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

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

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

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

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

[0003] For example, 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.

[0004] Non-Patent Document 1 describes that the relative dielectric constant of a polycrystalline TaO2F thin film is 60 at 1 MHz.

[0005] Japanese Patent Application Laid-Open No. 2005-294402

[0006] Journal of Materials Chemistry C, (English), 2020, Issue 14, p.4680-4684

[0007] The present disclosure provides a capacitor that is advantageous from the viewpoint of reducing the dielectric loss tangent while using fluorine-containing tantalum oxide.

[0008] The capacitor of 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, 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, and the fluorine concentration in the second portion is lower than the fluorine concentration in the first portion.

[0009] According to the present disclosure, a capacitor can be provided that is advantageous from the viewpoint of reducing the dielectric loss tangent while using fluorine-containing tantalum oxide.

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

[0011] (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 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 could be further improved if a dielectric material with a higher dielectric constant could be developed.

[0012] 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. Furthermore, the inventors have found through their studies that fluorine-containing tantalum oxides, even when amorphous, have a higher dielectric constant than fluorine-free tantalum oxide TaO. Based on these findings, it is expected that the use of fluorine-containing tantalum oxide in capacitors will increase the capacitance of the capacitor. Meanwhile, the inventors' studies have revealed that a capacitor equipped with a fluorine-containing tantalum oxide film may exhibit a high dielectric loss tangent. A low dielectric loss tangent of the dielectric is advantageous in capacitors to reduce electrical energy loss.

[0013] According to Patent Document 1, the dielectric layer is formed by anodizing a tantalum anode in an aqueous solution containing fluorine ions. It has been reported that the equivalent series resistance (ESR) of an electrolytic capacitor is reduced when the dielectric layer is made of fluorine-containing tantalum oxide. Meanwhile, the inventors' studies have found that there are conditions under which the dielectric dissipation factor of a film obtained by anodizing tantalum in an aqueous solution containing fluorine ions is high. It has been found that in such films, fluorine accumulates at the interface between the 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 the ion diffusion rate of oxide ions, and depending on the anodization conditions, fluorine may accumulate at the interface between the tantalum oxide and elemental tantalum, forming a region with a high fluorine concentration. It is believed that the formation of a region with a high fluorine concentration at the interface between the tantalum oxide and elemental tantalum increases the dielectric dissipation factor of the film.

[0014] In light of these circumstances, the present inventors conducted extensive research into the configuration of a capacitor that uses fluorine-containing tantalum oxide and reduces the dielectric loss tangent. As a result, they discovered that a tantalum oxide film having a specific configuration is advantageous for reducing the dielectric loss tangent. Based on this new finding, the present inventors have completed the capacitor of the present disclosure.

[0015] (Summary of one aspect of the present disclosure) A capacitor according to a first aspect of the present disclosure comprises: 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 that is located closer to the metallic tantalum than the first portion in the thickness direction of the tantalum oxide film, and the fluorine concentration in the second portion is lower than the fluorine concentration in the first portion.

[0016] According to the first aspect, the fluorine concentration is unlikely to become high near the metallic tantalum of the tantalum oxide film, and therefore, although the tantalum oxide film includes the first portion containing fluorine, the dielectric loss tangent of the capacitor is likely to be low.

[0017] In a second aspect of the present disclosure, for example, in the capacitor according to the first aspect, the first portion may be amorphous, which allows the capacitor to have a high capacitance while preventing current leakage due to a crystalline phase.

[0018] In a third aspect of the present disclosure, for example, in the capacitor according to the first or second aspect, the first portion is made of TaO x F y The composition may be expressed by the formula: where x satisfies the condition 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 the present disclosure, for example, in the capacitor according to the third aspect, the composition may further satisfy the condition y≧0.015, in which 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 the present disclosure, for example, in the capacitor according to the fourth aspect, the composition may further satisfy the condition y≦0.40. In this case, fluorine contained in the tantalum oxide film is likely to be prevented from diffusing toward the metal tantalum due to the influence of an electric field, heat, etc., and the tantalum oxide film is unlikely to be altered. This makes it easier to stabilize the performance of the capacitor.

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

[0022] In a seventh aspect of the present disclosure, for example, in the capacitor according to any one of the first to sixth aspects, the second portion may have a thickness of more than 5 nm and not more than 100 nm. According to the seventh aspect, the tantalum oxide film is likely to have a high dielectric constant, and the capacitor is likely to have a high capacitance. In addition, since the thickness of the second portion is greater than 5 nm, fluorine diffusion toward the tantalum metal is likely to be prevented, and the dielectric loss tangent of the capacitor is likely to be lower. The thickness of the native oxide film formed on the surface of the tantalum metal is typically about 5 nm.

[0023] In an eighth aspect of the present disclosure, for example, the 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 is likely to have a high capacitance.

[0024] An electric circuit according to a ninth aspect of the present disclosure includes the capacitor according to any one of the first to eighth aspects. According to the ninth aspect, the tantalum oxide film of the capacitor includes a first portion containing fluorine, and the dielectric loss tangent of the capacitor is likely to be low, making it easier for the electric circuit to exhibit desired performance.

[0025] A circuit board according to a tenth aspect of the present disclosure includes the capacitor according to any one of the first to eighth aspects. According to the tenth aspect, the tantalum oxide film of the capacitor includes a first portion containing fluorine, and the dielectric loss tangent of the capacitor is likely to be low, making it easier for the circuit board to exhibit desired performance.

[0026] An apparatus according to an eleventh aspect of the present disclosure includes the capacitor according to any one of aspects 1 to 8. According to the eleventh aspect, the tantalum oxide film of the capacitor includes a first portion containing fluorine, and the dielectric loss tangent of the capacitor is likely to be low, making it easier for the apparatus to exhibit desired performance.

[0027] A method for producing a capacitor according to a twelfth aspect of the present disclosure includes anodizing the tantalum metal in a state in which the tantalum metal is in contact with a fluorine-free aqueous solution, and anodizing the tantalum oxide layer formed on the tantalum metal by the anodization in a state in which the tantalum oxide layer is in contact with a fluorine-containing aqueous solution, thereby obtaining a tantalum oxide film containing fluorine in a surface region of the tantalum oxide layer. According to the twelfth aspect, a capacitor can be produced in which the tantalum oxide film includes a portion containing fluorine and has a low dielectric loss tangent.

[0028] (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.

[0029] 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 disposed in contact with the metal tantalum 10 and between the metal tantalum 10 and the conductor 20. The tantalum oxide film 30 includes a layer-like first portion 31 containing fluorine and a layer-like second portion 32. The first portion 31 corresponds to a region (surface region) on the surface side of the tantalum oxide film 30 in the thickness direction of the tantalum oxide film 30. 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 addition, the fluorine concentration in the second portion 32 is lower than the fluorine concentration in the first portion 31.

[0030] Because the tantalum oxide film 30 includes the layered first portion 31 containing fluorine, it is likely to have a high dielectric constant. Therefore, the capacitor 1a is likely to have a high capacitance. Because the tantalum oxide film 30 includes the layered second portion 32, which has a lower fluorine concentration, located closer to the tantalum metal 10 than the first portion 31, the fluorine concentration at the interface between the tantalum oxide film 30 and the tantalum metal 10 is unlikely to become high. Therefore, the dielectric loss tangent of the capacitor 1a is likely to be low.

[0031] The dielectric loss tangent of the 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 an interface that is visible when a cross section of the tantalum oxide film 30 taken along the thickness direction is viewed with a scanning electron microscope (SEM) or a transmission electron microscope (TEM). The boundary between the first portion 31 and other portions in the tantalum oxide film 30 may be a virtual one, and the interface between the first portion 31 and other portions may not be visible when a cross section of the tantalum oxide film 30 taken along the thickness direction is viewed with a SEM or a TEM. The boundary between the second portion 32 and other portions in the tantalum oxide film 30 may be an interface that is visible when a cross section of the tantalum oxide film 30 taken along the thickness direction is viewed with a SEM or a TEM. The boundary between the second portion 32 and other portions in the tantalum oxide film 30 may be a virtual one, and the interface between the second portion 32 and other portions may not be visible when a cross section of the tantalum oxide film 30 taken along the thickness direction is viewed with a SEM or a TEM.

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

[0034] 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°.

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

[0036] 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 x F y This composition satisfies the condition of 0<x<2.5, for example. 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 y≧0.015 is satisfied. In this case, the tantalum oxide film 30 is more likely to have a high dielectric constant, and the capacitor 1a is more likely to have a high capacitance. In the above composition, the condition 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, or the condition y≧0.2 may be satisfied, or the condition y≧0.3 may be satisfied. In addition, the above composition may satisfy the conditions 0<x<2.5 and 0<y<0.015.

[0038] The above composition may further satisfy, for example, the condition y≦0.40. In this case, fluorine contained in the tantalum oxide film 30 is 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 tantalum oxide film 30 is unlikely to be altered. The above composition may also satisfy the condition 0<y≦0.40, 0<y<0.40, or 0.015≦y≦0.40.

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

[0040] The concentration of fluorine in the second portion 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, based on the number of atoms.

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

[0042] The thickness of the second portion 32 is not limited to a specific value. The thickness is, for example, 100 nm or less. In this case, the proportion of the thickness of the second portion 32 in the overall thickness of the tantalum oxide film 30 is likely to be low. Because the fluorine concentration in the second portion 32 is lower than the fluorine concentration in the first portion 31, the second portion 32 is unlikely to have a high relative dielectric constant. Therefore, if the proportion of the thickness of the second portion 32 in the overall thickness of the tantalum oxide film 30 is low, the relative dielectric constant of the entire tantalum oxide film 30 is likely to be high, and the capacitor 1a is likely to have a high capacitance.

[0043] The thickness of second portion 32 may be greater than 5 nm and less than or equal to 100 nm. As described above, when second portion 32 is less than or equal to 100 nm, the relative dielectric constant of the entire tantalum oxide film 30 tends to be high, and capacitor 1a tends to have a high capacitance. When second portion 32 is more than 5 nm thick, fluorine is likely to be prevented from diffusing in tantalum oxide film 30 toward metal tantalum 10, and capacitor 1a tends to have a lower dielectric loss tangent.

[0044] The thickness of the second portion 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 portion 32 may be 90 nm or less, 80 nm or less, or 70 nm or less. The thickness of the second portion 32 may be within a predetermined range. The lower limit of the 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 the range is, for example, one selected from the group consisting of 70 nm, 80 nm, 90 nm, and 100 nm. When 5 nm is selected as the lower limit, the thickness of the second portion 32 is greater than 5 nm. When a value other than 5 nm is selected as the lower limit, the thickness of the second portion 32 is equal to or greater than the selected value. The thickness of the second portion 32 is equal to or less than the selected upper limit.

[0045] The method for manufacturing the capacitor 1a is not limited to a specific method. FIG. 2 is a flowchart showing an example of a method for manufacturing the capacitor 1a. The capacitor 1a is formed, for example, by a method including the following steps (I) and (II): (I) Anodizing the metallic tantalum while the metallic tantalum is in contact with a fluorine-free aqueous solution to form a tantalum oxide layer on the metallic tantalum. That is, a tantalum oxide layer in contact with the metallic tantalum is formed (step S101 in FIG. 2). (II) Anodizing the metallic tantalum while the tantalum oxide layer formed in step (I) is in contact with a fluorine-containing aqueous solution to obtain a tantalum oxide film 30 including a fluorine-containing first portion 31 and a second portion 32 (step S102 in FIG. 2).

[0046] In anodization, for example, a voltage of several volts to several hundred volts is applied between the anode and cathode with an electrolyte disposed between them. When metallic tantalum is used as the anode, anions attracted toward the metallic tantalum combine with ionized tantalum to form a chemically-converted film. Impurity ions or atoms derived from the electrolyte surrounding the anode may be incorporated into the chemically-converted 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, in the capacitor 1a, other elements, such as fluorine, may be present in the second portion 32 at impurity levels. By "impurity level," 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.

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

[0048] 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.

[0049] 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 this case, the capacitor 1a is provided as 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.

[0050] 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.

[0051] Figure 3 is a cross-sectional view showing another example of a capacitor according to the present disclosure. Capacitor 1b shown in Figure 3 has the same configuration as capacitor 1a, except for portions that will be specifically described. Components of capacitor 1b that are the same as or correspond to those of capacitor 1a are designated by the same reference numerals, and detailed descriptions thereof will be omitted. The description of capacitor 1a also applies to capacitor 1b, unless technically inconsistent.

[0052] 3, 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.

[0053] As shown in FIG. 3 , 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, as described above. An electrolyte 40 is disposed so as to fill the voids around the porous portion of the first electrode 10. 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.

[0054] 4A 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.

[0055] Fig. 4B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. As shown in Fig. 4B, 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.

[0056] FIG. 4C is a schematic diagram illustrating an example of a device according to the present disclosure. As shown in FIG. 4C , device 7 includes capacitor 1a. Device 7 includes, for example, circuit board 5 including capacitor 1a. Because device 7 includes capacitor 1a, device 7 is more likely to exhibit desired performance. Device 7 may be an electronic device, a communication device, a signal processing device, or a power supply. Device 7 may be a server, an AC adapter, an accelerator, or a flat panel display such as a liquid crystal display (LCD). 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. Device 7 may also include capacitor 1b.

[0057] 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.

[0058] Example 1 Metallic tantalum was immersed in a container filled with acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. After that, the acetone adhering to the surface of the metallic tantalum was evaporated, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere.

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

[0060] Next, the metal tantalum on which the oxide film was formed was placed as the anode and platinum foil as the cathode in an NH4HF2 aqueous solution. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative terminals of a power supply, respectively. The concentration of NH4HF2 in the aqueous solution was 0.5 mol / L. A current was applied from the power supply in a constant voltage state, and a voltage of 80 V was applied between the anode and cathode for 10 minutes to perform anodization. The anodized anode was then removed from the aqueous solution, washed with pure water, and dried. In this way, a sample according to Example 1 was obtained, in which a dielectric film was formed on the surface of metal tantalum.

[0061] Example 2 Metallic tantalum was immersed in a container filled with acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. After that, the acetone adhering to the surface of the metallic tantalum was evaporated, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere.

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

[0063] Next, the metal tantalum on which the oxide film was formed was placed as the anode and platinum foil as the cathode in an NH4HF2 aqueous solution. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative terminals of a power supply, respectively. The concentration of NH4HF2 in the aqueous solution was 1.0 mol / L. A current was applied from the power supply in a constant voltage state, and a voltage of 80 V was applied between the anode and cathode for 10 minutes to perform anodization. The anodized anode was then 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 metal tantalum.

[0064] Comparative Example 1: Metallic tantalum was immersed in a container filled with acetone and subjected to ultrasonic cleaning for 10 minutes to clean the surface of the metallic tantalum. After that, the acetone adhering to the surface of the metallic tantalum was evaporated, and the surface of the metallic tantalum was cleaned with pure water. The metallic tantalum was then dried in the atmosphere.

[0065] Next, tantalum metal was placed as the anode and platinum foil as the cathode in an NH4HF2 aqueous solution, 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. A current was applied from the power supply in a constant voltage state, and a voltage of 80 V was applied between the anode and cathode for 10 minutes to perform anodization. The anodized anode was then removed from the aqueous solution, washed with pure water, and dried. In this way, a sample according to Comparative Example 1 was obtained, in which a dielectric film was formed on the surface of tantalum metal.

[0066] Comparative Example 2: The surface of metallic tantalum was cleaned by ultrasonic cleaning for 10 minutes while immersed in a container filled with acetone. The acetone adhering to the surface of the metallic tantalum was then evaporated, and the surface of the metallic tantalum was washed with pure water. The metallic tantalum was then dried in the atmosphere.

[0067] Tantalum metal as an anode and platinum foil as a cathode were placed at a predetermined distance in an aqueous solution containing H3PO4. The portions of the anode and cathode not immersed in the aqueous solution were connected to the positive and negative terminals of a power supply, respectively. A constant voltage current was applied from the power supply, and a voltage of 80 V was applied between the anode and cathode for 30 minutes. An electrochemical reaction was induced on the surface of the tantalum metal anode, yielding a dielectric film, which was an oxide film. The tantalum metal with the oxide film formed was removed from the aqueous solution, washed with pure water, and dried in the air. In this way, a sample according to Comparative Example 2 was obtained, which had a dielectric film formed from fluorine-free tantalum oxide.

[0068] (X-ray Diffraction Measurement) An XRD pattern was obtained by 2θ / θ scanning of the dielectric film of the sample according to Example 1 using an X-ray diffraction (XRD) device Smartlab manufactured by Rigaku Corporation. Cu-Kα radiation was used as the X-ray source, and the voltage was adjusted to 40 kV, the current to 30 mA, and the scanning speed to 10 deg. / min. FIG. 5 shows the XRD pattern of the dielectric film of the sample according to Example 1. No peaks attributable to a crystalline structure were confirmed in the XRD pattern shown in FIG. 5, indicating that the tantalum oxide film of the sample according to Example 1 was amorphous.

[0069] (Elemental Composition Analysis) Using a Rutherford Backscattering Spectroscopy (RBS) apparatus, Pelletron 5SDH-2, RBS was performed on samples prepared from the surface regions of the dielectric layers of the samples according to Examples 1 and 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 ratio of the number of fluorine atoms to the number of tantalum atoms in the surface region of the dielectric layer of the sample according to Example 1 was 0.06, and the ratio of the number of fluorine atoms to the number of tantalum atoms in the surface region of the dielectric layer of the sample according to Example 2 was 0.40. According to the obtained RBS spectrum, the composition of the surface region of the dielectric layer of the sample according to 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 It was.

[0070] (TOF-SIMS) A fragment of a predetermined size was cut out from the sample according to Example 1 and embedded in resin to prepare a specimen for TOF-SIMS. Using a TOF-SIMS device TOF.SIMS5 manufactured by ION-TOF, TOF-SIMS was performed on the specimen prepared from the sample according to Example 1, and a composition analysis was performed in the depth direction of the oxide film of the dielectric film. In the 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 in TOF-SIMS of the sample according to Example 1. － , TaO ３－ , and O －6 is a graph showing the relationship between the signal intensity of each ion and the depth in the dielectric film. In Fig. 6, the vertical axis shows the signal intensity of each ion, and the horizontal axis shows the depth in the dielectric film.

[0071] For the sample according to Comparative Example 1, TOF-SIMS was performed in the same manner as in Example 1. FIG. － , TaO ３－ , and O － 7 is a graph showing the relationship between the signal intensity of each ion and the depth in the dielectric film. In Fig. 7, the vertical axis shows the signal intensity of each ion, and the horizontal axis shows the depth in the dielectric film.

[0072] 6, it can be seen that the dielectric film of the sample according to Example 1 is formed on metal tantalum and includes a region with a high fluorine concentration and a region with a low fluorine concentration. The region with a high fluorine concentration exists from the surface of the dielectric film to a depth of about 60 nm. On the other hand, the region with a low fluorine concentration exists from a depth of about 75 nm to a depth of about 150 nm in the dielectric film. F in the region with a low fluorine concentration of the dielectric film － From the signal intensity of , it can be understood that the fluorine concentration in this region is 0.5% or less on the basis of the number of atoms. The variation in fluorine concentration between the region with high fluorine concentration and the region with low fluorine concentration is small. － The signal intensity R F1 fluorine concentration in the tantalum oxide film 30 is low. － The signal intensity R F2 6, the depth of about 150 nm or more corresponds 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, as shown in FIG. 7 , the dielectric film of the sample according to Comparative Example 1 is understood to extend to a depth of approximately 180 nm from the surface. In the sample according to Comparative Example 1, an increased fluorine concentration was observed at the boundary between the metallic tantalum and the dielectric film. This is thought to be due to the fact that the diffusion rate of fluoride ions is much faster than that of oxide ions, causing fluoride ions to diffuse into the metallic tantalum and the generation of tantalum fluoride prior to the formation of a tantalum oxide film by anodization. The tantalum fluoride thus generated has poor electrical insulation properties and may degrade the dielectric properties required for a capacitor. In addition, the presence of such tantalum fluoride near the metallic tantalum may result in uneven formation of the tantalum oxide film, potentially causing peeling of the tantalum oxide film. Therefore, a dielectric with tantalum fluoride present near the metallic tantalum is hardly suitable as a dielectric for a capacitor. On the other hand, by performing a chemical conversion treatment using a fluorine-free solution in advance, as in Example 1, a fluorine-containing tantalum oxide film can be easily formed on the metallic tantalum without peeling.

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

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

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

[0078] The dielectric layers of the samples according to Example 1, Example 2, Comparative Example 1, and Comparative Example 2 were formed on tantalum metal with similar surface conditions, and it is understood that there was little difference in the surface area of ​​the dielectric layers of each sample. As shown in Figures 8A and 8B, the capacitances of the capacitors according to Example 1, Example 2, and Comparative Example 1 were higher than that of the capacitor according to Comparative Example 2. Although the capacitance of the capacitor according to Comparative Example 1 was high, as shown in Figures 9A and 9B, the dielectric loss tangent tanδ of the capacitor according to Comparative Example 1 was high. Tanδ corresponds to the energy consumed inside the capacitor, and it is understood that the capacitor according to Comparative Example 1 had a large loss of electrical energy. On the other hand, the dielectric loss tangent tanδ of the capacitors according to Examples 1 and 2 was low, remaining at a value equivalent to that of the capacitor according to Comparative Example 2. Therefore, it is understood that, overall, the capacitors according to Examples 1 and 2 were superior not only in terms of capacitance but also in terms of low electrical energy loss.

[0079] The capacitor according to the present disclosure is advantageous from the viewpoint of reducing the dielectric loss tangent.

Claims

1. Tantalum metal, A conductor; a tantalum oxide film disposed in contact with the tantalum metal and between the tantalum metal and the conductor; 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 a 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; Capacitor.

2. The first portion is amorphous. The capacitor of claim 1 .

3. The first portion is TaO x F y The composition is represented by The composition satisfies the condition 0<x<2.

5. The capacitor of claim 1 .

4. The composition further satisfies the condition y≧0.015; The capacitor according to claim 3 .

5. The composition further satisfies the condition y≦0.40; The capacitor according to claim 4.

6. The concentration of fluorine in the second portion is 0.4% or less based on the number of atoms. The capacitor of claim 1 .

7. The second portion has a thickness of more than 5 nm and not more than 100 nm. The capacitor of claim 1 .

8. Further comprising an electrolyte disposed between the tantalum oxide film and the conductor. The capacitor of claim 1 .

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

10. A circuit board comprising the capacitor according to claim 1 .

11. An apparatus comprising a capacitor according to any one of claims 1 to 8.

12. A method of producing a tantalum oxide film by anodizing a tantalum metal in a state where the tantalum metal is in contact with an aqueous solution not containing fluoride ions, and performing anodization in a state in which the tantalum oxide layer formed on the metal tantalum by the anodization is brought into contact with an aqueous solution containing fluoride ions, thereby obtaining a tantalum oxide film containing fluorine in a surface region of the tantalum oxide layer. How a capacitor is manufactured.