US20040165336A1

US20040165336A1 - Multi-layered unit including electrode and dielectic layer

Info

Publication number: US20040165336A1
Application number: US10/375,924
Authority: US
Inventors: Yukio Sakashita
Original assignee: TDK Corp
Current assignee: TDK Corp
Priority date: 2003-02-26
Filing date: 2003-02-26
Publication date: 2004-08-26
Anticipated expiration: 2023-02-26
Also published as: JPWO2004077463A1; WO2004077463A1; US6788522B1

Abstract

A multi-layered unit according to the present invention includes a support substrate formed of fused quartz, a buffer layer formed on the support substrate and formed of a dielectric material containing a bismuth layer structured compound oriented in the c axis direction, an electrode layer formed by epitaxially growing crystals of a conductive material on the buffer layer and oriented in the c axis direction, and a dielectric layer formed by epitaxially growing a dielectric material containing a bismuth layer structured compound on the electrode layer and oriented in the c axis direction. Since the thus constituted multi-layered unit includes the dielectric layer containing the bismuth layer structured compound oriented in the c axis direction, in the case of, for example, providing an upper electrode on the dielectric layer to form a thin film capacitor and applying a voltage between the electrode layer and the upper electrode, the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound contained in the dielectric layer. As a result, since the ferroelectric property of the bismuth layer structured compound contained in the dielectric layer can be suppressed and the paraelectric property thereof can be fully exhibited, it is possible to fabricate a thin film capacitor having a small size and large capacitance.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a multi-layered unit including an electrode and a dielectric layer and, particularly, to a multi-layered unit suitable for fabricating a thin film capacitor having a small size, large capacitance and an excellent dielectric characteristic and suitable for fabricating an inorganic EL (electro-luminescence) device capable of emitting light having high luminescence.

DESCRIPTION OF THE PRIOR ART

Recently, the operating frequency of LSIs (Large Scale Integrated circuits), typically CPUs (Central Processing Units), has become higher and higher. In the LSI having a high operating frequency, power supply noise is very likely to be generated, and once power supply noise occurs, a voltage drop occurs due to parasitic resistance and parasitic inductance of the power supply wiring, causing the LSI to operate erroneously.

In order to prevent such a voltage drop caused by power supply noise, a decoupling capacitor is generally connected between the terminals of the LSI power supply. In the case where a decoupling capacitor is connected between the terminals of the LSI power supply, the impedance of the power supply wiring decreases to effectively prevent voltage drop caused by power supply noise.

The impedance required of the power supply wiring is proportional to the operating voltage of the LSI and inversely proportional to the integration density of the LSI, the switching current of the LSI and the operating frequency of the LSI. Therefore, in current LSIs, which have high integration density, low operating voltage and high operating frequency, the impedance required of the power supply wiring is extremely low.

In order to achieve such low impedance of the power supply wiring, it is necessary to increase the capacitance of the decoupling capacitor and considerably lower the inductance of the wiring connecting the terminals of the LSI power supply and the decoupling capacitor.

As a decoupling capacitor having a large capacitance, an electrolytic capacitor or a multilayer ceramic capacitor is generally employed. However, since the size of an electrolytic capacitor or multilayer ceramic capacitor is relatively large, it is difficult to integrate it with an LSI. Therefore, the electrolytic capacitor or multilayer ceramic capacitor has to be mounted on a circuit substrate independently of the LSI and, as a result, the length of wiring for connecting the terminals of the LSI power supply and the decoupling capacitor is inevitably long. Accordingly, in the case where an electrolytic capacitor or a multilayer ceramic capacitor is employed as a decoupling capacitor, it is difficult to lower the inductance of the wiring for connecting the terminals of the LSI power supply and the decoupling capacitor.

In order to shorten the wiring for connecting the terminals of the LSI power supply and the decoupling capacitor, use of a thin film capacitor having a smaller size than that of an electrolytic capacitor or a multilayer ceramic capacitor is suitable.

Japanese Patent Application Laid Open No. 2001-15382 discloses a thin film capacitor having a small size and large capacitance which employs PZT, PLZT, (Ba, Sr) TiO ₃(BST), Ta₂O₅or the like as a dielectric material.

However, the thin film capacitor employing any one of the above mentioned materials is disadvantageous in that the temperature characteristic thereof is poor. For example, since the dielectric constant of BST has a temperature dependency of −1000 to −4000 ppm/° C., in the case where BST is employed as a dielectric material, the capacitance of the thin film capacitor at 80° C. varies between −6% and −24% in comparison with that at 20° C. Therefore, a thin film capacitor employing BST as a dielectric material is not suitable for use as a decoupling capacitor for a high operating frequency LSI whose ambient temperature frequently reaches 80° C. or higher owing to heat generated by electric power consumption.

Furthermore, the dielectric constant of a dielectric thin film formed of any one of the above mentioned materials decreases as the thickness thereof decreases and the capacitance thereof greatly decreases when an electric field of 100 kV/cm, for example, is applied thereto. Therefore, in the case where any one of the above mentioned materials is used as a dielectric material for a thin film capacitor, it is difficult to simultaneously make the thin film capacitor small and the capacitance thereof great.

In addition, Moreover, since the surface roughness of a dielectric thin film formed of any one of the above mentioned materials is high, its insulation performance tends to be lowered when formed thin.

It might be thought possible to overcome these problems by using a bismuth layer structured compound as a dielectric material for a thin film capacitor. The bismuth layer structured compound is discussed by Tadashi Takenaka in “Study on the particle orientation of bismuth layer structured ferroelectric ceramics and their application to piezoelectric or pyroelectric materials” Engineering Doctoral Thesis at the University of Kyoto (1984), Chapter 3, pages 23 to 36.

It is known that the bismuth layer structured compound has an anisotropic crystal structure and behaves as a ferroelectric material but that the bismuth layer structured compound exhibits only weak property as a ferroelectric material and behaves like as a paraelectric material along a certain axis of orientation.

The property of the bismuth layer structured compound as a ferroelectric material is undesirable when the bismuth layer structured compound is utilized as a dielectric material for a thin film capacitor since it causes variation in dielectric constant. Therefore, when a bismuth layer structured compound is used as a dielectric material for a thin film capacitor, it is preferable that its paraelectric property can be fully exhibited.

Therefore, a need has been felt for the development of a thin film capacitor of small size, large capacitance and excellent dielectric characteristic that has a dielectric layer in which a bismuth layer structured compound oriented in the axis of orientation along which the bismuth layer structured compound exhibits only weak property as a ferroelectric material and behaves like a paraelectric material.

On the other hand, it is necessary in order to fabricate an inorganic EL (electro-luminescence) device for emitting light having high luminescence to provide a dielectric layer having a high insulating property between an electrode and an inorganic EL device and it is therefore required to develop an inorganic EL device provided with a dielectric layer in which a bismuth layer structured compound oriented in the axis of orientation along which the bismuth layer structured compound exhibits only weak property as a ferroelectric material and behaves like a paraelectric material.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a multi-layered unit suitable for fabricating a thin film capacitor having a small size, large capacitance and an excellent dielectric characteristic and suitable for fabricating an inorganic EL (electro-luminescence) device capable of emitting light having high luminescence.

The above and other objects of the present invention can be accomplished by a multi-layered unit constituted by forming on a support substrate formed of a material on which crystals cannot be epitaxially grown, a buffer layer, which is formed of a material having an anisotropic property and enabling epitaxial growth of crystals of a conductive material thereon to form an electrode layer and is oriented in the [001] direction, the electrode layer formed by epitaxially growing crystals of a conductive material and oriented in the [001] direction, and a dielectric layer formed by epitaxially growing a dielectric material containing a bismuth layer structured compound on the electrode layer and oriented in the [001] direction in this order.

In the present invention, the [001] direction as termed herein means the [001] direction of a cubic crystal, a tetragonal crystal, a monoclinic crystal or an orthorhombic crystal.

According to the present invention, since the electrode layer is formed by epitaxially growing crystals of a conductive material on the buffer layer, which is formed of a material having an anisotropic property and enabling epitaxial growth of crystals of a conductive material thereon to form an electrode layer and is oriented in the [001] direction, it is possible to reliably orient the electrode layer in the [001] direction.

Further, according to the present invention, since the dielectric layer of a dielectric material containing a bismuth layer structured compound is formed by epitaxially growing the dielectric material containing the bismuth layer structured compound on the electrode layer oriented in the [001] direction, it is possible to easily orient the dielectric layer in the [001] direction, thereby improving the c axis orientation characteristic.

Therefore, according to the present invention, since the c axis of the bismuth layer structured compound contained in the dielectric layer can be oriented so as to be perpendicular to the electrode layer, in the case of, for example, providing an upper electrode on the dielectric layer and applying a voltage between the electrode layer and the upper electrode, the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound contained in the dielectric layer. Accordingly, since the ferroelectric property of the bismuth layer structured compound contained in the dielectric layer can be suppressed and the paraelectric property thereof can be fully exhibited, it is possible to fabricate a thin film capacitor having a small size and large capacitance.

Further, according to the present invention, since the dielectric layer of the dielectric material containing the bismuth layer structured compound whose c axis orientation is improved has a high insulating property, it is possible to form the dielectric layer thinner and therefore make a thin film capacitor much smaller.

Furthermore, since the dielectric layer of the dielectric material containing the bismuth layer structured compound whose c axis orientation is improved has a high insulating property, it is possible to cause an inorganic EL device to emit light in a desired manner and fabricate an inorganic EL device capable of emitting light having high luminescence by disposing the inorganic EL device on the dielectric layer of the multi-layered unit according to the present invention, disposing another electrode on the inorganic EL device and applying a voltage between the electrode layer and another electrode.

In the present invention, the dielectric material containing the bismuth layer structured compound may contain unavoidable impurities.

In the present invention, it is sufficient for the support substrate to be formed of a material on which crystals cannot be epitaxially grown and the material for forming the support substrate is not particularly limited. An amorphous substrate made of fused quartz or the like, a polycrystal substrate made of ceramic or the like, a heat-resistant glass substrate, a resin substrate or the like can be used as the support substrate.

In the present invention, the multi-layered unit includes a buffer layer oriented in the [001] direction, namely, the c axis direction on the support substrate. The buffer layer serves to ensure easy formation of an electrode layer thereon so as to be oriented in the [001] direction, namely, the c axis direction,

In the case of directly forming an electrode layer made of platinum or the like on the support substrate made of fused quartz or the like, since the electrode layer tends to be oriented in the [111] direction, it is difficult to epitaxially grow a dielectric layer of a dielectric material containing a bismuth layer structured compound on the electrode layer to form a dielectric layer of the dielectric material containing the bismuth layer structured compound oriented in the [001] direction, namely, the c axis direction. However, in the present invention, since the electrode layer is formed on the buffer layer, which is formed of a material having an anisotropic property and enabling epitaxial growth of crystals of a conductive material to form an electrode layer and is oriented in the [001] direction, namely, the c axis direction, the electrode can be formed so as to be reliably oriented in the [001] direction, namely, the c axis direction.

In the present invention, the material for forming the buffer layer is not particularly limited insofar as it has an anisotropic property and enables epitaxial growth of crystals of a conductive material thereon to form an electrode layer, and a bismuth layer structured compound and a copper oxide superconductor having a CuO ₂plane can be preferably used for forming the buffer layer.

The bismuth layer structured compound has a composition represented by the stoichiometric compositional formula: (Bi ₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W). In the case where the symbol A and/or B includes two or more elements, the ratio of the elements can be arbitrarily determined.

As shown in FIG. 1, the bismuth layer structured compound has a layered structure formed by alternately laminating

perovskite layers

1 each including perovskite lattices 1 a made of (m−1) ABO₃and (Bi₂O₂)²⁺

layers

2.

The number of laminates each consisting of the

perovskite layer

1 and the (Bi₂O₂)²⁺

layer

2 is not particularly limited and it is sufficient for the bismuth layer structured compound to include at least one pair of (Bi₂O₂)²⁺

layers

2 and one perovskite layer 1 sandwiched therebetween.

The c axis of the bismuth layer structured compound means the direction obtained by connecting the pair of (Bi ₂O₂)²⁺

layers

2, namely, the [001] direction.

Among the bismuth layer structured compounds represented by the above stoichiometric compositional formula, a bismuth layer structured compound where the symbol m is equal to 3 in the general stoichiometric compositional formula thereof, namely, that represented by the stoichiometric compositional formula: (Bi ₂O₂)²⁺ (A₃B₄O₁₃)²⁻ or Bi₂A₃B₄O₁₅, is most preferably employed since it can be easily oriented in the [001] direction, namely, the c axis direction,

As a copper oxide superconductor having a CuO ₂plane, compounds represented by the stoichiometric compositional formula: YBa₂Cu₃O₇-δ and Bi₂Sr₂CuO₆are preferably used for forming the buffer layer.

In the present invention, it is not absolutely necessary for the degree F of orientation in the [001] direction, namely, c axis orientation of the material having an anisotropic property and contained in the buffer layer to be 100% but it is sufficient for the degree F of c axis orientation of the material to be equal to or more than 80%. It is more preferable for the degree of c axis orientation of the material to be equal to or more than 90% and it is much more preferable for the degree of c axis orientation of the material to be equal to or more than 95%.

The degree F of the c axis orientation of the material having an anisotropic property is defined by the following formula (1).

F=(P−P ₀)/(1−P ₀)×100 (1)

In formula (1), P ₀is defined as the X-ray diffraction intensity of polycrystal whose orientation is completely random in the c axis direction, namely, the ratio of the sum Σ I₀(001) of reflection intensities I₀(001) from the surface of [001] of polycrystal whose orientation is completely random to the sum Σ I₀(hkl) of reflection intensities I₀(hkl) from the respective crystal surfaces of [hkl] thereof (Σ I₀(001)/Σ I₀(hkl), and P is defined as X-ray diffraction intensity of a material having an anisotropic property in the c axis direction, namely, the ratio of the sum Σ I (001) of reflection intensities I (001) from the surface of [001] of the material having an anisotropic property to the sum Σ I (hkl) of reflection intensities I (hkl) from the respective crystal surfaces of [hkl] thereof (Σ I (001)/Σ I (hkl). The symbols h, k and l can each assume an arbitrary integer value equal to or larger than 0.

In the above formula (1), since P ₀is a known constant, when the sum Σ I (001) of reflection intensities I (001) from the surface of [001] of the material having an anisotropic property and the sum Σ I (hkl) of reflection intensities I (hkl) from the respective crystal surfaces of [hkl] are equal to each other, the degree F of the c axis orientation of the material having an anisotropic property is equal to 100%.

In the present invention, the buffer layer can be formed using any of various thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a metal organic chemical vapor deposition process (MOCVD), a chemical solution deposition process (CSD process) such as a metal-organic decomposition process (MOD) and a sol-gel process or the like. Particularly, in the case where the buffer layer has to be formed at a low temperature, a plasma CVD process, a photo-CVD process, a laser CVD process, a photo-CSD process, a laser CSD process or the like is preferably used for forming the buffer layer.

In the present invention, the multi-layered unit includes an electrode layer of a conductive material oriented in the [001] direction, namely, the c axis direction on the buffer layer.

In the present invention, since the electrode layer is formed by epitaxially growing crystals of a conductive material on the buffer layer, which is formed of a material having an anisotropic property and enabling epitaxial growth of crystals of a conductive material thereon to form an electrode layer and is oriented in the [001] direction, namely, the c axis direction, it is possible to reliably orient an electrode layer in the [001] direction, namely, the c axis direction.

In the present invention, the material for forming the electrode layer is not particularly limited and can be a metal such as platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni) or the like, an alloy containing at least one of these metal as a principal component, a conductive oxide such as NdO, NbO, RhO ₂, OsO₂, IrO₂, RuO₂, SrMoO₃, SrRuO₃, CaRuO₃, SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃, Nb doped SrTiO₃or the like or a mixture of these.

It is preferable to select from among these materials a material having a small lattice mismatch with the material having an anisotropic property and forming the

buffer layer

4 and the bismuth layer structured compound for forming a dielectric layer.

In the present invention, the electrode layer can be formed using any of various thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a metal organic chemical vapor deposition process (MOCVD), a chemical solution deposition process (CSD process) such as a metal-organic decomposition process (MOD) and a sol-gel process or the like.

In the present invention, the multi-layered unit includes a dielectric layer of a dielectric material containing a bismuth layer structured compound oriented in the [001] direction, namely, the c axis direction on the electrode layer.

In the present invention, the dielectric layer is formed by epitaxially growing a dielectric material containing a bismuth layer structured compound on the electrode layer.

Since the dielectric layer is formed by epitaxially growing a dielectric material containing a bismuth layer structured compound on the electrode layer oriented in the [001] direction, it is possible to easily orient the bismuth layer structured compound contained in the dielectric layer in the [001] direction, namely, the c axis direction. Therefore, in the case where a thin film capacitor is fabricated using the multi-layered unit according to the present invention, since the bismuth layer structured compound contained in the dielectric layer does not function as a ferroelectric material but functions as a paraelectric material, it is possible to fabricate a thin film capacitor having a small size and large capacitance.

In the present invention, it is not absolutely necessary for the degree F of orientation in the [001] direction, namely, c axis orientation of the bismuth layer structured compound contained in the dielectric layer to be 100% and it is sufficient for the degree F of c axis orientation to be equal to or more than 80%. It is more preferable for the degree of c axis orientation of the bismuth layer structured compound to be equal to or more than 90% and it is much more preferable for the degree of c axis orientation of the bismuth layer structured compound to be equal to or more than 95%.

The degree F of the bismuth layer structured compound is defined by the formula (1).

The dielectric characteristic of a dielectric layer can be markedly improved by orienting the bismuth layer structured compound in the [001] direction, namely, the c axis direction in this manner.

More specifically, in the case where a thin film capacitor is fabricated by forming, for example, an upper electrode on the dielectric layer of the multi-layered unit according to the present invention, even if the thickness of the dielectric layer is equal to or thinner than, for example, 100 nm, a thin film capacitor having a relatively high dielectric constant and low loss (tan δ) can be obtained. Further, a thin film capacitor having an excellent leak characteristic, an improved breakdown voltage, an excellent temperature coefficient of the dielectric constant and an excellent surface smoothness can be obtained.

In the present invention, among bismuth layer structured compounds usable for forming the buffer layer, a bismuth layer structured compound having an excellent characteristic as a capacitor material can be used for forming the dielectric layer. The bismuth layer structured compound for forming the dielectric layer is not particularly limited insofar as it has an excellent characteristic as a capacitor material, and a bismuth layer structured compound where the symbol m is equal to 3 in the general stoichiometric compositional formula thereof, namely, that represented by the stoichiometric compositional formula: (Bi ₂O₂)²⁺ (A₂B₃O₁₀)²⁻ or Bi₂A₂B₃O₁₂, is preferably used since it has an excellent characteristic as a capacitor material.

In the present invention, it is particularly preferable that the bismuth layer structured compound contained in the dielectric layer has a composition represented by the stoichiometric compositional formula: Ca _xSr_(1−x)Bi₄Ti₄O₁₅, where x is equal to or larger than 0 and equal to or smaller than 1. If the bismuth layer structured compound having such a composition is used, a dielectric layer having a relatively large dielectric constant can be obtained and the temperature characteristic thereof can be further improved.

In the present invention, parts of the elements represented by the symbols A or B in the stoichiometric compositional formula of the bismuth layer structured compound contained in the dielectric layer are preferably replaced with at least one element Re (yttrium (Y) or a rare-earth element) selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb) and lutetium (Lu).

The preferable amount of replacement by the element Re depends upon the value of the symbol m. For example, in the case where the symbol m is equal to 3, in the compositional formula: Bi ₂A_(2−x)Re_xB₃O₁₂, x is preferably equal to or larger than 0.4 and equal to or smaller than 1.8 and more preferably equal to or larger than 1.0 and equal to or smaller than 1.4. If the amount of replacement by the element Re is determined within this range, the Curie temperature (phase transition temperature from ferroelectric to paraelectric) of the dielectric layer can be controlled preferably to be equal to or higher than −100° C. and equal to or lower than 100° C. and more preferably to be equal to or higher than −50° C. and equal to or lower than 50° C. If the Curie point is equal to or higher than −100° C. and equal to or lower than 100° C., the dielectric constant of the dielectric thin film 6 increases. The Curie temperature can be measured by DSC (differential scanning calorimetry) or the like. If the Curie point becomes lower than room temperature (25° C.), tan δ further decreases and, as a result, the loss value Q further increases.

Furthermore, in the case where the symbol m is equal to 4, in the compositional formula: Bi ₂A_(3−x)Re_xB₄O₁₅, x is preferably equal to or larger than 0.01 and equal to or smaller than 2.0 and more preferably equal to or larger than 0.1 and equal to or smaller than 1.0.

Although the dielectric layer of the multi-layered unit according to the present invention has an excellent leak characteristic even if it does not contain the element Re, it is possible to further improve the leak characteristic by replacing part of the elements represented by the symbols A or B with the element Re.

For example, even in the case where no part of the elements represented by the symbols A or B in the stoichiometric compositional formula of the bismuth layer structured compound is replaced with element Re, the leak current measured at the electric filed strength of 50 kV/cm can be controlled preferably to be equal to or lower than 1×10 ⁻⁷A/cm²and more preferably to be equal to or lower than 5×10⁻⁸A/cm²and the short circuit ratio can be controlled preferably to be equal to or lower than 10% and more preferably to be equal to or lower than 5%. However, in the case where parts of the elements represented by the symbols A or B in the stoichiometric compositional formula of the bismuth layer structured compound are replaced with element Re, the leak current measured under the same condition can be controlled preferably to be equal to or lower than 5×10⁻⁸A/cm²and more preferably to be equal to or lower than 1×10⁻⁸A/cm²and the short circuit ratio can be controlled preferably to be equal to or lower than 5% and more preferably to be equal to or lower than 3%.

In the present invention, the dielectric layer can be formed using any of various thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a metal organic chemical vapor deposition process (MOCVD), a chemical solution deposition process (CSD process) such as a metal-organic decomposition process (MOD) and a sol-gel process or the like. Particularly, in the case where the dielectric layer has to be formed at a low temperature, a plasma CVD process, a photo-CVD process, a laser CVD process, a photo-CSD process, a laser CSD process or the like is preferably used for forming the dielectric layer.

The above and other objects and features of the present invention will become apparent from the following description made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a drawing schematically showing the structure of a bismuth layer structured compound. [0062]
FIG. 2 is a schematic partial cross-sectional view showing a multi-layered unit which is a preferred embodiment of the present invention. [0063]
FIG. 3 is a schematic partial cross-sectional view showing a thin film capacitor fabricated using a multi-layered unit which is a preferred embodiment of the present invention.[0064]

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2 is a schematic partial cross-sectional view showing a multi-layered unit which is a preferred embodiment of the present invention. [0065]
As shown in FIG. 2, a [0066] multi-layered unit 1 according to this embodiment is constituted by laminating a buffer layer 3, an electrode layer 4 and a dielectric layer 5 on a support substrate 2 in this order.
In this embodiment, the [0067] support substrate 2 of the multi-layered unit 1 is formed of fused quartz.
As shown in FIG. 2, the [0068] multi-layered unit 1 according to this embodiment includes a buffer layer 3 of a dielectric material containing a bismuth layer structured compound on the support substrate 2.
In this embodiment, as a bismuth layer structured compound for forming the buffer layer, a bismuth layer structured compound having a composition represented by Bi[0069] ₄Ti₃O₁₂and having an excellent orientation characteristic is selected and the bismuth layer structured compound contained in the buffer layer 3 is oriented in the [001] direction, namely, the c axis direction.
In this embodiment, the [0070] buffer layer 3 of the dielectric material containing a bismuth layer structured compound having a composition represented by Bi₄Ti₃O₁₂is formed using a metal organic chemical vapor deposition process (MOCVD), for example.
In the case where a [0071] buffer layer 3 of the dielectric material containing a bismuth layer structured compound having a composition represented by Bi₄Ti₃O₁₂is formed by a metal organic chemical vapor deposition process (MOCVD), for example, Bi(CH₃)₃and Ti(O—i—C₃H₇)₄are used as constituent gases and the temperature of the support substrate 2 is maintained at 550° C., thereby forming a buffer layer 3 having a thickness of 50 nm and oriented in the [001] direction, namely, the c axis direction.
In this embodiment, the [0072] buffer layer 3 serves to ensure that an electrode layer 5 oriented in the [001] direction, namely, the c axis direction can be formed by epitaxially growing crystals of a conductive material thereon.
As shown in FIG. 2, the [0073] multi-layered unit 1 according to this embodiment includes an electrode layer 4 of platinum formed on the buffer layer 3.
An [0074] electrode layer 4 of platinum is formed on the buffer layer 4 so as to have a thickness of 100 nm, for example, by using argon gas having a pressure of 1 pascal (Pa) as a sputtering gas, setting the temperature of the buffer layer 4 to 400° C. and setting the electric power to 100 W
In the case of forming an [0075] electrode layer 4 of platinum on the support substrate 2 of fused quartz, since platinum has a cubic crystal structure, platinum is oriented in the most stable [111] direction. Therefore, even if a dielectric material containing a bismuth layer structured compound is epitaxially grown on the electrode layer 4, it is impossible to orient the bismuth layer structured compound in the [001] direction. As a result, since it is impossible to cause the bismuth layer structured compound contained in the dielectric layer 6 to function not as a ferroelectric material but as a paraelectric material, even if the multi-layered unit 1 is used, a thin film capacitor having a small size and large capacity cannot be fabricated.
However, in this embodiment, since the [0076] buffer layer 3 is formed of a dielectric material containing a bismuth layer structured compound having a composition represented by Bi₄Ti₃O₁₂which has an anisotropic property and can epitaxially grow crystals of a conductive material thereon and the bismuth layer structured compound contained in the buffer layer 3 is oriented in the [001] direction, namely, the c axis direction, an electrode layer 4 of platinum can be reliably epitaxially grown and oriented in the [001] direction.
As shown in FIG. 2, the [0077] multi-layered unit 1 according to this embodiment includes a dielectric layer 5 formed on the electrode layer 4.
In this embodiment, the [0078] dielectric layer 5 is formed of a dielectric material containing a bismuth layer structured compound having a composition represented by the stoichiometric compositional formula: SrBi₄Ti₄O₁₅where the symbol m is equal to 4 and the symbol A₃is replaced by Bi₂+Sr in the general stoichiometric compositional formula thereof and having an excellent characteristic as a capacitor characteristic.
In this embodiment, the [0079] dielectric layer 5 is formed on the electrode layer 4 using a metal organic deposition (MOD) process.
Concretely, a toluene solution of 2-ethyl hexanoate Sr, a 2-ethyl hexanoate solution of 2-ethyl hexanoate Bi and a toluene solution of 2-ethyl hexanoate Ti are stoichiometrically mixed so that the mixture contains 1 mole of 2-ethyl hexanoate Sr, 4 moles of 2-ethyl hexanoate Bi and 4 moles of 2-ethyl hexanoate Ti and is diluted with toluene. The resultant constituent solution is coated on the [0080] electrode layer 4 using a spin coating method and after drying the resultant dielectric layer 5 is tentatively baked at a temperature under which the dielectric layer 5 cannot be crystallized.
The same constituent solution is coated on the thus tentatively baked [0081] dielectric layer 5 using a spin coating method to form a coating layer and the coating layer is dried and tentatively baked. These operations are repeated.
When tentative baking is completed, the [0082] dielectric layer 5 is baked and a series of operations including coating, drying, tentative baking, coating, drying, tentative baking and baking are repeated until a dielectric layer 5 having a required thickness, for example, 100 nm is obtained.
During these processes, a dielectric material containing a bismuth layer structured compound is epitaxially grown and a [0083] dielectric layer 5 oriented in the [001] direction, namely, the c axis direction is formed.
According to this embodiment, since the [0084] multi-layered unit 1 has such a structure that the buffer layer 3, the electrode layer 4 and the dielectric layer 5 are laminated on the support substrate 2 of fused quartz and the electrode layer 4 is formed by epitaxially growing crystals of a conductive material on the buffer layer 3 formed of a material having an anisotropic property and capable of epitaxially growing crystals of a conductive material thereon to form an electrode layer 5 and oriented in the [001] direction, namely, the c axis direction, it is possible to reliably orient the electrode layer 4 in the [001] direction.
Further, according to this embodiment, since the [0085] dielectric layer 5 of a dielectric material containing a bismuth layer structured compound is formed by epitaxially growing the dielectric material containing the bismuth layer structured compound on the electrode layer 4 oriented in the [001] direction, namely, the c axis direction, it is possible to reliably orient the dielectric layer 5 in the [001] direction and improve the c axis orientation of the dielectric layer 5.
Therefore, according to this embodiment, since the [0086] multi-layered unit 1 includes a dielectric layer 5 formed of a dielectric material containing a bismuth layer structured compound oriented in the [001] direction, namely, the c axis direction, in the case of, for example, providing an upper electrode on the dielectric layer 5 of the multi-layered unit 1 according to this embodiment, thereby fabricating a thin film capacitor and applying a voltage between the electrode layer 4 and the upper electrode, the direction of an electric field substantially coincides with the c axis of the bismuth layer structured compound contained in the dielectric layer 5. As a result, since the ferroelectric property of the bismuth layer structured compound contained in the dielectric layer 5 can be suppressed and the paraelectric property thereof can be fully exhibited, it is possible to fabricate a thin film capacitor having a small size and large capacitance.
Further, according to this embodiment, since the [0087] multi-layered unit 1 includes the dielectric layer 5 formed of a dielectric material containing a bismuth layer structured compound oriented in the [001] direction, namely, the c axis direction and the dielectric layer 5 containing the bismuth layer structured compound whose c axis orientation is improved has a high insulating property, it is possible to make the dielectric layer 5 thinner and, therefore, make a thin film capacitor much smaller.
Furthermore, according to this embodiment, the [0088] buffer layer 3 having a thickness of 50 nm is formed using a metal organic chemical vapor deposition (MOCVD) process so that the electrode layer 5 can be reliably formed to be oriented in the [001] direction, namely, the c axis direction by epitaxially growing crystals of a conductive material thereon and, on the other hand, the dielectric layer 6 on which no layer is formed using an epitaxial growth process and which has a thickness larger than that of the buffer layer 4 is formed using a metal organic decomposition (MOD) process, which is an inexpensive process. Therefore, it is possible to decrease the cost of fabricating a multi-layered unit 1.
FIG. 3 is a schematic partial cross-sectional view showing a thin film capacitor fabricated using a multi-layered unit which is a preferred embodiment of the present invention. [0089]
As shown in FIG. 3, the [0090] thin film capacitor 10 includes the multi-layered unit 1 shown in FIG. 2 and an upper electrode 11 formed on the dielectric layer 5 of the multi-layered unit 1.
In this embodiment, the [0091] support substrate 2 of the multi-layered unit 1 serves to ensure the mechanical strength of the entire thin film capacitor 10.
Further, the [0092] electrode layer 4 of the multi-layered unit 1 serves as one of electrodes of the thin film capacitor 10 and as a base for orienting the c axis of a bismuth layer structured compound contained in the dielectric layer 5 substantially parallel to an electric field.
In this embodiment, the [0093] dielectric layer 5 of the multi-layered unit 1 serves as a dielectric layer of the thin film capacitor 10.
In this embodiment, the upper electrode [0094] 11 serving as the other of the electrodes of the thin film capacitor 10 is formed on the dielectric layer 5 of the multi-layered unit 1.
The process for forming the upper electrode [0095] 11 is not particularly limited and any process usable for forming the electrode layer 4 of the multi-layered unit 1 can be used for forming the upper electrode 11. It is preferable to form the upper electrode 11 using a sputtering process from the viewpoint of the film forming speed.
The material for forming the upper electrode [0096] 11 is not particularly limited insofar as it has conductivity and any material usable for forming the electrode layer 4 of the multi-layered unit 1 can be used for forming the upper electrode 11. Further, unlike the electrode layer 4 of the multi-layered unit 1, since it is unnecessary to consider the lattice mismatch with the material for forming the buffer layer 3 and the material for forming the dielectric layer 5, when a material for forming the upper electrode 11 is to be selected and it can be formed at room temperature, the upper electrode 11 can be formed using a base metal such as iron (Fe), cobalt (Co) or the like or an alloy such as WSi, MoSi or the like. The thickness of the upper electrode 11 is not particularly limited insofar as it can serve as the other of the electrodes of the thin film capacitor 10 and the upper electrode 11 can be formed so as to have a thickness of 10 to 10,000 nm, for example.
In the thus constituted [0097] thin layer capacitor 10, the bismuth layer structured compound contained in the dielectric layer 5 is oriented so that the c axis thereof is substantially perpendicular to the electrode layer 4 and the upper electrode 11. Therefore, when a voltage is applied between the electrode layer 4 and the upper electrode 11, the direction of the electric field substantially coincides with the c axis of the bismuth layer structured compound contained in the dielectric layer 5. As a result, since the ferroelectric property of the bismuth layer structured compound contained in the dielectric layer 5 can be suppressed and the paraelectric property thereof can be fully exhibited, it is possible to fabricate a thin film capacitor having a small size and large capacitance.
A [0098] thin film capacitor 10 having such characteristics can be preferably utilized as a decoupling capacitor, in particular, a decoupling capacitor for an LSI having a high operating frequency.
The present invention has thus been shown and described with reference to specific embodiments. However, it should be noted that the present invention is in no way limited to the details of the described arrangements but changes and modifications may be made without departing from the scope of the appended claims. [0099]
For example, in the above described embodiments, the [0100] multi-layered unit 1 is constituted by laminating on the support substrate 2, the buffer layer 3, the electrode layer 4 and the dielectric layer 5 in this order. However, the multi-layered unit 1 may be formed by further laminating a plurality of unit multi-layered elements each including at least an electrode layer 4 and a dielectric layer 5 on the dielectric layer 5 and a thin film capacitor may be fabricated by forming an upper electrode on the dielectric layer 5 of the uppermost unit multi-layered element. In the case where the multi-layered unit 1 is constituted by further laminating a plurality of unit multi-layered elements on the dielectric layer 5, if an electrode layer included in each of the unit multi-layered elements is not formed by epitaxially growing crystals of a conductive material on a dielectric layer 5, even if a dielectric material containing a bismuth layer structured compound is epitaxially grown on the electrode layer, it is difficult to orient the bismuth layer structured compound in the [001] direction and form a dielectric layer 5 of the dielectric material containing the bismuth layer structured compound oriented in the [001] direction. Therefore, it is required to form each unit multi-layered element so as to include an electrode layer, a buffer layer formed on the electrode layer and a dielectric layer formed of a dielectric material containing a bismuth layer structured compound on the buffer layer. It is further possible to laminate one or more unit multi-layered elements each including an electrode layer and a dielectric layer and one or more unit multi-layered elements each including an electrode layer, a buffer layer formed on the electrode layer and a dielectric layer formed on the buffer layer and formed of a dielectric material containing a bismuth layer structured compound on the dielectric layer 5 in an arbitrary order and form an upper electrode on the dielectric layer 5 of the uppermost unit multi-layered element, thereby fabricating a thin film capacitor.
Further, in the above described embodiments, although the [0101] support substrate 2 is formed of fused quartz, it is not absolutely necessary to employ the support substrate 2 formed of fused quartz. The material for forming the support substrate 2 is not particularly limited insofar as crystal cannot be epitaxially grown thereon. For example, instead of the support substrate 2 formed of fused quartz, another amorphous substrate can be used and further, a polycrystal substrate made of ceramic or the like, a heat-resistant glass substrate, a resin substrate or the like can be used as a support substrate.
Furthermore, in the above described embodiments, the [0102] buffer layer 3 formed on the support substrate 2 of the multi-layered unit 1 is formed of a dielectric material containing a bismuth layer structured compound having an excellent orientation characteristic and having a composition represented by Bi₄Ti₃O₁₂. However, it is not absolutely necessary to form the buffer layer 3 of the dielectric material containing the bismuth layer structured compound having an excellent orientation characteristic and having a composition represented by Bi₄Ti₃O₁₂and it is sufficient for the buffer layer to be formed of a material having an anisotropic property and enabling epitaxial growth of a conductive material thereon to form an electrode layer. The buffer layer 3 can be formed of another bismuth layer structured compound and the buffer layer 3 may be formed of a layer structured compound containing a copper oxide superconductor having a CuO₂plane.
Moreover, in the above described embodiments, although the [0103] buffer layer 3 of the multi-layered unit 1 is formed using a metal organic chemical vapor deposition process (MOCVD), it is not absolutely necessary to form the buffer layer 3 using a metal-organic chemical vapor deposition process and the buffer layer 3 may be formed using any of various thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD) and a chemical solution deposition process (CSD process) such as a metal-organic decomposition process (MOD) and a sol-gel process or the like.
Further, in the above described embodiments, although the [0104] multi-layered unit 1 includes the electrode layer 4 formed on the buffer layer 3 and formed of platinum, it is not absolutely necessary to form the electrode layer 4 of platinum and a material for forming the electrode layer 4 is not particularly limited insofar as it is conductive and has a very small lattice mismatch with a material used for forming the buffer layer 3 and a material used for forming the dielectric layer 5. Instead of platinum (Pt), the electrode layer 4 may be formed of a metal such as ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu), nickel (Ni) or the like, alloy containing at least one of these metal as a principal component, conductive oxide such as NdO, NbO, RhO₂, OsO₂, IrO₂, RuO₂, SrMoO₃, SrRuO₃, CaRuO₃, SrVO₃, SrCrO₃, SrCoO₃, LaNiO₃, Nb doped SrTiO₃or the like and a mixture of these.
Moreover, in the above described embodiments, although the [0105] electrode layer 4 of the multi-layered unit 1 is formed using a sputtering process, it is not absolutely necessary to form the electrode layer 4 using a sputtering process and instead of a sputtering process, the electrode layer 4 may be formed using any of various thin film forming processes such as a vacuum deposition process, a pulsed laser deposition process (PLD), a metal organic chemical vapor deposition process (MOCVD), a chemical solution deposition process (CSD process) such as a metal-organic decomposition process (MOD) and a sol-gel process or the like.
Furthermore, in the above described embodiments, although the [0106] multi-layered unit 1 includes on the electrode layer 4, the dielectric layer 5 formed of a dielectric material containing a bismuth layer structured compound having a composition represented by Bi₄Ti₃O₁₂wherein m is equal to 4 in the general stoichiometric compositional formula of a bismuth layer structured compound, it is not absolutely necessary to form on the electrode layer 4, the dielectric layer 5 of the dielectric material containing a bismuth layer structured compound having a composition represented by Bi₄Ti₃O₁₂wherein m is equal to 4 in the general stoichiometric compositional formula of a bismuth layer structured compound and the dielectric layer 5 may be formed of a dielectric material containing a bismuth layer structured compound wherein m is not equal to 4 in the general stoichiometric compositional formula of a bismuth layer structured compound and a dielectric material containing another bismuth layer structured compound whose constituent elements are different from Bi₄Ti₃O₁₂insofar as it has an excellent characteristic as a capacitor material.
Moreover, in the above described embodiments, although the [0107] dielectric layer 5 is formed using a metal-organic decomposition process (MOD), it is not absolutely necessary to form the dielectric layer 5 using a metal-organic decomposition process and the dielectric layer 5 may be formed using other thin film forming processes such as a vacuum deposition process, a sputtering process, a pulsed laser deposition process (PLD), a metal organic chemical vapor deposition process (MOCVD), other chemical solution deposition process (CSD process) such as a sol-gel process or the like.
Further, in the above described embodiments, although the [0108] multi-layered unit 1 is used as a component of a thin film capacitor, the multi-layered unit 1 can be used not only as a component of a thin film capacitor but also as a multi-layered unit for causing an inorganic EL device to emit light having high luminescence. Specifically, although an insulating layer having a high insulating property is necessary between an electrode layer 4 and an inorganic EL device in order to cause the inorganic EL device to emit light having high luminescence, since a dielectric layer 5 of a dielectric material containing a bismuth layer structured compound having an improved c axis orientation has a high insulating property, it is possible to cause an inorganic EL device to emit light in a desired manner by disposing the inorganic EL device on the dielectric layer 5, disposing another electrode on the inorganic EL device and applying a voltage between the electrode layer 3 and another electrode.
According to the present invention, it is possible to provide a multi-layered unit suitable for fabricating a thin film capacitor having a small size, large capacitance and an excellent dielectric characteristic and suitable for fabricating an inorganic EL (electro-luminescence) device capable of emitting light having high luminescence. [0109]

Claims

1. A multi-layered unit constituted by forming on a support substrate formed of a material on which crystals cannot be epitaxially grown, a buffer layer, which is formed of a material having an anisotropic property and enabling epitaxial growth of crystals of a conductive material thereon to form an electrode layer and is oriented in the [001] direction, the electrode layer formed by epitaxially growing crystals of a conductive material and oriented in the [001] direction, and a dielectric layer formed by epitaxially growing a dielectric material containing a bismuth layer structured compound on the electrode layer and oriented in the [001] direction in this order.

2. A multi-layered unit in accordance with claim 1, wherein the support substrate is formed of a material selected from a group consisting of an amorphous substrate, a polycrystal substrate and a heat-resistant glass substrate.

3. A multi-layered unit in accordance with claim 1, wherein the buffer layer contains a compound selected from a group consisting of a bismuth layer structured compound and a layer structured compound containing a copper oxide superconductor having a CuO₂plane.

4. A multi-layered unit in accordance with claim 2, wherein the buffer layer contains a compound selected from a group consisting of a bismuth layer structured compound and a layer structured compound containing a copper oxide superconductor having a CuO₂plane.

5. A multi-layered unit in accordance with claim 3, wherein the buffer layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

6. A multi-layered unit in accordance with claim 4, wherein the buffer layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

7. A multi-layered unit in accordance with claim 1, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

8. A multi-layered unit in accordance with claim 2, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

9. A multi-layered unit in accordance with claim 3, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

10. A multi-layered unit in accordance with claim 4, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

11. A multi-layered unit in accordance with claim 5, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

12. A multi-layered unit in accordance with claim 6, wherein the electrode layer contains at least one kind of metal selected from a group consisting of platinum (Pt), ruthenium (Ru), rhodium (Rh), palladium (Pd), iridium (Ir), gold (Au), silver (Ag), copper (Cu) and nickel (Ni).

13. A multi-layered unit in accordance with claim 1, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

14. A multi-layered unit in accordance with claim 2, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

15. A multi-layered unit in accordance with claim 3, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

16. A multi-layered unit in accordance with claim 4, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

17. A multi-layered unit in accordance with claim 5, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

18. A multi-layered unit in accordance with claim 6, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

19. A multi-layered unit in accordance with claim 7, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

20. A multi-layered unit in accordance with claim 8, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

21. A multi-layered unit in accordance with claim 9, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

22. A multi-layered unit in accordance with claim 10, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

23. A multi-layered unit in accordance with claim 11, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.

24. A multi-layered unit in accordance with claim 12, wherein the dielectric layer contains a bismuth layer structured compound having a composition represented by a stoichiometric compositional formula: (Bi₂O₂)²⁺ (A_m−1B_mO_3m+1)²⁻ or Bi₂A_m−1B_mO_3m+3, where the symbol m is a natural number, the symbol A is at least one element selected from a group consisting of sodium (Na), potassium (K), lead (Pb), barium (Ba), strontium (Sr), calcium (Ca) and bismuth (Bi), and the symbol B is at least one element selected from a group consisting of iron (Fe), cobalt (Co), chromium (Cr), gallium (Ga), titanium (Ti), niobium (Nb), tantalum (Ta), antimony (Sb), vanadium (V), molybdenum (Mo) and tungsten (W) and when the symbol A and/or B includes two or more elements, the ratio of the elements is arbitrarily determined.