Lithium metal oxide dispersion liquid for dielectric layer

Abstract

A lithium metal oxide dispersion liquid for a dielectric layer according to the present invention is for use in forming a dielectric layer. Further, a lithium metal oxide dispersion liquid for a dielectric layer according to the present invention is for use in forming a dielectric layer, and the dielectric layer contains a second metal oxide that has an ilmenite structure and is formed of LiTaO3 or LiNbO3 aligned in a certain direction. The maximum value of light transmittance of the lithium metal oxide dispersion liquid for a dielectric layer is 65%T or more in a wavelength range of 400-760 nm.

Description

Lithium Metal Oxide Dispersion for Dielectric Layers

[0001] The present invention relates to a lithium metal oxide dispersion for dielectric layers.

[0002] In the communication field, demand for frequency filters is increasing, and for example, demand for Surface Acoustic Wave (SAW) filters as frequency filters is growing. As piezoelectric materials for SAW filters, LiNbO ３ , or LiTaO ３ metal oxides having an ilmenite structure are used. Further, a laminated structure obtained by epitaxially growing a metal oxide having an ilmenite structure on a Si substrate and an electronic device including the laminated structure are known.

[0003] Patent Document 1 discloses a technique for a dielectric laminated thin film, wherein at least one epitaxially grown underlying film mainly containing zirconium oxide (ZrO ２ ) is formed on a single-crystal Si (111) substrate surface, and an epitaxially grown ilmenite structure film made of a dielectric material having an ilmenite structure is formed on the underlying film. It is also described that the dielectric laminated thin film has a (0001)-oriented LiNbO ３ , or LiTaO ３ film having an ilmenite structure formed on a Si (111) substrate.

[0004] Patent Document 2 discloses a technique for a film structure, which comprises a substrate, a buffer film formed on the substrate, and a piezoelectric film formed on the buffer film, wherein the substrate is a Si (100) substrate, or an SOI substrate including a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer made of a Si (100) film on the insulating layer, the buffer film contains ZrO ２ , and the piezoelectric film contains c-axis-oriented LiNbO ３ , or LiTaO ３ . It is described that the film structure comprises a Si (100) substrate, and c-axis-oriented LiNbO ３ , or LiTaO ３ having an ilmenite structure formed on the Si (100) substrate.

[0005] Patent Document 3 describes a piezoelectric device comprising a substrate, a lower electrode, a buffer layer disposed on the lower electrode, and LiNbO2 disposed on the buffer layer with its crystal orientation oriented in the (012) plane. ３ , or LiTaO ３ A piezoelectric film comprising and is disclosed, and a technique is disclosed in which the crystal orientation of the piezoelectric film is oriented in the (012) plane direction. Also, LiNbO ３ 36° Y-cut LiNbO ３ It is stated that when using a single crystal plate, the electromechanical coupling coefficient for quasi-longitudinal waves is approximately 50% at its maximum. Furthermore, LiNbO ３ Not only single crystal plates, but also LiTaO ３ A similar trend is expected for single-crystal plates.

[0006] Japanese Patent Publication No. 2013-173647, International Publication No. 2023 / 210309, Japanese Patent Publication No. 2022-159810

[0007] However, LiNbO is oriented (01-12) on the Si substrate. ３ , or LiTaO ３ It was difficult to epitaxially grow a dielectric film made of this material. In other words, it was difficult to easily epitaxially grow LiNbO in a (01-12) oriented state or in a state oriented to a plane different from the (0001) plane. ３ , or LiTaO ３ It was difficult to form a dielectric film with excellent crystallinity, including the aforementioned material, on a Si substrate.

[0008] In view of the above problems, the present invention provides LiNboO that can be easily epitaxially grown in a state oriented in a certain direction. ３ , or LiTaO ３ The objective is to provide a lithium metal oxide dispersion for dielectric layers that contains and is used to form a dielectric layer with excellent crystallinity.

[0009] The lithium metal oxide dispersion for dielectric layers of the present invention, which was developed to solve the above problems, is characterized by being a lithium metal oxide dispersion for dielectric layers used to form a dielectric layer. A dielectric layer formed using the lithium metal oxide dispersion for dielectric layers of the present invention exhibits excellent crystallinity. Examples of the lithium metal oxide dispersion for dielectric layers of the present invention include lithium niobate dispersion for dielectric layers and lithium tantalate dispersion for dielectric layers. In this specification, unless otherwise specified, the lithium metal oxide dispersion for dielectric layers of the present invention refers to both lithium niobate dispersion for dielectric layers and lithium tantalate dispersion for dielectric layers.

[0010] Here, it is assumed that the lithium niobate in the lithium niobate dispersion for dielectric layers of the present invention exists as an ion in which niobate and lithium are ionically bonded. In the lithium niobate dispersion for dielectric layers, hydroxide ions are present as anions, while halide ions such as fluoride ions and chloride ions are almost absent, and lithium is thought to exist as a cation, therefore niobium is NbO ３ － It is thought to exist as an anion like this, or as a polyoxometalate (polyacid) ion in which multiple niobium atoms and oxygen atoms are bonded together.

[0011] Furthermore, in the lithium metal oxide dispersion for dielectric layers of the present invention, it is presumed that the lithium tantalate in the lithium tantalate dispersion for dielectric layers exists in the dispersion as an ion in which tantalate and lithium are ionically bonded. In the lithium tantalate dispersion for dielectric layers, hydroxide ions are present as anions, while halide ions such as fluoride ions and chloride ions are almost absent, and lithium is thought to exist as a cation, therefore tantalum is TaO ３ － It is thought to exist either as an anion or as a polyoxometalate (polyacid) ion in which multiple tantalum atoms and oxygen atoms are bonded together.

[0012] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the dielectric layer has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ It is characterized by containing a second metal oxide. The dielectric layer formed using the lithium metal oxide dispersion for dielectric layers of the present invention has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ If it contains a second metal oxide, LiNboO can be easily epitaxially grown in a state oriented in a certain direction. ３ , or LiTaO ３ This material allows for the formation of a dielectric layer with excellent crystallinity, and a dielectric film formed by stacking these dielectric layers. Further details will be described later.

[0013] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the maximum value of the light transmittance in the wavelength range of 400 nm to 760 nm is 65% T or higher. The lithium metal oxide dispersion for dielectric layers of the present invention is preferable in that the maximum value of the light transmittance in the wavelength range of 400 nm to 760 nm is 65% T or higher, as it indicates a high degree of dispersion and excellent uniformity of the components in the liquid.

[0014] The maximum light transmittance of the lithium metal oxide dispersion for the dielectric layer of the present invention in the wavelength range of 400 nm to 760 nm is more preferably 70% T or higher, even more preferably 80% T or higher, particularly preferably 90% T or higher, and most preferably 100% T.

[0015] Furthermore, the lithium metal oxide dispersion for the dielectric layer of the present invention preferably has a light transmittance of 65%T or more at one or more wavelengths of 400 nm, 600 nm, and 750 nm, more preferably 70%T or more, even more preferably 80%T or more, particularly preferably 90%T or more, and most preferably 100%T. The light transmittance at one or more wavelengths of 400 nm, 600 nm, and 750 nm may be 70%T or more, 72%T or more, 74%T or more, 76%T or more, 78%T or more, 80%T or more, 90%T or more, 95%T or more, 97%T or more, 98%T or more, 99%T or more, or 100%T or more.

[0016] Furthermore, the lithium metal oxide dispersion for the dielectric layer of the present invention preferably has a light transmittance of 65%T or more in the wavelength range of 400 nm to 760 nm, more preferably 70%T or more, even more preferably 80%T or more, particularly preferably 90%T or more, and most preferably 100%T. The light transmittance in the wavelength range of 400 nm to 760 nm may be 70%T or more, 72%T or more, 74%T or more, 76%T or more, 78%T or more, 80%T or more, 90%T or more, 95%T or more, 97%T or more, 98%T or more, 99%T or more, or 100%T or more.

[0017] When the lithium metal oxide dispersion for dielectric layers of the present invention is a lithium niobate dispersion for dielectric layers, it is preferable that the light transmittance in the 400 nm wavelength region is 20%T or more, and the maximum value of the light transmittance in the 600 nm to 760 nm wavelength region is 70%T or more, as this indicates a high degree of dispersion and excellent uniformity of components in the liquid. It is more preferable that the light transmittance in the 400 nm wavelength region is 25%T or more, and even more preferable that it is 30%T or more. It is more preferable that the maximum value of the light transmittance in the 600 nm to 760 nm wavelength region is 72%T or more, even more preferable that it is 74%T or more, particularly preferable that it is 76%T or more, also particularly preferable that it is 78%T or more, even more particularly preferable that it is 80%T or more, also particularly preferable that it is 85%T or more, even more preferable that it is 90%T or more, even more preferable that it is 95%T or more, even more preferable that it is 97%T or more, especially preferable that it is 98%T or more, even more particularly preferable that it is 99%T or more, and most preferable that it is 100%T.

[0018] Furthermore, in the case of a lithium niobate dispersion for a dielectric layer, the light transmittance at one of the wavelengths of 400 nm, 600 nm, and 760 nm, or at two or more wavelengths, may be 70% T or higher. The light transmittance at one of the wavelengths of 400 nm, 600 nm, and 760 nm, or at two or more wavelengths, may be 72% T or higher, 74% T or higher, 76% T or higher, 78% T or higher, 80% T or higher, 85% T or higher, 90% T or higher, 95% T or higher, 97% T or higher, 98% T or higher, 99% T or higher, or 100% T or higher.

[0019] Furthermore, in the case of a lithium niobate dispersion for a dielectric layer, the light transmittance in the 400 nm wavelength region may be 20%T or higher, and the minimum light transmittance in the 600 nm to 760 nm wavelength region may be 70%T or higher. The light transmittance in the 400 nm wavelength region may be 25%T or higher, or 30%T or higher. The minimum light transmittance in the 600 nm to 760 nm wavelength region may be 72%T or higher, 74%T or higher, 76%T or higher, 78%T or higher, 80%T or higher, 85%T or higher, 90%T or higher, 95%T or higher, 97%T or higher, 98%T or higher, 99%T or higher, or 100%T or higher.

[0020] When the lithium metal oxide dispersion for dielectric layers of the present invention is a lithium tantalate dispersion for dielectric layers, it is preferable that the maximum value of light transmittance in the wavelength range of 400 nm to 760 nm is 70% T or higher, as this indicates a high degree of dispersion and excellent uniformity of components in the liquid. It is more preferable that the maximum value of light transmittance in the wavelength range of 400 nm to 760 nm is 72% T or higher, even more preferable that it is 74% T or higher, particularly preferable that it is 76% T or higher, particularly preferable that it is 78% T or higher, particularly preferable that it is 80% T or higher, particularly preferable that it is 85% T or higher, even more preferable that it is 90% T or higher, even more preferable that it is 95% T or higher, particularly preferable that it is 97% T or higher, especially preferable that it is 98% T or higher, even more preferable that it is 99% T or higher, and most preferable that it is 100% T.

[0021] Furthermore, in the case of a lithium tantalate dispersion for a dielectric layer, the light transmittance at one of the wavelengths of 400 nm, 600 nm, and 750 nm, or at two or more wavelengths, may be 70% T or higher. The light transmittance at one of the wavelengths of 400 nm, 600 nm, and 750 nm, or at two or more wavelengths, may be 72% T or higher, 74% T or higher, 76% T or higher, 78% T or higher, 80% T or higher, 85% T or higher, 90% T or higher, 95% T or higher, 97% T or higher, 98% T or higher, 99% T or higher, or 100% T or higher.

[0022] Furthermore, in the case of a lithium tantalate dispersion for a dielectric layer, the minimum light transmittance in the wavelength range of 400 nm to 760 nm may be 70% T or higher. The minimum light transmittance in the wavelength range of 400 nm to 760 nm may be 72% T or higher, 74% T or higher, 76% T or higher, 78% T or higher, 80% T or higher, 85% T or higher, 90% T or higher, 95% T or higher, 97% T or higher, 98% T or higher, 99% T or higher, or 100% T or higher.

[0023] In addition, due to measurement errors, etc., the measured value of the light transmittance described above may exceed 100%T. However, since the theoretical upper limit is 100%T, if the measured value exceeds 100%T, it shall be considered as 100%T. Furthermore, in this specification, unless otherwise specified, "light transmittance" includes both the "initial light transmittance" of the lithium metal oxide dispersion for dielectric layers of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "time-dependent light transmittance" of the lithium metal oxide dispersion for dielectric layers of the present invention after being left to stand for one month from the day it was produced in a constant temperature oven set to room temperature of 25°C. Furthermore, if the time-dependent variation range between the "initial light transmittance" and the "time-dependent light transmittance" of the lithium metal oxide dispersion for dielectric layers of the present invention is small, it is presumed that the time-dependent variation range of the light transmittance of the lithium metal oxide dispersion for dielectric layers of the present invention after being left to stand for more than one month from the day it was produced will also be small.

[0024] Here, the light transmittance described above is measured using a spectrophotometer for the lithium metal oxide dispersion for the dielectric layer of the present invention, according to the following light transmittance measurement conditions.

[0025] =Light transmittance measurement conditions= • Measurement device: Ultraviolet-Visible-Near Infrared Spectrophotometer UH4150 (manufactured by Hitachi High-Tech Science Co., Ltd.) • Measurement mode: Wavelength scan • Data mode: %T (transmission) • Measurement wavelength range: 200 nm to 2000 nm • Scan speed: 600 nm / min • Sampling interval: 2 nm

[0026] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the particle diameter (D50) of the particles in the lithium metal oxide dispersion for dielectric layers, as determined by dynamic light scattering, is 100 nm or less. The lithium metal oxide dispersion for dielectric layers of the present invention is preferable in that it has high dispersibility when the particle diameter (D50) of the particles in the lithium metal oxide dispersion for dielectric layers, as determined by dynamic light scattering, is 100 nm or less. Furthermore, when the particle diameter (D50) of the particles in the lithium metal oxide dispersion for dielectric layers is smaller, it is more stable because there is less change over time, and is also preferable from the viewpoint of forming a good coating film without uncovered areas during film formation and ensuring a sufficient coating weight. It is more preferable when the particle diameter (D50) of the particles in the lithium metal oxide dispersion for dielectric layers is 80 nm or less, even more preferable when it is 50 nm or less, particularly preferable when it is 30 nm or less, even more particularly preferable when it is 20 nm or less, even more particularly preferable when it is 10 nm or less, even more particularly preferable when it is 5 nm or less, and even more particularly preferable when it is 3 nm or less. Furthermore, if the particle size (D50) of particles in the lithium metal oxide dispersion for the dielectric layer falls below the particle size detection limit of the measurement device using dynamic light scattering, or if measurement becomes impossible, the particle size (D50) of those particles will be reduced to below the detection limit.

[0027] Here, dynamic light scattering is a method that involves irradiating a solution, such as a suspension, with light, such as laser light, to measure the light scattering intensity from a group of particles undergoing Brownian motion, and determining the particle size and distribution from the temporal variation of that intensity. Specifically, the particle size distribution is evaluated using a zeta potential, particle size, and molecular weight measurement system (Otsuka Electronics Co., Ltd.: ELSZ-2000) in accordance with JIS Z 8828:2019 "Particle size analysis - Dynamic light scattering method". Immediately before measurement, the solution to be measured is filtered through a 2 μm pore size filter to remove dust and other particles, and then ultrasonic treatment is performed at 28 kHz for 3 minutes using an ultrasonic cleaner (AS ONE Corporation: VS-100III). Furthermore, if the measured value shows an abnormal value, it is possible that it is due to dust that was not removed from the solution. In this case, if the measurement results from multiple measurement samples taken from the same solution are not reproducible, the point may be excluded as an anomaly. Furthermore, the particle diameter (D50) refers to the median diameter (D50), which is the particle diameter that represents the 50% integrated value of the integrated distribution curve. In addition, unless otherwise specified in this specification, "particle diameter (D50)" includes both "initial particle diameter D50," which indicates the particle diameter (D50) of particles in the lithium metal oxide dispersion for dielectric layers of the present invention immediately after it has been adjusted to a liquid temperature of 25°C, and "particle diameter over time D50," which indicates the particle diameter (D50) of particles in the lithium metal oxide dispersion for dielectric layers of the present invention after it has been left to stand for one month from the day it was produced in a constant temperature oven set to room temperature of 25°C.

[0028] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the maximum value of the light transmittance in the wavelength range of 400 nm to 760 nm of the lithium metal oxide dispersion for dielectric layers is 65%T or more, and the particle size (D50) of the particles in the lithium metal oxide dispersion for dielectric layers measured by dynamic light scattering is 100 nm or less. As described above, the lithium metal oxide dispersion for dielectric layers of the present invention is preferable in that it has a high degree of dispersion and excellent uniformity of components in the liquid when the maximum value of the light transmittance in the wavelength range of 400 nm to 760 nm of the lithium metal oxide dispersion for dielectric layers is 65%T or more, and the particle size (D50) of the particles in the lithium metal oxide dispersion for dielectric layers measured by dynamic light scattering is 100 nm or less.

[0029] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention has a niobium content in the lithium metal oxide dispersion for dielectric layers. ２ O ５ In conversion, or if the tantalum content is Ta ２ O ５ The present invention is characterized by having a niobium content of 0.1% by mass or more and less than 30% by mass. ２ O ５ In conversion, or if the tantalum content is Ta ２ O ５ In terms of conversion, a concentration of 0.1% by mass or more and less than 30% by mass is preferable in terms of achieving both practicality and stability for the lithium metal oxide dispersion for the dielectric layer of the present invention, more preferably 1 to 25% by mass, even more preferably 3 to 21% by mass, particularly preferably 4 to 20% by mass, and most preferably 4 to 5% by mass.

[0030] Here, the niobium content or tantalum content in the lithium metal oxide dispersion for dielectric layers of the present invention is determined by appropriately diluting the lithium metal oxide dispersion for dielectric layers with dilute hydrochloric acid as needed, and using ICP emission spectrometry (Agilent Technologies: AG-5110) in accordance with JIS K0116:2014, and determining the content of niobium oxide (Nb ２ O ５ ) Nb mass fraction converted to (Ta ２ O ５ The Ta mass fraction is calculated by measuring the Ta mass fraction in the conversion of the present invention. The niobium content in the lithium metal oxide dispersion for dielectric layers of the present invention is Nb ２ O ５ By expressing it in terms of conversion, multiple oxide states of niobium can be determined together. Furthermore, the tantalum content in the lithium metal oxide dispersion for dielectric layers of the present invention can be expressed as Ta ２ O ５By expressing the values ​​in conversion terms, multiple oxide states of tantalum can be determined collectively. Furthermore, the lithium content in the lithium metal oxide dispersion for dielectric layers of the present invention is calculated by measuring the Li mass fraction in Li equivalent terms. By specifying the niobium (mol) and lithium (mol), or tantalum (mol) and lithium (mol), in the lithium metal oxide dispersion for dielectric layers of the present invention, the molar ratio Li / Nb of lithium (Li) to niobium (Nb) in lithium niobate, or the molar ratio Li / Ta of lithium (Li) to tantalum (Ta) in lithium tantalate, can be specified.

[0031] Furthermore, the niobium content in the lithium metal oxide dispersion for the dielectric layer can also be expressed in terms of Nb. The above-mentioned niobium content expressed in terms of Nb is as follows: A niobium content of 0.1% by mass or more and 21.0% by mass or less in terms of Nb is preferable in terms of achieving both practicality and stability of the lithium metal oxide dispersion for the dielectric layer; a niobium content of 0.7% by mass or more and 17.5% by mass or less in terms of Nb is more preferable; a niobium content of 2.1% by mass or more and 14.7% by mass or less in terms of Nb is even more preferable; and a niobium content of 3.5% by mass or more and 14.0% by mass or less in terms of Nb is particularly preferable.

[0032] Furthermore, the tantalum content in the lithium metal oxide dispersion for the dielectric layer can also be expressed in terms of Ta. The above-mentioned tantalum content expressed in terms of Ta is as follows: A tantalum content of 0.08% by mass or more and 12.3% by mass or less in terms of Ta is preferable in terms of achieving both practicality and stability of the lithium metal oxide dispersion for the dielectric layer; a tantalum content of 0.08% by mass or more and 12.3% by mass or less in terms of Ta is more preferable; a tantalum content of 2.4% by mass or more and 8.2% by mass or less in terms of Ta is even more preferable; and a tantalum content of 4.1% by mass or more and 8.2% by mass or less in terms of Ta is particularly preferable.

[0033] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the molar ratio Li / Nb of lithium niobate in the lithium metal oxide dispersion for dielectric layers, or the molar ratio Li / Ta of lithium (Li) in lithium tantalate in the lithium metal oxide dispersion for dielectric layers, is 0.01 or more and 20 or less.

[0034] Here, the lithium metal oxide dispersion for dielectric layers of the present invention is a lithium niobate (LiNbO) dispersion in the dielectric layer. ３ When the molar ratio Li / Nb of lithium (Li) to niobium (Nb) is 0.01 or more and 20 or less, the stability of the lithium metal oxide dispersion for the dielectric layer is improved, such as by suppressing the occurrence of precipitate precipitation from the lithium metal oxide dispersion for the dielectric layer. Furthermore, a molar ratio of Li / Nb of 0.01 or more and 10 or less is more preferable, 0.5 or more and 5 or less is even more preferable, 0.5 or more and 2 or less is particularly preferable, 0.9 or more and 1.5 or less is even more preferable, 0.9 or more and 1.2 or less is even more preferable, and 1.0 or more and 1.1 or less is most preferable.

[0035] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention contains lithium tantalate (LiTaO) in the lithium metal oxide dispersion for dielectric layers. ３ A molar ratio of lithium (Li) to tantalum (Ta) of the product Li / Ta is preferable in that it improves dispersibility and solubility in water. Furthermore, a molar ratio of Li / Ta of 0.01 to 10 is more preferable, 0.5 to 5 is even more preferable, 0.5 to 2 is particularly preferable, 0.8 to 1.3 is even more preferable, 0.9 to 1.2 is even more preferable, and 1.0 to 1.1 is most preferable.

[0036] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized in that the lithium metal oxide dispersion for dielectric layers is an aqueous dispersion. Since the lithium metal oxide in the lithium metal oxide dispersion for dielectric layers of the present invention has high dispersibility in water and good solubility in water, pure water can be used as the solvent. Organic solvents may also be used as the solvent. Examples of organic solvents include alcohol solvents, ketone solvents, ether solvents, ester solvents, aromatic hydrocarbon solvents, aliphatic hydrocarbon solvents, etc., and a solvent may be a mixture of these organic solvents and pure water. It is preferable that the above-mentioned solvents and water are miscible. In addition, the lithium metal oxide dispersion for dielectric layers of the present invention may contain one or more solvents in any proportion as long as stability is not impaired.

[0037] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized by further containing ammonia.

[0038] Of the lithium metal oxide dispersions for dielectric layers of the present invention, the lithium niobate dispersion for dielectric layers will be described in detail in the manufacturing method of the lithium niobate dispersion for dielectric layers described later. In this manufacturing process, an acidic niobium dispersion is added to aqueous ammonia by a reverse neutralization method to produce a hydrated ammonium niobate cake, which is a precipitate slurry containing niobium. From this, the lithium niobate dispersion for dielectric layers of the present invention is produced. Therefore, it is considered that ammonia containing ammonium ions substituted with lithium ions exists as a cation in the lithium niobate dispersion for dielectric layers.

[0039] A method for measuring the ammonia content in a lithium niobate dispersion for dielectric layers involves adding sodium hydroxide to the lithium niobate dispersion, distilling and separating the ammonia, and quantifying the ammonia content using an ion meter, and measuring the N in the gasified sample. ２ Methods for quantifying ammonia content include using a thermal conductivity meter, the Kjeldahl method, gas chromatography (GC), gas chromatography-mass spectrometry (GC-MS), ion chromatography, liquid chromatography (LC), and liquid chromatography-mass spectrometry (LC-MS). In particular, a method for quantifying ammonia content using an ion meter is preferred.

[0040] The ammonia content of the lithium niobate dispersion for dielectric layers of the present invention, including ammonium ions, is preferably 0.001% by mass or more and 25% by mass or less, more preferably 0.5% by mass or more and 10% by mass or less, and even more preferably 1% by mass or more and 8% by mass or less.

[0041] Furthermore, the molar ratio of ammonia to niobium in the lithium niobate dispersion for the dielectric layer of the present invention, NH ３ / Nb is preferably 0 to 20, more preferably 0 to 10, and even more preferably 0 to 5.

[0042] Here, NH ３ NH in / Nb ３ This represents ammonia (mol) in the lithium niobate dispersion for the dielectric layer of the present invention. On the other hand, NH ３ In / Nb, Nb represents Nb (mol) in the lithium niobate dispersion for the dielectric layer of the present invention.

[0043] The molar ratio of lithium, ammonia, and niobium in the lithium niobate dispersion for dielectric layers of the present invention, (Li + NH ３ ) / Nb is preferably 0.5 or more and 20 or less, more preferably 0.5 or more and 10 or less, and even more preferably 0.5 or more and 5 or less.

[0044] Here, (Li + NH ３ In ) / Nb, Li represents Li (mol) in the lithium niobate dispersion for the dielectric layer of the present invention, and NH ３ This represents ammonia (mol) in the lithium niobate dispersion for the dielectric layer of the present invention. On the other hand, (Li + NH ３ In ) / Nb, Nb represents Nb (mol) in the lithium niobate dispersion for the dielectric layer of the present invention.

[0045] The molar ratio of lithium to ammonia in the lithium niobate dispersion for dielectric layers of the present invention, Li / NH ３The ratio is preferably 0.001 or higher, more preferably 0.01 or higher, even more preferably 0.1 or higher, and particularly preferably 1 or higher. Note that ammonia can be reduced in Li / NH by volatilizing the ammonia component during concentration adjustment after the production of the lithium niobate dispersion for the dielectric layer of the present invention. ３ The upper limit can be any value.

[0046] Here, Li / NH ３ In this case, Li represents Li (mol) in the lithium niobate dispersion for the dielectric layer of the present invention. On the other hand, Li / NH ３ NH in ３ This indicates the amount of ammonia (mol) in the lithium niobate dispersion for the dielectric layer of the present invention.

[0047] Furthermore, among the lithium metal oxide dispersions for dielectric layers of the present invention, the lithium tantalate dispersion for dielectric layers will be explained in detail in the manufacturing method of the lithium tantalate dispersion for dielectric layers described later. In this manufacturing process, an acidic aqueous solution of a tantalum complex is added to an alkaline aqueous solution, such as ammonia water, by a reverse neutralization method to produce a tantalum-containing precipitate slurry, such as a hydrated ammonium tantalate cake. From this, the lithium tantalate dispersion for dielectric layers of the present invention is produced. Therefore, it is considered that ammonia contains ammonium ions and exists as a cation in the lithium tantalate dispersion for dielectric layers.

[0048] The method for measuring the ammonia content present in the lithium tantalate dispersion for dielectric layers of the present invention is the same as the method for measuring the ammonia content present in the lithium niobate dispersion for dielectric layers of the present invention described above.

[0049] The ammonia content in the lithium tantalate dispersion for the dielectric layer of the present invention may be any amount. For example, the ammonia content may be greater than 0% by mass and 10% by mass or less, 0.001% by mass or more and 10% by mass or less, or 0.003% by mass or more and 5% by mass or less.

[0050] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized by further containing a surfactant. In addition to the water and organic solvents mentioned above, various surfactants may be added to the lithium metal oxide dispersion for dielectric layers of the present invention. Examples include nonionic surfactants, anionic surfactants, cationic surfactants, and the like.

[0051] Examples of nonionic surfactants include ester / ether type, ester type, ether type, polyvinylpyrrolidone, and amine oxide. Examples of ester / ether type, ester type, and ether type include polyoxyethylene glycol type (EO type), polyoxypropylene glycol type (PO type), and polyoxyalkylene type (AO type), which are obtained by adding one or more selected from polyoxyethylene glycol (EO), polyoxypropylene glycol (PO), and polyoxyalkylene (AO) to an alcohol or carboxylic acid.

[0052] Examples of anionic surfactants include carboxylates, sulfonates, phosphate esters, sulfate esters, and anionic fluorinated surfactants.

[0053] Examples of cationic surfactants include aliphatic amine salts, aliphatic quaternary ammonium salts, aromatic quaternary ammonium salts, heterocyclic quaternary ammonium salts, and fluorine-based surfactants.

[0054] Other examples include amphoteric fluorinated surfactants (boiling point: 180°C or higher).

[0055] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized by further containing an alcohol solvent. The lithium metal oxide dispersion for dielectric layers of the present invention may contain an alcohol solvent. Here, the alcohol solvent may be a monohydric alcohol, a dihydric alcohol, or a polyhydric alcohol with a valency of three or higher. Also, the alcohol solvent may be a primary alcohol, a secondary alcohol, or a tertiary alcohol. For example, it is preferable that it contains one or more selected from methanol, ethanol, propanol, 1-propanol, 2-propanol, butanol, 1-butanol, 2-butanol, tert-butanol, pentanol, 1-pentanol, hexanol, 1-hexanol, heptanol, 1-heptanol, octanol, 1-octanol, dodecanol, 1-dodecanol, tetradecanol, 1-tetradecanol, hexadecanol, 1-hexadecanol, stearyl alcohol, 1-stearyl alcohol, oleyl alcohol, 1-oleyl alcohol, ethylene glycol, propylene glycol, and glycerin.

[0056] Furthermore, if the alcohol solvent contains one or more selected from methanol, ethanol, 1-propanol, 2-propanol, and ethylene glycol, it is more preferable because it has a lower surface tension and higher wettability to the substrate than water. Moreover, if the alcohol solvent is methanol, ethanol, or 2-propanol, it is even more preferable because it has a lower boiling point than water and exhibits superior drying properties and volatility.

[0057] Furthermore, the alcohol solvent may be acetone or a high-boiling point solvent. Examples of high-boiling point solvents include polyhydric alcohol solvents and glycol solvents. Examples of polyhydric alcohol solvents include glycerin (boiling point: 290°C), 1,6-hexanediol (boiling point: 250°C), and 1,7-heptanediol (boiling point: 259°C). Glycol-based solvents include ethylene glycol (boiling point: 197.3°C), propylene glycol (boiling point: 188.2°C), diethylene glycol (boiling point: 244.3°C), triethylene glycol (boiling point: 287.4°C), oligoethylene glycol (boiling point: 287°C to 460°C), polyethylene glycol (PEG) (boiling point: 460°C or higher), polyethylene glycol (PEG)-polypropylene glycol (PPG) copolymer (boiling point: 460°C or higher), diethylene glycol monohexyl ether (boiling point: 260°C), polyoxyalkylene monoalkyl ether (boiling point: 260°C or higher), polyoxyethylene sorbitan monolaurate (boiling point: 321°C or higher), other anionic fluorinated surfactants (boiling point: 180°C or higher), amphoteric fluorinated surfactants (boiling point: 180°C or higher), nonionic fluorinated surfactants (boiling point: 180°C or higher), and amine oxides (boiling point: 180°C or higher). The boiling points mentioned above are those at 1 atmosphere of pressure.

[0058] Furthermore, the solvent of the lithium metal oxide dispersion for dielectric layers of the present invention described above may contain a binder such as a resin component. If the solvent of the lithium metal oxide dispersion for dielectric layers of the present invention contains a binder such as a resin component, the film-forming properties of the film formed using the lithium metal oxide dispersion for dielectric layers of the present invention can be improved. Examples of resin components that can be used as a binder include acrylic resins, polyurethanes, epoxy resins, polystyrenes, polycarbonates, glycol-based resins, cellulose-based resins, and mixed resins and copolymer resins thereof.

[0059] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is characterized by not containing hydrogen peroxide. In general, when niobium oxide is present as polyoxide ions in the lithium metal oxide dispersion for dielectric layers of the present invention, hydrogen peroxide is added to suppress decomposition by reaction with hydroxide ions and improve stability. However, the lithium niobate dispersion for dielectric layers of the present invention can ensure long-term stability even in the absence of hydrogen peroxide because ammonia is present in the lithium niobate dispersion for dielectric layers.

[0060] A method for detecting hydrogen peroxide in a lithium niobate dispersion for dielectric layers can be used, for example, by measuring the relative intensity of absorbance with a standard solution of hydrogen peroxide using the standard addition method. This allows for confirmation that the lithium niobate dispersion for dielectric layers does not contain hydrogen peroxide. Specifically, by examining the ultraviolet-visible absorption spectra of a standard solution containing a known content, e.g., 1% by mass of hydrogen peroxide, and a standard solution without added hydrogen peroxide, a wavelength region in which a change in absorbance associated with peroxo complex formation is observed can be identified. If the difference in absorbance between the standard solution without added hydrogen peroxide and a sample with an unknown hydrogen peroxide content in that wavelength region is less than 1%, it can be confirmed that the sample with an unknown hydrogen peroxide content substantially does not contain hydrogen peroxide. When hydrogen peroxide is present in a lithium niobate dispersion for dielectric layers, it reacts with the polyacid of niobium to form a peroxo complex. Therefore, by checking the difference in absorbance with a standard solution without added hydrogen peroxide, as described above, it can be confirmed that the lithium niobate dispersion for dielectric layers does not contain hydrogen peroxide. In addition to the standard addition method described above, qualitative and quantitative analysis of hydrogen peroxide in the lithium niobate dispersion for dielectric layers may also be performed by, for example, using a commercially available hydrogen peroxide measurement kit to add a reagent that reacts with hydrogen peroxide to the lithium niobate dispersion for dielectric layers and measuring the resulting color change, or by adding a reagent that reacts with hydrogen peroxide to the lithium niobate dispersion for dielectric layers and measuring the resulting luminescence.

[0061] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention is a lithium tantalate dispersion for dielectric layers, and if it is an aqueous dispersion, it is preferable that it does not contain organic acids. The lithium metal oxide dispersion for dielectric layers of the present invention is a lithium tantalate dispersion for dielectric layers, and if it is an aqueous dispersion, the absence of organic acids stabilizes the polyacid ions contained in the lithium tantalate dispersion for dielectric layers. In this specification, "aqueous dispersion" may refer to a mixed solvent in which water is the main component. Furthermore, in this specification, "main component" refers to the component that accounts for the highest proportion in the mixed solvent.

[0062] Furthermore, if the lithium metal oxide dispersion for dielectric layers of the present invention has an alcohol solvent as its main component, it may contain an organic acid, regardless of whether it is a lithium niobate dispersion for dielectric layers or a lithium tantalate dispersion for dielectric layers.

[0063] Examples of organic acids include carboxylic acids. Examples of carboxylic acids include saturated fatty acids, unsaturated fatty acids, hydroxy acids, aromatic carboxylic acids, dicarboxylic acids, tricarboxylic acids, oxocarboxylic acids, and carboxylic acid derivatives. Examples of saturated fatty acids include formic acid, acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, enanthic acid, caprylic acid, pelargonic acid, capric acid, lauric acid, myristic acid, palmitic acid, margaric acid, and stearic acid. Examples of unsaturated fatty acids include oleic acid, linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid, and sorbic acid. Examples of hydroxy acids include lactic acid, malic acid, citric acid, tartaric acid, glycolic acid, hydroxybutyric acid, and glyceric acid. Examples of aromatic carboxylic acids include benzoic acid, phthalic acid, isophthalic acid, terephthalic acid, salicylic acid, gallic acid, melitic acid, and cinnamic acid. Examples of dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, fumaric acid, and maleic acid. Examples of tricarboxylic acids include aconic acid. Examples of oxocarboxylic acids include pyruvate and oxaloacetate. Examples of carboxylic acid derivatives include amino acids and nitrocarboxylic acids. Examples of amino acids include alanine, arginine, and aspartic acid. Other examples of carboxylic acids include ethylenediaminetetraacetic acid. Alkali metal salts or alkaline earth metal salts of the organic acid may also be used. For example, sodium ethylenediaminetetraacetate and disodium ethylenediaminetetraacetate may be used.

[0064] Furthermore, it is preferable that the organic acid contains one or more selected from carboxylic acids, saturated fatty acids, citric acid, lactic acid, acetic acid, and their salts. Organic acids that do not contain nitrogen atoms are preferred, for example, carboxylic acids and saturated fatty acids are preferred, and it is more preferable that the organic acid contains one or more selected from citric acid, lactic acid, acetic acid, and their salts. The organic acid also includes various isomers (structural isomers, optical isomers, etc.) of the compounds described above. Furthermore, the organic acid may be one or more organic acids of the compounds described above.

[0065] Furthermore, among the lithium metal oxide dispersions for dielectric layers of the present invention, the lithium niobate dispersion for dielectric layers preferably has a pH of 9 or higher. A pH of 9 or higher for the lithium niobate dispersion for dielectric layers of the present invention is preferable because it stabilizes the polyacid ions contained in the lithium niobate dispersion for dielectric layers. Moreover, a pH of 10 or higher for the lithium niobate dispersion for dielectric layers of the present invention is more preferable, and 10.5 or higher is even more preferable. Furthermore, the pH of the lithium niobate dispersion for dielectric layers of the present invention may be 11 or higher, or 12 or higher.

[0066] Furthermore, among the lithium metal oxide dispersions for dielectric layers of the present invention, the lithium tantalate dispersion for dielectric layers of the present invention preferably has a pH greater than 7. A pH greater than 7 for the lithium tantalate dispersion for dielectric layers of the present invention is preferable because it stabilizes the polyacid ions contained in the lithium tantalate dispersion for dielectric layers. Moreover, a pH of 8 or higher is more preferable, 9 or higher is even more preferable, 10 or higher is particularly preferable, 11 or higher is particularly preferable, and it may also be 12 or higher. It is also preferable that the lithium tantalate dispersion for dielectric layers of the present invention does not contain organic acids, as the presence of organic acids lowers the pH.

[0067] Furthermore, unless otherwise specified in this specification, "pH" includes both the "initial pH" of the lithium metal oxide dispersion for dielectric layers of the present invention adjusted to a liquid temperature of 25°C immediately after production, and the "time-dependent pH" of the lithium metal oxide dispersion for dielectric layers of the present invention after being left to stand for one month from the day it was produced in a constant temperature oven set to room temperature of 25°C. In addition, if the time-dependent fluctuation range between the "initial pH" and the "time-dependent pH" of the lithium metal oxide dispersion for dielectric layers of the present invention is small, it can be inferred that the time-dependent fluctuation range of the pH of the lithium metal oxide dispersion for dielectric layers of the present invention after being left to stand for more than one month from the day it was produced will also be small.

[0068] Here, the pH of the lithium metal oxide dispersion for dielectric layers of the present invention is measured by immersing the electrode (HORIBA Standard ToupH Electrode 9615S-10D) of a pH meter (HORIBA Glass Electrode Type Hydrogen Ion Concentration Indicator D-51) in the lithium metal oxide dispersion for dielectric layers of the present invention, and after confirming that the liquid temperature has stabilized at 25°C, the measurement is performed.

[0069] In this invention, the term "dispersion" is not limited to a solute dispersed or mixed in a solvent as a single molecule, but also includes aggregates of multiple molecules attracted by intermolecular interactions, such as (1) polymer molecules, (2) solvated molecules, and (3) molecular clusters dispersed in a solvent. In this invention, it is preferable that the "dispersion" does not include sols containing colloidal particles exhibiting the Tyndall effect, as well as emulsions, gels, foams, suspensions, or other dispersion systems in which the optical path is visualized by light scattering.

[0070] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention may contain compounds such as Na, Mg, Al, Si, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Hf, Ta, Mo, Sn, Ba, La, Y, and W as additives. Here, examples of compounds include oxides, alkali metal salts of metal oxides, alkaline earth metal salts of metal oxides, chlorides, alkoxides of metal oxides, and polyoxometalates. In addition, when the total number of moles of each element that is an additive is X, the molar ratio X / Nb or X / Ta of the total number of moles of each element that is an additive to the number of moles of niobium (Nb) or the number of moles of tantalum (Ta) is preferably 0.0002 to 0.8. Furthermore, the molar ratio X / Nb or X / Ta may be 0.001 to 0.5, 0.001 to 0.4, or 0.001 to 0.01. Moreover, since the lithium metal oxide dispersion for dielectric layers of the present invention is a homogeneous dispersion, even if these compounds are in a suspended state, improved uniformity and reactivity (reaction rate) can be expected. In addition, when these compounds dissolve in the lithium metal oxide dispersion for dielectric layers of the present invention and become a homogeneous dispersion, the composite elements can be brought into the most reactive state.

[0071] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention may contain components other than those derived from lithium niobate (or lithium tantalate) and ammonia ("other components"), to the extent that they do not impair its effects. Examples of other components include Na, Mg, Al, Si, K, Ca, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Sr, Zr, Hf, Ta (or Nb), Mo, Sn, Ba, La, Y, and W. However, it is not limited to these. When the lithium metal oxide dispersion for dielectric layers of the present invention is considered to be 100% by mass, the content of other components is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. It should be noted that the lithium metal oxide dispersion for dielectric layers of the present invention is expected to contain unintended, unavoidable impurities. The content of unavoidable impurities is preferably 0.01% by mass or less.

[0072] The method for producing the lithium niobate dispersion for dielectric layers, which is one of the lithium metal oxide dispersions for dielectric layers of the present invention described above, will be explained below.

[0073] The present invention provides a method for producing a lithium niobate dispersion for dielectric layers, comprising the steps of: generating an acidic niobium solution containing niobium; obtaining a precipitated slurry containing niobium by a reverse neutralization method in which the acidic niobium solution is added to aqueous ammonia; and obtaining a lithium niobate dispersion for dielectric layers by mixing the obtained precipitated slurry containing niobium with lithium hydroxide and pure water, and maintaining the mixture at 20°C to 100°C while stirring.

[0074] First, in the step of producing an acidic niobium solution containing niobium, the acidic niobium solution refers to an acidic niobium solution containing fluoride ions obtained by solvent extraction of a solution obtained by dissolving niobium in an acidic solution containing hydrofluoric acid. Unless otherwise specified, the niobium referred to in this specification includes niobic acid compounds.

[0075] Here, an acidic niobium solution containing fluoride ions, such as an aqueous solution of niobium fluoride, is converted to Nb by adding water (e.g., pure water). ２ O５ It is preferable to prepare it so that it contains 1 to 100 g / L in conversion. In this case, the niobium content is Nb ２ O ５ A concentration of 1 g / L or more is preferable because it results in a water-soluble niobium compound hydrate, and from a productivity standpoint, 10 g / L or more is more preferable, and 20 g / L or more is even more preferable. On the other hand, if the niobium content is Nb ２ O ５ A concentration of 100 g / L or less is preferable because it results in a water-soluble niobium compound hydrate. To more reliably synthesize a water-soluble niobium compound hydrate, a concentration of 90 g / L or less is preferable, even preferable to 80 g / L or less, and particularly preferable to 70 g / L or less. The pH of the niobium fluoride aqueous solution is preferably 2 or less, and more preferably 1 or less, from the viewpoint of completely dissolving niobium or niobium oxide.

[0076] Next, in the step of obtaining a precipitate slurry containing niobium by a reverse neutralization method in which the acidic niobium solution is added to ammonia water (hereinafter referred to as the reverse neutralization step), it is preferable to obtain a precipitate slurry containing niobium by adding an acidic niobium solution containing fluoride ions to ammonia water of a predetermined content, i.e., by a reverse neutralization method.

[0077] The ammonia content of the ammonia solution used for reverse neutralization is preferably 10% to 30% by mass. When the ammonia content is 10% by mass or more, niobium is less likely to remain undissolved, and niobium or niobic acid can be completely dissolved in water. On the other hand, when the ammonia content is 30% by mass or less, it is preferable because it is close to a saturated aqueous solution of ammonia.

[0078] From this viewpoint, the ammonia content of aqueous ammonia is preferably 10% by mass or more, more preferably 15% by mass or more, even more preferably 20% by mass or more, and particularly preferably 25% by mass or more. On the other hand, the ammonia content is preferably 30% by mass or less, more preferably 29% by mass or less, and even more preferably 28% by mass or less.

[0079] During the reverse neutralization process, the amount of niobium fluoride aqueous solution added to the ammonia water is NH ３ / Nb ２ O ５ The molar ratio of is preferably 95 to 500, more preferably 100 to 450, and even more preferably 110 to 400. Furthermore, the amount of niobium fluoride aqueous solution added to the ammonia water is determined from the viewpoint of generating amines and niobium acid compounds that dissolve in dilute ammonia water, NH ３ The molar ratio of HF is preferably 3.0 or higher, more preferably 4.0 or higher, and even more preferably 5.0 or higher. On the other hand, from the viewpoint of cost reduction, NH ３ The molar ratio of HF is preferably 100 or less, more preferably 50 or more, and even more preferably 40 or more.

[0080] In the reverse neutralization step, the time required for adding the niobium fluoride aqueous solution to the ammonia water is preferably within 1 minute, more preferably within 30 seconds, and even more preferably within 10 seconds. In other words, rather than gradually adding the niobium fluoride aqueous solution over time, it is preferable to add it to the ammonia water in the shortest possible time, for example, by adding it all at once, to allow the neutralization reaction to occur. Furthermore, since the acidic niobium fluoride aqueous solution is added to the alkaline ammonia water in the reverse neutralization step, the neutralization reaction can be carried out while maintaining a high pH. Note that the niobium fluoride aqueous solution and ammonia water can be used at room temperature.

[0081] Furthermore, the present invention provides a method for producing a lithium niobate dispersion for dielectric layers, which includes a step of removing fluoride ions from a niobium-containing precipitate slurry obtained by a reverse neutralization method to obtain a niobium-containing precipitate from which fluoride ions have been removed. Since the niobium-containing precipitate slurry obtained by the reverse neutralization method contains fluorine compounds such as ammonium fluoride as impurities, it is preferable to remove these.

[0082] The method for removing fluorine compounds is arbitrary, but methods such as reverse osmosis filtration using ammonia water or pure water, ultrafiltration, microfiltration using membranes, centrifugation, and other known methods can be employed. When removing fluoride ions from a precipitate slurry containing niobium, temperature control is not particularly necessary, and the process may be carried out at room temperature.

[0083] Specifically, a niobium-containing precipitate slurry obtained by the reverse neutralization method is decanted using a centrifuge, and the washing process is repeated until the amount of free fluoride ions is 100 mg / L or less, thereby obtaining a niobium-containing precipitate from which fluoride ions have been removed.

[0084] The washing solution used to remove fluoride ions is preferably ammonia water. Specifically, ammonia water with a concentration of 5.0% by mass or less is preferred, 4.0% by mass or less is more preferred, 3.0% by mass or less is even more preferred, and 2.5% by mass is particularly preferred. When ammonia water with a concentration of 5.0% by mass or less is used, the ammonia containing ammonium ions is appropriate for fluoride ions, and unnecessary cost increases can be avoided.

[0085] In this way, by diluting the niobium-containing precipitate from which fluoride ions have been removed with pure water, a niobium-containing precipitate slurry from which fluoride ions have been removed is obtained. The niobium content of the niobium-containing precipitate slurry is determined by taking a sample of the slurry, drying it at 110°C for 24 hours, and then calcining it at 1,000°C for 4 hours, and then testing the Nb ２ O ５ This generates Nb. ２ O ５ The weight of the slurry can be measured, and the niobium content can be calculated from that weight.

[0086] Then, by stirring and maintaining a mixture of the niobium-containing precipitate slurry from which fluoride ions have been removed and lithium hydroxide monohydrate at 20°C to 100°C, the lithium niobate dispersion for dielectric layers of the present invention is obtained.

[0087] Specifically, the niobium content of the final mixture is Nb ２ O ５ A translucent white slurry is obtained by mixing the niobium-containing precipitate slurry obtained in an amount of 0.1 to 30% by mass and a lithium-to-niobium molar ratio Li / Nb of 0.01 to 20 with lithium hydroxide monohydrate. A colorless and transparent lithium niobate dispersion for dielectric layers of the present invention is obtained by stirring the translucent white slurry and maintaining the liquid temperature at 50°C to 100°C (for example, 70°C) for 1 to 24 hours. Furthermore, in order to remove the ammonia component contained in the obtained lithium niobate dispersion for dielectric layers of the present invention, the following concentration adjustment steps may be performed. In the concentration adjustment step, for example, the mixture is heated and stirred for 1 to 100 hours at 60°C to 90°C while adding solvent (pure water, etc.) to compensate for evaporation, and then cooled to room temperature. Alternatively, the mixture is heated and stirred at 60°C to 90°C for 1 to 100 hours, and then cooled to room temperature. After that, solvent (pure water, etc.) is added to replenish the evaporated solvent (pure water, etc.). The amount of solvent added is adjusted so that the niobium content of the lithium niobate dispersion for the dielectric layer after the ammonia component has been removed matches the niobium content of the lithium niobate dispersion for the dielectric layer before the ammonia component has been removed.

[0088] Alternatively, pure water or an alkaline aqueous solution, such as aqueous ammonia, may be added to a mixture of the niobium-containing precipitate slurry and lithium hydroxide monohydrate and mixed. The ammonia content of the aqueous ammonia added to the mixture can be any amount. For example, it may be 0.1% by mass or more and 30% by mass or 10% by mass or more and 25% by mass or less.

[0089] When the lithium niobate dispersion for dielectric layers of the present invention is obtained by the manufacturing method described above, it is preferable that the pH of the lithium niobate dispersion for dielectric layers is 9 or higher, as this ensures stability. Furthermore, it is more preferable that the pH of the lithium niobate dispersion for dielectric layers of the present invention is 10 or higher, and even more preferable that it is 10.5 or higher. In addition, the pH of the lithium niobate dispersion for dielectric layers of the present invention may be 11 or higher, or 12 or higher.

[0090] Next, the method for producing the lithium tantalate dispersion for dielectric layers, which is one of the lithium metal oxide dispersions for dielectric layers of the present invention described above, will be explained below.

[0091] The present invention provides a method for producing a lithium tantalate dispersion for dielectric layers, comprising a reaction step of adding hydrogen peroxide to an aqueous solution of tantalum fluoride to produce an aqueous solution of a tantalum compound, and a reverse neutralization step of adding the aqueous solution of the tantalum compound to an alkaline aqueous solution to produce a tantalum-containing precipitate.

[0092] First, an aqueous solution of tantalum fluoride is produced by reacting tantalum, tantalum oxide, or tantalum hydroxide with hydrofluoric acid (HF), such as an aqueous solution of hydrofluoric acid, to produce tantalum fluoride (H ２ TaF ７ ) and this can be prepared by dissolving it in water.

[0093] Here, an acidic tantalum solution containing fluoride ions, such as an aqueous solution of tantalum fluoride, is prepared by adding water (e.g., pure water) to the tantalum. ２ O ５ It is preferable to prepare it so that it contains 1 to 100 g / L in conversion. In this case, the tantalum concentration is Ta ２ O ５ A concentration of 1 g / L or more is preferable because it results in a water-soluble tantalate compound hydrate, and from a productivity standpoint, 10 g / L or more is more preferable, and 20 g / L or more is even more preferable. On the other hand, if the tantalum concentration is Ta ２ O ５ A concentration of 100 g / L or less is preferable because it results in a tantalum acid compound hydrate that is easily soluble in water. To more reliably synthesize a tantalum acid compound hydrate that is easily soluble in water, a concentration of 90 g / L or less is preferable, even preferable to 80 g / L or less, and particularly preferable to 70 g / L or less. The pH of the aqueous solution of tantalum fluoride is preferably 2 or less, and more preferably 1 or less, from the viewpoint of completely dissolving tantalum or tantalum oxide.

[0094] Next, in the reaction step of adding hydrogen peroxide to an aqueous tantalum fluoride solution to produce an aqueous tantalum compound solution, an aqueous tantalum compound solution is obtained by adding aqueous hydrogen peroxide to the aqueous tantalum fluoride solution and mixing them. It is presumed that at least a part of the obtained aqueous tantalum compound solution forms a peroxo complex.

[0095] Here, the hydrogen peroxide content of the aqueous hydrogen peroxide added to the aqueous tantalum fluoride solution is preferably 0.5% by mass to 35% by mass. Further, hydrogen peroxide has a molar ratio of hydrogen peroxide to tantalum H ２ O ２ / Ta is preferably added so as to be 0.6 or more and 1.5 or less, and since hydrogen peroxide may decompose during mixing, it is more preferably 0.7 or more and 1.2 or less.

[0096] In the reverse neutralization step of adding the obtained aqueous tantalum compound solution to an alkaline aqueous solution to produce a tantalic acid-containing precipitate, a tantalum-containing precipitation slurry is obtained by adding the aqueous tantalum compound solution to an alkaline aqueous solution, for example, aqueous ammonia, that is, by a reverse neutralization method. Then, by removing fluoride ions from the obtained tantalum-containing precipitation slurry, a tantalum-containing precipitate from which fluoride ions have been removed is obtained.

[0097] The ammonia content of the aqueous ammonia used for reverse neutralization is preferably 10% by mass to 30% by mass. When the ammonia content is 10% by mass or more, tantalum is less likely to remain undissolved, and tantalum or tantalic acid can be completely dissolved in water. On the other hand, when the ammonia content is 30% by mass or less, it is preferable because the solution is near a saturated aqueous solution of ammonia.

[0098] From this point of view, the ammonia content of the aqueous ammonia is preferably 10% by mass or more, more preferably 15% by mass or more, still more preferably 20% by mass or more, and particularly preferably 25% by mass or more. On the other hand, the ammonia content is preferably 30% by mass or less, more preferably 29% by mass or less, and still more preferably 28% by mass or less.

[0099] During the reverse neutralization process, the amount of tantalum fluoride aqueous solution added to the ammonia water is NH ３ The molar ratio of / Ta is preferably 95 to 500, more preferably 100 to 450, and even more preferably 110 to 400. Furthermore, the amount of aqueous tantalum fluoride solution added to the aqueous ammonia is determined from the viewpoint of generating amines and tantalum acid compounds that dissolve in dilute aqueous ammonia, NH ３ The molar ratio of HF is preferably 3.0 or higher, more preferably 4.0 or higher, and even more preferably 5.0 or higher. On the other hand, from the viewpoint of cost reduction, NH ３ The molar ratio of HF is preferably 100 or less, more preferably 50 or less, and even more preferably 40 or less.

[0100] In the reverse neutralization step, the time required for adding the tantalum fluoride aqueous solution to the ammonia water is preferably within 10 minutes, more preferably within 8 minutes, and even more preferably within 5 minutes. That is, rather than gradually adding the tantalum fluoride aqueous solution over time, it is preferable to add it to the ammonia water in the shortest possible time, for example, by adding it all at once, to allow the neutralization reaction to occur. Furthermore, since the acidic tantalum fluoride aqueous solution is added to the alkaline ammonia water in the reverse neutralization step, the neutralization reaction can be carried out while maintaining a high pH. Note that the tantalum fluoride aqueous solution and the ammonia water can be used at room temperature.

[0101] Then, in the reverse neutralization step, fluoride ions are removed from the tantalum-containing precipitate slurry obtained by the reverse neutralization method, thereby obtaining a tantalum-containing precipitate from which fluoride ions have been removed. Since the tantalum-containing precipitate slurry obtained by the reverse neutralization method contains fluorine compounds such as ammonium fluoride as impurities, it is preferable to remove these.

[0102] The method for removing fluorine compounds is arbitrary, but methods such as reverse osmosis filtration using ammonia water or pure water, ultrafiltration, microfiltration using membranes, centrifugation, and other known methods can be employed. Furthermore, when removing fluoride ions from a precipitate slurry containing tantalum, temperature control is not particularly necessary, and the process can be carried out at room temperature.

[0103] Specifically, the tantalum-containing precipitate slurry obtained by the reverse neutralization method is decanted using a centrifuge, and the washing is repeated until the amount of free fluoride ions is 100 mg / L or less, thereby obtaining a tantalum-containing precipitate from which fluoride ions have been removed. In addition, by repeating this washing, the hydrogen peroxide added in the reaction step is also removed.

[0104] The cleaning solution used to remove fluoride ions is preferably ammonia water. Specifically, ammonia water containing 1% to 35% by mass is preferred. With such ammonia water, the ammonia is appropriate for fluoride ions and unnecessary cost increases can be avoided.

[0105] Furthermore, the present invention provides a method for producing a lithium tantalate dispersion for dielectric layers, comprising the reaction step and the reverse neutralization step described above, followed by a step of mixing the resulting tantalate-containing precipitate with lithium hydroxide.

[0106] Through the above reaction step and reverse neutralization step, the generated tantalum-containing precipitate from which fluoride ions have been removed is diluted with pure water or the like, whereby a tantalum-containing precipitation slurry from which fluoride ions have been removed is obtained. Then, a mixture obtained by mixing the tantalum-containing precipitation slurry from which fluoride ions have been removed, for example, lithium hydroxide monohydrate, and pure water is maintained at 5°C to 100°C for 0.1 hours to 72 hours while being stirred, whereby the lithium tantalate dispersion for a dielectric layer of the present invention is obtained. Furthermore, in order to remove ammonia components contained in the obtained lithium tantalate dispersion for a dielectric layer of the present invention, the following concentration adjustment step may be performed. In the concentration adjustment step, for example, after heating and stirring at 60°C to 90°C for 1 hour to 100 hours, the mixture is cooled to room temperature. Thereafter, a solvent (pure water or the like) is added to replenish the evaporated solvent (pure water or the like). The addition amount of the solvent is adjusted such that the tantalum content of the lithium tantalate dispersion for a dielectric layer after removing the ammonia component matches the tantalum content of the lithium tantalate dispersion for a dielectric layer before removing the ammonia component.

[0107] Specifically, the tantalum content in the final mixture is expressed as Ta ２ O ５ By mixing the obtained tantalum-containing precipitation slurry, lithium hydroxide monohydrate, and pure water and stirring the mixture such that the content is 0.1 mass% or more and 15 mass% or less in terms of O, and the molar ratio Li / Ta of lithium to tantalum is 0.01 or more and 20 or less, the lithium tantalate dispersion for a dielectric layer of the present invention is obtained.

[0108] Said dielectric layer formed using the above-described lithium metal oxide dispersion for a dielectric layer of the present invention is formed on a buffer film formed on a substrate, and is laminated to form a dielectric film. The substrate is a Si substrate, or an SOI substrate comprising a base body formed of a Si substrate, an insulating layer on said base body, and an SOI layer formed of a Si film on said insulating layer. Said buffer film comprises a first metal oxide represented by the following compositional formula (1): (Hf １－ｘ Zr ｘ )xO ２ ...(1) wherein x preferably satisfies 0≦x<1 or x=1. Details will be described later.

[0109] A laminated structure having a dielectric layer formed by a wet method using the lithium metal oxide dispersion for dielectric layers of the present invention described above will be explained below.

[0110] The present invention relates to a laminated structure comprising a substrate, a buffer film formed on the substrate, and a dielectric film formed on the buffer film, wherein the buffer film contains a first metal oxide represented by the following compositional formula (1): (Hf １－ｘ Zr ｘ ) O ２ ... (1) The x satisfies 0 ≤ x < 1 or x = 1, the dielectric film includes stacked dielectric layers, and each layer of the dielectric layer is formed using the lithium metal oxide dispersion for dielectric layers of the present invention described above.

[0111] The laminated structure of the present invention will be described below with reference to Figures 1 to 5. Figure 1 is a cross-sectional view showing an example of a laminated structure according to an embodiment of the present invention. Figure 2 is a cross-sectional view showing another example of a laminated structure according to an embodiment of the present invention. Figure 3 shows LiNbO contained in the dielectric layer of the laminated structure according to an embodiment of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. Figure 4 shows LiNbO contained in the dielectric layer of the laminated structure according to an embodiment of the present invention. ３ Figure 5 is a schematic side view showing the orientation state of the crystal lattice. Figure 5 shows LiNbO having an ilmenite-type structure and (01-12) orientation included in the dielectric layer of an embodiment of the present invention. ３ This is a diagram showing the crystal structure.

[0112] The laminated structure 10 of the present invention shown in Figures 1 and 2 comprises a substrate 11 including a main surface 11p, a buffer film 12 formed on the main surface 11p, and a dielectric film 15 formed on the buffer film 12.

[0113] The substrate 11 is a Si substrate, or an SOI substrate comprising a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer.

[0114] The substrate 11 shown in Figure 1 is a Si (silicon) (111) substrate with the Si (111) surface as the main surface 11p. On the other hand, the substrate 11 shown in Figure 2 is an SOI (111) substrate that includes a base body 11a made of a Si substrate, an insulating layer 11b on the base body 11a, and an SOI (Silicon On Insulator) (111) layer (SOI layer 11c) made of a Si (111) film on the insulating layer 11b with the Si (111) surface as the main surface 11p.

[0115] The buffer film 12 is epitaxially grown on the main surface 11p, is (111) oriented in pseudocubic crystal representation, and contains the first metal oxide represented by the above compositional formula (1).

[0116] Here, among the first metal oxides represented by the above compositional formula (1), if x = 0, then HfO ２ And when x = 1, ZrO ２ However, the case where 0 < x < 1 is satisfied will be referred to as HZO below.

[0117] In this specification, when we say that the first metal oxide is (111) oriented in pseudocubic representation, we mean that the first metal oxide has a cubic crystal structure at room temperature and is (111) oriented in pseudocubic representation, or that even if it has a tetragonal or monoclinic crystal structure at room temperature, it undergoes a phase transition at high temperatures to have a cubic crystal structure and is (111) oriented in pseudocubic representation.

[0118] Furthermore, in this specification, if a film is said to be epitaxially grown, it means that the film is oriented in any of the three mutually orthogonal directions, that is, oriented in three dimensions.

[0119] The dielectric film 15 includes stacked dielectric layers 15a, and each layer of the dielectric layer 15a is formed using the lithium metal oxide dispersion for dielectric layers of the present invention. The dielectric film 15 may also include five or more dielectric layers 15a, or it may include ten or more dielectric layers 15a.

[0120] When each layer of the dielectric layer 15a is formed by spin-coating (applying) the lithium metal oxide dispersion for dielectric layers of the present invention onto a substrate, a different composition or bubbles exist at the boundaries between adjacent layers. Therefore, in images obtained by observing a cross-section using FIB-SEM (Focused Ion Beam - Scanning Electron Microscope) or STEM (Scanning Transmission Electron Microscope), the boundaries between layers can be detected by observing the periodic change in contrast corresponding to the layers and boundaries. Alternatively, the boundaries between layers can be detected by performing compositional analysis while etching in the depth direction, observing the periodic change in composition.

[0121] Furthermore, in the laminated structure of the present invention, each layer of the dielectric layer has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ It is characterized by containing a secondary metal oxide.

[0122] Furthermore, in the laminated structure of the present invention, each layer of the dielectric layer is epitaxially grown LiNbO on the buffer film. ３ , or LiTaO ３ It is characterized by containing a secondary metal oxide.

[0123] As shown in Figures 3 and 4, each layer of the dielectric layer 15a is preferably oriented such that the (0001) plane of the second metal oxide is tilted with respect to the main plane 11p by a predetermined angle, for example, a first angle θ11, and includes a first domain DM1, a second domain DM2, a third domain DM3, a fourth domain DM4, a fifth domain DM5, and a sixth domain DM6, in which the

[0001] axes of the second metal oxide are oriented in different directions. Note that in Figures 3 and 4, for the sake of simplicity, LiNbO is represented by a hexagonal crystal lattice instead of a trigonal crystal lattice. ３ The crystal lattice is further shown as a quadrangular prism. Also, for ease of understanding, the (0001) plane is hatched in Figure 3, and the second domain DM2 and the fourth domain DM4 are omitted from the illustration in Figure 4.

[0124] The second metal oxide is LiNbO ３ In this case, the first angle θ11 can be, for example, 52.24° to 70°, and can be, for example, 57.24°. On the other hand, if the second metal oxide is LiTaO ３ In this case, the first angle θ11 can be, for example, 52.02° to 75°, or for example, 57.02°.

[0125] Here, the second metal oxide is LiNbO ３ , or LiTaO ３ In this case, when the

[0001] direction of the second metal oxide in the first domain DM1 is defined as the first

[0001] direction, the

[0001] direction of the second metal oxide in the second domain DM2 is the direction rotated 60° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0126] Furthermore, the

[0001] direction of the second metal oxide in the third domain DM3 is a direction rotated 120° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0127] Furthermore, the

[0001] direction of the second metal oxide in the fourth domain DM4 is a direction rotated 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0128] Furthermore, the

[0001] direction of the second metal oxide in the fifth domain DM5 is a direction rotated 240° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0129] Furthermore, the

[0001] direction of the second metal oxide in the sixth domain is a direction rotated 300° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface (around the normal direction of the main surface 11p).

[0130] Furthermore, the orientation of the first domain DM1, second domain DM2, third domain DM3, fourth domain DM4, fifth domain DM5, and sixth domain DM6 contained in each layer of the dielectric layer 15a is substantially the same in each layer.

[0131] Furthermore, the dielectric film 15 may include 10 or more stacked dielectric layers 15a. For dielectric films 15 including such dielectric layers 15a, instead of a film deposition method in which the dielectric film 15 is deposited under a vacuum atmosphere in a deposition chamber equipped with a vacuum evacuation system, such as a sputtering method, a film deposition method in which the dielectric film 15 is deposited under atmospheric pressure, such as a wet method, can be used. As a result, the dielectric film 15 can be easily deposited on a large substrate with a large surface area, and the manufacturing cost of the laminated structure can be reduced.

[0132] Furthermore, the dielectric film 15 includes five or more stacked dielectric layers 15a, and each layer of the dielectric layer 15a is oriented in a certain direction. ３ , or LiTaO ３ Any substrate containing a second metal oxide is acceptable, and the substrate 11 does not have to be a Si(111) substrate with a Si(111) surface as the main surface, or an SOI(111) substrate containing an SOI(111) layer with a Si(111) surface as the main surface.

[0133] Thus, the lithium metal oxide dispersion for dielectric layers of the present invention is a (01-12) oriented LiNbO on a single crystal Si(111) substrate or an SOI(111) substrate. ３ , or LiTaO ３ A dielectric film 15 can be epitaxially grown from this material. Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention can be used to grow (01-12) oriented LiNbO on a single crystal Si(100) substrate or an SOI(100) substrate. ３ , or LiTaO ３ A dielectric film 15 can also be epitaxially grown. Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention can be used on a single crystal Si substrate, an SOI substrate, or various other substrates, with LiNbO ３ , or LiTaO ３The dielectric film 15 can also be epitaxially grown in a state where it is oriented to a plane different from the (0001) plane.

[0134] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention allows for the easy epitaxial growth of LiNbO in a (01-12) oriented state or in a state oriented to a plane different from the (0001) plane. ３ , or LiTaO ３ A dielectric layer with excellent crystallinity, including the above, and a dielectric film formed by stacking dielectric layers can be formed on a Si substrate.

[0135] Furthermore, if the lithium metal oxide dispersion for dielectric layers of the present invention includes, for example, a buffer film 12 that contains a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, then LiNbO can be easily epitaxially grown in a (01-12) oriented state or oriented on a plane different from the (0001) plane. ３ , or LiTaO ３ A dielectric film 15, which consists of a dielectric layer 15a with excellent crystallinity containing the above, can be formed on the buffer film 12.

[0136] Furthermore, the lithium metal oxide dispersion for the dielectric layer of the present invention contains LiNbO, which is a second metal oxide contained in the dielectric film 15. ３ , or LiTaO ３ Since it is oriented (01-12), LiNbO ３ , or LiTaO ３ The inclination angle of the (0001) surface relative to the main surface 11p can be easily controlled to be a constant angle. In addition, the (01-12) oriented LiNbO ３ The dielectric film 15 is made of 36° Y-cut LiNbO ３ It possesses an electromechanical coupling coefficient as high as that of a single crystal plate, as well as a high longitudinal wave velocity. Therefore, it is possible to realize electronic devices such as SAW filters with high electromechanical coupling coefficients and excellent filter characteristics.

[0137] In the laminated structure 10 of the present invention, a first conductive film 13 formed on the buffer film 12 and a second conductive film 14 formed on the first conductive film 13 may be formed between the buffer film 12 and the dielectric film 15 described above.

[0138] Preferably, the first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements such as platinum (Pt) oriented (111) in pseudocubic representation. In this specification, platinum group elements refer to elements located in the 5th and 6th periods, and groups 8, 9, and 10 of the periodic table, namely ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).

[0139] The second conductive film 14 is epitaxially grown on the first conductive film 13 and is (111) oriented in a pseudocubic crystal structure as strontium ruthenate (SrRuO ３ It is preferable that it contains ).

[0140] Furthermore, the buffer film 12 is not limited to a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, the first conductive film 13 is not limited to a platinum group element such as Pt epitaxially grown on the buffer film 12, and the second conductive film 14 is SrRuO epitaxially grown on the first conductive film 13. ３ It is not limited to this. Even in such cases, for example, by oriented the buffer film 12, the first conductive film 13, and the second conductive film 14 in a single direction, a dielectric film having an ilmenite-type structure or other various single-crystal high-quality dielectric films can be oriented in a certain direction on a Si substrate or SOI substrate, so that epitaxially grown LiNbO can be easily formed in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane. ３ , or LiTaO ３ A dielectric film 15 with excellent crystallinity, including the above, can be formed on a Si substrate or an SOI substrate.

[0141] Furthermore, a modified example of the laminated structure of the present invention will be described. The laminated structure 10a of this modified example differs from the laminated structure 10 of the present invention in that the main surface 11p of the substrate 11 is a Si(100) surface. Also, since the parts of the laminated structure 10a of this modified example other than the orientation direction of the substrate 11 and each layer are the same as the configuration of the laminated structure 10 of the present invention, their explanation will be omitted.

[0142] Figure 6 is a cross-sectional view showing an example of a modified laminated structure of the present invention. Figure 7 shows LiNbO, a second metal oxide contained in the dielectric layer of the modified laminated structure of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. Figure 8 shows LiNbO, a second metal oxide contained in the dielectric layer of a modified laminated structure of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. Note that in Figures 7 and 8, for the sake of ease of understanding, LiNbO is represented by a hexagonal crystal lattice instead of a trigonal one. ３ The crystal lattice is further represented by a quadrangular prism, with hatching applied to the (0001) face.

[0143] As shown in Figure 6, the substrate 11 in the laminated structure 10a of this modified example differs from the laminated structure 10 of the present invention in that it is made of a Si(100) substrate with the Si(100) surface as the main surface 11p. Note that, similar to Figure 2, the substrate 11 may be an SOI(100) substrate comprising a base body 11a made of a Si substrate, an insulating layer 11b on the base body 11a, and an SOI layer 11c made of a Si(100) film on the insulating layer 11b with the Si(100) surface as the main surface 11p.

[0144] Unlike the laminated structure 10 of the present invention, the buffer film 12 is epitaxially grown on the main surface 11p, is (100) oriented in pseudocubic crystal representation, and contains the first metal oxide represented by the above compositional formula (1). Furthermore, in the above compositional formula (1), x satisfies 0 ≤ x < 1 or x = 1.

[0145] Unlike the laminated structure 10 of the present invention, the first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements such as platinum (Pt) oriented (100) in pseudocubic representation.

[0146] Unlike the laminated structure 10 of the present invention, the second conductive film 14 is epitaxially grown on the first conductive film 13 and is (100) oriented in pseudocubic form as strontium ruthenate (SrRuO ３ ) includes.

[0147] The dielectric film 15 includes five or more stacked dielectric layers 15a, each of which is epitaxially grown on the second conductive film 14 and has an ilmenite-type structure and is (01-12) oriented LiNbO ３ , or LiTaO ３ It contains a secondary metal oxide.

[0148] Thus, in the laminated structure 10a of this modified example, the lithium metal oxide dispersion for the dielectric layer of the present invention is used, similar to the laminated structure 10 of the present invention, on a single crystal Si(100) substrate or SOI(100) substrate, with (01-12) oriented LiNbO ３ , or LiTaO ３ A dielectric film 15 can be epitaxially grown using the lithium metal oxide dispersion for dielectric layers of the present invention. ３ , or LiTaO ３ The dielectric film 15 can be epitaxially grown in a state where it is oriented to a plane different from the (0001) plane.

[0149] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention, in the laminated structure 10a of this modified example, allows for easy epitaxial growth of LiNbO in a state oriented (01-12) or oriented on a plane different from the (0001) plane, similar to the laminated structure 10 of the present invention. ３ , or LiTaO ３ A dielectric layer with excellent crystallinity, including the above, and a dielectric film formed by stacking these dielectric layers, can be formed on a Si substrate or an SOI substrate.

[0150] In addition, in this modified laminated structure 10a, similar to the laminated structure 10 of the present invention, the buffer film 12 is not limited to a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, the first conductive film 13 is not limited to a platinum group element such as Pt epitaxially grown on the buffer film 12, and the second conductive film 14 is SrRuO epitaxially grown on the first conductive film 13. ３It is not limited to this. Even in such cases, for example, by oriented the buffer film 12, the first conductive film 13, and the second conductive film 14 in a single direction, the lithium metal oxide dispersion for dielectric layers of the present invention can orient the dielectric film 15 having an ilmenite-type structure and other various single-crystal high-quality dielectric films 15 on the Si substrate in a certain direction, so that epitaxially grown LiNbO can be easily formed in a state oriented in (01-12) or in a state oriented in a plane different from the (0001) plane. ３ , or LiTaO ３ A dielectric layer with excellent crystallinity, including the above, and a dielectric film 15 formed by stacking the dielectric layers can be formed on a Si substrate.

[0151] Furthermore, the laminated structure 10a of this modified example does not necessarily have a first conductive film 13 and a second conductive film 14, similar to the laminated structure 10 of the present invention, and the dielectric film 15 may be formed directly on the buffer film 12. Even in such a case, for example, by including a first metal oxide epitaxially grown on the main surface 11p of the substrate 11, the lithium metal oxide dispersion for the dielectric layer of the present invention can easily epitaxially grow LiNbO in a (01-12) oriented state or oriented on a plane different from the (0001) plane. ３ , or LiTaO ３ A dielectric layer with excellent crystallinity, including the above, and a dielectric film formed by stacking the dielectric layers can be formed on the buffer film 12.

[0152] As shown in Figures 7 and 8, it is preferable that each layer of the dielectric layer 15a is oriented such that the (0001) plane of the second metal oxide is tilted with respect to the main plane by a predetermined angle, for example, a first angle θ11, and that it contains a first domain DM1, a second domain DM2, a third domain DM3, and a fourth domain DM4 in which the

[0001] axes of the second metal oxide are oriented in different directions. ３ When this is the case, the first angle θ11 can be set to, for example, 52.24 to 62.24°. On the other hand, the second metal oxide is LiTaO ３ When this occurs, the first angle θ11 can be set to, for example, 52.02 to 62.02°.

[0153] Here, the second metal oxide is LiNbO ３ , or LiTaO ３ In this case, when the

[0001] direction of the second metal oxide in the first domain DM1 is defined as the first

[0001] direction, the LiNbO contained in the second metal oxide in the second domain DM2 ３ , or LiTaO ３ The

[0001] direction is the direction rotated 90° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0154] Furthermore, LiNbO is included in the second metal oxide in the third domain DM3. ３ , or LiTaO ３ The

[0001] direction is the direction obtained by rotating 180° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0155] Furthermore, LiNbO is included in the second metal oxide in the fourth domain DM4. ３ , or LiTaO ３ The

[0001] direction is the direction rotated 270° counterclockwise from the first

[0001] direction when viewed from the normal direction of the main surface 11p (around the normal direction of the main surface 11p).

[0156] Furthermore, the orientation of the first domain DM1, second domain DM2, third domain DM3, and fourth domain DM4 contained in each layer of the dielectric layer 15a is substantially the same in each layer.

[0157] In such cases, LiNbO is contained in the second metal oxide of the dielectric film 15. ３ , or LiTaO ３ Since it is oriented (01-12), LiNbO ３ , or LiTaO ３ The inclination angle of the (0001) surface relative to the main surface 11p can be easily controlled to be a constant angle. In addition, the (01-12) oriented LiNbO ３ The dielectric film 15 is made of 36° Y-cut LiNbO ３It has an electromechanical coupling coefficient as high as that of a single crystal plate, and a high longitudinal wave velocity.

[0158] The method for manufacturing the laminated structure 10 of the present invention described above will be explained below.

[0159] The manufacturing method for the laminated structure 10 of the present invention comprises the steps of forming a buffer film 12 on a substrate 11 and forming a dielectric film 15 on the buffer film 12 by a wet method.

[0160] First, a buffer film 12 containing the first metal oxide represented by the above composition formula (1) is formed on the main surface 11p of the substrate 11 using an epitaxial growth method.

[0161] Specifically, the main surface 11p of the substrate 11 is treated with reactive ion etching (RIE), and after heating in the presence of oxygen to form a thermal oxide film, the first metal oxide represented by the above composition formula (1) of the deposition source and the oxygen in the oxide film on the substrate are thermally reacted by electron beam deposition without using oxygen, and a single crystal film of the first metal oxide as a buffer film 12 is formed on the substrate 11 according to the "(1-1) initial metal nucleus" described later.

[0162] Here, the substrate 11 is an SOI substrate that includes a Si substrate, or a substrate made of a Si substrate, an insulating layer on the substrate, and an SOI layer made of a Si film on the insulating layer. Alternatively, the substrate 11 is an SOI (111) substrate that includes a Si(111) substrate with the Si(111) surface as the main surface 11p, or a substrate made of a Si substrate, an insulating layer 11b on the substrate, and an SOI (Silicon On Insulator) (111) layer (SOI layer) made of a Si(111) film on the insulating layer with the Si(111) surface as the main surface 11p.

[0163] Next, oxygen is introduced, the temperature is lowered, and the pressure is increased, and annealing is performed according to "(1-2) Post-annealing" described later.

[0164] Furthermore, with oxygen flowing, the first metal oxide represented by the above compositional formula (1) of the deposition source is subjected to a thermal reaction with oxygen according to the "(1-3) HZO deposition" described later, thereby forming a single crystal film of the first metal oxide as a buffer film on the substrate 11.

[0165] In this way, the first metal oxide contained in the formed buffer film 12 grows epitaxially on the main surface 11p of the substrate 11 and is oriented (111) in a pseudocubic crystal representation, for example.

[0166] Then, a dielectric film 15, including a dielectric layer 15a, is formed on the buffer film 12 by a wet process using an epitaxial growth method. Each layer of the dielectric layer 15a has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ It includes.

[0167] Specifically, the process of forming a dielectric layer 15a by applying the lithium metal oxide dispersion for dielectric layers of the present invention described above onto a buffer film 12 and firing it is repeated, for example, 10 times to stack 10 layers under the same conditions. After that, the film is fired in an oxygen atmosphere to crystallize it, thereby forming a dielectric film 15 in which 10 layers of dielectric layers 15a are stacked.

[0168] Here, examples of the lithium metal oxide dispersion for the dielectric layer of the present invention include metal oxide solutions, metal organic compound solutions, and metal alkoxide solutions, with metal oxide solutions being preferred. Furthermore, the lithium metal oxide dispersion for the dielectric layer of the present invention may also be a metal compound particle dispersion (sol) in which the particle size (D50) of the particles measured by dynamic light scattering in the lithium metal oxide dispersion for the dielectric layer is 100 nm or less.

[0169] A film-forming material containing the lithium metal oxide dispersion for dielectric layers of the present invention is applied to a buffer film 12 and fired to epitaxially grow, resulting in an ilmenite-type structure and (01-12)-oriented LiNbO ３ , or LiTaO ３A dielectric layer 15a containing the above is formed on the buffer film 12 by a wet method. Specifically, ethanol is added to the lithium metal oxide dispersion for dielectric layers of the present invention to prepare a coating solution as a film-forming material.

[0170] In this way, the laminated structure 10 of the present invention can be manufactured, which has a substrate 11, a buffer film 12 formed on the substrate 11, and a dielectric film 15 formed on the buffer film 12 by a wet method.

[0171] Furthermore, the manufacturing method of the laminated structure 10 of the present invention may also include the steps of forming a buffer film 12 on a substrate 11, forming a first conductive film 13 on the buffer film 12, forming a second conductive film 14 on the first conductive film 13, and forming a dielectric film 15 on the second conductive film 14 by a wet method. Note that the step of forming the buffer film 12 on the substrate 11 is the same as the manufacturing method of the laminated structure 10 of the present invention described above, so its explanation is omitted.

[0172] As described above, a first conductive film 13 made of platinum group elements is formed on the formed buffer film 12 by sputtering according to the first sputtering conditions described later.

[0173] Thus, the formed first conductive film 13 is epitaxially grown on the buffer film 12, has a cubic crystal structure, and contains platinum group elements oriented (111) in a pseudocubic representation, for example.

[0174] Next, a second conductive film 14 made of SrRuO3 is formed on the first conductive film 13 by sputtering according to the second sputtering conditions described later.

[0175] Thus, the formed second conductive film 14 contains strontium ruthenate epitaxially grown on the first conductive film 13 and oriented (111) in a pseudocubic crystal structure.

[0176] Then, a dielectric film 15, including a dielectric layer 15a, is formed on the second conductive film 14 by a wet process using an epitaxial growth method. Note that the dielectric film 15, including the dielectric layer 15a, is obtained in the same manner as the manufacturing method of the laminated structure 10 of the present invention described above, so a detailed explanation is omitted.

[0177] The manufacturing method for the laminated structure 10 of the present invention described above can also be used to manufacture a laminated structure 10 of the present invention having a substrate 11, a buffer film 12 formed on the substrate 11, a first conductive film 13 formed on the buffer film 12, a second conductive film 14 formed on the first conductive film 13, and a dielectric film 15 formed on the second conductive film 14 by a wet method.

[0178] As described above, the lithium metal oxide dispersion for dielectric layers of the present invention is used to form a dielectric film by laminating a dielectric layer on a buffer film formed on a substrate using a wet method.

[0179] Furthermore, the lithium metal oxide dispersion for dielectric layers of the present invention comprises a dielectric film containing five or more stacked dielectric layers, each of which has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ It is used as a compound containing a secondary metal oxide.

[0180] In this specification, when we use the expression "X to Y" (where X and Y are any numbers), unless otherwise specified, it includes the meaning of "greater than or equal to X and less than or equal to Y," as well as the meaning of "preferably greater than X" or "preferably less than Y." Similarly, when we use the expression "greater than or equal to X" (where X is any number) or "less than or equal to Y" (where Y is any number), it also includes the meaning of "preferably greater than X" or "preferably less than Y."

[0181] The lithium metal oxide dispersion for dielectric layers of the present invention allows for the easy epitaxial growth of LiNbO in a state of orientation in a specific direction. ３ , or LiTaO ３ It is possible to form a dielectric layer with excellent crystallinity and a dielectric film formed by stacking dielectric layers.

[0182] This is a cross-sectional view showing an example of the laminated structure of the present invention. This is a cross-sectional view showing another example of the laminated structure of the present invention. LiNbO, a second metal oxide contained in the dielectric layer of the laminated structure of the present invention ３ This is a schematic plan view showing the orientation state of the crystal lattice. LiNbO is a second metal oxide contained in the dielectric layer of the laminated structure of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. The dielectric layer of the present invention contains an ilmenite-type structure and is (01-12) oriented LiNbO ３ This figure shows the crystal structure. This is a cross-sectional view showing an example of a modified laminated structure of the present invention. LiNbO is a second metal oxide contained in the dielectric layer of the modified laminated structure of the present invention. ３ This is a schematic plan view showing the orientation state of the crystal lattice. LiNbO is a second metal oxide contained in the dielectric layer of a modified laminated structure of the present invention. ３ This is a schematic side view showing the orientation state of the crystal lattice. This is a graph showing the diffraction pattern of the laminated structure of Example 1 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 1 of the present invention. This is a pole figure of the laminated structure of Example 1 of the present invention. This is a graph showing the diffraction pattern of the laminated structure of Example 2 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 2 of the present invention. This is a pole figure of the laminated structure of Example 2 of the present invention. This is a graph showing the diffraction pattern of the laminated structure of Example 3 of the present invention. This is a graph showing the φ scan of the laminated structure of Example 3 of the present invention. This is a pole figure of the laminated structure of Example 3 of the present invention.

[0183] The lithium metal oxide dispersions for dielectric layers according to embodiments of the present invention, namely lithium niobate dispersions for dielectric layers, lithium tantalate dispersions for dielectric layers, and coating structures, will be further described below with reference to the following examples. However, the following examples are not intended to limit the present invention.

[0184] (Example 1) The lithium niobate dispersion for the dielectric layer according to Example 1 was obtained as follows.

[0185] First, 100 g of niobium pentoxide is dissolved in 200 g of 55% hydrofluoric acid aqueous solution, and 830 mL of deionized water is added to convert the niobium into Nb２ O ５ It contains 100 g / L in conversion (Nb ２ O ５ = 8.84% by mass niobium fluoride aqueous solution was obtained. 200 mL of this niobium fluoride aqueous solution was mixed with ammonia water (NH₄). ３ Add to 1 L of 25% by mass (NH) in less than 1 minute. ３ / Nb ２ O ５ Mole ratio = 177.9, NH ３ (HF molar ratio = 12.2), a reaction solution (pH 11) was obtained. This reaction solution was a slurry of niobate compound hydrate, in other words, a slurry of niobium-containing precipitate.

[0186] Next, the reaction solution was decanted using a centrifuge and washed until the amount of free fluoride ions was 100 mg / L or less to obtain a niobium-containing precipitate from which the fluoride ions had been removed. Ammonia water was used as the washing solution.

[0187] Furthermore, the niobium-containing precipitate from which the fluoride ions were removed was diluted with pure water to obtain a slurry. A portion of this slurry was dried at 110°C for 24 hours, and then calcined at 1,000°C for 4 hours to obtain Nb ２ O ５ It generates Nb from its weight and the amount of Nb contained in the slurry. ２ O ５ The content was calculated.

[0188] Then, the slurry of the niobium-containing precipitate diluted with pure water is used to determine the niobium content of the final mixture. ２ O ５ A translucent slurry mixture was obtained by mixing lithium hydroxide monohydrate with pure water in an amount equivalent to 5% by mass, with a Li / Nb molar ratio of 1. This mixture was stirred and maintained for 1 hour at a liquid temperature of 50°C to 100°C, for example, 70°C, to obtain a colorless and transparent lithium niobate dispersion for dielectric layers according to Example 1. The pH of the lithium niobate dispersion for dielectric layers according to Example 1 was 11. The composition and physical properties of the lithium niobate dispersion for dielectric layers according to Example 1 are shown in Tables 1 and 2 below.

[0189] A laminated structure having a dielectric film formed using a film-forming material containing a lithium niobate dispersion for the dielectric layer according to Example 1 was obtained as follows (see Figure 1).

[0190] First, the crystal growth surface of the Si(111) substrate 11 was treated with reactive ion etching (RIE), and after heating in the presence of oxygen to form a thermal oxide film, an electron beam deposition method was used without using oxygen to thermally react the metal (Hf, Zr) of the deposition source with the oxygen in the oxide film on the Si(111) substrate, thereby forming a single crystal film of the first metal oxide as a buffer film 12 on the Si(111) substrate (see "(1-1) Initial Metal Nuclei" below).

[0191] (1-1) Metal initial nucleation deposition source: Hf, Zr Pressure: 2 × 10 －４ Pa thickness: 2 nm, Substrate temperature: 1000°C

[0192] Next, annealing was performed by flowing oxygen, lowering the temperature, and increasing the pressure (see "(1-2) Post-annealing" below).

[0193] (1-2) Post-annealing pressure: 2 × 10 －２ Pa Substrate temperature: 900℃ Time: 180sec

[0194] Furthermore, while oxygen was flowing, the metal (Hf, Zr) of the deposition source and the oxygen were subjected to a thermal reaction to form a single crystal film of the first metal oxide as a buffer film 12 on the Si substrate (see "(1-3) HZO Deposition" below). The conditions for the electron beam deposition method during this film formation were as follows. The Hf:Zr value was 25:75 (x in the above composition formula (1) was 0.75), which was the target value.

[0195] (1-3) HZO deposition source: Hf, Zr Pressure: 2 × 10 －２ Pa thickness: 10 nm, Substrate temperature: 900°C

[0196] Next, a metal film made of Pt was formed on the buffer film 12 as the first conductive film 13 by sputtering (see "First Sputtering Conditions" below).

[0197] =First sputtering conditions= Equipment: ULVAC sputtering machine QAM-4 Pressure: 1.20 × 10 －１ Pa Target: Pt Power: 100W (DC) Thickness: 80nm Substrate temperature: 450-600℃

[0198] Furthermore, on the first conductive film 13 made of Pt, SrRuO ３ A second conductive film 14 was formed by sputtering (see "Second Sputtering Conditions" below).

[0199] =Second Sputtering Conditions= Equipment: ULVAC QAM-4 sputtering system Power: 150W (RF) Gas: Ar Pressure: 1.8 Pa Substrate Temperature: 600℃ Thickness: 10 nm

[0200] And, SrRuO ３ On the second conductive film 14, which consists of LiNbO ３ A dielectric film 15 was formed by a wet process.

[0201] Specifically, a coating solution for film formation was prepared by adding ethanol to the lithium niobate dispersion for the dielectric layer according to Example 1 for coatability adjustment. The prepared coating solution was dropped onto a substrate and rotated at 1000 rpm for 15 seconds to spin-coat (apply) the coating solution to the substrate, thereby forming LiNbO ３ A film containing a precursor of (LN) was formed. Then, the solvent was evaporated and the film was dried by placing the substrate on a hot plate at a temperature of 200°C. This process was repeated 10 times to deposit 10 layers under the same conditions, after which oxygen (O) was added. ２ The precursor was oxidized and crystallized by heat treatment at 650°C for 5 seconds in an atmosphere. The dielectric film 15, which includes 10 dielectric layers 15a, is obtained by performing the above process and is composed of LiNbO ３ A dielectric film 15 containing a second metal oxide consisting of (LN) was obtained.

[0202] In this way, LiNbO is placed on the second conductive film 14. ３A dielectric film 15 containing a second metal oxide made of (LN) was formed by a wet method to obtain the laminated structure 10 according to Example 1. A first conductive film 13 made of Pt and SrRuO were formed on the buffer film 12. ３ Alternatively, the dielectric film 15 may be formed directly on the buffer film 12 without forming the second conductive film 14.

[0203] [X-ray Diffraction Measurement] For the laminated structure of Example 1, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the diffraction pattern of the laminated structure was measured by X-ray diffraction (XRD) measurement using the θ-2θ method, with the laminated structure positioned so that the diffraction plane was parallel to the main surface 11p. The measured diffraction pattern of the laminated structure of Example 1 is shown in Figure 9. The XRD measurement was performed using a Rigaku SmartLab X-ray diffractometer.

[0204] As shown in Figure 9, in the diffraction pattern of Example 1, there is a strong diffraction peak of the (111) plane of Si, a diffraction peak of the (111) plane in the pseudocubic representation of HZO, a strong diffraction peak of the (111) plane of Pt, and LiNbO ３ Strong diffraction peaks were observed on the (01-12) plane (LN(012)), (02-24) plane (LN(024)), and (03-36) plane (LN(036)) of (LN). Therefore, in Example 1, the HZO contained in the buffer film 12 was (111) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (111) oriented, and the LiNbO contained in the second metal oxide in the dielectric film 15 ３ It was revealed that (LN) has an ilmenite-type structure and is (01-12) oriented.

[0205] Although not shown in the diagram, after forming the second conductive film 14 on the main surface 11p of the substrate 11, and before forming the dielectric film 15, the diffraction pattern of the laminated structure is similarly measured to determine the amount of SrRuO contained in the second conductive film 14. ３ It was revealed that (SRO) is (111) oriented in a pseudocubic crystal representation.

[0206] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiNbO ３ With the laminated structure positioned (X-adjusted) so that no diffraction peaks other than those on the (01-12), (02-24), and (03-36) planes of (LN) were observed, a φ scan was performed on the (01-12) plane (2θ = 23.75°) of LN contained in the second metal oxide contained in the dielectric film 15. The φ scan measured for the laminated structure of Example 1 is shown in Figure 10.

[0207] As shown in Figure 10, in the φ scan, LiNbO ３ Six strong diffraction peaks were observed at 60° intervals on the (01-12) plane of (LN). In other words, diffraction peaks showing six-fold symmetry of LN were observed in the φ scan. Therefore, it became clear that the LN contained in the second metal oxide contained in the dielectric film 15 had crystal axes aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they were epitaxially grown.

[0208] Furthermore, regarding the laminated structure of Example 1, the LiNbO contained in the dielectric film 15 ３ A pole figure corresponding to the interplanar spacing d value (d value = 0.2308 nm, 2θ = 38.99° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LN) was measured. The measured pole figure is shown in Figure 11. Note that the values ​​of 2θ in this specification, including the 2θ value of the (01-12) plane mentioned above, are values ​​when using CuKα rays as X-rays.

[0209] As shown in Figure 11, in the pole figure of Example 1, LiNbO ３ Six diffraction peaks were observed at 60° intervals on the (0006) plane of (LN). That is, in the pole figure, diffraction peaks showing six-fold symmetry of LN were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 20° = 70° with respect to the main surface 11p. Therefore, it became clear that the polarization direction of LN contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0210] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 1, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0211] (Example 2) In Example 2, the same lithium niobate dispersion for the dielectric layer as in Example 1 was used, and the laminated structure of Example 2 was obtained in the same manner as in Example 1, except that a Si(100) substrate was used as the substrate 11 instead of a Si(111) substrate. The laminated structure of Example 2 is the laminated structure described above using Figure 6 in the modified example of the present invention. Note that the lithium niobate dispersion for the dielectric layer in Example 2 is the same as the lithium niobate dispersion for the dielectric layer in Example 1, so its description is omitted.

[0212] [X-ray diffraction measurement] For the laminated structure of Example 2, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the laminated structure was positioned so that the diffraction plane in the X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p, and the diffraction pattern of the laminated structure was measured by the said X-ray diffraction measurement. The measured diffraction pattern of the laminated structure of Example 2 is shown in Figure 12.

[0213] As shown in Figure 12, the diffraction pattern of Example 2 shows a strong diffraction peak on the (400) plane of Si, strong diffraction peaks on the (200) and (400) planes in the pseudocubic representation of HZO, a strong diffraction peak on the (200) plane of Pt, and SrRuO ３ Strong diffraction peaks on the (100) plane in the pseudocubic representation of (SRO), and LiNbO ３ A strong diffraction peak was observed on the (01-12) plane (LN(012)) of (LN). Therefore, in Example 2, the HZO contained in the buffer film 12 was (100) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (100) oriented, the SRO contained in the second conductive film 14 was (100) oriented in pseudocubic crystal representation, and the LiNbO contained in the second metal oxide in the dielectric film 15 ３It was revealed that (LN) has an ilmenite-type structure and is (01-12) oriented.

[0214] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiNbO ３ A φ scan was performed on the (01-12) plane (2θ = 23.75°) of the LN contained in the second metal oxide contained in the dielectric film 15, with the stacked structure in a state where diffraction peaks other than those on the (01-12), (02-24), and (03-36) planes of (LN) were not strongly observed. The φ scan measured for the stacked structure of Example 2 is shown in Figure 13.

[0215] As shown in Figure 13, in the φ scan, LiNbO ３ Four strong diffraction peaks were observed at 90° intervals on the (01-12) plane of (LN). In other words, diffraction peaks showing four-fold symmetry of LN were observed in the φ scan. Therefore, it became clear that the LN contained in the second metal oxide contained in the dielectric film 15 had crystal axes aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they were epitaxially grown.

[0216] Furthermore, regarding the laminated structure of Example 2, the LiNbO contained in the dielectric film 15 ３ The pole diagrams corresponding to the interplanar spacing d value (d value = 0.2308 nm, 2θ = 38.99° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LN) were measured. The measured pole diagrams are shown in Figure 14.

[0217] As shown in Figure 14, in the pole figure of Example 2, LiNbO ３ Four diffraction peaks were observed at 90° intervals on the (0006) plane of (LN). That is, in the pole figure, diffraction peaks showing four-fold symmetry of LN were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 35° = 55° with respect to the main surface 11p. Therefore, it became clear that the polarization direction of LN contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0218] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 2, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0219] (Example 3) Furthermore, SrRuO ３ On the second conductive film 14, which consists of LiNbO ３ Instead of the dielectric film 15 made of LiTaO ３ The laminated structure of Example 3 was obtained in the same manner as in Example 1, except that the dielectric film 15 was formed by a wet method.

[0220] The lithium tantalate dispersion for the dielectric layer according to Example 3, which was coated onto the second conductive film 14, was obtained as follows.

[0221] 137.9g ​​of tantalum hydroxide manufactured by Mitsui Mining & Smelting Co., Ltd. (Ta ２ O ５ Dissolve 66% by mass of tantalum fluoride in 120 g of 55% by mass hydrofluoric acid aqueous solution, and add 849 mL of deionized water to produce an aqueous solution of tantalum fluoride (Ta ２ O ５ A concentration of 8.2% by mass was obtained.

[0222] To 1,000 g of this tantalum fluoride aqueous solution, add 36.1 g of hydrogen peroxide solution (H ２ O ２ Add (H) (35% by mass) ２ O ２ An aqueous solution of tantalum compound was obtained by stirring for 5 minutes (Ta molar ratio = 1.0).

[0223] Add 1,000 g of this tantalum compound aqueous solution to 6.82 L of ammonia water (NH3 concentration 25% by mass) in less than 1 minute (NH ３ / Ta molar ratio = 245, NH ３ (HF molar ratio = 30.7), a reaction solution (pH 11) was obtained. This reaction solution was a slurry of tantalum compound hydrate, in other words, a slurry of tantalum-containing precipitate.

[0224] Next, the reaction solution was decanted using a centrifuge and washed until the amount of free fluoride ions was 100 mg / L or less to obtain a tantalum-containing precipitate from which the fluoride ions had been removed. Ammonia water was used as the washing solution.

[0225] Furthermore, the tantalum-containing precipitate from which the fluoride ions were removed was diluted with pure water to obtain a tantalum-containing precipitate slurry. A portion of this tantalum-containing precipitate slurry was dried at 110°C for 24 hours, and then calcined at 1,000°C for 4 hours to obtain Ta ２ O ５ This generates a tantalum-containing precipitate slurry, and its weight is used to determine the amount of Ta contained in the tantalum-containing precipitate slurry. ２ O ５ The concentration was calculated.

[0226] Then, the tantalum-containing precipitate slurry diluted with pure water, 0.54% by mass of lithium hydroxide, and pure water are mixed, and the tantalum content of the final mixture is Ta ２ O ５ A lithium tantalate dispersion for dielectric layers according to Example 3 was obtained by mixing the materials to a concentration of 5% by mass and a Li / Ta molar ratio of 1.0. The pH of the lithium tantalate dispersion for dielectric layers according to Example 3 was 12.2, and the ammonia concentration was 0.7% by mass. Furthermore, ethanol was added to the lithium tantalate dispersion for dielectric layers to prepare a coating solution for film formation. The composition and physical properties of the lithium tantalate dispersion for dielectric layers according to Example 3 are shown in Tables 1 and 2 below.

[0227] Next, the prepared coating solution was treated in the same manner as in Example 1 with LiTaO ３ A dielectric film 15 containing a second metal oxide made of (LT) was obtained.

[0228] In this way, LiTaO is placed on the second conductive film 14. ３ A dielectric film 15 made of (LT) was formed by a wet method to obtain the laminated structure 10 according to Example 3. A first conductive film 13 made of Pt and SrRuO were formed on the buffer film 12. ３ Alternatively, the dielectric film 15 may be formed directly on the buffer film 12 without forming the second conductive film 14.

[0229] [X-ray diffraction measurement] For the laminated structure of Example 3, after forming a dielectric film 15 on the main surface 11p of the substrate 11, the laminated structure was positioned so that the diffraction plane in the X-ray diffraction measurement using the θ-2θ method was parallel to the main surface 11p, and the diffraction pattern of the laminated structure was measured by the said X-ray diffraction measurement. The measured diffraction pattern of the laminated structure of Example 3 is shown in Figure 15.

[0230] As shown in Figure 15, in the diffraction pattern of Example 3, there is a strong diffraction peak of the (111) plane of Si, a diffraction peak of the (111) plane in the pseudocubic representation of HZO, a strong diffraction peak of the (111) plane of Pt, and LiTaO ３ Strong diffraction peaks were observed on the (01-12) plane (LT(012)) and the (03-36) plane (LT(036)) of (LT). Therefore, in Example 3, the HZO contained in the buffer film 12 was (111) oriented in pseudocubic crystal representation, the Pt contained in the first conductive film 13 had a cubic crystal structure and was (111) oriented, and the LiTaO contained in the second metal oxide in the dielectric film 15 ３ It was revealed that (LT) has an ilmenite-type structure and is (01-12) oriented.

[0231] Although not shown in the diagram, after forming the second conductive film 14 on the main surface 11p of the substrate 11, and before forming the dielectric film 15, the diffraction pattern of the laminated structure is similarly measured to determine the amount of SrRuO contained in the second conductive film 14. ３ It was revealed that (SRO) is (111) oriented in a pseudocubic crystal representation.

[0232] Furthermore, the diffraction plane in the X-ray diffraction measurement is inclined with respect to the main surface 11p, and LiTaO ３ With the stacked structure positioned (X-adjusted) so that no diffraction peaks other than those on the (01-12) and (03-36) planes of (LT) were observed, a φ scan was performed on the (3000) plane (2θ = 62.36°) of LT contained in the second metal oxide contained in the dielectric film 15. The φ scan measured for the stacked structure of Example 3 is shown in Figure 16.

[0233] As shown in Figure 16, in the φ scan, LiTaO ３ Six strong diffraction peaks were observed at 60° intervals on the (3000) plane of (LT). In other words, diffraction peaks showing 6-fold symmetry of LT were observed in the φ scan. Therefore, it was revealed that the crystal axes of the LT contained in the second metal oxide contained in the dielectric film 15 are aligned in the in-plane direction along the main surface 11p of the substrate 11, i.e., that they are epitaxially grown.

[0234] Furthermore, regarding the laminated structure of Example 3, the LiTaO contained in the dielectric film 15 ３ A pole figure corresponding to the interplanar spacing d value (d value = 0.2297 nm, 2θ = 39.18° when using CuKα rays) corresponding to the interplanar spacing of the (0006) plane of (LT) was measured. The measured pole figure is shown in Figure 17. Note that the values ​​of 2θ in this specification, including the 2θ value of the (3000) plane mentioned above, are values ​​when using CuKα rays as X-rays.

[0235] As shown in Figure 17, in the pole figure of Example 3, LiTaO ３ Six diffraction peaks were observed at 60° intervals on the (0006) plane of (LT). That is, in the pole figure, diffraction peaks showing 6-fold symmetry of LT were observed in an annular region (corresponding to a φ scan) that satisfies the condition where the diffraction plane is tilted 90° - 15° = 75° with respect to the main surface 11p. Therefore, it was revealed that the polarization direction of the LT contained in the second metal oxide contained in the dielectric film 15 is aligned in the in-plane direction along the main surface 11p of the substrate 11 (see Figure 1), i.e., that it is epitaxially grown.

[0236] Furthermore, although a detailed explanation will be omitted, even when the ratio of Hf:Zr is a ratio other than 25:75, and x in the above compositional formula (1) satisfies 0 ≤ x < 1 or x satisfies x = 1, the same results as in Example 3, where the ratio of Hf:Zr is 25:75 (x in the above compositional formula (1) is 0.75), were obtained.

[0237] The following physical properties were measured for the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3. Below, the measured physical properties and the method of measurement for those physical properties are shown, and the physical properties and measurement results for the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 are shown in Tables 1 and 2.

[0238] <Elemental Analysis> If necessary, the sample is appropriately diluted with dilute hydrochloric acid, and using ICP emission spectrometry (Agilent Technologies: AG-5110), in accordance with JIS K0116:2014, the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 were analyzed for Nb ２ O ５ Converted Nb mass%, Ta ２ O ５ The converted Ta mass% and the Li mass% on a Li atom basis were measured.

[0239] <pH Measurement> The electrodes of a pH meter (HORIBA: Standard ToupH Electrode 9615S-10D) were immersed in the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3. After confirming that the liquid temperature had stabilized at 25°C, the pH was measured. In Table 2, "Initial pH" refers to the pH of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3, which were adjusted to a liquid temperature of 25°C immediately after production. Furthermore, "pH over time" in Table 2 refers to the pH of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 after being left to stand for one month from the day they were produced in a constant temperature incubator set at room temperature of 25°C.

[0240] <Dynamic Light Scattering Method> The particle size distribution was evaluated using a zeta potential, particle size, and molecular weight measurement system (Otsuka Electronics Co., Ltd.: ELSZ-2000) and the dynamic light scattering method in accordance with JIS Z 8828:2019. Immediately before measurement, the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 were filtered using a 1 μm pore size filter to remove dust and other particles. Furthermore, D50 represents the particle size at which 50% of the volume fraction is reached. "Initial particle size D50 (nm)" in Table 2 refers to the particle size (D50) of the particles in the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 immediately after production. Furthermore, "Particle size D50 (nm) over time" in Table 2 refers to the particle size (D50) of particles in the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 after standing for one month from the day the two solutions were produced in a constant temperature incubator set at room temperature of 25°C.

[0241] <Transmittance Measurement> Three ml each of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 were placed in a synthetic quartz cell with a path length of 5 mm. The light transmittance of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 in the wavelength range of 400 nm to 760 nm (specifically, the light transmittance at wavelengths of 400 nm, 600 nm, and 750 nm) was measured using a spectrophotometer according to the light transmittance measurement conditions described above. "Initial light transmittance" in Table 2 refers to the light transmittance of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 after the liquid temperature was adjusted to 25°C immediately after production. Furthermore, "Time-dependent light transmittance" in Table 2 refers to the light transmittance of the lithium niobate dispersion for dielectric layers according to Example 1 and the lithium tantalate dispersion for dielectric layers according to Example 3 after being left to stand for one month from the day they were produced in a constant temperature oven set at room temperature of 25°C.

[0242] <Quantitative Analysis of Ammonia> 25 ml of sodium hydroxide solution (30 g / 100 ml) was added to 1-5 ml of the sample solution. This mixture was boiled and distilled, and the distillate (approximately 200 ml) was drained into a container containing 20 ml of pure water and 0.5 ml of sulfuric acid to separate the ammonia. Next, the separated ammonia was transferred to a 250 ml volumetric flask and diluted to 250 ml with pure water. Furthermore, 10 ml of the 250 ml solution was taken into a 100 ml volumetric flask, and 1 ml of sodium hydroxide solution (30 g / 100 mL) was added to the taken solution, and the volume was diluted to 100 ml with pure water. The ammonium ion concentration (mass%) in the solution was measured by quantitative analysis of the solution obtained in this way using an ion meter (main unit: HORIBA F-53, electrode: HORIBA 500 2A).

[0243] <Qualitative Analysis of Hydrogen Peroxide> Standard solution without added hydrogen peroxide, and H ２ O ２The ultraviolet-visible absorbance spectra of a standard solution to which hydrogen peroxide was added to a concentration equivalent to 1% by mass were measured, and the wavelength at which the rate of change in absorbance was greatest was defined as "λ". Next, for samples with an unknown hydrogen peroxide concentration, the absorbance at wavelength λ was measured in the same manner. If the ratio of the absorbance at wavelength λ of the sample with an unknown hydrogen peroxide concentration to the absorbance at wavelength λ of the standard solution without added hydrogen peroxide was 1% or less, it was determined that hydrogen peroxide had not been added to the sample.

[0244] The measurement conditions for the ultraviolet-visible absorption spectrum should be as follows: • Equipment: UH4150 spectrophotometer (Hitachi High-Tech Science Corporation) • Measurement mode: Wavelength scan • Data mode: %T (transmission) • Measurement wavelength range: 200–2,600 nm • Scan speed: 600 nm / min • Sampling interval: 2 nm

[0245]

[0246]

[0247] 10, 10a...Laminated structure 11...Substrate 11a...Base 11b...Insulating layer 11c...SOI layer 11p...Main surface 12...Buffer film 13...First conductive film 14...Second conductive film 15...Dielectric film 15a...Dielectric layer DM1...First domain DM2...Second domain DM3...Third domain DM4...Fourth domain DM5...Fifth domain DM6...Sixth domain

Claims

1. A lithium metal oxide dispersion for dielectric layers, characterized by being a lithium metal oxide dispersion for dielectric layers used to form a dielectric layer.

2. The dielectric layer has an ilmenite-type structure and is oriented in a certain direction. ３ , or LiTaO ３ A lithium metal oxide dispersion for a dielectric layer according to claim 1, characterized in that it contains a second metal oxide.

3. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the maximum value of the light transmittance in the wavelength range of 400 nm to 760 nm of the lithium metal oxide dispersion for dielectric layers is 65% T or more.

4. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the particle size (D50) of the particles in the lithium metal oxide dispersion for dielectric layers measured by dynamic light scattering is 100 nm or less.

5. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the maximum value of the light transmittance of the lithium metal oxide dispersion for dielectric layers in the wavelength range of 400 nm to 760 nm is 65% T or more, and the particle size (D50) of the particles in the lithium metal oxide dispersion for dielectric layers measured by dynamic light scattering is 100 nm or less.

6. The niobium content in the lithium metal oxide dispersion for the dielectric layer is Nb ２ O ５ In conversion, or if the tantalum content is Ta ２ O ５ A lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the amount is 0.1% by mass or more and less than 30% by mass when converted.

7. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the molar ratio Li / Nb of lithium niobate in the lithium metal oxide dispersion for dielectric layers, or the molar ratio Li / Ta of lithium (Li) in lithium tantalate in lithium tantalate, is 0.01 or more and 20 or less.

8. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the lithium metal oxide dispersion for dielectric layers is an aqueous dispersion.

9. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, further characterized by containing ammonia.

10. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, further characterized by containing a surfactant.

11. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, further characterized by containing an alcohol solvent.

12. The lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the lithium metal oxide dispersion for dielectric layers does not contain hydrogen peroxide.

13. The dielectric layer is formed on a buffer film formed on a substrate, and is stacked to form a dielectric film, the substrate is a Si substrate, or an SOI substrate comprising a base body made of a Si substrate, an insulating layer on the base body, and an SOI layer made of a Si film on the insulating layer, the buffer film comprises a first metal oxide represented by the following composition formula (1), (Hf １－ｘ Zr ｘ )O ２ ...(1) x satisfies 0≤x<1 or x=1, The lithium metal oxide dispersion for a dielectric layer according to claim 1 or 2, characterized by the above.

14. Use of the lithium metal oxide dispersion for dielectric layers according to claim 1 or 2 for forming a dielectric film by laminating a dielectric layer on a buffer film formed on a substrate using a wet method.

15. The use of the lithium metal oxide dispersion for dielectric layers according to claim 1 or 2, characterized in that the dielectric film comprises five or more stacked dielectric layers.

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