Dielectric, capacitor, electric circuit, circuit board, apparatus, and power storage device

Abstract

This dielectric 10 has a composition represented by BixMgyTizOk. This composition satisfies the conditions x ≥ 0.15, y ≤ 0.40, z ≥ 0.25, and x + y + z = 1.0. In this composition, k is a value for maintaining electrical neutrality.

Description

Dielectrics, capacitors, electric circuits, circuit boards, equipment, and power storage devices

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

[0002] Conventionally, capacitors using ceramics have been known. For example, Patent Document 1 describes a multilayer ceramic capacitor having dielectric ceramic layers containing an oxide having Ba, Ca, and Ti.

[0003] Patent Document 2 describes a dielectric composition having a perovskite-type crystal structure containing at least Bi, Na, Sr, and Ti. This dielectric composition contains specific particles having a core-shell structure with at least one core containing SrTiO. This dielectric composition can form a dielectric layer of a multilayer ceramic capacitor.

[0004] Patent Document 3 describes a capacitor having an insulating structure including a polymer layer and a composite layer. The composite layer is disposed on the polymer layer and includes a thermoplastic polymer containing at least one inorganic component. This capacitor can be used for power conversion with high energy density.

[0005] Non-Patent Document 1 describes the perovskite Bi(Mg 0.5 Ti x )O3 thin films are described, in which x is between 0.50 and 0.85.

[0006] Non-Patent Document 2 describes BiMg y Ti 0.5 O3 films are described in which y is between 0.50 and 0.62.

[0007] JP 2000-058378 A JP 2018-531858 A JP 2010-278430 A

[0008] Journal of Materials Chemistry C, 2019, vol.7, p.13632-13639Journal of the European Ceramic Society, 2020, vol.40, p.1243-1249

[0009] The techniques described in the above documents need to be reconsidered from the viewpoint of increasing the capacitance of a capacitor under conditions of high electric field strength. Therefore, the present disclosure provides a novel dielectric that is advantageous from the viewpoint of increasing the capacitance of a capacitor under conditions of high electric field strength.

[0010] The dielectric of the present disclosure is Bi 2x Mg y Ti z O k The composition satisfies the conditions of x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0, and in the composition, k is a value for maintaining electrical neutrality.

[0011] According to the present disclosure, a novel dielectric can be provided that is advantageous from the viewpoint of increasing the capacitance of a capacitor under conditions of high electric field strength.

[0012] FIG. 1 is a cross-sectional view showing an example of a capacitor according to the present disclosure. FIG. 2 is a cross-sectional view showing another example of a capacitor according to the present disclosure. FIG. 3A is a diagram schematically showing an example of an electric circuit according to the present disclosure. FIG. 3B is a diagram schematically showing an example of a circuit board according to the present disclosure. FIG. 3C is a diagram schematically showing an example of an apparatus according to the present disclosure. FIG. 3D is a diagram schematically showing an example of an electricity storage device according to the present disclosure. FIG. 4 is an X-ray diffraction (XRD) pattern of a dielectric film according to Examples 1 to 5. FIG. 5 is an XRD pattern of a dielectric film according to Comparative Examples 2 to 7.

[0013] (Findings that form the basis of the present disclosure) In recent years, with the miniaturization of devices and the increase in operating voltages, there has been a demand for similar miniaturization and increase in operating voltages for electronic components used in electric circuits. For example, if it were possible to provide a capacitor that is small and can exhibit high capacitance under conditions of high electric field strength, it would be possible to contribute to the miniaturization of devices and the increase in operating voltages.

[0014] Barium titanate and its derivatives have traditionally been used as dielectrics in capacitors. Multilayer ceramic capacitors, for example, are widely used. Since the capacitance of a capacitor of the same shape is proportional to the dielectric constant of the dielectric, increasing the dielectric constant of the dielectric leads to smaller capacitors and higher capacitance. For example, high-dielectric-constant multilayer ceramic capacitors can have a very high dielectric constant of 1000 or more.

[0015] According to Patent Document 1, a dielectric based on barium titanate to which a predetermined amount of a specific oxide is added is understood to have a relative dielectric constant of 1000 or more under the condition that no DC voltage is applied. In addition, it is understood that the multilayer ceramic capacitor described in Patent Document 1 has a reduced rate of capacitance change when a DC voltage is applied at an electric field strength of 5 kV / mm. It is understood that the dielectric composition described in Patent Document 2 has a relative dielectric constant of 1000 or more under the condition that no DC voltage is applied. In addition, it is understood that the dielectric composition described in Patent Document 2 has a small rate of capacitance change before and after application of a DC bias of 5 V / μm.

[0016] On the other hand, for example, a high DC voltage of several hundred volts may be applied to a snubber capacitor or smoothing capacitor in an on-board converter or on-board inverter. In order to achieve miniaturization of a capacitor that is expected to be used under conditions where a high DC voltage is applied, it is considered important to increase the capacitance of the capacitor at a higher electric field strength than the electric field strength used in the evaluation of the rate of capacitance change in Patent Documents 1 and 2.

[0017] The insulating structure of the capacitor described in Patent Document 3 has a dielectric constant ranging from about 3 to 100 and a dielectric strength of about 150 kV / mm. Although this insulating structure has a high dielectric strength, it is understood that the dielectric constant of the insulating structure is not very high because it includes a polymer layer. In addition, Patent Document 3 does not evaluate the dielectric constant of the insulating structure at high electric field strengths near the dielectric strength.

[0018] According to the descriptions in Non-Patent Documents 1 and 2, it is understood that by adding an excess amount of titanium or magnesium in the synthesis of magnesium bismuth titanate, the saturated polarization density decreases, but the dielectric strength increases, and the capacity of the material increases. On the other hand, Non-Patent Documents 1 and 2 also state that Bi(Mg 0.5 Ti x ) O3 thin film and BiMg y Ti 0.5 The dielectric constant of the O3 film has not been evaluated.

[0019] In view of these circumstances, the present inventors have conducted extensive research to develop a novel dielectric that is advantageous in terms of increasing the capacitance of a capacitor under conditions of high electric field strength. As a result of extensive trial and error, the present inventors have obtained new knowledge regarding the relationship between the contents of Bi, Mg, and Ti in an oxide containing Bi, Mg, and Ti and the dielectric properties under high electric field strength. Based on this new knowledge, the present inventors have devised the dielectric of the present disclosure.

[0020] (Summary of one aspect of the present disclosure) A dielectric according to a first aspect of the present disclosure includes: Bi 2x Mg y Ti z O k The composition satisfies the conditions of x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0, and in the composition, k is a value for maintaining electrical neutrality.

[0021] According to the first aspect, the dielectric constant of the dielectric tends to be high under conditions of high electric field strength, which is advantageous from the viewpoint of increasing the capacitance of the capacitor under conditions of high electric field strength.

[0022] In the second aspect of the present disclosure, for example, the dielectric according to the first aspect may contain crystalline BiTiO. According to the second aspect, the dielectric constant of the dielectric is likely to be higher under high electric field strength conditions, which is advantageous from the viewpoint of increasing the capacitance of the capacitor under high electric field strength conditions.

[0023] In the third aspect of the present disclosure, for example, the dielectric according to the first or second aspect is crystalline Bi4Ti3O12 , crystalline γ-BiO, and crystalline Bi(Mg 0.5 Ti 0.5 )O3. According to the third aspect, the dielectric constant of the dielectric is likely to be higher under conditions of high electric field strength. Therefore, the dielectric is more advantageous from the viewpoint of increasing the capacitance of the capacitor under conditions of high electric field strength.

[0024] In a fourth aspect of the present disclosure, for example, the dielectric according to any one of the first to third aspects is crystalline Bi4Ti3O 12 and crystalline γ-BiO. According to the fourth aspect, the dielectric constant of the dielectric is likely to be higher under conditions of high electric field strength. Therefore, the dielectric is more advantageous from the viewpoint of increasing the capacitance of the capacitor under conditions of high electric field strength.

[0025] In a fifth aspect of the present disclosure, for example, the dielectric according to any one of the first to third aspects may contain crystalline γ-Bi2O3. According to the fifth aspect, the dielectric constant of the dielectric is likely to be higher under high electric field strength conditions. Therefore, the dielectric is more advantageous from the viewpoint of increasing the capacitance of the capacitor under high electric field strength conditions.

[0026] In a sixth aspect of the present disclosure, for example, the dielectric according to any one of the first to fifth aspects may have a relative dielectric constant greater than 138 when the electric field strength is increased at an electric field strength of 0.5 MV / cm. In addition, the dielectric may have a relative dielectric constant greater than 100 when the electric field strength is decreased at an electric field strength of 0.5 MV / cm. The dielectric according to the sixth aspect is more advantageous from the viewpoint of increasing the capacitance of the capacitor under conditions of high electric field strength.

[0027] In a seventh aspect of the present disclosure, for example, the dielectric according to any one of the first to sixth aspects may have a relative dielectric constant greater than 138 when the electric field strength is increased at an electric field strength of 0.7 MV / cm. In addition, the dielectric may have a relative dielectric constant greater than 57 when the electric field strength is decreased at an electric field strength of 0.7 MV / cm. The dielectric according to the seventh aspect is more advantageous from the viewpoint of increasing the capacitance of the capacitor under conditions of high electric field strength.

[0028] In an eighth aspect of the present disclosure, for example, the dielectric according to any one of the first to seventh aspects may be at least one film selected from the group consisting of a pulsed laser deposited film, a vacuum evaporated film, a sputtered film, an atomic layer deposited film, a chemical vapor deposition film, and an anodized film. According to the eighth aspect, the dielectric can exist as a film such as a pulsed laser deposited film, which is advantageous from the viewpoint of increasing the capacitance of the capacitor.

[0029] In a ninth aspect of the present disclosure, for example, the dielectric according to any one of the first to eighth aspects may be used for a capacitor. According to the ninth aspect, the dielectric can be used to increase the capacitance of a capacitor under conditions of high electric field strength.

[0030] A capacitor according to a tenth aspect of the present disclosure comprises: a first electrode; a dielectric according to any one of the first to ninth aspects arranged on the first electrode; and a second electrode covering at least a portion of the dielectric.

[0031] According to the tenth aspect, the capacitance of the capacitor tends to increase under conditions of high electric field strength.

[0032] An electric circuit according to an eleventh aspect of the present disclosure includes the capacitor according to the tenth aspect. According to the eleventh aspect, when the capacitor is used under conditions of high electric field strength, the electric circuit is likely to exhibit desired performance.

[0033] A circuit board according to a twelfth aspect of the present disclosure includes the capacitor according to aspect 10. According to the twelfth aspect, when the capacitor is used under conditions of high electric field strength, the circuit board is likely to exhibit desired performance.

[0034] A circuit board according to a thirteenth aspect of the present disclosure includes the capacitor according to the tenth aspect. According to the thirteenth aspect, when the capacitor is used under conditions of high electric field strength, the device is likely to exhibit desired performance.

[0035] An electricity storage device according to a fourteenth aspect of the present disclosure includes the capacitor according to the tenth aspect. According to the fourteenth aspect, when the capacitor is used under conditions of high electric field strength, the electricity storage device is likely to exhibit desired performance.

[0036] (Embodiments) Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Note that the embodiments described below are all comprehensive or specific examples. Therefore, the numerical values, shapes, materials, components, component placement positions, connection forms, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. Furthermore, among the components in the following embodiments, components that are not recited in the independent claims that represent the highest concepts will be described as optional components. Furthermore, in the drawings, descriptions of components with the same reference numerals may be omitted. Furthermore, the drawings schematically illustrate each component to facilitate understanding, and the shapes, dimensional ratios, etc. may not be accurately represented.

[0037] 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 a dielectric 10. In other words, the dielectric 10 is a material for a capacitor. The dielectric 10 is made of Bi. 2x Mg y Ti z O k This composition satisfies the conditions x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0. In this composition, k is a value for maintaining electrical neutrality. With this configuration, the dielectric constant of the dielectric 10 tends to be high under conditions of high electric field strength. Therefore, the dielectric 10 is advantageous from the viewpoint of increasing the capacitance of the capacitor 1a under conditions of high electric field strength.

[0038] Dielectric 10 contains, for example, crystalline BiTiO. Such a configuration tends to increase the relative dielectric constant of dielectric 10 under conditions of high electric field strength, which is advantageous from the viewpoint of increasing the capacitance of capacitor 1a under conditions of high electric field strength.

[0039] When the above composition is satisfied in the dielectric, the dielectric does not necessarily contain crystalline Bi2Ti2O7. 0.5 Ti x ) O3 thin film and BiMg y Ti 0.5 According to the XRD patterns of the O3 films, it is understood that these films do not contain crystalline Bi2Ti2O7. On the other hand, according to the studies of the present inventors, even if a dielectric contains crystalline Bi2Ti2O7, unless the above compositional conditions are satisfied, the dielectric constant of the dielectric 10 is unlikely to be high under conditions of high electric field strength. In the dielectric 10, when both the above compositional conditions and the inclusion of crystalline Bi2Ti2O7 are satisfied, the dielectric constant of the dielectric 10 is likely to be higher under conditions of high electric field strength.

[0040] In the above composition, the condition x≦0.65 may be satisfied, or the condition x≦0.60 may be satisfied, or the condition x≦0.55 may be satisfied, or the condition x≦0.50 may be satisfied. In the above composition, the condition x≦0.45 may be satisfied, or the condition x≦0.40 may be satisfied. In the above composition, for example, the condition 0.15≦x≦0.65, 0.15≦x≦0.60, 0.15≦x≦0.55, 0.15≦x≦0.50, 0.15≦x≦0.45, or 0.15≦x≦0.40 is satisfied.

[0041] In the above composition, the condition y≧0.05 may be satisfied, the condition y≧0.10 may be satisfied, the condition y≧0.15 may be satisfied, or the condition y≧0.20 may be satisfied. In the above composition, for example, the condition 0.05≦y≦0.40, 0.10≦y≦0.40, 0.15≦y≦0.40, or 0.20≦y≦0.40 may be satisfied.

[0042] In the above composition, the condition z≦0.80 may be satisfied, the condition z≦0.75 may be satisfied, the condition z≦0.70 may be satisfied, the condition z≦0.65 may be satisfied, or the condition z≦0.60 may be satisfied. In the above composition, for example, the condition 0.25≦z≦0.80, 0.25≦z≦0.75, 0.25≦z≦0.70, 0.25≦z≦0.65, or 0.25≦z≦0.60 is satisfied.

[0043] The dielectric 10 may contain only Bi2Ti2O7 as the crystalline oxide, or may contain a crystalline oxide other than Bi2Ti2O7. 12 , crystalline γ-BiO, and crystalline Bi(Mg 0.5 Ti 0.5 ) O3. In this case, the relative dielectric constant of the dielectric 10 is likely to be higher under conditions of high electric field strength.

[0044] The dielectric 10 is crystalline Bi4Ti3O 12 and crystalline γ-Bi2O3. In this case, the relative dielectric constant of the dielectric 10 is likely to be higher under conditions of high electric field strength.

[0045] The dielectric 10 may contain crystalline γ-Bi2O3. In this case, the relative dielectric constant of the dielectric 10 tends to be higher under conditions of high electric field strength.

[0046] For example, at an electric field strength of 0.5 MV / cm, dielectric 10 has a relative dielectric constant greater than 138 when the electric field strength is increased, and a relative dielectric constant greater than 100 when the electric field strength is decreased. In this case, dielectric 10 has a high relative dielectric constant at a high electric field strength of 0.5 MV / cm, and the capacitance of capacitor 1a tends to be high under conditions of high electric field strength.

[0047] For example, at an electric field strength of 0.5 MV / cm, the dielectric 10 may have a relative dielectric constant of 140 or more, 150 or more, or 160 or more when the electric field strength is increased. For example, at an electric field strength of 0.5 MV / cm, the dielectric 10 may have a relative dielectric constant of 110 or more, 115 or more, or 120 or more when the electric field strength is decreased. At an electric field strength of 0.5 MV / cm, the dielectric 10 has a relative dielectric constant of, for example, 2000 or less, 1500 or less, or 1000 or less when the electric field strength is increased and when the electric field strength is decreased. At an electric field strength of 0.5 MV / cm, the dielectric 10 has a relative dielectric constant of, for example, more than 138 and 2000 or less, 1500 or less, or 1000 or less when the electric field strength is increased. The dielectric 10 has a relative dielectric constant of, for example, greater than 100 and not greater than 2000, not greater than 1500, or not greater than 1000 at an electric field strength of 0.5 MV / cm when the electric field strength is reduced.

[0048] For example, at an electric field strength of 0.7 MV / cm, dielectric 10 has a relative dielectric constant greater than 138 when the electric field strength is increased, and a relative dielectric constant greater than 57 when the electric field strength is decreased. In this case, dielectric 10 has a high relative dielectric constant at a high electric field strength of 0.7 MV / cm, and the capacitance of capacitor 1a tends to be high under conditions of high electric field strength.

[0049] For example, at an electric field strength of 0.7 MV / cm, the dielectric 10 may have a relative dielectric constant of 140 or more, 150 or more, or 160 or more when the electric field strength is increased. For example, at an electric field strength of 0.7 MV / cm, the dielectric 10 may have a relative dielectric constant of 60 or more, 80 or more, or 100 or more when the electric field strength is decreased. At an electric field strength of 0.7 MV / cm, the dielectric 10 has a relative dielectric constant of, for example, 2000 or less, 1500 or less, or 1000 or less when the electric field strength is increased and when the electric field strength is decreased. At an electric field strength of 0.7 MV / cm, the dielectric 10 has a relative dielectric constant of, for example, more than 138 and 2000 or less, 1500 or less, or 1000 or less when the electric field strength is increased. The dielectric 10 has a relative dielectric constant of, for example, greater than 57 and not greater than 2000, not greater than 1500, or not greater than 1000 at an electric field strength of 0.7 MV / cm when the electric field strength is reduced.

[0050] The shape of the dielectric 10 is not limited to a specific shape. The dielectric 10 is, for example, a film. The method for forming the film is not limited to a specific method. The film may be formed by, for example, a vapor deposition method or an anodic oxidation process. The dielectric 10 is, for example, at least one film selected from the group consisting of a pulsed laser deposition (PLD) film, a vacuum deposition film, a sputtering film, an atomic layer deposition (ALD) film, a chemical vapor deposition (CVD) film, and an anodic oxidation film. In this case, the relative dielectric constant of the dielectric 10 is likely to be higher under conditions of high electric field strength. In addition, Bi 2x Mg y Ti z O k The values ​​of x, y, and z in the composition can be easily adjusted to the desired range.

[0051] 1, the capacitor 1a includes a first electrode 21, a dielectric 10, and a second electrode 22. The dielectric 10 is disposed on the first electrode 21. The second electrode 22 covers at least a portion of the dielectric 10. Because the capacitor 1a includes the dielectric 10, it is likely to exhibit high capacitance under conditions of high electric field strength.

[0052] Fig. 2 is a cross-sectional view showing another example of a capacitor according to the present disclosure. Capacitor 1b shown in Fig. 2 has the same configuration as capacitor 1a, except for portions that will be particularly described. Components of capacitor 1b that are the same as or correspond to components of capacitor 1a are given the same reference numerals, and detailed description thereof will be omitted. The description of capacitor 1a also applies to capacitor 1b, unless technically inconsistent.

[0053] 2, in capacitor 1b, at least a portion of first electrode 21 is porous. This configuration tends to increase the surface area of ​​first electrode 21, and tends to increase the capacitance of capacitor 1b. Such a porous structure can be formed, for example, by etching a metal foil and sintering a powder.

[0054] 2, for example, a film of the dielectric 10 is formed on the surface of the porous portion of the first electrode 21. In this case, the method for forming the dielectric 10 can be an atomic layer deposition method (ALD method) or a chemical vapor deposition method such as a CVD method or a mist CVD method.

[0055] The first electrode 21 includes a valve metal such as Al, Ta, Nb, Zr, Hf, or Bi. The second electrode 22 may include, for example, a solidified silver-containing paste, a carbon material such as graphite, or both the solidified silver-containing paste and a carbon material.

[0056] The capacitors 1a and 1b may be electrolytic capacitors. In this case, for example, an electrolyte 23 is disposed between the first electrode 21 and the second electrode 22. The electrolyte 23 may also be disposed between the dielectric 10 and the second electrode 22. In the capacitor 1b, the electrolyte 23 is disposed so as to fill the voids around the porous portion of the first electrode 21, for example.

[0057] The electrolyte 23 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 23 may be a manganese compound such as manganese oxide. The electrolyte 23 may also include a solid electrolyte.

[0058] For example, an electric circuit including capacitor 1a or 1b can be provided. FIG. 3A is a diagram schematically showing an example of an electric circuit of the present disclosure. Electric circuit 3 includes capacitor 1a. Electric circuit 3 may be an active circuit or a passive circuit. Electric circuit 3 may be a discharge circuit, a smoothing circuit, a decoupling circuit, or a coupling circuit. Because electric circuit 3 includes capacitor 1a, when capacitor 1a is used under conditions of high electric field strength, electric circuit 3 is likely to exhibit desired performance. Electric circuit 3 may also include capacitor 1b.

[0059] For example, a circuit board including capacitor 1a or 1b can be provided. FIG. 3B is a diagram schematically illustrating an example of a circuit board according to the present disclosure. As shown in FIG. 3B, circuit board 5 includes capacitor 1a. For example, an electric circuit including capacitor 1a is formed on circuit board 5. Because circuit board 5 includes capacitor 1a, circuit board 5 is likely to exhibit the desired performance when capacitor 1a is used under conditions of high electric field strength. Circuit board 5 may also include capacitor 1b.

[0060] For example, a device including capacitor 1a or 1b can be provided. FIG. 3C is a diagram schematically illustrating an example of a device according to the present disclosure. As shown in FIG. 3C, device 7 includes capacitor 1a. Device 7 includes, for example, a circuit board 5 including capacitor 1a. Because device 7 includes capacitor 1a, device 7 is likely to exhibit desired performance when capacitor 1a is used under conditions of high electric field strength. Device 7 may also include capacitor 1b. Device 7 may be an electronic device, a communication device, a signal processing device, a power supply device, an inverter, or a converter. 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, a smartphone, or a tablet PC, or an Ethernet switch.

[0061] For example, an electricity storage device including capacitor 1a or 1b can be provided. FIG. 3D is a diagram schematically illustrating an example of an electricity storage device according to the present disclosure. As shown in FIG. 3D , the electricity storage device 9 includes capacitor 1a. Therefore, when capacitor 1a is used under conditions of high electric field strength, the electricity storage device 9 is likely to exhibit desired performance. The electricity storage device 9 may also include capacitor 1b. As shown in FIG. 3D , for example, an electricity storage system 50 can be provided using the electricity storage device 9. The electricity storage system 50 includes the electricity storage device 9 and a power generation device 2. In the electricity storage system 50, electricity obtained as a result of power generation in the power generation device 2 is stored in the electricity storage device 9. The power generation device 2 is, for example, a device for solar power generation or wind power generation. The electricity storage device 9 includes, for example, a secondary battery such as a lithium-ion battery or a lead-acid battery.

[0062] The present disclosure will be described in more detail below based on examples, although the present disclosure is not limited to the following examples.

[0063] (Examples 1 to 5 and Comparative Examples 2 to 7) A Pt thin film was formed on an Al2O3 (0001) substrate by sputtering using a Pt target to obtain a lower electrode. The Pt thin film was in contact with the substrate. During sputtering, the substrate environment was maintained at 0.3 Pa with argon gas occupying 100% by volume. In addition, the substrate temperature was adjusted to 500°C.

[0064] PLD films for samples according to Examples 1 to 5 and Comparative Examples 2 to 7 were formed on the lower electrode using a PLD method using Bi2O3, MgO, and TiO2 targets. The PLD conditions were adjusted to achieve a PLD film thickness of 100 nm. During PLD, the substrate environment was maintained at a pressure of 0.01 Pa, with 100% oxygen gas by volume. In addition, the substrate was not heated. The composition ratio of Bi, Mg, and Ti in the dielectric film of each sample was adjusted by adjusting the film formation time by opening and closing the shutter. Then, using an Advance Riko variable atmosphere lamp annealing system VHC-P616C, the PLD films were heat-treated at 640°C for 2 minutes in an environment consisting of 80% argon gas by volume and 20% oxygen gas by volume. This resulted in the dielectric films according to Examples 1 to 5 and Comparative Examples 2 to 7. Next, a Pt thin film having a diameter of 100 μm and a thickness of 100 nm was formed on the dielectric film by sputtering using a Pt target, thereby obtaining the upper electrode. In this manner, samples according to Examples 1 to 5 and Comparative Examples 2 to 7 were obtained.

[0065] (Identification of Composition) Before forming the upper electrode, the dielectric film of each sample was subjected to X-ray fluorescence analysis using a Shimadzu Corporation micro EDX-1400 X-ray fluorescence analyzer to quantitatively analyze the elements in each dielectric film. The fundamental parameter method (FP method) was used as the quantitative analysis method. From the results of the quantitative analysis, the atomic ratios of Bi, Mg, and Ti in the dielectric film of each sample were determined. The results are shown in Table 1. In Table 1, x is half the number of Bi atoms / (half the number of Bi atoms + number of Mg atoms + number of Ti atoms). y is the number of Mg atoms / (half the number of Bi atoms + number of Mg atoms + number of Ti atoms). z is the number of Ti atoms / (half the number of Bi atoms + number of Mg atoms + number of Ti atoms).

[0066] (Evaluation of Crystalline Phase) Before forming the upper electrode, X-ray diffraction measurements were performed on the dielectric film of each sample using a Bruker D8 Discover X-ray diffractometer, and 2θ / θ scan XRD patterns were obtained for each dielectric film. FIG. 4 shows XRD patterns for the dielectric films of the samples according to Examples 1 to 5. FIG. 5 shows XRD patterns for the dielectric films of the samples according to Comparative Examples 2 to 7. In FIGS. 4 and 5, the vertical axis represents the diffraction intensity in arbitrary units on a logarithmic scale, and the horizontal axis represents the diffraction angle 2θ. In FIGS. 4 and 5, the vertical axis represents the relative relationship between the diffraction intensities in one XRD pattern, not the relative relationship between the diffraction intensities in different XRD patterns. In this measurement, Cu-Kα radiation was used as the X-ray source, and the voltage was adjusted to 50 kV and the current to 100 mA. Measurements were performed using a two-dimensional detector and converted to 2θ.

[0067] (Dielectric Properties) The electric field strength dependence of the polarization density of the dielectric film of each sample at a frequency of 10 kHz was measured using a ferroelectric tester Precision Premier II manufactured by RADIANT TECHNOLOGIES, Inc. The dielectric constant at a specific electric field strength was calculated based on the differential capacitance (the amount of change in polarization density per unit change in electric field strength) at that electric field strength, based on the thickness of the dielectric film and the electrode area. The ambient temperature during measurement was 25°C. The results are shown in Table 1. In Table 1, the notation "OL" indicates that dielectric breakdown occurred and the dielectric constant could not be calculated.

[0068] A barium titanate-based multilayer ceramic capacitor was prepared as Comparative Example 1 to serve as a reference for dielectric constant evaluation. This multilayer ceramic capacitor was manufactured by Murata Manufacturing Co., Ltd., model number GRM188D71A106MA73D. This multilayer ceramic capacitor had a capacitance of 10 μF, a withstand voltage of 10 V, and dimensions of 1.6 × 0.8 × 0.8 mm. Using the ferroelectric tester described above, the field strength dependence of polarization density at a frequency of 10 kHz within the withstand voltage range was measured. A scanning electron microscope (SEM) was used to observe the cross section of the multilayer ceramic capacitor according to Comparative Example 1 to determine the thickness of the dielectric and the surface area of ​​the electrodes. The dielectric constant of the dielectric of the multilayer ceramic capacitor according to Comparative Example 1 was calculated using the same procedure as described above. The results are shown in Table 1.

[0069] The dielectric constants of the multilayer ceramic capacitor according to Comparative Example 1 at an electric field strength of 0.5 MV / cm were 138 and 100, respectively, when the voltage was increased and decreased. Increasing the voltage increased the electric field strength. Decreasing the voltage decreased the electric field strength. The dielectric constants of the multilayer ceramic capacitor according to Comparative Example 1 at an electric field strength of 0.7 MV / cm were 138 and 57, respectively, when the voltage was increased and decreased. Evaluation of the dielectric constant of a capacitor dielectric under high voltage conditions is often performed under conditions of an electric field strength of approximately several tens of kV / cm. However, in order to achieve miniaturization of capacitors to which a DC voltage of several hundred volts can be applied, such as capacitors used in automotive converters or automotive inverters, evaluating the dielectric constant of a dielectric at this electric field strength is considered insufficient. Therefore, taking into consideration the withstand voltage of the multilayer ceramic capacitor according to Comparative Example 1, the dielectric constants of the dielectrics were evaluated at electric field strengths of 0.5 MV / cm and 0.7 MV / cm, which are approximately 10 times greater than an electric field strength of approximately several tens of kV / cm, as described above.

[0070] As shown in Table 1, the dielectric constants of the dielectric films of the samples according to Examples 1 to 5 at 0.5 MV / cm exceeded 138 when the voltage was increased and exceeded 100 when the voltage was decreased. In addition, the dielectric constants of the dielectric films of the samples according to Examples 1 to 5 at 0.7 MV / cm exceeded 138 when the voltage was increased and exceeded 57 when the voltage was decreased. On the other hand, the dielectric constants of the dielectric films of the samples according to Comparative Examples 2 to 7 satisfied at least one of the following conditions (i), (ii), (iii), and (iv): (i) The dielectric constant at 0.5 MV / cm is 138 or less when the voltage is increased. (ii) The dielectric constant at 0.5 MV / cm is 100 or less when the voltage is decreased. (iii) The dielectric constant at 0.7 MV / cm is 138 or less when the voltage is increased. (iv) The dielectric constant at 0.7 MV / cm is 57 or less when the voltage is decreased.

[0071] 4 and 5, in the XRD patterns of the dielectric films of the samples according to Examples 1 to 5 and Comparative Examples 2 to 7, peaks are observed around 14.8°, 16.5°, 21.8°, 22.3°, 28.0°, 29.9°, 30.3°, 31.8°, 32.8°, 34.5°, 46.2°, 50.0°, 52.3°, 55.8°, 56.5°, 57.8°, 61.9°, 62.3°, and 63.5°. Of these, the peaks at 14.8°, 29.9°, 34.5°, 50.0°, 57.8°, and 62.3° are attributed to Bi2Ti2O7. The peaks around 16.5°, 21.8°, 61.9°, and 63.5° are attributed to Bi4Ti3O 12 The peaks around 28.0°, 30.3°, and 32.8° are attributed to γ-Bi2O3. The peaks around 22.3°, 31.8°, 46.2°, and 56.5° are attributed to Bi(Mg 0.5 Ti 0.5 )O3. The peaks near 52.3° and 55.8° are attributed to at least one selected from the group consisting of Bi2Ti2O7 and γ-Bi2O3. Incidentally, peaks are also observed near 39.8° and 41.7°, but these peaks are attributed to the lower electrode Pt and the substrate Al2O3, respectively, and are not related to the components of the dielectric film. The presence or absence of each crystalline phase in the dielectric films of the samples according to Examples 1 to 5 and Comparative Examples 2 to 7 is shown in Table 1. The dielectric films of the samples according to Examples 1 to 5 contained Bi2Ti2O7. In addition, the dielectric films of the samples according to Examples 1, 2, 4, and 5 contained Bi4Ti3O 12 , γ-Bi2O3, and Bi(Mg 0.5 Ti 0.5 ) O3.

[0072] From the above, it is suggested that a dielectric that satisfies both of the following conditions (I) and (II) is likely to have a high relative dielectric constant under conditions of high electric field intensity. (I) The dielectric is Bi 2x Mg y Ti z O kThis composition satisfies the conditions x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0. (II) The dielectric contains crystalline Bi2Ti2O7.

[0073] It should be noted that many modifications and other embodiments of the present disclosure will be apparent to those skilled in the art from the above description. Accordingly, the above description should be construed as illustrative only and is provided for the purpose of teaching those skilled in the art the best mode of carrying out the present disclosure. Substantial changes in operating conditions, composition, structure, and / or function can be made without departing from the spirit of the present disclosure.

[0074]

[0075] The dielectric materials of the present disclosure may be used in applications such as automotive capacitors.

Claims

1. Bi 2x Mg y Ti z O k The composition is represented by The composition satisfies the conditions of x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0, In the above composition, k is a value for maintaining electrical neutrality. Dielectrics (however, in the composition, excluding dielectrics which satisfy the conditions x=y and 10 / 37≦x≦1 / 3 and dielectrics which satisfy the conditions x=z and 25 / 81≦x≦1 / 3).

2. Crystalline Bi 2 Ti 2 O 7 Contains The dielectric material according to claim 1 .

3. The dielectric is a crystalline Bi 4 Ti 3 O 12 , crystalline γ-Bi 2 O 3 , and crystalline Bi(Mg 0.5 Ti 0.5 ) O 3 Contains at least one selected from the group consisting of: The dielectric material according to claim 1 .

4. The dielectric is a crystalline Bi 4 Ti 3 O 12 and crystalline γ-Bi 2 O 3 Contains at least one selected from the group consisting of: The dielectric material according to claim 1 .

5. The dielectric is a crystalline γ-Bi 2 O 3 Contains The dielectric material according to claim 1 .

6. The dielectric has a dielectric constant greater than 138 when the electric field strength is increased and a dielectric constant greater than 100 when the electric field strength is decreased at an electric field strength of 0.5 MV / cm. The dielectric material according to claim 1 .

7. The dielectric has a dielectric constant greater than 138 when the electric field strength is increased and a dielectric constant greater than 57 when the electric field strength is decreased at an electric field strength of 0.7 MV / cm. The dielectric material according to claim 1 .

8. The dielectric is at least one film selected from the group consisting of a pulsed laser deposition film, a vacuum deposition film, a sputtering film, an atomic layer deposition film, a chemical vapor deposition film, and an anodized film. The dielectric material according to claim 1 .

9. The dielectric is for a capacitor. The dielectric material according to claim 1 .

10. A composition represented by Bi2xMgyTizOk, The composition satisfies the conditions of x≧0.15, y≦0.40, z≧0.25, and x+y+z=1.0, In the above composition, k is a value for maintaining electrical neutrality, Contains crystalline Bi2Ti2O7; Dielectric.

11. A first electrode; A dielectric material according to claim 1 , disposed on the first electrode; A second electrode covering at least a portion of the dielectric. Capacitor.

12. An electric circuit comprising the capacitor of claim 11.

13. A circuit board comprising the capacitor according to claim 11.

14. An apparatus comprising the capacitor of claim 11.

15. An electricity storage device comprising the capacitor according to claim 11.