JPH03184412A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To suppress spurious resonance without blocking a main response by forming the contour shape of a cavity in non-circular shape so as to set the shortest distance from each corner part of a resonance electrode to the edge of the cavity at a range of two-three times the plate thickness of a piezoelectric ceramic substrate. CONSTITUTION:The shape of the cavity 10 is formed in such a way that the upper and lower parts of the resonance electrode are formed in circular arc shape and both side parts in non-circular shape forming linear shape. By forming the cavity 10 in such shape, it is possible to set the shortest distances d1 and d2 from each corner part of the oscillation electrode to the edge of the cavity 10 at the range of unmagnified to three times the plate thickness (t) of the piezoelectric ceramic substrate 1. In other words, by satisfying conditions t<=d1 and d2<=3t, it is possible to confine sufficient energy and to suppress the spurious resonance without blocking the main response required originally.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a piezoelectric resonator, particularly a dual mode resonator suitable as a piezoelectric monolithic filter.

[Conventional technology]

In general, a dual mode resonator has a pair of inputs and
A rectangular vibrating electrode 21.22 for output is formed, and a rectangular vibrating electrode 23 for grounding is formed on the other main surface at a portion facing the vibrating electrode 21.22.
The outer periphery of the piezoelectric ceramic substrate 20 is sealed with an exterior resin 25, leaving a cavity 24 around the piezoelectric ceramic substrate 23. Note that the rectangular vibrating electrode is more vertical and vertical than the circular vibrating electrode.
This is because by changing the lateral dimension ratio, a greater degree of freedom in characteristics can be achieved.

The method for forming the cavity 24 is to apply a cavity forming material such as wax or paraffin on the vibrating electrodes 21 to 23 in advance,
A method is used in which a cavity is formed by heating the exterior resin during or after sealing to melt the cavity-forming material and absorb it into the exterior resin (Japanese Patent Publication No. 45-22384).
Publication No.).

[Problem to be solved by the invention]

However, in the conventional case, since the shape of the cavity 24 is circular, there has been a problem that spurious vibrations become large. The cause of this is as shown in FIG.
The shortest path from the outer corner of the jlld to the periphery of the cavity 24
, the shortest path #d4 from the inner corner to the periphery of the cavity 24 is much larger, and the damping of the vibration propagating in the radial direction from the inner part of the vibrating electrode is insufficient.
This is because the spurious response becomes large. on the other hand,
FIG. 7 - The cavity 24 is arranged so that the periphery of the cavity 24 is located in the vicinity of the outer corner of the vibrating electrode 21.22, as shown by the dashed line.
If 4 is made small, the shortest distance d4 from the inner corner to the periphery of the cavity 24 is also made small, but this has the disadvantage that the main response of thickness longitudinal vibration is inhibited and transmission loss becomes large.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a piezoelectric resonator that can suppress spurious vibrations without inhibiting the main response even when the interval between vibrating electrodes becomes large.

(Means for solving !II!i!) In order to achieve the above object, the present invention forms a pair of rectangular vibration electrodes for input and output adjacent to one main surface of a piezoelectric ceramic substrate,
A rectangular vibrating electrode for grounding that includes the vibrating electrode is formed on the other principal surface at a portion facing the vibrating electrode, and the outer periphery of the piezoelectric ceramic substrate is sealed with an exterior resin, leaving a cavity around the vibrating electrode. In a piezoelectric resonator using an energy-trapped thickness longitudinal vibration mode, the cavity has a non-circular outline, and the shortest distance from each corner of the vibrating electrode is equal to the thickness of the piezoelectric ceramic substrate. It is characterized by being formed in a range of ~3 times as large.

[Effect]

The inventor conducted various studies and found that if the shortest distance from the corner of the vibrating electrode to the periphery of the cavity is smaller than the thickness of the piezoelectric ceramic substrate, the main response of the originally necessary thickness longitudinal vibration is suppressed and transmitted. On the other hand, if the shortest distance from the corner of the vibrating electrode to the periphery of the cavity is greater than three times the thickness of the piezoelectric ceramic substrate, energy confinement will be insufficient and spurious vibrations will not be suppressed. It turned out that. Therefore, it is necessary to set the shortest distance from each corner of the vibrating electrode to a range that is equal to or three times the thickness of the piezoelectric ceramic substrate, but a conventional circular cavity satisfies this condition. That is impossible.

Therefore, in the present invention, the contour shape of the cavity, in other words, the shape of the cavity forming material applied, is made into a non-circular shape that satisfies the above conditions.

〔Example〕

FIGS. 1 and 2 show an example in which the present invention is applied to an energy trap type piezoelectric monolithic filter, which has a structure in which two dual mode resonators are formed on the same substrate.

In the figure, a piezoelectric ceramic substrate 1 is polarized in its thickness direction, and has two pairs of input/output rectangular vibrating electrodes 2a, 4a, and 3a on its main surface.

4b is formed. The lower vibrating electrodes 2a and 3a are connected to the terminal electrodes 2c and 2c via lead electrodes 2b and 3b, respectively.
It is connected to 3c. In addition, the upper vibration orbit electrode 4a,
4b are electrically connected to each other via a connecting electrode 4c, and a capacitor electrode 4d is formed in the middle of the connecting electrode 4c. On the other hand, on the other main surface of the piezoelectric ceramic substrate 1,
Square vibrating electrodes 5a, 5b for grounding are provided at positions facing the vibrating electrodes 2a, 4a and 3a, 4b, and these vibrating electrodes 5a, 5b are connected to connecting electrodes 5c, 5d.
It is connected to a capacitor electrode 5e facing the capacitor electrode 4d, and further connected to a terminal electrode 5f.

As described above, the vibrating electrodes 2a, 4a and 5a facing each other with the piezoelectric ceramic substrate 1 in between constitute one double mode filter, and the vibrating electrodes 3a, 4b and 5b constitute the other double mode filter. do. and capacitor electrodes 4d facing each other with the piezoelectric ceramic substrate l in between;
5e constitutes a capacitor.

Input and output terminals 6.7 are connected to the terminal electrodes 2c and 3c by soldering, etc., and a ground terminal 8 is connected to the terminal electrode 5f.
However, they are connected by soldering, etc. As a result, the equivalent circuit shown in FIG. 3 is formed.

Vibrating electrodes 2a, 4a of the piezoelectric ceramic substrate l.

A cavity-forming material (not shown) made of wax, paraffin, etc. is applied onto 3a, 4b and 5a, 5b, respectively, and then sealed with exterior resin 9, so that the cavity-forming material is injected into exterior resin 9. Upon absorption, a cavity IO is formed. In this way, the cavity 10 is formed only in the vibrating electrode part, and the capacitor electrodes 4d and 5a are fixed with the exterior resin 9, so that the thickness longitudinal vibration is excited only in the part sandwiched between the vibrating electrodes of the piezoelectric ceramic substrate I. be done. For more information,
Dual modes of vibration, symmetric and asymmetric modes, are excited.

The shape of the cavity IO is such that the upper and lower parts of the vibrating electrode are arcuate,
It is formed into a non-circular shape with straight sides. Note that in order to form the cavity 10 having the above shape, the cavity forming material may be applied using a trowel whose tip end has substantially the same shape as the cavity IO. By making the cavity lO into such a shape, the shortest distance ddt (see Fig. 4) from each corner of the vibrating electrode to the periphery of the cavity lO can be made equal to or three times the thickness t of the piezoelectric ceramic substrate 1. It can be set to a range of . That is, t≦d,, dl≦31 By satisfying these conditions, sufficient energy can be trapped without inhibiting the originally necessary main response, and spurious vibrations can be suppressed. The inventor measured the spurious response (attenuation outside the passband) of a filter with a center frequency of 10.7 MH, and found that it was 40 d in the case of a conventional circular cavity.
B, whereas in the non-circular cavity 10 of the present invention, it was 45
I was able to improve it by dB. In addition, from each corner of the vibrating electrode, the cavity I
Of course, if the shortest paths gla+ and at to the periphery of O are made approximately equal distances, the characteristics will be further improved.

Furthermore, if the spacing δ between the vibrating electrodes 2a, 4a and 3a, 4b is increased in order to make the coupling between the symmetrical mode and the asymmetrical mode sparse, the above conditions can be met by making the cavity lO elongated in the vertical direction. can be easily satisfied.

Note that the shape of the cavity is not limited to the above-mentioned shape in which the upper and lower portions of the vibrating electrode are arcuate and both sides are linear, but can be changed to various shapes such as an elliptical shape or a rectangular shape.

Furthermore, the present invention is not limited to a piezoelectric monolithic filter in which two dual mode resonators are provided on the same substrate, but also a piezoelectric monolithic filter in which one double mode resonator is formed as shown in FIG.
It is also possible to form two or more dual mode resonators.

[Effects of the Invention] As is clear from the above description, according to the present invention, the contour shape of the cavity is such that the shortest distance from each corner of the vibrating electrode to the periphery of the cavity is equal to the thickness of the piezoelectric ceramic substrate. Since it is formed into a non-circular shape so as to have a range of ~3 times, spurious vibrations can be suppressed without interfering with the main response, and a dual mode resonator with excellent characteristics can be obtained.

[Brief explanation of drawings]

Fig. 1 is a front view of an example of a piezoelectric resonator according to the present invention, Fig. 2 is a sectional view taken along the line ■-■ in Fig. 1, Fig. 3 is an equivalent circuit diagram of the piezoelectric resonator, and Fig. 4 is a vibrating electrode. An enlarged view of the part, Figure 5 is a front view of a conventional piezoelectric resonator, and Figure 6 is the Vl-V of Figure 5.
7 is an enlarged view of the vibrating electrode portion. ! ...Piezoelectric ceramic substrate, 2a, 3a, 4a, 4
b, 5a, 5... Vibrating electrode, 9... Exterior resin, 10... Cavity.

Claims (1)

[Claims] (1) A pair of rectangular vibrating electrodes for input and output are formed adjacent to each other on one main surface of the piezoelectric substrate, and a rectangular vibrating electrode for grounding is formed on the other main surface of the piezoelectric substrate at a portion facing the above-mentioned vibrating electrode. In a piezoelectric resonator using an energy-trap thickness longitudinal vibration mode in which the outer periphery of the piezoelectric substrate is sealed with an exterior resin while leaving a cavity around the vibrating electrode, the cavity has a non-circular outline. A piezoelectric resonator characterized in that the shortest distance from each corner of the vibrating electrode is formed within a range of equal to three times the thickness of the piezoelectric substrate.