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JP2017085002

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DESCRIPTION JP2017085002
PROBLEM TO BE SOLVED: To provide a piezoelectric element which suppresses the occurrence
of strong spurious vibration and contributes to the improvement of sound quality particularly
when used for an acoustic generator, and an acoustic generator, an acoustic generator and an
electronic apparatus provided with the same. . SOLUTION: The piezoelectric element 1 of the
present invention comprises a piezoelectric body 11 as a plate-like piezoelectric element main
body, a surface electrode 12a and a surface electrode 12b provided on a first main surface of the
piezoelectric body 11, and a piezoelectric body 11. The surface electrode 12 c provided on the
second main surface 11 of the second embodiment and the external electrode 13 provided on at
least one side surface of the piezoelectric body 11 are provided in the thickness direction or
width direction of the piezoelectric body 11. In the cross section taken along, there is a portion
where the thickness changes along the thickness direction or the width direction. [Selected
figure] Figure 1
Piezoelectric element, acoustic generator provided with the same, acoustic generator, electronic
device
[0001]
The present invention relates to a piezoelectric element, an acoustic generator, an acoustic
generator, and an electronic device that can be suitably used as an acoustic generator.
[0002]
Conventionally, a piezoelectric element is used as a drive source of a vibration device or an
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acoustic generator.
In such applications, surface electrodes to which an electrical signal is applied are provided on
both main surfaces of the piezoelectric element, but in order to dispose the wiring member only
on the one main surface side, the electrode on the other main surface is on the one main surface
side An external electrode is provided on the side surface of the piezoelectric element for the
purpose of leading out and connecting the internal electrode and the surface electrode in the
case of a laminated type piezoelectric element consisting of a plurality of internal electrodes and
a piezoelectric layer. The thing of composition is known (for example, refer to patent documents
1).
[0003]
JP, 2007-109754, A
[0004]
Here, when such a piezoelectric element is used for an acoustic generator, the wave of vibration
of the piezoelectric element is reflected by the side surface of the piezoelectric element, and the
reflected wave is strongly expressed as spurious vibration, so There is a problem that the sound
quality may deteriorate due to the occurrence of peaks and dips due to the spurious vibration.
[0005]
Further, in the sound generator, the sound generator and the electronic device provided with
such a piezoelectric element, the sound quality may be deteriorated due to the above-mentioned
circumstances.
[0006]
The present invention has been made in view of the above circumstances, and suppresses the
occurrence of a strong spurious vibration, particularly when used in an acoustic generator, a
piezoelectric element that contributes to the improvement of sound quality, and an acoustic
generator provided with the same An object of the present invention is to provide a sound
generator and an electronic device.
[0007]
The piezoelectric element of the present invention comprises a plate-like piezoelectric element
body, a surface electrode provided on the main surface of the piezoelectric element body, and an
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external electrode provided on at least one side of the piezoelectric element body. The external
electrode is characterized in that it has a portion whose thickness changes along the thickness
direction or the width direction in a cross section along the thickness direction or the width
direction of the piezoelectric element main body.
[0008]
According to another aspect of the present invention, there is provided an acoustic generator
including the piezoelectric element having the above-described structure and a diaphragm
attached to the other main surface of the piezoelectric element.
[0009]
A sound generator according to the present invention is characterized by comprising the sound
generator of the above-mentioned configuration and a case for housing the sound generator.
[0010]
An electronic device according to the present invention includes the sound generator having the
above configuration, an electronic circuit connected to the piezoelectric element constituting the
sound generator, and a case for housing the sound generator and the electronic circuit. It is
characterized by
[0011]
According to the piezoelectric element of the present invention, the reflection position of the
reflected wave on at least one side face of the piezoelectric element is partially shifted to disperse
the spurious vibration caused by the reflected wave, particularly when used in an acoustic
generator, Sound pressure characteristics can be improved by suppressing peaks and dips caused
by spurious vibration.
[0012]
Further, according to the sound generator, the sound generator and the electronic device of the
present invention, high sound quality can be realized.
[0013]
It is a schematic perspective view which shows an example of the piezoelectric element of this
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embodiment.
It is a schematic perspective view which shows the other example of the piezoelectric element of
this embodiment.
It is a schematic perspective view which shows the other example of the piezoelectric element of
this embodiment.
It is a schematic perspective view which shows the other example of the piezoelectric element of
this embodiment.
(A) is a schematic plan view which shows the other example of the piezoelectric element of this
embodiment, (b) and (c) is a schematic sectional drawing which shows the other example of the
piezoelectric element of this embodiment.
It is a schematic perspective view which shows the other example of the piezoelectric element of
this embodiment.
It is a disassembled perspective view of the piezoelectric element shown in FIG.
It is a schematic perspective view which shows the other example of the piezoelectric element of
this embodiment.
It is a disassembled perspective view of the piezoelectric element shown in FIG.
(A) is a schematic plan view of an example of the sound generator according to the present
embodiment, (b) is a schematic cross-sectional view of an example cut along line AA shown in (a),
(c) is A shown in (a) It is a schematic sectional drawing of the other example cut | disconnected
by-A line.
It is a block diagram showing composition of an example of a sound generation device of this
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embodiment. It is a block diagram showing composition of an example of electronic equipment of
this embodiment. It is a graph which shows an example of the frequency characteristic of the
sound generator of this invention. It is a graph which shows an example of the frequency
characteristic of the sound generator of a comparative example.
[0014]
Hereinafter, an example of the piezoelectric element of the present embodiment will be described
in detail with reference to the attached drawings. Note that the present invention is not limited
by the embodiments described below.
[0015]
FIG. 1 is a schematic perspective view showing an example of the piezoelectric element of the
present embodiment. The piezoelectric element 1 shown in FIG. 1 includes a piezoelectric body
11 as a plate-like piezoelectric element main body, a surface electrode 12 a and a surface
electrode 12 b provided on the first main surface of the piezoelectric body 11, and The external
electrode 13 is provided with a surface electrode 12 c provided on the main surface 2 and an
external electrode 13 provided on at least one side surface (one end surface) of the piezoelectric
body 11. The external electrode 13 has a thickness direction or width of the piezoelectric body
11. The cross section along the direction has a portion where the thickness changes along the
thickness direction or the width direction. FIG. 1 shows an example in which the thickness of the
external electrode 13 changes in the width direction of the piezoelectric body 11. In the
following description, when describing the feature common to each surface electrode, it may only
be called a surface electrode.
[0016]
The piezoelectric body 11 as the piezoelectric element main body is, for example, a single-layered
plate-like body having a rectangular shape (shape of the first main surface seen from the top) in
plan view, and ceramics or the like having piezoelectric characteristics It is composed of a single
crystal. As such a material, 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 dimensions of the piezoelectric body 11 can be suitably set according to the application. In
order to obtain a large amount of displacement and generation force, it is preferable to have a
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piezoelectric constant d31 of 200 pm / V or more.
[0017]
Surface electrodes are respectively provided on the first main surface and the second main
surface (the main surface facing the first main surface) of the piezoelectric body 11. Here, the
first main surface and the second main surface are surfaces along a direction orthogonal to the
thickness direction of the piezoelectric body 11, and mean surfaces with a large area. Specifically,
surface electrode 12 a and surface electrode 12 b as a first surface electrode are provided on a
first main surface of piezoelectric body 11, and as a second surface electrode on a second main
surface of piezoelectric body 11. A surface electrode 12c is provided. Here, the surface electrode
12a provided on the first main surface and the surface electrode 12c provided on the second
main surface have large electrode patterns so as to have regions facing each other. As materials
of the surface electrode 12a, the surface electrode 12b and the surface electrode 12c, silver, a
silver compound containing silver and the like mainly containing silica, and nickel can be used.
[0018]
In addition, an external electrode 13 is provided on at least one side surface of the piezoelectric
body 11. In this example, at least one side surface is one end surface of a pair of end surfaces
opposed in the longitudinal direction of the piezoelectric body 11 having the longitudinal
direction and the short direction. Specifically, an external electrode 13 electrically connecting the
surface electrode 12 b and the surface electrode 12 c is provided on the end face of the
piezoelectric body 11. As a material of the external electrode 13, it is possible to use silver, a
silver compound containing silver or the like containing silver as a main component, silver, or the
like similar to the surface electrode 12 a, the surface electrode 12 b and the surface electrode 12
c. If necessary, an external electrode may be provided on the other end face opposite to one end
face.
[0019]
Then, in the piezoelectric element 1 of the present embodiment, the external electrode 13 has, in
a cross section along the thickness direction or the width direction of the piezoelectric body 11, a
portion where the thickness changes along the thickness direction or the width direction There
is. Here, the cross section along the thickness direction means a cross section cut to be divided in
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the width direction along the longitudinal direction of the piezoelectric element 1, and the cross
section along the width direction is the length of the piezoelectric element 1 It means a cross
section cut to divide in the thickness direction along the direction. Note that FIG. 1 shows an
example in which the thickness of the external electrode 13 changes along the width direction.
Specifically, there are thick regions at both ends in the width direction, and a central portion in
the width direction There are thin regions, and these boundaries are stepped. Although not
shown in the drawings, there are thin regions at both ends in the width direction, and there may
be thick regions at the center in the width direction, and these boundaries may be stepped.
[0020]
When a conventional piezoelectric element is used for an acoustic generator, the wave of
vibration of the piezoelectric element 1 is reflected on the outer surface of the piezoelectric
element 1 and the reflected wave is strongly expressed as spurious vibration, so that the spurious
vibration in sound pressure characteristics When the piezoelectric element 1 of this embodiment
is used as an acoustic generator, the reflected wave on at least one side surface of the
piezoelectric element 1 may occur, while the sound quality may be deteriorated due to the
occurrence of peaks and dips caused by In the sound pressure characteristic, it is possible to
suppress peaks and dips caused by the spurious vibration and to improve the sound quality.
[0021]
The difference between the thick portion and the thin portion of the external electrode 13 is, for
example, the most effective in terms of suppressing the generation of new peaks and dips due to
the division of spurious vibration and the sufficient effect due to the difference in reflection
position. When based on a thin part, it is set to have a thick part in the range of 120% to 200%.
[0022]
Here, as shown in FIG. 2, it is preferable that the thickness of the external electrode 13
continuously changes along the thickness direction or the width direction.
Note that FIG. 2 shows an example where the thickness of the external electrode 13 changes
continuously along the width direction.
Here, continuous change in thickness means a shape in which the thickness gradually changes
from a thick area to a thin area, and a step-like shape as shown in FIG. It means that it is not a
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shape having a boundary but a shape having no clear boundary.
[0023]
With such a configuration, the reflection position of the reflected wave on at least one side face
of the piezoelectric element 1 is continuously shifted, since it is directed in various directions at
different positions on the surface of the external electrode 13, Spurious vibration caused by the
reflected wave can be dispersed more broadly. Therefore, when used in an acoustic generator,
peaks and dips caused by spurious vibration can be efficiently damped in sound pressure
characteristics, and the sound quality can be further improved.
[0024]
1 and 2 show an example in which thick regions are present at both ends in the width direction
of the external electrode 13, but as shown in FIG. 3, thick regions may be present at both ends in
the thickness direction. Also, as shown in FIG. 4, there may be a thick region at the center in the
thickness direction. Further, although not shown, the thickness may be changed not only in one
of the thickness direction and the width direction but also in both the thickness direction and the
width direction. Furthermore, although not shown, the external electrode 13 may have a portion
whose thickness changes so as to have a surface having a corrugated shape along the thickness
direction or the width direction.
[0025]
However, as shown in FIGS. 1 to 3, it is preferable that the thickness of the central portion in the
thickness direction or the width direction of the external electrode 13 be the thinnest. With this
configuration, the traveling direction of the reflected wave is easily dispersed, so that spurious
vibration caused by the reflected wave can be further dispersed. Therefore, when it uses for a
sound generator, a sound quality can be improved further. When the thickness of the central
portion in both the thickness direction and the width direction is the thinnest, the traveling
direction of the reflected wave is more easily dispersed, and the spurious vibration caused by the
reflected wave can be further dispersed.
[0026]
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Further, as shown in FIGS. 5A to 5C, the external electrodes 13 are provided on a pair of
opposing side surfaces, and in the cross section along the thickness direction or the width
direction of the piezoelectric body 11, the respective external electrodes are provided. The outer
shape of 13 should be non-linearly symmetrical. Here, that the outer shape of each external
electrode 13 is non-linearly symmetrical means that when the piezoelectric element 1 is cut
along the longitudinal direction, it is not symmetrical about the central axis. doing. Note that the
pair of opposing side surfaces in this example are one end surface and the other end surface of
the piezoelectric body 11.
[0027]
With such a configuration, the reflection positions on both sides of the piezoelectric element 1
can be shifted to further disperse spurious vibration caused by the reflected wave, and in
addition, amplification of spurious vibration due to superposition of reflected waves from both
sides can be suppressed. In particular, when used in an acoustic device, the sound pressure
characteristics can be improved by further suppressing the peak / dip caused by the spurious
vibration.
[0028]
In the example shown in FIGS. 1 to 5, although the thickness of the external electrode 13
changes in all the area in the thickness direction or the width direction of the end face of the
piezoelectric body 11, it is not limited to this form. May change.
[0029]
On the other hand, the piezoelectric element 2 shown in FIGS. 6 and 7 is a piezoelectric element
provided with a laminated body 23 as a plate-like piezoelectric element main body, and is a
laminated body 23 in which a piezoelectric layer 21 and an internal electrode layer 22 are
laminated. And a surface electrode 24a as a first surface electrode provided on the first main
surface of the laminate 23 as surface electrodes provided on the first main surface and the
second main surface of the laminate 23, respectively. A surface electrode 24b, a surface
electrode 24c as a second surface electrode provided on the second principal surface of the
laminate 23, and a first outside provided on one side surface (first end surface) of the laminate
23 The first external electrode 25a and the second external electrode 25b are provided with the
electrode 25a and the second external electrode 25b provided on one side surface (the second
end surface) of the laminated body 23, and the thickness direction of the laminated body 23 or
In the cross section along the width direction, in the thickness or width direction It has a portion
in which the thickness is changing me.
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[0030]
The laminate 23 as a plate-like piezoelectric element main body is formed by laminating the
piezoelectric layer 21 and the internal electrode layer 22 and has, for example, a shape in plan
view (shape of the first main surface viewed from the top) Is a rectangular plate-like body.
[0031]
The plurality of piezoelectric layers 21 constituting the laminate 23 are made of ceramics having
piezoelectric characteristics, and as such ceramics, for example, a perovskite type mainly
composed of lead zirconate titanate (PbZrO 3 -PbTiO 3) An oxide, an oxide containing lithium
niobate (LiNbO 3) or lithium tantalate (LiTaO 3) as a main component can be used.
The thickness of one layer of the piezoelectric layer 21 is set to, for example, 0.01 to 0.1 mm.
Further, in order to obtain a large flexural vibration, the piezoelectric constant d31 is set to have,
for example, 200 pm / V or more.
[0032]
The plurality of internal electrode layers 22 constituting the laminate 23 are alternately stacked
with the plurality of piezoelectric layers 21 to sandwich the piezoelectric layers 21 from above
and below, and the piezoelectric layers 21 sandwiched between them are driven. It applies a
voltage.
In the internal electrode layer 22 shown in the figure, a first internal electrode layer 22a led out
to one side surface (first end surface) in a direction orthogonal to the thickness direction, and the
other side surface facing the first end surface (first And the second inner electrode layer 22b led
to the end face of the second embodiment.
As these materials, for example, a conductor containing silver or silver-palladium as a main
component which can be fired at a low temperature, or a conductor containing copper, platinum
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or the like can be used. Good.
[0033]
In addition, surface electrodes are provided on the first main surface and the second main
surface (the main surface facing the first main surface) of the laminate 23, respectively.
Specifically, a surface electrode 24a and a surface electrode 24b as a first surface electrode are
provided on a first main surface of the stacked body 23, and a second surface electrode is
provided on a second main surface of the stacked body 23. A surface electrode 24c is provided.
Here, the surface electrode 24a provided on the first main surface and the surface electrode 24c
provided on the second main surface are each formed in a large electrode pattern so as to have
regions facing each other. . As materials for the surface electrodes (surface electrode 24a, surface
electrode 24b and surface electrode 24c), silver, silver compounds containing glass containing
silver as a main component, silver, nickel, etc. can be used. Although the surface electrode 24c is
provided on the second main surface in the example shown in the figure, the present invention is
not limited to this embodiment, and the surface electrode as the second surface electrode is not
provided on the second main surface. It is also good.
[0034]
In addition, the laminated body 23 is provided with an external electrode which connects one
ends of the plurality of internal electrode layers 22 every other layer. Specifically, a first external
electrode 25a that electrically connects the first internal electrode layer 22a and the surface
electrode 24b is provided on one side surface (first end surface) of the stacked body 23. In
addition, a second external electrode 25 b electrically connecting the second internal electrode
layer 22 b, the surface electrode 24 a, and the surface electrode 24 c is provided on the other
side surface (second end surface) of the stacked body 23. As a material of the first external
electrode 25a and the second external electrode 25b, it is possible to use silver, a silver
compound containing silver or the like mainly containing silica, silver, nickel, or the like similar
to the surface electrode.
[0035]
In the piezoelectric element 2 shown in the figure, the thickness of the first external electrode
25a and the second external electrode 25b changes along the thickness direction or the width
direction in a cross section along the thickness direction or the width direction of the laminate
23 Part of the
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[0036]
When the piezoelectric element 2 of this embodiment is used as an acoustic generator, the
reflection positions of the reflected waves on one side surface and the other side surface of the
piezoelectric element 2 are partially shifted, and spurious vibration caused by the reflected waves
is dispersed. Therefore, it is possible to suppress peaks and dips caused by spurious vibration in
the sound pressure characteristic, and to improve the sound quality.
[0037]
In the example shown in the figure, the first external electrode 25a and the second external
electrode 25b are all in the thickness direction or width direction of one side surface (first end
surface) and the other side surface (second end surface) of the laminate 23 Although the
thickness changes in the region, the present invention is not limited to this form, and the
thickness may change in a partial region.
[0038]
In addition, as shown in FIGS. 8 and 9, the piezoelectric element 3 is a piezoelectric element 3
having a bimorph structure in which the laminated body 33 in which the piezoelectric layer 31
and the internal electrode layer 32 are laminated has a bimorph structure. The first external
electrode 35 a 1 and the second external electrode 35 a 2 including the electrode 35 a 1, the
second external electrode 35 a 2, and the third external electrode 35 b are spaced from the end
in the width direction to one side surface (first end surface) of the laminate 33 The third external
electrode 35b is provided on the other side surface (second end face) of the laminate 33 at a
distance from the end in the width direction, and all the external electrodes are laminated. The
cross section along the thickness direction or the width direction of 33 may have a portion where
the thickness changes along the thickness direction or the width direction.
Here, the bimorph structure is a structure in which the direction of polarization with respect to
the direction of the electric field applied at a certain moment is reversed between the first main
surface side and the second main surface side in the thickness direction. .
In the example shown in the figure, the piezoelectric layer 31, the first inner electrode layer 32a1
located on the first main surface side, the first inner electrode layer 32a2 located on the second
main surface side, the second inner electrode A stacked body 33 in which the layer 32b is
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stacked, and a surface electrode 34a as a first surface electrode provided on a first main surface
of the stacked body 33, a surface electrode 34b1, a surface electrode 34b2, a second of the
stacked body 33 A surface electrode 34c as a second surface electrode provided on the main
surface, and a first external electrode 35a1 and a second external electrode 35a2 provided on
the first end face, and a third external electrode provided on the second end face And 35b.
And, the first internal electrode layer 32a1 located on the first main surface side and the first
internal electrode layer 32a2 located on the second main surface side have different electrode
patterns, and an electrode with a narrow width It is led out to one side face (first end face)
through the lead-out part and is electrically connected to the different first external electrode
35a1 and second external electrode 35a2, respectively, and the second internal electrode layer
32b is the other It is derived | led-out to the side surface (2nd end surface), and it is comprised
so that it may be electrically connected with the 3rd exterior electrode 35b.
[0039]
With such a configuration, the piezoelectric element 3 itself is bent and displaced particularly
when used as a piezoelectric vibration device or an acoustic generator in which the piezoelectric
element 3 and the diaphragm are joined, and therefore the force at the joint surface with the
diaphragm Can be reduced, and the displacement amount and the generated force can be further
improved.
[0040]
The first external electrode 35a1, the second external electrode 35a2, and the third external
electrode 35b are provided at intervals from the end in the width direction, so that the corner or
ridge portion of the piezoelectric element 3 is an external one. Even if a chipping occurs, the
influence on these external electrodes can be suppressed.
[0041]
Next, a method of manufacturing the above-described piezoelectric elements 1, 2, and 3 will be
described.
[0042]
First, a ceramic molded body to be the piezoelectric body 11 or the piezoelectric body layers 21
and 31 is manufactured.
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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.
In addition, as a manufacturing method of a ceramic molded body, other suitable manufacturing
methods, such as press molding and extrusion molding, can be used.
[0043]
In the case of the piezoelectric elements 2 and 3, next, a conductive paste to be the internal
electrode layers 22 and 32 is produced. Specifically, a conductive paste is prepared by adding
and mixing a binder and a plasticizer to silver-palladium metal powder. The conductive paste is
applied on the above-mentioned ceramic green sheet in a desired pattern of the internal
electrode layer 22 using a screen printing method, and a plurality of ceramic green sheets on
which the conductive paste is printed are laminated.
[0044]
Then, after performing binder removal processing at a predetermined temperature, baking is
performed at a temperature of 900 ° C. to 1200 ° C., and grinding processing is performed
using a surface grinder or the like to obtain a predetermined shape, thereby obtaining a single
layer. Laminates 23 and 33 including the piezoelectric body 11 or the piezoelectric layers 21 and
31 and the internal electrode layers 22 and 32 alternately stacked are manufactured.
[0045]
It is to be noted that any manufacturing method may be used as long as it can produce a singlelayer piezoelectric body 11 or a laminate 23 or 33 formed by laminating a plurality of
piezoelectric layers 21 and 31 and internal electrode layers 22 and 32. Good.
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[0046]
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 prepared as a main surface of the piezoelectric body 11 or the laminates 23 and 33. The
surface electrodes 12a, 12b, 12c, 24a, 24b, 24c, 34a, 34b1, 34b2 are provided by printing and
drying using a screen printing method or the like.
[0047]
Next, similarly, 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 used as a side surface of the piezoelectric body 11 or the laminate 23 In
a predetermined pattern, screen printing, roller transfer, dispenser coating, etc., and then baking
is performed at a temperature of 600 ° C. to 800 ° C. The external electrode 25a, the second
external electrode 25b, the first external electrode 35a1, the second external electrode 35a2, and
the third external electrode 35b are formed.
[0048]
The external electrode 13, the first external electrode 25 a, the second external electrode 25 b,
the first external electrode 35 a 1, the second external electrode 35 a 2, and the third external
electrode 35 b are transferred by, for example, providing irregularities on the surface of the
roller. Sometimes it can be formed by changing the thickness.
The thickness can also be changed by changing the application speed of the dispenser.
[0049]
Thereafter, the piezoelectric body 11 or the laminates 23 and 33 are subjected to polarization
treatment to impart piezoelectric activity.
For the polarization process, a DC power supply is used, and in the case of the piezoelectric
element 1, the surface electrode 12a is connected to the negative electrode, and the surface
electrode 12b (and the third surface electrode 12c) is connected to the positive electrode. The
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potential difference of 3 kV / mm may be applied for several seconds as an application time at an
ambient temperature of 15 ° C. to 35 ° C.
In the case of the piezoelectric element 2, the surface electrode 24a may be connected to the
negative electrode, and the surface electrode 24b (and the surface electrode 24c) may be
connected to the positive electrode, and the same potential difference as described above may be
applied.
Further, in the case of the piezoelectric element 3, if the polarization directions of the
piezoelectric layer are symmetrical on the first principal surface side and the second principal
surface side, the same potential difference as described above is applied. Good. The voltage, the
ambient temperature, and the application time are suitably selected depending on the properties
of the piezoelectric material.
[0050]
Although a desired piezoelectric element can be obtained as described above, when a feeding
member is required, it may be disposed on the piezoelectric elements 1, 2, 3 by the following
method. For example, in the case of connecting and fixing (joining) the flexible wiring substrate
to the piezoelectric elements 1, 2, 3 using a conductive adhesive, a paste for conductive adhesive
is screen-printed at predetermined positions of the piezoelectric elements 1, 2, 3. Coating
formation is carried out using a technique such as Then, the flexible wiring board is connected
and fixed to the piezoelectric elements 1, 2, 3 by curing the conductive adhesive paste while the
flexible wiring board is in contact. The conductive adhesive paste may be applied and formed on
the flexible wiring substrate side.
[0051]
In addition, a lead wire which carried out insulation covering may be used as an electric power
feeding member, solder may be used as a joining member, and a member which has the same
function can be chosen suitably.
[0052]
The piezoelectric elements 1, 2, and 3 of the present embodiment can be manufactured by the
above manufacturing method.
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[0053]
Next, an example of the sound generator 10 of the present embodiment will be described.
[0054]
As shown in FIG. 10, in the sound generator 10 of the present embodiment, the above-described
piezoelectric element 2 and the piezoelectric element 2 are attached, and the diaphragm 20
vibrates due to the vibration of the piezoelectric element 2 and the outer periphery of the
diaphragm 20 And a frame 30 as a support for supporting the diaphragm 20.
In the present embodiment, the piezoelectric element 2 is used, but the piezoelectric elements 1
and 3 may be used.
Further, the frame 30 shown in FIG. 10 may not necessarily be provided, and the combination of
the piezoelectric element 2 and the diaphragm 20 can be used as a sound generator.
[0055]
The piezoelectric element 2 is an exciter that excites the diaphragm 20 by vibrating in response
to the application of a voltage.
The main surface of the piezoelectric element 2 and the main surface of the diaphragm 20 are
bonded by an adhesive such as epoxy resin, and the piezoelectric element 2 vibrates, whereby
the piezoelectric element 2 gives a constant vibration to the diaphragm 20 to make sound Can be
generated.
[0056]
The vibrating plate 20 vibrates together with the piezoelectric element 2 by the vibration of the
piezoelectric element 2. The diaphragm 20 can be formed using various materials such as resin
and metal. For example, the diaphragm 20 can be made of a resin film such as polyethylene,
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polyimide, or polypropylene having a thickness of 10 to 500 μm. In particular, by constituting
the diaphragm 20 by a resin film, the diaphragm 20 is bent and vibrated with a large amplitude,
and the width of the resonance peak in the frequency characteristic of the sound pressure is
made wide and the height is lowered to make the difference between the resonance peak and dip
Can be reduced. However, the diaphragm 20 is not limited to the resin film, and may be a resin
plate, a metal plate, a glass plate, etc. For example, a part of the case of an electronic device such
as a portable terminal or a part of the display functions as the diaphragm 20 It may be done.
[0057]
The frame 30 functions as a support that supports the outer peripheral portion of the main
surface of the diaphragm 20. By providing the vibration space by supporting the outer peripheral
portion of the diaphragm 20 with the frame 30, the amplitude of the diaphragm 20 can be
increased, and the sound pressure can be improved. The frame 30 can be formed using various
materials such as, for example, metals such as stainless steel, glass, acrylic resin, polycarbonate
resin, polybutylene terephthalate resin, and the like.
[0058]
The frame 30 is bonded to one main surface or the other main surface of the diaphragm 20 via a
bonding material. As the bonding material, a resin adhesive, a sheet obtained by molding a viscoelastic body into a sheet, a structure in which a base material layer and a layer made of a viscoelastic body are laminated, or the like can be used. An acrylic or epoxy adhesive or a rubber,
acrylic, silicone, urethane or other adhesive may be used. Moreover, as the base material layer,
acetate foam, acrylic foam, cellophane, polyethylene foam, paper, non-woven fabric is used.
[0059]
As in the example shown in FIG. 10, when the frame 30 is joined to the main surface of the
diaphragm 20 to which the piezoelectric element 2 is joined, particularly the total thickness of
the frame 30 and the joining material is larger than the thickness of the piezoelectric element 2
In this case, the piezoelectric element 2 can be protected by the frame 30.
[0060]
11-05-2019
18
This frame 30 may be formed of one frame member (upper frame member 301) as shown in FIG.
10 (b), and as shown in FIG. 10 (c), two frame members (upper frame member 301 and The
lower frame member 302) may be used.
In this case, the tension of the diaphragm 20 can be stabilized by sandwiching the diaphragm 20
with two frame members. The upper frame member 301 and the lower frame member 302 each
have a thickness of, for example, 100 to 5000 μm.
[0061]
In the sound generator 10 of this embodiment, at least a part of the surface of the piezoelectric
element 2 to the diaphragm 20 (for example, the peripheral portion of the piezoelectric element
2) as shown in FIGS. 10 (b) and 10 (c). It may further have a resin layer 40 provided so as to
cover up to. The resin layer 40 is formed to have, for example, a Young's modulus in the range of
1 MPa to 1 GPa, and an acrylic resin can be used, for example. Since the appropriate damper
effect can be induced by embedding the piezoelectric element 2 in the resin layer 40, the
resonance phenomenon can be suppressed, and the peak and dip in the frequency characteristic
of the sound pressure can be suppressed small. As shown in FIGS. 10B and 10C, the resin layer
40 may be formed to have the same height as the upper frame member 301.
[0062]
The sound generator 10 of the present embodiment is small in size and has high sound quality
because it is configured using the piezoelectric element 2 in which peaks and dips due to
spurious vibration are suppressed in sound pressure characteristics.
[0063]
Note that the combination of the piezoelectric element 2 and the diaphragm 20 described above
can be used as a piezoelectric vibration device instead of an acoustic generator.
[0064]
Moreover, as shown in FIG. 11, the above-mentioned sound generator 10 can be accommodated
in the housing | casing 70, and it can also be set as the sound generator 80. FIG.
11-05-2019
19
Here, a part of the housing may be the diaphragm 20 that constitutes the sound generator 10,
and that the housing 70 accommodates the sound generator 10 is a part of the sound generator
10 (piezoelectric element 1 , 2 and 3) are meant to be included.
[0065]
The housing internally resonates the sound emitted by the sound generator 10, and radiates the
sound to the outside from the opening provided in the housing 70.
By having such a housing 70, for example, the sound pressure in the low frequency band can be
increased.
[0066]
The sound generation device 80 can be used alone as a speaker, and can be suitably incorporated
into a portable terminal, a flat-screen television, a tablet terminal, or the like as described later. In
addition, it can be incorporated into home appliances such as refrigerators, microwave ovens,
vacuum cleaners, washing machines, etc., for which sound quality has not been emphasized
conventionally.
[0067]
Next, an example of the electronic device of the present embodiment will be described.
[0068]
As shown in FIG. 12, the electronic device 50 of the present example includes an acoustic
generator 10, an electronic circuit 60 connected to the acoustic generator 10, and a case 70
housing the electronic circuit 60 and the acoustic generator 10. Have.
[0069]
The electronic device 50 includes an electronic circuit 60.
11-05-2019
20
The electronic circuit 60 includes, for example, a controller 50a, a transmitting / receiving unit
50b, a key input unit 50c, and a microphone input unit 50d.
The electronic circuit 60 is connected to the sound generator 10 and has a function of outputting
an audio signal to the sound generator 10. The sound generator 10 generates a sound based on
an audio signal input from the electronic circuit 60.
[0070]
In addition, the electronic device 50 includes the display unit 50e, the antenna 50f, and the
sound generator 10, and the housing 70 that accommodates these devices. Although FIG. 12
shows a state in which all the devices including the controller 50a are housed in one housing 70,
the housing form of the devices is not limited. In the present embodiment, at least the electronic
circuit 60 and the sound generator 10 may be accommodated in one housing 70.
[0071]
The controller 50 a is a control unit of the electronic device 50. The transmitting and receiving
unit 50b transmits and 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 receives a key
input operation by the operator. The microphone input unit 50d is also an input device of the
electronic device 50, and receives a voice input operation and the like by the operator. The
display unit 50 e is a display output device of the electronic device 50, and outputs display
information based on the control of the controller 50 a.
[0072]
The sound generator 10 then operates as a sound output device in the electronic device 50. The
sound generator 10 is connected to the controller 50a of the electronic circuit 60, and emits a
sound in response to the application of a voltage controlled by the controller 50a.
11-05-2019
21
[0073]
Although the electronic device 50 has been described as a portable terminal device in FIG. 12,
the electronic device 50 does not ask 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 may be used for various products such as vacuum cleaners, washing machines,
refrigerators, microwave ovens and the like, as a matter of course, products having a function of
emitting sound, for example.
[0074]
The electronic device 50 according to the present embodiment is small and high because the
sound generator 10 according to the present embodiment is configured using the piezoelectric
element 2 in which peaks and dips due to spurious vibration are suppressed in the sound
pressure characteristic. It will have the sound quality.
[0075]
Next, a specific example of the piezoelectric element of the present embodiment will be
described.
[0076]
The piezoelectric element was in the form of a long plate having a length of 23.2 mm, a width of
3.3 mm, and a thickness of 0.77 mm.
The piezoelectric body was formed of lead zirconate titanate.
The surface electrode and the external electrode were made of silver glass. Here, as an example,
the external electrode was manufactured to have a shape as shown in FIG. 2 in which the thick
portion becomes 150% with respect to the thinnest portion in roller transfer. On the other hand,
as a comparative example, a flat external electrode was manufactured. Thus, the piezoelectric
element of the embodiment and the piezoelectric element of the comparative example were
manufactured.
11-05-2019
22
[0077]
These piezoelectric elements are attached to a diaphragm made of a resin film to produce an
acoustic generator as shown in FIG. 10 (b), a voltage of 50 Vp-p is applied to each acoustic
generator, and the voltage is 1 kHz. Sound pressure was measured at a distance of 10 cm, and
sound pressure characteristics were measured. The results are shown in FIG. 13 (example) and
FIG. 14 (comparative example).
[0078]
As a result, it can be seen that the sound generator of the embodiment shown in FIG. 13 is
improved in sound quality by suppressing peaks and dips as compared with the comparative
example shown in FIG.
[0079]
1, 2, 3 Piezoelectric element 11 Piezoelectric members 12a, 24a, 34a First surface electrodes
12b, 24b, 34b1 Second surface electrodes 12c, 24c, 34b2 Third surface electrode 34c Fourth
surface electrode 13 External electrode 21 , 31 piezoelectric layer 22, 32 internal electrode layer
22a first internal electrode layer 22b, 32b second internal electrode layer 32a1 first internal
electrode layer 32a2 located on the first principal surface side second principal surface side 1st
internal electrode layer 23, 33 laminated body 25a, 35a1 1st external electrode 25b, 35a 2 2nd
external electrode 35b 3rd external electrode 10 acoustic generator 20 diaphragm 4
piezoelectric vibration device 30 frame 301 upper frame member 302 lower frame member 40
resin layer 50 electronic device 60 electronic circuit 70 housing 80 sound generator
11-05-2019
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