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DESCRIPTION JP2006135924

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DESCRIPTION JP2006135924
An object of the present invention is to secure a larger sound pressure in a piezoelectric
sounding body used for various speakers and a sounding device using the same. In particular, a
resonance plate 6 is disposed on a diaphragm 3 constituting a piezoelectric sounding body 1 via
a frame 5. As a result, since the sound generated by vibrating the diaphragm resonates in the
space formed by the diaphragm, the frame and the resonance plate, a larger sound pressure can
be secured. [Selected figure] Figure 2
Piezoelectric sounding body and sounding device using the same
[0001]
The present invention relates to a piezoelectric sounding body used as a small speaker used for a
hearing aid or the like and a sounding device using the same.
[0002]
Generally, in portable electronic devices such as mobile phones and hearing aids, compactness
and power saving are listed as essential conditions for the electronic components that constitute
them.
[0003]
And under such circumstances, as a sounding body for constructing an acoustic system of a small
electronic device, piezoelectric sounding using a piezoelectric drive electrode as an actuator for
vibrating a diaphragm from the viewpoint of small number of component parts and excellent
power saving property The body was used.
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1
[0004]
In addition, as prior art literature information regarding this invention, patent document 1 is
known, for example.
Japanese Patent Application Laid-Open No. 11-7283
[0005]
However, in applications where the size is limited, the sound pressure is proportional to the drive
area and amplitude of the diaphragm, so it has been difficult to secure the sound pressure in a
compact piezoelectric speaker.
[0006]
Then, this invention solves such a problem, and it aims at ensuring bigger sound pressure in a
piezoelectric sounding body and a sounding apparatus using the same.
[0007]
In order to achieve this object, the present invention has a structure in which a resonance plate is
disposed via a frame to a diaphragm which particularly constitutes a piezoelectric speaker.
[0008]
With such a configuration, the sound generated by vibrating the diaphragm resonates in the
space formed by the diaphragm, the frame and the resonance plate, and a larger sound pressure
can be secured.
[0009]
Hereinafter, an embodiment of the present invention will be described with reference to the
drawings.
[0010]
FIG. 1 shows a sound producing apparatus in which the piezoelectric sounding body 1 according
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to an embodiment of the present invention is disposed inside a housing 2, which is used as a
microminiature speaker provided in a mobile phone, an inner ear type hearing aid, etc. It is a
thing.
[0011]
The basic structure is a configuration in which the piezoelectric sounding body 1 is disposed
inside the housing 2 having the opening 2a, and the housing 2 is produced by emitting a sound
from the piezoelectric sounding body 1 disposed inside the housing 2 It is a small-sized and
directivity sounding device with a structure that produces sound from the opening 2a provided
in the.
[0012]
Further, as shown in FIG. 2, the piezoelectric sounding body 1 disposed inside the housing body
2 is a piezoelectric drive region on the upper surface of the tongue-like vibration region 3 a
provided at the center of the thin plate-like diaphragm 3. The frame 5 is provided on the outer
peripheral portion of the diaphragm 3 so as to surround the tongue-shaped vibration area 3a
provided with the piezoelectric drive electrode 4 based on the structure in which the fourth
element 4 is disposed. A resonance plate 6 is provided so as to cover, and a sound hole 5a for
emitting the sound formed inside the piezoelectric sounding body 1 to the outside is provided on
the side surface of the frame 5.
[0013]
The piezoelectric drive electrode 4 has a piezoelectric thin film 4c made of PZT (lead zirconate
titanate) interposed between an upper electrode 4a made of Au and a lower electrode 4b made of
Pt, and between the upper electrode 4a and the lower electrode 4b When a voltage is applied to
the piezoelectric thin film 4c, the piezoelectric thin film 4c disposed therebetween is flexed, and
this flexing causes the vibrating region 3a of the diaphragm 3 to vibrate.
[0014]
Further, in the piezoelectric sounding body 1, since the upper surface side of the diaphragm 3 is
surrounded by the frame 5 and the resonance plate 6, the vibration generated by the
piezoelectric drive electrode 4 is particularly resonated by the resonance plate 6 facing the
diaphragm 3. Because the sound pressure of the sound emitted from the diaphragm 3 is
amplified by this resonance and output from the sound hole 5a, a larger sound pressure can be
secured without increasing the size of the diaphragm 3.
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[0015]
Further, as shown in FIG. 3, the frequency band of the piezoelectric speaker 1 can be expanded
by making the self resonance frequency f1 in the vibration region 3a of the diaphragm 3
different from the self resonance frequency f2 of the resonance plate 6 It is
[0016]
That is, since the self-resonant frequency f1 is determined by the length in the vibration area 3a
of the diaphragm 3, the range in the vibration area 3a is limited. However, the self-resonance
frequency of the vibration area 3a in the diaphragm 3 is By making f 1 different from the selfresonant frequency f 2 of the resonance plate 6, the range emitted from the piezoelectric speaker
1 is a frequency characteristic 9 in which the frequency characteristic 7 of the vibration region 3
a of the diaphragm 3 and the frequency characteristic 8 of the resonance plate 6 are combined.
As a result, since the vibration range 3a of the diaphragm 3 and the self-resonant frequencies f1
and f2 of the resonance plate 6 are made to coincide with each other, a wider sound range can be
secured.
[0017]
In addition, when such a piezoelectric sounding body 1 is used, as shown in the frequency
characteristic 9, the peak characteristic is shown for a specific frequency such as the selfresonant frequency f1, f2, etc. Since variations in the frequency characteristics are large, the
frequency characteristics shown by the solid line are not shown in FIG. 1 or FIG. 2 although the
resin elastic body (not shown) is coated on the surface of the diaphragm 3 in order to suppress
this. The peak characteristics can be suppressed as shown in FIG.
[0018]
In addition, when coating the resin elastic body which suppresses the peak characteristic
described above, if using an organo type silane member whose hardness is low among resin
materials, acoustic radiation by the resin elastic body provided on the diaphragm 3 is used. Of
the piezoelectric thin film 4c exposed at the end face of the piezoelectric drive electrode 4 by
covering the resin elastic body so as to cover the piezoelectric drive electrode 4 as well as the
diaphragm 3 region. The exposed surface can also be covered, and the moisture resistance of the
piezoelectric thin film 4c in this portion can be secured.
[0019]
Further, as shown in FIG. 2, when the resonance plate 6 is attached to the frame 5 by providing
the sound holes 5 a in the frame 5 at the lower end portion of the frame 5, that is, the contact
portion with the diaphragm 3. Since the end face of the frame 5 is a flat surface, the mounting
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accuracy of the resonance plate 6 is improved, and the sound quality deterioration of the
piezoelectric speaker 1 due to the mounting operation of the resonance plate 6 can be
suppressed.
[0020]
When the piezoelectric sounding body 1 is formed, first, as shown in FIG. 4, the lower electrode
4b is formed on the upper surface of the silicon substrate 11 obtained by processing a siliconbased member such as Si or SiO2 into a predetermined shape for forming the diaphragm 3. The
Pt electrode member 12 for forming the piezoelectric film is coated by high frequency sputtering,
and the PZT member 13 for forming the piezoelectric thin film 4 c is formed on the Pt electrode
member 12.
[0021]
Next, the PZT member 13 is formed into a predetermined shape by photolithographic processing,
and an insulating film 14 of a photosensitive resist as an etching mask is applied to the outer
peripheral end of the PZT member 13 and its peripheral portion.
The application of the insulating film 14 partially exposes the lower electrode 4b in order to form
the terminal portion 15 for external connection in the lower electrode 4b.
Thereafter, the Au electrode member 16 for forming the upper electrode 4a on the piezoelectric
thin film 4c and the insulating film is covered by vapor deposition.
[0022]
Next, the unnecessary Au electrode member 16, the insulating film 14 and the Pt electrode
member 12 are removed by dry etching.
Here, the reason why the insulating film 14 is left on the surface of the outer peripheral frame 1
is that the insulating film 14 stabilizes the electric field at the end face of the piezoelectric drive
electrode 4 and suppresses the occurrence of migration in this region. It is for ensuring the
insulation in the peripheral part of the thin film 4c.
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[0023]
Next, dry etching is performed to leave the outer peripheral portion of the lower surface of the
silicon substrate 11 forming the diaphragm 3 so that the outer peripheral portion is utilized as
the frame 3b and the thin plate portion inside thereof is utilized as the vibration region 3a. The
diaphragm 3 is formed.
Also, the hollow portion below the diaphragm 3 is used as an acoustic hole 3c.
[0024]
When the PZT member 13 for forming the piezoelectric thin film 4c is formed by sputtering on
the Pt electrode member 12 for forming the lower electrode 4b described above, the crystal axis
of Pt in the Pt electrode member 12 is oriented, By preferentially orienting the crystal axis of PZT
of the PZT member 13 laminated on the surface of the Pt electrode member 12, the adhesion
between the lower electrode 4b and the piezoelectric thin film 4c can be improved, and
delamination can be suppressed. By laminating the piezoelectric thin film 4c directly on the lower
electrode 4b, the adhesive layer used for this interlayer bonding can be removed, and the sound
pressure characteristics of the piezoelectric sounding body 1 can be improved.
The piezoelectric properties of the piezoelectric thin film 4c are also improved by enhancing the
adhesion between the lower electrode 4b and the piezoelectric thin film 4c.
[0025]
Then, the piezoelectric sounding body 1 can be formed by integrating the frame 5 and the
resonance plate 6 on the diaphragm 3 thus formed as shown in FIG.
[0026]
The piezoelectric sounding body according to the present invention has the effect of improving
the sound pressure characteristics of the piezoelectric sounding body, and is particularly useful
in small speaker applications such as hearing aids.
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[0027]
An exploded perspective view of the sound generation device according to an embodiment of the
present invention. A cross-sectional view of the sound generation device. A frequency
characteristic diagram showing a sound pressure characteristic of a piezoelectric sound
generator used in the sound generation device.
Explanation of sign
[0028]
DESCRIPTION OF SYMBOLS 1 piezoelectric sounding body 2 accommodation body 2a opening
part 3 diaphragm 4 piezoelectric drive electrode 5 frame 5a sound hole 6 resonance plate
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