JPH0758373A - Stacked piezoelectric element - Google Patents

Abstract

PURPOSE:To simplify the process of connection with every other inner electrode, and also, prevent the inferiority of connection such as short circuit, etc., in a stacked piezoelectric element used as an actuator. CONSTITUTION:In a piezoelectric element where piezoelectric material films 11 and inner electrodes 12 are stacked alternately, conductive projections 16 consisting of nickel chromium are made alternately at the ends of inner electrodes 12 exposed at the side, and flat sections 16a are made by polishing the pointed ends of the conductive projections 16, and a conductive film 13, which contains copper powder 31, is formed thereon. And, a copper foil (outer electrode) 15 and alternate conductive projections 16, in its turn inner electrodes 12 are electrically connected with each other by partially compressing the conductive films 13 by the projections 16, and arranging them so that the conductive particles 31 in compressed sections may contact with the flat sections 16 of the projections thereby selectively making them conductive sections 14.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric element in which a large number of thin films of piezoelectric material are laminated and a longitudinal displacement can be obtained by applying a voltage.

[0002]

2. Description of the Related Art When manufacturing a laminated piezoelectric element, it is necessary to connect internal electrodes every other layer. However, when the conventional multilayer capacitor method is used, the internal electrode area is smaller than the cross-sectional area of the element and the electric field is However, there is a fatal defect that not only does it not occur, but the displacement is hindered and stress concentration occurs in a non-uniform part, and finally it breaks. In addition, positioning at the time of stacking is difficult, and the number of stacked layers is limited to several tens at most. For the same applied voltage, the displacement amount of the element is proportional to the number of stacked layers. It was difficult to manufacture.

In order to solve this drawback, a method of printing and laminating electrodes on the entire surface of the piezoelectric sheet, that is, a structure in which the area of the internal electrode and the cross-sectional area of the element are made equal is common. In the case of a different structure, in order to connect the internal electrodes in every other layer, the method disclosed in JP-A-63-17354 (FIG. 9) and JP-A-62-21 are used.
Insulation must be performed using the method disclosed in Japanese Patent Publication No. 1974 (FIG. 10). That is, in the laminated piezoelectric element shown in FIG. 9, an insulating material (insulating layer) 41, such as glass, is attached every other layer by screen printing or electrophoresis, and then baked and fixed to form an external electrode. The silver paste 42 is applied to connect the internal electrodes 43 every other layer. In the laminated piezoelectric element shown in FIGS. 10A and 10B, an insulating layer 51 made of glass or the like is also formed, and an internal electrode 53 and an external electrode 52 formed on the insulating layer 51 are provided every other layer. It is electrically connected.

[0004]

However, in the piezoelectric element having the structure shown in FIGS. 9 and 10, the step of forming an insulating layer on the side surface of the element and the external electrode for connecting the internal electrode from the step are formed. Although a forming step is required, in either case, since the insulating layer is formed first and then the external electrode is formed, there is a disadvantage that the steps cannot be performed simultaneously and the number of steps increases. Further, in the case of the piezoelectric element having the structure shown in FIG. 9, the insulating layers 41 are formed every other layer at the end portions of the internal electrodes 43 exposed on the side surface. However, when screen printing is used as the method, it is very difficult. Accurate position accuracy is required, and in addition to printing misalignment, printing misalignment,
In some cases, due to bleeding or the like, the originally connected portion may have poor continuity, or the insulated portion may be short-circuited. Also in the case of the electrophoretic method, it is difficult to uniformly form the insulating layer 41 having a thickness that can withstand the driving voltage of the device, and there is a problem such as a short circuit due to dielectric breakdown.

On the other hand, in the piezoelectric element having the structure shown in FIG.
Although the insulating layer 51 can be formed relatively easily, it is difficult to connect the external electrode 52 and the internal electrode 53 on the insulating layer 51, and in the case of screen printing, in addition to the problem of positional accuracy, the device surface and the insulating layer are not easily separated. Since there is a step, it is difficult to print the conductive material paste on the step, and there is a problem of conduction failure and short circuit failure. Furthermore, whichever method is used, a step of firing the insulating layer and the external electrode paste at a high temperature is involved, which causes a rise in manufacturing cost.

The present invention has been made in order to solve the above-mentioned problems, and simplifies the process by omitting the step of forming an insulating layer, and at the same time, does not require special positioning, and external electrodes and internal electrodes. The purpose is to reliably connect and to prevent conduction failure and insulation failure.

[0007]

In order to achieve this object, a laminated piezoelectric element of the present invention has a conductive convex portion formed on an end portion of an internal electrode exposed on the side surface and a side surface of the piezoelectric element. A conductive film which is continuously formed on the conductive film and can be selectively made conductive by compression, and the conductive convex portion and the conductive film which are continuously formed on the conductive film. And an external electrode electrically connected to the conductive convex portion, and the tip of the conductive convex portion is formed flat. The conductive protrusion is formed by metal plating, and its tip is formed flat by machining. Further, the conductive film is made of a resin adhesive containing conductive particles.

[0008]

In the laminated piezoelectric element of the present invention having the above structure, only the external electrodes and the conductive film are provided on the side surface of the element, and the step of forming the insulating layer can be omitted.
Since there is no firing process at high temperature, the process is shortened significantly.
In addition, the conductive film is compressed by the conductive protrusions on the side surface of the element,
Since it is possible to selectively give conductivity, positioning is unnecessary, and since the tips of the conductive protrusions are formed flat and the contact area with the conductive particles increases, stable conductivity is ensured. It can be provided and the electrical connection can be made more reliable.

Further, the conductive convex portion can be accurately formed by metal plating with respect to the exposed end portion of the internal electrode, and at the same time the tip thereof is flattened by machining, and at the same time, the height by plating is increased. Misalignment is also eliminated, and it is possible to reliably connect every other internal electrode.

Further, since the conductive film is made of a resin adhesive containing conductive particles, a process such as baking at high temperature is not required, and the manufacturing cost of the element can be suppressed.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a cross-sectional view of a laminated piezoelectric element according to the present invention, in which a conductive convex portion 1 is provided every other layer on a side surface of a laminated body in which piezoelectric material films 11 and internal electrodes 12 are alternately superposed.
6 is formed, the conductive film 13 is formed so as to cover all the piezoelectric material films 11 in the stacking direction of the element, and the conductive parts 14 are in contact with the conductive convex parts 16 and the conductive parts 14 are provided in every other layer. Further, a copper foil 15 is formed as an external electrode on the conductive film 13, and is electrically connected to the conductive convex portion 16 and the internal electrode 12 via the conductive portion 14. The conductive film 13 has a one-layer structure in which conductive particles are contained and the concentration of the particles is continuously changed in the film thickness direction.

Next, a method of manufacturing the laminated piezoelectric element shown in FIG. 1 will be described with reference to FIGS.

First, a piezoelectric material containing PZT as a main component is mixed in a desired composition, and then the powder is calcined at 850.degree.
A binder and a small amount of a plasticizer and an antifoaming agent are added in parts by weight and dispersed in an organic solvent to form a slurry. This slurry is formed into a green sheet by a doctor blade method to a predetermined thickness. Pd paste is screen-printed as the internal electrodes 12 on the green sheet, and a predetermined number of punched out pieces are stacked and integrated by hot pressing. After degreasing, sintering is performed at about 1200 ° C., and as shown in FIG. 2, temporary external electrodes 22 and 23 are applied and baked onto the sintered body 21 cut at positions where the internal electrodes 12 are exposed every other layer. Then, cutting is performed so that another pair of side surfaces 24 and 25 is exposed.

Then, as shown in FIG. 3, on one side surface 24 of the sintered body 21, a portion other than the portion where the conductive convex portion is formed is masked with a tape, and the other side surface 25 is entirely masked with a tape. In this state, a temporary external electrode 22 is connected to the negative electrode of the DC power source and immersed in the nickel plating bath. When a current of 50 mA is applied for about 5 minutes in this state, nickel plating grows on the end surface of the internal electrode 12 connected to the temporary external electrode 22, and when the masking tape is peeled off, as shown in FIG. The convex portions 16 are formed in alternate layers.

Next, in order to form the conductive convex portion 16 also on the opposite side surface 25 by shifting the layer, the conductive convex portion 16 has already been formed.
After masking the entire side surface 24 on which is formed and a part of the side surface 25 with tape, the negative electrode is connected to the temporary external electrode 23 and nickel plating is grown. As a result, the conductive protrusions 16 are also formed on the side surfaces 25 so as to be offset by one layer from the side surfaces 24.

Next, the flat portion 1 is attached to the tip of the conductive convex portion 16.
In order to form 6a, the tips of the conductive convex portions 16 on the side surfaces 24 and 25 are ground by machining such as polishing to make the heights uniform.

Aside from the sintered body 21, as shown in FIG. 5, a resin adhesive containing copper powder (conductive particles) 31 having an average particle size of 20 to 30 μm on the copper foil 15, for example, thermosetting. Epoxy adhesive of 1 is evenly applied to a thickness of about 70 μm, and heated at a temperature lower than the curing temperature to make it softened
The copper powder (conductive particles) 31 is made to settle due to the difference in specific gravity, and is further in a semi-cured state. As a result, the conductive layer 13 has a one-layer structure in which the content concentration of the copper powder (conductive particles) 31 is continuously changed in the film thickness direction, that is, the copper powder (conductive particles) is closer to the copper foil 15. The content concentration of 31 is high,
The farther away from the copper foil 15, the lower the content concentration, and finally, the conductive film 13 having a one-layer structure containing little or no copper powder (conductive particles) 31 is formed.

Next, the conductive film 13 is cut into a required size for one element, for example, a width narrower than the width of the element, and the side surface 2 of the sintered body 21 on which the conductive convex portion 16 is formed.
4 and 25 are temporarily fixed to the conductive convex portions 16 with such lengths. Then, it is sandwiched between a pair of planar pressing jigs (one side is shown in FIG. 6) 35, and the whole is heated at 150 ° C. for 30 minutes while applying a uniform load. , The conductive film 13 near the protrusion
As shown in FIG. 6, only the copper powder (conductive particles) 31 having a high content concentration, in which the copper foil 15 is located on the ridge, is compressed.
It penetrates through the portion having a low content concentration and comes into contact with the flat portion 16a of the conductive convex portion 16 and also comes into contact with the copper foil 15 which is an external electrode to become the conductive portion 14, and the conductive film 13 is further cured by heat. The film 13 and the copper foil 15 are adhered to the element body, and the internal electrodes 12 and the copper foil 15 are electrically connected every other layer.

As described above, the sintered body 21 in which layers are staggered on the opposite side faces and connected every other layer is cut into one element at a position shown by a broken line in FIG. A lead wire for power supply is attached to the part, and a resin sheath and polarization treatment are applied to complete the product.

The conductive film 13 may be a conductive film 33 having a two-layer structure as shown in FIG. 8 as another embodiment.
That is, as shown in FIG.
A resin adhesive containing 0 to 30 μm of copper powder (conductive particles) 31, for example, a thermosetting epoxy adhesive is uniformly applied to a thickness of about 50 μm and heated at a temperature lower than the curing temperature. Then, a semi-cured state is obtained, and further, only the adhesive is similarly uniformly applied thereon and heated to be semi-cured. As a result, a conductive film 33 having a two-layer structure including a layer 33a made of an epoxy adhesive containing copper powder (conductive particles) 31 and a layer 33b made only of an epoxy adhesive.
To form.

Then, as in the previous embodiment, the conductive convex portion 1
The conductive film 33 is temporarily fixed to the side surfaces 24 and 25 of the sintered body 21 on which the conductive film 6 is formed so as to cover the conductive convex portions 16, respectively, and is sandwiched by a pair of planar pressing jigs to uniformly When the whole is heated at 150 ° C for 30 minutes while applying a load,
Due to the presence of the conductive convex portion 16, the conductive film 3 near the convex portion
Only 3 is compressed, the copper powder (conductive particles) 31 contained in the layer 33a breaks through the layer 33b containing no particles, contacts the flat portion 16a of the conductive convex portion 16, and
The copper foil 15 which is an external electrode also comes into contact with the copper foil 15 to form the conductive portion 14, and the layers 33a and 33b of the conductive film 33 are hardened by heat and adhered to the element body together with the copper foil 15. The copper foil 15 and the copper foil 15 are electrically connected.

Besides, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the invention. For example, as the conductive particles 31, metal powders such as nickel powder, aluminum, Invar alloy, and silver powder may be used instead of using the copper powder, or the conductive particles may be appropriately mixed and used. Good. Further, the shape and particle size of the conductive particles can be variously changed according to the film thickness of the piezoelectric material. Further, if one of the copper foils 15 is extended as it is, it can be used as a lead wire.

[0024]

As is apparent from the above description, in the laminated piezoelectric element of the present invention, the step of forming the insulating layer is omitted and there is no firing step at high temperature, so that the number of steps can be greatly reduced. Manufacturing cost can be suppressed. In addition, since the conductive projections on the side surface of the element compress the conductive film and the conductive particles contained in the conductive film are brought into contact with the conductive projections to selectively impart conductivity, positioning is unnecessary. It is extremely easy to manufacture. Furthermore, since the tips of the conductive protrusions are formed flat and the contact area with the conductive particles contained in the conductive film is increased, stable conductivity can be provided, and more reliable electrical connection can be achieved. Can be.

Further, the conductive convex portion can be accurately formed by metal plating on the exposed end portion of the internal electrode, and the tip end thereof is made flat by machining, and
Since unevenness in height due to plating is also eliminated, it is possible to reliably connect all the internal electrodes of every other layer.

Furthermore, since the conductive film is made of a resin adhesive containing conductive particles, a process such as baking at high temperature is not required, and the manufacturing cost of the element can be suppressed.

[Brief description of drawings]

FIG. 1 is a sectional view of a laminated piezoelectric element showing an embodiment of the present invention.

FIG. 2 is a perspective view of a cut laminated sintered body.

FIG. 3 is a perspective view of a laminated sintered body masked with a tape.

FIG. 4 is a perspective view of a laminated sintered body in which conductive protrusions are formed.

FIG. 5 is a cross-sectional view showing a copper foil and a conductive film having a one-layer structure.

FIG. 6 is an explanatory diagram of a state in which a conductive film and a copper foil are pressed.

FIG. 7 is a perspective view of a laminated sintered body on which a conductive film and a copper foil are formed.

FIG. 8 is a sectional view of a copper foil and a conductive film having a two-layer structure showing another embodiment.

FIG. 9 is a cross-sectional view of a conventional laminated piezoelectric element.

10A and 10B show another conventional laminated piezoelectric element, in which FIG. 10A is a side view and FIG. 10B is a sectional view taken along line BB of FIG. 10A.

[Explanation of symbols]

 Reference Signs List 11 piezoelectric material film 12 internal electrode 13 conductive film 14 conductive part 15 copper foil (external electrode) 16 conductive convex part 16a flat part 31 copper powder (conductive particle) 33 conductive film

Claims (5)

[Claims] 1. A laminated piezoelectric element in which a piezoelectric material and internal electrodes are alternately laminated, and a conductive convex portion formed at an end of the internal electrode exposed on a side surface of the laminated piezoelectric element. , A conductive film which is continuously formed on the side surface of the laminated piezoelectric element and which can be selectively made conductive by compression, and a conductive film which is continuously formed on the conductive film and A laminated piezoelectric element, comprising: a conductive convex portion and an external electrode electrically connected through a conductive film, wherein the conductive convex portion has a flat tip. 2. The laminated piezoelectric element according to claim 1, wherein the conductive convex portion is formed by metal plating. 3. The laminated piezoelectric element according to claim 2, wherein the tip of the conductive convex portion is formed flat by machining. 4. The conductive film comprises a layer made of a resin adhesive containing conductive particles and a layer made of a resin adhesive only.
4. The laminated piezoelectric element according to claim 1, which has a layered structure. 5. The laminated piezoelectric element according to claim 1, wherein the conductive film has a single-layer structure in which the concentration of conductive particles is changed in the film thickness direction.