JP2020161795A - Dielectric film, electronic component, thin film capacitor, and electronic circuit board - Google Patents

Abstract

To provide a thin film capacitor in which both of DC bias characteristics and withstand voltage characteristics are compatible with each other.SOLUTION: A dielectric film contains an oxide having a perovskite structure. The oxide contains (1) Bi, Na and Ti, (2) at least one of Ba and Ca, and (3) at least one element Ln selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y. In the oxide, when the rates of the atomic numbers of Bi, Ba, and Ca to the total atomic number of Bi, Na, Ba, and Ca are represented by XBi, XBa and XCa, 0.2≤XBi/(XBa+XCa)≤5 is satisfied.SELECTED DRAWING: Figure 1

Description

The present invention relates to dielectric films, electronic components, thin film capacitors, and electronic circuit boards.

The mounting space for electronic components allowed in an electronic device tends to shrink as the electronic device becomes smaller. Capacitors (often referred to as "capacitors" in Japan) are electronic components that are mounted on many electronic devices, and it is essential that they be made smaller and thinner. The thin film capacitor has thinner base material, dielectric film, insulating film, etc. than the conventional laminated ceramic capacitor by the thick film method, and can be made thinner and thinner. Therefore, thin film capacitors are expected as electronic components to be mounted in a small space with a low profile. Further, capacitors embedded in electronic component boards have been developed in recent years.

Many thin-film capacitors have a smaller electrical capacity than conventional multilayer ceramic capacitors. One of the methods for improving the electric capacity is to reduce the film thickness of the dielectric film. However, when the film thickness of the dielectric film is reduced, the DC electric field strength applied to the dielectric increases even if the DC voltage applied to both ends of the dielectric film is the same during actual use. Since the relative permittivity of a ferroelectric substance such as BaTiO ₃ has a so-called DC bias characteristic that it decreases as the DC electric field strength increases, the electric capacity cannot be improved even if the film thickness is reduced.

Further, if the DC electric field strength is increased by reducing the film thickness of the dielectric film, the risk of element destruction due to the electric field increases, so that high withstand voltage characteristics are also required.

Patent Document 1 discloses that the DC bias characteristic is improved by using a tungsten bronze type composite oxide containing K, Sr, Mg and Nb for the dielectric film.

Patent Document 2, on a conductive substrate having a Ti element on the surface, _Ba formed by hydrothermal synthesis method _{1-x Ca x Zr y Ti} 1-y O 3 ( where, 0 <x <0. It is disclosed that a high relative permittivity and a high withstand voltage characteristic are realized by providing a dielectric thin film represented by 2.0 <y <1).

Japanese Unexamined Patent Publication No. 2000-49045 Japanese Unexamined Patent Publication No. 2000-173349

However, even in Patent Documents 1 and 2, the withstand voltage characteristic and the DC bias characteristic cannot be compatible with each other.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a dielectric film, an electronic component, a thin film capacitor, and an electronic circuit board capable of achieving both DC bias characteristics and withstand voltage characteristics. And.

The dielectric film hanging on one aspect of the present invention is a dielectric film containing an oxide having a perovskite structure. Here, the oxides are (1) Bi, Na and Ti, (2) at least one of Ba and Ca, and (3) La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, It contains at least one element Ln, selected from the group consisting of Ho, Yb and Y. Further, when the ratio of the atomic numbers of Bi, Ba, and Ca to the total atomic number of Bi, Na, Ba, and Ca in the oxide is expressed as X _Bi , X _Ba , and X _Ca , respectively, 0.2 ≤ X _Bi / (X _Ba + X _Ca ) ≤ 5 is satisfied.

Here, in the oxide, when the ratio of the number of atoms of Na to the total number of atoms of Bi, Na, Ba and Ca is expressed as X _Na , 0.9 X _Bi ≤ X _Na ≤ 1.1 X _Bi is satisfied. be able to.

Further, in the oxide, the ratio of the atomic number of Ti to the total atomic number of Bi, Na, Ba and Ca can be 80% or more and 120% or less.

In the oxide, the ratio of the number of atoms of Ln to the total number of atoms of Bi, Na, Ba and Ca can be 0.5 to 20%.

The dielectric film hanging on the other aspect of the present invention is a dielectric film containing an oxide having a perovskite structure. Here, the oxide is at least one selected from the group consisting of (1) Bi, K, and Ti, (2) Ba, Sr, and Ca, and (3) La, Ce, Pr. , Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and at least one element Ln selected from the group consisting of Y. Further, in the oxide, the ratio of the atomic numbers of Bi, Ba, Sr, and Ca to the total atomic number of Bi, K, Ba, Sr, and Ca is set to X _Bi , X _Ba , and X _Sr , respectively. , And, when expressed as X _Ca , 0.2 ≦ X _Bi / (X _Ba + X _Sr + X _Ca ) ≦ 5 is satisfied.

Here, in the oxide, Bi, K, Ba, Sr, and a ratio of the number of atoms of K to the total number of atoms of Ca when expressed as _{X K, 0.9X Bi ≦ X K} ≦ 1. 1X _Bi can be satisfied.

Further, in the oxide, the ratio of the number of atoms of Ti to the total number of atoms of Bi, K, Ba, Sr, and Ca can be 80% or more and 120% or less.

In the oxide, the ratio of the number of atoms of Ln to the total number of atoms of Bi, K, Ba, Sr, and Ca can be 0.5 to 20%.
The thin film capacitor according to the present invention includes the above-mentioned dielectric film.
The electronic circuit board according to one aspect of the present invention includes the above-mentioned dielectric film.
The electronic circuit board according to one aspect of the present invention includes the above-mentioned electronic components.
The electronic circuit board according to one aspect of the present invention includes the above-mentioned thin film capacitor.

According to the present invention, a thin film capacitor or the like capable of achieving both DC bias characteristics and withstand voltage characteristics is provided.

FIG. 1 is a schematic cross-sectional view of a thin film capacitor according to an example of an electronic component according to the present embodiment. FIG. 2A is a schematic cross-sectional view of an electronic circuit board according to an embodiment of the present invention, and FIG. 2B is a portion 90A shown in FIG. 2A. It is an enlarged view of.

Hereinafter, the first embodiment of the present invention will be described in detail.

(Dielectric film)
The dielectric film according to the first embodiment of the present invention contains an oxide having a perovskite structure.
This oxide includes the following (1) to (3).
(1) Bi, Na and Ti
(2) At least one of Ba and Ca (3) At least one element Ln selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y.

In this oxide, when the ratio of the atomic numbers of Bi, Ba, and Ca to the total atomic number of Bi, Na, _Ba , and _Ca is expressed as X _Bi , X _Ba , and X _Ca , respectively,
0.2 ≤ X _Bi / (X _Ba + X _Ca ) ≤ 5 is satisfied. The upper limit is preferably 4.5 or less, and more preferably 4 or less.

In this oxide, Bi, Na, the atomic ratio of Na to the total number of atoms of Ba and Ca in the case expressed as _{X Na,} may satisfy 0.9X _Bi ≦ _{X Na} ≦ 1.1X _Bi .. Preferably, 0.95X _Bi ≤ X _Na ≤ 1.05X _Bi . Preferably, 0.98 X _Bi ≤ X _Na ≤ 1.02 X _Bi , and X _Na = X _Bi may be used.

In this oxide, the ratio of the number of atoms of Ti to the total number of atoms of Bi, Na, Ba and Ca can be 80% or more and 120% or less. The ratio of the number of atoms of the Ti may be 85% or more, 90% or more, 95% or more, 115% or less, 110% or less, 105% or less.

In this oxide, the ratio of the number of atoms of Ln to the total number of atoms of Bi, Na, Ba and Ca can be 0.5 to 20%. The ratio of the number of atoms of Ln is preferably 1 to 15%.

In this oxide, the ratio of the total number of atoms of Ba and Ca to the total number of atoms of Bi, Na, Ba and Ca can be 10 to 70%.

This oxide may contain at least one of Ba or Ca, but may contain both Ba and Ca. It is preferable that this oxide does not contain Sr.

Among the elements Ln, La is preferable.

The perovskite structure is a crystal structure generally represented by ABX ₃ . The A-site cation is located at the apex of the hexahedral unit cell, the B-site cation is located at the body center of this unit cell, and the X-site anion is located at the face center of this unit cell. In the present invention, cations (divalent or a combination of monovalent and trivalent) such as Ba ²⁺ , Ca ²⁺ , Bi ³⁺ , Na ⁺ , and Ln ions enter the A site, and Ti ⁴⁺ ions and the like enter the B site. The tetravalent cation of the above enters, and the divalent anion such as O ^2- ion enters the X site. Ln ions can also enter the B site.

The oxide may occupy 70% by mass or more of the dielectric film, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass. ..

The thickness of the dielectric film is not limited, but can be, for example, 10 nm to 2000 nm, preferably 50 nm to 1000 nm.

Such a dielectric film is excellent in both DC bias characteristics and withstand voltage characteristics. The reason for this is not clear, but the inventors think as follows.

The development of the relative permittivity in an oxide having a perovskite-type crystal structure is due to the displacement of the ions of each element with respect to the AC voltage, and when the voltage is strong, the displacement of the ions is saturated, resulting in a DC bias. The relative permittivity decreases. The combination of the bonds of A-site and B-site ions and oxygen ions is important for the ionic displacement of the perovskite-type crystal structure, and the perovskite-type crystal structure containing Bi, Na and Ti can be obtained from Ba and Ca. By satisfying 0.2 ≤ X _Bi / (X _Ba + X _Ca ) ≤ 5 when at least one selected is included, the degree of freedom of each bond is widened, and the displacement of ions is saturated. I think the size is getting bigger.

Further, the Curie point of the oxide having a perovskite structure containing Bi, Na and Ti is about 300 ° C., but Bi, Na and Ti are contained by containing at least one selected from Ba and Ca. It is considered that the absolute value of the relative permittivity increases and the relative permittivity when DC bias is applied also increases as the Curie point of the perovskite-type oxide approaches room temperature.

In addition, the valences of the La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y ions take multiple valences, including +3 valences, on both perovskite-structured AB sites. Since it is possible to enter, it is thought that by suppressing the movement of charges generated by defects such as oxygen defects, the concentration of charges is reduced and the withstand voltage is improved.

In addition to the above oxides, the dielectric film according to the present embodiment may contain trace impurities, subcomponents, and the like within the range in which the effects of the present invention are exhibited. Examples of such a component include Cr, Mo and the like.
For example, the dielectric film is Sc (scandium), Y (yttrium), La (lantern), Ce (cerium), Pr (placeodium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europyum). ), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (yttrium) and Lu (lutetium) at least one selected from the group. It may further contain rare earth elements. When the dielectric film further contains rare earth elements, the DC bias characteristics of the dielectric film may be improved.

Hereinafter, the second embodiment of the present invention will be described in detail.

(Dielectric film)
The dielectric film according to the second embodiment of the present invention contains an oxide having a perovskite structure.
This oxide includes the following (1) to (3).
(1) Bi, K, and Ti
(2) At least one selected from the group consisting of Ba, Sr, and Ca (3) Selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb, and Y. At least one element Ln

In this oxide, the ratio of the atomic numbers of Bi, Ba, Sr, and Ca to the total atomic number of Bi, K, Ba, Sr, and Ca is determined by X _Bi , X _Ba , X _Sr , and, respectively. , X _Ca , 0.2 ≦ X _Bi / (X _Ba + X _Sr + X _Ca ) ≦ 5. The upper limit is preferably 4.5 or less, and more preferably 4 or less.

In this oxide, Bi, K, Ba, Sr, and, when the ratio of the number of atoms of K to the total number of atoms of Ca expressed as _{X K,} a 0.9X _Bi ≦ _{X K} ≦ 1.1X _Bi Can be met. Preferably, 0.95 X _Bi ≤ X _K ≤ 1.05 X _Bi . Preferably, 0.98 X _Bi ≤ X _K ≤ 1.02 X _Bi , and X _K = X _Bi may be used.

In this oxide, the ratio of the number of atoms of Ti to the total number of atoms of Bi, K, Ba, Sr, and Ca can be 80% or more and 120% or less. The ratio of the number of atoms of the Ti may be 85% or more, 90% or more, 95% or more, 115% or less, 110% or less, 105% or less.

In this oxide, the ratio of the number of atoms of Ln to the total number of atoms of Bi, K, Ba, Sr, and Ca can be 0.5 to 20%. The ratio of the number of atoms of Ln is preferably 1 to 15%.

In this oxide, the ratio of the total number of atoms of Ba, Sr, and Ca to the total number of atoms of Bi, K, Ba, Sr, and Ca can be 10 to 70%.

This oxide may contain at least one of Ba, Sr, and Ca, but may also include a combination of Ba and Sr, a combination of Ba and Ca, and a combination of Sr and Ca, Ba, It may contain all combinations of Sr and Ca.

Among the elements Ln, La is preferable.

The perovskite structure is a crystal structure generally represented by ABX ₃ . The A-site cation is located at the apex of the hexahedral unit cell, the B-site cation is located at the body center of this unit cell, and the X-site anion is located at the face center of this unit cell. In the present invention, cations such as Ba ²⁺ , Sr ²⁺ , Ca ²⁺ , Bi ³⁺ , K ⁺ , and Ln ions (divalent or a combination of monovalent and trivalent) are contained in the A site, and Ti is contained in the B site. ^A tetravalent cation such as a ⁴⁺ ion enters, and a divalent anion such as an O2 ^- ion enters the X site. Ln ions can also enter the B site.

The oxide may occupy 70% by mass or more of the dielectric film, 80% by mass or more, 90% by mass or more, 95% by mass or more, 99% by mass or more, or 100% by mass. ..

The thickness of the dielectric film is not limited, but can be, for example, 10 nm to 2000 nm, preferably 50 nm to 1000 nm.

Such a dielectric film is excellent in both DC bias characteristics and withstand voltage characteristics. The reason for this is not clear, but the inventors think as follows.

The expression of the relative permittivity in an oxide having a perovskite-type crystal structure is due to the displacement of the ions of each element with respect to the AC voltage. The relative permittivity decreases. The combination of A-site and B-site ions and oxygen ion bonds is important for the ionic displacement of the perovskite-type crystal structure, and the perobskite-type crystal structure containing Bi, K, and Ti has Ba, Sr, and Ba, Sr. And when at least one selected from Ca is contained, by satisfying 0.2 ≦ X _Bi / (X _Ba + X _Sr + X _Ca ) ≦ 5, the degree of freedom of each bond is widened, and the displacement of ions is increased. We believe that the magnitude of the saturated DC bias is increasing.

Further, the Curie point of the oxide having a perovskite structure containing Bi, K, and Ti is about 300 ° C., but by containing at least one selected from Ba, Sr, and Ca, Bi It is considered that the absolute value of the relative permittivity increases and the relative permittivity when DC bias is applied also increases as the Curie point of the perovskite-type oxide containing, K, and Ti approaches room temperature.

In addition, the valences of the La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y ions take multiple valences, including +3 valences, on both perovskite-structured AB sites. Since it is possible to enter, it is thought that by suppressing the movement of charges generated by defects such as oxygen defects, the concentration of charges is reduced and the withstand voltage is improved.

In addition to the above oxides, the dielectric film according to the present embodiment may contain trace impurities, subcomponents, and the like within the range in which the effects of the present invention are exhibited. Examples of such a component include Cr, Mo and the like.
For example, the dielectric film is Sc (scandium), Y (yttrium), La (lantern), Ce (cerium), Pr (placeodium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europyum). ), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (yttrium) and Lu (lutetium) at least one selected from the group. It may further contain rare earth elements. When the dielectric film further contains rare earth elements, the DC bias characteristics of the dielectric film may be improved.

(Manufacturing method of dielectric film)
The above-mentioned dielectric film can be produced by various methods. Known film forming methods include, for example, vacuum vapor deposition, sputtering, pulsed laser deposition (PLD), metal-organic chemical vapor deposition (MOCVD), and organic metal decomposition. Examples include the method (Metal Organic Decomposition: MOD), the sol-gel method, and the chemical solution deposition method (CSD).

Specifically, the ratio of metal elements in the raw material composition used in each film forming method may be within the above range. The raw materials used for film formation (deposited materials, various target materials, organic metal materials, etc.) may contain trace amounts of impurities, subcomponents, etc. No problem.

For example, when the sputtering method is used, an oxide target having the above metal composition is first prepared. Specifically, powders of compounds containing each metal, for example, carbonates, oxides, hydroxides, etc. are prepared and mixed so that the ratio of metal elements is within the above range to obtain a mixed powder. .. Mixing is preferably carried out in water using, for example, a ball mill. Next, the mixed powder is molded to obtain a molded product. The molding pressure can be, for example, 10 to 200 Pa.

Then, the obtained molded product is fired to obtain a fired product. The firing conditions are such that the holding temperature is 900 to 1300 ° C., the temperature holding time is 1 to 10 hours, and the atmosphere is an oxidizing atmosphere such as air. Finally, the obtained fired body can be processed into a disk shape to obtain a target for sputtering.

Next, the obtained target is sputtered to form the above-mentioned dielectric film as a deposited film on the substrate. Sputtering conditions are not particularly limited, but high-frequency (RF) sputtering is preferable, the power can be 100 W to 300 W, and the atmosphere is preferably an oxygen-containing atmosphere, particularly an oxygen-containing argon gas atmosphere, and argon (Ar). The / oxygen (O ₂ ) ratio is preferably 1/1 to 5/1, and the substrate temperature can be preferably room temperature to 200 ° C.

It is also preferable to perform rapid thermal annealing (RTA) after forming a dielectric film by sputtering. As conditions for applying RTA, the atmosphere is preferably an atmospheric atmosphere, the heating rate is preferably 100 ° C./min or more, the annealing time is preferably 0.5 to 120 minutes, and the annealing temperature is 700. The temperature is preferably ℃ or more and 1000 ℃ or less.

(Thin film capacitor)
Subsequently, with reference to FIG. 1, a thin film capacitor will be described as an example of an electronic component having a dielectric film according to an embodiment of the present invention.

The thin film capacitor 100 according to the embodiment of the present invention has a substrate 10, an adhesive film 20, a lower electrode 30, a dielectric film 40, and an upper electrode 50 in this order.

(substrate)
The substrate 10 supports the adhesion film 20, the lower electrode 30, the dielectric film 40, and the upper electrode 50 formed on the substrate 10. The material of the substrate 10 is not particularly limited as long as it has a mechanical strength sufficient to support each of the above layers. Examples of the substrate 10 are Si single crystal, SiGe single crystal, GaAs single crystal, InP single crystal, SrTIO ₃ single crystal, MgO single crystal, LaAlO ₃ single crystal, ZrO ₂ single crystal, MgAl ₂ O ₄ single crystal, NdGaO ₃ Single crystal substrate such as single crystal; ceramic polycrystal substrate such as Al ₂ O ₃ polycrystal, ZnO polycrystal, SiO ₂ polycrystal; and from Ni, Cu, Ti, W, Mo, Al, Pt and alloys thereof. The metal substrate of choice. A Si single crystal substrate is preferable from the viewpoint of low cost and workability.

The thickness of the substrate 10 can be, for example, 10 μm to 5000 μm. If the thickness is too small, mechanical strength may not be ensured, and if the thickness is too large, there may be a problem that it cannot contribute to the miniaturization of electronic components.

The electrical resistivity of the above-mentioned substrate 10 differs depending on the material of the substrate. When the substrate is made of a material having a low electrical resistivity, a current leak to the substrate 10 side during operation of the thin film capacitor may occur, which may affect the electrical characteristics of the thin film capacitor. Therefore, when the electrical resistivity of the substrate 10 is low, it is preferable to perform an electrical insulation treatment on the surface thereof so that the current during the operation of the capacitor does not flow to the substrate 10.

For example, when the substrate 10 is a Si single crystal substrate, it is preferable that an insulating film is formed on the surface of the substrate 10. As long as sufficient insulation between the substrate 10 and the lower electrode 30 is ensured, the material constituting the insulating film and its thickness are not particularly limited. Examples of materials constituting the insulating film are SiO ₂ , Al ₂ O ₃ , and Si ₃ N _x . The thickness of the insulating film is preferably 0.01 μm or more. The insulating film is preferably provided on the adhesion film 20 side (lower electrode 30 side) of the substrate 10. The insulating film can be formed by a known film forming method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method.

(Adhesion film)
The adhesion film 20 is provided between the substrate 10 and the lower electrode 30, and improves the adhesion between the substrate 10 and the lower electrode 30. The material of the adhesion film 20 is not particularly limited as long as the material can sufficiently secure the adhesion between the substrate 10 and the lower electrode 30. For example, when the lower electrode 30 is a Cu film, the adhesive film 20 can be a Cr film, and when the lower electrode 30 is a Pt film, the adhesive film 20 can be a Ti film. The thickness of the adhesive film 20 can be, for example, 5 to 50 nm.

(Lower electrode)
The lower electrode 30 is formed in a thin film on the substrate 10 via the adhesion film 20. The lower electrode 30 is an electrode that sandwiches the dielectric film 40 together with the upper electrode 50 and functions as a capacitor. The material constituting the lower electrode 30 is not particularly limited as long as it is a conductive material. For example, metals such as Pt, Ru, Rh, Pd, Ir, Au, Ag, Cu, Ni, alloys thereof, conductive oxides and the like are exemplified.

The thickness of the lower electrode 30 is not particularly limited as long as it functions as an electrode. The thickness of the lower electrode 30 is preferably 10 nm or more, and preferably 300 nm or less from the viewpoint of thinning.

(Dielectric film)
The dielectric film 40 is the above-mentioned dielectric film. As described above, the thickness of the dielectric film 40 can be 10 nm to 2000 nm, preferably 50 nm to 1000 nm. The thickness of the dielectric film 40 is measured by drilling a thin film capacitor 100 containing the dielectric film 40 with a FIB (focused ion beam) processing device and observing the obtained cross section with a SEM (scanning electron microscope). Can be done.

(Upper electrode)
An upper electrode 50 is formed in a thin film on the upper surface of the dielectric film 40. The upper electrode 50 is an electrode that sandwiches the dielectric film 40 together with the lower electrode 30 described above and functions as a capacitor.

The material of the upper electrode 50 is not particularly limited as long as it is a conductive material like the lower electrode 30. Examples of the material are metals such as Pt, Ru, Rh, Pd, Ir, Au, Ag, Cu, Ni, alloys thereof, or conductive oxides, even if they are the same as the material of the lower electrode 30. It may be good or different. The thickness of the upper electrode 50 can be the same as that of the lower electrode 30.

Further, the thin film capacitor 100 may have a protective film 70 for covering the side surface of the dielectric film 40 and the like and blocking the dielectric film 40 from the external atmosphere. An example of the material of the protective layer is a resin such as epoxy.

The shape of the thin film capacitor 100 is not particularly limited, but is usually a rectangular parallelepiped shape when viewed from the thickness direction. Further, the dimensions are not particularly limited, and the thickness and length may be appropriate dimensions according to the application.

The lower electrode 30, the dielectric film 40, and the upper electrode 50 form a capacitor portion 60. When the lower electrode 30 and the upper electrode 50 are connected to an external circuit and a voltage is applied between the electrodes, the dielectric film 40 exhibits a predetermined capacitance and functions as a capacitor. In particular, in the present embodiment, since the above-mentioned dielectric film 40 is used, both high DC bias characteristics and high withstand voltage can be achieved at the same time.

(Manufacturing method of thin film capacitor)
Next, an example of the method for manufacturing the thin film capacitor 100 shown in FIG. 1 will be described below.

First, the substrate 10 is prepared, and the adhesion film 20 and the lower electrode 30 are formed on the substrate 10 by a known film forming method such as a sputtering method.

After the formation of the lower electrode 30, heat treatment may be performed for the purpose of improving the adhesion between the adhesion film 20 and the lower electrode 30 and improving the stability of the lower electrode 30. As the heat treatment conditions, for example, the heating rate is preferably 10 ° C./min to 2000 ° C./min, and more preferably 100 ° C./min to 1000 ° C./min. The holding temperature during the heat treatment is preferably 400 ° C. to 800 ° C., and the holding time is preferably 0.1 hour to 4.0 hours. When the heat treatment conditions are out of the above range, poor adhesion between the adhesion film 20 and the lower electrode 30 and unevenness on the surface of the lower electrode 30 are likely to occur. As a result, the dielectric properties of the dielectric film 40 are likely to be deteriorated.

Subsequently, the dielectric film 40 is formed on the lower electrode 30 by the method described above. If necessary, the annealing described above can be performed.

Next, the upper electrode 50 is formed on the formed dielectric film 40 by using a known film forming method such as a sputtering method.

Through the above steps, as shown in FIG. 1, a thin film capacitor 100 having a capacitor portion (lower electrode 30, dielectric film 40 and upper electrode 50) 60 formed on the substrate 10 via an adhesive film 20 is formed. can get. The protective film 70 that protects the dielectric film 40 may be formed by a known film forming method so as to cover at least the portion where the dielectric film 40 is exposed to the outside.

(Modification example)
Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and may be modified in various ways within the scope of the present invention.
For example, a dielectric film made of a material different from that of the dielectric film 40 may be further provided between the lower electrode 30 and the upper electrode 50. For example, a plurality of dielectrics can be obtained by forming a laminated structure of an amorphous film or a crystal film such as Si ₃ N _x , SiO _x , Al ₂ O _x , ZrO _x , Ta ₂ O _x and the above-mentioned dielectric film 40. It is possible to adjust the temperature change of impedance and relative permittivity of the entire film.

Further, in the above-described embodiment, the adhesion film 20 is formed in order to improve the adhesion between the substrate 10 and the lower electrode 30, but when the adhesion between the substrate 10 and the lower electrode 30 can be sufficiently ensured. The adhesive film 20 can be omitted. Further, when a metal such as Cu or Pt that can be used as an electrode, an alloy thereof, an oxide conductive material, or the like is used as the material constituting the substrate 10, the adhesive film 20 and the lower electrode 30 may be omitted. it can.

Further, the dielectric film according to the present embodiment can be used for electronic components such as electronic circuit boards and piezoelectric elements in addition to capacitors.
(Electronic circuit board)
The electronic circuit board according to this embodiment includes the above-mentioned dielectric film. The electronic circuit board may include electronic components such as a thin film capacitor containing the above-mentioned dielectric film. Electronic components such as thin film capacitors may be installed on the surface of the electronic circuit board. Electronic components such as thin film capacitors may be embedded in the electronic circuit board.
An example of the electronic circuit board is shown in (a) in FIG. 2 and (b) in FIG. The electronic circuit board 90 includes an epoxy-based resin substrate 92, a resin layer 93 covering the epoxy-based resin substrate 92, a thin film capacitor 91 installed on the resin layer 93, and an insulating coating covering the resin layer 93 and the thin film capacitor 91. A layer 94, an electronic component 95 installed on the insulating coating layer 94, and a plurality of metal wirings 96 may be provided. At least a 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. At least a part of the metal wiring 96 may be connected to the extraction electrodes 54 and 56 of the thin film capacitor 91, or the electronic component 95. 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. 2B, the thin film capacitor 91 according to the present embodiment includes a lower electrode 30, a dielectric film 40 provided on the surface of the lower electrode 30, and one of the upper surfaces of the dielectric film 40. The upper electrode 50 provided on the portion, the penetrating electrode 52 provided directly on the surface of the lower electrode 30 penetrating the other portion of the dielectric film 40, and the upper electrode 50, the dielectric film 40, and the penetrating electrode 52. The insulating resin layer 58 that covers the insulating resin layer 58, the take-out electrode 54 that penetrates the insulating resin layer 58 and is directly provided on the surface of the penetrating electrode 52, and the insulating resin layer 58 that penetrates the surface of the upper electrode 50 directly. The take-out electrode 56 provided may be provided.
The electronic circuit board 90 may be manufactured 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 the resin layer 93. The thin film capacitor 91 is installed on the surface of the uncured resin layer so that the base electrode of the thin film capacitor 91 faces the uncured resin layer. By covering the uncured resin layer and the thin film capacitor 91 with the insulating coating layer 94, the thin film capacitor 91 is sandwiched between the epoxy resin substrate 92 and the insulating coating layer 94. The resin layer 93 is formed by thermosetting the uncured resin layer. The insulating coating layer 94 is pressure-bonded to the epoxy resin substrate 92, the thin film capacitor 91, and the resin layer 93 by hot pressing. A plurality of through holes penetrating the laminated substrate are formed. Metal wiring 96 is formed in each through hole. After forming the metal wiring 96, the electronic component 95 is installed on the surface of the insulating coating layer 94. By the above method, the electronic circuit board 90 embedded in the thin film capacitor 91 can be obtained. Each metal wiring 96 may be made of a conductor such as Cu. The uncured resin layer may be a B-stage thermosetting resin (for example, epoxy resin or the like). The B-stage thermosetting resin is not completely cured at room temperature, but is completely cured by heating. The insulating coating layer 94 may be formed of an epoxy resin, a polytetrafluoroethylene resin, a polyimide resin, or the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the following examples.

(Example, comparative example)
First, the target for sputtering required for forming the dielectric film was prepared by the solid phase method as follows.

Raw material powders for target preparation include barium carbonate, strontium carbonate, calcium carbonate, titanium oxide, bismuth oxide, sodium carbonate, potassium carbonate, lanthanum hydroxide, cerium oxide, praseodymium oxide, neodymium oxide, samarium oxide, europium oxide, and gadolinium oxide. , Terbium oxide, dysprosium oxide, holonium oxide, ytterbium oxide, and yttrium oxide powder were prepared. These powders are weighed so that the number of atoms of each metal has the composition shown in Tables 1 and 2 for the first embodiment and the composition shown in Tables 3 and 4 for the second embodiment, respectively. did.

Wet mixing of the weighed raw material powder for target preparation was carried out in a ball mill using water as a solvent 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 product. The molding conditions were a pressure of 100 Pa, a temperature of 25 ° C., and a pressing time of 3 minutes.

Then, the obtained molded product was fired to obtain a fired product. The firing conditions were a holding temperature of 1100 ° C., a temperature holding time of 5 hours, and an atmosphere of air.

The obtained fired body was processed into a diameter of 80 mm and a thickness of 5 mm by a surface grinder and a cylindrical grinder to obtain a target for sputtering for forming a dielectric film.

Subsequently, a Si wafer having a thickness of 500 μm was heat-treated in a dry atmosphere of an oxidizing gas to form a SiO ₂ film having a thickness of 500 nm on the wafer surface to form a substrate. First, a Cr thin film as a base electrode was formed on the surface of this substrate by a sputtering method so as to have a thickness of 20 nm. Further, a Pt thin film was formed on the Cr thin film formed above by a sputtering method so as to have a thickness of 100 nm, and used as a lower electrode.

Next, a dielectric film having a thickness of 300 nm was formed on the lower electrode by a sputtering method using the target for sputtering prepared above. The sputtering conditions were atmosphere: Ar / O ₂ = 3/1, pressure: 1.0 Pa, high frequency power: 200 W, and substrate temperature: 100 ° C. After forming the dielectric film, the dielectric film was subjected to rapid thermal anneal treatment (RTA) at a heating rate of 900 ° C./min under the condition of 900 ° C. for 1 minute in an air atmosphere.

Next, a Pt thin film was formed on the obtained dielectric film by a sputtering method so as to have a diameter of 200 μm and a thickness of 100 nm using a mask, and used as an upper electrode. Through the above steps, a thin film capacitor having the configuration shown in FIG. 1 was obtained.

The crystal structure of the dielectric film was measured and analyzed by an X-ray diffraction method using an XRD measuring device (Rigaku, Smartlab). As a result, it was confirmed that the dielectric film has a perovskite-type crystal structure.

Further, the composition of the dielectric film was analyzed using XRF (X-ray Fluorescence Analysis), and it was confirmed that the composition was consistent with the composition shown in Table 1.

For all the obtained thin film capacitors, the relative permittivity when DC bias was applied was measured by the method shown below.

(Relative permittivity)
The relative permittivity when a DC bias is applied is an input at a room temperature of 25 ° C. and a frequency of 1 kHz while applying a DC bias of 10 V / μm in the thickness direction to the thin film capacitor using a digital LCR meter (Hewlet-Packard, 4284A). It was calculated from the capacitance, effective electrode area, inter-electrode distance and vacuum permittivity measured under the condition of signal level (measurement voltage) of 1.0 Vrms (no unit). As the dielectric film, it is preferable that the relative permittivity when DC bias is applied is high, and a sample having a relative permittivity of 600 or more when DC bias is applied is judged to be good. The results are shown in Table 1.

For reference, the relative permittivity was also measured without applying a DC bias. The measurement conditions were the same except that the DC bias was not marked. The results are shown in Table 1.

(Withstand voltage characteristics)
When a DC voltage was applied to a pair of electrodes of a thin film capacitor at a step-up rate of 1 V / sec starting from 0 V, the voltage when a current of 10 mA or more flowed between the electrodes was defined as the dielectric strength. In this example, the above evaluation was performed on 10 samples, and the samples having an average value of dielectric strength of 40 kV / mm or more were judged to be good.

From Tables 1 to 4, it was confirmed that the thin film capacitors according to the examples had a high relative permittivity when a DC bias was applied and also had a high withstand voltage characteristic.

10 ... Substrate, 20 ... Adhesive film, 30 ... Lower electrode, 40 ... Dielectric film, 50 ... Upper electrode, 90 ... Electronic circuit board, 91, 100 ... Thin film capacitor.

Claims (13)

A dielectric film containing an oxide having a perovskite structure.
The oxide is
(1) Bi, Na and Ti,
(2) At least one of Ba and Ca, and
(3) Containing at least one element Ln selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y.
When the ratio of the atomic numbers of Bi, Ba, and Ca to the total atomic number of Bi, Na, Ba, and Ca in the oxide is expressed as X _Bi , X _Ba , and X _Ca , respectively,
A dielectric film satisfying 0.2 ≤ X _Bi / (X _Ba + X _Ca ) ≤ 5. Claim that 0.9 X _Bi ≤ X _Na ≤ 1.1 X _Bi is satisfied when the ratio of the number of atoms of Na to the total number of atoms of Bi, Na, Ba and Ca in the oxide is expressed as X _Na. The dielectric film according to 1. The dielectric film according to claim 1 or 2, wherein in the oxide, the ratio of the atomic number of Ti to the total atomic number of Bi, Na, Ba and Ca is 80% or more and 120% or less. The dielectric according to any one of claims 1 to 3, wherein the ratio of the number of atoms of Ln to the total number of atoms of Bi, Na, Ba and Ca in the oxide is 0.5 to 20%. film. A dielectric film containing an oxide having a perovskite structure.
The oxide is
(1) Bi, K, and Ti,
(2) At least one selected from the group consisting of Ba, Sr, and Ca, and
(3) Containing at least one element Ln selected from the group consisting of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Yb and Y.
In the oxide, the ratios of the atomic numbers of Bi, Ba, Sr, and Ca to the total atomic numbers of Bi, K, Ba, Sr, and Ca are set to X _Bi , X _Ba , X _Sr , and, respectively. , X _Ca ,
A dielectric film satisfying 0.2 ≤ X _Bi / (X _Ba + X _Sr + X _Ca ) ≤ 5. In the oxide, Bi, K, Ba, Sr, and, when the ratio of the number of atoms of K to the total number of atoms of Ca expressed as _{X K,} a 0.9X _Bi ≦ _{X K} ≦ 1.1X _Bi The dielectric film according to claim 5, which is satisfied. The dielectric according to claim 5 or 6, wherein in the oxide, the ratio of the number of atoms of Ti to the total number of atoms of Bi, K, Ba, Sr, and Ca is 80% or more and 120% or less. film. In any one of claims 5 to 7, the ratio of the number of atoms of Ln to the total number of atoms of Bi, K, Ba, Sr, and Ca in the oxide is 0.5 to 20%. The dielectric film of the description. An electronic component comprising the dielectric film according to any one of claims 1 to 8. A thin film capacitor comprising the dielectric film according to any one of claims 1 to 8. An electronic circuit board comprising the dielectric film according to any one of claims 1 to 8. An electronic circuit board including the electronic component according to claim 9. An electronic circuit board comprising the thin film capacitor according to claim 10.

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