JPH06260696A - Partially polarizing method for piezoelectric element - Google Patents

Abstract

PURPOSE:To provide a method for partially polarizing a piezoelectric element component in which a defective product occurrence rate due to a crack caused by a stress concentration in the vicinity of a boundary between a polarized part and an unpolarized part can be reduced and which can obtain the component having excellent reliability. CONSTITUTION:Polarizing electrodes 12, 13 are partly formed on both main surfaces of a piezoelectric plate 11, and have a part having a wide gap and a part having a small or no gap so as to form gap regions in which ends are not superposed to one another. A method for partially polarizing a piezoelectric element comprises the steps of applying a DC voltage between the electrodes 12 and 13 to polarize superposed regions of the electrodes 12, 13 concentrically generating a crack at the piezoelectric element in the part having the wide gap, and removing the element having the crack after the polarization.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of partially polarizing a piezoelectric body, and more particularly, it can reduce defective products due to cracks in the piezoelectric body due to stress concentration near the boundary between a polarized portion and an unpolarized portion. It relates to a partial polarization method.

[0002]

2. Description of the Related Art For example, when an energy trapping type piezoelectric resonator and another circuit element such as a capacitor are formed by using one piezoelectric plate, the piezoelectric resonator portion is piezoelectric and the capacitor portion is a part. A partially polarized piezoelectric plate is used in order to fully exhibit the capacitance.
This partial polarization is performed by partially forming polarization electrodes on both main surfaces of the piezoelectric plate. That is, a DC voltage was applied between the partially formed polarization electrodes, and thereby the piezoelectric plate was partially polarized.

However, when the above partial polarization is performed, a large stress is concentrated near the boundary between the polarized portion and the non-polarized portion of the piezoelectric plate. As a result, there is a problem that the piezoelectric plate is broken or cracked. Therefore, it has been attempted to reduce the stress concentration near the boundary between the polarized portion and the unpolarized portion by devising the shape of the polarized electrode.

For example, as a first method, as shown in FIGS. 14 and 15, a method of forming polarization electrodes 2 and 3 of different sizes on both main surfaces 1a and 1b of the piezoelectric body 1 has been tried. ing. In this method, by forming a portion where the polarization electrode 2 and the polarization electrode 3 do not face each other with the piezoelectric plate 1 in between, that is, a gap region, stress concentration in the vicinity of the boundary between the unpolarized portion and the polarized portion is reduced. It is being alleviated.

Further, in the second method shown in FIG. 16, the edge of the polarization electrode 5 formed on the upper surface 4a of the piezoelectric plate 4 and the edge of the polarization electrode 6 formed on the lower surface are corrugated. In addition, the corrugated shape is a shape in which the phase is shifted by π radian between the polarization electrodes 5 and 6. As described above, since the edges of the polarization electrodes 5 and 6 are in the shape of a waveform whose phase is shifted by π radian, an electric field gap is formed, thereby relaxing stress concentration.

[0006]

However, in the above first and second methods for relaxing the stress concentration, the stress concentration in the vicinity of the edge of the polarization electrode is relaxed on one side, but rather on the other side. The electric field concentration became remarkable, stress concentration was promoted, and cracks were very likely to occur. That is, the method considered to alleviate the above-mentioned stress concentration is considered to be ineffective in reducing cracks and the like.

In particular, lead zirconate titanate-based piezoelectric ceramics, which are generally used as piezoelectric materials, have relatively large pores due to problems in the manufacturing method.
It has been considered that it is essentially impossible to avoid the occurrence of cracks as described above.

The object of the present invention is to reduce the occurrence of defective products due to cracks due to stress concentration near the boundary between the polarized portion and the non-polarized portion when the piezoelectric body is partially polarized, and therefore reliability is improved. Another object of the present invention is to provide a method for partially polarizing a piezoelectric body, which makes it possible to obtain excellent piezoelectric components.

[0009]

SUMMARY OF THE INVENTION The present invention is a method for partially polarizing a piezoelectric body, in which polarization electrodes are partially formed on both main surfaces of the piezoelectric body, and a voltage is applied between the polarization electrodes. When applied and polarized, the following steps are provided.

That is, according to the present invention, the polarization electrode edge on one main surface of the piezoelectric body and the polarization electrode edge on the other main surface form a gap region where they do not overlap each other through the piezoelectric body. In addition, the above-mentioned polarization electrode is formed such that there is a portion having a large width and a portion having a small width or a portion having no gap region. When a DC voltage is applied between the electrodes for polarization to cause polarization, cracks occur on the side of the piezoelectric region that is relatively large in the gap region.
Then, in the polarization method of the present invention, by removing the portion of the piezoelectric body in which cracks have occurred after polarization, a partially polarized piezoelectric body having no cracks can be obtained.

[0011]

In view of the fact that it is virtually impossible to prevent the occurrence of cracks due to stress concentration near the boundary between the polarized portion and the non-polarized portion during partial polarization of the piezoelectric body, the present invention has been described above. As described above, it is characterized in that the cracks are intentionally concentrated on the relatively large portion side of the gap region and the portions where the cracks are generated are removed after polarization.

That is, the present invention approves the generation of cracks that cannot be avoided in partial polarization, and then limits the position where the cracks are generated by devising the shape of the polarization electrode, which causes cracks. This facilitates the removal of the parts that have

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified below by describing non-limiting examples of the present invention. The piezoelectric body of the embodiment is composed of Pb (Ti, Zr) O _{3 having} a composition near the phase boundary between a tetragonal crystal and a rhombohedral crystal, and is 20 mm × 30 m
A piezoelectric plate having m × 0.185 mm thickness was prepared. Using this piezoelectric plate, a piezoelectric vibrator with a built-in load capacitance having an oscillation frequency of 12 MHz using the thickness extensional vibration mode was manufactured through the following steps.

First, as shown in FIG. 1, the piezoelectric plate 11 is used.
Polarizing electrodes 12 and 13 were formed on both main surfaces of the. The polarization electrode 13 has a shape similar to that of the polarization electrode 12, but in the region along the one end surface 11d of the piezoelectric plate 11, the edges of the polarization electrode 13 are the outer edge and the inner edge of the polarization electrode 12. It is formed so as to extend outside and inside (the edge of the protruding polarization electrode 13 is indicated by a broken line in FIG. 1). That is, the gap region having a width of 0.3 mm in which the polarization electrode 12 and the polarization electrode 13 do not overlap each other is in the direction along the end face 11d.
Are formed on both sides of.

Incidentally, other portions, for example, the end faces 11a to 11
In the direction along c, the edge of the electrode 12 for polarization and the edge of the electrode 13 for polarization are formed at positions overlapping in the thickness direction. No gap region is formed.

Although gap regions where the edges of the polarization electrode 12 and the polarization electrode 13 do not overlap each other may be formed in the portions along the end faces 11a to 11c, the gap regions are formed in the direction along the end face 11d. It is necessary that the width is narrower than that of the gap area.

Next, a direct current voltage was applied between the polarization electrodes 12 and 13 as shown in FIG. 2 to partially polarize the piezoelectric plate 11. This polarization was performed by applying a DC voltage of 700 V at a temperature of 60 ° C. for 20 minutes.

Due to the above-mentioned partial polarization, in the portion along the end face 11d where the gap region is formed,
As shown in FIG. 3, many cracks 14 were generated. This is because the stress concentration between the polarized portion and the non-polarized portion is relatively large in the portion where the gap region is formed, as compared with the region where the edges of the polarization electrodes 12 and 13 overlap each other. This is because the crack 14 has occurred at the portion where the gap region is provided.

The piezoelectric plate 11 in which the cracks 14 have been generated as described above is aged by being left in the atmosphere at a temperature of 150 ° C. for 1 hour, and then, as shown by a chain line A in FIG. The part along the end face 11d was cut and removed. As a result, the piezoelectric plate portion 11 in which the crack is generated
e is removed. As a result, the piezoelectric plate portion 11e in which the crack is generated is removed, so that the partially polarized piezoelectric plate 11 having no crack is obtained.

Next, as shown in FIG. 5, the polarization degree of the obtained partially-polarized piezoelectric plate 11 is confirmed by measuring the polarization degree of the spreading vibration of the piezoelectric plate so that the desired polarization degree is obtained. As shown in FIG. 5, a DC pulse voltage was applied in the forward direction or the reverse direction depending on the polarization degree. In this way
A partially polarized piezoelectric plate having a desired degree of polarization was obtained.

Next, the polarization electrodes 12 and 13 were removed by etching to obtain a partially polarized piezoelectric plate 11 having no electrodes on both principal surfaces, as shown in FIG. Furthermore, the piezoelectric plate 1
On both main surfaces of 1, by vapor deposition or sputtering,
An electrode film having a thickness of about several μm is formed on the entire surface. As the electrode film material, for example, Ag or Ag-Pd can be used.

Next, the formed entire electrodes on both main surfaces are etched to form the piezoelectric plate 1 as shown in FIGS. 7 (a) and 7 (b).
The excitation electrodes 15 and 16 and the capacitor electrodes 17 and 18 are dispersedly formed on both main surfaces of No. 1. Then, the piezoelectric plate 11 is cut along the alternate long and short dash lines B and C in FIG.
The piezoelectric vibrator 19 with a built-in load capacitance shown in (a) and (b) is obtained.

In the load capacity built-in type piezoelectric vibrator 19, the excitation electrodes 15 and 16 are formed in the polarized portion, and the capacitor electrodes 17 and 18 are formed in the unpolarized portion. Moreover, in the obtained piezoelectric vibrator 19, the element is configured by using the piezoelectric plate 11 having no crack.

Comparative Example 1 A piezoelectric plate having the same material and the same size as those used in the embodiment is prepared, and as shown in FIGS. 9 and 10, the piezoelectric plate 21 has the same shape and the same size on both main surfaces thereof. Polarization electrode 22,
No. 23 was formed so that the electrode edges overlap in the thickness direction. Next, as shown in FIG. 10, a DC voltage was applied from the polarization electrodes 22 and 23 under the same conditions as in the example to partially polarize the piezoelectric plate 21.

In this case, during partial polarization, stress concentration occurs at the boundary between the polarized portion and the non-polarized portion.
As shown in (a), there are no cracks,
As shown in FIG. 11B, a defective product having many cracks 24 was generated. The piezoelectric plate 21 partially polarized as described above is aged under the same conditions as in the embodiment, and thereafter, the subsequent steps are performed in the same manner as in the embodiment, whereby the piezoelectric vibrator with the built-in load capacitance ( The same as the piezoelectric vibrator shown in FIG. 8) was manufactured.

In Comparative Example 1, about 10% or more of the defective products had the cracks 24 shown in FIG. 11B due to the partial polarization as described above. Therefore, in manufacturing the piezoelectric vibrator, Therefore, the yield was inevitably lower than that of the example (the defective product rate was 1% or less).

Comparative Example 2 As shown in FIGS. 12 (a) and 12 (b), a polarization electrode 32 and a larger area than the polarization electrode 32 are formed on both main surfaces of the same piezoelectric plate 31 prepared in the embodiment. And the polarization electrode 33 of. As shown in the drawing, the edge of the polarization electrode 33 is located outside the edge of the polarization electrode 32 in all the regions, and there is a gap region where the polarization electrode 32 and the polarization electrode 33 do not overlap each other. The polarization electrodes 32 and 33 were formed so as to have the same width (0.3 mm) around the polarization part.

Using the piezoelectric plate 31 on which the polarization electrodes 32 and 33 are formed as described above, when a DC voltage is applied in the same manner as in the embodiment for partial polarization, the crack occurrence rate may be due to the existence of the gap region. Is about 50%, and the incidence of cracks is increased as compared with Comparative Example 1. That is, the crack generation rate was still high. However, there was regularity in the crack generation position. Therefore, when the polarization method of Comparative Example 2 is used, the yield of the piezoelectric vibrator decreases rather due to the occurrence of the cracks.

Comparative Example 3 As shown in the partially cutaway plan view of FIG. 13, a piezoelectric plate 41 having polarization electrodes 42 and 43 formed on both main surfaces thereof was prepared. The same piezoelectric plate 41 as that used in the example was prepared. The polarization electrodes 42 and 43 have a corrugated shape as shown, and the corrugated shape of the edge of the polarization electrode 42 is out of phase by π radian with respect to the corrugated shape of the edge of the polarization electrode 43. It is shaped like In addition, such a gap region has a maximum width of 0.3 mm, and the half-wavelength of the corrugated wave is 3 mm. When a DC voltage was applied from the polarization electrodes 42 and 43 to partially polarize in the same manner as in the example, the crack occurrence rate in the piezoelectric plate 41 was about 30%.
And was slightly reduced as compared with Comparative Example 2. However, the crack generation rate was still high, and there was no regularity in the crack generation position.

Therefore, also in the method of Comparative Example 3, the yield of the piezoelectric vibrator was inevitably low. In the methods of Comparative Examples 2 and 3, the rate of occurrence of cracks was rather increased, and small cracks were also generated in the center of the piezoelectric plate.
Therefore, it is impossible to avoid an increase in the defective product rate due to the occurrence of cracks as described above.

[0031]

As described above, according to the partial polarization method of the present invention, the gap regions where the polarization electrodes on both principal surfaces do not overlap each other are formed, and the large gap region and the small gap region or the gap region are formed. Since there is a non-existing portion, cracks are limitedly generated in a large portion of the gap region during polarization. Therefore, it is possible to easily remove the portion of the piezoelectric body in which a crack has occurred, and it is possible to reliably obtain a partially polarized piezoelectric body having no crack.

Therefore, when the present invention is utilized in the manufacture of a piezoelectric component that requires a piezoelectric body having a polarized portion and an unpolarized portion, such as a piezoelectric vibrator with a built-in load capacitance, the piezoelectric component can be manufactured. The yield and the reliability of the piezoelectric component can be improved.

[Brief description of drawings]

FIG. 1 is a plan view showing polarization electrodes formed on both principal surfaces of a piezoelectric plate in an example.

FIG. 2 is a schematic cross-sectional view for explaining a polarization process.

FIG. 3 is a plan view for explaining cracks generated after polarization in Examples.

FIG. 4 is a plan view for explaining a step of cutting / removing a cracked portion.

FIG. 5 is a schematic cross-sectional view for explaining a step of adjusting the polarization degree.

FIG. 6 is a plan view showing a piezoelectric plate from which a polarization electrode has been removed.

7 (a) and 7 (b) are a plan view showing a piezoelectric plate on which an excitation electrode and a capacitor electrode are formed, and a plan view showing an electrode on the back side through the piezoelectric plate.

8A and 8B are respectively a plan view for explaining the load capacity built-in type piezoelectric vibrator obtained in the example and a plan view showing electrodes on the back side through the piezoelectric plate.

9 is a plan view for explaining a piezoelectric plate prepared in Comparative Example 1 and polarization electrodes formed on both main surfaces of the piezoelectric plate. FIG.

FIG. 10 is a schematic cross-sectional view for explaining a polarization step in Comparative Example 1.

11 (a) and 11 (b) are plan views showing a partially-polarized piezoelectric plate obtained in Comparative Example 1,
(A) shows a good product, and (b) shows a defective product.

12A and 12B are a plan view and a side view showing a piezoelectric plate prepared in Comparative Example 2 and polarization electrodes formed on both main surfaces thereof.

FIG. 13 is a partially cutaway plan view for explaining shapes of a piezoelectric plate prepared in Comparative Example 3 and polarization electrodes formed on both main surfaces thereof.

FIG. 14 is a side view for explaining an example of a conventional partial polarization method.

15 is a partially cutaway plan view showing the piezoelectric plate and the polarization electrode shown in FIG.

FIG. 16 is a partially cutaway plan view for explaining another example of the conventional polarization method.

[Explanation of symbols]

 11 ... Piezoelectric plate 12, 13 ... Electrode for polarization

Claims (1)

[Claims] 1. A method of partially polarizing a piezoelectric body, comprising the steps of partially forming polarization electrodes on both main surfaces of the piezoelectric body and applying a voltage between the polarization electrodes for polarization. In order to form a gap region in which the polarization electrode edge on one main surface and the polarization electrode edge on the other main surface do not overlap with each other via the piezoelectric body, a large width portion and a small width portion of the gap area are formed. Alternatively, the electrodes for polarization are formed so that there is a portion where the gap region is not formed, and a voltage is applied between the electrodes for polarization to polarize the electrodes, and a piezoelectric body is formed on the side of the large width portion of the gap region. Causing cracks,
A method of partially polarizing a piezoelectric body, comprising: each step of removing a piezoelectric body portion in which a crack has occurred after polarization.