JP2006225235A - Method of suppressing decomposition of perovskite type compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To surely suppress the decomposition of a perovskite type compound at the time of heat-treating the perovskite type compound in the state that the compound is made into contact with glass. <P>SOLUTION: When the perovskite type compound containing the A-site element and a B-site element and expressed by ABO<SB>3</SB>is heat-treated in the state that the compound is made into contact with glass, a decomposition suppressing compound containing an element having smaller intensity for forming a cationic electric field than that of an A-site element is added. The intensity for forming the cationic electric field is obtained by the formula of (atomic valence)/(ionic radius)<SP>2</SP>. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a method for suppressing decomposition of a perovskite type compound such as CaRuO ₃ used as a conductive material in a thick film resistor, for example.

In a thick film resistor formed by applying a thick film resistor paste containing an insulating material (glass) or a conductive material on a substrate and firing, usually, ruthenium oxide (RuO ₂ ) or lead is used as the conductive material. Particles (conductive particles) such as ruthenium composite oxide (Pb ₂ Ru ₂ O ₆ ) are used, and PbO-based glass is used as the glass. Glass functions as a binder between the conductive particles and the substrate, and the resistance value can be adjusted by the ratio of the conductive particles to the glass.

In recent years, environmental problems have been actively discussed. For example, in solder materials and the like, it is required to exclude lead. Thick film resistors are no exception. Therefore, in consideration of the environment, the use of Pb ₂ Ru ₂ O ₆ which is a conductive material as well as PbO glass must be avoided. Under such circumstances, research has been made on lead-free thick film resistor pastes in which lead is excluded from the glass or conductive material used. For example, the Ru composite oxide described in Patent Document 1 Since a high resistance value can be realized as compared with ruthenium oxide, it is regarded as a promising conductive material in place of lead-ruthenium composite oxide.

Alternatively, for example, Patent Document 2 and Patent Document 3 describe a perovskite crystal structure such as CaTiO ₃ for the purpose of improving the temperature characteristics (TCR) and short-time overload (STOL) of a lead-free thick film resistor. It is disclosed that an oxide having an additive is added as an additive.
JP 2002-198203 A JP 2003-197405 A JP 2004-356266 A

By the way, the Ru composite oxide as the conductive material is typically a perovskite type compound such as CaRuO ₃ or SrRuO ₃ , but these perovskite type compounds are easily mixed with glass and subjected to heat treatment. There is a problem that it is decomposed to become ruthenium oxide and a desired resistance value cannot be obtained. In the thick film resistor paste, it is necessary to form a thick film resistor by firing, the decomposition of the conductive material (perovskite type compound) is inevitable, as a result, not only the resistance value variation, Other properties may be adversely affected.

  Similarly, an oxide having a perovskite crystal structure added as an additive also has a problem that when it is mixed with glass as a thick film resistor paste and heat-treated, it is easily decomposed and cannot fully function. is there.

  The present invention has been proposed in view of such conventional circumstances, and reliably suppresses the decomposition of the perovskite compound even when heat treatment is performed in a state where the perovskite compound is in contact with glass. It is an object of the present invention to provide a method for inhibiting the decomposition of a perovskite compound capable of undergoing

  In order to achieve the above-mentioned object, the present inventor has intensively studied for a long time. As a result, paying attention to the strength that creates the electric field of the cation, by selecting an element having an appropriate strength with respect to the A-site element of the perovskite type compound and adding a compound containing the element, the perovskite can be effectively used. It came to the knowledge that decomposition | disassembly of a type | mold compound could be suppressed.

The present invention has been completed on the basis of such findings, and when the perovskite type compound containing A-site element and B-site element and represented by ABO ₃ is heat-treated in the state of contact with glass, (Ion radius) A decomposition inhibiting compound containing an element having a smaller value of ² than the A-site element is added.

The intensity that creates the electric field of the cation is calculated by the valence / (ion radius) ² . For example, in the case of Ca ²⁺ , the valence is 2, the ionic radius is 0.99 、, and the strength for creating an electric field is calculated to be 2.04. Similarly, for each element, the intensity that creates a positive ion electric field can be calculated.

  In the present invention, the strength of the electric field of the cation is compared, various elements are selected for various perovskite compounds, and the compounds containing the elements are added to decompose the perovskite compounds. Suppress it. The criterion for selection of the element is the strength that creates the electric field of the cation, and an element that produces the electric field of the cation is smaller than the A-site element of the perovskite compound, and the compound is added as a decomposition inhibiting compound. . This suppresses the decomposition of the perovskite compound.

  The details of the reason why the decomposition of the perovskite type compound is suppressed by the addition of the decomposition suppressing compound is unknown. However, there is no doubt that the intensity of the cation electric field is involved in some way. For example, an element having a higher cation electric field intensity than the A-site element of a perovskite compound is almost not effective in suppressing the decomposition. Does not contribute.

  According to the present invention, even when heat treatment is performed in a state where the perovskite compound is in contact with glass, decomposition of the perovskite compound can be reliably suppressed. Therefore, for example, when a perovskite type compound as a conductive material or additive is mixed with glass or the like to form a thick film resistor paste, and this is fired to form a thick film resistor, its decomposition is sufficiently suppressed. And the functions of the perovskite type compound can be sufficiently exhibited.

  Hereinafter, a method for inhibiting decomposition of a perovskite compound to which the present invention is applied will be described in detail.

In the present invention, the perovskite type compound to be decomposed is a compound that contains an A site element and a B site element and is represented by the general formula ABO ₃ . In this case, the type is not particularly limited, and can be applied to suppress decomposition of all types of perovskite compounds. Specifically, CaRuO ₃ , SrRuO ₃ , BaRuO ₃ used as conductive materials for thick film resistors, and CaTiO ₃ , NiTiO ₃ , MnTiO ₃ , CoTiO ₃ , FeTiO ₃ that are also used as additives in thick film resistors. ₃ is a _{CuTiO 3, MgTiO 3, SrTiO 3} , BaTiO 3 , etc., but of course, not limited thereto.

  When the perovskite type compound is in contact with glass, for example, mixed with glass and subjected to heat treatment, the perovskite type compound is usually decomposed by the reaction between the perovskite type compound and glass, and after the heat treatment, the perovskite type compound is decomposed. A phenomenon occurs in which almost no type compound remains. When the perovskite type compound decomposes and does not remain, its function is lost. For example, it is difficult to obtain desired characteristics in a thick film resistor.

  Therefore, in the present invention, the decomposition of the perovskite compound is suppressed by the presence of a decomposition inhibiting compound during the heat treatment. However, in this case, it is necessary to use an appropriate compound as the decomposition inhibiting compound, and it is not necessary to add an arbitrary compound.

  In the present invention, in combination with a perovskite type compound to be decomposed, an element is selected on the basis of the strength that produces an electric field of a cation, and a compound containing the element is used as a decomposition inhibiting compound. Specifically, a compound of an element having a lower strength for generating the electric field than the A-site element of the perovskite type compound is used as the decomposition inhibiting compound.

As described above, the strength for generating an electric field of a cation is calculated by valence / (ion radius) ² . For example, in the case of Ca ²⁺ , the valence is 2, the ionic radius is 0.99 、, and the strength for creating an electric field is 2.04. When calculated in the same manner, for example, Mg, Co, and the like have a higher strength for creating an electric field than Ca. On the other hand, Ba, Sr, Na, K, and the like have a lower strength for creating an electric field than Ca. Therefore, when the A-site element of the perovskite type compound to be decomposed is Ca, a compound containing an element such as Ba, Sr, Na, or K, which has a lower strength than Ca, is used as the decomposition-inhibiting compound.

As the decomposition inhibiting compound, any compound can be used as long as it is a compound of an element that generates the electric field with a low strength. Usually, an oxide or a compound containing the oxide (such as a composite oxide) is used. Preferably, it is a perovskite type compound having a different B site element from the perovskite type compound to be decomposed. For example, when the perovskite compound to be decomposed is CaRuO ₃ , SrTiO ₃ , BaTiO ₃ , NaNbO ₃ or the like is suitable as the decomposition inhibiting compound.

  The amount of the decomposition inhibiting compound added is arbitrary, but if it is too small, there is a possibility that a sufficient effect cannot be obtained. On the other hand, if the amount is too large, other components must be reduced as a result, which is not preferable from the viewpoint of characteristics and the like. Therefore, the addition amount is preferably 1% by mass to 40% by mass with respect to the mass of the perovskite type compound to be decomposed. By setting the addition amount within the above range, a sufficient decomposition suppressing effect can be obtained, and adverse effects due to the addition can be minimized.

  Next, the method for suppressing decomposition according to the present invention will be described by taking the formation of a thick film resistor as an example.

  The thick film resistor is usually formed by baking (baking) a thick film resistor paste. The thick film resistor paste used includes a glass composition that is an insulating material, conductive particles, and, if necessary, additives, and these are mixed with an organic vehicle.

In the thick film resistor paste, the conductive particles have a role of imparting conductivity to the thick film resistor by being dispersed in the glass which is an insulator. In terms of environmental protection, it is preferable to use conductive particles that are substantially free of lead. Specific examples of the conductive particles substantially free of lead include ruthenium oxide. Examples of the ruthenium oxide include ruthenium oxide (RuO ₂ , RuO ₄ etc.), ruthenium-based pyrochlore (Bi ₂ Ru ₂ O ₇ , Tl ₂ Ru ₂ O ₇ etc.) and ruthenium composite oxides (SrRuO ₃ , BaRuO ₃ , CaRuO ₃ , LaRuO _3, etc.) are also included. Among these, it is preferable to apply the present invention when a perovskite type compound such as CaRuO ₃ , SrRuO ₃ , BaRuO ₃ is used.

  When the glass composition is a thick film resistor, it has a role of binding the conductive particles and additives to the substrate in the thick film resistor structure. Any glass composition may be used as long as it does not substantially contain lead. For example, CaO glass, SrO glass, Ba glass, ZnO glass, and the like are suitable.

Specifically, examples of the CaO glass include Ca—B—Si—Zr (Al) —Ta (Nb) —O glass. This Ca—B—Si—Zr (Al) —Ta (Nb) —O glass has CaO, SrO, or BaO as a main modified oxide component, and B ₂ O ₃ or SiO ₂ as a network-forming oxide component. And ZrO ₂ or Al ₂ O ₃ as the _second modified oxide component, and Ta ₂ O ₅ or Nb ₂ O ₅ as the third modified oxide component.

Alternatively, a Ca—B—Si—Mn—O based glass composition or the like can be used as the CaO based glass. The Ca—B—Si—Mn—O-based glass composition contains CaO, B ₂ O ₃ , SiO ₂ , and MnO, for example, CaO 10 to 30 mol%, B ₂ O ₃ 25 to 40 mol%. , SiO ₂ 15 to 30 mol%, MnO 10 to 40 mol% is composed of the composition ratio. As glass other than CaO-based glass, for example, Zn-B-Si-Mg-O glass, Ba-B-Si-Co-O glass, or the like can be used.

  As the organic vehicle, any of those used in this type of thick film resistor paste can be used. For example, binder resins such as ethyl cellulose, polyvinyl butyral, methacrylic resin, butyl methacrylate, terpineol, butyl carbitol, butyl A solvent such as carbitol acetate, toluene, various alcohols, and xylene can be mixed and used. At this time, various dispersants, activators, plasticizers, and the like can be appropriately used in accordance with the application.

  In addition to the glass composition and the conductive material, the thick film resistor paste may contain an additive for the purpose of adjusting the resistance value and the temperature characteristic. Examples of the additive include titanium compounds and metal oxides, which may be appropriately selected and used. For example, by using an alkaline earth metal titanate compound as an additive as a titanium compound, the TCR is greatly improved.

The titanate compound of an alkali earth _metal include _{BaTiO 3, SrTiO 3, CaTiO 3} , MgTiO 3, CoTiO 3, NiTiO perovskite compounds such as _3. These titanic acid compounds are preferably selected according to the resistance value, and in that case, the composition is preferably optimized. As a metal oxide, STOL can be further improved by using CuO, Cu ₂ O or the like.

In order to form the thick film resistor, the thick film resistor paste containing the above-described components may be printed (applied) on the substrate by a technique such as screen printing and fired at a temperature of about 850 ° C. As the substrate, a dielectric substrate such as an Al ₂ O ₃ substrate or a BaTiO ₃ substrate, a low-temperature fired ceramic substrate, an AlN substrate, or the like can be used. The substrate form may be any of a single layer substrate, a composite substrate, and a multilayer substrate. In the case of a multilayer substrate, the thick film resistor may be formed on the surface or inside.

  When forming a thick film resistor, a conductive pattern to be an electrode is usually formed on the substrate. This conductive pattern includes a good conductive material such as an Ag-based alloy containing Ag, Pt, Pd, or the like. It can be formed by printing a conductive paste. Further, a protective film (overglaze) such as a glass film may be formed on the surface of the formed thick film resistor.

The thick film resistor is formed as described above. When the thick film resistor is formed, as described above, the conductive material (CaRuO ₃ , SrRuO ₃ , BaRuO _3, etc.) or the additive (BaTiO ₃ , Firing (heat treatment) is performed in a state where a perovskite type compound such as SrTiO ₃ , CaTiO ₃ , MgTiO ₃ , CoTiO ₃ , NiTiO _3, etc.) is mixed with the glass composition. Therefore, after firing, the perovskite type compound is decomposed, and the respective functions cannot be sufficiently performed.

Therefore, in the present invention, when a perovskite type compound such as CaRuO ₃ , SrRuO ₃ , or BaRuO ₃ is used as the conductive material, an electric field is applied from the A site element (Ca, Sr, Ba, etc.) of the perovskite type compound. A compound of an element having a low strength is added to the thick film resistor paste as an additive. When a perovskite type compound such as BaTiO ₃ , SrTiO ₃ , CaTiO ₃ , MgTiO ₃ , CoTiO ₃ , NiTiO ₃ or the like is used as an additive, an element having a smaller electric field strength than the A site element of the perovskite type compound is used. The compound is added as a second additive to the thick film resistor paste. Thereby, the decomposition of the perovskite type compound used as the conductive material or additive is suppressed, the function of these compounds is sufficiently exhibited, and a thick film resistor having excellent characteristics can be formed.

  Hereinafter, specific examples of the present invention will be described based on experimental results.

Decomposition and suppression CaRuO ₃ 50 wt% of CaRuO _3, CaO-based glass 40 wt%, and additives of 10 wt% were mixed for 10 minutes at 850 ° C., it was baked. After baking, the abundance of CaRuO ₃ was confirmed. The abundance of CaRuO ₃ was calculated as the X-ray intensity ratio (CaRuO ₃ / RuO ₂ ) between CaRuO ₃ and RuO ₂ .

Using the additive having the strength to generate the electric field shown in Table 1, the difference in the abundance was examined. In addition, the intensity | strength which produces the electric field of Ca2 ⁺ is 2.04. For comparison, the same baking was performed without adding the added amount. In this case, 50% by mass of CaRuO _{3 and} 50% by mass of CaO-based glass were mixed and baked at 850 ° C. for 10 minutes. The results are shown in Table 1.

As is apparent from Table 1, when a compound containing Sr ²⁺ , Ba ²⁺ , and Na ⁺ having a lower strength than Ca ²⁺ is used, the decomposition of CaRuO ₃ is suppressed and remains after baking. I can see that When a compound containing Mg ²⁺ or Y ³⁺ having a higher strength for generating an electric field than Ca ²⁺ is used, CaRuO ₃ is decomposed and hardly remains after baking.

Decomposition and suppression MgTiO ₃ 50 wt% of the MgTiO _3, CaO-based glass 40 wt%, and additives of 10 wt% were mixed for 10 minutes at 850 ° C., it was baked. After baking, the abundance of MgTiO ₃ was confirmed. Abundance of MgTiO ₃ was calculated as MgTiO ₃ and the X-ray intensity ratio of MgO (MgTiO ₃ / MgO).

Using the additive having the strength to generate the electric field shown in Table 2, the difference in the abundance was examined. In addition, the intensity | strength which produces the electric field of Mg2 ⁺ is 3.85. For comparison, the same baking was performed without adding the added amount. In this case, 50% by mass of MgTiO _{3 and} 50% by mass of CaO glass were mixed and baked at 850 ° C. for 10 minutes. The results are shown in Table 2.

As is apparent from Table 2, when a compound containing Tb ³⁺ or Ca ²⁺ having a lower strength than that of Mg ²⁺ is used, the decomposition of MgTiO ₃ is suppressed and remains after baking. I understand. In the case of using a compound containing Ni ^+, which has a higher strength for creating an electric field than Mg ²⁺ , MgTiO ₃ is decomposed and hardly remains after baking.

Claims (9)

When the perovskite type compound containing A site element and B site element and represented by ABO ₃ is heat-treated in a state of being in contact with glass,
A method for inhibiting decomposition of a perovskite type compound, comprising adding a decomposition inhibiting compound containing an element having an atomic value / (ion radius) ² smaller than the A-site element.   2. The method for inhibiting decomposition of a perovskite compound according to claim 1, wherein the decomposition inhibiting compound is an oxide or composite oxide of an element whose value is smaller than the A-site element.   3. The method for inhibiting decomposition of a perovskite compound according to claim 2, wherein the decomposition inhibiting compound is a perovskite compound having a B site element different from that of the perovskite compound.   The method for inhibiting decomposition of a perovskite compound according to any one of claims 1 to 3, wherein the decomposition inhibiting compound is added when heat-treating a mixture of the perovskite compound and glass.   5. The method for inhibiting decomposition of a perovskite compound according to claim 4, wherein the mixture is a thick film resistor paste.   6. The method for inhibiting the decomposition of a perovskite compound according to claim 5, wherein the perovskite compound is a conductive material for a thick film resistor. The method for inhibiting decomposition of a perovskite compound according to claim 6, wherein the perovskite compound is one or more selected from CaRuO ₃ , SrRuO ₃ and BaRuO ₃ .   6. The method for inhibiting decomposition of a perovskite compound according to claim 5, wherein the perovskite compound is an additive for thick film resistors.   9. The method of inhibiting decomposition of a perovskite compound according to claim 8, wherein the perovskite compound is an alkaline earth metal titanate compound.