Capacitor

Abstract

This capacitor includes: a first electrode partially having a porous surface; a first dielectric layer positioned on the porous surface; a second dielectric layer positioned on the first dielectric layer; and a second electrode positioned on the second dielectric layer. The first electrode and the first dielectric layer are in contact with each other. The first dielectric layer includes a first dielectric component, and the first dielectric component is an oxide of a metal element contained in the first electrode layer. The second dielectric layer includes a second dielectric component different from the first dielectric component.

Description

capacitor

[0001] The present invention relates to a capacitor.

[0002] Patent Document 1 describes an invention relating to a capacitor and a method for manufacturing the same. The capacitor described in Patent Document 1 comprises a conductive porous substrate having pores, a dielectric layer located on the pores, and an upper electrode located on the dielectric layer. The dielectric layer is formed from a compound whose atoms originate differently from the conductive porous substrate.

[0003] Patent No. 6558439

[0004] An object of the present invention is to provide a capacitor with a high CR product and high reliability.

[0005] In order to achieve the above object, the capacitor of the present invention is a capacitor having a first electrode having a porous surface in part, a first dielectric layer located on the porous surface, a second dielectric layer located on the first dielectric layer, and a second electrode located on the second dielectric layer, wherein the first electrode and the first dielectric layer are in contact with each other, the first dielectric layer contains a first dielectric component, and the first dielectric component is an oxide of a metal element contained in the first electrode layer, and the second dielectric layer contains the second dielectric component different from the first dielectric component.

[0006] The first dielectric layer may have a lower dielectric constant than the second dielectric layer.

[0007] The second dielectric component may be an oxide of one or more elements selected from Al, Hf, Zr, Ta, Pb, Zn, Si, Ti, and Sr.

[0008] The second dielectric layer may be substantially free of the first dielectric component.

[0009] A third dielectric layer may be located between the second dielectric layer and the second electrode.

[0010] The third dielectric layer may include the first dielectric component.

[0011] The third dielectric layer may include a third dielectric component different from both the first and second dielectric components.

[0012] The third dielectric component may be an oxide of one or more elements selected from the group consisting of Al, Hf, Zr, Ta, Pb, Zn, Si, Ti, and Sr.

[0013] A fourth dielectric layer may be located between the third dielectric layer and the second electrode.

[0014] The fourth dielectric layer may include the second dielectric component.

[0015] The thickness of the first dielectric layer may be t1, and the total thickness of the dielectric layers included between the first electrode and the second electrode may be T, where 0.05<t1 / T<0.50 may be satisfied.

[0016] Fig. 1 is a cross-sectional view of a capacitor. Fig. 2 is a cross-sectional view of a capacitor. Fig. 3 is a cross-sectional view of a dielectric layer and its vicinity. Fig. 4 is a cross-sectional view of a dielectric layer and its vicinity. Fig. 5 is a cross-sectional view of a dielectric layer and its vicinity.

[0017] The following describes an embodiment of the present invention with reference to the drawings. The present invention is not limited to the following embodiment, and can be implemented by making appropriate modifications within the scope of the object of the present invention. Furthermore, where the description is redundant, it may be omitted as appropriate, but this does not limit the spirit of the invention.

[0018] (Overall Configuration of Capacitor) There are no particular limitations on the overall configuration of the capacitor according to this embodiment. For example, as shown in Figures 1 and 2, the capacitor according to this embodiment may have a first electrode 10, an insulating member 21 formed on the surface of the first electrode 10, a dielectric layer 12 located on the porous surface 10a, a second electrode 31 located on the porous surface 10a, a terminal electrode 51 connected to the first electrode 10 via a seed layer 40, and a terminal electrode 52 connected to the second electrode 31 via the seed layer 40. Figure 1 is a schematic cross-sectional view obtained by cutting the capacitor of Figure 2 along the longitudinal direction.

[0019] 1 , the second electrode 31 may be a thin film. In this case, the second electrode 31, which is a thin film, is formed on the surface of the dielectric layer 12 and in its vicinity, and the seed layer 40 is formed on the surface of the second electrode 31 and in its vicinity. Most of the area occupied by the seed layer 40 and the second electrode 31 located below the terminal electrode 52 in FIG. 1 becomes the terminal electrode 52.

[0020] 1 , the seed layer 40 connected to the terminal electrode 52 may also serve as the second electrode 31. In this case, the seed layer 40 also serving as the second electrode 31 is formed on the surface of the dielectric layer 12 and in the vicinity thereof. Most of the area occupied by the seed layer 40 and the second electrode 31 located below the terminal electrode 52 in FIG. 1 becomes the terminal electrode 52.

[0021] (Configuration of the dielectric layer and its vicinity) The capacitor of this embodiment has a first electrode 10 having a porous surface 10a, a dielectric layer 12 located on the porous surface 10a, and a second electrode 31 located on the dielectric layer 12.

[0022] Fig. 3 is an enlarged view of the dielectric layer 12 and its vicinity in Fig. 1. As shown in Fig. 3, the dielectric layer 12 has a first dielectric layer 12a located on the first electrode 10 and a second dielectric layer 12b located on the first dielectric layer 12a.

[0023] That is, the capacitor of this embodiment has a first electrode 10 having a porous surface 10a, a first dielectric layer 12a located on the porous surface 10a, a second dielectric layer 12b located on the first dielectric layer 12a, and a second electrode 31 located on the second dielectric layer 12b.

[0024] 3, the first electrode 10 and the first dielectric layer 12a are in contact with each other. The first dielectric layer 12a and the second dielectric layer 12b may be in contact with each other. The second dielectric layer 12b and the second electrode 31 may be in contact with each other.

[0025] In the capacitor according to this embodiment, the dielectric layer 12 may have the structure shown in Fig. 4. Specifically, the capacitor may have a first electrode 10 having a porous surface 10a, a first dielectric layer 12a located on the porous surface 10a, a second dielectric layer 12b located on the first dielectric layer 12a, a third dielectric layer 12c1 located on the second dielectric layer 12b, a fourth dielectric layer 12d located on the third dielectric layer 12c1, and a second electrode 31 located on the fourth dielectric layer 12d.

[0026] As shown in Fig. 4, the first electrode 10 and the first dielectric layer 12a are in contact with each other. The first dielectric layer 12a and the second dielectric layer 12b may be in contact with each other. The second dielectric layer 12b and the third dielectric layer 12c1 may be in contact with each other. The third dielectric layer 12c1 and the fourth dielectric layer 12d may be in contact with each other. The fourth dielectric layer 12d and the second electrode 31 may be in contact with each other.

[0027] In the capacitor according to this embodiment, the dielectric layer 12 may have the structure shown in Fig. 5. Specifically, the capacitor may have a first electrode 10 having a porous surface 10a, a first dielectric layer 12a located on the porous surface 10a, a second dielectric layer 12b located on the first dielectric layer 12a, a third dielectric layer 12c2 located on the second dielectric layer 12b, a fourth dielectric layer 12d located on the third dielectric layer 12c2, and a second electrode 31 located on the fourth dielectric layer 12d.

[0028] As shown in Fig. 5, the first electrode 10 and the first dielectric layer 12a are in contact with each other. The first dielectric layer 12a and the second dielectric layer 12b may be in contact with each other. The second dielectric layer 12b and the third dielectric layer 12c2 may be in contact with each other. The third dielectric layer 12c2 and the fourth dielectric layer 12d may be in contact with each other. The fourth dielectric layer 12d and the second electrode 31 may be in contact with each other.

[0029] The structure of the dielectric layer 12 of the capacitor according to this embodiment is not limited to the structures shown in Figures 3 to 5. The capacitor according to this embodiment has at least a first electrode 10 having a porous surface 10a, a first dielectric layer 12a located on the porous surface 10a, a second dielectric layer 12b located on the first dielectric layer 12a, and a second electrode 31 located on the second dielectric layer 12b, and the first electrode 10 and the first dielectric layer 12a are in contact with each other.

[0030] For example, only the third dielectric layer 12c1 or the third dielectric layer 12c2 may be included between the second dielectric layer 12b and the second electrode 31. At least one or more dielectric layers may be further included between the fourth dielectric layer 12d and the second electrode 31. Furthermore, the dielectric layers may not be in contact with each other.

[0031] Hereinafter, unless otherwise specified, it is assumed that the first electrode and the first dielectric layer are in contact with each other, the kth dielectric layer and the (k+1)th dielectric layer are in contact with each other (k=1, 2, ..., n), and the (n+1)th dielectric layer is in contact with the second electrode. n is an integer of 1 or more. There is no particular upper limit to n. For example, n may be 10 or less. (n+1) is the number of dielectric layers.

[0032] 1 indicates a surface of the first electrode 10 that is included in the porous portion of the first electrode 10. The porous portion has voids.

[0033] In the following description, "porosity" refers to the proportion of voids in the first electrode 10. A method for measuring voids will be described later. The voids in the porous portion may be filled with a material such as the dielectric layer 12 or the second electrode 31, as shown in FIG. 1 . However, the filled material is not taken into consideration when measuring voids. The voids are calculated by regarding the filled portions as voids.

[0034] An example of a method for measuring the porosity of the first electrode 10 will be described. First, the first electrode 10 is processed into a thin sample having a thickness of 60 nm or less, which allows an observation area of ​​3 μm x 3 μm to be set using an FIB microsampling method. An observation area is set on the thin sample, and a mapping analysis is performed using STEM-EDS. The observation area is set along the cross section shown in FIG. 1. The porosity is then obtained by dividing the area of ​​the portion of the observation area other than the first electrode 10 by the area of ​​the observation area.

[0035] In the first electrode 10, the porous portion is a portion having a higher porosity than the portions other than the porous portion, for example, the portions below and beside the porous portion shown in FIG.

[0036] The porous portion of the first electrode 10 has a large specific surface area, and therefore, the capacitance of the capacitor increases when the first electrode 10 has the porous portion.

[0037] There is no particular limitation on the porosity of the porous portion. From the viewpoint of increasing the capacitance of the capacitor, the porosity of the porous portion may be, for example, 20% or more. From the viewpoint of ensuring the mechanical strength of the porous portion, the porosity of the porous portion may be, for example, 90% or less.

[0038] In the porous portion of the first electrode 10, 5% or more of the entire porous portion may be occupied by portions where the thickness of the substrate between pores (the wall thickness of the porous portion) is 1.2 times or less the thickness (T described below) of the dielectric layer 12. When there are many portions where the wall thickness of the porous portion is small, the capacitance of the capacitor tends to be large.

[0039] In the porous portion of the first electrode 10, 80% or less of the entire porous portion may be occupied by portions where the substrate thickness between pores (wall thickness of the porous portion) is 1.2 times or less the thickness (T described below) of the dielectric layer 12. Fewer portions of the porous portion where the wall thickness is thin facilitates an improvement in the mechanical strength of the porous portion and also facilitates an improvement in the insulation resistance of the capacitor.

[0040] The thickness of the substrate between pores (the wall thickness of the porous portion) may be 50 nm or less and may account for 5% or more of the entire first electrode 10 included in the porous portion. Having many portions with thin walls in the porous portion tends to increase the capacitance of the capacitor.

[0041] The portions of the substrate between pores (the wall thickness of the porous portion) that are 50 nm or less may account for 80% or less of the entire first electrode 10 included in the porous portion. The fewer portions of the porous portion with thin wall thicknesses, the more likely it is that the mechanical strength of the porous portion will be improved, and the more likely it is that the insulation resistance of the capacitor will be improved.

[0042] The thickness of the substrate between the pores (the thickness of the walls of the porous portion) can be confirmed by setting an observation range in the porous portion of a thin film sample obtained by processing the first electrode 10 using the FIB microsampling method and observing it with a TEM.

[0043] (Materials of each electrode and each dielectric layer) The first electrode 10 contains one or more metal elements. There is no particular limit to the total content of the metal elements contained in the first electrode 10. For example, it may be 90 mass% or more, or 99 mass% or more. There is no particular limit to the type of metal element contained in the first electrode 10. For example, it may be one or more selected from Al, Ti, Ta, and Ni, or it may be one or more selected from Al, Ti, and Ta, or it may be Al.

[0044] There is no particular limitation on the thickness of the first electrode 10. For example, it may be 5 μm or more and 500 μm or less.

[0045] The first dielectric layer 12 a includes a first dielectric component, which is an oxide of a metal element included in the first electrode 10 .

[0046] When the first dielectric component is a complex oxide of two or more elements, the complex oxide is converted into a simple oxide of each element. The same applies to the second and third dielectric components described below.

[0047] Assuming that the total amount of metal elements contained in the first electrode 10 is 100 mass%, a metal element whose content in the first electrode 10 is 51 mass% or more is defined as a first electrode metal element. A metal element whose content in the first electrode 10 is 90 mass% or more may be defined as a first electrode metal element, or a metal element whose content in the first electrode 10 is 99 mass% or more may be defined as a first electrode metal element. An oxide of the first electrode metal element is defined as a first dielectric component.

[0048] The content of the first dielectric component in the first dielectric layer 12a is not particularly limited, and may be, for example, 50% by mass or more, 95% by mass or more, or 99.5% by mass or more.

[0049] The composition of elements other than oxygen contained in the first electrode 10 and the composition of elements other than oxygen contained in the first dielectric layer 12a may be identical by 50% or more, by 95% or more, or by 99.5% or more, on a mass basis.

[0050] The first dielectric layer 12a contains a first dielectric component that is an oxide of a metal element contained in the first electrode 10, thereby improving the adhesion of the dielectric layer 12 to the first electrode 10. Furthermore, the mountability of the capacitor is improved. As described above, the first dielectric layer 12a contains a first dielectric component that is an oxide of a metal element contained in the first electrode 10, thereby improving reliability.

[0051] The second dielectric layer 12b includes a second dielectric component different from the first dielectric component. There are no particular restrictions on the total content of the second dielectric component in the second dielectric layer 12b. For example, it may be 10% by mass or more, 50% by mass or more, 95% by mass or more, or 99.5% by mass or more.

[0052] The content of the first dielectric component in the second dielectric layer 12b may be 0% by mass or more and 50% by mass or less, 0% by mass or more and 5% by mass or less, or 0% by mass or more and 0.5% by mass or less. When the content of the first dielectric component in the second dielectric layer 12b is 0% by mass or more and 0.5% by mass or less, the second dielectric layer 12b is considered to be substantially free of the first dielectric component.

[0053] With the above-described configuration, the first dielectric layer 12a and the second dielectric layer 12b have different compositions. The different configurations of the first dielectric layer 12a and the second dielectric layer 12b can reduce the leakage path of the dielectric layer 12. As a result, the voltage resistance of the inductor is improved.

[0054] The type of the second dielectric component is not particularly limited. For example, it may be an oxide of one or more elements selected from Al, Hf, Zr, Ta, Pb, Zn, Si, Ti, and Sr, an oxide of one or more elements selected from Hf, Zr, and Ta, or an oxide of one or more elements selected from Hf and Zr. Alternatively, the second dielectric component may be only the oxide with the highest content in the second dielectric layer.

[0055] The dielectric constant of the first dielectric layer 12a may be lower than that of the second dielectric layer 12b. Specifically, the value obtained by dividing the dielectric constant of the first dielectric layer 12a by the dielectric constant of the second dielectric layer 12b may be 0.8 or less. When the dielectric constant of the first dielectric layer 12a is lower than that of the second dielectric layer 12b, the capacitance of the inductor is likely to be improved.

[0056] The dielectric constant of the first dielectric layer 12a may be considered to be the same as the dielectric constant of the first dielectric component, and the dielectric constant of the second dielectric layer 12b may be considered to be the same as the dielectric constant of the second dielectric component.

[0057] When one or more other dielectric layers are located between the second dielectric layer 12b and the second electrode 31 as shown in FIGS. 4 and 5, there are no particular restrictions on the composition of the other dielectric layers.

[0058] 4, a third dielectric layer 12c1 may be provided, which contains the first dielectric component and has a composition similar to that of the first dielectric layer 12a. The total content of the first dielectric component in the third dielectric layer 12c1 is not particularly limited. For example, it may be 50% by mass or more, 95% by mass or more, or 99.5% by mass or more.

[0059] As shown in FIG. 5, a third dielectric layer 12c2 may be located, which includes a third dielectric component different from both the first and second dielectric components and has a composition different from both the first and second dielectric layers 12a and 12b.

[0060] The type of the third dielectric component is not particularly limited. For example, it may be an oxide of one or more elements selected from Al, Hf, Zr, Ta, Pb, Zn, Si, Ti, and Sr (excluding the first and second dielectric components), an oxide of one or more elements selected from Hf, Zr, and Ta (excluding the first and second dielectric components), or an oxide of one or more elements selected from Hf and Zr (excluding the first and second dielectric components). Furthermore, the third dielectric component may be the oxide with the highest content, excluding the first and second dielectric components, among the oxides contained in the third dielectric layer. The total content of the third dielectric component in the third dielectric layer 12c2 is not particularly limited. For example, it may be 1% by mass or more, 10% by mass or more, 50% by mass or more, 95% by mass or more, or 99.5% by mass or more.

[0061] As shown in Fig. 4, a fourth dielectric layer 12d may be located between the third dielectric layer 12c1 and the second electrode 31. As shown in Fig. 5, a fourth dielectric layer 12d may be located between the third dielectric layer 12c2 and the second electrode 31.

[0062] The composition of the fourth dielectric layer 12d is not particularly limited. As shown in Figures 4 and 5, the fourth dielectric layer 12d may contain a second dielectric component and have a composition similar to that of the second dielectric layer 12b. The composition of the second dielectric layer 12b and the composition of the fourth dielectric layer 12d may be identical to each other by 50% or more, 95% or more, or 99.5% or more, on a mass basis.

[0063] Between the fourth dielectric layer 12d and the second electrode 31, a fifth dielectric layer, a sixth dielectric layer, . . . , an (n+1)th dielectric layer may be further positioned.

[0064] There are no particular restrictions on the material of the second electrode 31. Fig. 1 illustrates an example in which the second electrode 31 is made of a conductive resin.

[0065] (Thickness of First Dielectric Layer) As shown in Fig. 3, the thickness of the first dielectric layer 12a is defined as t1, and the total thickness of the dielectric layers included between the first electrode 10 and the second electrode 31, i.e., the thickness of the dielectric layer 12, is defined as T. In this case, the relationship 0.05 < t1 / T < 0.50 may be satisfied. The thickness of each dielectric layer may be the average thickness of the dielectric layers.

[0066] When t1 / T is greater than 0.05, the effect of forming the first dielectric layer 12a is easily obtained. When t1 / T is less than 0.50, the capacitance of the inductor is easily improved.

[0067] There is no particular limitation on t1, but it may be 0.1 nm or more and 10 nm or less.

[0068] Furthermore, the total thickness of the dielectric layers, the composition of which, by mass, is equal to or greater than 50% of the composition of elements other than oxygen contained in the first electrode 10, is defined as tA, and the relationship 0.05<tA / T<0.50 may be satisfied. When tA / T is less than 0.50, the capacitance of the inductor is likely to be improved.

[0069] Furthermore, tA is not particularly limited, but may be 0.1 nm or more and 15 nm or less, or 0.1 nm or more and 10 nm or less.

[0070] (Method of Manufacturing Capacitor) Hereinafter, as an example of a method of manufacturing a capacitor according to this embodiment, a method of manufacturing the capacitor shown in Figures 1 and 2 will be described. In this case, the case where dielectric layer 12 has a two-layer structure shown in Figure 3 will be described. However, the method of manufacturing a capacitor according to this embodiment is not limited to the method described below.

[0071] First, a metal foil is prepared as the material for the first electrode 10. Next, the portion of the surface of the metal foil where the porous portion will be formed is roughened. There are no particular limitations on the roughening method. For example, an etching method can be used. Another method is to attach metal powder to the surface of the metal foil and sinter it. By roughening a portion of the surface of the metal foil, the roughened portion becomes the porous portion.

[0072] Alternatively, a metal foil may be prepared whose entire surface is porous. Then, a portion of the surface of the metal foil may be planarized to form the non-porous portion. There are no particular limitations on the planarization method. Examples include electrolytic deposition and particle deposition.

[0073] Next, a first dielectric layer 12a is formed on the surface of the metal foil. There are no particular limitations on the method for forming the first dielectric layer 12a. For example, it can be formed by oxidizing the surface of the metal foil. There are no particular limitations on the method for oxidizing the surface of the metal foil. For example, an anodic oxidation method or a thermal oxidation method can be used.

[0074] Next, the second dielectric layer 12b is formed on the first dielectric layer 12a. There are no particular limitations on the method for forming the second dielectric layer 12b. For example, the ALD method, the CVD method, and the mist CVD method can be used.

[0075] Next, the insulating member 21 is formed on the second dielectric layer 12b in a portion other than the portion where the terminal electrode 51 and the terminal electrode 52 will ultimately be formed. There are no particular limitations on the method for forming the insulating member 21.

[0076] Next, the second electrode 31 is formed as needed. There are no particular limitations on the method for forming the second electrode 31. For example, a method of filling the porous portion and its surroundings with a conductive material, or a method of forming a conductive thin film on the surface of the second dielectric layer 12b may be used. It is also possible to not form the second electrode 31 at this stage. In this case, the seed layer 40 described below also serves as the second electrode 31.

[0077] When a conductive material is used for filling, there is no particular limitation on the type of conductive material, and a paste containing a conductive polymer (conductive resin), a carbon paste, or the like may be used as the conductive material.

[0078] When forming a conductive thin film, there is no particular limitation on the method for forming the conductive thin film. For example, the conductive thin film may be formed by a film formation method such as an ALD method, a CVD method, or a mist CVD method. Furthermore, there is no particular limitation on the type of the conductive thin film. The conductive thin film may be a film containing a metal, a film containing a conductive oxide, a film containing a conductive nitride, or the like.

[0079] Next, a portion of the dielectric layer is removed by a method such as reverse sputtering depending on the desired capacitor structure. Then, a seed layer 40 is formed on the portion exposed at this point. There are no particular limitations on the method for forming the seed layer 40. Examples include sputtering and vacuum deposition. Furthermore, if the second electrode 31 is not formed after the insulating member 21 is formed, the portion of the seed layer 40 formed at this point will also serve as the second electrode 31.

[0080] Next, a plating resist is appropriately formed in preparation for forming the terminal electrodes 51, 52. There are no particular restrictions on the type and position of the plating resist, as long as the terminal electrodes 51, 52 are ultimately formed in the desired positions and in the desired shapes.

[0081] Next, electrolytic plating is applied to the portions where no plating resist is formed to form the terminal electrodes 51 and 52 as appropriate.

[0082] Next, the plating resist is removed. There are no particular limitations on the method for removing the plating resist.

[0083] Next, the portion of the seed layer that is exposed to the surface at this stage is removed. There are no particular limitations on the method for removing the seed layer. By removing the seed layer, the terminal electrode 51 and the terminal electrode 52 are no longer electrically connected to each other.

[0084] 1 and 2 is obtained by the above steps. However, the present invention is not limited to the embodiments shown in the drawings. For example, the first electrode may also serve as a terminal electrode.

[0085] The present invention will be described below in more detail with reference to examples, but the present invention is not limited to these examples.

[0086] (Experimental Example 1) To finally fabricate the capacitor shown in Figs. 1 to 3 in which part of the seed layer 40 doubles as the second electrode 31, first, a first electrode 10 was prepared. Specifically, a metal foil was prepared which was made of a simple metal element shown in Table 1 and had porous portions formed only on part of one side of the surface. The thickness of the metal foil was 2 µm. When the metal element was Al, the specific surface area of ​​the porous portion was 0.2 m. 2When the metal element was Ti, the specific surface area of ​​the porous portion was 0.1 m / g. 2 When the metal element was Ta, the specific surface area in the porous portion was 0.1 m / g. 2 / g.

[0087] In all metal foils, the porosity of the porous portions was 50% or more and 80% or less. Portions in which the substrate thickness between pores (wall thickness of the porous portions) was 1.2 times or less the thickness of the dielectric layer 12 accounted for 50% or more and 80% or less of the entire porous portions. Portions in which the substrate thickness between pores (wall thickness of the porous portions) was 50 nm or less accounted for 1% or more and 10% or less of the entire first electrode 10 included in the porous portions.

[0088] Next, a first dielectric layer 12a was formed on the entire surface of the metal foil on which the porous portion was formed. Specifically, the metal foil was oxidized by anodization to form an oxide layer of the metal foil. The thickness t1 of the first dielectric layer 12a was set to the value shown in Table 1.

[0089] Next, a second dielectric layer 12b was formed on the first dielectric layer 12a. Specifically, a dielectric layer made of the second dielectric components shown in Table 1 was formed using the ALD method. The thickness of the second dielectric layer was set to the value shown in Table 1.

[0090] Next, an insulating member made of epoxy resin was formed on the second dielectric layer except for the portion where the two terminal electrodes were to be finally formed.

[0091] Next, the dielectric layer was removed by reverse sputtering from the portion where the dielectric layer 12 was not ultimately present, for example, the portion where the terminal electrode 51 was to be formed. After that, a seed layer 40 made of a Ni—Cu alloy and having a thickness of 500 nm was formed by sputtering. A part of the seed layer 40 also served as the second electrode 31.

[0092] Next, a plating resist was appropriately formed as a preparation for forming the terminal electrodes 51 and 52. Then, the terminal electrodes 51 and 52 made of Cu were formed by electrolytic plating on the portions where the plating resist was not formed.

[0093] (CR Product) The capacitance of the capacitor was measured using a digital LCR meter under the conditions of a reference temperature of 25°C, a frequency of 1.0 kHz, and a measurement voltage of 1.0 Vrms. The insulation resistance was measured using an insulation resistance meter after applying a DC voltage of 0.3 V to the capacitor for 1 minute at a reference temperature of 25°C. The CR product was calculated by multiplying the capacitance (unit: F) by the insulation resistance (unit: Ω). αE + β is expressed as α × 10 +β This means that αE-β is α×10 -β A CR product of 3.0 Ω·F or more was considered good, 3.5 Ω·F or more was considered even better, and 10.0 Ω·F or more was considered particularly good.

[0094] (Mounting Test) Five capacitor samples were prepared for each sample number. They were then observed using an optical microscope for mounting defects, i.e., the presence or absence of defects such as peeling, cracking, and swelling. The number of capacitors with mounting defects (number of defective capacitors) and the percentage of capacitors with mounting defects (defective rate) were measured. The results are shown in Table 1. A defective rate of 21% to 40% was considered good, a defective rate of 1% to 20% was considered even better, and a defective rate of less than 1% was considered particularly good.

[0095] (Adhesion Test) After the formation of the terminal electrode, the porous portion of each sample was subjected to an adhesion test in accordance with JIS K5400-8.5 (JIS D0202). First, 11 incisions were made using a cutter knife, extending from the terminal electrode to the first electrode. Next, the orientation of the capacitor sample was changed by 90°, and 11 more incisions were made.

[0096] Next, cellophane adhesive tape was applied to the cut surface so that it adhered to a depth of about 50 mm, and the tape was rubbed with an eraser to adhere to the coating. After 1 to 2 minutes, the edge of the tape was held at a right angle to the coating surface and instantly peeled off.

[0097] In accordance with JIS K5400-8.5 (JIS D0202), the appearance after peeling off the tape was evaluated on a 6-point scale of 0, 2, 4, 6, 8, or 10. A score of 8 was rated as good, and a score of 10 was rated as even better.

[0098]

[0099] For samples 1 to 9, the first electrode was made of Al, the first dielectric layer was made of Al2O3, and the second dielectric layer was made of HfO2, with the thicknesses of each layer varied. For samples 10 to 16, the first electrode was made of Al, the first dielectric layer was made of Al2O3, and the second dielectric layer was made of ZrO2, with the thicknesses of each layer varied. For samples 17 and 18, the first electrode was changed to Ti and Ta, and the first dielectric layer was made of TiO2 and Ta2O5, respectively. For sample 19, the first electrode was changed to Ni, the first dielectric layer was made of NiO, and the first and second dielectric thicknesses were changed. For sample 20a, the first electrode was changed to NiO5, and the first dielectric layer was made of Ta2O5. For sample 20b, the second dielectric layer was changed to Ta2O5. Sample No. 20c was prepared in the same manner as Sample No. 9, except that the second dielectric layer consisted of Ta2 O5.

[0100] Each of the examples having a predetermined configuration had a good CR product. Furthermore, each example also had good results in the mounting test and adhesion test, indicating good reliability.

[0101] In contrast, Samples 1 to 3, 10 to 12, and 20a, which did not have the first dielectric layer, did not perform well in the mounting test and / or adhesion test. Samples 4, 7, 13, and 15, which did not have the second dielectric layer, showed a decrease in CR product.

[0102] (Experimental Example 2) In sample number 21, a first dielectric layer made of Al2O3 and a second dielectric layer made of HfO2 were formed, as in sample number 9. Furthermore, a layer made of ZrO2 was formed on the second dielectric layer as a third dielectric layer, and a layer made of HfO2 was formed on the third dielectric layer as a fourth dielectric layer. In other words, the third dielectric layer was a layer made of a third dielectric component different from both the first and second dielectric components. The fourth dielectric layer, like the second dielectric layer, was a layer made of the second dielectric component. In Experimental Example 2, all dielectric layers except the first dielectric layer were formed using the ALD method. The test results are shown in Table 2.

[0103]

[0104] Sample No. 21, which has a predetermined configuration, exhibited a good CR product, and also achieved good results in the mounting test and adhesion test. Furthermore, examples having a third dielectric layer, such as sample No. 21, exhibited particularly good CR product compared to examples not having a third dielectric layer, such as sample No. 9. The results of the mounting test were also better for sample No. 21 than for sample No. 9.

[0105] (Experimental Example 3) Sample No. 31 had two layers containing the first dielectric component and two layers containing the second dielectric component. That is, Sample No. 31 had a dielectric layer structure in which layers containing the first dielectric component (Al2O3) and layers containing the second dielectric component (HfO2) were alternately repeated twice. In other words, a layer made of the first dielectric component and having the same thickness as the first dielectric layer was formed as the third dielectric layer. A layer made of the second dielectric component and having the same thickness as the second dielectric layer was formed as the fourth dielectric layer. In Experimental Example 3, all dielectric layers other than the first dielectric layer were formed using the ALD method. Sample No. 31 was fabricated under the same conditions as Sample No. 21, except that the third dielectric component was changed from ZrO2 to Al2O3.

[0106] For sample number 32, the number of repeated layers was three. That is, a fifth dielectric layer made of the first dielectric component and having the same thickness as the first dielectric layer was formed on the fourth dielectric layer of sample number 31. Furthermore, a sixth dielectric layer made of the second dielectric component and having the same thickness as the second dielectric layer was formed on the fifth dielectric layer. The test results for sample numbers 31 and 32 are shown in Table 3.

[0107]

[0108] Both sample numbers 31 and 32, which have the predetermined configuration, had good CR products and also achieved good results in the mounting test and adhesion test. Furthermore, examples having a third dielectric layer, such as sample numbers 31 and 32, had particularly good CR products compared to an example not having a third dielectric layer, such as sample number 9. The results of the mounting test for sample numbers 31 and 32 were also better than for sample number 9.

[0109] REFERENCE SIGNS LIST 10: First electrode 10a: Porous surface 12: Dielectric layer 12a: First dielectric layer 12b: Second dielectric layer 12c1, 12c2: Third dielectric layer 12d: Fourth dielectric layer 21: Insulating member 31: Second electrode 40: Seed layer 51, 52: Terminal electrodes

Claims

1. A capacitor having a first electrode having a porous surface in part, a first dielectric layer located on the porous surface, a second dielectric layer located on the first dielectric layer, and a second electrode located on the second dielectric layer, wherein the first electrode and the first dielectric layer are in contact, the first dielectric layer contains a first dielectric component, which is an oxide of a metal element contained in the first electrode layer, and the second dielectric layer contains the second dielectric component which is different from the first dielectric component.

2. The capacitor according to claim 1, wherein the relative dielectric constant of said first dielectric layer is lower than the relative dielectric constant of said second dielectric layer.

3. The capacitor according to claim 1 or 2, wherein the second dielectric component is an oxide of one or more elements selected from the group consisting of Al, Hf, Zr, Ta, Pb, Zn, Si, Ti and Sr.

4. A capacitor according to any one of claims 1 to 3, wherein said second dielectric layer is substantially free of said first dielectric component.

5. A capacitor according to any one of claims 1 to 4, wherein a third dielectric layer is located between the second dielectric layer and the second electrode.

6. The capacitor of claim 5, wherein said third dielectric layer comprises said first dielectric component.

7. The capacitor of claim 5 or 6, wherein said third dielectric layer comprises a third dielectric component different from said first dielectric component and said second dielectric component.

8. The capacitor of claim 7, wherein said third dielectric component is an oxide of one or more elements selected from the group consisting of Al, Hf, Zr, Ta, Pb, Zn, Si, Ti and Sr.

9. The capacitor according to any one of claims 5 to 8, wherein a fourth dielectric layer is located between the third dielectric layer and the second electrode.

10. The capacitor of claim 9, wherein said fourth dielectric layer comprises said second dielectric component.

11. The capacitor according to any one of claims 1 to 10, wherein t1 is the thickness of the first dielectric layer and T is the total thickness of the dielectric layers included between the first electrode and the second electrode, and the relationship 0.05<t1 / T<0.50 is satisfied.

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