JPH11355891A - Piezoelectric diaphragm and piezoelectric acoustic component using the piezoelectric diaphragm - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric acoustic component that has satisfactory acoustic concision efficiency, easily enabling obtaining low frequencies and is easily configured to be a surface mounting type. SOLUTION: Slits 2c are formed in parallel with a top plate of a metal plate 2 that is drawn into a cap shape to the metal plate 2 and a unimorph diaphragm 1 is configured by adhering face so as to face a rectangular piezoelectric plate 3 to part of the metal plate 2 between the slits 2c electrically and mechanically. The slits 2c of the diaphragm 1 are sealed with a flexible sealing material 4, a lower end of a circumferential wall of the metal plate 2 is adhered and fixed to a base plate 10 with a 1st electrode 11 and a 2nd electrode 12 for forming an acoustic space 5 between the metal plate 2 and the base 10. The metal plate 2 connects to the 1st electrode 11, a surface electrode 3a of the piezoelectric plate 3 is connected to the 2nd electrode 12 by a wire 6, the diaphragm 1 is covered in a contactless state and a cover 20 while sounding holes 21 is adhered and fixed to the base 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric acoustic component such as a piezoelectric buzzer or a piezoelectric receiver.

[0002]

2. Description of the Related Art Hitherto, piezoelectric acoustic components have been widely used as a piezoelectric buzzer or a piezoelectric receiver that generates an alarm sound or an operation sound in electronic devices, home appliances, mobile phones, and the like.

A piezoelectric acoustic component of this type is disclosed in, for example,
As described in JP-A-107593 and JP-A-7-203590, a diaphragm is formed by attaching a circular metal plate to a single-sided electrode of a circular piezoelectric plate, and a peripheral portion of the metal plate of the diaphragm is formed. In general, it is supported in a circular case, and the opening of the case is closed with a cover.

[0004]

However, when such a circular diaphragm is used, there has been a problem that the acoustic conversion efficiency is low and it is difficult to construct a surface mount type.

First, the acoustic conversion efficiency will be described. As shown in FIG. 1 (a), a disk-shaped diaphragm is hardly bent and displaced because its peripheral portion is fixed by a case or the like. Since the displacement point P is only the center point, the displacement volume is small. As a result, there is a disadvantage that the sound conversion efficiency is poor. Further, since the periphery of the diaphragm is constrained, the frequency becomes high, and there is a disadvantage that the radius dimension becomes large in order to obtain a low-frequency piezoelectric diaphragm.

Further, when a piezoelectric acoustic component is formed using a disk-shaped diaphragm, lead wires are often used for connection to the outside, and it is difficult to configure a surface-mounted type. For this reason, as described in Japanese Utility Model Laid-Open No. 3-125396, a device is known in which a lead terminal is integrally formed at a corner of a rectangular metal plate and a circular piezoelectric plate is bonded to the metal plate. However, in this structure, it is necessary to form the lead terminals integrally from the metal plate, so that the shape of the metal plate becomes complicated, and the shape of the case becomes complicated due to the lead terminals being drawn out. Since the lead terminals are in contact with or fixed to the piezoelectric plate, there is a problem that a mechanical load or a thermal load is easily applied to the piezoelectric plate. And there are many difficulties in terms of reliability.

An object of the present invention is to provide a piezoelectric vibrating plate which has good sound conversion efficiency and can easily obtain a low frequency. Another object of the present invention is to provide a piezoelectric acoustic component that can be easily configured in a surface mount type using the above-described piezoelectric vibration plate.

[0008]

In order to achieve the above object, according to the first aspect of the present invention, a slit is provided in parallel with a metal plate, and a rectangular piezoelectric plate is electrically and mechanically provided between the slits. A piezoelectric vibrating plate characterized by being joined face to face.

By joining a rectangular piezoelectric plate face-to-face to a portion between slits provided in the metal plate, a portion sandwiched between the slits of the metal plate constitutes a vibrating portion. When a predetermined frequency signal is input between the metal plate and the surface electrode of the piezoelectric plate, the piezoelectric plate expands and contracts in the length direction, and the vibrating part flexes and vibrates in response to this,
Pronounce. At this time, both ends in the length direction of the rectangular piezoelectric plate become nodes of vibration, and the center part in the length direction becomes an antinode of vibration. That is, as shown in FIG. 1B, since the maximum displacement point P exists along the longitudinal center line of the piezoelectric plate, the displacement volume increases. Since this displacement volume becomes energy for moving air, the sound conversion efficiency can be increased. Even if the peripheral portion of the metal plate is fixed to a substrate, a case, or the like, the portion sandwiched by the slits can be freely displaced, so that the sound conversion efficiency does not decrease. Further, since the portion where the piezoelectric plate is fixed can be freely displaced by the slit, a lower frequency can be obtained as compared with a conventional disk-shaped diaphragm. Conversely, if the same frequency is obtained, the size can be reduced.

In the present invention, since a rectangular piezoelectric plate is used, even when the piezoelectric plate is punched from the green sheet, the amount of scraps can be reduced and the material efficiency is high. In addition, since operations such as electrode formation and polarization can be performed in the state of the parent substrate, production efficiency is high. In addition, change the length or interval of the slit,
If the dimensions of the piezoelectric plate are changed, the electrical performance can be easily changed, so that other components (for example, a case, a board, a cover, etc.) do not need to be changed. Therefore, even if the number of kinds of products increases, a substrate or a case having a fixed shape can be used, and the production cost can be reduced.

According to a second aspect of the present invention, the metal plate of the piezoelectric vibrating plate according to the first aspect is drawn so as to have a top plate portion and a peripheral wall portion to form a slit parallel to the top plate portion.
The slit is sealed with a flexible sealing material, the lower end of the peripheral wall of the metal plate is adhesively fixed to a substrate having the first electrode and the second electrode, and an acoustic space is provided between the metal plate and the substrate. To form
The metal plate is connected to the first electrode of the substrate, the surface electrode of the piezoelectric plate is connected to the second electrode of the substrate, and the cover that covers the diaphragm in a non-contact state and has a sound emission hole is bonded and fixed on the substrate. Thus, a surface-mounted piezoelectric acoustic component can be obtained.

In this case, since the metal plate is formed in a cap shape, an acoustic space can be easily formed between the metal plate and the substrate by fixing the lower end of the peripheral wall portion to the flat substrate. . Moreover, by forming the slit on the top plate,
A large mounting area (vibration area) for the piezoelectric plate can be secured, and the sound conversion efficiency can be further increased.

The slit of the metal plate is sealed with a sealing material to prevent air leakage, but since this sealing material has flexibility, it does not hinder displacement of a portion sandwiched between the slits.
As the sealing material, a material having flexibility such as silicone rubber is desirable.

Further, since the cover for covering the diaphragm in a non-contact state is adhered and fixed on the substrate, the periphery of the diaphragm can be made substantially closed. Then, the first and second electrodes provided on the substrate are routed to the side edge or the back surface of the substrate, whereby the component can be easily configured as a surface mount type component.

[0015]

FIG. 2 to FIG. 7 show a piezoelectric buzzer as an example of a piezoelectric acoustic component according to the present invention. The piezoelectric buzzer generally includes a unimorph-type diaphragm 1, a substrate 10,
And a cover 20.

The vibration plate 1 includes a metal plate 2 formed in a cap shape, and a rectangular piezoelectric plate 3 electrically and mechanically joined to the metal plate 2. The metal plate 2 is made of a material having both good conductivity and spring elasticity, such as phosphor bronze and 42Ni. When the metal plate 3 is made of 42Ni, since its thermal expansion coefficient is close to that of ceramic (PZT or the like),
A more reliable product can be obtained. As shown in FIG.
A top plate portion 2a and a peripheral wall portion 2b are integrally formed on the metal plate 2 by drawing, and two parallel slits 2c, 2c are formed in the top plate portion 2a. It is joined to a portion 2d between 2c and 2c. The length L of the slit 2c is longer than the interval W between the slits 2c, 2c, and the length x and the width y of the piezoelectric plate 3 are equal to or slightly shorter than the length L and the interval W of the slit 2c, respectively.

The piezoelectric plate 3 is made of a piezoelectric ceramic such as PZT, and electrodes 3a and 3b are formed on the front and back surfaces thereof, and the back electrode 3b is joined to the portion 2d of the metal plate 2 so as to be electrically conductive. . The back electrode 3b may be omitted, and the back surface of the piezoelectric plate 3 may be used as the back electrode 3b by directly bonding the back surface of the piezoelectric plate 3 to the metal plate 2 via a conductive adhesive or the like.

The piezoelectric plate 3 is connected to the slits 2c, 2c of the metal plate 2.
After joining to the portion 2d between the slits 2c, the slits 2c, 2c are sealed with a flexible sealing material 4 such as silicone rubber. Note that the sealing step of the sealing material 4 may be performed after the diaphragm 1 is bonded to the substrate 10 as described later.

The diaphragm 1 is bonded and fixed to an insulating substrate 10 made of a glass epoxy substrate or the like, and an acoustic space 5 is formed between the diaphragm 1 and the substrate 10. Note that the acoustic space 5 does not need to be completely sealed. For example, the substrate 10 may be appropriately provided with a braking hole or the like so as to communicate with the outside. Substrate 1
0, a first electrode 11 and a second electrode 12 are formed.
The electrode 11 is formed so as to extend from the upper surface on one end side of the substrate 10 to the rear surface side via the side edge, and the second electrode 12 is similarly wrapped from the upper surface on the other end side of the substrate 10 to the rear surface side via the side edge. It is formed as follows.

A conductive adhesive is applied to the lower end of the peripheral portion 2b of the metal plate 2 by transfer or the like, and is adhered to the substrate 10 to fix the metal plate 2 to the substrate 10, Electrical connection with the first electrode 11 is performed simultaneously. Note that the metal plate 2 is positioned at a distance so as not to contact the second electrode 12. Also, the upper surface of the diaphragm 1,
That is, the surface electrode 3a of the piezoelectric plate 3 is covered with the coated metal wire 6
Through the second electrode 12 of the substrate 10. The reason why the coated metal wire 6 is used is to prevent short-circuit between the wire 6 and the metal plate 2.

A cover 20 for covering the diaphragm 1 in a non-contact state is adhered and fixed on the substrate 10. A sound emission hole 21 is formed in the ceiling surface of the cover 20, and a buzzer sound can be emitted from the hole 21 to the outside. The material of the cover 20 may be a metal or a resin. When the metal cover 20 is used, the metal cover 20 and one of the electrodes 11 or 12 may be electrically connected.

Next, a manufacturing process of the piezoelectric acoustic component will be described with reference to FIG. First, a metal plate 2 and a rectangular piezoelectric plate 3 which are processed into a cap shape as shown in FIG. The metal plate 2 has a slit 2 at the same time as or before and after drawing.
Process c. Next, the piezoelectric plate 3 is bonded to a portion 2d of the metal plate 2 sandwiched by the slits 2c with a conductive adhesive or the like as shown in FIG. Next, (c)
The slit 2c is filled with the silicone rubber 4 and the slit 2c is sealed. On the other hand, the substrate 10 on which the electrodes 11 and 12 are patterned in advance is prepared. Next, an acoustic space 5 is formed between the diaphragm 1 and the substrate 10 by bonding the diaphragm 1 to the substrate 10 as shown in FIG. In addition,
At this time, the metal plate 2 is connected and fixed to the first electrode 11 of the substrate 10 with a conductive adhesive. Then, the surface electrode 3 a of the piezoelectric plate 3, which is the upper surface of the vibration plate 1, and the second electrode 12 are connected by the wire 6. It is desirable that the connection position of the wire 6 with respect to the surface electrode 3 a be a longitudinal end portion that serves as a node of vibration of the piezoelectric plate 3. Next, a cover 20 that covers the diaphragm 1 in a non-contact state as shown in FIG. The sound emission hole 21 of the cover 20 is located immediately above the piezoelectric plate 3. As described above, the surface-mounted piezoelectric acoustic component shown in (f) can be obtained.

In the above-described piezoelectric acoustic component, the surface electrode 3a of the piezoelectric plate 3 and the second electrode 12 of the substrate 10 are connected by the metal wire 6, but instead of this, as shown in FIG. May be connected to the surface electrode 3a of the piezoelectric plate 3 by soldering or the like, and the other end of the wire 7 may be connected to the inner surface of the metal cover 20 using the conductive paste 8. In this case, the wiring space can be reduced by using the metal cover 20 as a part of the conductive path.

The metal plate 2 and the first electrode 11 of the substrate 10
A conductive adhesive was used to make the connection between the metal plate 2 and the substrate 10 with a normal insulating adhesive, and then the solder, the conductive adhesive, or the lead was used. The metal plate 2 and the first electrode 11 may be connected using a wire or the like. In short, the connection method between the metal plate 2 and the first electrode 11 and the connection method between the surface electrode 3a of the piezoelectric plate 3 and the second electrode 12 are not limited to the above embodiment, and any method may be used. it can.

FIG. 9 shows a second embodiment of the piezoelectric acoustic component according to the present invention.
An example will be described. In this embodiment, case 3 is the same as before.
0 and the cover 40. A circular concave portion 31 is formed in the case 30, and a step portion 32 is formed on an inner peripheral surface of the concave portion 31. The piezoelectric vibration plate 50 is formed by providing two parallel slits 52 in a disc-shaped metal plate 51 and electrically and mechanically facing each other to a piezoelectric plate 53 at a portion between the slits 52. The slit 52
Is sealed with a sealing material 54 such as silicone rubber. The periphery of the diaphragm 50 is the step 3 of the case 30.
2 and closely fixed with an adhesive or the like. Thus, an acoustic space is formed between the case 30 and the diaphragm 50. The cover 40 is adhered to the upper surface of the case 30 to complete the piezoelectric acoustic component.

The metal plate 51 and the surface electrode 53a of the piezoelectric plate 53
In order to connect to the outside, a lead wire (not shown) may be connected, or a lead terminal may be used.
Since both connection methods are known, description thereof is omitted here.

In the embodiment shown in FIG. 9, the outer shapes of the case 30, the cover 40 and the diaphragm 50 can be arbitrarily changed. For example, the case 30 and the cover 40 may have a rectangular shape, and the metal plate 51 may have a rectangular shape.

In the above embodiment, two slits are formed on one metal plate, and one piezoelectric plate is fixed between the slits. However, a plurality of pairs of slits are provided on the metal plate. A plurality of piezoelectric plates may be fixed between these slits. In this case, no vibration is transmitted by the slit between the adjacent piezoelectric plates, so that the acoustic characteristics are not disturbed. Also,
If a plurality of electrodes are formed on the substrate and these electrodes are individually connected to the surface electrodes of each piezoelectric plate, different sounds can be generated from each piezoelectric plate portion. Further, in the above-described embodiment, a unimorph type vibration plate in which a piezoelectric plate is attached to one surface of a metal plate has been described, but a bimorph type vibration plate in which a piezoelectric plate is attached to both surfaces of a metal plate may be used.

[0029]

As is apparent from the above description, claim 1
According to the invention described in (1), since the diaphragm is formed by providing slits in parallel with the metal plate and electrically and mechanically joining the rectangular piezoelectric plate face-to-face between the slits, The board can flex and vibrate greatly,
The sound conversion efficiency is improved, and a low frequency can be easily obtained.

According to the second aspect of the present invention, an acoustic space can be easily obtained by using a cap-shaped metal plate and a flat substrate, and the components can be simplified. By forming electrodes on the substrate,
A surface-mounted piezoelectric acoustic component can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a comparison diagram of a displacement distribution between a conventional example and the present invention.

FIG. 2 is a perspective view of a piezoelectric buzzer as an example of the piezoelectric acoustic component according to the present invention.

FIG. 3 is an exploded perspective view of the piezoelectric buzzer of FIG.

FIG. 4 is a sectional view taken along line IV-IV of FIG. 2;

FIG. 5 is a sectional view taken along line VV of FIG. 2;

FIG. 6 is an exploded perspective view of a diaphragm and a substrate.

FIG. 7 is a diagram showing a manufacturing process of the piezoelectric buzzer.

8 is a sectional view of a modification of the piezoelectric buzzer shown in FIG.

FIG. 9 is an exploded perspective view of a second embodiment of the piezoelectric acoustic component according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vibration plate 2 Metal plate 2c Slit 3 Piezoelectric plate 3a Surface electrode 4 Sealing material 5 Acoustic space 6 Conductive wire 10 Substrate 11 1st electrode 12 2nd electrode 20 Cover 21 Sound emission hole

Claims (2)

[Claims] 1. A piezoelectric vibrating plate wherein slits are provided in parallel with a metal plate, and a rectangular piezoelectric plate is electrically and mechanically face-to-face joined to a portion between the slits. 2. A metal plate of the piezoelectric vibrating plate according to claim 1 is drawn so as to have a top plate portion and a peripheral wall portion, and a slit parallel to the top plate portion is formed. It is sealed with a flexible sealing material, and the lower end of the peripheral wall of the metal plate is bonded and fixed to a substrate having a first electrode and a second electrode, so that an acoustic space is formed between the metal plate and the substrate. A metal plate is connected to a first electrode of the substrate, a surface electrode of the piezoelectric plate is connected to a second electrode of the substrate, and a cover that covers the diaphragm in a non-contact state and has a sound emission hole is formed on the substrate. A piezoelectric acoustic component characterized by being adhered and fixed to a substrate.