JPH0251908A - Piezoelectric resonator - Google Patents

Abstract

PURPOSE:To give damping to the thickness vibration and to reduce a spurious level based on the thickness vibration by using a sintered body having at least two piezoelectric ceramic layers with different porosity. CONSTITUTION:Piezoelectric ceramic layers 2-4 are laminated in the sintered body 1 in the broadwise direction and the middle piezoelectric ceramic layer 3 is made of a porous layer having porosity with diameter of 10-100mum and the piezoelectric ceramic layers 2, 4 at both sides are made of dense piezoelectric ceramic sintered layers. Then the entire sintered body 1 is subject to polarization treatment in a direction orthogonal to the broadwise direction. Since the piezoelectric ceramic layer 3 with different porosity is provided, in the case of utilizing the spread vibration, the spurious level based on the thickness longitudinal vibration is reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an improvement of a piezoelectric resonator device that utilizes imaging due to a piezoelectric transverse effect such as spreading vibration, and in particular to a structure that suppresses spurious waves based on thickness vibration. Concerning what is provided.

[Conventional technology]

Conventionally, kHz band filters and oscillators that utilize the spreading vibration of piezoelectric ceramics such as lead zirconate titanate have been widely used.

This type of piezoelectric resonator includes one in which electrodes are formed on both sides of a piezoelectric ceramic, and a multilayer type in which piezoelectric ceramic layers are laminated via internal electrodes.

[Technical problem to be solved by the invention] However,
In the impedance-frequency characteristics of this type of piezoelectric resonator, as shown in Fig. 2, the peak A based on the spreading vibration is
In addition, a response B occurs due to relatively large thickness vibrations. That is, when spreading vibration is used, thickness vibration is inevitably induced, and the response level based on this thickness vibration becomes a large spurious.

In applications such as ultrasonic sensors, piezoelectric output coefficient g8. However, by changing the composition of the piezoelectric material, the piezoelectric constant d! can be increased. When 2 is increased, the dielectric constant tsx also increases to -m. Therefore, it is difficult to increase the piezoelectric output coefficient g0 by changing the composition.

Therefore, an object of the present invention is to be able to effectively reduce spurious waves due to thickness vibration when using vibrations due to transverse effects such as spreading vibrations, and to achieve large power output in applications such as ultrasonic sensors. An object of the present invention is to provide a piezoelectric resonator device having a structure that can realize the following.

[Means for solving technical problems]

The present invention provides a piezoelectric resonator that utilizes vibration based on a transverse effect such as a spreading vibration mode, which includes a sintered body having at least two piezoelectric ceramic layers having different porosity and arranged so as to overlap in the thickness direction; It is characterized by comprising an electrode provided on the surface of this sintered body.

The at least two piezoelectric ceramic layers having different porosity and arranged so as to overlap in the thickness direction can be constructed by using one or more of the piezoelectric ceramic layers as a porous layer. In order to form this porous layer, a substance that can be scattered during sintering, such as carbon or an organic binder, may be added to the piezoelectric ceramic green sheet before sintering and then fired.

Furthermore, as is clear from the following examples, among the piezoelectric ceramic layers having different porosities, the layer with the highest porosity is 5
It is preferable to form a layer with a porosity of ~10%, and the remaining piezoelectric ceramic layers to be composed of a dense normal sintered body layer.
If it is less than 10%, the effect of reducing the spurious level based on thickness vibration will not be sufficient, and if it exceeds 10%, the electrical characteristics such as relative dielectric constant, frequency constant, and electromechanical coupling coefficient of spread vibration will gradually deteriorate. This is because it is not desirable.

[Effect]

In the present invention, since a sintered body having at least two piezoelectric ceramic layers having different porosity is used, thickness vibrations are effectively damped by the piezoelectric ceramic layer having a large porosity. Therefore, it is possible to effectively reduce the spurious level based on thickness vibration.

[Explanation of Examples]

FIG. 1 is a sectional view of a piezoelectric resonator device according to an embodiment of the present invention. In FIG. 1, piezoelectric ceramics J12 to J4 are arranged in the thickness direction in the sintered body l. Here, the central piezoelectric ceramic layer 3 is composed of a porous layer having pores with a diameter of 10-100 μm, and the piezoelectric ceramic layers 2.4 on both sides are composed of dense piezoelectric ceramic sintered bodies. The entire sintered body 1 is polarized in a direction perpendicular to the thickness direction. Note that 5 and 6 indicate electrodes for driving.

In this embodiment, as is clear from the detailed explanation below, since the piezoelectric ceramic layer 3 with different porosity is provided, when using the spreading vibration, the spurious level based on the longitudinal thickness vibration can be effectively reduced. It is believed that it is possible to reduce the

This example will be described in more detail with reference to the manufacturing process of the example shown in FIG.

First, a plurality of first piezoelectric ceramic green sheets are prepared by a normal doctor blade method. On the other hand, an equal volume of organic powder (
A second piezoelectric ceramic green sheet is prepared by the same doctor blade method using a slurry obtained by mixing materials that can be scattered at the firing temperature of the ceramic sintered body.

Above mentioned 1. As shown in FIG. 3, the second ceramic green sheets were overlapped to a desired thickness, pressed together, and then fired to obtain a sintered body. In addition, in FIG. 3, the green sheet indicated by reference number 7.8 is
The first ceramic green sheet, designated by reference number 9, is the second ceramic green sheet.

The sintered body obtained as described above was subjected to polarization treatment, and then electrodes were formed on both surfaces to obtain the piezoelectric resonator shown in FIG. 1.

In addition, as shown in FIG. 3, the first ceramic green sheets 7, 7..., the second ceramic green sheets 9, 9..., and the first ceramic green sheets 8
, 8, . . . can be laminated continuously by using a laminating apparatus shown in FIG. 4, for example. That is, as shown in FIG. 4, the rollers 11 and 12 rotated in the direction of the arrow X shown in the figure are brought relatively close to each other.
At least one of the rollers 11 and 12 is rotated while being pressed against the other side. Between such rollers 11 and 12,
1st. If the second ceramic green sheets 7 to 9 are supplied as shown in the figure (in FIG. 4, one ceramic green sheet 7 to 9 is shown for ease of illustration, but in reality A number of green sheets corresponding to the number of stacked sheets are supplied between rollers 11 and 12.), rollers 11,
12 to obtain a laminated sheet 13.

In addition, 1. The second ceramic green sheets 7 to 9 must be formed into a sheet shape and dried in advance, but it is desirable to apply water to the sheet surface in advance when pressing and laminating them between the rollers 11 and 12. This is because the binder contained in the ceramic green sheet is water-soluble, and therefore, if water is applied to the surface, pressure bonding becomes easier.

As mentioned above, using the rollers 11 and 12 shown in FIG. 4, a laminate of sheets of different materials can be easily obtained by extrusion molding.

However, in order to form piezoelectric ceramic layers having different porosity using the piezoelectric resonator of the present invention, it is not necessarily necessary to use the laminating apparatus shown in FIG. 4. As shown in FIG. The first cut rectangle. The second ceramic green sheets 7 to 9 may be stacked one on top of the other and pressed together from above and below using an arbitrary pressure device to obtain a molded body, and the molded body may be sintered.

Next, specific experimental results of the embodiment shown in FIG. 1 will be explained. In FIG. 3, the number of laminated ceramic green sheets (7, 8, and 9) is T.

Among T,,T', let,T,-T',T,/T,
Various piezoelectric resonant devices were obtained by changing the . In this way, the impedance-frequency characteristics were investigated when the ratio of the number of 11 layers of the second ceramic green sheets 9 to the number of stacked layers of the first ceramic green sheets 7 or 8 was changed. The results are shown in Figure 5.

Figure 5 shows the peak-to-valley ratio of the spread vibration and thickness vibration when varying T, /T, 20Xj! og [(impedance value at anti-resonant frequency/impedance value at resonant frequency)].

As is clear from Fig. 5, compared to when T is 0 (corresponding to the conventional example), as T increases, the response of the spreading vibration does not change much, but the peaks and valleys due to the thickness longitudinal vibration do not change much. It can be seen that the ratio decreases rapidly as Th increases.

Therefore, it can be seen from FIG. 3 that when the number of laminated second ceramic green sheets 9 for forming a porous layer is increased, spurious noise due to thickness vibration can be reduced. However, as is clear from Figure 5, Th
/T- exceeds 0.5, the effect of reducing spurious noise based on thickness vibration approaches the saturation point. On the other hand,
The peak-to-valley ratio of the spreading vibration also decreases slightly as T, /T, increases, so if both are taken into account, T, /T, becomes 0.
．． It is thought that it is preferable that it is 5 or less.

Further, in the embodiment of FIG. 1, changes in relative dielectric constant e and piezoelectric output coefficient g0 with respect to the lamination ratio of FIG. 3, that is, T, /T, are shown in FIG.

As is clear from FIG. 7, in this example, the value of the piezoelectric output coefficient g is more than twice that of a normal piezoelectric resonator (1-0) that does not include a porous layer. Therefore,
It becomes possible to configure high-performance pressure sensors, ultrasonic microphones, etc.

In the example shown in Fig. 1, the piezoelectric ceramic layer 3 with high porosity is formed in the center, but unlike the sintered body in which two or more piezoelectric ceramic layers with high porosity are laminated inside, Even if a sintered body is used in which a piezoelectric ceramic layer with a high porosity is provided on both sides of a piezoelectric ceramic layer with a high porosity, spurious noise due to longitudinal thickness vibration can be similarly reduced. Examples of these structures are shown in FIGS. 8 and 9.

In the embodiment shown in FIG. 8, porous piezoelectric ceramic layers 25, 26 with high porosity are laminated within the sintered body 21 between dense piezoelectric ceramic layers 22, 23, 24.

Note that 27 and 28 indicate electrodes.

In addition, in the sintered body 31 shown in FIG. 9, a dense piezoelectric ceramic layer 32 is formed at the center in the thickness direction, and piezoelectric ceramic layers 33 and 34 with relatively high porosity are laminated on both sides of the dense piezoelectric ceramic layer 32. . 35 and 36 indicate electrodes.

The sintered bodies 21.31 shown in FIGS. It is obtained by selecting the number of second ceramic green sheets to have the thickness shown in FIGS. 8 and 9, laminating them, and sintering them.

FIG. 10 is a diagram showing the relationship between the peak-to-valley ratio of the thickness *i motion and Tl/Ta in the embodiment shown in FIGS. 8 and 9. FIG.

1. 'rb/T' corresponds to the thickness of the porous piezoelectric ceramic layer 25 or 26 with high porosity in the structure shown in FIG. 8, and T corresponds to the thickness of the central dense piezoelectric ceramic layer 21. . Similarly, in the structure of FIG. 9, T is the thickness of the high-porosity piezoelectric ceramic N33.34 on both sides,
T corresponds to the thickness of the central dense piezoelectric ceramic Ji32.

In each of the embodiments shown in FIGS. 8 and 9, the porous piezoelectric ceramic layer 25.26 or 33.34 was used, so as is clear from FIG. It can be seen that as /T- increases, it decreases rapidly.

Next, specific experimental examples will be explained.

A mixture of lead zirconate titanate piezoelectric ceramic powder, 4% by weight of methylcellulose binder, 3% by weight of glycerin as a plasticizer, and 10% by weight of water (pure water) was mixed with three rolls. went. Thereafter, a 0.2 m first green sheet was extruded using a vacuum extruder, dried using a film dryer, and wound into a roll.

Next, the same kind and amount of binder, glycerin, and water were added to the same lead zirconate titanate piezoelectric ceramic powder, and then 3% by weight of insoluble cellulose was mixed and kneaded with three rolls. A second green sheet having a thickness of 0.2 mm was extruded and wound into a roll in the same manner as the first green sheet.

1. obtained as above. The second green sheet was pressed and laminated between the rolls 11 and 12 of the laminating apparatus described above to obtain a laminated sheet.

In addition, upon lamination, water was applied to the surface of each green sheet in advance. Also, between rolls 11 and 12,
Both ceramic green sheets were crimped together so that a pressure of 1Q kg/cj was applied.

The obtained laminated green sheet was punched out into 30 mm squares, stored in an alumina box, and fired at a temperature of 1160° C. for 2 hours. Silver paste was applied to the surface of the obtained sintered body, and 8
The electrode was baked at a temperature of 0.000C for 0.5 hours to form an electrode.

Furthermore, polarization was performed using a DC electric field of 3 kV/-, and 15
After drying at 0'C for 0.5 hours, impedance-frequency characteristics were measured. As a result, the impedance-frequency characteristics shown in FIG. 6 were obtained.

The impedance value at the anti-resonant frequency was reduced to 115 compared to the conventional one, and the resonant impedance value was, on the contrary, about 10 times as large. Therefore, it can be seen that damping of thickness longitudinal vibration is effectively performed.

After mixing and kneading 4% by weight of methylcellulose binder, 3% by weight of glycerin as a plasticizer, and 100% by weight of water into lead zirconate titanate-based piezoelectric ceramic powder, the mixture was kneaded using a vacuum extruder. The sheet was extruded, dried and wound into rolls.

On the other hand, a certain weight of water-insoluble cellulose was kneaded into a 5% aqueous solution of methylcellulose to prepare a sheet adhesive. The reason why water-insoluble cellulose was mixed is to form a layer with high porosity in the sintered body.

Prepare two of the ceramic green sheets described above, apply the sheet adhesive described above to the surface of each sheet by squeegee printing, etc., and press and press with a pressure of IL/cd using a pressure roller to form a laminated sheet. I got it.

The obtained laminated sheet was cut out into a 30+m++ square, and fired at a temperature of 1160°C for 2 hours using an alumina mold to obtain a sintered body with a thickness of 500 μm and a porous layer with a thickness of 20 to 3 otIm formed in the center. Ta. A silver paste was applied to the surface of the sintered body and baked at a temperature of 760° C. for 30 minutes to form an electrode.

Next, the film was polarized in the thickness direction using a DC electric field of 3 kV/power for 30 minutes, and after drying at 150° C. for 30 minutes, the characteristics of spreading vibration and thickness vibration were measured.

As a result, the results shown in FIGS. 11(a) to (d) were obtained. In other words, when the porosity of a high-porosity part constructed using a sheet adhesive is 5 to 10%, the spurious level based on longitudinal thickness vibration is less than OdB, and the level of spreading vibration is also low. It can be seen that it is possible to maintain the range without deterioration.

Note that if the porosity of the porous piezoelectric ceramic layer is 5% or less, the spurious level of longitudinal thickness vibration will be a positive value (see Figure 11 (a)), and if it is 10% or more, the spurious level will be positive. , dielectric constant, frequency constant and electromechanical coupling coefficient (
The deterioration of characteristics such as (spreading vibration) will increase, making it impossible to obtain what is needed. Therefore, the porosity of the porous piezoelectric ceramic layer is preferably 5 to 10%.

[Effects of the Invention] As described above, in the present invention, a piezoelectric resonator is constructed using a sintered body in which piezoelectric ceramic layers having different porosities are laminated, so that piezoelectric transverse effects such as spreading vibrations are avoided. When using the vibration based on this, it becomes possible to effectively reduce the spurious caused by the thickness longitudinal vibration, which has been unavoidable. Also, the piezoelectric output coefficient g. can be effectively increased, making it possible to obtain high-performance ultrasonic microphones, pressure sensors, etc.

[Brief explanation of the drawing]

Figure 1 is a sectional view of an embodiment of the present invention, Figure 2 is a diagram showing the impedance-frequency characteristics of a conventional example, and Figure 3 is a perspective view of a ceramic green sheet used to construct the embodiment of Figure 1. , FIG. 4 is a schematic side view showing a laminating apparatus for laminating ceramic green sheets, and FIG. 5 is a schematic side view showing a laminating apparatus for laminating ceramic green sheets.
A diagram showing changes in the peak-to-valley ratio of spreading vibration and thickness vibration when the laminated number ratio of ceramic green sheets is changed,
FIG. 6 is a diagram showing the impedance-frequency characteristics of Example 1, and FIG. 7 is the piezoelectric output coefficient gzs and T, /T. , FIG. 8 is a cross-sectional view showing another embodiment of the present invention, FIG. 9 is a cross-sectional view showing still another embodiment of the present invention, and FIG. 10 is a cross-sectional view showing another embodiment of the present invention. Figure 9 is a diagram showing the relationship between the peak-to-valley ratio of thickness longitudinal vibration and T b / T in the example,
FIGS. 11(a) to 11(d) are diagrams showing the characteristics of Example 2. In the figure, 1,21.31 is a sintered body, 2,422.2
3.24 is a dense piezoelectric ceramic layer, 3°25.26.
32 is a porous piezoelectric ceramic layer, 5.6, 27.2
8, 35, and 36 indicate electrodes. Figure 1 Figure 2 Tomo Suku Number Figure 6 Figure 6 Area Pos Figure 5 Tb /Ta Figure 7 θ ρ, 5 7b/Ta Figure 9 Figure 1 O θ, 5 Down/Down a

Claims (1)

[Scope of Claim] A piezoelectric resonator device that utilizes vibration caused by a piezoelectric transverse effect, comprising: a sintered body having at least two layers of piezoelectric ceramics having different porosity and arranged so as to overlap in the thickness direction;
and an electrode provided on the surface of the sintered body.