Electrostatic actuator and power generator

This electrostatic actuator includes an electret film and a conductor layer formed on the electret film, and the conductor layer is so formed as to have a sectional shape reduced in width upward from the side closer to the electret film.

CROSS-REFERENCE TO RELATED APPLICATIONS

The priority application number JP2007-221041, electrostatic actuator, Aug. 28, 2007, Yoshiki Murayama, Naoteru Matsubara, upon which this patent application is based is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an electrostatic actuator and a power generator, and more particularly, it relates to an electrostatic actuator and a power generator each comprising an electret film.

2. Description of the Background Art

An electrostatic actuator and a power generator each comprising an electret film are known in general.

A conventional power generator (electrostatic actuator) comprises a first substrate including a conductive region having a rectangular section with angular edges and a second substrate, opposed to the first substrate, having an electret region (electret film). The conventional power generator can obtain electromotive force by changing the relative positions of the first and second substrates thereby changing the quantity of charges stored in the conductive region.

SUMMARY OF THE INVENTION

An electrostatic actuator according to a first aspect of the present invention comprises an electret film and a conductor layer formed on the electret film, and the conductor layer is so formed as to have a sectional shape reduced in width upward from the side closer to the electret film.

A power generator according to a second aspect of the present invention comprises an electret film, a conductor layer formed on the electret film and a collector opposed to the electret film and so provided as to be relatively movable with respect to the electret film, to be capable of generating power by electrostatic induction due to relative movement of the electret film and the collector, while the conductor layer is so formed as to have a sectional shape reduced in width from the side closer to the electret film toward the side closer to the collector.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

The structure of an electrostatic induction power generator1according to a first embodiment of the present invention is described with reference toFIGS. 1 to 3. This embodiment of the present invention is applied to the electrostatic induction power generator1employed as an exemplary electrostatic actuator.

In the electrostatic induction power generator1according to the first embodiment, a first electrode portion10and a second electrode portion20are opposed to each other, as show inFIG. 1. The electrostatic induction power generator1comprises a bridge rectifier circuit2for rectifying generated power and a DC-DC converter3for converting the voltage of a direct current. A load4driven by the power generated by the electrostatic induction power generator1is connected to the DC-DC converter3. The DC-DC converter3and the load4are grounded respectively.

As shown inFIG. 1, an electret film12of fluororesin such as polytetrafluoroethylene (PTFE) or silicon oxide having a thickness t1(seeFIG. 3) of about 100 μm to about 1000 μm is formed on the surface of a substrate11made of a conductor. The electret film12is controlled to a potential of about −20 V to about −2000 V by negative charges injected into the overall surface by corona discharge and entirely distributed therein.

According to the first embodiment, a guard electrode13is formed on the surface of the electret film12. The guard electrode13is an example of the “conductor layer” in the present invention. This guard electrode13has a function of inhibiting an electric field resulting from the charges stored in the electret film12from spreading. The guard electrode13may be employed as a wire connecting elements formed on the electret film12with each other, or as a spacer or a stopper for preventing a collector22, described later, opposed to the electret film12from coming into contact with the electret film12. The guard electrode13is made of a conductor such as Al or W, and has a thickness of about 0.05 μm to about 1 μm. According to the first embodiment, portions around the upper and lower ends of the guard electrode13are so formed as to have tapered sections reduced in width (tapered) upward from the side closer to the electret film12, as shown inFIG. 3. The guard electrode13is so formed that the taper angle θ is about 20° to about 50°. According to the first embodiment, the sectional shapes of corners on the upper end portions of the guard electrode13are so rounded as to have a radius R1of curvature of about 0.1 μm to about 1 μm. The side of the guard electrode13in contact with the electret film12is so concavely rounded that the width thereof is gradually increased toward the electret film12, to have a radius R2of curvature of about 0.1 μm to about 1 μm.

According to the first embodiment, the guard electrode13is interdigitally formed in plan view and corners131of the guard electrode13are so rounded as to have the radius R1of curvature of about 0.1 μm to about 1 μm, as shown inFIG. 2. The width W1of teeth forming the interdigital guard electrode13and the interval W2between the teeth are about 100 μm to about 1000 μm respectively. The guard electrode13is grounded.

As sown inFIG. 1, the collector22of Al or W having a thickness t3of about 0.05 μm to about 1 μm is formed on the lower surface of another substrate21made of insulating glass. The collector22is formed interdigitally or in a stripped manner similarly to the guard electrode13shown inFIG. 2, and the width W3of teeth forming the collector22and the interval W4between the teeth are about 100 μm to about 1000 μm respectively. The interval W2between the teeth forming the guard electrode13and the width W3of the teeth forming the collector22satisfy the relation W3≧W2.

The power generating operation of the electrostatic induction power generator1according to the first embodiment of the present invention is now described with reference toFIG. 1.

When no vibration is applied to the electrostatic induction power generator1, the surface of the electret film12and the collector22are opposed to each other at a prescribed interval, as shown inFIG. 1. The surface of the electret film12is controlled to the negative potential (about −20 V to about −2000 V), and hence the collector22electrostatically induces positive charges.

When horizontal vibration (along arrow X) is applied to the electrostatic induction power generator1, the electret film12and the collector22so relatively move that the collector22is opposed to the guard electrode13. Thus, the potential opposed to the collector22changes from the potential (about −20 V to about −2000 V) of the electret film12to the potential (ground potential) of the guard electrode13, to change the quantity of the charges electrostatically induced by the collector22. This change in the quantity of the charges forms a current, which in turn is output to the load4through the bridge rectifier circuit2and the DC-DC converter3. Then, the electret film12and the collector22are opposed to each other again by vibration, whereby the collector22stores positive charges. Thus, the electrostatic induction power generator1continuously generates power due to repetitive relative movement of the electret film12and the collector22.

According to the first embodiment, as hereinabove described, the electrostatic power generator1comprises the guard electrode13for inhibiting the electric field resulting from the charges stored in the electret film12from spreading and the guard electrode13is so formed as to have the sectional shape reduced in width upward from the side closer to the electret film12, whereby the collector22and the guard electrode13can be inhibited from catching each other when coming into contact with each other, due to the inclined side surfaces of the guide electrode13. Thus, the electret film12provided with the guard electrode13on the surface thereof can smoothly vibrate.

According to the first embodiment, as hereinabove described, the sectional shapes of the corners on the upper end portions of the guard electrode13are so rounded that the collector22and the guard electrode13can be further inhibited from catching each other when coming into contact with each other, due to the rounded end portions on the surface of the guard electrode13.

According to the first embodiment, as hereinabove described, the side surfaces of the guard electrode13are so tapered upward from the side closer to the electret film12that the collector22and the guard electrode13can be inhibited from catching each other when coming into contact with each other, due to the tapered side surfaces of the guard electrode13.

According to the first embodiment, as hereinabove described, the guard electrode13is so interdigitally formed in plan view that a portion inhibiting the electric field from spreading and a portion allowing the electric field to spread can be easily formed.

According to the first embodiment, as hereinabove described, the sectional shape on the lower end portion of the guard electrode13is so concavely rounded that the width thereof is gradually increased toward the electret film12, whereby the guard electrode13can be stably formed with respect to the electret film12.

Second Embodiment

Referring toFIG. 4, a first electrode portion10aof an electrostatic induction power generator according to a second embodiment of the present invention is so formed that side surfaces131aof a guard electrode13aare perpendicular to the surface of an electret film12, dissimilarly to the aforementioned first embodiment.

In the first electrode portion10aof the electrostatic induction power generator according to the second embodiment, the guard electrode13afor inhibiting an electric field resulting from charges stored in the electret film12from spreading is formed on the surface of the electret film12, as shown inFIG. 4. The guard electrode13ais an example of the “conductor layer” in the present invention. The guard electrode13ahas a thickness t4of about 0.05 μm to about 1 μm. The guard electrode13ahas a sectional shape reduced in width from the side in contact with the electret film12toward a side not in contact with the electret film12, and is so formed that the side surfaces131athereof are perpendicular to the surface of the electret film12. According to the second embodiment, sectional shapes on ends of the surface of the guard electrode13aare so rounded as to have a radius R3of curvature of about 0.1 μm to about 1 μm. The side of the guard electrode13ain contact with the electret film12is gradually increased in width toward the electret film12, to have a radius R4of curvature of about 0.1 μm to about 1 μm.

The guard electrode13ais interdigitally formed in plan view as shown inFIG. 2, similarly to the guard electrode13of the electrostatic induction power generator1according to the aforementioned first embodiment. The width W5of teeth forming the guard electrode13aand the interval W6between the teeth are about 100 μm to about 1000 μm respectively. The guard electrode13ais grounded.

The remaining structure of the electrostatic induction power generator according to the second embodiment is identical to that of the electrostatic induction power generator1according to the aforementioned first embodiment.

According to the second embodiment, as hereinabove described, the ends of the surface of the guard electrode13aon the side not in contact with the electret film12are so rounded that a collector22(seeFIG. 1) and the guard electrode13acan be inhibited from catching each other when coming into contact with each other, due to the rounded sectional shapes of the ends of the surface of the guard electrode13a.

According to the second embodiment, as hereinabove described, the side surfaces131aof the guard electrode13aare so formed as to have sectional shapes substantially perpendicular to the surface of the electret film12so that an electric field formed between the guard electrode13aand the electret film12spreads along the perpendicular side surfaces131aof the guard electrode13a, thereby spreading perpendicularly to the surfaces of the guard electrode13aand the electret film12. Thus, stable electric induction takes place between the guard electrode13aand the electret film12, whereby the electrostatic induction power generator can stably generate power.

Third Embodiment

Referring toFIG. 5, a first insulating film14is formed on a surface of an electret film12not provided with a guard electrode13in a first electrode portion10bof an electrostatic induction power generator according to a third embodiment of the present invention, dissimilarly to the aforementioned first embodiment.

In the first electrode portion10bof the electrostatic induction power generator according to the third embodiment, the first insulating film14consisting of at least any one of an MSQ (methyl silsesquioxane) film, an SiOC film and an SiN film is formed on the surface of the electret film12not provided with the guard electrode13, as shown inFIG. 5. The first insulating film14has a function of inhibiting charges from flowing out of the surface of the electret film12. The first insulating film14has a thickness t5of about 0.01 μm to about 1 μm, which is identical to or smaller than the thickness t2of the guard electrode13.

The remaining structure of the electrostatic induction power generator according to the third embodiment is identical to that of the electrostatic induction power generator1according to the aforementioned first embodiment.

According to the third embodiment, as hereinabove described, the first insulating film14is so formed on the surface of the electret film12not provided with the guard electrode13as to inhibit the charges from flowing out of the surface of the electret film12not provided with the guard electrode13, whereby the surface potential of the electret film12can be prevented from reduction.

According to the third embodiment, as hereinabove described, the first insulating film14is so made of a material capable of inhibiting the charges from flowing out of the electret film, whereby the surface potential of the electret film12can be prevented from reduction.

According to the third embodiment, as hereinabove described, the first insulating film14is so formed by at least any one of an MSQ film, an SiOC film and an SiN film that the charges can be inhibited from flowing out of the surface of the electret film12.

The remaining effects of the third embodiment are similar to those of the aforementioned first embodiment.

Fourth Embodiment

Referring toFIG. 6, a protective film15is formed on the surface of a guard electrode13in a first electrode portion10cof an electrostatic induction power generator according to a fourth embodiment of the present invention, dissimilarly to the aforementioned third embodiment.

In the first electrode portion10cof the electrostatic induction power generator according to the fourth embodiment, the protective film15is formed on the surface of the guard electrode13, as shown inFIG. 6. The protective film15may be an insulating film formed by at least any one of an MSQ film, an SiOC film and an SiN film, or may be a conductive film. The protective film15is so formed as to have a thickness t6of about 0.01 μm to about 1 μm, which is identical to or smaller than the thickness t2of the guard electrode13. Sectional shapes on end portions of the surface of the protective film15are so rounded as to have a radius R5of curvature of about 0.1 μm to about 1 μm. Further, the protective film15is so formed that the width thereof is gradually increased toward the electret film12, to have a radius R6of curvature of about 0.1 μm to about 1 μm. The radii R5and R6of curvature are identical to or larger than the radii R1and R2(seeFIG. 3) of curvature of the guard electrode13. Thus, a collector22and the guard electrode13more hardly catch each other as compared with a case where no protective film15is formed, whereby the electret film12can more smoothly vibrate.

The remaining structure of the electrostatic induction power generator according to the fourth embodiment is identical to that of the electrostatic induction power generator1according to the aforementioned first embodiment.

According to the fourth embodiment, as hereinabove described, the protective film15is so formed on the surface of the guard electrode13as to prevent the guard electrode13and the collector22from coming into contact with each other, whereby charges stored in the collector22can be inhibited from flowing out toward the guard electrode13.

According to the fourth embodiment, as hereinabove described, the protective film15is formed by at least any one of an MSQ film, an SiOC film and an SiN film, thereby preventing the guard electrode13and the collector22from coming into contact with each other.

The remaining effects of the fourth embodiment are similar to those of the aforementioned first embodiment.

Fifth Embodiment

Referring toFIG. 7, a first insulating film14has a thickness t5larger than the thickness t7of a protective film15ain a first electrode portion10dof an electrostatic induction power generator according to a fifth embodiment of the present invention, dissimilarly to the aforementioned fourth embodiment.

In the first electrode portion10dof the electrostatic induction power generator according to the fifth embodiment, the protective film15aconsisting of at least any one of an MSQ film, an SiOC film and an SiN film is formed on the surface of a guard electrode13, as shown inFIG. 7. According to the fifth embodiment, the first insulating film14is so formed that the thickness t5thereof is larger than the thickness t7of the protective film15a.

The remaining structure of the electrostatic induction power generator according to the fifth embodiment is identical to that of the electrostatic induction power generator according to the aforementioned fourth embodiment.

According to the fifth embodiment, as hereinabove described, the first insulating film14is so formed that the thickness t5thereof is larger than the thickness t7of the protective film15a, whereby the first insulating film14can be prevented from damage exposing the electret film12even if the protective film15ais damaged to expose the guard electrode13, due to the thickness t5of the first insulating film14larger than the thickness t7of the protective film15a. Thus, the surface potential of the electret film12can be prevented from reduction resulting from such damage.

The remaining effects of the third embodiment are similar to those of the aforementioned fourth embodiment.

Sixth Embodiment

Referring toFIG. 8, an electret film12ais provided with projecting portions121ain a first electrode portion10eof an electrostatic induction power generator according to a sixth embodiment of the present invention, dissimilarly to the electrostatic induction power generator according to the aforementioned fifth embodiment.

As shown inFIG. 8, the electret film12ahaving the projecting portions121ais formed on the surface of a substrate11in the first electrode portion10eof the electrostatic induction power generator according to the sixth embodiment, as shown inFIG. 8. The projecting portions121aare interdigitally formed in plan view, in response to the shape of a guard electrode13. The projecting portions121ahave a thickness t8of about 0.64 μm. The guard electrode13is formed on the surfaces of the projecting portions121aof the electret film12a. Thus, charges stored in the surfaces of recess portions121bof the electret film12acan be inhibited from flowing out toward the guard electrode13. Further, a first insulating film14aconsisting of at least any one of an MSQ film, an SiOC film and an SiN film and having a thickness of about 1.55 μm is formed on the surfaces of the recess portions121bof the electret film12a. Thus, the charges stored in the surfaces of the recess portions121bof the electret film12acan be further inhibited from flowing out. A protective film15bconsisting of an MSQ film, an SiOC film and an SiN film and having a thickness t10of about 0.28 μm is formed on the surface of the guard electrode13. The thickness t8of the projecting portions121aof the electret film12a, the thickness t9of the first insulating film14aand the thickness t10of the protective film15bare in ratios of about 2.2:5.5:1.0.

The remaining structure of the electrostatic induction power generator according to the sixth embodiment is identical to that of the electrostatic induction power generator according to the aforementioned fifth embodiment.

According to the sixth embodiment, as hereinabove described, the guard electrode13is so formed on the surfaces of the projecting portions121athat the charges stored in the surfaces of the recess portions121bof the electret film12acan be inhibited from flowing out toward the guard electrode13.

According to the sixth embodiment, as hereinabove described, the first insulating film14ais so formed on the surfaces of the recess portions121bthat the charges stored in the surfaces of the recess portions121bof the electret film12acan be further inhibited from flowing out.

The remaining effects of the sixth embodiment are similar to those of the aforementioned fifth embodiment.

Seventh Embodiment

Referring toFIG. 9, a second insulating film16is formed on the surface of an electret film12in a first electrode portion10fof an electrostatic induction power generator according to a seventh embodiment of the present invention, dissimilarly to the aforementioned sixth embodiment.

In the first electrode portion10fof the electrostatic induction power generator according to the seventh embodiment, the second insulating film16consisting of an HDP (high density plasma) oxide film is formed on the surface of the electret film12, as shown inFIG. 9. The second insulating film16is interdigitally formed in plan view, in response to the shape of a guard electrode13. The guard electrode13is formed on the surface of the second insulating film16. The second insulating film16can inhibit charges stored in a surface of the electret film12not provided with the second insulating film16from flowing out toward the guard electrode13. A first insulating film14aconsisting of at least any one of an MSQ film, an SiOC film and an SiN film is formed on the surface of the electret film12not provided with the second insulating film16. Thus, the charges stored in the surface of the electret film12not provided with the second insulating film16can be further inhibited from flowing out. A protective film15bconsisting of at least any one of an MSQ film, an SiOC film and an SiN film is formed on the surface of the guard electrode13.

The remaining structure of the electrostatic induction power generator according to the seventh embodiment is identical to that of the electrostatic induction power generator according to the aforementioned sixth embodiment.

According to the seventh embodiment, as hereinabove described, the second insulating film16is so formed between the electret film12and the guard electrode13that the charges stored in the surface of the electret film12not provided with the second insulating film16can be inhibited from flowing out toward the guard electrode13.

The remaining effects of the seventh embodiment are similar to those of the aforementioned sixth embodiment.

Eighth Embodiment

Referring toFIG. 10, an insulating film and a protective film15care integrally formed by the same material in a first electrode portion10gof an electrostatic induction power generator according to an eighth embodiment of the present invention, dissimilarly to the aforementioned fifth embodiment.

In the first electrode portion10gof the electrostatic induction power generator according to the eighth embodiment, the protective film15cconsisting of at least any one of an MSQ film, an SiOC film and an SiN film is formed on a surface of an electret film12not provided with a guard electrode13and on the surface of the guard electrode13, as shown inFIG. 10. The protective film15cformed on the surface of the electret film12not provided with the guard electrode13functions as the insulating film inhibiting charges from flowing out of the surface of the electret film12. Thus, the insulating film and the protective film15ccan be integrally formed by the same material at the same time dissimilarly to a case of forming the insulating film inhibiting the charges from flowing out of the surface of the electret film12and the protective film15cthrough separate steps, whereby the steps of manufacturing the electrostatic induction power generator can be simplified. Further, the thickness t11of the portion of the protective film15cformed on the surface of the electret film12not provided with the guard electrode13can be easily rendered larger than the thickness t12of the portion of the protective film15cformed on the surface of the guard electrode13by employing spin coating.

The remaining structure of the electrostatic induction power generator according to the eighth embodiment is identical to that of the electrostatic induction power generator according to the aforementioned fifth embodiment.

According to the eighth embodiment, as hereinabove described, the insulating film formed on the surface of the electret film12not provided with the guard electrode13and the protective film15cformed on the surface of the guard electrode13are integrally formed by the same material on the surface of the electret film12so that the insulating film and the protective film15ccan be integrally formed by the same material dissimilarly to the case of forming the insulating film and the protective film15cthrough separate steps, whereby the structure of the electrostatic induction power generator can be simplified.

The remaining effects of the eighth embodiment are similar to those of the aforementioned fifth embodiment.

Ninth Embodiment

Referring toFIG. 11, insulating films and a protective film15dare integrally formed by the same material in a first electrode portion10hof an electrostatic induction power generator according to a ninth embodiment of the present invention, dissimilarly to the aforementioned sixth embodiment.

In the first electrode portion10hof the electrostatic induction power generator according to the ninth embodiment, the protective film15dconsisting of at least any one of an MSQ film, an SiOC film and an SiN film is so formed as to cover the side surfaces of projecting portions121aof an electret film12a, the surfaces of recess portions121band the surface of a guard electrode13, as shown inFIG. 11. The portions of the protective film15dformed on the surfaces of the recess portions121bof the electret film12afunction as the insulating films inhibiting charges from flowing out of the surface of the electret film12a.

The remaining structure of the electrostatic induction power generator according to the ninth embodiment is identical to that of the electrostatic induction power generator according to the aforementioned sixth embodiment.

According to the ninth embodiment, as hereinabove described, the insulating films formed on the recess portions121band the protective film15dformed on the surface of the guard electrode13are integrally formed by the same material on the surface of the electret film12so that the insulating films and the protective film15dcan be integrally formed by the same material dissimilarly to a case of forming the insulating films and the protective film15dthrough separate steps, whereby the structure of the electrostatic induction power generator can be simplified.

The remaining effects of the ninth embodiment are similar to those of the aforementioned sixth embodiment.

Tenth Embodiment

Referring toFIG. 12, an insulating film and a protective film15eare integrally formed in a first electrode portion10iof an electrostatic power generator according to a tenth embodiment of the present invention, dissimilarly to the aforementioned seventh embodiment.

In the first electrode portion10iof the electrostatic power generator according to the tenth embodiment, a second insulating film16is formed on the surface of an electret film12, as shown inFIG. 12. The protective film15econsisting of at least any one of an MSQ film, an SiOC film and an SiN film is so formed as to cover surface portions of the electret film12not provided with a guard electrode13, the side surfaces of the second insulating film16and the surface of the guard electrode13. The protective film15eformed on the surface portions of the electret film12not provided with the guard electrode13functions as the insulating film inhibiting charges from flowing out of the surface of the electret film12.

The remaining structure of the electrostatic induction power generator according to the tenth embodiment is similar to that of the electrostatic induction power generator according to the aforementioned seventh embodiment.

Further, the remaining effects of the electrostatic induction power generator according to the tenth embodiment are also similar to those of the electrostatic induction power generator according to the aforementioned seventh embodiment.

For example, while each of the aforementioned first to tenth embodiments is applied to the electrostatic induction power generator employed as an exemplary electrostatic actuator, the present invention is not restricted to this but is also applicable to another electrostatic actuator such as an electrostatic induction actuator or an electrostatic induction sensor, so far as the same includes an electret film.

While the substrate11made of a conductor is employed in each of the aforementioned first to tenth embodiments, the present invention is not restricted to this but a substrate made of an insulator may alternatively be employed. In this case, however, a conductor layer must be formed between the substrate made of an insulator and the electret film12or12a.

While the guard electrode13or13ais grounded in each of the aforementioned first to tenth embodiments, the present invention is not restricted to this but the guard electrode13or13amay alternatively be not grounded. Further, a prescribed voltage reverse in polarity to the surface potential of the electret film12or12amay be applied to the guard electrode13or13a.

While the interval W4between the teeth forming the collector22is larger than the interval W2between the teeth forming the interdigital guard electrode13or13ain each of the aforementioned first to tenth embodiments, the present invention is not restricted to this but the width W1of the teeth forming the guard electrode13or13amay alternatively be rendered larger than the width W3of the teeth forming the collector22.

While the thickness t3of the collector22is substantially identical to the thickness t2of the guard electrode13or13ain each of the aforementioned first to tenth embodiments, the present invention is not restricted to this but the thickness t2of the guard electrode13or13amay alternatively be rendered larger than the thickness t3of the collector22.