Patent Grant
10375482
This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2015-050100, filed on Mar. 12, 2015, and International Patent Application No. PCT/JP2016/057630, filed on Mar. 10, 2016, the contents of which are incorporated herein by reference in their entirety.
The present application relates to a capacitance type transducer and to an acoustic sensor including the capacitance type transducer. More specifically, the present invention relates to a capacitance type transducer and an acoustic sensor constituted by a capacitor structure made up of a vibrating electrode film formed using MEMS technology and a back plate.
Conventionally, small microphones have sometimes utilized an acoustic sensor called an ECM (Electret Condenser Microphone). However, since ECMs are sensitive to heat and microphones (hereinafter, also referred to as MEMS microphones) utilizing a capacitance type transducer manufactured using MEMS (Micro Electro Mechanical Systems) technology are superior in terms of readiness for digitization, downsizing, and the like, more MEMS microphones are recently being adopted (for example, refer to PTL 1).
Such capacitance type transducers include those using MEMS technology to realize a form where a vibrating electrode film which vibrates when subjected to pressure is arranged so as to oppose, across a gap, a back plate to which an electrode film is fixed. A capacitance type transducer in the form described above can be realized by a process involving, for example, after forming a vibrating electrode film and a sacrificial layer covering the vibrating electrode film on a silicon substrate, forming a back plate on top of the sacrificial layer and subsequently removing the sacrificial layer. Since MEMS technology applies semiconductor manufacturing technology in this manner, an extremely small capacitance type transducer can be obtained.
On the other hand, since a capacitance type transducer fabricated using MEMS technology is constituted by a thinned vibrating electrode film and a back plate, there is a risk that the vibrating electrode film may deform significantly and break when subjected to excessive pressure and the like. Such inconveniences may occur when, for example, high sound pressure is applied inside the capacitance type transducer as well as when air blowing is performed in a mounting process and when the capacitance type transducer is dropped.
While such inconveniences can conceivably be addressed by providing the vibrating electrode film with a hole for releasing pressure and releasing pressure from the hole when excessive pressure is applied, such a measure may cause a deterioration in frequency characteristics as a capacitance type transducer, particularly a decline in sensitivity in a low-frequency range.
In addition, a known invention of a MEMS transducer includes a vibrating electrode film and a plug section which is a section created by dividing and separating the vibrating electrode film with a slit, wherein the plug section is supported at a same height as other portions of the vibrating electrode film by a supporting structure with respect to a back plate or a substrate. In this invention, as the vibrating electrode film deforms in response to a difference in pressure between both sides of the film, a flow path between the vibrating electrode film and the plug section expands to release excessive pressure (for example, refer to PTL 2).
However, in the invention described above, since the plug section and a supporting member are separate members, the invention not only necessitates a more complicated manufacturing process but also entails a risk that the plug section may become detached from the supporting member and impair functionality. Therefore, the invention described above is unable to achieve sufficiently high reliability.
One or more embodiments of the present invention provides a technique enabling an excessive deformation of a vibrating electrode film to be suppressed and damage to the vibrating electrode film to be avoided when excessive pressure is applied to the vibrating electrode film, while maintaining favorably frequency characteristics during acoustic detection with a simpler configuration.
According to one or more embodiments of the present invention, in a capacitance type transducer which converts a displacement of a vibrating electrode film into a change in capacitance between the vibrating electrode film and a back plate, when the vibrating electrode film deforms under excessive pressure, the pressure applied to the vibrating electrode film is released by increasing a flow channel area of an air flow channel formed by a gap between a protruding portion integrally provided on the back plate and a part of the vibrating electrode film due to a relative movement of the protruding portion and the vibrating electrode film.
More specifically, the present invention provides a capacitance type transducer including:
a substrate with an opening on a surface thereof;
a back plate arranged to oppose the opening of the substrate; and
a vibrating electrode film arranged to oppose the back plate across a gap between the vibrating electrode film and the back plate,
the capacitance type transducer converting a displacement of the vibrating electrode film into a change in capacitance between the vibrating electrode film and the back plate,
the capacitance type transducer further including a pressure releasing flow channel which is an air flow channel formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate and which is configured to, when the vibrating electrode film deforms under pressure, release the pressure applied to the vibrating electrode film by increasing a flow channel area due to a relative movement of the vibrating electrode film and the protruding portion integrally provided on the back plate.
According to this configuration, for example, when excessive pressure is applied in the capacitance type transducer and the vibrating electrode film deforms significantly, the flow channel area of the pressure releasing flow channel increases due to a relative movement of the vibrating electrode film and the protruding portion integrally provided on the back plate. Consequently, when excessive pressure is applied in the capacitance type transducer and the vibrating electrode film deforms significantly, the pressure applied to the vibrating electrode film can be automatically released. As a result, damage to the vibrating electrode film due to excessive pressure can be suppressed.
In addition, according to this configuration, since the pressure releasing flow channel is formed by a gap between a part of the vibrating electrode film and a protruding portion integrally provided on the back plate, members themselves which inherently move when subjected to pressure can be utilized without modification and apparatus configuration can be simplified.
In addition, in the present invention, at least a part of a peripheral section of the back plate may bend to form a side surface and the back plate may be fixed to the substrate in a tip section of the side surface,
the pressure releasing flow channel may be formed by a gap between an end surface of the vibrating electrode film and a protruding portion integrally formed on the side surface of the back plate, and
when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film may be released by increasing the gap between the end surface of the vibrating electrode film and the side surface of the back plate as the end surface of the vibrating electrode film and the protruding portion formed on the side surface of the back plate relatively move and deviate.
In other words, in this case, the back plate is coupled to the substrate as at least a part of the peripheral section of the back plate is bent to form a side surface and a tip section of the side surface is fixed to the substrate. In addition, the pressure releasing flow channel is formed by a gap between an end surface of the vibrating electrode film and the protruding portion integrally formed on the side surface of the back plate. Furthermore, when the vibrating electrode film deforms under pressure, as the end surface of the vibrating electrode film and the protruding portion formed on the side surface of the back plate relatively move and deviate, the gap between the end surface of the vibrating electrode film and the side surface of the back plate increases. As a result, the flow channel area of the pressure releasing flow channel increases and the pressure applied to the vibrating electrode film is released.
According to this configuration, by a simple configuration of, for example, bending outward the side surface of the back plate midway to form a protruding section opposing the end surface of the vibrating electrode film, damage to the vibrating electrode film when subjected to excessive pressure can be suppressed.
In addition, in the present invention, the protruding portion may be a protruding pillar structure, the pressure releasing flow channel may be formed by a gap between a hole provided in the vibrating electrode film and a protruding pillar structure integrally provided from the back plate to a side of the vibrating electrode film,
at least a tip section of the protruding pillar structure may have a smaller diameter than a diameter of the hole and the protruding pillar structure may penetrate into the hole in a state prior to the vibrating electrode film deforming under pressure, and
when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film may be released as the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the penetration of the protruding pillar structure into the hole is canceled.
In other words, in this case, the pressure releasing flow channel is formed by a gap between a hole provided in the vibrating electrode film and the protruding pillar structure integrally provided from the back plate to the side of the vibrating electrode film. In addition, at least a tip section of the protruding pillar structure has a smaller diameter than a diameter of the hole and the protruding pillar structure penetrates into the hole in a state prior to the vibrating electrode film deforming under pressure. Furthermore, when the vibrating electrode film deforms under pressure, the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the protruding pillar structure withdraws from the hole to expose an entire surface of the hole. As a result, the pressure applied to the vibrating electrode film is released.
According to this configuration, in a state prior to the vibrating electrode film deforming under pressure, the penetration of the protruding pillar structure of the back plate into the hole of the vibrating electrode film enables leakage of air from the hole to be suppressed and frequency characteristics of an acoustic sensor to be preferably maintained in a more reliable manner. In addition, when the vibrating electrode film deforms by a prescribed amount due to being subjected to excessive pressure, since the protruding pillar structure of the back plate withdraws from the hole of the vibrating electrode film and the hole is released, the flow channel area of the pressure releasing flow channel is stably maintained at a small area until applied pressure reaches prescribed pressure and increases rapidly once the applied pressure reaches the prescribed pressure.
Therefore, the frequency characteristics of the capacitance type transducer can be maintained as favorably as possible until a last moment before the applied pressure reaches the prescribed pressure described above. In addition, once the applied pressure reaches the prescribed pressure, the pressure can be released at one time. Moreover, even in a state where the protruding pillar structure of the back plate withdraws from the hole of the vibrating electrode film and the hole is released, since air flowing into the hole passes through the gap between the vibrating electrode film and the protruding pillar structure integrally provided from the back plate to the side of the vibrating electrode film, the fact that the pressure releasing flow channel is formed by the gap between a part of the vibrating electrode film and the protruding portion integrally formed on the back plate remains unchanged. It should be noted that “penetration” in the above description indicates a state where the protruding pillar structure penetrates the hole of the vibrating electrode film and includes both a case where a tip of the protruding pillar structure reaches a surface on an opposite side of the vibrating electrode film or the tip further protrudes from the opposite side surface and a case where the tip of the protruding pillar structure stops at a midway point of a thickness of the vibrating electrode film.
In addition, in the present invention, the protruding portion may be a protruding pillar structure, the pressure releasing flow channel may be formed by a gap between a hole provided in the vibrating electrode film and a protruding pillar structure integrally provided from the back plate to a side of the vibrating electrode film,
the protruding pillar structure may have a larger diameter than a diameter of the hole and a tip of the protruding pillar structure may cover the hole from a side of the back plate in a state prior to the vibrating electrode film deforming under pressure, and
when the vibrating electrode film deforms under pressure, the pressure applied to the vibrating electrode film may be released as the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the tip of the protruding pillar structure separates from the hole.
In other words, also in this case, the pressure releasing flow channel is formed by a gap between a hole provided in the vibrating electrode film and the protruding pillar structure integrally provided from the back plate to the side of the vibrating electrode film. In addition, a diameter of the protruding pillar structure is set larger than a diameter of the hole of the vibrating electrode film and a tip of the protruding pillar structure covers the hole of the vibrating electrode film from a side of the back plate in a state prior to the vibrating electrode film deforming under pressure. Furthermore, when the vibrating electrode film deforms under pressure, the vibrating electrode film and the protruding pillar structure of the back plate relatively move and the tip of the protruding pillar structure separates from the hole of the vibrating electrode film to enable air to readily flow into the hole. As a result, the pressure applied to the vibrating electrode film is released.
According to this configuration, in accordance with an amount of deformation of the vibrating electrode film from a state before deforming under pressure to a state of deforming under pressure, the flow channel area of the pressure releasing flow channel can be gradually increased. Therefore, an operation of the vibrating electrode film can be stabilized and reliability and durability of the apparatus in an environment where the apparatus is frequently subjected to excessive pressure can be improved.
In addition, in the present invention, in a state prior to the vibrating electrode film deforming under pressure, the protruding pillar structure may penetrate through the hole and the tip of the protruding pillar structure may be positioned on an opposite side of the vibrating electrode film to the back plate.
According to this configuration, instead of the protruding pillar structure of the back plate withdrawing from the hole of the vibrating electrode film immediately after the vibrating electrode film starts deforming, a certain pressure range or more in which the frequency characteristics of the capacitance type transducer is favorably maintainable can be secured. In addition, by appropriately setting a position of the tip of the pillar structure, a pressure value as a threshold to be applied when rapidly increasing the flow channel area of the pressure releasing flow channel can be appropriately set.
Furthermore, in the present invention, a diameter of the protruding pillar structure may increase from the tip of the pillar structure toward the back plate or may be constant. According to the former configuration, before the protruding pillar structure withdraws from the hole of the vibrating electrode film, the flow channel area of the protruding pillar structure can be gradually increased and a flow rate of air for releasing pressure can be gradually increased. Meanwhile, according to the latter configuration, before the protruding pillar structure withdraws from the hole of the vibrating electrode film, the flow channel area of the protruding pillar structure can be set constant and a flow rate of air for releasing pressure can be set constant until the protruding pillar structure withdraws from the hole. In this manner, variations of modes of releasing pressure until the protruding pillar structure withdraws from the hole of the vibrating electrode film can be expanded.
In addition, in the present invention, the protruding pillar structure may be formed by a film forming process which differs from that of the vibrating electrode film. Alternatively, the protruding pillar structure may be formed by a same film forming process as that of the back plate. By forming the protruding pillar structure in the same film forming process as that of the back plate, the manufacturing process can be simplified, integration of the protruding pillar structure and the back plate can be further enhanced, and reliability can be improved.
Furthermore, in the present invention, the vibrating electrode film may be fixed to the substrate at an anchor section and the vibrating electrode film may not be in contact with the substrate and the back plate at locations other than the anchor section. According to this configuration, a movement or a displacement of the vibrating electrode film can be made smoother and the operation of the capacitance type transducer can be further stabilized.
In addition, in the present invention, the back plate may have a plurality of perforations. Furthermore, the substrate may be arranged to avoid a portion opposing the protruding pillar structure integrally provided on the back plate. As a result, when penetration into the protruding pillar structure is canceled, pressure can be released more efficiently. Furthermore, in the present invention, the back plate may be arranged to oppose the substrate, the protruding pillar structure may be provided from the back plate toward a side of the substrate, and the tip of the protruding pillar structure may be positioned on a same plane as a surface of the substrate on the back plate side or further toward the back plate side than the surface. According to this configuration, the back plate and the protruding pillar structure can be more readily integrally formed on the substrate by film formation.
In addition, in the present invention, the back plate may have a stationary electrode film in a central section, and the protruding portion may be provided on an outer side of the stationary electrode film on the back plate. Accordingly, an area of the stationary electrode film can be secured and sensitivity of the transducer can be improved. Furthermore, in the present invention, the protruding portion may be provided in a central section of the back plate. Accordingly, the protruding portion is to be formed in a portion which deforms with higher sensitivity and, when the vibrating electrode film is subjected to large pressure, pressure can be released with higher sensitivity.
In addition, in the present invention, a side surface of the protruding pillar structure may form a tapered surface and an inclination angle of the tapered surface with respect to the back plate may be set to 60 degrees or more and 85 degrees or less. According to this configuration, stress concentration on the side surface of the protruding pillar structure can be suppressed and strength of the protruding pillar structure can be relatively increased. In addition, when depositing and forming the protruding pillar structure by a semiconductor manufacturing process, film quality itself of the side surface can be improved, which also contributes to increasing strength. Furthermore, for example, when the side surface of the protruding pillar structure is vertically formed, a decline in a state of film formation at a bottom of the protruding pillar structure and reduced film thickness of a film forming the bottom section may result in a decline in strength. However, by setting the inclination angle of the side surface of the protruding pillar structure to the range described above, such a decline in strength can be suppressed.
Furthermore, in the present invention, the vibrating electrode film may have an approximately rectangular shape and may be fixed at fixing sections provided in four corners of the vibrating electrode film, and the protruding portion may be provided at four locations in portions at the four corners of the vibrating electrode film which correspond to a further inner side than the fixing sections in a plan view on the back plate.
According to this configuration, since the protruding portion can be arranged on an outer side of the stationary electrode film of the back plate, an effect on acoustic performance can be suppressed without reducing an area of the stationary electrode film on the back plate. In addition, since the protruding portion is only formed in portions which are close to the fixing sections and which have a small amount of displacement of the vibrating electrode film, the protruding section is relatively less likely to withdraw from the pressure release hole and frequency characteristics can be maintained up to high sound pressure. Furthermore, a balance can be achieved between air pressure resistance and frequency characteristics and a degree of freedom of design can be increased.
In addition, in the present invention, the protruding portion may be provided at one location in a central section of the back plate. According to this configuration, since the protruding portion is only provided in a small number, a variation in frequency characteristics can be reduced. Furthermore, since the protruding portion is only formed in the central section where the amount of displacement of the vibrating electrode film is large, the protruding portion is more readily withdrawn from the pressure release hole and the pressure releasing function can even be exhibited under low pressure. In addition, even when the substrate overlaps with the vibrating electrode film and the back plate in a plan view, a distance between a center-side end surface of the substrate and the protruding portion can be increased and an effect of overlapping can be suppressed.
Furthermore, in the present invention, the protruding portion may be further provided at four locations in portions of the back plate, which correspond to central sections of four sides of the vibrating electrode film in a plan view, so as to be provided at a total of eight locations. According to this configuration, the flow channel area of the pressure releasing flow channel can be increased as a whole and air pressure resistance can be improved. In addition, since the protruding portion does not withdraw from the hole until large pressure is applied, frequency characteristics can be maintained even under high sound pressure. Furthermore, since the protruding portion is installed so as to avoid the central section of the back plate, warpage deformation of the back plate can be reduced. In addition, an effect on acoustic performance can be suppressed without reducing an area of the stationary electrode film on the back plate in a portion where the amount of displacement of the vibrating electrode film is large.
Furthermore, in the present invention, the protruding portion may be further provided at one location in the central section of the back plate so as to be provided at a total of nine locations. According to this configuration, air pressure resistance can be further improved. In addition, since the protruding portion does not withdraw from the hole until large pressure is applied, frequency characteristics can be maintained even under high sound pressure (advantageous to use under high sound pressure).
In addition, in the present invention, in a state where the protruding pillar structure has penetrated into the hole before the vibrating electrode film deforms under pressure where, the gap between the protruding strip pillar structure and the hole may be set to 0.2 μm or more and 20 μm or less on one side. According to this configuration, a favorable balance can be achieved between an amount of attenuation in a low-frequency region in frequency characteristics as acoustic characteristics and a risk of contact between the protruding portion and the hole.
Furthermore, in the present invention, the back plate may include the stationary electrode film positioned to avoid a location where the protruding portion is provided in a plan view, and a distance between the protruding strip portion and the stationary electrode film may be set to 1 μm or more and 15 μm or less. According to this configuration, a favorable balance can be achieved between a loss reduction effect of an electrode area of the stationary electrode film by providing the protruding portion and a risk of short-circuit when conductive foreign objects infiltrate a vicinity of the protruding portion.
In addition, in the present invention, a size of the gap between the back plate and the vibrating electrode film may be set larger within a prescribed range in a periphery of the protruding portion, as compared to outside of the prescribed range. According to this configuration, when conductive foreign objects infiltrate a vicinity of the protruding portion, an amount of displacement of the vibrating electrode film due to the foreign objects can be reduced and an effect on frequency characteristics as acoustic characteristics can be reduced.
Moreover, in the present invention, a size of a sound hole in the back plate may be set smaller within a prescribed range in a periphery of the protruding portion, as compared to outside of the prescribed range. According to this configuration, a probability of infiltration by foreign objects from sound holes in the vicinity of the protruding portion can be reduced and a probability of foreign objects becoming deposited or getting caught in the vicinity of the protruding portion of the back plate can be reduced.
In addition, in the present invention, a sound hole within a prescribed range in a periphery of the protruding portion of the back plate and a hole provided in the vibrating electrode film may be arranged so that at least parts thereof overlap with each other in a plan view. According to this configuration, a space penetrating through both the vibrating electrode film and the back plate can be formed in a periphery of the protruding portion and foreign objects can more readily pass through this space. As a result, the probability of foreign objects becoming deposited or getting caught in the vicinity of the protruding portion of the back plate can be reduced.
Furthermore, the present invention may be an acoustic sensor which includes the capacitance type transducer described above, wherein the acoustic sensor converts sound pressure into a change in capacitance between the vibrating electrode film and the back plate and detects the capacitance change. According to this configuration, with respect to the acoustic sensor, damage to the vibrating electrode film can be avoided when excessive pressure is applied to the vibrating electrode film by suppressing excessive deformation of the vibrating electrode film, while maintaining favorably frequency characteristics during acoustic detection. As a result, an acoustic sensor with favorable frequency characteristics and high reliability can be obtained.
Moreover, means for solving the problem described above can be used in various combinations as appropriate.
According to the present invention, with respect to a capacitance type transducer, damage to a vibrating electrode film can be avoided when excessive pressure is applied to the vibrating electrode film by suppressing excessive deformation of the vibrating electrode film, while maintaining favorably frequency characteristics during detection of pressure. As a result, reliability of the capacitance type transducer can be improved, while maintaining more favorably performance thereof.
Hereinafter, embodiments of the invention of the present application will be described with reference to the drawings. The embodiments described below merely represent aspects of the invention of the present application and are not intended to limit the technical scope of the present invention. While the invention of the present application can be applied to all electrostatic transducers, a case where an electrostatic transducer is used as an acoustic sensor will be described below. However, a sound transducer according to the present invention can be used as sensors other than an acoustic sensor as long as a displacement of a vibrating electrode film can be detected. For example, in addition to a pressure sensor, a sound transducer according to the present invention may be used as an acceleration sensor, an inertial sensor, and the like. In addition, a sound transducer according to the present invention may be used as elements other than a sensor such as a speaker which converts an electrical signal into a displacement.
In this case, the silicon substrate 3 can be formed of, for example, single crystal silicon. In addition, the vibrating electrode film 5 can be formed of, for example, conductive polycrystalline silicon. The vibrating electrode film 5 is a thin film with an approximately rectangular shape, and a fixing section 12 is provided at four corners of an approximately quadrilateral vibrating section 11 which vibrates. Furthermore, the vibrating electrode film 5 is arranged on the upper surface of the silicon substrate 3 so as to cover the back chamber 2 and is fixed to the silicon substrate 3 at the four fixing sections 12 as anchor sections. The vibrating section 11 of the vibrating electrode film 5 vibrates up and down in reaction to sound pressure.
In addition, the vibrating electrode film 5 contacts neither the silicon substrate 3 nor the back plate 7 at locations other than the four fixing sections 12. Therefore, the vibrating electrode film 5 is capable of vibrating up and down more smoothly in response to sound pressure. Furthermore, a vibrating film electrode pad 9 is provided in one of the fixing sections 12 located at the four corners of the vibrating section 11. The stationary electrode film 8 provided on the back plate 7 is provided so as to correspond to a vibrating portion of the vibrating electrode film 5 excluding the fixing sections 12 at the four corners. This is because the fixing sections 12 at the four corners of the vibrating electrode film 5 do not vibrate in response to sound pressure and capacitance between the vibrating electrode film 5 and the stationary electrode film 8 does not change.
When sound reaches the acoustic sensor 1, the sound passes through the sound holes and applies sound pressure to the vibrating electrode film 5. In other words, the sound holes enable sound pressure to be applied to the vibrating electrode film 5. In addition, providing the sound holes enables air inside an air gap between the back plate 7 and the vibrating electrode film 5 to more readily escape outside and, consequently, thermal noise and noise can be reduced.
In the acoustic sensor 1, due to the structure described above, the vibrating electrode film 5 vibrates when receiving sound and a distance between the vibrating electrode film 5 and the stationary electrode film 8 changes. When the distance between the vibrating electrode film 5 and the stationary electrode film 8 changes, capacitance between the vibrating electrode film 5 and the stationary electrode film 8 changes. Therefore, by applying DC voltage between the vibrating film electrode pad 9 which is electrically connected to the vibrating electrode film 5 and the stationary electrode pad 10 which is electrically connected to the stationary electrode film 8 and extracting a change in the capacitance as an electrical signal, sound pressure can be detected as an electrical signal.
Next, an inconvenience which may occur in the conventional acoustic sensor 1 described will be explained.
Measures such as that shown in
Another conceivable measure involves providing a vibrating electrode film and a plug section which is a section created by dividing and separating the vibrating electrode film with a slit, and supporting the plug section at a same height as other portions of the vibrating electrode film by a supporting structure with respect to a back plate. According to this measure, as the vibrating electrode film deforms in response to a difference in pressure between both sides of the film, a flow channel between the vibrating electrode film and the plug section expands and releases excessive pressure (for example, refer to PTL 2).
However, this measure entails the following inconveniences. First, since the plug section is constructed using a section of the extremely thin vibrating electrode film, the plug section is susceptible to damage. In addition, since a lid-shaped plug section is supported by a supporting structure made of separate rod-like members with respect to the back plate, not only does the manufacturing process become complicated but there is also a risk that the plug section may break off or become detached from the supporting structure.
Furthermore, according to this measure, as the vibrating electrode film deforms in response to a difference in pressure between both sides of the film, a flow path between the vibrating electrode film and the plug section which is a section created by dividing and separating the vibrating electrode film with a slit expands and releases excessive pressure. Specifically, since a gap between two thin films, namely, the vibrating electrode film and the plug section which is a section created by dividing and separating the vibrating electrode film, is used as a flow channel, when an amplitude of the vibrating electrode film increases under relatively large pressure, there is a risk that positions of the plug section and the vibrating electrode film may deviate by their film thickness or more to create a state where the flow channel is somewhat enlarged and destabilize frequency characteristics of the acoustic sensor 1 even when the relatively large pressure is within a working pressure range.
In consideration of such inconveniences, in the present embodiment: the vibrating electrode film is provided with a hole for releasing applied pressure; in a state prior to deformation of the vibrating electrode film, a pillar structure which constitutes a part of the back plate and which is formed on a protruding shape penetrates through the hole and closes at least a part thereof; and in a state where the vibrating electrode film has deformed under pressure, a relative movement of the vibrating electrode film and the back plate causes the penetration through the hole by the pillar structure to be canceled and the entire hole to be exposed to release the pressure applied to the vibrating electrode film.
Next, actions of the pressure release hole 15b and the protruding section 17b described above will be explained with reference to
However, when excessive pressure is applied to the vibrating electrode film 15, the pressure causes the vibrating electrode film 15 to deform significantly in a direction of separation from the back plate 17 as shown in
As described above, in the present embodiment, during normal operation or, in other words, when excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, since the protruding section 17b penetrates through and closes the pressure release hole 15b, deterioration of frequency characteristics of an acoustic sensor 1 can be suppressed. In addition, in a state where excessive pressure is applied to the vibrating electrode film 15 and the vibrating electrode film 15 has deformed significantly, since the protruding section 17b withdraws from the pressure release hole 15b (the penetration of the pressure release hole 15b by the protruding section 17b is canceled) and the closure is terminated, pressure can be sufficiently released from the pressure release hole 15b. As a result, further deformation of the vibrating electrode film 15 can be suppressed and damage to the vibrating electrode film 15 caused when excessive pressure is applied to the acoustic sensor 1 can be avoided.
Furthermore, in the present embodiment, since the functions described above are realized by utilizing a relative movement of a protruding section 17b integrally provided on the back plate 17 and the pressure release hole 15b provided in the vibrating electrode film 15, the structure can be simplified and reliability can be improved.
In addition,
As shown in
In contrast, according to the present embodiment, even when relatively large pressure is applied and a displacement of the vibrating electrode film 15 becomes approximately equal to or larger than the film thickness, as long as a state where the protruding section 17b penetrates through the vibrating electrode film 15 is maintained as shown in
In addition, as shown in
In contrast, according to the present embodiment, even when a vicinity of the pressure release hole 15b of the vibrating electrode film 15 warps and planarity deteriorates during a manufacturing process, as long as a state where the protruding section 17b penetrates through the vibrating electrode film 15 is maintained as shown in
Furthermore, according to the conventional art described above, during actual operation, since a capacitor is not formed unless voltage is applied between the vibrating electrode film 105 and the back plate 107 and charge is accumulated, sound pressure is received while voltage is being applied between the vibrating electrode film 105 and the back plate 107. In other words, in an initial state where voltage is not applied, operation is performed in a state where the vibrating electrode film 105 as a whole is already attracted towards the side of the back plate 107. Therefore, overlapping of the plug section 105a and the peripheral vibrating electrode film 105 in a film thickness direction may become even smaller from the initial state and become unstable. Furthermore, another inconvenience is that a variation in applied voltage may cause the overlapping of the plug section 105a and the peripheral vibrating electrode film 105 in the film thickness direction to vary.
In contrast, according to the present embodiment, there are no inconveniences such as the overlapping of the plug section 105a and the peripheral vibrating electrode film 105 in the film thickness direction becoming unstable from an initial state or a variation in applied voltage causing the overlapping of the plug section 105a and the peripheral vibrating electrode film 105 in the film thickness direction to vary.
In addition, in the acoustic sensor 1, the amount of protrusion described above is desirably larger than an amount of displacement of the vibrating electrode film 15 when maximum sound pressure within a working volume range is applied. According to this configuration, as long as the acoustic sensor 1 is used within the working volume range, stable frequency characteristics can be obtained. Furthermore, the penetration of the pressure release hole 15b by the protruding section 17b is desirably canceled when applied pressure is equal to or higher than 200 Pa. Accordingly, stable frequency characteristics of the acoustic sensor 1 can be obtained within a pressure range of lower than 200 Pa.
Moreover, in the present embodiment, when pressure is applied to the vibrating electrode film 15 from the side of the back plate 17, since the protruding section 17b withdraws from the pressure release hole 15b and the closure thereof is terminated as described earlier, an excessive deformation of the vibrating electrode film 15 can be prevented. On the other hand, when pressure is applied to the vibrating electrode film 15 from the side opposite to the back plate 17, since the vibrating electrode film 15 deforms in a direction approaching the back plate 17, the protruding section 17b does not withdraw from the pressure release hole 15b.
In this case, to be exact, the protruding section 17b has a truncated conic shape of which a diameter slightly increases toward the side of the back plate 17 and slightly decreases toward the side opposite to the back plate 17. Therefore, the gap between the protruding section 17b and the pressure release hole 15b is configured to widen when pressure is applied to the vibrating electrode film 15 from the side opposite to the back plate 17. According to this configuration, even when the protruding section 17b does not withdraw from the pressure release hole 15b, a level at which pressure is released from the pressure release hole 15b increases (a flow rate of air in the pressure release hole 15b increases) as the deformation of the vibrating electrode film 15 increases and acts to suppress deformation of the vibrating electrode film 15.
On the other hand, the gap between the protruding section 17b and the pressure release hole 15b is configured to conversely become narrower when pressure is applied to the vibrating electrode film 15 from the side opposite to the back plate 17. In this case, a diameter of a portion with a largest sectional area of the protruding section 17b or, in other words, a diameter of a root portion of the protruding section 17b is desirably smaller than the diameter of the pressure release hole 15b. Accordingly, even when excessive pressure is applied to the vibrating electrode film 15 and the vibrating electrode film 15 deforms significantly toward the side of the back plate 17, a situation where the protruding section 17b and the pressure release hole 15b come into contact with each other and inhibit the operation of the vibrating electrode film 15 can be prevented.
In addition, according to the present embodiment, when the vibrating electrode film 15 deforms significantly toward the side of the back plate 17, the vibrating electrode film 15 abuts with, and is supported by, the back plate 17 and further deformation of the vibrating electrode film 15 is suppressed. Therefore, in this case, damage to the vibrating electrode film 15 can be avoided even when the protruding section 17b does not withdraw from the pressure release hole 15b to terminate the closure of the pressure release hole 15b. Moreover, in the present embodiment, the shape of the protruding section 17b need not necessarily be a truncated conic shape as described above. For example, the protruding section 17b may have a columnar shape with an approximately constant diameter at any location thereof.
Moreover, in the present embodiment, in a state where excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, the gap between the protruding section 17b and a peripheral section of the pressure release hole 15b in a state where the protruding section 17b penetrates through the pressure release hole 15b functions as a pressure releasing flow channel. In addition, in a state where excessive pressure is applied to the vibrating electrode film 15 and the vibrating electrode film 15 has significantly deformed, the protruding section 17b has withdrawn from the pressure release hole 15b and the gap between the protruding section 17b and the vibrating electrode film 15 in this state and the pressure release hole 15b function as a pressure releasing flow channel. Furthermore, in the present embodiment, the protruding section 17b corresponds to the protruding portion and to the protruding pillar structure.
Next, a relationship between the protruding section 17b and the silicon substrate 13 will be described with reference to
Moreover, the acoustic sensor according to the present embodiment can be realized by a process in which, after forming the vibrating electrode film 15 and a sacrificial layer covering the vibrating electrode film 15 on the silicon substrate 13, the back plate 17 and the protruding section 17b are formed on top of the sacrificial layer in the same process and the sacrificial layer is subsequently removed. Since the acoustic sensor according to the present embodiment applies semiconductor manufacturing technology in this manner, the acoustic sensor can be formed in an extremely small size and a positional relationship among the vibrating electrode film 15, the back plate 17, and the protruding section 17b can be formed with accuracy.
As described above, in the present embodiment, the protruding section 17b is formed by a film forming process which differs from that of the vibrating electrode film 15 and is formed by a same film forming process as that of the back plate 17. Therefore, the manufacturing process of the back plate 17 and the protruding section 17b can be simplified, integration of the protruding section 17b and the back plate 17 can be further enhanced, and reliability can be improved. This manufacturing process is roughly common to the embodiments described below. In addition, as shown in
In addition, in the present embodiment, a case has been described in which, in a state where excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, the protruding section 17b penetrates through the pressure release hole 15b and the tip of the protruding section 17b protrudes from an opposite-side surface of the vibrating electrode film. Alternatively, in a state where excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, the protruding section 17b may only penetrate into the pressure release hole 15b and the tip of the protruding section 17b may not protrude from the surface on the opposite side of the vibrating electrode film.
In this case, the protruding section 17b more readily withdraws from the pressure release hole 15b due to a displacement of the vibrating electrode film 15 and a pressure range, in which the frequency characteristics of the acoustic sensor 1 can be favorably maintained, becomes smaller. Except for this disadvantage, an effect can be produced which is comparable to a case where, in a state where excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, the protruding section 17b penetrates through the pressure release hole 15b and the tip of the protruding section 17b protrudes from an opposite-side surface of the vibrating electrode film. In this case, a configuration may be adopted in which, in a state where excessive pressure is not applied to the vibrating electrode film 15 and the vibrating electrode film 15 has not significantly deformed, the tip of the protruding section 17b is positioned at center of the thickness of the vibrating electrode film 15. Accordingly, as long as pressure is within a certain pressure range, the tip of the protruding section 17b can be positioned within a range of the film thickness of the vibrating electrode film 15 and the positional relationship between the protruding section 17b and the pressure release hole 15b can be similarly maintained.
Next, a second embodiment according to the present invention will now be described. In the first embodiment, an example has been described in which, when the protruding section 17b penetrates through the pressure release hole 15b of the vibrating electrode film 15 to close the pressure release hole 15b and excessive pressure is applied to the vibrating electrode film 15, the penetration of the pressure release hole 15b by the protruding section 17b is canceled and the entire pressure release hole 15b is exposed.
In contrast, in the second embodiment, an example will be described in which a protruding section of a back plate covers a pressure release hole of a vibrating electrode film in a state of normal use prior to the vibrating electrode film deforming significantly and the protruding section separates from the pressure release hole when excessive pressure is applied to the vibrating electrode film.
Actions of a pressure release hole 25b of a vibrating electrode film 25 and a protruding section 27b of a back plate 27 according to the present embodiment will be described with reference to
In this state, when pressure is applied to the vibrating electrode film 25 from the side of the back plate 27, a gap between a tip of the protruding section 27b and the vibrating electrode film 25 is narrow and a flow channel of air is substantially closed. Therefore, an amount of air passing through the pressure release hole 25b is small and the pressure release hole 25b is substantially closed.
However, when excessive pressure is applied to the vibrating electrode film 25, the pressure causes the vibrating electrode film 25 to deform significantly in a direction of separation from the back plate 27 as shown in
As a result, further deformation of the vibrating electrode film 25 is suppressed and damage to the vibrating electrode film 25 can be avoided. Moreover, also in the present embodiment, desirably, a silicon substrate is not present on a lower side of the pressure release hole 25b or, in other words, a back chamber is desirably arranged on the lower side of the pressure release hole 25b. Accordingly, a flow channel in which air having passed through the pressure release hole 25b flows more smoothly is formed and pressure can be released more efficiently.
As described above, in the present embodiment, during normal operation or, in other words, when excessive pressure is not applied to the vibrating electrode film 25, since the tip of the protruding section 27b covers and closes the pressure release hole 25b, deterioration of frequency characteristics of an acoustic sensor can be suppressed. In addition, in a state where excessive pressure is applied to the vibrating electrode film 25 and the vibrating electrode film 25 has deformed significantly, since the protruding section 27b separates from the pressure release hole 25b and the closure is terminated, a further deformation of the vibrating electrode film 25 can be prevented. As a result, damage to the vibrating electrode film 25 caused when excessive pressure is applied to the acoustic sensor can be avoided. Moreover, in the present embodiment, the gap between the tip of the protruding section 27b and the vibrating electrode film 25, and the pressure release hole 25b, correspond to a pressure releasing flow channel. Furthermore, in the present embodiment, the protruding section 27b corresponds to the protruding portion and to the protruding pillar structure.
Next, a third embodiment according to the present invention will now be described. In the third embodiment, an example will be described in which a protruding section is provided on a side surface of a back plate and, when excessive pressure is applied to a vibrating electrode film, a gap between the protruding section and an end surface of the vibrating electrode film increases to release pressure.
Actions of vibrating electrode films 35, 45, 55 and protruding sections 37b, 47b, and 57b of back plates 37, 47, and 57 according to the present embodiment will be described with reference to
First, the example shown in
In addition, when excessive pressure is applied to the vibrating electrode film 35, as depicted by a solid line in
Next, the example shown in
In addition, when excessive pressure is applied to the vibrating electrode film 45, as depicted by a solid line in
Next, the example shown in
In addition, when excessive pressure is applied to the vibrating electrode film 55, as depicted by a solid line in
As described above, in the present embodiment, a protruding section is provided on a side surface of a back plate. In addition, during normal operation or, in other words, when a vibrating electrode film is not significantly deformed due to excessive pressure, since a gap between the protruding section and an end surface of the vibrating electrode film is narrow and a flow channel area of a pressure releasing flow channel is small, deterioration of frequency characteristics of an acoustic sensor can be suppressed. Furthermore, in a state where excessive pressure is applied to the vibrating electrode film and the vibrating electrode film deforms significantly, since the end surface of the vibrating electrode film and the protruding section relatively move and deviate in a vertical direction in the diagrams, the gap between the protruding section and the end surface of the vibrating electrode film increases discontinuously and the flow channel area of the pressure releasing flow channel increases discontinuously. Accordingly, a further deformation of the vibrating electrode film can be suppressed. As a result, damage to the vibrating electrode film caused when excessive pressure is applied to the acoustic sensor can be avoided.
Moreover, while examples in which the protruding section provided on the side surface of the back plate is formed by bending the side surface outward have been described above, a method of forming the protruding section is not limited thereto. The protruding section may be formed by increasing a thickness of the side surface of the back plate or, in other words, increasing a width of the side surface of the back plate in a horizontal direction. Furthermore, in the present embodiment, the protruding sections 37b, 47b, and 57b correspond to the protruding portion and to the protruding pillar structure.
In addition, examples have been described above in which at least a part of a peripheral section of the back plate is bent to forma side surface, the back plate is fixed to a substrate at a tip section of the side surface, and a protruding section is provided on the side surface. However, the side surface of the back plate according to the present invention is not limited to that formed by bending a part of the back plate. A side surface may be formed by a spacer which is a separate member at least in portions where a protruding section is not formed.
Next, a fourth embodiment according to the present invention will now be described. In the first embodiment, an example has been described in which, when the protruding section 17b penetrates through the pressure release hole 15b of the vibrating electrode film 15 to close the pressure release hole 15b and excessive pressure is applied to the vibrating electrode film 15, the penetration of the pressure release hole 15b by the protruding section 17b is canceled and the entire pressure release hole 15b is exposed.
In contrast, in the fourth embodiment, an example will be described in which: a protruding section penetrates through a pressure release hole of a vibrating electrode film to close the pressure release hole; a diameter of the protruding section is smaller on a tip side than on a back plate side; and when excessive pressure is applied to the vibrating electrode film, a change in a portion penetrating through the pressure release hole of the protruding section causes an area where the pressure release hole is closed to change and, accordingly, a flow channel area of a pressure releasing flow channel changes.
However, when excessive pressure is applied to the vibrating electrode film 65, the pressure causes the vibrating electrode film 65 to deform significantly in a direction of separation from the back plate 67 as shown in
As described above, in the present embodiment, during normal operation or, in other words, in a state where the vibrating electrode film 65 has not significantly deformed due to excessive pressure, since the protruding section 67b penetrates through and closes the pressure release hole 65b, deterioration of frequency characteristics of the acoustic sensor can be suppressed. In addition, in a state where excessive pressure is applied to the vibrating electrode film 65 and the vibrating electrode film 65 has deformed significantly, since a state where the small-diameter protruding section tip section 67c of the protruding section 67b penetrates through the pressure release hole 65b is created and a flow channel area of air for releasing pressure increases, a further deformation of the vibrating electrode film 65 can be suppressed. As a result, damage to the vibrating electrode film 65 caused when excessive pressure is applied to the acoustic sensor can be avoided.
Moreover, while the description of the present embodiment given above is premised on the diameter of the protruding section 67b changing in two steps, the manner in which the diameter of the protruding section changes is not limited thereto.
Moreover, in the present embodiment, the gaps between the protruding sections 67b and 77b or the protruding section tip section 67c and peripheral sections of the pressure release holes 65b and 75b correspond to a pressure releasing flow channel. In addition, the protruding sections 67b and 77b and the protruding section tip section 67c correspond to the protruding portion and to the protruding pillar structure.
Moreover, in all of the embodiments described above, the flow channel area signifies a sectional area of a flow channel which dictates a flow rate of air passing through the flow channel. In addition, in the embodiment described above, the protruding section of the back plate may be formed at any position of the back plate. However, the protruding section is desirably provided in a region outside of the stationary electrode film provided on the back plate.
Accordingly, the protruding section can be formed without reducing an area of the stationary electrode film and sensitivity of the acoustic sensor can be secured. Alternatively, instead of arranging the protruding section in a peripheral section of the back plate, the protruding section may be provided at a position of the back plate which corresponds to a central section of the vibrating electrode film and the pressure release hole may be provided in the central section of the vibrating electrode film. According to this configuration, since pressure can be released at a location where the vibrating electrode film has a largest amount of displacement, sensitivity when releasing pressure can be improved. In addition, cross-sectional shapes of the protruding section and the pressure release hole need not be circular and may be elliptical or polygonal. Furthermore, the numbers of the protruding section and the pressure release hole are not particularly limited. There may be only one set or a plurality of sets such as five sets or more may be provided.
In addition, with respect to the acoustic sensor according to the embodiment described above, a mode in which a vibrating electrode film is arranged on a silicon substrate and a back plate is arranged on the vibrating electrode film has been described. However, an acoustic sensor to which the present invention is applied is not limited to this mode. The present invention may be applied to an acoustic sensor configured such that arrangements of the back plate and the vibrating electrode film are reversed.
Next, a fifth embodiment of the present invention will be described. In the present embodiment, an example in which a protruding section particularly has a shallow pan-like structure with a flat bottom surface will be described.
By shaping the protruding section 87b as described above, a difference in level of the protruding section 87b from the back plate 87 can be suppressed and an inclination angle on the tapered side surface can be made gradual. According to this configuration, stress concentration at the level difference can be suppressed and strength of the protruding section 87b can be relatively increased. In addition, when depositing and forming the protruding section 87b by a semiconductor manufacturing process, film quality itself of the side surface can be improved, which also contributes to increasing strength of the protruding section 87b.
Specifically, for example, when the side surface of the protruding section 87b is vertically formed, a decline in a state of film formation particularly at the bottom of the protruding section 87b and a reduction in film thickness of a film forming the bottom section may cause a decline in strength. From these perspectives, a slope angle of the side surface of the protruding section 87b is desirably 60 degrees or more and 85 degrees or less with respect to a plane of the back plate. In particular, when a pressure release hole 85b formed in the vibrating electrode film 85 has a large diameter of several μm or more, it is known that a state of the protruding section 87b becomes particularly stable by forming the side surface of the protruding section 87b as a tapered surface.
In addition, according to the present embodiment, as the vibrating electrode film 85 deforms downward and the protruding section 87b moves in a direction of withdrawal from the pressure release hole 85b, a gap between the protruding section 87b and an end surface of the pressure release hole 85b widens. Therefore, there is an advantage that foreign objects having infiltrated between the vibrating electrode film 85 and the back plate 87 are removed from the gap and a probability of foreign objects becoming deposited or getting caught in the vicinity of the protruding section 87b is reduced. Moreover, a diameter of the protruding section 87b can be selected in accordance with specifications from a range of 2 μm or more and 100 μm or less. As an example,
Next, a sixth embodiment of the present invention will be described. In the present embodiment, variations in the number of sets of a pressure release hole provided on a vibrating electrode film and a protruding section provided on a back plate, and characteristics of the variations, will be explained.
On the other hand, disadvantages when providing one pair of the pressure release hole 5b and the protruding section 7b include: since an area of the pressure release hole 5b in the vibrating electrode film 5 as a whole is small even in a state where the protruding section 7b has withdrawn from the pressure release hole 5b, air pressure resistance is relatively low.
Generally, since a vibrating electrode film is often fixed at end sections (in a case of a rectangular shape, four corners), this configuration enables a pressure release hole and a protruding section to be formed in a portion in which an amount of displacement of the vibrating electrode film is large regardless of the shape of the vibrating electrode film. As a result, a pressure releasing function can be exhibited with greater sensitivity or higher reliability.
Next,
Next,
Moreover, since the pairs of the pressure release hole and the protruding section are arranged symmetrical with respect to the central section of the back plate in all of the four examples shown in
In addition, when the protruding section withdraws from the pressure release hole to release air, air present in the periphery of each pressure release hole translationally moves toward the pressure release hole and subsequently reaches an opposite side of the vibrating electrode film through the pressure release hole. Therefore, according to the present embodiment, arranging the pairs of the pressure release hole and the protruding section as far away as possible from each other enables a larger amount of air as a whole to be released from the pressure release holes and enables pressure to be released more efficiently. Conversely, when the pairs of the pressure release hole and the protruding section are close to each other, since the pressure release hole of a single pair is only capable of releasing air in a nearby region, only a limited amount of air can be released and efficiency of releasing pressure declines. The arrangements of the pairs of the pressure release hole and the protruding section according to the present embodiment represent, for each number of pairs, an example of an arrangement in which the pairs are as far away as possible from each other.
Next, a seventh embodiment of the present invention will be described. In the present embodiment, an example will be described which adopts measures against foreign objects involving increasing a gap in a thickness direction between a back plate and a vibrating electrode film in a periphery of a protruding section of the back plate.
Foreign objects may infiltrate a space between a back plate and a vibrating electrode film in an acoustic sensor through sound holes. When foreign objects infiltrate into the acoustic sensor, the foreign objects may become deposited or may get caught between a protruding section of the back plate and a pressure release hole of the vibrating electrode film in accordance with air flow. As a result, due to a change in a gap between the back plate and the vibrating electrode film, frequency characteristics of the acoustic sensor may become affected. In addition, while such situations may conceivably be addressed by increasing a basic gap between the back plate and the vibrating electrode film, such a measure may cause sensitivity as a condenser microphone to decline. In consideration thereof, in the present embodiment, by increasing the gap between the back plate and the vibrating electrode film only in a periphery of a protruding section of the back plate, even when foreign objects infiltrate in a vicinity of the protruding section and a pressure release hole, an effect on the gap between the back plate and the vibrating electrode film is reduced.
Next, an effect produced by the acoustic sensor according to the present embodiment will be described with reference to
In addition, even when a major portion of the distribution of the sizes of foreign objects is larger than the size g of the gap between the back plate 127 and the vibrating electrode film 125 in a region near the protruding section 127b as shown in
Moreover, in the present embodiment, while a range in which the gap between the back plate 127 and the vibrating electrode film 125 is widened is desirably as small as possible in consideration of sensitivity as an acoustic sensor, a distance dg from a side surface of the protruding section 127b may be set to a range expressed as 0≤dg≤g in consideration of a particle size of the foreign objects. Alternatively, a wider range may be adopted.
Next, an eighth embodiment of the present invention will be described. In the present embodiment, an example will be described which adopts measures against foreign objects involving reducing an area ratio of sound holes in a periphery of a protruding section of a back plate.
A state where foreign objects infiltrate inside an acoustic sensor and become deposited or get caught between a protruding section of a back plate and a pressure release hole of a vibrating electrode film is conceivably more likely to occur when the foreign objects enter from sound holes in a vicinity of the protruding section of the back plate. Therefore, a measure of not providing sound holes in a vicinity of the protruding section of the back plate is conceivable. However, since the sound holes of the back plate may be used as chemical insertion ports in etching of a sacrificial layer during a semiconductor process and are also necessary in order to reduce thermal noise in an air gap, eliminating the sound holes altogether is not feasible. In consideration thereof, the present embodiment adopts measures against foreign objects involving reducing an area ratio of sound holes in a vicinity of the protruding section of the back plate.
In the present embodiment, as shown in
In the present embodiment, as shown in
Moreover, while the area ratio of sound holes is reduced in the present embodiment by reducing a diameter of the sound holes 137a in a region near the protruding section 137b in comparison to regions distanced from the protruding section 137b, for example, the area ratio of sound holes may be reduced by increasing distances between sound holes 137a (reducing a density of sound holes 137a) in a region near the protruding section 137b in comparison to regions distanced from the protruding section 137b.
In addition, in the present embodiment, a range in which the area ratio of the sound holes 137a is reduced in the back plate 137 may be, for example, a range in which a distance from the side surface of the protruding section 137b is equal to or less than twice the diameter of the protruding section 137b. Alternatively, a wider range may be adopted.
Next, a ninth embodiment of the present invention will be described. In the present embodiment, an example will be described in which measures against foreign objects involve adopting a configuration in which a sound hole in a periphery of a protruding section of a back plate and a pressure release hole of a vibrating electrode film overlap with each other in a plan view.
In the present embodiment, as shown in
As shown in the present embodiment, by forming a space penetrating through both the vibrating electrode film 145 and the back plate 147, an increase in attenuation of sensitivity of an acoustic sensor in a low-frequency region is expected and, at the same time, an improvement in a pressure releasing function when large pressure is applied and the protruding section 147b withdraws from the pressure release hole 145b is expected. Therefore, according to the present embodiment, in addition to enhancing measures against foreign objects, air pressure resistance can be improved while causing sensitivity of the acoustic sensor in a low-frequency region to attenuate at a constant level.
Next, a desirable state of dimensions of the respective parts according to the embodiments described above will be considered.
<Amount of Protrusion of Protruding Section from Vibrating Electrode Film>
In
In addition, as the amount of protrusion of the tip of the protruding section 17b from the vibrating electrode film 15 decreases, there is an advantage that: (1) since the protruding section 17b withdraws from the pressure release hole 15b even when relatively low sound pressure is applied, deposition of foreign objects between the back plate 17 and the vibrating electrode film 15 in a periphery of the protruding section 17b can be suppressed even during use under relatively low sound pressure. On the other hand, there are disadvantages such as: (1) even when relatively low sound pressure is applied, the protruding section 17b withdraws from the pressure release hole 15b and an abnormality in acoustic characteristics may occur; and (2) tolerance of variations in arrangements of respective members with respect to a longitudinal direction of the protruding section 17b decreases. From these perspectives, an amount of protrusion of 0.1 μm or more and 10 μm or less described in the first embodiment conceivably represents appropriate values.
<Clearance Between Protruding Section of Back Plate and Pressure Release Hole of Vibrating Electrode Film>
In
<Distance Between Protruding Section of Back Plate and Stationary Electrode Film>
In
<Distance Between Protruding Section of Back Plate and Semiconductor Substrate Edge>
In
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-050100 | Mar 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/057630 | 3/10/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/143867 | 9/15/2016 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 8111871 | Zhang et al. | Feb 2012 | B2 |
| 8692340 | Ata et al. | Apr 2014 | B1 |
| 8737171 | Jenkins et al. | May 2014 | B2 |
| 9695038 | Cargill | Jul 2017 | B2 |
| 20080175418 | Zhang et al. | Jul 2008 | A1 |
| 20080192963 | Sato | Aug 2008 | A1 |
| 20090060232 | Hirade et al. | Mar 2009 | A1 |
| 20090175477 | Suzuki et al. | Jul 2009 | A1 |
| 20090309171 | Schrank | Dec 2009 | A1 |
| 20110108933 | Nakatani | May 2011 | A1 |
| 20130069179 | Ishimoto et al. | Mar 2013 | A1 |
| 20140084396 | Jenkins et al. | Mar 2014 | A1 |
| 20140299948 | Wang et al. | Oct 2014 | A1 |
| Number | Date | Country |
|---|---|---|
| 101242682 | Aug 2008 | CN |
| 101374373 | Feb 2009 | CN |
| 103347808 | Oct 2013 | CN |
| 104053104 | Sep 2014 | CN |
| 2011-250170 | Dec 2011 | JP |
| 10-2008-0006579 | Jan 2008 | KR |
| 10-2009-0015834 | Feb 2009 | KR |
| 2010-004766 | Jan 2010 | WO |
| Entry |
|---|
| Office Action in corresponding Korean Application No. 10-2017-7005904, dated Sep. 21, 2017 (6 pages). |
| International Preliminary Report on Patentability issued in PCT/JP2016/057630, dated Sep. 12, 2017 (7 pages). |
| International Search Report issued in corresponding application No. PCT/JP2016/057630 dated May 10, 2016 (3 pages). |
| Written Opinion of the International Searching Authority issued in corresponding application No. PCT/JP2016/057630 dated May 10, 2016 (4 pages). |
| Office Action issued in Chinese Application No. 201680002574.X, dated Oct. 17, 2018 (25 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20170289702 A1 | Oct 2017 | US |
