JP2000286474A - Multilayered piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure electrical conductivity of the electrode layer of a multilayered piezoelectric element, and in addition, to prevent cracking of the electrode layer when the layer is baked. SOLUTION: A laminate is formed by laminating piezoelectric ceramic layers 11 (green sheets), each carrying an electrode layer 12 formed by printing Ag-Pd alloy conductor paste on one surface upon another and simultaneously baking the laminated ceramic layers 11. The Ag-Pd alloy conductor paste used for printing the electrode layers 12 contains small-diameter Ag-Pd alloy particles having a mean particle diameter of 0.5-3 μm and large-diameter Ag-Pd alloy particles having a mean particle diameter of 4-10 μm as main components and the weight percent ratio between the small- and large-diameter Ag-Pd alloy particles is varied in the range of 1:10 to 20:1, depending on the particle diameters. Therefore, the security of the electrical conductivity of the electrode layer 12 and the prevention of the cracking of the layer 12 at baking of the layer 12 which have conventionally been an antinomic theme can be made compatible.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-layer piezoelectric element in which the amount of displacement is increased by forming a plurality of piezoelectric ceramic layers.

[0002]

2. Description of the Related Art Piezoelectric elements are used as driving sources (piezoelectric actuators) for various devices by utilizing the characteristic of converting electric energy into mechanical displacement by a piezoelectric effect. A general piezoelectric element has a structure in which a conductive paste is printed and fired on both surfaces of a piezoelectric ceramic layer such as PZT (lead zirconate titanate) to form an electrode layer.
When a large displacement is required because the displacement is small, a plurality of piezoelectric ceramic layers are stacked to increase the displacement. When manufacturing such a multilayer piezoelectric element, an electrode layer is printed with a conductive paste on one side of a piezoelectric ceramic layer (green sheet) before firing, and a plurality of piezoelectric ceramic layers are laminated. And the electrode layer are fired simultaneously.

[0003]

When simultaneously firing a multilayer piezoelectric element, a firing crack may occur due to a difference in firing shrinkage behavior between the piezoelectric ceramic layer and the electrode layer. As the number increases, the influence of the difference in firing shrinkage behavior becomes more pronounced and firing cracks are more likely to occur. The difference in firing shrinkage behavior is caused by the fact that the electrode layer starts firing shrinkage before the piezoelectric ceramic layer because the sintering temperature or the sintering start temperature of the electrode layer (conductor paste) is lower than that of the piezoelectric ceramic layer. .

In general, the sintering temperature or the sintering start temperature of the electrode layer (conductor paste) varies depending on the particle size of the conductive particles in the conductive paste. As the particle size of the conductive particles increases, the sintering temperature or the sintering temperature of the electrode layer increases. The sintering start temperature rises, and the difference in firing shrinkage behavior with the piezoelectric ceramic layer decreases. Therefore, it is more advantageous to use conductor particles having a large particle diameter in order to prevent a firing crack.

However, if the particle size of the conductive particles is large, the voids between the conductive particles become large, so that the amount of shrinkage in firing of the electrode layer increases, and the pores (voids) generated in the electrode layer increase.
Electrical continuity failure is likely to occur. Therefore, when conductive particles having a large particle diameter are used, it is necessary to increase the thickness of the electrode layer in order to secure electrical conductivity. However, when the thickness of the electrode layer is increased, in the multi-layer element, the thickness dimension of the element itself increases, and the stress caused by the difference in firing shrinkage behavior with the piezoelectric ceramic layer increases, so that a firing crack is easily generated. .

Therefore, in order to reduce the stress caused by the difference in firing shrinkage behavior, it is necessary to reduce the thickness of the electrode layer. However, when reducing the thickness of the electrode layer, it is necessary to reduce the occurrence of pores. It is necessary to use conductive particles having a small particle size. However, when the conductive particles having a small particle size are used, the sintering temperature or the sintering start temperature of the electrode layer decreases, and the difference in firing shrinkage behavior with the piezoelectric ceramic layer increases, and firing cracks are easily generated. .

[0007] In short, if the particle size of the conductive particles is increased to reduce the difference in firing shrinkage behavior between the electrode layer and the piezoelectric ceramic layer, the pores generated in the electrode layer increase and the electrical conductivity decreases. Conversely, if the particle size of the conductive particles is reduced, the difference in firing shrinkage behavior between the electrode layer and the piezoelectric ceramic layer increases, and firing cracks are more likely to occur.

The present invention solves such a conflicting problem. Therefore, an object of the present invention is to make it possible to ensure both the electrical conductivity of the electrode layer and the prevention of firing cracks. It is another object of the present invention to provide a multi-layer piezoelectric element capable of realizing both improvement in quality and improvement in yield.

[0009]

In order to achieve the above object, a multi-layer piezoelectric element according to claim 1 of the present invention comprises a small Ag / Pd alloy particle having an average particle diameter of 0.5 to 3 μm and an average particle diameter of 0.5 to 3 μm. Has an electrode layer formed by using a conductive paste mainly composed of Ag—Pd alloy particles having a large diameter of 4 to 10 μm. Here, a small diameter Ag.
The Pd alloy particles play a role in reducing pores (voids) generated in the electrode layer and improving electrical conductivity. on the other hand,
Ag / Pd alloy particles having a large average diameter of 4 to 10 μm increase the sintering temperature or the sintering start temperature of the electrode layer,
It serves to reduce the difference in firing shrinkage behavior with the piezoelectric ceramic layer and to prevent firing cracks. As a result, it is possible to ensure both electrical conductivity of the electrode layer and prevention of firing cracks, both of which have been conflicting problems in the related art.

In this case, the weight ratio between the small-diameter Ag / Pd alloy particles and the large-diameter Ag / Pd alloy particles varies depending on the particle size.
It is preferable to set the weight ratio between the d alloy particles and the large diameter Ag / Pd alloy particles in the range of 1:10 to 20: 1.
Within this range, both the effect of ensuring electrical conductivity by the small-diameter Ag / Pd alloy particles and the effect of preventing sintering cracks by the large-diameter Ag / Pd alloy particles can be obtained.
In order to increase the electrical conductivity, the weight ratio of the small-diameter Ag / Pd alloy particles may be increased, and in order to enhance the fire crack preventing effect, the weight ratio of the large-diameter Ag / Pd alloy particles may be increased. .

When the present invention is applied to a multilayer piezoelectric element having 100 or more piezoelectric ceramic layers, a great effect can be obtained. Conventional multi-layer piezoelectric elements
When lamination is performed on more than 00 layers, the influence of the difference in firing shrinkage behavior between the piezoelectric ceramic layer and the electrode layer appears more and more remarkably,
Although it was very difficult to achieve both the prevention of firing cracks and the securing of electrical conductivity, in the present invention, even with 100 layers or more,
The prevention of firing cracks and the securing of electrical conductivity can be achieved at the same time, and the displacement can be greatly increased by increasing the number of layers while improving the yield and quality.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below. First, the structure of the multilayer piezoelectric element will be described with reference to FIG. The piezoelectric ceramic layer 11 of each layer is formed of, for example, a PZT-based piezoelectric ceramic material, has a layer thickness of, for example, 80 to 150 μm, and has a lamination number of, for example, 100 or more. On the surface of the piezoelectric ceramic layer 11 of each layer,
The electrode layer 12 is formed by printing and baking an Ag / Pd alloy-based conductor paste having a composition described later. The thickness of the electrode layer 12 of each layer is 1.5 to 7.5 μm, more preferably,
2 to 5 μm. The electrode layers 12 of each layer are alternately led out to the opposite side surface and connected to a side surface electrode (not shown).

Ag / P used for printing the electrode layer 12 of each layer
d alloy-based conductor paste has an average particle size of 0.5 to 3 μm
Ag / Pd with small diameter (preferably 1.5 to 2.5 μm)
Alloy particles having an average particle size of 4 to 10 μm (preferably 5 to 10 μm)
Ag / Pd alloy particles having a large diameter of 8 μm) as a main component,
In addition, the weight ratio of the small diameter Ag / Pd alloy particles to the large diameter Ag / Pd alloy particles is set in the range of 1:10 to 20: 1 (preferably 1: 2 to 8: 1) according to the particle diameter. are doing.
The Ag / Pd alloy particles had a composition ratio of Ag and Pd of 7
The ratio is preferably set to 5:25 to 65:35.

In this case, the Ag / Pd alloy particles having a small diameter and the Ag / Pd alloy particles having a large diameter may be separately produced and mixed at the above-mentioned weight ratio. Ag with a particle size distribution such that it has an average particle size and weight ratio
Pd alloy particles may be manufactured. In the case of manufacturing repeatedly, the Ag.
The stability is higher when the Pd alloy particles are mixed. Ag ・ Pd
The alloy-based conductor paste is prepared by mixing a resin (eg, ethyl cellulose, acrylic resin, etc.) and a solvent (eg, butyl carbitol acetate, terpineol, etc.) with Ag / Pd alloy particles having the above composition, and kneading them. Ag / Pd alloy particles and organic vehicle (resin + solvent)
Is preferably 50:50 to 70:30, more preferably 55:45 to 65:35.

Next, a method of manufacturing the multi-layer piezoelectric element having the above configuration will be described. For example, a green sheet of piezoelectric ceramic is tape-formed by a doctor blade method using a slurry of a PZT-based piezoelectric ceramic material. Thereafter, the electrode layer 12 is printed on the surface of the green sheet using the conductive paste containing the Ag / Pd alloy particles in the above-described average particle size and weight ratio.

After printing, the green sheet is cut into a product size, divided into individual piezoelectric ceramic layers 11, and 100 or more piezoelectric ceramic layers 11 are laminated and thermocompression bonded. Thereafter, the laminate is fired at a peak temperature of 1100 ° C. to manufacture a multilayer piezoelectric element.

[0017]

The multilayer piezoelectric element of the present invention described above was used to evaluate the incidence of firing cracks and poor conduction.
A sample was created as follows.

First, Ag having a composition ratio of Ag to Pd of 7: 3 is used.
Using Pd alloy particles, a small diameter Ag · Pd alloy particle having an average particle diameter of 2 μm and a large diameter Ag having an average particle diameter of 6 μm
-Pd alloy particles are blended at a weight ratio of 2: 1. Then, a resin containing ethyl cellulose as a main component and a solvent containing butyl carbitol acetate as a main component are added to the Ag / Pd alloy particles after blending, with the Ag / Pd alloy particles: resin:
Solvent = blended in a weight ratio of 60: 5: 35, kneaded,
An Ag / Pd alloy-based conductor paste is prepared.

A green sheet of piezoelectric ceramic is tape-formed by a doctor blade method using a slurry of a PZT-based piezoelectric ceramic material. And the above Ag
Printing a 3 μm electrode layer on the surface of the green sheet using a Pd alloy-based conductor paste.

After printing, the green sheet is cut into a product size, divided into individual piezoelectric ceramic layers, and 300 piezoelectric ceramic layers are laminated and thermocompression bonded. Thereafter, this laminate is fired at a peak temperature of 1100 ° C. to produce a sample (Example) of a multilayer piezoelectric element.

When the thus manufactured 300-layer multilayer piezoelectric element was inspected for the presence of fired cracks or poor conduction, no fired cracks or poor conduction occurred.
The incidences of firing cracks and poor conduction were both 0%.

For comparison, the average particle size was 2 μm.
When a 300-layer multilayer piezoelectric element was manufactured in the same manner using a conductive paste containing only Ag / Pd alloy particles having small diameters as conductive particles in the same manner, firing cracks occurred in half of the samples, and the rate of occurrence of firing cracks was reduced. It has reached 50%.
The reason for this is presumed that if only small-diameter Ag / Pd alloy particles are used, the sintering temperature or sintering start temperature of the electrode layer decreases, and the difference in firing shrinkage behavior with the piezoelectric ceramic layer increases. Is done.

As another comparative example, the average particle size was 6 μm.
When a multilayer piezoelectric element having 300 layers was produced by the same method using a conductive paste containing only Ag / Pd alloy particles having a large diameter of m as conductive particles, conduction failure occurred in all samples, and conduction failure occurred. The rate has reached 100%. The reason for this is that if only large diameter Ag / Pd alloy particles are used, A
It is presumed that the voids between the g · Pd alloy particles are increased, the firing shrinkage of the electrode layer is increased, and pores (voids) generated in the electrode layer are increased.

On the other hand, as in the present invention, a small-diameter Ag
-When a conductor paste containing Pd alloy particles and large-diameter Ag / Pd alloy particles is used, the small-diameter Ag / Pd alloy particles reduce pores (voids) generated in the electrode layer, resulting in electrical conductivity. The Ag / Pd alloy particles having a large diameter increase the sintering temperature or the sintering start temperature of the electrode layer to reduce the difference in firing shrinkage behavior with the piezoelectric ceramic layer, thereby reducing the firing crack. Play a role in preventing. As a result, it is possible to ensure both the electrical conductivity of the electrode layers and the prevention of firing cracks, both of which have been contradictory problems in the related art. Can be reduced to both 0%, yield,
While improving the quality, the displacement amount can be greatly increased by increasing the number of layers.

According to the experimental results of the present inventor, when the average particle diameter of the small-diameter Ag / Pd alloy particles is 0.5 to 3 μm, the pores generated in the electrode layer are reduced and the electrical conductivity is improved. The effect of improving the electrical conductivity is obtained, and when the thickness is set to 1.5 to 2.5 μm, the effect of improving the electrical conductivity becomes more remarkable.

On the other hand, if the average particle diameter of the large diameter Ag / Pd alloy particles is 4 to 10 μm, the effect of preventing sintering cracks can be obtained, and if the average diameter is 5 to 8 μm, the effect of preventing sintering cracks can be improved. It will be even more pronounced.

The weight ratio between the small-diameter Ag / Pd alloy particles and the large-diameter Ag / Pd alloy particles varies depending on the particle size, but the small-diameter Ag / Pd alloy particles and the large-diameter Ag / Pd alloy particles are different from each other.
When the weight ratio with the Pd alloy particles is 1:10 to 20: 1, the effect of securing electrical conductivity by the small-diameter Ag / Pd alloy particles and the effect of preventing the sintering crack by the large-diameter Ag / Pd alloy particles are provided. Can be obtained at the same time, and if the weight ratio is 1: 2 to 8: 1, the above-mentioned effect becomes more remarkable.

By the way, instead of the Ag / Pd alloy particles,
It is conceivable to use a mixed powder or coprecipitated powder of Ag particles and Pd particles. However, a mixed powder or coprecipitated powder of Ag particles and Pd particles is easily oxidized in the resin removal temperature region, and the piezoelectric ceramic has In the vicinity of the sintering temperature, on the contrary, it is reduced and oxygen is rapidly released and released. In addition, the mixed powder and the coprecipitated powder tend to have a lower sintering start temperature than the alloy powder. For this reason,
Delamination, swelling, warpage, and cracks are likely to occur in the multilayer piezoelectric element.

In this regard, the use of Ag / Pd alloy particles obtained by alloying Ag and Pd as in the present invention makes it possible to suppress the oxidation and reduction of Ag and Pd in the firing process, and to solve the above-mentioned problems. it can.

The piezoelectric ceramic used in the present invention is P
Not limited to ZT, other piezoelectric ceramics such as nickel-niobate-titanate-lead zirconate, magnesium-niobate-lead titanate, barium titanate, and lead titanate may be used.

In addition, the present invention may be applied to a multilayer piezoelectric element having 100 layers or less, and the layer thickness of the piezoelectric ceramic layer and the electrode layer may be appropriately changed. Various changes can be made within the embodiment.

[0032]

As is clear from the above description, according to the multilayer piezoelectric element of the first aspect of the present invention, the average particle diameter is 0.5
Ag / Pd alloy particles with a small diameter of ~ 3 µm and an average particle size of 4 ~
Since the electrode layer was formed using a conductive paste mainly composed of Ag / Pd alloy particles having a large diameter of 10 μm,
The effect of ensuring electrical conductivity by the g · Pd alloy particles and the effect of preventing sintering cracks by the large-diameter Ag / Pd alloy particles can be obtained, and both quality improvement and yield improvement can be realized.

According to the second aspect, a small diameter Ag · P
Since the weight ratio between the d alloy particles and the large diameter Ag / Pd alloy particles was set in the range of 1:10 to 20: 1,
The weight ratio can be optimized.

Further, in the third aspect, the present invention is applied to a multi-layer piezoelectric element having 100 or more piezoelectric ceramic layers, so that a multi-layer piezoelectric element having 100 or more layers can improve the yield and quality while improving the yield and quality. The displacement can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a multilayer piezoelectric element showing one embodiment of the present invention.

[Explanation of symbols]

 11: piezoelectric ceramic layer, 12: electrode layer.

Claims (3)

[Claims] 1. A multilayer piezoelectric element comprising a large number of piezoelectric ceramic layers and electrode layers alternately laminated, wherein the electrode layer has a small diameter of 0.5 to 3 μm.
・ Pd alloy particles and large diameter Ag having an average particle diameter of 4 to 10 μm
・ Print conductor paste mainly composed of Pd alloy particles
A multilayer piezoelectric element formed by firing. 2. The weight ratio of said small diameter Ag.Pd alloy particles to said large diameter Ag.Pd alloy particles is 1: 10-2.
2. The multilayer piezoelectric element according to claim 1, wherein the ratio is set in a range of 0: 1. 3. The method according to claim 1, wherein the number of laminated piezoelectric ceramic layers is 100.
The multilayer piezoelectric element according to claim 1, wherein the multilayer piezoelectric element has at least two layers.