JP2007295516A - Condenser microphone - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a condenser microphone having an improved vibration characteristic of a diaphragm by a simple manufacturing process, reduced parasitic capacitance, and an improved sensitivity. <P>SOLUTION: The diaphragm 10 is structured such that it is formed to be a gear shape including a center portion 12 and arms 14 and tips of the arms 14 are suspended by spacers 52 and suspension portions 20b or the like. A back plate 20 is also formed to be a gear shape including a center portion 22 and six arms 24. The center portion 22 of the back plate 20 concentrically corresponds to the center portion 12 of the diaphragm 10, and the radius of the center portion 22 is smaller than the radius of the center portion 12. Further, the arms 14 of the diaphragm 10, and the arms 24 of the back plate 20 have no correspondence relationship with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a condenser microphone, and more particularly to a condenser microphone as a MEMS sensor.

  Conventionally, a condenser microphone that can be manufactured by applying a semiconductor device manufacturing process is known. In the condenser microphone, a diaphragm and a plate that are vibrated by sound waves form a movable electrode and a fixed electrode, and the diaphragm and the plate are supported in a state of being separated from each other by an insulating spacer. That is, the diaphragm and the plate form the counter electrode of the capacitor.

  In such a condenser microphone, when the diaphragm vibrates due to sound waves, the capacitance of the capacitor changes due to the displacement, and the change in capacitance is converted into an electrical signal and output. The sensitivity of the condenser microphone is increased by increasing the ratio of the diaphragm displacement to the distance between the counter electrodes, that is, by improving the vibration characteristics of the diaphragm, and by reducing the parasitic capacitance that does not contribute to the capacitance change of the capacitor. improves.

  Non-Patent Document 1 discloses a condenser microphone in which each of a plate and a diaphragm is formed of a conductive thin film. However, since the entire periphery of the diaphragm is fixed to the spacer, when a sound wave propagates to the diaphragm, the displacement due to the vibration of the diaphragm is large at the center, but is extremely small at the outer periphery fixed to the spacer. As a result, the vibration of the diaphragm is efficiently detected as a change in capacitance mainly at the central portion of the diaphragm, and the outer peripheral portion of the diaphragm produces only parasitic capacitance. This parasitic capacitance is a factor that reduces the sensitivity of the condenser microphone.

  Patent Documents 1 and 2 disclose condenser microphones in which vibration characteristics of the diaphragm are improved and sensitivity is improved by providing a structure that acts as a spring in the support portion of the diaphragm. Specifically, the diaphragm is provided with a slit, and a region sandwiched between the slits has a spring function. However, since the plate corresponding to the entire diaphragm including the region with the spring function is arranged, parasitic capacitance is also generated in the region where the displacement due to the diaphragm vibration is small, which causes a decrease in sensitivity of the condenser microphone. It becomes.

  In Patent Document 3, a plate facing a diaphragm forming a movable electrode is formed of an insulating material, and a surface of the plate facing the diaphragm (hereinafter referred to as “diaphragm facing surface”) corresponds to a central portion of the diaphragm. A condenser microphone is disclosed in which a back electrode is provided only at a portion so that a capacitance change only at the center portion of the diaphragm can be efficiently detected, and a parasitic capacitance at the outer peripheral portion of the diaphragm is reduced to improve sensitivity. . However, since it is necessary to provide the back electrode only on a certain portion of the diaphragm facing surface of the plate made of an insulating material, there is a problem that the manufacturing process becomes complicated, the manufacturing yield decreases, and the manufacturing cost increases. In addition, in the step of etching away the sacrificial layer interposed between the diaphragm and the plate to form a gap, the insulating material that fixes the back electrode of the plate is also etched to some extent. Since it becomes necessary to be incorporated into the manufacturing process, the manufacturing cost is further increased.

The Institute of Electrical Engineers of Japan MSS-01-34 JP 9-508777 A US Patent No. 4776019 Special table 2004-506394

  An object of the present invention is to provide a condenser microphone that improves the vibration characteristics of the diaphragm, reduces the parasitic capacitance of the condenser, and improves the microphone sensitivity without complicating the manufacturing process.

(1) A condenser microphone for achieving the above object has a central portion and a plurality of arm portions extending radially outward from the central portion, and a conductive diaphragm that vibrates in response to sound waves, and the diaphragm And a conductive plate provided opposite to the diaphragm and a cavity provided on the opposite side of the plate to relieve pressure applied to the diaphragm from the opposite side of the plate. A substrate, a spacer having a lower end surface bonded to the tip end portions of the plurality of arm portions of the diaphragm, a suspension portion having an inner end portion bonded to the upper end surface of the spacer, and an outer end portion of the suspension portion; An insulating first support portion for supporting the outer peripheral portion of the plate on the substrate, and an insulating second support portion for supporting an outer edge portion of the plate on the substrate. Comprising serial central portion and a support means forming a gap between said plate.
In such a condenser microphone, since the diaphragm has a unique planar shape having a central portion and a plurality of arms extending radially outward from the central portion, the vibration characteristics of the diaphragm with respect to sound waves are improved. In addition, since the diaphragm is suspended from the suspension part supported on the substrate by the first support part via the spacer, the stress of the diaphragm is relieved and the vibration characteristics are further improved. . In addition, since there is no correspondence between the diaphragm and the plate facing each other, at least in the notch portion sandwiched between the plurality of diaphragm arm portions, there is no parasitic capacitance in that portion, and the parasitic capacitance as a whole is Decrease. In addition, since both the diaphragm and the plate are formed of a conductive material, a complicated manufacturing process is not required, in which an electrode is provided only on a certain portion of the diaphragm facing surface of the plate made of an insulating material, and the manufacturing process is simplified. Can be achieved. Therefore, without making the manufacturing process complicated, the vibration characteristics of the diaphragm can be improved, the parasitic capacitance of the capacitor can be reduced, and the microphone sensitivity can be improved.
In the specification of the present application, “diaphragm” and “plate” mean that the plane including the diaphragm and the plane including the plate are in a parallel or substantially parallel positional relationship, and the “corresponding” relationship. “Present” means that a certain part of the diaphragm and a certain part of the plate are in a positional relationship overlapping each other.

(2) In the condenser microphone described above, it is preferable that the distance from the center to the outer edge of the plate is shorter than the distance from the center of the central portion of the diaphragm to the tip of the arm portion.
In this case, since the correspondence between the diaphragm and the plate does not occur even in the portion including at least a part of the arm portion of the diaphragm located outside the outer edge of the plate, the parasitic capacitance does not occur in the portion, and the entire parasitic capacitance is generated. The capacity is further reduced. Also, since the planar shape of the plate can be made relatively small compared to the diaphragm, the rigidity of the plate is relatively increased. As a result, the diaphragm can be enlarged without degrading the stability of the microphone operation. can do. Accordingly, the microphone sensitivity can be improved by further reducing the parasitic capacitance of the capacitor and further improving the vibration characteristics of the diaphragm.

(3) In the above condenser microphone, it is preferable that a portion of the plate corresponding to the arm portion of the diaphragm is notched.
In this case, no parasitic capacitance is generated between the plate and the arm portion of the diaphragm, and electrostatic capacitance is mainly generated between the plate and the central portion of the diaphragm, so that the overall parasitic capacitance is greatly reduced. Therefore, the microphone sensitivity can be improved by further reducing the parasitic capacitance of the capacitor.

(4) In the condenser microphone, it is preferable that the second support portion is located between the plurality of arm portions of the diaphragm.
In this case, since the second support portion that supports the outer edge portion of the plate is located between the plurality of arm portions of the diaphragm, that is, in the cutout portion sandwiched between the plurality of arm portions, the planar shape of the plate is compared with that of the diaphragm. Accordingly, the rigidity of the plate is relatively increased. As a result, the diaphragm can be enlarged without deteriorating the stability of the microphone operation. Furthermore, since the diaphragm and the plate are each supported on the substrate, a particularly complicated manufacturing process is not required. Therefore, the diaphragm sensitivity can be further improved without complicating the manufacturing process, and the microphone sensitivity can be improved.

(5) In the above condenser microphone, it is preferable that the suspension portion is made of the same material as the plate and is formed simultaneously with the plate.
In this case, an independent process is not required to form the suspension part, and the suspension part can be formed simultaneously in the process of forming the plate. Therefore, it is possible to avoid a complicated manufacturing process.

(6) In the above condenser microphone, it is preferable that a plurality of through holes are provided in the suspension portion.
In this case, the rigidity of the suspension part is lowered by the amount of the plurality of through holes provided, the deformation in the suspension part during vibration of the diaphragm is facilitated, and the displacement in the center part is increased. Becomes even better. In addition, the plurality of through holes provided in the suspension portions are used to remove etching solution when the sacrificial layer interposed between the plate and the diaphragm is removed by etching and a gap is formed therebetween in the condenser microphone manufacturing process. Also functions as an entrance hole. Therefore, it can contribute to simplifying the manufacturing process.

(7) In the condenser microphone, it is preferable that an acoustic resistance higher than an acoustic resistance between the plurality of arms is formed by a peripheral portion of the cavity of the substrate and the diaphragm.
In this case, even if the diaphragm has a planar shape having a plurality of arm portions, the acoustic resistance higher than the acoustic resistance between the plurality of arm portions is formed by the peripheral portion of the cavity of the substrate and the diaphragm. The sound waves that reach the diaphragm are unlikely to pass between the arms.

(8) In the above condenser microphone, it is preferable that the cavity has an opening formed along the inner side of the outer edge of the diaphragm.
In this case, the cavity has a sufficient volume because its opening corresponds to almost the entire diaphragm, and as a result, the air spring constant of the cavity becomes sufficiently small, so that the vibration characteristics of the diaphragm are maintained well. Is possible. Therefore, the microphone sensitivity can be improved. In addition, since the opening of the cavity is formed along the inside of the outer edge of the diaphragm, a passage is formed between the substrate around the cavity and the diaphragm, and the acoustic resistance between the arms of the diaphragm is formed by this passage. Since a higher acoustic resistance is formed, the sound wave reaching the diaphragm is less likely to pass between the plurality of arms.

Embodiments of the present invention will be described below based on a plurality of examples. In each of the embodiments, the component having the same reference sign corresponds to the component of the other embodiment having the reference sign.
(First Example)
1A is a plan view schematically showing the configuration of the condenser microphone according to the first embodiment, FIG. 1B is a cross-sectional view taken along line AA ′ in FIG. 1A, and FIG. 1C is a cross-sectional view taken along line BB ′ in FIG. .

  As shown in FIG. 1A, FIG. 1B, and FIG. 1C, the condenser microphone has a diaphragm 10 that constitutes a counter electrode of the condenser, a back plate 20 as a plate, and a supporting means that supports the diaphragm 10 and the back plate 20 while insulating them. The support substrate 30 provided is provided.

  The diaphragm 10 is made of a conductive thin film made of polysilicon doped with, for example, P (phosphorus) as an impurity, and has a disk-shaped central portion 12 and, for example, six arms extending radially outward from the central portion 12. A substantially gear shape having a portion 14 is formed. Here, the thickness of the diaphragm 10 is about 0.5 μm, the radius of the central portion 12 is about 0.35 mm, and the length of the arm portion 14 is about 0.15 mm.

  The back plate 20 is disposed in parallel with the diaphragm 10 with a gap 40 having a predetermined interval, for example, an interval of about 4 μm. The back plate 20 is also made of a conductive thin film made of polysilicon doped with P, for example, and has a disk-like central portion 22 and, for example, six arm portions 24 extending radially outward from the central portion 22. Has a substantially gear shape. A large number of through holes 26 are continuously provided in the central portion 22 and the six arm portions 24. These through holes 26 function as acoustic holes for allowing sound waves from the outside to pass through to reach the diaphragm 10. Here, the thickness of the back plate 20 is about 1.5 μm, the radius of the central portion 22 is about 0.3 mm, and the length of the arm portion 24 is about 0.1 mm.

  The central portion 22 of the back plate 20 is disposed concentrically with the diaphragm 10, and the radius of the central portion 22 of the back plate 20 is smaller than the radius of the central portion 12 of the diaphragm 10. Further, the six arm portions 24 of the back plate 20 are located at positions corresponding to the six notch portions sandwiched between the six arm portions 14 of the diaphragm 10. Conversely, the six arm portions 14 of the diaphragm 10 are at positions corresponding to the six cutout portions sandwiched between the six arm portions 24 of the back plate 20. The distance from the center of the center portion 22 of the back plate 20 to the tip of the arm portion 24 is longer than the radius of the center portion 12 of the diaphragm 10 and the center of the center portion 12 of the diaphragm 10 to the tip of the arm portion 14. Shorter than the distance to.

  The lower end surface of the insulating spacer 52 is joined to the distal ends of the six arm portions 14 of the diaphragm 10. The inner end portion of the suspension portion 20b is joined to the upper end surface of the spacer 52. The suspension portion 20 b is made of the same material as the plate 20, that is, a conductive polysilicon thin film, and is formed simultaneously with the plate 20. And the outer side edge part has comprised the strip | belt shape which surrounds the outer side of the substantially gear-shaped outer edge of the diaphragm 10 circularly. The outer end portion of the suspension portion 20b is supported on the support substrate 30 by an insulating first support portion 54b. A plurality of through holes 26a are provided in a portion sandwiched between the spacer 52 and the first support portion 54b of the suspension portion 20b. Further, the front end portions of the six arm portions 24 of the back plate 20 are supported by the insulating second support portions 54 located at the six cutout portions sandwiched between the six arm portions 14 of the diaphragm 10. 30 is supported. The insulating spacer 52 and the first support portion 54b are made of, for example, a silicon oxide film.

  The second support portion 54 that supports the back plate 20 includes insulating films 541 and 543 and a conductive film 542. The insulating films 541 and 543 are made of, for example, a silicon oxide film. The conductive film 542 is preferably formed simultaneously with the diaphragm 10 which is a conductive film, and is made of, for example, polysilicon to which P (phosphorus) is added as an impurity. As will be described later, the conductive film 542 is set to the same potential as the back plate 20 or the substrate 30 and functions as a guard electrode for reducing the parasitic capacitance of the condenser microphone. Note that the conductive film 542 may be omitted.

  The support substrate 30 is made of, for example, a silicon substrate having a thickness of 500 to 600 μm, and a cavity 32 including an opening that penetrates the support substrate 30 and reaches the diaphragm 10 is provided at a position corresponding to the substantially gear shape of the diaphragm 10. Yes. The cavity 32 is formed along the inside of the substantially gear-shaped outer edge of the diaphragm 10 and functions as a pressure buffering chamber for relieving the pressure applied to the diaphragm 10 from the side opposite to the plate. Further, the support substrate 30 around the cavity 32 and the diaphragm 10 are provided with a passage 34 that forms an acoustic resistance higher than the acoustic resistance between the arm portions 14 of the diaphragm 10. The acoustic resistance is controlled by the height H of the passage 34 (that is, the distance between the diaphragm 10 and the support substrate 30) and the length L (that is, the distance from the substantially gear-shaped outer edge of the diaphragm 10 to the end of the cavity 32). By controlling, an acoustic resistance higher than the acoustic resistance between the arm portions 14 of the diaphragm 10 is formed, so that the sound wave reaching the diaphragm 10 does not leak through the plurality of arm portions 14. Here, the height H of the passage 34 is, for example, 2 μm, and the length L thereof is, for example, 15 μm.

FIG. 4A is a circuit diagram for explaining a detection circuit that detects a change in electrostatic capacitance between the diaphragm 10 and the back plate 20 as an electric signal.
A stable bias voltage is applied to the diaphragm 10 by a charge pump CP or the like. Capacitance changes of the back plate 20 and the diaphragm 10 are input to the amplifier A as voltage signals. Since the substrate 30 and the diaphragm 10 are short-circuited, a parasitic capacitance is formed between the back plate 20 and the substrate 30 if the conductive film 542 shown in FIGS. 1C and 4B does not exist.

  In the case where the conductive film 542 is provided, the conductive film 542 can function as a guard electrode by connecting the output terminal of the preamplifier A to the conductive film 542 as shown in FIG. That is, the parasitic capacitance generated between the back plate 20 and the conductive film 542 can be removed by controlling the back plate 20 and the conductive film 542 to the same potential by the voltage follower circuit. Further, by short-circuiting the substrate 30 and the diaphragm 10, the capacitance between the conductive film 542 and the substrate 30 becomes irrelevant to the output of the preamplifier A. Thus, by providing the conductive film 542 to form the guard electrode, the parasitic capacitance of the condenser microphone can be further reduced.

  As described above, according to the condenser microphone according to the first embodiment, the diaphragm 10 and the back plate 20 both have a substantially gear shape, and the central portion 12 of the diaphragm 10 and the central portion 22 of the back plate 20 correspond to each other. It is in. On the other hand, the six arm portions 24 of the back plate 20 are positioned at six cutout portions sandwiched between the six arm portions 14 of the diaphragm 10, and the six arm portions 14 of the diaphragm 10 are the back plate. 20, the arm portions 14 and 24 of the back plate 20 do not have a corresponding relationship, and as a result, parasitic capacitance occurs. Absent. Therefore, as a whole, a capacitance is mainly generated between the central portions 12 and 22 of the diaphragm 10 and the back plate 20, and this capacitance becomes a signal capacitance contributing to the capacitance change of the capacitor, while other portions. Since the parasitic capacitance at is greatly reduced, the microphone sensitivity can be greatly improved.

  The diaphragm 10 has a structure in which the tip ends of the six arm portions 14 are suspended by the spacer 52, the suspension portion 20b, and the first support portion 54b, and the spacer 10 extends from the center of the center portion 12 of the diaphragm 10. Since the distance to 52 is longer than the distance from the center of the central portion 22 of the back plate 20 to the second support portion 54 that supports the tip portions of the six arm portions 24, the outer edge portion of the diaphragm is directly on the support substrate. The vibration characteristics of the diaphragm 10 can be improved even when compared with the structure where the diaphragm is supported and when the planar shapes of the diaphragm and the back plate are substantially the same.

Further, the back plate 20 has a radius of the central portion 22 smaller than that of the central portion 12 of the diaphragm 10, and a distance from the center of the central portion 22 to the second support portion 54 is the central portion 12 of the diaphragm 10. Since the distance between the center of the diaphragm and the spacer 52 is shorter than the case where the planar shape of the diaphragm and the back plate is substantially the same, the rigidity of the back plate 20 is increased, and the diaphragm 10 does not deteriorate the stability of the microphone operation. And the vibration characteristics of the diaphragm 10 can be improved.
In addition, since the plurality of through holes 26a are provided in the suspension portion 20b, the rigidity of the arm portion 14 of the suspension portion 20b is reduced, and the suspension portion 20b can be easily deformed during vibration. The vibration characteristics can be further improved.

The inventors of the present application conducted the following experiment and simulation in order to confirm the effect of the condenser microphone according to the first embodiment as described above.
Here, FIGS. 2A and 2B are a plan view and a cross-sectional view schematically showing the configuration of a conventional condenser microphone, respectively, and FIGS. 3A and 3B are planes schematically showing the configuration of a capacitor microphone prepared for an experiment, respectively. It is a figure and sectional drawing.

  As shown in FIGS. 2A and 2B, the condenser microphone having the conventional structure is a disk-shaped diaphragm 100 having a radius equivalent to the distance from the center of the central portion 12 to the tip of the arm portion 14 of the diaphragm 10 of the first embodiment. However, the entire periphery thereof is supported on the support substrate 300 by the first support portion 500. A disc-shaped back plate 200 is disposed so as to cover the entire surface of the diaphragm 100, and the entire periphery thereof is supported on the support substrate 300 by the second support portion 540.

Further, as shown in FIGS. 3A and 3B, the condenser microphone of the experimental structure has an outer periphery supported by the first support portion 500 of the diaphragm 100 at the peripheral portion of the back plate 200 of the condenser microphone having the conventional structure. Six cutout portions 700 for reducing parasitic capacitance are provided at positions corresponding to the vicinity.
2A and 2B, the experimental structure shown in FIGS. 3A and 3B, and the condenser microphones of the first embodiment shown in FIGS. 1A, 1B, and 1C, the electrode withstand voltage, the vibration displacement When the amount and the microphone sensitivity were measured, the results shown in the following table were obtained.

Here, the electrode withstand voltage is a state in which a sacrificial oxide film is interposed between the diaphragm and the support substrate, that is, a state in which the entire diaphragm is fixed to the support substrate, and a voltage is applied between the diaphragm and the back plate. This is the voltage value when the back plate deformed by the attraction force is in contact with the diaphragm and energized, and serves as a measure of the strength of the back plate.
The vibration displacement amount is a displacement amount at the center of the diaphragm when a predetermined sound pressure is applied to the diaphragm.
The microphone sensitivity refers to the output voltage of the microphone when a predetermined sound pressure is applied to the diaphragm, and is expressed by the following equation.
Microphone sensitivity ∝Vibration displacement x Applied voltage between electrodes x {Signal capacitance / (Signal capacitance + Parasitic capacitance)}
The numbers in the table specify the electrode withstand voltage, the vibration displacement amount, and the microphone sensitivity in the case of a conventional condenser microphone as 1.0, and are displayed as relative values with respect to this reference.

  In the above table, the electrode breakdown voltage of the experimental structure is reduced to 0.8 times that of the conventional structure. This is considered to be due to the fact that the strength of the back plate 120 is reduced due to the installation of the notch 121 for reducing the parasitic capacitance. Such a decrease in electrode breakdown voltage causes instability in microphone operation.

  Moreover, although the back plate 20 of the first embodiment has a substantially gear shape and has a structure equivalent to that provided with a notch on the outer periphery, the electrode breakdown voltage is 1.2 times that of the conventional structure. It is high. This is because the second support portion 54 that supports the distal end portion of the arm portion 24 of the back plate 20 of the first embodiment is located in a notch portion sandwiched between the arm portions 14 of the diaphragm 10, and the central portion 22 of the back plate 20. The distance from the center to the second support part 54 is shorter than the distance from the center of the diaphragm 100 having the conventional structure to the first support part 500, and therefore the rigidity of the back plate 20 is relatively high. It is thought to be caused. Such an increase in the electrode breakdown voltage contributes to an increase in the stability of the microphone operation.

  Further, the vibration displacement amount of the diaphragm 10 of the first embodiment is 8.0 times higher than that in the conventional structure. This is because the diaphragm 10 of the first embodiment has a substantially gear shape and has a structure in which the distal end portion of the arm portion 14 is supported, and further, the distal end portion of the arm portion 14 is supported. Compared to the conventional structure in which the entire periphery of the diaphragm 110 is fixed by the support structure, the structure is a structure that is suspended by the spacer 52, the suspension part 20 or the like. It is considered that this is because the vibration characteristics of the diaphragm 10 are greatly improved.

  Further, the microphone sensitivity of the first embodiment is 12.0 times higher than that of the conventional structure. This is because the vibration displacement amount of the diaphragm 10 of the first embodiment is significantly higher than that of the conventional structure, and as described above, it is mainly between the central portions 12 and 22 of the diaphragm 10 and the back plate 20. On the other hand, it is considered that the parasitic capacitance is not generated because no correspondence relationship is generated in each of the arm portions 14 and 24, and the parasitic capacitance is greatly reduced as a whole.

Next, a method for manufacturing the condenser microphone according to the first embodiment will be described.
The condenser microphone according to the first embodiment is a so-called silicon microphone, which is manufactured using a semiconductor manufacturing process, and is basically the same as a normal silicon microphone manufacturing method.
First, for example, a P-doped polysilicon layer is formed on a support substrate 30 made of a semiconductor substrate such as a single crystal silicon substrate via a first insulating film (first sacrificial film) made of a silicon oxide film, for example. A first conductive layer is formed, and the first conductive layer is etched into a predetermined shape to form the diaphragm 10 and the guard electrode 542. As shown in FIG. 1A, the diaphragm 10 has a substantially gear shape having a disk-shaped central portion 12 and six arm portions 14 that radially extend from the central portion 12.

  Next, a second conductive layer made of, for example, a polysilicon layer to which P is added is formed on the diaphragm 10 and the first insulating film via a second insulating film (second sacrificial film) made of, for example, a silicon oxide film. Then, the second conductive layer is etched into a predetermined shape to form the back plate 20 and the suspension portion 20b. As shown in FIG. 1A, the back plate 20 has a substantially gear shape having a disc-shaped central portion 22 and six arm portions 24 extending radially outward from the central portion 22, A plurality of through holes 26a are formed in the suspension portion 20b.

  Further, as shown in FIG. 1A, the center portion 22 of the back plate 20 corresponds to the center portion 12 of the diaphragm 10 concentrically, and the radius of the center portion 22 of the back plate 20 is equal to the center portion 12 of the diaphragm 10. Is smaller than the radius. Further, the six arm portions 24 of the back plate 20 are located at positions corresponding to the six notch portions sandwiched between the six arm portions 14 of the diaphragm 10. Conversely, the six arm portions 14 of the diaphragm 10 are at positions corresponding to the six cutout portions sandwiched between the six arm portions 24 of the back plate 20. The distance from the center of the center portion 22 of the back plate 20 to the tip of the arm portion 24 is longer than the radius of the center portion 12 of the diaphragm 10 and the center of the center portion 12 of the diaphragm 10 to the tip of the arm portion 14. Shorter than the distance to.

Further, as shown in FIG. 1A, the suspension portion 20b has an inner end portion in a position overlapping the tip portions of the six arm portions 14 of the diaphragm 10, and an outer end portion of the suspension portion 20b having a substantially gear shape. It forms a band shape that surrounds the outside of the outer edge of the outer periphery.
Next, after the third insulating film 56 made of, for example, a silicon oxide film is formed on the back plate 20, the suspension 20b, and the second insulating film 52a, the back surface of the support substrate 30 is ground to adjust its thickness. Subsequently, for example, the support substrate 30 is selectively removed by an anisotropic etching technique commonly called deep RIE to form an opening reaching the first insulating film. This opening is at a position along the inside of the substantially gear-shaped outer edge of the diaphragm 10.

  Next, using the predetermined photoresist pattern as a mask, the third insulating film, the second insulating film, and the first insulating film are selectively etched away by a wet etching technique using, for example, buffered HF. . At this time, the plurality of through holes 26 formed in the central portion 22 and the arm portion 24 of the back plate 20 and the plurality of through holes 26 a formed in the suspension portion 20 b are interposed between the back plate 20 and the diaphragm 10. When the second insulating film is removed by etching, it functions as an entrance hole for the etchant. Further, the buffered hydrofluoric acid selectively removes the first insulating film and the like from the opening side of the support substrate 30 by etching.

  In this way, the second insulating film between the back plate 20 and the diaphragm 10 is removed, and a gap 40 is formed there. Further, the first insulating film is removed, and the opening of the support substrate 30 is expanded until reaching the diaphragm 10 to form a cavity 32, and a desired acoustic wave is formed between the support substrate 30 and the diaphragm 10 around the cavity 32. A passage 34 for forming a resistance is formed.

At the same time, the spacers 52 are formed by intentionally leaving the second insulating film between the tip portions of the six arm portions 14 of the diaphragm 10 and the suspension portion 20b. Further, the first support portion 54b is formed between the suspension portion 20b and the support substrate 30 by leaving the stacked insulating film in which the first insulating film and the second insulating film are intentionally stacked. Further, the second support portion 54 is formed by intentionally leaving the laminated insulating film between the front end portions of the six arm portions 24 of the back plate 20 and the support substrate 30.
In this way, the condenser microphone according to the first embodiment shown in FIGS. 1A, 1B and 1C is manufactured.

  As described above, according to the method of manufacturing the condenser microphone according to the first embodiment, it is possible to follow the conventional manufacturing process almost as it is, except that the resist mask pattern used in each photolithography process is different. In addition, it is possible to prevent an increase in manufacturing cost because a process that causes a decrease in manufacturing yield, such as a process of providing a back electrode only on a predetermined portion of the diaphragm facing surface of a plate made of an insulating material, is not required.

(Second embodiment)
The condenser microphone according to the second embodiment is the same as the condenser microphone according to the first embodiment shown in FIGS. 1A, 1B, and 1C. The entire back plate 20 has a disk shape, and the radius thereof is that of the central portion 12 of the diaphragm 10. It is longer than the radius and shorter than the distance from the center of the central portion 12 of the diaphragm 10 to the inner end of the suspension portion 20b.

Even in this case, since the diaphragm 10 has a substantially gear shape having the central portion 12 and the six arm portions 14, the notch portion sandwiched between the arm portions 14 of the diaphragm 10 is connected to the back plate 20. There is no correspondence between them, and as a result, no parasitic capacitance occurs. Similarly, no parasitic capacitance is generated in the arm portion 14 of the diaphragm 10 located outside the outer edge of the back plate 20. Therefore, as compared with the case of the conventional structure shown in FIGS. 2A and 2B, the parasitic capacitance can be reduced as a whole.
However, a portion of the arm portion 14 of the diaphragm 10 that is inside the outer periphery of the disk-shaped back plate 20 generates a parasitic capacitance with the back plate 20. Only the parasitic capacitance increases.

1A is a plan view schematically showing the configuration of the condenser microphone according to the first embodiment, FIG. 1B is a cross-sectional view taken along the line AA ′ of FIG. 1A, and FIG. 1C is a partially enlarged view of FIG. 1B. FIG. 2A is a plan view schematically showing the configuration of a conventional condenser microphone, and FIG. 2B is a sectional view thereof. 3A is a plan view schematically showing the configuration of a condenser microphone having an experimental structure, and FIG. 3B is a cross-sectional view thereof. 4A and 4B are circuit diagrams according to the first embodiment.

Explanation of symbols

  10: Diaphragm, 12: Center part (center part of diaphragm), 14: Arm part (arm part of diaphragm), 20: Back plate, 20b: Suspension part, 22: Center part (center part of back plate), 24: Arm (back plate arm), 26, 26a: through hole, 30: support substrate, 32: cavity, 34: passage, 40: gap, 52: spacer, 54: second support, 54b: first support Department.

Claims (8)

A conductive diaphragm that has a central portion and a plurality of arms extending radially outward from the central portion, and vibrates in response to sound waves;
A conductive plate provided opposite to the diaphragm;
A substrate provided on the opposite side of the plate with respect to the diaphragm, and forming a cavity for relieving pressure applied to the diaphragm from the opposite side of the plate;
A spacer having a lower end surface joined to tip ends of the plurality of arm portions of the diaphragm, a suspension portion having an inner end joined to an upper end surface of the spacer, and an outer end portion of the suspension portion as the substrate An insulating first supporting portion for supporting the upper edge of the plate; and an insulating second supporting portion for supporting an outer edge portion of the plate on the substrate; and between the central portion of the diaphragm and the plate. A supporting means forming a void in
Condenser microphone with In the plate, the distance from the center to the outer edge is shorter than the distance from the center of the central portion of the diaphragm to the tip of the arm portion,
The condenser microphone according to claim 1. The plate is cut out at a portion corresponding to the arm portion of the diaphragm.
The condenser microphone according to claim 1 or 2. The second support portion is located between the plurality of arm portions of the diaphragm.
The condenser microphone according to any one of claims 1 to 3. The suspension is made of the same material as the plate and is formed simultaneously with the plate.
The condenser microphone according to any one of claims 1 to 4. A plurality of through holes are provided in the suspension part,
The condenser microphone according to any one of claims 1 to 5. The acoustic resistance higher than the acoustic resistance between the plurality of arms of the diaphragm is formed by the peripheral portion of the cavity of the substrate and the diaphragm.
The condenser microphone according to any one of claims 1 to 6. The cavity has an opening formed along the inside of the outer edge of the diaphragm.
The condenser microphone according to claim 7.

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