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DESCRIPTION JP2004096225

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DESCRIPTION JP2004096225
The present invention provides a piezoelectric sounding element capable of securing sound
quality, bass reproduction, and low voltage drive in a well-balanced manner. A piezoelectric
diaphragm 25 includes piezoelectric elements 23A and 23B and a metal plate 22 to which the
piezoelectric elements 23A and 23B are attached. The entire surface of at least one surface of the
piezoelectric diaphragm 25 is a piezoelectric diaphragm. It is covered with a resin sheet 26
having an area of 25 or more. [Selected figure] Figure 1
Piezoelectric sounding element
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric sounding element incorporated in various electronic devices. 2. Description of the
Related Art Electronic devices are becoming more sophisticated and smaller year by year. For
example, the miniaturization and high functionality of mobile phones, personal digital assistants
(PDAs), personal computers, portable video devices and the like. At the same time, with the
introduction of Internet technology and the development of communication technology, there is
an environment where you can easily obtain video and music data anytime and anywhere. As
described above, it is becoming possible to obtain a large amount of information “anytime and
anywhere”, but on the other hand, technological developments regarding the interface between
such information and human beings are also progressing. For example, TFT (thin film transistor)
liquid crystal, organic electroluminescence (organic EL) and the like as "image display device",
small switches and touch panels as "input device", microspeakers as "sound generation element"
and the like. With regard to the “sound generation element”, the main force at present is a
microdynamic speaker using a neodymium magnet. The diameter of this speaker is small and has
been put to practical use from about 12 mm in diameter (φ). Basically, when the speaker
aperture becomes smaller, it is difficult to secure the volume, so a magnet with a strong magnetic
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force such as neodymium is often used to secure the volume. On the other hand, a speaker using
a piezoelectric element is also in practical use. A conventional piezoelectric buzzer is often used.
In general, when using piezoelectric, there is an advantage that the efficiency is high and the
consumption output can be suppressed compared to the magnet speaker, but the flatness of the
frequency characteristic of the sound pressure and the low frequency reproduction ability are
inferior and the sound quality is bad. There is a drawback of that. In order to improve these
drawbacks, some piezoelectric speakers have been improved in sound quality. For example, a
resin sheet extending to the outside of the diaphragm is adhered to both sides of the peripheral
portion of the diaphragm on which the piezoelectric ceramic plate is attached, and the resin sheet
is supported only by the resin sheet to improve sound quality in the low range. A piezoelectric
speaker that has been made possible has been proposed (see Japanese Patent Application LaidOpen No. 11-113094). Problems to be Solved by the Invention [0005] Demands for "high
performance" and "small size, light weight and thinness" of portable devices are high, and in
order to satisfy these requirements, the size of each device should be reduced. We have to go. In
the following, the problem of the "sound generation element" will be described in consideration
of this point. When incorporating a sounding element in a portable device, the options can be
roughly divided into two: "magnetic speaker" and "piezoelectric speaker".
<Problems of Magnet Speaker> As shown in FIG. 16, the basic structure of the magnet speaker 1
is integrally formed with a diaphragm (cone) 2 and a coil 3 formed thereon with a predetermined
distance. The diaphragm 2 is supported by the frame 7 via the damper 8 and the coil 3 is
disposed between the magnet 4 and the yoke 6. In the magnet speaker 1, the diaphragm 2 is
vibrated by receiving a force from the magnet 4 by supplying a current to the coil 3. Therefore,
there is a limit to reducing the thickness T1 of the speaker 1. As an example of a magnet speaker
currently used, for example, the thickness T1 of a speaker with a diameter of 16 mm is about 3
mm. On the other hand, in order to increase the volume, it is necessary to increase the diameter
of the speaker, but generally, if the diameter is increased, it is difficult to reduce the volume of
the speaker element because the thickness T1 also increases. <Problems of Piezoelectric
Speaker> As shown in FIG. 17, the basic structure of the piezoelectric speaker 11 is constituted
by a simple structure of only the piezoelectric diaphragm 14 in which the metal diaphragm 12
and the piezoelectric element 13 are bonded. . The thickness of the metal diaphragm 12 is about
0.1 mm or less, the thickness of the piezoelectric element 13 is 0.1 mm or less, and a thin
speaker having a total thickness T2 of about 0.2 mm can be obtained. On the other hand, in
order to secure a certain volume, a diameter of 25 mm or more is required. However, the volume
of the speaker element is smaller than that of the magnet speaker, and the device is suitable for
portable devices. However, the problem with the poor sound quality of the piezoelectric speaker
itself is that it is difficult to secure the volume as low as that of the magnet speaker. A general
portable device uses a lithium ion battery or the like as a power supply, and the drive voltage is
about 3 to 4 VDC. The piezoelectric element is generally a high impedance element, and is
suitable for high voltage driving, so the driving voltage is low at the operating voltage of the
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portable device, and it is difficult to secure the necessary volume. For example, although it is
possible to raise the drive voltage of the piezoelectric speaker by boosting with a DC-DC
converter or the like, this leads to an increase in cost and the number of parts, which is not
desirable. Another problem is that due to the increase in area, the deterioration of the low
frequency output when mounted in a minimal enclosure is significant. As mentioned above, the
area of the piezoelectric speaker tends to be larger than that of the magnet speaker, but the
space inside the high-density mounted portable device is only a few ml.
Under such conditions, since the area of the back pressure received by the diaphragm is large
due to the large area, vibration disturbance easily occurs, and the output deterioration
particularly in the low range becomes remarkable. For the above reasons, there are very few
cases where a piezoelectric speaker is introduced to a portable device because it is difficult to
secure the necessary volume and sound quality despite the excellent mounting efficiency. The
problems of the piezoelectric speaker will be described in more detail. 1) In the piezoelectric
speaker, the resonance of the diaphragm occurs in the audible range (several 10 Hz to 20 kHz
band), and a significant change in sound pressure at the frequency of the resonance occurs. As a
result, peaks (large output) and valleys (small output) of the sound pressure characteristics can
be generated. In the case of a general piezoelectric buzzer, the difference in sound pressure
between the peaks and valleys reaches as high as 20 dB to 30 dB, which is a factor in the
deterioration of the sound quality. 2) Piezoelectric speakers have lower bass reproduction
capability than magnet speakers. The sound pressure generated from the speaker diaphragm is
correlated with the displacement volume due to the vibration of the diaphragm (the product of
the area of the diaphragm and the stroke of the movement of the diaphragm, the amount of air
forced by the vibration of the diaphragm). It is necessary to increase the excluded volume as you
go to the area. However, the piezoelectric speaker is a rigid plate in which a piezoelectric element
and a metal diaphragm are integrated, and is not suitable for large vibration. On the contrary,
this also has the effect of being suitable for high-pitched sound reproduction. For this reason, the
piezoelectric speaker has an area larger than that of the magnet speaker to increase the excluded
volume even if the amplitude is small, but the internal volume of the box mounting the speaker
(hereinafter referred to as the enclosure volume) The bass reproduction capability can be
secured under conditions (eg, several tens of ml to several hundreds of ml) where a certain
degree of freedom is secured, but the deterioration of the bass reproduction capability is
remarkable when only a few ml of enclosure volume such as portable equipment is permitted.
Especially, it is inconvenient for the reproduction of a sound source whose power spectrum is
concentrated to 1 kHz or less such as music and voice. 3) Piezoelectric speakers are not suitable
for low voltage driving. For example, although the impedance of the magnet speaker is 8 Ω or 16
Ω, the piezoelectric element is basically a capacitive element and a high impedance element (for
example, the impedance at 1 kHz is several hundreds Ω). Therefore, although it is originally
desirable to drive at a voltage of 10 V or more, in the case of a portable device, the power supply
voltage is low and it is not suitable for driving a piezoelectric speaker at a low voltage. In view of
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the above-described points, the present invention provides a piezoelectric sounding element that
can ensure sound quality, bass reproduction, and low voltage drive in a well-balanced manner.
In particular, it is intended to provide a piezoelectric sounding element which achieves the
balance at a low cost and in consideration of the device mounting efficiency while achieving wellbalanced characteristics required for the application of the portable device. The piezoelectric
sounding element according to the present invention has a piezoelectric diaphragm formed of a
piezoelectric element and a metal plate to which the piezoelectric element is attached, and at
least one of the piezoelectric diaphragms. The entire surface is covered with a resin sheet having
a larger area than the piezoelectric diaphragm. The piezoelectric sounding element according to
the present invention has a piezoelectric vibrating plate consisting of a piezoelectric element and
a metal plate to which the piezoelectric element is attached, and the entire surface of both sides
of the piezoelectric vibrating plate is covered with a resin sheet. Either one has a larger area than
the piezoelectric diaphragm. The shape of the free vibration area of the piezoelectric sounding
element is preferably non-square, preferably rectangular. The outermost peripheral portion of
the resin sheet doubles as a mounting portion to a support member for supporting the
piezoelectric sound emitting element. In the piezoelectric sounding element of the present
invention, since the resin sheet is coated on the entire surface of at least one surface of the
piezoelectric diaphragm, the resin sheet has a large attenuation ratio with respect to the metal
sheet specific attenuation ratio. Damping effect of the piezoelectric diaphragm is enhanced. As a
result, the sound pressure difference between the peaks and valleys near the resonance point is
suppressed, and the sound pressure frequency characteristics can be flattened. When the shape
of the free vibration region of the piezoelectric sounding element is non-square, preferably
rectangular, the resonance points of the eigenmodes are deviated in the long side direction and
the short side direction, and the resonance points of the entire diaphragm are dispersed (for
example, 1) Two large resonance acuities (Q-factors) are distributed to a plurality of small
resonance acuities), which enables flattening of the sound pressure frequency characteristics.
Also, the sound pressure level in the low range is higher than in the case of the square. Since the
outermost periphery of the resin sheet also serves as an attachment portion to the support
member for supporting the piezoelectric sounding element, when the piezoelectric sounding
element is attached to the support member, the soft reproduction improves the sound
reproduction. As described above, the low frequency side is extended, and the acoustic
characteristics are improved by the flattening of the sound pressure frequency characteristics,
thereby enabling low voltage driving. DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
The piezoelectric sounding element according to the present invention uses a resin sheet having
flexibility for suppressing the difference between peaks and valleys (so-called peaks and valleys)
of sound pressure that degrades sound pressure frequency characteristics, and uses metal plate
to piezoelectrically Affixing on at least one surface, preferably both surfaces of a piezoelectric
diaphragm formed by bonding elements, and using a part of this resin sheet also as a mounting
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portion (adhesion portion) to a support member such as a housing of a device Configure to
Also, the shape of the free vibration area is formed to be non-square, preferably rectangular. The
piezoelectric sounding element of the present invention is applied to a speaker, a receiver, other
sounding elements, and the like. FIG. 1 shows a basic configuration of an embodiment of a
piezoelectric sounding element according to the present invention. In the piezoelectric sounding
element 21 according to the present embodiment, the piezoelectric elements 23 [23A, 23B] are
attached to both sides with the metal plate 22 in between, and the piezoelectric elements 23A
and 23B are provided on the surface opposite to the metal plate 22. A piezoelectric diaphragm
25 having electrodes 24A and 24B formed thereon is provided, and both surfaces of the
piezoelectric diaphragm 25 are coated with resin sheets 26 [26A, 26B] having an area larger
than that of the piezoelectric diaphragm 25. . The outer shape of the metal plate 22 is smaller
than the support member to which the piezoelectric sounding element 21 is attached, for
example, the inner periphery of a frame, and the possible vibration area, that is, the outermost
periphery of a so-called free vibration area is formed only by the resin sheet 26. One lead wire
27 is led out from the terminal portion of the metal plate 22, and the other lead wire 28 is led
out from the terminal portion of the electrode 24 [24A, 24B] of the piezoelectric element 23
[23A, 23B]. The lead wire 28 can be derived by connecting the lead wires respectively derived
from the electrodes 24A and 24B to the outside. The outer shape of the resin sheet 26 is larger
than the inner periphery of the frame to be attached, and the outermost peripheral portion 26 c
of the resin sheet 26, specifically, a portion 26 d thereof is a region to be adhered to the frame.
In this case, the frame to be attached may be, for example, a housing of a portable device or a
part of a mounting component. Further, the adhesion method may be an adhesion method or a
thermocompression bonding method. In the embodiment, as described later, a resin sheet is
selected so as to obtain appropriate sound pressure characteristics in accordance with the
bonding method. The piezoelectric sound element 21 is non-square in shape, preferably the outer
dimension of the resin sheet 26 is X> P, the dimension of the free vibration area is XS> PS, and
the outer dimension of the metal plate 22 as shown in FIG. Are rectangular so that the external
dimensions of the piezoelectric element 24 are XP> YP. In fact, with respect to the ratio of XS to
YS, XS / YS is set to 1.1 to 4.0, preferably 1.1 to 2.0. According to the piezoelectric sounding
element 21 configured such that the piezoelectric vibration plate 25 is covered with the resin
sheet 26 as described above, the following effects can be obtained. (1) The damping ratio of the
resin sheet 26 is large relative to the damping ratio inherent to the material of the metal or
material constituting the piezoelectric diaphragm 25, and the damping effect of the resin sheet
26 reduces the damping effect of the piezoelectric diaphragm 25 itself. Can be raised.
Due to this effect, it is possible to suppress the sound pressure difference between the peaks and
valleys near the resonance point. Thereby, the flatness of the sound pressure frequency
characteristic is obtained. (2) By covering all of the piezoelectric diaphragm 25 with the resin
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sheet 26, all the electrode surfaces other than the terminal portions are covered with the resin
sheet 26 so as to ensure insulation of the electrode surfaces. At the same time, it also has the
effect of suppressing the occurrence of cracks and cracks in the piezoelectric element portion
due to external force. (3) The resin sheet 26 has the effects of (1) and (2) and at the same time
has the function of bonding to the device. That is, as shown in FIG. 2, the adhesive property of
the portion 26c of the outer peripheral margin of the resin sheet 26 enables direct mounting on
the support member, for example, the support portion 30 in the housing 29 of the device. The
conventional speaker performs, for example, screw freezing or fitting using a nail of a molded
part. Also, there are many examples in which the conventional piezoelectric speaker also has a
frame with a predetermined thickness at the outer peripheral part, or one without the frame is
attached to the device with an adhesive. By using the structure of this embodiment, it is possible
to directly mount a piezoelectric sound emitting element, for example, a piezoelectric speaker, on
a device. (4) The case bonding portion outside the free vibration area (XS × YS) of the
piezoelectric sound emitting element 21, that is, the outermost peripheral portion 26c of the
piezoelectric sound emitting element 21 is an area of only the resin sheet. Therefore, the resin
sheet 26 also has an edge for supporting the piezoelectric diaphragm 25 and needs to have a
certain level of strength. For example, if the resin part is cracked by some external force, the
sealing property before and after the diaphragm can not be secured, and the acoustic
characteristic is deteriorated. In the present embodiment, for example, by combining a resin
sheet 26 having a certain degree of strength, such as a thermoplastic resin sheet having a
predetermined thickness, a polypropylene adhesive tape, a polyethylene adhesive tape, etc., the
strength of the resin portion is secured. The reliability of the Since the portion supporting the
piezoelectric diaphragm 25 is the resin sheet 26 and has appropriate flexibility, it can cope with
large vibrations and bass reproduction is improved. Further, the shape of the piezoelectric sound
emitting element 21 is non-square, preferably rectangular as shown in FIG. 1 such that X> Y (XS>
Y, XK> YS, XP> YP). Since the length of X is larger than the length in the Y direction, it is possible
to lower the natural mode frequency in the X direction to be lower than the natural mode
frequency in the Y direction. Therefore, the resonance points of the entire diaphragm are
dispersed to enable flattening of the sound pressure frequency characteristics, and the sound
pressure level in the low region becomes higher than in the case of the square.
In addition, when pressure is applied to the projection area (S = XS × YS) of the same
piezoelectric sound element, the case of XS> YS (rectangle) with respect to XS = YS (square) is the
diaphragm. Because it is possible to reduce the displacement of this, that is, to reduce the
influence of pressure, it is suitable for a speaker mounted on a very small enclosure. As described
above, the low frequency side of the sound pressure frequency characteristic is extended, and the
improvement of the acoustic characteristic by the flattening of the sound pressure frequency
characteristic enables the low voltage drive. FIG. 3 shows an embodiment in which the
piezoelectric sounding element of the present invention is applied to a piezoelectric speaker for
portable devices. In the piezoelectric speaker 31 according to the present embodiment, the
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piezoelectric elements 23 [23A, 23B] are attached to both sides of the metal plate 22 in the same
manner as described above, and opposite to the metal plates 22 of both piezoelectric elements
23A and 23B. Piezoelectric diaphragms 25 each having electrodes 24A and 24B are provided on
the side surface, and both sides of the piezoelectric diaphragm 25 are coated with resin sheets
26 [26A, 26B] having an area larger than that of the piezoelectric diaphragm 25. Is configured.
The outer shape of the metal plate 22 is smaller than the inner periphery of the support member
to which the piezoelectric speaker 31 is attached, and the outermost periphery of the free
vibration area is formed of only the resin sheet 26. The outer shape of the piezoelectric speaker
31 is formed in a rectangular shape. The outer dimension Y × X of the piezoelectric speaker 31
is a required dimension, which is 24 mm × 30 mm in this example, and the dimension YS × XS
of the free vibration area is the required dimension, which is 22 mm × 28 mm in the present
example. Therefore, the area for bonding the piezoelectric speaker 31 to the support member, for
example, the support portion 29 of the case 28 of the portable device of FIG. 2 has a width Yc =
Xc = 1 mm of the outermost periphery of the speaker. This bonding area is a so-called bonding
margin, and is selected to have an arbitrary width Yc and Xc of the portion 26c of the resin sheet
26 alone. The bonding area is a portion 26d in this example. On the other hand, the external
dimension YK × XK of the metal plate 22 for bonding the piezoelectric elements 23 [23A, 23B]
is a required dimension, 21 mm × 27 mm in this example. Therefore, in this case, the portions
Yd and Xd of only the resin sheet 26 in the free vibration area are 0.5 mm at the outermost
periphery of the free vibration area. Further, the external dimension YP × XP of the piezoelectric
element 23 [23A, 23B] is a required dimension, which is 20 mm × 25 mm in this example. As
the resin sheet 26, a thermoplastic resin sheet, a polypropylene resin sheet, a polyester resin
sheet or the like can be selected and used.
In this example, among the resin sheets 26 covering both surfaces of the piezoelectric diaphragm
25, one of the resin sheets 26A is a polypropylene adhesive sheet, and the other resin sheet 26B
is a thermoplastic resin sheet. As shown in FIG. 3, the polypropylene adhesive sheet 26A of this
example is formed of an adhesive tape based on the polypropylene resin sheet 33 and having an
adhesive layer 34 formed on the surface on the piezoelectric element 23A side. Regarding the
thickness, the thickness of the polypropylene resin sheet 33 is, for example, about 20 to 40 μm,
and the total thickness including the adhesive layer 34 is, for example, about 60 to 80 μm.
Polypropylene is suitable for an acoustic material as a general-purpose tape, as well as heat
resistance and strength, and its mechanical resonance sharpness (Q value) specific to the
material is lower than that of other polyester and Teflon (trade name). The polypropylene
adhesive sheet 26A is attached to one surface of the piezoelectric diaphragm 25 to improve the
acoustic characteristics and to secure the insulation of the electrode 24A and the protection of
the piezoelectric element 23A. The thermoplastic resin sheet 26 B of this example has a thickness
of about 50 μm to 100 μm, and is attached to the other surface of the piezoelectric diaphragm
25 by thermocompression bonding. Thermoplastic resin can be easily adhered to the supporting
member by reheating / pressurizing the outermost peripheral portion of the completed
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piezoelectric speaker 31, that is, the adhering portion 26d to the supporting member, because
the adhesiveness reproduces by heating. It becomes possible. The Young's modulus of the
thermoplastic resin sheet 26B itself is small, and by combining with the polypropylene resin
sheet 26A described above, it is possible to provide the resin sheet portion with appropriate
strength. The metal plate 22 to which the piezoelectric element 23 is attached preferably has a
high Young's modulus. In the case of a bimorph structure in which two piezoelectric elements 23
[23A, 23B] are bonded together, a larger bending displacement can be generated as the thickness
of the metal plate 22 is thinner. Further, since it is desirable that the thickness of the
piezoelectric speaker itself is also thin, the metal plate 22 is desirably 100 μm or less. In this
example, in consideration of solderability, a metal foil of 30 μm to 50 μm in thickness of 42
alloy material is used. The piezoelectric element 23 is made of, for example, a piezoelectric
material such as PZT (lead zirconate titanate), and is desirably as thin as possible. Assuming that
the thickness of the piezoelectric elements 23A and 23B is d, the electric field E when the voltage
V is applied is E = V / d, and the electric field E between the electrodes of the piezoelectric
element 23 (ie, the metal plate 22 and the electrode 24) is large. In order to do this, it is
necessary to reduce the thickness d.
However, the reduction of the thickness d is to make the piezoelectric element 23 thinner, and by
making the thickness thin, the strength of the piezoelectric element 23 is significantly reduced,
so it is necessary to determine the balance with the shape (size, area) in consideration of the cost.
There is. In this example, each thickness d of the piezoelectric element 23 is set to 60 to 80 μm.
The electrodes 24 [24A, 24B] deposited on one side of the piezoelectric element 23 [23A, 23B]
can be formed of a metallized electrode film of, for example, Ag, Ni, Au or the like. By combining
the above-described members, the thickness D of the piezoelectric speaker 31 of this example is
(piezoelectric element 23) × 2 sheets + metal plate 22 + polypropylene adhesive sheet 26A +
thermoplastic as the portion excluding the lead wire lead-out portion Specifically, the total
amount of the resin sheet 26B is about (60 to 80 μm) × 2 + (30 to 50 μm) + (50 to 100 μm) =
260 μm to about 390 μm. When the size of the piezoelectric speaker 31 is 24 mm × 30 mm,
the volume of the piezoelectric speaker itself is approximately 24 mm × 30 mm × (0.26 to 0.39
mm) = 187.2 to 280.8 mm <3>. This is, for example, 1/3 to 1/2 of the volume of 602.9 mm <3>
for the magnet speaker having a diameter (.phi.) Of 16 mm (thickness 3 mm). As for the weight,
the above-mentioned present example piezoelectric speaker 31 is about 0.5 to 0.7 g and can be
made lighter than the magnet speaker. Next, a basic manufacturing method of the piezoelectric
speaker 31 according to the above-described embodiment will be described. The adhesion
between the piezoelectric element 23 [23A, 23B] and the metal plate 22 can be made, for
example, using an anaerobic-curing addition type ultraviolet-curing adhesive (hereinafter,
anaerobic UV adhesive), one-component epoxy resin, or other structural adhesives. It can be
done. The application of the adhesive 36 is generally applied to the piezoelectric element
bonding sites on both sides of the metal plate 22 as shown in FIG. 4 by, for example, a screen
printing method or a transfer method. Thereafter, with the piezoelectric elements 23A and 23B
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positioned at predetermined positions with respect to both sides of the metal plate 22, the
piezoelectric elements 23A and 23B are pressed against both sides of the metal plate 22 and
thereafter matched to the curing conditions of the adhesive 36, The piezoelectric elements 23A
and 23B are attached to the metal plate 22 by heating, pressurizing or irradiating with ultraviolet
rays, etc. Thereafter, as shown in FIG. 5, the piezoelectric elements 23 [23A, 23B] and the metal
plate 22 are leaded Attach the wires 28a, 28b and 27.
That is, each of the piezoelectric elements 23A and 23B is polarized in the direction of arrow a
(the same direction), and both electrodes 24A and 24B are connected via lead wires 28a and 28b.
The lead terminal 27 is led out from the metal plate 22 and the other terminal is led out. By
supplying the audio signal SG between the two terminals, the free vibration area of the
piezoelectric speaker 31 vibrates. In this case, as shown in FIG. 6, a missing portion (a relief
portion) 37 is provided in a part of the metal plate 22 to short circuit the front electrodes 24 A
and 24 B of the two piezoelectric elements 23 A and 23 B. It is also possible to lead the lead wire
28 from either one of the electrodes, for example, the electrode 24A, after this. Further, as shown
in FIG. 7, a part of the metal plate 22 is protruded and extended so as to have a terminal shape,
and another projecting terminal 39 having a symmetrical shape is formed via the protruding
terminal 22a and the insulating layer 38, Even if the electrodes 24 [24A, 24B] of the two
piezoelectric elements 23 [23A, 23B] are interconnected in the notch 37 of the plate 22 to
connect the lead 28 from the electrode 24A to the other projecting terminal 39 good. In this
case, the projecting terminal 22 a is a terminal on the metal plate 22 side, and the other
projecting terminal 39 is a terminal on the electrode 24 side of the piezoelectric element 23. As
shown in FIG. 8, the electrode-connected piezoelectric diaphragm 25 is laminated on both sides
with a polypropylene adhesive sheet 26A and a thermoplastic resin sheet 26B. At this time, it is
necessary to apply predetermined pressure and adhere so that air bubbles do not enter between
the polypropylene adhesive sheet 26A and the piezoelectric element 23 and the metal plate 22.
Further, in order to bond the thermoplastic resin sheet 26B, it is necessary to perform
predetermined pressure and heating. The heating and pressing conditions of the thermoplastic
resin sheet differ depending on the characteristics of the thermoplastic resin used, but the heat
resistance of the piezoelectric element 23 (the heat resistance mentioned here is a factor for the
deterioration of the polarization state of the piezoelectric element) There is a need. If a
thermoplastic resin having a relatively low softening temperature is selected, pressure bonding at
100 ° C. or less is possible. When laminating the polypropylene adhesive sheet 26A and the
thermoplastic resin sheet 26B on both sides of the piezoelectric vibration plate 25 and bonding
between pressure rollers (at least one of which is a heat and pressure roller), the thermoplastic
resin sheet 26B is isolated Heat and press through paper. Next, the outer shape of the
piezoelectric speaker 31 in which the piezoelectric diaphragm 25 is covered with the resin sheets
26A and 26B is removed. The outermost peripheral portion of the speaker 31 is a region of only
the resin sheet 26 [26A, 26B], and can be performed by a general flexible substrate, a generalpurpose label, a die cutting method such as a seal or the like.
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At this time, it is necessary not to cut the lead wires 27 and 28 described above. The above is the
basic manufacturing method of the piezoelectric speaker 31 of the present embodiment. Next, a
method of mounting the piezoelectric speaker 31 of the present embodiment on a device will be
described. The outermost surface of the piezoelectric speaker 31 has a polypropylene adhesive
sheet 26A on one side and a thermoplastic resin sheet 26B on the other side. The piezoelectric
speaker 31 is, for example, as shown in FIG. 9 when it is mounted on the housing 41 of the
device. The material of the housing 41 may be, for example, acrylonitrile butadiene styrene
copolymer (ABS), an aluminum alloy, a magnesium alloy, or the like. The piezoelectric speaker
attachment portion of the housing 41 has a two-step counterbore shape having a first
counterbore portion 42 and a second counterbore portion 43. In the lower side plate 44 formed
by the second counterbore portion 43, several through holes 45 for releasing the sound wave
from the speaker 31 to the outside of the device are opened. In the first counterbore portion 42,
the outer dimension of the piezoelectric speaker 31 has a margin for a dimension tolerance. After
the piezoelectric speaker 31 is housed in the first counterbore portion 42, a pressure bonding jig
incorporating a heater for pressurizing and heating only the bonding portion 26 d of the
piezoelectric speaker 31, so-called thermo-compression bonding jig 47 Pressurize and heat. That
is, by raising the heater to a predetermined temperature, the adhesive portion 26 d of only the
resin sheet 26 of the piezoelectric speaker 31 is heated and pressurized to make the first
counterbore portion 42 and the second counterbore portion of the housing 41. It is bonded to
the step 43, that is, the support 48. At this time, the thermocompression bonding jig 47 does not
touch the thermoplastic resin sheet 26B directly and presses from the polypropylene adhesive
sheet 26A side, so when the thermoplastic resin sheet 26B is softened and melted, the
thermoplastic resin is transferred to the thermocompression bonding jig 47. It prevents the sheet
26B from being adhered. FIG. 9 shows the case of a two-step counterbore, however, as shown in
FIG. It is possible. Further, as shown in FIG. 11, a projection 49 serving as a support is provided
at a position surrounding the side plate region where the through hole 45 of the housing 41 is
formed, and the piezoelectric speaker 31 is bonded on the projection 49. Is also possible. These
will be selected in accordance with the internal design of the actual device. In the above
embodiment, although two piezoelectric elements 23 [23 A and 23 B] are used, the present
invention can be applied to a configuration using only one piezoelectric element 23.
FIG. 12 shows the embodiment. In the piezoelectric speaker 51 according to the present
embodiment, the piezoelectric diaphragm 52 to which one piezoelectric element 23 is attached is
provided on one surface of the metal plate 22, and the same resin sheet as described above is
provided on both sides of the piezoelectric diaphragm 52. It is comprised by covering by 26A
and 26B. In this case, what is important is the thickness of the metal plate 22. Generally, one
having a larger Young's modulus of the metal plate 22 or one having a larger thickness is
selected as compared with the case where two piezoelectric elements are used. For example, in
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the case of the 42 alloy material, the metal plate 22 having a thickness of about 80 to 100 μm is
selected. 13 and 14 show still another embodiment of the piezoelectric speaker of the present
invention. The piezoelectric speaker 54 which concerns on embodiment of FIG. 13 is comprised
so that it can adhere | attach to a supporting member using the outermost periphery of the
polypropylene adhesive sheet 26A. That is, one surface of the piezoelectric diaphragm 25 having
the two piezoelectric elements 23 [23A, 23B] is covered with a polypropylene adhesive sheet
26A which is a size larger than the piezoelectric diaphragm 25 and the outermost periphery of
the polypropylene adhesive sheet 26A. A release paper 55 is attached to the adhesive layer, and
the other surface of the piezoelectric diaphragm 25 is coated with a resin sheet 26 B having the
same size as the piezoelectric diaphragm 25. The other resin sheet 26B may be either a
polypropylene adhesive sheet or a thermoplastic resin sheet. When the piezoelectric speaker 54
is attached to the support member, the release paper 55 is peeled off and the polypropylene
adhesive sheet 26A is directly stuck to the support member. The piezoelectric speaker 57
according to the embodiment of FIG. 14 is configured such that it can be adhered to a support
member using the outermost periphery of the polypropylene adhesive sheet 26A. That is, one
surface of the piezoelectric diaphragm 25 having the two piezoelectric elements 23 [23A, 23B] is
covered with a polypropylene adhesive sheet 26A which is a size larger than the piezoelectric
diaphragm 25 and the outermost periphery of the polypropylene adhesive sheet 26A. A release
paper 55 is adhered to the adhesive layer. In this configuration, the other surface of the
piezoelectric diaphragm 25 is not coated with the resin sheet 23B. When the piezoelectric
speaker 57 is attached to the support member, the release paper 55 is peeled off and the
polypropylene adhesive sheet 26A is directly attached to the support member. The piezoelectric
speakers 54 and 57 according to the embodiments shown in FIGS. 13 and 14 can be maintained
at the same level as that of the one using the thermoplastic resin sheet on one side.
A major difference from the embodiment of FIG. 9 is the method of bonding the piezoelectric
speaker to the support member. In FIGS. 13 and 14, although not shown, resin sheet 26A is
formed of a thermoplastic resin sheet, and resin sheet 26B. It is also possible to form a
polypropylene resin sheet or a thermoplastic resin sheet. FIG. 15 is an example of a sound
pressure frequency characteristic diagram comparing characteristics of the piezoelectric speaker
according to the present invention and the conventional magnet speaker using the configuration
of FIG. The measuring distance is 10 cm and the enclosure volume is 4 ml. In the figure, curve I is
the piezoelectric speaker of the present invention, and curve II is the conventional magnet
speaker. According to this FIG. 15, the piezoelectric speaker of the present invention can ensure
the same or more characteristics under the condition of about 4 ml of enclosure volume, as
compared with the conventional magnet speaker of 15 mm in diameter. As a result, it is possible
to secure the sound quality equal to or better than that of the magnet speaker by making use of
the thin, lightweight, low power consumption, and nonmagnetic characteristics originally
possessed by the piezoelectric speaker. Furthermore, as shown in the present invention, it
becomes possible to mount directly on a case or other supporting member, and not only for
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11
portable devices, but in combination with an ultra thin display area such as a thin display or
electronic paper, Application to the field of wall-mounted audio, robots, etc. becomes possible.
According to the piezoelectric sounding element according to the present invention, since the
resin sheet covers one surface, preferably both surfaces, of the piezoelectric diaphragm, the
sound of peaks and valleys in the vicinity of the resonance point is produced. The pressure
difference can be suppressed to flatten the sound pressure frequency characteristics. Since the
outermost periphery of the resin sheet also serves as the mounting portion of the piezoelectric
sounding element, the sound pressure in the low range can be improved by the flexible support.
By making the shape of the piezoelectric vibration element free vibration region non-square,
preferably rectangular, it is possible to flatten the frequency characteristics of sound pressure
and to increase the sound pressure level in the low region compared to the square. Can.
Therefore, it is possible to provide a piezoelectric sounding element capable of securing sound
quality, low frequency reproduction, and low voltage drive in a well-balanced manner. In
particular, the characteristics required for the application of the portable device can be secured
in a well-balanced manner, and a piezoelectric sounding element can be provided at low cost and
in consideration of the device mounting efficiency. BRIEF DESCRIPTION OF THE DRAWINGS FIG.
1A is a plan view showing an embodiment of a piezoelectric sounding element according to the
present invention. B is a cross-sectional view of the piezoelectric sounding element of FIG. 1A.
FIG. 2 is a cross-sectional view showing an example of mounting of the piezoelectric sounding
element of the present embodiment.
3A is a plan view showing an embodiment in which the present invention is applied to a
piezoelectric speaker. FIG. B is a cross-sectional view of the piezoelectric speaker of FIG. 3A. FIG.
4 is an exploded perspective view for explaining connection of the metal plate of the piezoelectric
diaphragm and the piezoelectric element according to the present embodiment; FIG. 5A is a
perspective view showing connection of a piezoelectric diaphragm according to the present
embodiment. It is sectional drawing of B principal part. FIG. 6 is a perspective view of an
essential part showing an example of an electrode connection method of the piezoelectric
diaphragm according to the present embodiment. FIG. 7 is a perspective view of the main parts
showing another example of the method of connecting electrodes of the piezoelectric diaphragm
according to the present embodiment. FIG. 8 is an explanatory view for describing coating
(lamination) of a resin sheet on a piezoelectric diaphragm according to the present embodiment;
FIG. 9 is an explanatory view showing a process of bonding the piezoelectric speaker according
to the present embodiment to a support member. FIG. 10 is a cross-sectional view showing
another example of the bonding state of the piezoelectric speaker to the support member
according to the present embodiment. FIG. 11 is a cross-sectional view showing another example
of the state of adhesion of the piezoelectric speaker to the support member according to the
present embodiment. FIG. 12 is a cross-sectional view showing another embodiment of a
piezoelectric speaker according to the present invention. FIG. 13 is a cross-sectional view
showing another embodiment of the piezoelectric speaker according to the present invention.
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FIG. 14 is a cross-sectional view showing another embodiment of the piezoelectric speaker
according to the present invention. FIG. 15 is a sound pressure frequency characteristic diagram
comparing characteristics of the piezoelectric speaker according to the present invention and the
conventional magnet speaker. FIG. 16A is a cross-sectional view showing an example of a
conventional magnet speaker. B is a plan view showing an example of a conventional magnet
speaker. FIG. 17A is a cross-sectional view showing an example of a conventional piezoelectric
buzzer. B is a plan view showing an example of a conventional piezoelectric buzzer. [Description
of the code] 21 ... piezoelectric sounding element, 22 ... metal plate, 23 [23A, 23B] ... piezoelectric
element, 24 [24A, 24B] ... electrode, 26 [26A, 26B] · · Resin sheet, 27, 28 · · · Electrodes 31, 51,
54, 57 · · · Piezoelectric speaker, adhesive, 41 · · · Case, 55 · · · release paper
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