WO2017208923A1

WO2017208923A1 - Organic thin film transistor and image display device

Info

Publication number: WO2017208923A1
Application number: PCT/JP2017/019327
Authority: WO
Inventors: 典昭池田
Original assignee: 凸版印刷株式会社
Priority date: 2016-05-31
Filing date: 2017-05-24
Publication date: 2017-12-07
Also published as: JPWO2017208923A1

Abstract

Provided are: an organic thin film transistor which is produced with use of a printing method, and which is able to be stably driven by ensuring the capacitance of a capacitor and thereby maintaining the voltage holding ratio even in cases where a sufficient capacitor electrode area is not able to be ensured; and an image display device. This organic thin film transistor has, on an insulating substrate, at least a gate electrode, a capacitor electrode, a first insulating layer that is formed so as to cover at least the gate electrode, a second insulating layer that is formed so as to cover at least a part of the capacitor electrode, a source electrode, a drain electrode and a semiconductor layer that contains an organic semiconductor material. This organic thin film transistor is configured such that the film thickness of the second insulating layer is thinner than the film thickness of the first insulating layer.

Description

Organic thin film transistor and image display device

The present invention relates to an organic thin film transistor and an image display device.

Thin film transistors are widely used in active matrix display devices and sensors such as liquid crystal display devices (LCD), organic electroluminescence (EL) display devices, and electronic paper display devices.

As semiconductor materials used for thin film transistors, those using amorphous silicon, polycrystalline silicon, oxide semiconductors, and the like have become mainstream, and thin film transistors using these semiconductor materials are formed using a vacuum film formation method. In general, after film formation, patterning is performed by a photolithography method or the like.

In recent years, organic thin-film transistors using organic materials as semiconductor layers have attracted attention. In organic thin-film transistors, devices such as semiconductor materials, conductive materials and insulating materials can be formed on plastic substrates at low temperatures by using wet film formation methods such as coating and printing techniques, and at low cost. Since there is a possibility of device manufacturing and the printing method performs film formation and patterning processes at the same time, the material utilization efficiency is high compared to the vacuum film formation process using the conventional photolithography process, and development and etching are performed. Since no process is required, it is also expected to have a low environmental impact.

Japanese Unexamined Patent Publication No. 2015-142091

In the formation of organic thin-film transistors by printing methods, various printing methods are used according to the characteristics of each layer of the thin-film transistors. However, since they are inferior in alignment accuracy and patterning accuracy compared to conventional photolithography processes, transistor manufacturing In consideration of the yield, it is preferable to design with a margin in the dimensions of each layer of the thin film transistor.

However, if the design is made with a sufficient size, the area of the thin film transistor portion becomes large, and it becomes difficult to produce a high-definition thin film transistor pattern. In addition, since the area of the thin film transistor portion is increased, the area of the capacitor electrode that functions as an auxiliary capacitor for driving an active matrix image display device using a thin film transistor is limited, so that it is difficult to obtain a sufficient capacity. It becomes.

In an active matrix image display device, a capacitor installed in a thin film transistor plays a role of assisting voltage holding at the time of writing of each pixel, and if the capacity is insufficient, the voltage holding ratio at the selection time decreases. Measures such as increasing the writing voltage or increasing the number of writings are required, and as a result, the writing time and power consumption of the image display device are increased.

The present invention has been made in view of the above points, and in an organic thin film transistor manufactured using a printing method, even when a sufficient capacitor electrode area cannot be ensured, by securing the capacitance of the capacitor, An object of the present invention is to provide an organic thin film transistor and an image display device which can maintain a voltage holding ratio and can be stably driven.

One aspect of the present invention for solving the above problems includes at least a gate electrode, a capacitor electrode, a first insulating layer formed so as to cover at least the gate electrode, and at least a capacitor electrode on an insulating substrate. An organic thin film transistor having a second insulating layer formed so as to cover a part, a source electrode, a drain electrode, and a semiconductor layer containing an organic semiconductor material, wherein the thickness of the second insulating layer is This is an organic thin film transistor formed thinner than the thickness of one insulating film.

In another aspect of the present invention, at least a gate electrode, a capacitor electrode, a first insulating layer formed to cover at least the gate electrode, and at least a part of the capacitor electrode are formed on an insulating substrate. An organic thin film transistor having a second insulating layer formed to cover, a source electrode, a drain electrode, and a semiconductor layer containing an organic semiconductor material, wherein the dielectric constant of the second insulating layer is the first insulating layer It is an organic thin film transistor having a dielectric constant greater than

The first insulating layer may be formed by stacking two or more insulating materials.

The second insulating layer may be formed by stacking two or more insulating materials.

If the second insulating layer is composed of multiple layers, a part of the layer may be formed of the same material and composition as the first insulating layer.

According to another aspect of the present invention, there is provided a first insulation formed on an insulating substrate so as to cover at least a source electrode, a drain electrode, a semiconductor layer containing an organic semiconductor material, and the source electrode and the semiconductor layer. An organic thin film transistor having a layer, a second insulating layer formed so as to cover at least a part of the drain electrode, a gate electrode, and a capacitor electrode, wherein the second insulating layer has a film thickness of It is an organic thin film transistor characterized by being thinner than the thickness of one insulating layer.

Further, the dielectric constant of the second insulating layer may be larger than the dielectric constant of the first insulating layer.

Further, the first insulating layer may be formed by stacking two or more insulating materials.

Further, another aspect of the present invention is an image display device using the above-described organic thin film transistor.

According to the present invention, in an organic thin film transistor manufactured using a printing method, even when a sufficient capacitor electrode area cannot be secured, the voltage holding ratio is maintained and stabilized by securing the capacitance of the capacitor. Thus, it is possible to provide an organic thin film transistor and an image display device that exhibit device characteristics that can be driven.

FIG. 1 is a schematic cross-sectional view of an organic thin film transistor according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view of an organic thin film transistor according to the second embodiment of the present invention. FIG. 3 is a schematic cross-sectional view of an organic thin film transistor according to the third embodiment of the present invention. FIG. 4 is a schematic cross-sectional view of an organic thin film transistor according to the fourth embodiment of the present invention. FIG. 5 is a schematic cross-sectional view of an organic thin film transistor according to the fifth embodiment of the present invention. FIG. 6 is a schematic cross-sectional view of an organic thin film transistor according to a sixth embodiment of the present invention. FIG. 7 is a schematic cross-sectional view of an organic thin film transistor according to a seventh embodiment of the present invention. FIG. 8 is a schematic cross-sectional view of an organic thin film transistor according to an eighth embodiment of the present invention. FIG. 9 is a schematic cross-sectional view of an organic thin film transistor according to a ninth embodiment of the present invention. FIG. 10 is a schematic cross-sectional view of an organic thin film transistor according to Comparative Example 1. FIG. 11 is a schematic cross-sectional view of an organic thin film transistor according to Comparative Example 2. FIG. 12 is a schematic cross-sectional view of an organic thin film transistor according to Comparative Example 3.

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

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing an organic thin film transistor 100 according to a first embodiment of the present invention.

The organic thin film transistor 100 includes a gate electrode 2 and a capacitor electrode 3 formed on an insulating substrate 1, a first insulating layer 4 formed so as to cover at least the gate electrode 2, and at least one capacitor electrode 3. At least a second insulating layer 5 formed so as to cover the portion, a source electrode 6 and a drain electrode 7, and a semiconductor layer 8 made of an organic semiconductor material. A protective layer 9 for protecting the semiconductor layer 8 is also preferably used.

Further, by providing the organic thin film transistor 100 with the interlayer insulating film 10, the pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a second substrate (not shown), an image display device can be obtained. The structure of the counter electrode and the second substrate can be appropriately changed depending on the type of display element used.

Hereinafter, each component of the organic thin film transistor 100 will be described along the manufacturing process of the organic thin film transistor 100.

First, the substrate 1 is prepared. As the material of the substrate 1, polycarbonate, polyethylene sulfide, polyethersulfone, polyethylene terephthalate, polyethylene naphthalate, cycloolefin polymer, triacetyl cellulose, polyvinyl fluoride film, ethylene-tetrafluoroethylene copolymer resin, weather resistant polyethylene terephthalate, Weatherable polypropylene, glass fiber reinforced acrylic resin film, glass fiber reinforced polycarbonate, polyimide, fluorine resin, cyclic polyolefin resin, glass, quartz glass, and the like can be used, but are not limited thereto. These may be used alone, but can also be used as a composite substrate 1 in which two or more kinds are laminated.

In the case where the substrate 1 is an organic film, a transparent gas barrier layer (not shown) can be formed to improve the durability of the organic thin film transistor 100. Examples of the gas barrier layer include aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC), and diamond-like carbon (DLC). It is not limited to. These gas barrier layers can also be used by laminating two or more layers. The gas barrier layer may be formed only on one side of the substrate 1 using an organic film, or may be formed on both sides. The gas barrier layer can be formed using a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD (Chemical Vapor Deposition) method, a hot wire CVD method, a sol-gel method, and the like. It is not limited to these.

Further, an adhesion layer can be provided in order to improve the adhesion between the gate electrode 2 and the capacitor electrode 3 formed on the substrate 1 and the substrate 1, or surface treatment or the like may be performed on the surface of the substrate 1.

Next, the gate electrode 2 and the capacitor electrode 3 are formed on the substrate 1. The gate electrode 2, the capacitor electrode 3, the source electrode 6, and the drain electrode 7 do not need to be clearly separated from each other in the electrode portion and the wiring portion, and are hereinafter referred to as electrodes as components of each organic thin film transistor.

The gate electrode 2 and the capacitor electrode 3 include aluminum (Al), copper (Cu), molybdenum (Mo), silver (Ag), chromium (Cr), titanium (Ti), gold (Au), platinum (Pt), Metal materials such as tungsten (W) and manganese (Mn), and conductive materials such as indium oxide (InO), tin oxide (SnO), zinc oxide (ZnO), indium tin oxide (ITO), and indium zinc oxide (IZO) Although a metal oxide material can be used, it is not limited to these. These materials may be used as a single layer, or may be used as a laminate or an alloy.

The gate electrode 2 and the capacitor electrode 3 can be formed by vacuum film-forming methods such as vacuum deposition and sputtering, sol-gel methods using precursors of conductive materials, methods using nanoparticles, and the like. A method of forming an ink and forming it by a wet film forming method such as screen printing, letterpress printing, or an ink jet method can be used, but the method is not limited to these, and a known general method can be used. Patterning can be performed by, for example, protecting a pattern forming portion with a resist or the like using a photolithography method and removing an unnecessary portion by etching, or patterning directly using a printing method or the like. Also, the method is not limited to these methods, and a known general patterning method can be used.

Next, a first insulating layer 4 is formed so as to cover at least the gate electrode 2.

The first insulating layer 4 includes oxide-based insulating materials such as silicon oxide (SiOx), aluminum oxide (AlOx), tantalum oxide (TaOx), yttrium oxide (YOx), zirconium oxide (ZrOx), and hafnium oxide (HfOx). Materials, organic insulating materials such as silicon nitride (SiNx), silicon oxynitride (SiON), polyacrylates such as polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylphenol (PVP), and self-assembled films However, the present invention is not limited to these materials. These may be a single layer or a laminate of two or more layers, may be an inorganic-organic hybrid thin film, or may have a composition inclined in the growth direction.

When a self-assembled film is used for the first insulating layer 4, it is possible to control the dielectric constant and insulation of the insulating layer by using a multilayer film structure in which different self-assembled materials are laminated. Furthermore, it is also possible to improve insulation by making a self-assembled multilayer film into a repeated structure. It is also possible to improve the performance of the organic thin film transistor 100 by selecting the functional group on the surface according to the type of the semiconductor layer 8 formed on the surface of the first insulating layer 4 and controlling the surface energy. .

The first insulating layer 4 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 100 and the image display device 200.

Next, the second insulating layer 5 is formed on the capacitor electrode 3. The second insulating layer 5 is formed so as to cover at least a part of the capacitor electrode 3, and forms a capacitor structure by the drain electrode 7 formed so as to overlap the capacitor electrode 3 on the second insulating layer 5. Thus, it functions as a capacitor of an image display device using the organic thin film transistor 100. The formation of the first insulating layer 4 and the second insulating layer 5 is not limited to this order, and the first insulating layer 4 may be formed after the second insulating layer 5 is formed.

The second insulating layer 5 includes oxide-based insulating materials such as silicon oxide (SiOx), aluminum oxide (AlOx), tantalum oxide (TaOx), yttrium oxide (YOx), zirconium oxide (ZrOx), and hafnium oxide (HfOx). Materials, organic insulating materials such as silicon nitride (SiNx), silicon oxynitride (SiON), polyacrylates such as polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyvinylphenol (PVP), and self-assembled films However, the present invention is not limited to these materials. These may be a single layer or a laminate of two or more layers, may be an inorganic-organic hybrid thin film, or may have a composition inclined in the growth direction.

When a self-assembled film is used for the second insulating layer 5, it is possible to control the dielectric constant and insulation of the insulating layer by adopting a multilayer film structure in which different self-assembled materials are laminated. Furthermore, it is also possible to improve insulation by making a self-assembled multilayer film into a repeated structure.

The second insulating layer 5 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 100 and the image display device.

The second insulating layer 5 forms a capacitor structure by insulating the capacitor electrode 3 and the drain electrode 7 in the organic thin film transistor 100. The film thickness of the second insulating layer 5 is the first insulating thickness in order to secure the capacitance of the capacitor. It is preferable to make it thinner than the layer 4. In the organic thin film transistor 100, the second insulating layer 5 is formed to be thinner than the first insulating layer 4, thereby increasing the capacitance of the capacitor while keeping the leakage current in the first insulating layer 4 low. Is possible.

The second insulating layer 5 may use the same material and composition as the first insulating layer 4, or may use different materials and can be formed in various combinations without being limited thereto. It is.

By using a material having a relative dielectric constant higher than that of the first insulating layer 4 as the material of the second insulating layer 5, the capacitance of the capacitor can be increased. The relative dielectric constant of the first insulating layer 4 is preferably 2 or more and 5 or less. The relative dielectric constant of the second insulating layer 5 is 3 or more, preferably 5 or more, and more preferably 20 or more, but is not limited thereto.

The first insulating layer 4 and the second insulating layer 5 are formed using a vacuum film-forming method such as a vacuum deposition method or a sputtering method, a sol-gel method using a metal complex or the like as a precursor, or nanoparticles. For example, a method of forming by a wet coating method such as a slit coating method, a spin coating method, screen printing, letterpress printing, or an ink jet method can be used, but the method is not limited to these, and a known general method can be used. .

Next, the source electrode 6 and the drain electrode 7 are formed on the first insulating layer 4 and the second insulating layer 5. The source electrode 6 and the drain electrode 7 can be formed by the same material and method as the gate electrode 2 and the capacitor electrode 3 described above.

The source electrode 6 and the drain electrode 7 may have a bottom contact structure in which the source electrode 6 and the drain electrode 7 are formed before the semiconductor layer 8, or the source electrode 6 and the drain electrode 7 may be formed after the semiconductor layer 8 is formed. A top contact structure may be formed.

In the case of applying the bottom contact structure, the source electrode 6 and the drain electrode 7 can be subjected to a surface treatment or the like in order to reduce contact resistance in electrical connection with the semiconductor layer 8.

Next, a semiconductor layer 8 is formed on the first insulating layer 4, the source electrode 6 and the drain electrode 7. For the semiconductor layer 8, low molecular semiconductors such as pentacene and derivatives thereof, and polymer organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymers, and derivatives thereof can be used. It is not limited to these.

The semiconductor layer 8 can be formed by a wet film forming method such as letterpress printing, screen printing, ink jet method, or nozzle printing using a solution in which an organic semiconductor material is dissolved or dispersed as ink, but is not limited thereto. Instead, it is also possible to use known general methods.

The organic thin film transistor 100 can be suitably provided with a protective layer 9 for protecting the semiconductor layer 8 from external influences.

When the protective layer 9 is provided, it is preferably formed so as to cover at least the channel region of the semiconductor layer 8.

Examples of the material of the protective layer 9 include inorganic materials such as silicon oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconium oxide, and titanium oxide, or polyacrylates such as PMMA (polymethyl methacrylate), Examples thereof include, but are not limited to, insulating materials such as PVA (polyvinyl alcohol), PVP (polyvinylphenol), and fluorine resins.

About the material of the protective layer 9, in order to suppress the leakage current of the organic thin-film transistor 100 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

The protective layer 9 is formed by any one of an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method using a solution in which the protective layer material or its precursor is dissolved or dispersed. . These protective layers 9 may be used as a single layer or may be used by laminating two or more layers. Further, the composition may be inclined in the growth direction.

In an image display device using the organic thin film transistor 100, an interlayer insulating film 10, a pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a counter substrate (not shown) are preferably provided.

The interlayer insulating film 10 is formed mainly for the purpose of preventing a source-drain leak through the pixel electrode 11 by insulating the source electrode 6 and the pixel electrode 11.

Examples of the material for the interlayer insulating film 10 include inorganic materials such as silicon oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconium oxide, and titanium oxide, or polyacrylates such as PMMA (polymethyl methacrylate). Insulating materials such as PVA (polyvinyl alcohol), PVP (polyvinylphenol), and fluorine-based resins are included, but are not limited thereto.

About the material of the interlayer insulation film 10, in order to suppress the leakage current of the organic thin-film transistor 100 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

The interlayer insulating film 10 is formed by any one of an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method using a solution in which a protective layer material or a precursor thereof is dissolved or dispersed. The These interlayer insulating films 10 may be used as a single layer or may be used by stacking two or more layers. Further, the composition may be inclined in the growth direction.

The pixel electrode 11 is formed for the purpose of improving the aperture ratio of the image display device.

The pixel electrode 11 includes aluminum (Al), copper (Cu), molybdenum (Mo), silver (Ag), chromium (Cr), titanium (Ti), gold (Au), platinum (Pt), tungsten (W), Metal materials such as manganese (Mn) and conductive metal oxide materials such as indium oxide (InO), tin oxide (SnO), zinc oxide (ZnO), indium tin oxide (ITO), and indium zinc oxide (IZO) Although it can be used, it is not limited to these. These materials may be used as a single layer, or may be used as a laminate or an alloy.

The pixel electrode 11 can be formed by vacuum film-forming methods such as vacuum deposition and sputtering, sol-gel methods using a precursor of a conductive material, a method using nanoparticles, screen printing by converting them into ink, A method of forming by a wet film forming method such as letterpress printing or an ink jet method can be used, but the method is not limited to these, and a known general method can be used. Patterning can be performed by, for example, protecting a pattern forming portion with a resist or the like using a photolithography method and removing an unnecessary portion by etching, or patterning directly using a printing method or the like. Also, the method is not limited to these methods, and a known general patterning method can be used.

Also, by using an opaque material for the pixel electrode 11, it is possible to prevent the semiconductor layer 8 from being irradiated with light from the outside.

As the display element, liquid crystal, electrophoretic particles, microcapsules containing electrophoretic particles, organic electroluminescence, or the like can be used. In the image display apparatus, it is possible to use these known general display elements without being limited to either a reflection type or a transmission type. Further, depending on the display element to be used, it is possible to use a configuration in which a plurality of organic thin film transistors 100 are installed in one pixel.

The display element may be formed on the counter substrate on which the counter electrode is formed, and then combined with the organic thin film transistor 100 formed up to the pixel electrode 11 to form an image display device. After the display element is formed on the pixel electrode 11, the counter electrode In addition, an image display device may be formed by laminating a counter substrate, and the process can be selected in accordance with a display element to be used.

(Second Embodiment)
FIG. 2 is a schematic cross-sectional view showing an organic thin film transistor 110 according to a second embodiment of the present invention.

The difference between the organic thin film transistor 100 and the organic thin film transistor 110 is a region where the second insulating layer 5 is formed. As shown in FIG. 2, the second insulating layer 5 is laminated so as to cover the capacitor electrode 3 and the gate electrode 2 simultaneously. The first insulating layer 4 is laminated so as to cover the gate electrode 2 from above the second insulating layer 5.

By forming the first insulating layer 4 and the second insulating layer 5 in this way, the film thickness of the second insulating layer 5 can be reduced as compared with the first insulating layer 4. It is possible to increase the capacitance of the capacitor while keeping the leakage current in the insulating layer 4 low.

(Third embodiment)
FIG. 3 is a schematic sectional view showing an organic thin film transistor 120 according to the third embodiment of the present invention.

The difference between the organic thin film transistor 100 and the organic thin film transistor 120 is the film thickness of the second insulating layer 5 and the material used for the second insulating layer 5. As shown in FIG. 2, the second insulating layer 5 is formed so as to cover the capacitor electrode 3, and the film thickness thereof is the same as that of the first insulating layer 4. The second insulating layer 5 is formed of a material having a higher dielectric constant than that of the first insulating layer 4.

By using a material having a dielectric constant higher than that of the first insulating layer 4 as the material of the second insulating layer 5, the leakage current in the first insulating layer 4 can be kept low even if both films have the same thickness. However, the capacitance of the capacitor can be increased.

(Fourth embodiment)
FIG. 4 is a schematic cross-sectional view showing an organic thin film transistor 130 according to the fourth embodiment of the present invention.

The organic thin film transistor 130 includes a gate electrode 2 and a capacitor electrode 3 formed on an insulating substrate 1, a first insulating layer 4 formed so as to cover at least the gate electrode 2, and at least one capacitor electrode 3. At least a second insulating layer 5 formed so as to cover the portion, a source electrode 6 and a drain electrode 7, and a semiconductor layer 8 containing an organic semiconductor material. A protective layer 9 for protecting the semiconductor layer 8 is also preferably used.

Further, by providing the organic thin film transistor 130 with the interlayer insulating film 10, the pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a second substrate (not shown), an image display device can be obtained. . The structures of the counter electrode and the second substrate can be appropriately changed depending on the type of display element used.

Hereinafter, each component of the organic thin film transistor 130 will be described along the manufacturing process of the organic thin film transistor 130.

When the substrate 1 is an organic film, a transparent gas barrier layer (not shown) can be formed in order to improve the durability of the organic thin film transistor 130. Examples of the gas barrier layer include aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC), diamond-like carbon (DLC), and the like. However, it is not limited to these. These gas barrier layers can be used by laminating two or more layers. The gas barrier layer may be formed only on one side of the substrate 1 using an organic film, or may be formed on both sides. The gas barrier layer can be formed using a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD (Chemical Vapor Deposition) method, a hot wire CVD method, a sol-gel method, etc. It is not limited to these.

In addition, an adhesion layer can be provided in order to improve the adhesion between the gate electrode 2 and the capacitor electrode 3 formed on the substrate 1 and the substrate 1, or the surface of the substrate 1 may be subjected to a surface treatment or the like. .

Next, the gate electrode 2 and the capacitor electrode 3 are formed on the substrate 1. The gate electrode 2, the capacitor electrode 3, the source electrode 6, and the drain electrode 7 do not need to be clearly separated from each other in the electrode portion and the wiring portion, and are hereinafter referred to as electrodes as components of each organic thin film transistor. .

When a self-assembled film is used for the first insulating layer 4, it is possible to control the dielectric constant and insulation of the insulating layer by using a multilayer film structure in which different self-assembled materials are laminated. Furthermore, it is also possible to improve insulation by making a self-assembled multilayer film into a repeated structure. It is also possible to improve the performance of the organic thin film transistor 130 by selecting the surface functional group according to the type of the semiconductor layer 8 formed on the surface of the first insulating layer 4 and controlling the surface energy. is there.

The first insulating layer 4 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 130 and the image display device.

Next, the second insulating layer 5 is formed on the capacitor electrode 3. The second insulating layer 5 is formed so as to cover at least a part of the capacitor electrode 3, and forms a capacitor structure by the drain electrode 7 formed so as to overlap the capacitor electrode 3 on the second insulating layer 5. Thus, it functions as a voltage holding capacitor of an image display device using the organic thin film transistor 130. The formation of the first insulating layer 4 and the second insulating layer 5 is not limited to this order, and the first insulating layer 4 may be formed after the second insulating layer 5 is formed.

The second insulating layer 5 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 130 and the image display device.

The second insulating layer 5 forms a capacitor structure by insulating the capacitor electrode 3 and the drain electrode 7 in the organic thin film transistor 130, and in order to secure the capacitance of the capacitor, the dielectric constant thereof is changed to the first insulating layer. It is preferable to make it larger than that of the layer 4. In the organic thin film transistor 130, the capacitance of the capacitor can be increased by making the dielectric constant of the second insulating layer 5 larger than the dielectric constant of the first insulating layer 4. The relative dielectric constant of the first insulating layer 4 is preferably 2 or more and 5 or less. The relative dielectric constant of the second insulating layer 5 is 3 or more, preferably 5 or more, and more preferably 20 or more, but is not limited thereto.

When the second insulating layer 5 is composed of multiple layers, the same material and composition as the first insulating layer 4 may be used for a part of the second insulating layer 5, or all different materials may be used. Without being limited thereto, various combinations can be formed.

By making the thickness of the second insulating layer 5 thinner than that of the first insulating layer 4, it is possible to further increase the capacitance of the capacitor while keeping the gate leakage current in the first insulating layer 4 low. Become.

Next, a semiconductor layer 8 is formed on the first insulating layer 4, the source electrode 6 and the drain electrode 7. For the semiconductor layer 8, low molecular semiconductors such as pentacene and derivatives thereof, and polymer organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymers, and derivatives thereof can be used. It is not limited to.

The organic thin film transistor 130 can be suitably provided with a protective layer 9 for protecting the semiconductor layer 8 from external influences.

Examples of the material of the protective layer 9 include inorganic materials such as silicon oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconium oxide, and titanium oxide, or polyacrylates such as PMMA (polymethyl methacrylate), Organic insulating materials such as PVA (polyvinyl alcohol), PVP (polyvinylphenol), and fluorine-based resin are exemplified, but the invention is not limited thereto.

About the material of the protective layer 9, in order to suppress the leak current of the organic thin-film transistor 130 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

The protective layer 9 is formed by any one of an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method using a solution in which the protective layer material or its precursor is dissolved or dispersed. . These protective layers 9 may be used as a single layer, or two or more layers may be laminated. Further, the composition may be inclined in the growth direction.

In an image display device using the organic thin film transistor 130, the interlayer insulating film 10, the pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a counter substrate (not shown) are preferably provided.

Examples of the material for the interlayer insulating film 10 include inorganic materials such as silicon oxide, aluminum oxide, tantalum oxide, yttrium oxide, hafnium oxide, hafnium aluminate, zirconium oxide, and titanium oxide, or polyacrylates such as PMMA (polymethyl methacrylate). Insulating materials such as PVA (polyvinyl alcohol), PVP (polyvinylphenol), and fluorine-based resin are not limited thereto.

About the material of the interlayer insulation film 10, in order to suppress the leakage current of the organic thin-film transistor 130 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

As the display element, liquid crystal, electrophoretic particles, microcapsules containing electrophoretic particles, organic electroluminescence, or the like can be used. In the image display apparatus, it is possible to use these known general display elements without being limited to either a reflection type or a transmission type. Further, depending on the display element to be used, a configuration in which a plurality of organic thin film transistors 130 are installed in one pixel can be used.

The display element may be formed on the counter substrate on which the counter electrode is formed, and then combined with the organic thin film transistor 130 formed up to the pixel electrode 11 to form an image display device, or after being formed on the pixel electrode 11, the counter electrode The counter substrate may be stacked to form an image display device, and the process can be selected in accordance with the display element to be used.

(Fifth embodiment)
FIG. 5 is a schematic cross-sectional view showing an organic thin film transistor 140 according to the fifth embodiment of the present invention.

The difference between the organic thin film transistor 130 and the organic thin film transistor 140 is a region where the second insulating layer 5 is formed. As shown in FIG. 5, the second insulating layer 5 is laminated so as to cover the capacitor electrode 3 and the gate electrode 2 simultaneously. The first insulating layer 4 is laminated so as to cover the gate electrode 2 from above the second insulating layer 5.

By forming the first insulating layer 4 and the second insulating layer 5 in this way, the amount of charge accumulated in the channel portion of the thin film transistor is increased without changing the surface property of the first insulating layer 4. Therefore, it is possible to increase not only the capacitor capacity but also the ON current of the thin film transistor.

(Sixth embodiment)
FIG. 6 is a schematic cross-sectional view showing an organic thin film transistor 150 according to the sixth embodiment of the present invention.

The difference between the organic thin film transistor 130 and the organic thin film transistor 150 is a region where the first insulating layer 4 is formed. As shown in FIG. 6, the first insulating layer 4 is formed so as to cover the gate electrode 2 and the capacitor electrode 3 simultaneously. The second insulating layer 5 is laminated so as to cover the capacitor electrode 3 from above the first insulating layer 4. The second insulating layer 5 is formed of a material having a higher dielectric constant than that of the first insulating layer 4.

By using a material having a dielectric constant higher than that of the first insulating layer 4 as the material of the second insulating layer 5, it is possible to increase the capacitance of the capacitor while suppressing the leakage current.

(Seventh embodiment)
FIG. 7 is a schematic cross-sectional view showing an organic thin film transistor 160 according to a seventh embodiment of the present invention.

The organic thin film transistor 160 is formed so as to cover the source electrode 6 and the drain electrode 7 formed on the insulating substrate 1, the semiconductor layer 8 containing an organic semiconductor material, and the source electrode 6 and the semiconductor layer 8. At least an insulating layer 4, a second insulating layer 5 formed so as to cover at least a part of the drain electrode 7, a gate electrode 2, and a capacitor electrode 3 are provided.

Further, by providing the organic thin film transistor 160 with the interlayer insulating film 10, the pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a second substrate (not shown), an image display device can be obtained. . The structures of the counter electrode and the second substrate can be appropriately changed depending on the type of display element used.

Hereinafter, each component of the organic thin film transistor 160 will be described along the manufacturing process of the organic thin film transistor 160.

When the substrate 1 is an organic film, a transparent gas barrier layer (not shown) can be formed in order to improve the durability of the organic thin film transistor 160. Examples of the gas barrier layer include aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO), silicon nitride (SiN), silicon oxynitride (SiON), silicon carbide (SiC), diamond-like carbon (DLC), and the like. However, it is not limited to these. These gas barrier layers can be used by laminating two or more layers. The gas barrier layer may be formed only on one side of the substrate 1 using an organic film, or may be formed on both sides. The gas barrier layer can be formed using a vacuum deposition method, an ion plating method, a sputtering method, a laser ablation method, a plasma CVD (Chemical Vapor Deposition) method, a hot wire CVD method, a sol-gel method, etc. It is not limited to these.

In addition, an adhesion layer can be provided to improve the adhesion of the source electrode 6, the drain electrode 7, and the semiconductor layer 8 formed on the substrate 1 to the substrate 1, and a surface treatment or the like is performed on the surface of the substrate 1. May be applied.

Next, the source electrode 6 and the drain electrode 7 are formed on the substrate 1. The source electrode 6, drain electrode 7, gate electrode 2, and capacitor electrode 3 do not need to be clearly separated from each other in the electrode portion and the wiring portion, and are hereinafter referred to as electrodes as components of each organic thin film transistor. .

The source electrode 6 and the drain electrode 7 include aluminum (Al), copper (Cu), molybdenum (Mo), silver (Ag), chromium (Cr), titanium (Ti), gold (Au), platinum (Pt), Metal materials such as tungsten (W) and manganese (Mn), and conductive materials such as indium oxide (InO), tin oxide (SnO), zinc oxide (ZnO), indium tin oxide (ITO), and indium zinc oxide (IZO) Although a metal oxide material can be used, it is not limited to these. These materials may be used as a single layer, or may be used as a laminate or an alloy.

The source electrode 6 and the drain electrode 7 can be formed by vacuum film-forming methods such as vacuum deposition and sputtering, sol-gel methods using precursors of conductive materials, methods using nanoparticles, and the like. A method of forming an ink and forming it by a wet film forming method such as screen printing, letterpress printing, or an ink jet method can be used, but the method is not limited to these, and a known general method can be used. Patterning can be performed by, for example, protecting a pattern forming portion with a resist or the like using a photolithography method and removing an unnecessary portion by etching, or patterning directly using a printing method or the like. Also, the method is not limited to these methods, and a known general patterning method can be used.

In the case of applying the bottom contact structure, the source electrode 6 and the drain electrode 7 can be subjected to a surface treatment or the like in order to reduce the contact resistance in electrical connection with the semiconductor layer 8.

Next, a semiconductor layer 8 is formed on the insulating substrate 1, the source electrode 6, and the drain electrode 7. For the semiconductor layer 8, low molecular semiconductors such as pentacene and derivatives thereof, and polymer organic semiconductor materials such as polythiophene, polyallylamine, fluorenebithiophene copolymers, and derivatives thereof can be used. It is not limited to these.

Next, the first insulating layer 4 is formed so as to cover at least the source electrode 6 and the semiconductor layer 8.

The first insulating layer 4 includes oxide-based insulating materials such as silicon oxide (SiOx), aluminum oxide (AlOx), tantalum oxide (TaOx), yttrium oxide (YOx), zirconium oxide (ZrOx), and hafnium oxide (HfOx). Materials, silicon nitride (SiNx), silicon oxynitride (SiON), polyacrylates such as polymethyl methacrylate (PMMA), organic insulating materials such as polyvinyl alcohol (PVA), polyvinylphenol (PVP), etc. may be used. However, it is not limited to these. These may be a single layer or a laminate of two or more layers, may be an inorganic-organic hybrid thin film, or may have a composition inclined in the growth direction.

The first insulating layer 4 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 160 and the image display device.

Next, the second insulating layer 5 is formed on the drain electrode 7. The second insulating layer 5 is formed so as to cover at least a part of the drain electrode 7, and a capacitor structure is formed by the capacitor electrode 3 formed so as to overlap the drain electrode 7 on the second insulating layer 5. Thus, it functions as a capacitor of an image display device using the organic thin film transistor 160. The formation of the first insulating layer 4 and the second insulating layer 5 is not limited to this order, and the first insulating layer 4 may be formed after the second insulating layer 5 is formed.

The second insulating layer 5 desirably has a resistivity of 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more, in order to suppress leakage current in the organic thin film transistor 160 and the image display device.

The second insulating layer 5 forms a capacitor structure by insulating the drain electrode 7 and the capacitor electrode 3 in the organic thin film transistor 160. The film thickness of the second insulating layer 5 is the first insulating thickness in order to secure the capacitance of the capacitor. It is preferable to make it thinner than the layer 4. In the organic thin film transistor 160, the second insulating layer 5 is formed to be thinner than the first insulating layer 4, so that the leakage current in the transistor portion where the first insulating layer 4 is formed can be kept low while the capacitance of the capacitor is reduced. The electric capacity can be increased.

By using a material having a higher dielectric constant than that of the first insulating layer 4 as the material of the second insulating layer 5, the capacitance of the capacitor can be further increased. The relative dielectric constant of the first insulating layer 4 is preferably 2 or more and 5 or less. The relative dielectric constant of the second insulating layer 5 is 3 or more, preferably 5 or more, and more preferably 20 or more, but is not limited thereto.

Next, the gate electrode 2 and the capacitor electrode 3 are formed on the first insulating layer 4 and the second insulating layer 5. The gate electrode 2 and the capacitor electrode 3 can be formed by the same material and method as the source electrode 6 and the drain electrode 7 described above.

In an image display device using the organic thin film transistor 160, the interlayer insulating film 10, the pixel electrode 11, a display element (not shown), a counter electrode (not shown), and a counter substrate (not shown) are preferably provided.

The interlayer insulating film 10 mainly prevents gate-drain and capacitor-drain leakage through the pixel electrode 9 by insulating the gate electrode 2 and capacitor electrode 3 from the pixel electrode 9. It is formed.

About the material of the interlayer insulation film 10, in order to suppress the leakage current of the organic thin-film transistor 160 low, it is desirable that the resistivity is 10 ¹¹ Ωcm or more, more preferably 10 ¹⁴ Ωcm or more.

The interlayer insulating film 10 is formed by any one of an inkjet method, a relief printing method, a planographic printing method, an intaglio printing method, and a screen printing method using a solution in which a protective layer material or a precursor thereof is dissolved or dispersed. The These interlayer insulating films 9 may be used as a single layer or may be used by stacking two or more layers. Further, the composition may be inclined in the growth direction.

As the display element, liquid crystal, electrophoretic particles, microcapsules containing electrophoretic particles, organic electroluminescence, or the like can be used. In the image display apparatus, it is possible to use these known general display elements without being limited to either a reflection type or a transmission type. Further, depending on the display element to be used, it is possible to use a configuration in which a plurality of organic thin film transistors 160 are installed in one pixel.

The display element may be formed on the counter substrate on which the counter electrode is formed, and then combined with the organic thin film transistor 160 formed up to the pixel electrode 11 to form an image display device. After the display element is formed on the pixel electrode 11, the counter electrode The counter substrate may be stacked to form an image display device, and the process can be selected in accordance with the display element to be used.

(Eighth embodiment)
FIG. 8 is a schematic sectional view showing an organic thin film transistor 170 according to the eighth embodiment of the present invention.

The difference between the organic thin film transistor 160 and the organic thin film transistor 170 is a region where the second insulating layer 5 is formed. As shown in FIG. 8, the first insulating layer 4 is laminated so as to cover the semiconductor layer 8. The second insulating layer 5 is laminated on the first insulating layer 4 so as to cover the source electrode 6, the semiconductor layer 8, and a part of the drain electrode 7.

By forming the first insulating layer 4 and the second insulating layer 5 in this way, the thickness of the capacitor portion formed by the drain electrode 7 and the capacitor electrode 3 can be reduced in the transistor portion where the semiconductor layer 8 is formed. Since it can be made thinner than the film thickness, it is possible to increase the capacitance of the capacitor while keeping the leakage current of the transistor portion low.

(Ninth embodiment)
FIG. 9 is a schematic cross-sectional view showing an organic thin film transistor 180 according to a ninth embodiment of the present invention.

The difference between the organic thin film transistor 160 and the organic thin film transistor 180 is the thickness of the first insulating layer 4 and the second insulating layer 5 and the material used for the second insulating layer 5. As shown in FIG. 9, the second insulating layer 5 is formed so as to cover a part of the drain electrode 7, and the film thickness thereof is thinner than that of the first insulating layer 4. The second insulating layer 5 is formed of a material having a higher dielectric constant than that of the first insulating layer 4.

By using a material having a dielectric constant higher than that of the first insulating layer 4 as the material of the second insulating layer 5, the capacitance of the capacitor can be further increased.

As Example 1, an organic thin film transistor 100 shown in FIG.

Non-alkali glass with a thickness of 0.7 mm was used as the substrate 1. Molybdenum (Mo) was formed into a film thickness of 400 nm on the glass substrate 1 using DC magnetron sputtering, and was patterned into a desired shape by a photolithography method to obtain a gate electrode 2 and a capacitor electrode 3.

A photosensitive acrylic resin is applied to the substrate on which the gate electrode 2 and the capacitor electrode 3 are formed by a slit coat method, exposed and developed, patterned into a desired shape, baked at 200 ° C., and the second insulating layer 5 Formed. Thereafter, the first insulating layer 4 was formed in the same manner as the second insulating layer 5. The film thickness of the first insulating layer 4 was 1 μm, and the film thickness of the second insulating layer 5 was 0.5 μm. The relative permittivity of the photosensitive acrylic resin is 3.4.

Subsequently, a solution in which silver nanoparticles were dispersed was used as an ink, and was patterned into a desired shape using an ink jet method, and baked at 150 ° C. for 1 hour to form a source electrode 6 and a drain electrode 7.

Thereafter, a mesitylene solution in which poly (3-hexylthiophene) as an organic semiconductor material was dissolved at a concentration of 0.1% by weight was patterned by an ink jet method to form a semiconductor layer 8.

As Example 2, an organic thin film transistor 110 shown in FIG.

Non-alkali glass with a thickness of 0.7 mm was used as the substrate 1. On the glass substrate 1, Mo was formed into a film having a thickness of 400 nm by using DC magnetron sputtering, and patterned into a desired shape by a photolithography method to form the gate electrode 2 and the capacitor electrode 3.

Aluminum oxide (Al ₂ O ₃ ) was formed to a thickness of 50 nm on the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 were formed using an atomic layer deposition (ALD) method. Thereafter, a photosensitive acrylic resin is applied by a slit coating method, patterned by a photolithography method, and baked at 200 ° C., so that a region to be the first insulating layer 4 has a laminated structure of aluminum oxide and a photosensitive acrylic resin. The region to be the second insulating layer 5 was formed to be a layer made only of aluminum oxide. The film thickness of the photosensitive acrylic resin is 1 μm. Note that an unnecessary aluminum oxide layer such as an electrode extraction portion was removed by using a photolithography method and a dry etching method. The relative dielectric constant of aluminum oxide is 9.3, and the relative dielectric constant of the photosensitive acrylic resin is 3.4.

Subsequently, the ink in which the silver nanoparticles were dispersed was patterned into a desired shape using an ink jet method, and baked at 150 ° C. for 1 hour to form the source electrode 6 and the drain electrode 7.

As Example 3, an organic thin film transistor 120 shown in FIG.

A photosensitive polystyrene resin was applied to the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 were formed by a slit coating method, patterned by a photolithography method, and baked at 200 ° C. to form a first insulating layer 4. Subsequently, a photosensitive acrylic resin having a different dielectric constant from that of Examples 1 and 2 was applied and patterned by photolithography to form a second insulating layer 5. The film thicknesses of the first insulating layer 4 and the second insulating layer 5 are both 1 μm. The relative dielectric constant of the first insulating layer 4 is 2.5, and the relative dielectric constant of the second insulating layer is 4.2.

As Example 4, an organic thin film transistor 130 shown in FIG.

Non-alkali glass with a thickness of 0.7 mm was used as the substrate 1. Molybdenum (Mo) was formed into a film thickness of 400 nm on the glass substrate 1 using DC magnetron sputtering, and patterned into a desired shape by a photolithography method to form the gate electrode 2 and the capacitor electrode 3.

A photosensitive silicone resin is applied to the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 are formed by a slit coating method, exposed and developed, patterned into a desired shape, and baked at 200 ° C. to form a first insulating layer 4 was formed. Thereafter, the second insulating layer 5 was formed in the same manner as the first insulating layer 4. The film thicknesses of the first insulating layer 4 and the second insulating layer 5 were both 1 μm. The relative dielectric constant of the first insulating layer 4 is 2.5, and the relative dielectric constant of the second insulating layer 5 is 4.2.

Subsequently, a solution in which silver nanoparticles were dispersed was used as an ink, and was patterned into a desired shape using an ink jet method, and baked at 180 ° C. for 1 hour to form a source electrode 6 and a drain electrode 7.

As Example 5, an organic thin film transistor 140 shown in FIG.

Aluminum oxide (Al ₂ O ₃ ) was formed to a thickness of 100 nm on the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 were formed by using an atomic layer deposition method (ALD method). Thereafter, a photosensitive silicone resin is applied by a slit coating method, patterned by a photolithography method, and baked at 200 ° C., so that a region to be the first insulating layer 4 has a laminated structure of aluminum oxide and a photosensitive acrylic resin. The region to be the second insulating layer 5 on the capacitor electrode 3 was formed to be a layer made only of aluminum oxide. The film thickness of the photosensitive acrylic resin is 1 μm. Note that an unnecessary aluminum oxide layer such as an electrode extraction portion was removed by using a photolithography method and a dry etching method. The relative dielectric constant of aluminum oxide is 9.3, and the relative dielectric constant of photosensitive silicone resin is 2.5.

Subsequently, the ink in which the silver nanoparticles were dispersed was patterned into a desired shape using an ink jet method, and baked at 180 ° C. for 1 hour to form the source electrode 6 and the drain electrode 7.

As Example 6, an organic thin film transistor 150 shown in FIG.

A photosensitive silicone resin was applied to the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 were formed by a slit coating method, patterned by a photolithography method, and baked at 200 ° C. to form a first insulating layer 4. The film thickness of the first insulating layer 4 was 1 μm on the gate electrode 2 and 0.5 μm on the capacitor electrode 3. Subsequently, a photosensitive acrylic resin was applied and patterned by photolithography to form the second insulating layer 5 with a thickness of 0.5 μm. The relative dielectric constant of the first insulating layer 4 is 2.5, and the relative dielectric constant of the second insulating layer 5 is 4.2.

As Example 7, an organic thin film transistor 160 shown in FIG.

Non-alkali glass with a thickness of 0.7 mm was used as the substrate 1. A solution in which silver (Ag) nanoparticles are dispersed on a glass substrate 1 is used as an ink, and is patterned into a desired shape using an ink-jet method, followed by baking at 150 ° C. for 1 hour, and the source electrode 6 and the drain electrode 7 are formed. Formed.

A mesitylene solution in which poly (3-hexylthiophene) as an organic semiconductor material is dissolved at a concentration of 0.1% by weight is patterned on the substrate 1 on which the source electrode 6 and the drain electrode 7 are formed, thereby forming a semiconductor layer 8. did.

Thereafter, a fluororesin is applied by an ink jet method to form the first insulating layer 4 and the second insulating layer 5. As shown in FIG. 7, the second insulating layer 5 was formed so as to be thinner than the first insulating layer 4. The film thickness of the first insulating layer 4 was 1 μm, and the film thickness of the second insulating layer 5 was 0.5 μm. The relative dielectric constant of the resin used is 2.0.

Subsequently, a solution in which silver nanoparticles were dispersed was used as an ink, and was patterned into a desired shape using an ink jet method, and baked at 150 ° C. for 1 hour to form the gate electrode 2 and the capacitor electrode 3.

As Example 8, an organic thin film transistor 170 shown in FIG.

Thereafter, a fluororesin was applied with a film thickness of 1 μm by an inkjet method so as to cover a part of the semiconductor layer 8, the source electrode 6, and the drain electrode 7, thereby forming the first insulating layer 4. As shown in FIG. 8, aluminum oxide (Al ₂ O ₃ ) was formed as the second insulating layer 5 to a thickness of 100 nm by using an atomic layer volume method (ALD method). Note that an unnecessary aluminum oxide layer formed on a connection portion with the outside of the electrode or the like was removed by using a photolithography method and a dry etching method. The relative dielectric constant of the first insulating layer 4 is 2.0, and the relative dielectric constant of the second insulating layer 5 is 9.3.

Subsequently, the ink in which the silver nanoparticles were dispersed was patterned into a desired shape using an ink jet method, and baked at 150 ° C. for 1 hour to form the gate electrode 2 and the capacitor electrode 3.

As Example 9, an organic thin film transistor 180 shown in FIG.

After a film having a thickness of 100 nm is formed on a part of the drain electrode 7 of the substrate 1 on which the source electrode 6 and the drain electrode 7 are formed using an atomic layer volume method (ALD method), an unnecessary aluminum oxide layer is formed by photolithography. The second insulating layer 5 was formed by removing using a dry etching method. The relative dielectric constant of the second insulating layer 5 is 9.3.

Next, a mesitylene solution in which poly (3-hexylthiophene) as an organic semiconductor material is dissolved at a concentration of 0.1% by weight as an organic semiconductor material so as to cover a part of the source electrode 6, the drain electrode 7, and the substrate 1 is formed by an inkjet method. The semiconductor layer 8 was formed by patterning.

Thereafter, a fluororesin was applied to a part of the semiconductor layer 8, the source electrode 6, and the drain electrode 7 with a film thickness of 1 μm by an ink jet method to form the first insulating layer 4. The relative dielectric constant of the first insulating layer 4 is 2.0.

(Comparative Example 1)
As Comparative Example 1, an organic thin film transistor 200 shown in FIG.

A photosensitive acrylic resin having a dielectric constant different from that of Examples 1 to 3 is applied to the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 are formed by a slit coating method, patterned by a photolithography method, and baked at 200 ° C. Only the first insulating layer 4 was formed on the gate electrode 2 and the capacitor electrode 3. The film thickness of the first insulating layer 4 is 1 μm, and the relative dielectric constant is 3.3.

(Comparative Example 2)
As Comparative Example 2, an organic thin film transistor 210 shown in FIG.

Photosensitive silicone resin is applied to the substrate 1 on which the gate electrode 2 and the capacitor electrode 3 are formed by slit coating, patterned by photolithography, and baked at 200 ° C. Only one insulating layer 4 was formed. The film thickness of the first insulating layer 4 is 1 μm and the relative dielectric constant is 2.5.

(Comparative Example 3)
As Comparative Example 3, an organic thin film transistor 220 shown in FIG.

Thereafter, a fluororesin was applied with a film thickness of 1 μm by a slit coating method so as to cover the semiconductor layer 8, the source electrode 6, and the drain electrode 7, thereby forming the first insulating layer 4. The relative dielectric constant of the first insulating layer 4 is 2.0.

Through the above steps, organic thin film transistors according to Examples 1 to 9 and Comparative Examples 1 to 3 were produced. In Example 1, the capacitance of the capacitor could be doubled compared to the organic thin film transistor 200 by making the thickness of the second insulating layer 5 about half that of the first insulating layer 4. In Example 2, by using a film having a high dielectric constant for the second insulating layer 5, the capacitance of the capacitor could be significantly increased as compared with the organic thin film transistor 200. Further, in Example 3, the capacitance of the capacitor is increased as compared with the organic thin film transistor 200 by selecting the second insulating layer 5 having a relative dielectric constant higher than that of the first insulating layer 4. I was able to. In any of the embodiments, by increasing the capacitance of the capacitor, it is possible to improve the holding ratio of the writing voltage of the image display device and to drive the image display device stably.

In Example 4, the capacitance of the capacitor could be 1.6 times that of the organic thin film transistor 210 by using the second insulating layer 5 having a dielectric constant larger than that of the first insulating layer 4. . In Example 5, by using a film having a high dielectric constant for the second insulating layer 5, the capacitance of the capacitor could be significantly increased by about 75 times compared to the organic thin film transistor 210. Further, in Example 6, by selecting a material having a relative dielectric constant of the second insulating layer 5 higher than that of the first insulating layer 4, the capacitance of the capacitor is about 1 compared with that of the organic thin film transistor 210. It was possible to increase it 6 times. In any of the embodiments, by increasing the capacitance of the capacitor, it is possible to improve the holding ratio of the writing voltage of the image display device and to drive the image display device stably.

In Example 7, the capacitance of the capacitor could be doubled compared to the organic thin film transistor 220 by making the film thickness of the second insulating layer 5 about half that of the first insulating layer 4. In Example 8, by using a film having a high dielectric constant for the second insulating layer 5, the capacitance of the capacitor could be significantly increased as compared with the organic thin film transistor 220. Further, in Example 9, the capacitance of the capacitor is increased as compared with the organic thin film transistor 220 by selecting the second insulating layer 5 having a higher relative dielectric constant than that of the first insulating layer 4. I was able to. In any of the embodiments, by increasing the capacitance of the capacitor, it is possible to improve the holding ratio of the writing voltage of the image display device and to drive the image display device stably.

As described above, according to the present invention, the dielectric constant of the second insulating layer 5 formed between the capacitor electrode 3 and the drain electrode 7 is increased, so that the leakage current in the thin film transistor can be suppressed and the capacitor can be kept low. The capacity can be increased. In addition, by reducing the film thickness of at least the second insulating layer 5 formed between the capacitor electrode 3 and the drain electrode 7, it is possible to further increase the capacitor capacity and improve the voltage holding ratio. .

Therefore, according to the present invention, even in a case where a sufficient capacitor electrode area cannot be secured in an organic thin film transistor using a printing method, an element capable of maintaining a voltage holding ratio and stably driving by securing a capacitance. It becomes possible to provide an organic thin film transistor and an image display device exhibiting characteristics.

The present invention can be suitably used for an image display device and various sensors.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Capacitor electrode 4 First insulating layer 5 Second insulating layer 6 Source electrode 7 Drain electrode 8 Semiconductor layer 9 Protective layer 10 Interlayer insulating film 11 Pixel electrode 100 to 180, 200 to 220 Organic thin film transistor

Claims

On the insulating substrate, at least a gate electrode, a capacitor electrode, a first insulating layer formed to cover at least the gate electrode, and a second electrode formed to cover at least a part of the capacitor electrode An organic thin film transistor having an insulating layer, a source electrode, a drain electrode, and a semiconductor layer containing an organic semiconductor material,
An organic thin film transistor in which the film thickness of the second insulating layer is thinner than the film thickness of the first insulating film.
On the insulating substrate, at least a gate electrode, a capacitor electrode, a first insulating layer formed to cover at least the gate electrode, and a second electrode formed to cover at least a part of the capacitor electrode An organic thin film transistor having an insulating layer, a source electrode, a drain electrode, and a semiconductor layer containing an organic semiconductor material,
An organic thin film transistor, wherein a dielectric constant of the second insulating layer is larger than a dielectric constant of the first insulating layer.
The organic thin film transistor according to claim 1 or 2, wherein the first insulating layer is formed by laminating two or more insulating materials.
The organic thin film transistor according to any one of claims 1 to 3, wherein the second insulating layer is formed by laminating two or more insulating materials.
The organic thin film transistor according to any one of claims 1 to 4, wherein the second insulating layer is formed of a multilayer, and a part of the layer has the same material and composition as the first insulating layer.
At least a source electrode, a drain electrode, a semiconductor layer containing an organic semiconductor material, a first insulating layer formed so as to cover the source electrode and the semiconductor layer, and at least the drain electrode on an insulating substrate An organic thin film transistor having a second insulating layer formed so as to cover a part, a gate electrode, and a capacitor electrode,
An organic thin film transistor, wherein the thickness of the second insulating layer is thinner than the thickness of the first insulating layer.
The organic thin film transistor according to claim 6, wherein a dielectric constant of the second insulating layer is larger than a dielectric constant of the first insulating layer.
The organic thin film transistor according to claim 6 or 7, wherein the first insulating layer is formed by laminating two or more insulating materials.
9. The organic thin film transistor according to claim 6, wherein the second insulating layer is formed by laminating two or more insulating materials.
An image display device using the organic thin film transistor according to any one of claims 1 to 9.