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JP2006109193

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DESCRIPTION JP2006109193
A diaphragm made of silicon manufactured by a MEMS method is provided which has a function
suitable as a diaphragm for a photoacoustic conversion device without deformation. A light
emitting unit (2) and a light receiving unit (3) are disposed at a position facing a vibrating unit
(1a) of a diaphragm (1A) having a pressure receiving surface, and the light emitting unit is
disposed in the vibrating unit (1a). A photoacoustic conversion device made of silicon which
emits light from (2), receives reflected light from the vibrating portion (1a) by the light receiving
portion (3), and detects a change in position of the vibrating portion (1a) And a slit (1s) is formed
on the diaphragm (1A) by the MEMS semiconductor manufacturing method. [Selected figure]
Figure 1
Vibrator plate of photoacoustic converter
[0001]
The present invention relates to a diaphragm of a photoacoustic transducer, and more
particularly to the structure of the diaphragm.
[0002]
A conventional acoustoelectric converter using light (hereinafter referred to as a photoacoustic
converter).
An example of will be described with reference to FIG. Of the light emitting element 2 and the
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light receiving element 3 mounted on the frame 4 with the planar diaphragm 1 shown in FIG. 9
fixed to the frame 4, the light emitted from the light emitting element 2 is reflected by the
diaphragm 1 The reflected light is received by the light receiving element 3 to convert the
position of the diaphragm 1, that is, the vibration into an electrical signal.
[0003]
Basically, the diaphragm 1 for converting sound into an electrical signal is preferably sensitive to
the sound pressure, and the diaphragm 1 is light in weight, high in strength and appropriate in
compliance with this requirement. In recent years, silicon thin films have attracted attention
because of their reliability against environmental changes, and MEMS (Micro Electro Mechanical
System) are used to produce thin films etc. and to perform microfabrication on the micron level.
It is a well-known fact that it becomes possible to achieve the purpose, and that this method
produces a diaphragm for an acoustic transducer (for Electric Condenser Micrphon) made of
silicon.
[0004]
However, it is well known that silicon diaphragms are heavy, hard and brittle due to their nature.
With regard to the weight, which is a defect as a diaphragm for an acoustic conversion device, it
is possible to compensate for this defect by being able to obtain a thickness of 1/10 or less than
the thickness of a conventional diaphragm. However, in terms of hardness and brittleness, silicon
diaphragms still have that property, and have a structure for fixing the outer periphery of the
diaphragm, similar to the structure of a conventional diaphragm for general acoustic transducers.
It is not a theory that it is difficult to increase the amplitude of the diaphragm.
[0005]
Overcoming this drawback is crucial as a diaphragm for acoustic conversion devices, and in
particular it can be said that it is an important issue for the diaphragms of photoacoustic
conversion devices. Regardless of the silicon diaphragm, it is common practice to increase the
compliance of the diaphragm by slitting the diaphragm, and the inventor of the present
application has already slitted the diaphragm. It is proposed in Japanese Patent Application No.
2001-351355. However, when the diaphragm made of silicon is manufactured by the processing
method of the MEMS method in particular, the following problems have been encountered.
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[0006]
Of course, the portion to be the diaphragm is made in the form of a thin film. It is well known
that stress is applied to this thin film portion during film formation and tension is applied to this
thin film portion, and slitting this thin film portion tears and tears this thin film portion, that is,
the thin film subjected to tension. As a matter of course, when the torn part is pulled, the side
part constituted by this slit is deformed, and depending on the shape of the slit, the side part and
the corner part are warped, and the desired shape is What can not be obtained is a well-known
fact among those who are involved in MEMS. Therefore, it has been extremely difficult to obtain
a desired flatness for a silicon thin film obtained by the MEMS method, that is, a diaphragm in
which the outer peripheral portion of the silicon diaphragm is slit.
[0007]
Incidentally, the inventor of the present invention also produced the diaphragm by the MEMS
method and confirmed the above-mentioned event. Hereinafter, with reference to FIGS. 10 to 12,
the 0.39 mm thick silicon substrate 1b is processed by the MEMS method, and the thin film
portion, that is, the vibrating portion 1a has a thickness of about 1 μm to 1.5 μm. As seen, the
size of the vibrating portion 1a is 1.9 mm square, and the outer peripheral portion of the thin
film vibrating portion 1a is integrated with the outer substrate Ib as shown in FIG. The silicon
substrate 1b in a state in which the side 12 and the corner 13 of the portion 1a are completely
fixed is a square of 3.4 mm on a side, and the vibrating portion 1a is the diaphragm 1 for a
photoacoustic conversion device of 1.9 mm square as described above. Obtained. When this
diaphragm 1 was measured at a sound pressure of 1 kHz and 94 db, the diaphragm 1 having an
amplitude of about 0.1 μm was obtained by Peek to Peek.
[0008]
Furthermore, slit 1 s processing was performed to diaphragm 1 in this state as follows. Referring
to FIG. 11, the slit 1s is processed along the side portion 12. The width of the slit 1s is about 3
μm, and the width of the cantilever suspension 11 configured by the slit 1s is about 10 μm. The
diaphragm 1 processed in this manner is warped at a pair of corner portions 13 of the vibrating
portion 1a as shown in FIG. 12, including a portion near the connecting portion between the
vibrating portion 1a and the tip portion of the cantilever suspension 11 In other words, extreme
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shape change occurred, and it was not possible to obtain the shape of the diaphragm requiring
the desired flatness.
[0009]
When the diaphragm 1 is deformed as shown in FIG. 12, it is impossible to mount other
components such as an optical sensor in a later process, that is, not only the assembly as a
photoacoustic conversion device becomes impossible, but also this deformation However, since
other problems also occur, it can be said that the shape is not suitable as the diaphragm 1 for the
photoacoustic conversion device. However, when the amplitude performance of the diaphragm 1
is measured, Peek to Peek obtains an amplitude of about 20 μm or more at 1 kHz and 85 db,
and with respect to the diaphragm 1 having no slit 1s described in FIG. The cantilevered
suspension 11 configured of the slit 1s and the slit 1s can obtain an extremely large amplitude
more than necessary, and the slit 1s exerts an effective effect on the amplitude of the vibrating
portion 1a Together.
[0010]
Further, in the photoacoustic conversion device, the vicinity of the central portion of the
vibrating portion 1a is naturally the reflection portion, but in order to improve the reflection
efficiency, the reflection portion of the diaphragm 1 is coated with a metal such as gold. When
coated, there is a defect that distortion is easily generated in the diaphragm 1. Patent documents
1: Unexamined-Japanese-Patent No. 2003-153396, Paragraph 0021, FIG.
[0011]
The present invention is to solve the problems of the diaphragm for the photoacoustic transducer
in the prior art. That is, it is an object of the present invention to provide a diaphragm made of
silicon manufactured by the MEMS method, in particular, having a function suitable as a
diaphragm for a photoacoustic conversion device without deformation.
[0012]
The inventor of the present invention creates the thin film, that is, the diaphragm by the MEMS
method as described above, and performs slit processing along with the phenomenon that the
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outer peripheral portion of the diaphragm is largely deformed when slit processing is performed
on the diaphragm. As a result, an event in which the amplitude increase of the diaphragm was
extremely large was also confirmed at the same time.
[0013]
Then, in order to obtain a diaphragm having a larger amplitude than that of the conventional
diaphragm by the diaphragm formed by the conventional MEMS method, the thin film portion,
that is, the diaphragm is slit even when the thin film portion, that is, the diaphragm is slitted. It is
important that the diaphragm has a desired flatness without deformation, and in the shape of a
cantilever-like suspension configured by slit processing, the length dimension is a length suitable
for the amplitude. Made clear that it is desirable.
[0014]
In order to solve the problem, when observing the event, that is, the deformed shape of the
diaphragm, that is, the state of warpage, attention was paid to the fact that the direction of
warpage is definite.
Referring to FIG. 12, only the outside of the diaphragm, particularly the pair of opposing corner
portions 13, 13 is curved upward, and the other pair of corners 13, 13 maintain flatness.
The meaning of this deformed state is that before the slit 1s processing, it is presumed that the
tension in the diaphragm 1 works in the central direction of the diaphragm 1 from the side 12
and the corner 13 of the diaphragm 1 It is.
[0015]
That is, the phenomenon that the diaphragm 1 is warped means that the thin film portion, that is,
the diaphragm 1 is under tension before the slit 1s is processed. However, if the direction of
tension is irregular, the direction of deformation, that is, the warpage and the direction are also
irregular, and does not appear as warpage in a certain direction as in the prior art. Therefore,
based on the fact that the tension works in the central direction, the deformation of the
diaphragm 1 is prevented by devising the arrangement of the cantilever-like spences 11
constituted by the slit 1s or the slit 1s. Was judged to be possible.
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[0016]
For example, in the slit processing 1s in the experimental example, the corner portion 13 around
the vibrating portion 1a is equal to a state separated from the substrate 1b, and this portion is
largely deformed by the tension in the central direction of the diaphragm 1 . Moreover, since the
cantilevered suspension 11 is disposed parallel to the direction from the corner 13 to the side 12
of the diaphragm 1, the cantilevered suspension 11 is also naturally affected by the tension, so
that the diaphragm 1 is deformed. Both are deformed along the way.
[0017]
From the above, it is arranged that the cantilevered suspension 11 different from the
conventional example is disposed, specifically, in the case where the cantilevered suspension 11
is disposed on the side 12 and the corner 13 of the diaphragm 1, vibration is caused.
Arrangement that provides a fixing portion of cantilevered suspension 11 radially outward from
the central portion of plate 1 and from a connecting portion of side portion 12 and corner
portion 13 of vibrating portion 1a and cantilevered portion 11 to the outside. As a structure, the
tension applied to the outer peripheral portion of the diaphragm 1 is fixed in the radial direction,
and deformation to the side portion 12 and the corner portion 13 of the vibrating portion 1a,
that is, warpage, particularly warpage at the corner portion 13 occurs. The structure is made
difficult, the deformation of the entire diaphragm 1 is within an allowable range, and a
diaphragm for a practical photoacoustic transducer is obtained.
[0018]
According to the diaphragm for the photoacoustic conversion device of the present invention, the
diaphragm made of silicon manufactured by the MEMS method does not deform, and the
compliance is large, and the function suitable as the diaphragm for the photoacoustic conversion
device is provided. be able to.
[0019]
[0020]
The first to eighth embodiments of the diaphragm according to the present invention will be
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described with reference to FIGS. 1 to 8, respectively. The parts common to the conventional
example, such as the slit 1s and the cantilever suspension 11, are the same .
The method of manufacturing the diaphragm 1A of Example 1 shown in FIG. 1 processes a
silicon substrate of 0.39 mm in thickness by the MEMS method in the same manner as in the
above-mentioned experimental example, The thin film portion constituting a square vibration
portion 1a whose side portion 12 of the vibration portion 1a viewed from the front is 1.24 mm,
and the thin film portion constituting a cantilevered suspension 11 for supporting the vibration
portion 1a And at an angle of 45 degrees from the center line of the diaphragm, the direction
from the outside of the diaphragm 1, that is, the radial direction from the center of the vibrating
portion 1a, is about a width from the corner 13 A thin film portion having a length of 89 μm
and a length of 900 μm (hereinafter referred to as a radiation direction thin film portion).
) Was produced.
[0021]
Furthermore, as shown in FIG. 1, slit processing having a width of about 6 μm is applied to the
side 12 of the square in the vibrating part 1a and the radial direction thin film part provided at
the corner 13 of the vibrating part 1a. Thus, as shown in FIG. 1, a square vibration supported by
a cantilevered suspension 11 having a width of 20 μm at the connecting portion of the vibrating
portion 1a and a width of 10 μm at the fixing portion and a length of approximately 800 μm
The plate 1A is prepared, and the thin film portion constituting the vibrating portion 1a is further
thinned except the outer peripheral portion of the vibrating portion 1a, and the thickness of the
vibrating portion 1a is further thinned from about 1 μm to 1.5 μm. There is.
Accordingly, the outer peripheral portion of the vibrating portion 1a is surrounded by the
vibrating portion 1a having a height of 1 to 1.5 μm and a width of about 60 μm and a rib 14
integrally formed.
[0022]
Furthermore, in the case of the present embodiment, the reflecting portion made of metal coat or
the like originally provided at the central portion of the diaphragm 1 is a gold coating of the
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diaphragm 1 and all of the 11 parts of the cantilever suspension in the diaphragm 1A. And
coated to complete a diaphragm 1A for a photoacoustic transducer. Of course, it is also possible
to coat only the central portion of the diaphragm 1A.
[0023]
Furthermore, as Examples 2 and 3, as shown in FIGS. 2 and 3, diaphragms (hereinafter,
diaphragm 1B and diaphragm 1C) in which the lengths (360 μm and 60 μm, respectively) of
the cantilever suspension 11 are changed are described. In addition, as in the fourth, fifth, and
sixth embodiments, as illustrated in FIGS. 4, 5, and 6, a diaphragm in which the vicinity of the
connecting portion of the cantilever suspension 11 with the vibrating portion 1 a has an arc
shape. (The suspension 11 has a length of 530 μm) (hereinafter referred to as a diaphragm 1D).
And the diaphragm (in the following, the diaphragm 1E and the diaphragm 1F) in which the
length of the cantilever suspension 11 is changed to 140 μm and 0 mμ (the length of the
minimum width portion) respectively in the diaphragm shape. Furthermore, as Examples 7 and 8,
radial lines from the center of the vibrating portion 1a as shown in FIGS. 7 and 8, respectively,
that is, lines divided at 45 degrees as viewed from the front of the diaphragm. A diaphragm
having eight cantilevered suspensions 11 disposed outside the diaphragm, and a diaphragm in
which the length of the cantilever suspension is changed in the shape of the diaphragm
(hereinafter referred to as a diaphragm 1G (suspension And the diaphragm 1H (suspension
length 20 μm). ) Was produced.
[0024]
In the case of the diaphragm 1G and the diaphragm 1H in which the cantilever suspension 11 is
disposed at the 45 degree division, it goes without saying that the cantilever suspension 11 is
disposed at a portion corresponding to the side portion 12 of the diaphragm and at the corner
13a. In the case of the present embodiment, as shown in the figure, a corner 13a is newly
provided on the side 12, and the cantilever suspension 11 is arranged outward from the corner
13a. is there. Of course, depending on the purpose of use, the side portion 12 may be provided
with no corner portion 13a.
[0025]
The above-described diaphragm is a diaphragm having a shape that can withstand practical use,
that is, the flatness of the diaphragm without causing deformation as in the conventional
example, and each diaphragm 1 is made to have a sound pressure of 1 kHz and 94 db. When the
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amplitude of Peek to Peek is measured, the diaphragm 1A becomes a diaphragm having an
amplitude of about 2.98 μm, and in the following order, the diaphragm 1B is 1.16 μm, the
diaphragm 1C is 0.372 μm, and the diaphragm is To obtain diaphragms with amplitude values
of 1D: 2.14 μm, diaphragm 1E: 0.864 μm, diaphragm 1F: 0.624 μm, diaphragm 1 G: 0.412
μm, diaphragm 1 H: 0.232 μm It was possible.
Effect of the embodiment
[0026]
In a diaphragm made of silicon or the like manufactured by a semiconductor manufacturing
method such as MEMS, it is on a line passing through the top of the polygonal corner 13 from
the center of the diaphragm as in this embodiment, and the vibration By forming the shape of the
cantilever-like suspension 11 radially outward from the corner of the plate, the deformation is
significantly reduced, and the effect of obtaining flatness that can withstand practical use is
exhibited, and in particular, a silicon thin film having a thickness of 3 μm or less In the
diaphragm, it is possible to apply substantially free slit 1s processing without causing
deformation.
[0027]
In addition, as in the thin film diaphragm made of silicon or the like manufactured by a
semiconductor manufacturing method such as MEMS, slit processing 1s with a thin film (3 μm
or less) which was impossible conventionally is possible as in the embodiment of the present
invention. Because the amplitude of the diaphragm can be significantly increased compared to
that without slitting, and the slits ls provided on the outer peripheral portion of the diaphragm
can be made into a desired shape, It is also possible to arbitrarily set the length and the width of
the cantilever suspension 11 constituted by the slit 1 s, and there is an advantage that a free
design can be made according to the purpose.
[0028]
Furthermore, in the preparation of a thin film diaphragm made of silicon or the like
manufactured by a semiconductor manufacturing method such as MEMS, as in the embodiment
of the present invention, the shape of the cantilever suspension 11 is a connecting portion with
the vibrating portion 1a or a cantilever shape. It has been confirmed that the occurrence of
resonance in the high frequency band of the diaphragm is changed by providing the desired arcshaped portion at the suspension 11 and its proximal end.
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Therefore, it is possible to change the shape of the cantilevered suspension 11 depending on the
purpose of use, and it has the effect of obtaining the freedom of design.
[0029]
Also, in the means for changing the shape of the cantilevered suspension 11 depending on the
purpose of use, the thickness of the cantilevered suspension 11 may be formed to have a
different thickness at a desired position or to be given a corrugated shape. Of course, the effect
of gaining design freedom is even greater.
[0030]
Also, in the manufacture of a thin film diaphragm made of silicon or the like manufactured by a
semiconductor manufacturing method such as MEMS, as in the example of the present invention,
the width dimension of the cantilevered suspension 11 of the diaphragm of thin film (3 μm or
less) is 50 μm. In the following, preferably, by setting the width to 20 μm or less, the amplitude
can be easily obtained, and an effect that the mass productivity is not impaired can be obtained.
[0031]
Furthermore, in the preparation of a thin film diaphragm made of silicon or the like
manufactured by a semiconductor manufacturing method such as MEMS, it is preferable that the
slit 1s width dimension of the thin film (3 μm or less) diaphragm be smaller as in the
embodiment of the present invention. As it becomes smaller, a phenomenon occurs in which the
wall constituting the slit is attracted by static electricity.
Therefore, as in the present embodiment, by setting the width dimension to 0.5 μm or more and
20 μm or less according to the purpose, it is possible to obtain the shape of the diaphragm
stable, and the mass productivity is not impaired. Be
[0032]
In manufacturing a thin film diaphragm made of silicon or the like manufactured by a
semiconductor manufacturing method such as MEMS, as in the embodiment of the present
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invention, the surface of a thin film (3 μm or less) diaphragm, preferably the outer peripheral
portion (side portion) of the diaphragm 12. By providing a rib structure thicker than the
thickness of the diaphragm on the corner portions 13), it is effective in preventing deformation
of the diaphragm itself, and a large effect can be obtained to obtain a practical flatness.
Furthermore, the rib portion may be provided in the vicinity of the central portion of the
diaphragm, which can be used depending on the purpose of use, and an effect of increasing the
degree of freedom in design can be obtained.
[0033]
In manufacturing a thin film diaphragm made of silicon or the like manufactured by a
semiconductor manufacturing method such as MEMS, as in the embodiment of the present
invention, the reflector provided on the reflective surface side of the thin film (3 μm or less)
diaphragm is the outside of slit 1s processing It is possible to prevent the deformation of the
diaphragm by exerting up to the end, and by coating the reflection material up to the
cantilevered suspension 11, the resonance generation frequency of the suspension portion or the
diaphragm portion, the frequency characteristic, etc. Can be changed, and the effect of increasing
the degree of freedom in design can be obtained.
[0034]
Furthermore, not only the reflector but also the diaphragm or the cantilever-like suspension 11
can laminate at least a plurality of different materials, so that the resonance frequency and
frequency characteristics of the diaphragm can be changed. It has the effect of increasing the
degree.
[0035]
1 (a) is a perspective view showing a diaphragm according to a first embodiment of the present
invention, FIG. 1 (b) is a plan view showing the same diaphragm, and FIG. 1 (c) is a partially
enlarged view in FIG. FIG. 1D is a cross-sectional view showing the same diaphragm.
Fig.2 (a) is a perspective view which shows the diaphragm which is Example 2 of this invention,
FIG.2 (b) is a top view which shows the same diaphragm, FIG.2 (c) is the elements on larger scale
in FIG.2 (b). FIG. 2D is a cross-sectional view showing the same diaphragm.
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3 (a) is a perspective view showing a diaphragm according to a third embodiment of the present
invention, FIG. 3 (b) is a plan view showing the same diaphragm, and FIG. 3 (c) is a partially
enlarged view in FIG. 3 (d) is a cross-sectional view showing the same diaphragm.
4 (a) is a perspective view showing a diaphragm according to a fourth embodiment of the present
invention, FIG. 4 (b) is a plan view showing the same diaphragm, and FIG. 4 (c) is a partially
enlarged view in FIG. FIG. 4D is a cross-sectional view showing the same diaphragm.
5 (a) is a perspective view showing a diaphragm according to a fifth embodiment of the present
invention, FIG. 5 (b) is a plan view showing the same diaphragm, and FIG. 5 (c) is a partially
enlarged view in FIG. 5 (b) FIG. 5 (d) is a cross-sectional view showing the same diaphragm. 6 (a)
is a perspective view showing a diaphragm according to a sixth embodiment of the present
invention, FIG. 6 (b) is a plan view showing the same diaphragm, and FIG. 6 (c) is a partially
enlarged view in FIG. FIG. 6D is a cross-sectional view showing the same diaphragm. 7 (a) is a
perspective view showing a diaphragm according to a seventh embodiment of the present
invention, FIG. 7 (b) is a plan view showing the same diaphragm, and FIG. 7 (c) is a partially
enlarged view in FIG. 7 (b) FIG. 7D is a cross-sectional view showing the same diaphragm. 8 (a) is
a perspective view showing a diaphragm according to an eighth embodiment of the present
invention, FIG. 8 (b) is a plan view showing the same diaphragm, and FIG. 8 (c) is a partially
enlarged view in FIG. 8 (b) 8 (d) is a cross-sectional view showing the same diaphragm. It is
sectional drawing which shows the example of the conventional photoacoustic converter. 10 (a)
is a perspective view showing a diaphragm of a conventional photoacoustic transducer, FIG. 10
(b) is a plan view showing the same diaphragm, and FIG. 10 (c) is a side view showing the same
diaphragm. (D) is a cross-sectional view showing the same vibration. 11 (a) is a plan view
showing a diaphragm of a conventional photoacoustic transducer, FIG. 11 (b) is a partial enlarged
view of FIG. 11 (a), and FIG. 10 (c) is a sectional view showing the same diaphragm. is there. It is
a perspective view showing the slit processing state in the example of an experiment of the
diaphragm.
Explanation of sign
[0036]
DESCRIPTION OF SYMBOLS 1 diaphragm, 1a vibration part 1A, 1B, 1C, 1D, 1E, 1F, 1H
diaphragm 1b silicon substrate part 1s slit 2 light emission part 3 light reception part 4 frame 11
cantilever-like suspension 12 side part 13, 13a corner part 14 ribs
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