JP2003168800A - Thin film transistor substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that the temperature is high in an ordinary film forming process, and the thermal resistance is insufficient in a transparent plastic film which is used in the conventional technique, so that these plastic films can not be used when it is required to form a thin film transistor on a plastic film substrate, for another case, a low temperature film forming process has been proposed, but it requires a special technique and the cost is high. <P>SOLUTION: An ordinary film forming process is performed on a substrate formed of a polyimide film which is excellent in transparency and thermal resistance, thereby obtaining the thin film transistor substrate on which a thin film transistor is formed. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor substrate in which a thin film transistor is formed on a substrate made of a polyimide film having excellent transparency and heat resistance, and is used in a display device such as a liquid crystal display device and an organic EL display device. Used.

[0002]

2. Description of the Related Art In a display device, an active matrix display device using a thin film transistor substrate in which a thin film transistor is formed as a pixel switch element on a glass substrate can meet the demands for large size, high definition and high brightness of the device. Therefore, it has been adopted in recent years. If a plastic film substrate can be used instead of a glass substrate, it is possible to obtain a display device that is thin, light, and difficult to break.
Already, for a passive matrix display device that does not use a thin film transistor, Japanese Patent Application Laid-Open No. 9-169074 and Japanese Patent Application Laid-Open No.
As disclosed in 001-52530, a transparent plastic film such as polyethylene terephthalate, polycarbonate, or polyether sulfone is used as a substrate.

However, in the process of manufacturing an ordinary thin film transistor, the deposition temperature of the polycrystalline silicon film reaches 400 ° C. or higher even in the low temperature process, and the deposition temperature reaches 250 ° C. or higher even in the case of the amorphous silicon film. The above-mentioned conventionally used transparent plastic film has insufficient heat resistance, and it is extremely difficult to form a thin film transistor on the film substrate to obtain a thin film transistor substrate.

Further, Japanese Patent Application Laid-Open No. 9-116158 discloses a method of providing a heat dissipation means so that the temperature at the time of film formation of silicon does not rise, and Japanese Patent Application Laid-Open No. 10-270711 discloses a special method for film formation operation. A method of lowering the film forming temperature by adopting the method is disclosed. According to these methods,
Although it is possible to form a thin film transistor on an existing plastic film substrate, there is a drawback that the cost is high due to the use of a special technique.

On the other hand, a polyimide resin is known as a resin having excellent heat resistance and dimensional stability. The wholly aromatic polyimide resin obtained by the polycondensation reaction of aromatic tetracarboxylic dianhydride and aromatic diamines can be used at a high temperature of 400 ° C or higher, has a small coefficient of thermal expansion, and has excellent dimensional stability. As a raw material for films, electric wire coatings, adhesives, paints, etc. that have excellent characteristics and are used at high temperatures,
It is used in various fields, mainly in the electronics industry. However, since such a wholly aromatic polyimide resin is colored from pale yellow to reddish brown, it is not suitable for a film substrate of a thin film transistor substrate used in an active matrix display device.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to obtain an active matrix display device which is thin, light and hard to break at a low cost. It is to provide a thin film transistor substrate in which a thin film transistor is formed using a film forming process.

[0007]

[Means for Solving the Problems] The inventors of the present invention have made extensive studies to solve the above problems and arrived at the present invention. That is, the present invention relates to a thin film transistor substrate in which a thin film transistor is formed on a substrate made of a polyimide film having a repeating unit represented by the following general formula I.

[Chemical 2] (In the formula, R is a tetravalent aliphatic group having 4 to 39 carbon atoms,
Φ is a divalent aliphatic group having 1 to 39 carbon atoms or an aromatic group)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The aliphatic polyimide of the general formula I used in the present invention comprises a tetravalent aliphatic tetracarboxylic acid and
It is a polyimide having a valent diamine as a constituent component, and is obtained by reacting an aliphatic tetracarboxylic acid or its derivative with a diamine or its derivative. Examples of the aliphatic tetracarboxylic acid or a derivative thereof include an aliphatic tetracarboxylic acid, an aliphatic tetracarboxylic acid ester, and an aliphatic tetracarboxylic acid dianhydride, but an aliphatic tetracarboxylic acid dianhydride is preferable. Is. Examples of the diamine and its derivative include diamine, diisocyanate, and diaminodisilanes, and diamine is preferable.

The aliphatic tetracarboxylic acid dianhydride used in the synthesis of the aliphatic polyimide of the present invention is 1,
2,3,4-cyclobutanetetracarboxylic dianhydride,
1,2,4,5-cyclopentanetetracarboxylic dianhydride, 1,2,4,5-cyclohexanetetracarboxylic dianhydride, bicyclo [2,2,2] oct-7-ene-
Examples thereof include 2,3,5,6-tetracarboxylic dianhydride, and particularly preferred is 1,2,4,5-cyclohexanetetracarboxylic dianhydride. In general, a polyimide having an aliphatic diamine as a constituent component is difficult to polymerize because a polyamic acid and a diamine, which are intermediate products, form a strong complex, and thus a solvent having a relatively high solubility of the complex-for example, cresol- It is necessary to devise such as using. However, in a polyimide containing 1,2,4,5-cyclohexanetetracarboxylic dianhydride and an aliphatic diamine as components, the polyamic acid-diamine complex is bonded by a relatively weak bond, and Easy molecular weight conversion,
A flexible film is easily obtained.

The diamine used in the synthesis of the aliphatic polyimide of the present invention may be an aliphatic diamine, an aromatic diamine or a mixture thereof, but an aliphatic diamine is particularly preferable. When an aromatic diamine is used in combination with the aliphatic diamine, the total light transmittance decreases as the weight ratio of the aromatic diamine to the aliphatic diamine increases, so the mixing weight ratio is preferably 3: 1 or less.

Examples of the aliphatic diamine used in the synthesis of the aliphatic polyimide of the present invention include ethylenediamine, hexamethylenediamine, polyethylene glycol bis (3-aminopropyl) ether, polypropylene glycol bis (3-aminopropyl) ether, 1,
Examples thereof include 3-bis (aminomethyl) cyclohexane, 1,4-bis (aminomethyl) cyclohexane, metaxylylenediamine, paraxylylenediamine, isophoronediamine, norbornanediamine and siloxanediamines.

Further, examples of the aromatic diamine used for synthesizing the aliphatic polyimide of the present invention include, for example, 4,
4'-diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl sulfone, 2,2-bis (4-aminophenyl) propane, metaphenylenediamine, paraphenylenediamine, diaminobenzophenone, 2,6 -Diaminonaphthalene, 1,5-diaminonaphthalene and the like.

In producing the polyimide resin used in the present invention, for example, N-methyl-2-pyrrolidone, N, N-dimethylacetamide, N, N-dimethylformamide, dimethyl sulfoxide, hexamethylphosphoramide, tetramethyl Solvents such as methylene sulfone, P-chlorophenol, m-cresol, 2-chloro-4-hydroxytoluene are used.

The polyimide film used in the present invention is prepared by adding an acid dianhydride to a solution of diamine, or adding a diamine to a solution of acid dianhydride, preferably at a temperature of 80 ° C. or lower, particularly around room temperature or lower. The polyamic acid solution is obtained by keeping the temperature at 80 ° C., the solution is applied on a substrate such as a glass plate or a metal plate, and heated at 200 ° C. to 350 ° C. to carry out a dehydration reaction. In addition, after directly preparing a polyimide solution by the following method, the solution is applied on a substrate such as a glass plate or a metal plate, and the temperature is 200 ° C to
It is manufactured by heating at 350 ° C. to evaporate the solvent.

An azeotropic dehydration solvent such as toluene or xylene is added to the polyamic acid solution of the reaction intermediate, and the dehydration reaction is performed while removing the produced water from the system by azeotropic distillation to obtain a polyimide solution. After imidizing the polyamic acid solution of the reaction intermediate with a dehydrating agent such as acetic anhydride, a solvent with poor polyimide solubility such as methanol is added to precipitate the polyimide, which is then solidified by filtration, washing and drying. Separated as
A polyimide solution dissolved in a solvent such as N, N-dimethylacetamide is obtained. In the case of imidica, a tertiary amine such as triethylamine, pyridine or β-picoline can be used together as a catalyst. A polyamic acid solution is prepared using a high-boiling solvent such as cresol, kept at 150 ° C. or higher to be polyimidized, and then a solvent having poor polyimide solubility such as methanol is added to precipitate the polyimide, followed by filtration. Separation as a solid by washing and drying to obtain a polyimide solution dissolved in a solvent such as N, N-dimethylacetamide.

The thin film transistor in the present invention can be manufactured by a known method. In an amorphous silicon thin film transistor, as an example, first, a gate electrode is provided by, for example, forming a chromium film on a polyimide substrate by a sputtering method and then etching the chromium film. Next, plasma CVD
A silicon nitride film is formed by a method to form a gate insulating film. Further, after forming an amorphous silicon film by a plasma CVD method or the like, a predetermined shape is obtained by dry etching. Next, a source electrode and a drain electrode are provided by forming a chromium film by sputtering and then etching. After that, unnecessary portions of the amorphous silicon film are removed by dry etching. Finally, a silicon nitride film is formed by a plasma CVD method and used as a protective film, whereby an amorphous silicon thin film transistor is manufactured.

A polycrystalline silicon thin film transistor is also manufactured through the same steps, but after the amorphous silicon film is obtained, a step of crystallizing silicon by laser annealing is added as an example.

Through the above steps, a thin film transistor substrate in which a thin film transistor is formed on a transparent plastic film substrate can be obtained.

[0019]

EXAMPLES The present invention will be specifically described below with reference to examples. However, the present invention is not limited to these examples. Reference Example 1,2,4,5-Synthesis of cyclohexanetetracarboxylic dianhydride A catalyst in which 552 g of pyromellitic acid and Rh on activated carbon were carried in a Hastelloy (HC22) autoclave having an internal volume of 5 liters (NE Chemcat ( 200)
g and 1656 g of water were charged, and the inside of the reactor was replaced with nitrogen gas while stirring. Next, the inside of the reactor was replaced with hydrogen gas, the hydrogen pressure in the reactor was set to 5.0 MPa, and the temperature was raised to 60 ° C. The reaction was carried out for 2 hours while maintaining the hydrogen pressure at 5.0 MPa. The hydrogen gas in the reactor was replaced with nitrogen gas, the reaction solution was extracted from the autoclave, and the reaction solution was filtered while hot to separate the catalyst. The filtrate was concentrated by removing water under reduced pressure with a rotary evaporator to precipitate crystals. The precipitated crystals are solid-liquid separated at room temperature and dried to
2,4,5-Cyclohexanetetracarboxylic acid 481g
(Yield 85.0%) was obtained.

Subsequently, 450 g of the 1,2,4,5-cyclohexanetetracarboxylic acid thus obtained and 4000 g of acetic anhydride.
Were charged in a 5-liter glass separable flask (with a Dimroth cooling tube), and the inside of the reactor was replaced with nitrogen gas while stirring. The temperature was raised to the reflux temperature of the solvent under a nitrogen gas atmosphere, and the solvent was refluxed for 10 minutes. The mixture was cooled to room temperature with stirring to precipitate crystals. The precipitated crystals were solid-liquid separated and dried to obtain primary crystals. Furthermore, the separated mother liquor was concentrated under reduced pressure with a rotary evaporator to precipitate crystals. The crystals were solid-liquid separated and dried to obtain secondary crystals. 1,2,4,5-including primary and secondary crystals
375 g of cyclohexanetetracarboxylic dianhydride were obtained (anhydrous yield 96.6%).

EXAMPLE A 500 mL five-necked flask equipped with a thermometer, a stirrer, a nitrogen introducing ring, a dropping funnel with a side tube, and a condenser tube with a partial condenser,
11.2 g (0.05 mol) of 1,2,4,5-cyclohexanetetracarboxylic dianhydride synthesized in Reference Example and 37.7 g of N-methyl-2-pyrrolidone as a solvent were charged and dissolved in an ice water bath. Was used to cool to 5 ° C. While maintaining the same temperature, a solution prepared by dissolving 10.0 g (0.05 mol) of 4,4′-diaminodiphenyl ether in 40.0 g of N-methyl-2-pyrrolidone was added dropwise from a dropping funnel over 30 minutes, After completion of dropping, the ice water bath was removed and the mixture was stirred at room temperature for 2 hours. Next, xylene 3 is used as an azeotropic dehydration solvent.
0.0 g was added and the temperature was raised to 170 ° C, and while distilling off the distillate, the temperature was raised to 200 ° C over 4 hours to complete the reaction, and the reaction was performed by air cooling until the internal temperature reached 60 ° C. The liquid was taken out. The weight of this solution was 87.9 g, and the total weight of the distillate was 37.7 g. The obtained solution was applied to a glass plate and dried on a hot plate at 50 ° C for 1 hour, and then peeled from the glass plate to obtain a self-supporting film, which was fixed on a stainless steel fixing jig and then at 200 ° C in a hot air dryer. After drying for 1 hour, a flexible film having a thickness of 100 μm was obtained. The IR spectrum of this film is shown in FIG. ν (C = O) 1
Generation of imide was confirmed from 772, 1700 (cm ⁻¹ ). Further, 0.5 g of this film was dissolved in 10 ml of concentrated sulfuric acid and the intrinsic viscosity η measured at a temperature condition of 30 ° C. was
0.58, glass transition temperature measured by DSC is 315 ° C
Met. Moreover, although this film was colored in light brown, the total light transmittance was measured with a haze meter (Z-Σ80 manufactured by Nippon Denshoku Co., Ltd.) according to JIS K7105, and it was a high value of 85%. showed that.

A chromium film having a thickness of 300 nm was formed on the obtained polyimide film by a sputtering method. After photoprocessing, etching was performed to form a gate electrode having a predetermined shape. Next, a 300-nm-thick silicon nitride film was formed by a plasma CVD method to form a gate insulating film. After that, a high resistance amorphous silicon film having a thickness of 120 nm was formed by a plasma CVD method, and a low resistance amorphous silicon film having a thickness of 30 nm was formed thereon. After photoprocessing, dry etching was performed to obtain a silicon film having a predetermined shape. Then, a chromium film having a thickness of 40 nm was formed by a sputtering method and then etched to form a source electrode and a drain electrode. After that, the low resistance amorphous silicon film between the source electrode and the drain electrode was removed by dry etching. Next, a 500-nm-thick silicon nitride film was formed by a plasma CVD method, and dry etching was performed after photoprocessing, whereby a protective film and an insulating film having a predetermined shape were formed. Through the above steps, it was possible to obtain a visible light transmissive thin film transistor substrate in which an amorphous silicon thin film transistor was formed on a polyimide film substrate.

[0023]

According to the present invention, a thin film transistor substrate in which a thin film transistor is formed on a transparent plastic film substrate by using a normal film forming process can be obtained, which can be used for an active matrix display device which is thin, light and hard to break. You can

[Brief description of drawings]

FIG. 1 is an infrared absorption spectrum of the polyimide film obtained in Example.

FIG. 2 is a diagram showing a thin film transistor substrate of an example.

[Explanation of symbols]

1: Polyimide film 2: Gate electrode 3: Gate insulation film 4: High resistance amorphous silicon film 5: Low resistance amorphous silicon film 6: Source electrode 7: Drain electrode 8: Protective film

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Koji Kado             2-5-3 Marunouchi, Chiyoda-ku, Tokyo             Ryo Gas Chemical Co., Ltd. F term (reference) 2H090 JB03 JB05 JD01 LA01 LA04                 2H092 JA24 KA05 NA25 PA01                 4J043 PA02 QB14 QB26 QB31 RA34                       SA06 TA14 TA22 UA042                       UA111 ZB50                 5C094 AA43 AA44 BA27 BA43 EB10                 5F110 AA30 BB01 CC07 DD01 EE04                       EE44 FF03 FF30 GG02 GG13                       GG15 GG24 GG45 HK04 HK09                       HK16 HK21 HK33 HK35 NN04                       NN24 NN35 PP03

Claims (4)

[Claims] 1. A thin film transistor substrate in which a thin film transistor is formed on a substrate made of a polyimide film having a repeating unit represented by the following general formula I. [Chemical 1] (In the formula, R is a tetravalent aliphatic group having 4 to 39 carbon atoms,
Φ is a divalent aliphatic group having 1 to 39 carbon atoms or an aromatic group) 2. The thin film transistor substrate according to claim 1, wherein R in the general formula I is a cyclohexane ring. 3. The thin film transistor substrate according to claim 1, wherein Φ in the general formula I is a divalent aliphatic group having 1 to 39 carbon atoms. 4. An organic EL device comprising at least a light emitting layer and a cathode for injecting electrons, which are laminated on the thin film transistor substrate according to claim 1.