JP3336720B2 - Piezoelectric element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is an improvement in which an actuator used for a precision machine tool or the like which performs a mechanical operation by controlling an applied voltage to expand or contract the length is formed. It relates to a piezoelectric element.

[0002]

2. Description of the Related Art For example, a PZT actuator in which a large number of piezoelectric elements are laminated as an actuator for controlling a valve mechanism or the like by an electric signal in a component of an automobile, or as an actuator for controlling a position or an operation in a precision machine tool precisely. It has been known.

An actuator of this type includes a plurality of disk-shaped piezoelectric (PZT) elements, for example, as shown in FIG.
Are coaxially stacked. (B)
The figure shows the one piezoelectric element 11 taken out.
Electrode layers 131 and 132 are formed on both surfaces of a piezoelectric pellet 12 formed by compressing a PZT material into a disk.

Each of the piezoelectric elements 111, 112,... Having the electrode layers 131 and 132 formed on both sides thereof is laminated with electrode plates 141, 142,. The electrode plates 141, 142, ...
, Lead terminals are alternately taken out in the opposite direction according to the stacking order, and connected to the lead-out leads 151 and 152. Then, a DC power supply 16 is connected between the lead-out leads 151 and 152, and the stacked piezoelectric elements 111, 112,.
Are connected in parallel to the DC power supply.

That is, a switch for controlling the DC power supply 16
The piezoelectric elements 111 and 11 are controlled by turning on and off the
The laminated structure of 2... Expands and contracts in the length in the laminating direction, and an actuator that can linearly obtain a driving force is configured.

Here, the surface of the piezoelectric pellet 12 constituting the piezoelectric element 11 is polished after firing to achieve the surface roughness, so that the electrode layers 131 and 132 are formed on the surface. . However, since the piezoelectric pellet 12 is composed of an aggregate of a large number of particles, when viewed microscopically, fine irregularities are present on the surface thereof. Therefore, when the electrode layers 131 and 132 are joined to the surface having such irregularities, the contact area between the electrode layers 131 and 132 and the surface of the piezoelectric pellet 12 is compared with the area of the electrode layers 131 and 132. And slightly smaller.

The electrode layer 131 is formed on the surface of the piezoelectric pellet 12.
After bonding of the electrodes 132 and 132, only the convex portions of the irregularities on the surface of the piezoelectric pellet 12 are brought into contact with the surfaces of the electrode layers 131 and 132, and a large load is likely to be applied to these convex portions compared to the concave portions. When an actuator is configured, a mechanical load acts in the stacking direction, and each of the piezoelectric elements 111, 112,.
The load acts in each thickness direction. For this reason,
Although the concentration of stress occurs slightly on these protrusions, it may be difficult to sufficiently exert the reliability together with the performance of the piezoelectric element at present.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and in particular, the surface of a piezoelectric pellet on which an electrode layer is formed is smoothed to sufficiently reduce the contact resistance with the electrode layer. An object of the present invention is to provide a piezoelectric element which can be made smaller and which can effectively avoid unnecessary concentration of stress, and which can constitute an actuator which has improved strength against compressive force and can obtain reliability. It is.

[0009]

A piezoelectric element according to the present invention is formed by molding and firing a piezoelectric material, and is provided on a smoothed surface of a piezoelectric pellet which has been subjected to surface processing so as to be smoothed. A piezoelectric skin layer is formed by applying a solution in which the same composition as the composition of the material constituting the piezoelectric element pellets is chemically dispersed, and then drying and baking to form a piezoelectric skin layer. It was made to be joined. here,
The piezoelectric pellet is made of a PZT-based material,
The piezoelectric skin layer is formed of a layer coated with a sol-gel in which a PZT-based material is chemically dispersed, and the sol-gel is formed of, for example, an alkoxide solution in which a PZT material is dispersed.

[0010]

In the piezoelectric element constructed as described above, the piezoelectric pellet is formed by molding a PZT material into a predetermined shape and then sintering the material. ing. However, in this state, there are still fine irregularities on the surface of the piezoelectric pellet,
A solution having the same composition as that of the material constituting the piezoelectric pellet is applied to the surface of the pellet by a method such as depink or spin coating, and dried and sintered to fill the irregularities with the PZT material contained in the solution. As a result, the surface is formed into a dense structure, so that the unevenness is improved. Therefore, if the electrode layer is bonded to the surface with the improved unevenness, the contact resistance between the electrode layer and the piezoelectric pellet is effectively reduced, and even when a compressive load is applied,
Unnecessary stress concentration does not occur, and the piezoelectric element has sufficient reliability.

[0011]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows a cross-sectional structure of one piezoelectric element 20 for forming a multilayer actuator as shown in FIG. 3, for example, and shows a PZT-based piezoelectric pellet 21 formed in a disk shape. Although not shown in detail, the surface of the fired body is polished. Piezoelectric skin layers 221 and 222 are formed on both the front and back surfaces of the piezoelectric pellet 21 where minute irregularities still exist.

The piezoelectric skin layers 221 and 222 are formed, for example, as follows. In other words, a PZT solution such as an alkoxide PZT solution having the same composition as the composition of the material constituting the piezoelectric pellet 21 is formed on the front and back surfaces of the piezoelectric pellet 21.
A sol in which a ZT-based material is chemically dispersed is uniformly applied. For example, PZ is applied to both front and back surfaces of the piezoelectric pellet 21 by a dipping method in which the piezoelectric pellet is immersed in a container filled with a predetermined sol solution, or by a spin coating method.
A film of the T sol solution is formed.

More specifically, the dipping conditions are as follows: the dipping / pulling-up speed is set to 10 cm / min. In the spin coating method, the piezoelectric pellet 21 is rotated at 2000 rpm / min and a predetermined sol is applied to the surface thereof. The solution is added dropwise. Then, if a film of the PZT solution is formed on both sides of the piezoelectric pellet 21 in this manner, it is gelled by vacuum drying or drying at 80 ° C. for several tens of minutes in air, and at 500 ° C. to 650 ° C. in air. Bake for 30 minutes.

The piezoelectric skin layers 221 and 222 having the same composition as the pellet 21 and having very few surface irregularities are formed on the front and back surfaces of the piezoelectric pellet 21 in this manner. On each of the 222 surfaces, a conductive material is applied by vacuum, electrochemical,
The electrode layers 231 and 232 are formed by a coating method, a bonding method, or the like. The piezoelectric element 20 with electrodes is configured in this manner.By stacking a plurality of such piezoelectric elements 20 via an electrode plate,
The actuator as shown in FIG. 3 is configured.

[0015] Japanese Patent Laid-Open Publication No. Hei 4-260663 discloses a method of firing a piezoelectric pellet by applying a slurry containing PZT powder to the surface of a piezoelectric element and firing the slurry. This is proposed as a means for preventing the deposition of lead from the pellet surface when the piezoelectric element is fired, but the slurry is obtained by dispersing PZT powder in water or ethanol. It is difficult to allow the powder to penetrate into minute irregularities on the surface of the piezoelectric pellet.
That is, since the dispersed multi-PZT powder has a non-uniform particle size and a large size of 2 to 3 μm, it can cover the surface of the piezoelectric pellet, but rather covers the unevenness of the pellet surface. In addition, the unevenness of the surface may be increased, which may cause a further problem when forming the electrode layer.

On the other hand, as shown in the embodiment, PZT
When the sol-gel in which the system material is chemically dispersed is uniformly applied, the sol-gel is a solution and the piezoelectric pellet 21 is used.
It is easy to penetrate into the fine irregularities on the surface. That is, the substance of the sol-gel solution in this case is, for example, 0.1.
The sol-gel particles are densely formed of 1 μm or less and easily penetrate into the fine irregularities on the surface of the piezoelectric pellet 21 and are sintered in this state to form a very dense surface. .

The surface of the piezoelectric skin layers 221 and 222 formed on the surface of the piezoelectric pellet 21 in this way has an extremely small unevenness as compared with the surface of the piezoelectric pellet 21 itself. Therefore, in contrast to the case where the electrode layer is formed directly on the surface of the piezoelectric pellet 21, after the piezoelectric coating layers 221 and 222 are formed on the surface of the piezoelectric pellet 21, the electrode layers 231 and 222 are formed on the piezoelectric coating layers 221 and 222. When the 232 is bonded, the contact resistance of the electrode layers 231 and 232 to the piezoelectric pellet 21 is significantly reduced.

Assuming that the composite impedance Z of the piezoelectric element 20 is expressed as Z = R + jX, a Cole-Cole plot in which the imaginary axis resistance X is on the vertical axis and the real axis resistance R is on the horizontal axis is shown in FIG. It becomes as shown by. In this figure, R1 is the contact resistance, and R2 is the resistance of the piezoelectric pellet. The element resistance R is the same as that shown in the embodiment and the piezoelectric skin layers 221, 22
As shown in Table 1 below, the contact resistance is reduced in the piezoelectric element 20 shown in the embodiment.

[0019]

[Table 1] Table 2 shows a comparison between the example showing the element characteristics of the piezoelectric element 20 in the embodiment and the conventional example.

[0020]

[Table 2]

That is, PZT is applied to the surface of the piezoelectric pellet 21.
Applying a sol-gel solution in which the material is dissolved, drying and sintering to form the piezoelectric coating layers 221 and 222, and then forming the electrode layers 231 and 232 on the surface, compared with the conventional case where no piezoelectric coating layer is formed As a result, the contact resistance is effectively reduced, and the element characteristics are improved. Further, by improving the unevenness of the surface of the piezoelectric pellet 21, unnecessary stress concentration does not occur even when a large compressive load is applied,
Therefore, the load resistance is improved, and the reliability as an actuator is greatly improved.

[0022]

As described above, in the piezoelectric element according to the present invention, the contact resistance between the piezoelectric pellet and the electrode layer is reduced, so that the element characteristics are effectively improved. Is improved, the load-bearing performance when the actuator is configured is greatly improved, and the reliability thereof is improved.

[Brief description of the drawings]

FIG. 1 is a view for explaining a cross-sectional structure of a piezoelectric element according to one embodiment of the present invention.

FIG. 2 is a view showing a Cole-Cole plot of the piezoelectric element.

FIG. 3A is a view for explaining an actuator using a conventionally known piezoelectric element, and FIG. 3B is a side view showing one of the piezoelectric elements constituting the actuator.

[Explanation of symbols]

20: Piezoelectric element, 21: Piezoelectric pellet, 221, 222: Piezoelectric skin layer, 231, 232: Electrode layer.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-141678 (JP, A) JP-A-5-9054 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 41/09

Claims (3)

(57) [Claims] 1. A piezoelectric pellet which is formed by molding and firing a piezoelectric material, and is subjected to surface processing so as to be smoothed, and the piezoelectric element pellet is formed on the smoothed surface of the piezoelectric pellet. A piezoelectric skin layer formed by applying a solution in which the same composition as the composition of the material to be chemically dispersed is applied and then drying and firing; and an electrode layer joined to the piezoelectric skin layer. Piezoelectric element. 2. The piezoelectric pellet according to claim 1, wherein the piezoelectric pellet is made of a PZT material, and the piezoelectric skin layer is made of a layer coated with a sol-gel solution in which a PZT material is chemically dispersed. Piezoelectric element. 3. The piezoelectric element according to claim 2, wherein said sol-gel is constituted by an alkoxide solution in which a PZT material is dispersed.