Acoustic transducer and microphone

An acoustic transducer has a substrate having a cavity, a vibrating electrode plate disposed above the substrate and having a void portion that allows pressure to escape, a fixed electrode plate disposed above the substrate opposite the vibrating electrode plate, a plurality of sensing portions configured by the vibrating electrode plate and the fixed electrode plate, at least one of the vibrating electrode plate and the fixed electrode plate being divided into a plurality of regions, and a sensing portion being configured by the vibrating electrode plate and the fixed electrode plate in each of the divided regions, and a leak pressure regulation portion that hinders leakage of air pressure passing through the void portion when the vibrating electrode plate is not undergoing deformation.

BACKGROUND

Field

The present invention relates to an acoustic transducer and a microphone. Specifically, the present invention relates to a capacitance type of acoustic transducer configured by a capacitor structure made up of a vibrating electrode plate (diaphragm) and a fixed electrode plate. The present invention also relates to a microphone that employs this acoustic transducer. In particular, the present invention relates to a very small-sized acoustic transducer created using MEMS (Micro Electro Mechanical System) technology.

Related Art

In recent years, there has been demand for microphones to detect sounds with high sensitivity in a range from low sound pressure to high sound pressure. In general, the maximum input sound pressure of a microphone is limited by the harmonic distortion rate (total harmonic distortion). This is because when a microphone attempts to detect a sound having a high sound pressure, harmonic distortion occurs in the output signal, and the sound quality and precision become impaired. Accordingly, if the harmonic distortion rate can be reduced, it is possible to raise the maximum input sound pressure and widen the detectable sound pressure range (referred to hereinafter as the “dynamic range”) of the microphone.

However, in general microphones, there is a trade-off relationship between an improvement in the acoustic vibration detection sensitivity and a reduction in the harmonic distortion rate, and it has been difficult to provide a microphone with a wide dynamic range from low-volume (low sound pressure) sounds to high-volume (high sound pressure) sounds.

In this technical background, a method of using of an acoustic sensor structured as shown inFIGS. 1A and 1Bhas been proposed as a method for realizing a microphone that has a wide dynamic range.FIG. 1Ais a cross-sectional diagram of an acoustic sensor11according to a conventional example, andFIG. 1Bis a plan view of a state where a back plate19has been removed.

In the acoustic sensor11, a first diaphragm16aand a second diaphragm16bthat are divided by a slit17are arranged above a substrate12that has a cavity13. The first diaphragm16ahas a relatively larger area and is supported on the upper surface of the substrate12by anchors18a. The second diaphragm16bhas a relatively smaller area and is supported on the upper surface of the substrate12by anchors18b. A back plate19is provided on the upper surface of the substrate12so as to cover the two diaphragms16aand16b, and a first fixed electrode plate20aand a second fixed electrode plate20bare arranged on the lower surface of the back plate19so as to oppose the first diaphragm16aand the second diaphragm16b. A large number of acoustic holes21are formed in the back plate19and the fixed electrode plates20aand20b.

In the acoustic sensor11, a high-sensitivity first acoustic sensing portion14that can detect low-volume (low sound pressure) sounds is configured by the first diaphragm16aand the first fixed electrode plate20athat oppose each other. Also, a low-sensitivity second acoustic sensing portion15that can detect high-volume (high sound pressure) sounds is configured by the second diaphragm16band the second fixed electrode plate20bthat oppose each other. Also, the output from the acoustic sensor11is switched between output from the first acoustic sensing portion14and output from the second acoustic sensing portion15according to the volume, thus making it possible to detect sounds with high sensitivity in a range from low sound pressure to high sound pressure. One example of such an acoustic sensor is disclosed in JP 2012-147115A.

JP 2012-147115A is an example of background art.

SUMMARY

However, when a large degree of pressure is applied to the diaphragms16aand16bin this capacitance type of acoustic sensor11, there are cases where the diaphragms16aand16band the back plate19become damaged. Examples of situations in which a large degree of pressure is applied to the diaphragms16aand16binclude the case where the diaphragms16aand16bare subjected to the pressure of air entering through the cavity13in a drop test performed on the acoustic sensor11, the case where the device, such as a mobile phone, that includes the acoustic sensor11is dropped, the case where air is forcefully blown into the mouthpiece of a mobile phone that includes the acoustic sensor11, and the case where the mouthpiece is tapped by a finger or the like. In these cases, a pressure of several hundred Pa or more is applied to the diaphragms16aand16b(the maximum measurable sound pressure of the acoustic sensor is up to 200 Pa).

For example,FIG. 2shows the acoustic sensor11mounted on a casing22. In this structure, a sound introduction hole23is formed in the casing22in opposition to the cavity13of the acoustic sensor11, and acoustic vibration enters the acoustic sensor11through the sound introduction hole23and is detected by the first diaphragm16aand the second diaphragm16b. If the casing22with the acoustic sensor11included therein is dropped on a floor24, the air pressure inside the cavity13rises due to the air current entering through the sound introduction hole23, and the diaphragms16aand16bundergo large deformation due to the pressure load.

If a large degree of pressure P is applied to the diaphragms16aand16bin this way, as shown inFIGS. 3A to 3C, the diaphragms16aand16bbend a large amount due to the pressure P, the diaphragms16aand16bcollide with the back plate19, and the back plate19also undergoes deformation. Here,FIGS. 3A, 3B, and 3Care respectively a schematic cross-sectional diagram taken along a line X1-X1inFIG. 1B, a schematic cross-sectional diagram taken along a line X2-X2inFIG. 1B, and a schematic cross-sectional diagram taken along a line X3-X3inFIG. 1B. There are cases where the diaphragms16aand16band the back plate19become damaged or cracked as a result of undergoing large deformation or due to shock during an impact, and the damage resistance of the acoustic sensor11may be poor. In particular, as shown inFIG. 3C, the second diaphragm16bfor high-volume sounds has increased rigidity and a reduced area in order to operate optimally in the case of high sound pressure, and therefore is likely to become damaged due to undergoing steep deformation and the occurrence of large distortion.

One or more embodiments of the present invention provides a capacitance type of acoustic transducer that can maintain the frequency characteristics in acoustic vibration detection while also being able to avoid the concentration of stress and damage to a vibrating electrode plate (diaphragm) and a back plate by suppressing deformation of the vibrating electrode plate when a large degree of air pressure is applied.

An acoustic transducer according to one or more embodiments of the present invention includes: a substrate having a cavity; a vibrating electrode plate arranged above the substrate and having a void portion configured to allow pressure to escape; a fixed electrode plate arranged above the substrate so as to oppose the vibrating electrode plate; a plurality of sensing portions configured by the vibrating electrode plate and the fixed electrode plate, at least one of the vibrating electrode plate and the fixed electrode plate being divided into a plurality of regions, and a sensing portion being configured by the vibrating electrode plate and the fixed electrode plate in each of the divided regions; and a leak pressure regulation portion arranged so as to hinder leakage of air pressure passing through the void portion when the vibrating electrode plate is not undergoing deformation, and to become separated from the void portion and allow pressure to escape by passing through the void portion when the vibrating electrode plate undergoes deformation due to being subjected to pressure. Here, the void portion need only be able to allow pressure to escape, and can be an opening, a recession (notch), a hole, a slit-shaped gap, or the like.

In the acoustic transducer of one or more embodiments of the present invention, a void portion for the escape of pressure is provided in the vibrating electrode plate, and the leakage of air pressure passing through the void portion is hindered by the leak pressure regulation portion when the vibrating electrode plate is not undergoing deformation due to excessive pressure, thus making it unlikely for air pressure to escape through the void portion in the normal operating state. Accordingly, the measurement sensitivity of the acoustic transducer in the low frequency range is not likely to decrease, regardless of the fact that the void portion is provided in the vibrating electrode plate. On the other hand, when the vibrating electrode plate is subjected to excessive pressure and the vibrating electrode plate undergoes large deformation, the void portion is opened and the excessive pressure (high-load pressure) escapes through the void portion, thus suppressing deformation of the vibrating electrode plate due to the excessive pressure. For this reason, the vibrating electrode plate is not likely to become damaged even if the acoustic transducer is dropped or excessive pressure is applied.

In an acoustic transducer according to one or more embodiments of the present invention, the plurality of sensing portions output signals with different sensitivities. Accordingly, the dynamic range of the acoustic transducer can be widened by compositing or switching the signals from the sensing portions.

In an acoustic transducer according to one or more embodiments of the present invention, the void portion is a gap between divided regions of the vibrating electrode plate. Accordingly, the vibrating electrode plate can be divided into a plurality of regions by the gap. It is therefore possible for the void portion for the escape of air pressure to also serve as the opening for dividing the vibrating electrode plate into multiple regions, and the structure of the vibrating electrode plate can be simplified. Also, the total opening area in the vibrating electrode plate (the sum of the area of the void portion for the escape of air pressure and the area of the opening for dividing the vibrating electrode plate) is reduced, thus contributing to a reduction in the size of the acoustic transducer and also improving the strength of the vibrating electrode plate.

Also, in one or more embodiments of the present invention, the leak pressure regulation portion is a plate-shaped member that is accommodated in the gap in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation. Accordingly, the leakage of pressure through the gap is hindered by the leak pressure regulation portion in the normal operating state, but when the vibrating electrode plate undergoes large deformation due to excessive pressure, the gap in the vibrating electrode plate moves away from the leak pressure regulation portion so as to open and allow the escape of pressure.

In an acoustic transducer according to one or more embodiments of the present invention, the void portion is an opening formed in the vibrating electrode plate. In one or more embodiments of the present invention, the leak pressure regulation portion may be a plate-shaped member that is accommodated in the opening in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation. Accordingly, the leakage of pressure through the opening can be hindered by the leak pressure regulation portion in the normal operating state, but when the vibrating electrode plate undergoes large deformation due to excessive pressure, the opening in the vibrating electrode plate moves away from the leak pressure regulation portion so as to open and allow the escape of pressure through the opening.

In an acoustic transducer according to one or more embodiments of the present invention, the void portion is a recession that is formed in an edge of the vibrating electrode plate and is recessed toward the interior of the vibrating electrode plate. In one or more embodiments of, the leak pressure regulation portion may be a plate-shaped member that is located in the recession in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation. Accordingly, the leakage of air pressure through the recession can be hindered by the leak pressure regulation portion in the normal operating state, but when the vibrating electrode plate undergoes large deformation due to excessive pressure, the recession in the vibrating electrode plate moves away from the leak pressure regulation portion so as to open and allow the escape of pressure through the recession.

In an acoustic transducer according to one or more embodiments of the present invention, the leak pressure regulation portion is located in the void portion in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation, and a slit is formed between an edge of the leak pressure regulation portion and an edge of the void portion. This is because if the slit is not formed between the leak pressure regulation portion and the void portion, the leak pressure regulation portion and the vibrating electrode plate will partially be in contact, and therefore the vibration of the vibrating electrode plate will be hindered by the leak pressure regulation portion, and the sensitivity of the acoustic transducer and the like will be influenced. Also, if the width of the slit is less than or equal to 10 μm, a reduction in the sensitivity of the acoustic transducer in the low frequency range can be sufficiently suppressed.

Also, in one or more embodiments of the present invention, in which the gap between the regions obtained by division of the vibrating electrode plate serves as the leak pressure regulation portion, it is desirable that an end of a slit formed between the leak pressure regulation portion and a divided region of the vibrating electrode plate located on one side across the gap and an end of a slit formed between the leak pressure regulation portion and a divided region of the vibrating electrode plate located on another side across the gap intersect with an angle of 90°. Accordingly, stress is not likely to concentrate in the leak pressure regulation portion, and it is possible to avoid the formation of a portion having a large opening area in part of the gap.

In another mode of the leak pressure regulation portion, the leak pressure regulation portion may be a portion of an upper surface of the substrate that is located so as to block the lower opening of the void portion in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation. Also, the leak pressure regulation portion may be arranged in opposition to an upper side or a lower side of the vibrating electrode plate so as to block one of an upper opening and a lower opening of the void portion in the vibrating electrode plate when the vibrating electrode plate is not undergoing deformation (note that blockage by the leak pressure regulation portion in this description does not mean hermitic sealing).

In an acoustic transducer according to one or more embodiments of the present invention, a back plate may be arranged above the substrate so as to oppose the vibrating electrode plate, a support portion may be provided on a surface of the back plate that opposes the vibrating electrode plate, and the leak pressure regulation portion may be fixed to the support portion. Accordingly, the leak pressure regulation portion does not undergo deformation even when subjected to excessive pressure, thus making it possible to reliably open the void portion in the vibrating electrode plate when excessive pressure is applied.

In this case, it is desirable that the horizontal cross-sectional area of the support portion is smaller than the area of the leak pressure regulation portion. Accordingly, a space for the escape of pressure can be ensured between the vibrating electrode plate and the outer peripheral surface of the support portion.

Also, the leak pressure regulation portion may be supported by a plurality of support portions. If the leak pressure regulation portion is supported by multiple support portions, the rigidity of the leak pressure regulation portion increases, and the leak pressure regulation portion is not likely to undergo deformation even when subjected to excessive pressure.

Also, in the case where a plurality of support portions are provided, a through-hole may be provided in the back plate between adjacent support portions. Accordingly, excessive pressure can be more efficiently allowed to escape to the outside.

Also, the leak pressure regulation portion may be fixed to a support portion provided on an upper surface of the substrate.

In an acoustic transducer according to one or more embodiments of the present invention, a back plate is arranged above the substrate so as to oppose the vibrating electrode plate, the fixed electrode plate is provided on the back plate so as to oppose the vibrating electrode plate, a plurality of acoustic holes are formed in the back plate and the fixed electrode plate, and a portion of the acoustic holes are overlapped with the void portion in a view from a direction perpendicular to the upper surface of the substrate. Accordingly, excessive pressure can be allowed to smoothly escape to the outside.

In an acoustic transducer according to one or more embodiments of the present invention, a back plate is arranged above the substrate so as to oppose the vibrating electrode plate, the fixed electrode plate is provided on the back plate so as to oppose the vibrating electrode plate, a plurality of acoustic holes are formed in the back plate and the fixed electrode plate, and a portion of the acoustic holes are overlapped with the slit in a view from a direction perpendicular to the upper surface of the substrate. Accordingly, the path for the escape of excessive pressure is short, and therefore excessive pressure can be allowed to smoothly escape to the outside.

In an acoustic transducer according to one or more embodiments of the present invention, a back plate is arranged above the substrate so as to oppose the vibrating electrode plate, the fixed electrode plate is provided on the back plate so as to oppose the vibrating electrode plate, a plurality of acoustic holes are formed in the back plate and the fixed electrode plate, and the width of the leak pressure regulation portion is greater than the distance between adjacent acoustic holes in a view from a direction perpendicular to the upper surface of the substrate. Accordingly, the acoustic holes located above the leak pressure regulation portion are not likely to be blocked by the vibrating electrode plate, and excessive pressure can be reliably discharged.

In an acoustic transducer according to one or more embodiments of the present invention, a back plate is arranged above the substrate so as to oppose the vibrating electrode plate, and the fixed electrode plate is provided on the back plate so as to oppose the vibrating electrode plate and not oppose the leak pressure regulation portion. Accordingly, the parasitic capacitance generated between the leak pressure regulation portion and the fixed electrode plate can be reduced.

In an acoustic transducer according to one or more embodiments of the present invention, the fixed electrode plate is divided into a plurality of regions, and a barrier electrode for blocking electrical signal leakage is provided between divided regions of the fixed electrode plate. Accordingly, it is possible to prevent the leakage of signals and the transmission of noise between adjacent sensing portions.

In an acoustic transducer according to one or more embodiments of the present invention, a back plate is arranged above the substrate so as to oppose the vibrating electrode plate, and a protrusion is provided on the back plate so as to oppose a region of the vibrating electrode plate that is adjacent to the void portion. Accordingly, when the vibrating electrode plate undergoes large deformation, it is not likely to adhere to the fixed electrode plate due to being hindered by the protrusions.

In an acoustic transducer according to one or more embodiments of the present invention, the divided regions of the vibrating electrode plate and the leak pressure regulation portion are in the same plane and are formed using the same material. Accordingly, the vibrating electrode plate and the leak pressure regulation portion can be created at the same time using the same process.

The acoustic transducer according to one or more embodiments of the present invention is applicable to a microphone.

A scope of the present invention includes combinations of the above-described constituent elements, and many variations to disclosed embodiments are possible according to the combination of the constituent elements.

DETAILED DESCRIPTION

The following describes embodiments of the present invention with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiments, and various design modifications can be made within the scope of the present invention. In embodiments of the invention, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to one of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid obscuring the invention.

The following describes the structure of an acoustic sensor according to Embodiment 1 of the present invention with reference toFIGS. 4 to 7.FIG. 4is an exploded perspective view of an acoustic transducer according to Embodiment 1 of the present invention, that is to say an acoustic sensor31.FIG. 5is a cross-sectional diagram of the acoustic sensor31.FIG. 6is a plan view of the acoustic sensor31.FIG. 7is a plan view of the acoustic sensor31from which a back plate38, a protective film50, and the like have been removed, and shows a state in which a diaphragm33(vibrating electrode plate) and a fixed electrode plate39are overlapped with each other above a substrate32.

The acoustic sensor31is a capacitance type of device created using MEMS technology. As shown inFIGS. 4 and 5, in the acoustic sensor31, the diaphragm33is provided on the upper surface of a substrate32, which is made of a silicon substrate or the like, via anchors36aand36b, a canopy portion34is arranged above the diaphragm33via a very small air gap40, and the canopy portion34is fixed to the upper surface of the substrate32.

A cavity35(front chamber, back chamber) is formed in the substrate32so as to pass from the upper surface to the lower surface. Although the cavity35shown here is surrounded by surfaces that are perpendicular to the upper surface of the substrate32, the wall surfaces of the cavity35may be surfaces that are inclined with respect to the upper surface of the substrate32.

The diaphragm33is arranged above the substrate32so as to cover the cavity35. As shown inFIGS. 4 and 7, the diaphragm33is formed in a substantially rectangular shape. The diaphragm33is formed by a conductive polysilicon thin film, and the diaphragm33itself serves as a vibrating electrode plate. A void portion for allowing pressure to escape, that is to say an opening33cthat extends in a direction parallel to the short sides of the diaphragm33, is provided in the diaphragm33, and the diaphragm33is divided into a first diaphragm33aand a second diaphragm33bby the opening33c. The first diaphragm33aand the second diaphragm33bare partially connected on one of the long sides of the diaphragm33. The first diaphragm33aand the second diaphragm33bare both substantially rectangular, and the first diaphragm33ahas a larger area than the second diaphragm33b.

Leg pieces46provided in corner portions of the first diaphragm33aare supported on the upper surface of the substrate32by anchors36a, and thus the first diaphragm33ais supported so as to float above the upper surface of the substrate32. Between the adjacent anchors36a, a narrow vent hole42afor allowing the passage of acoustic vibration is formed between the upper surface of the substrate32and the lower surface of the outer peripheral portion of the first diaphragm33a.

The two short sides of the second diaphragm33bare supported on the upper surface of the substrate32by anchors36b, and thus the second diaphragm33bis supported so as to float above the upper surface of the substrate32. A narrow vent hole42bfor allowing the passage of acoustic vibration is formed between the upper surface of the substrate32and the lower surface of a long side of the second diaphragm33b. The vent hole42aand the vent hole42bare gaps having the same height.

A leak pressure regulation portion37(referred to hereinafter as simply the regulation portion37) made of a polysilicon thin film is provided in the opening33cbetween the first diaphragm33aand the second diaphragm33b. As shown inFIG. 5, the regulation portion37is supported horizontally below the later-described back plate38by multiple support portions48that extend downward from the back plate38. A slit-shaped gap, that is to say a slit47(a portion of the opening33e), is formed over the entire circumference of the regulation portion37, and thus the regulation portion37is completely separated from the first diaphragm33aby the slit47, and also completely separated from the second diaphragm33bby the slit47.

A lead-out interconnect49aprovided on the upper surface of the substrate32is connected to the diaphragm33. Furthermore, a strip-shaped base portion41is formed on the upper surface of the substrate32so as to surround the diaphragm33. The anchors36aand36band the base portion41are formed by SiO2.

As shown inFIG. 5, the canopy portion34is obtained by providing the fixed electrode plate39, which is made of a conductive polysilicon thin film, on the lower surface of the back plate38, which is made of SiN. The canopy portion34is shaped as a dome and has a cavity portion on its underside, and the diaphragm33is covered by the cavity portion. A very small air gap40is formed between the lower surface of the fixed electrode plate39and the upper surface of the diaphragm33.

The fixed electrode plate39is divided into a first fixed electrode plate39athat opposes the first diaphragm33aand a second fixed electrode plate39bthat opposes the second diaphragm33b, and the fixed electrode plates39aand39bare electrically separated from each other. The first fixed electrode plate39ahas a larger area than the second fixed electrode plate39b. A lead-out interconnect49bextends from the first fixed electrode plate39a, and a lead-out interconnect49cextends from the second fixed electrode plate39b.

A first acoustic sensing portion43ahaving a capacitor structure is formed by the first diaphragm33aand the first fixed electrode plate39athat oppose each other across the air gap40. Also, a second acoustic sensing portion43bhaving a capacitor structure is formed by the second diaphragm33band the second fixed electrode plate39bthat oppose each other across the air gap40. The gap distance of the air gap40in the first acoustic sensing portion43ais the same as the gap distance of the air gap40in the second acoustic sensing portion43b.

A large number of acoustic holes44for allowing acoustic vibration to pass are formed in the back plate38and the fixed electrode plate39so as to pass from the upper surface to the lower surface. Note that in the illustrated example, the hole diameter and pitch of the acoustic holes44are the same in the first acoustic sensing portion43aand the second acoustic sensing portion43b, but there are cases where the hole diameter and pitch of the acoustic holes44are different in the two acoustic sensing portions43aand43b.

As shown inFIGS. 6 and 7, the acoustic holes44are in a regular arrangement in both of the two acoustic sensing portions43aand43b. The acoustic holes44are arranged in a triangular shape along three directions that form 120° angles with each other in the illustrated example, but they may be arranged in a rectangular shape, concentric circles, or the like.

As shown inFIG. 5, in both the first acoustic sensing portion43aand the second acoustic sensing portion43b, very small stoppers45(protrusions) shaped as circular columns project from the lower surface of the canopy portion34. The stoppers45integrally project from the lower surface of the back plate38, pass through the first and second fixed electrode plates39aand39b, and project from the lower surface of the canopy portion34. The stoppers45are insulating due to being made of SiN likewise to the back plate38. The stoppers45are for preventing the diaphragms33aand33bfrom adhering to and not separating from the fixed electrode plates39aand39bdue to electrostatic force. Also, multiple support portions48extend downward from locations opposing the regulation portion37as described above, and the regulation portion37is horizontally supported on the lower ends of the support portions48.

A protective film50extends in a continuous manner around the entire circumference of the outer peripheral edge of the canopy-shaped back plate38. The protective film50covers the base portion41and the surface of the silicon substrate outward thereof.

A common electrode pad51, a first electrode pad52a, a second electrode pad52b, and a grounding electrode pad53are provided on the upper surface of the protective film50. The other end of the lead-out interconnect49aconnected to the diaphragm33is connected to the common electrode pad51. The lead-out interconnect49bextending from the first fixed electrode plate39ais connected to the first electrode pad52a, and the lead-out interconnect49cextending from the second fixed electrode plate39bis connected to the second electrode pad52b. Also, the grounding electrode pad53is connected to the substrate32and held at ground potential.

Next, operations when the acoustic sensor31detects acoustic vibration and operations of the acoustic sensor31when a large degree of high-load pressure is applied to the diaphragm33will be described.FIG. 5is a cross-sectional diagram of the acoustic sensor31in a state in which high-load pressure is not being applied to the diaphragm33.FIG. 9is a schematic cross-sectional diagram of the acoustic sensor31in a state in which high-load pressure is being applied to the diaphragm33.

In the case where the acoustic sensor31is not being subjected to a large degree of high-load pressure and is detecting only acoustic vibration, the diaphragm33vibrates upward and downward with a small amplitude, centered about the flat state shown inFIG. 5. When the diaphragms33aand33bvibrate in response to acoustic vibration that entered the acoustic sensor31from the cavity35, a change occurs in the capacitance of the variable capacitor configured by the first fixed electrode plate39aand the first diaphragm33a(the capacitance of the first acoustic sensing portion43a), and a change occurs in the capacitance of the variable capacitor configured by the second fixed electrode plate39band the second diaphragm33b(the capacitance of the second acoustic sensing portion43b). As a result, in the acoustic sensing portions43aand43b, the acoustic vibration (change in sound pressure) detected by the diaphragms33aand33bbecomes change in the respective capacitances and is output as electrical signals with different sensitivities.

Also, since the area of the second diaphragm33bis smaller than the area of the first diaphragm33a, the second acoustic sensing portion43bis a low-sensitivity acoustic sensor for a sound pressure range of mid volume to high volume, and the first acoustic sensing portion43ais a high-sensitivity acoustic sensor for a sound pressure range of low volume to mid volume. Accordingly, the two acoustic sensing portions43aand43bare hybridized and output signals by processing circuits, thus making it possible to widen the dynamic range of the acoustic sensor31. For example, assuming that the dynamic range of the first acoustic sensing portion43ais approximately 30 to 120 dB, and that the dynamic range of the second acoustic sensing portion43bis approximately 50 to 140 dB, combining the two acoustic sensing portions43aand43bmakes it possible to widen the dynamic range to approximately 30 to 140 dB. Also, if the acoustic sensor31is divided into the first acoustic sensing portion43afor range of low volume to mid volume and the second acoustic sensing portion43bfor the range of mid volume to high volume, it is possible to not use the output of the first acoustic sensing portion43ain the case of a high volume, and therefore there may be no issues even if there is a large amount of harmonic distortion in the large sound pressure range of the first acoustic sensing portion43a. Accordingly, it is possible to raise the sensitivity of the first acoustic sensing portion43awith respect to low volume.

Furthermore, in the acoustic sensor31, the first acoustic sensing portion43aand the second acoustic sensing portion43bare formed on the same substrate. Moreover, the first acoustic sensing portion43aand the second acoustic sensing portion43bare configured by the first diaphragm33aand the second diaphragm33bobtained by dividing the diaphragm33, and the first fixed electrode plate39aand the second fixed electrode plate39bobtained by dividing the fixed electrode plate39. In other words, the sensing portion that was originally one sensing portion is divided into two so as to hybridize the first acoustic sensing portion43aand the second acoustic sensing portion43b, and therefore the first acoustic sensing portion43aand the second acoustic sensing portion43bhave similar variation regarding detection sensitivity in comparison to a conventional acoustic sensor in which two independent sensing portions are provided on a single substrate or a conventional acoustic sensor in which sensing portions are provided on separate substrates. As a result, detection sensitivity variation between the two acoustic sensing portions43aand43bcan be reduced. Also, since the diaphragm and the fixed electrode plate are common to the two acoustic sensing portions43aand43b, it is possible to suppress mismatching regarding frequency characteristics and acoustic characteristics such as the phase.

Next, the relationship between the frequency characteristics of the acoustic sensor31and the regulation portion37will be described. If the regulation portion37were not present, the opening33cwould be in an open state between the first diaphragm33aand the second diaphragm33b, and therefore acoustic vibration would be more likely to pass through the opening33cthan pass through the narrow vent holes42aand42b. For this reason, acoustic resistance in the acoustic path between the upper side and the lower side of the diaphragm33would be smaller. Assume that curve Q1shown by the solid line inFIG. 8shows the frequency characteristics of the acoustic sensor in the case where the opening33cis not formed in the diaphragm33. In the case where the opening is open, the acoustic resistance decreases, and therefore the sensitivity of the acoustic sensor in the low frequency range decreases as shown by a curve Q2shown by the dashed line inFIG. 8.

With the acoustic sensor31of Embodiment 1, the opening33cis formed between the first diaphragm33aand the second diaphragm33b, but the opening33cis substantially blocked by the regulation portion37in the normal acoustic vibration detection mode, and therefore the leakage of air pressure is hindered by the regulation portion37, acoustic resistance is not likely to decrease, and the sensitivity of the acoustic sensor in the low frequency range is not likely to decrease.

If the two diaphragms33aand33band the regulation portion37are in contact with each other, vibration of the diaphragms33aand33bis hindered by the regulation portion37, and there is the risk of a decrease in the sensitivity of the acoustic sensor31and a decrease in the S/N ratio. For this reason, the area of the regulation portion37is made somewhat smaller than the opening area of the opening33csuch that the diaphragms33aand33band the regulation portion37are separated from each other. Specifically, the slit47having a substantially constant width w is provided between the inner peripheral surface of the opening33cand the outer peripheral surface of the regulation portion37.

On the other hand, if the width w of the slit47is too large, there is the risk that the ventilation effect will intensify, too much air pressure will pass through the slit47, the roll-off frequency will decrease, and the low frequency characteristics will degrade. This point will be described in detail below.

AforementionedFIG. 8shows typical frequency characteristics in a MEMS microphone, and the horizontal axis and the vertical axis in this figure respectively indicate the frequency of acoustic vibration (unit: Hz) and the relative sensitivity (unit: dB/dB). InFIG. 8, the range in which the plotted line is horizontal is a range in which sound waves can be favorably detected since the relative sensitivity is not dependent on the frequency of the sound waves. The frequency at the lower limit of this range will be referred to as the roll-off frequency f roll-off.

In general, the roll-off frequency f roll-off is dependent on the acoustic resistance R venthole in the acoustic vibration path and the compliance of air in the cavity35(air spring constant) C chamber, and is expressed by the following expression.
froll-off ∝1/(Rventhole×Cchamber)  Exp. 1

The acoustic resistance R venthole is also influenced by the length of the slit47, and decreases as the width w of the slit47increases. Therefore, according to Exp. 1 above, the roll-off frequency f roll-off will increase, and the low frequency characteristics will degrade as a result. For example, if the width w of the slit47is 10 μm, the roll-off frequency f roll-off will be 500 Hz or more. For this reason, if the width w of the slit47exceeds 10 μm, the low frequency characteristics degrade significantly, and sound quality is impaired. It is therefore desirable that the width w of the slit47is less than or equal to 10 μm.

Next, the state in which high-load pressure is applied to the first diaphragm33aand the second diaphragm33bof the acoustic sensor31will be described with reference toFIG. 9. The diaphragms33aand33bare subjected to a large degree of high-load pressure P in cases such as where the acoustic sensor31is subjected to a drop test, the device that includes the acoustic sensor31is dropped, or air is forcefully blown into the acoustic sensor31. When a large degree of pressure is applied to the acoustic sensor31from the cavity35side, the first diaphragm33aand the second diaphragm33bare subjected to the large degree of pressure P and undergo large deformation due to having a low elasticity and being flexible. In contrast, the regulation portion37is supported by the support portions48, and therefore does not move along with the two diaphragms33aand33b. Also, since the regulation portion37has a smaller area than the diaphragms33aand33band is rigid, the regulation portion37does not undergo deformation along with the diaphragms33aand33beven when subjected to a large degree of pressure. For this reason, when the first diaphragm33aand the second diaphragm33bundergo large deformation, the regulation portion37comes out of the opening33csuch that the opening33cis opened, and thus a space is formed for allowing the passage of the pressure P between the outer peripheral surface of the support portions48and the edge of the opening33c. As a result, as shown inFIG. 9, the pressure P escapes to the outside through the opening33cand the acoustic holes44, and the pressure applied to the diaphragms33aand33bis reduced, and therefore the amount of deformation of the diaphragms33aand33bdecreases. This reduces the shock that diaphragms33aand33bapply to the back plate38, a large amount of stress is not likely to be applied to the diaphragms33aand33band the back plate38, and the diaphragms33aand33band the back plate38are not likely to become damaged or cracked (i.e., the damage resistance improves).

In contrast, although the slit17is provided between the first diaphragm16aand the second diaphragm16bin the acoustic sensor11of JP 2012-147115A as well, if the width of the slit17is increased so as to allow a large degree of pressure to escape, the acoustic resistance decreases, and the low frequency characteristics of the acoustic sensor11degrade.

In the acoustic sensor31of Embodiment 1, in order for the pressure P that passed through the opening33cto smoothly escape to the outside through the acoustic holes44, it is desirable that a portion of the acoustic holes44are overlapped with the slit47between the diaphragms33aand33band the regulation portion37in a view from a direction perpendicular to the upper surface of the substrate32as shown inFIG. 10. If the slit47and the acoustic holes44are not overlapped with each other, and are out of alignment in the horizontal direction as shown inFIG. 11A, the path for the escape of the pressure P applied to the diaphragms33aand33bis long, and it becomes difficult for the pressure P to escape. In contrast, if the slit47and the acoustic holes44are overlapped with each other as shown inFIG. 11B, the path for the escape of the pressure P applied to the diaphragms33aand33bis short, the pressure P easily escapes, and it is possible to efficiently reduce the pressure applied to the diaphragms33aand33b.

Also, the regulation portion37is suspended from the back plate38by multiple support portions48arranged along the length direction of the regulation portion37as shown inFIG. 10. Furthermore, one or more through-holes54are provided in the back plate38at respective positions between adjacent support portions48. The through-holes54may be some of the acoustic holes44. If the regulation portion37is supported by multiple support portions48, the rigidity of the regulation portion37can be raised, and regulation portion37is less likely to undergo deformation due to high-load pressure P. If the regulation portion37undergoes deformation due to the pressure P, the path between the regulation portion37and the diaphragms33aand33bbecomes narrower, but if the rigidity of the regulation portion37is raised so as to make it less likely to undergo deformation, the path of the pressure P can be ensured. Moreover, providing the through-holes54between adjacent support portions48makes it possible for the pressure P to escape more efficiently.

Also, the cross-sectional area of the support portions48is smaller than the area of the regulation portion37, and in particular, the diameter of the support portions48is shorter than the width of the regulation portion37. According to this configuration, as shown inFIG. 9, it is possible to widen the path that is for allowing the pressure P to escape and is formed between the outer peripheral surface of the support portions48and the edges of the deformed first diaphragm33aand second diaphragm33b. Furthermore, as shown inFIG. 12A, the width D of the regulation portion37is greater than the distance d between adjacent acoustic holes44(distance between their edges). This is because if the width D of the regulation portion37is smaller than the distance d between adjacent acoustic holes44(distance between their edges) as shown inFIG. 12B, the acoustic holes44are blocked by the edges of the diaphragms33aand33b, and the path for allowing the escape of the pressure P is blocked.

Also,FIG. 13is an enlarged view of a portion Z inFIG. 7. It is desirable that the angle of intersection θ between the end portion of the slit47formed between the edge of the first diaphragm33aand the regulation portion37and the end portion of the slit47formed between the edge of the second diaphragm33band the regulation portion37is substantially 90° as shown inFIG. 13. If the intersection between the portions of the slit47is acutely angled as shown inFIG. 14A, there is the possibility of breakdown of the stacked thin-film structure including the polysilicon thin film, a sacrifice layer, and the like in the manufacturing process due to residual stress in the polysilicon thin film making up the diaphragm33and the regulation portion37in the manufacturing process for the acoustic sensor31. Also, if the acutely angled location inFIG. 14Ais rounded as shown inFIG. 14Bin order to mitigate the concentration of stress in the polysilicon thin film, a region55having a large opening area is formed in the slit47, acoustic vibration is likely to leak from this region, and the characteristics of the acoustic sensor31in the low frequency range degrade. In contrast, if portions of the slit47are gradually curved such that end portions of the slit47intersect at an angle of approximately 90° as shown inFIG. 13, the concentration of stress in the polysilicon thin film (regulation portion37) can be mitigated without allowing degradation of the characteristics of the acoustic sensor31in the low frequency range.

Next, as is shown inFIGS. 5 and 9, it is desirable that neither the first fixed electrode plate39anor the second fixed electrode plate39bis provided in a region that is overlapped with the regulation portion37in a view from a direction perpendicular to the upper surface of the substrate32. This is because the parasitic capacitance generated between the regulation portion37and the fixed electrode plate39increases if they oppose each other.

Also, since the regulation portion37is arranged between the first diaphragm33aand the second diaphragm33bin Embodiment 1, the distance between the first acoustic sensing portion43aand the second acoustic sensing portion43bcan be increased. In particular, the distance between the first diaphragm33aand the second fixed electrode plate39band the distance between the second diaphragm33band the first fixed electrode plate39acan be increased. As a result, it is possible to reduce mutual interference between signals from the first acoustic sensing portion43aand the second acoustic sensing portion43b, and to reduce the harmonic distortion rate of the acoustic sensor31. Furthermore, since the regulation portion37is arranged between the first diaphragm33aand the second diaphragm33b, the opening33cfor the arrangement of the regulation portion37can also serve as the opening for separating the diaphragms33aand33bfrom each other, and it is possible to increase the area of the opening33cfor allowing the escape of a high-load pressure P, while also reducing the size of the acoustic sensor31by logically arranging the opening33c. Moreover, the regulation portion37and the opening33ccan be arranged without a large decrease in the area (electrode area) of the first diaphragm33aand the second diaphragm33b, thus making it possible to reduce a decrease in the sensitivity of the acoustic sensor31even if the size of the acoustic sensor31is the same.

Also, in Embodiment 1, when the diaphragm33is not undergoing deformation, the diaphragm33and the regulation portion37are in the same plane and are merely separated by the slit47, and therefore the diaphragm33and the regulation portion37can be created using the same material and using the same film formation process, thus making it possible to simplify the manufacturing process. Moreover, since the slit47can be formed by performing photolithography one time and etching one time, the slit47can be formed so as to have a narrow width, and the acoustic resistance can be reduced.

Furthermore, a portion of the stoppers45are arranged in a region of the lower surface of the back plate38that opposes the edge portions of the first diaphragm33aand the second diaphragm33b(particularly the regions that undergo large deformation). If stoppers45are provided at these positions, it is possible to prevent the diaphragms33aand33bfrom adhering to and not separating from the fixed electrode plates39aand39bwhen they have undergone large deformation due to a large degree of pressure P.

Variations of Embodiment 1

A variation of Embodiment 1 of the present invention will be described below with reference toFIGS. 15 to 18.FIG. 15Ais a plan view showing an acoustic sensor according to a variation of Embodiment 1 of the present invention, in a state in which the back plate has been removed. In this variation, a circular opening33cis provided in the substantially central portion of the first diaphragm33a. When the first diaphragm33ais not undergoing deformation, the circular regulation portion37provided on the lower end of the support portion48extending downward from the back plate38is located inside the opening33cand blocks the opening33c. Note that a slit-shaped opening56is for separating the first diaphragm33aand the second diaphragm33b, and extends parallel to the short side direction of the diaphragm33.

In the variation shown inFIG. 15A, the first diaphragm33aand the second diaphragm33bundergo large deformation when high-load pressure is applied to the diaphragm33, and the regulation portion37comes out of the opening33cwhen the first diaphragm33aundergoes deformation. For this reason, the pressure P escapes through the opening33c, and deformation of the first diaphragm33aand of course the second diaphragm33bas well is suppressed.

Also, the opening33cand the regulation portion37may be provided in the substantially central portion of the second diaphragm33bas in another variation shown inFIG. 15B. Alternatively, there may be no issues if both the first diaphragm33aand the second diaphragm33bare provided with an opening33cand a regulation portion37, although this is not shown.

Also, the opening33cand the regulation portion37may be rectangular or polygonal as in yet another variation shown inFIG. 16A. Note that if the corner portions of the opening33cand the regulation portion37are rounded in this case, it is possible to mitigate the concentration of stress and prevent damage to the diaphragm33and the regulation portion37.

Furthermore, an opening33cand a regulation portion37that are elongated in one direction and extend in a direction parallel to the slit-shaped opening56may be provided in the vicinity of the slit-shaped opening56as shown inFIG. 16B.

If the opening33cis provided in the first diaphragm33aor the second diaphragm33bas shown inFIGS. 15A, 15B, 16A, and 16B, the area of the diaphragm33can be reduced, thus making it possible to contribute to a reduction in the size of the acoustic sensor31.

With the diaphragm33shown inFIG. 7, the first diaphragm33aand the second diaphragm33bare partially connected at the bottom of the figure, but the first diaphragm33aand the second diaphragm33bmay be partially connected at the top of the figure as shown inFIG. 17A. Also, the first diaphragm33aand the second diaphragm33bmay be partially connected at the top and the bottom of the figure as shown inFIG. 17B.

Also, the first diaphragm33aand the second diaphragm33bmay be completely separated mechanically and electrically as shown inFIG. 18. In this case, there may be no issues if the first fixed electrode plate39aand the second fixed electrode plate39bare continuous with each other.

FIG. 19Ais a plan view showing an acoustic sensor61according to Embodiment 2 of the present invention, in a state in which a back plate38has been removed.FIG. 19Bis a schematic cross-sectional diagram showing a state in which high-load pressure P has been applied to the acoustic sensor61. In the acoustic sensor61of Embodiment 2, recessions62that are recessed toward the interior of the diaphragm33in the shape of a notch (void portions for allowing pressure to escape) are formed in the sides (outer peripheral portions) of the diaphragm33as shown inFIG. 19A. Specifically, the recessions62are provided in regions between adjacent leg pieces46on the sides of the first diaphragm33athat are not adjacent to the second diaphragm33b. Alternatively, the recessions62may be provided on the long side of the second diaphragm33bthat is not adjacent to the first diaphragm33a, or the recessions62may be provided on the sides of both the first diaphragm33aand the second diaphragm33b. According to one or more embodiments of the present invention, the recessions62reaches the vicinity of the cavity35, and may reach the top of the cavity35. Also, regulation portions37are positioned so as to fit into the recessions62. The regulation portions37are positioned at the same height as the diaphragm33, and are separated from the diaphragms33aand33bby slits63. The other structures and variations are similar to Embodiment 1. According to one or more embodiments of the present invention, the width of the slits63is less than or equal to 10 μm, acoustic holes44are formed directly above the slits63in an overlapping manner, the acutely angled portion of the regulation portion37is rounded, and so on.

With the acoustic sensor61as well, when the diaphragm33is subjected to high-load pressure P from the cavity35side, the sides of the first diaphragm33aand the second diaphragm33bfloat upward as well as shown inFIG. 19B, and gaps for allowing pressure to escape are formed at the positions of the recessions62. Accordingly, deformation of the first diaphragm33aand the second diaphragm33bcan be reduced by allowing the high-load pressure P to escape, and damage to the diaphragms33aand33band the back plate38can be avoided.

Also, in Embodiment 2, the recessions62are provided at locations away from the regions of the first diaphragm33aand the second diaphragm33bthat primarily function as an electrode (i.e., the central portions), thus reducing the negative influence on the sensitivity of the acoustic sensor61. Note that since the area of a single recession62cannot be made too large in Embodiment 2, it is desirable that multiple separate recessions62are provided.

FIG. 20Ais a schematic cross-sectional diagram of an acoustic sensor71according to Embodiment 3 of the present invention.FIG. 20Bis a plan view of the acoustic sensor71in a state in which the back plate38has been removed. In the acoustic sensor71of Embodiment 3, a barrier electrode72is provided in a region of the lower surface of the back plate38that opposes the regulation portion37. The barrier electrode72is formed by a conductive polysilicon thin film, and is created using the same material and the same process as the first fixed electrode plate39aand the second fixed electrode plate39bin the manufacturing process for the acoustic sensor71. The barrier electrode72extends along the boundary between the first diaphragm33aand the second diaphragm33b, that is to say substantially from end to end along the length direction of the regulation portion37. Note that the barrier electrode72may be grounded, or may be kept at a certain potential.

If the barrier electrode72is provided, it is possible to prevent noise and signals from being transmitting from the first fixed electrode plate39ato the second fixed electrode plate39bor from the second fixed electrode plate39bto the first fixed electrode plate39a, and it is possible to prevent a reduction in the S/N ratio of the first acoustic sensing portion43aand the second acoustic sensing portion43band the occurrence of crosstalk. Also, by providing the barrier electrode72so as to be overlapped with the regulation portion37in a view from a direction perpendicular to the upper surface of the substrate32, the barrier electrode72and the regulation portion37can be arranged logically, and the size of the acoustic sensor71can be reduced.

Also, the barrier electrode72may be provided parallel to the regulation portion37at a position separated from the regulation portion37as shown inFIGS. 21A and 21B.

Although the diaphragm33is divided into two regions, namely the first diaphragm33aand the second diaphragm33b, in the acoustic sensors of one or more of the above embodiments, the diaphragm33may be divided into three or more regions.FIG. 22is a plan view of an acoustic sensor according to Embodiment 4 of the present invention, in a state in which the back plate has been removed, and the diaphragm33has been divided into three regions. The fixed electrode plate39is also divided into three regions in correspondence with the diaphragm33, and thus the acoustic sensor has three acoustic sensing portions.

The diaphragm33shown inFIG. 22is divided into a first diaphragm33ahaving the largest area, a second diaphragm33bhaving the smallest area, and a third diaphragm33dhaving an intermediate area. The first diaphragm33aand the second diaphragm33bare divided by the opening33c, and the first diaphragm33aand the third diaphragm33dare divided by an opening33e(a void portion for allowing pressure to escape). A regulation portion37is accommodated in the openings33cand33e, and a slit47is formed around each of the regulation portions37. Although not shown, the regulation portions37are each supported horizontally on the lower end of a support portion48extending downward from the back plate38, similarly to the case in Embodiment 1.

The first diaphragm33ahaving the largest area is paired with the corresponding fixed electrode plate so as to configure a high-sensitivity sensing portion for low volume. The second diaphragm33bhaving the smallest area is paired with the corresponding fixed electrode plate so as to configure a low-sensitivity sensing portion for high volume. The third diaphragm33dhaving an intermediate area is paired with the corresponding fixed electrode plate so as to configure an intermediate-sensitivity sensing portion for intermediate volume. Accordingly, Embodiment 4 enables providing an acoustic sensor with a wide dynamic range.

With this acoustic sensor as well, if the diaphragms33a,33b, and33dundergo deformation due to the acoustic sensor being dropped for example, the openings33cand33eopen and high-load pressure escapes such that deformation of the diaphragms33a,33b, and33dis suppressed, and damage to the diaphragms33a,33b, and33dand the back plate38is prevented.

FIG. 23is a cross-sectional diagram of an acoustic sensor81according to Embodiment 5 of the present invention, a feature of which is that diaphragms33aand33bare provided above the fixed electrode plates39aand39b. In the acoustic sensor81, a flat plate-shaped back plate38is provided on the upper surface of the substrate32via an insulation layer82. The fixed electrode plates39aand39bare formed on the upper surface of the back plate38. Multiple acoustic holes44are formed in the back plate38and the fixed electrode plates39aand39babove the cavity35. Also, the diaphragms33aand33bare arranged so as to oppose the fixed electrode plates39aand39babove the back plate38. The diaphragms33aand33bare supported by anchors36aand36bprovided on the upper surface of the back plate38.

The diaphragm has the same structure as the diaphragm33used in the acoustic sensor31of Embodiment 1 for example. Specifically, the diaphragm is divided into the first diaphragm33aand the second diaphragm33b, and the opening33cis provided between the first diaphragm33aand the second diaphragm33b. The regulation portion37is accommodated in the opening33c, and the regulation portion37is fixed to the upper end of the support portion48standing on the upper surface on the back plate38.

In one or more of the above embodiments, the opening33cprovided in the diaphragm33is substantially blocked by the regulation portion37in the normal operating state, but a configuration is possible in which the opening33c, which is the void portion for allowing pressure to escape, is covered by the upper surface of the substrate32so as to hinder the leakage of air pressure in the opening33c.

FIG. 24Ais a schematic cross-sectional diagram of an acoustic sensor91according to Embodiment 6 of the present invention.FIG. 24Bis a schematic cross-sectional diagram of the acoustic sensor91in a state in which a large degree of high-load pressure is being applied to the two diaphragms from below. Also,FIG. 25Ais a plan view of the acoustic sensor91in a state in which the back plate has been removed.FIG. 25Bis a plan view of the substrate32used in the acoustic sensor91.

As shown inFIG. 25A, in the acoustic sensor91, the diaphragm33is divided into the first diaphragm33aand the second diaphragm33b, and the opening33cis formed between the two diaphragms33aand33b. On the other hand, as shown inFIG. 25B, a protrusion portion92that is shaped as a partition wall or a beam and extends parallel to the length direction of the opening33cis provided in the cavity35of the substrate32, and the underside of the opening33cis blocked by the upper surface of the substrate32, or more specifically the upper surface of the protrusion portion92. Accordingly, a portion of the upper surface of the substrate32, that is to say the upper surface of the protrusion portion92, serves as the regulation portion37.

When normal acoustic vibration is being detected in the acoustic sensor91, the leakage of air pressure in the opening33cis hindered by the upper surface of the substrate32(protrusion portion92) as shown inFIG. 24A, and therefore the acoustic resistance of the acoustic sensor91is not likely to decrease, and it is possible to maintain the characteristics of the acoustic sensor91in the low frequency range. In contrast, when the diaphragm33is subjected to high-load pressure P from below, the diaphragms33aand33bfloat upward as shown inFIG. 24Bso as to open the opening33cand allow the pressure P to escape through the opening33c.

FIG. 26Ais a schematic cross-sectional diagram of an acoustic sensor101according to a variation of Embodiment 7 of the present invention. Also,FIG. 26Bis a plan view of the acoustic sensor101in a state in which the back plate has been removed. In the acoustic sensor101, the regulation portion37located in the opening33cis fixed to the upper surface of the substrate32, that is to say the upper surface of the support portion48provided on the upper surface of the protrusion portion92. Also, the leg pieces46of the diaphragm33and the two end portions of the second diaphragm33bare fixed to the lower ends of the anchors36aand36bextending downward from the lower surface of the back plate38.

The electrode portions are not limited to being rectangular, and may be circular.FIG. 27is a plan view showing an acoustic sensor111according to Embodiment 8 of the present invention.FIG. 28is a cross-sectional diagram of the acoustic sensor111.FIG. 29Ais a plan view showing a barrier electrode72and fixed electrode plates39aand39bprovided on the lower surface of the back plate38in the acoustic sensor111.FIG. 29Bis a plan view of the diaphragm33used in the acoustic sensor111.

As shown inFIG. 28, in the acoustic sensor111, a circular diaphragm33is provided on the upper surface of the substrate32. One leg piece46extends from the outer peripheral portion of the circular diaphragm33, and the diaphragm33is supported in a cantilever manner by the leg piece46, which is supported by an anchor36. As shown inFIG. 29B, the opening33cis formed in the central portion of the diaphragm33. Also, as shown inFIGS. 27 and 29B, a lead-out interconnect49aextends from the leg piece46, and the lead-out interconnect49ais connected to a common electrode pad51. The regulation portion37is arranged in the opening33cof the diaphragm33, and the opening33cis blocked by the regulation portion37. Note that the slit47is formed between the diaphragm33and the regulation portion37so as to prevent them from coming into contact and causing interference. The regulation portion37is supported horizontally by a support portion48that extends downward from the back plate38for example.

On the other hand, as shown inFIGS. 28 and 29A, a disk-shaped first fixed electrode plate39ais provided in the central portion of the lower surface of the back plate38. A circular ring-shaped barrier electrode72is provided outside of the first fixed electrode plate39aso as to not come into contact with the first fixed electrode plate39a. A circular disk-shaped second fixed electrode plate39bis provided outside of the barrier electrode72so as to not come into contact with the barrier electrode72. As shown inFIGS. 27 and 29A, a lead-out interconnect49bextends from the outer peripheral portion of the first fixed electrode plate39a, and the lead-out interconnect49bis connected to a first electrode pad52a. A lead-out interconnect49cextends from the second fixed electrode plate39b, and the lead-out interconnect49cis connected to a second electrode pad52b.

In the acoustic sensor111, a circular low-volume high-sensitivity acoustic sensing portion is configured by the central portion of the diaphragm33and the first fixed electrode plate39a. Also, a circular ring-shaped high-volume low-sensitivity acoustic sensing portion is configured by the outer peripheral portion of the diaphragm33and the second fixed electrode plate39b.

Also, in the acoustic sensor111as well, when the diaphragm33is subjected to high-load pressure, the diaphragm33undergoes large deformation so as to open the opening33cand allow the high-load pressure to escape through the opening33c.

FIG. 30is a schematic cross-sectional diagram showing the structure of an acoustic sensor121according to Embodiment 9 of the present invention. In the acoustic sensor91of Embodiment 6 (FIG. 24), the leakage of air pressure is hindered by arranging the upper surface of the substrate32in opposition to the lower opening of the void portion (opening33c), but a leak pressure regulation portion37that is separate from the substrate may be used. Specifically, a plate-shaped or thin film-shaped leak pressure regulation portion37may be arranged in opposition to the upper side or the lower side of the diaphragm33so as to substantially block either the upper opening or the lower opening of the void portion of the diaphragm33when it is not undergoing deformation. In the example shown inFIG. 30, the leak pressure regulation portion37is fixed by a support portion48provided on the upper surface of the substrate32, and the opening33cbetween the first diaphragm33aand the second diaphragm33bis blocked from the lower side by the leak pressure regulation portion37.

Application in Microphone

FIG. 31is a schematic cross-sectional diagram of a bottom port type of microphone131including an acoustic sensor according to one or more embodiments of the present invention, such as the acoustic sensor31of Embodiment 1. This microphone131has the acoustic sensor31and a signal processing circuit135(ASIC), which is a circuit portion, built into a package made up of a circuit substrate132and a cover133. The acoustic sensor31and the signal processing circuit135are mounted on the upper surface of the circuit substrate132. A sound introduction hole134for the introduction of acoustic vibration into the acoustic sensor31is formed in the circuit substrate132. The acoustic sensor31is mounted on the upper surface of the circuit substrate132such that the lower opening of the cavity35is aligned with the sound introduction hole134and covers the sound introduction hole134. Accordingly, the cavity35of the acoustic sensor31is the front chamber, and the space inside the package is the back chamber.

The acoustic sensor31and the signal processing circuit135are connected by a bonding wire136. Furthermore, the signal processing circuit135is connected to the circuit substrate132by a bonding wire137. Note that signal processing circuit135has a function of supplying power to the acoustic sensor31and a function of outputting a capacitance change signal from the acoustic sensor31to the outside.

A cover133is attached to the upper surface of the circuit substrate132so as to cover the acoustic sensor31and the signal processing circuit135. The package has an electromagnetic shielding function, and protects the acoustic sensor31and the signal processing circuit135from mechanical shock and electrical disturbances from the outside.

In this way, acoustic vibration that has entered the cavity35through the sound introduction hole134is detected by the acoustic sensor31, and then output after being subjected to amplification and signal processing by the signal processing circuit135. Since the space inside the package is the back chamber in this microphone131, the area of the back chamber can be increased, and the sensitivity of the microphone131can be increased.

Note that in this microphone131, the sound introduction hole134for introducing acoustic vibration into the package may be formed in the upper surface of the cover133. In this case, the cavity35of the acoustic sensor31is the back chamber, and the space inside the package is the front chamber.