JP2005045463A - Sound-to-electric transducer element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sound-to-electric transducer element of a simple small-area structure which has a wide dynamic range and is usable for various purposes. <P>SOLUTION: The sound-to-electric transducer element is equipped with a diaphragm 2 which is equipped with a diffraction grating and vibrates with sound pressure, a light source 1 which irradiates the diffraction grating with light, and an optical detector 3 which detects and converts the light diffracted by the diffraction grating into an electric signal. The optical detector 3 uses an image sensor such as a photodiode array. The optical detector 3 detects the diaphragm 2 being displaced in two dimensions by detecting not a difference in light intensity, but a two-dimensional image of a diffraction image. When the light emitted by the light source 1 is incident on the diaphragm 2, the light wave emitted by the light source 1 is reflected by the diaphragm 2 since the reflection diffraction grating is formed on the diaphragm 2 to form the diffraction image on the surface of the photodiode array 3. The optical detector 3 optically detects the diaphragm 2 with the reflection diffraction grating being displaced and further converts the displacement into the electric signal. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an acoustoelectric transducer.
[0002]
[Prior art]
The conventional microphone has a diaphragm attached with a certain tension, and the resonance frequency is uniquely determined by the mass of the diaphragm and the spring constant. Nominally, even though the frequency characteristic is defined to be flat, it is a matter of course that the sensitivity may decrease as the distance from the resonance frequency inherent in the diaphragm increases. As a technique for realizing a microphone with a wide dynamic range, a technique of arranging a plurality of diaphragms having different diaphragm sizes and spring constants has been reported (see Patent Document 1 and Patent Document 2).
[0003]
On the other hand, compared to a condenser microphone that detects the vibration displacement of the diaphragm due to sound pressure as a capacitance, light is irradiated to the diaphragm that vibrates due to sound pressure, and the change in the light intensity of the reflected light is reflected in the vibration of the diaphragm. An optical microphone detected as a displacement is expected to have excellent characteristics from the viewpoints of directivity and noise resistance. However, the conventional optical microphone irradiates the output light of a gas laser, a solid-state laser or a semiconductor laser diode on the vibration plate, and detects the change in the light intensity of the reflected light as vibration displacement of the vibration plate.
[0004]
[Patent Document 1]
JP 2001-292498 A
[0005]
[Patent Document 2]
JP 2001-231100 A
[0006]
[Non-Patent Document 1]
Rossi, Kuniya Fukuda, Yoshio Nakai, Toshizo Kato, Physics Series "Optics", Yoshioka Shoten (1967)
[0007]
[Problems to be solved by the invention]
The methods proposed in Patent Document 1 and Patent Document 2 have problems due to mechanical structure and dimensional constraints. Also in mounting, there is a concern that the yield will decrease because the product group increases.
[0008]
In the conventional optical microphone structure, high optical accuracy is required in the incident optical system for the light incident on the diaphragm and the reflective optical system for guiding the reflected light to a predetermined photodetector. Therefore, an optical fiber and a light guide are used to allow the incident light and the reflected light to take arbitrary optical paths. Also, in order to greatly increase the reflected light movement width corresponding to the vibration displacement of the diaphragm on the photodetector surface, measures such as installing a lens element between the substrate on which the light receiving / emitting element is mounted and the diaphragm are taken. I'm taking it. That is, in the conventional optical microphone condensing method, the light wave reflected from the diaphragm spreads, so a strong light intensity is required to detect the vibration displacement of the minute diaphragm with a photodetector and detect the difference in light intensity. For this purpose, it is necessary to assist the optical path and to correct it. Therefore, in addition to the light emitting / receiving element and the diaphragm, an optical element that performs advanced alignment and a new system are required, and high-precision optical alignment is required. Therefore, there is a risk of reducing the yield as a product. Accompanying this, the cost of the system also increases. In addition, when an optical fiber or a light guide is used, its use range and application are limited at a stretch.
[0009]
An object of the present invention is to provide an acoustoelectric transducer having a simpler and smaller area structure, a wider dynamic range, and usable for a wide range of applications.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention is characterized in that (a) a diffraction grating is provided and vibrates by sound pressure, (b) a light source that irradiates light to the diffraction grating, and (c) diffraction by the diffraction grating. The gist of the present invention is an acoustoelectric conversion element that includes a photodetector that detects the converted light and converts it into an electric signal, and converts the displacement of the diaphragm into an electric signal.
[0011]
In the characteristics of the present invention, it is preferable to use an image sensor such as a photodiode array for the photodetector. That is, the photodetector does not detect the difference in light intensity, but detects the displacement of the two-dimensional diaphragm by detecting the two-dimensional image of the diffraction image. For this reason, the image sensor has a sufficiently large area for the diffracted light so that the diffraction image can be detected without omission.
[0012]
According to the feature of the present invention, since the diffracted light is self-imaged by the diffraction grating, the lens for narrowing the reflected light from the diaphragm, which is necessary for the conventional acoustoelectric transducer, and the light wave are guided in an arbitrary direction. Therefore, the need for a waveguide such as an optical fiber or a light guide is eliminated. Since the image is formed by the diffraction effect, focusing can be performed on the image sensor surface, and detection can be performed with high resolution. In addition, restrictions on the optical path of incident light incident on the diaphragm are greatly reduced. The optical restriction of incident / reflected light on the diaphragm is reduced, a simple system can be configured, miniaturization is possible, and the usable applications are expanded. Furthermore, by using an image sensor for the photodetector, it is possible to perform digital conversion simultaneously with detection on the pixel, eliminating the need for an A / D converter, improving the response speed, and reducing the circuit scale. As a result, the device cost can be reduced.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Next, first and second embodiments of the present invention will be described with reference to the drawings. 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 dimensions, the ratio of the thickness of each layer, and the like are different from the actual ones. Therefore, specific thicknesses and dimensions should be determined in consideration of the following description. Moreover, it is a matter of course that portions having different dimensional relationships and ratios are included between the drawings.
[0014]
Further, the following first and second embodiments exemplify apparatuses and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is a component part. The material, shape, structure, arrangement, etc. are not specified below. The technical idea of the present invention can be variously modified within the scope of the claims.
[0015]
(First embodiment)
As shown in FIG. 1, the acoustoelectric transducer according to the first embodiment of the present invention includes a diffraction grating 2 that vibrates due to sound pressure, and a light source 1 that irradiates light to the diffraction grating. And a photodetector 3 that detects light diffracted by the diffraction grating and converts it into an electrical signal.
[0016]
An image sensor such as a photodiode array is preferably used for the photodetector 3 shown in FIG. That is, the light detector 3 does not detect the difference in light intensity, but detects the displacement of the two-dimensional diaphragm 2 by detecting a two-dimensional image of the diffraction image. Therefore, the photodiode array 3 has a sufficiently wide area for the diffracted light so that the diffraction image can be detected without omission.
[0017]
In the acoustoelectric transducer according to the first embodiment, when the light irradiated from the light source 1 is incident on the diaphragm 2, a reflection type diffraction grating is formed on the diaphragm 2. The light wave emitted from the light is reflected by the diffraction grating and produces a diffraction image on the surface of the photodiode array 3. As described above, the acoustoelectric conversion element according to the first embodiment optically detects the displacement of the diaphragm 2 provided with the reflective diffraction grating by the optical detector 3, and further converts it into an electric signal. .
[0018]
For this reason, the diaphragm 2 is suspended from the fixing portions 4a and 4b by the elastic connection portions 5a and 5b. Specifically, as shown in FIG. 2, the diaphragm 2 is suspended from the fixing portions 4a and 4b provided on the support substrate 11 via the elastic connection portions 5a and 5b. When viewed as a planar pattern, the fixing portions 4 a and 4 b have a frame shape surrounding the hollow portion 9 </ b> R provided on the upper surface of the support substrate 11. And the diaphragm 2 is arrange | positioned as a diaphragm-like lid | cover in the upper part of the hollow part 9R whose cross section as shown in FIG. 2 is boat-shaped.
[0019]
Each of the fixing portions 4a and 4b includes a buried insulating film 12, an element isolation insulating film 13, an interlayer insulating film 14, and a passivation film 15, which are sequentially deposited on a support substrate 11 made of single crystal Si. The diaphragm 2 also has a laminated structure including a buried insulating film 12, an element isolation insulating film 13, an interlayer insulating film 14, and a passivation film 15.
[0020]
The elastic connection portions 5 a and 5 b are constituted by a buried insulating film 12, an element isolation insulating film 13, and an interlayer insulating film 14, and polysilicon connectors 21 a and 21 b are embedded in the element isolation insulating film 13 layer.
[0021]
The reflection type diffraction grating provided on the diaphragm 2 may be a two-dimensional diffraction grating shown in FIG. 3A or a one-dimensional diffraction grating shown in FIG. In FIG. 3A, a plurality of holes (concave portions) H arranged in a matrix on the diaphragm 2 are illustrated._i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}Shows an example in which a two-dimensional diffraction grating is constructed. In FIG. 3B, a plurality of grooves G periodically arranged on the diaphragm 2 are used.₁, G₂, G₃, ..., G₆Shows an example in which a one-dimensional diffraction grating is constructed.
[0022]
As shown in FIG. 4, a plurality of diaphragms Q_{i-1, j-1}, Q_{i-1, j}, Q_{i-1, j + 1}, ..., Q_{i, j-1}, Q_{i, j}, Q_{i, j + 1}, ..., Q_{i + 1, j-1}, Q_{i + 1, j}, Q_{i + 1, j + 1},... May be arranged in a matrix. In FIG. 4, a plurality of diaphragms Q_{i-1, j-1}, Q_{i-1, j}, Q_{i-1, j + 1}, ..., Q_{i, j-1}, Q_{i, j}, Q_{i, j + 1}, ..., Q_{i + 1, j-1}, Q_{i + 1, j}, Q_{i + 1, j + 1},... Are suspended from fixing portions 4a and 4b formed in a lattice pattern on the surface of the support substrate via two bent elastic connection portions 5a and 5b. The elastic connecting portion 5a is sandwiched between the slits 6a and 6b and has one L-shaped bent portion. On the other hand, the elastic connecting portion 5b is sandwiched between the slits 6a and 6b and has two L-shaped bent portions. 2 corresponds to a cross-sectional view as seen from the direction AA in FIG.
[0023]
In FIG. 4, diaphragms Q arranged in the row direction._{i-1, j-1}, Q_{i-1, j}, Q_{i-1, j + 1}Are elastically coupled directly to each other to form a vibrator chain (vibrator chain)._{i, j-1}, Q_{i, j}, Q_{i, j + 1}, ... constitute a vibrator chain (vibrator chain), and diaphragm Q_{i + 1, j-1}, Q_{i + 1, j}, Q_{i + 1, j + 1},... Constitute an oscillator chain (oscillator chain), and an oscillator chain having a different resonance frequency for each row can provide an extremely wide-band acoustoelectric transducer. Alternatively, a similar vibrator chain may be formed in the column direction so that the vibrator chains have different resonance frequencies for each column. Further, both the fixed portions 4a and 4b traveling in the row direction and the column direction are caused to function as fixed beams, and each diaphragm Q_{i-1, j-1}, Q_{i-1, j}, Q_{i-1, j + 1}, ..., Q_{i, j-1}, Q_{i, j}, Q_{i, j + 1}, ..., Q_{i + 1, j-1}, Q_{i + 1, j}, Q_{i + 1, j + 1}A vibration mode that vibrates independently is also possible. The individual diaphragms Q arranged as a two-dimensional matrix_{i-1, j-1}, Q_{i-1, j}, Q_{i-1, j + 1}, ..., Q_{i, j-1}, Q_{i, j}, Q_{i, j + 1}, ..., Q_{i + 1, j-1}, Q_{i + 1, j}, Q_{i + 1, j + 1}If all the resonance frequencies of... Are made different, an extremely wide band acoustoelectric transducer can be provided.
[0024]
In the state shown in FIG. 1, when sound pressure is input to the diaphragm 2 having a diffraction grating having a structure as shown in FIGS. 2 to 4, the diaphragm 2 has elastic connecting portions 5a and 5b and fixed portions 4a, It vibrates using the boundary with 4b as a fulcrum. In FIG. 1, the diffraction image before the diaphragm 2 is displaced is indicated by a thick solid line and a thick broken line. When diaphragm 2 is stationary, that is, when there is no voice input, it is diffracted on the surface of photodiode array 3 by the light emitted from light source 1 at intervals as shown by the thick solid line and thick broken line in FIG. An image appears.
[0025]
When there is a voice input and the distance f between the diaphragm 2 and the photodiode array 3 changes, the interval between the diffraction images on the surface of the photodiode array 3 is two-dimensionally shown by thin solid lines and thin broken lines. Change. A thin solid line and a thin broken line in FIG. 1 indicate that the interval of the diffraction images has changed with the vibration of the diaphragm 2.
[0026]
In this way, in the diffraction image obtained on the photodiode array 3, a difference is obtained on the photodiode array 3 before and after vibration when attention is paid to a certain diffraction image in the same direction and orientation. By detecting the displacement of the diffraction image on the photodiode array 3, the vibration displacement of the diaphragm 2 is output.
[0027]
According to the acoustoelectric transducer according to the first embodiment, the reflected light from the diaphragm 2 required for the conventional acoustoelectric transducer is narrowed down by using the diffracted light that is self-formed by the diffraction grating. Therefore, it is not necessary to install a waveguide such as an optical fiber or a light guide for guiding a light wave in an arbitrary direction. Since the diffraction effect of the light wave is used, an image is formed by itself without using a lens or the like, so that focusing can be performed on the surface of the photodiode array 3 and detection can be performed with high resolution. In addition, restrictions on the optical path of incident light incident on the diaphragm 2 are greatly reduced.
[0028]
Since the optical restriction of incident / reflected light on the diaphragm 2 is reduced, the acoustoelectric transducer according to the first embodiment can be used for a simple system and can be downsized. Applications that can be expanded.
[0029]
Furthermore, according to the acoustoelectric conversion element according to the first embodiment, by using the photodiode array 3 for the photodetector 3, digital conversion is performed simultaneously with detection on the pixel. For this reason, an A / D converter becomes unnecessary, the response speed is improved, and the circuit scale can be reduced. In the reflection type diffraction grating as shown in FIG. 1, the light source 1, the power source of the photodiode array 3, the drive circuit, and the processing circuit can be formed on the same substrate. Furthermore, like the photodiode array 3 and its peripheral circuits, the diaphragm 2 formed with a diffraction grating can be manufactured by a semiconductor manufacturing process.
[0030]
As a result, it becomes possible to reduce the manufacturing cost of the acoustoelectric transducer according to the first embodiment.
As can be easily understood from FIG. 2, it is useful to use a semiconductor manufacturing process when forming the diffraction grating on the diaphragm 2, that is, when forming the groove / grating on the substrate. By using a semiconductor manufacturing process, a diffraction grating having an arbitrary grating period can be formed with good reproducibility, which is suitable for mass production.
[0031]
Further, since the semiconductor substrate used as the support substrate 11 has various physical properties, the mass and the spring constant of the diaphragm 2 can be easily changed. For example, if silicon (Si) is used for the diaphragm 2 (see FIG. 15), a laser having a wavelength λ = 1000 nm or less is used for the light source 1, and a highly reflective material is coated on the side wall of the grating, the silicon portion is coated. The incident light is absorbed, and only the diffracted light from the grating side wall is diffracted onto the photodiode array 3, so that the stray light to the photodiode array 3 can be cut and the S / N can be improved as a result.
[0032]
In describing the acoustoelectric transducer according to the first embodiment of the present invention, the phenomenon in which the displacement of the diffraction image changes on the detection surface due to the vibration of the diaphragm 2 is a two-dimensional structure formed of a yz plane. A diffraction grating will be described as an example. As shown in FIG. 5, two orthogonal axes y and z on the lattice plane are set in parallel with the straight line in which the holes are arranged, and the distance between the holes in the y-axis direction and the z-axis direction is set to h._y, H_zAnd Taking the center of one particular hole as the origin, the coordinates (y, z) of all other holes are h_y, H_zIs an integer multiple of.
[0033]
As shown in FIG. 6, the angle θ formed by the direction of the diffracted light diffracted on the yz plane and the y axis._yCosine of (cosθ_y) To γ_y= Cosθ_yAnd the angle θ between the direction of the diffracted light and the z-axis_zCosine of (cosθ_z) To γ_z= Cosθ_zAnd the order k in the y direction_yLet be an integer:
h_yγ_y  = K_yλ (1)
Under the condition, the disturbance generated from the holes arranged in parallel in the y-axis direction reaches the focal plane with the same phase. Similarly, k_zLet (order in the z direction) be an integer:
h_zγ_z  = K_zλ (2)
Under the conditions satisfying the above, the disturbance generated from the holes arranged in parallel with the z-axis is in phase.
[0034]
For the diffraction grating, the disturbances generated from all the holes are in phase at the point corresponding to the direction satisfying the equations (1) and (2) at the same time. When there are a large number of holes, the light intensity is concentrated very close to the point determined by the equations (1) and (2). Therefore, on the focal plane of the photodiode array 3, bright spots are arranged in a rectangular lattice pattern on a dark background. FIG. 7A shows this. Each of the spots is considered as a separate image of the point light source 1. Focal length is f_aThen, the interval p between the spots along the y-axis direction_yIs:
p_y= F_aλ / h_y      (3)
And the interval p along the z-axis direction_zIs:
p_z  = F_aλ / h_z      (4)
It becomes. In FIG. 7A, the numbers attached to the spots are k._yAnd k_zIs shown. FIG. 7B is a diffraction image generated when a one-dimensional diffraction grating is used.
[0035]
Here, since the photodiode array 3 side for detecting the light wave is a fixed body, while the diaphragm 2 on which the diffraction grating is formed is a movable body, the diaphragm 2 on which the diffraction grating is formed vibrates due to sound pressure. Therefore, the focal length between the diffraction grating and the photodiode array 3 changes. That is, the diaphragm 2 on which the diffraction grating is formed vibrates due to the sound pressure, and the focal length of the diffraction grating is f as shown in FIG._aTo f_bSince the grating period carved in the diffraction grating is not changed, the distance p between the spots along the y-axis direction on the photodiode array 3 from the equations (3) and (4) is unchanged._y ^mdIs:
p_y ^md= F_bλ / h_y      (5)
And the interval p along the z-axis direction_z ^mdIs:
p_z ^md= F_bλ / h_z      (6)
It becomes.
[0036]
The two-dimensional diffraction grating vibrates and the focal length is f_aTo f_bFIG. 9 schematically shows a state in which the interval between spots changes on the surface of the photodiode array 3 when it changes to. The 0th-order diffraction image (points expressed as 0, 0 in FIG. 7A) is such that the diaphragm 2 vibrates and the focal length f_aIs f_bEven if it changes to, it will not be displaced. As indicated by the equations (3), (4), (5), and (6), each diffraction image is displaced two-dimensionally on the surface of the photodiode array 3. When attention is paid to a certain diffraction image (diffracted image other than the 0th order), it shows a behavior of two-dimensional displacement on the surface of the photodiode array 3 corresponding to the vibration of the diaphragm 2. Due to this behavior, on the photodiode array 3, the area where the light wave is taken in and the area where the light wave is not taken change with the vibration of the diaphragm 2 every minute time.
[0037]
Also, the one-dimensional diffraction grating vibrates and the focal length is f_aTo f_bFIG. 10 schematically shows a state in which the interval between spots changes on the surface of the photodiode array 3 when it changes to.
[0038]
In the acoustoelectric transducer according to the first embodiment, an arbitrary time t = t₁In this case, it is assumed that the diffraction image is two-dimensionally arranged on the image sensor including the photodiode array 3 as shown in FIG. In this state, the sound pressure is applied t = t₁+ T₂At this time, since the diaphragm 2 sinks downward, the diffraction image shifts. Next, the diaphragm 2 repels and t = t₁+ T₂+ T₃, T = t₁+ T₂+ T₃+ T₄And t = t at the first position₁+ T₂+ T₃+ T₄+ T₅Return later. This is the vibration of the diaphragm 2 corresponding to the frequency of one input sound.
[0039]
t = t₁+ T₂+ T₃+ T₄+ T₅The period of vibration of the diaphragm 2 is obtained by calculating this time. Also, which cell (photodiode) portion of the photodiode array 3 is preliminarily memorized, and when the vibration is applied and the sensitivity is recognized again in the memorized cell (photodiode) portion. Can be recognized as a period of one vibration. Further, detection with higher sensitivity is made possible by referring to which cell (photodiode) is sensitive in time series with respect to the period of one vibration of the diaphragm 2.
[0040]
As described above, in the acoustoelectric conversion element according to the first embodiment, the displacement of the diffraction image before and after the input of the sound pressure is detected by the photodiode array 3 arranged regularly at a minute interval, and the diaphragm 2 A signal corresponding to the amount of displacement is output. By manufacturing the drive circuit and the signal processing circuit integrally on the substrate on which the photodiode array 3 is installed by a semiconductor manufacturing process, it is possible to provide a more compact and lower cost. In addition, a system with good reactivity can be realized by forming the same substrate. Furthermore, it is possible to suppress electrical resistance caused by the wiring, and it becomes electrically stable.
[0041]
Here, in consideration of detecting the two-dimensional displacement of the diffraction image with higher resolution, the cell area per one of the photodiodes constituting the photodiode array 3 and the mutual space between the cells are small. It is desirable to do.
[0042]
A method for manufacturing the acoustoelectric transducer according to the first embodiment of the present invention shown in FIG. 2 will be described with reference to FIGS. Note that the method for manufacturing an acoustoelectric conversion element described below is an example, and it is needless to say that the method can be realized by various other manufacturing methods including this modification.
[0043]
(A) First, as shown in FIG. 12A, a buried insulating film (SOI oxide film) 12 and a single crystal Si layer (SOI layer) 10 are sequentially stacked on a support substrate 11 made of single crystal Si. A so-called SOI substrate is prepared. Next, the single crystal Si layer 10 is selectively etched away by a technique such as a reactive ion etching (RIE) method. In FIG. 12A, it is shown as if it was completely removed by etching, but the single crystal Si layer 10 is left in the peripheral circuit formation scheduled region and the like.
[0044]
Then, the element isolation insulating film 13 is formed by a technique such as a chemical vapor deposition (CVD) method, and planarized as shown in FIG. 12B by a chemical mechanical polishing (CMP) method or the like. In the planarization step shown in FIG. 12B, a so-called “active region” is defined in the peripheral circuit formation scheduled region surrounded by the element isolation insulating film 13.
[0045]
(B) Next, the element isolation insulating film 13 in the regions where the polysilicon connectors 21a and 21b shown in FIG. 2 are to be formed is selectively etched away by, for example, the RIE method or the like, as shown in FIG. Groove portions 20a and 20b are formed. A peripheral circuit (not shown) is simultaneously formed in a normal standard MOS integrated circuit manufacturing method. Although details are omitted, the surface of the single crystal Si layer 10 exposed as an active region is thermally oxidized to form a gate oxide film having a thickness of 50 nm to 100 nm. At this time V_thControl ion implantation may be added. Next, a polysilicon film is deposited on the entire surface of the gate oxide film by a CVD method to a thickness of about 300 nm to 600 nm, for example, 400 nm. At this time, the polysilicon film is also buried in the grooves 20a and 20b (FIG. 12D). Next, a photoresist film (hereinafter simply referred to as “photoresist”) is spin-coated on the surface of the polysilicon film. Then, the photoresist is patterned by a photolithography technique. Then, using this photoresist as a mask, the polysilicon film is etched by RIE or the like to form a gate electrode and a polysilicon wiring (not shown). Thereafter, the photoresist is removed, and a new photoresist is spin-coated on the surface of the gate electrode. Then, using photolithography technology, an ion implantation opening is formed in the MOS transistor formation region to expose the polysilicon gate electrode. Then, using the exposed polysilicon gate electrode and a new photoresist as a mask, arsenic ions (⁷⁵As⁺) Dose amount 10¹⁵cm^-2Ion implantation in the order of. At this time, the arsenic (⁷⁵As⁺) Is implanted. After removing the new photoresist, the single crystal Si layer 10 is heat-treated, and the implanted impurity ions are activated and diffused to form an n-type source region and an n-type drain region in the active region of the single crystal Si layer 10. To do. However, the active region in the single-crystal Si layer 10, the n-type source region, the n-type drain region, the n-type impurity region, the n-type impurity region, and the like inside are not shown. When embedding the polysilicon film in the trenches 20a and 20b, a planarization process such as etch back is employed as necessary.
[0046]
(C) Next, as shown in FIG. 13E, an interlayer insulating film 14 is formed on the entire surface of the element isolation insulating film 13. The interlayer insulating film 14 is also deposited on the polysilicon gate electrode in the peripheral circuit formation scheduled region (not shown). After the interlayer insulating film 14 is formed on the entire surface, the surface of the interlayer insulating film 14 is planarized by the CMP method. Further, as shown in FIG. 13F, a passivation film 15 is formed on the interlayer insulating film 14 using the CVD method.
[0047]
(D) Next, the passivation film 15 is selectively removed by etching using a photolithography technique, an RIE method, or the like to form a hole H constituting a reflective two-dimensional diffraction grating._i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Is formed as shown in FIG. At this time, as shown in FIG. 13G, grooves 22a and 22b are formed at positions above the polysilicon connectors 21a and 21b and their peripheral portions.
[0048]
(E) Next, the interlayer insulating film 14, the element isolation insulating film 13, and the buried insulating film (SOI oxide film) 12 around the trenches 22 a and 22 b are formed by photolithography, RIE, ECR ion etching, or the like. Etching is performed to form grooves 23a, 23b, 23c, and 23d as shown in FIG.
[0049]
(F) Thereafter, a part of the surface of the support substrate (single crystal Si) 11 exposed by the formation of the grooves 23a, 23b, 23c, and 23d is formed on a single crystal Si anisotropic etchant such as tetramethylammonium hydroxide (TMAH). When anisotropic etching is performed using a chemical solution such as), a cavity 9R is formed as shown in FIG. 14 (i), and the acoustoelectric transducer according to the first embodiment of the present invention is completed. To do.
[0050]
FIG. 15 shows a cross-sectional structure of an acoustoelectric transducer according to a modification (first modification) of the first embodiment of the present invention. As in FIG. 2, the diaphragm 2 is suspended from the fixing portions 4a and 4b provided on the support substrate 11 via the elastic connection portions 5a and 5b. The fixed portions 4a and 4b are provided in a frame shape on the upper surface of the support substrate 11, and the diaphragm 2 is a diaphragm arranged as a lid on the upper portion of the flat hollow portion 9R. Each of the fixing portions 4a and 4b includes a buried insulating film 12, a single crystal Si layer (SOI layer) 10, and a passivation film 15 which are sequentially deposited on a support substrate 11 made of single crystal Si. The diaphragm 2 has a laminated structure including the single crystal Si layer 10 and the passivation film 15. The elastic connection portions 5 a and 5 b also have a laminated structure composed of the single crystal Si layer 10 and the passivation film 15.
[0051]
Even when the diaphragm 2 having a reflection type diffraction grating as shown in FIG. 15 is used, when the vibration displacement of the diaphragm 2 oscillated by the sound pressure is detected by light, the diaphragm 2 itself has an imaging performance. Therefore, an element for guiding the optical path becomes unnecessary. Further, by detecting with the photodiode array 3, the vibration displacement of the diaphragm 2 can be replaced with a two-dimensional plane displacement.
A method for manufacturing the acoustoelectric transducer according to the first modification will be described with reference to FIGS. The method for manufacturing the acoustoelectric conversion element described below is an example, and it is needless to say that the method can be realized by various other manufacturing methods including this example.
[0052]
(A) First, as shown in FIG. 16A, a buried insulating film (SOI oxide film) 12 and a single crystal Si layer (SOI layer) 10 are sequentially laminated on a support substrate 11 made of single crystal Si. A so-called SOI substrate is prepared. Next, an element isolation region is defined using a photolithography technique, and the single crystal Si layer 10 where the element isolation region is to be formed is etched away by a technique such as RIE. Then, as shown in FIG. 16B, as the element isolation insulating films 16a, 16b, 16c, and 16d, silicon oxide films (SiO₂The film is buried by a CVD method or the like and planarized by a technique such as a CMP method. In the planarization step shown in FIG. 16B, a so-called “active region” is defined by being surrounded by the element isolation insulating film 13 in the region where the peripheral circuit is to be formed (in the following description, description of the peripheral circuit is omitted). To do.)
[0053]
(B) Next, the single crystal Si layer 10 is selectively etched using a photolithographic technique, an RIE method, or the like, so that a hole constituting a reflective two-dimensional diffraction grating is formed as shown in FIG. H_i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Form. At this time, hole H_i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Is formed higher than the bottom of the single crystal Si layer 10.
[0054]
(C) Next, as shown in FIG. 16D, a photoresist 32 is applied and patterned by exposure drawing, and the single crystal Si layer 10 and the buried insulating film 12 are RIE using the photoresist 32 as an etching mask. Etching is performed by a method or the like to form grooves 41a and 41b.
[0055]
(D) Next, as shown in FIG. 17E, a silicon nitride film (Si₃N₄Film) is formed by a low pressure CVD method or the like,_i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6The grooves 41a and 41b are embedded. Further, a photoresist 33 is applied and patterned by exposure drawing. Using the photoresist 33 as an etching mask, as shown in FIG.₃N₄A part of the film 15 is selectively removed by etching.
[0056]
(E) Next, the photoresist 33 is removed, and a passivation film (Si₃N₄Film) 15 is used as an etching mask, and isolation insulating films 16a, 16b, 16c and 16d and silicon oxide film (SiO 2 as buried insulating film 12)₂If the film is removed by etching, a cavity 9R is selectively formed at the bottom of the diaphragm 2 as shown in FIG. 17 (g), and a modified example (first example) of the first embodiment of the present invention is shown. The acoustoelectric transducer according to the modification is completed.
[0057]
FIG. 18 shows a cross-sectional structure of an acoustoelectric transducer according to another modification (second modification) of the first embodiment of the present invention. As in FIGS. 2 and 15, the diaphragm 2 is suspended from the fixing portions 4 a and 4 b provided on the support substrate 11 via the elastic connection portions 5 a and 5 b. The fixed portions 4a and 4b are provided in a frame shape on the upper surface of the support substrate 11, and the diaphragm 2 is a diaphragm arranged as a lid on the upper portion of the boat-shaped cavity portion 9R. Each of the fixing portions 4a and 4b is formed of a silicon nitride film (Si) sequentially deposited on the support substrate 11 made of single crystal Si.₃N₄Film) 17, buried Si layers 18 a and 18 e made of a polysilicon layer, and a passivation film 15. The diaphragm 2 is made of Si₃N₄The film 17 has a laminated structure including a buried Si layer 18 c made of a polysilicon layer and a passivation film 15. The elastic connection parts 5a and 5b are also Si.₃N₄The film 17 has a laminated structure composed of buried Si layers 18 b and 18 d made of a polysilicon layer and a passivation film 15.
[0058]
Even when the diaphragm 2 having a reflection type diffraction grating as shown in FIG. 18 is used, when the vibration displacement of the diaphragm 2 oscillated by the sound pressure is detected by light, the diaphragm 2 itself has an imaging performance. Therefore, an element for guiding the optical path becomes unnecessary. Further, by detecting with the photodiode array 3, the vibration displacement of the diaphragm 2 can be replaced with a two-dimensional plane displacement.
A method for manufacturing an acoustoelectric transducer according to a second modification will be described with reference to FIGS. The method for manufacturing the acoustoelectric conversion element described below is an example, and it is needless to say that the method can be realized by various other manufacturing methods including this example.
[0059]
(A) First, as shown in FIG. 19A, a so-called SOI substrate in which a buried insulating film (SOI oxide film) 12 and a single crystal Si layer 10 are sequentially laminated on a support substrate 11 made of single crystal Si. prepare. Next, an element isolation region is defined using a photolithography technique, and the single crystal Si layer 10 where the element isolation region is to be formed is etched away by a technique such as RIE. Then, as shown in FIG. 19B, the element isolation insulating films 16a, 16b, 16c, and 16d are embedded by a CVD method or the like and planarized by a technique such as a CMP method. By this planarization step, in the peripheral circuit formation scheduled region, a so-called “active region” is defined by being surrounded by the element isolation insulating film (in the following description, description of the peripheral circuit is omitted). Further, the single crystal Si layer 10 in the region where the diffraction grating is to be formed is selectively removed using a photolithography technique to obtain the structure shown in FIG. In FIG. 19B, the single crystal Si layer 10 is shown to be completely removed by etching, but the single crystal Si layer 10 is left in the peripheral circuit formation scheduled region and the like.
[0060]
(B) Next, after selectively etching the buried insulating film 12 by using a photolithography technique, an RIE method, or the like, as shown in FIG. 19C, a silicon nitride film (Si₃N₄Film) 17 is formed by the CVD method.
[0061]
(C) Next, Si₃N₄A polysilicon layer is deposited on the entire surface by the CVD method on the film 17, and is flattened until the upper surfaces of the isolation insulating films 16a, 16b, 16c, and 16d are exposed by a technique such as a CMP method as shown in FIG. Turn into. As a result, buried Si layers 18a, 18b, 18c, 18d, and 18e made of a polysilicon layer are buried between the isolation insulating films 16a, 16b, 16c, and 16d.
[0062]
(D) Next, a part of the embedded Si layer 18c is selectively etched by using a photolithography technique, an RIE method, or the like to form a reflective two-dimensional diffraction grating as shown in FIG. Hole H_i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Form. At this time, hole H_i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Is formed higher than the bottom of the single crystal Si layer 10. Further, as the passivation film 15, Si₃N₄A film is formed on the entire surface by a CVD method or the like, and as shown in FIG._i1, H_i2・ ・ ・ ・ ・ ・ ・ ・ H_i6Embed.
[0063]
(E) Next, as shown in FIG. 20G, a photoresist 31 is applied and patterned by exposure drawing, and the upper surfaces of the isolation insulating films 16a, 16b, 16c, and 16d using the photoresist 31 as an etching mask. Passivation film (Si₃N₄A part of the film 15 is removed by etching by RIE or the like.
[0064]
(F) Next, the photoresist 31 is removed, and a passivation film (Si₃N₄Film) 15 and Si₃N₄With the film 17 as a mask, the isolation insulating films 16a, 16b, 16c, 16d and the silicon oxide film (SiO 2 as the buried insulating film 12)₂If the film is removed by etching, a cavity 9R is selectively formed at the bottom of the diaphragm 2 as shown in FIG. Furthermore, if anisotropic etching is performed on a part of the surface of the support substrate (single crystal Si) 11 exposed by this etching using a chemical liquid such as an anisotropic etchant of single crystal Si, for example, TMAH, FIG. As shown to (i), the cavity 9R is formed under the diaphragm 2, and the acoustoelectric conversion element which concerns on the other modification (2nd modification) of the 1st Embodiment of this invention is completed. .
[0065]
FIG. 22 shows a cross-sectional structure of an acoustoelectric transducer according to still another modification (third modification) of the first embodiment of the present invention.
[0066]
The acoustoelectric transducer according to the third modification is an SOI substrate in which a buried insulating film (SOI oxide film) 12 and a single crystal Si layer (SOI layer) 10 are sequentially laminated on a support substrate 11 made of single crystal Si. It is provided on the surface. The fixing parts 4a and 4b of the acoustoelectric transducer according to the third modification are provided in a frame shape surrounding a ship-shaped cavity 9R provided on the upper surface of the single crystal Si layer 10, and the diaphragm 2 is provided in the cavity. It is composed of a flat bridge structure that protrudes upward from the top of 9R. The diaphragm 2 is a diaphragm made of a polysilicon layer 50. The polysilicon layer 50 has a hole H_i1, H_i2, ..., H_i6,... Are formed to constitute a reflective two-dimensional diffraction grating. Each of the fixing portions 4a and 4b includes an SOI substrate and a passivation film 53 on the upper portion thereof. The elastic connecting portions 5a and 5b are configured using the inclined portion at the end of the polysilicon layer 50 having a bridge structure.
[0067]
Even when the diaphragm 2 having a reflection type diffraction grating as shown in FIG. 22 is used, when the vibration displacement of the diaphragm 2 oscillated by the sound pressure is detected by light, the diaphragm 2 itself has an imaging performance. Therefore, an element for guiding the optical path becomes unnecessary. Further, by detecting with the photodiode array 3, the vibration displacement of the diaphragm 2 can be replaced with a two-dimensional plane displacement.
In the structure of the acoustoelectric transducer according to the third modification shown in FIG. 22, a sacrificial oxide film in the shape of a ship-shaped cavity 9R is embedded in advance, and a polysilicon layer 50 is deposited thereon to perform two-dimensional diffraction. Holes H constituting the lattice_i1, H_i2, ..., H_i6After opening, hole H_i1, H_i2, ..., H_i6,... Can be easily manufactured by injecting an etching solution and removing the sacrificial oxide film.
[0068]
(Second Embodiment)
As shown in FIG. 23, the acoustoelectric transducer according to the second embodiment of the present invention includes a diffraction grating, a diaphragm 2 that vibrates due to sound pressure, a light source 1 that irradiates light to the diffraction grating, and And a photodetector 3 that detects light diffracted by the diffraction grating and converts it into an electrical signal. And the point by which the transmission type diffraction grating is formed in the diaphragm 2 is a point different from the acoustoelectric conversion element which concerns on 1st Embodiment. The point that the diaphragm 2 is suspended from the fixing portions 4a and 4b by the elastic connection portions 5a and 5b is the same as the acoustoelectric conversion element according to the first embodiment.
[0069]
As in the first embodiment, an image sensor such as a photodiode array is preferably used for the photodetector 3 shown in FIG. That is, the light detector 3 does not detect the difference in light intensity, but detects the displacement of the two-dimensional diaphragm 2 by detecting a two-dimensional image of the diffraction image. Therefore, the photodiode array 3 has a sufficiently wide area for the diffracted light so that the diffraction image can be detected without omission.
[0070]
In the acoustoelectric transducer according to the second embodiment of the present invention, the light emitted from the light source 1 is incident on the diaphragm 2, and a transmissive diffraction grating is formed on the diaphragm 2. The light wave emitted from the light source 1 passes through the diaphragm 2 and produces a diffraction image on the surface of the photodiode array 3.
[0071]
FIG. 23 shows a state in which the diaphragm 2 on which the diffraction grating is formed vibrates by the input of sound and the displacement of the diffraction image on the photodiode array 3 changes. When the diaphragm 2 is stationary, that is, when there is no input by sound, a diffracted image is formed on the surface of the photodiode array 3 by light irradiated from the light source 1 at intervals as shown by a thick solid line and a thick broken line in FIG. Appears. Next, when sound pressure is input in this state, the diaphragm 2 vibrates using the boundary between the elastic connecting portions 5a and 5b and the substrate as a fulcrum. Accordingly, the distance f between the diaphragm 2 and the photodiode array 3 changes, and the interval between the diffraction images on the surface of the photodiode array 3 changes two-dimensionally with a thin solid line and a thin broken line. A thin solid line and a thin broken line in FIG. 23 indicate that the interval between the diffraction images has changed with the vibration of the diaphragm 2.
[0072]
Here, regarding a diffraction image obtained on the photodiode array 3, if attention is paid to a diffraction image having the same order and orientation, a difference is obtained on the photodiode array 3 before and after vibration. By detecting the displacement of the diffraction image on the photodiode array 3, the vibration displacement of the diaphragm 2 is output. At this time, the vibration of the continuous diaphragm 2 is detected and output not only when the diaphragm 2 is stationary or vibrating. The diaphragm 2 on which the diffraction grating is formed is designed so as to exhibit flat characteristics with respect to all frequencies of the input sound, but the elastic connecting portion that connects the mass or fixed surface of the diaphragm 2 and the diaphragm 2. A plurality of diaphragms 2 having different spring constants 5a and 5b may be provided to have a structure having higher sensitivity in a wide band with respect to the frequency of the input sound.
[0073]
Similarly to the photodiode array 3 and its peripheral circuits, the diaphragm 2 formed with a diffraction grating can also be manufactured by a semiconductor manufacturing process. In particular, when forming a diffraction grating on the diaphragm 2, that is, when forming a groove / grating on the substrate, it is useful to use a semiconductor manufacturing process, and a diffraction grating having an arbitrary grating period can be formed with good reproducibility. Suitable for mass production. Moreover, since it has various physical properties, the mass and spring constant of the diaphragm 2 can be easily changed. For example, if silicon (Si) is used for the diaphragm 2 and a laser having a wavelength λ = 1000 nm or less is used for the light source 1 and a highly reflective material is coated on the side wall of the grating, the light incident on the silicon portion is absorbed. Since only the diffracted light from the grating side wall is diffracted onto the photodiode array 3, stray light to the photodiode array 3 can be cut, and the S / N can be improved as a result.
[0074]
Specifically, as shown in FIG. 24, the acoustoelectric transducer according to the second embodiment of the present invention is connected to the fixing portions 4a and 4b provided on the support substrate 11 via the elastic connection portions 5a and 5b. The diaphragm 2 is suspended. The fixing portions 4a and 4b are provided in a frame shape so as to surround the hollow portion 9T penetrating the support substrate 11, and the diaphragm 2 is a diaphragm arranged as a lid on the upper portion of the hollow portion 9T.
[0075]
Each of the fixing portions 4a and 4b includes a buried insulating film 12, an element isolation insulating film 13, an interlayer insulating film 14, and a passivation film 15, which are sequentially deposited on a support substrate 11 made of single crystal Si. The diaphragm 2 also has a laminated structure including a buried insulating film 12, an element isolation insulating film 13, an interlayer insulating film 14, and a passivation film 15.
[0076]
The elastic connection portions 5 a and 5 b are constituted by a buried insulating film 12, an element isolation insulating film 13, and an interlayer insulating film 14, and polysilicon connectors 21 a and 21 b are embedded in the element isolation insulating film 13 layer.
[0077]
The transmission type diffraction grating provided on the diaphragm 2 may be a two-dimensional diffraction grating shown in FIG. 25A or a one-dimensional diffraction grating shown in FIG. In FIG. 25A, a plurality of holes (through holes) H arranged in a matrix on the diaphragm 2._i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}Shows an example in which a two-dimensional diffraction grating is constructed. In FIG. 25B, a plurality of grooves (slits) G periodically arranged on the diaphragm 2.₁, G₂, G₃, ..., G₆Shows an example in which a one-dimensional diffraction grating is constructed.
[0078]
In FIG. 24, the through hole H penetrates through the laminated structure composed of the buried insulating film 12, the element isolation insulating film 13, the interlayer insulating film 14, and the passivation film 15._i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}Are formed to constitute a transmission type two-dimensional diffraction grating.
[0079]
Since the horizontal level of the elastic connecting portions 5a and 5b is lower than the horizontal level of the top of the diaphragm 2, a plurality of holes (through holes) H_i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}The light diffracted by the two-dimensional diffraction grating can be easily separated from the reflected light from the elastic connecting portions 5a and 5b, and the structure is advantageous in terms of improving the S / N ratio and sensitivity. Since the vibration mode of the elastic connecting portions 5a and 5b is different from the vibration mode of the diaphragm 2, the reflected light from the elastic connecting portions 5a and 5b functions as a noise component for the light diffracted by the two-dimensional diffraction grating. is there.
[0080]
FIG. 26 shows a cross-sectional structure of an acoustoelectric transducer according to a modification (first modification) of the second embodiment of the present invention. Similarly to FIG. 24, the diaphragm 2 is suspended from the fixing portions 4a and 4b provided on the support substrate 11 via the elastic connection portions 5a and 5b. The fixed portions 4 a and 4 b are provided in a frame shape on the upper surface of the support substrate 11, and the diaphragm 2 is a diaphragm arranged as a lid on the upper portion of the hollow portion 9 T that penetrates the support substrate 11. Each of the fixing portions 4a and 4b is formed of a silicon nitride film (Si) sequentially deposited on the support substrate 11 made of single crystal Si.₃N₄Film) 17, buried Si layers 18 a and 18 e made of a polysilicon layer, and a passivation film 15. The diaphragm 2 is made of Si₃N₄The film 17 has a laminated structure including a buried Si layer 18 c made of a polysilicon layer and a passivation film 15. The elastic connection parts 5a and 5b are also Si.₃N₄The film 17 has a laminated structure composed of buried Si layers 18 b and 18 d made of a polysilicon layer and a passivation film 15. In FIG. 26, Si₃N₄A through-hole H is formed through the laminated structure including the film 17, the buried Si layer 18 c and the passivation film 15._i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}Are formed to constitute a transmission type two-dimensional diffraction grating. Through hole H_i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}A passivation film 15 is also deposited on the inner wall portion of the film.
[0081]
Even when the diaphragm 2 having a transmission type diffraction grating as shown in FIG. 26 is used, when the vibration displacement of the diaphragm 2 oscillated by the sound pressure is detected by light, the diaphragm 2 itself has an imaging performance. Therefore, an element for guiding the optical path becomes unnecessary. Further, by detecting with the photodiode array 3, the vibration displacement of the diaphragm 2 can be replaced with a two-dimensional plane displacement.
FIG. 27 shows a cross-sectional structure of an acoustoelectric transducer according to another modification (second modification) of the second embodiment of the present invention. The acoustoelectric transducer according to the second modification is an SOI substrate in which a buried insulating film (SOI oxide film) 12 and a single crystal Si layer (SOI layer) 10 are sequentially laminated on a support substrate 11 made of single crystal Si. Is provided on the surface. The fixing portions 4a and 4b of the acoustoelectric conversion element according to the second modification are provided in a frame shape so as to surround the cavity portion 9T penetrating the SOI substrate, and the diaphragm 2 is projected upward on the cavity portion 9T. It consists of a flat bridge structure. The diaphragm 2 is a diaphragm made of a polysilicon layer 50. The polysilicon layer 50 has a hole H_i1, H_i2, ..., H_i6,... Are formed to constitute a transmission type two-dimensional diffraction grating. Each of the fixing portions 4a and 4b includes an SOI substrate and a passivation film 53 on the upper portion thereof. The elastic connecting portions 5a and 5b are configured using the inclined portion at the end of the polysilicon layer 50 having a bridge structure.
[0082]
Even when the diaphragm 2 having a transmission type diffraction grating as shown in FIG. 27 is used, when the vibration displacement of the diaphragm 2 oscillated by the sound pressure is detected by light, the diaphragm 2 itself has an imaging performance. Therefore, an element for guiding the optical path becomes unnecessary. Further, by detecting with the photodiode array 3, the vibration displacement of the diaphragm 2 can be replaced with a two-dimensional plane displacement.
[0083]
(Other embodiments)
As described above, the present invention has been described according to the first and second embodiments. However, it should not be understood that the description and drawings constituting a part of this disclosure limit the present invention. From this disclosure, various alternative embodiments, examples and operational techniques will be apparent to those skilled in the art.
[0084]
In the description of the first and second embodiments already described, the diffraction grating having a geometrical shape such as a hole or a groove has been described. A dimensional diffraction grating may be realized.
[0085]
Further, for example, a diaphragm 2 as shown in FIG. 28 may be used. The diaphragm 2 shown in FIG. 28 (a) has a frame-shaped fixed frame 51 and both ends fixed to the fixed frame 51, and extends in the row direction and the column direction orthogonal to the row direction. A plurality of fixed beams 52 arranged so as to form a lattice in a space surrounded by the fixed frame 51, and a plurality of vibrators X respectively arranged in a window portion of the lattice_{i, j}(I = 1 to 3, j = 1 to 3) and a plurality of transducers X_{i, j}Elastic beam la connecting each of the beam and fixed beam 52_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}(I = 1 to 3, j = 1 to 3). In other words, each of the diaphragm-shaped vibrators X that becomes one main mass_{i, j}And 4 elastic beams la_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}Are connected. 4 elastic beams la_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}Each function as a small secondary cell.
[0086]
As shown in FIG. 28 (b), the diaphragm 2 has an edge e of the fixed beam 52._a, Vibrator X_{i, j}Edge of e_b, Elastic beam la_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}Edge of e_cDiffraction pattern images can be detected respectively. Edge e_aIn FIG. 5, since the mass of the fixed beam 52 is large, it has sensitivity in a low frequency band._{i, j}Edge of e_b, Elastic beam la_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}Edge of e_cTherefore, it is possible to construct a broadband frequency with a so-called single diaphragm 2. That is, each edge e_a, E_b, E_cConsidering the mass related to the edge e_a, E_b, E_cThe resonance frequency of f_a0, F_b0, F_c0given that
f_a0<F_b0<F_c0                            (7)
The relationship is obtained. Diffraction images arranged in three different arrangements appear on the sensor surface, but by using the diffraction image with the largest displacement for detection, an arbitrary frequency can be followed.
[0087]
As described above, the present invention naturally includes various embodiments not described herein. Therefore, the technical scope of the present invention is defined only by the invention specifying matters according to the scope of claims reasonable from the above description.
[0088]
【The invention's effect】
According to the present invention, it is possible to provide an acoustoelectric conversion element that has a simple and small area structure, a wide dynamic range, and can be used for a wide range of applications.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a configuration of an acoustoelectric transducer according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a specific structural example of the acoustoelectric transducer according to the first embodiment of the invention.
3A is a bird's-eye view showing a reflective two-dimensional diffraction grating, and FIG. 3B is a bird's-eye view showing a reflective one-dimensional diffraction grating.
FIG. 4 is a plan view of the acoustoelectric transducer according to the first embodiment of the present invention when a plurality of diaphragms are arranged in a matrix.
FIG. 5 is a schematic diagram illustrating a two-dimensional diffraction grating.
FIG. 6 is a schematic diagram for explaining a phase relationship of diffracted light.
FIG. 7A is a diffraction image generated when a two-dimensional diffraction grating is used, and FIG. 7B is a diffraction image generated when a one-dimensional diffraction grating is used.
FIG. 8 is a schematic diagram for explaining a change in the focal length of a diffraction grating.
FIG. 9 shows that the two-dimensional diffraction grating vibrates and the focal length is f._aTo f_bIt is a figure which shows typically the change of the space | interval of the spot on the surface of a photodiode array when it changes to.
FIG. 10 shows that the one-dimensional diffraction grating vibrates and the focal length is f._aTo f_bIt is a figure which shows typically the change of the space | interval of the spot on the surface of a photodiode array when it changes to.
FIG. 11 is a schematic diagram illustrating a method for obtaining a vibration period of a diaphragm.
FIG. 12 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the first embodiment of the present invention (No. 1).
13 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the first embodiment of the present invention (No. 2). FIG.
14 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the first embodiment of the present invention (No. 3). FIG.
FIG. 15 is a cross-sectional view showing a specific structural example of the acoustoelectric transducer according to the modification (first modification) of the first embodiment of the present invention.
FIG. 16 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the first modification of the first embodiment of the present invention (No. 1).
FIG. 17 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the first modification of the first embodiment of the present invention (No. 2).
FIG. 18 is a cross-sectional view showing a specific structural example of an acoustoelectric transducer according to another modification (second modification) of the first embodiment of the present invention.
FIG. 19 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the second modification of the first embodiment of the present invention (No. 1).
FIG. 20 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the second modification of the first embodiment of the present invention (No. 2).
FIG. 21 is a process cross-sectional view illustrating the manufacturing method of the acoustoelectric transducer according to the second modification of the first embodiment of the present invention (No. 3).
FIG. 22 is a cross-sectional view showing a specific structure example of an acoustoelectric transducer according to still another modification example (third modification example) of the first embodiment of the present invention;
FIG. 23 is a schematic diagram showing a configuration of an acoustoelectric transducer according to a second embodiment of the present invention.
FIG. 24 is a cross-sectional view showing a specific structural example of an acoustoelectric transducer according to a second embodiment of the present invention.
FIG. 25A is a bird's-eye view showing a transmission type two-dimensional diffraction grating, and FIG. 25B is a bird's-eye view showing a transmission type one-dimensional diffraction grating.
FIG. 26 is a cross-sectional view showing a specific structural example of an acoustoelectric transducer according to a modification (first modification) of the second embodiment of the present invention.
FIG. 27 is a cross-sectional view showing a specific structural example of an acoustoelectric transducer according to another modification (second modification) of the second embodiment of the present invention;
FIG. 28 is a plan view of an acoustoelectric transducer according to another embodiment of the present invention.
[Explanation of symbols]
1 ... Light source
2 ... Diaphragm
3 ... Photodetector (photodiode array)
4a, 4b ... fixed part
5a, 5b ... elastic connection part
9R, 9T ... cavity
10: Single crystal Si layer (SOI layer)
11 ... Supporting substrate
12 ... Embedded insulating film
13: Element isolation insulating film
14 ... Interlayer insulating film
14 ... Interlayer insulating film
15, 53 ... Passivation film
16a ... element isolation insulating film
17 ... Silicon nitride film (Si₃N₄film)
18a, 18b, 18c, 18d, 18e ... buried Si layer
20a, 20b ... groove
21a, 21b ... polysilicon connection body
22a, 22b, 23a, 213b, 23c, 23d, 41a, 41b ... groove
31, 32, 33 ... Photoresist
50. Polysilicon layer
51 ... Fixed frame
52. Fixed beam
G₁, G₂, G₃, ..., G₆…groove
H_i-1,1, ..., H_{i, 1}, H_{1, 2}, H_1,3, ..., H_{i + 2,6}... Hole (recess or through hole)
Q_{i-1, j-1}, Q_{i-1, j}, ..., Q_{i, j-1}, ..., Q_{i + 1, j}, Q_{i + 1, j + 1}・ ・ ・ ・ ・ ・ ・ ・ ・ ・ ・ Diaphragm
X_{i, j}... vibrator
e_a, E_b, E_c... Edge
la_{i, j}, Lb_{i, j}, Lc_{i, j}, Ld_{i, j}... elastic beams

Claims (9)

A diaphragm that includes a diffraction grating and vibrates by sound pressure;
A light source for irradiating the diffraction grating with light;
An acoustoelectric conversion element comprising: a photodetector that detects light diffracted by the diffraction grating and converts the light into an electric signal; and converts the displacement of the diaphragm into an electric signal. The acoustoelectric transducer according to claim 1, wherein the diffraction grating is a transmission diffraction grating or a reflection diffraction grating. The acoustoelectric transducer according to claim 1, wherein the diffraction grating is a one-dimensional diffraction grating or a two-dimensional diffraction grating. The acoustoelectric transducer according to claim 1 or 2, wherein a two-dimensional diffraction grating is constituted by a plurality of holes arranged in a matrix on the diaphragm. The acoustoelectric transducer according to claim 1 or 2, wherein a one-dimensional diffraction grating is constituted by a plurality of grooves periodically arranged on the diaphragm. The acoustoelectric conversion according to any one of claims 1 to 5, wherein one or a plurality of the diaphragms are suspended from a fixed portion provided on a support substrate via an elastic connection portion. element. The acoustoelectric transducer according to claim 6, wherein the diaphragm is suspended from a cavity provided in the support substrate via the elastic connection portion. 8. The acoustoelectric device according to claim 1, comprising a plurality of the diaphragms, wherein the plurality of diaphragms include a plurality of the diaphragms having different resonance frequencies. Conversion element. The diaphragm is
A fixed frame,
A plurality of fixed beams fixed at both ends to the fixed frame, extending in a row direction and a column direction perpendicular to the row direction, and arranged to form a lattice in a space surrounded by the fixed frame;
A plurality of vibrators respectively disposed in the window portion of the lattice;
The acoustoelectric transducer according to claim 1, further comprising an elastic beam connecting each of the plurality of vibrators and the fixed beam.

Images