JPH11322419A - 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 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) Laα (Sn1/3 Nb2/3 )ATiBZrCO3 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 polarized 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<=A<=0.05, 0.46<=B<=0.78, 0.25<=C<=0.45 and A+B+C=1.

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]

The piezoelectric ceramic composition used for the filter is compatible with surface-mount type chip components, so that it has heat resistance enough to withstand the soldering mounting temperature and uses under severe environments of electronic devices. Prerequisite 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. I needed 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
_While realizing ₁₁ ^T / ε ₀ and the electromechanical coupling coefficient k ₁₅ , good heat resistance and moisture resistance and a change in resonance frequency due to a temperature cycle 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 partial La substitution of Pb improves 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 voltage
Was. In addition, the relative permittivity 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]

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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
Then short-circuit the electrodes for polarization of this polarized sintered body,
Producing a piezoelectric ceramic composition, comprising: a fourth step of performing heat treatment at a temperature of 150 to 250 ° C. under a condition that a product of a heat treatment temperature (° C.) and a heat treatment time (hour) is 1800 or more. This method has a relatively large electromechanical coupling coefficient suitable for a broadband filter using thickness-shear mode resonance, and has little deterioration in electrical characteristics even at a soldering mounting temperature near 280 ° C, has excellent moisture resistance, and has resonance due to temperature cycling. 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 , 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 solution of polyvinyl alcohol as a binder was added, and the mixture was granulated and then 1 ton /
Pressure molding was performed at a pressure of cm ² to obtain a molded body having a length of 50 mm, a width of 45 mm, and a height of 7 mm. The molded body obtained here was fired in a closed furnace at a temperature of 1150 to 1290 ° C. for 1 hour, and a thickness-shear vibration resonator was manufactured from the obtained piezoelectric ceramic as follows.

First, a piezoelectric ceramic rectangular plate is polished to a thickness of 5 mm.
After baking silver electrodes on both sides
After forming the electrode 3, in silicon oil at 125-185 ° C
To apply a DC electric field of 3.0 to 4.0 kV / mm for 30 minutes
Then, a polarization treatment was performed, and then a heat treatment was performed under predetermined conditions.
Next, cut to a thickness of 0.5 mm in the thickness direction,
Cut off the resonance electrode 2 composed of a two-layer deposited film of Cr-1 μm Au.
Formed in cross section and cut in the direction of polarization shown in FIG.
Thus, a rectangular plate-shaped thickness shear mode resonator was obtained. these
Density ρ, relative permittivity ε per sample₁₁ ^T/ Ε₀Electromechanical coupling
Coefficient k_FifteenWas measured. The heat resistance is as follows.
After holding on the plate for 1 minute, 30 minutes later
k_FifteenAnd the change rate of the resonance frequency was measured. k_Fifteen≧ 0.
3, | k _FifteenChange rate | ≦ 5%, | resonance frequency change rate | ≦
One having a heat resistance of 0.3% was judged to have good 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 Samples 1 to 3 when the polarization conditions and 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
Sample 4 has a large change in resonance frequency after the moisture resistance test (0.
Sample 7 with α> 0.08 has a Curie temperature of 3
Since the temperature dropped to 00 ° C. or less and depolarized in the heat resistance test, it was excluded from the scope of the present invention.

Samples 8 and 9 with β <0.002 show a large change in the resonance frequency due to the temperature cycle (0.3% or more), and Sample 12 with β> 0.05 has a low piezoelectricity (k ₁₅ <
0.3) was excluded from the scope of the present invention.

Sample 13 with A <0.02 has reduced heat resistance (| resonance frequency change rate |> 0.3%), and sample 16 with A> 0.05 has a Curie temperature of 30.
Since the temperature dropped to 0 ° C. or less and depolarized in the heat resistance test, it was excluded from the scope of the present invention.

Furthermore, Sample 17 with B <0.46
Has a large change rate of the resonance frequency due to the temperature cycle (0.
Sample 20 with B> 0.78 was excluded from the scope of the present invention because the piezoelectricity was reduced (k ₁₅ <0.3).

Sample 21 with C <0.25 has reduced sinterability and piezoelectricity (k ₁₅ <0.3).
The sample 24 having a ratio of> 0.45 had a rate of change in resonance frequency after heat resistance of more than 0.3% and a rate of change in resonance frequency due to temperature cycling as large as 0.3% or more, and thus was excluded from the scope of the present invention. .

Regarding the addition amount of Cr ₂ O ₃ and Mn ₃ O ₄ (at least one type) as the sub-components, samples 25, 26, and 3 were less than 0.05% by weight based on 100% by weight of the main component.
In Examples 1 and 35, the change rate of the resonance frequency due to the temperature cycle was as large as 0.3% or more, and in Samples 29, 34 and 38 exceeding 0.8% by weight, the sintered body density was 7.5 g / cm ^3.
And the piezoelectricity decreases (k ₁₅ <
0.3), and thus excluded from the scope of the present invention.

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 polarization is higher than 180 ° C. (processing condition d). The resistance of the piezoelectric ceramic 1 is reduced to 3.0 kV / m
m or more cannot be applied. Also, the DC applied voltage during polarization was excluded from the scope of the present invention because the polarization was not saturated at 3.0 kV / mm or less (processing condition E) even in the polarization temperature range of the present invention.

As to the heat treatment conditions after polarization (Table 4) and Table 5 (Table 5), the samples heat-treated without short-circuiting between the polarization electrodes 3 (working condition key) showed remarkable depolarization and k ₁₅ <0.3. This is because the piezoelectric ceramic 1 of the present invention has a relatively large pyroelectric effect, and the surface charge 6 and the floating charge 5 of the polarization electrode 3 are balanced after polarization as shown in FIG. However, when the piezoelectric ceramic 1 is heat-treated at a temperature of 150 ° C. or more for a long time without short-circuiting between the polarization electrodes 3, the polarization in the direction opposite to the polarization vector 4 is canceled as shown in FIG. Since such an anti-electric field 7 is generated,
This is because the polarization decreases as shown in FIG. When the heat treatment temperature is 150 ° C. or less (processing condition C), the resonance frequency change rate after solder heat resistance is as large as 0.3% or more.
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 is 1800 (° C. · hour) or more, the depolarization becomes large (k ₁₅ <0.3). Excluded. Even in the temperature range of 150 to 250 ° C., the product of the heat treatment temperature and the heat treatment time is 1800 (° C.
· Hr) or less (excluding from the scope of the present invention for the resonance frequency change or k ₁₅ changes after the heat resistance when machining conditions scan) is large.

[0038]

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 (Chemical Formula 1), and at least one of Cr ₂ O ₃ and Mn ₃ O ₄ as a subcomponent is 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 (Chemical Formula 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 with respect to 100% by weight of the main component. A first step of adding and mixing 0.8% 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 130 to 180 ° C. to polarize, and then short-circuiting between the polarizing electrodes of the polarized sintered body to obtain 150 to 250 ° C. The product of the heat treatment temperature (° C.) and the heat treatment time (hour) is 18
And a fourth step of performing a heat treatment under a condition of at least 00. Embedded image