JP2003125491A - Piezoelectric acoustic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric acoustic device which can be made thin easily. SOLUTION: The piezoelectric acoustic device 1 comprises a piezoelectric element 30 having an electrode film 31 formed on the opposite sides, and a diaphragm 20 bonded to one electrode film of the piezoelectric element 30 wherein a plurality of stripe lead-out electrodes 32 of the piezoelectric element 30 extending radially in the outer circumferential direction from positions where expanding/contracting displacement of the piezoelectric element 30 is minimized are bonded to the electrode film 21 of the piezoelectric element 30 through an adhesive exhibiting viscosity and conductivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric acoustic device used in electronic acoustic equipment, communication equipment and the like, and more particularly to the 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 according to its application, and has been widely used in the fields of mobile phones, personal digital assistants, electronic calculators, 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.

The piezoelectric speaker 100 includes disk-shaped piezoelectric elements 110 and 120, a diaphragm 130 attached to one surface of the piezoelectric elements 110 and 120, and a diaphragm 130.
And an annular case (not shown) for fixing the peripheral portion of the.

The piezoelectric elements 110 and 120 have a structure in which a piezoelectric body and internal electrodes are laminated. Piezoelectric element 110, 1
Electrode films (not shown) are formed on both surfaces of 20.
The electrode film is connected to the internal electrode via a through hole (not shown).

As the material for the piezoelectric layer of the piezoelectric elements 110 and 120, piezoelectric ceramics (lead zirconate titanate (PZT for short), barium titanate, lead zirconate,
Ceramics containing lead titanate as a main component is used.

The vibrating plate 130 includes piezoelectric elements 110 and 120.
It consists of a disk-shaped metal plate with a slightly larger diameter. Diaphragm 1
As the material of 30, for example, a Fe—Ni-based stainless material is used. The vibrating plate 130 is used for the piezoelectric element 11
It is electrically connected to the electrode films of 0 and 120.

The piezoelectric speaker 100 has lead wires 1
50 and 151 are connected by soldering. The lead wire 150 is soldered to the electrode film of the one piezoelectric element 110. Further, the lead wire 151 is connected to the diaphragm 130.
Is soldered to. Further, one piezoelectric element 110
And the electrode film of the piezoelectric element 120 on the other side are the wiring 152
Are electrically connected.

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. However, since the piezoelectric elements 110 and 120 are fixed to the diaphragm 130 and the peripheral edge of the diaphragm 130 is fixed to the case, the piezoelectric elements 110 and 120 and the diaphragm 13 are fixed.
0 vibrates up and down. As a result, the piezoelectric speaker 100
Sounds in accordance with the drive signal.

[0009]

By the way, with regard to such a piezoelectric acoustic device, there is an increasing demand for a thinner device as the equipment used is made smaller. In order to meet this demand, the piezoelectric elements 110 and 120 and the diaphragm 130 are being made thinner by advancing the lamination technology and optimizing the piezoelectric material. Specifically, the piezoelectric elements 110, 1
A piezoelectric speaker 100 has been developed in which the thickness of 20 is 60 μm and the thickness of the diaphragm 130 is 30 μm.

However, in the piezoelectric speaker 100 having the conventional structure, the piezoelectric elements 110 and 120 and the diaphragm 130 are used.
As the thickness becomes thinner, the lead wires 150 and 151 and the wiring 1
The thickness of the solder fillet 160 of 52 cannot be ignored. Specifically, the thickness of the solder fillet 160 is usually about 300 μm to 500 μm. Therefore, the piezoelectric speaker 100 having the conventional structure has a limitation in thinning.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a piezoelectric acoustic device capable of easily realizing a thin structure.

[0012]

In order to achieve the above object, in claim 1, a piezoelectric element having electrode films formed on both surfaces thereof and a vibration plate bonded to one electrode film of the piezoelectric element are provided. In the piezoelectric acoustic device, the strip-shaped extraction electrodes radially extending in the outer peripheral direction of the piezoelectric element from the position where the expansion and contraction displacement of the piezoelectric element is minimal are formed on the electrode film of the piezoelectric element by an adhesive having adhesiveness and conductivity. We propose the one characterized by being bonded.

According to the present invention, the strip-shaped lead electrode is adhered to the electrode film of the piezoelectric element by the adhesive having adhesiveness and conductivity, so that the connecting portion between the lead electrode and the piezoelectric element can be formed thin. Further, the extraction electrode extends radially from the position where the expansion and contraction displacement of the piezoelectric element is minimal to the outer peripheral direction of the piezoelectric element, so that even if the expansion and contraction of the piezoelectric element, the connection between the extraction electrode and the piezoelectric element is reliable. It will be 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 center position.

According to a second aspect of the present invention, in the piezoelectric acoustic device according to the first aspect, the piezoelectric elements are provided on both surfaces of the diaphragm, and the extraction electrodes bonded to the respective piezoelectric elements are electrically connected to each other. Suggest things.

According to the present invention, since the lead-out electrodes adhered to the respective piezoelectric elements are electrically connected to each other, it is not necessary to separately provide wiring for connecting the piezoelectric elements. Therefore, the piezoelectric acoustic device can be manufactured at low cost.

[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.
FIG. 1 is an exploded perspective view of the piezoelectric acoustic device, and FIG. 2 is a schematic cross-sectional view of a piezoelectric speaker for explaining the attachment structure of the extraction electrode.

As shown in FIGS. 1 and 2, the piezoelectric acoustic device 1 has a structure in which the piezoelectric speaker 10 is housed in a case 50. The piezoelectric speaker 10 includes a disc-shaped diaphragm 20 and
Piezoelectric elements 30 and 40 attached to both sides of the diaphragm 20
It has and.

The vibration plate 20 is made of a disk-shaped metal plate having a diameter slightly larger than that of the piezoelectric elements 30 and 40. As the material of the diaphragm 20, for example, a material such as Fe—Ni-based stainless steel, aluminum, or copper is used. This diaphragm 20
At the peripheral edge of the
3, 24 are formed at equal intervals.

The piezoelectric elements 30 and 40 are formed in a disk shape slightly smaller than the diaphragm 20. This piezoelectric element 30,
40 has a structure in which a piezoelectric body and an internal electrode are laminated. Electrode films 31 and 41 are formed on both surfaces of the piezoelectric elements 30 and 40. The electrode films 31 and 41 are, for example, A
It is formed by applying and firing a conductive paste containing metal particles made of a noble metal such as g, Pd, Au or an alloy thereof, a base metal such as Cu or Ni, or an alloy thereof. In the present embodiment, Ag-Pd
However, Ag is also preferable from the viewpoint of cost reduction.

By the way, in order to reduce the thickness of the entire device, it is preferable that the electrode films 31 and 41 are 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 is non-uniform due to the aggregation of metal particles. Specifically, the electrode films 31 and 41 are the piezoelectric elements 30 and 4.
It is formed in a mesh shape or a grid shape on the surface of 0. Electrode film 3
1, 41 are connected to internal electrodes via through holes (not shown).

As a material for the piezoelectric body of the piezoelectric elements 30 and 40, piezoelectric ceramics (lead zirconate titanate (PZT for short), barium titanate, lead zirconate, lead titanate and the like as a main component) are used. Is used.

One surface of the piezoelectric element 30 is bonded to one surface of the vibration plate 20. On the other hand, one surface of the piezoelectric element 40 is joined to the other surface 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, the piezoelectric element 3
An acrylic adhesive was used to bond the 0 and 40 to the diaphragm 20. As is well known, this acrylic adhesive is an insulator, but since the electrode films 31 and 41 have unevenness on the surface, the adhesive filled in the recesses ensures the bonding strength while the projections vibrate. It abuts the plate 20 to ensure electrical continuity.
In order to obtain such a bonded state, a predetermined pressure may be applied to the bonding surface between the piezoelectric elements 30 and 40 and the vibration plate 20 at the time of bonding.

Extraction electrodes 32 and 42 are attached to the electrode films 31 and 41 of the piezoelectric elements 30 and 40, respectively. Extraction electrode 32,
Reference numeral 42 is a strip-shaped member radially extending in a plurality of outer circumferential directions from a position where the expansion and contraction displacement of the piezoelectric elements 30 and 40 is minimum. In the present embodiment, the piezoelectric elements 30 and 40 are disk-shaped, so the extraction electrodes 32 and 42 extend radially from the central position of the elements. Extraction electrode pieces 32a, 32b, 32c, 3 extending radially from the piezoelectric elements 30, 40.
2d, 42a, 42b, 42c, 42d are arranged at equal intervals. In the present embodiment, the extraction electrodes 32 and 42 extend from the piezoelectric elements 30 and 40 in four directions at equal intervals.
The extraction electrodes 32 and 42 are arranged so as to overlap each other via the piezoelectric element 30, the vibration plate 20, and the piezoelectric element 40, respectively.

The end portions of the extraction electrodes 32 and 42 are connected to the vibration plate 20.
Outside the terminal, the terminal plates 25, 26, 2 having conductivity.
They are connected to each other via 7, 28. As a result, the one electrode film 31 of the piezoelectric element 30 and the one electrode film 41 of the piezoelectric element 40 are electrically connected. The terminal plates 25 to 28 are made of the same material as the diaphragm 20. The diaphragm 20 is provided with an insulator 29 at a position overlapping the extraction electrodes 32 and 42. With this insulator 29, the extraction electrodes 32, 4
The electrical connection between the diaphragm 2 and the diaphragm 20 is prevented.

The material of the extraction electrodes 32 and 42 is
Examples include metals such as Cu and Al. Extraction electrode 3
The electrodes 2 and 42 and the electrode films 31 and 41 are joined by an adhesive agent having a conductivity and flexibility (a conductive adhesive agent). In the present embodiment, a copper tape having one surface coated with a conductive adhesive in advance (manufactured by DIC: model number E-
1100 CD). The conductive adhesive has conductivity by containing metal particles such as Cu, Ni and Ag in the adhesive.

The extraction electrodes 32, 42 are covered with insulating covering members 33, 43 attached from both sides. The covering members 33 and 43 are at least the extraction electrodes 3
The joints between the piezoelectric elements 30 and 40 are covered.
The covering members 33 and 43 protect the extraction electrodes 32 and 42, and ensure the conductive connection between the extraction 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 this embodiment, the covering member 3
As 3,43, transparent polyethylene terephthalate was used.

The case 50 is an annular member having a substantially L-shaped cross section in the radial direction. The circumferential portion of the diaphragm 20 is supported by an adhesive on the stepped portion formed inside the case 50. Further, the case 50 is formed with notches 51, 52, 53, 54 for drawing out the terminal portion 21 and the terminal plate 25 of the diaphragm 20 to the outside of the case 50.

According to the piezoelectric acoustic device 1 as described above, the strip-shaped lead-out electrodes 32 and 42 are made of the piezoelectric element 3 by the conductive adhesive.
Since it is adhered to the electrode films 31 and 41 of 0 and 40, the thickness of the lead-out portions of the piezoelectric elements 30 and 40 can be formed thin as compared with the conventional method of soldering lead wires. As a result, the piezoelectric acoustic device as a whole can be made thinner. As a specific example, the thickness of the diaphragm 20 is 30 μm.
m, the piezoelectric elements 30 and 40 each have a thickness of 60 μm, the extraction electrodes 32 and 42 each have a thickness of 50 μm, and the covering members 33 and 34 each have a thickness of 20 μm, so that the piezoelectric sounding body 10 has a thickness of about 300 μm. Can be

Further, in this piezoelectric acoustic device 1, since the extraction electrodes 32 and 42 extend radially from the centers of the piezoelectric elements 30 and 40 at equal intervals, the extraction electrode 32 is expanded and contracted even if the piezoelectric elements 30 and 40 expand and contract. , 42 can reduce the concentration of stress due to expansion and contraction at the center position. This is the piezoelectric element 30, 40.
Expands and contracts in the radial direction, but each piece 32 of the extraction electrodes 32, 42
This is because the stresses applied to a to 32d and 42a to 42d cancel each other out at the center position. As a result, the bonding between the piezoelectric elements 30 and 40 and the extraction electrodes 30 and 40 can be reliably maintained. In addition, the extraction electrode 3 is provided in a plurality of directions.
Since the 2, 42 end portions are arranged, the degree of freedom in the directionality of the piezoelectric acoustic device 1 becomes high during mounting. This facilitates the mounting of the piezoelectric acoustic device 1.

The amplitude of the diaphragm will be described with reference to FIG. FIG. 3 is a diagram for explaining the state of the amplitude of the diaphragm with the cutting electrode forming position as the cutting line. This piezoelectric acoustic device 1
Then, expansion / contraction of the piezoelectric elements 30 and 40 is 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 the present 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 than that of However, in the present embodiment, the extraction electrode pieces 32a to 3a.
2d and 42a to 42d are radially arranged at equal intervals from the central portions of the piezoelectric elements 30 and 40. Therefore, FIG.
As shown in FIG. 3, the amplitude amounts are symmetrical in the horizontal direction of FIG. In general, when the amplitude becomes asymmetrical as shown by the alternate long and short dash line in FIG. 3, the sound is distorted. However, in the present embodiment, the sound is symmetric as indicated by the solid line in FIG. 3, so that it is possible to reproduce clear sound with less nonlinear distortion.

Although the embodiment of the present invention has been described above, the present invention is not limited to this. The scope of the invention is indicated by the claims and all the modifications are included in the invention.

For example, in the present embodiment, the piezoelectric element 3
Each of the extraction electrode pieces 32a in four directions from the center position of 0, 40
32d, 42a to 42d extend and each extraction electrode piece 32
Although the extraction electrodes 32 and 42 are formed so that a to 32d and 42a to 42d are equidistant from each other, the extraction electrodes 32 and 42 may be formed in three or five directions as long as they are two or more directions. In this case, it is preferable that each extraction electrode piece be arranged so as to be point-symmetrical with respect to the center of the piezoelectric element, or be arranged line-symmetrically with respect to a line passing through one extraction electrode piece. Is. 4 and 5 show a modification of the present invention. In this case, it is preferable from the viewpoint of acoustic characteristics that the number of extraction electrode pieces is even.

Further, in the present embodiment, the covering members 33,
Although 43 is formed so as to cover the entire extraction electrodes 32, 42, it may be provided only at the central portions of the extraction electrodes 32, 42 as shown in FIG. 6, for example.

Further, in the above embodiment, the piezoelectric acoustic device in which the piezoelectric speaker is housed in the case has been described.
In the present invention, the presence or absence of the case is irrelevant. Therefore, the piezoelectric acoustic device as shown in FIG. 7 may be used. The piezoelectric acoustic device will be described below.

As shown in FIG. 7, this piezoelectric acoustic device 70
Is the piezoelectric speaker 10 described in the above embodiment and a pair of flexible sheets 71 that cover the piezoelectric speaker 10 from both sides.
And a pair of support frames 72 that sandwich the flexible sheet 71 from both sides. In this piezoelectric sounding body 10, the terminal portion 21 and the terminal plate 25 of one vibration plate 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, the piezoelectric acoustic device 70 functions as a speaker having excellent reproducibility particularly in the low frequency range.

Further, in the above embodiment, the extraction electrode 3
The electrode films 31, 4 of the piezoelectric elements 30, 40 are formed on the entire surfaces of 2, 2, 42.
Although it was adhered to No. 1 with an adhesive having conductivity and tackiness,
You may make it adhere | attach only in the center part of the piezoelectric elements 30 and 40.

[0037]

As described in detail above, according to the present invention,
Since the strip-shaped extraction electrode is adhered to the electrode film of the piezoelectric element with the adhesive having adhesiveness and conductivity, the connection portion between the extraction electrode and the piezoelectric element can be formed thin. Further, since the extraction electrode extends radially from the position where the expansion and contraction displacement of the piezoelectric element is minimal to the outer peripheral direction of the piezoelectric element, even if the piezoelectric element expands and contracts, the extraction electrode can be securely joined to the piezoelectric element. It will be 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 center position.

[Brief description of drawings]

FIG. 1 is an exploded perspective view of a piezoelectric acoustic device.

FIG. 2 is a schematic cross-sectional view of a piezoelectric speaker for explaining the attachment structure of the extraction electrode.

FIG. 3 is a diagram for explaining a state of amplitude of the diaphragm with the cutting electrode forming position as a cutting line.

FIG. 4 is a plan view of a piezoelectric speaker according to another example.

FIG. 5 is a plan view of a piezoelectric speaker according to another example.

FIG. 6 is a plan view of a piezoelectric speaker according to another example.

FIG. 7 is a plan view of a piezoelectric acoustic device according to another example.

FIG. 8 is a side view of a conventional piezoelectric acoustic device.

[Explanation of symbols]

1, 70 ... Piezoelectric acoustic device, 10 ... Piezoelectric sounding body, 20 ... Vibration plate, 21, 22, 23, 24 ... Terminal portion, 25, 26,
27, 28 ... Terminal plate, 29 ... Insulator, 30, 40 ... Piezoelectric element, 31, 41 ... Electrode film, 32, 42 ... Extraction electrode, 3
3, 43 ... Covering member, 50 ... Case, 71 ... Flexible sheet, 72 ... Support frame

Claims (2)

[Claims] 1. A piezoelectric element having electrode films formed on both surfaces,
In a piezoelectric acoustic device including a vibrating plate joined to one electrode film of this piezoelectric element, strip-shaped extraction electrodes radially extending in a plurality of outer peripheral directions of the piezoelectric element from a position where expansion and contraction displacement of the piezoelectric element is minimal, A piezoelectric acoustic device characterized by being adhered to an electrode film of a piezoelectric element with an adhesive having adhesiveness and conductivity. 2. The piezoelectric acoustic device according to claim 1, wherein piezoelectric elements are provided on both sides of the vibration plate, and the extraction electrodes adhered to the respective piezoelectric elements are electrically connected to each other.