Capacitors, electrical circuits, circuit boards, devices, and methods for manufacturing capacitors

Abstract

This capacitor 1a comprises a metal tantalum 10, a conductor 20, and a tantalum oxide film 30. The tantalum oxide film 30 is disposed in contact with the metal tantalum 10, and is disposed between the metal tantalum 10 and the conductor 20. The tantalum oxide film 30 includes a first part 31 and a second part 32 containing fluorine. The second part 32 exists at a position closer to the metal tantalum 10 than the first part 31 in the thickness direction of the tantalum oxide film 30. Additionally, the concentration of fluorine in the second part 32 is lower than the concentration of fluorine in the first part 31.

Description

[Technical Field]

[0001] This disclosure relates to capacitors, electrical circuits, circuit boards, equipment, and methods for manufacturing capacitors. [Background technology]

[0002] Traditionally, tantalum oxide containing fluorine has been used in capacitors.

[0003] For example, Patent Document 1 describes a solid electrolytic capacitor having a dielectric layer made of tantalum oxide containing fluorine. The dielectric layer is formed by anodizing an anode made of tantalum in an aqueous solution containing fluoride ions.

[0004] Non-patent document 1 states that the relative permittivity of a polycrystalline TaO2F thin film at 1 MHz is 60. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2005-294402 [Non-patent literature]

[0006] [Non-Patent Document 1] Journal of Materials Chemistry C, (English), 2020, Issue 14, p.4680-4684 [Overview of the project] [Problems that the invention aims to solve]

[0007] This disclosure provides a capacitor that is advantageous in terms of reducing dielectric loss tangent while using fluorine-containing tantalum oxide. [Means for solving the problem]

[0008] The capacitor of the present disclosure is tantalum metal, a conductor, a tantalum oxide film disposed in contact with the tantalum metal and disposed between the tantalum metal and the conductor, and the tantalum oxide film includes a first portion containing fluorine and a second portion existing at a position closer to the tantalum metal than the first portion in the thickness direction of the tantalum oxide film, the concentration of fluorine in the second portion is lower than the concentration of fluorine in the first portion.

Effect of the Invention

[0009] According to the present disclosure, it is possible to provide an advantageous capacitor from the viewpoint of reducing the dielectric loss tangent while using a tantalum oxide containing fluorine.

Brief Description of the Drawings

[0010] [Figure 1] FIG. 1 is a cross-sectional view showing an example of the capacitor of the present disclosure. [Figure 2] FIG. 2 is a flowchart showing an example of the manufacturing method of the capacitor of the present disclosure. [Figure 3] FIG. 3 is a cross-sectional view showing another example of the capacitor of the present disclosure. [Figure 4A] FIG. 4A is a diagram schematically showing an example of the electric circuit of the present disclosure. [Figure 4B] FIG. 4B is a diagram schematically showing an example of the circuit board of the present disclosure. [Figure 4C] FIG. 4C is a diagram schematically showing an example of the device of the present disclosure. [Figure 5] FIG. 5 is a graph showing the XRD pattern of the dielectric film of the sample according to Example 1. [Figure 6] FIG. 6 is a graph showing the relationship between the signal intensities of F-, TaO3-, and O- and the depth in the dielectric film in the time-of-flight secondary ion mass spectrometry (TOF-SIMS) of the sample according to Example 1. [Figure 7]Figure 7 is a graph showing the relationship between the signal intensities of F-, TaO3-, and O- in TOF-SIMS of the tantalum oxide film sample for Comparative Example 1 and the depth in the dielectric film. [Figure 8A] Figure 8A is a graph showing the relationship between the capacitance of an example capacitor and frequency. [Figure 8B] Figure 8B is a graph showing the relationship between the capacitance of an example capacitor and frequency. [Figure 9A] Figure 9A is a graph showing the relationship between the dielectric loss tangent tanδ and frequency for an example capacitor. [Figure 9B] Figure 9B is a graph showing the relationship between the dielectric loss tangent tanδ and frequency for an example capacitor. [Modes for carrying out the invention]

[0011] (Knowledge that forms the basis of this disclosure) For example, there is a continuous demand for improving the processing performance of electronic devices. The performance of electronic components such as capacitors greatly affects the performance of the electronic devices in which they are incorporated. For this reason, an increasing need for small, high-performance capacitors is anticipated. Electrolytic capacitors are a well-known example of a capacitor. In electrolytic capacitors, a dielectric film consisting of a thin oxide layer is formed on the surface of metallic aluminum or metallic tantalum through a 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, limitations have been observed in such attempts, and it is believed that the performance of capacitors could be further improved if dielectric materials with higher dielectric constants could be developed.

[0012] For example, the polycrystalline TaO2F thin film described in Non-Patent Document 1 has a high dielectric constant. It is believed that the polycrystalline oxyfluoride of tantalum has a different crystalline state from tantalum oxide Ta2O5, resulting in greater polarization and a high dielectric constant. In addition, the inventors have found that fluorine-containing tantalum oxide has a higher dielectric constant than fluorine-free tantalum oxide Ta2O5, even when the tantalum oxide is amorphous. From these findings, it is expected that using fluorine-containing tantalum oxide in a capacitor will increase the capacitance of the capacitor. On the other hand, the inventors' studies have revealed that a phenomenon of high dielectric loss tangent of the film can occur in a capacitor equipped with a fluorine-containing tantalum oxide film. It should be noted that a low dielectric loss tangent of the dielectric is advantageous in reducing electrical energy loss in a capacitor.

[0013] According to Patent Document 1, the dielectric layer is formed by anodizing a tantalum anode in an aqueous solution containing fluoride ions. It has been reported that the equivalent series resistance (ESR) of an electrolytic capacitor is reduced when the dielectric layer is made of tantalum oxide containing fluoride. On the other hand, our own research has shown that there are conditions under which the dielectric loss tangent of a film obtained by anodizing tantalum in an aqueous solution containing fluoride ions becomes high. In such a film, it was found that fluorine accumulates at the interface between tantalum oxide and elemental tantalum, forming a region with a high fluorine concentration. The reason for this is that the ion diffusion rate of fluoride ions is more than twice that of oxide ions, and depending on the anodizing conditions, fluorine can accumulate at the interface between tantalum oxide and elemental tantalum, forming a region with a high fluorine concentration. It is thought that the dielectric loss tangent of the film is increased by the formation of a region with a high fluorine concentration at the interface between tantalum oxide and elemental tantalum.

[0014] In view of such circumstances, the inventors of the present invention have intensively studied the configuration of a capacitor for reducing the dielectric loss tangent while using a tantalum oxide containing fluorine. As a result, they newly found that a tantalum oxide film having a specific configuration is advantageous for reducing the dielectric loss tangent. Based on this new finding, the inventors of the present invention have completed the capacitor of the present disclosure.

[0015] (Summary of one aspect according to the present disclosure) The capacitor according to the first aspect of the present disclosure is metallic tantalum, a conductor, 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 existing at a position closer to the metallic tantalum than the first portion in the thickness direction of the tantalum oxide film, [[ID=!6]]the concentration of fluorine in the second portion is lower than the concentration of fluorine in the first portion.

[0016] According to the first aspect, it is difficult for the concentration of fluorine near the metallic tantalum of the tantalum oxide film to increase. Therefore, although the tantalum oxide film includes the first portion containing fluorine, the dielectric loss tangent of the capacitor is likely to be low. [[ID=2!]]

[0017] In the second aspect of the present disclosure, for example, in the capacitor according to the first aspect, the first portion may be amorphous. According to the second aspect, it is possible to prevent current leakage derived from the crystal phase while the capacitor has a high capacitance.

[0018] In the third aspect of the present disclosure, for example, in the capacitor according to the first aspect or the second aspect, the first portion may have a composition represented by TaO x F y and the composition may satisfy the condition of 0 < x < 2.5. In this case, the tantalum oxide film is likely to have a high relative dielectric constant, and the capacitor is likely to have a high capacitance.

[0019] In a fourth aspect of this disclosure, for example, in the capacitor according to the third aspect, the composition may further satisfy the condition y≧0.015. In this case, the tantalum oxide film is more likely to have a high dielectric constant, and the capacitor is more likely to have a high capacitance.

[0020] In a fifth aspect of this disclosure, for example, in the capacitor according to the fourth aspect, the composition may further satisfy the condition y ≤ 0.40. In this case, the fluorine contained in the tantalum oxide film is less likely to diffuse toward the metallic tantalum due to the effects of electric fields and heat, and the tantalum oxide film is less likely to deteriorate. As a result, the performance of the capacitor is more stable.

[0021] In a sixth aspect of this disclosure, for example, in a capacitor according to any one of the first to fifth aspects, the concentration of fluorine in the second part may be 0.4% or less on an atomic basis. According to the sixth aspect, the concentration of fluorine near the metallic tantalum in the tantalum oxide film is less likely to be high, and the dielectric loss tangent of the capacitor is more likely to be low.

[0022] In the seventh aspect of this disclosure, for example, in a capacitor according to any one of the first to sixth aspects, the second portion may have a thickness greater than 5 nm and less than or equal to 100 nm. According to the seventh aspect, the tantalum oxide film tends to have a high relative permittivity, and the capacitor tends to have a high capacitance. In addition, because the thickness of the second portion is greater than 5 nm, the diffusion of fluorine toward the metallic tantalum is more easily prevented, and the dielectric loss tangent of the capacitor tends to be lower. The thickness of the native oxide film formed on the surface of metallic tantalum is usually about 5 nm.

[0023] In the eighth aspect of this disclosure, for example, a capacitor according to any one of the first to seventh aspects may further include an electrolyte disposed between the tantalum oxide film and the conductor. According to the eighth aspect, the capacitor can be configured as an electrolytic capacitor, and the capacitor tends to have a high capacitance.

[0024] An electrical circuit according to the ninth aspect of this disclosure comprises a capacitor according to any one of the first to eighth aspects. According to the ninth aspect, the tantalum oxide film of the capacitor contains a first portion containing fluorine, while the dielectric loss tangent of the capacitor tends to be low, and the electrical circuit tends to exhibit the desired performance.

[0025] A circuit board according to the tenth aspect of this disclosure comprises a capacitor according to any one of the first to eighth aspects. According to the tenth aspect, the tantalum oxide film of the capacitor contains a first portion containing fluorine, while the dielectric loss tangent of the capacitor tends to be low, and the circuit board tends to exhibit the desired performance.

[0026] The device according to the 11th aspect of this disclosure comprises a capacitor according to any one of the first to eighth aspects. According to the 11th aspect, the tantalum oxide film of the capacitor contains a first portion containing fluorine, while the dielectric loss tangent of the capacitor tends to be low, and the device tends to exhibit the desired performance.

[0027] A method for manufacturing a capacitor according to a twelfth aspect of this disclosure includes anodic deposition of metallic tantalum while in contact with a fluorine-free aqueous solution, and anodic deposition of the tantalum oxide layer formed on the metallic tantalum by the anodic deposition while in contact with a fluorine-containing aqueous solution to obtain a tantalum oxide film containing fluorine in the surface region of the tantalum oxide layer. According to the twelfth aspect, a capacitor with a low dielectric loss tangent can be manufactured while the tantalum oxide film contains fluorine-containing portions.

[0028] (Embodiment) The embodiments of this disclosure will be described below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0029] Figure 1 is a cross-sectional view showing an example of a capacitor according to the present disclosure. As shown in Figure 1, the capacitor 1a comprises metallic tantalum 10, a conductor 20, and a tantalum oxide film 30. The tantalum oxide film 30 is positioned in contact with the metallic tantalum 10 and between the metallic tantalum 10 and the conductor 20. The tantalum oxide film 30 includes a layered first portion 31 containing fluorine and a layered second portion 32. The first portion 31 corresponds to the surface region (surface region) of the tantalum oxide film 30 in the thickness direction. The second portion 32 is located closer to the metallic tantalum 10 than the first portion 31 in the thickness direction of the tantalum oxide film 30. In addition, the concentration of fluorine in the second portion 32 is lower than the concentration of fluorine in the first portion 31.

[0030] The tantalum oxide film 30 contains a layered first region 31 that contains fluorine, and therefore tends to have a high dielectric constant. For this reason, the capacitor 1a tends to have a high capacitance. The tantalum oxide film 30 has a layered second region 32 with a lower fluorine concentration located closer to the metallic tantalum 10 than the first region 31, so the fluorine concentration at the interface between the tantalum oxide film 30 and the metallic tantalum 10 does not tend to be high. For this reason, the dielectric loss tangent of the capacitor 1a tends to be low.

[0031] The dielectric loss tangent of capacitor 1a is, for example, 0.20 or less at frequencies from 1 Hz to 10 kHz.

[0032] The boundary between the first portion 31 and other portions in the tantalum oxide film 30 may be a visible interface when viewing a cross-section along the thickness direction of the tantalum oxide film 30 with a scanning electron microscope (SEM) or transmission electron microscope (TEM). The boundary between the first portion 31 and other portions in the tantalum oxide film 30 may be virtual, and the interface between the first portion 31 and other portions may not be visible when viewing a cross-section along the thickness direction of the tantalum oxide film 30 with an SEM or TEM. The boundary between the second portion 32 and other portions in the tantalum oxide film 30 may be a visible interface when viewing a cross-section along the thickness direction of the tantalum oxide film 30 with an SEM or TEM. The boundary between the second portion 32 and other portions in the tantalum oxide film 30 may be virtual, and the interface between the second portion 32 and other portions may not be visible when viewing a cross-section along the thickness direction of the tantalum oxide film 30 with an SEM or TEM.

[0033] As long as the second portion 32 is located closer to the metallic tantalum 10 than the first portion 31 in the thickness direction of the tantalum oxide film 30, the position of the first portion 31 is not limited to a specific position. For example, the first portion 31 is located at a depth of 100 nm or less from the main surface closest to the conductor 20 in the thickness direction of the tantalum oxide film 30.

[0034] The first region 31 may be crystalline or amorphous. Even if the first region 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 a broad halo pattern is shown in the XRD pattern of the target using Cu-Kα lines at diffraction angles 2θ from 10° to 50°, the target can be determined to be amorphous.

[0035] The second part 32 may be crystalline or amorphous.

[0036] As long as the concentration of fluorine in the second part 32 is lower than the concentration of fluorine in the first part 31, the composition of the first part 31 is not limited to a specific composition. For example, the first part 31 does not contain silicon and titanium. The first part 31 is, for example, TaO x F y and has a composition represented by. This composition satisfies the condition of, for example, 0 < x < 2.5. In this case, the tantalum oxide film 30 is likely to have a high relative dielectric constant, and the capacitor 1a is likely to have a high capacitance.

[0037] In the above composition, for example, the condition of y ≧ 0.015 is satisfied. 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 the above composition, the conditions of y ≧ 0.016, y ≧ 0.017, y ≧ 0.018, y ≧ 0.019, y ≧ 0.02, y ≧ 0.03, y ≧ 0.05, or y ≧ 0.1 may be satisfied, the condition of y ≧ 0.2 may be satisfied, and the condition of y ≧ 0.3 may be satisfied. Also, the above composition may satisfy the conditions of 0 < x < 2.5 and 0 < y < 0.015.

[0038] In the above composition, for example, the condition of y ≦ 0.40 may be further satisfied. In this case, the fluorine contained in the tantalum oxide film 30 is likely to be prevented from diffusing toward the metallic tantalum 10 due to the influence of an electric field, heat, etc., and the tantalum oxide film 30 is unlikely to be deteriorated. In the above composition, the conditions of 0 < y ≦ 0.40, 0 < y < 0.40, or 0.015 ≦ y ≦ 0.40 may be satisfied.

[0039] As long as the fluorine concentration in the second part 32 is lower than the fluorine concentration in the first part 31, the fluorine concentration in the second part 32 is not limited to a specific value. The fluorine concentration in the second part 32 is, on an atomic number basis, for example, 0.4% or less. In other words, the ratio of the number of fluorine atoms to the total number of atoms contained in the second part 32 is 0.4% or less. In this case, it is difficult for the fluorine concentration near the metallic tantalum 10 of the tantalum oxide film 30 to become higher, and the dielectric loss tangent of the capacitor 1a is likely to become lower. The fluorine concentration in the second part 32 can be determined, for example, based on the results of TOF-SIMS. The fluorine concentration in the second part 32 may be determined by combining TOF-SIMS with another analysis method such as Rutherford backscattering spectrometry (RBS).

[0040] The fluorine concentration in the second part 32 may be 0.3% or less, 0.2% or less, or 0.1% or less, 0.05% or less, or 0.01% or less on an atomic number basis.

[0041] The signal intensity ratio R of F in the TOF-SIMS of the tantalum oxide film 30 - is not limited to a specific value. The signal intensity ratio R F is the ratio of the second signal intensity R F to the first signal intensity R F1 . The first signal intensity R F2 is the signal intensity of F at the depth corresponding to the first part 31 of the TOF-SIMS of the tantalum oxide film 30 F1 . The second signal intensity R - is the signal intensity of F at the depth corresponding to the second part 32 of the TOF-SIMS of the tantalum oxide film 30 F2 . The signal intensity ratio R - is, for example, 0.0026 or more. In this case, it is difficult for the fluorine concentration near the metallic tantalum 10 of the tantalum oxide film 30 to become higher, and the dielectric loss tangent of the capacitor 1a is likely to become lower. The signal intensity ratio R F is, for example, 0.0026 or more. In this case, it is difficult for the fluorine concentration near the metallic tantalum 10 of the tantalum oxide film 30 to become higher, and the dielectric loss tangent of the capacitor 1a is likely to become lower. The signal intensity ratio R FThe signal intensity ratio R may be 0.005 or greater, 0.01 or greater, or 0.05 or greater. F For example, it is 0.1 or less.

[0042] The thickness of the second portion 32 is not limited to a specific value. Its thickness is, for example, 100 nm or less. In this case, the proportion of the thickness of the second portion 32 to the total thickness of the tantalum oxide film 30 tends to be low. Since the fluorine concentration in the second portion 32 is lower than that in the first portion 31, the second portion 32 does not tend to have a high relative permittivity. For this reason, when the proportion of the thickness of the second portion 32 to the total thickness of the tantalum oxide film 30 is low, the overall relative permittivity of the tantalum oxide film 30 tends to be high, and the capacitor 1a tends to have a high capacitance.

[0043] The thickness of the second portion 32 may be greater than 5 nm and less than or equal to 100 nm. As described above, if the thickness of the second portion 32 is 100 nm or less, the overall relative permittivity of the tantalum oxide film 30 tends to be higher, and the capacitor 1a tends to have a higher capacitance. If the thickness of the second portion 32 is greater than 5 nm, the diffusion of fluorine toward the metallic tantalum 10 in the tantalum oxide film 30 is more easily prevented, and the dielectric loss tangent of the capacitor 1a tends to be lower.

[0044] The thickness of the second part 32 may be 11 nm or more, 12 nm or more, 15 nm or more, or 20 nm or more. The thickness of the second part 32 may be 90 nm or less, 80 nm or less, or 70 nm or less. The thickness of the second part 32 may fall within a predetermined range. The lower limit of this range is, for example, one selected from the group consisting of 5 nm, 7 nm, 12 nm, 15 nm, and 20 nm. The upper limit of this range is, for example, one selected from the group consisting of 70 nm, 80 nm, 90 nm, and 100 nm. If 5 nm is selected as the lower limit, it means that the thickness of the second part 32 is greater than 5 nm. If a value other than 5 nm is selected as the lower limit, it means that the thickness of the second part 32 is greater than or equal to the selected value. The thickness of the second part 32 is less than or equal to the selected upper limit.

[0045] The method for manufacturing capacitor 1a is not limited to a specific method. Figure 2 is a flowchart of an example of a method for manufacturing capacitor 1a. Capacitor 1a is formed by, for example, a method including (I) and (II) below. (I) Metallic tantalum is brought into contact with a fluorine-free aqueous solution, and an anodic deposition is performed on the metallic tantalum to form a tantalum oxide layer on the metallic tantalum. That is, a tantalum oxide layer is formed in contact with the metallic tantalum (step S101 in Figure 2). (II) The tantalum oxide layer formed in (I) above is brought into contact with a fluorine-containing aqueous solution and anodized with metallic tantalum to obtain a tantalum oxide film 30 containing a first portion 31 and a second portion 32 containing fluorine (step S102 in Figure 2).

[0046] In anodic deposition, for example, an electrolyte is placed between the anode and cathode, and a voltage ranging from several volts to several hundred volts is applied between the anode and cathode. When metallic tantalum is the anode, anions attracted to the metallic tantalum combine with the ionized tantalum to form a deposition film. At that time, ions or atoms, which are impurities from the electrolyte present around the anode, may be incorporated into the deposition film. For this reason, in anodic deposition using metallic tantalum as the anode, it is practically impossible to form a film consisting of only two specific elements, such as tantalum and oxygen. For this reason, in capacitor 1a, other elements such as fluorine may be present in the second part 32 at an impurity level. An impurity level means, for example, that other elements such as fluorine, other than tantalum and oxygen, may be present in the second part 32 at a concentration of 0.4% or less on an atomic basis.

[0047] Next, in step S103, a tantalum oxide film 30 is placed between the metallic tantalum and the conductor 20. In other words, in step S103, the conductor 20 is placed on the opposite side of the tantalum oxide film 30 from the metallic tantalum 10. For example, a capacitor 1a is obtained in this way.

[0048] In capacitor 1a, the conductor 20 is not limited to a specific material. The conductor 20 may contain valve metals such as aluminum, tantalum, niobium, and bismuth, or it may contain precious metals such as gold and platinum, or it may contain nickel. The conductor 20 may also contain carbon materials such as graphite.

[0049] As shown in Figure 1, the capacitor 1a includes, for example, an electrolyte 40. The electrolyte 40 is placed between the tantalum oxide film 30 and the conductor 20. In this case, the capacitor 1a is provided as an electrolytic capacitor. In the capacitor 1a, the electrolyte 40 is, for example, in layers. The electrolyte 40 may be omitted in the capacitor 1a.

[0050] The electrolyte 40 is not limited to a specific electrolyte. The electrolyte 40 includes, for example, at least one selected from the group consisting of an electrolyte solution and a conductive polymer. Examples of conductive polymers are polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte 40 may also be a manganese compound such as manganese oxide. The electrolyte 40 may also include a solid electrolyte.

[0051] Figure 3 is a cross-sectional view showing another example of a capacitor of the present disclosure. Capacitor 1b shown in Figure 3 is configured similarly to capacitor 1a, except for parts that are not specifically described. Components of capacitor 1b that are the same as or correspond to components of capacitor 1a are denoted by the same reference numerals, and detailed descriptions are omitted. Descriptions of capacitor 1a also apply to capacitor 1b, to the extent that they do not technically contradict each other.

[0052] As shown in Figure 3, in capacitor 1b, at least a portion of the metallic tantalum 10 is porous. With this configuration, the surface area of ​​the metallic 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 metal foil and sintering powder.

[0053] As shown in Figure 3, a tantalum oxide film 30 is placed on the surface of a porous portion of metallic tantalum 10. The tantalum oxide film 30 is formed, for example, by anodic deposition, as described above. Metallic tantalum The electrolyte 40 is arranged to fill the voids around the 10 porous portions. The electrolyte 40 includes, for example, at least one selected from the group consisting of manganese oxide, an electrolyte solution, and a conductive polymer. Examples of conductive polymers are polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte 40 may also be a manganese compound such as manganese oxide. The electrolyte 40 may also include a solid electrolyte. In the capacitor 1b, for example, the cathode is composed of a conductor 20 and an electrolyte 40. The conductor 20 may include, for example, a solidified silver-containing paste, a carbon material such as graphite, or both of the above solidified material and the carbon material.

[0054] Figure 4A is a schematic diagram showing an example of an electrical circuit of the present disclosure. Electrical circuit 3 includes a capacitor 1a. Electrical circuit 3 may be an active circuit or a passive circuit. Electrical circuit 3 may be a discharge circuit, a smoothing circuit, a decoupling circuit, or a coupling circuit. Because electrical circuit 3 includes a capacitor 1a, electrical circuit 3 is more likely to exhibit desired performance. For example, noise is more easily reduced in electrical circuit 3. Electrical circuit 3 may also include a capacitor 1b.

[0055] Figure 4B is a schematic diagram showing an example of a circuit board of the present disclosure. As shown in Figure 4B, the circuit board 5 includes a capacitor 1a. For example, an electrical circuit 3 including the capacitor 1a is formed on the circuit board 5. Because the circuit board 5 includes the capacitor 1a, the circuit board 5 is more 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.

[0056] Figure 4C is a schematic diagram showing an example of the device of this disclosure. As shown in Figure 4C, the device 7 includes a capacitor 1a. The device 7 includes, for example, a circuit board 5 including a capacitor 1a. Because the device 7 includes a capacitor 1a, the device 7 is able to easily achieve the desired performance. The device 7 may be an electronic device, a communication device, a signal processing device, or a power supply device. 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, smartphone, or tablet PC, or an Ethernet switch. The device 7 may also include a capacitor 1b. [Examples]

[0057] The present disclosure will be further described below with reference to examples. The following examples are illustrative and the present disclosure is not limited to these examples.

[0058] <Example 1> The surface of the tantalum metal was cleaned by ultrasonic cleaning for 10 minutes while immersed in a container filled with acetone. Afterward, the acetone adhering to the surface of the tantalum metal was evaporated, and the surface was rinsed with pure water. Finally, the tantalum metal was dried in the air.

[0059] In an aqueous solution containing H3PO4, metallic tantalum and platinum foil as a counter electrode were placed at predetermined intervals. The portion of metallic tantalum not immersed in the aqueous solution was connected to the positive electrode of a power supply, and the portion of platinum foil not immersed in the aqueous solution was connected to the negative electrode of the power supply. Current was supplied from the power supply under constant voltage conditions, and a voltage of 64V was applied between the metallic tantalum and the counter electrode for 30 minutes. An electrochemical reaction occurred on the surface of the metallic tantalum, which was the anode, and an oxide film was obtained. The metallic tantalum with the oxide film formed on it was removed from the aqueous solution, washed with pure water, and dried in the air.

[0060] Next, in an NH4HF2 aqueous solution, metallic tantalum with an oxide film formed on it was placed as the anode, and platinum foil as the cathode. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative electrodes of a power supply, respectively. The concentration of NH4HF2 in the aqueous solution was 0.5 mol / liter (mol / L). Current was passed from the power supply under constant voltage conditions, and a voltage of 80V was applied between the anode and cathode for 10 minutes to perform anodic conversion treatment. After that, the anode after anodic conversion treatment was removed from the aqueous solution, washed with pure water, and dried. In this way, a sample according to Example 1, in which a dielectric film was formed on the surface of metallic tantalum, was obtained.

[0061] <Example 2> The surface of the tantalum metal was cleaned by ultrasonic cleaning for 10 minutes while immersed in a container filled with acetone. Afterward, the acetone adhering to the surface of the tantalum metal was evaporated, and the surface was rinsed with pure water. Finally, the tantalum metal was dried in the air.

[0062] In an aqueous solution containing H3PO4, metallic tantalum and platinum foil as a counter electrode were placed at predetermined intervals. The portion of metallic tantalum not immersed in the aqueous solution was connected to the positive electrode of a power supply, and the portion of platinum foil not immersed in the aqueous solution was connected to the negative electrode of the power supply. Current was supplied from the power supply under constant voltage conditions, and a voltage of 64V was applied between the metallic tantalum and the counter electrode for 30 minutes. An electrochemical reaction occurred on the surface of the metallic tantalum, which was the anode, and an oxide film was obtained. The metallic tantalum with the oxide film formed on it was removed from the aqueous solution, washed with pure water, and dried in the air.

[0063] Next, in an NH4HF2 aqueous solution, metallic tantalum with an oxide film formed on it was placed as the anode, and platinum foil as the cathode. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative electrodes of a power supply, respectively. The concentration of NH4HF2 in the aqueous solution was 1.0 mol / L. Current was passed from the power supply under constant voltage conditions, and a voltage of 80 V was applied between the anode and cathode for 10 minutes to perform anodic conversion treatment. After that, the anode after anodic conversion treatment was removed from the aqueous solution, washed with pure water, and dried. In this way, a sample according to Example 2 was obtained in which a dielectric film was formed on the surface of metallic tantalum.

[0064] <Comparative Example 1> The surface of the tantalum metal was cleaned by ultrasonic cleaning for 10 minutes while immersed in a container filled with acetone. Afterward, the acetone adhering to the surface of the tantalum metal was evaporated, and the surface was rinsed with pure water. Finally, the tantalum metal was dried in the air.

[0065] Next, in an NH4HF2 aqueous solution, metallic tantalum was placed as the anode and platinum foil as the cathode, and the portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative electrodes of a power supply, respectively. The concentration of NH4HF2 in the aqueous solution was 0.5 mol / L. Current was passed from the power supply under constant voltage conditions, and a voltage of 80 V was applied between the anode and cathode for 10 minutes to perform anodic conversion treatment. After that, the anode after anodic conversion treatment was removed from the aqueous solution, washed with pure water, and dried. In this way, a sample relating to Comparative Example 1 was obtained in which a dielectric film was formed on the surface of metallic tantalum.

[0066] <Comparative Example 2> The surface of the tantalum metal was cleaned by ultrasonic cleaning for 10 minutes while immersed in a container filled with acetone. Afterward, the acetone adhering to the surface of the tantalum metal was evaporated, and the surface was rinsed with pure water. Finally, the tantalum metal was dried in the air.

[0067] In an aqueous solution containing H3PO4, metallic tantalum as the anode and platinum foil as the cathode were placed at predetermined intervals. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative electrodes of a power supply, respectively. Current was supplied from the power supply under constant voltage conditions, and a voltage of 80V was applied between the anode and cathode for 30 minutes. An electrochemical reaction occurred on the surface of the metallic tantalum anode, yielding a dielectric film, which is an oxide film. The metallic tantalum with the oxide film formed on it was removed from the aqueous solution, washed with pure water, and dried in the air. In this way, a sample relating to Comparative Example 2, having a dielectric film formed of fluorine-free tantalum oxide, was obtained.

[0068] (X-ray diffraction measurement) An XRD pattern of the dielectric film of the sample according to Example 1 was acquired by 2θ / θ scanning using a Rigaku Smartlab X-ray diffraction (XRD) system. Cu-Kα rays were used as the X-ray source, the voltage was adjusted to 40kV, the current to 30mA, and the scanning speed to 10deg. / min. Figure 5 shows the XRD pattern of the dielectric film of the sample according to Example 1. No peaks originating from the crystal structure were observed in the XRD pattern shown in Figure 5, indicating that the tantalum oxide film of the sample according to Example 1 is amorphous.

[0069] (Elemental composition analysis) Using a Rutherford backscatter spectroscopy (RBS) instrument, Pelletron 5SDH-2, RBS was performed on samples prepared from the surface of the dielectric layers of the samples from Example 1 and Example 2. During RBS, the samples were irradiated with an ion beam under predetermined conditions to obtain RBS spectra. According to the obtained RBS spectra, the ratio of fluorine atoms to tantalum atoms in the surface of the dielectric layer of the sample from Example 1 was 0.06, and the ratio of fluorine atoms to tantalum atoms in the surface of the dielectric layer of the sample from Example 2 was 0.40. According to the obtained RBS spectra, the composition of the surface of the dielectric layer of the sample from Example 1 was TaO 2.47 F 0.06 The composition of the surface portion of the dielectric layer of the sample according to Example 2 is TaO 2.30 F 0.40 That was the case.

[0070] (TOF-SIMS) A fragment of a predetermined size was cut from the sample according to Example 1, and a sample for TOF-SIMS was prepared by resin embedding. TOF-SIMS was performed on the sample prepared from the sample according to Example 1 using the TOF.SIMS5 instrument manufactured by ION-TOF, and the compositional analysis of the oxide film in the depth direction of the dielectric film was performed. In TOF-SIMS, a Bi beam was used as the primary ion beam. O2 was used as the sputtering ion species. Figure 6 shows the F of the sample according to Example 1 in TOF-SIMS. -TaO 3- , and O - This graph shows the relationship between the signal intensity and the depth in the dielectric film. In Figure 6, the vertical axis represents the signal intensity of each ion, and the horizontal axis represents the depth in the dielectric film.

[0071] TOF-SIMS was performed on the sample related to Comparative Example 1 in the same manner as in Example 1. Figure 7 shows the F of the sample related to Comparative Example 1 in TOF-SIMS. - TaO 3- , and O - This graph shows the relationship between the signal intensity and the depth in the dielectric film. In Figure 7, the vertical axis represents the signal intensity of each ion, and the horizontal axis represents the depth in the dielectric film.

[0072] According to Figure 6, the dielectric film of the sample according to Example 1 is formed on metallic tantalum and is understood to contain areas with high fluorine concentration and areas with low fluorine concentration. The areas with high fluorine concentration exist from the surface of the dielectric film to a depth of approximately 60 nm. On the other hand, the areas with low fluorine concentration exist from a depth of approximately 75 nm to approximately 150 nm in the dielectric film. - Based on the signal intensity, the fluorine concentration in this region is understood to be 0.5% or less on an atomic basis. There is little variation in fluorine concentration in both the high-fluorine and low-fluorine concentration regions. TOF-SIMS F in the high-fluorine concentration region of tantalum oxide film 30 - Signal intensity R F1 In contrast, the F of TOF-SIMS in the region of the tantalum oxide film 30 with a low fluorine concentration. - Signal intensity R F2 The ratio was approximately 0.1 or less. In Figure 6, depths of approximately 150 nm or more are understood to correspond to metallic tantalum. No increase in fluorine concentration was observed at the boundary between metallic tantalum and the dielectric film.

[0073] On the other hand, according to Figure 7, the dielectric film of the sample according to Comparative Example 1 is understood to exist to a depth of approximately 180 nm from its surface. In the sample according to Comparative Example 1, an increase in fluorine concentration is observed at the boundary between the metallic tantalum and the dielectric film. This is thought to be because the diffusion rate of fluoride ions is much faster than the diffusion rate of oxide ions, so the diffusion of fluoride ions into the metallic tantalum and the formation of tantalum fluoride occurred prior to the formation of the tantalum oxide film by anodic conversion. The tantalum fluoride thus formed has poor electrical insulation properties and can degrade the dielectric properties required for capacitors. In addition, the presence of such tantalum fluoride near the metallic tantalum may lead to uneven formation of the tantalum oxide film and may cause peeling of the tantalum oxide film. For this reason, dielectrics in which tantalum fluoride is present near the metallic tantalum are not suitable as dielectrics for capacitors. On the other hand, as in Example 1, if a chemical conversion treatment using a fluorine-free solution is performed in advance, a fluorine-containing tantalum oxide film can be easily formed on the metallic tantalum without peeling.

[0074] (Capacitance and dielectric loss tangent) The sample from Example 1 was mounted in an electrochemical cell manufactured by BAS, and the dielectric properties of the capacitor according to Example 1 were evaluated according to the AC impedance method with platinum as the counter electrode. In this evaluation, an AC voltage was applied to the capacitor according to Example 1 in the range of amplitude from 10 to 100 mV and frequency from 1 MHz to 0.1 Hz, and the capacitance was calculated from the resistance value at each frequency. Figures 8A and 8B are graphs showing the relationship between the capacitance of the capacitor and frequency. In Figures 8A and 8B, the vertical axis represents capacitance and the horizontal axis represents frequency. Figure 8B is an enlarged view of a part of Figure 8A. In addition, based on the results of this evaluation, the dielectric loss tangent tanδ of the capacitor according to Example 1 was determined at each frequency. Figures 9A and 9B are graphs showing the relationship between the dielectric loss tangent tanδ of the capacitor and frequency. In Figure 9A, the vertical axis represents tanδ and the horizontal axis represents frequency. Figure 9B is an enlarged view of a part of Figure 9A.

[0075] The sample according to Example 2 was mounted in an electrochemical cell manufactured by BAS, and the capacitance and dielectric loss tangent tanδ of the capacitor according to Example 2 were determined in the same manner as in Example 1, using the AC impedance method with platinum as the counter electrode. The results are shown in Figures 8A to 9B.

[0076] The sample for Comparative Example 1 was mounted in an electrochemical cell manufactured by BAS, and the capacitance and dielectric loss tangent tanδ of the capacitor for Comparative Example 1 were determined in the same manner as in Example 1, using the AC impedance method with platinum as the counter electrode. The results are shown in Figures 8A to 9B.

[0077] The sample for Comparative Example 2 was mounted in an electrochemical cell manufactured by BAS, and the capacitance and dielectric loss tangent tanδ of the capacitor for Comparative Example 2 were determined in the same manner as in Example 1, using the AC impedance method with platinum as the counter electrode. The results are shown in Figures 8A to 9B.

[0078] The dielectric layers of the samples in Example 1, Example 2, Comparative Example 1, and Comparative Example 2 are formed on metallic tantalum with equivalent surface conditions, and it is understood that there is no significant difference in the surface area of ​​the dielectric layers of each sample. According to Figures 8A and 8B, the capacitance of the capacitors in Example 1, Example 2, and Comparative Example 1 is higher than that of the capacitor in Comparative Example 2. Although the capacitance of the capacitor in Comparative Example 1 is high, as shown in Figures 9A and 9B, the dielectric loss tangent tanδ of the capacitor in Comparative Example 1 is high. tanδ corresponds to the energy consumed inside the capacitor, and it is understood that the capacitor in Comparative Example 1 has a large loss of electrical energy. On the other hand, the dielectric loss tangent tanδ of the capacitors in Example 1 and Example 2 is low and remains at a value equivalent to that of the capacitor in Comparative Example 2. Therefore, overall, it is understood that the capacitors in Example 1 and Example 2 are superior not only in terms of capacitance but also in terms of low electrical energy loss. [Industrial applicability]

[0079] The capacitor described herein is advantageous in terms of reducing the dielectric loss tangent.

Claims

1. Metallic tantalum and, Conductors and, The system comprises a tantalum oxide film disposed in contact with the metallic tantalum and positioned 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 part is lower than the fluorine concentration in the first part. Capacitor.

2. The aforementioned first part is amorphous. The capacitor according to claim 1.

3. The first part is TaO x F y Having a composition represented by, The above composition satisfies the condition 0 < x < 2.

5. The capacitor according to claim 1.

4. The above composition further satisfies the condition y ≥ 0.

015. The capacitor according to claim 3.

5. The above composition further satisfies the condition y ≤ 0.

40. The capacitor according to claim 4.

6. The concentration of fluorine in the second site is 0.4% or less on an atomic basis. The capacitor according to claim 1.

7. The second portion has a thickness greater than 5 nm and less than or equal to 100 nm. The capacitor according to claim 1.

8. The system further comprises an electrolyte disposed between the tantalum oxide film and the conductor. The capacitor according to claim 1.

9. An electrical circuit comprising a capacitor according to any one of claims 1 to 8.

10. A circuit board comprising a capacitor according to any one of claims 1 to 8.

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

12. The first anodic deposition is performed on the metallic tantalum while it is in contact with an aqueous solution that does not contain fluoride ions (F-). The process involves performing a second anodic reaction on the tantalum oxide layer on the metallic tantalum formed by the first anodic reaction, while in contact with an aqueous solution containing fluoride ions (F-), thereby obtaining a tantalum oxide film containing fluorine in the surface region of the tantalum oxide layer. The applied voltage in the second anodic formation is higher than the applied voltage in the first anodic formation. Capacitor manufacturing method.

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