JPS62118627A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To decrease the static capacitance and to improve the spurious characteristic by forming at least one electrode in a shape cancelling a surface electric charge of opposite polarity produced at the peripheral part and in a diagonal direction of the major surface of a piezoelectric substrate in the two-terminal type piezoelectric resonator formed with the electrode to both the major surfaces opposed to each other on the piezoelectric substrate. CONSTITUTION:In the piezoelectric resonator 11, a rectangle ring part 12 having a prescribed width formed to the peripheral part of the major surface 7a of the piezoelectric substrate 7 and an electrode 15 comprising crossing diagonal line parts 13, 14 prolonged from the ring part 12 in directions of diagonal lines l1, l2 of the piezoelectric substrate 7 are formed. Thus, the opposed area between both the opposed electrodes is decreased, the surface electric charges of the opposite polarities due to the undesired vibration mode generated at the peripheral part of the major surface of the piezoelectric substrate and in diagonal line directions are cancelled, the static capacitance is decreased and the piezoelectric resonator with excellent spurious characteristic is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a two-terminal piezoelectric resonator used in ladder filters, oscillators, and the like.

(Prior art) - As shown in Figure 3, the IIGI gate filter has a series resonator 5 and a parallel resonator 6 between the input terminal 1.2 and the output terminal 3.4. It has a so-called ladder-like connected structure. The series resonator 5 and the parallel resonator 〇 are both two-terminal piezoelectric resonators.

By the way, in order to reduce the size of the ladder filter as described above, it is necessary to use as few series resonators 5 and parallel resonators 6 as possible, and to obtain the necessary filter characteristics. is preferred. In this way, in order to reduce the number of series resonators 5 and parallel resonators 6 used and obtain the necessary filter characteristics, the ratio of the capacitances of the series resonators 5 and parallel resonators 6 should be increased. The deterioration of the shave factor of the filter characteristics caused by this is caused by the series resonator 5 and the parallel resonator 6.
A material with a large mechanical Q (Qm) may be used. As mentioned above, in order to increase the capacitance ratio between the series resonator 5 and the parallel resonator 6, the dielectric constant and thickness of the piezoelectric substrate constituting the series resonator 5 must be made small, and the thickness must be increased, while the parallel It is necessary to increase the dielectric constant and reduce the thickness of the piezoelectric substrate constituting the resonator 6. However, if the thickness of the piezoelectric substrate of the series resonator 5 is increased, the shape of the filter becomes larger.
Furthermore, when the thickness of the piezoelectric substrate of the parallel resonator 6 is reduced, the mechanical strength of this piezoelectric substrate is reduced.

Therefore, as shown in FIGS. 4(a), 4(b), and 4(C), the series resonator 5 conventionally has two opposing main surfaces 7a, Of the electrodes 8 and 9 formed on the main surface 7a, the dimensions of one of the electrodes 8 and 9 formed on the main surface 7a are reduced to reduce the opposing area between the electrodes 8 and 9, thereby reducing the capacitance. I was trying to do that.

However, as mentioned above, if the dimensions of the electrode 8 of the series resonator 5 are reduced, the resonant frequency will be 1.5 times, 3 times, and 5 times
A ladder filter using such a series resonator 5 has a problem in that the spurious characteristics in the double and seven times frequency bands are degraded, and the spurious outside the pass frequency band becomes large.

(Object of the Invention) An object of the present invention is to provide a piezoelectric resonator that has small capacitance and good spurious characteristics.

(Structure of the Invention) Therefore, the present invention provides that at least one of the electrodes formed on both opposing main surfaces of a rectangular piezoelectric substrate is formed on the peripheral edge of the main surface of the piezoelectric substrate on which the electrode is formed. It is characterized by comprising a ring-shaped part and a diagonal part extending from the ring-shaped part in a diagonal direction of the main surface.

That is, the present invention provides a two-terminal piezoelectric resonator in which electrodes are formed on both opposing main surfaces of a piezoelectric substrate, in which at least one electrode has different polarity that occurs at the periphery and diagonal direction of the main surface of the piezoelectric substrate. The shape is such that it cancels out the surface charge.

These characteristics of the present invention were obtained based on the following considerations by the inventor of the present application.

The inventor of the present application first used the same piezoelectric material as the piezoelectric substrate 7 of the series resonator 5 having the configurations shown in FIGS. 4(a), 4(b), and 4(C), and It has almost the same dimensions as the substrate 7, 4.9 mm square, thickness 0, . A 5 mm piezoelectric substrate (not shown) was manufactured, electrodes were formed on both main surfaces thereof, and the impedance characteristics of this piezoelectric substrate were measured, and the results shown in FIG. 5 were obtained.

On the other hand, with the development of computers, the impedance characteristics of the piezoelectric substrate model described above were determined through simulation calculations using finite element method analysis, which has recently been put into practical use, and a good agreement with that shown in Figure 5 was found. It was done.

Therefore, by computer-assisted finite element analysis, we determined the surface charge distribution generated on the surface of the piezoelectric substrate model in response to displacement and strain. In the impedance characteristics shown in Figure 5, we found that the fundamental vibration a1 Surface charge distributions as shown in FIGS. 6(a) to (J2) were obtained corresponding to spurious signals b to Q, respectively. Here, as is clear from Fig. 5, spurious c, g, h, and i are modes that are difficult to excite, so they will be excluded from the following discussion, and Fig. 6 (b)
, (d).

As is clear from the surface charge distribution patterns of (e), (D, (D, (k) and (12)), the spurious b
,d,e.

It can be seen that the surface charge distribution of the piezoelectric substrate corresponding to ,j, and ρ has charges with different signs distributed along the periphery and diagonal direction of the main surface of the piezoelectric substrate.

By the way, there is a certain unnecessary vibration mode of the piezoelectric substrate, namely,
It is known that in order to suppress spurious components, the electrode shape should be such that the surface charges generated on the surface of the piezoelectric substrate in the vibration mode are exactly canceled out.

Therefore, from the above simulation results and the above facts, if electrodes are formed diagonally to the main surface of the piezoelectric substrate, the surface charge on the piezoelectric substrate surface will be canceled out in response to spurious vibrations, and spurious vibrations will be suppressed. It is considered that On the other hand, if the dimensions of the electrode 8 are made smaller in the series resonator 5 having the rectangular electrode 8 as shown in FIGS. 4(a), 4(b), and 4(c),
The amount of charges canceled out on one main surface of the piezoelectric substrate 5 becomes unbalanced between positive and negative. Therefore, it is understood that spurious characteristics deteriorate in a ladder filter using a series resonator having such an electrode configuration.

The present invention has been made based on such consideration.

(Effects of the Invention) According to the present invention, at least one electrode of a two-terminal piezoelectric resonator is formed along the peripheral edge and diagonal direction of the main surface of the piezoelectric substrate on which it is formed, so that The opposing area between the two electrodes is reduced, and the surface charges of different polarities due to unnecessary vibration modes generated at the periphery and diagonal of the main surface of the piezoelectric substrate are canceled out, resulting in a small capacitance and improved spurious characteristics. A good piezoelectric resonator can be obtained.

(Example) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1(a), FIG. 1(b) and FIG. 1(C) show an embodiment of a piezoelectric resonator according to the present invention.

The piezoelectric resonator II has a piezoelectric substrate instead of the small rectangular electrode 8 in the series resonator 5 explained in FIG. 4(a), FIG. 4(b), and FIG. 4(C). a square ring-shaped part 12 having a predetermined width formed on the peripheral edge of the main surface 7a of the piezoelectric substrate 7; and a cross-shaped diagonal part extending from the ring-shaped part 12 in the direction of the diagonal lines g1 and Q of the piezoelectric substrate 7. 13 and 14, an electrode 15 is formed.

In addition, Fig. 1(a), Fig. 1(b) and Fig. 1(c)
In Fig. 4(a), Fig. 4(b) and Fig. 4(
Parts corresponding to C) are shown with corresponding symbols, and redundant explanations will be omitted.

With such a configuration, the piezoelectric resonator 11 has the fifth
The surface charges on the main surface 7a of the piezoelectric substrate 7 corresponding to the spurious waves d, e, f, j, and g shown in the figure are
5 by diagonal portions 13 and 14. Thereby, spurious d, ej, j, and Q can be suppressed. Further, due to the presence of the ring-shaped portion 12 of the electrode 15, spurious components b, e, and r are suppressed. On the other hand, since the electrode 15 is formed on a part of the main surface 7a of the piezoelectric substrate 7, the opposing area between the electrode 15 and the electrode 9 becomes small, the capacitance of the piezoelectric resonator 11 becomes small, and the ladder filter It can be suitably used as a series resonator.

In the above embodiment, the electrode 15 may have one of the diagonal portions 13 and 14 omitted, as shown in FIG. 2, for example. In addition, the above electrode 1
5 may have partially different widths or may have recesses or protrusions. Furthermore, the piezoelectric substrate 7 may have a parallelogram shape.

The present invention can be applied not only to piezoelectric resonators used in ladder filters but also to oscillators and the like.

[Brief explanation of drawings]

FIG. 1(a) and FIG. 1(b) are a plan view and a bottom view of an embodiment of a piezoelectric resonator according to the present invention, respectively.
-)IJ 纺1 1'i'71/ -)/T'l NT
nT 灼1-; 8A KCFF+M Fig. 2 is a plan view of a modification of the above embodiment, Fig. 3 is a circuit diagram of a ladder filter, Fig. 4(a) and Fig. 4(b) are respectively the conventional A top view and a bottom view of the piezoelectric resonator, FIG. 4(c) is a sectional view taken along the line ■-■ in FIG. 4(a),
FIG. 5 is an impedance characteristic diagram of a piezoelectric substrate of a conventional piezoelectric resonator, and FIGS. 6(a) to 12) are explanatory diagrams of surface charge patterns generated on the main surface of the piezoelectric substrate, respectively. 5...Series resonator, 6...Parallel resonator, 7...
・Piezoelectric substrate, 7 a, 7 b...Main surface, 9...
- Electrode, 11... Piezoelectric resonator, 12... Ring-shaped part, 13.14... Diagonal part, I5... Electrode, g, , 12. ···diagonal.

Claims (1)

[Claims] (1) In a piezoelectric resonator in which electrodes are formed on both opposing main surfaces of a square piezoelectric substrate, at least one of the electrodes is formed on the periphery of the main surface of the piezoelectric substrate on which it is formed. The main surface of the piezoelectric substrate is made of A piezoelectric resonator characterized in that generated surface charges of different polarities cancel each other out.