JP2003160313A - Compound for forming metal oxide thin film, method for producing metal oxide and metal oxide thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compound for forming a metal oxide thin film to be able to produce a thin coating film having a sufficient thickness by one coating operation not applying an impractical step such as a drying step at high temperature and the like and the metal oxide thin film. <P>SOLUTION: A solution contains a metal alkoxide or a metal alkoxide and a metallic salt. The compound for forming the metal oxide thin film contains an alkanediol whose melting point is 30°C or more and carbon number is 5-12 in the compound. The compound is used for producing a metal oxide and for the metal oxide thin film. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention can be used in all fields requiring functional ceramic thin films such as optical, electronic, information, chemical, mechanical, medical, and the like, and a solution of a metal alkoxide or a metal salt can be obtained. The present invention relates to a composition for forming a metal oxide thin film as a coating liquid, a method for producing a metal oxide, and a metal oxide thin film.

[0002]

2. Description of the Related Art Metal oxide thin films have been conventionally used for hard coating films, optical coating films, etc., and in recent years, their electrical characteristics have been paid attention to, and in the field of electronics, transparent conductive films, ferroelectric thin films, and dielectric films. Its application fields are expanding as thin films.

In particular, for example, ITO or SnO ₂ thin film is used as a transparent conductive film as an electrode layer of a solar cell or a liquid crystal display, and PZT, BaTiO ₃ , BST.
The perovskite type ferroelectric thin film is known for its wide range of applications such as a capacitor, an infrared sensor, an actuator, a non-volatile memory, a display and a transducer by utilizing its ferroelectricity and high dielectric constant characteristics.

Conventionally, such a method for forming a metal oxide thin film is a vacuum evaporation method such as a vacuum evaporation method, a sputtering method or a CVD method, or a precursor solution for forming a metal oxide thin film is applied to a substrate. MO that forms a film by firing
The D method and the sol-gel method are known.

The sol-gel method is generally a method in which a predetermined amount of water is added to a metal alkoxide dissolved in a solvent, and a precursor solution of a sol having an MOM bond formed by hydrolysis and polycondensation reaction is applied to a substrate. It is a method of forming a film by baking after drying, drying. In addition, MOD (Metallo-Or
The ganic decomposition method is a method of forming a film by dissolving a metal salt of a carboxylic acid having an MO bond in an organic solvent to form a precursor solution, coating and drying the precursor solution on the substrate, and then baking the solution. Here, the precursor solution refers to a solution containing an intermediate compound produced by dissolving a raw material compound in a solvent in a film forming method such as a sol-gel method or a MOD method.

The sol-gel method and the MOD method are not completely separate methods but are generally used in combination with each other. For example, when forming a PZT film, it is common to prepare a solution using lead acetate as a Pb source and alkoxides as Ti and Zr sources. The two methods of the sol-gel method and the MOD method may be collectively referred to as the sol-gel method. In either case, the precursor solution is applied to the substrate and baked to form a film. Then, the solution coating firing method is used.

In both the sol-gel method and the MOD method, the solution coating and firing method uniformly mixes the elements constituting the oxide thin film in the order of submicron or less, so that the method using ceramic powder sintering can be used. In comparison, it is possible to synthesize a dielectric at an extremely low temperature, and since it is easy to strictly adjust the chemical composition when preparing a precursor solution, it is particularly desirable to use a functional composite oxide such as a ferroelectric thin film. This is a preferable film forming method for synthesizing a thin film.

Further, unlike a vapor deposition method using a vacuum such as a sputtering method or a CVD method, a large area film can be formed under normal pressure without requiring expensive manufacturing equipment, and therefore, as a low cost film forming method. Is also preferable.

However, the conventional sol-gel method and MOD
In a method of forming a metal oxide thin film using a solution coating baking method such as a method, an extremely large volume contraction occurs in a process from a solution state immediately after coating a precursor solution on a substrate to an oxide solid state after baking. If an oxide thin film having a thickness of about 0.1 μm or more is formed by coating and baking once, the film has cracks or peeling during drying or baking, which makes it unusable.

Therefore, in order to form an oxide thin film having a large film thickness by using the solution coating and baking method, it is necessary to repeat coating, drying and baking many times. However, such a method is poor in productivity because of low productivity and high cost, and it is difficult to put the method of forming a thick oxide thin film by the solution coating and baking method into practical use.

In particular, in the case of a functional oxide thin film such as a ferroelectric thin film, it is difficult to form a thick film because the functionality of the film cannot be obtained unless the film thickness exceeds a certain value. This is a major weakness of the coating and firing method.

In order to solve such a problem, in order to obtain a thick oxide thin film without cracks by one-time coating and firing using the solution coating and firing method, it was attempted to add an organic substance additive to the precursor solution. Has been.

For example, Journal of Materials Science 30
(1995) 2507-2516 used a sol-gel precursor solution of PZT formed by introducing 1,3-propanediol addition during the synthesis process.
Dry on a hot plate at 0 ℃ to 450 ℃ (pre-baking)
It is disclosed that a thick PZT film having a maximum of 1 μm without cracks can be formed by one-time application and baking by performing main baking at 700 ° C. after performing the above.

At this time, the substrate coated with the solution is heated to 350.degree.
If the film obtained is dried at a temperature other than 450 ° C., cracks and peeling will occur in the obtained film, so this high temperature hot plate drying is an essential step.

However, since the sol-gel precursor solution using addition of 1,3-propanediol remains in a solution state when applied to a substrate, it becomes very difficult to handle the applied substrate. Further, since drying requires heating by a hot plate having a very high temperature of 350 ° C. to 450 ° C., it is difficult to handle the high temperature hot plate, the problem of damage due to rapid heating of the substrate, the processing of a large area substrate, etc. There were a lot of problems and it was not practical.

[0016]

An object of the present invention is to enable production of a thick oxide thin film by a solution coating and baking method in a single film forming operation without passing through steps of low practicality such as a high temperature drying step. A method for forming a metal oxide thin film, a method for producing a metal oxide thin film, and a metal oxide thin film are provided.

[0017]

That is, the above object is achieved by the following constitution of the present invention. (1) A composition for forming a metal oxide thin film, which contains a metal alkoxide or a metal alkoxide and a metal salt in a solution, and contains an alkanediol having a melting point of 30 ° C. or higher and a carbon number of 5 to 12 in the composition. (2) The composition for forming a metal oxide thin film according to (1) above, wherein the alkanediol is neopentyl glycol. (3) The metal of the metal alkoxide and the metal salt is
At least alkaline earth metal, or Pb, Ti, Zr, H
The composition for forming a metal oxide thin film according to (1) or (2) above, which is one or more selected from f, Sn, Nb, Ta, and La. (4) The metal alkoxide is one or two of Ti alkoxide and Zr alkoxide,
The composition for forming a metal oxide thin film according to any one of (1) to (3) above, wherein the metal salt is a Pb salt. (5) A metal oxide thin film in which the composition for forming a metal oxide thin film according to any one of (1) to (4) above is applied onto a substrate, dried at a temperature not higher than the melting point of the added alkanediol, and then baked. Production method. (6) A metal oxide thin film having a film thickness of 0.4 μm or more, obtained by the composition for forming a metal oxide thin film according to any one of (1) to (4) above.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The composition for forming a metal oxide thin film of the present invention contains a metal alkoxide or a metal alkoxide and a metal salt in a solution, and has a melting point of 30 ° C. or higher and a carbon number of 5 to 5. It contains 12 alkanediols.

By containing an alkanediol having a melting point of 30 ° C. or higher and a carbon number of 5 to 12 as described above, a thick film can be formed without causing cracks, cracks or chips during drying or firing (heat treatment). A metal oxide thin film is obtained.

The alkanediol used in the present invention has 5 to 12 carbon atoms, preferably 5 to 11 carbon atoms, and particularly 5 to 5 carbon atoms.
8 If the number of carbon atoms is less than this range, the melting point will be outside the range, and if the number of carbon atoms is more than this range, the mass of the alkanediol bonded to the metal alkoxide will be too large and cracks will occur. . Further, as the number of carbons increases, the range of manufacturing conditions such as firing conditions becomes narrower, production management becomes stricter, and manufacturing costs tend to increase.

Specific examples of such alkane diols include neopentyl glycol (= 2,2-dimethyl-1,3-propanediol), 2,2-diethyl-1,3-propanediol and 2-methyl-. 2-ethyl-
1,3-propanediol, 2-methyl-2-propyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 2,2-dibutyl-1,
3-propanediol, 3,3-dimethyl-1,2-butanediol, pinacol (= 2,3-dimethyl-2,
3-butanediol), 2,2,4-trimethyl-1,
3-pentanediol, 2,5-dimethyl-2,5-hexanediol, 1,6-hexanediol, 1,2-
Octanediol, 1,8-octanediol, 1,2
-Decanediol, 1,10-decanediol, 1,1
2-dodecanediol etc. are mentioned. Among them,
Neopentyl glycol is preferred because it has a relatively high melting point of around 130 ° C. and thus has a wide drying temperature range and is relatively inexpensive and available.

The present inventor has studied various organic additives in order to prepare a composition for forming a metal oxide thin film, which enables a thick oxide thin film to be produced by a single film-forming operation by the solution coating and baking method. By using the above-mentioned alkanediol as an organic additive, the maximum film thickness that can form various oxide thin films without cracks by coating and baking once is 0.1 μm.
From the front and back, it was found that it can be greatly increased to 0.4 μm to 1 μm or more, particularly 0.5 μm or more.

Further, the composition for forming a metal oxide thin film using the above-mentioned alkanediol as an organic additive can be dried at a relatively low temperature from room temperature to a melting point of the organic additive or lower after coating on the substrate, and further The drying conditions do not need to be strict except for the temperature, and if the drying temperature is below the melting point of the organic additive, a thick thin film of 1 μm or more can be formed even if a drying step is included before firing by one coating firing. I found that.

As described above, when alkanediol is used, cracks and the like do not occur during firing, and a thick metal oxide thin film can be obtained because the alkane bonded to the metal alkoxide by the ligand exchange reaction. It is considered that the diol does not desorb up to a relatively high temperature when the temperature rises and imparts the stress relaxation ability to the gel film. Further, it is presumed that one of the reasons why the cracks do not occur during drying is that the unbound alkanediol remains without being evaporated and the state of the coating film is stable.

The melting point of the alkanediols is 30 ° C. or higher, preferably 50 ° C. or higher, particularly 100 ° C. or higher. The upper limit is about 200 ° C., but there is no problem, but 150 ° C. or less is preferable. For example, neopentyl glycol is around 130 ° C. and 1,6-hexanediol is 4 ° C.
It is around 0 ° C. If the melting point is lower than the above temperature, work at room temperature will be hindered.

Here, the temperature of 150 ° C. or lower is approximately the same as the post-application drying temperature of the photosensitive photoresist which is widely used in microfabrication of semiconductors by photolithography, for example. Therefore, a special hot plate having a high temperature of 350 ° C. or higher, which was required when forming an oxide thin film by a solution coating and baking method using a conventional precursor solution using 1,3-propanediol, was used. It is extremely practical because it can be dried over a large area uniformly and at low cost using a conventional industrially established apparatus without requiring drying.

The amount of the alkanediol to be mixed is 0.1 to 8 mol, particularly 0.2 to 3 mol, and further 0.5 to 1 with respect to 1 mol of the metal atom of the metal source (metal alkoxide, metal salt). 0.5 mol is preferred. If the added amount is too small, the effect of the present invention cannot be obtained, and if the added amount is too large, cracks occur and the film quality deteriorates.

Further, the solution composition for forming a metal oxide thin film of the present invention can form a similar thick film by directly putting it in a baking furnace and baking it after coating without using the above-mentioned drying step.

The composition for forming a metal oxide thin film of the present invention comprises
It can be used for forming an extremely wide oxide thin film.
For example, SnO₂ , ZnO, TiO₂ , Ta₂O_Five , N
b₂O _Five , Al₂O₃ , Various thin oxides such as ITO and MgO
It can be used for film formation.

Further, the composition for forming a metal oxide thin film of the present invention can be preferably used particularly for forming a composite oxide thin film.

As such a composite oxide thin film,
Ferroelectric materials can be used. For example, ABO₃ Indicated by
The perovskite type complex oxide and its complex system
Alkali metal or
Arranging potash earth metal or Pb, T at the B site
Also one selected from i, Zr, Hf, Sn, Nb, Ta
It is mainly composed of substances composed of multiple elements.
BaTiO 3 as a specific example of the substance₃ ,
SrTiO₃ , CaTiO₃ , PbTiO₃ , BaSn
O₃ , Pb (Zr_1-xTi_x ) O₃ , PLZT, (Ba
_1-xSr_x ) (Zr _1-yTi_y ) O₃ , KNbO₃ , KT
aO₃ Etc.

Further, Pb (Mg _1/3 Nb _2/3 ) O ₃ , Pb
It can also be used for a perovskite reluxer-type composite oxide typified by (Fe _1/2 Nb _1/2 ) O ₃ , Pb (Fe _2/3 W _1/3 ) O _{3, and the} like (Sr _{1- x} Ba _x ) Nb ₂ O ₆
, PbNb ₂ O _{6 and the} like, and can also be used for forming a tungsten bronze type ferroelectric thin film.

The metal source of the metal oxide forming composition of the present invention is a metal alkoxide or a metal alkoxide and a metal salt dissolved in a solvent.

As the metal source, for example, when forming a TiO ₂ thin film, a Ti alkoxide may be used. As such a metal alkoxide, Ti alkoxide may be titanium tetramethoxide, titanium tetraethoxide or titanium tetran. -Propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra
Examples thereof include i-butoxide, titanium tetra-sec-butoxide, titanium tetra-t-butoxide, titanium tetramethoxyethoxide, and the like, and an alkoxide having a β-diketone group such as titanium diisopropoxybisacetylacetonate can also be used.

Similarly, when forming a ZrO ₂ thin film, Zr alkoxide may be used, for example, zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra n-propoxide, zirconium tetraisopropoxide, zirconium tetra n. -Butoxide, zirconium tetra i-butoxide, zirconium tetra sec-butoxide, zirconium tetra t-butoxide and the like.

As a metal source for forming the SnO ₂ thin film, tin tetraethoxide, tin tetraisopropoxide,
Examples thereof include tin tetra n-butoxide, and when forming an ITO thin film, indium trimethoxide, indium triethoxide, indium triisopropoxide, etc. are used as an In source together with the Sn compound as a metal source. Good.

In the case of a Ta oxide thin film such as Ta ₂ O ₅ ,
Tantalum pentamethoxide, tantalum pentaethoxide, tantalum pentaisopropoxide, tantalum penta
Alkoxides such as n-propoxide, tantalum penta n-butoxide, tantalum penta i-butoxide, tantalum penta sec-butoxide and tantalum penta t-butoxide can be preferably used, and in the case of Nb oxide thin film such as Nb ₂ O ₅ , niobium Pentamethoxide, niobium pentaethoxide, niobium pentaisopropoxide, niobium penta n-propoxide, niobium penta n-butoxide, niobium penta
i-Butoxide and niobium penta sec-butoxide can be used.

When forming a ZnO thin film, zinc dimethoxide, zinc diethoxide, zinc di-n-propoxide,
Zinc di-n-butoxide or the like can be used, and Al ₂ O ₃
When forming a thin film, aluminum trimethoxide, aluminum triethoxide, aluminum tri n-propoxide, aluminum triisopropoxide, aluminum tri n-butoxide, aluminum triisobutoxide, aluminum tri sec-butoxide, aluminum tri t. -Butoxide and the like can be used.

As the metal source for forming the perovskite complex oxide thin film preferably used in the present invention, the metal of the metal alkoxide is an alkaline earth metal, Pb,
Ti, Zr, Sn, Nb and Ta are preferable, and Ti and Zr are particularly preferable.

Examples of such metal alkoxide include T
Examples of i alkoxides include titanium tetramethoxide, titanium tetraethoxide, titanium tetra n-propoxide, titanium tetraisopropoxide, titanium tetra n-butoxide, titanium tetra i-butoxide, titanium tetra sec-butoxide, and titanium tetra t-butoxide. , Titanium tetramethoxyethoxide, etc., and an alkoxide having a β-diketone group such as titanium diisopropoxybisacetylacetonate can also be used. The same applies to other metals, for example, zirconium tetramethoxide, zirconium tetraethoxide, zirconium tetra n-propoxide, zirconium tetraisopropoxide, zirconium tetra n-butoxide, zirconium tetra i-butoxide, zirconium tetra sec. -Butoxide, zirconium tetra-t-butoxide, tin tetraethoxide, tin tetraisopropoxide, tin tetra n-butoxide, niobium pentamethoxide, niobium pentaethoxide, niobium pentaisopropoxide, niobium penta
n-propoxide, niobium penta n-butoxide, niobium penta i-butoxide, niobium penta sec-butoxide, tantalum pentamethoxide, tantalum pentaethoxide, tantalum pentaisopropoxide, tantalum penta n-propoxide, tantalum penta n-butoxide, tantalum Alkoxides such as penta i-butoxide, tantalum penta sec-butoxide and tantalum penta t-butoxide can be preferably used.

As the metal of the metal salt, an alkaline earth metal or a metal salt of Pb is preferable, and Pb is particularly preferable. Specifically, acetate (lead acetate, barium acetate, etc.), nitrate (lead nitrate, barium nitrate, etc.), 2-ethylhexanoate (2
-Lead ethylhexanoate, barium 2-ethylhexanoate, etc.) and the like. It is also possible to include a rare earth metal salt such as lanthanum acetate as a doping element.

As the solvent of the composition for forming an oxide thin film of the present invention, a non-aqueous solvent such as alcohol, carboxylic acid, ester or ketone can be used. Among them,
Particularly preferably usable are 2-methoxyethanol, 2-ethoxyethanol, alkoxy alcohols such as 1-ethoxy-2-propanol, ethanol,
1-propanol, 2-propanol, 1-butanol, 2-butanol, 2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol, 2-methyl
-2-Alkanols such as pentanol, and carboxylic acids such as acetic acid and propionic acid.

The concentration of the metal source is preferably 5 to 40% by mass (concentration as oxide) with respect to the solvent, particularly 10 to 40% by mass. When the concentration is lower than 5% by mass, the final film thickness to be formed becomes thin, which is not preferable, and when the concentration is higher than 40% by mass, precipitation or the like is likely to occur and the long-term stability of the solution deteriorates. The optimum value of the range varies depending on the material used and the coating method. For example, in the case of spin coating PZT, the content is preferably 20% by mass or more.

The method of dissolving the alkoxide in the solvent is
As is generally used, the solvent may be stirred in the solvent using a means such as a stirrer to dissolve the alkoxide.

The temperature at the time of dissolution may be in the range of room temperature to a temperature not higher than the boiling point of the solvent depending on the reactivity of the alkoxide with the solvent, and the reaction time at this time is 10 min to 48 hours.
Is. Further, when the reaction is carried out for a long time, it is preferable to reflux the reaction.

In the case of a complex oxide, when a metal salt is used as a part of the metal source of the composition, the metal salt may be dissolved in a solvent and then the alkoxide may be mixed. Alternatively, the metal salt and the alkoxide may be dissolved in different solvents and the solvents may be mixed.

For example, when 2-methoxyethanol is used as a solvent, lead acetate anhydrous is used as a Pb source, and titanium tetraisopropoxide is used as a Ti source as a PbTiO ₃ thin film forming composition, first, the temperature is maintained at 60 to 90 ° C. 2-
Anhydrous lead acetate may be dissolved in methoxyethanol, and titanium tetraisopropoxide may be further added and mixed.

When barium acetate is used as a Ba source and titanium tetraethoxide is used as a Ti source in a composition for forming a BaTiO ₃ thin film, acetic acid is used as a solvent for barium acetate and ethanol is used as a solvent for titanium tetraethoxide. It is also possible to use each solution separately, and then mix and react each solution.

In the present invention, a chelating agent may be contained in the solution for stabilizing the solution. Examples of the chelating agent contained in the solution include acetylacetone, β-diketones such as dipivaloylmethane, and alkanolamines such as monoethanolamine, diethanolamine and triethanolamine. Acetylacetone is preferred.

The content of the chelating agent is preferably 0.1 to 2 mol with respect to 1 mol of the metal alkoxide.

As a mixing method, the chelating agent may be reacted with the alkoxide in advance, but it is also possible to mix the alkoxide in the solvent and then the chelating agent.

After mixing the alkoxide, the solution is mixed with alkanediol. The amount of the alkanediol mixed is preferably 0.1 to 8 mol with respect to 1 mol of the metal atom.

The method for mixing the alkanediol is 5
A predetermined amount of alkanediol may be mixed in the solution maintained at 0 to 120 ° C., sufficiently stirred using a stirrer, and reacted for a predetermined time.

The composition for forming a metal oxide thin film of the present invention comprises
A commonly used coating method, for example, dip coating,
It is applied on the substrate by spin coating, spray coating, knife coating, roll coating, etc., and dried and gelled.

Further, when the film thickness is controlled by the spin coating method, in order to increase the film thickness in particular, for example, the time of the first press pin having a low rotational speed may be adjusted.

As a drying method, the temperature may be maintained at room temperature to a temperature not higher than the melting point of alkanediol for 10 seconds to 10 minutes. Specifically, a hot plate held at a predetermined temperature or an oven may be used. Alternatively, it may be dried by leaving it at room temperature. The sol-gel film of the present invention does not cause cracks or the like even when left at room temperature and dried, and a good gel film can be obtained.

The gel film obtained was further heat-treated,
It is crystallized into a metal oxide thin film. The heat treatment condition varies depending on the composition of the oxide to be formed, but it is usually carried out in an oxidizing atmosphere such as oxygen or air at 500 ° C. or higher and 900 ° C. or lower for 5 minutes to 8 hours.

The composition for forming a metal oxide thin film of the present invention comprises
It can be widely used for various applications requiring a thick film of submicron to micron order. In particular, it is preferably used for forming an oxide thin film such as a ferroelectric perovskite oxide thin film such as PZT that requires a film thickness of submicron or more in order to develop the characteristics such as ferroelectricity, high dielectric constant characteristics, and piezoelectricity. be able to.

Specifically, it can be used, for example, as a flattening layer or a dielectric layer itself of the following thin film EL element.

The thin film EL device to which the present invention is applied is, for example, a lower electrode / thick film dielectric layer / metal oxide thin film layer of the present invention / light emitting layer / upper insulating layer (thin film insulating layer) / upper part on a substrate. It has a structure in which electrodes (transparent electrodes) are sequentially laminated, or a structure in which a multi-layered dielectric layer in which the metal oxide thin film of the present invention is laminated plural times is used instead of the thick film dielectric layer.

The substrate of the EL element is not particularly limited as long as it has electrical insulation and can maintain a predetermined heat resistance strength without contaminating the lower electrode layer and the dielectric layer formed thereon. Instead, for example, heat resistant ceramics such as alumina (Al ₂ O ₃ ), forsterite (2MgO · SiO ₂ ), zirconia (ZrO ₂ ), magnesia (MgO), high strain point glass, high heat resistant crystallized glass, quartz glass ( A substrate such as SiO ₂ ) can be used.

In the case of a simple matrix type, the lower electrode layer is formed to have a plurality of stripe patterns. The material for the lower electrode layer is preferably a material that has high conductivity, is not damaged during the formation of the dielectric layer, and has low reactivity with the dielectric layer or the light emitting layer. Specifically, Au, Pt, Noble metals such as Pd, Ir and Ag can be used. As a method for forming the lower electrode layer, a known technique such as a sputtering method, a vapor deposition method, a plating method may be used.

When the thick film dielectric layer is used, the thick film dielectric layer must have a high dielectric constant and a high breakdown voltage.
Further, in consideration of the heat resistance of the substrate, it is required to be a substance that can be fired at a low temperature.

Here, the thick film dielectric layer is a ceramic layer formed by firing a powdery insulating material by a so-called thick film method. This thick-film dielectric layer is formed by, for example, printing an insulating paste made by mixing a powdery insulating material with a binder and a solvent on a substrate on which a lower electrode layer is formed, and firing it. be able to. Alternatively, a green sheet may be formed by casting an insulating paste, and the green sheets may be stacked.

Various materials can be considered as such a high dielectric constant thick film material, but a high dielectric constant ceramic composition that can be formed at a low temperature is required in consideration of the heat resistance of the substrate material. Perovskite structure dielectric material such as (Zr _x Ti _1-x ) O ₃ or Pb (Mg _1/3 Ni _2/3 )
A composite perovskite relaxor type ferroelectric material typified by O ₃ or the like and a tungsten bronze type ferroelectric material typified by PbNbO ₆ or the like are preferably used.

The film thickness of the thick film dielectric is required to be thick in order to eliminate pin steps formed by the steps of electrodes and dust in the manufacturing process, and at least 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more is required.

However, the light emitting layer formed on the thick film dielectric layer is only several hundred nm, which is about 1/100 of the thickness of the thick film dielectric layer. Therefore, the surface of the thick film dielectric layer must be smooth at a level equal to or less than the thickness of the light emitting layer, but the surface roughness of the thick film does not fall below the crystal grain size of the polycrystalline sintered body. The surface becomes uneven with submicron size or more.

To improve the flatness of the surface of such a thick dielectric layer, a surface flattening layer using a solution coating firing method is effective. If the solution coating and baking method is used, a step of coating and baking the precursor solution is performed, so that a thick layer is formed in the concave portion of the base and a thin layer is formed in the convex portion, and as a result, the surface of the base layer is formed on the surface of this film. A film having a flat surface can be obtained without reflecting irregularities or steps. Therefore, by forming the surface flattening layer using the solution coating baking method, it is possible to greatly improve the uniformity of the thin film light emitting layer formed thereon.

The film thickness of the surface flattening layer is sufficient if it can sufficiently fill the irregularities on the surface of the thick dielectric layer, and is usually 0.5.
μm or more, preferably 1 μm or more, more preferably 2 μm
That is all. The composition for forming a metal oxide thin film of the present invention is 1
A film of 0.4 μm to 1 μm or more can be formed by coating and baking once,
Since a target thick surface flattening layer can be formed with a small number of times of coating and baking, it can be preferably used for forming such a surface flattening layer.

The relative permittivity of the surface flattening layer is desirably as high as possible, preferably 50 or more, more preferably 50.
It is 0 or more. Examples of materials having such a high dielectric constant include (ferroelectric) dielectric materials having a perovskite structure such as PbTiO ₃ , PZT, and PLZT, and TiO _{2 and the} like, for forming the metal oxide thin film of the present invention. The composition is preferably applicable.

As another structure, only a multilayer dielectric layer formed by repeating coating and firing with the composition for forming a metal oxide thin film of the present invention a plurality of times without providing a thick dielectric layer may be provided. Good. In this case, the thickness of the multilayer dielectric layer is preferably 2 to 3 μm or more, but if the composition for forming a metal oxide thin film of the present invention is used, one layer is about 0.1 μm as in the conventional solution coating baking method. Compared with the case of laminating the metal oxide thin film of (1), it is possible to form the multilayer dielectric layer with a smaller number of times of coating and firing, and the manufacturing cost can be reduced.

The phosphor material forming the light emitting layer is not particularly limited, and any phosphor material such as ZnS doped with Mn may be used. The thickness of the light emitting layer is not particularly limited, but if it is too thick, the driving voltage increases, and if it is too thin, the luminous efficiency decreases. Specifically, the thickness is preferably about 100 to 2000 nm, though it depends on the light emitting material.

As the method for forming the light emitting layer, a vapor deposition method can be used. As the vapor deposition method, a physical vapor deposition method such as a sputtering method or a vapor deposition method, or a chemical vapor deposition method such as a CVD method is preferable.

Although the thin film insulator layer may be omitted, it is preferable to have it.

This thin film insulator layer has a resistivity of 10
^It is preferably ⁸ Ω · cm or more, particularly about 10 ¹⁰ to 10 ¹⁸ Ω · cm. A substance having a relatively high relative permittivity is preferable, and the relative permittivity ε is preferably ε =
It is 3 or more. As the constituent material of this thin film insulator layer,
For example, silicon oxide (SiO ₂ ), silicon nitride (Si ₃
N ₄ ), tantalum oxide (Ta ₂ O ₅ ), yttrium oxide (Y ₂ O ₃ ), zirconia (ZrO ₂ ), silicon oxynitride (SiON), alumina (Al ₂ O ₃ ), and the like can be used. . As a method for forming the thin film insulator layer, a sputtering method, a vapor deposition method, or a CVD method can be used. The thickness of the thin film insulator layer is preferably 10 to 1000 nm, particularly preferably 20 to 20 nm.
It is about 0 nm.

For the transparent electrode layer, an oxide conductive material such as ITO, SnO ₂ (nesa film), ZnO—Al or the like having a film thickness of 0.2 μm to 1 μm is used. As a method of forming the transparent electrode layer, a known technique such as a vapor deposition method other than the sputtering method may be used.

Although the EL element described above has only a single light emitting layer, the EL element to which the present invention is applied is not limited to such a structure, and a plurality of light emitting layers are laminated in the film thickness direction. Alternatively, the light emitting layers (pixels) of different types may be combined in a matrix and arranged in a plane.

As described above, the EL device to which the present invention is applied has extremely good smoothness of the surface of the dielectric layer on which the light emitting layer is laminated, has a high withstand voltage and is free from defects. Therefore, it is possible to easily construct a high-performance and high-definition display having high brightness and long-term reliability of brightness. In addition, the manufacturing process is easy and the manufacturing cost can be kept low.

Further, according to the composition for forming a metal oxide thin film of the present invention, it is possible to form a thick dielectric film having a maximum of 1 μm or more by one firing even by the solution coating firing method alone, and further repeat a plurality of times. As a result, even a dielectric layer having a thickness of about 10 μm can be formed in a process within a practical range. Therefore, the solution coating baking method is directly applied to the substrate without using the thick film dielectric layer described in the above example. Thus, it is possible to form a thin film EL element by forming a dielectric layer having a thickness of 2 to 3 μm or more.

[0080]

Example 1 A PZT thin film forming solution containing neopentyl glycol, lead acetate, titanium tetraisopropoxide, zirconium tetra n-propoxide, 2-methoxyethanol and acetylacetone was prepared. Lead acetate trihydrate was dissolved in 2-methoxyethanol in a reaction vessel and dehydrated at 110 to 120 ° C. for 15 minutes. Zirconium tetra-n-propoxide and titanium tetraisopropoxide were added thereto, reacted at 110 to 120 ° C. for 30 minutes, and neopentyl glycol and acetylacetone dissolved in 2-methoxyethanol were added to prepare a solution. .

The molar ratio of each component was changed within the following range. Table 1 shows the compositions evaluated. The oxide conversion concentration was adjusted by the amount of 2-methoxyethanol. Neopentyl glycol (NPG): Lead acetate: Titanium tetraisopropoxide: Zirconium tetra n-propoxide: Acetylacetone (acacH) = 0.5-5: 1.1:
0.465: 0.535: 0-2

The solution thus prepared was spin-coated on an alumina substrate (press pin 250 rpm 40 s).
After that, it was applied at 1000 rpm for 30 s), dried on a hot plate set at 100 ° C. for 10 minutes, placed in an electric furnace at 700 ° C. and heat-treated for 10 minutes to form a PZT thin film. The film forming operation consisting of spin coating and baking was basically performed only once, and repeated coating as used in the solution coating and baking method was not performed.

The film properties of this PZT thin film were investigated by the following method, and the results are summarized in Table 1.

[Presence or absence of cracks] Confirmed by an optical microscope and SEM after heat treatment. The case where no crack was found was marked with ◯, and the case where a crack was found was marked with x. [Film thickness (μm)] The average film thickness was obtained by confirming by SEM observation of the film cross section.

[0085]

[Table 1]

No crack was observed in any of the films, and it was possible to form a crack-free PZT film with a maximum of 1 μm in one film forming operation. 1 and 2 in Table 1,
The SEM photograph of the film surface of sample 7 and a cross section is each shown. As is clear from this SEM photograph, it can be seen that the metal oxide thin film of the present invention can obtain a good film that is smooth and uniform on both the surface and the cross section.

A liquid having the composition of Sample 7 in Table 1 was applied on an alumina substrate having a gold electrode and baked to form a film of about 1 μm, and the relative dielectric constant of this PZT film was measured. It was about 600 (at 100 kHz).

[Comparative Examples 1 and 2] A coating liquid was prepared in the same manner as in Example 1 except that neopentyl glycol was not added, and the coating liquid was coated on a substrate, dried and baked to measure the film characteristics.
The composition and the results are shown in Table 1.

Comparative Example 3 A coating solution was prepared by using propylene glycol having 3 carbon atoms in place of neopentyl glycol in Example 1. Using this coating solution, coating on a substrate, drying and baking were carried out in the same manner as in Example 1, and the film characteristics were measured. The composition and the results are shown in Table 1.

[Example 2] 2,2-as alkanediol
A solution was prepared in the same manner as in Example 1 except that diethyl-1,3-propanediol was used. The oxide conversion concentration was adjusted to be 25% by mass. Using this coating solution,
Film characteristics were measured by coating, drying and baking on a substrate in the same manner as in Example 1 except that the hot plate was dried at a temperature of 50 ° C. The composition and the results are shown in Table 2.

[0091]

[Table 2]

[Example 3] 2,5-as alkanediol
A solution was prepared in the same manner as in Example 1 except that dimethyl-2,5-hexanediol was used. The oxide conversion concentration was adjusted to be 25% by mass. Using this coating solution,
The film characteristics were measured by coating, drying and baking on the substrate in the same manner as in Example 1 except that the drying temperature of the hot plate was 70 ° C. The composition and the results are shown in Table 2.

[Example 4] 1,6-as alkanediol
A solution was prepared in the same manner as in Example 1 except that hexanediol was used. The oxide conversion concentration was adjusted to be 25% by mass. Using this coating solution, coating on a substrate, drying and baking were carried out in the same manner as in Example 1 except that the drying by the hot plate was replaced by the drying by leaving at room temperature for 30 minutes, and the film characteristics were measured. The composition and the results are shown in Table 2.

Example 5 A PbTiO ₃ thin film forming solution containing neopentyl glycol, lead acetate, titanium tetraisopropoxide, 2-ethoxyethanol and acetylacetone was prepared. 2-lead acetic acid trihydrate in a reaction vessel
Dissolve in ethoxyethanol and add 1 at 110-120 ℃
It was dehydrated for 5 minutes. Titanium tetraisopropoxide was added thereto and reacted at 110 to 120 ° C for 30 minutes,
A solution was prepared by adding neopentyl glycol and acetylacetone dissolved in ethoxyethanol. The molar ratio of each component used for the preparation is as follows.
Further, it was adjusted with 2-ethoxyethanol so that the oxide conversion concentration was 24% by mass.

NPG: Lead acetate: Titanium tetraisopropoxide: acacH = 2: 1.1: 1: 1

A film was formed using this solution in the same manner as in Example 1 to form a PbTiO ₃ thin film on an alumina substrate.

The surface of the obtained thin film was observed with an optical microscope and SEM.
As a result, it was confirmed that there was no crack or the like and the surface was homogeneous. Further, the film thickness was confirmed by SEM and the average film thickness was determined, and it was 0.65 μm.

Example 6 Neopentyl glycol, titanium tetraisopropoxide, 2-methoxyethanol,
A TiO ₂ thin film forming solution containing diethanolamine was prepared. 2-Methoxyethanol, titanium tetraisopropoxide and diethanolamine were mixed in a reaction vessel, reacted at 110 ° C. for 30 minutes, and neopentyl glycol dissolved in 2-methoxyethanol was added to prepare a solution. The molar ratio of each component used for the preparation is as follows. Further, it was adjusted with 2-methoxyethanol so that the oxide conversion concentration would be 10% by mass.

NPG: Titanium tetraisopropoxide: Diethanolamine = 1: 1: 2

Using this solution, a TiO ₂ thin film was formed on an alumina substrate in the same manner as in Example 1 except that the press-pin time of spin coating was 10 seconds.
Homogeneous TiO _{2 with} an average film thickness of 0.55 μm and no cracks
A thin film was obtained.

[Example 7 (Example of EL device fabrication)] 99.
A commercially available Au paste was printed on a 6% -purity alumina substrate by a screen printing method so that the film thickness after firing was 1 μm on the entire surface of the substrate, and firing was performed at 850 ° C. This lower electrode layer is formed with a width of 300 μm by photoetching.
It was patterned into a large number of stripes each having m and a space of 30 μm.

A dielectric ceramics thick film was further formed on the substrate on which the lower electrode was formed by screen printing. As thick film paste, 4210C manufactured by ESL
Using thick film dielectric paste, screen printing and drying were repeated so that the film thickness after firing was 30 μm.

After printing and drying, the thick film was baked for 20 minutes at 850 ° C. in an atmosphere in which sufficient air was supplied using a belt furnace. The dielectric constant of this thick film alone was about 4000.

Next, a surface flattening layer was formed by using a solution coating baking method. In this solution coating and firing method, the PZT thin film forming solution prepared in the same manner as in Example 1 sample 7 was used as the precursor solution. The precursor solution is applied to the surface of the thick film dielectric layer by spin coating, and the temperature is 700 ° C.
The surface flattening layer having a film thickness of 2 μm was formed by repeating baking for 15 minutes twice.

Next, with the substrate heated to 200 ° C.,
A ZnS vapor deposition source doped with Mn was used to form a light emitting layer of ZnS: Mn having a thickness of 0.7 μm by vapor deposition and then annealed in vacuum at 500 ° C. for 10 minutes.

Next, a thin film EL device sample was obtained by sequentially forming a Si ₃ N ₄ thin film as an upper insulator layer and an ITO thin film as an upper electrode layer by a sputtering method. The upper electrode layer was patterned into a stripe shape in which line-shaped electrodes having a width of 1 mm were arranged by using a metal mask during film formation.

With respect to these samples, the electrodes were drawn out from the lower electrode layer and the upper electrode layer, respectively, and 1 kH
An electric field of z and a pulse width of 50 μs was applied at an intensity at which the emission brightness was saturated.

As a result, a good EL was obtained at an applied voltage of 150V.
Luminescence was observed and the saturation brightness was 6700 cd / m ² .

From the above results, it is understood that the composition for forming a metal oxide thin film of the present invention is extremely effective when applied to an EL device. Further, its application range is not limited to EL, and sub-micron or more is required for exhibiting characteristics such as ferroelectric perovskite oxide thin film such as PZT, ferroelectricity, high dielectric constant characteristics, piezoelectricity and the like. It can be widely applied to elements and devices using an oxide thin film that requires a film thickness.

[0110]

As described above, according to the present invention, it is possible to manufacture a coating thin film having a sufficient thickness by a single film forming operation without passing through a process of low practicality such as a drying process at a high temperature. A composition for forming a metal oxide thin film and a metal oxide thin film can be provided.

[Brief description of drawings]

FIG. 1 is a drawing-substitute SEM photograph showing a film surface of Sample 7.

FIG. 2 is a drawing-substitute SEM photograph showing a cross section of Sample 7.

Continued front page    (72) Inventor Masatoshi Takizawa             1-13-1, Nihonbashi, Chuo-ku, Tokyo             -In DC Inc. F term (reference) 4G042 DA01 DB10 DC01 DD02 DE03                       DE09 DE12 DE14                 4G047 CA02 CB06 CB08 CC02 CD02                 4G048 AA02 AB02 AB05 AC02 AD02                       AE05 AE08

Claims (6)

[Claims] 1. A composition for forming a metal oxide thin film, which contains a metal alkoxide or a metal alkoxide and a metal salt in a solution, and contains an alkanediol having a melting point of 30 ° C. or higher and a carbon number of 5 to 12 in the composition. . 2. The composition for forming a metal oxide thin film according to claim 1, wherein the alkanediol is neopentyl glycol. 3. The metal of the metal alkoxide and metal salt is at least an alkaline earth metal, or Pb, Ti,
The composition for forming a metal oxide thin film according to claim 1 or 2, which is one or more selected from Zr, Hf, Sn, Nb, Ta and La. 4. The composition for forming a metal oxide thin film according to claim 1, wherein the metal alkoxide is one or two of a Ti alkoxide and a Zr alkoxide, and the metal salt is a Pb salt. . 5. A method for producing a metal oxide thin film, which comprises coating the composition for forming a metal oxide thin film according to any one of claims 1 to 4 on a substrate, drying the composition at a temperature equal to or lower than the melting point of the added alkanediol, and then firing the composition. Method. 6. A metal oxide thin film having a film thickness of 0.4 μm or more, which is obtained by the composition for forming a metal oxide thin film according to claim 1.