JPS6224983Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a piezoelectric vibrator, and more particularly to a piezoelectric vibrator that utilizes a bending vibration mode of a piezoelectric element plate.

FIG. 1 is a structural perspective view showing an example of a conventional piezoelectric vibrator using a bending vibration mode, which is the background of this invention. FIG. 2 is a diagram showing the polarization direction of the piezoelectric element plate. The piezoelectric vibrator 1 shown in FIG.
For example, a longitudinal piezoelectric element plate 11 made of ceramic such as PZT, parallel electrodes 14 and 15 formed on one main surface of the piezoelectric element plate 11, and parallel electrodes 14 and 15 formed on the other main surface of the piezoelectric element plate 11. It has parallel electrodes or ground electrodes 12 and 13 opposite to 14 and 15, respectively. Then, one of the parallel electrodes 14 and 15, for example 14
is used as an electrode on the input side, and 15 is used as an electrode on the output side, and ground electrodes 12 and 13 are grounded. In this way, bending vibration is excited in the piezoelectric element plate 11. Piezoelectric vibrators using such a bending vibration mode are already well known, and detailed explanation thereof will be omitted here.

The conventional piezoelectric vibrator as shown in FIG.
5 and 13, the piezoelectric element plate 11 has a second
As shown in the figure, polarization treatment is performed in the same direction. The frequency characteristic is shown by the dotted line A in Figure 3.
As shown in , for example, the amount of attenuation is the minimum at 57kHz. As can be seen from the dotted line A in Fig. 3, in the conventional device shown in Fig. 1 (Fig. 2), the degree of attenuation is flat on the low frequency side, and therefore the selectivity is particularly low on the low frequency side. The characteristics were not very good.

Therefore, the present applicant previously proposed an improved piezoelectric vibrator for the purpose of improving such selectivity characteristics on the low frequency side. The proposed piezoelectric vibrator is
As shown in FIG. 4, the piezoelectric element plate 11 is polarized in different directions individually for each electrode 14 and 15. As shown in FIG. In this way, when the polarization direction is changed, the frequency characteristic is such that one attenuation pole is formed on the low frequency side, as shown by the dotted line A in Figure 5, and the selectivity characteristic on the low frequency side is thereby changed. This is a dramatic improvement over that shown by dotted line A in FIG.

On the other hand, recently, as ICs and LSIs have become more practical, devices have become smaller and thinner. Accordingly, components are required to be smaller and thinner, and piezoelectric vibrators that utilize a bending vibration mode are no exception. If you try to downsize a piezoelectric vibrator that uses a bending vibration mode, it is natural that the parallel electrodes 14 and 1
The interval between 5 becomes narrower. On the other hand, the interelectrode capacitance is
This depends on the spacing between the electrodes, and as the spacing between the electrodes becomes smaller with miniaturization, the stray capacitance increases. If the stray capacitance becomes large, it will affect the selectivity characteristics and make it worse. Therefore, conventionally, two such oscillators were used to obtain the necessary selectivity characteristics. In addition, in order to reduce the interelectrode capacitance, as shown in FIG. 6, it is considered to make the parallel electrodes 14 and 15 thinner, thereby preventing an increase in stray capacitance and, therefore, a deterioration in selectivity characteristics. It was getting worse. However, the smaller the width of the electrode, the more difficult it is to process it, and when miniaturized, it is no longer possible to improve the selectivity characteristics with the conventional electrode structure.

Therefore, the main purpose of this invention is to provide a piezoelectric vibrator that can be miniaturized and can obtain desired selectivity characteristics, and also utilizes a bending vibration mode.

In summary, this idea is to select the length of at least one of the parallel electrodes to be shorter than the longitudinal dimension of the piezoelectric element plate, thereby reducing the interelectrode capacitance and improving the selectivity characteristics. be.

The above objects and other objects and features of the present invention will become clearer from the following detailed description with reference to the drawings.

FIG. 7 is an illustrative perspective view showing an example of this invention. This embodiment is characterized in that the parallel electrodes 1
The dimensions of 4' and 15' are shorter than those shown in FIG. That is, the first
In the conventional device shown in the figure, the lengths of the electrodes 14 and 15 are the same as the longitudinal dimension of the piezoelectric element plate 11. However, in this embodiment, the dimensions of the electrodes 14' and 15' are made shorter than the longitudinal dimension of the piezoelectric element plate 11. In this way, the stray capacitance or interelectrode capacitance between electrodes 14' and 15' is reduced compared to the conventional one shown in FIG. Therefore, looking at the frequency characteristics, in the case of the polarization process shown in Figure 2, the third
The characteristics are shown by the solid line B in the figure, and the polarization treatment shown in FIG. 4 has the characteristics shown by the solid line B in FIG. 5. As can be seen from FIGS. 3 and 5, it can be seen that according to this example, the selectivity characteristics are improved as compared to the conventional one. For example, in the polarization process shown in FIG. 2, the attenuation amount is improved by about 5 to 7 dB in the frequency range of 0 to 40 kHz. Further, in the polarization processing shown in FIG. 4, the attenuation amount is similarly improved by about 15 to 17 dB.

The specific dimensions for shortening the electrodes 14' and 15' are selected to be about 0.75 to 0.8, assuming that the interelectrode capacitance of the conventional device shown in FIG. 1 is 1. It has been experimentally found that if this is done, the attenuation amount is improved, that is, the selectivity characteristic is most significantly improved. As a result of such improvement in selectivity characteristics, desired characteristics can be obtained even if the device is made smaller or the width of the electrodes is not made so small.

FIG. 8 is a structural perspective view showing another embodiment of this invention. In this embodiment as well, the parallel electrode 1
4' and 15' are each shorter than the longitudinal dimension of the piezoelectric element plate 11. In this embodiment, the ground electrode formed on the other main surface of the piezoelectric element plate 11 is configured as a full-surface electrode or a common electrode 16. Then, parallel electrodes 14' and 1
5', a convex portion 141 and a convex portion 151 are formed at positions corresponding to nodes of bending vibration, respectively. These convex portions 141 and 151 serve as target points when, for example, lead wires are soldered to the electrodes 14' and 15'. Therefore, such a leader line is always located at a vibration node, and does not adversely affect the bending vibration of the vibrator 1. Further, the ground electrode 16 is connected to the piezoelectric element plate 1
A parallel electrode 1 is formed almost entirely on the other main surface of 1.
4' and 15'. This has the advantage of improving workability during polarization treatment and increasing mass productivity, compared to the conventional method (FIG. 1) in which ground electrodes are provided separately. Furthermore, since the common electrode is used in this way, the method of supporting the device, especially when it is housed in a case, becomes simpler, and its mass productivity is further improved.

Similarly to the embodiment shown in FIG. 7, in the embodiment shown in FIG. 8, the characteristics shown by the solid line B in FIG. For those subjected to the polarization treatment shown in
The characteristics indicated by the solid line B in the figure are obtained.

In the above embodiment, both the parallel electrodes 14' and 15' are made shorter than the longitudinal dimension of the piezoelectric element plate 11, but it is also possible to make only one of the electrodes shorter. . Even in this case, it is possible to make the interelectrode capacitance 0.75 to 0.8 compared to the conventional one shown in FIG.

It goes without saying that the entire surface electrode 16 shown in FIG. 8 can be used in the embodiment shown in FIG. 7 as well.

As described above, according to this invention, since the length of at least one of the parallel electrodes is made shorter than the longitudinal dimension of the piezoelectric element plate, the stray capacitance between the parallel electrodes can be made smaller than that of the conventional one. Can be done. Therefore, even if the device is downsized, desired selectivity characteristics can be obtained without significantly reducing the width of the parallel electrodes. Therefore, the piezoelectric vibrator can be easily mass-produced, and can be miniaturized without deteriorating the selectivity characteristics, making it possible to obtain a very useful piezoelectric vibrator.

[Brief explanation of the drawing]

FIG. 1 is a structural perspective view showing an example of a conventional piezoelectric vibrator using a bending vibration mode, which is the background of this invention. FIG. 2 is an illustrative diagram showing the polarization direction of the conventional piezoelectric vibrator shown in FIG. FIG. 3 is a graph showing the frequency characteristics of the conventional vibrator in the polarization direction shown in FIG. 2 and the embodiment of this invention.
FIG. 4 is an illustrative diagram showing another example of the polarization direction.
FIG. 5 is a graph showing the frequency characteristics of the conventional and embodiments of the present invention in the polarization direction shown in FIG. FIG. 6 is an illustrative diagram showing an electrode for explaining the background of this invention. FIG. 7 is a structural perspective view showing an embodiment of this invention. FIG. 8 is a structural perspective view showing another embodiment of this invention. In the figure, 11 is a piezoelectric element plate, 14' and 15' are parallel electrodes, 16 is a ground electrode, and 141 and 151 are convex portions.

Claims (1)

[Claims for Utility Model Registration] (1) A piezoelectric vibrator that utilizes a bending vibration mode, comprising a piezoelectric element plate, a parallel plate formed on one main surface of the piezoelectric element plate in the longitudinal direction of the piezoelectric element plate an electrode, and a ground electrode formed on the other main surface of the piezoelectric element plate to face the parallel electrode,
Furthermore, the piezoelectric vibrator is characterized in that at least one of the parallel electrodes has a length shorter than the longitudinal dimension of the piezoelectric element plate. (2) The piezoelectric vibrator according to claim 1, wherein both of the parallel electrodes have a length shorter than the longitudinal dimension of the piezoelectric element plate. (3) The piezoelectric device according to claim 2, wherein one of the parallel electrodes is shortened from one end of the piezoelectric element plate, and the other is shortened from the other end of the piezoelectric element plate. vibrator. (4) The length of the shorter one of the parallel electrodes increases the stray capacitance between the parallel electrodes compared to when the length of the short one is the same as the length of the longitudinal dimension of the piezoelectric element plate.
Utility model registration claims Paragraphs (1) to 1, which are selected as short as approximately 0.75 to 0.8.
A piezoelectric vibrator according to any of paragraph (3).