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DESCRIPTION JP2006005801

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DESCRIPTION JP2006005801
To provide a thin piezoelectric speaker having good sound reproducibility by forming a stable
electrical connection state. A piezoelectric element (14) having an electrode layer (16) on its
surface is attached to the main surface of a diaphragm (12) of a piezoelectric speaker (10). The
piezoelectric element 14 has a structure in which at least three or more piezoelectric layers and
electrode layers are alternately stacked in order to obtain a sufficient driving force. On the front
surface of the electrode layer 16, a conductive path 20 made of a strip-like metal foil provided
with a first conductive connection portion 22 made of a conductive adhesive material layer on
the back surface is provided. The rigidity is low and the volume resistance is low so as to cross
the conductive path 20 from the upper side of the conductive path 20 to the upper side of the
conductive path 20 and the surface of the electrode layer 16 on both sides of the conductive
path 20. A conductive paste having a high rate is applied to form a second conductive connection
24 (to 26, 28). [Selected figure] Figure 1
Piezoelectric speaker
[0001]
The present invention relates to a piezoelectric speaker, and more specifically, to improvement in
sound reproducibility of a thin piezoelectric speaker.
[0002]
Conventionally, for example, an ultra thin piezoelectric speaker having a thickness of 1 mm or
less has a structure in which a piezoelectric element (piezoelectric thin plate) polarized in the
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thickness direction is attached to one side or both sides of a metal diaphragm. .
In order to obtain a sufficient sound pressure, it is necessary to make this piezoelectric element
into a laminated body in which a piezoelectric body (piezoelectric layer) and an electrode layer
are laminated. Therefore, it is necessary to co-fire the electrode, and a silver / palladium alloy
electrode is used as a material that can withstand the firing. Then, as a conductive path for
applying a signal to the electrode on the surface of the piezoelectric body, a thin metal foil with a
conductive adhesive material having a thickness of 0.1 mm or less is used to ensure the thinness
of the entire speaker (for example, Patent Document 1). Further, since a method of reducing the
palladium ratio in the electrode is effective to reduce the cost, the silver / palladium ratio is, for
example, about 9: 1 by using a piezoelectric material sintered at a low temperature. However, in
an electrode with such a reduced palladium content, the contraction proceeds at a lower
temperature than the base piezoelectric material, so the piezoelectric element is deformed or
broken by the stress generated by the contraction mismatch during sintering. I will do it.
Therefore, a method is used in which the same piezoelectric material as that of the base material
is added to the electrode to match the contraction rate. Patent Document 1: Japanese Patent
Application Laid-Open No. 2003-078995
[0003]
However, since the piezoelectric material added to the electrode as described above is excluded
from the metal during sintering, particles of the piezoelectric material are precipitated on the
surface of the electrode in the external electrode of the piezoelectric element. Since the
piezoelectric material itself is a nonconductor, it becomes an obstacle when taking an electrical
contact with the conductive adhesive material, and the contact between the conductive adhesive
material and the electrode becomes unstable. Due to this, there is a problem that the contact
resistance changes with the vibration and the reproducibility of the sound is significantly
impaired.
[0004]
The present invention focuses on the above points, and an object thereof is to provide a thin
piezoelectric speaker having excellent sound reproducibility by forming a stable electrical
connection state.
[0005]
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In order to achieve the above object, the present invention is a piezoelectric speaker including a
piezoelectric element having an electrode layer on at least one main surface of a piezoelectric
body, and a diaphragm attached to the other main surface of the piezoelectric element. A
conductive path made of a strip-shaped metal foil conductively fixed on the electrode layers to
electrically connect the electrode layers of the piezoelectric elements or any one electrode layer
of the piezoelectric elements and an external circuit; A first conductive connection portion
formed of a conductive adhesive layer provided on the back surface of the conductive path, a
conductive layer provided from the surface of the electrode layer to the upper surface of the
conductive path by application of a conductive paste And a second conductive connection
portion to be formed, and the second conductive connection portion is formed to be connected to
the electrode layer at a plurality of locations along the edge of the conductive path. Do.
Preferably, the second conductive connections are formed on both sides of the conductive path
or across the conductive path. One of the main modes is characterized in that the conductive
layer constituting the second conductive connection portion has a Young's modulus of 100 MPa
or less and a volume resistivity of 6 × 10 <-3> Ωcm or less.
[0006]
In another embodiment, the contact area between the surface of the electrode layer and the
conductive layer, and the contact area between the conductive path and the conductive layer are
each 0.8 mm <2> or more, and the thickness of the conductive layer is 0.2. It is characterized in
that it is 01 mm or more. Yet another mode is characterized in that a contact area between the
surface of the electrode layer and the conductive layer is preferably 20 mm or less. The
diaphragm is characterized in that it has a diameter of 10 mm to 50 mm.
[0007]
In still another mode, (1) the piezoelectric element is adhered to at least one main surface of the
diaphragm, (2) the piezoelectric element is formed by alternately laminating a plurality of
piezoelectric layers and electrode layers. It is characterized in that it has a laminated structure,
and (3) the piezoelectric element includes at least three or more piezoelectric layers. The above
and other objects, features and advantages of the present invention will be apparent from the
following detailed description and the accompanying drawings.
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[0008]
In the present invention, a conductive path of a strip-shaped metal foil provided with a first
conductive connection portion made of a conductive adhesive material layer on the back surface
is provided on the electrode layer on the surface of the piezoelectric element provided on the
main surface of the diaphragm. And connecting between the electrode layers or between the
electrode layer and the external circuit, using a conductive paste having low rigidity and high
volume resistivity, to extend from the surface of the electrode layer to the upper surface of the
conductive path, Second conductive connections are formed at a plurality of locations along the
edge so as to be connected to the electrode layer. For this reason, a stable electrical connection
state can be obtained, and a thin piezoelectric speaker with good sound reproducibility can be
obtained.
[0009]
Hereinafter, the best mode for carrying out the present invention will be described in detail
based on examples. FIG. 1 is a view showing the basic structure of the piezoelectric speaker of
the present invention, FIG. 1 (A) is a plan view of Embodiment 1, FIG. 1 (B) is a perspective view
thereof, and FIG. 1 (C) is a conductive path. FIG. 1D is a plan view of the second embodiment, and
FIG. 1E is a plan view of the third embodiment.
[0010]
As shown in FIG. 1, in the piezoelectric speaker 10 of the present invention, a piezoelectric
element 14 provided with an electrode layer 16 on at least one main surface of a laminate of
piezoelectric bodies is attached to a diaphragm 12 made of metal. is there. The piezoelectric
speaker 10 may be a unimorph type in which the piezoelectric element 14 is provided on one of
the main surfaces of the diaphragm 12 or a bimorph type in which the piezoelectric element 14
is provided on both surfaces of the diaphragm 12. In order to make the total thickness of the
piezoelectric speaker 10 1 mm or less, for example, the thickness of the diaphragm 12 is 0.1 mm
or less. Further, in order to obtain a sufficient driving force, the piezoelectric element 14 has a
laminated structure in which at least three or more piezoelectric layers are alternately laminated
with electrode layers, and the total thickness does not exceed 0.1 mm.
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[0011]
The material of the electrode layer 16 between the layers of the piezoelectric element 14 and the
front and back surfaces is, for example, an alloy or silver having a ratio (molar ratio) of silver /
palladium = 9/1 to 10/0, which can be co-fired with the piezoelectric body. It is used. The
electrode layer 16 is formed by applying an alloy (or silver) and a piezoelectric powder to a
suitable solvent together with a binder to form a paste, and forming the green sheet of the
piezoelectric by screen printing, for example. A strip-shaped metal foil having a thickness of 0.1
mm or less, on which the first conductive connection portion 22 is provided, is attached to the
electrode layer 16 on the surface of the piezoelectric element 14 as described above. The metal
foils form conductive paths 20 for connecting the electrode layers 16 to each other, and the
electrode layers 16 and an external circuit. The first conductive connection portion 22 is formed
of a conductive adhesive layer. For this reason, in order to prevent a short circuit with the
diaphragm 12, it is necessary to appropriately take measures for insulation, such as sticking the
insulating tape 23 on the portion where the adhesive material layer and the diaphragm 12
contact (see FIG. 1C). is there.
[0012]
Then, a conductive paste having a low rigidity and a high volume resistivity is applied from above
the conductive path 20 so as to extend over the conductive path 20 and the surface of the
electrode layer 16, and a second conductive connection made of a conductive layer Form The
application shape of the conductive paste may be formed so as to be connected to the electrode
layer 16 at a plurality of locations along the edge of the conductive path 20, but preferably it is
formed on both sides of the conductive path 20, Alternatively, it is formed to cross the
conductive path 20. For example, as in the piezoelectric speaker 10 shown in FIG. 1 (A), it is
convenient to form two circular conductive connections 24 or to make it rectangular as the
conductive connections 26 shown in FIG. 1 (D). As in the piezoelectric speaker 10 shown in FIG.
1 (E), when the position of the conductive path 20 is close to the edge of the piezoelectric
element 14, as in the example of FIG. 1 (A) or (D), It can not be applied on both sides, but in this
case, it can be coped with by applying a circular conductive connection portion 28 at two places
on one side of the conductive path 20 and the tip.
[0013]
A conductive paste having low rigidity and high volume resistivity is used as the second
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conductive connection portions 24, 26 and 28. Specifically, it is preferable to meet the physical
properties of Young's modulus of 100 MPa or less and volume resistivity of 6 × 10 <-3> Ωcm or
less. If the Young's modulus is more than this, it can not withstand the stress when the
diaphragm 12 is deformed and breaks. For example, Table 1 below is an example showing the
relationship between the Young's modulus of the conductive paste used as the conductive layer
forming the second conductive connection portion and the presence or absence of breakage due
to driving of the piezoelectric speaker 10. The used paste A uses a polyester-based resin, the
used paste B uses a silicone-based resin, the used paste C uses an epoxy-based resin, and the
used paste D utilizes a polyimide-based resin. Both of the used pastes contain silver as a
conductive filler. As can be seen from Table 1, although the used pastes B to D satisfy the
condition that the volume resistivity is 6 × 10 <−3> Ωcm or less, they are broken by driving
because the rigidity is too high.
[0014]
Further, Table 2 below shows the change in sound pressure when the second conductive
connection portion 26 having the shape shown in FIG. 1D is formed by the conductive paste and
the Young's modulus of the conductive paste is changed. . As can be seen from the results in
Table 2, it is found that the upper limit of the Young's modulus of the conductive paste is 100
MPa in order to suppress the sound pressure deterioration to, for example, 0.1 dB or less.
Therefore, it is understood that it is preferable to set the Young's modulus of the conductive
paste to 100 MPa or less in order to prevent breakage due to driving and to minimize
deterioration in sound quality.
[0015]
Further, if the volume resistivity is 6 × 10 <-3> Ωcm or more, the contact resistance can not be
sufficiently reduced. The application shape of the conductive paste may be formed on either side
of the conductive path 20 as described above, or may be any shape such as circular or
rectangular as long as it crosses the conductive path 20. The portion overlapping with the
conductive path 20 and the portion overlapping with the electrode layer 16 are both 0.8 mm <2>
or more. If the area is smaller than this, the resistance value of the conductive paste portion (the
second conductive connection portions 24, 26, 28) is not sufficiently low, and a stable contact
state can not be obtained. Moreover, the sound pressure deterioration at the time of changing the
application area of the electrically conductive paste (electrically conductive connection part
24,26,28) on the electrode layer 16 is shown in the following Table 3 using the electrically
conductive paste of Young's modulus 60MPa. There is. As shown in Table 3, since the sound
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pressure deterioration exceeds 0.1 dB when the area is larger than 20 mm <2>, the coated area
on the electrode layer 16 is preferably 20 mm <2> or less. The influence of the application area
of the conductive paste on the sound quality is remarkable in the case of a relatively small
piezoelectric speaker having a diameter of about 10 to 50 mm of the diaphragm 12. This is
because, in the case of a relatively small piezoelectric speaker, the rigidity of the diaphragm 12 is
high, and therefore, the influence of the conductive paste is less likely to occur. As a method of
applying the conductive paste, for example, various known methods such as a printing method
and a spray method can be used. Also, the thickness of the second conductive connection portion
24 (to 26 and 28) is, for example, 0.01 mm (10 μm) or more. If the thickness is smaller than
this, the resistance value becomes too high to form a stable contact state. By curing the
conductive paste by a predetermined method such as ultraviolet irradiation or heating after the
application, the piezoelectric speaker 10 in which the contact state is stable can be obtained.
[0016]
Next, examples of the present invention and comparative examples will be described. FIG. 2
shows main cross sections of the piezoelectric speakers of the example and the comparative
example. First, the first embodiment will be described. The piezoelectric speaker 30 of the first
embodiment is a bimorph type in which the piezoelectric elements 34 and 40 having a laminated
structure are bonded to both the front and back sides of the diaphragm 32. In the electrode
layers 38A and 44A on the surface of 40, conductive paths 46A and 46B made of strip metal foil
are provided. As the vibrating plate 32, for example, an iron-nickel alloy having a diameter of 23
mm and a thickness of 0.03 mm is used. The piezoelectric element 34 is a laminate in which
three piezoelectric layers 36A to 36C and four electrode layers 38A to 38D are alternately
stacked, and the piezoelectric layers 36A to 36C have a diameter of 19 mm and a thickness, for
example. 0.018 mm (18 μm) lead zirconate titanate is used, and as the electrode layers 36A to
36C, for example, a silver-palladium alloy having a diameter of 18.5 mm and a thickness of
0.001 mm is used. The electrode layers 38A to 38D are connected to each other by through
holes or the like. The other piezoelectric element 40 also has the same configuration as the
piezoelectric element 34, and has a laminated structure in which three piezoelectric layers 42A
to 42C and four electrode layers 44A to 44D are alternately laminated.
[0017]
The conductive paths 46A and 46B are copper foils provided with first conductive connecting
portions 48A and 48B formed of a conductive adhesive material layer on the back surface, and
for example, a thickness of 0.07 mm, a length of 10 mm, and a width One with a size of 2 mm is
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used. Furthermore, insulating tapes 50A and 50B are attached to the insides of the conductive
paths 46A and 46B in order to prevent a short circuit in a portion where metal is exposed at the
peripheral portion of the diaphragm 32. . Then, from above such conductive paths 46A and 46B,
a polyester-based conductive paste using silver as a conductive filler (product name: DW-250H-5,
manufactured by Toyobo Co., Ltd., Young's modulus: 60 MPa, volume resistance: 1 × 10) <-3> Ω
cm) is applied to form second conductive connections 52A and 52B. The application shape is, as
shown in FIG. 1A, made two rounds of 1.0 mm in diameter by spray method, and the areas on the
conductive paths 46A (46B) and the electrode layers 38A (44A) are respectively 0. 9 mm <2>,
and the thickness was 0.015 mm. The obtained piezoelectric speaker 30 was installed in a jig for
fixing the periphery, and a sine wave having a voltage of 3 Vrms and a frequency of 1 kHz was
applied to the terminal. Then, the generated sound was collected by a microphone, and the signal
amplified by the preamplifier was confirmed by an oscilloscope to observe the presence or
absence of waveform distortion. The results are shown in Table 4 below. In Table 4, those with
waveform distortion were judged as unstable contact states, and those without distortion were
judged as stable contact states.
[0018]
A conductive paste under the same conditions as in Example 1 is applied from the top of the
conductive paths 46A and 46B by the printing method, and as shown in FIG. The conductive
connection portions 52A and 52B are formed. The areas on the conductive path 46A (46B) and
the electrode layer 38A (44A) were controlled to be 3.2 mm <2>, and the thickness was
controlled to be 0.03 mm. The presence or absence of distortion of the waveform of the
produced piezoelectric speaker was observed under the same conditions as in Example 1 above.
[0019]
Comparative Example 1 In the same manner as in Example 1 described above, a piezoelectric
speaker not using a conductive paste, ie, a piezoelectric speaker in which the second conductive
connection portions 52A and 52B were not formed, was manufactured, and the waveform
distortion was We observed the presence or absence.
[0020]
Comparative Example 2 For comparison with Example 2, the Young's modulus of the second
conductive connection portions 52A and 52B was 1000 MPa, the volume resistivity was 2 × 10
<-3> Ω cm, and the thickness was 0.02 mm. A piezoelectric speaker was produced, and the
presence or absence of waveform distortion was observed by the method described above.
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[0021]
Comparative Example 3 For comparison with Example 1, a piezoelectric speaker having a second
conductive connecting portion 52A, 52B having a Young's modulus of 40 MPa and a volume
resistivity of 1 × 10 <−1> Ω cm is manufactured. The presence or absence of waveform
distortion was observed by the method mentioned above.
[0022]
Comparative Example 4 For comparison with Example 2, a piezoelectric speaker in which the
thickness of the second conductive connection portions 52A and 52B was 0.005 mm was
created, and the presence or absence of waveform distortion was observed by the method
described above. The
[0023]
Table 4 shows the physical properties, the application shape, the application area, and the
thickness of the second conductive connection portions 52A and 52B, and the presence or
absence of the waveform distortion of the produced piezoelectric speaker in the examples 1 and
2 and the comparative examples 1 to 4. It is shown.
[0024]
As seen from the results, the conditions specified in the present invention, that is, the second
conductive connections 52A and 52 are provided, the Young's modulus of the conductive
connections 52A and 52A is 100 MPa or less, and the volume resistance is 6 × 10 <-3. > Ω cm
or less, the contact area between the electrode layer 38A (44A) and the conductive connection
52A (52B), and the contact area between the conductive path 46A (46B) and the conductive
connection 52A (52B) are each 0.8 mm <2 As described above, in Examples 1 and 2 in which the
thickness of the conductive connection portions 52A and 52B satisfies 0.01 mm (10 μm) or
more, the result that no waveform distortion is observed regardless of the application shape is
obtained. .
That is, it was confirmed that it was a stable contact state.
[0025]
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On the other hand, in Comparative Example 1 in which the conductive paste was not used, in
addition to the generation of waveform distortion, no sound was generated.
In addition, in Comparative Examples 2 to 4 manufactured by changing the physical property
and thickness of the conductive paste and produced out of the range of the above-mentioned
conditions, it is understood that waveform distortion is all generated and good sound
reproducibility can not be obtained. .
In particular, in the case of Comparative Example 2 in which a conductive paste having a high
Young's modulus was used, the conductive paste was broken by vibration, and no sound was
generated.
[0026]
Thus, in a piezoelectric speaker comprising a piezoelectric element having an electrode layer on
at least one main surface and a diaphragm, a conductive path of a strip-like metal foil having a
first conductive connection portion comprising a conductive adhesive material layer on the back
surface Connects between the electrode layers or between the electrode layer and the external
circuit, and utilizes the conductive paste having low rigidity and high volume resistivity to extend
from the surface of the electrode layer to the upper surface of the conductive path, The second
conductive connection portion is formed to be connected to the electrode layer at a plurality of
locations along the edge portion of the
As a result, a conductive path having a low resistance value is formed, so even if piezoelectric
fine particles as a barrier are deposited on the surface of the electrode layer by the simultaneous
sintering method using a low cost electrode material, vibration is caused by vibration. A stable
electrical connection state can be formed without fluctuation in the contact resistance value, and
a thin piezoelectric speaker with low cost and good sound reproducibility can be obtained.
[0027]
The present invention is not limited to the embodiments described above, and various
modifications can be made without departing from the scope of the present invention.
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For example, the following are also included. (1)The materials, shapes, and dimensions shown in
the above-described embodiments are merely examples, and can be appropriately changed to
exhibit the same function. For example, the application shape of the second conductive
connection portions 24, 26, 28, 52A, 52B is an example, and may be formed on both sides of the
conductive path or may be formed to cross the conductive path. For example, the application
shape may be appropriately changed within the range of the conditions (area, thickness)
described above. Also, for example, when the piezoelectric speaker is a bimorph type, the second
conductive connection portion formed on the electrode layer of one piezoelectric element and the
second conductive connection portion formed on the electrode layer of the other piezoelectric
element The shape of may be made different.
[0028]
(2)
The number of laminations of the piezoelectric layer and the electrode layer may be changed as
necessary. In the above embodiment, three piezoelectric layers are stacked in order to obtain a
sufficient driving force, but if the total thickness of the stacked body does not exceed 0.1 mm, it
is difficult to stack more layers. It is not a thing. In addition, the connection structure of the
internal electrode layer can be appropriately changed as needed.
[0029]
(3)
Preferred applications of the present invention include speakers of various electronic devices
such as mobile phones (including PHS), personal digital assistants (PDAs), voice recorders, and
PCs (personal computers). Of course, it does not prevent applying to other various applications.
[0030]
According to the present invention, the conductive path of the strip-like metal foil provided with
the first conductive connection portion made of the conductive adhesive layer on the back
surface on the electrode layer on the surface of the piezoelectric element provided on the main
surface of the diaphragm The conductive layer is provided to connect the electrode layers to
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each other or to an external circuit, and the conductive paste having low rigidity and high volume
resistivity is used to extend the surface of the electrode layer to the upper surface of the
conductive path. A second conductive connection is formed to be connected to the electrode
layer at a plurality of locations along the edge of the path. For this reason, a stable electrical
connection state can be obtained, which can be applied to the use of a thin piezoelectric speaker.
In particular, it is suitable for the application of the ultra thin piezoelectric speaker whose
thickness is 1 mm or less.
[0031]
BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows the basic structure of the
piezoelectric speaker of this invention, (A) is a top view of Embodiment 1, (B) is a perspective
view of Embodiment 1, (C) shows the back of the conductive path of Embodiment 1. (D) is a plan
view of Embodiment 2, (E) is a plan view of Embodiment 3. FIG. FIG. 1 is a main cross-sectional
view of a piezoelectric speaker according to an embodiment of the present invention.
Explanation of sign
[0032]
10: Piezoelectric speaker 12: Diaphragm 14: Piezoelectric element 16: Electrode layer 20:
Conductive path 22: First conductive connection portion 23: Insulating tape 24, 26, 28: second
conductive connection portion 30: Piezoelectric speaker 32 : Vibrating plate 34, 40: Piezoelectric
element 36A to 36C, 42A to 42C: Piezoelectric layer 38A to 38D, 44A to 44D: electrode layer
46A, 46B: conductive path 48A, 48B: first conductive connecting portion 50A, 50B: insulation
Tape 52A, 52B: second conductive connection
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