Thin film capacitor, power supply module, and electronic device

Abstract

To provide a thin film capacitor, etc., of high adhesiveness and high voltage resistance.SOLUTION: The present invention relates to a thin film capacitor having a laminated structure configured by successively laminating a first electrode, a first dielectric film, a second dielectric film and a second electrode. The second dielectric film and the second electrode are in contact. The first dielectric film contains a perovskite compound. The second dielectric film contains a perovskite compound or an oxide of M. An absolute value of average oxide production energy of cation elements contained in a B site of the perovskite compound contained in the first dielectric film is defined as X1. An absolute value of average oxide production energy of cation elements contained in a B site of the perovskite compound contained in the second dielectric film is defined as X2a, and an absolute value of average oxide production energy of M is defined as X2b. It leads X2a<X1 and X2a≤1000 kJ / mol or it leads X2b<X1 and X2b≤1000 kJ / mol.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a thin film capacitor, a power module, and an electronic device.

Background Art

[0002] With the miniaturization of power modules used in electronic devices, the demand for miniaturization of electronic components such as capacitors used in power modules is increasing.

[0003] The miniaturization of the power module is achieved by increasing the switching frequency of the power supply. However, when the switching frequency is high, the parasitic inductance generated from the wiring and the parasitic inductance of the mounted components themselves are likely to cause voltage fluctuations in the power supply circuit. Voltage fluctuations may cause unexpected high voltage abnormalities (such as surge voltage and ringing), which may destroy the switching element. Even if the switching element is not destroyed, the loss may increase or noise may occur. Therefore, it is necessary to configure a power supply circuit that is less affected by high voltage abnormalities and to select components that are less affected by high voltage abnormalities. Therefore, it is desired to suppress voltage fluctuations.

[0004] In order to suppress voltage fluctuations, a snubber circuit including a snubber capacitor may be formed around the switching element. By forming a snubber circuit, high voltage abnormalities can be suppressed. Also, attempts have been made to reduce parasitic inductance. Since thin film capacitors have a small parasitic inductance, research on using thin film capacitors in power modules has been underway.

[0005] Thin film capacitors may be used as decoupling capacitors arranged near the LSI. In this case, since the thin film capacitor is driven at a relatively low voltage, high breakdown voltage is not so much required.

[0006] On the other hand, since the thin-film capacitor used in the power supply circuit near the switching element is driven at a relatively high voltage, high breakdown voltage is required. Generally, there is an inverse relationship between the dielectric constant and the breakdown voltage. In order to obtain a thin-film capacitor with a high breakdown voltage, it is necessary to use a dielectric film with a low dielectric constant. However, when manufacturing a thin-film capacitor using such a dielectric film, the adhesion between the dielectric film and the electrode may decrease.

[0007] Patent Document 1 describes an invention related to a semiconductor device, and a second insulator that suppresses the diffusion of excess oxygen from an insulator having an excess oxygen region to a conductor is described. However, it is unclear to what extent the second insulator contributes to the adhesion between the insulator and the conductor.

[0008] Patent Document 2 describes an invention related to an electronic component. In order to ensure the adhesion between the electrode film and the dielectric film, an adhesion metal layer is provided between the main conductive layer and the dielectric film. However, there is a concern that metals such as Cr, Ti, and Ta contained in the adhesion metal layer may oxidize and diffuse due to the contact between the main conductive layer and the dielectric film. In that case, there is a concern that it may adversely affect the characteristics of the dielectric film.

[0009] Patent Document 3 describes an invention related to a ceramic electronic component. By forming two thin-film portions with different orientations of the dielectric thin films, leakage is reduced and the breakdown voltage is improved. However, there is no description regarding the adhesion between the dielectric thin film and the electrode.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0011] An object of the present invention is to provide a thin film capacitor or the like having high adhesion and high withstand voltage.

Means for Solving the Problems

[0012] A thin film capacitor according to a first aspect of the present invention is a thin film capacitor having a laminated structure in which a first electrode, a first dielectric film, a second dielectric film, and a second electrode are laminated in this order, the second dielectric film and the second electrode are in contact with each other, the first dielectric film and the second dielectric film contain a perovskite-type compound, the absolute value of the average oxide formation energy of the cation element contained in the B-site of the perovskite-type compound contained in the first dielectric film is defined as X1, the absolute value of the average oxide formation energy of the cation element contained in the B-site of the perovskite-type compound contained in the second dielectric film is defined as X2a, and X2a < X1 and X2a ≤ 1000 kJ / mol.

[0013] A thin film capacitor according to a second aspect of the present invention is a thin film capacitor having a laminated structure in which a first electrode, a first dielectric film, a second dielectric film, and a second electrode are laminated in this order, the second dielectric film and the second electrode are in contact with each other, the first dielectric film contains a perovskite-type compound, the second dielectric film contains an oxide of M, the absolute value of the average oxide formation energy of the cation element contained in the B-site of the perovskite-type compound contained in the first dielectric film is defined as X1, the absolute value of the average oxide formation energy of M contained in the second dielectric film is defined as X2b, and X2b < X1 and X2b ≤ 1000 kJ / mol.

[0014] The relative permittivity of the first dielectric film is ε 1 , the film thickness of the first dielectric film is d 1 , the relative permittivity of the second dielectric film is ε 2 , the film thickness of the second dielectric film is d 2 , ε 1 and ε 2 Let the composite permittivity of and be ε. Then, ε ≥ 0.8 × ε 1 × ((d 1 + d 2 ) / d 1 ) may be satisfied.

[0015] The breakdown voltage of the first dielectric film may be 0.30 kV / μm or more.

[0016] The power module of the present invention has the above thin-film capacitor.

[0017] The electronic device of the present invention has the above power module.

Brief Description of the Drawings

[0018]

Figure 1

Embodiments for Carrying Out the Invention

[0019] (First Embodiment) Hereinafter, the first embodiment of the present invention will be described in detail in the following order. 1. Thin-film capacitor 1.1. Overall configuration of the thin-film capacitor 1.2. Dielectric film 1.3. Substrate 1.4. First electrode 1.5. Second electrode 2. Manufacturing method of the thin-film capacitor

[0020] (1. Thin-film capacitor) First, the thin-film capacitor according to the first embodiment of the present invention will be described.

[0021] (1.1. Overall configuration of the thin-film capacitor) As shown in FIG. 1, a thin-film capacitor 100 as an example of a dielectric element according to the present embodiment has a structure in which a substrate 10, a first electrode 30, a dielectric film 40, and a second electrode 50 are laminated in this order. When the first electrode 30 and the second electrode 50 are connected to an external circuit and a voltage is applied, the dielectric film 40 exhibits a predetermined capacitance and can function as a capacitor. Detailed descriptions of each component will be given later.

[0022] Note that the shape of the thin-film capacitor is not particularly limited, but it is usually in a rectangular parallelepiped shape. Also, its dimensions are not particularly limited, and the thickness and length may be appropriate dimensions according to the application.

[0023] (1.2. Dielectric Film) In the present embodiment, the dielectric film 40 includes a first dielectric film 41 and a second dielectric film 42. And, as shown in FIG. 1, the thin-film capacitor 100 has a laminated structure 60 in which the first electrode 30, the first dielectric film 41, the second dielectric film 42, and the second electrode 50 are laminated in this order. Further, the second dielectric film 42 and the second electrode 50 are in contact with each other.

[0024] The first electrode 30 and the first dielectric film 41 may be in contact with each other. The first dielectric film 41 and the second dielectric film 42 may be in contact with each other.

[0025] Other dielectric films may be included between the first electrode 30 and the first dielectric film 41, or between the first dielectric film 41 and the second dielectric film 42. There are no particular restrictions on the composition and thickness of the other dielectric films in the case of including other dielectric films, as long as the realization of high adhesion and high breakdown voltage is not inhibited.

[0026] The first dielectric film 41 and the second dielectric film 42 contain a perovskite-type compound. The perovskite-type compound according to the present embodiment is a perovskite-type oxide represented by the general formula ABO 3 wherein A is a cation element constituting the A site, and B is a cation element constituting the B site.

[0027] Also, in the first dielectric film 41 and the second dielectric film 42, a compound other than the perovskite-type compound may be included as long as it does not inhibit the realization of high adhesion and high breakdown voltage. For example, in the first dielectric film 41, the compound other than the perovskite-type compound may be included in an amount less than 50 mol%. For example, in the second dielectric film 42, the compound other than the perovskite-type compound may be included in an amount less than 50 mol%.

[0028] There is no particular limitation on the type of A in the perovskite-type compound contained in the first dielectric film or the perovskite-type compound contained in the second dielectric film. Any cation element that enters the A site in a general perovskite compound may be used. For example, it is at least one selected from calcium (Ca), strontium (Sr), and barium (Ba).

[0029] There is no particular limitation on the type of B in the perovskite-type compound contained in the first dielectric film or the perovskite-type compound contained in the second dielectric film. Any cation element that enters the B site in a general perovskite compound may be used. For example, it is at least one selected from titanium (Ti), zirconium (Zr), hafnium (Hf), tin (Sn), niobium (Nb), tantalum (Ta), magnesium (Mg), zinc (Zn), and nickel (Ni). It may also be at least one selected from Ti, Zr, Mg, and Ta. However, in the perovskite-type compound contained in the first dielectric film, it is preferable that the ratio of Ti to the cation element entering the B site is small. Specifically, in the perovskite-type compound contained in the first dielectric film, it is preferable that the ratio of Ti to 100 mol parts of the cation element entering the B site is 50 mol parts or less. When the ratio of Ti in the cation element entering the B site is large, the breakdown voltage tends to be low.

[0030] In this embodiment, let the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the first dielectric film 41 be X1, and the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the second dielectric film 42 be X2a. Then, X2a < X1 and X2a ≤ 1000 kJ / mol.

[0031] Since the second dielectric film 42 with a small X2a is included in the dielectric film 40, the adhesion between the dielectric film 40 and the second electrode 50 can be improved. The reason for the improved adhesion will be explained below.

[0032] In order to improve the adhesion between the electrode and the dielectric film, it is necessary to firmly bond the electrode and the dielectric film at the interface between them. To strengthen the bond between the electrode and the dielectric film, it is necessary to make the bonding states of the atoms contained in the electrode and the bonding states of the atoms contained in the dielectric film closer to each other.

[0033] Generally, the atoms contained in the electrode are bonded by metal-metal bonds. On the other hand, generally, the atoms contained in the dielectric film are bonded by covalent bonds. Therefore, the adhesion between the electrode and the dielectric film tends to be low.

[0034] Here, when the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the dielectric film is small, the dielectric film is likely to be oxidized and reduced. That is, the dielectric film is likely to be oxidized and reduced at the atomic layer level of the interface in contact with the electrode. Therefore, when the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the dielectric film is small, the bonding state of atoms at the interface on the dielectric film side is close to a metal-metal bond. Therefore, when the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the dielectric film is small, the adhesion between the electrode and the dielectric film is improved. Further, in order to improve the adhesion between the electrode and the dielectric film by the above mechanism, it is preferable that the electrode contains a base metal.

[0035] The oxide formation energy of each element is obtained by subtracting the standard formation Gibbs energy of each element from the standard formation Gibbs energy of the oxide of each element at a standard temperature of 298.15 K and a standard pressure of 1.01325×10 5 Pa. The standard formation Gibbs energy of each element at the standard temperature and standard pressure is known. Also, the standard formation Gibbs energy of the oxide of each element at the standard temperature and standard pressure is known. The average oxide formation energy can be calculated by weighted-averaging the oxide formation energy of each element according to the content ratio (mole fraction) of each element.

[0036] There is no particular limitation on the composition of the perovskite-type compound contained in the first dielectric film 41.

[0037] The composition of the perovskite-type compound can be represented by the general formula xA 1 O-yB 1 ´O-zB 1 ´´ 2 O 5 (atomic ratio). The cation element constituting the A-site is A 1 and A 1 is, for example, one or more selected from Ca, Sr, and Ba. The cation element constituting the B-site is B1 ' and B 1 It is divided into '' and B 1 ' is, for example, one or more selected from Mg, Zn, Ni. B 1 '' is, for example, one or more selected from Ti, Nb, Zr, Ta.

[0038] Regarding the composition of the perovskite-type compound contained in the first dielectric film 41, for example, x, y, z may be within the following ranges. x + y + z = 1.000 0.375 ≤ x ≤ 0.563 0.250 ≤ y ≤ 0.500 x / 3 ≤ z ≤ x / 3 + 1 / 9

[0039] There is no particular limitation on the composition of the perovskite-type compound contained in the second dielectric film 42.

[0040] The relative permittivity of the first dielectric film 41 is ε 1 , the film thickness of the first dielectric film 41 is d 1 , the relative permittivity of the second dielectric film 42 is ε 2 , the film thickness of the second dielectric film 42 is d 2 , ε 1 and ε 2 Taking the composite relative permittivity of and as ε, ε ≥ 0.8 × ε 1 × ((d 1 + d 2 ) / d 1 ) may be satisfied.

[0041] The case where the dielectric film 40 includes the first dielectric film 41 and does not include the second dielectric film 42 is compared with the case where the dielectric film 40 includes the first dielectric film 41 and the second dielectric film 42. If the thickness of the dielectric film 40 is the same, the breakdown voltage in the case where the dielectric film 40 includes the first dielectric film 41 and the second dielectric film 42 decreases compared with the case where the dielectric film 40 includes the first dielectric film 41 and does not include the second dielectric film 42. If the thickness of the dielectric film 40 is increased, the breakdown voltage of the dielectric film 40 increases, but the capacitance of the thin film capacitor 100 decreases. ε ≥ 0.8 × ε 1 × ((d 1 + d 2 ) / d 1) When the condition is satisfied, the reduction rate of the capacitance of the thin film capacitor 100 when the thickness of the dielectric film 40 is increased without changing the breakdown voltage is 20% or less.

[0042] Hereinafter, the calculation method of ε will be described. Let the electrode area of the thin film capacitor 100 be S, and V 1 = Sd 1 , V 2 = Sd 2 , α:β = V 1 / (V 1 + V 2 ):V 2 / (V 1 + V 2 ), assuming α + β = 1, the following equation holds. logε can be calculated according to the following equation, and ε can be calculated from logε. Note that all logs in the following equation have a base of 10. logε = αlogε 1 + βlogε 2 = (d 1 logε 1 + d 2 logε 2 ) / (d 1 + d 2 )

[0043] There is no particular limitation on the breakdown voltage of the first dielectric film 41. It may be 0.10 kV / μm or more, 0.30 kV / μm or more, or 0.50 kV / μm or more.

[0044] There is no particular limitation on the breakdown voltage of the dielectric film 40. It may be 0.10 kV / μm or more, 0.30 kV / μm or more, or 0.50 kV / μm or more.

[0045] There is no particular limitation on the thickness of the dielectric film 40. Preferably, it is 1.0 μm to 6.0 μm. There is no particular limitation on d 1 . Preferably, it is 0.5 μm to 5.5 μm. There is no particular limitation on d 2 . Preferably, it is 0.1 μm to 0.5 μm.

[0046] The thickness of the dielectric film 40 can be measured by processing the thin-film capacitor including the dielectric film 40 with a FIB (Focused Ion Beam) processing apparatus and observing the obtained cross-section with an SEM (Scanning Electron Microscope). d 1 And d 2 can also be measured by the same method. In addition, when the first dielectric film 41 and the second dielectric film 42 cannot be distinguished by SEM, they may be distinguished using, for example, crystal orientation observation by a transmission electron microscope (TEM), crystal orientation observation by electron backscatter diffraction (EBSD), etc.

[0047] (1.3. Substrate) There is no particular limitation on the type of the substrate 10. The substrate 10 may be composed of a material that is chemically and thermally stable and that can keep the surface smoothness of the substrate 10 with little stress generated in the substrate 10. For example, a single-crystal substrate composed of a Si single crystal, a sapphire single crystal, a SrTiO 3 single crystal, a MgO single crystal, etc.; a ceramic polycrystalline substrate composed of alumina (Al 2 O 3 ), magnesia (MgO), forsterite (2MgO·SiO 2 ), steatite (MgO·SiO 2 ), mullite (3Al 2 O 3 ·2SiO 2 ), beryllia (BeO), zirconia (ZrO 2 ), aluminum nitride (AlN), silicon nitride (Si 3 N 4 ), silicon carbide (SiC), etc.; a glass-ceramics substrate (LTCC substrate) composed of alumina (crystalline phase) and silicon oxide (glass phase) obtained by firing at 1000°C or lower; a glass substrate such as quartz glass; a metal substrate composed of an Fe-Ni alloy, etc. Further, a metal foil made of nickel (Ni) or copper (Cu) may also be used.

[0048] The metal foil can also serve as the substrate 10 and the first electrode 30. When the metal foil serves as both the substrate 10 and the first electrode 30, the insulating layer 20 described later is not formed. When the metal foil serves as both the substrate 10 and the first electrode 30, it becomes easier to mount the thin film capacitor 100 on the electronic circuit board. Therefore, using the metal foil as the substrate 10 can contribute to further thinning of the thin film capacitor 100, improvement of flexibility, and reduction of substrate cost. There is no particular limitation on the thickness of the metal foil when it serves as both the substrate 10 and the first electrode 30. For example, it may be 1 um or more and 1000 um or less.

[0049] Hereinafter, unless otherwise specified, the case where the metal foil does not serve as both the substrate 10 and the first electrode 30 will be described.

[0050] There is no particular limitation on the thickness of the substrate 10. It may be 10 um to 5000 um.

[0051] The resistivity of the substrate 10 varies depending on the material used. When the substrate 10 is made of a material with a low resistivity, current leakage from the stacked structure 60 to the substrate 10 may occur during the operation of the thin film capacitor 100. As a result, it may affect the electrical characteristics of the thin film capacitor 100. Therefore, when the electrical resistivity of the substrate 10 is low, it is preferable to perform an insulation treatment on the surface of the substrate 10 on the side of the stacked structure 60 to make it difficult for the current generated during the operation of the thin film capacitor 100 to flow into the substrate 10.

[0052] For example, when the substrate 10 is a single crystal Si substrate, it is preferable that an insulating layer 20 is formed on the surface of the substrate 10. There is no particular limitation on the material constituting the insulating layer 20, and any material that can sufficiently ensure insulation between the substrate 10 and the stacked structure 60 may be used. For example, SiO 2 , Al 2 O 3 , Si 3 N x etc. may be mentioned. Also, there is no particular limitation on the thickness of the insulating layer 20. It may be 0.01 um or more and 1 um or less.

[0053] (1.4. First Electrode) As shown in FIG. 1, a first electrode 30 is formed on a substrate 10 via an insulating layer 20. The first electrode 30 may be in a thin film shape. That is, the first electrode 30 may be an electrode film. The first electrode 30, together with a second electrode 50, sandwiches a dielectric film 40 and is an electrode for causing a thin film capacitor 100 to function as a capacitor. The first electrode 30 only needs to be made of a conductive material. Examples of the conductive material include simple metals such as Au, Pt, Ag, Ir, Ru, Co, Ni, Fe, Cu, and Al; alloys composed of the above metals; semiconductors such as Si, GaAs, GaP, InP, and SiC; ITO, ZnO, SnO 2 and other conductive metal oxides. It is preferable to use a material containing a base metal as the conductive material. As the material containing a base metal, it is particularly preferable to use simple Ni, simple Cu, or a Ni-Cu alloy.

[0054] There is no particular limitation on the thickness of the first electrode 30. The thickness of the first electrode 30 only needs to be a thickness that functions as an electrode. The thickness of the first electrode 30 may be 0.01 μm or more and 1 μm or less.

[0055] In order to improve the adhesion between the substrate 10 and the first electrode 30, an adhesion layer may be formed on the substrate 10 before forming the first electrode 30. The material for forming the adhesion layer is not particularly limited as long as it can improve the adhesion between the substrate 10 and the first electrode 30. For example, titanium oxide and chromium oxide are exemplified. When the insulating layer 20 is formed, the above substrate 10 is read as the insulating layer 20.

[0056] (1.5. Second Electrode) As shown in FIG. 1, a second electrode 50 is formed on the surface of the dielectric film 40. The second electrode 50 may be in a thin film shape. That is, the second electrode 50 may be an electrode film. The second electrode 50, together with the above-described first electrode 30, sandwiches the dielectric film 40 and is an electrode for causing a thin film capacitor 100 to function as a capacitor. Therefore, the second electrode 50 has a polarity different from that of the first electrode 30.

[0057] The second electrode 50 may be made of a conductive material, just like the first electrode 30. Examples of the conductive material include simple metals such as Au, Pt, Ag, Ir, Ru, Co, Ni, Fe, Cu, and Al; alloys composed of the above metals; semiconductors such as Si, GaAs, GaP, InP, and SiC; and conductive metal oxides such as ITO, ZnO, and SnO 2 etc. It is preferable to use a material containing a base metal as the conductive material. It is particularly preferable to use a simple Ni, a simple Cu, or a Ni-Cu alloy as the material containing a base metal. This is because the adhesion is likely to be improved particularly when a material containing a base metal is used for the second electrode 50 in contact with the second dielectric layer 42.

[0058] There is no particular limitation on the thickness of the second electrode 50. The thickness of the second electrode 50 may be a thickness that functions as an electrode. The thickness of the second electrode 50 may be 0.01 μm or more and 100 μm or less.

[0059] (2. Method for manufacturing a thin-film capacitor) Next, an example of the method for manufacturing the thin-film capacitor 100 shown in FIG. 1 will be described below.

[0060] First, a substrate 10 is prepared. When a Si single-crystal substrate is prepared as the substrate 10, an insulating layer 20 is formed on one main surface of the Si single-crystal substrate as necessary. There is no particular limitation on the method for forming the insulating layer 20. For example, it may be formed using a known film-forming method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method.

[0061] Subsequently, an adhesion layer is formed on the formed insulating layer 20 (or on the substrate 10 if the insulating layer 20 is not formed) using a known film-forming method as necessary.

[0062] Subsequently, the first electrode 30 is formed on the substrate 10, on the insulating layer 20, or on the adhesion layer using a known film-forming method.

[0063] In addition, when the metal foil also serves as the substrate 10 and the first electrode 30, a metal foil that also serves as the substrate 10 and the first electrode 30 is prepared.

[0064] Subsequently, a dielectric film 40 is formed on the first electrode 30. Specifically, after forming the first dielectric film 41, the second dielectric film 42 is formed on the first dielectric film 41. There is no particular limitation on the method for forming the first dielectric film 41 and the second dielectric film 42. Each dielectric film is formed as a deposited film in which the material constituting each dielectric film is deposited in a thin film state by a known film formation method.

[0065] Examples of known film formation methods include, for example, vacuum evaporation, sputtering, PLD (pulsed laser deposition), MO-CVD (metalorganic chemical vapor deposition), MOD (metalorganic decomposition), sol-gel method, and CSD (chemical solution deposition).

[0066] The raw materials (evaporation materials, various target materials, metalorganic materials, etc.) used during the film formation of each dielectric film may contain trace amounts of impurities, sub-components, etc., as long as they do not inhibit the realization of high adhesion and high breakdown voltage.

[0067] Next, a second electrode 50 is formed on the formed dielectric film 40 using a known film formation method.

[0068] Annealing treatment may be performed before or after forming the second electrode 50. There is no particular limitation on the annealing treatment conditions. For example, annealing treatment may be performed in an atmosphere where the electrode does not oxidize at an annealing temperature of 300°C to 1000°C and an annealing time of 30 minutes to 120 minutes. By performing the annealing treatment, the components contained in each dielectric film can be surely made into a perovskite-type compound. The atmosphere where the electrode does not oxidize means an atmosphere with an oxygen content of 1% or less. Specifically, an atmosphere that can be created with a mixed gas composed of hydrogen, nitrogen, and water vapor, and an atmosphere that can be created by utilizing the dissociation of oxygen in carbon monoxide and carbon dioxide are exemplified. The atmosphere where the electrode does not oxidize may be a vacuum atmosphere of 100 Pa or less.

[0069] Further, a passivation layer (protective layer) may be formed as needed. As the material of the passivation layer, inorganic materials such as SiO 2 and Al 2 O 3 and organic materials such as epoxy resin and polyimide resin can be used.

[0070] Through the above steps, as shown in FIG. 1, a thin film capacitor 100 having a stacked structure 60 (first electrode 30, dielectric film 40, and second electrode 50) formed on a substrate 10 is obtained. Note that the protective film 70 for protecting the dielectric film 40 may be formed by a known film formation method so as to cover at least the portion where the dielectric film 40 is exposed to the outside. There is no particular limitation on the material of the protective film 70, and any material known as a protective film for protecting a dielectric film may be used.

[0071] (Second Embodiment) Hereinafter, a second embodiment of the present invention will be described. Regarding the content not particularly described, it is the same as that of the first embodiment.

[0072] In this embodiment, the first dielectric film 41 contains a perovskite-type compound. The perovskite-type compound according to this embodiment is a perovskite-type oxide represented by the general formula ABO 3 . A is a cation element constituting the A site, and B is a cation element constituting the B site.

[0073] The second dielectric film 42 contains an oxide of M. There is no particular limitation on the type of M. For example, Si, Ti, Zn, Al, Fe, Hf, Ta, Nb, and Zr can be mentioned. The oxide of M may be a single-element oxide. A single-element oxide is a compound of one element selected from elements other than oxygen and oxygen.

[0074] In addition, in the first dielectric film 41, a compound other than the perovskite-type compound may be included as long as it does not inhibit the realization of high adhesion and high breakdown voltage. In the second dielectric film 42, a compound other than the oxide of M may be included as long as it does not inhibit the realization of high adhesion and high breakdown voltage. For example, in the first dielectric film 41, the compound other than the perovskite-type compound may be included in an amount of less than 50 mol%. For example, in the second dielectric film 42, the compound other than the oxide of M may be included in an amount of less than 50 mol%.

[0075] In the present embodiment, the absolute value of the average oxide formation energy of the cation element contained in the B-site in the perovskite-type compound contained in the first dielectric film 41 is defined as X1, and the absolute value of the average oxide formation energy of M in the oxide of M contained in the second dielectric film 42 is defined as X2b, and X2b < X1 and X2b ≤ 1000 kJ / mol.

[0076] Since the second dielectric film 42 with a small X2b is included in the dielectric film 40, the adhesion between the dielectric film 40 and the second electrode 50 can be improved. The reason for the improved adhesion will be described below.

[0077] In order to improve the adhesion between the electrode and the dielectric film, it is necessary to firmly bond the electrode and the dielectric film at the interface between the electrode and the dielectric film. In order to strengthen the bond between the electrode and the dielectric film, it is necessary to bring the bonding state of the atoms contained in the electrode closer to the bonding state of the atoms contained in the dielectric film.

[0078] Generally, the atoms contained in the electrode are bonded by a metal-metal bond. On the other hand, generally, the atoms contained in the dielectric film are bonded by a covalent bond. Therefore, the adhesion between the electrode and the dielectric film tends to be low.

[0079] Here, when the absolute value of the average oxide formation energy of M in the oxide of M contained in the dielectric film is small, the dielectric film is likely to be oxidized and reduced. That is, at the atomic layer level of the interface in contact with the electrode, the dielectric film is likely to be oxidized and reduced. Therefore, when the absolute value of the average oxide formation energy of M in the oxide of M contained in the dielectric film is small, the bonding state of atoms at the interface on the dielectric film side is close to a metal-metal bond. Therefore, when the absolute value of the average oxide formation energy of M contained in the oxide of M contained in the dielectric film is small, the adhesion between the electrode and the dielectric film is improved.

[0080] As described above, the first embodiment and the second embodiment have been described. However, the present invention is not limited to the above embodiments, and various modifications may be made within the scope of the present invention.

[0081] There is no particular limitation on the use of the thin film capacitor of each embodiment. For example, a snubber capacitor used in a DC-DC converter, an AC-AC converter, a DC-AC inverter, etc. can be mentioned. In addition, a power module on which a thin film capacitor is mounted can be mentioned. Furthermore, electronic devices including the power module, such as digital TVs, servers, in-vehicle devices, etc. can be mentioned.

Examples

[0082] Hereinafter, the present invention will be described in more detail using examples and comparative examples. However, the present invention is not limited to the following examples.

[0083] (Experimental Example 1) First, targets for forming the first dielectric film and the second dielectric film were produced as follows.

[0084] As raw material powders for the target, strontium carbonate (SrCO 3 ), calcium carbonate (CaCO 3 ), barium carbonate (BaCO 3 ), titanium oxide (TiO 2 ), zirconium oxide (ZrO2 ) Magnesium oxide (MgO) and tantalum oxide (Ta 2 O 5 ) powders were prepared. These powders were weighed so as to have the compositions of the dielectric films shown in Tables 1 and 2.

[0085] Using water as a solvent in a ball mill, wet mixing of the weighed raw material powders of the target was carried out for 20 hours. The obtained mixed powder slurry was dried at 100 °C to obtain mixed powder. The obtained mixed powder was press-molded by a press machine to obtain a molded body. The molding conditions were a pressure of 100 Pa, a temperature of 25 °C, and a pressing time of 3 minutes.

[0086] Subsequently, the obtained molded body was fired to obtain a sintered body. The firing conditions were a holding temperature of 1300 - 1400 °C, a holding time of 2 - 5 hours, and the atmosphere was air.

[0087] The obtained sintered body was processed to a diameter of 200 mm and a thickness of 6 mm by a surface grinding machine and a cylindrical grinding machine to obtain a target for forming each dielectric film.

[0088] Subsequently, Ni foil and Cu foil were prepared as metal foils that also serve as a substrate and a first electrode. The dimensions of the metal foil were 100 mm × 100 mm × 0.05 mm.

[0089] Subsequently, using the target for forming the first dielectric film, the first dielectric film was formed on the metal foil by sputtering to a thickness d shown in Tables 1 and 2 1 so as to be.

[0090] Subsequently, using the target for forming the second dielectric film, the second dielectric film was formed on the first dielectric film by sputtering to a thickness d shown in Tables 1 and 2 2 so as to be.

[0091] The film formation conditions for each dielectric film were a substrate temperature of 400 °C and a film formation pressure of 0.1 Pa.

[0092] Next, before forming the second electrode, reduction firing was performed at 600 °C. Thereafter, on the second dielectric film, a thin film of the metal elements shown in Tables 1 and 2 was formed as the second electrode by sputtering, thereby obtaining thin film capacitor samples shown in Tables 1 and 2.

[0093] For all samples, the compositions of the first dielectric film and the second dielectric film were analyzed using XRF (X-ray fluorescence elemental analysis), and it was confirmed that they were consistent with the compositions described in Tables 1 and 2. Also, the thicknesses of the first dielectric film and the second dielectric film were taken as the values measured by processing the thin film capacitor sample with FIB and observing the obtained cross-section with SEM (scanning electron microscope).

[0094] For all the obtained thin film capacitors, the relative permittivity, breakdown voltage, and adhesion strength were measured by the methods shown below.

[0095] The relative permittivity was calculated from the capacitance measured under the conditions of room temperature 25 °C and measurement frequency 1 kHz (1 Vrms) using an impedance analyzer (E4980A) for the thin film capacitor sample, the electrode dimensions of the thin film capacitor sample, and the distance between the electrodes.

[0096] The relative permittivity ε 1 of the first dielectric film was taken as the relative permittivity of a thin film capacitor sample fabricated under the same conditions except that the second dielectric film was not formed. The results are shown in Tables 1 and 2.

[0097] The relative permittivity ε 2 of the second dielectric film was taken as the relative permittivity of a thin film capacitor sample fabricated under the same conditions except that the first dielectric film was not formed. The results are shown in Tables 1 and 2.

[0098] The composite permittivity ε was calculated by the above method. The results are shown in Tables 1 and 2. Also, the relative permittivity of each thin film capacitor was measured and it was confirmed that it was substantially consistent with the composite permittivity ε.

[0099] The breakdown voltage was measured by applying a direct current at a voltage increase rate of 1 V / s and measuring the voltage at the point when a current exceeding 50 mA flowed. Also, regarding the breakdown voltage, the breakdown voltage of each sample and the breakdown voltage of a thin-film capacitor sample (the breakdown voltage of the first dielectric film) prepared under the same conditions except that the second dielectric film was not formed for each sample were measured. The results are shown in Tables 1 and 2. For the breakdown voltage of the first dielectric film, it was considered good when it was 0.10 kV / μm or more, even better when it was 0.30 kV / μm or more, and even better when it was 0.50 kV / μm or more. For the breakdown voltage of each sample, it was considered good when it was 0.10 kV / μm or more, even better when it was 0.30 kV / μm or more, and even better when it was 0.50 kV / μm or more.

[0100] The adhesion strength was measured by attaching and pulling an Al stud pin. The following is an explanation of the method for measuring the adhesion strength.

[0101] As the Al stud pin 、first An Al stud pin with an epoxy adhesive and a diameter of 2.7 mm at the end (manufactured by Quad Group) was prepared. Next, the Al stud pin was adhered to the second electrode layer of the evaluation sample. Specifically, the surface of the Al stud pin with the epoxy adhesive was pressed against the second electrode layer and heated at 150°C for 1 hour. Then, a cut was made in the second electrode layer around the part where the stud pin was adhered.

[0102] Separately, a clamp was attached to a digital force gauge RZ-50 (manufactured by AIKO Engineering).

[0103] Then, the evaluation sample was fixed and the stud pin was clamped with the clamp. After that, the stud pin was pulled vertically upward at a speed of 15 mm / min. The maximum value of the tensile stress when the stud pin was pulled up was measured and taken as the adhesion strength.

[0104] The adhesion strength is 10.0 N / mm 2It was considered good when it was as described above. The adhesion strength is 10.0 N / mm 2 or more, and 1.0 N / mm or more higher than the adhesion strength when the second dielectric film is not formed 2 or more. It was considered even better when it was higher.

[0105] [Table 1]

[0106] [Table 2]

[0107] From Table 1 and Table 2, in the examples where X2a < X1 and X2a ≤ 1000 kJ / mol were satisfied, the adhesion strength and breakdown voltage were good. On the other hand, in the comparative examples where X2a was too large, the adhesion strength decreased. Also, in the perovskite-type compound contained in the first dielectric film, in the examples where the ratio of Ti to 100 mol parts of the cation element entering the B site was 50 mol parts or less, the adhesion strength was greatly improved in comparison with the case where it was carried out under the same conditions except for the absence of the second dielectric film. Furthermore, in the examples where the ratio of Ti to 100 mol parts of the cation element entering the B site was 50 mol parts or less, the breakdown voltage also increased.

[0108] (Experimental Example 2) In Experimental Example 2, the second dielectric film is different from that in Experimental Example 1. Hereinafter, the method for forming the second dielectric film will be described.

[0109] As the raw material powder of the target for forming the second dielectric film, silicon oxide (SiO 2 ), titanium oxide (TiO 2 ), zinc oxide (ZnO 2 ), aluminum oxide (Al 2 O 3 ), iron oxide (Fe 2 O 3 ), hafnium oxide (HfO 2 ), tantalum oxide (Ta 2 O 5Each powder of was prepared. These powders were weighed so as to have the composition of the second dielectric film shown in Tables 3 and 4.

[0110] Using water as a solvent in a ball mill, wet mixing of the weighed raw material powders of the target was carried out for 20 hours. The obtained mixed powder slurry was dried at 100 °C to obtain a mixed powder. The obtained mixed powder was press-molded by a press machine to obtain a molded body. The molding conditions were a pressure of 100 Pa, a temperature of 25 °C, and a press time of 3 minutes.

[0111] Thereafter, the obtained molded body was fired to obtain a sintered body. The firing conditions were a holding temperature of 1300 to 1400 °C, a holding time of 2 to 5 hours, and the atmosphere was air.

[0112] The obtained sintered body was processed to a diameter of 200 mm and a thickness of 6 mm by a surface grinding machine and a cylindrical grinding machine to obtain a target for forming a second dielectric film.

[0113] Regarding other points, it was carried out under the same conditions as in Experimental Example 1. The results are shown in Tables 3 and 4.

[0114]

Table 3

[0115]

Table 4

[0116] From Tables 3 and 4, in the examples satisfying X2b < X1 and X2b ≤ 1000 kJ / mol, the adhesion strength and the withstand voltage were good. On the other hand, in the comparative examples where X2b was too large, the adhesion strength decreased. Further, in the perovskite-type compound contained in the first dielectric film, in the examples where the ratio of Ti to 100 mol parts of the cation element entering the B site was 50 mol parts or less, the adhesion strength was greatly improved in comparison with the case where it was carried out under the same conditions except that the second dielectric film was not present. Furthermore, in the examples where the ratio of Ti to 100 mol parts of the cation element entering the B site was 50 mol parts or less, the withstand voltage also increased.

[0117] For reference, Table 5 shows the oxide formation energies of the respective elements used for calculating X1, X2a, and X2b in the above-described embodiments.

[0118] [Table 5] [Description of Reference Numerals]

[0119] 100... thin film capacitor 10... substrate 20... insulating layer 30... first electrode 40... dielectric film 41... first dielectric film 42... second dielectric film 50... second electrode 60... laminated structure 70... protective film

Claims

1. A thin-film capacitor having a stacked structure in which a first electrode, a first dielectric film, a second dielectric film, and a second electrode are stacked in this order, wherein the second dielectric film is in contact with the second electrode, the first dielectric film and the second dielectric film contain a perovskite-type compound, the cation element contained in the A site in the perovskite-type compound contained in the first dielectric film is one or more selected from calcium (Ca), strontium (Sr), and barium (Ba), the ratio of Ti to 100 mol parts of the cation element entering the B site in the perovskite-type compound contained in the first dielectric film is 50 mol parts or less, let the absolute value of the average oxide formation energy of the cation element contained in the B site in the perovskite-type compound contained in the first dielectric film be X1, let the absolute value of the average oxide formation energy of the cation element contained in the B site in the perovskite-type compound contained in the second dielectric film be X2a, a thin-film capacitor in which X2a < X1 and X2a ≦ 1000 kJ / mol.

2. Let the relative permittivity of the first dielectric film be ε 1 and the film thickness of the first dielectric film be d 1 Let the relative permittivity of the second dielectric film be ε 2 and the film thickness of the second dielectric film be d 2 ε 1 and ε 2 Let the composite permittivity of them be ε. The thin-film capacitor according to claim 1 satisfies ε ≥ 0.8 × ε 1 × ((d 1 + d 2 ) / d 1 ).

3. The thin-film capacitor according to claim 1 or 2, wherein the breakdown voltage of the first dielectric film is 0.30 kV / um or more.

4. A power module having the thin-film capacitor according to any one of claims 1 to 3.

5. An electronic device having the power module according to claim 4.

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