1. Field of the Invention
The present invention relates to a sonic sensor and a diaphragm.
2. Description of the Background Art
A microphone (sonic sensor) sonically vibrating a diaphragm and extracting an electric signal corresponding to sound on the basis of change in the vibration is known in general (refer to Japanese Patent No. 3556676, for example).
A microphone comprising a diaphragm constituted of a piezoelectric substance is also known as another exemplary sonic sensor extracting an electric signal corresponding to sound through a diaphragm. As shown in
In the microphone according to Japanese Patent No. 3556676 shown in
The present invention has been proposed in order to solve the aforementioned problems, and an object of the present invention is to provide a sonic sensor and a diaphragm therefor, which can improve sensitivity of the sonic sensor such as a microphone while enabling downsizing thereof.
A sonic sensor according to a first aspect of the present invention comprises an electrode plate and a diaphragm including a charge storage member opposed to the electrode plate at a prescribed distance and provided in a vibratory manner and a power generation member constituted of a piezoelectric substance capable of generating power upon vibration with the charge storage member, while the charge storage member is so formed as to store charges supplied by the power generation member, for converting sound to an electrical signal on the basis of change in the capacitance between the diaphragm and the electrode plate.
In the sonic sensor according to the first aspect of the present invention, the diaphragm is provided with the vibratory charge storage member so formed as to store charges and the power generation member capable of generating power upon vibration with the charge storage member so that the power generation member constituted of the piezoelectric substance is also vibrated when the charge storage member is sonically vibrated, whereby the charge storage member stores charges generated by the power generation member to cause potential difference between the electrode plate and the diaphragm. When the diaphragm is vibrated in the state causing potential difference between the same and the electrode plate, the distance between the electrode plate and the diaphragm so changes as to change the capacitance of a capacitor formed by the electrode plate and the diaphragm as well as the potential of the electrode plate. The sonic sensor can convert sound or the like to an electrical signal by outputting the potential change as an electric signal. Further, the sonic sensor, capable of storing charges in the charge storage member by vibrating the power generation member constituted of the piezoelectric substance, requires no booster circuit or the like for applying a voltage to the diaphragm. Thus, a control circuit of the sonic sensor can be downsized, thereby downsizing the sonic sensor. In addition, the power generation member repetitively generates power due to the vibration, whereby the charge storage member can store a large quantity of charges. Thus, large potential difference can be caused between the electrode plate and the diaphragm including the charge storage member, thereby increasing potential change of the electrode plate corresponding to change of the capacitance of the capacitor formed by the electrode plate and the diaphragm. Therefore, sensitivity of the sonic sensor can be improved without increasing the size of the diaphragm. According to the first aspect, therefore, the sonic sensor can be improved in sensitivity and downsized.
In the aforementioned sonic sensor according to the first aspect, a rectifier suppressing outflow of charges is preferably electrically connected to the power generation member. According to this structure, the flow of charges generated by the power generation member can be unidirectionally fixed toward the charge storage member while outflow of the charges stored in the charge storage member can be suppressed, whereby the charge storage member hardly loses the charges supplied from the power generation member. Thus, the sonic sensor can efficiently store the charges in the charge storage member.
In the aforementioned sonic sensor according to the first aspect, the power generation member constituted of the piezoelectric substance is preferably arranged on the outer periphery of the charge storage member. According to this structure, the sonic sensor can supply charges generated by the power generation member to the charge storage member from the outer periphery thereof while ensuring vibrational performance of a maximumly vibrated portion of the charge storage member by arranging the power generation member on the outer periphery of the charge storage member having a circular shape when the circular charge storage member is maximumly vibrated on the central portion, for example.
In the aforementioned sonic sensor having the power generation member arranged on the outer periphery of the charge storage member, the power generation member constituted of the piezoelectric substance preferably includes a power generation film constituted of the piezoelectric substance, and is preferably so formed as to generate either positive charges or negative charges on the outer periphery of the power generation film in plan view and to generate either negative charges or positive charges on the inner periphery of the power generation film, on which the charge storage member is located, in plan view. According to this structure, external negative charges are attracted by positive charges generated on the outer periphery of the power generation film to flow into the sonic sensor when the power generation member is so formed as to generate positive charges on the inner periphery of the power generation film and to generate negative charges on the inner periphery of the power generation film. These negative charges flow from the outer periphery toward the inner periphery of the power generation film, whereby the charge storage member can store the negative charges. When the power generation member is so formed as to generate negative charges on the outer periphery of the power generation film and to generate positive charges on the inner periphery of the power generation film, on the other hand, external positive charges are attracted by negative charges generated on the outer periphery of the power generation film, to flow into the sonic sensor. These positive charges flow from the outer periphery toward the inner periphery of the power generation film, whereby the charge storage member stores the positive charges. Thus, the sonic sensor can unidirectionally fix the flow of positive and negative charges generated by the power generation film, thereby more efficiently storing the charges in the charge storage member.
In this case, the power generation film constituted of the piezoelectric substance may be so polarized as to generate positive charges on the outer periphery of the power generation film and to generate negative charges on the inner periphery of the power generation film.
In the aforementioned sonic sensor having the power generation member arranged on the outer periphery of the charge storage member, the power generation member constituted of the piezoelectric substance is preferably so formed as to enclose the outer periphery of the charge storage member in plan view. According to this structure, the power generation member can supply charges to the charge storage member from the overall outer periphery of the charge storage member, thereby supplying a larger quantity of charges to the charge storage member.
In the aforementioned sonic sensor having the power generation member enclosing the outer periphery of the charge storage member, the charge storage member is preferably circularly formed in plan view, and the power generation member is preferably so annularly formed as to enclose the circular charge storage member. According to this structure, the power generation member can easily enclose the charge storage member.
In the aforementioned sonic sensor according to the first aspect, the charge storage member may include a conductive semiconductor film.
In the aforementioned sonic sensor according to the first aspect, the charge storage member and the power generation member are preferably so formed as to at least partially overlap with each other. According to this structure, the power generation member can be easily mounted on the charge storage member.
A diaphragm according to a second aspect of the present invention comprises a charge storage member opposed to an electrode plate at a prescribed distance and provided in a vibratory manner and a power generation member constituted of a piezoelectric substance capable of generating power upon vibration with the charge storage member, while the charge storage member is so formed as to store charges supplied by the power generation member.
As hereinabove described, the diaphragm according to the second aspect of the present invention is provided with the vibratory charge storage member so formed as to store charges and the power generation member capable of generating power upon vibration with the charge storage member so that the power generation member constituted of the piezoelectric substance is also vibrated when the charge storage member is sonically vibrated, whereby the charge storage member stores charges generated by the power generation member to cause potential difference between the electrode plate and the diaphragm. When the diaphragm is vibrated in the state causing potential difference between the same and the electrode plate, the distance between the electrode plate and the diaphragm so changes as to change the capacitance of a capacitor formed by the electrode plate and the diaphragm as well as the potential of the electrode plate. The diaphragm can convert sound or the like to an electrical signal by outputting the potential change as an electric signal. Further, the diaphragm, capable of storing charges in the charge storage member by vibrating the power generation member constituted of the piezoelectric substance, requires no booster circuit or the like for applying a voltage thereto. Thus, a control circuit of the diaphragm can be downsized, thereby downsizing a sonic apparatus such as a sonic sensor to which the diaphragm is applied. In addition, the power generation member repetitively generates power due to the vibration, whereby the charge storage member can store a large quantity of charges. Thus, large potential difference can be caused between the electrode plate and the diaphragm including the charge storage member, thereby increasing potential change of the electrode plate corresponding to change of the capacitance of the capacitor formed by the electrode plate and the diaphragm. Thus, the extracted electric signal can be intensified. Consequently, sensitivity of a sonic sensor or the like can be improved without increasing the size of the diaphragm.
In the aforementioned diaphragm according to the second aspect, a rectifier suppressing outflow of charges is preferably electrically connected to the power generation member. According to this structure, the flow of charges generated by the power generation member can be unidirectionally fixed toward the charge storage member while outflow of the charges stored in the charge storage member can be suppressed, whereby the charge storage member hardly loses the charges supplied from the power generation member. Thus, the diaphragm can efficiently store the charges in the charge storage member.
In the aforementioned diaphragm according to the second aspect, the power generation member constituted of the piezoelectric substance is preferably arranged on the outer periphery of the charge storage member. According to this structure, the diaphragm can supply charges generated by the power generation member to the charge storage member from the outer periphery thereof while ensuring vibrational performance of a maximumly vibrated portion of the charge storage member by arranging the power generation member on the outer periphery of the charge storage member having a circular shape when the circular charge storage member is maximumly vibrated on the central portion, for example.
In the aforementioned diaphragm having the power generation member arranged on the outer periphery of the charge storage member, the power generation member constituted of the piezoelectric substance preferably includes a power generation film constituted of the piezoelectric substance, and is preferably so formed as to generate either positive charges or negative charges on the outer periphery of the power generation film in plan view and to generate either negative charges or positive charges on the inner periphery of the power generation film, on which the charge storage member is located, in plan view. According to this structure, external negative charges are attracted by positive charges generated on the outer periphery of the power generation film to flow into the diaphragm when the power generation member is so formed as to generate positive charges on the inner periphery of the power generation film and to generate negative charges on the inner periphery of the power generation film. These negative charges flow from the outer periphery toward the inner periphery of the power generation film, whereby the charge storage member can store the negative charges. When the power generation member is so formed as to generate negative charges on the outer periphery of the power generation film and to generate positive charges on the inner periphery of the power generation film, on the other hand, external positive charges are attracted by negative charges generated on the outer periphery of the power generation film, to flow into the diaphragm. These positive charges flow from the outer periphery toward the inner periphery of the power generation film, whereby the charge storage member stores the positive charges. Thus, the diaphragm can unidirectionally fix the flow of positive and negative charges generated by the power generation film, thereby more efficiently storing the charges in the charge storage member.
In this case, the power generation film constituted of the piezoelectric substance may be so polarized as to generate positive charges on the outer periphery of the power generation film and to generate negative charges on the inner periphery of the power generation film.
In the aforementioned diaphragm having the power generation member set on the outer periphery of the charge storage member, the power generation member constituted of the piezoelectric substance is preferably so formed as to enclose the outer periphery of the charge storage member in plan view. According to this structure, the power generation member can supply charges to the charge storage member from the overall outer periphery of the charge storage member, thereby supplying a larger quantity of charges to the charge storage member.
In the aforementioned diaphragm having the power generation member enclosing the outer periphery of the charge storage member, the charge storage member is preferably circularly formed in plan view, and the power generation member is preferably so annularly formed as to enclose the circular charge storage member. According to this structure, the power generation member can easily enclose the charge storage member.
In the aforementioned diaphragm according to the second aspect, the charge storage member may include a conductive semiconductor film.
In the aforementioned diaphragm according to the second aspect, the charge storage member and the power generation member are preferably so formed as to at least partially overlap with each other. According to this structure, the power generation member can be easily mounted on the charge storage member.
In the aforementioned diaphragm according to the second aspect, the electrode plate may include a plurality of sonic holes, and the diaphragm may be applied to an audio.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.
FIGS. 4 to 13 are sectional views for illustrating a fabrication process for the diaphragm according to the embodiment shown in
An embodiment of the present invention is now described with reference to the drawings. In the following description, the present invention is applied to a microphone, which is a kind of sonic sensor.
The structure of a microphone including a diaphragm according to the embodiment of the present invention is described with reference to FIGS. 1 to 3.
In the microphone according to this embodiment, SiO2 layers 2 and 3 each having a thickness of about 250 nm are formed on the back and front surfaces of a silicon substrate 1 respectively, as shown in
An SiN layer 8 having a thickness of about 100 nm is partially formed on the upper surfaces of the polysilicon layer 5a and the SiO2 layer 3. A polysilicon layer 9 having a thickness of about 3 μm is formed on the SiN layer 8. This polysilicon layer 9 is doped with an n-type impurity (phosphorus (P)), to have conductivity. A portion of the polysilicon layer 9 opposed to the diaphragm 7 functions as a back plate 10. The back plate 10 is an example of the “electrode plate” in the present invention. A space 11 for insulating the back plate 10 and the diaphragm 7 from each other is formed between the SiN layer 8 and the polysilicon layers 5a and 5b and the power generation film 7. The distance between the back plate 10 and the diaphragm 7 in this space 11 is about 3 μm to about 5 μm. Another SiN layer 12 having a thickness of about 100 nm is formed on the polysilicon layer 9. A plurality of circular sonic holes 13 (see
A fabrication process for the diaphragm according to the embodiment of the present invention and the periphery thereof is now described with reference to
First, the back and front surfaces of the silicon substrate 1 are polished, for thereafter forming the SiO2 layers 2 and 3 each having the thickness of about 250 nm thereon by thermal oxidation respectively, as shown in
Then, a piezoelectric layer (not shown) of PbTiO3 is formed on the overall surface by a sol-gel process, and thereafter patterned by photolithography and dry etching with argon, oxygen and CF4, thereby forming the annular power generation film 6 of PbTiO3 having the thickness of about 1 μm, the outer diameter of about 1 mm and the inner diameter of about 0.5 mm, as shown in
As shown in
As shown in
As shown in
As shown in
As shown in
As shown in
FIGS. 14 to 22 are plan views and sectional views for illustrating the circuit structure and operations of the microphone according to this embodiment. The circuit structure of the microphone according to this embodiment is now described with reference to
As shown in
The operations of the microphone according to this embodiment are now described with reference to FIGS. 14 to 22. When the microphone receives no sound, the diaphragm 7 remains unvibrational, as shown in
When the microphone receives sound along arrow A as shown in
When the diaphragm 7 is flattened as shown in
Thus, the polysilicon layer 5b stores the negative charges as shown in
When the polysilicon layer 5b storing the negative charges and causing potential difference between the same and the back plate 10 is sonically vibrated to reduce the distance between the same and the back plate 10 as shown in
According to this embodiment, as hereinabove described, the diaphragm 7 is provided with the vibratory polysilicon layer 5b capable of storing charges and the power generation film 6 capable of generating power upon vibration with the polysilicon layer 5b so that the power generation film 6 constituted of the piezoelectric substance is also vibrated when the polysilicon layer 5b is sonically vibrated, whereby the polysilicon layer 5b stores charges generated by the power generation film 6 to cause potential difference between the back plate 10 and the diaphragm 7. When the diaphragm 7 is vibrated in the state causing the potential difference between the same and the back plate 10, the distance between the back plate 10 and the diaphragm 7 changes to change the capacitance of a capacitor formed by the back plate 10 and the diaphragm 7 as well as the potential of the back plate 10. The amplification circuit 26 amplifies this potential change and outputs the same as an electric signal, so that the microphone can output sound with an electrical signal. According to this embodiment, further, the power generation film 6 constituted of the piezoelectric substance is so vibrated that the polysilicon layer 5b can store charges, whereby the microphone requires no booster circuit or the like for applying a voltage between the diaphragm 7 and the back plate 10. Thus, a structure related to control including the amplification circuit 26 around the diaphragm 7 etc. can be so downsized as to downsize the microphone. In addition, the power generation film 6 repetitively generates power by vibration, whereby the polysilicon layer 5b can store a large quantity of charges. Thus, large potential difference can be caused between the back plate 10 and the diaphragm 7 including the polysilicon layer 5b, whereby potential change corresponding to change of the capacitance of the capacitor formed by the back plate 10 and the diaphragm 7 can be increased. Thus, the extracted electric signal can be intensified. Consequently, sensitivity of the microphone can be improved without increasing the size of the diaphragm 7. According to this embodiment, therefore, the microphone can be improved in sensitivity and downsized due to the diaphragm 7.
The diaphragm 7 is formed by the power generation film 6 constituted of the piezoelectric substance (PbTiO3 (Curie temperature: about 490° C.), for example) having higher heat resistance as compared with an electret film formed by an organic film and the polysilicon layer 5b, whereby heat resistance of the diaphragm 7 can be improved as compared with a diaphragm formed by an electret film. Thus, the power generation film 6 and the polysilicon layer 5b can be manufactured through a semiconductor fabrication process, whereby the diaphragm 7 can be downsized. Further, soldering can be automatically performed due to the improved heat resistance.
According to this embodiment, the diode 27 is so electrically connected to the power generation film 6 that the flow of charges generated by the power generation film 6 can be unidirectionally fixed from the power generation film 6 toward the polysilicon layer 5b and outflow of the charges stored in the polysilicon layer 5b can be suppressed, whereby the polysilicon layer 5b hardly loses the charges supplied from the power generation film 6. Thus, the polysilicon layer 5b can efficiently store charges.
According to this embodiment, the power generation film 6 is arranged on the outer periphery of the polysilicon layer 5b, whereby vibrational performance of a maximumly vibrated portion of the circular polysilicon layer 5b can be ensured. Further, the power generation film 6 is so formed as to enclose the polysilicon layer 5b, thereby supplying charges from the overall outer periphery of the polysilicon layer 5b. Thus, the power generation film 6 can supply a larger quantity of charges to the polysilicon layer 5b. In the fabrication process, the power generation film 6 constituted of the piezoelectric substance is so polarized as to generate positive charges on the outer periphery of the power generation film 6 and to generate negative charges on the inner periphery of the power generation film 6, on which the polysilicon layer 5b is located. Thus, external negative charges are attracted by the positive charges generated on the outer periphery of the power generation film 6, to flow into the microphone. These negative charges flow from the outer periphery toward the inner periphery of the power generation film 6. Consequently, the microphone can unidirectionally fix the flow of charges generated by the power generation film 6, thereby efficiently supplying charges to the polysilicon layer 5b.
Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.
For example, while the present invention is applied to the microphone which is a kind of sonic sensor in the aforementioned embodiment, the present invention is not restricted to this but is also applicable to another sonic sensor other than the microphone or a speaker.
While the power generation film 6 and the polysilicon layer 5b partially overlap with each other in the aforementioned embodiment, the present invention is not restricted to this but a power generation member 30 may alternatively be so formed as to cover the overall surface of a polysilicon layer 5b included in a diaphragm 31 as in a modification of the embodiment of the present invention shown in
While the piezoelectric substance constituting the power generation film 6 is prepared from PbTiO3 in the aforementioned embodiment, the present invention is not restricted to this but a single-crystalline substance such as quartz, LiNbO3, LiTaO3 or KNbO3, a thin film of ZnO or AlN, a sintered body of polarized PZT or a piezoelectric polymer membrane of polyvinylidene fluoride (PVDF) or the like may alternatively be employed for constituting the power generation film 6.
While the power generation film 6 is so polarized that positive charges concentrate on the outer periphery of the power generation film 6 and negative charges concentrate on the inner periphery thereof in the aforementioned embodiment, the present invention is not restricted to this but the power generation film 6 may alternatively be so polarized that negative charges concentrate on the outer periphery of the power generation film 6 and positive charges concentrate on the inner periphery thereof. In this case, the diode 27 must be arranged reversely to the arrangement in the aforementioned embodiment. In this case, further, negative charges concentrate on the outer periphery of the power generation film and positive charges concentrate on the inner periphery thereof upon vibration of the power generation film, whereby positive charges are attracted toward the polysilicon layer provided on the outer periphery of the power generation film through the diode. The potential of the polysilicon layer provided on the outer periphery of the power generation film is increased due to these positive charges, whereby negative charges flow out from the polysilicon layer provided on the inner periphery of the power generation film. Consequently, the potential of the polysilicon layer provided on the inner periphery of the power generation film is increased to cause potential difference between the same and the back plate.
While the power generation film 6 is so formed as to enclose the outer periphery of the polysilicon layer 5b for storing charges in the aforementioned embodiment, the present invention is not restricted to this but the power generation film 6 may alternatively be so formed as to partially support the outer periphery of the polysilicon layer 5b for storing charges.
While the diode 27 is formed by a Schottky diode or a p-n junction diode in the aforementioned embodiment, the present invention is not restricted to this but a diode prepared by forming an insulating film between a p region and an electrode of a p-n junction diode may alternatively be employed as a rectifier. When this diode is employed as the rectifier, outflow of stored charges can be further suppressed.
Number | Date | Country | Kind |
---|---|---|---|
JP2005-190856 | Jun 2005 | JP | national |