JPH09266332A - Lamination type piezoelectric element, its manufacturing method and polarization - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the damage of element by crack on operation, to prevent formation of drum shape deformation and generation of internal stress at the polarization processing, by the polarization of the protecting layer part together with the piezoelectric layer part. SOLUTION: Silver palladium alloy is printed on a green sheet as an internal electrode. After cutting the green sheet, a piezoelectric part is prepared by laminating the sheets. The block of a lamination type piezoelectric element is obtained by arranging protective layers to the top and the bottom of the piezoelectric part. After printing the electrodes for polarization on the surfaces of the protective layer parts at the top and the bottom of the block and performing the polarizing process by applying electric field, external electrodes are attached and the lamination type piezoelectric element is completed. In the lamination type piezoelectric element, the piezoelectric layer part 11 is formed by laminating piezoelectric material 3 and internal electrode 1 alternately and the protective part 12 is formed by laminating the piezoelectric material only. An electrode 4 indicates the electrode for polarizing process prepared on the surface of protective layer 12 for the polarizing process.

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 and a method for manufacturing the same.

[0002]

2. Description of the Related Art Piezoelectric materials are distorted by an electric field. The direction of this strain is a random direction within the piezoelectric element, and as it is, the strain caused by the electric field is offset and the strain is not displaced. However, when an electric field above a certain level is applied, the directions of distortion are aligned. This is called polarization processing. Therefore, the piezoelectric element is always polarized before use.

Conventionally, a laminated piezoelectric element is composed of a piezoelectric layer portion in which piezoelectric materials and internal electrodes are alternately laminated, and a protective layer portion disposed above and below the piezoelectric layer portion that does not include internal electrodes. An external electrode is formed on the side surface of the piezoelectric layer portion and connected to the internal electrodes every other layer, and an electric field is applied between the internal electrodes of the piezoelectric element through the external electrodes to perform polarization processing. With this polarization process, the piezoelectric element expands in the direction of the electric field, contracts in the vertical direction, and deforms like a drum.

FIG. 4 is a schematic cross-sectional view of a piezoelectric element polarized by a conventional manufacturing method. In FIG. 4, 1 is an internal electrode, 2 is an external electrode that is connected to the internal electrode every other layer, and 3
Is a piezoelectric material. Reference numeral 11 is a piezoelectric layer portion in which the piezoelectric material 3 and the internal electrode 1 are alternately laminated, and 12 is a protective layer portion in which only the piezoelectric material is laminated. In the conventional polarization method for a laminated piezoelectric element as described above, a voltage is applied to the external electrode 2,
Since a high electric field acts between the internal electrodes 1 connected to different external electrodes 2, the piezoelectric layer portion 11 is polarized, but the electric field is not applied to the protective layer portion 12 and is not polarized. For this reason,
The polarized piezoelectric layer portion 11 expands in the direction of the electric field and contracts in the vertical direction, but the protective layer portion 12 does not change in size because it is not polarized, and the piezoelectric element deforms like a drum as shown in FIG. Stress is generated at the boundary between the portion 12 and the piezoelectric layer portion 11.

Further, since the polarization treatment is usually performed after cutting a piezoelectric element made of a large block into several pieces and polishing the pieces to obtain elements having a predetermined size, they are deformed by polarization as described above, The dimensional accuracy becomes poor. Therefore, there has been a strong demand for a method of manufacturing a laminated piezoelectric element that eliminates this deformation and does not generate stress inside.

[0006]

DISCLOSURE OF THE INVENTION The present invention is directed to a method of manufacturing a laminated piezoelectric element having excellent shape and dimension accuracy, a method of polarization, and a method of polarization in which a drum-shaped deformation and internal stress are not generated in the step of polarizing the laminated piezoelectric element. An object is to provide a laminated piezoelectric element obtained by this method.

[0007]

To achieve this object, the present invention provides a piezoelectric layer portion in which piezoelectric materials and internal electrodes are alternately laminated, and internal electrodes arranged above and below the piezoelectric layer portion. A laminated piezoelectric element obtained by integrally firing a protective layer portion not containing the above, wherein both the protective layer portion and the piezoelectric layer portion are polarized.

Further, according to the present invention, the piezoelectric layer portion in which the piezoelectric material and the internal electrode are alternately laminated and the protective layer portion disposed above and below the piezoelectric layer portion and not including the internal electrode are integrally fired. In the method for manufacturing a laminated piezoelectric element, the steps of applying an electric field between the upper and lower surfaces of the upper and lower protective layer portions to polarize the protective layer portion and the piezoelectric layer portion at the same time, and cutting into a predetermined shape are performed. An object of the present invention is to solve the problems by a method for manufacturing a laminated piezoelectric element characterized by having the above. Further, in the step of simultaneously polarizing the protective layer portion and the piezoelectric layer portion, the electrodes for polarization are provided on the surfaces of the upper and lower protective layer portions, a voltage is applied between the electrodes for polarization, and the protective layer portion and the piezoelectric layer portion are simultaneously formed. Provided is a method of polarizing and / or a method of simultaneously polarizing a protective layer portion and a piezoelectric layer portion by inserting a fired piezoelectric element between electrodes to which a voltage is applied.

Further, a laminate obtained by integrally firing a piezoelectric layer portion in which piezoelectric materials and internal electrodes are alternately laminated and a protective layer portion disposed above and below the piezoelectric layer portion and not including internal electrodes. In the polarization method of the laminated piezoelectric element, an electric field is applied between the upper surface and the lower surface of the laminated piezoelectric element to polarize both the protective layer portion and the piezoelectric layer portion. Is what you are trying to do.

[0010]

According to the present invention, since both the protective layer portion and the piezoelectric layer portion are polarized, both the protective layer portion and the piezoelectric layer portion shrink in the same direction in the direction perpendicular to the electric field and have the same size. Therefore, no stress is applied to the boundary portion between the protective layer portion and the piezoelectric layer portion.

In the present invention, when an electric field is applied to a large block after firing, the entire block is polarized,
The same deformation occurs in both the protective layer portion and the piezoelectric layer portion. That is, both the protective layer portion and the piezoelectric layer portion extend in the stacking direction and contract in the vertical direction. Therefore, it does not deform like a drum and no internal stress is generated at the boundary between the protective layer portion and the piezoelectric layer portion. Furthermore, since the cutting process is performed after polarization, the processing accuracy is not affected by the deformation due to polarization. Therefore, the processing accuracy does not decrease.

The present invention will be further described below based on examples.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Ceramic powders such as Pb (Zr, Ti) O ₃ are pulverized with a sand mill, and a binder, a dispersant, an activator, and an antifoaming agent are added to the mixture, and the mixture is kneaded in a vacuum to defoam and then the doctor blade method is used. A green sheet was produced using the above. The thickness of the obtained green sheet was 100 μm. A silver-palladium alloy was printed as an internal electrode on this sheet by using a screen printing method. Next, after cutting into a size of 100 × 100 mm, 130 sheets on which internal electrodes were printed were laminated to prepare a piezoelectric portion. Separately from this, 20 green sheets are laminated and press-molded, and the protective layer portions are provided above and below the piezoelectric portion, press-bonded with a press, and heat degreased and fired to form a laminated piezoelectric material. A block of devices was obtained.

After the electrodes for polarization were baked on the surface of the protective layer portions above and below the block thus obtained (or may be dried only), an electric field of 2 kV / mm was applied for polarization treatment. Thereafter, this block was cut and polished, and then external electrodes were attached to obtain a laminated piezoelectric element. FIG. 1 is a schematic sectional view of a laminated piezoelectric element polarized by this manufacturing method. In FIG. 1, 1 is an internal electrode and 3 is a piezoelectric material. Reference numeral 11 is a piezoelectric layer portion in which the piezoelectric material 3 and the internal electrode 1 are alternately laminated, and 12 is a protective layer portion in which only the piezoelectric material is laminated. 4 is the protective layer portion 1 for polarization treatment
2 is an electrode for polarization treatment provided on the surface of 2. Since the laminated piezoelectric element manufactured by the present manufacturing method polarizes both the piezoelectric layer portion and the protective layer portion at the same time, it is not deformed like a drum as shown in FIG. 1. Therefore, the protective layer portion 12 and the piezoelectric layer portion are not deformed. 1
At the boundary of 1, no stress is generated by the polarization treatment.

The polarization method is not limited to the method of providing the polarization electrodes 4 on the protective layer portions 12 above and below the block, but by inserting the block between the electrodes to which a voltage is applied, an electric field is applied to the block to cause piezoelectricity. Both the layer portion and the protective layer portion may be polarized at the same time. The electrode and the block may or may not be in close contact.

Further, in the present manufacturing method, the manufacturing method in which the block is subjected to the polarization treatment and then the cutting processing is performed, but the point of the polarization method of the present invention is that both the piezoelectric layer portion and the protective layer portion are polarized. Therefore, after processing the unit element, an electric field may be applied by providing electrodes on the upper surface and the lower surface of the element or by inserting the element between electrodes to which a voltage is applied.

The piezoelectric element manufactured by the manufacturing method of the present invention was processed with a height of ± 0.01 mm and a parallelism of 0.01 mm. A device manufactured by the conventional method has a height of ± 0.0
It was processed with 1 mm and a parallelism of 0.01 mm, but then, due to polarization, the height became +0.00 to +0.04 mm and the parallelism was 0.05 mm.

The device according to the present invention and the device prepared by the conventional method were subjected to a drive test by fixing the protective layer portion to the plate with the adhesive 4 (FIGS. 2 and 3). When a voltage is applied to the element to drive it, the piezoelectric portion expands vertically and contracts horizontally due to the electric field. At this time, since the protective layer portion to which the electric field is not applied does not expand or contract, it is deformed into a drum shape. The element by the conventional method was originally deformed during the polarization process and accumulated internal stress, and further the deformation and internal stress due to this displacement added, so cracks occurred at the boundary between the protective layer part and the piezoelectric layer part. There was something to do (Fig. 2). On the other hand, the element obtained in the present invention was also deformed by driving, but no crack was generated because of no deformation or internal stress due to polarization treatment (FIG. 3).

[0019]

As described above, by polarizing the protective layer portion together with the piezoelectric layer portion, drum-like deformation and internal stress due to the polarization treatment do not occur. Therefore, when the element is driven, the protective layer portion and the piezoelectric layer portion. It is possible to obtain a laminated piezoelectric element in which destruction of the element due to cracks does not occur in the vicinity of the boundary. Also,
The processing accuracy is improved, and it is extremely easy to deal with equipment that requires assembly accuracy.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a laminated piezoelectric element according to an embodiment of the present invention after processing.

FIG. 2 is a cross-sectional view of a drive test of a conventional laminated piezoelectric element.

FIG. 3 is a cross-sectional view of a drive test of a laminated piezoelectric element according to an example of the present invention.

FIG. 4 is a cross-sectional view of a conventional laminated piezoelectric element after polarization.

[Explanation of symbols]

1 Internal Electrode 2 External Electrode 3 Piezoelectric Material 4 Polarizing Electrode 11 Piezoelectric Layer Part 12 Protective Layer Part 21 Schematic Diagram of Cracks Generated by Driving Test

Claims (5)

[Claims] 1. A laminate obtained by integrally firing a piezoelectric layer portion in which a piezoelectric material and an internal electrode are alternately laminated and a protective layer portion disposed above and below the piezoelectric layer portion and not including the internal electrode. A laminated piezoelectric element, wherein the protective layer portion and the piezoelectric layer portion are both polarized. 2. A piezoelectric layer portion in which a piezoelectric material and an internal electrode are alternately laminated and a protective layer portion disposed above and below the piezoelectric layer portion, which does not include the internal electrode, are integrally fired and processed. The method for manufacturing a laminated piezoelectric element may include a step of applying an electric field between the upper and lower surfaces of the upper and lower protective layer portions to polarize the protective layer portion and the piezoelectric layer portion at the same time, and a step of cutting into a predetermined shape. A method of manufacturing a laminated piezoelectric element having a feature. 3. The step of polarizing the protective layer portion and the piezoelectric layer portion at the same time includes the steps of providing polarization electrodes on the surfaces of the upper and lower protective layer portions and applying a voltage between the polarization electrodes to form the protective layer portion. 3. The method for manufacturing a laminated piezoelectric element according to claim 2, further comprising the step of simultaneously polarizing the piezoelectric layer portion. 4. The step of simultaneously polarizing the protective layer portion and the piezoelectric layer portion simultaneously polarizes the protective layer portion and the piezoelectric layer portion by inserting a fired piezoelectric element between electrodes to which a voltage is applied. The method for manufacturing a laminated piezoelectric element according to claim 2, wherein the method is a step. 5. A laminate obtained by integrally firing a piezoelectric layer portion in which a piezoelectric material and an internal electrode are alternately laminated and a protective layer portion disposed above and below the piezoelectric layer portion and not including the internal electrode. In the method of polarizing a laminated piezoelectric element, an electric field is applied between the upper surface and the lower surface of the laminated piezoelectric element to polarize both the protective layer portion and the piezoelectric layer portion.