JPH0685345A - PZT-based piezoelectric element polarization method - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a PZT-based piezoelectric element polarization method capable of avoiding spark cracking of a piezoelectric body and ameliorating problems of environmental pollution and workability while eliminating the use of silicone oil. A PZT-based piezoelectric element including a piezoelectric body and a pair of electrode layers formed on both front and back surfaces of the piezoelectric body is used. And
Piezoelectric substance (thickness 0.33 m in the atmosphere of 70 to 120 ° C)
m) voltage of 400V to 870V, that is, 1.2kV /
An electric field of mm to 2.6 kV / mm is applied to polarize the piezoelectric body. Stir the atmosphere with a fan to achieve uniform heating.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for polarizing a PZT type piezoelectric element.

[0002]

2. Description of the Related Art PZT-based piezoelectric elements are used in actuators and the like. The PZT-based piezoelectric element is manufactured through a raw material powder forming step, a firing step, an electrode layer forming step, and a polarization step. This PZT-based piezoelectric material is a ferroelectric material, and in order to utilize its piezoelectricity, it is necessary to apply an electric field to polarize it. Therefore, a polarization process is performed.

By the way, conventionally, for the polarization of a PZT type piezoelectric element, as disclosed in Japanese Patent Laid-Open No. 60-123079, silicon oil, which is an electrical insulator, is used.
This is performed by immersing the piezoelectric body in silicon oil at 0 to 100 ° C. and applying an electric field of 2 kV / mm to 3 kV / mm to the piezoelectric body in the silicon oil. The reason for polarization in silicon oil, which is an electrical insulator, is to prevent cracking of the piezoelectric body due to sparks.

[0004]

However, since silicone oil is used, it is necessary to take measures against environmental pollution.
Further, there is a problem that workability is not sufficient. The present invention has been made in view of the above circumstances, and an object thereof is to eliminate the use of silicon oil and to avoid spark cracking of the piezoelectric body as much as possible, and to improve environmental pollution and workability problems. To provide a polarization method.

[0005]

[Means for Solving the Problems] Based on the above purpose,
The present inventor proceeded with the development of a method for polarization in the atmosphere. Then, a piezoelectric body having a thickness of 0.33 mm, which is frequently used, was subjected to polarization treatment in the atmosphere at 70 to 120 ° C., and the relationship between the capacitance and the polarization voltage was examined. As indicated by the characteristic line A1 of
It was found that the electrostatic capacitance rapidly increased in the range of 300 V and then saturated with a slight increase. Further, when the spark crack of the piezoelectric body was examined, when the polarization voltage in the atmosphere exceeds 870 V, as shown in FIG. 2, the crack due to the spark frequently occurs in the piezoelectric body. Therefore, in order to obtain the necessary piezoelectric characteristics while preventing spark cracks, the piezoelectric body with a thickness of 0.33 mm used is 400 to
A polarization voltage of 870 V is suitable, and it is confirmed by a test that the piezoelectric substance can be favorably polarized by atmospheric polarization in this region, and that the piezoelectric characteristics of the piezoelectric element are not much different from those polarized in silicon oil. The method of the present invention has been completed.

The polarization voltage of 400 to 870V is 1
Electric field of 212 V / mm to 2636 V / mm, that is,
This corresponds to an electric field of 1.2 kV / mm to 2.6 kV / mm. That is, the PZT-based piezoelectric element polarization method of the present invention uses a PZT-based piezoelectric element including a piezoelectric body and a pair of electrode layers formed on both front and back surfaces of the piezoelectric body, in the atmosphere at 70 to 120 ° C. , 1.2 kV / mm to 2.6 kV / mm for piezoelectric body
Is applied to polarize the piezoelectric body.

The method of the present invention is directed to a PZT type piezoelectric element. The PZT system means a general term for solid solutions of lead zirconate (PbZrO ₃ ) and lead titanate (PbTiO ₃ ),
If necessary, a third component such as Nb or Co may be included. In the method of the present invention, an electric field is applied to the piezoelectric body in the atmosphere at 70 to 120 ° C to polarize the piezoelectric body. The temperature of the atmosphere affects the degree of polarization. Generally, when the temperature is low,
It is necessary to increase the electric field. The time required for polarization is selected according to the characteristics required of the piezoelectric element and the like, but generally about 10 to 100 minutes is preferable.

In the method of the present invention, when a large number of piezoelectric elements are polarized at once in a closed chamber such as a furnace chamber, the atmosphere is preferably soaked. This is because the temperature during polarization affects the degree of polarization as described above. In this sense, the polarization process can be performed while stirring the heated air with a stirring means such as a fan.

[0009]

In the piezoelectric element which is polarized in the atmosphere by the method of the present invention, necessary piezoelectric characteristics can be obtained.

[0010]

Embodiments of the method of the present invention will be described below with reference to the drawings. A schematic diagram of the apparatus used in this example is shown in FIG. As shown in FIG. 3, the apparatus 1 includes a furnace body 10, a frame 11 arranged in the furnace body 10, and a mounting portion 13 having a large number of voltage applying portions 12 arranged in parallel in the frame 11.
And a high voltage generator 16 for applying a high DC voltage to the voltage applying section 12 via the lead wires 14 and 15.
The voltage applying unit 12 includes a fixing unit 121 having an electrode 120,
And an elevating part 124 having an electrode 123. Furthermore, the furnace body 1
The heater 20 disposed inside the furnace 0 and the heater driving unit 21 that drives the heater 20 are provided. Further, the fan 22 that stirs the air in the furnace body 10 and the fan driving unit 23 that drives the fan 22 are provided. Equipped. The temperature inside the furnace is detected by the temperature sensor 25, and the control unit 27 controls the heater driving unit 21 and the fan driving unit 23 in accordance with the temperature inside the furnace to make the temperature inside the furnace constant. As a result, the temperature during the polarization treatment is set to about 100 ° C.

A schematic cross section of the piezoelectric element 3 used in this example is shown in FIG.
Shown in. As shown in FIG. 5, the piezoelectric element 3 uses a chip-shaped piezoelectric body 30 made of PZT-based ceramics, and a silver paste is screen-printed on both front and back surfaces of the piezoelectric body 30 and dried to form a pair of electrode layers 31. It is formed by stacking layers. The piezoelectric body 30 has a thickness of 0.33 m.
m, the outer diameter is 14.7 mm, and the inner diameter is 4.6 mm. The piezoelectric body 30 is made of PZT ceramics, and is made of PbZr.
O ₃ is 62.4%, PbTiO ₃ is 34.5%, Nb ₂
It contains 3.1% of O ₅ and SrO.

As can be understood from FIG. 4, the elevating part 124 of the voltage applying part 12 is lifted, and the electrode 123 of the elevating part 124 and the electrode 120 of the fixed part 121 sandwich the piezoelectric element 3. In that state, power is supplied from the high voltage generator 16 to each voltage application unit 12. As a result, a voltage of 650 V is applied to each piezoelectric body 30 in the atmosphere of 100 ° C., and the piezoelectric bodies 30 are collectively polarized. The polarization time is 10
100 minutes.

As another test example, polarization treatment is performed even at a voltage of 750V. Here, since the thickness of the piezoelectric body 30 used in this example is 0.33 mm, the voltage of 650 V is about 2.0 V.
Corresponding to an electric field of / mm, a voltage of 750V is about 2.3V /
This corresponds to an electric field of mm. If atmospheric polarization is performed under this condition, cracking of the piezoelectric body 30 due to sparks can be avoided or greatly reduced.

After that, the piezoelectric element 3 is aged under the condition of 100 ° C. × 60 minutes. When the polarization amount of the piezoelectric element 3 formed in this way was examined, the result as shown by ● in FIG. 6 was obtained, and the necessary capacitance was secured even in the atmospheric polarization in which the use of silicon oil was abolished. That
I was grasped. The polarization amount of the piezoelectric element polarized in silicon oil under the conventional conditions (voltage of 990 V and electric field of about 3 kV / mm when the thickness of the piezoelectric body 30 is 0.33 mm) is indicated by a circle in FIG. . As is clear from this result, the amount of polarization is not so different between the one polarized in the atmosphere and the one polarized in silicon oil.

Further, as the piezoelectric characteristics, the resonance resistance R ₁ , the electrostatic capacitance Cf, the radial electromechanical coupling coefficient Kp and the mechanical quality coefficient Qm were examined, and the results are shown by ● in FIG. The polarization amount of the piezoelectric element polarized in silicon oil under the conventional conditions is indicated by ◯ in FIG. 7. As is clear from this result, according to this example, it is understood that the piezoelectric element 3 having a piezoelectric characteristic that is not much different from that polarized in silicon oil under the conventional condition can be obtained.

Therefore, according to this example, since the silicone oil used in the polarization treatment can be eliminated, it is advantageous in terms of preventing environmental pollution and cost, and further, the step of cleaning the silicone oil adhering to the piezoelectric element 3 is performed. Since the step of drying the piezoelectric element 3 after cleaning can be omitted, the number of steps can be reduced. Further, in this embodiment, the air is agitated by the fan 22 and the furnace body 10
Since it is possible to equalize the temperature inside, it is advantageous to avoid variations in the degree of polarization of each piezoelectric element 3 even when a large number of piezoelectric elements 3 are collectively polarized.

(Other Examples) In the above embodiment, the fan 2 is used.
In step 2, the air is agitated to obtain a uniform temperature, but in some cases,
The stirring process by the fan 22 may be omitted.

[0018]

According to the method of the present invention, a piezoelectric element having necessary piezoelectric characteristics can be obtained even if the use of silicon oil in the polarization treatment is eliminated. Furthermore, since silicon oil can be eliminated, it is advantageous in terms of environmental pollution prevention and cost, and further, the step of washing the silicone oil adhering to the piezoelectric element and the step of drying the piezoelectric element after washing can be eliminated, It is possible to reduce the process.

[Brief description of drawings]

FIG. 1 is a graph showing a relationship between a polarization voltage and an electrostatic capacitance in atmospheric polarization.

FIG. 2 is a graph showing the relationship between the polarization voltage in atmospheric polarization and the incidence of spark cracking.

FIG. 3 is a conceptual diagram of an apparatus used in Examples.

FIG. 4 is a front view showing a state in which a piezoelectric element is set in a voltage applying section.

FIG. 5 is a cross-sectional view of a piezoelectric element.

FIG. 6 is a graph showing the relationship between the polarization voltage and the polarization amount.

FIG. 7 is a graph showing piezoelectric characteristics.

[Explanation of symbols]

In the figure, 16 is a high voltage generator, 3 is a piezoelectric element, 30 is a piezoelectric body, and 31 is an electrode layer.

Claims (1)

[Claims] 1. A PZT-based piezoelectric element comprising a piezoelectric body and a pair of electrode layers formed on both front and back surfaces of the piezoelectric body is used.
1.2 kV / mm to the piezoelectric body in the atmosphere of ~ 120 ° C
A polarization method for a PZT-based piezoelectric element, which comprises applying an electric field of up to 2.6 kV / mm to polarize the piezoelectric body.