Film and method for producing same

Abstract

The present disclosure relates to a film comprising an oxide of a transition metal element and comprising at least one selected from the group consisting of a carboxy group, a hydroxy group, and salts thereof, wherein the oxide of the transition metal element includes at least one among a trivalent transition metal element and a tetravalent transition metal element. According to the present disclosure, provided are: a metal oxide-based film which exhibits proton conductivity not only at a relatively high temperature but also at a relatively low temperature, and which has heat resistance against a relatively high temperature; and a method for producing the same.

Description

Membrane and method for producing same

[0001] The present disclosure relates to membranes and methods for making the same.

[0002] Until now, in electronics based on silicon (Si) technology, devices that control the flow of electrons have contributed to technological advances as the most important element in all electronic devices. However, in the accelerating Internet of Things (IoE) / Internet of Things (IoB) society, it is expected that a world in which all objects, including the human body, are organically connected will be realized. This will require the creation of devices with unprecedented functions and ultimate power saving.

[0003] In recent years, iontronics, which utilizes the functions of ions in addition to conventional electrons, has been attracting attention. Ions are expected to lead to the creation of devices with a wide range of physical properties, including high capacity density due to electric double layers, low voltage operation, and biomimetic devices that utilize electrochemical reactions. One example of iontronics that utilizes the functions of ions is the proton conductor, which utilizes the conduction of protons (hydrogen ions).

[0004] Proton conductors are broadly classified into organic polymer-based proton conductors and oxide-based proton conductors. JP 2011-168785 A (Patent Document 1) proposes a proton conductive membrane containing a polymer acid.

[0005] As an oxide-based proton conductor, the following Non-Patent Document 1 describes amorphous microporous silicon oxide (SiO ２ ) film having a perovskite crystal structure has been proposed. ３ ) based metal oxides have been proposed.

[0006] JP 2011-168785 A

[0007] Applied Physics Letters, 2009, 95, 222905 "Role of Substituting Element Y and Influence of Ba Deficiency in Proton-Conducting Metal Oxide BaZrO3", Materia, Japan Institute of Metals, 2015, Vol. 54, No. 7 "Development of Proton-Conducting SOFC", Panasonic Technical Journal, Vol. 63, No. 1, May 2017

[0008] Organic polymer proton conductors are organic membranes that have high water absorption, which tends to result in low membrane density. Therefore, when organic polymer proton conductors are used in batteries, gas crossover (mixing) can occur between the anode and cathode. Organic polymer proton conductors also have insufficient heat resistance, only being able to withstand temperatures of around 100°C.

[0009] On the other hand, many perovskite-type oxides, which are representative oxide-based proton conductors, do not exhibit high conductivity in their parent materials. Therefore, their conductivity can sometimes be enhanced by introducing oxygen vacancies into their crystal structure. However, the enhancement of conductivity by introducing oxygen vacancies into the crystal structure is due to hopping conduction, in which electrons and holes hop between molecules, resulting in the flow of current. Therefore, relatively high temperatures (e.g., temperatures above 500°C) are often required to achieve high conductivity. Furthermore, proton trapping, in which oxygen vacancies trap protons, can occur. Therefore, proton conductivity tends to decrease significantly at relatively low temperatures (e.g., temperatures between room temperature and 500°C or lower). Furthermore, the presence of oxygen vacancies in the film tends to reduce the film density more easily than that of bulk solids.

[0010] An object of the present disclosure is to provide a metal oxide membrane that exhibits proton conductivity not only at relatively high temperatures but also at relatively low temperatures and has heat resistance at relatively high temperatures, and a method for producing the same.

[0011] The film according to the present disclosure includes an oxide of a transition metal element, and includes at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and salts thereof. The oxide of the transition metal element includes at least one of a trivalent transition metal element and a tetravalent transition metal element.

[0012] According to the present disclosure, it is possible to provide a metal oxide membrane that exhibits proton conductivity not only at relatively high temperatures but also at relatively low temperatures and has heat resistance at relatively high temperatures, and a method for producing the same.

[0013] FIG. 1 is a schematic cross-sectional view illustrating proton conduction. FIG. 2 is a schematic cross-sectional view illustrating an example of a transistor. FIG. 3 is a schematic flowchart illustrating a method for manufacturing a film of this embodiment. FIG. 4 is a graph illustrating the relationship between the electrical conductivity and samarium content of a film of this embodiment. FIG. 5 is a scanning electron microscope image of a cross section of a film of this embodiment. FIG. 6 is a graph illustrating the relationship between film density and samarium content. FIG. 7 is a graph illustrating the frequency response of the dielectric constant of a film. FIG. 8 is a graph illustrating the results of infrared spectroscopy analysis of COOH groups in the film. FIG. 9 is a graph illustrating the results of infrared spectroscopy analysis of OH groups in the film. FIG. 10 is a graph illustrating the results of secondary ion mass spectroscopy analysis of the film of this embodiment in the thickness direction. FIG. 11 is a graph illustrating the frequency response of the dielectric constant of a film of this embodiment. FIG. 12 is a graph illustrating the frequency response of the dielectric loss of a film of this embodiment. FIG. 13 is a graph illustrating the results of X-ray diffraction analysis of a film of this embodiment. FIG. 14 is a graph illustrating the frequency response of the dielectric constant of a film of this embodiment. Fig. 15 is a graph showing the frequency response of the dielectric loss of the film of this embodiment. Fig. 16 is a graph showing the frequency response of the relative dielectric constant of the film of this embodiment. Fig. 17 is a graph showing the frequency response of the dielectric loss of the film of this embodiment. Fig. 18 is a graph showing the Id-Vg curve and Ig-Vg curve of a field effect transistor.

[0014] The film of the present disclosure contains an oxide of a transition metal element (hereinafter also referred to as a first metal oxide). The first metal oxide contains at least one of a trivalent transition metal element and a tetravalent transition metal element. A transition metal element refers to a metal element present in Groups 3 to 11 of the periodic table. A trivalent transition metal element and a tetravalent transition metal element refer to transition metal elements that can become trivalent cations and tetravalent cations, respectively. The presence of a film containing a first metal oxide and a second metal oxide described below can be confirmed, for example, by X-ray photoelectron spectroscopy (XPS).

[0015] The membrane contains a first metal oxide as a major component. The major component refers to the component that is most abundant in mass terms among the components constituting the membrane. The content (mol %) of the first metal oxide in the membrane may be 50 mol % or more, 60 mol % or more, 70 mol % or more, 80 mol % or more, 90 mol % or more, 95 mol % or more, or 99 mol % or more relative to all substances in the membrane. When the membrane contains the first metal oxide in a proportion within the above range, heat resistance tends to be more easily exhibited. In the present disclosure, the heat resistance temperature of the membrane can be the upper limit of the temperature at which the membrane can exhibit proton conductivity. The temperature at which the membrane can exhibit heat resistance may be, for example, 100°C or more, 300°C or more, or 600°C or more, or may be, for example, 800°C or less.

[0016] The first metal oxide can be present in the film in an amorphous (non-crystalline) state. The first metal oxide may be present entirely in an amorphous state in the film. The first metal oxide may be present in the film mostly in an amorphous state, with a small amount of the first metal oxide being microcrystalline in the film. The presence of the first metal oxide in an amorphous state in the film can be confirmed, for example, by analysis using X-ray diffraction (XRD).

[0017] The membrane of the present disclosure contains at least one selected from the group consisting of a carboxy group (—COOH), a hydroxy group (—OH), and salts thereof. By including at least one selected from the group consisting of a carboxy group (—COOH), a hydroxy group (—OH), and salts thereof, the membrane of the present disclosure tends to have increased proton conductivity. This is presumably because protons are more easily supplied into the membrane, and water is more easily absorbed into the membrane despite being a dense membrane containing an oxide of a transition metal element, which results in increased proton conductivity.

[0018] Proton conduction is the transfer of protons (H ＋ ) in the capacitor using the membrane of the present disclosure. When an electric field is applied to the capacitor 1, protons (H ＋ ) is a water molecule (H ２ O) to the electrode 2 side, whereby proton conduction occurs. Since the membrane of the present disclosure has moisture present even inside the membrane, it can exhibit proton conductivity even in a relatively low temperature range (for example, from room temperature to a temperature of 500°C or less).

[0019] The proton conductivity of the membrane can be confirmed by, for example, calculating the Cole-Cole plot obtained by measuring the electrical conductivity of the membrane using an LCR meter or an AC impedance measurement method. The electrical conductivity of the membrane is, for example, 1.0 × 10 at room temperature. －３ (S / cm) or more. Alternatively, when the relative dielectric constant (hereinafter also referred to as the relative dielectric constant of the film) calculated from the capacitance of a capacitor measured when the film is used as a dielectric of the capacitor is 100 or more, it is suggested that proton conduction occurs in the film. The capacitance density of the capacitor measured when the film is used as a dielectric of the capacitor is, for example, 200 nF / mm ２ It is suggested that the less the capacity decreases up to the high frequency region in the capacity frequency characteristics, the higher the proton conductivity.

[0020] The water content in the film can be measured by, for example, deuterium-substituted secondary ion mass spectrometry (SIMS) or thermal desorption spectrometry (TDS). The water content in the depth of the film measured by deuterium-substituted SIMS is 1×10 ２０ The water content in the film measured by TDS analysis may be, for example, 3.2×10 １６ The amount of residual hydrogen in the film measured by sensor gas chromatography analysis may be, for example, 20 ppm or more. The amount of residual hydrogen in the film measured by TDS analysis may be, for example, 1.0 × 10 １５ There may be more than one.

[0021] The first metal oxide may be an oxide containing only trivalent transition metal elements as transition metal elements, an oxide containing only tetravalent transition metal elements as transition metal elements, or an oxide containing only trivalent transition metal elements and tetravalent transition metal elements as transition metal elements.

[0022] The first metal oxide may contain two or more transition metal elements. When the first metal oxide contains two or more transition metal elements, the first metal oxide may be, for example, an oxide containing one or more trivalent transition metal elements and one or more tetravalent transition metal elements, or may be an oxide containing two or more trivalent transition metal elements, or may be an oxide containing two or more tetravalent transition metal elements.

[0023] Examples of trivalent transition metal elements include samarium (Sm), yttrium (Y), and lanthanum (La). When the membrane contains a trivalent transition metal element, the trivalent transition metal element is preferably samarium or yttrium from the viewpoint of proton conductivity (dielectric constant of the membrane).

[0024] Examples of tetravalent transition metal elements include hafnium (Hf), zirconium (Zr), and titanium (Ti). When the membrane contains a trivalent transition metal element, the tetravalent transition metal element is preferably hafnium or titanium from the viewpoint of proton conductivity (frequency response of the dielectric constant of the membrane).

[0025] From the viewpoint of the denseness of the membrane and the proton conductivity, the first metal oxide is preferably an oxide containing a trivalent transition metal element and a tetravalent transition metal element (hereinafter also referred to as the second metal oxide). In the second metal oxide, examples of combinations of two kinds of transition metal elements include samarium and hafnium; samarium and zirconium; yttrium and zirconium; lanthanum and hafnium; lanthanum and zirconium; and lanthanum and titanium. Among them, from the viewpoint of the proton conductivity and heat resistance, the combination of samarium and hafnium is preferred.

[0026] The second metal oxide can be a compound having an (AB)O type structure, where A is a trivalent transition metal element, B is a tetravalent transition metal element, and O is an oxygen atom. Examples of combinations of A and B include the above-mentioned examples of combinations of trivalent transition metal elements and tetravalent transition metal elements. The notation "(AB)" indicates that the sum of the molar ratios in parentheses is 1. Examples of the structure of the second metal oxide include (SmHf)O, (SmZr)O, (YZr)O, (LaHf)O, (LaZr)O, and (LaTi)O. Among these, (SmHf)O is preferred from the viewpoints of proton conductivity and heat resistance.

[0027] The mass content of the trivalent transition metal element relative to all transition metal elements contained in the membrane is preferably 0 mol % or more and 70 mol % or less, more preferably 0 mol % or more and 50 mol % or less, and even more preferably 30 mol %, from the viewpoints of proton conductivity and membrane density.

[0028] When the membrane contains samarium, the content of samarium relative to all transition metal elements contained in the membrane is preferably more than 0 mol % and not more than 70 mol %, more preferably more than 0 mol % and not more than 50 mol %, and even more preferably 30 mol %, from the viewpoints of proton conductivity and membrane density.

[0029] The second metal oxide preferably has a molar ratio (A / B) of the trivalent transition metal element (A) to the tetravalent transition metal element (B) of more than 0 and not more than 7 / 3, more preferably more than 0 and not more than 1, and even more preferably 3 / 7, from the viewpoints of proton conductivity, membrane density, and denseness. ０．３ B ０．７ It has an O-type structure.

[0030] When the membrane contains samarium and hafnium, the molar ratio of samarium to hafnium is preferably greater than 0 and less than 7 / 3, more preferably greater than 0 and less than 1, and even more preferably 3 / 7, from the viewpoints of proton conductivity, membrane density, and compactness. When the second metal oxide contains samarium and hafnium, the second metal oxide is preferably Sm ０．３ Hf ０．７ The transition metal element content in the film and the first and second metal oxides can be adjusted by adjusting the blending amount of a precursor compound, which will be described later and is used as a starting material when producing the film.

[0031] When the membrane contains a tetravalent transition metal element, the membrane density may be, for example, 80% or more, or 100% or less, when the membrane density of a bulk oxide of the tetravalent transition metal element is taken as 100%. When the membrane contains a trivalent transition metal element and a tetravalent transition metal element, the membrane density may be, for example, 95% or more, or 120% or less, when the membrane density of a bulk oxide of the trivalent transition metal element is taken as 100%. When the membrane density is in the above range, proton conductivity tends to be easily increased.

[0032] When the film contains a trivalent transition metal element and a tetravalent transition metal element, the film density is, for example, 8.0 g / cm ３ or more or 8.3 g / cm ３ or more, and ３ or less than 9.2 g / cm ３ It may be the following:

[0033] The thickness of the film may be, for example, 1 nm or more, or 10 nm or more, or 50 nm or more. The thickness of the film may be, for example, 10 μm or less, or 1 μm or less and 500 nm or less.

[0034] The film of the present disclosure can be used in, for example, capacitors, transistors, solid-state batteries, etc. The film of the present disclosure is suitable as a gate insulating film for a field-effect transistor. A field-effect transistor using the film of the present disclosure can exhibit high current drive due to the proton electric double layer. Furthermore, since the field-effect transistor using the film of the present disclosure is an inorganic solid-state device, it is suitable for application to electronic devices. Furthermore, the field-effect transistor using the film of the present disclosure can also be applied to sensors, ionic devices, neurodevices, etc.

[0035] 2 shows a schematic cross-sectional view of an example of a transistor using the film of the present disclosure. The transistor 10 can be a field-effect transistor. The transistor 10 includes a source electrode 11 and a drain electrode 12 disposed on a semiconductor film or ion-conductive film 15, and a gate electrode 13 disposed on a substrate 16. A film 14 of the present disclosure is disposed between the semiconductor film or ion-conductive film 15 and the substrate 16, covering the gate electrode 13. The film 14 may be disposed in direct contact with the semiconductor film or ion-conductive film 15, the substrate 16, and the gate electrode 13. The film 14 can function as an insulating film. The substrate 16 can be made of, for example, SiO ２ The film 14 may be, for example, a film having a (SmHf)O type structure.

[0036] The film of the present disclosure can be produced using, for example, a CSD (Chemical Solution Deposition) method. As shown in FIG. 3 , the film production method of the present disclosure can include, for example, the following steps: a first step (A) of applying a film-forming solution to a substrate to form a first coating film, and a second step (B) of baking the first coating film. The film production method of the present disclosure may also include a solvent removal step between the first and second steps of removing the solvent from the first coating film. The film-forming solution can include at least one compound selected from the group consisting of acetyl-based, alkoxide-based, and carboxylic acid-based compounds containing a trivalent transition metal element or a tetravalent transition metal element (hereinafter also referred to as a precursor compound), an alkylcarboxylic acid-based additive, and a solvent. Examples of acetyl-based compounds include metal acetylacetonates. Examples of alkoxide-based compounds include metal isopropoxides. Examples of carboxylic acid-based compounds include metal acetates.

[0037] As examples of the trivalent transition metal element and the tetravalent transition metal element contained in the precursor compound, the examples of the trivalent transition metal element and the tetravalent transition metal element given in the above description of the film are applicable.

[0038] The precursor compound is preferably an acetyl-based compound containing a trivalent transition metal element or a tetravalent transition metal element. Examples of acetyl-based compounds containing a trivalent transition metal element include samarium(III) acetylacetonate (Sm-acac), yttrium(III) acetylacetonate (Y-acac), and lanthanum(III) acetylacetonate (La-acac). Examples of acetyl-based compounds containing a tetravalent transition metal element include hafnium(IV) acetylacetonate (Hf-acac), hafnium(IV) isopropoxide (Hf-ip), zirconium(IV) acetylacetonate (Zr-acac), and titanyl(IV) acetylacetonate (Ti-acac).

[0039] The coating film-forming solution may contain two or more precursor compounds. When the coating film-forming solution contains two or more precursor compounds, the coating film-forming solution may contain, for example, one or more precursor compounds containing a trivalent transition metal element and one or more precursor compounds containing a tetravalent transition metal element, or may contain two or more precursor compounds containing a trivalent transition metal element, or may contain two or more precursor compounds containing a tetravalent transition metal element. When the coating film-forming solution contains two or more precursor compounds, the types and blending ratios of the precursor compounds can be adjusted depending on the types and mass ratios of the transition metal elements in the metal oxide finally obtained.

[0040] Examples of alkyl carboxylic acid additives include saturated carboxylic acids having a straight chain or one or more branched chains and having 2 to 15 carbon atoms. The alkyl carboxylic acid additive may be, for example, propionic acid. The content of the alkyl carboxylic acid additive in the coating film-forming solution (including the carboxylic acid in the mixed solvent described below) may be 10 to 50 parts by mass per 100 parts by mass of the precursor compound.

[0041] As the solvent, for example, an alcohol can be used. Examples of the alcohol include monohydric alcohols such as methanol and ethanol, and dihydric alcohols such as ethylene glycol. The solvent may also be a mixed solvent of an alcohol and a carboxylic acid such as propionic acid. The content of the solvent in the coating film-forming solution may be, for example, 50 to 3,000 parts by mass or 50 to 1,500 parts by mass per 100 parts by mass of the solid content.

[0042] In the first step, the first coating film can be formed by spin coating. Specifically, the coating film-forming solution is dropped onto the substrate, and the substrate is then rotated to coat the coating film-forming solution with a uniform thickness, thereby forming the first coating film.

[0043] When the film of the present disclosure includes a solvent removal step, the solvent can be evaporated in the solvent removal step by, for example, placing the substrate on which the first coating film has been formed on a hot plate heated to a temperature of 100 to 300°C for 1 to 15 minutes.

[0044] In the second step, the first coating film is calcined. Calcination can be carried out, for example, in an oxygen atmosphere at a temperature of 600 to 900°C for 10 minutes to 1 hour. Calcination can be carried out using a calcination furnace. The temperature rise time can be, for example, 50 to 600°C / min. The film of the present disclosure can be adjusted to a desired thickness by repeating the steps from the first step to the second step. When the method for producing a film of the present disclosure includes a solvent removal step, the steps up to the first step and the solvent removal step, or the steps up to the first step, the solvent removal step, and the second step can be repeated to adjust to a desired thickness.

[0045] <Film Preparation> A coating film-forming solution was prepared by mixing 100 parts by mass of a first precursor compound (hereinafter referred to as precursor 1) and / or a second precursor compound (hereinafter referred to as precursor 2) shown in Table 1, 25 to 80 parts by mass of an alkylcarboxylic acid having 2 to 15 carbon atoms, and a solvent (a mixed solvent of alcohol and propionic acid) (210 parts by mass per 100 parts by mass of solids) so that the content of the precursor compounds was 0.2 mol / kg. When precursor 1 and precursor 2 were blended, precursor 1 and precursor 2 were blended in the molar ratio (precursor 1:precursor 2) shown in Table 1. Note that for sample 6, a coating film-forming solution was prepared without adding alkylcarboxylic acid. For sample 6, samarium nitrate (Sm-NO ) was used as precursor 1. ３ ), and hafnium isopropoxide (Hf-ip) was used as precursor 2.

[0046] The coating film-forming solution was dropped onto a substrate made of platinum (Pt), and a first coating film was formed by spin coating (2000 rpm). The first coating film was placed on a hot plate at a temperature of 100 to 300°C and heat-treated for 1 to 15 minutes to remove the solvent, thereby forming a second coating film. This process was repeated six times. The second coating film was then placed in a baking furnace and baked in an oxygen atmosphere at a temperature increase rate of 50 to 600°C / min at the baking temperature shown in Table 1, to produce films of Samples 1 to 17. The thickness of the obtained film was 100 to 200 nm in all test examples.

[0047] "*" indicates samples not in accordance with this disclosure.

[0048] [Measurement of Electrical Conductivity] A Pt substrate was placed on the surface of the sample opposite the substrate, and a capacitor was fabricated in which the film was sandwiched between two electrodes made of Pt substrates. An AC signal with an amplitude of 10 to 50 mV and a frequency of approximately 1 to 100 kHz was applied to the upper and lower electrodes, and the L, C, and R components (AC impedance) of the sample were measured from the phase shift of the applied signal. The conductivity (S / cm) was calculated from the resistance component (R) of this data. Figure 4 shows the electrical conductivity (S / cm) versus the mass ratio of Sm at room temperature. High electrical conductivity was confirmed at room temperature for all of Samples 1 to 5. When the molar ratio of samarium to hafnium was 30:70, the electrical conductivity at room temperature was 1.1 x 10 －３ (S / cm).

[0049] 5 shows scanning electron microscope (SEM) images of cross sections in the thickness direction of Samples 1 to 5. It was confirmed that dense films were formed in Samples 2 to 4, which contained samarium and hafnium.

[0050] [Measurement of Film Density] The film density was measured by the XRR method (X-ray reflectivity). X-rays were incident on the sample surface at a very shallow angle, and the reflected intensity was measured. The reflected X-ray intensity profile obtained by this measurement was compared with the simulation results, and the simulation parameters were optimized to determine the film thickness and film density of the sample. The film thickness of Samples 1 to 4 and 6 was measured, and then the mass of the film separated from the substrate was measured. The film density per unit volume (g / cm) was calculated from the film area and film thickness. ３ ) was calculated. Figure 6 shows the film density of samples 1 to 4 and 6. The film density of samples 1 to 4 was 8.2 g / cm ３ The film densities of samples 1 to 4 were the same as those of bulk hafnium oxide (film density 9.68 g / cm ３ The film densities of samples 1 to 4 were 80% or more of the film density of bulk samarium oxide (film density 8.35 g / cm ３ ) had a film density equivalent to or higher than that of the other films.

[0051] [Evaluation of Frequency Dependence of Dielectric Constant] The capacitance (C) measured in the above-mentioned electrical conductivity measurement was calculated using the following formula: ε ｒ= (C × d) / (S × ε ０ ) (where ε ｒ is the relative dielectric constant of the film, ε ０ is the dielectric constant of a vacuum, C is the capacitance of the capacitor, d is the thickness of the sample film, and S is the area of ​​the electrode).

[0052] FIG. 7 shows the relative dielectric constant (ε ｒ As shown in FIG. 7, Sample 7 exhibited a higher relative dielectric constant than Sample 6. The capacitance density of Sample 7 was 200 to 300 nF / mm ２ It was.

[0053] The results of infrared spectroscopy (IR analysis) performed on Samples 6 and 7 are shown in Figures 8 and 9. In IR analysis, infrared light is incident on the top surface of a thin film sample, and the reflected or transmitted infrared absorption spectrum is measured. Information on the molecular structure can be obtained by measuring the infrared absorption due to molecular vibration. Sample 7 exhibited higher peaks for both carboxyl groups (-COOH) and hydroxyl groups (-OH) than Sample 6. The carboxyl groups detected in Sample 6 are residual components derived from the carboxylic acid solvent, and are thought not to contribute to proton generation or the high dielectric constant. The reason why Sample 6 did not achieve a high dielectric constant (proton conductivity) is that nitrate (Sm-NO ) was used as Precursor 1 in Sample 6. ３ ), and alkoxide (Hf-isopropoxide) was used as precursor 2, which made it difficult for ligand exchange to occur between the solvent and precursor (i.e., metal-carboxylate salts were unlikely to exist), and the oxidative thermal decomposition reaction proceeded as precursors 1 and 2. As a result, it was thought that the reason for this was that "metal-carboxylate salts" that could be a proton generation source were unlikely to remain in the film after firing. Sample 7 contained many carboxyl groups and hydroxyl groups, and as a result, protons (H ＋ ) and moisture were present, which is presumed to have caused Grotus conduction of protons.

[0054] To support this assumption, Figure 10 shows the results of secondary ion mass spectrometry (SIMS) in the thickness direction of Sample 7 after substitution with deuterium. As shown in Figure 10, hydrogen was confirmed to be present even near the substrate side. Since deuterium is present even near the substrate side of the membrane of the present disclosure, it is inferred that water is easily absorbed into the membrane. This indicates that the membrane of the present disclosure exhibits proton conductivity. In SIMS analysis, when ions are incident on the sample surface, various particles such as electrons, neutral particles, and ions are emitted from the sample surface. By detecting ions among these particles and measuring the detected amount at each mass, qualitative and quantitative evaluation of the components contained in the sample can be performed. SIMS analysis was performed in the depth direction of the membrane on a sample immersed in deuterium at a temperature of 80°C for 12 hours or more, and the amount of deuterium (D) in the membrane was measured. It is suggested that the deuterium detected here is hydrogen derived from water absorption.

[0055] FIG. 11 shows the relative dielectric constant (ε ) calculated from the capacitance measured for the capacitors fabricated using Samples 8 to 11 fabricated at different firing temperatures. ｒ ) is shown. It can be seen that the relative dielectric constant is maintained at 200 to 1600 even when the firing temperature is in the range of 450°C to 700°C. Figure 12 shows the dielectric loss (tan δ) for Samples 8 to 11. Almost no change in dielectric loss was observed when the firing temperature was in the range of 450°C to 700°C. It can be seen that the membrane of the present disclosure exhibits proton conduction not only at relatively high temperatures but also at relatively low temperatures. Figure 13 shows the results of XRD analysis of Sample 11. As shown in Figure 13, no peaks due to metal oxides were observed. It can be seen that the metal oxide is present in an amorphous state in the membrane of Sample 11.

[0056] FIG. 14 shows the relative dielectric constant (ε ｒ ) shows the frequency dependence of the dielectric constant. Samples 7 to 9 all showed a higher relative dielectric constant than Sample 6. Figure 15 shows the dielectric loss (tan δ) of Samples 12 to 14. No significant change in the dielectric loss was observed for Samples 12 to 14.

[0057] FIG. 16 shows the relative dielectric constant (ε ｒ) shows the frequency dependence. Figure 17 shows the dielectric loss (tan δ) of Samples 15 to 17. Samples 15 to 17 all exhibited higher relative dielectric constants than Sample 2. Sample 17 tended to have a higher relative dielectric constant in the high frequency range than Samples 15 and 16. It can be seen that Sample 17, which contains hafnium, tends to have a higher frequency response than Sample 15, which contains zirconium, and Sample 16, which contains titanium.

[0058] <Fabrication of Field-Effect Transistor> A field-effect transistor having the configuration shown in FIG. 2 was fabricated. ２ / The insulating film of the gate electrode arranged on the Si substrate was made of Sm in the same manner as in Sample 2. ０．３ Hf ０．７ A film containing a metal oxide with an O-type structure was used. An indium tin oxide (ITO) film was used as the oxide film. The Id-Vg and Ig-Vg characteristics of the field-effect transistor were evaluated. The results are shown in FIG. 18. The large proton electric double layer capacitance exhibited by the transistor's gate insulating film (the sample of the present disclosure) enabled steep switching operation at an extremely low gate voltage of 1 V or less.

[0059] In the above-described embodiments, configurations that can be combined may be combined with each other.

[0060] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

[0061] It will be appreciated by those skilled in the art that the exemplary embodiments described above are examples of the following aspects.

[0062] (Item 1) The film of the present disclosure includes an oxide of a transition metal element, and includes at least one selected from the group consisting of a carboxyl group, a hydroxyl group, and salts thereof. The oxide of the transition metal element includes at least one of a trivalent transition metal element and a tetravalent transition metal element.

[0063] (Item 2) In the film according to item 1, the oxide of a transition metal element contains two or more kinds of transition metal elements.

[0064] (Item 3) In the film according to item 1 or 2, the oxide of the transition metal element contains a trivalent transition metal element and a tetravalent transition metal element.

[0065] (Item 4) In the film according to any one of Items 1 to 3, the oxide of a transition metal element contains at least one combination of transition metal elements selected from the group consisting of the following combinations of two types of transition metal elements: samarium and hafnium; samarium and zirconium; yttrium and zirconium; lanthanum and hafnium; lanthanum and zirconium; and lanthanum and titanium.

[0066] (Item 5) In the film according to any one of items 1 to 4, the molar ratio of trivalent transition metal elements to the transition metal elements contained in the film is 0 mol % or more and 70 mol % or less.

[0067] (Item 6) In the film according to any one of items 1 to 5, the molar ratio of trivalent transition metal elements to the transition metal elements contained in the film is 0 mol % or more and 50 mol % or less.

[0068] (Item 7) A transistor according to the present disclosure is a transistor comprising a source electrode and a drain electrode disposed on a semiconductor film or an ion conductive film, and a gate electrode disposed on a substrate, in which the film according to any one of items 1 to 6 is disposed between the semiconductor film or the ion conductive film and the substrate, covering the gate electrode.

[0069] (Item 8) A method for producing a film according to any one of Items 1 to 6, comprising a first step of applying a coating film-forming solution onto a substrate to form a first coating film, and a second step of baking the first coating film, wherein the coating film-forming solution contains at least one compound selected from the group consisting of acetyl-, alkoxide-, and acetate-based compounds containing a trivalent transition metal element or a tetravalent transition metal element, an alkylcarboxylic acid-based additive, and a solvent.

[0070] 1 capacitor, 2, 3 electrode, 4 film, 10 transistor, 11 source electrode, 12 drain electrode, 13 gate electrode, 14 film, 15 semiconductor film or ion-conducting film, 16 substrate.

Claims

1. A film containing an oxide of a transition metal element, the film containing at least one selected from the group consisting of a carboxy group, a hydroxy group, and salts thereof, wherein the oxide of the transition metal element contains at least one of a trivalent transition metal element and a tetravalent transition metal element.

2. The film according to claim 1, wherein the oxide of a transition metal element comprises two or more transition metal elements.

3. The film according to claim 1 or 2, wherein the oxide of the transition metal element includes a trivalent transition metal element and a tetravalent transition metal element.

4. The film according to any one of claims 1 to 3, wherein the oxide of a transition metal element comprises at least one combination of transition metal elements selected from the group consisting of the following combinations of two transition metal elements: samarium and hafnium; samarium and zirconium; yttrium and zirconium; lanthanum and hafnium; lanthanum and zirconium; and lanthanum and titanium.

5. A film according to any one of claims 1 to 4, wherein the molar ratio of the trivalent transition metal element to all transition metal elements contained in the film is 0 mol % or more and 70 mol % or less.

6. A film according to any one of claims 1 to 5, wherein the molar ratio of the trivalent transition metal element to all transition metal elements contained in the film is 0 mol % or more and 50 mol % or less.

7. A transistor comprising a source electrode and a drain electrode disposed on a semiconductor film or an ion conductive film, and a gate electrode disposed on a substrate, wherein the film according to any one of claims 1 to 6 is disposed between the semiconductor film or the ion conductive film and the substrate, covering the gate electrode.

8. A method for producing a film according to any one of claims 1 to 6, comprising: a first step of applying a coating film-forming solution onto a substrate to form a first coating film; and a second step of baking the first coating film, wherein the coating film-forming solution contains at least one compound selected from the group consisting of acetyl-based, alkoxide-based, and acetate-based compounds containing a trivalent transition metal element or a tetravalent transition metal element, an alkylcarboxylic acid-based additive, and a solvent.

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