JPH05335644A - Lamination-type electrostrictive/piezoelectric element - Google Patents

Abstract

PURPOSE:To prevent generation of stress breakdown due to concentration of stress strain at the boundary between an active region and an inactive region, prevent insulation breakdown, and then increase the amount of displacement to be generated. CONSTITUTION:A number of thin plates 10 where an internal electrode 14 is formed are laminated on the surface of an electrostrictive/piezoelectric material 12 and then each internal electrode is alternately connected at every other layer by a pair of external electrodes. Each thin plate is provided with an electrode leading part 16 for continuing the internal electrode to one of external electrodes and an electroless part 18 for preventing continuity between the internal electrode and the other external electrode. N types of electroless parts which are different in width are avaliable (N; an integer) >=2). Then, assuming that their relationship is W1<W2<...<Wn, each thin plate is laminated in the order of W1, W2,..., Wn, Wn, ..., W2, W1, W2,... depending on the width of the electroless part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated electrostrictive / piezoelectric actuator element. More specifically, by adopting an internal electrode structure that gives a gradual electric field intensity distribution at the boundary between the inactive region and the active region inside the element, internal stress is dispersed and damage due to stress strain is prevented. The present invention relates to a laminated electrostrictive / piezoelectric element.
The element of the present invention is useful, for example, as an actuator for opening and closing a hydraulic valve, printing for a dot printer, and precision positioning.

[0002]

2. Description of the Related Art As a laminated electrostrictive / piezoelectric element,
There are a structure in which sintered ceramic thin plates made of a piezoelectric material are laminated and bonded and integrated, and a structure in which unsintered sheets are stacked and integrally sintered. In any case, a large number of thin plates each having an internal electrode formed on the surface of the electrostrictive / piezoelectric material are laminated, and each internal electrode is alternately connected by a pair of conductors.

As a structure in which internal electrodes are partially (not over the entire surface) formed in the laminate and are connected to each other, the through holes formed in the electrostrictive / piezoelectric materials are uniform as a whole when viewed from the lamination direction. And the internal electrodes are connected to each other through the through holes (Japanese Patent Laid-Open No. 2-79482). The internal electrodes are separated from the ends by an appropriate distance so that the internal electrodes do not reach the ends at every other layer. There is a method in which the internal electrodes are exposed to the end face for each layer so that they are different on both sides, and are connected by the external electrodes.

In these laminated electrostrictive / piezoelectric elements, a portion where the internal electrodes are superposed and a predetermined driving electric field strength is applied becomes an active region (a portion where a predetermined displacement is caused by the electrostrictive / piezoelectric effect). The other parts are inactive areas.

[0005]

In the above-mentioned conventional structure, the electric field strength changes abruptly at the boundary between the active region and the inactive region. A large displacement occurs according to the electric field strength in the active region, and a displacement occurs in the inactive region without restraint, so that a large stress strain occurs and stress fracture occurs. Moreover, there is a possibility that dielectric breakdown may occur due to a rapid change in electric field strength. In order to prevent the breakdown and the dielectric breakdown of these elements, the only method is to keep the driving electric field strength low, but if this is done, an electrostrictive / piezoelectric element with a large displacement cannot be obtained.

The internal electrodes are applied to the entire surface of the electrostrictive / piezoelectric material to make the entire surface an active region, and the edges of all the internal electrodes exposed on the side surfaces are alternately covered with an electric insulator and exposed without being covered. There is also a method of connecting the inner electrode edge with an external electrode. However, this structure is more difficult to manufacture and the cost is higher as the thickness of the electrostrictive / piezoelectric material is thinner. Usually, an electrophoretic method is used to provide an electrical insulation part, but due to variations in the deposition of electrical insulation, or residual ions after dipping the laminate in a plating solution or suspension containing glass powder. Therefore, there is a drawback that dielectric breakdown is likely to occur.

An object of the present invention is to devise the electric field strength at the boundary between the active region and the inactive region so that the electric field strength at the boundary between the active region and the inactive region changes gradually in a stepwise manner. Laminated electrostriction that prevents stress breakdown due to concentration of stress strain, prevents dielectric breakdown, and increases displacement
It is to provide a piezoelectric element.

[0008]

According to the present invention, a large number of thin plates having internal electrodes partially (not on the entire surface) formed on the surface of an electrostrictive / piezoelectric material are stacked, and each internal electrode is formed by a pair of external electrodes. It is a laminated element in which every other layer is alternately connected. Therefore, each thin plate is provided with an electrodeless portion for preventing conduction between the internal electrode formed on the thin plate and the external electrode on one side. Here, the feature of the present invention resides in the shape and the stacking order of the electrodeless portion formed on each thin plate. There are n types of electrodeless portions having different widths (where n is an integer of 2 or more). If the magnitude relation of the widths is W ₁ <W ₂ <... <W _n , each thin plate is ... W ₁ , W ₂ , ..., W _n , W _n ,.
₂ , W ₁ , W ₂ , ... Are laminated in this order.

More preferably, electrode lead-out portions which are continuous with the respective internal electrodes and reach the end of the thin plate and which are electrically connected to the external electrodes are alternately provided at the same position, and there is no space between both electrode lead-out portion forming positions. The structure is such that an electrode portion is provided. The change in the width of the electrodeless portion is set substantially equal to each other. The value of n is preferably 2 or 3. Further, the thin plate is formed in a quadrangular shape, the electrode lead-out portion is located on one side of one side, the rest of the same side is an electrodeless portion, and the inner electrodes are formed on all other three sides up to the end. The structure is optimal.

[0010]

The electrostriction / piezoelectric element produces a displacement amount according to the electric field strength applied to the electrostriction / piezoelectric material. When the electrodeless portion exists inside the element, the electric field strength changes at the boundary between the electrodeless portion and the electrode portion, and stress strain occurs. The more rapidly the electric field strength changes, the greater the stress strain that occurs.

A thin plate made of an electrostrictive / piezoelectric material and partially having an internal electrode is formed according to the width of the electrodeless portion.
W ₁ , W ₂ , ..., W _n , W _n , ..., W ₂ , W ₁ , W ₂ ,
When the layers are laminated in this order, the positions of the boundary lines of the internal electrodes are sequentially displaced and the electric field strength at the element end changes gradually in a stepwise manner. Therefore, stress strain is relaxed. Also, dielectric breakdown can be prevented.

For example, the electrodeless portion has two widths (n = 2), the layer thickness is t, and the voltage applied between layers is V (electric field strength E =
V / t), the electric field strength at the end is 0, and the electric field strength at a position inside the end by a width W ₁ is E /
3. The electric field strength is E at the position that is inward from the outermost end by the width W ₂ , and the change in the electric field strength at the end is gradual. As the number of widths (the number of n) of the electrodeless portion is increased, the change in the electric field strength becomes more gradual. But,
If it is increased too much, the area of the active region becomes small, the structure becomes complicated, and the effectiveness is not improved so much,
It is preferable that n = 2 or 3.

[0013]

1 is an exploded perspective view showing an embodiment of a laminated electrostrictive / piezoelectric element according to the present invention, FIG. 2 is an electrode pattern diagram of each thin plate, and FIG. 3 is an assembly diagram. In this embodiment, the width of the electrodeless portion is 2 (n = 2). This electrostrictive / piezoelectric element has a laminated structure in which a large number of thin plates 10 each having an internal electrode formed on the surface of an electrostrictive / piezoelectric material are laminated and each internal electrode is connected by a pair of external electrodes 20a and 20b. ing. The structure may be an integrally bonded structure of sintered ceramic thin plates or an integrally sintered structure of unsintered sheets.

In this embodiment, each thin plate 10 has a quadrangular shape, and the electrode patterns formed on them are a total of four types (A to D). This is because there are two types of widths of the electrodeless portions, but there are two types of formation positions of the electrode lead portions for each of them (so that they are connected to a pair of external electrodes, respectively). In both cases, the internal electrode 14 covers most of the surface of the electrostrictive / piezoelectric material 12. The electrode lead-out portion 16 is located on one side of one side of the electrostrictive / piezoelectric material 12, the remaining portion of the same side is an electrodeless portion 18, and the inner electrodes 14 extend to the end portions of the other three sides. Electrode drawer 1
6 has a shape in which one is electrically connected to the internal electrode 14 and the other end is electrically connected to the external electrode by reaching the end of the thin plate 10. The electrode patterns A and D have the same width of the electrodeless portion 18 (W ₁ )
Moreover, the positions of the electrode lead-out portions 16 are reversed, and the electrode patterns B and C have the same width of the electrodeless portion 18 (W ₂ ).
Moreover, the position of the electrode lead-out portion 16 is reversed. However,
The width of the electrodeless portion 18 is W ₁ <W ₂ , and 2W ₁ ≈W
There is a relationship of ₂ .

A thin plate having such an electrode pattern is
A, B, C, D, C, B, A, B, ... Are laminated in this order. As a result, the electrode lead-out portions 16 are alternately located at the same position every other layer, and exposed from the end of the thin plate. Then, the electrodeless portion 18 is located between both electrode lead-out portion forming positions. Therefore, as shown in FIG.
By forming a and 20b, the internal electrodes can be alternately connected one by one. Looking at this in terms of the width of the electrodeless portion 18, two types (W ₁ <W ₂ ) having different widths are arranged in the order of W ₁ , W ₂ , W ₂ , W ₁ , W ₂ , ... In accordance with the width. Will be stacked in.

FIG. 4 schematically shows the state of the internal electrodes when the electrostrictive / piezoelectric element is viewed from the side. When the thickness of the electrostrictive / piezoelectric material is t and the voltage applied between the layers is V, the electric field strength E can be expressed by E = V / t. The electric field strength at the extreme end (position) of the element is zero because no voltage is applied because there is no electrode. The electric field strength at the position where the width W _{1 is} entered from the outermost end is three layers of electrostrictive / piezoelectric material (interval is 3
Since there are electrodes every t), V / 3t = E / 3. Furthermore, the electric field strength at the position where the width W _{2 is} entered from the outermost portion is V / t = E because the electrodes are present in each layer. Since the internal electrodes are all present inside the position, the electric field strength is E (constant). from these things,
The electric field strength distribution at the end of the element is as shown in FIG.
The electric field strength at the end of the element gradually changes gradually, and therefore stress strain can be suppressed to a small level.

By increasing the types of electrode patterns, the change in electric field strength can be made more gradual. Examples thereof are shown in FIGS. In this embodiment, the width n of the electrodeless portion is set to 3. The electrode patterns A and F have the same width of the electrodeless portion 18 (W ₁ ) and the positions of the electrode lead-out portions 16 are opposite, and the electrode patterns B and E have the width of the electrodeless portion 18. _{They are the} same (W ₂ ) and the positions of the electrode lead-out portions 16 are reversed. Further, the electrode patterns C and D have the same width of the electrodeless portion 18 (W ₃ ) and the electrode lead-out portion 16
The position of is the opposite. However, the width of the electrodeless portion 18 is W ₁ <
W ₂ <W ₃ , where W ₂ ≈ 2W ₁ and W ₃ ≈ 3
The relationship is W ₁ .

A large number of thin plates having such an electrode pattern are formed by A, B, C, D, E, F, E, D, C, B, A,
B, ... are stacked in this order. As a result, the electrode lead-out portion 1
6 are alternately arranged at the same position every other layer and exposed from the end of the thin plate. Then, the electrodeless portion 18 is located between both electrode lead-out portion forming positions. The internal electrodes are alternately connected one by one by the external electrodes. Thus, regarding the width of the electrodeless portion 18, three kinds (W ₁ <
W ₂ <W ₃ ) depends on its width, W ₁ , W ₂ , W ₃ ,
It means that W ₃ , W ₂ , W ₁ , W ₂ , ... Are laminated in this order.

FIG. 8 schematically shows the state of the internal electrodes when the electrostrictive / piezoelectric element is viewed from the side surface. The electric field strength at the extreme end (position) of the element is zero because no voltage is applied because there is no electrode. The electric field strength at the position where the width W _{1 is} entered from the outermost portion is E / 5 because there are electrodes every 5 layers. The electric field strength at the position where the width W ₂ enters from the outermost end is (E + E / 3) / 2 = 2 on average.
It is E / 3. Further, the electric field strength at the position where the width W _{3 is} entered from the outermost end is E because the electrodes are present in each layer. Since the internal electrodes are all present inside the position, the electric field strength is E (constant). The electric field strength distribution at the end of the element is as shown in FIG. The electric field strength at the end of the element changes more gradually, so that the occurrence of stress strain can be further suppressed.

The electrodes are formed by a screen printing method or the like. In the case of a bonded integrated structure of sintered ceramic plates,
It can be formed by baking silver paste or the like. In the case of a sintered integrated structure of unsintered ceramic sheets, a high melting point electrode material such as platinum is used.

The two preferred embodiments of the present invention have been described above, but the present invention is not limited to such a configuration. In each case, the electrode pattern A starts from A, B, and C, but may start from another electrode pattern. The above concept can be applied to the width n of the electrodeless portion of 4 or more. Then, although the distribution of the electric field strength at the end portion of the element can be made gentler by this, the number of kinds of required electrode patterns is increased to 2n, which makes the manufacture complicated. Therefore, in practice, the value of n is preferably about 2 or 3. Although the electrode lead-out portion is provided at the corner portion of the electrostrictive / piezoelectric material in the above-described embodiment, it is not particularly limited to the corner portion. The shape of the electrostrictive / piezoelectric material may be changed as appropriate. In each embodiment, the electrode shape that gives a stepwise electric field intensity distribution is applied to only one side of the electrostrictive / piezoelectric material, but it is also possible to apply it to some or all of the other sides.

[0022]

As described above, according to the present invention, the width of the electrodeless portion of each layer inside the element is changed and the arrangement order of the thin plates is defined, so that the electric field strength distribution at the edge of the element is gradually increased. As a result, the internal stress can be dispersed. Therefore, damage due to stress strain can be prevented. Further, since the electric field strength distribution becomes gentle, dielectric breakdown can be prevented. As a result, the laminated electrostrictive / piezoelectric element according to the present invention can be driven at a high voltage, so that even a small element can generate a large displacement.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing an embodiment of a laminated electrostrictive / piezoelectric element according to the present invention.

FIG. 2 is an explanatory view of the electrode pattern.

FIG. 3 is a perspective view after the assembly.

FIG. 4 is an explanatory diagram showing a state of internal electrodes viewed from the side surface thereof.

FIG. 5 is an explanatory diagram of an electric field strength distribution at an element end portion.

FIG. 6 is an explanatory diagram of an electrode pattern showing another embodiment of the electrostrictive / piezoelectric element according to the present invention.

FIG. 7 is an explanatory view showing a state of the internal electrodes seen from the side surface after assembly.

FIG. 8 is an explanatory diagram of an electric field intensity distribution at an element end portion.

[Explanation of symbols]

 10 Thin Plate 12 Electrostrictive / Piezoelectric Material 14 Internal Electrode 16 Electrode Leading Part 18 No Electrode Part

Claims (5)

[Claims] 1. A laminated element in which a plurality of thin plates each having an internal electrode formed on the surface of an electrostrictive / piezoelectric material are laminated and each internal electrode is alternately connected by a pair of external electrodes.
The thin plate is provided with an electrodeless portion for blocking conduction between an internal electrode formed on the thin plate and an external electrode on one side, and the electrodeless portion has n types having different widths (where n is an integer of 2 or more, The size of the width of each electrodeless portion is W ₁ <W ₂ <... <W _n ), and these thin plates are arranged according to the width of the electrodeless portion.
W ₁ , W ₂ , ..., W _n , W _n , ..., W ₂ , W ₁ , W ₂ ,
A laminated electrostrictive / piezoelectric element characterized by being laminated in this order. 2. A laminated element in which a large number of thin plates each having an internal electrode formed on the surface of an electrostrictive / piezoelectric material are laminated and each internal electrode is alternately connected by a pair of external electrodes.
Electrode lead-out portions that are continuous with each internal electrode, reach the end of the thin plate, and are electrically connected to the external electrodes are alternately present at the same position every other layer,
Further, an electrodeless portion is provided between both electrode lead-out portion forming positions, and these electrodeless portions have n types of different widths (where n is an integer of 2 or more, and the width of each electrodeless portion is large or small). Is W ₁
<W ₂ <... <W _n ), and the thin plates are arranged according to the width of the electrodeless portion, ..., W ₁ , W ₂ , ..., W _n , W _n ,
, W ₂ , W ₁ , W ₂ , ... Laminated electrostrictive / piezoelectric elements, which are laminated in this order. 3. The device according to claim 1, wherein the change in the width of the electrodeless portion is set substantially equal to each other. 4. The device according to claim 1, wherein the value of n is 2 or 3. 5. The thin plate has a quadrangular shape, an electrode lead-out portion is located on one side of one side thereof, the remaining portion of the same side is an electrodeless portion, and the other three sides are all internal electrodes up to the end portion. The element according to claim 3, wherein the element is formed.