Patent Application
20090136064
1. Field of the Invention
The present invention relates to vibration transducers and in particular to wave transducers such as miniature condenser microphones serving as MEMS sensors. The present invention also relates to manufacturing methods of vibration transducers.
The present application claims priority on Japanese Patent Application No. 2007-256905 and Japanese Patent Application No. 2007-256906, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Various types of vibration transducers have been developed and disclosed in various documents such as Patent Documents 1, 2, 3 and Non-Patent Document 1.
Miniature condenser microphones have been conventionally known as typical types of vibration transducers and have been produced by way of semiconductor device manufacturing processes.
Condenser microphones are referred to as MEMS microphones (where MEMS stands for Micro Electro Mechanical System). A typical example of condenser microphones is constituted of a substrate, a diaphragm, and a plate. The diaphragm and plate serving as opposite electrodes, which are distanced from each other, are composed of films deposed on the substrate and are supported above the substrate. When the diaphragm vibrates due to sound waves relative to the plate, the electrostatic capacitance between the diaphragm and the plate varies due to the displacement of the diaphragm, and then variations of electrostatic capacitance are converted into electric signals. This condenser microphone (or vibration transducer) is designed such that the peripheral portion of the plate joins an insulating film.
In the structure in which the plate joins the insulating film, however, a parasitic capacitance occurs between the diaphragm or the substrate and the plate which joins the insulating film serving as a dielectric layer in the peripheral portion, thus reducing the sensitivity of the vibration transducer.
It is an object of the present invention to provide a vibration transducer having high sensitivity.
It is another object of the present invention to provide a manufacturing method of the vibration transducer.
In a first aspect of the present invention, a vibration transducer includes a diaphragm having a conductive property, a plate having a conductive property, which is positioned opposite to the diaphragm, and a plurality of first spacers having pillar shapes which are formed using a deposited film having an insulating property joining the plate and which supports the plate relative to the diaphragm with a gap therebetween, wherein an electrostatic capacitance formed between the diaphragm and the plate is varied when the diaphragm vibrates relative to the plate.
In the fixed region of the diaphragm which does not vibrate relative to the plate, a parasitic capacitance is formed between the diaphragm and the plate, which are positioned opposite to each other; hence, it is preferable that the first spacers each having a high dielectric constant (higher than that of the air) be each reduced in area in plan view. That is, the plate is supported by the first spacers, which are not formed in ring shapes but are formed in a pillar shape, whereby it is possible to reduce the electrostatic capacitance between the diaphragm and the plate, thus improving the sensitivity. The geometric shapes of the first spacers are not necessarily limited to pillar shapes but can also be formed in flat shapes. The present invention does not need the support having a structurally closed shape but multiple supports which are formed in any shape for supporting the plate. It may be possible to reduce the parasitic capacitance by forming the plate or the diaphragm by use of an insulating substance in the region in which the diaphragm and the plate is positioned opposite to each other; however, this causes complexity in film structure with respect to at least one of the diaphragm and the plate
The aforementioned vibration transducer is manufactured in such a way that a plurality of holes are formed in the plate; isotropic etching is performed using the plate as a mask so as to remove a part of the deposited film, thus forming the gap between the plate and the diaphragm; and the first spacers are formed by use of the remaining deposited film. Since the plate is used as the etching mask so as to form the first spacers, it is possible to reduce the total number of masks, thus reducing the manufacturing cost.
That is, it is preferable that the plate has a plurality of holes which allow an etchant to transmit therethrough in isotropic etching, thus simultaneously forming the first spacers and the gap between the plate and the diaphragm.
The vibration transducer further includes a substrate and a plurality of second spacers having pillar shapes which are formed using a deposited film having an insulating property and which support the plate relative to the substrate with a gap therebetween, wherein an electrostatic capacitance formed between the diaphragm and the plate is varied when the diaphragm vibrates relative to the plate.
In consideration of a parasitic capacitance formed in the region in which the plate and the substrate are positioned opposite to each other via the second spacers having high dielectric constants (higher than the dielectric constant of the air) therebetween, it is preferable that the second spacers each be reduced in area in plan view. That is, the plate is supported by the second spacers which are formed not in ring shapes but in pillar shapes, whereby it is possible to reduce the electrostatic capacitance between the substrate and the plate, thus improving the sensitivity of the vibration transducer. The geometric shapes of the second spacers are not necessarily limited to pillar shapes but can also be formed in flat shapes. The present invention does not need the support having a structurally closed shape but multiple supports which are formed in any shapes for supporting the plate. It may be possible to reduce the parasitic capacitance in the region in which the plate and the substrate are positioned opposite to each other with the second spacers therebetween by forming the prescribed region of the plate joining the second spacers by use of an insulating substance; however, this causes complexity in the film structure of the plate.
The vibration transducer is manufactured in such a way that a plurality of holes is formed in the plate; isotropic etching is performed using the plate as a mask so as to remove a part of the deposited film, thus forming the gap between the plate and the substrate; and the second spacers are formed using the remaining of the deposited film. Since the plate is used as an etching mask for use in the formation of the second spacers, it is possible to reduce the number of masks, thus reducing the manufacturing cost.
That is, it is preferable that the plate has a plurality of holes allowing an etchant to transmit therethrough in isotropic etching, thus simultaneously forming the second spacers and the gap between the plate and the substrate.
In the vibration transducer, the distance between the center and the external end of the plate is smaller than the distance between the center and the external end of the diaphragm. In the region in which the diaphragm causes a relatively small amplitude of vibration or causes substantially no vibration, the electrostatic capacitance between the diaphragm and the plate varies very little or is not varied substantially. In the foregoing structure in which the external portion of the diaphragm is fixed to its upper or lower film, it causes a very small amplitude of vibration. The vibration transducer is designed such that the distance between the center and the external end of the plate becomes smaller than the distance between the center and the external end of the diaphragm, thus inhibiting the external portion of the diaphragm from being positioned opposite to the plate. When the plate and the diaphragm are both formed in a circular shape or when they have no recess in the outlines thereof, it is required that the external end of the plate is positioned inwardly of the external end of the diaphragm. When the plate and the diaphragm are both formed in a circular shape or when they have no recess in the outlines thereof, it is required that the shortest distance between the center and the external end of the plate be shorter than the shortest distance between the center and the external end of the diaphragm. Even when the plate is formed in a circular shape or does not have a recess in the outline thereof and even when the diaphragm has recesses in the outline thereof, it is required that the shortest distance between the center and the external end of the plate be shorter than the shortest distance between the center and the external end of the diaphragm. The aforementioned structure of the vibration transducer is capable of reducing the parasitic capacitance between the diaphragm and the plate, thus improving the sensitivity. In this connection, it may be possible to reduce the parasitic capacitance by forming the external portion of the diaphragm by use of an insulating substance or by forming the external region of the plate positioned opposite to the external portion of the diaphragm by use of an insulating substance, whereas this causes complexity in the film structure of at least one of the plate and the diaphragm.
Alternatively, the vibration transducer further includes a plurality of third spacers having pillar shapes which are formed using a deposited film having an insulating property which joins the substrate and the diaphragm and which supports the diaphragm relative to the substrate with a gap therebetween. When a parasitic capacitance is formed between the diaphragm and the substrate in the region in which they are positioned opposite to each other via the third spacers, it is preferable that the area of the third spacer (whose dielectric constant is higher than that of the air) be as small as possible. Each of the third spacers is not formed in a ring shape but in a pillar shape, whereby the diaphragm is supported by multiple third spacers; thus, it is possible to reduce the parasitic capacitance between the substrate and the diaphragm, thus improving the sensitivity. The geometric shapes of the third spacers are not necessarily limited to pillar shapes but can be formed in flat shapes. It is required that the third spacer not be formed in a closed wall structure, but a plurality of third spacers be formed in any shape for supporting the diaphragm. In this connection, it may be possible to reduce the parasitic capacitance between the diaphragm and the substrate in the region in which they are positioned opposite to each other via the third spacers by forming joint portions of the diaphragm joining the third spacers by use of insulating materials; however, this causes complexity in the film structure of the diaphragm.
Moreover, the plate is constituted of a center portion and a plurality of arms which are extended outwardly in a radial direction from the center portion, whereby the diaphragm is not positioned opposite to the plate at the arms and in the cutout regions between the arms. Due to the formation of the arms which are extended outwardly in a radial direction from the center portion of the plate, it is possible to reduce the parasitic capacitance formed between the diaphragm and the plate.
In a second aspect of the present invention, a vibration transducer includes a substrate, a diaphragm having a conductive property which is constituted of a center portion and a plurality of arms extended outwardly in a radial direction from the center portion, a plate having a conductive property which is constituted of a center portion, which is positioned opposite to the center portion of the diaphragm, and a plurality of arms extended outwardly in a radial direction from the center portion thereof, a plurality of plate supports for supporting the plate, and a plurality of diaphragm supports having pillar shapes which are positioned between the cutouts formed between the arms of the plate and which are positioned outwardly of the plate supports in the radial direction of the plate so as to support the diaphragm. The width of each arm of the diaphragm in the circumferential direction of the diaphragm becomes shortest in the intermediate region between the center portion and the joint portion at which each arm joins each diaphragm support but becomes longer in proximity to the joint portion. Herein, an electrostatic capacitance formed between the diaphragm and the plate is varied when the diaphragm vibrates relative to the plate.
In the above, the arms of the diaphragm are positioned alternately with the arms of the plate in plan view, wherein the distance between the plate supports which are positioned opposite to each other so as to support the plate is shorter than the distance between the diaphragm supports which are positioned opposite to each other so as to support the diaphragm. That is, the diaphragm supports which join the arms of the diaphragm and the substrate are positioned between the plate supports in the circumferential direction of the plate and are positioned externally of the plate supports in the radial direction of the plate. This increases the rigidity of the plate to be relatively higher than the rigidity of the diaphragm. The joint strength between the arms of the diaphragm and the diaphragm supports increase as the joint areas therebetween increase; thus, it is possible to increase the durability of the vibration transducer. When the joint areas are increased by increasing the lengths of the diaphragm supports in the radial direction of the diaphragm, the rigidity of the diaphragm is not changed (so that the sensitivity is not increased) irrespective of the substantial length of the diaphragm between the diaphragm supports, whereas the vibration transducer may be increased in size. To cope with such a possible drawback, the widths of the arms of the diaphragm in its circumferential direction are broadened at the joint areas so as to broaden the joint areas between the arms of the diaphragm and the diaphragm supports. This makes it possible to increase the sensitivity and durability of the vibration transducer without increasing its size. The geometric shapes of the diaphragm supports are not necessarily limited to pillar shapes but can be formed in flat shapes. That is, it is required for the diaphragm support to not have a structurally closed-wall structure but should be formed in any shape for supporting the diaphragm.
The rigidity of the diaphragm decreases as the widths of the arms of the diaphragm become short; hence, it is preferable that the widths of the arms of the diaphragm should be mostly broadened at the joint regions joining the diaphragm supports. That is, it is preferable that the widths of the arms of the diaphragm become longest at the joint regions joining the diaphragm supports.
It is preferable that the widths of the diaphragm supports be longer than the shortest width of the arm of the diaphragm at the intermediate position between the diaphragm support and the center portion of the diaphragm.
These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings.
The present invention will be described in further detail by way of examples with reference to the accompanying drawings.
(A) Constitution
The sensor chip of the condenser microphone 1 is composed of multiple films deposited on a substrate 100, i.e., a lower insulating film 110, a lower conductive film 120, an upper insulating film 130, an upper conductive film 160, and a surface insulating film 170. The lamination of films included in the MEMS structure of the condenser microphone 1 will be described below.
The substrate 100 is composed of a P-type monocrystal silicon; but this is not a restriction. The material of the substrate 100 should be determined to ensure the adequate rigidity, thickness, and strength in supporting multiple thin films deposited on a base substrate. A through-hole having an opening 100a is formed in the substrate 100, wherein the opening 100a corresponds to the opening of a back cavity C1.
The lower insulating film 110 joining the substrate 100, the lower conductive film 120, and the upper insulating film 130 is a deposited film composed of silicon oxide (SiOx). The lower insulating film 110 is used to form a plurality of third spacers 102 which are aligned in a circular manner with equal spacing therebetween, a plurality of guard spacers 103 which are aligned in a circular manner with equal spacing therebetween and are positioned internally of the third spacers 102, and a ring-shaped portion (actually, a rectangular-shaped portion having a circular opening) 101 which insulates a guard ring 125c and a guard lead 125d from the substrate 100.
The lower conductive film 120 joining the lower insulating film 110 and the upper insulating film 130 is a deposited film composed of polycrystal silicon entirely doped with impurities such as phosphorus (P). The lower conductive film 120 forms the diaphragm 123 and a guard portion 127 which is constituted of guard electrodes 125a and guard connectors 125b as well as the guard ring 125c and the guard lead 125d.
The upper insulating film 130 joining the lower conductive film 120, the upper conductive film 160, and the lower insulating film 110 is a deposited film composed of silicon oxide. The upper insulating film 130 forms a plurality of first spacers 131 which are aligned in a circular manner with prescribed distances therebetween, and a ring-shaped portion (actually a rectangular-shaped portion having a circular opening) 132 which is positioned outside of the first spacers 131, which supports an etching ring 161, and which insulates a plate lead 162d from the guard lead 125d.
The upper conductive film 160 joining the upper insulating film 130 is a deposited film composed of polycrystal silicon entirely doped with impurities such as phosphorus (P). The upper conductive film 160 forms the plate 162, the plate lead 162d, and the etching stopper 161.
The surface insulating film 170 joining the upper conductive film 160 and the upper insulating film 130 is a deposited film composed of silicon oxide having an insulating property.
The MEMS structure of the condenser microphone 1 has four terminals 125e, 162e, 123e, and 100b, which are formed using a pad conductive film 180 (which is a deposited film composed of AlSi having a conductive property), a bump film 210 (which is a deposited film composed of Ni having a conductive property), and a bump protection film 220 (which is a deposited film composed of Au having a superior anti-corrosion property and a conductive property). The side walls of the terminals 125e, 162e, 123e, and 100b are protected by means of a pad protection film 190 (which is a deposited film composed of SiN having an insulating property) and a surface protection film 200 (which is a deposited film composed of silicon oxide having an insulating property).
Next, the mechanical structure of the MEMS structure of the condenser microphone 1 will be described below.
The diaphragm 123 is formed using a thin single-layered deposited film having a conductive property and is constituted of a center portion 123a and a plurality of arms 123c which are extended outwardly in a radial direction from the center portion 123a. The diaphragm 123 is positioned in parallel with the substrate 100 and is supported by prescribed distances with the substrate 100 and the plate 162 while being insulated from the plate 162 by means of the third spacers 102 having pillar shapes which join the peripheral portion of the diaphragm 123 at multiple points. Specifically, the third spacers 102 join the arms 123c of the diaphragm 123 in proximity to their distal ends. Due to the cutouts formed between the arms 123c adjoining together in the diaphragm 123, the diaphragm 123 is reduced in rigidity compared with the foregoing diaphragm having no cutout. A plurality of diaphragm holes 123b is formed in each of the arms 123c, which is thus reduced in rigidity. Each arm 123c is elongated in length in the circumferential direction towards the center portion 123a of the diaphragm 123. This reduces concentration of stress at the boundary between the center portion 123a and each arm 123c. The diaphragm 123 is designed such that no bent portion is formed in the outline of each arm 123c in proximity to the boundary with the center portion 123a, thus preventing stress from being concentrated at the bent portion.
The third spacers 102 are aligned in the circumferential direction with equal spacing therebetween in the surrounding area of the opening 100a of the back cavity C1. Each of the third spacers 102 is formed using a deposited film having an insulating property in a pillar shape. The diaphragm 123 is supported above the substrate 100 by the third spacers 102 such that the center portion 123a thereof covers the opening 100a of the back cavity C1 in plan view. A gap C2 whose height substantially corresponds to the height or thickness of the third spacer 102 is formed between the substrate 100 and the diaphragm 123. The gap C2 is required to establish a balance between the internal pressure of the back cavity C1 and the atmospheric pressure. The gap C2 is reduced in height and is elongated in length in the radial direction of the diaphragm 123 so as to form a maximum acoustic resistance in a path which propagate sound waves (for vibrating the diaphragm 123) to reach the opening 100a of the back cavity C1.
A plurality of diaphragm bumps 123f is formed in the backside of the diaphragm 123 which is positioned opposite to the substrate 100. The diaphragm bumps 123f are projections for preventing the diaphragm 123 from being attached (or stuck) to the substrate 100. They are formed using the waviness of the lower conductive film 120 forming the diaphragm 123. Thus, dimples (or small recesses) are formed on the distal ends of the diaphragm bumps 123f.
The diaphragm 123 is connected to the diaphragm terminal 123e via a diaphragm lead 123d which is extended from the distal end of one of the arms 123c. The diaphragm lead 123d is formed using the lower conductive film 120 as similarly to the diaphragm 123 in such a way that the width thereof becomes smaller than the width of the arm 123c. The diaphragm lead 123d is elongated to pass through the gap of the guard ring 125c toward the diaphragm terminal 123e. Since the diaphragm terminal 123e is short-circuited to the substrate terminal 100b via a circuit chip (not shown) as shown in
A parasitic capacitance occurs between the substrate and the diaphragm 123 when the potential of the substrate 100 differs from the potential of the diaphragm 123. Herein, the diaphragm 123 is supported by the third spacers 102 which adjoin each other with an air gap therebetween; hence, it is possible to reduce the parasitic capacitance in the condenser microphone 1 compared with the foregoing condenser microphone whose diaphragm is supported by a spacer having a ring-shaped wall structure.
The plate 162 is formed using a thin single-layer deposited film having a conductive property and is constituted of a center portion 162b and a plurality of arms 162a which are extended outwardly in a radial direction from the center portion 162b. The plate 162 is supported by the first spacers 131 having pillar shapes which join the peripheral portion of the plate 162 at multiple points. The plate 162 is positioned in parallel with the diaphragm 123 such that the center of the plate 162 substantially matches the center of the diaphragm 123 in plan view. Herein, the distance between the center of the plate 162 (i.e., the center of the center portion 162b) and the external end of the center portion 162b, i.e., the shortest distance between the center and the periphery of the plate 162, is shorter than the distance between the center of the diaphragm 123 (i.e., the center of the center portion 123a) and the external end of the center portion 123a, i.e, the shortest distance between the center and the periphery of the diaphragm 123. That is, the plate 162 is not positioned opposite to the peripheral portion of the diaphragm 123 causing a small amplitude of vibration. Cutouts are formed between the arms 162a of the plate 162 adjoining each other; hence, the plate 162 is not positioned opposite to the peripheral portion of the diaphragm 123 at the cutout regions thereof. The arms 123c of the diaphragm 123 are extended in the cutout regions of the plate 162. This increases the effective length of the diaphragm 123 causing vibration without increasing the parasitic capacitance.
A plurality of plate holes 162c is formed in the plate 162. The plate holes 162c serve as passages for propagating sound waves towards the diaphragm 123, and they also serve as through-holes for transmitting an etchant used for isotropic etching performed on the upper insulating film 130. The remaining parts of the upper insulating film 130 after etching are used to form the first spacers 131 and the ring-shaped portion 132, while the other parts removed by etching are used to form a gap C3 between the diaphragm 123 and the plate 162. That is, the plate holes 162c serve as through-holes allowing the etchant to reach the upper insulating film 130 so as to simultaneously form the first spacers 131 and the gap C3. For this reason, the plate holes 162c are appropriately aligned in consideration of the height of the gap C3, the shapes of the first spacers 130, and the etching speed. Specifically, the plate holes 162c are collectively formed with equal spacing therebetween in the center portion 162b and the arms 162a except for the joint portions of the plate 162 joining with the first spacers 131. As the distances between the adjacent plate holes 162c get smaller, it is possible to reduce the width of the ring-shaped portion 132 (formed using the upper insulating film 130), thus reducing the overall size of a chip. On the other hand, the rigidity of the plate 162 gets smaller as the distances between the adjacent plate holes 162c get smaller.
The first spacers 131 join the guard electrodes 125a, which are positioned at the same position as the diaphragm 123 and which are formed using the lower conductive film 120 forming the diaphragm 123. The first spacers 131 are formed using the upper insulating film 130, i.e., a deposited film having an insulating property joined to the plate 162. The first spacers 131 are aligned with equal spacing therebetween in the surrounding area of the opening 100a of the back cavity C1. Since the first spacers 131 are positioned in the cutout regions between the arms 123c adjoining each other in the diaphragm 123, it is possible to reduce the maximum diameter of the diaphragm 123 to be smaller than the maximum diameter of the plate 162. This relatively increases the rigidity of the plate 162 while reducing the parasitic capacitance between the plate 162 and the substrate 100.
The plate 162 is supported above the substrate 100 by means of a plurality of second spacers 129 having pillar shapes which are constituted of the guard spacers 103, the guard electrodes 125a, and the first spacers 131. The second spacers 129 are each formed in a multilayered structure including deposited films. The gap C3 is formed between the plate 162 and the diaphragm 123 by the second spacers 129, so that the gaps C2 and C3 are formed between the plate 162 and the substrate 100. Due to insulating properties of the guard spacers 103 and the first spacers 131, the plate 162 is insulated from the substrate 100.
When the potential of the plate 162 differs from the potential of the substrate 100 due to absence of the guard electrodes 125a, a parasitic capacitance occurs in the prescribed region in which the plate 162 and the substrate 100 are positioned opposite to each other in plan view, wherein the parasitic capacitance may increase by way of the intervention of insulating substances arranged therebetween (see
A plurality of plate bumps 162f is formed on the backside of the plate 162 positioned opposite to the diaphragm 123. The plate bumps 162f are formed using a silicon nitride film (SiN) joining the upper conductive film 160, and a polycrystal silicon film joining the silicon nitride film. The plate bumps 162f prevent the diaphragm 123 from being attached (or stuck) to the plate 162.
A plate lead 162d whose width is smaller than the width of the arm 162a is extended from the distal end of the arm 162a of the plate 162 toward the plate terminal 162e. The plate lead 162d is formed using the upper conductive film 160 forming the plate 162. The wiring path of the plate lead 162d substantially overlap the wiring path of the guard lead 125d in plan view; hence, it is possible to reduce the parasitic capacitance formed between the plate lead 162d and the substrate 100.
(B) Operation
Next, the overall operation of the condenser microphone 1 will be described with reference to
Sound waves (entered from a through-hole of a package, not shown) are transmitted through the plate holes 162c and the cutout regions between the arms 162a of the plate 162 so as to reach the diaphragm 123. Since sound waves of the same phase are propagated along both of the surface and backside of the plate 162, the plate 162 would not vibrate substantially. Sound waves reaching the diaphragm 123 make the diaphragm 123 vibrate relative to the plate 162. When the diaphragm 123 vibrates due to sound waves, the electrostatic capacitance of a parallel-plate condenser constituted of opposite electrodes (corresponding to the diaphragm 123 and the plate 162) is varied. Variations of electrostatic capacitance are converted into electric signals, which are then amplified by an amplifier A included in the circuit chip. The amplifier A should be necessarily installed in the package because of the high-impedance output of the sensor chip.
Since the diaphragm 123 is short-circuited with the substrate 100, a parasitic capacitance is formed between the substrate 100 and the plate 162 (which does not vibrate relatively) in the circuitry of
It is possible to incorporate the constituent elements of the circuit chip such as the charge pump P and the amplifier A into the sensor chip, thus forming the condenser microphone 1 having a single-chip structure.
(C) Manufacturing Method
Next, the manufacturing method of the condenser microphone 1 will be described with reference to
In a first step of the manufacturing method shown in
In a second step of the manufacturing method shown in
In a third step of the manufacturing method shown in
In a fourth step of the manufacturing method shown in
In a fifth step of the manufacturing method shown in
In a sixth step of the manufacturing method shown in
In a seventh step of the manufacturing method shown in
In an eighth step of the manufacturing method shown in
In a ninth step of the manufacturing method shown in
The film formation process is completed with respect to the surface side of the substrate 100 by way of the aforementioned steps. After completion of the film formation process in the surface side of the substrate 100, a photoresist mask R1 having a through-hole H6 (used for the formation of the back cavity C1) is formed on the backside of the substrate 100 in a tenth step of the manufacturing method shown in
Subsequently, in an eleventh step of the manufacturing method shown in
In a twelfth step of the manufacturing method shown in
In a thirteenth step of the manufacturing method shown in
Lastly, the photoresist mask R2 is removed, then the substrate 100 is subjected to dicing, thus completing the production of the sensor chip of the condenser microphone 1. Thereafter, the sensor chip and the circuit chip are bonded onto the substrate of the package; the aforementioned terminals are connected together by way of wire bonding; then, a package cover (not shown) is mounted on the substrate of the package; thus, it is possible to close the back cavity C1 in an airtight manner in the backside of the substrate 100.
The second embodiment of the present invention is directed to the condenser microphone 1, which is described with reference to
As described in the first embodiment in which the sensitivity can be increased by increasing the rigidity of the plate 162, while it is possible to reduce the rigidity of the diaphragm 123, to reduce the stress occurring during the film formation process, and to reduce the parasitic capacitance by supporting the diaphragm 123 by use of pillar structures. However, the “miniature” condenser microphone 1 whose diaphragm 123 is supported using pillar structures may have a difficulty in achieving an adequate durability. In this sense, the second embodiment is designed to increase the sensitivity and durability of the condenser microphone 1 in which the diaphragm 123 is supported using pillar structures without substantially increasing the size of the condenser microphone 1.
Since the condenser microphone 1 according to the second embodiment has a constitution substantially identical to that of the first embodiment, the detailed description thereof will not be repeated, whereas the second embodiment can be explained in more detail by way of the following descriptions.
Each of the arms 123c of the diaphragm 123 is increased in width in each of the joint regions at which the arms 123c join the diaphragm supports 102 and is elongated in length in the circumferential direction of the diaphragm 123. Specifically, each of the arms 123c of the diaphragm 123 becomes narrow in width in proximity to the center portion 123a in the direction departing from the center portion 123a, while it becomes wider in width in proximity to and toward each of the diaphragm supports 102. That is, the width of the arm 123c in the circumferential direction of the diaphragm 123 becomes shortest in the intermediate region between the center portion 123a and the diaphragm support 102 but becomes longer in the region at which the arm 123c joins the diaphragm support 102. For this reason, it is possible to increase the durability while increasing the overall joint area between the diaphragm 123 and the diaphragm supports 102 without substantially increasing the overall radius of the diaphragm 123. Since the width of the arm 123c (lying in the circumferential direction of the diaphragm 123) becomes longest in the region in which the arm 123c joins the diaphragm support 102, it is possible to secure high joint strength of the diaphragm 123 while reducing the rigidity of the diaphragm 123.
In addition, the diaphragm supports 102 are positioned between the arms (or joint portions) 162a of the plate 162 and externally of the plate supports 129 in the radial direction of the plate 162. This reduces the rigidity of the diaphragm 123 compared with the rigidity of the plate 162. The widths of the diaphragm supports 102 (in the circumferential direction of the diaphragm 123) are longer than the widths of the arms 123c in their regions positioned between the center portion 123a of the diaphragm 123 and the diaphragm supports 102. Thus, it is possible to secure an adequate joint strength between the arms 123c of the diaphragm 123 and the diaphragm supports 102. The gap C2 whose height substantially matches the thickness of the diaphragm supports 102 is formed between the substrate 100 and the diaphragm 123. As described above, the gap is required to establish a balance between the internal pressure of the back cavity C1 and the atmospheric pressure.
The overall operation of the condenser microphone 1 of the second embodiment is identical to that of the first embodiment which is described with reference to
The manufacturing method of the condenser microphone 1 of the second embodiment is identical to that of the first embodiment which is described with reference to
The diaphragm 123 adapted to the second embodiment is identical to that of the first embodiment shown in
In the first and second embodiments, the aforementioned materials and dimensions are merely illustrative and not restrictive, wherein the descriptions regarding the addition, deletion, and change of order of steps in manufacturing, which may be obvious to those skilled in the art are omitted for the sake of simplicity of the explanation. For example, the film composition, film formation method, outline formation methods of films, and order of steps in manufacturing are not necessarily limited those described above but can be appropriately selected in consideration of the combination of materials of films having desired properties, thicknesses of films, required precisions for defining outlines of films, and the like.
Lastly, the present invention is not necessarily limited to the first and second embodiments and variations, which can be further modified within the scope of the invention as defined by the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-256905 | Sep 2007 | JP | national |
| 2007-256906 | Sep 2007 | JP | national |
