JP4511323B2 - Multilayer ceramic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor and a method for producing the same, and more particularly to a small-sized, high-capacity and highly reliable multilayer ceramic capacitor in which a dielectric layer is composed of barium titanate crystal particles having different Ca component concentrations 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.
JP 2003-40671 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.

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

Multilayer ceramic capacitor of the present invention, in the multilayer ceramic capacitor comprising a capacitor body formed by alternately laminating dielectrics layers and internal electrode layers, the dielectric layer is, Ca component concentration than 0.2 atomic% and barium titanate crystal grains (BT crystal grains) of, Ca component concentration is from 0.4 atomic% or more of barium titanate crystal grains (BCT crystal grains), the BT crystal grain and the BCT crystal grains is Mg, as well as rare earth element (RE) and Mn, the total amount of Ba potassium and Ca is a moles, when the titanium B mol, in molar ratio, 1.003 ≦ a / B ≦ 1.00 7 with satisfying the relationship, the Mg contained in the BCT crystal grains, the total content of the rare earth element (RE) and Mn, included in the BT crystal grains by mass Mg, rare Characterized by comprising the high dielectric ceramic than the content of the sum of s elements (RE) and Mn.

In the multilayer ceramic capacitor, barium constituting the BT crystal grain and the BCT crystal grains, the total amount of the oxides of titanium and Ca is 100 mass parts
, Mg in terms of MgO is 0 . 04 to 0.14 parts by weight, the rare earth element and (RE) 0.2 to 0.9 parts by weight in terms _{of RE} 2 _{O 3,} it is desirable to have 0.04 to 0.15 parts by weight containing a Mn in terms of MnO. Further, a multilayer ceramic capacitor, temperature 250 ° C., when exposed to a high temperature load atmosphere at a voltage 3 V, the grain boundaries of the resistance reduction ratio of the dielectric layer of the AC impedance measurement at the before and after 0.7% / Min. Less is and this is desirable.

The manufacturing method of the multilayer ceramic capacitor of the present invention is the manufacturing method of the above-mentioned multilayer ceramic capacitor, and is a perovskite-type barium titanate powder (BCT powder) in which a part of the A site is replaced with Ca and a perovskite containing no Ca. In each type of barium titanate powder (BT powder), the total content of Mg, rare earth element (RE) and Mn contained in the BCT powder is Mg, rare earth element (RE) contained in the BT powder by mass. Mg, rare earth element (RE) and Mn are coated so as to be larger than the total content of Mg and Mn, and Mg, rare earth element (RE) and Mn are converted to MgO, converted to RE ₂ O _{3 and} converted to MnO. To a mixed powder contained in a total of 0.5 to 1.5 parts by mass, to a total of 100 parts by mass of the BCT powder and the BT powder. To a green sheet containing alumina dielectric powder and an organic resin content was a 1 to 1.4 parts by weight and barium carbonate 0.1 weight% or less of the glass were added 0.01 parts by weight of to prepare a capacitor body forming body configured and internal electrode patterns are alternately laminated, characterized by a Turkey to firing the capacitor green body.

According to the multilayer ceramic capacitor of the present invention, the dielectric layer constituting the multilayer ceramic capacitor is composed of BCT crystal particles and BT crystal particles, and these crystal particles contain Mg, rare earth elements and Mn, the ratio of the a site and titanium B sites of barium in a molar ratio, by using a satisfies a relationship of 1.003 ≦ a / B ≦ 1.00 7 , reduce variations in grain growth of BCT crystal grains It is possible to improve the dielectric constant, temperature characteristics and high temperature load test characteristics. 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.

Further , according to the method for producing a multilayer ceramic capacitor of the present invention, a perovskite-type barium titanate powder (BCT powder) in which a part of the A site is substituted with Ca and a perovskite-type barium titanate powder (BT) containing no Ca The total content of Mg, rare earth element (RE) and Mn contained in the BCT powder is greater than the total content of Mg, rare earth element (RE) and Mn contained in the BT powder by mass. Mg, rare earth element (RE) and Mn are coated so as to increase, and Mg, rare earth element (RE) and Mn are 0.5 to 1. in total in terms of MgO, RE ₂ O ₃ and MnO. The mixed powder contained in 5 parts by mass has an alumina content of 0.1% by mass or less with respect to 100 parts by mass in total of the BCT powder and the BT powder. Capacitor body constituted by alternately laminating green sheets and internal electrode patterns containing dielectric powder and organic resin added with 1 to 1.4 parts by weight of glass and 0.01 to 1 part by weight of barium carbonate By producing a molded body and firing the capacitor body molded body, even in the mass production of multilayer ceramic capacitors, even if a large tunnel-type firing furnace with a large variation in the maximum temperature during firing in the firing furnace is used, the BCT the dielectric constant and temperature characteristic of the dielectric layer to the crystal grain and the BT crystal grain and the main crystal grains, and are stable high temperature load test characteristic as well, a high yield laminated ceramic capacitor easily can obtain Rukoto .

(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 includes 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 because it can be achieved.

  The crystal particles 9 constituting the dielectric layer 5 according to the present invention are perovskite-type barium titanate crystal particles having different Ca component concentrations. That is, it is composed of perovskite-type barium titanate crystal particles (BCT crystal particles) 9a in which a part of the A site is substituted with Ca and perovskite-type barium titanate crystal particles (BT crystal particles) 9b not containing substituted Ca. . That is, the crystal particle 9 according to the present invention contains the BCT crystal particle 9a and the BT crystal particle 9b, and has excellent characteristics due to the coexistence of these two kinds of crystal particles as described above. Indicates. Of the perovskite barium titanate crystal particles according to the present invention, the BT crystal particle 9b is a barium titanate crystal particle having a Ca component concentration of 0.2 atomic% or less, while the BCT crystal particle 9a has a Ca component concentration. Barium titanate having a Ca component concentration of 0.5 to 2.5 atomic% in terms of maintaining a function as a ferroelectric having a high relative dielectric constant of BCT crystal particles 9a, particularly 0.4 atomic% or more. Crystal grains are desirable.

  The average grain size of the 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 diameters of the BCT crystal particles 9a and the BT crystal particles 9b is 0.15 μm or more because the dielectric constant of the dielectric layer 5 is increased and the temperature dependence of the dielectric constant is suppressed. preferable.

Here, the BCT crystal particle 9a which is one crystal particle constituting the crystal particle 9 is a perovskite-type barium titanate in which a part of the A site is substituted with Ca as described above, and ideally (Ba _1-x Ca _x ) TiO ₃ In the present invention, the amount of Ca substitution in the A site in the BCT crystal particles 9a is preferably X = 0.01 to 0.2, particularly preferably X = 0.02 to 0.07. If the amount of Ca substitution is within this range, the phase transition point near room temperature is shifted to a sufficiently low temperature side, and due to the coexistence structure with the BT crystal particles 9b, excellent temperature characteristics and DC bias characteristics in the temperature range used as a capacitor. This is because it can be secured.

On the other hand, the BT crystal particles 9b are perovskite-type barium titanate containing no substituted Ca, and are ideally represented by BaTiO ₃ . In the present invention, the BT crystal particles 9b have a Ca concentration of 0.2 atomic% or less as an analytical value.

In the present invention, the BCT crystal particles 9a and the BT crystal particles 9b constituting the crystal particles 9 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 Ca concentration is defined. When the ratio of the BCT crystal particles 9a is A _BCT 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 _BCT = 0.1-3 is established. it is desirable to coexist in a tissue proportions having, in particular, dielectric constant, preferably _a BT _{/ a} BCT = _0.3~2 in that further improve the temperature characteristics and the DC bias characteristics.

Also, B CT crystal grain 9a and the BT crystal grain 9b are each, Mg, characterized by containing a rare earth element and Mn, their BCT crystal grain 9a and the BT crystal grain 9b
The content of Mg, rare earth elements and Mn contained in Mg is 100 parts by mass when the total amount of oxides of barium, titanium and Ca constituting the BT crystal particles and BCT crystal particles is Mg in terms of MgO. If 0.04 to 0.14 parts by mass, the rare earth element (RE) is 0.2 to 0.9 parts by mass in terms of RE ₂ O ₃ , and Mn is 0.04 to 0.15 parts by mass in terms of MnO , It can stabilize the temperature characteristics of capacitance and improve the reliability in high-temperature load tests.

Furthermore, in terms of improving the reliability of stabilization and high-temperature load test of the temperature characteristic of the capacitance, Mg contained in the BCT crystal grain 9a, rare earth elements and Mn in the sum of the content of BT crystal grain 9b included Mg, multi Ikoto than the content of total rare earth element and Mn in is important. Since these Mg, rare earth elements and Mn are derived from the sintering aid, these elements are solid-solved in the BCT 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 5 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 BCT crystal particles 9a, while Mn is a BT crystal particle generated by firing in a reducing atmosphere. 9b, oxygen defects in the BCT crystal particles 9a can be compensated, and 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 crystal grain 9 has a concentration gradient from the surface of the crystal grain 9 to the inside of the grain with the grain boundary layer 11 as the grain surface being the highest concentration, and 0.05 It is desirable to be at least atomic% / nm. 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 BCT crystal particles 9a and the BT crystal particles 9b coexist. In such a coexistence system, the BCT crystal particles 9a and the BT crystal particles 9b are derived from the sintering aid on the particle surface side from 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.

  In general, the BT crystal particle 9b exhibits a large relative dielectric constant exceeding 4000 due to atomic fluctuations associated with successive phase transitions. Therefore, the relative permittivity 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 is hardly changed 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, the major factor that the BT crystal particle 9b exhibits a high dielectric constant is an increase in atomic fluctuations, which is a precursor of structural phase transition near room temperature and at a lower temperature, so that part of the A site is replaced with Ca. In the BCT crystal particle 9a, 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 characteristic is greatly improved. That is, in the dielectric ceramic according to the present invention, by realizing a coexistence structure of the BT crystal particles 9b having a high relative dielectric constant and excellent temperature characteristics and the BCT crystal particles 9a excellent in DC bias characteristics, It exhibits excellent DC bias characteristics compared to the particles 9b, has a higher dielectric constant than the BCT crystal particles 9a, and exhibits low temperature dependence and DC bias dependence of the dielectric characteristics.

In addition the present invention is, in barium titanate constituting the crystal grain 9, the molar ratio of the A site and titanium B site, barium and Ca, satisfy the relation: 1.003 ≦ A / B ≦ 1.00 7 Furthermore, the molar ratio A / B between the A site (barium) and the B site (titanium) in the BCT crystal particle, which is one of the main constituent crystal particles of the crystal particle 9, is 1.003. The above is desirable. In the conventional BCT crystal particles 9a, when mixed with Mg and rare earth elements, it is said that grain growth is likely to occur with the diffusion of Ca. In the present invention, the A / of barium calcium titanate (BCT crystal particles) is used. By defining the B ratio as described above, the grain growth of the BCT crystal particles 9a can be suppressed.

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

  FIG. 2 is a schematic diagram showing an evaluation method of the resistance of the grain boundary in the dielectric layer using the AC impedance measurement according to the present invention. In FIG. 2, 20a is a thermostatic chamber for controlling the temperature by mounting a multilayer ceramic capacitor as a sample, 20b is a HALT measuring device for applying a DC voltage to the sample, and 20c is an impedance measuring device having an AC power source. FIG. 3 is a representative example of the resistance evaluation result of the grain boundary in the dielectric layer using the AC impedance measurement of the present invention.

In the present invention, a multilayer ceramic capacitor, temperature 250 ° C., allowed to stand in a high temperature load atmosphere at voltage 3V. Then, the resistance reduction rate of the grain boundary layer in the dielectric layer in the AC impedance measurement is measured under the same conditions before and after being left in the high temperature load atmosphere under the above conditions. FIG. 3 is a graph showing the impedance change at the interface between the core (center part), shell (outer peripheral part), grain boundary layer, and internal electrode 7 and dielectric layer 5 of the crystal grain 9 in the multilayer ceramic capacitor according to the present invention. In this evaluation, as shown in the equivalent circuit of the figure, the dielectric layer 5 is formed at the core (center portion), shell (outer peripheral portion), grain boundary layer 11 and the interface between the internal electrode 7 and the dielectric layer 5. The graph is divided into four components: the horizontal axis of the graph shows the real part of the impedance signal, the vertical axis shows the imaginary part, the graph showing the change in impedance shows the difference before and after the accelerated life test (HALT), and fitting by simulation In the present invention, attention is particularly paid to the resistance change in the grain boundary layer 11, and it is desirable that the rate of change of the real part is 0.7% / min.

This evaluation can be obtained, for example, by dividing the Cole-Cole plot of FIG. 3 before and after the accelerated life test (HALT) into the above four components by using dedicated software.

  Here, the temperature is reduced to a Curie temperature in that the diffusion of ions and the movement of electrons in the dielectric layer 5 before and after the high-temperature load atmosphere treatment are increased, and the resistance reduction rate of the grain boundary layer 11 can be seen remarkably. The voltage is preferably 2/5 V or more of the rated voltage.

(Manufacturing method)
Next, the manufacturing method of the multilayer ceramic capacitor according to the present invention will be described in detail. FIG. 4 is a process diagram showing a method for producing the multilayer ceramic capacitor of the present invention.

The manufacturing method of the multilayer ceramic capacitor of the present invention uses dielectric powder obtained by previously coating dielectric powder of BCT powder and BT powder with oxide powder of Mg, rare earth elements, and Mn. That is, the manufacturing method of the multilayer ceramic capacitor of the present invention includes a perovskite-type barium titanate powder (BCT powder) in which a part of the A site is substituted with Ca, and a perovskite-type barium titanate powder (BT powder) containing no Ca. The total content of Mg, rare earth element (RE) and Mn contained in the BCT powder is greater than the total content of Mg, rare earth element (RE) and Mn contained in the BT powder by mass. Mg, rare earth element (RE) and Mn are coated so as to increase, and Mg, rare earth element (RE) and Mn are 0.5 to 1. in total in terms of MgO, RE ₂ O ₃ and MnO. The mixed powder contained in 5 parts by mass has an alumina content of 0.1% by mass or less with respect to a total of 100 parts by mass of the BCT powder and the BT powder. Capacitor configured green sheets of glass containing a 1 to 1.4 parts by weight and the dielectric powder and an organic resin and the barium carbonate was added 0.01 parts by mass and the internal electrode patterns are stacked alternately and wherein the benzalkonium be fired green body. In this case, compared with the case where 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 BCT powder can be suppressed, and a more fine thing can be used about BT powder and BCT powder to be used from this. BT and BCT powder are coated with Mg, rare earth element and Mn oxide by mixing a predetermined amount of Mg, rare earth element and Mn oxide into BT powder and BCT powder and then coated by mechanochemical method. it can. And in this invention, since BCT and BT powder can be coat | covered with Mg, rare earth elements, and Mn individually, the coating amount can be changed. In the present invention, it is desirable that the total content of Mg, rare earth element and Mn contained in the BCT powder is higher than the total content of Mg, rare earth element and Mn contained in the BT powder. By making the total content of Mg, rare earth elements and Mn contained in the BCT powder higher than the total content of Mg, rare earth elements and Mn contained in the BT powder, Grain growth can be effectively suppressed. At the same time, the diffusion of Ca from the BCT powder can be suppressed.

  FIG. 4 is a process diagram showing a method for producing the multilayer ceramic capacitor of the present invention.

  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.

Dielectric which is a perovskite type barium titanate powder (BCT powder) in which a part of A site used in the production method of the present invention is substituted with Ca and a perovskite type barium titanate powder (BT powder) which does not contain substituted Ca The powder is a raw material powder represented by (Ba _1-x Ca _x ) TiO ₃ and BaTiO ₃ , respectively. Here, the Ca substitution amount in the A site in the BCT powder is preferably X = 0.01 to 0.2, particularly preferably X = 0.03 to 0.1. Further, it is desirable that the BCT powder has an atomic ratio A / B of A site (barium) and B site (titanium), which are constituent components, of 1.003 or more. These BT powder and BCT powder are synthesized by mixing a compound containing a Ba component, a Ca 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 barium calcium titanate powder (BCT 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, 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 the ratio of the peak of the index _{(100) P BB} indicating is _P AA _{/ P BB} is 1.1 or more.

If you form constituting the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention, the mixing ratio of the BCT powder and the BT powder, in the ceramic obtained after firing, in particular, the relative dielectric constant, temperature characteristic and DC bias characteristic In view of further improving the BCT, the W _BCT / W _BT ratio is preferably in the range of 0.95 to 1.05, where the BCT powder amount is W _BCT and the BT powder amount is W _BT .

Moreover, Mg is added to the dielectric powder, to the mixed Goko powder of 100 parts by mass of the BCT powder and the BT powder, 0.04 to 0.14 parts by weight in terms of MgO, rare earth element (RE) is BCT against mixing Goko powder of 100 parts by mass of the powder and the BT powder, 0.2 to 0.9 parts by mass in terms _{of RE} 2 _{O 3,} and Mn mixed Goko powder 100 weight of the BCT powder and the BT powder It is preferable that it is 0.04-0.15 mass part with respect to a part in conversion of MnO .

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 0.7 to 2 parts by mass with respect to 100 parts by mass of the dielectric powder, which is a mixture of the BCT powder and the 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.

  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 the BCT powder and the 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 mixing 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. The ceramic powder is preferably a BT powder having a low Ca concentration. However, the internal electrode layer 7 according to the present invention connects the upper and lower dielectric layers 5 through the electrode layer by containing the ceramic powder in the conductor paste. Thus, 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 is formed around the internal electrode pattern 23 with substantially the same thickness as the internal electrode pattern 23 in order to eliminate the step due to the internal electrode pattern 23 on the ceramic green sheet 21. Is preferred. 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 the internal electrode patterns 23 are formed are stacked, a plurality of ceramic green sheets 21 on which the internal electrode patterns 23 are not formed are the same, and the upper and lower layers are the same. The temporary laminated body is formed by overlapping the number of sheets. 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 laminated body 29 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) and (c2) of FIG. 4 are cut in parallel to the longitudinal direction of the internal electrode pattern 23 to form a capacitor body molded body so that the end 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 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 of 0.5 to 4 hours, rate of cooling from the maximum temperature to 1000 ° C. is 200 to 500 ° C./h, atmosphere is hydrogen-nitrogen, heat treatment after firing (re- Oxidation treatment) It is preferable that the maximum temperature is 900 to 1100 ° C. and the atmosphere is nitrogen.

  Next, an external electrode paste is applied to the opposite ends of the capacitor body 1 and baked to form the external electrode 1. A plating film is formed on the surface of the external electrode 3 in order to improve mountability.

  The BCT 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 BCT crystal particles 9a having a fine particle size smaller than 0.2 μm can easily generate solid solution / growth and suppress the movement of atoms between the particles. If 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. Therefore , in the present invention, the molar ratio A / B between the A site (barium) and the B site (titanium) in the barium / calcium titanate crystal particles is set to 1.003 or more together with the microcrystal raw material, and Mg and Y introducing such a rare earth element as an additive, further by adjusting the firing conditions, it is possible to obtain a fine particle sintered body that reflects the size of the raw material grains. When the element ratio on the A-site side is increased in barium titanate or barium / calcium titanate, barium or barium / calcium is present on the particle surface, so that these barium and other additives are diffused on the particle surface. by forming the phase, suppression with promoting sintering, BT is a mother phase present in the vicinity of the grain boundary and the grain boundary, Ba among BCT crystal grains, Ca, and suppressing grain growth and movement of the Ti atoms 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. Thus, Mg and rare earth element-shell structure which is eccentrically distributed on the particle surface. 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 BCT powder used here had an A / B site ratio of 1.003. However, sample No. The A / B ratio of the BT and BCT powders used for 9 and 10 was 1.001. The particle size of BT powder and BCT powder was mainly 0.2 to 0.4 μm. The composition of the glass powder was SiO ₂ = 50, BaO = 20, CaO = 20, and Li ₂ O = 10 (mol%).

Next, BT powder and BCT powder were wet mixed by adding a mixed solvent of toluene and alcohol as a solvent using zirconia balls having a diameter of 5 mm. 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 heating rate of 10 ° C./h, and the temperature rising rate from 500 ° C. was 300 ° C./h. -Firing in nitrogen at 1150-1200 ° C for 2 hours, followed by cooling to 1000 ° C at a rate of temperature decrease of 300 ° C / h, reoxidation treatment at 1000 ° C for 4 hours in a nitrogen atmosphere, and temperature decrease of 300 ° C / h The capacitor body was manufactured by cooling at a speed. The size of the capacitor body was 2 × 1 × 1 mm ³ and the thickness of the dielectric layer was 2 μm.

Next, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends of the capacitor 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 was manufactured work is the area ratio of each crystal grains in the cross section of the crystal structure, the ratio of the BCT crystal grains A _BCT, the proportion of _BT crystal grains when the A _{BT, ABT} / _ABCT = 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.

  In the high-temperature load test, evaluation (MTTF) was performed at a temperature of 125 ° C., a voltage of 9.45 V, and up to 1000 hours. The number of samples was 30.

The average particle size of B T crystal grains and BC T crystal grains 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) )

  Regarding the Ca concentration, an arbitrary place near the center was analyzed using a transmission electron microscope and EDS. 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.

As the evaluation of the grain boundary phase, it was separately measured using the AC impedance method. The high-temperature load conditions in this case, the temperature 250 ° C., the voltage applied to the external electrodes of the product layer ceramic capacitor was 3V. The voltage during measurement was 0.1 V, the frequency was 10 mHz to 10 kHz, and the AC impedance before and after the treatment was evaluated for 30 samples.

As a comparative example, a mixture powder such as BT powder and BCT powder in which no barium carbonate was added, only BT powder was coated with Mg, Y, Mn, and BCT powder was not coated. the B-sites ratio which was 1.001 was prepared by the same method as above. The results are shown in Tables 1-4.

  As is apparent from the results of Tables 1 to 4, Samples 1 to 1 according to the present invention include Mg, Y, Mn in the BT powder and BCT powder, and the A / B site ratio of Ba and Ti is 1.003 or more. 8 and 11-13, the relative dielectric constant is 3080 or more and the temperature characteristics are within -17% at 125 ° C. in all temperature regions fired at a firing temperature of 1150 to 1200 ° C., and the dielectric breakdown voltage ( BDV) was 107 V or more, the durability time in a high temperature load test (125 ° C., 9.45 v) was 510 hours or more, and the resistance change rate by the AC impedance method was −1.07% or less.

  Both BT powder and BCT powder are coated with a predetermined amount of Mg, Y, Mn, and a dielectric powder having an A / B site ratio of Ba and Ti of 1.003 or more is used. Sample No. defining the coating amount of Mn. In 2 to 4, 6 to 8, 12, and 13, in all temperature regions fired at a firing temperature of 1150 to 1200 ° C., the relative dielectric constant is 3080 or more, and the temperature characteristics are in a range of −15% or less at 125 ° C. In addition, the dielectric breakdown voltage (BDV) was 107 V or higher, no defect was found even in the high temperature load test (125 ° C., 9.45 V, 1000 hours), and the resistance change rate by the AC impedance method was −1% or lower.

On the other hand, with respect to the BT powder and the BCT powder having an A / B site ratio of 1.001 or less, sample No. 1 in which barium carbonate was not added was used. 9 and sample No. 1 in which only BT powder was coated with Mg, Y, Mn but not BCT powder. 10, in the temperature range where the firing temperature was 1150 to 1200 ° C., the characteristics at 1170 ° C. showed the same dielectric constant as that of the sample of the present invention, but the temperature was higher than 1170 ° C. at 1185 ° C. or higher. A sample calcined at a temperature of 1150 ° C. had a large capacitance temperature characteristic, and the maximum resistance change rate by the AC impedance method was −1.08% or less.

It is a longitudinal cross-sectional view of the multilayer ceramic capacitor of this invention. It is a schematic diagram which shows the evaluation method of the resistance of the grain boundary in the dielectric material layer using the alternating current impedance measurement concerning this invention. It is a typical example of the resistance evaluation result of the grain boundary in a dielectric material layer using the alternating current impedance measurement 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 Crystal particle 9a BCT crystal particle 9b BT crystal particle 21 Ceramic green sheet 23 Internal electrode pattern 25 Ceramic pattern 29 Laminate

Claims (4)

In a multilayer ceramic capacitor having a capacitor body formed by alternately laminating dielectric layers and internal electrode layers, the dielectric layer is composed of barium titanate crystal particles (BT crystal) having a Ca component concentration of 0.2 atomic% or less. Particles) and barium titanate crystal particles (BCT crystal particles) having a Ca component concentration of 0.4 atomic% or more, and the BT crystal particles and the BCT crystal particles contain Mg, rare earth elements (RE) and Mn as well as, the total amount of Ba potassium and Ca is a moles, when the titanium B mol, in molar ratio, as well as satisfy the relation of 1.003 ≦ a / B ≦ 1.00 7 , the BCT The total content of Mg, rare earth element (RE) and Mn contained in the crystal particles is the total content of Mg, rare earth element (RE) and Mn contained in the BT crystal particles by mass. Multilayer ceramic capacitor characterized by comprising the high dielectric ceramic than the amount. Wherein 0 barium constituting the BT crystal grain and the BCT crystal grains, the total amount of the oxides of titanium and Ca is 100 parts by mass, the Mg in terms of MgO. 04 to 0.14 parts by weight, 0.2 to 0.9 parts by weight of a rare earth element and (RE) in terms _{of RE} 2 _{O 3,} and characterized in that it has 0.04 to 0.15 parts by weight containing a Mn in terms of MnO The multilayer ceramic capacitor according to claim 1 . The multilayer ceramic capacitor, temperature 250 ° C., conductive upon exposure to a high temperature load atmosphere at pressures 3V, the grain boundary resistivity reduction rate of the dielectric layer of the AC impedance measurement at the before and after 0.7% / min . The multilayer ceramic capacitor according to claim 1 or 2, wherein: 4. A method for producing a multilayer ceramic capacitor according to claim 1, wherein a perovskite-type barium titanate powder (BCT powder) in which a part of the A site is substituted with Ca and a perovskite containing no Ca. In each type of barium titanate powder (BT powder), the total content of Mg, rare earth element (RE) and Mn contained in the BCT powder is Mg, rare earth element (RE) contained in the BT powder by mass. Mg, rare earth element (RE) and Mn are coated so as to be larger than the total content of Mg and Mn, and Mg, rare earth element (RE) and Mn are converted to MgO, converted to RE ₂ O _{3 and} converted to MnO. To a mixed powder contained in a total of 0.5 to 1.5 parts by mass with respect to a total of 100 parts by mass of the BCT powder and the BT powder. Green sheets and internal electrode pattern in which the content of Na contains the added dielectric powder and an organic resin 0.01 parts by 1 to 1.4 parts by weight and barium carbonate 0.1 weight% or less of the glass to prepare a capacitor body forming body configured by alternately laminating bets, preparation of multilayer ceramic capacitors, wherein the benzalkonium be fired the capacitor body forming body.

Images