JP2006179675A - Multilayer ceramic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor and its manufacturing method wherein, if a dielectric porcelain composed of BST crystal particles and BT crystal particles is used as a dielectric layer, variations of the particle growth of the BST crystal particles are small, and even in a mass production using a tunnel type large-sized sintering furnace, a specific inductive capacity, a temperature characteristic, and a high temperature load test characteristic can be enhanced. <P>SOLUTION: A main crystal particle is a crystal particle in which Ba and Ti are main components and an Sr component concentration is different, and which contains Mg, an rare earth element and Mn. When Ba or a combined amount of Ba and Ca is A mol and Ti is B mol, there is provided a capacitor body 1 obtained by alternately stacking a dielectric layer 5 which satisfies a relationship of A/B≥1.003 at a mol ratio and an internal electrode layer 7. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a monolithic ceramic capacitor and a method for producing the same, and more particularly to a monolithic ceramic capacitor having a small size and a high capacity and high reliability and a method for producing the same.

  In recent years, with the spread of mobile devices such as mobile phones and the high speed and high frequency of semiconductor elements, which are the main components of personal computers, multilayer ceramic capacitors mounted on such electronic devices are required to be smaller and have higher capacities. Increasingly.

  Therefore, the dielectric layer constituting the multilayer ceramic capacitor has been made thin and highly laminated. For example, in Patent Document 1, a part of the A site is Ca in the dielectric powder constituting the dielectric ceramic. The barium titanate crystal particles in the dielectric layer after firing using a mixture of barium titanate powder (BCT powder) substituted with bismuth and barium titanate powder (BT powder) not containing substituted Ca The DC bias characteristics are improved along with the improvement of the atomization and the relative dielectric constant.

  By the way, among the barium titanate crystal particles constituting the dielectric ceramic described in Patent Document 1, the BCT crystal particles are added with Mg, rare earth elements, etc. which are indispensable for controlling the temperature characteristics of the relative dielectric constant. When mixed with the ingredients and fired, grain growth is likely to occur with the diffusion of Ca contained in the BCT powder, and strict control of conditions in firing is required. In particular, a raw material having a particle size of submicron or less is used. In such a case, it is known that it is not easy to produce a sintered body made of fine barium titanate crystal particles because of significant grain growth.

Therefore, in the above-mentioned Patent Document 1, in order to suppress grain growth of BCT crystal particles during firing, when mixing BT powder coated with Mg and rare earth element oxide and BCT powder, MnCO ₃ , By adding MgO and rare earth oxide, a coating layer composed of a highly insulating composite oxide is formed almost uniformly on the surface of the BT crystal particles after firing, and an excess of Mg and rare earth elements with respect to the BCT crystal particles. Suppresses solid solution and grain growth.

In recent years, (Ba _1-x Sr _x ) TiO _{3 in} which the Ca site of the BCT powder is replaced with Sr is used as the high dielectric constant material for the multilayer ceramic capacitor as well as the BT powder and the BCT powder. It has been found and used for dielectric layers of high-capacity multilayer ceramic capacitors and thin film capacitors (Patent Documents 2 and 3).
JP 2003-40671 A JP 2004-262717 A JP 2004-281446 A

According to the manufacturing method described in Patent Document 1, in the case of adopting firing conditions using a small experimental firing furnace capable of highly controlling the firing temperature, BT coated with the above-described Mg and rare earth oxides is used. When the powder and the BCT powder are mixed, a sample satisfying the desired relative dielectric constant, temperature characteristics, and high temperature load test can be formed even by using a method of adding MnCO ₃ , MgO, and rare earth oxide.

However, at the control level of the firing temperature for a large tunnel-type firing furnace used for mass production of multilayer ceramic capacitors, there is a large variation in the maximum temperature during firing in the firing furnace, and thus grain growth of BCT crystal grains. There is a problem in that the variation in the number of particles is likely to occur, and there are many cases where the relative permittivity, temperature characteristics, and high temperature load test characteristics are not satisfied, and the yield in mass production decreases. Further, such a problem in mass production also occurred in the same manner when the (Ba _1-x Sr _x ) TiO ₃ -based high dielectric constant material introduced as Patent Documents 2 and 3 was used.

  Therefore, the present invention suppresses grain growth of BST crystal particles even when a dielectric ceramic composed of BST crystal particles and BT crystal particles is used as a main crystal particle as a dielectric layer, and uses a tunnel-type large firing furnace. An object of the present invention is to provide a multilayer ceramic capacitor capable of improving the relative permittivity, temperature characteristics, and high temperature load test characteristics even in mass production, and a method for producing the same.

  The multilayer ceramic capacitor of the present invention is (1) a multilayer ceramic capacitor comprising a capacitor body in which dielectric layers composed of main crystal grains and grain boundary phases and internal electrode layers are alternately stacked. The particles are mainly composed of Ba and Ti and have different Sr component concentrations, and contain Mg, rare earth elements and Mn, and the dielectric layer has a molar amount of Ba or Ba and Sr. When Ti is B mole, the relationship of A / B ≧ 1.003 is satisfied in terms of molar ratio.

In the multilayer ceramic capacitor, (2) the main crystal particles are composed of BT crystal particles having a Sr component concentration of 0.2 atomic% or less and BST crystal particles having a Sr component concentration of 0.4 atomic% or more, and When the total amount of Ba and Sr in the BST crystal grains having an Sr component concentration of 0.4 atomic% or more is A mol and Ti is B mol, the relationship of A / B ≧ 1.003 is given as the molar ratio. (3) the combined concentration of Mg, rare earth element and Mn contained in the BST crystal particles is higher than the combined concentration of Mg, rare earth element and Mn contained in the BT crystal particles; (4) The average grain size of the main crystal particles is 0.4 μm or less, (5) the thickness of the dielectric layer is 3 μm or less, and the number of stacked layers is 100 or more,
The manufacturing method of the multilayer ceramic capacitor of the present invention is as follows: (6) A multilayer ceramic capacitor for firing a capacitor main body formed by alternately laminating green sheets containing dielectric powder and organic resin and internal electrode patterns. In the manufacturing method, the dielectric powder is (a) a mixed powder mainly composed of at least two kinds of Ba and Ti having different Sr component concentrations, and the mixed powder includes (a) Mg, a rare earth element, And an oxide of Mn, (c) a glass powder having an alumina content of 1% by mass or less, and (d) a barium carbonate powder.

  The method for producing a multilayer ceramic capacitor according to the present invention includes: (7) a multilayer ceramic capacitor for firing a capacitor main body formed by alternately laminating green sheets containing dielectric powder and organic resin and internal electrode patterns. In the manufacturing method, the dielectric powder is (f) coated with Mg, rare earth element and Mn oxide, respectively. (G) Ba and Ti in which part of the A site is substituted with Sr as main components. A powder (BST powder), a mixed powder with a powder containing Ba and Ti as main components (BT powder) not containing Sr, and the mixed powder has (a) alumina content. 1% by mass or less of glass and (g) barium carbonate powder are added.

  In the above method for producing a multilayer ceramic capacitor, (8) when B and B in the BST powder are A and Ti is B, the molar ratio is A / B is 1.003 or more; (9) BST powder (10) BST powder, BT powder, glass powder and barium carbonate, wherein the total concentration of Mg, rare earth element and Mn contained in the BT powder is higher than the total concentration of Mg, rare earth element and Mn contained in the BT powder. It is desirable that the average particle diameter of the powder is 0.5 μm or less.

  According to the multilayer ceramic capacitor of the present invention, the BST crystal particles and BT crystal particles constituting the dielectric layer constituting the multilayer ceramic capacitor contain Mg, rare earth elements and Mn, and Ba or a combination of Ba and Ca. When the amount is A mole and Ti is B mole, by using a material satisfying the relationship of A / B ≧ 1.003 in terms of molar ratio, variation in grain growth of BST crystal grains can be reduced, and the ratio Dielectric constant, temperature characteristics and high temperature load test characteristics can be improved. In addition, the above dielectric constant can be used in the mass production of a multilayer ceramic capacitor using a tunnel-type large firing furnace that has a large variation in the maximum temperature during firing in the firing furnace. And temperature characteristics and high-temperature load test characteristics are stabilized, and the yield can be increased.

  That is, according to the method for producing a multilayer ceramic capacitor of the present invention, as the dielectric powder, for example, (a) for a mixed powder mainly containing at least two types of Ba and Ti having different Sr component concentrations, (B) By adding Mg, rare earth elements, and Mn oxides, (c) glass having an alumina content of 1% by mass or less, and (d) barium carbonate powder, In mass production, the relative permittivity of a dielectric layer having BST crystal particles and BT crystal particles as main crystal particles can be obtained even when a tunnel-type large-scale firing furnace having a large variation in the maximum temperature during firing in the firing furnace is used. The temperature characteristics and the multilayer ceramic capacitor high-temperature load test characteristics including the dielectric layer are stabilized, and the yield can be easily increased.

(Construction)
The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic sectional view of FIG. FIG. 1 is a schematic cross-sectional view showing a multilayer ceramic capacitor of the present invention. The enlarged drawing of the drawer is a schematic diagram showing the main crystal grains and the grain boundary layer constituting the dielectric layer. In the multilayer ceramic capacitor of the present invention, external electrodes 3 are formed at both ends of the capacitor body 1. The external electrode 3 is formed, for example, by baking Cu or an alloy paste of Cu and Ni.

  The capacitor body 1 is configured by alternately laminating dielectric layers 5 and internal electrode layers 7. The dielectric layer 5 is composed of main crystal grains 9 and a grain boundary layer 11. The thickness is preferably 3 μm or less, and particularly preferably 2.5 μm or less in order to reduce the size and capacity of the multilayer ceramic capacitor. Further, in the present invention, in order to stabilize the capacitance variation and the capacitance-temperature characteristics, It is more desirable that the thickness variation of the dielectric layer 5 is within 10%.

  The internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) in that the manufacturing cost can be suppressed even if the internal electrode layer 7 is highly laminated. In particular, simultaneous firing with the dielectric layer 5 according to the present invention is possible. Nickel (Ni) is more preferable in that it can be achieved.

  The average grain size of the main crystal grains 9 according to the present invention is preferably 0.4 μm or less and d90 is 0.7 μm or less in terms of achieving high capacity and high insulation by thinning the dielectric layer 5. d90 is a 90% cumulative cumulative value by mass in the particle size distribution. On the other hand, the lower limit of the particle size of the BST crystal particles and the BT crystal particles is preferably 0.15 μm or more because it increases the relative dielectric constant of the dielectric layer and suppresses the temperature dependence of the relative dielectric constant.

  The main crystal particles 9 constituting the dielectric layer 5 according to the present invention are crystal particles mainly composed of Ba and Ti and having different Sr component concentrations. That is, it consists of perovskite-type barium titanate crystal particles (BST crystal particles) in which a part of the A site is substituted with Sr and perovskite-type barium titanate crystal particles (BT crystal particles) that do not contain substituted Sr.

That is, the main crystal particle 9 according to the present invention contains the BST crystal particle 9a and the BT crystal particle 9b, and is excellent by the coexistence of such two kinds of crystal particles as described above. Show the characteristics. Of the main crystal particles 9 according to the present invention, the BT crystal particles 9b are ideally represented by BaTiO ₃ . In the present invention, the BT crystal particle 9b not containing Sr has an Sr concentration of 0.2 atomic% or less as an analytical value, but the Sr component contained in the BST crystal particle 9a is small. And those which diffuse into the BT crystal particles 9b.

  On the other hand, the BST crystal particles have a Sr component concentration of 0.4 atomic% or more, and in particular, the SST component concentration is 0.5 to 5 in that the BST crystal particles maintain the function as a ferroelectric having a high relative dielectric constant. It is desirable to be 2.5 atomic%.

Here, the BST crystal particle 9a which is one crystal particle constituting the main crystal particle 9 is a perovskite type barium titanate in which a part of the A site is substituted with Sr as described above. represented by _{Ba 1-x Sr x) TiO} 3. In the present invention, the amount of Sr substitution in the A site in the BST crystal particle 9a is preferably X = 0.01 to 0.2, particularly preferably X = 0.02 to 0.07. If the Sr substitution amount is within this range, the phase transition point near room temperature is shifted to a sufficiently low temperature side, and the coexistence structure with BT crystal particles provides excellent temperature characteristics and DC bias characteristics in the temperature range used as a capacitor. This is because it can be secured.

In the present invention, the BST crystal particles 9a and the BT crystal particles 9b constituting the main crystal particles of the dielectric layer 5 are obtained by evaluating the cross section or surface of the dielectric layer 5 in the evaluation based on the index when the Sr concentration is defined. When the ratio of the BST crystal particles 9a is A _BST and the ratio of the BT crystal particles 9b is A _{BT in} the area ratio of each crystal particle in the crystal structure, the relationship of A _BT / A _BST = 0.1-3 is established. it is desirable to coexist in a tissue proportions having, in particular, dielectric constant, preferably _a BT _{/ a} BST = _0.3~2 in that further improve the temperature characteristics and the DC bias characteristics.

Each of the BST crystal particles 9a and the BT crystal particles 9b contains Mg, rare earth elements, and Mn. The contents of Mg, rare earth elements, and Mn contained in these crystal particles are mainly With respect to 100 parts by mass of crystal particles, Mg is 0.04 to 0.14 parts by mass in terms of MgO, rare earth elements are 0.2 to 0.9 parts by mass in terms of Re ₂ O ₃ , and Mn is 0 in terms of MnCO _3. If it is 0.04 to 0.15 parts by mass (in the case of coating, it is in the form of MnO), the temperature characteristics of the capacitance can be further stabilized and the reliability in the high temperature load test can be improved.

  Furthermore, the total concentration of Mg, rare earth element and Mn contained in the BST crystal particle 9a is changed to the BT crystal particle 9b in terms of stabilizing the temperature characteristic of the capacitance and improving the reliability in the high temperature load test. More preferably, it is higher than the total concentration of Mg, rare earth element and Mn contained. Since these Mg, rare earth elements and Mn are derived from the sintering aid, these elements are solid-solved in the BST crystal particles 9a and BT crystal particles 9b, but partly exist in the grain boundary layer 11. In particular, it tends to exist as an amorphous material. That is, in the dielectric layer according to the present invention, Mg and rare earth elements are components having the core-shell structure of the BT crystal particles 9b and the BST crystal particles 9a, while Mn is a BT crystal particle 9b generated by firing in a reducing atmosphere. , Oxygen defects in the BST crystal particles 9a can be compensated for, and the insulation and high temperature load life can be improved.

  Further, in the dielectric layer 5 according to the present invention, the rare earth element contained in the main crystal grain 9 has a concentration gradient from the crystal grain surface to the inside of the grain with the grain boundary layer 11 as the grain surface being the highest concentration, and 0.05 atom % / Nm or more is desirable. In other words, if the concentration gradient of the rare earth element is such a condition, the X7R standard can be satisfied in terms of the capacitance temperature characteristics as well as the improvement of the relative permittivity and the high temperature load life. Here, the rare earth element in the present invention is preferably at least one of La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Y, Er, Tm, Yb, Lu, and Sc.

  Further, in the dielectric layer 5 according to the present invention, the amount of impurities of alumina contained in the porcelain is 1% by mass or less because the relative dielectric constant of the dielectric layer 5 can be maintained high and the resistance in the acceleration test is increased. It is desirable that

  As described above, the dielectric ceramic according to the present invention is characterized in that the BST crystal particles 9a and the BT crystal particles 9b coexist. In such a coexistence system, the BST crystal particles 9a and the BT crystal particles 9b are derived from the sintering aid on the particle surface side of the particle center, and in particular, form a core-shell type structure in which Mg and rare earth elements are unevenly distributed, As a result, the dielectric constant becomes high, and the temperature dependence and DC bias dependence of the relative dielectric constant are extremely small.

  Next, the characteristic expression mechanism of the main crystal particles 9 of barium titanate according to the present invention will be described. In general, BT crystal particles exhibit a large relative dielectric constant exceeding 4000 due to atomic fluctuation accompanying sequential phase transition, but because of the high relative dielectric constant due to atomic fluctuation, which is a precursor of sequential phase transition. The relative dielectric constant is greatly reduced by applying the DC bias. On the other hand, the phase transition temperature at the highest temperature (about 125 ° C.) among the three sequential phase transition points found in the BT crystal particles hardly changes even when a part of the A site is replaced with Sr. The structural phase transition point near room temperature and lower than that shifts to a low temperature in proportion to an increase in the amount of substituted Sr. That is, the major factor that the BT crystal particles exhibit a high dielectric constant is an increase in atomic fluctuation, which is a precursor of the structural phase transition near room temperature and at a lower temperature. Therefore, BST in which a part of the A site is substituted with Sr. In the crystal grains, the transition point near room temperature and at a lower temperature is shifted to a lower temperature side, and although the relative permittivity is decreased, the DC bias characteristics are greatly improved. That is, the dielectric ceramic according to the present invention realizes a coexistence structure of BT crystal particles exhibiting a high relative dielectric constant and excellent temperature characteristics and BST crystal particles excellent in DC bias characteristics, thereby making it possible to compare with BT crystals. It exhibits excellent DC bias characteristics, a high dielectric constant compared to the BST crystal, and low temperature dependence and DC bias dependence of the dielectric characteristics.

  In addition, in the present invention, the main crystal particle 9 is a crystal particle mainly composed of Ba and Ti and having different Sr component concentrations, and contains Mg, rare earth elements and Mn, and a combination of Ba or Ba and Ca. When the amount is A mole and Ti is B mole, it is important to satisfy the relationship of A / B ≧ 1.003 in terms of molar ratio. Furthermore, the crystal grains constituting the main crystal grain 9 When the total amount of Ba and Sr in the BST crystal particle 9a, which is one of the main, is A mole and Ti is B mole, it is desirable that A / B is 1.003 or more in terms of molar ratio. In the conventional BST crystal particle 9a, when it is mixed with Mg and rare earth elements, it is said that grain growth is likely to occur with the diffusion of Sr. In the present invention, the Ba, Sr site and Ti site of the BST crystal particle 9a By defining the A / B ratio, which is the ratio, as described above, the grain growth of the BST crystal grains 9a can be suppressed.

  On the other hand, when the BST crystal particles 9a do not contain Mg, rare earth elements, and Mn, or when the A / B ratio is 1.002 or less, the BST crystal particles 9a are likely to grow, resulting in a decrease in insulation. , Defects at high temperature load are likely to occur.

(Manufacturing method)
Next, the manufacturing method of the multilayer ceramic capacitor according to the present invention will be described in detail. FIG. 2 is a process diagram showing a method for producing the multilayer ceramic capacitor of the present invention.

  The method for producing a multilayer ceramic capacitor of the present invention is a method for producing a multilayer ceramic capacitor in which a capacitor body molded body configured by alternately laminating green sheets containing dielectric powder and organic resin and internal electrode patterns is fired. The dielectric powder is a mixed powder of a perovskite-type barium titanate powder (BST powder) in which part of the A site is substituted with Sr and a perovskite-type barium titanate powder (BT powder) that does not contain substituted Sr. On the other hand, it is characterized by adding oxides of Mg, rare earth elements and Mn, glass having an alumina content of 1% by mass or less, and barium carbonate powder.

  In this case, the dielectric powder includes a perovskite-type barium titanate powder (BST powder) in which a part of the A site is substituted with Sr, and a perovskite-type barium titanate powder (BT powder) that does not contain substituted Sr. With respect to 100 parts by mass of the mixed powder, Mg, rare earth elements, and Mn are converted into oxides, and the total content of 0.05 to 1.5 parts by mass of alumina is 0.5% by mass or less. ~ 1.4 parts by weight, 0.01 to 1 part by weight of barium carbonate powder added, desirable because of high dielectric constant, high insulation, temperature characteristics of dielectric constant and high temperature load life .

  Step (a): In the production method of the present invention, first, a ceramic slurry is prepared by mixing the following raw material powder with an organic resin such as polyvinyl butyral resin and a solvent such as toluene and alcohol using a ball mill or the like, The ceramic green sheet 21 is formed from the ceramic slurry using a sheet forming method such as a doctor blade method or a die coater method. The thickness of the ceramic green sheet 21 is preferably 1 to 4 μm from the viewpoint of thinning the dielectric layer for increasing the capacity and maintaining high insulation.

The dielectric powders that are BST powder in which part of the Ba site is substituted with Sr and BT powder not containing Sr used in the production method of the present invention are (Ba _1-x Sr _x ) TiO ₃ and BaTiO _{3, respectively.} It is the raw material powder represented by these. Here, the amount of Sr substitution in the A site in the BST powder is preferably X = 0.01 to 0.2, particularly preferably X = 0.03 to 0.1. The BST powder preferably has an atomic ratio A / B of A site (barium) and B site (titanium), which is a constituent component, of 1.003 or more. These BT powder and BST powder are synthesized by mixing compounds containing a Ba component, an Sr component, and a Ti component so as to have a predetermined composition. These dielectric powders are obtained by a synthesis method selected from a solid phase method, a liquid phase method (including a method of generating via oxalate), a hydrothermal synthesis method, and the like. Among these, the dielectric powder obtained by the hydrothermal synthesis method is desirable because the particle size distribution of the obtained dielectric powder is narrow and the crystallinity is high.

  The particle size distribution of the barium titanate powder (BT powder) and the barium calcium titanate powder (BST powder), which are dielectric powders according to the present invention, facilitates thinning of the dielectric layer 5 and It is desirable to be 0.15 to 0.4 μm from the viewpoint of increasing the relative dielectric constant.

Further, shown as a high dielectric powder having thus the dielectric constant, the crystallinity when evaluated using X-ray diffraction, for example, the peak of index (001) P _AA indicating tetragonal, cubic It is desirable that the ratio of the index (100) P _{BB to} the peak is P _AA / P _BB is 1.1 or more.

In the case of constituting the dielectric layer of the present invention, the mixing ratio of the BST powder and the BT powder is a ceramic obtained after firing, particularly in terms of further improving the relative permittivity, temperature characteristics, and DC bias characteristics. When the BST powder amount is W _BST and the BT powder amount is W _BT , the W _BST / W _BT ratio is preferably in the range of 0.95 to 1.05 by mass ratio.

  Mg, rare earth element and Mn added to the dielectric powder are each 0.04 to 0.14 parts by mass in terms of oxides with respect to 100 parts by mass of dielectric powder which is a mixture of BST powder and BT powder. It is preferable that they are 0.2-0.9 mass part and 0.04-0.15 mass part.

The glass powder added to the dielectric powder is composed of Li ₂ O, SiO ₂ , BaO and CaO as constituent components. The addition amount of the glass powder is preferably 0.5 to 1.4 parts by mass with respect to 100 parts by mass of the dielectric powder, which is a mixture of BST powder and BT powder, from the viewpoint of enhancing the sinterability of the porcelain. The composition is desirably Li ₂ O = 5 to 15 mol%, SiO ₂ = 40 to 60 mol%, BaO = 10 to 30 mol%, and CaO = 10 to 30 mol%. In the glass powder according to the present invention, In particular, it is important that the content of alumina is 1% by mass or less, and particularly 0.1% by mass or less is preferable. When the content of alumina is more than 1% by mass, the main crystal grains grow, the temperature characteristics of relative permittivity increase, and the high temperature load life decreases. The barium carbonate powder is preferably 0.01 to 1 part by mass with respect to 100 parts by mass of the dielectric powder, which is a mixture of BST powder and BT powder, for the purpose of suppressing grain growth.

  (B) Step: Next, a rectangular internal electrode pattern 23 is printed and formed on the main surface of the ceramic green sheet 21 obtained above. The conductor paste used as the internal electrode pattern 23 is prepared by using Ni, Cu or an alloy powder thereof as a main component metal, mixing ceramic powder as a co-material with this, and adding an organic binder, a solvent and a dispersant. As the metal powder, Ni is preferable because it enables simultaneous firing with the dielectric powder and is low in cost. BT crystal particles having a low Sr concentration are preferable as the ceramic powder. However, the internal electrode layer 7 according to the present invention connects the upper and lower dielectric layers 5 through the electrode layer by including the ceramic powder in the conductor paste. As a result, columnar ceramics are formed. Thereby, peeling between the dielectric layer 5 and the internal electrode layer 7 can be prevented. The ceramic powder used here can suppress abnormal grain growth of columnar ceramics during firing, and can increase mechanical strength. Moreover, the capacitance temperature dependency of the multilayer ceramic capacitor can be reduced by suppressing the abnormal grain growth of the columnar ceramics formed in the internal electrode layer. The thickness of the internal electrode pattern 23 is preferably 1 μm or less because the multilayer ceramic capacitor is miniaturized and the steps due to the internal electrode pattern 23 are reduced.

  According to the present invention, the ceramic pattern 25 may be formed with substantially the same thickness as the internal electrode pattern 23 around the internal electrode pattern in order to eliminate the step due to the internal electrode pattern 23 on the ceramic green sheet 21. preferable. As the ceramic component constituting the ceramic pattern 25, it is preferable to use the dielectric powder in terms of making the firing shrinkage in the simultaneous firing the same.

  Step (c): Next, a desired number of ceramic green sheets 21 on which internal electrode patterns are formed are stacked, a plurality of ceramic green sheets 21 on which no internal electrode pattern is formed, and the same number of upper and lower layers. The temporary laminated body is formed by overlapping. The internal electrode pattern in the temporary laminate is shifted by a half pattern in the longitudinal direction. By such a laminating method, the internal electrode patterns 23 can be alternately exposed on the end faces of the cut laminate.

  In the present invention, as described above, in addition to the method of forming and laminating the internal electrode pattern in advance on the main surface of the ceramic green sheet, after the ceramic green sheet is once in close contact with the underlying equipment, After the internal electrode pattern is printed and dried, a ceramic green sheet on which the internal electrode pattern is not printed is superimposed on the printed and dried internal electrode pattern and temporarily adhered, and the ceramic green sheet is adhered. And an internal electrode pattern can be formed by a method of sequentially printing.

  Next, the temporary laminate is pressed at a temperature higher and higher than the temperature and pressure at the time of the temporary laminate to form a laminate 29 in which the ceramic green sheet and the internal electrode pattern are firmly adhered.

  Next, the laminated body is cut along the cutting line h, that is, approximately at the center of the ceramic pattern 29 formed in the laminated body in a direction perpendicular to the longitudinal direction of the internal electrode pattern 25 ((c1 in FIG. 4). ) And (c2) of FIG. 4, the capacitor body molded body is formed so as to be cut in parallel to the longitudinal direction of the internal electrode pattern so that the end portion of the internal electrode pattern is exposed. On the other hand, in the widest portion of the internal electrode pattern, the internal electrode pattern is formed in an unexposed state on the side margin portion side.

Next, this capacitor body molded body is fired under a predetermined atmosphere at a temperature condition to form a capacitor body. In some cases, the capacitor body is chamfered at the ridge line portion, and from the opposite end surface of the capacitor body. Barrel polishing may be performed to expose the exposed internal electrode layer. In the production method of the present invention, degreasing is in the temperature range up to 500 ° C., the heating rate is 5 to 20 ° C./h, the firing temperature is in the range of 1130 to 1230 ° C., and the heating rate from degreasing to the maximum temperature is 200 to 500 ° C./h, holding time at the maximum temperature is 0.5 to 4 hours, the rate of temperature decrease from the maximum temperature to 1000 ° C. is 200 to 500 ° C./h, and the atmosphere (oxygen concentration PO ₂ ) is 10 ⁻⁷ to 10 ⁻⁵ Pa, heat treatment (reoxidation treatment) maximum temperature after firing is 900 to 1100 ° C.,
The atmosphere is preferably in nitrogen.

  Next, an external electrode paste is applied to the opposite ends of the capacitor body 3 and baked to form the external electrodes 5. A plating film is formed on the surface of the external electrode 5 in order to improve mountability.

    Next, the case where another dielectric powder according to the present invention is used will be described. In the production method of the multilayer ceramic capacitor of the present invention, apart from the method of adding Mg, rare earth element, Mn oxide powder to the BST powder and BT powder as described above, dielectric powder such as BST powder and BT powder. In addition, a dielectric powder previously coated with oxide powders of Mg, rare earth elements, and Mn can be used. In this case, the steps (a) to (c) in FIG. 4 are the same except that the dielectric powder is different.

  That is, the manufacturing method of the multilayer ceramic capacitor of the present invention is a multilayer ceramic that fires a capacitor body molded body formed by alternately laminating green sheets containing dielectric powder and organic resin and internal electrode patterns. In the method of manufacturing a capacitor, the dielectric powder is coated with an oxide of Mg, rare earth element, and Mn, and a perovskite-type barium titanate powder (BST powder) in which a part of the A site is substituted with Sr, 0.5 to 1.4 parts by mass of glass having an alumina content of 1% by mass or less with respect to 100 parts by mass of mixed powder with perovskite-type barium titanate powder (BT powder) not containing substituted Sr, It is preferable to add 0.01 to 1 part by mass of barium carbonate.

  In this case, compared with the case where the oxides of Mg, rare earth elements and Mn are added, there are few oxides of Mg, rare earth elements and Mn, and in particular, the amount of Mg and rare earth elements can be reduced. For this reason, the fall of the dielectric constant of BT powder and BST powder can be suppressed, and a more fine thing can be used about BT powder and BST powder used from this.

  The BT and BST powders can be coated with Mg, rare earth elements and Mn oxides by mixing a predetermined amount of Mg, rare earth elements and Mn oxides with the BT and BST powders, and by a mechanochemical method.

  In the present invention, since the BST and BT powders can be individually coated with Mg, rare earth elements, and Mn, the coating amount can be changed. In the present invention, the total concentration of Mg, rare earth element and Mn contained in the BST powder is preferably higher than the total concentration of Mg, rare earth element and Mn contained in the BT powder. By making the total concentration of Mg, rare earth element and Mn contained in the BST powder higher than the total concentration of Mg, rare earth element and Mn contained in the BT powder, grains of the BST powder that are more likely to grow during firing Growth can be effectively suppressed. At the same time, diffusion of Sr from the BST powder can be suppressed.

  The BST crystal particles and BT crystal particles according to the present invention described above generally tend to cause grain growth by atomic diffusion during sintering, and it is difficult to obtain a dense sintered body having a fine particle diameter. In particular, when the raw material particle size to be used is smaller than submicron, the surface area occupies a large proportion with respect to the particle volume, and the surface energy is large, resulting in an energetically unstable state. For this reason, during firing, grain growth is caused by atomic diffusion, the surface area is reduced, and stabilization is caused by a reduction in surface energy. Therefore, grain growth is likely to occur, and it is difficult to obtain a dense sintered body made of fine particles.

  Specifically, the sintered body composed of BT crystal particles 9b and BST crystal particles 9a having a fine particle size smaller than 0.2 μm easily causes solid solution / growth and suppresses movement of atoms between the particles. If no is introduced between the particles, a sintered body having a large particle size exceeding 1 μm is formed, and it is difficult to obtain a dense sintered body having a fine particle size of submicron or less. However, in the present invention, the microcrystal raw material is added with a molar ratio A / B of the total amount of Ba and Sr in the BST crystal particles 9a and Ti of 1.003 or more, and a rare earth element such as Mg and Y is added. By introducing it as an agent and adjusting the firing conditions, a fine particle sintered body reflecting the size of the raw crystal particles can be obtained. In the BT crystal particle 9b or the BST crystal particle 9a, when the element ratio on the Ba and Sr side is increased, the Ba and other additives are present on the surface of the main crystal particle 9, so that these Ba and other additives are diffused to the particle surface. Sintering is promoted by forming a phase, and the growth of Ba, Sr, and Ti atoms between BT and BST crystal grains that are in the vicinity of and at the grain boundary is suppressed and grain growth is suppressed. To do. As a result, a crystal phase in which Mg and rare earth elements are diffused and dissolved in addition to barium is formed on the crystal particle surface. That is, a core-shell structure in which Mg and rare earth elements are unevenly distributed on the particle surface is formed. The formation of such a core-shell structure can be confirmed by observing these crystal particles with a transmission electron microscope.

A multilayer ceramic capacitor was produced as follows. Table 1 shows the type of raw material powder used, the average particle size, the amount added, and the firing temperature. The BT powder and BST powder used here had A / B site ratios of 1.001 and 1.003. BT and BST powders having a main particle size of 0.2 to 0.4 μm were used. The composition of the glass powder was SiO ₂ = 50, BaO = 20, CaO = 20, and Li ₂ O = 10 (mol%). “With or without coating” in Table 1 means that BT powder or BST powder was coated with Mg, Y, or Mn with an oxide, and glass powder containing alumina in the amount shown in Table 1 was used.

  Using a zirconia ball having a diameter of 5 mm, the above powder was wet mixed by adding a mixed solvent of toluene and alcohol as a solvent. Next, a polyvinyl butyral resin and a mixed solvent of toluene and alcohol are added to the wet-mixed powder, and wet-mixed using a zirconia ball having a diameter of 5 mm to prepare a ceramic slurry, and a ceramic green sheet having a thickness of 3 μm by the doctor blade method. Was made.

  Next, a plurality of rectangular internal electrode patterns mainly composed of Ni were formed on the upper surface of the ceramic green sheet. The conductor paste used for the internal electrode pattern was Ni powder having an average particle size of 0.3 μm, and 30 parts by mass of BT powder used for a green sheet as a co-material with respect to 100 parts by mass of Ni powder.

Next, 360 ceramic green sheets on which internal electrode patterns were printed were laminated, and 20 ceramic green sheets on which the internal electrode patterns were not printed were laminated on the upper and lower surfaces, respectively, using a press machine at a temperature of 60 ° C. and pressure The layers were laminated together under the conditions of 10 ⁷ Pa and time 10 minutes, and cut into predetermined dimensions.

Next, the laminated molded body was subjected to binder removal treatment at 300 ° C./h in the atmosphere at a temperature rising rate of 10 ° C./h, and the temperature rising rate from 500 ° C. was 1155 ° C. at a temperature rising rate of 300 ° C./h. ˜1200 ° C. (calcined at an oxygen partial pressure of 10 ⁻⁶ Pa for 2 hours, then cooled to 1000 ° C. at a temperature drop rate of 300 ° C./h, re-oxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere, The capacitor body was manufactured by cooling at a temperature lowering rate of h. The size of the capacitor body was 2 × 1 × 1 mm ³ and the thickness of the dielectric layer was 2 μm.

  Next, after the sintered electronic component body was barrel-polished, an external electrode paste containing Cu powder and glass was applied to both ends of the electronic component body, and baked at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, Ni plating and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor.

The dielectric layer constituting the multilayer ceramic capacitor produced above has an area ratio of crystal grains in a cross-sectional crystal structure, and the ratio of BST crystal particles is A _BST and the ratio of BT crystal particles is A _BT . _ABT / _ABST = 0.8 to 1.2. In addition, the rare earth element (yttrium) contained in the barium titanate crystal particles had a concentration gradient of 0.05 atomic% / nm or more from the crystal particle surface to the inside of the particle with the grain boundary layer on the particle surface being the highest concentration. .

  Next, the following evaluation was performed on these multilayer ceramic capacitors.

  The temperature characteristics of the capacitance, relative permittivity, and relative permittivity were measured under the measurement conditions of a frequency of 1.0 kHz and a measurement voltage of 0.5 Vrms. The relative dielectric constant was calculated from the capacitance, the effective area of the internal electrode layer, and the thickness of the dielectric layer. The high temperature load test was evaluated until the initial failure occurred under the conditions of 125 ° C. and 9.45V.

  The average particle size of the BT type crystal particles and the BST type crystal particles constituting the dielectric layer was determined by a scanning electron microscope (SEM). The polished surface was etched, 20 crystal particles in the electron micrograph were arbitrarily selected, the maximum diameter of each crystal particle was determined by the intercept method, and the average value thereof was determined.

The Sr concentration was analyzed at an arbitrary location near the center using a transmission electron microscope and EDS (elemental analyzer). At that time, dielectric particles having a high Sr concentration were used for those having a Sr concentration higher than 0.4 atomic% (rounded to the second decimal place). This analysis was performed on 100 to 150 main crystal particles.

  As is clear from the results in Tables 1 and 2, in the sample according to the present invention in which BT powder and BST powder contain Mg, Y, Mn and the A / B site ratio of Ba and Ti is 1.003 or more, Sample No. using glass powder with high alumina content. Except 2, the dielectric constant is 3500 or more, the temperature characteristics are within -15% at 125 ° C., and the dielectric breakdown voltage (BDV) is in all the temperature ranges fired at a firing temperature of 1155 to 1200 ° C. The durability time in a high-temperature load test (125 ° C., 9.45 v) was 1000 hours or more at 150 V or more.

  On the other hand, in the sample in which the barium carbonate was not added to the BT and BST powder having an A / B site ratio of 1.001 or less, in the temperature range where the firing temperature was 1155 to 1200 ° C, The characteristic showed the same dielectric constant as the sample of the present invention, but the temperature characteristic of the capacitance was large for the sample fired at a temperature higher than 1170 ° C. or higher than 1185 ° C. or 1150 ° C. There was no durability in a high temperature load test (125 degreeC, 9.45v). Further, even in a sample in which the amount of alumina contained in the glass powder was outside the range of the present invention, the temperature characteristics of the sample fired at 1200 ° C. did not satisfy the X7R characteristics and the high temperature load life.

It is a longitudinal cross-sectional view of the multilayer ceramic capacitor of this invention. It is process drawing which shows the manufacturing method of the multilayer ceramic capacitor of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Main crystal particle 9a BST crystal particle 9b BT crystal particle 21 Ceramic green sheet 23 Internal electrode pattern 25 Ceramic pattern 29 Laminate

Claims (10)

In a multilayer ceramic capacitor having a capacitor body in which dielectric layers composed of main crystal grains and grain boundary phases and internal electrode layers are alternately stacked, the main crystal grains are mainly composed of Ba and Ti, Crystal grains having different Sr component concentrations and containing Mg, rare earth elements and Mn, and when the dielectric layer is Ba or the total amount of Ba and Sr is A mol and Ti is B mol, A multilayer ceramic capacitor characterized by satisfying a relationship of A / B ≧ 1.003 in terms of a molar ratio. The main crystal particles are composed of BT crystal particles having an Sr component concentration of 0.2 atomic% or less and BST crystal particles having an Sr component concentration of 0.4 atomic% or more, and the Sr component concentration is 0.4 atomic%. 2. The multilayer ceramic according to claim 1, wherein when the total amount of Ba and Sr in the BST crystal particles is A mol and Ti is B mol, the molar ratio satisfies the relationship of A / B ≧ 1.003. Capacitor. The multilayer ceramic capacitor according to claim 1 or 2, wherein a total concentration of Mg, rare earth element and Mn contained in the BST crystal particles is higher than a total concentration of Mg, rare earth element and Mn contained in the BT crystal particles. 4. The multilayer ceramic capacitor according to claim 1, wherein an average particle size of the main crystal particles is 0.4 μm or less. 5. The multilayer ceramic capacitor according to claim 1, wherein the dielectric layer has a thickness of 3 μm or less and the number of laminated layers is 100 or more. In the method of manufacturing a multilayer ceramic capacitor in which a capacitor body formed by alternately laminating green sheets containing dielectric powder and an organic resin and internal electrode patterns is laminated, the dielectric powder comprises (a) Sr. A mixed powder mainly composed of at least two kinds of Ba and Ti having different component concentrations. The mixed powder contains (a) an oxide of Mg, a rare earth element, and Mn, and (c) an alumina. A method for producing a multilayer ceramic capacitor, comprising a glass powder having an amount of 1% by mass or less and (d) a barium carbonate powder. In the method of manufacturing a multilayer ceramic capacitor in which a capacitor main body formed by alternately laminating green sheets containing dielectric powder and an organic resin and internal electrode patterns is laminated, the dielectric powder comprises: , Mg, rare earth elements and Mn oxides, and (x) Ba and Ti powders (BST powder) in which part of A site is replaced by Sr, not containing Sr A mixed powder of powders (BT powder) containing Ba and Ti as main components, and (g) a glass having an alumina content of 1% by mass or less with respect to the mixed powder, and (g) barium carbonate powder A method for producing a multilayer ceramic capacitor characterized by comprising: The method for producing a multilayer ceramic capacitor according to claim 6 or 7, wherein A / B is 1.003 or more in terms of molar ratio, where Ba and Sr in the BST powder are A and Ti is B. The multilayer ceramic capacitor according to any one of claims 6 to 8, wherein a total concentration of Mg, rare earth element and Mn contained in the BST powder is higher than a total concentration of Mg, rare earth element and Mn contained in the BT powder. The manufacturing method. 10. The method for producing a multilayer ceramic capacitor according to claim 6, wherein the BST powder, the BT powder, the glass powder, and the barium carbonate powder all have an average particle size of 0.5 μm or less.

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