JP2006073774A - Thin film transistor and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a thin film transistor which is reduced in cost, improved in carrier mobility, has an improved ON/OFF ratio of a current, and is kept high in reliability; and to provide its manufacturing method. <P>SOLUTION: The thin film transistor is equipped with an insulating board 3 which is uniform in thickness and provided with a first and a second flat main surfaces, a gate electrode 4 formed on the first main surface of the insulating board 3, a channel layer 2 formed on the second main surface of the insulating board 3 and composed of an organic semiconductor, carbon nanotubes or an organic dispersing material containing, at least, carbon nanotubes, and a source electrode 1 and a drain electrode 5 which are formed on the channel layer 2 interposing the gate electrode 4 between them. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

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

  Thin film transistors are mainly used to drive each pixel of flat panel displays typified by liquid crystal displays and organic electroluminescence displays, but the active layers of conventional thin film transistors are made of inorganic semiconductors such as silicon. It has become.

  In general, amorphous silicon (a-Si: H) is used as an inorganic semiconductor, but in recent years, organic semiconductors such as pentacene for low molecular weight materials and thiophene derivative materials for high molecular weight materials have made significant progress. Yes.

  In the background, conventional inorganic semiconductors have the following two problems. The first problem is that it is very difficult to obtain a display having an arbitrary shape because inorganic semiconductors have poor flexibility. The second problem is that a thin film transistor using an inorganic semiconductor requires a complicated process and a high-cost and sophisticated device such as a high vacuum device.

  Therefore, by adopting an organic semiconductor as an active layer of the thin film transistor, it becomes possible to use a liquid phase process such as ink jet printing and spin coating, and the cost can be reduced. Be flexible.

  FIG. 14 is a diagram showing a structure of a conventional thin film transistor in a sectional view. In this conventional thin film transistor, a gate electrode 4 is formed on a substrate 10, a gate insulating film 9 is formed thereon, a channel layer 2 made of an organic semiconductor is formed on the gate insulating film 9, and the channel layer 2 is formed on the channel layer 2. A source electrode 1 and a drain electrode 5 are formed.

  In addition, in order to obtain a high electric field mobility at a low operating voltage, there is one that uses BST (barium strontium titanate) having a high dielectric constant as an insulating material formed on a substrate (see, for example, Patent Document 1). . In this configuration, a substrate for holding an insulating material is required as a field effect transistor structure.

In some cases, a substrate made of an inorganic material such as silicone, ceramic, glass, or a plastic material such as polyvinylene chloride or polyolefin is used to support the transistor structure (see, for example, Patent Document 2).
Japanese Patent No. 3304299 JP 09-232589 A

  A conventional general thin film transistor requires at least a gate electrode, a source electrode and a drain electrode, a gate insulating film, a channel layer using a semiconductor, and a substrate for holding them. In such a configuration, for example, as shown in FIG. 14, the gate electrode 4, the gate insulating film 9, the channel layer 2, the source electrode 1 and the drain electrode 5 are stacked on the substrate 10. Is necessary, which has hindered cost reduction. In addition, since a multi-stage manufacturing process such as formation of the gate electrode 4 and formation of the gate insulating film 9 is performed before the formation of the channel layer 2, the surface of the gate insulating film 9 below the channel layer 2 is thereby formed. The difference in height between the top and bottom is increased, the surface of the channel layer 2 formed on the top and bottom is also swelled up and down, and the channel layer 2 cannot be formed with a uniform film thickness. A part arises. There is a problem in that the carrier mobility in the channel layer 2 is rate-limited by the thin portion, the carrier mobility is lowered, and the current ON / OFF ratio is also lowered. Further, in the portion where the channel layer 2 is thin, deterioration due to moisture, deterioration due to chemical reaction with other than water, and deterioration due to heat generation become significant, and the above-described carrier mobility and current ON / OFF ratio are reduced. There has been a problem that the deterioration of characteristics is remarkably advanced and the life is shortened. These problems are common when the channel layer 2 is composed of an organic semiconductor, a carbon nanotube, or an organic dispersion material containing at least a carbon nanotube.

  Therefore, a first object of the present invention is to provide a highly reliable thin film transistor and a method for manufacturing the same, which can reduce costs and have improved carrier mobility and current ON / OFF ratio.

  The present invention also provides an active matrix type display in which a plurality of thin film transistors having improved carrier mobility and current ON / OFF ratio, and a thin film transistor having improved carrier mobility and current ON / OFF ratio. A second object is to provide a wireless ID tag and a portable device used in the integrated circuit portion.

  In order to solve the above-described problem, a thin film transistor according to the present invention includes an insulating substrate having a flat first surface and a second main surface and a uniform thickness, and the first substrate of the insulating substrate. A gate electrode formed on a main surface, a channel layer formed on the second main surface of the insulating substrate and made of an organic semiconductor, a carbon nanotube, or an organic dispersion material containing at least a carbon nanotube; And a source electrode and a drain electrode formed on the channel layer or between the channel layer and the insulating substrate and on both sides of the gate electrode.

  According to this configuration, the insulating substrate, which is a gate insulating layer, is flat on both main surfaces and has a uniform thickness, so that the capacitance component is uniform in the substrate surface and a thin film transistor with stable characteristics is realized. it can. In addition, since the insulating substrate also serves as the gate insulating layer, and the channel layer is formed on the flat second main surface opposite to the first main surface of the insulating substrate on which the gate electrode is formed, A highly reliable thin film transistor with improved uniformity of channel layer thickness and improved carrier mobility and current ON / OFF ratio characteristics in the channel layer can be realized. In addition, since the insulating substrate also serves as the gate insulating layer, the cost can be reduced by reducing the number of components and the number of manufacturing processes.

  In the present invention, a first insulating protective layer covering the first main surface on which the gate electrode of the insulating substrate is formed, the channel layer of the insulating substrate, the source electrode and the drain electrode are formed. It is preferable that at least one of the insulating protective layers is provided with the second insulating protective layer covering the second main surface. By providing the insulating protective layer in this way, it is possible to prevent intrusion of moisture and the like from the side where the insulating protective layer is provided, prevent deterioration of the channel layer due to aging, and further improve the reliability and extend the life. be able to.

  In this case, the insulating protective layer may be made of any one of acrylic, epoxy, urethane, silicone, polyimide, undoped polyaniline, and parylene, or a polymer material containing any of these. preferable.

  In the present invention, the insulating substrate is any one of polyester, polyvinyl, polycarbonate, polypropylene, polyethylene, polyacetate, and polyimide, or a polymer material made of any one of these, or It is preferable that it is made of an oxide material.

  In the present invention, the gate electrode, the source electrode, and the drain electrode are made of chromium, titanium, copper, aluminum, molybdenum, tungsten, palladium, nickel, gold, platinum, conductive polyaniline, conductive polypyrrole, and conductive polythiophene. It is preferable that it is comprised with the material containing at least any one of them.

  In the present invention, the organic semiconductor is preferably an acene molecular material made of any one of naphthalene, anthracene, tetracene, pentacene, and hexacene, or any derivative thereof.

  In the present invention, the organic semiconductor is preferably a material made of any one of polyacetylene, polythiophene, polypyrrole, polyaniline, and fullerene, or any derivative thereof.

  The method of manufacturing a thin film transistor according to the present invention (first manufacturing method) includes a step of forming a gate electrode on a first main surface of an insulating substrate and a step of forming a channel layer on the second main surface of the insulating substrate. And forming a source electrode and a drain electrode on the channel layer.

  A thin film transistor manufacturing method (second manufacturing method) according to the present invention includes a step of forming a gate electrode on a first main surface of an insulating substrate, and a source electrode and a drain electrode on the second main surface of the insulating substrate. Forming a channel layer on the second main surface on which the source electrode and the drain electrode are formed.

  According to the first and second manufacturing methods, the insulating substrate also serves as the gate insulating layer, and is formed on the second main surface opposite to the first main surface of the insulating substrate on which the gate electrode is formed. Since the channel layer is formed, it is possible to manufacture a highly reliable thin film transistor in which the uniformity of the thickness of the channel layer is improved and the characteristics of carrier mobility and current ON / OFF ratio in the channel layer are improved. In addition, since the insulating substrate also serves as the gate insulating layer, the cost can be reduced by reducing the number of components and the number of manufacturing processes.

  In the first and second manufacturing methods, the insulating substrate is pulled out from a roll around which the insulating substrate is wound, and the gate electrode, the organic semiconductor layer, the source electrode, After performing each step of forming each with the drain electrode, the portion of the insulating substrate subjected to each step is wound up in a roll shape. By using such a roll-to-roll process, the production efficiency is much higher than that of the batch process, which is preferable for cost reduction.

  In the first and second manufacturing methods, the first insulating protective layer covering the first main surface on which the gate electrode of the insulating substrate is formed, the channel layer and the source electrode of the insulating substrate. It is preferable to include a step of forming at least one of the insulating protective layer among the second insulating protective layer covering the second main surface on which the drain electrode and the drain electrode are formed. By forming the insulating protective layer in this way, it is possible to prevent the intrusion of moisture and the like from the side where the insulating protective layer is provided, prevent deterioration of the channel layer due to aging, improve reliability, and extend the life. Can be planned.

  In this case, it is preferable to have a step of flattening the surface of the insulating protective layer. As a result, there is no step on the surface of the insulating protective layer, so that stress concentration when bent with flexibility can be relaxed.

  In the first and second manufacturing methods, the step of forming the channel layer, the step of forming the gate electrode, and the step of forming the source electrode and the drain electrode include vapor deposition, sputtering, chemical vapor deposition, electrodeposition. Including at least one of deposition, spin coating, electroless plating, electropolymerization, molecular beam deposition, self assembly from solution, screen printing, and stamping.

  The active matrix display according to the present invention employs a configuration in which a plurality of thin film transistors according to the present invention are arranged as switching elements for driving pixels. With this configuration, a sheet-like or paper-like display with good characteristics can be realized at low cost.

  The wireless ID tag according to the present invention adopts a configuration in which the thin film transistor according to the present invention is used as a semiconductor element for forming an integrated circuit. With this configuration, the wireless ID tag can be attached to objects or materials of various shapes. In addition, a wireless ID tag that can be formed into an arbitrary shape can be realized.

  The portable device according to the present invention adopts a configuration in which the thin film transistor according to the present invention is used as a semiconductor element for forming an integrated circuit. Here, examples of the portable device include a portable television, a communication terminal, a PDA, and a portable medical device. However, the present invention is not limited to these portable devices, and includes any portable device such as a portable AV device and a portable computer. With this configuration, it is possible to add advantages such as low cost, flexibility, impact resistance, and ability to be formed into an arbitrary shape to portable devices such as portable televisions, communication terminals, PDAs, and portable medical devices.

  The present invention has the configuration described above, and can provide a highly reliable thin film transistor and a method for manufacturing the same that can reduce costs, have improved carrier mobility and ON / OFF ratio of current. Play.

  In addition, an active matrix type display in which a plurality of thin film transistors with improved carrier mobility and current ON / OFF ratio, and a thin film transistor with improved carrier mobility and current ON / OFF ratio are used for an integrated circuit portion. It is possible to provide a wireless ID tag, a portable device, and the like.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In many cases, the dimensions of the device function are in the range of a micrometer or less, and in the drawings, the scale is designed with emphasis placed on the legibility rather than the accuracy of the dimensions.

(Embodiment 1)
FIG. 1 is a diagram showing a structure in a cross-sectional view of a thin film transistor of a first configuration example according to the first embodiment of the present invention. In this thin film transistor, the gate electrode 4 is provided on the first main surface of the insulating substrate 3, the channel layer 2 is provided on the second main surface, and the source electrode is formed on the channel layer 2 in alignment with the gate electrode 4. 1 and a drain electrode 5 are provided. The gate electrode 4 is provided between the source electrode 1 and the drain electrode 5 in plan view. The insulating substrate 3 also serves as a gate insulating layer, and the insulating substrate 3 has a flat first surface and a second main surface and a uniform thickness. Accordingly, the first main surface and the second main surface are parallel to each other. This thin film transistor has a so-called bottom gate type field transistor structure.

  The insulating substrate 3 is a polymer material selected from polyester, polyvinyl, polycarbonate, polypropylene, polyethylene, polyacetate, polyimide, or derivatives thereof, or an oxide material (for example, tantalum oxide, niobium oxide, silica, barium titanate). It is necessary to select the most suitable transistor configuration from the dielectric constant and thickness of these materials. More preferably, since the water absorption rate, moisture permeability, and oxygen permeability greatly affect the lifetime of the transistor, it is necessary to use those having low values. As a specific example, polyethylene terephthalate has a dielectric constant of 3.2 and exhibits characteristics almost equal to the dielectric constant of silica of 3.8, which is conventionally used, and at the same time, a film having a thickness of about 10 μm is available. Therefore, it is desirable as a material. In particular, it is desirable that the film be thin because a lower gate voltage can be achieved by using a thinner film. The insulating substrate 3 desirably has a high dielectric constant and low hysteresis. However, when a transistor has a memory function, it is necessary to increase hysteresis.

  The gate electrode 4, the source electrode 1 and the drain electrode 5 are made of chromium, titanium, copper, aluminum, molybdenum, tungsten, palladium, nickel, gold, platinum, conductive polyaniline, conductive polypyrrole, and conductive polythiophene. It is desirable that it is made of a material including at least one of them, such as any one or a combination thereof.

  The channel layer 2 can be configured using a conductive polymer material or a low molecular material organic semiconductor. As an organic semiconductor of a low molecular material, an acene molecular material containing at least naphthalene, anthracene, tetracene, pentacene, hexacene, or a derivative thereof may be used, and as an organic semiconductor of a high molecular material, polyacetylene, polythiophene, polypyrrole, polyaniline , Fullerene, or a material containing at least a derivative thereof may be used. From the viewpoint of high electron mobility, it is desirable to use an acene molecular material containing at least naphthalene, anthracene, tetracene, pentacene, hexacene, fullerene, or a derivative thereof.

  From the viewpoint of further high electron mobility, it is desirable to use carbon nanotubes or an organic dispersion material containing at least carbon nanotubes as the channel layer 2. The production of the organic dispersion material requires an organic solvent and a dispersion aid. Desirable organic solvents are tetrahydrofuran (THF), dimethylformamide (DMF), benzene, dichloromethane (DCM), sodium dodecyl sulfate (SDS), and dispersion aids are polycarbonate (PC), polystyrene (PS), polymethyl methacrylate. (PMMA) is preferred.

  FIG. 2 is a process cross-sectional view illustrating a method of manufacturing the thin film transistor shown in FIG.

  As shown in FIG. 2A, the gate electrode 4 is formed by patterning on the first main surface of the insulating substrate 3. Next, as shown in FIG. 2B, the channel layer 2 is formed by patterning on the second main surface of the insulating substrate 3. Next, as shown in FIG. 2C, the source electrode 1 and the drain electrode 5 are formed by patterning on the channel layer 2.

  The channel layer 2, the gate electrode 4, the source electrode 1 and the drain electrode 5 are formed by vapor deposition, sputtering, chemical vapor deposition, electrodeposition, spin coating, electroless plating, baking, electropolymerization, molecular beam deposition, self- Desirably, any one or a combination of assembly, deposition through a mask, screen printing, stamping, blanket film patterning, shadow mask deposition, and lithographic patterning methods may be formed.

  Also, a series of steps shown in FIGS. 2A, 2B, and 2C can be performed using a roll-to-roll process shown in FIG. In this method, the insulating substrate 3 is unwound and transferred from the roll 8a, and the gate electrode 4, the channel layer 2, the source electrode 1 and the drain electrode 5 are sequentially patterned by a method such as vapor deposition from the material supply source 7, and the roll It is a method of winding up to 8b. When a polymer material is used for the insulating substrate 3, since it has flexibility, such a roll-to-roll process can be used. In this case, the production efficiency is very high as compared with the batch process, which is preferable in terms of cost reduction.

  In the above description, the gate electrode 4 is formed first, but the gate electrode 4 may be formed at any time. For example, the gate electrode 4 may be formed after the channel layer 2, the source electrode 1 and the drain electrode 5 are formed.

  FIG. 4 is a diagram showing a structure in a cross-sectional view of the thin film transistor of the second configuration example according to the first embodiment of the present invention. The thin film transistor of FIG. 4 has a configuration in which an insulating protective layer 6 is further provided on both surfaces of the thin film transistor of FIG. By using acrylic, epoxy, urethane, silicone, polyimide, parylene, undoped polyaniline, or the like as the material of the insulating protective layer 6, it is possible to prevent intrusion of moisture or the like. In addition, when polyimide, parylene, or undoped polyaniline is used, there is an effect of protecting the thin film transistor from processing exposure at the time of further photolithography and an external atmosphere such as water and oxygen.

  Further, after the insulating protective layer 6 is applied to both surfaces of the insulating substrate 3, the surface of the insulating protective layer 6 is flattened to adjust the film thickness of the thin film transistor including the insulating protective layer 6 to be uniform over the entire surface. Since there is no level difference on the surface of the insulating protective layer 6, the stress concentration when bent with flexibility can be relaxed.

  In the case of FIG. 4, after the thin film transistor having the configuration shown in FIG. 1 is formed, the insulating protective layer 6 is finally formed. Also in this case, a series of steps until the insulating protective layer 6 is formed can be performed using a roll-to-roll process as shown in FIG.

  In FIG. 4, the insulating protective layer 6 is provided on both surfaces of the insulating substrate 3. However, even if the insulating protective layer 6 is provided only on one surface, the effect of protecting the thin film transistor on one surface can be obtained. Also in this case, after applying the insulating protective layer 6 to one surface of the insulating substrate 3, the surface of the insulating protective layer 6 is flattened to eliminate the level difference on the surface of the insulating protective layer 6 provided on one surface. It is possible to alleviate stress concentration on one side when bent with a thickness. In addition, when providing the insulating protective layer 6 only on one side, it is more desirable to provide it on the formation side of the channel layer 2 so that the channel layer 2 may be protected.

  As described above, in the first embodiment, the insulating substrate 3 also serves as the gate insulating layer, and the flat second main surface opposite to the first main surface of the insulating substrate 3 on which the gate electrode 4 is formed. Since the channel layer 2 is formed on the surface, the uniformity of the film thickness of the channel layer 2 is improved, and the highly reliable thin film transistor with improved carrier mobility and current ON / OFF ratio characteristics in the channel layer 2 Can be realized. Further, since the insulating substrate 3 also serves as the gate insulating layer, the cost can be reduced by reducing the number of components and the number of manufacturing processes. Further, the insulating substrate 3 which is a gate insulating layer is flat on both main surfaces and has a uniform thickness, so that the capacitance component is uniform in the substrate surface, and a thin film transistor having stable characteristics can be realized.

  Further, as in the second configuration example, by providing the insulating protective layer 6, it is possible to prevent intrusion of moisture and the like, prevent deterioration of the channel layer 2 due to aging, improve reliability, and extend the life. Can be planned.

  In order to clarify the effects of the first embodiment described above, specific examples of the first configuration example and the second configuration example in the first embodiment will be referred to as Example 1 and Example 2, respectively. A specific example of the conventional thin film transistor shown in FIG.

[Example 1]
In Example 1, a plurality of thin film transistors of the first configuration example (FIG. 1) were formed by performing a roll-to-roll process as shown in FIG. Here, a polyethylene terephthalate (PET) film (film thickness: 12.5 μm, dielectric constant: 3.2) was used as the insulating substrate 3. The channel layer 2 was formed to have a thickness of 100 nm by resistance heating vapor deposition using a material obtained by purifying pentacene (manufactured by Aldrich, purity 98%) and improving the purity as a material. The source electrode 1, the drain electrode 5, and the gate electrode 4 were formed to have a film thickness of 100 nm by resistance heating evaporation using masking patterning using oxidation-resistant Au (gold) as a material. The shortest distance between the source electrode 1 and the drain electrode 5 was 50 nm. In addition, the formation order of each part formed in order of the gate electrode 4, the channel layer 2, the source electrode 1, and the drain electrode 5 similarly to FIG.

  A plurality of thin film transistors were formed as described above. Then, in order to evaluate the characteristics of the thin film transistor in Example 1, 10 thin film transistor circuits were cut out from the roll and covered with an insulating layer or the like on the source electrode 1, drain electrode 5 and gate electrode 4 of each thin film transistor. A silver wire having a diameter of 0.1 mmΦ was wired with a silver paste on the part that was not present. Then, the carrier mobility and current ON / OFF ratio (ON current / OFF current) of the thin film transistor immediately after fabrication and the carrier mobility and current ON / OFF ratio after being left in the humidification tester for 7 days are measured. Compared. Humidification conditions in the humidification tester are a temperature of 65 ° C. and a humidity of 85%. The average value of the measurement results of 10 thin film transistors is shown in FIG.

As shown in FIG. 5, the carrier mobility immediately after the fabrication of the thin film transistor of Example 1 was 0.214 cm ² / Vs (average of 10), and the current ON / OFF ratio was 5.2 × 10 ⁷ (average of 10). )was gotten. Next, the carrier mobility after being left in the humidification tester was 0.108 cm ² / Vs (average of 10), and the current ON / OFF ratio was 2.8 × 10 ⁴ (average of 10), compared to immediately after fabrication. Carrier mobility decreased by 49.5%, and the current ON / OFF ratio decreased by three orders of magnitude.

[Example 2]
In Example 2, a plurality of thin film transistors of the second configuration example (FIG. 4) were formed by performing a roll-to-roll process as shown in FIG. Also in Example 2, as in Example 1, a polyethylene terephthalate (PET) film (film thickness 12.5 μm, dielectric constant 3.2) was used as the insulating substrate 3. The channel layer 2 was formed to have a thickness of 100 nm by resistance heating vapor deposition using a material obtained by purifying pentacene (manufactured by Aldrich, purity 98%) and improving the purity as a material. The source electrode 1, the drain electrode 5, and the gate electrode 4 were formed to have a film thickness of 100 nm by resistance heating evaporation using masking patterning using oxidation-resistant Au (gold) as a material. The shortest distance between the source electrode 1 and the drain electrode 5 was 50 nm. Furthermore, in Example 2, the insulating protective layers 6 provided on both surfaces of the insulating substrate 3 are respectively screen-coated with silicone together with a curing agent, flattened to a thickness of 10 μm by pressure heating, and unevenness on the surface (both surfaces) of the thin film transistor is obtained. Reduced. In addition, the formation order of each part formed the insulating protective layer 6 after forming the gate electrode 4, the channel layer 2, the source electrode 1, and the drain electrode 5 in order like the Example 1. FIG.

  A plurality of thin film transistors were formed as described above. Then, in order to evaluate the characteristics of the thin film transistor in Example 2, 10 thin film transistor circuits were cut out from the roll and covered with an insulating layer or the like on the source electrode 1, drain electrode 5 and gate electrode 4 of each thin film transistor. A silver wire having a diameter of 0.1 mmΦ was wired with a silver paste on the part that was not present. Then, the carrier mobility and current ON / OFF ratio (ON current / OFF current) of the thin film transistor immediately after fabrication and the carrier mobility and current ON / OFF ratio after being left in the humidification tester for 7 days are measured. Compared. Humidification conditions in the humidification tester are a temperature of 65 ° C. and a humidity of 85%. The average value of the measurement results of 10 thin film transistors is shown in FIG.

As shown in FIG. 5, the carrier mobility immediately after fabrication of the thin film transistor of Example 2 was 0.208 cm ² / Vs (average of 10), and the current ON / OFF ratio was 4.9 × 10 ⁷ (average of 10). )was gotten. Next, the carrier mobility after being left in the humidification tester is 0.171 cm ² / Vs (average of 10 pieces), and the current ON / OFF ratio is 8.4 × 10 ⁶ (average of 10 pieces), compared to immediately after the production. Carrier mobility decreased by 17.8%, and the current ON / OFF ratio decreased by an order of magnitude.

[Comparative Example 1]
In Comparative Example 1, a plurality of conventional (FIG. 14) thin film transistors were formed by performing a roll-to-roll process as shown in FIG. As a material of the substrate 10 shown in FIG. 14, a polyethylene terephthalate (PET) film (film thickness 12.5 μm, dielectric constant 3.2) is used and fixed to the roll part shown in FIG. It was.

  First, the gate electrode 4 is formed on the substrate 10 drawn from the roll. The gate electrode 4 was formed to a thickness of 100 nm by resistance heating vapor deposition using masking patterning using oxidation-resistant Au (gold) as a material. Next, as the gate insulating film 9, PVP (polyvinylphenol) was formed to a thickness of 50 μm by screen printing. Next, the channel layer 2 is formed. The channel layer 2 was made of pentacene (manufactured by Aldrich, purity 98%) with improved purity as a material, mask patterning was performed, and a thickness of 100 nm was formed by resistance heating vapor deposition. Next, the source electrode 1 and the drain electrode 5 are formed. The source electrode 1 and the drain electrode 5 were formed to a thickness of 100 nm by resistance heating vapor deposition using masking patterning using oxidation-resistant Au (gold) as a material. The shortest distance between the source electrode 1 and the drain electrode 5 was 50 nm.

  A plurality of thin film transistors were formed as described above. Then, in order to evaluate the characteristics of the thin film transistor in Comparative Example 1, ten thin film transistor circuits were cut out from the roll and covered with an insulating layer or the like on the source electrode 1, drain electrode 5, and gate electrode 4 of each thin film transistor. A silver wire having a diameter of 0.1 mmΦ was wired with a silver paste on the part that was not present. Then, the carrier mobility and current ON / OFF ratio (ON current / OFF current) of the thin film transistor immediately after fabrication and the carrier mobility and current ON / OFF ratio after being left in the humidification tester for 7 days are measured. Compared. Humidification conditions in the humidification tester are a temperature of 65 ° C. and a humidity of 85%. The average value of the measurement results of 10 thin film transistors is shown in FIG.

As shown in FIG. 5, the carrier mobility immediately after the fabrication of the thin film transistor of Comparative Example 1 was 0.155 cm ² / Vs (average of 10), and the current ON / OFF ratio was 1.6 × 10 ⁶ (average of 10). )was gotten. Next, the carrier mobility after being left in the humidification tester is 0.020 cm ² / Vs (average of 10 pieces), and the current ON / OFF ratio is 6.3 × 10 ¹ (average of 10 pieces), which is compared with that immediately after fabrication. The carrier mobility decreased by 87.1%, and the current ON / OFF ratio decreased by 5 digits.

  As described above, from the evaluation results of Examples 1 and 2 and Comparative Example 1, the structure according to the embodiment of the present invention in Examples 1 and 2 is compared with the conventional structure in Comparative Example 1 immediately after the production and after being left for humidification for 7 days. Both show high performance and high reliability in terms of carrier mobility and current ON / OFF ratio.

  Moreover, although there is no big difference in the evaluation result immediately after production between Example 1 and Example 2, Example 2 shows higher reliability than Example 1 in the evaluation result after being left humidified for 7 days. Yes. This is considered to be a result of the insulating protective layer 6 blocking moisture that causes deterioration of the organic semiconductor material constituting the channel layer 2. Although not mentioned in this experiment, the mechanical strength of Example 2 is expected to be improved due to the flatness of the surface of the insulating protective layer 6 as compared with Comparative Example 1.

(Embodiment 2)
FIG. 6 is a view showing a structure of the thin film transistor in the second embodiment of the present invention in a sectional view. In this thin film transistor, the gate electrode 4 is provided on the first main surface of the insulating substrate 3, the source electrode 1 and the drain electrode 5 are provided on the second main surface so as to be aligned with the gate electrode 4, and the source electrode 1 The channel layer 2 is provided on the drain electrode 5 and the second main surface of the insulating substrate 3. The gate electrode 4 is provided between the source electrode 1 and the drain electrode 5 in plan view. The insulating substrate 3 also serves as a gate insulating layer, and the insulating substrate 3 has a flat first surface and a second main surface and a uniform thickness. Accordingly, the first main surface and the second main surface are parallel to each other. The thin film transistor according to the second embodiment includes a source electrode 1 and a drain electrode 5 formed on the second main surface of the insulating substrate 3 in the configuration of the first configuration example (FIG. 1) of the first embodiment. The top and bottom arrangement with respect to the channel layer 2 is simply reversed.

  7 is a process cross-sectional view illustrating a method of manufacturing the thin film transistor shown in FIG.

  As shown in FIG. 7A, the gate electrode 4 is formed by patterning on the first main surface of the insulating substrate 3. Next, as shown in FIG. 7B, the source electrode 1 and the drain electrode 5 are formed by patterning on the second main surface of the insulating substrate 3. Next, as shown in FIG. 7C, the channel layer 2 is formed by patterning on the second main surface of the source electrode 1, the drain electrode 5 and the insulating substrate 3.

  The insulating substrate 3, channel layer 2, gate electrode 4, source electrode 1, and drain electrode 5 can be made of the same materials as in the first embodiment, and the channel layer 2, gate electrode 4, source electrode 1 can be used. In addition, the drain electrode 5 can be formed by the same method as in the first embodiment. Further, the series of steps shown in FIGS. 7A, 7B, and 7C can be performed using a roll-to-roll process as shown in FIG. In the above description, the gate electrode 4 is formed first, but the gate electrode 4 may be formed at any time. For example, the gate electrode 4 may be formed after the channel layer 2 is formed.

  In the second embodiment, the upper and lower arrangements of the source electrode 1 and the drain electrode 5 and the channel layer 2 are merely opposite to those in the first configuration example of the first embodiment. Since the portion functioning as the channel between the source electrode 1 and the drain electrode 5 is formed in contact with the second main surface of the insulating substrate 3 as in the first configuration example of the first embodiment. Thus, the uniformity of the film thickness of the portion functioning as the channel can be improved. Therefore, the same effect as the first configuration example of the first embodiment can be obtained.

  Further, similarly to the second configuration example in the first embodiment, by providing the insulating protective layer 6 (FIG. 4) on both sides or one side, the same effect as the second configuration example can be obtained.

(Embodiment 3)
In Embodiment 3 of the present invention, as an application example using the thin film transistor (hereinafter referred to as TFT) described in Embodiments 1 and 2, a sheet-like flexible display, a wireless ID tag, a mobile TV, a communication terminal, a mobile phone A portable device such as a medical device will be described.

  First, a configuration example of an active matrix display using an organic EL as a display unit as a sheet-like flexible display will be described.

  FIG. 8 is a perspective view schematically showing a configuration of an active matrix display using the organic EL in the third embodiment as a display unit.

  As shown in FIG. 8, in the active matrix display according to the third embodiment, TFT drive circuits 110 connected to pixel electrodes are arranged in an array on a plastic substrate 101. In addition, an organic EL layer 102 and a protective film 104 are disposed. A transparent electrode 103 is provided on the upper surface of the organic EL layer 102. Here, the organic EL layer 102 is formed by laminating layers such as an electron transport layer, a light emitting layer, and a hole transport layer. The source electrode line 105 and the gate electrode line 106 extending from predetermined electrodes of each TFT are each connected to a control circuit (not shown). Here, an enlarged view of one configuration example of the TFT drive circuit unit 110 is shown in FIG. FIG. 9A is a plan view of the surface (second main surface) side of the insulating substrate 3, and FIG. 9B shows the back surface (first main surface) side of the insulating substrate 3 from the surface side. It is the top view seen through. The laminated structure of the TFT itself in this example is basically the same as the laminated structure shown in FIG. 1 in the first embodiment, and the same reference numerals are given to portions corresponding to FIG. As shown in FIG. 9A, an organic EL pixel electrode 107, a source electrode line 105, and a TFT channel layer 2 are formed on an insulating substrate 3, and a drain electrode 5 formed on the channel layer 2 is The source electrode 1 electrically connected to the pixel electrode 107 and formed on the channel layer 2 is connected to the source electrode line 105. Further, as shown in FIG. 9B, a gate electrode line 106 is formed on the back side of the insulating substrate 3, and the gate electrode 4 is gated so as to be positioned between the source electrode 1 and the drain electrode 5 in plan view. It is connected to the electrode line 106. Here, the insulating substrate 3 corresponds to the plastic substrate 101 of FIG.

  In this manner, by forming an active matrix type display using the TFTs described in Embodiments 1 and 2, the TFT portion can be manufactured by a low-cost process, so that the display as a whole is inexpensive and mechanically flexible. A sheet-like display excellent in heat resistance and impact resistance can be realized. Further, by improving the carrier mobility of the TFT, it is possible to provide an active matrix display having a high display speed (reaction speed).

  Note that although the case where an organic EL is used for the display portion has been described in this embodiment mode, the effect of the present invention is not limited to an active matrix display having this configuration. That is, the effect is similarly exhibited if the display is an active matrix type that requires a TFT circuit.

  Further, the structure of the driver circuit portion for driving the pixels is not limited to the structure shown in this embodiment mode. In other words, for example, a current driving TFT and a switching TFT for controlling the current driving TFT may be combined to drive one pixel. Further, it is possible to have a circuit configuration in which a plurality of TFTs are combined.

  Next, a case where the TFT according to the present invention is applied to a wireless ID tag will be described.

  FIG. 10 is a perspective view schematically showing a configuration of a wireless ID tag using TFTs in the third embodiment.

  As shown in FIG. 10, the wireless ID tag 120 in the third embodiment uses a film-like plastic substrate 121 as a base material. An antenna part 122 and a memory IC part 123 are provided on the substrate 121. Here, the memory IC portion 123 can be configured using the TFT described in the first and second embodiments, and a plastic substrate 121 may be used as the insulating substrate 3 of the TFT. The wireless ID tag 120 can be used by being attached to a non-flat item such as a candy bag or a drink can by giving an adhesive effect to the back surface. A protective film is provided on the surface of the wireless ID tag 120 as necessary.

  As described above, by configuring the wireless ID tag using the TFTs described in Embodiments 1 and 2, it is possible to realize wireless ID tags that can be attached to various shapes or materials. Become. Further, by improving the carrier mobility of the TFT, it is possible to provide a wireless ID tag having a high reaction speed (processing speed).

  The effects of the present invention are not limited to the configuration of the wireless ID tag shown in FIG. Therefore, the arrangement and configuration method of the antenna unit and the memory IC unit can be arbitrarily set. In addition, for example, the ethics circuit unit can be incorporated into a wireless ID tag.

  In this embodiment mode, the antenna portion 122 and the memory IC portion 123 are formed in advance on the plastic substrate 121. However, the present invention is not limited to this embodiment, and the inkjet printing is performed. It is also possible to directly form a wireless ID tag on an object using such a method. At this time, a high-performance wireless ID tag using a TFT with improved carrier mobility and current ON / OFF ratio in an integrated circuit portion can be obtained at low cost by using the TFT structure according to the present invention. It becomes possible to produce.

  Finally, the case where the TFT according to the present invention is applied to a portable device will be described. 11 to 13 show some specific application examples of portable devices using TFTs according to the present invention.

  First, the case where the TFT according to the present invention is applied to a portable television will be described.

  FIG. 11 is a front view schematically showing a configuration of a portable television using the TFT according to the third embodiment.

  As shown in FIG. 11, portable television 130 according to the third embodiment is capable of receiving a broadcast wave composed of a display unit 131 composed of a liquid crystal display device or the like that displays television images, and a telescopic rod antenna here. Unit 132, a power switch 133 for controlling the power on / off of the portable television 130, and a volume adjustment of an audio output output from an audio output device 135, which will be described later, and a channel of a television broadcast to be received. An operation switch 134, an audio output unit 135 including a speaker for outputting TV sound, an input / output terminal 136 for inputting or outputting an audio signal or a video signal to or from the portable TV 130, and a received TV broadcast or the like Recording medium insertion unit 13 for inserting a recording medium on which the audio signal and the video signal are recorded as necessary It is equipped with a door.

  Although not particularly shown in FIG. 11, the portable television 130 has an integrated circuit such as an IC or LSI therein. An integrated circuit using the TFT according to the present invention is appropriately used as an arithmetic element, a memory element, a switching element, or the like that constitutes the portable television 130. Thereby, the portable television 130 functions as a portable television broadcast receiver.

  Next, a case where the TFT according to the present invention is applied to a communication terminal will be described. Here, a mobile phone is illustrated as the communication terminal.

  FIG. 12 is a front view schematically showing the configuration of a mobile phone using TFTs in the third embodiment.

  As shown in FIG. 12, the mobile phone 140 according to the third embodiment can transmit and receive communication radio waves including a display unit 141 including a liquid crystal display device that displays a telephone number and the like, and a retractable whip antenna here. Transmission / reception unit 142, audio output unit 143 including a speaker or the like for outputting communication audio, camera unit 144 having a CCD element capable of taking a photograph, and folding movable unit 145 for folding the mobile phone 140 as necessary. And a plurality of operation switches 146 for inputting telephone numbers and characters, and a voice input unit 147 composed of a condenser microphone or the like for inputting communication voice.

  Although not particularly shown in FIG. 12, the mobile phone 140 has an integrated circuit such as an IC or LSI therein. An integrated circuit using the TFT according to the present invention is appropriately used as an arithmetic element, a memory element, a switching element, or the like that constitutes the mobile phone 140. Thereby, the mobile phone 140 functions as a mobile communication terminal.

  Next, the case where the TFT according to the present invention is applied to a portable medical device will be described.

  FIG. 13 is a perspective view schematically showing a configuration of a portable medical device using the TFT according to the third embodiment. Here, as an example of the portable medical device, a portable medical device that automatically performs medical treatment such as drug administration on the patient based on the acquired biological information is illustrated. In FIG. 13, a patient's arm 155, which will be described later, is shown in perspective.

  As shown in FIG. 13, the portable medical device 150 according to the third embodiment includes a display unit 151 including a liquid crystal display device that displays an operation state of the device, acquired biological information, and the like, and a portable medical device 150. The operation switch 152 for performing settings related to the operation of the patient and the biological information acquired by the percutaneous contact unit 154 to be described later, and the drug for the patient via the percutaneous contact unit 154 based on the processing result A medical treatment unit 153 that performs medical treatment such as administration, and a percutaneous contact unit 154 that sequentially collects biological information of the patient for the medical treatment and substantially performs the medical treatment on the patient are provided. .

  When a medical procedure is performed on a patient using the portable medical device 150, the portable medical device 150 is wound around the patient's arm 155 and carried as shown in FIG. In the wearing state shown in FIG. 13, the percutaneous contact portion 154 and the surface of the patient's arm 155 are in close contact with each other. And the portable medical device 150 acquires the biological information for medical treatment from the arm 155 via the percutaneous contact part 154 in the wearing state shown in FIG. When the biological information of the patient is acquired, the acquired biological information is input to the medical treatment unit 153. The medical treatment unit 153 performs predetermined processing for medical treatment of the acquired biological information. Based on the result of the processing, the medical treatment unit 153 performs medical treatment such as drug administration to the patient via the percutaneous contact unit 154.

  The portable medical device 150 has an integrated circuit such as an IC or LSI therein, although not particularly shown in FIG. An integrated circuit using the TFT according to the present invention is appropriately used as an arithmetic element, a memory element, a switching element, or the like that constitutes the portable medical device 150. Thereby, the portable medical device 150 functions as a portable medical device.

  In this way, by configuring the portable device using the integrated circuit using the TFT described in the first and second embodiments, the following effects can be obtained. In other words, various elements using semiconductor characteristics such as arithmetic elements, storage elements, and switching elements can be considered as integrated circuits used in the above-described portable equipment. When the performance mentioned as advantages of organic materials such as impact resistance, environmental resistance at the time of disposal, light weight, and low cost is required, a part of the performance is configured by using the TFT according to the present invention. A high-performance element can be realized at low cost. As a result, a portable device having the above-described advantages can be manufactured at low cost.

  In the third embodiment, some examples of portable devices to which the TFT according to the present invention is applied have been described. However, the configurations of these exemplified devices are not limited to the above-described configurations. Further, portable devices to which the TFT according to the present invention can be applied are not limited to the above-described devices. For example, PDA terminals, wearable AV devices, portable computers, wristwatch-type communication devices, etc., portable devices that require mechanical flexibility, impact resistance, environmental friendliness when discarded, light weight, low cost, etc. On the other hand, the TFT according to the present invention can be preferably applied.

  The thin film transistor and the method for manufacturing the thin film transistor according to the present invention are useful as a thin film transistor in which the cost can be reduced, the carrier mobility and the current ON / OFF ratio are improved, and the method for manufacturing the thin film transistor. The thin film transistor according to the present invention is useful for configuring a sheet-like or paper-like active matrix display, a portable device such as a wireless ID tag, a portable TV, and a cellular phone.

It is a figure which shows the structure in the cross sectional view of the thin-film transistor of the 1st structural example in Embodiment 1 of this invention. It is process sectional drawing which shows the manufacturing method of the thin-film transistor of the 1st structural example in Embodiment 1 of this invention. It is a schematic diagram which shows the roll-to-roll process used for the manufacturing method of the thin-film transistor of the 1st structural example in Embodiment 1 of this invention. It is a figure which shows the structure in the cross sectional view of the thin-film transistor of the 2nd structural example in Embodiment 1 of this invention. It is a figure which shows the evaluation result of the thin-film transistor in Embodiment 1 of this invention. It is a figure which shows the structure in the cross sectional view of the thin-film transistor in Embodiment 2 of this invention. It is process sectional drawing which shows the manufacturing method of the thin-film transistor in Embodiment 2 of this invention. It is a perspective view which shows typically the structure of the active matrix type display which used organic EL in Embodiment 3 of this invention for the display part. FIG. 9 is an enlarged plan view showing a configuration of a thin film transistor driving circuit unit in FIG. 8. It is the perspective view which showed typically the structure of the radio | wireless ID tag using the thin-film transistor in Embodiment 3 of this invention. It is the front view which showed typically the structure of the portable television using the thin-film transistor in Embodiment 3 of this invention. It is the front view which showed typically the structure of the mobile telephone using the thin-film transistor in Embodiment 3 of this invention. It is the perspective view which showed typically the structure of the portable medical device using the thin-film transistor in Embodiment 3 of this invention. It is a figure which shows the structure in the cross sectional view of the conventional thin-film transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Source electrode 2 Channel layer 3 Insulating substrate 4 Gate electrode 5 Drain electrode 6 Insulating protective layer 7 Material supply source 8a, 8b Roll 9 Gate insulating film 10 Substrate 110 Thin film transistor drive circuit part 101 Plastic substrate 102 Organic EL layer 103 Transparent electrode 104 Protective film 105 Source electrode line 106 Gate electrode line 107 Pixel electrode 120 Wireless ID tag 121 Plastic substrate 122 Antenna unit 123 Memory IC unit 130 Mobile TV 131 Display unit 132 Reception unit 133 Power switch 134 Operation switch 135 Audio output unit 136 Input / output terminal 137 Recording media insertion unit 140 Mobile phone 141 Display unit 142 Transmission / reception unit 143 Audio output unit 144 Camera unit 145 Folding movable unit 146 Operation switch 147 Audio input unit 150 Portable medical device 151 Display Unit 152 operation switch 153 medical treatment unit 154 transcutaneous contact unit 155 arm

Claims (16)

An insulating substrate in which the first main surface and the second main surface are flat and have a uniform thickness;
A gate electrode formed on the first main surface of the insulating substrate;
A channel layer formed on the second main surface of the insulating substrate and made of an organic semiconductor, a carbon nanotube, or an organic dispersion material containing at least a carbon nanotube;
A thin film transistor comprising a source electrode and a drain electrode formed on the channel layer or between the channel layer and the insulating substrate and on both sides of the gate electrode.   The first insulating protective layer covering the first main surface on which the gate electrode of the insulating substrate is formed, the second layer on which the channel layer, the source electrode and the drain electrode of the insulating substrate are formed. The thin film transistor according to claim 1, wherein at least one of the second insulating protective layers covering the main surface is provided.   3. The insulating protective layer according to claim 2, wherein the insulating protective layer is made of any one of acrylic, epoxy, urethane, silicone, polyimide, undoped polyaniline, and parylene, or a polymer material containing any one of these. Thin film transistor.   The insulating substrate is made of any one of polyester, polyvinyl, polycarbonate, polypropylene, polyethylene, polyacetate, and polyimide, or a polymer material or an oxide material made of any of these derivatives. The thin film transistor according to claim 1.   The gate electrode, the source electrode, and the drain electrode are at least one of chromium, titanium, copper, aluminum, molybdenum, tungsten, palladium, nickel, gold, platinum, conductive polyaniline, conductive polypyrrole, and conductive polythiophene. The thin film transistor according to claim 1, wherein the thin film transistor is made of a material containing two.   2. The thin film transistor according to claim 1, wherein the organic semiconductor is an acene molecular material made of any one of naphthalene, anthracene, tetracene, pentacene, and hexacene, or a derivative of any of these.   2. The thin film transistor according to claim 1, wherein the organic semiconductor is a material made of any one of polyacetylene, polythiophene, polypyrrole, polyaniline, and fullerene, or a derivative thereof. Forming a gate electrode on the first main surface of the insulating substrate;
Forming a channel layer on the second main surface of the insulating substrate;
Forming a source electrode and a drain electrode on the channel layer. Forming a gate electrode on the first main surface of the insulating substrate;
Forming a source electrode and a drain electrode on the second main surface of the insulating substrate;
Forming a channel layer on the second main surface on which the source electrode and the drain electrode are formed.   Each step of pulling out the insulating substrate from the roll around which the insulating substrate is wound and forming each of the gate electrode, the organic semiconductor layer, the source electrode, and the drain electrode on the extracted portion of the insulating substrate is performed. 10. The method of manufacturing a thin film transistor according to claim 8, wherein the insulating substrate in a portion subjected to each of the steps is wound up in a roll shape.   The first insulating protective layer covering the first main surface on which the gate electrode of the insulating substrate is formed, the second layer on which the channel layer, the source electrode and the drain electrode of the insulating substrate are formed. 10. The method of manufacturing a thin film transistor according to claim 8, further comprising a step of forming at least one of the second insulating protective layers covering the main surface.   The method of manufacturing a thin film transistor according to claim 11, further comprising a step of planarizing a surface of the insulating protective layer.   The step of forming the channel layer, the step of forming the gate electrode, and the step of forming the source electrode and the drain electrode include vapor deposition, sputtering, chemical vapor deposition, electrodeposition, spin coating, electroless plating, electropolymer line. The method of manufacturing a thin film transistor according to claim 8 or 9, comprising at least one of the following processes: zestation, molecular beam deposition, self-assembly from solution, screen printing, and stamping.   An active matrix display in which a plurality of thin film transistors according to claim 1 are arranged as switching elements for driving pixels.   A wireless ID tag in which the thin film transistor according to claim 1 is used as a semiconductor element for constituting an integrated circuit.   A portable device, wherein the thin film transistor according to claim 1 is used as a semiconductor element for constituting an integrated circuit.

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