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DESCRIPTION JP2003125491

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DESCRIPTION JP2003125491
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric acoustic device used for an electronic acoustic device, a communication device, etc.,
and more particularly to a structure of an extraction electrode.
[0002]
2. Description of the Related Art This type of piezoelectric acoustic device is called a piezoelectric
speaker or a piezoelectric buzzer depending on its application, and has been widely used in the
field of portable telephones, portable information terminals, electronic computers, etc. in recent
years. A conventional piezoelectric speaker will be described with reference to FIG. FIG. 8 is a
side view of a conventional piezoelectric speaker.
[0003]
The piezoelectric speaker 100 includes a disk-shaped piezoelectric element 110, 120, a
diaphragm 130 bonded to one surface of the piezoelectric element 110, 120, and an annular
case (not shown) for fixing the peripheral portion of the diaphragm 130. And).
[0004]
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The piezoelectric elements 110 and 120 have a structure in which a piezoelectric body and an
internal electrode are stacked.
Electrode films (not shown) are formed on both sides of the piezoelectric elements 110 and 120.
The electrode film is connected to the internal electrode through a through hole (not shown).
[0005]
Piezoelectric ceramics (lead zirconate titanate (abbreviated as PZT), ceramics mainly composed of
barium titanate, lead zirconate, lead titanate, etc.) are used as the material of the piezoelectric
layer of the piezoelectric elements 110 and 120. Be
[0006]
The diaphragm 130 is formed of a disk-shaped metal plate having a diameter slightly larger than
that of the piezoelectric elements 110 and 120.
As a material of the diaphragm 130, for example, an Fe-Ni-based stainless steel material is used.
The vibrating plate 130 is conductively connected to the electrode films of the piezoelectric
elements 110 and 120.
[0007]
Lead wires 150 and 151 are connected to the piezoelectric speaker 100 by soldering. The lead
wire 150 is soldered to the electrode film of one of the piezoelectric elements 110. Also, the lead
wire 151 is soldered to the diaphragm 130. Further, the electrode film of one piezoelectric
element 110 and the electrode film of the other piezoelectric element 120 are electrically
connected by the wiring 152.
[0008]
In such a piezoelectric speaker 100, when a drive signal is applied between the lead wires 150
and 151, the piezoelectric elements 110 and 120 expand and contract in the radial direction.
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However, since the piezoelectric elements 110 and 120 are fixed to the diaphragm 130 and the
peripheral portion of the diaphragm 130 is fixed to the case, the piezoelectric elements 110 and
120 and the diaphragm 130 vibrate vertically. Thereby, the piezoelectric speaker 100 generates
sound according to the drive signal.
[0009]
By the way, with regard to such a piezoelectric acoustic device, there is an increasing demand for
thinning along with the miniaturization of the equipment to be used. Then, in order to satisfy this
demand, thinning of the piezoelectric elements 110 and 120 and the diaphragm 130 is
progressing by upgrading the layering technology and optimizing the piezoelectric material.
Specifically, a piezoelectric speaker 100 in which the thickness of each of the piezoelectric
elements 110 and 120 is 60 μm and the thickness of the diaphragm 130 is 30 μm has been
developed.
[0010]
However, in the piezoelectric speaker 100 having a conventional structure, as the piezoelectric
elements 110 and 120 and the diaphragm 130 become thinner, the thickness of the solder fillet
160 of the lead wires 150 and 151 and the wiring 152 can not be ignored. The Specifically, the
thickness of the solder fillet 160 is usually about 300 μm to 500 μm. Therefore, there is a limit
to thinning of the piezoelectric speaker 100 having the conventional structure.
[0011]
The present invention has been made in view of the above-mentioned circumstances, and an
object of the present invention is to provide a piezoelectric acoustic device capable of easily
realizing thinning.
[0012]
[Means for Solving the Problems] In order to achieve the above object, according to claim 1, a
piezoelectric element having electrode films formed on both sides, and a diaphragm joined to one
electrode film of the piezoelectric element are provided. In the piezoelectric acoustic device, striplike lead electrodes radially extending in a plurality of outer peripheral directions of the
piezoelectric element from a position where the expansion and contraction displacement of the
piezoelectric element is minimized are made into an electrode film of the piezoelectric element by
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an adhesive having adhesiveness and conductivity. We propose something that is characterized
by being glued.
[0013]
According to the present invention, since the strip-like lead-out electrode is adhered to the
electrode film of the piezoelectric element by the adhesive having adhesiveness and conductivity,
the connection portion between the lead-out electrode and the piezoelectric element can be
formed thin.
Further, since the extraction electrode radially extends from the position where the expansion
and contraction displacement of the piezoelectric element is minimized in the plurality of outer
peripheral directions of the piezoelectric element, even if the piezoelectric element is expanded
and contracted, the connection with the piezoelectric element with the extraction electrode is
assured It becomes a thing.
This is because, even if the piezoelectric element expands and contracts in the radial direction,
the stress applied to the radially extending extraction electrode is canceled at the central
position.
[0014]
According to a second aspect of the present invention, in the piezoelectric acoustic device
according to the first aspect, piezoelectric elements are provided on both sides of the diaphragm,
and lead electrodes bonded to the respective piezoelectric elements are conductively connected
to each other. Do.
[0015]
According to the present invention, since the lead-out electrodes bonded to the respective
piezoelectric elements are conductively connected to each other, it is not necessary to separately
provide a wire for connecting the piezoelectric elements.
Therefore, the piezoelectric acoustic device can be manufactured inexpensively.
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[0016]
BEST MODE FOR CARRYING OUT THE INVENTION A piezoelectric acoustic device according to
an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG.
FIG. 1 is an exploded perspective view of the piezoelectric acoustic device, and FIG. 2 is a
schematic cross-sectional view of a piezoelectric sounding body for explaining the attachment
structure of the lead-out electrode.
[0017]
As shown in FIGS. 1 and 2, the piezoelectric acoustic device 1 has a structure in which the
piezoelectric sounding body 10 is housed in a case 50. The piezoelectric speaker 10 includes a
disk-shaped diaphragm 20 and piezoelectric elements 30 and 40 attached to both sides of the
diaphragm 20.
[0018]
The diaphragm 20 is formed of a disk-shaped metal plate having a diameter slightly larger than
that of the piezoelectric elements 30 and 40. As a material of the diaphragm 20, for example, a
material such as Fe-Ni-based stainless steel, aluminum, copper or the like is used. Terminal
portions 21, 22, 23, 24 protruding outward are formed at equal intervals at the peripheral edge
portion of the diaphragm 20.
[0019]
The piezoelectric elements 30 and 40 are formed in a disc shape slightly smaller than the
diaphragm 20. The piezoelectric elements 30 and 40 have a structure in which a piezoelectric
body and an internal electrode are laminated. Electrode films 31 and 41 are formed on both sides
of the piezoelectric elements 30 and 40, respectively. The electrode films 31 and 41 are formed,
for example, by applying and baking a conductive paste containing a noble metal such as Ag, Pd,
Au or an alloy thereof, a base metal such as Cu, Ni or an alloy thereof. It is formed. Although
Ag̶Pd is used in the present embodiment, Ag is also preferable from the viewpoint of cost
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reduction.
[0020]
By the way, in order to reduce the thickness of the entire device, it is preferable that the film
thickness of the electrode films 31 and 41 be thin. In the present embodiment, as a result of
making the coating thickness of the conductive paste as thin as possible in order to meet this
demand, the film thickness of the electrode films 31 and 41 after firing becomes uneven due to
the aggregation of metal particles. Specifically, the electrode films 31 and 41 are formed on the
surfaces of the piezoelectric elements 30 and 40 in a net shape or a lattice shape. The electrode
films 31 and 41 are connected to the internal electrodes through through holes (not shown).
[0021]
Piezoelectric ceramics (ceramics containing lead zirconate titanate (abbreviated as PZT), barium
titanate, lead zirconate, lead titanate, etc. as a main component) are used as the material of the
piezoelectric body of the piezoelectric elements 30 and 40 .
[0022]
One side of the piezoelectric element 30 is bonded to one side of the diaphragm 20.
On the other hand, one side of the piezoelectric element 40 is joined to the other side of the
diaphragm 20. Here, the electrode films 31 and 41 of the piezoelectric elements 30 and 40 are
joined so as to be conductively connected to the diaphragm 20. In the present embodiment, an
acrylic adhesive is used to bond the piezoelectric elements 30 and 40 and the diaphragm 20.
Although this acrylic adhesive is an insulator as is well known, since the electrode films 31 and
41 have irregularities on the surface, the adhesive is filled in the concave portion, and the convex
portion vibrates while securing the bonding strength. It is in contact with the plate 20 to ensure
conduction. In order to obtain such a bonding state, a predetermined pressure may be applied to
the bonding surfaces of the piezoelectric elements 30 and 40 and the diaphragm 20 at the time
of bonding.
[0023]
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Extraction electrodes 32 and 42 are attached to the electrode films 31 and 41 of the
piezoelectric elements 30 and 40, respectively. The lead-out electrodes 32 and 42 are formed of
band-like members radially extending in the outer peripheral direction from the position where
the expansion and contraction displacement of the piezoelectric elements 30 and 40 is
minimized. In the present embodiment, since the piezoelectric elements 30 and 40 have a disk
shape, the lead-out electrodes 32 and 42 radially extend from the central position of the element.
The lead-out electrode pieces 32a, 32b, 32c, 32d, 42a, 42b, 42c, 42d extending radially from the
piezoelectric elements 30, 40 are arranged at equal intervals. In the present embodiment, the
lead-out electrodes 32 and 42 extend from the piezoelectric elements 30 and 40 at equal
intervals in four directions. The lead-out electrodes 32 and 42 are disposed so as to overlap with
each other via the piezoelectric element 30, the diaphragm 20, and the piezoelectric element 40,
respectively.
[0024]
The ends of the extraction electrodes 32 and 42 are connected to each other on the outside of
the diaphragm 20 via the conductive terminal plates 25, 26, 27 and 28. Thereby, one electrode
film 31 of the piezoelectric element 30 and one electrode film 41 of the piezoelectric element 40
are electrically connected. The terminal plates 25 to 28 are formed of the same material as the
diaphragm 20. An insulator 29 is provided on the diaphragm 20 at a position overlapping the
lead electrodes 32 and 42. The insulator 29 prevents conduction between the lead-out electrodes
32 and 42 and the diaphragm 20.
[0025]
Examples of the material of the lead-out electrodes 32 and 42 include metals such as Cu and Al.
The extraction electrodes 32 and 42 and the electrode films 31 and 41 are joined by an adhesive
(conductive adhesive) having conductivity and flexibility. In the present embodiment, it is formed
using a kappa tape (manufactured by DIC Corporation: model number E-1100CD) on one side of
which a conductive adhesive is previously applied. The conductive pressure-sensitive adhesive
obtains conductivity by containing metal particles such as Cu, Ni, Ag, etc. in the pressuresensitive adhesive.
[0026]
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The lead-out electrodes 32, 42 are covered with insulating covering members 33, 43 attached
from both sides. The covering members 33 and 43 cover at least the joint between the lead
electrodes 32 and 42 and the piezoelectric elements 30 and 40. The covering members 33 and
43 protect the lead-out electrodes 32 and 42 and ensure conductive connection between the
lead-out electrodes 32 and 42 and the piezoelectric elements 30 and 40. Examples of the
material of the covering members 33 and 43 include polyvinyl chloride, polyvinylidene chloride,
polyethylene, polypropylene, polyethylene terephthalate, polybutyl terephthalate, and polyimide.
In the present embodiment, transparent polyethylene terephthalate is used as the covering
members 33 and 43.
[0027]
The case 50 is formed of an annular member whose cross section in the radial direction is
substantially L-shaped. The circumferential portion of the diaphragm 20 is supported by an
adhesive on the step portion formed inside the case 50. Further, in the case 50, notches 51, 52,
53, 54 for forming the terminal portion 21 of the diaphragm 20 and the terminal plate 25 out of
the case 50 are formed.
[0028]
According to such a piezoelectric acoustic device 1, since the strip-like lead electrodes 32 and 42
are bonded to the electrode films 31 and 41 of the piezoelectric elements 30 and 40 with a
conductive adhesive, the lead wire is soldered as in the prior art. As compared with the method of
attaching, the thickness of the lead-out portion of the piezoelectric elements 30 and 40 can be
formed thin. As a result, it is possible to make the entire piezoelectric acoustic device thinner. As
a specific example, the diaphragm 20 has a thickness of 30 μm, the piezoelectric elements 30
and 40 each has a thickness of 60 μm, the lead electrodes 32 and 42 each has a thickness of 50
μm, and the covering members 33 and 34 each has a thickness of 20 μm. By using the
piezoelectric sounding body 10, the thickness of the piezoelectric sounding body 10 can be about
300 μm.
[0029]
Further, in the piezoelectric acoustic device 1, since the lead-out electrodes 32 and 42 radially
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extend at equal intervals from the center of the piezoelectric elements 30 and 40, even if the
piezoelectric elements 30 and 40 expand and contract, At the central position, concentration of
stress due to expansion and contraction can be reduced. This is because the piezoelectric
elements 30 and 40 expand and contract in the radial direction, but the stresses applied to the
pieces 32 a to 32 d and 42 a to 42 d of the lead electrodes 32 and 42 cancel each other at the
central position. Thus, the bonding between the piezoelectric elements 30 and 40 and the lead
electrodes 30 and 40 can be reliably maintained. Further, since the end portions of the lead-out
electrodes 32 and 42 are arranged in a plurality of directions, the degree of freedom in the
directionality of the piezoelectric acoustic device 1 is high during mounting. This facilitates the
mounting of the piezoelectric acoustic device 1.
[0030]
The state of the amplitude of the diaphragm will be described with reference to FIG. FIG. 3 is a
view for explaining the state of the amplitude of the diaphragm in which the formation position
of the lead-out electrode is taken as a cutting line. In the piezoelectric acoustic device 1,
expansion and contraction of the piezoelectric elements 30 and 40 are restricted by the
extraction electrodes 32 and 42. Therefore, as shown in FIG. 3, the amplitude of the diaphragm
of the piezoelectric acoustic device 1 according to this embodiment (see the solid line in FIG. 3) is
the amplitude of the diaphragm in the conventional piezoelectric acoustic device (see the dotted
line in FIG. 3). The amplitude is smaller compared to. However, in the present embodiment, the
lead-out electrode pieces 32 a to 32 d and 42 a to 42 d are radially arranged at equal intervals
from the central portion of the piezoelectric elements 30 and 40. Therefore, as shown in FIG. 3,
the amount of amplitude becomes symmetrical in the lateral direction of FIG. Generally,
distortion occurs in the sound when this amplitude is left-right asymmetry as indicated by the
dashed line in FIG. However, in the present embodiment, as shown by the solid line in FIG. 3, the
left and right symmetry is achieved, so that it is possible to reproduce a clear sound with less
non-linear distortion.
[0031]
Although the embodiments of the present invention have been described above, the present
invention is not limited thereto. The scope of the present invention is indicated by the claims, and
all the modifications are included in the present invention.
[0032]
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For example, in the present embodiment, the lead-out electrode pieces 32a to 32d and 42a to
42d extend in four directions from the center position of the piezoelectric elements 30 and 40,
and the lead-out electrode pieces 32a to 32d and 42a to 42d are equally spaced from one
another. The lead-out electrodes 32 and 42 are formed in such a manner that they may be three
or five directions as long as they are two or more. In this case, the lead-out electrode pieces are
preferably arranged so as to be point-symmetrical with respect to the center of the piezoelectric
element, or line-symmetrically based on a line passing through one lead-out electrode piece. It is.
4 and 5 show a modification of the present invention. In this case, if the number of the lead-out
electrode pieces is even, it is preferable from the viewpoint of acoustic characteristics.
[0033]
Further, in the present embodiment, the covering members 33 and 43 are formed so as to cover
the whole of the lead electrodes 32 and 42. However, for example, as shown in FIG. May be
[0034]
Furthermore, in the above embodiment, the piezoelectric acoustic device in which the
piezoelectric sounding body is housed in the case has been described, but in the present
invention, the presence or absence of the case does not matter.
Therefore, a piezoelectric acoustic device as shown in FIG. 7 may be used. The piezoelectric
acoustic device will be described below.
[0035]
As shown in FIG. 7, the piezoelectric acoustic device 70 includes the piezoelectric sounding body
10 described in the above embodiment, a pair of flexible sheets 71 covering the piezoelectric
sounding body 10 from both sides, and a flexible sheet 71. And a pair of support frames 72
which are held by In the piezoelectric sounding body 10, the terminal portion 21 and the
terminal plate 25 of one diaphragm 20 are extended to the outside of the support frame 72. In
such a piezoelectric acoustic device 70, since the flexible sheet 71 vibrates together with the
diaphragm 20, it functions as a speaker having excellent reproducibility in the low frequency
range.
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[0036]
Furthermore, in the above embodiment, the entire surfaces of the lead electrodes 32, 42 are
bonded to the electrode films 31, 41 of the piezoelectric elements 30, 40 with an adhesive
having conductivity and adhesiveness. You may make it adhere only in the part.
[0037]
As described above in detail, according to the present invention, the strip-like lead electrode is
adhered to the electrode film of the piezoelectric element by the adhesive having the adhesive
property and the conductive property. The connection part with can be formed thin.
Further, since the extraction electrode radially extends from the position where the expansion
and contraction displacement of the piezoelectric element is minimized in the plurality of outer
peripheral directions of the piezoelectric element, even if the piezoelectric element is expanded
and contracted, the connection with the piezoelectric element with the extraction electrode is
assured It becomes a thing. This is because, even if the piezoelectric element expands and
contracts in the radial direction, the stress applied to the radially extending extraction electrode
is canceled at the central position.
[0038]
Brief description of the drawings
[0039]
Fig. 1 An exploded perspective view of the piezoelectric acoustic device
[0040]
Fig. 2 A schematic sectional view of a piezoelectric sounding body for explaining the attachment
structure of the lead-out electrode
[0041]
3 is a diagram for explaining the state of the amplitude of the diaphragm with the formation
position of the lead-out electrode as a cutting line
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[0042]
Fig. 4 A plan view of a piezoelectric speaker according to another example
[0043]
Fig. 5 A plan view of a piezoelectric speaker according to another example
[0044]
6 is a plan view of a piezoelectric speaker according to another example.
[0045]
7 is a plan view of a piezoelectric acoustic device according to another example.
[0046]
Fig. 8 Side view of the conventional piezoelectric acoustic device
[0047]
Explanation of sign
[0048]
DESCRIPTION OF SYMBOLS 1, 70 ... Piezoelectric acoustic device, 10 ... Piezoelectric sounding
body, 20 ... Diaphragm, 21, 22, 23, 24 ... Terminal part, 25, 26, 27, 28 ... Terminal board, 29 ...
Insulator, 30, 40 ... Piezoelectric element 31, 41: Electrode film 32, 42: Extraction electrode, 33,
43: Coating member, 50: Case, 71: Flexible sheet, 72: Support frame
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