JPS6134279B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a piezoelectric ceramic element that reduces deterioration of piezoelectricity of the piezoelectric ceramic that occurs during heat treatment when processing a polarized piezoelectric ceramic element.

In piezoelectric ceramics, the polarization axis of spontaneous polarization points in an arbitrary direction in the sintered state, and it does not exhibit piezoelectricity as a whole. However, when polarization treatment is performed by applying a high DC electric field, the direction of the polarization axis changes depending on the electric field. Oriented in the direction of , it exhibits piezoelectricity. This piezoelectricity disappears when the temperature reaches the Curie point due to the disappearance of residual polarization. However, piezoelectricity deterioration occurs gradually at temperatures below the Curie point.

In the processing of piezoelectric ceramic elements, polarized elements are often heated during cutting, bonding with resin, curing of adhesive, vacuum deposition, soldering, and the like. Therefore, deterioration of piezoelectricity due to heat has become a problem. Furthermore, even though high temperatures are required for processing, it has often been necessary to keep the temperature lower due to problems with piezoelectricity deterioration.

The present invention aims to reduce the deterioration of piezoelectricity of piezoelectric ceramic elements, which was a conventional drawback, in processing that involves heating after polarization treatment of piezoelectric ceramic elements using thickness shear vibration. In order to prevent the polarization from being weakened by the charge generated by the pyroelectric effect when the temperature of the element changes, we leave both electrodes that were used for polarization between the two electrodes when using thickness shear vibration. This is a method to cancel the charge generated by the effect.

Hereinafter, the effects of the present invention will be explained based on Examples. A ternary piezoelectric ceramic material of Pb(Mg1/3Nb2/3)O ₃ -PbTiO ₃ -PbZrO ₃ was used and polarized in silicone oil at 100°C with a DC electric field of 3KV/mm, as shown in Figure 1a. When the block of the piezoelectric ceramic element 1 is cut out as shown in Fig. 1b, leaving the electrode 2 used for polarization, and the electrode 3 for using thickness shear vibration is attached to the entire surface as shown in Fig. 1c (this whole surface electrode 3 short-circuits both electrodes 2 during polarization)
and the case where electrode 2 used for polarization is dropped and electrode 3 is attached when thickness shear vibration is used (i.e., the space between the two electrodes during polarization is open), as was conventionally done. The degree of piezoelectricity deterioration was investigated. The heat treatment was performed using a constant temperature bath, and the measurement of piezoelectricity after the heat treatment was performed after the heat treatment was sufficiently stabilized. Regarding the sample of the present invention in which the electrode 2 during polarization remained, the electrode 2 was dropped before the measurement and the measurement was performed. When actually used, the electrode 2 used for polarization is removed after heat treatment. Figure 2 shows case A of the present invention method in which the electrodes 2 are short-circuited and heat treated during polarization, and case B of the conventional method in which heat treatment is performed with the electrodes 2 open (however, heat treatment here includes temperature raising and lowering). of
It shows the degree of deterioration of K ₁₅ (electromechanical coupling coefficient of thickness shear vibration, coefficient K ₁₅ ′ after heat treatment). The Curie point of this material is 326℃, and the coercive electric field is 1KV/
mm, K ₁₅ is 0.70.

As in this example, if the electrode used for thickness-shear vibration is the entire surface electrode 3, leave the electrode 2 used for polarization and attach the electrode 3 used for thickness-shear vibration between the two electrodes 2 during polarization. can conduct. The deterioration that occurs when both electrodes 2 are short-circuited during polarization is purely due to the disappearance of a portion of residual polarization due to the heat treatment temperature, and in this case and when both electrodes 2 are opened during polarization. The difference between the deterioration and the deterioration in this case is the deterioration of piezoelectricity due to the pyroelectric effect.
According to the method of the present invention, deterioration of piezoelectricity due to this pyroelectric effect can be prevented. In addition, Figure 1a,
In b, c and FIG. 3, A is the direction of polarization, and B is the cut plane.

As described above, according to the method of the present invention, in a piezoelectric ceramic element that utilizes thickness shear vibration, the electrodes at the time of polarization, which were previously removed because they were not needed after the polarization process, remain, and heating is involved. By establishing continuity between these two electrodes during processing, deterioration of piezoelectricity due to heat treatment can be greatly reduced, and this is extremely useful in processing involving heating of piezoelectric ceramic elements that utilize thickness shear vibration. This is particularly effective for materials with a large pyroelectric effect and materials with a low coercive electric field.

[Brief explanation of the drawing]

FIG. 1a is a cross-sectional view of a piezoelectric ceramic block after polarization treatment to explain the method of the present invention, FIG. 1b is a cross-sectional view of a piezoelectric ceramic element using thickness shear vibration cut out from the block of FIG. FIG. 1c is a cross-sectional view of the piezoelectric ceramic element of FIG. 1b with electrodes attached to the entire surface when thickness shear vibration is utilized, and FIG. 2 is a diagram showing how the piezoelectricity deteriorates due to heat treatment temperature. 1... Piezoelectric ceramic element, 2... Electrode during polarization, 3
...An electrode when using thickness-shear vibration.

Claims (1)

[Claims] 1. In manufacturing piezoelectric ceramic elements using thickness-shear vibration, by leaving the electrodes used for polarization processing and forming electrodes when using thickness-shear vibration, the gap between the two electrodes used for polarization processing during processing that involves heating is left behind. 1. A method for manufacturing a piezoelectric ceramic element, characterized in that heat treatment is performed by conducting.