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JP2005203944

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2005203944
PROBLEM TO BE SOLVED: To provide a compact, thin and environmentally resistant optical
microphone having high directivity. SOLUTION: A semiconductor substrate 11 having a
diffraction grating and a vibrating plate 113 vibrating with sound pressure, a light emitting
element 21 for irradiating light to the diffraction grating, and light diffracted by the diffraction
grating are detected and converted into an electric signal The mounting substrate 15 having the
light receiving element 23 is stacked on one another, and the displacement of the diaphragm 113
is converted into an electric signal. The semiconductor substrate 11 is bonded onto the
semiconductor substrate 11 via the transparent substrate 13. [Selected figure] Figure 1
Optical microphone and method of manufacturing the same
[0001]
The present invention relates to a high-performance small-sized microphone used in speech
recognition and the like, and more particularly to an optical microphone using a micro-electromechanical system (MEMS) method and a method of manufacturing the same.
[0002]
Condenser microphones are used as small microphones.
The condenser microphone detects the amount of vibration displacement of the diaphragm from
the change in capacitance with the lower electrode.
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[0003]
In addition, as an optical microphone, a reflection type is mainstream. Employs a structure in
which the vertical surface light emitting element and the light receiving element are arranged
concentrically around the vertical surface light emitting element having a substantially uniform
luminous intensity distribution concentrically, and the difference between the outputs from the
plurality of light receiving elements as differential signals An optical microphone that detects and
outputs an output is also proposed (see Patent Document 1). In the invention described in Patent
Document 1, a stable signal output is obtained by reducing the influence of a temperature change
of the light emitting element, a drive current change, etc., as compared with the case where an
output signal is formed using a single light receiving element. . Japanese Patent Application
Publication No. 2001-169394
[0004]
Since the condenser microphone detects the amount of vibration displacement of the diaphragm
from the change of the capacitance with the lower electrode, sharp directivity can not be realized.
For this reason, a "microphone array" which realizes unidirectivity by using a plurality of
condenser microphones and utilizing the delay sum is required. In addition, the sensitivity of the
condenser microphone is improved as the gap between the diaphragm and the lower electrode is
smaller, but the stability is impaired, and the problem of the vibration between the diaphragm
and the lower electrode in the gap formation process often causes a drop in yield. It is a factor.
[0005]
If the optical microphone is of the reflection type, the back surface of the diaphragm can be
opened, so that an ideal eight-shaped bi-directionality can be obtained which captures sound
from all directions and cancels out the ambient noise. However, since reflected light usually has a
large spread compared to incident light, it is difficult to observe a minute vibration displacement
of the diaphragm as a large difference of the reflected light intensity, and a solution such as an
optical fiber or a light guide In order to add a transmission path, various problems such as an
increase in cost, an increase in size of the system, and a limitation in the range of use occur.
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[0006]
In view of the above problems, it is an object of the present invention to provide an optical
microphone that has high directivity, is small and thin, and is environmentally resistant, and a
method of manufacturing the same.
[0007]
In order to achieve the above object, a first feature of the present invention is (a) a
semiconductor substrate having a diffraction grating and a vibrating plate vibrating with sound
pressure, and (b) a light emitting element for irradiating light to the diffraction grating And a
mounting substrate having a light receiving element for detecting light diffracted by a diffraction
grating and converting the light into an electric signal, and the light microphone is an optical
microphone for converting displacement of a diaphragm into an electric signal.
[0008]
According to a second feature of the present invention, (a) forming a diaphragm having a
diffraction grating on a semiconductor substrate, and (b) forming a recess for a light emitting
element and a recess for a light receiving element on a mounting substrate; And d) mounting a
light emitting element for emitting light to the concave portion for the light emitting element,
and mounting a light receiving element for detecting light diffracted by the diffraction grating to
the electric light receiving element recess and converting the light into an electrical signal; The
gist of the present invention is a method of manufacturing an optical microphone, including the
steps of: making a concave portion for a light receiving element and a concave portion for a light
receiving element opposite to a diaphragm;
[0009]
According to the present invention, it is possible to provide an optical microphone that has high
directivity, is small and thin, and is environmentally resistant, and a method of manufacturing the
same.
[0010]
Before describing the first to fourth embodiments of the present invention, the principle of an
optical microphone which is the basis of these embodiments will be described.
First, the basic of the optical microphone is the diffraction phenomenon of light by the diffraction
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grating on the vibrating film.
Strictly speaking, two-dimensional diffraction phenomena must be dealt with, but a onedimensional model is used as an approximation for principle explanation and conceptual design.
The intensity distribution of the interference fringes by the diffraction grating is expressed by the
equation (1) (by Toshihiro Arai and Masamitsu Hirai, “Introduction to Optoelectronics”, see
Kodansha Scientific.): I = I 0 (sin β / β) <2> (2 sin Nγ / γ) <2> (1) where parameters γ and β
are the angle θ with the optical axis, wavelength λ, speed of light c, grating spacing h, grating
width b, number of gratings N Is defined as follows: γ = k · h · sin θ / 2 (2) β = k · b · sin θ / 2
(3) where k = ω / C, ω = 2πc / λ.
As is apparent from equation (1), a sharp bright line appears in the direction represented by
equation (4), where n is an integer: sin θ = ± nλ / h (4) If the bright line represented is
detected by the light detection element, a signal corresponding to the displacement of the
diaphragm can be obtained.
[0011]
Details will be described in the following first to fourth embodiments of the present invention
with reference to the drawings.
[0012]
In the following description of the drawings, the same or similar parts are denoted by the same
or similar reference numerals.
However, it should be noted that the drawings are schematic, and the relationship between the
thickness and the planar dimension, the ratio of the thickness of each layer, and the like are
different from actual ones. Therefore, specific thicknesses and dimensions should be determined
in consideration of the following description. Moreover, it is needless to say that parts having
different dimensional relationships and proportions are included among the drawings. Also, the
first to fourth embodiments described below illustrate apparatuses and methods for embodying
the technical idea of the present invention, and the technical idea of the present invention is a
component Material, shape, structure, arrangement, etc. are not specified to the following.
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Various changes can be added to the technical idea of the present invention within the scope of
the claims.
[0013]
First Embodiment As shown in FIG. 1B, the optical microphone according to the first embodiment
of the present invention has a diffraction grating and is vibrated by the sound pressure of a
sound wave 入射 incident from below. A semiconductor substrate 11 having a diaphragm 113, a
surface emitting semiconductor laser (light emitting element) 21 for irradiating light to a
diffraction grating, and a photodiode (light receiving element) 23 for detecting light diffracted by
the diffraction grating and converting it into an electric signal And the mounting substrate 15 are
stacked on each other. The semiconductor substrate 11 and the mounting substrate 15 are
bonded to each other via a glass substrate (transparent substrate) 13. As a result, the first threelayer structure has a mounting substrate 15, a glass substrate (transparent substrate) 13 under
the mounting substrate 15, and a semiconductor substrate 11 disposed under the glass substrate
(transparent substrate) 13. The optical microphone according to the embodiment is configured to
convert the displacement of the diaphragm 113 due to the sound pressure into an electric signal.
This three-layer structure may be integrated by, for example, heat fusion technology or an
adhesive.
[0014]
FIG. 1A is a plan view showing the pattern on the back surface of the mounting substrate 15. As
shown in FIG. 1A, in the light emitting element 21 mounted in the light emitting element recess
155, the bonding pads on the light emitting element 21 and the wirings 152c and 152d are
connected by bonding wires 162c and 162d (note that When the back surface of the light
emitting element 21 is one of the electrodes, for example, the wiring 152 d may be led to the
back surface of the light emitting element 21 and the bonding pad on the light emitting element
21 may be connected to the wiring 152 c by the bonding wire 162 c. ). The bonding pads on the
light emitting element 21 are electrically connected to the pads (electrode pads) 151c and 151d
through the wirings 152c and 152d formed on the surface of the mounting substrate 15,
respectively.
[0015]
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Similarly, the bonding pads on the light receiving element 23 mounted in the light receiving
element recess 156 are connected to the wires 152a and 152b by the bonding wires 162a and
162b (note that the back surface of the light receiving element 23 becomes one electrode) In this
case, for example, the wire 152b may be guided to the back surface of the light receiving element
23, and the bonding pad on the light receiving element 23 and the wire 152a may be connected
by the bonding wire 162a. Then, the bonding pads on the light receiving element 23 are led to
the pads (electrode pads) 151a and 151b through the wirings 152a and 152b formed on the
surface of the mounting substrate 15, as shown in FIG. 1A. .
[0016]
As can be understood with reference to FIG. 1 (b), since a part of the pads 151a to 151d appears
in the vicinity of both ends of the glass substrate (transparent substrate) 13, the wiring for
driving the light emitting element 21 is And the electrical connection of the signal extraction
wiring from the light receiving element 23 is possible.
[0017]
As a material of the mounting substrate 15, various organic synthetic resins, inorganic materials
such as ceramic, glass, semiconductor and the like can be used.
As an organic resin material, a phenol resin, a polyester resin, an epoxy resin, a polyimide resin, a
fluorine resin, etc. can be used, and a substrate to be a core when forming a plate is paper, glass
cloth, glass base Materials are used. A common inorganic base material is ceramic or
semiconductor. When a metal substrate or a transparent substrate is required to enhance the
heat dissipation characteristics, glass is used. As a material of the ceramic substrate, alumina
(Al2O3), mullite (3Al2O3.2SiO2), beryllia (BeO), aluminum nitride (AlN), silicon nitride (SiC) or
the like can be used. Furthermore, a metal-based substrate (metal insulating substrate) may be
used, in which a polyimide resin plate having high heat resistance is laminated on a metal such as
iron and copper to form a multilayer. Among these materials, it is preferable to use a
semiconductor substrate as the mounting substrate 15 because the light emitting element recess
155 and the light receiving element recess 156 can be easily formed by the photolithography
technique and the etching technique similar to the manufacturing process of the semiconductor
integrated circuit. .
[0018]
The semiconductor substrate 11 is illustrated as if it were a single-layer semiconductor substrate
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in FIG. 1, but it may be a composite film or the like such as an SOI substrate described later.
[0019]
As shown in FIG. 2, the semiconductor vibrating film (diaphragm) 113 has a plurality of holes
(concave portions) Hi-1, 1. , 2, Hi, 3,..., Hi + 2, 6 are arranged to constitute a two-dimensional
diffraction grating.
The semiconductor vibrating film (diaphragm) 113 in which such a periodic pattern (twodimensional diffraction grating) is formed is fixed to the bottom cavity sidewall 117 provided in
the semiconductor substrate 11 by the elastic beams 115a and 115b. There is. As shown by a
two-dot chain line in FIG. 1A, when viewed as a plane pattern, the bottom cavity 17 is provided in
the shape of a rectangular frame on the semiconductor substrate. And as shown in FIG. 1, the
diaphragm 113 is arrange | positioned in the inside of the bottom part hollow part 17 in the
shape of a rectangular diaphragm. In FIG. 1A, the elastic beams 115a and 115b are also indicated
by two-dot chain lines.
[0020]
The beam of the semiconductor laser (light emitting element) 21 is diffracted by the diffraction
grating of the semiconductor vibrating film (diaphragm) 113 after passing through the glass
substrate (transparent substrate) 13 as shown in FIG. The light passes through 13 and is detected
by a photodiode (light receiving element) 23. At this time, as shown in FIG. 3, since the incident
position of the photodiode (light receiving element) 23 changes by ΔX depending on the
displacement ΔY of the semiconductor vibrating film (diaphragm) 113 by the sound wave Φ, the
output signal is temporally Change to Assuming that a bright line of first-order diffraction with
high diffraction intensity is used, n = 1 in equation (4), and sin θ = λ / h. At this time, the
displacement ΔY of the semiconductor vibrating film (diaphragm) 113 in the Y direction due to
the sound wave Φ and the displacement ΔX of the incident position of the photodiode (light
receiving element) 23 in the X direction are: ΔX = ΔY tan θ 5) It becomes a relation. A timevarying signal dependent on the displacement ΔX is a sound wave signal.
[0021]
From the equation (4), the following equation must be approximately satisfied between the
distance L between the light emitting device 21 and the diaphragm 113 and the distance M
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between the light emitting device 21 and the light receiving device 23: M / L = tan θ (6)
However, strictly speaking, it is necessary to consider the beam shift due to the refraction
phenomenon in the glass substrate (transparent substrate) 13.
[0022]
For simplicity, λ / h = 1⁄2, ie, if the wavelength λ of the laser beam is half the grating spacing h,
then sin θ = 0.5.
At this time, since tan θ = 1 / √3 to 0.577, M / L to 0.577 can be obtained from the equation
(6). Therefore, when the distance L between the light emitting element 21 and the diaphragm
113 is 2 mm, the distance M between the light emitting element 21 and the light receiving
element 23 may be designed to be 2 × 0.577 = about 1.15 mm. When the distance L between
the light emitting element 21 and the diaphragm 113 is 1 mm, the distance M between the light
emitting element 21 and the light receiving element 23 may be designed to be 577 μm.
[0023]
As described above, if the optical microphone according to the first embodiment of the present
invention is designed to satisfy the expression (6), all of the mounting substrate 15, the glass
substrate (transparent substrate) 13, and the semiconductor substrate 11 can be obtained. A thin
film of about 60 μm to about 600 μm, preferably about 100 μm to about 300 μm, can be
bonded to three layers, which is suitable for downsizing and thinning.
[0024]
Furthermore, according to the first embodiment of the present invention, it is possible to observe
a minute vibration displacement of the diaphragm as a large difference of the reflected light
intensity, and realize an optical microphone which is low in cost and limited in limited use range.
it can.
Therefore, it is possible to provide an optical microphone that has high directivity, is excellent in
stability, is small and thin, has environmental resistance, and has a high manufacturing yield.
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[0025]
The optical microphone according to the first embodiment of the present invention can be
manufactured by the following procedure. Note that the method of manufacturing the optical
microphone described below is an example, and the optical microphone according to the first
embodiment can be realized by various manufacturing methods other than this including this
modification. Of course.
[0026]
(A) First, a so-called SOI substrate in which a buried insulating film (SOI oxide film) and a single
crystal Si layer (SOI layer) are sequentially stacked on a supporting substrate made of single
crystal Si is prepared as a semiconductor substrate 11. Next, a photoresist film (hereinafter
simply referred to as "photoresist". ) Is spin-coated on the surface of the SOI layer. Then, the
photoresist is patterned by photolithography. Then, using this photoresist as a mask, the SOI
layer is etched by RIE or the like to cut out the pattern of the diaphragm 113. At this time, the
patterns of the elastic beams 115a and 115b are also formed.
[0027]
(B) Thereafter, a new photoresist is spin-coated on the surface of the SOI layer. That is, the SOI
layer is selectively etched by the RIE method or the ECR ion etching method using the
photolithography technique and the RIE method or the like to form fine holes Hi − as shown in
FIG. 1, 1, ..., Hi, 1, Hi, 2, Hi, 3, ..., Hi + 2, 6 are dug to form a reflective two-dimensional diffraction
grating. Thereafter, the photoresist is removed.
[0028]
(C) Thereafter, spin-coating a new photoresist on the entire surface. A window is formed in the
photoresist by photolithography to expose a region between the elastic beam 115 a and the
elastic beam 115 b around the diaphragm 113. Then, using this photoresist as a mask, the SOI
oxide film exposed in the window is selectively removed by RIE or the like to expose the support
substrate at the bottom of the window.
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[0029]
(D) Then, a chemical solution such as tetramethyl ammonium hydroxide (TMAH) is introduced
through the window portion to an anisotropic etchant of single crystal Si, for example, to
selectively anisotropically etch the supporting substrate, Cavity) is formed under the diaphragm
113. Furthermore, by etching the support substrate from the back surface to form the bottom
cavity 17, the diaphragm 113 having a diffraction grating as shown in FIGS. 1 and 2 is formed in
the bottom cavity 17 of the semiconductor substrate 11. Ru.
[0030]
(E) On the other hand, a single crystal Si substrate is prepared as the mounting substrate 15.
Then, if the single crystal Si substrate as the mounting substrate 15 is anisotropically etched by
TMAH or the like using the photoresist or the like as a mask by photolithography technology, the
light emitting element recess 155 and the light receiving element recess 156 are mounted. It is
formed on the surface of the substrate 15. After that, a metal film of aluminum (Al), aluminum
alloy (Al-Si, Al-Cu-Si), copper (Cu), gold (Au) is deposited by CVD, vacuum evaporation, sputtering
or the like, photolithography technology, RIE The metal film is patterned using an etching
technique such as, for example, to form patterns of pads 151a to 151d and wirings 152a to
152d. For patterning of the pads 151a to 151d and the wirings 152a to 152d, a lift off method
may be used, or a selective plating method using a mask similar to the lift off method may be
used. Alternatively, patterns such as the pads 151a to 151d and the wirings 152a to 152d may
be formed by a screen printing technique or the like.
[0031]
(F) Then, the light emitting element 21 for emitting light to the light emitting element recess 155
of the mounting substrate 15 is detected, and the light diffracted from the diffraction grating for
the light receiving element recess 156 is detected and converted to an electric signal Implement
each As shown in FIG. 1B, in order to incline the optical axis of the surface emitting
semiconductor laser (light emitting element) 21, the bottom of the light emitting element recess
155 is mounted to be inclined with respect to the main surface of the mounting substrate 15. In
this structure, the light emitting element 21 may be mounted by inserting a spacer in which the
bottom of the light emitting element 21 is inclined into the flat bottom light emitting element
recess 155 formed by anisotropic etching. For example, a structure in which the bottom of the
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light emitting element 21 is substantially inclined with respect to the main surface of the
mounting substrate 15 may be realized substantially by the shapes of the solder and the
conductive adhesive when mounting the light emitting element 21. Then, the bonding pads on
the light emitting element 21 and the wirings 152c and 152d are connected by the bonding
wires 162c and 162d. Similarly, the bonding pads on the light receiving element 23 and the
wirings 152a and 152b are connected by bonding wires 162a and 162b.
[0032]
(G) Then, the concave portion 155 for the light emitting element and the concave portion 156 for
the light receiving element are made to face the diaphragm 113, and the mounting substrate 15
is a semiconductor as shown in FIG. When laminated on the substrate 11, the optical microphone
according to the first embodiment is completed.
[0033]
Second Embodiment The light emitting element 21 is not limited to a surface emitting
semiconductor laser, and may be an edge emitting semiconductor laser.
The optical microphone according to the second embodiment of the present invention has a
three-layer structure as shown in FIG. 4, and an edge emitting semiconductor laser (light emitting
element) 21 and a light receiving element 23 from the top, respectively The semiconductor
substrate 11 has the mounting substrate 15 provided in the light emitting element recess 155
and the light receiving element recess 156, the glass substrate (transparent substrate) 13, and
the diaphragm 113.
[0034]
Similar to the optical microphone according to the first embodiment, this three-layer structure is
integrated by heat fusion technology or an adhesive. In addition, the periodic pattern (diffraction
grating) is formed on the diaphragm 113 by semiconductor process technology (etching
technology or photolithography technology), as in the optical microphone according to the first
embodiment. . The beam of the end face light emitting type semiconductor laser (light emitting
element) 21 is reflected by the reflecting mirror 159 provided on the wall of the recess 155 for
light emitting element, and after being transmitted through the glass substrate (transparent
substrate) 13, it is diffracted by the diffraction grating of the diaphragm 113 The light passes
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through the glass substrate (transparent substrate) 13 again and is detected by the light
receiving element 23.
[0035]
When a single crystal Si substrate is used for the mounting substrate 15, after forming the light
emitting element recess 155 and the light receiving element recess 156 by anisotropic etching
such as TMAH, gold (Au) or the like is formed on the side wall of the light emitting element
recess 155. The reflective mirror 159 can be formed by depositing a metal thin film having a
high reflectance as follows by vacuum deposition or sputtering. However, the side wall of the
light emitting element recess 155 is a mirror surface only by anisotropic etching, so that the
deposition process of the metal thin film with high reflectance can be omitted.
[0036]
As in the optical microphone according to the first embodiment, the light beam changes the
incident position of the light receiving element 23 depending on the displacement of the
diaphragm 113, so that the output signal temporally changes. This signal becomes a sound wave
signal corresponding to voice.
[0037]
The other points such as a point in which the wirings 152a to 152d are formed on the
semiconductor substrate 11, a manufacturing method of the optical microphone, and the like are
the same as those of the optical microphone according to the first embodiment.
[0038]
According to the second embodiment of the present invention, similarly to the optical
microphone according to the first embodiment, it is possible to provide an optical microphone
which has high directivity, is small and thin, and has environmental resistance.
[0039]
Third Embodiment As shown in FIG. 5, an optical microphone according to a third embodiment of
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the present invention has a mounting having a surface emitting semiconductor laser (light
emitting element) 21 and a light receiving element 23 from the top. It has a three-layer structure
of a semiconductor substrate 11 having a substrate 15, a transparent tape (transparent
substrate) 14, and a diaphragm 113.
FIG. 5A is a plan view seen through the back surface of the mounting substrate 15 from the back
surface of the transparent tape (transparent substrate) 14, but the plane surface of the
transparent tape (transparent substrate) 14 is larger than the planar dimensions of the mounting
substrate 15. The dimensions are designed to be larger.
[0040]
The three-layer structure shown in FIG. 5 is integrated by heat fusion technology or an adhesive.
Periodic patterns (diffraction gratings) are formed on the diaphragm 113 by semiconductor
process technology (etching technology or photolithography technology). The beam of the light
emitting element 21 is transmitted through the transparent tape (transparent substrate) 14,
diffracted by the diffraction grating of the diaphragm 113, transmitted again through the
transparent tape (transparent substrate) 14, and detected by the light receiving element 23. At
this time, as shown in FIG. 3, the incident position of the light receiving element 23 changes
depending on the displacement of the diaphragm 113, so that the output signal changes
temporally. This signal becomes a sound wave signal corresponding to voice.
[0041]
In the optical microphone according to the third embodiment, the tape-shaped mounting wirings
141, 142, 143, 144 are formed on the transparent tape (transparent substrate) 14, and the pads
provided on the periphery of the mounting substrate 15 ( The electrode pads are electrically
connected to 153a, 153b, 153c and 153d, respectively. Then, in the light emitting element 21
mounted in the light emitting element recess 155, as shown in FIG. 5A, the bonding pad on the
light emitting element 21 and the chip side wiring 154a, 154d are connected by the bonding
wires 164a, 164d. (When the back surface of the light emitting element 21 is one of the
electrodes, for example, the chip side wiring 154a is led to the back surface of the light emitting
element 21 and the bonding pad on the light emitting element 21 and the chip side wiring 154d
are It may be connected by a bonding wire 164d). The bonding pads on the light emitting
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element 21 are electrically connected to the pads (electrode pads) 153a and 153d through chip
side wirings 154a and 154d formed on the surface of the mounting substrate 15, respectively.
[0042]
Similarly, the bonding pads on the light receiving element 23 mounted in the light receiving
element recess 156 are connected to the chip side wires 154b and 154c by the bonding wires
164b and 164c (note that the back surface of the light receiving element 23 is one electrode) In
this case, for example, the chip side wiring 154c may be guided to the back surface of the light
receiving element 23, and the bonding pad on the light receiving element 23 and the chip side
wiring 154b may be connected by the bonding wire 164b. Then, as shown in FIG. 5A, the
bonding pads on the light receiving element 23 are respectively connected to the pads (electrode
pads) 153b and 153c through the chip side wirings 154b and 154c formed on the surface of the
mounting substrate 15. Led. The pads 153a to 153d and the chip side wirings 154a to 154d can
be formed by the chip wiring technology as described in the method of manufacturing the optical
microphone according to the first embodiment. Thus, electrical connection between the drive
wiring of the light emitting element 21 and the signal extraction wiring from the light receiving
element 23 is possible through the mounting wirings 141, 142, 143, 144 on the transparent
tape (transparent substrate) 14.
[0043]
The other points such as the manufacturing method of the optical microphone are substantially
the same as those of the optical microphones according to the first and second embodiments, and
thus the redundant description will be omitted.
[0044]
According to the third embodiment of the present invention, as in the optical microphones
according to the first and second embodiments, it is possible to provide a compact, thin,
environment-resistant optical microphone having high directivity. Can.
[0045]
Fourth Embodiment As shown in FIG. 6, in the fourth embodiment of the present invention, the
plurality of light emitting elements 21B and 21A and the plurality of light receiving elements
23B and 23A have different resonance characteristics. An optical microphone having a function
of selecting a frequency component of sound by independently obtaining vibration information
from the plurality of diaphragms 113B and 113A will be described.
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[0046]
FIG. 6 is a plan view showing the pattern on the back surface of the mounting substrate 15.
In the optical microphone according to the fourth embodiment, as shown in FIG. 6, the high
frequency light emitting element 21B is in the light emitting element recess 155B, the low
frequency light emitting element 21A is in the light emitting element recess 155A, and the light
receiving element recess is A high frequency light receiving element 23B is mounted on the light
receiving element 156B, and a low frequency light receiving element 23A is mounted on the light
receiving element recess 156A.
Although the cross-sectional structure is not shown, it is basically the same as the optical
microphone according to the first embodiment, and the mounting substrate 15 on which the light
emitting elements 21B and 21A and the light receiving elements 23B and 23A are mounted from
above It has a three-layer structure of a semiconductor substrate 11 provided with a substrate
(transparent substrate) 13, a high frequency diaphragm 113B, and a low frequency diaphragm
113A.
In FIG. 6, the low frequency diaphragm 113A, which is larger in area than the high frequency
diaphragm 113B and the high frequency diaphragm 113B, and the area of the bottom cavity 17
that accommodates these are shown by imaginary lines. The diaphragm 113B for high frequency
and the diaphragm 113A for low frequency may be an integrated diaphragm as long as they are
divided into a vibration region for high frequency and a vibration region for low frequency.
[0047]
In the high frequency light emitting element 21B mounted in the light emitting element recess
155B, as shown in FIG. 6, the bonding pads on the high frequency light emitting element 21B
and the wires 152c and 152d are connected by bonding wires 162c and 162d ( When the back
surface of the high frequency light emitting element 21B is one of the electrodes, for example,
the wire 152d is led to the back surface of the high frequency light emitting element 21B, and
the bonding pad on the high frequency light emitting element 21B and the wire 152c are bonded
It may be connected by a wire 162c). The bonding pads on the high frequency light emitting
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element 21B are electrically connected to the pads (electrode pads) 151c and 151d via the
wirings 152c and 152d formed on the surface of the mounting substrate 16, respectively.
[0048]
Similarly, the bonding pads on the high frequency light receiving element 23B mounted in the
light receiving element recess 156B are connected to the wires 152a and 152b by bonding wires
162a and 162b (note that the back surface of the high frequency light receiving element 23B is
one side) In the case of the electrode, for example, the wire 152b may be guided to the back
surface of the high frequency light receiving element 23B, and the bonding pad on the high
frequency light receiving element 23B and the wire 152a may be connected by the bonding wire
162a. The bonding pads on the high frequency light receiving element 23B are respectively led
to the pads (electrode pads) 151a and 151b through the wirings 152a and 152b formed on the
surface of the mounting substrate 16, as shown in FIG.
[0049]
On the other hand, in the low frequency light emitting element 21A mounted in the light emitting
element recess 155A, as shown in FIG. 6, the bonding pads on the low frequency light emitting
element 21A and the wires 152g and 152h are connected by bonding wires 162g and 162h. (If
the back surface of the low frequency light emitting element 21A is one of the electrodes, for
example, lead the wire 152h to the back surface of the low frequency light emitting element 21A
and bond it on the low frequency light emitting element 21A. The pad and the wiring 152g may
be connected by the bonding wire 162g. The bonding pads on the low frequency light emitting
element 21A are electrically connected to the pads (electrode pads) 151g and 151h via the
wirings 152g and 152h formed on the surface of the mounting substrate 16, respectively.
[0050]
Similarly, the bonding pads on the low frequency light receiving element 23A mounted in the
light receiving element recess 156A are connected to the wires 152e and 152f by bonding wires
162e and 162f (note that the back surface of the low frequency light receiving element 23A) In
the case where the electrode is one of the electrodes, for example, the wiring 152f may be guided
to the back surface of the low frequency light receiving element 23A, and the bonding pad on the
low frequency light receiving element 23A and the wiring 152e may be connected by the
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bonding wire 162e. ). The bonding pads on the low frequency light receiving element 23A are led
to the pads (electrode pads) 151e and 151f through the wirings 152e and 152f formed on the
surface of the mounting substrate 16 as shown in FIG. .
[0051]
The pads 151a to 151h and the wirings 152a to 152h can be formed by the chip wiring
technology as described in the method of manufacturing the optical microphone according to the
first embodiment. Similar to FIG. 1 (e), parts of 151a to 151h near the both ends of the glass
substrate (transparent substrate) 13 have faces, so the high frequency light emitting element 21B
and the low frequency light emitting element 21A It is possible to electrically connect the drive
wiring and the signal extraction wiring from the high frequency light receiving element 23B and
the low frequency light receiving element 23A.
[0052]
The other points such as the manufacturing method of the optical microphone are substantially
the same as those of the optical microphones according to the first to third embodiments, and
thus the redundant description will be omitted.
[0053]
According to the optical microphone of the fourth embodiment shown in FIG. 6, as shown in FIG.
7, the vibration spectrum of the high frequency from the high frequency light emitting element
21B, the high frequency light receiving element 23B and the high frequency diaphragm 113B. B
can be obtained, and a low frequency vibration spectrum A from the low frequency light emitting
element 21A, the low frequency light receiving element 23A, and the low frequency diaphragm
113A can be obtained.
As described above, by obtaining vibration information of different vibration spectra, it is
possible to add a function of selecting frequency components of speech. Note that, by obtaining
vibration information from a portion having different resonance characteristics on the integrated
diaphragm 113 by the plurality of light emitting elements 21B and 21A and the plurality of light
receiving elements 23B and 23A, the frequency component of sound is selected. A function may
be added.
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[0054]
(Other Embodiments) As described above, the present invention has been described by the first
to fourth embodiments, but it is understood that the statements and drawings that form a part of
this disclosure limit the present invention. should not do. Various alternative embodiments,
examples and operation techniques will be apparent to those skilled in the art from this
disclosure.
[0055]
In the optical microphones according to the first to fourth embodiments already described, a
photodiode array or a CCD as shown in FIG. 8 may be used as the light receiving element 23.
Although FIG. 8 illustrates a photodiode array including four photodiodes PD1, PD2, PD3, and
PD4, the number of photodiodes is not limited to four, and may be a one-dimensional
arrangement or a two-dimensional arrangement. If a photodiode array or a CCD is used, not only
the first order diffracted light but also the second order diffracted light can be detected to
improve the sensitivity. Furthermore, diffracted light from the plurality of diaphragms 113A and
113B described in the fourth embodiment can be simultaneously detected as a time series.
[0056]
Further, in the optical microphones according to the first to fourth embodiments, by making the
transparent substrates 13 and 14 have wavelength selectivity, the wavelength of the light
emitting element 21 is transmitted but the background light from the outside is blocked. Noise
characteristics may be improved. It is possible to reduce noise from background light and to
increase sensitivity while reducing the light transmittance of portions of the transparent
substrates 13 and 14 other than the region through which the light beam passes.
[0057]
Furthermore, as shown in FIG. 9, the microlenses 135A and 135B may be formed on the
transparent substrate (glass substrate) 13 to form a microlens array, and the diameter reduction
of the light beam from the light emitting element 21 and the utilization efficiency may be
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18
improved. . The micro lenses 135A and 135B may be formed at positions where the optical path
from the light emitting element 21 to the light receiving element 23 through the diffraction
grating formed on the diaphragm 113 intersects the transparent substrate (glass substrate) 13.
And 135B may be omitted. In the first, second and fourth embodiments, since a normal glass
substrate is used as the transparent substrate 13, the diameter of the light beam emitted from
the light emitting element 21 is initially small, but the light receiving element (photodiode array)
23 It will spread considerably at the stage of reaching. Therefore, a part of the light beam
deviates from the sensitive area of the light receiving element (photodiode array) 23 and leads to
the desensitization. On the other hand, as shown in FIG. 9, when the microlenses 135A and 135B
are formed on the transparent substrate (glass substrate) 13 by the etching technique or the
laser processing technique, the diameter of the light beam is narrowed and the sensitivity
becomes high. This is because when the light beam diameter is reduced, even a slight change in
beam position can be detected by the light receiving element (photodiode array) 23.
[0058]
Furthermore, in the optical microphones according to the first to fourth embodiments, the
transparent substrates 13 and 14 can be omitted in certain cases. For example, as shown in FIG.
10A, a second semiconductor substrate 18 in which a surface emitting semiconductor laser (light
emitting element) 21 and a photodiode (light receiving element) 23 are integrated is used as a
mounting substrate, and a semiconductor vibrating film (diaphragm) It may be a two-layer
structure in which the first semiconductor substrate 11 on which the semiconductor device 113
is formed is directly bonded by a bonding method. In FIG. 10A, the light emitting element 21 and
the light receiving element 23 are formed using the epitaxial growth layer 19 formed on the
second semiconductor substrate 18 made of a compound semiconductor, and between the light
emitting element 21 and the light receiving element 23 Are electrically isolated by an element
isolation region 181 which is formed of an insulating film and a high resistance region by proton
(H <+>) irradiation. The first semiconductor substrate 11 is preferably silicon (Si) in consideration
of the mechanical strength of the thin semiconductor vibration film (diaphragm) 113, but may be
a compound semiconductor substrate. However, although it is necessary to design the depth
from the surface of the first semiconductor substrate 11 to the surface of the semiconductor
vibrating film (diaphragm) 113 to satisfy the expression (6), a surface emitting semiconductor
laser (light emitting device 21) The distance between the photodiode 21 and the photodiode
(light receiving element) 23 can be designed by photolithography, so that miniaturization is easy
and the structure is excellent in miniaturization and thinning.
[0059]
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19
The light emitting element 21 includes an n-side Bragg reflection film 191, an n-side cladding
layer 192, an active layer 193, a p-side cladding layer, a p-side Bragg reflection film 195, a p-side
electrode 182 and the like as shown in FIG. What is necessary is just to comprise with the
surface emitting semiconductor laser provided. If the surface emitting semiconductor laser
shown in FIG. 10B is used as a photodiode as the light receiving element 23, the photodiode
having the same forbidden band width as the surface emitting semiconductor laser is used, and
the resonance effect of the wavelength is obtained. It is possible to realize an extremely sensitive
optical microphone that is not affected by noise or stray light.
[0060]
Thus, it is a matter of course that the present invention includes various embodiments and the
like which are not described herein. Accordingly, the technical scope of the present invention is
defined only by the invention-specifying matters according to the scope of claims appropriate
from the above description.
[0061]
FIG. 1 (a) is a plan view showing a pattern viewed from the back of a mounting substrate which is
an element of the optical microphone according to the first embodiment of the present invention,
and FIG. 1 (b) is a first embodiment of the present invention. It is a schematic cross section
explaining the 3 layer structure which consists of the mounting substrate of the optical
microphone which concerns on a form, a glass substrate (transparent substrate), and a
semiconductor substrate. It is a typical bird's-eye view for demonstrating the two-dimensional
diffraction grating formed in the surface of the semiconductor diaphragm (diaphragm) which is
an element of the optical microphone concerning a 1st embodiment of the present invention. The
optical microphone which concerns on the 1st Embodiment of this invention WHEREIN: It is a
schematic diagram for demonstrating the relationship between the distance of a light emitting
element and a diaphragm, and the distance of a light emitting element and a light receiving
element. FIG. 4 (a) is a plan view showing a pattern viewed from the back of the mounting
substrate which is an element of the optical microphone according to the second embodiment of
the present invention, and FIG. 4 (b) is a second embodiment of the present invention. It is a
schematic cross section explaining the 3 layer structure which consists of the mounting substrate
of the optical microphone which concerns on a form, a glass substrate (transparent substrate),
and a semiconductor substrate. FIG. 5 (a) is a plan view seen through the back of the mounting
substrate from the back of the transparent tape (transparent substrate) which is an element of
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the optical microphone according to the third embodiment of the present invention, and FIG.
These are typical sectional drawings explaining the 3 layer structure which consists of the
mounting substrate of the optical microphone which concerns on 3rd Embodiment, a transparent
tape (transparent substrate), and a semiconductor substrate. It is a top view showing the pattern
seen from the back of the mounting board which is an element of the optical microphone
concerning a 4th embodiment of the present invention. It is a frequency spectrum for
demonstrating the function which selects the frequency component of the audio | voice of the
optical microphone which concerns on the 4th Embodiment of this invention. It is a typical
sectional view for explaining the photo diode array of the optical microphone concerning other
embodiments of the present invention. It is a typical sectional view for explaining the micro lens
array of the optical microphone concerning another embodiment of the present invention. It is a
typical sectional view explaining the 2 layer structure which consists of the 1st and 2nd
semiconductor substrate of the optical microphone concerning another embodiment of the
present invention.
Explanation of sign
[0062]
11 semiconductor substrate (first semiconductor substrate) 13 transparent substrate (glass
substrate) 14 transparent substrate (transparent tape) 15 concave portion 15, 16 mounting
substrate 17 bottom hollow portion 18 second semiconductor substrate 19 epitaxial growth
layer 21 light emitting element 21A low frequency light emitting element 21B high frequency
light emitting element 23 light receiving element 23A low frequency light receiving element 23B
high frequency light receiving element 113 diaphragm 113A low frequency diaphragm 113B
high frequency vibration Plates 115a, 115b: Elastic beam 117: Bottom cavity side wall 135A,
135B: Micro lens array 141, 142, 143, 144: Mounting wiring 151a to 51h, 153a to 153d: Pad
152a to 152h: Wiring 154a to 154d: Chip side Wiring 162a to 162h, 164a to 164d ... bonding
Ear 155, 155A, 155B, 156, 156A, 156B ... recessed part 159 ... reflector 181 ... element
separation area 182 ... p-side electrode 191 ... n-side Bragg reflection film 192 ... n-side cladding
layer 193 ... active layer 194 ... p-side cladding Layer 195 ... p-side Bragg reflection film ... ...
sound wave PD1, PD2, PD3, PD4 ... photodiode
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