JP2001332778A - Method of polarizing piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polarize many thin plates consisting of piezoelectric material efficiently and easily with less processing loss, and also to polarize them easily without forming an electrode (conductive film)for polarization. SOLUTION: This method is for polarizing the thin plates consisting of piezoelectric material in its in-plane direction (a direction vertical to the thickness direction of the plate). Plural sheets of thin plates 20 consisting of piezoelectric material are stacked on top of one another, and then high voltage is applied to both their opposite sides of the stack, thereby polarizing the piled thin plates consisting of piezoelectric materials en block. A method of forming conductive films 22 directly on the films consisting of piezoeiectric material and polarizing them utilizing the conductive film, and a method of polarizing them utilizing conductive sheets without forming conductive films, are available.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of polarizing a thin plate made of a piezoelectric material in an in-plane direction (a direction perpendicular to the thickness direction). More specifically, the present invention relates to a method of polarizing a thin plate made of a plurality of piezoelectric materials. The present invention relates to a method for collectively performing polarization processing in a state where thin plates are stacked. This polarization processing method
In particular, it is useful for manufacturing a thin plate-type shearing type piezoelectric element.

[0002]

2. Description of the Related Art Piezoelectric materials are used in actuators, sound generators, vibrators, etc. by utilizing the function of converting electrical signals into mechanical displacements. Sensors utilizing the function of converting mechanical displacements into electrical signals. It is widely used for filters and the like by combining both functions.

In order to produce a piezoelectric effect on a piezoelectric material, especially a piezoelectric ceramic material composed of a polycrystalline material, a high voltage (a voltage higher than the coercive voltage of the piezoelectric material) is applied to the fine particles forming the piezoelectric ceramic. A step of aligning the direction of the spontaneous polarization with the polarization direction is required. This polarization treatment is generally performed by forming a conductive film (such as a thick silver film-baked electrode) on a member made of a piezoelectric material and applying a high voltage to the film.

There are various types of devices using piezoelectric ceramics, and a typical example thereof is a piezoelectric device utilizing a longitudinal effect and a lateral effect of electric field induced strain. In this type of piezoelectric element, driving electrodes or detection electrodes are provided on both surfaces perpendicular to the polarization direction. Therefore, the conductive film for polarization formed on both surfaces perpendicular to the polarization direction can be used as it is as a drive electrode or a detection electrode.

Devices using piezoelectric ceramics include:
In addition, there is a shear-type piezoelectric element that slides and vibrates along a surface. This is a special structure in which the direction of polarization of the piezoelectric element and the direction connecting both driving electrodes or detection electrodes (the direction of applying an electric field or the direction of detecting an electric field) are orthogonal to each other. This shear type piezoelectric element is schematically shown in FIG. The piezoelectric body 10 is polarized in the direction of the arrow, and the electrodes 12 are provided on the entire front and back surfaces. When a voltage is applied between both electrodes, the piezoelectric body 1
A value of 0 causes a shear strain as shown by a dotted line. Conversely, when an external force is applied in the polarization direction to generate shear strain, a voltage is generated between the electrodes on the front and back surfaces.

In such a shear-type piezoelectric element, as described above, since the polarization direction and the driving electric field direction are orthogonal to each other, the electrode used for polarization processing cannot be used as a driving electrode. . Therefore, the thin plate type shearing type piezoelectric element has been subjected to a polarization treatment by a method as shown in FIG. This is a method in which a band-like polarization electrode 16 is formed on one surface of a thin plate 14 made of a piezoelectric material or at the same position on both front and back surfaces at intervals and a high voltage is applied to perform polarization. Piezoelectric element 1
There is also a method of performing polarization processing on individual piezoelectric elements. If the piezoelectric elements are small, a polarization electrode is formed in a strip shape on a thin plate of a plurality of pieces, and after polarization, cut and separated into individual piezoelectric elements. There is also a way to do it.

[0007]

In such a conventional method, the electrodes for polarization must be formed one by one on the surface of the thin plate in alignment with each other, and it takes time and effort to form the electrodes. The thin plates must be polarized one by one. Even if a plurality of piezoelectric elements are cut out from one thin plate, the efficiency of the whole manufacturing process is not significantly improved even though the complexity of the polarization operation is somewhat reduced.

[0008] The polarization electrode formed on the surface of the thin plate,
After the polarization treatment, it is unnecessary as a product, and therefore, the portion on which the polarization electrode is formed must be cut and removed. Therefore, the loss of the piezoelectric material is very large.

An object of the present invention is to provide a method capable of efficiently and easily polarizing a large number of thin plates made of a piezoelectric material with little processing loss. Another object of the present invention is to provide a method for easily polarizing a large number of thin plates made of a piezoelectric material without forming a conductive film for polarization.

[0010]

SUMMARY OF THE INVENTION The present invention is a method for polarizing a thin plate made of a piezoelectric material in an in-plane direction (a direction perpendicular to the thickness direction of the plate). In the present invention, a plurality of thin plates made of a piezoelectric material are stacked, and a high voltage is applied between opposing side surfaces of the stacked body to collectively polarize the thin plates made of the piezoelectric material. I do. Here, the thin plate made of a piezoelectric material is a thin plate-shaped sintered body made of a piezoelectric ceramic such as lead zirconate titanate, and is held by a method of clamping with a jig using a spring. The high voltage applied during the polarization process refers to a voltage equal to or higher than the coercive voltage of the piezoelectric material. By forming electrodes on both the front and back surfaces of the thin plate after the polarization treatment, a shear-type piezoelectric element that performs thickness-shear vibration can be obtained.

According to the present invention, there is provided a method of forming a conductive film directly on a thin plate made of a piezoelectric material and performing a polarization treatment using the conductive film, and a method of using a conductive member without forming the conductive film. And a polarization treatment.

In the method of forming a conductive film, a thin plate made of a piezoelectric material is prepared by forming a conductive film for polarization on both end surfaces thereof in advance, and a plurality of such films may be stacked. A plurality of thin plates made of a material having a uniform length may be stacked, and a conductive film for polarization may be formed on both sides of the stacked body facing each other. In any case, a high voltage is applied between the conductive films for polarization to collectively polarize the stacked thin plates made of the piezoelectric material. The conductive film for polarization to be formed is, for example, a thick-film silver electrode coated with a silver paste and baked. Of course, a sputtered film or a deposited film of a conductive material may be used.

[0013] More preferably, a plurality of thin plates made of piezoelectric material are held in a stacked state, and opposing side surfaces of the stacked body are ground to make the length uniform and surfaced. There is a method in which a conductive film for polarization is formed on a thin film, and a high voltage is applied between the conductive films to collectively polarize the stacked thin sheets of piezoelectric material. By exposing it, a beautiful conductive film can be formed,
The contact state with the metal plate for voltage application described below is also improved.

In these methods, a metal plate for applying a voltage is brought into contact with both of the polarizing conductive films of the stacked thin plates made of a piezoelectric material, and a lead wire is connected to the metal plate for applying a voltage. It is preferable to perform polarization processing by applying a voltage.

The conductive films for polarization can be removed at a time by grinding both side surfaces of the piezoelectric thin plates that have been subjected to the polarization treatment in a stacked state.

In the method of performing a polarization treatment without forming a conductive film, a plurality of thin plates made of a piezoelectric material and having a uniform length are stacked, and elasticity is applied to opposing side surfaces of the stack. A flexible conductive member is disposed, the conductive member is pressed from outside with a metal plate for voltage application, and a high voltage is applied between the metal plates for voltage application to form a stack of piezoelectric materials. The thin plate is collectively polarized.

Here, as in the case of forming the conductive film, in a state where a plurality of thin plates made of a piezoelectric material are stacked, opposing both side surfaces of the stacked body are ground to make the lengths uniform and surface-projected. It is preferable that flexible conductive sheets having elasticity are arranged on both sides of the exposed and exposed surfaces. An example of a flexible conductive sheet having elasticity is a conductive rubber sheet.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Powder of a piezoelectric material (for example, a lead zirconate-based piezoelectric ceramic material), an organic binder and a solvent are kneaded to form a slurry, which is formed into a thin sheet by a doctor blade method or the like. Then, it is cut into a predetermined thin plate size and fired in a state where many sheets are stacked.
Thus, a sintered thin plate made of a piezoelectric material is obtained. Here, the shape of the thin plate is, for example, about 20 mm in length, 10 mm in width, and about 0.2 to 0.3 mm in thickness.

FIG. 1 is an explanatory view showing one embodiment of the method of the present invention, in which a conductive film for polarization is provided. Thin plate 2 made of piezoelectric material fired as described above
0 (several tens to several hundreds) are stacked and held (FIG. 1)
A). The holding may be performed by using a jig (not shown) and using a spring or spring tightening force or the like to hold the jig. Then, both side surfaces (upper and lower surfaces in the drawing) perpendicular to the polarization direction are ground, and the length is adjusted and surfaced.

Next, as shown in FIG. 1B, while a plurality of thin plates 20 made of a piezoelectric material are stacked and held, conductive films 22 for polarization are provided on both exposed side surfaces. The conductive film 22 is formed by, for example, applying a silver paste or the like by a screen printing method and baking. Of course, the conductive film may be formed by a sputtering method, an evaporation method, or the like.

Then, as shown in FIG. 1C, a metal plate 24 for applying a voltage is arranged outside the conductive coating 22 while a plurality of thin plates 20 made of a piezoelectric material are stacked, and between the two metal plates. Polarization is performed by applying a high voltage. This polarization operation is usually performed in order to reduce the load voltage required for polarization and to prevent dielectric breakdown due to corona discharge or the like.
The immersion is performed by dipping in insulating oil such as silicone oil heated to 120 ° C. The high voltage applied at the time of polarization is a voltage equal to or higher than a coercive voltage previously determined according to the piezoelectric material, and is applied to the piezoelectric material. For example, 20k
V / width is about 10 mm. The application of this high voltage is usually
Perform for several minutes to one hour.

After the polarization treatment, the stacked thin plates are taken out and the attached silicone oil is washed. Then, the conductive film for polarization is removed by grinding. When it is necessary to grasp the direction of polarization in a later step, one corner of the thin plate may be chamfered by grinding while being stacked. This becomes a marking, and even if the sheets are separated one by one, it is possible to determine the polarization direction at the position of the chamfered corner.

In order to form a shear-type piezoelectric element, driving electrodes are formed on both front and back surfaces of the polarized thin plate manufactured as described above. The driving electrode is formed by a sputtering method or the like so that the piezoelectric body is heated to a temperature equal to or higher than the Curie temperature and spontaneous polarization aligned with the high voltage application direction does not turn to an arbitrary direction again (depolarization). It is formed by an evaporation method. If the thin plates are larger than the element size, they are cut one by one or collectively in a stacked state.

FIG. 2 is an explanatory view showing another embodiment of the method of the present invention, in which a conductive film for polarization is not provided. A large number (several tens to several hundreds) of thin plates 20 made of fired piezoelectric material are stacked and held as shown in FIG.

Then, as shown in FIG. 2B, while a large number of thin plates 20 made of a piezoelectric material are stacked, elastic and flexible conductive sheets 30 are provided on both sides perpendicular to the polarization direction. Install. As mentioned above, the polarization operation is usually
In order to lower the load voltage required for polarization and to prevent dielectric breakdown due to corona discharge or the like, immersion is performed in an insulating oil such as silicone oil heated to 80 to 120 ° C. Therefore, the conductive sheet 3 for applying a high voltage
For 0, a material having good heat resistance is used. Degraded by high temperature such as silicone rubber as base material of conductive sheet,
Materials that do not cure are suitable. In addition, when there is a variation in the dimensions of the polarizing thin plate, a material having excellent flexibility such as a gelled silicone resin is desirable. The conductivity may be imparted by dispersing a metal powder, a metal fiber, a carbon powder, or the like in a base material, or by adding an ion-conductive substance, for example, a powder such as lithium chloride.

Then, as shown in FIG. 2C, a metal plate 32 for applying a voltage is disposed outside the conductive sheet 30, and a high voltage is applied between the two metal plates 32 to perform a polarization process. This polarization operation is performed to reduce the load voltage required for polarization and to prevent dielectric breakdown due to corona discharge or the like.
It is immersed in insulating oil such as silicone oil heated to 20 ° C., and is performed for several minutes to one hour.

After the polarization treatment, the stacked thin plates are taken out, and the attached silicone oil is washed. When it is necessary to grasp the direction of polarization in a later step, one corner of the thin plate may be chamfered by grinding while being stacked. Driving electrodes are formed on both sides of the polarized thin plate manufactured as described above by a sputtering method or a vapor deposition method so that depolarization does not occur. After that, depending on the size of the thin plate, the thin plate is cut into a specified element size, and a plurality of piezoelectric elements are cut out.

[0028]

EXAMPLES Pb (Sb _1/2 Nb _1/2 ) O ₃ -PbZrO
_{Using a 3-} PbTiO ₃ -based piezoelectric material and providing a conductive coating shown in FIG. 1 (Polarization method A), the piezoelectric d ₃₁ value when polarized and a method using a conductive sheet shown in FIG. 2 (Polarization method) Table 1 shows a comparison result of the piezoelectric d ₁₅ value when polarized according to B). The sample was adjusted and measured in accordance with EMAS-6005 (Test method for piezoelectric ceramic vibrator-Thickness sliding vibration of rectangular plate vibrator), which is a technical standard of the Electronic Materials Industries Association. The sample had a length of 20 mm, a width of 10 mm, and a thickness of 2.5 mm, and was polarized in the width direction.

The conductive film of the polarization method A is a silver thick film baked electrode. The conductive sheet used in the polarization method B is obtained by dispersing metal fibers in silicone rubber. Polarization was performed by applying an electric field of 2 kV / mm in silicone oil at 120 ° C. and holding for 1 hour. Polarization method A
Then, after the polarization treatment, the conductive film was removed by grinding. After forming a gold electrode on the sample by sputtering,
The sheet was cut into a size of 10 mm × 2.5 mm to obtain a thickness sliding oscillator, and the piezoelectric characteristics were measured. As a result, it was found that the piezoelectric characteristics hardly changed in both methods.

[0030]

[Table 1]

[0031]

As described above, the present invention is a method of performing a polarization process at a time in a state in which a plurality of thin plates made of a piezoelectric material are stacked, so that a large number of thin plates made of a piezoelectric material can be efficiently and easily formed. Can be polarized. Further, the processing loss can be almost eliminated, and the effective use of the piezoelectric material can be achieved.

Further, in the method using a conductive member, the step of forming and removing the conductive film for polarization is not required, and the conductive member can be used repeatedly, so that the cost can be significantly reduced. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of a polarization processing method according to the present invention.

FIG. 2 is an explanatory view showing another example of the polarization processing method according to the present invention.

FIG. 3 is an explanatory view showing an example of the structure and operation of a shear-type piezoelectric element.

FIG. 4 is a diagram showing an example of a conventional polarization method.

[Explanation of symbols]

 Reference Signs List 20 thin plate made of piezoelectric material 22 conductive coating for polarization 24 metal plate for applying voltage 30 conductive member 32 metal plate for applying voltage

Claims (7)

[Claims] 1. A method for polarizing a thin plate made of a piezoelectric material in an in-plane direction, comprising: stacking a plurality of thin plates made of a piezoelectric material, and applying a high voltage between opposing side surfaces of the stacked body. A polarization processing method for a piezoelectric element, comprising applying a voltage to collectively polarize stacked thin plates made of a piezoelectric material. 2. A method for polarizing a thin plate made of a piezoelectric material in an in-plane direction, comprising: stacking a plurality of thin plates made of a piezoelectric material having a uniform length, and opposing opposite sides of the stacked body. Applying a high voltage between the conductive films for polarization provided on the surface,
A polarization processing method for a piezoelectric element, wherein a plurality of thin plates made of a piezoelectric material are subjected to polarization processing at a time. 3. A method for polarizing a thin plate made of a piezoelectric material in an in-plane direction, wherein a plurality of thin plates made of a piezoelectric material are held in a stacked state, and opposing side surfaces of the stacked body are ground. The length is aligned and surfaced, a conductive film for polarization is formed on both sides of the surface, and a high voltage is applied between the conductive films.
A polarization processing method for a piezoelectric element, wherein a plurality of thin plates made of a piezoelectric material are subjected to polarization processing at a time. 4. The polarization treatment of a piezoelectric element according to claim 2, wherein the polarization treatment is performed by contacting the voltage-applying metal plates to both the conductive films for polarization of the stacked thin plates made of the piezoelectric material. Method. 5. The polarization treatment of a piezoelectric element according to claim 2, wherein both sides of the polarization-treated piezoelectric thin plates are ground and the conductive film for polarization is collectively removed. Method. 6. A method for polarizing a thin plate made of a piezoelectric material in an in-plane direction, comprising stacking a plurality of thin plates made of a piezoelectric material having a uniform length, and opposing opposite sides of the stacked body. On the surface, a flexible conductive member having elasticity is arranged, the conductive member is pressed from outside with a metal plate for voltage application, and a high voltage is applied between the metal plates for voltage application to be stacked. Polarizing processing of a thin plate made of a piezoelectric material at a time. 7. The method according to claim 6, wherein the elastic and flexible conductive member is a conductive rubber sheet.