JPH0828643B2 - Piezoelectric vibrator - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a piezoelectric vibrator used for a filter or the like in a weak electric circuit.

(Prior Art) A piezoelectric body made of a single crystal, for example, a multimode crystal filter using a crystal is used in a weak electric circuit.
This crystal filter has an extremely high Q value showing the electrical resonance characteristic of the crystalline lens, that is, the resonance characteristic is sharp, so that the crystal filter has excellent electrical characteristics such as propagation characteristics. Since the crystalline lens is normally excited by a thickness-based vibration mode and exhibits a good temperature characteristic of a cubic curve, it has been used as a filter for high-grade communication equipment for business use, especially for a narrow band. . In recent years, due to an increase in the amount of information and the like, there is a demand for a crystal filter having a wide pass band width and a sufficient guaranteed attenuation amount outside the pass band.

FIG. 4 is a diagram showing a conventional example of a multimode crystal filter, in which FIG. 4 (a) is a sectional view and FIG. 4 (b) is a plan view.

This crystal filter forms a pair of input electrodes 11a, 11b and output electrodes 12a, 12b on both main plate surfaces of the crystal plate 10, and the input and output electrodes 11b, 12b on one plate surface side. Each is grounded to a common potential. In addition, 13 shown in FIG.
Is an extraction electrode extending from the respective input / output electrodes (11a, 11b), (12a, 12b) to the outer peripheral portion. Then, as shown in the displacement distribution curve diagram of FIG. 5, this crystal filter has an input on one plate surface side, an input on the other plate surface facing the output electrodes 11a, 12a, and output electrodes 11b, 12b. The symmetric mode Fs is excited by the pair of input electrodes 11a and 11b, and the output electrode 12a.
And 12b excite the obliquely symmetric mode Fa to make it a multiple mode. Then, normally, as shown in the resonance characteristic diagram of FIG. 6, the pass band width BW of the crystal filter is approximately between the resonance frequency fs ₁ of the symmetric mode Fs and the anti-resonance frequency fa ₂ of the oblique symmetry mode Fa. I am trying to design it. In addition,
In FIG. 6, the horizontal axis is the vibration frequency (f), the vertical axis is the reactance (X), Fs is the symmetric mode, Fa is the resonance characteristic of the oblique symmetric mode, fs ₂ is the anti-resonant frequency of the symmetric mode, fa ₁ indicates the resonance frequency of the obliquely symmetric mode.

Then, generally, the pass band width BW of the crystal filter is determined by the inter-electrode distance G (fourth electrode) between the input side electrode 11a and the output side electrode 12a.
(Fig.) Is adjusted to determine the degree of acoustic coupling. However, the variable distance G between electrodes is due to
Since the capacitance C between the input and output electrodes of a and the electrode 12a on the output side is changed, the guaranteed attenuation outside the pass band is affected. That is, as the capacitance C between the input and output electrodes is larger, the attenuation pole is more likely to occur in the vicinity of the pass band and the guaranteed attenuation amount is smaller, and if the acoustic coupling between the input and output electrodes is strengthened and the pass band width BW is widened, There is a problem that the capacitance C between the input and output electrodes becomes large and a sufficient guaranteed attenuation cannot be obtained.

FIG. 7 is a cross-sectional view of a reverse connection type crystal filter.
That is, this crystal filter is one conventional example for solving the above-mentioned problems, and of the input and output electrodes (11a, 11b) and (12a, 12b) formed on both main plate surfaces of the piezoelectric plate 10. ,
Input electrode 11b on one plate surface side and output electrode 1 on the other plate surface side
2a has a common potential. And by this,
The interelectrode capacitance C between the input and output of the output electrodes 11a and 12b is reduced to increase the guaranteed attenuation amount and to widen the pass band width BWB.

FIGS. 8 (a) and 8 (b) are cross-sectional views of a reverse connection type crystal filter in which the pass band width is further widened, and the input and output electrodes 11b and 12a having the above-mentioned common potential are provided on the piezoelectric plate 10 respectively. 2
The protrusions 11c and 12c are provided so as to extend to the center line that divides them equally (a in the same figure). Alternatively, the mass 14 is added to the piezoelectric plate portion on the center line between the input and output electrodes (FIG. 8B). And
The resonance frequency fs ₁ of the symmetric mode Fs is mainly lowered and the pass band width BW is widened due to the additional effect of the protrusions 11c and 12c or the mass 14.

(Problems to be Solved by the Invention) By the way, in the crystal filter of FIG. 8 (a), the input and output electrodes (11
a, 11b) and (12a, 12b) are added to the surface to obtain the desired characteristics. For example, pass bandwidth BW
When trying to widen the
Is the maximum, and is the minimum in the oblique symmetry mode Fa.
On the center line (p) of 10, add mass and perform fine adjustment.
For this reason, the adjustment film made of metal as a mass adheres to the surface of the piezoelectric plate around the electrode and acts as an electrode, which causes adverse effects such as changes in various characteristics during design. To prevent this adverse effect, it is conceivable to add mass to the protrusions 11c and 12c, for example. However, in this case, the amount of change in the resonance frequency of the symmetric mode Fs is too small, and for example, the symmetry of the additional mass is lost with respect to the center line, so that the vibration characteristics are impaired and spurious is generated, which lowers the electrical performance. Is causing

In addition, in the crystal filter of FIG.
Because it is difficult to control the mechanical amount and position of
There is a problem that the passband width BW varies and the productivity deteriorates.

As described above, in the conventional reverse connection type crystal filter, workability and electrical characteristics are good, the pass band is wide, and sufficient attenuation is ensured due to the relationship of the electrode arrangement for multimode. It was difficult to get the quantity.

The present invention has been made in view of the above problems,
It is an object of the present invention to provide a piezoelectric vibrator filter which can maintain a guaranteed attenuation amount outside the pass band, widen the pass band width, and have good workability and electrical characteristics.

(Means for Solving the Problems) According to the present invention, two pairs of electrodes facing each other are arranged on the front and back main surfaces of the piezoelectric plate, and two electrodes are arranged in a diagonal direction when viewed from the cross-sectional direction.
In the piezoelectric vibrator, the two electrodes are electrically commonly connected, and the remaining one electrode and the above-mentioned facing electrode are used as input ends, and the other facing electrodes are used as output ends. The plate is integrally formed by a circular or rectangular piezoelectric element, and the electrodes are formed on the piezoelectric plate with the same width in the direction perpendicular to the vibration propagation direction and are electrically commonly connected to each other. The ends of the two diagonal electrodes are extended toward the center of the piezoelectric plate so that they face each other with the piezoelectric plate sandwiched between them. Provided is a piezoelectric vibrator having a width of 0.8 times or less in the direction.

(Operation) In the present invention, the end portions of the two electrodes in the diagonal direction are extended to face each other with the piezoelectric plate sandwiched therebetween, and the portions of the electrodes facing each other have a predetermined size. Therefore, the guaranteed attenuation outside the pass band is obtained. Can be maintained and a predetermined pass bandwidth can be obtained.

(Example) Next, the Example of this invention is described in detail using drawing.

FIG. 1 is a sectional view showing an embodiment of the piezoelectric vibrator according to the present invention, and FIG. 2 is a plan view thereof.

In FIGS. 1 and 2, reference numeral 1 denotes a crystal plate, which uses a disk-shaped crystal piece that is cut out from a crystal body of quartz as a piezoelectric material, for example, by AT cutting, and vibrates in a thickness system. .
A pair of rectangular electrodes (2a, 2b), (3a, 3b) are provided on both main surfaces of the crystal plate 1, and further extraction electrodes (2c, 2d), ( 3c, 3d),
It is provided so as to extend to the outer peripheral end of the crystal plate 1. The paired electrodes 2a and 2b are, for example, the input side, and the other paired electrodes 3a and 3b are the output side.

Input side electrode 2a provided on one side of the crystal plate 1
And the output-side electrode 3b provided on the other plate surface
They are arranged symmetrically with respect to a center line P that divides the x-axis direction of x, y ', z'into two halves, and are formed in the same area. Further, the electrode 2b forming a pair with the electrode 2a has an end portion in the outer peripheral direction arranged in the same arrangement with the end portion of the electrode 2a sandwiching the crystal plate 1 and has an area larger than that of the electrode 2a. Is provided so as to extend beyond the center line P in the direction of the electrode 3b on the same plate surface. The electrode 3a forming a pair with the electrode 3b has an end portion in the outer peripheral direction aligned with the electrode 3b and has an area larger than that of the electrode 3b. It is provided so as to project in the direction of the electrode 2a on the surface. Therefore, since the electrode 2b and the electrode 3a are arranged on the respective plate surfaces beyond the center line P, the electrode 2b and the electrode 3a have opposing portions a with the crystal plate 1 interposed therebetween. When
A reverse connection type piezoelectric vibrator is configured by grounding 3a and 3a together and applying a common potential.

FIGS. 3 (a) and 3 (b) are diagrams showing the frequency propagation characteristics thereof, and depending on the length of the dimension a of the facing overlapping portion of the electrode 2b and the electrode 3a, in the pass band, FIG. It is shown that spurious is generated outside the pass band and in FIG. In FIG. 3 (c), the length of the facing overlapping portion a is the electrode.
A curve diagram showing the relationship between the value of the ratio to the length of 2a or 3b (ratio of the opposed overlapping portion a) and the generation position of the spurious frequency fo1, where the horizontal axis is the ratio of the opposed overlapping portion a and the vertical axis is the center frequency fo This is the position where the spurious frequency fo1 is generated. The position where the spurious frequency fo1 is generated is standardized by dividing the difference (fo1-fo) from the center frequency fo by the band frequency BW. That is, in the curve diagram of FIG. 3 (c), when the ratio of the opposed overlapping portion a is gradually increased from 0, the generation position of the spurious frequency fo1 approaches the center frequency fo. Then, when the ratio of the opposed overlapping portions a is about 0.8, the spurious fo1 generation position is close to the upper limit frequency of the pass band BW because (fo1-fo) / BW is 0.5. Then, when the ratio of the opposed overlapping portion a is approximately 0.5, (fo1 / fo) / BW is 0.
9, that is, 0.4 BW from the upper limit of the pass bandwidth BW. When the ratio of the opposed overlapping portion a is about 0.4, the falling position of the spurious fs indicated by the symbol a is outside the pass band width BW and the characteristics in the pass band are not deteriorated.

Then, when the ratio of the opposed overlapping portion a is set to about 0.5 or less, the spurious generation position is 0.
Since the positions are 4 BW or more apart, it is possible to prevent the effect of practical spurious outside the pass band.

In this embodiment having such a configuration, since the two pairs of electrodes are formed as a reverse connection type piezoelectric vibrator,
The input-side electrode 2a and the output-side electrode 3b are on opposite plate surfaces and form an equipotential surface in the piezoelectric plate between the electrodes for input and output, so the capacitance C between the input and output electrodes is small. Therefore, when used as a filter, it is possible to obtain a predetermined non-damping pole type damping characteristic. In addition, electrodes 2b and 3a, which are at a common potential,
Since and are opposed to each other beyond the center line P, the resonance of the symmetric mode is compared with the anti-resonance frequency of the oblique symmetric mode due to the mass addition effect of the minimum displacement part of the oblique symmetric mode and the maximum displacement part of the symmetric mode. It works by lowering the frequency to widen the passband.

Then, a value obtained by comparing the length of the facing portion a of the electrodes 2b and 3a having the common potential with the length of the electrode 2a or 3b is 0.
When the value is set to 8 or less, the position of the spurious fo1 is separated from the center frequency fo and is out of the band, so that the deterioration of the characteristics due to the generation of spurious in the band can be prevented.

Incidentally, in the above-mentioned embodiment, using a disk-shaped crystal piece cut out from a crystal body of quartz as the piezoelectric material, the piezoelectric vibrator provided with a rectangular electrode has been described, the present invention is a quartz material as the piezoelectric material. Without limitation, for example LiTaO ₃ ,, L
A piezoelectric material made of a single crystal such as iNbO _{3 is} also used, and the shapes of the piezoelectric plate and the electrodes are not limited to the above shapes.

(Effects of the Invention) As described in detail above, according to the present invention, one electrode on the input side and the electrode on the output side provided on the opposite plate surface are grounded to have a common potential. Since the portions facing each other beyond the center line are provided, at the time of fine adjustment of the frequency, a predetermined mass can be attached to the opposing portions, and there is no direct attachment to the piezoelectric plate surface. Adjustments can be made without damaging the characteristics of the piezoelectric vibrator,
The effect of improving productivity is produced.

Further, according to the present invention, the opposing electrode portions lower the resonance frequency of the symmetric mode as compared with the anti-resonance frequency of the oblique symmetry mode due to the correspondence between the oblique symmetry mode and the symmetry mode. Has the effect of being spread.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the piezoelectric vibrator according to the present invention, FIG. 2 is a plan view thereof, and FIGS. 3 (a) and 3 (b) are views showing frequency propagation characteristics thereof. FIG. 4 (c) shows the relationship between the spurious emission position ratio (fo1-fo) / BW in FIG. 3 (b) and the ratio of the opposed overlapping portion a shown in FIG. 1, and FIG. Is a sectional view of an example of a conventional crystal filter, a plan view, FIG. 5 is a displacement distribution diagram of the crystal filter, FIG. 6 is a resonance characteristic diagram of the crystal filter, FIG. 7 is a cross-sectional view of a reverse connection type crystal filter, FIG. 8 is an explanatory diagram of frequency adjustment of the reverse connection type crystal filter. 1 ... Quartz plate, 2a, 2b, 3a, 3b ... Electrode, a ... Electrode part facing each other.

Claims (1)

[Claims] 1. Two pairs of electrodes facing each other on the front and back main surfaces of a piezoelectric plate are arranged, two electrodes in a diagonal direction as viewed from the cross-sectional direction are electrically commonly connected, and the remaining one electrode faces the above-mentioned facing. In the piezoelectric vibrator having the electrodes as input ends and the electrodes facing the other remaining electrodes as output ends, the piezoelectric plate is integrally formed by a circular or rectangular piezoelectric element, and each electrode is The piezoelectric plate is formed with the same width in the direction perpendicular to the vibration propagating direction, and the two diagonally connected electrically common electrodes are formed.
Extend the ends of the two electrodes toward the center of the piezoelectric plate so that they face each other with the piezoelectric plate sandwiched between them.
A piezoelectric vibrator characterized by being 0.8 times or less.