JP2006261493A - Thin film transistor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor whose transistor characteristic is improved by using an inexpensive insulating film of high insulation property, and also to provide its manufacturing method. <P>SOLUTION: In the thin film transistor 10, a gate electrode 13 is formed at least in one surface of a first gate insulating film 11, and a second gate insulating film 12 whose specific inductive capacity is lower than that of the first gate insulating film is formed in the other surface. A source electrode 14, a drain electrode 14, and a semiconductor film 15, are formed thereon. A resin film is used as the first gate insulating film 11. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  In recent years, the spread of electronic paper, RFID tags, and the like has attracted attention, and a reduction in the price has been demanded. These require transistors. However, the current transistor manufacturing process requires a vacuum process and a photo process, and its manufacturing cost is high. Therefore, in order to make them real, it is necessary to produce them at a lower cost and in a larger amount than conventional transistors. There is also a demand for forming a transistor on a flexible substrate.

  For this reason, a transistor using a printing method, particularly an organic transistor, has attracted attention (for example, see Patent Document 1). This method is attracting attention for the following reasons.

  First, since processing at a low temperature is possible, it is possible to use a resin film as a substrate. Further, since the semiconductor is an organic substance, it can be processed by a printing method using a solution obtained by dissolving the semiconductor in a solvent in the same manner as the printing ink. For this reason, a resin film is used as a base material, and this can be manufactured by a printing method in a so-called roll-to-roll process in which the film is supplied in a roll form to a manufacturing apparatus. Therefore, a large number of transistors can be manufactured at low cost.

  As a method of manufacturing a thin film transistor using an organic substance as a semiconductor, there are many reports using a silicon as a substrate and a thermal oxide film as a gate insulating film for a gate insulating film, and an example using a gate insulating film by a small number of solution processes. However, there are many methods for spin coating. The reason is that in spin coating, it is possible to easily obtain a thin film having a thickness of about 1 micrometer or less necessary for a gate insulating film.

  However, spin coating is difficult to apply to a roll-to-roll process, and it is necessary to form a gate insulating film by other methods. However, in this case, there are the following restrictions.

  That is, when the electrode is formed by the printing method, the screen printing method is optimal at present, but in that case, from the practical viewpoint of avoiding the conductivity and disconnection of the electrode material, the thickness is usually from 10 It is required to be 20 microns.

  Therefore, in this case, that is, when the gate electrode is formed on a predetermined substrate by screen printing, it is necessary to form a gate insulating film on the surface with a uniform film thickness without a pinhole. In order to follow the unevenness of the substrate surface due to the thickness, the thickness of the gate insulating film needs to be the same as that of the gate electrode.

  However, in this case, since the gate insulating film becomes too thick, even if the thin film transistor can be actually formed, the gate voltage for operating the thin film transistor becomes very high, so that it is practically difficult to use.

  As one means for avoiding this, it is conceivable to use a resin film formed in advance as a gate insulating film.

  Non-patent documents 1 and 2 can be cited as research reports on actually producing organic transistors by that means.

  However, in these studies, vacuum processes and photo processes are used for semiconductors and electrodes, resulting in a high-cost transistor manufacturing process. There is no mention of a specific roll-to-roll process.

  On the other hand, it has been pointed out that the form of the semiconductor film formed on the gate insulating film differs depending on the relative dielectric constant of the gate insulating film, and the transistor characteristics obtained are different (Non-Patent Document 3).

  According to Non-Patent Document 3, when the relative dielectric constant of the gate insulating film is high, carriers are localized in the semiconductor film due to the influence of the polarity of the gate insulating film at the interface with the semiconductor film. .

When a resin film is used as the gate insulating film, a polyester film is mainly used because of problems such as cost and thermal stability. In this case, the relative dielectric constant is about 3, and the carriers in the semiconductor film are localized, and the resulting carrier movement The degree is lowered.
JP 2003-249656 A Garnier et al. Science Vol. 265, pages 1884 to 1886 (1994) Bonfiglio et al. Applied Physics Letters Vol. 82, No. 20, pages 3550 to 3552 (2003) Veres et al. Advanced Functional Materials Vol.13, No.3, pages 199 to 204 (2003)

  The present invention has been made in view of such problems, and it is an object of the present invention to provide a thin film transistor and a method of manufacturing the same, which are inexpensive and have an improved insulating property using an insulating film having high insulating properties. .

  According to a first aspect of the present invention, a gate electrode is provided on at least one surface of the first gate insulating film, and a second gate insulating film having a relative dielectric constant lower than that of the first gate insulating film is provided on the other surface. A thin film transistor in which a source electrode, a drain electrode, and a semiconductor film are formed and a resin film is used as the first gate insulating film.

  A second aspect of the present invention is the thin film transistor according to the first aspect, wherein the second gate insulating film has a relative dielectric constant of 1.5 to 2.5.

  A third aspect of the present invention is the thin film transistor according to the first or second aspect, wherein the second gate insulating film is an organic substance.

  The invention described in claim 4 is the thin film transistor according to any one of claims 1 to 3, wherein the second gate insulating film is porous.

  A fifth aspect of the present invention is the thin film transistor according to any one of the first to fourth aspects, wherein the semiconductor is an organic semiconductor.

A sixth aspect of the present invention is the method of manufacturing a thin film transistor according to any one of the first to fifth aspects, wherein a gate electrode is formed on one side of a resin film used as the first gate insulating film, and the resin film is inverted. After that, a second gate insulating film is formed, and a source electrode, a drain electrode, and a semiconductor film are formed on the second gate insulating film.

  According to a seventh aspect of the present invention, in the method for manufacturing a thin film transistor according to any one of the first to fifth aspects, a second gate insulating film is formed on one side of a resin film used as the first gate insulating film, and the second gate insulating film is formed thereon. Forming a gate electrode by forming a source electrode, a drain electrode, and a semiconductor film, and bonding them to the other surface of the resin film so as to face a gate electrode previously provided on another support substrate. The method of manufacturing the thin film transistor is as follows.

  The invention according to claim 8 is a step of unwinding at least a web-like resin film, a gate electrode on one side of the unwound resin film, a second gate insulating film on the other side, a source electrode, a drain electrode, and a semiconductor film And a step of winding the resin film on which the gate electrode, the second gate insulating film, the source electrode, the drain electrode, and the semiconductor film are formed.

  The invention according to claim 9 is the thin film transistor manufacturing method according to any one of claims 1 to 5, wherein at least the step of unwinding the web-like resin film, the second gate insulation on one surface of the unrolled resin film A step of forming a film, a source electrode, a drain electrode, and a semiconductor film, and a step of forming a gate electrode on the other surface of the resin film by facing the gate electrode provided in advance on another supporting substrate. And a step of winding a resin film on which a gate electrode, a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film are formed.

  A tenth aspect of the present invention is the method of manufacturing a thin film transistor according to any one of the sixth to ninth aspects, wherein the second gate insulating film is formed by a coating method.

  The invention described in claim 11 is the method of manufacturing a thin film transistor according to claim 10, wherein the coating method is gravure printing or die coating.

  The invention according to claim 12 is characterized in that at least one of the gate electrode, the source electrode, and the drain electrode is formed by a printing method, and the method of manufacturing a thin film transistor according to any one of claims 6 to 11, It is a thing.

  As described above, according to the present invention, a resin film is used as the first gate insulating film, and the first gate insulating film is formed on one surface of the resin film, that is, the surface on which the semiconductor film is formed. By providing a layer having a relative dielectric constant lower than that of the gate insulating film, a thin film transistor having high transistor characteristics while maintaining high insulation can be obtained, and a method for manufacturing the thin film transistor.

  The material used for the first gate insulating film in the embodiment of the present invention is not particularly limited. Examples of commonly used materials include polyesters such as polyethylene terephthalate (PET) and polyethylene naphthalate (PEN), polyimide, and polyethylene. , Polypropylene, polyethersulfone, polycarbonate and the like. However, polyesters such as PET and PEN are desirable in consideration of cost and thermal stability as described above.

  The first gate insulating film preferably has a thickness in the range of 0.1 to 2 microns. If it exceeds 2 microns, the gate voltage for operating the transistor increases, and if it is 0.1 microns or less, the strength as a film cannot be maintained.

  The material used for the second gate insulating film in the embodiment of the present invention is not particularly limited as long as it has a lower dielectric constant than the resin film used for the first gate insulating film. A material having a ratio of less than 1.5 is difficult to obtain at present, and the dielectric constant is made lower than that of the first gate insulating film, and carriers in the semiconductor film are localized at the interface with the semiconductor film. In order to suppress it, 2.5 or less is desirable. In addition, as a method for reducing the relative permittivity, a porous material containing air may be used. Commonly used materials include fluorinated resins, perfluorocyclic polymers, fluorinated resins such as fluorinated polyimide, polyphenylene oxide resins, amorphous polyolefin resins, syndiotactic polystyrene, etc., but heat resistance, solvent resistance, solution In view of the film formation by coating method, perfluoro cyclic polymer is desirable. As the method for forming the second gate insulating film, a known method such as a dry film forming method such as vapor deposition or sputtering, or a wet film forming method such as gravure printing or die coating can be used.

  The thickness of the second gate insulating film is preferably 1 micron or less. This is because, as described above, when the total thickness of the gate insulating film is thick, the gate voltage when the transistor is operated becomes high. In addition, the second gate insulating film only needs to cover the surface of the first gate insulating film, and thus may have a thickness equal to or greater than that of the monomolecular film.

  In the embodiment of the present invention, the material used as the electrode material is not particularly limited, but generally used materials include metals such as gold, platinum, nickel, and indium tin oxide, or thin films of oxide or poly ( Ethylenedioxythiophene) / polystyrene sulfonate (PEDOT / PSS), conductive polymers such as polyaniline, and solutions in which metal colloidal particles such as gold, silver and nickel are dispersed, or metal particles such as silver, carbon and nickel are used as conductive materials The thick film paste using a solution in which metal colloidal particles are dispersed or the metal particles as a conductive material is preferable in consideration of forming electrodes by a printing method in consideration of cost. In addition, as a method for forming the electrode, a known method such as a film forming method such as vapor deposition or sputtering, or a coating method such as gravure printing, screen printing, or inkjet can be used.

In the embodiment of the present invention, a material used as a semiconductor is not particularly limited, but it is desirable to use an organic semiconductor to which a printing method can be applied in consideration of cost reduction, flexibility, and area increase. That is, high molecular organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymers, and derivatives thereof, and low molecular organic semiconductor materials such as pentacene, tetracene, copper phthalocyanine, perylene, and derivatives thereof. Can be used. Carbon compounds such as carbon nanotubes or fullerenes, semiconductor nanoparticle dispersions, and the like can also be used as semiconductor materials. Furthermore, as the semiconductor layer, an oxide semiconductor such as InGaZnO-based, InGaO-based, ZnGaO-based, InZnO-based, ZnO, or SnO ₂ can be used.

  As a method for printing the organic semiconductor, known methods such as gravure printing, offset printing, screen printing, and inkjet method can be used. In general, since the organic semiconductor has a low solubility in a solvent, it is desirable to use an inkjet method or gravure printing suitable for printing a low viscosity solution.

In addition, a supporting substrate can be further bonded to the thin film transistor of the present invention. As such a supporting base material, a resin film such as polyester, polyimide, polyethylene, polypropylene, polyethersulfone, and polycarbonate can be used, but a polyester film is the best in consideration of cost and thermal stability.

  In the thin film transistor of the present invention, a gate electrode, a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film are formed by the above-described method using a resin film as a first gate insulating film as a base material. . Further, in the present invention, as shown in FIG. 1, a web-like resin film is unwound, and a gate electrode is formed on one surface, and a second gate insulating film, source electrode, drain electrode, and semiconductor film are formed on the other surface. Can be manufactured using a so-called roll-to-roll method.

  Furthermore, as shown in FIG. 3, when forming a gate electrode, a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film on a resin film by a roll-to-roll method, weak adhesion that can be peeled off to the resin film A support having an adhesive layer can be bonded and peeled off after formation.

  Further, as shown in FIG. 5, a web-like resin film is unwound, a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film are formed on one surface, and the other surface is previously placed on another supporting substrate. The gate electrode can also be formed by being attached to face the provided gate electrode.

  Hereinafter, specific description will be given based on examples.

  As shown in FIG. 1, a PEN film having a thickness of 1.2 microns (Teonex Q70 manufactured by Teijin DuPont, relative dielectric constant 2.9) is used as the first gate insulating film 11, and silver and carbon are conductive as the gate electrode 13. Using a thick film paste (manufactured by Asahi Chemical Research Laboratories) as a material, printing was performed with a screen printer 20 and drying was performed with a dryer 23 at 150 ° C. for 30 minutes. Subsequently, as a pretreatment for improving adhesion, the first gate insulating film is treated with oxygen plasma, and the second gate insulating film 12 is a perfluoro cyclic polymer (Cytop, manufactured by Asahi Glass Co., Ltd., having a relative dielectric constant of 2.1). A solution (CTX-805A) dissolved in a system solvent (Asahi Glass Co., Ltd. CT-Solv.180) was formed into a film with a die coater 21 and dried with a dryer 23 at 100 ° C. for 30 minutes to form a film thickness of 0.4 microns. . Argon plasma treatment is performed on the second gate insulating film to improve adhesion and screen printing is performed using a thick film paste (manufactured by Asahi Chemical Research Laboratories) using silver and carbon as the conductive material for the source and drain electrodes 14. It was formed by printing with a machine 20 and drying with a dryer 23 at 150 ° C. for 30 minutes. Thereafter, an anisole solution of poly (3-hexylthiophene) (manufactured by Sigma-Aldrich Japan) was printed as the semiconductor film 15 with the ink jet device 22 and dried at 100 ° C. with the dryer 23. As a result, a resin film is used as the first gate insulating film as shown in FIG. 2, the gate electrode on one side, the second gate insulating film having a relative dielectric constant lower than that of the first gate insulating film on the other side, and the source A thin film transistor 10 in which an electrode, a drain electrode, and a semiconductor film were formed could be formed.

As shown in FIG. 3, a PEN film having a thickness of 1.2 microns (Teonex Q70 manufactured by Teijin DuPont, relative dielectric constant 2.9) is used as the first gate insulating film 11, and a supporting substrate having a thickness of 100 microns is used. A re-peeling adhesive film 16 (PSamar-made by Somar) with a thermal foaming adhesive layer formed on PET and a laminator 24 were attached. The gate electrode 13 is formed by using a thick film paste (manufactured by Asahi Chemical Research Laboratories) using silver and carbon as a conductive material, printed by a screen printer 20 and dried by a dryer 23 at 150 ° C. for 30 minutes. Then, the support base material with the foamed heat foaming adhesive layer was peeled off. Subsequently, an adhesive film 17 (TP300 manufactured by Nitto Denko) as a supporting base material is pasted together with a laminator 24, and then the first gate insulating film is subjected to oxygen plasma treatment as a pretreatment for improving adhesion, thereby providing a second gate insulation. A film (CTX-805A) in which a perfluorocyclic polymer (Cytop from Asahi Glass Co., relative dielectric constant 2.1) is dissolved in a fluorine-based solvent (CT-Solv. 180 manufactured by Asahi Glass Co., Ltd.) is formed into a film by the die coater 21. The film was dried with a dryer 23 at 100 ° C. for 30 minutes to form a film having a thickness of 0.4 microns. Argon plasma treatment is performed on the second gate insulating film to improve adhesion and screen printing is performed using a thick film paste (manufactured by Asahi Chemical Research Laboratories) using silver and carbon as the conductive material for the source and drain electrodes 14. It was formed by printing with a machine 20 and drying with a dryer 23 at 150 ° C. for 30 minutes. Thereafter, an anisole solution of poly (3-hexylthiophene) (manufactured by Sigma-Aldrich Japan) was printed as the semiconductor film 15 with the ink jet device 22 and dried at 100 ° C. with the dryer 23. As a result, a pressure sensitive adhesive film as shown in FIG. 4 is used as a first gate insulating film on a supporting substrate, a gate electrode on one side, and a relative dielectric constant lower than that of the first gate insulating film on the other side. A thin film transistor in which the second gate insulating film, the source electrode, the drain electrode, and the semiconductor film were formed could be formed.

  As shown in FIG. 5, a PEN film having a thickness of 1.2 microns (Teonex Q70 manufactured by Teijin DuPont, relative dielectric constant 2.9) is used as the first gate insulating film 11, and then, the first gate insulating film 11 is used to improve adhesion. As the treatment, the first gate insulating film was subjected to oxygen plasma treatment, and as the second gate insulating film 12, a perfluorocyclic polymer (Cytop manufactured by Asahi Glass Co., relative dielectric constant 2.1) was used as a fluorine-based solvent (CT-Solv. Manufactured by Asahi Glass Co., Ltd.). The solution (CTX-805A) dissolved in 180) was formed into a film with a die coater 21 and dried with a dryer 23 at 100 ° C. for 30 minutes to form a film having a thickness of 0.4 microns. Argon plasma treatment is performed on the second gate insulating film to improve adhesion and screen printing is performed using a thick film paste (manufactured by Asahi Chemical Research Laboratories) using silver and carbon as the conductive material for the source and drain electrodes 14. It was formed by printing with a machine 20 and drying with a dryer 23 at 150 ° C. for 30 minutes. Thereafter, an anisole solution of poly (3-hexylthiophene) (manufactured by Sigma-Aldrich Japan) was printed as the semiconductor film 15 with the ink jet device 22 and dried at 100 ° C. with the dryer 23. On the other hand, a 125 micron thick PEN film (Teonex Q51 made by Teijin DuPont) is used as the support substrate 18, and a thick film paste (made by Asahi Chemical Research Laboratories) using silver and carbon as the conductive material is used as the gate electrode 13. It was formed by printing with a screen printer 20 and drying with a dryer 23 at 150 ° C. for 30 minutes. Subsequently, 0.2 μm of unsaturated polyester (Byron 300 manufactured by Toyobo Co., Ltd.) was applied as an adhesive 19 with a gravure printing machine 25 and dried at 80 ° C. for 20 minutes. Thereafter, the source electrode and the drain electrode formed on the first gate insulating film and the gate electrode on the supporting base material were made to face each other with a laminator. As a result, a gate electrode previously formed on another supporting substrate as shown in FIG. 6 and a second gate insulating film, source electrode, drain electrode, and semiconductor film formed on the first gate insulating film are obtained. A thin film transistor could be fabricated by pasting together.

It is explanatory drawing which shows an example of the manufacturing method of the thin-film transistor of this invention. It is explanatory drawing which showed one example of the thin-film transistor of this invention in the cross section. It is explanatory drawing which shows the other example of the manufacturing method of the thin-film transistor of this invention. It is explanatory drawing which showed the other example of the thin-film transistor of this invention in the cross section. It is explanatory drawing which shows the other example of the manufacturing method of the thin-film transistor of this invention. It is explanatory drawing which showed the other example of the thin-film transistor of this invention in the cross section.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Thin-film transistor 11 ... 1st gate insulating film 12 ... 2nd gate insulating film 13 ... Gate electrode 14 ... Source electrode, drain electrode 15 ... Semiconductor film 16 ... Re-peeling adhesive film 17 ... Adhesive film 18 ... Support base material 19 ... Adhesive 20 ... Screen printer 21 ... Die coater 22 ... Inkjet device 23 ... Dryer 24 ... Laminator 25 ... Gravure printer

Claims (12)

  A gate electrode is formed on at least one surface of the first gate insulating film, and a second gate insulating film having a relative dielectric constant lower than that of the first gate insulating film is formed on the other surface, and a source electrode and a drain electrode are formed thereon. A thin film transistor in which a semiconductor film is formed, wherein a resin film is used as the first gate insulating film.   2. The thin film transistor according to claim 1, wherein a relative dielectric constant of the second gate insulating film is 1.5 to 2.5.   3. The thin film transistor according to claim 1, wherein the second gate insulating film is an organic material.   The thin film transistor according to claim 1, wherein the second gate insulating film is porous.   The thin film transistor according to claim 1, wherein the semiconductor is an organic semiconductor.   6. The method of manufacturing a thin film transistor according to claim 1, wherein a gate electrode is formed on one surface of a resin film used as the first gate insulating film, and the resin film is inverted, and then the second gate insulating film. And a source electrode, a drain electrode, and a semiconductor film are formed thereon.   6. The method of manufacturing a thin film transistor according to claim 1, wherein a second gate insulating film is formed on one side of a resin film used as the first gate insulating film, and a source electrode, a drain electrode, and a semiconductor are formed thereon. A method of manufacturing a thin film transistor, comprising: forming a film, and forming a gate electrode on the other surface of the resin film so as to be opposed to a gate electrode previously provided on another supporting substrate.   A step of unwinding at least a web-like resin film, a step of forming a gate electrode on one side of the unwound resin film, a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film on the other side, a gate electrode, A method for manufacturing a thin film transistor, comprising a step of winding a resin film on which a second gate insulating film, a source electrode, a drain electrode, and a semiconductor film are formed.   6. The method of manufacturing a thin film transistor according to claim 1, wherein at least a step of unwinding the web-shaped resin film, a second gate insulating film, a source electrode, a drain electrode on one surface of the unwound resin film, A step of forming a semiconductor film, a step of forming a gate electrode on the other surface of the resin film by facing a gate electrode provided in advance on another supporting substrate, a gate electrode, and a second gate A method of manufacturing a thin film transistor, comprising a step of winding up a resin film on which an insulating film, a source electrode, a drain electrode, and a semiconductor film are formed.   The method for manufacturing a thin film transistor according to claim 6, wherein the second gate insulating film is formed by a coating method.   The method of manufacturing a thin film transistor according to claim 10, wherein the coating method is gravure printing or die coating.   The method for manufacturing a thin film transistor according to claim 6, wherein at least one of the gate electrode, the source electrode, and the drain electrode is formed by a printing method.