JP2011176533A - Acoustic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve the noise elimination effect of an acoustic sensor by improving the transmission efficiency of mechanical vibrations between an acoustic sensing part and a vibration sensing part. <P>SOLUTION: Two back chambers 31a, 31b are formed on a silicon substrate 28. On the upper surface of the silicon substrate 28, the acoustic sensing part 29 is prepared by a vibration electrode plate 33a formed to cover one back chamber 31a and a fixed electrode plate 34a facing the vibration electrode plate 33a. Also, the vibration sensing part 30 is prepared by a vibration electrode plate 33b formed to cover the other back chamber 31b and a fixed electrode plate 34b facing the vibration electrode plate 33b. Also, the fixed electrode plate 34a of the acoustic sensing part 29 includes an acoustic hole 43 for making acoustic vibrations pass through. The fixed electrode plate 34b of the vibration sensing part 30 is formed to cover the vibration electrode plate 33b and the fixed electrode plate 34b does not have an acoustic hole or other holes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an acoustic sensor, and more particularly to a MEMS acoustic sensor having a function of removing external vibration noise.

  An acoustic sensor used for a microphone or the like detects acoustic vibration using air as a transmission medium. However, since it is usually installed in some device, noise is likely to be generated due to external mechanical vibration.

  In order to reduce noise (external vibration noise) due to such external mechanical vibration, a conventional condenser microphone combines an acoustic detection unit that detects acoustic vibration and a vibration detection unit that detects only mechanical vibration. . As such a noise elimination type condenser microphone, there is one disclosed in Patent Document 1.

  The structure of the capacitor microphone disclosed in Patent Document 1 is shown in FIG. In this condenser microphone 11, an acoustic detection unit 12 and a vibration detection unit 13, which are electret condenser microphone units having substantially the same structure, are housed in a rigid holder 14. In both the acoustic detection unit 12 and the vibration detection unit 13, a vibration film 15 for vibration detection is held in the casings 12 a and 13 a, and an acoustic hole 16 is opened facing the vibration film 15. The sound detection unit 12 and the vibration detection unit 13 are accommodated in substantially parallel delivery units 17 and 18 provided in the holder 14. The acoustic hole 16 of the acoustic detection unit 12 housed in the delivery unit 17 is opened to the outside by an opening 19 of the delivery unit 17. On the other hand, the acoustic hole 16 of the vibration detection unit 13 housed in the delivery unit 18 is closed by the holder 14.

  Therefore, the acoustic vibration is detected only by the acoustic detector 12 through the opening 19. Further, extraneous mechanical vibrations are detected by the acoustic detection unit 12 and the vibration detection unit 13 through the holder 14. 2A shows an example of a signal waveform (acoustic vibration with external vibration noise) output from the acoustic detection unit 12, and FIG. 2B shows a signal waveform output from the vibration detection unit 13 (mechanical). An example of vibration). In FIG. 2, the signal waveform of the acoustic vibration is assumed to be a sine wave.

  In order to remove external vibration noise using such two types of signal waveforms, a differential amplifier or a noise canceling circuit is generally used. When a differential amplifier is used, an acoustic vibration waveform carrying external vibration noise as shown in FIG. 2A and a mechanical vibration waveform as shown in FIG. To output a differential signal of both signal waveforms. Since the output waveform of the vibration detection unit 13 shown in FIG. 2B is the same as the noise component riding on the acoustic vibration output from the acoustic detection unit 12, the signal waveform of FIG. If the difference signal of the signal waveform of b) is output, the external vibration noise is removed and only the acoustic vibration waveform can be extracted.

Japanese Utility Model Publication No. 4-53394

  However, even with such a capacitor microphone, if there is a phase difference (temporal shift) between the mechanical vibration detected by the acoustic detection unit 12 and the mechanical vibration detected by the vibration detection unit 13, the noise is removed. There was considerable noise left in the signal. The external mechanical vibration is transmitted to the vibration film 15 of both detection units 12 and 13 through the holder 14 and the casings 12a and 13a to vibrate the vibration film 15. However, the acoustic detection unit 12 depends on the direction and way of transmission of vibration. There may be a time lag between the mechanical vibration transmitted to the vibration film 15 and the mechanical vibration transmitted to the vibration film 15 of the vibration detector 13. Therefore, even if it is attempted to remove external vibration noise from the output signal of the acoustic detection unit 12 using the output signal of the vibration detection unit 13, the acoustic vibration waveform as shown in FIG.

  The present invention has been made in view of such technical problems, and an object of the present invention is to improve the transmission efficiency of mechanical vibration between the acoustic detection unit and the vibration detection unit, thereby improving the acoustic sensor. It is to improve the noise removal effect.

  In order to achieve such an object, an acoustic sensor according to the present invention includes, on a single substrate, a first transducer that senses acoustic vibrations and mechanical vibrations and outputs an electrical signal, and only mechanical vibrations. A second transducer that senses and outputs an electrical signal is provided.

  In the acoustic sensor of the present invention, the first transducer and the second transducer are provided on a common substrate. Therefore, when mechanical vibration is applied to the acoustic sensor, the first vibration electrode of the first transducer. The time lag between the mechanical vibration transmitted to the plate and the mechanical vibration transmitted to the second vibrating electrode plate of the second transducer and the magnitude of the signal intensity of the mechanical vibration can be reduced. In particular, in the case of an acoustic sensor (sensor body) manufactured using MEMS technology, a hard material having a large elastic modulus such as silicon is used as a substrate material. Therefore, a machine transmitted to each vibration electrode plate of both transducers. The time difference of the mechanical vibration and the magnitude of the signal intensity of the mechanical vibration can be made very small. Therefore, the external vibration noise can be accurately removed from the output signal of the first transducer using the mechanical vibration detected by the second transducer, and the S / N ratio of the acoustic sensor can be improved. In addition, when an acoustic sensor is manufactured using the MEMS technology, the first transducer and the second transducer can be manufactured on the same substrate in the same process, and the mass productivity of the acoustic sensor is improved. Sensitivity variation with respect to mechanical vibration in the first transducer and the second transducer can be reduced. The acoustic sensor may be a capacitance type or a piezoresistive type.

  In an embodiment of the acoustic sensor according to the present invention, the first transducer is provided on the surface of the substrate so as to cover the first back chamber formed on the substrate and the first back chamber. The first vibration electrode plate and the first fixed electrode plate facing the first vibration electrode plate and having an acoustic hole opened therein, and the first vibration electrode plate is displaced by the displacement of the first vibration electrode plate. An electric signal is output based on a change in capacitance between the vibrating electrode plate and the first fixed electrode plate, and the second transducer is a second vibrating electrode plate provided on the surface of the substrate. And a second fixed electrode plate facing the second vibration electrode plate and having no opening, and the second vibration electrode plate and the second fixed due to displacement of the second vibration electrode plate Electrical signal based on the change in capacitance between electrode plates It is characterized in that the output.

  In this embodiment, since the first transducer has an acoustic hole in the first fixed electrode plate, acoustic vibration can reach the first vibrating electrode plate through the acoustic hole, and the first transducer Sensing vibrations and external mechanical vibrations. On the other hand, since the second transducer does not have an opening in the second fixed electrode plate, the acoustic vibration does not reach the second vibration electrode plate, and the second transducer senses only external mechanical vibration.

  In the second transducer of this embodiment, it is desirable to form a second back chamber on the substrate so as to face the second vibrating electrode plate. In this embodiment, the second fixed electrode plate of the second transducer is not provided with an opening, but is provided with the second back chamber, so that in the acoustic sensor manufacturing process, the substrate surface and the second fixed electrode are provided. The sacrificial layer that was present between the plates can be etched away through the second back chamber.

  In another embodiment of the present invention, the first transducer includes a first back chamber formed on the substrate and a first back chamber provided on the surface of the substrate so as to cover the first back chamber. The first vibration electrode plate and the first fixed electrode plate facing the first vibration electrode plate and having an acoustic hole opened therein, the first vibration caused by displacement of the first vibration electrode plate An electrical signal is output based on a change in capacitance between the electrode plate and the first fixed electrode plate, and the second transducer is provided on the surface of the substrate where the back chamber is not formed. The second vibration electrode plate, and a second fixed electrode plate provided opposite to the second vibration electrode plate, and the second vibration electrode due to displacement of the second vibration electrode plate Capacitance between the plate and the second fixed electrode plate It is characterized by outputting an electric signal based on the change.

  In this alternative embodiment, the first transducer has the first back chamber on the back side of the first vibrating electrode plate, so that the first vibrating electrode plate is resistant to the acoustic vibration propagated from the acoustic hole. The first transducer senses acoustic vibrations and extraneous mechanical vibrations. On the other hand, since the second transducer is provided in a region on the substrate where the back chamber is not formed, the second vibrating electrode plate is not sensitive to acoustic vibration, and the second transducer is an external machine. Sense only dynamic vibration.

  In another embodiment, it is desirable to provide an opening in the second fixed electrode plate. In this other embodiment, since the opening is provided in the second fixed electrode plate of the second transducer, the sacrificial layer that exists between the substrate surface and the second fixed electrode plate in the manufacturing process of the acoustic sensor is removed. Etching can be performed through the opening of the second fixed electrode plate.

  In still another embodiment of the present invention, the first transducer is provided on the surface of the substrate so as to cover the first back chamber formed on the substrate and the first back chamber. A first stationary electrode plate facing the first vibrating electrode plate and having an acoustic hole opened, the first vibrating electrode plate being displaced by a displacement of the first vibrating electrode plate; An electric signal is output based on a change in capacitance between the vibrating electrode plate and the first fixed electrode plate, and the second transducer is provided on the surface of the substrate and has a vent hole opened. The second vibration electrode plate having a second vibration electrode plate and a second fixed electrode plate provided to face the second vibration electrode plate, and the displacement of the second vibration electrode plate And change in capacitance between the second fixed electrode plate and the second fixed electrode plate It is characterized in that outputs an electric signal Zui.

  In this further embodiment, acoustic vibrations can reach the first vibrating electrode plate through the acoustic holes, and the first transducer senses acoustic vibrations and extraneous mechanical vibrations. On the other hand, since the second transducer has a vent hole formed in the second vibrating electrode plate, the acoustic vibration that has reached the surface of the second vibrating electrode plate passes through the vent hole and passes through the second vibrating electrode plate. It is transmitted to the back side. As a result, no pressure difference is generated between the front and back surfaces of the second vibrating electrode plate, the second vibrating electrode plate does not vibrate substantially due to acoustic vibration, and the second transducer senses only external mechanical vibration.

  In the second transducer of this further embodiment, an opening formed in the second fixed electrode plate and a second transducer formed on the substrate facing the second vibrating electrode plate. It is desirable to provide at least one of the back chambers. In this alternative embodiment, in the manufacturing process of the acoustic sensor, the sacrificial layer that existed between the substrate surface and the second fixed electrode plate through the opening of the second fixed electrode plate or the second back chamber of the substrate. Can be removed by etching. Moreover, since the second vibrating electrode plate also has a vent hole, when etching the sacrificial layer, the etching solution passes through the second vibrating electrode plate through the vent hole, so that the etching is performed more reliably. The etching time can be shortened.

  In still another embodiment of the present invention, the first transducer is provided on the surface of the substrate so as to cover the first back chamber formed on the substrate and the first back chamber. A first stationary electrode plate facing the first vibrating electrode plate and having an acoustic hole opened, the first vibrating electrode plate being displaced by a displacement of the first vibrating electrode plate; An electrical signal is output based on a change in capacitance between the vibrating electrode plate and the first fixed electrode plate, and the second transducer includes a second back chamber formed on the substrate, A second vibration electrode plate provided on a surface of the substrate so as to cover a second back chamber; a second fixed electrode plate facing the second vibration electrode plate and provided with an opening; Second back chamber and external air And an electrical signal based on a change in capacitance between the second vibrating electrode plate and the second fixed electrode plate due to displacement of the second vibrating electrode plate. It is characterized by output.

  In this further embodiment, since the first transducer has an acoustic hole opened in the first fixed electrode plate, the acoustic vibration can reach the first vibrating electrode plate through the acoustic hole, and the first transducer The transducer senses acoustic vibrations and extraneous mechanical vibrations. On the other hand, since the second transducer has a passage in the substrate that connects the second back chamber and the external space, the acoustic vibration propagated through the opening of the second fixed electrode plate; The acoustic vibration propagated through the passage and the second back chamber reaches the front and back of the second vibrating electrode plate. As a result, no pressure difference is generated between the front and back surfaces of the second vibrating electrode plate, the second vibrating electrode plate does not vibrate substantially due to acoustic vibration, and the second transducer senses only external mechanical vibration.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

FIG. 1 is a cross-sectional view of the acoustic sensor disclosed in Patent Document 1. As shown in FIG. 2A is a diagram showing an output waveform of the acoustic detection unit in the condenser microphone of FIG. 1, FIG. 2B is a diagram showing an output waveform of the vibration detection unit in the capacitor microphone of FIG. 1, and FIG. It is a figure which shows the waveform which removed the noise from the output waveform of Fig.2 (a) using the output waveform of FIG.2 (b). FIG. 3 is a schematic cross-sectional view showing the structure of the acoustic sensor according to Embodiment 1 of the present invention. FIG. 4 is an exploded perspective view of a sensor main body used in the acoustic sensor of the first embodiment. 5A is a diagram illustrating an output waveform from the acoustic detection unit of the acoustic sensor according to the first embodiment, FIG. 5B is a diagram illustrating an output waveform from the vibration detection unit of the acoustic sensor according to the first embodiment, and FIG. (C) is a figure which shows the waveform which removed the noise from the output waveform of Fig.5 (a) using the output waveform of FIG.5 (b). FIG. 6 is a schematic cross-sectional view showing a comparative example. FIG. 7 is a schematic cross-sectional view showing a part of an acoustic sensor according to Embodiment 2 of the present invention. FIG. 8 is an exploded perspective view of the sensor body in the second embodiment. FIG. 9 is a schematic cross-sectional view showing a part of an acoustic sensor according to Embodiment 3 of the present invention. FIG. 10 is an exploded perspective view of the sensor body in the third embodiment. FIG. 11 is a schematic cross-sectional view showing a part of an acoustic sensor according to Embodiment 4 of the present invention. FIG. 12 is an exploded perspective view of the sensor body in the fourth embodiment.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

(First embodiment)
Hereinafter, the acoustic sensor 21 according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 3 is a schematic sectional view of the acoustic sensor 21. As shown in FIG. 3, the acoustic sensor 21 mainly includes a sensor main body 22 and circuit elements 23 and 24 (IC chips). The sensor main body 22 and the lower surfaces of the circuit elements 23 and 24 have wiring patterns formed thereon. It is fixed to the upper surface of the substrate 25 with an adhesive. The sensor body 22 and the circuit elements 23 and 24 are covered with an electromagnetic shielding cover 26 bonded to the upper surface of the wiring board 25, and are housed in a space 27 formed by the wiring board 25 and the cover 26. .

FIG. 4 is an exploded perspective view showing the structure of the sensor body 22. The sensor body 22 is a MEMS element manufactured using MEMS (Micro Electro Mechanical Systems) technology, and an acoustic detection unit 29 (first transducer) and a vibration detection unit 30 are formed on a single silicon substrate 28 (substrate). (Second transducer) is provided. The silicon substrate 28 has two back chambers 31a (first back chamber) and a back chamber 31b (second back chamber) penetrating from the front surface to the back surface. The inner surfaces of the back chambers 31a and 31b may be vertical surfaces or may be inclined in a tapered shape. The size of the silicon substrate 28 is such that the length of one side is several mm or less and the thickness is about 400 to 500 μm in plan view. An insulating film 32 made of an oxide film (SiO ₂ film) or the like is formed on the upper surface of the silicon substrate 28.

  The acoustic detection unit 29 is disposed above the back chamber 31a with the vibration electrode plate 33a (first vibration electrode plate) and the fixed electrode plate 34a (first fixed electrode plate) facing each other on the upper surface of the silicon substrate 28. It is configured by Further, the vibration detection unit 30 causes the vibration electrode plate 33b (second vibration electrode plate) and the fixed electrode plate 34b (second fixed electrode plate) to face each other on the upper surface of the silicon substrate 28 above the other back chamber 31b. It is configured by arranging. That is, the vibrating electrode plates 33a and 33b are provided on the upper surface of the silicon substrate 28 so as to cover the respective back chambers 31a and 31b, and above the vibrating electrode plates 33a and 33b via a minute gap (gap). Fixed electrode plates 34a and 34b are provided.

  The vibrating electrode plates 33a and 33b are formed of a polysilicon thin film having a thickness of about 1 μm. The vibration electrode plates 33a and 33b are substantially rectangular thin films, and support legs 35a and 35b extend diagonally outward at the four corners. Further, extending portions 36a and 36b extend from one of the support legs 35a and 35b. The vibrating electrode plates 33a and 33b are arranged on the upper surface of the silicon substrate 28 so as to cover the upper surfaces of the respective back chambers 31a and 31b, and the support legs 35a and 35b and the extending portions 36a and 36b at the four corners are formed on the insulating coating 32. It is fixed on the top. Of the vibrating electrode plates 33a and 33b, portions supported in the air above the back chambers 31a and 31b (in this embodiment, portions other than the support legs 35a and 35b and the extending portions 36a and 36b) are diaphragms 37a and 37b, respectively. 37b (vibration membrane).

  The fixed electrode plates 34a and 34b are formed by providing fixed electrodes 39a and 39b made of a metal thin film on the upper surfaces of back plates 38a and 38b made of a nitride film. As shown in FIG. 4, the fixed electrode plates 34a and 34b cover the diaphragms 37a and 37b with a small gap of about 3 μm in the regions facing the diaphragms 37a and 37b, respectively. The fixed electrodes 39a and 39b are diaphragms. A capacitor is configured to face 37a and 37b. The outer peripheral portions of the fixed electrode plates 34a and 34b, that is, the outer portions of the regions facing the diaphragms 37a and 37b are fixed to the upper surface of the silicon substrate 28 with an insulating coating 32 made of an oxide film or the like.

  Extending portions 40a and 40b extend from the fixed electrodes 39a and 39b, and electrode pads 41a and 41b (Au films) respectively connected to the fixed electrodes 39a and 39b are provided at the tips of the extracted portions 40a and 40b. Yes. Furthermore, the fixed electrode plates 34a and 34b are provided with electrode pads 42a and 42b (Au film) that are joined to the extending portions 36a and 36b of the vibrating electrode plates 33a and 33b and are electrically connected to the vibrating electrode plates 33a and 33b. Yes. The electrode pads 42a and 42b are disposed on the upper surfaces of the back plates 38a and 38b, and the electrode pads 42a and 42b are located in the openings of the back plates 38a and 38b.

  The fixed electrode 39a and the back plate 38a have an acoustic hole 43 (acoustic hole) through which acoustic vibrations pass so as to penetrate from the upper surface to the lower surface, and the diaphragm 37a and the back chamber 31a are acoustically connected. linked. On the other hand, acoustic holes and other holes are not opened in the fixed electrode 39b and the back plate 38b, and the fixed electrode plate 34b covers the vibration electrode plate 33b in an airtight manner. The vibrating electrode plates 33a and 33b vibrate in resonance with acoustic vibrations and mechanical vibrations. Therefore, the vibrating electrode plates 33a and 33b are thin films of about 1 μm. Therefore, the thickness is 2 μm or more, for example.

  A circuit element 23 for processing the output signal of the acoustic detection unit 29 is bonded to the upper surface of the wiring substrate 25 by a thermosetting resin, and the acoustic detection unit 29 and the circuit element 23 are bonded by a bonding wire or a wiring substrate. The connection is made through 25 wiring patterns. Similarly, a circuit element 24 for processing the output signal of the vibration detection unit 30 is bonded to the upper surface of the wiring board 25 by a thermosetting resin, and the vibration detection unit 30 and the circuit element 24 are bonded by a bonding wire. Alternatively, they are connected through the wiring pattern of the wiring board 25.

  The cover 26 has an outer peripheral back surface bonded to the wiring board 25 with a conductive adhesive, and the cover 26 is electrically connected to the ground pattern of the wiring board 25. The gap between the lower surface of the cover 26 and the wiring board 25 is sealed with a conductive adhesive. The cover 26 has an electromagnetic shielding function for blocking electromagnetic noise from the outside. For this purpose, the cover 26 itself may be formed of a conductive metal, or the inner surface of the resin cover may be covered with a metal film such as plating. The cover 26 has an opening 44, and the space between the opening 44 and the sound detection unit 29 is a path for propagating acoustic vibration.

  In the acoustic sensor 21, when acoustic vibration (sound pressure) propagates from the opening 44, acoustic vibration enters the acoustic detection unit 29 through the acoustic hole 43 and vibrates the diaphragm 37 a. When the diaphragm 37a vibrates, the gap distance between the diaphragm 37a and the fixed electrode 39a changes, thereby changing the capacitance between the diaphragm 37a and the fixed electrode 39a. Therefore, if a DC voltage is applied between the electrode pads 41a and 42a and this change in capacitance is taken out as an electrical signal, the acoustic vibration can be converted into an electrical signal and detected. it can.

  On the other hand, in the vibration detection unit 30, since the fixed electrode plate 34 b does not have an acoustic hole, even if acoustic vibration enters from the opening 44, the acoustic vibration is not transmitted to the diaphragm 37 b, and the acoustic vibration is not detected by the vibration detection unit 30. .

  On the other hand, the mechanical vibration is transmitted to the diaphragm 37a of the acoustic detection unit 29 and the diaphragm 37b of the vibration detection unit 30 through the silicon substrate 28, so that both the acoustic detection unit 29 and the vibration detection unit 30 detect the mechanical vibration. Moreover, the acoustic detection unit 29 and the vibration detection unit 30 are configured to detect mechanical vibration with the same sensitivity.

  Since the external mechanical vibration is not a detection target in the acoustic detection unit 29, when the mechanical vibration is transmitted simultaneously with the acoustic vibration, the output signal from the acoustic detection unit 29 is mechanical as shown in FIG. The vibration becomes noise on the acoustic vibration waveform. On the other hand, the vibration detection unit 30 detects only mechanical vibrations, and the vibration detection unit 30 outputs mechanical vibrations corresponding to the noise of the acoustic detection unit 29 as shown in FIG. Therefore, for example, the output signal of the acoustic detection unit 29 and the output signal of the vibration detection unit 30 are respectively input to an external differential amplifier so that a difference signal between the output of the acoustic detection unit 29 and the output of the vibration detection unit 30 is output. If so, noise is removed and only acoustic vibration is output.

  In addition, the acoustic detection unit 29 and the vibration detection unit 30 are formed on a single silicon substrate 28. Since the silicon substrate 28 has high hardness and a large elastic constant, mechanical vibration transmitted through the silicon substrate 28 is acoustic. The time difference between the detection unit 29 and the vibration detection unit 30 becomes very small, and the phase difference and attenuation of the mechanical vibration detected by both the detection units 29 and 30 are almost eliminated. As a result, noise can be accurately removed from the output of the acoustic detector 29, and a clean acoustic vibration waveform can be extracted as shown in FIG.

  The acoustic sensor shown in FIG. 6 is a comparative example, and the acoustic detection unit 29 and the vibration detection unit 30 are formed on separate silicon substrates 28a and 28b, respectively. In the case of such a comparative example, reflection of mechanical vibration and time delay occur at the interface between the silicon substrates 28a and 28b, and noise is not sufficiently removed as in the conventional condenser microphone (FIG. 2 ( c)).

  Moreover, in the acoustic sensor 21 of this embodiment, since the MEMS element is used as the acoustic detection part 29 and the vibration detection part 30, the acoustic sensor 21 can be reduced in size. Furthermore, since the acoustic detection unit 29 and the vibration detection unit 30 are formed on a single silicon substrate 28, the manufacturing process of the sensor body 22 and the mounting process on the wiring board 25 are simplified, and the acoustic sensor 21 Manufacturing efficiency is improved.

(Second Embodiment)
FIG. 7 is a schematic sectional view showing a part of an acoustic sensor according to Embodiment 2 of the present invention. Since the structure of the acoustic sensor of the second embodiment is the same as that of the first embodiment except for the sensor main body, only the portion of the sensor main body 51 is shown in FIG. 7 (the same applies to the third and fourth embodiments). FIG. 8 is an exploded perspective view of the sensor main body 51 of the second embodiment.

  In the sensor main body 51, the vibration detection unit 30 is not sensitive to acoustic vibration by eliminating the back chamber (31b) on the vibration detection unit 30 side. That is, the back chamber 31a is provided only on the acoustic detection unit 29 side, and no back chamber is provided on the vibration detection unit 30 side.

  Further, since the back chamber does not exist in the vibration detector 30, the sacrificial layer (semiconductor layer to be the back plate 38a) existing between the surface of the silicon substrate 28 and the fixed electrode plate 34b in the manufacturing process is formed. The support layer (not shown) cannot be removed from the back side of the silicon substrate 28 by etching. Therefore, in this embodiment, the etching hole 52 is opened in the fixed electrode plate 34 b of the vibration detection unit 30, and the sacrificial layer is removed from the etching hole 52 by etching.

  The vibration detection unit 30 of the sensor main body 51 does not have a back chamber under the diaphragm 37b. Therefore, even if the etching electrode 52 is opened in the fixed electrode plate 34b, the vibration detection unit 30 is not sensitive to acoustic vibration. Only mechanical vibration is detected.

  Since the acoustic detection unit 29 and the vibration detection unit 30 are formed on a single silicon substrate 28, the mechanical vibration detected by the acoustic detection unit 29 and the vibration detection unit 30 is unlikely to cause a time difference or attenuation. External vibration noise due to mechanical vibration can be accurately removed. In addition, the production efficiency of the acoustic sensor is improved.

(Third embodiment)
FIG. 9 is a schematic cross-sectional view showing a sensor main body 61 which is a part of an acoustic sensor according to Embodiment 3 of the present invention. FIG. 10 is an exploded perspective view of the sensor main body 61 according to the third embodiment.

  In the sensor main body 61, in the vibration detection unit 30, an etching hole 62 (or an acoustic hole) is provided in the fixed electrode plate 34b, and a vent hole 63 penetrating the front and back is provided in the diaphragm 37b. The back chamber 31b on the vibration detection unit 30 side may not be provided.

  In this sensor main body 61, even if acoustic vibration enters from the etching hole 62, the acoustic vibration passes through the vent hole 63 of the diaphragm 37b, so that the acoustic vibration (sound pressure) is applied from the front and back of the diaphragm 37b. There is no pressure difference between the front and back. As a result, the diaphragm 37b does not vibrate, has no sensitivity to acoustic vibrations, and detects only mechanical vibrations.

  Since the acoustic detection unit 29 and the vibration detection unit 30 are formed on a single silicon substrate 28, the mechanical vibration detected by the acoustic detection unit 29 and the vibration detection unit 30 is unlikely to cause a time difference or attenuation. External vibration noise due to mechanical vibration can be accurately removed. In addition, the production efficiency of the acoustic sensor is improved. Furthermore, in this embodiment, when the back chamber 31b is not provided, the etching solution passes through the vent hole 63 when the sacrificial layer between the surface of the silicon substrate 28 and the vibration electrode plate 33b is removed by etching. It becomes easy to reach the lower surface of 33b, and it becomes easy to perform sacrificial layer etching.

(Fourth embodiment)
FIG. 11 is a schematic cross-sectional view showing a sensor main body 71 which is a part of an acoustic sensor according to Embodiment 4 of the present invention. FIG. 12 is an exploded perspective view of the sensor main body 71 of the fourth embodiment.

  In the sensor main body 71, the vibration detection unit 30 is provided with an etching hole 62 (or acoustic hole) in the fixed electrode plate 34 b and a passage 72 for communicating the outside of the sensor main body 71 and the back chamber 31 b in the silicon substrate 28. Forming. In the illustrated example, the passage 72 is formed in the shape of a horizontal hole in the silicon substrate 28, but it may have any position and shape.

  In this sensor main body 71, the acoustic vibration that has entered from the etching hole 62 and the acoustic vibration that has been transmitted through the passage 72 and the back chamber 31b are applied to the front and back of the diaphragm 37b, so that the diaphragm 37b does not vibrate due to the acoustic vibration. It has no sensitivity to.

  Since the acoustic detection unit 29 and the vibration detection unit 30 are formed on a single silicon substrate 28, the mechanical vibration detected by the acoustic detection unit 29 and the vibration detection unit 30 is unlikely to cause a time difference or attenuation. External vibration noise due to mechanical vibration can be accurately removed. In addition, the production efficiency of the acoustic sensor is improved.

21, 51, 61, 71 Acoustic sensor 22 Sensor body 25 Wiring substrate 28 Silicon substrate 29 Acoustic detection unit 30 Vibration detection unit 31a, 31b Back chamber 33a, 33b Vibration electrode plate 34a, 34b Fixed electrode plate 37a, 37b Diaphragm 38a, 38b Back plate 39a, 39b Fixed electrode 43 Acoustic hole 52, 62 Etching hole 72 Passage

Claims (8)

  A single substrate is provided with a first transducer that senses acoustic vibration and mechanical vibration and outputs an electrical signal, and a second transducer that senses only mechanical vibration and outputs an electrical signal. A characteristic acoustic sensor. The first transducer includes a first back chamber formed on the substrate, a first vibrating electrode plate provided on a surface of the substrate so as to cover the first back chamber, and the first transducer A first fixed electrode plate facing the vibration electrode plate and having an acoustic hole opened between the first vibration electrode plate and the first fixed electrode plate due to displacement of the first vibration electrode plate. An electrical signal is output based on the change in capacitance,
The second transducer includes a second vibrating electrode plate provided on the surface of the substrate, and a second fixed electrode plate facing the second vibrating electrode plate and having no opening, and the second transducer The electrical signal is output based on a change in electrostatic capacitance between the second vibrating electrode plate and the second fixed electrode plate due to the displacement of the vibrating electrode plate. Acoustic sensor.   3. The acoustic sensor according to claim 2, wherein in the second transducer, a second back chamber is formed on the substrate so as to face the second vibrating electrode plate. The first transducer includes a first back chamber formed on the substrate, a first vibrating electrode plate provided on a surface of the substrate so as to cover the first back chamber, and the first transducer A first fixed electrode plate facing the vibration electrode plate and having an acoustic hole opened between the first vibration electrode plate and the first fixed electrode plate due to displacement of the first vibration electrode plate. An electrical signal is output based on the change in capacitance,
The second transducer includes a second vibrating electrode plate provided on a surface of a region where the back chamber of the substrate is not formed, and a second fixed electrode provided opposite to the second vibrating electrode plate. And an electrical signal is output based on a change in capacitance between the second vibrating electrode plate and the second fixed electrode plate due to displacement of the second vibrating electrode plate. The acoustic sensor according to claim 1.   The acoustic sensor according to claim 4, wherein an opening is provided in the second fixed electrode plate. The first transducer includes a first back chamber formed on the substrate, a first vibrating electrode plate provided on a surface of the substrate so as to cover the first back chamber, and the first transducer A first fixed electrode plate facing the vibration electrode plate and having an acoustic hole opened between the first vibration electrode plate and the first fixed electrode plate due to displacement of the first vibration electrode plate. An electrical signal is output based on the change in capacitance,
The second transducer includes a second vibrating electrode plate provided on the surface of the substrate and having a vent hole, and a second fixed electrode plate provided opposite to the second vibrating electrode plate. And an electrical signal is output based on a change in capacitance between the second vibrating electrode plate and the second fixed electrode plate due to displacement of the second vibrating electrode plate. The acoustic sensor according to claim 1.   In the second transducer, at least one of an opening formed in the second fixed electrode plate and a second back chamber formed in the substrate facing the second vibrating electrode plate is provided. The acoustic sensor according to claim 6, wherein: The first transducer includes a first back chamber formed on the substrate, a first vibrating electrode plate provided on a surface of the substrate so as to cover the first back chamber, and the first transducer A first fixed electrode plate facing the vibration electrode plate and having an acoustic hole opened between the first vibration electrode plate and the first fixed electrode plate due to displacement of the first vibration electrode plate. An electrical signal is output based on the change in capacitance,
The second transducer includes a second back chamber formed on the substrate, a second vibrating electrode plate provided on the surface of the substrate so as to cover the second back chamber, and the second transducer A second fixed electrode plate facing the vibration electrode plate and provided with an opening; and a passage in the substrate for connecting the second back chamber and an external space, the second vibration electrode plate 2. The acoustic sensor according to claim 1, wherein an electrical signal is output based on a change in electrostatic capacitance between the second vibrating electrode plate and the second fixed electrode plate due to a displacement of the first electrode.

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