JP4423052B2 - Multilayer ceramic capacitor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a multilayer ceramic capacitor and a method for manufacturing the same, and is used in particular for small-sized and high-functional electronic devices such as mobile phones, and is configured by alternately laminating extremely thin dielectric layers and internal electrode layers, respectively. The present invention relates to a small-sized and large-capacity monolithic ceramic capacitor having excellent characteristics and reliability such as a high-temperature load life and a method for manufacturing the same.

  In recent years, with the downsizing and higher density of electronic devices, the multilayer ceramic capacitors used for this purpose have been required to be smaller and have higher capacity. For this reason, the number of laminated dielectric layers has increased and the dielectric layers themselves have become thinner. In addition, as a characteristic of the multilayer ceramic capacitor, improvement of reliability such as a capacity-temperature characteristic and a high temperature load life is achieved.

  As such multilayer ceramic capacitors, for example, those disclosed in Patent Documents 1 and 2 below are known.

First, in the multilayer ceramic capacitor disclosed in Patent Document 1, when preparing a dielectric ceramic, optimization of the composition of various oxides such as Mg, Mn, and rare earth elements added to BaTiO ₃ and glass components is possible. Has been done.

On the other hand, in the multilayer ceramic capacitor disclosed in Patent Document 2, in preparation of the dielectric ceramic, BaTiO ₃ and MgO are calcined in advance, and then various kinds of rare earth elements and acceptor elements are applied to the calcined powder. A method of adding an oxide is used. By adopting such a two-stage mixing method, even after firing, diffusion of rare earth elements and acceptor-type elements added later into the BaTiO ₃ crystal particles is suppressed by Mg. It is described that can be improved.
JP-A-6-84692 JP 2001-230149 A

  However, the multilayer ceramic capacitor disclosed in Patent Document 1 described above has an accelerated life of insulation resistance and X7R standard (temperature range: −55 ° C. to 125 ° C. Although a capacitor satisfying the capacitance-temperature characteristic with a capacitance change rate of ± 15% can be obtained, if the thickness of the dielectric layer is reduced to, for example, 2.5 μm or less, the accelerated life of the insulation resistance is reduced, and the capacitance-temperature characteristic is reduced. There was a problem that it deviated from the X7R standard.

On the other hand, the multilayer ceramic capacitor disclosed in Patent Document 2 employs a preliminary process in which BaTiO ₃ and MgO are mixed and calcined in advance, so that the dielectric constant of the dielectric ceramic is increased. In addition, the capacitance temperature characteristic satisfies the B characteristic (temperature range: −25 ° C. to 85 ° C., capacitance change rate ± 10%), but this multilayer ceramic capacitor still has the capacitance temperature characteristic as X7R. It did not meet the standards.

  Accordingly, an object of the present invention is to provide a small-sized and high-capacity monolithic ceramic capacitor excellent in reliability such as capacity-temperature characteristics and high-temperature load life even when the dielectric layer is thinned, and a method for manufacturing the same.

  The multilayer ceramic capacitor of the present invention is a multilayer ceramic capacitor comprising a capacitor body in which dielectric layers and internal electrode layers are alternately stacked, wherein the dielectric layer is composed of Ba, Ti, rare earth elements as metal elements. , Comprising crystal grains made of a perovskite complex oxide containing Mg and Mn and a grain boundary phase, wherein the crystal grains contain Mg, Mn and rare earth elements, and these Mg, Mn and rare earth elements are centered on the crystal grains And a concentration gradient in which the concentration increases from the particle surface to the particle surface, and the concentration gradient of the rare earth element among the Mg, Mn, and rare earth elements is 0.02 atomic% / nm or more.

  As described above, the crystal particles constituting the dielectric ceramic have a concentration gradient that increases from the center to the particle surface, and among these elements, in particular, by defining the concentration gradient of rare earth elements, Along with the improvement of the relative permittivity and the high temperature load life, the capacitance temperature characteristic satisfying the X7R standard can be obtained.

  In the multilayer ceramic capacitor, Y is desirable as a rare earth element contained in the crystal particles in terms of increasing the dielectric constant.

  In the multilayer ceramic capacitor, it is desirable that the dielectric layer has a thickness of 2.5 μm or less and the average diameter of crystal grains is 0.4 μm or less. If the average diameter of the crystal particles is 0.4 μm or less, high insulation can be obtained even when the thickness of the dielectric layer is as thin as 2.5 μm or less. The allowable stability with respect to the standard can be increased.

  In addition, since the dielectric layers having the above-described configuration have excellent reduction resistance, the dielectric layers are alternately laminated together with such dielectric layers in terms of reducing the manufacturing cost of the multilayer ceramic capacitor. The internal electrode layer is preferably composed mainly of a base metal.

Preparation of multilayer ceramic capacitor of the present invention, the (a) BaTiO ₃ powder and the mixed powder of MgO was calcined at 750 ° C. below the temperature, the coating BaTiO ₃ powder MgO is coated formed on BaTiO ₃ powder surface A step of preparing;
(B) mixing the raw material powder containing rare earth element, Mn as a metal element and additive powder containing Si with the coated BaTiO ₃ powder, and preparing a slurry;
(C) forming a dielectric green sheet using the slurry;
(D) forming an internal electrode pattern on the main surface of the dielectric green sheet; and (e) stacking a plurality of dielectric green sheets on which the internal electrode pattern is formed to form a capacitor body molded body. And a step of firing.

In this production method, the calcining temperature of the mixed powder of BaTiO ₃ powder and MgO when preparing the coated BaTiO ₃ powder in the step (a) is set to 800 ° C. or less, so that the capacity temperature characteristic and the high temperature load life characteristic are obtained. An excellent multilayer ceramic capacitor can be easily obtained.

In the method for manufacturing the multilayer ceramic capacitor, Y is selected as the rare earth element, the average particle diameter of the BaTiO ₃ powder is 0.4 μm or less, the thickness of the dielectric green sheet is 3 μm or less, and the internal electrode layer By using a base metal as the main component, it is easy to manufacture a small-sized, high-capacity, low-cost multilayer ceramic capacitor.

  The multilayer ceramic capacitor of the present invention will be described in detail based on the schematic sectional view of FIG. The multilayer ceramic capacitor of the present invention is configured by forming external electrodes 3 at both ends of a 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 formed by alternately laminating dielectric layers 5 and internal electrode layers 7. The dielectric layer 5 is composed of crystal grains 11 and grain boundary phases 13, and the thickness is preferably 2.5 μm or less. In particular, the dielectric layer 5 is 2 μm or less in terms of increasing capacitance, while maintaining high insulation. In terms of point, 0.5 μm or more, particularly 1 μm or more is desirable. Furthermore, in the present invention, it is more desirable that the thickness variation of the dielectric layer 5 is within 10% in order to stabilize the capacitance variation and capacitance temperature characteristics.

  The internal electrode layer 7 is preferably a base metal such as Ni or Cu from the viewpoint that the manufacturing cost can be suppressed even if the internal electrode layer 7 is made highly laminated, and particularly Ni is more preferable from the viewpoint of simultaneous firing with the dielectric layer of the present invention. . The thickness of the internal electrode layer 7 is preferably 1 μm or less on average.

  The dielectric layer 5 of the present invention is characterized by comprising crystal grains 11 made of a perovskite complex oxide containing Ba, Ti, rare earth elements, Mg and Mn as metal elements and a grain boundary phase 13. In addition, the average particle diameter of the crystal particles 11 constituting the dielectric layer 5 is preferably 0.4 μm or less, particularly 0.3 μm or less in terms of stabilizing the capacity-temperature characteristics. In terms of increasing, it is more preferably 0.1 μm or more, particularly 0.2 μm or more. Furthermore, in the present invention, the variation of the average particle diameter of the crystal particles 11 is further that the CV value (= standard deviation / average value) is 0.5 or less in that the capacity-temperature characteristic is stabilized. desirable.

  FIG. 2 is a schematic diagram showing concentration distributions of rare earth elements, Mg and Mn contained in crystal grains forming the dielectric layer. The crystal particle 11 of the present invention is composed of a perovskite type complex oxide containing Ba, Ti, rare earth element, Mg and Mn as metal elements, and these Mg, Mn and rare earth elements have concentrations from the center of the crystal particle 11 to the particle surface. It is important that the concentration gradient of the rare earth element is 0.02 atomic% / nm or more among the Mg, Mn, and rare earth elements as well as the concentration gradient increasing. By defining the concentration gradient of the rare earth element in this way, it is possible to obtain a material that satisfies the X7R standard as a capacitance temperature characteristic as well as an improvement in relative permittivity and high temperature load life. The concentration gradients of Mg and Mn are preferably 0.003 atomic% / nm or more and 0.02 atomic% / nm or more, respectively. On the other hand, when the concentration gradient of the rare earth element is smaller than 0.02 atomic% / nm, the capacity-temperature characteristic does not satisfy X7R.

  Here, as the rare earth element of the present invention, including Y, at least one selected from the group of La, Ce, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Eb, Tm, Yb and the like is preferable. Although selected, Y is more desirable in the present invention in terms of increasing the relative dielectric constant of the dielectric layer 5.

The process of the present invention, the preparation of (a) BaTiO ₃ powder and the mixed powder of MgO was calcined at 750 ° C. below the temperature, the coating BaTiO ₃ powder MgO is coated formed on BaTiO ₃ powder surface Features. In this case, MgO is preferably present on the surface of the BaTiO ₃ powder. The main raw material BaTiO ₃ powder used here is preferably a powder obtained by a hydrothermal synthesis method because of its narrow particle size distribution and high crystallinity, and its average particle size is 0.1 μm or more and 0.4 μm or less, particularly 0.2 μm or more and 0.3 μm or less are desirable. In addition, the specific surface area of such a fine powder is preferably 1.7 to 6.6 (m ² / g).

That is, in the present invention, it is necessary to prepare a highly reactive powder for the reason that the coated BaTiO ₃ is formed by low-temperature calcining. It is desirable to keep it.

The calcining temperature in the production method of the present invention is particularly preferably 800 ° C. or lower and 750 ° C. or lower because the solid solution of MgO in the coated BaTiO ₃ is suppressed. On the other hand, the BaTiO ₃ powder surface is coated with MgO. For reasons of certainty, 600 ° C. or higher, particularly 650 ° C. or higher is desirable. The average particle size of the MgO powder used here is preferably 0.3 μm or less. In the present invention, by using BaTiO ₃ powder preliminarily calcined with MgO in this way, the additive containing rare earth elements, Mn, and Si is not easily dissolved in the BaTiO ₃ crystal particles. Can be present on the crystal grain surface side.

Next, (b) this coated BaTiO ₃ powder is mixed with a raw material powder containing rare earth elements and Mn as metal elements and an additive powder containing Si to prepare a slurry. The raw material powder containing rare earth element and Mn as a metal element used here is preferably an oxide in that it is the same form as the main raw material BaTiO ₃ powder and is easy to mix, and their average particle size is It is desirable that it is 0.3 μm or less. As additive powder containing Si, Si-Li-Ca-based glass powder is suitable as a sintering aid.

  Subsequently, (c) using this slurry, a dielectric green sheet is formed using a sheet forming method such as a die coater. The thickness of the dielectric green sheet is preferably 3 μm or less, particularly preferably 2.5 μm or less.

  Next, (d) an internal electrode pattern is formed in a predetermined region on the main surface of the dielectric green sheet. The internal electrode pattern is formed, for example, by screen printing of a base metal powder such as Ni or Cu that is pasted together with an organic resin or a solvent. The thickness of the internal electrode pattern is preferably less than the thickness of the dielectric green sheet and 2 μm or less in terms of reducing the level difference on the dielectric green sheet.

  Next, (e) a plurality of dielectric green sheets on which internal electrode patterns are formed are stacked, then heated and pressed to form a base stack, and cut at a predetermined position to form a capacitor body molded body. Thereafter, the capacitor body is debindered at 400 to 500 ° C. at a temperature increase rate of 40 to 80 ° C./h in the atmosphere, and then the temperature increase rate from 500 ° C. to 100 to 400 ° C. in a reducing atmosphere. / H, baked at a temperature of 1100 to 1300 ° C. for 2 to 5 hours, subsequently cooled at a cooling rate of 80 to 400 ° C./h, and reoxidized at 750 to 1100 ° C. in an air atmosphere.

  Finally, the external electrode 3 is formed by applying an external electrode paste on both end faces of the fired capacitor body and baking it in nitrogen, whereby the multilayer ceramic capacitor of the present invention can be obtained.

The multilayer ceramic capacitor of the present invention was produced as follows. First, 100 parts by mass of BaTiO ₃ synthesized in advance and 0.1 part by mass of MgO were weighed, mixed sufficiently, and heated at the temperature shown in Table 1 for 2 hours. Next, with respect to BaTiO ₃ 100 parts by weight of this calcined, 0.3 parts by weight of _MgO, of Y 2 _{O 3} and 1 part by mass, MnCO ₃ and 0.1 part by weight, and Li ₂ O and SiO ₂ 0.5 parts by mass of an additive component composed of CaO was mixed, and this mixed powder was wet pulverized by a ball mill using ZrO ₂ balls having a diameter of 5 mmφ, and an organic binder was added to prepare a slurry. Next, using this slurry, a dielectric green sheet having a thickness of 2.5 μm was produced by a doctor blade.

  Next, a conductive paste containing Ni metal was screen printed on the dielectric green sheet to form an internal electrode pattern.

  Next, 100 dielectric 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 upper and lower surfaces, and are integrated using a press. A laminate was obtained.

  Thereafter, the base laminate was cut into a lattice shape to produce a capacitor body molded body of 2.3 mm × 1.5 mm × 1.5 mm.

Next, this capacitor body molded body was debindered at 500 ° C. in the air at a temperature rising rate of 50 ° C./h, and the temperature rising rate from 500 ° C. was 1270 ° C. Calcination for 2 hours at a temperature of -1 ° C to 1300 ° C (oxygen partial pressure 10 ^-11 atm), followed by cooling to 800 ° C at a temperature decrease rate of 200 ° C / h, followed by reoxidation treatment at 800 ° C for 4 hours in an air atmosphere The capacitor body was manufactured by cooling at a temperature drop rate of ° C / h. The thickness of the dielectric layer was 2 μm.

  Next, the fired capacitor body was barrel-polished, and then an external electrode paste containing Cu powder and glass was applied to both ends thereof, followed by baking in nitrogen at 850 ° C. to form external electrodes. Thereafter, using an electrolytic barrel machine, the surface of the external electrode was sequentially plated with Ni and Sn to produce a multilayer ceramic capacitor.

  Next, the capacitance and dielectric loss of these samples, which were the produced 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 Vrms. The relative dielectric constant was calculated from the capacitance, the effective area of the internal electrode layer, and the thickness of the dielectric layer. Subsequently, the temperature characteristics of the capacitance were measured in a range of −55 to 125 ° C. with reference to the capacitance at 25 ° C. The high temperature load test was performed for 1000 hours under the conditions of a temperature of 85 ° C. and a voltage of 9.5 V, and the change in insulation resistance was measured for 100 samples. In this case, the short was regarded as defective. The crystal particle diameter and its variation were measured using an electron microscope. In addition, the presence of Y, Mg, and Mn components in the crystal particles constituting the dielectric layer was evaluated using an analytical electron microscope for a sample whose cross-section was polished. In the sample of the present invention, a concentration gradient similar to that of the Y element was observed not only for Mn but also for the Mg element due to the two-stage Mg addition. The concentration gradient was 0.003 atomic% / nm or more for Mg and 0.02 atomic% / nm or more for Mn. The average particle size of the crystal particles in the sample of the present invention was 0.4 μm or less, and the variation was 0.5 or less.

As Comparative Example 1, a mixed powder of BaTiO ₃ and MgO was heated at 900 ° C. for 2 hours to prepare a calcined powder. The other additive compositions and procedures were substantially the same as the above-described step of the present invention except that the firing temperature was 1130 ° C.

As Comparative Example 2, a raw material powder obtained by batch mixing the raw material powders used in the present invention was granulated using a spray dryer, and a multilayer ceramic capacitor was produced using the granulated powder by the same process as that of the present invention. For the samples of the above two comparative examples, the average grain size of the crystal grains was both 0.6 μm or more, and the variation was 0.8 or more. The concentration gradient of Mg was 0.002 atomic% / nm or less, and the concentration gradient of Mn was 0.015 atomic% / nm or less.

  As is apparent from the results in Table 1, sample Nos. Produced using the production method of the present invention. 3 to 6, all have a Y concentration gradient of 0.02 atomic% / nm or more, a relative dielectric constant of 2850 or more, a capacity-temperature characteristic that satisfies the X7R standard, and a high-temperature load test that satisfies 1000 hours. Met.

  On the other hand, in the samples of Comparative Examples 1 and 2, the Y concentration gradient was 0.018 atomic% / nm or less, and none of the capacity-temperature characteristics satisfied the X7R standard and the high temperature load life.

It is a schematic sectional drawing of the multilayer ceramic capacitor of this invention. It is a schematic diagram which shows the density | concentration distribution of the rare earth elements, Mg, and Mn contained in the crystal grain which forms a dielectric material layer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Capacitor body 5 ... Dielectric layer 7 ... Internal electrode layer 11 ... Crystal grain 13 ... Grain boundary phase

Claims (10)

A multilayer ceramic capacitor comprising a capacitor body in which dielectric layers and internal electrode layers are alternately laminated, wherein the dielectric layer contains Ba, Ti, rare earth elements, Mg and Mn as metal elements A crystal grain made of a composite oxide and a grain boundary phase, wherein the crystal grain contains Mg, Mn and a rare earth element, and the concentration of Mg, Mn and rare earth element increases from the center of the crystal grain to the grain surface. A multilayer ceramic capacitor having a concentration gradient, wherein the concentration gradient of rare earth elements among the Mg, Mn, and rare earth elements is 0.02 atomic% / nm or more. The multilayer ceramic capacitor according to claim 1, wherein the rare earth element is Y. The multilayer ceramic capacitor according to claim 1 or 2, wherein the average grain size of the crystal grains is 0.4 µm or less. The multilayer ceramic capacitor according to claim 1, wherein the dielectric layer has a thickness of 2.5 μm or less. The multilayer ceramic capacitor according to claim 1, wherein the internal electrode layer contains a base metal as a main component. (A) a mixed powder of BaTiO ₃ powder and MgO and calcined at temperatures below 750 ° C., a step of MgO to prepare a coating BaTiO ₃ powder coated formed on BaTiO ₃ powder surface,
(B) mixing the raw material powder containing rare earth element, Mn as a metal element and additive powder containing Si with the coated BaTiO ₃ powder, and preparing a slurry;
(C) forming a dielectric green sheet using the slurry;
(D) forming an internal electrode pattern on the main surface of the dielectric green sheet; and (e) stacking a plurality of dielectric green sheets on which the internal electrode pattern is formed to form a capacitor body molded body. A method for producing a multilayer ceramic capacitor comprising the step of firing. The method for producing a multilayer ceramic capacitor according to claim 6, wherein the rare earth element is Y. The method for producing a multilayer ceramic capacitor according to claim 6 or 7, wherein the average particle diameter of the BaTiO ₃ powder is 0.4 µm or less. The method for producing a multilayer ceramic capacitor according to claim 6, wherein the dielectric green sheet has a thickness of 3 μm or less. The method for producing a multilayer ceramic capacitor according to claim 6, wherein the internal electrode layer contains a base metal as a main component.

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