JP2001044524A - Multilayer piezoelectric body - Google Patents

Abstract

(57) [Abstract] [Problem] To eliminate internal stress remaining before and after polarization treatment,
An object of the present invention is to provide a laminated piezoelectric body in which cracks are suppressed and product reliability is improved. A laminated piezoelectric body (1) alternately laminates piezoelectric layers (2) and electrode layers (3) formed on a main surface of the piezoelectric layers (2), and separates the electrode layers (3) from each piezoelectric layer (2). The electrode layers 3 are partially opposed to each other by extending in different end face directions. In the opposed region D, the polarization directions of the adjacent piezoelectric layers 2 are opposite to each other. In the laminated piezoelectric body formed in (1), the polarization direction of each piezoelectric layer 2 in the region E other than the region D is configured to be a fixed direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated piezoelectric body in which piezoelectric layers and electrode layers are alternately laminated.

[0002]

2. Description of the Related Art Hitherto, a laminated piezoelectric material in which a plurality of piezoelectric layers are laminated as a resonator or a filter utilizing mechanical resonance of a dielectric has been disclosed in, for example, Japanese Patent Application Laid-Open No. 9-275325.

[0003] As shown in FIG. 4, this laminated piezoelectric body has a piezoelectric layer 34 and an electrode layer 3 formed on the main surface of the piezoelectric layer 34.
6 are alternately stacked, and the electrode layers 36 are extended to the respective piezoelectric layers 34 in different end face directions, so that the center of the main surface of the stacked piezoelectric layers 34 (hereinafter referred to as piezoelectric blocks 35) is formed. In the region D where the electrode layers 36 face each other
Is formed.

On almost the entire surface at both ends of the piezoelectric block 35, every other piezoelectric layer 34 is provided with external electrodes 38, 4 connected to the electrode layer 36 extended to the end face side of the piezoelectric layer 34.
0 is applied, and a polarization process is applied to each piezoelectric layer 34 by applying a DC voltage 37 to these external electrodes 38 and 40.

At this time, a DC voltage 37 of 1 to 2 KV / mm is applied between adjacent electrode layers 36 in the piezoelectric block 35 for about 20 to 30 seconds.
Since a DC voltage is alternately applied in the opposite direction to the region D facing each electrode layer 36, the polarization direction of the adjacent piezoelectric layer 34 is polarized in the opposite direction in the region D facing each electrode layer 36. Will be.

[0006]

However, in such a laminated piezoelectric material that is polarized only in the region D of the piezoelectric block 35, the piezoelectric block 35 is polarized before and after the polarization of the piezoelectric block 35. A difference in thickness change occurs between the region D and the other region E. Therefore, when such a laminated piezoelectric body is used as a resonator, if the resonator itself continues to vibrate at a high frequency, this difference in thickness changes causes internal stress of the piezoelectric block 35 and exists in the piezoelectric layer. The area D of the piezoelectric block 35 starts from a minute defect.
There is a problem that cracks occur at the boundary between the region E and the region E to change the resonance characteristics, and a short circuit occurs at the crack portion.

The present invention has been devised in view of the above-mentioned problems, and has as its object to eliminate internal stress remaining before and after the polarization treatment of a laminated piezoelectric body, to suppress the occurrence of cracks,
An object of the present invention is to provide a laminated piezoelectric body having improved product reliability.

[0008]

In order to solve the above-mentioned problems, a laminated piezoelectric material according to the present invention has a structure in which polarized piezoelectric layers and electrode layers are alternately laminated, and each of the piezoelectric layers is sandwiched therebetween. A laminated piezoelectric body in which the electrode layers are opposed to each other and each electrode layer is alternately extended in a different end face direction, wherein each of the adjacent piezoelectric layers has a reverse polarization direction of a region sandwiched between the electrode layers,
This is because the polarization directions of the other regions are the same.

According to the present invention, the adjacent piezoelectric layers are arranged such that the polarization directions of the regions sandwiched between the electrode layers (hereinafter referred to as opposing regions) are opposite to each other, and the polarization directions other than the opposing regions are the same. As a result, the thickness change in the laminated piezoelectric body before and after the polarization treatment is substantially the same in the opposing region and the other region, and thereby, the inner portion remaining in the laminated piezoelectric material at the boundary between the opposing region and the other region is reduced. It is possible to provide a laminated piezoelectric body that does not exert stress, suppresses the occurrence of cracks, can effectively prevent short-circuit failure due to cracks, and does not affect resonance characteristics.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laminated piezoelectric body according to the present invention will be described with reference to FIGS. FIG. 1 is a perspective view illustrating the configuration of the laminated piezoelectric body 1, and FIG. 2 is a sectional view taken along line AA of FIG. 2 illustrating the internal configuration of the laminated piezoelectric body 1. As shown in FIGS. 1 and 2, the laminated piezoelectric body 1 of the present invention is formed by alternately laminating electrode layers 3 formed on the main surface of a piezoelectric body layer 2 to form a piezoelectric body block 20. Further, the electrode layer 3 is alternately extended in a different end face direction for each of the piezoelectric layers 2 to form the opposing region D of the region sandwiched between the electrode layers 3 and the other region E.

On almost the entire surface at both ends of the piezoelectric block 20, external electrodes 4 and 5, which are connected to the electrode layer 3 drawn out to the end face side of the piezoelectric layer 2, are provided every other piezoelectric layer 2. Is formed.

The piezoelectric layer 2 is formed in a strip shape.
As a material of the piezoelectric layer 2 having a thickness of about 300 μm, for example, a material mainly containing lead titanate (PT), lead zirconate titanate (PZT), or the like is used. Note that, as the vibration mode, for example, spreading vibration, stretching vibration, or the like is used.

The piezoelectric block 20 includes piezoelectric layers 2-1 and 2-2.
-5 are stacked, and as the polarization direction, in the opposing region D, for example, the adjacent piezoelectric layers 2-1 and 2-2 are arranged.
-2 is formed so that the polarization direction is reversed, and
In the region E, the polarization direction is changed to the piezoelectric layers 2-1 to 2-
5 are aligned in the same direction (downward in the figure). Therefore, since the polarization direction of the region E is the same direction, each of the piezoelectric layers 2-1 to 2-5 needs to be in the same direction, and the direction does not matter.

The electrode layer 3 is used as a vibrating electrode for generating vibration, and its material is, for example, Ag, Ag-Pd
It is formed of a highly conductive material such as

The external electrodes 4 and 5 are formed of a material having high conductivity as the material of the electrode layers 3. Also,
The external electrodes 4 and 5 are configured to be able to apply a DC voltage (not shown) so that the polarization directions of the piezoelectric layers 2-1 to 2-5 adjacent to each other in the facing region D of the piezoelectric block 20 are opposite. Is subjected to a polarization treatment.

The operation of the laminated piezoelectric body having such a configuration will be described. A description will be given of a case where spread vibration is used as a vibration mode of the piezoelectric layer 2. That is, the piezoelectric block 20
And the piezoelectric block 2
Driving is performed by connecting to a power supply from the external electrodes 4 and 5 formed at both ends of the zero. When an AC voltage is applied between the external electrodes 4 and 5, the piezoelectric layers 2-1 and 2-2 sandwiched between all the electrode layers 3 are formed.
At -5, an AC voltage is applied. This allows
The expansion and contraction occur in the thickness direction according to the polarization of each of the piezoelectric layers 2-1 to 2-5, and at the same time, the vibration also expands in the plane direction.

Next, a production example of the laminated piezoelectric body of the present invention will be described. A green sheet (piezoelectric layer) made of a piezoelectric ceramic is molded, and an electrode layer 3 made of Ag-Pd is printed on both main surfaces of the green sheet by a screen printing method. At this time, the printing pattern extends to the end face side of the green sheet, and the electrode layer 3 is printed. Thereafter, a green sheet on which the electrode layer 3 is printed is laminated. in this case,
The printed electrode layers 3 and the green sheets are formed so as to be alternately laminated, and the electrode layers 3 are further extended in the direction of different end faces for each green sheet so that the electrode layers 3 face each other. Arrange.

Next, through a crimping step, the piezoelectric block 20 is formed by cutting into a desired size of the piezoelectric body.
Co-firing at 0 ° C. In the baked product, each electrode layer 3 is exposed on the side surface, and the electrode layer 3 is exposed on every other side of the piezoelectric layer on the end surface.

Next, primary polarization processing of the baked piezoelectric block 20 is performed. A plane electrode made of conductive rubber is pressed between both main surfaces of the piezoelectric block 20, and a DC voltage of 1 to 2 KV / mm is applied between the plane electrodes. This allows
For example, polarization can be obtained in the direction of the downward arrow formed at both ends of the dielectric block 20 in FIG.

Next, external electrodes 4 and 5 are formed on the end faces of the piezoelectric block 20 by sputtering. Thereby, each electrode layer 3 passes through each end face of the piezoelectric block 20.
Are connected every other layer of the piezoelectric layer 2.

Next, a voltage is applied between the external electrodes 4 and 5 formed on both end faces of the piezoelectric block 20 to perform secondary polarization processing. The polarization direction at this time is determined by the piezoelectric layers 2-1 to 2-5 adjacent to each other in the facing region D of the piezoelectric block 20.
Is reversed. That is, as shown in FIG.
1 is upward, the piezoelectric layer 2-2 is downward, and the piezoelectric layer 2-3
Is upward ... Thereby, a laminated piezoelectric body is manufactured.

Next, a change in thickness due to the primary and secondary polarization processes will be schematically described with reference to FIG. The horizontal axis in FIG. 3 is the polarization voltage V, and the vertical axis is the thickness change ΔT. When a predetermined voltage is applied by the primary polarization processing, the change in thickness is zero.
→ a → b becomes a miracle. At this time, the piezoelectric block 20
In both regions D and E, the thickness after polarization is a thickness change at the position b.

In this state, secondary polarization is performed. The thickness changes only in the facing region D of the piezoelectric block 20. The change in the thickness is, for example, a locus of b → c → d → e. That is, in a layer in which the voltage of the secondary polarization is opposite in polarity to the voltage of the primary polarization, once the thickness returns to the initial state with the reversal of the polarization, the polarization is completed at the point d via the point c, Thereafter, when the voltage is turned off, a point e is reached, which is at substantially the same position as the point b. As a result, there is a difference in the polarization direction, but the internal deformation is the same, that is, the laminated piezoelectric body in which the change in the thickness of the region D after the secondary polarization is substantially the same as the change in the thickness of the region E after the primary polarization is obtained. Can be manufactured. As a result, the residual internal stress applied at the boundary between the regions D and E of the piezoelectric block 20 is eliminated.

In the present invention, the example of the resonator in the laminated piezoelectric body has been described. However, the present invention is not limited to this, and it can be used as a laminated actuator. In this case, the extraction of the electrode layer 3 may be taken directly from the external electrode, or appropriate terminal electrodes may be provided on the upper and lower surfaces. In particular, if the longitudinal direction in FIG. 2 is made large, an actuator which can easily obtain a large displacement can be achieved.

According to the structure of the present invention, the polarized piezoelectric layers 2 and the electrode layers 3 are alternately laminated, and each piezoelectric layer 2
A laminated piezoelectric body 1 in which the electrode layers 3 are opposed to each other with -1 to 2-5 interposed therebetween and the electrode layers 3 are alternately extended in different end face directions. 1 to
2-5, the polarization direction of the opposing region D sandwiched between the electrode layers 3 is opposite, and the polarization direction of the other region E is the same direction. The thickness change in the piezoelectric body 1 becomes substantially the same, so that at the boundary between the facing region D and the region E,
The multilayer piezoelectric body 1 does not affect the resonance characteristics while preventing the occurrence of cracks, effectively preventing short-circuit defects caused by cracks, without applying internal stress remaining on the piezoelectric element 1.
Can be provided.

[0026]

As described above, according to the present invention, the adjacent piezoelectric layers are arranged so that the polarization directions of the opposing regions sandwiched between the electrode layers are opposite, and the polarization directions of the other regions are the same. The thickness change in the laminated piezoelectric body before and after the polarization treatment is substantially the same in the opposing region and the other region because of the orientation, so that the layer remains in the laminated piezoelectric material at the boundary between the opposing region and the other region. It is possible to provide a laminated piezoelectric body that does not receive internal stress, suppresses the occurrence of cracks, can effectively prevent short-circuit failure due to cracks, and does not affect resonance characteristics. Therefore, the reliability of the laminated piezoelectric body can be significantly improved.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an embodiment of a laminated piezoelectric body of the present invention.

FIG. 2 is a diagram illustrating an internal configuration of a laminated piezoelectric body according to the present invention.
FIG. 3 is a sectional view taken along line A.

FIG. 3 is a diagram illustrating a change in thickness when a polarization treatment is performed on the laminated piezoelectric body of the present invention.

FIG. 4 is a cross-sectional view illustrating a conventional laminated piezoelectric body.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Laminated piezoelectric body 2 ... Piezoelectric layer 20 ... Dielectric block 3 ... Electrode layer 4, 5 ... External electrode D ... Opposing area | region (area where an electrode layer opposes) E ... Areas other than facing areas

Claims (1)

[Claims] 1. A polarization-processed piezoelectric layer and an electrode layer are alternately laminated, each electrode layer is opposed to each other with each piezoelectric layer interposed, and each electrode layer is alternately extended in a different end face direction. Wherein each of the adjacent piezoelectric layers has a polarization direction opposite to that of a region sandwiched between electrode layers, and a polarization direction of another region is the same.