JP2006005800A - Piezoelectric speaker - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric speaker with a low profile wherein a power loss can be reduced by decreasing a contact resistance without deteriorating the sound quality. <P>SOLUTION: A piezoelectric element 14 on the surface of which an electrode layer is provided is adhered to a principal face of a diaphragm 12 of the piezoelectric speaker 10. The piezoelectric element 14 is formed to have a structure wherein at least three or more piezoelectric layers 16 and electrode layers 16 are alternately laminated to obtain a sufficient drive force. A conduction path 20 comprising a belt-like metallic foil and on the rear side of which an adhesive layer 22 is provided is provided to the surface of the electrode layer 16. Further, it does not matter whether or not the adhesive layer 22 has conductivity. Conductive paste with low rigidity and a high volume resistivity is coated over the conduction path 20 and the surface of the electrode layer 16 to form conductive layers 24 to 26 whose Young's modulus is 100 MPs or below and whose volume resistivity is 6 × 10<SP>-3</SP>Ωcm or below. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric speaker, and more specifically to improvement of power loss and sound pressure drop of a thin piezoelectric speaker.

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 thickness direction is attached to one or both surfaces of a metal diaphragm. . In order to obtain a sufficient sound pressure, the piezoelectric element needs to be a laminated body in which a piezoelectric body (piezoelectric layer) and an electrode layer are laminated. Therefore, it is necessary to fire the electrodes simultaneously, and a silver / palladium alloy electrode is used as a material that can withstand the firing. 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 ensured as a whole speaker (for example, below) Patent Document 1). Further, since a method of reducing the palladium ratio in the electrode is effective for reducing the cost, for example, the silver / palladium ratio is set to about 9: 1 by using a piezoelectric body that is sintered at a low temperature. However, in such an electrode with a reduced palladium content, since the shrinkage proceeds at a lower temperature than the base piezoelectric material, the piezoelectric element may be deformed or broken due to the stress generated by shrinkage mismatch during sintering. I will do. Therefore, a method is used in which the same piezoelectric material as the base material is added to the electrode to match the shrinkage rate.
JP 2003-078995 A

  However, since the piezoelectric material added to the electrode as described above is excluded from the metal during the sintering, particles of the piezoelectric material are deposited on the electrode surface in the external electrode of the piezoelectric element. Since the piezoelectric material itself is a nonconductor, the contact resistance is increased by the precipitated particles, and the power consumed at the contact portion is increased. Therefore, there is a problem that energy that is effectively converted into sound is reduced, and conversion efficiency is lowered. In order to avoid this problem, there is a method of increasing the area of the conductive path (metal foil) and reducing the contact resistance. However, in this method, the conductive path interferes with the vibration of the diaphragm. There is an inconvenience that the frequency increases and the sound pressure decreases.

  The present invention focuses on the above points, and an object of the present invention is to provide a thin piezoelectric speaker that can reduce power loss by reducing contact resistance without deteriorating sound quality.

In order to achieve the above object, the present invention provides 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 side of the piezoelectric element. In addition, the electrode layers of the piezoelectric elements or one of the electrode layers of the piezoelectric elements and an external circuit are conductively connected, and are fixed to the electrode layers by an adhesive material layer provided on the back surface. A conductive path made of a strip-shaped metal foil, formed by coating a conductive paste, has a Young's modulus of 100 MPa or less and a volume resistivity of 6 × 10 ⁻³ Ωcm or less provided from the surface of the electrode layer to the upper surface of the conductive path A conductive layer.

One of the main forms is that the contact area between the electrode layer surface 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. .01 mm or more. In another embodiment, the contact area between the electrode layer surface and the conductive layer is preferably 20 mm ² or less. The diameter of the diaphragm is 10 mm to 50 mm.

  Still another embodiment is (1) a structure in which the piezoelectric element is attached to at least one main surface of the diaphragm, and (2) the piezoelectric element has a plurality of alternately laminated piezoelectric layers and electrode layers. (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 become apparent from the following detailed description and the accompanying drawings.

In the present invention, a conductive path made of a strip-shaped metal foil having an adhesive material layer provided 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. A conductive layer having a Young's modulus of 100 MPa or less and a volume resistivity of 6 × 10 ⁻³ Ωcm or less is formed using the conductive paste having a low rigidity and a high volume resistivity while connecting to an external circuit. The surface is formed so as to extend from the surface to the upper surface of the conductive path. For this reason, it is possible to obtain a thin piezoelectric speaker with high efficiency while maintaining low contact resistance without deteriorating sound quality and preventing power loss of signals.

  Hereinafter, the best mode for carrying out the present invention will be described in detail based on examples. FIG. 1 is a diagram showing a basic structure of a piezoelectric speaker according to the present invention. FIG. 1 (A) is a plan view of Embodiment 1, FIG. 1 (B) is a perspective view thereof, and FIG. FIG. 1D is a plan view of the second embodiment.

  As shown in FIG. 1, a piezoelectric speaker 10 of the present invention is obtained by attaching a piezoelectric element 14 made of a laminated piezoelectric material having an electrode layer 16 on at least one main surface to a metal diaphragm 12. The piezoelectric speaker 10 may be a unimorph type in which the piezoelectric element 14 is provided on one main surface of the diaphragm 12 or may be a bimorph type provided on both surfaces of the diaphragm 12. In order to make the total thickness of the piezoelectric speaker 10 1 mm or less, the diaphragm 12 has a thickness of 0.1 mm or less, for example. 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.

  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 of silver / palladium = 9/1 to 10/0 ratio (molar ratio) that can be fired simultaneously with the piezoelectric body. Used. The electrode layer 16 is formed by pasting an alloy (or silver) and piezoelectric powder into a paste by adding an appropriate solvent together with a binder to a piezoelectric green sheet by, for example, screen printing. A band-shaped metal foil having a thickness of 0.1 mm or less and having an adhesive layer 22 provided on the back surface is attached to the electrode layer 16 on the surface of the piezoelectric element 14. The metal foil forms conductive paths 20 for connecting the electrode layers 16 to each other and for connecting the electrode layers 16 and external circuits. The pressure-sensitive adhesive layer 22 used here may be conductive or non-conductive. However, in the case where the conductive adhesive layer 22 is used, in order to insulate, for example, an insulating tape (not shown) is attached to a portion where the adhesive layer 22 and the diaphragm 12 touch in order to prevent a short circuit with the diaphragm 12. It is necessary to take appropriate measures.

  Next, a conductive paste having a low rigidity and a low volume resistivity is applied from the conductive path 20 over the conductive path 20 and the surface of the electrode layer 16 to form a conductive layer. As for the application shape of the conductive paste, for example, two circular conductive layers 24 may be formed as in the piezoelectric speaker 10 shown in FIG. 1 (A), or the conductive layer 26 shown in FIG. 1 (D). It is good also as arbitrary shapes, such as making it a rectangle like.

表１から分かるように、使用ペーストＢ〜Ｄは、体積抵抗率は６×１０^−３Ωｃｍ以下の条件を満たすものの、剛性が高すぎるため駆動によって破壊してしまう。 Specifically, the conductive layers 24 to 26 preferably have a Young's modulus of 100 MPa or less and a volume resistivity of 6 × 10 ⁻³ Ωcm or less. When the Young's modulus is equal to or greater than the above value, the diaphragm 12 cannot withstand the stress when the diaphragm 12 is deformed and breaks, and becomes a resistance against the displacement of the diaphragm 12, thereby deteriorating sound quality. For example, Table 1 below is an example showing the relationship between the Young's modulus of a conductive paste used as a conductive layer and the presence or absence of breakage due to driving of the piezoelectric speaker 10. The used paste A uses polyester, the used paste B uses silicone, the used paste C uses epoxy, and the used paste D uses polyimide-based resin. Both used pastes contain silver as a conductive filler.

As can be seen from Table 1, the used pastes B to D satisfy the condition that the volume resistivity is 6 × 10 ⁻³ Ωcm or less, but are too high in rigidity so that they are destroyed by driving.

表２の結果から分かるように、音圧劣化を例えば０．１ｄＢ以内におさめるためには、導電ペーストのヤング率は１００ＭＰａが上限であることがわかる。従って、駆動による破壊を防止し、音質の劣化を最小限にするためには、導電ペーストのヤング率を１００ＭＰａ以下にするのが好ましいことが分かる。 Table 2 below shows changes in sound pressure when the conductive layer 26 having the shape shown in FIG. 1D is formed from 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 can be seen that the upper limit of the Young's modulus of the conductive paste is 100 MPa in order to suppress the sound pressure degradation within, for example, 0.1 dB. Therefore, it can be seen 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 minimize deterioration of sound quality.

前記導電ペーストの塗布方法としては、例えば、印刷法，スプレー法など公知の各種の方法を用いることができる。また、導電層２４又は２６の厚みは、例えば、０．０１ｍｍ（１０μｍ）以上とする。これより厚みが少ないと、抵抗値が高くなり過ぎて安定した接触状態を形成できない。塗布後に導電ペーストを紫外線照射や加熱などの所定の方法で硬化させることにより、接触状態が安定した圧電スピーカ１０を得ることができる。 Further, when the volume resistivity is 6 × 10 ⁻³ Ωcm or more, the contact resistance cannot be sufficiently reduced. The application shape of the conductive paste can be any shape such as a circle or a rectangle as described above, but both the portion overlapping the conductive path 20 and the portion overlapping the electrode layer 16 are 0.8 mm ² or more. Like that. In an area smaller than this, the contact resistance value is not sufficiently low. Table 3 below shows the sound pressure degradation when the application area of the conductive paste (conductive layers 24 to 26) on the electrode layer 16 is changed using a conductive paste having a Young's modulus of 60 MPa. As shown in Table 3, since the sound pressure deterioration exceeds 0.1 dB when the area is larger than 20 mm ² , the coating area on the electrode layer 16 is preferably 20 mm ² or less. Note that the effect of the application area of the conductive paste on the sound quality is remarkable in the case of a relatively small piezoelectric speaker having the diaphragm 12 having a diameter of about 10 to 50 mm. This is because, in the case of a relatively small piezoelectric speaker, the rigidity of the diaphragm 12 is increased, and therefore, it is less susceptible to the influence of the conductive paste.

As a method for applying the conductive paste, various known methods such as a printing method and a spray method can be used. Moreover, the thickness of the conductive layer 24 or 26 shall be 0.01 mm (10 micrometers) or more, for example. If the thickness is less 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 having a stable contact state can be obtained.

  Next, examples and comparative examples of the present invention will be described. FIG. 2 shows a main cross section of the piezoelectric speaker of the example and the comparative example. First, a description will be given of the first embodiment. The piezoelectric speaker 30 of the first embodiment is a bimorph type in which piezoelectric elements 34 and 40 having a laminated structure are bonded to both front and back surfaces of a diaphragm 32. The piezoelectric element 34, Conductive paths 46A and 46B made of a strip-shaped metal foil are provided on the electrode layers 38A and 44A on the surface of 40. As the diaphragm 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. The piezoelectric layers 36A to 36C have, for example, a diameter of 19 mm and a thickness. 0.018 mm (18 μm) lead zirconate titanate is used, and for example, a silver-palladium alloy having a diameter of 18.5 mm and a thickness of 0.001 mm is used as the electrode layers 36A to 36C. The electrode layers 38A to 38D are connected to each other by through holes or the like. The other piezoelectric element 40 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.

The conductive paths 46A and 46B are copper foils having conductive adhesive layers 48A and 48B provided on the back surface, and for example, those having dimensions of thickness 0.07 mm, length 10 mm, and width 2 mm are used. . The adhesive material layers 48A and 48B may be non-conductive. Furthermore, in order to prevent a short circuit in the portion where the metal around the diaphragm 32 is exposed, insulating tapes 50A and 50B are affixed inside the conductive paths 46A and 46B. . Then, from above the conductive paths 46A and 46B, a polyester 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 Ωcm) is applied to form conductive layers 52A and 52B. As in the form shown in FIG. 1A, the application shape is formed by setting a circular shape having a diameter of 1.0 mm at two locations by a spray method, and the areas on the conductive path 46A (46B) and the electrode layer 38A (44A) are set to 0. 9 mm ^2, the conductive layer 52A, the thickness of the 52B was 0.015 mm. The resistance values between the conductive paths 46A and 46B of the obtained piezoelectric speaker and the electrode layers 38A and 44A on the surfaces of the piezoelectric bodies 34 and 40 were measured by a four-terminal method, and the results are shown in Table 4 below.

A conductive paste having the same conditions as in Example 1 was applied by printing from above the conductive paths 46A and 46B, and a rectangular conductive layer of 1.6 × 4 mm as shown in FIG. 1D. 52A and 52B were formed. The areas on the conductive path 46A (46B) and the electrode layer 38A (44A) were controlled to 3.2 mm ² and the thickness to 0.03 mm, respectively. The resistance value between the conductive paths 46A and 46B of the produced piezoelectric speaker and the electrode layers 38A and 44A was measured under the same conditions as in Example 1.

[Comparative Example 1]
A piezoelectric speaker that does not use a conductive paste, that is, a piezoelectric speaker that does not form the conductive layers 52A and 52B, was manufactured in the same manner as in Example 1 described above, and the resistance value was measured by the method described above.

[Comparative Example 2]
For comparison with Example 2, a piezoelectric speaker in which the Young's modulus of the conductive layers 52A and 52B was 1000 MPa, the volume resistivity was 2 × 10 ⁻³ Ωcm, and the thickness was 0.02 mm was prepared. The value was measured.

[Comparative Example 3]
For comparison with Example 1, a piezoelectric speaker in which the Young's modulus of the conductive layers 52A and 52B was 40 MPa and the volume resistivity was 1 × 10 ⁻¹ Ωcm was produced, and the resistance value was measured by the method described above. .

[Comparative Example 4]
For comparison with Example 2, a piezoelectric speaker in which the thickness of the conductive layers 52A and 52B was 0.005 mm was prepared, and the resistance value was measured by the method described above.

Table 4 shows the contact resistance between the conductive paths 46A and 46B of the produced piezoelectric speaker and the electrode layers 38A and 44A on the surfaces of the piezoelectric elements 34 and 40 for Examples 1 and 2 and Comparative Examples 1 to 4. The measured values of are shown.

Looking at the results in Table 4, the conditions defined in the embodiment of the present invention, that is, the Young's modulus of the conductive layers 52A and 52A is 100 MPa or less, the volume resistance is 6 × 10 ⁻³ Ωcm or less, and the electrode layer 38A (44A) The contact area between the conductive layer 52A (52B) and the contact area between the conductive path 46A (46B) and the conductive layer 52A (52B) is 0.8 mm ² or more, and the thickness of the conductive layers 52A and 52B is 0.01 mm. In Example 1 and Example 2 satisfying (10 μm) or more, the contact resistances were 0.11Ω and 0.08Ω, respectively, regardless of the coating shape. That is, it was confirmed that the contact resistance can be kept at 0.5Ω or less, and a high-efficiency thin piezoelectric speaker can be realized by suppressing the power loss of the signal.

  On the other hand, in Comparative Example 1 in which no conductive paste was used, the contact resistance was very large at 4.22Ω. Further, in Comparative Example 3 for comparison with Example 1, the Young's modulus satisfies the above-described conditions, but the volume resistivity is larger than the above conditions, and the contact resistance is 2.09Ω. In Comparative Example 2 for comparison with Example 2, although the thickness and volume resistivity satisfy the above conditions, the Young's modulus is larger than the above condition, and the contact resistance is 1.86Ω. Similarly, in Comparative Example 4 for comparison with Example 2, the Young's modulus and volume resistivity satisfy the above conditions, but the thickness was thinner than 0.01 mm and the contact resistance was 3.33Ω. From the above results, it can be seen that in the piezoelectric speaker manufactured under the condition outside the above-described range, the contact resistance is 1Ω or more, and the power loss in this portion is large.

  In this way, in a piezoelectric speaker comprising a piezoelectric element having an electrode layer on at least one main surface and a diaphragm, the electrode layers or electrode layers are formed by a conductive path made of a strip-shaped metal foil provided with an adhesive material layer on the back surface. The conductive layer is formed so as to extend from the surface of the electrode layer to the upper surface of the conductive path using a conductive paste having low rigidity and high volume resistivity. For this reason, it is possible to obtain a thin piezoelectric speaker with high efficiency while maintaining low contact resistance (for example, 0.5Ω or less) without deteriorating sound quality and preventing power loss of signals.

In addition, this invention is not limited to the Example mentioned above, A various change can be added in the range which does not deviate from the summary of this invention. For example, the following are also included.
(1) The materials, shapes, and dimensions shown in the above-described embodiments are examples, and can be appropriately changed so as to achieve the same effect. For example, the coating shape of the conductive layers 24, 26, 52A, and 52B is an example, and the coating shape may be appropriately changed as long as the above-described conditions (area and thickness) are satisfied. Of course, the position where the conductive path is provided may be arbitrarily changed, and the application shape may be appropriately changed according to the position of the conductive path. For example, when the piezoelectric speaker is a bimorph type, the shape of the conductive layer formed on the electrode layer of one piezoelectric element may be different from the shape of the conductive layer formed on the electrode layer of the other piezoelectric element. Good.

  (2) The number of stacked piezoelectric layers and electrode layers may be changed as necessary. In the above embodiment, three piezoelectric layers are laminated in order to obtain a sufficient driving force. However, if the total thickness of the laminated body does not exceed 0.1 mm, a large number of piezoelectric layers are prevented from being laminated. It is not a thing. Further, the connection structure of the internal electrode layers can be appropriately changed as necessary.

  (3) In the above embodiment, the adhesive layers 48A and 48B are made of conductive materials, but non-conductive materials may be used.

  (4) As a preferred application example of the present invention, there is a speaker of various electronic devices such as a mobile phone (including PHS), a personal digital assistant (PDA), a voice recorder, and a PC (personal computer). Of course, this does not prevent application to various other uses.

According to the present invention, on the electrode layer on the surface of the piezoelectric element provided on the main surface of the diaphragm, a conductive path made of a strip-shaped metal foil having an adhesive material layer provided on the back surface is provided, and the electrode layers or electrodes are provided. A conductive layer having a Young's modulus of 100 MPa or less and a volume resistivity of 6 × 10 ⁻³ Ωcm or less using a conductive paste having a low rigidity and a high volume resistivity, and connecting the layer to an external circuit. The layer is formed so as to extend from the surface of the layer to the upper surface of the conductive path. For this reason, the contact resistance can be kept low without deteriorating the sound quality, signal loss can be prevented, and high efficiency can be realized. Therefore, the present invention can be applied to thin piezoelectric speakers. In particular, it is suitable for an ultra-thin piezoelectric speaker having a thickness of 1 mm or less.

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 surface of the electrical conduction path of Embodiment 1. FIG. A perspective view and (D) are plan views of the second embodiment. It is principal sectional drawing of the piezoelectric speaker of the Example of this invention.

Explanation of symbols

10: Piezoelectric speaker 12: Vibration plate 14: Piezoelectric element 16: Electrode layer 20: Conductive path 22: Adhesive material layer 24, 26: Conductive layer 30: Piezoelectric speaker 32: Vibration plate 34, 40: Piezoelectric elements 36A to 36C, 42A -42C: Piezoelectric layers 38A-38D, 44A-44D: Electrode layers 46A, 46B: Conductive paths 48A, 48B: Adhesive material layers 50A, 50B: Insulating tapes 52A, 52B: Conductive layers

Claims (7)

A piezoelectric speaker comprising 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 side of the piezoelectric element,
A band-shaped metal foil which is electrically connected to the electrode layers of the piezoelectric elements or one of the electrode layers of the piezoelectric elements and an external circuit, and is fixed to the electrode layers by an adhesive layer provided on the back surface. A conductive path consisting of,
A conductive layer formed by applying a conductive paste and having a Young's modulus of 100 MPa or less and a volume resistivity of 6 × 10 ⁻³ Ωcm or less provided from the surface of the electrode layer to the upper surface of the conductive path;
A piezoelectric speaker characterized by comprising: The contact area between the electrode layer surface 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 0.01 mm or more. The piezoelectric speaker according to claim 1. The piezoelectric speaker according to claim 2, wherein a contact area between the electrode layer surface and the conductive layer is preferably 20 mm ² or less.   The piezoelectric speaker according to claim 1, wherein the diaphragm has a diameter of 10 mm to 50 mm.   The piezoelectric speaker according to any one of claims 1 to 4, wherein the piezoelectric speaker has a structure in which the piezoelectric element is attached to at least one main surface of the diaphragm.   The piezoelectric speaker according to claim 1, wherein the piezoelectric element has a laminated structure in which a plurality of piezoelectric layers and electrode layers are alternately laminated. The piezoelectric speaker according to claim 6, wherein the piezoelectric element includes at least three piezoelectric layers.

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