JPH0443685A - Laminated bimorph type piezoelectric element - Google Patents

Abstract

PURPOSE:To be excellent in durability and to obtain a large displacement amount and a large generation power by a method wherein a planar piezoelectric is laminated on one face of a substrate, a planar piezoelectric ceramic is laminated on the other face and a resistant electric field on the other face is made larger than a resistant electric field on one face. CONSTITUTION:A planar piezoelectric ceramic A1 having a thickness of t1 is laminated on one face of a substrate 1; in addition, a planar piezoelectric ceramic A2 having a thickness of t2 is laminated on the planar ceramic A1;t1-t2>0 is satisfied. A planar piezoelectric ceramic B is laminated on the other face; the resistant electric field Ecb of the planar piezoelectric piezoelectric ceramic B and the resistant electric field Eca of the planar piezoelectric ceramics A1, A2 are set so as to satisfy Ecb>Eca. When they are laminated, the + side of polarization is set to the side of the substrate 1 at the planar piezoelectric ceramic A1 and the - side of polarization is set to the planar piezoelectric ceramic A1 at the planar piezoelectric ceramic A2. The -side of polarization is set to the side of the substrate 1 at the planar piezoelectric ceramic B. An electric field is applied to the individual planar piezoelectric ceramics A1, A2 in the same direction as their polarization direction and to the planar piezoelectric ceramic B in the direction of its polarization direction.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a laminated bimorph piezoelectric element.

[Conventional technology]

PZT converts electrical energy into mechanical energy
A bimorph piezoelectric element is conventionally known as a bending displacement type piezoelectric element using a piezoelectric material such as the following.

For example, as shown in FIG.
An elastic substrate 12 formed of a metal plate or the like so that two rectangular piezoelectric bodies 10 and 11 are polarized in the same direction.
By applying electric fields in opposite directions with the substrate 12 as a boundary, one piezoelectric body 10 is contracted perpendicularly to the polarization direction, and the other piezoelectric body 11 is expanded perpendicularly to the polarization direction. As a result, it becomes bent and displaced by Q%.

[Problem to be solved by the invention]

However, in such a bimorph type, an electric field is applied to one piezoelectric body in the same direction as its polarization direction, and an electric field is applied to the other piezoelectric body in the opposite direction to its polarization direction. When the applied electric field in the direction approaches the coercive electric field of the piezoelectric material, polarization reversal occurs, resulting in a significant decrease in displacement and generated force.Also, since the electric field is applied in the opposite direction, long-term use is difficult. and the polarization becomes weaker.

On the other hand, as seen in Japanese Unexamined Patent Publication No. 59-63782, as a conventional technique, a material with a high coercive electric field is used for the ceramic on the side where a voltage is applied in the opposite direction to the polarization direction, and the durability is improved by preventing polarization reversal. There are examples of improving However, with this method, it is not very possible to increase the amount of displacement or generated force, and on the contrary, the characteristics may deteriorate. Generally, in order to improve the displacement characteristics of the element, a material with a large piezoelectric constant d31 is used for the ceramic on the side to which a voltage is applied in the same direction as the polarization direction, since polarization reversal cannot occur even if the coercive electric field Ec is small.

The present invention was made against this background, and it is an object of the present invention to provide a bimorph type piezoelectric element that is difficult to cause polarization reversal even after long-term use, is convenient for durability, and has a large amount of displacement and generated force.

[Means to solve the problem]

That is, the present invention provides a first plate-shaped piezoelectric ceramic A having a thickness of t on one surface of a substrate, and further provides a first plate-shaped piezoelectric ceramic A having a thickness of t2 on the surface of this first plate-shaped piezoelectric ceramic A. A second plate-shaped piezoelectric ceramic A2 is provided, and n pieces of plate-shaped piezoelectric ceramics are sequentially laminated (n is a natural number of 2 or more, preferably 2 to 4), and the n-th plate-shaped Piezoelectric ceramics A. The thickness of t. If you close it,
The thickness of each plate-shaped piezoelectric ceramic is set to be t11t6+1>0, and a plate-shaped piezoelectric ceramic B having a thickness of t8 is laminated on the other surface of the substrate. An electric field is applied to each of the plate-shaped piezoelectric ceramics A, ~A1 in the same direction as the polarization direction, and the plate-shaped piezoelectric ceramics B
is configured to apply an electric field in a direction opposite to the polarization direction, and the coercive electric field EC of the plate-shaped piezoelectric ceramic B is applied to the first
It is a laminated bimorph type piezoelectric element having a coercive electric field Ec larger than that of the plate-shaped piezoelectric ceramic A, ~An.

Here, the substrate needs to have flexibility or elasticity, and is selected to be piezoelectrically inactive, that is, not to expand or contract when an electric field is applied. When the substrate itself is used as an electrode, the substrate must be made of metal, but when forming a thin film electrode between the piezoelectric ceramic and the substrate, it may be made of ceramics, synthetic resin, etc. instead of metal. The thickness of the substrate is preferably IOμm~1
m m.

Particularly preferably, the thickness is 30 μm to 200 μm.

Next, plate-shaped piezoelectric ceramics are typified by PZT, but are not limited to this. This plate-shaped piezoelectric ceramic is polarized perpendicularly to its surface direction, that is, in its thickness direction.

The thickness of each piezoelectric ceramic is preferably 1
0 μm to 1 mm, particularly preferably 30 μm to 200 μm
Good.

In the present invention, such plate-shaped piezoelectric ceramics are laminated. Each of the plate-shaped piezoelectric ceramics laminated on one surface of the substrate is configured such that its J7 becomes thinner as it moves away from the substrate. That is, the height of the first plate-shaped piezoelectric ceramic laminated on the substrate is [,], and the thickness of the second, third, etc. n-th U is t2, tl,
・・１． , then t, -tn,>O.

By making the thickness of the plate-shaped piezoelectric ceramic thinner as the substrates are separated from each other by ω, when the same voltage is applied to each plate-shaped piezoelectric ceramic in the same direction as the polarization direction, the The electric field (-voltage//!J) applied to the piezoelectric ceramic becomes larger than the electric field applied to the n-th plate-shaped piezoelectric ceramic having a wide electrode interval. Therefore, the shrinkage rate in the direction perpendicular to the polarization is greater for the (n+1)th plate-shaped piezoelectric ceramic than for the n-th plate-shaped piezoelectric ceramic.

When stacking plate-shaped piezoelectric ceramics, a force is applied to stack the layers so that the polarization direction is opposite between the odd-numbered layer and the even-numbered layer from the substrate side (this is preferable for the following reasons).

In other words, when laminating layers, an electrode is inserted between each layer and an electric field is applied to the piezoelectric ceramic plate through this electrode.8 If the polarization is the same between the odd and even layers,
The odd-numbered positive electrode and the even-numbered negative electrode are adjacent to each other between the plate-shaped piezoelectric ceramics, and an insulating layer must be provided between them. On the other hand, if the odd-numbered and even-numbered piezoelectric ceramics are stacked so that the polarization direction is opposite, only one electrode is provided between the piezoelectric ceramic plates, and that electrode can be used as the negative or positive electrode for both adjacent piezoelectric ceramic plates. It has the advantage that it can be shared as a single device, and the circuit can be simplified.

Such electrodes are formed by printing and applying a metal paste on both sides of a sintered plate-shaped piezoelectric ceramic and then baking it, or by depositing metal on the piezoelectric ceramic surface using a PVD method such as sputtering.

Furthermore, the force for providing the plate-shaped piezoelectric ceramic B on the other surface of the substrate \ The coercive electric field Ec thereof is larger than the coercive electric field Ec of the first to nth plate-shaped piezoelectric ceramics A, ~An.

As a result, the plate-shaped piezoelectric ceramic A,
Compared to the case where a voltage is applied in the opposite direction to the polarization direction, the polarization reversal induced by the polarization is less likely to occur, which has the advantage of superior durability and the ability to apply a higher voltage to the entire device. arise.

Here, the coercive electric field refers to the electric field at which polarization reversal occurs when a certain electric field is exceeded when an electric field is applied in the opposite direction to the polarization direction.

Further, it is preferable that the polarization directions of the plate-shaped piezoelectric ceramic B and the first plate-shaped piezoelectric ceramic A are the same in order to facilitate the circuit configuration.

[Effect]

In the present invention, by laminating a plurality of plate-shaped piezoelectric ceramics, it is possible to obtain a large amount of displacement and a large amount of generated force. In addition, since an electric field is applied to piezoelectric ceramic A in the same direction as the polarization direction, the problem of polarization reversal may occur.Also, since the coercive electric field of piezoelectric ceramic B is large,
A large voltage can be applied to the element as a whole.

The element of the present invention can be used, for example, as a piezoelectric actuator, a vibrator, and the like.

〔Example〕

Hereinafter, one embodiment of the present invention will be described based on FIG.

A first plate-shaped piezoelectric ceramic A is provided on one surface of a substrate 1 made of phosphor bronze.Furthermore, a second plate-shaped piezoelectric ceramic A2 is provided on the first plate-shaped piezoelectric ceramic 2.

Further, a third plate-shaped piezoelectric ceramic B is provided on the other surface of the substrate l. The coercive electric field Ec of this plate-shaped piezoelectric ceramic B is 10 kV/cm, and the first
．． 2. Chiku electric field Ec of plate-shaped piezoelectric ceramics An A,
, is 5kV/cm and satisfies ECb>EC@.

Here, the 11th second plate-shaped piezoelectric ceramic AA2
are both Pb (Mg+7Jb2, s) s, xtsTis a
vsZrs, made of a sintered body of a compound containing taOx as a component, piezoelectric constant d, -380x 10-12 m/V
The main components of the plate-shaped piezoelectric ceramic B are Pb (Mg+73Nb2,3) @ 1t5Tis,
ztsZrs, asox+s, 52Mn02, piezoelectric constant d3. =240x 11"m/V.

In both cases, silver paste is printed and applied on both sides, baked, and then polarized perpendicular to the surface direction.

Then, the substrate 11 first plate-shaped piezoelectric ceramic A2
, the second plate-shaped piezoelectric ceramic A8, and the third plate-shaped piezoelectric ceramic B are each bonded with an adhesive.

First plate-shaped piezoelectric ceramic A for lamination.

so that the + side of the IL polarization is on the substrate 1 side, and
In the plate-shaped piezoelectric ceramic A2, one side of polarization is set to the first plate-shaped piezoelectric ceramic A, t4, and in the third plate-shaped piezoelectric ceramic B, one side of polarization is set to the substrate l side, As a result, the polarization direction is the first plate-shaped piezoelectric ceramic A and the third plate-shaped piezoelectric ceramic B.
The polarization directions of the two are in the same direction.

Then, the electrode Sl between the first plate-shaped piezoelectric ceramic AI and the second plate-shaped piezoelectric ceramic A2, and the electrode S on the side opposite to the substrate of the third plate-shaped piezoelectric ceramic B are connected to a power source 4, respectively. a substrate 1 which is connected to the negative electrode of and also serves as an electrode;
The positive electrode of the power source 4 is connected to the electrode S2 of the second plate-shaped piezoelectric ceramic A2 on the opposite side to the first plate-shaped piezoelectric ceramic 2, and each plate-shaped piezoelectric ceramic An
An electric field was applied to A in the same direction as the polarization direction, and to plate-shaped piezoelectric ceramics B in the opposite direction to the polarization method.As a result, each of the plate-shaped piezoelectric ceramics AnA.

shrinks and the plate-shaped piezoelectric ceramic B expands, so that the entire element does not undergo bending displacement.The thickness of the substrate 1 is 1. To μ First plate-shaped piezoelectric ceramic A
To the thickness t, μ of the second plate-shaped piezoelectric ceramic A2, t2μ, to the thickness t of the third plate-shaped piezoelectric ceramic B
Select 8μm appropriately, displacement amount δμm, generated force F (g)
The applied voltage V was measured for piezoelectric ceramics B.
Table 1 shows the results when the electric field was set to be 50% of the coercive electric field. Note that t is the thickness of the entire element, the width of the element is 10 mm, and the driving length is 20 mm.
It was set as constant mm.

(This page, blank space below) Table 1 Here, Comparative Example 1 is one of the conventional techniques. Measurement of an improved bimorph using a material with a high coercive electric field in ceramics where an electric field is applied in the opposite direction to the polarization direction (L .

On the other hand, Example 1 of the laminated bimorph type piezoelectric element f according to the present invention exhibited a larger displacement amount and generated force than Comparative Example 2, and the J7 thickness of the piezoelectric ceramic A2 was changed to an appropriate thickness. It can be seen that Example 2 shows an even larger displacement amount and generated force.

〔Effect of the invention〕

In the present invention, by laminating a plurality of plate-shaped piezoelectric ceramics, it is possible to obtain a large amount of displacement and a large amount of generated force, compared to the conventional pimorphous piezoelectric element.

Moreover, in the present invention, the thickness of the plate-shaped piezoelectric ceramics becomes thinner as the distance from the substrate increases on one surface of the substrate, so that when the same voltage is applied to each plate-shaped piezoelectric ceramic, the nth The electric field (=voltage/J'!) applied to the th plate-shaped piezoelectric ceramic is larger than the electric field applied to the n-th plate-shaped piezoelectric ceramic having a wide electrode interval.

Therefore, the shrinkage rate in the direction perpendicular to the polarization of the (n+1)th plate-shaped piezoelectric ceramic is greater than that of the n-th plate-shaped piezoelectric ceramic.

Further, the coercive electric field EC5 of the plate-shaped piezoelectric ceramics B is the first to n-th plate-shaped piezoelectric ceramics A, ~A,
Since the coercive electric field Ec is larger than the coercive electric field Ec, polarization reversal of the ceramic B to which an electric field is applied in the direction opposite to the polarization direction does not occur, and an element with excellent durability can be obtained. Furthermore, since it becomes possible to increase the voltage applied to the entire element, a larger displacement amount and generated force can be obtained.

This effect occurs.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of a laminated bimorph piezoelectric element of the present invention, and FIG. 2 is a sectional view showing an example of a conventional bimorph piezoelectric element. A. B・S, huh. First plate-shaped piezoelectric ceramics Second plate-shaped piezoelectric ceramics Third plate-shaped piezoelectric ceramics Power supply S3 electrode

Claims (1)

[Claims] (1) A first plate-shaped piezoelectric ceramic A_1 with a thickness t_1 is provided on one surface of the substrate, and a second plate-shaped piezoelectric ceramic with a thickness t_2 is further provided on the surface of this first plate-shaped piezoelectric ceramic A_1. Ceramic A_2 is provided, and n pieces of plate-shaped piezoelectric ceramics are sequentially laminated (n is a natural number of 2 or more), and the thickness of the n-th plate-shaped piezoelectric ceramic A_n is t.
_n, the thickness of each plate-shaped piezoelectric ceramic is in a relationship such that t_n-t_n_+_1>0, and further, a plate-shaped piezoelectric ceramic B having a thickness t_B is provided on the other surface of the substrate, and the above-mentioned Each plate-shaped piezoelectric ceramic is polarized perpendicular to the surface direction, and an electric field is applied to the plate-shaped piezoelectric ceramics A_1 to A_n in the same direction as the polarization direction, and an electric field is applied to the plate-shaped piezoelectric ceramic B in the opposite direction to the polarization direction. is configured to apply a coercive electric field Ec_b of the plate-shaped piezoelectric ceramics B to the first to n-th plate-shaped piezoelectric ceramics A_1 to A_n.
A laminated bimorph piezoelectric element characterized in that the coercive electric field Ec_a is larger than the coercive electric field Ec_a.