JP6250481B2 - Metal oxide film, metal oxide film manufacturing method, thin film transistor, and electronic device - Google Patents

Description

  The present invention relates to a metal oxide film, a method for manufacturing a metal oxide film, a thin film transistor, and an electronic device.

Transparent oxide semiconductors (TOS: Transparent Oxide Semiconductor) that are transparent, high mobility, and excellent in manufacturing suitability are attracting attention, and TOS-TFT using TOS as an active layer of a thin film transistor (TFT) is Research has been progressed until it is put into practical use as a drive element of a display device.
The active layer in the TOS-TFT that is currently in practical use is manufactured by a vacuum film forming method. However, in the case of the vacuum film forming method, the manufacturing cost tends to be high, so TOS that exhibits high characteristics by the solution coating process. On the other hand, research aimed at realizing this is prosperous.

  As a film forming method using a solution as a raw material, a solution raw material containing a metal alkoxide, an inorganic metal salt, or the like is applied, and a metal and oxygen network is formed by applying some energy to convert it into an oxide semiconductor, There has been considered a method of obtaining a TOS film composed of an aggregate of particles by applying a dispersion liquid in which oxide semiconductor particles in which a metal-oxygen network is formed in advance are dispersed in a solution.

For example, Non-Patent Document 1 describes a semiconductor film made of an aggregate of semiconductor nanoparticles.
Patent Document 1 discloses oxide nanoparticles for realizing TOS.
In Patent Documents 2 and 3, a dispersion containing zinc oxide particles is applied to form a porous film, and then a solution of a zinc compound such as a carboxylate, metal alkoxide, or ammonium compound is applied, and further heated. A method of manufacturing a semiconductor film by processing is disclosed.

Japanese Patent No. 4738931 Special table 2012-530033 gazette Special table 2008-547195

J. M. Luther et al., “Structural, Optical, and Electrical Properties of Self-Assembled Films of PbSe Nanocrystals Treated with 1,2-Ethanedithiol” ACS Nano (2008)

  In the method of obtaining a TOS film composed of an aggregate of particles by applying a dispersion in which oxide semiconductor particles in which a metal-oxygen network is formed in advance are dispersed in a solution, the TOS film can be obtained at a lower temperature. However, since it is difficult to synthesize desired oxide semiconductor particles and the electrical conductivity between the particles tends to be low, sufficiently high TFT characteristics are not obtained.

  Further, the semiconductor film described in Non-Patent Document 1 is not composed of an oxide, and the TFT characteristics are greatly deteriorated if the manufacturing process is not performed in an inert atmosphere. Further, since it is not transparent, TFT characteristics are greatly deteriorated by light irradiation.

  In addition, the oxide nanoparticles disclosed in Patent Document 1 are preferably a dispersant (ligand) having a relatively long-chain alkyl group in order to impart dispersibility. In the case of a TOS film formed by applying particles, the distance between particles tends to be large, and electric conduction through the particles may not be sufficiently obtained. Moreover, although the method of apply | coating by dispersing a semiconductor particle in a solvent without using a dispersing agent can be considered, the particles are likely to aggregate, and in this case, sufficient film flatness cannot be obtained.

In addition, in the methods disclosed in Patent Documents 2 and 3, a film having high electrical conductivity has not been obtained. This is presumably due to the use of an oxide semiconductor film based on zinc oxide, which is difficult to achieve high mobility at low temperatures.
When only the ligand is present around the particles, voids are likely to occur in the film, and it is difficult to increase the film density. As a result, it is difficult to realize high semiconductor characteristics. That is, a semiconductor film made of an aggregate of semiconductor particles and a TFT using the semiconductor film as an active layer can be manufactured in the air and it is difficult to achieve both high electrical characteristics.

  It is an object of the present invention to provide a metal oxide film having high conductivity or high semiconductor characteristics, which can be easily manufactured, a manufacturing method thereof, a thin film transistor excellent in electric characteristics, and an electronic device. .

In order to achieve the above object, the following invention is provided.
<1> an aggregate of metal oxide particles containing at least one metal element selected from In, Zn and Sn;
At least one selected from metal nitrates and metal oxides present in at least part of the metal oxide particles of the aggregate;
Metal oxide film containing
<2> The metal oxide film according to <1>, wherein the metal oxide particles are metal oxide particles containing at least In.
<3> The metal oxide film according to <1> or <2>, wherein the metal oxide particles are metal oxide particles containing In and at least one metal element selected from Sn, Ga, and Zn.
<4> The metal oxide film according to any one of <1> to <3>, wherein the metal nitrate is at least indium nitrate.
<5 > The metal oxide film according to any one of <1> to <4>, formed using metal oxide particles having a number average particle diameter of 3 to 50 nm.
<6> The metal oxide film according to any one of <1> to <5>, which is a semiconductor film.
<7> The metal oxide film according to any one of <1> to <5>, which is a conductive film.
<8> Aggregation of metal oxide particles by applying a dispersion liquid containing metal oxide particles having a number average particle diameter of 3 to 50 nm containing at least one metal element selected from In, Zn and Sn on a substrate. Forming an assembly film including a body;
Applying a solution containing metal nitrate to the aggregate film;
The manufacturing method of the metal oxide film which has this.
<9> The method for producing a metal oxide film according to <8>, including a step of heat-treating the aggregate film coated with a solution containing a metal nitrate under ultraviolet irradiation.
<10> The method for producing a metal oxide film according to <8> or <9>, wherein the metal nitrate contains at least indium nitrate.
<11> The method for producing a metal oxide film according to any one of <8> to <10>, wherein the metal oxide particles in the dispersion have a hydrocarbon-containing ligand.
<1 2> A thin film transistor including the metal oxide film according to any one of <1> to <7 > .
<1 3 > An electronic device having the thin film transistor according to <1 2 >.

  According to the present invention, there are provided a metal oxide film that has high conductivity or high semiconductor characteristics and can be easily manufactured, a manufacturing method thereof, a thin film transistor that is excellent in electrical characteristics, and an electronic device.

It is the schematic which shows the structure of an example (top gate-top contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (top gate-bottom contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (bottom gate-top contact type) of the thin-film transistor manufactured by this invention. It is the schematic which shows the structure of an example (bottom gate-bottom contact type) of the thin-film transistor manufactured by this invention. It is a schematic sectional drawing which shows a part of liquid crystal display device of embodiment. It is a schematic block diagram of the electrical wiring of the liquid crystal display device of FIG. It is a schematic sectional drawing which shows a part of organic EL display apparatus of embodiment. It is a schematic block diagram of the electrical wiring of the organic electroluminescent display apparatus of FIG. It is a schematic sectional drawing which shows a part of X-ray sensor array of embodiment. It is a schematic block diagram of the electrical wiring of the X-ray sensor array of FIG. FIG. 3 is a schematic view showing a process of manufacturing a simple TFT in Example 1. Examples 1,7, illustrates a, _V g -I _d characteristics of the simplified TFT manufactured in Comparative Example 1.

Hereinafter, the present invention will be specifically described with reference to the accompanying drawings.
In the drawings, members (components) having the same or corresponding functions are denoted by the same reference numerals and description thereof is omitted as appropriate. Further, in the present specification, when a numerical range is indicated by the symbol “to”, a lower limit value and an upper limit value are included.
<Oxide film>

  The metal oxide film of the present invention includes an aggregate of metal oxide particles containing at least one metal element selected from In, Zn, and Sn (hereinafter sometimes simply referred to as “metal oxide particles”), And at least one selected from metal nitrates and metal oxides, which are present in at least part of the metal oxide particles of the aggregate.

  In general, when a thin film is formed by applying a dispersion containing metal oxide particles, a certain amount of voids are generated between the particles. Therefore, in a metal oxide film having voids between particles, it is difficult to increase the film density as a whole film due to the presence of voids, and as a result, it is difficult to obtain high electrical conduction characteristics. Similarly, the presence of a ligand for dispersing grain boundaries and metal oxide particles may hinder electrical conduction between the particles, resulting in a decrease in electrical conductivity.

  On the other hand, in the metal oxide film of the present invention, metal nitrate or metal oxide is formed in at least part of voids between particles in an aggregate of metal oxide particles containing at least one metal element selected from In, Zn, and Sn. High electrical conductivity is realized by the presence of the object.

  The metal oxide particles contained in the metal oxide film of the present invention are desirably metal oxide particles containing at least In. The outer shell electron orbit of In is 5S, and higher electron mobility can be expected in the case of an oxide based on In.

  In addition to In, the metal oxide particles according to the present invention may contain at least one metal element selected from Sn, Ga, and Zn at an arbitrary ratio. When Sn is contained in the oxide crystal based on In, an increase in carrier concentration can be expected. On the other hand, when Ga is contained, oxygen deficiency can be suppressed. In addition, the transparency can be further increased by increasing the band gap, and as a result, the light stability can be increased. Moreover, increase in electron mobility can be expected by containing Zn.

In general, by using metal oxide particles having a wide band gap (˜3 eV), it is possible to produce a conductive film, a semiconductor film, and a TFT that are transparent and stable to light irradiation.
From the above viewpoint, specifically, the metal oxide particles constituting the aggregate according to the present invention are desirably formed of InO, InGaO, InZnO, InSnO, InGaZnO, InGaSnO, InSnZnO, or the like.

  The metal oxide particles according to the present invention may have a ligand on the particle surface. In the method for producing a metal oxide film, which will be described later, if a ligand (dispersible ligand) is present on the surface of the metal oxide particle, it is easy to disperse in the dispersion medium. When obtained, a uniform thin film having high flatness can be formed. In the metal oxide film of the present invention, at least one of metal nitrate and metal oxide is interposed between metal oxide particles, or a metal nitrate component is bonded to the particle surface as a ligand and is adjacent to each other. By increasing the interaction with the particles, high electrical conductivity can be obtained even if the dispersible ligand remains on the surface of the metal oxide particles. Specific ligands (dispersing ligands) will be described later.

The metal nitrate present between the particles of the aggregate of metal oxide particles desirably includes at least indium nitrate. In addition, examples of the metal oxide present between the particles of the aggregate of metal oxide particles include metal oxides derived from the above metal nitrates, and indium oxide is desirable.
It is possible to increase electrical conductivity by using an In material having a spatially large wave function. Moreover, the following two are mentioned as a merit of using an indium nitrate compound. (1) Since indium nitrate can be crosslinked and coordinated between particles, high conductivity can be obtained even if indium nitrate is not converted into an oxide. (2) Conversion to metal oxide is easy by using nitrate having particularly high decomposability among In-based materials.

The size of the metal oxide particles according to the present invention is more preferably 3 to 50 nm. The particle size referred to here refers to the number average particle diameter.
When the size of the metal oxide particles is 3 nm or more, it is suppressed that the number of particles per unit volume is excessive, and the influence of residual organic substances such as grain boundary scattering and a dispersing agent becomes relatively small and high. Electrical conductivity is easily obtained.
On the other hand, when the size of the metal oxide particles is 50 nm or less, for example, when dispersed in a specific solvent, it is difficult to cause particle sedimentation, and a sufficient film is obtained when a dispersion containing the metal oxide particles is applied. Flatness is easily obtained.

Note that whether or not a metal nitrate-derived component (metal nitrate or metal oxide) is present between the metal oxide particles is determined by, for example, X-ray photoelectron spectroscopy (XPS) measurement using a metal component and NO _3. and NO ₂ component can be confirmed by quantifying. For example, when a heat treatment under ultraviolet irradiation is performed in the method for producing a metal oxide film of the present invention described later, most of the NO ₃ component is converted to NO ₂ .

<Method for producing metal oxide film>
Next, the manufacturing method of the metal oxide film of this invention is demonstrated.
The method for producing the metal oxide film of the present invention is not particularly limited. For example, after applying a dispersion of metal oxide particles containing at least one metal element selected from In, Zn, and Sn on a substrate, the metal A two-step coating method in which a solution containing nitrate is applied and metal nitrate is filled between particles may be employed, or a coating solution in which metal nitrate is dissolved in a dispersion of metal oxide particles is used. You may form by the application | coating process of times. From the viewpoint of filling the gaps between the metal oxide particle aggregates with metal nitrate, it is preferable to produce the metal oxide particles by a two-step coating method.

That is, a preferred method for producing a metal oxide film according to the present invention is to apply a dispersion containing metal oxide particles containing at least one metal element selected from In, Zn and Sn onto a substrate, and then apply the metal oxide particles. A step of forming an aggregate film including the aggregate (aggregate film forming step) and a step of applying a solution containing metal nitrate to the aggregate film (solution coating step).
Further, from the viewpoint of improving electrical conductivity, it is preferable to perform a heat treatment step (heat treatment step) on the aggregate film coated with the solution containing the metal nitrate after the solution coating step, and ultraviolet (UV) It is more preferable to perform the heat treatment under irradiation.
Hereinafter, each step will be specifically described.

(Assembly film formation process)
A dispersion liquid containing metal oxide particles containing at least one metal element selected from In, Zn, and Sn is applied onto a substrate to form an aggregate film including an aggregate of metal oxide particles.

  The material and size (number average particle diameter) constituting the metal oxide particles are as described above, and a description thereof is omitted here.

The dispersion medium for dispersing the metal oxide particles is preferably an organic solvent, and specific examples include alkanes (n-hexane, n-octane, etc.), benzene, toluene, and the like.
Only one type of dispersion medium may be used, or a dispersion medium obtained by mixing two or more types may be used.

  The metal oxide particles may have a ligand on the particle surface. When a ligand is present on the surface of the metal oxide particles, it becomes possible to uniformly disperse the metal oxide particles in the dispersion medium, and an aggregate film of the metal oxide particles can be formed by applying the dispersion liquid. When obtained, a uniform assembly film with high flatness can be formed.

  In this case, in order for the metal oxide particles to be uniformly dispersed in the solvent, the metal oxide particles desirably have a ligand containing a hydrocarbon (for example, an alkyl group) on the surface. From the viewpoint of improving the dispersion of the metal oxide particles, the ligand imparting dispersibility is preferably a ligand having at least 6 carbon atoms in the main chain, and having 10 or more carbon atoms in the main chain. More desirably, it is a ligand. On the other hand, from the viewpoint of increasing the electrical conductivity by reducing the distance between the metal oxide particles in the aggregate film, it is desirable that the main chain is a ligand having 18 or less carbon atoms.

  The ligand present on the particle surface of the metal oxide particles according to the present invention may be either a saturated compound or an unsaturated compound. Specifically, decanoic acid, lauric acid, myristic acid, palmitic acid, stearic acid , Behenic acid, oleic acid, erucic acid, oleylamine, dodecylamine, dodecanethiol, 1,2-hexadecanethiol, trioctylphosphine, trioctylphosphine oxide, cetrimonium bromide and the like.

  The concentration of the metal oxide particles in the metal oxide particle dispersion may be selected according to the material, particle size, target electric conductivity, etc. of the metal oxide particles. 1 to 200 mg / ml is preferable, and 5 to 50 mg / ml is more preferable from the viewpoint of suppressing the aggregation of. When the concentration of the metal oxide particles is 1 mg / ml or more, high electrical conductivity is obtained, and when the concentration is 200 mg / ml or less, aggregation of the particles is suppressed and an aggregate film with high film thickness uniformity can be formed. it can.

  The method for applying the metal oxide particle dispersion on the substrate is not particularly limited, and a liquid phase method such as spin coating, bar coating, dip coating, spray coating, ink jet, dispenser, screen printing, letterpress printing, intaglio printing, etc. is used. Then, an aggregate film of metal oxide particles can be formed by coating on the substrate.

In addition, there is no restriction | limiting in particular about the shape of the board | substrate which forms the aggregate film of a metal oxide particle, a magnitude | size, etc., According to the objective, it can select suitably.
For example, the structure of the substrate may be a single layer structure or a laminated structure.

  As a material constituting the substrate, a substrate made of an inorganic material such as glass or YSZ (Yttria-Stabilized Zirconia), a resin, a resin composite material, or the like can be used. Among these, a substrate made of a resin or a resin composite material is preferable in terms of light weight and flexibility. Specifically, polybutylene terephthalate, polyethylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polystyrene, polycarbonate, polysulfone, polyethersulfone, polyarylate, allyl diglycol carbonate, polyamide, polyimide, polyamideimide, polyetherimide, Fluorine resin such as polybenzazole, polyphenylene sulfide, polycycloolefin, norbornene resin, polychlorotrifluoroethylene, liquid crystal polymer, acrylic resin, epoxy resin, silicone resin, ionomer resin, cyanate resin, crosslinked fumaric acid diester, cyclic polyolefin, Substrates made of synthetic resins such as aromatic ethers, maleimide-olefins, cellulose, episulfide compounds, A substrate composed of a composite plastic material of the above-mentioned synthetic resin and the like and silicon oxide particles, a substrate composed of a composite plastic material of the above-described synthetic resin and the like and metal nanoparticles, inorganic oxide nanoparticles or inorganic nitride nanoparticles, A substrate made of a composite plastic material of the aforementioned synthetic resin, etc. and carbon fiber or carbon nanotube, a substrate made of a composite plastic material of the aforementioned synthetic resin, etc., and glass fake, glass fiber or glass bead, the aforementioned synthesis A substrate made of a composite plastic material of a resin or the like and a clay mineral or particles having a mica-derived crystal structure, a laminated plastic substrate having at least one bonding interface between a thin glass and any of the above-described synthetic resins, an inorganic layer And organic layers (synthetic resin as described above) Improve surface insulation by applying oxidation treatment (for example, anodizing treatment) to a substrate made of a composite material having barrier properties, a stainless steel substrate, a metal multilayer substrate in which stainless steel and different metals are laminated, an aluminum substrate, or the surface An aluminum substrate with an oxide film and a silicon substrate with an oxide film can be used.

  The resin substrate is preferably excellent in heat resistance, dimensional stability, solvent resistance, electrical insulation, workability, low air permeability, low moisture absorption, and the like. The resin substrate may include a gas barrier layer for preventing permeation of moisture and oxygen, an undercoat layer for improving the flatness of the resin substrate and adhesion with the lower electrode, and the like.

  Further, a lower electrode or an insulating film may be provided on the substrate. In that case, the metal oxide film of the present invention is formed on the lower electrode or the insulating film on the substrate.

(Solution coating process)
A solution containing metal nitrate is applied to the aggregate film of metal oxide particles.
The metal nitrate in the solution applied to the aggregated film of metal oxide particles may be selected according to the target metal oxide semiconductor film, but the conductivity can be further improved by containing at least indium nitrate.

  The metal nitrate concentration of the solution containing metal nitrate is desirably 0.01 to 0.2 M (mol / L). If the concentration of metal nitrate in the solution applied to the aggregate film of metal oxide particles is 0.01M or more, the nitrate component remains between the particles after the solvent of the solution volatilizes, thereby increasing electron transfer. The effect of improving the degree is obtained. On the other hand, when the metal nitrate concentration in the solution is 0.2 M or less, the metal nitrate is sufficiently dissolved in the solvent, and the flatness of the film is suppressed from being lowered due to precipitation of solid components.

  As the solvent for dissolving the metal nitrate, a solvent having a low boiling point is desirable because the solubility of the metal nitrate is high and the coating is dried after coating. Specifically, methoxyethanol, ethanol, methanol, water, dimethylacetamide, ethylene glycol and the like are desirable.

  Through the above process, a metal oxide film in which metal nitrate is present at least partially between the metal oxide particles is obtained. In order to obtain a desired film thickness, the assembly film forming process and the solution coating process are repeated. May be. Further, when the assembly film forming process and the solution coating process are repeated, it is desirable to sufficiently dry the film every cycle. As a method for applying the metal nitrate solution, spin coating is performed after applying the nitrate solution on the metal oxide particles and waiting for the nitrate solution to penetrate between the particles (for example, about 1 minute). It is preferable to use a method of removing the excess nitrate solution, or a dip coater in which the nitrate solution easily permeates between the metal oxide particles.

(Heat treatment process)
By removing the solvent in the solution applied to the metal oxide particle aggregate film by drying or the like, a metal oxide film in which metal nitrate is present at least partially between the metal oxide particles is formed.
In the method for producing a metal oxide film of the present invention, it is preferable that the aggregate film coated with a solution containing metal nitrate is further subjected to heat treatment, and the heat treatment is performed under ultraviolet (UV) irradiation. It is more preferable that the process to be performed is included. At least a part of the metal nitrate present between the particles of the aggregate film is converted into a metal oxide by heat-treating the aggregate film coated with a solution containing metal nitrate, preferably under external line irradiation. In addition, higher electrical conductivity can be obtained.

From the viewpoint of converting at least a part of the metal nitrate present between the particles of the aggregate film into a metal oxide, the heat treatment for the aggregate film coated with the solution containing the metal nitrate is, for example, in the atmosphere at 100 to 100 It is preferable to carry out at 250 degreeC for 5 to 120 minutes.
The heating means is not particularly limited, and can be selected from hot plate heating, electric furnace heating, infrared heating, microwave heating, and the like.

  As a light source for ultraviolet irradiation, a UV lamp, a UV laser, and the like can be mentioned. A UV lamp is preferable from the viewpoint of performing ultraviolet irradiation uniformly with a large area and using inexpensive equipment. Examples of UV lamps include excimer lamps, deuterium lamps, low pressure mercury lamps, high pressure mercury lamps, ultrahigh pressure mercury lamps, metal halide lamps, helium lamps, carbon arc lamps, cadmium lamps, electrodeless discharge lamps, etc. It is preferable to use a mercury lamp because conversion from metal nitrate to metal oxide can be easily performed.

The heat treatment under ultraviolet irradiation may be performed until at least a part of the metal nitrate contained in the voids of the aggregate film is converted into a metal oxide. For example, ultraviolet light including wavelength light in the range of 180 to 300 nm is irradiated to the aggregate film with an illuminance of 5 mW / cm ² or more. The illuminance of ultraviolet light with respect to the film surface of the aggregate film is preferably 10 mW / cm ² or more, and more preferably 100 mW / cm ² or more. If the illuminance of ultraviolet light with respect to the film surface of the metal oxide precursor film is 10 mW / cm ² or more, a metal oxide film having high electron transfer characteristics can be obtained, and if it is 100 mW / cm ² or more, high electrons can be obtained in a shorter time. A metal oxide film having transfer characteristics can be obtained. In addition, it is preferable that the upper limit of illumination intensity is 500 mW / cm < ² > or less from a viewpoint of apparatus cost.

  Depending on the composition of metal nitrate, heating temperature, ultraviolet illuminance, etc., from the viewpoint of productivity, the heat treatment under ultraviolet irradiation is preferably 5 minutes to 120 minutes, preferably 5 minutes to 30 minutes. It is more preferable.

Through the above steps, a metal oxide film having conductor or semiconductor characteristics can be easily produced.
The metal oxide film of the present invention integrates metal oxide particles and metal nitrate or metal oxide converted from metal nitrate, so that it can be electrically used even in a low temperature annealing region where metal nitrate is not decomposed. An increase in conductivity is obtained.

By using metal oxide particles, a high-performance semiconductor film (preferably having a specific resistance of 10 ⁸ Ωcm or less) or a conductive film (preferably having a specific resistance of 10 ⁻² Ωcm or less) can be obtained without deterioration of the characteristics even in the atmosphere. can get. When the metal oxide film of the present invention is formed as the active layer, the mobility is preferably 0.2 cm ² / Vs or more, more preferably 0.5 cm ² / Vs or more, and further preferably 1 cm ² / Vs or more. A TFT having the same can also be manufactured.
In addition, since the metal-oxygen network is formed in advance in the oxide particles, there is no energy application step (for example, UV treatment) for forming the metal-oxygen network at a lower temperature, and high characteristics are obtained. It is done.

<Thin film transistor>
Since the metal oxide film of the present invention exhibits conductivity or semiconductivity, it is preferably used for an electrode (source electrode, drain electrode, or gate electrode) or active layer (oxide semiconductor layer) of a thin film transistor (TFT). it can.

  Hereinafter, although the form which applies the metal oxide film of this invention to the active layer of a thin-film transistor is mainly demonstrated, the metal oxide film of this invention is not limited to the active layer of TFT.

The element structure of the TFT according to the present invention is not particularly limited, and is either a so-called reverse stagger structure (also referred to as a bottom gate type) or a stagger structure (also referred to as a top gate type) based on the position of the gate electrode. Also good. Further, based on the contact portion between the active layer and the source and drain electrodes (referred to as “source / drain electrodes” as appropriate), either a so-called top contact type or bottom contact type may be used.
The top gate type is a form in which a gate electrode is disposed on the upper side of the gate insulating film and an active layer is formed on the lower side of the gate insulating film when the substrate on which the TFT is formed is the lowermost layer. The bottom gate type is a form in which a gate electrode is disposed below the gate insulating film and an active layer is formed above the gate insulating film. The bottom contact type is a mode in which the source / drain electrodes are formed before the active layer and the lower surface of the active layer is in contact with the source / drain electrodes. The top contact type is the type in which the active layer is the source / drain. In this embodiment, the upper surface of the active layer is in contact with the source / drain electrodes.

  FIG. 1 is a schematic diagram showing an example of a top contact type TFT according to the present invention having a top gate structure. In the TFT 10 shown in FIG. 1, the above-described oxide semiconductor film is stacked as an active layer 14 on one main surface of the substrate 12. A source electrode 16 and a drain electrode 18 are disposed on the active layer 14 so as to be separated from each other, and a gate insulating film 20 and a gate electrode 22 are sequentially stacked.

  FIG. 2 is a schematic view showing an example of a bottom contact type TFT according to the present invention having a top gate structure. In the TFT 30 shown in FIG. 2, the source electrode 16 and the drain electrode 18 are disposed on one main surface of the substrate 12 so as to be separated from each other. Then, the above-described oxide semiconductor film, the gate insulating film 20, and the gate electrode 22 are sequentially stacked as the active layer.

  FIG. 3 is a schematic diagram showing an example of a top contact type TFT according to the present invention having a bottom gate structure. In the TFT 40 illustrated in FIG. 3, the gate electrode 22, the gate insulating film 20, and the above-described oxide semiconductor film as the active layer 14 are sequentially stacked on one main surface of the substrate 12. A source electrode 16 and a drain electrode 18 are disposed on the surface of the active layer 14 so as to be separated from each other.

  FIG. 4 is a schematic view showing an example of a bottom contact type TFT according to the present invention having a bottom gate structure. In the TFT 50 shown in FIG. 4, the gate electrode 22 and the gate insulating film 20 are sequentially stacked on one main surface of the substrate 12. Then, the source electrode 16 and the drain electrode 18 are disposed on the surface of the gate insulating film 20 so as to be separated from each other, and the above-described oxide semiconductor film is stacked as the active layer 14.

  In the following embodiment, the top gate type thin film transistor 10 shown in FIG. 1 will be mainly described. However, the thin film transistor of the present invention is not limited to the top gate type and may be a bottom gate type thin film transistor.

(Active layer)
When the thin film transistor 10 of this embodiment is manufactured, first, metal oxide is formed on the substrate 12 by performing the above-described assembly film forming step and solution coating step, and further, if necessary, heat treatment or heat treatment under ultraviolet irradiation. A physical semiconductor film is formed.

  The metal oxide semiconductor film is patterned into the shape of the active layer. The patterning may be converted into a metal oxide semiconductor film by forming a metal oxide precursor film having an active layer pattern in advance by the above-described ink jet method, dispenser method, letterpress printing method, and intaglio printing method. Then, the metal oxide semiconductor film may be patterned into the shape of the active layer by photolithography and etching. In order to perform pattern formation by photolithography and etching, for example, a resist pattern is formed by photolithography on a portion where the metal oxide semiconductor film remains as an active layer, and hydrochloric acid, nitric acid, dilute sulfuric acid, or phosphoric acid, nitric acid, and acetic acid are used. The pattern of the active layer 14 is formed by etching with an acid solution such as a mixed solution.

  The thickness of the active layer 14 is preferably 5 nm or more and 50 nm or less from the viewpoint of flatness and time required for film formation.

  From the viewpoint of obtaining high mobility, the content of indium in the active layer 14 is preferably 50 atom% or more of the metal component contained in the active layer 14, and more preferably 80 atom% or more.

(Protective layer)
A protective layer (not shown) for protecting the active layer 14 is preferably formed on the active layer 14 when the source / drain electrodes 16 and 18 are etched. There is no particular limitation on the method for forming the protective layer, and the protective layer may be formed after the metal oxide semiconductor film or after the patterning of the metal oxide semiconductor film.
The protective layer may be a metal oxide layer or an organic material such as a resin. The protective layer may be removed after the source electrode 16 and the drain electrode 18 (referred to as “source / drain electrodes” as appropriate) are formed.

(Source / drain electrodes)
Source / drain electrodes 16 and 18 are formed on the active layer 14. The source / drain electrodes 16 and 18 each have a high electrical conductivity functioning as an electrode, for example, metals such as Al, Mo, Cr, Ta, Ti, Ag, Au, Al—Nd, Ag alloy, tin oxide, oxidation A metal oxide conductive film such as zinc, indium oxide, indium tin oxide (ITO), indium zinc oxide (IZO), or InGaZnO can be used.

  When the source / drain electrodes 16 and 18 are formed, a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method, or an ion plating method, a CVD (chemical vapor deposition), or a plasma CVD method. The film may be formed according to a method appropriately selected in consideration of suitability with a material to be used from among chemical methods such as the above.

  The film thickness of the source / drain electrodes 16 and 18 is preferably 10 nm or more and 1000 nm or less, preferably 50 nm or more and 100 nm or less in consideration of film forming properties, patterning properties by etching or lift-off methods, conductivity, and the like. More preferred.

  The source / drain electrodes 16 and 18 may be formed by patterning into a predetermined shape by, for example, etching or a lift-off method after forming a conductive film, or may be directly formed by an inkjet method or the like. At this time, it is preferable to pattern the source / drain electrodes 16 and 18 and wiring (not shown) connected to these electrodes simultaneously.

(Gate insulation film)
After the source / drain electrodes 16 and 18 and the wiring (not shown) are formed, the gate insulating film 20 is formed. The gate insulating film 20 is preferably made of a material having high insulating properties. For example, an insulating film such as SiO ₂ , SiN _x , SiON, Al ₂ O ₃ , Y ₂ O ₃ , Ta ₂ O ₅ , HfO ₂ , or a compound thereof is used. The insulating film may include two or more types, and may have a single layer structure or a stacked structure.
The gate insulating film 20 can be formed from a printing method, a wet method such as a coating method, a physical method such as a vacuum deposition method, a sputtering method or an ion plating method, or a chemical method such as a CVD or plasma CVD method. The film may be formed according to a method appropriately selected in consideration of suitability with the material to be used. The gate insulating film 20 may be an organic insulating film or an inorganic insulating film as long as it has gate insulating characteristics.

  The gate insulating film 20 needs to have a thickness for reducing leakage current and improving voltage resistance. On the other hand, if the thickness of the gate insulating film 20 is too large, the driving voltage is increased. Although the gate insulating film 20 depends on the material, the thickness of the gate insulating film 20 is preferably 10 nm to 10 μm, more preferably 50 nm to 1000 nm, and particularly preferably 100 nm to 400 nm.

(Gate electrode)
After forming the gate insulating film 20, a gate electrode 22 is formed. The gate electrode 22 is made of a material having high conductivity, for example, metal such as Al, CuMo, Cr, Ta, Ti, Ag, Au, Al—Nd, Ag alloy, tin oxide, zinc oxide, indium oxide, indium tin oxide ( It can be formed using a metal oxide conductive film such as ITO), indium zinc oxide (IZO), or InGaZnO. As the gate electrode 22, these conductive films can be used as a single layer structure or a stacked structure of two or more layers.

The gate electrode 22 is made of a material used from a wet method such as a printing method or a coating method, a physical method such as a vacuum deposition method, a sputtering method or an ion plating method, or a chemical method such as a CVD or plasma CVD method. The film is formed according to a method appropriately selected in consideration of the suitability of the above.
The film thickness of the metal film for forming the gate electrode 22 is preferably 10 nm or more and 1000 nm or less, preferably 50 nm or more and 200 nm or less in consideration of film forming properties, patterning properties by etching or lift-off methods, conductivity, and the like. More preferably.
After the film formation, the gate electrode 22 may be formed by patterning into a predetermined shape by an etching or lift-off method, or the pattern may be directly formed by an inkjet method or the like. At this time, it is preferable to pattern the gate electrode 22 and the gate wiring (not shown) at the same time.

Although there is no limitation in particular in the use of the thin-film transistor 10 of this embodiment demonstrated above, Since it shows a high transport characteristic, it can apply to various electronic devices. Specifically, it is suitable for manufacturing a flexible display using a driving element in a display device such as a liquid crystal display device, an organic EL (Electro Luminescence) display device, and an inorganic EL display device, and a resin substrate having low heat resistance.
Further, the thin film transistor manufactured according to the present invention is suitably used as a driving element (driving circuit) in various electronic devices such as various sensors such as an X-ray sensor and an image sensor, and a micro electro mechanical system (MEMS).

<Liquid crystal display device>
FIG. 5 shows a schematic sectional view of a part of a liquid crystal display device according to an embodiment of the present invention, and FIG. 6 shows a schematic configuration diagram of electrical wiring.

  As shown in FIG. 5, the liquid crystal display device 100 according to the present embodiment includes a top contact type TFT 10 having the top gate structure shown in FIG. 1 and a pixel lower electrode on the gate electrode 22 protected by the passivation layer 102 of the TFT 10. 104 and a liquid crystal layer 108 sandwiched between the counter upper electrode 106 and an R (red) G (green) B (blue) color filter 110 for developing different colors corresponding to each pixel. In this configuration, polarizing plates 112a and 112b are provided on the substrate 12 side and the RGB color filter 110, respectively.

  As shown in FIG. 6, the liquid crystal display device 100 according to the present embodiment includes a plurality of gate lines 112 that are parallel to each other and data lines 114 that are parallel to each other and intersect the gate lines 112. Here, the gate wiring 112 and the data wiring 114 are electrically insulated. The TFT 10 is provided in the vicinity of the intersection between the gate wiring 112 and the data wiring 114.

  The gate electrode 22 of the TFT 10 is connected to the gate wiring 112, and the source electrode 16 of the TFT 10 is connected to the data wiring 114. The drain electrode 18 of the TFT 10 is connected to the pixel lower electrode 104 through a contact hole 116 provided in the gate insulating film 20 (a conductor is embedded in the contact hole 116). The pixel lower electrode 104 forms a capacitor 118 together with the grounded counter upper electrode 106.

<Organic EL display device>
FIG. 7 shows a schematic sectional view of a part of an active matrix organic EL display device according to an embodiment of the present invention, and FIG. 8 shows a schematic configuration diagram of electrical wiring.

  The active matrix organic EL display device 200 of the present embodiment includes the TFT 10 having the top gate structure shown in FIG. 1 as a driving TFT 10a and a switching TFT 10b on a substrate 12 having a passivation layer 202. , 10b is provided with an organic EL light emitting element 214 composed of an organic light emitting layer 212 sandwiched between a lower electrode 208 and an upper electrode 210, and the upper surface is also protected by a passivation layer 216.

  As shown in FIG. 8, the organic EL display device 200 of this embodiment includes a plurality of gate wirings 220 that are parallel to each other, and data wirings 222 and driving wirings 224 that are parallel to each other and intersect the gate wirings 220. ing. Here, the gate wiring 220, the data wiring 222, and the drive wiring 224 are electrically insulated. The gate electrode 22 of the switching TFT 10 b is connected to the gate wiring 220, and the source electrode 16 of the switching TFT 10 b is connected to the data wiring 222. The drain electrode 18 of the switching TFT 10b is connected to the gate electrode 22 of the driving TFT 10a, and the driving TFT 10a is kept on by using the capacitor 226. The source electrode 16 of the driving TFT 10 a is connected to the driving wiring 224, and the drain electrode 18 is connected to the organic EL light emitting element 214.

  In the organic EL display device shown in FIG. 7, the upper electrode 210 may be a top emission type using a transparent electrode, or the lower electrode 208 and each electrode of a TFT may be a bottom emission type using a transparent electrode.

<X-ray sensor>
FIG. 9 shows a partial schematic cross-sectional view of an X-ray sensor according to an embodiment of the present invention, and FIG. 10 shows a schematic configuration diagram of electrical wiring.

  The X-ray sensor 300 of this embodiment includes the TFT 10 and the capacitor 310 formed on the substrate 12, the charge collection electrode 302 formed on the capacitor 310, the X-ray conversion layer 304, and the upper electrode 306. Composed. A passivation film 308 is provided on the TFT 10.

  The capacitor 310 has a structure in which an insulating film 316 is sandwiched between a capacitor lower electrode 312 and a capacitor upper electrode 314. The capacitor upper electrode 314 is connected to one of the source electrode 16 and the drain electrode 18 (the drain electrode 18 in FIG. 9) of the TFT 10 through a contact hole 318 provided in the insulating film 316.

The charge collection electrode 302 is provided on the capacitor upper electrode 314 in the capacitor 310 and is in contact with the capacitor upper electrode 314.
The X-ray conversion layer 304 is a layer made of amorphous selenium, and is provided so as to cover the TFT 10 and the capacitor 310.
The upper electrode 306 is provided on the X-ray conversion layer 304 and is in contact with the X-ray conversion layer 304.

  As shown in FIG. 10, the X-ray sensor 300 of this embodiment includes a plurality of gate wirings 320 that are parallel to each other and a plurality of data wirings 322 that intersect with the gate wirings 320 and are parallel to each other. Here, the gate wiring 320 and the data wiring 322 are electrically insulated. The TFT 10 is provided in the vicinity of the intersection between the gate wiring 320 and the data wiring 322.

  The gate electrode 22 of the TFT 10 is connected to the gate wiring 320, and the source electrode 16 of the TFT 10 is connected to the data wiring 322. The drain electrode 18 of the TFT 10 is connected to the charge collecting electrode 302, and the charge collecting electrode 302 is connected to the capacitor 310.

  In the X-ray sensor 300 of this embodiment, X-rays enter from the upper electrode 306 side in FIG. 9 and generate electron-hole pairs in the X-ray conversion layer 304. By applying a high electric field to the X-ray conversion layer 304 by the upper electrode 306, the generated charge is accumulated in the capacitor 310 and read out by sequentially scanning the TFT 10.

  Note that the liquid crystal display device 100, the organic EL display device 200, and the X-ray sensor 300 of the above embodiment include a top gate TFT, but are not limited to the top gate TFT. A TFT having the structure shown in FIG.

Examples will be described below, but the present invention is not limited to the following examples.
A semiconductor film or a conductive film exhibiting high conductivity by forming a film in which metal oxide converted from metal nitrate or metal nitrate exists in at least a part of the aggregate of metal oxide particles containing In or the like It was proved that

(Preparation of metal oxide particle dispersion 1)
In ₂ O ₃ nanoparticle dispersion liquid (metal oxide particle dispersion liquid 1) was prepared by the following method.
Add 30 mL octadecene, indium triacetate (1.2 mmol), 3.6 mL oleic acid, 4.8 mL oleylamine in a three-necked flask, and heat and stir at 150 ° C. under a nitrogen flow to dissolve the raw materials sufficiently. Degassing was performed for 1 hour.
Subsequently, the flask was heated to 230 ° C. or 270 ° C. and maintained for 150 minutes. It was confirmed that the solution was colored and particles were formed during heating. After cooling the obtained solution to room temperature, ethanol was added and centrifuged to precipitate particles. The supernatant was discarded and then dispersed in a hexane solvent.
Thus, metal oxide particle dispersion 1 (metal oxide particles: In ₂ O ₃ particles, number average particle size: 7 to 30 nm, ligand: oleic acid + oleylamine, solvent: hexane, concentration: 25 mg / ml) is prepared. did.

(Preparation of metal oxide particle dispersion 2)
In—Ga—O nanoparticle dispersion liquid (metal oxide particle dispersion liquid 2) was prepared by the following method.
30 mL of octadecene, indium triacetate (1.08 mmol), gallium (III) acetylacetone (0.12 mmol), 3.6 mL of oleic acid, and 4.8 mL of oleylamine were added to the three-necked flask, and the mixture was heated and stirred at 150 ° C. under a nitrogen flow. The raw material was sufficiently dissolved and deaerated for 1 hour.
Subsequently, the flask was heated to 270 ° C. and maintained for 150 minutes. It was confirmed that the solution was colored and particles were formed during heating. After cooling the obtained solution to room temperature, ethanol was added and centrifuged to precipitate particles. The supernatant was discarded and then dispersed in a hexane solvent.
Thus, metal oxide particle dispersion 2 (metal oxide particles: In—Ga—O particles (Ga: 10% dope), number average particle diameter: 8 nm, ligand: oleic acid + oleylamine, solvent: hexane, concentration: 25 mg / ml) was prepared.

(Preparation of metal oxide particle dispersion 3)
In—Sn—O nanoparticle dispersion (metal oxide particle dispersion 3) was prepared by the following method.
Add 30 mL of octadecene, indium triacetate (1.08 mmol), tin diacetate (0.12 mmol), 3.6 mL of oleic acid, and 4.8 mL of oleylamine in a three-necked flask and stir at 150 ° C. under a nitrogen flow. The raw material was sufficiently dissolved and deaerated for 1 hour.
Subsequently, the flask was heated to 270 ° C. and kept for 150 minutes. It was confirmed that the solution was colored and particles were formed during heating. After cooling the obtained solution to room temperature, ethanol was added and centrifuged to precipitate particles. The supernatant was discarded and then dispersed in a hexane solvent.
Thus, metal oxide particle dispersion 3 (metal oxide particles: In—Sn—O particles (Sn: 10% dope), number average particle diameter: 7 nm, ligand: oleic acid + oleylamine, solvent: hexane, concentration: 25 mg / ml) was prepared.

In order to control the thickness of the metal oxide particle aggregate film, the metal oxide particle dispersions 1 to 3 were further diluted with hexane to adjust the concentration. The relationship between the concentration and the target film thickness is as follows.
2.5 mg / ml: 10 nm thickness 5.0 mg / ml: 15 nm thickness 8.3 mg / ml: 25 nm thickness 25 mg / ml: 70 nm thickness

<Example 1>
(Formation of metal oxide film)
FIG. 11 schematically shows a process of forming the metal oxide film in the first embodiment.
First, a dispersion obtained by adjusting the In ₂ O ₃ particle concentration of the metal oxide particle dispersion 1 to 8.3 mg / ml is applied to the highly doped p-Si substrate 1 on which the thermal oxide film 2 having a thickness of 100 nm is formed. The aggregate film 3 of In ₂ O ₃ particles was formed by spin coating (1500 rpm) (FIG. 11A).

After forming the aggregate film 3 of metal oxide particles, a methanol solution of indium nitrate (nitric acid) is used as a solution for filling the voids in the aggregate film 3 (hereinafter referred to as a filling solution) into the aggregate film 3. Indium concentration: 0.1M) is prepared, applied onto the aggregate film 3 of metal oxide particles, and left to stand for about 30 seconds, and then spin-coated at 1500 rpm, so that indium nitrate 4 is interposed between the In ₂ O ₃ particles. Thus, a metal oxide film with the presence of C was obtained (FIG. 11B).

(Production and evaluation of TFT)
After forming the metal oxide film, an electrode 5 of Ti (10 nm thickness) / Au (40 nm thickness) was formed by using a vacuum evaporation method. The electrodes were formed using a shadow mask, and TFTs with L / W = 180 μm / 1000 μm were produced (FIG. 11C).
After the TFT was fabricated, heat treatment was performed for 1 hour at 150 ° C. in the atmosphere. The heating was performed by setting on a hot plate heated to a surface temperature of 150 ° C.

  Using the semiconductor parameter analyzer (manufactured by Agilent Technologies), the TFT fabricated as described above was subjected to measurement of transport characteristics by sweeping the gate voltage between −50 to 50 V with a drain voltage of 10 V applied, and field effect mobility. (Μ) was calculated.

<Examples 2 to 11 and Comparative Examples 1 to 7>
Except that the conditions of Example 1 were changed to the conditions shown in Table 1 below, a metal oxide film was formed, TFTs were fabricated, and evaluated in the same manner as Example 1.

In Table 1, “160 ° C. air + UV” in the heat treatment process means that heat treatment was performed in the air at 160 ° C. for 60 minutes under UV irradiation. After setting the sample on a hot plate heated to a surface temperature of 160 ° C. in the apparatus, a VUV dry processor (Oak Seisakusho, VUE-3400-F) equipped with a low-pressure mercury lamp is used as the ultraviolet irradiation apparatus. After waiting for 5 minutes, the shutter in the apparatus was opened, and an ultraviolet irradiation process was performed together with a heat treatment at 160 ° C. for 60 minutes. Moreover, when the ultraviolet illuminance of wavelength 185nm and 254nm in a sample position was measured using the ultraviolet light meter (Oak Seisakusho make, UV-M10, light receiver UV-25), the illuminance with respect to the irradiation wavelength of 254nm is 100mW /. cm ² .

  In Table 1, “250 ° C. atmosphere” means that heat treatment was performed in the atmosphere at 250 ° C. for 1 hour.

  Table 1 shows the dispersions, filling solutions, heat treatment conditions, and evaluation results used in Examples 1 to 11 and Comparative Examples 1 to 7.

As shown in Table 1, the TFTs of Examples 1 to 11 including a metal oxide film produced by applying a solution containing In nitrate as an aggregate film of metal oxide particles as an active layer have high field effect mobility. Obtained.
On the other hand, in the TFTs of Comparative Examples 1 to 4 in which the solution containing In nitrate was not applied to the aggregate film of metal oxide particles and the TFTs of Comparative Examples 6 and 7 in which a solution containing In acetate or In alkoxide was applied, the field effect In Comparative Example 5 in which the mobility was extremely low, an aggregate film of metal oxide particles was not formed, and only an In nitrate nitrate solution was applied, TFT driving was not observed.
Figure 12 shows, _V g -I _d characteristics of the simplified type TFT prepared in Example 1 and 7, Comparative Example 1.

<Examples 12 to 15 and Comparative Example 8>
(Production and evaluation of conductive film)
A metal oxide film was formed on the Si substrate in the same manner as in Example 1 except that the dispersion and filling solution shown in Table 2 were used.

  Next, the metal oxide film was subjected to heat treatment at 160 ° C. for 60 minutes under UV irradiation to obtain a conductive film exhibiting degenerate conduction. The specific resistance was calculated by forming a two-terminal electrode on the conductive film and measuring the resistance.

  Table 2 shows the dispersions, filling solutions, heat treatment conditions, and evaluation results used in Examples 12 to 15 and Comparative Example 8.

  As shown in Table 2, for the films of Examples 12 to 15 in which a metal oxide film was prepared by applying a solution containing In nitrate to an aggregate film of metal oxide particles, a solution containing In nitrate was applied. It was found that the specific resistance can be reduced by one digit or more as compared with the film of Comparative Example 8 that did not exist.

DESCRIPTION OF SYMBOLS 1 Si substrate 2 Thermal oxide film 3 Aggregate film | membrane 4 Indium nitrate 5 Electrode 10, 30, 40, 50 Thin-film transistor 12 Substrate 14 Active layer (oxide semiconductor layer)
16 Source electrode 18 Drain electrode 20 Gate insulating film 22 Gate electrode 100 Liquid crystal display device 200 Organic EL display device 300 X-ray sensor

Claims (13)

An aggregate of metal oxide particles containing at least one metal element selected from In, Zn and Sn;
At least one selected from metal nitrates and metal oxides present in at least part of the metal oxide particles of the aggregate;
Metal oxide film containing   The metal oxide film according to claim 1, wherein the metal oxide particles are metal oxide particles containing at least In.   The metal oxide film according to claim 1, wherein the metal oxide particles are metal oxide particles containing In and at least one metal element selected from Sn, Ga, and Zn.   The metal oxide film according to claim 1, wherein the metal nitrate contains at least indium nitrate. Metal oxide film according to any one of the metal oxide according to claim 1 to claim 4 in which the particles are formed using Sutaira average particle diameter of 3 to 50 nm.   It is a semiconductor film, The metal oxide film of any one of Claims 1-5.   It is a electrically conductive film, The metal oxide film of any one of Claims 1-5. A dispersion containing metal oxide particles having a number average particle diameter of 3 to 50 nm containing at least one metal element selected from In, Zn and Sn is applied onto a substrate to form an aggregate of the metal oxide particles. Forming an assembly film comprising:
Applying a solution containing metal nitrate to the aggregate film;
The manufacturing method of the metal oxide film which has this.   The method for producing a metal oxide film according to claim 8, comprising a step of performing a heat treatment under ultraviolet irradiation on the aggregate film to which the solution containing the metal nitrate is applied.   The method for producing a metal oxide film according to claim 8 or 9, wherein the metal nitrate contains at least indium nitrate.   The method for producing a metal oxide film according to any one of claims 8 to 10, wherein the metal oxide particles in the dispersion have a ligand containing a hydrocarbon. Thin film transistor comprising a metal oxide film according to any one of claims 1 to 7. Electronic device having a thin film transistor according to claim 1 2.