JP2011165947A - Thin film transistor and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor which can improve performance. <P>SOLUTION: A source electrode 4 and a drain electrode 5 are isolated from each other and overlap with an organic semiconductor layer 3. The state of the alignment of organic semiconductor molecules in the organic semiconductor layer 3 is different between portions P1 and P2 with which the source electrode 4 and the drain electrode 5 overlap and a portion P3 with which they do not overlap. The electric resistances R1Y and R2Y of the portions P1 and P2 in the thickness direction of the organic semiconductor layer 3 are smaller than the electric resistance R3Y of the portion P3 in the same direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a thin film transistor including an organic semiconductor layer and an electronic device using the same.

  In recent years, a thin film transistor (TFT) using an organic semiconductor layer as a channel layer has attracted attention and is called an organic TFT. In the organic TFT, since the channel layer can be formed by coating, the cost can be reduced. In addition, since the channel layer can be formed at a temperature lower than that of vapor deposition or the like, the organic TFT can be mounted on a low heat-resistant and flexible plastic film or the like.

  Similar to conventional TFTs (inorganic TFTs using an inorganic semiconductor layer as a channel layer), organic TFTs are widely used in electronic devices such as display devices as switching elements. Along with the organic semiconductor layer, a gate electrode, A source electrode and a drain electrode are provided. Also in this organic TFT, a structure such as a top contact type, a bottom contact type, a top gate type or a bottom gate type is used as in the conventional TFT. In particular, the top contact type in which the source electrode and the drain electrode are disposed so as to overlap the organic semiconductor layer is common.

  In an organic TFT, a current flows from a source electrode to a drain electrode via an organic semiconductor layer, and therefore the ease of current flow in the organic semiconductor layer has a great effect on performance. This is because the mobility and on / off ratio, which are important characteristics (index) of the organic TFT, change according to the electric resistance of the organic semiconductor layer. Therefore, various studies have been made to improve the performance of the organic TFT.

  Specifically, in a bottom contact type organic TFT, an organic molecular thin film (thiocresol) is inserted between the source and drain electrodes and the organic semiconductor layer (see, for example, Patent Document 1). As a result, the crystal grain size of the organic semiconductor layer increases, so that the electrical contact resistance between the source and drain electrodes and the organic semiconductor layer is reduced.

  In a bottom contact type organic TFT, a planarization layer is formed between a source electrode and a drain electrode, and then an organic semiconductor layer is formed on the planar surface (see, for example, Patent Document 2). ). Thereby, since the orientation of the molecular arrangement of the organic semiconductor crystal is improved, the contact resistance between the source and drain electrodes and the organic semiconductor layer is reduced.

JP 2007-158140 A JP 2007-266355 A

  Various electronic devices typified by display devices such as liquid crystal displays, organic electroluminescence (EL) displays, and electronic paper displays have been developed, and there is a strong demand for improving the performance of organic TFTs in order to improve their performance. ing. However, the performance, particularly mobility and on / off ratio, of organic TFTs are still not sufficient, and there is room for improvement.

  The present invention has been made in view of such problems, and an object of the present invention is to provide a thin film transistor and an electronic device capable of improving performance.

  The thin film transistor of the present invention includes an organic semiconductor layer including a plurality of organic semiconductor molecules, and a source electrode and a drain electrode that are separated from each other. The organic semiconductor layer includes a portion that overlaps the source electrode and the drain electrode (overlapping portion) and a portion that does not overlap (non-overlapping portion), and the alignment state of the plurality of organic semiconductor molecules includes an overlapping portion and a non-overlapping portion. Are different. The electronic device of the present invention includes the above-described thin film transistor of the present invention.

  According to the thin film transistor and the electronic device of the present invention, the alignment state of the plurality of organic semiconductor molecules in the organic semiconductor layer is different between the overlapping portion and the non-overlapping portion. This difference in orientation promotes charge injection from the source electrode to the organic semiconductor layer and charge discharge from the organic semiconductor layer to the drain electrode. Therefore, the mobility and the on / off ratio are improved, so that the performance can be improved.

It is sectional drawing showing the structure of the thin-film transistor in one Embodiment of this invention. It is sectional drawing for demonstrating the orientation state of the some organic-semiconductor molecule in an organic-semiconductor layer. It is sectional drawing for demonstrating the manufacturing method (1st manufacturing method) of a thin-film transistor. FIG. 4 is a cross-sectional view for explaining a step following the step in FIG. 3. FIG. 5 is a cross-sectional view for explaining a step following the step in FIG. 4. FIG. 6 is a cross-sectional view for explaining a step following the step in FIG. 5. It is sectional drawing for demonstrating the manufacturing method (2nd manufacturing method) of a thin-film transistor. FIG. 8 is a cross-sectional view for explaining a step following the step in FIG. 7. FIG. 9 is a cross-sectional view for explaining a step following the step in FIG. 8. FIG. 10 is a cross-sectional view for explaining a step following the step in FIG. 9. It is sectional drawing for demonstrating the process following FIG. It is sectional drawing for demonstrating the manufacturing method (3rd manufacturing method) of a thin-film transistor. It is sectional drawing for demonstrating the process following FIG. It is sectional drawing for demonstrating the process following FIG. It is sectional drawing showing the structure of the principal part of the liquid crystal display device which is an application example of a thin-film transistor. FIG. 16 is a diagram illustrating a circuit configuration of the liquid crystal display device illustrated in FIG. 15. It is sectional drawing showing the structure of the principal part of the organic electroluminescence display which is an application example of a thin-film transistor. FIG. 18 is a diagram illustrating a circuit configuration of the organic EL display device illustrated in FIG. 17. It is sectional drawing showing the structure of the principal part of the electronic paper display apparatus which is an application example of a thin-film transistor.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The order of explanation is as follows.

1. 1. Thin film transistor (organic TFT) and manufacturing method thereof Application example of thin film transistor (organic TFT) (electronic equipment)
2-1. Liquid crystal display device 2-2. Organic EL display device 2-3. Electronic paper display device

<1. Organic TFT and manufacturing method thereof>
[Overall structure of organic TFT]
FIG. 1 shows a cross-sectional configuration of an organic TFT which is a thin film transistor according to an embodiment of the present invention.

  In the organic TFT, the organic semiconductor layer 3 is disposed to face the gate electrode 1 through the gate insulating layer 2, and the source electrode 4 and the drain electrode 5 are connected to the organic semiconductor layer 3. The source electrode 4 and the drain electrode 5 are separated (separated) from each other and are disposed so as to overlap the organic semiconductor layer 3, respectively.

  The organic TFT described here is a top contact / bottom gate type in which the gate electrode 1 is located below the organic semiconductor layer 3 and the source electrode 4 and the drain electrode 5 overlap the organic semiconductor layer 3.

The gate electrode 1 is formed of, for example, one or more of a metal material, an inorganic conductive material, an organic conductive material, and a carbon material. Examples of the metal material include aluminum (Al), copper (Cu), molybdenum (Mo), titanium (Ti), chromium (Cr), nickel (Ni), palladium (Pd), gold (Au), and silver (Ag). Platinum (Pt) or an alloy containing them. Examples of the inorganic conductive material include indium oxide (In ₂ O ₃ ), indium tin oxide (ITO), indium zinc oxide (IZO), and zinc oxide (ZnO). The organic conductive material is, for example, polyethylene dioxythiophene (PEDOT) or polystyrene sulfonic acid (PSS). The carbon material is, for example, graphite. Note that the gate electrode 1 may be formed by laminating two or more layers of the various materials described above, and may be laminated such that the gate insulating layer 2, the organic semiconductor layer 3, the source electrode 4 and The same applies to the drain electrode 5.

The gate insulating layer 2 is formed of, for example, one or more of an inorganic insulating material and an organic insulating material. Examples of the inorganic insulating material include silicon oxide (SiO _x ), silicon nitride (SiN _x ), aluminum oxide (AlO _x ), titanium oxide (TiO ₂ ), hafnium oxide (HfO _x ), and barium titanate (BaTiO ₃ ). Etc. Examples of the organic insulating material include polyvinylphenol (PVP), polyimide, polymethacrylic acid acrylate, photosensitive polyimide, photosensitive novolak resin, and polyparaxylylene.

  The organic semiconductor layer 3 includes a plurality of organic semiconductor molecules, and is formed of, for example, one or more of semiconductor materials such as a low molecular material, a soluble low molecular material, or a high molecular material described below. Has been. The low molecular weight material is a material that is generally difficult to dissolve in a solvent. For example, pentacene, anthradithiophene, dinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2-b] thienophene. 2,9-diphenyl-peri-xanthenoxanthene or peri-xanthenoxanthene compounds such as 2,9-dinaphthyl-peri-xanthenoxanthene, or copper phthalocyanine. The soluble low molecular weight material is a material whose solubility is improved by chemically modifying the low molecular weight material, such as 6,13-bis (triisopropylsilylethynyl) pentacene, 2,7-didodecyl [1] benzothieno [ 3,2-b] [1] benzothiophene or 2,9-bis (p-ethylphenyl) -peri-xanthenoxanthene. Examples of the polymer material include α-quaterthiophene, poly- (β-hexylthiophene) or poly (2,5-bis (3-dodecyl-5- (3-dodecylthiophen-2-yl) thiophen-2-yl. ) Thiazolo [5,4-d] thiasol.

In addition, the semiconductor material may be, for example, the following material. Acene compounds such as tetracene, anthracene, 2,9-dimethylpentacene, rubrene or perfluoropentacene. Anthradithiophene compounds such as α, ω-dialkylanthradithiophene. Peri-xanthenoxanthene compounds such as 2,9-bis (p-propylphenyl) -peri-xanthenoxanthene. Naphtho [1,8-bc: 5,4-b′c ′] dithiophene compounds such as 2,6-di (2-naphthyl) naphtho [1,8-bc: 5,4-b′c ′] dithiophene It is. Benzodithiophene compounds such as 2,6-diphenylbenzo [1,2-b: 4,5-b ′] dithiophene. [1] benzothieno [3,2-b] [1] benzothiophene compounds such as 2,7-diphenyl [1] benzothieno [3,2-b] [1] benzothiophene. Oligothiophene and oligoselenophene compounds such as α-quaterselenophene. Β-substituted thiophene polymers and oligomeric compounds such as poly- (3,3 ′ ″-didodecyl silk thiophene). Α, ω-substituted thiophene oligomeric compounds such as α, ω-dihexyl silk water thiophene. Dithiophene) and the like, and thiophene-phenylene oligomers such as 2,5-bis (4-n-hexylphenyl) thiophene, and 5,5′-bis- (7-hexyl). -9H-fluoren-2-yl)-[2,2 ′] bithiophene and other thiophene-fluorene oligomeric compounds such as 6,6′-dihexyl- [2,2 ′] bianthracenyl and other thiophene-acene oligomeric compounds Phthalocyanines such as phthalocyanine or zinc phthalocyanine A down-class compounds. A fullerene compound such as .C ₆₀ is a porphyrin compound such as tetrabenzoporphyrin.

  The organic semiconductor layer 3 does not overlap any of the portion P1 that overlaps the source electrode 4, the portion P2 that overlaps the drain electrode 5, and neither the source electrode 4 nor the drain electrode 5 (between the portions P1 and P2). Part P3). The parts P1, P2 (overlapping part) and the part P3 (non-overlapping part) may be integrated or separated. The term “integrated” refers to a state where the parts P1 to P3 are formed in one step and thus cannot be separated (there is no interface between two adjacent parts). On the other hand, the separation is a state in which the parts P1 to P3 are formed in separate steps and thus can be separated (there is an interface between two adjacent parts). Whether or not the portions P1 to P3 are integrated is determined by an organic TFT manufacturing method (a procedure for forming the organic semiconductor layer 3) described later.

  The source electrode 4 and the drain electrode 5 are made of, for example, the same material as that of the gate electrode 1 described above, and are preferably in ohmic contact with the organic semiconductor layer 3.

  In this organic TFT, a current C flows from the source electrode 4 through the organic semiconductor layer 3 to the drain electrode 5, so that charges move along the flow path. Details of the charge transfer path are as follows. First, charges injected from the source electrode 4 into the organic semiconductor layer 3 (part P1) move downward in the part P1 from the top to the bottom. This lowermost part is a so-called active region of the organic semiconductor layer 3. Subsequently, the electric charge that has reached the lowermost part of the portion P1 moves in the lateral direction at the lowermost part. In this case, the charge moves from the portion P1 to the portion P2 via the portion P3. Finally, the electric charges that have reached the bottom of the portion P2 move upward in the portion P2 from the bottom to the top, and are then discharged from the organic semiconductor layer 3 to the drain electrode 5.

  In this way, when electric charges move inside the organic semiconductor layer 3, two types of electrical resistance are generated. Electrical resistances R1Y and R2Y generated when charges move in the vertical direction (upward or downward) inside the parts P1 and P2, and electrical resistance R3X generated when charges move in the horizontal direction inside the part P3 It is. The electric resistances R1Y and R2Y are electric resistances (so-called bulk resistance) in the thickness direction of the organic semiconductor layer 3, and the electric resistance R3X is an electric resistance (so-called channel resistance) in a direction crossing the thickness direction of the organic semiconductor layer 3. ).

  Details regarding the above-described charge transfer path are reported in Applied Physics Letters by T. Minari et al. (T. Minari et al., Applied Physics Letters 91, p.053508, 2007).

  Note that the organic TFT may include other components other than those described above. Examples of such other components include a substrate that supports an organic TFT. The substrate may be, for example, a substrate such as glass, a plastic material, or a metal material, a film such as a plastic material or a metal material, or paper (general paper). Examples of the plastic material include polyethersulfone (PES), polycarbonate (PC), polyimide (PI), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and polyethyl ether ketone (PEEK). Examples of the metal material include aluminum, nickel, and stainless steel. The surface of the substrate may be provided with various layers such as a buffer layer for ensuring adhesion and a gas barrier layer for preventing gas release.

[Configuration of organic semiconductor layer]
2 shows the orientation state of the organic semiconductor molecules M, (A) shows the organic semiconductor layer 3 shown in FIG. 1, and (B) shows the organic semiconductor layer 103 as a comparative example.

  In the organic semiconductor layer 3, the orientation state (crystallinity) of the organic semiconductor molecule M is different between the portions P1, P2 and the portion P3. In this case, for example, as shown in FIG. 2A, in the portion P3, the orientation state of the organic semiconductor molecules M is regular and the major axis direction is aligned in a predetermined direction. In the portions P1 and P2, the orientation state of the organic semiconductor molecules M may be irregular, and the major axis direction may vary. In FIG. 1, the hatching applied to a part (parts P1, P2) of the organic semiconductor layer 3 indicates that the orientation state of the organic semiconductor molecules M is different from the part P3 in the parts P1, P2. In addition, for example, the alignment state of the organic semiconductor molecules M is regular in the portions P1 to P3, but the alignment method (orientation (tilt) angle, etc.) of the organic semiconductor molecules M is between the portions P1, P2 and the portion P3. May be different.

  In order to examine the orientation state of the organic semiconductor molecule M, the organic semiconductor layer 3 may be observed using various microscopes such as a transmission electron microscope (TEM) or an atomic force microscope (AFM). Further, the organic semiconductor layer 3 may be analyzed using, for example, X-ray diffraction or Raman spectroscopy. From these observations or analyses, it can be confirmed whether the orientation state of the organic semiconductor molecule M is different between the portions P1, P2 and the portion P3. It can also be confirmed whether or not the orientation state is regular.

  Here, when the electric resistance (bulk resistance) R3Y in the thickness direction of the portion P3 is taken into account, the electric resistances R1Y and R2Y of the portions P1 and P2 are the electric resistance of the portion P3 due to the difference in the orientation state of the organic semiconductor molecules M described above. It is smaller than R3Y. This is because charges are less likely to move in the thickness direction in the portion P3, whereas charges are more likely to move in the portions P1 and P2 than in the portion P3 in the thickness direction.

In the organic semiconductor layer 103, the alignment state of the organic semiconductor molecules M is consistent between the portions P1 to P3. For example, as shown in FIG. 2B, the alignment state is regular. In this case, unlike the organic semiconductor layer 3 shown in FIG. 2A, the electric resistances R1Y and R2Y of the portions P1 and P2 are equal to the electric resistance R3Y of the portion P3.
ing.

[Manufacturing method of organic TFT]
Several procedures can be used to produce this organic TFT. 3 to 14 are for explaining a method of manufacturing an organic TFT, and all show a cross-sectional configuration corresponding to FIG. Below, since the formation material of a series of component was already demonstrated, those description is abbreviate | omitted as needed. In addition, the manufacturing method of the organic TFT demonstrated below is an example to the last, and the formation material of each component, a formation method, etc. can be changed suitably.

[First production method]
First, as shown in FIG. 3, the gate electrode 1 is formed. In this case, for example, after forming a metal material layer, a mask (not shown) such as a resist pattern is formed on the metal material layer. Subsequently, after the metal material layer is etched using the mask, the mask is removed using an ashing method or an etching method. Examples of the method for forming the metal material layer include a vacuum film forming method, a coating method, and a plating method. Examples of the vacuum film forming method include a vacuum deposition method, a flash deposition method, a sputtering method, a physical vapor deposition method (PVD), a chemical vapor deposition method (CVD), a pulse laser deposition method (PLD), or an arc discharge method. Etc. Examples of the coating method include spin coating, slit coating, bar coating, and spray coating. Examples of the plating method include an electrolytic plating method and an electroless plating method. In the case of forming a resist pattern, for example, after applying a photoresist to form a photoresist film, the photoresist film is formed using a photolithography method, a laser drawing method, an electron beam drawing method, an X-ray drawing method, or the like. Pattern. However, the resist pattern may be formed using a resist transfer method or the like. The metal material layer etching method is, for example, a dry etching method or a wet etching method using an etchant solution, and the dry etching method is, for example, ion milling or reactive ion etching (RIE). The etching method for removing the mask is the same. In addition, the formation method of the gate electrode 1 may be a printing method such as an inkjet method, a screen printing method, a gravure printing method, or a gravure offset printing method. Further, a metal pattern or the like may be formed instead of the resist pattern as a mask by using a laser ablation method, a mask vapor deposition method, a laser transfer method, or the like. Of course, in order to form the gate electrode 1, an inorganic conductive material layer, an organic conductive material layer, a carbon material layer, or the like may be formed instead of the metal material layer.

  Subsequently, a gate insulating layer 2 is formed so as to cover the gate electrode 1. The formation procedure of the gate insulating layer 2 varies depending on, for example, the forming material. The formation procedure in the case of using an inorganic insulating material is the same as that in the case of forming the gate electrode 1 except that, for example, the coating method may be a sol-gel method. The formation procedure in the case of using the organic insulating material is the same as that in the case of forming the gate electrode 1 except that the photosensitive material may be patterned using, for example, a photolithography method.

  Subsequently, the organic semiconductor layer 6 is formed on the gate insulating layer 2. The organic semiconductor layer 6 is a preparation layer for forming the organic semiconductor layer 3, and the same material as that of the organic semiconductor layer 3 is used as a forming material thereof. In this case, the same procedure as in the case where the gate electrode 1 is formed is used. Specifically, after forming the organic semiconductor layer 6 so as to cover the gate insulating layer 2, the organic semiconductor layer 6 is etched. The formation method of the organic semiconductor layer 6 differs depending on, for example, the formation material. A forming method in the case of using a low molecular material is, for example, a vacuum film forming method similar to that in the case where the gate electrode 1 is formed. The forming method in the case of using a soluble low molecular weight material is, for example, the same vacuum film forming method, coating method, or printing method as in the case of forming the gate electrode 1. A forming method in the case of using a polymer material is, for example, a coating method or a printing method similar to the case where the gate electrode 1 is formed. In general, it is preferable to use a coating method or a printing method when a highly soluble material is used, and to use a vacuum film forming method or the like when a low soluble material or an insoluble material is used. . In the organic semiconductor layer 6, the alignment state of the organic semiconductor molecules M is consistent with the whole as in the organic semiconductor layer 103 shown in FIG.

  Subsequently, a mask (stopper layer) 7 is formed on the organic semiconductor layer 6. In this case, for example, the same procedure as that when the gate electrode 1 is formed is used. Specifically, after forming a layer for forming the mask 7 on the organic semiconductor layer 6, the layer is etched using the resist pattern or the like as a mask. In addition, the mask 7 is aligned so as to be disposed on the portion of the organic semiconductor layer 6 that finally becomes the portion P3. As a material for forming the layer for forming the mask 7, for example, an insulating material such as polyparaxylylene, polyvinyl alcohol (PVA), or silicon oxide is used.

  Subsequently, the organic semiconductor layer 6 is brought into contact with a solvent such as an organic solvent to form the organic semiconductor layer 3 (parts P1 to P3) as shown in FIG. In this case, since only a part of the organic semiconductor layer 6 (the part not covered with the mask 7) is exposed to the solvent, the orientation state of the organic semiconductor molecules in the part changes. Specifically, since a part of the organic semiconductor layer 6 is partly dissolved or swollen by the solvent, the orientation state of the organic semiconductor molecules M is disturbed in that part. The type of the solvent can be arbitrarily selected according to the material for forming the organic semiconductor layer 6. For example, an alcohol such as isopropyl alcohol or ethanol. In addition, acetone or propylene glycol monoether acetate (PGMEA) may be used. In order to bring the organic semiconductor layer 6 into contact with the solvent, the organic semiconductor layer 6 may be immersed in the solvent, or the solvent may be dropped into the organic semiconductor layer 6.

  Details regarding the change in the orientation state of the organic semiconductor molecules by the solvent described above are reported in Applied Physics Letters by D.J. Gundlach et al. (D.J. Gundlach et al., Applied Physics Letters 74, p. 3302, 1999).

  Subsequently, as shown in FIG. 5, an electrode layer 8 is formed so as to cover the organic semiconductor layer 3, the mask 7 and the surrounding gate insulating layer 2. The electrode layer 8 is a preparation layer for forming the source electrode 4 and the drain electrode 5, and the same material as that of the source electrode 4 and the drain electrode 5 is used as a forming material thereof. The method for forming the electrode layer 8 is the same as, for example, when the gate electrode 1 is formed, and a method that hardly damages the organic semiconductor layer 3 is particularly preferable.

  Finally, the electrode layer 8 is selectively etched to form the source electrode 4 and the drain electrode 5 as shown in FIG. In this case, the same procedure as in the case where the gate electrode 1 is formed is used. Specifically, after forming a resist pattern or the like on the electrode layer 8, the electrode layer 8 is etched using the resist pattern as a mask. In particular, the etching method of the electrode layer 8 is preferably, for example, a wet etching method that hardly damages the organic semiconductor layer 3. Thereby, the organic TFT is completed.

  Although the mask 7 used to form the organic semiconductor layer 3 is left until the subsequent steps, the mask 7 may be removed using RIE or wet etching after the organic semiconductor layer 3 is formed. In this case, the thin film transistor shown in FIG. 1 is manufactured. The mask 7 may be removed in this way as in the second and third manufacturing methods described later.

  In addition, the organic semiconductor layer 6 is brought into contact with the solvent in order to change the alignment state of the organic semiconductor molecules, but other methods may be used. Examples of such other methods include a method of exposing the organic semiconductor layer 6 to a solution or gas containing a specific material or irradiating the organic semiconductor layer 6 with a specific light beam. May be. The specific material is, for example, iodine (I) or bromine (Br). The specific light beam is, for example, a laser, an electron beam, an X-ray, an ultraviolet ray, an infrared ray, or visible light. A method of using both in combination is, for example, ultraviolet ozone treatment. In these cases, since a part of the organic semiconductor layer 6 reacts or changes in quality, the alignment state of the organic semiconductor molecules changes in that part.

  Details regarding the change in the orientation state of organic semiconductor molecules due to the specific solution or gas described above are reported in Journal of Applied Physics Letters by T. Minakata et al. (T. Minakata et al., Journal of Applied Physics Letters 69, p.7354, 1991).

  In the first manufacturing method, the organic semiconductor layer 6 that has been subjected to additional treatment with a solvent or the like becomes the organic semiconductor layer 3, and thus the portions P <b> 1 to P <b> 3 are integrated in the organic semiconductor layer 3.

[Second production method]
First, after forming from the gate electrode 1 to the mask 7 by the same procedure as the first manufacturing method (see FIG. 3), as shown in FIG. 7, the organic semiconductor layer 6 is selectively intermediated using the mask 7 as shown in FIG. Etch until. The etching method of the organic semiconductor layer 6 is, for example, the same method as when the gate electrode 1 is formed, such as RIE using an etching gas (reactive gas) or a wet etching method using an etchant solution. In addition, an ultraviolet (UV) ozone method that can etch organic substances at a low speed may be used. In this case, only a part of the organic semiconductor layer 6 (part not covered with the mask 7) reacts with the etching gas or the etchant solution during etching, and the orientation state of the organic semiconductor molecules changes in that part. The kind of etching gas or etchant solution can be arbitrarily selected according to the material for forming the organic semiconductor layer 6. The etching gas is, for example, oxygen (O ₂ ), ozone (O ₃ ), or carbon tetrafluoride (CF ₄ ), and the etchant solution is, for example, toluene or xylene.

  Subsequently, as shown in FIG. 8, an additional organic semiconductor layer 9 is formed to supplement the etched portion of the organic semiconductor layer 6. The additional organic semiconductor layer 9 becomes a part of the organic semiconductor layer 3. The material for forming the additional organic semiconductor layer 9 may be the same material as the organic semiconductor layer 6 or a different material. The method for forming the additional organic semiconductor layer 9 is the same as the method for forming the organic semiconductor layer 6, for example. In this case, conditions such as the film formation temperature or the substrate temperature are controlled so that the orientation state of the organic semiconductor molecules is different from that of the organic semiconductor layer 6 in the additional organic semiconductor layer 9. Thereby, the organic semiconductor layer 3 (parts P1 to P3) including the additional organic semiconductor layer 9 is formed.

  In addition, when forming the additional organic-semiconductor layer 9, you may co-evaporate the formation material with another material. Such other materials are, for example, tetracyanoquinodimethane (TCNQ). In this case, since other materials such as TCNQ act as acceptors, in the additional organic semiconductor layer 9, not only the orientation state of the organic semiconductor molecules is different from that of the organic semiconductor layer 6 but also the electrical resistance is higher than that of the organic semiconductor layer 6. Is also significantly reduced.

  Finally, as shown in FIG. 9, the source electrode 4 and the drain electrode 5 are formed by the same procedure as the first manufacturing method (see FIGS. 5 and 6). Thereby, the organic TFT is completed.

  In addition, after etching a part of the organic semiconductor layer 6 halfway, the additional organic semiconductor layer 9 was formed in order to supplement the etched part. However, the present invention is not limited to this. For example, after part of the organic semiconductor layer 6 is etched, the additional organic semiconductor layer 9 may be formed in order to supplement the etched part. In this case, the organic TFT shown in FIG. 10 is manufactured.

  In addition, although the additional organic semiconductor layer 9 is formed after partially etching the organic semiconductor layer 6, the additional organic semiconductor layer 9 may not be formed. This is because it is not always necessary to form the additional organic semiconductor layer 9 if there are portions P1 and P2 that remain without being etched. In this case, the organic TFT shown in FIG. 11 is formed.

  In the second manufacturing method, since the additional organic semiconductor layer 9 is formed in a separate process from the organic semiconductor layer 6, in the organic semiconductor layer 3, part or all of the parts P1 and P2 are separated from the part P3. .

[Third production method]
First, after forming from the gate electrode 1 to the mask 7 by the same procedure as the second manufacturing method (see FIGS. 3 and 7), the organic semiconductor layer 6 is formed using the mask 7 as shown in FIG. Selectively etch. In this case, a part of the organic semiconductor layer 6 (a part not covered with the mask 7) is completely removed.

  Subsequently, a surface treatment TR is performed on a part of the gate insulating layer 2 (a surface not covered with the mask 7) using the mask 7. The surface treatment TR may be a coating treatment using a solution such as a silane coupling agent, or may be an exposure treatment using a heat vaporized product thereof. In any case, the surface physical properties of the gate insulating layer 2 subjected to the surface treatment TR are modified.

  Subsequently, as shown in FIG. 13, an additional organic semiconductor layer 10 is formed to supplement the etched portion of the organic semiconductor layer 6. This additional organic semiconductor layer 10 becomes a part of the organic semiconductor layer 3, and the same material as that of the organic semiconductor layer 3 is used as a forming material thereof. The material for forming the additional organic semiconductor layer 10 may be the same material as the organic semiconductor layer 6 or a different material. The method for forming the additional organic semiconductor layer 10 is the same as the method for forming the organic semiconductor layer 6, for example. In this case, since the additional organic semiconductor layer 10 is formed on the surface of the gate insulating layer 2 on which the surface treatment TR has been applied, in the additional organic semiconductor layer 10, the orientation state of the organic semiconductor molecules is the organic semiconductor layer 6. And change. Thereby, the organic semiconductor layer 3 including the additional organic semiconductor layer 10 as the portions P1 and P2 is formed.

  Finally, as shown in FIG. 14, the source electrode 4 and the drain electrode 5 are formed by the same procedure as the first manufacturing method (see FIGS. 5 and 6). Thereby, the organic TFT is completed.

  In the third manufacturing method, since the additional organic semiconductor layer 10 is formed in a separate process from the organic semiconductor layer 6, the parts P1 and P2 are separated from the part P3 in the organic semiconductor layer 3.

[Operations and effects of organic TFT and its manufacturing method]
According to the above-described organic TFT and its manufacturing method, as shown in FIGS. 1 and 2A, the orientation state of the organic semiconductor molecules M in the organic semiconductor layer 3 is between the portions P1, P2 and the portion P3. Different. For this reason, the electrical resistances R1Y and R2Y of the portions P1 and P2 are smaller than the electrical resistance R3Y of the portion P3. In this case, since the orientation state of the organic semiconductor molecule M is coincident between the portions P1, P2 and the portion P3, the organic semiconductor layer 103 in which the electrical resistances R1Y and R2Y are equal to the electrical resistance R3Y (FIG. 2B )), The current C easily flows through the organic semiconductor layer 3. Specifically, since the electric resistance R1Y is lower than the electric resistance R3Y, charges are easily injected from the source electrode 4 to the organic semiconductor layer 3. In addition, since the electric resistance R2Y is lower than the electric resistance R3Y, electric charges are easily discharged from the organic semiconductor layer 3 to the drain electrode 5. Thereby, the injection and discharge of charges in the organic semiconductor layer 3 are promoted. Therefore, the mobility and the on / off ratio are improved, so that the performance can be improved.

<2. Application example of organic TFT (electronic equipment)>
Next, application examples of the organic TFT described above will be described. This organic TFT can be applied to several electronic devices, for example, as will be described in order below.

<2-1. Liquid crystal display>
The organic TFT is applied to, for example, a liquid crystal display device. 15 and 16 show a cross-sectional configuration and a circuit configuration of the main part of the liquid crystal display device, respectively. Note that the device configuration (FIG. 15) and circuit configuration (FIG. 16) described below are merely examples, and the configurations can be changed as appropriate.

  The liquid crystal display device described here is, for example, an active matrix driving type transmissive liquid crystal display using organic TFTs, and the organic TFTs are used as elements for switching (pixel selection). In this liquid crystal display device, as shown in FIG. 15, a liquid crystal layer 41 is sealed between a drive substrate 20 and a counter substrate 30.

  The drive substrate 20 has, for example, an organic TFT 22, a planarization insulating layer 23, and a pixel electrode 24 formed in this order on one surface of a support substrate 21, and a plurality of organic TFTs 22 and pixel electrodes 24 arranged in a matrix. It is. However, the number of organic TFTs 22 included in one pixel may be one or two or more. 15 and FIG. 16, for example, shows a case where one organic TFT 22 is included in one pixel.

  The support substrate 21 is made of, for example, a transmissive material such as glass or plastic material, and the organic TFT 22 has the same configuration as the organic TFT described above. The kind of plastic material is the same as that described for the organic TFT, for example, and the same applies to the cases described below. The planarization insulating layer 23 is made of, for example, an insulating resin material such as polyimide, and the pixel electrode 24 is made of, for example, a transmissive conductive material such as ITO. Note that the pixel electrode 24 is connected to the organic TFT 22 through a contact hole (not shown) provided in the planarization insulating layer 23.

  The counter substrate 30 is, for example, one in which the counter electrode 32 is formed on the entire surface of the support substrate 31. The support substrate 31 is made of, for example, a transmissive material such as glass or plastic material, and the counter electrode 32 is made of, for example, a transmissive conductive material such as ITO.

  The drive substrate 20 and the counter substrate 30 are disposed so that the pixel electrode 24 and the counter electrode 32 face each other with the liquid crystal layer 41 interposed therebetween, and are bonded to each other with a sealing material 40. The type of liquid crystal molecules contained in the liquid crystal layer 41 can be arbitrarily selected.

  In addition, the liquid crystal display device may include other components (all not shown) such as a retardation plate, a polarizing plate, an alignment film, and a backlight unit.

  For example, as shown in FIG. 16, the circuit for driving the liquid crystal display device includes a capacitor 45 together with an organic TFT 22 and a liquid crystal display element 44 (an element portion including the pixel electrode 24, the counter electrode 32, and the liquid crystal layer 41). Contains. In this circuit, a plurality of signal lines 42 are arranged in the row direction and a plurality of scanning lines 43 are arranged in the column direction, and the organic TFT 22, the liquid crystal display element 44 and the capacitor 45 are arranged at positions where they intersect. Has been. The connection destination of the source electrode, the gate electrode, and the drain electrode in the organic TFT 22 is not limited to the mode shown in FIG. 16, and can be arbitrarily changed. The signal line 42 and the scanning line 43 are connected to a signal line driving circuit (data driver) and a scanning line driving circuit (scanning driver) (not shown), respectively.

  In this liquid crystal display device, when the liquid crystal display element 44 is selected by the organic TFT 22 and an electric field is applied between the pixel electrode 24 and the counter electrode 32, the alignment of the liquid crystal molecules in the liquid crystal layer 41 according to the electric field strength. The state changes. Thereby, the light transmission amount (transmittance) is controlled in accordance with the alignment state of the liquid crystal molecules, so that a gradation image is displayed.

  According to this liquid crystal display device, since the organic TFT 22 has the same configuration as the above-described organic TFT, its mobility and on / off ratio are improved. Therefore, display performance can be improved. The liquid crystal display device is not limited to the transmissive type, but may be a reflective type.

<2-2. Organic EL display>
The organic TFT is applied to, for example, an organic EL display device. 17 and 18 show a cross-sectional configuration and a circuit configuration of the main part of the organic EL display device, respectively. Note that the device configuration (FIG. 17) and circuit configuration (FIG. 18) described below are merely examples, and the configurations can be changed as appropriate.

  The organic EL display device described here is, for example, an active matrix driving type organic EL display using organic TFTs as switching elements. This organic EL display device has a drive substrate 50 and a counter substrate 60 bonded together with an adhesive layer 70, and is, for example, a top emission type that emits light via the counter substrate 60.

  The drive substrate 50 includes, for example, an organic TFT 52, a protective layer 53, a planarization insulating layer 54, a pixel isolation insulating layer 55, a pixel electrode 56, an organic layer 57, a counter electrode 58, and a protective layer 59 in this order on one surface of the support substrate 51. It is formed. The plurality of organic TFTs 52, the pixel electrodes 56, and the organic layer 57 are arranged in a matrix. However, the number of organic TFTs 52 included in one pixel may be one or two or more. 17 and 18 show a case where two organic TFTs 52 (selection TFT 52A and drive TFT 52B) are included in one pixel, for example.

  The support substrate 51 is formed of, for example, glass or a plastic material. Since light is extracted from the counter substrate 60 in the top emission type, the support substrate 51 may be formed of either a transmissive material or a non-transmissive material. The organic TFT 52 has the same configuration as the organic TFT described above, and the protective layer 53 is formed of a polymer material such as PVA or polyparaxylylene. The planarization insulating layer 54 and the pixel isolation insulating layer 55 are made of an insulating resin material such as polyimide, for example. The pixel isolation insulating layer 55 is preferably formed of a photosensitive resin material that can be formed by photopatterning or reflowing, for example, in order to simplify the formation process and enable the pixel isolation insulating layer 55 to be formed into a desired shape. Note that the planarization insulating layer 54 may be omitted if sufficient planarity is obtained by the protective layer 53.

  The pixel electrode 56 is formed of a reflective material such as aluminum, silver, titanium, or chromium, and the counter electrode 58 is formed of a transparent conductive material such as ITO or IZO. However, it may be formed of a permeable metal material such as calcium (Ca) or an alloy thereof, or a permeable organic conductive material such as PEDOT. The organic layer 57 includes a light emitting layer that generates light such as red, green, or blue, and may have a stacked structure including a hole transport layer, an electron transport layer, and the like as necessary. The material for forming the light emitting layer can be arbitrarily selected according to the color of the light to be generated. The pixel electrode 56 and the organic layer 57 are arranged in a matrix while being separated by the pixel isolation insulating layer 55, whereas the counter electrode 58 is continuous while facing the pixel electrode 56 through the organic layer 57. It extends to. The protective layer 59 is made of a light transmissive dielectric material such as silicon oxide, aluminum oxide, silicon nitride, polyparaxylylene, or urethane. The pixel electrode 56 is connected to the organic TFT 52 through a contact hole (not shown) provided in the protective layer 53 and the planarization insulating layer 54.

  The counter substrate 60 is, for example, one in which a color filter 62 is provided on one surface of a support substrate 61. The support substrate 61 is made of, for example, a transmissive material such as glass or plastic material, and the color filter 62 has a plurality of color regions corresponding to the color of light generated in the organic layer 57. However, the color filter 62 may not be provided.

  The adhesive layer 70 is an adhesive such as a thermosetting resin, for example.

  A circuit for driving the organic EL display device includes, for example, an organic TFT 52 (selection TFT 52A and drive TFT 52B) and an organic EL display element 73 (pixel electrode 56, organic layer 57, and counter electrode as shown in FIG. A capacitor 74 is included. In this circuit, an organic TFT 52, an organic EL display element 73, and a capacitor 74 are arranged at a position where a plurality of signal lines 71 and scanning lines 72 intersect. The connection destination of the source electrode, the gate electrode, and the drain electrode in the selection TFT 52A and the driving TFT 52B is not limited to the mode illustrated in FIG. 18, and can be arbitrarily changed.

  In this organic EL display device, for example, when the organic EL display element 73 is selected by the selection TFT 52A, the organic EL display element 73 is driven by the driving TFT 52B. Accordingly, when an electric field is applied between the pixel electrode 56 and the counter electrode 58, light is generated in the organic layer 57. In this case, for example, red, green, or blue light is generated in each of the three adjacent organic EL display elements 73. Since the combined light of these lights is emitted to the outside via the counter substrate 60, a gradation image is displayed.

  According to this organic EL display device, since the organic TFT 52 has the same configuration as the organic TFT described above, the display performance can be improved in the same manner as the liquid crystal display device.

  The organic EL display device is not limited to the top emission type, but may be a bottom emission type that emits light via the driving substrate 50, or emits light via both the driving substrate 50 and the counter substrate 60. A dual emission type may be used. In this case, of the pixel electrode 56 and the counter electrode 58, the electrode on the side from which light is emitted is formed of a transmissive material, and the electrode on the side from which light is not emitted is formed of a reflective material.

<2-3. Electronic paper display>
The organic TFT is applied to, for example, an electronic paper display device. FIG. 19 illustrates a cross-sectional configuration of the electronic paper display device. The device configuration described below (FIG. 19) and the circuit configuration described with reference to FIG. 16 are merely examples, and the configurations can be changed as appropriate.

  The electronic paper display device described here is, for example, an active matrix drive type electronic paper display using organic TFTs as switching elements. In this electronic paper display device, for example, a driving substrate 80 and a counter substrate 90 including a plurality of electrophoretic elements 93 are bonded together via an adhesive layer 100.

  In the drive substrate 80, for example, an organic TFT 82, a protective layer 83, a planarization insulating layer 84, and a pixel electrode 85 are formed in this order on one surface of the support substrate 81, and a plurality of organic TFTs 82 and the pixel electrodes 85 are arranged in a matrix. It is arranged. The support substrate 81 is made of, for example, glass or plastic material, and the organic TFT 82 has the same configuration as the organic TFT described above. The protective layer 83 and the planarization insulating layer 84 are made of, for example, an insulating resin material such as polyimide, and the pixel electrode 85 is made of, for example, a metal material such as silver (Ag). Note that the pixel electrode 85 is connected to the organic TFT 82 through a contact hole (not shown) provided in the protective layer 83 and the planarization insulating layer 84. Further, the planarization insulating layer 84 may be omitted as long as sufficient planarity is obtained by the protective layer 83.

  In the counter substrate 90, for example, a counter electrode 92 and a layer including a plurality of electrophoretic elements 93 are laminated in this order on one surface of the support substrate 91, and the counter electrode 92 is formed on the entire surface. The support substrate 91 is formed of a transmissive material such as glass or plastic material, and the counter electrode 92 is formed of a transmissive conductive material such as ITO. The electrophoretic element 93 is, for example, one in which charged particles are dispersed in an insulating liquid and are encapsulated in microcapsules. The charged particles include, for example, black particles such as graphite fine particles and white particles such as titanium oxide fine particles.

  In addition, the electronic paper display device may include other components (not shown) such as a color filter, for example.

  A circuit for driving the electronic paper display device has the same configuration as the circuit of the liquid crystal display device shown in FIG. 16, for example. The circuit of the electronic paper display device includes an organic TFT 82 and an electronic paper display element (an element portion including a pixel electrode 85, a counter electrode 92, and an electrophoretic element 93) instead of the organic TFT 22 and the liquid crystal display element 44, respectively.

  In this electronic paper display device, when an electronic paper display element is selected by the organic TFT 82 and an electric field is applied between the pixel electrode 85 and the counter electrode 92, black particles in the electrophoretic element 93 are generated according to the electric field. Alternatively, white particles are attracted to the counter electrode 92. Thereby, since contrast is expressed by the black particles and the white particles, a gradation image is displayed.

  According to this electronic paper display device, since the organic TFT 82 has the same configuration as that of the organic TFT described above, the display performance can be improved in the same manner as the liquid crystal display device.

  The present invention has been described with reference to the embodiment. However, the present invention is not limited to the aspect described in the embodiment, and various modifications can be made. For example, the structure of the thin film transistor of the present invention is not limited to the top contact / bottom gate type, but may be a bottom contact / bottom gate type, a top contact / top gate type, or a bottom contact / top gate type. Taking the bottom contact / top gate type as an example, in this case, after forming the source electrode 4 and the drain electrode 5 and the organic semiconductor layer 3 (parts P1 to P3) in this order, the gate insulating layer 2 and the gate electrode 1 may be formed in this order. Also in these cases, since the source electrode and the drain electrode overlap with the organic semiconductor layer, charge injection from the source electrode to the organic semiconductor layer and charge discharge from the organic semiconductor layer to the drain electrode are promoted. Therefore, the same effect as the top contact / bottom gate type can be obtained.

  In addition, for example, an electronic device to which the thin film transistor of the present invention is applied is not limited to a liquid crystal display device, an organic EL display device, or an electronic paper display device, and may be another display device. Examples of such other display devices include a MEMS (Micro Electro Mechanical Systems) display unit (MEMS type display). Even in this case, the display performance can be improved.

  Furthermore, for example, the thin film transistor of the present invention may be applied to electronic devices other than display devices. Examples of such an electronic device include a sensor matrix, a memory sensor, an RFID tag (Radio Frequency Identification), or a sensor array. Even in this case, the mobility and on / off ratio of the thin film transistor are improved, so that the performance can be improved.

  DESCRIPTION OF SYMBOLS 1 ... Gate electrode, 2 ... Gate insulating layer, 3, 6 ... Organic-semiconductor layer, 4 ... Source electrode, 5 ... Drain electrode, 7 ... Mask, 8 ... Electrode layer, 9, 10 ... Additional organic-semiconductor layer, M ... Organic Semiconductor molecule, P1 to P3... Part, R1Y, R2Y, R3X, R3Y.

Claims (5)

An organic semiconductor layer including a plurality of organic semiconductor molecules, and a source electrode and a drain electrode spaced apart from each other,
The organic semiconductor layer includes a portion that overlaps the source electrode and the drain electrode (overlapping portion) and a portion that does not overlap (non-overlapping portion),
The orientation state of the plurality of organic semiconductor molecules is different between the overlapping portion and the non-overlapping portion.
Thin film transistor.   2. The thin film transistor according to claim 1, wherein the alignment state of the plurality of organic semiconductor molecules is regular in the non-overlapping portion but irregular in the overlapping portion.   The thin film transistor according to claim 1, wherein an electric resistance in a thickness direction of the organic semiconductor layer is smaller in the overlapping portion than in the non-overlapping portion.   The thin film transistor according to claim 1, wherein the overlapping portion and the non-overlapping portion are integrated. A thin film transistor including an organic semiconductor layer including a plurality of organic semiconductor molecules, and a source electrode and a drain electrode spaced apart from each other;
The organic semiconductor layer includes a portion that overlaps the source electrode and the drain electrode (overlapping portion) and a portion that does not overlap (non-overlapping portion),
The orientation state of the plurality of organic semiconductor molecules is different between the overlapping portion and the non-overlapping portion.
Electronics.

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