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JPWO2013171918

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DESCRIPTION JPWO2013171918
PROBLEM TO BE SOLVED: To provide a piezoelectric actuator, a piezoelectric vibration device,
and a portable terminal which improve the bonding reliability between a flexible wiring board
and a piezoelectric element and stably drive for a long time. SOLUTION: The piezoelectric
actuator 1 of the present invention comprises a laminate 4 in which an internal electrode 2 and a
piezoelectric layer 3 are laminated, and a surface electrode electrically connected to the internal
electrode 2 on at least one main surface of the laminate 4 5 and a flexible wiring board 6 having
a wiring conductor 61 partially connected to the one main surface and electrically connected to
the surface electrode 5, and electrically connecting the surface electrode 5 and the wiring
conductor 61 Are characterized by a plurality of conductive particles 7 interspersed with each
other. [Selected figure] Figure 1
Piezoelectric actuator, piezoelectric vibration device and portable terminal
[0001]
The present invention relates to a piezoelectric vibration device, a piezoelectric actuator suitable
for a portable terminal, a piezoelectric vibration device, and a portable terminal.
[0002]
As a piezoelectric actuator, as shown in FIG. 12, one using a bimorph-type piezoelectric element
10 in which a surface electrode 104 is formed on the surface of a laminated body 103 in which a
plurality of internal electrodes 101 and piezoelectric layers 102 are laminated, The piezoelectric
element 10 and the flexible wiring board 105 are joined by the conductive connection member
106 to electrically connect the surface electrode 104 of the piezoelectric element 10 and the
wiring conductor 107 of the flexible wiring board 105 (see Patent Document 1). It is known that
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this is done (see Patent Document 2).
[0003]
Furthermore, there is known a piezoelectric vibration device in which a central portion and one
end in a longitudinal direction of a bimorph piezoelectric element are fixed to a diaphragm (see
Patent Documents 3 and 4).
[0004]
Patent Document 1: JP-A-2002-10393 Patent Document 2: JP-A-6-14396 Patent Document 2:
International Publication No. 2005/004535 Patent Document 2: JP-A-2006-238072
[0005]
In recent years, the piezoelectric actuator of the piezoelectric vibration device used for these
portable terminals and the like 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.
[0006]
Here, in bonding 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 a result, a
part of the flexible wiring substrate 105 is joined on one main surface of the laminate 103.
When the piezoelectric element 10 is repeatedly driven in a temperature environment below
freezing, the flexible wiring board 105 itself is harder than in a room temperature environment,
so the conductive connecting member 106 connecting the flexible wiring board 105 and the
piezoelectric element 10 The stress is concentrated at the end of the metal, and micro cracks are
gradually generated, which may lower the bonding reliability.
[0007]
The present invention has been made in view of the above problems, and an object thereof is to
improve the bonding reliability between a flexible wiring board and a piezoelectric element, and
to provide a piezoelectric actuator which is stably driven for a long period of time, and
piezoelectric vibration. It is providing an apparatus and a portable terminal.
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[0008]
The piezoelectric actuator according to the present invention comprises 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 major surface of the laminate, and a surface
electrode on the one major surface. And a flexible wiring board provided with a wiring conductor
electrically connected to the surface electrode, and a plurality of conductive particles are
electrically connected between the surface electrode and the wiring conductor. It is characterized
by
[0009]
The piezoelectric vibration device according to the present invention is characterized by
including the piezoelectric actuator and a vibrating plate joined to the other main surface of the
piezoelectric element.
[0010]
The portable terminal of the present invention includes the piezoelectric actuator, an electronic
circuit, a display, and a housing, and the other principal surface of the piezoelectric actuator is
joined to the display or the housing. It features.
[0011]
According to the present invention, there is provided a piezoelectric actuator, a piezoelectric
vibration device, and a portable terminal capable of stably and stably driving for a long period of
time by improving the bonding reliability between the flexible wiring substrate and the
piezoelectric element by increasing the electric and mechanical bonding strength. can do.
For example, even in use under a severe environment such as driving a piezoelectric element in a
temperature environment below freezing, a portable terminal capable of transmitting highquality sound information with high reliability can be obtained.
[0012]
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(A) is a schematic perspective view which shows an example of embodiment of the piezoelectric
actuator of this invention, (b) is the schematic sectional drawing cut | disconnected by the AA
shown to (a).
It is a schematic enlarged view of 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 the schematic sectional drawing cut | disconnected
by the AA 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.
FIG. 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. It is the schematic
sectional drawing cut | disconnected by the AA shown in FIG. It is the schematic sectional
drawing cut | disconnected by the BB line shown in FIG. 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 shown to (a).
[0013]
An example of the embodiment of the piezoelectric actuator of the present invention will be
described in detail with reference to the drawings.
[0014]
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FIG. 1 is a schematic perspective view showing an example of the embodiment of the
piezoelectric actuator of the present invention, FIG. 2 (a) is a schematic sectional view cut along
the line AA shown in FIG. 1 (b), FIG. It is the schematic enlarged view of the area | region A
shown to 1 (b).
[0015]
The piezoelectric actuator 1 of the present embodiment shown in FIG. 1 has a laminated body 4
in which the internal electrode 2 and the piezoelectric layer 3 are laminated, and a surface
electrically connected to the internal electrode 2 on at least one main surface of the laminated
body 4. An electrode 5 and a flexible wiring board 6 provided with a wiring conductor 61
partially connected to one main surface and electrically connected to the surface electrode 5 are
provided. It is characterized in that the connection is made by a plurality of conductive particles
7 scattered.
[0016]
The piezoelectric actuator 1 includes a piezoelectric element 10, and a laminate 4 constituting
the piezoelectric element 10 is formed by laminating the internal electrode 2 and the
piezoelectric layer 3 and an active portion in which a plurality of internal electrodes 2 overlap in
the laminating direction 41 and the other inactive part 42, for example, are formed in a long
shape.
In the case of a piezoelectric actuator attached to a display or a housing of a portable terminal,
the length of the laminate 4 is preferably 18 mm to 28 mm, for example, and more preferably 22
mm to 25 mm.
The width of the laminate 4 is preferably, for example, 1 mm to 6 mm, and more preferably 3
mm to 4 mm.
0.2 mm-1.0 mm are preferable, for example, and, as for the thickness of the laminated body 4,
0.4 mm-0.8 mm are still more preferable.
[0017]
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The internal electrode 2 constituting the laminate 4 is formed by co-firing with the ceramic
forming the piezoelectric layer 3 and comprises 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. The piezoelectric layer 3 is alternately stacked with the
piezoelectric layer 3 to sandwich the piezoelectric layer 3 from the upper and lower sides, and
the first pole 21 and the second pole 22 are arranged in the stacking order, thereby sandwiching
the piezoelectric body A driving voltage is applied to the layer 3. As the forming material, for
example, a conductor containing silver or silver-palladium alloy as a main component having low
reactivity with piezoelectric ceramics, or a conductor containing copper, platinum or the like can
be used. You may make it contain.
[0018]
In the example shown in FIG. 1, the end portions of the first pole 21 and the second pole 22 are
respectively alternately drawn to a pair of opposing side surfaces of the laminate 4. In the case of
a piezoelectric actuator attached to a display or a housing of a portable 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. The width of the internal electrode 2 is preferably, for example, 1 mm to 5 mm, and
more preferably 2 mm to 4 mm. The thickness of the internal electrode 2 is preferably, for
example, 0.1 to 5 μm.
[0019]
The piezoelectric layer 3 constituting the laminate 4 is formed of a ceramic having piezoelectric
properties, and as such a ceramic, for example, a perovskite oxide made of lead zirconate titanate
(PbZrO 3 -PbTiO 3), Lithium niobate (LiNbO 3), lithium tantalate (LiTaO 3) or the like can be
used. The thickness of one layer of the piezoelectric layer 3 is preferably set to, for example, 0.01
to 0.1 mm in order to drive at a low voltage. Moreover, in order to obtain a large bending
vibration, it is preferable to have a piezoelectric d31 constant of 200 pm / V or more.
[0020]
A front 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 is composed
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of a first surface electrode 51 with a large area, a second surface electrode 52 with a small area,
and a third surface electrode 53. For example, the first surface electrode 51 is electrically
connected to the internal electrode 2 serving as the first electrode 21, and the second surface
electrode 52 is an internal electrode serving as the second electrode 22 disposed on the one
principal surface side. 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 a housing of a portable terminal, the
length of the first surface electrode 51 is, for example, preferably 17 mm to 23 mm, and more
preferably 19 mm to 21 mm. The width of the first surface electrode 51 is preferably, for
example, 1 mm to 5 mm, and more preferably 2 mm to 4 mm. The lengths of the second surface
electrode 52 and the third surface electrode 53 are preferably, for example, 1 mm to 3 mm. The
width of the second surface electrode 52 and the third surface electrode 53 is preferably, for
example, 0.5 mm to 1.5 mm.
[0021]
In addition, the piezoelectric actuator 1 has a flexible wiring board 6 partially connected to one
main surface of the laminate 4 constituting the piezoelectric element 10.
[0022]
The flexible wiring board 6 is, for example, a flexible printed wiring board in which 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 There is.
[0023]
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 the plurality of conductive particles 7 scattered.
[0024]
The conductive particles 7 include, for example, gold, silver, copper, an alloy such as silverpalladium, or metal particles obtained by plating gold on a metal such as Ni, and having an
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average particle diameter of, for example, 0.05 to 50 μm. That's good.
Further, it is preferable that 50 to 10000 particles of the plurality of dispersed conductive
particles 7 be distributed, for example, per 1 mm <2>.
[0025]
When the surface electrode 5 and the wiring conductor 61 are joined by a conductive connection
member such as solder, the thermal expansion coefficient of the conductive connection member
is large, and the surface electrode 5 and the conductive connection member restrained by the
piezoelectric layer 3 The piezoelectric element 10 is driven in a severe environment where shear
stress is likely to be concentrated at the junctions between the two and the junctions of the
wiring conductor 61 of the flexible wiring board 6 and the conductive connection member, and
further embrittlement under freezing. Then, microcracks may be generated in the joint of the
front surface electrode 5 and the conductive connection member or in the joint of the wiring
conductor 61 of the flexible wiring board 6 and the conductive connection member, which may
cause the piezoelectric actuator 1 to stop. was there.
[0026]
On the other hand, the surface electrode 5 and the wiring conductor 61 are connected by the
plurality of conductive particles 7 scattered like in the present invention, compared with the case
where the conductive connecting member as a bulk body is used. The thermal expansion
difference between the electrode 5 and the wiring conductor 61 can be reduced.
[0027]
As a result, even if the piezoelectric element 10 is driven in a severe environment such as below
freezing, generation of microcracks at the junctions between the plurality of conductive particles
7 and the surface electrode 5 and the wiring conductor 61 is suppressed, and the piezoelectric
actuator The displacement amount of 1 does not decrease, and unnecessary vibration does not
occur to deteriorate the vibration characteristic, so that stable driving can be performed for a
long time.
[0028]
Here, as shown in FIG. 3, it is preferable that a resin adhesive 73 be provided between the
plurality of dispersed conductive particles 7.
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The resin adhesive 73 is, for example, one having a low elastic modulus (Young's modulus) such
as polyimide, polyamide imide, silicone rubber, synthetic rubber and the like.
[0029]
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 substrate 6
can be kept high while the stress due to the thermal expansion difference is low.
In addition, since the resin adhesive 73 having a low elastic modulus is provided, vibrations that
do not follow the vibrations of the piezoelectric element 10 of the flexible wiring substrate 6
occur due to external vibration, resonance of the flexible wiring substrate 6 itself, etc. Also, it is
possible to suppress stress concentration at the end of the root or the like of the joint of the
flexible wiring board 6.
[0030]
Furthermore, as shown in FIG. 4, the plurality of conductive particles 7 may be those in which the
conductive film 72 is coated on the surface of the particle main body 71 made of resin.
[0031]
The particle main body 71 is made of, for example, a resin such as an acrylic resin having a high
elastic modulus (Young's modulus), an imide resin, an amide resin, an epoxy resin, and a
polypropylene resin.
The conductive film 72 coated on the surface of the particle main body 71 is, for example, an Au
plating film or the like.
[0032]
The conductive film 72 coated on the surface of the particle main body 71 contributes to
electrical bonding, and is rich in ductility even under freezing point, so that deterioration such as
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embrittlement can be suppressed.
[0033]
Furthermore, as shown in FIG. 5 or FIG. 6, a part of the conductive film 72 coated on the surface
of the particle main body 71 may be missing.
[0034]
In FIG. 5, a part of the conductive film 72 is missing at the contact point of the conductive
particle 7 with the surface electrode 5 and the wiring conductor 61. According to this
configuration, the machine of the surface electrode 5 and the wiring conductor 61 Connection is
formed by the particle main body 71 having a high elastic modulus, and the electrical connection
is a connection in which the conductive film 72 spreads around the connection portion between
the resin adhesive 73 and the surface electrode 5 and the wiring conductor 61 to widen the
connection area. Form an electrical connection.
By doing this, the mechanical connection can be made stronger, the junction area of the electrical
connection can be expanded, and the electrical resistance can be lowered.
[0035]
Further, in FIG. 6, the region where the conductive film 72 is not provided is provided in the
region other than the contact point with the surface electrode 5 and the wiring conductor 61.
According to this configuration, the plurality of conductive particles 7 are scattered. In order to
directly bond the particle main body 71 and the resin adhesive 73 when the resin adhesive 73 is
provided between the two, the conductive film 72 adheres to the resin when the conductive
particles 7 and the resin adhesive 73 flow in the bonding process. It can be reduced by the agent
73 to be peeled off.
As a result, the electrical connection between the surface electrode 5 and the wiring conductor
61 can be made reliable.
[0036]
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Further, as shown in FIG. 7, it is preferable that the resin adhesive 73 have an air gap 74
communicating with the wiring conductor 61 from the surface electrode 5.
This is because the voids 74 contribute to stress relaxation as a result of lowering the elastic
modulus of the resin adhesive 73 as a bulk.
[0037]
Furthermore, as shown in FIG. 3 and FIG. 7, in the case where a plurality of surface electrodes 5
are provided adjacent to each other on one main surface of laminated body 4, an insulating
region between adjacent surface electrodes 5 and surface electrode 5. Preferably, a plurality of
conductive particles 7 are disposed. This is because the thermal resistance can be lowered by
arranging the plurality of conductive particles 7 having high thermal conductivity even in a
portion thicker than the region forming the electrical junction. Furthermore, for the same effect,
it is preferable that a plurality of conductive particles 7 be disposed also in the insulating region
outside the surface electrode 5.
[0038]
As shown in FIGS. 1 to 7, one conductive particle 7 is in contact with surface electrode 5 and
wiring conductor 61, that is, each conductive particle 7 between surface electrode 5 and wiring
conductor 61. Is preferably in contact with the surface electrode 5 and the wiring conductor 61.
Further, by making the other main surface of the piezoelectric element 10 flat, for example, the
other main object (for example, a diaphragm to be described later) When the surfaces are
bonded, it becomes easy to cause bending vibration integrally with the object to which vibration
is applied, and it is possible to increase the efficiency of bending vibration as a whole.
[0039]
The piezoelectric actuator 1 shown in FIG. 1 is a so-called bimorph type piezoelectric actuator,
which receives an electric signal from the surface electrode 5 and bends and vibrates so that one
main surface and the other main surface become bending surfaces. The piezoelectric actuator of
the present invention is not limited to the bimorph type, and may be a unimorph type. For
example, the other principal surface of the piezoelectric actuator is bonded (bonded) to a
diaphragm described later. It can be done.
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[0040]
Next, a method of manufacturing the piezoelectric actuator 1 of the present embodiment will be
described.
[0041]
First, a ceramic green sheet to be the piezoelectric layer 3 is manufactured.
Specifically, a ceramic slurry is prepared by mixing a calcined powder of a piezoelectric ceramic,
a binder made of an organic polymer such as acrylic and butyral, and a plasticizer.
Then, a ceramic green sheet is produced using this ceramic slurry by using a tape forming
method such as a doctor blade method or a calender roll method.
Any piezoelectric ceramic may be used as long as it has piezoelectric characteristics, and, for
example, a perovskite oxide made of lead zirconate titanate (PbZrO 3 -PbTiO 3) can be used.
Further, as a plasticizer, dibutyl phthalate (DBP), dioctyl phthalate (DOP) or the like can be used.
[0042]
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 metal powder of a silverpalladium alloy. This conductive paste is applied on the above-mentioned ceramic green sheet in
the pattern of the internal electrodes 2 using a screen printing method. Further, a plurality of
ceramic green sheets on which the conductive paste is printed are laminated, subjected to
debinding treatment at a predetermined temperature, and fired at a temperature of 900 to 1200
° C. The laminated body 4 provided with the internal electrode 2 and the piezoelectric material
layer 3 laminated | stacked alternately is produced by giving a grinding process so that it may
become a shape of.
[0043]
The laminate 4 is not limited to one manufactured by the above manufacturing method, and any
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manufacturing method may be used as long as the laminate 4 formed by laminating a plurality of
internal electrodes 2 and piezoelectric layers 3 can be manufactured. It may be produced.
[0044]
Thereafter, a silver glass-containing conductive paste prepared by adding a binder, a plasticizer
and a solvent to a mixture of conductive particles containing silver as a main component and
glass is made to have the main surface of the laminate 4 in the pattern of the surface electrode 5
After printing and drying on the side and the side by a screen printing method or the like, baking
is performed at a temperature of 650 to 750 ° C. to form the surface electrode 5.
[0045]
When the surface electrode 5 and the internal electrode 2 are electrically connected, a via
penetrating the piezoelectric layer 3 may be formed and connected, or a side electrode may be
formed on the side surface of the laminate 4, It may be produced by any manufacturing method.
[0046]
Next, the flexible wiring board 6 is connected and fixed (joined) to the piezoelectric element 10
using the plurality of conductive particles 7 scattered.
[0047]
First, a paste containing a plurality of conductive particles 7 and a resin adhesive 73 is applied
and formed on a predetermined position of the piezoelectric element 10 using a method such as
screen printing.
Then, the flexible wiring board 6 is connected and fixed to the piezoelectric element 10 by curing
the paste in a state where the flexible wiring board 6 is in contact.
The paste may be applied and formed on the flexible wiring substrate 6 side.
[0048]
When the resin adhesive is made of a thermoplastic resin, a paste is applied and formed on a
predetermined position of the piezoelectric element 10 or the flexible wiring board 6, and then
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the piezoelectric element 10 and the flexible wiring board 6 are brought into contact with each
other via the paste. The thermoplastic resin is softened and flowed by heating and pressing in a
compressed state, and then the thermoplastic resin is cured again by returning to normal
temperature, and the flexible wiring substrate 6 is connected and fixed to the piezoelectric
element 10.
[0049]
In particular, it is necessary to control the amount of pressure so that the adjacent conductive
particles 7 do not contact.
[0050]
The piezoelectric vibration device of the present invention has a piezoelectric actuator 1 and a
diaphragm 81 joined to the other main surface of the piezoelectric actuator 1, as shown in FIG.
[0051]
The diaphragm 81 has a rectangular thin plate shape.
The diaphragm 81 can be formed by suitably using a material having high rigidity and elasticity
such as acrylic resin or glass.
The thickness of the diaphragm 81 is set to, for example, 0.4 mm to 1.5 mm.
[0052]
The vibrating plate 81 is bonded to the other main surface of the piezoelectric actuator 1 via a
bonding 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.
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[0053]
The bonding member 82 has a film-like shape.
The bonding member 82 is formed of a material that is softer and easier to deform 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 joint member 82 is deformable and deforms more than the diaphragm 81 when the
same force is applied. The other main surface (main surface on the −z direction side in the
drawing) of the piezoelectric actuator 1 is entirely fixed to one main surface (the main surface on
the + z direction side in the drawing) of the bonding member 82. 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 (the main surface on the −z direction side in the drawing).
[0054]
The bonding member 82 may be a single member or a composite of several members. As such a
joining member 82, for example, a double-sided tape in which an adhesive is attached to both
sides of a base material made of non-woven fabric or the like, various elastic adhesives which are
adhesives having elasticity, etc. can be suitably used. Further, the thickness of the bonding
member 82 is desirably larger than the amplitude of the flexural vibration of the piezoelectric
actuator 1, but since the vibration is attenuated if the thickness is too thick, it is set to, for
example, 0.1 mm to 0.6 mm. 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 harder than the diaphragm 81 and less likely to be deformed. Further, depending
on the case, a configuration without the bonding member 82 may be employed.
[0055]
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 electrical signal, thereby vibrating the diaphragm 81. The other end in the
lengthwise direction of the diaphragm 81 (the end in the −y direction in the figure, the
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peripheral edge of the diaphragm 81, etc.) may be supported by a support member (not shown).
[0056]
Since the piezoelectric vibration device of this example is configured using the piezoelectric
actuator 1 in which the generation of unnecessary vibration is reduced, the piezoelectric
vibration device can be reduced in which the generation of unnecessary vibration is reduced.
[0057]
Further, in the piezoelectric vibration device of this example, the diaphragm 81 is joined to the
flat other main surface of the piezoelectric actuator 1.
As a result, it is possible to obtain a piezoelectric vibration device in which the piezoelectric
actuator 1 and the diaphragm 81 are firmly joined.
[0058]
The portable terminal according to the present invention includes the piezoelectric actuator 1, an
electronic circuit (not shown), a display 91, and a housing 92, as shown in FIGS. 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 cross-sectional view cut along
line AA shown in FIG. 9, and FIG. 11 is line BB shown in FIG. It is a schematic sectional view cut
at.
[0059]
Here, it is preferable that the piezoelectric actuator 1 and the housing 92 be joined using a
deformable joining member. That is, in FIG. 5 and FIG. 6, the joining member 82 is a deformable
joining member.
[0060]
By bonding the piezoelectric actuator 1 and the housing 92 with the deformable bonding
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member 82, when vibration is transmitted from the piezoelectric actuator 1, the deformable
bonding member 82 deforms more than the housing 92.
[0061]
At this time, since the vibration in the opposite phase reflected from the housing 92 can be
mitigated by the deformable bonding member 82, the piezoelectric actuator 1 transmits strong
vibration to the housing 92 without being affected by surrounding vibration. It can be done.
[0062]
In particular, at least a part of the bonding member 82 is made of a visco-elastic body, so that the
strong vibration from the piezoelectric actuator 1 is transmitted to the housing 92, while the
bonding member 82 transmits the weak vibration reflected from the housing 92. It is preferable
at the point which can absorb.
For example, a double-sided tape in which an adhesive is attached to both sides of a substrate
made of non-woven fabric or a bonding member having a configuration including an adhesive
having elasticity can be used, and the thickness thereof is, for example, 10 μm to 2000 μm. It
can be used.
[0063]
Then, in this example, the piezoelectric actuator 1 is attached to a part of a housing 92 which is a
cover of the display 91, and a part of the housing 92 functions as a diaphragm 922.
[0064]
Although the piezoelectric actuator 1 is joined to the housing 92 in this example, the
piezoelectric actuator 1 may be joined to the display 91.
[0065]
The housing 92 has a box-shaped housing body 921 with one surface open, and a diaphragm
922 for closing the opening of the housing body 921.
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The housing 92 (the housing body 921 and the diaphragm 922) can be formed preferably using
a material such as a synthetic resin having high rigidity and elastic modulus.
[0066]
The peripheral portion of the diaphragm 922 is vibratably attached to the housing body 921 via
a bonding material 93.
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 is deformable, and deforms more than the diaphragm 922 when
the same force is applied.
[0067]
The bonding material 93 may be a single material or a composite of several members. As such a
bonding material 93, for example, a double-sided tape or the like in which an adhesive is
attached to both sides of a base material made of non-woven fabric or the like can be suitably
used. The thickness of the bonding material 93 is set so as not to be too thick and the vibration is
attenuated, and is set to, for example, 0.1 mm to 0.6 mm. However, in the portable terminal of
the present invention, the material of the bonding material 93 is not limited, and the bonding
material 93 may be formed harder than the diaphragm 922 and less likely to be deformed. In
addition, depending on the case, the bonding material 93 may not be provided.
[0068]
As the electronic circuit (not shown), for example, a circuit that processes image information to
be displayed on the display 91 or audio information transmitted by the mobile terminal, a
communication circuit, and the like can be exemplified. At least one of these circuits may be
included, or all of the circuits may be included. Alternatively, a circuit having another function
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may be used. Furthermore, a plurality of electronic circuits may be included. The electronic
circuit and the piezoelectric actuator 1 are connected by a connection wiring (not shown).
[0069]
The display 91 is a display device having a function of displaying image information. For
example, known displays 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. In
addition, the cover (diaphragm 922) of the display 91 may have an input device such as a touch
panel. Furthermore, the entire display 91 or a part of the display 91 may function as a
diaphragm.
[0070]
Also, the portable terminal of the present invention is characterized in that the display 91 or the
housing 92 generates a vibration that transmits sound information through the cartilage or air
conduction of the ear. The portable terminal of this example can transmit sound information by
transmitting vibration to the cartilage of the ear by bringing the diaphragm (the display 91 or the
housing 92) into contact with the ear directly or through another object. That is, sound
information can be transmitted by transmitting vibration to the cartilage of the ear by bringing
the diaphragm (the display 91 or the housing 92) into contact with the ear directly or indirectly.
Thereby, for example, a portable terminal capable of transmitting sound information even when
the surrounding area is noisy can be obtained. An object interposed between the diaphragm (the
display 91 or the housing 92) and the ear may be, for example, a cover of a portable terminal, a
headphone or an earphone, and it may be one that can transmit vibration. Anything will do. In
addition, the portable terminal may be one that transmits sound information by propagating the
sound generated from the diaphragm (the display 91 or the housing 92) into the air.
Furthermore, it may be a portable terminal that transmits sound information via a plurality of
routes.
[0071]
Since the portable terminal of this example transmits sound information using the piezoelectric
actuator 1 in which generation of unnecessary vibration is reduced, high quality sound
information can be transmitted.
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[0072]
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
manufactured, and its characteristics were measured.
[0073]
The piezoelectric actuator had a length of 23.5 mm, a width of 3.3 mm, and a thickness of 0.5
mm. The piezoelectric actuator had a structure in which 30 μm thick piezoelectric layers and
internal electrodes were alternately stacked, and the total number of piezoelectric layers was 16.
The piezoelectric layer was formed of lead zirconate titanate in which a part of Zr was replaced
with Sb.
[0074]
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 substrate and the
surface electrode, a conductive particle of an about 5 μm particle diameter is prepared by
combining gold coated with Ni plating as a base coat on a particle body made of acrylic resin.
The paste dispersed in the rubber-based adhesive was prepared and printed on the surface
electrode by screen printing, and then the flexible wiring board was pressed while being heated.
[0075]
When the conductive particles are crushed, a part of the conductive film is peeled off from the
resin and a chipping occurs, but it is used that the resistance between the wiring conductor and
the surface electrode changes to the high resistance side by the partial chipping of the
conductive film. Then, the resistance was measured while pressing the flexible wiring board while
heating, and after the conductive particles joined and the resistance reached the minimum value
and stabilized, the pressure was applied again and the resistance changed by about 1%. By the
way, the pressure was released and cooled.
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[0076]
Then, the glass plate was attached to a metal frame with double-sided tape, and the other main
surface of the piezoelectric actuator was attached to the center of one surface of the glass plate
with double-sided tape, 1 mm away from the other surface of the glass plate I installed a
microphone at the position.
[0077]
And the sine wave signal of effective value 3.0V which changed frequency in the range of 0.3-3.4
kHz was input into the piezoelectric actuator, and the sound pressure detected with the
microphone was measured.
Furthermore, 100,000 cycles of sine wave signals were continuously added to compare sound
pressure levels before and after continuous measurement.
[0078]
As a result, high sound pressure characteristics were obtained even with low input.
As a result, it has been confirmed that the connection reliability between the flexible wiring
board and the piezoelectric element is good, and stable driving for a long time is achieved.
[0079]
1: Piezoelectric actuator 10: Piezoelectric element 2: Internal electrode 21: first pole 22: second
pole 3: piezoelectric layer 4: laminate 41: active portion 42: inactive portion 5: surface electrode
51: first Surface electrode 52: second surface electrode 53: third surface electrode 6: flexible
wiring substrate 61: wiring conductor 7: conductive particles 71: particle main body 72:
conductive film 73: resin adhesive 81: diaphragm 82: bonding Member 91: Display 92: Case 921:
Case body 922: Diaphragm 93: Bonding material
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