JPH06151996A - Polarizing treatment for piezoelectric ceramic - Google Patents

Abstract

PURPOSE:To prevent the mechanical breakdown during polarizing treatment for piezoelectric ceramics and to improve the yield rate in manufacturing. CONSTITUTION:Heat treatment is performed for a long time for piezoelectric ceramics beforehand at a temperature higher than polarization treatment temperature. Immediately after the heat treatment, a DC voltage is applied, and the polarization treatment is performed. Since the applying time of the DC-voltage applying time required for the polarization treatment is greatly shortened, the discharging frequency during the polarization treatment is decreased, and the mechanical breakdowns of the piezoelectric ceramics caused by the discharge are decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polarization treatment method for piezoelectric ceramics, and more particularly to a polarization treatment method for a piezoelectric longitudinal effect vertical oscillator which is difficult to perform polarization treatment.

[0002]

2. Description of the Related Art Piezoelectric ceramics do not exhibit piezoelectricity in the as-sintered state. In order to impart piezoelectricity to this, a polarization treatment for aligning the directions of spontaneous electric polarization in the piezoelectric ceramics is required. The polarization treatment is performed by applying a DC electric field higher than the coercive electric field between a pair of electrodes provided on the surface of the piezoelectric ceramic.

[0003]

The polarization treatment is generally
It is performed in a state in which the piezoelectric ceramic is immersed in insulating oil heated to about 00 ° C. The higher the polarization treatment temperature and the higher the electrode treatment electric field, the shorter the polarization treatment is.

However, when the temperature exceeds the Curie point, spontaneous electric polarization disappears, so that the upper limit of the polarization treatment temperature becomes the Curie point.

Further, as the temperature rises, the insulation resistance decreases and a large electric field cannot be applied, so that the polarization treatment temperature is also restricted from this point. On the other hand, the upper limit of the polarization electric field is determined by the dielectric breakdown voltage of the piezoelectric ceramic.

Generally, in the piezoelectric vertical effect vertical vibrator, the distance between the electrodes becomes long. Therefore, a high DC voltage must be applied between the electrodes in order to provide the electric field strength necessary for the polarization treatment. However, when a high voltage is applied, a discharge often occurs between the electrodes, resulting in mechanical breakdown of the piezoelectric ceramic during the polarization process. It is empirically known that this discharge phenomenon occurs even when the piezoelectric ceramics are immersed in insulating oil, and that the frequency of the discharge phenomenon is not proportional to the electric field strength but is approximately proportional to the absolute value of the voltage applied between the electrodes. Has been. Therefore, the manufacturing yield during the polarization process becomes worse as the ceramic having a longer distance between the electrodes.

An object of the present invention is to provide a polarization treatment method for piezoelectric ceramics which prevents a discharge phenomenon during polarization treatment and improves the production yield of piezoelectric ceramics.

[0008]

In order to achieve the above-mentioned object, the polarization treatment method for piezoelectric ceramics according to the present invention is a polarization treatment method for piezoelectric ceramics having a pretreatment and a polarization treatment. The piezoelectric ceramic is preliminarily subjected to a heat treatment at a temperature higher than the polarization treatment temperature for a long time. In the polarization treatment, a direct current voltage is applied immediately after heating to subject the piezoelectric ceramic to the polarization treatment.

[0009]

The discharge phenomenon occurs more frequently as the polarization treatment time for applying the DC voltage becomes longer, so that shortening the time for applying the DC voltage leads to improvement in yield.

From this point of view, the present invention is characterized in that the piezoelectric ceramics are preliminarily heat-treated at a temperature equal to or higher than the polarization treatment temperature for a long time, and immediately after that, the direct-current voltage is applied to perform the polarization treatment.

According to the present invention, the time required for the polarization treatment is shortened, the frequency of electric discharge is reduced correspondingly, and the manufacturing yield is improved.

[0012]

The present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is a perspective view showing a piezoelectric longitudinal effect vertical vibrator according to a first embodiment of the present invention.

In FIG. 1, reference numeral 1 indicates a dimension of 30 m in length.
It is a piezoelectric ceramics NEPEC-61 manufactured by Tokin Co., Ltd. having a width of m, a width of 5 mm and a thickness of 5 mm. Moreover, 2 has shown the baking silver electrode.

The ordinate of FIG. 2 shows the value obtained by normalizing the electromechanical coupling coefficient k ₃₃ of the piezoelectric longitudinal effect longitudinal vibration by its saturation values k ₃₃ and ₅ , and the abscissa shows the polarization treatment time. There is. The polarization treatment is performed by applying a DC voltage of 50 KV in insulating oil at 100 ° C.

In the figure, 21 is the sample ceramics at 100 ° C.
2 shows the relationship between the polarization time and the electromechanical coupling coefficient when the sample is immersed in insulating oil for 10 minutes and the sample temperature becomes equal to the ambient temperature, and then a voltage of 50 KV is applied for polarization treatment. . It takes about 70 minutes for the polarization to be saturated.

Numeral 22 is the sample ceramics at 100 ° C.
After heating for 0 minutes, a DC voltage of 50 KV is applied to polarize the sample. In this case, the polarization is saturated when the voltage application time is about 50 minutes.

Reference numeral 23 is a sample ceramic 120
This shows the result of polarization after heating at 100 ° C. for a minute, and the polarization is saturated if the polarization treatment is performed for about 40 minutes.

When the sample is subjected to the heat treatment before the polarization treatment as described above, the polarization treatment is completed within a shorter time as the treatment time becomes longer.

FIG. 3 shows a result obtained by subjecting the sample ceramics to a heating treatment at 150 ° C. in advance and then applying a DC voltage of 50 KV to the polarization treatment. Reference numerals 31 and 32 correspond to heating times of 30 minutes and 60 minutes, respectively.

In addition, FIG.
After heating at 0 ° C., the result of polarization at a DC voltage of 50 KV is shown, where 41 is 60 minutes and 42 is 12
It corresponds to a heat treatment time of 0 minutes.

As is clear from the above results, even if the polarization treatment voltage and the polarization treatment temperature are constant, if the heat treatment conditions applied before the polarization treatment are different, the polarization treatment time required for the sample ceramics to undergo saturated polarization is Change. The higher the heat treatment temperature and the longer the heat treatment time, the shorter the polarization treatment time.

(Embodiment 2) FIG. 5 shows a piezoelectric vertical-effect vertical oscillator used in another embodiment of the present invention. The dimensions are 40 mm in length, 8 mm in width, and 0.5 mm in thickness. .
In the figure, 51 is a piezoelectric ceramic (N manufactured by Tokin Co., Ltd.
EPEC-61), 52 shows a baked silver electrode having a length of 5 mm.

FIG. 6 shows the relationship between the polarization treatment time and the electromechanical coupling coefficient of the sample ceramics. In the figure, reference numeral 61 shows the result when the sample ceramic was immersed in insulating oil heated to 100 ° C. for 10 minutes, and after the sample temperature reached 100 ° C., a DC voltage of 50 KV was applied between the electrodes. .

In order to saturate the polarization, it is necessary to perform the polarization treatment for about 80 minutes. Reference numeral 62 shows a result of performing a heat treatment at a temperature of 180 ° C. for 60 minutes in advance and then performing a polarization treatment under the same conditions as above, and the polarization treatment time could be reduced to half or less.

As is clear from Examples 1 and 2, the heat treatment of the sample ceramics in advance can shorten the polarization treatment time. Further, the higher the heat treatment temperature and the longer the heat treatment time, the greater the heat treatment effect.

The sample ceramics of Example 1 is shown in FIG.
As a result of the polarization treatment under the above conditions, 83 samples out of 100 samples were discharged and destroyed during the polarization treatment. However, when the polarization treatment is performed under the condition of 42 in FIG.
Only 0 out of 0 samples broke during the polarization process.

[0028]

As described above, according to the present invention, the DC voltage application time during the polarization treatment can be greatly shortened.
The frequency of the discharge phenomenon that occurs during the polarization treatment is reduced, and the manufacturing yield can be improved.

[Brief description of drawings]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a diagram showing the polarization time dependence of the electromechanical coupling coefficient of the ceramics shown in FIG.

3 is a diagram showing the polarization time dependence of the electromechanical coupling coefficient of the ceramics shown in FIG.

4 is a diagram showing the polarization time dependence of the electromechanical coupling coefficient of the ceramics shown in FIG.

FIG. 5 is a perspective view showing another embodiment of the present invention.

6 is a diagram showing the polarization time dependence of the electromechanical coupling coefficient of the ceramics shown in FIG.

[Explanation of symbols]

 1,51 Piezoelectric ceramics 2,52 Electrodes

Claims (1)

[Claims] 1. A polarization treatment method for piezoelectric ceramics, comprising a pretreatment and a polarization treatment, wherein the pretreatment comprises preliminarily heating the piezoelectric ceramics at a temperature higher than the polarization treatment temperature for a long time. Is a method for polarization treatment of piezoelectric ceramics, in which a direct current voltage is applied immediately after heating to perform polarization treatment on the piezoelectric ceramics.