JP2006237218A - Piezoelectric element and stacked piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tight piezoelectric element or stacked piezoelectric element of good piezoelectric characteristics in which an electrode layer and a piezoelectric sintered body main component of niobic acid alkali metal are provided by simultaneous sintering. <P>SOLUTION: A stacked piezoelectric element 1 comprises a piezoelectric sintered body layer 2 whose main component is niobic acid alkali metal, and internal electrode layers 3A and 3B which are formed by simultaneous sintering with it and laminated alternately. The internal electrode layers 3A and 3B comprise Pt, and the piezoelectric sintered body layer 2 is tight. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a piezoelectric element and a multilayer piezoelectric element.

  Conventionally, piezoelectric elements using piezoelectric ceramic compositions have been used in various fields such as vibration detection applications, pressure detection applications, piezoelectric actuators, and piezoelectric devices. Among them, the laminated piezoelectric element is used as a piezoelectric actuator such as precision positioning or a fuel injection device, or a sensor such as a vehicle-mounted sensor (for example, a knocking sensor or a combustion pressure sensor).

By the way, as such a piezoelectric ceramic composition, a piezoelectric ceramic composition containing lead such as lead zirconate titanate is often used.
However, in consideration of the influence of lead on the environment, high-performance lead-free piezoelectric ceramic compositions have been developed. One of them is a piezoelectric ceramic composition (see Patent Document 1) mainly composed of an alkali metal niobate oxide.
On the other hand, as an electrode material used for the piezoelectric ceramic composition, an electrode material containing a large amount of Ag, such as Ag or Ag-Pd, is often used because of cost, conductivity, and the like.

International Publication No. WO2004 / 106264

However, the inventors have included a large amount of Ag as an electrode layer in a piezoelectric element or laminated piezoelectric element provided with a piezoelectric sintered body mainly composed of alkali metal niobate and an electrode layer by simultaneous sintering. It has been found that when an electrode material is used, a porous piezoelectric sintered body (piezoelectric sintered body layer) in which a large number of pores remain is obtained, and piezoelectric characteristics and mechanical strength are lowered. This is considered that the sinterability of the piezoelectric sintered body (piezoelectric sintered body layer) was lowered by Ag in the electrode layer.
The present invention has been made on the basis of such knowledge, and is a piezoelectric element or a laminated piezoelectric element in which a piezoelectric sintered body mainly composed of an alkali metal niobate and an electrode layer are provided by simultaneous sintering. An object of the present invention is to provide a dense piezoelectric element or a laminated piezoelectric element having good piezoelectric characteristics.

  The solution is a piezoelectric sintered body mainly composed of alkali metal niobate, and an electrode layer formed by simultaneous sintering with the piezoelectric sintered body and in contact with the piezoelectric sintered body, wherein Pt, Pd And an electrode layer having an Ag content of less than 10 mol% (including 0).

As described above, when a piezoelectric sintered body mainly composed of an alkali metal niobate is simultaneously sintered together with an electrode layer containing a large amount of Ag such as Ag or 70Ag-30Pd, a large amount of Ag is used. It has been found that the sintering of the piezoelectric sintered body is hindered and it is difficult to obtain a dense piezoelectric sintered body.
On the other hand, in the piezoelectric element of the present invention, Ag that lowers the sinterability of the piezoelectric sintered body mainly containing at least one of Pt and Pd as the electrode layer and containing the alkali metal niobate as the main component. In a composition containing less than 10 mol% or no Ag.
Therefore, the piezoelectric element which can suppress the sinterability fall about a piezoelectric sintered compact by a large amount of Ag, has a dense piezoelectric sintered compact and an electrode layer, and has a favorable piezoelectric characteristic and mechanical characteristics. Can be obtained. In addition, since the electrode layer does not contain a large amount of Ag, there is an advantage that the migration resistance is excellent.

Examples of the alkali metal in the alkali metal niobate include K, Na, and Li. Examples of the alkali metal niobate include KNbO ₃ , NaNbO ₃ , (K _x Na _1-x ) NbO ₃ (where 0 <x <1), (K _x Li _y Na _1-xy ) NbO ₃ ( However, a perovskite oxide represented by 0 <x <1, 0 <y <1, 0 <x + y <1) can be given. In addition, there may be mentioned those obtained by substituting part of Nb of these oxides with Ta or Sb. Furthermore, the alkali metal niobate that is a perovskite oxide may have a composition in which elements located at the A site are partially lost.
In addition to the alkali metal niobate, the piezoelectric sintered body should contain auxiliary components such as CaTiO ₃ , NiO, CuO, BaTiO _{3 in} order to improve piezoelectric characteristics or to improve sinterability. Can do.

In the above-described piezoelectric element, the electrode layer is preferably a piezoelectric element that does not substantially contain Ag. This is because, by not using Ag that lowers the sinterability of the piezoelectric sintered body for the electrode layer, the piezoelectric sintered body can be sintered more reliably and densely.
Note that “substantially free of Ag” means that it does not contain intentionally added Ag, and is intended to allow when a very small amount of Ag is included as an inevitable impurity.

  Another solution is a dense piezoelectric sintered body mainly composed of alkali metal niobate and an electrode layer formed by simultaneous sintering with the piezoelectric sintered body and in contact with the piezoelectric sintered body. And an electrode layer mainly composed of at least one of Pt and Pd.

  In the piezoelectric element of the present invention, the electrode layer has at least one of Pt and Pd as a main component, and the piezoelectric sintered body is dense. In this piezoelectric element, a decrease in sinterability of the piezoelectric sintered body due to Ag can be suppressed, and the piezoelectric element has good piezoelectric characteristics and mechanical characteristics.

  Still another solution is a piezoelectric sintered body layer mainly composed of alkali metal niobate, and an electrode layer formed by simultaneous sintering with the piezoelectric sintered body layer and in contact with the piezoelectric sintered body layer. , Pt, Pd as a main component, and an Ag layer having an Ag content of less than 10 mol% (including 0), and a stacked piezoelectric element that is alternately stacked.

In the multilayer piezoelectric element of the present invention, as the electrode layer, Ag that lowers the sinterability of a piezoelectric sintered body layer mainly containing at least one of Pt and Pd and having an alkali metal niobate as a main component. The composition contained less than 10 mol% or no Ag.
Therefore, a decrease in sinterability of the piezoelectric sintered body layer due to a large amount of Ag can be suppressed, and a dense piezoelectric sintered body layer and an electrode layer are alternately laminated to provide excellent piezoelectric characteristics and mechanical characteristics. It is possible to obtain a laminated piezoelectric element having In addition, since the electrode layer does not contain a large amount of Ag, there is an advantage that the migration resistance is excellent.

  Still another solution is a dense piezoelectric sintered body layer mainly composed of an alkali metal niobate, and an electrode formed by simultaneous sintering with the piezoelectric sintered body layer and in contact with the piezoelectric sintered body layer This is a multilayer piezoelectric element in which electrode layers mainly composed of at least one of Pt and Pd are alternately laminated.

  In the multilayer piezoelectric element of the present invention, as the electrode layer, at least one of Pt and Pd is a main component, and the piezoelectric sintered body layer is dense. Therefore, in this multilayer piezoelectric element, a decrease in sinterability of the piezoelectric sintered body layer due to Ag can be suppressed, and a multilayer piezoelectric element having good piezoelectric characteristics and mechanical characteristics can be obtained.

  Of the embodiments of the present invention, a laminated piezoelectric element will be described in Example 1, and a ring-type piezoelectric element will be described in Example 2.

  The laminated piezoelectric element according to Example 1 will be described with reference to FIGS. As shown in FIG. 1, the multilayer piezoelectric element 1 of Example 1 has a substantially rectangular parallelepiped shape having four side surfaces 1A, 1B, 1C, and 1D. Out of the four side surfaces 1A, 1B, 1C, and 1D, extraction electrodes 4A and 4B that are mainly composed of Ag and extend linearly are formed on the opposing extraction electrode formation surfaces 1A and 1B.

  As shown in FIG. 2, the multilayer piezoelectric element 1 has a form in which flat piezoelectric sintered body layers 2 and internal electrode layers 3A and 3B are alternately laminated. Further, the internal electrode layers 3A and the internal electrode layers 3B are alternately arranged. Of these, the internal electrode layer 3A is pulled down from the extraction electrode formation surface 1B, but is exposed to the extraction electrode formation surface 1A, and is electrically connected to the extraction electrode 4A formed on the extraction electrode formation surface 1A. . On the contrary, the internal electrode layer 3B is pulled down from the extraction electrode formation surface 1A, but is exposed to the extraction electrode formation surface 1B, and is electrically connected to the extraction electrode 4B formed on the extraction electrode formation surface 1B. is doing.

In the multilayer piezoelectric element 1, the piezoelectric sintered body layer 2 is made of a piezoelectric ceramic composition mainly composed of an alkali metal niobate. Specifically, the charged composition has a composition in which CuO and NiO are added to a perovskite oxide represented by the chemical formula 0.95 (K _0.50 Na _0.45 ) NbO ₃ —0.05CaTiO ₃ . Note that the perovskite oxide represented by the above chemical formula has a composition in which a part of the Na amount is lost stoichiometrically. In addition, the amount of O in the chemical formula (K _0.50 Na _0.45 ) NbO ₃ is expressed stoichiometrically, and actually, the value is shifted according to the shift of the Na amount from the stoichiometric composition. It is thought that.
The internal electrode layers 3A and 3B are both made of Pt and substantially free of Ag.

  FIG. 3 shows the state of the cross section of the piezoelectric sintered body layer 2 and the internal electrode layers 3A and 3B shown by part E in FIG. 2 in the multilayer piezoelectric element 1 of the first embodiment. As can be seen from this figure, in the multilayer piezoelectric element 1 of Example 1, the piezoelectric sintered body layer 2 has almost no voids, and the piezoelectric sintered body layer 2 is dense. I understand. Therefore, the mechanical strength such as compressive strength and tensile strength of the piezoelectric sintered body layer 2 is also high. In addition, in such a multilayer piezoelectric element 1, for example, the piezoelectric characteristics such as d33 are sufficiently obtained by sufficiently obtaining the characteristics that can be obtained from the composition of the piezoelectric ceramic composition.

  In the case where the composition of the internal electrode layer is made of Pd, similarly, the piezoelectric sintered body layer has almost no voids, and the piezoelectric sintered body layer becomes dense, and the mechanical strength and It has been confirmed that the piezoelectric characteristics are also good.

  On the other hand, in the multilayer piezoelectric element 1 of Example 1, the multilayer piezoelectric element 101 according to Comparative Example 1 was produced by replacing only the composition of the internal electrode layers 103A and 103B with 70Ag-30Pd. FIG. 4 shows a cross-sectional view of a portion corresponding to the portion E of FIG. 2 in the piezoelectric sintered body layer 102 and the internal electrode layers 103A and 103B of the multilayer piezoelectric element 101 according to the comparative example 1. As can be seen from this figure, in the multilayer piezoelectric element 101 of Comparative Example 1, it can be seen that the piezoelectric sintered body layer 102 has a large number of pores PO and is porous. Since the piezoelectric sintered body layer 102 is porous, mechanical strength such as compressive strength and tensile strength is insufficient. Further, in such a multilayer piezoelectric element 101, for example, the piezoelectric characteristics such as d33 can be obtained with extremely low characteristics as compared with the characteristics that would be obtained from the composition of the piezoelectric ceramic composition. In order to make the piezoelectric sintered body layer 102 dense rather than porous, a sample with a high firing temperature was made, but it was still confirmed that the piezoelectric sintered body layer 102 could not be densified.

  In addition, even when the composition of the internal electrode layer is made of Ag, it has been confirmed that the piezoelectric sintered body layer is porous with a large number of pores PO.

  As described above, when a large amount of Ag is present in the internal electrode layer, the reason why a large number of pores PO are generated in the piezoelectric sintered body layer is not clear. However, if a large amount of Ag is present in the internal electrode layer, a large amount of Ag is baked in the piezoelectric ceramic composition during simultaneous sintering with the piezoelectric ceramic composition mainly composed of alkali metal niobate. It is understood that it produces an action that inhibits ligation.

  On the other hand, when the Pt is used as the composition of the internal electrode layers 3A and 3B as in the laminated piezoelectric element 1 of the first embodiment, or the internal electrode layer mainly composed of Pd, and further Pt and Pd. It can be seen that the piezoelectric sintered body layer 2 of the multilayer piezoelectric element 1 can be made dense, and the mechanical characteristics and piezoelectric characteristics can also be improved.

  In the laminated piezoelectric element 1 of Example 1, a piezoelectric ceramic composition mainly composed of alkali metal niobate was used for the piezoelectric sintered body layer 2, and internal electrode layers 3A and 3B made of Pt were used. Is manufactured by employing a known method for manufacturing a multilayer piezoelectric element.

  That is, a prepared powder obtained by adding 0.25 parts by weight of CuO powder and NiO powder to 100 parts by weight of the starting material powder prepared so as to be a perovskite type oxide represented by the above chemical formula at 1 to 600 ° C. After calcining for 10 hours, a polyvinyl butyral resin and dibutyl phthalate are mixed and pulverized, a green sheet is produced by a known doctor blade method, and then cut into a predetermined shape (for example, 150 mm □). On the other hand, a conductive paste is prepared by previously mixing and kneading Pt powder, ethyl cellulose, butyl carbidol or terpineol, and a conductive paste layer having a predetermined pattern is formed by screen printing on the green sheet having the predetermined shape. This conductive paste layer becomes an internal electrode layer after sintering. Next, a required number of green sheets on which the conductive paste layer is formed are stacked and pressed to form a laminate. From this laminate, a prismatic unfired multilayer piezoelectric element is cut out and degreased and sintered at 1000 to 1200 ° C. Thereby, the piezoelectric sintered body layer 2 and the internal electrode layers 3A and 3B are simultaneously sintered. After sintering, side surfaces 1A, 1B, 1C, and 1D are surface ground to adjust each dimension, and an Ag paste is applied to extraction electrode forming surfaces 1A and 1B, and baked at 600 to 800 ° C. to extract electrodes 4A and 4B. Form. The electrode for polarization is brought into contact with the extraction electrodes 4A and 4B, or the lead wire is taken out from the extraction electrodes 4A and 4B, and the direct current is connected between the extraction electrodes 4A and 4B, and therefore between the internal electrode layers 3A and 3B. A voltage is applied to polarize the piezoelectric sintered body layer 2.

  Next, a ring-type piezoelectric element according to Example 2 will be described with reference to FIG. The ring-type piezoelectric element 11 of Example 2 is formed by ring-shaped piezoelectric sintered body 12 having a through-hole 12H in the center, and simultaneous sintering with the piezoelectric sintered body 12. It has ring-shaped electrode layers 13A and 13B in contact with the lower surface.

Of this ring-type piezoelectric element 11, the piezoelectric sintered body 12 is also made of a piezoelectric ceramic composition containing an alkali metal niobate as a main component, as in Example 1. Specifically, the charged composition has a composition in which CuO and NiO are added to a perovskite oxide represented by the chemical formula 0.95 (K _0.50 Na _0.45 ) NbO ₃ —0.05CaTiO ₃ . The perovskite oxide represented by the above chemical formula also has a composition in which some defects are stoichiometrically generated with respect to the amount of Na, as in Example 1. In addition, the amount of O in the chemical formula (K _0.50 Na _0.45 ) NbO ₃ is expressed stoichiometrically, and actually, the value is shifted according to the shift of the Na amount from the stoichiometric composition. It is thought that.
The electrode layers 13A and 13B are both made of Pt and substantially free of Ag.

  Also in the piezoelectric element 11 of the second embodiment, as in the stacked piezoelectric element 1 of the first embodiment (see FIG. 3), the piezoelectric sintered body 12 has almost no holes, and the piezoelectric sintered body 12 is dense. It became quality. Accordingly, the piezoelectric sintered body 2 has high mechanical strength such as compressive strength and tensile strength. Also, with this piezoelectric element 11, for example, with respect to piezoelectric characteristics such as kr, sufficient characteristics that would be obtained from the composition of the piezoelectric ceramic composition were obtained, and good piezoelectric characteristics were obtained.

  On the other hand, the piezoelectric element 111 according to Comparative Example 2 was manufactured by replacing only the composition of the electrode layer with that composed of 70Ag-30Pd. Then, as in the above-described Comparative Example 1 (see FIG. 4), in this piezoelectric element 111, the piezoelectric sintered body 112 had a large number of pores PO and was porous. Since the piezoelectric sintered body 112 is porous, mechanical strength such as compressive strength and tensile strength is insufficient. Further, regarding the piezoelectric characteristics such as kr, only extremely low characteristics were obtained as compared with the characteristics that would be obtained from the composition of the piezoelectric ceramic composition. As in Comparative Example 1, a prototype with a high firing temperature was made in order to make the piezoelectric sintered body layer 112 dense rather than porous, but the piezoelectric sintered body layer 112 still cannot be densified. It has been confirmed.

  If a large amount of Ag is present in the electrode layers 113A and 113B as in Comparative Example 2, the cause of the large number of holes PO in the piezoelectric sintered body 12 is not clear. However, if Ag is present in a large amount in the electrode layer 113A or the like, Ag present in a large amount is sintered in the piezoelectric ceramic composition upon simultaneous sintering with the piezoelectric ceramic composition mainly composed of alkali metal niobate. It is understood that it produces an action that inhibits ligation.

  On the other hand, when the Pt is used as the composition of the electrode layers 13A and 13B as in the piezoelectric element 11 of the second embodiment, or when an electrode layer mainly composed of Pd and further Pt and Pd is used. It can be seen that the piezoelectric sintered body 12 of the piezoelectric element 11 can be made dense, and the mechanical characteristics and piezoelectric characteristics can also be improved.

In the above, the present invention has been described with reference to the first and second embodiments. However, the present invention is not limited to the above-described embodiments and the like, and it can be applied as appropriate without departing from the scope of the present invention. Not too long.
For example, in Examples 1 and 2, (K _0.50 Na _0.45 ) NbO ₃ was used as the alkali metal niobate, but the composition ratio of K and Na was changed to (K _x Na _1-x ) NbO ₃ (where 0 <x <1), or KNbO ₃ , NaNbO ₃ , (K _x Li _y Na _1-xy ) NbO ₃ (where 0 <x <1, 0 <y <1, Alkali metal niobates having other compositions such as 0 <x + y <1) can also be used.

  In Examples 1 and 2, examples in which the electrode layers 3A, 3B, 13A, and 13B are composed of Pt or Pd are shown. However, in order to further increase the adhesion with the piezoelectric sintered body layer 2 (piezoelectric sintered body 12), the composition of the electrode layer is mainly composed of either Pt or Pd, while the piezoelectric sintered body layer 2 (piezoelectric layer 2). It is good also as what contains the material which comprises the sintered compact 12).

1 is a perspective view showing an outer shape of a multilayer piezoelectric element according to Example 1 and Comparative Example 1. FIG. 2 is a longitudinal sectional view showing an internal structure of a multilayer piezoelectric element according to Example 1 and Comparative Example 1. FIG. FIG. 3 is an explanatory view showing, in an enlarged manner, cross sections of a piezoelectric sintered body layer and an electrode layer at a portion E in FIG. It is explanatory drawing which expands and shows the state of a piezoelectric sintered body layer and an electrode layer among the lamination type piezoelectric elements concerning the comparative example 1. FIG. 6 is a perspective view showing an outer shape of a ring-type piezoelectric element according to Example 2 and Comparative Example 2. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laminated piezoelectric element 1A, 1B, 1C, 1D Side surface 1A, 1B (Extraction electrode formation surface) 2 Piezoelectric sintered body layer 3A, 3B Internal electrode layer (electrode layer)
4A, 4B Extraction electrode PO Hole 11 Ring type piezoelectric element (piezoelectric element)
12 Piezoelectric sintered body 12H Through hole 13A, 13B Electrode layer

Claims (4)

A piezoelectric sintered body mainly composed of alkali metal niobate;
An electrode layer formed by simultaneous sintering with the piezoelectric sintered body and in contact with the piezoelectric sintered body,
A piezoelectric element comprising: an electrode layer having at least one of Pt and Pd as a main component and an Ag content of less than 10 mol% (including 0). A dense piezoelectric sintered body mainly composed of alkali metal niobate,
An electrode layer formed by simultaneous sintering with the piezoelectric sintered body and in contact with the piezoelectric sintered body,
And an electrode layer mainly composed of at least one of Pt and Pd. A piezoelectric sintered body layer mainly composed of alkali metal niobate;
An electrode layer formed by simultaneous sintering with the piezoelectric sintered body layer and in contact with the piezoelectric sintered body layer,
A multi-layer piezoelectric element in which electrode layers containing at least one of Pt and Pd as a main component and an Ag content of less than 10 mol% (including 0) are alternately laminated. A dense piezoelectric sintered body layer mainly composed of alkali metal niobate,
An electrode layer formed by simultaneous sintering with the piezoelectric sintered body layer and in contact with the piezoelectric sintered body layer,
A laminated piezoelectric element in which electrode layers containing at least one of Pt and Pd as main components are alternately laminated.

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