JP6236778B2 - Metal oxide film forming coating solution, metal oxide film, field effect transistor, and method of manufacturing field effect transistor - Google Patents

Description

  The present invention relates to a coating solution for forming a metal oxide film, a metal oxide film, a field effect transistor, and a method for manufacturing a field effect transistor.

  Conventionally, metal oxides such as antimony-doped tin oxide (ATO) and tin-doped indium oxide (ITO) are used as transparent conductive films as electrodes for display elements such as liquid crystal display elements and electroluminescence display elements, as well as automobiles, aircraft, and architecture. It is used as a heating resistor for preventing fogging of windows and other objects and for preventing freezing.

In recent years, it has been found that an oxide semiconductor such as ZnO, In ₂ O ₃ , or In—Ga—Zn—O, which is a kind of metal oxide, is a semiconductor that exhibits higher carrier mobility than amorphous silicon. Has been. And development of the field effect transistor (FET; Field Effect Transistor) which used these oxide semiconductors for the active layer is activated.

As a method for forming such a metal oxide thin film, a vacuum deposition method, a sputtering method, or the like is generally used. For example, it contains indium, positive divalent elements (especially zinc, magnesium, copper, cobalt, nickel, calcium) and oxygen using a vacuum film formation technique such as sputtering, and has a specific resistance of 10 ⁻¹ Ωcm to 10 ⁸ Ωcm. A semiconductor thin film has been proposed (see, for example, Patent Document 1).
However, the implementation of these methods has the problem of requiring complex and expensive equipment. There is also a problem that it is difficult to form a large-area thin film.

Therefore, as a simpler method that can increase the area, a coating solution in which an inorganic metal compound or an organic metal compound is dissolved in an organic solvent or the like, and another metal is added as an activator to impart higher conductivity. And a coating method using the coating solution have been studied.
For example, for the purpose of forming a thin film having high conductivity and transmittance, a composition for forming a transparent conductive film containing an inorganic indium compound, a magnesium compound, and an organic compound capable of coordinating with indium has been proposed (for example, , See Patent Document 2). In addition, a composition for forming a transparent conductive film in which an indium nitrate, a polyhydric alcohol condensate, and an active agent are dissolved in an organic solvent has been proposed (see, for example, Patent Document 3).
However, these proposed techniques are composition techniques for forming a transparent conductive film, and the obtained transparent conductive film cannot be used as an active layer of a field effect transistor and can be used. There is a problem that various applications are limited.

Further, the metal oxide precursor is an inorganic metal salt, a metal oxide precursor solution in which an inorganic metal salt is dissolved in water or ethanol as a solvent, and the metal oxide precursor solution is applied on a substrate. A method for manufacturing an oxide semiconductor has been proposed (see Patent Document 4). In the proposed technique, the obtained oxide semiconductor is studied for an active layer of a field effect transistor.
However, this proposed technique has a problem that when the metal oxide precursor solution is applied onto the base material, the coating liquid spreads thinly on the base material, so that the shape accuracy of the obtained oxide semiconductor is low.

  Therefore, it is required to provide a coating solution for forming a metal oxide film that can easily and easily produce a metal oxide film having a desired volume resistivity in a large area and that has a high accuracy for forming a metal oxide film having a desired shape. This is the current situation.

  An object of the present invention is to solve the above-described problems and achieve the following objects. That is, the present invention provides a metal oxide film-forming coating solution that can easily produce a metal oxide film having a desired volume resistivity in a large area and has a high accuracy for forming a metal oxide film of a desired shape. The purpose is to provide.

Means for solving the problems are as follows. That is,
The coating liquid for forming a metal oxide film of the present invention contains an inorganic indium compound, a barium compound, and an organic solvent.

  According to the present invention, the conventional problems can be solved, a metal oxide film having a desired volume resistivity can be easily produced in a large area, and a metal oxide film having a desired shape is formed. A coating solution for forming a metal oxide film with high accuracy can be provided.

FIG. 1 is a schematic configuration diagram showing an example of a bottom gate / bottom contact field effect transistor. FIG. 2 is a schematic configuration diagram showing an example of a bottom gate / top contact field effect transistor. FIG. 3 is a schematic configuration diagram showing an example of a top-gate / bottom-contact field effect transistor. FIG. 4 is a schematic configuration diagram illustrating an example of a top gate / top contact field effect transistor. FIG. 5A is a diagram showing an example of a method for producing a field effect transistor according to the present invention (part 1). FIG. 5B is a diagram showing an example of the method for producing the field effect transistor according to the present invention (part 2). FIG. 5C is a diagram showing an example of the method for producing the field effect transistor according to the present invention (part 3). FIG. 5D is a diagram showing an example of the method for producing the field effect transistor according to the present invention (part 4). FIG. 6 is a schematic view showing a state in which the coating property of the coating solution for forming a metal oxide film is good. FIG. 7 is a schematic diagram showing a state where the coating property of the coating liquid for forming a metal oxide film is poor. FIG. 8 is a graph showing the relationship between the gate voltage Vgs and the source-drain current Ids of the field effect transistor produced in Example 1.

(Coating liquid for forming metal oxide film)
The coating solution for forming a metal oxide film of the present invention contains at least an inorganic indium compound, a barium compound, and an organic solvent, and further contains other components as necessary.

By using the metal oxide film-forming coating solution, a metal oxide film having a desired volume resistivity can be obtained.
Note that the metal oxide film forming coating solution has a volume resistance of a metal oxide film (for example, an oxide semiconductor film) obtained depending on the conditions, specifically, the type of solvent to be dissolved and the concentration of the compound. It is possible to control the rate. The volume resistivity can also be controlled by substituting a part of each element constituting the In—Ba-based oxide with another metal element.
The volume resistivity can also be controlled by the heat treatment conditions after coating, more specifically, the firing temperature, firing time, temperature rise rate, temperature drop rate, and atmosphere (gas fraction and pressure) during firing.
Furthermore, the raw material decomposition | disassembly and reaction promotion effect by light can be utilized. In addition, since the volume resistivity is changed by annealing after the film is formed, a method of optimizing the annealing temperature and atmosphere is also effective.

<Inorganic Indium Compound>
There is no restriction | limiting in particular as said inorganic indium compound, According to the objective, it can select suitably, For example, an indium oxo acid, an indium halide, an indium hydroxide, an indium cyanide etc. are mentioned.
Examples of the indium oxoacid include indium nitrate, indium sulfate, indium carbonate, and indium phosphate.
Examples of the indium halide include indium chloride, indium bromide, and indium iodide.
Among these, in terms of high solubility in various solvents, indium oxoacid and indium halide are preferable, and indium nitrate, indium sulfate, and indium chloride are more preferable.

  There is no restriction | limiting in particular as said indium nitrate, According to the objective, it can select suitably, For example, the hydrate of an indium nitrate etc. are mentioned. Examples of the indium nitrate hydrate include indium nitrate trihydrate and indium nitrate pentahydrate.

  There is no restriction | limiting in particular as said indium sulfate, According to the objective, it can select suitably, For example, anhydrous indium sulfate, a hydrate of indium sulfate, etc. are mentioned. Examples of the hydrate of indium sulfate include indium sulfate nonahydrate.

  There is no restriction | limiting in particular as said indium chloride, According to the objective, it can select suitably, For example, the hydrate of an indium chloride etc. are mentioned. Examples of the hydrate of indium chloride include indium chloride tetrahydrate.

  As these inorganic indium compounds, synthesized ones or commercially available products may be used.

<Barium compound>
There is no restriction | limiting in particular as said barium compound, According to the objective, it can select suitably, For example, an organic barium compound, an inorganic barium compound, etc. are mentioned.

The organic barium compound is not particularly limited as long as it is a compound having barium and an organic group, and can be appropriately selected according to the purpose. The barium and the organic group are bonded by, for example, an ionic bond, a covalent bond, or a coordinate bond.
The organic group is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include an alkoxy group which may have a substituent, an acyloxy group which may have a substituent, and a substituent. And an acetylacetonate group which may have As said alkoxy group, a C1-C6 alkoxy group etc. are mentioned, for example. As said acyloxy group, a C1-C10 acyloxy group etc. are mentioned, for example.
Examples of the substituent include a halogen and a tetrahydrofuryl group.

Examples of the organic barium compound include the following compounds.
Barium bistetrahydrofurfuryl oxide
Barium 2-ethylhexanoate
Barium acetylacetonate As said x in the said structural formula, the integer of 0-2 is mentioned, for example.

Examples of the inorganic barium compound include barium oxoacid, barium halide, barium hydroxide, and barium cyanide.
Examples of the barium oxoacid include barium nitrate, barium acetate, barium carbonate, and barium phosphate.
Examples of the barium halide include barium chloride, barium bromide, and barium iodide.

  The barium chloride is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include anhydrous barium chloride and barium chloride hydrate. Examples of the hydrate of barium chloride include barium chloride dihydrate.

  The barium bromide is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include anhydrous barium bromide and hydrates of barium bromide. Examples of the hydrate of barium bromide include barium bromide dihydrate.

  The barium iodide is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include anhydrous barium iodide and barium iodide hydrate. Examples of the hydrate of barium iodide include barium iodide monohydrate and barium iodide dihydrate.

  Of these, barium bistetrahydrofurfuryl oxide, barium nitrate, barium carbonate, barium acetate, barium hydroxide, barium chloride, barium bromide, and barium iodide are preferred, with barium bistetrahydrofurfuroxide being preferred because of their high solubility in various solvents. More preferred are furyl oxide, barium chloride, barium bromide, and barium iodide.

  As these barium compounds, synthesized ones or commercially available products may be used.

It is preferable that the number of indium atoms (A) of the inorganic indium compound and the number of barium atoms (B) of the barium compound in the coating solution for forming a metal oxide film satisfy the following formula (1).
0.040 ≦ [B / (A + B)] ≦ 0.200 Formula (1)
Here, the indium atom and the barium atom may be in an ionic state.

  The coating liquid for forming a metal oxide film that satisfies the formula (1) can also be referred to as a coating liquid for forming an oxide semiconductor film.

It is known that an indium oxide film formed by sputtering can be obtained as a low resistance film of about 10 ⁻³ Ωcm to about 10 ⁻⁴ Ωcm by adding several to 20% of tin, zinc, gallium or the like. However, such a low volume resistivity does not function effectively as an active layer of a field effect transistor.

  The metal oxide film-forming coating solution satisfies the above-described formula (1), so that the volume resistivity of the oxide semiconductor film formed by applying the metal oxide film-forming coating solution is changed to a field effect type. A volume resistivity that effectively functions as an active layer of a transistor can be obtained.

  When [B / (A + B)] is less than 0.040 or exceeds 0.200, the volume resistivity of the obtained oxide semiconductor film is too high, and the field effect using the oxide semiconductor film as an active layer The type transistor has a low on / off ratio and may not exhibit good transistor characteristics.

An oxide semiconductor film used for an active layer of a field effect transistor used in a display driver circuit or the like is required to have high carrier mobility and so-called normally-off characteristics. In order to achieve high carrier mobility and normally-off characteristics, the volume resistivity of the oxide semiconductor film is preferably 10 ⁻² Ωcm to 10 ⁹ Ωcm.

When the volume resistivity of the metal oxide film used for the active layer is high, it may be difficult to achieve high carrier mobility in an on state by gate voltage control. Therefore, the volume resistivity of the metal oxide film is more preferably 10 ⁶ Ωcm or less.
When the volume resistivity of the metal oxide film used for the active layer is low, it may be difficult to reduce Ids (drain-source current) in an off state by gate voltage control. Therefore, the volume resistivity of the metal oxide film is more preferably 10 ⁻¹ Ωcm or more.
The volume resistivity ρ (Ωcm) of the metal oxide follows the following formula (2).
ρ = 1 / nQμ Equation (2)
In the above formula, Q (C) represents carrier charge, n (pieces / m ³ ) represents carrier density, and μ (m ² / V / s) represents carrier mobility.
Therefore, the volume resistivity can be controlled by changing these n, Q, and μ.
As a specific method of controlling the volume resistivity of the metal oxide film, there is generally a method of changing the carrier density by adjusting the amount of oxygen (oxygen defect density) in the film.

The metal oxide film forming coating solution can control the volume resistivity by satisfying the formula (1), and obtain an oxide semiconductor film effective as an active layer of a field effect transistor.
As a method for controlling the volume resistivity of the oxide semiconductor film formed from the metal oxide film forming coating solution, it is most effective to satisfy the range of the formula (1).

<Organic solvent>
There is no restriction | limiting in particular as said organic solvent, Although it can select suitably according to the objective, Glycol ethers and diol are preferable. That is, it is preferable that the coating liquid for forming a metal oxide film contains at least one of the glycol ethers and the diols.

-Glycol ethers-
Since the glycol ethers dissolve the inorganic indium compound and the barium compound well and have high stability after dissolution, the glycol ethers can be uniformly used by using the coating liquid for forming the metal oxide film. Thus, a metal oxide film (eg, an oxide semiconductor film) having high properties and few defects can be obtained.
Further, by using the glycol ether in the coating solution for forming the metal oxide film, a metal oxide film having a desired shape (for example, an oxide semiconductor film) can be formed with high accuracy.
The glycol ethers are considered to work as a reducing agent. Since an In—Ba-based oxide semiconductor that is an n-type semiconductor generates conduction electrons due to generation of oxygen defects, a material having higher conductivity can be obtained by moving the equilibrium to the reduction side. Therefore, when the coating liquid for forming a metal oxide film contains the glycol ethers, a reducing action acts during heat treatment after coating, and an oxide semiconductor film having a lower volume resistivity can be obtained.

There is no restriction | limiting in particular as said glycol ether, Although it can select suitably according to the objective, An alkylene glycol monoalkyl ether is preferable. As carbon number of the said glycol ethers, 3-6 are preferable.
The alkylene glycol monoalkyl ether is preferably at least one of ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoisobutyl ether. These alkylene glycol monoalkyl ethers have a boiling point of about 120 ° C. to 180 ° C. and dry quickly, so that the coating solution for forming a metal oxide film is difficult to spread. With such a preferable compound, the firing temperature is lowered, and firing in a relatively short time is possible. In addition, a metal oxide film (eg, an oxide semiconductor film) with few impurities after baking is obtained. As a result, since the carrier mobility increases, in the graph showing the relationship between the gate voltage Vgs and the source-drain current Ids of the field effect transistor using the oxide semiconductor film as the active layer, the rising edge is switched from off to on. , The switching characteristics are improved, and the driving voltage for obtaining the required on-current is lowered.
These may be used individually by 1 type and may use 2 or more types together.

  There is no restriction | limiting in particular as content of the said glycol ether in the said coating liquid for metal oxide film formation, Although it can select suitably according to the objective, 10 mass%-80 mass% are preferable. When the content is less than 10% by mass, the above-described effect when the glycol ether is contained (the effect that a metal oxide film having high uniformity and few defects can be obtained, and a desired shape The effect that the metal oxide film can be formed with high accuracy and the effect that a lower volume resistivity oxide semiconductor film can be obtained) may not be obtained. In some cases, the thickness of a metal oxide film (eg, an oxide semiconductor film) that can be formed is reduced.

-Diols-
The glycol ethers are preferably used in combination with diols. When the glycol ethers and the diols are used in combination, clogging due to solvent drying in the ink jet nozzle during application by the ink jet method can be eliminated by the action of the diols. Furthermore, it is possible to quickly dry the coating liquid adhered to the substrate or the like by the action of the glycol ethers, and to prevent the coating liquid from spreading to unnecessary portions. For example, it is possible to quickly dry a coating solution attached to a channel when manufacturing a field effect transistor and to prevent the coating solution from spreading outside the channel region.
In addition, since the glycol ethers usually have a low viscosity of about 1.3 cp to 3.5 cp, the coating liquid for forming a metal oxide film can be easily mixed with diols having a high viscosity. The viscosity can be adjusted.

  The diols are considered to function to increase the thermal stability of the metal salt by coordinating with the indium salt, barium salt, calcium salt, strontium salt, magnesium salt, and zinc salt.

There is no restriction | limiting in particular as said diol, Although it can select suitably according to the objective, Alkanediol and dialkylene glycol are preferable. As carbon number of the said diols, 2-4 are preferable. When the number of carbon atoms is 5 or more, the volatility is low, and the remaining metal oxide film (for example, an oxide semiconductor film) is likely to remain, and the fired metal oxide film (for example, an oxide semiconductor) May reduce the density of the film. When the density of the oxide semiconductor film is reduced, carrier mobility may be reduced and on-state current may be reduced.
Since diols having 2 to 4 carbon atoms have a boiling point of about 180 ° C. to 250 ° C., they volatilize during firing after applying the metal oxide film-forming coating solution, and metal oxide films (for example, oxidation It is difficult to remain in the (semiconductor film). Further, since the viscosity is about 10 cp to 110 cp, when the metal oxide film forming coating solution is applied by an ink jet method, the metal oxide film forming coating solution spreads when landing on a substrate or the like. There is an effect to suppress.
Examples of the diol include diethylene glycol, 1,2-ethanediol, 1,2-propanediol, and 1 from the viewpoint of the firing temperature and the denseness of the fired metal oxide film (for example, an oxide semiconductor film). , 3-butanediol is more preferable.
These may be used individually by 1 type and may use 2 or more types together.

  There is no restriction | limiting in particular as content of the said organic solvent in the said coating liquid for metal oxide film formation, Although it can select suitably according to the objective, 50 mass%-97 mass% are preferable, and 80 mass%- 97 mass% is more preferable. When the content is less than 50% by mass, the concentration of the inorganic metal compound is too high and the inorganic metal compound is likely to be precipitated due to solvent evaporation at the nozzle tip. In addition, in the case where water is a typical inorganic solvent, most of the remaining portion has a large surface tension of 72 dyn / cm, poor ejection characteristics with an inkjet, and a low boiling point of 100 ° C. May dry quickly and the nozzle may become clogged. When the content exceeds 97% by mass, the amount of the inorganic metal compound deposited after drying the coating solution is small, so the number of overcoating times for obtaining a metal oxide film having a required thickness increases, and the productivity decreases. There are things to do. When the content is within the more preferable range, the surface tension is reduced, which is advantageous in terms of dischargeability and drying property.

  In the coating solution for forming the metal oxide film, as a ratio of the raw material of the metal oxide film (for example, the inorganic indium compound and the barium compound) to the organic solvent (for example, the diols and glycol ethers), There is no restriction | limiting in particular, Although it can select suitably according to the objective, 0.1 mol-0.5 mol of the sum total of the said inorganic indium compound and the said barium compound is preferable with respect to 1 L of said organic solvents. When the content ratio is less than 0.1 mol, the thickness of the metal oxide film formed after firing becomes too thin, and it may be difficult to form a continuous film. Also, it may be necessary to repeat application and drying in order to obtain the required thickness. When the content ratio exceeds 0.5 mol, the frequency of nozzle clogging at the tip of the ink jet nozzle may increase when applied by the ink jet method.

<Other ingredients>
Examples of the other components include inorganic magnesium compounds, inorganic zinc compounds, inorganic calcium compounds, and inorganic strontium compounds.
Magnesium contained in the inorganic magnesium compound, zinc contained in the inorganic zinc compound, calcium contained in the inorganic calcium compound, and strontium contained in the inorganic strontium compound were coated with the coating solution for forming the metal oxide film. The metal oxide film (for example, an oxide semiconductor film) obtained in this manner functions as a dopant for replacing indium sites and has an effect of doping holes.

-Inorganic magnesium compound-
There is no restriction | limiting in particular as said inorganic magnesium compound, According to the objective, it can select suitably, For example, magnesium oxo acid, magnesium halide, magnesium hydroxide, magnesium cyanide etc. are mentioned.
Examples of the magnesium oxo acid include magnesium nitrate, magnesium sulfate, magnesium carbonate, and magnesium phosphate.
Examples of the magnesium halide include magnesium chloride, magnesium bromide, and magnesium iodide.
These may be anhydrides or hydrates.

-Inorganic zinc compounds-
There is no restriction | limiting in particular as said inorganic zinc compound, According to the objective, it can select suitably, For example, oxo acid zinc, a halogenated zinc, zinc hydroxide, zinc cyanide etc. are mentioned.
Examples of the zinc oxoacid include zinc nitrate, zinc sulfate, zinc carbonate, and zinc phosphate.
Examples of the zinc halide include zinc chloride, zinc bromide, and zinc iodide.
These may be anhydrides or hydrates.

-Inorganic calcium compounds-
There is no restriction | limiting in particular as said inorganic calcium compound, According to the objective, it can select suitably, For example, a calcium oxo acid, a calcium halide, a calcium hydroxide, a calcium cyanide etc. are mentioned.
Examples of the calcium oxoacid include calcium nitrate, calcium sulfate, calcium carbonate, and calcium phosphate.
Examples of the calcium halide include calcium chloride, calcium bromide, and calcium iodide.
Among these, calcium oxoacid and calcium halide are preferable, and calcium nitrate, calcium sulfate, and calcium chloride are more preferable in terms of high solubility in various solvents.

  There is no restriction | limiting in particular as said calcium nitrate, According to the objective, it can select suitably, For example, the hydrate etc. of calcium nitrate are mentioned. Examples of the calcium nitrate hydrate include calcium nitrate trihydrate and calcium nitrate hexahydrate.

  There is no restriction | limiting in particular as said calcium sulfate, According to the objective, it can select suitably, For example, the hydrate of calcium sulfate etc. are mentioned. Examples of the calcium sulfate hydrate include calcium sulfate monohydrate and calcium sulfate heptahydrate.

  There is no restriction | limiting in particular as said calcium chloride, According to the objective, it can select suitably, For example, the hydrate of calcium chloride etc. are mentioned. Examples of the calcium chloride hydrate include calcium chloride hexahydrate.

  As these inorganic calcium compounds, synthesized ones or commercially available products may be used.

-Inorganic strontium compounds-
There is no restriction | limiting in particular as said inorganic strontium compound, According to the objective, it can select suitably, For example, strontium oxo acid, strontium halide, strontium hydroxide, strontium cyanide etc. are mentioned.
Examples of the strontium oxoacid include strontium nitrate, strontium sulfate, strontium carbonate, and strontium phosphate.
Examples of the strontium halide include strontium chloride, strontium bromide, and strontium iodide.
Among these, strontium oxoacids and strontium halides are preferable in terms of high solubility in various solvents, and strontium nitrate, strontium sulfate, and strontium chloride are more preferable.

  There is no restriction | limiting in particular as said strontium nitrate, According to the objective, it can select suitably, For example, the hydrate of strontium nitrate etc. are mentioned. Examples of the hydrate of strontium nitrate include strontium nitrate trihydrate and strontium nitrate hexahydrate.

  The strontium sulfate is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include anhydrous strontium sulfate and hydrated strontium sulfate. Examples of the strontium sulfate hydrate include strontium sulfate dihydrate and strontium sulfate heptahydrate.

  The strontium chloride is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include anhydrous strontium chloride and strontium chloride hydrate. Examples of the strontium chloride hydrate include strontium chloride dihydrate and strontium chloride tetrahydrate.

  As these inorganic strontium compounds, synthesized ones or commercially available products may be used.

The content of the inorganic magnesium compound, the inorganic zinc compound, the inorganic calcium compound, and the inorganic strontium compound in the coating solution for forming the metal oxide film is not particularly limited and may be appropriately selected depending on the purpose. However, the sum (C) of the number of magnesium atoms, the number of zinc atoms, the number of calcium atoms, and the number of strontium atoms is preferably 1% to 30% with respect to the number of indium atoms (A).
Here, the indium atom, the magnesium atom, the zinc atom, the calcium atom, and the strontium atom may be in an ionic state.

<Method for producing coating solution for forming metal oxide film>
The method for preparing the coating solution for forming the metal oxide film is not particularly limited and can be appropriately selected depending on the purpose. For example, a nitrate diol solution and a nitrate glycol ether solution are respectively prepared and mixed. The method of doing is mentioned.
Specifically, the following production methods can be mentioned.
An example of using a commercially available barium compound solution such as a barium bistetrahydrofurfuryl oxide solution (manufactured by Sigma-Aldrich) as the barium compound will be described.
First, indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) is dissolved in diols to prepare a nitrate diol solution. Diethylene glycol, 1,2-ethanediol, 1,2-propanediol, and 1,3-butanediol, which are the diols, can dissolve indium nitrate to a concentration of 1 mol / L or more at room temperature by stirring. is there. During the dissolution, the dissolution time can be shortened by heating.
Subsequently, indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) is dissolved in glycol ethers to prepare a nitrate glycol ether solution. The glycol ethers, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoisobutyl ether, are mixed with indium nitrate by stirring. It can be dissolved at room temperature up to a concentration of 1 mol / L or more. During the dissolution, the dissolution time can be shortened by heating.
Then, the prepared nitrate diol solution and the nitrate glycol ether solution are mixed at a desired mixing ratio to obtain a mixed solution of nitrate.
Finally, a barium bistetrahydrofurfuryl oxide solution (manufactured by Sigma-Aldrich) and a mixed solution of the nitrate are mixed at a desired mixing ratio to obtain a coating solution for forming a metal oxide film.
The barium bistetrahydrofurfuryl oxide solution is composed of 40% by mass of barium bistetrahydrofurfuryl oxide, 36% by mass of ethyl alcohol, and 24% by mass of tetrahydrofurfuryl alcohol.

Next, an example in which a solid raw material is dissolved in a solvent to produce a coating solution for forming a metal oxide film will be described.
First, indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) and barium chloride (BaCl ₂ .2H ₂ O) are dissolved in diols to prepare a diol solution. Diethylene glycol, 1,2-ethanediol, 1,2-propanediol, and 1,3-butanediol, which are the diols, are mixed with indium nitrate and barium chloride to a concentration of 1 mol / L or more by stirring. It can be dissolved at room temperature. During the dissolution, the dissolution time can be shortened by heating.
Subsequently, indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) and barium chloride (BaCl ₂ .2H ₂ O) are dissolved in glycol ethers to prepare a glycol ether solution. The glycol ethers such as ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol monopropyl ether, ethylene glycol monoisopropyl ether, ethylene glycol monobutyl ether, and ethylene glycol monoisobutyl ether are mixed with indium nitrate, And barium chloride can be dissolved at a room temperature to a concentration of 1 mol / L or more. During the dissolution, the dissolution time can be shortened by heating.
Then, the prepared diol solution and the glycol ether solution are mixed at a desired mixing ratio to obtain a coating solution for forming a metal oxide film.

  The coating solution for forming a metal oxide film of the present invention is suitable for a coating solution for producing a metal oxide film, and in particular, a coating solution for forming a metal oxide film (oxide) satisfying the formula (1). The semiconductor film forming coating solution is suitable as a coating solution for forming an active layer of a field effect transistor.

(Metal oxide film)
The metal oxide film of the present invention is obtained by applying the metal oxide film-forming coating solution of the present invention to an object to be coated and drying it, followed by firing.
Examples of the metal oxide film include an oxide semiconductor film.
When the metal oxide film forming coating solution (the oxide semiconductor film forming coating solution) satisfying the formula (1) is used as the metal oxide film forming coating solution, the active layer of the field effect transistor is used. An oxide semiconductor film particularly suitable for the above can be obtained.

There is no restriction | limiting in particular as said to-be-coated article, According to the objective, it can select suitably, For example, a glass base material, a plastic base material, etc. are mentioned.
When the metal oxide film is used as an oxide semiconductor film for an active layer of a field effect transistor, examples of the object to be coated include a base material and a gate insulating layer. There is no restriction | limiting in particular as a shape, a structure, and a magnitude | size of the said base material, According to the objective, it can select suitably. There is no restriction | limiting in particular as a material of the said base material, According to the objective, it can select suitably, For example, a glass base material, a plastic base material, etc. are mentioned.

  The application method is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include screen printing, roll coating, dip coating, spin coating, ink jet, and nanoimprint. . Among these, in the production of a metal oxide film having a desired shape, for example, a field effect transistor, the amount of coating liquid to be deposited is that a designed channel width (in other words, a desired active layer shape) can be obtained. An ink jet method and a nanoimprint method capable of controlling the temperature are preferable. When applying by the inkjet method and the nanoimprint method, it can be applied even at room temperature, but heating the substrate (application object) to about 40 ° C. to 100 ° C. is a coating solution immediately after adhering to the substrate surface. Is preferable in that it is possible to suppress spreading and spreading.

  The drying is not particularly limited as long as it can remove volatile components in the coating solution for forming a metal oxide film, and can be appropriately selected according to the purpose. In the drying, it is not necessary to completely remove the volatile component, and it is sufficient if the volatile component can be removed to such an extent that firing is not hindered.

The firing temperature is not particularly limited as long as it is not less than the temperature at which indium, barium, calcium, strontium, magnesium, zinc forms an oxide and not more than the heat deformation temperature of the substrate (coating object), Although it can select suitably according to the objective, 250 to 600 degreeC is preferable.
There is no restriction | limiting in particular as said baking atmosphere, According to the objective, it can select suitably, For example, the atmosphere containing oxygen, such as in oxygen and air, is mentioned. Further, by setting the firing atmosphere to an inert gas such as nitrogen gas, the amount of oxygen in the formed metal oxide film (eg, oxide semiconductor film) is reduced, and a low-resistance metal oxide film ( For example, an oxide semiconductor film or the like can be obtained.
After firing, the electrical properties, reliability, and uniformity of metal oxide film (eg, oxide semiconductor film) are further improved by annealing in air, inert gas, or reducing gas atmosphere. can do.
There is no restriction | limiting in particular as time of the said baking, According to the objective, it can select suitably.

  There is no restriction | limiting in particular as average thickness of the metal oxide film (for example, oxide semiconductor film etc.) formed, Although it can select suitably according to the objective, 1 nm-200 nm are preferable, and 5 nm-100 nm are more preferable.

There is no restriction | limiting in particular as a use of the said metal oxide film, According to the objective, it can select suitably. For example, when the volume resistivity of the metal oxide film is less than 10 ⁻² Ωcm, it can be used for a transparent conductive film. For example, when the volume resistivity of the metal oxide film is 10 ⁻² Ωcm or more and 10 ⁹ Ωcm or less, the metal oxide film can be used for an active layer of a field effect transistor. For example, when the volume resistivity of the metal oxide film exceeds 10 ⁹ Ωcm, it can be used as an antistatic film.

(Field effect transistor)
The field effect transistor of the present invention includes at least a gate electrode, a source electrode, a drain electrode, an active layer, and a gate insulating layer, and further includes other members as necessary.

  The field effect transistor of the present invention can be manufactured, for example, by the method for manufacturing a field effect transistor of the present invention.

<Gate electrode>
The gate electrode is not particularly limited as long as it is an electrode for applying a gate voltage, and can be appropriately selected according to the purpose.
The material of the gate electrode is not particularly limited and may be appropriately selected depending on the purpose. For example, platinum, palladium, gold, silver, copper, zinc, aluminum, nickel, chromium, tantalum, molybdenum, titanium, etc. Metals, alloys thereof, mixtures of these metals, and the like. In addition, conductive oxides such as indium oxide, zinc oxide, tin oxide, gallium oxide, and niobium oxide, composite compounds thereof, mixtures thereof, and the like can be given.
There is no restriction | limiting in particular as average thickness of the said gate electrode, Although it can select suitably according to the objective, 40 nm-2 micrometers are preferable, and 70 nm-1 micrometer are more preferable.

<Gate insulation layer>
The gate insulating layer is not particularly limited as long as it is an insulating layer formed between the gate electrode and the active layer, and can be appropriately selected according to the purpose.
There is no restriction | limiting in particular as a material of the said gate insulating layer, According to the objective, it can select suitably, For example, an inorganic insulating material, an organic insulating material, etc. are mentioned.
Examples of the inorganic insulating material include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, yttrium oxide, lanthanum oxide, hafnium oxide, zirconium oxide, silicon nitride, aluminum nitride, and mixtures thereof.
Examples of the organic insulating material include polyimide, polyamide, polyacrylate, polyvinyl alcohol, and novolac resin.
There is no restriction | limiting in particular as average thickness of the said gate insulating layer, Although it can select suitably according to the objective, 50 nm-3 micrometers are preferable, and 100 nm-1 micrometer are more preferable.

<Source electrode and drain electrode>
The source electrode and the drain electrode are not particularly limited as long as they are electrodes for taking out current, and can be appropriately selected according to the purpose.
There is no restriction | limiting in particular as a material of the said source electrode and the said drain electrode, According to the objective, it can select suitably, For example, the same material as the material described in description of the said gate electrode is mentioned.
There is no restriction | limiting in particular as average thickness of the said source electrode and the said drain electrode, Although it can select suitably according to the objective, 40 nm-2 micrometers are preferable, and 70 nm-1 micrometer are more preferable.

<Active layer>
The active layer is an active layer made of an oxide semiconductor formed between the source electrode and the drain electrode, and is an oxide formed by applying the metal oxide film forming coating solution of the present invention. Made of semiconductor.
There is no restriction | limiting in particular as average thickness of the said active layer, Although it can select suitably according to the objective, 1 nm-200 micrometers are preferable, and 5 nm-100 micrometers are more preferable.

The structure of the field effect transistor is not particularly limited and may be appropriately selected depending on the purpose. For example, a bottom gate / bottom contact type (FIG. 1), a bottom gate / top contact type (FIG. 2), Examples include a top gate / bottom contact type (FIG. 3) and a top gate / top contact type (FIG. 4).
1 to 4, 1 is a base material, 2 is a gate electrode, 3 is a gate insulating layer, 4 is a source electrode, 5 is a drain electrode, and 6 is an active layer.

  The field effect transistor of the present invention can be suitably used for a pixel drive circuit such as a liquid crystal display, an organic EL display, and an electrochromic display, and a field effect transistor for a logic circuit.

(Method for producing field-effect transistor)
The manufacturing method (first manufacturing method) of the field effect transistor of the present invention includes:
A gate electrode forming step of forming a gate electrode on the substrate;
Forming a gate insulating layer on the gate electrode; and
A source electrode and drain electrode forming step of forming a source electrode and a drain electrode apart from each other on the gate insulating layer;
An active layer forming step of forming an active layer made of an oxide semiconductor on the gate insulating layer in the channel region between the source electrode and the drain electrode.

Moreover, the manufacturing method (second manufacturing method) of the field effect transistor of the present invention includes:
A source electrode and drain electrode forming step of separately forming a source electrode and a drain electrode on a substrate;
An active layer forming step of forming an active layer made of an oxide semiconductor on the base material in the channel region between the source electrode and the drain electrode;
A gate insulating layer forming step of forming a gate insulating layer on the active layer;
Forming a gate electrode on the gate insulating layer.

<First manufacturing method>
The first manufacturing method will be described.

-Base material-
There is no restriction | limiting in particular as a shape, a structure, and a magnitude | size of the said base material, According to the objective, it can select suitably.
There is no restriction | limiting in particular as said base material, According to the objective, it can select suitably, For example, a glass base material, a plastic base material, etc. are mentioned.
There is no restriction | limiting in particular as a material of the said glass base material, According to the objective, it can select suitably, For example, an alkali free glass, silica glass, etc. are mentioned.
There is no restriction | limiting in particular as a material of the said plastic base material, According to the objective, it can select suitably, For example, a polycarbonate (PC), a polyimide (PI), a polyethylene terephthalate (PET), a polyethylene naphthalate (PEN) etc. Is mentioned.
In addition, it is preferable that pretreatments, such as oxygen plasma, UV ozone, and UV irradiation washing | cleaning, are performed for the said base material at the point of the cleaning of a surface, and adhesive improvement.

-Gate electrode formation process-
The gate electrode forming step is not particularly limited as long as it is a step of forming a gate electrode on the substrate, and can be appropriately selected according to the purpose. For example, (i) sputtering method, dip coating method Examples include a step of patterning by photolithography after film formation by a method such as (ii) a step of directly forming a desired shape by a printing process such as ink jet, nanoimprint, and gravure.

-Gate insulation layer formation process-
The gate insulating layer forming step is not particularly limited as long as it is a step of forming a gate insulating layer on the gate electrode, and can be appropriately selected according to the purpose. For example, (i) sputtering, dip Examples include a step of patterning by photolithography after film formation by a coating method or the like, and (ii) a step of directly forming a desired shape by a printing process such as inkjet, nanoimprint, or gravure.

-Source and drain electrode formation process-
The source electrode and drain electrode forming step is not particularly limited as long as it is a step of forming the source electrode and the drain electrode separately on the gate insulating layer, and can be appropriately selected according to the purpose. (I) A step of patterning by photolithography after film formation by a sputtering method, a dip coating method, or the like, and (ii) a step of directly forming a desired shape by a printing process such as ink jet, nanoimprint, or gravure. .

-Active layer formation process-
As the active layer forming step, the metal oxide film forming coating solution of the present invention is applied to the channel region between the source electrode and the drain electrode and on the gate insulating layer to form an oxide semiconductor. If it is the process of forming the active layer which consists of, there will be no restriction | limiting in particular, According to the objective, it can select suitably.

  In the active layer forming step, the ratio of the number of indium atoms (A) of the inorganic indium compound in the coating liquid for forming a metal oxide film to the number of barium atoms (B) of the barium compound [B / (A + B )] Is preferably adjusted to control at least one of volume resistivity, carrier mobility, and carrier density of the oxide semiconductor. By doing so, a field effect transistor having a desired characteristic (for example, an on / off ratio) can be obtained.

  In the active layer forming step, the coating liquid for forming a metal oxide film contains the glycol ethers and the diols, and the glycol ethers and the diols in the coating liquid for forming a metal oxide film. It is preferable to control the viscosity of the coating liquid for forming a metal oxide film by adjusting the mixing ratio. By doing so, it is possible to obtain a field effect transistor having excellent coating properties and a good channel formation state.

There is no restriction | limiting in particular as a method of apply | coating the said coating liquid for metal oxide film formation, and forming an oxide semiconductor, According to the objective, it can select suitably, For example, the said coating liquid for metal oxide film formation Is applied to the base material on which the gate insulating layer is formed, dried, and then fired.
The application method is not particularly limited and may be appropriately selected depending on the intended purpose. Examples thereof include screen printing, roll coating, dip coating, spin coating, ink jet, and nanoimprint. . Among these, in the production of a field effect transistor, an inkjet method and a nanoimprint method capable of controlling the amount of coating solution to be deposited are preferable in that a designed channel width (in other words, a desired active layer shape) can be obtained.
The drying is not particularly limited as long as it can remove volatile components in the coating solution for forming a metal oxide film, and can be appropriately selected according to the purpose. In the drying, it is not necessary to completely remove the volatile component, and it is sufficient if the volatile component can be removed to such an extent that firing is not hindered.
There is no restriction | limiting in particular as the temperature of the said baking, Although it can select suitably according to the objective, 250 to 600 degreeC is preferable.

In the first manufacturing method, the order of the source electrode and drain electrode formation step and the active layer formation step is not limited, and the active layer formation step may be performed after the source electrode and drain electrode formation step. The source electrode and drain electrode formation step may be performed after the active layer formation step.
In the first manufacturing method, when the active layer forming step is performed after the source electrode and drain electrode forming step, a bottom gate / bottom contact type field effect transistor can be manufactured.
In the first manufacturing method, when the source electrode and drain electrode forming step is performed after the active layer forming step, a bottom gate / top contact type field effect transistor can be manufactured.

Here, a manufacturing method of a bottom gate / bottom contact type field effect transistor will be described with reference to FIGS. 5A to 5D.
First, a conductor film made of aluminum or the like is formed on a base material 1 made of a glass substrate or the like by sputtering or the like, and the formed conductor film is patterned by etching to form the gate electrode 2 (FIG. 5A). ).
Next, a gate insulating layer 3 made of SiO ₂ or the like is formed on the gate electrode 2 and the base material 1 by sputtering or the like so as to cover the gate electrode 2 (FIG. 5B).
Next, a conductor film made of ITO or the like is formed on the gate insulating layer 3 by sputtering or the like, and the formed conductor film is patterned by etching to form the source electrode 4 and the drain electrode 5 (FIG. 5C). .
Next, the metal oxide film-forming coating solution is applied on the gate insulating layer 3 by an inkjet method or the like so as to cover a channel region formed between the source electrode 4 and the drain electrode 5, and heat treatment is performed. Then, an active layer 6 made of an oxide semiconductor is formed (FIG. 5D).
Thus, a field effect transistor is manufactured.

<Second production method>
The second manufacturing method will be described.

-Base material-
There is no restriction | limiting in particular as said base material, According to the objective, it can select suitably, For example, the same base material as the base material illustrated in the said 1st manufacturing method is mentioned.

-Source and drain electrode formation process-
The source electrode and drain electrode forming step is not particularly limited as long as the source electrode and the drain electrode are separately formed on the base material, and can be appropriately selected according to the purpose. The process similar to the process illustrated in the said source electrode and drain electrode formation process of 1 manufacturing method is mentioned.

-Active layer formation process-
As the active layer forming step, the metal oxide film-forming coating solution of the present invention is applied to the base material in the channel region between the source electrode and the drain electrode, and the oxide semiconductor is used. If it is the process of forming the active layer which becomes, there will be no restriction | limiting in particular, According to the objective, it can select suitably.
There is no restriction | limiting in particular as a method of apply | coating the said coating liquid for metal oxide film formation, and forming an oxide semiconductor, According to the objective, it can select suitably, For example, the said activity of the said 1st manufacturing method The method similar to the method illustrated in the layer formation process is mentioned.

  In the active layer forming step, the ratio of the number of indium atoms (A) of the inorganic indium compound in the coating liquid for forming a metal oxide film to the number of barium atoms (B) of the barium compound [B / (A + B )] Is preferably adjusted to control at least one of volume resistivity, carrier mobility, and carrier density of the oxide semiconductor. By doing so, a field effect transistor having a desired characteristic (for example, an on / off ratio) can be obtained.

  In the active layer forming step, the coating liquid for forming a metal oxide film contains the glycol ethers and the diols, and the glycol ethers and the diols in the coating liquid for forming a metal oxide film. It is preferable to control the viscosity of the coating liquid for forming a metal oxide film by adjusting the mixing ratio. By doing so, it is possible to obtain a field effect transistor having excellent coating properties and a good channel formation state.

-Gate insulation layer formation process-
The gate insulating layer forming step is not particularly limited as long as it is a step of forming a gate insulating layer on the active layer, and can be appropriately selected according to the purpose. For example, in the first manufacturing method, A step similar to the step exemplified in the gate insulating layer forming step can be given.

-Gate electrode formation process-
The gate electrode forming step is not particularly limited as long as it is a step of forming a gate electrode on the gate insulating layer, and can be appropriately selected according to the purpose. The process similar to the process illustrated in the gate electrode formation process is mentioned.

In the second manufacturing method, the order of the source electrode and drain electrode formation step and the active layer formation step is not limited, and the active layer formation step may be performed after the source electrode and drain electrode formation step. The source electrode and drain electrode formation step may be performed after the active layer formation step.
In the second manufacturing method, when the active layer forming step is performed after the source electrode and drain electrode forming step, a top gate / bottom contact type field effect transistor can be manufactured.
In the second manufacturing method, when the source electrode and drain electrode forming step is performed after the active layer forming step, a top gate / top contact type field effect transistor can be manufactured.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

Example 1
<Preparation of coating solution for forming metal oxide film>
In a beaker, weigh 3.55 g of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O), add 20 mL of 1,2-ethanediol and 20 mL of ethylene glycol monomethyl ether, mix and dissolve at room temperature, and add nitric acid. An indium solution was prepared.
Subsequently, 0.36 g of a barium bistetrahydrofurfuryl oxide solution manufactured by Sigma-Aldrich made of 40% by weight barium bistetrahydrofurfuryl oxide, 36% by weight ethyl alcohol, and 24% by weight tetrahydrofurfuryl alcohol was weighed, A metal oxide film forming coating solution was prepared by mixing with the indium nitrate solution.
[B / (A + B)] (A represents the number of indium atoms and B represents the number of barium atoms) in the obtained coating solution for forming a metal oxide film, the content (mass%) of glycol ethers, The ratio of raw materials to 1 L of diols and glycol ethers, and the ratio of the number of indium atoms (A) to the sum of the number of magnesium atoms, the number of zinc atoms, the number of calcium atoms, and the number of strontium atoms (C) ((C) / (A) (%)) is shown in Table 2.

<Fabrication of field effect transistor>
-Formation of gate electrode-
A molybdenum film was formed on a glass substrate by DC sputtering so as to have an average thickness of about 100 nm. Thereafter, a photoresist was applied, and a resist pattern similar to the pattern of the gate electrode to be formed was formed by pre-baking, exposure by an exposure apparatus, and development. Further, etching was performed with an etching solution composed of phosphoric acid-nitric acid-acetic acid, and the molybdenum film in the region where the resist pattern was not formed was removed. Thereafter, the gate electrode was formed by removing the resist pattern.

-Formation of gate insulation layer-
An SiO ₂ film was formed on the formed gate electrode and the glass substrate by RF sputtering so as to have an average thickness of about 200 nm. Thereafter, a photoresist was applied, and a resist pattern similar to the pattern of the gate insulating layer to be formed was formed by pre-baking, exposure with an exposure apparatus, and development. Furthermore, the SiO ₂ film in the region where the resist pattern was not formed was removed by etching using buffered hydrofluoric acid, and then the resist pattern was also removed to form a gate insulating layer.

-Formation of source and drain electrodes-
An ITO film (In ₂ O ₃ —SnO ₂ (5 mass%)), which is a transparent conductive film, was formed on the formed gate insulating layer by DC sputtering so as to have an average thickness of about 100 nm. Thereafter, a photoresist was applied on the ITO film, and a resist pattern similar to the pattern of the source electrode and drain electrode to be formed was formed by pre-baking, exposure with an exposure apparatus, and development. Further, the ITO film in the region where the resist pattern was not formed was removed by etching using an oxalic acid-based etching solution. Thereafter, the resist pattern was also removed to form a source electrode and a drain electrode made of an ITO film. At this time, the channel width defined by the source electrode width was 50 μm, and the channel length defined between the source and drain electrodes was 50 μm.

-Formation of active layer-
The metal oxide film-forming coating solution was applied to the channel between the formed source electrode and the drain electrode by an inkjet apparatus.
The substrate was dried on a hot plate heated to 120 ° C. for 10 minutes, then baked at 350 ° C. for 1 hour in an air atmosphere, and further annealed at 300 ° C. for 3 hours in an air atmosphere to obtain an active layer. The average thickness of the channel portion of the obtained active layer was about 15 nm.
Thus, a field effect transistor was manufactured.

<Evaluation>
-Channel formation state (applicability)-
In the production of the field effect transistor, the spread of the coating solution when the coating solution for forming a metal oxide film was applied with an inkjet apparatus was observed with an optical microscope, and the channel formation state was evaluated according to the following evaluation criteria. The results are shown in Table 3.
○: The active layer spreads between the source electrode and the drain electrode and does not protrude from the gate electrode (see FIG. 6).
X: The active layer spreads except between the source electrode and the drain electrode, and protrudes from the gate electrode (see FIG. 7).

-Volume resistivity-
With respect to the obtained field effect transistor, the current when a voltage of 0 V to ± 20 V is applied between the source and the drain using a semiconductor parameter analyzer (manufactured by Agilent Technologies, semiconductor parameter analyzer 4156C) is a two-terminal method. And the volume resistivity of the active layer was measured. The results are shown in Table 3.

-Carrier mobility and on / off ratio-
With respect to the obtained field effect transistor, the gate voltage Vgs and the source-drain current Ids when the source-drain voltage Vds is set to 20 V using a semiconductor parameter analyzer apparatus (manufactured by Agilent Technologies, semiconductor parameter analyzer 4156C). Sought a relationship with. The results are shown in the graph of FIG. It can be confirmed from FIG. 8 that good transistor characteristics are obtained. In FIG. 8, “E” represents “power of 10”. For example, “E-04” is “0.0001”.
Carrier mobility was calculated in the saturation region. In addition, the on / off ratio was determined. In the on / off ratio, the on value is an Ids value at 30V. The results are shown in Table 3.

(Examples 2 to 5 and Examples 24 to 35)
<Preparation of coating solution for forming metal oxide film>
In Example 1, the metals of Examples 2 to 5 and Examples 24 to 35 were the same as Example 1 except that the formulation of the coating solution for forming a metal oxide film was changed to the formulation shown in Table 1. A coating solution for forming an oxide film was prepared.
[B / (A + B)] (A represents the number of indium atoms and B represents the number of barium atoms) in the obtained coating solution for forming a metal oxide film, the content (mass%) of glycol ethers, The ratio of raw materials to 1 L of diols and glycol ethers, and the ratio of the number of indium atoms (A) to the sum of the number of magnesium atoms, the number of zinc atoms, the number of calcium atoms, and the number of strontium atoms (C) ((C) / (A) (%)) is shown in Table 2.

(Example 6)
<Preparation of coating solution for forming metal oxide film>
In a beaker, weigh 3.55 g of indium nitrate (In (NO ₃ ) ₃ .3H ₂ O) and 0.11 g of barium chloride (BaCl ₂ .2H ₂ O), 20 mL of 1,2-ethanediol and ethylene glycol. 20 mL of monomethyl ether was added and mixed and dissolved at room temperature to prepare a coating solution for forming a metal oxide film.
[B / (A + B)] (A represents the number of indium atoms and B represents the number of barium atoms) in the obtained coating solution for forming a metal oxide film, the content (mass%) of glycol ethers, The ratio of raw materials to 1 L of diols and glycol ethers, and the ratio of the number of indium atoms (A) to the sum of the number of magnesium atoms, the number of zinc atoms, the number of calcium atoms, and the number of strontium atoms (C) ((C) / (A) (%)) is shown in Table 2.

(Examples 7 to 23 and Comparative Examples 1 to 4)
<Preparation of coating solution for forming metal oxide film>
In Example 6, the metals of Examples 7 to 23 and Comparative Examples 1 to 4 were the same as Example 6 except that the formulation of the coating solution for forming a metal oxide film was changed to the formulation shown in Table 1. A coating solution for forming an oxide film was prepared.
[B / (A + B)] (A represents the number of indium atoms and B represents the number of barium atoms) in the obtained coating solution for forming a metal oxide film, the content (mass%) of glycol ethers, The ratio of raw materials to 1 L of diols and glycol ethers, and the ratio of the number of indium atoms (A) to the sum of the number of magnesium atoms, the number of zinc atoms, the number of calcium atoms, and the number of strontium atoms (C) ((C) / (A) (%)) is shown in Table 2.
However, in Comparative Example 2, the B is the number of copper atoms. In Comparative Example 3, B is the number of cobalt atoms. In Comparative Example 4, B is the number of nickel atoms.

<Fabrication and evaluation of field effect transistor>
Using the metal oxide film-forming coating solutions obtained in Examples 2-35 and Comparative Examples 1-4, a field effect transistor was fabricated in the same manner as in Example 1, and the same as in Example 1 Evaluation was performed. The results are shown in Table 3.

In Table 1, (* 1) represents water.
In Table 1, indium nitrate represents In (NO ₃ ) ₃ · 3H ₂ O, indium sulfate represents In ₂ (SO ₄ ) ₃ · 9H ₂ O, and indium chloride represents InCl ₃ · 4H ₂ O. Barium chloride represents BaCl ₂ .2H ₂ O, barium bromide represents BaBr ₂ .2H ₂ O, barium iodide represents BaI ₂ .2H ₂ O, and barium nitrate represents Ba (NO ₃ ) ₂ · H ₂ O, barium acetate represents (CH ₃ COO) ₂ Ba, barium hydroxide represents Ba (OH) ₂ , and zinc nitrate represents Zn (NO ₃ ) ₂ · 6H ₂ O Magnesium nitrate represents Mg (NO ₃ ) ₂ .6H ₂ O, calcium nitrate represents Ca (NO ₃ ) ₂ .4H ₂ O, strontium chloride represents SrCl ₂ .6H ₂ O, Copper nitrate is , Cu (NO ₃ ) ₂ .3H ₂ O, cobalt nitrate represents Co (NO ₃ ) ₂ .6H ₂ O, and nickel nitrate represents Ni (NO ₃ ) ₂ .6H ₂ O.
In Table 1, the compounding quantity of barium bistetrahydrofurfuryl oxide (following structural formula) is the barium bistetrahydrofurfuryl oxide solution (40 mass% barium bistetrahydrofurfuryl oxide, 36 mass% ethyl alcohol, the Sigma-Aldrich company). And a solution comprising 24% by mass of tetrahydrofurfuryl alcohol).

In Table 3, “-” represents that measurement is impossible.

  The coating liquids for forming metal oxide films of Examples 1 to 35 of the present invention were excellent in coating properties, and thus the channel formation state was good. In addition, in a field effect transistor using an oxide semiconductor obtained by applying the metal oxide film forming coating solution as an active layer, the volume resistivity of the active layer is required for the active layer of the field effect transistor. It was suitable for resistivity, high carrier mobility, large on / off ratio, and good transistor characteristics.

  On the other hand, the coating liquid for forming an oxide semiconductor film of Comparative Example 1 was poor in coating properties, and the channel formation state was insufficient, and the field effect transistor could not be evaluated.

  Further, the oxide film forming coating solutions of Comparative Examples 2 to 4 did not show semiconductor characteristics because the source-drain current hardly changed even when the gate voltage Vgs was changed.

As an aspect of this invention, it is as follows, for example.
<1> A coating solution for forming a metal oxide film comprising an inorganic indium compound, a barium compound, and an organic solvent.
<2> The inorganic indium compound is at least one of indium nitrate, indium sulfate, and indium chloride,
The metal oxide according to <1>, wherein the barium compound is at least one of barium bistetrahydrofurfuryl oxide, barium nitrate, barium carbonate, barium acetate, barium hydroxide, barium chloride, barium bromide, and barium iodide. It is a coating liquid for film formation.
<3> The metal oxidation according to any one of <1> to <2>, wherein the number of indium atoms (A) of the inorganic indium compound and the number of barium atoms (B) of the barium compound satisfy the following formula (1): This is a coating solution for forming a physical film.
0.040 ≦ [B / (A + B)] ≦ 0.200 Formula (1)
<4> The coating solution for forming a metal oxide film according to any one of <1> to <3>, wherein the organic solvent is at least one of glycol ethers and diols.
<5> A metal oxide obtained by applying the metal oxide film-forming coating solution according to any one of <1> to <4> to an object to be coated, followed by drying and firing. It is a material film.
<6> a gate electrode for applying a gate voltage;
A source electrode and a drain electrode for extracting current;
An active layer made of an oxide semiconductor formed between the source electrode and the drain electrode;
A gate insulating layer formed between the gate electrode and the active layer;
A field effect transistor, wherein the oxide semiconductor is an oxide semiconductor formed by applying the metal oxide film-forming coating solution according to any one of <1> to <4>. is there.
<7> a gate electrode forming step of forming a gate electrode on the substrate;
Forming a gate insulating layer on the gate electrode; and
A source electrode and drain electrode forming step of forming a source electrode and a drain electrode apart from each other on the gate insulating layer;
An active layer forming step of forming an active layer made of an oxide semiconductor on the gate insulating layer in the channel region between the source electrode and the drain electrode,
The active layer forming step forms the active layer made of the oxide semiconductor by applying the metal oxide film forming coating solution according to any one of <1> to <4> on the gate insulating layer. A method of manufacturing a field effect transistor.
<8> A source electrode and drain electrode forming step of forming a source electrode and a drain electrode separately on a base material;
An active layer forming step of forming an active layer made of an oxide semiconductor on the base material in the channel region between the source electrode and the drain electrode;
A gate insulating layer forming step of forming a gate insulating layer on the active layer;
Forming a gate electrode on the gate insulating layer, and
The active layer forming step forms the active layer made of the oxide semiconductor by applying the metal oxide film forming coating solution according to any one of <1> to <4> on the base material. It is a manufacturing method of a field effect transistor characterized by being a process.
<9> In the active layer forming step, the ratio of the number of indium atoms of the inorganic indium compound (A) in the coating solution for forming the metal oxide film to the number of barium atoms (B) of the barium compound [B / (A + B)] In the method for producing a field effect transistor according to any one of <7> to <8>, wherein at least one of volume resistivity, carrier mobility, and carrier density of the oxide semiconductor is controlled by adjusting is there.
<10> The coating liquid for forming a metal oxide film contains glycol ethers and diols,
In the active layer forming step, the viscosity of the coating solution for forming a metal oxide film is controlled by adjusting a mixing ratio of the glycol ethers and the diols in the coating solution for forming a metal oxide film. <7> to <9>. The method for producing a field effect transistor according to any one of <9>.

DESCRIPTION OF SYMBOLS 1 Base material 2 Gate electrode 3 Gate insulating layer 4 Source electrode 5 Drain electrode 6 Active layer

International Publication No. 2007/058248 Pamphlet JP-A-6-96619 Japanese Patent Laid-Open No. 7-320541 JP 2009-177149 A

Claims (8)

Containing an inorganic indium compound, a barium compound, and an organic solvent,
A coating solution for forming a metal oxide film, wherein the inorganic indium compound is at least one of indium oxoate, indium halide, indium hydroxide, and indium cyanide. Containing an inorganic indium compound, a barium compound, and an organic solvent,
The barium compound is at least one of barium bistetrahydrofurfuryl oxide, barium 2-ethylhexanoate, barium acetylacetonate, barium oxoate, barium halide, barium hydroxide, and barium cyanide. A coating solution for forming a metal oxide film. Containing an inorganic indium compound, a barium compound, an organic solvent, an inorganic magnesium compound, an inorganic zinc compound, an inorganic calcium compound, and an inorganic strontium compound,
The inorganic magnesium compound is at least one of magnesium oxoacid, magnesium halide, magnesium hydroxide, and magnesium cyanide;
The inorganic zinc compound is at least one of zinc oxoacid, zinc halide, zinc hydroxide, and zinc cyanide;
The inorganic calcium compound is at least one of calcium oxoacid, calcium halide, calcium hydroxide, and calcium cyanide;
A coating solution for forming a metal oxide film, wherein the inorganic strontium compound is at least one of strontium oxoacid, strontium halide, strontium hydroxide, and strontium cyanide. Containing an inorganic indium compound, a barium compound, and an organic solvent,
The coating liquid for forming a metal oxide film, wherein the organic solvent is at least one of glycol ethers and diols.   A coating solution for forming a metal oxide film, comprising an inorganic indium compound, a barium compound, an organic solvent, and at least one of an inorganic magnesium compound, an inorganic calcium compound, and an inorganic strontium compound.   6. A metal oxide film, wherein the metal oxide film-forming coating solution according to claim 1 is applied to an object to be coated, dried, and then fired to obtain a metal oxide film. Manufacturing method. A gate electrode forming step of forming a gate electrode on the substrate;
Forming a gate insulating layer on the gate electrode; and
A source electrode and drain electrode forming step of forming a source electrode and a drain electrode apart from each other on the gate insulating layer;
An active layer forming step of forming an active layer made of an oxide semiconductor on the gate insulating layer in the channel region between the source electrode and the drain electrode,
The active layer forming step is a step of forming the active layer made of the oxide semiconductor by applying the metal oxide film forming coating solution according to claim 1 on the gate insulating layer. A method for manufacturing a field effect transistor, which is characterized by the following. A source electrode and drain electrode forming step of separately forming a source electrode and a drain electrode on a substrate;
An active layer forming step of forming an active layer made of an oxide semiconductor on the base material in the channel region between the source electrode and the drain electrode;
A gate insulating layer forming step of forming a gate insulating layer on the active layer;
Forming a gate electrode on the gate insulating layer, and
The said active layer formation process is a process of apply | coating the coating liquid for metal oxide film formation in any one of Claim 1 to 5 on the said base material, and forming the said active layer which consists of the said oxide semiconductor. A method of manufacturing a field effect transistor.