Capacitor, electrical circuit, circuit board, device, and method for manufacturing capacitor

Abstract

A capacitor 1a includes tantalum metal 20 and a dielectric layer 10. The dielectric layer 10 covers the tantalum metal and contains tantalum oxide. The dielectric layer 10 contains fluorine and phosphorus. The dielectric layer 10 includes, for example, a first portion 11 and a second portion 12. The first portion 11 is separate from the tantalum metal 20 in the thickness direction of the dielectric layer 10. The second portion 12 is in contact with the tantalum metal 20 in the thickness direction of the dielectric layer 10.

Description

Capacitor, electric circuit, circuit board, device, and method for manufacturing capacitor

[0001] The present disclosure relates to capacitors, electric circuits, circuit boards, devices, and methods for manufacturing capacitors.

[0002] Conventionally, attempts have been made to use fluorine-containing tantalum oxide in capacitors.

[0003] For example, Patent Document 1 describes a capacitor with a dielectric containing an amorphous tantalum compound containing fluorine and oxygen. This dielectric has a higher dielectric constant than a dielectric that does not contain fluorine. This dielectric is obtained by, for example, sputtering or anodic oxidation.

[0004] Patent Document 2 describes a capacitor including metallic tantalum, a conductor, and a tantalum oxide film. The tantalum oxide film is disposed in contact with the metallic tantalum and is disposed between the metallic tantalum and the conductor. The tantalum oxide film includes a first portion containing fluorine and a second portion. The second portion is located closer to the metallic tantalum than the first portion in the thickness direction of the tantalum oxide film. The fluorine concentration in the second portion is lower than the fluorine concentration in the first portion. This capacitor has a reduced dielectric loss tangent. The tantalum oxide film is formed, for example, by anodic oxidation.

[0005] Patent No. 7122617 International Publication No. 2023 / 234343

[0006] The present disclosure provides a capacitor that is advantageous in terms of capacitance and withstand voltage.

[0007] The capacitor of the present disclosure comprises: metallic tantalum; and a dielectric layer covering the metallic tantalum and including tantalum oxide, the dielectric layer including fluorine and phosphorus.

[0008] According to the present disclosure, a capacitor that is advantageous in terms of capacity and withstand voltage can be provided.

[0009] FIG. 1 is a cross-sectional view showing an example of a capacitor according to the present disclosure. FIG. 2 is a cross-sectional view showing another example of a capacitor according to the present disclosure. FIG. 3A is a diagram schematically showing an example of an electric circuit according to the present disclosure. FIG. 3B is a diagram schematically showing an example of a circuit board according to the present disclosure. FIG. 3C is a diagram schematically showing an example of an apparatus according to the present disclosure. FIG. 4 is a flowchart showing an example of a method for manufacturing a capacitor according to the present disclosure. FIG. 5 is a diagram showing F in a depth profile obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) of a sample according to Example 1. - , P.O. 2- , TaO 3- , and O - 6 is a graph showing the relationship between signal intensity and depth of the sample according to Example 2 and metal tantalum by X-ray diffraction (XRD) measurement.

[0010] (Knowledge Forming the Basis of the Present Disclosure) For example, there is a continuous demand for improving the processing performance of electronic devices. The performance of electronic components such as capacitors has a significant impact on the performance of electronic devices incorporating those electronic components. For this reason, it is expected that there will be an increasing need for capacitors that are small and can exhibit high performance. For example, electrolytic capacitors are known as capacitors. In electrolytic capacitors, a dielectric consisting of a thin oxide film is formed on the surface of metallic aluminum or metallic tantalum by chemical conversion treatment of aluminum or tantalum. In electrolytic capacitors, attempts have been made to increase the capacitance mainly by increasing the specific surface area of ​​the dielectric. However, such attempts have shown limitations, and it is believed that the performance of capacitors could be further improved if dielectric materials with higher dielectric constants and higher withstand voltages could be developed.

[0011] According to Patent Document 1, a dielectric containing amorphous tantalum oxide containing fluorine exhibits a higher dielectric constant than a dielectric containing tantalum oxide not containing fluorine. Thus, by using fluorine-containing tantalum oxide in a capacitor, it is expected that the capacitance of the capacitor will be increased.

[0012] According to Patent Document 2, the dielectric layer is obtained by anodizing tantalum in an aqueous solution containing fluorine ions. Patent Document 2 also discloses that there are conditions under which the dielectric loss tangent of the anodic oxide film is increased. Furthermore, Patent Document 2 reveals that anodizing tantalum in a fluorine-free aqueous solution followed by additional anodization in a fluorine-containing aqueous solution reduces the dielectric loss tangent of the fluorine-containing amorphous tantalum oxide dielectric. Thus, by using a specific fluorine-containing tantalum oxide in a capacitor, it is expected that the dielectric loss tangent of the dielectric contained in the capacitor can be reduced. A low dielectric loss tangent of the dielectric is advantageous for reducing electrical energy loss in a capacitor. A high withstand voltage of the capacitor is also important.

[0013] In view of these circumstances, the present inventors have conducted extensive research into a configuration that can increase the capacitance and withstand voltage of a capacitor having a dielectric layer containing fluorine-containing tantalum oxide. As a result, the present inventors have newly discovered that the capacitance and withstand voltage of a capacitor can be increased by providing a dielectric layer with a specific configuration. Based on this new finding, the present inventors have completed the method for manufacturing a capacitor disclosed herein.

[0014] (Embodiments) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The present disclosure is not limited to the following embodiments.

[0015] FIG. 1 is a cross-sectional view showing an example of a capacitor according to the present disclosure. As shown in FIG. 1, the capacitor 1a includes a tantalum metal 20 and a dielectric layer 10. The dielectric layer 10 covers the tantalum metal and contains tantalum oxide. The tantalum oxide is, for example, amorphous. The tantalum oxide may also contain crystalline material. The dielectric layer 10 contains fluorine and phosphorus. This configuration tends to increase the capacitance and withstand voltage of the capacitor 1a. The capacitor 1a is manufactured by, for example, a method including the following (I) and (II). The fluorine contained in the dielectric layer 10 originates from, for example, a fluoride contained in the solution (I) below. At least a portion of the phosphorus contained in the dielectric layer 10 originates from, for example, a pH adjuster contained in the solution (I) below.

[0016] In the capacitor 1a, the dielectric layer 10 has a withstand voltage of, for example, 4V or more, and preferably 10V or more.

[0017] 1 , the dielectric layer 10 includes, for example, a first portion 11 and a second portion 12. The first portion 11 is a portion that is separated from the metal tantalum 20 in the thickness direction of the dielectric layer 10. The second portion 12 is a portion that is in contact with the metal tantalum 20 in the thickness direction of the dielectric layer 10. The first portion 11 and the second portion 12 contain fluorine. The phosphorus concentration in the first portion 11 is higher than the phosphorus concentration in the second portion 12. With this configuration, the capacitance and withstand voltage of the capacitor 1a are likely to be higher.

[0018] The second portion 12 may not contain phosphorus.

[0019] 1, the first portion 11 includes the surface 10p of the dielectric layer 10. The surface 10p is the surface of the dielectric layer 10 that is farther away from the metal tantalum 20 in the thickness direction of the dielectric layer 10. In other words, the surface 10p of the dielectric layer 10 contains phosphorus. With this configuration, the capacitance and withstand voltage of the capacitor 1a are likely to be higher.

[0020] 1, the capacitor 1b includes a first electrode 21 and a second electrode 22. The first electrode 21 includes metal tantalum 20. The dielectric layer 10 is disposed, for example, between the first electrode 21 and the second electrode 22 in the thickness direction of the dielectric layer 10. The first electrode 21 has a principal surface 21p made of metal tantalum 20. One principal surface of the dielectric layer 10 is in contact with the principal surface 21p. The second electrode 22 has, for example, a principal surface 22p parallel to the principal surface 21p. The other principal surface of the dielectric layer 10 is in contact with the principal surface 22p.

[0021] The first electrode 21 may be, for example, an anodizable alloy containing metal tantalum 20 as a main component.

[0022] The second electrode 22 may contain an electrolyte solution or a conductive polymer. The second electrode 22 may also contain a conductor used in an upper electrode that is disposed away from the base material of a circuit board on which the capacitor 1 a is mounted.

[0023] Fig. 2 is a cross-sectional view showing another example of a capacitor according to the present disclosure. Capacitor 1b shown in Fig. 2 has the same configuration as capacitor 1a, except for portions that will be particularly described. Components of capacitor 1b that are the same as or correspond to components of capacitor 1a are given the same reference numerals, and detailed descriptions thereof will be omitted. The description of capacitor 1a also applies to capacitor 1b, unless technically inconsistent.

[0024] 2, in the capacitor 1b, the first electrode 21 contains metal tantalum 20, at least a portion of which is porous. With this configuration, the surface area of ​​the metal tantalum 20 tends to be large, and the capacitor 1b tends to have a high capacitance. Such a porous structure can be formed, for example, by etching a metal foil and sintering a powder.

[0025] The dielectric layer 10 is disposed on the surface of the porous portion of the metal tantalum 20. As described above, the dielectric layer 10 is, for example, an anodic oxide film.

[0026] 2, the capacitor 1b further includes an electrolyte 23. The electrolyte 23 is disposed between the first electrode 21 and the second electrode 22. With this configuration, the capacitor 1b is more likely to have a high capacitance.

[0027] The electrolyte 23 is not limited to a specific electrolyte. For example, the electrolyte 23 includes at least one selected from the group consisting of an electrolytic solution, a solid electrolyte, and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte may also be a manganese compound such as manganese oxide.

[0028] The electrolyte 23 is disposed, for example, so as to fill voids around the porous portion of the metal tantalum 20. The second electrode 22 may include, for example, a solidified silver-containing paste, a carbon material such as graphite, or both the above-mentioned solidified paste and a carbon material.

[0029] 3A is a diagram schematically illustrating an example of an electric circuit according to the present disclosure. The electric circuit 3 includes a capacitor 1a. The electric circuit 3 may be an active circuit or a passive circuit. The electric circuit 3 may be a discharge circuit, a smoothing circuit, a decoupling circuit, or a coupling circuit. Because the electric circuit 3 includes the capacitor 1a, the electric circuit 3 is likely to exhibit the desired performance. For example, noise is likely to be reduced in the electric circuit 3. The electric circuit 3 may also include a capacitor 1b.

[0030] 3B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. As shown in FIG. 3B, the circuit board 5 includes a capacitor 1a. For example, an electric circuit 3 including the capacitor 1a is formed on the circuit board 5. Since the circuit board 5 includes the capacitor 1a, the circuit board 5 is likely to exhibit the desired performance. The circuit board 5 may be an embedded board or a motherboard. The circuit board 5 may also include a capacitor 1b.

[0031] FIG. 3C is a schematic diagram illustrating an example of a device according to the present disclosure. As shown in FIG. 3C , the device 7 includes a capacitor 1a. The device 7 includes, for example, a circuit board 5 including the capacitor 1a. Because the device 7 includes the capacitor 1a, the device 7 is likely to exhibit desired performance. The device 7 may be an electronic device, a communication device, a signal processing device, or a power supply. The device 7 may be a server, an AC adapter, an accelerator, or a flat panel display such as a liquid crystal display (LCD). The device 7 may be a USB charger, a solid-state drive (SSD), an information terminal such as a PC, a smartphone, or a tablet PC, or an Ethernet switch. The device 7 may also include a capacitor 1b.

[0032] In manufacturing a capacitor having a dielectric layer containing fluorine-containing tantalum oxide, it is considered to form the dielectric layer by anodizing using a solution containing fluorine ions, as described in Patent Documents 1 and 2. It is considered advantageous to extend the anodizing time to some extent in order to densify the anodized film and reduce the variation in the properties of the anodized film. Densifying the anodized film can contribute to improving the withstand voltage. However, the inventors' research has newly discovered that forming a dielectric layer containing fluorine-containing tantalum oxide by anodizing for a long period of time does not necessarily result in an increase in the capacitance and withstand voltage of the capacitor.

[0033] In view of these circumstances, the present inventors have conducted extensive research into methods for increasing the capacitance and withstand voltage of a capacitor when a dielectric layer containing fluorine-containing tantalum oxide is formed by long-term anodization. As a result, the present inventors have newly discovered that by performing anodization using a specific solution, a dielectric layer can be formed that can increase the capacitance and withstand voltage of a capacitor even if the anodization time is long. Based on this new finding, the present inventors have completed the method for manufacturing a capacitor disclosed herein.

[0034] 4 is a flowchart showing an example of a method for manufacturing a capacitor according to the present disclosure. As shown in FIG. 4, the capacitor is manufactured by a method including the following steps (I) and (II): (I) adding fluoride ions (F ‐ (II) A solution containing a fluoride containing fluorine-containing fluoride and a pH buffer is brought into contact with metallic tantalum or a tantalum oxide covering metallic tantalum. In this state, the metallic tantalum or the tantalum oxide is brought into contact with the solution, and a dielectric layer covering the metallic tantalum is formed by anodization.

[0035] The solution used for anodization contains a fluoride, which allows the formation of a dielectric layer containing fluorine-containing tantalum oxide. In addition, the solution contains a pH buffer, which makes it easier to increase the capacitance and withstand voltage of the capacitor even if the anodization time is long.

[0036] For example, if the anodization time is long and the solution does not contain a pH buffer, the pH near the surface of the anode may locally decrease during the anodization, which may dissolve the oxide film or increase the fluorine concentration at the interface between the tantalum metal and the dielectric layer. As a result, the insulating properties of the dielectric layer may decrease, making it difficult to manufacture a capacitor with the desired capacitance and withstand voltage.

[0037] During anodization, if the pH of a fluorine-containing solution decreases, hydrogen fluoride may be generated. In this case, measures to deal with the generated hydrogen fluoride are required, which may complicate the manufacturing equipment. According to the above manufacturing method, the pH of the solution is unlikely to decrease due to the pH buffer, and therefore hydrogen fluoride is unlikely to be generated. Therefore, the above manufacturing method is advantageous from the viewpoints of safety and manufacturing costs.

[0038] The pH of the solution is not limited to a specific value as long as a capacitor can be produced. The pH of the solution is, for example, 4 or more and 12 or less. In this case, a capacitor with high performance is likely to be produced. When the pH of the solution is 4 or more, the dielectric layer is likely to have the desired insulating properties, and hydrogen fluoride is unlikely to be generated, which tends to increase the safety of the capacitor production method. When the pH of the solution is 12 or less, metal tantalum can be prevented from dissolving in the solution.

[0039] As long as a capacitor can be manufactured, the concentrations of the fluoride and the pH buffer in the solution are not limited to specific values. The fluoride concentration in the solution is, for example, greater than 0 mol / L and less than or equal to 15 mol / L. The pH buffer concentration in the solution is, for example, greater than 0 mol / L and less than or equal to 1.5 mol / L. In this case, a capacitor with high performance is likely to be manufactured.

[0040] As long as a capacitor can be produced, the fluoride in the solution is not limited to a specific fluoride, and the pH buffer in the solution is not limited to a specific pH buffer. The fluoride may include, for example, at least one selected from the group consisting of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride. Additionally, the pH buffer may include at least one selected from the group consisting of sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, potassium hydrogen phthalate, sodium citrate, sodium hydrogen carbonate, and sodium borate. In this case, a capacitor with high performance is likely to be produced.

[0041] Other examples of fluorides are sodium hydrogen fluoride, potassium hydrogen fluoride, lithium fluoride, cesium fluoride, strontium fluoride, lithium monofluorophosphate, sodium monofluorophosphate, potassium monofluorophosphate, lithium hexafluorophosphate, sodium hexafluorophosphate, potassium hexafluorophosphate, ammonium hexafluorophosphate, sodium tetrafluoroborate, potassium tetrafluoroborate, and ammonium tetrafluoroborate.

[0042] An example of a pH buffering agent, sodium hydrogen phosphate, is an aqueous solution containing sodium dihydrogen phosphate and disodium hydrogen phosphate, and the pH of the solution is adjusted to, for example, about 7. The pH of the solution can also be adjusted by adjusting the ratio of the amount of sodium dihydrogen phosphate added to the amount of disodium hydrogen phosphate added. Another example of a pH buffering agent, sodium hydrogen phosphate, is an aqueous solution containing trisodium phosphate and disodium hydrogen phosphate, and the pH of the solution is adjusted to, for example, about 11. The pH of the solution can also be adjusted by adjusting the ratio of the amount of trisodium phosphate added to the amount of disodium hydrogen phosphate added. The pH buffering agent may also be an aqueous solution containing sodium dihydrogen phosphate and dipotassium hydrogen phosphate, and the pH of the solution can be adjusted to, for example, about 7. The pH of the solution can also be adjusted by adjusting the ratio of the amount of sodium dihydrogen phosphate added to the amount of dipotassium hydrogen phosphate added. As in these examples, the combination of various components functioning as pH buffering agents and the ratio of their contents can be appropriately adjusted within the scope of the capacitor manufacturing method of the present disclosure to prepare the above solution.

[0043] Other examples of pH buffers are as follows: Tris(hydroxymethyl)aminomethane + hydrochloric acid (pH range: 7 to 9) (orthophosphoric acid + glacial acetic acid + boric acid) mixed acid + sodium hydroxide (pH range: 4 to 12) (citric acid + potassium dihydrogen phosphate + boric acid + diethylbarbituric acid + hydrochloric acid) mixed acid + sodium hydroxide (pH range: 4 to 12) (boric acid + citric acid) + trisodium phosphate (pH range: 4 to 12) Potassium hydrogen phthalate + sodium hydroxide (pH range: 4 to 6.2) Potassium dihydrogen phosphate + sodium hydroxide (pH range: 5.8 to 8) (boric acid + potassium chloride) + sodium hydroxide (pH range: 7.8 to 10) 2,4,6-trimethylpyridine + hydrochloric acid (pH range: 6.4 to 8.3) Tris(hydroxymethyl)aminomethane + hydrochloric acid (pH range: 7.2 to 9.1) 2-Amino-2-methyl-1,3-propanediol + hydrochloric acid (pH range: 7.8 to 9.7) 3-[4-(2-hydroxyethyl)-1-piperazinyl]-1-propanesulfonic acid + sodium hydroxide (pH range: 5.3 to 8.1) Potassium hydrogen citrate + sodium hydroxide (pH range: 4 to 6) Succinic acid + borax (pH range: 4 to 5.8) Potassium hydrogen citrate + borax (pH range: 4 to 6) Potassium dihydrogen phosphate + borax (pH range: 5.8 to 9.2) Borax + sodium carbonate (pH range: 9.2 to 11) Hydrochloric acid + sodium carbonate (pH range: 10.2 to 11.2) Disodium hydrogen phosphate + sodium hydroxide (pH range: 11 to 12) Disodium hydrogen phosphate + citric acid (pH range: 4 to 8) Tartaric acid + sodium tartrate (pH range: 4 to 4.5) Lactic acid + sodium lactate (pH range: 4 to 5.3) Acetic acid + sodium acetate (pH range: 4 to 6.2) Ammonium chloride + aqueous ammonia (pH range: 8 to 11) (Sodium diethylbarbiturate + sodium acetate) + hydrochloric acid (pH range: 4 to 9.2) Sodium diethylbarbiturate + hydrochloric acid (pH range: 6.8 to 9.2) N,Sodium N-dimethylglycinate + hydrochloric acid (pH range: 8.6 to 10.6) (Glycine + sodium chloride) + hydrochloric acid (pH range: 4 to 4.6) (Glycine + sodium chloride) + sodium hydroxide (pH range: 8.6 to 12) Sodium citrate + hydrochloric acid (pH range: 4 to 4.9) Sodium citrate + sodium hydroxide (pH range: 5 to 6.7) Borax + hydrochloric acid (pH range: 7.6 to 9.2) Borax + sodium hydroxide (pH range: 9.3 to 12),

[0044] As shown in Fig. 4, for example, in step S11, metallic tantalum or tantalum oxide covering metallic tantalum is immersed in the above-mentioned solution, and the solution comes into contact with the metallic tantalum or tantalum oxide. The tantalum oxide covering metallic tantalum can be obtained, for example, by anodizing metallic tantalum. Next, in step S12, a predetermined voltage is applied between the metallic tantalum and a counter electrode in the solution, with the metallic tantalum and the counter electrode disposed at a predetermined distance, to perform anodization. As a result, a dielectric layer containing fluorine-containing tantalum oxide is formed on the metallic tantalum. Step S12 may be followed by a heat treatment and an anodization treatment under different conditions.

[0045] Next, in step S13, a cathode is formed. The cathode is formed so that the dielectric layer is located between the cathode and the metal tantalum in the thickness direction of the dielectric layer. The cathode is formed, for example, according to a method known as a method for forming a cathode in an electrolytic capacitor. In this manner, a capacitor can be manufactured. After the dielectric layer is formed, terminals are attached and sealing treatment, etc. are performed as necessary.

[0046] (Additional Notes) From the above, the following technologies are disclosed. (Technology 1) A capacitor comprising: metallic tantalum; and a dielectric layer covering the metallic tantalum and containing tantalum oxide, wherein the dielectric layer contains fluorine and phosphorus. (Technology 2) The capacitor according to Technology 1, wherein the dielectric layer comprises a first portion separated from the metallic tantalum in the thickness direction of the dielectric layer and a second portion in contact with the metallic tantalum in the thickness direction of the dielectric layer, wherein the first portion and the second portion contain fluorine, and wherein the concentration of phosphorus in the first portion is higher than the concentration of phosphorus in the second portion. (Technology 3) The capacitor according to Technology 2, wherein the first portion includes the surface of the dielectric layer. (Technology 4) The capacitor according to any one of Technologies 1 to 3, wherein the dielectric layer contains phosphorus on a surface opposite to the metallic tantalum in the thickness direction of the dielectric layer. (Technology 5) The capacitor according to any one of Technologies 1 to 4, wherein the tantalum oxide is amorphous. (Technology 6) An electric circuit comprising the capacitor according to any one of Technologies 1 to 5. (Technology 7) A circuit board comprising the capacitor according to any one of Technologies 1 to 5. (Technology 8) An apparatus comprising the capacitor according to any one of Technologies 1 to 5. (Technology 9) A method for manufacturing a capacitor, comprising: bringing metal tantalum or a tantalum oxide covering the metal tantalum into contact with a solution containing a fluoride containing fluoride ions and a pH buffer; and forming a dielectric layer covering the metal tantalum by anodizing the metal tantalum or the tantalum oxide while the metal tantalum or the tantalum oxide is in contact with the solution. (Technology 10) The method for manufacturing a capacitor according to Technology 9, wherein the pH of the solution is 4 or more and 12 or less. (Technology 11) The method for manufacturing a capacitor according to Technology 9 or 10, wherein the concentration of the fluoride in the solution is greater than 0 mol / L and less than 15 mol / L, and the concentration of the pH buffer in the solution is greater than 0 mol / L and less than 1.5 mol / L.(Technology 12) The method for manufacturing a capacitor according to any one of Technologies 9 to 11, wherein the fluoride includes at least one selected from the group consisting of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride, and the pH buffer includes at least one selected from the group consisting of sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, potassium hydrogen phthalate, sodium citrate, sodium hydrogen carbonate, and sodium borate.

[0047] The present disclosure will be described in more detail below with reference to examples. Note that the following examples are illustrative and the present disclosure is not limited to the following examples.

[0048] (Example 1) A flat plate of metallic tantalum was immersed in acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. The acetone adhering to the surface of the metallic tantalum was then dried by nitrogen blowing, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere to obtain an anode foil.

[0049] The anode foil and a metal tantalum plate serving as a counter electrode were placed at a predetermined distance so that they were immersed in the phosphoric acid aqueous solution. The portion of the anode foil not immersed in the phosphoric acid aqueous solution was connected to the positive terminal of a power supply, and the portion of the metal tantalum plate not immersed in the phosphoric acid aqueous solution was connected to the negative terminal of the power supply. A voltage of 15 V was applied between the anode foil and the metal tantalum plate for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode foil. The anode foil was then removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air.

[0050] Next, the anode foil with the oxide layer formed thereon and a metal tantalum plate as a counter electrode were placed at a predetermined distance so as to be immersed in the fluoride-containing aqueous solution of Example 1. The fluoride-containing aqueous solution of Example 1 contained ammonium hydrogen fluoride and ammonium dihydrogen phosphate and diammonium hydrogen phosphate as pH buffers. The concentration of ammonium hydrogen fluoride in the fluoride-containing aqueous solution of Example 1 was 0.1 mol / L, and the concentration of the buffer in Example 1 was 0.05 mol / L. The fluoride-containing aqueous solution of Example 1 further contained sodium hydroxide. The pH of the fluoride-containing aqueous solution of Example 1 was 6.5. The portion of the anode foil not immersed in the fluoride-containing aqueous solution of Example 1 was connected to the positive electrode of a power supply, and the portion of the metal tantalum plate not immersed in the fluoride-containing aqueous solution was connected to the negative electrode of the power supply. A voltage of 45 V was applied between the anode foil and the metal tantalum plate for 4 hours to form a fluorine-containing tantalum oxide layer. The anode foil was removed from the fluoride-containing aqueous solution, washed with pure water, and then dried in the air. In this way, a sample according to Example 1 was obtained, in which a dielectric layer was formed on the surface of metallic tantalum.

[0051] Comparative Example 1: A flat plate of metallic tantalum was immersed in acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. The acetone adhering to the surface of the metallic tantalum was then dried by nitrogen blowing, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere to obtain an anode foil.

[0052] The anode foil and a metal tantalum plate serving as a counter electrode were placed at a predetermined distance so that they were immersed in the phosphoric acid aqueous solution. The portion of the anode foil not immersed in the phosphoric acid aqueous solution was connected to the positive terminal of a power supply, and the portion of the metal tantalum plate not immersed in the phosphoric acid aqueous solution was connected to the negative terminal of the power supply. A voltage of 15 V was applied between the anode foil and the metal tantalum plate for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode foil. The anode foil was then removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air.

[0053] Next, the anode foil with the oxide layer formed thereon and a metal tantalum plate serving as a counter electrode were placed at a predetermined distance so as to be immersed in a 0.1 mol / L aqueous solution of ammonium bifluoride. The pH of the aqueous solution was 3.0. The portion of the anode foil not immersed in the aqueous solution of ammonium bifluoride was connected to the positive terminal of a power supply, and the portion of the metal tantalum plate not immersed in the aqueous solution of ammonium bifluoride was connected to the negative terminal of the power supply. A voltage of 45 V was applied between the anode foil and the metallic tantalum plate for 4 hours to form a fluorine-containing tantalum oxide layer. The anode foil was removed from the aqueous solution of ammonium bifluoride, washed with pure water, and then dried in the air. In this manner, a sample according to Comparative Example 1 was obtained, in which a dielectric layer was formed on the surface of the metallic tantalum.

[0054] (Evaluation of Capacity and Dielectric Loss Tangent) The samples according to Example 1 and Comparative Example 1 were mounted in a plate electrode evaluation cell manufactured by BAS Corporation, and the capacitance and dielectric loss tangent were evaluated according to the AC impedance method using a sulfuric acid aqueous solution as the electrolyte and platinum as the counter electrode. The values ​​of the capacitance and dielectric loss tangent were measured at 120 Hz. The evaluation was carried out at room temperature (20°C to 30°C). The results are shown in Table 1.

[0055] (Evaluation of Withstand Voltage) The samples according to Example 1 and Comparative Example 1 were mounted in a plate electrode evaluation cell manufactured by BAS Corporation, and the withstand voltage was evaluated by chronovoltammetry using a phosphoric acid aqueous solution as the electrolyte and platinum as the counter electrode. The constant current value in chronovoltammetry was 1 μA, and the voltage value after 5 minutes was taken as the withstand voltage value. The evaluation was carried out at room temperature (20° C. to 30° C.). The results are shown in Table 1.

[0056] As shown in Table 1, the sample according to Comparative Example 1 had a large leakage current and a low withstand voltage, so that the capacitance and dielectric loss tangent could not be evaluated. Therefore, it is difficult to say that the dielectric layer of the sample according to Comparative Example 1 is suitable for a capacitor. On the other hand, the sample according to Example 1 exhibited a capacitance, dielectric loss tangent, and withstand voltage that are desirable from the viewpoint of use as a capacitor. A comparison between Example 1 and Comparative Example 1 suggests that, when a long-term anodizing treatment is performed using a fluoride-containing aqueous solution, it is advantageous from the viewpoint of increasing the capacitance and withstand voltage of the capacitor for the fluoride-containing aqueous solution to contain a pH buffer.

[0057]

[0058] (Examples 2 to 7) A flat plate of metallic tantalum was immersed in acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. The acetone adhering to the surface of the metallic tantalum was then dried by nitrogen blowing, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere to obtain an anode foil.

[0059] The anode foil and a metal tantalum plate as a counter electrode were placed at a predetermined distance so that they were immersed in the phosphoric acid aqueous solution. The portion of the anode foil that was not immersed in the phosphoric acid aqueous solution was connected to the positive electrode of a power supply, and the portion of the metal tantalum plate that was not immersed in the phosphoric acid aqueous solution was connected to the negative electrode of the power supply. A voltage of 18 V was applied between the anode foil and the metal tantalum plate for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode foil. The anode foil was then removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air.

[0060] Next, the anode foil with the oxide layer formed thereon and a metal tantalum plate as a counter electrode were placed at a predetermined distance so as to be immersed in the fluoride-containing aqueous solution of each Example shown in Table 2. Table 2 shows the type and concentration of fluoride and pH buffer in the fluoride-containing aqueous solution of each Example 2 to Example 7, as well as the pH of the fluoride-containing aqueous solution of each Example 2 to Example 7. The portion of the anode foil not immersed in the fluoride-containing aqueous solution of each Example was connected to the positive electrode of a power supply, and the portion of the metal tantalum plate not immersed in the fluoride-containing aqueous solution was connected to the negative electrode of the power supply. A voltage of 45 V was applied between the anode foil and the metal tantalum plate for 4 hours to form a fluorine-containing tantalum oxide layer. The anode foil was removed from the fluoride-containing aqueous solution, washed with pure water, and then dried in the air.

[0061] Next, the anode foil with the fluorine-containing oxide layer formed thereon was subjected to a heat treatment in air at 260°C for 2 hours. After the heat treatment, the anode foil was allowed to cool to room temperature. The anode foil and a metal tantalum plate serving as a counter electrode were then placed at a predetermined distance so as to be immersed in a phosphoric acid aqueous solution. The portion of the anode foil not immersed in the phosphoric acid aqueous solution was connected to the positive terminal of a power supply, and the portion of the metal tantalum plate not immersed in the phosphoric acid aqueous solution was connected to the negative terminal of the power supply. A voltage of 44.5 V was applied between the anode foil and the metal tantalum plate for 30 minutes to perform repair chemical conversion. The anode foil was removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in air. In this manner, samples according to Examples 2 to 7, in which a dielectric layer was formed on the surface of the metal tantalum, were obtained.

[0062] (Comparative Example 2) A flat plate of metallic tantalum was immersed in acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. The acetone adhering to the surface of the metallic tantalum was then dried by nitrogen blowing, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere to obtain an anode foil.

[0063] The above-mentioned anode foil and a metal tantalum plate as a counter electrode were placed at a predetermined distance so as to be immersed in the phosphoric acid aqueous solution. The portion of the anode foil not immersed in the phosphoric acid aqueous solution was connected to the positive terminal of a power supply, and the portion of the metal tantalum plate not immersed in the phosphoric acid aqueous solution was connected to the negative terminal of the power supply. A voltage of 40 V was applied between the anode foil and the metal tantalum plate for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode foil. The anode foil was then removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air. In this way, a sample according to Comparative Example 2 was obtained, in which a dielectric layer was formed on the surface of the metal tantalum.

[0064] (Evaluation of Q Value) The samples according to Examples 2 to 7 and Comparative Example 2 were mounted in a plate electrode evaluation cell manufactured by BAS Corporation, and the capacity was evaluated according to the AC impedance method using a sulfuric acid aqueous solution as the electrolyte and platinum as the counter electrode. The capacity value was measured at 120 Hz. The evaluation was carried out at room temperature (20°C to 30°C).

[0065] The samples according to Examples 2 to 7 and Comparative Example 2 were mounted in a plate electrode evaluation cell manufactured by BAS Corporation, and the withstand voltage was evaluated by chronovoltammetry using a phosphoric acid aqueous solution as the electrolyte and a platinum counter electrode. The constant current value in chronovoltammetry was 1 μA, and the voltage value after 5 minutes was taken as the withstand voltage value. The evaluation was carried out at room temperature (20°C to 30°C).

[0066] The Q value, which is the product of the capacitance and the withstand voltage, was calculated, and the Q values ​​of the samples according to Examples 2 to 7 were compared with the Q value of the sample according to Comparative Example 2 (Q ref This normalization allows us to evaluate the improvement in capacitor performance that comes from the inclusion of fluorine in the dielectric layer.

[0067] As shown in Table 2, the capacitance and withstand voltage of the samples according to Examples 2 to 7 could be measured, and the Q values ​​of these samples confirmed that the inclusion of fluorine in the dielectric layer improved the performance of the capacitor.

[0068]

[0069] (Examples 8 to 13) One longitudinal end of a rod-shaped anode lead made of metallic tantalum was embedded in metallic tantalum powder, and the tantalum powder was molded into a rectangular parallelepiped shape to obtain a compact. This compact was sintered to obtain an anode body having a porous structure in which one end of the anode lead was embedded.

[0070] The above-mentioned anode body and a similar metallic tantalum porous body as a counter electrode were placed at a predetermined distance so as to be immersed in an aqueous phosphoric acid solution. The rod portion of the anode body that was not immersed in the aqueous phosphoric acid solution was connected to the positive electrode of a power supply, and the rod portion of the metallic tantalum porous body that was not immersed in the aqueous solution was connected to the negative electrode of the power supply. A voltage of 50 V was applied between the anode body and the metallic tantalum porous body for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode body. The anode body was then removed from the aqueous solution, washed with pure water, and then dried in the air.

[0071] Next, the anode body with the oxide layer formed thereon and a porous metal tantalum body serving as a counter electrode were placed at a predetermined distance so as to be immersed in the fluoride-containing aqueous solution of each Example shown in Table 3. Table 3 shows the type and concentration of fluoride and pH buffer in the fluoride-containing aqueous solution of Examples 8 to 13, as well as the pH of the fluoride-containing aqueous solution of Examples 8 to 13. The rod portion of the anode body that was not immersed in the fluoride-containing aqueous solution was connected to the positive electrode of a power supply, and the rod portion of the porous metal tantalum that was not immersed in the fluoride-containing aqueous solution was connected to the negative electrode of the power supply. A voltage of 95 V was applied between the anode body and the porous metal tantalum body for 4 hours, forming a fluorine-containing tantalum oxide layer. The anode body was removed from the fluoride-containing aqueous solution, washed with pure water, and then dried in the air.

[0072] Next, the anode body with the fluorine-containing oxide layer formed thereon was subjected to a heat treatment in air at 200°C for 30 minutes. After the heat treatment, the anode body was allowed to cool to room temperature, and a porous metal tantalum body serving as a counter electrode was placed at a predetermined distance so as to be immersed in an aqueous phosphoric acid solution. The rod portion of the anode body not immersed in the aqueous phosphoric acid solution was connected to the positive electrode of a power supply, and the rod portion of the porous metal tantalum body not immersed in the aqueous phosphoric acid solution was connected to the negative electrode of the power supply. A voltage of 94 V was applied between the anode body and the porous metal tantalum body for 30 minutes to perform repair chemical conversion. The anode body was removed from the aqueous phosphoric acid solution, washed with pure water, and then dried in air. In this manner, samples according to Examples 8 to 13, in which a dielectric layer was formed on the surface of the metallic tantalum, were obtained.

[0073] Comparative Example 3 One longitudinal end of a rod-shaped anode lead made of metallic tantalum was embedded in metallic tantalum powder, and the tantalum powder was molded into a rectangular parallelepiped shape to obtain a compact. This compact was sintered to obtain an anode body having a porous structure in which one end of the anode lead was embedded.

[0074] The above anode body and a similar porous metal tantalum body serving as a counter electrode were arranged at a predetermined distance so that they were immersed in the phosphoric acid aqueous solution. The rod portion of the anode body that was not immersed in the phosphoric acid aqueous solution was connected to the positive electrode of a power supply, and the rod portion of the porous metal tantalum that was not immersed in the phosphoric acid aqueous solution was connected to the negative electrode of the power supply. A voltage of 80 V was applied between the anode body and the porous metal tantalum body for 13 hours, forming an oxide layer containing tantalum oxide on the surface of the anode body. The anode body was then removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air. In this manner, a sample according to Comparative Example 3 was obtained, in which a dielectric layer was formed on the surface of the metallic tantalum.

[0075] (Evaluation of Q Value) The capacitance was evaluated by AC impedance method using the samples according to Examples 8 to 13 and Comparative Example 3 as the working electrode, an aqueous sulfuric acid solution as the electrolyte, and a porous metal tantalum as the counter electrode. The capacitance value was measured at 120 Hz. The evaluation was carried out at room temperature (20°C to 30°C).

[0076] The withstand voltage was evaluated by chronovoltammetry using the samples of Examples 8 to 13 and Comparative Example 3 as the working electrode, a phosphoric acid aqueous solution as the electrolyte, and a SUS plate as the counter electrode. The constant current value in chronovoltammetry was 1 μA, and the value after 5 minutes was taken as the withstand voltage value. The evaluation was performed at room temperature (20°C to 30°C).

[0077] The Q value, which is the product of the capacitance and the withstand voltage, was calculated, and the Q values ​​of the samples according to Examples 8 to 13 were compared with the Q value of the sample according to Comparative Example 3 (Q ref This normalization allows us to evaluate the improvement in capacitor performance that comes from the inclusion of fluorine in the dielectric layer.

[0078] As shown in Table 3, the capacitance and withstand voltage could be measured for the samples according to Examples 8 to 13, and the Q values ​​of these samples confirmed that the inclusion of fluorine in the dielectric layer improved the performance of the capacitor.

[0079]

[0080] (Elemental Composition Analysis) A fragment of a predetermined size was cut out from the sample according to Example 1 and embedded in resin to prepare a sample for time-of-flight secondary ion mass spectrometry (TOF-SIMS). Using a TOF-SIMS device TOF.SIMS5 manufactured by ION-TOF, the sample prepared from the sample according to Example 1 was subjected to TOF-SIMS measurement, and composition analysis in the depth direction of the dielectric layer was performed. In TOF-SIMS, a Bi ion beam was used as the primary ion beam. O was used as the sputtering ion species. 2+ was used.

[0081] FIG. 5 shows the F in the depth profile by TOF-SIMS of the sample according to Example 1. - , P.O. 2- , TaO 3- , and O -5 is a graph showing the relationship between signal intensity and depth of ions. In FIG. 5, the vertical axis represents the signal intensity of each ion, and the horizontal axis represents the depth in the dielectric layer. From FIG. 5, it can be seen that the dielectric layer of the sample according to Example 1 exists from its surface to a depth of approximately 90 nm and is formed on metallic tantalum. The fluorine-containing portion was present from the surface of the dielectric layer to a depth of approximately 90 nm. On the other hand, the phosphorus-containing portion was present from the surface of the dielectric layer to a depth of approximately 26 nm. The fluorine-containing portion may include a portion with a high fluorine concentration on the surface side of the dielectric layer and a portion with a low fluorine concentration on the metallic tantalum side. On the other hand, to fully demonstrate the effect of adding fluorine to improve capacitor performance, it is advantageous for fluorine to be present throughout the entire thickness direction of the dielectric layer. In this case, the anodization conditions are adjusted so that fluorine is present in the so-called inner layer of the anodic oxide film. Therefore, a fluorine-containing portion may exist in a deeper region of the anodic oxide film, closer to the metallic tantalum than the portion containing fluorine and phosphorus. The sample according to Example 1 is an example in which fluorine is present as deep as possible, and the areas with low fluorine concentration are reduced as much as possible, while there are areas containing fluorine closer to the metal tantalum than the areas containing fluorine and phosphorus.

[0082] (X-ray Diffraction) An XRD pattern was obtained by 2θ / θ scanning of the sample prepared from the sample according to Example 2 using an X-ray diffractometer, X'Pert PRO, manufactured by PANalytical. Cu-Kα radiation was used as the X-ray source, with the voltage adjusted to 45 kV and the current adjusted to 40 mA. The wavelength of Cu-Kα radiation was 0.15418 nm. FIG. 6 is a graph showing the results of X-ray diffraction (XRD) measurements of the sample according to Example 2 and metallic tantalum. In FIG. 6, the vertical axis represents the diffraction intensity in arbitrary units, and the horizontal axis represents the diffraction angle 2θ. As shown in FIG. 6, the XRD measurement results of the sample according to Example 2 confirmed diffraction peaks attributable to metallic tantalum, but an overall broad profile was observed. This indicates that the fluorine-containing tantalum oxide contained in the dielectric layer of the sample according to Example 2 is amorphous. Considering the sample preparation conditions, etc., it is believed that the fluorine-containing tantalum oxide contained in the dielectric layers of the samples according to the other Examples is also amorphous.

[0083] The capacitor of the present disclosure is useful when high capacitance and withstand voltage are required.

Claims

1. A capacitor comprising: metallic tantalum; and a dielectric layer comprising tantalum oxide overlying said metallic tantalum, said dielectric layer comprising fluorine and phosphorus.

2. The capacitor according to claim 1, wherein the dielectric layer comprises a first portion that is separated from the metallic tantalum in the thickness direction of the dielectric layer and a second portion that is in contact with the metallic tantalum in the thickness direction of the dielectric layer, the first portion and the second portion contain fluorine, and the concentration of phosphorus in the first portion is higher than the concentration of phosphorus in the second portion.

3. The capacitor according to claim 2, wherein the first portion includes a surface of the dielectric layer.

4. The capacitor according to claim 1, wherein the dielectric layer contains phosphorus on a surface opposite to the metal tantalum in the thickness direction of the dielectric layer.

5. The capacitor according to claim 1, wherein the tantalum oxide is amorphous.

6. An electric circuit comprising a capacitor according to any one of claims 1 to 5.

7. A circuit board comprising a capacitor according to any one of claims 1 to 5.

8. A device comprising a capacitor according to any one of claims 1 to 5.

9. A method for manufacturing a capacitor, comprising: bringing a solution containing a fluoride containing fluoride ions and a pH buffer into contact with metallic tantalum or a tantalum oxide covering metallic tantalum; and forming a dielectric layer covering the metallic tantalum by anodization while the metallic tantalum or the tantalum oxide is in contact with the solution.

10. The method for manufacturing a capacitor according to claim 9, wherein the pH of the solution is 4 or more and 12 or less.

11. The method for manufacturing a capacitor according to claim 9, wherein the concentration of the fluoride in the solution is greater than 0 mol / L and less than or equal to 15 mol / L, and the concentration of the pH buffer in the solution is greater than 0 mol / L and less than or equal to 1.5 mol / L.

12. The method for manufacturing a capacitor according to claim 9, wherein the fluoride includes at least one selected from the group consisting of sodium fluoride, potassium fluoride, ammonium hydrogen fluoride, and ammonium fluoride, and the pH buffer includes at least one selected from the group consisting of sodium hydrogen phosphate, potassium hydrogen phosphate, ammonium hydrogen phosphate, potassium hydrogen phthalate, sodium citrate, sodium hydrogen carbonate, and sodium borate.

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