WO2013171918A1

WO2013171918A1 - Piezoelectric actuator, piezoelectric vibration device, and mobile terminal

Info

Publication number: WO2013171918A1
Application number: PCT/JP2012/072264
Authority: WO
Inventors: 健岡村; 中村　成信
Original assignee: 京セラ株式会社
Priority date: 2012-05-15
Filing date: 2012-08-31
Publication date: 2013-11-21
Also published as: KR20140089031A; JPWO2013171918A1

Abstract

[Problem] To provide a mobile terminal, a piezoelectric vibration device, and a piezoelectric actuator capable of improving bonding reliability between a flexible wiring board and a piezoelectric element, and capable of stably driving for extended periods of time. [Solution] This piezoelectric actuator (1) is characterized by being provided with: a stacked body (4) having, stacked therein, internal electrodes (2) and piezoelectric layers (3); surface electrodes (5) on at least one main surface of the stacked body (4), said surface electrodes (5) being electrically connected with the internal electrodes (2); and a flexible wiring board (6) which has a portion thereof bonded to the one main surface, and which is provided with a wiring conductor (61) electrically connected with the surface electrodes (5). The piezoelectric actuator (1) is further characterized in that the electric connection between the surface electrodes (5) and the wiring conductor (61) is formed by a plurality of interspersed conductive particles (7).

Description

Piezoelectric actuator, piezoelectric vibration device, and portable terminal

The present invention relates to a piezoelectric vibration device, a piezoelectric actuator suitable for a mobile terminal, a piezoelectric vibration device, and a mobile terminal.

As a piezoelectric actuator, as shown in FIG. 12, a bimorph type piezoelectric element 10 in which a surface electrode 104 is formed on the surface of a laminate 103 in which a plurality of internal electrodes 101 and a plurality of piezoelectric layers 102 are laminated, (See Patent Document 1) The piezoelectric element 10 and the flexible wiring board 105 are joined by the conductive connecting member 106, and the surface electrode 104 of the piezoelectric element 10 and the wiring conductor 107 of the flexible wiring board 105 are electrically connected. It is known (see Patent Document 2).

Furthermore, there is known a piezoelectric vibration device in which a central portion or one end in the length direction of a bimorph type piezoelectric element is fixed to a diaphragm (see Patent Documents 3 and 4).

Japanese Patent Laid-Open No. 2002-10393 Japanese Patent Laid-Open No. 6-14396 International Publication No. 2005/004535 JP 2006-238072 A

In recent years, the piezoelectric actuator of the piezoelectric vibration device used for such portable terminals has been required to be used for a long time not only in a room temperature environment but also in a temperature environment below freezing point.

Here, in joining of the flexible wiring board 105 having the wiring conductor 107 and the piezoelectric element 10, the surface electrode 104 and the wiring conductor 107 are electrically connected via the conductive connection member 106 (solder or conductive resin). As described above, a part of the flexible wiring board 105 is bonded to one main surface of the laminate 103. When the piezoelectric element 10 is repeatedly driven in a temperature environment below freezing point, the flexible wiring board 105 itself is harder than the room temperature environment. Therefore, the conductive connecting member 106 connecting the flexible wiring board 105 and the piezoelectric element 10 is used. There was a risk that stress was concentrated at the end of the metal and micro cracks were gradually generated, resulting in a decrease in bonding reliability.

The present invention has been devised in view of the above-mentioned problems, and its purpose is to improve the bonding reliability between the flexible wiring board and the piezoelectric element, and to stably drive the piezoelectric actuator for a long period of time and the piezoelectric vibration. An apparatus and a mobile terminal are provided.

The piezoelectric actuator of the present invention includes a laminate in which an internal electrode and a piezoelectric layer are laminated, a surface electrode electrically connected to the internal electrode on at least one main surface of the laminate, and one on the one main surface. And a flexible wiring board having a wiring conductor electrically connected to the surface electrode, and a plurality of conductive particles interspersed with electrical connection between the surface electrode and the wiring conductor. It is characterized by that.

The piezoelectric vibration device according to the present invention includes the piezoelectric actuator and a vibration plate bonded to the other main surface of the piezoelectric element.

The portable terminal of the present invention includes the piezoelectric actuator, an electronic circuit, a display, and a housing, and the other main surface of the piezoelectric actuator is bonded to the display or the housing. Features.

According to the present invention, there are provided a piezoelectric actuator, a piezoelectric vibration device, and a portable terminal that can be stably driven for a long period of time by improving electrical and mechanical joint strength between a flexible wiring board and a piezoelectric element to improve joint reliability. can do. For example, a portable terminal capable of transmitting sound information with high reliability and high quality can be obtained even in a severe environment such as driving a piezoelectric element in a temperature environment below freezing point.

(A) is a schematic perspective view which shows an example of embodiment of the piezoelectric actuator of this invention, (b) is a schematic sectional drawing cut | disconnected by the AA line | wire shown to (a). It is a schematic enlarged view of the area | region A shown in FIG.1 (b). (A) is a schematic perspective view which shows the other example of embodiment of the piezoelectric actuator of this invention, (b) is a schematic sectional drawing cut | disconnected by the AA line shown to (a). It is a schematic enlarged view which shows the other example of FIG. It is a schematic enlarged view which shows the other example of FIG. It is a schematic enlarged view which shows the other example of FIG. It is a schematic perspective view which shows the other example of embodiment of the piezoelectric actuator of this invention. 1 is a schematic perspective view schematically showing a piezoelectric vibration device according to an embodiment of the present invention. It is a schematic perspective view which shows typically the portable terminal of embodiment of this invention. FIG. 10 is a schematic cross-sectional view taken along line AA shown in FIG. 9. FIG. 10 is a schematic sectional view taken along line BB shown in FIG. 9. It is a schematic perspective view which shows an example of embodiment of the conventional piezoelectric actuator, (b) is a schematic sectional drawing cut | disconnected by the AA line shown to (a).

An example of an embodiment of a piezoelectric actuator of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a schematic perspective view showing an example of an embodiment of the piezoelectric actuator of the present invention, FIG. 2 (a) is a schematic cross-sectional view taken along line AA shown in FIG. 1 (b), and FIG. It is a schematic enlarged view of the area | region A shown to 1 (b).

The piezoelectric actuator 1 of this embodiment shown in FIG. 1 includes a laminate 4 in which an internal electrode 2 and a piezoelectric layer 3 are laminated, and a surface electrically connected to the internal electrode 2 on at least one main surface of the laminate 4. The electrode 5 and a flexible wiring board 6 having a wiring conductor 61 partially joined to one main surface and electrically connected to the surface electrode 5 are provided. The electrical connection between the surface electrode 5 and the wiring conductor 61 is provided. The connection is made by a plurality of conductive particles 7 which are scattered.

The piezoelectric actuator 1 includes a piezoelectric element 10, and a laminated body 4 constituting the piezoelectric element 10 is formed by laminating an internal electrode 2 and a piezoelectric layer 3, and an active portion in which a plurality of internal electrodes 2 overlap in the laminating direction. 41 and other inactive portions 42 are formed, for example, in a long shape. In the case of a piezoelectric actuator attached to a display or casing of a mobile terminal, the length of the laminate 4 is preferably, for example, 18 mm to 28 mm, and more preferably 22 mm to 25 mm. For example, the width of the laminate 4 is preferably 1 mm to 6 mm, and more preferably 3 mm to 4 mm. For example, the thickness of the laminate 4 is preferably 0.2 mm to 1.0 mm, and more preferably 0.4 mm to 0.8 mm.

The internal electrode 2 constituting the laminated body 4 is formed by simultaneous firing with ceramics forming the piezoelectric layer 3 and includes a first electrode 21 and a second electrode 22. For example, the first electrode 21 is a ground electrode, and the second electrode 22 is a positive electrode or a negative electrode. Piezoelectric layers 3 are alternately stacked to sandwich the piezoelectric layers 3 from above and below, and the first pole 21 and the second pole 22 are arranged in the stacking order, so that the piezoelectric body sandwiched between them. A driving voltage is applied to the layer 3. As this forming material, for example, a conductor mainly composed of silver or a silver-palladium alloy having a low reactivity with piezoelectric ceramics, or a conductor containing copper, platinum, or the like can be used. You may make it contain.

In the example shown in FIG. 1, the end portions of the first pole 21 and the second pole 22 are alternately led to a pair of side surfaces facing each other of the stacked body 4. In the case of a piezoelectric actuator attached to a display or casing of a mobile terminal, the length of the internal electrode 2 is preferably 17 mm to 25 mm, for example, and more preferably 21 mm to 24 mm. For example, the width of the internal electrode 2 is preferably 1 mm to 5 mm, and more preferably 2 mm to 4 mm. The thickness of the internal electrode 2 is preferably 0.1 to 5 μm, for example.

The piezoelectric layer 3 constituting the multilayer body 4 is formed of ceramics having piezoelectric characteristics. As such ceramics, 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 3 is preferably set to 0.01 to 0.1 mm, for example, so as to be driven at a low voltage. In order to obtain a large bending vibration, it is preferable to have a piezoelectric d31 constant of 200 pm / V or more.

A surface electrode 5 electrically connected to the internal electrode 2 is provided on one main surface of the laminate 4. The surface electrode 5 in the form shown in FIG. 1 includes a first surface electrode 51 having a large area, a second surface electrode 52 having a small area, and a third surface electrode 53. For example, the first surface electrode 51 is electrically connected to the internal electrode 2 to be the first electrode 21, and the second surface electrode 52 is the internal electrode to be the second electrode 22 disposed on one main surface side. 2 and the third surface electrode 53 is electrically connected to the internal electrode 2 serving as the second electrode 22 disposed on the other main surface side. In the case of a piezoelectric actuator attached to a display or casing of a portable terminal, the length of the first surface electrode 51 is preferably, for example, 17 mm to 23 mm, and more preferably 19 mm to 21 mm. The width of the first surface electrode 51 is preferably 1 mm to 5 mm, for example, and more preferably 2 mm to 4 mm. The lengths of the second surface electrode 52 and the third surface electrode 53 are preferably 1 mm to 3 mm, for example. The widths of the second surface electrode 52 and the third surface electrode 53 are preferably 0.5 mm to 1.5 mm, for example.

The piezoelectric actuator 1 also has a flexible wiring board 6 that is partly bonded to one main surface of the laminate 4 constituting the piezoelectric element 10.

The flexible wiring board 6 is a flexible printed wiring board in which, for example, two wiring conductors 61 are embedded in a resin film, and a connector (not shown) for connecting to an external circuit is connected to one end. Yes.

The surface electrode 5 and the wiring conductor 61 are electrically connected. Here, the electrical connection between the surface electrode 5 and the wiring conductor 61 is made by a plurality of conductive particles 7 which are scattered.

Examples of the conductive particles 7 include gold, silver, copper, an alloy such as silver-palladium, or metal particles obtained by plating gold on a metal such as Ni. For example, the conductive particles 7 have an average particle diameter of 0.05 to 50 μm. It is good. Further, it is preferable that the plurality of scattered conductive particles 7 are distributed, for example, 50 to 10,000 per 1 mm ² .

When the surface electrode 5 and the wiring conductor 61 are joined by a conductive connecting member such as solder, the conductive electrode has a large coefficient of thermal expansion, and the surface electrode 5 and the conductive connecting member constrained by the piezoelectric layer 3. The piezoelectric element 10 is driven in a harsh environment where shear stress tends to concentrate at the joint between the wiring conductor 61 and the conductive conductor 61 of the flexible wiring board 6 and the conductive connecting member, and further embrittlement occurs below freezing point. Then, microcracks are generated at the joint between the surface electrode 5 and the conductive connection member and at the joint between the wiring conductor 61 of the flexible wiring board 6 and the conductive connection member, and the piezoelectric actuator 1 may stop due to progress. was there.

On the other hand, by connecting the surface electrode 5 and the wiring conductor 61 with a plurality of conductive particles 7 interspersed as in the present invention, the surface is compared with the case where a conductive connecting member as a bulk body is used. The difference in thermal expansion between the electrode 5 and the wiring conductor 61 can be reduced.

As a result, even when the piezoelectric element 10 is driven under a severe environment such as below freezing point, the occurrence of microcracks at the joints between the plurality of conductive particles 7 and the surface electrode 5 or the wiring conductor 61 is suppressed. The displacement amount of 1 does not become small, or unnecessary vibrations are not generated and the vibration characteristics are not deteriorated, so that stable driving can be performed for a long time.

Here, as shown in FIG. 3, it is preferable that a resin adhesive 73 is provided between the plurality of conductive particles 7 scattered. Examples of the resin adhesive 73 are those having a low elastic modulus (Young's modulus) such as polyimide, polyamideimide, silicone rubber, and synthetic rubber.

With such a configuration, even if the piezoelectric element 10 generates heat due to vibration, the bonding strength between the piezoelectric element 10 and the flexible wiring board 6 can be kept high while the stress due to the difference in thermal expansion remains low. Further, since the resin adhesive 73 having a low elastic modulus is provided, vibration that does not follow the vibration of the piezoelectric element 10 of the flexible wiring board 6 occurs due to external vibration or resonance of the flexible wiring board 6 itself. In addition, the stress concentration at the end portion such as the root of the joint portion of the flexible wiring board 6 can be suppressed.

Furthermore, as shown in FIG. 4, the plurality of conductive particles 7 may be one in which the surface of a particle body 71 made of resin is coated with a conductive film 72.

The particle body 71 is made of a resin such as an acrylic resin, an imide resin, an amide resin, an epoxy resin, or a polypropylene resin having a high elastic modulus (Young's modulus). The conductive film 72 covered on the surface of the particle body 71 is, for example, an Au plating film.

Since the conductive film 72 coated on the surface of the particle body 71 contributes to electrical bonding and is highly ductile even below freezing, it is possible to suppress deterioration such as embrittlement.

Furthermore, as shown in FIG. 5 or FIG. 6, a part of the conductive film 72 coated on the surface of the particle body 71 may be missing.

In FIG. 5, a part of the conductive film 72 is missing at the contact point between the surface electrode 5 and the wiring conductor 61 in the conductive particle 7. The electrical connection is formed by the particle body 71 having a high elastic modulus, and the electrical connection is made by connecting the conductive film 72 around the connection portion between the resin adhesive 73, the surface electrode 5, and the wiring conductor 61, thereby increasing the connection area. An electrical connection is formed in the form. By doing in this way, mechanical connection can be strengthened more, the junction area of electrical connection can be expanded, and electrical resistance can be lowered.

In FIG. 6, the region lacking the conductive film 72 is provided in a region other than the contact point with the surface electrode 5 and the wiring conductor 61, but according to this configuration, the plurality of scattered conductive particles 7 are scattered. When the resin adhesive 73 is provided between the particles, the particle main body 71 and the resin adhesive 73 are directly bonded. Therefore, the conductive film 72 is bonded to the resin when the conductive particles 7 and the resin adhesive 73 flow in the bonding process. It can be reduced that the agent 73 is pulled and peeled off. As a result, the electrical connection between the surface electrode 5 and the wiring conductor 61 can be ensured.

In addition, as shown in FIG. 7, it is preferable to have a gap 74 between the surface electrode 5 and the wiring conductor 61 between the resin adhesives 73. This is because the gap 74 contributes to stress relaxation as a result of lowering the elastic modulus of the resin adhesive 73 as a bulk.

Further, as shown in FIGS. 3 and 7, when a plurality of surface electrodes 5 are provided adjacent to one main surface of the laminate 4, an insulating region between the adjacent surface electrodes 5 and the surface electrodes 5 is used. In addition, it is preferable that a plurality of conductive particles 7 be disposed. This is because the thermal resistance can be lowered by arranging the plurality of conductive particles 7 having high thermal conductivity even at a location thicker than the region where the electrical junction is formed. Furthermore, for the same effect, it is preferable that a plurality of conductive particles 7 are also disposed in the insulating region outside the surface electrode 5.

As shown in FIGS. 1 to 7, one conductive particle 7 is in contact with the surface electrode 5 and the wiring conductor 61, that is, each conductive particle 7 between the surface electrode 5 and the wiring conductor 61. It is preferable that the surface electrode 5 and the wiring conductor 61 are in contact with each other. By making the other main surface of the piezoelectric element 10 flat, for example, the other main surface is applied to an object (for example, a vibration plate described later) to which vibration is applied. When the surfaces are bonded together, it becomes easy to cause bending vibration integrally with the object to which vibration is applied, and the efficiency of bending vibration can be improved as a whole.

The piezoelectric actuator 1 shown in FIG. 1 is a so-called bimorph type piezoelectric actuator that receives an electric signal from the surface electrode 5 and bends and vibrates so that one main surface and the other main surface are bent surfaces. The piezoelectric actuator of the present invention is not limited to the bimorph type, and may be a unimorph type. For example, by bending (bonding) the other main surface of the piezoelectric actuator to a diaphragm described later, the unimorph type is also bent and vibrated. Can be made.

Next, a method for manufacturing the piezoelectric actuator 1 according to this embodiment will be described.

First, a ceramic green sheet to be the piezoelectric layer 3 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 2 is produced. Specifically, a conductive paste is prepared by adding and mixing a binder and a plasticizer to a silver-palladium alloy metal powder. This conductive paste is applied on the ceramic green sheet in the pattern of the internal electrode 2 using a screen printing method. Further, a plurality of ceramic green sheets printed with this conductive paste are laminated, subjected to a binder removal treatment at a predetermined temperature, fired at a temperature of 900 to 1200 ° C., and then subjected to a predetermined grinding using a surface grinder or the like. By performing a grinding process so as to obtain a shape, a laminated body 4 including the internal electrodes 2 and the piezoelectric body layers 3 that are alternately laminated is manufactured.

The laminate 4 is not limited to the one produced by the above manufacturing method, and any production method can be used as long as the laminate 4 formed by laminating a plurality of internal electrodes 2 and piezoelectric layers 3 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 used to form a main surface of the laminate 4 in a pattern of the surface electrode 5. After the surface is printed by screen printing or the like and dried, a baking process is performed at a temperature of 650 to 750 ° C. to form the surface electrode 5.

When the surface electrode 5 and the internal electrode 2 are electrically connected, a via that penetrates the piezoelectric layer 3 may be formed or connected, or a side electrode may be formed on the side surface of the multilayer body 4. It may be produced by any manufacturing method.

Next, the flexible wiring board 6 is connected and fixed (bonded) to the piezoelectric element 10 using a plurality of conductive particles 7 scattered.

First, a paste containing a plurality of conductive particles 7 and a resin adhesive 73 is applied and formed at a predetermined position of the piezoelectric element 10 using a technique such as screen printing. Then, the flexible wiring board 6 is connected and fixed to the piezoelectric element 10 by curing the paste with the flexible wiring board 6 in contact. This paste may be applied and formed on the flexible wiring board 6 side.

When the resin adhesive is made of a thermoplastic resin, the paste is applied and formed at a predetermined position on the piezoelectric element 10 or the flexible wiring board 6, and then the piezoelectric element 10 and the flexible wiring board 6 are brought into contact with each other via the paste. By heating and pressing in this state, the thermoplastic resin softens and flows, and then returns to room temperature, whereby the thermoplastic resin is cured again, and the flexible wiring board 6 is connected and fixed to the piezoelectric element 10.

In particular, it is necessary to control the amount of pressurization so that adjacent conductive particles 7 do not come into contact.

The piezoelectric vibration device of the present invention has a piezoelectric actuator 1 and a diaphragm 81 bonded to the other main surface of the piezoelectric actuator 1 as shown in FIG.

The diaphragm 81 has a rectangular thin plate shape. The vibration plate 81 can be preferably formed using a material having high rigidity and elasticity such as acrylic resin or glass. Further, the thickness of the diaphragm 81 is set to 0.4 mm to 1.5 mm, for example.

The diaphragm 81 is joined to the other main surface of the piezoelectric actuator 1 via a joining member 82. The entire surface of the other main surface may be bonded to the diaphragm 81 via the bonding member 82, or substantially the entire surface may be bonded.

The joining member 82 has a film shape. Further, the joining member 82 is formed of a material that is softer and more easily deformed than the diaphragm 81, and has a smaller elastic modulus and rigidity such as Young's modulus, rigidity, and bulk modulus than the diaphragm 81. That is, the joining member 82 is deformable and deforms more greatly than the diaphragm 81 when the same force is applied. Then, the other main surface (main surface on the −z direction side in the drawing) of the piezoelectric actuator 1 is fixed to the one main surface (main surface on the + z direction side in the drawing) of the bonding member 82 as a whole. A part of one main surface (main surface on the + z direction side in the drawing) of the diaphragm 81 is fixed to the other main surface (main surface on the −z direction side in the drawing).

The joining member 82 may be a single member or a composite composed of several members. As such a joining member 82, for example, a double-sided tape in which a pressure-sensitive adhesive is attached to both surfaces of a substrate made of a nonwoven fabric or the like, various elastic adhesives which are adhesives having elasticity, and the like can be suitably used. The thickness of the joining member 82 is desirably larger than the amplitude of the flexural vibration of the piezoelectric actuator 1, but if it is too thick, the vibration is attenuated, so it is set to 0.1 mm to 0.6 mm, for example. However, in the piezoelectric vibration device of the present invention, the material of the bonding member 82 is not limited, and the bonding member 82 may be formed of a material that is harder and less deformable than the vibration plate 81. In some cases, a configuration without the joining member 82 may be used.

The piezoelectric vibration device of this example having such a configuration functions as a piezoelectric vibration device that causes the piezoelectric actuator 1 to bend and vibrate by applying an electric signal, thereby vibrating the vibration plate 81. Note that the other end in the length direction of the diaphragm 81 (the end in the −y direction in the figure, the peripheral edge of the diaphragm 81, and the like) may be supported by a support member (not shown).

Since the piezoelectric vibration device of this example is configured using the piezoelectric actuator 1 in which generation of unnecessary vibration is reduced, the piezoelectric vibration device in which generation of unnecessary vibration is reduced can be obtained.

Further, in the piezoelectric vibration device of this example, the vibration plate 81 is joined to the other flat main surface of the piezoelectric actuator 1. Thereby, a piezoelectric vibration device in which the piezoelectric actuator 1 and the vibration plate 81 are firmly joined can be obtained.

As shown in FIGS. 9 to 11, the portable terminal of the present invention includes the piezoelectric actuator 1, an electronic circuit (not shown), a display 91, and a housing 92. The main surface is joined to the housing 92. 9 is a schematic perspective view schematically showing the portable terminal of the present invention, FIG. 10 is a schematic sectional view cut along the line AA shown in FIG. 9, and FIG. 11 is a line BB shown in FIG. It is the schematic sectional drawing cut | disconnected by.

Here, it is preferable that the piezoelectric actuator 1 and the housing 92 are joined using a deformable joining member. That is, in FIG. 5 and FIG. 6, the joining member 82 is a deformable joining member.

By joining the piezoelectric actuator 1 and the housing 92 with the deformable joining member 82, when the vibration is transmitted from the piezoelectric actuator 1, the deformable joining member 82 is deformed more greatly than the housing 92.

At this time, since the anti-phase vibration reflected from the casing 92 can be mitigated by the deformable joining member 82, the piezoelectric actuator 1 transmits strong vibration to the casing 92 without being influenced by the surrounding vibration. Can be made.

In particular, since at least a part of the joining member 82 is formed of a viscoelastic body, strong vibration from the piezoelectric actuator 1 is transmitted to the housing 92, while weak vibration reflected from the housing 92 is transmitted to the joining member 82. It is preferable in that it can be absorbed. For example, a double-sided tape in which a pressure-sensitive adhesive is attached to both surfaces of a base material made of a nonwoven fabric or the like, or a joining member including an adhesive having elasticity can be used, and the thickness thereof is, for example, 10 μm to 2000 μm Can be used.

In this example, the piezoelectric actuator 1 is attached to a part of the casing 92 that becomes the cover of the display 91, and a part of the casing 92 functions as the diaphragm 922.

In this example, the piezoelectric actuator 1 is bonded to the housing 92, but the piezoelectric actuator 1 may be bonded to the display 91.

The casing 92 includes a box-shaped casing main body 921 having one surface opened, and a diaphragm 922 that closes the opening of the casing main body 921. The casing 92 (the casing main body 921 and the diaphragm 922) can be preferably formed using a material such as a synthetic resin having high rigidity and elastic modulus.

The peripheral edge of the diaphragm 922 is attached to the housing main body 921 via a bonding material 93 so as to vibrate. The bonding material 93 is formed of a material that is softer and easier to deform than the diaphragm 922, and has a smaller elastic modulus and rigidity such as Young's modulus, rigidity, and bulk modulus than the diaphragm 922. That is, the bonding material 93 can be deformed, and deforms more greatly than the diaphragm 922 when the same force is applied.

The bonding material 93 may be a single material or a composite made up of several members. As such a bonding material 93, for example, a double-sided tape in which an adhesive is attached to both surfaces of a base material made of a nonwoven fabric or the like can be suitably used. The thickness of the bonding material 93 is set so that the vibration is not attenuated due to being too thick, and is set to, for example, 0.1 mm to 0.6 mm. However, in the mobile terminal of the present invention, the material of the bonding material 93 is not limited, and the bonding material 93 may be formed of a material that is harder and more difficult to deform than the diaphragm 922. In some cases, a configuration without the bonding material 93 may be used.

Examples of the electronic circuit (not shown) include a circuit that processes image information displayed on the display 91 and audio information transmitted by the mobile 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 and the piezoelectric actuator 1 are connected by a connection wiring (not shown).

The display 91 is a display device having a function of displaying image information. For example, a known display such as a liquid crystal display, a plasma display, and an organic EL display can be suitably used. The display 91 may have an input device such as a touch panel. Further, the cover (diaphragm 922) of the display 91 may have an input device such as a touch panel. Further, the entire display 91 or a part of the display 91 may function as a diaphragm.

In addition, the portable terminal of the present invention is characterized in that the display 91 or the casing 92 generates vibration that transmits sound information through the ear cartilage or air conduction. The portable terminal of this example can transmit sound information by transmitting a vibration to the cartilage of the ear by bringing the diaphragm (display 91 or housing 92) into contact with the ear directly or via another object. That is, sound information can be transmitted by bringing a diaphragm (display 91 or housing 92) into direct or indirect contact with the ear and transmitting vibration to the cartilage of the ear. Thereby, for example, a portable terminal capable of transmitting sound information even when the surroundings are noisy can be obtained. Note that the object interposed between the diaphragm (display 91 or housing 92) and the ear may be, for example, a cover of a mobile terminal, a headphone or an earphone, and any object that can transmit vibration. Anything can be used. Further, it may be a portable terminal that transmits sound information by propagating sound generated from the diaphragm (display 91 or housing 92) in the air. Furthermore, it may be a portable terminal that transmits sound information via a plurality of routes.

Since the portable terminal of this example transmits sound information using the piezoelectric actuator 1 in which occurrence of unnecessary vibration is reduced, it can transmit high-quality sound information.

Next, a specific example of the piezoelectric vibration device of the present invention will be described. A piezoelectric vibration device using the piezoelectric actuator shown in FIG. 7 was produced and its characteristics were measured.

The piezoelectric actuator had a long shape with a length of 23.5 mm, a width of 3.3 mm, and a thickness of 0.5 mm. The piezoelectric actuator 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 16. The piezoelectric layer was formed of lead zirconate titanate in which part of Zr was replaced with Sb.

Next, the wiring conductor of the flexible wiring board and the surface electrode were electrically connected. Here, in order to connect the wiring conductor of the flexible wiring board and the surface electrode, a conductive particle having a particle diameter of about 5 μm and a particle body made of acrylic resin coated with gold plating with Ni plating as a base coat is synthesized. A paste dispersed in a rubber-based adhesive was prepared, printed on the surface electrode by screen printing, and then pressed while heating the flexible wiring board.

When the conductive particles are crushed, a part of the conductive film is peeled off from the resin, resulting in chipping. However, the resistance between the wiring conductor and the surface electrode changes to the high resistance side due to part of the conductive film being chipped. Then, the resistance value was measured while pressing the flexible wiring board, and after the conductive particles joined and the resistance value reached the lowest value and stabilized, the resistance value was changed by about 1% by applying pressure again. By the way, the pressure was released and cooling was performed.

And while sticking a glass plate to a metal frame with a double-sided tape, the other main surface of the piezoelectric actuator was stuck to the center of one surface of the glass plate with a double-sided tape, and 1 mm away from the other surface of the glass plate A microphone was installed at the position.

Then, a sine wave signal having an effective value of 3.0 V with the frequency changed in the range of 0.3 to 3.4 kHz was input to the piezoelectric actuator, and the sound pressure detected by the microphone was measured. Furthermore, 100,000 cycles of sine wave signals were continuously added to compare the sound pressure levels before and after the continuous measurement.

As a result, high sound pressure characteristics were obtained even with low input. As a result, it was confirmed that the bonding reliability between the flexible wiring board and the piezoelectric element was good, and it was driven stably for a long time.

1: Piezoelectric actuator
10: Piezoelectric element 2: Internal electrode
21: First pole
22: Second pole 3: Piezoelectric layer 4: Laminate
41: Active part
42: Inactive part 5: Surface electrode
51: First surface electrode
52: Second surface electrode
53: Third surface electrode 6: Flexible wiring board
61: Wiring conductor 7: Conductive particles
71: Particle body
72: Conductive film
73: Resin adhesive
81: Diaphragm
82: Joining member
91: Display
92: Housing
921: Housing body
922: Diaphragm
93: Bonding material

Claims

A laminated body in which an internal electrode and a piezoelectric layer are laminated; a surface electrode electrically connected to the internal electrode on at least one main surface of the laminated body; A flexible wiring board having wiring conductors electrically connected to the electrodes,
A piezoelectric actuator comprising a plurality of conductive particles interspersed with electrical connection between the surface electrode and the wiring conductor.
2. The piezoelectric actuator according to claim 1, wherein a resin adhesive is provided between the plurality of conductive particles.
3. The piezoelectric actuator according to claim 1, wherein the plurality of conductive particles are obtained by coating a conductive film on a surface of a particle main body made of a resin.
4. The piezoelectric actuator according to claim 3, wherein a part of the conductive film coated on a surface of the particle main body is missing.
3. The piezoelectric actuator according to claim 2, wherein a gap is provided between the resin adhesive and communicated from the surface electrode to the wiring conductor.
The plurality of surface electrodes are provided adjacent to one main surface of the laminate, and the plurality of conductive particles are also disposed in an insulating region between adjacent surface electrodes. The piezoelectric actuator according to claim 5.
7. The piezoelectric actuator according to claim 1, wherein the one conductive particle is in contact with the surface electrode and the wiring conductor.
8. A piezoelectric vibration device comprising: the piezoelectric actuator according to claim 1; and a vibration plate joined to the other main surface of the piezoelectric element.
9. The piezoelectric vibration device according to claim 8, wherein the piezoelectric actuator and the diaphragm are joined using a deformable joining member.
The piezoelectric actuator according to any one of claims 1 to 7, an electronic circuit, a display, and a housing,
A portable terminal, wherein the other main surface of the piezoelectric actuator is joined to the display or the housing.
11. The portable terminal according to claim 10, wherein the piezoelectric actuator and the display or the casing are joined using a deformable joining member.
The mobile terminal according to claim 10 or 11, wherein the display or the casing generates vibrations for transmitting sound information through ear cartilage or air conduction.