JP4281320B2 - Method for producing organic thin film transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a thin film transistor (TFT) having an organic semiconductor material in an active layer and a method for manufacturing the same.
[0002]
[Prior art]
Organic semiconductor materials are currently being studied for use as active layers in various devices such as light emitting diodes, TFTs such as metal-insulator-semiconductor organic thin film transistors (MIS-FETs) (Patent Document 1, etc.). Organic semiconductor materials have the advantage of workability such as compatibility with flexible plastic substrates and ease of formation by spin coating. However, in order for such organic semiconductor materials to be useful in TFT devices, the resulting device must have an on / off ratio suitable for the particular application. In general, a TFT device should have an on / off ratio of at least about 10 ³ . The properties of organic semiconductor materials that govern the on / off ratio are carrier mobility and electrical conductivity.
[0003]
In general, an organic semiconductor material used for a TFT device should have at least a carrier mobility μ of about 10 ⁻³ cm ² / Vs or more and an electric conductivity of about 10 ⁻⁵ S / cm or less. By using such an organic semiconductor material, a TFT device having an on / off ratio of at least about 10 ³ can be produced.
[0004]
Examples of such an organic material include pentacene (Patent Documents 2 and 3), regioregular polythiophene (Patent Document 4), and the like.
However, such an organic material has a problem that its characteristics deteriorate due to moisture and oxygen, and the on / off ratio becomes 10 ³ or less. That is, the organic material is denatured due to the influence of moisture, oxygen, etc., so that predetermined transistor characteristics cannot be obtained, and quality cannot be maintained.
[0005]
[Patent Document 1]
JP-A-5-55568 [Patent Document 2]
US Pat. No. 5,946,551 [Patent Document 3]
US Pat. No. 5,982,970 [Patent Document 4]
US Pat. No. 6,107,117 Specification
[Problems to be solved by the invention]
An object of the present invention is to produce an organic thin film transistor in which the organic semiconductor material is not deteriorated by moisture, oxygen or the like, and to provide a long-life organic thin film transistor capable of maintaining the initial performance for a long time.
[0007]
[Means for Solving the Problems]
The invention of claim 1 is an organic thin film transistor including an active layer comprising a gas barrier layer, a gate electrode, a source electrode, a drain electrode, an insulating layer, and an organic semiconductor on at least a plastic substrate. A step of drying under heating and reducing the water content to 0.2% or less by weight, a step of forming a gas barrier layer on the surface of the plastic substrate, and then the plastic substrate on which the gas barrier layer is formed. A step of forming an active layer comprising a gate electrode, a source electrode, a drain electrode, an insulating layer and an organic semiconductor on the material, and a step of heating and drying the plastic substrate on which the gas barrier layer and the active layer are formed under reduced pressure The manufacturing method of the organic thin-film transistor characterized by including.
[0008]
In the invention of claim 2, the moisture content of the electrode material used for each of the electrodes, the insulating layer material used for the insulating layer, and the active layer material used for the active layer is 0.2% or less by weight. The method for producing an organic thin film transistor according to claim 1.
[0009]
The invention according to claim 3 is an organic thin film transistor that constitutes each device in a device such as a liquid crystal display, an organic EL display, an RFID, and a sensor using the organic thin film transistor manufactured by the method according to claims 1 and 2. A method for manufacturing a device, wherein the moisture content of the other members is 0.2% or less.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
An embodiment of the present invention will be described with reference to the drawings, but the present invention is not limited thereto.
As an example of the present invention, FIG. 1 shows an example of a metal-insulator-semiconductor field effect transistor (MISFET type) device having an organic semiconductor material in an active layer. In the MISFET of FIG. 1, a metal electrode 3 and an insulating layer 4 are formed on a plastic substrate 1 with a barrier layer 2. Further, two metal electrodes 5 and 6 are formed on the insulating layer 4. An organic semiconductor layer 7 is formed on and between the metal electrodes 5 and 6.
[0011]
For the plastic substrate 1 used in the present invention, polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfene, polymethyl methacrylate, polycarbonate, polyallylate and the like can be used.
[0011]
Since such a plastic substrate 1 is made of a polymer compound, it contains a certain amount of moisture. The contained moisture diffuses in the base material and affects the organic semiconductor. If the water content of the plastic substrate 1 is lowered, the total amount of water vapor is lowered even when the diffusion rate is high, and the deterioration of the organic TFT can be reduced. When the moisture content is 0.2% or more, the deterioration is rapid, and it is desirable that the moisture content is 0.2% or less. More preferably, it is 0.1% or less, and particularly preferably 0.05% or less.
The moisture content can be measured by, for example, the Karl Fischer titration method (Mitsubishi Kasei Coulometric Titration Moisture Analyzer CA-06).
[0012]
As a method of reducing the moisture content, positively adopting a method using a plastic substrate 1 such as polypropylene or cycloolefin polymer which is inherently difficult to absorb water, and a plastic substrate 1 such as polyamide or polyester which is inherently easy to absorb water. There is a method of drying. By drying, not only moisture but also gases such as oxygen, monomers, and solvents may be removed, which is effective in preventing element deterioration.
[0013]
As a method for drying the plastic substrate 1 described above, a vacuum drying method, a method combining these, and the like can be used in addition to a normal heat drying method. In particular, a vacuum drying method that can remove moisture and other gas molecules inside the plastic substrate 1 in a short time is desirable.
[0014]
The moisture diffusion of the plastic substrate 1 described above is affected by the moisture content of the substrate and the magnitude of the diffusion of water vapor in the substrate.
In the present invention, by forming the gas barrier layer 2 on the surface of the plastic substrate 1, it is possible to reduce the diffusion of water vapor and to reduce the speed of element deterioration. As a method of reducing the element deterioration rate by reducing the diffusivity, there is a method of forming a gas barrier layer 2 having a water vapor barrier performance on at least the surface side of the surface of the plastic substrate 1 in contact with the organic semiconductor layer or on both surfaces. The reason why the gas barrier layer 2 having the water vapor barrier performance is formed at least on the surface side in contact with the organic semiconductor layer is that the surface is in direct contact with the organic semiconductor layer, and the influence of water vapor diffusion is large. The gas barrier layer 2 having water vapor barrier performance may have not only water vapor barrier performance but also barrier performance against other gases such as oxygen barrier performance. In particular, it is desirable to have oxygen barrier performance.
Moreover, it is more preferable that the plastic substrate 1 to be used is within the range of the moisture content described above.
[0015]
As the gas barrier layer 2, known materials such as organic thin films such as polyvinyl chloride, polyvinylidene chloride and polychlorotrifluoroethylene, inorganic thin films such as aluminum oxide and silicon oxide, and composite films and laminated films thereof are used. Is possible. Among these, inorganic oxides such as aluminum oxide and silicon oxide are particularly preferable because they have not only water vapor permeability but also low oxygen permeability. In addition, it is desirable to form a film by a winding-type vacuum film forming method from the viewpoint of barrier performance and manufacturing cost.
[0016]
For the electrodes 3, 5, and 6 of the present invention, gold, silver, copper, chromium, titanium, indium tin oxide (ITO), a conductive polymer, or the like can be used. The film thickness of the electrodes 3, 5 and 6 is at least 0.01 μm or more. The electrodes 3, 5, and 6 can be formed by a known method such as a vacuum deposition method or a spin coating method.
[0017]
The insulating material used for the insulating layer 4 of the present invention is not particularly limited, but an organic material can be used. For example, polyethylene terephthalate, polyethylene naphthalate, polypropylene, cycloolefin polymer, polyamide, polyethersulfene, polymethyl methacrylate, polycarbonate, polyallylate and the like can be used. In order to suppress the leakage current between the metal electrodes, it is preferable that the insulating material has a conductivity of about 10 ⁻¹² S / cm or less. The insulating layer is formed using a conventional method such as spin coating, dip coating, screen printing, letterpress printing, intaglio printing, planographic printing, and ink jet method. The film thickness of the insulating layer is desirably 0.1 to 1 μm. In addition, an inorganic material can be used as the insulating material, but care must be taken so that the process temperature does not become high. As the inorganic insulating material, silicon dioxide, silicon nitride, aluminum oxide, or the like can be formed by a known method such as a CVD method or a sol-gel method.
[0018]
The organic semiconductor material used for the organic semiconductor layer 7 of the present invention is perylene tetracarboxylic dianhydride (PTCDA), naphthalene tetracarboxyl dianhydride (NTCDA), copper phthalocyanine, copper fluoride phthalocyanine, tetracene, pentacene, Various known materials such as thiophene oligomers, α-sexual thiophene, regioregular poly (thiophene) can be used.
[0019]
The organic semiconductor layer 7 is formed using a dry process such as a vacuum deposition method, or a wet process such as spin coating, dip coating, screen printing, letterpress printing, intaglio printing, planographic printing, and ink jet printing. The thickness of the organic semiconductor layer is desirably at least 0.01 μm.
[0020]
In the present invention, a protective layer can be further provided on the organic semiconductor layer 7. A known material can be used for the protective layer. Further, by providing the protective layer with gas barrier properties, it can be protected from moisture and oxygen from the side opposite to the plastic substrate.
[0021]
The organic thin film transistor of the present invention can be used for devices such as a liquid crystal display, an organic EL display, RFID (Radio Frequency Identification), and a sensor.
[0022]
When used in these devices, a gas barrier layer may be provided on an interlayer other than the organic thin film transistors constituting these devices and on the surface of the layers to prevent moisture and oxygen from entering the organic thin film transistors.
[0023]
In addition, it is desirable that the moisture content of the counter substrate other than the organic thin film transistor constituting these devices, a functional thin film such as a liquid crystal layer or an EL layer, and a member such as a sealant is 0.2% or less. More preferably, it is 0.1% or less, and particularly preferably 0.05% or less. In this way, moisture and oxygen can be prevented from entering the organic thin film transistor.
[0024]
【Example】
<Example 1>
As Example 1, the MISFET shown in FIG.
First, polyethylene terephthalate (PET) was used for the plastic substrate 1. The plastic substrate 1 was dried in vacuum at 100 ° C. for 24 hours. After drying, the water content of the substrate 1 was 0.2% or less. Next, an aluminum oxide layer was vapor-deposited on both sides of this PET by an electron beam heating method to form a gas barrier layer 2 having a thickness of 0.1 μm.
Next, a gold film having a thickness of 0.1 μm was formed as a gate electrode 3 on the gas barrier layer 2 by a vacuum deposition method. Next, a polymethyl methacrylate (PMMA) layer having a film thickness of 0.3 μm was formed as the insulating layer 4 by spin coating. Next, a gold film having a thickness of 0.1 μm was formed as the source electrode 5 and the drain electrode 6 by a vacuum deposition method. Here, the channel length was 50 μm and the channel width was 500 μm.
Next, an organic semiconductor layer 7 having a thickness of 0.1 μm was formed as an active layer by spin coating. As the organic semiconductor material, regioregular poly (3-hexylthiophene) (Aldrich) was used. The linkage in this polymer was at least 98.5% HT (head-to-tail) linkage. 1 mg / ml of regioregular poly (3-hexylthiophene) was dissolved in chloroform at room temperature and filtered through a polytetrafluoroethylene (PTFE) membrane filter having a pore size of 0.2 μm.
Next, after the organic semiconductor layer 7 was formed, it was dried in vacuum at 100 ° C. for 24 hours. After drying, the water content of the substrate 1, the insulating layer 4, and the organic semiconductor layer 7 was 0.2% or less.
When the carrier mobility and conductivity of the fabricated MISFET type TFT were measured, they were 1 × 10 ⁻² cm ² / Vs and 1 × 10 ⁻⁴ S / cm, respectively. The on / off ratio was about 10 ⁴ .
[0025]
<Comparative Example 1>
A MISFET was produced in the same manner as in Example 1 except that the gas barrier layer was not provided except for the vacuum drying process.
The manufactured MISFET type TFT had a water content of 0.4%, and the carrier mobility and conductivity were measured to be 1 × 10 ⁻³ cm ² / Vs and 1 × 10 ⁻⁵ S / cm, respectively. there were. On / off ratio was about 10 ^2.
[0026]
【The invention's effect】
According to the present invention, by reducing the amount of moisture contained in the materials and materials constituting the organic thin film transistor, the influence of moisture, oxygen, etc. is eliminated as much as possible, long-term organic that can maintain initial performance for a long time with little deterioration over time. A thin film transistor and a manufacturing method thereof can be provided. In addition, by providing a gas barrier layer on the surface of the plastic substrate surface on which the organic thin film transistor is formed, moisture, oxygen, and the like can be blocked, deterioration with time can be reduced, and a long-life organic thin film transistor that can maintain initial performance for a long time can be provided.
[0027]
[Brief description of the drawings]
FIG. 1 is an explanatory view showing a cross-sectional structure of an example of an organic thin film transistor of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Plastic base material 2 Gas barrier layer 3 Gate electrode 4 Insulating layer 5 Source electrode 6 Drain electrode 7 Organic-semiconductor layer

Claims (3)

In an organic thin film transistor including at least a gas barrier layer, a gate electrode, a source electrode, a drain electrode, an insulating layer, and an active layer made of an organic semiconductor on a plastic substrate, the plastic substrate before the gas barrier layer is formed is dried by heating under reduced pressure. A weight fraction of 0.2% or less, a step of forming a gas barrier layer on the surface of the plastic substrate, a gate electrode and a source on the plastic substrate on which the gas barrier layer is formed. A step of forming an active layer comprising an electrode, a drain electrode, an insulating layer and an organic semiconductor; and a step of drying the plastic substrate on which the gas barrier layer and the active layer are formed by heating under reduced pressure. Manufacturing method of organic thin-film transistor. Claims, characterized in that the electrode material used for the electrodes, the moisture content of the active layer material used for the insulating layer material and the active layer is used in the insulating layer is not more than 0.2% Both the weight fraction 2. A method for producing an organic thin film transistor according to 1. In devices such as a liquid crystal display, an organic EL display, an RFID, and a sensor using the organic thin film transistor manufactured by the method according to claim 1 and 2, the moisture content of members other than the organic thin film transistor constituting each device Is 0.2% or less, A device manufacturing method,

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