Capacitor, circuit, circuit board and device

Abstract

A capacitor 1a is provided with a tantalum metal 10, a conductor 20, and a tantalum oxide film 30. And a tantalum oxide film (30) that is in contact with the tantalum metal (10) and is disposed between the tantalum metal (10) and the conductor (20). The tantalum oxide film 30 includes a first site 31 and a second site 32. The first site 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. In the tantalum oxide film (30), the concentration of fluorine in the second region (32) is lower than the concentration of fluorine in the first region (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 0.8 or less.

Description

Capacitors, circuits, circuit boards and equipment Technical Field

[0001] This disclosure relates to capacitors, circuits, circuit boards, and devices. Background Technology

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

[0003] For example, Non-Patent Document 1 describes a polycrystalline TaO2F thin film with a relative permittivity of 60 at 1 MHz.

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

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

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent Application Publication No. 2005-294402

[0009] Patent Document 2: Japanese Patent No. 7122617

[0010] Non-patent literature

[0011] Non-patent literature 1: Journal of Materials Chemistry C, (English), 2020, Issue 14, pp. 4680-4684 Summary of the Invention

[0012] This disclosure provides a capacitor that uses fluorine-containing tantalum oxide and is advantageous from the viewpoints of capacitance and dielectric loss tangent of the tantalum oxide film.

[0013] The capacitor disclosed herein comprises tantalum metal, a conductor, and a tantalum oxide film.

[0014] The tantalum oxide film is disposed in contact with the metallic tantalum and between the metallic tantalum and the conductor.

[0015] The tantalum oxide film includes a first portion containing fluorine and a second portion located closer to the metallic tantalum in the thickness direction of the tantalum oxide film than the first portion.

[0016] The concentration of fluorine in the second part is lower than the concentration of fluorine in the first part.

[0017] The ratio of the thickness of the first portion to the thickness of the tantalum oxide film is greater than 0.4 and less than 0.8.

[0018] According to this disclosure, it is possible to provide a capacitor that uses fluorine-containing tantalum oxide and is advantageous from the viewpoints of capacitance and dielectric loss tangent of the tantalum oxide film. Attached Figure Description

[0019] Figure 1 is a cross-sectional view showing an example of the capacitor of this disclosure.

[0020] Figure 2 is a cross-sectional view showing another example of the capacitor of this disclosure.

[0021] Figure 3A is a schematic diagram illustrating an example of a circuit according to the present disclosure.

[0022] Figure 3B is a schematic diagram illustrating an example of a circuit board according to the present disclosure.

[0023] Figure 3C is a schematic diagram illustrating an example of the device of this disclosure.

[0024] Figure 4 is a graph showing the results of X-ray diffraction (XRD) measurements of the sample and tantalum metal in Example 1B.

[0025] Figure 5A shows the depth profile of the sample from Example 1A obtained by time-of-flight secondary ion mass spectrometry (TOF-SIMS). - TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film.

[0026] Figure 5B shows the depth distribution of the sample from Example 1B obtained by TOF-SIMS in the F-axis. - TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film.

[0027] Figure 6A shows the depth distribution of the sample in Comparative Example 1 obtained by TOF-SIMS, in terms of F. - TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film.

[0028] Figure 6B shows the depth distribution of the sample in Comparative Example 2 obtained by TOF-SIMS, in terms of F. - TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film.

[0029] Figure 7A is a graph showing the relationship between the capacitance rise rate and the ratio of the thickness of the first part to the thickness of the tantalum oxide film for the samples of Example 2A, Example 2B, Comparative Example 3, Comparative Example 4 and Comparative Example 5.

[0030] Figure 7B is a graph showing the relationship between the dielectric loss tangent tanδ of the tantalum oxide film of the samples of Examples 2A, 2B, Comparative Example 3, Comparative Example 4 and Comparative Example 5 and the ratio of the thickness of the first part to the thickness of the tantalum oxide film. Detailed Implementation

[0031] (The insights that form the basis of this disclosure)

[0032] For example, there is a continuous demand for improved processing performance in electronic devices. The performance of electronic components such as capacitors significantly impacts the performance of electronic devices in which these components are assembled. Therefore, the demand for small capacitors capable of high performance is anticipated to be high. Electrolytic capacitors are known as examples of capacitors. In electrolytic capacitors, a dielectric consisting of a thin oxide film is formed on the surface of metallic aluminum or tantalum through a chemical conversion process. In electrolytic capacitors, the primary approach to increasing capacitance is to increase the specific surface area of ​​the dielectric. However, limitations have been identified in these attempts, suggesting that further improvements in capacitor performance could be achieved by developing dielectric materials with higher dielectric constants.

[0033] For example, the polycrystalline TaO2F thin film described in Non-Patent Document 1 has a high relative permittivity. It is believed that the polycrystalline form of tantalum fluoride oxide has a different crystallization state than tantalum oxide Ta2O5, thereby increasing polarization and resulting in a high relative permittivity. As described in Patent Document 2, fluorine-containing tantalum oxides, even when amorphous, can have a higher relative permittivity than fluorine-free tantalum oxide Ta2O5. Thus, by using fluorine-containing tantalum oxides in capacitors, an increase in capacitor capacitance can be expected.

[0034] According to Patent Document 1, the dielectric layer is formed by anodizing an anode made of tantalum in an aqueous solution containing fluoride ions. According to Patent Document 1, the dielectric layer is made of fluorine-containing tantalum oxide, thereby resulting in a small equivalent series resistance (ESR) for the electrolytic capacitor. On the other hand, according to the inventors' research, the dielectric loss tangent of the film sometimes obtained by anodizing tantalum in an aqueous solution containing fluoride ions is high.

[0035] In view of this situation, the inventors have repeatedly and diligently studied whether it is possible to improve the capacitance of a capacitor and maintain a low dielectric loss tangent when using fluorine-containing tantalum oxide as a dielectric. As a result, the inventors have made a new discovery: from the viewpoint of simultaneously 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 itself is within a specified range. Based on this new insight, the inventors have completed the capacitor of this disclosure.

[0036] (Implementation Method)

[0037] The embodiments of this disclosure will now be described with reference to the accompanying drawings. This disclosure is not limited to the following embodiments.

[0038] Figure 1 is a cross-sectional view showing an example of the capacitor of this disclosure. As shown in Figure 1, the capacitor 1a includes a tantalum metal 10, a conductor 20, and a tantalum oxide film 30. The tantalum oxide film 30 is in contact with the tantalum metal 10 and disposed between the tantalum metal 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 tantalum metal 10 in the thickness direction of the tantalum oxide film 30 than the first portion 31. The second portion 32 is in contact with the tantalum metal 10, for example. In 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. 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 less than 0.8. With this configuration, the capacitance of the capacitor 1a is easily increased, and the dielectric loss tangent of the tantalum oxide film 30 is difficult to increase. Therefore, the capacitor 1a easily achieves the desired performance.

[0039] With a ratio d1 / d0 greater than 0.4, the material constituting the tantalum oxide film 30 tends to have a high relative permittivity, and the capacitance of capacitor 1a tends to be high. From the viewpoint of improving the capacitance of capacitor 1a, a ratio d1 / d0 of 0.42 or higher is preferred, more preferably 0.45 or higher, and even more preferably 0.5 or higher.

[0040] With a d1 / d0 ratio below 0.8, the dielectric loss tangent of the tantalum oxide film 30 is difficult to increase. The d1 / d0 ratio can be below 0.80, below 0.7, or below 0.6.

[0041] As shown in Figure 1, the first part 31 and the second part 32 are each, for example, layered parts.

[0042] The thickness of the first portion 31 in the tantalum oxide film 30 can be determined, for example, based on the depth distribution obtained by TOF-SIMS. For instance, in the depth distribution obtained by TOF-SIMS, the thickness of the fluoride ion (F...) portion is determined... -The maximum signal intensity within the range that can be accurately analyzed from the signal of fluoride ions is defined. The reason for limiting the range to be considered in determining the maximum value is that, in analyses based on TOF-SIMS, the signal intensity sometimes changes in the early stages of analysis due to the influence of surface deposits, etc. The fluoride ion (F...) range is then used to determine the maximum value. - The thickness d1 of the range where the maximum value of the signal strength is greater than or equal to half of that maximum value is determined as the thickness of the first part 31. Furthermore, the method for determining the thickness of the first part 31 is not limited to the TOF-SIMS-based method described above; for example, it can also be determined similarly in depth distributions such as RBS and TEM-EDX.

[0043] In capacitor 1a, the thickness of the tantalum oxide film 30 can be determined, for example, based on the depth distribution obtained by TOF-SIMS. For instance, in the depth distribution, the thickness of the tantalate ion (TaO) film can be determined. 3- The maximum signal intensity within the range that can be accurately analyzed from the signal is determined. The reasons for limiting the scope of the target range in determining the maximum value are as described above. Tantalate ions (TaO) are then identified within the aforementioned target range. 3- The thickness d0 of the tantalum oxide film 30 is defined as the range of signal strengths that are at least half of the maximum value. Furthermore, the method for determining the thickness of the tantalum oxide film 30 is not limited to the TOF-SIMS-based method described above; it can also be determined similarly using depth distributions such as RBS and TEM-EDX.

[0044] The above-mentioned TOF-SIMS can be performed at any point in the in-plane direction of the tantalum oxide film 30. Thus, the thickness d1 of the first part 31 and the thickness d0 of the tantalum oxide film 30 can be determined. As the value obtained by subtracting the thickness d1 from the thickness d0 (d0-d1), the thickness d2 of the second part 32 can also be determined.

[0045] The dielectric loss tangent of the tantalum oxide film 30 is, for example, less than 0.12 at 120 Hz.

[0046] The rate of increase in capacitance of capacitor 1a is, for example, 5% or more. The rate of increase in capacitance is based on the capacitance C of capacitor 1a. 1a And the capacitance C0 of the capacitor in the reference example, expressed as a percentage (C 1a -C0) / C0. The capacitor in the reference example is a capacitor that has a fluorine-free tantalum oxide film instead of the tantalum oxide film 30. Capacitance C 1a The capacitance C0 can be determined, for example, according to the method described in the embodiments.

[0047] The thickness of the tantalum oxide film 30 is not limited to a specific thickness. For example, the tantalum oxide film 30 may be 1 μm or less. In this case, the tantalum oxide film 30 can be formed by anodic oxidation. The tantalum oxide film 30 may be, for example, an anodic oxide film. The tantalum oxide film 30 may be, for example, 1 nm or more.

[0048] The first part 31 can be crystalline or amorphous. Even if the first part 31 is amorphous, the tantalum oxide film 30 tends to have a high relative permittivity, and the capacitor 1a tends to have a high capacitance. For example, if the XRD pattern of an object obtained using Cu-Kα rays at a diffraction angle 2θ of 10° to 50° shows a wide halo pattern, it can be determined that the object is amorphous.

[0049] The second part 32 can be crystalline or amorphous.

[0050] The composition of the first portion 31 is not limited to a specific composition, provided that the concentration of fluorine in the second portion 32 is lower than that in the first portion 31. For example, the first portion 31 may not contain silicon or titanium. The first portion 31 may, for example, contain TaO. x1 F y1 The composition is represented by the condition 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 permittivity, and the capacitor 1a is more likely to have a high capacitance. In addition, it is easier to prevent the fluorine contained in the tantalum oxide film 30 from diffusing into the metallic tantalum 10 due to the influence of electric field and heat, and the dielectric loss tangent of the tantalum oxide film 30 is less likely to become high.

[0051] The composition of the second portion 32 is not limited to a specific composition, provided that the concentration of fluorine in the second portion 32 is lower than that in the first portion 31. For example, the second portion 32 may not contain silicon or titanium. The second portion 32 may, for example, contain TaO. x2 F y2 The composition is represented. This composition, for example, satisfies the conditions 0 < x² < 2.5 and 0 < y² < 0.015. In this case, the concentration of fluorine in the portion of the tantalum oxide film 30 near the metallic tantalum 10 is less likely to increase, and the dielectric loss tangent of the tantalum oxide film 30 is less likely to increase.

[0052] The values ​​of x1, x2, y1, and y2 in the above components can be determined, for example, based on the results of Rutherford backscattering analysis (RBS). Alternatively, the values ​​of x1, x2, y1, and y2 can be determined by combining TOF-SIMS with other analytical methods such as Rutherford backscattering analysis (RBS).

[0053] As shown in Figure 1, 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, capacitor 1a is provided, for example, as an electrolytic capacitor. In capacitor 1a, the electrolyte 40 is, for example, formed as a layer. The electrolyte 40 may also be omitted in capacitor 1a.

[0054] Electrolyte 40 is not limited to a specific electrolyte. Electrolyte 40 may include, for example, at least one selected from electrolytes and conductive polymers. Examples of conductive polymers are polypyrrole, polythiophene, polyaniline, and their derivatives. Electrolyte 40 may also be a manganese compound such as manganese oxide. Electrolyte 40 may comprise a solid electrolyte.

[0055] In capacitor 1a, the conductor 20 is not limited to a specific material. The conductor 20 may include valve metals such as aluminum, tantalum, niobium, and bismuth, precious metals such as gold and platinum, and nickel. The conductor 20 may also include carbon materials such as graphite.

[0056] The method for forming the tantalum oxide film 30 is not limited to a specific method. The tantalum oxide film 30 may be formed, for example, by a method comprising (I) and (II) below.

[0057] (I) Anodic chemical conversion of tantalum metal is performed while it is in contact with a fluorine-free aqueous solution to form an oxide layer in contact with the tantalum metal.

[0058] (II) Anodic chemical conversion of tantalum metal is performed while the oxide layer formed in (I) above is in contact with an aqueous solution containing fluorine to obtain a tantalum oxide film 30 containing a first part 31 and a second part 32 containing fluorine.

[0059] In anodic chemical conversion, 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 tantalum is used as the anode, anions attracted toward the tantalum combine with the ionized tantalum to form a chemical conversion film. At this time, ions or atoms of impurities from the electrolyte present around the anode are sometimes incorporated into the chemical conversion film. Therefore, in anodic chemical conversion using tantalum as the anode, it is practically impossible to form a film composed of only two specific elements, such as tantalum and oxygen. Therefore, for example, in the second part 32, other elements such as fluorine, besides tantalum and oxygen, may be present at a concentration of less than 0.4% on an atomic basis.

[0060] The ratio d1 / d0 can be adjusted by factors such as the magnitude of the voltage applied between the anode and cathode during anodic chemical conversion and the temperature of the electrolyte. For example, when the voltage applied between the anode and cathode is constant during anodic chemical conversion in (II) above, the larger the voltage applied between the anode and cathode during anodic chemical conversion in (I) above, the easier it is for the ratio d1 / d0 to decrease. In addition, the higher the temperature of the electrolyte during anodic chemical conversion, the easier it is for the thickness of the tantalum oxide film 30 to increase.

[0061] Figure 2 is a cross-sectional view showing another example of the capacitor of this disclosure. The capacitor 1b shown in Figure 2 is constructed in the same manner as capacitor 1a, except where specifically described. The same reference numerals are used to denote the constituent elements of capacitor 1b that are the same as or correspond to those of capacitor 1a, and detailed descriptions are omitted. The description of capacitor 1a applies to capacitor 1b as long as it is not technically contradictory.

[0062] As shown in Figure 2, in capacitor 1b, at least a portion of the tantalum metal 10 is porous. With this configuration, the surface area of ​​the tantalum metal 10 can easily be increased, and capacitor 1b can easily have a high capacitance. Such a porous structure can be formed, for example, by etching of a metal foil or sintering of powder.

[0063] As shown in Figure 2, a tantalum oxide film 30 is disposed on the surface of the porous portion of the tantalum metal 10. The tantalum oxide film 30 is formed, for example, by anodic chemical conversion. An electrolyte 40 is disposed to fill the voids surrounding the porous portion of the tantalum oxide film 30. The electrolyte 40 comprises, for example, at least one selected from manganese oxide, an electrolyte, and a conductive polymer. Examples of conductive polymers are polypyrrole, polythiophene, polyaniline, and their derivatives. The electrolyte 40 may also be a manganese compound such as manganese oxide. The electrolyte 40 may comprise a solid electrolyte. In the capacitor 1b, a cathode is constructed, for example, using a conductor 20 and an electrolyte 40. The conductor 20 may comprise, for example, a cured material containing silver paste, a carbon material such as graphite, or both of the above-mentioned cured materials and carbon materials.

[0064] Figure 3A is a schematic diagram illustrating an example of a circuit according to the present disclosure. Circuit 3 includes capacitor 1a. Circuit 3 can be an active circuit or a passive circuit. Circuit 3 can be a discharge circuit, a smoothing circuit, a decoupling circuit, or a coupling circuit. Because circuit 3 includes capacitor 1a, circuit 3 can easily achieve the desired performance. For example, noise can be easily reduced in circuit 3. Circuit 3 can also include capacitor 1b.

[0065] Figure 3B is a schematic diagram illustrating an example of a circuit board according to the present disclosure. As shown in Figure 3B, the circuit board 5 includes a capacitor 1a. For example, circuit 3 including capacitor 1a is formed in the circuit board 5. Because the circuit board 5 includes capacitor 1a, the circuit board 5 can easily achieve the desired performance. The circuit board 5 can be an embedded board or a motherboard. The circuit board 5 may also include capacitor 1b.

[0066] Figure 3C is a schematic diagram illustrating an example of the device of this disclosure. As shown in Figure 3C, device 7 includes capacitor 1a. Device 7 may include, for example, a circuit board 5 containing capacitor 1a. Because device 7 includes capacitor 1a, device 7 can easily achieve the desired performance. Device 7 can be an electronic device, a communication device, a signal processing device, or a power supply device. Device 7 can be a server, an AC adapter, an accelerator, or a flat panel display such as a liquid crystal display (LCD). Device 7 can be a USB charger, a solid-state drive (SSD), an information terminal such as a PC, smartphone, or tablet PC, or an Ethernet switch. Device 7 may also include capacitor 1b.

[0067] (Postscript)

[0068] Based on the above records, the following technologies are disclosed.

[0069] (Technology 1)

[0070] A capacitor comprising tantalum metal, a conductor, and a tantalum oxide film,

[0071] The tantalum oxide film is disposed in contact with the metallic tantalum and between the metallic tantalum and the conductor.

[0072] The tantalum oxide film includes a first portion containing fluorine and a second portion located closer to the metallic tantalum in the thickness direction of the tantalum oxide film than the first portion.

[0073] The concentration of fluorine in the second part is lower than the concentration of fluorine in the first part.

[0074] The ratio of the thickness of the first portion to the thickness of the tantalum oxide film is greater than 0.4 and less than 0.8.

[0075] (Technology 2)

[0076] The capacitor according to technology 1

[0077] The first part is amorphous.

[0078] (Technology 3)

[0079] The capacitor according to technique 1 or 2

[0080] The first part has TaO x1 F y1 The composition of the representation,

[0081] The composition satisfies the conditions 0 < x1 < 2.5 and 0 < y1 ≤ 0.4.

[0082] (Technology 4)

[0083] The capacitor according to any one of techniques 1 to 3

[0084] The second part has TaO x2 F y2 The composition of the representation,

[0085] The composition satisfies the conditions 0 < x2 < 2.5 and 0 < y2 ≤ 0.015.

[0086] (Technology 5)

[0087] The capacitor according to any one of techniques 1 to 4

[0088] It also includes an electrolyte disposed between the tantalum oxide film and the conductor in the thickness direction of the tantalum oxide film.

[0089] (Technology 6)

[0090] A circuit comprising a capacitor as described in any one of techniques 1 to 5.

[0091] (Technology 7)

[0092] A circuit board comprising a capacitor as described in any one of techniques 1 to 5.

[0093] (Technology 8)

[0094] An apparatus comprising a capacitor as described in any one of techniques 1 to 5.

[0095] Example

[0096] The present disclosure is further described in detail below through examples. Furthermore, the following examples are illustrative and the present disclosure is not limited to these examples.

[0097] <Example 1A and Example 1B>

[0098] The surface of the tantalum metal is cleaned by ultrasonic cleaning for 10 minutes while immersing a flat sheet of acetone in a container. Then, the acetone adhering to the surface of the tantalum metal is evaporated, and the surface of the tantalum metal is rinsed with pure water. Finally, the tantalum metal is dried in atmospheric air. This yields the anode foil.

[0099] The aforementioned anode foil and platinum foil, serving as the counter electrode, are arranged at a predetermined interval while immersed in an aqueous phosphoric acid solution. The portion of the anode foil not immersed in the phosphoric acid solution is connected to the positive terminal of a power supply, and the portion of the platinum foil not immersed in the phosphoric acid solution is connected to the negative terminal of the power supply. In Examples 1A and 1B, voltages of 50V and 40V, respectively, are applied between the anode foil and the platinum foil for predetermined times, forming an oxide layer containing Ta₂O₅ on the surface of the anode foil. The anode foil is then removed from the phosphoric acid solution, washed with pure water, and then dried in air.

[0100] Next, the anode foil with the oxide layer formed and the platinum foil serving as the counter electrode were arranged at a predetermined interval by immersing them 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 the 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 90V was applied between the anode foil and the platinum foil for a predetermined time to form a fluorine-containing tantalum oxide film. This yielded samples of Examples 1A and 1B, in which a tantalum oxide film was formed on the surface of metallic tantalum.

[0101] <Comparative Example 1>

[0102] In the formation of the oxide layer using an aqueous phosphoric acid solution, the voltage applied between the anode foil and the platinum foil was changed to 30V. Otherwise, the process was carried out in the same manner as in Examples 1A and 1B, resulting in the sample of Comparative Example 1.

[0103] <Comparative Example 2>

[0104] In the formation of the oxide layer using an aqueous phosphoric acid solution, the voltage applied between the anode foil and the platinum foil was changed to 60V. Otherwise, the process was carried out in the same manner as in Examples 1A and 1B, resulting in the sample of Comparative Example 2.

[0105] (X-ray diffraction measurement)

[0106] Using an X'Pert PRO X-ray diffractometer manufactured by PANalytical, XRD patterns based on 2θ / θ scans were obtained for samples prepared from the sample of Example 1B. Cu-Kα rays were used as the X-ray source, with the voltage adjusted to 45 kV and the current adjusted to 40 mA. The wavelength of the Cu-Kα rays was 0.15418 nm. Figure 4 is a graph showing the X-ray diffraction (XRD) measurements of the sample of Example 1B and metallic tantalum. In Figure 4, the vertical axis represents the diffraction intensity in arbitrary units, and the horizontal axis represents the diffraction angle 2θ. As shown in Figure 4, based on the XRD measurements of the sample of Example 1B, diffraction peaks originating from metallic tantalum were confirmed, but a broad profile was observed overall. Therefore, it is shown that the tantalum oxide film of the sample of Example 1B is amorphous. Similarly, this suggests that the tantalum oxide films of the samples of other examples are amorphous.

[0107] (Elemental composition analysis)

[0108] The sample prepared from the dielectric film of Comparative Example 2 was subjected to RBS analysis using a Pelletron 5SDH-2 Rutherford backscattered spectroscopy (RBS) apparatus. In RBS, the sample was irradiated with an ion beam under specified conditions to obtain the RBS spectrum. Based on the obtained RBS spectrum, the surface region of the dielectric layer of the sample in Comparative Example 2 was composed of TaO. 2.27 F 0.03 In the dielectric film of Comparative Example 2, at the contact point between the dielectric film and tantalum metal, the molar ratio of O to Ta was 2.48, and the F content was below the analytical limit.

[0109] (TOF-SIMS)

[0110] Prescribed fragments were cut from the samples of Examples 1A and 1B, as well as Comparative Examples 1 and 2, and TOF-SIMS samples were prepared by resin embedding. TOF-SIMS analysis of the depth direction composition of the tantalum oxide film was performed on the samples prepared from Examples 1A and 1B, as well as Comparative Examples 1 and 2, using a TOF.SIMS5 TOF-SIMS apparatus manufactured by ION-TOF Corporation. In TOF-SIMS, a Bi ion beam was used as the primary ion beam. O2 was used as the sputtering ion type. + Figures 5A and 5B respectively show the depth distribution of the samples from Example 1A and Example 1B obtained by TOF-SIMS, in terms of F. - TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film. Figures 6A and 6B respectively show the F signal intensity in TOF-SIMS of Comparative Example 1 and Comparative Example 2.- TaO 3- and O - The graph shows the relationship between signal intensity and depth in the tantalum oxide film. In Figures 5A, 5B, 6A, and 6B, the vertical axis represents the signal intensity of each ion, and the horizontal axis represents the depth in the dielectric film. Additionally, in Figures 5A, 5B, 6A, and 6B, black arrows at both ends indicate the direction of fluoride ion concentration (F₂). - ) and tantalate ions (TaO) 3- The range used is the maximum value of ).

[0111] Based on Figures 5A, 5B, 6A, and 6B, it can be understood that the tantalum oxide films of the samples from Examples 1A and 1B, as well as Comparative Examples 1 and 2, are formed on metallic tantalum and contain a first region with a high concentration of fluorine and a second region with a low concentration of fluorine. From Figures 5A, 5B, 6A, and 6B, fluorine ions (F) in the first region are identified. - The thickness d1 of the first part is calculated by taking the signal strength of the fluoride ion (F) signal at a value greater than half of its maximum value. - The maximum signal intensity is defined as the range within which the signal can be accurately analyzed (in Figures 5A, 5B, 6A, and 6B, indicated by the arrows at both ends). In this compositional analysis, the influence of surface deposits, etc., was observed in the depth range of 0 to approximately 40 nm; therefore, this range was not used to determine the concentration of fluoride ions (F). - The maximum signal strength was determined. Furthermore, the tantalate ions (TaO) in the tantalum oxide film 30 were identified. 3- The thickness d0 of the tantalum oxide film 30 was calculated by taking the signal strength of the sample from Example 1A and Example 1B, and Comparative Example 1 and Comparative Example 2, at least half of the maximum value. The thickness d0 of the tantalum oxide film was then calculated. The results are shown in Table 1.

[0112]

[0113] <Examples 2A and 2B>

[0114] With one end of an anode lead made of rod-shaped tantalum metal embedded in tantalum powder along its length, the tantalum powder is shaped into a cuboid to obtain a molded body. This molded body is then sintered to obtain a porous anode body with the anode lead embedded at one end.

[0115] Next, the anode body is immersed in an aqueous phosphoric acid solution, and a voltage of 50V or 40V is applied to the anode body using the anode lead for a specified time, forming an oxide layer containing Ta2O5 on the surface of the anode body. The anode body is then removed from the aqueous phosphoric acid solution, washed with pure water, and dried in the atmosphere.

[0116] Next, the anode body with the oxide layer formed was immersed in a mixed aqueous solution of NaF and sodium phosphate buffer, and a voltage of 90V was applied to the anode body for a specified time using the 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 then removed from the mixed solution and washed with pure water, and dried in a drying oven at 100°C for 10 minutes to obtain samples of 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. Therefore, it is assumed that the ratio d1 / d0 of the thickness d1 of the first portion in the samples of Examples 2A and 2B to the thickness d0 of the tantalum oxide film is the same as the value of the ratio d1 / d0 in the samples of Examples 1A and 1B.

[0117] <Comparative Example 3>

[0118] Except that the voltage applied to the anode body when using an aqueous phosphoric acid solution to form the oxide layer was changed to 30V, the same procedures as in Examples 2A and 2B were followed to obtain the sample of Comparative Example 3. 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 in the sample of Comparative Example 1. Therefore, it is assumed that the ratio d1 / d0 of the thickness d1 of the first portion in the sample of Comparative Example 3 to the thickness d0 of the tantalum oxide film is the same as the value of the ratio d1 / d0 in the sample of Comparative Example 1.

[0119] <Comparative Example 4>

[0120] The voltage applied to the anode body when using an aqueous phosphoric acid solution to form the oxide layer was changed to 60V. Otherwise, the process was the same as in Examples 2A and 2B, resulting in Comparative Example 4. 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 in Comparative Example 2. Therefore, it is assumed that the ratio d1 / d0 of the thickness d1 of the first portion in Comparative Example 4 to the thickness d0 of the tantalum oxide film is the same as the value of d1 / d0 in the sample according to Comparative Example 2.

[0121] <Comparative Example 5>

[0122] An anode body prepared in the same manner as in Examples 2A and 2B was immersed in an aqueous phosphoric acid solution. A voltage of 80V was applied to the anode body using an anode lead for a specified time, forming an oxide layer containing Ta₂O₅ on the surface of the anode body. The anode body was then removed from the aqueous phosphoric acid solution and washed with pure water. It was then dried in a drying oven at 100°C for 10 minutes to obtain the sample of Comparative Example 5. In Comparative Example 5, no fluorine-containing tantalum oxide film was formed; therefore, the ratio d₁ / d₀ in Comparative Example 5 was 0.

[0123] (Tangent of capacitance and dielectric loss)

[0124] The dielectric properties of the samples from Examples 2A, 2B, Comparative Examples 3, 4, and 5 were evaluated using the AC impedance method. In this evaluation, the amplitude was adjusted to 500 mV. Furthermore, while varying the frequency within the range of 200 Hz to 80 Hz, the capacitance was calculated based on the resistance values ​​at five different frequencies within this range. The capacitance at 120 Hz was calculated using an approximate straight line obtained from the data at these five points. Similarly, the dielectric loss tangent tanδ at 120 Hz was calculated.

[0125] Figure 7A is a graph showing the relationship between the capacitance rise rate and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film for the samples of Examples 2A, 2B, Comparative Examples 3, 4, and 5. Figure 7B is a graph showing the relationship between the dielectric loss tangent tanδ of the tantalum oxide film for the samples of Examples 2A, 2B, 3, 4, and 5 and the ratio of the thickness of the first portion to the thickness of the tantalum oxide film. In Figures 7A and 7B, the plot where the ratio d1 / d0 is 0 corresponds to Comparative Example 5. The capacitance rise rate is expressed as a percentage as the ratio of the difference obtained by subtracting the capacitance of the sample of Comparative Example 5 from the capacitance of the samples of Examples 2A, 2B, 3, and 4 to the capacitance of the sample of Comparative Example 5.

[0126] The tantalum oxide films of the samples in Examples 2A, 2B, Comparative Examples 3, 4, and 5 were formed on metallic tantalum with the same surface condition, and it was assumed that the surface area of ​​the tantalum oxide films of each sample was not significantly different. According to Figures 7A and 7B, the smaller the ratio of the thickness of the first region to the thickness of the tantalum oxide film, the lower the dielectric loss tangent tanδ of the tantalum oxide film, but the capacitance increase rate also decreases. If the ratio d1 / d0 is greater than 0.4 and less than 0.8, the dielectric loss tangent tanδ of the tantalum oxide film is not as high as that of the tantalum oxide film of Comparative Example 5. Furthermore, if the ratio d1 / d0 is greater than 0.4 and less than 0.8, it can be said that the capacitance has effectively increased compared to the capacitance of the sample of Comparative Example 5.

[0127] Industrial availability

[0128] The capacitor disclosed herein is advantageous from the viewpoint of capacitance and dielectric loss tangent of tantalum oxide film.

Claims

1. A capacitor comprising a tantalum metal, a conductor, and a tantalum oxide film, the tantalum oxide film being disposed in contact with the tantalum metal and between the tantalum metal and the conductor, the tantalum oxide film comprising a first portion containing fluorine and a second portion present in the thickness direction of the tantalum oxide film at a position closer to the tantalum metal than the first portion, the concentration of fluorine in the second portion being lower than the concentration of fluorine 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 less than 0.

8.

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

3. The capacitor according to claim 1, wherein the first portion has a material made of TaO x1 F y1 The composition is represented by the condition that 0 < x1 < 2.5 and 0 < y1 ≤ 0.

4.

4. The capacitor according to claim 1, wherein the second portion has a component made of TaO x2 F y2 The composition is represented by the condition that 0 < x2 < 2.5 and 0 < y2 ≤ 0.

015.

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

6. A circuit comprising a capacitor as described in any one of claims 1 to 5.

7. A circuit board comprising a capacitor as described in any one of claims 1 to 5.

8. An apparatus comprising a capacitor as described in any one of claims 1 to 5.

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