Capacitor, electric circuit, circuit board, and apparatus

Abstract

A capacitor 1a includes metallic tantalum 10, a conductor 20, and a tantalum oxide film 30. The tantalum oxide film 30 is disposed in contact with the metallic tantalum 10 between said metallic tantalum 10 and the conductor 20. The tantalum oxide film 30 includes a first portion 31 and a second portion 32. The first portion 31 contains fluorine. The second portion 32 is present at a position closer to the metallic tantalum 10 than the first portion 31 in the thickness direction of the tantalum oxide film 30. The concentration of fluorine in the second portion 32 is lower than the concentration of fluorine in the first portion 31 in the tantalum oxide film 30. The ratio d1 / d0 of the thickness d1 of the first portion to the thickness d0 of the tantalum oxide film 30 is greater than 0.4 but not more than 0.8.

Description

Capacitors, electric circuits, circuit boards, and devices

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

[0002] It is known that fluorine-containing tantalum oxide is used in capacitors.

[0003] For example, Non-Patent Document 1 describes that the relative dielectric constant of a polycrystalline TaO2F thin film is 60 at 1 MHz.

[0004] Patent Document 1 describes a solid electrolytic capacitor having a dielectric layer made of fluorine-containing tantalum oxide, which is formed by anodizing a tantalum anode in an aqueous solution containing fluorine ions.

[0005] Patent Document 2 describes a capacitor having a dielectric containing an amorphous tantalum compound containing fluorine and oxygen.

[0006] JP 2005-294402 A Japanese Patent No. 7122617 A

[0007] Journal of Materials Chemistry C, (English), 2020, Issue 14, pp.4680-4684

[0008] The present disclosure provides a capacitor that uses fluorine-containing tantalum oxide and is advantageous in terms of the capacitance of the capacitor and the dielectric loss tangent of the tantalum oxide film.

[0009] A capacitor according to the present disclosure comprises: metallic tantalum; a conductor; and a tantalum oxide film disposed in contact with the metallic tantalum and disposed between the metallic tantalum and the conductor; the tantalum oxide film includes a first portion containing fluorine and a second portion 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; and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film is greater than 0.4 and equal to or less than 0.8.

[0010] According to the present disclosure, it is possible to provide a capacitor that is advantageous in terms of the capacitance of the capacitor and the dielectric loss tangent of the tantalum oxide film while using fluorine-containing tantalum oxide.

[0011] 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 graph showing the results of X-ray diffraction (XRD) measurements of a sample according to Example 1B and metal tantalum. FIG. 5A is a graph showing F in a depth profile obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the sample according to Example 1A. - , TaO 3- , and O - 5B is a graph showing the relationship between the signal intensity of F and the depth in the tantalum oxide film in the TOF-SIMS depth profile of the sample according to Example 1B. - , TaO 3- , and O - 6A is a graph showing the relationship between the signal intensity of F and the depth in the tantalum oxide film in the TOF-SIMS depth profile of the sample according to Comparative Example 1. - , TaO 3- , and O - 6B is a graph showing the relationship between the signal intensity of F and the depth in the tantalum oxide film in the TOF-SIMS depth profile of the sample according to Comparative Example 2. - , TaO 3- , and O - 7A is a graph showing the relationship between the signal intensity of the signal at the capacitance increasing rate and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film for the samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5. FIG. 7B is a graph showing the relationship between the dielectric loss tangent tanδ of the tantalum oxide film and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film for the samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5.

[0012] (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 of the capacitor 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 can be further improved if a dielectric material with a higher dielectric constant could be developed.

[0013] For example, the polycrystalline TaOF thin film described in Non-Patent Document 1 has a high dielectric constant. It is believed that polycrystalline tantalum oxyfluorides have a different crystalline state from tantalum oxide TaO, resulting in increased polarization and a high dielectric constant. As described in Patent Document 2, fluorine-containing tantalum oxides can have a higher dielectric constant than fluorine-free tantalum oxide TaO, even when the tantalum oxide is amorphous. Thus, the use of fluorine-containing tantalum oxides in capacitors is expected to increase the capacitance of the capacitor.

[0014] According to Patent Document 1, the dielectric layer is formed by anodizing an anode made of tantalum in an aqueous solution containing fluorine ions. According to Patent Document 1, the dielectric layer is made of tantalum oxide containing fluorine, so that the equivalent series resistance (ESR) of the electrolytic capacitor is small. On the other hand, according to the studies of the present inventors, the dielectric loss tangent of the film obtained by anodizing tantalum in an aqueous solution containing fluorine ions can be high.

[0015] In view of these circumstances, the present inventors have conducted extensive research into whether it is possible to simultaneously increase the capacitance of a capacitor and maintain a low dielectric loss tangent of the tantalum oxide while using fluorine-containing tantalum oxide as a dielectric. As a result, the present inventors have newly discovered that, from the perspective of achieving both, it is important that the ratio of the thickness of the fluorine-containing portion of the tantalum oxide to the thickness of the tantalum oxide be within a predetermined range. Based on this new finding, the present inventors have completed the capacitor of the present disclosure.

[0016] (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.

[0017] FIG. 1 is a cross-sectional view showing an example of a capacitor according to the present disclosure. As shown in FIG. 1 , a capacitor 1a includes metal tantalum 10, a conductor 20, and a tantalum oxide film 30. The tantalum oxide film 30 is in contact with the metal tantalum 10 and disposed between the metal tantalum 10 and the conductor 20. The tantalum oxide film 30 includes a first portion 31 and a second portion 32. The first portion 31 contains fluorine. The second portion 32 is located closer to the metal tantalum 10 than the first portion 31 in the thickness direction of the tantalum oxide film 30. The second portion 32 is in contact with the metal tantalum 10, for example. In the tantalum oxide film 30, the fluorine concentration in the second portion 32 is lower than the fluorine concentration in the first portion 31. The ratio d1 / d0 of the thickness d1 of the first portion to the thickness d0 of the tantalum oxide film 30 is greater than 0.4 and not greater than 0.8. With this configuration, the capacitance of the capacitor 1a is likely to be high, and the dielectric loss tangent of the tantalum oxide film 30 is unlikely to be high, which makes it easier for the capacitor 1a to exhibit the desired performance.

[0018] When the ratio d1 / d0 is greater than 0.4, the material forming the tantalum oxide film 30 tends to have a high relative dielectric constant, and the capacitance of the capacitor 1a tends to be high. From the viewpoint of improving the capacitance of the capacitor 1a, the ratio d1 / d0 is preferably 0.42 or more, more preferably 0.45 or more, and even more preferably 0.5 or more.

[0019] When the ratio d1 / d0 is 0.8 or less, the dielectric loss tangent of the tantalum oxide film 30 is unlikely to become high. The ratio d1 / d0 may be 0.80 or less, 0.7 or less, or 0.6 or less.

[0020] As shown in FIG. 1, each of the first portion 31 and the second portion 32 is, for example, a layered portion.

[0021] The thickness of the first portion 31 in the tantalum oxide film 30 can be determined according to a depth profile obtained by, for example, TOF-SIMS. For example, in the depth profile obtained by TOF-SIMS, fluoride ions (F - The maximum value of the signal intensity within the range in which the signal of fluoride ion (F) can be accurately analyzed is specified. The reason for limiting the target range in specifying the maximum value is that in analysis by TOF-SIMS or the like, the signal intensity may change in the early stage of analysis due to the influence of surface deposits, etc. Within the target range, - ) is identified, and a thickness d1 in a range where the thickness is equal to or greater than half of this maximum value is determined as the thickness of the first portion 31. Note that the method for determining the thickness of the first portion 31 is not limited to the above-described TOF-SIMS method, and the thickness may also be determined in a similar manner using depth profiles such as RBS and TEM-EDX.

[0022] In the capacitor 1a, the thickness of the tantalum oxide film 30 can be determined according to a depth profile obtained by, for example, TOF-SIMS. For example, in the depth profile, tantalum oxide ions (TaO 3- The maximum value of the signal intensity in the range where the signal of tantalum oxide ions (TaO) can be accurately analyzed is specified. The reason for limiting the target range in specifying the maximum value is as described above. 3- ) is identified, and the thickness d0 in the range where the thickness is equal to or greater than half of this maximum value is determined as the thickness of the tantalum oxide film 30. Note that the method for determining the thickness of the tantalum oxide film 30 is not limited to the above-described TOF-SIMS method, and it may also be determined in the same manner using depth profiles such as RBS and TEM-EDX.

[0023] The above-mentioned TOF-SIMS may be performed on any one location in the in-plane direction of the tantalum oxide film 30, thereby determining the thickness d1 of the first portion 31 and the thickness d0 of the tantalum oxide film 30, and also determining the thickness d2 of the second portion 32 as the value (d0 - d1) obtained by subtracting the thickness d1 from the thickness d0.

[0024] The dielectric loss tangent of the tantalum oxide film 30 is, for example, 0.12 or less at 120 Hz.

[0025] The capacitance increase rate of the capacitor 1a is, for example, 5% or more. 1a and based on the capacitance C0 of the capacitor according to the reference example, (C 1a -C0) / C0 expressed as a percentage. The capacitor according to the reference example is a capacitor provided with a tantalum oxide film that does not contain fluorine instead of the tantalum oxide film 30. 1a and capacitance C0 can be determined, for example, according to the method described in the examples.

[0026] The thickness of the tantalum oxide film 30 is not limited to a specific thickness. For example, the tantalum oxide film 30 is 1 μm or less. In this case, the tantalum oxide film 30 can be formed by anodic oxidation. For example, the tantalum oxide film 30 is an anodic oxide film. For example, the tantalum oxide film 30 is 1 nm or more.

[0027] The first portion 31 may be crystalline or amorphous. Even if the first portion 31 is amorphous, the tantalum oxide film 30 is likely to have a high dielectric constant, and the capacitor 1a is likely to have a high capacitance. For example, the object can be determined to be amorphous when a broad halo pattern is shown in an XRD pattern of the object using Cu-Kα radiation at a diffraction angle 2θ of 10° to 50°.

[0028] The second portion 32 may be crystalline or amorphous.

[0029] The composition of the first portion 31 is not limited to a specific composition as long as the concentration of fluorine in the second portion 32 is lower than the concentration of fluorine in the first portion 31. The first portion 31 does not contain, for example, silicon or titanium. The first portion 31 may contain, for example, TaO x1 F y1 This composition satisfies, for example, the conditions 0<x1<2.5 and 0<y1≦0.40. In this case, the tantalum oxide film 30 is more likely to have a high relative dielectric constant, and the capacitor 1a is more likely to have a high capacitance. In addition, the fluorine contained in the tantalum oxide film 30 is more likely to be prevented from diffusing toward the metal tantalum 10 due to the influence of an electric field, heat, and the like, and the dielectric loss tangent of the tantalum oxide film 30 is less likely to become high.

[0030] The composition of the second portion 32 is not limited to a specific composition as long as the concentration of fluorine in the second portion 32 is lower than the concentration of fluorine in the first portion 31. The second portion 32 does not contain, for example, silicon or titanium. The second portion 32 may contain, for example, TaO x2 F y2 This composition satisfies, for example, the conditions 0<x2<2.5 and 0<y2<0.015. In this case, the fluorine concentration in the tantalum oxide film 30 near the metal tantalum 10 is less likely to become high, and the dielectric loss tangent of the tantalum oxide film 30 is less likely to become high.

[0031] The values ​​of x1, x2, y1, and y2 in the above composition can be determined based on the results of, for example, Rutherford backscattering spectroscopy (RBS). The values ​​of x1, x2, y1, and y2 may also be determined by combining TOF-SIMS with another analytical method such as Rutherford backscattering spectroscopy (RBS).

[0032] 1, the capacitor 1a includes, for example, an electrolyte 40. The electrolyte 40 is disposed between the tantalum oxide film 30 and the conductor 20 in the thickness direction of the tantalum oxide film 30. In this case, the capacitor 1a is provided as, for example, an electrolytic capacitor. In the capacitor 1a, the electrolyte 40 forms, for example, a layer. The electrolyte 40 may be omitted from the capacitor 1a.

[0033] The electrolyte 40 is not limited to a specific electrolyte. For example, the electrolyte 40 includes at least one selected from the group consisting of an electrolytic solution and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte 40 may be a manganese compound such as manganese oxide. The electrolyte 40 may also include a solid electrolyte.

[0034] In the capacitor 1a, the conductor 20 is not limited to a specific material. The conductor 20 may include a valve metal such as aluminum, tantalum, niobium, or bismuth, a noble metal such as gold or platinum, or nickel. The conductor 20 may also include a carbon material such as graphite.

[0035] The method for forming the tantalum oxide film 30 is not limited to any particular method. The tantalum oxide film 30 can be formed, for example, by a method including the following two methods (I) and (II): (I) Anodizing the tantalum metal in a state where the tantalum metal is in contact with a fluorine-free aqueous solution to form an oxide layer in contact with the tantalum metal; (II) Anodizing the tantalum metal in a state where the oxide layer formed in (I) is in contact with a fluorine-containing aqueous solution to obtain the tantalum oxide film 30 including the first portion 31 and the second portion 32 containing fluorine.

[0036] In anodization, for example, a voltage of several volts [V] to several hundred volts [V] is applied between the anode and cathode with an electrolyte disposed between them. For example, a voltage of 5 volts [V] to 300 volts [V] is applied. When metallic tantalum is used as the anode, anions attracted toward the metallic tantalum combine with ionized tantalum to form a chemical film. Impurities such as ions or atoms derived from the electrolyte present around the anode may be incorporated into the chemical film. For this reason, it is virtually impossible to form a film consisting of only two specific elements, such as tantalum and oxygen, in anodization using metallic tantalum as the anode. Therefore, for example, the second portion 32 may contain elements other than tantalum and oxygen, such as fluorine, at a concentration of 0.4% or less by atomic number.

[0037] The ratio d1 / d0 can be adjusted by the magnitude of the voltage applied between the anode and cathode during anodization, the temperature of the electrolyte, and the like. For example, when the voltage applied between the anode and cathode during anodization in (II) above is constant, the ratio d1 / d0 tends to decrease as the voltage applied between the anode and cathode during anodization in (I) above increases. Furthermore, the thickness of the tantalum oxide film 30 tends to increase as the temperature of the electrolyte during anodization increases.

[0038] 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 description thereof will be omitted. The description of capacitor 1a also applies to capacitor 1b, unless technically inconsistent.

[0039] 2, in capacitor 1b, at least a portion of metal tantalum 10 is porous. With this configuration, the surface area of ​​metal tantalum 10 tends to be large, and 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.

[0040] As shown in FIG. 2 , a tantalum oxide film 30 is disposed on the surface of the porous portion of the metal tantalum 10. The tantalum oxide film 30 is formed, for example, by anodization. An electrolyte 40 is disposed so as to fill the voids around the porous portion of the tantalum oxide film 30. The electrolyte 40 includes, for example, at least one selected from the group consisting of manganese oxide, an electrolytic solution, and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte 40 may be a manganese compound such as manganese oxide. The electrolyte 40 may also include a solid electrolyte. In the capacitor 1b, for example, the conductor 20 and the electrolyte 40 form a cathode. The conductor 20 may include, for example, a solidified silver-containing paste, a carbon material such as graphite, or both the solidified material and a carbon material.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] (Additional Notes) From the above description, the following technologies are disclosed. (Technology 1) A capacitor comprising: metallic tantalum; a conductor; and a tantalum oxide film arranged in contact with the metallic tantalum and arranged between the metallic tantalum and the conductor, wherein the tantalum oxide film includes a first portion containing fluorine and a second portion 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 being lower than the fluorine concentration in the first portion, and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film being greater than 0.4 and equal to or less than 0.8. (Technology 2) A capacitor according to Technology 1, wherein the first portion is amorphous. (Technology 3) The first portion is TaO x1 F y1 The capacitor according to Technology 1 or Technology 2, wherein the second portion has a composition represented by the formula: x2 F y2 The capacitor according to any one of Technologies 1 to 3, having a composition represented by the formula: wherein the composition satisfies the conditions of 0<x2<2.5 and 0<y2≦0.015. (Technology 5) The capacitor according to any one of Technologies 1 to 4, further comprising an electrolyte disposed between the tantalum oxide film and the conductor in the thickness direction of the tantalum oxide film. (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) A device comprising the capacitor according to any one of Technologies 1 to 5.

[0045] 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.

[0046] <Example 1A and Example 1B> A flat metal tantalum foil was immersed in a container filled with acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metal tantalum. The acetone adhering to the surface of the metal tantalum was then evaporated, and the surface of the metal tantalum was washed with pure water. The metal tantalum foil was then dried in the atmosphere. In this manner, an anode foil was obtained.

[0047] The anode foil and a platinum foil 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 platinum foil not immersed in the phosphoric acid aqueous solution was connected to the negative terminal of the power supply. In Examples 1A and 1B, a voltage of 50 V and 40 V was applied between the anode foil and the platinum foil, respectively, for a predetermined period of time, forming an oxide layer containing TaO on the surface of the anode foil. The anode foil was removed from the phosphoric acid aqueous solution, washed with pure water, and then dried in the air.

[0048] Next, the anode foil with the oxide layer formed thereon and a platinum foil serving as a counter electrode were placed at a predetermined distance so as to be immersed in a mixed aqueous solution of NaF and sodium phosphate buffer. The portion of the anode foil not immersed in the mixed aqueous solution was connected to the positive terminal of a power supply, and the portion of the platinum foil not immersed in the mixed aqueous solution was connected to the negative terminal of the power supply. A voltage of 90 V was applied between the anode foil and the platinum foil for a predetermined time, forming a fluorine-containing tantalum oxide film. In this way, samples according to Examples 1A and 1B, in which a tantalum oxide film was formed on the surface of metallic tantalum, were obtained.

[0049] <Comparative Example 1> A sample according to Comparative Example 1 was obtained in the same manner as in Example 1A and Example 1B, except that the voltage applied between the anode foil and the platinum foil in forming the oxide layer using the phosphoric acid aqueous solution was changed to 30 V.

[0050] <Comparative Example 2> A sample according to Comparative Example 2 was obtained in the same manner as in Example 1A and Example 1B, except that the voltage applied between the anode foil and the platinum foil in forming the oxide layer using the phosphoric acid aqueous solution was changed to 60 V.

[0051] (X-ray Diffraction Measurement) An XRD pattern was obtained by 2θ / θ scanning of the sample prepared from the sample of Example 1B using an X-ray diffractometer X'Pert PRO manufactured by PANalytical. Cu-Kα radiation was used as the X-ray source, and the voltage was adjusted to 45 kV and the current to 40 mA. The wavelength of Cu-Kα radiation was 0.15418 nm. FIG. 4 is a graph showing the results of X-ray diffraction (XRD) measurement of the sample of Example 1B and metallic tantalum. In FIG. 4, the vertical axis represents the diffraction intensity in arbitrary units, and the horizontal axis represents the diffraction angle 2θ. As shown in FIG. 4, the results of the XRD measurement of the sample of Example 1B confirmed diffraction peaks attributable to metallic tantalum, but an overall broad profile was confirmed. This indicated that the tantalum oxide film of the sample of Example 1B was amorphous. Similarly, this suggests that the tantalum oxide films of the samples of the other examples were amorphous.

[0052] (Elemental Composition Analysis) Using a Rutherford Backscattering Spectroscopy (RBS) device Pelletron 5SDH-2, RBS was performed on a sample prepared from the dielectric film of the sample according to Comparative Example 2. In the RBS, an ion beam was irradiated onto the sample under predetermined conditions to obtain an RBS spectrum. According to the obtained RBS spectrum, the composition of the surface portion of the dielectric layer of the sample according to Comparative Example 2 was TaO. 2.27 F 0.03 In the portion of the dielectric film of the sample according to Comparative Example 2 in contact with metallic tantalum, the molar ratio of the O content to the Ta content was 2.48, and the F content was below the lower analytical limit.

[0053] (TOF-SIMS) Pieces of a predetermined size were cut out from the samples according to Example 1A and Example 1B and Comparative Examples 1 and 2, and samples for TOF-SIMS were prepared by embedding them in resin. Using a TOF-SIMS device TOF.SIMS5 manufactured by ION-TOF, TOF-SIMS was performed on the samples prepared from the samples according to Example 1A and Example 1B and Comparative Examples 1 and 2, and composition analysis was performed in the depth direction of the tantalum oxide film. In TOF-SIMS, a Bi ion beam was used as the primary ion beam. O2 was used as the sputtering ion species.+ 5A and 5B show the F in the depth profiles by TOF-SIMS of the samples according to Example 1A and Example 1B, respectively. - , TaO 3- , and O - 6A and 6B are graphs showing the relationship between the signal intensity of F and the depth in the tantalum oxide film in TOF-SIMS for the samples according to Comparative Example 1 and Comparative Example 2, respectively. - , TaO 3- , and O - 5A, 5B, 6A, and 6B, the vertical axis indicates the signal intensity of each ion, and the horizontal axis indicates the depth in the dielectric film. In addition, in FIGS. 5A, 5B, 6A, and 6B, the signal intensity of fluoride ions (F - ) and tantalum oxide ions (TaO 3- The range used to calculate the maximum value of ( ) is indicated by the black double arrow.

[0054] 5A, 5B, 6A, and 6B, it can be seen that the tantalum oxide films of the samples according to Examples 1A and 1B and Comparative Examples 1 and 2 are formed on metallic tantalum and include a first region with a high fluorine concentration and a second region with a low fluorine concentration. - The thickness d1 of the first region was calculated by specifying the range where the signal intensity of the first region was at least half the maximum value of the signal intensity of the fluoride ion (F - ) signal in the range where accurate analysis was possible (the range indicated by double arrows in Figures 5A, 5B, 6A, and 6B). In this composition analysis, the influence of surface deposits was observed in the range from 0 to about 40 nm in depth, so this range was determined to be the range where fluoride ions (F - ) in the tantalum oxide film 30. 3-) was more than half the maximum value of the signal intensity, and the thickness d0 of the tantalum oxide film 30 was calculated. This allowed the ratio d1 / d0 of the thickness d1 of the first portion to the thickness d0 of the tantalum oxide film to be determined for the samples of Example 1A, Example 1B, and Comparative Example 1 and Comparative Example 2. The results are shown in Table 1.

[0055]

[0056] Example 2A and Example 2B 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 compact. This compact was sintered to obtain an anode body having a porous structure in which one end of the anode lead was embedded.

[0057] Next, the anode body was immersed in an aqueous phosphoric acid solution, and a voltage of 50 V or 40 V was applied to the anode body using an anode lead for a predetermined time to form an oxide layer containing TaO on the surface of the anode body. The anode body was then removed from the aqueous phosphoric acid solution, washed with pure water, and dried in the air.

[0058] Next, the anode body with the oxide layer formed thereon was immersed in a mixed aqueous solution of NaF and sodium phosphate buffer, and a voltage of 90 V was applied to the anode body for a predetermined time using an anode lead. This resulted in the formation of a fluorine-containing tantalum oxide film on the surface of the anode body. The anode body was removed from the mixed solution, washed with pure water, and dried for 10 minutes in a drying oven adjusted to 100°C, yielding samples according to Examples 2A and 2B. The conditions for forming the oxide layer and the conditions for forming the fluorine-containing tantalum oxide film in Examples 2A and 2B were adjusted to be the same as those in Examples 1A and 1B, respectively. Therefore, the ratio d / d of the thickness d of the first portion to the thickness d of the tantalum oxide film in the samples according to Examples 2A and 2B was assumed to be the same as the value of the ratio d / d in the samples according to Examples 1A and 1B, respectively.

[0059] Comparative Example 3 A sample according to Comparative Example 3 was obtained in the same manner as in Examples 2A and 2B, except that the voltage applied to the anode body when forming the oxide layer using an aqueous phosphoric acid solution was changed to 30 V. The conditions for forming the oxide layer and the conditions for forming the fluorine-containing tantalum oxide film in Comparative Example 3 were adjusted to be the same as those for the sample according to Comparative Example 1. Therefore, it was assumed that the ratio d1 / d0 of the thickness d1 of the first portion to the thickness d0 of the tantalum oxide film in the sample according to Comparative Example 3 was the same as the value of the ratio d1 / d0 in the sample according to Comparative Example 1.

[0060] Comparative Example 4 A sample according to Comparative Example 4 was obtained in the same manner as in Examples 2A and 2B, except that the voltage applied to the anode body when forming the oxide layer using an aqueous phosphoric acid solution was changed to 60 V. The conditions for forming the oxide layer and the conditions for forming the fluorine-containing tantalum oxide film in Comparative Example 4 were adjusted to be the same as those for the sample according to Comparative Example 2. Therefore, it was assumed that the ratio d1 / d0 of the thickness d1 of the first portion to the thickness d0 of the tantalum oxide film in the sample according to Comparative Example 4 was the same as the value of the ratio d1 / d0 in the sample according to Comparative Example 2.

[0061] Comparative Example 5 An anode body prepared in the same manner as in Examples 2A and 2B was immersed in an aqueous phosphoric acid solution, and a voltage of 80 V was applied to the anode body using an anode lead for a predetermined period of time to form an oxide layer containing TaO on the surface of the anode body. The anode body was then removed from the aqueous phosphoric acid solution, washed with pure water, and dried for 10 minutes in a drying oven adjusted to 100°C, yielding a sample according to Comparative Example 5. In Comparative Example 5, a fluorine-containing tantalum oxide film was not formed, and therefore the ratio d / d is 0.

[0062] (Capacitance and Dielectric Loss Tangent) The dielectric properties of the samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5 were evaluated by an AC impedance method. In this evaluation, the amplitude was adjusted to 500 mV. In addition, while changing the frequency in the range from 200 Hz to 80 Hz, the capacitance was calculated from the resistance values ​​at five different frequencies within this range, and the capacitance at 120 Hz was calculated from an approximate straight line obtained from the data at the five points. Similarly, the dielectric loss tangent tanδ at 120 Hz was calculated.

[0063] 7A is a graph showing the relationship between the rate of increase in capacity and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film for samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5. FIG. 7B is a graph showing the relationship between the dielectric loss tangent tanδ of the tantalum oxide film and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film for samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5. In FIGS. 7A and 7B , the plots where the ratio d / d is 0 correspond to Comparative Example 5. The rate of increase in capacity is expressed as a percentage, which is the ratio of the difference between the capacity of the sample according to Comparative Example 5 and the capacity of the sample according to Example 2A, Example 2B, Comparative Example 3, and Comparative Example 4 minus the capacity of the sample according to Comparative Example 5.

[0064] The tantalum oxide films of the samples according to Example 2A, Example 2B, Comparative Example 3, Comparative Example 4, and Comparative Example 5 were formed on metallic tantalum with similar surface conditions, and it is believed that there was little difference in the surface area of ​​the tantalum oxide film among the samples. According to Figures 7A and 7B, the smaller the ratio of the thickness of the first portion to the thickness of the tantalum oxide film, the lower the dielectric loss tangent tanδ of the tantalum oxide film, but the lower the rate of capacitance increase. When the ratio d1 / d0 is greater than 0.4 and equal to or less than 0.8, the dielectric loss tangent tanδ of the tantalum oxide film is not significantly higher than the dielectric loss tangent tanδ of the tantalum oxide film of Comparative Example 5. Additionally, when the ratio d1 / d0 is greater than 0.4 and equal to or less than 0.8, it can be said that the capacitance is effectively increased compared to that of the sample according to Comparative Example 5.

[0065] The capacitor according to the present disclosure is advantageous in terms of the capacitance of the capacitor and the dielectric loss tangent of the tantalum oxide film.

Claims

1. A capacitor comprising: metallic tantalum; a conductor; and a tantalum oxide film disposed in contact with the metallic tantalum and disposed between the metallic tantalum and the conductor, wherein the tantalum oxide film includes a first portion containing fluorine and a second portion that 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 being lower than the fluorine concentration in the first portion, and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film being greater than 0.4 and equal to or less than 0.

8.

2. The capacitor according to claim 1, wherein the first portion is amorphous.

3. The first portion is TaO x1 F y1 2. The capacitor according to claim 1, having a composition expressed by the following formula: wherein the composition satisfies the conditions of 0<x1<2.5 and 0<y1≦0.

4.

4. The second portion is TaO x2 F y2 2. The capacitor according to claim 1, having a composition expressed by the following formula: wherein the composition satisfies the conditions 0<x2<2.5 and 0<y2≦0.

015.

5. The capacitor according to claim 1, further comprising an electrolyte disposed between said tantalum oxide film and said conductor in the thickness direction of said tantalum oxide film.

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.

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