JP2018139261A - Capacitor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitor with high effective capacity.SOLUTION: A capacitor comprises: a capacitor body 1 in which a plurality of dielectric layers 5 and a plurality of internal electrode layers 7 are alternately laminated; and an external electrode 3 provided on an edge face from which the internal electrode layers 7 of the capacitor body 1 are exposed. The dielectric layers 5 are each formed by dielectric ceramic made of crystal grains 9 having barium titanate as its main constituent and containing vanadium. The crystal grains 9 each have the maximum concentration of the vanadium in the depth ranging from 1 to 20 nm from a surface 9a of each of the crystal grains 9. Also, the concentration of vanadium in the depth range deeper than 20 nm from the surface 9a is 0.05 atom% or lower.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to capacitors.

  2. Description of the Related Art Conventionally, a multilayer capacitor is known that is manufactured by alternately stacking a plurality of dielectric layers and internal electrode layers and then firing them integrally (see, for example, Patent Document 1). Capacitors are required to be further reduced in size and capacity in order to cope with small electronic devices typified by mobile phones in recent years.

JP 2011-129841 A

  In a capacitor in which the number of laminated dielectric layers and internal electrode layers is several hundred, for example, it is difficult to obtain desired dielectric characteristics because the crystal grains constituting the dielectric layer are fine particles. Yes. In particular, there is a problem that the electrostatic capacity (hereinafter referred to as effective capacity) when a voltage is applied to the capacitor cannot be increased.

  Therefore, this indication aims at providing a capacitor with high effective capacity.

  A capacitor according to the present disclosure includes a capacitor main body in which a plurality of dielectric layers and internal electrode layers are alternately laminated, and an external electrode provided on an end surface of the capacitor main body where the internal electrode layer is exposed. The dielectric layer is made of a dielectric ceramic composed of crystal particles containing barium titanate as a main component and containing vanadium, and the crystal particles have a depth of not less than 1 nm and not more than 20 nm from the surface of the crystal particles. In this range, the vanadium concentration has a maximum value, and the vanadium concentration in a range where the depth from the surface is deeper than 20 nm is 0.05 atomic% or less.

  According to the present disclosure, a capacitor having a high effective capacity can be obtained.

(A) is a perspective view which shows an example of the capacitor | condenser of this embodiment, (b) is the sectional view on the AA line of (a). (A) is the transmission electron microscope photograph which image | photographed a part of cross section of a dielectric material ceramic, (b) is the analytical data of the element in the range shown by the arrow in the photograph of (a). (A) is a scanning electron micrograph of the cross section of the dielectric ceramic, and (b) is the particle size distribution data of the crystal particles in the cross section of (a).

The capacitor of the present embodiment has a configuration in which external electrodes 3 are provided at opposite ends of the capacitor body 1. The capacitor body 1 has a configuration in which dielectric layers 5 and internal electrode layers 7 are alternately stacked over a plurality of layers. The shape of the capacitor body 1 is a rectangular parallelepiped shape. The dielectric layer 5 has a rectangular shape when viewed from above. The internal electrode layer 7 disposed in the main surface of the dielectric layer 5 has a rectangular shape like the dielectric layer 5. The internal electrode layers 7 are alternately extended to the external electrode 3 side in the stacking direction and connected to the external electrode 3. The capacitor body 1 shown in FIG. 1B shows a small number of laminated dielectric layers 5 and internal electrode layers 7, but the present embodiment is not limited to this, and the number of laminated layers reaches several hundred. It goes without saying that it is included.

The dielectric layer 5 is a dielectric ceramic in which crystal grains 9 are sintered via grain boundaries 11. The crystal particles 9 are mainly composed of barium titanate and contain vanadium. In this case, when barium titanate is the main component, the ratio of the total amount of titanium oxide (in terms of TiO ₂ ) and barium oxide (in terms of BaO) when the elemental analysis of the dielectric ceramic is performed is 60. The thing which is the mass% or more is said. The state in which the crystal particles 9 contain vanadium is detected when X-rays indicating vanadium are detected when an analysis is performed by applying an electron beam to arbitrarily selected crystal particles (the number is 10 to 30). Say things. The dielectric ceramic according to the present embodiment includes 90% or more of crystal particles 9 in which vanadium is detected.

  Here, as shown in FIGS. 2 (a) and 2 (b), the crystal particles 9 have a distribution in which the concentration of vanadium is maximized in a depth range from 1 nm to 20 nm from the surface 9a. In the range where the depth from the surface 9a is deeper than 20 nm, the concentration of vanadium is 0.05 atomic% or less.

  When the crystal grains 9 constituting the dielectric layer 5 exhibit such vanadium concentration distribution, it is possible to suppress a decrease in capacitance under the condition that a voltage is applied to the capacitor. The applied voltage (DC voltage) in this case is 15 to 20 V / μm per unit thickness (1 μm) of the dielectric layer 5. That is, according to the capacitor of this embodiment, a high effective capacity can be obtained.

  In addition, the capacitor of the present embodiment is not limited to vanadium, and may include other elements such as rare earth elements. When the crystal particle 9 contains a rare earth element, the concentration of the rare earth element is 0.3 atom% or more and 0.7 atom% or less, particularly 0.4 atom% or more and 0.6 atom% in the entire region of the crystal particle 9. It should be less than atomic percent.

  When the crystal grains 9 contain vanadium and a rare earth element in a state of concentration distribution as described above, it is possible to obtain a capacitor having a high effective capacity even at a temperature higher than room temperature (for example, 85 ° C.). . This is because vanadium which is easily diffused is localized in the vicinity of the surface 9 a of the crystal particle 9, so that many ferroelectric portions remain in the crystal particle 9. Moreover, since rare earth elements are distributed at a high concentration throughout, defects such as oxygen vacancies contained in the crystal grains 9 are reduced throughout.

  Further, the crystal particles 9 may contain elements other than vanadium and rare earth elements (for example, magnesium and manganese). The concentration of these magnesium and manganese is 0.05 atom in the entire region of the crystal particles 9. % Or less is good.

Here, the concentrations of vanadium and other elements contained in the crystal particles 9 are measured using a scanning electron microscope or a transmission electron microscope provided with an elemental analysis instrument. The sample used for the measurement is a mirror-polished cross section of the dielectric layer 5 or, if necessary, further polished by ion milling. At this time, the spot size of the electron beam is set to 2 to 5 nm. Moreover, the locations to be analyzed are, for example, 4 to 5 points on the arrow drawn from the surface 9a of the crystal particle 9 toward the center, as shown in FIG. The vanadium concentration detected from each measurement point thus obtained is plotted as shown in FIG. Such an analysis is performed on about 5 to 10 crystal grains 9, and the change in vanadium concentration in the crystal grains 9 is obtained. The vanadium concentration plot shown in FIG. 2 (b) is obtained by measuring the concentration in the range from the surface 9a of the analyzed crystal particle to almost the center.

  In the capacitor according to the present embodiment, it is preferable that the crystal layer 9 having a large particle size exists in the dielectric layer 5 and has a wide particle size distribution. When the dielectric layer 5 contains crystal grains 9 having a large particle size, a capacitor having a higher effective capacity can be obtained.

  FIG. 3A shows a scanning electron micrograph of a cross section of the dielectric ceramic. FIG. 3B shows the particle size distribution data of the crystal particles in the cross section of FIG. FIG. 3A shows a crystal structure in which the grain boundary 11 component is dissolved and removed.

  For example, it is preferable that the dielectric ceramic has a particle size distribution as shown in FIG. The particle size distribution shown in FIG. 3 (b) has two or more peaks (FIG. 3 (b)) in a large particle size range with respect to the particle size peak showing the maximum frequency (peak 1 in FIG. 3 (b)). It has a state having peaks 2 and 3). In this case, if two or more peaks other than the peak indicating the maximum frequency (Peak 1) are so prominent that the remarkable frequency can be seen from the base of the peak indicating the maximum frequency, the particle size distribution graph has a mountain shape. Not only the shape, but also a shoulder shape such as peak 2 in the range of 270 to 320 nm in FIG.

  In the case of manufacturing a capacitor having such a particle size distribution, a barium titanate powder whose particle size distribution shows a normal distribution is used as the main component of the barium titanate powder. In the case of forming a dielectric ceramic having a plurality of peaks in the particle size distribution, it is prepared by mixing barium titanate powders having a normal particle size distribution and different average particle sizes.

  As a raw material of vanadium, it is preferable to use an organometallic compound in which a compound containing vanadium is prepared in a sol form. As firing conditions, as described later, it is preferable to adopt conditions with a high temperature increase rate.

  The capacitor according to the present embodiment uses an organometallic compound prepared in a sol form as a compound containing vanadium, and adopts a condition with a high rate of temperature rise as a firing condition, so that vanadium is on the surface 9a of the crystal particle 9. Crystal grains 9 stopped in the vicinity can be formed.

As a composition of the dielectric ceramic capable of realizing such crystal grains 9, the content of vanadium with respect to 100 moles of barium titanate is set to be 0.2 in terms of V ₂ O ₅ from the viewpoint that the temperature characteristic of capacitance can be stabilized. 02-0.10 mol is good. As for other additive components, the rare earth element (RE) is 0.5 to 1.5 mol in terms of RE ₂ O ₃ , magnesium is 0.5 to 1.5 mol in terms of MgO, and manganese is 0 in terms of MnO. .1 to 0.3 mol is a suitable range.

  In the capacitor of this embodiment, from the standpoint of increasing the effective capacity, most of the added magnesium and manganese stays at the grain boundaries 11 of the crystal grains 9 mainly composed of barium titanate, and solidifies inside the crystal grains 9. It is better to have a lower proportion of dissolution.

  The rare earth element (RE) is preferably at least one selected from yttrium, dysprosium, holmium, terbium and ytterbium.

  The average particle size of the crystal particles 9 is preferably 0.1 to 0.8 μm. Furthermore, the average thickness of the dielectric layer 5 is preferably 0.3 to 2 μm. In this case, the internal electrode layer 7 may have the same average thickness. The material of the internal electrode layer 7 is preferably nickel (Ni) in that the manufacturing cost can be suppressed even when the number of layers is increased, and simultaneous firing with the dielectric layer 5 can be achieved.

  Hereinafter, the capacitor of this embodiment was specifically manufactured and dielectric characteristics were evaluated. First, the raw material powder has a purity of 99.9% by mass, a particle size distribution range of 0.05 to 0.2 μm, an average particle size (D50) of 0.1 μm, and a Ba / Ti molar ratio of 1.005. Barium titanate powder (BT1 powder in Table 1) was prepared. Further, as barium titanate powders having different average particle diameters, barium titanate having the same Ba / Ti molar ratio, a particle size distribution range of 0.1 to 0.5 μm, and an average particle diameter (D50) of 0.2 μm. A powder (BT2 powder in Table 1) and a barium titanate powder (BT3 powder in Table 1) having a particle size distribution range of 0.3 to 0.9 μm and an average particle diameter (D50) of 0.45 μm were prepared.

Dielectric powders were prepared by adding the following components to these raw material powders. The composition of the dielectric powder is 0.05 mole of an organometallic compound containing V in terms of V ₂ O ₅ , 1 mole of MgO powder, and rare earth element (Dy ₂ O ₃ ) with respect to 100 moles of barium titanate powder. Oxide powder is 0.85 mol, MnCO ₃ powder is 0.2 mol, and glass powder of sintering aid (SiO ₂ = 55, BaO = 20, CaO = 15, Li ₂ O = 10 (mol%)). 1 part by mass with respect to 100 parts by mass of barium titanate powder. Hereinafter, sample No. 1-4 are capacitors produced using a sol-shaped organometallic compound as a raw material for vanadium. Sample No. Reference numeral 5 denotes a capacitor manufactured using V ₂ O ₅ powder as a raw material for vanadium.

  Next, the obtained dielectric powder is put into a mixed solvent of polyvinyl butyral resin, toluene and alcohol, and wet-mixed using a zirconia ball having a diameter of 1 mm to prepare a ceramic slurry. A 1.7 μm 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 20 parts by mass of barium titanate powder to 100 parts by mass of Ni powder having an average particle size of 0.3 μm.

Next, 420 ceramic green sheets printed with internal electrode patterns were stacked, 20 ceramic green sheets not printed with internal electrode patterns were stacked on each of the upper and lower surfaces, and a temperature of 60 ° C. and pressure was applied using a press. 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, after the raw molded body to be the capacitor body is treated to remove the binder in the air, firing is performed in hydrogen-nitrogen at a heating rate of 800 to 1000 ° C./h and a maximum temperature of 1200 ° C. A capacitor body 1 was produced. A roller hearth kiln was used for this baking.

Subsequently, the manufactured capacitor body was re-oxidized in a nitrogen atmosphere at a maximum temperature of 1000 ° C. and a holding time of 5 hours. The size of the capacitor body is 1.6 mm × 1.0 mm × 0.8 mm, the thickness of the dielectric layer is 1.3 μm, the thickness of the internal electrode layer is about 1 μm, and the effective area of one layer of the internal electrode layer is 1 mm ^2. Met. Here, the effective area is an area of overlapping portions of the internal electrode layers formed alternately in the stacking direction so as to be exposed at different end faces of the capacitor body. The design value of the capacitance of the produced capacitor was set to 10 μF.

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 obtain a capacitor.

  Next, these capacitors were evaluated as follows. The capacitance is LCR meter (manufactured by Hewlett-Packard Company), the frequency is 1.0 kHz, the AC voltage is 1.0 V / μm, no DC voltage is applied (0 V / μm), and the DC voltage is 15 V / μm. It measured on the conditions which applied. The measurement temperature was room temperature (25 ° C.) and 85 ° C. Also, the insulation resistance of the capacitor was measured under the same temperature condition of 85 ° C. The number of samples for each measurement of capacitance and insulation resistance was 30 pieces.

The high temperature load life test was conducted under conditions of a temperature of 170 ° C. and 30V. The life in the high temperature load test was set to the time when the insulation resistance became 10 ⁶ Ω or less. The number of samples for the high temperature load life test was 300.

  The average particle size of the crystal particles is obtained by processing the contours of the crystal particles from a photograph of the cross section of the dielectric layer taken using a scanning electron microscope, obtaining the area of each particle, and replacing it with a circle having the same area. The diameter was calculated from the average value.

  As shown in FIG. 3B, the particle size distribution of the crystal particles was obtained by re-plotting the data obtained by dividing the average particle size into data obtained by dividing the particle size every 60 nm.

  The concentration distribution of elements such as vanadium contained in the crystal particles was determined using a transmission electron microscope equipped with an analyzer. The sample for analysis was produced as follows. First, a capacitor sample was cut into a predetermined size, and finally ion milling was performed to prepare a sample in which the cross section (polished surface) of the dielectric ceramic was exposed. Next, elemental analysis was performed on individual crystal particles present in the cross section of the prepared sample. At this time, the spot size of the electron beam was set to 2 to 3 nm from the performance of the apparatus. The locations to be analyzed were 4 to 6 points from the grain boundary on a straight line drawn from the grain boundary toward the center of each crystal grain. Next, the concentration of vanadium detected from each measurement point was determined and plotted as shown in FIG. Such analysis was performed by analyzing three locations for each sample, and calculating an average value of concentration change. The concentration distribution of other elements was also obtained by the same method.

  Table 1 shows the preparation composition of the dielectric powder and the results of the concentration distribution of each element. Table 2 shows the dielectric characteristics of the capacitor.

  Sample No. 1-4, the vanadium concentration change in the crystal grain shows the maximum value within the range of the depth of 1 nm to 20 nm from the surface of the crystal grain, while the vanadium concentration in the range where the depth from the surface is deeper than 20 nm. Was 0.05 atomic% or less.

  In contrast, sample no. No. 5 shows a maximum change in vanadium concentration within a depth range of 1 nm or more and 20 nm or less from the surface of the crystal grain, but the vanadium concentration in the range where the depth from the surface is deeper than 20 nm is 0. It was 1 atomic%.

  The concentration of the rare earth element is the sample no. In any of 1-4, it was 0.5 atomic% in the whole area | region of the crystal grain. Sample No. The rare earth element 5 concentration was 0.3 atomic%.

  Sample No. 1 and sample no. 2 is different from the crystal grain size distribution. Sample No. Reference numeral 1 denotes a capacitor having a dielectric layer that is a dielectric ceramic whose crystal particle size distribution has a single peak. Sample No. Reference numeral 2 denotes a capacitor having a dielectric layer made of a dielectric ceramic having a particle size distribution having three peaks (peaks 1 to 3 in FIG. 3B) within a particle size range of 30 to 700 nm.

  Samples with different heating rates (sample No. 3: 900 ° C./h, sample No. 4: 800 ° C./h) were prepared with sample No. 3 manufactured at a heating rate of 1000 ° C./h. Compared with 2, the concentration of magnesium and manganese at a position of a distance of 50 nm from the surface of the crystal grain was higher.

  For the dielectric properties shown in Table 2, sample no. 1-4 are sample numbers. Compared to 5, the electrostatic capacity under the condition that no DC voltage was applied at room temperature (25 ° C.) and the effective capacity at room temperature (25 ° C.) and high temperature (85 ° C.) were higher. In this case, sample no. 1-4 are sample no. 5, the change rate of the effective capacitance based on the electrostatic capacitance measured at room temperature (25 ° C.) without applying a DC voltage ((B−A) / A (%) in Table 2, ( C−A) / A (%)) was also small. Furthermore, sample no. 1-4 are sample numbers. Compared to 5, the insulation resistance at high temperature was high, and the number of failures was small for the high temperature load life.

  In addition, the sample No. 1 in which the particle size distribution of the crystal particles was changed. 1 and sample no. 2, sample no. 2 is the sample No. 2. Compared to 1, the electrostatic capacity, effective capacity and rate of change thereof, insulation resistance at high temperature, and high temperature load life were all excellent.

  Sample No. 2 to 4, sample No. 1 with a heating rate of 1000 ° C./h was used. No. 2 showed higher values of capacitance and effective capacity than the samples (sample Nos. 3 and 4) in which the heating rate was slowed to 800 to 900 ° C./h.

DESCRIPTION OF SYMBOLS 1 Capacitor body 3 External electrode 5 Dielectric layer 7 Internal electrode layer 9 Crystal grain 9a (crystal grain) surface 11 Grain boundary

Claims (4)

  A capacitor comprising a capacitor body in which a plurality of dielectric layers 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, The body layer is made of a dielectric ceramic composed of crystal particles containing barium titanate as a main component and containing vanadium, and the crystal particles are in the range of 1 nm to 20 nm in depth from the surface of the crystal particles. And a vanadium concentration in a range where the depth from the surface is deeper than 20 nm is 0.05 atomic% or less.   2. The capacitor according to claim 1, wherein the crystal particles include a rare earth element, and the concentration of the rare earth element is 0.3 atomic percent or more and 0.7 atomic percent or less in the entire region of the crystal particles.   The capacitor according to claim 2, wherein the crystal particles further include magnesium and manganese, and the concentration of magnesium and manganese is 0.05 atomic% or less in the entire region of the crystal particles.   The capacitor according to any one of claims 1 to 3, wherein a particle size distribution of the crystal particles constituting the dielectric layer has at least three peaks in a particle size range of 30 to 700 nm.