The electrode portion 11a is provided on the main surface 10a and extends in direction D2. The electrode portion 11b is provided on the main surface 10b. The electrode portion 11c is provided on the side surface 10c. The electrode portion 11c is connected to the electrode portions 11a and 11b.

[0021] The external electrode 12 has electrode portions 12a, 12b, and 12c. The electrode portion 12a is provided on the main surface 10a and extends in direction D2. The electrode portion 12b is provided on the main surface 10b. The electrode portion 12c is provided on the side surface 10c. The electrode portion 12c is connected to the electrode portions 12a and 12b.

[0022] The external electrode 13 has electrode portions 13a, 13b, and 13c. The electrode portion 13a is provided on the main surface 10a and extends in direction D2. The electrode portion 13b is provided on the main surface 10b. The electrode portion 13c is provided on the side surface 10c. The electrode portion 13c is connected to the electrode portions 13a and 13b.

[0023] The length L6 of electrode portion 11a in direction D2, the length L7 of electrode portion 12a in direction D2, and the length L8 of electrode portion 13a in direction D2 are each 50% or more, and preferably 60% or more, of the length L9 of main surface 10a in direction D2. In this embodiment, the length is 60%. The lengths L6, L7, and L8 are, for example, equal to each other.

[0024] The piezoelectric element 2 includes a plurality of internal electrodes 15, 16, and 17 provided within the element body 10. The internal electrodes 15, 16, and 17 are made of, for example, Ag or an Ag alloy. The internal electrodes 15, 16, and 17 are stacked together with the plurality of element body layers 14 in the direction D1.

[0025] The internal electrode 15 includes a main electrode portion 15a and a connecting portion 15b. The main electrode portion 15a is spaced apart from the four side surfaces 10c, 10d, 10e, and 10f. The connecting portion 15b extends from the main electrode portion 15a in direction D2 and is exposed at the side surface 2c. The connecting portion 15b is connected to the electrode portion 11c. The width of the connecting portion 15b in direction D3 is equal to the width L1.

[0026] The internal electrode 16 includes a main electrode portion 16a and a connecting portion 16b. The main electrode portion 16a is spaced apart from the four side surfaces 10c, 10d, 10e, and 10f. The connecting portion 16b extends from the main electrode portion 16a in direction D2 and is exposed at the side surface 2c. The connecting portion 16b is connected to the electrode portion 12c. The width of the connecting portion 16b in direction D3 is equal to the width L2.

[0027] The internal electrode 17 includes a main electrode portion 17a and a connecting portion 17b. The main electrode portion 17a is spaced apart from the four side surfaces 10c, 10d, 10e, and 10f. The connecting portion 17b extends from the main electrode portion 17a in direction D2 and is exposed at the side surface 2c. The connecting portion 17b is connected to the electrode portion 13c. The width of the connecting portion 17b in direction D3 is equal to the width L3.

[0028] Main electrode portions 15a, 16a, and 17a have the same shape and overlap when viewed from direction D1. Connection portion 15b overlaps electrode portion 11a when viewed from direction D1. Connection portion 16b overlaps electrode portion 12a when viewed from direction D1. Connection portion 17b overlaps electrode portion 13a when viewed from direction D1. Connection portions 15b, 16b, and 17b are spaced apart from each other in direction D3.

[0029] The stacking order of the multiple internal electrodes 15, 16, 17 will be described with reference to Figure 3. If the element layer 14 including the main surface 10a is the first element layer 14, an internal electrode 15 is arranged on the second element layer 14. An internal electrode 17 is arranged on the third element layer 14. An internal electrode 15 is arranged on the fourth element layer 14. An internal electrode 17 is arranged on the fifth element layer 14. An internal electrode 15 is arranged on the sixth element layer 14. An internal electrode 16 is arranged on the seventh element layer 14. An internal electrode 15 is arranged on the eighth element layer 14. An internal electrode 16 is arranged on the ninth element layer 14. An internal electrode 15 is arranged on the tenth element layer 14.

[0030] That is, the internal electrodes 15 and 17 are alternately stacked on the upper side (main surface 10a side) of the element body 10, and the internal electrodes 15 and 16 are alternately stacked on the lower side (main surface 10b side) of the element body 10. The internal electrode 15 arranged on the second element layer 14 is arranged closest to the main surface 10a among the multiple internal electrodes 15, 16, 17. The internal electrode 15 arranged on the tenth element layer 14 is arranged closest to the main surface 10b among the multiple internal electrodes 15, 16, 17.

[0031] 4 to 6, the element body 10 has a piezoelectrically active region R1 and a piezoelectrically inactive inactive region R2. The active region R1 includes active regions R11, R12, R13, and R14. The active regions R11 and R12 are regions disposed between the internal electrodes 15, 16, and 17. More specifically, the active region R11 is a region sandwiched between the internal electrodes 15 and 16. The active region R12 is a region sandwiched between the internal electrodes 15 and 17.

[0032] Active regions R11 and R12 are shown in perspective in Fig. 2. As shown in Fig. 2, when viewed from direction D1, active regions R11 and R12 are spaced apart from the outer edge of element body 10. When viewed from direction D1, active regions R11 and R12 are surrounded on all sides by inactive region R2 (Figs. 4 to 6).

[0033] As shown in Fig. 5, the active region R13 is a region sandwiched between the external electrode 12 and the internal electrode 15 arranged on the second element layer 14 (see Fig. 3). As shown in Fig. 6, the active region R14 is a region sandwiched between the external electrode 13 and the internal electrode 15 arranged on the second element layer 14 (see Fig. 3). The inactive region R2 is a region of the element body 10 other than the active region R1.

[0034] When a voltage is applied between the external electrodes 11 and 12, the active region R11 expands and contracts due to the electric field generated between the internal electrodes 15 and 16, and the active region R13 expands and contracts due to the electric field generated between the external electrode 12 and the internal electrode 15. When a voltage is applied between the external electrodes 11 and 13, the active region R12 expands and contracts due to the electric field generated between the internal electrodes 15 and 17, and the active region R14 expands and contracts due to the electric field generated between the external electrode 13 and the internal electrode 15.

[0035] The active regions R11 and R13 are polarized in the same direction. The active regions R12 and R14 are polarized in the same direction. The polarization direction of the active regions R11 and R13 is opposite to the polarization direction of the active regions R12 and R14. Therefore, by applying a first voltage to the external electrode 11 and a second voltage different from the first voltage to both the external electrodes 12 and 13, the active regions R11 and R13 and the active regions R12 and R14 can be expanded and contracted in opposite directions.

[0036] 2 and 4, the electrode portion 11a includes an overlapping region 11d that overlaps with the active regions R11 and R12 when viewed from the direction D1. When viewed from the direction D1, the area of ​​the overlapping region 11d is 50% or more of the area of ​​the electrode portion 11a.

[0037] 2 and 5, the electrode portion 12a includes an overlapping region 12d that overlaps with the active regions R11 and R12 when viewed from the direction D1. When viewed from the direction D1, the area of ​​the overlapping region 12d is 50% or more of the area of ​​the electrode portion 12a.

[0038] 2 and 6, the electrode portion 13a includes an overlapping region 13d that overlaps with the active regions R11 and R12 when viewed from the direction D1. When viewed from the direction D1, the area of ​​the overlapping region 13d is 50% or more of the area of ​​the electrode portion 13a.

[0039] 1, 4 to 6, the wiring member 3 electrically connects the piezoelectric element 2 to an external control circuit (not shown) and applies a voltage to the piezoelectric element 2. The wiring member 3 is, for example, a flexible printed circuit (FPC) or a flexible flat cable (FFC). The wiring member 3 is disposed on the main surface 10a and joined to the main surface 10a by joining members 4 and 5. The wiring member 3 is drawn out from the side surface 10d of the main surface 10a along direction D2. The wiring member 3 is in the shape of a plate, a sheet, or a strip.

[0040] The bonding member 4 is an electrically insulating resin layer that does not contain conductive particles. The bonding member 4 is, for example, a hot-melt resin whose main components are reactive phenol resin and nitrile rubber. The bonding member 4 is arranged along the long side of the main surface 10a on the side surface 10d side. The bonding member 4 bonds the entire width direction (direction D3) of the wiring member 3 to the main surface 10a. The bonding member 4 is spaced from the bonding member 5 in direction D2.

[0041] The bonding member 5 is a resin layer containing a plurality of conductive particles (not shown). The conductive particles are, for example, metal particles or gold-plated particles. The bonding member 5 contains, for example, a thermosetting elastomer. The bonding member 5 is formed, for example, by hardening an anisotropic conductive paste or an anisotropic conductive film. The bonding member 5 electrically connects the wiring member 3 and the electrode portions 11a, 12a, and 13a.

[0042] The electrode portion 11a includes a bonding region 11e that is bonded to the wiring member 3 by the bonding member 5. The electrode portion 12a includes a bonding region 12e that is bonded to the wiring member 3 by the bonding member 5. The electrode portion 13a includes a bonding region 13e that is bonded to the wiring member 3 by the bonding member 5.

[0043] In this embodiment, overlapping region 11d includes the entire bonding region 11e. Overlapping region 12d includes the entire bonding region 12e. Overlapping region 13d includes the entire bonding region 13e. Overlapping region 11d further includes exposed region 11f that is exposed from wiring member 3. Overlapping region 12d further includes exposed region 12f that is exposed from wiring member 3. Overlapping region 13d further includes exposed region 13f that is exposed from wiring member 3.

[0044] The wiring member 3 has conductor layers 31 and 32, a base 33, and a cover 34. The conductor layers 31 and 32 are made of, for example, Cu. The base 33 and the cover 34 are resin layers made of, for example, polyimide resin. The conductor layers 31 and 32 are disposed between the base 33 and the cover 34. The conductor layers 31 and 32 are adhered to the base 33 and the cover 34 by, for example, an adhesive layer (not shown).

[0045] The conductor layers 31 and 32 extend in direction D2 on the main surface 10a and are spaced apart from each other in direction D3. One end of each of the conductor layers 31 and 32 in direction D2 is exposed from the cover 34. The one end of the conductor layer 31 exposed from the cover 34 faces the bonding region 11e in direction D1 and is electrically connected to the bonding region 11e by the bonding member 5. The one end of the conductor layer 32 exposed from the cover 34 faces the bonding regions 12e and 13e in direction D1 and is electrically connected to the bonding regions 12e and 13e by the bonding member 5.

[0046] In the piezoelectric element 2, the largest displacement occurs in the center of the element body 10, more specifically, in the portion overlapping the center of gravity of the main surface 10a when viewed from the direction D1. Resonance occurring in this large displacement portion can increase the volume of sound at certain frequencies, potentially resulting in inconsistent sound quality. In the piezoelectric element 2, the area of ​​the overlapping regions 11d, 12d, and 13d is more than half the area of ​​the electrode portions 11a, 12a, and 13a. In other words, when viewed from the direction D1, the electrode portions 11a, 12a, and 13a are located more over the active regions R11 and R12 than in the region where the active regions R11 and R12 are not located. Therefore, the active regions R11 and R12 are held down by the overlapping regions 11d, 12d, and 13d, suppressing displacement in the center of the element body 10. This allows for uniform displacement of the piezoelectric element 2 and consistent sound quality.

[0047] The lengths L6, L7, and L8 of the electrode portions 11a, 12a, and 13a in the direction D2 are 50% or more of the length L9 of the main surface 10a in the direction D2. This further suppresses displacement of the central portion of the element body 10. This makes the displacement of the piezoelectric element 2 more uniform, resulting in more uniform sound quality.

[0048] When viewed from direction D1, the active regions R11 and R12 are spaced apart from the outer edge of the element body 10. As a result, the active regions R11 and R12 are surrounded by the inactive region R2, and the resonance point of the piezoelectric element 2 shifts to the lower frequency side. As a result, when the piezoelectric element 2 is applied to an acoustic device, a sound pressure that is sufficiently high for practical use can be obtained.

[0049] The overlapping regions 11d, 12d, and 13d include bonding regions 11e, 12e, and 13e that are bonded to the wiring member 3. The bonding regions 11e, 12e, and 13e are located on the active regions R11 and R12. Since the wiring member 3 displaces following the displacement of the active regions R11 and R12, it is more difficult to disconnect the wiring member 3 than when the wiring member 3 is not located on the active regions R11 and R12.

[0050] The overlapping regions 11d, 12d, and 13d also include exposed regions 11f, 12f, and 13f that are exposed from the wiring member 3. Therefore, it is difficult to suppress the displacement of the active regions R13 and R14 that are formed between the internal electrode 15 that is closest to the main surface 10a among the multiple internal electrodes 15, 16, and 17, and the exposed regions 12f and 13f. Therefore, the displacement of the piezoelectric element 2 can be improved.

[0051] The region sandwiched between the internal electrode 15 arranged closest to the main surface 10a and the external electrodes 12 and 13 is the active region R13 and R14, while the region sandwiched between the internal electrode 15 arranged closest to the main surface 10a and the external electrode 11 is the inactive region R2. This prevents the internal electrodes 15 and 16 from being electrically affected from the outside, improving reliability.

[0052] [Second embodiment] The resonation device 1A according to the second embodiment shown in FIG. 7 differs from the resonation device 1 mainly in that the wiring member 3 is drawn from the side surface 10c of the main surface 10a along the direction D2. In this embodiment, the electrode portions 11a, 11b, and 11c are entirely covered with the wiring member 3. That is, the overlapping regions 11d, 12d, and 13d do not include the exposed regions 11f, 12f, and 13f, respectively. Since the overlapping regions 11d, 12d, and 13d are not exposed, corrosion of the overlapping regions 11d, 12d, and 13d can be suppressed. Furthermore, since the wiring member 3 suppresses displacement of the active regions R13 and R14, the piezoelectric element 2 can be displaced in a balanced manner between the side surface 10c and the side surface 10d.

[0053] Although the embodiments of the present invention have been described above, the present invention is not necessarily limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0054] The piezoelectric element 2 may be a monomorph type. The wiring member 3 may be drawn out from the side surface 10e or 10f of the main surface 10a. The piezoelectric element 2 may be used in, for example, a haptic device.

[0055] The above-described embodiments and modifications may be combined as appropriate.

[0056] As can be understood from the above description of the embodiments and modifications, this specification includes disclosure of the following aspects. (Appendix 1) an element body having a first main surface and a second main surface opposing each other in a first direction, and a first side surface and a second side surface opposing each other in a second direction perpendicular to the first direction and connecting the first main surface and the second main surface; a plurality of internal electrodes provided within the element body and stacked in the first direction; a plurality of external electrodes, each having a first electrode portion provided on the first side surface and connected to a corresponding internal electrode, and a second electrode portion provided on the first main surface and connected to the first electrode portion; the element body includes a piezoelectrically active region disposed between the plurality of internal electrodes; the second electrode portion includes an overlapping region that overlaps the active region when viewed from the first direction, The area of ​​the overlapping region is 50% or more of the area of ​​the second electrode portion. Piezoelectric element. (Appendix 2) The length of the second electrode portion in the second direction is 50% or more of the length of the first main surface in the second direction. 2. The piezoelectric element according to claim 1. (Appendix 3) When viewed from the first direction, the active region is spaced apart from an outer edge of the element body. 3. The piezoelectric element according to claim 1 or 2. (Appendix 4) The overlapping region includes a bonding region to be bonded to a wiring member. 4. The piezoelectric element according to any one of claims 1 to 3. (Appendix 5) The overlapping region includes an exposed region exposed from the wiring member. 5. The piezoelectric element according to claim 4. (Appendix 6) The overlapping region is entirely covered by the wiring member. 5. The piezoelectric element according to claim 4. [Explanation of symbols]

[0057] 2...piezoelectric element, 10...element body, 3...wiring member, 11, 12, 13...external electrodes, 15, 16, 17...internal electrodes, 11d, 12d, 13d...overlapping regions, 11e, 12e, 13e...bonding regions, 11f, 12f, 13f...exposed regions, R1, R11, R12, R13, R14...active regions.

Claims

1. an element body having a first main surface and a second main surface opposing each other in a first direction, and a first side surface and a second side surface opposing each other in a second direction perpendicular to the first direction and connecting the first main surface and the second main surface; a plurality of internal electrodes provided within the element body and stacked in the first direction; a plurality of external electrodes, each having a first electrode portion provided on the first side surface and connected to a corresponding internal electrode, and a second electrode portion provided on the first main surface and connected to the first electrode portion; the element body includes a piezoelectrically active region disposed between the plurality of internal electrodes; the second electrode portion includes an overlapping region that overlaps the active region when viewed from the first direction, an area of ​​the overlapping region is 50% or more of an area of ​​the second electrode portion; a length of the second electrode portion in the second direction is 50% or more of a length of the first main surface in the second direction; Piezoelectric element.

2. When viewed from the first direction, the active region is spaced apart from an outer edge of the element body. The piezoelectric element according to claim 1 .

3. The overlapping region includes a bonding region to be bonded to a wiring member. The piezoelectric element according to claim 1 or 2.

4. The overlapping region includes an exposed region exposed from the wiring member. The piezoelectric element according to claim 3 .

5. The overlapping region is entirely covered by the wiring member. The piezoelectric element according to claim 3 .

Images