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DESCRIPTION JP2009267616

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DESCRIPTION JP2009267616
A piezoelectric speaker using a conventional PZT has poor compatibility with a CMOS
semiconductor process used for a dedicated driver IC in terms of its manufacturing process, so
the piezoelectric speaker and a signal processing circuit are integrated. It was difficult to do. Even
with bulk MEMS technology and piezoelectric thin films, integration with signal processing
circuits formed on semiconductor substrates has not been achieved. The signal processing circuit
had to be provided separately, which made it difficult to miniaturize. An acoustic transducer
according to the present invention includes a signal processing circuit formed on a
semiconductor substrate, and a diaphragm unit that functions as an acoustic transducer
integrally with the substrate. In the acoustic transducer, the diaphragm portion is partitioned by
a space portion or cavity formed between the diaphragm and the substrate. [Selected figure]
Figure 1
Acoustic transducer and method of manufacturing the same
[0001]
The present invention relates to an acoustic transducer and a method of manufacturing the same.
More specifically, the present invention relates to an acoustic transducer such as a microphone
using a piezoelectric body, a micro speaker, and an ultrasonic sensor.
[0002]
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1
2. Description of the Related Art In recent years, with the progress of downsizing and thinning of
mobile phones, parts used for mobile phones are required to be particularly compact and low in
back. Conventionally, microspeakers used in mobile phones are dynamic types. Generally, a
dynamic type micro speaker is excellent in driving force, but it is difficult to reduce the height
because it incorporates a voice coil and a magnet. Furthermore, the large current consumption is
also a drawback.
[0003]
For this reason, in the microspeaker, more attention has been paid to dynamic to piezoelectric
speakers. This is because, unlike the dynamic type, the piezoelectric type can be made thinner,
and has the advantage of smaller current consumption. The piezoelectric speaker currently put to
practical use is configured by forming and bonding electrodes on both sides of a thin plate
formed by ceramic firing or a thin plate obtained by cutting a ferroelectric crystal. Examples of
the ceramic firing material include lead zirconate titanate (hereinafter referred to as PZT).
[0004]
While the piezoelectric speaker has the above-mentioned advantages, the sound pressure level is
lower than that of the dynamic speaker. Therefore, in order to ensure the same sound pressure
as that of the dynamic type speaker, a dedicated driver circuit for driving the piezoelectric type
speaker with a high voltage is required. Further, in the micro speaker, it is known that the sound
pressure level significantly decreases in a low frequency range of 1 kHz or less, and the sound
quality is also degraded in terms of the frequency characteristics of the reproduced sound. For
example, Patent Document 1 describes a conventional piezoelectric speaker.
[0005]
As other microspeakers, studies of a type using MEMS (Micro Electro Machining Systems) are
also being conducted (Non-Patent Document 1).
[0006]
Patent Document 1: JP-A-2004-96225 "Piezoelectric Microspeaker with Compressive Nitride
Diaphragm", Seung Hwan Yi, Eun Sok Kim, IEEE 16th.
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2
International Micro Electro Mechanical Conference (MEMS '02), pp. 269-263, 2002.
[0007]
As described above, from the viewpoint of space saving, there is an increasing demand for
downsizing of speakers used in small electronic devices such as mobile phones. However, when a
conventional piezoelectric speaker is used, a dedicated driver IC is required to secure a sufficient
sound pressure level. Also in the cellular phone, the dedicated driver IC is configured separately
from the microspeaker, and the dedicated driver IC and the microspeaker are currently
implemented separately. As described above, in the piezoelectric speaker, since a dedicated signal
processing circuit for securing the sound pressure level is required, the current situation is that
the area saving is hindered.
[0008]
In the piezoelectric speaker described in Patent Document 1, the piezoelectric speaker and the
signal processing circuit can not be integrated, and sufficient miniaturization can not be achieved
due to the difference in the manufacturing process described above.
[0009]
Although the piezoelectric speaker described in Non-Patent Document 1 uses bulk MEMS
technology and a piezoelectric thin film, integration with a signal processing circuit formed on a
semiconductor substrate has not yet been achieved.
The signal processing circuit had to be provided separately, and it was still difficult to
miniaturize.
[0010]
The present invention has been made in view of such problems, and an object thereof is to
provide a compact and high-performance acoustic transducer by integrating a transducer such as
a speaker and a signal processing circuit.
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[0011]
In order to achieve the above object, the present invention is characterized in that a signal
processing circuit and a signal terminal for performing signal input / output with respect to the
signal processing circuit are formed on a semiconductor substrate. A semiconductor circuit
portion, and a laminated body integrally formed on the semiconductor circuit portion with the
semiconductor circuit portion, wherein the laminated body is formed on the semiconductor
circuit portion and has a cavity inside. A first metal layer formed on the insulating layer in a
region corresponding to the cavity, a piezoelectric layer formed on the first metal layer, and the
piezoelectric layer And a second metal layer formed to be opposite to the first metal layer in a
region corresponding to the cavity, the second metal layer and the second metal layer being
sequentially laminated, and the first metal layer and the second metal layer are formed. The
metal layer and the signal terminal are electrically connected An acoustic transducer,
characterized in that it comprises and.
Here, the laminate functions as a diaphragm of an acoustic transducer.
[0012]
The invention according to claim 2 is the acoustic transducer according to claim 1, wherein the
signal processing circuit is formed by a semiconductor manufacturing process.
[0013]
The invention according to claim 3 is the acoustic transducer according to claim 1 or 2, wherein
the signal processing circuit transmits the first metal film and the second metal layer based on an
audio input signal. The drive circuit is characterized by comprising a drive circuit that controls a
voltage applied to the piezoelectric layer, and a booster circuit that generates a voltage higher
than an input power supply voltage and supplies the voltage to the drive circuit.
[0014]
The invention as set forth in claim 4 is the acoustic transducer according to claim 3, wherein the
signal processing circuit further comprises a harmonics generation unit for generating a
frequency component of natural number times the frequency component of the input signal. It is
characterized by
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[0015]
The invention according to claim 5 is the acoustic transducer according to any one of claims 1 to
3, wherein the piezoelectric layer is made of aluminum nitride.
As the piezoelectric body, it is also possible to use zirconia oxide (ZnO), PZT or the like.
Since aluminum nitride can be formed into a film at a temperature of about 300 to 400 ° C., it
does not damage the signal processing circuit, and the material is made of aluminum and
nitrogen. It is optimal in that it does not have to bring in materials.
[0016]
The invention according to claim 6 comprises the steps of: forming a first insulating layer on a
semiconductor circuit portion in which a signal processing circuit and a signal terminal of the
signal processing circuit are formed on a semiconductor substrate, and the first insulating layer
Forming a recessed region in the semiconductor device, depositing amorphous silicon in the
recessed region, depositing a second insulating layer on the first insulating layer and the
amorphous silicon, and the second insulating layer A step of sequentially laminating a first metal
layer, a piezoelectric layer and a second metal layer thereon, wherein the first metal layer and the
second metal layer correspond to the region corresponding to the recessed region Forming an
electrode pair facing each other with the piezoelectric layer interposed therebetween, and
connecting the first metal film and the second metal film and the signal terminal of the signal
processing circuit with metal wiring, Said first metal layer Forming an opening formed through
the piezoelectric layer and the second metal layer to be connected to the amorphous silicon, and
selectively removing the amorphous silicon through the opening; And a step of manufacturing an
acoustic transducer.
The recessed area functions as a cavity formed in the first insulating layer.
[0017]
The invention according to claim 7 is the manufacturing method according to claim 6,
characterized in that the piezoelectric body is made of aluminum nitride.
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[0018]
According to the present invention, a compact and high-performance acoustic transducer is
realized by forming an acoustic transducer using a piezoelectric body as a diaphragm on a
substrate including a signal processing circuit and integrating the acoustic transducer and the
signal processing circuit board. can do.
[0019]
Hereinafter, embodiments of the present invention will be described with reference to the
drawings.
[0020]
FIG. 1 is a structural view showing the configuration of the acoustic transducer of the present
invention.
FIG. 1A shows a top view seen from above the surface of the substrate 1 constituting the acoustic
transducer, and FIG. 1B shows a cross-sectional view seen from the side of the substrate 1.
The acoustic transducer of the present invention is characterized in that a signal processing
circuit formed on a semiconductor substrate and a diaphragm unit which functions as an
acoustic transducer integrally with the substrate are formed.
In the acoustic transducer, the diaphragm portion is partitioned by a space portion or a cavity
formed between the diaphragm portion and the substrate.
[0021]
Hereinafter, first, an outline of the configuration of the present invention will be described, and a
method of manufacturing the acoustic transducer of the present invention will be described so as
to facilitate understanding of the configuration. FIG. 1A is a top view of the substrate 1 on which
the acoustic transducer is formed, as viewed from above. The state which removed the protective
layer formed in the outermost surface mentioned later is shown.
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[0022]
A thin film layer 10 made of a piezoelectric material such as aluminum nitride is formed on the
substrate 1, and circular first electrodes 9 and second circular electrodes are formed on the
upper and lower sides of the thin film layer 10 in the thickness direction. An electrode 11 is
formed. The thin film layer 10 and the two electrodes 9 and 11 are laminated and configured as
an integral laminate. Here, the shape of the two electrodes is not limited to a circular shape, and
may be any shape as long as it has an acoustic conversion effect as an acoustic transducer such
as an elliptical shape. The first electrode 9 and the second electrode 11 are connected to the
signal output terminals 2b and 2a, respectively.
[0023]
(B) of FIG. 1 shows the configuration of the cross section along line Ib-Ib of (a). Referring to (b),
the insulating film 5 is formed on the substrate 1 and the thin film layer 10 is further formed. A
cavity 6 is formed in the insulating layer 5 corresponding to the formation region of the first
electrode 9 and the second electrode 11. A signal processing circuit 18 is formed on the
substrate 1. The signal processing circuit 18 and the acoustic transducer are connected via the
signal output terminals 2b and 2a.
[0024]
FIG. 2 is a view showing the acoustic transducer of the present invention in another cross section.
(A) is a top view, and is the same as (a) of FIG. (B) of FIG. 2 is a figure which shows the structure
of the cross section in the IIb-IIb line which does not straddle an electrode in (a). The cavity 6 in
the insulating layer 5 is formed via the via holes 17a and 17b as described later. As is clear from
(b), the diaphragm portion 19 is separated from the substrate 1 at least on the cross section C-D,
and provides mechanical freedom to function as an acoustic transducer. The shape of the cavity
6 is shown as a low-height cylindrical shape in FIGS. 1 and 2, but is not limited thereto. That is, it
should be noted that any shape corresponding to the shape of the two electrodes 9 and 11 may
be used as long as it can function as an acoustic transducer. Next, the function of the acoustic
transducer of the present invention having the above-described specific structure will be
described.
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[0025]
FIG. 3 is a diagram showing the configuration of the acoustic transducer of the present invention
and the function including signal processing in association with each other. FIG. 3A is a block
diagram specifically showing the function of the signal processing circuit including the
diaphragm portion of the acoustic transducer. (B) shows the cross-sectional structure of the
acoustic transducer, which is the same as (b) in FIG. As shown in (a), the acoustic transducer of
the present invention includes a signal processing circuit unit 18 and a diaphragm unit 19. The
signal processing circuit unit 18 includes signal input terminals 21a and 21b to which an audio
input signal from the outside is input, and a preamplifier 24 for amplifying the audio input
signal. After passing through the preamplifier unit 24, the audio signal is further amplified by the
class D amplifier 25 and amplified to a voltage level required to drive the diaphragm unit 19. The
drive signal from the class D amplifier 25 is connected to the diaphragm 19 via the output
terminals 22a and 22b.
[0026]
The signal processing circuit 18 further includes a booster circuit and a voltage regulator unit 23
for boosting and stabilizing a power supply voltage supplied from an external battery or the like
via the input terminal 20. The booster circuit / voltage regulator unit 23 boosts and stabilizes the
power supply voltage supplied from the battery or the like to a predetermined voltage higher
than the power supply voltage, and supplies it to the class D amplifier 25. By supplying a
predetermined voltage higher than the power supply voltage to class D amplifier 25, a high drive
voltage is applied to diaphragm portion 19, and a high sound pressure level can be obtained. The
acoustic transducer of this embodiment is a micro speaker.
[0027]
Other means for driving the diaphragm 19 include a class A amplifier, a class AB amplifier and
the like, but a class D amplifier is particularly preferable in view of low distortion. The booster
circuit includes, for example, a charge pump circuit, and as the voltage regulator circuit, a circuit
including a DC-DC converter is particularly preferable.
[0028]
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Referring to (b) of FIG. 3, in the acoustic transducer of the present invention, the signal
processing circuit 18 is formed on the substrate 1, and the diaphragm portion 19 formed above
the substrate 1 via the cavity is a substrate 1. It is characterized in that it is integrally formed
with the The signal processing circuit 18 and the diaphragm unit 19 are connected by output
electrodes 22 a and 22 b formed on the substrate 1. Although the signal input terminals 21a and
21b and the power input terminal 20 are not shown in FIG. 3B, they can be formed in the same
manner as the output electrodes 22a and 22b. Next, a method of manufacturing the acoustic
transducer of the present invention will be described together with more specific examples.
[0029]
4 and 5 are flow diagrams illustrating the steps of making the acoustic transducer of the present
invention. In each of the drawings, a cross-sectional view for explaining each step from (1) to (9)
and a description corresponding to each cross-sectional view are sequentially shown from the
top to the bottom. In the process described below, the signal processing circuit 18 and the
electrodes 2a and 2b for connecting the signal processing circuit to an external circuit and the
like are already formed on the substrate 1. The signal processing circuit 18 and the electrodes 2a
and 2b are formed using a conventional semiconductor circuit manufacturing process. An
exemplary process is described below.
[0030]
In the step (1) of FIG. 4, first, the first insulating film 5 is formed. A portion 3 surrounded by a
dashed line in (1) indicates the semiconductor circuit portion 3 in which the signal processing
circuit 18 is already formed on the semiconductor substrate 1. Furthermore, in the
semiconductor circuit portion 3, terminals 2a and 2b for inputting or outputting a signal from
the signal processing circuit 18 are formed. The protective layer 4 is already formed on the
semiconductor substrate 1. As the protective layer 4, a silicon oxide film, a silicon nitride film, a
polyimide, or a combination thereof is used.
[0031]
In the step (1), first, the first insulating film 5 is deposited and formed on the semiconductor
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substrate 1. Here, the semiconductor substrate 1 is preferably silicon or a compound
semiconductor such as gallium arsenide (GaAs). As the first insulating film 5 formed on the
semiconductor substrate 1, a silicon oxide film or a silicon nitride film is preferable. In the
present embodiment, a silicon oxide film was deposited to a thickness of 5.0 μm by plasma CVD.
A feature of the manufacturing process of the acoustic transducer of the present invention is that
the formation of the first insulating film 5 is performed at a low temperature so as not to damage
the signal processing circuit 18 already formed on the substrate. The deposition temperature of
the first insulating film 5 is preferably 300 ° C. or less, and plasma CVD, sputtering or the like
can be used. Subsequently, a recess region 6 which will later constitute a cavity region is formed
in the first insulating film 5 using the RIE (Reactive Ion Etching) method. The depth of the
recessed area 6 is, for example, 4.0 μm.
[0032]
The shape of the recessed area 6 is determined according to the shape of the diaphragm to be
formed. For example, if the diaphragm defined by the circular shaped upper and lower electrodes
is formed, the recessed area 6 may be substantially cylindrical in shape. However, as described in
detail in step (9) later, recessed region 6 has a shape including a region for a via hole portion to
be formed to remove amorphous silicon to be a sacrificial layer by dry etching. Please be careful.
[0033]
In the step (2), after the recessed region 6 is formed, the entire first insulating film 5 is covered
to be formed by depositing amorphous silicon 7. For example, a 6.0 μm-thick is deposited by
sputtering. The formation temperature of amorphous silicon is preferably 300 ° C. or less so as
not to damage the signal processing circuit 18 formed on the substrate 1. Amorphous silicon can
be deposited even at room temperature and is preferred because it does not damage the signal
processing circuit 18. After depositing amorphous silicon 7 on the entire surface, the surface is
polished by CMP (Chemical Mechanical Polishing) to remove amorphous silicon. It is preferable
to finish the CMP when the amorphous silicon in a place other than the recess region is removed.
In practice, it is necessary to completely remove the amorphous silicon outside the recess region
by overpolishing. Also, over-polish needs to be adjusted to minimize the recession of the
amorphous silicon in the recessed area 6.
[0034]
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In the step (3), after removing the amorphous silicon 7 other than the recessed region 6, the
second insulating film 8 is deposited and formed. The second insulating film 8 is deposited to a
thickness of 1.0 μm by plasma CVD or sputtering. As the second insulating film 8, a silicon oxide
film or a silicon nitride film is particularly preferable, but it is more preferable to use the same
material as the first insulating film 5.
[0035]
In the step (4), after the second insulating film 8 is formed, a first metal film 9 to be a lower
electrode (first electrode) is deposited later. As a material of the first metal film 9, for example,
tungsten / titanium can be used. Each layer is deposited to a thickness of 0.2 μm / 0.05 μm by
sputtering, and then patterned by photolithography to form the lower electrode 9 having a
predetermined shape by dry etching.
[0036]
In the step (5), after the lower electrode 9 is formed, an aluminum nitride thin film 10 is
deposited and formed as a piezoelectric layer on the entire surface. The aluminum nitride thin
film 10 is deposited to a thickness of 1.0 μm by sputtering. It is desirable to deposit the
aluminum nitride thin film 10 at a film forming temperature of 300 ° C. or less so as not to
damage the signal processing circuit 18 already formed on the substrate 1. After depositing the
aluminum nitride thin film 10, a second metal film 11 to be an upper electrode (second
electrode) is deposited by sputtering. As a material of the second metal film 11, for example,
aluminum / titanium can be used. Each layer is deposited to a thickness of 0.2 μm / 0.05 μm by
sputtering, and then patterned by photolithography to form the upper electrode 11 having a
predetermined shape by dry etching.
[0037]
In the acoustic transducer of the present invention, a diaphragm is formed by the two electrodes
of the lower electrode 9 and the upper electrode 11, and the aluminum nitride thin film 10
sandwiched between these electrodes. Therefore, the lower electrode 9 and the upper electrode
11 may have substantially the same shape except for the connection wiring portion with the
outside. For example, as shown in (a) of FIG. However, the shape is not limited to the circular
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11
shape, and the lower electrode 9 and the upper electrode 11 may have different shapes as long
as they function as the diaphragm of the acoustic transducer.
[0038]
Advances in sputtering technology make it possible to produce a highly crystalline aluminum
nitride film stably in the temperature range of 300 to 400 ° C. Therefore, the matching with the
CMOS semiconductor process is also good, and there is an advantage that the film can be formed
even after the signal processing circuit 18 is formed on the substrate 1.
[0039]
Further, as the first metal film and the second metal film constituting the lower electrode 9 and
the upper electrode 11, respectively, aluminum, platinum, tungsten, titanium, titanium tungsten
or molybdenum is preferable. The first metal film and the second metal film may be used in
combination with different materials. Next, the subsequent steps (6) to (9) will be described with
reference to FIG.
[0040]
In the step (6), after the upper electrode 11 is formed, a silicon oxide film 12 is deposited and
formed on the entire surface. The silicon oxide film 12 is deposited to a thickness of 0.2 μm by
sputtering. The silicon oxide film 12 is used to protect the aluminum nitride layer 10 from the
damage when peeling off the resist after the formation of the via hole in the step (9) described
later. In general, aluminum nitride is easily damaged by alkali, and this step is necessary to
prevent aluminum nitride from being exposed to a resist stripping solution.
[0041]
In the step (7), after the silicon oxide film 12 is deposited, the via holes 13, 14 and 15a for taking
electrical contact with the terminals for extracting signals from the lower electrode 9, the upper
electrode 11 and the signal processing circuit 18, respectively. , 15b are formed by RIE. In the
subsequent wiring formation step, in order to ensure step coverage in the via holes of the wiring,
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the shape of each via hole is preferably a forward tapered shape.
[0042]
In the step (8), after the via holes are formed, the metal film 16 is deposited and formed on the
entire surface. The metal film 16 is deposited to a thickness of 0.6 μm by sputtering. The
material of the metal film 16 can be, for example, aluminum / titanium. After depositing the
metal film 16, wiring is formed by patterning and dry etching. Wiring is formed to electrically
couple the upper electrode 11 and the lower electrode 9 sandwiching the aluminum nitride layer
10 to the input / output terminals 2 a and 2 b of the signal processing circuit 18 formed on the
substrate 1. be able to. As an electrical means for coupling the first metal film and the second
metal film to the input terminal of the signal processing circuit or the like, a wiring forming step
of a semiconductor process can be used, or a bonding wire or the like can be used.
[0043]
In the step (9), after the wiring 16 is formed, the via holes 17a and 17b are connected to the
amorphous silicon 7 formed in the recess region 6 in the first insulating film 5 in the abovementioned step (2). Form. It should be noted that (9) of FIG. 5 shows a cross section different
from the cross sections of (1) to (8) described above which do not extend over the wiring layer to
simplify the description. That is, for example, it corresponds to the cross section on the line C-D
in (a) of FIG. The via holes 17a and 17b are used to remove the amorphous silicon 7 to be a
sacrificial layer by dry etching. For selective removal of the amorphous silicon 7, sulfur
hexafluoride (SF6) and zenonfluoride (XeF2) are preferable as an etching gas. In particular,
Zenon fluoride is optimum from the viewpoint of the selectivity to the silicon oxide film. After the
via holes 17a and 17b are formed, the amorphous silicon 7 is selectively removed by dry etching
with, for example, Zenon fluoride, and a cavity 6 defined by the recess region and the second
insulating film 8 in step (2) is formed. Ru.
[0044]
By the above-described steps (1) to (9), the diaphragm 19 operating as a piezoelectric layer of
aluminum nitride is formed above the semiconductor substrate 1 on which the signal processing
circuit 18 is formed. The diaphragm 19 in the acoustic transducer of the present invention is
configured as a laminate formed by sequentially laminating the second insulating film 8, the
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lower electrode 9, the aluminum nitride layer 10 and the upper electrode 11 on the cavity 6. .
[0045]
In the diaphragm 19, when a voltage is applied to the aluminum nitride layer 10 through the
upper electrode 11 and the lower electrode 9, the aluminum nitride layer 10 expands and
contracts. The aluminum nitride layer 10 can be vibrated by the bimorph effect of the second
insulating film 8, the upper electrode 11 and the lower electrode 9. The audio input signal
voltage from the outside is subjected to signal processing in the signal processing circuit 18 and
applied to the lower electrode 9 and the upper electrode 11 via the input / output terminals 2a
and 2b.
[0046]
The above-described manufacturing process can form an acoustic transducer having the unique
configuration of the present invention. The substrate 1 including the signal processing circuit
and the diaphragm unit configured as a laminate can be integrally formed by one manufacturing
process. By forming an acoustic transducer using aluminum nitride as a diaphragm above the
signal processing circuit and integrating the acoustic transducer and the substrate including the
signal processing circuit, a compact and high-performance acoustic transducer can be realized.
[0047]
FIG. 6 is a block diagram illustrating another signal processing circuit configuration that may be
utilized with the acoustic transducer of the present invention. In the signal processing circuit
having the configuration shown in FIG. 3A, it is generally known that reproduction of bass is
difficult with a micro speaker. In order to solve this problem, it is known to use the missing
fundamental phenomenon. Instead of difficult-to-play bass, by playing its overtones (voice signal
with a frequency several times the natural frequency of the voice signal of a certain frequency), it
is audible in spite of playing in the reproducible band of the speaker Good bass feeling can be
improved.
[0048]
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In addition to the signal processing circuit shown in FIG. 3A, the signal processing circuit shown
in FIG. 6 improves the bass feeling of the reproduced sound from the speaker by including a
circuit for inserting harmonics in the output signal. . Specifically, a fundamental frequency
component is extracted from the audio input signal input to the input terminals 21a and 21b
through the low pass filter 26. Further, the overtone generation unit 27 creates an audio signal
having a frequency that is a natural number multiple of the fundamental tone. Thereafter, the
output from the class D amplifier 25 and the output from the overtone generation unit 27 are
added together in the addition units 28a and 28b. The summed signal drives the acoustic
transducer 19 through the terminals 22a, 22b. By further including the harmonic overtone
generation unit 27, it becomes possible to correct the frequency characteristics of the
reproduced sound of the acoustic transducer. By improving the bass feeling, it has the effect of
improving the overall sound quality from the acoustic transducer.
[0049]
By applying the signal processing circuit having the configuration shown in FIG. 6 to the acoustic
transducer of the present invention, it compensates for the lack of bass feeling that was difficult
with the microspeaker, and the microspeaker is smaller and has high sound pressure level and
excellent sound quality. Can be realized.
[0050]
The present invention can be used for small-sized, high-performance acoustic transducers.
In particular, it can be used for systems such as mobile phones.
[0051]
It is a structural diagram which shows the structure of the acoustic transducer of this invention.
It is a structural view showing the composition which saw the acoustic transducer of the present
invention from another section. It is the figure which matched and demonstrated the structure of
the acoustic transducer of this invention, and the function containing signal processing. FIG. 2 is
a flow diagram illustrating the steps of making the acoustic transducer of the present invention.
FIG. 2 is a flow diagram illustrating the steps of making the acoustic transducer of the present
invention. FIG. 6 is a circuit block diagram illustrating another signal processing circuit
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configuration that can be used with the acoustic transducer of the present invention.
Explanation of sign
[0052]
DESCRIPTION OF SYMBOLS 1 substrate 2a, 2b signal output terminal 3 semiconductor circuit
part 4 protective film 5 1st insulating film 6 recessed area (cavity) 7 amorphous silicon 8 2nd
insulating film 9 lower electrode (1st electrode) 10 thin film layer (nitriding Aluminum 11 Upper
electrode (second electrode) 12 Silicon oxide film 13, 14, 15a, 15b, 17a, 17b Via hole 16 Wiring
layer 18 Signal processing circuit section 19 Acoustic transducer (diaphragm) 20 Power supply
voltage input terminal 21a, 21b Voice Signal input terminal 22a, 22b Output electrode 23 Stepup circuit and voltage regulator section 24 Pre-amplifier 25 Class D amplifier 26 Low-pass filter
27 Harmonic generation section 28a, 28b Addition section 29 Acoustic transducer input terminal
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