Multilayer body, capacitor, electrical circuit, circuit board, apparatus, and multilayer body manufacturing method

Abstract

A multilayer body 1a is provided with metal tantalum 10 and a dielectric layer 20. The dielectric layer 20 is in contact with the metal tantalum 10 and contains an oxide containing tantalum and tungsten. At 120 Hz, the dielectric layer 20 has a relative permittivity greater than 27 and equal to or smaller than 41.7.

Description

Laminate, capacitor, electric circuit, circuit board, device, and method for manufacturing laminate

[0001] The present disclosure relates to a laminate, a capacitor, an electric circuit, a circuit board, a device, and a method for manufacturing the laminate.

[0002] Conventionally, a technique for improving the dielectric constant by anodic oxidation has been known.

[0003] For example, Patent Document 1 describes a high-dielectric-constant composite oxide film of a metal selected from metals belonging to Groups IIIa, IVa, and Va, containing 1 to 50 wt % of the central atom of an anion of an inorganic oxoacid salt. This high-dielectric-constant composite oxide film has a relative dielectric constant that is at least twice that of the oxide of the metal. This high-dielectric-constant composite oxide film is produced by electrolytic anodizing of a metal selected from metals belonging to Groups IIIa, IVa, and Va in a nonaqueous electrolyte containing an inorganic oxoacid salt and having a water content of 5 wt % or less.

[0004] Patent Document 2 describes a method for manufacturing a solid capacitor. This manufacturing method includes a step of forming a dielectric oxide film layer on the surface of a metal substrate and a step of surface-treating the dielectric oxide film layer. In the step of surface-treating the dielectric oxide film layer, the part on which the dielectric oxide film layer is formed is immersed in a surface-treatment aqueous solution containing one or more of phosphotungstic acid, molybdic acid, phosphomolybdic acid, or salts thereof. For example, an aluminum anodic oxide film layer can be immersed in a solution of phosphotungstic acid (H3(PW 12 O 40 The aluminum anodized film is then immersed in an aqueous solution to form a thin inorganic oxide layer of P2O5WO3 on the aluminum anodized film. The metal substrate may be a tantalum foil, a tantalum sintered body, or the like.

[0005] Patent Document 3 describes a tantalum solid electrolytic capacitor, which uses tungsten-doped tantalum metal powder.

[0006] Patent Document 4 describes a two-terminal nonlinear element that is manufactured by a method including a step of anodizing a first conductive film made of tantalum in a predetermined non-aqueous chemical conversion solution to form an insulating film on the surface of the first conductive film.

[0007] Non-Patent Document 1 describes the formation of an anodic film on a Ta-W alloy magnetron sputtered film. The anodic film consists of two layers: an outer TaO thin film containing no tungsten species, and an inner layer containing both tantalum and tungsten species.

[0008] JP 8-134696 JP 10-154639 JP 9-293647 JP 10-275949

[0009] Masatoshi ISHIZUKA, Etsushi TSUJI, Yoshitaka AOKI, Hiroki HABAZAKI: “Formation and Dielectric Properties of Anodic Films Formed on Ta-W Alloys at Various Formation Voltages”, 81, p.840-844 (2013)

[0010] The present disclosure provides a novel stack comprising a selected dielectric layer on tantalum metal.

[0011] The laminate of the present disclosure comprises: metallic tantalum; and a dielectric layer in contact with the metallic tantalum and containing an oxide containing tantalum and tungsten, wherein the dielectric layer has a relative dielectric constant greater than 27 and not greater than 41.7 at 120 Hz.

[0012] According to the present disclosure, a novel laminate can be provided that includes a predetermined dielectric layer on metal tantalum.

[0013] FIG. 1 is a cross-sectional view showing an example of a laminate according to the present disclosure. FIG. 2 is a potential-pH diagram showing the state of tungsten in water. FIG. 3 is a flowchart showing an example of a method for manufacturing a laminate according to the present disclosure. FIG. 4 is a cross-sectional view showing an example of a capacitor according to the present disclosure. FIG. 5 is a cross-sectional view showing another example of a capacitor according to the present disclosure. FIG. 6A is a diagram schematically showing an example of an electric circuit according to the present disclosure. FIG. 6B is a diagram schematically showing an example of a circuit board according to the present disclosure. FIG. 6C is a diagram schematically showing an example of a device according to the present disclosure. FIG. 7 is a graph showing the relationship between the oxygen and tungsten concentrations in a sample according to Example 1 and the depth from the surface of the sample.

[0014] (Findings underlying the present disclosure) According to the technology described in Patent Document 1, electrolytic anodization of metal is performed in a nonaqueous electrolyte containing an inorganic oxoacid salt and having a water content of 5 wt % or less, and the oxygen source required to form a dielectric film is substantially limited to the oxygen contained in the oxoacid. For this reason, it is difficult to oxidize, for example, metallic tantalum to a state corresponding to its highest oxidation state. This is hardly advantageous from the perspective of reducing current leakage when a voltage is applied to the dielectric.

[0015] According to the technique described in Patent Document 2, it is necessary to form a dielectric oxide film layer by anodization or the like before the surface treatment using a surface treatment aqueous solution containing phosphotungstic acid or the like.

[0016] It is understood that the techniques described in Patent Document 3 and Non-Patent Document 1 form a dielectric containing tungsten and an oxide containing tantalum by anodizing an alloy of tantalum and tungsten. However, these techniques require an alloy of tantalum and tungsten, which may cause limitations in terms of mass production.

[0017] The technology described in Patent Document 4 relates to a two-terminal nonlinear element in which the element capacitance of the MIM element is sufficiently small, and the relative dielectric constant of the MIM element according to the embodiment is 17.7 to 20.5.

[0018] In view of these circumstances, the present inventors have conducted extensive research into whether it is possible to obtain a laminate comprising, on metal tantalum, a dielectric layer containing an oxide containing tantalum and tungsten and having a predetermined dielectric constant. After extensive trial and error, the present inventors have discovered a new method for obtaining such a laminate. Based on this new finding, the present inventors have devised the laminate of the present disclosure.

[0019] (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.

[0020] FIG. 1 is a cross-sectional view showing an example of a laminate of the present disclosure. As shown in FIG. 1, the laminate 1a includes a tantalum metal 10 and a dielectric layer 20. The dielectric layer 20 is in contact with the tantalum metal 10 and contains an oxide containing tantalum and tungsten. The dielectric layer 20 has a relative dielectric constant greater than 27 and equal to or less than 41.7 at 120 Hz. The relative dielectric constant of the dielectric layer formed on the tantalum metal can be determined, for example, according to the method described in the Examples.

[0021] The dielectric constant values ​​of metal oxides that can be formed by anodizing metals are shown in Table 1. As shown in Table 1, WO obtained by anodizing is amorphous and has the highest dielectric constant among the amorphous metal oxides listed below. For this reason, for example, if the metal oxide obtained by anodizing metal tantalum contains tungsten in addition to tantalum, it is expected that the dielectric constant of the dielectric layer obtained by anodizing metal tantalum will be high.

[0022]

[0023] Figure 2 is a potential-pH diagram showing the state of tungsten in water. As shown in Figure 2, tungsten is water-soluble when the pH is equal to or greater than a predetermined value in the range of 4 to 7, depending on its concentration in water. Therefore, when anodizing metallic tantalum using an aqueous solution of a tungsten compound having a pH equal to or greater than a predetermined value in the range of 4 to 7, the tungsten incorporated into the dielectric layer formed by the anodization may re-dissolve in the aqueous solution due to a reverse reaction. For example, in the technology described in Non-Patent Document 1, an ammonium borate aqueous solution is used to anodize a Ta-W alloy. The pH of the ammonium borate aqueous solution is generally about 8.2. Therefore, it is thought that tungsten dissolves into the ammonium borate aqueous solution from the surface of the dielectric formed by the anodizing of the Ta-W alloy.

[0024] The laminate 1a can be manufactured by, for example, a method including the following steps (I) and (II). Figure 3 is a flowchart showing an example of a method for manufacturing the laminate 1a. (I) Metallic tantalum is brought into contact with an acidic solution containing a tungsten compound. (II) While the metallic tantalum is in contact with the above solution, the metallic tantalum is anodized.

[0025] First, in step S11, metallic tantalum is brought into contact with an acidic solution containing a tungsten compound. The solution is preferably an aqueous solution having a pH of 4 or less. This makes it difficult for tungsten to dissolve from the dielectric layer formed by anodizing metallic tantalum, and the tungsten concentration in the dielectric layer is likely to be high. This makes it easy to adjust the relative dielectric constant of the dielectric layer to a desired range. The pH of the aqueous solution may be 3.5 or less, 3.0 or less, 2.5 or less, 2.0 or less, 1.5 or less, or 1.0 or less.

[0026] The tungsten compound contained in the solution is not limited to a specific compound. The solution may contain, for example, an electrolyte containing polytungstic acid or polytungstate, which contains two or more tungsten atoms per anion molecule. In this case, tungsten is likely to be stable in the solution, and the tungsten concentration in the dielectric layer is likely to be high. Therefore, the relative permittivity of the dielectric layer can be easily adjusted to a desired range.

[0027] The polytungstic acid or polytungstate preferably has a heteroatom with a valence of 3 or more, which tends to lower the pH of the aqueous solution. Examples of heteroatoms are phosphorus and silicon.

[0028] The concentration of the tungsten compound in the solution is not limited to a specific value. The concentration is, for example, 0.5 mass % or more. In this case, the concentration of tungsten in the dielectric layer is likely to be high, and the relative dielectric constant of the dielectric layer is likely to be adjusted to a desired range.

[0029] The concentration of the tungsten compound in the solution is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 2.5% by mass or more. This concentration may be 5% by mass or more, 10% by mass or more, 15% by mass or more, or 20% by mass or more. This concentration may be, for example, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, or 30% by mass or less. This concentration may be, for example, 0.5% by mass or more to 50% by mass or less, preferably 1% by mass or more to 50% by mass or less, more preferably 2% by mass or more to 50% by mass or less, and even more preferably 2.5% by mass or more to 50% by mass or less.

[0030] The above solution satisfies, for example, at least one condition selected from the group consisting of (i) and (ii) below. This makes it easy to increase the tungsten concentration in the dielectric layer and adjust the dielectric constant of the dielectric layer to a desired range. Heteropolytungstic acid is a polytungstic acid whose anion, an oxoacid ion, contains an oxyacid of an element (heteroatom) other than Group V elements and Group VI elements (V, Nb, Ta, Mo, and W). (i) The solution contains an electrolyte containing heteropolytungstic acid or heteropolytungstate, in which one molecule of the anion contains two or more tungsten atoms. (ii) The concentration of the tungsten compound in the solution is 0.5% by mass or more.

[0031] Next, in step S12, the tantalum metal is brought into contact with the solution and anodized. For example, a predetermined voltage is applied between the tantalum metal and a counter electrode in the solution, with the tantalum metal and the counter electrode positioned at a predetermined distance, to perform anodization. For example, the tantalum metal is used as the anode, and platinum is used as the cathode. Anions such as oxide ions attracted toward the tantalum metal (the anode) combine with the ionized tantalum to produce tantalum oxide. At this time, tungsten contained in the solution is incorporated into the dielectric layer. As a result, a dielectric layer 20 containing an oxide containing tantalum and tungsten is formed on the tantalum metal 10, resulting in a laminate 1a. In this manner, the dielectric layer 20 is, for example, an anodized oxide film.

[0032] The dielectric layer 20 may be manufactured by a method other than anodization, for example, sputtering. The dielectric layer 20 may be a sputtered film.

[0033] The relative dielectric constant of the dielectric layer 20 may be, for example, 28 or more, or 29 or more, or 40 or less.

[0034] The average tungsten concentration in the dielectric layer 20 is not limited to a specific value. The average value is, for example, 0.1 mass % or more and 20 mass % or less. In this case, the dielectric layer 20 is likely to have a desired relative dielectric constant. In addition, oxygen deficiency is less likely to occur in the dielectric layer 20, and the durability of products including the laminate 1a is likely to be high. The average tungsten concentration in the dielectric layer 20 may be 0.15 mass % or more or 0.2 mass % or more, or may be 15 mass % or less, 10 mass % or less, 5 mass % or less, 4 mass % or less, 3 mass % or less, 2 mass % or less, or 1 mass % or less. The average tungsten concentration in the dielectric layer 20 can be determined, for example, according to the method described in the Examples.

[0035] In measurements of the dielectric layer 20 by time-of-flight secondary ion mass spectrometry (TOF-SIMS), the intensity of the signal of ions derived from tungsten is lower than the intensity of the signal of ions derived from, for example, tantalum oxide.

[0036] The thickness of the dielectric layer 20 is not limited to a specific value. The thickness is, for example, 10 nm or more and 1000 nm or less. The thickness of the dielectric layer 20 may be determined based on, for example, the measurement results of TOF-SIMS, or may be determined based on observation of a cross section of the dielectric layer using an electron microscope such as a scanning electron microscope (SEM) or a transmission electron microscope (TEM).

[0037] The dielectric layer 20 includes, for example, a portion 21. The portion 21 has a tungsten concentration of 0.15 mass % or more and a thickness of 10 nm or more. In this case, the dielectric layer 20 is more likely to have a desired relative dielectric constant, and the durability of a product including the laminate 1a is likely to be increased. The thickness of the portion 21 may be 20 nm or more, 50 nm or more, or 100 nm or more, or 1000 nm or less, 500 nm or less, or 200 nm or less.

[0038] The tungsten concentration in the dielectric layer 20 may, for example, decrease continuously or discontinuously with increasing distance from the surface of the dielectric layer 20 (the surface not in contact with the metal tantalum 10) in the thickness direction of the dielectric layer 20. The dielectric layer 20 may include a portion where the tungsten concentration increases with increasing distance from the surface of the dielectric layer 20.

[0039] There is no particular limitation on the shape of the metal tantalum 10. The metal tantalum 10 may be in the form of a plate or foil, or may be in the form of particles or fibers, or may be porous.

[0040] 4 is a cross-sectional view showing an example of a capacitor according to the present disclosure. As shown in FIG. 4, the capacitor 2a includes a first electrode 11 containing metal tantalum 10, a second electrode 12, and a dielectric layer 20. The dielectric layer 20 is disposed between the first electrode 11 and the second electrode 12. The dielectric layer 20 contains an oxide containing tantalum and tungsten. The dielectric layer 20 has a relative dielectric constant greater than 27 and equal to or less than 41.7 at 120 Hz. This configuration allows the capacitor 2a to have a high capacitance.

[0041] The capacitor 2a can be manufactured, for example, by forming or disposing the second electrode 12 on the surface of the dielectric layer 20 in the laminate 1a. Therefore, the dielectric layer 20 in the capacitor 2a can have the structure and properties derived from the dielectric layer 20 in the laminate 1a.

[0042] The second electrode 12 is not limited to a specific material as long as it is conductive. The second electrode 12 may include, for example, a valve metal such as aluminum, tantalum, niobium, or bismuth, a noble metal such as gold or platinum, or nickel. The second electrode 12 may also include a carbon material such as graphite.

[0043] In the capacitor 2a, the surface of the dielectric layer 20 may be in contact with an electrolyte. In this case, the second electrode 12 may contain an electrolyte. This electrolyte is not limited to a specific electrolyte. For example, the electrolyte contains at least one selected from the group consisting of an electrolytic solution, a solid electrolyte, and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte may also be a manganese compound such as manganese oxide.

[0044] Fig. 5 is a cross-sectional view showing another example of a capacitor according to the present disclosure. Capacitor 2b shown in Fig. 5 has the same configuration as capacitor 2a, except for portions that will be specifically described. Components of capacitor 2b that are the same as or correspond to those of capacitor 2a are designated by the same reference numerals, and detailed descriptions thereof will be omitted. The description of capacitor 2a also applies to capacitor 2b, unless technically inconsistent.

[0045] 5, in capacitor 2b, dielectric layer 20 and first electrode 11 form a porous body 15. Second electrode 12 fills pores 15p of porous body 15. With this configuration, the area of ​​first electrode 11 is increased, and capacitor 2b is therefore likely to have a higher capacitance.

[0046] Porous body 15 can be obtained, for example, by anodizing porous tantalum metal 10 in contact with an acidic solution containing a tungsten compound. Porous tantalum metal 10 can be obtained, for example, by etching a tantalum metal foil or sintering a tantalum metal powder.

[0047] In the capacitor 2b, the second electrode 12 includes, for example, an electrolyte. The electrolyte includes, for example, at least one selected from the group consisting of an electrolytic solution, a solid electrolyte, and a conductive polymer. Examples of the conductive polymer include polypyrrole, polythiophene, polyaniline, and derivatives thereof. The electrolyte may also be a manganese compound such as manganese oxide.

[0048] 6A is a diagram schematically illustrating an example of an electric circuit according to the present disclosure. The electric circuit 3 includes a capacitor 2a. 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 2a, 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 2b.

[0049] Fig. 6B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. As shown in Fig. 6B, the circuit board 5 includes a capacitor 2a. For example, an electric circuit 3 including the capacitor 2a is formed on the circuit board 5. Since the circuit board 5 includes the capacitor 2a, 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 2b.

[0050] FIG. 6C is a schematic diagram illustrating an example of a device according to the present disclosure. As shown in FIG. 6C , the device 7 includes a capacitor 2a. The device 7 includes, for example, a circuit board 5 including the capacitor 2a. Because the device 7 includes the capacitor 2a, the device 7 is likely to exhibit desired performance. The device 7 may be an electronic device, a communication device, a signal processing device, or a power supply. The device 7 may be a server, an AC adapter, an accelerator, or a flat panel display such as a liquid crystal display (LCD). The device 7 may be a USB charger, a solid-state drive (SSD), an information terminal such as a PC, a smartphone, or a tablet PC, or an Ethernet switch. The device 7 may also include a capacitor 2b.

[0051] (Additional Notes) From the above, the following technologies are disclosed. (Technology 1) A laminate comprising metallic tantalum and a dielectric layer in contact with the metallic tantalum and containing an oxide containing tantalum and tungsten, wherein the dielectric layer has a relative dielectric constant greater than 27 and equal to or less than 41.7 at 120 Hz. (Technology 2) The laminate according to Technology 1, wherein the average tungsten concentration in the dielectric layer is 0.1 mass% or more and 20 mass% or less. (Technology 3) The laminate according to Technology 1 or 2, wherein the dielectric layer includes a portion having a tungsten concentration of 0.15 mass% or more and a thickness of 10 nm or more. (Technology 4) A capacitor comprising a first electrode containing metallic tantalum, a second electrode, and a dielectric layer disposed between the first electrode and the second electrode and containing an oxide containing tantalum and tungsten, wherein the dielectric layer has a relative dielectric constant greater than 27 and equal to or less than 41.7 at 120 Hz. (Technology 5) An electric circuit comprising the capacitor according to Technology 4. (Technology 6) A circuit board comprising the capacitor according to Technology 4. (Technology 7) An apparatus comprising the capacitor according to Technology 4. (Technology 8) A method for producing a laminate, comprising: bringing metallic tantalum into contact with an acidic solution containing a tungsten compound; and anodizing the metallic tantalum while the metallic tantalum is in contact with the solution. (Technology 9) A method for producing a laminate according to Technology 8, wherein the solution satisfies at least one condition selected from the group consisting of (i) and (ii) below: (i) The solution contains an electrolyte containing heteropolytungstic acid or heteropolytungstate, which contains two or more tungsten atoms in one molecule of anion. (ii) The concentration of the tungsten compound in the solution is 0.5 mass% or more. (Technology 10) A method for producing a laminate according to Technology 8 or 9, wherein the solution is an aqueous solution having a pH of 4 or less. (Technology 11) The method for producing a laminate according to any one of Technologies 8 to 10, wherein the solution satisfies the condition (i). (Technology 12) The method for producing a laminate according to any one of Technologies 8 to 10, wherein the solution satisfies the condition (ii).(Technology 13) The method for producing a laminate according to any one of Techniques 8 to 12, wherein the solution satisfies the conditions (i) and (ii). (Technology 14) The method for producing a laminate according to Technique 8, wherein the heteropolytungstic acid or heteropolytungstate salt has a heteroatom having a valence of 3 or more.

[0052] 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.

[0053] 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.

[0054] H4SiW at a concentration of 100 mmol (millimol) / L 12 O 40 In the aqueous solution, a metal tantalum electrode and a counter electrode were placed at a predetermined distance. The pH of the aqueous solution was less than 1. 12 O 40 The concentration of was 22% by mass. The portion of the metallic tantalum not immersed in the aqueous solution was connected to the positive electrode of a power supply, and the portion of the metallic tantalum not immersed in the aqueous solution, serving as the counter electrode, was connected to the negative electrode of the power supply. A current was applied from the power supply at a constant voltage, and a voltage of 95 V was applied between the metallic tantalum connected to the positive electrode and the metallic tantalum serving as the counter electrode for 10 hours. An electrochemical reaction was induced on the surface of the metallic tantalum serving as the anode, yielding an oxide film. The metallic tantalum on which the oxide film had been formed was removed from the aqueous solution, washed with pure water, and dried in the air. In this manner, a sample according to Example 1 was obtained, in which a dielectric film, an oxide film, was formed on the surface of the metallic tantalum.

[0055] Example 2: H3PW at a concentration of 100 mmol / L 12 O 40 The aqueous solution was 12 O 40A sample according to Example 2 was obtained in the same manner as in Example 1, except that H3PW was used instead of an aqueous solution. 12 O 40 The pH of the aqueous solution was less than 1. 12 O 40 The concentration was 22% by mass.

[0056] Example 3 H4SiW 12 O 40 A sample according to Example 3 was obtained in the same manner as in Example 1, except that the concentration of the aqueous solution was changed to 10 mmol / L. 12 O 40 The pH of the aqueous solution was 1.4. 12 O 40 The concentration was 2.8% by mass.

[0057] Comparative Example 1: Aqueous H3PO4 solution was mixed with H4SiW 12 O 40 A sample according to Comparative Example 1 was obtained in the same manner as in Example 1, except that the aqueous solution was used instead.

[0058] (Film Thickness Measurement and Elemental Composition Analysis) Using a scanning electron microscope (SEM) ISM7900F manufactured by JEOL Ltd., the cross sections of the samples according to Examples 1, 2, and 3 were observed. In this observation, the cross sections of the samples of each Example were polished using a cross-section polisher, and the cross sections were observed perpendicular to the cross sections to determine the film thickness of the dielectric film. Furthermore, energy dispersive X-ray fluorescence analysis (EDX) was performed on the SEM, and the tungsten concentration in the dielectric film was calculated by averaging the tungsten concentration at four locations to smooth out errors due to the spot location. The results are shown in Table 2. The spot diameter of the device used to determine the concentration was approximately 100 nm to 200 nm, and since smoothing was performed at multiple locations, this concentration is understood to correspond to the average tungsten concentration in the dielectric film.

[0059]

[0060] (Elemental Concentration Distribution Measurement) Glow Discharge Optical Emission Spectroscopy (GD-OES) was performed on samples prepared from the surface regions of the dielectric films of the samples according to Examples 1 and 2 using a GD-Profiler 2 glow discharge optical emission spectroscopy (GD-OES) system manufactured by Horiba, Ltd. In the GD-OES, argon gas was sputtered onto the sample under specified conditions to obtain an emission spectrum. The emission spectrum was converted to mass concentration using software provided with the GD-Profiler 2. Because GD-OES is a semi-quantitative analytical method, the absolute values ​​of the concentrations of the elements of interest are not necessarily highly reliable. Therefore, the GD-OES measurement results are used only to evaluate the concentration distribution of the elements of interest in the thickness direction of the dielectric film of each example sample. The value based on the EDX described above was used as the average tungsten concentration in the dielectric film.

[0061] FIG. 7 is a graph showing the relationship between the oxygen and tungsten concentrations and the depth from the surface of the sample according to Example 1. This graph was obtained based on GD-OES of the sample according to Example 1. In FIG. 7, the upper graph shows the relationship between the oxygen concentration and the depth from the surface of the sample. In this graph, the vertical axis represents the oxygen concentration [mass %], and the horizontal axis represents the depth from the surface of the sample. In FIG. 7, the lower graph shows the relationship between the tungsten concentration and the depth from the surface of the sample. In this graph, the vertical axis represents the tungsten concentration [mass %], and the horizontal axis represents the depth from the surface of the sample.

[0062] In the lower graph of Figure 7 , the portion corresponding to a tungsten concentration of 0.1 mass % or less is considered to be background noise resulting from the similarity between the Ta and W emission spectra. As shown in Table 2, the dielectric film of the sample according to Example 1 had a thickness of 183 nm, and the oxygen and tungsten concentrations also rapidly decrease at depths of 180 nm or more in the graph of Figure 7 . According to the lower graph of Figure 7 , the tungsten concentration is higher than the background noise at the depth corresponding to the dielectric film, suggesting that tungsten is present throughout the entire thickness of the dielectric film. In other words, the dielectric film of the sample according to Example 1 can be said to contain an oxide containing tantalum and tungsten. Similarly, in the dielectric films of the samples according to Examples 2 and 3, tungsten is considered to be present throughout the entire thickness of the dielectric film.

[0063] (Dielectric Constant Measurement) The sample according to Example 1 was immersed in a sulfuric acid solution, and the dielectric properties of the dielectric films of the samples according to Examples 1, 2, and 3, and Comparative Example 1 were evaluated according to the AC impedance method using platinum as the counter electrode. The results are shown in Table 3. A Modulab XM manufactured by Solartron Analytics was used for the AC impedance measurement. In this evaluation, an AC voltage was applied to the capacitor according to Example 1 with an amplitude of 10 mV to 100 mV and a frequency range of 1 MHz to 0.1 Hz, and the capacitance C was calculated from the complex impedance at 120 Hz. The relative dielectric constant ε was calculated according to the following formula (1) using the calculated capacitance C, the thickness t of the dielectric film calculated from SEM observation, and the electric constant ε, which is the dielectric constant of vacuum. In formula (1), S is the surface area of ​​the metal tantalum on which the dielectric film is formed. ε=(C·t) / (εS) Formula (1)

[0064]

[0065] As shown in Table 3, a comparison between Examples 1 to 3 and Comparative Example 1 shows that the inclusion of tungsten in the dielectric film increases the dielectric constant of the dielectric film. In addition, according to Table 2, the tungsten concentration in the dielectric film of the sample according to Example 1 is higher than the tungsten concentration in the dielectric film of the sample according to Example 2. In addition, the tungsten concentration in the dielectric film of the sample according to Example 2 is higher than the tungsten concentration in the dielectric film of the sample according to Example 3. A comparison between Examples 1 and 2 and a comparison between Examples 2 and 3 shows that a high tungsten concentration in the dielectric film is advantageous in increasing the dielectric constant of the dielectric film.

[0066] The laminate of the present disclosure can be suitably used in electronic components such as capacitors.

Claims

1. A laminate comprising: metallic tantalum; and a dielectric layer in contact with the metallic tantalum, the dielectric layer containing an oxide containing tantalum and tungsten, wherein the dielectric layer has a relative dielectric constant greater than 27 and less than or equal to 41.7 at 120 Hz.

2. The laminate according to claim 1, wherein the average tungsten concentration in the dielectric layer is 0.1 mass % or more and 20 mass % or less.

3. The laminate according to claim 1, wherein the dielectric layer includes a portion having a tungsten concentration of 0.15 mass % or more and a thickness of 10 nm or more.

4. A capacitor comprising: a first electrode containing metallic tantalum; a second electrode; and a dielectric layer disposed between the first electrode and the second electrode and containing an oxide containing tantalum and tungsten, wherein the dielectric layer has a relative dielectric constant greater than 27 and not greater than 41.7 at 120 Hz.

5. An electric circuit comprising the capacitor according to claim 4.

6. A circuit board comprising the capacitor according to claim 4.

7. A device comprising the capacitor according to claim 4.

8. A method for producing a laminate, comprising: bringing metallic tantalum into contact with an acidic solution containing a tungsten compound; and anodizing the metallic tantalum while the metallic tantalum is in contact with the solution, wherein the solution satisfies at least one condition selected from the group consisting of (i) and (ii). (i) The solution contains an electrolyte containing heteropolytungstic acid or heteropolytungstate, which contains two or more tungsten species per molecule of anion. (ii) The concentration of the tungsten compound in the solution is 0.5 mass% or more.

9. The method for producing a laminate according to claim 8, wherein the solution is an aqueous solution having a pH of 4 or less.

10. The method for producing a laminate according to claim 8, wherein the solution satisfies the condition (i).

11. The method for producing a laminate according to claim 8, wherein the solution satisfies the condition (ii).

12. The method for producing a laminate according to claim 8, wherein the solution satisfies the conditions (i) and (ii).

13. The method for producing a laminate according to claim 8, wherein the heteropolytungstic acid or heteropolytungstate salt has a heteroatom with a valence of 3 or more.

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