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JP2006100955

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DESCRIPTION JP2006100955
The present invention provides a structure of a piezoelectric acoustic transducer capable of being
made into an extremely small shape with a high vibration level in the audible range while being a
piezoelectric type capable of driving with low power consumption, and a method of
manufacturing the same. The purpose is A substrate (1) having a recess (12) on one side and a
cavity (10a) adjacent to the other surface, and a part of the substrate (1) provided with the recess
(12) as a first vibrating portion (2) The first conductive layer 3 is provided on the vibrating
portion 2, the piezoelectric layer 4 is provided on the first conductive layer 3, and the second
conductive layer 5 is provided on the piezoelectric layer 4. A second actuator having at least one
through hole 11 formed at a predetermined position where the formed actuator 6 and the
actuator 6 of the first vibrating portion 2 are not formed, and the upper surface of the cavity 10a.
It is set as the structure provided with the vibration part 8a. [Selected figure] Figure 2
Piezoelectric acoustic transducer and method of manufacturing the same
[0001]
The present invention relates to bilaterally converting sound or vibration and an electrical signal,
and more particularly to a piezoelectric acoustic transducer that is required to be miniaturized,
such as an earphone, a micro receiver, a hearing aid, and a method of manufacturing the same.
[0002]
Heretofore, there are the following types of acoustic transducers of this type.
[0003]
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1
For example, in a hearing aid, a sound wave transmitted in the air is accurately captured and
converted into an electric signal, and the electric signal is subjected to signal processing such as
amplification processing and wavelength adjustment by a DSP etc. There is.
Thus, in the hearing aid, an acoustic transducer that converts sound waves into electrical signals
and an acoustic transducer that converts electrical signals into sound waves are used.
And the hearing aids in which these are incorporated are appropriately set in the user's ear canal.
[0004]
In addition, there are various methods as an acoustic transducer used for these, for example, a
method of converting a sound wave into an electric signal using change in capacity of a capacitor
due to vibration of sound wave, a current flowing in a coil to generate a magnetic field. There is a
type that generates an electric signal by converting an electric signal into a sound wave by
vibrating the diaphragm portion by the interaction force between the magnetic field and the
peripheral magnetic field.
[0005]
Here, a small acoustic transducer is required for use as a hearing aid, and a small battery is also
required, so power consumption is also required to be small.
On the other hand, in the electromagnetic method, for example, it is difficult to install a magnet
as the size is reduced, and there is a problem that the battery life is short because the power
consumption is large.
[0006]
On the other hand, the piezoelectric method is suitable for miniaturization because the
piezoelectric element can be bonded to a metal plate or in the form of a thin film, and the
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2
piezoelectric drive can realize low power consumption. Therefore, it is used as a sound source
such as a mobile phone of various small portable terminals, a sound source such as a personal
computer, or a microphone (see, for example, Patent Document 1). JP 2000-152385 A
[0007]
However, the above-mentioned conventional configuration is not used for a device which is
further required to be miniaturized, for example, a hearing aid having a very small shape which
completely enters a human ear canal.
[0008]
This is because the resonant frequency of the piezoelectric vibrating unit is increased by
reducing the area of the vibrating unit that generates or receives the vibration of the acoustic
wave as the size is reduced.
As a result, since the vibration level in the audible range of 100 to 20000 Hz, particularly in the
low frequency range, is reduced, the conversion efficiency of the acoustic wave is significantly
reduced, making it difficult to realize a piezoelectric acoustic transducer having a small shape.
[0009]
The present invention solves the above-mentioned conventional problems, and an object of the
present invention is to provide a small-sized piezoelectric acoustic transducer excellent in sound
pressure characteristics in the audio frequency band and a method of manufacturing the same.
[0010]
In order to achieve this object, the present invention comprises a substrate provided with a
recess on one side and a cavity on the other side, and a part of the substrate corresponding to the
bottom of this recess is used as a first vibrating portion. An actuator is formed by providing a
first conductive layer on one vibrating portion, providing a piezoelectric layer on the first
conductive layer, and providing a second conductive layer on the piezoelectric layer. Providing at
least one first through hole at a predetermined location where the actuator of the first vibration
unit is not formed, and providing a second vibration unit having a second through hole on the
upper surface of the cavity The configuration is as follows.
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[0011]
In the acoustic conversion device and the method of manufacturing the same according to the
present invention, a portion of the substrate provided with the recess is used as a first vibrating
portion, an actuator is provided on the first vibrating portion, and a cavity is provided adjacent to
the recess. By providing a second vibrating portion having a through hole on the upper surface of
this cavity and vibrating the second vibrating portion while resonating with the first vibrating
portion, a small size excellent in sound pressure characteristics in the audio frequency band A
piezoelectric acoustic transducer and a method of manufacturing the same can be realized.
[0012]
Embodiment 1 Hereinafter, a piezoelectric acoustic transducer according to Embodiment 1 of the
present invention will be described with reference to the drawings.
[0013]
FIG. 1 is a perspective view of a piezoelectric acoustic transducer according to a first embodiment
of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA in FIG.
FIG. 3 is a cross-sectional view of another example of the piezoelectric acoustic transducer
according to the first embodiment.
[0014]
In FIGS. 1 and 2, the substrate 1 is made of, for example, silicon or the like, and the first vibrating
portion 2 is formed at a predetermined position of the substrate 1.
The first vibrating portion 2 can be formed by removing the single side of the substrate 1 by
etching or the like to form a recess 12 on one side of the substrate 1 and forming a thin first
vibrating portion 2 at the bottom portion. .
Since the resonance frequency can be reduced by forming the first vibrating portion 2 thinner at
this time, in order to satisfy the sound pressure characteristics in the audio frequency band in a
small-sized hearing aid that enters the ear canal, 10 μm or less It is desirable that the thickness
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of the
Furthermore, by forming the first vibration unit 2 integrally with the substrate 1, it is possible to
realize a piezoelectric acoustic transducer having sound pressure characteristics in a high
accuracy, highly homogeneous audio frequency band. In particular, by using silicon as the
substrate 1 and processing this silicon by etching, it is possible to control the shape and accuracy
of the first vibrating portion 2 with high accuracy.
[0015]
Further, by forming the recess 12 on one side of the substrate 1 as described above, the portion
of the substrate 1 which is not etched around the first vibrating portion 2 functions as a frame 7
supporting the first vibrating portion 2. Further, since the frame 7 can be integrally formed with
the first vibrating portion 2, it is possible to realize the structure of the acoustic conversion
device for supporting the first vibrating portion 2 firmly and precisely. Therefore, it is also
possible to solve the problems such as the change of the sound pressure characteristics due to
the expansion coefficient, the temperature characteristics, etc. which are found in the
piezoelectric acoustic transducer by assembling different materials.
[0016]
Further, since the thickness of the frame 7 can also be processed to about 200 μm, the size can
be further reduced.
[0017]
In order to realize such a configuration of the frame 7 and the first vibrating portion 2 as an
integral structure, it is desirable to form the substrate 1 by etching, and the material used for the
substrate 1 is mechanical characteristics, processability, production It is most preferable to use
silicon from the viewpoint of properties.
As the other material, a material having excellent rigidity is suitable, and glass, quartz, single
crystal or the like can also be used.
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[0018]
Next, a first conductive layer 3 is formed on the upper surface of the first vibrating portion 2
using platinum or the like, and made of lead zirconate titanate which is a piezoelectric material
on the first conductive layer 3 The actuator 6 is formed by forming the piezoelectric layer 4 and
further laminating and forming the second conductive layer 5 made of gold on the piezoelectric
layer 4. The actuator 6 applies an electrical signal to the first conductive layer 3 and the second
conductive layer 5 to expand and contract the piezoelectric layer 4 to vibrate the first vibrating
portion 2. In the procedure of converting this electrical signal into an acoustic wave, an electrical
signal having the same frequency as the frequency of the acoustic wave to be generated is first
applied between the first conductive layer 3 and the second conductive layer 5. Elongate
according to the electric field strength with frequency. On the other hand, since the first vibrating
portion 2 is fixed to the first conductive layer 3, distortion occurs as the piezoelectric layer 4
expands and contracts. This distortion vibrates the first vibrating portion 2 in the thickness
direction, and can generate air vibration, that is, an acoustic wave.
[0019]
Here, in order to generate a large acoustic wave, it is necessary to increase the vibration
displacement of the first vibration unit 2. The vibration displacement possessed by the first
vibrating portion 2 is determined by the hardness possessed by the first vibrating portion 2; if it
is soft, the vibration displacement becomes large, and if the hardness possessed by the first
vibrating portion 2 is hard The displacement is smaller.
[0020]
In addition, the resonance frequency of the first vibration unit 2 is affected by the hardness of
the first vibration unit 2, and when the first vibration unit 2 is soft, the resonance frequency
decreases, and when it is hard, the resonance frequency increases. .
[0021]
From these facts, for example, the hardness of the first vibrating portion 2 depends on the
thickness of the first vibrating portion 2, and when the thickness of the first vibrating portion 2
is thin, the vibration displacement increases and the resonant frequency Since the vibration
displacement in the low frequency region can be increased, the acoustic conversion can be
performed more efficiently.
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[0022]
Also, by providing at least one slit-like through hole 11 at a predetermined location where the
actuator 6 of the first vibration unit 2 is not formed, the resonance frequency is reduced and the
sound pressure characteristic is improved. It can be an acoustic transducer.
[0023]
In the first embodiment, by making the shape (area) of the piezoelectric layer 4 50% to 70% of
the shape (area) of the first vibrating portion 2, the vibration displacement of the first vibrating
portion 2 is the largest. It becomes large and can perform efficient sound conversion.
[0024]
For example, when the shape of the piezoelectric layer 4 is extremely small compared to the
shape of the first vibrating portion 2, the generated force of the piezoelectric layer 4 as the
actuator 6 is small, and the entire first vibrating portion 2 is moved. The sufficient driving force
can not be obtained, and the vibration displacement of the first vibrating portion 2 becomes
small.
When the shape of the piezoelectric layer 4 is made extremely large, the hardness of the portion
bent when the first vibrating portion 2 vibrates becomes hard, and the vibration displacement of
the first vibrating portion 2 decreases.
[0025]
In addition, by making the shape of the first vibration unit 2 into any one of a circle, an ellipse,
and a polygon, a piezoelectric acoustic transducer having a desired shape and characteristics in
sound pressure characteristics, timbre, etc. is realized. be able to.
[0026]
Next, a second vibrating portion 8 a is provided at a predetermined position adjacent to the first
vibrating portion 2.
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In the first embodiment, the second vibrating portion 8a has the same thickness as that of the
first conductive layer 3, and a very thin vibrating film can be formed.
The second vibrating portion 8a is designed to resonate with the first vibrating portion 2 so that
it resonates adjacent to the first vibrating portion 2 and vibrates.
[0027]
The second vibrating portion 8a is formed of a single material, and in FIG. 1, is formed of
platinum which is the same material as the first conductive layer 3.
The second vibrating portion 8a can be formed simultaneously with the first conductive layer 3
by a thin film process by using any of chromium, platinum, titanium, iridium and gold, thereby
enhancing productivity efficiency and as a vibrating film Can also exhibit excellent
characteristics.
[0028]
In addition to this, by forming a vibrating film of inorganic oxide containing silicon dioxide by
sputtering or the like separately from the second vibrating section 8a, to realize a piezoelectric
acoustic transducer having different sound pressure characteristics and timbre. Can.
[0029]
In addition, by making the second vibrating portion 8a of a resin film, it is possible to realize a
piezoelectric acoustic transducer having different sound pressure characteristics and timbre.
[0030]
Since the vibration of the second vibrating portion 8a provided in this manner can be formed as a
very thin vibrating film made of a single material, it is excellent in sound pressure characteristics
and is also a piezoelectric acoustic having a vibration mode with little distortion. A converter can
be realized.
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In addition, the transmission loss can be minimized by disposing the second vibrating portion 8 a
in proximity to the first vibrating portion 2.
The sound pressure characteristic as the piezoelectric acoustic conversion device in the first
embodiment acts as a synthesized acoustic characteristic of the first vibrating portion 2 and the
second vibrating portion 8a.
[0031]
Therefore, by designing the shape, material, and the like of the first vibrating portion 2 and the
second vibrating portion 8a, it is possible to realize a piezoelectric type acoustic transducer
having a desired sound pressure characteristic and less distortion.
[0032]
Here, it is important that the second vibrating portion 8a form a single very thin vibrating film,
and the thickness of the second vibrating portion 8a is a very thin vibrating plate of 0.1 to 3 μm.
be able to.
With such a thickness, it is possible to significantly lower the resonance frequency, and further,
since the second vibrating portion 8a is made of a single material, the sound pressure
characteristic with the distortion of the vibration significantly reduced. Can be realized.
[0033]
As a material of the second diaphragm 8a, a metal containing any one of chromium, platinum,
titanium, iridium and gold can be used.
[0034]
It is also possible to use an inorganic oxide film containing silicon dioxide or a resin film such as
an epoxy resin, polyimide resin, Teflon (registered trademark) resin or the like, and according to
the desired sound pressure characteristics or sound quality. It is possible to realize the second
vibration unit 8a.
[0035]
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Further, by making the area of the second vibrating part 8a larger than the area of the first
vibrating part 2, the sound pressure characteristic of the second vibrating part 8a can be further
improved, and the sound pressure characteristic with less distortion can be obtained. It can be
realized.
[0036]
Further, by providing a slit-like through hole on the outer periphery of the through hole 9a of the
second vibrating portion 8a, the second vibrating portion 8a is easily vibrated, and vibration
characteristics with less distortion and less resonance frequency can be obtained. It can be set as
the piezoelectric type acoustic converter which it has.
[0037]
Next, as shown in FIG. 3, the piezoelectric pressure type is further enhanced by providing the
second vibrating portions 8a and 8b having the cavities 10a and 10b and the through holes 9a
and 9b on both surfaces of the substrate 1, respectively. An acoustic converter can be realized.
[0038]
Next, a through hole 9a is formed substantially at the center of the second vibrating portion 8a.
The through hole 9a is provided to form the cavity 10a by etching, and the etching solution or
etching gas can be made to penetrate from the through hole 9a to form the cavity 10a.
Therefore, from the viewpoint of sound pressure characteristics, it is desirable that the shape of
the through hole 9a be small.
Moreover, after forming the cavity 10a by etching, it is also possible to further improve the
sound pressure characteristic by closing the through hole 9a.
[0039]
With the above-described configuration, it is possible to realize a piezoelectric acoustic
transducer that is excellent in sound pressure characteristics in a very small audio frequency
band and has little distortion.
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[0040]
That is, each one shown in FIG. 2 or FIG. 3 includes the first vibrating portion 2 and the second
vibrating portion 8a, and both of them can generate sound or detect sound. There is.
[0041]
For example, at the time of generation of sound, an electric signal is supplied between the first
and second conductive layers 3 and 5, whereby the piezoelectric layer 4 is distorted, the first
vibrating portion 2 is vibrated, and the vibration is Can be transmitted to the vibration unit 8a,
and resonate, whereby a large sound vibration can be achieved.
[0042]
Conversely, at the time of detection of sound, the first and second vibration parts 2 and 8a
vibrate in resonance due to the sound, and the vibration is extracted as an electrical signal from
between the first and second conductive layers 3 and 5 After amplification, it plays with other
speakers.
That is, at this time, it functions as a hearing aid.
[0043]
A method of manufacturing the piezoelectric acoustic transducer configured as described above
will be described below.
[0044]
4 to 9 are cross-sectional views for explaining the method of manufacturing a piezoelectric
acoustic transducer according to the first embodiment of the present invention.
[0045]
First, a substrate 1 made of silicon as shown in FIG. 4 is prepared, and a platinum layer 14 is
formed on the upper surface of the substrate 1 by vapor deposition and sputtering.
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[0046]
Next, as shown in FIG. 5, lead zirconate titanate was formed as the piezoelectric layer 4 on the
platinum layer 14, and gold was sequentially formed as the second conductive layer 5 on the
piezoelectric layer 4. .
[0047]
Here, the formation of platinum and lead zirconate titanate is preferably sputtering from the
viewpoint of piezoelectric properties and productivity, and gold is preferably vapor deposition
and sputtering from the viewpoint of productivity.
Since the piezoelectric layer 4 formed by such a thin film process can have high crystallinity and
orientation, and has excellent piezoelectric characteristics, electro-acoustic conversion can be
efficiently performed.
[0048]
The same effect as described above can be exhibited by forming the first conductive layer 3 and
the second conductive layer 5 as thin film electrodes made of a material containing any one of
platinum, titanium, iridium, gold and chromium. be able to.
[0049]
Thereafter, a resist mask (not shown) is formed in a predetermined pattern, and then gold, lead
zirconate titanate, and platinum layer 14 are etched to form the second conductive layer 5 and
the piezoelectric body as shown in FIG. An actuator 6 consisting of the layer 4 and the first
conductive layer 3 is formed.
As an etching method at this time, either wet etching or dry etching can be used.
After the actuator 6 is formed, the resist mask is removed.
[0050]
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It is also possible to form the actuator 6 directly on the shape of the actuator 6 using a thin film
process using a metal mask or the like.
[0051]
Next, as shown in FIG. 7, a resist mask (not shown) is formed into a predetermined pattern, and
silicon etching is performed to a predetermined depth from the upper surface of the substrate 1
to form slit-like through holes 11.
After etching, the resist mask is removed.
Moreover, dry etching is desirable in order to form the slit-like through holes 11 as narrow as
possible as this etching method.
[0052]
Thereafter, as shown in FIG. 8, a resist mask 15 is formed in a predetermined pattern on the back
surface of the substrate 1 and etched from the lower surface side of the substrate 1 to obtain a
predetermined shape of a predetermined vibration portion 2 on one surface of the substrate 1.
The recess 12 and the slit-like through hole 11 are formed in the
After the recess 12 is formed, the resist mask 15 is removed.
[0053]
Here, as a method of etching the substrate 1 made of silicon, a dry process is performed by
mixing a gas suppressing etching, such as C4F8 and CHF3, and a gas promoting etching, such as
SF6, CF4, XeF2, etc. It is desirable to etch.
The etching is performed vertically from the lower surface side of the substrate 1 by repeating
the process of forming a protective film on the wall surface of the substrate 1 etched by the gas
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suppressing etching after performing a small amount of etching with a gas that promotes
etching. It can be advanced.
By using two gases having such different properties, it is possible to form the fine slit-like
through hole 11 and the recess 12 with high precision.
[0054]
Next, as shown in FIG. 9, a resist mask 16 is formed on the other surface side of the substrate 1,
and etching is performed while infiltrating the etching gas from the through holes 9a to form a
cavity 10a.
After the cavity 10a is formed, the resist mask 16 is removed.
At this time, the cavity 10 a can be efficiently formed by performing dry etching using only a gas
that promotes etching.
[0055]
Thus, the piezoelectric acoustic transducer provided with the first vibrating portion 2 and the
second vibrating portion 8a can be manufactured.
[0056]
In the first embodiment, the first vibrating portion 2 has a circular shape, but in this case, the
vibration of the vibrating portion 2 is point-symmetrical with respect to the center of the circle,
and the vibration of the first vibrating portion 2 is Distortion of vibration due to split vibration
can be minimized.
[0057]
In still another method, the vibration resonance mode of the first vibrating portion 2 is changed
by making the shape of the first vibrating portion 2 elliptical or polygonal to control the
frequency characteristics of the piezoelectric acoustic transducer. By forming the first vibrating
portion 2 having an optimal shape in accordance with a desired external shape, a piezoelectric
acoustic transducer optimum for miniaturization can be realized.
04-05-2019
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[0058]
According to the manufacturing method as described above, it is possible to produce a
piezoelectric acoustic transducer having the first vibrating portion 2 and the second vibrating
portion 8 a having a diameter of 0.5 to 5.0 mmφ.
[0059]
As described above, with such a configuration, it is possible to realize a small-sized piezoelectric
acoustic transducer having excellent sound pressure characteristics in the audio frequency band
and little distortion, and a method of manufacturing the same.
[0060]
As described above, the piezoelectric acoustic transducer according to the present invention and
the method of manufacturing the same are capable of enabling a piezoelectric acoustic
transducer that is compact and has sufficient sound pressure characteristics even in the audio
frequency band. It can be applied to applications such as ultra-small speakers and microphones.
[0061]
1 is a perspective view of a piezoelectric acoustic transducer according to Embodiment 1 of the
present invention, and FIG. 2 is a sectional view of the piezoelectric acoustic transducer
according to Example 1 of the present invention. FIG. 2 is a sectional view for explaining a
method of manufacturing the piezoelectric acoustic transducer. Cross sectional view same cross
sectional view same cross sectional view same cross sectional view same cross sectional view
Explanation of sign
[0062]
Reference Signs List 1 substrate 2 first vibration unit 3 first conductive layer 4 piezoelectric layer
5 second conductive layer 6 actuator 7 frame 8a, 8b second vibration unit 9a, 9b through hole
10a, 10b cavity 11 through hole 12 recess 14 platinum layer 15 resist mask 16 resist mask
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