JPH0660713A - Conductive paste for piezoelectric element - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a conductive paste for a piezoelectric element, which can sufficiently exhibit the original electrical characteristics of the piezoelectric element having a large displacement amount. [Structure] Particles of a base metal or a noble metal and a noble metal compound that decomposes by heating are used as a conductive material. The fine noble metal (Pd) particles 4 generated by being decomposed at the boundary of the metal (Al) particles 3 and the interface of the piezoelectric element 1 by heating are dispersed. Since a good ohmic contact property with the piezoelectric element 1 is secured, the amount of displacement of the piezoelectric element 1 is large.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric paste for forming a piezoelectric element electrode, and more particularly to a piezoelectric paste having a large displacement.

[0002]

2. Description of the Related Art In recent years, as various mechanical driving elements, instead of actuators utilizing electromagnetic force, laminated piezoelectric actuators utilizing the piezoelectric effect of ceramics such as lead zirconate titanate (PZT) porcelain have been widely used. ing. This multi-layer piezoelectric actuator generates less heat, is small, and can be driven at high speed.
Since displacement characteristics can be expected, it is extremely promising as various mechanical drive elements. However, since the mechanical displacement due to the piezoelectric effect is extremely small in nature, it is provided as a piezoelectric laminate having a structure in which piezoelectric elements and electrodes are alternately laminated in multiple layers to obtain a large displacement amount and covered with an insulating protective layer. There is.

For example, in Japanese Unexamined Patent Publication No. 62-165381, a plurality of piezoelectric elements having a disk shape are laminated, and electrodes are respectively interposed between the plurality of piezoelectric elements. There is disclosed a laminated piezoelectric actuator in which a plurality of piezoelectric elements are connected in parallel. In this laminated piezoelectric actuator, when the electrodes are energized, the piezoelectric element extends in the axial direction and operates as an actuator.

Conventionally, a noble metal material such as silver, silver-palladium, platinum or gold is mainly used as the conductive material of the conductive paste for forming the internal electrodes of the piezoelectric element. Since this noble metal material has a good ohmic contact property with the piezoelectric element, the piezoelectric element can exhibit excellent electrical characteristics, but it has a drawback of high cost. Therefore, in recent years, low-cost base metal materials have begun to be used as the conductive paste, as reported in, for example, Japanese Patent Laid-Open No. 3-233805.

[0005]

When the base metal material is used as the conductive material of the conductive paste, since the base metal material has a lower ohmic contact with the piezoelectric element than the noble metal material, the displacement amount of the piezoelectric element is small. Fell. Therefore, there is a problem that the conductive paste using a base metal material as the conductive material cannot fully utilize the original characteristics of the piezoelectric element. Further, in the industry, there is a demand for a conductive paste for a piezoelectric element, which can obtain a higher displacement amount than the conductive paste for a piezoelectric element using a conventional noble metal as a conductive material.

The present invention has been made in view of the above circumstances, and a piezoelectric element electrode capable of sufficiently exhibiting the original electrical characteristics of the piezoelectric element, which can obtain a high displacement amount, and a high displacement amount can be obtained. It is an object of the present invention to provide not only a low-cost conductive paste for piezoelectric elements.

[0007]

A conductive paste for a piezoelectric element according to the present invention which solves the above-mentioned problems is a conductive paste for a piezoelectric element which is composed of a conductive material, a glass frit and a spreading agent. As the material, metal particles and a compound of a noble metal which is decomposed by heating to become a noble metal are used.

[0008]

The electroconductive paste for a piezoelectric element of the present invention is applied onto the piezoelectric element by screen printing or the like to form a film. Then, it heat-processes for baking. In this process, the spreading agent is volatilized and the noble metal compound is decomposed to become an extremely fine noble metal. On the other hand, the glass frit sinters with each other and integrates with the metal particles and fine noble metal. Here, since the noble metal generated by thermal decomposition is extremely fine, the fine noble metal covers the surfaces of the metal particles and the interface of the piezoelectric element. Since the noble metal fine particles generated at the interface of the piezoelectric element enhance the ohmic contact property with the piezoelectric element, the electrical characteristics of the piezoelectric element are improved, and the piezoelectric element is superior to the one using only base metal particles as the conductive material. The amount of displacement increases significantly.

Since many precious metal particles having good ohmic contact with the piezoelectric element come into contact with the piezoelectric element,
The polarizability of the piezoelectric element also becomes good.

[0010]

EXAMPLES Examples of the present invention will be specifically described below. Example 1 Using aluminum particles having an average particle size of 3 μm and palladium acetate (Pd (OCOCH ₃ ) ₂ ) powder,
Sample No. shown in Table 1 1 to No. Five kinds of conductive materials up to 5 were prepared. The numbers in parentheses in Table 1 indicate the weight composition of the conductive material when converted to metallic palladium. 100 g of these conductive materials, 10 g of low-melting-point glass frit, 2 g of ethyl cellulose, and 20 g of terpineol were blended and sufficiently kneaded with a raking machine to prepare a total of 132 g of five conductive pastes for piezoelectric elements.

[0011]

[Table 1] Each of these pastes was added to PZT (PbZrO ₃ · P
Both sides of a disk-shaped piezoelectric element (φ17 mm × t0.5 mm) made of bTio ₃ ) -based ceramics were printed with a 300 mesh screen printer. After this, dry (120 ℃
10 minutes), and heat-treated at a temperature of 600 to 900 ° C. for 10 to 30 minutes in the air atmosphere and baked. A piezoelectric element 1 having the electrode 2 thus obtained is shown in FIG. The five types of piezoelectric elements having the electrodes 2 formed as described above were subjected to polarization treatment by applying a DC voltage of 1.5 kV to both surfaces of the electrodes 2 in silicone oil.

Next, each of these five types of piezoelectric elements is
A pulse voltage of 200 to +600 V was applied for pulse driving, and the displacement amount of each piezoelectric element was measured. The measured amounts of displacement are also shown in Table 1. For reference, a conductive paste for a piezoelectric element was prepared by the above method using 100 g of aluminum particles having an average particle size of 3 μm without using palladium acetate, and the electrode of the piezoelectric element was prepared using this paste. Was formed and similarly polarized, the displacement amount of this piezoelectric element was measured in the same manner. The amount of displacement of this piezoelectric element was 0.67 μm. Also, using a commercially available conventional conductive paste for piezoelectric elements that uses silver powder as the conductive material, similarly form the electrodes of the piezoelectric element, polarize in the same manner, and then measure the displacement amount of that piezoelectric element in the same manner. did. The displacement amount of this piezoelectric element was 0.73 μm.

Using the conductive paste for piezoelectric element prepared by using only aluminum powder as the conductive material, the conductive paste for piezoelectric element shown in Table 1 is prepared with reference to the displacement amount of the piezoelectric element having electrodes. The displacement amount of the piezoelectric element formed by using each is shown in FIG. In FIG. 2, the horizontal axis represents the compounding amount of the palladium compound used as the conductive material of the conductive paste for a piezoelectric element (100 of the conductive material as a whole).
Weight% ), And the vertical axis represents the improvement rate of the displacement amount by blending the palladium compound in%.

As is apparent from FIG. 2, when the palladium compound was blended in an amount of 1% by weight, the displacement amount of the piezoelectric element was improved by about 5%, and when it was blended in an amount of 5% by weight or more, the displacement amount was improved by 20% and remained constant. The amount of displacement of the piezoelectric element of the conductive paste for piezoelectric element prepared by blending 5% by weight of the palladium compound is compared with the amount of displacement of the piezoelectric element of the conductive paste for piezoelectric element using conventional silver powder. It is about 10% higher.

A conductive paste for a piezoelectric element prepared by blending a palladium compound in an amount of more than 30% by weight is P
The adhesion strength with the ZT piezoelectric element was low, and the electrode peeled off, which was unsuitable. Sample No. suitable as a conductive paste for piezoelectric elements, which has a large amount of displacement and does not peel off. The state of the interface between the electrode and the piezoelectric element in which the electrode was formed using the paste of No. 3 was observed with a microscope. The results are shown in the schematic diagram of FIG. Under the microscope, the size of the palladium particles 4 was observed to be 0.03 to 0.05 μm in diameter. Reference numeral 3 for aluminum particles, reference numeral 1 for piezoelectric elements, reference numeral 2 for electrodes
Indicated by.

For reference, only aluminum particles are used as the conductive material, and the average particle size of the aluminum particles is 1
A conductive paste for piezoelectric element was prepared in the same manner as above with a thickness of μm or less, and electrodes were formed using this paste. As a result, submicron-order aluminum particles were remarkably oxidized in the air or during firing, resulting in an electric resistance value. Has an average particle size of 3
It is more than 10 times higher than that of μm. Also, the adhesion strength with the piezoelectric element was significantly reduced. Therefore, it is not preferable to make the average particle size of the base metal particles as the conductive material smaller than 1 μm. This applies to all base metal particles. (Example 2) Nickel (Ni) particles were used in place of aluminum particles as base metal particles (average particle size 1 µm was used to prepare a conductive paste for a piezoelectric element in the same manner as in Example 1. Nickel as the base metal particles was used. Among the conductive pastes for piezoelectric elements using particles, the one containing 6% by weight of palladium acetate gave the maximum displacement improvement rate, which was 17%, and the conventional silver powder was used. compared to the displacement of the piezoelectric element of the piezoelectric element for the conductive paste was about 7% higher. (example 3) chloroauric instead of palladium acetate in example 1 (I) [AuCl (C ₈ H ₁₄ )] was used, and otherwise the conductive paste for a piezoelectric element was prepared in the same manner as in Example 1. In the conductive paste for a piezoelectric element using chlorogold (I) as the noble metal compound, The one in which 6 wt% of gold (I) was mixed gave the maximum displacement improvement rate, which was 18%, which was almost the same tendency as in Example 1. (Example 4) Silver particles (average particle size: 0.6 μm) were used in place of the aluminum particles of Example 1. A conductive paste for a piezoelectric element was prepared in the same manner as in Example 1 except for the above.
In the conductive paste for piezoelectric elements using silver particles as the metal particles, the one containing 6% by weight of palladium acetate gave the maximum displacement improvement rate. The amount of displacement at this time was 5% higher than the amount of displacement of the conductive paste for piezoelectric elements using only silver powder having an average particle size of 0.6 μm as the conductive material.

In the above examples, base particles of aluminum particles and nickel particles and silver particles of noble metal particles were used as the metal particles. As base metal particles, in addition to aluminum particles and nickel particles, cobalt (Co)
Particles, zinc (Zn) particles, tin (Sn) particles, iron (Fe)
Particles can be used. The average particle size of the base metal particles is 1 μm.
It must be m or more. As precious metal particles,
Besides silver particles, gold (Au) particles, platinum (Pt) particles, palladium (Pd) particles, and rhodium (Rh) particles can be used. It is particularly effective when the average particle size of the noble metal particles is 0.5 μm or more.

Palladium acetate and chlorogold (I) were used as the noble metal compound. In the present invention, in addition to these noble metal compounds, other noble metal compounds that decompose to form fine noble metals by heating can be used. It is preferable that substances other than noble metals are scattered by vaporization during decomposition.
From this viewpoint, an organic compound of a noble metal is preferable. However, it is considered that noble metal halogen compounds and the like are also suitable for use because the halogen element scatters during the heat treatment. Examples of noble metal compounds other than those shown in the examples that can be used include dichloropalladium [PdCl (C ₈ H ₁₂ )], bispalladium [Pd (η-C ₃ H ₅ )], and chloroplatinic acid [H ₂ PtCl].
₆ · 6H ₂ O], rhodium chloride, can be exemplified palladium chloride.

The mixing ratio of the metal particles and the noble metal compound in the conductive material is such that when the noble metal compound is converted to a metal and the metal particles are base metals, the ratio of the noble metal compound is 0.5% by weight to 21% by weight. (Remainder metal particles) are preferred. Also,
If the metal particles are noble metals, the ratio of noble metal compounds is 1.0
% To 21% by weight (residual metal particles) are preferred. In both cases, when the compounding ratio of the noble metal compound is small, the displacement amount improving effect is small. On the contrary, when the compounding ratio of the noble metal compound increases, the adhesion strength with the PZT piezoelectric element decreases.

As the glass frit and the spreading agent which are components other than the conductive material constituting the conductive paste for a piezoelectric element of the present invention, the same ones as the conventional one can be used. The glass frit content is preferably about 5 to 10% when the total paste is 100% by weight. In addition, the spreader is 10
About 23% is preferable. Further, as the piezoelectric element, PZ
Besides the T element, it can be applied to a PT element, a BLSF element, and the like.

[0021]

As described in detail above, according to the present invention, metal particles and a noble metal compound are used as the conductive material. The noble metal compound decomposes during heat treatment to produce extremely fine noble metal. Therefore, the conductive paste for a piezoelectric element of the present invention has excellent ohmic contact with the piezoelectric element, and the amount of displacement of the piezoelectric element increases. In particular, when a base metal is used as the metal particles, the cost can be reduced by using the base metal particles.

Further, the driving voltage of the piezoelectric element can be reduced as compared with the conventional piezoelectric element electrode made of only a base metal.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which electrodes for a piezoelectric element are formed on both surfaces of a piezoelectric element.

FIG. 2 is a diagram showing a relationship between a compounding amount of a palladium compound and a displacement amount of a piezoelectric element.

FIG. 3 is an enlarged schematic diagram of an interface portion between the piezoelectric element electrode and the piezoelectric element according to the first embodiment.

[Explanation of symbols]

 Reference numeral 1 is a piezoelectric element, and 2 is an electrode.

Claims (1)

[Claims] 1. A conductive paste for a piezoelectric element, comprising a conductive material, a glass frit and a spreading agent, wherein the conductive material is composed of metal particles and a noble metal compound which decomposes into a noble metal when heated. A conductive paste for a piezoelectric element, which is characterized in that