KR20090106057A - Thin film transistor having active layer with stacking of carbon nano tube layer and organic semiconductor layer and method for fabricating the same - Google Patents

Abstract

PURPOSE: A thin film transistor including an active layer of a structure in which a carbon nano tube layer and an organic semiconductor layer are laminated is provided to reduce an off leakage current and to increase an operating current of a thin film transistor by improving mobility of an electric charge inside the active layer. CONSTITUTION: A thin film transistor includes a gate electrode, a gate insulation layer, an active layer(14), a source electrode, and a drain electrode. The gate electrode is formed on a substrate. The gate insulation layer covers the gate electrode on the substrate. The active layer has a structure in which a carbon nano tube layer and an organic semiconductor layer(25) are laminated on the gate insulation layer. The source electrode and the drain electrode are formed on the active layer, and are separated each other.

Description

A thin film transistor comprising an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are laminated, and a method of manufacturing the same.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a method for manufacturing the same. In particular, a carbon nanotube layer (CNT layer) and an organic semiconductor may be used to improve mobility of charge in an active layer. A thin film transistor (TFT) including an active layer having a structure in which an organic semiconductor layer (OSC layer) is stacked, and a method of manufacturing the same.

Thin Film Transistors (TFTs) are switching devices that operate each pixel in a display device such as an organic light emitting display (OLED) or a liquid crystal display (LCD). Widely used. In general, the thin film transistor includes a gate electrode, a gate insulating layer, an active layer, a source electrode and a drain electrode, and may be classified into an inorganic thin film transistor and an organic thin film transistor according to a material used as an active layer. That is, when the active layer is formed of an inorganic semiconductor layer such as a silicon layer (Si), it is called an inorganic thin film transistor, and the active layer is formed of an organic semiconductor layer, such as pentacene, or an organic semiconductor layer (OSC layer). It is called an organic thin film transistor.

In recent years, interest in organic thin film transistors has increased due to the trend toward larger area, lower cost, and more flexible. In order to form the inorganic semiconductor layer, a high-temperature vacuum processor is required, which leads to a high production cost, and due to the limitation of the process equipment, it is very difficult to form a large area thin film. In addition, when the inorganic thin film transistor is bent, mechanical stress is generated in the active layer formed of the inorganic semiconductor layer, and electrical characteristics of the inorganic thin film transistor are deteriorated due to the generated mechanical stress, or the inorganic thin film transistor does not operate normally. This is because a fatal problem occurs. On the other hand, the organic thin film transistor has an advantage of easily forming a large area thin film using a solution process-based roll-to-roll process. In addition, even when the organic thin film transistor is bent, mechanical stress does not occur in the active layer formed of the organic semiconductor layer.

1 is a cross-sectional view showing a thin film transistor having an active layer made of an organic semiconductor layer according to the prior art.

As shown in FIG. 1, a thin film transistor according to the related art includes a gate electrode 12 formed on a substrate 11, a gate insulating layer 13 formed on a substrate 11, and a gate electrode 12 covered on a substrate 11. It is formed on the insulating layer 13, and includes an active layer 14 made of an organic semiconductor layer, a source electrode 15A and a drain electrode 15B formed on the active layer 14.

However, in the above-described prior art, the organic semiconductor layer constituting the active layer 14 has a very fast movement of charge, electrons or holes in the molecule, but hopping of charges between molecules is hopping. Because of this, there is a problem that the mobility of the charge in the active layer 14 is low. The low charge mobility of the active layer 14 causes a problem of lowering the operating characteristics of the thin film transistor.

The present invention has been proposed to solve the above problems of the prior art, and an object thereof is to provide a thin film transistor and a method of manufacturing the same which can improve the mobility of charge in the active layer.

According to one aspect of the present invention, a thin film transistor includes: a gate electrode formed on a substrate; A gate insulating layer formed on the substrate to cover the gate electrode; An active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked on the gate insulating layer, and a source electrode and a drain electrode formed spaced apart from each other on the active layer.

The carbon nanotube layer is characterized in that semiconductor characteristics are superior to metal characteristics. In addition, the carbon nanotube layer may include any one selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes and bundled carbon nanotubes. In addition, the carbon nanotube layer has a carbon nanotube in the range of 0.5 ~ 1.5 carbon nanotubes per unit area (㎛ ² ), the carbon nanotube has a diameter in the range of 0.8nm ~ 1.4nm and a length in the range of 5㎛ ~ 20㎛ Can have

The organic semiconductor layer may include pentacene (pentacene).

The gate insulating layer is characterized by having a hydrophobic surface. In addition, the gate insulating layer may be a single layer made of an inorganic insulating material or an organic insulating material, or may include a composite layer in which an inorganic insulating material and an organic insulating material are mixed.

The substrate is characterized in that the flexible substrate.

According to another aspect of the present invention, a method of manufacturing a thin film transistor includes: forming a gate electrode on a substrate; Forming a gate insulating layer on the substrate to cover the gate electrode; Forming a carbon nanotube layer on the gate insulating layer; And forming an organic semiconductor layer on the gate insulating layer including the carbon nanotube layer and forming a source electrode and a drain electrode on the organic semiconductor layer.

The forming of the carbon nanotube layer may include preparing a carbon nanotube dispersion solution in which carbon nanotubes are dispersed in a dispersion solution; Applying the carbon nanotube dispersion solution on the gate insulating layer and removing the dispersion solution from the carbon nanotube dispersion solution applied on the gate insulating layer to leave carbon nanotubes on the gate insulating layer. It may include. At this time, the concentration of the carbon nanotubes in the carbon nanotube dispersion solution is characterized in that it is formed to have a range of 25mg / L ~ 35mg / L. In addition, the carbon nanotubes may include any one or two or more selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes and bundled carbon nanotubes. In addition, the carbon nanotubes may use carbon nanotubes having a diameter in the range of 0.8 nm to 1.4 nm and a length in the range of 5 μm to 20 μm.

The coating of the carbon nanotube dispersion solution on the gate insulating layer may be performed to have carbon nanotubes in a range of 0.5 to 1.5 carbon atoms per unit area (μm ² ). In addition, the coating of the carbon nanotube dispersion solution on the gate insulating layer may include spin coating, slit coating, drop casting, dip casting, and dip casting. ), An ink jet method, a printing method, or an imprint method may be used.

The organic semiconductor layer may include pentacene (pentacene).

The gate insulating layer may be formed as a single layer using an inorganic insulating material or an organic insulating material, or may be formed as a composite layer by mixing an inorganic insulating material and an organic insulating material. In addition, when the gate insulating layer is formed using the inorganic insulating material, the polymer coating may be applied on the gate insulating layer or the surface of the gate insulating layer may be formed to be hydrophobic by plasma treatment of the surface of the gate insulating layer. It features.

The thin film transistor of the present invention based on the above-described problem solving means has an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked, whereby the mobility of charge in the active layer can be improved. This has the effect of improving the operating characteristics of the thin film transistor.

In addition, the present invention provides a carbon nanotube layer in which semiconductor characteristics are superior to metal characteristics, thereby improving the mobility of charge in the active layer, thereby increasing the operating current of the thin film transistor and reducing the off leakage current.

In addition, the present invention is provided with a carbon nanotube layer to improve the mobility of the charge in the active layer, there is an effect that can improve the operating characteristics of the thin film transistor without reducing the flexible characteristics of the thin film transistor.

In addition, the present invention has the effect of improving the operating characteristics of the thin film transistor by forming the surface of the gate insulating layer to have a hydrophobicity to improve the interface characteristics between the gate insulating layer and the organic semiconductor layer.

Hereinafter, the most preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention.

The present invention described below includes a charge, electron, or hole in an active layer in a thin film transistor (TFT) including an active layer including an organic semiconductor layer (OSC layer). The present invention provides a thin film transistor and a method of manufacturing the same.

To this end, the present invention is to form an active layer acting as a channel having a structure in which a carbon nanotube layer (CNT layer) and an organic semiconductor layer (OSC layer) is laminated to improve the charge mobility in the active layer On principle. At this time, the active layer has a structure in which an organic semiconductor layer is stacked on a carbon nanotube layer (carbon nanotube / derivative conductor layer), and a structure in which a carbon nanotube layer is laminated on an organic semiconductor layer (derived organic layer / carbon nanotube layer) , A structure in which a carbon nanotube layer is interposed between organic semiconductor layers (oil-based conductor layer / carbon nanotube / oil-based conductor layer) and a structure in which an organic semiconductor layer is interposed between carbon nanotube layers (carbon nanotube layer / derivative semiconductor layer) / Carbon nanotube layer) may be any one selected from the group consisting of.

In the embodiment of the present invention to be described below, a case where the technical principle of the present invention is applied to a thin film transistor having a bottom gate type structure will be described. In addition, the technical principles of the present invention may be equally applicable to thin film transistors having a bottom contact type, a top contact type, or a top gate type. In addition, the structure of the above-described thin film transistor may be partially modified without departing from the object of the present invention.

2A to 2C illustrate a thin film transistor according to an exemplary embodiment of the present invention. 2A is a perspective view and FIG. 2B is a cross-sectional view taken along the line X-X ′ of FIG. 2A. 2C is a plan view for explaining charge transfer in the active layer of the present invention.

As shown in FIGS. 2A and 2B, the thin film transistor according to the exemplary embodiment of the present invention may include a gate electrode 22 formed on the substrate 21 and a gate insulation formed to cover the gate electrode 22 on the substrate 21. Source electrode formed on the active layer 26 and the active layer 26 having a structure in which the carbon nanotube layer (CNT, 24) and the organic semiconductor layer 25 are stacked on the layer 23 and the gate insulating layer 23 27A and the drain electrode 27B.

The substrate 21 may use various materials within a range that does not impair the object of the present invention. For example, a glass substrate, a silicon substrate, an ITO glass, a quartz or a plastic substrate can be used. At this time, when the thin film transistor of the present invention is applied to the flexible device, it is preferable that the substrate 21 uses a flexible substrate having flexible characteristics. Flexible substrates include polycarbon ester (PolyCarbonate, PC), polymethyl methacrylate (PolyMethylMetaAcrlate, PMMA), polydimethylsiloxane (PDMS), polyetherimide (PEI), polyetheretherketone (polyetheretherketone) PEEK), polyimide (PI), polyethersulfone (PES), polyetherimide (PEI), polyester (Polyester, PET), polyethylene naphthalate (PEN) or cyclic olefin copolymer (Cyclic Olefin Copolymer, COC) can be used.

The gate electrode 22, the source electrode 27A, and the drain electrode 27B may be formed of a conductive material, for example, a metal material or a metal compound material. In this case, the gate electrode 22 may be formed to have a thickness in the range of 50 nm to 250 nm, preferably 150 nm. The source electrode 27A and the drain electrode 27B may be formed to have a thickness in the range of 150 nm to 350 nm, preferably 250 nm.

Here, the metal material is gold (Au), silver (Ag), platinum (Pt), chromium (Cr), titanium (Ti), copper (Cu), aluminum (Al), tantalum (Ta), molybdenum (Mo), tungsten (W), nickel (Ni) or palladium (Pd) can be used. The metal compound may be indium tin oxide (ITO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), al doped zinc oxide (AZO), or gallium zinc oxide (GZO).

Here, the source electrode 27A and the drain electrode 27B are conductive materials having a work function similar to that of the organic semiconductor layer 25, for example, 6.02 eV, which is the highest Occupied Molecular Orbital (HOMO) of pentacene. It is preferable to form. For example, the source electrode 27A and the drain electrode 27B may be formed using gold (Au, a work function of 5.01 eV), which is a conductive material having a work function similar to pentacene. As such, the reason for forming the source electrode 27A and the drain electrode 27B using a conductive material having a work function similar to that of the organic semiconductor layer 25 is to lower the potential barrier between them. For sake. The lower the potential barrier between them, the easier the charge transfer between them can improve the electrical properties of the thin film transistor. For reference, HOMO in the organic semiconductor layer 25 means the highest energy of the valence band of the organic semiconductor layer 25, and can be regarded as the same concept as the work function of a general inorganic semiconductor.

In addition, the thin film transistor of the present invention may further include a potential barrier control layer (not shown) interposed between the organic semiconductor layer 25, the source electrode 27A, and the drain electrode 27B. The potential barrier control layer is used to improve charge transfer efficiency between the organic semiconductor layer 25, the source electrode 27A, and the drain electrode 27B, and constitutes the organic semiconductor layer 25. It can be formed using a conductive material having a work function between the work function of the material and the work function of the material constituting the source electrode 27A and the drain electrode 27B (eg, work function <potential of the organic semiconductor layer). Work function of the barrier control layer <work function of the source electrode and the drain electrode, or work function of the organic semiconductor layer> work function of the potential barrier control layer> work function of the source electrode and the drain electrode). Specifically, when the work function difference between the work function of the organic semiconductor layer 25 and the source electrode 27A and the drain electrode 27B is large, a high potential barrier is formed between them, which causes the organic semiconductor layer 25 The charge transfer between the source electrode 27A and the drain electrode 27B becomes difficult. Therefore, by interposing a potential barrier control layer having a work function between the work function of the organic semiconductor layer 25 and the work function of the source electrode 27A and the drain electrode 27B, the charge is transferred to the source electrode 27A. And a scaffold to more easily move from the drain electrode 27B to the organic semiconductor layer 25.

The gate insulating layer 23 may be formed of a single layer made of any one of an inorganic insulating material and an organic insulating material, or may be formed of a composite layer in which an inorganic insulating material and an organic insulating material are mixed. In addition, the gate insulating layer 23 may be formed to have a thickness in the range of 300 nm to 700 nm, preferably 450 nm, based on the top surface of the gate electrode 22.

As the inorganic insulating material, any one selected from the group consisting of oxides, nitrides and oxynitrides can be used. Oxides include silicon oxide (SiO ₂ ), Boron Phosphorus Silicate Glass (BPSG), Phosphorus Silicate Glass (PSG), Tetra Ethyle Ortho Silicate (TEOS), Un-doped Silicate Glass (USG), High Density Plasma , HDP), spin on glass (SOG), or spin on dielectric (SOD) may be used. Silicon nitride (Si ₃ N ₄ ) may be used as the nitride, and silicon oxynitride (SiON) may be used as the oxynitride.

Here, when the gate insulating layer 23 is formed using the inorganic insulating material, it is preferable to use the spin-on glass or the spin-on insulating film among the above-described inorganic insulating materials. Since the spin on glass or the spin on insulating film can be formed based on a solution process, the gate insulating layer 23 can be easily formed at low cost. As a result, the production cost of the thin film transistor may be reduced and manufacturing yield may be improved. Specifically, when the gate insulating layer 23 is formed using spin-on-glass or spin-on-insulating film, spin including any one selected from the group consisting of siloxane, silozne and silicate It is preferable to use a spin-on insulating film containing on glass or polysilazane. For reference, in the solution process, a material to be formed into a thin film is dissolved in a solvent to form a liquid material, and then the liquid material is transferred to a desired position, and then the solvent is removed to form a thin film. to be.

Organic insulating materials include parylene, epoxy, polyimide (PI), polyamide (PA), polyvinyl chloride (PVC), benzocyclobutene (BCB) , Polyvinyl alcohol (polyvinyl alcohol, PVA) polyvinylphenol (polyvinylphenol, PVP) or cyclopentene (cyclopentene, CyPe) can be used.

In addition, the gate insulating layer 23 preferably has a hydrophobic surface. Here, having the hydrophobic surface of the gate insulating layer 23 means that the surface energy of the gate insulating layer 23 is low. More specifically, it means that the surface energy of the gate insulating layer 23 is less than 50mJ / m ² . For reference, although there is a slight difference depending on the type and composition of the thin film, in general, if the surface energy is less than 50mJ / m ² is called a hydrophobic surface, when the surface energy is greater than 50mJ / m ² is called a hydrophilic surface. When the gate insulating layer 23 has a hydrophobic surface, the interfacial characteristics between the active layer 26 formed on the gate insulating layer 23, in particular, the organic semiconductor layer 25 serving as a channel and the gate insulating layer 23. Can improve. If the surface of the gate insulating layer 23 has hydrophilicity, the adhesive strength decreases due to the repulsive force between the gate insulating layer 23 and the organic semiconductor layer 25 having generally hydrophobicity. . When the adhesive force decreases between the gate insulating layer 23 and the organic semiconductor layer 25, there may be a peeling effect of the organic semiconductor layer 25. In addition, when the gate insulating layer 23 has a hydrophilic surface, the interfacial state becomes unstable due to the repulsive force at the interface where the gate insulating layer 23 and the organic semiconductor layer 25 contact each other. There is a fear that a defect occurs at the interface. At this time, when a defect occurs at the interface between the gate insulating layer 23 and the organic semiconductor layer 25, the defect acts as a trap site of the charge, thereby lowering the mobility of the charge in the organic semiconductor layer 25. Let's do it. Therefore, when the surface of the gate insulating layer 23 has a hydrophilic property, for example, when the gate insulating layer 23 is formed using an inorganic insulating material having a hydrophilic property, the surface of the gate insulating layer 23 may be coated with a polymer coating ( It is preferable to remove the hydroxyl group (—OH) present on the surface of the gate insulating layer 23 by performing a polymer coating or by plasma treatment. For reference, when a hydroxyl group exists on the surface of the gate insulating layer 23, the surface of the gate insulating layer 23 is hydrophilic by the hydroxyl group. Therefore, by removing the hydroxyl groups present on the surface of the gate insulating layer 23, the surface of the gate insulating layer 23 can be changed from hydrophilic to hydrophobic.

In addition, the smaller the surface roughness of the gate insulating layer 23, that is, the more flat the surface of the gate insulating layer 23 is. This is because the roughness of the gate insulating layer 23 increases the probability that a defect occurs at an interface between the gate insulating layer 23 and the organic semiconductor layer 25. As mentioned above, when a defect occurs at the interface between the gate insulating layer 23 and the organic semiconductor layer 25, the generated defect acts as a trap site for the charge, so that the mobility of the charge in the organic semiconductor layer 25 is increased. Decreases.

The active layer 26 has a structure in which a carbon nanotube layer 24 and an organic semiconductor layer 25 are stacked. More specifically, the active layer 26 is an organic semiconductor layer 25 formed on the gate insulating layer 23 including the carbon nanotube layer 24 and the carbon nanotube layer 24 formed on the gate insulating layer 23. ). In addition, the active layer 26 has a structure in which a carbon nanotube layer 24 is stacked on the organic semiconductor layer 25 (the organic semiconductor layer 25 / the carbon nanotube layer 24), and the organic semiconductor layer 25. The organic semiconductor layer 25 between the structure in which the carbon nanotube layer 24 is disposed (the organic base layer 25 / carbon nanotube 24 / the organic base layer 25) and the carbon nanotube layer 24. It may be of any one type selected from the group consisting of the published structure (carbon nanotube layer 24 / oil-based conductor layer 25 / carbon nanotube layer 24).

The organic semiconductor layer 25 functions as a channel, ie, providing a movement path of electric charges such as electrons or holes. Here, the organic semiconductor layer 25 may be formed using various materials according to the purpose of use of the thin film transistor or required characteristics. For example, the organic semiconductor layer 25 may be formed of pentacene (pentacene), tip-pentacene (6,13-bis (triisopropylsilylethynyl) pentacene), tetracene (tetracene), anthracene, naphthalene, alpha-6 -Thiophene (α-6-thiophene), alpha-4-thiophene (α-4-thiophene), perylene and its derivatives, rubrene and its derivatives, coronene and its Derivatives, perylene tetracarboxylic diimide and derivatives thereof, perylene tetracarboxylic dianhydride and derivatives thereof, polythiophene and derivatives thereof, polyparaphenyl ((Poly (p-phenylene vinylene) and its derivatives, polyparaphenylene and its derivatives, polyfluorene and its derivatives, polythiophenevinylene and its derivatives, polythiophene-heterocyclic aromatic Copolymers and derivatives thereof, oligoacenes of naphthalene and derivatives thereof, Among oligothiophenes and derivatives thereof of pa-5-thiophene, phthalocyanines and derivatives thereof, with or without metals, pyromellitic dianhydrides and derivatives thereof or pyromellitic diimides and derivatives thereof It may be formed using any one, or may be formed by mixing two or more thereof, but is not necessarily limited thereto.

The tanno nanotube layer 24 may be formed as a network in which a plurality of carbon nanotubes (CNTs) are irregularly connected, and the movement of charge in the active layer 26 also acts as a channel. It serves to improve the mobility of the charge in the organic semiconductor layer (25). This will be described in more detail with reference to FIG. 2C. 2C illustrates the movement of electrons e in the organic semiconductor layer 25 for convenience of description.

As shown in FIG. 2C, the transfer of charge between the molecules 28 and 28 in the active layer 14 consisting of only the organic semiconductor layer of the thin film transistor according to the prior art illustrated in FIG. The charge mobility is very low because the charge moves between the molecules 28 and 28. In contrast, in the present invention, a carbon nanotube layer 24 composed of a network in which a plurality of carbon nanotubes (CNTs) are connected irregularly is electrically connected between the molecules 28 and the molecules 28 in the organic semiconductor layer 25. have. That is, the carbon nanotubes constituting the carbon nanotube layer 24 perform a function of a connecting road for electrically connecting molecules between molecules in the organic semiconductor layer 25. Therefore, the charge transfer between the molecules 28 and 28 in the organic semiconductor layer 25 is not through hopping but through carbon nanotubes (CNTs), so that the charges in the organic semiconductor layer 25 are transferred. Can improve the degree. That is, the mobility of the charge in the active layer 26 can be improved.

Here, the number of carbon nanotubes forming the carbon nanotube layer 24 is increased in order to improve the mobility of charge in the organic semiconductor layer 25 and to reduce the off leakage current of the thin film transistor. It is preferred to have a number ranging from 0.5 to 1.5 per area (1 μm ² ) (see FIG. 5). The reason for this is as follows.

Carbon nanotubes have semiconductor characteristics or metal characteristics depending on the dried form, surface area, etc., and semiconductor characteristics are generally superior. At this time, when there are more than 1.5 carbon nanotubes per unit area in the carbon nanotube layer 24, the total surface area of the carbon nanotubes constituting the carbon nanotube layer 24 increases, thereby making the metal properties superior to the semiconductor properties. . Specifically, even if the carbon nanotube layer 24 is made of carbon nanotubes in which semiconductor characteristics are superior to metal properties, when the carbon nanotube layer 24 exceeds 1.5 per unit area, the total surface area of the carbon nanotubes is increased, thereby increasing the carbon nanotube layer 24. ) Has a higher metal characteristic than semiconductor characteristics. In this case, the off-leakage current of the thin film transistor is increased, thereby deteriorating electrical characteristics of the thin film transistor. On the other hand, if there are less than 0.5 carbon nanotubes per unit area in the carbon nanotube layer 24, the total surface area of the carbon nanotubes constituting the carbon nanotube layer 24 is reduced, resulting in not only metal characteristics but also semiconductor characteristics. As a result, the mobility of charge in the active layer 26 cannot be improved. For reference, as the surface area of the carbon nanotubes increases, the metal properties are superior to the semiconductor properties.

In addition, the carbon nanotube layer 24 is preferably formed using carbon nanotubes having a diameter in the range of 0.8 nm to 1.4 nm. This is because it is determined that the carbon nanotubes have either the semiconductor characteristics or the metal characteristics, depending on the diameter of the carbon nanotubes. Specifically, when the diameter of the carbon nanotubes is less than 0.8 nm, the mobility of the charge in the active layer 26 cannot be improved because the carbon nanotubes do not exhibit not only metal properties but also semiconductor properties. In addition, when the diameter of the carbon nanotube exceeds 1.4 nm, the metal characteristics are superior to the semiconductor characteristics, so that the off-leakage current of the thin film transistor is increased, thereby deteriorating the electrical characteristics of the thin film transistor.

 In addition, the length of the carbon nanotubes constituting the carbon nanotube layer 24 preferably has a length in the range of 5㎛ ~ 20㎛ in order to effectively form a network (network) of irregularly connected carbon nanotubes.

The carbon nanotube layer 24 described above is any one selected from the group consisting of single-walled carbon nanotubes (SWNTs), double-walled carbon nanotubes, multi-walled carbon nanotubes, and bundle carbon nanotubes. These can be mixed and used for formation. Preferably, it is preferable to form the carbon nanotube layer 24 using single-walled carbon nanotubes which can effectively improve the mobility of charge due to the same volume density (surface area).

In summary, the carbon nanotube layer 24 is preferably made of carbon nanotubes in which semiconductor characteristics are superior to metal characteristics. Specifically, the carbon nanotube layer 24 is a semiconductor rather than a metal property by controlling the conditions of any one or two or more of the number of carbon nanotubes per unit area, the diameter of the carbon nanotubes, the length of the carbon nanotubes, or the type of carbon nanotubes. It is preferable to form the carbon nanotube layer 24 so that the characteristic is superior.

As described above, the present invention includes an active layer 26 having a structure in which the carbon nanotube layer 24 and the organic semiconductor layer 25 are stacked, whereby the mobility of charge in the active layer 26 can be improved. As a result, the operating characteristics of the thin film transistor including the active layer 26 including the organic semiconductor material may be improved. This will be described in more detail through the operation principle of the thin film transistor of the present invention having the above-described structure. Here, for convenience of description, the case where the active layer 26 specifically, the organic semiconductor layer 25 has a P-type conductivity is described as an example.

First, when a current flows between the source electrode 27A and the drain electrode 27B, a current proportional to the voltage flows under a low voltage. In this case, when a positive voltage, for example, a voltage of 0 V or more is applied to the gate electrode 22, all holes having positive charges due to the electric field generated by the applied voltage are all organic semiconductors. The upper region of the layer 25, that is, the region of the organic semiconductor layer 25 and the source electrode 27A and the drain electrode 27B is pushed up. That is, the thin film transistor is turned off. Therefore, a depletion layer free of conductive charges is formed in the lower region of the organic semiconductor layer 25, that is, the region adjacent to the interface between the organic semiconductor layer 25 and the gate insulating layer 23. At this time, since the carbon nanotube layer 24 formed on the gate insulating layer 23 also has semiconductor characteristics, a depletion layer is formed in the same manner as the organic semiconductor layer 25 due to the voltage applied to the gate electrode 27. In this situation, even when a voltage is applied between the source electrode 27A and the drain electrode 27B, since a conductable charge is reduced due to the depletion layer, a very small current flows between the source electrode 27A and the drain electrode 27B. If the carbon nanotube layer 24 formed on the gate insulating layer 23 has a higher metal characteristic than the semiconductor characteristic, the lower region of the active layer 26, that is, the gate insulating layer 23 and the organic semiconductor layer 25. Even if the depletion layer is formed at the interface where)), the carbon nanotube layer 24 may flow a lot of current regardless of the depletion layer. That is, the off-leakage current may occur due to the carbon nanotube layer 24, and as a result, electrical characteristics of the thin film transistor may be degraded. Therefore, the carbon nanotube layer 24 is preferably formed so that the semiconductor characteristics are superior to the metal characteristics.

On the contrary, when a negative voltage is applied to the gate electrode 22, a positive charge is induced in the lower region of the organic semiconductor layer 25 adjacent to the gate insulating layer 23 due to the electric field by the applied voltage. Accumulation layer is formed. That is, the thin film transistor is turned on. At this time, since there are many conducting charge carriers between the source electrode 27A and the drain electrode 27B, more current can flow than when the thin film transistor is turned off. In this case, the present invention includes an active layer 26 having a structure in which a carbon nanotube layer 24 and an organic semiconductor layer 25 are stacked, thereby improving the mobility of charge in the active layer 26, thereby operating characteristics of the thin film transistor. Can improve.

Hereinafter, an embodiment of a method of manufacturing a thin film transistor including an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked according to the present invention will be described in detail with reference to the accompanying drawings. In the following process description, known technologies are not described in the descriptions related to the manufacturing method of the thin film transistor or the related film formation method, which means that the technical scope of the present invention is not limited by these known technologies. do.

3A to 3C are cross-sectional views illustrating a method of manufacturing a thin film transistor according to an exemplary embodiment of the present invention.

As shown in FIG. 3A, the gate electrode 22 is formed on the substrate 21. The substrate 21 may use various materials within a range that does not impair the object of the present invention. For example, a glass substrate, a silicon substrate, an ITO glass, a quartz or a plastic substrate can be used. At this time, when the thin film transistor of the present invention is applied to the flexible device, it is preferable that the substrate 21 uses a flexible substrate having flexible characteristics. Flexible substrates include polycarbon ester (PC), polymethyl methacrylate (PolyMethylMetaAcrlate, PMMA), polydimethylsiloxane (PDMS), polyetherimide (PEI), polyetheretherketone (polyetheretherketone) PEEK), polyimide (PI), polyethersulfone (PES), polyetherimide (PEI), polyester (Polyester, PET), polyethylene naphthalate (PEN) or cyclic olefin copolymer (Cyclic Olefin Copolymer, COC) can be used.

The gate electrode 22 may be formed using a conductive material, for example, a metal material or a metal compound material. In addition, the gate electrode 22 may be formed to have a thickness in the range of 50 nm to 250 nm, preferably 150 nm. Here, the metal material is gold (Au), silver (Ag), platinum (Pt), chromium (Cr), titanium (Ti), copper (Cu), aluminum (Al), tantalum (Ta), molybdenum ( Mo), tungsten (W), nickel (Ni) or palladium (Pd) may be used, and the metal compound may be indium tin oxide (ITO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), or AZO ( Al doped Zinc Oxide) or GZO (Gallium Zinc Oxide) may be used.

Here, the gate electrode 22 can be formed using various known methods. For example, a method of forming and then patterning a conductive film on the entire surface of the substrate 21, a method of forming using a metal shadow mask, and forming a photoresist pattern on the substrate 21 and then depositing a conductive film on the entire surface of the substrate 21. It may be formed using a lift-off method for removing the photoresist pattern, printing using a metal paste, or the like.

Next, the gate insulating layer 23 is formed on the substrate 21 to cover the gate electrode 22. The gate insulating layer 23 may be formed as a single layer using either an inorganic insulating material or an organic insulating material, or may be formed as a composite layer using a mixture of an inorganic insulating material and an organic insulating material. In addition, the gate insulating layer 23 may be formed to have a thickness in the range of 300 nm to 700 nm, preferably 450 nm, based on the top surface of the gate electrode 22.

In addition, the gate insulating layer 23 is preferably formed to have a hydrophobic surface. This is to improve the interface characteristics between the active layer to be formed on the gate insulating layer 23, in particular, the organic semiconductor layer and the gate insulating layer 23 through a subsequent process. If the surface of the gate insulating layer 23 has a hydrophilic property-when the surface energy of the gate insulating layer 23 is large and the surface energy is approximately larger than 50 mJ / m ^2- , the gate insulating layer The adhesive strength between (23) and the organic semiconductor layer having a hydrophobic property is generally lowered, and a peeling effect of the organic semiconductor layer may occur. In addition, the interface state between the gate insulating layer 23 and the organic semiconductor layer is unstable, and there is a possibility that defects occur at these interfaces. In this case, a defect generated at an interface between the gate insulating layer 23 and the organic semiconductor layer may act as a trap site to reduce the mobility of charge in the organic semiconductor layer.

In general, since the organic insulating material has hydrophobicity, when the gate insulating layer 23 is formed using the organic insulating material, the gate insulating layer 23 having the hydrophobic surface may be formed without a separate process. On the other hand, since the inorganic insulating material generally has hydrophilicity, when the gate insulating layer 23 is formed using the inorganic insulating material, the surface of the gate insulating layer 23 is formed to have hydrophobicity through a separate process. desirable. For example, a method of forming the surface of the gate insulating layer 23 to have hydrophobicity may include coating a polymer having hydrophobicity on the surface of the gate insulating layer 23, or performing a plasma treatment to perform gate insulation. A method of removing hydroxyl (-OH) present on the surface of layer 23 can be used. For reference, when a hydroxyl group exists on the surface of the gate insulating layer 23, the surface of the gate insulating layer 23 is hydrophilic by the hydroxyl group. Therefore, by removing the hydroxyl groups present on the surface of the gate insulating layer 23, the surface of the gate insulating layer 23 can be changed from hydrophilic to hydrophobic.

In addition, it is preferable to form so that the surface roughness of the gate insulating layer 23 is small. That is, it is preferable to form the surface of the gate insulating layer 23 to be flat. This is because the roughness of the surface of the gate insulating layer 23 increases the probability that a defect occurs at an interface between the gate insulating layer 23 and the organic semiconductor layer to be formed through a subsequent process. As mentioned above, when a defect occurs at an interface between the gate insulating layer 23 and the organic semiconductor layer, the generated defect acts as a trap site to lower the mobility of charge in the organic semiconductor layer.

As the inorganic insulating material that can be used as the gate insulating layer 23, any one selected from the group consisting of oxide, nitride, and oxynitride may be used. Oxides include silicon oxide (SiO ₂ ), Boron Phosphorus Silicate Glass (BPSG), Phosphorus Silicate Glass (PSG), Tetra Ethyle Ortho Silicate (TEOS), Un-doped Silicate Glass (USG), High Density Plasma, HDP), spin on glass (SOG), or spin on dielectric (SOD) may be used. Silicon nitride (Si ₃ N ₄ ) may be used as the nitride, and silicon oxynitride (SiON) may be used as the oxynitride.

Here, when the gate insulating layer 23 is formed using the inorganic insulating material, it is most preferable to use the spin on glass or the spin on insulating film among the above-described inorganic insulating materials. This is because the spin-on glass or the spin-on insulating film can be easily formed at a low cost since it can be formed based on a solution process. Specifically, when the gate insulating layer 23 is formed using spin-on-glass or spin-on-insulating film, spin including any one selected from the group consisting of siloxane, silozne and silicate It is preferable to use a spin-on insulating film containing on glass or polysilazane.

For example, a method of forming the gate insulating layer 23 using the spin-on insulating film will be described in detail as follows.

First, a spin on insulating film is formed on the entire surface of the substrate 21 by using spin coating. The coating composition for this may include a liquid material in which polysilazane is dissolved in a solvent. At this time, the solvent may be an aromatic, aliphatic or ether type solvent. For example, the solvent may be selected from toluene, benzene, benzene, xylene, dibutylether, dibutylether, diethylether, tetrahydrofuran, or hexane. Here, instead of the spin coating method, the slit coating method, the drop casting method, the dip casting method, the ink jet method, the inkjet method, the printing method or the imprint method may be used. Either method may be used to form the spin-on insulating film.

Next, heat treatment is performed to remove the solvent contained in the spin-on insulating film and to form the spin-on insulating film silicon-oxygen (Si-O) network. The heat treatment can be carried out in the air for 1 to 10 minutes at a temperature in the range of 80 ° C. to 230 ° C. using a furnace or hot plate.

Organic insulators that can be used as the gate insulating layer 23 include parylene, epoxy, polyimide (PI), polyamide (PA), and polyvinyl chloride (PVC). , Benzocyclobutene (BCB), polyvinyl alcohol (polyvinyl alcohol, PVA) polyvinylphenol (polyvinylphenol, PVP) or cyclopentene (cyclopentene, CyPe) can be used.

For example, a method of forming the gate insulating layer 23 using polyvinylphenol (PVP) will be described in detail as follows.

First, polyvinylphenol is formed on the entire surface of the substrate 21 by using spin coating. The coating composition for this may include a liquid material in which polyvinylphenol powder is dissolved in a solvent. In this case, PGMEA (propylene glycol monomethyl ether acetate) may be used as the solvent. At this time, the coating composition for forming the polyvinylphenol is more easily formed cross-linking in the polyvinylphenol, cross-linking derivative (cross-) in order to lower the surface energy of the polyvinylphenol linking agent), for example, may further comprise poly melamine-co-formaldehyde methylated. Here, instead of the spin coating method, the slit coating method, the drop casting method, the dip casting method, the ink jet method, the inkjet method, the printing method or the imprint method may be used. Either method may be used to form the polyvinylphenol.

Next, heat treatment is performed to remove the solvent contained in the polyvinylphenol and to form a crosslink in the polyvinyl phenol. The heat treatment can be carried out using a furnace or a hot plate in the atmosphere. For example, when the heat treatment is performed using the furnace, the heat treatment may be performed for a time in the range of 30 minutes to 60 minutes at a temperature in the range of 130 ° C to 170 ° C. When the heat treatment is performed using a hot plate, the heat treatment may be performed at a temperature ranging from 180 ° C. to 220 ° C. for a time ranging from 5 minutes to 10 minutes.

As shown in FIG. 3B, the carbon nanotube layer 24 is formed on the gate insulating layer 23. The carbon nanotube layer 24 may be formed as a network in which a plurality of carbon nanotubes are irregularly connected, and serves to improve the mobility of charge in the organic semiconductor layer to be formed through a subsequent process (FIG. 2c and FIG. 5). In this case, it is preferable that the carbon nanotubes constituting the carbon nanotube layer 24 have superior semiconductor properties than metal properties.

In addition, the carbon nanotube layer 24 is 0.5 to 1.5 per unit area (1 μm ² ) in order to improve the mobility of charge in the organic semiconductor layer to be formed through a subsequent process and to reduce the off leakage current of the thin film transistor. It is preferable to form so as to have a carbon nanotube of a range. Because carbon nanotubes have semiconductor characteristics or metal characteristics depending on the dried form, surface area, etc., generally, semiconductor characteristics are superior to metal characteristics. In this case, when there are more than 1.5 carbon nanotubes per unit area in the carbon nanotube layer 24, the carbon nanotubes constituting the carbon nanotube layer 24 are superior to the metal properties even though the semiconductor characteristics are superior to the metal properties. The total surface area of the carbon nanotubes constituting the layer 24 increases, so that the metal properties are superior to the semiconductor properties. In this case, the off-leakage current of the thin film transistor is increased, thereby deteriorating electrical characteristics of the thin film transistor. On the other hand, if there are less than 0.5 carbon nanotubes per unit area in the carbon nanotube layer 24, the total surface area of the carbon nanotubes constituting the carbon nanotube layer 24 is reduced, resulting in not only metal characteristics but also semiconductor characteristics. Therefore, the mobility of charge in the active layer cannot be improved.

In addition, the carbon nanotube layer 24 is preferably formed using carbon nanotubes having a diameter in the range of 0.8 nm to 1.4 nm. This is because when the diameter of the carbon nanotubes is less than 0.8 nm, the mobility of the charges in the active layer 26 cannot be improved because the carbon nanotubes do not exhibit not only metal characteristics but also semiconductor characteristics. When the diameter of the carbon nanotubes exceeds 1.4 nm, the metal characteristics are superior to those of the semiconductor characteristics, so that the off-leakage current of the thin film transistor may be increased.

 In addition, the length of the carbon nanotubes constituting the carbon nanotube layer 24 preferably has a length in the range of 5㎛ ~ 20㎛ in order to effectively form a network (network) of irregularly connected carbon nanotubes.

In addition, the carbon nanotube layer 24 is any one selected from the group consisting of single-walled carbon nanotubes (SWNT), double-walled carbon nanotubes, multi-walled carbon nanotubes and bundle carbon nanotubes; These can be mixed and used for formation. Preferably, it is preferable to form the carbon nanotube layer 24 using single-walled carbon nanotubes which can effectively improve the mobility of charge due to the same volume density (surface area).

In summary, the carbon nanotube layer 24 is more semiconductor than metal properties by controlling one or more conditions of the number of carbon nanotubes per unit area, the diameter of carbon nanotubes, the length of carbon nanotubes, or the types of carbon nanotubes. It is preferable to form the carbon nanotube layer 24 so that the characteristic is superior.

For example, a method of forming the carbon nanotube layer 24 on the gate insulating layer 23 in which semiconductor characteristics are superior to metal characteristics will be described in detail.

First, a plurality of carbon nanotubes are formed using a known technique such as chemical vapor deposition (CVD). In this case, the carbon nanotubes may be formed of single-walled carbon nanotubes, and may be formed to have a diameter of 0.8 nm to 1.4 nm and a length of 5 μm to 20 μm.

Next, the carbon nanotubes are dispersed in a dispersion solution such as deionized water (DI). This is called a carbon nanotube dispersion solution. At this time, it is preferable to disperse the carbon nanotubes in the dispersion solution so that the concentration of carbon nanotubes in the dispersion solution of carbon nanotubes has a range of 25 mg / L to 35 mg / L. Herein, when the concentration of carbon nanotubes in the dispersion solution of carbon nanotubes is less than 25 mg / l, the number of carbon nanotubes (μm ² ) per unit area of the carbon nanotube layer 24 may be less than 0.5, and carbon nanotubes. When the concentration of the carbon nanotubes in the dispersion solution exceeds 35mg / l, the number of carbon nanotubes (μm ² ) per unit area of the carbon nanotube layer 24 may exceed 1.5.

In order to effectively disperse the carbon nanotubes in the process of forming the carbon nanotube dispersion solution, an appropriate amount of a conventional acid or base may be added or sonication may be performed within a range not impairing the object of the present invention. In addition, one or more other additives such as an organic binder, a photosensitive monomer, a photoinitiator, a viscosity modifier, a storage stabilizer, a humectant, and the like may be further added by those skilled in the art as appropriate depending on the use and need.

Next, a solution in which carbon nanotubes are dispersed is coated on the gate insulating layer 23. In this case, the coating method may be spin coating, slit coating, drop casting, dip casting, ink jet, printing, or the like. Or any method of imprint can be used.

Next, the dispersion solution, for example, deionized water, is removed from the carbon nanotube dispersion solution applied on the gate insulating layer 23 by heat treatment, and the carbon nanotubes are left on the gate insulating layer 23 to remove the carbon nanotube layer. To form (24). At this time, the heat treatment may be carried out in the atmosphere for 10 minutes to 20 minutes at a temperature range of 90 ℃ to 110 ℃ using a furnace (furnace) or hot plate (hot plate).

Meanwhile, the carbon nanotube layer 24 may be formed by directly growing the carbon nanotubes on the gate insulating layer 23 by using chemical vapor deposition without using a carbon nanotube dispersion solution. However, when the carbon nanotubes are grown on the gate insulating layer 23, the following problems may be caused.

First, the growth of carbon nanotubes using chemical vapor deposition generally requires a high temperature, for example, 600 ° C or higher. In such a high temperature environment, a flexible substrate, for example, a plastic substrate, introduced to apply the thin film transistor of the present invention to a flexible device may be damaged. In addition, when the gate insulating layer 23 is formed using an organic insulating material, it may be damaged in the above-described high temperature environment (600 ° C. or higher).

In addition, when growing the carbon nanotubes on the gate insulating layer 23, it is difficult to control the number of (μm ² ) carbon nanotubes per unit area, thereby forming a carbon nanotube layer 24 meeting the object of the present invention. Difficult to do

Therefore, it is not preferable to form the carbon nanotube layer 24 using a method of growing carbon nanobubbles directly on the gate insulating layer 23 using a known technique such as chemical vapor deposition.

As shown in FIG. 3C, the organic semiconductor layer 25 is formed on the gate insulating layer 23 on which the carbon nanotube layer 24 is formed. The organic semiconductor layer 25 functions as a channel, ie, providing a movement path of electric charges such as electrons or holes. Here, the organic semiconductor layer 25 may be formed using various materials according to the purpose of use of the thin film transistor or required characteristics. For example, the organic semiconductor layer 25 may be formed of pentacene (pentacene), tip-pentacene (6,13-bis (triisopropylsilylethynyl) pentacene), tetracene (tetracene), anthracene, naphthalene, alpha-6 -Thiophene (α-6-thiophene), alpha-4-thiophene, perylene and its derivatives, rubrene and its derivatives, coronene and Derivatives thereof, perylene tetracarboxylic diimide and derivatives thereof, perylene tetracarboxylic dianhydride and derivatives thereof, polythiophene and derivatives thereof, polypara Phenylene vinylene ((Poly (p-phenylene vinylene) and its derivatives, polyparaphenylene and its derivatives, polyfluorene and its derivatives, polythiophenevinylene and its derivatives, polythiophene-heterocycle Aromatic copolymers and derivatives thereof, oligoacenes of naphthalene and derivatives thereof, Among oligothiophenes and derivatives thereof of alpha-5-thiophene, phthalocyanines and derivatives thereof, with or without metals, pyromellitic dianhydrides and derivatives thereof or pyromellitic diimides and derivatives thereof It may be formed using any one, or may be formed by mixing two or more thereof, but is not necessarily limited thereto.

In addition, the organic semiconductor layer 25 may be formed using a vacuum deposition method or a roll-to-roll process based on a solution process. Preferably, the organic semiconductor layer 25 may be easily formed at a low cost and easily formed at a low cost. It is good to form using.

Through the above-described process, the active layer 26 in which the carbon nanotube layer 24 and the organic semiconductor layer 25 are stacked may be formed. In this case, the active layer 26 has a structure in which a carbon nanotube layer 24 is stacked on the organic semiconductor layer 25 (in addition to the structure shown in the drawing) (organic base layer 25 / carbon nanotube layer 24), and an organic layer. Between the semiconductor layer 25, a structure in which a carbon nanotube layer 24 is disposed (between the organic base layer 25 / carbon nanotube 24 / organic base layer 25) and the carbon nanotube layer 24 The organic semiconductor layer 25 may be formed in any one form selected from the group consisting of interposed structures (carbon nanotube layer 24 / organic semiconductor layer 25 / carbon nanotube layer 24).

For the convenience of the process, the organic semiconductor layer 25 and the carbon nanotube layer 24 are mixed instead of the stacked structure of the organic semiconductor layer 25 and the carbon nanotube layer 24 described above with the active layer 26 ( The active layer 26 may be formed by mixing. However, when the organic semiconductor layer 25 and the carbon nanotube layer 24 are mixed to form the active layer 26, the number of carbon nanotubes per unit area in the active layer 26, that is, the carbon nanotubes in the active layer 26. The problem arises that it is very difficult to uniformly control the distribution of the tubes. Because carbon nanotubes have a very large surface area, carbon nanotubes have a strong tendency to aggregate with each other. When the carbon nanotubes in the active layer 26 agglomerate with each other, the surface area of the carbon nanotubes increases, so that the metal properties are superior to the semiconductor properties, and thus, the off leakage current of the thin film transistor increases. In addition, the formation method that can be used to form the active layer 26 in which the organic semiconductor layer 25 and the carbon nanotube layer 24 are mixed is limited to the solution process based deposition method. In addition, since the organic semiconductor layer 25 and the carbon nanotube layer 24 must be dispersed in a solvent at the same time, there is a problem that the selection range of a solvent that can be used is also limited. Therefore, it is not preferable to form the active layer 26 by mixing the carbon nanotube layer 24 and the organic semiconductor layer 25.

Next, the source electrode 27A and the drain electrode 27B are formed on the active layer 26. The source electrode 27A and the drain electrode 27B may be formed of a conductive material, for example, a metal material or a metal compound material. The source electrode 27A and the drain electrode 27B may be formed to have a thickness in the range of 150 nm to 350 nm, preferably 250 nm.

Here, the metal material is gold (Au), silver (Ag), platinum (Pt), chromium (Cr), titanium (Ti), copper (Cu), aluminum (Al), tantalum (Ta), molybdenum ( Mo), tungsten (W), nickel (Ni) or palladium (Pd) can be used. The metal compound may be indium tin oxide (ITO), indium zinc oxide (IZO), indium tin zinc oxide (ITZO), al doped zinc oxide (AZO), or gallium zinc oxide (GZO).

Here, the source electrode 27A and the drain electrode 27B can be formed using various known methods. For example, a method of forming a conductive film on the entire surface of the organic semiconductor layer 25 and then patterning, a method of forming using a metal shadow mask, and forming a photoresist pattern on the organic semiconductor layer 25 and then It may be formed using a lift-off method of depositing a conductive film and removing a photoresist pattern, a printing method using a metal paste, or the like.

As described above, the present invention includes an active layer 26 having a structure in which the carbon nanotube layer 24 and the organic semiconductor layer 25 are stacked, whereby the mobility of charge in the active layer 26 can be improved. This has the effect of improving the operating characteristics of the thin film transistor.

In addition, according to the present invention, the carbon nanotube layer 24 is formed so that the semiconductor characteristics are superior to the metal characteristics, thereby improving the mobility of charge in the active layer 26 and suppressing the occurrence of off leakage current. Through this, the operating characteristics of the thin film transistor may be further improved.

In addition, according to the present invention, the surface of the gate insulating layer 23 is formed to have hydrophobicity to improve the interface characteristics between the gate insulating layer 23 and the organic semiconductor layer 25, thereby further improving the operating characteristics of the thin film transistor. It has an effect.

4 is an image bending the thin film transistor formed according to the embodiment of the present invention. Herein, the thin film transistor of the present invention is a case where a flexible substrate is formed based on a flexible substrate in order to be applied to a flexible flat panel display.

As shown in FIG. 4, the thin film transistor of the present invention can be easily formed based on a flexible substrate, and through this, the thin film transistor of the present invention can be confirmed to have flexible characteristics.

In this case, the thin film transistor of the present invention may include a carbon nanotube layer, thereby improving charge mobility in the organic semiconductor layer without degrading the flexible characteristics of the thin film transistor. Through this, the electrical characteristics of the thin film transistor may be improved.

FIG. 5 is an image of a carbon nanotube layer of a thin film transistor formed according to an embodiment of the present invention using an atomic force microscope (AFM).

As shown in Figure 5, the carbon nanotube layer formed in accordance with an embodiment of the present invention can be confirmed that a plurality of carbon nanotubes (CNT) form an irregularly connected network.

In addition, it can be seen that the carbon nanotube layer formed according to the embodiment of the present invention has 0.5 to 1.5 carbon nanotubes formed per unit area (μm ² ). Through this, it can be seen that the carbon nanotube layer formed according to the embodiment of the present invention is formed so that the semiconductor characteristics are superior to the metal characteristics.

6A to 6B are images for explaining gate insulating layer characteristics of a thin film transistor formed according to an exemplary embodiment of the present invention. FIG. 6A is an image for explaining surface energy of a gate insulating layer, and FIG. 6B is a gate insulating layer. The surface of is observed using atomic force microscope. In this case, the gate insulating layer is formed by using polyvinylphenol (PVP) as an example.

As shown in FIG. 6, when deionized water (DI) and ethylene glycol were dropped dropwise onto the gate insulating layer made of polyvinylphenol, the gate insulating layer was separated from the deionized water and ethylene glycol. The surface energy of the gate insulating layer can be obtained using the contact angle (θ) of. Here, the contact angle θ between the gate insulating layer and the deionized water is 69 degrees, and the contact angle θ between the gate insulating layer and ethylene glycol is 48 degrees.

The surface energy of the gate insulating layer may be obtained by substituting the above-described contact angle θ into the following Equation 1.

[Equation 1]

Where 'г _s ' is the surface energy of the gate insulating layer, 'г _r ' is the surface energy of deionized water and ethylene glycol, and the superscripts p and d of the surface energy are polar and dispersion surfaces, respectively. It means energy.

In addition, in order to obtain the surface energy of the gate insulating layer using Equation 1, it is necessary to know the surface energy values of known deionized water and ethylene glycol in addition to the contact angle θ between the gate insulating layer, deionized water and ethylene glycol. Known deionized water has a surface energy value of ^d ~ 21.80 mJ / m ² , and a ^p ~ 51.00 mJ / m ² . And the surface energy value of ethylene glycol is ^{g d} -29.29 mJ / m ² , g ^p ~ 18.91 mJ / m ² .

Using the above values and Equation 1, the surface energy of the gate insulating layer made of polyvinylphenol is 34.40 mJ / m ² . As mentioned earlier in FIGS. 2A-2C, it can generally be said that if the surface energy is 50 mJ / m ² or less, it has a hydrophobic surface.

In summary, since the gate insulating layer made of polyvinylphenol has a hydrophobic surface according to an embodiment of the present invention, peeling phenomenon due to a decrease in adhesion between the gate insulating layer and the organic semiconductor layer can be prevented. In addition, it is possible to stabilize the interface state of the interface between the gate insulating layer and the organic semiconductor layer to prevent the occurrence of defects at the interface between them. Through this, the operating characteristics of the thin film transistor may be improved.

As shown in FIG. 6B, according to the results of observing the gate insulating layer formed of polyvinylphenol according to the embodiment of the present invention using an atomic force microscope, the average roughness of the gate insulating layer formed according to the embodiment of the present invention. of root mean square) is 0.44 nm. In general, considering that the average roughness of the silicon oxide film (SiO ₂ ) formed by thermal oxidation, which is commonly used as a gate insulating layer in a semiconductor device, is 1.08 nm, the gate insulating layer formed according to the embodiment of the present invention is very It can be seen that it is formed flat.

Here, since the gate insulating layer is in contact with an active layer that acts as a channel, specifically, an organic semiconductor layer, it is possible to prevent defects from occurring at the interface between the gate insulating layer and the organic semiconductor layer as the gate insulating layer is flat. Through this, the operating characteristics of the thin film transistor may be improved.

7A to 7B illustrate organic semiconductor layer characteristics of a thin film transistor formed according to an exemplary embodiment of the present invention. FIG. 7A is an image of the surface of the organic semiconductor layer observed using an atomic force microscope (AFM). 7b is a graph showing the results of analyzing the organic semiconductor layer using XRD (X Ray Diffraction). Herein, the organic semiconductor layer is illustrated by using pentacene. For reference, pentacene is an active layer material, and a lot of research has been done, and it is an aromatic hydrocarbon material consisting of five banzen rings.

As shown in FIG. 7A, the organic semiconductor layer formed according to the exemplary embodiment of the present invention may be well formed even though the organic semiconductor layer is formed on the gate insulating layer on which the carbon nanotube layer is formed. The well formed crystal grains of the organic semiconductor layer means excellent molecular cross-packing in the organic semiconductor layer. Molecular density is an indicator that can indirectly explain the mobility of the charge in the organic semiconductor layer. The better the molecular density, the higher the mobility of charge.

As shown in FIG. 7B, when the organic semiconductor layer formed according to the embodiment of the present invention is analyzed using XRD, three peak values may be observed. At this time, the peak at 5.66˚ means that the organic semiconductor layer has a plane direction of (001`) called 'thin film phase', and the peak at 6.06˚ means that the organic semiconductor layer is called 'triclinic bulk phase' ( 001) means the plane direction. These two plane directions ((001`) and (001)) are observed when X-rays of pentacene with well-formed crystal grains are formed, and through this, an organic layer formed on the carbon nanotube layer according to an embodiment of the present invention. This results prove that the crystal grains of the semiconductor layer are well formed.

Here, the peak at 6.80 ° is a peak value irrelevant to the crystal grains of the organic semiconductor layer, and the crystal direction in the lower surface of the organic semiconductor layer in contact with the gate insulating layer due to the carbon nanotube layer is determined to be irregular. This can be inferred from the fact that the peak appears at 1.27 nm from the lower surface of the organic semiconductor layer when the thickness of the thin film is calculated using the peak value shown at 6.80 °. For reference, the carbon nanotube layer formed according to the embodiment of the present invention was formed using carbon nanotubes having a diameter ranging from 0.8 nm to 1.4 nm.

In summary, even though the organic semiconductor layer is formed on the carbon nanotube layer according to the embodiment of the present invention through FIGS. 7A and 7B, it can be seen that the physical properties of the organic semiconductor layer are not deteriorated.

8A is a graph showing the drain current ( _{D D} ) versus the drain voltage (V _D ) of a thin film transistor in which the active layer is formed of only an organic semiconductor layer, and FIG. 8B is a carbon nanotube layer of the present invention. A graph showing a drain current I _D versus a drain voltage V _D of a thin film transistor including an active layer having an organic semiconductor layer stacked thereon. Here, the gate voltage (V _G ) was increased from 0V to -10V and measured to -60V. The remaining thin film transistors except for the active layer are identical to each other.

As shown in FIGS. 8A and 8B, the drain to drain voltage of a thin film transistor including an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked is compared with a thin film transistor in which an active layer is formed of only an organic semiconductor layer. It can be seen that the magnitude of the current is very large. This is because, as described in FIG. 2C, the carbon nanotube layer electrically connects molecules between molecules in the organic semiconductor layer to facilitate charge transfer therebetween. Through this, the present invention can increase the operating current of the thin film transistor.

FIG. 9A is a graph illustrating drain current ( _ID ) vs. gate voltage (V _G ) of a thin film transistor in which an active layer is formed of only an organic semiconductor layer, and FIG. 9B is a carbon nanotube layer of the present invention. A graph showing a drain current I _D versus a gate voltage V _G of a thin film transistor including an active layer having an organic semiconductor layer stacked thereon. In this case, components of the thin film transistors except for the active layer are the same.

As shown in FIGS. 9A and 9B, the gate voltage drain of the thin film transistor including the active layer having the carbon nanotube layer and the organic semiconductor layer laminated according to the present invention is thinner than the thin film transistor including the active semiconductor layer only. It can be seen that the magnitude of the current is larger.

In addition, even though the thin film transistor of the present invention has a carbon nanotube layer, it can be confirmed that the thin film transistor having the same level of open leakage current as the thin film transistor having no carbon nanotube layer.

In addition, it can be seen that the thin film transistor of the present invention has a significantly reduced threshold voltage compared to the thin film transistor in which the active layer is formed of only the organic semiconductor layer. In general, as the threshold voltage decreases, the operating voltage of the thin film transistor can be reduced.

Hereinafter, the active layer shown in FIGS. 8A, 8B, 9A, and 9B through Table 1 includes a thin film transistor including only an organic semiconductor layer, and an active layer in which a carbon nanotube layer and an organic semiconductor layer of the present invention are stacked. The electrical characteristics of the thin film transistor are summarized.

TABLE 1

Active layer Threshold Voltage (V) Operating current (A) Charge Mobility (cm ² / V _S ) Organic semiconductor layer -15.5 1.1 × 10 ^-5 9.7 × 10 ^-2 Carbon nanotube layer / oil based conductor layer -7 2.9 × 10 ^-5 2.6 × 10 ^-1

The threshold voltage values shown in Table 1 were obtained using the slope of the drain current according to the gate voltages shown in FIGS. 9A and 9B. The operating current was calculated using the drain current value in the saturation region in the graph showing the drain current according to the drain voltage shown in FIGS. 8A and 8B. And, the charge mobility (μ) was calculated using the following equation (2).

[Equation 2]

Where 'I _D ' is the drain current (operating current), 'L' is the channel length, 'W' is the channel width, 'C _O ' is the capacitance of the gate insulation layer, 'V _G ' is the gate voltage, and 'V _T 'is the threshold voltage. Specifically, the channel width is 1000 μm, the channel length is 100 μm, and the capacitance of the gate insulating layer is 7.9 nF / cm ² . These were substituted in Equation 2 to obtain a charge mobility μ.

Looking at the charge mobility (μ) obtained through Equation 2 described above, the active layer has an active layer having a structure in which the carbon nanotube layer and the organic semiconductor layer are stacked in comparison to the charge mobility of the thin film transistor including the organic semiconductor layer only. It can be seen that the charge mobility of the thin film transistor is greater.

Although the technical spirit of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will appreciate that various embodiments within the scope of the technical idea of the present invention are possible.

1 is a cross-sectional view showing a thin film transistor having an active layer made of an organic semiconductor layer according to the prior art.

2A is a perspective view illustrating a thin film transistor according to an exemplary embodiment of the present invention.

FIG. 2B is a cross-sectional view of the thin film transistor according to the exemplary embodiment of the present invention along the line X-X ′ of FIG. 2A.

2C is a plan view illustrating movement of charge in an active layer of a thin film transistor according to an exemplary embodiment of the present invention.

3A to 3C are cross-sectional views illustrating a method of manufacturing a thin film transistor according to an exemplary embodiment of the present invention.

4 is an image bending a thin film transistor formed according to an embodiment of the present invention.

5 is an image of a carbon nanotube layer of a thin film transistor formed according to an embodiment of the present invention using an atomic force microscope (AFM).

6A to 6B are views for explaining gate insulating layer characteristics of a thin film transistor formed according to an exemplary embodiment of the present invention.

7A to 7B are views for explaining the characteristics of the organic semiconductor layer of the thin film transistor formed according to the embodiment of the present invention.

Figure 8a is a graph showing the active layer is a drain current (drain current, I _D) for the organic semiconductor layer, only the drain voltage (drain voltage, V _D) consisting of a thin film transistor.

8B is a graph showing the drain current (I _D ) versus the drain voltage (V _D ) of a thin film transistor having an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked.

Figure 9a is a graph showing the active layer is a drain current (drain current, I _D) for a gate voltage of the thin film transistor composed of only an organic semiconductor layer (gate voltage, V _G).

9B is a graph showing the drain current I _D versus the gate voltage V _G of a thin film transistor including an active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked.

* Description of symbols on the main parts of the drawings *

21 substrate 22 gate electrode

23: gate insulating layer 24: carbon nanotube layer

25: organic semiconductor layer 26: active layer

27A: source electrode 27B: gate electrode

28: molecule

Claims (19)

A gate electrode formed on the substrate; A gate insulating layer formed on the substrate to cover the gate electrode; An active layer having a structure in which a carbon nanotube layer and an organic semiconductor layer are stacked on the gate insulating layer; And Source and drain electrodes formed spaced apart from each other on the active layer Thin film transistor comprising a. The method of claim 1, The carbon nanotube layer is a thin film transistor made of carbon nanotubes, the semiconductor characteristics are superior to the metal characteristics. The method of claim 1, The carbon nanotube layer is a thin film transistor including a carbon nanotube in the range of 0.5 to 1.5 per unit area (㎛ ² ). The method of claim 1, The carbon nanotube layer includes any one or two or more selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and bundled carbon nanotubes. The method according to any one of claims 2 to 4, The carbon nanotubes are thin film transistors having a diameter ranging from 0.8 nm to 1.4 nm and a length ranging from 5 μm to 20 μm. The method of claim 1, The organic semiconductor layer is a thin film transistor containing pentacene (pentacene). The method of claim 1, And the gate insulating layer has a hydrophobic surface. The method of claim 7, wherein The gate insulating layer may be a single layer made of an inorganic insulating material or an organic insulating material, or may be a composite layer in which an inorganic insulating material and an organic insulating material are mixed. The method of claim 1, The substrate is a thin film transistor is a flexible substrate. Forming a gate electrode on the substrate; Forming a gate insulating layer on the substrate to cover the gate electrode; Forming a carbon nanotube layer on the gate insulating layer; Forming an organic semiconductor layer on the gate insulating layer including the carbon nanotube layer; And Forming a source electrode and a drain electrode on the organic semiconductor layer Thin film transistor manufacturing method comprising a. The method of claim 10, Forming the carbon nanotube layer, Preparing a carbon nanotube dispersion solution in which carbon nanotubes are dispersed in a dispersion solution; Applying the carbon nanotube dispersion solution on the gate insulating layer; And Removing the dispersion solution from the carbon nanotube dispersion solution applied on the gate insulating layer to leave carbon nanotubes on the gate insulating layer Thin film transistor manufacturing method comprising a. The method of claim 11, The carbon nanotube concentration in the carbon nanotube dispersion solution is a manufacturing method of a thin film transistor having a range of 25mg / l ~ 35mg / l. The method of claim 11, The carbon nanotubes include any one or two or more selected from the group consisting of single-walled carbon nanotubes, double-walled carbon nanotubes, multi-walled carbon nanotubes, and bundle-type carbon nanotubes. The method of claim 11, The carbon nanotube is a thin film transistor using a carbon nanotube having a diameter in the range of 0.8nm ~ 1.4nm and the length of 5㎛ ~ 20㎛ range. The method of claim 11, Applying the carbon nanotube dispersion solution on the gate insulating layer, A method of manufacturing a thin film transistor coated with a carbon nanotube in a range of 0.5 to 1.5 carbon atoms per unit area (μm ² ). The method of claim 11, The coating of the carbon nanotube dispersion solution on the gate insulating layer may include spin coating, slit coating, drop casting, dip casting, A method of manufacturing a thin film transistor, which is carried out using any one of an ink jet method, a printing method, or an imprint method. The method of claim 10, The organic semiconductor layer is a thin film transistor manufacturing method containing pentacene (pentacene). The method of claim 10, The gate insulating layer is formed of a single layer using an inorganic insulating material or an organic insulating material, or a thin film transistor manufacturing method of forming a composite layer by mixing an inorganic insulating material and an organic insulating material. The method of claim 18, When the gate insulating layer is formed using the inorganic insulating material, a thin film transistor is formed to have a polymer coating on the gate insulating layer or to form a surface of the gate insulating layer by performing a plasma treatment on the surface of the gate insulating layer. Way.

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