JPS622477B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of polarizing a piezoelectric material, and more particularly to a method of polarizing a piezoelectric film in a direction perpendicular to the thickness direction of the piezoelectric film.

The process of polarizing a piezoelectric body is usually carried out by forming polarizing electrodes on both sides in the direction to be polarized by vapor deposition or the like, and applying a DC voltage between the electrodes. The shape of a piezoelectric body is normally a flat plate as shown in FIG. 1, and such a piezoelectric body 1 can be polarized in the thickness direction (Z-axis) relatively easily by the above method. For example, Journal of the Institute of Electronics and Communication Engineers, January 1978 Vol.61, NO-1
According to “Piezoelectric and Pyroelectric Polymer Materials and Their Applications”, polyvinylidene fluoride (β type) film is
Poling at 50℃ for 30 minutes to increase the piezoelectric constant _d13 by 2x
To obtain about 10 ^-7 cgs, the electric field strength must be
It is said that 1000KV/cm is sufficient. Therefore, if the thickness of the film is 100μ, the polarization voltage required for poling may be about 1KV.

On the other hand, the surface of the piezoelectric material whose normal is the thickness direction
It is very difficult to polarize in a certain direction within the XY plane using the above method.

That is, the first possibility for polarizing in this direction is to provide a polarizing electrode between both end faces in the X or Y direction and apply a DC voltage as shown in FIG. Second
As shown in Fig. 2, one possibility is to mold a relatively thick piezoelectric film, place polarization electrodes 2 in the thickness direction, apply a polarization voltage, and then slice it very thinly in the thickness direction. It is possible to obtain a piezoelectric film with a polarization axis perpendicular to the thickness direction. Furthermore, the third possibility is that as shown in Fig. 3, the electrodes 2 are arranged on the surface of the piezoelectric sheet so that they are deviated from each other, and a DC voltage is applied to the upper and lower busbars 3, 3' to generate a voltage parallel to the surface of the piezoelectric sheet. Form components and perform polarization. The first method is dangerous because it requires a large polarization electrode.If the voltage that can be applied is lowered, the size of the piezoelectric sheet that can be polarized is limited. Also, in the second method, the width of the piezoelectric sheet cannot be made large;
It requires a difficult process of slicing it extremely thin.
The third method is that the electric field from the polarizing blind electrode through the inside of the piezoelectric sheet and returning to the blind electrode forms an arc as shown in Figure 4, making it difficult to polarize uniformly in a plane perpendicular to the thickness direction. be. That is, only the horizontal component of the electric field 4 in FIG. 4 is effective for polarization.

This invention has been made in view of the above-mentioned points, and its purpose is to use a relatively low polarization voltage and to achieve uniformity without unevenness in the direction perpendicular to the thickness direction of the membranous piezoelectric film. The purpose of the present invention is to provide a good polarization method for membranous piezoelectric films.

In order to achieve the above object, the present invention first folds a piezoelectric film into a wave shape before providing a polarizing electrode on the membrane piezoelectric film. Thereafter, silver paste or the like is applied to each wave head, and the anode of the polarization power source is brought into contact with the upper wave front group, and the cathode is brought into contact with the lower wave front group, and the DC voltage necessary for polarization is applied to polarize. Thereafter, by stretching this membranous piezoelectric film again, a piezoelectric film having a uniform polarization axis in the entire thickness direction on a plane perpendicular to the thickness direction of the membranous piezoelectric film is produced.

The present invention will be specifically explained below using examples.

FIGS. 5 and 6 show an embodiment of the present invention, in which a polyvinylidene fluoride (β type) piezoelectric film 11 with a thickness of 50 μm, a width of 5 cm, and a length of 6 cm is arranged in fifth rows at intervals of 1 mm in the length direction. Fold the piezoelectric film into a wave shape as shown in the figure. Then, as shown in FIG. 6, polarizing electrodes 12, 12' are brought into contact with each wavefront group, and a DC voltage of 10 KV is applied in silicone oil at 50°C. After 30 minutes, it was taken out, stretched, and returned to the original flat piezoelectric film.

The partial polarization carried out in the above process allows each region to be polarized with uniform strength in the thickness direction, and the boundary between each region can be made narrower than when using interdigital electrodes.

Furthermore, since electrodes bonded to the wave crests during polarization remain on both sides of the stretched piezoelectric film after polarization, these electrodes can be used as landmarks for the next patterning process.

In order to make it easier to fold the membranous piezoelectric film into a wave shape, it is also effective to make some cuts 13 at the top and bottom of the wave as shown in FIG.

[Brief explanation of the drawing]

Figures 1 to 4 are for explaining a conventional method of polarizing a piezoelectric material. Figure 1 shows a method in which a polarizing electrode is provided between both end faces of a piezoelectric film in the X or Y direction. Fig. 2 shows a relatively thick piezoelectric material with polarizing electrodes attached to both end faces, Fig. 3 shows a membrane piezoelectric material with polarizing interdigital electrodes, and Fig. 4 shows the same as Fig. 3. 5 and 6 show an example of the method of polarizing a piezoelectric material of the present invention, and FIG. This shows how a piezoelectric film is folded into a wave shape. Figure 6 shows the piezoelectric film in the state shown in Figure 5 with polarization electrodes attached to the top and bottom wave fronts. FIG. 7 shows a modification of the present invention, and is a diagram showing a state in which a cut is made at the wave crest of FIG. 5. 1, 11... membranous piezoelectric film, 2, 12...
Electrode for polarization.

Claims (1)

[Claims] 1 After folding a membranous piezoelectric film into a wave shape and forming polarization electrodes on both wave heads, applying a DC voltage to each of the polarization electrodes to polarize the film, and then folding the membranous piezoelectric film folded into a wave shape. A method of polarizing a piezoelectric material characterized by stretching it into a flat plate.