Patent Description:
There is a MEMS element known in the related art, which is manufactured by using an SOI (silicon-on-insulator) substrate and includes a fixed electrode, a movable electrode and an elastic support member for supporting the movable electrode, formed on an intermediate layer constituted with an insulating layer such as a silicon oxide layer that, in turn, is formed on a base constituted with a silicon substrate or the like. The fixed electrode includes a plurality of comb tooth electrodes, an electrode pad and a lead portion that connects the comb tooth electrodes with the electrode pad. The movable electrode includes a plurality of comb tooth electrodes that interdigitate with the comb tooth electrodes at the fixed electrode and the elastic support member includes a fixed end fixed to the base.

The fixed electrode, the movable electrode and the elastic support member are formed by adopting a MEMS machining technology. At the base, an opening, through which the comb teeth at the fixed electrode, the movable comb tooth electrodes and the area of the elastic support member excluding the fixed end are exposed, is formed. The fixed electrode is formed by forming a plurality of comb teeth, a linking portion that links the individual comb teeth with one another, the lead portion and the electrode pad all as integrated parts of the silicon oxide layer and the base, and its linking portion, lead portion and electrode pad, i.e., portions excluding the plurality of comb teeth, are fixed to the base via the intermediate layer (see, PTL <NUM>).

<CIT> discloses a semiconductor physical quantity sensor comprising a substrate made of silicon having an opening, a moving comb electrode supported by the substrate for displacing over the opening, a fixed electrode comb fixed to an edge of the substrate at the opening and disposed facing the moving electrode part, and a fixed electrode pad formed on the substrate next to the opening for connecting a wire that electrically connects the fixed comb electrode.

In the structure disclosed in PTL <NUM>, achieved by laminating the fixed electrode upon the base so that the entire surface of the fixed electrode to be fixed to the base faces opposite the base, the fixed electrode and the base face opposite each other over a large area. As a result, the parasitic capacitance occurring between the fixed electrode and the base is bound to be significant.

According to a 1st aspect of the present invention, a MEMS element, comprises: <NUM>. a base constituted with a silicon substrate, a device layer electrically insulated from the base, a fixed electrode and a movable electrode formed in the device layer, the fixed electrode having a plurality of fixed comb teeth, a fixed electrode pad and a support fastening portion. The movable electrode has a plurality of movable comb teeth which are interdigitated with the fixed comb teeth. The support fastening portion includes a comb tooth linking portion that connects the plurality of fixed comb teeth and the base comprises an opening, wherein the fixed electrode and the movable electrode are at least in part disposed over the opening. The base comprises a projecting portion which projects from an edge of the opening and extends along the comb tooth linking portion, wherein a fastening portion is disposed at the end of the projecting portion, wherein the end of the comb tooth linking portion is fixed to the fastening portion at the end of the projecting portion. A portion of the base, which would face opposite at least part of the comb tooth linking portion between the fastening portion and the fixed electrode pad, is removed, forming a gap between the projecting portion and the comb tooth linking portion.

According to a 2nd aspect of the present invention, a MEMS element comprises: a base constituted with a silicon substrate, a device layer electrically insulated from the base, a fixed electrode and a movable electrode formed in the device layer, the fixed electrode having a plurality of fixed comb teeth, a fixed electrode pad and a support fastening portion. The movable electrode has a plurality of movable comb teeth which are interdigitated with the fixed comb teeth. The support fastening portion includes a comb tooth linking portion that connects the plurality of fixed comb teeth, a lead portion that connects with the fixed electrode pad, a linking portion at which the comb tooth linking portion and the lead portion are linked. The base includes a fastening portion that fastens the linking portion or an end portion of the lead portion located toward the comb electrode, and a portion of the base, which would face opposite at least part of the lead portion at the fixed electrode, is removed.

According to embodiments of the invention, it is preferable that portions of the base, which would face opposite the entire fixed comb teeth and face opposite the entire movable comb teeth, are removed.

According to embodiments of the invention the MEMS element may further comprise:
an elastic support member that supports the movable electrode, wherein: a portion of the base, excluding a fixed end at which the elastic support member is fixed to the base and a connecting portion at which the elastic support member is connected to the movable electrode, is removed.

According to a further aspect of the invention, a vibration-driven energy harvesting device comprises a MEMS according to the invention wherein: an electret is formed at least at one of the movable electrode and the fixed electrode; and the vibration-driven energy harvesting device outputs electric power generated as the movable electrode vibrates.

According to the present invention, the parasitic capacitance between the fixed electrode and the base can be reduced.

The variants shown in <FIG>, <FIG> and <FIG> do not form part of the claimed invention.

A MEMS element and a vibration-driven energy harvesting device according to the present invention both relate to a structure that makes it possible to reduce a parasitic capacitance occurring in, for instance, wiring or the like, so as to extract a voltage having been generated through an external output terminal with a high level of efficiency.

The following is a description of the first embodiment of the present invention, given in reference to <FIG>.

<FIG> is a plan view illustrating the first embodiment of the vibration-driven energy harvesting device according to the present invention, and <FIG> shows the vibration-driven energy harvesting device in <FIG> in a sectional view taken through a line II-II. <FIG> does not include an illustration of an upper lid disposed on the top surface side (on the positive side along a z-axis), so as to provide a clear presentation of the structure of the MEMS element in the plan view. <FIG> is a plan view of the first embodiment of the MEMS element according to the present invention, <FIG> shows the MEMS element in <FIG> in a sectional view taken through line IVA-IVA, <FIG> is an enlarged view of a region IVB of the MEMS element in <FIG>, and <FIG> is a sectional view taken through line IVc-IVc in <FIG>. <FIG> is a plan view illustrating fastening portions via which a base and an intermediate layer of the MEMS element in <FIG> are fixed to each other, <FIG> is a sectional view taken through line VB-VB in <FIG>, illustrating a lead portion that is double-side supported. <FIG> is a top view of <FIG> shows a first stopper 15a formed so as to overhang at an opening 102a in a sectional view taken through line VD-VD in <FIG>.

It is to be noted that the following description will be given in reference to an x-axis, a y-axis and a z-axis running along the directions indicated in the figures. In addition, a line segment that forms a center line with respect to the x-axis (which extends along the left/right direction) is assigned with reference sign CLx and the line segment that forms a center line with respect to the y-axis (which extends along the up/down direction) is assigned with reference sign CLy in <FIG> and <FIG>.

A vibration-driven energy harvesting device <NUM> in <FIG> is a vibration-driven energy harvesting device having mounted thereat a MEMS element <NUM> that adopts a comb electrode structure. As shown in <FIG>, the vibration-driven energy harvesting device <NUM> comprises the MEMS element <NUM>, a case <NUM> at which the MEMS element <NUM> is installed and an upper lid <NUM> that covers the top of the case <NUM>, with the atmosphere within the case <NUM> sustaining a state of vacuum.

As shown in <FIG>, the MEMS element <NUM> comprises a base <NUM> constituted of Si (silicon), a device layer <NUM> constituted with an Si active layer, an intermediate layer <NUM> disposed between the base <NUM> and the device layer <NUM>, which is constituted of an inorganic insulating material such as a silicon oxide or a silicon nitride. Namely, the MEMS element <NUM> is configured by adopting a three-layer structure achieved by laminating the base <NUM>, the intermediate layer <NUM> and the device layer <NUM> constituted with an Si active layer along the z-axis, as illustrated in <FIG>. The MEMS element <NUM> adopting such a structure is normally manufactured through a standard MEMS machining technology by using an SOI (silicon-on-insulator) substrate.

The MEMS element <NUM> includes a first comb electrode structure <NUM> and a second comb electrode structure 300R respectively disposed on the left side and on the right side of the center line CLx. The first comb electrode structure <NUM> disposed on the left side of the center line CLx includes a pair of first movable electrodes <NUM> and a pair of first fixed electrodes <NUM>, whereas the second comb electrode structure 300R disposed on the right side of the center line CLx includes a pair of second movable electrodes <NUM> and a pair of second fixed electrodes <NUM>. The first and second movable electrodes <NUM> and <NUM> respectively include a plurality of movable comb teeth 131a and a plurality of movable comb teeth 132a connected to a movable unit <NUM> which functions as a comb tooth linking portion. The first and second fixed electrodes <NUM> and <NUM> respectively include a plurality of fixed comb teeth 141a and a plurality of fixed comb teeth 142a connected to comb tooth linking portions <NUM>. The movable comb teeth 131a and 132a are set so as to face opposite the fixed comb teeth 141a and 142a respectively and interdigitate with the respective fixed comb teeth 141a and 142a. A first electret is formed at either of or both of the first movable electrodes <NUM> and the first fixed electrodes <NUM>. In addition, a second electret is formed at either of or both of the second movable electrodes <NUM> and the second fixed electrodes <NUM>. The first and second movable electrodes <NUM> and <NUM> are elastically supported at the base <NUM> via elastic support members 133a and 133b, which will be explained later. At such a vibration-driven energy harvesting device <NUM>, power is generated as the comb teeth are displaced relative to each other.

While the structural concept of a comb electrode structure achieved in the first embodiment includes movable electrodes <NUM> (<NUM>), fixed electrodes <NUM> (<NUM>), a movable unit <NUM> and an elastic support member 133a (133b), the structural concept of the comb electrode structure may further include wiring portions, such as leads <NUM> that electrically connect the individual electrodes to electrode pads <NUM> and <NUM> functioning as external terminals, a stopper 15a (15b) and the like, as well as the electrode pads <NUM> and <NUM>.

A rectangular opening 102a is formed at the base <NUM> as illustrated in <FIG>. The first and second comb electrode structures <NUM> and 300R are disposed within the opening 102a in their entirety or in part. The first comb electrode structure <NUM> and the second comb electrode structure 300R include the first movable electrodes <NUM>, the first fixed electrodes <NUM>, the second movable electrodes <NUM> and the second fixed electrodes <NUM>, each disposed in one of the four areas partitioned by the center line CLy and the center line CLx within the opening 102a.

It is to be noted that this structural arrangement may be alternatively described as "the pair of first movable electrodes <NUM>, the pair of first fixed electrodes <NUM>, the pair of second movable electrodes <NUM> and the pair of second fixed electrodes <NUM> are each split so that one of the two electrodes is disposed above and the other electrode is disposed below relative to the center line CLy in the figure.

The first and the second comb electrode structures <NUM> and 300R are formed in the device layer <NUM>. Namely, the movable unit <NUM> extending along the center line CLy, the first movable electrodes <NUM> and the first fixed electrodes <NUM> disposed to the left relative to the center line CLx, the second movable electrodes <NUM> and the second fixed electrodes <NUM> disposed to the right relative to the center line CLx, a pair of elastic support members 133a and 133b that elastically support the movable unit <NUM> at the base <NUM>, the first stopper 15a disposed to the left relative to the center line CLx and the second stopper 15b disposed to the right relative to the center line CLx are formed in the device layer <NUM>.

As shown in <FIG>, weights <NUM> are fixed to the movable unit <NUM> with glue or the like, and the movable unit <NUM> and the weights <NUM> configure a movable assembly <NUM>. The weights <NUM> are fixed to the movable unit <NUM> in order to generate power with high efficiency even when the environmental vibration is slight by increasing the mass of the movable unit <NUM>.

The first movable electrodes <NUM> each include a plurality of movable comb teeth 131a, each extending toward the - side of the x-axis, which are disposed one after another over predetermined intervals along the y-axis on one side of a comb tooth linking portion <NUM>, whereas the second movable electrodes <NUM> each include a plurality of movable comb teeth 132a, each extending toward the + side of the x-axis, which are disposed one after another over predetermined intervals along the y-axis. The length of the movable comb teeth 131a of the first movable electrodes <NUM>, measured along the x-axis, and the length of the movable comb teeth 132a of the second movable electrodes <NUM>, measured along the x-axis, are substantially equal.

The movable comb teeth 131a and 132a of the first movable electrodes <NUM> and the second movable electrodes <NUM> are connected to the common comb tooth linking portion <NUM>, and the comb tooth linking portion <NUM>, in turn, is connected to the movable unit <NUM>. A left-end portion 103a of the movable unit <NUM> is supported at the base <NUM> via a pair of elastic support members 133a, one disposed above and the other disposed below the center line CLy. A right-end portion 103b of the movable unit <NUM> is supported at the base <NUM> via a pair of elastic support members 133b, one disposed above and the other disposed below the center line CLy. In the MEMS device <NUM> in the vibration-driven energy harvester <NUM> shown in <FIG>, the elastic support members 133a are disposed in the upper and lower areas on the left side and the elastic support members 133b are disposed in the upper and lower areas on the right side.

The first fixed electrodes <NUM> each include a plurality of fixed comb teeth 141a with which the plurality of movable comb teeth 131a of the first movable electrode <NUM> are interdigitated. The plurality of fixed comb teeth 141a are disposed one after another over equal intervals along the y-axis and each extend toward the + side of the x-axis. The first fixed electrodes <NUM> each include a comb tooth linking portion <NUM> via which the plurality of fixed comb teeth 141a are linked with one another, a fixed electrode pad <NUM> and a lead portion <NUM> that connects the comb tooth linking portion <NUM> to the fixed electrode pad <NUM>. The plurality of fixed comb teeth 141a, the comb tooth linking portion <NUM>, the lead portion <NUM> and the fixed electrode pad <NUM> of the first fixed electrode <NUM> are formed as an integrated unit in the device layer <NUM>, by adopting a MEMS machining technology.

Likewise, the second fixed electrodes <NUM> each include a plurality of fixed comb teeth 142a with which the plurality of movable comb teeth 132a of the second movable electrode <NUM> are interdigitated. The plurality of fixed comb teeth 142a are disposed one after another over equal intervals along the y-axis and each extend toward the - side of the x-axis. The second fixed electrodes <NUM> each include a comb tooth linking portion <NUM> via which the plurality of fixed comb teeth 142a are linked with one another, a fixed electrode pad <NUM> and a lead portion <NUM> that connects the comb tooth linking portion <NUM> to the fixed electrode pad <NUM>. The plurality of fixed comb teeth 142a, the comb tooth linking portion <NUM>, the lead portion <NUM> and the fixed electrode pad <NUM> of the second fixed electrode <NUM> are formed as an integrated unit in the device layer <NUM>, by adopting a MEMS machining technology.

It is to be noted that at each of the first fixed electrodes <NUM> and the second fixed electrodes <NUM>, a support fastening portion <NUM> is configured with the comb tooth linking portion <NUM> and the lead portion <NUM>. A middle part 112a of the lead portion <NUM> is not fixed to the base <NUM>. In other words, the base <NUM> is not present underneath the middle part 112a. As a result, the parasitic capacitance in the middle part 112a is reduced.

In addition, the comb tooth linking portion <NUM> and the fixed comb teeth 141a may be referred to, in a narrow sense, as a fixed electrode <NUM>.

The elastic support members 133a and the elastic support members 133b, which elastically support the movable unit <NUM>, adopt structures identical to one another. The elastic support members 133a and 133b each include three support beams <NUM> through <NUM>, a support beam linking portion <NUM> that links the support beams <NUM> through <NUM>, a fastening beam <NUM> and a linking portion <NUM> that links the support beam <NUM> to the fastening beam <NUM>.

The fastening structure adopted for the elastic support members 133a will be explained below.

The support beam <NUM>, disposed at a position furthest away from the fixed electrode <NUM> is connected to the first stopper 15a. The corresponding support beam <NUM>, disposed at a position closest to the same fixed electrode <NUM>, is connected to the fastening beam <NUM> via the linking portion <NUM>. The support beam <NUM>, disposed between the support beam <NUM> and the support beam <NUM> is connected at its one end to the linking portion <NUM> and is connected at its other end to the end 103a of the movable unit <NUM>. A fixed end 185a, which is an end of the fastening beam <NUM>, is fixed to a second fastening portion <NUM> (see <FIG>) disposed in the intermediate layer <NUM>.

The fastening structure adopted for the elastic support members 133b will be explained next.

The support beam <NUM>, disposed at a position furthest away from the fixed electrode <NUM> is connected to the second stopper 15b. The support beam <NUM>, disposed at a position closest to the same fixed electrode <NUM>, is connected to the fastening beam <NUM> via the linking portion <NUM>. The support beam <NUM>, disposed between the support beam <NUM> and the support beam <NUM>, is connected at its one end to the linking portion <NUM> and is connected at its other end to the end 103b of the movable unit <NUM>. A fixed end 185a, which is an end of the fastening beam <NUM>, is fixed to a second fastening portion <NUM> (see <FIG>) disposed in the intermediate layer <NUM>.

The first stopper 15a and the second stopper 15b have a function of regulating the amplitude with which the movable unit <NUM> vibrates. The first stopper 15a includes a projection 16a formed so as to face opposite one end 103a of the movable unit <NUM> in the x-axis. A movable electrode pad <NUM> is electrically connected to the first stopper 15a. The second stopper 15b includes a projection 16b formed so as to face opposite the other end 103b of the movable unit <NUM> in the x-axis. A movable electrode pad <NUM> is connected to the second stopper 15b.

If an abnormal condition or the like at the vibration source causes the movable unit <NUM> to move toward the - side of the x-axis by an extent greater than a predetermined degree, the one end 103a of the movable unit <NUM> will come into contact with the projection 16a of the first stopper 15a. If, on the other hand, the movable unit <NUM> moves toward the + side of the x-axis by an extent greater than a predetermined degree, the other end 103b of the movable unit <NUM> will come into contact with the projection 16b of the second stopper 15b. In this manner, the amplitude of the vibration of the movable unit <NUM> is regulated via the first stopper 15a and the second stopper 15b.

The first and second movable electrodes <NUM> and <NUM>, the movable unit <NUM>, the elastic support members 133a and 133b, the first and second stoppers 15a and 15b and the movable electrode pads <NUM> are formed as an integrated unit in the device layer <NUM> through a MEMS machining technology.

As described above, the plurality of fixed comb teeth 141a, the comb tooth linking portion <NUM>, the lead portion <NUM> and the fixed electrode pad <NUM> of each fixed electrode <NUM> are formed with the device layer <NUM> as an integrated unit by adopting a MEMS machining technology. In addition, the plurality of fixed comb teeth 142a, the comb tooth linking portion <NUM>, the lead portion <NUM> and the fixed electrode pad <NUM> of each second fixed electrode <NUM> are formed with the device layer <NUM> as an integrated unit by adopting a MEMS machining technology. In other words, the first comb electrode structure <NUM> and the second comb electrode structure 300R are each formed with the device layer <NUM> as an integrated unit through a MEMS machining technology.

The MEMS element <NUM> achieved in the first embodiment includes a wiring structure via which the first and second movable electrodes <NUM> and <NUM> are electrically connected to the movable electrode pads <NUM> and a wiring structure via which the comb tooth linking portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> are electrically connected to the fixed electrode pads <NUM>. These wiring structures are held fast and supported while, at the same time, they are insulated from the base <NUM>. The wiring structures include the first and second stoppers 15a and 15b, the lead portions <NUM>, the fixed electrode pads <NUM>, the movable electrode pads <NUM> and the elastic support members 133a and 133b. The following is a description of the wiring structures.

A first characteristic feature of the MEMS element <NUM> in the first embodiment is a reduction in the parasitic capacitance in the wiring on the fixed electrode-side. Namely, the lead portions <NUM> that connect the comb tooth linking portions <NUM> at the fixed electrodes <NUM> and <NUM> with the corresponding fixed electrode pads <NUM> are each double-side supported, i.e., supported on two ends, by fastening support portions <NUM> and <NUM> shown in <FIG>, and the base <NUM> is partially removed so that it is not present under the middle part 112a of the lead portion <NUM> supported on two ends by the fastening support portions <NUM> and <NUM>. The lead portion <NUM> and the fastening support portions <NUM> and <NUM> will be described in detail later in reference to <FIG>, <FIG>.

A second characteristic feature of the MEMS element <NUM> achieved in the first embodiment is that the base <NUM> is partially removed so that it is not present under the comb tooth linking portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> and under the plurality of comb teeth 141a and 142a.

<FIG> shows a region IVB of the MEMS element in <FIG> in an enlarged view, and <FIG> is a sectional view of <FIG> taken through line IVC - IVC.

Reference sign <NUM> in <FIG> indicates a peripheral fastening portion. The peripheral fastening portion <NUM> is formed so as to surround the lead portions <NUM> of the first and second fixed electrodes <NUM> and <NUM>, to surround the fixed electrode pads <NUM>, to surround the first and second stoppers 15a and 15b and to surround the movable electrode pads <NUM>. As shown in <FIG>, the peripheral fastening portion <NUM> is formed in the device layer <NUM>.

As <FIG> illustrate, a slit <NUM> is formed between the lead portion <NUM> and the peripheral fastening portion <NUM>. The lead portion <NUM> and the peripheral fastening portion <NUM> are physically separated from each other and electrically insulated from each other by the slit <NUM>.

Likewise, as <FIG> illustrates, the first and second stoppers 15a and 15b, together with corresponding electrode pads <NUM>, are each physically separated and electrically insulated from the peripheral fastening portion <NUM> by a slit <NUM>.

As explained earlier, the movable unit <NUM>, the first and second movable electrodes <NUM> and <NUM> and the first and second elastic support members 133a and 133b are disposed within the opening 102a of the base <NUM>. The fixed ends 185a of the elastic support members 133a and 133b are each supported at the second fastening portion <NUM> disposed at the intermediate layer <NUM> over the base <NUM> (see <FIG>, <FIG>).

The first stopper 15a is disposed so that its region 150A shown in <FIG> is fixed to the base <NUM> and so that its region 150B located on the side where the projection 16a is formed hangs over the opening 102a of the base <NUM>. In other words, the first stopper 15a is fixed to the base <NUM> over the region 150A ranging over half the length of the first stopper 15a measured along the x-axis.

Likewise, the second stopper 15b is disposed so that its region 150A shown in <FIG> is fixed to the base <NUM> and so that its region 150B located on the side where the projection 16b is formed hangs over the opening 102a of the base <NUM>. In other words, the second stopper 15b is fixed to the base <NUM> over the region 150A ranging over half its length measured along the x-axis.

The portions of the base <NUM> that would be present under the regions 150B of the first and second stoppers 15a and 15b are removed.

The comb tooth linking portion <NUM> and the lead portion <NUM> at each first fixed electrode <NUM> extend along directions substantially perpendicular to each other, and the comb tooth linking portion <NUM> and the lead portion <NUM> are linked with each other via a linking portion <NUM>. The linking portion <NUM> at the first fixed electrode <NUM> is fixed to the base <NUM> via the first fastening portion <NUM> formed in the intermediate layer <NUM> (see <FIG>, <FIG>). The fixed electrode pad <NUM> connected to the lead portion <NUM> of the first fixed electrode <NUM> and the end of the lead portion <NUM> located on the side where the fixed electrode pad <NUM> is present are fixed to the base <NUM> via the fourth fastening portion <NUM> formed in the intermediate layer <NUM> (see <FIG>, <FIG>). The middle part 112a of the lead portion <NUM> at the first fixed electrode <NUM>, which is located between the linking portion <NUM> and the end of the lead portion <NUM> located toward the fixed electrode pad <NUM>, is disposed within the opening 102a of the base <NUM>. The portion of the base <NUM>, which would be present under the lead middle part 112a, is removed (see <FIG>).

It is to be noted that an edge <NUM> of the opening 102a at the base <NUM> assumes a position substantially the same as that of a side surface of the lead portion <NUM> located on the outer side along the y-axis, over the region facing opposite the lead middle part 112a, i.e., the edge <NUM> matches with the side surface (however, the edge <NUM> in the illustration presented in <FIG> takes a position at which it does not overlap with the side surface of the lead portion <NUM> located on the outer side, so as to clearly indicate a position of the edge <NUM>).

Likewise, the plurality of fixed comb teeth 142a and the comb tooth linking portion <NUM> at each second fixed electrode <NUM> are disposed within the opening 102a of the base <NUM>. The comb tooth linking portion <NUM> and the lead portion <NUM> at the second fixed electrode <NUM> extend along directions substantially perpendicular to each other, and the comb tooth linking portion <NUM> and the lead portion <NUM> are linked with each other via a linking portion <NUM>. The linking portion <NUM> at the second fixed electrode <NUM> is fixed to the base <NUM> via the first fastening portion <NUM> formed in the intermediate layer <NUM> (see <FIG>). The fixed electrode pad <NUM> connected to the lead portion <NUM> at the second fixed electrode <NUM> and the end of the lead portion <NUM> located on the side where the fixed electrode pad <NUM> is present are fixed to the base <NUM> via the fourth fastening portion <NUM> formed in the intermediate layer <NUM> (see <FIG>). The middle part 112a of the lead portion <NUM> at the second fixed electrode <NUM>, which is located between the linking portion <NUM> and the end of the lead portion <NUM> located toward the fixed electrode pad <NUM>, is disposed within the opening 102a of the base <NUM>. The portion of the base <NUM>, which would be present under the lead middle part 112a, is removed (see <FIG>).

It is to be noted that the edge <NUM> of the opening 102a at the base <NUM> assumes a position substantially the same as that of a side surface of the lead portion <NUM> located on the outer side over the region facing opposite the lead middle part 112a, i.e., the edge <NUM> matches with the side surface.

<FIG> is a plan view showing fastening portions disposed at the base <NUM> and the intermediate layer <NUM> of the MEMS element <NUM> illustrated in <FIG>.

A substantially rectangular opening 102a is formed at the base <NUM>, and a pair of support portions <NUM> and a pair of support portions <NUM> are disposed at the opening 102a on the sides where the edges <NUM> are located. The support portions <NUM> and <NUM> each include the first fastening portion <NUM>, to which the linking portion <NUM> belonging to the corresponding fixed electrode, among the first and second fixed electrodes <NUM> and <NUM> is fixed. In addition, the second fastening portions <NUM>, to which the fixed ends 185a of the fastening beams <NUM> at the elastic support members 133a and 133b are fixed, are disposed in the intermediate layer <NUM> over the support portions <NUM> and <NUM>.

Two third fastening portions <NUM>, to which part of the first and second stoppers 15a and 15b and the movable electrode pads <NUM> are fixed, and four fourth fastening portions <NUM>, to which the fixed electrode pads <NUM> and the ends of the lead portions <NUM> located on the side where the fixed electrode pads <NUM> are present are fixed, are disposed over the peripheral region of the base <NUM>.

The fastening portions <NUM> through <NUM> are constituted with the intermediate layer <NUM> disposed between the device layer <NUM> and the base <NUM>.

As explained earlier, the edges <NUM> of the opening 102a take positions that substantially match with the outer side surfaces of the lead portions <NUM>. The edge <NUM> of the opening 102a project out relative to the support portions <NUM> and <NUM>. In other words, the portions of the base <NUM> that would face opposite the lead middle parts 112a, each located between a first fastening portion <NUM> and a fourth fastening portion <NUM>, are removed. As a result, the parasitic capacitance between the base <NUM> and the lead portions <NUM> can be reduced.

In addition to the portions of the base <NUM> that would face opposite the movable electrodes <NUM> and <NUM>, the portions of the base <NUM> that would face opposite the comb tooth linking portions <NUM> and the fixed comb teeth 141a and 142a at the first and second fixed electrodes <NUM> and <NUM> are removed. This structure makes it possible to further reduce the parasitic capacitance between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM>, in comparison to a structure in which only the portions of the base <NUM> that would face opposite the movable electrodes <NUM> and <NUM> are removed.

As <FIG> and <FIG> indicate, pad portions 114a constituted of an electrically conductive metal such as aluminum are formed on the fixed electrode pads <NUM>, each connected to a first fixed electrode <NUM> or a second fixed electrode <NUM>. In addition, pad portions 113a constituted of an electrically conductive metal such as aluminum are formed on the movable electrode pads <NUM>, one connected to the first stopper 15a and the other connected to the second stopper 15b. As shown in <FIG>, the pad portions 113a and 114a are connected, each via a wire <NUM>, respectively to electrodes 117a and 117b disposed at the case <NUM>.

The vibration-driven energy harvester <NUM> is installed at a vibration source to cause the movable unit <NUM> to vibrate along the x-axis. The pair of elastic support members 133a and the pair of elastic support members 133b are formed so as to achieve high levels of rigidity along the y-axis and along the z-axis and the movable unit <NUM> is set so that it is primarily engaged in vibration along the x-axis. For instance, as the movable unit <NUM> is displaced toward the + side along the x-axis, the facing area (overlapping area length) over which the fixed comb teeth 142a of the second fixed electrodes <NUM> and the movable comb teeth 132a of the second movable electrodes <NUM> face opposite each other increases and the facing area over which the fixed comb teeth 141a of the first fixed electrodes <NUM> and the movable comb teeth 131a of the first movable electrodes <NUM> face opposite each other decreases. As explained earlier, the first electret is formed at either of or both of the first movable electrodes <NUM> and the first fixed electrodes <NUM>, and the second electret is formed at either of or at both of the second movable electrodes <NUM> and the second fixed electrodes <NUM>. As the facing areas change, electric charges induced via the electrets change. Power is generated at the MEMS element <NUM> as the electric charges induced between the first fixed electrodes <NUM> and the first movable electrodes <NUM> and between the second fixed electrodes <NUM> and the second movable electrodes <NUM> change and the electric power thus generated is output from the vibration-driven energy harvesting device <NUM>.

In the first embodiment described above, the portions of the base <NUM> that would face opposite part of the lead portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> (that would face opposite the middle parts 112a) are removed and also the portions of the base <NUM> that would face opposite part of the comb tooth linking portions <NUM> excluding the linking portions <NUM> that link with the lead portions <NUM>, are removed. In other words, the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> only via the fixed electrode pads <NUM>, part of the lead portions <NUM> and part of the comb tooth linking portions <NUM>.

The MEMS element <NUM> in the example described above assumes four comb electrode structures defined by the center lines CLx and CLy. However, the present invention may instead be adopted in a MEMS element that includes just one of the four comb electrode structures, i.e., a single comb electrode structure defined by the center lines CLx and CLy.

It is to be noted that in the embodiment described above, the portions of the base <NUM> that would face opposite part of the lead portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> (that would face opposite the middle parts 112a) are removed and also the portions of the base <NUM> that would face opposite part of the comb tooth linking portions <NUM> excluding the linking portions <NUM>, which link with the lead portions <NUM>, are removed. In other words, the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> only via the fixed electrode pads <NUM>, part of the lead portions <NUM> and part of the comb tooth linking portions <NUM> in the example described above.

However, the fastening structure with which the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> allows for a number of variations and some such variations will be described below.

<FIG> shows variation <NUM> of the first embodiment in a plan view illustrating a fastening structure that may be adopted to fix the device layer and the base of a MEMS element to each other. <FIG> is a plan view showing fastening portions via which the device layer and the base of the MEMS element in <FIG> are fixed to each other. It is to be noted that <FIG> illustrate a region of the MEMS element <NUM> located at the upper left part of the MEMS element <NUM> which is one quarter of the entire MEMS element <NUM> in <FIG> and <FIG>, so as to simplify the drawings for better clarity.

At the MEMS element <NUM> achieved in the first embodiment illustrated in <FIG> and <FIG>, the first fixed electrodes <NUM> are each fixed to the base <NUM> only at a fixed electrode pad <NUM>, the end of a lead portion <NUM> located toward the electrode pad and a linking portion <NUM> that links the comb tooth linking portion <NUM> to the lead portion <NUM>. Namely, the portions of the base <NUM> that would be present under the middle part 112a of the lead portion <NUM> and under the comb tooth linking portion <NUM> are removed. In contrast, the first fixed electrode <NUM> at the MEMS element <NUM> in variation <NUM> is fixed to the base <NUM> only via a fixed electrode pad <NUM>, one end of a lead portion <NUM> located toward the electrode pad and another end of the lead portion <NUM> located on the side where the comb electrode is present. In other words, the comb tooth linking portion <NUM> of the first fixed electrode <NUM> is not fixed to the base <NUM>.

A support portion 121a in the MEMS element <NUM> achieved in variation <NUM> is disposed at a position set away (set apart) from the corresponding comb tooth linking portion <NUM>. As <FIG> illustrates, the support portion 121a includes a second fastening portion <NUM> to which a fixed end 185a of the fastening beam <NUM> is fixed and a fastening portion <NUM> to which the other end of the lead portion <NUM> located toward the comb electrode is fixed. The support portion 121a in the MEMS element <NUM> achieved in variation <NUM> does not include a fastening portion via which the comb tooth linking portion <NUM> is fixed to the base <NUM>. The comb tooth linking portion <NUM> is configured as an integrated part of the lead portion <NUM>, and is supported indirectly at the base <NUM> via the lead portion <NUM>, which is fixed at the fastening portion <NUM>. Although not shown, the second fixed electrodes <NUM>, too, are each fixed in a similar manner, and the comb tooth linking portions <NUM> of the second fixed electrodes <NUM> are not fixed to the base <NUM>.

As described above, in the MEMS element <NUM> in variation <NUM>, only the fixed electrode pads <NUM> and part of the lead portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM>, and the comb tooth linking portions <NUM> are not fixed to the base <NUM>.

Other structural features of variation <NUM> are similar to those illustrated in <FIG> and <FIG>, and the same reference signs are assigned to the corresponding structural features so as to preclude the necessity of a repeated explanation thereof.

At the MEMS element <NUM> achieved in the first embodiment as illustrated in <FIG> and <FIG>, the fixed electrode pads <NUM> of the first fixed electrodes <NUM> are fixed in their entirety to the base <NUM>. In contrast, the fixed electrode pads <NUM> of the first fixed electrodes <NUM> at the MEMS element <NUM> achieved in variation <NUM> are fixed to the base <NUM> only in part thereof.

As <FIG> illustrates, a side of a fixed electrode pad <NUM> at a first fixed electrode <NUM> is set so as to take a position at the opening 102a of the base <NUM> and the remainder of the fixed electrode pad <NUM> is positioned to sit on the base <NUM>. In other words, a region <NUM>-<NUM> of the fixed electrode pad <NUM>, located on the side where the lead portion <NUM> is present, is formed so as to overhang at the opening 102a. As shown in <FIG>, a fastening portion 154a having an area corresponding to the area of the portion of the first fixed electrode <NUM> positioned over the base <NUM> is disposed on the base <NUM>.

It is to be noted that as in variation <NUM>, only a second fastening portion <NUM> and a fastening portion <NUM>, to which the end of the lead portion <NUM> located toward the comb electrode is fixed, are formed at the support portion 121a, and the fastening structure does not include a fastening portion via which the comb tooth linking portion <NUM> is fixed to the base <NUM> in variation <NUM>.

As described above, only part of the fixed electrode pad <NUM> and part of the lead portion <NUM> are fixed to the base <NUM>, and the comb tooth linking portion <NUM> is not fixed to the base <NUM> in the MEMS element <NUM> in variation <NUM>.

At the MEMS element <NUM> achieved in the first embodiment as illustrated in <FIG> and Fig. SA, the portions of the base <NUM> that would face opposite part of the lead portions <NUM> (middle parts) at the first fixed electrodes <NUM> are removed and also the portions of the base <NUM> that would face opposite the regions of the comb tooth linking portions <NUM> excluding the linking portions <NUM>, which are linked with the lead portions <NUM> are removed. In contrast, the MEMS element <NUM> achieved in variation <NUM> adopts a structure in which the lead portion <NUM> of the fixed electrodes <NUM> are fixed in their entirety to the base <NUM> and the entire portion of the base <NUM> that would face opposite the comb tooth linking portions <NUM> are removed. In other words, the entire comb tooth linking portions <NUM> are positioned within the opening 102a.

As <FIG> illustrates, an edge 128a of the opening 102a of the base <NUM> is positioned further inward along the direction in which the y-axis extends, relative to the inner side surface of a lead portion <NUM> and the lead portion <NUM> is disposed in its entirety over the base <NUM>. As shown in <FIG>, a fastening portion <NUM>, which is connected to a fourth fastening portion <NUM> and extends in correspondence to substantially the entirety of the lead portion <NUM>, is disposed at the base <NUM>.

A projecting portion <NUM>, which projects from the edge 128a of the opening 102a and extends along a comb tooth linking portion <NUM> toward the movable unit <NUM> is disposed at the base <NUM>. A gap <NUM> between the projecting portion <NUM> and the comb tooth linking portion <NUM> separates the projecting portion <NUM> from the comb tooth linking portion <NUM> along the x-axis (see <FIG>).

An elastic support member 133a includes support beams <NUM> through <NUM> and a support beam linking portion <NUM> that links the support beams <NUM> through <NUM> at one end. However, the elastic support member 133a does not include a fastening beam <NUM> such as those shown in <FIG>, and a fixed end 181a of the support beam <NUM>, located at a front end on the side opposite from the support beam linking portion <NUM>, is laminated on the front end of the projecting portion <NUM>. A fastening portion 152a is disposed at the front end of the projecting portion <NUM> and the fixed end 181a of the support beam <NUM> at the elastic support member 133a is fixed to the fastening portion 152a of the projecting portion <NUM>.

In the MEMS element <NUM> achieved in variation <NUM> as described above, the portions of the base <NUM> that would face opposite the entirety of comb tooth linking portions <NUM> at the first fixed electrodes <NUM> are removed, and the lead portions <NUM> and the regions of the first fixed electrodes <NUM> that face opposite the fixed electrode pads <NUM> are fixed in their entirety to the base <NUM>.

Although not shown, a similar structure is adopted in conjunction with the second fixed electrodes <NUM>, such that the portions of the base <NUM> that would face opposite the entirety of the comb tooth linking portions <NUM> of the second fixed electrodes <NUM> are removed and the lead portion <NUM> and the regions of the second fixed electrodes <NUM> facing opposite the fixed electrode pads <NUM> are fixed in their entirety to the base <NUM>.

It is to be noted that in the structural example described above, the portions of the base <NUM> that would face opposite the comb tooth linking portions <NUM> over their entire areas at the first and second fixed electrodes <NUM> and <NUM> are removed. As an alternative, the comb tooth linking portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> may be fixed to the base <NUM> only in part. In other words, the comb tooth linking portions <NUM> may be only partially fixed to the base <NUM> and significant regions of the comb tooth linking portions <NUM> may be positioned within the opening 102a.

In more specific terms, the MEMS element <NUM> in variation <NUM> meets a structural requirement that portions of the base that would face opposite at least part of the comb tooth linking portions <NUM> at the first and second fixed electrodes <NUM> and <NUM> over substantially the entirety of its width, i.e., the length running along a direction (along the x-axis) perpendicular to the direction in which the fixed comb teeth 141a and 142a are disposed one after another (along the y-axis), be removed. In other words, a structure is achieved such that portions ranging over substantially the entire width of the comb tooth linking portions <NUM> along the x-axis and, more desirably, over the entirety of the width of the comb tooth linking portions <NUM> along the x-axis, are removed.

<FIG> shows variation <NUM> of the first embodiment in a plan view, illustrating a fastening structure that may be adopted to fix the device layer and the base of a MEMS element to each other. <FIG> is a plan view showing fastening portions via which the device layer and the base of the MEMS element in <FIG> are fixed to each other. It is to be noted that <FIG> illustrate a region of the MEMS element <NUM> located at the upper left part of the MEMS element <NUM> which is one quarter of the entire MEMS element <NUM> in <FIG> and Fig. SA, so as to simplify the drawings for better clarity.

At the MEMS element <NUM> achieved in the first embodiment as illustrated in <FIG> and <FIG>, the portions of the base <NUM> that would face opposite part of the lead portions <NUM> (middle parts 112a) at the first fixed electrodes <NUM> are removed and also the portions of the base <NUM> that would face opposite the regions of the comb tooth linking portions <NUM> excluding some part thereof (linking portions <NUM>) are removed. In contrast, the MEMS element <NUM> achieved in variation <NUM> adopts a structure in which the comb tooth linking portions <NUM> of the first fixed electrodes <NUM> are fixed substantially in their entirety to the base <NUM> and portions of the base <NUM> that would face opposite the lead portions <NUM> substantially in their entirety are removed.

As <FIG> illustrate, an edge <NUM> of the opening 102a at the base <NUM> is set at a position that matches with a side surface of a lead portion <NUM>, located on the outer side along the y-axis, as in the MEMS element <NUM> shown in <FIG> and <FIG>. At the base <NUM>, a projecting portion <NUM> projecting from the edge <NUM> of the opening 102a and extending along a comb tooth linking portion <NUM> toward the movable unit <NUM>, is formed. The projecting portion <NUM> is laminated under the comb tooth linking portion <NUM>, and a fastening portion <NUM> to which the comb tooth linking portion <NUM> is fixed is disposed over the projecting portion <NUM>.

As in variation <NUM>, a fastening portion 152a to which a fixed end 181a present at the front end of the support beam <NUM> at the elastic support member 133a is fixed, is disposed at the front end of the projecting portion <NUM>. As in variation <NUM>, a fixed electrode pad <NUM> is disposed so that a side portion thereof, located on the side where the comb tooth linking portion <NUM> is present, overhangs the opening 102a, and the fixed electrode pad <NUM> is only partially fixed to the fastening portion 154a at the base <NUM>.

As described above, at the MEMS element <NUM> achieved in variation <NUM>, the portions of the base <NUM>, which would face opposite the entire lead portions <NUM> of the first fixed electrodes <NUM> are removed and the entire comb tooth linking portions <NUM> are fixed to the base <NUM> via the fastening portions <NUM>.

Although not shown, a similar structure is adopted for the second fixed electrodes <NUM>, such that the portions of the base <NUM> that would face opposite the entire lead portions <NUM> of the second fixed electrodes <NUM> are removed and the entire comb tooth linking portions <NUM> are fixed to the base <NUM> via the fastening portions <NUM>.

It is to be noted that the lead portions <NUM> and the comb tooth linking portions <NUM> may be only partially fixed to the base <NUM>.

Namely, at the MEMS element <NUM> achieved in variation <NUM>, the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> only via part of the fixed electrode pads <NUM> and via substantially the whole of or part of the comb tooth linking portions <NUM>.

The following operational advantages are achieved through the first embodiment and variations <NUM> through <NUM>.

Namely, at least portions of the base <NUM> that would face opposite the regions of the comb tooth linking portions <NUM> excluding the part described above are removed. As a result, the parasitic capacitance between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM> can be reduced. This, in turn, makes it possible to reduce the electric charges accumulated between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM>. Consequently, greater power output can be achieved for a vibration-driven energy harvesting device <NUM> configured with the MEMS element <NUM>.

<FIG> shows the second embodiment of the MEMS element, and <FIG> is a plan view showing the fastening portions via which the device layer and the base of the MEMS element in <FIG> are fixed to each other.

A MEMS element 10A achieved in the second embodiment is distinguishable from the first embodiment having lead portions <NUM> included in the support fastening portions <NUM>, in that support fastening portions 104a at first and second fixed electrodes <NUM> and <NUM> thereof do not include lead portions <NUM>.

The following description will focus on structural features of the second embodiment distinguishable from those of the first embodiment.

As shown in <FIG>, the first and second fixed electrodes <NUM> and <NUM> each include a fixed electrode pad <NUM>. However, the first and second fixed electrodes <NUM> and <NUM> do not include lead portions <NUM>, such as those in the first embodiment. Namely, support fastening portions 104a of the first and second fixed electrodes <NUM> and <NUM> are each constituted with a comb tooth linking portion <NUM> alone, which is directly linked to the corresponding fixed electrode pad <NUM>.

The part of each fixed electrode pad <NUM>, located on the side where it is linked with the comb tooth linking portion <NUM>, is positioned at the opening 102a of the base <NUM>. In other words, the fixed electrode pad <NUM> is fixed only in part to a fastening portion 154b disposed at the base <NUM>, as illustrated in <FIG>. Fixed ends 185a of the fastening beams <NUM> at the elastic support members 133a and 133b are fixed to second fastening portions <NUM> at positions matching those assumed in the first embodiment.

Other structural features of the second embodiment are similar to those described in reference to the first embodiment, and the same reference signs are assigned to the corresponding structural features so as to preclude the necessity of a repeated explanation thereof.

The first and second fixed electrodes <NUM> and <NUM> in the second embodiment do not include lead portions <NUM> and the comb tooth linking portions <NUM> in their entirety are not fixed to the base <NUM>. In other words, the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> via only part of the fixed electrode pads <NUM>.

It is to be noted that in the structural example described above, the fixed electrode pads <NUM> are fixed to the base <NUM> only in part. However, the fixed electrode pads <NUM> may instead be fixed in their entirety to the base <NUM>.

The MEMS element 10A in the second embodiment comprises a base <NUM>, a first fixed electrode <NUM> and a second fixed electrode <NUM> each having a plurality of fixed comb teeth 141a or 142a, a fixed electrode pad <NUM> and a support fastening portion 104a, and first and second movable electrodes <NUM> and <NUM> respectively having a plurality of movable comb teeth 131a and a plurality of movable comb teeth 132a that are interdigitated with the fixed comb teeth 141a and the fixed comb teeth 142a respectively. The support fastening portions 104a each include a comb tooth linking portion <NUM> that links the plurality of fixed comb teeth 141a or 142a, and the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> via the entirety of the fixed electrode pads <NUM> or via part of the fixed electrode pads <NUM>. Namely, at least portions of the base <NUM> that would face opposite substantially the entirety of the comb tooth linking portions <NUM> are removed. As a result, the parasitic capacitance between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM> can be reduced. This, in turn, makes it possible to reduce the electric charges accumulated between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM>. Consequently, greater power output can be achieved for a vibration-driven energy harvesting device <NUM> configured with the MEMS element 10A.

<FIG> shows variation <NUM> of the second embodiment in a plan view, illustrating a fastening structure that may be adopted to fix the device layer and the base of a MEMS element to each other. <FIG> is a plan view showing fastening portions via which the device layer and the base of the MEMS element in <FIG> are fixed to each other.

It is to be noted that <FIG> illustrate a region of the MEMS element 10A located at the upper left part of the MEMS element 10A which is one quarter of the entire MEMS element 10A shown in <FIG> and <FIG> so as to simplify the drawings for better clarity.

Variation <NUM> of the second embodiment is distinguishable from the second embodiment, in which the comb tooth linking portions <NUM> are not fixed in their entirety to the base <NUM>, in that part of each comb tooth linking portion <NUM> is fixed to the base <NUM>.

As <FIG> illustrates, a projecting portion 123a, similar to that shown in <FIG>, is formed so as to project from an edge 128a of the opening 102a and extend along the comb tooth linking portion <NUM> toward the movable unit <NUM>. A gap <NUM> is present between the projecting portion 123a and the comb tooth linking portion <NUM>.

An elastic support member 133a does not include a fastening beam <NUM> (see <FIG>), and a fixed end 181a of a support beam <NUM> located on the side opposite from a support beam linking portion <NUM> is laminated on the front end of the projecting portion 123a. As illustrated in <FIG>, a fastening portion 152a is disposed at the front end of the projecting portion 123a, and the fixed end 181a of the support beam <NUM> at the elastic support member 133a is fixed to the fastening portion 152a disposed at the front end of the projecting portion 123a. In variation <NUM> of the second embodiment, another fastening portion <NUM> is disposed at the front end of the projecting portion 123a. The front end of the comb tooth linking portion <NUM> at each first fixed electrode <NUM> is fixed to the fastening portion <NUM>.

Although not shown, a structure similar to that pertaining to the first fixed electrodes <NUM> is adopted for the second fixed electrodes <NUM>, and the second fixed electrodes <NUM> are each fixed to the base <NUM> only via part of the fixed electrode pad <NUM> and part of the comb tooth linking portion <NUM>.

Other structural features of the variation <NUM> of the second embodiment are similar to those described in reference to the second embodiment and the same reference signs are assigned to the corresponding structural features so as to preclude the necessity of a repeated explanation thereof.

The first and second fixed electrodes <NUM> and <NUM> in variation <NUM> of the second embodiment do not include lead portions <NUM> and part of the comb tooth linking portions <NUM> is not fixed to the base <NUM>. Namely, the first and second fixed electrodes <NUM> and <NUM> are fixed to the base <NUM> only via part of the fixed electrode pads <NUM> and part of the comb tooth linking portions <NUM>.

The MEMS element 10A achieved in variation <NUM> of the second embodiment comprises a base <NUM>, a first fixed electrode <NUM> and a second fixed electrode <NUM> each having a plurality of fixed comb teeth 141a or 142a, a fixed electrode pad <NUM> and a support fastening portion 104a, and first and second movable electrodes <NUM> and <NUM> respectively having a plurality of movable comb teeth 131a and a plurality of movable comb teeth 132a that are interdigitated with the fixed comb teeth 141a and the fixed comb teeth 142a respectively. The support fastening portions 104a each include a comb tooth linking portion <NUM> that links the plurality of fixed comb teeth 141a or 142a, and the first and second fixed electrodes <NUM> and <NUM> adopt either a structure whereby the fixed electrode pads <NUM> are fixed to the base <NUM> in their entirety or only in part thereof or a structure whereby the fixed electrode pads <NUM> in their entirety or in part and only part of the comb tooth linking portions <NUM> are fixed to the base <NUM>.

Namely, at least portions of the base <NUM> that would face opposite the regions of the comb tooth linking portions <NUM> excluding the part described above are removed. As a result, the parasitic capacitance between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM> can be reduced. This, in turn, makes it possible to reduce the electric charges accumulated between the base <NUM> and the first and second fixed electrodes <NUM> and <NUM>. Consequently, greater power output can be achieved for a vibration-driven energy harvesting device <NUM> configured with the MEMS element 10A.

While the MEMS elements <NUM> and 10A achieved in the embodiments and variations are each configured by using an SOI substrate in the description provided above, a MEMS element <NUM> or 10A may be formed by using a silicon substrate instead of an SOI substrate. As an alternative, the MEMS element may be formed by combining a silicon substrate, glass, metal, alumina or the like.

The MEMS elements <NUM> and 10A in the examples cited in reference to the embodiments each configure a vibration-driven energy harvesting device <NUM>. However, the MEMS element according to the present invention may be a MEMS element for a vibration actuator that causes vibration of a movable electrode unit by applying a drive voltage sourced from the outside.

In addition, the present invention may be adopted in a micro-resonator adopting a structure in which a movable electrode and a fixed electrode are separated from each other via a slit, as disclosed in PTL <NUM> (<CIT>). The micro-resonator described in PTL <NUM> fulfills a function as a filter through which a vibration of a specific frequency in a vibration occurring between one fixed comb electrode and a movable comb electrode is extracted from another fixed comb electrode.

Moreover, the structures of the MEMS elements <NUM> and 10A achieved in the embodiments and variations may be adopted in various types of sensors.

Claim 1:
A MEMS element (<NUM>), comprising:
a base (<NUM>) constituted with a silicon substrate;
a device layer (<NUM>) electrically insulated from the base (<NUM>);
a fixed electrode (<NUM>, <NUM>) and a movable electrode (<NUM>, <NUM>) formed in the device layer (<NUM>);
the fixed electrode (<NUM>, <NUM>) having a plurality of fixed comb teeth (141a, 142a), a fixed electrode pad (<NUM>) and a support fastening portion (<NUM>); and
the movable electrode (<NUM>, <NUM>) having a plurality of movable comb teeth (131a, 132a) which are interdigitated with the fixed comb teeth (141a, 142a), wherein:
the support fastening portion (<NUM>) includes a comb tooth linking portion (<NUM>) that connects the plurality of fixed comb teeth (141a, 142a); and
the base comprises an opening (102a), wherein the fixed electrode (<NUM>, <NUM>) and the movable electrode are at least in part disposed over the opening (102a);
characterised in that the base (<NUM>) comprises a projecting portion (123a) which projects from an edge (128a) of the opening (102a) and extends along the comb tooth linking portion (<NUM>), wherein a fastening portion (<NUM>) is disposed at the end of the projecting portion (123a);
wherein the end of the comb tooth linking portion (<NUM>) is fixed to the fastening portion (<NUM>) at the end of the projecting portion (123a) and a portion of the base (<NUM>), which would face opposite at least part of the comb tooth linking portion (<NUM>) between the fastening portion (<NUM>) and the fixed electrode pad (<NUM>), is removed, forming a gap (<NUM>) between the projecting portion (<NUM>) and the comb tooth linking portion (<NUM>).