Patent Application
20240038411
The present invention relates to a dielectric, a capacitor, an electrical circuit, a circuit board, and an apparatus.
Capacitors including a metal oxide as a dielectric have been known.
For example, JP 2005-203529 A describes, as a common aluminum electrolytic capacitor, a capacitor element including an anode foil including a dielectric oxide film. The dielectric oxide film is formed on a surface of an aluminum foil by anodic oxidation, the surface having an effective surface area expanded by etching.
JP 2005-203529 A also describes a foil electrode manufacturing method in which aluminum is etched by applying an alternating current in an electrolyte solution. The electrolyte solution is an aqueous solution containing hydrochloric acid as its main component and at least one of sulfuric acid, oxalic acid, and phosphoric acid. In this manufacturing method, a current density at which the alternating current is applied is its maximum at the beginning of the etching, gradually decreases from the maximum, and becomes 0 in the middle of the etching. JP 2005-203529 A describes that according to this manufacturing method, the surface area of a foil electrode can be expanded by formation of minute etch pits at high density, so that the resulting aluminum electrolytic capacitor can have an increased capacitance.
WO 2017/026247 A1 describes a capacitor including a dielectric layer positioned on a porous portion of an electrically conductive porous substrate. WO 2017/026247 A1 describes metal oxides such as Al2O3 as the material of the dielectric layer. The dielectric layer is not an anodic film, and is formed by deposition such as atomic layer deposition.
The techniques described in Patent Literatures 1 and 2 leave room for reexamination from the viewpoint of maintaining the dielectric loss of the capacitor low and increasing the capacitance thereof. Therefore, the present disclosure provides a dielectric advantageous in maintaining the dielectric loss of a capacitor low and increasing the capacitance thereof.
The present disclosure provides a dielectric including a composite oxide having composition represented by CexAl1-xOk, the composite oxide being amorphous, wherein
The present disclosure provides a dielectric advantageous in maintaining the dielectric loss of a capacitor low and increasing the capacitance thereof.
(Findings on which the Present Disclosure is Based)
A porous portion can be formed by etching of a surface of a metallic foil. A capacitor including a metal oxide as a dielectric can be produced by subjecting a metallic foil having a porous portion to a conversion treatment, such as anodic oxidation, to form a metal oxide over a surface of a metal framework of the porous portion. The porous portion having a large surface area allows the capacitor to have a high capacitance. However, the surface area of the porous portion cannot be expanded without limitation. Moreover, in some applications of capacitors, it may be difficult to use the metallic foil having the porous portion as electrodes of the capacitors. It is also important to maintain dielectric losses of capacitors low.
In view of these circumstances, the present inventors made intensive studies to create a new dielectric having properties advantageous in maintaining the dielectric loss of a capacitor low and increasing the capacitance thereof. Through a lot of trial and error, the present inventors have newly found that a material including a given composite oxide including Ce and Al is advantageous in maintaining the dielectric loss of a capacitor low and increasing the capacitance thereof. The present inventors have consequently invented a dielectric and a capacitor of the present disclosure.
(Summary of One Aspect According to the Present Disclosure)
A dielectric according to a first aspect of the present disclosure includes a composite oxide having composition represented by CexAl1-xOk, the composite oxide being amorphous, wherein
The dielectric according to the first aspect is likely to have a high dielectric constant and a low dielectric loss tangent and is advantageous in maintaining the dielectric loss of a capacitor low and increasing the capacitance thereof.
According to a second aspect of the present disclosure, for example, the dielectric according to the first aspect may include a sputtered film. According to the second aspect, a dielectric film for capacitors can be formed by sputtering.
According to a third aspect of the present disclosure, for example, the dielectric according to the first or second aspect may be for a capacitor. According to the third aspect, the dielectric can be included in capacitors.
A capacitor according to a fourth aspect of the present disclosure includes:
According to the fourth aspect, the dielectric is likely to have a high dielectric constant and a low dielectric loss tangent. Consequently, the capacitance of the capacitor is likely to be increased and the dielectric loss of the capacitor is likely to be maintained low.
According to a fifth aspect of the present disclosure, for example, in the capacitor according to the fourth aspect, at least a portion of the first electrode may be a porous portion. According to the fifth aspect, the surface area of the first electrode is likely to be large, and the capacitance of the capacitor is likely to be increased.
According to a sixth aspect of the present disclosure, for example, in the capacitor according to the fourth or fifth aspect, the first electrode may include a valve metal. According to the sixth aspect, a member including a valve metal can be used as the first electrode.
According to a seventh aspect of the present disclosure, for example, in the capacitor according to the sixth aspect, the valve metal may include at least one selected from the group consisting of aluminum, tantalum, and niobium. According to the seventh aspect, a member including any of the above valve metals can be used as the first electrode.
According to an eighth aspect of the present disclosure, for example, in the capacitor according to any one of the fourth to seventh aspects, the second electrode may include at least one selected from the group consisting of aluminum, tantalum, niobium, gold, silver, platinum, and nickel. According to the eighth aspect, a member including any of the above metals can be used as the second electrode.
According to a ninth aspect of the present disclosure, for example, the capacitor according to the fifth aspect may further include an electrolyte in contact with the second electrode. Additionally, the electrolyte may fill the porous portion and may include at least one selected from the group consisting of an electrolyte solution, an electrically conductive polymer, and manganese oxide. According to the ninth aspect, a capacitor including an electrolyte such as an electrolyte solution can be provided.
An electrical circuit according to a tenth aspect of the present disclosure includes the capacitor according to any one of the fourth to ninth aspects. According to the tenth aspect, the capacitor is likely to have a low dielectric loss and a high capacitance, and thus the electrical circuit is likely to have improved properties.
A circuit board according to an eleventh aspect of the present disclosure includes the capacitor according to any one of the fourth to ninth aspects. According to the eleventh aspect, the capacitor is likely to have a low dielectric loss and a high capacitance, and thus the circuit board is likely to have improved properties.
An apparatus according to a twelfth aspect of the present disclosure includes the capacitor according to any one of the fourth to ninth aspects. According to the twelfth aspect, the capacitor is likely to have a low dielectric loss and a high capacitance, and thus the apparatus is likely to have improved properties.
Embodiments of the present disclosure will be described hereinafter with reference to the drawings. The present disclosure is not limited to the following embodiments.
The composite oxide included in the dielectric 10 is, for example, a solid solution of aluminum oxide and cerium oxide.
The value x is desirably 0.475 or more. In such cases, the dielectric 10 is likely to have a higher dielectric constant. The value x may be, in some cases, 0.500 or more, or 0.600 or more.
The value of x is desirably 0.880 or less, more desirably 0.850 or less, even more desirably 0.840 or less, and particularly desirably 0.830 or less. In such cases, the dielectric 10 is likely to have a low dielectric loss tangent.
The dielectric constant of the dielectric 10 is not limited to a particular value. The dielectric constant of the dielectric 10 is, for example, higher than that of Al2O3. The dielectric constant of the dielectric 10 at 10 kHz is, for example, 14.0 or more, desirably 15.0 or more, more desirably 18.0 or more. The dielectric constant of the dielectric 10 at 10 kHz may be, in some cases, 22.0 or more, or 25.0 or more. The dielectric constant of the dielectric 10 at 1 MHz is, for example, 13.0 or more, desirably 14.0 or more, more desirably 15.0 or more, even more desirably 17.0 or more. The dielectric constant of the dielectric 10 at 1 MHz may be, in some cases, 21.0 or more, or 24.0 or more.
The dielectric loss tangent of the dielectric 10 is not limited to a particular value. The dielectric loss tangents of the dielectric 10 at 10 kHz and 1 MHz are each, for example, 0.020 or less. The dielectric loss tangents of the dielectric 10 at 10 kHz and 1 MHz may be, for example, less than 0.020.
As described above, the composite oxide is amorphous. Since the dielectric 10 includes such a composite oxide, occurrence of a leak current in the dielectric 10 is less likely. The reason is presumably because occurrence of a leak current attributable to a grain boundary can be reduced in the composite oxide. As a result, the dielectric 10 is likely to have a high dielectric constant and a low dielectric loss tangent. For example, when a peak whose full width at half maximum is 5° or less and which is distinct from a background is not confirmed in an XRD pattern of the composite oxide at diffraction angles of 10° to 50°, the compound included in the dielectric 10 is concluded to be amorphous.
As shown in
As shown in
The materials of the first electrode 21 and the second electrode 22 are not limited to particular materials. The first electrode 21 and the second electrode 22 include, for example, a metal. For example, the first electrode 21 is desirably formed of an electrically conductive metal. The first electrode 21 includes, for example, a valve metal. Examples of the valve metal include aluminum, tantalum, and niobium. The first electrode 21 includes, for example, at least one selected from the group consisting of aluminum, tantalum, and niobium as the valve metal. The first electrode 21 may include a noble metal such as gold or platinum, or may include nickel.
The second electrode 22 is desirably, for example, an electrically conductive metal. The second electrode 22 may include, for example, a valve metal such as aluminum, tantalum, or niobium, may include a noble metal such as gold, silver, or platinum, or may include nickel. The second electrode 22 includes, for example, at least one selected from the group consisting of aluminum, tantalum, niobium, gold, silver, platinum, and nickel.
As shown in
As shown in
As shown in
In the capacitor 1b, the second electrode 22 is disposed, for example, to fill a space around the porous portion of the first electrode 21.
The second electrode 22 may include, for example, a valve metal such as aluminum, tantalum, or niobium, may include a noble metal such as gold, silver, or platinum, or may include nickel. The second electrode 22 includes, for example, at least one selected from the group consisting of aluminum, tantalum, niobium, gold, silver, platinum, and nickel.
The capacitors 1a and 1b may be electrolytic capacitors. In this case, for example, an electrolyte 23 is disposed between the first electrode 21 and the second electrode 22. The electrolyte 23 may be disposed between the dielectric 10 and the second electrode 22.
The electrolyte includes, for example, at least one selected from the group consisting of an electrolyte solution and an electrically conductive polymer. Examples of the electrically conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives of these. The electrolyte may be made of a manganese compound such as manganese oxide. The electrolyte may include a solid electrolyte.
The electrolyte including the electrically conductive polymer can be formed by performing chemical polymerization, electrolytic polymerization, or both chemical polymerization and electrolytic polymerization of a monomer as a raw material on the dielectric 10. The electrolyte including the electrically conductive polymer may be formed by adhering a solution or dispersion of the electrically conductive polymer onto the dielectric 10.
Hereinafter, the present disclosure will be described in more detail with reference to examples. The examples given below are just examples, and the present disclosure is not limited to them.
(Production of Sample)
Sputtering was performed using Ti and Pt as targets to form a lower electrode being a laminate of a thin Ti film and a thin Pt film on a substrate. The thin Ti film was in contact with the substrate. An alkali-free glass EAGLE XG manufactured by Corning Incorporated was used as the substrate. During the sputtering, an environment of the substrate was maintained at a pressure of 0.3 Pa, and an argon gas occupied the entire volume of the environment. Additionally, the temperature of the substrate was adjusted at 600° C.
Next, a dielectric film of each sample was formed on the lower electrode by co-sputtering using Al2O3 and CeO2 as targets. Co-sputtering conditions were adjusted so that the dielectric film would have a thickness of 100 nm. During the co-sputtering, an environment of the substrate was maintained at a pressure of 0.3 Pa, and an argon gas and an oxygen gas respectively occupied 90% and 10% of the volume of the environment. Additionally, the substrate was not heated. A composition ratio between Al and Ce in each sample was controlled by adjusting a film formation time by opening and closing a shutter. Dielectric films according to Samples 1 to 9 were obtained in this manner. Next, sputtering was performed using Pt as a target to form an upper electrode made of Pt and having a diameter of 104 μm and a thickness of 100 nm on each dielectric film. Samples 1 to 9 were obtained in this manner.
(Identification of Composition)
Before the formation of the upper electrode, the dielectric film according to each sample was subjected to fluorescent X-ray analysis using a fluorescent X-ray analyzer ZSX Primus IV manufactured by Rigaku Corporation, and quantitative analysis of elements in the dielectric film according to each sample was performed. The fundamental parameter method (FP method) was adopted as the quantitative analysis method. A ratio Ce/(Al+Ce) of the number of Ce atoms to the number of Al and Ce atoms in the dielectric film according to each sample was determined from the results of the quantitative analysis. Table 1 shows the results.
(Confirmation for Crystal Phase)
Before the formation of the upper electrode, the dielectric film according to each sample was subjected to X-ray diffraction measurement using an X-ray diffractometer D8 Discover manufactured by Bruker Corporation to obtain an XRD pattern of each dielectric film by 2θ/θ scan.
(Dielectric Properties)
A dielectric constant ε and a dielectric loss tangent tan δ of the dielectric film according to each sample were measured at 10 kHz and 1 MHz using an LCR meter. After measuring a capacitance of each sample, the dielectric constant was determined on the basis of the measurement value of the capacitance, the thickness of the dielectric film, and the areas of the electrodes. An ambient temperature was 25° C. in the measurement. Table 1 shows the results.
As shown in Table 1 and
As shown in Table 1 and
As shown in Table 1 and
The dielectric of the present disclosure can be suitably included in electronic components such as electrolytic capacitors.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2021-076877 | Apr 2021 | JP | national |
This application is a continuation of PCT/JP2022/011753 filed on Mar. 15, 2022, which claims foreign priority of Japanese Patent Application No. 2021-076877 filed on Apr. 28, 2021, the entire contents of both of which are incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2022/011753 | Mar 2022 | US |
| Child | 18486018 | US |
