JP6330408B2 - Thin film transistor and manufacturing method thereof - Google Patents

Description

  The present invention relates to a thin film transistor and a method for manufacturing the same.

  At present, a general flat and thin image display device is driven by an active matrix of a thin film transistor using amorphous silicon or polycrystalline silicon as a semiconductor layer.

  On the other hand, in recent years, attempts have been made to use a resin substrate instead of a glass substrate in order to further reduce the thickness, weight, and damage resistance of a flat and thin image display device.

  However, the manufacture of the above-described thin film transistor using silicon requires a relatively high temperature thermal process and is generally difficult to form directly on a resin substrate having low heat resistance.

  Therefore, development of a thin film transistor using an organic semiconductor that can be formed at a low temperature has been actively conducted.

  In addition, the organic semiconductor has an advantage that it can be patterned by a printing method. Furthermore, a thin film transistor using an organic semiconductor can be formed by printing not only the semiconductor layer but also the electrodes and the gate insulating layer by selecting materials that can be formed by a printing method, so that all layers constituting the thin film transistor can be formed by printing. .

  By using the printing method, a significant reduction in manufacturing cost is expected as compared with a silicon-based thin film and a transistor manufactured by vacuum film formation / photolithography.

  For example, in the case of a bottom gate / bottom contact type TFT, the organic semiconductor film is formed on the gate insulating layer and the source / drain electrodes. The organic semiconductor film can be formed by, for example, applying a coating solution containing an organic semiconductor material onto the gate insulating layer and the source / drain electrodes and then removing the solvent to form an organic semiconductor film on the transfer substrate. There is a method in which a coating liquid containing a semiconductor material is applied, the organic semiconductor material is crystallized on a transfer substrate, and the organic semiconductor film is transferred onto the gate insulating layer and the source / drain electrodes (Patent) References 1, 2).

  However, when the organic semiconductor film is formed, the surface energy of the gate insulating layer is different from that of the source / drain electrode. Therefore, the organic semiconductor film is easily formed on either the gate insulating layer or the source / drain electrode. On the other hand, there is a problem that it is difficult to form. When the organic semiconductor film is not sufficiently formed on the gate insulating layer, a portion where the organic semiconductor film does not exist in the channel is generated, so that the on-current of the thin film transistor is reduced and desired characteristics can be obtained in operating the device. It will not be. Even when the organic semiconductor film is not sufficiently formed on the source / drain electrodes, the contact area between the organic semiconductor film and the source / drain electrodes is small and the contact resistance is high, so that the on-current of the thin film transistor is reduced, and the device In this case, desired characteristics cannot be obtained.

Japanese Patent No. 3803342 Japanese Patent No. 4831406

  An object of this invention is to provide the thin-film transistor which can obtain a high on-current, and its manufacturing method.

One aspect of the present invention for solving the above problems is an insulating substrate, at least a gate electrode formed on the insulating substrate, a gate insulating layer, a source electrode, a drain electrode, and a channel layer including an organic semiconductor. include, between the source electrode surface and the drain electrode surface and the channel layer, it has a contact layer comprising an organic semiconductor, the channel layer and the contact layer is made of the same organic semiconductor material, a thin film transistor.

  Further, the channel layer or the contact layer may include a material having crystallinity.

  Another aspect of the present invention is a method for manufacturing a thin film transistor, including a step of forming a channel layer and / or a contact layer using a coating liquid containing an organic semiconductor material.

Further, in the step of forming the contact layer, the contact angle with the gate insulating layer surface of the coating liquid, the coating liquid may be applied so as to be larger than the contact angle against the source electrode and the drain electrodes.

Further, in the step of forming the contact layer, the contact angle with respect to the insulating substrate surface of the coating liquid, the coating liquid may be applied so as to be larger than the contact angle against the source electrode and the drain electrodes.

  Further, the step of forming the contact layer may include a step of forming an organic semiconductor film to be a contact layer by removing the solvent component from the coating solution after coating the coating solution.

  Further, in the step of forming the channel layer, a step of applying a coating liquid on the transfer substrate, a step of crystallizing an organic semiconductor material contained in the coating liquid on the transfer substrate, and forming an organic semiconductor film, A step of forming a channel layer by transferring an organic semiconductor film over an insulating substrate on which at least a source electrode, a drain electrode, and a contact layer are formed may be included.

  By having a contact layer containing an organic semiconductor material between the surface of the source and drain electrodes and the channel layer, the contact resistance between the channel layer and the source / drain electrodes is low, and a high on-current can be obtained.

  Since the channel layer and the contact layer have crystallinity, higher on-current can be obtained.

  When the channel layer and the contact layer contain the same organic semiconductor material, carriers in the semiconductor film can move smoothly and a higher on-current can be obtained.

  By forming the channel layer and the contact layer from a coating solution containing an organic semiconductor material, the channel layer and the contact layer can be manufactured using a printing method, and a low-cost thin film transistor can be realized.

  In the case of a bottom gate-bottom contact thin film transistor, when forming an organic semiconductor film to be a contact layer, the contact angle with respect to the gate insulating layer surface of the coating liquid containing the organic semiconductor material is defined as the contact angle with respect to the source electrode and drain electrode surfaces. By making it larger than this, when the coating solution sufficiently wets the source electrode and the drain electrode and the solvent dries, a contact layer can be sufficiently formed on the surface of the source electrode and the drain electrode.

  In the case of the top gate-bottom contact type thin film transistor, when forming the organic semiconductor film to be the contact layer, the contact angle of the coating liquid containing the organic semiconductor material with respect to the insulating substrate surface is determined from the contact angle with respect to the source electrode and drain electrode surfaces. By increasing the thickness, the coating liquid sufficiently wets the source electrode and the drain electrode, and the contact layer can be sufficiently formed on the surface of the source electrode and the drain electrode when the solvent is dried.

  An organic layer that becomes a contact layer on the source electrode and the drain electrode by the step of coating the coating solution containing the organic semiconductor material described above on the source electrode and the drain electrode and the step of removing the solvent component from the coating solution. A semiconductor film can be easily formed.

  Insulating substrate in which a coating liquid containing the above-mentioned organic semiconductor material is applied on a transfer substrate, a step of crystallizing the organic semiconductor material on the transfer substrate, and a source electrode, a drain electrode, and a contact layer are formed Further, a crystalline organic semiconductor film can be formed on the surface of the gate insulating layer or the insulating substrate without dissolving the contact layer by the step of transferring the organic semiconductor film.

It is the schematic showing the cross-sectional structure of the thin-film transistor which concerns on the 1st Embodiment and Example of this invention. It is the schematic showing the cross-section of the thin-film transistor concerning the 2nd Embodiment of this invention. It is the schematic showing the cross-sectional structure of the thin-film transistor which concerns on the comparative example of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the embodiments, the same components are denoted by the same reference numerals, and redundant description among the embodiments is omitted.

  FIG. 1 shows a thin film transistor 1 which is a first embodiment of the thin film transistor of the present invention. The thin film transistor has a bottom gate-bottom contact structure including a gate electrode 11, a gate insulating layer 12, a source electrode 13 and a drain electrode 14, a contact layer 15, and a channel layer (semiconductor layer) 16 on an insulating substrate 10.

  FIG. 2 shows a thin film transistor 2 which is a second embodiment of the thin film transistor of the present invention. A thin film transistor having a top gate-bottom contact structure including a gate electrode 11, a gate insulating layer 12, a source electrode 13 and a drain electrode 14, a contact layer 15, and a channel layer 16 on an insulating substrate 10.

A glass substrate or a resin substrate can be used as the insulating substrate 10 of the present invention. In the case of a resin substrate, for example, polyimide, polymethyl methacrylate, polyacrylate, polycarbonate, polystyrene, polyethylene sulfide, polyethersulfone (PES), polyolefin, polyethylene terephthalate, polyethylene naphthalate (PEN), cycloolefin polymer, polyethersulfene Triacetyl cellulose, polyvinyl fluoride film, ethylene-tetrafluoroethylene copolymer resin, glass fiber reinforced acrylic resin film, glass fiber reinforced polycarbonate, fluorine resin, cyclic polyolefin resin, and the like can be used. These substrates can be used alone, or a composite substrate in which two or more kinds are laminated can be used.
A gas barrier layer or an adhesive layer made of an organic film such as polyvinyl pyrrolidone or an inorganic film such as SiO ₂ may be provided on the insulating substrate.

  The gate electrode 11 of the present invention is formed by applying a low resistance metal material such as Ag, Cu, Au or the like in the form of an ink or paste by screen printing, transfer printing, letterpress printing, an ink jet method, or the like, and baking it. Can be formed. A conductive organic material such as PEDOT (polyethylenedioxythiophene) can also be used. Further, it can be formed by depositing a low resistance metal material such as Mo, Al, Cu or the like in vacuum and patterning using photolithography, but is not limited thereto.

  As the gate insulating layer 12 of the present invention, for example, a polymer solution such as polyvinylphenol, polymethyl methacrylate, polyimide, polyvinyl alcohol, parylene, fluororesin, epoxy resin, a solution in which particles such as alumina and silica gel are dispersed, Alternatively, a precursor solution of an inorganic material such as silicon oxide, silicon nitride, silicon oxynitride, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, zirconium oxide, titanium oxide, or the like is applied using a spin coating method, a slit die coating method, or the like. It can be formed by coating and baking. In addition, the inorganic material can be formed by using a vacuum film forming method and patterned by a photolithography method, but is not limited thereto.

  For the source electrode 13 and the drain electrode 14 of the present invention, a low resistance metal material such as Ag, Cu, Au or the like is applied in an ink form or a paste form by screen printing, transfer printing, letterpress printing, an inkjet method, etc. It can be formed by firing. A conductive organic material such as PEDOT (polyethylenedioxythiophene) can also be used. Further, it can be formed by depositing a low resistance metal material such as Mo, Al, Cu or the like in vacuum and patterning using photolithography, but is not limited thereto.

  The contact layer 15 of the present invention is formed using a coating solution containing an organic semiconductor material. As a specific example, a coating liquid containing an organic semiconductor material is applied onto a source electrode and a drain electrode using a printing method such as screen printing or letterpress printing, or an ink jet method, a dispenser method, and the like. There is a method for removing the solvent component. By manufacturing using a printing method, a low-cost thin film transistor can be realized. Moreover, the organic semiconductor film used as a contact layer can be easily formed on a source electrode and a drain electrode by the method of removing a solvent component from a coating liquid after coating. The method for forming the contact layer 15 is not limited to this. Since the material of the contact layer 15 can obtain a higher on-current, it is preferably a crystalline organic semiconductor material, but may be non-crystalline. Low molecular organic semiconductor materials such as pentacene, tetracene, copper phthalocyanine, and derivatives thereof, and high molecular organic semiconductor materials such as polythiophene, fluorenebithiophene copolymer, and derivatives thereof can be used. Moreover, you may add additives, such as a suitable dispersing agent and a stabilizer, to a solvent.

  As shown in FIGS. 1 and 2, the contact layer 15 is formed between the surface of the source electrode 13 and the drain electrode 14 and the channel layer 16. As a result, the contact resistance between the channel layer and the source / drain electrodes is low, and a high on-current can be obtained.

  In the case of the bottom gate-bottom contact type thin film transistor 1 shown in FIG. 1, when forming the organic semiconductor film to be the contact layer 15, the contact angle of the coating solution containing the organic semiconductor material with respect to the surface of the gate insulating layer 12 is expressed as the source. It is preferable that the contact angle of the surfaces of the electrode 13 and the drain electrode 14 with respect to the gate insulating layer 12 is larger. This is because when the coating solution sufficiently wets the source electrode 13 and the drain electrode 14 and the solvent is dried, a contact layer can be sufficiently formed on the surface of the source electrode 13 and the drain electrode 14.

  In the case of the top gate-bottom contact type thin film transistor 2 shown in FIG. 2, when forming the organic semiconductor film to be the contact layer 15, the contact angle of the coating liquid containing the organic semiconductor material with respect to the surface of the insulating substrate 10 is set. The contact angles of the source electrode 13 and the drain electrode 14 with respect to the surface of the insulating substrate 10 are preferably larger. This is because when the coating solution sufficiently wets the source electrode 13 and the drain electrode 14 and the solvent is dried, a contact layer can be sufficiently formed on the surface of the source electrode 13 and the drain electrode 14.

  Since the channel layer 16 of the present invention can obtain a higher on-current, a coating liquid containing an organic semiconductor material having crystallinity is applied onto the transfer substrate, and the organic semiconductor material is applied on the transfer substrate. Is formed by transferring the organic semiconductor film onto the insulating substrate 10 on which the source electrode 13, the drain electrode 14, and the contact layer 15 are formed. Through such a process, a crystalline organic semiconductor film can be formed on the surface of the gate insulating layer or on the insulating substrate without dissolving the contact layer 15. For the transfer of the organic semiconductor film, for example, a relief printing method, a reverse printing method, a micro contact printer method, or the like can be used. Examples of the material of the channel layer 16 include, but are not limited to, low molecular organic semiconductor materials such as pentacene, tetracene, copper phthalocyanine, and derivatives thereof. You may add additives, such as a suitable dispersing agent and a stabilizer, to a coating liquid. Further, since the carriers move smoothly in the semiconductor film and a higher on-current can be obtained, the contact layer 15 and the channel layer 16 may contain the same organic semiconductor material.

  Specific examples of the thin film transistor according to the present invention will be described below. Note that the present invention is not limited to each embodiment.

(Example)
A thin film transistor according to an example having a cross section as shown in FIG. 1 was produced.
On the polyethylene naphthalate (PEN) film used as the insulating substrate 10, Al was formed into a film by sputtering, and the gate electrode 11 was produced using the photolithographic method. Next, the polyvinyl phenol used as the gate insulating layer 12 was formed into a film by the spin coat method on the insulating substrate 10 containing the gate electrode 11, and baked at 180 degreeC for 1 hour, and the gate insulating layer 12 was obtained. Subsequently, after depositing Au as the source electrode 13 and the drain electrode 14 on the gate insulating layer 12, a pattern was formed using a photolithography method, and the source electrode 13 and the drain electrode 14 were obtained. Next, a coating solution in which 6,13-bis (triisopropylsilylethynyl) pentacene is dissolved in a solvent containing xylene is applied onto the source electrode 13 and the drain electrode 14 using a dispenser method, and dried at 100 ° C. for 60 minutes. The contact layer 15 was obtained. Finally, a coating solution in which 6,13-bis (triisopropylsilylethynyl) pentacene is dissolved in a solvent containing toluene and dimethyltetralin is crystallized on the transfer substrate, and the source electrode 13 and the drain electrode 14 are formed using a relief printing method. The channel layer 16 was formed by printing between the source electrode 13 and the drain electrode 14 so as to cover a part of the upper part and drying at 100 ° C. for 60 minutes. The manufactured thin film transistor has a channel length of 10 μm and a channel width of 200 μm.

The device characteristics of the thin film transistor according to the example manufactured as described above were an off current of 1.1 × 10 ⁻¹² A and an on current of 5.6 × 10 ⁻⁶ A, and a thin film transistor having a high on current was obtained. .

(Comparative example)
A thin film transistor 3 according to a comparative example having a cross section as shown in FIG. 3 was produced.
On the polyethylene naphthalate (PEN) film used as the insulating substrate 10, Al was formed into a film by sputtering, and the gate electrode 11 was produced using the photolithographic method. Next, the polyvinyl phenol used as the gate insulating layer 12 was formed into a film by the spin coat method on the insulating substrate 10 containing the gate electrode 11, and baked at 180 degreeC for 1 hour, and the gate insulating layer 12 was obtained. Subsequently, after depositing Au as the source electrode 13 and the drain electrode 14 on the gate insulating layer 12, a pattern was formed using a photolithography method, and the source electrode 13 and the drain electrode 14 were obtained. Finally, a coating solution in which 6,13-bis (triisopropylsilylethynyl) pentacene is dissolved in a solvent containing toluene and dimethyltetralin is crystallized on the transfer substrate, and the source electrode 13 and the drain electrode 14 are formed using a relief printing method. The channel layer 16 was formed by printing between the source electrode 13 and the drain electrode 14 so as to cover a part of the upper part and drying at 100 ° C. for 60 minutes. The manufactured thin film transistor 3 has a channel length of 10 μm and a channel width of 200 μm.

The device characteristics of the thin film transistor 3 manufactured as described above are an off-current of 1.0 × 10 ⁻¹² A and an on-current of 1.1 × 10 ⁻⁶ A, and a thin film transistor having a low on-current is obtained as compared with the example. It was.

  From the above results, it was confirmed that a thin film transistor with high on-current can be obtained according to the present invention.

  Such a thin film transistor can be used as a switching element such as flexible electronic paper and a pressure sensor.

1, 2, 3 Thin film transistor 10 Insulating substrate 11 Gate electrode 12 Gate insulating layer 13 Source electrode 14 Drain electrode 15 Contact layer 16 Channel layer

Claims (9)

Including an insulating substrate, at least a gate electrode formed on the insulating substrate, a gate insulating layer, a source electrode, a drain electrode, and a channel layer including an organic semiconductor;
Between the source electrode surface and the drain electrode surface and the channel layer, it has a contact layer comprising an organic semiconductor,
The channel layer and the contact layer are made of the same organic semiconductor material;
Thin film transistor.   The thin film transistor according to claim 1, wherein the channel layer has crystallinity.   The thin film transistor according to claim 1, wherein the contact layer has crystallinity. A method of manufacturing a thin film transistor according to any one of claims 1 to 3 ,
The manufacturing method of a thin-film transistor including the process of apply | coating the coating liquid containing an organic-semiconductor material, and forming the said channel layer. A method of manufacturing a thin film transistor according to any one of claims 1 to 3 ,
The manufacturing method of a thin-film transistor including the process of forming the said contact layer using the coating liquid containing an organic-semiconductor material. In the step of forming the contact layer, the contact angle with respect to the gate insulating layer surface of the coating solution, the applying the coating solution to be greater than the contact angle against the source electrode and the drain electrodes, claim 6. A method for producing a thin film transistor according to 5 . In the step of forming the contact layer, the contact angle with respect to the insulating substrate surface of the coating solution, the applying the coating solution to be greater than the contact angle against the source electrode and the drain electrodes, according to claim 5 A method for producing the thin film transistor according to 1. The step of forming the contact layer, after application of the coating liquid, by removing the solvent component from the coating liquid, comprising the step of forming an organic semiconductor film to be the contact layer, in any one of claims 5 to 7 The manufacturing method of the thin-film transistor of description. The step of forming the channel layer includes:
Applying the coating solution onto a transfer substrate;
Forming an organic semiconductor film by crystallizing an organic semiconductor material contained in the coating liquid on the transfer substrate;
5. The method of manufacturing a thin film transistor according to claim 4 , comprising: forming a channel layer by transferring the organic semiconductor film on the insulating substrate on which at least the source electrode, the drain electrode, and the contact layer are formed. .

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