JP4884101B2 - Multilayer ceramic capacitor - Google Patents

Description

The present invention relates to a multilayer ceramic con den Sa, particularly, it relates to a multilayer ceramic con den Sa small high capacitance with the dielectric layers and internal electrode layers formed by crystal grains mainly composed of barium titanate.

  In recent years, multilayer ceramic capacitors have been made thinner dielectric layers in response to demands for smaller size and higher capacity, and crystal grains such as barium titanate constituting the dielectric layers have been made finer. ing.

  In addition, since the internal electrode layer needs to be fired in a reducing atmosphere due to the formation of a base metal, barium titanate, which is the main component of the dielectric porcelain serving as the dielectric layer, contains additives such as rare earth elements, magnesium and manganese. In addition, the reduction resistance is improved.

  Crystal grains mainly composed of barium titanate containing the above-mentioned additive have a core portion with a large proportion of tetragonal crystals leaving a domain domain showing ferroelectricity, while the periphery of the core portion is When the additive is dissolved, a shell portion in which the crystal structure is changed from a tetragonal crystal to a cubic crystal is formed, and a core-shell structure is formed (for example, see Patent Document 1).

A dielectric ceramic layer composed mainly of such fine-grained barium titanate having a core-shell structure is used as a thin dielectric layer to produce a small-sized and high-capacity multilayer ceramic capacitor.
JP-A-6-5460

  However, there is a problem that the relative permittivity decreases when the crystal particle size is reduced because the crystal particles obtained from the dielectric powder mainly composed of barium titanate have a size effect. When it is increased, the number of grain boundaries formed in the dielectric layer having a predetermined thickness is reduced, so that the insulating property is lowered. For this reason, it has become difficult to ensure a high dielectric constant and high insulation in a thin dielectric layer.

Accordingly, the present invention aims at providing a multilayer ceramic con den support having a high dielectric constant by reducing the crystal grain size and highly insulating the dielectric layer obtained.

The multilayer ceramic capacitor of the present invention is composed of alternately laminated dielectric layers and internal electrode layers formed of a plurality of crystal particles containing barium titanate as a main component and magnesium, manganese and rare earth elements dissolved as oxides. In the multilayer ceramic capacitor, the crystal particles have a total solid solution amount of magnesium, manganese and rare earth elements at a depth of 20 nm from the grain boundary with respect to the total amount of Ba, Ti, magnesium, manganese and rare earth elements. The total solid solution amount of the first crystal grains of 0.05 to 0.15 atomic% and the magnesium, manganese, and rare earth elements at a depth of 20 nm from the grain boundary is Ba, Ti, magnesium, manganese, rare earth elements. and a second crystal grains is 0.2 to 0.4 atomic% of the total amount, the average particle diameter of the first crystal grains And characterized in a serial smaller this than the average grain size of the second crystal grains, in the multilayer ceramic capacitor, the average particle diameter of the first crystal grains is in the range of 0.271～0.316Myuemu, The average grain size of the second crystal particles is preferably in the range of 0.33 to 0.39 μm.

  The multilayer ceramic capacitor of the present invention is such that a dielectric layer is formed so that different crystal grains are mixed within the above-mentioned ranges of solid solution amounts of oxides of magnesium, manganese and rare earth elements. Crystal grains having a large solid solution amount of the oxide can obtain a high relative dielectric constant by grain growth, whereas crystal particles having a small solid solution amount of the oxide have a small crystal particle diameter due to the size effect. High insulation can be obtained.

  In this case, a high dielectric constant and a high insulating property can be obtained in a dielectric layer having a predetermined thickness by mixing crystal particles having a small solid solution amount of the oxide between the crystal particles having a large solid solution amount of the oxide. Can be secured.

  FIG. 1 is a schematic cross-sectional view showing a multilayer ceramic capacitor of the present invention. The multilayer ceramic capacitor of the present invention is provided with an external electrode 2 at the end of a capacitor body 1. The external electrode 2 is formed by baking, for example, Cu or an alloy paste of Cu and Ni. The capacitor body 1 is configured by alternately laminating dielectric layers 3 and internal electrode layers 4. The thickness of the dielectric layer 3 is desirably 1.5 μm or less, particularly 1.2 μm or less. If the thickness of the dielectric layer 3 is 1.5 μm or less, there is an advantage that the capacitance of the multilayer ceramic capacitor can be increased by making the dielectric layer 3 thinner. The thickness of the dielectric layer 3 is preferably 0.5 μm or more. When the thickness of the dielectric layer 5 is 0.5 μm or more, there is an advantage that a desired thickness capable of obtaining high insulation can be secured in the dielectric layer 5.

  The internal electrode layer 4 is preferably a base metal such as Ni or Cu in that the manufacturing cost can be suppressed even if the internal electrode layer 4 is highly laminated. In particular, simultaneous firing with the dielectric layer 3 constituting the multilayer ceramic capacitor of the present invention is intended. Ni is more desirable. The thickness of the internal electrode layer 4 is preferably 1 μm or less on average.

FIG. 2 is a schematic diagram showing a microstructure of a dielectric layer constituting the multilayer ceramic capacitor of the present invention. The dielectric ceramic forming the dielectric layer 3 is composed of crystal grains 5 and grain boundaries 6 mainly composed of at least barium titanate (BaTiO ₃ ) as elements. The crystal grains 5A and the second crystal grains 5B are configured. The average particle size of the crystal particles 5 is preferably 0.5 μm or less, particularly 0.4 μm or less. When the average grain size of the crystal grains 5 is 0.5 μm or less, there is an advantage that high insulation can be obtained when the dielectric layer 3 is thinned in the multilayer ceramic capacitor. The average particle size of the crystal particles 5 constituting the dielectric layer 3 of the present invention is preferably 0.1 μm or more. If the average particle size of the crystal particles 5 is 0.1 μm or more, there is an advantage that the crystallinity of the crystal particles 5 can be increased, and thus a high dielectric constant can be achieved.

FIG. 3 is a schematic diagram of crystal particles 5A and 5B having different core and shell ratios in the dielectric layer 3 constituting the multilayer ceramic capacitor of the present invention. FIG. 4 is a schematic diagram showing a change in the amount of solid solution from the grain boundary of the additive in the first crystal particle 5A and the second crystal particle 5B according to the present invention. The point where the broken line shown in FIG. 4 and the curves 5A and 5B intersect is the thickness of the shell portion 5b.

  That is, the crystal particles 5 constituting the dielectric layer 3 in the multilayer ceramic capacitor of the present invention are composed of a core part 5a showing tetragonal crystal inside and a shell part 5b showing cubic crystal around the core part 5a. The In addition, the shell portion 5b is solid-dissolved with oxides of magnesium (Mg), manganese (Mn) and rare earth elements (at least one selected from Y, Dy, Ho, Tb and Yb) as additives. .

The dielectric layer 3 constituting the multilayer ceramic capacitor of the present invention has different total solid solution amounts of oxides of magnesium, manganese and rare earth elements (at least one selected from Y, Dy, Ho, Tb and Yb). The first crystal particle 5A and the second crystal particle 5B are composed of two kinds of crystal particles, that is, a first crystal particle 5A and a second crystal particle 5B. magnesium those in which, but manganese and rare earth element dissolved amount of oxides of (Y, Dy, Ho, at least one selected from Tb and Yb) are turned into variable over inside the grain boundaries of crystal grains 5 is there.

In the present invention, the total solid solution amount of the magnesium, manganese, and rare earth element at a depth of 20 nm from the grain boundary is 0.05 to 0.15 atom relative to the total amount of Ba, Ti, magnesium, manganese, and rare earth element. % First crystal grains 5A , 0 . It is important to be composed of 2 to 0.4 atomic% of the second crystal particles 5B. In particular, the total solid solution amount of the magnesium, manganese and rare earth elements in the first crystal particles 5A is 0.00. Further, the total solid solution amount of the magnesium, manganese and rare earth elements in the second crystal particle 5B is in the range of 0.22 to 0.38 atomic%. desirable. In addition, it is desirable that the average particle diameter of the first crystal particles 5A is 0.271 to 0.316 μm and the average particle diameter of the second crystal particles 5B is in the range of 0.331 to 0.39 μm.

When the first crystal particles 5A and the second crystal particles 5B satisfy the above solid solution amount and average particle size ranges, the relative dielectric constant can be increased to 3610 or higher and the insulation resistance can be increased to 1 × 10 ⁹ Ω or higher. There is an advantage.

On the other hand, the crystal particles 5 constituting the dielectric layer 3 do not have a solid solution amount in which the solid solution amount of the oxide is divided into two ranges as in the present invention. In the case where it is composed only of crystal grains 5 indicating the amount, for example, even if the insulation resistance is 1 × 10 ⁸ Ω or more, the relative dielectric constant is 3000 or less, or the relative dielectric constant is 3960 or more. Resistance becomes 1 × 10 ⁷ Ω or less.

  The crystal particles 5 constituting the dielectric layer 3 in the multilayer ceramic capacitor of the present invention constitute a core-shell structure with components such as magnesium, manganese, and rare earth elements, and the crystal particles 5 mainly composed of barium titanate. There is an advantage that the reduction resistance can be enhanced. In the crystal particles 5 having a core-shell structure, the components such as magnesium, manganese, and rare earth elements are mainly unevenly distributed on the shell portion 5b side on the surface side of the crystal particles 5, and the core portion 5a has the above components than the shell portion 5b. It is desirable that the content of is low. When the core portion 5a has a small content of components such as magnesium, manganese, and rare earth elements, there is an advantage that the tetragonal ratio of barium titanate having a perovskite structure constituting the core portion 11a can be increased. In this case, the lattice constant ratio c / a is desirably 1.005 or more as an index indicating the tetragonal nature of the crystal grains 5.

Moreover, various additives are 0.5 to 1.2 mol parts in terms of MgO, 0.04 to 0.4 mol parts in terms of MnO, and 0.04 to 0.4 mol parts in terms of MnO with respect to 100 mol parts of barium titanate as the main component. It is desirable that the element is in the range of 0.2 to 3 mole parts in terms of RE ₂ O ₃ . When the composition of the dielectric ceramic constituting the dielectric layer 3 in the present invention is in the above range, there is an advantage that it has reduction resistance and can achieve high dielectric constant and high insulation as described above. Here, the rare earth element in the present invention is preferably at least one of Tb, Dy, Ho, Yb, and Y, and more preferably Y in terms of increasing the dielectric constant of the dielectric ceramic.

  In addition, the volume ratio of the core part 5a and the shell part 5b in the dielectric material layer 3 can be measured using the transmission electron microscope (TEM) which attached the EDS (energy dispersion analysis) apparatus.

In addition, as described above, the dielectric layer 3 of the present invention preferably contains Si in an amount of 0.6 mol part or more and 2 mol parts or less in terms of SiO ₂ with respect to 100 mol parts of BaTiO ₃ . When the Si content is 0.6 mol part or more in terms of SiO ₂ , there is an advantage that the effect as a sintering aid for the dielectric ceramic increases and the density after firing can be increased. When the content of Si is 2 mol parts or less in terms of SiO ₂ , the amount of solid solution of the additive in the crystal particles 5 is reduced, and the ratio of tetragonal crystals of the crystal particles 5 mainly composed of barium titanate can be maintained. This has the advantage that the dielectric constant of the dielectric layer 3 can be increased.

Next, a method for producing the multilayer ceramic capacitor of the present invention will be described. In the production method of the multilayer ceramic capacitor of the present invention, first, in a BaTiO ₃ powder as a raw material, a first dielectric powder mainly composed of barium titanate having a Ba / Ti ratio greater than 1, and a Ba / Ti ratio of 1 The following second dielectric powder mainly composed of barium titanate is mixed and used. Since the Ba / Ti ratio of the first dielectric powder and the second dielectric powder satisfies the volume ratio of the core portion 5a and the shell portion 5b described above, 1.005 to 1.02 and 0.98 to 1, respectively. Is desirable. The first dielectric powder mainly composed of barium titanate having a Ba / Ti ratio of greater than 1 is difficult to grow grains and the additive is difficult to dissolve. On the contrary, the second dielectric powder mainly composed of barium titanate having a Ba / Ti ratio of 1 or less is likely to grow grains and the additive is liable to be dissolved. Therefore, it is possible to form crystal grains having two types of core / shell volume ratios in simultaneous firing. When the Ba / Ti ratio is 1 or less, grains are likely to grow together with solid solutions of additives such as magnesium, manganese, and rare earth elements. Therefore, the first dielectric powder: the second dielectric powder mixing ratio by molar ratio of 6: 4-8: 2 is preferred.

The average particle diameter of the BaTiO ₃ powder used is preferably 0.05 μm or more and 0.2 μm or less for both the first dielectric powder and the second dielectric powder . If the average particle size of the BaTiO ₃ powder is 0.05 μm or more, the BaTiO ₃ powder having high crystallinity is used, and there is an advantage that the dielectric constant of the dielectric ceramic obtained after firing can be increased. On the other hand, when the average particle diameter of the BaTiO ₃ powder is 0.2 μm or less, there is an advantage that the grain boundary can be increased in the thinning of the dielectric layer and high insulation can be achieved.

Next, an additive and a sintering aid are added to the BaTiO ₃ powder in which the first dielectric powder and the second dielectric powder described above are mixed, and they are mixed using a ball mill, and polyvinyl butyral is added to the mixed powder. A slurry is prepared by adding an organic binder such as toluene and a solvent such as toluene.

  Next, this slurry is formed into a sheet shape by a doctor blade to form a green sheet. The thickness of the green sheet is preferably 0.4 μm or more and 3 μm or less. When the thickness of the green sheet is 0.4 μm or more, defects such as pinholes can be reduced, so that there is an advantage that a dielectric layer having excellent insulation can be formed. If the thickness of the green sheet is 3 μm or less, there is an advantage that the capacity can be increased by thinning the dielectric layer 3.

Next, a conductor paste is printed on the surface of the green sheet, and then a plurality of green sheets on which the conductor paste is printed as an internal electrode pattern are stacked to produce a base laminate. The thickness of the internal electrode pattern is preferably set to reduce 1.5μm hereinafter more 0.3μm because of suppressing the effective area due to excessive shrinkage after sintering while eliminating a level difference on the green sheet. Next, the matrix laminate is cut into a lattice shape to produce a capacitor body molded body with the internal electrode pattern exposed on the end face. Next, the capacitor body molded body is fired to prepare the capacitor body 1 , and the end face is coated with an external electrode paste and baked to obtain the multilayer ceramic capacitor of the present invention.

The multilayer ceramic capacitor of the present invention was produced as follows. First, 100 mol parts of BaTiO ₃ powder with an average particle diameter of 0.2 μm synthesized in advance, 1.0 mol part of MgO as additive powder, 0.3 mol part of MnO using manganese carbonate, and Y ₂ O ₃ were added. Each 1.0 mole part was weighed.

For Samples 1-5, as shown in Table 1, the BaTiO ₃ powder with one Ba / Ti ratio, the additive, and the SiO ₂ powder were mixed thoroughly as in the conventional method, and an organic binder was added. Adjusted the slurry. The amount of SiO ₂ powder was 1 mol part with respect to 100 mol parts of barium titanate powder in the mixed powder obtained by adding the additive powder to the barium titanate powder. When two rare earth elements were used, the addition amount was added in 0.5 mol parts (Sample No. 18).

On the other hand, for Samples 6 to 18 of the present invention, as shown in Table 2, a powder having a large Ba / Ti ratio and a small powder are mixed at a ratio of 7: 3, and the additive and SiO ₂ powder are added. Then, the slurry was adjusted by adding an organic binder. Also in this case, the amount of SiO ₂ powder was 1 mol part with respect to 100 mol parts of barium titanate powder in the mixed powder obtained by adding additive powder to barium titanate powder.

  Next, a green sheet having a thickness of 1.5 μm was produced by using this slurry with a doctor blade. Next, a conductive paste containing Ni metal was screen printed on the green sheet to form an internal electrode pattern. Next, 330 green sheets on which internal electrode patterns are formed are stacked, and 20 dielectric green sheets on which internal electrode patterns are not formed are stacked on the top and bottom surfaces of the green sheets and integrated using a press machine. Got the body. Thereafter, the base laminate was cut into a lattice shape to produce a capacitor body molded body.

Next, the molded body of the capacitor body was treated to remove the binder at 500 ° C. in the atmosphere, reduced and fired at 1250 ° C. for 2 hours, and reoxidized at 800 ° C. for 4 hours in the air atmosphere to produce a capacitor body. . Dimensions of the capacitor Body is an 1.6mm × 0.8mm × 0.8mm.
The thickness of the dielectric layer was 1.2 μm. The area contributing to the capacitance was 1.09 mm ² .

  Next, the fired capacitor body was barrel-polished, and then an external electrode paste was applied to both ends thereof and baked at 850 ° C. to form external electrodes. Then, using an electrolytic barrel machine, Ni and Sn plating were sequentially performed on the surface of the external electrode to produce a multilayer ceramic capacitor.

  The capacitances of these samples, which are the multilayer ceramic capacitors, were measured using an LCR meter 4284A at a frequency of 1.0 kHz and an input signal level of 1.0 V, and the relative dielectric constant was calculated from the area of the internal electrode and the dielectric thickness. Calculated. The number of samples was 10 each. Moreover, about insulation resistance (IR), it measured DC10V and room temperature.

  After polishing the fracture surface of the obtained multilayer ceramic capacitor, the average grain size of the crystal grains is taken by taking a picture of the internal structure using a scanning electron microscope and then imaging the outline of the crystal grains shown in the photograph Each particle was treated as a circle, and its diameter was obtained and averaged.

A transmission electron microscope apparatus (TEM) provided with an elemental analysis instrument (EDS) was used to measure the additive solid solution amount at 20 nm from the grain boundary. The multilayer ceramic capacitor was cross-cut, those thinned by FIB processing, the entire crystal grains forming the dielectric layers in the transmission electron microscope were selected as crystal grains for measuring what appears clearly. Elemental analyzes were performed by EDS device at the location of such approximately 20nm in countercurrent Ke in the center of the grain boundary for the crystal grains 50 composed mainly of titanium barium. EDS was Ba, Ti, magnesium, manganese, magnesium for the total amount to measure the components of the rare earth elements, manganese, and the solid solution amount total amount of rare earth elements.

As is apparent from the results of Tables 1 and 2, as an example of using BaTiO ₃ powder having a Ba / Ti ratio of one kind as in the conventional method, a sample using only a Ba / Ti ratio greater than 1 No. 1 to 3, the solid solution amount at a position 20 nm from the grain boundary is as small as 0.06 to 0.16 atomic%, the average particle size is 0.311 to 0.371 μm, the relative dielectric constant is 2330 to 2914, and the insulation resistance Was 1 × 10 ^{8 to} 3 × 10 ⁹ Ω.

On the other hand, sample No. using only barium titanate having a Ba / Ti ratio of 1 or less. 4 and 5, the solid solution amount at a position 20 nm from the grain boundary increases as 0.32 to 0.36 atomic%, the average particle diameter increases as 0.426 to 1.23 μm, and the relative dielectric constant is 3960 to Although it was 5630, the insulation resistance was 1 × 10 ⁷ or less.

In contrast, Sample No. of Ba / Ti ratio is greater than 1 barium titanate and Ba / Ti ratio was used and 1 less barium titanate 7 to 18, the amount of solid solution at a position 20 nm from the grain boundary is in the range of 0.06 to 0.17 atomic%, the first crystal grain having an average grain size of 0.21 to 0.32 μm, and the grain boundary To 20 nm, the solid solution amount is in the range of 0.13 to 0.41 atomic%, and the second crystal particles having an average particle diameter in the range of 0.22 to 0.4 μm coexist. The dielectric constant was 2930 or higher and the insulation resistance was 8 × 10 ⁸ Ω or higher, and a high dielectric constant and high insulation were obtained.

In particular, the solid solution amount of the oxide in the first crystal particles is in the range of 0.1 to 0.15 atomic%, the average particle size is 0.271 to 0.316 μm, and the above in the second crystal particles. In the case where the solid solution amount of the oxide is in the range of 0.24 to 0.38 atomic% and the average particle size satisfies the range of 0.33 to 0.39 μm, the relative dielectric constant is 3610 or more and the insulation resistance Was 1 × 10 ⁹ Ω or more.

It is a cross-sectional schematic diagram which shows the multilayer ceramic capacitor of this invention. It is a schematic diagram which shows the microstructure of the dielectric material layer which comprises the multilayer ceramic capacitor of this invention. It is a schematic diagram of the amount of additive dissolved in crystal grains having different core and shell ratios in the dielectric layer constituting the multilayer ceramic capacitor of the present invention. It is the schematic diagram which showed the change of the solid solution amount from the grain boundary of the additive in the crystal grain which concerns on this invention to a grain.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 Dielectric layer 5 Crystal particle 5a Core part 5b Shell part 5A 1st crystal particle 5B 2nd crystal particle

Claims (2)

  A multilayer ceramic capacitor in which dielectric layers and internal electrode layers formed of a plurality of crystal particles mainly composed of barium titanate and solid-dissolved as an oxide of magnesium, manganese and rare earth elements are alternately laminated. The crystal grains have a total solid solution amount of the magnesium, manganese, and rare earth elements at a depth of 20 nm from the grain boundary of 0.05 to 0.15 atoms relative to the total amount of Ba, Ti, magnesium, manganese, and rare earth elements. %, And the total solid solution amount of magnesium, manganese, and rare earth element at a depth of 20 nm from the grain boundary is 0.2 to about the total amount of Ba, Ti, magnesium, manganese, and rare earth element. Second crystal particles that are 0.4 atomic%, and the average particle size of the first crystal particles is smaller than the average particle size of the second crystal particles Multilayer ceramic capacitor, characterized in that.   The average particle size of the first crystal particles is in a range of 0.271 to 0.316 μm, and the average particle size of the second crystal particles is in a range of 0.33 to 0.39 μm. Item 2. The multilayer ceramic capacitor according to Item 1.

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