JPH0522069A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To obtain the piezoelectric resonator, which is miniaturized and hardly affected by unnecessitated sprious signals, by providing a piezoelectric plate polarized in a thickness-wise direction so as to fix a polarizing direction and a pair of resonant electrodes. CONSTITUTION:A piezoelectric plate A having a square-shaped plane is polarized so that the polarizing directions of four areas 7-10 divided by two diagonals 6a and 6b of the square can be reverse to the thickness-wise direction between the adjacent areas, and a piezoelectric resonator 15 is constituted by forming a pair of resonant electrodes 13 and 14 on both the entire main faces of the piezoelectric plate A. Namely, the areas 7 and 9 are polarized from up to down in the thickness-wise direction of the piezoelectric plate A, and the areas 8 and 10 are polarized from down to up on the piezoelectric plate A. By impressing AC electric fields from the resonant electrodes 13 and 14, the polarized piezoelectric plate A has a resonant point on the side of a frequency lower than a spread vibration mode, and the vibration mode whose apexes is vibrated is excited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric resonator using a piezoelectric plate having a square planar shape and utilizing a vibration mode having a lower frequency than a spreading vibration mode, for example, a KHz band oscillator or filter. The present invention relates to a piezoelectric resonator suitable for

[0002]

2. Description of the Related Art As a resonator in the KHz band, a resonator utilizing a spreading vibration mode of a piezoelectric plate having a square planar shape is widely used. A piezoelectric resonator using such a spreading vibration mode has a structure in which resonant electrodes are formed on both main surfaces of a piezoelectric plate having a square planar shape.

[0003]

The resonance frequency of the spreading vibration mode is determined by the outer diameter of the piezoelectric plate. for that reason,
For example, when a resonator having a resonance frequency of 455 KHz is configured, the size of the piezoelectric plate is inevitably as large as about 4.5 mm × 4.5 mm. In recent years, similar to other electronic components, there is a strong demand for miniaturization of elements in piezoelectric resonators, but in piezoelectric resonators that use the spreading vibration mode as described above, the resonance frequency is determined by the outer diameter dimension. Therefore, there is a problem that it is not possible to sufficiently cope with the miniaturization of the element.

Further, in the piezoelectric resonator utilizing the spreading vibration mode, there is a problem that the contour vibration is generated with a considerable intensity in the frequency range immediately above the resonance frequency, and the unnecessary spurious vibration due to the contour vibration cannot be ignored. there were. An object of the present invention is to provide a piezoelectric resonator that is smaller and less susceptible to the influence of unwanted spurious vibrations.

[0005]

The piezoelectric resonator of the invention described in claim 1 has a square planar shape, and the piezoelectric resonator has a square shape.
In four areas divided by diagonal lines of the book, piezoelectric plates polarized in the thickness direction so that the polarization directions are opposite to each other between adjacent areas, and formed on the entire surfaces of both main surfaces of the piezoelectric plate. It is a piezoelectric resonator provided with a pair of resonance electrodes.

In the piezoelectric resonator according to a second aspect of the present invention, the planar shape is a square, and the four regions separated by two diagonal lines of the square have polarization directions opposite to each other between adjacent regions. A piezoelectric plate polarized in the thickness direction and a pair of resonance electrodes formed on both main surfaces of the piezoelectric plate, and an unpolarized region is formed on the piezoelectric plate near the center point of the square. Alternatively, the piezoelectric resonator is characterized in that an electrode missing portion, in which the resonance electrode is missing, is provided in the vicinity of the center point of the square. That is,
The invention according to claims 1 and 2 of the present application is such that the planar shape is a square, and the polarization directions are opposite to each other between adjacent regions in four regions divided by two diagonal lines of the square. It is common to use a piezoelectric plate polarized in the direction.

[0007]

In the piezoelectric resonator according to the present invention as set forth in claims 1 and 2, the piezoelectric plate is polarized in the thickness direction so that the polarization directions are opposite to each other in the four adjacent regions of the piezoelectric plate. By applying an AC electric field from the pair of resonance electrodes, a vibration mode described below in which the vertices of a square vibrate is excited. Since this vibration mode vibrates in a lower frequency range than the spread vibration mode, it is possible to reduce the size of the piezoelectric resonator and reduce the influence of unnecessary spurious vibration. That is, the present invention is characterized in that the above-mentioned vibration mode different from the expansion vibration mode is used in view of the limitation of downsizing in the piezoelectric resonator using the expansion vibration mode.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Vibration Mode Used in the Present Invention FIG. 2 is a schematic plan view for explaining the vibration mode used in the present invention. In the present invention, the vibration mode in which the vertices 1 to 4 of the piezoelectric plate having a square planar shape indicated by the one-dot chain line A vibrates in the direction of the arrow shown in the figure is used. In this case, the vibration is generated by repeating the state shown by the solid line in the figure and the state in which each of the vertices 1 to 4 is at a considerable position on the opposite side with the original position shown by the one-dot chain line in between. . In this way, the vibration mode in which the vertices 1-4 vibrate in the direction of the arrow shown in the figure is
As is clear from the examples described below, vibration is generated in a lower frequency range than the spreading vibration mode.

FIG. 3 shows the generated charge distribution when the piezoelectric plate is vibrated as shown in FIG. As is clear from FIG. 3, when the above vibration is excited, charge concentration occurs so that adjacent regions have opposite polarities in the four regions formed by dividing the square 5 by two diagonal lines. Therefore,
In the present invention, as shown in FIG. 4, the first to fourth regions 7 to 10 formed by dividing the two square lines 6a and 6b of the piezoelectric plate A having a square planar shape into It is possible to excite the vibration by polarization as described above.

That is, the regions 7 and 9 are polarized from the upper surface to the lower surface in the thickness direction of the piezoelectric plate A as indicated by the downward arrows in the figure, and conversely, the regions 8 and 10 are processed.
Is polarized in a direction from the lower surface of the piezoelectric plate A toward the upper surface thereof, as indicated by an upward arrow. In other words, in the regions 7 to 10, the adjacent regions are polarized in the opposite direction in the thickness direction.

In the present invention, the piezoelectric plate that has been polarized as described above is used, but the polarization is performed through the process shown in FIG. 5, for example. First, the polarization electrodes 11 and 12 are formed on the entire surfaces of both main surfaces of the piezoelectric plate A, and the piezoelectric plate A is polarized in the thickness direction by applying a voltage. next,
As shown in FIG. 5, the polarization electrodes on both main surfaces of the piezoelectric plate A are removed in regions 7 and 9 of the regions divided by two diagonal lines, and the first polarization treatment is performed only in regions 8 and 10. A polarization is applied by applying a voltage in the opposite direction. In this way, the piezoelectric plate A in which the polarization directions of the regions 8 and 10 and the regions 7 and 9 are opposite to each other can be obtained.

First Embodiment FIG. 1 is a perspective view showing a piezoelectric resonator according to a first embodiment of the present invention. The piezoelectric plate A having a square planar shape is polarized by the method shown in FIG. That is, four regions that are configured by separating a square piezoelectric plate A with two diagonal lines 6a, 6b, as shown by the arrow P ₁ to P ₄ shown, reverse the polarization direction between adjacent regions Is polarized in the thickness direction so that A pair of resonance electrodes 13 and 14 are formed on both main surfaces of the piezoelectric plate A in the form of full-scale electrodes.

When driving the piezoelectric resonator 15 of the present embodiment, it is sufficient to apply an AC electric field from the resonance electrodes 13 and 14, and therefore, it is used in the same manner as a conventional piezoelectric resonator utilizing the spreading vibration mode. be able to. However, in the piezoelectric resonator 15 of the present embodiment, since the piezoelectric plate A is polarized as described above, the above-mentioned vibration mode that vibrates in a lower frequency range than the above-described spread vibration mode is excited. Therefore, it is possible to obtain a smaller piezoelectric resonator as compared with the piezoelectric resonator using the spreading vibration mode.

Next, the effect of this embodiment will be clarified by explaining a concrete experimental example. As the piezoelectric plate A,
A piezoelectric plate mainly composed of a piezoelectric material containing Pb (Zr _0.52 Ti ₀₄₈ ) O _{3 in} a proportion of 0.3% by weight of Cr ₂ O _{3, and} having a size of 15 mm × 15 mm × thickness 5 mm. Was prepared and polarized according to the method shown in FIG. 5 described above, and thereafter, a resonance electrode was formed on the entire surfaces of both main surfaces. The impedance-frequency characteristic of the piezoelectric resonator obtained as described above is shown by the solid line in FIG. For comparison, a conventional piezoelectric resonator utilizing a spreading vibration mode produced in the same manner as above except that the polarization direction of the piezoelectric plate is uniform in the thickness direction was obtained, and its impedance-frequency characteristic was measured. It was measured. The impedance-frequency characteristic of the conventional piezoelectric resonator is shown by the broken line in FIG.

As is apparent from FIG. 6, in the piezoelectric resonator of the embodiment, the conventional example (using the spreading vibration mode)
It can be seen that the above-mentioned vibration mode is excited on the lower frequency side, and the spreading vibration and the contour vibration are hardly excited. In addition, the electrical characteristics of the piezoelectric resonator of the above-described example and the piezoelectric resonator of the conventional example were measured. The results are shown in Table 1. In Table 1, the meaning of each symbol is as follows. Fr ... Resonance frequency, Zr ... Impedance value at resonance frequency, Fa ... Anti-resonance frequency, Za ... Impedance value at anti-resonance frequency, K
… Electromechanical coupling coefficient.

[0016]

[Table 1]

As is apparent from Table 1, in the piezoelectric resonator of the embodiment, when it is attempted to obtain the same resonance frequency as that of the conventional piezoelectric resonator using the spreading vibration mode, the outer diameter of the piezoelectric plate is 15 mm. It may be set to x15 mm (in the case of spreading vibration) to 12.7 mm x 12.7 mm (in the example). Therefore, according to this example, it is understood that the piezoelectric resonator can be downsized by about 15%. Further, as is clear from FIG. 6, in the piezoelectric resonator of the embodiment, the difference between the resonance frequency and the unnecessary spurious vibration frequency is about twice as wide as that of the conventional example, and therefore the spurious vibration is affected. I know that it is difficult.

Second Embodiment As shown in FIG. 6, in the first embodiment, unnecessary spurious vibrations due to spreading vibration and contour vibration other than the vibration mode in which the apex moves in the impedance-frequency characteristics are generated. I found it difficult to do. However, when a large number of piezoelectric resonators of the first embodiment are manufactured, spurious vibration that is considered to be based on a vibration mode that spreads to a higher frequency side than the vibration mode in which the apex moves in some cases, as shown in FIG. X sometimes occurred.

Then, as a result of further study, it was found that such spurious vibrations based on the spreading vibration mode occur when the four regions of the piezoelectric plate cannot be polarized completely symmetrically. That is, as shown in FIG. 4, if the piezoelectric plates are symmetrically polarized so that adjacent regions in the four regions are surely in opposite directions, spurious vibrations due to spreading vibrations as shown in FIG. It rarely happens. On the other hand, when the polarization state is not completely symmetrical, it was found that the unwanted spurious vibration X occurs as shown in FIG.

In the vibration mode in which the apex moves, which is excited on the lower frequency side than the above-described spread vibration mode, FIG.
As is clear from the charge distribution of, almost no charge is generated in the region near the center of the square. On the other hand, the charge distribution generated in the piezoelectric plate in the spreading vibration mode is shown in FIG.
It becomes as shown in. That is, the charges are concentrated most strongly in the central region of the square. Therefore, it is understood that if the vibration is suppressed in the vicinity of the center point of the square, the excitation of the spread vibration can be effectively suppressed without weakening the above-described vibration in which the apex moves.

Therefore, in the second embodiment, the polarized electrodes 21 to 2 shown in FIG. 9 are arranged along the contour lines of the generated charges in FIG.
4 is formed and a polarization process is performed. That is, the piezoelectric plate A
The polarized electrodes 21 to 24 are formed on one main surface, and the polarized electrodes are formed on the other main surface so as to face the polarized electrodes 21 to 24 with the piezoelectric plate A in between. Then, by applying a voltage of opposite polarity between the adjacent polarization electrodes on the main surface, in the four areas of the piezoelectric plate A divided by diagonal lines, the adjacent areas are polarized in the opposite direction in the thickness direction. Polarization process.

Next, the second resonator 25 shown in FIG. 10 can be obtained by forming a resonance electrode on the entire both main surfaces of the piezoelectric plate A polarized as described above. In FIG. 10, the region surrounded by the broken lines B to E and the peripheral edge of the piezoelectric plate A is the region that has been polarized.
In the piezoelectric resonator 25 of the second embodiment, the region F near the center point of the piezoelectric plate A is not polarized. Therefore, when an AC electric field is applied from the pair of resonance electrodes 26 and 27, the region F in the vicinity of the center point of the piezoelectric plate A is not driven, so that the above-described vibration in which the apex moves while suppressing the spreading vibration. Can be excited.

A specific experimental example of the second embodiment will be described. Using the same piezoelectric plate as in Example 1, polarization electrodes were formed as shown in FIG. 9 and subjected to polarization treatment to obtain a piezoelectric resonator of the second example, and its impedance-frequency characteristics were measured. The results are shown in Fig. 11. As is clear from FIG. 11, in this embodiment, since the region near the center point is not polarized, it can be seen that spurious due to spreading vibration is effectively suppressed. In the second embodiment, the region near the center point of the piezoelectric plate A is not polarized, so that the region near the center point is not driven. However, the first embodiment After performing the polarization process in the same manner as the example, as shown in FIG. 12, the resonance electrode 2 having the electrode missing portion 28 in the region near the center point of the piezoelectric plate A is provided.
If 9 is formed on both main surfaces, spurious due to spreading vibration can be effectively suppressed.

[0024]

According to the present invention, in the piezoelectric plate having a square planar shape, the four adjacent areas separated by two diagonal lines are polarized in different directions in the thickness direction. By applying an AC electric field from the resonance electrode formed on the substrate, the vibration that the apex of the piezoelectric plate moves is excited. The vibration in which the apex of the piezoelectric plate moves is generated on the lower frequency side than the spreading vibration. Therefore,
It is possible to provide a piezoelectric resonator that is smaller in size and less susceptible to the influence of unnecessary spurious vibrations such as contour vibrations, as compared with a conventional piezoelectric resonator that uses a spreading vibration mode.

Further, when the region near the center point of the piezoelectric plate is not driven as in the second aspect of the invention, the spreading vibration can be suppressed more effectively. It is possible to configure a piezoelectric resonator that is even less susceptible to spurious vibrations.

[Brief description of drawings]

FIG. 1 is a perspective view showing a piezoelectric resonator according to an embodiment of the present invention.

FIG. 2 is a schematic plan view for explaining a vibration mode used in the present invention.

FIG. 3 is a schematic plan view for explaining a charge distribution when a piezoelectric plate is excited in a vibration mode used in the present invention.

FIG. 4 is a schematic plan view for explaining the polarization direction of the piezoelectric plate used in the present invention.

FIG. 5 is a perspective view for explaining an example of a polarization method.

FIG. 6 is a diagram showing impedance-frequency characteristics of the piezoelectric resonator of the first embodiment and the piezoelectric resonator of the conventional example.

FIG. 7 is a diagram showing impedance-frequency characteristics showing an example in which spurious due to spreading vibration is generated.

FIG. 8 is a schematic plan view for explaining a charge distribution generated in a piezoelectric plate when a spreading vibration mode is excited.

FIG. 9 is a schematic plan view for explaining the polarization method in the second embodiment.

FIG. 10 is a perspective view of a piezoelectric resonator according to a second embodiment.

FIG. 11 is a diagram showing impedance-frequency characteristics of the piezoelectric resonator of the second embodiment.

FIG. 12 is a perspective view showing a piezoelectric resonator according to a third embodiment of the present invention.

[Explanation of symbols]

A ... Piezoelectric plate 5, 6 ... Diagonal line 7-10 ... area 13, 14 ... Resonant electrodes 15 ... Piezoelectric resonator

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yo Ando             2-10-10 Tenjin, Nagaokakyo, Kyoto Stock             Murata Manufacturing Co., Ltd. (72) Inventor Yukio Sakabe             2-10-10 Tenjin, Nagaokakyo, Kyoto Stock             Murata Manufacturing Co., Ltd.

Claims (2)

[Claims] 1. The plane shape is a square, and the square shape has two
Piezoelectric plates that are polarized in the thickness direction so that the polarization directions are opposite to each other in the four regions separated by diagonal lines of the book, and are formed on the entire both main surfaces of the piezoelectric plate. A piezoelectric resonator comprising a pair of resonance electrodes. 2. The planar shape is a square, and the square has
In four regions divided by a diagonal line of the book, a piezoelectric plate polarized in the thickness direction so that the polarization directions are opposite to each other between adjacent regions, and a pair of piezoelectric plates formed on both main surfaces of the piezoelectric plate. A resonance electrode is provided, and an unpolarized region that is not polarized in the piezoelectric plate is formed in the vicinity of the center point of the square, or an electrode missing portion where the resonance electrode is missing in the vicinity of the center point of the square. A piezoelectric resonator characterized by being provided.