JP7525974B2 - Multilayer ceramic capacitors and ceramic raw material powder - Google Patents

Description

The present invention relates to multilayer ceramic capacitors and ceramic raw material powders.

There is a demand for dielectric materials that provide sufficient reliability characteristics for multilayer ceramic capacitors with thin dielectric layers. For example, it has been found that a method of preliminarily dissolving specific elements in the raw material powder is effective. Patent Document 1 discloses a technology for adding donor elements with the aim of improving life characteristics.

JP 2016-139720 A

However, in recent years, as the thickness of the dielectric layer has become smaller and the number of layers has increased, there is a demand for further improvements in life characteristics. There is also a demand for improved insulation characteristics. Therefore, it is difficult to achieve even higher reliability simply by using donor elements to reduce the amount of oxygen vacancies.

The present invention has been made in consideration of the above problems, and aims to provide a multilayer ceramic capacitor and ceramic raw material powder that can achieve high reliability.

The multilayer ceramic capacitor according to the present invention comprises a laminate in which dielectric layers and internal electrode layers are alternately laminated, the main component of the dielectric layers is a ceramic material having a perovskite structure represented by a general formula ABO3 as a main phase, containing an element functioning as a donor in the B site, and containing a rare earth element in both the A site and the B site, the ratio of the amount of solid solution of the rare earth element solid-solved in the A site (A site solid solution amount) to the amount of solid solution of the rare earth element solid-solved in the B site (B site solid solution amount) satisfies 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25, the element functioning as a donor in the B site is substituted and solid-solved at 0.05 atm% or more and 0.3 atm% or less when the main component element in the B site is taken as 100 atm%, and the perovskite structure is selected from BaTiO ₃ , CaZrO ₃ , CaTiO ₃ , SrTiO ₃ , and Ba _1-x-y The composition is characterized in that it is any one of Ca _x Sr _y Ti _1-z Zr _z O ₃ (0≦x≦1, 0≦y≦1, 0≦z≦1).

The ceramic raw material powder according to the present invention has a perovskite structure represented by a general formula _ABO3 as a main phase, contains an element functioning as a donor in the B site, and contains a rare earth element in both the A site and the B site, the ratio of the amount of the rare earth element dissolved in the A site (A site solid solution amount) to the amount of the rare earth element dissolved in the B site (B site solid solution amount) satisfies 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25, the element functioning as a donor is substituted and solid-solved in the B site at 0.05 atm % or more and 0.3 atm % or less when the main component element in the B site is taken as 100 atm % , and the perovskite structure is BaTiO ₃ , CaZrO ₃ , CaTiO ₃ , SrTiO ₃ , or Ba _1-x-y Ca _x Sr _y Ti _1-z Zr _z O ₃ (0≦x≦1, 0≦y≦1, 0≦z≦1).

The present invention provides a multilayer ceramic capacitor and ceramic raw material powder that can achieve high reliability.

FIG. 2 is a partial cross-sectional perspective view of a multilayer ceramic capacitor. 1 is a diagram illustrating a flow of a method for manufacturing a multilayer ceramic capacitor. FIG. 1 is a diagram showing test results of examples and comparative examples.

The following describes the embodiment with reference to the drawings.

(Embodiment)
Fig. 1 is a partial cross-sectional perspective view of a multilayer ceramic capacitor 100 according to an embodiment. As illustrated in Fig. 1, the multilayer ceramic capacitor 100 includes a laminated chip 10 having a substantially rectangular parallelepiped shape, and external electrodes 20a, 20b provided on two opposing end faces of the laminated chip 10. Of the four faces of the laminated chip 10 other than the two end faces, the two faces other than the top and bottom faces in the stacking direction are referred to as side faces. The external electrodes 20a, 20b extend on the top, bottom and two side faces in the stacking direction of the laminated chip 10. However, the external electrodes 20a, 20b are spaced apart from each other.

The laminated chip 10 has a laminated structure in which dielectric layers 11 containing a ceramic material that functions as a dielectric and internal electrode layers 12 containing a base metal material are alternately stacked. The edges of each internal electrode layer 12 are alternately exposed to the end face of the laminated chip 10 on which the external electrode 20a is provided and the end face on which the external electrode 20b is provided. As a result, each internal electrode layer 12 is alternately conductive to the external electrode 20a and the external electrode 20b. As a result, the laminated ceramic capacitor 100 has a structure in which multiple dielectric layers 11 are stacked via the internal electrode layers 12. In addition, in the laminate of the dielectric layers 11 and the internal electrode layers 12, the internal electrode layer 12 is arranged on the outermost layer in the stacking direction, and the upper and lower surfaces of the laminate are covered by the cover layer 13. The cover layer 13 is mainly composed of a ceramic material. For example, the material of the cover layer 13 is the same as that of the dielectric layer 11 and the ceramic material.

The size of the multilayer ceramic capacitor 100 is, for example, 0.2 mm long, 0.125 mm wide, and 0.125 mm high, or 0.4 mm long, 0.2 mm wide, and 0.2 mm high, or 0.6 mm long, 0.3 mm wide, and 0.3 mm high, or 1.0 mm long, 0.5 mm wide, and 0.5 mm high, or 3.2 mm long, 1.6 mm wide, and 1.6 mm high, or 4.5 mm long, 3.2 mm wide, and 2.5 mm high, but is not limited to these sizes.

The internal electrode layer 12 is mainly composed of base metals such as Ni (nickel), Cu (copper), and Sn (tin). Noble metals such as Pt (platinum), Pd (palladium), Ag (silver), and Au (gold), or alloys containing these metals, may also be used as the internal electrode layer 12.

The dielectric layer 11 is mainly composed of a ceramic material having a perovskite structure represented by the general formula ABO ₃ as a main phase. The perovskite structure includes ABO _3-α , which is not a stoichiometric composition. For example, the ceramic material may be BaTiO ₃ (barium titanate), CaZrO ₃ (calcium zirconate), CaTiO ₃ (calcium titanate), SrTiO ₃ (strontium titanate), or Ba _1-x-y Ca _x Sr _y Ti _1-z Zr _z O ₃ (0≦x≦1, 0≦y≦1, 0≦z≦1) which forms a perovskite structure.

In order to make the multilayer ceramic capacitor 100 smaller and larger in capacity, it is desirable to make the dielectric layer 11 thinner. However, if one tries to make the dielectric layer 11 thinner, there is a risk that the life characteristics will deteriorate due to insulation breakdown, etc., and reliability will decrease.

Here, the deterioration of reliability will be described. Since the dielectric layer 11 is mainly composed of a ceramic material using a ceramic raw material powder having a perovskite structure represented by the general formula _ABO3 as a main phase, oxygen defects are generated in _ABO3 when the dielectric layer 11 is exposed to a reducing atmosphere during firing. When the multilayer ceramic capacitor 100 is used, a voltage is repeatedly applied to the dielectric layer 11. At this time, the oxygen defects move, destroying the barrier. In other words, the oxygen defects in the perovskite structure are a cause of the deterioration of the reliability of the dielectric layer 11.

Therefore, in this embodiment, an element that functions as a donor is included in the B site of the perovskite structure (substitutionally dissolved). Examples of elements that function as donors include Mo (molybdenum), Nb (niobium), Ta (tantalum), and W (tungsten). By substituting and dissolving the element that functions as a donor in the B site, oxygen defects in the perovskite structure are suppressed. This extends the life of the dielectric layer 11 and improves its reliability.

If there is too little element functioning as a donor in the B site, oxygen defects may not be sufficiently suppressed. Therefore, it is preferable to set a lower limit on the amount of the element functioning as a donor in the B site that is substituted and dissolved. For example, it is preferable that the element functioning as a donor in the B site is substituted and dissolved at 0.05 atm% or more, and more preferably 0.1 atm% or more, when the main component elements in the B site are taken as 100 atm%.

On the other hand, if there are too many elements functioning as donors in the B site, problems such as reduced insulation may occur. Therefore, it is preferable to set an upper limit on the amount of elements functioning as donors in the B site that are substituted in solid solution. For example, it is preferable that the elements functioning as donors in the B site are substituted in solid solution at 0.3 atm % or less, and more preferably substituted in solid solution at 0.25 atm % or less.

Next, the dielectric layer 11, which is mainly composed of a ceramic material using a ceramic raw material powder having a perovskite structure as the main phase, is fired in a reducing atmosphere, and then re-oxidized, thereby further suppressing oxygen defects. If rare earth elements are contained (substitutionally dissolved) in both the A site and the B site during re-oxidation, the amount of oxygen defects after firing is suppressed. This makes it possible to achieve long life characteristics while maintaining insulation (IR: Insulation Resistance) characteristics. As a result, high reliability can be achieved. Therefore, in this embodiment, rare earth elements are substituted and solid-solved in both the A site and the B site.

If the amount of rare earth element substituted into the A site (A site solid solution amount) is too large compared to the amount of rare earth element substituted into the B site (B site solid solution amount), the donor may be excessively added to the perovskite. In this case, the insulating characteristics may deteriorate. On the other hand, if the amount of B site solid solution is too large compared to the amount of A site solid solution, the acceptor may be excessively added to the perovskite. In this case, the amount of oxygen defects may increase and the life characteristics may deteriorate. Therefore, by making the ratio of the amount of A site solid solution to the amount of B site solid solution close to 1, the amount of oxygen defects after firing is suppressed, and high reliability with an excellent balance between insulating characteristics and life characteristics can be obtained. Specifically, 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25. From the viewpoint of further suppressing the state of excessive donor addition, it is preferable that (A-site solid solution amount/B-site solid solution amount)≦1.20, more preferably (A-site solid solution amount/B-site solid solution amount)≦1.10, and even more preferably (A-site solid solution amount/B-site solid solution amount)≦1.05. From the viewpoint of further suppressing the state of excessive acceptor addition, it is preferable that 0.90≦(A-site solid solution amount/B-site solid solution amount) and more preferably 0.95≦(A-site solid solution amount/B-site solid solution amount).

If the amount of rare earth elements in the A and B sites is too small, the amount of oxygen defects after firing may not be sufficiently suppressed. Therefore, it is preferable to set a lower limit for the total amount of rare earth elements in the A and B sites. For example, it is preferable that the total amount of rare earth elements in the A and B sites is 0.2 atm% or more, and more preferably 0.3 atm% or more. Here, atm% refers to the concentration when the B site elements of _ABO3 in the ceramic raw material powder are 100 atm%.

On the other hand, if there is too much rare earth element in the A site and B site, the tetragonality of the crystal grains may decrease, and problems such as a decrease in the dielectric constant may occur. Therefore, it is preferable to set an upper limit on the total amount of rare earth element substituted in solid solution in the A site and B site. For example, it is preferable that the total amount of rare earth element substituted in solid solution in the A site and B site is 1.0 atm% or less, and more preferably 0.9 atm% or less.

As the rare earth element, Y (yttrium), La (lanthanum), Ce (cerium), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), etc. can be used. Note that the ionic radius of the A site and the ionic radius of the B site are different. In order to substitute and dissolve the rare earth element in the A site and the B site in a well-balanced manner, it is preferable that the ionic radius of the rare earth element is between the ionic radius of the A site and the ionic radius of the B site. For example, in the case of using _BaTiO3 as perovskite, it is preferable to substitute and dissolve La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, etc., in Table 1. The source of Table 1 is "R.D. Shannon, Acta Crystallogr., A32, 751 (1976)".

Elements with relatively large ionic radii, such as La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, tend to be substituted and dissolved in the A site. On the other hand, elements with relatively small ionic radii, such as Er, Tm, and Yb, tend to be substituted and dissolved in the B site. Therefore, when La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd are substituted and dissolved in the B site, it is preferable to also substituted and dissolved Er, Tm, and Yb.

In addition, in perovskite (A _m BO ₃ ) in which an element functioning as a donor is substituted and dissolved in the B site and a rare earth element is substituted and dissolved in both the A site and the B site, if the value of "m" is too small, problems such as reduced insulation occur. Therefore, it is preferable to set a lower limit for the value of "m". Specifically, it is preferable that m≧1.002. On the other hand, if the value of "m" is too large, problems such as reduced sinterability occur. Therefore, it is preferable to set an upper limit for the value of "m". Specifically, it is preferable that m≦1.010.

The average crystal grain size of the main component ceramic in the dielectric layer 11 is preferably 80 nm to 300 nm, and more preferably 80 nm to 200 nm. If the average crystal grain size of the main component ceramic is small, the dielectric constant will be low and the desired capacitance may not be obtained. On the other hand, if the average crystal grain size is large, when the dielectric layer 11 has a thickness of 1.0 μm or less, the grain boundary area acting as a barrier to the movement of oxygen defects will be reduced, and this may result in a decrease in life characteristics.

It is also possible to obtain high reliability by making the dielectric layer 11 thicker. However, in this case, the multilayer ceramic capacitor 100 becomes larger. Therefore, this embodiment is particularly effective for a small multilayer ceramic capacitor 100. For example, this embodiment is particularly effective for a thin-layer multilayer ceramic capacitor in which the dielectric layer 11 is 1.0 μm or less thick. Furthermore, if the thickness of the dielectric layer 11 is 0.4 μm or less, a smaller and more reliable multilayer ceramic capacitor can be obtained. It is more preferable that the thickness of the dielectric layer 11 is 0.2 μm or more so as not to reduce the insulation resistance value.

Next, we will explain the manufacturing method of the multilayer ceramic capacitor 100. Figure 2 is a diagram illustrating the flow of the manufacturing method of the multilayer ceramic capacitor 100.

(Raw material powder preparation process)
First, a ceramic raw material powder is prepared in which a perovskite structure represented by the general formula _ABO3 is the main phase, an element functioning as a donor is substituted and dissolved in the B site, and rare earth elements are substituted and dissolved in both the A site and the B site. The ceramic material using the ceramic raw material powder is the main component of the dielectric layer 11. As a method for synthesizing the ceramic raw material powder, various methods have been known in the past, such as a solid-phase synthesis method, a sol-gel synthesis method, a hydrothermal synthesis method, and the like. In addition, when the amount of the rare earth element substituted and dissolved in the A site is the amount of solid solution in the A site, and the amount of the rare earth element substituted and dissolved in the B site is the amount of solid solution in the B site, 0.75≦(amount of solid solution in the A site/amount of solid solution in the B site)≦1.25 is set. As an example, the solid-phase synthesis method will be described. First, a slurry is prepared by mixing _TiO2 powder and _BaCO3 powder with a solvent such as pure water and a dispersant. Next, a solution in which rare earth elements are dissolved in acetic acid is neutralized and added to the slurry, and kneaded and dispersed. A molybdenum compound powder may be added to the slurry, and the molybdenum may be kneaded and dispersed in an ionized or complexed state. The kneading and dispersion is carried out for 20 to 30 hours using a bead mill or the like. The slurry is then dried to obtain a green material. The green material is subjected to a first calcination at 800°C to 1150°C to obtain a ceramic raw material powder.

The resulting ceramic raw material powder is added with a specific additive compound according to the purpose. Examples of additive compounds include oxides of Mg (magnesium), Mn (manganese), V (vanadium), and Cr (chromium), as well as oxides or glasses of Co (cobalt), Ni, Li (lithium), B (boron), Na (sodium), K (potassium), and Si (silicon).

For example, a compound containing an additive compound is mixed with the ceramic raw material powder and a second calcination is performed at 820 to 1150°C. Next, the mixture is wet mixed, dried and pulverized to prepare the ceramic material. For example, the average particle size of the ceramic material is preferably 50 to 150 nm from the viewpoint of thinning the dielectric layer 11. For example, the ceramic material obtained as described above may be pulverized as necessary to adjust the particle size, or may be combined with a classification process to adjust the particle size. The above steps produce the ceramic material that will be the main component of the dielectric layer.

(Lamination process)
Next, a binder such as polyvinyl butyral (PVB) resin, an organic solvent such as ethanol or toluene, and a plasticizer are added to the obtained ceramic material and wet mixed. Using the obtained slurry, a belt-shaped dielectric green sheet having a thickness of, for example, 3 μm to 10 μm is coated on a substrate by, for example, a die coater method or a doctor blade method, and then dried.

Next, a metal conductive paste for forming an internal electrode containing an organic binder is printed on the surface of the dielectric green sheet by screen printing, gravure printing, or the like to arrange an internal electrode layer pattern that is alternately drawn to a pair of external electrodes with different polarities. Ceramic particles are added to the metal conductive paste as a co-material. The main component of the ceramic particles is not particularly limited, but is preferably the same as the main component ceramic of the dielectric layer 11. For example, _BaTiO3 with an average particle size of 50 nm or less may be uniformly dispersed.

Then, the dielectric green sheet on which the internal electrode layer pattern is printed is punched out to a specified size, and the punched out dielectric green sheet is laminated in a specified number of layers (e.g., 100 to 500 layers) with the base material peeled off so that the internal electrode layers 12 and the dielectric layers 11 are alternated and the internal electrode layers 12 are alternately exposed at both longitudinal end faces of the dielectric layers 11 and drawn out alternately to a pair of external electrodes 20a, 20b of different polarity. Cover sheets for forming the cover layers 13 are pressed onto the top and bottom of the laminated dielectric green sheets, and the laminated dielectric green sheets are cut to the specified chip dimensions (e.g., 1.0 mm x 0.5 mm).

The obtained ceramic laminate is debindered in a _N2 atmosphere, and then a metal paste that contains a metal filler including the main component metal of the external electrodes 20a, 20b, a co-material, a binder, a solvent, etc. and that serves as a base layer for the external electrodes 20a, 20b is applied to both end faces and each side face of the ceramic laminate, and then dried.

(Firing process)
The molded body thus obtained is subjected to a binder removal process in a _N2 atmosphere at 250 to 500°C, and then fired for 10 minutes to 2 hours at 1100 to 1300°C in a reducing atmosphere with an oxygen partial pressure of ^10-5 to ^10-8 atm, causing the particles in the molded body to sinter and grow. In this way, a sintered body is obtained.

(Reoxidation treatment process)
After that, a re-oxidation process is performed in a _N2 gas atmosphere at 600° C. to 1000° C. This process suppresses oxygen defects.

(External electrode formation process)
Thereafter, the undercoat layers of the external electrodes 20a and 20b are coated with a metal such as Cu, Ni, Sn, etc. by plating.

According to the manufacturing method of this embodiment, in the ceramic raw material powder used in the raw material powder preparation process, an element that functions as a donor is substituted and solid-solved in the B site of the perovskite structure, so that oxygen defects in the perovskite structure are suppressed in the firing process. As a result, the dielectric layer 11 can be extended in life and improved in reliability. In addition, since rare earth elements are substituted and solid-solved in the A site and the B site, the amount of oxygen defects after firing is suppressed. As a result, long life characteristics can be achieved while maintaining the insulating characteristics. As a result, high reliability can be achieved. In addition, by making 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25, the amount of oxygen defects after firing is suppressed, and high reliability with an excellent balance between insulating characteristics and life characteristics can be obtained.

From the viewpoint of further suppressing the state of excessive donor addition, it is preferable that (A-site solid solution amount/B-site solid solution amount)≦1.20, more preferably that (A-site solid solution amount/B-site solid solution amount)≦1.10, and even more preferably that (A-site solid solution amount/B-site solid solution amount)≦1.05. From the viewpoint of further suppressing the state of excessive acceptor addition, it is preferable that 0.90≦(A-site solid solution amount/B-site solid solution amount) and more preferably that 0.95≦(A-site solid solution amount/B-site solid solution amount)

If there is too little element functioning as a donor in the B site, oxygen defects may not be sufficiently suppressed. Therefore, it is preferable to set a lower limit on the amount of the element functioning as a donor in the B site that is substituted and dissolved. For example, it is preferable that the element functioning as a donor in the B site is substituted and dissolved at 0.05 atm% or more, and more preferably 0.1 atm% or more, when the main component elements in the B site are taken as 100 atm%.

On the other hand, if there are too many elements functioning as donors in the B site, problems such as reduced insulation may occur. Therefore, it is preferable to set an upper limit on the amount of the elements functioning as donors in the B site. For example, it is preferable that the elements functioning as donors in the B site are substituted and dissolved at 0.3 atm % or less, and more preferably substituted and dissolved at 0.25 atm % or less.

If the amount of rare earth elements in the A and B sites is too small, the amount of oxygen defects after firing may not be sufficiently suppressed. Therefore, it is preferable to set a lower limit for the total amount of rare earth elements in the A and B sites. For example, it is preferable that the total amount of rare earth elements in the A and B sites is 0.2 atm% or more, and more preferably 0.3 atm% or more. Here, atm% means the concentration when the B site elements of _ABO3 in the ceramic raw material powder are 100 atm%.

On the other hand, if there is too much rare earth element in the A site and B site, the tetragonality of the crystal grains may decrease, causing problems such as a decrease in the dielectric constant. Therefore, it is preferable to set an upper limit on the total amount of rare earth element substituted in solid solution in the A site and B site. For example, it is preferable that the total amount of rare earth element substituted in solid solution in the A site and B site is 1.0 atm% or less, and more preferably 0.9 atm% or less.

As the rare earth element, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, etc. can be used. The ionic radius of the A site and the ionic radius of the B site are different. In order to substitute and dissolve the rare earth element in the A site and the B site in a well-balanced manner, it is preferable that the ionic radius of the rare earth element is between the ionic radius of the A site and the ionic radius of the B site. For example, from Table 1, when BaTiO ₃ is used as the perovskite, it is preferable to substitute and dissolve La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, etc.

Elements with relatively large ionic radii, such as La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd, tend to be substituted and dissolved in the A site. On the other hand, elements with relatively small ionic radii, such as Er, Tm, and Yb, tend to be substituted and dissolved in the B site. Therefore, when La, Ce, Pr, Nd, Pm, Sm, Eu, and Gd are substituted and dissolved in the B site, it is preferable to also substituted and dissolved Er, Tm, and Yb.

In addition, in perovskite (A _m BO ₃ ) in which an element functioning as a donor is substituted and dissolved in the B site and a rare earth element is substituted and dissolved in both the A site and the B site, if the value of "m" is too small, problems such as reduced insulation occur. Therefore, it is preferable to set a lower limit for the value of "m". Specifically, it is preferable that m≧1.002. On the other hand, if the value of "m" is too large, problems such as reduced sinterability occur. Therefore, it is preferable to set an upper limit for the value of "m". Specifically, it is preferable that m≦1.010.

The multilayer ceramic capacitor according to the embodiment was fabricated and its characteristics were investigated.

First, a ceramic raw material powder of _BaTiO3 was prepared in which an element functioning as a donor was substituted and dissolved in the B site, and rare earth elements were substituted and dissolved in both the A site and the B site. The average particle size was 150 nm. In all of Examples 1 to 11 and Comparative Examples 1 to 9, 0.2 atm % of Mo was substituted and dissolved in the B site when Ti was 100 atm %.

In Examples 1 and 2, a ceramic raw material powder in which 0.2 atm% Ho was substituted as a rare earth element and then 0.8 atm% Ho was added as Ho ₂ O _3. In Examples 3 to 7, a ceramic raw material powder in which 0.5 atm% Ho was substituted as a rare earth element and then 0.5 atm% Ho was added as Ho ₂ O _3. In Example 8, a ceramic raw material powder in which 0.25 atm% Gd and Yb were substituted as rare earth elements and then 0.25 atm% Gd was added as Gd ₂ O ₃ , and 0.25 atm% Yb was added as Yb _{2 O 3. In Examples 9 to 11, a ceramic raw material powder in which 1.0 atm% Ho was substituted as a rare earth element and then added as Ho 2} O ₃ . In Comparative Example 1, the ceramic raw material powder was not substituted with a rare earth element, and 1.0 atm% of Ho was added as Ho ₂ O _3. In Comparative Example 2, a ceramic raw material powder with 0.2 atm% of Ho substituted and solid-solved was used, and then 0.8 atm% of Ho was added as Ho ₂ O _3. In Comparative Examples 3 to 5, a ceramic raw material powder with 0.5 atm% of Ho substituted and solid-solved was used, and then 0.5 atm% of Ho was added as Ho ₂ O _3. In Comparative Example 6, a ceramic raw material powder with 0.2 atm% and 0.3 atm% of Gd and Yb substituted and solid-solved as rare earth elements was used, and then 0.2 atm% of Gd was added as Gd ₂ O ₃ , and 0.3 atm% of Yb was added as Yb ₂ O ₃ . _{In Comparative Example 7, a ceramic raw material powder in which 0.3 atm % and 0.2 atm % Gd and Yb, respectively, were substituted and solid-solved as rare earth elements was used, and then 0.3 atm % equivalent of Gd was added as Gd2O3 ,} and _0.2 atm % equivalent of Yb was added as _Yb2O3 . In Comparative Examples 8 and 9, a ceramic raw material powder in which 1.0 atm % of Ho was substituted and solid-solved as a rare earth element was used. In this paragraph, atm % means a concentration when the B site of _ABO3 of the ceramic raw material powder is 100 atm %.

In Example 1, (amount of solid solution at A site/amount of solid solution at B site) was 0.95. In Example 2, (amount of solid solution at A site/amount of solid solution at B site) was 1.10. In Example 3, (amount of solid solution at A site/amount of solid solution at B site) was 0.75. In Example 4, (amount of solid solution at A site/amount of solid solution at B site) was 0.95. In Example 5, (amount of solid solution at A site/amount of solid solution at B site) was 1.00. In Example 6, (amount of solid solution at A site/amount of solid solution at B site) was 1.05. In Example 7, (amount of solid solution at A site/amount of solid solution at B site) was 1.25. In Example 8, (amount of solid solution at A site/amount of solid solution at B site) was 1.10. In Example 9, (amount of solid solution at A site/amount of solid solution at B site) was 0.75. In Example 10, (A-site solid solution amount/B-site solid solution amount) was 1.03. In Example 11, (A-site solid solution amount/B-site solid solution amount) was 1.20. In Comparative Example 2, (A-site solid solution amount/B-site solid solution amount) was 1.32. In Comparative Example 3, (A-site solid solution amount/B-site solid solution amount) was 0.50. In Comparative Example 4, (A-site solid solution amount/B-site solid solution amount) was 1.35. In Comparative Example 5, (A-site solid solution amount/B-site solid solution amount) was 1.50. In Comparative Example 6, (A-site solid solution amount/B-site solid solution amount) was 0.70. In Comparative Example 7, (A-site solid solution amount/B-site solid solution amount) was 1.50. In Comparative Example 8, (A-site solid solution amount/B-site solid solution amount) was 0.66. In Example 9, the ratio (A site solid solution amount/B site solid solution amount) was 1.30.

The amount of substituted solid solution was measured by using a transmission electron microscope (TEM) and energy dispersive X-ray fluorescence spectrometry (EDS) on a sample made by etching the ceramic raw material powder into a hemispherical shape using Ar ions. The amount of (A-site solid solution amount/B-site solid solution amount) was measured on the same processed sample using high-angle annular dark-field scanning transmission microscopy (HADDF-STEM).

In all of Examples 1 to 11 and Comparative Examples 1 to 9, the value of "m" in A _m BO ₃ in which Mo is substituted and dissolved in the B site and a rare earth element is substituted and dissolved in both the A site and the B site was set to 1.002.

To the ceramic raw material powder, 1.0 mol% of MgO was added as an additive, 0.05 mol% each of _MnO and _V2O5 were added as additives, and 1.0 mol% each of _SiO2 and _BaCO3 were added as sintering aids. In this case, "mol%" is the value when the _ABO3 of the ceramic raw material powder is 100 mol%.

The ceramic raw material powder to which additives and sintering aids had been added was thoroughly wet mixed and ground in a ball mill to obtain a ceramic material. An organic binder and a solvent were added to the ceramic material, and a dielectric green sheet was produced by the doctor blade method. The coating thickness of the dielectric green sheet was set to 0.8 μm, and polyvinyl butyral (PVB) or the like was used as the organic binder, and ethanol, toluene acid, etc. were added as the solvent. In addition, plasticizers and the like were added. Next, a conductive paste for forming the internal electrode, which contains powder of the main component metal (Ni) of the internal electrode layer 12, a co-material (barium titanate), a binder (ethyl cellulose), a solvent, and other auxiliary agents as necessary, was produced in a planetary ball mill.

A conductive paste for forming an internal electrode was screen-printed on a dielectric sheet. 250 sheets on which the conductive paste for forming an internal electrode was printed were stacked, and a cover sheet was laminated on the top and bottom of each sheet. Then, a ceramic laminate was obtained by thermocompression bonding, and cut into a predetermined shape. After the obtained ceramic laminate was debindered in a _N2 atmosphere, a metal paste containing a metal filler mainly composed of Ni, a co-material, a binder, a solvent, etc., which would become the base layer of the external electrodes 20a, 20b was applied from both end faces to each side of the ceramic laminate, and then dried. Then, the metal paste was fired simultaneously with the ceramic laminate at 1100°C to 1300°C for 10 minutes to 2 hours in a reducing atmosphere to obtain a sintered body.

The dimensions of the obtained sintered body were length 0.6 mm, width 0.3 mm, and height 0.3 mm. The sintered body was reoxidized under conditions of _N2 atmosphere at 800°C, and then plated to form a Cu plating layer, a Ni plating layer, and a Sn plating layer on the surface of the base layer of the external electrodes 20a and 20b, thereby forming the external electrodes 20a and 20b, and the multilayer ceramic capacitor 100 was obtained.

(analysis)
Twenty samples were prepared for each of Examples 1 to 11 and Comparative Examples 1 to 9. A life characteristic test was conducted for each sample to measure the average life. The life characteristic test was conducted at 125° C. with a direct current voltage of 10 V applied, the leakage current value was measured with an ammeter, and the time until dielectric breakdown occurred was taken as the life value. An insulation resistance test was also conducted for each sample to measure the average insulation resistance. The insulation resistance test was conducted at room temperature with a direct current voltage of 10 V applied, and the resistance was measured from the current value after 60 seconds.

If the average life was 100 min or less, the life characteristics were judged to be unacceptable (x). If the insulation resistance was 10 MΩ or less, the insulation characteristics were judged to be unacceptable (x). If either the life characteristics or the insulation characteristics were judged to be unacceptable, the reliability was judged to be unacceptable. The results are shown in Figure 3.

In Comparative Example 1, both the life characteristics and the insulation characteristics were judged to be unacceptable. This is believed to be because the rare earth element was not substituted into a solid solution in the ceramic raw material powder used, and therefore it was not possible to sufficiently substitute and dissolve the rare earth element. In Comparative Examples 2, 4, 5, 7, and 9, the life characteristics were judged to be acceptable, but the insulation characteristics were judged to be unacceptable. This is believed to be because (A-site solid solution amount/B-site solid solution amount) exceeded 1.25. In Comparative Examples 3, 6, and 8, the insulation characteristics were judged to be acceptable, but the life characteristics were judged to be unacceptable. This is believed to be because (A-site solid solution amount/B-site solid solution amount) fell below 0.75.

In contrast, in all of Examples 1 to 11, both the life characteristics and the insulating characteristics were judged to be acceptable. This is believed to be because an element that functions as a donor was substituted and dissolved in the B site, and rare earth elements were substituted and dissolved in both the A site and the B site, so that (amount of solid solution in the A site/amount of solid solution in the B site) was in the range of 0.75 to 1.25.

In addition, in Examples 4 and 5, the insulation resistance and life characteristics are better than in Example 3. This is believed to be because (A-site solid solution amount/B-site solid solution amount) is 0.95 or more. In Example 2, the insulation resistance and life characteristics are better than in Example 7. This is believed to be because (A-site solid solution amount/B-site solid solution amount) is 1.10 or less. In Examples 5 and 6, the insulation resistance and life characteristics are better than in Example 2. This is believed to be because (A-site solid solution amount/B-site solid solution amount) is 1.05 or less. In Example 10, the life characteristics are better than in Example 9. This is believed to be because (A-site solid solution amount/B-site solid solution amount) is 0.95 or more. In addition, in Example 10, the life characteristics are better than in Example 11. This is believed to be because (A-site solid solution amount/B-site solid solution amount) is 1.05 or less.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and variations are possible within the scope of the gist of the present invention as described in the claims.

REFERENCE SIGNS LIST 10 laminated chip 11 dielectric layer 12 internal electrode layer 13 cover layer 20a, 20b external electrode 100 laminated ceramic capacitor

Claims (2)

The laminate is made up of dielectric layers and internal electrode layers stacked alternately,
The main component of the dielectric layer is a ceramic material having a perovskite structure represented by the general formula _ABO3 as a main phase, containing an element functioning as a donor in the B site, and containing rare earth elements in both the A site and the B site,
a ratio of the amount of the rare earth element dissolved in the A site (A site solid solution amount) to the amount of the rare earth element dissolved in the B site (B site solid solution amount) satisfies 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25,
In the B site, an element functioning as a donor is substituted and dissolved in an amount of 0.05 atm % or more and 0.3 atm % or less when the main component element of the B site is taken as 100 atm % ,
The multilayer ceramic capacitor _has a perovskite structure selected from the group consisting of BaTiO3 , _{CaZrO3 , CaTiO3} , _SrTiO3 , _and Ba1 _- xyCaxSryTi1 _{- zZrzO3} ( 0 ≦ x≦1, 0≦y≦1, 0≦z≦1) _. The main phase is a perovskite structure represented by the general formula _ABO3 , the B site contains an element that functions as a donor, and both the A site and the B site contain rare earth elements,
a ratio of the amount of the rare earth element dissolved in the A site (A site solid solution amount) to the amount of the rare earth element dissolved in the B site (B site solid solution amount) satisfies 0.75≦(A site solid solution amount/B site solid solution amount)≦1.25,
In the B site, an element functioning as a donor is substituted and dissolved in an amount of 0.05 atm % or more and 0.3 atm % or less when the main component element of the B site is taken as 100 atm % ,
The ceramic _raw material powder is characterized in that the perovskite structure is any one of BaTiO3, CaZrO3, CaTiO3, SrTiO3, or Ba1-x-yCaxSryTi1 - _zZrzO3 ( 0 _{≦ x} ≦ ₁ , ₀ ≦ _y ≦ _{1, 0} ≦ _z ≦ 1).

Images