JPH0752819B2 - Piezoelectric resonance device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an energy confinement type piezoelectric resonance device using harmonics of a thickness longitudinal vibration mode, and in particular, an electrode structure for energy confinement is improved. Regarding things

[Conventional technology]

BACKGROUND ART Conventionally, energy confinement type piezoelectric vibrators using a thickness longitudinal vibration mode using PZT-based piezoelectric ceramics have been known. This type of energy confinement type piezoelectric vibrator is configured by forming electrodes having a smaller area than the piezoelectric ceramic plate on both surfaces of the piezoelectric ceramic plate.

Further, as the piezoelectric ceramics, a material having an effective Poisson's ratio such as PZT is used is 1/3 or more. This is because, when a material having an effective Poisson's ratio of less than 1/3 was used, it was not possible to confine the frequency-decreasing energy of thickness longitudinal vibration.

On the other hand, there is a demand for a piezoelectric resonance device that can be used at higher frequencies. Therefore, a structure has been proposed that can be used for high frequencies by utilizing the second harmonic of the thickness longitudinal vibration (Japanese Patent Application No. 62-235948).

This not yet known prior art structure will be described with reference to FIGS. 2 and 3. As shown in FIG.
Prepare ceramic green sheets 1 and 2 made of PZT-based piezoelectric material. On the upper surface of the ceramic green sheet 1, electrode pastes 3 and 4 are applied in order to form an energy confining electrode and a connecting conductive portion (hereinafter, in the present specification, an energy confining electrode and a connecting conductive portion are formed). The same reference number as that given to the electrode paste portion is also given to the completed electrode and the connection conductive portion).

On the upper surface of the ceramic green sheet 2, the electrode paste 5,
Apply 6, respectively. Further, also on the lower surface of the ceramic green sheet 2, electrode pastes 7 and 8 are applied to portions that will become electrodes and portions that will become connection conductive portions.

Next, the ceramic green sheets 1 and 2 are laminated and subjected to polarization treatment after integral firing to obtain the piezoelectric resonance device shown in FIG.

In the piezoelectric resonance device of FIG. 3, electrodes for energy confinement are provided in the sintered body 10 through the piezoelectric ceramic layers 1 and 2 (which will be described by giving the same reference numbers as the original ceramic green sheets). 3,5,7 are overlapping. The second harmonic of the thickness longitudinal vibration is confined in the overlapping area A.

That is, the three electrodes 3, 5, 7 are arranged through the piezoelectric ceramic layer.
Since they are arranged so as to overlap with each other, the first response of the thickness extensional vibration appears in a higher frequency range as compared with the conventional single plate type piezoelectric resonance device. Therefore, it is possible to realize a piezoelectric resonance device that can be used in a higher frequency range. Not only that, but it is possible to confine the third harmonic of the thickness longitudinal vibration by using a piezoelectric material with a composition with an effective Poisson's ratio of less than 1/3, so various piezoelectric materials can be selected and used appropriately. It is possible to realize a piezoelectric resonance device having the same electrical characteristics as the fundamental wave of thickness longitudinal vibration in terms of response level.

[Technical problem to be solved by the invention]

When manufacturing the piezoelectric resonance device of FIG. 3, the electrodes 3, 5,
The seven must be formed so that they exactly overlap. That is, when the electrodes 3, 5, 7 are misaligned, the resonance characteristics largely vary. However, it is difficult to prevent such positional displacement between the electrodes, and therefore, the complicated work of measuring the characteristics of mass-produced piezoelectric resonance devices and selecting them according to the characteristics is required.

On the other hand, in order to eliminate the above variations in characteristics, it is possible to adopt a structure as shown in FIG. Here, by forming the entire surface electrode 5a on the upper surface of the ceramic green sheet 2, the influence of the positional deviation between the upper and lower electrodes 3 and 7 is prevented.

However, the spurious mode is excited in the frequency region between the resonance frequency and the antiresonance frequency due to the stray capacitance generated between the entire surface electrode 5a and the upper and lower connecting conductive portions 4 and 8. Furthermore, the anti-resonance frequency and anti-resonance resistance are reduced by this stray capacitance, the frequency region between the resonance frequency and the anti-resonance frequency is narrowed, and when applied to an oscillator or the like, defects such as oscillation stop occur. It was the cause.

Therefore, an object of the present invention is to effectively suppress spurious vibrations that are superimposed on higher harmonics of thickness longitudinal vibration, and to effectively reduce variations in characteristics due to displacement of electrodes for energy confinement. Another object is to provide a piezoelectric resonance device having a structure.

[Means for solving technical problems]

The present invention relates to an energy confinement type piezoelectric resonance device using harmonics of a thickness extensional vibration mode, including a plate-shaped main body made of a polarized piezoelectric material, and a piezoelectric layer in the thickness direction of the plate-shaped main body. In which at least three energy confining electrodes are arranged so as to overlap with each other through the gap, the shape relationship between the outermost electrode in the thickness direction and the remaining energy confining electrode is improved. Regarding things.

That is, of the energy confining electrodes, the area of at least one of the energy confining electrodes located in the outermost side in the thickness direction is overlapped with another energy confining electrode adjacent in the thickness direction without displacement. It is characterized in that it is made larger than the overlapping area when it is opened.

[Action]

At least one electrode of the energy confining electrodes located on the outermost side in the thickness direction is made larger than the inner energy confining electrode. Therefore, the permissible amount of the formation position of the inner energy confining electrode with respect to the outermost energy confining electrode is increased by making the outer energy confining electrode relatively large. Therefore, it is possible to reduce the variation in the resonance characteristics due to the displacement of the overlapping energy confining electrodes. Further, as is clear from the examples below, it is possible to effectively suppress the generation of spurious in the band between the antiresonance and the resonance frequency.

[Explanation of Examples]

First, with reference to FIG. 1, a manufacturing process of a piezoelectric resonance device according to an embodiment of the present invention will be described.

First and second ceramic green sheets 11.12 made of two PZT piezoelectric materials are prepared. On the upper surface of the first ceramic green sheet 11, electrode pastes 13 and 14 are applied to a portion which will be an electrode for energy confinement and a portion which constitutes a connection conductive portion.

The electrode paste 15 is applied in a rectangular shape on the upper surface of the second ceramic green sheet 12. This rectangular electrode paste 15 is applied at a position where it overlaps with the electrode paste 13 in the thickness direction when the ceramic green sheets 11 and 12 are superposed.

Further, in this embodiment, the width w of the rectangular electrode paste 15 is
The diameter a of the energy confining electrode paste 13 on the ceramic green sheet 11 is longer than that of the above. Therefore, when the ceramic green sheet 11 and the ceramic green sheet 12 are stacked, the electrode pastes 13, 15
Can be easily overlaid.

Further, electrode pastes 16 and 17 are also applied to the lower surface of the second ceramic green sheet 12 in order to form electrodes for energy confinement and connection conductive portions 17.

A ceramic resonance sheet shown in FIGS. 5 and 6 is obtained by stacking the ceramic green sheets 11 and 12 in the illustrated state, press-bonding them in the thickness direction, firing them, and subjecting them to a predetermined polarization treatment (described later). You can

Polarization is applied to the electrode 15 side exposed on the end surface of the sintered body by +
This is done by applying a negative potential to the upper and lower electrodes 13 and 17. As a result, in the direction of the arrow shown, that is, 2
The piezoelectric ceramic layers of the layers are polarized in opposite directions in the thickness direction.

During driving, the conductive part 14 connects the electrode 13 with + or-
One of the electric potentials can be resonated by periodically applying the other electric potential from the connecting conductive portion 18 to the electrode 17. In the piezoelectric resonator of the present embodiment, similarly to the structural example shown in FIG. 3, harmonics in the thickness extensional vibration mode are excited. Therefore, it is possible to realize a piezoelectric resonance device that can be used in a higher frequency range than the conventional single-plate piezoelectric resonance device.

Next, concrete experimental results will be described when the width w of the energy confining electrode 15 arranged inside is changed in the above-mentioned embodiment. Now, as the first and second ceramic green sheets 11 and 12, those of 3 × 3 mm × thickness of 0.25 mm are prepared, and the energy confining electrode 13 formed on the upper surface or the lower surface of each ceramic green sheet 11 and 12 is prepared. , 17 diameter
A piezoelectric resonance device was manufactured in which the width w of the rectangular energy confining electrode 15 disposed inside was 1.5 mm when the width was 1.5 mm. For comparison, a width w of the energy confining electrode disposed inside was set to 1.5 mm, and the other shapes were the same as those in the above-mentioned embodiment.

In manufacturing the piezoelectric resonance devices of the above-mentioned examples and comparative examples,
The center of the energy confining electrode 13 on the upper surface of the ceramic green sheet 11 and the center of the internal energy confining electrode 15 are in the x direction in FIG. 1, that is, the extending direction of the rectangular energy confining electrode 15. A large number of products were manufactured that were displaced by a distance 1 in the direction orthogonal to. FIG. 7 shows the relationship between the electromechanical coupling coefficient kt and the displacement amount l in the piezoelectric resonance devices of these examples and comparative examples.

As is clear from FIG. 7, in the piezoelectric resonance device of the present embodiment (when width w = 1.2 mm), deterioration of the electromechanical coupling coefficient is not observed unless the displacement amount l exceeds 0.15 mm. I understand. On the other hand, in the resonance device of the comparative example, when the positional displacement amount 1 exceeds 0, that is, even when the displacement amount 1 is small,
It can be seen that the electromechanical coupling coefficient kt deteriorates when there is a displacement between 3 and 15.

Further, when the spurious level in the band between the resonance frequency and the anti-resonance frequency in the piezoelectric resonance layers of the above-mentioned Examples and Comparative Examples was measured, the results shown in Table 1 below were obtained.

In Table 1 above, phase rotation was used when evaluating the spurious level. As shown in FIG. 8, in the frequency band between the resonance frequency fr and the anti-resonance frequency fa, when the impedance waveform is disturbed by spurious vibrations, the phase curve and the phase curve (shown by broken lines) Also spike-like disturbances occur. The depth of this spike-like turbulence is called phase rotation.
That is, the phase rotation can be regarded as an index indicating the spurious level.

As is apparent from Table 1, in the piezoelectric resonance device of the example, the spurious level in the frequency band between the resonance frequency and the antiresonance frequency is effectively reduced as compared with the piezoelectric resonance device of the comparative example. .

In the above-described embodiment, the three energy confining electrodes are formed so as to overlap each other in the thickness direction, but four or more energy confining electrodes are arranged so as to overlap with each other via the piezoelectric layer. It should be pointed out that the present invention can be applied to a resonance device in general.

Regarding the shape of the energy confining electrode, it is not always necessary to configure the outermost layer energy confining electrode in a circular shape and the inner energy confining electrode in a polygonal shape as in the illustrated example. According to the above, the shape of each energy confining electrode can be arbitrarily changed.

〔The invention's effect〕

As described above, according to the present invention, among the energy confining electrodes, at least one of the electrodes located in the outermost layer is formed relatively larger than the energy confining electrode located inside. It is possible to improve the overlapping precision of the energy confining electrodes in the laminated piezoelectric resonance device. Therefore, it is possible to reduce variations in resonance characteristics and the like due to the positional deviation with respect to the energy confining electrode located in the outermost layer of the internal electrode, and it is possible to improve the yield in mass production.

In addition, it is possible to effectively suppress the generation of spurious in the frequency band between the resonance frequency and the anti-resonant frequency, and for example, when using the oscillator, an accident such as an oscillation stop due to the spurious in the frequency band. It is also possible to prevent this, and it is possible to provide a high-performance piezoelectric resonance device.

[Brief description of drawings]

FIG. 1 is an exploded perspective view for explaining a manufacturing process of an embodiment of the present invention, and FIG. 2 is an exploded perspective view for explaining a process for obtaining a piezoelectric resonance device which triggered the present invention. FIG. 3 is a sectional view of the piezoelectric resonance device obtained through the process of FIG.
FIG. 4 is a cross-sectional view for explaining another example of the conventional piezoelectric resonance device, and FIG. 5 is a cross-sectional view of the piezoelectric resonance device of the embodiment obtained in the step of FIG. 1. 6 is a sectional view corresponding to a portion along the line VV, FIG. 6 is a sectional view of an example corresponding to a portion along the line VI-VI in FIG. 1, and FIG. 7 is an electromechanical coupling in the example and the comparative example. FIG. 8 is a diagram showing the relationship between the coefficient and the positional deviation amount l between the electrodes, and FIG. 8 is a diagram for explaining the relationship between spurious and phase rotation. In the figure, 10 is a main body, and 13, 15 and 17 are energy confining electrodes.

Claims (1)

[Claims] 1. An energy confinement type piezoelectric resonance device utilizing harmonics of a thickness longitudinal vibration mode, wherein a plate-shaped main body including a plurality of polarized piezoelectric layers is overlapped with the piezoelectric layer. And at least three energy confinement electrodes formed smaller than the main surface of the piezoelectric layer, and connection conduction electrically connected to the energy confinement electrodes and led to at least one end surface of the main body. And an area of at least one electrode of the energy confining electrodes located on the outermost side in the thickness direction is overlapped with another energy confining electrode adjacent in the thickness direction without deviation. The piezoelectric resonance device is characterized in that it is larger than the overlapping area.