JPH10303475A - Piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a piezoelectric element which relaxes the microscopic internal strain that the sintered piezoelectric material has. SOLUTION: This is a piezoelectric element consisting of a piezoelectric substance which includes a pair of external electrodes and piezoelectric material and conductive material arranged between the external electrodes, and the piezoelectric material and the conductive material are laminar as a piezoelectric layer and a conductive layer, respectively, and the piezoelectric layers and the conductive layers are stacked alternately in the direction of connecting the external electrodes in a pair with each other, and besides the conductive layer is insulated from the internal electrode, and also, the thickness is 1 μor under, and this piezoelectric element relaxes the internal strain, and a large quantity of strain can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element in which microscopic internal strain in a sintered piezoelectric material is alleviated.

[0002]

2. Description of the Related Art In recent years, piezoelectric elements have attracted attention as small and efficient actuators replacing electromagnetically driven components. A piezoelectric element is an element obtained by applying a high electric field to a ferroelectric substance typified by a material such as lead zirconate titanate (PZT) and polarizing the ferroelectric substance. When an electric field is applied to the element in the same direction as the polarization, the element is distorted in proportion to the electric field, and when an electric field is applied in the direction opposite to the polarization, the element is distorted in the opposite direction. The strain caused by the application of the electric field can be taken out and used as an actuator. For use in this actuator, development of a piezoelectric material having high strain performance is desired. For this reason, in the PZT-based piezoelectric material, composition improvement such as addition of a donor element and combination with a relaxer has been promoted to improve characteristics.

On the other hand, there has been proposed a laminated piezoelectric element in which a large number of piezoelectric plates are stacked in layers in order not only to improve the composition of the piezoelectric material but also to provide a piezoelectric element having high strain performance. In the laminated piezoelectric element, a piezoelectric material layer and an electrode layer are alternately laminated, and the strain of the piezoelectric material layer due to the application of a voltage between the electrode layers is added and taken out by the number of the laminated piezoelectric material layers. As a laminated piezoelectric element in which piezoelectric materials and electrodes are alternately laminated, an integrally fired piezoelectric element is known. This integrally fired piezoelectric element has an advantage that the driving voltage of the actual element can be reduced to several tens of volts because the thickness of one layer of piezoelectric material can be reduced to several tens of μm.

[0004]

Generally, a sintered piezoelectric material has microscopic internal strain, which hinders the manifestation of characteristics inherent to the piezoelectric material. In order to alleviate this internal strain, Japanese Patent Application No. Hei 8
In -290762, metal particles are dispersed in a piezoelectric material. The piezoelectric material in which the metal particles were dispersed in the piezoelectric material exhibited higher electric-field-induced strain performance than the piezoelectric material in which the metal particles were not dispersed. However, since the dispersed metal particles are scattered only at the grain boundaries of the piezoelectric material, the effect of relaxing the microscopic internal strain was small. Also,
If an attempt is made to increase the relaxation effect by increasing the dispersion amount of the metal particles, the spacing between the metal particles becomes narrower and dielectric breakdown occurs, so that the dispersion amount is limited and the relaxation effect is also limited.

In addition, in an integrally fired piezoelectric element in which piezoelectric materials and electrodes are alternately laminated, microscopic internal strain can be reduced because the electrode layer is present inside. However, this internal electrode layer is as thick as 1 to 5 μm and has irregularities on the order of several μm. Furthermore, if the internal electrode layer is soft, the electric field induced strain generated by the piezoelectric material is absorbed particularly under a compressive stress, and the original strain cannot be exhibited. In addition, when the internal electrode layer has irregularities, the distortion is absorbed when the piezoelectric material is expanded, and the original performance has not been generated.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a piezoelectric element having high strain performance in which microscopic internal strain of a piezoelectric material is alleviated. And That is, the piezoelectric element of the present invention is a piezoelectric element including a pair of external electrodes and a piezoelectric body disposed between the external electrodes and including a piezoelectric material and a conductive material, wherein the piezoelectric material and the conductive material are each a piezoelectric layer. And a layer as a conductive layer, wherein the piezoelectric layer and the conductive layer are alternately laminated in a direction connecting the pair of external electrodes / and the conductive layer is insulated from the external electrode and has a thickness of 1 μm.
It is characterized by the following.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric element according to the present invention has a conductive layer in an internal piezoelectric material, and the conductive layer is formed in parallel with an external electrode formed for applying a voltage to the piezoelectric element. The electrodes are insulated. Further, the thickness of the conductive layer is thin and is 1 μm or less. When the thickness of the conductive layer is 1 μm or more, the conductive layer absorbs electric field-induced strain, and the displacement performance of the piezoelectric element is reduced.

[0008] The conductive layer inside the piezoelectric material reduces microscopic internal strain by dispersing nonuniformity of electric charge generated at the grain boundary of the piezoelectric material in the conductive layer. By alleviating the internal strain, the displacement performance due to the electric field induced by the piezoelectric material can be exhibited, and for example, the displacement amount per unit drive voltage is improved. The conductive layer according to the present invention is not an electrode to which a voltage is externally applied. Therefore, the piezoelectric element of the present invention is different from the conventional laminated piezoelectric element.

[0009]

The present invention will be specifically described below with reference to examples. Note that PZT was used for the piezoelectric material and Pt was used for the conductive layer. (Preparation of PZT green sheet) Commercially available PZT powder (Fuji Titanium Co., Ltd., PE510) was added to 5 parts by weight of a binder (PVB), trace amounts of a plasticizer and a defoaming material, and dispersed in an organic solvent (toluene) A slurry was prepared.
This slurry was formed into a thickness of about 50 μm by a doctor blade method to form a green sheet.

Example 1 Pt was deposited on a green sheet to a thickness of about 0.2 μm using an ion coater.
This Pt-deposited green sheet is 40 × 40 mm
This was laminated into 20 layers, and an internal conductive layer of Pt was formed by integration by hot pressing. After degreasing, 1200 ° C
After sintering for 2 hours, cut and processed to 15 × 15
A 0.8 mm plate-like piezoelectric element was prepared. The upper and lower surfaces of the plate-like piezoelectric element were ion-coated with Pt to form external electrodes. 3kV in 100 ° C silicone oil
/ Mm electric field was applied for 10 minutes to polarize, thereby producing a piezoelectric element. The thickness of the internal conductive layer of this device was 0.2 μm, and the thickness of the piezoelectric layer was 40 μm.

(Example 2) A Pt paste to be an internal conductive layer was printed on a green sheet by screen printing. However, the average viscosity of the Pt particles in the Pt paste was 0.2 μm, and the paste viscosity was adjusted so that the print thickness was about 0.5 μm. After that, as in the case of the first embodiment, 40
It was cut into a size of × 40 mm, laminated into 20 layers, and integrated by hot pressing to form an internal conductive layer of Pd. After degreasing, 1200
After holding for 2 hours at ℃ and sintering, cut and processed to 15 × 1
A 5 × 0.8 mm plate-like piezoelectric element was prepared. The upper and lower surfaces of the plate-like piezoelectric element were ion-coated with Pt to form external electrodes. 3k in 100 ℃ silicone oil
An electric field of V / mm was applied for 10 minutes to polarize, thereby producing a piezoelectric element. The thickness of the internal conductive layer of this device was 0.5 μm, and the thickness of the piezoelectric layer was 40 μm.

Comparative Example 1 A Pt paste to be an internal conductive layer was printed on a green sheet by screen printing. The Pt particles in the Pt paste at this time have a coarse particle size,
Its average particle size is 1 μm. The printing thickness is 3μm
The viscosity of the Pt paste was adjusted to be as follows. After that, as in Example 1, it was cut into 40 × 40 mm, laminated into 20 layers, and integrated by hot pressing to form an internal conductive layer of Pt. After degreasing, holding at 1200 ° C for 2 hours and sintering, cutting,
This was processed to form a 15 × 15 × 0.8 mm plate-shaped piezoelectric element. The upper and lower surfaces of the plate-like piezoelectric element were ion-coated with Pt to form external electrodes. Furthermore, an electric field of 3 kV / mm was applied in silicone oil at 100 ° C. for 10 minutes to polarize, thereby producing a piezoelectric element. The thickness of the internal conductive layer of this device was 3 μm, and the thickness of the piezoelectric layer was 40 μm.

(Comparative Example 2) This is an element having no conductive layer inside, and after cutting a green sheet into 40 × 40 mm, 20 layers are laminated, integrated by hot pressing, degreased, and 1200 ° C. After sintering for 2 hours,
By cutting and processing, a plate-shaped piezoelectric element of 15 × 15 × 0.8 mm was prepared. The upper and lower surfaces of the plate-like piezoelectric element were ion-coated with Pt to form external electrodes. Furthermore, an electric field of 3 kV / mm was applied in silicone oil at 100 ° C. for 10 minutes to polarize, thereby producing a piezoelectric element.

(Evaluation of Sample) The displacement performance of the prepared piezoelectric element was measured by a micro-displacement measuring apparatus at room temperature and in the air at a compressive stress of 20 MPa, applying a voltage of 0.1 Hz and a voltage of 0 to 1 kV. FIG. 1 shows the measurement results. When the example of the present invention is compared with the comparative example 1, the strain amount of the comparative example is lower than that of the example. This means that the thickness of the conductive layer is 3 μm
This is because the conductive layer absorbs not only internal strain but also required strain, and the amount of strain is reduced.

Comparative Example 2 is an example of a piezoelectric element having no conductive material. Since there is no conductive material, internal strain is not relaxed, and a large strain cannot be obtained. However, a larger amount of strain is obtained than that of Comparative Example 1 having a thick conductive layer.

[0016]

When the conductive material is dispersed in the piezoelectric material, the internal strain of the piezoelectric material is relaxed and a large amount of strain can be exhibited.

[Brief description of the drawings]

FIG. 1 is a diagram showing the amount of strain of each sample of an example and a comparative example.

Claims (2)

[Claims] 1. A piezoelectric element comprising a pair of external electrodes and a piezoelectric body disposed between the external electrodes and including a piezoelectric material and a conductive material, wherein the piezoelectric material and the conductive material are a piezoelectric layer and a conductive layer, respectively. A piezoelectric element, wherein the piezoelectric layer and the conductive layer are alternately stacked in a direction connecting the pair of external electrodes, and the conductive layer is insulated from the external electrode. 2. The piezoelectric element according to claim 1, wherein the thickness of the conductive layer is 1 μm or less.