JP2003197997A - Method of manufacturing laminate type piezoelectric ceramic element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing a laminate type piezoelectric ceramic element, which is superior in piezoelectric characteristics and shows high reliability. <P>SOLUTION: In the laminate type piezoelectric ceramic element where inner electrodes containing alloy, which has Ag as main component, are formed via ceramic layers, the ceramic layers and the inner electrodes are simultaneously baked and are re-baked in atmosphere having oxygen concentration of 10% or less. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a piezoelectric ceramic element used for a piezoelectric resonator, a piezoelectric actuator, a piezoelectric filter, a piezoelectric buzzer, a piezoelectric transformer and the like. In particular, the present invention relates to a method for manufacturing a laminated piezoelectric ceramic element having an internal electrode of an alloy containing Ag as a main component.

[0002]

2. Description of the Related Art Conventionally, a piezoelectric ceramic element used for a piezoelectric resonator, a piezoelectric actuator, a piezoelectric filter, a piezoelectric buzzer, a piezoelectric transformer, etc., has no structural defects and is highly reliable, depending on each application. It is well known that firing under optimal conditions is essential to have the above-mentioned component characteristics, and various efforts have been made so far.

For example, in Japanese Unexamined Patent Publication No. 2-74566, the atmosphere in the furnace is maintained at an oxygen concentration of 50% by volume or more in the temperature rising process to the firing temperature, and the atmosphere in the furnace is maintained in the oxygen concentration in the holding process at the firing temperature. Is 1 / when the temperature rise process
It shows a process of firing under conditions of 2 to 10% by volume. This increases the oxygen concentration in the closed pores of the ceramic formed at this time in the temperature raising process under the high oxygen atmosphere condition where the oxygen concentration is 50% by volume or more, and then increases the oxygen concentration in the holding process at the firing temperature. If the volume of the heating step is set to 1/2 to 10% by volume, the difference in oxygen concentration between the closed pores of the ceramic and the outside air becomes large, and thus the diffusion rate of oxygen becomes large. It has been proposed that ceramics can be densely sintered with high productivity.

Further, Japanese Unexamined Patent Publication No. 4-357164 and Japanese Unexamined Patent Publication No. 10-95665 disclose a process of firing under an atmospheric condition where the oxygen concentration is 80% by volume or more in the entire firing profile. It is said that this makes it possible to obtain a dense and highly reliable piezoelectric ceramic element, particularly a piezoelectric resonator, in which voids and structural defects of the ceramic sintered body are suppressed.

Further, regardless of the type of internal electrode, there is also known a process of firing in the air, that is, in an atmosphere having an oxygen concentration of about 21% by volume in the entire firing profile, which is generally used in various piezoelectric ceramic parts. Has been applied to.

[0006]

However, in the case of the conventional firing process used in the piezoelectric ceramic element as described above, the unfired laminate in which the internal electrodes are made of an alloy containing Ag as a main component is used. When fired,
There is a problem in that Ag contained in the internal electrodes is taken into the ceramic particles in the piezoelectric ceramic layer to deteriorate the piezoelectric characteristics.

Therefore, an object of the present invention is to provide a method for manufacturing a laminated piezoelectric ceramic element having further excellent piezoelectric characteristics and high reliability.

[0008]

In order to achieve the above object, a method for manufacturing a laminated piezoelectric ceramic element of the present invention comprises:
A step of applying a conductive paste containing an alloy containing Ag as a main component on a ceramic green sheet containing a piezoelectric ceramic material, stacking the ceramic green sheets into a laminated body, and firing the laminated body first. Step (hereinafter referred to as main calcination) and the laminated calcination product have an oxygen concentration of 1
And a step of firing again in an atmosphere of 0% by volume or less (hereinafter referred to as re-firing).

Here, the oxygen concentration in the re-firing is set to 10% by volume or less, because when it exceeds 10% by volume, the effect that Ag incorporated in the ceramic grains in the main firing precipitates at the grain boundaries of the ceramics. This is because it is not sufficiently exhibited and the piezoelectric characteristics and reliability are not improved. On the other hand, the lower limit of the oxygen concentration in the re-baking is not particularly limited, but the effect is obtained at 0.05% by volume, and the oxygen concentration may be further lowered depending on the baking conditions.

For example, in the case of lead zirconate titanate (PZT) type compound, the oxygen concentration is about 21% by volume.
Is fired under the atmospheric condition or the atmospheric condition where the oxygen concentration is about 21% by volume or more. The firing temperature in the maximum temperature range is set to a temperature at which sintering of the laminated body is completed under the above-mentioned atmospheric conditions, specifically, a temperature at which the packing density of the laminated fired body is 99% or more of the theoretical density. . The holding time in the maximum temperature range is set according to the same idea as in the case of the above firing temperature.

Further, after maintaining the maximum temperature range in the main firing, the temperature may be lowered to 300 ° C. or lower, or the temperature may be once cooled to room temperature and then re-fired.

The heating rate and cooling rate in the main calcination are, for example, for lead zirconate titanate (PZT) type compounds, set in the range of 1 to 10 ° C. per minute, and the maximum temperature The retention time in the zone is set within the range of 1 to 10 hours.

On the other hand, the re-baking is carried out, for example, in the case of a lead zirconate titanate (PZT) -based compound, under an atmosphere condition where the oxygen concentration is 10% by volume or less. Further, the firing temperature in the highest temperature range in the re-firing is set lower than the firing temperature in the highest temperature range in the main firing. For example, in the case of lead zirconate titanate (PZT) -based compound, the temperature is set to be about 20 ° C. to 50 ° C. lower than the top temperature of main firing. This is to prevent the deterioration of the piezoelectric characteristics due to the evaporation of Pb.

Further, the rate of temperature increase and the rate of temperature decrease in the re-baking are, for example, for lead zirconate titanate (PZT) type compounds, set in the range of 1 to 10 ° C. per minute, and the maximum temperature. The retention time in the zone is set within the range of 1 to 10 hours.

However, the firing conditions for the main firing and the re-firing are not limited to the above-mentioned conditions, but the type (composition system) of the piezoelectric ceramic material containing the compound of the Pb element.
The optimum firing temperature, heating rate, holding time, and cooling rate may be selected according to

As the piezoelectric ceramic material in the ceramic green sheet, in addition to the lead zirconate titanate (PZT) -based compound shown above, a lead titanate (PbTiO ₃ ) -based compound and lead metaniobate ( PbN
b ₂ O ₆ ) -based compounds and lead metatantalate (PbT
a ₂ O ₆ ) -based compounds and the like.

The conductor contained in the conductive paste for internal electrodes is composed mainly of Ag and contains Ag in an amount of 100% by weight or Pd in an amount of 50% by weight or less.

The atmosphere having an oxygen concentration of 10% by volume or less is characterized by an atmosphere containing nitrogen as a main component.

In addition to nitrogen, the atmosphere gas may contain an inert gas such as argon or carbon dioxide in the atmosphere to the extent that the piezoelectric characteristics are not adversely affected.

Further, it is desirable that the main firing and the re-firing be performed by different firing devices.
This is because the atmosphere in the firing process can be accurately controlled.

As described above, according to the method of manufacturing a laminated piezoelectric ceramic element of the present invention, in the laminated piezoelectric ceramic element in which the internal electrode containing the alloy containing Ag as a main component is formed via the ceramic layer, By re-baking the above-mentioned internal electrode and the above-described internal electrode simultaneously in an atmosphere having an oxygen concentration of 10% by volume or less, Ag taken in the grains of the ceramic at the time of firing is precipitated in the grain boundary in the re-baking process. However, since the piezoelectric characteristics of the element, which have been degraded by incorporating Ag into the ceramic grains, are improved, it is possible to improve the piezoelectric characteristics and sufficiently secure high reliability.

Therefore, it becomes possible to obtain a laminated piezoelectric ceramic element having more excellent piezoelectric characteristics and reliability.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the method for manufacturing a laminated piezoelectric actuator, which is an example of the laminated piezoelectric ceramic element of the present invention, will be described in detail below with reference to examples.

[Example 1] First, Pb was used as a starting material.
₃ O ₄ , TiO ₂ , ZrO ₂ , and SrCO ₃ were prepared. Then, Pb _0.98 Sr _0.02 (Zr _0.45 Ti _0.55 ) O
_The above raw materials were weighed and wet mixed in a ball mill so that a piezoelectric ceramic composition of ₃ was obtained.

Further, the above mixture is dehydrated and dried,
By calcining at a temperature of 800 ° C for 2 hours and crushing,
A calcined powder was obtained.

Next, additives such as an acrylic organic binder, an organic solvent, and a plasticizer were added to the calcined powder, and the mixture was wet-mixed with a ball mill to obtain a slurry.

This slurry was molded by the doctor blade method to prepare a ceramic green sheet having a thickness of about 40 μm.

On this ceramic green sheet, Ag
/ Pd = 80% by weight / 20% by weight of a conductive paste containing a conductor is applied by a screen printing method so that the thickness after firing is 1.0 to 3.0 μm,
It was dried to obtain a ceramic green sheet on which a layer for internal electrodes was formed. After that, the ceramic green sheets were stacked and pressed by hot pressing to obtain an integrated laminate.

Next, this laminated body is preliminarily subjected to about 50
The binder component was sufficiently removed at a temperature of 0 ° C., and the main firing and the re-baking were performed using the firing profile and firing atmosphere shown in Table 1.

The main calcination and the re-calcination are carried out by different calcination apparatuses. In both the main calcination and the re-calcination, the temperature rising rate is 3 ° C. per minute, the holding time in the maximum temperature range is 2 hours, and the temperature is lowered. The rate was 4 ° C / min.

Further, in Table 1, those marked with * are outside the scope of the present invention, and all other items are within the scope of the present invention.

[0032]

[Table 1]

The laminated body after re-baking was cut into a predetermined size, and then external electrodes were applied and baked to form electrically connected internal electrodes, thereby obtaining a laminated piezoelectric actuator. .

Then, in insulating oil at 60 ° C., 4.0 k
A DC electric field of V / mm was applied for 60 minutes to perform polarization treatment. Then, in air at 120 to 200 ° C, 30 to 6
After aging for 0 minutes, the intended laminated piezoelectric actuator 10 as shown in FIG. 1 was obtained. In FIG. 1, 11 is an internal electrode, 12 is an external electrode, and 13 is a piezoelectric ceramic.

The piezoelectric strain constant | d ₃₁ | of these laminated piezoelectric actuators and the electrical resistivity ρ of the piezoelectric ceramics
I asked. The results are shown in Table 2.

│d ₃₁ │ was obtained by measuring the amount of strain with a laser Doppler vibrometer and calculating the piezoelectric strain constant in the 31 direction. Also, ρ is DC between the internal electrodes through the ceramic layer.
The insulation resistance when a voltage of 50 V was applied for 30 seconds was measured, the insulation resistance was multiplied by the electrode area, and this value was divided by the thickness of the ceramic layer between the internal electrodes.

│d ₃₁ │ represents an average value (in the table, referred to as AVE.) And 3σ (σ represents a standard deviation), and ρ represents an average value.

In Table 2, those marked with * are outside the scope of the present invention, and other than that are within the scope of the present invention.

[0039]

[Table 2]

As is clear from Tables 1 and 2, the oxygen concentration was higher than that of sample No. 4 which was re-fired in the air, that is, in the atmosphere in which the oxygen concentration was about 21%, after the main firing. According to the sample numbers 1, 2, and 3 which are re-fired in respective nitrogen atmospheres of 0.05% by volume, 1% by volume, and 10% by volume, the piezoelectric strain constant d ₃₁ and the electrical resistivity ρ of the piezoelectric ceramic are shown. It can be seen that is improved, and the characteristic variation of d ₃₁ is also reduced.

It is considered that this is largely due to the fact that the oxygen concentration was lowered in the atmosphere for re-firing.

That is, Ag that has been incorporated into the grains during firing is precipitated at the grain boundaries in the re-firing process, and the incorporation of Ag improves the piezoelectric characteristics of the element, which has been degraded.

As described above, the conditions for the firing atmosphere are:
In the re-firing process after the main firing, by satisfying the nitrogen atmosphere condition where the oxygen concentration is 10% by volume or less, it is possible to improve the piezoelectric characteristics and insulating properties.

Example 2 First, Pb was used as a starting material.
₃O_Four, TiO₂, ZrO₂, Cr₂O₃, And Sb ₂O₃To
I prepared. Then, 97% by weight of Pb (Zr_0.47Ti
_0.53) O₃1% by weight of Cr as an additive to₂O₃And 2 weight
% Sb₂O₃A piezoelectric ceramic composition containing
As above, weigh the above raw materials and wet mix them with a ball mill.
did. Further, the above mixture is dehydrated and dried to obtain 80
Calcination by calcination at 0 ° C for 2 hours and crushing
A powder was obtained.

Next, additives such as an acrylic organic binder, an organic solvent, and a plasticizer were added to this calcined powder, and the mixture was wet-mixed in a ball mill to obtain a slurry.

This slurry was molded by the doctor blade method to prepare a green sheet having a thickness of about 80 μm.

On this ceramic green sheet, Ag
/ Pd = 80% by weight / 20% by weight of a conductive paste containing a conductor is applied by a screen printing method so that the thickness after firing is 1.0 to 3.0 μm,
It was dried to obtain a ceramic green sheet on which a layer for internal electrodes was formed. After that, the ceramic green sheets were stacked and pressed by hot pressing to obtain an integrated laminate.

Next, this laminated body is preliminarily subjected to about 50
The binder component was sufficiently removed at a temperature of 0 ° C., and the main firing and the re-baking were performed using the firing profile and firing atmosphere shown in Table 3.

The main calcination and the re-calcination are carried out by different calcination apparatuses. In both the main calcination and the re-calcination, the temperature rising rate is 3 ° C. per minute, the holding time in the maximum temperature range is 2 hours, and the temperature is lowered. The rate was 4 ° C / min.

Further, in Table 3, those marked with * are outside the scope of the present invention, and other than that are within the scope of the present invention.

[0051]

[Table 3]

The laminated body after this re-baking was cut into a predetermined size, and then external electrodes were applied and baked to form an electrically connected internal electrode, thereby obtaining a laminated piezoelectric actuator. .

Then, in insulating oil at 60 ° C., 4.0 k
A DC electric field of V / mm was applied for 60 minutes to perform polarization treatment. Then, in air at 120 to 200 ° C, 30 to 6
Aging was performed for 0 minutes to obtain a desired laminated piezoelectric actuator 10 as shown in FIG.

The electromechanical coupling coefficient K ₃₁ and the mechanical quality coefficient Qm ₃₁ of these laminated piezoelectric actuators were measured with an impedance analyzer.

Further, ρ is measured by measuring the insulation resistance when a voltage of DC 50 V is applied for 30 seconds between the internal electrodes through the ceramic layers, multiplying the insulation resistance by the electrode area, and multiplying this value by the ceramic layer between the internal electrodes. Calculated by dividing by the thickness.

The results are shown in Table 4. K ₃₁ , Qm ₃₁ , ρ
All of the values of 1 indicate the average value (in the table, referred to as AVE.).

In Table 4, those marked with * are outside the scope of the present invention, and other than that are within the scope of the present invention.

[0058]

[Table 4]

As is clear from Tables 3 and 4, after the main firing
In the atmosphere, that is, an atmosphere where the oxygen concentration is about 21%
Compared to sample No. 8 which is re-fired in
0.05% by volume, 1% by volume, and 10% by volume, respectively
According to sample Nos. 5, 6, and 7, which are re-fired in an elementary atmosphere
For example, the electromechanical coupling coefficient of laminated piezoelectric actuators
K ₃₁, Mechanical quality factor Qm₃₁, And piezoceramic
It can be seen that the electrical resistivity ρ is improved.

It is considered that this is largely due to the fact that the oxygen concentration was lowered in the atmosphere for re-firing.

That is, Ag that has been incorporated into the grains during firing is precipitated at the grain boundaries in the re-firing process, and the reduced piezoelectric characteristics of the element are improved by incorporating Ag.

As described above, the conditions for the firing atmosphere are:
In the re-firing process after the main firing, by satisfying the nitrogen atmosphere condition where the oxygen concentration is 10% by volume or less, it is possible to improve the piezoelectric characteristics and insulating properties.

Although the above-mentioned embodiment shows the case of the laminated piezoelectric actuator, it is of course not limited to this case, and a piezoelectric resonator, a piezoelectric filter, a piezoelectric buzzer, and a piezoelectric transformer utilizing the piezoelectric effect. It goes without saying that the present invention can be applied to all laminated piezoelectric ceramic elements such as. FIG. 3 shows a perspective view of a laminated piezoelectric element 30 for an ink jet to which the present invention can be applied. Reference numeral 31 is a piezoelectric ceramic, 32 is an internal electrode, and 33 is an external electrode.

[0064]

As is apparent from the above description, according to the method for manufacturing a laminated piezoelectric ceramic element of the present invention, a laminated structure in which internal electrodes containing an alloy containing Ag as a main component are formed via ceramic layers. Type piezoelectric ceramic element, in which the ceramic layer and the internal electrode are simultaneously fired,
Further, by re-baking in an atmosphere having an oxygen concentration of 10% by volume or less, the Ag taken in the particles at the time of baking
However, the piezoelectric characteristics of the element, which have been precipitated at the grain boundaries in the re-firing process and deteriorated by incorporating Ag, are improved, so that the piezoelectric characteristics can be improved and high reliability can be sufficiently ensured. Therefore, it becomes possible to obtain a laminated piezoelectric ceramic element having more excellent piezoelectric characteristics and reliability.

[Brief description of drawings]

FIG. 1 is a perspective view showing a laminated piezoelectric actuator according to an embodiment of the present invention.

2 is a-b of the laminated piezoelectric actuator shown in FIG.
It is sectional drawing in a direction.

FIG. 3 is a perspective view showing an example of a laminated piezoelectric element for inkjet to which the present invention can be applied.

[Explanation of symbols]

10. Multilayer piezoelectric actuator 11. Internal electrode 12. External electrode 13. Piezoelectric ceramic 30. Multilayer piezoelectric element for inkjet 31. Piezoelectric ceramic 32. Internal electrode 33. External electrode

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01L 41/24 H01L 41/22 AF term (reference) 4G031 AA05 AA11 AA12 AA16 AA31 AA32 BA10 CA03 GA08 GA09 GA17

Claims (2)

[Claims] 1. A ceramic green sheet of a piezoelectric ceramic material containing a compound of a Pb element is coated with a conductive paste containing an alloy containing Ag as a main component, and the ceramic green sheets are stacked to form a laminate. And a step of first firing the laminated body, and a step of firing the laminated fired body again in an atmosphere having an oxygen concentration of 10% by volume or less. Production method. 2. The atmosphere having an oxygen concentration of 10% by volume or less is an atmosphere containing nitrogen as a main component,
A method of manufacturing the multilayer piezoelectric ceramic element according to claim 1.