JP2017117934A - Piezoelectric element, sound generator, sound generation device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric element excellent in durability and in which crack in the boundary of a surface electrode and a piezoelectric layer or exfoliation of the surface electrode is less likely to occur during high voltage driving, and to provide a sound generator, a sound generation device and an electronic apparatus including the piezoelectric element.SOLUTION: A piezoelectric element 1 is provided with a surface electrode 5 at least on one principal surface of a laminate 4 laminating a piezoelectric layer 2 and an internal electrode layer 3, and the outer periphery of the surface electrode 5 has irregularities, when viewing from the lamination direction. When the piezoelectric element 1 is displaced, a stress generated in the boundary of the piezoelectric layer 2 and surface electrode 5 is dispersed. Consequently, occurence of crack in the boundary of the surface electrode 5 and laminate 4 can be suppressed, and exfoliation of the surface electrode 5 from the laminate 4 can also be suppressed.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric element, an acoustic generator, an acoustic generator, and an electronic device.

  Piezoelectric actuators and sound generating elements are used as drive sources for vibration devices and acoustic equipment. In such applications, a laminated piezoelectric element having a surface electrode for applying voltage on its surface is used (see, for example, Patent Document 1).

JP 2007-173456 A

  In recent years, piezoelectric elements for use in vibration devices and acoustic equipment are required to have a larger displacement, and accordingly, a higher drive voltage is required. However, when the piezoelectric element is driven at a high voltage, there is a possibility that a crack is generated at the boundary between the surface electrode and the laminate, or the surface electrode is peeled off from the laminate.

  The present invention has been made in view of the above circumstances, and provides a piezoelectric element with excellent durability that is unlikely to cause cracks and electrode peeling in high-voltage driving, and an acoustic generator, an acoustic generator, and an electronic device including the piezoelectric element. The purpose is to provide.

  The piezoelectric element of the present invention is a piezoelectric element in which a surface electrode is provided on at least one main surface of a laminate in which a piezoelectric layer and an internal electrode layer are laminated, and the outer periphery of the surface electrode is viewed from the lamination direction. Is characterized by having irregularities.

  According to another aspect of the present invention, there is provided an acoustic generator including the piezoelectric element and a diaphragm attached to the other main surface of the piezoelectric element.

  According to another aspect of the present invention, there is provided a sound generator comprising: the sound generator described above; and a housing that houses the sound generator.

  According to another aspect of the invention, there is provided an electronic apparatus comprising: the above-described acoustic generator; an electronic circuit connected to the piezoelectric element constituting the acoustic generator; and a housing that houses the acoustic generator and the electronic circuit. It is characterized by that.

  According to the piezoelectric element of the present invention, it is possible to suppress the occurrence of cracks at the boundary between the surface electrode and the laminate, and to provide a highly durable piezoelectric element capable of suppressing the separation of the surface electrode from the laminate. Can do.

  Also, according to the acoustic generator of the present invention, peaks and dips are flattened due to the occurrence of spurious vibrations in the piezoelectric element, and acoustic performance such as sound pressure and sound quality can be improved.

In addition, according to the sound generator and the electronic apparatus of the present invention, the sound performance such as sound pressure and sound quality can be improved as in the case of the sound generator of the present invention.

(A) is a schematic perspective view which shows an example of the piezoelectric element of this embodiment, (b) is a schematic sectional drawing of an example cut | disconnected by the XX line shown to (a), (c) is Y shown to (a). It is a schematic sectional drawing of an example cut | disconnected by the -Y line | wire. It is a disassembled perspective view of an example of the piezoelectric element of this embodiment. It is the principal part enlarged plan view which expanded an example of the A section of Drawing 1 (a). It is the principal part enlarged plan view which expanded the other example of the A section of Fig.1 (a). (A) is a schematic plan view of an example of the piezoelectric element of this embodiment, (b) is a schematic sectional drawing of an example cut | disconnected by the ZZ line | wire shown to (a). (A), (b) is a schematic sectional drawing of the other example cut | disconnected by the ZZ line | wire shown to Fig.5 (a). (A) is a typical top view which shows schematic structure of embodiment of the acoustic generator of this embodiment, (b) is a schematic sectional drawing of an example cut | disconnected by the VV line | wire of (a), (C) is a schematic sectional drawing of the other example cut | disconnected by the VV line of (a). It is a block diagram showing an example of an embodiment of a sound generator of this embodiment. It is a block diagram which shows an example of embodiment of the electronic device of this embodiment. (A) is a graph which shows an example of the frequency-sound pressure characteristic of the sound generator which concerns on embodiment of this embodiment, (b) is a graph which shows the frequency-sound pressure characteristic of the conventional sound generator.

  Hereinafter, an example of an embodiment of a piezoelectric element of the present invention will be described in detail with reference to the accompanying drawings. In addition, this invention is not limited by embodiment shown below.

  1A is a schematic perspective view showing an example of the piezoelectric element of the present embodiment, FIG. 1B is a schematic cross-sectional view of an example cut along the line XX shown in FIG. 1A, and FIG. ) Is a schematic cross-sectional view of an example cut along line YY shown in FIG. FIG. 2 is an exploded perspective view of an example of the piezoelectric element of the present embodiment. 3 is an enlarged plan view of an essential part of an example of the A part in FIG. 1A, and FIG. 4 is an enlarged plan view of an essential part of another example of the A part in FIG. .

  1 to 4 is a piezoelectric element in which a surface electrode 5 is provided on at least one main surface of a laminate 4 in which a piezoelectric layer 2 and an internal electrode layer 3 are laminated. As seen from the stacking direction, the outer peripheral portion 8 of the surface electrode 5 has irregularities 10. For example, the piezoelectric element 1 in the example shown in FIG. 1 is a piezoelectric element including a laminate 4 in which a plurality of piezoelectric layers 2 and a plurality of internal electrode layers 3 are alternately laminated. The laminate 4 is a rectangular plate-like body having a main surface viewed from the plane (upper surface) having a length direction and a width direction. Therefore, the piezoelectric element 1 also has a rectangular shape having a length direction and a width direction in plan view.

The piezoelectric layer 2 is made of a ceramic having piezoelectric characteristics. As such a ceramic, for example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ -PbTiO ₃ ), lithium niobate (LiNbO ₃ ), Lithium tantalate (LiTaO ₃ ) or the like can be used. The thickness of one layer of the piezoelectric layer 2 is set to 0.01 to 0.1 mm, for example, in order to drive with a low voltage. Further, in order to obtain a large bending vibration, for example, the piezoelectric constant d31 is set to 200 pm / V or more.

The internal electrode layers 3 are disposed so as to face each other with the piezoelectric layer 2 interposed therebetween, and sandwich the piezoelectric layer 2 from above and below. As a material for the internal electrode layer 3, for example, a conductor mainly composed of silver or silver-palladium that can be fired at a low temperature, or a conductor containing copper, platinum, or the like can be used. You may let them.

  In addition, the piezoelectric element 1 includes a surface electrode 5 on at least one main surface of the laminate 4 as shown in FIGS. As a material of the surface electrode 5, silver, a silver compound containing silver or the like containing glass mainly containing silica, nickel, or the like can be used. Further, in the laminate 4, the folded electrode 7 is formed on the same surface as the one main surface on which the surface electrode 5 is formed. The folded electrode 7 is electrically separated from the surface electrode 5 and is not connected. As the material of the folded electrode 7, the same silver material as that of the surface electrode 5, silver, a silver compound containing silica as a main component, nickel, or the like can be used.

  Further, side electrodes 6 that are electrically connected to the surface electrode 5 and the folded electrode 7 are provided on the side surfaces (end surfaces) facing each other in the length direction of the multilayer body 4. As the material for the side electrode 6, silver, a silver compound containing silver or a glass containing silica as a main component, nickel, or the like, similar to the surface electrode 5, can be used.

  As a power supply member (wiring member) for supplying power to the piezoelectric element 1, a flexible wiring board, an insulation-coated lead wire or the like may be used, and this may be joined to the surface electrode 5 via a conductive adhesive or solder.

  A piezoelectric element 1 of the present invention is a piezoelectric element in which a surface electrode 5 is provided on at least one main surface of a laminate 4 in which a piezoelectric layer 2 and an internal electrode layer 3 are laminated. The outer peripheral portion 8 of the surface electrode 5 has irregularities 10. With such a configuration, when the piezoelectric element 1 is displaced, the stress generated at the boundary between the piezoelectric layer 2 and the surface electrode 5 is dispersed, and a crack is generated at the boundary between the surface electrode 5 and the laminate 4. It can suppress that the surface electrode 5 peels from the laminated body 4. FIG. As a result, the durability of the piezoelectric element 1 in high voltage driving can be improved. Further, with such a configuration, spurious vibrations are generated, and due to this effect, damping and division of natural vibrations occur, and strong expression of piezoelectric resonance at a specific frequency can be suppressed. Therefore, when used as a vibration source of the sound generator 11, since the peak and dip are flattened in the frequency-sound pressure characteristics, the vibration plate 12 is joined to the other main surface of the piezoelectric element 1 to generate the sound generator. The sound quality in the case of 11 can be improved.

  The example shown in FIGS. 3 and 4 is an example in which the convex portions 101 and the concave portions 102 are alternately and continuously connected in a wavy manner, and the outer peripheral portion 8 has a waveform. The example shown in FIG. 3 is an example in which the convex portion 101 and the concave portion 102 are regularly and continuously repeated even in the same waveform, in a semicircular arc shape having the same shape. Further, the example shown in FIG. 4 is an example in which the convex portions 101 and the concave portions 102 have different shapes even in the same waveform, and the convex portions 101 and the concave portions 102 are irregularly repeated. In the example shown in FIG. 3, the size of the unevenness 10 is such that the size t from the top of the convex portion 101 to the bottom of the concave portion 102 is, for example, 0.05 mm to 1.00 mm.

  The example shown in FIG. 3 shows the dimensions of the irregularities 10 in the outer peripheral portion 8 of the surface electrode 5. The length from the top of the convex portion 101 to the top of the next convex portion 101 or the length (pitch) p from the bottom of the concave portion 102 to the bottom of the next concave portion 102 is 0.05 mm to 1.00 mm. Is preferred. When the pitch p is within this range, the stress generated at the boundary between the piezoelectric layer 2 and the internal electrode layer 3 when the piezoelectric element 1 is displaced is further dispersed, and a crack is generated at the boundary between the surface electrode 5 and the laminate 4. Can be suppressed, and the surface electrode 5 can be prevented from peeling from the laminate 4. As a result, the durability of the piezoelectric element 1 in high voltage driving can be further improved.

In the example shown in FIG. 3, the angle θ at which the straight line connecting the apex of the convex portion 101 and the bottom of the concave portion 102 is inclined with respect to the straight line parallel to the adjacent side among the sides of the piezoelectric element 1 is 30 °. It is preferably ˜60 °. When the angle θ is within this range, the stress generated at the boundary between the piezoelectric layer 2 and the surface electrode 5 when the piezoelectric element 1 is displaced is further dispersed, and cracks are generated at the boundary between the surface electrode 5 and the laminate 4. Generation | occurrence | production can be suppressed and it can suppress that the surface electrode 5 peels from the laminated body 4. FIG. As a result, the durability of the piezoelectric element 1 in high voltage driving can be further improved.

  Moreover, it is preferable that the outer peripheral part 8 of the surface electrode 5 has the unevenness | corrugation 10 of a different shape like the example shown in FIG. The uneven shape 10 having different shapes means that the shapes of the convex portions 101 and the concave portions 102 are different. By adopting such a configuration, the stress generated at the boundary between the piezoelectric layer 2 and the surface electrode 5 when the piezoelectric element 1 is displaced is more dispersed by the convex portions 101 and the concave portions 102 having different shapes. It can suppress that a crack generate | occur | produces in the boundary of 5 and the laminated body 4, and can suppress that the surface electrode 5 peels from the laminated body 4. FIG. As a result, the durability of the piezoelectric element 1 in high voltage driving can be further improved. Furthermore, by adopting such a configuration, the symmetry of the surface electrode 5 is broken by the convex portions 101 and the concave portions 102 having different shapes, so that the symmetry of resonance is broken and spurious vibration is likely to occur. When the piezoelectric element 1 is used as a vibration source of the sound generator 11, the sound performance such as sound pressure and sound quality can be improved.

  FIG. 5A is a schematic plan view of an example of the piezoelectric element of the present embodiment, and FIG. 5B is a schematic sectional view of an example cut along the line ZZ shown in FIG. 5A. 6 (a) and 6 (b) are schematic cross-sectional views of another example cut along the line ZZ shown in FIG. 5 (a), and are cross-sectional views showing variations of the vertical cross-sectional shape of the surface electrode 5. is there. As shown in FIGS. 5 and 6, it is preferable that the outer peripheral portion 8 of the surface electrode 5 is thinner than the central portion 9. By adopting such a configuration, it is possible to reduce the residual stress accompanying the formation of the surface electrode 5 by baking and to reduce the superimposition of the residual stress on the stress generated during driving, thereby further suppressing the occurrence of cracks and electrode peeling. The durability in voltage driving can be further improved. The central portion 9 is indicated by reference numeral 9 in the central region of the surface electrode 5 in FIG. 5B, and is a portion of about 80% of the entire length. Moreover, the outer peripheral part 8 is shown by the code | symbol 8 in the outer peripheral area | region of the surface electrode 5 in FIG.5 (b), and is a part about 10% of the whole length.

  FIG. 6A shows a configuration in which the vertical cross-sectional shape of the surface electrode 5 is a two-step shape, and the thickness of the outer peripheral portion 8 is thinner than the thickness of the central portion 9. (B) is a configuration in which the vertical cross-sectional shape of the surface electrode 5 is a three-stepped shape, and the thickness of the outer peripheral portion 8 is thinner than the thickness of the central portion 9. On the other hand, FIG. 5B shows a configuration in which the surface electrode 5 gradually decreases in thickness from the central portion 9 toward the outer peripheral portion 8. In this way, by adopting the configuration as shown in FIG. 5B, the residual stress accompanying the electrode formation can be gradually reduced and the overlapping region of the residual stress on the stress generated during driving can be dispersed. Generation | occurrence | production of electrode peeling is further suppressed and durability in a high voltage drive can further be improved. In FIG. 5B, h1 is the thickness of the average value of the thickness of the central portion 9, h2 is the thickness at a position of 1/2 of the entire length of the outer peripheral portion 8, and the thickness h2 is the thickness of the thickness h1. It is preferable that it is 50% or less. Thereby, when the piezoelectric element 1 is displaced, the stress generated at the boundary between the piezoelectric layer 2 and the internal electrode layer 3 is further dispersed, and the generation of cracks at the boundary between the surface electrode 5 and the laminate 4 is suppressed. Moreover, it can suppress that the surface electrode 5 peels from the laminated body 4. FIG. As a result, the durability of the piezoelectric element 1 in high voltage driving can be further improved.

  Next, a method for manufacturing the piezoelectric element of this embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 2 is produced. Specifically, a ceramic slurry is prepared by mixing a calcined powder of piezoelectric ceramic, a binder made of an organic polymer such as acrylic or butyral, and a plasticizer. And a ceramic green sheet is produced using this ceramic slurry by using tape molding methods, such as a doctor blade method and a calender roll method. As the piezoelectric ceramic, any material having piezoelectric characteristics may be used. For example, a perovskite oxide made of lead zirconate titanate (PbZrO ₃ —PbTiO ₃ ) can be used. As the plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP), or the like can be used.

  Next, a conductive paste to be the internal electrode layer 3 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium metal powder. This conductive paste is applied on the above ceramic green sheet in a desired pattern of internal electrode layers using a screen printing method.

  Then, a plurality of ceramic green sheets printed with this conductive paste are laminated, subjected to binder removal treatment at a predetermined temperature, fired at a temperature of 900 ° C. to 1200 ° C., and predetermined using a surface grinder or the like. The laminated body 4 provided with the internal electrode layers 3 and the piezoelectric body layers 2 that are alternately laminated is manufactured by performing a grinding process so as to have the shape as described above.

  The laminate 4 is not limited to the one produced by the above production method, and any production method can be used as long as the laminate 4 formed by laminating a plurality of internal electrode layers 3 and piezoelectric layers 2 can be produced. May be produced.

  Thereafter, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer, and a solvent to a mixture of conductive particles mainly composed of silver and glass is screen-printed on the main surface and side surfaces of the laminate 4. After printing and the like by drying, a baking process is performed at a temperature of 600 ° C. to 800 ° C. to form the surface electrode 5, the side electrode 6, and the folded electrode 7.

  A method of forming the outer peripheral portion 8 of the surface electrode 5 so as to be uneven 10 is as follows.

  The surface electrode 5 is formed by the screen printing method as described above, and is combined with the screen mesh of the screen mesh plate to be used to create a plate plate having a resist thickness reduced to 5 μm or less. Further, in combination with printing conditions, printing is performed so as to leave a trace of the screen mesh, and the unevenness 10 is produced on the outer peripheral portion 8 of the surface electrode 5. Moreover, you may form by the printing method similarly using the platemaking which provided the uneven | corrugated pattern in the outer peripheral part 8 of the surface electrode 5. FIG.

  In order to electrically connect the surface electrode 5 and the internal electrode 3, it is formed so as to penetrate the piezoelectric layer 2 in place of the side electrode 6 formed on the side surface of the laminate 4 as described above. You may use the made through conductor.

  Thereafter, the laminate 4 is subjected to polarization treatment to impart piezoelectric activity. In the case of the piezoelectric element shown in FIGS. 1 and 2, for example, in the case of the piezoelectric element shown in FIGS. 1 and 2, the surface electrode is connected to the negative electrode, and the folded electrode 7 is connected to the positive electrode, for example, in the polarization process, for example, 2 kV / mm to 3 kV / mm The potential difference may be applied for several seconds as the application time at an ambient temperature of 15 ° C. to 35 ° C. The voltage, ambient temperature, and application time are suitably selected depending on the properties of the piezoelectric material.

  When the desired piezoelectric element 1 can be obtained as described above and a power supply member (wiring member) is required, the power supply member (wiring member) may be connected to the piezoelectric element 1 by the following method.

For example, when a flexible wiring substrate is connected and fixed (bonded) to the piezoelectric element 1 using a conductive adhesive, a conductive adhesive paste is applied and formed at a predetermined position of the piezoelectric element 1 using a technique such as screen printing. To do. Then, the flexible wiring board is connected and fixed to the piezoelectric element 1 by curing the conductive adhesive paste with the flexible wiring board being in contact therewith. The conductive adhesive paste may be applied and formed on the flexible wiring board side.

  In addition, as the power supply member (wiring member), an insulation-coated lead wire may be used, and solder may be used as the bonding material, and a member having the same function can be suitably selected.

  Next, an example of the sound generator of this embodiment will be described.

  As shown in FIG. 8, the acoustic generator 11 of the present embodiment includes the above-described piezoelectric element 1 and a vibration plate 12 to which the piezoelectric element 1 is attached and vibrates due to vibration of the piezoelectric element 1. Furthermore, the sound generator 11 shown in the drawing is provided on at least a part of the outer peripheral portion of the diaphragm 2 and includes a frame 13 as a support body that supports the diaphragm 12.

  The piezoelectric element 1 is an exciter that excites the diaphragm 12 by vibrating under application of a voltage. The main surface of the piezoelectric element 1 and the main surface of the diaphragm are joined by an adhesive such as an epoxy resin, and the piezoelectric element 1 bends and vibrates, so that the piezoelectric element 1 gives a certain vibration to the diaphragm 12 to generate sound. Can be generated.

  The peripheral edge of the diaphragm 12 is fixed to the frame 13, and vibrates with the piezoelectric element 1 by the vibration of the piezoelectric element 1. This diaphragm 12 can be formed using various materials, such as resin and a metal, for example, can be comprised with resin films, such as 10-200 micrometers thick, polyethylene, a polyimide, a polypropylene. The shape of the diaphragm 12 is not particularly limited, and may be a circular plate shape or an elliptical plate shape other than a polygonal plate shape such as a rectangular plate shape. When the diaphragm 12 is formed of a resin film, it is preferable that the peripheral edge portion is fixed to the frame body 13 in a state where tension is applied to the diaphragm 12. By configuring the diaphragm 12 with a resin film, the diaphragm 12 is bent and vibrated with a large amplitude, the width of the resonance peak in the frequency characteristics of the sound pressure is widened, and the height is lowered to reduce the difference between the resonance peak and the dip. Can be reduced. However, the vibration plate 12 is not limited to a resin film, and may be a resin plate, a metal plate, a glass plate, or the like. For example, a part of a casing of an electronic device such as a portable terminal or a part of a display functions as the vibration plate 12. You may do it.

  The frame body 13 functions as a support body that supports the outer peripheral portion of the main surface of the diaphragm 12. By providing the vibration space by supporting the outer peripheral portion of the diaphragm 12 with the frame 13, the amplitude of the diaphragm 12 is increased, and the sound pressure can be improved. The frame 13 can be formed using various materials such as metals such as stainless steel, glass, acrylic resin, polycarbonate resin, and polybutylene terephthalate resin.

  The frame body 13 is bonded to one main surface or the other main surface of the diaphragm 12 via a bonding material. As the bonding material, a resin-based adhesive, a viscoelastic material molded into a sheet shape, a structure in which a base material layer and a layer made of a viscoelastic material are laminated, or the like can be used. An acrylic or epoxy adhesive or a rubber, acrylic, silicone or urethane adhesive is used. As the base material layer, acetate foam, acrylic foam, cellophane, polyethylene foam, paper, and nonwoven fabric are used.

  The acoustic generator 11 may be configured not to include the frame body 13, but when the frame body 13 is joined to the main surface to which the piezoelectric element 1 of the diaphragm 12 is joined as in the example illustrated in FIG. 9. In particular, when the combined thickness of the frame 13 and the bonding material is larger than the thickness of the piezoelectric element 1, the piezoelectric element 1 can be protected by the frame 13. Further, the diaphragm 12 is supported, and the electronic device can be easily fixed to the housing or the like.

  The frame 13 may be composed of one frame member as shown in FIG. 7 (b), or may be composed of two upper and lower frame members as shown in FIG. 7 (c). In this case, the tension of the diaphragm 12 can be stabilized by sandwiching the diaphragm between the two frame members. The upper and lower frame members have a thickness of, for example, 100 to 5000 μm.

  In the acoustic generator of the present embodiment, as shown in FIGS. 7B and 7C, the piezoelectric element 1 to at least a part of the surface of the diaphragm 12 (for example, the peripheral part of the piezoelectric element 1). You may further have the resin layer 14 provided so that it might cover. The resin layer 14 is formed, for example, so that the Young's modulus is in the range of, for example, 1 MPa to 1 GPa. For example, an acrylic resin can be used. By embedding the piezoelectric in the resin layer 14, an appropriate damper effect can be induced, so that the resonance phenomenon can be suppressed and the peak or dip in the frequency characteristic of the sound pressure can be suppressed to a small level. In addition, as shown in FIG.7 (b) and FIG.7 (c), the resin layer 14 may be formed so that it may become the same height as the upper frame member in the frame 13. FIG.

  Since the sound generator according to the present embodiment is configured using a piezoelectric element that can flatten peaks and dips in the frequency-sound pressure characteristics, the sound generator has high sound quality. Such an acoustic generator includes, for example, a state in which the diaphragm 12 is mechanically fixed to a support portion provided in a housing of an electronic device or the like, or is fixed via a bonding material, or includes a small housing. The sound generation device can be used as a sound generation source of an electronic device in a state where the sound generation device is incorporated in the casing of the electronic device.

  Next, an example of the sound generator of this embodiment will be described.

  The sound generation device 100 is a sound generation device such as a so-called speaker. As shown in FIG. 8, the sound generation device 100 of this example includes a sound generator 111 and a housing 20 that houses the sound generator 11. Note that a part of the housing 20 may be the diaphragm 12 constituting the acoustic generator 11, and that the housing 20 accommodates the acoustic generator 11 means that a part of the acoustic generator 11 (piezoelectric element 1). ) Is also included.

  The housing 20 resonates the sound generated by the sound generator 11 and radiates sound to the outside from an opening (not shown) formed in the housing 20. The housing 20 can be formed using various materials such as metals such as aluminum and magnesium alloys, resins such as polycarbonate, and wood. By having such a housing | casing 20, the sound pressure in a low frequency band can be raised, for example.

  Such a sound generator 100 can be used alone as a speaker, and can be suitably incorporated into a portable terminal, a thin television, a tablet terminal, or the like, as will be described later. Moreover, it can also be incorporated into home appliances that have not been prioritized in terms of sound quality, such as refrigerators, microwave ovens, vacuum cleaners, and washing machines.

  Since the sound generator of the present embodiment described above is configured using a sound generator including a piezoelectric element that can flatten peaks and dips in frequency-sound pressure characteristics, it has high sound quality.

  Next, an example of the electronic apparatus of this embodiment will be described.

As shown in FIG. 9, the electronic device 50 according to the present embodiment includes an acoustic generator 11, an electronic circuit 60 connected to the acoustic generator 10, and a housing 70 that houses the electronic circuit 60 and the acoustic generator 11. And has a function of generating sound from the sound generator 11. In addition, as the electronic device 50, not only the acoustic generator 11 is accommodated in the casing 70 as it is, but also the acoustic generator 100 that accommodates the acoustic generator 11 (consisting of the acoustic generator 11 and the casing 20). Is included in the housing 70. In addition, a part of the housing 70 may be the diaphragm 12 constituting the sound generator 11.

  The electronic device 50 includes an electronic circuit 60. Examples of the electronic circuit 60 include a circuit for processing image information to be displayed on a display and audio information transmitted by a portable terminal, a communication circuit, and the like. At least one of these circuits may be included, or all the circuits may be included. Further, it may be a circuit having other functions. Furthermore, you may have a some electronic circuit. The electronic circuit 60 shown in the figure includes a controller 60a, a transmission / reception unit 60b, a key input unit 60c, and a microphone input unit 60d. The electronic circuit 60 is connected to the sound generator 11 and has a function of outputting an audio signal to the sound generator 11. The sound generator 11 generates sound based on the sound signal input from the electronic circuit 60.

  Moreover, the electronic device 50 includes a display unit 50a, an antenna 50b, and the sound generator 11, and includes a housing 70 that accommodates these devices. Although FIG. 9 shows a state in which each device including the controller 60a is housed in one housing, the housing form of each device is not limited. In the present embodiment, it is only necessary that at least the electronic circuit 60 and the sound generator 11 are accommodated in one housing 70.

  The controller 60 a is a control unit of the electronic device 50. The transmission / reception unit 60b transmits / receives data via the antenna 50b based on the control of the controller 60a. The key input unit 60c is an input device of the electronic device 50 and accepts a key input operation by an operator. The key input unit 60 c may be a button-like key or a touch panel integrated with the display unit 50. The microphone input unit 60d is also an input device of the electronic device 50, and receives a voice input operation by an operator. The display unit 50a is a display output device of the electronic device 50, and outputs display information based on the control of the controller 60a.

  The sound generator 11 operates as a sound output device in the electronic device 60. The sound generator 11 is connected to the controller 60a of the electronic circuit 60, and emits sound upon application of a voltage controlled by the controller 60a.

  In FIG. 9, the electronic device is described as a portable terminal device. However, the electronic device is not limited to the type of the electronic device, and may be applied to various consumer devices having a function of emitting sound. For example, flat-screen televisions and car audio devices can of course be used for products having a function of generating sound, for example, various products such as vacuum cleaners, washing machines, refrigerators, microwave ovens, and the like.

  The electronic apparatus of the present embodiment described above has high sound quality because it is configured using an acoustic generator including a piezoelectric element that can flatten peaks and dips in frequency-sound pressure characteristics.

  Next, a specific example of the sound generator of this embodiment will be described.

  The piezoelectric element was a long plate having a length of 34.0 mm, a width of 15.0 mm, and a thickness of 0.2 mm. The piezoelectric element has a structure in which piezoelectric layers having a thickness of 30 μm and internal electrodes are alternately stacked, and the total number of piezoelectric layers is 4 to 50 layers. The piezoelectric layer was formed of lead zirconate titanate in which part of Zr was substituted with Nb or the like, and silver palladium was used for the internal electrode.

  First, a plurality of conductive pastes made of silver-palladium printed on a ceramic green sheet were prepared, and these were laminated, and then press-contacted and cut into a predetermined size to produce a molded body. Thereafter, degreasing was performed at a predetermined temperature, followed by firing at 1000 ° C. to obtain a laminated sintered body.

  A conductive paste made of silver was printed on the surface and side surfaces of this laminated sintered body, dried, and then fired at 700 ° C. to form surface electrodes, side electrodes, and folded electrodes.

  The surface electrode was formed by screen printing using mesh-type production and sales. At that time, the type of screen mesh and printing conditions were selectively performed to form irregularities on the outer periphery of the surface electrode.

  Next, a voltage having a potential difference of 2 kV / mm was applied between the internal electrodes via the surface electrode at room temperature, and a polarization treatment was performed to manufacture a piezoelectric element.

  Next, using an acrylic anaerobic adhesive paste, after bonding the piezoelectric element to one end side in the length direction of an acrylic plate (diaphragm) having a length of 110 mm, a width of 60 mm, and a thickness of 0.5 mm, The lead wire with the insulation coating was joined to the surface electrode with solder to produce an acoustic generator.

  The outer circumferences of both main surfaces of the diaphragm of the sound generator according to the example produced as described above were fixed with a frame jig for sound pressure measurement made of polybutylene terephthalate, and applied voltage 30 Vp-p, measurement. Frequency-sound pressure characteristics were measured under the condition of a distance of 3 cm. The result is shown in FIG.

  On the other hand, the acoustic generator produced with the following method was prepared as a comparative example.

  When forming the surface electrode, the type of screen mesh and printing conditions were selectively performed to form a surface electrode having no irregularities on the outer periphery. Other manufacturing methods were the same as those in the above example, and a piezoelectric element was manufactured.

  Using this piezoelectric element, an acoustic generator was produced by the same method as in the above embodiment, and the outer circumferences of both main surfaces of the diaphragm of the acoustic generator were made of polybutylene terephthalate as in the above embodiment. The frequency-sound pressure characteristics were measured under the conditions of an applied voltage of 30 Vp-p and a measurement distance of 3 cm. The result is shown in FIG.

  In comparison between FIG. 10 (a) and FIG. 10 (b), when comparing the peak and dip of the sound pressure particularly at frequencies of 400 Hz to 2 kHz and frequencies of 5 kHz to 8 kHz, FIG. It can be seen that the difference is clearly smaller compared to FIG. 10B, which is a comparative example.

  Also, the lead wire was soldered and fixed to the surface electrode with a single piezoelectric element, and the surface electrode was peeled off in the comparative example as a result of checking the presence or absence of peeling of the surface electrode using a tensile test device. On the other hand, peeling of the surface electrode was not confirmed in this example.

  From the above, in the piezoelectric element, it was confirmed that the outer peripheral portion of the surface electrode had irregularities when viewed from the stacking direction, so that the surface electrode could be prevented from peeling from the stack. In addition, when such a piezoelectric element is used as a vibration source of an acoustic generator, the peak and dip are flattened in the frequency-sound pressure characteristics. Therefore, sound is generated by joining a diaphragm to the other main surface of the piezoelectric element. It has been confirmed that the sound quality can be improved when the device is used.

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 2 Piezoelectric layer 3 Internal electrode layer 4 Laminated body 5 Surface electrode 6 Side electrode 7 Folding electrode 8 Outer peripheral part 9 Center part 10 Concavity and convexity 101 Convex part 102 Concave part 11 Sound generator 12 Diaphragm 13 Frame 14 Resin layer 20 70 Housing 100 Sound generator 50 Electronic device 60 Electronic circuit

Claims (7)

  A piezoelectric element in which a surface electrode is provided on at least one main surface of a laminate in which a piezoelectric layer and an internal electrode layer are laminated, and the outer periphery of the surface electrode has irregularities when viewed from the lamination direction. A piezoelectric element characterized by comprising:   2. The piezoelectric element according to claim 1, wherein the outer peripheral portion of the surface electrode has irregularities with different shapes.   3. The piezoelectric element according to claim 1, wherein a thickness of the outer peripheral portion of the surface electrode is thinner than a thickness of a central portion.   The piezoelectric element according to claim 3, wherein the thickness of the surface electrode gradually decreases from the central portion toward the outer peripheral portion.   An acoustic generator comprising: the piezoelectric element according to any one of claims 1 to 4; and a diaphragm attached to the other main surface of the piezoelectric element.   An acoustic generator comprising: the acoustic generator according to claim 5; and a housing that accommodates the acoustic generator. The acoustic generator according to claim 5, an electronic circuit connected to the piezoelectric element constituting the acoustic generator, and a housing that houses the acoustic generator and the electronic circuit. Electronic equipment.