JP2748830B2 - Multilayer electrostrictive effect element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated electrostrictive element, and more particularly, to a full-electrode laminated electrostrictive element in which the planar shape of a ceramic layer exhibiting an electrostrictive effect and the planar shape of an internal electrode layer are the same. It relates to an effect element.

[0002]

2. Description of the Related Art As shown in a perspective view of FIG. 3, a laminated electrostrictive element has a thin ceramic layer which generates distortion due to an electrostrictive effect and an external power supply circuit (not shown). An electric field corresponding to the applied driving voltage is applied to the ceramic layer 1.
And a thin layer of an internal electrode to be applied alternately to the upper and lower sides. The internal electrode layers 2 are divided into two groups so as to have the same potential every other layer. For each group, external electrode layers 3A and 3B (left side surface) are provided on each of the opposing side surfaces of the element. (The upper external electrode layer 3B is hidden and cannot be seen.) In such a structure, when a driving voltage is applied from a power supply circuit provided outside between the two external electrode layers 3A and 3B, the driving voltage is applied between the internal electrode layers 2 sandwiching the respective ceramic layers 1. Ceramic layer 1
, An electric field is applied to each of the ceramic layers 1, so that a distortion is generated in each ceramic layer 1 in accordance with the drive voltage.

[0003] As a phenomenon that causes distortion in response to an externally applied electric field, a piezoelectric effect is known in addition to the electrostrictive effect. The following description is made for an electrostrictive effect element using the electrostrictive effect, but the difference between the piezoelectric effect and the electrostrictive effect is as follows.
The magnitude of the generated strain is proportional to the electric field (piezoelectric effect)
In the following description, “electrostriction” is all “piezoelectric” because there is only a difference of whether it is proportional to the square of the electric field (electrostrictive effect).
Can be read as In the present invention, the electrostrictive effect element refers to an element that generates a strain in response to an externally applied electric field, and is defined to include both an element using the electrostrictive effect and an element using the piezoelectric effect.

In the electrostrictive effect element having the above-described structure, the thickness of the ceramic layer 1 that generates strain is, for example, 100%.
Since these ceramic layers 1 are laminated as thin as about μm and their generated strains are connected in series, a large displacement in the direction indicated by an arrow is generated between both end surfaces of the element as a whole even with a low driving voltage. It has the feature that it can be done. In particular, in the full-electrode multilayer electrostrictive effect element to which the present invention is applied, the planar shape of the ceramic layer 1 and the planar shape of the internal electrode layer 2 are made the same, and the entire area of each ceramic layer 1 is formed. Since a uniform electric field is applied, the magnitude of the generated displacement and the reliability when used repeatedly are excellent.

As is apparent from the above-described structure, generally, in a laminated electrostrictive element, a technique of electrically connecting the internal electrode layers every other layer is essential. As such a technique, for example, a technique of a through hole or a via hole used in a multilayer printed wiring board or the like can be applied. According to this method, as shown in the sectional view of the laminate in FIG. 4, a through-hole is formed in the ceramic layer 1 and the connection conductor 4 is formed in the through-hole.
And the upper and lower internal electrode layers can be sequentially connected alternately. However, in this case, for example, for the through holes for connecting the odd-numbered internal electrode layers, an insulating space is provided around the through holes in the even-numbered internal electrode layers in order to avoid contact with the connection conductor 4. Must be provided. For this reason, no electric field is applied to the peripheral portion of the through hole of each ceramic layer 1, and no distortion occurs. As a result, when a drive voltage is applied, a portion where one strain is generated and a portion where no strain is generated occur in one ceramic layer, and a large stress is generated at a boundary portion thereof, so that the generated displacement of the element is reduced. At the same time, reliability is impaired. Therefore, in the full-electrode type electrostrictive effect element,
Such through-hole (or via-hole) technology,
In other words, it is difficult to apply the technique of connecting the internal electrode layers inside the laminate, and it is absolutely necessary to connect every other internal electrode layer outside the laminate as shown in FIG. 3 as an example. .

Referring again to FIG. 3, in the multilayered electrostrictive effect element of the full-electrode type shown in FIG. 3, odd-numbered (from the upper side of the paper) exposed portions of the internal electrode layer are formed on the right side of the laminate.
A plurality of insulator layers 5A that are individually insulated are formed. Furthermore, the external electrode layer 3A is formed in a belt shape thereon. Accordingly, even-numbered (same) internal electrode layers 2
Are electrically connected to the external electrode layer 3A at the portions exposed on the right side of the laminate, and all have the same potential. On the other hand, on the left side surface opposite to the side surface on which the insulator layer 5A and the external electrode layer 3A are formed, an insulator layer 5B for individually insulating exposed portions of the even-numbered internal electrode layers, and an odd-numbered And an external electrode layer 3B (hidden and invisible) connecting the exposed portions of the internal electrode layer.

A characteristic feature of the conventional electrostrictive element shown in FIG .
The insulator layers 5A and 5B that cover the exposed portions of the internal electrode layers 2 on the side surfaces of the laminate and insulate the internal electrode layers 2 and the external electrode layers 3A and 3B are independent for each internal electrode layer . Minute
Is that formed by the release. In order to form a plurality of independent and separated insulator layers as described above, a method of selectively forming a plurality of insulator layers on a predetermined portion and a method of forming an insulator layer as a whole and leaving only the insulator layer on a predetermined portion are left. And selective removal.

[0008] The selective formation method is described in JP-B-63-1.
As disclosed in Japanese Patent No. 7354 (hereinafter, referred to as a first publication), there is a method using a screen printing method.
Japanese Patent Application Laid-Open No. 59-115579 (hereinafter referred to as "second publication") discloses a technique for forming an insulator layer by electrophoresis followed by baking as another method for selectively forming an insulator layer. It has been disclosed.

On the other hand, as a method of forming an insulator layer by selective removal, Japanese Patent Laid-Open Publication No.
The publication discloses a method disclosed in US Pat. In this method, first, an insulating material is applied to the entire side surface of the laminate by screen printing or brush coating, and then baked. Then, unnecessary portions of the insulating material are removed by precision processing such as laser processing or water jet processing, and the inside is removed. The electrode layers are exposed every other layer.

As described above, one of the major characteristics of the laminated electrostrictive effect element is that the thickness of the ceramic layer 1 is, for example,
This is as thin as about 00 μm or less. Accordingly, the width of the insulator layers 5A and 5B in the laminating direction (the direction of element displacement indicated by an arrow in FIG. 3) is also very narrow, about 100 μm. Therefore, in particular, in a full-electrode type laminated electrostrictive effect element, in order to reliably connect and insulate the internal electrode layer and the external electrode layer,
It is indispensable to form a high-quality insulator layer 5A, 5B having a thickness of about 50 μm and a width of about 100 μm at a precise position with high dimensional accuracy. The above publications all attempt to solve such technical problems.

As described above, in each of the conventional laminated electrostrictive elements having the entire internal electrode structure, the insulator layer formed on the side surface of the element is independent and separated for each exposed portion of each internal electrode layer. It consists of multiple parts. In the first and second publications, such an insulator layer is selectively formed by screen printing or electrophoresis. Further, in the third publication, it is formed by selectively removing after forming the entire surface.

However, the feature of this type of laminated electrostrictive element is that a high electric field is applied to the ceramic layer even at a low driving voltage by making the ceramic layer thin and sandwiching the internal electrode layers from above and below. In order to sufficiently exhibit the feature of the conventional technology, it is difficult to reduce the cost of the device using the conventional technology, and in some cases, adverse effects such as sacrificing the reliability of the device may occur. The description is given below.

First, in the electrostrictive effect element described in the third publication, after forming an insulating layer continuous in the longitudinal direction (laminating direction) of the laminated body, this insulating layer body is subjected to laser processing with every other layer. It is selectively removed by a mechanical processing method such as thermal processing or water jet processing.However, when the thermal processing method is used, adverse effects such as generation of thermal cracks due to heat generation during processing are caused by the ceramic layer. And the insulating layer may induce the mechanical strength and electrical reliability of the device. Further, when the insulator layer is made of an organic material, the electrical characteristics of the element may be degraded due to the adhesion of carbon generated by the burning of the insulating material. On the other hand, the mechanical processing method generates a mechanical crack such as a micro crack at the time of processing, and similarly to the case of the thermal processing method, may cause a decrease in mechanical strength and a reduction in reliability during element driving. Furthermore, the formation of the insulator layer by such selective removal requires an additional step of partially removing the insulator layer in addition to the step of forming the insulator layer. It is difficult to remove all unnecessary portions of the insulator layer at once, and unnecessary portions must be removed one by one. Therefore, it takes a lot of processing time and is very disadvantageous in terms of cost. These effects become more remarkable as the number of layers is increased to improve the characteristics of the device.

On the other hand, in the method of selectively forming an insulator layer described in the first and second publications, a thermal and mechanical method as in the element described in the third publication is used. There is no problem such as deterioration of mechanical / electrical performance or deterioration of reliability due to stress. However, on the other hand, since it is necessary to selectively form the insulator layer in a narrow region, if an attempt is made to give the insulator layer a sufficient dielectric strength,
There are problems such as restrictions on thinning the ceramic layer and difficulty in reducing the cost.

For example, it is assumed that a practical electric field intensity applied to the ceramic layer is about 1.5 kV / mm.
In addition, glass (strength of dielectric breakdown: about 50 k)
V / mm or less), and in consideration of the transient phenomenon of the driving voltage and the long-term reliability of the element, the strength of the dielectric breakdown of the glass is estimated to be 1/10 of the above value. At this time, theoretically, the required dielectric strength is obtained when the thickness of the glass insulator layer is about 30 μm.

Here, as described in the first publication, when screen printing is used to form an insulator layer, the formation of a defective portion is inevitably avoided in the actual insulator layer formed. 50 μm minimum for practical use as body layer
A certain thickness is required. The thickness of this insulator layer is 50 μm
Is the minimum distance between the internal electrode layers, that is, the minimum thickness of the ceramic layer. The ceramic layer having such a thickness can be stably mass-produced even under the present circumstances due to the development of the lamination technology of the multilayer ceramic capacitor, and can be sufficiently thinned. However, on the other hand, considering the positioning accuracy and pattern dimensional accuracy in the current screen printing, a space of about 50 μm is required on both sides of each insulator layer, and the thickness of the ceramic layer does not need to be at least about 100 μm. Not be. In this way, an element having a thickness of each ceramic layer of 100 μm, a thickness of each insulator layer of 50 μm, a width in the stacking direction of 100 μm, and a driving voltage of 150 V is obtained. In short,
In the case of an element using screen printing for forming the glass insulator layer, the thickness of the ceramic layer is limited by the limit of the technology for forming the glass insulator layer and cannot be made sufficiently thin, and it can be said that the driving electric field cannot be further increased. .

On the other hand, the insulator layer forming technique based on the electrophoresis method disclosed in the second gazette does not cause displacement of the insulator layer with respect to the internal electrode layer due to the principle of formation thereof, so that the screen printing is performed. It is suitable for forming a fine and high-quality glass insulator layer as compared with the formation of an insulator layer by the method described above. However, in the electrostrictive effect element to which this technology is applied, the step of forming a temporary electrode, the step of masking the exposed portion of the internal electrode layer, and the step of electrodeposition are performed only for electrophoresis. It is necessary twice each for each side. Moreover, the electrical characteristics of the formed insulator layer are affected by the electrodeposition state of the insulator layer,
This electrodeposition condition is sensitive to the temperature and concentration of the bath, and its thickness and shape are easily affected by the voltage and time during electrodeposition.Therefore, in the actual manufacturing process, it is very important to control these electrodeposition conditions. If not strictly performed, the non-defective rate will be reduced.
As described above, in the electrostrictive effect element in which the insulator layer is formed by electrophoresis, it is necessary to reduce the manufacturing cost because the manufacturing process is complicated, the management of the manufacturing conditions is difficult, and the yield rate is easily varied. It's not easy.

The above-described insulator layer on the side surface of the element is connected to each internal electrode.
The device function associated with an independent and separate structure for each pole
Reduction of mechanical strength, deterioration of electrical characteristics, reduction of manufacturing cost
The difficulty is that the insulator layer must be
No) Avoid using continuous strips
Can be. FIG. 5 shows such a band-shaped insulator layer.
1 shows a perspective view of an example of a laminated electrostrictive element. As shown in this figure
The electrostriction effect element is disclosed in Japanese Patent Application Laid-Open No. 3-225975
Below, referred to as a fourth publication).
Eta element, which is continuous on the side surface of the laminate in the laminating direction.
A strip-shaped insulator layer 51A is formed. External electrode 3
1A is formed in a comb-teeth shape on the strip-shaped insulator layer 51A.
Have been. The teeth of each comb of the external electrode 31A are
The end protrudes from the insulator layer 51A to expose the internal electrode 2.
Connected to the unit.

The insulating layer is formed in a continuous band shape and
The electrodes are comb-shaped, which will be described in detail later.
As described above, the insulator layer is separated for each internal electrode,
The above problems are solved. The electrostrictive effect shown in FIG.
The element has a pair of external electrodes on opposite sides of the element.
The structures are formed one by one, as shown in FIG.
As shown, two external electrodes are connected to the same band insulator on one side.
Even if the structure is arranged side by side on the layer 51,
The same effect as solid can be obtained.

[0020]

As described above, the element
Insulation layer on the side is independent and separated for each internal electrode
Decrease in mechanical strength and electrical characteristics of the device
Problems such as deterioration of the manufacturing cost and difficulty in reducing the manufacturing cost
(Not an independent, separated structure)
Can be avoided by doing

However, when the insulator layer is continuous in the laminating direction,
In the case of a helical structure, the generated displacement of the element is reduced
With side effects. The insulator layer is located in the stacking direction
Where the displacement is constrained, this is called a continuum
In case of separate and independent structure for each internal electrode
Because the contact area between the insulator layer and the laminate increases.
is there.

Therefore, according to the present invention, the internal electrode has a full-surface electrode structure.
A continuous strip-shaped insulator layer and comb-shaped external
In a laminated electrostrictive effect element of a type having
Due to separate and independent layers for each internal electrode
Of the mechanical strength, electrical characteristics and
Ensuring the advantage of solving the difficulty of reducing manufacturing costs
While increasing the amount of displacement generated by the element.
Things.

The laminated electrostrictive effect element of the present invention is a laminate of a laminate in which ceramic layers exhibiting an electrostrictive effect and internal electrode layers having the same planar shape as the ceramic layer are alternately laminated. A first insulator layer that is continuous in a band shape in the laminating direction and partially covers an exposed portion of the internal electrode layer to the first side surface, on a first side surface parallel to an axis along a direction; A first external electrode provided on a first insulator layer and electrically connecting an exposed portion of the first internal electrode layer disposed on every other one of the internal electrode layers to the first side surface; A layer is provided, and on the second side surface parallel to the axis along the stacking direction of the stacked body, the exposed portion of the internal electrode layer exposed to the second side surface in a band shape in the stacking direction is partially formed. A second insulator layer covering the second insulator layer, the second electrode layer being provided on the second insulator layer; A second external electrode layer that electrically connects an exposed portion of the second internal electrode layer, which is different from the internal electrode layer, to the second side surface, wherein the first external electrode layer and the second external electrode layer are connected to each other. In the stacked electrostrictive effect element having a structure in which a portion connected to each internal electrode layer has a planar shape protruding in a comb-like shape from each insulator layer, the first insulator layer and the first insulator layer The planar shape of the second insulator layer is changed to a corner between the comb-shaped protrusions of the first external electrode layer and the second external electrode layer on a side parallel to the stacking direction. of
It is characterized by having a shape having a dent drawn with no smooth lines .

Further, in the laminated electrostrictive element according to the present invention, in the above-described laminated electrostrictive element, the side parallel to the laminating direction has no corner between the recess and a portion other than the recess.
It is characterized by being connected by smooth lines .

[0025]

Next, a preferred embodiment of the present invention will be described with reference to the drawings.

First, the laminated electrostrictive effect element of the present invention
In order to facilitate understanding of the manufacturing process of FIG.
Reference as shown in FIG. 7 in which the insulator layer has a continuous band structure.
Using the laminated electrostrictive effect element of the example,
The effect of the continuation-shaped insulator layer will be described.

FIG. 5 is a perspective view of the first reference example . Referring to FIG. 5 and FIG. 3, the reference example conventional entire internal power
The difference from the polar laminated electrostrictive element is that the insulator layer 51
A, 51B (The insulator layer 51B is not shown in the figure because it is formed on the side surface on the hidden side of the laminate)
And the structure of the external electrode layers 31A and 31B (same as above), particularly the planar shape when viewed from the direction perpendicular to the side surface of the element. The insulator layer in this reference example is different from the prior art in that the insulator layers 5A and 5B of the conventional device each consist of an isolated portion covering only the exposed portion and its periphery for each internal electrode layer. It has a continuous shape in the direction of a band. or,
The external electrode layer 31A (31B) of the present reference example is provided in a strip shape on the insulator layer 51A (51B). Only the portion connected to the exposed portion of the internal electrode layer 2 protrudes in a comb shape from the insulator layer 51A (51B) and electrically connects the odd-numbered (even-numbered) internal electrode layer 2. The insulator layer and the external electrode layer are formed by a screen printing method as described later. The thickness of the ceramic layer 1 is 110 μm
m.

The present inventor produced this reference example as described below. First, for example, Pb (Zr, Ti) O
A green sheet is prepared by mixing a polyvinyl butyral resin powder as an organic binder with a multi-component solid solution ceramic powder having a perovskite crystal structure as described above. Then, a silver-palladium paste to be an internal electrode layer is screen-printed on the entire surface and dried.
The layers are laminated and sintered at a high temperature of 1000 ° C. or more to form a laminated sintered body.

Next, a glass paste to be the insulator layer 51A is screen-printed and dried on the right side surface of the opposing side surfaces of the laminated sintered body. At this time, a band-like pattern as shown in FIG. 5 is used. This band-shaped glass paste has a thickness of 50 μm or more, and a width (width in a direction along the exposed portion of the internal electrode layer) is １ ／ of a width (same as above) of the laminated sintered body. Subsequently, on the opposite left side surface, similarly, a glass paste to be the insulator layer 51B (hidden and invisible) is screen-printed and dried. Body layer 51A, 5
1B (same as above).

Next, a silver paste to be the external electrode layer 31A is screen-printed and dried on the side surface on which the glass insulator layer 51A is formed. As shown in FIG. 5, the printing pattern of the silver paste is continuous in a band shape on the insulator layer 51A, and a part thereof protrudes in a comb-like shape in a direction perpendicular to the band portion and is odd-numbered (from the upper side of the paper). Are connected to the exposed portions of the internal electrode layer 2 of FIG. Similarly, the external electrode layer 31B is formed on the side surface on which the glass insulator layer 51B is formed.
Screen-print silver paste (hidden and invisible). The printed pattern of the silver paste is a pattern connected to the exposed portions of the even-numbered (from the upper side of the paper) internal electrode layers of the internal electrode layers. Thereafter, both surfaces are simultaneously fired at a temperature of 650 ° C. to simultaneously form the external electrode layers 31A and 31B. Each of these external electrode layers has a thickness of 10 μm and a width in the stacking direction of a comb-tooth-like portion that is in electrical contact with the internal electrode layer is 30 μm.
μm, and the width of the band-shaped portion on the glass insulator layer (the width in the direction along the exposed portion of the internal electrode layer) is ／ of the width of the glass insulator layer (the same).

Thereafter, lead wires (same as above) for connection to an external drive power supply circuit (not shown) are soldered to the external electrode layers 31A and 31B to complete the present reference example .

In the present embodiment , the width in the stacking direction of the comb-tooth-shaped protrusions of the external electrode layer for establishing conduction with the exposed portions of the internal electrode layer 2 is set to 30 μm, but this width is made wider than necessary. No need. This is because the electrostrictive effect element is basically not a current-driven element but a voltage-driven element. That is, in the electrostrictive effect element, the contact between the exposed portion of the internal electrode layer and the external electrode layer may be, in the extreme case, merely an electrical contact to transmit only the voltage. Therefore, it is not necessary to increase the contact area in consideration of the voltage drop due to the contact resistance between the internal electrode layer and the external electrode layer and the voltage drop due to the resistance component of the external electrode layer. On the other hand, in the electrostrictive effect element described in the first publication, the electric field applied to the ceramic layer, in other words, according to the strength of the electric field applied between the internal electrode layer and the external electrode layer with the glass insulator layer interposed therebetween. ,
This limits the thickness of the ceramic layer, as the width of the glass insulator layer must be kept above a certain level.

Now, referring to FIG. 6 (a) showing an enlarged main part of a side surface of a conventional electrostrictive element in which an independent insulator layer is formed for each internal electrode layer, the thickness of each ceramic layer 1 is shown. T
_C1, the width of the insulating layer 5A and w _1, the insulator layer 5A is for the internal electrode layer 2 _{n + 1,} (in the figure, indicated by a solid line) a normal position and displaced from a distance d (equal, (Indicated by dashed lines).
At this time, since the insulator layer 5A must not cover the adjacent internal electrode layer 2 _n , (1/2) w ₁ + d <t _C1 must be satisfied. On the other hand, since the dielectric strength between the internal electrode layer 2 _{n + 1} and the external electrode layer must be ensured, (1/2) w ₁ -d ≧ t _BD must be satisfied (however, _tBD is the thickness of the insulator layer 5A for obtaining a necessary dielectric strength).

Therefore, the minimum value t of the thickness of the ceramic layer 1
_C1min is represented by t _C1min > t _BD + 2d from the following equations.

On the other hand, with reference to FIG. 6B which shows an enlarged view of a main part of the element side surface of this embodiment , each ceramic layer 1
Is the thickness of t _C2 , and the width of the comb-like portion of the external electrode layer 31A is
_{2. If} the amount of displacement of the external electrode layer 31A with respect to the internal electrode layer 2 _{n + 1} is d, the external electrode layer 31
(Shown by a broken line) A is from having to keep the contact with the internal electrode layer 2 _{n + 1} and not contacting the internal electrode layer 2 _n, the thickness t _C2 of each ceramic layer 1 , (1/2) w ₂ + d <t _C2, and (1/2) w ₂ −d> 0.

Accordingly, the ceramic layer 1 in this embodiment is
The minimum value t _C2min of the thickness of the following equation is t _C2 ≧ 2d from the following equations.

Here, comparing the equations, it is found that the conventional electrostrictive effect element in which an insulator layer is independently formed for each internal electrode layer has a good effect even if the precision of the insulator layer formation is improved. While the thinning of the ceramic layer is subject to the limitations associated with the dielectric strength of the insulator layer, in this reference example, it is possible to reduce the thickness of the ceramic layer by improving the accuracy of screen printing. See what you can do. Especially,
In electrostrictive effect element of the first publication to use screen printing to form the present embodiment similarly to the insulating layer, the difference of the effects of the present embodiment is remarkable.

Further, in the present embodiment , since the insulator layer and the external electrode layer are formed by screen printing, unlike the electrostrictive effect element described in the second publication, there is no need to form any insulator layer. No new technology or manufacturing process is required, and of course, no manufacturing equipment and complicated manufacturing condition management are required. Therefore, the present embodiment can greatly reduce the manufacturing cost as compared with the electrostrictive effect element described in the second publication. In the present embodiment, as an example, the number of processing steps per 1000 pieces can be reduced to 1/3 of that in the case of electrophoresis.

Further, as in the electrostrictive effect element described in the third publication, the thermal and electrical characteristics and the reliability are not deteriorated due to the selective removal of the insulator layer. .

In this embodiment , the insulator layers 51A (51B)
Has a continuous band shape, so that the band-shaped inorganic insulator layer reduces the amount of displacement caused by restricting the strain generation of the ceramic layer on the side of the element, and the insulator when repeated displacement occurs. It is somewhat disadvantageous in comparison with the electrostrictive effect elements described in the first and second publications in that a failure occurs due to stress applied to the layer. However, in recent years, the use of this type of electrostrictive effect element has been widespread, and thus, for example, a mass flow controller (precision gas flow control device) used in a semiconductor manufacturing apparatus, a mirror for positioning an optical fiber, or a mirror in an optical device. In applications where the displacement is relatively small, such as about 10 μm or less, such as for position control, in applications where DC servo-like operations are not repeated frequently, and when it is easy to replace in case of failure, The advantage of low cost can be exhibited.

Here, in order to reduce the amount of displacement generated and the occurrence of failure due to the above-mentioned band-like inorganic insulator layer, as described in the second publication, an organic material based material having elasticity is used. It is preferable to use an insulator layer. Conventionally, organic insulating materials have not had sufficient dielectric breakdown strength as compared with inorganic insulating materials, but in recent years, the electrical properties of organic materials have been significantly improved. Since the dielectric breakdown strength is several hundred kV / mm, which is not inferior to that of glass, it can be practically used as a material for an insulator layer of an electrostrictive effect element.

In the above-described reference example , the insulator layer 51A
And a side surface (right side surface) on which the external electrode layer 31A is formed;
Although the side surface (left side surface) on which the insulator layer 51B and the external electrode layer 31B are formed is different from each other, these surfaces may be the same side surface. Further, as shown in the perspective view of FIG. 7, the external electrode layer 31A and the external electrode layer 31B may have a structure in which the same one insulator layer 51 is shared on the same side surface.

Next, a description will be given of an embodiment of the present invention in which a reduction in the amount of displacement caused by the above-mentioned band-shaped insulator layer and occurrence of a failure are reduced. FIG. 1 shows a laminated type according to an embodiment of the present invention.
It is a perspective view of an electrostriction effect element . In the following description, for the sake of simplicity, the insulator layer 52A on the right side of the two insulator layers opposed to each other will be described as an example.

Referring to FIG. 1, the present embodiment employs an insulating layer 5
The pattern of 2A is different from that of the reference example shown in FIG. Pattern of the insulator layer 52A in the present embodiment, as shown in FIGS. 1 and 2 (a), an insulator layer 52A
The semi-circular recess 6 is provided between the comb-shaped protrusions of the external electrode layer 31A.

The provision of the recess 6 reduces the contact area between the side surface of the laminate and the insulator layer 52A. Further, for example, as can be seen from a comparison between a straight cylindrical metal pipe and a bellows-shaped metal pipe, the insulating layer 52A has elasticity due to the shape effect provided by the concave portion 6. In the present embodiment, by reducing the contact area and imparting the elasticity, the restraining force of the insulator layer 52A against the displacement of the stacked body and the resulting reduction in the amount of displacement are reduced.

When a vertical force is applied to the insulator layer 52A as the laminate is displaced in the vertical direction on the paper,
In the recess 6, the tensile force on the side of the insulator layer 52A is dispersed. Therefore, for example, as shown in FIG. 2A, even when a minute defect occurs at the time of screen printing in the concave portion 6, the concentration of the stress on the minute defect is as shown by a short arrow in FIG. Be relaxed. On the other hand, in the linear insulator layer 51A shown in FIG. 2B, there is no dispersion of the tensile force at the side of the insulator layer 51A as described above. As a result, when a small defect similar to that described above occurs in the peripheral portion of the insulator layer 51A, a large concentration of stress occurs at this defective portion as indicated by a long arrow in the drawing, and displacement is repeated. Accordingly, the rupture of the insulator layer 51A proceeds from this defect. Therefore, if the density of the micro defects generated on the side portions of the insulator layer is the same between the present embodiment shown in FIG. 2A and the linear insulator layer shown in FIG. In this embodiment, the probability of rupture from a microdefect in the layer is lower, and there is less failure when the element is repeatedly displaced. still,
The shape of the recess 6 is not limited to a semicircle. It may be a part of an ellipse or a part of a sine curve. Furthermore,
A shape formed by connecting a plurality of straight lines smoothly without any corners may be used.

In the above-described embodiment, the concave portion 6 of the insulator layer 52A and other portions (flat portions in the longitudinal direction of the strip-shaped insulator layer) are formed.
(The edge of the line) is connected at an angle . Therefore, generation site of minute defects during screen printing, the contact
There is a small possibility that stress will be concentrated on the straight portion other than the sharp corner portion or the concave portion 6 of the connecting point and the element will fail, although this is small. Failure of the element due to such a cause can be further reduced by forming the pattern of the insulator layer into the shape shown in FIG. That is, referring to FIG. 2C, the pattern of the insulator layer 53A shown in FIG. 2C is such that the portion corresponding to the comb-shaped protrusion of the external electrode layer is formed in a semicircular convex shape, and the concave portion 6 is smoothly formed. Connected to In the insulator layer 53A having such a shape, the tensile force is dispersed in any part around the insulator layer.
The occurrence of device failures due to minute defects is reduced. Here, in this example, the convex semicircle and the concave semicircle are continuous, but the shape of each is not limited to the semicircle. A similar effect can be obtained even if it is a part of an ellipse or a sinusoidal curve. Of course, the external electrode layer of the insulator layer
The part corresponding to the comb-shaped protrusion of
And smoothly connect the straight line to the semicircular recess
However, the effect of stress dispersion can be obtained.

In the embodiment described so far, the pattern of the external electrode layer 31A is formed in such a shape that the comb-like projections protrude in both directions with respect to the band-like portion as shown in FIG. Although the pattern in which the tooth-shaped protrusions are provided back to back is used, it is a matter of course that the pattern may be such that the comb-shaped protrusions protrude only to one side as shown in FIG. Further, two insulator layers may be formed on the same side surface of the laminate, and further, at this time, two external electrode layers may share the same insulator layer, as described above. This is the same as in the reference example .

[0049]

As described above, according to the present invention, in a laminated electrostrictive effect element having an entire internal electrode structure, the exposed portion of the internal electrode layer exposed on the side surface of the laminate is insulated from the external electrode layer. Insulator layers and external electrode layers for connecting the internal electrode layers every other layer are formed by screen printing, and the shape of the insulator layers is insulated from all internal electrode layers by one continuous insulator layer. The shape of the external electrode layer is such that a portion connected to the exposed portion of the internal electrode layer protrudes in a comb-like shape from the strip portion of the insulator layer.

Thus, according to the present invention, the thickness of the ceramic layer can be determined only by the screen printing accuracy of the external electrode layer without being limited by the dielectric strength of the insulator layer. Accordingly, the ceramic layer can be made thinner and driven by a high electric field, as compared with a conventional electrostrictive element in which an independent insulator layer is formed for each internal electrode layer.

Further, unlike an element in which an insulator layer is formed by an electrophoresis method, no new process is required for forming the insulator layer and the external electrode layer, and strict control of manufacturing conditions is required. Because there is no such, manufacturing cost can be greatly reduced.

Furthermore, since there is no thermal or mechanical damage at the time of manufacturing the device as compared with a device in which the insulator layer is formed by the selective removal method, the electrical and mechanical characteristics associated with these damages are reduced. There are no problems such as deterioration and reliability.

Further, according to the present invention, a concave portion drawn by a continuous line is provided in a portion of the external electrode layer sandwiched between the comb-shaped protrusions with respect to a side extending in the stacking direction of the insulator layer. I have.
Accordingly, it is possible to reduce the amount of displacement caused by forming the insulator layer into a strip-shaped continuum and to reduce the occurrence of failure of the element due to breakage of the insulator layer when the insulator layer is repeatedly displaced.

The electrostrictive effect element of the present invention is used for applications where the amount of displacement is relatively small, for applications where DC servo operation is performed without frequent repetition, and for applications where replacement is easy in case of failure. In particular, the advantage of low cost is greatly exhibited.

[Brief description of the drawings]

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2A is a diagram showing a state of stress when a minute defect occurs in an insulator layer in the embodiment shown in FIG. FIG. 5B is a diagram showing a state of stress when a minute defect occurs in the insulator layer in the reference example shown in FIG. FIG. 4C is a diagram showing another example of the pattern of the insulator layer in the embodiment of the present invention .

FIG. 3 is a perspective view of an example of a conventional laminated electrostrictive element.

FIG. 4 is a cross-sectional view of another example of the conventional laminated electrostrictive effect element.

FIG. 5 is a perspective view of a laminated electrostrictive effect element of a reference example .

FIG. 6 shows a structure in which an insulator layer is separated and independent for each internal electrode.
In the multilayered electrostrictive element and the multilayer electrostrictive element of the reference example, the relationship between the thickness of the ceramic layer and the width of the insulator layer, and the relationship between the width of the ceramic layer and the width of the external electrode layer FIG.

FIG. 7 is a perspective view showing another example of the structure of the insulator layer and the external electrode layer in the multilayer electrostrictive effect element of the reference example .

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Ceramic layer 2 Internal electrode layer 3A, 3B External electrode layer 4 Connection conductor 5A, 5B Insulator layer 6 Depression 31A, 31B External electrode layer 51, 51A, 51B, 52A, 52B, 53A, 53
B Insulator layer

Claims (2)

(57) [Claims] A first layer parallel to an axis along a laminating direction of a laminate formed by alternately laminating ceramic layers exhibiting an electrostrictive effect and internal electrode layers having the same planar shape as the ceramic layer. A first insulator layer continuous in a strip shape in the laminating direction and partially covering an exposed portion of the internal electrode layer to the first side surface; and provided on the first insulator layer. And
A first external electrode layer that electrically connects exposed portions of the first internal electrode layer to the first side surface disposed every other of the internal electrode layers; A second insulator layer that is continuous in a band shape in the laminating direction and partially covers an exposed portion of the internal electrode layer to the second side surface, the second insulator layer being parallel to an axis along the axis; A second electrode provided on a second insulator layer and electrically connecting an exposed portion of the internal electrode layer to the second side surface of a second internal electrode layer different from the first internal electrode layer; 2 external electrode layers, and the planar shape of the first external electrode layer and the second external electrode layer is changed so that a portion connected to each internal electrode layer protrudes in a comb-like shape from each insulator layer. In the laminated electrostrictive effect element having the structure described above, the planar shape of the first insulator layer and the second insulator layer is A shape having a concave portion drawn by a smooth line with no corners at a portion between sides of the first external electrode layer and the second external electrode layer which are parallel to the layer direction and between the comb-shaped protrusions. A stacked electrostrictive effect element comprising: 2. The laminated electrostrictive effect element according to claim 1, wherein the side parallel to the laminating direction is connected by a smooth line so that the recess and a portion other than the recess have no corner. A laminated electrostrictive effect element characterized by being formed.