JP2010272816A - Method of forming organic semiconductor film to polysilsesquioxane thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of uniformly forming an organic semiconductor film to a polysilsesquioxane thin film without incurring a deterioration in the characteristic of an organic semiconductor. <P>SOLUTION: In the method of forming the organic semiconductor film to the polysilsesquioxane thin film, an organic semiconductor solution containing phenyl group-modified colloidal silica is applied onto the polysilsesquioxane thin film, and a coating film is dried. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for forming an organic semiconductor film on a polysilsesquioxane thin film.

  Thin film transistors made of organic materials (organic thin film transistors: organic TFTs) are lightweight, flexible, and impact resistant, so that they have shape-flexible electronic materials such as flexible display and electronic paper display device fields, information tags Applications to portable electronic devices and the like are attracting attention.

  For example, a polysilsesquioxane thin film is known as a gate insulating film of an organic TFT. The polysilsesquioxane thin film is a gate insulating film that can obtain a field effect mobility μ higher than that of a silicon thermal oxide film. Then, an organic semiconductor film such as poly-3-hexylthiophene (P3HT), 6,13-triisopropylsilylethynylpentacene (TIPS-pentacene), fullerene, or the like is formed on the gate insulating film.

  However, it is not easy to form an organic semiconductor film on a polysilsesquioxane thin film. For example, TIPS-pentacene and fullerene have a problem that they cannot be uniformly formed (dewetting occurs) due to low wettability on a polysilsesquioxane thin film. This is because the polysilsesquioxane thin film is extremely water-repellent and TIPS-pentacene has a low molecular weight and high crystallinity structure. In Non-Patent Document 1, it has been reported that TIPS-pentacene is mixed with a polymer and applied to improve the coating property to the silicon thermal oxide film. However, when the polymer content increases, It is not a good idea because it leads to deterioration of semiconductor characteristics.

  In view of the above, development of a technique for uniformly forming an organic semiconductor film on a polysilsesquioxane thin film without causing deterioration of the characteristics of the organic semiconductor is demanded.

Organic thin film transistors using 6,13-bis (triisopropylsilylethynyl) pentacene embedded into polymer binders, Kwon et al., APPLIED PHYSICS LETTERS 94, 013506 (2009)

  An object of the present invention is to provide a method for uniformly forming an organic semiconductor film on a polysilsesquioxane thin film without causing deterioration of characteristics of the organic semiconductor.

  As a result of intensive studies to achieve the above object, the present inventor has achieved the above object when using a specific surface-modified colloidal silica in forming an organic semiconductor film on a polysilsesquioxane thin film. The inventors have found that this can be achieved and have completed the present invention.

That is, the present invention relates to the following method for forming an organic semiconductor film.
1. A method for producing an organic semiconductor film on a polysilsesquioxane thin film, comprising applying an organic semiconductor solution containing phenyl group-modified colloidal silica onto a polysilsesquioxane thin film and drying the coating film.
2. 2. The film forming method according to item 1, wherein the organic semiconductor is at least one selected from the group consisting of 6,13-triisopropylsilylethynylpentacene (TIPS-pentacene) and fullerene.
3. Item 3. The film forming method according to Item 1 or 2, wherein the organic semiconductor solution is a toluene solution.
4). The organic thin-film transistor which comprises the organic-semiconductor film formed into a film by the film-forming method in any one of said claim | item 1-3.

  Hereinafter, the organic semiconductor film forming method of the present invention will be described in detail.

  The method for forming an organic semiconductor film of the present invention is a method for forming an organic semiconductor film on a polysilsesquioxane thin film, wherein an organic semiconductor solution containing phenyl group-modified colloidal silica is applied to the polysilsesquioxane thin film. It is characterized in that it is applied to and dried.

  The method for producing an organic semiconductor film of the present invention having the above-described characteristics is that an organic semiconductor solution that is a coating liquid contains a phenyl group-modified colloidal silica. Even if it is a semiconductor, a uniform coating film can be formed on the polysilsesquioxane thin film without deteriorating the characteristics of the organic semiconductor. And a uniform organic-semiconductor film | membrane can be formed into a film by drying this coating film. The film forming method of the present invention is highly useful in that an organic semiconductor film such as TIPS-pentacene or fullerene, which has been difficult to form, can be formed uniformly.

  As the polysilsesquioxane thin film used in the method for producing an organic semiconductor film of the present invention, those known as gate insulating films in the field of organic TFTs can be used as they are. For example, polymethylsilsesquioxane (PMSQ) can be suitably used as the polysilsesquioxane thin film. In addition, polymethylphenylsilsesquioxane (PMPSQ) whose surface is modified with PhTMS can also be used.

  The organic semiconductor is not limited, and a polysilsesquioxane thin film that has been considered difficult to form can be applied. In particular, TIPS-pentacene (6,13-triisopropylsilylethynylpentacene), fullerene, and the like are used in the present invention. It can be suitably applied to. These organic semiconductors, as they are, have low wettability with the polysilsesquioxane thin film, so-called dewetting (surface repelling) occurs, and uniform film formation is difficult, but according to the film formation method of the present invention, A uniform film can be formed on a highly water-repellent polysilsesquioxane thin film.

  In the film forming method of the present invention, an advantageous effect can be obtained by including phenyl group-modified colloidal silica in the organic semiconductor solution which is a coating liquid. The phenyl group-modified colloidal silica can be prepared, for example, by surface-modifying a known silica sol obtained using alkoxysilane as a raw material with a phenyl group-containing silane coupling agent (JP-A-2005-314197, etc.) reference).

  Examples of the phenyl group-containing silane coupling agent include phenyltrimethoxysilane and diethoxymethylphenylsilane. Further, as the dispersion medium for colloidal silica, a hydrophobic organic solvent is preferable, and saturated or unsaturated aliphatic hydrocarbons, alicyclic hydrocarbons, aromatic hydrocarbons and their halides, ethers, esters. Aldehydes, ketones and the like. Specifically, saturated aliphatic hydrocarbons such as hexane, heptane, octane, nonane, decane, undecane, dodecane; unsaturated aliphatic hydrocarbons such as hexene, heptene, octene; cyclohexane, methylcyclohexane, decalin, etc. Alicyclic hydrocarbons; aromatic hydrocarbons such as benzene, toluene, xylene, mesitylene, dodecylbenzene, methylnaphthalene; halides such as methylene chloride, chloroform, ethylene chloride, chlorobenzene; dibutyl ether, dipentyl ether, dihexyl ether , Ethers such as diheptyl ether and dioctyl ether; esters such as ethyl acetate, butyl acetate, butyl acrylate, methyl methacrylate, hexamethylene diacrylate and trimethylolpropane triacrylate ; Ketones such as methyl ethyl ketone and methyl isobutyl ketone, cyclohexanone; naphtha, and the like can be exemplified petroleum distillates classification such as kerosene. Of these hydrophobic organic solvents, n-heptane, toluene, xylene, and mesitylene are preferably used, and toluene is particularly preferable.

  The silica concentration of the phenyl group-modified colloidal silica is preferably 20% by weight or more, and more preferably 40 to 50% by weight.

  In the present invention, the phenyl group-modified colloidal silica is not particularly limited as long as the surface of the dispersoidal silica is surface-modified (surface-modified) with a phenyl group. For example, “Part No. PL-1-TOL, silica concentration Commercial products such as “40% by weight, toluene dispersion, manufactured by Fuso Chemical Industry Co., Ltd.” can be used. As an average particle diameter of silica, about 10-50 nm is preferable and about 10-15 nm is more preferable.

  In the film forming method of the present invention, when preparing the coating liquid, for example, the organic semiconductor solution and the phenyl group-modified colloidal silica (for example, toluene dispersion) can be mixed. Examples of the organic semiconductor solution include a toluene solution of an organic semiconductor.

  The content of the organic semiconductor and the phenyl group-containing colloidal silica in the coating liquid is not limited, but the organic semiconductor: phenyl group-containing colloidal silica (solid content weight ratio) is preferably about 1: 3, more preferably about 1: 2. A ratio of about 1: 1 is most preferable. That is, it is preferable to set appropriately from the range of 1: 3-1.

  The coating method of the coating liquid is not limited, and a coating method by an inkjet method including a coating method known in the field of organic TFTs such as a spin coating method, a casting method, and a bar coating method can also be used. What is necessary is just to dry the coating film after coating by either natural drying or heat drying. In the case of heat drying, the temperature is preferably about 50 to 150 ° C, more preferably about 100 to 120 ° C. Although drying time can be suitably adjusted according to temperature, about 0.2 to 3 hours are preferable and about 0.5 to 1 hour are more preferable. Thereby, an organic semiconductor film is uniformly formed on the polysilsesquioxane thin film.

  The present invention also includes an organic TFT having an organic semiconductor film obtained by the film forming method. That is, it includes an organic TFT having a structure in which a polysilsesquioxane thin film is used as a gate insulating film and an organic semiconductor film is formed thereon by the film forming method. In this invention, the structure of a well-known organic TFT can be used except the kind of gate insulating film and the film forming method of an organic semiconductor film being as above-mentioned.

  The organic semiconductor film-forming method of the present invention is an organic semiconductor that has low wettability and is difficult to apply uniformly, particularly by including phenyl group-modified colloidal silica in the organic semiconductor solution that is the coating liquid. However, a uniform coating film can be formed on the polysilsesquioxane thin film without deteriorating the characteristics of the organic semiconductor. And a uniform organic-semiconductor film | membrane can be formed into a film by drying this coating film. The film forming method of the present invention is highly useful in that an organic semiconductor film such as TIPS-pentacene or fullerene, which has been difficult to form, can be formed uniformly.

(A) is an optical microscope observation image of the TIPS-pentacene film obtained in Comparative Example 1, and (b) is an optical microscope observation image of the TIPS-pentacene film obtained in Example 1. 3 is an optical microscope observation image of a TIPS-pentacene film obtained in Example 2. 2 is a schematic view of an organic TFT produced in Test Example 1. FIG. It is a figure which shows the transistor characteristic ((A) is an output characteristic, (B) is a transmission characteristic) of the organic TFT (Test Example 1) which comprises the TIPS-pentacene film obtained in Example 1.

The present invention will be specifically described below with reference to examples and comparative examples. However, the present invention is not limited to the examples.
(Synthesis of PMSQ)
To a 100 ml two-necked flask equipped with a magnetic stir bar, methyltrimethoxysilane (10 g, 0.073 mol) as a main raw material and 10 g of propylene glycol monomethyl ether acetate (PGMEA) as a solvent were added. Water (3.96 g, 0.22 mol) and formic acid (1.01 g, 0.022 mol) were slowly added to this solution, and then the mixture was stirred at room temperature for 30 minutes for hydrolysis. Thereafter, the condensation reaction was carried out by stirring at 70 ° C. for 1 hour, and methanol produced as a by-product was distilled off while stirring at 70 ° C. and 200 Torr for 2 hours. The reaction solution was returned to room temperature and diluted with PGMEA to prepare 30% by weight. The reaction formula is as follows.

Thereby, PMSQ was synthesized.
(Preparation of PMSQ thin film)
Using a 30 wt% PMSQ solution, spin coating was performed on a glass substrate under the conditions of 500 rpm for 10 sec and 3000 rpm for 20 sec. This thin film was heated at 100 ° C. for 1 hour and 150 ° C. for 1 hour to obtain a cured PMSQ thin film.

Example 1
A toluene solution of TIPS-pentacene (concentration 1 wt%) and a toluene dispersion of phenyl group-modified colloidal silica (product number “PL-1-TOL”, silica concentration 40 wt%, manufactured by Fuso Chemical Industry Co., Ltd.) -Using a coating solution in which the weight ratio of pentacene and phenyl group-modified colloidal silica was 1: 1, spin coating was performed on a PMSQ thin film under conditions of 500 rpm for 10 sec and 1000 rpm for 10 sec. Next, the coating film was dried to form a TIPS-pentacene film.

  An optical micrograph of the TIPS-pentacene film is shown in FIG. Since a film with high crystallinity was confirmed by an optical micrograph, identification of the crystal by X-ray diffraction confirmed peaks of about 1000 and 750 at 6 ° and 17 ° in the X-ray diffraction spectrum, and TIPS- It was found that pentacene crystals were formed.

Comparative Example 1
A TIPS-pentacene film was formed on the PMSQ thin film in the same manner as in Example 1 except that only the TIPS-pentacene toluene solution (concentration 1 wt%) was used as the coating liquid.

  An optical micrograph of the TIPS-pentacene film is shown in FIG. As apparent from FIG. 1A, almost no TIPS-pentacene film was formed, and in some cases, ring-shaped coating spots called coffee stains were also observed.

Example 2
A TIPS-pentacene film was formed on the PMSQ thin film in the same manner as in Example 1 except that the spin coating method was changed to the casting method (the solution was dropped on the substrate and dried at room temperature for about 3 to 6 hours).

  An optical micrograph of the TIPS-pentacene film is shown in FIG. As is apparent from FIG. 2, a needle-like and uniform film with high crystallinity was confirmed.

Example 3
A fullerene solution in toluene (concentration 1% by weight) and a phenyl group-modified colloidal silica toluene dispersion (product number "PL-1-TOL", silica concentration 40% by weight, manufactured by Fuso Chemical Industry Co., Ltd.), fullerene and phenyl Using a coating solution mixed so that the weight ratio of the group-modified colloidal silica was 1: 1, spin coating was performed on the PMSQ thin film at 500 rpm for 10 sec and 1000 rpm for 10 sec. Next, the coating film was dried to form a uniform fullerene film.

Test Example 1 (Production and evaluation of organic TFT)
Cut the ITO glass substrate to 17mm square, ultrasonically wash with acetone and IPA for 5 minutes, apply conductive paste, dry the paste well, drop the PMSQ solution above, drop at 10rpm at 500rpm, 20sec at 3000rpm It spin-coated on the conditions of this. This thin film was heated at 100 ° C. for 1 hour and 150 ° C. for 1 hour to obtain a cured PMSQ thin film.

After forming a TIPS-pentacene film on the PMSQ thin film under the conditions of Example 1, Au serving as a source electrode and a drain electrode is vacuum-deposited on the surface of the TIPS-pentacene film using a mask (conditions 5 × 10 ⁻⁵ Torr or less) did.

  Thereby, an organic TFT (conceptual diagram shown in FIG. 3) was obtained.

  The characteristics of the organic TFT were analyzed using an analyzer (Keithley 2400 source meter). Specifically, evaluation was performed by calculating mobility, threshold voltage, and On / Off ratio from two graphs obtained by measuring transfer characteristics and output characteristics of TFTs.

  FIGS. 4A and 4B show graphs of the transfer characteristics and output characteristics of the manufactured organic TFT.

From the transfer characteristic of FIG. 4A, when V _D (V) is changed, I _D (A) changes and reaches the saturation region. From the output characteristic of FIG. 4B, V _G = −80 V when, on / Off ratio it was found that organic TFT are normally driven from the fact that a 1.3 × 10 ^3.

  The mobility, threshold voltage, and On / Off ratio of Test Example 1 are shown in Table 1 below (results of changing conditions are also shown for reference).

Claims (4)

  A method for producing an organic semiconductor film on a polysilsesquioxane thin film, comprising applying an organic semiconductor solution containing phenyl group-modified colloidal silica onto a polysilsesquioxane thin film and drying the coating film.   2. The film forming method according to claim 1, wherein the organic semiconductor is at least one selected from the group consisting of 6,13-triisopropylsilylethynylpentacene (TIPS-pentacene) and fullerene.   The film forming method according to claim 1, wherein the organic semiconductor solution is a toluene solution.   The organic thin-film transistor which comprises the organic-semiconductor film formed into a film by the film-forming method in any one of Claims 1-3.

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