JPH11322420A - Piezoelectric porcelain composition and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric porcelain compsn. having a relatively high electromechanical coupling factor, hardly changing in electrical characteristics even at a soldering package temp. and hardly changing in resonance frequency due to a temp. cycle by adding a specified amt. of Cr2 O3 and/or Mn3 O4 as a subsidiary component to a principal component represented by a specified relation. SOLUTION: A mixture is prepd. by adding 0.05-0.8 wt.% Cr2 O3 and/or Mn3 O4 as a subsidiary component to 100 wt.% principal component represented by the formula Pb(1-3/2α+β) Ndα (B1 B2 )XTiYZrZO3 and mixing them. The mixture is molded and fired to obtain a sintered body. Electrodes for polarization are formed on the surface of the sintered body, the sintered body is plarized by applying a DC electric field of >=3.0 kV/mm at 130-180 deg.C and a short circuit is caused between the electrodes. The sintered body is then heat-treated at 150-250 deg.C under such conditions that the product of the heat treatment temp. ( deg.C) and heat treatment time (hr) is made >=1,800. In the formula, 0.02<=α<=0.08, 0.002<=β<=0.05, 0.02<=X<=0.05, 0.46<=Y<=0.73, 0.25<=Z<=0.49, X+Y+Z=1 and B1 and B2 are each Nb, Ta, Sb or Sn with the exception of B1 ≠B2 and a combination of (Sb, Sn).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is particularly used for a filter utilizing thickness-shear mode resonance, and has a relatively large electromechanical coupling coefficient, good heat resistance and moisture resistance, and a change in resonance frequency before and after a temperature cycle. The present invention relates to a small piezoelectric ceramic composition and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, piezoelectric ceramic compositions include lead zirconate porcelain titanate, lead zirconate porcelain magnesium niobate, and lead zirconate zinc niobate porcelain. Has been improved.

[0003]

SUMMARY OF THE INVENTION The piezoelectric ceramic composition used for a filter is intended to be used in a severe environment of an electronic device and a heat resistance capable of withstanding a soldering mounting temperature in order to correspond to a chip component of a surface mounting type. Reliability (especially moisture resistance) is required.

Further, the conventional piezoelectric ceramic composition has a problem that the resonance frequency changes before and after a temperature cycle, which is one of reliability which is important for practical use. We had to keep it low.

Accordingly, the present invention has a relatively large electromechanical coupling coefficient suitable for a filter utilizing thickness-shear mode resonance, and has a small deterioration in electric characteristics even at a soldering mounting temperature near 280 ° C. It is an object of the present invention to provide a piezoelectric ceramic composition which is less deteriorated and has less change in resonance frequency due to a temperature cycle.

[0006]

In order to achieve this object, the piezoelectric ceramic composition of the present invention comprises a main component represented by the general formula (Chemical Formula 3) and Cr ₂ O ₃ and Mn ₃ O as subcomponents. ₄ is formed by adding at least one of 0.05 to 0.8% by weight to 100% by weight of the main component.

[0007]

Embedded image

According to this configuration, a relatively large relative dielectric constant ε
₁₁ ^T / ε ₀ and the electromechanical coupling coefficient k ₁₅ can be realized, and at the same time, good heat resistance, moisture resistance, and a change in resonance frequency due to temperature cycles can be reduced.

Further, the amount of Pb is made slightly larger than the stoichiometric ratio.
This reduces the effect of PbO scattering during firing and
Sinterability is improved, and Pb is partially substituted with Nd to improve moisture resistance.
Changes in resonance frequency due to temperature and temperature cycles,
Cr as_TwoO_ThreeAnd Mn _ThreeO_FourAt least one of
Improves heat resistance without lowering piezoelectricity
Was. In addition, the relative dielectric constant ε₁₁ ^T/ Ε₀Is on
The advantage is that the bandwidth can be widened by the filter.
You.

As a result, the above object can be achieved.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is characterized in that at least one of Cr ₂ O ₃ and Mn ₃ O ₄ is added as a sub-component to the main component represented by the general formula (Formula 4). A piezoelectric ceramic composition formed by adding 0.05 to 0.8% by weight with respect to 100% by weight of a main component, and has a relatively large electromechanical coupling coefficient suitable for a filter utilizing thickness-shear mode resonance, and Even at a soldering mounting temperature of around ℃, there is little deterioration in electrical characteristics, excellent moisture resistance, and little change in resonance frequency due to temperature cycling.

[0012]

Embedded image

The invention according to claim 2 is a compound of the general formula (5)
And Cr ₂ O ₃ and Mn as accessory components
_A first step of adding and mixing at least one type of ₃ O _{4 in} an amount of 0.05 to 0.8% by weight based on 100% by weight of the main component, and then molding and firing the mixture to obtain a sintered body; A second step of obtaining the electrode, and then forming a polarization electrode on the surface of the sintered body, and setting the polarization electrode to 3.0 kV /
a third step of applying a DC electric field of at least mm and polarizing, and then short-circuiting between the polarizing electrodes of the polarized sintered body to obtain 1
Producing a piezoelectric ceramic composition comprising: a fourth step of performing a heat treatment under a condition in which a product of a heat treatment temperature (° C.) and a heat treatment time (hour) is 1800 or more at a temperature of 50 to 250 ° C. This method has a relatively large electromechanical coupling coefficient suitable for a broadband filter using thickness-shear mode resonance, has little electrical property deterioration even at a soldering mounting temperature near 280 ° C, has excellent moisture resistance, and has resonance due to temperature cycles. A piezoelectric ceramic composition with a small frequency change can be obtained.

[0014]

Embedded image

An embodiment of the present invention will be described below with reference to the drawings. (Embodiment) FIG. 1 is a perspective view of a thickness-shear mode resonator according to the present embodiment, in which a resonance electrode 2 is formed on both upper and lower surfaces of a piezoelectric ceramic 1. In addition, FIG.
(B), (c) is sectional drawing for demonstrating the depolarization mechanism at the time of the heat treatment of the polarized piezoelectric ceramic by a pyroelectric effect.
Is a polarization electrode, 4 is a polarization vector, 5 is a floating charge, 6 is a surface charge, and 7 is an anti-electric field.

First, as raw materials PbO, TiO ₂ , Zr
O ₂ , Ta ₂ O ₅ , Sb ₂ O ₃ , SnO ₂ , Nb ₂ O ₅ , Cr ₂
O ₃ and Mn ₃ O ₄ were accurately weighed so as to have the composition shown in Table 1 and mixed well by a ball mill.

[0017]

[Table 1]

The raw materials are not limited to these, and other compounds may be used as long as they produce the piezoelectric ceramic composition shown in (Chem. 5) by a chemical reaction. Next, the mixture was calcined at a temperature of 850 ° C. and further pulverized by a ball mill. After drying, an aqueous polyvinyl alcohol solution as a binder was added, and the mixture was granulated, and then 1 ton / c.
and pressing at a pressure of m ^2, vertical 50 mm, lateral 45 mm, thickness 7mm
Was obtained. The molded body obtained here was placed in a closed furnace for 11 hours.
It was baked at a temperature of 50 to 1290 ° C. for 1 hour, and a thickness shear vibration resonator was produced from the obtained piezoelectric ceramic as follows.

First, a piezoelectric ceramic rectangular plate is polished to obtain a piezoelectric ceramic 1 having a thickness of 5 mm. Then, silver electrodes are baked on both sides to form polarized electrodes 3, and then 2.9 to 3 in silicon oil at 125 to 185 ° C. A DC electric field of 0.5 kV / mm was applied for 30 minutes to perform polarization treatment, and then heat treatment was performed under predetermined conditions. Next, cut at a thickness of 0.5 mm in the thickness direction to obtain a 0.05 μm Cr-1
A resonance electrode 2 composed of a two-layer deposited film of μmAu was formed on the cut surface, and cut in the polarization direction to obtain a rectangular plate-shaped thickness-shear mode resonator shown in FIG. For these samples, the density ρ, relative permittivity ε ₁₁ ^T / ε ₀ , electromechanical coupling coefficient k
₁₅ were measured. The heat resistance was measured by measuring the change rate of k ₁₅ and the resonance frequency after 30 minutes, after holding the resonator on a hot plate at 280 ° C. for 1 minute. k ₁₅ ≧ 0.3, |
k ₁₅ change rate | ≦ 5%, | resonance frequency change rate | ≦ 0.3%
Was determined to be good in heat resistance.

Regarding the moisture resistance, the resonance frequency change rate and k after exposing the rectangular plate-shaped thickness-slip mode resonator to an atmosphere at a temperature of 60 ° C. and a relative humidity of 90 to 95% for 200 hours are described.
₁₅ rates of change were measured. k ₁₅ ≧ 0.3, | k ₁₅ change rate | ≦
Those having 5%, | resonance frequency change rate | ≦ 0.2% were determined to have good moisture resistance.

Based on the above results, the porcelain firing temperature (maximum density)
(Table 2) and (Table 3).

[0022]

[Table 2]

[0023]

[Table 3]

As shown in (Table 4), the resonator characteristics of the samples 1 to 5 when the polarization conditions and the post-polarization heat treatment conditions were variously changed are shown in (Table 5).

[0025]

[Table 4]

[0026]

[Table 5]

Further temperature cycles (out 1) variations in the resonant frequency before and after ((value of _{f r -f r0) / f r0} ;%) was also measured by the resonator (Table 3), in (Table 5) Indicated.

[0028]

[Outside 1]

With respect to the variation of the resonance frequency due to the temperature cycle, those having a resonance frequency of 0.3% or less were judged to be good.

Hereinafter, the present embodiment will be described with reference to a table. According to Tables 1 to 5, α <0.02
In sample 6, the change in resonance frequency after the moisture resistance test was large (0.
Sample 9 having α> 0.08 was excluded from the scope of the present invention because the Curie temperature decreased to 300 ° C. or lower and depolarized in a heat resistance test.

Samples 10 and 11 with β <0.002 show large changes in resonance frequency due to temperature cycling (0.3% or more), and Sample 13 with β> 0.05 has low piezoelectricity (k ₁₅ <
0.3) was excluded from the scope of the present invention.

Sample 14 where X <0.02 has reduced heat resistance (| resonance frequency change rate |> 0.3%), and X>
Sample 16 having a value of 0.05 has reduced piezoelectricity (k ₁₅ <
0.3), and thus excluded from the scope of the present invention.

Sample 17 in which Y <0.46 has a large change rate of the resonance frequency due to the temperature cycle (0.3% or more).
Y is limited to the range of 0.46 ≦ Y ≦ 0.73 since Y ≦ 0.73 when X and Y are within the range of the present invention.

Sample 20 with Z <0.25 has reduced sinterability and piezoelectricity (k ₁₅ <0.3), so that Z>
Sample 17, which was 0.49, was excluded from the scope of the present invention because the rate of change in resonance frequency after heat resistance exceeded 0.3% and the rate of change in resonance frequency due to temperature cycling was 0.3% or more.

Regarding the added amount of the sub-components Cr ₂ O ₃ and Mn ₃ O ₄ (at least one type), Samples 24, 25, and 2 each containing less than 0.05% by weight based on 100% by weight of the main component.
Since the resonance frequency change rate by temperature cycling in 6,27 is as large as 0.3% or more, the sintered density of the samples 34, 35, 36 falls below 7.5 g / cm ³ greater than 0.8 wt% And the piezoelectricity decreases (k ₁₅ <0.
31) Therefore, it was excluded from the scope of the present invention.

The reason why the combination of (Sn, Sb) is excluded from B1 and B2 is that when Sn is +2 and Sb is +3, Sn _a Sb _1-a becomes +4 and 0 <a <1. Is not present in the range.

As shown in (Table 4) and (Table 5), the polarization condition is that the polarization is not saturated when the polarization temperature is lower than 130 ° C. (processing condition a), and the piezoelectricity is higher when the polarization temperature exceeds 180 ° C. (processing condition d). The resistance of the porcelain 1 decreases, so that a voltage of 3.0 kV / mm or more cannot be applied. Further, the DC applied voltage during polarization is 3.0 even in the polarization temperature range of the present invention.
At kV / mm or less (processing condition (e)), the polarization becomes unsaturated, so that it was excluded from the scope of the present invention.

As to the heat treatment conditions after the polarization (Table 4), as shown in (Table 5), in the sample heat-treated without short-circuiting between the polarization electrodes 3 (processing condition G), the depolarization was remarkable and k ₁₅ <0.31.

This is because the piezoelectric ceramic 1 of the present invention has a relatively large pyroelectric effect, and as shown in FIG. 2A, after polarization, the surface charge 6 of the polarization electrode 3 and the floating charge 5 are balanced. However, when the piezoelectric ceramic 1 is heat-treated at a temperature of 150 ° C. or more for a long time, as shown in FIG. 2 (b), the anti-electric field 7 cancels the polarization in the direction opposite to the polarization vector 4.
This causes the piezoelectric ceramic 1 to be stabilized but the polarization to be reduced, as shown in FIG. 2 (c). Therefore, in order to prevent this, it is desirable to perform the heat treatment in a state where the electrodes for polarization 3 are short-circuited.

At a heat treatment temperature of 150 ° C. or less (processing condition C), the resonance frequency change rate after solder heat resistance is 0.3%.
At 250 ° C. or higher (processing conditions), if heat treatment is performed for such a time that the product of heat treatment temperature × heat treatment time exceeds 1800 (° C. · hour), depolarization is large (k ₁₅ <0.3).
2) Therefore, it was excluded from the scope of the present invention. Even if the heat treatment temperature after polarization is in the temperature range of 150 to 250 ° C., if the product of the heat treatment temperature and the heat treatment time is 1800 (° C. · Hr) or less (processing conditions), the resonance frequency change after heat resistance or k ₁₅ Since the change was large, it was excluded from the scope of the present invention.

[0041]

As described above, according to the present invention, a piezoelectric ceramic for an oscillator or a filter utilizing thickness-shear mode resonance can be fired at a relatively low temperature, has a relatively large electromechanical coupling coefficient, and has a soldering temperature of about 280 ° C. It is possible to provide a piezoelectric ceramic composition having little change in electric characteristics even at the mounting temperature and little change in resonance frequency due to a temperature cycle.

[Brief description of the drawings]

FIG. 1 is a perspective view of a thickness-shear mode resonator according to an embodiment of the present invention.

FIG. 2A is a cross-sectional view of a piezoelectric ceramic after polarization for explaining a depolarization mechanism during heat treatment of a polarized piezoelectric ceramic due to a pyroelectric effect in one embodiment of the present invention; Figure (c) Sectional view after heat treatment

[Explanation of symbols]

 Reference Signs List 1 piezoelectric ceramic 2 resonant electrode 3 electrode for polarization 4 polarization vector 5 floating charge 6 surface charge 7 demagnetizing field

Claims (2)

[Claims] 1. A main component represented by the general formula (Chem. 1), and at least one of Cr ₂ O ₃ and Mn ₃ O ₄ as an auxiliary component is added in an amount of 0.05 to 0. A piezoelectric ceramic composition formed by adding 8% by weight. Embedded image 2. A main component represented by the general formula (Chem. 2), and at least one of Cr ₂ O ₃ and Mn ₃ O ₄ as subcomponents in an amount of 0.05 to 0. A first step of adding and mixing 8% by weight, a second step of forming and firing this mixture to obtain a sintered body, and then forming a polarizing electrode on the surface of the sintered body; A third step of applying a DC electric field of 3.0 kV / mm or more in a temperature range of -180 ° C to polarize, and then short-circuiting between the polarizing electrodes of the polarized sintered body to obtain a temperature of 150-250 ° C. Under the temperature, the product of the heat treatment temperature (° C.) and the heat treatment time (hour) is 1800.
And a fourth step of performing a heat treatment under the conditions described above. Embedded image