JPH08222777A - Piezoelectric element and its manufacture - Google Patents

Abstract

PURPOSE: To provide a piezoelectric element and its manufacturing method which can surely prevent a defect like electrode continuity failure in the junction part of laminated green sheets. CONSTITUTION: A piezoelectric element 20 consists of a piezoelectric active part 21 which is expanded and contracted by applying a voltage, substrate parts 30 which hold the active part 21 from both sides, outer electrodes 32, 33, etc., which are electrically connected with inner electrodes 23, 24 of the active part 21. The piezoelectric active part 21 is constituted by laminating many PZT sheets, and inner electrodes 23, 24, 24a are alternately formed between layers. The piezoelectric active parts 21 and the substrates 30 are closely brought into contact with each other, and then hardened to be in a unified body by baking. Viewing from the thickness direction of the piezoelectric element 20, a region where the inner electrodes 23, 24, 24a on both sides of PZT sheet turning to a piezoelectric layer mutually overlap, and a region where they do not overlap are formed. The region 25 where they do not overlap is out of the end portion 30a of the substrate part 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element obtained by laminating and sintering green sheets formed by kneading ceramic powder with a binder and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a laminated ceramic product, for example, a green sheet made of a ceramic material such as PZT0 (lead zirconate titanate) is cut into a predetermined size by using a mold, and then, for example, Ag-Pd. (Silver-
An electrode paste composed of palladium or the like is applied to the green sheet by screen printing. At that time, two types of patterns of a positive electrode and a negative electrode are used as a screen mask. Further, a positive electrode green sheet and a negative electrode green sheet are alternately laminated, pressed, and then fired to obtain a laminated ceramic having internal electrodes. After that, external electrodes are attached to connect with the internal electrodes.

FIG. 7 is an exploded perspective view showing an example of a laminated ceramic product. This laminated ceramic product is an intermediate product before cutting out a piezoelectric element, and is a piezoelectric active part 1 in which a large number of PZT sheets are laminated and internal electrodes are formed between the respective layers.
Then, similarly, two substrate parts 2 in which a large number of PZT sheets are laminated are closely adhered to each other, and then fired to obtain a hardened ceramic product. The substrate unit 2
A penetrating window 3 is preformed near the center of the.

[0004]

FIG. 8 (a) is an exploded sectional view of the laminated ceramic product shown in FIG. In such a laminated ceramic product, two types of electrode patterns, a positive electrode 4 and a negative electrode 5, are formed as internal electrodes of the piezoelectric active portion 1 and are drawn out to both end faces. When a voltage is applied between both electrodes, an electric field in the thickness direction is generated in a region where the electrodes overlap each other to perform a piezoelectric operation.

The electrode pattern has a positive electrode 4 and a negative electrode 5.
A certain gap is formed so as not to short-circuit each other. Further, although the internal electrodes themselves are quite thin, when a large number of layers are stacked, the total thickness of the element differs between the regions where the internal electrodes overlap and the regions where they do not overlap. Therefore, the dummy electrode 5a is formed in a region that does not contribute to the piezoelectric operation,
The thickness variation is suppressed as much as possible.

However, in the regions where a certain gap is formed to prevent short circuits, that is, in the regions 6 and 7 where the internal electrodes 4, 5 and 5a do not overlap with each other, the number of electrodes is small and the thickness is insufficient. Who will happen.

FIG. 8B is a sectional view showing a state in which the piezoelectric active portion 1 and the substrate portion 2 are joined. End part 2 of substrate part 2
Since a is located in the regions 6 and 7, a shape defect 1 such as a constriction or a pull-in due to a dent or shoulder sag at the joint portion.
0 has occurred. Therefore, as shown in FIG. 8C, when the external electrode 11 is formed on the surfaces of the piezoelectric active portion 1 and the substrate portion 2 by utilizing vapor deposition, sputtering, or the like, conduction failure occurs at the shape defect 10. I will end up. Therefore, the manufacturing yield of the piezoelectric element is low.

An object of the present invention is to provide a piezoelectric element and a method for manufacturing the same, which can reliably prevent defects such as poor electrode conduction at the joints of laminated green sheets.

[0009]

According to the present invention, a piezoelectric active portion in which piezoelectric layers made of a piezoelectric material and internal electrodes are alternately laminated, and a substrate portion partially bonded to the surface of the piezoelectric active portion are provided.
In a piezoelectric element formed on the surfaces of a substrate portion and a piezoelectric active portion and having an external electrode connected to an internal electrode on the end face of the piezoelectric active portion, internal electrodes on both sides of the piezoelectric layer when viewed in the thickness direction of the piezoelectric element. The piezoelectric element is characterized in that an overlapping region and a non-overlapping region are formed, and the non-overlapping region is deviated from an end portion of the substrate portion. The present invention also includes a step of preparing a laminated green sheet for a substrate portion by punching out a window portion after laminating a plurality of green sheets, and printing an electrode paste on the surface of the green sheet to form a first electrode pattern. A step of preparing a 1st green sheet and a 2nd green sheet having a 2nd electrode pattern, and alternately laminating them to prepare a laminated green sheet for a piezoelectric active portion; A method for manufacturing a piezoelectric element, comprising the steps of joining sheets, followed by firing, and cutting the laminated ceramic obtained by firing into a predetermined shape, and then forming external electrodes, wherein the piezoelectric element has a thickness direction. As seen from the above, the electrode is formed so that the region where the first electrode pattern and the second electrode pattern do not overlap is deviated from the end of the window. It is a method for producing a child.

[0010]

According to the present invention, as seen from the thickness direction of the piezoelectric element, the regions where the internal electrodes on both sides of the piezoelectric layer do not overlap with each other are separated from the end portion of the substrate portion. Shape defects such as pulling in at the joint portion with the portion are eliminated. Therefore, when the external electrode is formed on the surface, electrode conduction at the joint can be surely realized, and defects such as defective conduction can be prevented.

Further, according to the manufacturing method of the present invention, the electrode is formed so that the region where the first electrode pattern and the second electrode pattern do not overlap with each other deviates from the end of the window when viewed from the thickness direction of the piezoelectric element. As a result, shape defects such as pulling in do not occur at the joint between the piezoelectric active portion and the substrate portion. Therefore, the electrode continuity failure is eliminated when the external electrodes are attached after firing, so that a highly reliable piezoelectric element can be obtained.

[0012]

FIG. 1 is a constitutional view showing a piezoelectric element according to an embodiment of the present invention, and FIGS. 1A to 1D show various examples of arrangement of internal electrodes. FIG. 2 is a perspective view of the piezoelectric element shown in FIG. The piezoelectric element 20 includes a piezoelectric active portion 21 that expands and contracts when a voltage is applied, a substrate portion 30 that holds the piezoelectric active portion 21 from both sides, an internal electrode 23 of the piezoelectric active portion 21,
The external electrodes 32 and 33 are electrically connected to the external electrode 24.

The piezoelectric active portion 21 is constructed by laminating a large number of PZT sheets, and internal electrodes 23 and 24 are alternately formed between the layers. Further, if necessary, the dummy internal electrode 2 that does not participate in the piezoelectric operation is provided in the same plane as the internal electrodes 23 and 24.
3a and 24a are formed, and the thickness of the entire element is made uniform.

The substrate portion 30 is similarly constructed by laminating a large number of PZT sheets. After the piezoelectric active portion 21 and the substrate portion 30 are brought into close contact with each other, they are cured by firing and integrated. After that, the external electrodes 32 and 33 are formed on the surfaces and end faces of the piezoelectric active portion 21 and the substrate portion 30 by using vapor deposition or sputtering. The internal electrode 24 is exposed on the front end surface (left side in FIGS. 1 and 2) of the piezoelectric active portion 21 and is connected to the external electrode 32. The internal electrode 23 is formed on the rear end surface of the piezoelectric active portion 21 (on the right side of FIGS. 1 and 2).
Is exposed and is connected to the external electrode 33.

Next, the operation of the piezoelectric element 20 will be described. When a voltage is applied to the external electrodes 32 and 33, an electric field is generated between the internal electrode 23 and the internal electrode 24, the PZT layer of the piezoelectric active portion 21 is polarized in the thickness direction, and stress is generated by the piezoelectric effect. The stress causes a longitudinal strain in the thickness direction in the piezoelectric active portion 21, and further a lateral strain corresponding to the Poisson's ratio in the longitudinal direction of the piezoelectric element 20. Therefore, if the rear side of the piezoelectric element 20 is fixed, the tip is linearly displaced according to the applied voltage. In this way, the piezoelectric element 20 which converts an electric signal into a mechanical displacement is obtained.

First, in FIG. 1A, as viewed in the thickness direction of the piezoelectric element 20, a region 25 where the internal electrodes 23, 24, 24a on both sides of the PZT sheet to be a piezoelectric layer overlap and a region 25 where they do not overlap are formed. To be done. Non-overlapping area 2
5 is formed closer to both end portions than the conventional one shown in FIG. 8 and is separated from the end portion 30a of the substrate portion 30.

Further, in FIG. 1B, the region 25 where the internal electrodes 23, 24 and 24a do not overlap with each other when viewed from the thickness direction of the piezoelectric element 20 is formed closer to the inner side than the conventional one shown in FIG. It is removed from the end portion 30a of the substrate portion 30.

Further, in FIGS. 1C and 1D, when viewed from the thickness direction of the piezoelectric element 20, the internal electrodes 23,
One of the regions 25 where 24 and 24a do not overlap is formed closer to the inner side and the other is formed closer to the end, and both regions 25 are separated from the end 30a of the substrate unit 30.

Thus, the region 2 where the internal electrodes do not overlap each other
The influence of the dent or shoulder sag generated at 5 does not extend to the joint near the end 30a, and shape defects such as constriction and pull-in are eliminated, and defective conduction of the external electrode 32 can be prevented.

FIG. 3 is a process drawing showing the method of manufacturing the piezoelectric element 20. Hereinafter, the piezoelectric element 20 shown in FIG. 2 will be described as an example. First, in step S1, PZT powder, a binder, a plasticizer, a dispersant, a surfactant, an antifoaming agent, pure water, and the like are mixed at a predetermined ratio to prepare a slurry-like green sheet raw material. Next, in step S2, the slurry-like raw material is placed on a moving PET (polyethylene terephthalate) film and uniformly spread to a thickness of about 26 to 27 μm using a blade to form a green sheet, and then a green sheet. The PET film is peeled off and wound into rolls.

From here, steps S3 to S7 of the piezoelectric active portion 21 are performed.
And the steps S8 to S12 of the substrate unit 30. In step S3, while unrolling the rolled green sheet, it is cut into a size of, for example, 100 mm × 90 mm, and in step S4, the cut sheet is irradiated with transmitted light to check for the presence of defects such as pinholes and foreign substances. Inspect and remove defective sheets. In step S5, the internal electrodes 23, 24,
Using two types of print patterns corresponding to the shape of 24a, screen-print the electrode paste on the cutting sheet,
In step S6, the ink surface is left to stand for 2 minutes at room temperature for leveling, and then left at 60 ° C. for 4 minutes to be dried. A total of 19 sheets obtained by printing the two types of electrode patterns obtained in this manner are alternately laminated, and two sheets without printing are laminated on both sides to form the piezoelectric active portion 2.
1 to obtain a laminated green sheet before firing.

On the other hand, in steps S8-S9, steps S3-S
Similar to 4, the roll-shaped green sheet is unwound and cut into a predetermined size, and then a defect inspection is performed. In step S10,
After stacking 14 cutting sheets, store them in a vinyl chloride resin bag and evacuate for about 100 seconds to seal, then store in another bag and evacuate for about 30 seconds to seal and waterproof. A vacuum bag with a double bag structure is applied to improve the performance.
In step S11, a laminated green sheet in a vacuum-packed state is put into a high-pressure container filled with a liquid such as water by using a WIL (hot water isostatic laminating) device, and the temperature is 60 ° C.
Isostatic pressing is performed under conditions of a hydrostatic pressure of 500 kg / cm ² and a pressure holding time of 5 minutes. This isotropic pressure press uses the principle of Pascal, and compared to a mechanical press that sandwiches it from both sides, even if the surface shape has irregularities, the magnitude and direction of the applied pressure will be uniform, so the laminated green The adhesion of the sheet can be significantly improved. Next, step S1
The vacuum pack is opened at 2, the laminated green sheet is set in the mold, and the shearing process is performed by punching, and the substrate portion 3
Form a window at 0.

Next, in step S13, the laminated green sheets for the substrate portion 30 obtained in step S12 are placed on both sides of the laminated green sheet for the piezoelectric active portion 21 obtained in step S7, and a jig is used. They are mutually positioned, coated with a water-based glue, and pressed under the conditions of a temperature of 40 ° C., a pressure of 40 kg / cm ² , and a pressing time of 5 seconds to temporarily press-bond the laminated green sheets.

FIG. 4 is an exploded sectional view of the laminated green sheet obtained in step S13, and FIG. 5 is a plan view thereof.
The PZT sheet 22 having the internal electrodes 23 printed with the first electrode pattern and the PZT sheets 22 having the internal electrodes 24 and 24 a printed with the second electrode pattern are alternately laminated to form the piezoelectric active portion 21. At this time, when viewed from the element thickness direction,
An electrode is formed so that a region where the first electrode pattern and the second electrode pattern overlap with each other and a region where they do not overlap each other are separated from the end of the window.

Further, the substrate portion 30 having the window 31 formed thereon is brought into close contact with the upper and lower surfaces of the piezoelectric active portion 21. 8 × 6 windows 31 are formed in the substrate portion 30 and are arranged so that the front ends and the rear ends of the piezoelectric elements 20 are continuously provided.
In the region of the window 31, the internal electrodes 23 and 24 are printed so as to overlap each other, and after firing, the portion sandwiched between the internal electrodes 23 and 24 performs a piezoelectric operation. In addition, in order to make the entire thickness uniform, even in the wide portion other than the window 31, the dummy internal electrode 2 is formed.
Although 4a is formed, the internal electric field is not applied to this portion and the piezoelectric operation is not performed.

Returning to FIG. 3, in step S14, step S1
The same double bag structure vacuum packing as 0 is applied, and the process S15
, And left in a WIL apparatus at a temperature of 65 ° C. for 20 minutes and then in a WIL apparatus container at a temperature of 60 ° C. for 2 minutes, then at a temperature of 60 ° C. and a hydrostatic pressure of 1000 kg / cm ² ,
Isotropic pressing is performed under the condition that the pressure holding time is 20 minutes.

Next, in step S16, the laminated green sheets are sandwiched between setter substrates made of MgO, and then the temperature is set to 5
The mixture is heated at 00 ° C. for 1.5 hours to perform calcination to vaporize the binder in the green sheet, and the temperature is set to 11 in step S17.
When the main firing is performed by heating at 55 ° C for 3 hours, the thickness is 1
A laminated ceramic of about mm is obtained.

Next, in step S18, the laminated ceramic is fixed to the silicon wafer with wax and cut into a predetermined shape using a dicing saw.

FIG. 6A is a plan view of the laminated ceramic cut in step S18. In the arrangement of the windows 31 shown in FIG. 5, when the center of the narrow portion and the wide portion other than the windows 31 is cut, a shape having eight windows 31 shown in FIG. 6A is obtained, and the narrow portion is piezoelectric. The wide portion corresponds to the front end of the element 20, and the wide portion corresponds to the rear end of the piezoelectric element 20.

Returning to FIG. 3, in step S19, after the surface of the cut laminated ceramic is polished, the internal electrodes 23,
The end face is polished so that 24 is exposed. In step S20, the laminated ceramic is subjected to ultrasonic cleaning and steam cleaning with a chlorocene solvent to remove wax, and in step S21, ultrasonic cleaning is performed using a surfactant, pure water, isopropyl alcohol, etc., and then thoroughly dried. Let

Next, in step S22, the laminated ceramic is stored in a masking jig, and then Cr (thickness: 0.2 μm), Ni (thickness: 0.4 μm) is used by vapor deposition or sputtering.
m) and Au (thickness 0.2 μm) in this order,
External electrodes 32 and 33 as shown in (b) are formed. According to the present invention, when this external electrode is attached, a shape defect such as a constriction is eliminated at the step portion where the substrate portion 30 and the piezoelectric active portion 21 are joined together, so that no conduction failure occurs.

Next, in step S23, the monolithic ceramic shown in FIG. 5B is divided into eight pieces, and as shown in FIG.
1 is cut into one monolithic ceramic, width 80
When cut to about μm, a large number of piezoelectric elements 20 shown in FIG. 2 are obtained.

[0033]

As described in detail above, according to the present invention, shape defects such as pull-in do not occur at the joint between the piezoelectric active portion and the substrate portion. Therefore, when the external electrode is formed on the surface, the electrode conduction at the bonding portion is surely realized, so that there is no defect such as conduction failure and a highly reliable piezoelectric element can be obtained.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a piezoelectric element according to an embodiment of the present invention, and FIGS. 1A to 1D show various arrangement examples of internal electrodes.

FIG. 2 is a perspective view of the piezoelectric element shown in FIG.

FIG. 3 is a process drawing showing the method of manufacturing the piezoelectric element 20.

FIG. 4 is an exploded cross-sectional view of a laminated green sheet obtained in step S13.

FIG. 5 is a plan view of a laminated green sheet obtained in step S13.

6A is a plan view of the laminated ceramic cut in step S18, and FIG. 6B is a plan view of a state in which external electrodes 32 and 33 are formed in step S22.
(C) is a plan view of the state cut in step S23.

FIG. 7 is an exploded perspective view showing an example of a laminated ceramic product.

8 (a) is an exploded cross-sectional view of the monolithic ceramic product shown in FIG. 7, and FIG. 8 (b) is a cross-sectional view showing a bonded state of the piezoelectric active portion 1 and the substrate portion 2. FIG. 8 (c) is a partially enlarged view showing a conduction failure due to a shape defect.

[Explanation of symbols]

 20 Piezoelectric element 21 Piezoelectric active part 22 PZT sheet 23, 23a, 24, 24a Internal electrode 30 Substrate part 30a End part 31 Window 32, 33 External electrode

Claims (2)

[Claims] 1. A piezoelectric active part in which piezoelectric layers made of a piezoelectric material and internal electrodes are alternately laminated, a substrate part partially bonded to the surface of the piezoelectric active part, and surfaces of the substrate part and the piezoelectric active part. A piezoelectric element having an external electrode connected to the internal electrode at the end face of the piezoelectric active portion, the area where the internal electrodes on both sides of the piezoelectric layer overlap and the area where the internal electrodes do not overlap when viewed from the thickness direction of the piezoelectric element. The piezoelectric element is characterized in that the region where the gap is formed and the non-overlapping region is separated from the end portion of the substrate portion. 2. A step of preparing a laminated green sheet for a substrate portion by punching out a window portion after laminating a plurality of green sheets, and printing an electrode paste on the surface of the green sheet,
A step of preparing a first green sheet having an electrode pattern and a second green sheet having a second electrode pattern, and alternately stacking the green sheets to prepare a laminated green sheet for a piezoelectric active portion; A method of manufacturing a piezoelectric element, comprising: a step of firing a laminated green sheet for a substrate part, followed by firing; and a step of cutting the laminated ceramic obtained by firing into a predetermined shape and then forming an external electrode. When viewed from the thickness direction of the element, the first electrode pattern and the second electrode pattern
A method for manufacturing a piezoelectric element, comprising forming an electrode so that a region that does not overlap with the electrode pattern deviates from an end portion of the window portion.