JP2007104641A - Capacitor microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-sensitivity capacitor microphone capable of preventing pull-in occurrence. <P>SOLUTION: A capacitor microphone is provided with: a plate having a stationary electrode; a diaphragm in which the rigidity of a center portion forming a vibrating electrode with respect to the stationary electrode is higher than the rigidity of a near-end portion that is closer to a fixed end rather than the center portion, and which vibrates in response to sound waves; and a spacer that forms an air gap between the plate and the diaphragm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a condenser microphone, and more particularly to a condenser microphone using a semiconductor film.

  Conventionally, a condenser microphone that can be manufactured by applying a semiconductor device manufacturing process is known. The condenser microphone has an electrode on each of the plate and the diaphragm that is vibrated by sound waves, and the plate and the diaphragm are supported in a state of being separated from each other by an insulating spacer. The condenser microphone converts a capacitance change caused by the displacement of the diaphragm formed by the plate and the diaphragm into an electric signal and outputs the electric signal. The sensitivity of the condenser microphone is improved by increasing the ratio of the displacement of the diaphragm to the distance between the electrodes, reducing the leakage current of the spacer, and reducing the parasitic capacitance.

  Non-Patent Document 1 discloses a condenser microphone in which each of a plate and a diaphragm that is vibrated by sound waves is formed of a conductive thin film. However, since the rigidity of the diaphragm is uniform, even if sound waves propagate through the diaphragm, only the center of the diaphragm vibrates at the maximum displacement, and the displacement due to the diaphragm vibration decreases from the center toward the outer periphery fixed to the spacer. Become. That is, the sensitivity of the condenser microphone is reduced at portions other than the center of the diaphragm having uniform rigidity. On the other hand, if the ratio of the maximum displacement of the diaphragm to the distance between the plate and the diaphragm is increased in order to increase the sensitivity of the condenser microphone, the diaphragm is attracted to the plate by the electrostatic attraction force due to the bias when the diaphragm approaches the plate. There is a problem that so-called pull-in occurs.

Tajima, Nishiguchi, Kondo, Saito, Chiba, Morita, Esashi, “Mechanical characteristics of condenser-type silicon microphones”, The Institute of Electrical Engineers of Japan, November 21, 22nd, 2001

  An object of the present invention is to provide a highly sensitive condenser microphone that can prevent the occurrence of pull-in.

(1) A condenser microphone for solving the above-mentioned problems is a near end where the rigidity of the plate forming the stationary electrode and the central part forming the vibration electrode for the stationary electrode is closer to the fixed end than the central part A diaphragm that is higher than the rigidity of the portion and vibrates by sound waves, and a spacer to which the plate and the fixed end of the diaphragm are fixed and a gap is formed between the plate and the diaphragm.
The definitions of terms used to define this invention are as follows. The center part and the near end part of the diaphragm are both part names of the diaphragm. A part of the diaphragm belongs to either the central portion or the near end portion, and the near end portion refers to a portion closer to the fixed end than the central portion. The central portion is a region having only one, and the near end portion is a region having one or more. The rigidity of the central part means a strain generated when a tensile force is applied to the outer periphery of the central part. However, the diaphragm strain referred to here is a value obtained by dividing the deformation amount with respect to the tensile force by the original distance between the two points to which the tensile force is applied. The rigidity of the near end portion means a strain generated when a tensile force is applied to both ends of the near end portion. However, the boundary between the near end and the center is defined as one end of the near end, and the fixed end of the diaphragm is defined as the other end of the near end. Further, the near end strain here is a value obtained by dividing the deformation amount with respect to the tensile force by the original distance between the two points to which the tensile force is applied.
In this condenser microphone, since the rigidity of the central portion of the diaphragm is higher than the rigidity of the near end portion of the diaphragm, the deformation amount of the central portion of the diaphragm with respect to the sound pressure is smaller than when the partial rigidity of the diaphragm is uniform. That is, in this condenser microphone, the displacement deviation at each point in the center of the diaphragm is smaller than when the diaphragm has a uniform partial rigidity. Therefore, the condenser microphone is formed by the plate and diaphragm without increasing the maximum displacement of the diaphragm. It is possible to increase the capacitance component (hereinafter referred to as variable capacitance) that varies due to the sound wave of the capacitor (hereinafter referred to as microphone capacitor). Thereby, it is possible to increase the sensitivity of the condenser microphone while preventing the occurrence of pull-in.

(2) At least the outer peripheral portion of the central portion of the diaphragm may be thicker than the proximal end portion of the diaphragm.
By making at least the outer peripheral part of the center part of the diaphragm thicker than the near end part, the rigidity of the center part of the diaphragm can be made higher than that of the near end part.

(3) The proximal end portion of the diaphragm is formed of a first film, and the central portion of the diaphragm includes a first film and a second film having a hardness higher than that of the first film. It may consist of a layer film.
Even if the first film is made of a low-hardness material in order to reduce the rigidity of the near end of the diaphragm, the central part of the diaphragm is formed with the first film and the second film having a higher hardness than the first film. By comprising the multi-layer film including the rigidity of the central portion of the diaphragm can be increased.

(4) The proximal end portion of the diaphragm is formed of a first film, and the central portion of the diaphragm includes a first film and a second film having a lower density than the first film. It may consist of a layer film.
The central part of the diaphragm is composed of a multilayer film that includes a first film and a second film having a lower density than the first film, thereby increasing the rigidity of the central part of the diaphragm and reducing the weight of the central part of the diaphragm. Can be By reducing the weight of the central portion of the diaphragm, the sensitivity of the condenser microphone to high frequency sound can be increased.

(5) The partial rigidity of the diaphragm may gradually increase from the outer periphery of the diaphragm toward the center of the diaphragm.
Here, the partial rigidity of the diaphragm refers to a strain generated in a part when a tensile force is applied to the outer periphery of a part of the diaphragm. However, the strain referred to here is a value obtained by dividing the deformation amount with respect to the tensile force by the original distance between the two points to which the tensile force is applied.
Since the partial rigidity of the diaphragm is gradually increased from the outer periphery toward the center, the stress at the time of diaphragm deformation can be dispersed throughout the diaphragm, so that the diaphragm can be formed thin. By reducing the thickness of the diaphragm, the rigidity of the entire diaphragm can be reduced, so that the diaphragm can be vibrated with a large amplitude. Further, by forming the diaphragm thin, it is possible to increase the sensitivity of the condenser microphone to high frequency sound.

(6) The diaphragm may have a thin-walled portion and a thick-walled portion whose formation density gradually increases from the outer periphery of the diaphragm toward the center of the diaphragm.
By forming a thick-walled portion in the diaphragm in which the formation density gradually increases from the outer periphery of the diaphragm toward the center of the diaphragm, the rigidity of the diaphragm can be gradually increased from the outer periphery toward the center.

(7) The thin portion may be formed of a first film, and the thick portion may be formed of a multilayer film including the first film and a second film having a hardness higher than that of the first film. Good.
By configuring the thin part of the diaphragm with the first film and the thick part of the diaphragm with the multilayer film including the first film and the second film having higher hardness than the first film, The rigidity of the thick part can be increased.

(8) The thin portion may be formed of a first film, and the thick portion may be formed of a multilayer film including the first film and a second film having a lower density than the first film. Good.
By forming the thin part of the diaphragm with the first film, and forming the thick part of the diaphragm with the multilayer film including the first film and the second film having a lower density than the first film, While increasing the rigidity of the thick part, the thick part of the diaphragm can be reduced in weight. By reducing the thickness of the thick part of the diaphragm, the entire diaphragm is reduced in weight, so that the lowest resonance frequency of the condenser microphone is increased. As a result, the sensitivity of the condenser microphone with respect to high frequency sound can be increased.

Embodiments of the present invention will be described below based on a plurality of examples.
(First Example)
2 and 3 are schematic views showing the configuration of the condenser microphone 1 according to the first embodiment. 3A is a top view of the back plate 20 of the condenser microphone 1, and FIG. 3B is a bottom view of the diaphragm 10 of the condenser microphone 1.
The condenser microphone 1 is a so-called silicon microphone manufactured using a semiconductor manufacturing process. The condenser microphone 1 includes a sound sensing unit drawn as a cross-sectional view in FIG. 2 and a detection unit drawn as a circuit diagram in FIG. Hereinafter, the configuration of the sound sensing unit, the configuration of the detection unit, and the manufacturing method of the condenser microphone 1 will be described in this order.

(Configuration of sound sensor)
As shown in FIG. 2, the sound sensing part of the condenser microphone 1 includes a diaphragm 10, a back plate 20, a spacer 30, a base 40, and the like.
The diaphragm 10 includes a portion of the conductive film 110 that is not fixed to the insulating film 102 and the insulating film 112 (hereinafter referred to as a non-fixed portion of the conductive film 110), and a conductive film 108 that is fixed to the conductive film 110. It consists of That is, the outer periphery of the diaphragm 10 is fixed to the insulating film 102 and the insulating film 112. The conductive film 108 and the conductive film 110 are both semiconductor films such as polycrystalline silicon doped with impurities (hereinafter referred to as polysilicon). The conductive film 108 is disposed at the center of the non-fixed portion of the conductive film 110. That is, the near end portion near the outer periphery of the diaphragm 10 is composed of only the conductive film 110, and the central portion of the diaphragm 10 is composed of the conductive film 110 and the conductive film 108. Thus, by making the central portion of the diaphragm 10 thicker than the proximal end portion of the diaphragm 10, the rigidity of the central portion of the diaphragm 10 can be made higher than the rigidity of the proximal end portion of the diaphragm 10. The conductive film 110 corresponds to the “first film” recited in the claims, and the conductive film 108 corresponds to the “second film” recited in the claims.

Note that the conductive film 108 and the conductive film 110 may be formed using the same material or different materials. In the case where the conductive film 108 and the conductive film 110 are formed using different materials, the conductive film 108 is preferably formed using a material whose hardness is higher than that of the conductive film 110. Even if the conductive film 110 is formed of a low-hardness material in order to reduce the rigidity of the near end portion of the diaphragm 10 by forming the conductive film 108 of a high-hardness material, the conductive film 108 and the conductive film 110 are configured. The rigidity of the central portion of the diaphragm 10 can be increased. For example, when the conductive film 110 is formed of polysilicon, the conductive film 108 can be SiCx, SiGe, SiGeC, or a material whose specific resistance is adjusted by doping impurities therein.
The conductive film 108 is preferably formed using a material having a lower density than the conductive film 110. By forming the conductive film 108 with a low-density material, the center portion of the diaphragm 10 including the conductive film 108 and the conductive film 110 can be reduced in weight. By reducing the weight of the central portion of the diaphragm 10, the sensitivity of the condenser microphone 1 with respect to high-frequency sound can be increased.

  Moreover, the center part of the diaphragm 10 may protrude to the base 40 side as shown in FIG. 2, may protrude to the back plate 20 side, or may protrude to both sides. Moreover, although the diaphragm 10 which consists of an electrically conductive film as an example was illustrated, the diaphragm may be comprised with the electrode arrange | positioned in the center part of an insulating film whose center part is thicker than a near end part, and an insulating film. For example, an insulating film may be used instead of the conductive film 108, or an insulating film may be used instead of the conductive film 110. In the case where an insulating film is used instead of the conductive film 110, the outer shape of the conductive film 108 is designed so as to be connected to a connection pad with the detection portion. Further, the diaphragm 10 may have a disk shape as shown in FIG. 3B, or may have another shape.

  As shown in FIG. 2, the back plate 20 as a plate is configured by a portion of the conductive film 114 that is not fixed to the insulating film 112. The conductive film 114 is a semiconductor film such as polysilicon. A plurality of through holes 22 are formed in the back plate 20. The through hole 22 of the back plate 20 allows sound waves from the sound source to pass through. As a result, the sound wave from the sound source is propagated to the diaphragm 10. Note that the back plate 20 may have a disk shape as shown in FIG. Further, the through-hole 22 may be circular as shown in FIG.

As shown in FIG. 2, the spacer 30 is composed of an insulating film 112. The insulating film 112 is an oxide film such as SiO ₂ . The spacer 30 supports the diaphragm 10 and the back plate 20 while insulating them, and forms a gap 32 between the diaphragm 10 and the back plate 20.
The base 40 is composed of the insulating film 102 and the substrate 100. The substrate 100 is, for example, a single crystal silicon substrate. The insulating film 102 is an oxide film such as SiO ₂ . A through hole 42 that functions as a back cavity is formed in the base 40.
The condenser microphone 1 may be configured such that the diaphragm 10 is positioned closer to the sound source than the back plate 20, and sound waves propagate directly to the diaphragm 10. In this case, the through hole 22 of the back plate 20 functions as a passage through which the gap 32 formed between the diaphragm 10 and the back plate 20 communicates with the recess 42 of the base 40, that is, the back cavity.

(Configuration of detector)
Diaphragm 10 is connected to resistor 300, and back plate 20 is connected to ground. Specifically, for example, a lead wire 302 connected to one end of the resistor 300 is connected to the conductive film 110 constituting the diaphragm 10, and a lead wire 304 connected to the ground of the substrate on which the condenser microphone 1 is mounted. The conductive film 114 constituting the back plate 20 is connected. A lead wire 308 connected to the output terminal of the bias power supply circuit 306 is connected to the other end of the resistor 300. A resistor 300 having a large resistance value is used. Specifically, the resistor 300 preferably has an electrical resistance on the order of GΩ. A lead wire 314 connected to one end of the capacitor 312 is connected to the input end of the preamplifier 310. The lead wire 302 connecting the diaphragm 10 and the resistor 300 is also connected to the other end of the capacitor 312.

(Condenser microphone operation)
When the sound wave passes through the through hole 22 of the back plate 20 and propagates to the diaphragm 10, the diaphragm 10 vibrates with respect to the back plate 20. When the diaphragm 10 vibrates, the distance between the back plate 20 and the diaphragm 10 changes, and the capacitance of a capacitor (hereinafter referred to as a microphone capacitor) constituted by the diaphragm 10 and the back plate 20 changes.

Since the diaphragm 10 is connected to the resistor 300 having a large resistance value as described above, even if the capacitance of the microphone capacitor is changed by the vibration of the diaphragm 10, the electric charge accumulated in the microphone capacitor is changed to the resistor 300. There is almost no flow. That is, the charge accumulated in the microphone capacitor can be regarded as not changing. Therefore, the change in the capacitance of the microphone capacitor can be taken out as a change in the voltage between the diaphragm 10 and the back plate 20.
The condenser microphone 1 amplifies a change in voltage with respect to the ground of the diaphragm 10 by the preamplifier 310, and outputs a very slight change in the capacitance of the capacitor as an electric signal. That is, the condenser microphone 1 converts a change in sound pressure applied to the diaphragm 10 into a change in capacitance of the microphone capacitor, and converts a change in capacitance of the microphone capacitor into a change in voltage, thereby changing the sound pressure. An electrical signal correlating to is output.

  Incidentally, as shown in FIG. 4, in the conventional condenser microphone 400 including the diaphragm 410 having uniform partial rigidity, only the center of the diaphragm 410 vibrates at the maximum displacement, and the displacement due to the vibration of the diaphragm 410 is a spacer from the center. It becomes smaller toward the outer periphery fixed to 30. As a result, portions other than the center of the diaphragm 410 reduce the sensitivity of the condenser microphone 400 by reducing the total displacement amount of the diaphragm 410 (see a region 460 indicated by hatching in FIG. 4). Here, the total amount of displacement of the diaphragm is the total sum of displacement at each part of the diaphragm. On the other hand, when the maximum displacement of the diaphragm 410 (see the arrow 464 shown in FIG. 4) is increased with respect to the distance between the back plate 20 and the diaphragm 410 (see the arrow 462 shown in FIG. 4) to increase the sensitivity of the condenser microphone 400, When approaching the back plate 20, there is a problem that pull-in occurs because the diaphragm 410 is attracted to the back plate 20 by electrostatic attraction due to bias.

FIG. 1 is a schematic diagram for explaining the operation of the condenser microphone 1 according to the first embodiment.
As described above, the rigidity of the central portion of the diaphragm 10 is higher than the hardness of the proximal end portion of the diaphragm 10. As a result, the amount of deformation that occurs at the center of the diaphragm 10 during vibration is smaller than in the prior art, and the deformation concentrates on the near end of the diaphragm 10. That is, the deviation of the displacement of the central portion of the diaphragm 10 is reduced, and the entire central portion vibrates with an amplitude close to the maximum amplitude (see arrow 64 shown in FIG. 1). By reducing the deviation of the amplitude of the central portion of the diaphragm 10, compared to the total displacement amount of the diaphragm having uniform partial rigidity and the same maximum displacement (area 460 indicated by hatching in FIG. 4), The total displacement amount of the diaphragm 10 (the area of the region 60 indicated by the oblique lines in FIG. 1) can be increased. That is, the variable capacitance of the microphone capacitor formed by the diaphragm 10 and the back plate 20 can be increased without increasing the maximum displacement of the diaphragm 10. Thereby, the sensitivity of the condenser microphone 1 can be enhanced while preventing the occurrence of pull-in. Of course, the maximum displacement of the diaphragm 10 with respect to the distance between the diaphragm 10 and the back plate 20 may be increased within a range where pull-in does not occur.

(Production method)
5 and 6 are cross-sectional views showing a method for manufacturing the condenser microphone 1. FIG. The partial diagram (An) is a diagram showing a cross section taken along line A1-A1 shown in (B1) for the corresponding partial diagram (Bn). The fractional view (Bn) is a plan view.
First, as illustrated in FIG. 5A1, the insulating film 102 is formed over the substrate 100. The substrate 100 is, for example, a single crystal silicon wafer. Specifically, for example, SiO ₂ is deposited on the surface of the substrate 100 by CVD (Chemical Vapor Deposition) or the like, thereby forming the insulating film 102 of SiO ₂ on the substrate 100. Note that this step can be omitted by using an SOI substrate.

  Next, as shown in FIGS. 5A2 and 5B2, a recess 104 is formed in the insulating film. Specifically, the recess 104 is formed as follows, for example. First, a resist film 106 that exposes a portion of the insulating film 102 where the recess 104 is to be formed is formed on the insulating film 102 by lithography. More specifically, a resist is applied to the insulating film 102 to form a resist film. Then, a mask having a predetermined shape is arranged, and the resist film is exposed and developed to remove unnecessary resist films. Thereby, a resist film 106 is formed on the insulating film 102. For removing the resist film, a resist stripping solution such as NMP (N-methyl-2-pyrrolidone) is used. Next, the insulating film 102 exposed from the resist film 106 is etched by RIE (Reactive Ion Etching) or the like, thereby forming a recess 104 in the insulating film 102. Then, the resist film 106 is removed. A conductive film 108 constituting the diaphragm 10 is formed in the recess 104 in a process described later. Therefore, the recess 104 may be formed according to the shape of the conductive film 108.

Next, as shown in FIGS. 5A3 and 5B3, a conductive film 108 that forms the central portion of the diaphragm 10 is formed in the recess 104 of the insulating film 102. Specifically, the conductive film 108 is formed as follows, for example. First, a P ⁺ polysilicon film for burying the recess 104 is formed on the insulating film 102 by CVD or the like. Here, the P ⁺ polysilicon is polysilicon containing impurities serving as acceptors. More specifically, a polysilicon film is formed on the insulating film 102 by CVD or the like, and B (boron) or the like as an impurity is ion-implanted into the polysilicon layer. Then, the P ⁺ polysilicon film is formed by annealing the polysilicon layer after the ion implantation. Then, the P ⁺ polysilicon film and the insulating film 102 are polished and planarized by CMP (Chemical Mechanical Polishing) or the like, so that the P ⁺ polysilicon is left only in the recess 104 on the insulating film 102. As a result, a conductive film 108 of P ⁺ polysilicon is formed.

Next, as shown in FIGS. 5A4 and 5B4, a conductive film 110 that forms the diaphragm 10 is formed on the surfaces of the insulating film 102 and the conductive film 108 by CVD or the like. For example, the conductive film 110 is a P ⁺ polysilicon film or the like.
Next, an insulating film 112 constituting the spacer 30 is formed on the conductive film 110 by CVD or the like. The insulating film 112 is preferably formed using the same material as the insulating film 102. By forming the insulating film 102 and the insulating film 112 with the same material, the etching rate of both can be made the same. As a result, the etching amount of the insulating film can be easily controlled in the step of removing a part of the insulating film described later.

Next, a conductive film 114 constituting the back plate 20 is formed on the insulating film 112 by CVD or the like. For example, the conductive film 114 is a P ⁺ polysilicon film or the like.
Next, as illustrated in FIGS. 6A5 and 6B5, the through hole 22 is formed in the conductive film 114. Specifically, the through hole 22 is formed as follows, for example. First, a resist film 118 that exposes a portion of the conductive film 114 where the through hole 22 is to be formed is formed on the conductive film 114 by lithography. Next, the conductive film 114 exposed from the resist film 118 is etched by RIE or the like until reaching the insulating film 112, thereby forming the through hole 22 in the conductive film 114. Then, the resist film 118 is removed.

  Next, as shown in FIGS. 6A6 and 6B6, a part of the conductive film 110 is exposed. Specifically, for example, first, a resist film 120 that masks a portion where the conductive film 114 remains is formed on the conductive film 114 by lithography. Next, the conductive film 110 and the insulating film 112 exposed from the resist film 120 are etched by RIE or the like until the conductive film 110 is reached, thereby exposing the conductive film 110. Then, the resist film 120 is removed. By exposing a part of the conductive film 110, the conductive film 110 and the detection unit can be connected.

  Next, as shown in FIG. 6 (A7), an opening 122 that forms the through hole 42 is formed in the substrate 100. Specifically, the opening 122 is formed as shown below. First, a resist film 124 that exposes only a portion of the substrate 100 where the opening 122 is to be formed is formed by lithography. Next, an opening 122 is formed in the substrate 100 by removing the portion exposed from the resist film 124 of the substrate 100 with Deep RIE or the like until reaching the insulating film 102. Then, the resist film 124 is removed.

Next, as illustrated in FIG. 6A8, the insulating film 102 and the insulating film 112 (hereinafter referred to as an insulating film) are formed as a part of the insulating film 102 serving as the base 40 and the insulating film 112 serving as the spacer 30. Remove all parts. Specifically, the insulating film is removed by wet etching, for example. For example, the insulating film of SiO ₂ is removed using an etchant such as hydrofluoric acid. The etching solution reaches the insulating film 102 and the insulating film 112 through the opening 122 of the substrate 100 and the through hole 22 of the conductive film 114 and dissolves the insulating film. Thereby, the air gap 32 between the diaphragm 10 and the back plate 20 is formed, and the sound sensing part of the condenser microphone 1 is obtained.

(Second embodiment)
FIG. 7 is a schematic diagram showing the configuration of the condenser microphone 2 according to the second embodiment. (A) is a sectional view of the condenser microphone 2, and (B) is a bottom view of the diaphragm 210 of the condenser microphone 2. The detection unit of the condenser microphone 2 is substantially the same as the detection unit of the condenser microphone 1.

  The diaphragm 210 includes the conductive film 110 and the convex portion 200. The convex portions 200 are formed of, for example, a semiconductor film such as polysilicon as the second film, and are arranged radially with the center of the non-fixed portion of the conductive film 110 as the first film. That is, the formation density of the convex portions 200 gradually increases from the outer periphery of the diaphragm 210 toward the center of the diaphragm 210. Such a convex part 200 is equivalent to what changed the outline shape of the electrically conductive film 108 of a 1st Example. The portion of the diaphragm 210 that is configured only by the conductive film 110 corresponds to the “thin portion” described in the claims, and the portion of the diaphragm 210 that is configured by the conductive film 110 and the convex portion 200 is described in the claims. Corresponds to “thick part”.

  Note that the second film only needs to have a gradually increasing density from the outer periphery of the diaphragm 210 toward the center of the diaphragm 210, and is not limited to the convex portion 200 illustrated. For example, as long as the formation density is as described above, the arrangement of the protrusions 200 may not be radial. Further, for example, the convex portion 200 may have any shape, and may have a shape extending radially around the center of the diaphragm 210 as shown in FIG. Further, as shown in FIG. 7, the convex portion 200 may be disposed on the back plate 20 side of the conductive film 110, may be disposed on the base 40 side of the conductive film 110, or may be disposed on both surfaces of the conductive film 110. May be. In addition, the diaphragm 210 may be composed of the conductive film 110 and an insulating film and electrodes corresponding to the protrusions 200.

  According to the present embodiment, since the diaphragm 210 can be reduced in weight, the sensitivity of the condenser microphone 2 with respect to a high frequency sound can be increased.

(Third embodiment)
FIG. 9 is a view showing a third embodiment of the condenser microphone according to the present invention. As shown in FIG. 9, the central portion 14 of the diaphragm 11 has a two-layer structure including a conductive film 23 and a conductive film 110. The conductive film 110 functions as a reinforcing film that increases the rigidity of the central portion 14. The near end 15 of the diaphragm 11 is made of a conductive film 110 and is a plurality of portions that function as a structure that spans the central portion 14 over the spacer 30. The near end 15 is bent zigzag so as to function as a spring. Therefore, the rigidity of the near end portion 15 is remarkably low with respect to the central portion 14, and the deformation that occurs when the sound wave propagates to the diaphragm 11 is concentrated on the near end portion 15. Even if the sound wave propagates to the diaphragm 11, the central portion 14 hardly deforms, and therefore the central portion 14 vibrates in a motion state close to parallel movement.
Since the amplitude of the near end portion 15 is smaller than that of the central portion 14, the average parasitic capacitance per area formed by the near end portion 15 is larger than that of the central portion 14 if the distance between the counter electrodes is the same. According to this embodiment, since the conductive film 23 is bonded to the back plate 20 side of the conductive film 110, the distance between the back plate 20 and the diaphragm 11 is narrow at the central portion 14 and wide at the near end portion 15. Therefore, the condenser microphone 3 according to this embodiment can reduce the parasitic capacitance as compared with the first embodiment.

(Fourth embodiment)
FIG. 10 is a diagram showing a third embodiment of the condenser microphone according to the present invention. As shown in FIG. 10, the conductive film 24 that increases the rigidity of the central portion 16 of the diaphragm 12 may be formed annularly or substantially annularly only in the peripheral portion of the central portion 16.

(Fifth embodiment)
FIG. 11 is a diagram showing a fifth embodiment of the condenser microphone according to the present invention. As shown in FIG. 11, the central portion 18 of the diaphragm 13 may be suspended from the near end portion 19. The near end portion 19 includes a connection portion 27 constituted by a part of the insulating film 112 and a part of the conductive film 114, and supports the central portion 18 at a plurality of locations. The notch 28 mechanically separates the back plate 20 and the proximal end portion 19 of the diaphragm 13. The near end portion 19 enables the diaphragm 13 to be contracted by a stress generated during manufacturing, and brings about an effect of reducing the stress of the diaphragm 13 by the contraction. The conductive film 25 that increases the rigidity of the central portion 13 is formed in an annular shape or a substantially annular shape only in the peripheral portion of the central portion 18. Note that the conductive film 25 is a film that has a function of increasing the rigidity of the central portion 18 and may be formed of an insulating film made of SiN, SiON, or the like.

(Sixth embodiment)
FIG. 12 is a diagram showing a sixth embodiment of the condenser microphone according to the present invention. As shown in FIG. 12, the rigidity of the central portion 18 of the diaphragm 13 may be increased by the connecting portion 27. That is, the circumferential length of the connecting portion 27 is extended from that of the fifth embodiment, a plurality of connecting portions 27 form a substantially ring shape, and the connecting portion 27 forms a central portion 18 in which the outer peripheral portion is formed. Also good. Even if the connecting portion 27 is divided in the circumferential direction of the central portion 18 of the diaphragm 13, if the connecting portion 27 forms most of the outer periphery of the central portion 18, the rigidity of the entire central portion 18 is increased. . In this case, it is not necessary to provide a reinforcing film as used in the fifth embodiment on the outer peripheral portion of the surface on the opposite side of the back plate 20 of the central portion 18 of the diaphragm 13.
On the other hand, if the circumferential length of the connecting portion 27 is extended, the rigidity of the back plate 20 is lowered. Therefore, it is desirable to increase the thickness of the back plate 20 when the circumferential length of the connecting portion 27 is extended. Specifically, for example, it is desirable to make the thickness of the back plate 20 thicker than the proximal end portion 19 of the diaphragm 16.

(Other examples)
Note that the rigidity of the diaphragm made of a semiconductor film may be controlled by implanting impurity ions. Specifically, for example, impurity ions that increase the rigidity of the semiconductor film may be injected into the central portion of the diaphragm, or impurity ions that decrease the rigidity of the semiconductor film may be injected into the near end portion of the diaphragm. Thus, a diaphragm having a small amplitude deviation at the center can be obtained. More specifically, if SiC is formed in the central portion of the diaphragm by implanting C ions into the central portion of the Si diaphragm, the rigidity of the central portion of the diaphragm can be increased. Also, by implanting Ar ions at a high dose into the near end of the diaphragm made of a semiconductor film, Ar ions enter between the Si crystals constituting the near end of the diaphragm, thereby reducing the bonding force between the Si crystals. If so, the rigidity of the near end of the diaphragm can be reduced. Further, impurity ions that increase the rigidity of the semiconductor film may be implanted into the diaphragm so that the ratio of the implanted region to the non-implanted region gradually increases from the outer periphery of the diaphragm toward the center of the diaphragm. Impurity ions that lower the rigidity of the semiconductor film may be implanted into the diaphragm so that the ratio of the implanted region to the non-implanted region gradually increases toward the outer periphery of the diaphragm.

FIG. 3 is a schematic cross-sectional view showing the operation of the condenser microphone according to the first embodiment. 1 is a schematic cross-sectional view showing the configuration of a condenser microphone according to a first embodiment. (A) is a top view which shows the backplate which concerns on a 1st Example. (B) is a top view which shows the diaphragm which concerns on a 1st Example. FIG. 6 is a schematic cross-sectional view showing the operation of a conventional condenser microphone. The figure which shows the manufacturing method of the condenser microphone by a 1st Example. The figure which shows the manufacturing method of the condenser microphone by a 1st Example. The schematic cross section which shows the structure of the capacitor | condenser microphone by a 2nd Example. (A) is a top view which shows the diaphragm of the modification based on 2nd Example. (B) is sectional drawing of the B1-B1 line | wire shown to (A). (A) is a schematic cross section showing the configuration of a condenser microphone according to a third embodiment. (B) is sectional drawing of the BB line shown to (A). (A) is a schematic cross section showing the configuration of a condenser microphone according to a fourth embodiment. (B) is sectional drawing of the BB line shown to (A). (A) is a schematic cross section showing the configuration of a condenser microphone according to a fifth embodiment. (B) is a partial top view of the condenser microphone according to the fifth embodiment. (C) is sectional drawing of the CC line shown to (A). (A) is a schematic cross section showing the configuration of a condenser microphone according to a sixth embodiment. (B) is a partial top view of the condenser microphone according to the sixth embodiment. (C) is sectional drawing of the CC line shown to (A).

Explanation of symbols

1, 2, 3, 4, 5: Condenser microphones 10, 11, 12, 13, 210: Diaphragm, 20, 220: Back plate (plate), 22: Through hole, 30: Spacer, 32: Air gap, 40: Base, 108: conductive film (second film), 200, 201: rib (second film)

Claims (8)

A plate forming a stationary electrode;
A diaphragm that vibrates by sound waves, the rigidity of the central part forming the vibrating electrode with respect to the stationary electrode is higher than the rigidity of the near end part closer to the fixed end than the central part;
A spacer that fixes the plate and the fixed end of the diaphragm, and forms a gap between the plate and the diaphragm;
Condenser microphone with At least the outer peripheral portion of the central portion of the diaphragm is thicker than the proximal end portion of the diaphragm,
The condenser microphone according to claim 1. The proximal end of the diaphragm is composed of a first film,
The central portion of the diaphragm is formed of a multilayer film including the first film and a second film having higher hardness than the first film.
The condenser microphone according to claim 2. The proximal end of the diaphragm is composed of a first film,
The central portion of the diaphragm is composed of a multilayer film including the first film and a second film having a lower density than the first film.
The condenser microphone according to claim 2. The partial rigidity of the diaphragm is gradually increased from the outer periphery of the diaphragm toward the center of the diaphragm.
The condenser microphone according to claim 1. The diaphragm has a thin-walled portion and a thick-walled portion whose formation density gradually increases from the outer periphery of the diaphragm toward the center of the diaphragm.
The condenser microphone according to claim 5. The thin portion is composed of a first film,
The thick part is composed of a multilayer film including the first film and a second film having higher hardness than the first film.
The condenser microphone according to claim 6. The thin portion is composed of a first film,
The thick part is composed of a multilayer film including the first film and a second film having a lower density than the first film.
The condenser microphone according to claim 6.

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