JPH0568889B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of the Invention] The present invention relates to a laminated body using a sintered body in which ceramic green sheets are laminated via internal electrodes so as to overlap each other in the thickness direction and are sintered as one body. This invention relates to improvements in the structure of type piezoelectric elements.

[Prior Art] Conventionally, a flat piezoelectric element 1 shown in perspective and cross-sectional views in FIGS. 2 and 3 has been used as a piezoelectric element that utilizes radial vibration, that is, spreading vibration. Here, electrodes 3 and 4 are formed on the top and bottom surfaces of the polarized piezoelectric ceramic 2, and by applying a voltage from the electrodes 3 and 4, a desired spreading vibration can be extracted. By the way, in this type of flat piezoelectric element 1, the resonance frequency can usually be adjusted by polishing the end face, that is, the outer circumferential face.

However, for example, the second part of the ladder filter
When low impedance is required, such as when used for a resonator, the second
The piezoelectric element 1 shown in FIG. 3 and FIG. 3 was insufficient.

Therefore, a laminated piezoelectric element 11 as shown in a schematic cross-sectional view in FIG. 5 has been developed in recent years. Here, a plurality of ceramic layers 11a...11c are laminated with internal electrodes 13b, 13c interposed therebetween and fired as one body. Note that the electrodes 13a and 13d are
It can be formed simultaneously with the internal electrodes 13b and 13c or after firing. The electrodes 13a...13d are electrically connected to every other layer by external electrodes 15 and 16, respectively. Therefore, the electrodes 15 and 16
A voltage is applied to polarize each ceramic layer 11a...11c in the direction shown by the arrow in FIG. It is said that it is possible to expand and contract.

FIG. 4 is a schematic perspective view showing an example of a specific structure of the laminated piezoelectric element as shown in FIG.
It should be noted that it is not yet known to use this specific example as a second resonator of a ladder type filter. Here, the electrode 13a
a protrusion 21 extending to the end surface of the sintered body;
A main area 22 in the center is used. Although not particularly shown in the figure, the electrodes 13b, 13c, and 13d disposed on the lower side also have similar shapes, so that the protruding portions are arranged on the left and right sides of FIG. 4 every other layer. It is pulled out to the end face in the direction. The protruding parts of the electrodes 13a to 13d drawn out every other layer in this way are electrically connected by external electrodes 15 and 16, respectively.

[Problems to be solved by the invention] Regarding the laminated piezoelectric element as described above,
Compared to the conventional flat plate type piezoelectric element 1, it is possible to greatly reduce impedance with the same size. However, when adjusting the frequency to vibrate to a desired resonance frequency, it is not possible to adopt a method of polishing the end face of the sintered body. That is, in the case of the laminated piezoelectric element 11 as shown in FIGS. 4 and 5, the external electrode 1
Since the external electrodes 5 and 16 are formed on the end faces of the sintered body, when the end faces are polished, the external electrodes 15 and 16 are removed, and the resonator cannot function as a resonator.

Therefore, an object of the present invention is to provide a multilayer piezoelectric element that utilizes a spread vibration mode that allows easy and reliable frequency adjustment.

[Means for Solving the Problems] The present invention uses a sintered body in which a plurality of ceramic green sheets are laminated via internal electrodes so as to overlap each other in the thickness direction, and are sintered integrally. It is a laminated piezoelectric element that utilizes a spreading vibration mode, and when viewed from the lamination direction, notches extending in the lamination direction are formed at at least two or more locations on the outer periphery of the sintered body, and the notches extend in the lamination direction. Only the ends of the internal electrodes to be connected are exposed, and a conductive part is formed to electrically connect the internal electrodes to be connected, and the outer periphery of the sintered body is polished. This is a piezoelectric element that allows frequency adjustment. Note that in the following description of this specification, the term "internal electrode" refers to
The term is defined to include not only electrodes formed between ceramic layers but also electrodes formed on the upper and lower surfaces of the sintered body.

The end portion of the internal electrode facing the notch has a width approximately equal to the maximum width of the notch and is formed to protrude outward from the central main region of the internal electrode, and the central main region of the internal electrode is Except for the protruding portion, the cutout may be formed closer to the center than the depth of the notch.

Further, the ends of the internal electrodes are exposed in the same notch in every other layer, so that every other layer can be electrically connected to each other by the same conductive part.

[Function] According to the present invention, the conductive part that electrically connects the internal electrodes to be connected is formed in the notch, and therefore the side where the notch is formed is equal to the thickness of the conductive part. Even if the end faces of the internal electrodes are polished, the electrical connection between the internal electrodes can be ensured.

[Description of Embodiments] FIG. 1 is a schematic perspective view of an embodiment of the present invention, and FIG. 6 is a plan view showing a plurality of ceramic green sheets used to obtain the embodiment shown in FIG. 1. It is a diagram.

As shown in FIG. 6, when producing the embodiment shown in FIG. 1, three ceramic green sheets 31a, 31b, and 31c are prepared. In addition,
On one side of each ceramic green sheet 31a...13c, there are electrode patterns 32a...3 serving as internal electrodes.
2c are formed respectively. Further, on the other side of the ceramic green sheet 31c, an electrode pattern 32 of the ceramic green sheet 31c is provided.
When viewed from side c, an electrode pattern 32d is formed having a shape as shown in FIG. Therefore, the ceramic green sheet 31c is drawn with imaginary lines.)

By the way, each electrode pattern 32a...32d is
Ceramic green sheets 31a...3, respectively.
The main area portion 3 has protrusions 33a...33d extending on one side of 1c, and has protrusions 33a...33d other than the protrusions 33a...33d.
4a...34d are ceramic green sheets 31
a...31c is formed closer to the center so as not to reach any of the sides of 31c. This distance will be described later.

The ceramic green sheets 31a...31c prepared as described above are laminated in the state shown in FIG. 6 and fired simultaneously to obtain a sintered body laminated with internal electrodes 32b and 32c interposed therebetween. be able to.

Next, a pair of notches extending in the stacking direction are formed in the outer peripheral portion of the sintered body thus obtained. As shown by the broken line in FIG.
3d and at the opposite side of each ceramic green sheet 31a...31c to the side where the protrusion is provided. That is, the two notches are formed on opposing side surfaces of the sintered body, each extending in the stacking direction.

By the way, the size of this notch is, for example, 6th
Broken line A on the ceramic green sheet 31a in the figure.
As shown, the maximum width is approximately equal to the width of the protrusion 33a of the electrode pattern 32a. Therefore, after the notch is formed in the sintered body, the end of the protruding portion 33a is exposed in the notch. On the other hand, the depth of the notch is determined by the distance X (sixth
(see figure). Therefore,
Even after the notches are formed, none of the portions of the electrode patterns 32a to 32d other than the protrusions 33a to 33d, that is, the main regions 34a to 34d, are located in the notches.

After the notches are formed as described above, conductive portions 36 and 37 are formed in the notches as shown in FIG. The conductive parts 36 and 37 can be formed, for example, by baking silver paste. The cross-sectional view of the example shown in FIG. 1 obtained in this way is
It is shown in FIG. As is clear from FIG. 7, each internal electrode 32a...32d has a conductive portion 3 at every other layer.
6 and 37 are electrically connected. Therefore, by applying a voltage from the conductive parts 36 and 37 to perform polarization treatment, each ceramic layer 31a...31c can be polarized in the direction shown by the arrow in FIG. 36,
When a voltage is applied through 37, spreading vibration is generated in the same way as the conventional laminated piezoelectric element shown in FIG.

By the way, the piezoelectric element 3 of the embodiment shown in FIG.
In No. 1, the conductive parts 36 and 37 that function to connect the internal electrodes 32a...32d are formed in the notches, so the conductive parts 36 and 37 are formed thickly in the notches, and the conductive parts 36 and 37 are formed thickly in the notches. Even if the side surfaces are polished by the thickness, the internal electrode 32a and the internal electrode 32
c, and the electrical connection between the internal electrodes 32b and 32d can be ensured. That is, as clearly illustrated in FIG. 7, it is possible to polish the end face by the thickness of the conductive parts 36 and 37 which will become the external electrodes. Therefore, it can be seen that, unlike the conventional laminated piezoelectric element shown in FIGS. 4 and 5, it is possible to easily adjust the frequency by polishing the end face.

In the above embodiment, since frequency adjustment is performed, even if the end face (side surface) of the sintered body is polished, the polishing does not reach the internal electrodes 32a to 32d. However, for reasons discussed below, frequency adjustments can be made almost independently of that.

Generally, the resonant frequency of a piezoelectric plate is determined by the sound speed (v) of waves traveling through the plate and the shape (length of the sides) of the plate. That is, the resonance frequency r=v/(2×side length), and the resonance frequency fr is inversely proportional to the side length of the piezoelectric plate. Therefore, as described above, by polishing the end surface (side surface) of the sintered body, the resonance frequency of the piezoelectric element can be adjusted.

As a supplementary explanation, in the sintered body,
The sound speed of the wave is different between the part sandwiched by the internal electrodes and the part not sandwiched. That is, the speed of sound v
is v=√1−, where ρ is the density and s is the elastic constant (compliance). Here, there is a difference in elastic constant between the part sandwiched by the internal electrodes and the part not sandwiched, but the difference is only about 10% at most. And since the speed of sound is inversely proportional to the square root of this,
At most, the difference is only about 5%. It is true that the speed of sound is determined by the overall equilibrium elastic constant brought about by the contribution of the elastic constants of the part sandwiched between the electrodes and the part not sandwiched between the electrodes. The sintered body included in the piezoelectric element 31 shown has a structure in which most of the sintered body is sandwiched between electrodes. Therefore, the average elastic constant and sound velocity of the entire sintered body are close to the elastic constant and sound velocity of the part sandwiched between the electrodes, respectively, and even if the part not sandwiched between the electrodes is removed by polishing, , the average elastic constant of the entire sintered body remains almost unchanged, and as a result, the resonant frequency depends almost exclusively on the dimensions of the sintered body.

What has been described above also applies to the following examples.

FIG. 8 is a schematic perspective view showing a second embodiment of the present invention, and FIG. 9 is a plan view showing each electrode pattern used to obtain the piezoelectric element of the embodiment shown in FIG. It is.

As is clear from FIGS. 8 and 9, two protrusions are formed in each of the electrode patterns 42a to 42d. for example,
The electrode pattern 42a has protrusions 43a and 53a formed on two mutually orthogonal sides of the ceramic green sheet 41a, respectively. Similarly,
Two protrusions 43b, 53b...43d, 53d are also formed in the other electrode patterns 42b...42d. Regarding the electrode pattern 42d,
Similar to the electrode pattern 32d shown in FIG. 6, it is drawn to show the state seen from above of the ceramic green sheet 42c, and therefore the ceramic green sheet 41c is shown with imaginary lines.

Each ceramic green sheet 4 shown in Figure 9
A sintered body can be obtained by simultaneously firing 1a...41c in the same manner as in the production of the embodiment shown in FIG. Here, notches are formed on the four sides of the sintered body in correspondence with the provision of two protrusions in each of the electrode patterns 42a...42d as described above. The position where this notch is formed is indicated by a broken line in FIG. The depth and width of this notch can be formed in the same manner as in the embodiment shown in FIG. 1 described above.

After forming the above-mentioned notches in the side surface of the sintered body, conductive parts 46, 47, 48, and 49 are formed in each of the notches. In this way, the piezoelectric element 41 shown in FIG. 8 can be obtained. Here, internal electrode 42a and internal electrode 42c are connected by conductive parts 46 and 48, and internal electrode 42b and internal electrode 42d are connected by conductive parts 47 and 49, respectively. Therefore, polarization can be performed by applying a voltage from either one of the conductive parts 46, 48 and one of the conductive parts 47, 49, and it is possible to drive in the same way. .

Furthermore, when polishing the end faces when adjusting the frequency, even if all the end faces of the piezoelectric element 41 shown in FIG. It is possible to obtain more ideal spreading vibration than in the embodiment shown in the figure.

FIG. 10 shows a cross-sectional view of the embodiment shown in FIG. 8, and even here, even if the conductive parts 46, 47 are polished by the thickness, the electrical connection between the internal electrodes 42a42c and 42b, 42d is ensured. I know what I'm getting. It goes without saying that even when cutting along a plane passing through the conductive parts 48 and 49, a similar cross section appears.

The amount of end face polishing in the piezoelectric element of the example shown in FIGS. 1 and 8 obtained as described above,
The relationship with the resonance frequency _r is shown in FIG. 11th
As is clear from the figure, it can be seen that a substantially linear relationship is established between the end face polishing amount and the resonance frequency _r in all the examples.

Also, in Figures 12 to 15, respectively,
The impedance-frequency characteristics of the conventional flat piezoelectric element shown in Fig. 2, the conventional multilayer piezoelectric element shown in Fig. 4, the embodiment shown in Fig. 1, and the embodiment shown in Fig. 8 are shown. . Figures 12 to 15
As is clear from the figure, the laminated piezoelectric element (Fig. 4,
It can be seen that in the examples shown in FIGS. 1 and 8), harmonics that become spurious waves of spreading vibration can be significantly reduced. In addition, the first embodiment which is an embodiment of this invention
It can be seen that the piezoelectric elements 31, 41 shown in FIG. 8 and FIG. 8 can also significantly reduce spurious noise based on thickness vibration that appears around 3.5 to 4.0×10 ³ kHz. This is considered to be because, in the piezoelectric elements 31 and 41 of the embodiments shown in FIGS. 1 and 8, spurious waves due to thickness vibration are suppressed by the node cuts.

In the above-described embodiments, the number of laminated ceramic layers was three, but it goes without saying that the present invention can be applied to piezoelectric elements having a larger number of layers. Furthermore, it goes without saying that the planar shape of the notch is not limited to an arcuate shape, but may be any other suitable shape such as a quadrangular shape.

In the above example, ceramic green sheets were stacked to form a laminate, which was fired to obtain a sintered body, and a notch extending in the stacking direction was formed on the outer periphery of the sintered body. The formed green sheets may be stacked with their notch positions aligned, and the laminate may be fired to obtain a sintered body having notches extending in the stacking direction.

In addition, using a large ceramic green sheet, holes corresponding to the above notches are formed in this green sheet in advance, and when the green sheets are stacked and fired and cut to obtain a single piezoelectric element, the holes pass through the holes. A plurality of single piezoelectric elements each having a notch extending in the stacking direction may be obtained by cutting at a certain position.

Further, the shape of the internal electrodes is not limited to that shown in the above embodiment, but has a shape slightly inward from the ceramic green sheets 61a, 61b, such as internal electrodes 62a, 62b shown in a plan view in FIG. It can also be used as a salad. That is, electrode 6
In 2a, the ceramic green sheet 61
The internal electrodes 62 correspond to the notches 63a and 73a of a.
A notch is also provided in the notch 63a, and an electrode protrusion 64a extending to the notch 63a is provided on one notch 63a side. Similarly, regarding the internal electrode 62b on the ceramic green sheet 61b, the notches 63b, 73
A protrusion 64 extending to one notch 73b of b.
form b. In this way, the internal electrodes 62a, 62
b is ceramic green sheet 61a, 61b
Since the notches 63b...73b are formed to extend outward from the innermost portions, the internal electrodes 62a, 62
It can be seen that the area b is increased, and therefore the piezoelectricity can be further enhanced.

More preferably, as shown in FIG. 17, by using internal electrodes 82a and 82b that extend to the edge of the ceramic green sheet except for the portions near the notches 83a, 93a, 83b, and 93b, the electrode area can be increased. Therefore, the piezoelectricity can be further enhanced.

[Effects of the Invention] As described above, according to the present invention, notches extending in the stacking direction are formed at at least two or more locations on the outer circumference of the sintered body when viewed from the stacking direction, and the cutouts extend in the stacking direction. Since only the ends of the internal electrodes to be connected are exposed, and a conductive part is formed to electrically connect the internal electrodes to be connected, polishing the sides allows easy and reliable connection. A piezoelectric element whose frequency can be adjusted can be obtained.

It should be pointed out that the piezoelectric element of the present invention is suitable for, for example, the second resonator of a Cedar type filter, but can also be used for other oscillators or resonators in general.

[Brief explanation of the drawing]

FIG. 1 is a schematic perspective view showing an embodiment of the present invention. FIG. 2 is a schematic perspective view showing an example of a conventional piezoelectric element. FIG. 3 is a cross-sectional view of the piezoelectric element shown in FIG. 2. FIG. 4 is a schematic perspective view showing another example of a conventional piezoelectric element. FIG. 5 is a sectional view of the piezoelectric element shown in FIG. 4. FIG. 6 is a plan view for explaining the electrode pattern used to create the embodiment shown in FIG. FIG. 7 is a sectional view of the embodiment shown in FIG. 1. FIG. 8 is a schematic perspective view showing a second embodiment of the invention. FIG. 9 is a plan view for explaining the electrode pattern used to create the embodiment shown in FIG. 8. FIG. 10 is a sectional view of the embodiment shown in FIG. 8. FIG. 11 is a diagram showing the relationship between the amount of end face polishing and the resonant frequency in an embodiment of the present invention. FIG. 12 is a diagram showing the impedance-frequency characteristics of the conventional piezoelectric element shown in FIG. 1. FIG. 13 is a diagram showing the impedance-frequency characteristics of the conventional piezoelectric element shown in FIG. 4. FIG. 14 is a diagram showing the impedance-frequency characteristics of the embodiment shown in FIG. 1. FIG. 15 is a diagram showing the impedance-frequency characteristics of the embodiment shown in FIG. 8. FIG. 16 is a plan view showing another example of the shape of the internal electrodes.
FIG. 17 is a plan view showing still another example of the shape of the internal electrodes. In the figure, 31 is a piezoelectric element, 31a...31c
3 is a ceramic layer, 32a...32d is an internal electrode, and 3
3a...33d are protruding parts, 34a...34d are main regions, 36, 37 are conductive parts, 41 is a piezoelectric element, 41
a...41c is a ceramic layer, 42a...42d are internal electrodes, 43a...43d, 53a...53d are protrusions, 44a...44d are main regions, 46, 47, 4
8, 49 are conductive parts, 61a, 61b are ceramic green sheets, 62a, 62b are internal electrodes, 6
3a, 63b, 73a, 73b are notches, 64a,
64b is a protrusion, 82a and 82b are internal electrodes, 8
3a, 83b, 93a, 93b are notches, 84a,
84b indicates a protrusion.

Claims (1)

[Scope of Claims] 1. Lamination using a spreading vibration mode using a sintered body in which a plurality of ceramic green sheets are laminated via internal electrodes so as to overlap each other in the thickness direction and sintered as one body. type piezoelectric element, when viewed from the stacking direction, cutouts extending in the stacking direction are formed at at least two or more locations on the outer circumferential part of the sintered body, and the cutouts include internal connections to be connected. Frequency adjustment is performed by polishing the outer periphery of the sintered body, in which only the ends of the electrodes are exposed and a conductive part is formed to electrically connect the internal electrodes to be connected. possible piezoelectric element. 2. The end portion of the internal electrode facing the notch is formed to protrude outward from the central main region with a width approximately equal to the maximum width of the notch, and the central main region of the internal electrode is formed to protrude outward from the central main region. 2. The frequency-adjustable piezoelectric element according to claim 1, wherein the piezoelectric element is formed closer to the center than the depth of the notch except for the formed end portion. 3. The internal electrode is notched at the notch portion in a shape that follows the notch, and the notch portion of the internal electrode to be connected is provided with a protrusion, so that the notch of the sintered body is provided with a protrusion. The frequency adjustable piezoelectric element according to claim 1, wherein the internal electrode is exposed. 4. The internal electrode extends to the end face of the sintered body except for a notch portion shaped to follow the notch of the sintered body, and the exposed width of the electrode protrusion is wider than the width of the notch of the sintered body. 4. The frequency-adjustable piezoelectric element according to claim 3, wherein the piezoelectric element is narrow. 5. Claims 1 to 4, wherein the internal electrodes have their ends exposed in the same notch in every other layer, and are thereby electrically connected to each other by the conductive part. The frequency-adjustable piezoelectric element according to any one of paragraphs.