Stacked electro-mechanical energy conversion element and method of manufacturing the same

A stacked electro-mechanical energy conversion element includes a plurality of layers having a circular shape each of which is formed of a material having an electro-mechanical energy conversion function and has a through-hole in the center thereof, a plurality of electrode portions formed at least on one surface of the layers and separated from each other by a plurality of first non-electrode portions, a plurality of wiring conductors which penetrate the plurality of layers and electrically connect electrode portions of the different layers, and a plurality of second non-electrode portions formed in the periphery of the wiring conductors so as to prevent the wiring conductors from being rendered conductive to the electrode portions, wherein the wiring conductors are formed at least on or in the vicinity of an edge of an outer diameter of each layer, and the electrode portions are formed over the edge of the outer diameter except for portions at which the second non-electrode portions are formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a stacked electro-mechanical energy conversion element such as a piezoelectric element and a method of manufacturing the stacked electro-mechanical energy conversion element, and more particularly to a through-hole that forms a connection between the respective layers of the stacked electro-mechanical energy conversion element.

2. Related Background Art

Up to now, a piezoelectric material having an electro-mechanical energy conversion function is employed as various piezoelectric elements or piezoelectric devices. As a recent tendency, those piezoelectric elements and piezoelectric devices take not a single plate but a structure in which a large number of thin sheets are superimposed on each other so as to be stacked.

One main reason is that a large deformation or distortion or a large force can be obtained by a low supply voltage in a stacked piezoelectric element as compared with a single plate-like piezoelectric element. Also, another reason is that a sheet molding method or a manufacturing method for stacking have been spread, the thickness of each layer is thinned, and a stacked piezoelectric element and piezoelectric device which are downsized and high in performance are readily manufactured.

For example, a stacked piezoelectric element for a vibration wave motor which is an example of a vibration wave driving device has been disclosed by U.S. Pat. Nos. 6,046,526 and 5,770,916. The stacked piezoelectric element is not limited to a vibration wave driving device but employed for various devices such as a vibration gyro or a piezoelectric transformer.

The stacked electro-mechanical energy conversion element is of the structure in which a plurality of laminate materials each having an electro-mechanical energy conversion function on which an electrode region is formed are superimposed on each other. As a representative example, there is a structure in which a plurality of piezoelectric ceramics layers (hereinafter referred to as “piezoelectric layer”) on a surface of which an electrode layer formed of an electrode material (hereinafter referred to as “inner electrode”) is provided are stacked on each other.

As disclosed in U.S. Pat. Nos. 6,046,526 and 5,770,916, there is a structure that uses through-holes (or called “via holes”) formed by embedding an electrically conductive material (electrode material) in holes defined in the piezoelectric layer as interlayer wirings for connecting a plurality of stacked inner electrodes.

FIG. 10shows a stacked piezoelectric element disclosed in U.S. Pat. No. 5,770,916, in which a stacked piezoelectric element71has a through-hole76for connecting the inner electrodes.

InFIG. 10, the stacked piezoelectric element71is of a columnar shape in the center of which a through-hole is formed, in which through-holes76indicated by black circles are formed at an inner diameter side. The through-holes76render the respective stacked piezoelectric layers conductive. On the surfaces of two kinds of piezoelectric layers72and73that constitute the stacked piezoelectric element71are formed an inner electrode (or called “electrode pattern”)74divided into four electrode portions (74-1,74-2,74-3,74-4) and an inner electrode75divided into four electrode portions (75-1,75-2,75-3,75-4). The piezoelectric layers72and73are alternately stacked on each other on a second layer to a twenty-fifth layer except for a first layer that is an upper surface layer.

Eight through-holes76indicated by black circles are formed at the inner diameter sides of the respective piezoelectric layers in the figure. Among them, four through-holes76render the electrode portions positioned at an inphase of the second layer, the fourth layer, the sixth layer, . . . the 24th layer (piezoelectric layer72) conductive to each other.

Also, the remaining four through-holes76render the electrode portions positioned at an inphase of the third layer, the fifth layer, the seventh layer, . . . the 25th layer (piezoelectric layer73) conductive to each other. Only the 25th layer is different in structure from other layers in that no through-holes are formed in the 25th layer because no layer is disposed below the 25th layer.

Also, the through-holes that are rendered conductive to the inner electrode74of the piezoelectric layer72are not rendered conductive to the inner electrode75of the piezoelectric layer73whereas the through-holes that are rendered conductive to the inner electrode75of the piezoelectric layer73are not rendered conductive to the inner electrode74of the piezoelectric layer72.

Then, those eight through-holes76are rendered nonconductive to each other, and the end portions of the through-holes76are exposed on the surface of the stacked piezoelectric element71to form a surface electrode77. Also, the respective inner electrodes74and75are not formed up to the edges of the outer diameter and the inner diameter, and non-electrode regions are formed at the edges of the outer diameter and the inner diameter.

The stacked piezoelectric element71thus structured as shown inFIG. 10is subjected to the following polarizing process.

In the respective piezoelectric layers73that structure the third layer, the fifth layer, the seventh layer, . . . the 25th layer, the electrode portions having a positional relationship of 180 degrees have polarized polarities different from each other so that the electrode portions75-1and75-3are polarized to +(plus) and −(minus), respectively, and the electrode portions75-2and75-4are polarized to +(plus) and −(minus), respectively.

As shown inFIG. 10, it is assumed that the electrode portions75-1and75-3are A+ and A− respectively, the electrode portions75-2and75-4are B+ and B− respectively, and those electrode portions are phase A and phase B, respectively. Also, it is assumed that the electrode portions74-1and74-3of the piezoelectric layer72which face the electrode portions75-1and75-3are a phase AG, the electrode portions74-2and74-4of the piezoelectric layer72which face the electrode portions75-2and75-4are a phase BG, and those electrode portions are electrically grounded.

FIG. 11is a cross-sectional view showing a bar-shaped vibration wave motor140that functions as a vibration wave driving device where the stacked piezoelectric element71are incorporated in a vibration member141. The stacked piezoelectric element71and a wiring board149that comes in direct contact with the stacked piezoelectric element71are disposed between metal parts142and143which are elastic members of the vibration member141are fixed by fastening a bolt144. The eight surface electrodes of the stacked piezoelectric element71and the electrode pattern of the wiring substrate149are electrically connected to each other.

The drive principle of the bar-shaped vibration wave motor140is as follows: two bending vibrations that are orthogonal to each other are produced in the vibration member141in which the stacked piezoelectric element71is incorporated, and a rotor147that comes in pressure contact with the vibration member141is driven by a frictional force. The rotor147is brought in pressure contact with the metal part142though a spring145and a spring support member146.

The phase AG and the phase BG which face the phase A and the phase B are grounded, and a high frequency voltage that is substantially identical with a natural vibration frequency is applied to the phase A. Also, a high frequency voltage of the same vibration frequency as that of the phase A but electrically different in phase from the phase A by 90 degrees is applied to the phase B that is spatially different in phase from the phase A by 90 degrees, and drive vibrations are obtained by synthesizing those two bending vibrations produced in the vibration member141.

Then, the rotor147that is in pressure contact with one surface of the metal part142is frictionally driven by the drive vibrations generated in the vibration member141, and a drive force is outputted from the gear148that functions as an output member that rotates integrally with the rotor147.

It is necessary to notch the inner electrode75and dispose an insulating portion (non-electrode region79inFIG. 10) in the periphery of the through-hole so that the through-hole that is rendered conductive to the inner electrode74of the piezoelectric layer72is not rendered conductive to the inner electrode75of the piezoelectric layer73. The same is applied to the piezoelectric layer72.

When the outer diameter of the stacked piezoelectric element is made small as the through-holes remain at the inner diameter side as in the stacked piezoelectric element shown inFIG. 10, because the circular insulating portion is disposed in the periphery of the through-hole, it is difficult to satisfactorily broaden a region of a piezoelectric active portion (a portion interposed between the inner electrode74and the inner electrode75) necessary to drive the vibration wave motor. For that reason, there is a limit of downsizing the stacked piezoelectric element71.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-mentioned related art, and therefore an object of the present invention is to provide a stacked piezoelectric element that is suitable for downsizing by the provision of a broad piezoelectric active portion.

According to an aspect of the present invention, there is provided a stacked electro-mechanical energy conversion element having a plurality of electrode portions on a surface thereof, and a plurality of layers each having an electro-mechanical energy conversion function in which wiring conductors (through-holes) that penetrate the plurality of layers and electrically connect the electrode portions of the different layers is formed, wherein the wiring conductors are formed at the end portions of the layers or in the vicinity of the end portions.

Preferably, each of the plurality of layers is shaped into a circle having a through-hole in the center thereof, and a non-electrode portion for preventing the conduction of each of the wiring conductors and each of the plurality of electrode portions is formed, and the electrode portions are formed over an outer diameter edge or an inner diameter edge except for a portion on which the non-electrode is formed.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, a description will be given in more detail of preferred embodiments of the present invention with reference to the accompanying drawings.

FIG. 1shows a first embodiment of the present invention.

A stacked piezoelectric element1that functions as a stacked electro-mechanical energy conversion element according to this embodiment is designed such that through-holes are formed in the center thereof to obtain conductions between stacked piezoelectric layers.

As a second layer to a 25th layer except for a first layer that is a surface layer (uppermost layer), piezoelectric layers2and3are alternately disposed one by one. That is, the stacked piezoelectric element1includes the piezoelectric layers2that form the second layer, the fourth layer, the sixth layer, . . . , and the 24th layer, and the piezoelectric layers3that form the third layer, the fifth layer, the seventh layer, . . . , and the 25th layer. Then, inner electrodes4and5disposed on the surfaces of the respective piezoelectric layers2and3reach the edges of the outer diameters and the inner diameters of disc-shaped piezoelectric bodies that constitute the respective layers.

A cross-shaped slit (non-electrode formation portion) that passes through diameter portions is formed on a surface of each of two kinds of piezoelectric layers2and3that constitute the stacked piezoelectric element1. Through the slits, the inner electrode4is divided into four segments consisting of electrode portions4-1,4-2,4-3and4-4, and the inner electrode5is divided into four segments consisting of electrode portions5-1,5-2,5-3and5-4.

In the piezoelectric layers2and the piezoelectric layers3, eight through-holes6indicated by black circles in the figure are formed at positions that approach the outer diameter ends as much as possible, respectively.

The respective piezoelectric layers are stacked so that all of eight through-holes6are inphase with each other, and the respective through-holes6are coupled to each other in a thickness direction of the stacked piezoelectric element to render the respective piezoelectric layers conductive.

Each of the electrode portions of the piezoelectric layers2and the piezoelectric layers3has one through-hole formed therein so that the electrode portions of the piezoelectric layers2which are positioned in the same phase are rendered conductive, and the electrode portions of the piezoelectric layers3which are positioned in the same phase are rendered conductive. In this situation, each of the through-holes that pass through the electrode portions of the piezoelectric layers2passes through each of the non-electrode portions of the piezoelectric layers3, and each of the through-holes that pass through the electrode portions of the piezoelectric layers3passes through each of the non-electrode portions of the piezoelectric layers2.

In other words, when those through-holes are viewed as eight linear through holes coupled to each other in the thickness direction of the piezoelectric elements, each one of those eight linear through-holes alternately passes through the electrode portions and the non-electrode portion.

Since the 25th layer is a lowermost layer and no layer is disposed below the 25th layer, no through-holes are formed in the 25th layer.

Those eight linear through-holes6are out of contact with each other and are not rendered conductive to each other. Also, the respective end portions of those eight through-holes6are exposed to the surface of the stacked piezoelectric element1, and the eight surface electrodes7that are identical in size with the diameters of the through-holes are formed on the first layer.

After the stacked piezoelectric element1has been structured as described above, the stacked piezoelectric element1is subjected to the following polarizing process as in the related art so as to be given polarization polarity suitable for the vibration wave motor.

In the piezoelectric layers3that constitute the third layer, the fifth layer, the seventh layer, . . . , and the 25th layer of the stacked piezoelectric element1, the electrode portion5-1and the electrode portion5-3are polarized to +(plus) and −(minus), and the electrode portion5-2and the electrode portion5-4are polarized to +(plus) and −(minus), respectively, so that the electrode portions having a positional relationship of 180 degrees have polarization polarities different from each other.

That is, as shown inFIG. 1, assuming that the electrode portions5-1and5-3are set to A+ and A−, and the electrode portions5-2and5-4are set to B+ and B−, those electrode portions are set to a phase A and a phase B. The electrode portions4-1and4-3of the piezoelectric layer2which face the electrode portions5-1and5-3are set to a phase AG, the electrode portions4-2and4-4of the piezoelectric layer2which face the electrode portions5-2and5-4are set to a phase BG, and those electrode portions are electrically grounded.

FIG. 3is a diagram showing a structure in which the stacked piezoelectric element1is incorporated in a vibration member101that constitutes the bar-shaped vibration wave motor100. The vibration member101is set to be smaller in diameter than the conventional one.

The stacked piezoelectric element1and a wiring substrate109are disposed between the metal parts102and103which are elastic members of the member101, and fitted by fastening a bolt104. The wiring substrate109comes in close contact with the stacked piezoelectric element1by a nipping force exerted at this time. The rotor107comes in pressure contact with the metal part102through the spring105and the spring support member106.

The wiring substrate109is disposed with a wiring electrode pattern which is rendered conductive to the respective surface electrodes7of the stacked piezoelectric element1to electrically connect an external power supply and the stacked piezoelectric element1.

The wiring substrate109is structured by patterning a copper foil which is 35 μm in thickness for wiring on a normally used sheet made of polyimide which is 25 μm in thickness.

Then, as in the conventional example, the phase AG and the phase BG that face the phase A and the phase B are grounded, a high-frequency voltage that is substantially identical with the natural vibration frequency of the vibration member is applied to the phase A, and a high frequency voltage of the same vibration frequency which is electrically different in phase from the phase A by 90 degrees is applied to the phase B spatially different in phase from the phase A by 90 degrees. In this way, in the drive vibration obtained by synthesizing two bending vibrations of the vibration member101, the rotor107that is in pressure contact with one surface of the metal part102that is an elastic member is frictionally driven, and a driving force is outputted from the gear108that functions as an output member that rotates integrally with the rotor107.

The above-mentioned conventional stacked piezoelectric element71is 10 mm in outer diameter, 2.8 mm in inner diameter, 2.3 mm in thickness, about 90 μm in the thickness of the piezoelectric layer, 2 to 3 μm in the thickness of the inner electrode, and 25 in the total number of piezoelectric layers.

On the contrary, the stacked piezoelectric element1according to this embodiment is 6 mm in outer diameter, 1.7 mm in inner diameter, about 1.6 mm in thickness, about 60 μm in the thickness of the piezoelectric layer, 2 to 3 μm in the thickness of the inner electrode, 25 in the total number of piezoelectric layers, and 24 in the number of layers having inner electrode. Also, the diameter of the through-holes is 0.1 mm. The outer diameter of the metal parts22and24which are elastic members are also 6 mm which is the same as that of the stacked piezoelectric element1.

The stacked piezoelectric element1according to this embodiment is smaller in the outer diameter than the conventional stacked piezoelectric element71, and the thickness of each of the layers is also thinned.

A method of manufacturing a stacked piezoelectric element according to this embodiment will be described. Silver and palladium powder paste are screen-printed on a green sheet made of piezoelectric ceramic powders that will form the piezoelectric layer and organic binder to form an inner electrode. Subsequently, silver and palladium powders are filled in the through hole portions, and the respective sheets are superimposed on each other and pressurized while being heated so as to be stacked. Then, a hole is penetrated in the center of the stacked sheets by machining to form an inner diameter portion before being sintered. Thereafter, after the stacked sheets are sintered at about 1100° C. in a lead atmosphere and subjected to sintering and polarizing processes, a both-surface lapping process is conducted on the stacked sheets, and the outer diameter portion is finally adjusted by a mechanical (cutting) process.

In the existing circumstances, because a positional precision of the through-holes with respect to the outer diameter in the manufacture is finally ±0.1 mm after machining, in this embodiment, the through-holes are so formed as to be set to 0.25 mm inwardly from the edge of the outer diameter. Under this condition, there is no case in which no through-holes are formed in the outer peripheral portion with the margin of 0.1 mm at the minimum.

In order to reduce an area of the insulating portion in the periphery of the through-hole as much as possible, the through-hole is allowed to approach the edge of the outer diameter as much as possible. Also, the insulating portion (non-electrode portion) in the periphery of each the through-hole includes the outer diameter edge and a slit so as to be shaped into a fan which is substantially ¼ of a circle. In this embodiment, each the through-hole is in the vicinity of the slit, but if the through-hole is formed at a position apart from the slit, it is desirable that the insulating portion in the periphery of the through-hole is shaped into a substantially semi-circle including the edge of the outer diameter. The radius of the insulating portion from the center of the through-hole is set to about 0.5 mm, and the slit that divides a plurality of electrode layers is set to about 0.4 mm.

Those values are dimensions by which the insulation is surely taken in use, and are determined taking into consideration the positional displacements of the respective electrode portions of the stacked piezoelectric element and the through-holes in the manufacture, the use conditions and so on. If an improvement of the manufacturing technique is advanced, the stacked piezoelectric element1can be further reduced.

In the stacked piezoelectric element1according to this embodiment, the through-holes6and the surface electrodes7are made to extremely approach the outer diameter end side of the element, to thereby reduce an area of the insulating portion around each the through-hole. In addition, each the inner electrode is extended up to a region ranging from the outer diameter portion to the inner diameter portion (a region indicated by hatching in FIG.1). With this structure, the area of the piezoelectric active portion of the stacked piezoelectric element1can be enlarged as compared with the conventional one.

As a result, the rotation speed of the vibration wave motor, the rotating torque or the drive efficiency can be improved. That is, the vibration wave motor can be more downsized with the similar level in performance.

FIG. 2shows a second embodiment of the present invention.

The stacked piezoelectric element11according to this embodiment is different from that shown inFIG. 1in that the through-holes16are formed in four in the vicinity of the inner diameter and the outer diameter, respectively. The method of manufacturing the stacked piezoelectric element11and the driving method are identical with those of the stacked piezoelectric element1shown in FIG.1.

In the second layer to the 25th layer except for the first layer that is a surface layer, piezoelectric layers12and13are alternately disposed one by one. A cross-shaped slit (non-electrode formation portion) that passes through diameter portions is formed on a surface of each of the piezoelectric layers12and13. Through the slits, the inner electrode14is divided into four segments consisting of electrode portions14-1,14-2,14-3and14-4by the slit, and the inner electrode15is divided into four segments consisting of electrode portions15-1,15-2,15-3and15-4. Those electrode portions reach the edges of the outer diameter and the inner diameter of the disc-shaped piezoelectric member.

Through-holes16indicated by black circles in the figure are formed extremely in the vicinity of the outer diameter and the inner diameter of each piezoelectric layer. In this embodiment, all of the dimensions of the stacked piezoelectric element are identical with the stacked piezoelectric element1shown inFIG. 1except for the positions at which the through-holes are formed, and the through-holes16are formed such that the inner side of the outer diameter is 0.25 mm and the outer side of the inner diameter is 0.25 mm. With this dimensions, the through-holes are not exposed to the outer periphery thereof. Then, each of the insulating portions (non-electrode portion) is made to approach the edge of the outer diameter or the inner diameter as much as possible so as to be shaped into a substantially semicircle with the through-hole used as its center, to thereby reduce the area of the insulating portion as much as possible.

In the piezoelectric layers12that constitute the second layer, the fourth layer, the sixth layer, . . . , and the 24th layer, each of the through-holes16formed in the vicinity of the outer diameter passes through the electrode portion, and each of the through-holes16formed in the vicinity of the inner diameter passes through the non-electrode portion. In the piezoelectric layers13that constitute the third layer, the fifth layer, the seventh layer, . . . , and the 25th layer, each of the through-holes16formed in the vicinity of the inner diameter passes through the electrode portion, and each of the through-holes16formed in the vicinity of the outer diameter passes through the non-electrode portion. Since the 25th layer is a lowermost layer and no layer is disposed below the 25th layer, no through-hole16is disposed.

FIG. 3is a diagram in which the stacked piezoelectric element11is incorporated in the vibration member101that constitutes the bar-shaped vibration wave motor100. The stacked piezoelectric element11and a wiring substrate119are disposed between the metal parts102and103which are elastic members of the vibration member101, and fitted by fastening a bolt104. The wiring substrate119comes in close contact with the stacked piezoelectric element1by a nipping force exerted at this time. The rotor107comes in pressure contact with the metal part102through the spring105and the spring support member106.

The stacked piezoelectric element11shown inFIG. 2has the through-holes on the inner diameter portions which is different from that of FIG.1. This structure has such an advantage that a plurality of through-holes are dispersed toward the outer diameter side and the inner diameter side with the result that a margin can be provided in the space of the wiring electrode pattern of the wiring substrate119to simplify the design. This advantage in the actual use is significant in the development of a compact vibration wave motor. Moreover, the same performance as that of the stacked piezoelectric element1shown inFIG. 1is provided as the driving source of the vibration wave motor.

FIG. 4is a third embodiment of the present invention.

A stacked piezoelectric element according to this embodiment is different from that shown inFIG. 1in the positions at which the through-holes are formed. The through-holes of the stacked piezoelectric element1shown inFIG. 1are formed in the vicinity of the outer diameter of the stacked piezoelectric element1, but the through-holes26of the stacked piezoelectric element21according to this embodiment are formed on the outer diameter end of the stacked piezoelectric element21.

The above-mentioned conventional stacked piezoelectric element is 10 mm in outer diameter, 2.8 mm in inner diameter, about 2.3 mm in thickness, about 90 μm in the thickness of the piezoelectric layer, 2 to 3 μm in the thickness of the inner electrode, and 25 in the total number of piezoelectric layers.

The stacked piezoelectric element21according to this embodiment is specifically 6 mm in outer diameter, 1.7 mm in inner diameter, about 1.6 mm in thickness, about 60 μm in the thickness of the piezoelectric layer, 2 to 3 μm in the thickness of the inner electrode, 25 in the total number of piezoelectric layers, and 24 in the number of inner electrode layers. Also, the diameter of the through-holes is 0.35 mm. The outer diameter of the metal parts22and23which are elastic members are also 6 mm which is the same as that of the stacked piezoelectric element21.

The stacked piezoelectric element21according to this embodiment is smaller in the outer diameter than the conventional stacked piezoelectric element71, and the thickness of each of the layers is also thinned.

However, a difference in the rotation speed of the vibration wave motor and the rotary torque hardly occurs between the vibration wave motor140in which the stacked piezoelectric element71is incorporated and the vibration wave motor in which the stacked piezoelectric element21is incorporated.

A method of manufacturing the stacked piezoelectric element according to this embodiment will be described. Holes for forming the through-holes are pierced in a green sheet made of piezoelectric ceramic-powders which will form the piezoelectric layer and organic binder, and silver and palladium powder paste are filled in the holes. Then, silver and palladium powder paste which will form the inner electrode are screen-printed on the green sheet, and the respective sheets are superimposed on each other and pressurized while being heated so as to be stacked. Then, a hole is penetrated in the center of the stacked sheets by machining to form an inner diameter portion before being sintered. Thereafter, after the stacked sheets are sintered at about 1100 C in a lead atmosphere and subjected to sintering and polarizing processes, a both-surface lapping process is conducted on the stacked sheets, and the outer diameter portion is finally adjusted by a mechanical (cutting) process.

A plurality of piezoelectric layers are obtained from one large green sheet. For example, one green sheet that is formed into a rectangle is folded so as to be superimposed on each other and sintered. After being sintered, the sheet is machined into a circular outer configuration by machining.

In a completed product of the stacked piezoelectric element21, the through-holes26are shaped into a semicircle at the outer diameter ends of the piezoelectric layers22and23. However, in a state of the through-holes26before sintering, as shown inFIG. 9A, each of the through-holes26is formed in a circle (0.35 mm in diameter before sintering) indicated by oblique lines with a position that forms the outer diameter end as a center. That is because in a final process of manufacturing the stacked piezoelectric element21, while the outer diameter of the stacked piezoelectric element21is formed in a circle by machining, parts of the through-holes26are cut and the through-holes are formed in a substantially semicircle indicated by dual oblique lines in FIG.9A.

In this embodiment, the through-holes are formed at the outer diameter end. In the existing circumstances, because a positional precision of the through-holes with respect to the outer diameter in the manufacture is finally ±0.1 mm after machining, the diameter of the through-holes is set to be slightly larger, that is, 0.35 mm so that the filler within the through-holes is prevented from being scrapped off.

Also, the radius of the insulating portion which is formed into a substantially ¼ circle in the periphery of the through-hole is set to be about 0.6 mm from the through-hole on the outer diameter, and the slit that divides the electrode layer is set to be about 0.4 mm.

Those values are dimensions by which the insulation is surely taken in use as in the first embodiment, and are determined taking into consideration the positional displacements of the respective electrode portions of the stacked piezoelectric element and the through-holes in the manufacture, the use conditions and so on. If an improvement of the manufacturing technique is advanced, the stacked piezoelectric element21can be further reduced.

FIG. 5shows a fourth embodiment of the present invention.

A stacked piezoelectric element shown inFIG. 5is different from the stacked piezoelectric element11shown inFIG. 2in the positions at which the through-holes are formed. The through-holes of the stacked piezoelectric element11shown inFIG. 2are formed in the vicinity of the inner diameter and in the vicinity of the outer diameter of the stacked piezoelectric element11, but the through-holes36of the stacked piezoelectric element31according to this embodiment are formed on the inner diameter end and the outer diameter end of the stacked piezoelectric element31.

The method of manufacturing the stacked piezoelectric element31is identical with that in the third embodiment.

In the embodiment shown inFIG. 5, the through-holes which become shaped in a substantially semicircle are formed on the inner diameter end and the outer diameter end, respectively. However, all of the through-holes may be disposed on the inner diameter end side. However, as described above, the periphery of the inner diameter becomes smaller in area because of downsizing, to thereby make it difficult to design the wiring electrode pattern on the wiring substrate. Therefore, it is preferable that the through-holes are formed on the outer diameter, or dispersed on the outer diameter and the inner diameter. Similarly, in this embodiment, the stacked piezoelectric element31having the same dimensions as those of the stacked piezoelectric element21shown inFIG. 4is manufactured.

FIG. 6shows a fifth embodiment of the present invention.

A stacked piezoelectric element41according to this embodiment is identical with the stacked piezoelectric element21according to the third embodiment shown inFIG. 4except that the first layer that is a surface layer is formed of a piezoelectric layer48having not through-hole. In the second layer to the 25th layer except for the first layer, the piezoelectric layers22and the piezoelectric layers23are alternately disposed one by one. Since the 25th layer is a final layer, and no layer that is rendered conductive exists below the 25th layer, no through-hole is formed in the 25th layer.

Then, the stacked piezoelectric element41exposes the cross section of the through holes from the outer peripheral surface except for the first layer and the 25th layer. All of other forms, driving method, manufacturing method and so on are identical with those in the third embodiment.

FIG. 7is a diagram showing a structure in which the stacked piezoelectric element41shown inFIG. 6is incorporated in the vibration member121that constitutes the bar-shaped vibration wave motor120. The stacked piezoelectric element41is disposed between the metal parts122and123which are elastic members of the vibration member and fitted by fastening a bolt124. The rotor127is in pressure contact with the metal part122through the spring125and spring support member126.

The cross-sections of linear through-holes46are exposed from the outer peripheral portion of the stacked piezoelectric element41. For that reason, unlike that shown inFIG. 3, the wiring substrate129is wound around the stacked piezoelectric element41, and conduction between the external power source and the stacked piezoelectric element41are made by the exposed through-holes46.

Since the wiring substrate is made of normal polyimide resin, the vibration attenuation is large. For that reason, as compared with the structure in which the wiring substrates109and119are held between the metal parts102and103which are elastic members as shown inFIG. 3, a structure in which the wiring substrate129is not held between the metal parts122and123that are elastic members as shown inFIG. 7is very useful particularly in downsizing the vibration wave motor.

In this example, it is unnecessary to expose the through-holes from all of the layers of the stacked piezoelectric element41when the conduction between the wiring substrate129and the stacked piezoelectric element41is taken, but if there is one layer from which the cross sections of the through-holes are exposed, the stacked piezoelectric element41and the external power supply can be rendered conductive.

Alternatively, positions at which the through-holes are exposed to the outer peripheral portion may be different for each of the through-holes. In this case, because an interval of a joint portion of the stacked piezoelectric element41and the wiring substrate129becomes large, the electrode pattern is readily designed.

FIG. 8shows a sixth embodiment of the present invention.

A stacked piezoelectric element51according to this embodiment is identical with the stacked piezoelectric element21according to the third embodiment shown inFIG. 4in appearance.

The stacked piezoelectric element51according to this embodiment is different from the stacked piezoelectric element21shown inFIG. 4in the configuration of the through-hole. When manufacturing the stacked piezoelectric element21shown inFIG. 4, the through-holes26shaped in a circle of 0.35 mm in diameter are formed. If the diameter of the through-holes is larger than that value, because the electrode material filled in the through-holes increase, the costs increases, and there is a tendency that clacks are liable to occur.

Under the above circumstance, in this embodiment, two through-holes56small in diameter shown inFIG. 9Bare aligned and formed in the stacked piezoelectric element that has not yet been sintered in the radial direction of the stacked piezoelectric element. Those two through-holes56aligned in the radial direction are slightly overlapped on each other. Those two through-holes56are so formed as to have the respective centers at a regular distance outward and inward in the radial direction through the outer diameter end of the piezoelectric layer52or53that has been completed.

Those two through-holes56are aligned and formed so as to have a slightly overlapped portion along the radial direction, and thereafter sintered. Then, the electrode material filled in the stacked piezoelectric element and the piezoelectric layer per se are contracted, with the result that each of the through-holes is shaped in a substantially oval that extends in the radial direction.

In this embodiment, the diameter of each of the through-holes is set to 0.2 mm.

Since each of the through-holes is thus shaped in a substantially oval having a longitudinal axis in the radial direction, even if the positional precision of the through-holes in the manufacture is slightly deteriorated, the through-holes can be formed on the outer diameter end portion and the inner diameter end portion. All of other forms, manufacturing method, driving method and so on are identical with those in the third embodiment.

It is needless to say that the through-hole forming method can be applied to the through-holes of the stacked piezoelectric element21shown inFIG. 4, the through-holes of the stacked piezoelectric element31shown inFIG. 5, or the through-holes of the stacked piezoelectric element41shown in FIG.6.

The stacked piezoelectric elements21,31and51inFIGS. 4,5and8can be incorporated in the bar-shaped vibration wave motor shown in FIG.3. Any one of the stacked piezoelectric elements21,31and51and a wiring substrate are disposed between the metal parts102and103which are elastic members of the vibration member, and then fitted by fastening a bolt104. The wiring substrate comes in close contact with the stacked piezoelectric element21,31and51by a nipping force exerted at this time. The rotor107comes in pressure contact with the metal part102through the spring105and the spring support member106.

The stacked piezoelectric element21,31,41or51shown inFIG. 4,5,6or8reduces an area of the insulating portion in the periphery of each of the through-holes and can enlarge the area of the inner electrode as compared with the stacked piezoelectric elements1and11shown inFIGS. 1 and 2. With such structures, the area of the piezoelectric active portion of the stacked piezoelectric element can be increased more than the conventional one.

As a result, the rotation speed of the vibration wave motor, the rotating torque or the drive efficiency can be improved. That is, the vibration wave motor can be more downsized with the similar level in performance.

Also, the through-holes that are exposed to the outer peripheral portion are also effective as positioning marks in the circumferential direction of the stacked piezoelectric element when the vibration wave motor is incorporated.