capacitor

Abstract

A capacitor includes a laminate and an external electrode on a surface thereof. The laminate has dielectric layers and internal electrode layers alternately laminated in multiple layers. The laminate also has an intermediate layer between the dielectric layers and the internal electrode layers, the intermediate layer containing a dielectric component of the dielectric layers and a conductive component of the internal electrode layers. The intermediate layer has a concentration gradient in which the concentration of the conductive component decreases from the internal electrode layers to the dielectric layers.

Description

Technical Field

[0001] This disclosure relates to multilayer capacitors. Background Technology

[0002] An example of the prior art is described in Patent Document 1.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 10-4027 Summary of the Invention

[0006] The capacitor disclosed herein comprises: a laminate having alternately stacked dielectric layers and internal electrode layers, and an external electrode located on the surface of the laminate and electrically connected to the internal electrode layers. The laminate further comprises an intermediate layer located between the dielectric layers and the internal electrode layers, the intermediate layer containing a dielectric component of the dielectric layers and a conductive component of the internal electrode layers. The intermediate layer has a concentration gradient of the conductive component that decreases from the internal electrode layers to the dielectric layers. Attached Figure Description

[0007] The purpose, features, and advantages of this disclosure will become clearer from the following detailed description and accompanying drawings.

[0008] Figure 1 This is a 3D view of the capacitor's appearance.

[0009] Figure 2 yes Figure 1 A sectional view at the section line.

[0010] Figure 3 This is an enlarged schematic diagram of the cross-section of the laminated body.

[0011] Figure 4A It is a comparative chart showing the changes in nickel concentration in the intermediate layer.

[0012] Figure 4B This is a graph from Example 2 showing the variation in nickel concentration in the intermediate layer. Detailed Implementation

[0013] For capacitors that form the basis of this disclosure and are one of the electronic components mounted on electronic devices, high electrostatic capacitance is required and improvements in various characteristics are desired.

[0014] For example, the multilayer ceramic capacitor described in Patent Document 1 diffuses the internal electrode material within the ceramic body, such that the diffusion distance of the internal electrode material is 3 to 30% of the distance between the internal electrodes, thereby resulting in small temperature changes in the electrostatic capacitor and high reliability under high temperature conditions.

[0015] The capacitor of this disclosure will now be described with reference to the accompanying drawings. However, the capacitor of this disclosure is not limited to the specific embodiments described below. The capacitor of this disclosure encompasses various forms as long as they conform to the spirit or scope of the general concept defined by the appended claims.

[0016] Figure 1 This is a 3D view of the capacitor's appearance. Figure 2 yes Figure 1 A cross-sectional view at the section line. As an example of an embodiment of this disclosure, the capacitor 100 includes a laminate 1 and an external electrode 3 located on its surface. The laminate 1 has a dielectric layer 5 and an internal electrode layer 7, which are alternately stacked. In this embodiment, the laminate 1 is, for example, rectangular, and in a top view viewed from the stacking direction, both the dielectric layer 5 and the internal electrode layer 7 are rectangular. One side of the internal electrode layer 7 is exposed on the side of the laminate 1, and the external electrode 3 electrically connects the internal electrode layer 7 and the external electrode 3 by covering this side. Figure 2 In this paper, the number of layers of dielectric layer 5 and internal electrode layer 7 is simplified to a few layers, but the number of layers of dielectric layer 5 and internal electrode layer 7 can be, for example, hundreds of layers.

[0017] Figure 3 This is an enlarged schematic diagram of the cross-section of the dielectric layer. The dielectric layer 5 is, for example, composed of multiple grains containing titanate. The grains can be grains containing a dielectric component with titanate as the main component. Here, the main component refers to the component most abundant in the grain. Having titanate as the main component means that the content of titanate in the grain is greater than the content of other components. Examples of titanates include barium titanate, magnesium titanate, and lanthanum titanate. Multiple titanates can be mixed and used. Using barium titanate, which has a high dielectric constant, can improve the electrostatic capacitance of capacitor 100.

[0018] The titanate-containing grains are grains with an average grain size of, for example, 0.1 to 0.5 μm. The average grain size is determined by, for example, the following steps: First, the fracture surface of the sample, which is the sintered laminate 1, is ground. Then, a photograph of the internal structure of the ground sample is taken using a scanning electron microscope, and a circle comprising 50 to 100 grains is drawn on the photograph. Grains falling within and around the circle are selected. Next, the outline of each grain contained in the area is extracted using an existing image analysis program to calculate the cross-sectional area. Based on the obtained cross-sectional area, the diameter of the equivalent circle of each grain is calculated, and the average grain size is obtained from the average value of this circle.

[0019] The inner electrode layer 7 is composed of conductive components such as metals, for example, nickel (Ni), copper (Cu), palladium (Pd), and silver (Ag). Alternatively, alloys containing these metals can be used. The outer electrode 3 can also be made of the same or similar metal material as the inner electrode layer 7.

[0020] In this embodiment, the laminate 1 further includes an intermediate layer 6 located between the dielectric layer 5 and the inner electrode layer 7. The intermediate layer 6 contains the dielectric component of the dielectric layer 5 and the conductive component of the inner electrode layer 7. The intermediate layer 6 has a concentration gradient of the conductive component, decreasing from the inner electrode layer 7 to the dielectric layer 5. This layer containing a concentration gradient of components is called a so-called gradient layer. In the intermediate layer 6, the concentration of the conductive component gradually changes along the thickness direction. The concentration of the conductive component is highest on the side of the inner electrode layer 7 and lowest on the side of the dielectric layer 5.

[0021] In the laminate 1, the conductive component contained in the inner electrode layer 7 enters the dielectric layer 5, forming a region containing both the dielectric component of the dielectric layer 5 and the conductive component of the inner electrode layer 7. Conventionally, in the region where the conductive component enters the dielectric layer 5, the conductive component is typically present uniformly or randomly. Furthermore, the concentration of the diffused conductive component is low. In this embodiment, as described above, the intermediate layer 6 is a gradient layer with a concentration gradient of the conductive component, which mitigates the thermal stress generated between the dielectric layer 5 and the inner electrode layer 7 under high-temperature conditions. This improves the reliability of the capacitor 100 in high-temperature environments with strong thermal shock.

[0022] The thickness of the intermediate layer 6 is 0.04–0.2 μm. If the thickness exceeds 0.2 μm, the content of conductive components in the intermediate layer 6 increases, and correspondingly, the conductive components in the inner electrode layer 7 decrease, the continuity of the inner electrode layer 7 decreases, and the electrostatic capacitance may decrease.

[0023] The conductive component content of the intermediate layer 6 is 0.005 to 0.035 mol%. This means that the conductive component content on the inner electrode layer 7 side of the intermediate layer 6, where the conductive component concentration is highest, is, for example, a maximum of 0.035 mol%, and the conductive component content on the dielectric layer 5 side of the intermediate layer 6, where the conductive component concentration is lowest, is, for example, a minimum of 0.005 mol%. The concentration gradient of the conductive component in the intermediate layer 6 only needs to be within the range of 0.005 to 0.035 mol%. For example, the intermediate layer 6 may have a concentration gradient where the conductive component content on the inner electrode layer 7 side is 0.015 mol% and the conductive component content on the dielectric layer 5 side is 0.005 mol%. Furthermore, for example, the intermediate layer 6 may have a concentration gradient where the conductive component content on the inner electrode layer 7 side is 0.02 mol% and the conductive component content on the dielectric layer 5 side is 0.01 mol%. Furthermore, for example, the intermediate layer 6 may have a concentration gradient where the content of the conductive component on the side of the internal electrode layer 7 is 0.035 mol% and the content of the conductive component on the side of the dielectric layer 5 is 0.02 mol%.

[0024] The following description uses barium titanate as the dielectric component of dielectric layer 5 and nickel as the conductive component of inner electrode layer 7. Intermediate layer 6 contains barium titanate and nickel, and has a nickel concentration gradient that decreases from inner electrode layer 7 to dielectric layer 5. For example, it is known that nickel diffuses into barium titanate during firing, but the amount diffused is only trace. It was discovered that in the firing process of laminate 1, after heat treatment in an oxidizing atmosphere, by performing heat treatment (formal firing) in the same reducing atmosphere as before, nickel can be present in barium titanate at a high concentration. The specific mechanism is not yet clear, but it is speculated as follows: Through heat treatment in an oxidizing atmosphere, a portion of the nickel is oxidized to form nickel oxide. The generated nickel oxide has a higher affinity for unsintered barium titanate than nickel and enters into the barium titanate. Through subsequent heat treatment in a reducing atmosphere, barium titanate is sintered and nickel oxide is reduced to nickel. In the obtained laminate 1, an intermediate layer 6 with a nickel concentration gradient is formed between the dielectric layer 5 and the inner electrode layer 7.

[0025] Since the thickness of intermediate layer 6, the nickel content in intermediate layer 6, and the slope of the concentration gradient are determined by the penetration depth and amount of nickel oxide into barium titanate, they can be controlled by the composition of the atmosphere gas, the heat treatment temperature, and the heat treatment time during the oxidizing atmosphere heat treatment. During heat treatment, the oxygen partial pressure of the atmosphere gas composition can be used to control whether it is an oxidizing atmosphere that oxidizes nickel, a reducing atmosphere that reduces nickel oxide, or a reducing atmosphere that prevents nickel oxidation. The oxygen partial pressure of the atmosphere gas composition is determined by the partial pressures of hydrogen and water vapor in the atmosphere gas. The higher the ratio of hydrogen to water vapor in the atmosphere gas, the lower the oxygen partial pressure. Furthermore, the higher the temperature of the atmosphere gas, the higher the oxygen partial pressure. When the oxygen partial pressure of the atmosphere gas is higher than the equilibrium oxygen partial pressure of nickel, it becomes an oxidizing atmosphere where nickel is oxidized; when the oxygen partial pressure of the atmosphere gas is lower than the equilibrium oxygen partial pressure of nickel, it becomes a reducing atmosphere where nickel is reduced.

[0026] For example, when the ratio of hydrogen to water vapor (H2 / H2O) in the atmosphere is set to 1 / 2000 and the temperature is set to 700–800°C, the oxygen partial pressure of the atmosphere becomes higher than the parallel oxygen partial pressure, thus becoming an oxidizing atmosphere. By heat treatment under this oxidizing atmosphere, nickel is oxidized and incorporated into the unsintered barium titanate. Then, for example, when the ratio of hydrogen to water vapor (H2 / H2O) in the atmosphere is set to 1 / 20 and the temperature is set to 800°C or higher, the oxygen partial pressure of the atmosphere becomes lower than the parallel oxygen partial pressure, thus becoming a reducing atmosphere. In this reducing atmosphere, the barium titanate is sintered and the nickel oxide is reduced, resulting in a laminate 1 containing the intermediate layer 6.

[0027] The above explanation uses nickel as a conductive component, but the same applies to other conductive components. The oxidizing and reducing atmospheres for copper can be controlled based on the relationship between the partial pressure of oxygen in the atmosphere gas and the equilibrium partial pressure of conductive components such as copper.

[0028] The method for manufacturing the capacitor according to this embodiment will be described.

[0029] First, a ceramic slurry is prepared by using a ball mill or similar method with dielectric powder, organic resins such as polyvinyl butyral resin, and solvents such as toluene and ethanol. Then, a ceramic green sheet is formed on a substrate using a sheet forming method such as a doctor blade method or a die-casting method. From the perspective of achieving high capacity and thinning of the dielectric layer 5 while maintaining high insulation, the thickness of the ceramic green sheet is preferably 0.8 to 1.5 μm.

[0030] However, the dielectric material used to manufacture multilayer ceramic capacitors can be barium titanate (BaTiO3, hereinafter referred to as BT powder), depending on the required dielectric properties. Alternatively, it can be BaTiO3, which is produced by dissolving alkaline earth metal elements such as calcium or strontium at barium sites. 1-x Ca xTiO3 (x = 0.01–0.1, hereinafter referred to as BCT powder) powder or Ba 1-x Sr x TiO3 (x = 0.01–0.1, hereinafter referred to as BST powder) powder, or, by solidifying calcium in the barium sites of barium titanate and solidifying zirconium in the titanium sites of Ba 1- x Ca x Ti 1-y Zr y O3 (x = 0.01 to 0.1, y = 0.05 to 0.5, hereinafter referred to as BCTZ powder) powder.

[0031] Among the aforementioned powders, BT powder is preferred because it allows for the production of multilayer ceramic capacitors with relatively small temperature variation rates of electrostatic capacitance over a wide temperature range centered at room temperature. The Ba / Ti molar ratio of the BT powder is 1.001 to 1.009, and its average particle size is 0.1 to 0.2 μm. Therefore, the dielectric layer 5 can be easily thinned, and using BT powder, a multilayer ceramic capacitor exhibiting excellent high-temperature load life can be obtained according to the firing conditions described later.

[0032] Furthermore, the dielectric powder used in manufacturing the multilayer ceramic capacitor of this embodiment can be a powder containing sintering aids such as vanadium, magnesium, rare earth elements (RE), manganese, and glass powder with SiO2 as the main component. Using these powders, a capacitor with high-temperature load life and high capacitance per unit volume can be obtained.

[0033] For example, BT powder with a purity of 99.9% or higher, a Ba / Ti molar ratio of 1.001 to 1.009, and an average particle size of 0.1 to 0.2 μm may be mixed with V₂O₅ powder, MgO powder, an oxide powder of at least one rare earth element (RE) selected from Y₂O₃ powder, Dy₂O₃ powder, Ho₂O₃ powder, and Yb₂O₃ powder, and a powder containing manganese (here, MnCO₃ powder is used). In this case, the composition may be such that, relative to 100 moles of BT powder, 0.03 to 0.08 moles of V₂O₅ powder, 0.9 to 1.1 moles of MgO powder, 0.4 to 0.6 moles of an oxide powder of at least one rare earth element (RE) selected from Y₂O₃ powder, Dy₂O₃ powder, Ho₂O₃ powder, and Yb₂O₃ powder, and 0.2 to 0.3 moles of a powder containing manganese.

[0034] Next, within the aforementioned range, glass powder with SiO2 as the main component is added to BT powder containing V2O5 powder, MgO powder, rare earth element (RE) oxide powder and manganese powder, organic binder and solvent are added and mixed to prepare ceramic slurry.

[0035] The glass powder used contains SiO2, BaO, CaO and Li2O as the main components. Its composition can be that when SiO2 is 1 mole, it contains 0.15 to 0.70 moles of BaO, 0.15 to 0.70 moles of CaO and 0.05 to 0.45 moles of Li2O.

[0036] Furthermore, the purity of these raw materials and reagents is preferably 99.5% or higher, from the perspective of reducing impurities mixed into the sintered body that serves as the dielectric layer 5 and obtaining high dielectric properties.

[0037] Next, a rectangular internal electrode pattern is printed and formed on the surface of the obtained ceramic green sheet. The conductive paste that forms the internal electrode pattern is prepared by mixing a ceramic powder (in this case, BT powder or the dielectric powder used in the ceramic green sheet) as a co-material with nickel (Ni) or its alloy powder as the main component metal, and adding an organic binder, solvent, and dispersant. Furthermore, to eliminate the steps caused by the internal electrode pattern on the ceramic green sheet, a ceramic pattern can be formed around the internal electrode pattern with a thickness substantially the same as the internal electrode pattern. In this case, the ceramic component constituting the ceramic pattern can also use the dielectric powder used in the ceramic green sheet to ensure that the firing shrinkage during simultaneous firing is the same.

[0038] Next, a desired number of ceramic green sheets with internal electrode patterns are overlapped, and multiple ceramic green sheets without internal electrode patterns are overlapped on top of each other, with the same number of sheets in each layer, to form a temporary laminate. The internal electrode patterns in the temporary laminate are staggered by half a pattern along their length. This lamination method allows the internal electrode patterns to be alternately exposed on the end faces of the cut laminate.

[0039] In addition to the method of pre-forming the internal electrode pattern on the main surface of the ceramic green sheet before stacking, the stacked ceramic capacitor of this embodiment can also be formed by the following method: after temporarily attaching the ceramic green sheet to the substrate on the lower layer side, printing the internal electrode pattern and drying it, stacking the ceramic green sheet without the internal electrode pattern on the printed and dried internal electrode pattern and pre-attaching it, and then sequentially attaching the ceramic green sheet and printing the internal electrode pattern.

[0040] Next, the temporary laminate is pressed under high temperature and high pressure conditions, which are higher than those during the temporary lamination process, to form a molded body in which the ceramic green sheet and the internal electrode pattern are firmly attached. By cutting the molded body into a grid pattern, a laminated body (unfired) with the ends of the internal electrode pattern exposed is obtained.

[0041] Next, the unfired laminate is fired under specified firing conditions to form laminate 1. Depending on the situation, the edges of laminate 1 may be chamfered, and the inner electrode layer 7 may be exposed by tumbling to expose the opposite end faces of laminate 1. Regarding the firing conditions, as described above, heat treatment can be performed in an oxidizing atmosphere with an oxygen partial pressure higher than the equilibrium oxygen partial pressure of nickel, and firing can be performed in a reducing atmosphere by changing the composition and temperature of the atmosphere.

[0042] Next, external electrode paste is applied to the opposite ends of the laminate 1 and sintered to form external electrodes 3. Furthermore, depending on the situation, a coating is formed on the surface of the external electrodes 3 to improve mounting performance. Thus, the capacitor of this embodiment is obtained.

[0043] Example

[0044] Next, the manufacturing method of the capacitor in the embodiment will be described. A barium titanate raw material powder with a purity of 99.9%, an average particle size of 0.2 μm, and a Ba / Ti molar ratio of 1.005 was prepared. Dysprosium was added as a rare earth element, specifically as Dy₂O₃. Other additives included calcium carbonate powder (CaCO₃), manganese carbonate powder (MnCO₃), and glass powder (containing SiO₂, BaO, CaO, and Li₂O as main components). These powders were wet-mixed using zirconia spheres with a diameter of 5 mm and a mixed solvent containing toluene and ethanol.

[0045] Next, the wet-mixed powder is added to a mixed solvent of toluene and ethanol containing polyvinyl butyral resin, and ceramic slurry is prepared by wet mixing using zirconia balls with a diameter of 5 mm. Ceramic green sheets with a thickness of about 3 μm are then formed on a molding film by a doctor blade method.

[0046] Nickel powder was used as the metal for forming the metal paste of the internal electrode layer. Ethyl cellulose was used as the resin for preparing the metal paste. Dihydroterpene alcohol solvent and butyl cellosolve were used as solvents in a mixture.

[0047] Next, metal paste is printed onto the prepared ceramic green sheet to create a green sheet with metal paste. Then, 400 layers of the prepared green sheet with metal paste are stacked, with ceramic green sheets overlapped on both the upper and lower surfaces as covering layers to create a shaped body. Finally, the shaped body is cut to create an unfired laminate.

[0048] The firing process was carried out under the following conditions. During firing, after heat treatment in an oxidizing atmosphere, a formal firing was performed in a reducing atmosphere. Examples 1-4 were obtained by changing the concentration gradient of the intermediate layer by varying the oxidizing atmosphere. Specifically, the heat treatment time in the oxidizing atmosphere was set to 20 minutes, and the temperature conditions and composition ratio (hydrogen to water vapor ratio (H2 / H2O)) were varied as shown in Table 1. In the formal firing in the reducing atmosphere, Examples 1-4 used the same conditions. Specifically, the temperature was maintained at the highest temperature of 1200°C for 30 minutes, and the hydrogen to water vapor ratio (H2 / H2O) was set to 1 / 10. The resulting laminate had dimensions of 2.0 mm × 1.25 mm × 1.25 mm.

[0049] After tumbling the obtained laminate 1, an external electrode paste was applied to both ends of the laminate 1, and sintering was performed at 800°C to form external electrodes. The external electrode paste used a material containing Cu powder and glass. Then, using an electrolytic tumbling mill, a Ni plating layer and a Sn plating layer were sequentially formed on the surface of the external electrodes to obtain a capacitor. The designed capacitance of the fabricated capacitor was set to 10.0 μF.

[0050] Except for the firing process, the comparative examples were manufactured using the same manufacturing method as the examples. In the firing process, the comparative examples did not undergo heat treatment in an oxidizing atmosphere, but were fired only in a reducing atmosphere.

[0051] Thermal shock resistance was evaluated using a solderability test. In the solderability test, 100 capacitors from Examples 1-4 and the comparative example were immersed in a solder bath maintained at 305°C for 5 seconds. After removal, the number of cracks was counted. The result is expressed as the number of cracks generated / the number of capacitors immersed, as shown in Table 1.

[0052] In addition, for the intermediate layer, the intermediate layer thickness, the concentration on the internal electrode layer side (maximum concentration), and the concentration on the dielectric layer side (minimum concentration) were measured. The measurement methods are described below. Stripped samples from Examples 1-4 were prepared, exposing the intermediate layer. The stripping of the internal electrode layer was performed by electrochemical nickel dissolution treatment to ensure no internal electrode layer residue remained on the surface of the intermediate layer. Nickel was quantified along the depth direction from the surface of the intermediate layer of the stripped sample using secondary ion mass spectrometry (SIMS). The SIMS measurement conditions are shown below. Furthermore, for the comparative examples, the nickel concentration in the dielectric layer was also measured by SIMS in the same or similar manner. The measurement results are shown in Table 1.

[0053] Analytical method: Time-of-flight secondary ion mass spectrometry (ToF-SIMS)

[0054] Analytical apparatus: ULVAC-PHI nano ToF II; Primary ions: Bi cluster ions

[0055] Measurement area: 100μm square

[0056] Depth-direction sputtering: Ar ions 4keV

[0057] [Table 1]

[0058]

[0059] As shown in Table 1, in the weld resistance test, compared with the comparative example, the number of cracks generated in Examples 1-4 was significantly reduced, resulting in excellent thermal shock resistance. Furthermore, it can be seen that the thickness, maximum concentration, and minimum concentration of the intermediate layer in Examples 1-4 all varied, indicating that the intermediate layer could be controlled according to the oxidizing atmosphere conditions. In the comparative example, the nickel concentration in the dielectric layer 5 was lower than the minimum concentration in the examples, and no concentration change was observed in the thickness direction of the dielectric layer.

[0060] Figure 4A and Figure 4B The text shows an example of a measurement result based on SIMS. Figure 4A This indicates the results of the comparative measurements. Figure 4B The results of Example 2 are shown in Figure 4. In the graph, the vertical axis represents the nickel content (mol%), and the horizontal axis represents the depth (nm) from the sample surface. In the comparative example, the nickel content was constant at 0.003 mol%, regardless of depth. In Example 2, it was confirmed that the nickel content decreased with depth, forming an intermediate layer with a concentration gradient.

[0061] This disclosure may be implemented in the following ways.

[0062] The capacitor disclosed herein comprises: a laminate having alternately stacked dielectric layers and internal electrode layers, and an external electrode located on the surface of the laminate and electrically connected to the internal electrode layers. The laminate further comprises an intermediate layer located between the dielectric layers and the internal electrode layers, the intermediate layer containing a dielectric component of the dielectric layers and a conductive component of the internal electrode layers. The intermediate layer has a concentration gradient of the conductive component that decreases from the internal electrode layers to the dielectric layers.

[0063] The capacitor disclosed herein can improve the reliability of the capacitor under high temperature conditions.

[0064] The embodiments of this disclosure have been described in detail above. Furthermore, this disclosure is not limited to the above embodiments, and various changes and modifications can be made without departing from the spirit of this disclosure. It goes without saying that all or part of the embodiments described above can be combined within an appropriate and non-contradictory scope.

[0065] Symbol Explanation

[0066] 1-layer stack

[0067] 3 External Electrodes

[0068] 5 Dielectric layer

[0069] 6 intermediate layers

[0070] 7 Internal Electrode Layer

[0071] 100 capacitor

Claims

1. A capacitor, possessing: A laminate having alternating layers of dielectric and internal electrode layers, and An external electrode located on the surface of the laminate and electrically connected to the internal electrode layer; The laminate further comprises an intermediate layer located between the dielectric layer and the inner electrode layer, the intermediate layer containing the dielectric component of the dielectric layer and the conductive component of the inner electrode layer; The dielectric component comprises barium titanate, and the conductive component comprises nickel; The intermediate layer has a concentration gradient of the conductive component that decreases from the inner electrode layer to the dielectric layer; The content of the conductive component in the intermediate layer is 0.005 to 0.035 mol.

2. The capacitor according to claim 1, wherein the thickness of the intermediate layer is 0.04 to 0.2 μm.

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