JP2009238885A - Laminated ceramic capacitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a laminated ceramic capacitor having high permittivity, small in a temperature change rate of relative permittivity and a D.C. bias characteristic, high in a service life characteristic in a high-temperature load test, and excelling in capacitance stability. <P>SOLUTION: This laminated ceramic capacitor contains barium titanate as a main constituent, and has a first crystal group formed of crystalline particles 9a wherein the concentration of calcium is not larger than 0.2 atomic% and a second crystal group formed of crystalline particles 9b wherein the concentration of calcium is not smaller than 0.4 atomic% at a predetermined ratio. In the laminated ceramic capacitor, the average particle diameters of the first crystalline particles 9a and the second crystalline particles 9b are 0.18-0.3 μm, and the average particle diameter of the first crystalline particles 9a is smaller than that of the second crystalline particles 9b by 0.05 μm or more. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a multilayer ceramic capacitor, and more particularly to a small and high capacity multilayer ceramic capacitor in which a dielectric layer is composed of barium titanate having different Ca concentrations.

  Multilayer ceramic capacitors are constructed by forming external electrodes on the exposed end surfaces of the capacitor body, which are formed by alternately laminating dielectric layers and internal electrode layers. In response to the demand for capacitance, the dielectric layers and internal electrode layers have been made thinner and multi-layered.

  By the way, as a dielectric porcelain serving as a dielectric layer constituting a multilayer ceramic capacitor, a dielectric constant material mainly composed of barium titanate has been conventionally used. However, in recent years, barium titanate powder and titanic acid have been used. A composite dielectric material in which these dielectric materials coexist is developed by mixing powder in which calcium is dissolved in barium, and applied to a multilayer ceramic capacitor (see, for example, Patent Document 1). ).

Dielectric porcelain produced using the above-mentioned barium titanate powder or powder in which calcium is dissolved in barium titanate, magnesium, rare earth elements and manganese oxides are used as additives. These additives can be dissolved in the vicinity of each surface of barium titanate powder or barium calcium titanate powder in which calcium is dissolved in barium titanate to improve the relative permittivity and temperature characteristics of relative permittivity. It is illustrated.
JP 2001-156450 A

  A multilayer ceramic capacitor having a dielectric ceramic layer composed of the above-described crystal particles as a dielectric layer has an improved relative dielectric constant and a relative dielectric constant temperature characteristic of X5R (relative dielectric relative to 25 ° C.). Although the temperature change rate of the rate satisfies the range of ± 15% at −55 to 85 ° C.), if the thickness of the dielectric layer is reduced to, for example, about 2 μm, the life characteristics in the high temperature load test are greatly reduced. There has been a problem that the capacitance is greatly reduced (DC bias characteristics are large) when a DC voltage is applied to the multilayer ceramic capacitor.

  Accordingly, an object of the present invention is to provide a multilayer ceramic capacitor having a high dielectric constant, a small temperature change rate of a relative dielectric constant, a high life characteristic in a high temperature load test, and a small DC bias characteristic.

The multilayer ceramic capacitor of the present invention has a capacitor body in which dielectric layers composed of dielectric ceramics mainly composed of barium titanate and internal electrode layers are alternately stacked, and the internal electrode layer of the capacitor body is exposed. In the multilayer ceramic capacitor having an external electrode provided on an end face, the dielectric ceramic is composed of 0.2 to 1 mol of magnesium in terms of MgO and manganese in 100 mol of titanium constituting the barium titanate. 0.2 to 0.5 mol in terms of MnO, one kind of first rare earth element (RE) selected from the group of holmium, yttrium, erbium, thulium, ytterbium and lutetium, and a group of samarium, europium, gadolinium, terbium and dysprosium one second rare earth element selected from the (RE) _RE 2 O Convert summed together to 0.7 to 3 moles contained in the main as a crystalline phase, as a main component the barium titanate, a first crystal group concentration of calcium consists of first crystal grains of less than 0.2 atomic% And a second crystal group consisting of second crystal particles having the barium titanate as a main component and a calcium concentration of 0.4 atomic% or more, and the first crystal particles and the second crystal particles The average particle size is 0.18 to 0.3 μm, the average particle size of the first crystal particles is 0.05 μm or more smaller than the average particle size of the second crystal particles, and 3 μm on the polished surface of the dielectric ceramic. The b / (a + b) is 0.5 to 0.8, where a is the number of the first crystal particles found in the region of 3 μm and b is the number of the second crystal particles 9b. And

  The average grain size of the first crystal particles is preferably smaller by 0.1 μm or more than the average grain size of the second crystal particles.

  Furthermore, it is desirable that an average particle size of the first crystal particles and the second crystal particles is 0.22 to 0.27 μm.

Furthermore, with respect to 100 mol of titanium constituting the barium titanate, the magnesium is 0.5 to 1 mol in terms of MgO, the manganese is 0.2 to 0.4 mol in terms of MnO, the first rare earth element ( RE) containing 0.6 to 0.8 mol of yttrium in terms of Y ₂ O ₃ and 0.2 to 0.5 mol of terbium in terms of Tb ₂ O ₃ as the second rare earth element (RE) Is desirable.

  The first rare earth element and the second rare earth element are both represented as RE, which is based on the English representation of the rare earth element (Rare earth) in the periodic table.

  According to the present invention, it is possible to obtain a multilayer ceramic capacitor having a high dielectric constant, a low relative dielectric constant temperature change rate, a high life characteristic in a high temperature load test, and a small DC bias characteristic.

  The multilayer ceramic capacitor of the present invention will be described in detail with reference to FIGS. FIG. 1 is a schematic cross-sectional view showing one embodiment of the multilayer ceramic capacitor of the present invention, and FIG. 2 is an enlarged view of a dielectric layer constituting the multilayer ceramic capacitor of FIG. It is a schematic diagram which shows.

  This multilayer ceramic capacitor has a capacitor body 1 in which dielectric layers 5 made of dielectric ceramics and internal electrode layers 7 are alternately laminated, and both ends of the capacitor body 1 where one end of the internal electrode layer 7 is exposed. The external electrode 3 is formed.

  The dielectric layer 5 made of a dielectric ceramic is composed of crystal grains 9 and grain boundary phases 11, and the thickness thereof is preferably 2 μm or less, particularly preferably 1 μm or less, thereby reducing the size and capacity of the multilayer ceramic capacitor. Can be realized. In addition, when the thickness of the dielectric layer 5 is 0.4 μm or more, the variation in capacitance can be reduced, and the capacitance-temperature characteristic can be stabilized.

  The conductor component constituting the internal electrode layer 7 is preferably a base metal such as nickel (Ni) or copper (Cu) from the viewpoint that the manufacturing cost can be suppressed even when the number of layers is increased, and is particularly composed of a dielectric ceramic described later. Nickel (Ni) is more desirable because it can be fired simultaneously with the dielectric layer 5. Further, as the conductor component constituting the external electrode 3, for example, Cu or an alloy of Cu and Ni can be used. After applying paste containing these conductor components to the end face of the capacitor body 1, baking is performed. It is formed by.

  In FIG. 1, the laminated state of the dielectric layer 5 and the internal electrode layer 7 is shown in a simplified manner. However, the multilayer ceramic capacitor of the present invention has several hundred layers of the dielectric layer 5 and the internal electrode layer 7. It is also a laminated body.

By the way, the dielectric porcelain constituting the dielectric layer 5 is composed of barium titanate as a main component, and is a first type selected from the group consisting of calcium, magnesium and manganese, and holmium, yttrium, erbium, thulium, ytterbium and lutetium. A sintered body containing a rare earth element (RE) and one second rare earth element (RE) selected from the group consisting of samarium, europium, gadolinium, terbium and dysprosium, and with respect to 100 moles of titanium constituting barium titanate The magnesium is converted to 0.2 to 1 mol in terms of MgO, the manganese is converted to 0.2 to 0.5 mol in terms of MnO, and the first rare earth element (RE) and the second rare earth element (RE) are converted to RE ₂ O _3. The total content is 0.7-3 mol.

  In addition, the dielectric ceramic is composed of first crystal particles 9a constituting a first crystal group composed of crystal particles mainly composed of barium titanate and having a calcium concentration of 0.2 atomic% or less, and barium titanate. The main crystal phase is provided with crystal grains 9 composed of the second crystal grains 9b constituting the second crystal group consisting of crystal grains having a main component and a calcium concentration of 0.4 atomic% or more.

  Furthermore, the average grain size of the first crystal particles 9a constituting the first crystal group and the second crystal particles 9b constituting the second crystal group is 0.18 to 0.3 μm, and the first crystal group Is smaller than the average particle diameter of the second crystal particles 9b constituting the second crystal group by 0.05 μm or more.

  Furthermore, when the number of the first crystal particles found in the 3 μm × 3 μm region on the polished surface of the dielectric ceramic is a and the number of the second crystal particles 9b is b, b / (a + b) is 0.5 to 0.8.

  Such a dielectric ceramic has a relative dielectric constant of 3500 or more at room temperature (25 ° C.) and a temperature characteristic of the relative dielectric constant of X5R (the rate of temperature change of the relative dielectric constant with respect to 25 ° C. is −55 to 85. Furthermore, the DC bias characteristic (capacity change rate when a DC voltage of 2 V / μm is applied to a DC imprint) can be reduced to 30% or less. For this reason, the multilayer ceramic capacitor of the present invention including the dielectric layer 5 made of this dielectric ceramic has a dielectric property with a small decrease in capacitance even in actual use where a DC bias is applied, and excellent capacitance stability. .

  Here, when the content of magnesium contained in the dielectric ceramic constituting the dielectric layer 5 is less than 0.2 mol in terms of MgO with respect to 100 mol of titanium constituting the barium titanate, On the other hand, the temperature change rate of the relative dielectric constant at 85 ° C. does not satisfy X5R, and the life characteristics in the high temperature load test are greatly deteriorated. On the other hand, when the content of magnesium is more than 1 mol in terms of MgO with respect to 100 mol of titanium constituting barium titanate, the relative dielectric constant becomes lower than 3500.

  Further, if the content of manganese contained in the dielectric ceramic serving as the dielectric layer 5 is less than 0.2 mol in terms of MnO with respect to 100 mol of titanium constituting the barium titanate, the high temperature load life is greatly impaired. It is. On the other hand, when the manganese content is more than 0.5 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate, the dielectric constant of the dielectric ceramic is also lower than 3500 in this case.

Furthermore, when the content of the first rare earth element (RE) and the second rare earth element (RE) is less than 0.7 mol in terms of RE ₂ O ₃ with respect to 100 moles of titanium constituting the barium titanate. In addition, the temperature change rate of the relative permittivity increases, and the X5R cannot be satisfied, and the life characteristics in the high temperature load test are greatly deteriorated. On the other hand, if the total content of the first rare earth element (RE) and the second rare earth element (RE) in terms of RE ₂ O ₃ is more than 3 moles with respect to 100 moles of titanium constituting barium titanate, The dielectric constant is lower than 3500.

Therefore, with respect to 100 moles of titanium constituting barium titanate, magnesium is 0.2 to 1 mole in terms of MgO, manganese is 0.2 to 0.5 moles in terms of MnO, the first rare earth element (RE) and A total of 0.7 to ₃ mol of the second rare earth element (RE) in terms of RE ₂ O _{3 is} contained. Further, it is desirable that the content of the first rare earth element is larger than the content of the second rare earth element.

  In the dielectric layer 5 constituting the multilayer ceramic capacitor of the present invention, a glass component may be contained as an auxiliary for enhancing the sinterability as long as desired dielectric characteristics can be maintained.

  In the present invention, the dielectric ceramic constituting the dielectric layer 5 of the multilayer ceramic capacitor includes a first crystal group consisting of crystal grains 9a having a calcium concentration of 0.2 atomic% or less, and barium titanate as a main component. And a second crystal group consisting of crystal grains 9b having a calcium concentration of 0.4 atomic% or more.

  The ratio of the first crystal particles 9a and the second crystal particles 9b constituting the first crystal group is the number of the first crystal particles found in a 3 μm × 3 μm region on the polished surface of the dielectric ceramic. a, b / (a + b) is 0.5 to 0.8, where b is the number of second crystal grains 9b. In this case, when b / (a + b) is smaller than 0.5, the dielectric constant of the dielectric ceramic is lower than 3500, and when b / (a + b) is larger than 0.8, the DC bias characteristic is 30. Greater than%. Therefore, b / (a + b) is preferably in the range of 0.5 to 0.8, particularly preferably 0.6 to 0.8.

  Here, the calcium concentration of the second crystal particles is preferably 0.5 to 2.5 atomic%. When the calcium concentration is within this range, the solid solution of Ca in the barium titanate can be made sufficient, and the Ca compound remaining in the grain boundaries without being dissolved can be reduced. Since the dependency of the AC voltage on the AC voltage increases, it is possible to increase the dielectric constant. The first crystal particles 9a include those having a calcium concentration of zero.

  Regarding the concentration of calcium in the crystal particles 9, a transmission type in which element analysis equipment is 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 an electron microscope. At this time, the spot size of the electron beam is 5 nm, and the analysis points 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 to the center of the crystal grain 9. Find the average value of. In this case, the ratio of Ca when the total amount of Ba, Ti, Ca, Mg, first and second rare earth elements and Mn detected from each measurement point of the crystal particle 9 is 100% is obtained as the calcium concentration.

  The crystal particles 9 to be measured are drawn on a circle of 20 to 50 crystal particles 9 on the photograph, and the crystal particles 9 that fall within and around the circle are selected, and image processing is performed from the outline of each crystal particle 9. Obtain the area of each particle, calculate the diameter when replaced with a circle having the same area, and the diameter of the obtained crystal particle 9 is in the range of ± 50% of the average particle diameter obtained by the method described above Nine.

  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 9 is a region from the grain boundary of the crystal grain 9 to the inside of 5 nm. is there. For the inscribed circle of the crystal particle 9, the image projected by the transmission electron microscope is taken into a computer, and the inscribed circle is drawn on the crystal particle 9 on the screen to determine the center of the crystal particle 9. To do. Further, the number ratio (b / a + b) in the first crystal particle 9a and the second crystal particle 9b is obtained from the group of crystal particles 9 in which the calcium concentration is specified.

  The average grain size of the first crystal particles 9a constituting the first crystal group and the second crystal particles 9b constituting the second crystal group is 0.18 to 0.3 μm. The average grain size of the constituting crystal grains 9 is preferably 0.22 to 0.27 μm.

  In the present invention, the average particle diameter of the crystal particles 9a constituting the first crystal group is smaller than the average particle diameter of the crystal particles 9b constituting the second crystal group, and the difference is 0.05 μm or more, It is desirable that it is 0.1 μm or more.

  The average grain size of the crystal particles 9 constituting the dielectric layer 5 is determined by polishing the fracture surface of the sintered capacitor body 1 and then taking a photograph of the internal structure using a scanning electron microscope. Draw a circle containing 20 to 50 crystal grains 9, select crystal grains in and around the circle, perform image processing on the outline of each crystal grain 9, find the area of each grain, and have the same area Calculate the diameter when it is replaced with a circle, and find the average value.

  In the multilayer ceramic capacitor of the present invention, when the average grain size of the crystal grains 9a constituting the first crystal group and the crystal grains 9b constituting the second crystal group is 0.22 to 0.27 μm, room temperature ( 25 ° C.) with a relative dielectric constant of 3570 or more and a temperature characteristic of the relative dielectric constant satisfying X5R (temperature change rate of relative dielectric constant with respect to 25 ° C. is ± 15% at −55 to 85 ° C.), In the DC bias characteristics, the capacity change rate when a direct current of 2 V / μm is applied to no DC application is 29% or less, and a high temperature load test (temperature: 85 ° C., voltage: 1. of rated voltage). 5 times, test time: 1000 hours), a highly reliable multilayer ceramic capacitor free from defects can be obtained.

  Further, when the difference between the average grain size of the first crystal grains 9a constituting the first crystal group and the second crystal grains 9b constituting the second crystal group is 0.1 μm or more, the temperature is room temperature (25 ° C.). The dielectric constant is 3560 or more, the temperature characteristics of the dielectric constant satisfy X5R (the temperature change rate of the dielectric constant with respect to 25 ° C. is ± 15% at −55 to 85 ° C.), and the high temperature load test ( 2V / μm direct current was applied to the DC impressed DC bias characteristic while maintaining the life characteristics at 85 ° C., voltage: 1.5 times the rated voltage, and test time: 1000 hours. In this case, the capacity change rate can be 28% or less.

Further, the composition of the dielectric porcelain is 0.5 to 1 mol in terms of MgO and 0.2 to 0.4 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate. Yttrium as a rare earth element (RE) is 0.6 to 0.8 mol in terms of Y ₂ O ₃ and terbium is contained as a second rare earth element (RE) in an amount of 0.2 to 0.5 mol in terms of Tb ₂ O _3. Assuming that the temperature characteristic of relative permittivity satisfies X5R (temperature change rate of relative permittivity with respect to 25 ° C is within ± 15% at -55 to 85 ° C), and high temperature load test (temperature : 85 ° C., voltage: 1.5 times the rated voltage, test time: 1000 hours), no defect occurred, and the DC bias characteristics were the capacity when DC of 2V / μm was applied to the DC imprint Change rate is 30 %, The dielectric constant at room temperature (25 ° C.) can be increased to 3710 or more.

  Furthermore, the average grain size of the crystal grains 9a constituting the first crystal group and the crystal grains 9b constituting the second crystal group is set to 0.23 to 0.27 μm, and b / (a + b) is set to 0.6 to Assuming 0.8, the temperature characteristic of the dielectric constant satisfies X5R (the temperature change rate of the dielectric constant relative to 25 ° C. is ± 15% at −55 to 85 ° C.), and the high temperature load test ( While maintaining the life characteristics at a temperature of 85 ° C., a voltage of 1.5 times the rated voltage, and a test time of 1000 hours, a relative dielectric constant of 3800 or more at room temperature (25 ° C.) and a DC bias characteristic of DC The capacitance change rate when a direct current of 2 V / μm is applied can be reduced to 28% or less.

  Next, a method for producing the multilayer ceramic capacitor of the present invention will be described.

  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, a solvent such as toluene and alcohol, and then the ceramic slurry is subjected to a sheet molding method such as a doctor blade method or a die coater method. A ceramic green sheet is formed on the substrate. The thickness of the ceramic green sheet is preferably 1 to 3 μm from the viewpoint of reducing the thickness of the dielectric layer 5 to increase the capacity and maintaining high insulation.

The dielectric powder used in the manufacturing method of the multilayer ceramic capacitor of the present invention includes BT powder represented by BaTiO ₃ as barium titanate powder, and Ba _1-x Ca as barium calcium titanate in which a part of Ba is substituted with Ca. Mixed powder with BCT powder represented by _x TiO ₃ powder (x = 0.01 to 0.2: BCT powder) is used.

  In particular, these BT powders and BCT powders have a molar ratio A / B of 1.003 or more when the total content of the constituent components Ba and Ca is A mol and the content of Ti is B mol. It is desirable that the grain growth of the first and second crystal grains 9a and 9b can be suppressed, and therefore, high insulation can be achieved, the high temperature load life can be improved, and the DC bias characteristics can be improved.

  The average particle size of the BT powder and BCT powder is preferably 0.1 to 0.2 μm. This facilitates thinning of the dielectric layer 5 and allows the BT powder and BCT powder to be made into crystal particles 9a and 9b suitable for high dielectric constant and DC bias characteristics under the firing conditions described later.

Next, when the total amount of the BT powder or BCT powder is 100 mol as an additive for improving the reduction resistance of the dielectric ceramic and enhancing the dielectric property to the BT powder or BCT powder or a mixed powder thereof. In addition, 0.2 to 1 mol of MgO powder, 0.2 to 0.5 mol of MnCO ₃ powder as MnO, Ho ₂ O ₃ powder, Y ₂ O ₃ powder, Er ₂ O ₃ powder, Tm ₂ O ₃ powder , Yb ₂ O ₃ powder and Lu ₂ O ₃ powder, one kind of first rare earth element (RE) and Sm ₂ O ₃ powder, Eu ₂ O ₃ powder, Gd ₂ O ₃ powder, Tb ₂ O ₃ and Dy _A total of 0.7 to 3 mol of a powder of a second rare earth element (RE) selected from ₂ O ₃ powder is added.

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. The composition is preferably Li ₂ O = 1-15 mol%, SiO ₂ = 40-60 mol%, BaO = 15-35 mol%, and CaO = 5-25 mol%. 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.

  Next, a rectangular internal electrode pattern is printed and formed on the main surface of the obtained ceramic green sheet. The conductor paste used as the internal electrode pattern 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. Further, in order to eliminate the step due to the internal electrode pattern on the ceramic green sheet, it is preferable to form the ceramic pattern with substantially the same thickness as the internal electrode pattern around the internal electrode pattern. In this case, it is preferable to use the dielectric powder used for the ceramic green sheet as the ceramic component constituting the ceramic pattern in that the firing shrinkage in the simultaneous firing is the same.

  Next, a desired number of ceramic green sheets with internal electrode patterns are stacked, and a plurality of ceramic green sheets without internal electrode patterns are stacked on top and bottom of the ceramic green sheets so that the upper and lower layers have the same number. Form the body. The internal electrode patterns in the temporary laminate are shifted by half patterns in the longitudinal direction. By such a laminating method, the internal electrode pattern can be formed so as to be alternately exposed on the end face of the cut laminate.

  The multilayer ceramic capacitor of the present invention has a method of laminating after the internal electrode pattern is formed in advance on the main surface of the ceramic green sheet. Is printed, dried, and the ceramic green sheet without the internal electrode pattern printed thereon is temporarily adhered to the printed and dried internal electrode pattern, and the adhesion of the ceramic green sheet and the printing of the internal electrode pattern are sequentially performed. It can also be formed by a construction method.

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

  Next, the capacitor body molded body in which the end portions of the internal electrode patterns are exposed is formed by cutting the laminate into a lattice shape.

  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.

  Next, the obtained capacitor body molded body is degreased and fired. Firing is preferably performed in a hydrogen-nitrogen atmosphere at a temperature rising rate of 1000 to 1600 ° C./h, a maximum temperature of 1040 to 1200 ° C., a holding time of 0.1 to 4 hours, The temperature rate is 1200 to 1500 ° C./h, and the maximum temperature is more preferably 1050 to 1150 ° C. Then, the capacitor body 1 is obtained by performing reoxidation treatment in the temperature range of 900 to 1100 ° C. By performing the firing under such conditions, the average particle diameter of the crystal particles 9 constituting the dielectric layer 5 is in the range of 0.18 to 0.3 μm, and the average of the crystal grains 9a constituting the first crystal group is set. Dielectric porcelain having crystal grains 9a and 9b having a grain size smaller than the average grain size of crystal grains 9b constituting the second crystal group and having b / (a + b) of 0.5 to 0.8 The capacitor body 1 having the body layer 5 can be obtained.

  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. Thus, the multilayer ceramic capacitor of the present invention can be obtained.

First, as the raw material powder, BT powder, BCT powder (composition _{(Ba 1-x Ca x)} TiO 3, X = 0.05), MgO powder, MnCO ₃ powder, _Ho 2 _{O 3 powder,} Y 2 _{O 3} powder , Er2O ₃ powder, _Tm 2 _{O 3} powder, _Yb 2 _{O 3} powder, _Lu 2 _{O 3} powder, _Sm 2 _{O 3} powder, _Eu 2 _{O 3} powder, _Gd 2 _{O 3} powder, _Tb 2 _{O 3} and _Dy 2 _{O 3} A powder was prepared. These various powders were mixed in the ratios shown in Tables 1 and 2. However, MgO powder, MnCO ₃ powder, Ho ₂ O ₃ powder, Y ₂ O ₃ powder, Er ₂ O ₃ powder, Tm ₂ O ₃ powder, Yb ₂ O ₃ powder, Lu ₂ O ₃ powder, Sm ₂ O ₃ powder , Eu ₂ O ₃ powder, Gd ₂ O ₃ powder, Tb ₂ O ₃ and Dy ₂ O ₃ powder are ratios when the total amount of BT powder and BCT powder is 100 mol. As the BT powder and the BCT powder, those having a molar ratio A / B of 1.005 when the total content of Ba and Ca was A mol and the content of Ti was B mol were used. These raw material powders all have a purity of 99.9%, and are MgO powder, MnCO ₃ powder, Ho ₂ O ₃ powder, Y ₂ O ₃ powder, Er ₂ O ₃ powder, Tm ₂ O ₃ powder, Yb ₂ O. ₃ powder, Lu ₂ O ₃ powder, Sm ₂ O ₃ powder, Eu ₂ O ₃ powder, Gd ₂ O ₃ powder, Tb ₂ O ₃ and Dy ₂ O ₃ powder having an average particle diameter of 0.1 μm were used. . Further, a glass powder having the composition _{SiO 2 = 55, BaO = 20} , CaO = 15, Li 2 O = 10 as a sintering aid (mol%). The addition amount of the glass powder was 1 part by mass with respect to a total of 100 parts by mass of the BT powder and BCT powder.

  Next, these raw material powders were wet mixed using a zirconia ball having a diameter of 1 mm and a mixed solvent consisting of toluene and alcohol as a solvent.

  Next, the wet-mixed powder is put into a mixed solvent of polyvinyl butyral resin and toluene and alcohol, and wet-mixed using a zirconia ball having a diameter of 1 mm to prepare a ceramic slurry, and a thickness of 2 μm is obtained by a doctor blade method. A ceramic green sheet was prepared.

  Next, a plurality of conductive pastes containing Ni as a main component were formed on the upper surface of the ceramic green sheet so as to form a rectangular internal electrode pattern. The conductor paste for forming the internal electrode pattern was obtained by adding BT powder to 100 parts by mass of Ni powder having an average particle size of 0.3 μm.

Next, 200 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 A laminated body was prepared by closely adhering under conditions of 10 ⁷ Pa and time 10 minutes, and then the laminated body was cut into a predetermined size to form a capacitor body molded body.

Next, the capacitor body molded body was treated to remove the binder in the air and then fired at 1040 to 1200 ° C. in hydrogen-nitrogen to produce a capacitor body. In this firing, a roller hearth kiln is used under conditions where the temperature rise rate is 1000 to 2000 ° C./h, and a conventional tunnel firing furnace is used under conditions where the temperature rise rate is 300 ° C./h. Went. The produced capacitor body was subsequently reoxidized at 1000 ° C. for 4 hours in a nitrogen atmosphere. The size of the capacitor body was 0.95 × 0.48 × 0.48 mm ³ , the thickness of the dielectric layer was 1.5 μm, and the effective area of one internal electrode layer was 0.3 mm ² . The effective area is the area of the overlapping portion of the internal electrode layers that are alternately formed in the stacking direction so as to be exposed at different end faces of the capacitor body.

  Next, after barrel-polishing the capacitor body, 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.

  Next, the following evaluation was performed on these multilayer ceramic capacitors. The relative dielectric constant at room temperature (25 ° C.) was measured using an LCR meter (manufactured by Hewlett-Packard) with a capacitance of 25 ° C., a frequency of 1.0 kHz, and a measurement voltage of 1 Vrms. It calculated | required from the effective area of the electrode layer. Moreover, the temperature characteristic of the relative dielectric constant was measured by measuring the capacitance in the range of temperature -55 to 85 ° C. As for the temperature characteristic of the relative dielectric constant, a case where X5R (within ± 15% with respect to 25 ° C. in the range of −55 to 85 ° C.) was satisfied was evaluated as “◯”, and a case where it was not satisfied was evaluated as “X”. The high temperature load test was performed under conditions of a temperature of 85 ° C., an applied voltage of 6 V, and 1000 hours. The number of samples in the high-temperature load test was 20 for each sample, and those that did not have a short circuit up to 1000 hours were regarded as non-defective products.

  The DC bias characteristics are measured by applying a DC voltage of 3V to the manufactured multilayer ceramic capacitor, measuring the capacitance, c1 when no DC voltage is applied, and c2 when applying 3V. It was calculated from ((c1-c2) / c1) × 100 (%).

  The average particle size of the crystal particles constituting the dielectric layer is determined by polishing the fracture surface of the sample that is the capacitor body after firing, and then taking a picture of the internal structure using a scanning electron microscope. Draw a circle that contains 30 circles, select the crystal particles that fall within and around the circle, image the outline of each crystal particle, determine the area of each particle, and replace it with a circle with the same area Was calculated from the average value.

  Further, regarding the concentration of calcium in the crystal particles, a transmission type in which element analysis equipment is attached to about 30 crystal particles existing on the polished surface obtained by polishing the cross section of the dielectric layer 5 constituting the multilayer ceramic capacitor. Elemental analysis was performed using an electron microscope. At this time, the spot size of the electron beam is set to 3 nm, and the location to be analyzed is 4 to 5 points at approximately equal intervals from the grain boundary on the straight line drawn from the vicinity of the grain boundary toward the center. The average value was obtained. In this case, the ratio of Ca when the total amount of Ba, Ti, Ca, Mg, the first and second rare earth elements and Mn detected from each measurement point of the crystal particles was 100% was determined as the Ca concentration.

  The crystal particles for determining the calcium concentration are drawn on a circle of 20 to 50 crystal particles on the photograph, and the crystal particles in and around the circle are selected, and image processing is performed from the outline of each crystal particle. The diameter of each particle is obtained by calculating the diameter when replaced with a circle having the same area, and the obtained crystal particle diameter is in the range of ± 50% of the average particle diameter obtained by the method described above. Particles were used. Note that the center of the crystal grain is the center of the inscribed circle of the crystal grain, and the vicinity of the grain boundary of the crystal grain is a region from the grain boundary of the crystal grain to the inside of 5 nm. For the inscribed circle of the crystal particles, an image projected by a transmission electron microscope was taken into a computer, and an inscribed circle was drawn on the crystal particles on the screen to determine the center of the crystal particles.

  Next, the number ratio (b / a + b) between the first crystal particles and the second crystal particles was determined from the crystal particles whose calcium concentration was evaluated.

  Moreover, the composition analysis of the sample which is the obtained sintered body was performed by ICP (Inductively Coupled Plasma) analysis or atomic absorption analysis. In this case, the obtained dielectric porcelain mixed with boric acid and sodium carbonate and dissolved in hydrochloric acid is first subjected to qualitative analysis of the elements contained in the dielectric porcelain by atomic absorption spectrometry, and then specified. The diluted standard solution for each element was used as a standard sample and quantified 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.

  The composition and firing conditions are shown in Tables 1 to 4, the composition of each element in the sintered body in terms of oxides is shown in Tables 5 to 8, and the first and second crystal particles after firing and the average of these combined Particle size, ratio of first and second crystal particles (b / a + b), characteristics (relative permittivity, relative permittivity (determined from temperature characteristics of capacitance)), DC bias characteristics, high temperature load test Tables 9 to 12 show the results of the lifetimes.

  As is clear from the results in Tables 1 to 12, the sample No. 4 to 11, 16 to 32, 35 to 38, 41 to 52, 64 to 66, 69, 70 and 73 to 75, the relative dielectric constant at room temperature (25 ° C.) is 3500 or more, and the temperature characteristic of the relative dielectric constant is X5R. (The rate of change in temperature of relative permittivity with respect to 25 ° C. is ± 15% at −55 to 85 ° C.), and in DC bias measurement in which a DC voltage of 3 V is applied, no DC voltage is applied. When the value is used as a reference, the decrease rate of the capacitance value when 3 V is applied is 30% or less, and further, a high temperature load test (temperature: 85 ° C., voltage: 1.5 times the rated voltage, test time: 1000) A highly reliable monolithic ceramic capacitor free from defects in time) could be obtained.

  Sample Nos. 1 and 2 having an average particle size of 0.22 to 0.27 μm of the crystal grains constituting the dielectric ceramic were used. 4 to 10, 16 to 32, 36, 37, 41 to 52, 64 to 66, 69, 70 and 73 to 75, while satisfying the temperature characteristics of the relative permittivity and the life characteristics in the high temperature load test, The relative dielectric constant at 25 ° C. was 3570 or more, and the decrease rate of the capacitance value in the measurement of the DC bias characteristic was suppressed to 29% or less.

  In addition, the sample No. 1 in which the difference between the average particle diameter of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group was 0.1 μm or more. 4 to 10, 16 to 32, 36, 37, 38, 41 to 52, 64 to 66, 69, 73 and 74, the relative dielectric constant at room temperature (25 ° C.) is 3600 or more, the temperature characteristics of the relative dielectric constant and the high temperature While satisfying the life characteristics in the load test (temperature: 85 ° C, voltage: 1.5 times the rated voltage, test time: 1000 hours), the capacity change rate in the measurement of DC bias characteristics can be suppressed to 28% or less. It was.

Further, the composition of the dielectric porcelain is 0.5 to 1 mol in terms of MgO and 0.2 to 0.4 mol in terms of MnO with respect to 100 mol of titanium constituting barium titanate. As a rare earth element (RE), yttrium is contained in an amount of 0.6 to 0.8 mol in terms of Y ₂ O ₃ , and terbium is contained as a second rare earth element (RE) in an amount of 0.2 to 0.5 mol in terms of Tb ₂ O _3. Furthermore, the average grain size of the crystal grains constituting the first crystal group and the crystal grains constituting the second crystal group is set to 0.23 to 0.27 μm, and b / (a + b) is set to 0.6 to 0. Sample No. 8 7 to 9, 36, 64, 65, 73 and 74, the temperature characteristics of the dielectric constant and the life characteristics in the high temperature load test (temperature: 85 ° C., voltage: 1.5 times the rated voltage, test time: 1000 hours) The relative dielectric constant at room temperature (25 ° C.) was 3800 or more and the capacitance change rate in the DC bias characteristics was suppressed to 28% or less.

  On the other hand, sample no. 1 to 3, 12 to 15, 33, 34, 39, 40, 53 to 63, 67, 68, 71, 72, and 76, the relative dielectric constant at room temperature (25 ° C.) is 3500 or more, and the temperature characteristics of the relative dielectric constant Satisfies X5R (temperature change rate of relative permittivity with respect to 25 ° C. is within ± 15% at −55 to 85 ° C.) In DC bias measurement applying 3 V DC, no DC voltage is applied When the capacitance value is 3V, the decrease rate of the capacitance value at 3 V applied is 30% or less and a high temperature load test (temperature: 85 ° C., voltage: 1.5 times the rated voltage, test time: 1000) Any of the following characteristics were not satisfied.

It is a schematic sectional drawing which shows the example of the multilayer ceramic capacitor of this invention. FIG. 2 is an enlarged view of a dielectric layer constituting the multilayer ceramic capacitor of the example of FIG. 1, and is a schematic diagram showing crystal grains and grain boundary phases.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal grain 9a 1st crystal grain 9b 2nd crystal grain 11 Grain boundary phase

Claims (4)

A capacitor body in which dielectric layers composed of dielectric ceramics mainly composed of barium titanate and internal electrode layers are alternately laminated; and an external electrode provided on an end surface of the capacitor body where the internal electrode layer is exposed; In the multilayer ceramic capacitor, the dielectric ceramic is 0.2 to 1 mol in terms of MgO and 0.2 to 0 in terms of MnO with respect to 100 mol of titanium constituting the barium titanate. .5 mol, one first rare earth element (RE) selected from the group of holmium, yttrium, erbium, thulium, ytterbium and lutetium and one second selected from the group of samarium, europium, gadolinium, terbium and dysprosium be 0.7 to 3 mol containing a rare earth element and (RE) in total in terms _RE 2 _{O 3} In addition, as the main crystal phase, the first crystal group consisting of the first crystal particles having the barium titanate as a main component and a calcium concentration of 0.2 atomic% or less, and the barium titanate as the main component, the calcium And a second crystal group consisting of second crystal particles having a concentration of 0.4 atomic% or more, and an average particle size of the first crystal particles and the second crystal particles is 0.18 to 0.3 μm And the first crystal grains having an average particle size of 0.05 μm or more smaller than the average particle size of the second crystal particles and found in a region of 3 μm × 3 μm on the polished surface of the dielectric ceramic. A multilayer ceramic capacitor, wherein b / (a + b) is 0.5 to 0.8, where a is the number of particles and b is the number of second crystal particles 9b.   2. The multilayer ceramic capacitor according to claim 1, wherein an average particle size of the first crystal particles is 0.1 μm or more smaller than an average particle size of the second crystal particles.   3. The multilayer ceramic capacitor according to claim 1, wherein an average particle size of the first crystal particles and the second crystal particles is 0.22 to 0.27 μm. 4. For 100 mol of titanium constituting the barium titanate, the magnesium is 0.5 to 1 mol in terms of MgO, the manganese is 0.2 to 0.4 mol in terms of MnO, and the first rare earth element (RE) The yttrium is contained in an amount of 0.6 to 0.8 mol in terms of Y ₂ O ₃ , and the terbium as a second rare earth element (RE) is contained in an amount of 0.2 to 0.5 mol in terms of Tb ₂ O _3. The multilayer ceramic capacitor according to claim 3.

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