JP2008109120A - Multilayer ceramic capacitor and its fabrication process - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multilayer ceramic capacitor exhibiting a high permittivity even if the mean particle diameter of crystal grains is made smaller than 0.5 μm in which high temperature loading lifetime can be enhanced while reducing the temperature variation rate of dielectric constant. <P>SOLUTION: A dielectric layer 5 contains 0.5-2 mol parts of Mg in terms of MgO, and 0.2-0.5 mol parts of Mn in terms of MnO for 100 mol parts of titanic acid barium, one kind of first rare earth element selected from Ho, Y, Er, Tm, Yb and Lu, and one kind of second rare earth element selected from Sm, Eu, Gd, Tb and Dy wherein the mean particle diameter of crystal grains composing the dielectric layer 5 is 0.15-0.3 μm, concentration gradient from the grain boundary to the central portion of crystal particles of the first rare earth element is in the range from -0.005 to -0.05 atm%/nm, and concentration gradient from the grain boundary to the central portion of crystal particles of the second rare earth element is in the range from -0.0005 to -0.005 atm%/nm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a monolithic ceramic capacitor used in electronic equipment, and more particularly to a monolithic ceramic capacitor having an internal electrode layer made of nickel or a nickel alloy and a method for producing the same.

  Multilayer ceramic capacitors are constructed by forming external electrodes on the exposed end face of the capacitor body, which is composed of alternately laminated dielectric layers and internal electrode layers. In order to meet the demand for a reduction in thickness, the dielectric layers and internal electrode layers have been made thinner and multi-layered.

  For example, a dielectric material mainly composed of barium titanate powder is used for the dielectric layer constituting such a multilayer ceramic capacitor, and a base metal such as Ni is preferably used for the internal electrode layer in terms of low cost. It has been. When a base metal such as Ni is used for the internal electrode layer, firing is usually performed in a hydrogen-nitrogen mixed gas atmosphere. However, in such an atmosphere, the dielectric layer is reduced and becomes a semiconductor. was there.

  In order to solve such a problem, for example, a dielectric material (for example, Patent Document 1) in which the ratio of barium sites to titanium sites of the barium titanate powder is larger than the stoichiometric ratio, or barium titanate powder is used. Dielectric materials to which additives such as MnO, rare earth element oxides, and MgO have been added have been proposed (for example, Patent Document 2).

  The proposed dielectric material has high resistance to reduction and exhibits a high relative dielectric constant, so that it can be suitably used for multilayer ceramic capacitors having a dielectric layer having a thickness of 10 μm or more that has been mass-produced so far. I came. However, for a dielectric layer having a thickness of 5 μm or less like a thin multilayer ceramic capacitor in recent years, the above-mentioned dielectric material is likely to grow grains, and crystals existing in one layer of the dielectric layer. Due to the decrease in the number of particles, the insulating property is lowered, and the reliability of the high temperature load life cannot be obtained.

Therefore, recently, a novel dielectric material having a high relative dielectric constant and high insulation even when the thickness of the dielectric layer is reduced to 5 μm or less has been further proposed (for example, Patent Document 3). In the dielectric material disclosed in Patent Document 3, the content of alkali metal oxides contained as impurities in the main component barium titanate powder (hereinafter referred to as BT powder) is set to 0.02% by weight or less. Above, with respect to this BT powder, at least one selected from scandium oxide and yttrium oxide, and at least one selected from gadolinium oxide, terbium oxide and dysprosium oxide, two different ionic radii The above rare earth element oxide is added.
Japanese Examined Patent Publication No. 57-42588 Japanese Patent Laid-Open No. 61-101458 JP-A-10-223471

  However, as in the multilayer ceramic capacitor disclosed in Patent Document 3, when the average particle size of the crystal particles mainly composed of barium titanate constituting the dielectric layer is 0.5 μm or more, a high dielectric constant and Although high insulation was obtained, when the average grain size of the crystal grains is made smaller than 0.5 μm, the dielectric constant of the dielectric layer decreases and the temperature characteristics of the capacitance increase. At the same time, there is a problem that the high temperature load life is shortened and the reliability is lowered.

  Therefore, the present invention provides a multilayer ceramic capacitor that has a high dielectric constant even when the average grain size of crystal grains is smaller than 0.5 μm, has a small temperature change rate of relative permittivity, and can improve a high temperature load life. It aims at providing the manufacturing method.

The multilayer ceramic capacitor of the present invention is a multilayer ceramic capacitor comprising a dielectric layer, an internal electrode layer formed between the dielectric layers, and an external electrode electrically connected to the internal electrode layer. The body layer has crystal particles having barium titanate as a main component and an average crystal grain size of 0.15 to 0.3 μm, and magnesium is converted to 0.5 mg in terms of MgO with respect to 100 mol parts of the barium titanate. ~ 2 mol part, manganese 0.2-0.5 mol part in terms of MnO, one first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium and samarium, europium, gadolinium, terbium and 0.7 to 3 molar parts containing one of the second rare earth element selected from dysprosium total converted _RE 2 _{O 3} And the crystal grains contain the first rare earth element and the second rare earth element so that the amount of the first rare earth element is larger than the amount of the second rare earth element, and the crystal of the first rare earth element. The concentration gradient from the grain boundary of the grain to the central part is −0.005 atomic% / nm or more and −0.05 atomic% / nm or less, and the grain of the second rare earth element from the grain boundary to the central part. It is characterized by comprising a dielectric ceramic having a concentration gradient of −0.0005 atomic% / nm or more and −0.005 atomic% / nm or less.

  Further, in the multilayer ceramic capacitor, the crystal particles constituting the dielectric ceramic have a first crystal group consisting of crystal particles having a Ca component concentration of 0.2 atomic% or less, and a Ca component concentration of 0.4 atomic%. A composite particle in which the second crystal group including the above crystal particles is mixed is preferable.

  Furthermore, in the multilayer ceramic capacitor, when the total content of Ba and Ca in the dielectric ceramic is A mol and the content of Ti is B mol, the relationship of A / B ≧ 1.003 may be satisfied. preferable.

Further, 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 main body formed by alternately laminating green sheets containing dielectric powder and internal electrode patterns is fired. The body powder is selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium on the surface of barium titanate powder, barium calcium titanate powder having a mean particle size of 0.15 to 0.3 μm, or a mixed powder thereof. A first powder in which 0.6 to 2 mol parts of one kind of rare earth element oxide is coated on 100 mol parts of the barium titanate powder, the barium calcium titanate powder, or a mixed powder thereof is prepared. The first powder includes the barium titanate powder or the Against Tan barium calcium powder or mixed powder 100 molar parts of, 0.5 to 2 parts by mole of MgO powder, 0.2 to 0.5 parts by mole of MnCO ₃ powder, samarium, europium, gadolinium, terbium and What added 0.1-1 mol part of oxide powders of 1 type of 2nd rare earth elements chosen from dysprosium is used, It is characterized by the above-mentioned.

  Furthermore, in the manufacturing method of the multilayer ceramic capacitor of this invention, it is preferable that the temperature of this baking at the time of baking the said capacitor body molded object is 1050-1150 degreeC.

Furthermore, in the method for producing a multilayer ceramic capacitor of the present invention, it is preferable that the barium calcium titanate powder is Ba _1-x Ca _x TiO ₃ powder (where x = 0.01 to 0.2).

Furthermore, in the method for producing a multilayer ceramic capacitor of the present invention, the total content of Ba and Ca in the Ba _1-x Ca _x TiO ₃ powder (where x = 0.01 to 0.2) is C mol, Ti. It is preferable to use a material satisfying the relationship of C / D ≧ 1.003 when the content is D mol.

Note that both the first rare earth element and the second rare earth element are represented as RE and the oxide thereof is represented as RE ₂ O ₃ , which is based on the English language representation (Rare earth) of the rare earth element in the periodic table.

  According to the present invention, two kinds of rare earth elements having different ionic radii in which a predetermined amount of magnesium, manganese and rare earth elements are contained in the dielectric layer constituting the multilayer ceramic capacitor, and the crystal grains mainly composed of barium titanate are different in ion radius. By containing each element with the above-mentioned concentration gradient, even when the average crystal grain size of the crystal grains constituting the dielectric layer is 0.15 to 0.3 μm, the temperature change rate of the relative permittivity is high and the dielectric constant is high. And the high temperature load life can be improved.

  In the present invention, the crystal particles constituting the dielectric ceramic are the first crystal group consisting of crystal particles having a Ca component concentration of 0.2 atomic% or less and the crystal particles having a Ca component concentration of 0.4 atomic% or more. In the case of the composite particles in which the second crystal group consisting of is mixed, the dielectric constant of the dielectric layer can be further increased, and the temperature change rate of the dielectric constant can be further reduced.

  Further, in the present invention, when the total amount of Ba and Ca in the dielectric ceramic is A mol and Ti is B mol, if the relationship of A / B ≧ 1.003 is satisfied, Since growth is suppressed, the high temperature load life can be further improved.

  In addition, according to the method for producing a multilayer ceramic capacitor of the present invention, as a dielectric powder forming a green sheet, barium titanate powder or barium calcium titanate powder having an average particle diameter of 0.15 to 0.3 μm or these Using the mixed powder, a first powder in which the surface of the powder is coated with an oxide of a first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium, and lutetium is prepared. On the other hand, by using a dielectric powder obtained by adding one second rare earth element oxide powder selected from samarium, europium, gadolinium, terbium and dysprosium, MgO powder, and MnO powder, the average grain size after firing For crystal grains having a diameter of 0.15 to 0.3 μm, the first rare earth element Crystal grains having different concentration gradients of the second rare earth element and the second rare earth element can be easily formed in the dielectric layer, thereby having a high dielectric constant, excellent temperature characteristics of the dielectric constant, and high temperature load life. An excellent multilayer ceramic capacitor can be easily obtained.

  Further, in the present invention, by setting the main firing temperature when firing the capacitor body molded body to 1050 to 1150 ° C., it has a high relative dielectric constant, excellent temperature characteristics of the relative dielectric constant, and high temperature load life. Can be obtained.

Furthermore, in the present invention, when Ba _1-x Ca _x TiO ₃ powder (x = 0.01 to 0.2) is used as the barium calcium titanate powder used for the first powder, the relative dielectric constant is higher and the ratio A multilayer ceramic capacitor excellent in the temperature characteristics of dielectric constant can be easily obtained.

Furthermore, in the present invention, when using the _{Ba 1-x} Ca _x TiO ₃ powder as barium calcium titanate powder used in the first powder (x = 0.01 to 0.2), the _{Ba 1-x} Ca _x TiO Satisfying the relationship of C / D ≧ 1.003 when the total content of Ba and Ca in ₃ powders (however, x = 0.01 to 0.2) is C mol and the content of Ti is D mol By using this, the grain growth of the crystal grains after firing can be suppressed, so that a multilayer ceramic capacitor having further excellent high-temperature load life can be obtained.

  The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic cross-sectional views of FIGS. Fig.1 (a) is a schematic sectional drawing which shows the multilayer ceramic capacitor of this invention. The enlarged view of the drawer in (b) is a schematic diagram showing crystal grains and grain boundaries constituting a dielectric ceramic serving as a 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 crystal grains 9 mainly composed of barium titanate and a grain boundary 11. The thickness of the dielectric layer 5 is preferably 2 μm or less, particularly 1.5 μm or less. 0.5 μm or more is desirable in terms of maintaining high insulation per layer. This makes it possible to obtain a small and high capacity multilayer ceramic capacitor.

  The internal electrode layer 7 is preferably a base metal such as nickel (Ni) or a nickel alloy in that the manufacturing cost can be suppressed even if the internal electrode layer 7 is highly laminated, and in particular, nickel (Ni) in that the simultaneous firing with the dielectric layer 5 can be achieved. ) Is more desirable.

In the multilayer ceramic capacitor of the present invention, the crystal grains 9 constituting the dielectric ceramic serving as the dielectric layer 5 are mainly composed of barium titanate, and the average crystal grain size is 0.15 to 0.3 μm. In addition, the composition of the dielectric porcelain used as the dielectric layer 5 is 0.5 to 2 mol parts in terms of MgO and 0.2 to 0 in terms of MnO with respect to 100 mol parts of barium titanate. 0.5 mol part, and further, one first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium and one second rare earth element selected from samarium, europium, gadolinium, terbium and dysprosium along with containing 0.7 to 3 parts by mol in total in terms _RE 2 _{O 3,} of these rare earth elements, ho One kind of first rare earth element selected from the group consisting of mium, yttrium, erbium, thulium, ytterbium and lutetium is contained in the crystalline particle 9 more than the second kind of rare earth element selected from samarium, europium, gadolinium, terbium and dysprosium. Further, the concentration gradient from the grain boundary to the center of the first rare earth element in the crystal grains is −0.005 atomic% / nm or more and −0.05 atomic% / nm or less, the second rare earth element When the concentration gradient from the grain boundary to the central part is −0.0005 atomic% / nm or more and −0.005 atomic% / nm or less, the average crystal grain size of the crystal grains 9 is 0.15 to 0.005. Even if it is 3 μm, the temperature change rate of the relative dielectric constant at 85 ° C. when the relative dielectric constant is 1760 or more and 25 ° C. is within −15.9%. The rate of decrease in intergranular resistance in a high temperature load test can be reduced to 1.09% / min or less, even with fine particles, the dielectric constant is high, the temperature characteristics of relative permittivity are stable, and the high temperature load life is excellent. A laminated ceramic capacitor can be obtained. In the present invention, when the decrease rate of the resistance at the grain boundary in the high temperature load test is 1.1% / min or less, under the conditions described later (temperature 85 ° C., applied voltage 6.3 V / μm), The high temperature load life can satisfy 1000 hours or more, so that the high temperature load life can be increased.

The dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention is composed of crystal particles 9 mainly composed of barium titanate. In this case, a perovskite structure composite oxide expressed as BaTiO ₃ in the chemical formula is preferable for the reason that the crystal particle 9 has a high dielectric constant, but Ca is dissolved together with the crystal particle 9b expressed as BaTiO ₃ . A mixture of crystal particles 9a represented as Ba _1-x Ca _x TiO ₃ may be used. In particular, a first crystal group composed of crystal particles 9b having a Ca component concentration of 0.2 atomic% or less and a second crystal group composed of crystal particles 9a having a Ca component concentration of 0.4 atomic% or more were mixed. A composite particle is desirable. As a result, it is possible to increase the relative permittivity and reduce the rate of change of the temperature characteristic of the capacitance.

  Here, the crystal particle 9a constituting the second crystal group has a Ca component concentration of 0.4 atomic% or more, particularly 0.5 to 2.5 atomic%, because it maintains a perovskite structure. Is desirable.

  Further, in the present invention, the area occupied by the crystal grains 9b of the first crystal group found on the polished surface obtained by polishing the surface of the dielectric layer 5 is a, and the area occupied by the crystal grains 9a of the second crystal group is b. Sometimes, it is desirable that b / (a + b) is 0.7 to 0.8. When the area ratio b / (a + b) of the crystal grains 9a of the second crystal group is 0.7 or more, the relative dielectric constant of the dielectric layer 5 is increased, and b / (a + b) is 0.8 or less. There is an advantage that the reduction rate of the grain boundary resistance can be reduced and the high temperature load life can be increased.

  Here, with respect to the Ca concentration in the crystal particles 9, an elemental analysis device was attached to about 30 crystal particles 9 existing on the polished surface obtained by polishing the cross section of the dielectric layer 5 constituting the multilayer ceramic capacitor. Elemental analysis is performed using a transmission electron microscope. At this time, the spot size of the electron beam is set to 5 nm, and the points to be analyzed are 4 to 5 points at almost equal intervals from the grain boundary on the straight line drawn from the vicinity of the grain boundary toward the center of the crystal grain 9. Let the average value of the measured value be Ca density | concentration. In this case, assuming that the total amount of Ba, Ti, Ca, Mg, rare earth elements and Mn detected from each measurement point of the crystal particles is 100%, the Ca concentration at that time is obtained.

  The crystal particle 9 to be selected is obtained by calculating the area of each crystal particle from its contour by image processing, calculating the diameter when the crystal particle 9 is replaced with a circle having the same area, and obtaining the diameter of the obtained crystal particle by a method described later. The crystal grain 9 is in the range of ± 30% of the average crystal grain size.

  The center of the crystal grain 9 is the center of the inscribed circle of the crystal grain 9, and the vicinity of the grain boundary of the crystal grain is a region from the grain boundary of the crystal grain 9 to the inside of 5 nm. Further, the inscribed circle of the crystal particle 9 is obtained by taking an image projected by a transmission electron microscope into a computer and drawing the inscribed circle with respect to the crystal particle 9 on the screen to determine the center of the crystal particle.

  The area ratios of the crystal grains 9b of the first crystal group and the crystal grains 9a of the second crystal group are calculated from the area data when the Ca concentration is obtained. In this case, crystal grains having a Ca concentration of 0.2 atomic% or less are defined as crystal grains 9b of the first crystal group, and crystal grains having a Ca concentration of 0.4 atomic% or more are defined as crystal grains 9a of the second crystal group. To do.

  Further, in the present invention, the crystal particles 9 are a first crystal group composed of crystal particles 9b having a Ca component concentration of 0.2 atomic% or less and a second crystal particle 9a having a Ca component concentration of 0.4 atomic% or more. A / B ≧ 1.003 when the total content of Ba and Ca in the dielectric ceramic is A mol and the content of Ti is B mol. It is desirable to satisfy the relationship. As a result, the dielectric constant can be increased and the temperature characteristics of the relative dielectric constant can be stabilized, and the high-temperature load life can be further increased.

  In the present invention, it is important that the average crystal grain size of the crystal grains 9 is 0.15 to 0.3 μm, particularly 0.165 to 0.28 μm, and further 0.165 to 0.193 μm. Is more desirable. As a result, even if the dielectric layer 5 is thinned, high capacity and high insulation can be achieved.

  That is, when the average crystal grain size of the crystal particles 9 is smaller than 0.15 μm, the dielectric constant of the dielectric layer 5 is lower than 1760, while when the average crystal grain size of the crystal particles 9 is larger than 0.3 μm. Although the relative permittivity is increased, the temperature change rate of the relative permittivity is also larger than −15.9% and the high temperature load life is decreased.

  Here, the total average crystal grain size of the crystal grains 9 consisting of the crystal grains 9b constituting the first crystal group and the crystal grains 9a constituting the second crystal group is obtained by polishing the cross section of the dielectric layer 5. For the polished surface, the image displayed by the transmission electron microscope is taken into a computer, a diagonal line is drawn on the screen, the contour of the crystal particle existing on the diagonal line is image-processed, and the area of each particle is obtained. The diameter when replaced with a circle having the same area is calculated and obtained as an average value of about 50 calculated crystal particles.

  The average crystal grain size of each of the crystal grains 9b constituting the first crystal group constituting the dielectric layer 5 and the crystal grains 9a constituting the second crystal group is the value obtained when the Ca concentration is obtained. It is calculated from the data of the area of the crystal grains 9b constituting the first crystal group and the crystal grains 9a constituting the second crystal group. In this case, with respect to the polished surface obtained by polishing the cross section of the dielectric layer 5, an image displayed by a transmission electron microscope is taken into a computer, and the outline of the crystal particles 9 existing on the screen is subjected to image processing. The area of crystal grains is obtained, the diameter when replaced with a circle having the same area is calculated, and the average value of about 50 calculated crystal grains is obtained.

  FIG. 2A is a schematic diagram showing the concentration gradients of the first rare earth element and the second rare earth element in the crystal particles constituting the dielectric layer of the multilayer ceramic capacitor of the present invention. (B) is a schematic diagram showing crystal grains outside the scope of the present invention in which the concentration gradient of the first rare earth element is smaller than the concentration gradient of the second rare earth element and the concentration gradient of the rare earth element. (C) is a schematic diagram showing a crystal particle and a concentration gradient of the rare earth element when the content of the second rare earth element is larger than the content of the first rare earth element.

  Here, each concentration gradient from the grain boundary to the center of the crystal grains of the first rare earth element and the second rare earth element is measured using a transmission electron microscope provided with an element analyzer (EDS). In this case, as a sample to be analyzed, a multilayer ceramic capacitor is polished in the stacking direction, and crystal particles 9 are extracted on the surface of the polished dielectric layer 5. Further, the first crystal group in which the crystal particle 9 is composed of crystal particles having a Ca component concentration of 0.2 atomic% or less and the second crystal group in which the Ca component concentration is 0.4 atomic% or more are mixed. In the case of the composite particles, the crystal particles 9b of the first crystal group and the crystal particles 9a of the second crystal group determined by the above-described measurement of the Ca concentration are extracted.

  For each crystal particle 9 (or crystal particle 9a, 9b) to be extracted, the area of each crystal particle is obtained from its contour by image processing, and the diameter when replaced with a circle having the same area is calculated, and the measurement described above The crystal grains are in the range of ± 30% of the average crystal grain diameter of each crystal grain 9 (or crystal grain 9a, 9b) determined by the method. Ten crystal grains 9b of the first crystal group and ten crystal grains 9a of the second crystal group in this range are extracted.

  The spot size of the electron beam when performing elemental analysis is set to 1 to 3 nm. Further, the location to be analyzed is a point that exists on a straight line at an interval of 5 nm from the grain boundary to the center of the crystal grain, and each crystal grain 9 is measured in one direction. The grain boundary of the crystal grain is a region within 3 nm from the surface of the crystal grain, and the center part of the crystal grain is the center of the inscribed circle of the crystal grain. In this case, for the inscribed circle of the crystal particles, an inscribed circle is drawn on the screen of a computer on the image projected by the transmission electron microscope, and the center of the crystal particle is determined from the image on the screen.

  Thus, the analysis is performed from the grain boundary to the center of each crystal grain 9, and the total amount of Ba, Ti, Ca, Mg, rare earth element and Mn detected from each measurement point is 100%. The respective concentrations of the second rare earth element are obtained. Next, the relationship between the concentration of the first rare earth element and the second rare earth element obtained at each measurement point of the crystal grain 9 and the distance from the grain boundary as the measurement point to the center is plotted on a graph (coordinates). The X-axis is the distance from the grain boundary to the center, and the Y-axis is the concentration of each of the first rare earth element and the second rare earth element.) From the plotted points, the first rare earth element and the second The concentration gradient of each rare earth element is obtained.

  As described above, the concentration gradient of the first rare earth element or the second rare earth element in the present invention is, for example, from the interface of the crystal grain 9 when the grain size of the crystal grain 9 is taken as the X axis in FIG. It is represented by the concentration change of the rare earth element at the distance to the center C.

  In the present invention, the crystal grains 9 constituting the dielectric layer 5 in the multilayer ceramic capacitor are holmium (Ho), yttrium (Y), erbium (Er), thulium (Tm), ytterbium (Yb) having an ionic radius of 0.106 nm or less. ) And lutetium (Lu), a first rare earth element, and samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb) and dysprosium (Dy) having an ionic radius of 0.107 nm or more. It is important to contain the second rare earth element selected from the above in the crystal grains 9 so that the amount of the first rare earth element is larger than the amount of the second rare earth element. In this case, the amount of the first rare earth element is larger than the amount of the second rare earth element is when the concentration of the first rare earth element is higher than the concentration of the second rare earth element on the surface of the crystal particle 9.

  In the present invention, since the first rare earth element is contained at a higher concentration than the second rare earth element as described above, a decrease in the dielectric constant due to the presence of a large amount of the second rare earth element in the crystal grains 9 and It is possible to suppress a decrease in insulation when the first rare earth element is small.

  Among these rare earth elements having different ionic radii, any one of Ho, Y, Er, and Tm is selected as the first rare earth element, and Sm, Eu, Gd, Tb, and Dy are selected as the second rare earth element. It is desirable to select any one of them and combine them. As a result, the dielectric constant of the dielectric layer 5 is increased, and the high temperature load life can be improved. In particular, Y having an ionic radius of 0.106 nm and Ho having a 0.105 nm, Tb having an ionic radius of 0.109 nm and 0.11 nm. A combination with Gd is more desirable.

  In the present invention, the concentration gradient of the first rare earth element from the grain boundary 11 to the central portion C of each crystal grain 9a, 9b is −0.005 atomic% / nm or more and −0.05 atomic% / nm or less, In addition, it is important that the concentration gradient of the second rare earth element from the grain boundary 11 to the central portion C of each crystal grain 9a, 9b is −0.0005 atomic% / nm or less and −0.005 atomic% / nm or more. is there.

  That is, in the present invention, each of the crystal grains 9a and 9b constituting the dielectric layer 5 has a steep concentration gradient from the grain boundary 11 to the center C, while the second rare earth element Two kinds of rare earth elements are contained so as to have a gradual concentration gradient from the grain boundary 11 to the center C of the crystal grains 9a, 9b.

  That is, in the present invention, in each crystal particle 9a, 9b, the first rare earth element contained in a high concentration is unevenly distributed near the grain boundary 11 so that the internal concentration is lowered, thereby forming each crystal particle 9a. , 9b and the vicinity of the grain boundary 11 can be improved, and the tetragonal nature of the crystal grains 9a, 9b can be maintained, whereby a high dielectric constant can be obtained.

  Further, by containing the second rare earth element at a low concentration in each of the crystal particles 9a and 9b, the carrier density such as oxygen vacancies in each of the crystal particles 9a and 9b can be reduced. This can improve the high temperature load life.

  On the other hand, in the case of only the first rare earth element or only the second rare earth element, the rate of decrease in the resistance of the grain boundary 11 is large and the high temperature load life is reduced. Further, even when a rare earth element other than the first rare earth element and the second rare earth element is used, the central portion C extends from the grain boundary 11 of each of the crystal grains 9a and 9b mainly composed of the barium titanate of the first rare earth element. From the grain boundary 11 of each of the crystal grains 9a, 9b whose main component is the second rare earth element barium titanate, the concentration gradient to −0.005 atomic% / nm to −0.05 atomic% / nm. Since the concentration gradient to the central portion C cannot be in the range of −0.0005 atomic% / nm or more and −0.005 atomic% / nm or less, the high temperature load life is reduced.

  Further, the total content of the first rare earth element and the second rare earth element is large with respect to each crystal particle 9a, 9b, and the concentration gradient of the first rare earth element from the grain boundary 11 to the central portion C is −0. If the concentration gradient of the second rare earth element from the grain boundary 11 to the central portion C of each crystal grain 9a, 9b is greater than −0.005 atomic% / nm, the ratio is greater than 05 atoms / nm. The dielectric constant is greatly reduced.

  Further, the content of the first rare earth element and the second rare earth element in the crystal grains 9a and 9b is small, and the concentration gradient from the grain boundary 11 to the central portion C of the first rare earth element is -0.005 atom / nm. Or when the concentration gradient from the grain boundary 11 of the second rare earth element to the central portion C is smaller than −0.0005 atom / nm, the temperature change rate of the relative permittivity increases and the high temperature load is increased. The service life is reduced.

  In the present invention, it is important that the total content of the first rare earth element and the second rare earth element is 0.7 to 3 mole parts in total with respect to 100 mole parts of barium titanate. In particular, when the content of the first rare earth element and the second rare earth element is in the above range, the relative permittivity can be increased, the temperature change rate of the relative permittivity can be reduced, and at the same time, the high temperature load life is improved. it can. In particular, the first rare earth element is 0.6 to 2 mole parts with respect to 100 mole parts of barium titanate, and the second rare earth element is 0.1 to 1 mole parts with respect to 100 mole parts of barium titanate. preferable.

  Further, in the present invention, the dielectric ceramic serving as the dielectric layer 5 contains magnesium and manganese in addition to the rare earth element, and the content thereof is 0 in terms of MgO with respect to 100 mol parts of barium titanate. It is important that 0.5 to 2 mol parts and manganese are 0.2 to 0.5 mol parts in terms of MnO. As a result, the reduction resistance of the dielectric layer 5 can be enhanced, the temperature characteristics of the relative permittivity can be stabilized, the insulation properties are increased, and the high temperature load life is improved.

  On the other hand, when the content of magnesium contained in the dielectric ceramic serving as the dielectric layer 5 is less than 0.5 mole parts in terms of MgO with respect to 100 mole parts of barium titanate, On the other hand, the temperature change rate of the dielectric constant at 85 ° C. increases to −18.2%, and the reduction rate of the grain boundary resistance increases to 1.2% / min. On the other hand, when the magnesium content is more than 2 mol parts in terms of MgO with respect to 100 mol parts of barium titanate, the relative dielectric constant decreases to 1700.

  Further, when the content of manganese contained in the dielectric ceramic serving as the dielectric layer 5 is less than 0.2 mol parts in terms of MnO with respect to 100 mol parts of barium titanate, the reduction rate of the resistance of the grain boundary is reduced. 3.3% / min, the high temperature load life is greatly impaired.

  Further, when the manganese content is more than 0.5 mol parts in terms of MnO with respect to 100 mol parts of barium titanate, the relative dielectric constant decreases to 1720.

  FIG. 3 is a schematic diagram showing a method for evaluating the resistance of the grain boundary in the dielectric layer by the AC impedance method. This evaluation method can simply evaluate the high-temperature load life of the multilayer ceramic capacitor, and has an advantage that the high-temperature load life can be evaluated in a short time compared to a high-temperature load test that is usually performed. In FIG. 3, 20a is a thermostatic chamber for controlling the temperature by mounting a multilayer ceramic capacitor as a sample, 20b is an accelerated life test (HALT) device for applying a DC voltage to the sample, and 20c is an impedance measuring device having an AC power source. is there.

  FIG. 4A is a graph of impedance change (Cole-Cole plot) for the multilayer ceramic capacitor of the present invention, in which crystal grains 9 (core (center part), shell (outer peripheral part)), grain boundaries 11, and internal electrode layers are shown. 7 represents the impedance of the interface 12 between the dielectric layer 5 and the dielectric layer 5. FIG. 4B shows each component of the crystal grains 9, the grain boundaries 11, and the interface 12 between the internal electrode 7 and the dielectric layer 5 constituting the multilayer ceramic capacitor by an equivalent circuit.

  In this evaluation, as shown in the equivalent circuit of FIG. 4B, the dielectric layer 5 is divided into three components: crystal grains 9, grain boundaries 11, and interfaces 12 between the internal electrodes 7 and the dielectric layer 5. The horizontal axis of the graph indicates the real part of the impedance signal, and the vertical axis indicates the imaginary part. The graph showing the change in impedance is the difference between before and after the accelerated life test (HALT) and the fitting by simulation. In this evaluation, attention is paid to a resistance change at the grain boundary 11. In the above evaluation, for example, the Cole-Cole plot of FIG. 4A before and after the accelerated life test (HALT) is obtained by using dedicated software, and the crystal grains 9 (core (central part), shell (outer peripheral part)), grain boundaries 11 It can be obtained by dividing into three components of the interface 12 between the internal electrode layer 7 and the dielectric layer 5.

  In the present invention, the standing time is changed to a high temperature load state at a temperature higher than the Curie temperature indicated by the crystal grains 9 constituting the dielectric ceramic serving as the dielectric layer 5 and a voltage equal to or higher than 1/3 of the rated voltage of the multilayer ceramic capacitor. Test. Then, the AC impedance measurement under the same conditions is performed before and after being left in a high temperature load condition under the above conditions, and the resistance change of the grain boundary 11 in the dielectric layer 5 is measured. The resistance change is evaluated as time dependency (amount of change per unit time) by evaluating a change in the standing time. In this case, it is desirable that the resistance change in the real part of the impedance is 1% / min or less.

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

As described above, the dielectric ceramic constituting the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention may contain components other than barium titanate, magnesium, rare earth elements and manganese in a range of 2 mass% or less. For example, when a glass component containing SiO ₂ as a main component is included, there is an advantage that the sinterability can be enhanced without impairing the characteristics of the dielectric ceramic serving as the dielectric layer 5.

  Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. FIG. 5 is a process diagram showing a method for producing a multilayer ceramic capacitor of the present invention.

  (A) Step: In the production method of the present invention, first, a ceramic slurry is prepared by using a ball mill or the like together with a dielectric powder, an organic resin such as polyvinyl butyral resin, and a solvent such as toluene and alcohol, and then the ceramic slurry is doctor blade. The ceramic green sheet 21 is formed using a sheet forming method such as a method or a die coater method. The thickness of the ceramic green sheet 21 is preferably 1 to 3 μm from the viewpoint of reducing the thickness of the dielectric layer 5 for increasing the capacity and maintaining high insulation.

The dielectric powder used in the method for producing the multilayer ceramic capacitor of the present invention uses BT powder represented by BaTiO ₃ as the barium titanate powder, or Ba ₁₋ as the barium calcium titanate in which a part of Ba is replaced by Ca. A BCT powder represented by _x Ca _x TiO ₃ powder (x = 0.01 to 0.2: BCT powder) or a mixed powder of BT powder and BCT powder is used.

In particular, in the BCT powder, when the total content of its constituent components Ba and Ca is C mol and the content of Ti is D mol, the molar ratio C / D is 1.003 or more, particularly 1.003. It is desirable to be ˜1.007. When the molar ratio C / D of Ba and Ca and Ti constituting the BCT powder is 1.003 or more, the grain growth of the crystal grains 9a constituting the second crystal group can be suppressed, and thus high insulating properties are achieved. The high temperature load life can be improved. In addition, when the C / D ratio is 1.007 or less, the crystal particles mainly composed of barium titanate can maintain the crystal structure of the ferroelectric perovskite structure, and the dielectric constant can be increased. The BCT powder is synthesized by mixing a compound containing a Ba component, a Ca component and a Ti component so as to have a predetermined composition. For example, it can be obtained by a synthesis method selected from a solid phase method, a liquid phase method (including a method of producing via oxalate), a hydrothermal synthesis method and the like. Among these, the powder obtained by the hydrothermal synthesis method is preferable because the particle size distribution of the obtained dielectric powder is narrow and the crystallinity is high.

  In the present invention, it is important that the average particle size of the BT powder and the BCT powder used in the method for producing the multilayer ceramic capacitor is 0.15 to 0.3 μm. This facilitates thinning of the dielectric layer 5 and makes it possible to obtain a high dielectric constant powder as the BT powder and the BCT powder.

  When the average particle size of the BT powder and the BCT powder is smaller than 0.15 μm, the relative dielectric constant is lowered, and the temperature change rate of the relative dielectric constant at 85 ° C. is increased with respect to 25 ° C. On the other hand, if the average particle size of the BT powder and the BCT powder is larger than 0.15 μm, the rate of decrease in the resistance of the grain boundary increases, and the high temperature load life decreases.

  In the present invention, next, a plurality of rare earth elements are dissolved in the BT powder, the BCT powder, or a mixed powder thereof as an additive for improving the reduction resistance of the dielectric ceramic and enhancing the dielectric characteristics.

  The total amount of rare earth elements to be dissolved in the BT powder, BCT powder, or mixed powder thereof is 0.7-3 mole parts when the BT powder, BCT powder, or mixed powder thereof is 100 mole parts. An oxide of a first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium having an ionic radius of 0.106 nm or less is coated on the surface of BT powder, BCT powder, or a mixed powder thereof. A first powder is produced. The coating amount is set to 0.6 to 2 mol parts with respect to 100 mol parts of BT powder, BCT powder or mixed powder thereof.

  Next, one second rare earth element selected from samarium, europium, gadolinium, terbium and dysprosium is applied to the first powder which is a BT powder or BCT powder coated with a predetermined amount of the first rare earth element or a mixed powder thereof. Add the oxide powder. The addition amount is 0.1-1 mol part with respect to 100 mol parts of the first powder.

In addition, when the oxide powder of the second rare earth element is added, the MgO powder and the MnCO ₃ powder are added in an amount of 0.5 to 2 mol, respectively, with respect to 100 mol parts of the BT powder, BCT powder or mixed powder thereof. And 0.2 to 0.5 mole parts are added and mixed. MnCO ₃ powder is suitable in terms of fine particles and high purity.

  These magnesium oxide, rare earth element oxide and manganese oxide are dissolved in the crystal grains 9b constituting the first crystal group and the crystal grains 9a constituting the second crystal group. It tends to exist in the boundary 11 and also acts as a sintering aid.

  In the present invention, as described above, the surface of BT powder, BCT powder, or a mixed powder thereof is coated with an oxide of a first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium, and lutetium. Then, by adopting a method of adding one second rare earth element oxide powder selected from samarium, europium, gadolinium, terbium and dysprosium thereafter, the second BT powder or BCT powder or a mixed powder thereof is obtained. It becomes possible to suppress solid solution of rare earth elements. As a result, in the crystal grains 9 constituting the dielectric layer 5 which is a sintered body after firing, the concentration gradient of the first rare earth element from the grain boundary 11 to the center portion C is −0.005 to −0.05 atoms. % / Nm, and the concentration gradient of the second rare earth element can be in the range of −0.0005 to −0.005 atomic% / nm.

  On the other hand, when the oxide of the first rare earth element and the oxide of the second rare earth element are collectively added to the BT powder, the BCT powder, or the mixed powder thereof, the crystal particles after firing the BT powder, the BCT powder, or the mixed powder thereof The concentration gradient of the first rare earth element to less than −0.005 atomic% / nm, and thus the temperature change rate of the relative dielectric constant at 85 ° C. increases to −18.4%, and the grain boundary The resistance reduction rate is 1.21% / min or more, and the high temperature load life is low.

In the present invention, as long as desired dielectric characteristics can be maintained, in addition to components such as magnesium, first rare earth element, second rare earth element and manganese, a glass component as an auxiliary agent for enhancing sinterability. In this case, the addition amount of the sintering aid is preferably 0.5 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. This can further enhance the sinterability of the dielectric ceramic, and its composition is Li ₂ O = 1-15 mol%, SiO ₂ = 40-60 mol%, BaO = 15-35 mol%, and CaO. = 5-25 mol% is preferable. The average particle size of the glass powder used as a sintering aid is preferably in the range of 0.1 to 0.3 μm because it increases the dispersibility when added to the dielectric powder.

  (B) Process: Next, the rectangular internal electrode pattern 23 is printed and formed on the main surface of the obtained ceramic green sheet 21. The conductive paste to be the internal electrode pattern 23 is prepared by mixing Ni 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. BT powder is preferable as the ceramic powder. Columnar ceramics are formed so that the ceramic powder contained in the conductor paste penetrates the internal electrode layer 7 and connects the upper and lower dielectric layers 5. Thereby, peeling between the dielectric layer 5 and the internal electrode layer 7 can be prevented. The thickness of the internal electrode pattern 23 is preferably 1 μm or less because the multilayer ceramic capacitor is downsized and the level difference due to the internal electrode pattern 23 is 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. It is preferable. As the ceramic component constituting the ceramic pattern 25, it is preferable to use the dielectric powder used for the ceramic green sheet 21 in that the firing shrinkage in the simultaneous firing is 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. A 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 formed so as to be alternately exposed on the end faces of the cut laminate.

  In the manufacturing method of the multilayer ceramic capacitor of the present invention, the ceramic green sheet 21 is once brought into close contact with the lower layer equipment in addition to the method of laminating the internal electrode pattern 23 on the main surface of the ceramic green sheet 21 in advance. After that, the internal electrode pattern 23 is printed and dried, and the ceramic green sheet 21 on which the internal electrode pattern 23 is not printed is overlapped and temporarily adhered onto the printed and dried internal electrode pattern 23, and the ceramic green sheet 21 is printed. Can be formed by a method of sequentially performing the adhesion and printing of the internal electrode pattern 23.

  Next, the temporary laminate is pressed under conditions of higher temperature and higher pressure than the temperature pressure at the time of temporary lamination to form a laminate 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 to form a capacitor body molded body in which the end portion of the internal electrode pattern 23 is exposed. In this case, the cutting is performed in such a manner that the approximate center of the ceramic pattern 25 formed in the laminate 29 is perpendicular to the longitudinal direction of the internal electrode pattern 23 ((c1) in FIG. 5 and (c2) in FIG. 5). In parallel with the longitudinal direction of the internal electrode pattern 23, the process is performed. In this case, the internal electrode pattern 23 is exposed on the end margin side, but the internal electrode pattern 23 is not exposed on the side margin portion side.

  Next, the capacitor body 1 is formed by firing the capacitor body molded body in a predetermined atmosphere under temperature conditions. In some cases, the ridge line portion of the capacitor body 1 may be chamfered, and barrel polishing may be performed to expose the internal electrode layer 7 exposed from the opposite end surface of the capacitor body 1.

  Degreasing is performed at a temperature rising rate of 5 to 20 ° C./h and in a temperature range from room temperature to 500 ° C. Firing is preferably performed in a hydrogen-nitrogen atmosphere at a temperature elevation rate of 200 to 500 ° C./h, a maximum temperature of 1040 to 1200 ° C., a holding time of 0.5 to 4 hours, The temperature is more preferably 1050 to 1150 ° C. By performing the firing under such conditions, the average grain size of the crystal grains 9 constituting the dielectric layer 5 is in the range of 0.15 to 0.3 μm, and two kinds of rare earth elements having different ionic radii are used. Each can be contained so as to have the above-mentioned concentration gradient, and in particular, by setting the maximum firing temperature in the range of 1050 to 1150 ° C., the concentration gradient of the first rare earth element in the crystal particles 9 is −0. The concentration gradient of the second rare earth element can be in the range of -0.001 to -0.0048 atom% / nm in the range of 0051 to -0.0046 atom% / nm. The resistance reduction rate can be less than 1.09% / min.

  Then, the capacitor body 1 is obtained by performing reoxidation treatment in the temperature range of 900 to 1100 ° C.

  Next, an external electrode paste is applied to the opposing ends of the capacitor body 1 and baked to form the external electrodes 3. In some cases, a plating film is formed on the surface of the external electrode 3 in order to improve mountability.

A multilayer ceramic capacitor was produced as follows. As barium titanate powder, BT powder (BaTiO ₃ ) and BCT powder (Ba _1-x Ca _x TiO ₃ x = 0.05) coated with oxides of the first rare earth elements shown in Tables 1, 3 and 5 were used. Got ready. The A / B ratio of the used BT powder and BCT powder was 1-1.09.

The first powder BT powder and BCT powder or a mixed powder thereof was coated with a rare earth element by mixing an aqueous solution containing the first rare earth element by a liquid phase method and then heating. As the second rare earth element, an oxide powder having an average particle diameter of 0.05 μm was used. The addition amounts of the first rare earth oxide and the second rare earth oxide are shown in Tables 1, 3 and 5. Further, MgO and MnO were added in proportions shown in Tables 1, 3 and 5 with respect to 100 mol parts of BT powder or BCT powder as the first powder or mixed powder thereof. MnO was added in the form of MnCO ₃ . The average particle diameters of MgO powder and MnCO ₃ powder were both 0.2 μm. Further, a glass powder having an average particle size of 0.3 μm and a composition of Li ₂ O = 10, BaO = 20, CaO = 20, and SiO ₂ = 50 (mol%) was used as a sintering aid. The addition amount of the glass powder was 1.2 parts by mass with respect to 100 parts by mass of the dielectric powder mainly composed of barium titanate powder.

Next, a dielectric powder containing rare earth element oxide powder, MgO powder and MnCO ₃ powder is mixed with BT powder, BCT powder, or a mixed powder thereof using zirconia balls having a diameter of 5 mm, and toluene and alcohol are mixed as a solvent. Solvent was added and wet mixed. 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, and a ceramic slurry is prepared. The thickness is 2.5 μm by the doctor blade method. A ceramic green sheet was prepared.

  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 the ceramic green sheet as a co-material was added to 100 parts by mass of Ni powder.

Next, 100 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, and a temperature of 60 ° C. and pressure were used using a press. 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 degreased at about 300 ° C./h in the atmosphere at a temperature increase rate of 10 ° C./h, and then the temperature increase rate from 500 ° C. was switched to 300 ° C./h. Firing was carried out in hydrogen-nitrogen for 2 hours at the maximum temperatures shown in 1, 3 and 5. Subsequently, after cooling to 1000 ° C. at a temperature lowering rate of 300 ° C./h, reoxidation treatment was performed at 1000 ° C. for 4 hours in a nitrogen atmosphere to obtain a capacitor body. The size of the obtained capacitor body was 1 × 0.5 × 0.5 mm ³ , and the thickness of the dielectric layer was 1.8 μm. The effective area contributing to the capacitance per internal electrode layer was 0.258 mm ² .

  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, Ni plating and Sn plating were sequentially performed on the surface of the external electrode by using an electrolytic barrel machine to produce a multilayer ceramic capacitor.

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

  The dielectric constant of the dielectric layer was calculated from the effective area of the internal electrode layer and the thickness of the dielectric layer after measuring the capacitance under measurement conditions of a frequency of 1.0 kHz and a measurement voltage of 0.5 Vrms.

  The temperature change rate of the relative dielectric constant was also measured by measuring the capacitance at 25 ° C. and 85 ° C. under the condition of frequency and measurement voltage when the capacitance was measured, and 85 when 25 ° C. was used as a reference. The rate of change in relative dielectric constant at 0 ° C. (that is, the temperature characteristic of capacitance) was determined. The number of samples was 30 each.

  The total average crystal grain size of the crystal grains comprising the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group is determined by using a transmission electron microscope on the polished surface obtained by polishing the cross section of the dielectric layer. The image shown in is taken into a computer, a diagonal line is drawn on the screen, the contours of crystal grains existing on the diagonal line are image-processed, the area of each particle is obtained, and it is replaced with a circle with the same area The diameter was calculated, and an average value of about 50 calculated crystal particles was obtained.

  Regarding the Ca concentration in the crystal particles, a transmission electron microscope provided with an elemental analysis device was used for about 30 crystal particles existing on the surface of the dielectric layer obtained by polishing the cross section in the stacking direction of the multilayer ceramic capacitor. Elemental analysis was performed. At this time, the spot size of the electron beam was 5 nm, and the locations to be analyzed were five locations from the vicinity of the crystal grain boundary to the center. The crystal particles to be selected are obtained by calculating the area of each particle by image processing from the outline, and calculating the diameter when replaced with a circle having the same area. The diameter of the crystal particle thus obtained is the average crystal Crystal particles in the range of ± 30% of the particle diameter were used. Crystal grains having a Ca concentration of 0.2 atomic% or less were taken as the first crystal group, and crystal grains having a Ca concentration of 0.4 atomic% or more were taken as the second crystal group.

  The average crystal grain sizes of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group are the crystal grains constituting the first crystal group and the first crystal grains when the Ca concentration is determined. It calculated from the data of the area of the crystal grain which comprises 2 crystal groups. In this case, for the polished surface obtained by polishing the cross section of the dielectric layer, an image projected by a transmission electron microscope is taken into a computer, and the outline of the crystal particles present on the screen is image-processed. The area was calculated, the diameter when replaced with a circle having the same area was calculated, and the average value of about 50 calculated crystal particles was determined.

  Following this analysis, the area ratio (b / (a + b) of the crystal grains constituting the first crystal group and the second crystal group constituting the dielectric layer (b / (a + b)) The area of the crystal particles 1b constituting the crystal grains 1b and the area of the crystal grains 1a constituting the second crystal group b) are calculated from the area data obtained by calculating the average crystal grain size of each crystal grain for the above about 50 particles. did. In this case, the one having a Ca concentration higher than 0.4 atomic% (rounded to the second decimal place) was used as the crystal grains of the second crystal group. As shown in Tables 1 to 6, in the sample in which the BT powder and the BCT powder were mixed, the Ca concentration was 0.4 atom due to the diffusion of Ca during the firing relative to the mixing ratio of the BT powder and the BCT powder after firing. The proportion of crystal particles with a concentration of at least% increased, but crystal particles with a Ca concentration of 0.2 atomic percent or less and crystal particles with a Ca concentration of 0.4 atomic percent or more were mixed.

  Each concentration gradient from the grain boundary to the center of the crystal grains of the first rare earth element and the second rare earth element was measured using a transmission electron microscope equipped with an element analyzer (EDS) as follows. . In this case, as a sample to be analyzed, a multilayer ceramic capacitor was polished in the stacking direction, and crystal particles were extracted on the surface of the polished dielectric layer.

  Further, the first crystal group in which the crystal particles are composed of crystal particles having a Ca component concentration of 0.2 atomic% or less and the second crystal group composed of crystal particles in which the Ca component concentration is 0.4 atomic% or more are mixed. In the case of composite particles, the crystal particles 9b of the first crystal group and the crystal particles 9a of the second crystal group determined by the above-described measurement of the Ca concentration were extracted.

  The spot size of the electron beam when performing elemental analysis was set to 1 to 3 nm. Moreover, the location to analyze was made into the point which exists on a straight line in the space | interval of 5 nm from the grain boundary of a crystal grain to a center part. This measurement was performed in one direction for each crystal particle.

  The grain boundary of the crystal grain was set to a region within 3 nm from the surface of the crystal grain, and the center part of the crystal grain was set to the center of the inscribed circle of the crystal grain. In this case, the inscribed circle of the crystal grain was drawn on the screen of a computer with an image projected by a transmission electron microscope, and the center part of the crystal grain was determined from the image on the screen. Thus, the analysis is performed from the grain boundary to the center of each crystal grain, and the total amount of Ba, Ti, Ca, Mg, rare earth elements and Mn detected from each measurement point is 100%, and the first rare earth element at each measurement point The respective concentrations of the second rare earth element were determined.

  Next, the relationship between the concentration of each of the first rare earth element and the second rare earth element obtained at each measurement point of the crystal particle and the measurement point is plotted on a graph, and the first rare earth element and the second rare earth element are measured using the least square method. The concentration gradient of each of the two rare earth elements was determined. At this time, the measurement point of the grain boundary was set to the coordinate origin side.

  The high temperature load life was obtained by evaluating the reduction rate of the grain boundary resistance using the AC impedance method. As high temperature load conditions in this case, the temperature was 250 ° C., and the voltage applied to the external electrode of the multilayer ceramic capacitor was 2 V / μm. The voltage at the time of measurement was 0.1 V, the frequency was 10 mHz to 10 kHz, the standing time was 1 hour, and the AC impedance before and after the treatment was measured for each sample. The number of samples was 30 each.

  In addition, 30 samples were extracted from the same lot and subjected to a high temperature load test for 1000 hours at a temperature of 85 ° C. and an applied voltage of 6.3 V / μm. In these measurements, the grain boundary resistance decrease rate of 1.1% / min or less satisfied 1000 hours or more at a temperature of 85 ° C. and an applied voltage of 6.3 V / μm.

  The composition analysis of the sample, which was the obtained multilayer ceramic capacitor, was performed by ICP analysis or atomic absorption analysis. In this case, a dielectric layer obtained by cutting from the obtained multilayer ceramic capacitor is mixed with boric acid and sodium carbonate and melted, dissolved in hydrochloric acid, and first contained in the dielectric layer by atomic absorption analysis. Qualitative analysis of the element was performed, and then, the diluted standard solution for each identified element was used as a standard sample for quantification by ICP emission spectroscopic analysis. Further, the amount of oxygen was determined using the valence of each element as the valence shown in the periodic table. In this example, the composition of the dielectric layer after firing was not different from the prepared composition. Further, the molar ratio when the total content of Ba and Ca constituting the dielectric layer was A mol and the content of Ti was B mol was also determined by this analysis.

In this case, the composition of the sintered body obtained by using MnCO ₃ as the additive as MnO was not different from the prepared composition.

As a comparative example, the ratio of the first rare earth element or the second rare earth element or other additive component deviated from the scope of the present invention, the oxide powder of the first rare earth element and the oxide powder of the second rare earth element. Multilayer ceramic capacitors were produced by the same production method as above using the batch addition, BT powder, and BCT powder whose average particle diameters were not within the scope of the present invention, and the same evaluation was performed. The results are shown in Tables 1-6.

As is apparent from the results of Tables 1 to 6, with respect to 100 mol parts of barium titanate, Mg is 0.5 to 2 mol parts in terms of MgO, Mn is 0.2 to 0.5 mol parts in terms of MnO, While containing at least one rare earth element (RE) selected from Ho, Y, Er, Tm, Yb, Lu, Sm, Eu, Gd, Tb and Dy in an amount of 0.7 to ₃ moles in terms of RE ₂ O _3. The crystal particles include one kind of first rare earth element selected from Ho, Y, Er, Tm, Yb and Lu, and one kind of second rare earth element selected from Sm, Eu, Gd, Tb and Dy. The content of the first rare earth element is greater than the amount of the second rare earth element, and the concentration gradient from the grain boundary to the center of the crystal grain of the first rare earth element is −0.005 to −0.05 atomic%. / Nm and second rare earth element crystals Samples of the present invention (sample Nos. 4 to 10, 17 to 45, 55 to 63, 66 to 69) in which the concentration gradient from the grain boundary to the central part was −0.0005 to −0.005 atomic% / nm. 71, 72, 75, 76, 78, 81 and 83 to 86), even if the average crystal grain size of the crystal grains mainly composed of barium titanate is 0.153 to 0.286 μm, the relative dielectric constant Is 1760 or more, the change rate of the relative dielectric constant at 85 ° C. is within −15.9%, the decrease rate of the resistance of the grain boundary as an index of the high temperature load life is 1.09% / min or less, and the high temperature load The lifetime was 1000 hours or more.

  Further, the dielectric layer includes a first crystal group composed of crystal particles having a Ca component concentration of 0.2 atomic% or less and a second crystal group composed of crystal particles having a Ca component concentration of 0.4 atomic% or more. Samples composed of mixed composite particles (sample Nos. 4 to 10, 17 to 45, 57 to 63, 66 to 69, 71, 72, 75, 76, 78, 81, and 83 to 86) have a relative dielectric constant. It became 1760 or more, and the rate of change of the relative dielectric constant at 85 ° C. was within −15.1%.

  Further, in the composite particles constituting the dielectric layer, when the total content of Ba and Ca is A mol and the content of Ti is B mol, a sample in which A / B is 1.003 to 1.005 ( Sample Nos. 4 to 10, 17 to 45, 58, 60 to 63, 66 to 69, 71, 72, 75, 76, 78, 81, and 83 to 86) have a relative dielectric constant of 1770 or more at 85 ° C. The rate of change of the relative dielectric constant was within -15%, the rate of decrease in the grain boundary resistance was 1.08% / min or less, and the high temperature load life was improved.

  Furthermore, the dielectric layer is formed of composite particles, the molar ratio A / B is 1.003 to 1.005, and the average crystal grain size of the crystal particles is 0.165 to 0.193 μm (sample No. 4 to 10, 17 to 37, 58, 66 to 69, 71, 72, 75, 76 and 78), the relative dielectric constant is 2110 or more, and the rate of change of the relative dielectric constant at 85 ° C. is within −15%. The rate of decrease in grain boundary resistance was 1% / min or less, and the high temperature load life was further improved.

  On the other hand, in samples outside the scope of the present invention (sample Nos. 1-3, 11-16, 46-54, 64, 65, 70, 73, 74, 77, 79, 80, 82 and 87), The relative dielectric constant is 1700 or less, the change rate of the relative dielectric constant at 85 ° C. is larger than −15.9%, or the decrease rate of the grain boundary resistance is larger than 1.09% / min. A dielectric constant of 1760 or more, a change rate of relative dielectric constant at 85 ° C. within −15.9%, and a decrease rate of resistance at grain boundaries of 1.09% / min or less were not obtained.

Fig.1 (a) is a schematic sectional drawing which shows the multilayer ceramic capacitor of this invention. The enlarged view of the drawer of (b) is a schematic diagram showing crystal grains and a grain boundary phase constituting the dielectric layer. (A) is a schematic diagram which shows the concentration gradient of the 1st rare earth element and the 2nd rare earth element in the crystal grain which comprises the dielectric material layer of the multilayer ceramic capacitor of this invention. (B) is a schematic diagram showing crystal grains outside the scope of the present invention in which the concentration gradient of the first rare earth element is smaller than the concentration gradient of the second rare earth element and the concentration gradient of the rare earth element. (C) is a schematic diagram showing a crystal particle and a concentration gradient of the rare earth element when the content of the second rare earth element is larger than the content of the first rare earth element. It is a schematic diagram which shows the evaluation method of the resistance of the grain boundary in the dielectric material layer by an alternating current impedance method. (A) is a graph (Cole-Cole plot) of impedance change at the interface between the crystal grains (core (central part), shell (outer peripheral part)), grain boundaries, and internal electrode layer and dielectric layer in the multilayer ceramic capacitor of the present invention. (B) represents each component of the crystal grains, the grain boundaries, and the interface between the internal electrode and the dielectric layer constituting the multilayer ceramic capacitor in an equivalent circuit. 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 grain 9a Crystal grain 9b which forms 2nd crystal group Crystal grain 21 which forms 1st crystal group Ceramic green sheet 23 Internal electrode pattern 25 Ceramic pattern 29 Laminate

Claims (7)

In a multilayer ceramic capacitor comprising a dielectric layer, an internal electrode layer formed between the dielectric layers, and an external electrode electrically connected to the internal electrode layer, the dielectric layer comprises barium titanate. It has crystal grains having an average crystal grain size of 0.15 to 0.3 μm as a main component, and 0.5 to 2 mole parts of magnesium in terms of MgO and manganese to MnO with respect to 100 mole parts of barium titanate. 0.2 to 0.5 mol in terms of conversion, one first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium and one first selected from samarium, europium, gadolinium, terbium and dysprosium 2 rare earth element with containing 0.7 to 3 parts by mol in total in terms _RE 2 _{O 3,} the crystal grains, the second The rare earth element and the second rare earth element are contained so that the amount of the first rare earth element is larger than the amount of the second rare earth element, and the concentration gradient of the first rare earth element from the grain boundary to the center portion thereof −0.005 atomic% / nm or more and −0.05 atomic% / nm or less, and the concentration gradient of the second rare earth element from the grain boundary to the central portion of the crystal grain is −0.0005 atomic% / nm. A multilayer ceramic capacitor comprising a dielectric ceramic having −0.005 atomic% / nm or less. The crystal particles include a first crystal group composed of crystal particles having a Ca component concentration of 0.2 atomic% or less and a second crystal group composed of crystal particles having a Ca component concentration of 0.4 atomic% or more. The multilayer ceramic capacitor according to claim 1, wherein the multilayer ceramic capacitor is a composite particle. 3. The relationship of A / B ≧ 1.003 is satisfied, where the total content of Ba and Ca in the dielectric ceramic is A mol, and the content of Ti is B mol. The multilayer ceramic capacitor described. In the method for producing a multilayer ceramic capacitor for firing a capacitor body molded body constituted by alternately laminating green sheets containing dielectric powder and internal electrode patterns, the dielectric powder has an average particle size of 0.15 to 0.15. On the surface of 0.3 μm barium titanate powder or barium calcium titanate powder or a mixed powder thereof, an oxide of one kind of first rare earth element selected from holmium, yttrium, erbium, thulium, ytterbium and lutetium, A first powder coated with 0.6 to 2 mole parts with respect to 100 mole parts of the barium titanate powder, the barium calcium titanate powder, or a mixed powder thereof is prepared, and the barium titanate powder is applied to the first powder. Or the barium calcium titanate powder or a mixture thereof. Against powder 100 parts by mole, 0.5 to 2 parts by mole of MgO powder, MnCO ₃ powder 0.2 to 0.5 molar parts, samarium, europium, gadolinium, of one selected from terbium and dysprosium second What is claimed is: 1. A method of producing a multilayer ceramic capacitor, comprising using 0.1 to 1 mole part of rare earth element oxide powder. 5. The method for producing a multilayer ceramic capacitor according to claim 4, wherein the firing temperature when firing the capacitor main body is 1050 to 1150 ° C. 6. 6. The multilayer ceramic capacitor according to claim 4, wherein the barium calcium titanate powder is Ba _1-x Ca _x TiO ₃ powder (x = 0.01 to 0.2). 7. Manufacturing method. When the total content of Ba and Ca in the Ba _1-x Ca _x TiO ₃ powder (x = 0.01 to 0.2) is C mol, and the Ti content is D mol, C / D The method for producing a multilayer ceramic capacitor according to claim 6, wherein a material satisfying a relationship of ≧ 1.003 is used.

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