JP2007188963A - Conductive paste and method of manufacturing laminated ceramic element employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrode paste with which a laminated ceramic element having high reliability can be produced while suppressing deterioration in characteristics of the laminated ceramic element to be produced, and to provide a method of producing the laminated ceramic element employing the same. <P>SOLUTION: The electrode paste (conductive paste) 22 contains Ag as a main metal component; and further contains a solvent, a binder and an additive made of WO<SB>3</SB>. Thus, when the electrode paste 22 is used for manufacture of a piezoelectric actuator 10, an additive agent WO<SB>3</SB>bonds with the Ag of the main metal component in the electrode paste 22 in baking to form a composite. In this way, since the main metal component of the electrode paste remains in an electrode layer, the situation can be suppressed that the main metal component is diffused in a dielectric layer or remains in an interface between the dielectric layer and the electrode layer. According to this conductive paste, the laminated ceramic element having high reliability can be produced while suppressing the deterioration in the laminated ceramic element to be produced. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive paste and a method for producing a multilayer ceramic element using the same.

  A piezoelectric element is known as one of representative ceramic elements. The piezoelectric element is an element including a piezoelectric layer and an electrode layer, and typical piezoelectric elements include a piezoelectric actuator, a piezoelectric buzzer, a sound generator, a piezoelectric sensor, and the like. In recent years, the advantage of being small and providing a large mechanical / physical displacement with a small voltage is suitable for today's industrial requirements. It is being advanced.

  Such a laminated piezoelectric element (piezoelectric actuator) is also used for an actuator that requires a large amount of displacement, such as an actuator for fuel injection control of an internal combustion engine such as an automobile, and the number of laminated layers is 300 to 400. It extends to the layer. A multilayer piezoelectric element having a so-called array structure in which individual displacement portions are formed in a matrix in one piezoelectric element is also known.

  As a general method of manufacturing the multilayer piezoelectric element as described above, first, a ceramic powder mainly composed of lead zirconate titanate (PZT) is slurried and formed into a sheet to prepare a green sheet. . Next, an electrode paste containing Ag as a metal component is applied on the green sheet. Then, a plurality of the green sheets coated with the electrode paste are stacked to produce a laminate in which green sheets and electrode paste layers are alternately stacked. Thereafter, the obtained laminate is fired, and finally an external electrode for applying a voltage is provided, thereby completing the production of a laminated piezoelectric element in which piezoelectric layers (dielectric layers) and electrode layers are alternately laminated. To do.

  However, in such a method for manufacturing a piezoelectric element, the metal component in the electrode paste diffuses into the green sheet while the laminate is fired. The metal component diffused in the green sheet hindered the grain growth of the piezoelectric material of the green sheet during firing, and deteriorated the piezoelectric characteristics of the multilayer piezoelectric element. In particular, when Ag or Cu is contained in the metal component of the electrode paste, such diffusion is significant.

Therefore, as a technique for suppressing the metal component of the electrode layer from entering the dielectric layer, a technique for adding an auxiliary oxide such as WO ₃ or MoO ₃ to the dielectric layer is disclosed in Patent Document 1 below.
JP 2002-255646 A

  However, the above-described prior art has the following problems. That is, the metal component of the electrode layer that is prevented from entering the dielectric layer remains at the interface between the dielectric layer and the electrode layer, and as a result, migration of the metal component at the interface may occur when the element is driven. An element having high reliability could not be obtained.

  Therefore, the present invention has been made to solve the above-described problems, and it is possible to produce a multilayer ceramic element having high reliability while suppressing deterioration of characteristics of the produced multilayer ceramic element. It is an object of the present invention to provide a conductive paste and a method for producing a multilayer ceramic element using the same.

The conductive paste according to the present invention includes Ag or Cu as a main metal component, and further includes a solvent, a binder, and an additive composed of at least one of WO ₃ and MoO ₃ .

When this conductive paste is used in the production of a multilayer ceramic element, the additives WO ₃ and MoO ₃ are combined with Ag and Cu as main metal components of the conductive paste to form a compound during firing. As a result, the main metal component of the conductive paste remains in the electrode layer, so that the situation where the main metal component diffuses into the dielectric layer or stays at the interface between the dielectric layer and the electrode layer is suppressed. Therefore, according to the conductive paste according to the present invention, a multilayer ceramic element having high reliability can be fabricated while suppressing deterioration of characteristics of the multilayer ceramic element to be fabricated.

  Moreover, it is preferable that the addition amount of an additive is 0.1 wt% or more and 30 wt% or less. In this case, sufficient particle growth is realized during firing, and a good electrode interface can be obtained.

The method for producing a multilayer ceramic element according to the present invention further comprises a solvent, a binder, and an additive comprising at least one of WO ₃ and MoO ₃ containing Ag or Cu as a main metal component on a ceramic green sheet. A step of applying a conductive paste, a step of forming a laminate in which a plurality of ceramic green sheets coated with the conductive paste are laminated, and a step of firing the laminate.

In this method for manufacturing a multilayer ceramic element, during firing, WO ₃ and MoO ₃ as additives of the conductive paste are combined with Ag and Cu as main metal components to form a compound. As a result, the main metal component of the conductive paste remains in the electrode layer, so that the situation where the main metal component diffuses into the dielectric layer or stays at the interface between the dielectric layer and the electrode layer is suppressed. Therefore, according to the method for manufacturing a ceramic element according to the present invention, a multilayer ceramic element having high reliability is manufactured while suppressing deterioration of characteristics of the manufactured multilayer ceramic element.

  Moreover, it is preferable that the addition amount of an additive is 0.1 wt% or more and 30 wt% or less. In this case, sufficient particle growth is realized during firing, and a good electrode interface can be obtained.

  Further, the ceramic green sheet may include a piezoelectric ceramic whose main component is Pb oxide.

  ADVANTAGE OF THE INVENTION According to this invention, while suppressing the characteristic deterioration of the produced multilayer ceramic element, the electrically conductive paste which can produce the highly reliable multilayer ceramic element, and manufacture of a multilayer ceramic element using the same A method is provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, embodiments that are considered to be the best in carrying out the invention will be described in detail with reference to the accompanying drawings. In addition, the same code | symbol is attached | subjected about the same or equivalent element, and the description is abbreviate | omitted when description overlaps.

  FIG. 1 shows a schematic cross-sectional view of a multilayer ceramic element according to an embodiment of the present invention. As shown in FIG. 1, a multilayer piezoelectric actuator 10 which is a kind of multilayer ceramic element has two surface layers 11 and 11 which are outermost layers, and 20 piezoelectric layers (functions) sandwiched between the surface layers 11 and 11. Layer) 12 and a hexahedral actuator body 16 having an internal electrode layer 14 interposed between the piezoelectric layers 12 disposed above and below. That is, the actuator body 16 has a laminated structure, and the piezoelectric layers 12 and the internal electrode layers 14 are alternately laminated. A pair of end surfaces 16a and 16b extending in the thickness direction of the actuator body 16 and facing each other out of the end surfaces of the actuator body 16 so as to cover the entire area of the end surfaces 16a and 16b. External electrodes 18 and 18 are provided.

  Further, the internal electrode layers 14 arranged above and below are electrically insulated from each other by the piezoelectric layer 12 and are connected to one external electrode 18 different from each other. Therefore, when a predetermined voltage is applied between the pair of external electrodes 18, 18, the piezoelectric layers 12 sandwiched between the internal electrode layers 14 facing each other vertically are deformed in the thickness direction by the piezoelectric effect. Occurs. And in the piezoelectric actuator 10, since the several piezoelectric layer 12 is piled up in the thickness direction, a big deformation | transformation is obtained.

Both the surface layer 11 and the piezoelectric layer 12 are layers mainly composed of a piezoelectric material represented by the general formula Pb [(Zn _1/3 Nb _2/3 ) _0.1 Ti _0.435 Zr _0.465 ] O _3. The thickness of each surface layer 11 is approximately 60 μm, and the thickness of each piezoelectric layer 12 is 5 to 200 μm (for example, 30 μm). The surface layer 11 and the piezoelectric layer 12 are formed by firing a later-described green sheet.

  The internal electrode layer 14 is a metal layer containing Ag as a main metal component, and has a thickness of 0.1 to 5 μm (for example, 2 μm). If the thickness of the electrode layer 14 exceeds 5 μm, delamination is likely to occur due to the shrinkage difference between the electrode layer 14 and the piezoelectric layer 12 during firing. Further, if the thickness is less than 0.1 μm, it is difficult to ensure a sufficient covering state of the electrode.

  Each external electrode 18 is formed by sputtering Au, but Ag or Cu can also be used in addition to Au as another constituent material.

  Hereinafter, a method for manufacturing the above-described piezoelectric actuator 10 will be described with reference to FIGS.

  First, prior to the description of the procedure for manufacturing the piezoelectric actuator 10, the procedure for preparing ceramic powder necessary for manufacturing the piezoelectric actuator 10 will be described with reference to the flowchart of FIG.

For preparation of ceramic powder (piezoelectric ceramic), PbO, ZrO ₂ , TiO ₂ , ZnO and Nb ₂ O ₅ are prepared as main raw materials and weighed by a predetermined amount. Then, these oxide raw materials are wet mixed by a ball mill (step 1) and then dried (step 2). Thereafter, temporary firing is performed (step 3), and after the preliminary firing, fine pulverization is performed by wet pulverization using a ball mill (step 4). Finally, by drying the mixed and pulverized oxide raw material (step 5), the general formula Pb [(Zn _1/3 Nb _2/3 ) _0.1 Ti necessary for manufacturing the piezoelectric actuator 10 is obtained. _0.435 Zr _0.465] ceramic powder represented by _{O 3} is obtained.

  Next, a procedure for manufacturing the piezoelectric actuator 10 will be described with reference to the flowchart of FIG.

  First, the ceramic powder and an organic binder / organic solvent are mixed to form a slurry (step 11). The paste obtained by the slurrying is formed into a sheet on a carrier film such as a PET film by using a doctor blade method to produce 20 green sheets 20 having a predetermined thickness (step 12). In addition, two green sheets 21 that are thicker than the green sheet 20 and are to be the surface layer 11 are prepared.

  In parallel with the production of the green sheets 20 and 21, an electrode paste (conductive paste) 22 to be the internal electrode layer 14 is also prepared. The electrode paste 22 is a mixture of metal powder and an organic binder, organic solvent, common material, additive, and the like.

  The metal powder is an Ag—Pb alloy and is prepared by blending Ag and Pd at a ratio of 7: 3. The metal powder may be appropriately changed to an Ag-Pd alloy, Ag alone, or Cu alone. In addition, it is preferable that the average particle diameter of metal powder is 0.1-2 micrometers (for example, 0.8 micrometer). If the average particle size of the metal powder exceeds 2 μm, delamination is likely to occur during firing. If the average particle size of the metal powder is less than 0.1 μm, the particle size is too fine, and it is difficult to ensure a sufficient covering state of the electrode.

  The common material is the same as the ceramic powder described above. Thus, by adding the ceramic powder to the electrode paste 22, the shrinkage ratio and the sintering start temperature between the electrode paste 22 and the green sheet 20. The difference is eased. The amount of the ceramic powder added is 10 wt% with respect to the total weight of the metal powder.

The additive is WO ₃ and the amount added is preferably 0.1 wt% or more and 30 wt% or less with respect to the total weight of the metal powder. Incidentally, additives, other be composed only of WO _3, can also be configured with or be composed only MoO _3, and WO ₃ and MoO _3.

  Subsequently, as shown in FIG. 4, a predetermined pattern of electrode paste 22 is applied to the surface 20a of the green sheet 20 by a screen printing method and dried (step 13). That is, the electrode paste 22 is applied to a region other than the edge region of the three sides in the rectangular region 24 (for example, 3 mm × 12 mm) corresponding to one piezoelectric actuator on the green sheet surface 20a.

  As shown in FIG. 5A, the green sheet 20 coated with the electrode paste 22 as described above is laminated on the green sheet 21 with the electrode paste 22 facing upward. In addition, 20 green sheets 20 produced by the same manufacturing method are sequentially laminated so that the positions of the electrode pastes 22 are alternately changed (see FIG. 5B). Then, the green sheet 21 to which nothing is applied is put on the laminated green sheet 20 and pressed under the conditions of about 60 ° C. and 100 MPa from the laminating direction, so that the adjacent green sheet 21, green sheet 20 and electrode The pastes 22 are pressed together. In this way, a laminate 26 in which the green sheets 20 and the electrode pastes 22 are alternately laminated is produced (step 14).

  Then, a degreasing process (debinding process) is performed on the laminated body 26 at 400 ° C. for 10 hours in an air atmosphere. Subsequently, each rectangular region 24 corresponding to one piezoelectric actuator is cut into chips (see FIG. 5C). Then, the green sheet 21, the green sheet 20, and the electrode paste 22 were each mentioned above by baking the laminated body 26 made into a chip | tip at 800-1150 degreeC (for example, 1050 degreeC) for 2 hours in a sealed mortar (sheath). The surface layer 11, the piezoelectric layer 12, and the internal electrode layer 14 are formed, and the stacked body 26 is an actuator body 16 in which the piezoelectric layers 12 and the internal electrode layers 14 are alternately stacked. If the firing temperature exceeds 1150 ° C., sufficient coating cannot be performed due to a melting point problem or the like, and therefore Ag or Cu cannot be used for the electrode paste. Further, when the firing temperature is less than 800 ° C., remarkable diffusion of Ag or Cu into the piezoelectric layer 12 does not occur.

  When the metal component of the electrode paste 22 is Cu, it is necessary to degrease / fire the laminated body 26 in a low oxygen atmosphere.

  Subsequently, the external electrode 18 is formed by sputtering so as to cover the pair of end faces 16a and 16b extending in the stacking direction and facing each other among the end faces of the actuator body 16 to complete the piezoelectric actuator 10 (FIG. 5 (d)). The external electrode 18 can be formed by baking, vapor deposition, electroless plating, or the like.

  After the external electrode 18 is formed, the piezoelectric actuator 10 is subjected to polarization treatment under a predetermined condition (for example, applying an electric field having an electric field strength of 2 to 3 kV / mm for about 3 minutes at a temperature of 120 ° C.). It comes to function as a piezoelectric element.

  The electrode paste 22 used for the manufacturing method of the piezoelectric actuator 10 demonstrated above is demonstrated.

As described above, WO ₃ is added to the electrode paste 22 as an additive. As a result of intensive studies, the inventors have added such an additive to the electrode paste 22 so that Ag in the electrode paste 22 diffuses into the piezoelectric layer 12 (green sheet 21) when the laminate 26 is fired. A new finding that the situation is suppressed. This is presumably because the additive WO ₃ and the main metal component Ag combine to form a compound such as AgWO ₄ during the firing of the laminate 26, and Ag remains in the electrode paste 22. Conventionally, Ag diffuses into the piezoelectric layer and dissolves in the piezoelectric layer, so that the amount of Pb component (A site component) in the piezoelectric layer is apparently excessive. As a result, the piezoelectric of the piezoelectric layer The grain growth of the material was hindered, and the piezoelectric characteristics of the device were deteriorated.

That is, by using the electrode paste 22 to which the additive is added in the production of the piezoelectric actuator 10, the situation where the main metal component diffuses into the piezoelectric layer 12 is suppressed, and the deterioration of the piezoelectric characteristics of the piezoelectric actuator 10 is suppressed. The Incidentally, as an additive, MoO _3, or in the case of using both the WO ₃ and MoO _3, the same above effect in the case of using WO ₃ as additives were also confirmed to be obtained.

In addition, in the prior art in which WO ₃ or MoO ₃ is added to the dielectric layer, the metal component of the electrode paste stays at the interface between the dielectric layer and the electrode layer, and the migration of the metal component at the interface during the driving of the element As a result, the reliability of the element was reduced. However, when the electrode paste 22 to which the above additive is added is used for the production of the piezoelectric actuator 10, Ag remains in the electrode paste 22, and such a problem is significantly eliminated.

As described in detail above, the method of manufacturing a piezoelectric actuator 10, during firing of the stack 26, the additive WO ₃ of electrode paste 22 is bonded to the Ag in the main metal component compounds (AgWO ₄₎ Form. As a result, Ag of the electrode paste 22 stays in the electrode layer 14, so that the situation where Ag diffuses into the piezoelectric layer 12 or stays at the interface between the piezoelectric layer 12 and the electrode layer 14 is suppressed. Therefore, according to the method of manufacturing the piezoelectric actuator 10 using the electrode paste 22, the deterioration of the piezoelectric characteristics of the piezoelectric actuator 10 is suppressed, and high reliability of the piezoelectric actuator 10 is realized.

The present invention is not limited to the above embodiment, and various modifications are possible. For example, the multilayer ceramic element is not limited to a piezoelectric actuator, and may be other piezoelectric elements (for example, a piezoelectric buzzer, a piezoelectric sensor, a sound generator, etc.), and includes a dielectric layer as a functional layer instead of the piezoelectric layer. It may be an element (for example, a capacitor, an inductor, a varistor, an NTC thermistor, etc.). The ceramic powder only needs to contain Pb oxide, and its structure may be a pyrochlore structure (for example, Pb ₂ Nb ₂ O ₇ or the like). Further, the number of stacked elements is not limited to 20 layers, and can be appropriately increased or decreased between 2 and 400 layers.

  Hereinafter, in order to further clarify the effects of the present invention, description will be made using examples.

  The piezoelectric actuator sample used in the examples is a 12 mm × 3 mm square plate produced by the same manufacturing method as the piezoelectric actuator 10 described above, and is obtained by stacking 20 piezoelectric layers having a thickness of 30 μm.

As a sample, the sample 7-11 Sample 1-6 additive added to the electrode paste consisting only of WO _3, additive consisting only of MoO _3, the additive is composed of WO ₃ and MoO ₃ Three types of samples 12 to 17 were prepared.

  Then, for each of the above samples, the particle growth and the state of the electrode interface were examined. Note that the particle growth was determined by whether or not particle growth equal to or greater than that obtained when firing with a single material (single plate) was observed. Further, the state of the electrode interface was determined by whether or not a gap of a predetermined size or larger was observed at the interface between the electrode layer and the piezoelectric layer.

Table 1 below is a table showing the results of Samples 1 to 6 with different amounts of WO ₃ added.

  As is apparent from Table 1, Sample 1 did not have sufficient particle growth. This is thought to be because the metal component of the electrode paste diffused into the piezoelectric layer and the particle growth of the piezoelectric layer was inhibited because the amount of the additive was too small. In sample 6, voids were observed, and there were problems such as delamination.

  On the other hand, Sample 2 to Sample 5 in which the amount of the additive was 0.1 wt% or more and 30 wt% or less gave good results for both “particle growth” and “electrode interface state”.

Table 2 below is a table showing the results of Samples 7 to 11 with different amounts of MoO ₃ added.

  As is apparent from Table 2, sufficient particle growth was not observed in Sample 7. This is thought to be because the metal component of the electrode paste diffused into the piezoelectric layer and the particle growth of the piezoelectric layer was inhibited because the amount of the additive was too small. Further, in sample 11, voids were observed and there were defects such as delamination.

  On the other hand, Sample 8 to Sample 10 in which the amount of the additive was 0.1 wt% or more and 30 wt% or less gave good results for both “particle growth” and “electrode interface state”.

Table 3 below is a table showing the results of Samples 12 to 17 having different addition amounts of WO ₃ and MoO ₃ . In addition, the addition amount of WO ₃ and MoO ₃ is shown in parentheses in the term of addition amount.

  As is apparent from Table 3, the sample 12 did not show sufficient particle growth. This is thought to be because the metal component of the electrode paste diffused into the piezoelectric layer and the particle growth of the piezoelectric layer was inhibited because the amount of the additive was too small. In Sample 17, voids were observed, and there were problems such as delamination.

  On the other hand, Sample 13 to Sample 16 in which the amount of the additive was 0.1 wt% or more and 30 wt% or less gave good results for both “particle growth” and “electrode interface state”.

From the above results, even when any of “WO ₃ only”, “MoO ₃ only” and “WO ₃ and MoO ₃ ” is used as an additive for the electrode paste, the amount of the additive is 0.1 wt. It was confirmed that good results were obtained for both “particle growth” and “state of electrode interface” by setting the content to not less than 30% and not more than 30 wt%.

It is a schematic sectional drawing of the piezoelectric actuator which concerns on embodiment of this invention. It is the flowchart which showed the procedure which produces the ceramic powder used for preparation of the piezoelectric actuator shown in FIG. It is the flowchart which showed the procedure which produces the piezoelectric actuator shown in FIG. It is the elements on larger scale which showed the printing pattern of the green sheet. It is the figure which showed the procedure which produces the piezoelectric actuator shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Piezoelectric actuator, 12 ... Piezoelectric layer, 14 ... Internal electrode layer, 18 ... External electrode, 20, 21 ... Green sheet, 22 ... Electrode paste, 26 ... Laminated body.

Claims (5)

Ag or Cu containing as a main metal component, further comprising a solvent, a binder, and an additive comprising at least one of WO ₃ and MoO _3, the conductive paste.   The electrically conductive paste of Claim 1 whose addition amount of the said additive is 0.1 to 30 wt%. A step of applying a conductive paste that contains Ag or Cu as a main metal component on the ceramic green sheet, and further includes a solvent, a binder, and an additive composed of at least one of WO ₃ and MoO ₃ ;
Forming a laminate in which a plurality of the ceramic green sheets coated with the conductive paste are laminated;
Firing the laminate;
A method for manufacturing a multilayer ceramic element.   The method for manufacturing a multilayer ceramic element according to claim 3, wherein the additive is added in an amount of 0.1 wt% or more and 30 wt% or less. 5. The method for manufacturing a multilayer ceramic element according to claim 3, wherein the ceramic green sheet includes a piezoelectric ceramic mainly composed of a Pb oxide.

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