JP2022154797A - Dielectric element and electronic circuit board - Google Patents

Abstract

To provide a dielectric element comprising a dielectric film having a relatively high specific dielectric constant while relatively reducing a leak current even in a case where an electrode consists of a base metal and heat treatment is applied to the dielectric film under a reductive atmosphere, and an electronic circuit board on which the dielectric element is mounted.SOLUTION: The present invention relates to a dielectric element comprising a first electrode consisting of a base metal, a dielectric film and a second electrode. The dielectric film has a laminated structure in which a first dielectric film containing a composite oxide expressed by a chemical formula ABO3 as a main component and a second dielectric film containing a composite oxide expressed by a chemical formula A'B'O3 as a main component are directly in contact with each other. In the dielectric film, in the chemical formulas, A is at least one selected from the group consisting of barium, strontium and calcium; B is titanium; A' is at least one selected from the group consisting of barium, strontium and calcium; and B' is at least one selected from the group consisting of zirconium and hafnium.SELECTED DRAWING: Figure 2A

Description

The present invention relates to dielectric elements and electronic circuit boards. In particular, the present invention relates to a dielectric element such as a thin film capacitor having a thin dielectric film.

In recent years, electronic devices such as mobile phones and computers have become increasingly demanding for higher functionality and lower power consumption. It is required to reduce the operating voltage and reduce the operating voltage.

Since this IC is accompanied by variations in impedance during operation, high-frequency noise is generated in the power supply line when various logic operations are performed. This high-frequency noise becomes noise to the power supply voltage of other ICs in the circuit and destabilizes its operation. do.

As a capacitor for a decoupling circuit, there is a demand for a small and low-profile capacitor that can be embedded inside a substrate near the IC in order to reduce the inductance of the wiring that connects the IC and the capacitor. A thin film capacitor, which is an example of a dielectric element, is known as such a capacitor.

Patent Document 1 describes a dielectric laminated thin film having a structure in which an intermediate dielectric layer is sandwiched between a bulk dielectric layer and an electrode. It is described that such a dielectric laminated thin film can increase the height of the Schottky barrier formed at the interface between the electrode and the dielectric, thereby reducing leakage current.

Further, Patent Document 2 discloses a thin-film capacitor containing a perovskite-type composite oxide, manganese, and at least one element M selected from vanadium, niobium, and tantalum, and containing these elements within a predetermined range. is described. It is described that such a thin film capacitor increases the insulation resistance value and improves the reliability.

JP-A-2003-45987 JP 2010-267953 A

In recent years, in order to reduce the cost of thin film capacitors, the electrodes have been made of base metals. On the other hand, in order to increase the capacitance density of a thin film capacitor, a dielectric film formed by a film forming method is heat-treated at a high temperature to increase the crystallinity of the dielectric material forming the dielectric film.

However, when the electrode is made of a base metal, the electrode is oxidized by heat treatment at a high temperature under a high oxygen partial pressure such as air. Therefore, in order to prevent oxidation of the base metal, it is necessary to perform heat treatment at high temperature in a reducing atmosphere.

However, if the heat treatment is performed in a reducing atmosphere, part of the dielectric material forming the dielectric film is conversely reduced, resulting in a decrease in insulation resistance. As a result, the dielectric film becomes more conductive, increasing leakage current. Further, when a thin film capacitor is mounted on a substrate and embedded with resin, protons resulting from hydrogen contained in the atmosphere during the embedding process may form a solid solution in the dielectric film. When such protons form a solid solution, carriers tend to move in the dielectric, further increasing leakage current.

Patent Documents 1 and 2 do not assume that the electrodes are made of a base metal, and there is a problem that no consideration is given to the deterioration of the dielectric properties of the thin film capacitor due to heat treatment in a reducing atmosphere.

The present invention has been made in view of such a situation, and even when the electrode is made of a base metal and the dielectric film is heat-treated in a reducing atmosphere, the leakage current can be relatively reduced and the current can be relatively reduced. An object of the present invention is to provide a dielectric element having a dielectric film having a high dielectric constant, and an electronic circuit board on which the dielectric element is mounted.

In order to achieve the above object, aspects of the present invention are as follows.
[1] A dielectric element having a first electrode made of a base metal, a dielectric film, and a second electrode,
The dielectric films are composed of a first dielectric film mainly composed of a complex oxide represented by the chemical formula _ABO3 and a second dielectric film mainly composed of a complex oxide represented by the chemical formula _A'B'O3 . having a laminated structure in which the dielectric film and the are in direct contact with each other,
In the chemical formula, A is at least one selected from the group consisting of barium, strontium and calcium, B is titanium, A' is at least one selected from the group consisting of barium, strontium and calcium, and B ' is a dielectric element which is at least one selected from the group consisting of zirconium and hafnium.

[2] When t2 is the thickness of the second dielectric film and T is the total thickness of the first dielectric film and the second dielectric film, t2/T is 10% or more and 50% or less. A dielectric element according to a certain [1].

[3] When t2/T is 10% or more and 30% or less, the first dielectric film is in direct contact with both the first electrode and the second electrode, or the second dielectric A dielectric element according to [2], wherein the film is in direct contact with both the first electrode and the second electrode.

[4] The first dielectric film contains, as an auxiliary component, at least one selected from the group consisting of yttrium and aluminum with respect to 100 mols of the composite oxide represented by the chemical formula ABO ₃ . The dielectric element according to any one of [1] to [3], containing 0 mol or less of manganese and 0.3 mol or less of vanadium.

[5] In the laminated structure, the diffraction angle 2θ of the strongest peak among the diffraction peaks of the (110) plane of the composite oxide in the X-ray diffraction measurement of the composite oxide represented by the chemical formula ABO ₃ is The dielectric according to any one of [1] to [4], which is 0.5° or more larger than the diffraction angle 2θ of the strongest peak among the diffraction peaks of the (110) plane of the reference when the reference is subjected to X-ray diffraction measurement. is a body element.

[6] An electronic circuit board on which the dielectric element according to any one of [1] to [5] is mounted.

According to the present invention, even when the electrode is made of a base metal and the dielectric film is heat-treated in a reducing atmosphere, a dielectric film having a relatively high dielectric constant can be obtained while reducing leakage current. It is possible to provide a dielectric element provided with the dielectric element and an electronic circuit board on which the dielectric element is mounted.

FIG. 1 is a schematic cross-sectional view of a thin film capacitor as a dielectric element according to one embodiment of the present invention. FIG. 2A is a schematic cross-sectional view of a thin film capacitor for explaining a laminated structure of dielectric films. FIG. 2B is a schematic cross-sectional view of a thin film capacitor for explaining a laminated structure of dielectric films. FIG. 2C is a schematic cross-sectional view of a thin film capacitor for explaining a laminated structure of dielectric films. FIG. 2D is a schematic cross-sectional view of a thin film capacitor for explaining the laminated structure of dielectric films. FIG. 3A is a schematic cross-sectional view of an electronic circuit board on which a thin film capacitor is mounted. FIG. 3B is an enlarged view of 90A in FIG. 3A.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail in the following order based on specific embodiments with reference to the drawings.
1. Thin film capacitor 1.1 Overall configuration of thin film capacitor 1.2 Dielectric film 1.3 First electrode 1.4 Second electrode 2. 2. Manufacturing method of thin film capacitor. electronic circuit board4. Modification

(1. Thin film capacitor)
First, a thin film capacitor having a thin dielectric film will be described as an example of the dielectric element according to the present embodiment.

(1.1 Overall Configuration of Thin Film Capacitor)
As shown in FIG. 1, a thin film capacitor 1 as an example of a dielectric element according to this embodiment includes a first electrode 10, a dielectric film 30, and a second electrode 20 laminated in this order. have a configuration. Dielectric film 30 includes a first dielectric film and a second dielectric film.

When the first electrode 10 and the second electrode 20 are connected to an external circuit and a voltage is applied, the dielectric film 30 exhibits a predetermined capacitance and can function as a capacitor. A detailed description of each component will be given later. If the first electrode and the second electrode are made of different materials, one electrode may be the upper electrode and the other electrode may be the lower electrode in order to distinguish the vertical direction of the thin film capacitor.

Although the shape of the thin film capacitor is not particularly limited, it is usually rectangular parallelepiped. Moreover, there are no particular restrictions on the dimensions thereof, and the thickness and length may be set appropriately according to the application.

The thickness of the dielectric film 30 is not particularly limited, and can be arbitrarily set according to desired properties, applications, and the like. In this embodiment, the thickness of the dielectric film 30 is preferably 30 nm to 1000 nm, more preferably 30 nm to 600 nm. In addition, when the dielectric film 30 is composed of the first dielectric film and the second dielectric film, the thickness of the dielectric film 30 is equal to the thickness of the first dielectric film and the second dielectric film. Matches the total thickness of the membrane.

Note that the thickness of the dielectric film 30 is determined by processing a thin film capacitor including the dielectric film 30 with an FIB (focused ion beam) processing apparatus, and examining the obtained cross section with a scanning electron microscope (SEM) or a transmission electron microscope ( TEM) or the like to observe and measure.

Further, in the present embodiment, the first dielectric film and the second dielectric film forming the dielectric film 30 are thin films formed by a known film forming method. Since such thin films are usually formed by depositing atoms on a substrate, the dielectric film is preferably a dielectric deposited film. Therefore, the dielectric film according to the present embodiment does not include a sintered body (obtained by a solid-phase reaction) obtained by firing a molded body obtained by molding dielectric raw material powder. Note that the dielectric film 30 is crystalline in this embodiment.

In this embodiment, the first electrode is composed of a base metal. Base metals are less expensive than noble metals, and the cost of thin film capacitors can be reduced by forming the electrodes from base metals.

In a thin-film capacitor, a dielectric material forming a dielectric film is formed on the first electrode by a known film-forming method. A dielectric film formed by a known film formation method often has low crystallinity, and as a result, the relative dielectric constant of the dielectric film tends to be low. If the relative dielectric constant of the dielectric film is low, it becomes difficult to increase the capacity density of a thin film capacitor with a low profile.

Therefore, in order to increase the relative dielectric constant of the dielectric film, the dielectric film after deposition is heat-treated at a high temperature to promote crystallization of the dielectric film and improve crystallinity. Since base metals are easily oxidized in heat treatment at such high temperatures, the heat treatment is performed in a reducing atmosphere in order to prevent oxidation of the base metals.

However, heat treatment in a reducing atmosphere conversely reduces a portion of the dielectric material forming the dielectric film, thereby lowering the insulation resistance of the dielectric film. As a result, the dielectric film becomes more conductive and the leak current increases.

In this embodiment, the first electrode is made of a base metal, and even when heat treatment is performed in a reducing atmosphere, the leakage current is kept relatively low and the capacitance density of the thin film capacitor is increased. A first dielectric film having a relatively high dielectric constant but being relatively easily reduced and a second dielectric film having a relatively low dielectric constant but being relatively difficult to be reduced are in contact with each other through an interface. A laminated structure is formed. A thin film capacitor having such a laminated structure can maintain a relatively low leakage current and obtain a higher dielectric constant than a thin film capacitor using only a dielectric material having resistance to reduction.

The above first dielectric film has a composite oxide represented by the chemical formula _ABO3 as a main component. In this embodiment, it is preferable that the main component is contained in an amount of 80 mol % or more and 100 mol % or less in the entire first dielectric film (100 mol %).

In the above chemical formula, "A" is at least one selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), and "B" is titanium (Ti). Such a composite oxide is a composite oxide having a perovskite structure, and can be represented, for example, by the composition formula Ba _x Sr _y Ca _1-xy TiO ₃ (0≦x≦1, 0≦y≦1). can be done. "A" preferably contains at least barium, more preferably barium.

Also, the above-described second dielectric film has a composite oxide represented by the chemical formula A'B'O ₃ as a main component. In this embodiment, it is preferable that the main component is contained in an amount of 80 mol % or more and 100 mol % or less in the entire second dielectric film (100 mol %).

In the above chemical formula, "A'" is at least one selected from the group consisting of barium (Ba), strontium (Sr) and calcium (Ca), and "B'" is zirconium (Zr) and hafnium (Hf). ) is at least one selected from the group consisting of Such a composite oxide is a composite oxide having a perovskite structure, and has, for example, a composition formula of Ba _s Sr _t Ca _1- st Zr _m Hf _1-m O ₃ (0≦s≦1, 0≦t ≤1, 0≤m≤1). "A'" preferably contains at least barium, more preferably barium. "B'" preferably contains at least zirconium, more preferably zirconium.

As shown in FIG. 2A, the dielectric film 30 has a laminated structure in which a first dielectric film 31 and a second dielectric film 32 are laminated. In this laminated structure, the first dielectric film 31 and the second dielectric film 32 are in direct contact. That is, an interface is formed between the first dielectric film 31 and the second dielectric film 32 .

When a dielectric film having such a laminated structure is heat treated in a reducing atmosphere, oxygen is deprived from the composite oxide (ABO ₃ ) contained in the first dielectric film, which is relatively easily reduced, resulting in oxygen defects and free radicals. generated by electrons. On the other hand, since the first dielectric film and the second dielectric film are in direct contact with each other, from the composite oxide (A'B'O ₃ ) contained in the second dielectric film, the ABO ₃ side can transfer oxygen to and supply ABO ₃ with oxygen. That is, some of the oxygen defects generated in ABO ₃ are compensated by oxygen supplied from A'B'O ₃ . As a result, reduction of ABO ₃ is moderated, and leakage current due to carriers generated by the reduction is reduced. In addition, since ABO ₃ has a dielectric constant higher than that of A'B'O ₃ , the leakage current is reduced while the dielectric film is made of A'B'O ₃ . A high dielectric constant can be obtained.

Although the complex oxide (A'B'O ₃ ) contained in the second dielectric film and the complex oxide (ABO ₃ ) contained in the first dielectric film have the same crystal structure, , the lattice constants are different, and 'A', 'B', 'A'' and 'B'' are the elements mentioned above, the lattice constant of A'B'O ₃ is greater than that of ABO ₃ is also big. At this time, when oxygen moves from A'B'O ₃ to ABO ₃ , the lattice of ABO ₃ is distorted and contracted. As a result, the lattice spacing of ABO ₃ becomes smaller, so that when X-ray diffraction measurement is performed on ABO ₃ after the lattice contraction, the position of the diffraction peak (diffraction angle 2θ) of the predetermined lattice plane is on the high angle side. shift to

Such lattice contraction occurs when oxygen moves from _A'B'O3 to _ABO3 . Therefore, if the deposited ABO ₃ is not heat-treated in a reducing atmosphere, the deposited ABO ₃ is not subjected to the energy associated with the heat treatment, so no shrinkage from the deposited lattice occurs. . In the thin film capacitor according to the present embodiment, the base metal needs to have sufficient conductivity in order to function as an electrode, so an atmosphere in which the base metal is oxidized is not taken into consideration.

Therefore, if the ABO ₃ immediately after film formation, which has not undergone a heat treatment in a reducing atmosphere, is used as a reference, the value of the diffraction angle 2θ of the diffraction peak of the predetermined lattice plane of the reference ABO ₃ ( The value (P) of the diffraction angle 2θ of the diffraction peak of the lattice plane of ABO ₃ after heat treatment of the dielectric film having the above laminated structure in a reducing atmosphere is larger than P _r ).

In this embodiment, _Pr and P are calculated for the strongest peak among the diffraction peaks of the (110) plane of _ABO3 . The strongest peak lies within the diffraction angle 2θ range of 30° to 34°, which varies with the composition of ABO ₃ .

The value (P) of the strongest peak diffraction angle 2θ of the ₍ 110) plane of ABO ₃ of the thin film capacitor according to the present embodiment is the value (P _r ) by at least 0.5°.

It can be inferred that when P is greater than Pr by 0.5° or more, oxygen moves from A'B'O ₃ to ABO ₃ and the reduction of ABO ₃ is moderated, resulting in the above effect. be.

Further, when the total thickness of the first dielectric and the second dielectric is T, and the thickness of the second dielectric film is t2, t2/T is 10% or more and 50% or less. preferable. That is, by setting the thickness of the second dielectric film to be equal to or less than the thickness of the first dielectric film, the above effect can be improved.

Furthermore, the thin film capacitor including the above dielectric film may be mounted on an electronic circuit board and embedded in resin. In the embedding process, the thin-film capacitor is usually exposed to an atmosphere containing hydrogen derived from resin, and protons derived from the atmosphere may form a solid solution in the dielectric film. In particular, when protons are solid-dissolved in the first dielectric film, migration of protons or migration of carriers via protons occurs, resulting in an increase in leakage current. However, since the thin film capacitor according to the present embodiment has the laminated structure described above, it is possible to suppress the migration of protons and the like, and to further reduce the leakage current.

The above effect can also be obtained with a laminated structure other than the laminated structure shown in FIG. 2A. In FIG. 2A, the first dielectric film 31 is formed on the first electrode 10. However, if the first electrode and the second electrode are made of different materials, as shown in FIG. A laminated structure in which the second dielectric film 32 is formed on one electrode 10 and the first dielectric film 31 is laminated on the second dielectric film 32 may be employed.

Alternatively, as shown in FIGS. 2C and 2D, the dielectric film may have a three-layer structure, and a laminated structure may be formed by sandwiching one dielectric film between two other dielectric films. . By having such a laminated structure, the same dielectric film is in contact with the first electrode and the second electrode showing different polarities. Characteristic changes are less likely to occur.

A laminated structure (FIG. 2C) in which a second dielectric film 32 is sandwiched between two first dielectric films 31, and a laminated structure in which a first dielectric film 31 is sandwiched between two second dielectric films 32 (FIG. 2C). The laminated structure (FIG. 2D) may be selected according to the characteristics to be emphasized. For example, when emphasizing that the characteristics of the thin film capacitor are unlikely to change due to the voltage application direction, the laminated structure shown in FIG. 2D is preferable. 2D, the thickness t2 of the second dielectric film 32 is the total thickness of the two second dielectric films 32. As shown in FIG.

Further, if the first dielectric film and the second dielectric film are in direct contact with each other, the total number of layers of the first dielectric film and the second dielectric film is four. You may have the above laminated structures.

The first dielectric film may have subcomponents in addition to the main component (ABO ₃ ). As an auxiliary component, at least one selected from the group consisting of yttrium (Y) and aluminum (Al) is preferably contained in an amount of more than 0 mol and 0.3 mol or less per 100 mol of ABO ₃ . Moreover, it is preferable that more than 0 mol and 0.3 mol or less of manganese (Mn) is included with respect to 100 mol of ABO ₃ . Moreover, it is preferable that more than 0 mol and 0.3 mol or less of vanadium (V) is included with respect to 100 mol of ABO ₃ . Furthermore, with respect to 100 mols of ABO ₃ , at least one selected from the group consisting of yttrium and aluminum, more than 0 mols and 0.3 mols or less, manganese more than 0 mols and 0.3 mols or less, vanadium more than 0 mols and 0.3 mols or less. It is more preferable to contain 3 mol or less. By including such an element in the first dielectric film, it is possible to suppress the migration of protons and the like after being embedded in the resin. As a result, leakage current can be further reduced.

Further, the second dielectric film may contain trace amounts of impurities, subcomponents, etc. within the range where the effects of the present invention can be obtained.

(1.4. First electrode)
As shown in FIG. 1, the first electrode 10 is an electrode for sandwiching a dielectric film 30 together with a second electrode 20, which will be described later, to function as a capacitor. The material forming the first electrode 10 is a conductive base metal, as described above. Examples of such base metals include nickel (Ni), copper (Cu), iron (Fe), and alloys containing at least two selected from these.

In this embodiment, nickel, copper and iron are preferred, with nickel being more preferred. The higher the purity of nickel, the better. For example, it is more preferably 99.99% by mass or more.

In this embodiment, the first electrode 10 also serves as a substrate, and is preferably a metal plate such as metal foil. In this case, in addition to being able to make the thin film capacitor thinner, it becomes easier to mount the thin film capacitor on the electronic circuit board.

The thickness of the first electrode 10 is preferably 5 μm or more and 100 μm or less, more preferably 20 μm or more and 70 μm or less. If the thickness of the first electrode 10 is too small, it tends to be difficult to handle the first electrode 10 when manufacturing the thin film capacitor 1 .

(1.5. Second electrode)
As shown in FIG. 1, a second electrode 20 is formed as a thin film on the surface of the dielectric film 30 as an upper electrode. The second electrode 20 is an electrode for sandwiching the dielectric film 30 together with the above-described first electrode 10 and functioning as a capacitor. The second electrode 20 thus exhibits a different polarity than the first electrode 10 .

The material forming the second electrode 20 is not particularly limited as long as it is a conductive material when the second electrode is formed after heat treatment of the dielectric film in a reducing atmosphere. For example, gold (Au), platinum (Pt), silver (Ag), iridium (Ir), ruthenium (Ru), cobalt (Co), nickel (Ni), iron (Fe), copper (Cu), aluminum (Al ), or alloys thereof; semiconductors such as silicon (Si), GaAs, GaP, InP, SiC; and conductive metal oxides such as ITO, ZnO, _SnO2 .

When the dielectric film is heat-treated in a reducing atmosphere after the second electrode is formed, the material constituting the second electrode may be the above-described base metal as in the case of the first electrode. preferable.

As with the first electrode 10, the thickness of the second electrode 20 is not particularly limited as long as it is thick enough to function as an electrode. In this embodiment, the thickness is preferably 0.01 μm or more.

(2. Manufacturing method of thin film capacitor)
Next, an example of a method for manufacturing the thin film capacitor 1 shown in FIG. 2A will be described below.

First, the first electrode 10 is prepared. In this embodiment, a base metal foil is prepared as the first electrode 10 . The base metal foil is the lower electrode and also serves as the substrate.

Subsequently, a dielectric film 30 is formed by depositing a material constituting the dielectric film on the first electrode 10 . In this embodiment, a known film formation method is used to form a first dielectric film 31 as a dielectric deposition film on the first electrode 10, and then, on the first dielectric film 31, A second dielectric film 32 is formed as a dielectric deposition film.

Examples of known film forming methods include vacuum deposition, sputtering, PLD (pulsed laser deposition), MO-CVD (metal-organic chemical vapor deposition), MOD (metal-organic decomposition), sol-gel method, and CSD. (chemical solution deposition method) is exemplified. In this embodiment, the sputtering method is preferable from the viewpoint of cost and the like.

Raw materials used for film formation (vapor deposition materials, various target materials, organometallic materials, etc.) may contain trace amounts of impurities and subcomponents. No problem.

For example, when the sputtering method is used, a target for forming the first dielectric film is used to form the first dielectric film 31 on the first electrode 10 as the substrate. As film formation conditions, the substrate temperature is preferably 100 to 500.degree. Also, the pressure during film formation is preferably 0.05 to 10 Pa.

Subsequently, a second dielectric film 32 is formed on the first dielectric film 31 . The method of forming the second dielectric film may be any known film forming method. As well-known film formation methods as in the formation of the first dielectric film, for example, vacuum deposition method, sputtering method, PLD (pulse laser deposition method), MO-CVD (metalorganic chemical vapor deposition method), Examples include MOD (metal organic decomposition method), sol-gel method, and CSD (chemical solution deposition method). In this embodiment, from the viewpoint of cost and the like, it is preferable that the film formation method is the same as the film formation method for forming the first dielectric film, and the sputtering method is preferable.

For example, when the first dielectric film and the second dielectric film are formed by a sputtering method, after the first dielectric film 31 is formed, the substrate (first electrode 10) is heated while the first dielectric film is formed. The target for forming the first dielectric film is switched to the target for forming the second dielectric film, and the first dielectric film 31 is formed under the same conditions as the first dielectric film. A second dielectric film 32 is formed. That is, as film formation conditions, the substrate temperature is preferably 300° C. or less. Also, the pressure during film formation is preferably 0.05 to 10 Pa. Any layered structure other than the layered structure shown in FIG. 2A can be formed by appropriately changing the order of forming the first dielectric film and the second dielectric film.

In this embodiment, after forming a dielectric film having a desired laminated structure, the dielectric film is heat-treated. The heat treatment is performed using, for example, a tubular furnace in which the atmosphere can be controlled. The dielectric film 30 (the first dielectric film 31 and the second dielectric film 32) formed on the first electrode 10 is placed in a tubular furnace, and the partial pressure of oxygen in the furnace is set to the first value. The heat treatment is controlled to such an extent that the electrodes 10 (base metal foil) are not oxidized. The holding temperature during the heat treatment is preferably 1000° C. or less, and the holding time is 1 to 600 minutes.

The oxygen partial pressure in the furnace is achieved, for example, by circulating a mixed gas containing nitrogen, oxygen, hydrogen, water vapor, etc., as atmospheric gas in the furnace.

By performing such a heat treatment, the crystallization of the dielectric film 30 is promoted and the crystallinity of the dielectric film 30 is enhanced. As a result, the capacity density of the thin film capacitor 1 can be increased.

After the heat treatment, the second electrode 20 is formed by forming a thin film of a material for forming the second electrode on the second dielectric film 32 using a known film forming method.

Through the above steps, as shown in FIG. 2A, a thin film capacitor 1 in which a first electrode 10, a first dielectric film 31, a second dielectric film 32 and a second electrode 20 are formed in this order. is obtained.

(3. Electronic circuit board)
The electronic circuit board according to this embodiment is mounted with the thin film capacitor described above. Further, the electronic circuit board may include other electronic components in addition to the thin film capacitors. An electronic component such as a thin film capacitor may be placed on the surface of the electronic circuit board or embedded in the electronic circuit board. The thin film capacitor provided on the electronic circuit board has base metal foil as the substrate and the first electrode (lower electrode) as described above.

An example of an electronic circuit board is shown in FIGS. 3A and 3B. The electronic circuit board 90 shown in FIG. 3A includes an epoxy resin substrate 92, a resin layer 93 covering the epoxy resin substrate 92, a thin film capacitor 1 provided on the resin layer 93, and the resin layer 93 and the thin film capacitor 1. An insulating coating layer 94 for covering, an electronic component 95 placed on the insulating coating layer 94, and a plurality of metal wirings 96 are provided.

At least part of the metal wiring 96 may be drawn out to the surface of the epoxy resin substrate 92 or the insulating coating layer 94 . Moreover, at least a part of the metal wiring 96 may be connected to the extraction electrodes 54 and 56 of the thin film capacitor 1 or the electronic component 95 . Moreover, at least a part of the metal wiring 96 may penetrate the electronic circuit board 90 in the direction from the front surface to the back surface of the electronic circuit board 90 .

As shown in FIG. 3B, the thin film capacitor 1 according to this embodiment includes a lower electrode (first electrode) 10, a dielectric film 30 provided on the surface of the lower electrode 10, and a dielectric film 30 on the upper surface of the dielectric film 30. and an upper electrode (second electrode) 20 provided on a portion thereof. In addition to these, the thin film capacitor 1 includes a through electrode 52 directly provided on the surface of the lower electrode 10 through the other portion of the dielectric film 30 , the upper electrode 20 , the dielectric film 30 and the through electrode 52 . The covering insulating resin layer 58, the extraction electrode 54 penetrating the insulating resin layer 58 and directly provided on the surface of the through electrode 52, and the insulating resin layer 58 penetrating and directly provided on the surface of the upper electrode 20 It may be provided with an extraction electrode 56 .

Electronic circuit board 90 is manufactured, for example, by the following procedure. First, the surface of the epoxy resin substrate 92 is covered with an uncured resin layer. The uncured resin layer is a precursor of resin layer 93 . A thin film capacitor 1 is placed on the surface of the uncured resin layer so that the lower electrode of the thin film capacitor 1 faces the uncured resin layer. By covering the uncured resin layer and the thin film capacitor 1 with the insulating coating layer 94 , the thin film capacitor 1 is sandwiched between the epoxy resin substrate 92 and the insulating coating layer 94 . A resin layer 93 is formed by thermosetting the uncured resin layer. Further, the insulating coating layer 94 is pressure-bonded to the epoxy resin substrate 92, the thin film capacitor 1 and the resin layer 93 by hot pressing, and the thin film capacitor 1 is embedded in the substrate with the resin.

In the process of embedding a thin film capacitor in a resin, the capacitor is usually exposed to an atmosphere containing hydrogen derived from the resin. There is When protons enter the dielectric film, the protons or carriers via the protons move easily in the dielectric, the insulation resistance of the dielectric film decreases, and the leakage current increases.

However, in this embodiment, since the dielectric film of the thin film capacitor has the above-described laminated structure, it is possible to suppress an increase in leakage current due to migration of protons and the like.

Subsequently, a plurality of through holes are formed through the laminated substrate. A metal line 96 is formed in each through hole. After forming the metal wiring 96 , the electronic component 95 is placed on the surface of the insulating coating layer 94 .

By the above method, the electronic circuit board 90 in which the thin film capacitor 1 is embedded is obtained. Each metal wiring 96 is a conductor and is made of copper, for example. The uncured resin layer may be a B-stage thermosetting resin (eg, epoxy resin, etc.). B-stage thermosets are not fully cured at room temperature and are fully cured upon heating. The insulating coating layer 94 may be made of epoxy resin, polytetrafluoroethylene resin, polyimide resin, or the like.

(4. Modification)
In the above-described embodiments, the case where the dielectric film is composed only of the first dielectric film and the second dielectric film has been described. It may further have a different dielectric film.

Although the embodiments of the present invention have been described above, the present invention is by no means limited to the above embodiments, and may be modified in various ways within the scope of the present invention.

The present invention will be described in more detail in the following examples. However, the present invention is not limited to the following examples.

(Experiment 1)
First, nickel foil, iron foil, copper foil, and platinum foil having a thickness of 30 μm were prepared as the first electrode. The dimensions of these metal foils were 80 mm long by 80 mm wide.

Subsequently, sputtering targets necessary for forming the first dielectric film and the second dielectric film were produced by a solid-phase method as follows.

Powders of BaCO ₃ , SrCO ₃ , CaCO ₃ , TiO ₂ and ZrO ₂ and powders of Y ₂ O ₃ , Al ₂ O ₃ , MnO ₂ and V ₂ O ₅ were prepared as target raw material powders. Raw materials for the target for the first dielectric film were weighed so as to have the composition shown in Table 1. Materials for the target for the second dielectric film were weighed so as to have the composition shown in Table 1.

Wet mixing of the weighed raw material powders of the target for the first dielectric film was performed for 20 hours in a ball mill using water as a solvent. The obtained mixed powder slurry was dried at 100° C. to obtain a mixed powder. The obtained mixed powder was press-molded by a pressing machine to obtain a compact. The molding conditions were a pressure of 100 Pa, a temperature of 25° C., and a pressing time of 3 minutes.

After that, the obtained molded body was fired to obtain a sintered body.

The obtained sintered body was processed to have a diameter of 200 mm and a thickness of 6 mm using a surface grinder and a cylindrical grinder to obtain a sputtering target for forming the first dielectric film. A sputtering target for forming the second dielectric film was also prepared in the same manner as the sputtering target for forming the first dielectric film.

Next, the laminated structure shown in Table 1 was formed on the nickel foil as the first electrode using the sputtering target for the first dielectric film and the sputtering target for the second dielectric film prepared above. A dielectric film having a thickness of 200 nm, which is composed of the first dielectric film and the second dielectric film, was formed by the sputtering method by switching the target so as to obtain the desired result. The film formation conditions were pressure: 1.5 Pa, substrate (first electrode) temperature: 500° C. or less. Incidentally, in Comparative Example 1, the first dielectric film was not formed. In Example 24, copper foil was used instead of nickel foil, in Example 25 iron foil was used instead of nickel foil, and in comparative example 2 platinum foil was used instead of nickel foil.

Except for Comparative Example 2, the dielectric film formed on the first electrode was placed in a tubular furnace, and a mixed gas composed of nitrogen, oxygen, hydrogen, and water vapor was passed through the furnace to obtain nickel. The oxygen partial pressure was adjusted so that the foil, copper foil and iron foil would not be oxidized. In this state, heat treatment was performed by increasing the temperature at a rate of temperature increase of 20° C./min or less and maintaining the temperature at 700° C. or more for 1 minute or more.

After the heat treatment, nickel was formed on the second dielectric film by sputtering at room temperature. Thereafter, a metal foil having a dielectric film formed thereon was supported on a substrate, a resist was coated on the nickel, exposed and developed, and only the nickel was etched to form a pattern as a second electrode. . A thin film capacitor sample was obtained through the above steps. In Comparative Example 2, the second electrode was formed without heat-treating the dielectric film after forming the second dielectric film.

The obtained thin film capacitor sample was subjected to heat treatment in a reducing atmosphere containing 3% hydrogen by heating to 200° C. and holding for 1 hour. This heat treatment simulates the process of mounting a thin film capacitor on a substrate and embedding it in resin.

In Table 1, “BT” in the “first dielectric” column indicates barium titanate (BaTiO ₃ ), “ST” indicates strontium titanate (SrTiO ₃ ), and “CT” indicates calcium titanate. (CaTiO ₃ ), and "BZ" in the "second dielectric" column indicates barium zirconate (BaZrO ₃ ).

In the column of "layer structure", "1st" indicates the first electrode, and "2nd" indicates the second electrode. showing. That is, Examples 1 to 7 had the laminated structure shown in FIG. 2C. Examples 8-13 and 20-28 had the laminate structure shown in FIG. 2A. Examples 14-19 and Comparative Example 2 had the laminate structure shown in FIG. 2D.

In addition, the compositions of the first dielectric film and the second dielectric film were analyzed using XRF (X-ray fluorescence elemental analysis) for all samples, and were consistent with the compositions listed in Table 1. It was confirmed. The thickness of the dielectric film was obtained by processing the thin film capacitor with FIB, observing the obtained cross section with TEM, and measuring the length.

(XRD measurement)
XRD measurement was performed on the first dielectric film included in the dielectric film after heat treatment to obtain an X-ray diffraction chart. In the obtained X-ray diffraction chart, the diffraction angle 2θ of the strongest peak of the (110) plane of the composite oxide having a perovskite structure was calculated. Table 1 shows the results. The same XRD measurement was also performed on the first dielectric film included in the dielectric film of Comparative Example 2, which was not subjected to heat treatment, and the diffraction angle 2θ of the strongest peak of the (110) plane was calculated. That is, the diffraction angle 2θ of Comparative Example 2 was the reference (P _r ).

For all the obtained thin film capacitor samples, the dependence of the leakage current value, dielectric constant and dielectric loss on the voltage application direction was measured by the method shown below.

(leak current value)
First, using a digital ultra-high resistance meter (R8340A manufactured by Advantest), a DC voltage was applied so that the electric field strength applied to the thin film capacitor was 0.3 MV/cm, and the insulation resistance was measured at room temperature. . A leakage current value was calculated from the obtained insulation resistance and the electrode area of the second electrode. It is ^preferable that the ^{leak current} value is small. was judged to be good. Table 1 shows the results.

(relative permittivity)
The dielectric constant was measured by applying an AC voltage to the thin film capacitor sample at a reference temperature of 25° C. using a digital LCR meter (Keysight E4980A) at a frequency of 1 kHz so that the input signal level (measurement voltage) was 1 Vrms. and the thickness of the dielectric film obtained above (no units). The dielectric constant is preferably higher than the dielectric constant of the thin film capacitor (comparative example 1) composed only of the second dielectric film, and in this example, 55 or more was considered good. Table 1 shows the results.

(Dependence of dielectric loss on voltage application direction)
First, for the thin film capacitor sample, at a reference temperature of 25° C., a digital LCR meter (Keysight E4980A) was used to sweep the DC bias voltage so that the electric field strength applied to the thin film capacitor was 0.5 MV/cm. Then, the dielectric loss (tan δ _forward ) was calculated.

Next, the dielectric loss (tan δ _reverse ) was similarly calculated by changing the application direction of the DC bias voltage (inverted).

The absolute value of the common logarithm (log(tan δ _forward /tan δ _reverse )) of the obtained dielectric loss ratio was calculated. The closer the absolute value is to 0, the less dependence there is on the voltage application direction. Table 1 shows the results.

From Table 1, it was confirmed that the thin-film capacitor having the above configuration exhibited a high dielectric constant while maintaining a relatively low leakage current.

The dielectric element according to the present invention can exhibit a high dielectric constant while maintaining a relatively low leakage current by having the above-described configuration. Therefore, such a dielectric element is suitable, for example, as a thin film capacitor embedded in an electronic circuit board.

REFERENCE SIGNS LIST 1 thin film capacitor 10 first electrode 30 dielectric film 31 first dielectric film (ABO ₃ )
32 Second dielectric film (A'B'O ₃ )
20... second electrode

Claims (6)

A dielectric element having a first electrode made of a base metal, a dielectric film, and a second electrode,
The dielectric films include a first dielectric film having a composite oxide represented by the chemical formula ABO ₃ as a main component and a second dielectric film having a composite oxide represented by the chemical formula A'B'O ₃ as a main component. has a laminated structure in which is in direct contact with the dielectric film of
In the chemical formula, A is at least one selected from the group consisting of barium, strontium and calcium, B is titanium, A' is at least one selected from the group consisting of barium, strontium and calcium, and B ' is at least one selected from the group consisting of zirconium and hafnium. When the thickness of the second dielectric film is t2 and the total thickness of the first dielectric film and the second dielectric film is T, t2/T is 10% or more and 50% or less. A dielectric device according to claim 1. When t2/T is 10% or more and 30% or less, the first dielectric film is in direct contact with both the first electrode and the second electrode, or the second dielectric film 3. A dielectric element according to claim 2, wherein the body film is in direct contact with both said first electrode and said second electrode. The first dielectric film contains, as an auxiliary component, at least one selected from the group consisting of yttrium and aluminum in excess of 0 mol and 0.3 mol or less per 100 mol of the composite oxide represented by the chemical formula _ABO3 . 4. The dielectric element according to any one of claims 1 to 3, containing more than 0 mol and 0.3 mol or less of manganese, and more than 0 mol and 0.3 mol or less of vanadium. In the laminated structure, the diffraction angle 2θ of the strongest peak among the diffraction peaks of the (110) plane of the composite oxide in the X-ray diffraction measurement of the composite oxide represented by the chemical formula ABO ₃ is the reference of the composite oxide. 5. The dielectric element according to any one of claims 1 to 4, wherein the diffraction angle 2[theta] of the strongest peak among the diffraction peaks of the (110) plane of the reference is 0.5[deg.] or more when measured by X-ray diffraction. An electronic circuit board on which the dielectric element according to any one of claims 1 to 5 is mounted.

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