Coating liquid, metal compound thin film formed by using coating liquid, and method for forming the same

The present invention relates to a coating liquid used for forming a conductive thin film, a conductive thin film, a method for forming the same, and a product having the conductive thin film formed on the surface.

Conductive thin films are applied in a wide range of fields, and are indispensable for most display devices such as plasma displays (PDP), liquid crystal displays (LCD), and organic EL displays (OLED), especially in display-related applications. It has become.

Most of these display-related applications are carried out by vapor phase methods such as sputtering. This is because the thin film formed by the vapor phase method is dense, so that the resistivity is low and the film uniformity is excellent.

However, in the gas phase method such as sputtering, the above-mentioned equipment is increased in size, the vacuum is maintained during large area film formation, high energy is required during film formation, the yield is poor, and the utilization efficiency of the target is poor. Therefore, there is a problem that the utilization efficiency of raw materials is low.

As a method for solving these problems, there is a liquid phase method shown below. According to the liquid phase method, there is an advantage that a large device is not required and energy consumption is low.

(i) A technique for drying ITO fine particles together with a binder to form a film (see Patent Document 1).

(ii) A technique of spraying a solution of an organic metal or an inorganic salt onto a heated substrate from an atomizer to precipitate a solid phase from the liquid phase and deposit it as a thin film on the substrate (see Patent Document 2).

(iii) A technique for immobilizing indium tin oxide and tin oxide in a sol containing a metal alkoxide obtained by a sol-gel method (see Patent Document 3).

(iv) A technique of coating a solution of an organometallic (indium or tin) compound (complex) to form a film, producing a thin film without going through a sol-gel reaction process, and firing the film (see Patent Document 4).<patcit num="1"><text>Japanese Patent Application Laid-Open No. 6-119816</text></patcit><patcit num="2"><text>Japanese Unexamined Patent Publication No. 2006-73267</text></patcit><patcit num="3"><text>Japanese Unexamined Patent Publication No. 10-237078</text></patcit><patcit num="4"><text>Japanese Unexamined Patent Publication No. 2002-42583</text></patcit>

<p num="0010"> However, in the technique (i) above, a binder is required to hold the conductive particles on the surface, and since the binder resin is usually an insulator such as silica, there is a limit to reducing the resistance of the thin film to be formed. is there.</p><p num="0011"> In the technique (ii) described above, in order to obtain a low resistivity, it is usually necessary to spray several tens to several hundreds of times, and there is a problem that the time efficiency of the process is poor.</p><p num="0012"> In the above technique (iii), since the progress of the polycondensation reaction varies greatly depending on the temperature and humidity, it is necessary to strictly control the film forming conditions in order to always obtain a uniform thin film. In addition, the sol of the coating liquid is often unstable, and there are many problems to be solved in implementation, such as the need to maintain the viscosity of the sol and to prevent the solid matter from settling.</p><p num="0013"> In the technique (iv) above, a chemically stable solution of an organic indium zuzu complex is applied, and a thin film is produced and calcined without going through a sol-gel reaction process. However, in the conventionally used complex molecule containing a ligand, since the organic part of the ligand occupies a large volume, the volume shrinkage at the time of firing to form a metal oxide is large, and the adhesion strength is high. Therefore, the durability may be insufficient depending on the application.</p><p num="0014"> Further, depending on the conditions, the adhesion to the substrate may be poor and peeling may occur, or even if the adhesion is adhered, a large number of cracks may occur. In the case of a transparent conductive film, the generation of fine cracks leads to an increase in turbidity (haze), which is not practically preferable. Further, since the problems of cracks and adhesion are prominent especially when a thick film is produced, it becomes necessary to strictly control the film thickness in order to obtain a good film.</p><p num="0015"> The present invention has been made in view of these problems, and an object of the present invention is to provide a technique relating to a conductive thin film having high transparency, high conductivity, and high adhesion to a substrate.</p>

<p num="0016"> The first invention of the present application made to solve such a problem is Reacts with the ligand represented by Chemical Formula 1<u style="single">An organometallic complex represented by Chemical Formula 2 or Chemical Formula 3,</u>The gist is a coating solution containing indium (In), tin (Sn) or indium (In) and tin (Sn) and both metal materials.</p><p num="0017"><chemistry num="1"><img id="000002" he="50" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry></p><p num="0018"> R in formula 1₂₁~ R₂₄Is one of the following (1) to (11), respectively, and X₁₁, X₁₂Is complex<u style="single">atom</u>Or it is a carboxylic acid.</p><p num="0019"> (1) C_lH_{2l + 1}Group represented by (where l is an integer from 0 to 4) (2) C_mH_2mGroup represented by (where m is an integer from 2 to 4) (3) C_nH_2n-1Group represented by (where n is an integer from 2 to 4) (4) A group represented by COOR (however, the above R is C_pH_{2p + 1}(However, p is an integer from 0 to 4) or R = C₆H₅Group represented by) (5) Aldehydes, ketones, COC_qH_{2q + 1}Group represented by (where q is an integer from 0 to 4) or benzophenone (6) Hydroxy (OH) or ethers (7) Amine (NH)₂) Or alkylamine (8) Amide (9) Halogen (10) Nitrile (CN) (11) Nitro (NO)₂)<chemistry num="2"><img id="000003" he="53" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry><chemistry num="3"><img id="000004" he="42" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></chemistry><u style="single">R in Chemical Formula 2 and Chemical Formula 3</u>_{<u style="single">11</u>}<u style="single">~ R</u>_{<u style="single">20</u>}<u style="single">Is any of (1) to (11) in claim 1, and X</u>_{<u style="single">1</u>}<u style="single">~ X</u>_{<u style="single">10</u>}<u style="single">Is a complex atom or carboxylic acid.</u> By using the coating liquid of the present invention, a conductive thin film can be formed on the surface of the substrate. For example, when the coating liquid of the present invention is applied to the surface of a substrate, the surface of the substrate contains indium (hereinafter, also referred to as In), tin (hereinafter, also referred to as Sn), or both In and Sn. A coating film containing a metal compound is formed. Next, when the coating film is fired, the above metal compound is thermally decomposed, the ligand disappears, and a metal oxide thin film (conductive thin film) containing In, Sn, or both In and Sn is formed. ..</p><p num="0020"> The conductive thin film formed by using the coating liquid of the present invention has a high film density, does not cause cracks, and has excellent adhesion to the substrate. Moreover, since the film density is high, the conductivity is high. Further, since cracks do not occur, the turbidity (haze) is low, so that a transparent conductive thin film can be obtained.</p><p num="0021"> As described above, the reason why the film density is high and cracks do not occur is presumed as follows. That is, the metal material that reacts with the ligand represented by Chemical Formula 1 and contains In, Sn, or both In and Sn has a flat structure as is clear from the molecular structure represented by Chemical Formula 1. Therefore, when the coating liquid is applied to the surface of the substrate to form a coating film, a molecular assembly structure (stacking) is formed in which the metal materials overlap each other due to the interaction between the metal materials.</p><p num="0022"> The interaction between aromatic rings contained in the ligand also contributes to the formation of the above-mentioned molecular assembly structure. As a result, even if the ligand disappears during firing, volume shrinkage in the direction parallel to the surface of the substrate is suppressed, and crack generation and peeling are suppressed.</p><p num="0023"> The reason why cracks and poor adhesion were generated when the metal oxide thin film was formed from the conventionally used organometallic complex is considered as follows. That is, when metal atoms form a complex, a bond is formed using the d-orbital of the outermost shell, and this bond extends in the direction of each apex of the octahedron centered on the metal atom, and its tip. Since the substituent of the ligand is present in, the ordinary organic metal complex has a three-dimensional structure centered on the metal, for example, as in the molecular structure shown in FIG. Therefore, when the coating film composed of the organometallic complex is fired and the ligand disappears by thermal decomposition, a large volume shrinkage occurs in the three-dimensional direction, and as a result, cracks and peeling due to size mismatch with the substrate occur. It will occur.</p><p num="0024"> Further, the conductive thin film formed by using the coating liquid of the present invention has high hardness. Further, since the conductive thin film formed by using the coating liquid of the present invention is smooth and has high transparency, for example, when the conductive thin film is formed on the surface of glass, the permeability can be maintained. When a conductive thin film is formed on the surface of the mirror, the reflectance can be maintained.</p><p num="0025"> Further, the coating liquid of the present invention can form a durable conductive thin film even if it does not contain a binder. Therefore, the concentration of In oxide, Sn oxide, or In-Sn oxide in the formed thin film is not diluted with that of the binder, and thus In oxide, Sn oxide, or In-Sn oxidation. High action by objects (for example, conductive action).</p><p num="0026"> Moreover, since the coating liquid of the present invention is stable, it can be stored for a long period of time.</p><p num="0027"> Further, the metal oxide thin film (conductive thin film) formed by using the coating liquid of the present invention functions as a transparent conductive film.</p><p num="0028"> The coating liquid of the present invention can be easily produced. For example, an indium-tin complex is produced by adding an appropriate amount of catechol, which is a ligand, to an indium or tin atom to a raw material such as indium alkoxide or tin chloride in a suitable solvent, and then heating the mixture. Depending on the situation, it is only necessary to filter or evaporate the solvent for recovery.</p><p num="0029"> Since this indium-tin complex has a planar structure, it forms a molecular structure in which complex molecules overlap each other in a coated and dried state (stacking). The interaction between aromatic rings also contributes to this molecular structure.</p><p num="0034"> The coating liquid of the present invention contains, for example, alcohols (eg, methanol, ethanol, 2-propanol, n-butanol, isobutanol), ethers (eg, diethyl ether, MTBE, THF), ethylene glycol, ethylene as solvents. Glycol monomethyl ether, ethylene glycol dimethyl ether, hydrocarbons (eg octane, n-hexane, cyclohexane, benzene, toluene, xylene), dimethyl sulfoxide (DMSO), amides (eg dimethylformamide), lactams (eg dimethylformamide) N-Methylpyrrolidinone (NMP)), halides (eg carbon tetrachloride, chloroform, dibromomethane, dichloromethane), ketones (eg acetone, methyl ethyl ketone (MEK)), β-ketones (eg acetylacetone (acac)) )), Esters (eg, ethyl acetate), lactones (eg, γ-butyrolactone, ε-caprolactone), nitroalkane (eg, nitroethane, nitromethane), water and the like.</p><p num="0035"> The concentration of the organometallic complex in the coating liquid is not particularly limited as long as it does not exceed the solubility of the organometallic complex, but for example, a concentration of 0.1 M to 0.8 M is preferable. When forming a composite conductive thin film in which two or more kinds of metals are uniformly mixed, the corresponding organometallic complexes may be mixed and used in a desired ratio.</p><p num="0036"> The second invention of the present application is By applying the coating liquid of the first invention to the surface of the substrate to form a coating film and firing, one or more selected from the group consisting of the metal material contained in the coating film is transformed into a conductive thin film. The gist is a method for forming a conductive thin film, which is characterized by the fact that</p><p num="0037"> The conductive thin film formed by the present invention does not cause cracks, has excellent adhesion to the substrate, and has high hardness. Further, as described above, since cracks do not occur, the film thickness of the conductive thin film can be increased.</p><p num="0038"> Further, since the conductive thin film formed by the present invention is hard, smooth and highly transparent, for example, when a conductive thin film is formed on the surface of glass, the transparency can be maintained, and the mirror can be maintained. When a conductive thin film is formed on the surface, the reflectance can be maintained.</p><p num="0039"> Further, the coating liquid used in the present invention can form a durable conductive thin film even if it does not contain a binder. Therefore, the concentration of In oxide, Sn oxide, or In-Sn oxide in the formed thin film is not diluted with that of the binder, and thus In oxide, Sn oxide, or In-Sn oxidation. High action by objects (for example, conductive action).</p><p num="0040"> The substrate is not particularly limited, but when the firing method is used in the step of forming the conductive thin film, it is desirable that the substrate is a substance that can withstand the temperature at the time of firing. Specific examples of the substrate include heat-resistant polymers of glass (eg, PYREX® glass, normal glass, quartz glass), ceramics (eg, alumina, zirconia, silica), and resins (eg, polyimide resin). Can be mentioned.</p><p num="0041"> The coating method can be widely used as long as it is a wet method capable of forming a coating film of a coating liquid, and examples thereof include commonly used coating methods such as spin coating, dip coating, and spray coating. .. After applying the coating liquid, it is preferable that the coating film is naturally dried under normal temperature and pressure. After this, for example, the coating film can be fired.</p><p num="0042"> As a method of changing the organometallic compound into a conductive thin film, for example, there is a method of firing a coating film formed by applying a coating liquid. The firing temperature is preferably in the range of 350 to 1000 ° C, for example.</p><p num="0043"> When the firing temperature is 350 ° C. or higher, a dense film can be formed, so that a conductive thin film having conductivity and transparency can be obtained. Further, when the firing temperature is 700 ° C. or higher, a dense film can be formed, so that a transparent conductive thin film having higher conductivity can be obtained.</p><p num="0044"> Further, if the calcination is performed in the atmosphere and further in a reducing atmosphere (for example, in a mixed gas atmosphere of nitrogen and hydrogen), a conductive thin film having a lower resistivity can be formed.</p><p num="0045"> As described above, since the firing temperature may be as low as about 350 ° C., the conductive thin film can be formed on the surface of the heat-sensitive substrate by using the coating liquid of the present invention. Further, even when the substrate is ordinary glass, a conductive thin film can be formed without an undercoat. The firing temperature can be adjusted according to the type of metal M and the desired crystal phase of the conductive thin film.</p><p num="0046"> The third invention of the present application is The gist is a conductive thin film formed by the method for forming a conductive thin film, which is the second invention.</p><p num="0047"> The conductive thin film of the present invention does not crack, has high hardness, and has excellent adhesion to the substrate. Further, since the conductive thin film of the present invention is smooth and highly transparent, for example, when a conductive thin film is formed on the surface of glass, the transparency can be maintained and the surface of the mirror is conductive. When a thin film is formed, the reflectance can be maintained.</p><p num="0048"> Further, since the conductive thin film of the present invention does not have to contain a binder, the concentration of In oxide, Sn oxide, or In-Sn oxide in the formed thin film is thinner than that of the binder. There is no such thing, and the action of In oxide, Sn oxide, or In-Sn oxide (for example, conductive action) is high.</p><p num="0049"> The fourth invention of the present application is The gist of the present invention is a conductive thin film-coated product comprising a substrate and a conductive thin film formed on the surface of the substrate according to the second invention.</p><p num="0050"> In the conductive thin film-coated product of the present invention, the conductive thin film does not crack, has high hardness, and has excellent adhesion to the substrate. Further, since the conductive thin film in the present invention is smooth and highly transparent, for example, when the substrate is glass, transparency can be maintained, and when the substrate is a mirror, the reflectance can be increased. Can be maintained. Further, since the conductive thin film in the present invention does not have to contain a binder, the concentration of In oxide, Sn oxide, or In-Sn oxide in the formed thin film is thinner than that of the binder. There is no such thing, and the action of In oxide, Sn oxide, or In-Sn oxide (for example, conductive action) is high.</p><p num="0051"> The substrate is not particularly limited, but when the firing method is used in the step of forming the conductive thin film, it is desirable that the substrate is a substance that can withstand the temperature at the time of firing. Specific examples of the substrate include heat-resistant polymers of glass (eg, PYREX® glass, normal glass, quartz glass), ceramics (eg, alumina, zirconia, silica), and resins (eg, polyimide resin). Can be mentioned.</p>

<figref num="1">It is explanatory drawing which shows the molecular structure of the iminodiethanol complex.</figref>

Hereinafter, the present invention will be described based on examples. [Example] The present invention will be described with reference to examples.

(a) Production of metal complex Prepare a solution in which the amount of compound A shown in Table 1 below is dissolved in an appropriate amount of solvent (xylene), and indium acetate and tin (IV) butoxide finely crushed in a mortar are added to the following amounts (tin, tin). Butoxide was added dropwise) and mixed. Then, the mixed solution was refluxed for 1 hour, and then distilled at 132 ° C. until the amount of the mixed solution was halved. After distillation, the volatile components of the remaining mixture were evaporated under reduced pressure on the rotary evaporator. The remaining solid content was further heated to 100 ° C. under vacuum using a vacuum dryer to completely remove the remaining volatile components. The yield of solids is shown in Table 1.

The solid content did not change chemically even after storage for 6 months or more, and the electrical and optical properties did not change from the sample produced immediately after synthesis even when coating was performed 6 months or more after synthesis.

<tables num="1"><img id="000005" he="78" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

(b) Manufacture of coating liquid (Changes due to In and Sn composition of coating liquid) The powders obtained in Example 1 and Example 2 shown in Table 1 are dissolved in a solution in which 5 mL of acetylacetone and toluene are mixed at a ratio shown in Table 2 below at a ratio of 1: 1 to prepare a coating solution having a metal ion concentration of 0.5 M. Obtained.

0.4 mL of the solution was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired at 900 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film. Table 2 shows the sheet resistance, total transmittance, and turbidity of the formed conductive thin film.

The sheet resistance of the conductive thin film is measured using the NPS resistance measuring instrument Σ-5 (using the KS-TC-40-TF-VR probe) based on JIS R 1635, and the total transmittance and turbidity are measured using Nippon Denshoku Kogyo NDH5000W. It was used and measured based on JIS Z 8722.

<tables num="2"><img id="000006" he="114" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above results, it was found that the ratio of In and Sn in forming a conductive thin film is about 5 atom.% (Sn (doping amount)), which is the lowest sheet resistance. Therefore, all the following Examples / Comparative Examples were performed with this composition (In: Sn = 95: 5).

(Change due to solid content concentration of coating liquid) Based on the above results, the powder of Example 3 synthesized with the optimum composition of In and Sn precursors was dissolved in a solution of 100 mL of acetylacetone and toluene mixed in a ratio of 1: 1 as shown in Table 3 below. , A coating solution was obtained. The coating liquid did not precipitate even after 4 months or more after production, was chemically stable, and could be used in the same manner as immediately after production.

0.4 mL of the solution was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired at 900 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film.

The sample with the lowest resistivity was then N₂96% H₂Annealing (temperature rise 10 ° C / min, natural cooling) at 500 ° C. under a 4% reduction atmosphere (Example 11-4A). Table 3 shows the composition of the coating liquid before firing, the film thickness and resistivity after firing, the sheet resistance, the total transmittance, the turbidity and the film hardness.

The sheet resistance and resistivity of the conductive thin film are measured using the NPS resistance measuring instrument Σ-5 (using the KS-TC-40-TF-VR probe) based on JIS R 1635, and the total transmittance and turbidity are measured by Nippon Denshoku. Measured based on JIS Z 8722 using industrial NDH5000W. For the film thickness, measure the absorption of the substrate at a light wavelength of 250 nm with a spectrophotometer (Hitachi U-3310), check the corresponding film thickness with SEM (Hitachi S-4800), and use the following formula. Obtained the coefficient .. For other samples, the coefficient was used to determine the film thickness from the absorption of light.

Equation for determining the extinction coefficient: Abs. = 0.4343 αl Abs .: Absorbance α :: Absorption coefficient l :: Film thickness The hardness measurement conditions were based on the pencil scratch test (JIS K 5400).

<tables num="3"><img id="000007" he="59" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

As can be seen from the above results, the film thickness changed in proportion to the solid content concentration of the coating liquid. The hardness of the film was as high as&gt; 9H even when the film thickness became thicker. As the film thickness increased, both the resistivity and the sheet resistance decreased. After annealing, the resistivity and sheet resistance were further reduced.

(Change due to firing temperature) The powder obtained in Example 3 shown in Table 1 was dissolved in an appropriate amount in a 1: 1 mixture of 5 mL of acetylacetone and toluene to obtain a coating solution having a metal ion concentration of 0.75 M. 0.4 mL of the solution was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired in the range of 350 to 1000 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film. Table 4 below shows the resistivity and sheet resistance of the formed conductive thin film.

<tables num="4"><img id="000008" he="72" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above results, it was found that the conductivity was exhibited even when firing at 350 ° C, and the optimum firing temperature was 900 ° C when firing was for 1 hour.

(Change due to recoating) The powder obtained in Example 3 shown in Table 1 was dissolved in an appropriate amount in a 1: 1 mixture of 5 mL of acetylacetone and toluene to obtain a coating solution having a metal ion concentration of 0.25 M. 0.4 mL of the solution was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired at 900 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film. After that, the resistivity, sheet resistance and optical characteristics, and film hardness of the conductive thin film were measured, and the coating process and firing were repeated 5 times. After firing, the sample showing the lowest resistivity was annealed at 500 ° C for 1 hour in a reducing atmosphere (heating temperature 10 ° C / min, natural cooling) (Example 13-5A).

Table 5 below shows the resistivity, sheet resistance and optical characteristics of the formed conductive thin film.

<tables num="5"><img id="000009" he="60" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above results, the film thickness became thicker as the number of coatings increased, and even if the film thickness became thicker, the film hardness was as high as&gt; 9H. At the same time, as the film thickness increased, the resistivity and sheet resistance decreased. There was almost no change in optical characteristics.

(Changes due to differences in ligands and solvents) The powders obtained in Examples 3 to 9 shown in Table 1 were dissolved in the solvent shown in Table 6 below in the amounts shown in Table 6 to obtain a coating liquid having a metal ion concentration of 0.25 M. Then, 0.4 mL of the solution was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired at 900 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film. Then, the resistivity, sheet resistance and optical characteristics of the conductive thin film were measured.

<tables num="6"><img id="000010" he="77" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above results, the conductivity and the transparency of the substrate were confirmed even if the solvent and the ligand were other than those shown in Example 3 shown in Table 1.

(c) Comparative example (Comparative example 1) Prepare a solution in which 4.180 g of ethylhexanoic acid is dissolved in 20 mL of solvent (xylene), and add 2.630 g of indium acetate finely crushed in a mortar and 0.206 g of tin (IV) butoxide (tin and butoxide are added dropwise). , Mixed. Then, the mixed solution was refluxed for 1 hour, and then distilled at 132 ° C. until the amount of the mixed solution was halved. After distillation, the volatile components of the remaining mixture were evaporated under reduced pressure on the rotary evaporator. The remaining solid content was further heated to 100 ° C. under vacuum using a vacuum dryer to completely remove the remaining volatile components. The yield of solids was 5.24 g. The obtained powder was dissolved in 5 mL of toluene in an amount of 1.38 g to obtain a coating solution having a metal ion concentration of 0.5 M.

(Comparative example 2) Add 0.692 g of indium acetate finely crushed in a dairy pot and 0.054 g of tin (IV) butoxide to a mixed solution of 2.5 mL of acetylacetone + 2.5 mL of toluene (by dropping tin butoxide) to obtain a coating solution with a metal ion concentration of 0.5 M. It was.

(Comparative example 3) 0.840 g of indium nitrate trihydrate and 0.054 g of tin (IV) butoxide were added to a mixed solution of 2.5 mL of acetylacetone + 2.5 mL of toluene (by dropping tin butoxide) to obtain a coating solution having a metal ion concentration of 0.5 M. ..

(Performance of comparative example) 0.4 mL of the coating liquid obtained in Comparative Examples 1 to 3 was coated on a quartz glass plate (50 × 50 × 2 t mm) by spin coating (rotation speed at the time of application: 750 rpm). Then, the coated glass substrate was fired at 900 ° C. for 1 hour (heating temperature 10 ° C./min, natural cooling) to obtain a conductive thin film. Table 7 below shows the film thickness, resistivity, sheet resistance and optical characteristics of the conductive thin film.

<tables num="7"><img id="000011" he="40" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

(Comparison 1: Comparison by ligand) Table 8 below shows a comparison between Examples and Comparative Examples with different ligands. All samples are coated with 0.5M solution.

<tables num="8"><img id="000012" he="47" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above, it can be seen that even when the solutions having the same concentration are used, the resistivity and the sheet resistance of the examples are lower and the turbidity is lower than those of the other comparative examples, although the film thickness is thicker. This indicates that the examples have a dense and highly transparent film.

Next, in order to measure the density of the film, the refractive index at a light wavelength of 550 nm was measured with an ellipsometer (Mizojiri Optical Co., Ltd. DHA-XAVW / S6), and the porosity of the film was calculated by the following formula. Table 9 below shows the comparison. Porosity calculation formula P = 1-(n_p²-1) / (n_d²-1) P: Porosity N_p: Refractive index of dense film N_d: Refractive index of porous membrane

<tables num="9"><img id="000013" he="22" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above, it can be seen that in the examples, the membrane is denser (porosity is low) and the resistivity is also low.

(Comparison 2: Comparison by recoating) Table 10 below shows a comparison between the case where a low-concentration coating liquid is repeatedly applied and fired and the case where a high-concentration coating liquid is applied.

<tables num="10"><img id="000014" he="46" wi="159" file="JP5226512B2_D0001.tif" img-format="tif" img-content="drawing" /></tables>

From the above, it was found that there is almost no difference in performance between the coating liquid having a low concentration and being repeatedly coated and fired as compared with the coating liquid having a high concentration once. This indicates that the coating liquid of the example can be used to form a thick, dense and highly transparent film with a single application.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention can be carried out in various modes without departing from the present invention.