JPH06315196A - Characteristic control method for piezoelectric body - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric body whose piezoelectric characteristic will not be changed even when a thermal shock is added by performing a polarization processing to the piezoelectric body, and performing an inverse polarization processing so that a difference between a preliminarily decided resonance frequency and an antiresonance frequency can be obtained. CONSTITUTION:Each kind of oxide Pb3O4, SnO2, Sb2O3, Nb2O5, ZrO2, TiO2 and MnCO3 is used to mix so that the oxide is composed with Zr and Ti of 50-100mol, and Sn, Sb, and Nb of 50-0mol for Pb of 100mol, and molded by adding an organic binder, and the molded body is baked. So that a piezoelectric porcelain can be manufactured. The polarization processing is performed to this piezoelectric body in almost 2 hours at 100-160 deg.C by impressing a high electric field which is 40-60kV/cm. The frequency characteristic of the piezoelectric body to which the polarization processing is operated is measured, and a difference DELTAf between a resonance frequency fa and an antiresonance frequency fr is obtained. Next, the frequency of the piezoelectric body is made close to a specific frequency by decreasing the DELTAf by impressing (inverse polarizing) the electric field having a constant strength to a direction different from the polarizing direction of the piezoelectric body.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling the characteristics of a piezoelectric body, and more specifically, it controls the characteristics of a piezoelectric body used as a sounding body such as a piezoelectric buzzer or a piezoelectric speaker, a filter, a resonator, a discriminator or an actuator. Regarding the method.

[0002]

2. Description of the Related Art Piezoelectric parts that utilize the piezoelectric effect in which electric polarization is generated by applying stress and mechanical strain is generated by an electric field, are used in various fields today.
Typical examples of the piezoelectric material include so-called PZT-based porcelain containing lead titanate and lead zirconate as main components. The PZT-based porcelain is used for various purposes, and one of them is used, for example, as a piezoelectric resonator.

The ferroelectric ceramics constituting the piezoelectric resonator or the like can be obtained by sintering a raw material under specific conditions, but generally the polarization directions of the domains are not aligned immediately after sintering. The direction of the polarization axis is obtained by applying a so-called polarization treatment to this sintered body, for example, by applying a high electric field of 40 to 60 kV / cm at 100 to 160 ° C., which is a temperature lower than the Curie point of the piezoelectric body, for about 2 hours. Are aligned, and the piezoelectric effect described above is exhibited.

However, the polarized state of the piezoelectric body after the polarization treatment is relaxed with or without use, and the piezoelectric characteristics are deteriorated by long-term use or standing.

Also in the PZT-based porcelain, its piezoelectric characteristics are apt to deteriorate due to long-term use and leaving, and especially the piezoelectric characteristics are likely to change due to thermal shock.

[0006] Therefore, as a method for reducing such changes in piezoelectric characteristics over time and changes in piezoelectric characteristics due to thermal shock, conventionally, heat insulation is performed at 60 to 120 ° C higher than room temperature and lower than the Curie temperature of the piezoelectric body for several hours, The so-called aging has been performed in which the change in piezoelectric characteristics is forcibly reduced in a short time by leaving it at a low temperature of −100 to 0 ° C. lower than room temperature for several hours, or by applying a thermal shock in advance.

As the aging method of applying the thermal shock, for example, with the electrodes of the piezoelectric body open, the piezoelectric body is placed in a constant temperature bath having a temperature of about 100 to 200 ° C. lower than the Curie point of the piezoelectric body and left for several hours. After that, a method of rapidly cooling to room temperature again can be mentioned.

[0008]

However, in the above-mentioned aging method, the processing conditions such as the processing temperature and the processing time are not clear, and the aging method allows sufficient aging so that the piezoelectric characteristics do not change with the passage of time. Since it is unclear whether or not it is difficult to guarantee the reliability of the piezoelectric characteristics.

The present invention has been invented in view of the above-mentioned problems, and it is a characteristic control of a piezoelectric body that can clarify the conditions of aging and ensure the reliability of piezoelectric characteristics by the aging. It is intended to provide a way.

[0010]

In order to achieve the above object, a method for controlling the characteristics of a piezoelectric body according to the present invention is to apply an electric field in a direction different from the polarization direction to a piezoelectric body that has been previously polarized. Polarization or reverse polarization) to bring the difference between the resonance frequency and the anti-resonance frequency of the piezoelectric material close to a specific frequency that has been obtained in advance. Hereinafter, the method is also referred to as a reverse polarization method.

Further, in the method for controlling the characteristics of the piezoelectric body according to the present invention, an electric field in a direction different from the polarization direction is applied to the piezoelectric body which has been subjected to the polarization treatment in advance, and the electromechanical coupling coefficient of the piezoelectric body is obtained in advance. It is characterized in that it approaches the specific electromechanical coupling coefficient.

In the method of controlling the characteristic of the piezoelectric body according to the present invention, first, the frequency characteristic of the piezoelectric body which has been subjected to the polarization treatment in advance is measured, and the resonance frequency fa and the anti-resonance frequency f are measured.
The difference Δf (= fa−fr) of r is obtained. The conditions of the polarization treatment include, for example, conditions of applying a high electric field of 40 to 60 kV / cm at 100 to 160 ° C. for about 2 hours.

Next, by applying an electric field of a constant strength in a direction different from the polarization direction of the piezoelectric body (reverse polarization), Δf is decreased, and Δf of the piezoelectric body subjected to the reverse polarization treatment is reduced.
f is measured. In this case, if the direction of the electric field applied with the reverse polarization is different from the direction applied with the polarization first,
The direction does not necessarily have to be 180 ° opposite, and may be any direction in three dimensions. After that, in the piezoelectric body, for example, in a state where the electrodes of the piezoelectric body are opened as described above, after being placed in a constant temperature bath set at a temperature of 100 to 200 ° C. lower than the Curie point of the piezoelectric body and left for several hours. ,
A thermal shock is applied again such that the temperature is rapidly cooled to room temperature, and how much Δf changes is measured.

Next, it is made of the same material as the piezoelectric body,
For a piezoelectric body having the same shape, electrode position, and electrode shape, change the strength and direction of the electric field when performing reverse polarization processing, and
Then, f is lowered and the same thermal shock is applied, and Δf before the thermal shock and Δf after the thermal shock are measured.
The results obtained by the series of experiments described above will be examined to determine the conditions under which the value of Δf does not change before and after thermal shock.

Since the piezoelectric property of the material having the value of Δf obtained by the above method does not change due to thermal shock, it is considered that the piezoelectric property does not change even if it is subjected to thermal shock again or it is used for a long time.

Therefore, a material which has been subjected to a polarization treatment in advance is
By performing the reverse polarization treatment so as to be as close as possible to the value of Δf thus obtained, it is possible to obtain a piezoelectric body whose piezoelectric characteristics do not change due to thermal shock or long-term use.

It has been conventionally known that the piezoelectric property is suppressed by performing the reverse polarization treatment, but it has been known until now that the thermal shock resistance can be controlled by performing the reverse polarization treatment. There wasn't.

Further, by obtaining the relationship between Δf before thermal shock and Δf after thermal shock in the above-mentioned method, conversely, if Δf after reverse polarization treatment is measured,
It is possible to predict how much Δf will shift if a thermal shock is applied.

[0019]

According to the method of controlling the characteristics of the piezoelectric body according to the present invention,
A thermal shock is generated by applying an electric field in a direction different from the polarization direction to a piezoelectric body that has been subjected to a polarization process in advance, and bringing the difference between the resonance frequency and the antiresonance frequency of the piezoelectric body close to a specific frequency that has been obtained in advance. The piezoelectric characteristic is controlled so that the piezoelectric characteristic does not change even when the voltage is applied, and the piezoelectric characteristic is controlled so that the piezoelectric characteristic does not change even when used for a long time.

Further, according to the method of controlling the characteristics of the piezoelectric body according to the present invention, an electric field having a direction different from the polarization direction is applied to the piezoelectric body that has been subjected to the polarization treatment in advance, and the electromechanical coupling coefficient of the piezoelectric body is obtained in advance. By approaching the specified electromechanical coupling coefficient, the piezoelectric characteristics are controlled so that the piezoelectric characteristics do not change even when a thermal shock is applied, as in the case described above, and even after long-term use, the piezoelectric characteristics are controlled. The piezoelectric characteristics are controlled so that the characteristics do not change.

[0021]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of the method for controlling the characteristics of the piezoelectric material according to the present invention will be described below. In this embodiment, P is used as the material of the piezoelectric resonator utilizing the spreading vibration mode.
A ZT type piezoelectric ceramic was used.

First, as a raw material for a piezoelectric ceramic, Pb ₃ O
₄ , SnO ₂ , Sb ₂ O ₃ , Nb ₂ O ₅ , ZrO ₂ , T
Various oxides of iO ₂ and MnCO ₃ were used, and these oxides were blended in a composition of 50 to 100 moles of Zr and Ti and 50 to 0 moles of Sn, Sb and Nb with respect to 100 moles of Pb, and then mixed in a pot mill. Wet mixing was performed for 24 hours.
Next, after drying the mixed raw material, 700-950 degreeC
It was calcined in the temperature range of. Further, an appropriate amount of organic binder was added and dry-mixed, and the mixture was passed through a mesh container for sizing.
Then, 1000 to 1500 kg / cm for the sized powder.
A pressure of ² was applied to prepare a 100 × 100 × 50 (mm) plate-shaped molded body, and main firing was performed in a temperature range of 1000 to 1300 ° C. to obtain a piezoelectric ceramic. Furthermore, after lapping the thickness of this sintered body to 0.5 mm, the electrode pattern of the vibrating electrode was produced by silver vapor deposition, and 1 to 10 KV / mm
Then, a direct current voltage was applied to perform polarization treatment, and then cutting processing was performed to obtain a piezoelectric resonator. The piezoelectric resonator thus obtained had a width of 4.5 mm and a length of 4.5 mm.

After the polarization treatment, the frequency characteristic of impedance was measured, and a value of Δf≈60 (kHz) was obtained as the difference (Δf) between the resonance frequency and the antiresonance frequency.

The points to be noted here are fr, fa, and Δf.
Depends on the vibration mode, the size of the piezoelectric resonator, and the density of the piezoelectric material after firing, so that basically the same manufacturing lot is preferable. In particular, in the spreading vibration mode taken up in this embodiment, the frequency is given by the following mathematical formula 1, so it is necessary to fix the dimensions. Further, although the piezoelectric density and the like described above affect the frequency constant N, they are not greatly affected if the manufacturing conditions are controlled.

[0025]

[Equation 1]

Next, an electric field of various strengths is applied to the piezoelectric resonator to subject it to reverse polarization to reduce Δf, and Δf after the reverse polarization is measured, and a thermal shock test is conducted. It was measured how much each of Δf, fr, and fa changed.

In the thermal shock test, the piezoelectric resonator is placed in a thermostat at 150 ° C. in an electrically open state, left for 1 hour, and then rapidly cooled to room temperature again. went.

Tables 1 to 3 show the results,
Table 1 shows the relationship between Δf before the thermal shock test and the change rate of Δf after the thermal shock test, and Table 2 shows the relationship between the Δf before the thermal shock test and the change rate of fr after the thermal shock test, Table 3 shows the relationship between Δf before the thermal shock test and the rate of change of fa after the thermal shock test. In addition, as shown in Tables 1-3, the same test was repeated twice in the examples.

[0029]

[Table 1]

[0030]

[Table 2]

[0031]

[Table 3]

From Tables 1 to 3, Δf and f after the thermal shock test
It can be seen that the values of Δf before thermal shock where r and fa do not change are both Δf≈45 (kHz). Also, Table 2
From ~ 3, it can be seen that not only Δf does not change when Δf≈45 (kHz), but also the values of fa and fr do not change, and the piezoelectric body has excellent thermal shock resistance. Furthermore, since the value does not change even if the same test is performed twice, the reproducibility is good and the reliability is very high.

Further, as is generally well known, a material having stable properties against thermal shock is less likely to change with time. Therefore, the piezoelectric body subjected to the method of the present invention is also excellent in stability with time. It can be easily estimated. Further, the electromechanical coupling coefficient Kp is approximately equal to the anti-resonance frequency fr and the resonance frequency f.
Since it can be obtained from a, the electromechanical coupling coefficient K
Similarly, p can be controlled. For example, in the spreading vibration mode, the value varies depending on the size of the piezoelectric resonator, but is given by the following mathematical expression 2.

[0034]

[Equation 2]

Next, as a comparative example, the same porcelain was used, and Δf was changed by changing the conditions of the first polarization treatment.
The reverse polarization treatment was not performed, and then a thermal shock test under the same conditions as described above was performed to examine the relationship between the value of Δf before the thermal shock test and the rate of change of Δf, fa, fr after the thermal shock test. The results are shown in Tables 4-6.

[0036]

[Table 4]

[0037]

[Table 5]

[0038]

[Table 6]

As is clear from Tables 4 to 6, there is no condition that the change rate of Δf becomes 0 after the thermal shock test only by the first polarization treatment, and the value of Δf always decreases due to the thermal shock. In addition, since both fr and fa are considerably changed, it can be understood that the thermal shock resistance cannot be improved only by the first polarization treatment. Further, this data shows an unfavorable result that the larger the Δf is and the better the piezoelectric characteristics are, the larger the rate of change of fr and fa due to thermal shock is.

As described above, in the method of controlling the characteristics of the piezoelectric body according to the present embodiment, after the polarization process is performed, the specific Δf
It is considered that by performing the reverse polarization treatment so that the piezoelectric property does not change even when a thermal shock is applied, the change over time can be reduced.

[0041]

As described in detail above, in the method for controlling the characteristics of a piezoelectric body according to the present invention, an electric field in a direction different from the polarization direction is applied to a piezoelectric body that has been subjected to a polarization treatment in advance. Since the method of bringing the difference between the resonance frequency and the anti-resonance frequency close to the specific frequency that was previously obtained is adopted, its piezoelectric characteristics do not change even when a thermal shock is applied, and even after long-term use It is possible to obtain a piezoelectric body having a piezoelectric characteristic in which the piezoelectric characteristic does not change, and by comparing how much the value of Δf after reverse polarization processing differs from a specific frequency obtained in advance, it is possible to obtain It is possible to predict changes in piezoelectric characteristics.

Further, in the method of controlling the characteristics of the piezoelectric body according to the present invention, an electric field in a direction different from the polarization direction is applied to the piezoelectric body that has been subjected to the polarization treatment in advance, and the electromechanical coupling coefficient of the piezoelectric body is calculated in advance. Since the method of approaching the specified electromechanical coupling coefficient is adopted, the piezoelectric characteristics do not change even when a thermal shock is applied as in the case above, and the piezoelectric characteristics remain unchanged even after long-term use. It is possible to obtain a piezoelectric body having a piezoelectric characteristic that does not change, and by comparing how the value of Δf after reverse polarization treatment differs from a specific frequency that has been obtained in advance, the electromechanical coupling coefficient due to thermal shock can be obtained. Can also predict changes in

Claims (2)

[Claims] 1. An electric field having a direction different from the polarization direction is applied to a piezoelectric body that has been subjected to a polarization process in advance to bring the difference between the resonance frequency and the anti-resonance frequency of the piezoelectric body close to a specific frequency that has been obtained in advance. A characteristic control method for a piezoelectric body, comprising: 2. An electric field in a direction different from the polarization direction is applied to a piezoelectric body that has been subjected to a polarization treatment in advance so as to bring the electromechanical coupling coefficient of the piezoelectric body close to a specific electromechanical coupling coefficient that has been obtained in advance. A characteristic control method for a piezoelectric body.