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JP2007329533

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DESCRIPTION JP2007329533
The present invention relates to a piezoelectric sounding body used as a speaker, and its object is
to widen a reproduction band. A speaker according to the present invention includes a support
6A and a plurality of vibrating body sound pieces 1 to 5 supported by the support 6A and having
different sizes. By changing the size of each of the vibrating body sound pieces 1 to 5, it is
possible to reproduce sound in a wide band and to suppress unnecessary vibration and reduce
acoustic vibration loss. [Selected figure] Figure 1
Piezoelectric speaker
[0001]
The present invention relates to a piezoelectric speaker used for a small speaker used in various
electronic devices, a micro speaker for a hearing aid, and the like.
[0002]
As a conventional piezoelectric speaker, there is one shown in FIG.
9 shows a rubber 31 applied to the metal diaphragm 35, a piezoelectric 32 of PZT bonded to the
back of the metal diaphragm 35 by adhesion, 33 an edge for holding the end face of the metal
diaphragm 35, 34 Is a frame covering the edge 33.
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[0003]
In addition, as prior art document information regarding the invention of this application, patent
document 1 is known, for example. Unexamined-Japanese-Patent No. 11-164396 gazette
[0004]
The conventional piezoelectric speaker has a configuration in which one piezoelectric material
32 of PZT is provided on one metal diaphragm 35, and the reproduction characteristic is
determined by the resonance characteristic of itself, so that reproduction of a wider band sound
can be obtained. Was difficult. That is, the mechanical resonance sharpness Qm of the vibration
due to the piezoelectric body 32 and the metal vibrating plate 35 is high, and the acoustic
reproduction band is narrowed.
[0005]
An object of the present invention is to provide a piezoelectric speaker capable of reproducing
wide-band sound.
[0006]
And in order to achieve this object, in the present invention, a plurality of vibrating body sound
pieces having different sizes are supported by a support.
[0007]
As described above, since the piezoelectric sounding body of the present invention is made by
supporting a plurality of vibrating body sound pieces having different sizes by a support,
vibrators of a plurality of different bands can be formed, and reproduction of sound in a wide
band is realized. In addition, since the piezoelectric thin film is directly formed on a
predetermined portion of the lower electrode, unnecessary vibration can be suppressed and
acoustic vibration loss can be reduced.
[0008]
FIG. 1, FIG. 2, and FIG. 3 respectively show structural examples of the piezoelectric sounding
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body.
The structure shown in FIG. 1 is composed of five vibrating body sound pieces 1 to 5 and a
support 6A supporting all of them, and the support 6A has the ends of five vibrating body sound
pieces 1 to 5 different in size. It has a held structure.
The vibrating body sound pieces 1 to 5 have different sizes, specifically different lengths, so that
the resonant frequencies of the vibrating body sound pieces 1 to 5 are made different.
Similarly, FIG. 2 shows a configuration in which five vibrating body sound pieces 7 to 11 are
supported by a support 6B. The shape of the vibrating body sound pieces 7 to 11 is different
from the length in the longitudinal direction as well as the width dimension, and the resonance
frequencies of the vibrating body sound pieces 7 to 11 are made different. FIG. 3 is characterized
in that the width and length of the three vibrating body sound pieces 12 to 14 supported by the
support 6C are different from each other, and the resonance frequencies of the vibrating body
sound pieces 12 to 14 are different. In these FIGS. 1 to 3, since the widths and lengths of the
vibrating body sound pieces 1 to 5, 7 to 11, and 12 to 14 are different among the supports 6A to
6C respectively, the resonance frequencies are different from each other. Thus, the sound can be
faithfully reproduced in a wide band range.
[0009]
A more detailed description will now be given on the basis of the embodiment of FIG. Reference
numerals 15 and 16 in FIG. 3 denote lead wires for feeding the vibrating body sound pieces 12
to 14, respectively, for guiding an AC signal from the outside to the vibrating body sound pieces
12 to 14. Reference numerals 17 and 18 denote feed terminals for connecting the lead wires 15
and 16 to the piezoelectric sounding body. Next, the cross section of the portion of the broken
line 19 shown in FIG. 3 will be described with reference to FIG.
[0010]
Reference numerals 20 and 21 in FIG. 4 denote silicon (Si) plates. The silicon plate 20 plays a
role as a substrate, and the silicon plate 21 plays a role as a diaphragm. Reference numeral 22
denotes a lower electrode, which forms a lower electrode of a piezoelectric thin film 23 of lead
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titanate / lead zirconate (PZT). The PZT piezoelectric thin film 23 converts the electrical signal
into mechanical displacement. Reference numeral 24 denotes an insulating film made of an
insulating resin, and serves both as insulation and protection so that the electrode material
provided on the PZT piezoelectric thin film 23 does not cause migration. Reference numeral 25
denotes an upper electrode for applying a voltage from above the PZT piezoelectric thin film 23.
26 is a cavity as a sound hole.
[0011]
Based on the cross-sectional view of FIG. 4, the process of the process will be sequentially
described with reference to FIG. 5. As shown in FIG. 5A, steam is added to a silicon plate 20
having a predetermined thickness, for example, 500 μm, as a support, and heat treatment is
performed at a temperature of 1000 ° C. or more to oxidize the surface of the silicon plate 20.
Form a thin film. The silicon plate 21 is further stacked thereon by anodic bonding, and both the
silicon plate 20 and the silicon plate 21 are sandwiched from both sides of the oxide film of SiO
2, after which the thickness of the silicon plate 21 is processed to about 50 μm. Form a
substrate. The SiO 2 film layer is omitted (in FIG. 5A) because it is very thin (about 0.2 μm).
[0012]
Then, as shown in FIG. 5B, the lower electrode 22 is formed on the upper surface of the silicon
plate 21 by high frequency sputtering, preferably using Pt or the like as an electrode material, as
shown in FIG. 5C. The piezoelectric thin film 23 of PZT is formed on the lower electrode 22.
[0013]
By this configuration, the adhesion between the lower electrode 22 and the piezoelectric thin film
23 is improved, and the orientation of the PZT crystal axis of the piezoelectric thin film 23 is
promoted, and a stable piezoelectric thin film 23 can be formed.
Moreover, peeling can be suppressed by the improvement of adhesiveness. Further, the adhesive
for transfer, which has conventionally been required for bonding the piezoelectric thin films 23,
is adhesiveless according to this embodiment. Furthermore, by forming the lower electrode 22 on
the entire silicon plate 21, the conductor resistance is reduced, so the electro-acoustic conversion
efficiency is improved.
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[0014]
Next, as shown in FIG. 5D, the piezoelectric thin film 23 of PZT is photolithographically
processed into vibrating body sound pieces 12 to 14 with one free end. Here, the piezoelectric
thin film 23 of PZT may be an ellipse or a polygon other than a rectangle, and is not particularly
limited as long as it can be photolithographically processed. Then, as shown in FIG. 5E, an
insulating film 24 of photosensitive resist as an etching mask is applied on the periphery of the
piezoelectric thin film 23 of PZT and the lower electrode 22 to expose the lower electrode
terminal 27. In this way, the electric field at the end face of the electrode can be stabilized by the
insulating film 24 in the peripheral portion, migration of the electrode can be prevented, and the
insulation in the peripheral portion of the piezoelectric thin film 23 can be secured.
[0015]
Then, as shown in FIG. 5F, the upper electrode 25 is formed on the piezoelectric thin film 23 and
the insulating film 24 preferably by vapor deposition of Au. The upper electrode 25 can apply a
stable uniform electric field to the piezoelectric thin film 23 of PZT, and the upper electrode 25 is
formed on the insulating film 24 and the entire piezoelectric thin film 23 to reduce the conductor
resistance. The electro-acoustic conversion efficiency is improved.
[0016]
Next, as shown in FIG. 5G, a photoresist film 28 is formed on a predetermined portion of the
other surface of the silicon plate 20, and as shown in FIG. 5H, the SiO2 film is dry etched from
this surface. It is exposed and a cavity as a sound hole 26 is formed below the piezoelectric thin
film 23. Then, the resist film 28 is removed to obtain a piezoelectric speaker.
[0017]
Next, as shown in FIG. 5I, the lead wire 15 is fixed to the lower electrode terminal portion 27
with a conductive paste, and the lead wire 16 is similarly fixed to the upper portion of the upper
electrode 25 with a conductive paste. Thereby, a piezoelectric speaker is obtained.
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[0018]
With this configuration, the resonance frequency can be set to a predetermined value, and the
band of the sound to be reproduced can be freely set, so that a wide band sound can be
reproduced. Furthermore, since the cavity as the sound hole 26 is formed below the piezoelectric
thin film 23 and the vibrating body sound pieces 12 to 14, the electro-acoustic conversion
efficiency is improved.
[0019]
FIG. 6 shows the frequency at which the piezoelectric sounding body obtained by FIG. 5
reproduces and the characteristic of reproducing wide-band sound. As shown in FIG. 6, the lower
band A of the sound to be reproduced is a long vibrating body sound piece 14, and the middle
band B is a medium length vibrating body sound piece 12, and the high band C is a shorter
vibrating body sound. By playing back with the piece 13, it is possible to play broadband sound.
[0020]
Also, an example of mounting and assembling as a device is shown in FIG. 7 below. FIG. 7 is a
mounting assembly view, and the element of the piezoelectric sounding body obtained in FIG. 5
(i) is hereinafter referred to as the piezoelectric sounding body 30, and the outer cover 29 and
the piezoelectric sounding body 30 are integrated in the sound storing outer case 36. After the
lead wires 15 and 16 penetrate the outer lid 29 and are drawn out, the portion of the
piezoelectric sounding body 30 is coated with an organosilane material to a thickness of 5 μm
or less. If the organosilane material is thicker than this, the drive impedance of the acoustic
vibration increases due to the addition of mass, causing drive loss. In addition, if it is coated at an
extremely thin (0.01 μm) or less, it is difficult to obtain the moisture resistance effect.
[0021]
FIG. 8 shows a side view of the configuration of FIG. 7 in detail. The piezoelectric sounding body
30 of FIG. 8 is fixed to the bottom of the sound storing outer case 36 by an adhesive, and the
sound from the diaphragm obtained by energizing the piezoelectric sounding body 30 is emitted
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from the upper portion of the piezoelectric sounding body 30 It comes off to the left through the
left opening of the storage outer case 36. On the other hand, the sound in the lower direction of
the vibrating body sound pieces 12 to 14 is blocked by the sound storing outer case 36 and
works as an air damper, so that the resonance Qm near the resonance point is reduced and
frequency characteristics slow against frequency change can be obtained. . The sound sources
from the vibrating body sound pieces 12 to 14 are once squeezed at the opening and emitted
from one place, so that a uniform sound source free from distortion and uniform in phase is
secured. As a result, it is possible to provide an ultra-compact piezoelectric thin film type more
stable sound generator with frequency characteristics.
[0022]
As described above, since the piezoelectric sounding body according to the present invention
uses a plurality of vibrating body sound pieces having different sizes, it is possible to reproduce
sound in a wide band, which is extremely useful as a speaker.
[0023]
The perspective view which shows one Embodiment of this invention The perspective view which
shows other embodiment of this invention The perspective view which shows further another
embodiment of this invention Sectional drawing (a)-(i) of FIG. 3 shows a manufacturing process
Cross-section frequency characteristic diagram exploded perspective view showing mounting and
assembly state Cross-sectional view showing conventional mounting and assembly state
Explanation of sign
[0024]
Reference Signs List 1 vibration body sound piece 2 vibration body sound piece 3 vibration body
sound piece 4 vibration body sound piece 5 vibration body sound piece 6A support 7 vibration
body sound piece 8 vibration body sound piece 9 vibration body sound piece 10 vibration body
sound piece 11 vibration 12 vibrating body sound pieces 14 vibrating body sound pieces 20
silicon plate 21 silicon plate 22 lower electrode 23 piezoelectric thin film of PZT 24 insulating
film 25 upper electrode 26 sound hole 27 lower electrode terminal portion
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