JPH0818373A - Manufacture of piezoelectric resonance element - Google Patents

Abstract

PURPOSE:To obtain the piezoelectric resonance element which varies a little in resonance frequency and resonance impedance owing to a thermal shock by heating piezoelectric ceramic up to specific temperature after baking, and then annealing it at a necessary temperature drop speed. CONSTITUTION:A piezoelectric composition is used and the piezoelectric ceramic is baked and heated up to higher Curie temperature and lower than grain growth start temperature. Then the temperature area including the Curie temperature is annealed at the drop speed of -50 deg.C/Hr--10 deg.C/Hr. Then a polarization electrode 2 is formed. This method relaxes thermodynamic unstableness generated in the crystal phase of the piezoelectric ceramic and the internal strain is also reduced. Even when a thermal shock is applied to the piezoelectric ceramic after polarization, variation in piezoelectric characteristics are suppressed small and the piezoelectric element which varies a little in resonance frequency and resonance impedance owing to the thermal shock is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a piezoelectric resonance element.

[0002]

2. Description of the Related Art A piezoelectric resonance element is formed by firing a piezoelectric ceramic, and conventionally, natural firing is performed in a furnace after firing. In addition, no intentional heat treatment was performed after polarization (excluding heat treatment when assembling the resonator).

[0003]

Among lead zirconic acid titanate porcelains, which are typical piezoelectric ceramics, a phase boundary between a tetragonal crystal and a rhombohedral crystal having a large electromechanical coupling coefficient suitable for a piezoelectric resonator. In the vicinity composition, the composition ratio of the crystal layer is unstable.

In the above-mentioned conventional natural cooling, the temperature is lowered before the thermodynamic equilibrium is reached when the temperature is lowered, and as a result, the crystal phase is thermodynamically unstable and the internal strain becomes large. Therefore, when the thermal shock is applied, the composition ratio of the crystal phase and the distribution of the internal strain are easily changed, and accordingly, the change of the resonance characteristic is also large.

An object of the present invention is to provide a piezoelectric resonance element in which the fluctuation of resonance characteristics due to thermal shock is small.

[0006]

To achieve this object, according to the present invention, after firing a piezoelectric ceramic, heating is performed to a temperature above the Curie temperature and below a grain growth start temperature, and then a temperature range including the Curie temperature is The film is annealed at a temperature lowering rate of 50 ° C./Hr to −10 ° C./Hr, after which polarization and electrode formation are performed.

[0007]

With this structure, the thermodynamic instability generated in the crystal phase of the piezoelectric ceramic during firing is relaxed, and the internal strain is also reduced. As a result, even if a thermal shock is applied to the piezoelectric ceramic after polarization, the change in piezoelectric characteristics can be suppressed to a small level.

[0008]

Embodiments of the present invention will be described below with reference to FIGS.

[0009] When producing a _{resonator, Pb (Mg 1/3 Nb 2/} 3) as a piezoelectric ceramic having good characteristics Ti _0.01 Zr
_A composition of _0.46 O ₃ +0.1 wt% MnO ₂ +0.1 wt% NiO is disclosed in Japanese Patent Publication No. 45-14935. This porcelain composition will be described.

First, as raw materials, PbO, TiO ₂ , Zr
_{O 2, MgO, Nb 2 O} 5, MnCO 3, and, NiO and so that the above composition was accurately weighed and mixed well in a ball mill. Next, the mixture was calcined at 850 ° C., and further pulverized with a ball mill. After drying this, add a polyvinyl alcohol aqueous solution as a binder,
Granulated. Then, 20 * 20 * 7 at a pressure of 1 ton / cm ^2.
It is pressed into a rectangular columnar shaped body of mm and it is placed in a closed furnace for 12
The piezoelectric ceramic 1 was obtained by firing at a temperature of 30 ° C. for 1 hour. Next, this piezoelectric ceramic 1 was lapped in the thickness direction to a thickness of 5.0 mm, and after lapping, vapor-deposited silver electrodes were formed on both lower surfaces, and then 4 kV in 100 ° C. silicon oil.
A direct current electric field of / mm was applied for 30 minutes to perform polarization treatment.
Next, after cutting this in the polarization direction and lapping in the polarization direction, the resonance electrode (silver electrode) 2 is vapor-deposited on both upper and lower surfaces and cut, and the thickness shear vibration resonator (5.0 * 0.
5 * 0.5 mm) was prepared.

The Curie temperature of the piezoelectric ceramic 1 was 318 ° C. according to the measurement of the coefficient of thermal expansion. From this,
Determine the heat treatment temperature profile of this piezoelectric ceramic 1,
Pre-polarization treatment and post-polarization annealing were performed under the conditions shown in (Table 1) to fabricate a resonator as described above.

[0012]

[Table 1]

Next, these resonators were placed on a hot plate at 250 ° C. for 1 minute before and after heat treatment for 1 minute. The rate of change of the resonant frequency f _r of the thickness shear mode resonant fundamental wave, the rate of change of the resonant impedance Z _r , and the electromechanical coupling. The rate of change of the coefficient k ₁₅ was measured and is shown in (Table 2).

[0014]

[Table 2]

The resonance characteristic after the heat treatment was measured 30 minutes after the heat treatment. Here, the rate of change of the resonance frequency f _r, the rate of change and the rate of change of the electromechanical coupling factor k ₁₅ of the resonant impedance Z _r was calculated by the following equation.

X (%) = 100 * (X ₁ −X ₀ ) / X ₀ X ... Rate of change X ₀ …… Value before heat treatment X ₁ …… Value after heat treatment (Table 2) The one in which the change rate of the resonance frequency characteristic due to the heat treatment for one minute at 250 ° C. that simulates the mounting thermal shock of the resonator is within 0.1% is within the scope of the claims of the present invention. It can be seen that these are Samples 1, 7, 10, and 12. Further, it can be seen that these samples also have small rates of change in resonance impedance and electromechanical coupling coefficient.

As described above, the piezoelectric resonance element of the present invention has an extremely small change in resonance characteristics due to thermal shock during mounting.

In this embodiment, Pb (Mg _1/3 Nb _2/3 ) O ₃ -PbTiO ₃ -PbZ is used as the piezoelectric ceramic 1.
rO ₃ system Pb (Mg _1/3 Nb _2/3 ) Ti _0.01 Zr _0.46 O ₃
+ 0.1wt% MnO ₂ + 0.1wt% NiO Pb (Mg
The porcelain composition of _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃ was used, but the same effect can be obtained by using another lead zirconate titanate-based material.

Further, the temperature-decreasing rate when the piezoelectric ceramic 1 is heated after firing and gradually cooled is set to -10 ° C / Hr.
It may be from -10 ° C / Hr. The temperature after annealing the piezoelectric ceramic 1 was Curie temperature (T _c ) + 5 ° C., but it may be annealed at the Curie temperature (T _c ) ± 10 ° C. for 2 hours or more. Furthermore, the piezoelectric ceramic 1 after polarization was annealed at a temperature of 0.63 times and 0.4 times the Curie temperature for 1 hour, but 0.4 times or more of the Curie temperature and 0.1.
Annealing may be performed at a temperature of 8 times or less for 30 minutes or more. The reason for leaving it at room temperature for 48 hours or more is to wait for the frequency constant (element thickness * resonance frequency) to stabilize, as can be seen from FIG. Here, when the thickness of the piezoelectric ceramic 1 is polished in order to adjust the resonance frequency within 48 hours after the annealing is performed, the resonance frequency changes after polishing and deviates from the target resonance frequency.

[0020]

As described above, according to the present invention, after firing the piezoelectric ceramic, the temperature is heated to the Curie temperature or higher and the grain growth start temperature or lower, and then the temperature range including the Curie temperature is -50 ° C / Hr to -10 ° C /
Gradually cool at the Hr cooling rate, or use the Curie temperature ±
Annealing is performed for 2 hours or more in a temperature range of 10 ° C., and then polarization and electrode formation are performed to form electrodes to obtain a piezoelectric resonance element. As a result, the thermodynamic instability generated in the crystal phase of the piezoelectric ceramic is relaxed during firing, and the internal strain is also reduced. As a result, even if a thermal shock is applied to the piezoelectric ceramic after polarization, the change in piezoelectric characteristics can be suppressed to a small level.

When the piezoelectric ceramic is polarized and then annealed at a temperature of 0.4 to 0.8 times the Curie temperature for 30 minutes or more, most of the polarization component due to mounting heat of the polarization component is removed. It is possible to reduce the depolarization due to the heat treatment when actually used. Then, at room temperature, 4
By leaving it for 8 hours or more, the frequency constant of the resonance frequency of the piezoelectric resonance element is stabilized.

[Brief description of drawings]

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

FIG. 2 is a characteristic curve diagram of a frequency constant depending on the elapsed time of annealing after polarization.

[Explanation of symbols] 1 Piezoelectric ceramic 2 Resonance electrode

Claims (6)

[Claims] 1. A piezoelectric ceramic formed by using a piezoelectric ceramic composition is fired, and then heated to a temperature above the Curie temperature and below a grain growth start temperature, and thereafter, a temperature region including the Curie temperature is −50 ° C. / Hr to −10 ° C./Hr, which is a method for manufacturing a piezoelectric resonance element in which the material is gradually cooled at a temperature lowering rate, and then polarization and electrode formation are performed. 2. After the piezoelectric ceramic is polarized, the Curie temperature of 0.
Anneal at a temperature of 4 times or more and 0.8 times or less for 30 minutes or more,
Next, the method for manufacturing a piezoelectric resonant element according to claim 1, wherein the piezoelectric ceramic is left at room temperature until the frequency constant becomes stable. 3. After the piezoelectric ceramic is polarized, the Curie temperature of 0.
Anneal at a temperature of 4 times or more and 0.8 times or less for 30 minutes or more,
Next, the method for manufacturing a piezoelectric resonant element according to claim 1, wherein the piezoelectric ceramic is left at room temperature for 48 hours or more. 4. A piezoelectric resonance in which a piezoelectric ceramic formed by using the piezoelectric ceramic composition is fired, and then annealed in a temperature range of Curie temperature ± 10 ° C. for 2 hours or more, after which polarization and electrode formation are performed. Device manufacturing method. 5. After the piezoelectric ceramic is polarized, the Curie temperature of 0.
Anneal at a temperature of 4 times or more and 0.8 times or less for 30 minutes or more,
5. The method for manufacturing a piezoelectric resonant element according to claim 4, wherein the piezoelectric ceramic is left at room temperature until the frequency constant becomes stable. 6. After the piezoelectric ceramic is polarized, the Curie temperature of 0.
Anneal at a temperature of 4 times or more and 0.8 times or less for 30 minutes or more,
Next, the method for manufacturing a piezoelectric resonant element according to claim 4, wherein the piezoelectric ceramic is left at room temperature for 48 hours or more.