Multilayer ceramic structure, manufacturing method therefor and piezoelectric actuator

The present application is a continuation of International application No. PCT/JP2014/076926, filed Oct. 8, 2014, which claims priority to Japanese Patent Application No. 2013-219302, filed Oct. 22, 2013, the entire contents of each of which are incorporated herein by reference.

The present invention relates to a multilayer ceramic structure including a multilayer ceramic body in which a plurality of ceramic layers are stacked on top of one another and to a manufacturing method therefor, and in particular relates to a multilayer ceramic structure to be divided into a plurality of piezoelectric actuators, to a manufacturing method therefor and to the piezoelectric actuator.

To date, a variety of piezoelectric actuators employing a multilayer ceramic body have been proposed. For example, in a piezoelectric actuator described in below-listed Patent Document 1, a plurality of ceramic layers composed of a piezoelectric ceramic are stacked on top of one another. An active layer in which a ceramic layer and an inner electrode are alternately stacked is arranged inside the multilayer ceramic body. Inactive layers, which do not contain an inner electrode, are stacked outside of the active layer in the stacking direction. In the piezoelectric actuator, the active layer is driven and undergoes bending vibration. An electrode is not provided on a lower surface of the multilayer ceramic body.

Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-023186

In the piezoelectric actuator described in Patent Document 1, detachment of particles of the ceramic making up the multilayer ceramic body occurs due to the bending vibration. There is a risk that when detachment of particles occurs these particles will become attached to the surrounding components and so forth and have an adverse effect.

On the other hand, it has been necessary to make electrical connections for poling and inspection of electrical characteristics using side surfaces of the piezoelectric actuator described in Patent Document 1 or at the stage of a mother multilayer body for obtaining the piezoelectric actuator. Consequently, handling has been complicated. Furthermore, when the electrical characteristics have been inspected using the side surfaces, since the side surfaces are portions that undergo expansion and contraction, the measurement accuracy has not been sufficient.

An object of the present invention is to provide a multilayer ceramic structure in which detachment of particles is not likely to occur and that can be easily subjected to poling and inspection of electrical characteristics and to provide a manufacturing method for the multilayer ceramic structure.

Another object of the present invention is to provide a piezoelectric actuator in which detachment of particles is not likely to occur at the time of operation and that can be easily subjected to inspection of electrical characteristics.

A first invention of the present application is a multilayer ceramic structure extending in a first direction and for forming a plurality of piezoelectric actuators by being divided along a second direction orthogonal to the first direction. The multilayer ceramic structure according to the first invention includes a rectangular-parallelepiped-shaped multilayer ceramic body in which a plurality of ceramic layers are stacked, the multilayer ceramic body having an upper surface, a lower surface, first and second side surfaces that oppose each other and first and second end surfaces that oppose each other, the upper surface, the lower surface and the first and second side surfaces extending in the first direction and the first and second end surfaces extending in the second direction, an upper surface opposing electrode provided on the upper surface of the multilayer ceramic body, a lower surface opposing electrode provided on the lower surface of the multilayer ceramic body, inner opposing electrodes provided inside the multilayer ceramic body and arranged parallel to the upper surface and the lower surface, a first side surface electrode provided on the first side surface, and a second side surface electrode provided on the second side surface, where the upper surface opposing electrode, the lower surface opposing electrode and the inner opposing electrodes form opposing portions superposed with each other when viewed in plan, the upper surface opposing electrode extends so as to reach the first side surface and is electrically connected to the first side surface electrode, and an inner opposing electrode positioned uppermost amongst the inner opposing electrodes is led out to the second side surface and is electrically connected to the second side surface electrode, the upper surface opposing electrode, the inner opposing electrodes and the lower surface opposing electrode are led out to the first side surface electrode or the second side surface electrode alternately in a vertical direction of the multilayer ceramic structure, and a slit extending in the first direction is provided in a portion of a region between the opposing portion of the upper surface opposing electrode and the first side surface.

In a certain specific aspect of the multilayer ceramic structure according to the first invention, at the opposing portions where the upper surface opposing electrode, the inner opposing electrodes and the lower surface opposing electrode are stacked on top of one another, ceramic layers interposed between the opposing electrodes are polarized in a thickness direction and a polarization direction of each ceramic layer is opposite to that of adjacent ceramic layers.

In another specific aspect of the multilayer ceramic structure according to the first invention, the slit is provided in a portion located in a region between the opposing portion of the upper surface opposing electrode and the first side surface electrode so as to not reach end portions of the upper surface opposing electrode on both sides in the first direction.

In another specific aspect of the multilayer ceramic structure according to the first invention, the slit does not reach an end portion of the upper surface opposing electrode on one side but reaches an end portion of the upper surface opposing electrode on another side in a portion located in a region between the opposing portion of the upper surface opposing electrode and the first side surface electrode.

In another specific aspect of the multilayer ceramic structure according to the first invention, the upper surface opposing electrode is divided into a first upper surface opposing electrode portion and a second upper surface opposing electrode portion by the slit, and the slit includes a silt main portion extending in the first direction, a first slit extending portion extending from an end portion of the silt main portion on one side in the first direction so as to reach the first side surface of the multilayer ceramic body, and a second silt extending portion extending from another end of the silt main portion in the first direction so as to reach the first side surface electrode, the slit is surrounded by the first upper surface opposing electrode portion, the second upper surface opposing electrode portion is surrounded by the slit, and the first upper surface opposing electrode portion and the second upper surface opposing electrode portion are provided so as to reach the first side surface.

In another specific aspect of the multilayer ceramic structure according to the first invention, an inspection electrode provided on the upper surface of the multilayer ceramic body so as to be separated from the upper surface opposing electrode and so as to extend in the first direction inside the slit is further included.

A second invention of the present application is a multilayer ceramic structure manufacturing method for manufacturing the multilayer ceramic structure formed in accordance with the first invention and includes a step of preparing the multilayer ceramic body provided with the upper surface opposing electrode, the inner opposing electrodes and the lower surface opposing electrode, and a step of performing poling in which different potentials are applied between the first and second side surface electrodes of the multilayer ceramic body.

In a certain specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of measuring electrical characteristics using the upper surface opposing electrode and the lower surface opposing electrode is further included.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of dividing the multilayer ceramic body by performing cutting in a direction that links the first side surface and the second side surface at a plurality of positions along the first direction after measuring the electrical characteristics is further included.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of measuring the electrical characteristics using the upper surface opposing electrode and the lower surface opposing electrode in a portion outside of the portion in which the slit is provided in the first direction after the step of dividing the multilayer ceramic body is further included.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of providing an inspection electrode on the upper surface of the multilayer ceramic body so as to be separated from the upper surface opposing electrode and so as to extend in the first direction inside the slit is further included.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of inspecting the presence or absence of a short circuit between the inspection electrode and the upper surface opposing electrode is further included.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, when forming the upper surface opposing electrode on the upper surface of the multilayer ceramic body, the slit including the slit main portion extending in the first direction, the first slit extending portion extending from one end of the silt main portion in the first direction to the first side surface, and the second silt extending portion extending from another end of the silt main portion in the first direction so as to reach the side surface of the multilayer ceramic body, and the first upper surface opposing electrode portion, and the second upper surface opposing electrode portion surrounded by the slit are provided.

In another specific aspect of the multilayer ceramic structure manufacturing method according to the second invention, a step of inspecting the presence or absence of a short circuit between the first upper surface opposing electrode portion and the second upper surface opposing electrode portion is further included.

An third invention of the present application is a piezoelectric actuator including a rectangular-parallelepiped-shaped actuator body in which a plurality of ceramic layers are stacked, the actuator body having an upper surface, a lower surface, first and second side surfaces that oppose each other and first and second end surfaces that oppose each other, a direction that links the first and second end surfaces being a first direction, an upper surface opposing electrode provided on the upper surface of the actuator body, a lower surface opposing electrode provided on the lower surface of the actuator body, an inner opposing electrode arranged inside the actuator body and provided parallel to the upper surface and the lower surface, a first side surface electrode provided on the first side surface of the actuator body, and a second side surface electrode provided on the second side surface of the actuator body, where the upper surface opposing electrode, the inner opposing electrode and the lower surface opposing electrode have opposing portions that are superposed with each other when viewed in plan, the upper surface opposing electrode is a float electrode not electrically connected to the first and second side surface electrodes, the inner opposing electrode and the lower surface opposing electrode are alternately in a vertical direction of the actuator body led out to the second side surface or the first side surface and are electrically connected to the second side surface electrode or the first side surface electrode, and a ceramic layer interposed between opposing electrodes adjacent to each other in the vertical direction among the inner opposing electrode and the lower surface opposing electrode is polarized in a thickness direction and a ceramic layer adjacent to the ceramic layer in the thickness direction is polarized in the opposite direction.

A fourth invention of the present application is a multilayer ceramic structure extending in a first direction and for forming a plurality of piezoelectric actuators by being divided along a direction orthogonal to the first direction, the multilayer ceramic structure including a rectangular-parallelepiped-shaped multilayer ceramic body in which a plurality of ceramic layers are stacked and having first and second side surfaces extending in the first direction, the multilayer ceramic body having an upper surface, a lower surface, the first and second side surfaces that oppose each other and first and second end surfaces that oppose each other, the upper surface, the lower surface and the first and second side surfaces extending in the first direction and the first and second end surfaces extending in a second direction, an upper surface opposing electrode provided on the upper surface of the multilayer ceramic body, a lower surface opposing electrode provided on the lower surface of the multilayer ceramic body, inner opposing electrodes provided inside the multilayer ceramic body and arranged parallel to the upper surface and the lower surface, a first side surface electrode provided on the first side surface, and a second side surface electrode provided on the second side surface, where the upper surface opposing electrode, the lower surface opposing electrode and the inner opposing electrodes form opposing portions superposed with each other when viewed in plan, the upper surface opposing electrode extends so as to reach the first side surface and is electrically connected to the first side surface electrode, and an inner opposing electrode positioned uppermost amongst the inner opposing electrodes is led out to the first side surface and is electrically connected to the first side surface electrode, and the inner opposing electrodes and the lower surface opposing electrode are led out to the first side surface electrode or the second side surface electrode alternately in a vertical direction of the multilayer ceramic structure.

In a certain specific aspect of the multilayer ceramic structure according to the fourth invention, a ceramic layer between the upper surface opposing electrode and the uppermost inner opposing electrode is not polarized, and at the opposing portions where the inner opposing electrodes including the uppermost inner opposing electrode and the lower surface opposing electrode are stacked on top of one another, ceramic layers interposed between the opposing electrodes are polarized in a thickness direction and a polarization direction of each ceramic layer is opposite to that of adjacent ceramic layers.

A fifth invention of the present application is a piezoelectric actuator, the piezoelectric actuator including a rectangular-parallelepiped-shaped actuator body in which a plurality of ceramic layers are stacked, the actuator body having an upper surface, a lower surface, first and second side surfaces that oppose each other and first and second end surfaces that oppose each other, a direction that links the first and second end surfaces being a first direction, an upper surface opposing electrode provided on the upper surface of the actuator body, a lower surface opposing electrode provided on the lower surface of the actuator body, inner opposing electrodes arranged inside the actuator body and provided parallel to the upper surface and the lower surface, a first side surface electrode provided on the first side surface of the actuator body, and a second side surface electrode provided on the second side surface of the actuator body, where the upper surface opposing electrode, the inner opposing electrodes and the lower surface opposing electrode have opposing portions that are superposed with each other when viewed in plan, a ceramic layer between the upper surface opposing electrode and the inner opposing electrode positioned uppermost is not polarized, in the portion where the inner opposing electrodes including the inner opposing electrode positioned uppermost and the lower surface opposing electrode are stacked on top of one another, ceramic layers interposed between the opposing electrodes are polarized in a thickness direction and adjacent ceramic layers are polarized in opposite directions in the thickness direction when two or more ceramic layers oppose each other, and the upper surface opposing electrode and the inner opposing electrode positioned uppermost are led out to the first side surface electrode, and in the portion where the inner opposing electrodes including the inner opposing electrode positioned uppermost and the lower surface opposing electrode are stacked on top of one another, the inner opposing electrodes and the lower surface opposing electrode are alternately in a vertical direction of the actuator body led out to the first side surface or the second side surface and electrically connected to the first side surface electrode or the second side surface electrode.

With the multilayer ceramic structure according to the first invention and with the second invention which is the manufacturing method therefor, a multilayer ceramic structure is provided in which detachment of particles is not likely to occur and that can be easily subjected to poling and inspection of electrical characteristics.

In addition, in the piezoelectric actuator according to the third invention, detachment of particles is not likely to occur at the time of operation and electrical characteristics can be easily inspected.

With the multilayer ceramic structure according to the fourth invention, there can be obtained a multilayer ceramic structure for obtaining the piezoelectric actuator according to the fifth invention in which detachment of particles is not likely to occur that the time of operation, and a multilayer ceramic structure can be provided that can be easily subjected to poling and inspection of electrical characteristics.

With the fifth invention, a piezoelectric actuator can be provided in which detachment of particles is not likely to occur at the time of operation and that can be easily subjected to inspection of electrical characteristics.

FIG. 1 is a perspective view of a multilayer ceramic structure according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a portion along line A-A in FIG. 1 .

FIG. 3 is a sectional view of a portion along line B-B in FIG. 1 .

FIG. 4 is a schematic plan view for explaining a step of dividing the multilayer ceramic structure along a second direction in the first embodiment of the present invention.

FIG. 5 is a perspective view illustrating a piezoelectric actuator obtained in the first embodiment of the present invention.

FIG. 6 is a perspective view illustrating a multilayer ceramic structure according to a second embodiment of the present invention.

FIG. 7 is a perspective view illustrating a multilayer ceramic structure according to a third embodiment of the present invention.

FIG. 8 is a sectional view of a portion along line A 2 -A 2 in FIG. 7 .

FIG. 9 is a sectional view of a portion along line B 2 -B 2 in FIG. 7 .

FIG. 10 is a perspective view for explaining a first modification of the multilayer ceramic structure according to the first embodiment of the present invention.

FIG. 11 is a perspective view for explaining a multilayer structure of a second modification of the multilayer ceramic structure according to the first embodiment of the present invention.

FIG. 12 is a perspective view of the multilayer ceramic structure according to the second modification of the first embodiment of the present invention.

FIG. 13 is a perspective view of a multilayer ceramic structure according to a fourth embodiment of the present invention.

FIG. 14 is a sectional view of a portion along line A 3 -A 3 in FIG. 13 .

FIG. 15 is a perspective view of a piezoelectric actuator obtained in the fourth embodiment of the present invention.

FIG. 16 is a sectional view of a multilayer ceramic structure according to a fifth embodiment of the present invention.

FIG. 17 is a sectional view of a multilayer ceramic structure according to a sixth embodiment of the present invention.

Hereafter, the present invention will be made clearer by describing specific embodiments of the present invention while referring to the drawings.

FIG. 1 is a perspective view of a multilayer ceramic structure according to a first embodiment of the present invention. FIGS. 2 and 3 are sectional views of portions along line A-A and line B-B in FIG. 1 , respectively.

A multilayer ceramic structure 1 includes a multilayer ceramic body 2 . The multilayer ceramic body 2 has a rectangular parallelepiped shape. More specifically, the multilayer ceramic body 2 has an upper surface 2 a , a lower surface 2 b , first and second side surfaces 2 c and 2 d that oppose each other, and first and second end surfaces 2 e and 2 f that oppose each other. A direction that connects the first end surface 2 e and the second end surface 2 f is a first direction. That is, the upper surface 2 a , the lower surface 2 b and the first and second side surfaces 2 c and 2 d extend in the first direction.

In addition, a direction that connects the first side surface 2 c and the second side surface 2 d is a second direction that is orthogonal to the first direction.

The multilayer ceramic structure 1 of this embodiment is used to form a plurality of piezoelectric actuators by being divided along a direction parallel to the second direction. In other words, the multilayer ceramic structure 1 is a mother structure for obtaining a large number of piezoelectric actuators.

In the multilayer ceramic body 2 , a plurality of ceramic layers composed of a piezoelectric ceramic are stacked on top of one another. A stacking direction of the plurality of ceramic layers is a direction that connects the upper surface 2 a and the lower surface 2 b.

An upper surface opposing electrode 3 is provided on the upper surface 2 a of the multilayer ceramic body 2 . A lower surface opposing electrode 4 is provided on the lower surface 2 b as illustrated in FIG. 2 and FIG. 3 .

In addition, a plurality of inner opposing electrodes 5 and 6 are provided parallel to the upper surface 2 a and the lower surface 2 b inside the multilayer ceramic body 2 .

The upper surface opposing electrode 3 is provided so as to not reach an edge formed by the first end surface 2 e and the upper surface 2 a and so as to not reach an edge formed by the upper surface 2 a and the second end surface 2 f . In other words, regions 2 a 1 and 2 a 2 in which the upper surface opposing electrode 3 is not provided are provided outside of the upper surface opposing electrode 3 in the first direction.

Although not specifically illustrated, the lower surface opposing electrode 4 provided on the lower surface 2 b does not reach regions superposed with the regions 2 a 1 and 2 a 2 .

The upper surface opposing electrode 3 has a slit 3 a . The slit 3 a has a long thin rectangular shape that extends in the first direction. As a result of the slit 3 a being provided, part of the upper surface 2 a is exposed through the slit 3 a.

The upper surface opposing electrode 3 is connected to a first side surface electrode 7 provided on the first side surface 2 c . The first side surface electrode 7 is provided so as to cover the first side surface 2 c and so as to reach to part of the lower surface 2 b . However, the first side surface electrode 7 need not reach the lower surface 2 b.

As illustrated in FIG. 2 and FIG. 3 , a second side surface electrode 8 is provided on the second side surface 2 d . The lower surface opposing electrode 4 is electrically connected to the second side surface electrode 8 .

The inner opposing electrode 5 is an inner opposing electrode that is positioned uppermost among the plurality of inner opposing electrodes 5 and 6 . The inner opposing electrode 5 is led out to the second side surface 2 d and is electrically connected to the second side surface electrode 8 . On the other hand, the inner opposing electrode 6 is led out to the first side surface 2 c and is electrically connected to the first side surface electrode 7 .

The upper surface opposing electrode 3 , the inner opposing electrode 5 , the inner opposing electrode 6 and the lower surface opposing electrode 4 are superposed with each other in a central region of the multilayer ceramic body 2 in the second direction when viewed in plan. These superposed portions form opposing portions in the present invention.

The above-described slit 3 a is provided so as to extend in the first direction in a region between the opposing portion and the first side surface 2 c.

In the multilayer ceramic body 2 , a plurality of ceramic layers 2 g , 2 h and 2 i are stacked on top of one another. In addition, as illustrated by the arrows in FIG. 2 and FIG. 3 , the ceramic layers 2 g , 2 h and 2 i are polarized in the thickness direction. More specifically, the polarization directions of the ceramic layer 2 g and the ceramic layer 2 h , which are ceramic layers that are adjacent to each other, are opposite to each other. Similarly, the polarization directions of the ceramic layer 2 h and the ceramic layer 2 i , which are ceramic layers that are adjacent to each other, are also opposite to each other. In other words, the plurality of ceramic layers 2 g to 2 i are alternately polarized in opposite directions in the vertical direction.

The ceramic layers 2 g to 2 i may be formed using a suitable piezoelectric ceramic. For example, a PZT-based ceramic may be suitably used as the piezoelectric ceramic.

On the other hand, the various electrodes such as the upper surface opposing electrode 3 , the lower surface opposing electrode 4 , the inner opposing electrodes 5 and 6 and the first and second side surface electrodes 7 and 8 may be formed of a suitable metal or alloy such as Ag, Ag—Pd or Pt.

At the time of manufacture, the inner opposing electrode 6 is printed on a ceramic green sheet having a piezoelectric ceramic as a main constituent. A ceramic green sheet on which the inner opposing electrode 5 has been printed and a ceramic green sheet on which the upper surface opposing electrode 3 has been printed are separately prepared. These ceramic green sheets are then stacked on top of one another. Next, a conductive paste for forming the lower surface opposing electrode 4 and the first and second side surface electrodes 7 and 8 is applied to the obtained multilayer body. Next, the multilayer body is fired.

After the firing the ceramic layers 2 g to 2 i are subjected to poling. In this way, the multilayer ceramic structure 1 can be obtained.

The upper surface opposing electrode 3 , the first and second side surface electrodes 7 and 8 and the lower surface opposing electrode 4 may be formed by for example applying and then baking a conductive paste or by sputtering or vapor depositing after sintering.

At the time of poling, it is sufficient that the upper surface opposing electrode 3 and the lower surface opposing electrode 4 be connected to a power supply and that a direct-current voltage be applied. Therefore, it is easy to make the electrical connections at the time of poling.

The multilayer ceramic structure 1 expands and contracts in a direction d 31 at the time of poling. Therefore, it is not likely bending will occur in the multilayer ceramic structure 1 .

Furthermore, electrical characteristics may be measured at the stage of the multilayer ceramic structure 1 . It is sufficient that the upper surface opposing electrode 3 and the lower surface opposing electrode 4 be electrically connected to a measurement apparatus when measuring electrical characteristics in this way. Therefore, the electrical characteristics can be easily measured.

In addition, since the electrical characteristics can be measured by holding the upper surface 2 a and the lower surface 2 b , the measurement accuracy is increased. This is because the electrical characteristics can be measured without there being a restriction in the direction of expansion and contraction.

In addition, at the time of poling, all the ceramic layers 2 g to 2 i expand and contract in the direction d 31 . Therefore, it is unlikely that bending will occur in the multilayer ceramic body 2 at the time of poling.

In addition, at least the opposing portions are covered by the upper surface opposing electrode 3 and the lower surface opposing electrode 4 at the upper surface 2 a and the lower surface 2 b of the multilayer ceramic body 2 . Therefore, it is unlikely that detachment of particles will occur at the time of poling or at the time of measurement of electrical characteristics.

After obtaining the multilayer ceramic structure 1 , in this embodiment, the multilayer ceramic structure 1 is divided at a plurality of positions along directions parallel to the second direction as illustrated in the plan view of FIG. 4 . In other words, the solid lines C in FIG. 4 represent cutting lines extending parallel to the second direction. By dividing the multilayer ceramic structure 1 along the plurality of cutting lines, a piezoelectric actuator 11 illustrated in FIG. 5 can be obtained. The piezoelectric actuator 11 corresponds to a portion cut from the multilayer ceramic structure 1 in the portion where the slit 3 a is provided. The electrical characteristics may be measured using the upper surface opposing electrode 3 and the lower surface opposing electrode 4 in a portion further toward the outside than the portion where the slit 3 a is provided in the first direction after dividing the multilayer ceramic body 2 .

As illustrated in FIG. 5 , in the piezoelectric actuator 11 , an actuator body 2 A of a unit piezoelectric actuator 11 is formed by the multilayer ceramic body 2 being divided. An upper surface opposing electrode 3 A is formed on an upper surface of the actuator body 2 A and a lower surface opposing electrode 4 A is formed on a lower surface of the actuator body 2 A. In addition, inner opposing electrodes 5 A and 6 A are arranged inside the actuator body 2 A. Furthermore, first and second side surface electrodes 7 A and 8 A are provided so as to cover a first side surface 2 A 1 and a second side surface 2 A 2 .

As is clear from FIG. 5 , the ceramic layers 2 g to 2 i have been subjecting to poling similarly to the case of the multilayer ceramic structure 1 illustrated in FIG. 1 , but a voltage is not applied to the ceramic layer 2 g at the time of driving. The upper surface opposing electrode 3 A is isolated from the first side surface electrode 7 A. In other words, the upper surface opposing electrode 3 A is isolated from the first side surface electrode 7 A in a portion where the slit 3 a of FIG. 4 is provided. Therefore, a voltage is not applied to the ceramic layer 2 g at the time of driving. Therefore, the ceramic layer 2 g is an inactive layer.

When a voltage is applied between the first side surface electrode 7 A and a second side surface electrode 8 A, the ceramic layer 2 h and the ceramic layer 2 i are driven as active layers and the ceramic layers 2 h and 2 i expand and contract. As described above, the ceramic layer 2 g is an inactive layer.

In the above-mentioned Patent Document 1, the upper surface of the multilayer ceramic body is covered by an electrode but an electrode is not provided on the lower surface of the multilayer ceramic body and therefore detachment of particles is likely to occur on the lower surface side.

In contrast, the upper surface of the actuator body 2 A is covered by the upper surface opposing electrode 3 A and the lower surface of the actuator body 2 A is covered by the lower surface opposing electrode 4 A even if bending occurs at the time of driving. Therefore, detachment of ceramic particles is not likely to occur.

At the time of manufacture of the piezoelectric actuator 11 , after preferably affixing a plurality of the multilayer ceramic structures 1 onto an adhesive sheet, it is preferable that the multilayer ceramic structures 1 be divided along the solid lines C in FIG. 4 as previously described on the adhesive sheet. Thus, the piezoelectric actuators 11 are preferably provided in a state in which a plurality of the divided piezoelectric actuators 11 are affixed to the adhesive sheet in this way. In this case, the electrical characteristics of the individual piezoelectric actuators 11 obtained by the division can be easily inspected while the actuators are held by the adhesive sheet.

In addition, with the piezoelectric actuator 11 , not only is it unlikely that detachment of particles will occur at the time of driving as described above, measurement of electrical characteristics can be easily performed using the lower surface opposing electrode 4 A and the first side surface electrode 7 A.

FIG. 6 is a perspective view of a multilayer ceramic structure according to a second embodiment of the present invention. In a multilayer ceramic structure 21 , a slit 3 a of an upper surface opposing electrode 3 is not closed at an end portion of the upper surface opposing electrode 3 on a second end surface 2 f side and is open toward the second end surface 2 f side. Thus, the slit 3 a may be open toward the second end surface 2 f side. Alternatively, the slit 3 a may be open toward a first end surface 2 e side rather than the second end surface 2 f side. However, it is necessary that an electrical connection be made to portions on both sides of the slit 3 a of the upper surface opposing electrode 3 in order to perform poling.

The rest of the configuration of the multilayer ceramic structure 21 is the same as that of the multilayer ceramic structure 1 and therefore the same effect as in the first embodiment is exhibited.

FIG. 7 is a perspective view of a multilayer ceramic structure according to a third embodiment of the present invention. A multilayer ceramic structure 31 of the third embodiment includes a multilayer ceramic body 32 . The multilayer ceramic body 32 has a rectangular parallelepiped shape. The multilayer ceramic body 32 has an upper surface 32 a , a lower surface 32 b , a first side surface 32 c , a second side surface 32 d , a first end surface 32 e and a second end surface 32 f . In FIGS. 7 to 9 , the first and second side surfaces 32 c and 32 d are positioned on the opposite sides to the first and second side surfaces 2 c and 2 d illustrated in FIGS. 1 to 3 . In this embodiment, an upper surface opposing electrode 33 is formed on the upper surface 32 a similarly to as in the first embodiment. In addition, as illustrated in FIG. 8 and FIG. 9 , a lower surface opposing electrode 34 is provided on the lower surface 32 b.

A silt 33 a is provided in the upper surface opposing electrode 33 . The silt 33 a extends in the first direction similarly to the slit 3 a . In this embodiment, the silt 33 a is closed at both ends in the first direction, but may be open at one end as in the above-described second embodiment.

In the multilayer ceramic structure 31 of this embodiment, an inner opposing electrode 35 is provided inside the multilayer ceramic body 32 . The inner opposing electrode 35 is led out to the second side surface 32 d and is electrically connected to a second side surface electrode 38 . The difference between this embodiment and the first embodiment is as follows.

As illustrated in FIGS. 8 and 9 , only one inner opposing electrode 35 is formed. The upper surface opposing electrode 33 is led out to the first side surface 32 c side and is electrically connected to a first side surface electrode 37 provided on the first side surface 32 c . The lower surface opposing electrode 34 is similarly electrically connected to the first side surface electrode 37 .

The multilayer ceramic body 32 includes two ceramic layers 32 g and 32 h . At the time of poling, a direct-current voltage is applied between the first and second side surface electrodes 37 and 38 . As a result, in the multilayer ceramic body 32 , the ceramic layers 32 g and 32 h undergo poling in opposite directions in the thickness direction. The polarization directions are indicated by arrows in FIGS. 8 and 9 .

A plurality of ceramic layers may be arranged inside the multilayer ceramic body as in this embodiment.

By cutting the multilayer ceramic body 32 in directions parallel to the second direction in a portion where the silt 33 a is provided, piezoelectric actuators can be obtained similarly to as in the first embodiment. In this case, as is deduced from FIG. 9 , when a voltage is driven between the first and second side surface electrodes 37 and 38 in an obtained piezoelectric actuator, a voltage is applied only between the inner opposing electrode 35 and the lower surface opposing electrode 34 , that is, only in the ceramic layer 32 h . The ceramic layer 32 g is an inactive layer.

In this embodiment as well, in the obtained piezoelectric actuator, at least regions where the opposing portions are projected onto the upper surface and the lower surface are covered by the upper surface opposing electrode and the lower surface opposing electrode. Therefore, detachment of particles at the time of driving can be effectively suppressed.

Furthermore, also in this embodiment, poling and inspection of electrical characteristics can be easily performed at the stage of the multilayer ceramic structure 31 , similarly to as in the first and second embodiments. In addition, the accuracy of electrical characteristics can be made high. In addition, the electrical characteristics can also be easily measured in a piezoelectric actuator obtained by dividing the multilayer ceramic structure 31 .

As is clear from the first to third embodiments, in the multilayer ceramic structures 1 , 21 and 31 , three or two ceramic layers are stacked on top of one another, but the number of stacked ceramic layers is not especially limited and may be an even number of 4 or more or an odd number of 5 or more.

FIG. 13 is a perspective view of a multilayer ceramic structure according to a fourth embodiment of the present invention.

A multilayer ceramic structure 41 includes a rectangular-parallelepiped-shaped multilayer ceramic body 42 . The multilayer ceramic body 42 has an upper surface 42 a , a lower surface 42 b , first and second side surfaces 42 c and 42 d , and first and second end surfaces 42 e and 42 f.

In addition, in the multilayer ceramic body 42 , ceramic layer 42 g and 42 h , which are composed of a piezoelectric ceramic, are stacked one of top of the other.

An upper surface opposing electrode 43 is formed on the upper surface 42 a . The upper surface opposing electrode 43 is different from that of the first embodiment and does not have a slit. The upper surface opposing electrode 43 is led out to an edge formed by the upper surface 42 a and the first side surface 42 c . The upper surface opposing electrode 43 is electrically connected to a first side surface electrode 47 . The first side surface electrode 47 is provided so as to cover the first side surface 42 c and so as to reach to part of the lower surface 42 b as illustrated in FIG. 14 . However, the first side surface electrode 47 need not reach the lower surface 42 b.

A lower surface opposing electrode 44 is provided on the lower surface of the multilayer ceramic body 42 . The lower surface opposing electrode 44 is provided so as to reach an edge formed by the lower surface 42 b and the second side surface 42 d . A second side surface electrode 48 is provided on the second side surface 42 d . As illustrated in FIG. 14 , the lower surface opposing electrode 44 is electrically connected to the second side surface electrode 48 .

An inner opposing electrode 45 is provided inside the multilayer ceramic body 42 . That is, one inner opposing electrode 45 is provided between two ceramic layers 42 g and 42 h.

The upper surface opposing electrode 43 , the inner opposing electrode 45 and the lower surface opposing electrode 44 are provided so that parts thereof are superposed with each other when viewed in plan, that is, so as to form opposing portions.

In the multilayer ceramic structure 41 of this embodiment, it is sufficient that a direct-current voltage be applied between the upper surface opposing electrode 43 and the lower surface opposing electrode 44 when performing poling. As a result, as illustrated by the arrow in FIG. 14 , the ceramic layer 42 h is polarized in the thickness direction. On the other hand the ceramic layer 42 g is not polarized.

Therefore, the ceramic layer 42 g is an inactive layer that is not driven in the finally obtained piezoelectric actuator.

In the multilayer ceramic structure 41 as well, poling can be performed by applying a voltage using the upper surface opposing electrode 43 and the lower surface opposing electrode 44 . Therefore polarization is easily performed. In addition, at the time of inspection of electrical characteristics, the electrical characteristics can be measured by electrically connecting the upper surface opposing electrode 43 and the lower surface opposing electrode 44 to the outside or holding the upper surface and lower surface sides. Therefore, inspection of electrical characteristics can be performed easily and with high accuracy.

At the time of obtaining piezoelectric actuators from the multilayer ceramic structure 41 , it is sufficient that the multilayer ceramic structure 41 be divided in directions parallel to the second direction orthogonal to the first direction similarly to as in the first embodiment. In this case, individual piezoelectric actuators 49 illustrated in FIG. 15 can be obtained from the portion in which the upper surface opposing electrode 43 is provided.

The piezoelectric actuator 49 includes an actuator body 42 A obtained by cutting the multilayer ceramic body 42 . An upper surface opposing electrode 43 A is formed on the upper surface of the actuator body 42 A and an inner opposing electrode 45 A is formed inside the actuator body 42 A. A lower surface opposing electrode 44 A is located on the lower surface. In addition, first and second side surface electrodes 47 A and 48 A are located so as to cover the first and second side surfaces.

Therefore, the piezoelectric actuator 49 can be driven by applying a direct-current voltage between the inner opposing electrode 45 A and the lower surface opposing electrode 44 A.

In the piezoelectric actuator 49 as well, upper and lower surfaces of opposing portions that undergo bending vibration at the time of driving are covered by the upper surface opposing electrode 43 A and the lower surface opposing electrode 44 A. Therefore, detachment of particles can be prevented with certainty. Of course, since the ceramic layer 42 g is an inactive layer, there is a risk that the multilayer ceramic body 42 will bend at the time of poling.

In this embodiment, since it is not necessary to provide the slit, the processing steps can be simplified.

In the first to third embodiments, there are portions where the upper surface opposing electrode continues in the first direction toward the outside beyond the portion where the slit is provided. These portions of the upper surface opposing electrode connected to both sides of the slit are portions that cannot be extracted as piezoelectric actuators in the first to third embodiments. Therefore, in the first to third embodiments, the number of piezoelectric actuators extracted from the multilayer ceramic structure is reduced.

In contrast, in the fourth embodiment, it is possible to cut out piezoelectric actuators from the entirety of a portion extending the whole length of the upper surface opposing electrode 43 in the first direction. Therefore, when preparing multilayer ceramic structures of the same dimensions, a greater number of piezoelectric actuators can be extracted with the fourth embodiment than with the first to third embodiments.

FIG. 16 is a sectional view of a multilayer ceramic structure according to a fifth embodiment of the present invention. A multilayer ceramic structure 51 of the fifth embodiment corresponds to a modification of the multilayer ceramic structure 41 of the fourth embodiment. That is, three inner opposing electrodes 55 a to 55 c are provided inside a multilayer ceramic body 52 in this embodiment and accordingly four ceramic layers 52 g to 52 j are stacked on top of one another. The ceramic layers 52 h to 52 j are polarized as indicated by the illustrated arrows. The inner opposing electrodes 55 a and 55 c are electrically connected to the first side surface electrode 47 . The inner opposing electrode 55 b located in the center is electrically connected to the second side surface electrode 48 .

The multilayer ceramic structure 51 of this embodiment is the same as that of the fourth embodiment except for the structure inside the multilayer ceramic body 52 being different from the multilayer ceramic body 42 of the fourth embodiment. Therefore, the same reference symbols as for the multilayer ceramic body 42 denote the remaining portions. Thus, four ceramic layers 52 g to 52 j may be formed inside the multilayer ceramic body 52 . In this case as well, the uppermost ceramic layer 52 g is not polarized and is an inactive layer.

FIG. 10 is a perspective view for explaining a first modification of the multilayer ceramic structure according to the first embodiment illustrated in FIG. 1 . In a multilayer ceramic structure 80 according to the modification illustrated in FIG. 10 , an inspection electrode 81 is provided on the upper surface 2 a of the multilayer ceramic body 2 . The inspection electrode 81 has a long, thin strip-like shape. The inspection electrode 81 extends in the above-described first direction inside the slit 3 a . In addition, the inspection electrode 81 is separated from the upper surface opposing electrode 3 with the slit 3 a interposed therebetween.

The inspection electrode 81 is composed of a conductive material such as a suitable metal. It is preferable that the inspection electrode 81 be composed of the same metal as the upper surface opposing electrode 3 . Therefore, the upper surface opposing electrode 3 and the inspection electrode 81 can be formed with the same process.

Except for the provision of the inspection electrode 81 , the multilayer ceramic structure 80 is the same as the multilayer ceramic structure 1 according to the first embodiment. Therefore, the same reference symbols are used so that description of the same portions may be omitted.

As a result of providing the inspection electrode 81 , the presence or absence of a short circuit between the upper surface opposing electrode 3 and the inspection electrode 81 can be inspected.

In the multilayer ceramic structure 1 according to the first embodiment, if the film thickness of the upper surface opposing electrode 3 is small, it is difficult to visually check whether the slit 3 a has been correctly formed. Furthermore, this check cannot be performed electrically. If the silt 3 a has not been correctly formed, there is a risk of portions of the upper surface opposing electrode on both sides of the slit 3 a in the second direction short circuiting. Therefore, there is a risk that the finally cut out piezoelectric actuator will not correctly operate.

In contrast, when the inspection electrode 81 is provided, it is possible to inspect that there is no short circuit between the upper surface opposing electrode 3 and the inspection electrode 81 . Therefore, it is possible to electrically check with certainty that no short circuit is generated at portions of the upper surface opposing electrode on both sides of the slit 3 a in the second direction.

FIG. 11 is a perspective view for explaining a manufacturing step of a second modification of the first embodiment and FIG. 12 is a perspective view of a multilayer ceramic structure of the second modification.

As illustrated in FIG. 11 , a first upper surface opposing electrode portion 3 x and a second upper surface opposing electrode portion 3 y are formed as the upper surface opposing electrode 3 on the upper surface 2 a of the multilayer ceramic body 2 . The first upper surface opposing electrode portion 3 x and the second upper surface opposing electrode portion 3 y are separated from each other by the slit 3 a . The slit 3 a includes a silt main portion 3 a 1 and first and second slit extending portions 3 a 2 and 3 a 3 . The silt main portion 3 a 1 extends in the first direction. The first slit extending portion 3 a 2 is connected to one end of the silt main portion 3 a 1 in the first direction. The first slit extending portion 3 a 2 is provided so as to reach the first side surface 2 c from the one end of the silt main portion 3 a 1 . The second slit extending portion 3 a 3 is provided so as to reach the first side surface 2 c from the other end of the silt main portion 3 a 1 in the first direction.

Although not particularly limited, the first and second slit extending portions 3 a 2 and 3 a 3 extend in the second direction.

The first upper surface opposing electrode portion 3 x is shaped so as to surround the slit 3 a when viewed in plan. In addition, the second upper surface opposing electrode portion 3 y is shaped so as to be surrounded by the slit 3 a when viewed in plan. The second upper surface opposing electrode portion 3 y has a strip-like planar shape extending in the first direction. In addition the second upper surface opposing electrode portion 3 y is provided so as to extend along an edge formed by the side surface 2 c and the upper surface 2 a.

The first upper surface opposing electrode portion 3 x includes extending portions 3 x 1 and 3 x 2 that reach from the both ends of the first upper surface opposing electrode portion 3 x in the first direction to the edge formed by the side surface 2 c and the upper surface 2 a.

Therefore, the first upper surface opposing electrode portion 3 x and the second upper surface opposing electrode portion 3 y are provided so as to be separated from each other and so as to each reach the edge formed by the side surface 2 c and the upper surface 2 a.

Next, a first side surface electrode 7 x is formed as illustrated in FIG. 12 . The first side surface electrode 7 x is provided so as to cover the first side surface 2 c . In addition, the first side surface electrode 7 x is electrically connected to the first and second upper surface opposing electrode portions 3 x and 3 y at the edge formed by the upper surface 2 a and the side surface 2 c.

A multilayer ceramic structure 82 according to the second modification illustrated in FIG. 12 is the same as the multilayer ceramic structure 1 of the first embodiment except for the upper surface opposing electrode 3 being formed as described above. Therefore, the same portions are denoted by the same reference symbols and description thereof is accordingly omitted.

In the second modification, it is sufficient that the presence or absence of a short circuit between the first upper surface opposing electrode portion 3 x and the second upper surface opposing electrode portion 3 y be electrically investigated in the state illustrated in FIG. 11 , that is, before formation of the first side surface electrode 7 x . In other words, in the case where no short circuit has occurred, it can be confirmed with certainty that the first upper surface opposing electrode portion 3 x and the second upper surface opposing electrode portion 3 y positioned on both sides of the silt main portion 3 a 1 of the slit 3 a in the first direction are insulated from each other.

Furthermore, as illustrated in FIG. 12 , the first and second upper surface opposing electrode portions 3 x and 3 y become electrically connected to each other after formation of the first side surface electrode 7 x . Therefore, poling and checking of characteristics can be performed in the same way as in the first embodiment.

FIG. 17 is a sectional view of a multilayer ceramic structure according to a sixth embodiment of the present invention. A multilayer ceramic structure 61 of the sixth embodiment corresponds to a modification of the multilayer ceramic structure 41 of the fourth embodiment. Here, a multilayer ceramic body 62 has a structure in which three ceramic layers 62 g to 62 i are arranged in order from the upper surface side. Two inner opposing electrodes 65 a and 65 b are superposed with each other with the ceramic layer 62 h interposed therebetween.

In the multilayer ceramic body 62 , the uppermost ceramic layer 62 g is not subjected to poling. The ceramic layers 62 h and 62 i are polarized as indicated by the illustrated arrows.

The rest of the configuration of the multilayer ceramic structure 61 is the same as that of the multilayer ceramic structure 41 . Therefore, the same reference symbols as for the multilayer ceramic body 42 denote the remaining portions. An odd number of ceramic layers 62 g to 62 i may be stacked inside the multilayer ceramic body 62 as in this embodiment.

The rest of the structures of the multilayer ceramic structures 51 and 61 of the fifth and sixth embodiments are the same as that of the multilayer ceramic structure 41 of the fourth embodiment. Therefore, the same effect as in the fourth embodiment is exhibited.

As is clear from the fourth to sixth embodiments, in a multilayer ceramic structure in which the uppermost ceramic layer is an inactive layer, the number of stacked ceramic layers may be an odd number or may be even number and is not particularly limited.

1 . . . multilayer ceramic structure

2 . . . multilayer ceramic body

2 A . . . actuator body

2 A 1 , 2 A 2 . . . first, second side surface

2 a . . . upper surface

2 a 1 , 2 a 2 . . . region

2 b . . . lower surface

2 c , 2 d . . . first, second side surface

2 e , 2 f . . . first, second end surface

2 g to 2 i . . . ceramic layer

3 , 3 A . . . upper surface opposing electrode

3 x , 3 y . . . upper surface opposing electrode portion

3 x 1 , 3 x 2 . . . extending portion

3 a . . . slit

3 a 1 . . . silt main portion

3 a 2 , 3 a 3 . . . slit extending portion

4 , 4 A . . . lower surface opposing electrode

5 , 5 A, 6 , 6 A . . . inner opposing electrode

7 , 7 A, 7 x . . . first side surface electrode

8 , 8 A . . . second side surface electrode

11 . . . piezoelectric actuator

21 , 31 . . . multilayer ceramic structure

32 . . . multilayer ceramic body

32 a . . . upper surface

32 b . . . lower surface

32 c , 32 d . . . first, second side surface

32 e , 32 f . . . first, second end surface

32 g , 32 h . . . ceramic layer

33 . . . upper surface opposing electrode

33 a . . . slit

34 . . . lower surface opposing electrode

35 . . . inner opposing electrode

37 , 38 . . . first, second side surface electrode

41 , 51 , 61 . . . multilayer ceramic structure

42 , 52 , 62 . . . multilayer ceramic body

42 A . . . actuator body

42 a . . . upper surface

42 b . . . lower surface

42 c , 42 d . . . first, second side surface

42 e , 42 f . . . first, second end surface

42 g , 42 h , 52 g to 52 j , 62 g to 62 i . . . ceramic layer

43 , 43 A . . . upper surface opposing electrode

44 , 44 A . . . lower surface opposing electrode

45 , 45 A, 55 a to 55 c , 65 a , 65 b . . . inner opposing electrode

47 , 47 A . . . first side surface electrode

48 , 48 A . . . second side surface electrode

49 . . . piezoelectric actuator

80 , 82 . . . multilayer ceramic structure

81 . . . inspection electrode