KR100922444B1 - Composition for the improvement of coating property of organic passivation layer and organic thin film transistor using it - Google Patents

Abstract

The present invention relates to a method for forming an organic protective thin film for device stability of an organic thin film transistor (OTFT) that can be applied to the next-generation flexible display. That is, as a new method for improving the thin film characteristics of the organic material used in the protective film forming technology through the solution process, there is an effect of improving the sealing properties and the uniformity of the thin film for the process after the protective film. The organic material used as the organic protective film is dissolved in a solvent which does not damage the lower layer of the organic protective film to form a protective film. In this case, coating properties and thin film uniformity can be improved by introducing an appropriate surfactant for improving the coating property into the organic protective film solution. . These technologies are new technologies that have not been reported previously.

The present invention is a technology that must be applied in the process for the application of the array device of the organic thin film transistor (OTFT) and improves the uniformity of the protective film thin film by improving the organic protective film coating property, It is a technology that can reduce process defects.

Organic protective film, layered silicon compound, polyvinyl alcohol, organic thin film transistor

Description

Composition for the improvement of coating property of organic passivation layer and organic thin film transistor using it}

1 shows a change in the contact angle of the organic protective film according to the content of the surfactant.

FIG. 2 is a cross-sectional view illustrating a structure of a top-contact organic thin film transistor to which an organic protective film having improved coating property of the present invention is applied.

3 is an atomic force microscopy (AFM) surface photograph of the surface of the PVA organic protective film thin film containing a surfactant and the surface of the PVA organic protective film thin film not containing a surfactant in the present invention.

4 is a graph showing the mobility performance change of the organic thin film transistor to which the PVA organic protective film including the surfactant of the present invention and the PVA organic protective film without the surfactant are applied.

Explanation of symbols on the main parts of the drawing

1-substrate 2-gate electrode

3-insulating film 4-organic active layer

5-source and drain electrodes 6-protective layer

The present invention relates to a composition for forming an organic protective thin film (hereinafter referred to as a 'protective layer') for device stability of an organic thin film transistor (OTFT) that can be applied as a driving device in a next-generation flexible display and the like, and a method of manufacturing the same.

In the past, a method of forming a multilayer of organic and inorganic layers using vacuum equipment has been mainly used (J. Vac. Sci. Technol. B, Vol. 20. No. 3. 958, 2002. IBM Research Institute and Recently, the protective film itself uses organic materials that can be solution-processed to realize the organic devices. (UV curable Resin, Appl. Phys. Lett 83, 1644, 2003, Polyvinyl Alcohol, Appl. Phys. Lett 88, 073519, 2006, PMMA, self encapsulation, Adv. Mater. 18, 2900, 2006). However, since the device itself for introducing the organic protective film is an organic material, it is impossible to form an organic protective film using an organic solvent. Therefore, organic materials of water-soluble components that do not deteriorate the characteristics of the organic material of the device and damage the thin film are often used as the organic protective thin film. Typical examples include water-soluble polyvinyl alcohol (PVA) and acrylate resins. These organic protective film materials have a protective film forming process in a polar aqueous solution in order to prevent damage to the lower layer, even though the organic material of the lower layer has a non-polar surface property. Accordingly, there has been a problem that a result of deterioration of thin film uniformity due to coating nonuniformity and a deterioration of device protection characteristics due to a decrease in uniformity is caused, and furthermore, a defect of a subsequent process performed after the protective film process.

Therefore, in the present invention, the surfactant is introduced into the organic protective film solution of the aqueous solution component and the coating property is decreased in forming the organic protective film on the organic active layer (or organic semiconductor layer, hereinafter referred to as "organic active layer") due to the difference in the interface polarity. And to solve the film non-uniformity.

That is, it is intended to improve the coating property and thin film uniformity by introducing a surfactant containing hydrophilic and hydrophobic properties into the organic protective film solution.

The present invention relates to a protective film composition incorporating a surfactant in a water-soluble polymer that is frequently used as an organic protective film of an organic transistor, and an organic transistor device including the same, and is applicable to a driving device and various organic electronic devices in the next-generation flexible display, etc. An organic protective thin film formation process for device stability of a thin film transistor (OTFT).

In general, in the case of an organic thin film transistor using an organic semiconductor, a protective film for preventing device characteristics is essential. Such organic protective film materials have a polar polarity selected from water or alcohols to prevent damage to the organic layer of the lower layer even though the organic material of the lower layer is non-polar. Was formed and the thin film process was performed. Accordingly, there has been a problem that a result of deterioration of thin film uniformity due to coating nonuniformity and a deterioration of device protection characteristics due to a decrease in uniformity is caused, and furthermore, a defect of a subsequent process performed after the protective film process.

In the present invention, in order to solve the above problems, in order to improve the coating property of the organic protective film, a surfactant was added to prepare an organic protective film composition, and the organic thin film transistor was coated using the solution to form an organic protective film layer. The organic protective film is a water-soluble polymer other than polyvinyl alcohol (PVA), and any material that does not damage the organic semiconductor can be applied. In the case of the surfactant, the material has a hydrophilicity and hydrophobicity. It is possible.

More specifically, the present invention relates to a composition for organic thin film transistor protective film and an organic transistor using the same as a protective layer, characterized in that in the composition for an organic thin film transistor protective film, a water-soluble polymer and a surfactant are mixed.

Referring to the method of manufacturing the organic thin film transistor of the present invention, the organic protective film manufacturing process and the application to the organic thin film transistor according to the present invention is largely subjected to the following three steps.

(a) Dissolving a water-soluble polymer to prepare a protective film solution in aqueous solution

(b) introducing surfactants to the coating solution to improve coating properties

(c) Application of an organic protective film to an organic thin film transistor (OTFT)

The step (a) is to prepare an organic protective film solution to prepare a polyvinyl alcohol aqueous solution by dissolving a polyvinyl alcohol (PVA), which is a water-soluble polymer in powder form commonly used as an organic thin film transistor organic protective film. The organic protective film that can be used in the manufacturing process of the improved organic protective film of the present invention is indispensable to use an aqueous solution in order to avoid damage to the organic semiconductor layer of the organic thin film transistor can be used a water-soluble polymer. In addition, a method of forming an organic protective film using a water-soluble monomer and forming a protective film through a curing process through heat or exposure is possible. In general, water-soluble polymers such as water-soluble polyvinyl alcohol (PVA), polyvinyl alcohol copolymerized polymers, and water-soluble acrylate resins may be used as the organic protective film. In general, the organic semiconductor layer of the organic thin film transistor to be introduced into the protective film has a hydrophobic surface property, which has a problem that the formation of a thin film because the surface polarity shows a lot of difference.

In the step (b), in order to improve the coating property of the organic protective film layer on the aqueous solution, a surfactant containing hydrophilic and hydrophobic groups is added to the organic protective film solution. For example, Novec 4200 from 3M mixed at 25% by weight of ammonium fluoroalkylsulfonimide and 75% by weight of water. Surfactant which can be used is not limited to this, Any surfactant which can be disperse | distributed in aqueous solution can be used. The amount of the surfactant added varies depending on the type of the organic protective film and the type of the surfactant, but the surfactant may be introduced at a concentration having a lower contact angle than the contact angle of the organic protective film on the organic semiconductor as compared with the introduction of the surfactant.

In the step (c), an organic thin film transistor (OTFT) device manufacturing step and an organic protective film introduction step may be divided into an organic thin film transistor to which the organic protective film may be applied as an organic protective film to which a surfactant is added to the organic thin film transistor ( OTFT devices are applicable regardless of transistor structures such as top gate or bottom gate, top contact or bottom contact. In addition, the organic active layer to be used can be applied to both a solution-type polymer such as polythiophene or poly pulloene derivative, which is a deposition type such as oligothiophene or pentacene. In addition, the organic protective film forming process may be formed by various methods such as spin coating, inkjet printing, roll coating, and screen printing.

Hereinafter, the present invention will be described in more detail.

The present invention relates to a mixed composition for an organic thin film transistor protective film, comprising a water-soluble polymer, a polar solvent, and a surfactant.

The water-soluble polymer constituting the organic protective film of the organic thin film transistor according to the present invention is preferably a polymer or copolymer prepared from at least one monomer having a hydroxy group (-OH). The water-soluble polymer is soluble in a polar solvent, specifically, can be used without limitation if the solubility in the polar solvent is about 1 to 50% by weight, more preferably a water-soluble poly with a weight average molecular weight of 5,000 to 1,000,000. Any one or more selected from urethane, polyvinyl alcohol, polyvinyl alcohol copolymer, a water-soluble acrylate resin having a hydroxy group (-OH), and polyethylene glycol can be used.

The surfactant is soluble in a polar solvent, and may be used without limitation as long as it is a water-soluble surfactant containing a hydrophilic and hydrophobic group. For example, anionic surfactant, primary amine salt, secondary amine salt, tertiary amine salt, quaternary ammonium salt, phosphonium salt, such as carboxylate, sulfonate, sulfate ester salt, phosphate ester salt, and phosphonate salt Cationic surfactants such as sulfonium salts, fatty acid monoglycerine esters, fatty acid polyglycol esters, fatty acid sorbitan esters, fatty acid sucrose esters, fatty acid alkanolamides, polyethylene glycol condensation types and the like; Amphoteric surfactants containing sulfonic acid salts and sulfuric ester salts, and cations include amines, especially quaternary ammonium nitrogen groups, and more preferably linear alkylbenzenesulfonate sodium, alpha alpha sulfonic acid and alpha olefin sulfonic acid. Sodium, alcohol polyoxyethylene ether, alcohol polyoxyethylene ether sodium sulfonate, ammonium fluoroal This mid-sulfonic and the like are available.

As the polar solvent, alcohols such as water or isopropyl alcohol can be used.

In the present invention, the mixed composition is preferably 1 to 50% by weight of water-soluble polymer, 10 to 40,000 ppm (0.001 to 40% by weight) of the surfactant, and the remainder is made of a polar solvent. More specifically, the content of the polar solvent may be used in 10 to 90% by weight. When the content of the water-soluble polymer is less than 1% by weight, the effect is insignificant, and when the content exceeds 50% by weight, the viscosity rises sharply, and solubility of the resin is not preferable. In addition, the content of the surfactant in the water-soluble polymer solution is preferably used in 0.001 to 40% by weight, when used in less than 0.001% by weight of the coating improvement effect is insignificant, if it exceeds 40% by weight of the protective film It is not preferable because the protective film properties are degraded due to the increase in ionic properties.

When manufacturing an organic protective film solution for improving the organic protective film coating property according to the present invention with a specific example, as follows. Organic thin film transistor A polyvinyl alcohol aqueous solution is prepared by dissolving polyvinyl alcohol (PVA), a water-soluble polymer in powder form, which is frequently used as an organic protective film. A polyvinyl alcohol solution for an organic protective film is prepared by adding a surfactant containing a hydrophilic and hydrophobic group to the prepared polyvinyl alcohol aqueous solution to an organic protective film solution.

2 is an organic thin film transistor comprising a gate electrode, an organic insulating film, an organic active layer, a source / drain electrode, and a protective layer on a glass or plastic substrate, wherein the protective layer is a water-soluble polymer according to the present invention. And a mixed composition containing a polar solvent and a surfactant. The organic thin film transistor (OTFT) device can be applied regardless of a transistor structure such as a top gate or a bottom gate, a top contact, or a bottom contact. In addition, the organic active layer used may be any of a deposition type such as oligothiophene or pentacene or a solution type polymer such as polythiophene or polyfluoene derivative.

Fabrication of the organic thin film transistor to which the organic protective film (hereinafter referred to as a protective layer) for improving the coating property proposed in the present invention may be prepared by the following steps.

In the case of using a Si substrate as an example, HMDS (1,1,1,3,3,3-hexamethyldisilazane), which is a surface treatment agent, is used to improve insulator surface properties on a substrate in which SiO ₂ is laminated on a Si wafer as an insulator. After the treatment, the pentacene having excellent properties is vacuum deposited with the organic active layer. According to FIG. 2, an organic thin film transistor was manufactured by depositing gold (Au) using a shadow mask to introduce a source electrode and a drain electrode.

Next, the protective layer forming process may be formed by various methods such as spin coating, inkjet printing, roll coating, screen printing, and dipping using the mixed composition prepared above. That is, an organic thin film transistor to which a protective layer is applied was manufactured by performing an annealing step of forming a thin film from the organic thin film transistor prepared above using a mixed composition and removing water from a vacuum oven.

In the present invention, the protective layer preferably has a thickness of 30 nm to 3000 nm. If the protective layer is less than 30nm, the effect of inhibiting moisture and oxygen permeation is insignificant, while if the protective layer is greater than 3000nm, the increase of the effect of inhibiting moisture and oxygen permeation is minimal, while acting as an obstacle to high integration and ultra-thin film formation of the organic thin film transistor.

In addition, the organic active layer may be pentacene, tetracene (tetracene), oligo thiophene (polythiophene), polythiophene (polythiophene), metal phthalocyanine, polyphenylene (polyphenylene), polyvinylene phenylene (polyvinylenephenylene), poly It is preferably selected from fluorene, C ₆₀ , fluorinated phthalocyanine and derivatives thereof.

In addition, display elements such as an organic light emitting display, an electronic paper, and a liquid crystal display using the organic thin film transistor according to the present invention are also within the scope of the present invention.

The organic thin film transistor of the present invention as described above has a feature that the field effect charge mobility of 0.01 to 10 cm ² / Vs.

Hereinafter, the present invention will be described in more detail, but for the purpose of the present invention, the present invention is not limited thereto.

Example 1

Polyvinyl alcohol ( PVA ) And organic protective film mixed solution prepared with surfactant

Polyvinyl alcohol (PVA) (weight average molecular weight 10,000) in the form of powder was dissolved in water to prepare a 10 wt% polyvinyl alcohol aqueous solution. The completely dissolved aqueous polyvinyl alcohol solution was filtered with a 0.45 μm pore size membrane filter for aqueous solution to remove impurities.

25 parts by weight of Novec 4200 (ammonium fluoroalkylsulfonimide) of 3M at concentrations of 500 ppm (0.05% by weight), 1000 ppm (0.1%) and 2000 ppm (0.2% by weight), respectively, based on the filtered 10% by weight polyvinyl alcohol aqueous solution % And 75% by weight of water) hydrophilic surfactant was added to prepare a mixed composition.

Comparative Example 1

Polyvinyl alcohol (PVA) (weight average molecular weight 10,000) in the form of powder was dissolved in water to prepare a 10 wt% polyvinyl alcohol aqueous solution. The completely dissolved aqueous polyvinyl alcohol solution was filtered with a 0.45 μm pore size membrane filter for aqueous solution to remove impurities.

Experimental Example 1

In order to measure the coating properties of the mixed compositions of Example 1 and Comparative Example 1, after dropping the mixed composition to the surface of the organic active layer (pentacene) to be added dropwise, the contact angle was measured.

As a result, as shown in FIG. 1, the water contact angle was 59.93 degrees in the case of Comparative Example 1, in which the surfactant was not added at all, but in Example 1, the concentration was 54.90 degrees and 1000 ppm when the surfactant was added at 500 ppm. When it was added to the 52.64 degrees, 2000 ppm concentration was added to 47.35 degrees was measured, and as the concentration of the added surfactant was confirmed that the water contact angle on the upper surface of the organic semiconductor of the organic protective film solution accordingly was lowered. Therefore, it was found that the coating property of the hydrophilic organic protective film solution on the hydrophobic organic active layer was improved by the addition of the surfactant.

Example 2

Organic thin film transistor manufacturing

The substrate was used by cutting a 60-mm-thick silicon wafer (Poltec, 4inch (100) orientation, <0.005 ohm-cm) with 2 cm x 2 cm of p-doped silicon oxide, and the transistor structure was a top-contact structure. The transistor was produced. Substrate cleanliness is one of the most important factors in the manufacture of electronic devices, so ultrasonic cleaning with detergent, distilled water, acetone and isopropyl alcohol was used, followed by drying sufficiently in an oven.

In order to improve the surface properties of the well-cleaned substrate, it was coated with HMDS (1,1,1,3,3,3, -Hexamethyldisilazane) treatment and dried at 120 ℃.

Pentacene, an organic semiconductor, was deposited on the HMDS-treated SiO ₂ to a thickness of 50 nm using thermal vacuum deposition in a vacuum of 1 × 10 ⁻⁶ torr. At this time, the temperature of the substrate having a great influence on the crystallization of pentacene was kept constant at 90 ℃. Finally, gold was deposited to a thickness of 60 nm using a shadow mask to form a source and a drain electrode.

In the pentacene organic thin film transistor, 10 wt% PVA aqueous solution containing 2000 ppm of the surfactant prepared according to Example 1 was spin coated at 1000 rpm to form an organic protective thin film having a thickness of 1.0 μm.

Comparative Example 2

The organic thin film transistor was introduced into the organic thin film transistor through the same process as Example 2, except that the mixed composition of Comparative Example 1, which does not contain a surfactant, was used as a comparative object. That is, an organic protective thin film having a thickness of 1.0 μm was formed by spin coating in the same manner as in Example 2.

Experimental Example 2

Surface roughness  Measure

Figure 3 shows the surfactant at 2000 ppm concentration Atomic force microscopy (AFM) surface photographs of the PVA organic protective film thin film surface (Example 2) included and the PVA organic protective film thin film surface (Comparative Example 2) containing no surfactant were shown.

As shown in the photo, the surface uniformity of the PVA organic protective film containing the surfactant is very good at about 0.944 nm (RMS value), whereas the poor interface property of the PVA organic protective film without the surfactant with the hydrophobic organic semiconductor of the lower layer. As a result, it was found that the surface uniformity was significantly reduced to 1.678 nm (RMS value). Uneven organic protective film thin film properties (pinhole, thickness variation, etc.) act as a deterioration factor of the organic thin film transistor. Of surfactant Due to the introduction, the coating property of the organic protective film was improved and the surface uniformity of the thin film was also improved.

Experimental Example 3

Characteristics of Organic Thin Film Transistors with Time

The characteristics of the devices fabricated in Example 2 and Comparative Example 2 were measured according to the drain voltage-drain current and drain voltage according to the gate voltage using an Agilent Technology probe station (E5272) equipment. The gate voltage-drain current curves were measured and overall characteristics were evaluated using the following current and voltage relationship in saturation.

와 V_gs 의 그래프로부터 I_ds 가 0인 게이트 전압으로 결정되고 전계효과 전하이동도는

와 V_gs의 그래프의 기울기로부터 산출하였다. I _ds is the source-drain current, V _T is the threshold voltage, V _gs is the applied gate voltage, is the field effect charge mobility, W and L are the width and length of the channel, and C is the capacitance of the insulating film. Threshold voltage

From the graphs of V _gs and V _gs , we determine the gate voltage with I _ds 0 and the field effect charge mobility

It was computed from the slope of the graph of and V _gs .

4 is a result showing the characteristics change with time of the pentacene organic thin film transistor in which the PVA organic protective film containing the surfactant (Example 2) and the PVA organic protective film containing the surfactant (Comparative Example 2) were respectively introduced. .

In the case of a transistor device in which a PVA organic protective film containing a surfactant is introduced, it can be seen that the time-dependent decrease in mobility, which is an important parameter of device characteristics, is much slower than that in which a protective film containing no surfactant is applied. This shows that in the case of the protective film containing the surfactant, a thin film having uniformity is obtained and thus shows the effect of preventing the penetration of oxygen or moisture locally due to the uneven surface. That is, in the case of a protective film without a surfactant, the surface is poor in coating property and becomes uneven because of no pinhole or coating locally, so that moisture or oxygen penetrates into the part and consequently deteriorates the characteristics of the thin film transistor more quickly. Could know.

The present invention is a novel method of improving the thin film properties of the organic material used in the protective film forming technology through a solution process has the effect of improving the sealing properties and the uniformity of the thin film for the post-protective process.

The organic material used as the organic protective film is dissolved in a solvent that does not damage the lower layer of the organic protective film to form a protective film. The coating property and the uniformity of the thin film could be improved by introducing an appropriate surfactant to improve the coating property in the organic protective film solution. .

In addition, the water contact angle of the organic protective film on the organic active layer due to the introduction of the surfactant was confirmed that the wettability (wetting) is improved because it is lowered from 59.93 to 47.35 degrees compared to before the introduction into the surfactant, the roughness of the interface of the protective film formed As a result, it was confirmed that the surface roughness (RMS value) was improved from 1.678 nm to 0.944 nm. This is thought to reduce the probability of failure in later array processes. In addition, when the protective film containing the surfactant is applied to the actual organic thin film transistor, the decrease in characteristics (mobility) with time occurs much more slowly than the device to which the protective film without the surfactant is applied.

That is, through the method of improving the coating property of the organic protective film of the present invention, it was possible to obtain excellent results of improving the coating property of the organic protective film, improving the uniformity of the thin film, and improving the electrical properties of the protective device. This technology is a new technology that has not been reported previously, and is an essential technology to be applied when the organic thin film transistor is applied to a real device in the next generation of organic electronics. In other words, it is an essential technology for improving the characteristic reliability of the device.

Claims (15)

In the composition for an organic thin film transistor protective film, Water-soluble polymers, polar solvents, and any one or more interfaces selected from linear alkylbenzenesulfonic acid sodium, alpha alpha sulfonate, alpha olefin sodium sulfonate, alcohol polyoxyethylene ether, alcohol polyoxyethylene ether sulfonate, ammonium fluoroalkylsulfonimide A mixed composition for an organic thin film transistor protective film, comprising an activator. The method of claim 1, The water-soluble polymer is a mixed composition for an organic thin film transistor protective film, characterized in that any one or more selected from water-soluble polyurethane, polyvinyl alcohol, polyvinyl alcohol copolymer, water-soluble acrylate resin, polyethylene glycol having a weight average molecular weight of 5,000 ~ 1,000,000. . delete delete The method of claim 1, The mixed composition is a mixed composition for an organic thin film transistor protective film, characterized in that 1 to 50% by weight of water-soluble polymer, 0.001 to 40% by weight of surfactant and the remainder is composed of a polar solvent. An organic thin film transistor comprising a gate electrode, an organic insulating film, an organic active layer, a source / drain electrode, and a protective layer on a glass or plastic substrate, The protective layer is an organic thin film transistor, characterized in that the mixed composition for the protective film of any one selected from claim 1, 2 or 5. The method of claim 6, The protective layer is an organic thin film transistor, characterized in that formed on top of the organic active layer and the source / drain electrode. The method of claim 6, The protective layer is an organic thin film transistor, characterized in that applied by any one method selected from spin coating, inkjet printing or dipping method. The method of claim 8, The thickness of the protective layer is an organic thin film transistor, characterized in that 30 nm to 3000 nm. The method of claim 6, The organic active layer is pentacene, tetracene (tetracene), oligo thiophene (polythiophene), polythiophene (polythiophene), metal phthalocyanine, polyphenylene (polyphenylene), polyvinylene phenylene (polyvinylenephenylene), polyfluorene (polyfluorene), C ₆₀ , fluorinated phthalocyanine and derivatives thereof. The method of claim 10, The organic thin film transistor, characterized in that the electric field mobility of the organic thin film transistor is in the range of 0.01 ~ 10cm ² / Vs. A display element comprising the organic thin film transistor according to claim 6. The method of claim 12, The display device may be any one selected from an organic light emitting display, an electronic paper, and a liquid crystal display. delete delete

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