JP6431086B2 - Piezoelectric element, sound generator, sound generator, and electronic device - Google Patents

Description

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

  Conventionally, a multilayer piezoelectric element in which a plurality of internal electrode layers and piezoelectric layers are stacked is known. As an element of an actuator, a resonator, a filter, or a vibration of an acoustic generator such as a buzzer or a panel speaker. Used as a source. In such a piezoelectric element, it is important from the viewpoint of ensuring reliability to suppress the generation of stress and local stress concentration inside the element during driving. For example, a multi-layer piezoelectric element that suppresses such stress concentration by providing a non-electrode forming portion at the periphery of the internal electrode layer is known (see, for example, Patent Document 1).

JP 2001-025268 A

  By the way, in the piezoelectric element having the above-described structure, the positions of the internal electrode layers having the periphery as the non-electrode forming portion are aligned in the stacking direction. Therefore, when the piezoelectric element is used as a vibration source for an acoustic generator, the position of the expanding and contracting piezoelectric active region is uniform, so that there is a possibility that the resonance frequency is matched and the piezoelectric resonance is strongly developed. Therefore, there is a problem that a peak or dip increases in the frequency-sound pressure characteristics of the sound generator provided with this piezoelectric element, and the sound quality may be deteriorated. Similarly, there has been a problem that the sound quality of the acoustic generator and the electronic apparatus including the piezoelectric element may be deteriorated.

  The present invention has been made in view of the above circumstances, a piezoelectric element capable of suppressing the strong expression of piezoelectric resonance at a specific frequency and improving the sound quality of an acoustic generator, and an acoustic equipped with this piezoelectric element. It aims at providing a generator, a sound generator, and an electronic device.

The piezoelectric element of the present invention has a rectangular plate shape having a length direction and a width direction in which the first internal electrode layer and the second internal electrode layer are alternately stacked so as to face each other through the piezoelectric layer. A piezoelectric element, wherein the first internal electrode layer is provided so as to reach both side surfaces in the width direction when viewed from the stacking direction, and the second internal electrode layer is disposed between both side surfaces in the width direction. provided so as to at least partially there is a gap, the distance between the second internal electrode layer and the side surface have different portions when viewed the entire area of said gap, said second internal electrode The shape of the gap between the layer and one side is different from the shape of the gap between the second internal electrode layer and the other side .

  According to another aspect of the present invention, there is provided an acoustic generator comprising: the above-described piezoelectric element; and a diaphragm to which the piezoelectric element is attached and which vibrates due to vibration of the piezoelectric element.

  According to another aspect of the present invention, there is provided a sound generation apparatus including the above-described sound generator and a housing that houses the sound generator.

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

  According to the piezoelectric element of the present invention, strong expression of piezoelectric resonance at a specific frequency can be suppressed. Therefore, when used as a vibration source of an acoustic generator, peaks and dips in the frequency-sound pressure characteristics are flattened, and the sound quality of the acoustic generator can be improved. In addition, according to the sound generator, sound generator, and electronic apparatus of the present invention, the sound performance can be improved.

(A) is a schematic perspective view which shows an example of the piezoelectric element of this embodiment, (b) is pattern explanatory drawing of the internal electrode layer of the piezoelectric element shown to (a), (c) is a piezoelectric element shown to (a). It is a disassembled perspective view. (A) is a schematic perspective view which shows the other example of the piezoelectric element of this embodiment, (b) is pattern explanatory drawing of the internal electrode layer of the piezoelectric element shown to (a), (c) is a piezoelectric shown to (a). It is a disassembled perspective view of an element. (A)-(d) is explanatory drawing of the variation of the pattern of a 2nd internal electrode layer. (A) is a schematic perspective view which shows another example of the piezoelectric element of this embodiment, (b) is explanatory drawing at the time of the drive of a bimorph type piezoelectric element. (A)-(d) is explanatory drawing of the variation of the relationship between the space | interval d1 and the space | interval d2. (A) And (b) is explanatory drawing of the variation of the pattern of the 2nd internal electrode layer from which an area differs. (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 AA line of (a), (C) is a schematic sectional drawing of the other example cut | disconnected by the AA 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.

  FIG. 1A is a schematic perspective view showing an example of the piezoelectric element of the present embodiment, FIG. 1B is an explanatory diagram of patterns of internal electrode layers of the piezoelectric element shown in FIG. 1A, and FIG. It is a disassembled perspective view of the piezoelectric element shown to Fig.1 (a). 2A is a schematic perspective view showing another example of the piezoelectric element of the present embodiment, FIG. 2B is a pattern explanatory diagram of the internal electrode layer of the piezoelectric element shown in FIG. FIG. 3C is an exploded perspective view of the piezoelectric element shown in FIG.

  The piezoelectric element 1 of the present embodiment shown in FIGS. 1 and 2 is a laminate in which the first internal electrode layers 11 and the second internal electrode layers 12 are alternately stacked so that they face each other via the piezoelectric layer 13. A rectangular plate-shaped piezoelectric element having a body 14 and having a length direction and a width direction, and the second internal electrode layer 12 is located between both side surfaces in the width direction of the stack 14 when viewed from the stacking direction. The gap 120 is provided in at least a part of the gap 120, and when the entire area of the gap 120 is viewed, there is a portion where the distance d between the second internal electrode layer 12 and the side surface is different.

  The piezoelectric element 1 is a rectangular plate-shaped piezoelectric element in which a first internal electrode layer 11 and a second internal electrode layer 12 are alternately stacked so as to face each other via a piezoelectric layer 13. More specifically, the first internal electrode layer 11, the second internal electrode layer 12, and the piezoelectric layer 13 are composed of the piezoelectric layer 13, the first internal electrode layer 11, the piezoelectric layer 13, and the second internal layer. It has a laminate 14 in which an electrode layer 12 and a piezoelectric layer 13 are laminated in this order. This laminated body 14 is a rectangular plate-like body in which the shape of the main surface viewed from the plane (upper surface) has a length direction (longitudinal direction) and a width direction (short direction). Therefore, the piezoelectric element 1 also has a rectangular shape having a length direction and a width direction in plan view.

  The first internal electrode layer 11 and the second internal electrode layer 12 constituting the multilayer body 14 are arranged so as to face each other via the piezoelectric layer 13 and sandwich the piezoelectric layer 13 from above and below. As these materials, for example, a conductor mainly composed of silver or silver-palladium which can be fired at a low temperature, or a conductor containing copper, platinum or the like can be used. Good.

The plurality of piezoelectric layers 13 constituting the laminated body 14 are made of ceramics having piezoelectric characteristics. As such ceramics, for example, perovskite oxides 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 13 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.

  Moreover, the laminated body 14 shown in the figure includes a surface electrode 15. Specifically, the surface electrode 15 includes a first surface electrode 151 electrically connected to the first internal electrode 11 and a second surface electrode 152 electrically connected to the second internal electrode 12. And. The surface electrode 15 is provided on at least one main surface of the multilayer body 14. As a material of the surface electrode 15, silver, a silver compound containing silver or the like containing glass mainly containing silica, nickel, or the like can be used.

  In addition, on the side surfaces (end surfaces) facing each other in the length direction of the multilayer body 14, the first side electrode 161 that electrically connects the first internal electrode layer 11 and the first surface electrode 151, and the second A second side electrode 162 that electrically connects the internal electrode layer 12 and the second surface electrode 152 is provided. As the material for the first side electrode 161 and the second side electrode 162, the same as the surface electrode 15, silver, silver, a silver compound containing silica as a main component, nickel, or the like is used. it can.

  1 and 2, the side surface (end surface) in the length direction of the laminate 14 is used to connect the surface electrode 15 and the internal electrode layers (the first internal electrode layer 11 and the second internal electrode layer). The side electrodes (the first side electrode 161 and the second side electrode 162) provided on the first side electrode 11 are replaced with one end portion of the first internal electrode layer 11 and the piezoelectric body. A penetrating conductor that penetrates the layer 13, a penetrating conductor that penetrates one end of the second internal electrode layer 12 and the piezoelectric layer 13 may be used. At this time, the other end portion of the second internal electrode layer 12 is laminated so that the through conductor electrically connected to the first internal electrode layer 11 is not electrically connected to the second internal electrode layer 12. A desired gap may be provided between the body 14 and the end face. Further, the other end of the first internal electrode layer 11 and the laminated body are arranged so that the through conductor electrically connected to the second internal electrode layer 12 is not electrically connected to the first internal electrode layer 11. It is sufficient that there is a desired gap between the 14 end faces.

  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 15 via a conductive adhesive or solder.

  The piezoelectric element 1 may have a shape in which the first internal electrode layer 11 has a gap at least partially between both side surfaces of the stacked body 14 in the width direction. The first internal electrode layer 11 may have a shape provided so as to reach both side surfaces in the width direction when viewed from the side. By providing the first internal electrode layer 11 so as to reach both side surfaces in the width direction, the piezoelectric active region can be increased by the edge effect. Therefore, when a diaphragm is joined to the other main surface of the piezoelectric element 1 to obtain a sound generator, a high sound pressure can be ensured.

  In addition, the piezoelectric element 1 has a shape in which the second internal electrode layer 12 is provided so that there is a gap 120 at least partly between both side surfaces in the width direction of the multilayer body 14, in other words, the second internal electrode The layer 12 may have a shape provided so that at least a part of the layer 12 reaches one of both sides in the width direction of the multilayer body 14. However, as illustrated, the gap 120 has the second internal electrode layer. It is good to provide over the whole region between 12 and the both sides | surfaces of the width direction. Thereby, it can suppress that a migration and a short circuit arise through the side surface of the laminated body 14. FIG.

  Furthermore, when the entire area of the gap 120 between the second internal electrode layer 12 and both side surfaces in the width direction of the multilayer body 14 is viewed, the distance d between the second internal electrode layer 12 and the side surface of the multilayer body 14 is Have different parts. Here, the entire area of the gap 120 between the second internal electrode layer 12 and both side surfaces in the width direction of the multilayer body 14 is between the second internal electrode layer 12 and one side surface of the multilayer body 14. It means both the gap and the area of the gap between the second internal electrode layer 12 and the other side surface of the multilayer body 14.

  As an example in which the distance d between the second internal electrode layer 12 and the side surface of the multilayer body 14 is different, the second internal electrode layer 12 has an oblique pattern inclined with respect to the length direction. There are some forms. In FIG. 1, all the second internal electrode layers 12 are electrically connected to the second side electrode 162 at a position closer to one side surface, and with respect to the length direction so as to approach the other side surface as moving away from this. The structure is a slanted and inclined pattern. In FIG. 2, the second side electrode 162 is electrically connected at a position closer to one side surface, and the diagonal pattern is inclined with respect to the length direction so as to approach the other side surface as the distance from the second side electrode 162 increases. The second internal electrode layer 12 is electrically connected to the second side electrode 162 at a position closer to the other side surface, and an oblique pattern inclined with respect to the length direction so as to approach one side surface as the distance from the inner electrode layer 12 increases. The second internal electrode layer 12 is included.

  Note that when the entire area of the gap 120 is viewed, the second internal electrode layer 12 and the laminated body 14 have a portion where the distance d between the second internal electrode layer 12 and the side surface of the laminated body 14 is different. This means that it is not uniform (non-uniform) when looking over the entire area of the distance d from the side surface. Specifically, in any one of the plurality of second internal electrode layers 12, the gap 120a on one side surface in the width direction of the multilayer body 14 is compared with the gap 120b on the other side surface, This means that it includes both the case where the intervals between the arbitrary one of the two are different, and the case where each of the gaps 120a and 120b has different portions. In particular, when each of the gaps 120a and 120b has a different portion, the interval may change continuously, for example, gradually increasing, or the interval may change discontinuously, for example, spreading in steps. It may be. About the space | interval d, a narrow site | part is set to 50-250 micrometers, for example, and the difference of a wide site | part and a narrow site | part is set to 100-500 micrometers, for example.

  For example, when the second internal electrode layer 12 is led out to the side surface (end face) of the stacked body 14 via a lead-out region whose width is narrower than other regions, the lead-out region is not included. Using the region (region other than the lead-out region) as the second internal electrode layer 12, it is determined whether or not the second internal electrode layer 12 and the side surface of the multilayer body 14 have different portions.

  By adopting such a configuration, a difference is provided in the position of the piezoelectric active region as viewed from the stacking direction, and spurious vibrations are generated in addition to the shape-specific vibrations. Due to this effect, damping and division of the natural vibration occur, and strong expression of piezoelectric resonance at a specific frequency can be suppressed. Therefore, when used as a vibration source of an acoustic generator, the peak and dip are flattened in the frequency-sound pressure characteristics. Therefore, a diaphragm is joined to the other main surface of the piezoelectric element 1 to obtain an acoustic generator. The sound quality in case can be improved.

  Here, in the piezoelectric element 1, the shape of the gap 120a between the second internal electrode layer 12 and one side surface is the shape of the gap 120b between the second internal electrode layer 12 and the other side surface when viewed from the stacking direction. And are preferably different. The shape of the gap 120a between the second internal electrode layer 12 and one side surface when viewed from the stacking direction is the same as the shape of the gap 120b between the second internal electrode layer 12 and the other side surface. In addition to being exactly the same shape, it is meant to include the same shape when reversed, or a shape that is line-symmetric with respect to the central axis in the longitudinal direction. Therefore, these shapes are different from each other, meaning that they are not the same even if they are inverted, and do not correspond to a shape that is line-symmetric with respect to the central axis in the longitudinal direction.

  The shape of the gap 120a between the second internal electrode layer 12 and one side surface when viewed from the stacking direction is different from the shape of the gap 120b between the second internal electrode layer 12 and the other side surface. As shown in FIG. 3, the shape of the second internal electrode layer 12 is a curved shape (FIG. 3A) when the second internal electrode layer 12 is viewed in plan, or a wavy shape ( 3 (b)), a bent shape (FIG. 3 (c)), a rectangular shape that is shifted so that the distance d is different between one and the other in the width direction ((FIG. 3 (d)), etc. can also be adopted. 3A to 3C have portions where the gaps 120a and 120b have different intervals d, and the gaps 120a and 120b themselves also have portions having different intervals d. FIG. 3 (d) shows an example in which only the gaps 120a and 120b differ in the distance d. Is an example having a portion that. This distance d is specifically set in narrow sites for example 50 to 250 [mu] m, the difference between the wide portion and a narrow portion, for example 100 to 500 [mu] m.

  It should be noted that all layers are different in that the shape of the gap 120a between the second internal electrode layer 12 and one side surface is different from the shape of the gap 120b between the second internal electrode layer 12 and the other side surface. It may be over. Here, the shape of the gap 120a between the second internal electrode layer 12 and one side surface is the same in all layers, and the shape of the gap 120b between the second internal electrode layer 12 and the other side surface is the same. All layers may have the same shape. Moreover, when each layer is viewed, the shape may change alternately. Furthermore, the shape may change with an arbitrary piezoelectric layer 13 as a boundary.

  With such a configuration, the resonance in the width direction can be divided, and spurious vibrations are generated in addition to the vibrations inherent in the shape. By this effect, damping and division of natural vibrations occur, and the strong expression of piezoelectric resonance at a specific frequency can be further suppressed. Therefore, when used as a vibration source of an acoustic generator, a peak or dip on the high frequency side or low frequency side can be further flattened in the frequency-sound pressure characteristics, so that a diaphragm is provided on the other main surface of the piezoelectric element 1. When the sound generator is joined, the sound quality on the high frequency side can be further improved.

  Here, the piezoelectric element 1 shown in FIG. 1 is a piezoelectric element having a unimorph structure, but as shown in FIG. 4A, a region 141 on the one main surface side and a region 142 on the other main surface side, which are different from each other in the expansion and contraction state. A bimorph structure having As shown in FIG. 4B, the bimorph structure includes a region 141 on one main surface side and a region 142 on the other main surface side, and the electric field direction and polarization direction during driving (FIG. 5B This means a structure in which the relationship (direction of P shown in FIG. 4)) is the same or different, and the expansion and contraction states during driving are reversed.

  With such a configuration, the piezoelectric element 1 itself bends and vibrates, so that mechanical loss at the joint surface with the diaphragm described later can be reduced and the displacement of the diaphragm can be increased. When a diaphragm is joined to the other main surface to form a sound generator, the sound pressure can be further improved.

  Here, when the piezoelectric element 1 has a bimorph structure as shown in FIG. 5, the distance d11 between the second internal electrode layer 12 and the one side surface on the one main surface side, and the second internal electrode on the other main surface side. The distance d12 between the layer 12 and one side surface is different, the distance d21 between the second internal electrode layer 12 and the other side surface on the one main surface side, and the second internal electrode layer 12 on the other main surface side The distance d22 from the other side surface may be different. In FIG. 5, the intervals d11 and d21 and the intervals d12 and d22 are shown only for the uppermost or lowermost second internal electrode layer 12.

  In particular, as shown in FIGS. 5A and 5B, on one main surface side, the distance d11 between the second internal electrode layer 12 and one side surface is equal to the second internal electrode layer 12 and the other side surface. The distance d21 between the second internal electrode layer 12 and the one side surface is smaller than the distance d22 between the second internal electrode layer 12 and the other side surface. May be. Moreover, as shown in FIG.5 (c) and FIG.5 (d), the magnitude | size may be a reverse structure. Note that the difference between the distance between the second internal electrode layer 12 and the one side surface and the distance between the second internal electrode layer 12 and the other side surface is set to, for example, 50 to 500 μm.

  Furthermore, as shown in FIG. 6, when the piezoelectric element 1 has a bimorph structure, the area of the second internal electrode layer 121 located on the one main surface side and the second internal electrode layer 122 located on the other main surface side. The area may be different.

  A difference in piezoelectric active region between the region on the one principal surface side and the region on the other principal surface side in the piezoelectric element 1 causes further spurious vibrations. By this effect, damping and division of natural vibration are promoted, and strong expression of piezoelectric resonance at a specific frequency can be further suppressed. Therefore, when used as a vibration source of an acoustic generator, the peak and dip on the high frequency side and the low frequency side can be further flattened in the frequency-sound pressure characteristics, so that a diaphragm is provided on the other main surface of the piezoelectric element 1. The sound quality can be further improved when the sound generator is joined.

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

First, a ceramic green sheet to be the piezoelectric layer 13 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 an internal electrode layer (first internal electrode layer 11 and second internal electrode layer 12) is prepared. 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.

  At this time, the structure which has the part from which the space | interval of the 2nd internal electrode layer 12 and a side surface differs by changing and applying the position of the application pattern by the screen printing method of the electrically conductive paste used as the 2nd internal electrode layer 12 It can be.

  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 14 provided with the internal electrode layers (the first internal electrode layer 11 and the second internal electrode layer 12) and the piezoelectric body layer 13 which are alternately laminated is manufactured by performing a grinding process so as to have the shape of To do.

  In addition, when the ceramic green sheets are laminated, the position of the ceramic green sheets is changed in order to obtain a configuration (non-uniformity) having a portion where the distance between the facing region and the side surface of the second internal electrode layer 12 is different. They can be stacked.

  The laminate 14 is not limited to the one produced by the above manufacturing method, and any production method can be used as long as the laminate 14 formed by laminating a plurality of internal electrode layers and piezoelectric layers 13 can be produced. It 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 14. After being printed and dried by, for example, a baking process is performed at a temperature of 600 ° C. to 800 ° C., and the surface electrode 15 (first surface electrode 151 and second surface electrode 152) and side electrode (first side electrode) 161 and the second side electrode 162).

  In order to electrically connect the surface electrode and the internal electrode, instead of the side electrodes (the first side electrode 161 and the second side electrode 162) formed on the side surface of the laminate 14 as described above. A through conductor formed so as to penetrate the piezoelectric layer 13 may be used.

  Thereafter, the laminate 14 is subjected to polarization treatment to impart piezoelectric activity. For the polarization treatment, for example, in the case of a unimorph piezoelectric element as shown in FIGS. 1 and 2, the first surface electrode is connected to the negative electrode, and the second surface electrode is connected to the positive electrode. For example, a potential difference of 2 kV / mm to 3 kV / mm may be applied for several seconds as an 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.

  On the other hand, in the case of a piezoelectric element having a bimorph structure as shown in FIG. 4, for example, the first surface electrode is used as the ground electrode, the second surface electrode is used as the positive electrode, and the third surface is used. The electrodes may be connected to the negative electrode and polarized.

  Although a desired piezoelectric element can be obtained as described above, when a power feeding member (wiring member) is required, the power feeding member (wiring member) may be connected to the piezoelectric element by the following method. For example, when a flexible wiring board is connected and fixed (bonded) to a piezoelectric element using a conductive adhesive, a conductive adhesive paste is applied and formed at a predetermined position of the piezoelectric element using a technique such as screen printing. Then, the flexible wiring board is connected and fixed to the piezoelectric element 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. 7, the acoustic generator 10 of the present embodiment includes the above-described piezoelectric element 1 and the diaphragm 2 to which the piezoelectric element 1 is attached and vibrates due to vibration of the piezoelectric element 1. Furthermore, the sound generator 10 shown in the drawing is provided on at least a part of the outer peripheral portion of the diaphragm 2 and includes a frame 3 as a support that supports the diaphragm 2.

  The piezoelectric element 1 is an exciter that excites the diaphragm 2 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 2 to generate sound. Can be generated.

  The peripheral edge of the diaphragm 2 is fixed to the frame 3, and vibrates with the piezoelectric element 1 by the vibration of the piezoelectric element 1. This diaphragm 2 can be formed using various materials, such as resin and 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 2 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 2 is formed of a resin film, it is preferable that the peripheral edge portion is fixed to the frame 3 in a state where the diaphragm 2 is in tension. By configuring the diaphragm 2 with a resin film, the diaphragm 2 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 diaphragm 2 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 diaphragm 2. You may do it.

  The frame body 3 functions as a support body that supports the outer peripheral portion of the main surface of the diaphragm 2. By providing the vibration space by supporting the outer peripheral portion of the diaphragm 2 with the frame 3, the amplitude of the diaphragm 2 is increased, and the sound pressure can be improved. The frame 3 can be formed using various materials such as metals such as stainless steel, glass, acrylic resin, polycarbonate resin, polybutylene terephthalate resin, and the like.

  The frame 3 is bonded to one main surface or the other main surface of the diaphragm 2 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 sound generator 10 may be configured not to include the frame 3, but when the frame 3 is joined to the main surface to which the piezoelectric element 1 of the diaphragm 2 is joined as in the example illustrated in FIG. 8. In particular, when the total thickness of the frame 3 and the bonding material is larger than the thickness of the piezoelectric element 1, the piezoelectric element 1 can be protected by the frame 3. Further, the diaphragm 2 is supported, and the electronic device can be easily fixed to the housing or the like.

  The frame 3 may be composed of one frame member (upper frame member 31) as shown in FIG. 7 (b), and two frame members (upper frame member 31 and upper frame member 31) as shown in FIG. 7 (c). The lower frame member 32) may be used. In this case, the tension of the diaphragm 2 can be stabilized by sandwiching the diaphragm between the two frame members. The upper frame member 31 and the lower frame member 32 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 2 (for example, the peripheral part of the piezoelectric element 1). You may further have the resin layer 4 provided so that it might cover. The resin layer 4 is formed, for example, with a Young's modulus in the range of 1 MPa to 1 GPa, for example, and an acrylic resin can be used, for example. By embedding piezoelectric material in the resin layer 4, an appropriate damper effect can be induced, so that a resonance phenomenon can be suppressed and a peak or dip in the frequency characteristic of sound pressure can be suppressed to a small value. In addition, as shown in FIG.7 (b) and FIG.7 (c), the resin layer 4 may be formed so that it may become the same height as the upper frame member 31. 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 2 is mechanically fixed to a support portion provided in a housing of an electronic device or the like, or is fixed through 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 10 and a housing 20 that houses the sound generator 10. Note that a part of the housing 20 may be the diaphragm 2 constituting the acoustic generator 10, and that the housing 20 accommodates the acoustic generator 10 means that a part of the acoustic generator 10 (piezoelectric element 1). ) Is also included.

  The housing 20 resonates the sound generated by the sound generator 10 inside, 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 of the present embodiment includes an acoustic generator 10, an electronic circuit 60 connected to the acoustic generator 10, and a housing 70 that houses the electronic circuit 60 and the acoustic generator 10. And has a function of generating sound from the sound generator 10. In addition, as the electronic device 50, not only the acoustic generator 10 is accommodated in the casing 70 as it is, but also the acoustic generator 100 that accommodates the acoustic generator 10 (consisting of the acoustic generator 1 and the casing 5). Is included in the housing 70. Further, a part of the housing 70 may be the diaphragm 2 constituting the sound generator 10.

  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 10 and has a function of outputting an audio signal to the sound generator 10. The sound generator 10 generates sound based on the sound signal input from the electronic circuit 60.

  Further, the electronic device 50 includes a display unit 50a, an antenna 50b, and the sound generator 10, 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 10 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 10 operates as a sound output device in the electronic device 60. The sound generator 10 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 had a long plate shape with a length of 23.5 mm, a width of 3.3 mm, and a thickness of 0.9 mm. The piezoelectric element had a structure in which piezoelectric layers having a thickness of 30 μm and internal electrodes were alternately laminated, and the total number of piezoelectric layers was 28. 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 conductive paste made of silver palladium was printed on a ceramic green sheet to prepare a ceramic green sheet for the first internal electrode layer and a second ceramic green sheet for the internal electrode layer whose printing position was changed by a predetermined amount. . After laminating these ceramic green sheets, they were pressed and adhered to each other and cut into predetermined dimensions to produce molded bodies. Here, what was produced is that of the pattern shown in FIG. 1 as the pattern of the second internal electrode layer.

  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 and side electrodes. 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.

  A second ceramic green sheet for an internal electrode layer having a fixed printing position was prepared, and other manufacturing methods were the same as those in the above example to produce a piezoelectric element.

  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 a frequency of 400 Hz to 2 kHz and a frequency of 10 kHz to 20 kHz, FIG. It can be seen that this is clearly smaller than the comparative example of FIG.

  From the above, in the piezoelectric element, the first internal electrode layer is provided so as to reach both side surfaces in the width direction when viewed from the stacking direction, and the second internal electrode layer is provided between the both side surfaces in the width direction. The gap between the second internal electrode layer and the side surface is non-uniform when the entire gap is viewed, so that a sudden change in sound pressure at a specific frequency is suppressed. It was confirmed that the characteristics were flattened and the sound quality could be improved.

DESCRIPTION OF SYMBOLS 1 Piezoelectric element 11 1st internal electrode layer 12 2nd internal electrode layer 120 Gap | interval 13 Piezoelectric layer 14 Laminate body 141 Area on one main surface side Area 15 on the other main surface side Surface electrode 151 First surface electrode 152 Second surface electrode 161 First side electrode 162 Second side electrode 10 Sound generator 2 Diaphragm 3 Frame 31 Upper frame member 32 Lower frame member 4 Resin layer 100 Sound generator 50 Electronic device 60 Electronic circuit 20 70 body

Claims (10)

A rectangular plate-shaped piezoelectric element having a length direction and a width direction, in which a first internal electrode layer and a second internal electrode layer are alternately stacked so as to face each other with a piezoelectric layer therebetween. The first internal electrode layer is provided so as to reach both side surfaces in the width direction when viewed from the direction, and the second internal electrode layer has a gap at least partially between both side surfaces in the width direction. And when the entire area of the gap is viewed, the second internal electrode layer has a portion where the distance between the side surface is different from the side surface, The piezoelectric element is characterized in that the shape of the gap is different from the shape of the gap between the second internal electrode layer and the other side surface . 2. The piezoelectric element according to claim 1, wherein the gap is provided over the entire area between the second internal electrode layer and both side surfaces in the width direction.   The shape of the gap between the second internal electrode layer and one side surface and the shape of the gap between the second internal electrode layer and the other side surface are not the same when reversed, and 3. The piezoelectric element according to claim 1, wherein the piezoelectric element is not line-symmetric with respect to a central axis in a length direction. The piezoelectric element according to any one of claims 1 to 3 , wherein the piezoelectric element has a bimorph structure having a region on one main surface side and a region on the other main surface side that are different from each other in a stretched state. element. The interval between the second internal electrode layer and the one side surface in the region on the one main surface side is different from the interval between the second internal electrode layer and the one side surface in the region on the other main surface side. And the distance between the second internal electrode layer and the other side surface in the region on the one main surface side is different from the distance between the second internal electrode layer and the other side surface on the other main surface side. The piezoelectric element according to claim 4 , wherein: In the region on the one main surface side, the interval between the second internal electrode layer and the one side surface is larger than the interval between the second internal electrode layer and the other side surface, and the other main surface side 6. The region according to claim 5 , wherein the interval between the second internal electrode layer and one side surface is smaller than the interval between the second internal electrode layer and the other side surface. Piezoelectric element. Claim 4, characterized in that different the area of the one second inner electrode layer located in the second area an area of the other main surface side of the internal electrode layer positioned in the region of the main surface side The piezoelectric element according to claim 6 . The piezoelectric element according to any one of claims 1 to 7, the piezoelectric element is mounted, sound generator, characterized by comprising a vibration plate that vibrates by the vibration of the piezoelectric element vessel. An acoustic generator comprising: the acoustic generator according to claim 8 ; and a housing that accommodates the acoustic generator. 9. An electronic device comprising: the sound generator according to claim 8; an electronic circuit connected to the sound generator; and a housing that houses the electronic circuit and the sound generator.

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