JP2022088333A - Nanosheet containing niobate dielectric and dielectric thin film containing the same - Google Patents

Abstract

To provide a nanosheet having a high dielectric constant and low dielectric loss characteristics.SOLUTION: A nanosheet comprises a niobate dielectric having a composition of Formula 1 and having a high dielectric constant and low dielectric loss characteristics. (Formula 1): Sr2(1-x)Bi2xNb3O10 (wherein x is 0<x≤0.2).SELECTED DRAWING: Figure 1

Description

The present specification relates to a niobate dielectric nanosheet having a high dielectric constant and a low dielectric loss characteristic and a dielectric thin film containing the same, and more specifically, a characteristic having an extremely low dielectric loss while maintaining a high dielectric constant dielectric constant. The present invention relates to a niobate dielectric nanosheet showing the above and a dielectric thin film containing the same.

In recent years, duplexers for mobile communication terminals, Band Pass Filters, insulators for transistors, electronic components such as frequency filters, multilayer ceramic capacitors (MLCCs), and gate oxidation of transistors. With the integration and ultra-miniaturization of various electronic devices such as gate oxides, the dielectric materials used in them are also required to be smaller and have higher performance.

In addition, with the development of high-performance semiconductor devices equipped with high-addition functions such as smartphones, smart cards, and Bluetooth (registered trademark) for vehicles, the demand for higher-performance capacitors is increasing, and semiconductor processing technology With the development, it is essential to develop more integrated ultra-small high-capacity ceramic capacitors. In order to realize a high-capacity ceramic capacitor such as MLCC suitable for next-generation devices, it is essential to reduce the thickness of the dielectric layer to an ultra-thin layer. There is a big limit to reducing.

As the material of the dielectric layer typically used, titanium oxide having a high dielectric constant (Ba, Sr) TiO ₃ , CaTiO ₃ , or a composition in which these are combined is mainly used. However, in such a perovskite-based titanium oxide dielectric material, when it is manufactured with a thin thin film having a thickness of several tens of nanometers, it is caused by the problem of interface deterioration with the substrate, composition deviation, and many crystal grain interfaces shown in the heat treatment process. It causes deterioration of dielectric properties and high dielectric loss.

In addition, in order to realize ultra-thin film formation by using a screen printing method that synthesizes existing dielectric materials to produce ceramic capacitors, there is only the difficulty that the dielectric material must be synthesized with several nanoparticles. Not only that, the durability under high temperature load deteriorates, and there is a limit to achieving high stacking. Therefore, in order to realize ultra-compact and high-capacity ceramic capacitors or capacitors that can be applied to next-generation devices, it is essential to research and develop dielectric materials that have excellent properties even in thin films at the nano-thickness level. ..

Not only that, even if a dielectric material with excellent properties is developed, if the size of the nanosheet particles is too small, a large dielectric loss will occur at many grain boundaries. In addition, when manufacturing a thin film with the developed nanosheet, if a uniform and flat thin film cannot be obtained in the process, not only a large leakage current will be caused but also the uniformity of thin film production will decrease. Therefore, nanosheets are used. A manufacturing method capable of producing a more dense and uniform thin film is indispensable.

In order to solve such a problem, a realization example of the present invention is to synthesize a KSr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ dielectric material, which is a perovskite material having a layered structure, under various conditions. Provided are methods for synthesizing Sr _{2 (1-x)} Bi ₂ x Nb ₃ O ₁₀ single crystal nanosheets of various sizes obtained by cation substitution of K + ions.
Further, the present invention provides a method for producing a more uniform and flat dielectric thin film in a solution vapor deposition step using a nanosheet dispersion solution.

ここで、ｘは０＜ｘ≦０．２ In order to achieve the above-mentioned object, in one embodiment of the present invention, a nanosheet containing a niobate dielectric having a composition represented by the following chemical formula 1 and having a high dielectric constant and a low dielectric loss property is provided. ..

Here, x is 0 <x ≦ 0.2.

In one embodiment, the nanosheets may have an average diameter of 50 nm to 50 μm.

In one embodiment, the nanosheets may have a thickness of 10 nm or less.

In one embodiment, the nanosheet may exhibit a dielectric constant of 500 or more with a thickness of 10 nm or less.

In one embodiment of the present invention, a step of forming a precursor mixture; a step of calcining the precursor mixture to form a bulk niobate dielectric; and a step of peeling the bulk niobate dielectric in layers to form nanosheets. Provided is a method for producing a nanosheet, which comprises the stage of forming the nanosheet.

In one embodiment, the precursor mixture may include K ₂ CO ₃ , SrCO ₃ , Bi ₂ O ₃ , and Nb ₂ O ₅ .

In one embodiment, the precursor mixture may be formed by wet mixing in a ball mill step.

In one embodiment, the bulk niobate dielectric may be formed by sintering at a temperature of 700 to 1300 ° C.

In one embodiment, prior to sintering, calcination may be performed at a temperature of 700 to 1100 ° C. for 5 to 20 hours.

In one embodiment of the present invention, a dielectric layer containing a plurality of nanosheets according to the embodiment of the present invention is included, and the plurality of nanosheets are arranged in a single-layer structure with a dielectric layer. A thin film is provided.

In one embodiment, the niobate dielectric thin film may have a multi-layered laminated structure including a plurality of dielectric layers.

In one embodiment, the niobate dielectric thin film may further include a lower substrate.

In one embodiment, the lower substrate comprises one or more selected from the group consisting of a conductive perovskite substrate, a glass substrate, a plastic substrate, a metal electrode, and an oxide transparent electrode having an oxide / metal / oxide structure. It's fine.

In one embodiment, the nanosheets may have 90% or more coverage.

In one embodiment, the niobate dielectric thin film may exhibit a dielectric constant of 500 or more with a thickness of 10 nm or less.

In one embodiment, the niobate dielectric thin film may have a roughness (RMS) in the range 0.1-3.0 nm.

In one embodiment of the present invention, a niobate dielectric thin film comprising a step of developing a dispersion solution in which a plurality of nanosheets according to the embodiment of the present invention are dispersed; and a step of depositing the nanosheets on a lower substrate. A manufacturing method is provided.

In one embodiment, the vapor deposition step may be vapor deposition by an electrophoresis method or a Langmuir Brodget method.

In one embodiment, the developed dispersion may be stabilized for 5-20 minutes prior to deposition.

In one embodiment, the lower substrate may be moved to form a dielectric layer while maintaining a predetermined vapor deposition pressure at the vapor deposition step.

In one embodiment, the vapor deposition pressure may be reached at a barrier moving speed of 0.1 to 20 mm / min at the vapor deposition step.

In one embodiment, the vapor deposition pressure may be in the range of 5 to 30 mN / m at the vapor deposition step.

The niobate dielectric nanosheet according to the present invention has a large dielectric constant and a low dielectric loss, and is applied to the fabrication of a low-temperature element capable of realizing insulation characteristics with linear and excellent dielectric constant even at a nano-level thickness. It is possible to provide a dielectric material in the form of a possible nanosheet. Further, not only can the grain interface be reduced to the maximum by producing the starting particles in the form of a non-spherical sheet, but also when a crystalline sheet is used, there is an advantage that a heat treatment step is not required.

In addition, since it eliminates the need for vacuum equipment and expensive vapor deposition equipment required in the conventional dielectric element manufacturing process, it has made it possible to design an element manufacturing process that satisfies low cost and early manufacturing time.
Furthermore, we will provide a technique that can adjust the size of nanosheets according to the conditions for synthesizing niobate dielectrics, synthesize nanosheets of a size suitable for the application, and provide a method that can produce a more uniform thin film when applied to devices. ..

Therefore, it can solve the deterioration problem between the substrate and the dielectric material that occurs in the conventional element manufacturing process, and is applied to various types of electronic devices such as next-generation laminated ceramic capacitors, microwave dielectrics, transistor gates, and next-generation TFTs. obtain. Further, since the element of the present invention is manufactured at room temperature, it can be applied to various types of polymer substrates, paper substrates, etc., and an element having a novel structure that can be composited and laminated with an organic substance can be produced. It can be used as a dielectric material for molecular electronics. The dielectric element using the present invention can replace the conventional material with a thin thickness, and realizes high dielectric constant and good insulating properties at the same time, so that a huge economic ripple effect can be expected. can.

Scanning electron micrograph of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet changed according to the sintering conditions of KSr _1.8 Bi _0.2 Nb ₃ O ₁₀ of the mother composition according to one embodiment of the present invention. Is shown. It shows the C-AFM photograph of the Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet monolayer film which concerns on one Example of this invention. It is a TEM photograph of an Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nano-thin film laminated in 10 layers under various surface pressure conditions according to an embodiment of the present invention. The following is a cross-sectional electron micrograph of a Pt / Sr _1.8 Bi _0.2 Nb _{3O 10} / Nb-SrTiO ₃ capacitor manufactured according to an embodiment of the present invention. It is a scanning electron micrograph of a sample produced as Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet which concerns on one Example of this invention at a sintering temperature of 1225 ° C. It is a scanning electron micrograph of a sample manufactured at a sintering temperature of 1250 ° C. as an Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet according to an embodiment of the present invention. It is a scanning electron micrograph of a sample produced as Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet which concerns on one Example of this invention at a sintering temperature of 1275 ° C. It is a scanning electron micrograph of a sample manufactured as Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet which concerns on one Example of this invention at a sintering temperature of 1300 ℃. It shows the dielectric constant and the dielectric loss value of the Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet thin film measured according to one embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in more detail.
The examples of the present invention disclosed in the text are exemplified only for the purpose of explanation, and the examples of the present invention can be carried out in various forms and are limited to the examples described in the text. Should not be interpreted as being done.

Although the present invention can be modified in various ways and can have various forms, the examples are not intended to limit the present invention to a specific disclosed form, and the idea and technical scope of the present invention are not limited to the present invention. It should be understood to include all modifications, equivalents or alternatives contained in.

Singular expressions include multiple expressions unless explicitly mentioned in the context. Terms such as "include" or "have" in this application are meant to indicate the existence of the features, numbers, stages, actions, components, parts or combinations thereof described herein. It should be understood that it is not intended to preclude the existence or addability of one or more other features or numbers, stages, actions, components, parts or combinations thereof.

ここで、ｘは０＜ｘ≦０．２
一方、Ｂｉの置換量に関連して、ｘが０．２以上である場合、Ｓｒイオンの位置を置換するよりは二次相を形成して層状構造が破壊され得る。 Niobate Dielectric Nanosheet In order to achieve the above-mentioned object, in one embodiment of the present invention, the niobate dielectric having the composition represented by the following chemical formula 1 is contained, and has high dielectric constant and low dielectric loss characteristics. Provide nanosheets.

Here, x is 0 <x ≦ 0.2.
On the other hand, when x is 0.2 or more in relation to the substitution amount of Bi, the layered structure can be destroyed by forming a secondary phase rather than substituting the position of the Sr ion.

In one embodiment, the nanosheets may have an average diameter of 50 nm to 50 μm.

In one embodiment, the nanosheets may have a thickness of 10 nm or less.

In one embodiment, the nanosheet may exhibit a dielectric constant of 500 or more with a thickness of 10 nm or less.

Method for Producing Nanosheets In one embodiment of the present invention, a step of forming a precursor mixture; a step of sintering the precursor mixture to form a bulk niobate dielectric; and a step of forming the bulk niobate dielectric in layers; Provided is a method for producing nanosheets, which comprises a step of peeling to form nanosheets;

First, a precursor mixture may be formed.
In an exemplary embodiment, the precursor mixture may comprise a potassium precursor, a strontium precursor, a bizmas precursor, and a niobate precursor, eg, the potassium precursor, a strontium precursor, a bizmas precursor, a niobate. The precursors may be, but are not limited to, K ₂ CO ₃ , SrCO ₃ , Bi ₂ O ₃ , and Nb ₂ O ₅ , respectively.

In an exemplary embodiment, the precursor mixture uses the general formula KSr _{2 (1-x)} Bi with K2 CO ₃ , SrCO ₃ , Bi ₂ O ₃ and Nb ₂ O ₅ with a purity of 99% or greater. After nominated with a composition ratio satisfying _{(y / 3) x} Nb ₃ O _{10 + δ} , a precursor mixture using ethanol as a solvent may be formed.

In an exemplary embodiment, the precursor mixture may be wet-mixed to form, specifically, wet-mixed with zirconia balls by a ball mill step to form a precursor mixture.

（前記化学式２中、モル分率ｘは０＜ｘ≦０．２の範囲である。） The precursor mixture may then be calcined to form a bulk niobate dielectric.
Specifically, the formed precursor mixture may be dried in an oven at 100 ° C. and then sintered at 1200 ° C. to obtain KSBNO.
Here, KSBNO may be a bizmas niobate dielectric having a composition represented by the following chemical formula 2 and having a high dielectric constant and a low dielectric loss characteristic.

(In the chemical formula 2, the mole fraction x is in the range of 0 <x ≦ 0.2.)

The dielectric represented by the chemical formula 2 is produced by substituting Bi, which is a Group 15 element, with Sr sites based on the KSr ₂ Nb ₃ O ₁₀ dielectric substance having a layered structure. For example, in order to produce the KSBNO dielectric, the Sr site of the KSr ₂ Nb ₃ O ₁₀ ceramic having a layered structure is replaced with Bi to produce a dielectric material represented by the general formula KSBNO, but compared to Sr ions. Since Bi ions have a small ionic radius, when x = 0.2 or more, a secondary phase is formed and the layered structure is destroyed rather than replacing the site of Sr ions. In the chemical formula 2, the oxidation number of Bi is 3+, and it is possible to have better dielectric properties when Bi is substituted with 3+ ions than when Bi is substituted with 2+ ions.

In one embodiment, the bulk niobate dielectric may be formed by sintering at a temperature of 700 to 1300 ° C. By adjusting the sintering temperature, the size of the nanoparticles formed can be controlled. If the sintering temperature is less than 700 ° C., the phase may not be synthesized, and if it is more than 1300 ° C., a secondary phase may occur.

On the other hand, prior to sintering, calcining may be performed at a predetermined temperature and time, whereby the size of the nanosheet particles can be controlled. The calcining may be carried out at a temperature of 700 to 1100 ° C. for 2 to 24 hours. Pre-baking at a temperature of 700 to 1100 ° C. for 2 to 24 hours can be synthesized in the desired single phase, and the grain size may increase as the pre-baking time increases. In particular, if the particles are calcined at a predetermined temperature and time prior to sintering as compared with the case where only the sintering step is performed, the size of the synthesized particles can be increased, and the particles are formed later by the peeling step. It is advantageous because the size of the particles of the nanosheet can be greatly controlled.

Next, the bulk niobate dielectric may be exfoliated in layers to form nanosheets.
In an exemplary implementation, the stripping step may be to chemically strip the bulk niobate dielectric in layers to form nanosheets. Specifically, after synthesizing a KSBNO dielectric having high dielectric properties due to changes in composition, the non-linear dielectric properties of KSBNO are linearly dielectric properties by substituting K + ions with H + ions based on the KSBNO dielectric. By changing to the above to reduce the dielectric loss, it is possible to synthesize an HSBNO dielectric having a high dielectric constant, a low dielectric loss, and a linear dielectric property. After that, the SBNO dielectric may be produced by substituting the H + ions of the HSBNO dielectric with TBA + ions and exfoliating them.

（前記化学式３中、モル分率ｘは０＜ｘ≦０．２の範囲である。） In an exemplary embodiment, K + ions may be cationically substituted with H + ions in KSBNO represented by Chemical Formula 2 and calcined to produce an HSBNO dielectric represented by Chemical Formula 3.

(In the chemical formula 3, the mole fraction x is in the range of 0 <x ≦ 0.2.)

For example, the synthesized KSBNO powder for producing the HSBNO dielectric composition is stirred with 5M or 7M acids such as HNO ₃ , HCl, H ₂ SO ₄ for 4 days and inserted between SBNOs. The existing K + ion is replaced with H + ion. The replaced solution is washed several times with DI Water using a centrifuge. Then, it is dried at 50 degreeC for 24 hours, and HSBNO can be obtained.

Further, in the exemplary embodiment, the H + ion of the HSBNO dielectric represented by the chemical formula 3 is replaced with a TBA + ion and peeled off to obtain a nanosheet containing the niobate dielectric having the composition represented by the chemical formula 1. Can be done. Specifically, for example, when the HSBNO dielectric sample is stirred in a tetrabutylammonium (TBAOH) solution for several days, it exists between Sr _{2 (1-x)} Bi _{(y / 3) x} Nb ₃ O _{10 + δ} layers. The H + ions are stabilized by the TBA + ions, and the bulk specimen becomes colloidal and is peeled off one by one on the Sr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ single crystal sheet.

The KSBNO and HSBNO dielectrics according to one embodiment of the present invention exhibit extremely low dielectric loss while maintaining a high dielectric constant. Especially in the case of _HSBNO to which Bi is added in an excessive amount, as a ^high dielectric constant material, er = 460 and a constant dielectric constant value of 0 <x ≦ 0.25 in the frequency range between 102 Hz and ¹⁰⁷ Hz. Has a dielectric loss between. Further, since the HSBNO exhibits linear dielectric properties, it can be used for laminated ceramic capacitors, microwave dielectrics, dielectric films of next-generation TFTs, and the like.

Niobate Dielectric Thin Film In one embodiment of the present invention, a dielectric layer containing a plurality of nanosheets according to one embodiment of the present invention is included, and the plurality of nanosheets are arranged in a single layer structure with a dielectric layer. , Niobate Dielectric Thin Films are provided.

In one embodiment, the niobate dielectric thin film may have a multi-layered laminated structure including a plurality of dielectric layers. For example, the niobate dielectric thin film may have a multi-layered laminated structure including two or more dielectric layers. In the case of a single-layer laminated structure, the dielectric thin film cannot completely cover the lower substrate (for example, about 100% coverage). Therefore, when a niobate dielectric thin film having a single-layer laminated structure is applied to a device, a leak current (leakage) is applied. Currant) may occur significantly.

In one embodiment, the niobate dielectric thin film may further include a lower substrate.

In one embodiment, the lower substrate is a conductive perovskite substrate (eg, Nb-SrTiO ₃ and SrRuO ₃ , etc.), a glass substrate, a plastic substrate, a metal electrode (eg, gold and aluminum, etc.), and an oxide / metal / oxide. It may contain one or more selected from the group consisting of oxide transparent electrodes having a structure, and is not particularly limited as long as it is a substrate capable of uniformly depositing niobium dielectric nanosheets.

In one embodiment, the surface roughness (RMS) value of the niobate dielectric thin film may be controlled at the level of several nm, and in particular, when laminated with a plurality of dielectric layers, the niobate dielectric nanosheets are uniformly vapor-deposited. It is important to control the surface roughness. Specifically, the niobate dielectric thin film may have a roughness (RMS) in the range of 0.1 nm to 3 nm. If the roughness value exceeds 3 nm, the interfacial bondability with the thin film laminated on the upper portion may be lowered, and the uniformity of the upper thin film may be lowered.

In one embodiment, the dielectric thin film may have different nanosheet coverage depending on the field of application, and may have a high coverage value when specifically applied to gated dielectrics such as ceramic capacitors and transistors. It may be advantageous. For example, the nanosheets may have 90% or more coverage, and the nanosheets may have 95% or more, 98% or more coverage. If the coverage is less than the above-mentioned range, the dielectric thin film layer cannot completely cover the lower substrate (for example, about 100% coverage). Therefore, when a niobate dielectric thin film having a single-layer laminated structure is applied to the device, a leak occurs. A large current (leakage leakage) may be generated.

On the other hand, when the dielectric thin film is applied to a fuel cell, a water splitting electrode, etc., it has a low coverage of 90% or less because the characteristics may deteriorate if the surface of the electrode is completely covered. good.

In one embodiment, the niobate dielectric thin film may exhibit a dielectric constant of 500 or more with a thickness of 10 nm or less. Therefore, the niobate dielectric thin film according to the embodiment of the present invention has excellent dielectric properties, and therefore can be applied to laminated ceramic capacitors, microwave dielectrics, dielectric films of next-generation TFTs, and the like.

Method for Producing Niobate Dielectric Thin Film In one embodiment of the present invention, a step of developing a dispersion solution in which nanosheets according to one embodiment of the present invention are dispersed; and the developed nanosheets are vapor-deposited on a lower substrate. A method for producing a niobate dielectric thin film is provided, which comprises a step of forming a dielectric layer containing nanosheets.

First, a dispersion solution in which a plurality of nanosheets are dispersed may be developed.
In the exemplary embodiment, the dispersion solution may be a dispersion solution in which nanosheets containing a niobate dielectric having the composition represented by Chemical Formula 1 are dispersed as described above.
For example, an opaque colloidal solution in which Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheets having a perovskite structure are dispersed may be dispersed in ultrapure water filled with an LB (Langmuir-Blodgett) trough.

The nanosheets may then be deposited on the lower substrate.
In one embodiment, the vapor deposition step may be performed by a solution vapor deposition step, specifically in one or more of the electrophoresis, Langmuir-Bloggett, LBL, and spin-coating processes. It may be vapor-deposited. In particular, it is possible to provide a condition capable of obtaining a uniform thin film capable of precise control one by one by the Langmuir-Blodgett method.

Further, for example, after adjusting the concentration by dispersing the dielectric nanosheet colloid in a solution such as acetone or ethanol, the lower electrode substrate is positioned on the (+) pole, and the Pt plate is placed on the (-) pole as the mating electrode. A dielectric thin film can be vapor-deposited by electrophoresis by applying an electric field at a position and DC power supply.

In one embodiment, the developed dispersion may be stabilized for 5-20 minutes prior to deposition. By such a stabilization process, the water surface of the dispersion solution can be stabilized and the temperature of the underlying solution can be kept constant.

In one embodiment, the lower substrate may be moved to form a dielectric layer while maintaining a predetermined vapor deposition pressure at the vapor deposition step. When the lower substrate is moved in the vertical direction in this way, the developed nanosheets are vapor-deposited on the lower substrate, which may reduce the vapor deposition pressure of the nanosheets deployed on the water surface. The stability of the vapor-filmed dielectric layer may be impaired. Therefore, in order to maintain the vapor deposition pressure, a method of moving the barrier at a predetermined moving speed with an LB (Langmuir-Blodgett) trough may be used. For example, in the vapor deposition step, the surface pressure of the dispersion solution can be reached to a desired vapor deposition pressure by using barriers on both sides having a moving speed of 0.1 to 20 mm / min. After moving the barrier to reach the vapor deposition pressure, the substrate is lowered vertically or horizontally at a speed of 0.1 to 20 mm / min, and a single-layer film is formed on the surface of the substrate while maintaining the surface pressure by moving the barriers on both sides. Can be transferred. If the moving speed of the barrier is less than 0.1 mm / min, the stability of the nanosheet particles may decrease and it may take a long time to reach the desired pressure by sinking from the surface, and the movement of the barrier may occur. If the speed is more than 20 mm / min, the nanosheets may overlap with each other due to the moving speed being too fast.

In one embodiment, the vapor deposition pressure may be maintained in the range of 5 to 30 mN / m at the vapor deposition step. If the vapor deposition pressure is less than 5 mN / m, the nanosheet may be vaporized in a form having a coverage of 10% or less due to a decrease in the uniformity of the thin film in a gas phase state, and the vapor deposition pressure is 30 mN. If it exceeds / m, many portions where nanosheets overlap are generated in the liquid-condensed phase state, and the coverage is excellent at 98% or more, but the surface roughness of the thin film may deteriorate.

In the exemplary embodiment, the step of depositing the nanosheets may be repeated several times, whereby a niobate dielectric thin film having a multi-layered laminated structure can be formed by including a plurality of dielectric layers which are a single layer of nanosheets. For example, the nanosheet vapor deposition step is repeated twice or more, and the film can be formed so that the lower substrate is not exposed. In the case of a single-layer laminated structure, the dielectric thin film cannot completely cover the lower substrate (for example, about 100% coverage). Therefore, when a niobate dielectric thin film having a single-layer laminated structure is applied to a device, a leak current (leakage) is applied. Currant) may occur significantly.

On the other hand, prior to the vapor deposition, the lower substrate may be washed with ethanol and / or acetone and then irradiated with UV to be surface-treated so as to have a hydrophilic surface. Since the vapor deposition of the nanosheet thin film is transferred at the air-water interface, a hydrophilic surface can be formed and better bonding properties can be obtained.

In an exemplary embodiment, after the vapor deposition step, the Pt or Au electrodes may be sputtered and vapor-deposited to form the dielectric thin film capacitor, the upper electrode required for the dielectric gate layer of the thin film transistor.

In addition, organic substances may be removed by UV-Ozone or UV treatment. On the other hand, the niobate dielectric thin film may be heat-treated at 500 ° C. or lower to remove organic substances.

Therefore, the perovskite nanosheet thin film formed by the method for producing a niobate dielectric thin film according to the embodiment of the present invention has a high relative permittivity of 500 or more and excellent insulating properties even with a thin film thickness of 10 nm or less. , Can be used as a next-generation material that surpasses existing high dielectric constant oxide materials.

Examples Hereinafter, the configuration and effects of the present invention will be described in more detail with reference to examples. It should be noted that these examples are provided only for the purpose of illustration to help understanding of the present invention, and the scope and scope of the present invention are not limited by the following examples.

[Example 1] Manufacture of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheets (calcination temperature 900 ° C., sintering temperature 1200 ° C.)
Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheets were obtained using a chemical stripping method. K ₂ CO ₃ , SrCO ₃ , Bi ₂ O ₃ and Nb ₂ O ₅ are used as the mother composition for obtaining the nanosheet, and the composition ratio satisfies the general formula KSr _1.8 Bi _0.2 Nb ₃ O ₁₀ . After weighing, wet mixing with zirconia balls using ethanol as a solvent using a ball mill step, drying in an oven at 100 ° C., and selecting a sintering temperature of 1200 ° C. for bulk Sr _1.8 Bi _0.2 . Nb ₃ O ₁₀ was obtained. At this time, in order to adjust the size of the particles of the obtained nanosheets, calcining was performed at 900 ° C. for 10 hours before sintering to adjust the size of the particles of the mother composition.
Then, HSr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ niobate composition was obtained by cation substitution using HNO ₃ , HCl, H ₂ SO ₄ , etc., and single crystal Sr was obtained by organic cation substitution such as TBAOH, TMAOH. _{A 2 (1-x)} Bi _2x Nb ₃ O ₁₀ niobium dielectric nanosheet composition was obtained. Specifically, the KSr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ specimen of the present invention having a layered structure in which K + ions are inserted between Sr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ layers. Was stirred with an acid solution for several days to replace the K + ions existing between the Sr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ layers with H + ions, and stirred with a cationic organic substance TBA ⁺ ion solution for several days. Then, the bulk specimen was colloidalized and peeled off as a nanosheet of Sr _{2 (1-x)} Bi _2x Nb ₃ O ₁₀ single crystal (“900 to 1200 ° C. synchronize” in FIG. 1).
A photograph of a colloidalized nanosheet thin film analyzed by high-resolution electron microscope observation is shown in FIG. The nanosheet shown in FIG. 1 has a particle size of 100 nm in width and length, but is not limited to this, and may have a particle size of several tens of m. It was confirmed that the peeled nanosheets were composed of 5 nm or less in thickness, and the horizontal and vertical sizes of the particles were 50 nm to 50 μm (FIG. 1).

[Example 2] Production of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet (sintering temperature 1200 ° C.)
Nanosheets were produced in the same manner as in Example 1 except that the calcination at 900 ° C. for 10 hours was omitted (“1200 ° C. synchronize” in FIG. 1).

[Example 3] Production of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheets (sintering temperature 1225 ° C., 1250 ° C., 1275 ° C., 1300 ° C.)
Nanosheets were produced in the same manner as in Example 1 except that the sintering temperatures were 1225 ° C, 1250 ° C, 1275 ° C, and 1300 ° C, respectively.

[Example 4] Thin-film deposition of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ niobate dielectric single-layer structure by Langmuir-Blodgett method The nanosheets produced in Examples 1 and 2 are vapor-deposited on a lower substrate and niobate. A dielectric thin film was manufactured.
The lower electrode substrate is washed with ethanol and acetone and then irradiated with UV to treat it so that it has a hydrophilic surface. Then, an opaque colloidal solution in which Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheets having a perovskite structure were dispersed was dispersed in ultrapure water filled with an LB (Langmuir-Blodgett) trough. After developing the dispersion solution, after having a stabilization time of 10 minutes for the purpose of stabilizing the water surface and keeping the temperature of the lower layer liquid constant, the solution is vertically or horizontally lowered using a Si substrate on which a Pt lower electrode is vapor-deposited. The barrier was compressed at a rate of 0.1 mm / sec to maintain a surface pressure of 12 mN / m on both sides, and the monolayer film was transferred to the surface of the substrate. On the other hand, the surface pressure was measured by sensing the surface pressure with an ultrasensitive pressure sensor mounted on the Langmuir-Blodgett equipment, and the standardized Wilhelmy method was used together with the platinum plate for the pressure sensing.
By the nuclear microscopic analysis shown in FIG. 2, it can be confirmed that the nanosheets are deposited flatly and densely on the lower electrode at the atomic level. In addition, it can be confirmed from the nuclear micrographs measured by applying an electric field to the single-layer film shown on the right of FIG. 2 that the film has non-conductivity.

[Example 5] Thin film deposition of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ niobate dielectric multilayer structure by Langmuir-Blodgett method The vapor deposition method of Example 4 is repeated several times to form a perovskite nanosheet thin film having a multilayer structure. The organic polymer remaining in the prepared thin film was removed by UV treatment. Then, a Pt or Au electrode was deposited as an upper electrode by a sputtering method. A transmission electron micrograph of the dielectric element thus produced is shown in FIG.

[Experimental Example 1] Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ Measurement of Dielectric Characteristics of Niobium Dielectric Thin Film UVO treatment was performed to remove organic substances remaining in the niobium dielectric thin film of Example 4. Then, Pt used as an upper electrode was vapor-deposited in an electron scanning microscope.
A cross-sectional electron micrograph of the produced Pt / Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ / Nb-SrTiO ₃ capacitor is shown in FIG. 4, and the measured dielectric properties are shown in FIG. Nanosheets exhibited excellent dielectric properties of 500 or more and excellent dielectric loss values even at thicknesses of 10 nm or less.
Therefore, since the niobate dielectric thin film according to the embodiment of the present invention has a high relative permittivity of 500 or more and excellent insulating properties even with a thin film thickness of 10 nm or less, the existing high dielectric constant oxide material can be used. It can be used as a next-generation material that surpasses.

[Experimental Example 2] Change in particle size of Sr _1.8 Bi _0.2 Nb ₃ O ₁₀ nanosheet mother composition according to sintering temperature The mother composition of the nanosheet produced in Example 3 is analyzed by scanning electron microscope observation. The results are shown in FIGS. 5a to 5d.
As a result, it was confirmed that the particle size of the nanosheet matrix composition, which determines the particle size of the nanosheet, increases as the sintering temperature increases.

The aforementioned embodiments of the present invention should not be construed as limiting the technical ideas of the present invention. The scope of protection of the present invention is limited by the matters described in the claims, and a person having ordinary knowledge in the technical field of the present invention can improve and change the technical idea of the present invention in various forms. be. Therefore, such improvements and changes are self-evident to those of ordinary knowledge and fall within the scope of protection of the present invention.

Claims (22)

A nanosheet containing a niobate dielectric having the composition represented by Chemical Formula 1 and having high dielectric constant and low dielectric loss characteristics.

In the above formula, x is 0 <x ≦ 0.2. The nanosheet according to claim 1, wherein the nanosheet has an average diameter of 50 nm to 50 μm. The nanosheet according to claim 1, wherein the nanosheet has a thickness of 10 nm or less. The nanosheet according to claim 1, wherein the nanosheet has a thickness of 10 nm or less and a dielectric constant of 500 or more. The stage of forming a precursor mixture;
A method for producing nanosheets, comprising a step of sintering the precursor mixture to form a bulk niobate dielectric; and a step of exfoliating the bulk niobate dielectric in layers to form nanosheets. The method for producing nanosheets according to claim 5, wherein the precursor mixture contains K ₂ CO ₃ , SrCO ₃ , Bi ₂ O ₃ , and Nb ₂ O ₅ . The method for producing nanosheets according to claim 5, wherein the precursor mixture is formed by wet mixing in a ball mill step. The method for producing nanosheets according to claim 5, wherein the bulk niobate dielectric is formed by sintering at a temperature of 700 to 1300 ° C. The method for producing nanosheets according to claim 8, wherein the nanosheets are calcined at a temperature of 700 to 1100 ° C. for 5 to 20 hours prior to sintering. A dielectric layer comprising a plurality of the nanosheets according to claim 1 is included.
The plurality of nanosheets are niobate dielectric thin films arranged in a single layer structure with a dielectric layer. The niobate dielectric thin film according to claim 10, wherein the niobate dielectric thin film has a multilayer laminated structure including a plurality of dielectric layers. The niobate dielectric thin film according to claim 10, wherein the niobate dielectric thin film further includes a lower substrate. The lower substrate comprises one or more selected from the group consisting of a conductive perovskite substrate, a glass substrate, a plastic substrate, a metal electrode, and an oxide transparent electrode having an oxide / metal / oxide structure. The niobate dielectric thin film according to claim 10. The niobate dielectric thin film according to claim 10, wherein the nanosheet has a coverage of 90% or more in the dielectric layer. The niobate dielectric thin film according to claim 10, wherein the niobate dielectric thin film has a roughness (RMS) in the range of 0.1 to 3 nm. The niobate dielectric thin film according to claim 10, wherein the niobate dielectric thin film exhibits a dielectric constant of 500 or more at a thickness of 10 nm or less. A niobate comprising the step of developing the dispersion solution in which the nanosheets according to claim 1 are dispersed on the water surface; and the step of depositing the developed nanosheets on a lower substrate to form a dielectric layer containing the nanosheets. A method for manufacturing a dielectric thin film. The method for producing a niobate dielectric thin film according to claim 17, wherein the vapor deposition step is vapor deposition by an electrophoresis method or a Langmuir Brodget method. The method for producing a niobate dielectric thin film according to claim 17, wherein the developed dispersion solution is stabilized for 5 to 20 minutes prior to vapor deposition. The method for producing a niobate dielectric thin film according to claim 17, wherein the lower substrate is moved to form a dielectric layer while maintaining a predetermined vapor deposition pressure at the vapor deposition step. The method for producing a niobate dielectric thin film according to claim 17, wherein the vapor deposition pressure is reached at a barrier moving speed of 0.1 to 20 mm / min in the vapor deposition step. The method for producing a niobate dielectric thin film according to claim 17, wherein the vapor deposition pressure is maintained in the range of 5 to 30 mN / m at the vapor deposition step.

Images