JP2006179773A - Multilayer ceramic capacitor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor which can suppress growth of barium titanium crystalline grains (BCTZ crystalline grains) even when a dielectric layer is made of a dielectric ceramic containing, as main crystalline grains, the BCTZ crystalline grains having part of an A site substituted for Ca and having part of a B site substituted for Zr, and BT crystalline grains; and which can improve a relative permittivity, a temperature characteristic, and a high-temperature load test characteristic even in mass production using a tunnel type large-scale baking furnace; and also to provide a method for manufacturing the ceramic capacitor. <P>SOLUTION: In the multilayer ceramic capacitor comprising a capacitor body 1 made of a dielectric layer 5 an internal electrode layer 7 alternately laminated, barium titanium crystalline grains having different Ca and Zr component concentrations are used as main crystalline grains 9. The barium titanium crystalline grains contain Mg, rare earth element, and Mn. When the dielectric layer contains a total of an A mole of Ba or Ba and Ca and a total of a B mole of Ti or Ti and Zr, the dielectric layer satisfies a relation, A/B≥1.003 in mole ratio. <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, as a high dielectric constant material for multilayer ceramic capacitors, together with the BT powder and BCT powder, the Ti site of the BCT powder is partially replaced with Zr (Ba _1-x Ca _x ) _m (Ti _1-y Zr _y ) O ₃ has been found as a high dielectric constant material, and is used for dielectric layers of high-capacity multilayer ceramic capacitors and thin film capacitors (Patent Document 2).
JP 2003-40671 A JP-A-11-157828

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. Moreover, the problem is, similarly to the case of using introduced the _{(Ba 1-x Ca x)} m (Ti 1-y Zr y) O 3 based high-permittivity material as Patent Document 2 in such mass production It occurred.

  Therefore, the present invention suppresses the grain growth of the BCTZ crystal particles even when the dielectric ceramic composed of BCTZ crystal particles and BT crystal particles is used as the dielectric layer, and uses a large tunnel-type 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 particle is a crystal particle mainly composed of Ba and Ti and having different Ca and Zr component concentrations, and contains Mg, rare earth element and Mn, and the total amount of Ba or Ba and Ca in the dielectric layer is determined. It is characterized by satisfying the relationship of A / B ≧ 1.003, where A mole is Ti and the total amount of Ti or Ti and Zr is B mole.

  In the multilayer ceramic capacitor, (2) the main crystal particles are composed of BT crystal particles having a Ca component concentration of 0.2 atomic% or less and BCTZ crystal particles having a Ca component concentration of 0.4 atomic% or more, and When the total amount of Ba and Ca in the BCTZ crystal particles having a Ca component concentration of 0.4 atomic% or more is A mol and the total amount of Ti and Zr is B mol, the molar ratio is A / B ≧ Satisfying the relationship of 1.003, (3) the total concentration of Mg, rare earth element and Mn contained in BCTZ crystal particles is higher than the total concentration of Mg, rare earth element and Mn contained in BT crystal particles (4) It is desirable that the average particle diameter of the barium titanate crystal particles is 0.4 μm or less, and (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 production method, the dielectric powder contains (a) a mixed powder containing two or more types of Ba and Ti having different Ca component concentration and Zr component concentration as a main component. In addition, a rare earth element and an oxide of Mn, (c) glass powder having an alumina content of 1% by mass or less, and (d) barium carbonate powder are added.

  In the method for manufacturing the multilayer ceramic capacitor, (7) the mixed powder is composed of BCTZ powder and BT powder, and the mixed powder is coated with Mg, a rare earth element, and an oxide of Mn, respectively (8 ) When the total amount of Ba and Ca in the BCTZ powder is A mol and the total amount of Ti and Zr is B mol, A / B is 1.003 or more, (9) Mg contained in the BCTZ powder The total concentration of rare earth elements and Mn is higher than the total concentration of Mg, rare earth elements and Mn contained in the BT powder, (10) Average particle diameter of BCTZ powder, BT powder, glass powder and barium carbonate powder Is desirably 0.5 μm or less.

  According to the multilayer ceramic capacitor of the present invention, the BT crystal particles and the BCTZ crystal particles constituting the dielectric layer of the multilayer ceramic capacitor have Ba or the total amount of Ba and Ca as A mole, and Ti or Ti and Zr. When the total amount is B mol, by using the one satisfying the relationship of A / B ≧ 1.003 in terms of molar ratio, variation in grain growth of BCTZ crystal grains can be reduced, and the relative dielectric constant and temperature characteristics In addition, 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, the dielectric powder is, for example, (a) a mixed powder mainly containing two or more kinds of Ba and Ti having different Ca component concentrations and Zr component concentrations. (I) Mg, rare earth element, and Mn oxide, (c) glass powder having an alumina content of 1% by mass or less, and (d) barium carbonate powder were added to the mixed powder. Thus, in mass production of multilayer ceramic capacitors, even if a tunnel type large firing furnace having a large variation in the maximum temperature during firing in the firing furnace is used, the BCTZ crystal particles and the BT crystal particles are separated from the main crystal particles. The dielectric constant and temperature characteristics of the dielectric layer to be used and the high-temperature load test characteristics of the multilayer ceramic capacitor equipped with the dielectric layer are stable, which facilitates the yield. It is Mel possible.

(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 drawing is a schematic diagram showing the main crystal grains and the grain boundary phase 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 grain boundary phases 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 BCTZ crystal particles 9a and the BT crystal particles 9b is 0.15 μm or more because it increases the relative dielectric constant of the dielectric layer 5 and suppresses the temperature dependence of the relative dielectric constant. preferable.

  The main crystal grains 9 constituting the dielectric layer 5 according to the present invention are crystal grains mainly composed of Ba and Ti and having different Ca and Zr component concentrations. That is, a perovskite-type barium titanate crystal particle (BCTZ crystal particle 9a) in which a part of the A site is substituted with Ca and a part of the B site is substituted with Zr, and a perovskite-type titanium containing no Ca and Zr It consists of barium acid crystal particles (BT crystal particles 9b).

That is, the main crystal particle 9 according to the present invention contains the BCTZ crystal particle 9a and the BT crystal particle 9b. As described above, the main crystal particle 9 is excellent because the two kinds of crystal particles coexist. 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 particles 9b not containing Ca and Zr have an analytical value of Ca and Zr concentration of 0.2 atomic% or less, but the Ca contained in the BCTZ crystal particles 9a. Also included are those in which the Zr component slightly diffuses into the BT crystal particles 9b.

  On the other hand, the BCTZ crystal particle 9a has a Ca component concentration of 0.4 atomic% or more, and in particular, the Ca component concentration is 0 in that the BCTZ crystal particle 9a maintains the function as a ferroelectric having a high relative dielectric constant. It is desirable to be 5 to 2.5 atomic%.

Here, the BCTZ crystal particle 9a which is one crystal particle constituting the main crystal particle 9 is a perovskite in which a part of the A site is substituted with Ca and a part of the B site is substituted with Zr as described above. a type barium titanate, _ideally represented by _{(Ba 1-x Ca x)} m (Ti 1-y Zr y) O 3. In the present invention, the amount of Ca substitution in the A site in the BCTZ crystal particle 9a is x = 0.01 to 0.2, particularly x = 0.02 to 0.07, y = 0.15 to 0. .25, particularly preferably X = 0.175 to 0.225. If the Ca substitution amount is within this range, the phase transition point near room temperature is sufficiently shifted to the low temperature side, and due to the coexistence structure with the BT crystal particles 9b, excellent temperature characteristics and DC in the temperature range used as the multilayer ceramic capacitor This is because the bias characteristic can be secured. Further, if the Zr substitution amount is within this range, the dielectric loss is reduced and the relative dielectric constant is increased.

In the present invention, the BCTZ crystal particles 9a and the BT crystal particles 9b constituting the main crystal particles 9 of the dielectric layer 5 are the cross section or surface of the dielectric layer 5 in the evaluation based on the index when the Ca concentration is defined. in the area ratio of each crystal grain in the crystal structure, the ratio of _{a BCTZ} the BCTZ crystal grain 9a, a proportion of the BT crystal grain 9b is taken as _{a BT, a BT / a BCTZ} = 0.1~3 relationship it is desirable to coexist in a tissue proportions with, in particular, dielectric constant, preferably _a BT _{/ a} BCTZ = _0.3~2 in that further improve the temperature characteristics and the DC bias characteristics.

The BCTZ crystal particles 9a and BT crystal particles 9b both contain Mg, rare earth elements and Mn, and 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, particularly 0.04 to 0.1 parts by mass, and rare earth elements are 0.2 to 0 in terms of Re ₂ O _3. .9 parts by mass, especially 0.22 to 0.5 parts by mass, Mn is 0.04 to 0.15 parts by mass in terms of MnCO ₃ , especially 0.05 to 0.1 parts by mass (in the case of coating) In this case, 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 elements and Mn contained in the BCTZ crystal particle 9a is included in 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 combined concentration of Mg, rare earth elements and Mn. These Mg, rare earth element and Mn are dissolved in the BCTZ crystal particles 9a and the BT crystal particles 9b, but are partly present in the grain boundary phase 11. In the dielectric layer 5 according to the present invention, Mg and rare earth elements are components in which the BT crystal particles 9b and the BCTZ crystal particles 9a have a core-shell structure, and in particular, grain growth of the BCTZ crystal particles 9a can be suppressed. Mn compensates for oxygen defects in the BT crystal particles 9b and BCTZ crystal particles 9a produced by firing in a reducing atmosphere, and can improve insulation and high-temperature load life.

  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 phase 11 which is the grain surface as the maximum density, and 0.05 atoms. % / 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.

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

  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

  Next, the characteristic expression mechanism of the main crystal particle 9 mainly composed of barium titanate according to the present invention will be described. In general, the BT crystal particle 9b exhibits a large relative dielectric constant exceeding 4000 due to the atomic fluctuation accompanying the sequential phase transition, but the high relative dielectric constant due to the atomic fluctuation which is a precursor of the sequential phase transition. Therefore, the relative permittivity is greatly reduced by applying the DC bias. Of the three sequential phase transition points found in the BT crystal particles 9b, the phase transition temperature at the highest temperature (about 125 ° C.) hardly changes even when a part of the A site is replaced with Ca. 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 Ca. That is, a major factor that the BT crystal particles exhibit a high dielectric constant is due to an increase in atomic fluctuation, which is a precursor of structural phase transition near room temperature and at a lower temperature.

  On the other hand, the BCTZ crystal particle 9a functions as a depressor for flattening the temperature characteristic of the relative dielectric constant by Ca and acts as an element for increasing the insulation resistance value, and Zr mainly has a Curie point on the low temperature side. Therefore, the transition point near room temperature and further at low temperature is shifted to the low temperature side, and the relative permittivity near room temperature can be greatly improved.

  That is, in the dielectric ceramic of the present invention, by realizing a coexistence structure of the BT crystal particles 9b exhibiting a high relative dielectric constant and excellent in temperature characteristics and the BCTZ crystal particles 9a having an extremely high relative dielectric constant near room temperature. The dielectric constant is higher than that of the BT crystal particle 9b, and the temperature dependence of the dielectric property is lower than that of the BCTZ crystal particle 9a.

  In addition, in the present invention, the main crystal particle 9 is a crystal particle mainly composed of Ba and Ti and having different Ca and Zr component concentrations, and contains Mg, rare earth element and Mn, and Ba or Ba and Ca and Ca. When the total amount of A is A mole and the total amount of Ti or Ti and Zr is B mole, it is important to satisfy the relationship of A / B ≧ 1.003 in terms of molar ratio. The molar ratio A / B between the A site (Ba, Ca) and the B site (Ti, Zr) in the BCTZ crystal particle 9a, which is one of the main crystal particles constituting the main crystal particle 9, is 1.003 or more. It is desirable. In the conventional BCTZ crystal particle 9a, when Mg and rare earth elements are mixed, grain growth is likely to occur as Ca diffuses. In the present invention, the A / B ratio of BCTZ crystal particle 9a is as described above. In particular, grain growth of the BCTZ crystal grain 9a can be suppressed.

  On the other hand, when the BCTZ crystal particle 9a does not contain Mg, rare earth element and Mn, or when the A / B ratio is 1.002 or less, the grain growth of the BCTZ crystal particle 9a is likely to occur and the insulating property is lowered. However, defects in the high temperature load test 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. In the dielectric powder, a perovskite-type barium titanate powder (BCTZ powder) in which a part of the A site is substituted with Ca and a part of the B site is substituted with Zr, and a perovskite type that does not contain Ca and Zr. A mixture powder of barium titanate powder (BT powder) with Mg, rare earth element and Mn oxide, glass having an alumina content of 1% by mass or less, and barium carbonate powder. It is characterized by being.

  Here, the dielectric powder contains perovskite-type barium titanate powder (BCTZ powder) in which a part of the A site is substituted with Ca and a part of the B site is substituted with Zr, and Ca and Zr. Mg, rare earth elements, and Mn in terms of oxides in a total amount of 0.05 to 1.5 parts by mass with respect to 100 parts by mass of mixed powder with no perovskite-type barium titanate powder (BT powder). It is desirable to add 1 to 1.4 parts by mass of glass having a content of 1% by mass or less and 0.01 to 1 part by mass of barium carbonate powder.

  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 reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

The dielectric powders which are BCTZ powder and BT powder used in the production method of the present invention are raw material powders represented by (Ba _1-x Ca _x ) _m (Ti _1-y Zr _y ) O ₃ and BaTiO ₃ , respectively. . Here, the amount of Ca substitution in the A site in the BCTZ powder is x = 0.01 to 0.2, particularly x = 0.02 to 0.07, y = 0.15 to 0.25, particularly X is preferably 0.175 to 0.225.

  The BCTZ powder preferably has an atomic ratio A / B of A site (Ba, Ca) and B site (Ti, Zr), which is a constituent component, of 1.003 or more. These BT powder and BCTZ powder are synthesized by mixing a compound containing a Ba component, a Ca component, a Ti component, and a Zr 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 diameters of the BT powder and BCTZ powder, which are dielectric powders according to the present invention, are 0.15 to 0.00 in terms of facilitating thinning of the dielectric layer 5 and increasing the dielectric constant of the dielectric powder. It is desirable to be 4 μm.

Further, as a dielectric powder having such a high relative dielectric constant, its crystallinity is evaluated by, for example, an index (001) _PAA peak indicating a tetragonal crystal and a cubic crystal when evaluated using X-ray diffraction. It is desirable that the ratio of the index (100) P _BB shown to P _AA / P _BB is 1.1 or more.

Further, the mixing ratio of the BCTZ powder and the BT powder in the case of constituting the dielectric layer 5 of the present invention further improves the relative permittivity, the temperature characteristic and the DC bias characteristic particularly in the ceramic obtained after firing. In this regard, when the BCTZ powder amount is W _BCTZ and the BT powder amount is W _BT , the W _BCTZ / W _BT ratio is desirably in the range of 0.95 to 1.05 in terms of mass ratio.

  In this case, Mg, rare earth element, and Mn added to the dielectric powder are 0.04 to 0.14 parts by mass, 0 parts by weight in terms of oxides with respect to 100 parts by mass of the mixed powder of BCTZ powder and BT powder, respectively. It is preferable that they are 2-0.9 mass parts and 0.04-0.15 mass parts.

The glass powder added to the dielectric powder is present as a _component, Li 2 _O, composed of SiO 2, BaO and CaO. The addition amount of the glass powder is more preferably 1 to 1.3 parts by mass with respect to 100 parts by mass of the dielectric powder, which is a mixture of BCTZ powder and BT powder, in terms of enhancing the sintering property 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. The average particle size is preferably 0.5 μm or less because the dispersibility of the glass powder is increased and the region of the grain boundary phase 11 can be narrowed.

  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 BCTZ 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. As the ceramic powder, BT powder having a low Ca and Zr concentration is preferable because abnormal grain growth of columnar ceramics during firing can be suppressed. Thus, the internal electrode layer 7 according to the present invention includes ceramic powder as a conductor paste. By containing, columnar ceramics are formed so as to connect the upper and lower dielectric layers 5 through the electrode layers, thereby preventing peeling between the dielectric layers 5 and the internal electrode layers 7, and mechanical strength. Can be high. 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 23 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 the internal electrode pattern 23 in advance on the main surface of the ceramic green sheet 21 and laminating it, the ceramic green sheet 21 is once brought into close contact with the lower layer side equipment. After the internal electrode pattern 23 is printed and dried, the ceramic green sheet 21 on which the internal electrode pattern 23 is not printed is overlaid and temporarily adhered onto the printed and dried internal electrode pattern 23. It can also be formed by a method in which the adhesion of the ceramic green sheet 21 and the printing of the internal electrode pattern 23 are sequentially performed.

  Next, the temporary laminated body is pressed under conditions of higher temperature and higher pressure than the temperature pressure during the temporary lamination to form a laminated body 29 in which the ceramic green sheet 21 and the internal electrode pattern 23 are firmly adhered.

  Next, the multilayer body 29 is cut along the cutting line h, that is, the approximate center of the ceramic pattern 29 formed in the multilayer body is 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 23 so that the end portion of the internal electrode pattern 23 is exposed. On the other hand, in the widest portion of the internal electrode pattern 23, the internal electrode pattern 23 is not exposed on the side margin 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 1250 ° C., and the heating rate from degreasing to the maximum temperature is 200 to 500 ° C./h, retention time at the maximum temperature of 0.5 to 4 hours, temperature decrease rate from the maximum temperature to 1000 ° C. of 200 to 500 ° C./h, atmosphere (oxygen partial pressure PO ₂ ) of 10 ⁻⁷ 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 opposing 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 method for producing a multilayer ceramic capacitor according to the present invention, dielectric powders such as BCTZ powder and BT powder, in addition to the method of adding Mg, rare earth element and Mn oxide powder to BCTZ powder and BT powder as described above. 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 method for producing a multilayer ceramic capacitor of the present invention is a method of firing a capacitor body molded body that is formed by alternately laminating ceramic green sheets containing dielectric powder and organic resin and internal electrode patterns. In the method of manufacturing a ceramic capacitor, each of the dielectric powders is coated with Mg, a rare earth element, and an oxide of Mn, and a part of the A site is replaced with Ca and a part of the B site is replaced with Zr. The perovskite-type barium titanate powder (BCTZ powder) and the mixed powder of perovskite-type barium titanate powder (BT powder) not containing substituted Ca have an alumina content of 1% by mass or less. 1 to 1.4 parts by mass of glass and 0.01 to 1 part by mass of barium carbonate are added.

  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 BCTZ powder can be suppressed, and a more fine thing can be used about BT powder and BCTZ powder used from this.

  The BT and BCTZ 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 BCTZ powders and then coated by a mechanochemical method.

  In the present invention, since BCTZ and BT powder can be individually coated with Mg, rare earth elements, and Mn, the content thereof can be changed. In the present invention, the total concentration of Mg, rare earth element and Mn contained in the BCTZ 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 elements and Mn contained in the BCTZ powder higher than the total concentration of Mg, rare earth elements and Mn contained in the BT powder, grains of BCTZ powder which are more likely to grow during firing Growth can be effectively suppressed. At the same time, the diffusion of Ca from the BCTZ powder can be suppressed.

  The BCTZ crystal particles 9a and BT crystal particles 9b according to the present invention described above generally tend to cause grain growth due to atomic diffusion during sintering, and it is difficult to obtain a dense sintered body having a small 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 of the BT crystal particles 9b and the BCTZ crystal particles 9a having a fine particle size smaller than 0.2 μm can easily cause solid solution / growth and suppress the movement of atoms between the particles. If it is not 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. In the present invention, however, the molar ratio A / B between the A site (Ba, Ca) and the B site (Ti, Zr) in the BCTZ crystal particles is set to 1.003 or more together with the microcrystal raw material, and Mg and Y By introducing such a rare earth element as an additive and further adjusting the firing conditions, a fine particle sintered body reflecting the size of the raw crystal grains can be obtained. When the element ratio on the A site side is increased in the BT crystal particle 9b or the BCTZ crystal particle 9a, barium, barium, or Ca is present on the particle surface, so that these barium and other additives are diffused on the particle surface and become a liquid phase. And promotes the sintering, and suppresses the movement of Ba, Ca, Ti, and Zr atoms between the BT crystal particles 9b and the BCTZ crystal particles 9a that are present in the vicinity of and at the grain boundaries. Grain growth is suppressed. 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 BCTZ powder used here were equimolar, and those having A / B site ratios of 1.001 and 1.003. The particle size of BT and BCTZ powders was mainly 0.2 to 0.4 μm. A BCTZ powder having a composition of (Ba _0.95 Ca _0.05 ) _m (Ti _0.8 Zr _0.2 ) O ₃ was used. The glass powder contained alumina in the amount shown in Table 1, and the composition used was a glass powder of SiO ₂ = 50, BaO = 20, CaO = 20, Li ₂ O = 10 (mol%). “With coating” means that BT powder and BCTZ powder are coated with oxides of Mg, Y and Mn, respectively.

  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 are formed on the upper surface of the ceramic green sheet, and a ceramic pattern of the same ceramic component as the ceramic green sheet is formed at substantially the same height around the inner electrode pattern. . 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. ˜1245 ° 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 × 1.3 × 1.3 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.

Dielectric layer constituting a multilayer ceramic capacitor prepared above is the area ratio of each crystal grains in the cross section of the crystal structure, A _BCTZ the ratio of BCTZ crystal _grain, the ratio of the _BT crystal grain is taken as A _BT, It was _{a BT} / a BCTZ = 0.8~1.2. Further, 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 phase on the particle surface being the highest concentration. .

  Next, the following evaluation was performed on these multilayer ceramic capacitors. The number of samples in the following evaluation was 100.

  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 at 125 ° C., 9.45 V, up to 1000 hours.

  The average particle size of the BT type crystal particles and BCTZ type crystal particles constituting the dielectric layer was determined by a scanning electron microscope (SEM). The polished surface is etched, 20 crystal particles in the electron micrograph are arbitrarily selected, the maximum diameter of each crystal particle is obtained by the intercept method, and the average value thereof and D90 (90% cumulative value from small to large diameter) ) In this case, the number of samples was five.

About Ca density | concentration, the arbitrary places of the central part vicinity were analyzed using the transmission electron microscope and EDS (elemental analyzer). At that time, dielectric particles having a high Ca concentration were used for those having a Ca concentration higher than 0.4 atomic% (rounded to the second decimal place). This analysis was performed on 100 to 150 main crystal particles in one sample.

  As is clear from the results in Tables 1 and 2, in the sample according to the present invention in which BT powder and BCTZ 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 for 2, the dielectric constant is 5850 or more, the temperature characteristics are less than −18.6% at 125 ° C., and the temperature characteristics at −55 ° C. Was within ± 15%, and there was no defect in the high temperature load test.

  On the other hand, with respect to the BT and BCTZ powders having an A / B site ratio of 1.001 or less, in the sample in which barium carbonate was not added, the characteristics at 1215 ° C. were obtained at the firing temperature of 1155 to 1245 ° C. The specific permittivity of the same degree as that of the above sample was shown, but the temperature characteristic of the capacitance was large for the sample fired at a temperature higher than 1215 ° C. or higher than 1215 ° C. or 1155 ° C. Defects were seen.

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 BCTZ 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 Ca and Zr component concentrations and containing Mg, rare earth elements and Mn, and the total amount of Ba or Ba and Ca in the dielectric layer is A mole, and Ti or Ti and Zr A multilayer ceramic capacitor characterized by satisfying a relationship of A / B ≧ 1.003 when the total amount is B mol. The main crystal particles are composed of BT crystal particles having a Ca component concentration of 0.2 atomic% or less and BCTZ crystal particles having a Ca component concentration of 0.4 atomic% or more, and the Ca component concentration is 0.4 atom. 2. The relationship of A / B ≧ 1.003 is satisfied when the total amount of Ba and Ca in BCTZ crystal grains of at least% is A mol and the total amount of Ti and Zr is B mol. Multilayer ceramic capacitor. 3. The multilayer ceramic capacitor according to claim 1, wherein a total concentration of Mg, rare earth element, and Mn contained in the BCTZ 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 a method for producing a multilayer ceramic capacitor in which a capacitor main body formed by alternately laminating green sheets containing dielectric powder and organic resin and internal electrode patterns is laminated, the dielectric powder comprises (a) Ca A mixed powder mainly composed of two or more kinds of Ba and Ti having different component concentrations and Zr component concentrations; and (b) an oxide of Mg, rare earth element, and Mn, and (c) A method for producing a multilayer ceramic capacitor, comprising 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 claim 6, wherein the mixed powder is composed of BCTZ powder and BT powder, and the mixed powder is coated with an oxide of Mg, rare earth element and Mn, respectively. The multilayer ceramic capacitor according to claim 6 or 7, wherein A / B is 1.003 or more when the total amount of Ba and Ca in the BCTZ powder is A mol and the total amount of Ti and Zr is B mol. Manufacturing method. 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 BCTZ powder is higher than a total concentration of Mg, rare earth element and Mn contained in the BT powder. Manufacturing method. 11. The method for producing a multilayer ceramic capacitor according to claim 6, wherein the average particle diameters of the BCTZ powder, the BT powder, the glass powder, and the barium carbonate powder are all 0.5 μm or less.

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