JP6434373B2 - Piezoelectric actuator, piezoelectric vibration device including the same, sound generator, sound generator, electronic device - Google Patents

Description

  The present invention relates to a piezoelectric actuator suitable as an acoustic generator, a piezoelectric vibration device including the piezoelectric actuator, an acoustic generator, an acoustic generator, and an electronic apparatus.

  The piezoelectric actuator includes a laminated body in which a piezoelectric layer and an internal electrode layer are laminated, and an external electrode is provided on a side surface from which the internal electrode layer of the laminated body is led, and the laminated body is connected to the external electrode. A piezoelectric element having a main surface provided with a surface electrode and a structure in which a wiring member is bonded to the surface electrode of the piezoelectric element via a conductive bonding material are known.

  In addition, an acoustic generator in which such a piezoelectric actuator is attached to a diaphragm is known (see, for example, Patent Document 1). This sound generator is used by being incorporated into a small electronic device such as a mobile computing device.

JP 2002-199493 A

  In the piezoelectric actuator described above, the conductive bonding material for bonding the wiring members may not be able to follow the vibration of the piezoelectric element, and may break and break.

  Also, in the acoustic generator using the above piezoelectric actuator, there is a difference in vibration mode between the part where the wiring member is joined and the part away from this joined part, and a large distortion occurs in a specific frequency region. Unnecessary vibration was generated due to distortion. Then, due to the resonance of the unnecessary vibration, a dip occurs in the sound pressure, and there is a possibility that the sound quality is deteriorated.

  The present invention has been made in view of the above circumstances, and includes a piezoelectric actuator that suppresses breakage of a conductive bonding material that joins wiring members, a piezoelectric vibration device including the piezoelectric actuator, an acoustic generator, an acoustic generator, and an electronic device. The purpose is to provide.

The piezoelectric actuator of the present invention includes a piezoelectric element having a surface electrode on an upper surface, and a wiring member having an end portion electrically connected to the surface electrode via a conductive bonding material, and the piezoelectric element and the wiring member In the cross-section of the connection portion, the width of the wiring member extending from the piezoelectric element is surrounded by the surface electrode, the wiring member, and the conductive bonding material in the extending direction. There is a gap larger than the length in the vertical direction .

  According to another aspect of the present invention, there is provided a piezoelectric vibration device including the above-described piezoelectric actuator and a vibration plate attached to a lower surface of the piezoelectric element.

  According to another aspect of the present invention, there is provided an acoustic generator including the piezoelectric actuator described above and a frame that supports an outer peripheral portion of the diaphragm.

  According to another aspect of the present invention, there is provided an acoustic generator including the above-described piezoelectric actuator and a housing that houses the piezoelectric actuator.

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

  According to the piezoelectric actuator of the present invention, it is possible to suppress the breakage of the conductive bonding material for bonding the wiring member and to suppress the disconnection.

  Moreover, according to the piezoelectric vibration device of the present invention, since it is configured using the piezoelectric actuator that suppresses breakage of the conductive bonding material and suppresses disconnection, it can be excellent in long-term reliability.

  Moreover, according to the acoustic generator of the present invention, since it is configured using the piezoelectric actuator that suppresses breakage of the conductive bonding material and suppresses disconnection, it can be excellent in long-term reliability. Furthermore, since the conductive bonding material constituting the piezoelectric actuator is easily deformed, the dip caused by the distortion is reduced, so that an acoustic generator having excellent sound quality can be obtained.

  Further, according to the sound generator of the present invention, it is possible to provide a sound generator having excellent long-term reliability and sound quality and further improved sound pressure.

  Further, according to the electronic device of the present invention, a high-performance electronic device excellent in long-term reliability and sound quality can be obtained.

(A) is a schematic plan view which shows an example of the piezoelectric actuator of this embodiment, (b) is a schematic expanded sectional view of an example which cut | disconnected the broken-line area | region shown in (a) by the AA line, (c ) Is an enlarged cross-sectional view of a main part of an example cut along line BB shown in (b). It is a schematic longitudinal cross-sectional view of the piezoelectric element shown in FIG. (A) And (b) is a principal part expanded sectional view of the other example cut | disconnected by the BB line shown to FIG.1 (b). It is a principal part expanded sectional view of the other example cut | disconnected by the BB line shown in FIG.1 (b). It is a schematic perspective view which shows an example of the piezoelectric vibration apparatus of this embodiment. (A) is a schematic plan view which shows an example of the acoustic generator of this embodiment, (b) is a schematic sectional drawing which shows an example of the cross section cut | disconnected by the AA line shown to (a), (c) is It is a schematic sectional drawing which shows the other example of the cross section cut | disconnected by the AA line shown to (a). It is a figure which shows the structure of an example of the sound generator of this embodiment. It is a figure which shows the structure of an example of the electronic device of this embodiment. It is a figure which shows the distortion characteristic of the acoustic generator of this embodiment and a comparative example.

  Hereinafter, an example of the piezoelectric actuator of the present embodiment will be described with reference to the drawings.

  FIG. 1A is a schematic plan view showing an example of the piezoelectric actuator of the present embodiment, and FIG. 1B is a schematic cross-sectional view of the broken line area shown in FIG. FIG.1 (c) is the schematic sectional drawing cut | disconnected by the BB line | wire shown in FIG.1 (b).

A piezoelectric actuator 10 shown in FIG. 1 includes a piezoelectric element 1 having a surface electrode 11 on an upper surface, and a wiring member 3 having an end portion electrically connected to the surface electrode 11 via a conductive bonding material 2. In the cross section of the connection portion between the element 1 and the wiring member 3, there is a gap 4 surrounded by the surface electrode 11, the wiring member 3, and the conductive bonding material 2.

  The piezoelectric element 1 constituting the piezoelectric actuator 10 is attached to the main surface of the diaphragm, for example, and excites the diaphragm by vibrating under application of voltage. For example, as shown in FIG. In addition, a laminated body in which piezoelectric layers 12 made of four ceramic layers and three internal electrode layers 13 are alternately laminated, and formed on one main surface (upper surface) and the other main surface (lower surface) of the laminated body. And the external electrode 14 formed on the side surface from which the internal electrode layer 13 is derived.

  The piezoelectric layer 12 constituting the piezoelectric element 1 is formed of ceramics having piezoelectric characteristics, and as such ceramics, lead zirconate titanate, lithium niobate, lithium tantalate, Bi layer shape Conventionally used piezoelectric ceramics such as compounds and lead-free piezoelectric materials such as tungsten bronze structure compounds can be used. The thickness of one layer of the piezoelectric layer 12 is set to 0.01 to 0.1 mm, for example, in order to drive with a low voltage. In order to obtain a large bending vibration, it is preferable to have a piezoelectric constant d31 of 200 pm / V or more.

  Further, the internal electrode layer 13 constituting the piezoelectric element 1 is formed by simultaneous firing with the ceramic forming the piezoelectric layer 12, and the first internal electrode layer led to one side surface and the other side surface are formed. It consists of the derived | led-out 2nd internal electrode layer. The internal electrode layers 13 are alternately stacked with the piezoelectric layers 12 to sandwich the piezoelectric layers 12 from above and below, and the first internal electrode layer and the second internal electrode layer are arranged in the stacking order. As a material for forming the internal electrode layer 13, various metal materials can be used. For example, a conductor mainly composed of silver or silver-palladium suitable for low-temperature firing, or a conductor containing copper, platinum, or the like can be used, but a ceramic component or a glass component may be contained therein. In the case where the internal electrode layer 13 is made of a material containing a metal component composed of silver and palladium and a ceramic component that constitutes the piezoelectric layer 12, the firing shrinkage difference between the piezoelectric layer 12 and the internal electrode layer 13. Therefore, the piezoelectric element 1 free from stacking faults can be obtained.

  As the piezoelectric element 1, for example, the main surface on the upper surface side and the lower surface side may be a polygonal shape such as a rectangular shape or a square shape, or a circular shape or an elliptical shape. The piezoelectric element 1 may have a unimorph structure, but preferably has a bimorph structure as shown in FIG. That is, it is preferable that the direction of polarization with respect to the direction of the electric field applied at a certain moment is polarized so as to be reversed between one side and the other side in the thickness direction. As a result, it is possible to reduce the thickness of the acoustic generator when the piezoelectric actuator 10 is attached to the diaphragm to form an acoustic generator, and to efficiently vibrate the diaphragm with less energy. In addition, since the piezoelectric element 1 itself undergoes flexural vibration, mechanical loss at the joint surface with the diaphragm can be reduced, which can contribute to improvement in sound pressure.

  An end portion of the wiring member 3 is electrically connected to the surface electrode 11 of the piezoelectric element 1 through the conductive bonding material 2.

  As the wiring member 3, for example, a flexible substrate in which a wiring made of a metal foil such as copper is provided on a resin film such as polyimide, or a plate-like body such as a metal plate formed in a slit in the width direction as necessary can be used. The width of the wiring member 3 (the width in the direction perpendicular to the direction extending from the piezoelectric element 1) is set to 0.8 to 2.0 mm, for example.

As the conductive bonding material 2 for bonding the end portion of the wiring member 3 to the surface electrode 11, a silver paste, solder, a conductive adhesive containing metal particles and a resin, or the like can be used. The conductive bonding material 2 is provided, for example, at a distance of 1.0 to 2.3 mm in the longitudinal direction of the wiring member 3 (direction extending from the piezoelectric element 1) in consideration of bonding strength, electric resistance, and the like. The width direction will be described later.

  Then, as shown in FIG. 1B, there is a gap 4 surrounded by the surface electrode 11, the wiring member 3, and the conductive bonding material 2 in the cross section of the connection portion between the piezoelectric element 1 and the wiring member 3.

  The gap 4 is formed to have a width of, for example, 40 to 85% with respect to 100% of the width of the wiring member 3. At this time, the conductive bonding material 2 has sunk a distance of, for example, 7.5 to 30% with respect to 100% of the width of the wiring member 3 from one side and the other side in the width direction of the wiring member 3 to the inside. It has a shape. Moreover, the height of the space | gap 4, in other words, the space | interval of the surface electrode 11 and the wiring member 3 is 0.05-0.2 mm, for example. In addition, the conductive bonding material 2 has a shape in which a distance of, for example, 7.5 to 30% protrudes from the one side and the other side in the width direction of the wiring member 3 toward the outside with respect to 100% of the width of the wiring member 3. It has become.

  According to such a piezoelectric actuator 10, since the conductive bonding material 2 is easily deformed due to the presence of the gap 4 in the conductive bonding material 2, the conductive bonding material 2 is electrically conductive by vibration of the piezoelectric element 1 or heat generated by continuous driving. The stress applied to the conductive bonding material 2 can be relaxed. Therefore, breakage of the conductive bonding material 2 can be suppressed and disconnection can be suppressed.

  In addition, since the conductive bonding material 2 is easily deformed, a difference in vibration mode between a portion where the wiring member 3 is bonded and a portion away from the bonding portion is reduced. Therefore, the distortion when attached to the diaphragm and used as a sound generator can be reduced, the dip of the sound pressure due to resonance of unnecessary vibration can be reduced, and the sound quality can be improved.

  Here, as shown in FIG. 3, it is preferable that the space | gap 4 is opening at least one of the front end side and rear end side of a connection part. 3 (a) and 3 (b) are enlarged cross-sectional views of the main part of another example cut along line BB shown in FIG. 1 (b). Specifically, the gap 4 is crossed. It is sectional drawing which cut | disconnected so that it might see and looked at the wiring member 3 side.

  In the form shown in FIG. 1, the conductive bonding material 2 is connected in the width direction on the front end side and the rear end side of the connection portion, whereas in FIG. 3, the gap 4 is the front end side and the rear end of the connection portion. At least one of the sides is opened, and the conductive bonding material 2 is not connected in the width direction at least one of the front end side and the rear end side of the connecting portion.

  Thereby, the conductive bonding material 2 is more easily deformed, and the stress applied to the conductive bonding material 2 due to vibration generated when the piezoelectric element 1 is driven or heat generated by continuous driving can be further relaxed. Therefore, damage to the conductive bonding material can be further suppressed.

  In addition, since the conductive bonding material 2 is more easily deformed, distortion when attached to the diaphragm and used as an acoustic generator can be further reduced, and sound quality can be further improved.

  Here, FIG. 3A shows a configuration in which the gap 4 is open on the rear end side of the connection portion, and FIG. 3B is a view in which the gap 4 opens on both the front end side and the rear end side of the connection portion. However, the configuration of FIG. 3B is more effective in terms of ease of deformation.

Moreover, as shown in FIG. 4, it is preferable that the inner surface of the conductive bonding material 2 facing the gap 4 has a shape with irregularities. In particular, the unevenness is preferably a curved unevenness. Thereby, it becomes easier to relieve stress applied when the conductive bonding material 2 is deformed, and the damage of the conductive bonding material 2 due to vibration or thermal shock can be further suppressed. Note that the distance L from the lowest concave bottom point to the highest convex vertex when seen in a plan view is appropriately set within a range of 0.1% to 22.5% of the width of the wiring member 3, for example.

  Further, although not shown, the outer surface of the conductive bonding material 2 may have an uneven shape, and the stress applied when the conductive bonding material 2 is deformed can also be reduced by this configuration.

  Next, a method for manufacturing the piezoelectric actuator 10 of this embodiment will be described.

First, a ceramic green sheet to be a piezoelectric layer and 12 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 13 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 pattern of internal electrodes using a screen printing method. Furthermore, after laminating a plurality of ceramic green sheets printed with this conductive paste and performing a binder removal treatment at a predetermined temperature, firing at a temperature of 900 to 1200 ° C., using a surface grinder or the like By performing a grinding process so as to obtain a shape, a laminated body including the piezoelectric layers 12 and the internal electrode layers 13 that are alternately laminated is manufactured.

  A laminated body is not limited to what is produced by said manufacturing method, You may produce by what kind of manufacturing method.

  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 laminated in a pattern of the surface electrode 11 and the external electrode 14. After printing and drying on the main surface and the side surface of the substrate by a screen printing method or the like, baking is performed at a temperature of 650 to 750 ° C. to form the surface electrode 11 and the external electrode 14.

  When the surface electrode 11 and the internal electrode layer 13 are electrically connected, a via that penetrates the piezoelectric layer 12 may be formed and connected.

  Next, the end of the wiring member 3 is bonded to the surface electrode 11 of the piezoelectric element 1 using the conductive bonding material 2. At this time, the paste of the conductive bonding material 2 is applied in a pattern in which the gap 4 is formed, or the conductive bonding material 2 formed in a sheet shape of such a pattern is connected to the wiring member 3 and the surface electrode 11. They may be joined by heating and pressurization while sandwiched between them. Further, the wiring member 3 is placed at a predetermined position of the piezoelectric element 1 and the conductive bonding material 2 is applied and formed on the wiring member 3 so that a gap 4 is formed between the wiring member 3 and the surface electrode 11. Thus, it is possible to produce a form in which at least one of the gaps is open.

  The piezoelectric actuator 10 of this embodiment can be manufactured by the above manufacturing method.

  Next, an example of the piezoelectric vibration device of the present embodiment will be described.

FIG. 5 is a schematic perspective view illustrating an example of the piezoelectric vibration device according to the present embodiment. The piezoelectric vibration device 20 illustrated in FIG. 5 is provided on the lower surface of the piezoelectric actuator 10 described above and the piezoelectric element 1 constituting the piezoelectric actuator 10. And an attached diaphragm 5. In FIG. 5, the conductive bonding material 2 and the wiring member 3 are omitted.

  The diaphragm 5 is, for example, a rectangular thin plate, and can be formed by suitably using a resin material having high rigidity and elasticity such as acrylic resin or glass. Moreover, the thickness of the diaphragm 5 is set to, for example, 0.3 mm to 1.5 mm. The diaphragm 5 is bonded to the other main surface (lower surface) of the piezoelectric element 1 constituting the piezoelectric actuator 10 via a bonding member. As this joining member, 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 structure containing an adhesive having elasticity, for example, a thickness of 10 μm to 2000 μm is used. The entire surface of the other main surface of the piezoelectric element 1 may be bonded to the diaphragm 5 via a bonding member, or there may be a region that is not bonded to a part.

  The piezoelectric vibration device of this example having such a configuration functions as a piezoelectric vibration device that causes the piezoelectric element 1 to bend and vibrate by applying an electrical signal, thereby vibrating the diaphragm 5.

  Since the piezoelectric vibration device 20 of the present example is configured using the piezoelectric actuator 10 that suppresses breakage of the conductive bonding material 2 and suppresses disconnection, the piezoelectric vibration device 20 is excellent in long-term reliability. it can.

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

  FIG. 6 is a schematic cross-sectional view showing an example of the sound generator of the present embodiment. The sound generator 30 shown in FIG. 6 includes the above-described piezoelectric actuator 10 and the diaphragm 5 attached to the lower surface of the piezoelectric element 1. And a frame 6 that supports the outer peripheral portion of the diaphragm 5. In FIG. 6B and FIG. 6C, the wiring member 3 and the conductive bonding material 2 constituting the piezoelectric actuator 10 are omitted.

  The piezoelectric element 1 is an exciter that vibrates the diaphragm 5 by receiving a voltage and vibrating. The main surface of the piezoelectric element 1 and the main surface of the diaphragm 5 are joined by an adhesive such as an epoxy resin, and the piezoelectric element 1 flexurally vibrates, so that the piezoelectric element 1 gives a certain vibration to the diaphragm 5. Sound can be generated.

  The outer periphery of the vibration plate 5 is fixed to the frame body 6 in a tensioned state, and vibrates together with the piezoelectric element 1 by the vibration of the piezoelectric element 1. The diaphragm 5 can be formed using various materials such as resin and metal. For example, the diaphragm 5 can be made of a resin film such as polyethylene, polyimide, or polypropylene having a thickness of 10 to 200 μm. Since the resin film is a material having a lower elastic modulus and mechanical Q value than a metal plate or the like, the diaphragm 5 is made of a resin film, so that the diaphragm 20 bends and vibrates with a large amplitude, thereby reducing the sound pressure. It is possible to reduce the difference between the resonance peak and the dip by widening the width of the resonance peak and reducing the height in the frequency characteristics.

  The frame body 6 functions as a support body that supports the diaphragm 5 at the outer peripheral portion of the diaphragm 5, and can be formed using various materials such as metals such as stainless steel and resins. The frame 6 may be composed of one frame member (upper frame member 61) as shown in FIG. 6 (b), and two frame members (upper frame member 61 and upper frame member 61 and as shown in FIG. 6 (c)). The lower frame member 62) may be used. In this case, the tension of the diaphragm 5 can be stabilized by sandwiching the diaphragm 5 between the two frame members. The upper frame member 61 and the lower frame member 62 have a thickness of, for example, 100 to 5000 μm.

  In the acoustic generator 30 of this example, as shown in FIGS. 6B and 6C, the resin layer 7 covering the upper surface of the piezoelectric element 1, the end of the wiring member 3, and the conductive bonding material 2 is provided. Furthermore, it is preferable to have. As the resin layer 7, for example, an acrylic resin can be used. By embedding the piezoelectric element 1 in the resin layer 7, 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 small. Note that, as shown in FIGS. 6B and 6C, the resin layer 7 may be formed to be the same height as the upper frame member 61.

  Since the acoustic generator 30 of the present example is configured using the piezoelectric actuator 10 that suppresses breakage of the conductive bonding material 2 and suppresses disconnection, the acoustic generator 30 can be an acoustic generator having excellent long-term reliability. it can. Further, since the conductive bonding material 2 constituting the piezoelectric actuator 10 is easily deformed, the dip caused by the distortion is reduced, so that an acoustic generator having excellent sound quality can be obtained.

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

  The sound generation device 40 is a sound generation device such as a so-called speaker, and includes, for example, a piezoelectric actuator 10 and a housing 70 that houses the piezoelectric actuator 10 as illustrated in FIG. 7. Here, the acoustic generator 40 may have a configuration in which the piezoelectric actuator 10 is attached to the inside of the casing 70 with a part of the casing 70 as the diaphragm 5 as shown in FIG. 5, for example. Moreover, the acoustic generator 40 is used as an acoustic generator 30 in which the piezoelectric actuator 10 includes the diaphragm 5 and the frame body 6 as shown in FIG. 6, for example. A housed configuration may be used.

  The housing 70 resonates the sound emitted by the piezoelectric actuator 10 or the sound generator 30 and radiates sound from an opening (not shown) formed in the housing 70 to the outside. By having such a casing 70, a resonance space can be secured, so that, for example, sound pressure in a low frequency band can be increased.

  Such a sound generator 40 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 40 of this example is configured using the piezoelectric actuator 10 described above, it can be a sound generator excellent in long-term reliability and sound quality and further improved in sound pressure.

  Next, an electronic device equipped with an acoustic generator will be described with reference to FIG. FIG. 8 is a diagram illustrating a configuration of the electronic device 50 according to the embodiment. In addition, in both figures, only the component required for description is shown and description about a general component is abbreviate | omitted.

As shown in FIG. 8, the electronic apparatus 50 of this example includes the piezoelectric actuator 10, an electronic circuit 80 connected to the piezoelectric actuator 10, and a housing 70 that houses the electronic circuit 80 and the piezoelectric actuator 10. Here, the electronic device 50 may have a configuration in which the piezoelectric actuator 10 is attached to the inside of the housing 70 with a part of the housing 70 as the diaphragm 5 as illustrated in FIG. 5, for example. Further, in the electronic device 50, the piezoelectric actuator 10 is used as an acoustic generator 30 including a diaphragm 5 and a frame body 6 as shown in FIG. It may also be configured. Further, the electronic device 50 includes the piezoelectric actuator 1
The sound generator in which 0 is housed in another housing may be housed in the housing 70.

  The electronic device 50 includes an electronic circuit 80. The electronic circuit 80 includes, for example, a controller 50a, a transmission / reception unit 50b, a key input unit 50c, and a microphone input unit 50d. The electronic circuit 80 is connected to the piezoelectric actuator 10 and has a function of outputting an audio signal to the piezoelectric actuator 10. The piezoelectric actuator 10 generates sound based on the audio signal input from the electronic circuit 80.

  The electronic device 50 includes a display unit 50e, an antenna 50f, and the sound generator 10. Further, the electronic device 50 includes a housing 70 that accommodates these devices. Although FIG. 11 shows a state in which each device including the controller 50a is accommodated in one casing 70, the accommodation form of each device is not limited. In the present embodiment, it is sufficient that at least the electronic circuit 80 and the piezoelectric actuator 10 are accommodated in one housing 70.

  The controller 50 a is a control unit of the electronic device 50. The transmission / reception unit 50b transmits / receives data via the antenna 50f based on the control of the controller 50a. The key input unit 50c is an input device of the electronic device 50 and accepts a key input operation by an operator. The microphone input unit 50d is also an input device of the electronic device 50, and accepts a voice input operation by an operator. The display unit 50e is a display output device of the electronic device 50 and outputs display information based on the control of the controller 50a. For example, a known display such as a liquid crystal display or an organic EL display can be used.

  The piezoelectric actuator 10 operates as an acoustic output device in the electronic device 50. The piezoelectric actuator 10 is connected to the controller 50a of the electronic circuit 60, and emits sound in response to application of a voltage controlled by the controller 50a.

  In FIG. 8, the electronic device 50 is described as a portable terminal device. However, the electronic device 50 is not limited to the type of the electronic device 50, and may be applied to various consumer devices having a function of emitting sound. . For example, flat-screen TVs and car audio devices can of course be used for products having a function of emitting sound such as "speak", for example, various products such as vacuum cleaners, washing machines, refrigerators, microwave ovens, etc. .

  Since such an electronic device 50 is configured using the piezoelectric actuator 10 described above, it can be a high-performance electronic device excellent in long-term reliability and sound quality.

  An embodiment of the sound generator will be described. Specifically, the sound generator shown in FIG. 6C was manufactured as shown below.

  The piezoelectric element had a structure in which piezoelectric layers having a length of 14 mm, a width of 20 mm, and a thickness of 30 μm were alternately laminated, and the total number of piezoelectric layers was eight. The piezoelectric layer was formed of lead zirconate titanate. As the internal electrode, an alloy of silver palladium was used.

  The diaphragm was a film made of polyethylene terephthalate, and the frame was made of stainless steel having an outer circumference of 20 mm in length and 30 mm in width, an inner circumference of 17 in length, 27 mm in width and 3 mm in width.

As the wiring member, a flexible substrate having a width of 1.2 mm formed by attaching a copper foil to a polyimide film was used.

  A silver paste was used as the conductive bonding material for bonding the wiring member to the piezoelectric element.

  Here, a conductive bonding material having a void was prepared as a present example, and a conductive bonding material having no void was prepared as a comparative example.

  Specifically, the conductive bonding material of this example is 0.1 mm from one side in the width direction under the flexible substrate, 0.2 mm from the other side, and 0.1 mm from the tip side, and is placed outside the flexible substrate. Was formed with a width of 0.2 mm on one side in the width direction, 0.15 mm on the other side, and 0.2 mm on the tip side. Note that the height of the gap (the distance between the surface electrode and the wiring member) was 0.1 mm.

  On the other hand, the conductive bonding material of the comparative example is formed on the outer side of the flexible substrate with a width of 0.2 mm on one side in the width direction, 0.15 mm on the other side, and 0.2 mm on the tip side. Used a structure that was embedded in the entire region so that voids were not formed. The distance between the surface electrode and the wiring member was 0.1 mm.

  When the above two types of acoustic generators were driven at a voltage of 7 Vrms and the reliability of continuous driving was confirmed, the acoustic generator of the comparative example without gaps confirmed that the conductive bonding material was damaged in about 1200 hours. However, disconnection caused by this occurred. On the other hand, in the sound generator according to the embodiment of the present invention having a gap, it was confirmed that the conductive bonding material was not damaged at the same time, and the reliability was improved.

  Moreover, distortion was measured about two types of sound generators, as shown in the graph of FIG. In the graph shown in FIG. 9, the vertical axis represents strain and the horizontal axis represents frequency, and the acoustic generator of the embodiment of the present invention is indicated by a solid line, and the acoustic generator of a comparative example is indicated by a broken line.

  As shown in the graph of FIG. 9, when the distortions of the two are compared, the distortion of the sound generator of the embodiment of the present invention having a gap is about 20% to about 10% compared to the sound generator of the comparative example having no gap. It can be seen that it has been improved to%. In particular, it can be seen that there is a significant improvement near 3 kHz.

  Thus, according to this embodiment, it can be seen that the frequency characteristics can be improved by improving the reliability and simultaneously reducing the distortion.

1 .. Piezoelectric element 11 .. Surface electrode 12 .. Piezoelectric layer 13 .. Internal electrode layer 14 .. External electrode 2 .. Conductive bonding material 3 .. Wiring member 4 .. Air gap 20. · · Diaphragm 30 · · Sound generator 6 · · Frame body 61 · · Upper frame member 62 · · Lower frame member 40 · · Sound generator 50 · · Electronic equipment 70 · · Case 80 · · Electronic circuit

Claims (7)

In the cross section of the connection portion between the piezoelectric element and the wiring member, comprising: a piezoelectric element having a surface electrode on the upper surface; and a wiring member whose end is electrically connected to the surface electrode via a conductive bonding material. The length of the wiring member extending in the direction extending from the piezoelectric element is greater than the length in the width direction perpendicular to the extending direction, being surrounded by the surface electrode, the wiring member, and the conductive bonding material. A piezoelectric actuator characterized by having an air gap.   2. The piezoelectric actuator according to claim 1, wherein the gap opens at least one of a front end side and a rear end side of the connection portion.   3. The piezoelectric actuator according to claim 1, wherein an inner surface of the conductive bonding material facing the gap has an uneven shape.   A piezoelectric vibration device comprising: the piezoelectric actuator according to claim 1; and a vibration plate attached to a lower surface of the piezoelectric element.   A piezoelectric actuator according to any one of claims 1 to 3, a diaphragm attached to a lower surface of the piezoelectric element, and a frame body that supports an outer peripheral portion of the diaphragm. A featured sound generator.   An acoustic generator comprising: the piezoelectric actuator according to any one of claims 1 to 3; and a housing that accommodates the piezoelectric actuator.   A piezoelectric actuator according to any one of claims 1 to 3, an electronic circuit connected to the piezoelectric actuator, and a housing that houses the electronic circuit and the piezoelectric actuator. Electronic equipment.