JPH04273183A - Piezoelectric effect element and electrostriction effect element and its manufacture - Google Patents

Abstract

PURPOSE:To satisfy requirements to high temperature resistance properties from the side of a system whose mutual bonding strength of sintered bodies does not deteriorate even if it is exposed to a high temperature by using glass- based inorganic adhesive as adhesive. CONSTITUTION:A green sheet is manufactured in kneading process and film formation process. Then, inside electrode print process, cutting process and thermal bonding process are carried out. Furthermore, cutting process, binder removal process and burning process are carried out. A lamination body which is acquired through the processes is provided with outside electrodes 3a, 3b in outside electrode print process and burning process, and becomes a sintered body 5 of lamination ceramic chip capacitor structure. In the next process, inorganic paste containing lead borosilicate as the main component, organic binder, solvent and plasticizer is applied to a bonding side by a dispenser. After 10 sintered bodies are laminated and dried at about 150 deg.C to remove organic solvent, heating is further carried out at about 680 deg.C to burn inorganic matter.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric effect element, an electrostrictive effect element, and a method for manufacturing the same, and more particularly to a laminated piezoelectric effect element, an electrostrictive effect element, and a method for manufacturing the same.

0002

[Prior Art] A piezoelectric/electrostrictive effect element is a solid-state piezoelectric/electrostrictive element.
A transducer that converts electrical energy into mechanical energy using electrostrictive effects. Specifically, piezoelectric
Metal electrodes are provided on two opposing surfaces of a solid material with strong piezoelectric and electrostrictive effects, such as electrostrictive ceramics, and the strain in the solid material that occurs when a potential difference is applied between these electrodes is utilized.

[0003] In the above piezoelectric/electrostrictive effects, usually,
Since the strain that occurs in the direction parallel to the electric field (longitudinal effect strain) is larger than the strain that occurs in the direction perpendicular to the electric field (transverse effect strain), it is more advantageous to use the former and also improves the electrical/mechanical energy conversion efficiency. It's also expensive.

In a piezoelectric/electrostrictive element (hereinafter referred to as an element) that utilizes this longitudinal effect strain, the amount of displacement per unit length of the element increases as the applied electric field strength increases. Therefore, in order to obtain a large amount of displacement as an element, it is effective to apply a high voltage between the opposing electrodes or to make the piezoelectric/electrostrictive material into a thin layer to reduce the distance between the opposing electrodes.

However, increasing the voltage requires a large and expensive power source and also increases the risk of handling, which is not desirable.

[0006] For this reason, in order to obtain a large strain, the actual device has a structure in which the electric field strength is increased by reducing the thickness of the piezoelectric/electrostrictive material and narrowing the spacing between the electrodes, and then laminating multiple layers of these materials. , a so-called stacked type element is being considered.

An example of such a stacked element is shown in FIG. 4(a).
) and (b). FIG. 4(a) is a cross-sectional view of the element, and FIG. 4(b) is a projected view in the stacking direction. The following explanation uses a piezoelectric effect element as an example, but the difference between the piezoelectric effect and the electrostrictive effect is that the strain that occurs when an electric field is applied to a dielectric material is proportional to the electric field or proportional to the square of the electric field. However, since the materials, structures, manufacturing methods, etc. of the elements are the same, "piezoelectric effect" may be replaced with "electrostrictive effect" in the following description of the piezoelectric effect element.

In the device shown in FIGS. 4A and 4B, internal electrodes 2a and 2b are formed inside the piezoelectric material 1 at regular intervals. And every other internal electrode is connected to external electrodes 3a, 3b. Since such a structure is often used in multilayer ceramic chip capacitors, such a structure will hereinafter be referred to as a multilayer ceramic chip capacitor structure.

With such a structure, the thickness of the layer of piezoelectric material 1 can be made as thin as several tens of micrometers by using ordinary film thinning technology for multilayer ceramic chip capacitors. Moreover, since these layers are laminated, it is possible to realize an element that utilizes the longitudinal effect and generates a large displacement even at a low voltage.

By the way, in an element having this structure, when the element is viewed from the stacking direction, as can be seen from FIG. is the cross section of the element (the part surrounded by the outermost line in the figure)
It is inside. That is, basically, the overlapping parts of the internal electrodes deform in response to the electric field, but the other parts do not try to deform.

[0011] Therefore, in this structure, when applying a voltage from the outside to drive this element, there is constraint from the peripheral portion, which is disadvantageous for extracting a large displacement. Furthermore, when a high voltage is applied to obtain a large displacement, the boundary between the deformable part and the hard-to-deform part (Fig. 4(a)
A large amount of stress is concentrated in the area (the part surrounded by the broken line), and in extreme cases, mechanical failure may occur in this part. In particular, the uppermost and lowermost portions of the above-mentioned boundary portion are prone to breakage because stress accumulates in these portions.

[0012] In order to improve the drawbacks of such conventional elements, it has been proposed to break down the above-mentioned elements into several units and synthesize them into one element.

That is, the structure is such that a sintered body having a multilayer ceramic chip capacitor structure having a height that is 1/n of the height required for one element is made and n pieces of this sintered body are stacked. An element having such a structure is shown in FIG. Figure 5 (a
) is a cross-sectional view of the element, and FIG. 5(b) is a projected view in the stacking direction. In this element, each sintered body 5 is connected by bonding only the center portion of the surface of the sintered body 5 with an organic adhesive 6 such as epoxy.

[0014] With this arrangement, when a voltage is applied to this element, each sintered body deforms as a unit, as shown in FIG. Therefore, in the element as a whole, the stress applied to the boundary portion described above is dispersed in each sintered body unit and is relaxed as a whole.

One way to use piezoelectric effect elements is to operate them by repeatedly applying a driving voltage in the form of pulses. According to the element structure described above, even when used in this way, mechanical The lifespan until destruction can be extended. Moreover, the displacement of the element can also be increased.

[0016]

[Problem to be Solved by the Invention] As mentioned above, FIG.
In the conventional multilayer device shown in FIG. 1, an organic adhesive (for example, epoxy resin, etc.) 6 is used when bonding a sintered body 5 having a multilayer ceramic chip capacitor structure.

However, when this element is incorporated into an electronic equipment system and used, the element itself may be exposed to high temperatures due to requests from the system side. For example, when passing a board on which this element is mounted through a solder reflow oven,
Exposure to temperatures close to 0°C. Under such conditions, the adhesive strength of the organic adhesive 6 may deteriorate and, in some cases, it may peel off at the adhesive surface.

[0018]

[Means for solving the problems] The piezoelectric effect element of the present invention (
An electrostrictive element (electrostrictive effect element) has a structure in which layers of material exhibiting a piezoelectric effect (electrostrictive effect) and layers of internal electrodes are laminated alternately, and each internal electrode is connected to one of two external electrodes. A type of piezoelectric effect element (electrostrictive effect element) in which at least two or more bodies are stacked in the stacking direction, where the surfaces of adjacent sintered bodies perpendicular to the stacking direction have glass as the main component. It is characterized by being bonded via an inorganic adhesive layer.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be described with reference to the drawings. FIG. 1(a) is a sectional view showing the structure of the first embodiment of the present invention, and FIG. 1(b) is a projected view of the first embodiment in the stacking direction. Further, FIG. 2 is a flowchart showing the manufacturing process of this embodiment.

This embodiment differs from the conventional element shown in FIG. 5 in that an inorganic adhesive layer 7 containing glass as a main component is used to bond the sintered bodies 5 together in FIG.

This example is manufactured as follows. First, the starting material of this example is a nickel-niobate-titanate-lead zirconate-based material exhibiting a piezoelectric effect.

First, in the kneading step and the film forming step, an organic solvent, a binder and a plasticizer are added to the pre-fired powder of the above material, and a green sheet with a thickness of about 130 μm is produced by a doctor blade method.

Next, the internal electrode printing process, cutting process and thermocompression bonding process are carried out. Here, the green sheet is dried,
An internal electrode paste containing silver-palladium alloy powder as a main component is printed thereon, cut into a predetermined shape, and then a predetermined number of sheets are laminated and thermocompressed to obtain a green laminate.

Further, a cutting process, a binder removal process and a firing process are performed. Here, the green laminate described above is cut into predetermined dimensions, heated at about 500°C to remove the organic binder, and then fired at a temperature of about 1100°C.

The laminate obtained through the above steps is then subjected to an external electrode printing process and a firing process to form external electrodes 3.
a, 3b are formed. Then, a sintered body 5 having a multilayer ceramic chip capacitor structure is obtained. The external electrodes 3a and 3b are made of paste containing silver-palladium alloy powder as a main component.
It is formed by firing at a temperature of 0°C.

The structure of the above sintered body has a cross section in the stacking direction of 5 mm x 5 mm and a height of 1 mm, and the area of the overlapped portion of the internal electrodes 2a and 2b is 4.7 mm x 4.7 mm.
It is. Further, the distance between the internal electrodes 2a and 2b is approximately 10
It is 0 μm. Although FIG. 1 schematically depicts the structure of the element and only four internal electrodes are shown inside each sintered body 5, there are ten internal electrodes in the actual sintered body. It is formed. In this example, ten sintered bodies having the above-mentioned multilayer ceramic chip capacitor structure were bonded together in the following inorganic coating process and firing process.

In this step, first, an inorganic paste containing lead borosilicate glass as a main component, an organic binder, a solvent, and a plasticizer is applied to the surface to be bonded using a dispenser. Then, ten sintered bodies are stacked and dried at about 150° C. to remove the organic solvent, and then further heated at about 680° C. to bake the inorganic material. As a result, the glass and the piezoelectric material 1 in the sintered body 5 are bonded to each other, so that an element having a structure in which ten sintered bodies 5 are connected via the inorganic adhesive layer 7 is obtained. The adhesive area of the inorganic adhesive layer 7 is approximately 1.5 m.
It is mφ.

Finally, the external electrodes of each sintered body 5 are electrically connected by soldering the lead wires 4a and 4b with high-temperature solder to complete the device of this embodiment.

Next, tests were conducted to confirm the effects of the present invention. The samples were an element according to this example and an element with a conventional structure bonded with epoxy resin, each with 10
There are 0 pieces each. These samples were left in a constant temperature bath at 230°C for 60 minutes.

[0030] As a result, while all of the conventional elements showed deterioration in adhesive strength and peeling from the adhesive surface, none of the elements according to the present example showed any deterioration in adhesive strength. It was confirmed that the adhesive strength of the device of this example did not deteriorate up to 240° C., which is the melting point of the solder.

[0031] A similar investigation was also attempted on an element using an electrostrictive material based on magnesium niobate-lead titanate instead of the piezoelectric material, but results exactly the same as those described above were obtained.

Furthermore, in place of the above-mentioned inorganic paste, exactly the same effect was obtained when an inorganic paste containing 5, 10, or 15 weight percent alumina added to glass as its main component was used.

Next, a second embodiment of the present invention will be described. FIG. 3(a) is a sectional view showing the structure of a second embodiment of the present invention, and FIG. 3(b) is a projected view of the second embodiment in the stacking direction.

The difference between this embodiment and the first embodiment shown in FIG. 1 is that in each sintered body, glass is provided between the inorganic adhesive layer 7 and the internal electrodes 2c and 2d closest to the inorganic adhesive layer 7. The difference is that a diffusion prevention layer 8 is provided. The material of this glass diffusion prevention layer 8 is a fired paste containing the same silver-palladium alloy powder as the main component used for the internal electrodes of the first embodiment.

The device according to this example is manufactured using the same materials and the same manufacturing process as in the first example. However, in the case of this example, in order to provide the glass diffusion prevention layer 8, the following sub-processes were added to the film forming process, internal electrode printing process, and lamination process in the flowchart of the manufacturing process shown in FIG. be done.

First, when a green sheet for the piezoelectric material 1 is produced in the film forming process and the internal electrode printing process, a green sheet for the glass diffusion prevention layer 8 is produced separately. The material of this green sheet is the same as the green sheet for piezoelectric material 1, and the size is also the same. However, the thickness is 10
Make it as thin as μm.

Next, when printing the internal electrode paste on the green sheet for piezoelectric material 1 in the internal electrode printing process,
The same paste for internal electrodes is printed on the grease sheet for glass diffusion prevention 8 described above. In this case, the printing pattern is
As shown in FIG. 3(b), the size is 3 mm x 3 mm and the thickness after completion is adjusted to 3 μm.

After that, the green sheet for piezoelectric material 1 and the green sheet for glass diffusion prevention layer 8 are laminated.

In this case, green sheets for the piezoelectric material 1 are laminated to have the same structure as in the first embodiment, and a glass diffusion prevention layer 8 is further formed on the outside thereof as shown in FIG. 3(b).
Stack one green sheet. At this time, the green sheets for glass diffusion prevention layer 8 are laminated so that the paste for internal electrodes faces inward.

Thereafter, by the same manufacturing process as in the first embodiment, a sintered body 5 is produced from the green laminate obtained as described above, and this sintered body 5 is bonded with an inorganic adhesive layer 7. Through these steps, the device of the second embodiment is completed.

In the device manufactured in this way, the glass diffusion prevention layer 8 has an area of 3 mm×3 mm and a thickness of 3 μm.
It is. In addition, this glass diffusion prevention layer 8 and the inorganic adhesive layer 7
The distance between them is approximately 8 μm.

In the device according to the second embodiment, the dielectric strength voltage between the internal electrodes 2c and 2d closest to the inorganic adhesive layer 7 of the sintered body 5 bonded with the inorganic adhesive layer 7 in between is the highest. It is expected that the device will be better than the device according to the first embodiment.

This can be considered as follows. That is, in the element of the first embodiment, the glass, which is the main component of the inorganic adhesive layer 7, reacts with the piezoelectric material 1 to form the reaction layer 9, but this reaction layer 9 has many pores and is dense. is not good. Therefore, when a voltage higher than 5 is applied between the internal electrodes 2c and 2d, dielectric breakdown tends to occur near the reaction layer 9.

On the other hand, in the element of the second embodiment, the glass diffusion prevention layer 8 provided between the inorganic adhesive layer 7 and the internal electrodes 2c and 2d prevents the diffusion of glass, and the ceramic for piezoelectric material Since a dense layer similar to the above is left thick, the dielectric strength voltage between the internal electrodes 2c and 2d remains high.

When the vertical cross section of the element of the second embodiment was actually observed using an optical microscope, it was found that the shape of the particles was different in the part inside the glass diffusion prevention layer 8 compared to the other part of the piezoelectric material 1. On the other hand, it was observed that the portions outside the glass diffusion prevention layer 8 were deteriorated in quality. That is, it can be considered that the glass diffusion prevention layer 8 prevents the diffusion of glass, which is the main component of the inorganic adhesive layer 7 .

Next, a test was conducted to confirm the above. The samples were 50 elements of the first example and 50 elements of the second example. These samples were subjected to a humidity load life test by applying a rated DC voltage of 150 V under conditions of a temperature of 40° C. and a humidity of 90 to 95% RH.

As a result, within 2000 hours after the start of energization, two insulation breakdown defects occurred in the element of the first example, whereas no defects occurred in the element of the second example. There wasn't.

[0048] In place of the piezoelectric material, a similar investigation was attempted with respect to an element using an electrostrictive material based on magnesium niobate-lead titanate, and results exactly the same as those described above were obtained.

It has also been confirmed that similar results can be obtained when an inorganic paste containing 5, 10, or 15 weight percent alumina is used in place of the above-mentioned inorganic paste.

[0050]

[Effects of the Invention] As explained above, the present invention uses glass instead of conventional organic adhesives such as epoxy when bonding sintered bodies of a multilayer ceramic chip capacitor structure to make an element. An inorganic adhesive is used as the main component.

Therefore, according to the present invention, it is possible to obtain an element that can satisfy the requirements for high temperature resistance from the system side, in which the adhesive strength between sintered bodies does not deteriorate even when exposed to high temperatures. It will be done.

Furthermore, by providing an inorganic diffusion prevention layer for this element, it is possible to prevent the components in the inorganic adhesive from diffusing and forming a reaction layer with low dielectric strength. A highly reliable element with excellent dielectric strength can be provided.

[Brief explanation of the drawing]

FIG. 1 (a) is a sectional view of a first embodiment of the present invention. Part (b) is a projected view of the first embodiment of the present invention in the stacking direction.

FIG. 2 is a flowchart diagram for explaining the manufacturing process of the first embodiment and the second embodiment of the present invention.

FIG. 3 (a) is a cross-sectional view of a second embodiment of the invention. Part (b) is a projected view of the second embodiment of the present invention in the stacking direction.

FIG. 4 (a) is a cross-sectional view of a first example of a conventional element. Part (b) is a projected view of the first example of the conventional element in the stacking direction.

FIG. 5(a) is a cross-sectional view of a second example of a conventional element. Part (b) is a projection view of a second example of a conventional element in the stacking direction.

6 is a schematic diagram for explaining a deformed state of the element shown in FIG. 5 during operation; FIG.

[Explanation of symbols]

1 Piezoelectric materials 2a, 2b, 2c, 2d Internal electrodes 3a, 3b,
External electrodes 4a, 4b Lead wire 5 Sintered body 6 Adhesive 7 Inorganic adhesive layer 8 Glass diffusion prevention layer 9 Reaction layer

Claims (8)

[Claims] Claim 1: A sintered body having a structure in which layers of a material exhibiting a piezoelectric effect and layers of internal electrodes are alternately laminated and each internal electrode is connected to one of two external electrodes. It is a type of piezoelectric effect element in which two or more are stacked one on top of the other, and the surfaces of adjacent sintered bodies perpendicular to the stacking direction are bonded together via an inorganic adhesive layer mainly composed of glass. A piezoelectric effect element. Claim 2: A sintered body having a structure in which layers of a material exhibiting an electrostrictive effect and layers of internal electrodes are alternately laminated and each internal electrode is connected to one of two external electrodes in the lamination direction. An electrostrictive effect element of a type in which at least two or more are stacked, and the surfaces of adjacent sintered bodies perpendicular to the stacking direction are bonded to each other via an inorganic adhesive layer mainly composed of glass. An electrostrictive effect element characterized by: 3. The piezoelectric effect element according to claim 1, wherein the sintered body has an inorganic diffusion prevention layer between the internal electrode closest to the inorganic adhesive layer and the inorganic adhesive layer. A characteristic piezoelectric effect element. 4. The electrostrictive effect element according to claim 2, wherein the sintered body has an inorganic diffusion prevention layer between the internal electrode closest to the inorganic adhesive layer and the inorganic adhesive layer. An electrostrictive effect element characterized by: 5. The piezoelectric effect element according to claim 3, wherein the inorganic diffusion prevention layer is formed by firing a paste containing a silver-palladium alloy powder as a main component. effect element. 6. The electrostrictive effect element according to claim 4, wherein the inorganic diffusion prevention layer is formed by firing a paste containing a silver-palladium alloy powder as a main component. Electrostrictive effect element. 7. The method of manufacturing a piezoelectric effect element according to claim 1, claim 3, and claim 5, wherein the surface of the sintered body that comes into contact with another adjacent sintered body contains glass as a main component. 1. A method for manufacturing a piezoelectric effect element, comprising the steps of: applying an inorganic paste; and stacking a predetermined number of sintered bodies coated with the inorganic paste and firing them. 8. The method of manufacturing an electrostrictive effect element according to claim 2, claim 4, and claim 6, wherein glass is mainly used on the surface of the sintered body that comes into contact with another adjacent sintered body. A method for manufacturing an electrostrictive effect element, comprising the steps of applying an inorganic paste as a component, and stacking and firing a predetermined number of sintered bodies coated with the inorganic paste.