1. Field of the Invention
The present invention relates to electroacoustic transducers such as speakers and microphones.
This application claims priority on Japanese Patent Application No. 2006-222382, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, it is required that electroacoustic transducers such as speakers and microphones be reduced in size and weight. U.S. Patent Application Publication No. 2003/0044029 teaches an example of an electroacoustic transducer adapted to MEMS technology. This kind of electroacoustic transducer is formed using a fixed electrode (having a planar shape) and a diaphragm electrode, wherein the peripheral portions of the fixed electrode and diaphragm electrode are fixed to a ring-shaped housing and are thus positioned opposite to each other with a spacing therebetween, and wherein the fixed electrode and diaphragm electrode are arranged inside of the housing.
When the electroacoustic transducer having the aforementioned constitution serves as a speaker, the diaphragm electrode vibrates due to elastic deformation in response to a certain voltage being applied between the fixed electrode and the diaphragm electrode.
Since the peripheral portion of the diaphragm electrode is fixed in the aforementioned electroacoustic transducer, it is very difficult to produce adequate amplitude when the electroacoustic transducer serves as a speaker; hence, it is very difficult to produce sound having high sound pressure.
It is an object of the present invention to provide an electroacoustic transducer having reduced size and weight, which causes vibration of a diaphragm with relatively high amplitude.
An electroacoustic transducer of the present invention includes a housing having a cavity that is opened in the exterior, a fixed electrode having a planar shape, which is positioned opposite to the opening and which forms a part of the housing, a diaphragm having an electrode, which is positioned between the opening and the fixed electrode, and an elastic deformation portion for supporting the diaphragm with respect to the housing and for allowing the diaphragm to vibrate in its thickness direction, wherein the fixed electrode is electrically insulated from the electrode of the diaphragm, wherein the diaphragm is distanced from the fixed electrode by means of the elastic deformation portion in a balanced state, and wherein the elastic deformation portion is subjected to elastic deformation so that the diaphragm comes in contact with the fixed electrode.
When the electroacoustic transducer serves as a speaker, a DC voltage is applied between the fixed electrode and the diaphragm in advance, so that the diaphragm is attracted and attached to the fixed electrode due to electrostatic attraction exerted therebetween. In the attracted and attached condition, the elastic deformation portion produces an elastic force for distancing the diaphragm from the fixed electrode. By increasing the electrostatic attraction to be greater than the elastic force, it is possible to maintain the attracted and attached condition. Since the electrode of the diaphragm is electrically insulated from the fixed electrode, it is possible to prevent an electric current from flowing between the electrode of the diaphragm and the fixed electrode in the attracted and attached condition.
By releasing voltage applied between the fixed electrode and the diaphragm, it is possible for the electroacoustic transducer to generate sound. At this time, the diaphragm is distanced from the fixed electrode due to the elastic force of the elastic deformation portion so that the elastic deformation portion is placed in the balanced state; then, the elastic deformation portion is further deformed so that the diaphragm moves toward the position opposite to the attracted and attached position due to the inertia thereof. Due to the elastic force still being applied to the elastic deformation portion and the inertia of the diaphragm, the elastic deformation portion is further deformed so that the diaphragm moves close to the fixed electrode and is then returned to the attracted and attached position. As described above, the diaphragm vibrates so as to generate sound, which is emitted from the opening of the housing toward the exterior.
When the diaphragm vibrates and is the returned close to the fixed electrode again, it is necessary to apply a relatively high voltage between the fixed electrode and the electrode of the diaphragm again. Thus, even when energy is lost with respect to the vibration of the diaphragm due to air pressure so that the diaphragm cannot be returned to the attracted and attached position by way of the elastic force of the elastic deformation portion and the inertia of the diaphragm, it is possible for the diaphragm to be reliably attracted to the fixed electrode.
The electroacoustic transducer is further equipped with a power unit for selectively applying either an AC voltage or DC voltage between the fixed electrode and the electrode of the diaphragm, wherein the frequency of the AC voltage is substantially identical to the resonance frequency of the diaphragm based on the elastic modulus of the elastic deformation portion and the weight of the diaphragm.
When the power unit applies the AC voltage whose frequency is substantially identical to the resonance frequency between the fixed electrode and the electrode of the diaphragm in the balanced state, it is possible for the diaphragm to be efficiently attracted and attached to the fixed electrode. This is because the amplitude of the diaphragm gradually increases due to an AC electric field occurring between the fixed electrode and the electrode of the diaphragm, so that the diaphragm is moved close to the fixed electrode. When the diaphragm comes in contact with the fixed electrode, or when the diaphragm moves very close to the fixed electrode, the power unit applies the DC voltage between the fixed electrode and the electrode of the diaphragm, so that the diaphragm is attracted and attached to the fixed electrode.
In the above, prior to the generation of sound, the diaphragm is attracted and attached to the fixed electrode upon application of the AC voltage or DC voltage. This makes it possible for the diaphragm to be compulsorily attracted and attached to the fixed electrode irrespective of the elastic force of the elastic deformation portion in advance. When the diaphragm vibrates to generate sound by releasing the attracted and attached condition of the diaphragm, it is possible to reliably increase the vibration displacement of the diaphragm by use of the elastic force.
At least one of the diaphragm and the fixed electrode is formed using an electret film. That is, when voltage is applied such that an electric charge whose polarity is inverse to the polarity of permanent charge of the electret film is applied to the diaphragm and the fixed electrode, electrostatic attraction occurs due to the application of the voltage, and another electrostatic attraction is exerted between the electret film and the diaphragm or the fixed electrode. This makes it possible for the diaphragm to be attracted and attached to the fixed electrode even when the voltage applied between the diaphragm and fixed electrode is reduced. When the voltage is applied such that the electric charge whose polarity is identical to the polarity of the permanent charge of the electret film is applied to the diaphragm and the fixed electrode, it is possible to produce repulsion between the diaphragm and the fixed electrode; hence, it is possible to realize efficient operation of the electroacoustic transducer.
Alternatively, an electroacoustic transducer includes a housing having a cavity opened in the exterior, a fixed electrode having a planar shape, which is positioned opposite to the opening and which forms a part of the housing, a diaphragm that is positioned between the opening and the fixed electrode, and an elastic deformation portion for supporting the diaphragm with respect to the housing and for allowing the diaphragm to vibrate in its thickness direction, wherein the diaphragm is distanced from the fixed electrode by means of the elastic deformation portion in a balanced state, wherein the elastic deformation portion is subjected to elastic deformation such that the diaphragm comes in contact with the fixed electrode, and wherein the diaphragm is composed of an electret, which is charged in either the positive polarity or negative polarity.
In the above, when the electroacoustic transducer serves as a speaker, a DC voltage is applied such that an electric charge whose polarity is inverse to the polarity of the permanent charge of the electret is applied to the fixed electrode, so that the diaphragm is attracted and attached to the fixed electrode due to electrostatic attraction exerted between the diaphragm and the fixed electrode. In the attracted and attached condition, an elastic force occurs in the elastic deformation portion so that the diaphragm is distanced from the fixed electrode. However, by increasing the electrostatic attraction to be greater than the elastic force, it is possible to maintain the attracted and attached condition.
When the electroacoustic transducer generates sound, the aforementioned voltage is released, or voltage is applied such that an electric charge whose polarity is identical to the polarity of the permanent charge is applied to the fixed electrode to which the diaphragm is attracted, so that the diaphragm vibrates due to the inertia thereof and the elastic force of the elastic deformation portion and is thus returned to the attracted and attached position. That is, the diaphragm vibrates so that sound is emitted from the opening of the housing toward the exterior.
When the diaphragm is moved close to the fixed electrode again, a relatively high voltage is applied such that an electric charge whose polarity is inverse to the polarity of the permanent charge is applied to the fixed electrode, so that the diaphragm is reliably attracted and attached to the fixed electrode.
Since the diaphragm is compulsorily subjected to vibration from the attracted and attached state, which is initially established irrespective of the elastic force of the elastic deformation portion, it is possible to cause a relatively large amplitude of vibration with respect to the diaphragm; hence, it is possible to generate sound with relatively high sound pressure. Since the electroacoustic transducer has a simple structure in which the fixed electrode, diaphragm, and elastic deformation portion are installed in the housing, it is possible to reduce the size and weight of the electroacoustic transducer with ease. Furthermore, the electroacoustic transducer is capable of operating with low power when a reduced voltage is applied between the diaphragm and the fixed electrode.
These and other objects, aspects, and embodiments of the present invention will be described in more detail with reference to the following drawings, in which:
The present invention will be described in further detail by way of examples with reference to the accompanying drawings.
An electroacoustic transducer according to a first embodiment of the present invention will be described with reference to
The fixed electrode 7 is composed of a conductive material, wherein an electret film 13 is formed on a surface 7a positioned opposite to the diaphragm 5. The electret film 13 is covered with an electrically insulating film 15. The electret film 13 is composed of an organic material such as a fluorine-contained resin or is composed of an inorganic material such as SiO2, for example.
The diaphragm 5 is arranged between the opening 3a and the fixed electrode 7 substantially in parallel with the fixed electrode 7, wherein it is supported by the housing 3 by means of an elastic deformation portion 17, which is integrally formed with the diaphragm 5. The elastic deformation portion 17 includes a bellows portion 19 substantially having a cylindrical shape and a flange 21 having a membrane shape, which project externally from the upper portion thereof in a radial direction. The external circumferential portion of the flange 21 is fixed and sandwiched between the upper portion of the side wall 9 and the cover 11. Thus, the upper end of the bellows portions 19 is fixed to the circumferential portion of the opening 3a of the cover 11.
The lower end of the bellows portion 19 is integrally interconnected to the external circumferential portion of the diaphragm 5, whereby the diaphragm 5 is hung down from the circumferential portion of the opening 3a of the cover 11 by means of the bellows portion 19. The bellows portion 19 is formed in an elastically deformed manner so that the diaphragm 5 can vibrate in the thickness direction (i.e., direction A-B).
In a balanced state in which no elastic force is applied to the bellows portion 19, the elastic deformation portion 17 makes the diaphragm 5 retract away from the fixed electrode 7. As shown in
The diaphragm 5 and the elastic deformation portion 17 having the aforementioned constitutions can be integrally formed by use of a mold F shown in
In the formation of the diaphragm 5 and the elastic deformation portion 17 by use of the mold F, a polyimide film 23 having a membranous shape is arranged on the surface F1 of the heated mold F; and air in the recess F2 is evacuated, so that the polyimide film 23 is shaped to match the bottom and bellows of the recess F2 as shown in
Lastly, as shown in
As shown in
Both of the fixed electrode 7 and the electrode 29 of the diaphragm 5 are connected to a power unit 35, which can selectively apply an AC voltage or DC voltage between the fixed electrode 7 and the electrode 29. The power unit 35 is designed to turn on or off the voltage applied to the fixed electrode 7 and the electrode 29. Herein, the frequency of the AC voltage supplied from the power unit 35 is substantially identical to the resonance frequency of the diaphragm 5 based on the elastic modulus of the bellows portion 19 and the weight of the diaphragm 5.
Even when the bellows portion 19 is elastically deformed so that the diaphragm 5 comes in contact with the fixed electrode 7 as shown in
The cavity S1 of the housing 3 is partitioned into a space S2 (positioned in proximity to the opening 3a) and a back space S3 (positioned in proximity to the fixed electrode 7) by means of the diaphragm 5 having the aforementioned constitution and the elastic deformation portion 17. A plurality of holes 9a are formed in the side wall 9 so as to allow communication between the back space S3 and the exterior, thus preventing vibration of the diaphragm 5 from being disturbed due to an increase and decrease of pressure applied to the back space S3. Due to the formation of the holes 9a in the side wall 9, it is possible to emit sound from the holes 9a due to the vibration of the diaphragm 5.
Next, the operation of the electroacoustic transducer 1 having the aforementioned constitution, which serves as a speaker, will be described.
In the electroacoustic transducer 1, a permanent charge is formed in the electret film 13 by way of a high voltage or corona discharge in advance. Specifically, a negative charge is concentrated at the surface of the electret film 13 opposite to the diaphragm 5, while a positive charge is concentrated at the backside of the electret film 13 that comes in contact with the fixed electrode 7.
Before sound emission, in the condition in which the bellows portion 19 of the elastic deformation portion 17 is elastically deformed and expanded so that the diaphragm 5 comes in contact with the fixed electrode 7 as shown in
In the attracted and attached condition, the DC voltage is applied in such a way that a charge whose polarity is inverse to the polarity of the permanent charge concentrated at the surface of the electret film 13 is concentrated at the electrode 29 of the diaphragm 5. For example, when a negative charge is concentrated at the surface of the electret film 13, the DC voltage is applied such that a positive charge is concentrated at the diaphragm 5. This realizes electrostatic attraction exerted between the electret film 13 and the diaphragm 5 in addition to electrostatic attraction caused by applying the DC voltage; hence, it is possible to reliably fix the diaphragm 5 to the fixed electrode 7 even when the voltage applied between the diaphragm 5 and the fixed electrode 7 is reduced.
In the aforementioned condition, the elastic force is applied to the bellows portion 19 such that the diaphragm 5 is separated from the fixed electrode 7. By increasing the sum of electrostatic attractions so as to be higher than the elastic force, it is possible to maintain the attracted and attached condition. Since the fixed electrode 7 is electrically insulated from the electrode 29 of the diaphragm 5 by means of the insulating film, substantially no current may flow between the fixed electrode 7 and the electrode 29 of the diaphragm 5 in the attracted and attached condition.
In order to generate sound by means of the electroacoustic transducer 1, the power unit 35 releases a voltage applied between the fixed electrode 7 and the diaphragm 5 in the aforementioned condition. At this time, the diaphragm 5 is separated from the fixed electrode 7 due to the elastic force of the bellows portion 19; hence, the bellows portion 19 is positioned in the balanced state as shown in
When the diaphragm 5 vibrates and is thus returned to proximity of the fixed electrode 7, it is necessary to apply a high DC voltage between the fixed electrode 7 and the electrode 29 of the diaphragm 5 again. Thus, it is possible to reliably attract and fix the diaphragm 5 to the fixed electrode 7 even when energy is lost due to air resistance during the vibration of the diaphragm 5, so that the diaphragm 5 cannot be returned to the attracted and attached position due to the elasticity of the bellows portion 19 and the inertia of the diaphragm 5.
In order to generate sound by means of the electroacoustic transducer 1, it is possible to apply a predetermined voltage to the electrode 29 of the diaphragm 5 of which charge whose polarity is identical to the polarity of the permanent charge concentrated at the surface of the electret film 13 appears. This causes repulsion between the diaphragm 5 and the fixed electrode 7; hence, it is possible to realize efficient operation of the electroacoustic transducer 1.
In order for the diaphragm 5, which is once positioned in the balanced state as shown in
That is, when the aforementioned AC voltage is applied between the fixed electrode 7 and the diaphragm 5 in the balanced state of the diaphragm 5, the amplitude of the diaphragm 5 gradually increases due to an AC electric field being applied between the fixed electrode 7 and the electrode 29 of the diaphragm 5; hence, the diaphragm 5 can move close to the fixed electrode 7. When the diaphragm 5 comes in contact with the fixed electrode 7, or when the diaphragm 5 moves very close to the fixed electrode 7, the power unit 35 applies a DC voltage between the fixed electrode 7 and the electrode 29 of the diaphragm 5, so that the diaphragm 5 is reliably attracted and attached to the fixed electrode 7.
In order to realize the absorption and fixation, it is necessary to apply a predetermined voltage so that an electrostatic attraction is applied between the electrode 29 of the diaphragm 5, which is in the balanced state, and the fixed electrode 7. In this case, it is possible to move the diaphragm 5 by way of an electrostatic attraction exerted between the electrode 29 of the diaphragm 5 and the electret film 13. This makes it possible to reduce the applied voltage in the electroacoustic transducer 1 compared with another electroacoustic transducer not having the electret film 13.
Prior to sound emission, the aforementioned electroacoustic transducer 1 can cause vibration of the diaphragm 5, which is compulsorily attracted and attached to the fixed electrode 7 irrespective of the elasticity of the bellows portion 19 in advance; hence, it is possible to realize a relatively high amplitude of the diaphragm 5. This makes it possible to increase the displacement of the diaphragm 5 so as to generate sound at a relatively high sound pressure.
Since the electroacoustic transducer 1 has a simple structure in which the housing 3 includes the fixed electrode 7, the diaphragm 5, and the elastic deformation portion 17, it can be easily reduced in size and weight.
Even when the diaphragm 5 is placed in the balanced state, the power unit 35 applies the AC voltage whose frequency is substantially identical to the resonance frequency of the diaphragm 5, so that the diaphragm 5 can be efficiently attracted and attached to the fixed electrode 7.
Due to the provision of the electret film 13, it is possible to reduce the voltage applied to the electroacoustic transducer 1 such as a predetermined voltage for attracting and fixing the diaphragm 5, which is initially placed in the balanced state, to the fixed electrode 7 and a predetermined voltage for maintaining the attracted and attached condition of the diaphragm 5. That is, the present embodiment makes it possible for the electroacoustic transducer 1 to operate with low power.
The present embodiment is designed such that the diaphragm 5 is attracted and attached to the fixed electrode 7 by applying an AC voltage between the diaphragm 5 and the fixed electrode 7 prior to sound emission. However, the present invention is not necessarily limited to the present embodiment. That is, the present embodiment can be modified such that the diaphragm 5 is attracted and attached to the fixed electrode 7 by applying the DC voltage between the diaphragm 5 and the fixed electrode 7.
The present embodiment is designed such that the electret film 13 is formed on the surface 7a of the fixed electrode 7 positioned opposite to the diaphragm 5. Instead, the present embodiment can be modified such that the electret film 13 is formed on the surface 5a of the diaphragm 5 positioned opposite to the fixed electrode 7. In this constitution, it is preferable that the electret film 13 be arranged to cover the electrode 29 of the diaphragm 5. In addition, it is preferable that the electret film 13 be covered with the insulating film 15. With such a modification, it is possible to reduce the voltage applied between the diaphragm 5 and the fixed electrode 7; this makes it possible for the electroacoustic transducer 1 to operate with low power.
The present embodiment is designed such that the diaphragm 5 and the fixed electrode 7 are formed by way of the formation of the electret film 13; however, the electret film 13 does not need to be formed. When the electret film 13 is not formed, it is necessary to form the insulating film 15 on either the surface 5a of the diaphragm 5 or the surface 7a of the fixed electrode 7, thus avoiding the occurrence of short-circuiting between the fixed electrode 7 and the electrode 29 of the diaphragm 5. In order to attract the diaphragm 5 to the fixed electrode 7 with a low voltage, it is preferable that the insulating film 15 be reduced in thickness. Specifically, it is preferable that the thickness of the insulating film 15 be set to several micro-meters.
In the present embodiment, the elastic deformation portion 17 is composed of the polyimide film 23; however, this is not a restriction. That is, it is required that the elastic deformation portion 17 be composed of a prescribed material realizing elastic deformation.
In the present embodiment, the diaphragm 5 is composed of the polyimide film 23 and the glass epoxy resin 27; however, this is not a restriction. That is, it is required that the diaphragm 5 be formed in a planar shape that does not cause elastic deformation.
In the present embodiment, the electrode 29 is attached to the surface 5a of the diaphragm 5; however, this is not a restriction. That is, it is possible to form the diaphragm 5 by use of a conductive material, so that the diaphragm 5 can entirely serve as an electrode.
An electroacoustic transducer according to a second embodiment of the present invention will be described with reference to
In
The cover 47 is composed of a conductive material so as to form an electrode 49 positioned opposite to the fixed electrode 7. Similar to the electroacoustic transducer 1, the fixed electrode 7 and the electrode 49 used in the electroacoustic transducer 41 are connected to the power unit 35. That is, the power unit 35 applies a voltage between the fixed electrode 7 and the electrode 49 in the electroacoustic transducer 41. A plurality of elastic deformation portions 53 are fixed to the interior of the side wall 45.
As shown in
The elastic deformation portions 53 are elongated in a plane direction from the circumferential periphery of the diaphragm 51, wherein the distal ends thereof are fixed to the side wall 45 of the housing 43. Each of the elastic deformation portions 53 meanders from the diaphragm 51 to the side wall 45; hence, each of them can be elastically deformed with ease. The elastic deformation portions 53, which are integrally formed together with the diaphragm 51, are arranged in a circumferential direction of the diaphragm 51 with equal spacing therebetween.
Due to elastic deformation of the elastic deformation portions 53, the diaphragm 51 can vibrate in the thickness direction (i.e., direction C-D shown in
Both of the diaphragm 51 and the elastic deformation portions 53 are integrally formed together by means of an electret 55 composed of an organic material such as a fluorine-contained resin or composed of an inorganic material such as SiO2. The diaphragm 51 and the elastic deformation portions 53 can be integrally formed by way of etching of the electret 55 having a planar shape by use of a resist pattern forming the diaphragm 51 and the elastic deformation portions 53. Herein, etching is performed with respect to the elastic deformation portions 53, each having a thickness that is reduced to realize elastic deformation.
Since the diaphragm 51 is composed of the electret 55 (i.e., a dielectric), the electric charge may not move between the diaphragm 51 and the fixed electrode 7 or the electrode 49 even when the diaphragm 51 comes in contact with the fixed electrode 7 or the electrode 49.
A plurality of partition plates 57, which project inwardly of the side wall 45, are formed to occupy the gap formed between the diaphragm 51 and the side wall 45. The diaphragm 51 and the partition plates 57 are arranged to partition the cavity S1 into the cavity S2 in proximity to the opening 43a and the back cavity S3 in proximity to the fixed electrode 7. That is, they prevent air flow from occurring between the cavity S2 and the back cavity S3.
Next, the operation of the electroacoustic transducer 41, which serves as a speaker, will be described. In the electroacoustic transducer 41, the diaphragm 51 composed of the electret 55 is subjected to a high voltage or corona discharge and is thus charged with either the positive polarity or negative polarity in advance.
In addition, a DC voltage is applied to the fixed electrode 7 so that a charge whose polarity is inverse to the polarity of a permanent charge of the electret 55 is applied to the fixed electrode 7 in the condition in which the elastic deformation portions 53 are elastically deformed and expanded so that the diaphragm 51 comes in contact with the fixed electrode 7, whereby the diaphragm 51 is attracted and attached to the fixed electrode due to an electrostatic attraction exerted between the diaphragm 51 and the fixed electrode 7. In the attracted and attached condition, an elastic force occurs in the elastic deformation portions 53 so as to distance the diaphragm 51 from the fixed electrode 7. However, the attracted and attached condition can be maintained by increasing the electrostatic attraction to be greater than the elastic force.
In the second embodiment, similar to the first embodiment, the electroacoustic transducer 41 is capable of generating sound when the power unit 35 releases the voltage applied between the fixed electrode 7 and the electrode 49 because the diaphragm 51 vibrates due to the elastic force of the elastic deformation portions 53 and the inertia thereof so that the diaphragm 51 is returned to the attracted and attached position. That is, vibration of the diaphragm 51 causes sound, which is emitted from the opening 43a of the housing 43 toward the exterior.
When the diaphragm 51 vibrates and is thus moved close to the fixed electrode 7, the DC voltage is applied between the fixed electrode 7 and the electrode 49 again, thus reliably fixing the diaphragm 51 to the fixed electrode 7.
Incidentally, the electroacoustic transducer 41 is capable of generating sound upon the application of the voltage such that the electric charge whose polarity is identical to the polarity of permanent charge of the electret 55 is applied to the fixed electrode 7 in the attracted and attached condition of the diaphragm 51. In this case, repulsion occurs between the diaphragm 51 and the fixed electrode 7 so as to realize efficient operation of the electroacoustic transducer 41.
In the electroacoustic transducer 41, the diaphragm 51, which is once placed in the balanced state, is attracted and attached to the fixed electrode 7 when the power unit 35 applies the AC voltage whose frequency is identical to the resonance frequency of the diaphragm 51 between the fixed electrode 7 and the electrode 49.
When the AC voltage is applied between the fixed electrode 7 and the electrode 49 in the balanced state of the diaphragm 51, the amplitude of the diaphragm 51 gradually increases due to an AC electric field being applied between the fixed electrode 7 and the diaphragm 51 or between the electrode 49 and the diaphragm 51, so that the diaphragm 51 moves close to the fixed electrode 7 or the electrode 49. When the diaphragm 51 comes in contact with the fixed electrode 7, or when the diaphragm 51 moves very close to the fixed electrode 7, the power unit 35 applies a voltage between the fixed electrode 7 and the electrode 49 in such a way that an electric charge whose polarity is inverse to the polarity of permanent charge of the electret 55 is applied to the fixed electrode 7, so that the diaphragm 51 is reliably attracted to the fixed electrode 7.
The electroacoustic transducer 41 of the second embodiment provides effects similar to those of the electroacoustic transducer 1 of the first embodiment. In this constitution, when the power unit 35 applies an AC voltage whose frequency is identical to the resonance frequency of the diaphragm 51 between the fixed electrode 7 and the electrode 49 in the balanced state of the diaphragm 51, it is possible to efficiently increase the amplitude of the diaphragm 51 due to an AC electric field being applied between the electrode 49 and the diaphragm 51 in addition to an AC electric field being applied between the fixed electrode 7 and the diaphragm 51. Compared with the electroacoustic transducer 1 of the first embodiment, the electroacoustic transducer 41 of the second embodiment allows the diaphragm 51 to be attracted and attached to the fixed electrode 7 in a short period of time.
The electroacoustic transducer 41 of the second embodiment is designed such that the entire area of the cover 47 forms the electrode 49 positioned opposite to the fixed electrode 7; but this is not a restriction. That is, the second embodiment requires that at least a prescribed portion of the cover 47 corresponding to the peripheral portion of the opening 43a of the housing 43 forms an electrode positioned opposite to the fixed electrode 7, allowing the diaphragm 51 to come in contact with the electrode due to the elastic deformation of the elastic deformation portions 53.
Each of the elastic deformation portions 53 is not necessarily formed in a meandering shape elongated in the radial direction of the diaphragm 51. For example, it is formed in a meandering shape elongated in a direction along a part of the external periphery of the diaphragm 51, or it is formed in a corrugated shape.
In the second embodiment, the elastic deformation portions 53 are each formed using the electret 55, which is also used for the formation of the diaphragm 51; but this is not a restriction. That is, both of the elastic deformation portions 53 and the diaphragm 51 can be formed using the same material, or they can be formed using different materials. That is, the second embodiment simply requires that the elastic deformation portions 53 be elastically deformable together with the diaphragm 51 by appropriately selecting shapes and materials thereof.
In the second embodiment, the diaphragm 51 is entirely formed using the electret 55; but this is not a restriction. That is, the second embodiment requires that at least a part of the diaphragm 51 be formed using the electret 55.
It is not necessary that the elastic deformation portions 53 be directly connected to the diaphragm 51; that is, it is possible to design variations as shown in
In case of
In the variations, the elastic deformation portions 53 are each formed using the electret 55, which is also used for the formation of the diaphragm 51; but this is not a restriction. That is, both of the elastic deformation portions 53 and the diaphragm 51 can be formed using the same material, or they can be formed using different materials. That is, the variations simply require that the elastic deformation portions 53 be elastically deformable together with the diaphragm 51 by appropriately selecting shapes and materials thereof.
In the variations, the diaphragm 51 is entirely formed using the electret 55; but this is not a restriction. That is, the variations require that at least a part of the diaphragm 51 be formed using the electret 55.
Each of the diaphragm 51 and the elastic deformation portions 53 is of an electrostatic capacitance type, in which it is partially formed using the electret 55; but this is not a restriction. That is, the diaphragm 51 can be designed as a condenser type, wherein the diaphragm 51 is formed using conductive materials and is connected to an external terminal (not shown). Herein, the diaphragm 51 can vibrate by varying the voltage applied between the diaphragm 51, the fixed electrode 7, and the opposite electrode 49.
Next, the manufacturing method of the electroacoustic transducer 41 that is manufactured using a silicon substrate by way of semiconductor manufacturing processes will be described with reference to
An upper substrate 70 (see
The partition plates 57 are formed in proximity to the opening 43a in such a way that etching is performed using a resist mask so as to form the recess S (see
Phosphorus doping (or phosphorus ion implantation) is performed using a resist 104 suiting the shape of the opening 43a so as to form a plurality of ring-shaped conductive layers 201 on the surface of the substrate 101 having the recess S (see FIG. 12D), thus forming impurities-diffused regions (or n+-doped regions) 105. After completion of the doping, the resist 104 is removed from the substrate 101, which is then subjected to thermal treatment so as to form the conductive layers (or diffusion layers) 201 (see
Insulating films 202 are formed on the conductive layers 201 in such a way that silicon oxide whose thickness ranges from 100 A° to 250 A° (realizing pad oxidation) is deposited on the surface of the substrate 101, and then, silicon nitride (realizing an insulating film) whose thickness ranges from 1000 A° to 3000 A° is deposited (see
Thereafter, silicon oxide is deposited so as to form a stopper layer 107 (see
A polysilicon film 108 of 0.5 μm thickness, which is doped with impurities such as phosphorus so as to form the diaphragm 51 and the elastic deformation portions 53, is deposited on the surface of the stopper layer 107 (see
Anisotropic etching such as reactive ion etching (RIE) is performed using a photoresist mask on the polysilicon film 108, which is thus selectively etched and processed into the diaphragm 51 and the elastic deformation portions 53 (see
Silicon oxide is deposited to form a stopper layer 110 that covers the polysilicon film 108 subjected to etching. Herein, the planation of the stopper layer 110 is performed as necessary (see
The upper substrate 70 can be formed by performing etching on the substrate 101 subjected to deposition. Herein, the backside of the substrate 101 is subjected to anisotropic etching such as Deep RIE in conformity with the opening 43a in such a way that the polysilicon film 108 is etched to expose the silicon oxide film (see
After completion of the etching on the silicon oxide (or pad oxidation) and the silicon nitride (or the insulating film) in conformity with the opening 43a, wet etching is performed using buffered hydrofluoric acid (or Buffered HF) so as so selectively remove the silicon oxide (or a stopper layer 110) in the periphery of the diaphragm 51 (see
Next, the lower substrate 80 is produced as shown in
By adhering the upper substrate 70 and the lower substrate 80 together, it is possible to completely produce the electroacoustic transducer 41.
In the aforementioned manufacturing method, the diaphragm 51 and the elastic deformation portions 53 are each formed using the polysilicon film doped with impurities such as phosphorus (P); but this is not a restriction. The diaphragm 51 can be formed using the silicon nitride film (SiN film) and silicon oxide nitride film (SiON film); it can be formed in a layered structure combining the SiN film and SiON film; it can be formed in a layered structure in which the polysilicon film is covered with the insulating film such as the SiN film and SiON film; and it can be formed using the silicon oxide film, for example. Then, the diaphragm 51, which is formed using the aforementioned insulating materials, is charged with either a positive polarity or a negative polarity by way of high voltage application or corona discharge, whereby it is possible to manufacture the electroacoustic transducer 41 of the electrostatic capacitance type by way of the semiconductor device manufacturing processes.
Each of the aforementioned embodiments and variations teaches a single electroacoustic transducer; but this is not a restriction. That is, a plurality of electroacoustic transducers can be arranged in an array, thus realizing a digital speaker for reproducing analog waveforms. Herein, an array including plural electroacoustic transducers can serve as a single speaker for producing a relatively high sound pressure. In addition, it is possible to simultaneously form a plurality of electroacoustic transducers on a single wafer by way of semiconductor device manufacturing processes.
In the aforementioned embodiments, the housings 3 and 43 are constituted of the fixed electrodes 7, the side walls 9 and 45, and the covers 11 and 47; but this is not a restriction. That is, the present invention requires that the electroacoustic transducer include the fixed electrode 7 and the cavity S1 opened in the exterior thereof. For example, it is possible to modify the aforementioned embodiments such that the side walls 9 and 45 and the covers 11 and 47 are integrally formed.
In the aforementioned embodiments, the diaphragms 5 and 51 are positioned substantially in parallel with the fixed electrode 7 and the electrode 49. The present invention requires that the diaphragms 5 and 51 be positioned substantially in parallel with the fixed electrode 7 and the electrode 49 in the balanced states of the diaphragm 5 and 51 and in the attracted and attached conditions in which the diaphragms 5 and 51 are attracted and attached to the fixed electrodes 7. In addition, it is required that, during vibration, the diaphragms 5 and 51 be substantially positioned in parallel with the fixed electrode 7 and the electrode 49 even when they are slightly inclined with respect to the fixed electrode 7 and the electrode 49.
The electroacoustic transducers 1 and 41 are not necessarily limited to speakers, but they can be used as microphones for detecting sounds. That is, the electroacoustic transducers 1 and 41 are capable of detecting sounds, which are transmitted to the diaphragms 5 and 51 via the openings 3a and 43a of the housings 3 and 43, by detecting vibrations of the diaphragms 5 and 51. In the electroacoustic transducer 1 of the first embodiment, for example, vibration of the diaphragm 5 can be detected in response to variations of electrostatic capacitance between the fixed electrode 7 and the electrode 29 of the diaphragm 5. In the electroacoustic transducer 41 of the second embodiment, vibration of the diaphragm 51 can be detected by detecting variations of electrostatic capacitance between the diaphragm 51 and the fixed electrode 7 or the electrode 49.
Lastly, the present invention is not necessarily limited to the aforementioned embodiments and variations, which can be further modified in a variety of ways within the scope of the invention defined by the appended claims.
Number | Date | Country | Kind |
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P2006-222382 | Aug 2006 | JP | national |
Number | Name | Date | Kind |
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20030044029 | Gabriel et al. | Mar 2003 | A1 |
20030068055 | Tanabe et al. | Apr 2003 | A1 |
20060210106 | Pedersen | Sep 2006 | A1 |
Number | Date | Country |
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10-2000-0059183 | Apr 2002 | KR |
Number | Date | Country | |
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20080181437 A1 | Jul 2008 | US |