JPS63131587A - Laminated piezoelectric element - Google Patents

Abstract

PURPOSE:To reduce the deterioration in displacement characteristics and reliability by bringing the thickness of ceramics layers at the upper and lower end sections of an element to 25% or less of the thickness of another ceramics layer held by internal electrodes. CONSTITUTION:In a laminated piezoelectric element in which a large number of the sheets of piezoelectric ceramics 1a, 1b, on both surfaces or one surfaces of which electrodes are set up, are laminated, the thickness of ceramics layers not displaced substantially existing at the end sections of the element is brought to 25% or less of the thickness of other displaced ceramics layers held by internal electrodes 2a, 2b. That is, five piezoelectric elements are sampled from piezoelectric elements having conventional structure, and the ceramics layers 1b at upper and lower end sections are polished and worked until the thickness of the layers 1b is brought to 25% of the thickness of other ceramics layers 1a. Accordingly, the laminated piezoelectric element having high displacement characteristics and high reliability can be acquired.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a laminated piezoelectric element used as an actuator in the fields of mechatronics, microelectronics, etc. This invention relates to the structure of a laminated piezoelectric element formed by laminating a large number of thin plates of piezoelectric ceramics.

[Prior Art] Generally, a laminated piezoelectric element is manufactured by laminating and crimping a plurality of green sheets each having electrodes on both or one side, and then removing the binder and sintering the crimped body. ,
Both upper and lower ends of the element (both ends in the stacking direction) are used to protect internal electrodes during sintering and insulate during driving.
A pressed body is produced by further laminating a plurality of green sheets without electrodes, and the binder is removed and sintered. According to such a manufacturing method.

The obtained laminated piezoelectric element consists of a piezoelectric ceramic layer 1a sandwiched between internal electrodes 2, as shown in FIG.
The thicker layer 1b exists at the upper and lower ends of the piezoelectric element.

[Problems to be Solved by the Invention] When a voltage is applied to the external electrodes 3a, 3b of the laminated piezoelectric element having the above structure via the electrode terminals 4a, 4b.

Each ceramic layer 1a sandwiched between internal electrodes 2a and 2b
, respectively, elongate in the vertical direction (laminated direction), and cause distortion in the direction perpendicular to it, such as shrinkage.

However, since the layers 1b at the upper and lower ends are not sandwiched between electrodes, no voltage is applied and no distortion occurs.

For this reason, there was a problem in that the strain in the adjacent ceramic layer 1a was suppressed and the displacement characteristics of the element were deteriorated. In addition, while conducting various experimental studies, the present inventors discovered that the above-mentioned strain suppressing force causes a shear path force to be generated at the boundary between adjacent ceramic layers, and as a result, peeling occurs at the boundary. I also noticed that there is a problem that reduces reliability.

An object of the present invention is to reduce the deterioration in displacement characteristics and reliability caused by the ceramic layers present at the upper and lower ends of the laminated piezoelectric element having the conventional structure.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a laminated piezoelectric element formed by laminating a large number of piezoelectric ceramic thin plates each having electrodes on both or one side. The present invention is characterized in that the thickness of the existing ceramic layer that does not substantially displace is 25% or less of the thickness of the other displaceable ceramic layer sandwiched between the internal electrodes.

In the present invention, the thinner the piezoelectric ceramic layer that is present at the upper and lower ends and which does not substantially displace, the better the displacement characteristics. It will not be possible to sufficiently protect the internal electrodes during sintering, insulate during driving, and work as a processing adjustment allowance for changes in shape and dimensions due to molding distortion caused during lamination crimping and surface roughness during sintering. ,
It is desirable that the thickness be at least 10 μm or more.

[Example] Hereinafter, the present invention will be explained in detail based on examples.

FIG. 1 is a side view of a laminated piezoelectric element showing one embodiment of the present invention. In the figure, la and lb are piezoelectric ceramic layers, and 2a and 2b are internal electrodes, respectively.

First, PVB (polybutyl alcohol) as an organic binder was added to P b (Z r + Ti) 03 powder.
Adding BPBG (butylphthalyl butyl glycolate) as a plasticizer and trichlene as an organic solvent,
After crosstalk, a green sheet of piezoelectric ceramics with a thickness of 200 μl was formed using the doctor blade method.
This green sheet is screen-printed with platinum paste that will become the internal electrode material (in Figures 1 and 3, it will become the displacing ceramic layer 1a) 50
and 5 green sheets each with no platinum paste printed on them (in Figures 1 and 3, the ceramic layer 1b that does not displace) are stacked on both ends of the 50 sheets 1 for a total of 60 sheets. A stack of piezoelectric ceramic green sheets was formed and pressed together. Thereafter, a plurality of laminates were obtained by cutting into predetermined dimensions and shapes.6Then, the obtained laminates were sintered at about 1250° C. for 2 hours to obtain ioam square sintered bodies.

Next, the side surfaces of these sintered bodies are polished, and external electrodes 3a and 3b are formed by applying and baking silver paste on the side surfaces, and terminals 4a and 4b are taken out to form a laminated structure of the conventional structure shown in FIG. A type piezoelectric element was formed. In order to obtain a multilayer piezoelectric element having the structure according to the present invention as shown in FIG. thickness,
It was polished to 25% of its diameter.

Each of the laminated piezoelectric elements thus obtained had four
A voltage of 0.00 mm was applied for 5 minutes to carry out polarization treatment, and then the relationship between the applied voltage and the amount of displacement was measured. The results are shown in FIG.

In FIG. 2, a hysteresis curve A is a curve showing the relationship between the applied voltage and the amount of displacement of the laminated piezoelectric element having the structure of the present invention. Further, in the figure, a curve B shows the relationship between the applied voltage and the amount of displacement of a conventional laminated piezoelectric element in which the thickness of the ceramic layer 1b at both the upper and lower ends is large. From the figure, the amount of displacement of the element according to the present invention is 0.0 at 100V compared to the conventional element.
4μm, 0°8μm at 200V, 1.4μm at 300V
It can be seen that m is large.

Note that the thickness of the ceramic layer 1b that does not displace at the upper and lower ends is 75% of the thickness of the other ceramic layer 1a that displaces.
Similar measurements were made for the element with 50%, but
There was no difference from the measurement results of the conventional element.

In addition, a life test was conducted by applying a voltage of 300 V to each of the laminated piezoelectric element according to the present invention and the piezoelectric element having a conventional structure, and driving the piezoelectric element repeatedly 1 million times. Although peeling occurred at the boundary with the non-conforming ceramic layer, resulting in loss of differential operation, the laminated piezoelectric element according to the present invention did not exhibit any abnormality. Therefore, it was confirmed that the shear path force acting between the layer at the end of the element and the adjacent layer is smaller in the laminated piezoelectric element having the structure according to the present invention than in the laminated piezoelectric element having the conventional structure. .

[Effects of the Invention] As described above, the present invention has the advantage that a multilayer piezoelectric element having high displacement characteristics and high reliability can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing applied voltage and displacement amount in the embodiment of the present invention,
FIG. 3 is a side view showing a conventional laminated piezoelectric element. 1: piezoelectric ceramic, 2: internal electrode, 3: external electrode, 4
: External electrode terminal. Figure 1 Figure 3 Figure 2 Applied voltage (V)

Claims (1)

[Claims] In a multilayer piezoelectric element made by laminating a large number of piezoelectric ceramic thin plates with electrodes on both or one side, the thickness of the ceramic layer at the top and bottom ends of the element is equal to the thickness of the other ceramic layers sandwiched between internal electrodes. A laminated piezoelectric element characterized by having a thickness of 25% or less.