JP2012169419A - Organic thin-film transistor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic thin-film transistor in which a dielectric voltage of a gate insulator can be increased and which can be operated on a low voltage.SOLUTION: The organic thin-film transistor includes a gate electrode 20 and a gate insulator 30 formed on the gate electrode. The gate insulator has a laminated structure in which a polymer insulating film 32 is formed on a self-assembled molecular film 31.

Description

  The present invention relates to an organic thin film transistor, and more particularly to an organic thin film transistor in which a gate insulating film is formed on a gate electrode.

  In recent years, research on transistors using organic semiconductors (organic TFTs, thin film transistors) has become active from the viewpoint of flexibility and weight reduction. In general, when an organic semiconductor is used, a coating film can be formed from a solution, a large area process using various printing methods can be applied, and the cost can be greatly reduced. In addition, since it is a low-temperature manufacturing process, there is an advantage that a flexible substrate such as plastic can be used.

  The field of application of organic TFT is wide, and it is considered as a driving element that actively drives display devices such as organic EL (Electro Luminescence) display, liquid crystal, and electronic paper, and application to RFID (Radio Frequency Identification) tags, sensors, etc. Yes. However, the current organic TFT has not reached a practical level in terms of mobility, operating voltage, and driving stability. Therefore, there is an urgent need to improve not only organic semiconductors but also various aspects such as element configuration and manufacturing process.

  In general, organic TFTs have a problem of high driving voltage, and a characteristic that the operating voltage is about several tens to 100 V has been reported. In an actual electronic device, when used in a logic circuit or the like, it is necessary to set an operating voltage of 5 V or less and a display driving circuit of 20 V or less.

  There are two methods for reducing the operating voltage of the organic TFT. One is a method of thinning the gate insulating film. Specifically, a method using a self-assembled monomolecular film has been proposed (for example, see Non-Patent Document 1). According to the method described in Non-Patent Document 1, by using a self-assembled monomolecular film as a gate insulating film, the thickness of the gate insulating film can be reduced to about several nm, and the gate capacitance can be increased. Can do. As a result, the operating voltage of the organic TFT can be significantly reduced to 3 V or less.

  Another method is to increase the dielectric constant of the gate insulating film (for example, see Non-Patent Document 2). According to the method described in Non-Patent Document 2, it is possible to flow a larger amount of current with a small voltage by increasing the dielectric constant of the gate insulating film, thereby reducing the operating voltage of the organic TFT. Can do.

Nature, Vol.364, No. 6436, published July 29, 1993, p.745 Yoshiki Iino et al, "Organic Thin Film Transistors on a Plastic Substrate with Anodically Oxide High-Dielectric-Constant Insulators", Japanese Journal of Applied Physics, Vol. 42 (2003) pp. 299-304

  However, most of the polymer insulating materials used in organic TFTs are materials with a small dielectric constant, and the method of reducing the operating voltage of organic TFTs is almost limited to the method of reducing the thickness of the gate insulating film, The method described in Non-Patent Document 2 described above is not realistic.

  On the other hand, when the operating voltage of the organic TFT is reduced by thinning the gate insulating film as in the method described in Non-Patent Document 1 described above, there is a problem that the withstand voltage is lowered. Since the gate insulating film using the self-assembled monomolecular film reported in Non-Patent Document 1 has a film thickness of about several nanometers, dielectric breakdown occurs at a voltage of about 4V. Therefore, there is a problem that this insulating film cannot be used for an organic TFT of a display driving circuit whose operating voltage is about 20V. Although the operating voltage can be reduced by thinning the polymer insulating material, the dielectric breakdown voltage of the polymer insulating material is generally as low as about 1 MV / cm. There was a problem that the film could not be thinned.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an organic thin film transistor that can increase the withstand voltage of a gate insulating film and can be operated at a low voltage.

To achieve the above object, an organic thin film transistor according to an embodiment of the present invention is an organic thin film transistor having a gate electrode and a gate insulating film formed over the gate electrode,
The gate insulating film has a laminated structure in which a polymer insulating film is formed on a self-assembled monomolecular film.

  The self-assembled monolayer may be a phosphate-based self-assembled monolayer.

The phosphate self-assembled monolayer may have a long-chain alkyl group represented by n-alkyl-PO (OH) ₂ (n is an integer of 8 or more).

  The polymer insulating film may be a hydrophobic film.

  The gate electrode may be made of aluminum and the surface may be subjected to oxygen plasma treatment.

  According to the present invention, the withstand voltage of the gate insulating film can be improved, and the transistor operation can be performed at a low voltage.

1 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor according to Embodiment 1. FIG. It is explanatory drawing of the manufacturing method of the organic thin-film transistor which concerns on Embodiment 1. FIG. FIG. 2A illustrates an example of a gate electrode formation process. FIG. 2B is a diagram illustrating an example of a gate electrode surface treatment process. FIG. 2C is a diagram showing an example of a self-assembled monolayer forming process. FIG. 2D is a diagram showing an example of a polymer gate insulating film forming process. FIG. 2E is a diagram showing an example of a source / drain electrode formation step. FIG. 2F is a diagram illustrating an example of an organic semiconductor layer forming process. 5 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor according to Embodiment 2. FIG. 5 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor according to Embodiment 3. FIG. It is a transistor characteristic view of the organic thin-film transistor concerning Example 1 and Comparative Examples 1 and 2. FIG. 5A is a graph showing the change characteristics of the drain current with respect to the gate voltage of the organic thin film transistors according to Example 1 and Comparative Examples 1 and 2. FIG. 5B is a change characteristic diagram of the gate current with respect to the gate voltage of the organic thin film transistor according to Example 1 and Comparative Examples 1 and 2. It is the figure which showed the measurement result of the current voltage characteristic of the organic thin-film transistor which concerns on Example 2 and Comparative Examples 3 and 4. FIG.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.

Embodiment 1
FIG. 1 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor (hereinafter, may be referred to as “organic TFT”) according to Embodiment 1 of the present invention. In FIG. 1, the organic thin film transistor according to the first embodiment includes an insulating substrate 10, a gate electrode 20, a gate insulating film 30, a source electrode 40, a drain electrode 41, and an organic semiconductor layer 50. The gate insulating film 30 includes a self-assembled monomolecular film 31 and a polymer gate insulating film 32.

  In FIG. 1, a gate electrode 20 is formed on an insulating substrate 10, a self-assembled monomolecular film 31 is formed on the gate electrode 20, and a polymer gate insulating film 32 is formed on the self-assembled monomolecular film 31. Have a laminated structure. The source electrode 40 and the drain electrode 41 are formed on the surface of the polymer gate insulating film 32 so as to cover both ends of the gate electrode 20 in a top view. In addition, an organic semiconductor layer 50 is formed on the polymer gate insulating film 32 between the source electrode 40 and the drain electrode 41, and the organic semiconductor layer 50 has inner end portions of the source electrode 40 and the drain electrode 41. Covering. The structure shown in FIG. 1 is a structure called a bottom gate / bottom contact structure.

  The insulating substrate 10 may be composed of various substrates made of an insulating material. For example, a glass substrate such as quartz or silicon, polyethylene terephthalate (PET), polyethersulfone (PES), polyethylene naphthalate (PEN), polyimide Plastic films such as (PI), polyetherimide (PEI), polystyrene (PS), polyvinyl chloride (PVC), polyethylene (PE), polypropylene (PP), nylon, and polycarbonate can be used. Further, a metal foil or the like can be used as the insulating substrate 10 as long as the surface is treated with an insulating treatment.

  The gate electrode 20 is an electrode serving as an input of the organic thin film transistor according to the first embodiment, and may be made of aluminum, for example. A self-assembled monolayer 31 is formed on the surface of the gate electrode 20. The surface of the gate electrode 20 is subjected to a necessary surface treatment in order to form the self-assembled monolayer 31 in a stacked manner. It's okay.

  The gate insulating film 30 is a film that covers the periphery of the gate electrode 20 and insulates the gate electrode 20. The gate insulating film 30 of the organic thin film transistor according to the present embodiment has a stacked structure in which a polymer gate insulating film 32 is stacked on a self-assembled monomolecular film 31. In the organic thin film transistor, when a voltage is applied to the gate electrode 20, a channel is formed in the organic semiconductor layer 50, and the source electrode 40 and the drain electrode 41 are electrically connected to perform transistor operation. If the dielectric strength of 30 is lower than that required for an actual circuit, the organic thin film transistor cannot be operated as a device in the actual circuit. In the organic thin film transistor according to this embodiment, the withstand voltage of the gate insulating film 30 is increased by adopting a stacked structure in which the polymer gate insulating film 32 is formed on the self-assembled monolayer 31.

  The self-assembled monolayer 31 is a film having such a property that, when a specific treatment is performed on the insulating substrate 10, organic molecules adhere to one molecule by a chemical reaction. As a film, for example, a phosphate-based self-assembled monolayer 31 is known. The self-assembled monolayer 31 has an advantage that a film with very few defects and extremely high uniformity can be formed. However, there is no growth property in the thickness direction, and a thick film cannot be formed. Therefore, the thickness of the self-assembled monomolecular film 31 is almost constant, and for example, only a film having a thickness of about several nm can be formed. In this case, although a dielectric breakdown voltage of about 2 to 3 V can be obtained, the display drive circuit requires a breakdown voltage of 20 V, and cannot be used in an actual circuit as it is.

  Therefore, in the organic thin film transistor according to the present embodiment, the gate insulating film 30 is configured by laminating the polymer gate insulating film 32 on the self-assembled monomolecular film 31. The polymer gate insulating film 32 has many defects such as pinholes, and when used alone, a large withstand voltage cannot be obtained. However, unlike the self-assembled monomolecular film 31, the polymer gate insulating film 32 is grown and formed in the thickness direction. And has the advantage that the thickness of the membrane can be controlled. Therefore, the withstand voltage of the entire gate insulating film 30 can be improved by forming the self-assembled monomolecular film 31 with a necessary thickness. For example, a gate oxide film having a breakdown voltage of about 5 to 10 V is formed by stacking a polymer gate oxide film 32 having a thickness of about several tens of nm, for example, about 50 nm on a self-assembled monolayer 31 of several nm. 30 can be configured. Therefore, after forming the self-assembled monomolecular film 31 on the gate electrode 20, the polymer gate insulating film 32 is formed by adjusting the thickness, thereby forming the gate insulating film 30 having a desired breakdown voltage. Can do.

  As described above, in the organic thin film transistor according to the present embodiment, the gate insulating film 30 has a stacked structure of the self-assembled monomolecular film 31 and the polymer gate insulating film 32 to obtain a desired withstand voltage. Can do.

As the self-assembled monolayer 31, various films having the property of self-assembly can be used. For example, when using a phosphate-based self-assembled monolayer, the gate electrode 20 is made of aluminum. It is preferable to comprise. This is because the phosphoric acid-based self-assembled monolayer 31 formed on the gate electrode 20 is most easily bonded to the oxide film Al ₂ O _{3 on} the Al surface and has good compatibility. The aluminum gate electrode 20 may be formed by various methods.

  The polymer gate insulating film 32 may be composed of various polymer polymer insulating films. The material used for the polymer gate insulating film 32 is, for example, polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinylphenol (PVP), polyvinyl alcohol (PVA), polymethyl methacrylate (PMMA), CYTOP, An insulating polymer such as Teflon (registered trademark) can be used.

  Note that it is preferable to select a combination of materials for the self-assembled monomolecular film 31 and the polymer gate insulating film 32 so as to increase the degree of adhesion between them. For example, since the phosphoric acid-based self-assembled monolayer 31 has water repellency, it is necessary to select a hydrophobic solvent for the polymer gate insulating film 32. In this case, for example, by using a hydrophobic fluorine-based film as the polymer gate insulating film 32, the gate insulating film 30 having a laminated structure can be appropriately configured.

  The source electrode 40 and the drain electrode 41 are output electrodes of an organic thin film transistor, and can be composed of various materials. Examples of the material of the source electrode 40 and the drain electrode 41 include a solution in which metal colloidal particles such as gold, silver, and nickel are dispersed or a paste that uses metal particles such as silver as a conductive material. Also, for example, a metal, an alloy, or a transparent conductive film material is formed on the entire surface by sputtering or vapor deposition, and a resist pattern is used to form a desired resist pattern by photolithography or screen printing. A desired pattern can be formed by etching with an etching solution such as the above. In addition, a desired pattern can be directly formed from a metal, an alloy, or a transparent conductive film material by a sputtering method or a vapor deposition method using a mask. Examples of metal materials that can be used for these sputtering and vapor deposition methods include aluminum, molybdenum, chromium, titanium, tantalum, nickel, copper, silver, gold, platinum, and palladium, and examples of the transparent conductive film material include ITO.

The organic semiconductor layer 50 is an active semiconductor region that forms a channel during transistor operation, and is composed of an organic semiconductor film. The organic semiconductor layer 50 may be composed of various materials, for example, polycyclic aromatic hydrocarbons such as pentacene, anthracene, and lebran, low molecular compounds such as tetracyanoquinodimethane (TCNQ), polyacetylene, poly- Polymers such as 3-hexylthiophene (P ₃ HT) and polyparaphenylene vinylene (PPV) may be used.

  Although not shown in FIG. 1, the organic thin film transistor according to this embodiment may be provided with a sealing layer, a light shielding layer, and the like as necessary.

  Next, the manufacturing method of the organic thin-film transistor which concerns on Embodiment 1 of this invention is demonstrated using FIG. FIG. 2 is a view for explaining the method of manufacturing the organic thin film transistor according to the first embodiment. In FIG. 2, an example using a phosphoric acid self-assembled monolayer of the self-assembled monolayer 31 will be described.

FIG. 2A illustrates an example of a gate electrode formation process. In the gate electrode formation step, the gate electrode 20 is formed on the insulating substrate 10. Since the phosphoric acid-based self-assembled monolayer 31 formed on the gate electrode 20 is most easily bonded to the oxide film Al ₂ O _{3 on} the Al surface, it is necessary to use Al for the gate electrode 20. Therefore, the gate electrode 20 is made of Al. In addition, the formation method of the gate electrode 20 is not ask | required.

  FIG. 2B is a diagram illustrating an example of a gate electrode surface treatment process. In the gate electrode surface treatment step, the surface of the gate electrode 20 is oxidized with oxygen plasma. Specifically, after forming an aluminum film to be the gate electrode 20, the aluminum electrode surface is subjected to oxygen plasma treatment to form a very thin alumina layer. Note that the surface oxidation treatment by plasma may be performed on the entire surface including the gate electrode 20 and the insulating substrate 10.

FIG. 2C is a diagram showing an example of a self-assembled monolayer forming process. In the self-assembled monolayer formation step, the self-assembled monolayer 31 is formed on the plasma-treated gate electrode 20 using a phosphoric acid surface treatment agent having an alkyl chain length of 14 carbon atoms. In other words, the alumina layer formed in the gate electrode surface predetermined process is surface-treated with a phosphoric acid-based self-assembled monomolecular film, thereby reacting with the phosphoric acid-based self-assembled film, and this monomolecular film becomes an alumina layer. Formed on top. The molecular structure of the phosphoric acid-based self-assembled monolayer 31 is not limited, but it is more effective to use a phosphoric acid treating agent having an alkyl chain length of 8 or more carbon atoms. In order to control the wettability of the surface after the self-assembled monolayer 31 is formed, a phosphating agent in which the terminal structure of the alkyl chain is changed can also be used. For example, the phosphoric acid-based self-assembled monolayer 31 may use a phosphoric acid treatment agent represented by n-alkyl-PO (OH) ₂ (n is an integer of 8 or more).

  FIG. 2D is a diagram showing an example of a polymer gate insulating film forming process. In the polymer gate insulating film forming step, a polymer gate insulating material is applied onto the gate electrode 20 on which the self-assembled monomolecular film 31 is formed, and the polymer gate insulating film 32 is formed. Thereby, the gate insulating film 30 is completed.

  FIG. 2E is a diagram showing an example of a source / drain electrode formation step. In the source / drain electrode formation step, the source electrode 40 and the drain electrode 41 are formed on the polymer gate insulating film 32 of the gate insulating film 30. The source electrode 40 and the drain electrode 41 are formed above the both end portions of the gate electrode 20 so that the central region of the gate electrode 20 is an opening, and are formed so as to partially overlap the both end portions of the gate electrode 20. Is done. Since the source electrode 40 and the gate strength 41 are made of the same material, the source electrode 40 and the drain electrode 41 may be interchanged. The formation method and material of the source electrode 40 and the drain electrode 41 do not matter. For example, it may be formed by a printing method such as a screen printing method, an ink jet method, a flexographic printing method, and a reverse offset printing method in addition to a photolithography method and a dispenser method. As described above, a film may be formed using a sputtering method or a vapor deposition method, and then a predetermined pattern may be formed by photolithography or screen printing, or a predetermined pattern may be formed by a sputtering method or a vapor deposition method using a mask. A film may be formed. Various materials can be used as described with reference to FIG.

  FIG. 2F is a diagram illustrating an example of an organic semiconductor layer forming process. In the organic semiconductor layer forming step, the organic semiconductor film is formed in the opening of the source electrode 40 and the drain region 41 where the polymer gate insulating film 32 is exposed. The formation method of the organic semiconductor layer 50 is not limited and may be formed by various methods. The organic semiconductor layer 50 is formed on the polymer gate insulating film 32 and is formed so as to cover the opening side end portions of the source electrode 40 and the drain strength 41. The organic semiconductor layer 50 may also be composed of various materials as described in FIG.

  For example, the organic thin film transistor according to the first embodiment is manufactured through such a process. Since a vacuum process is not required and a process at a low temperature is sufficient, an organic thin film transistor capable of operating at a low voltage can be manufactured with a simple process.

[Embodiment 2]
FIG. 3 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor according to Embodiment 2 of the present invention. The organic thin film transistor according to the second embodiment includes an insulating substrate 10, a gate electrode 20, and a gate insulating film 30, and is configured by sequentially laminating these from the bottom. It is the same. In addition, the gate insulating film 30 has a configuration in which a polymer gate insulating film 32 is formed on a self-assembled monomolecular film 31 in the same manner as the organic thin film transistor according to the first embodiment. Therefore, these components are denoted by the same reference numerals as those in the first embodiment, and description thereof is omitted.

  The organic thin film transistor according to the second embodiment is implemented in that the organic semiconductor layer 51 is formed on the entire surface of the polymer gate insulating film 32, and the source region 42 and the drain region 43 are formed on the organic semiconductor layer 51. This is different from the organic thin film transistor according to the first embodiment.

  The organic thin film transistor according to the second embodiment has a structure called a bottom gate / top contact structure. Thus, the organic thin film transistor according to the present invention may have a top contact structure as long as the gate insulating film 30 is formed on the gate electrode 20. Even in this case, since the self-assembled monolayer 31 is formed on the gate electrode 20 and the polymer gate insulating film 32 is formed on the self-assembled monolayer 31, An organic thin film transistor that can operate at a low voltage by improving the dielectric strength of the film 30 can be configured.

  It should be noted that the source electrode 40 and the drain strength 41 are formed on the organic semiconductor layer 50 in the thickness direction and are different from those in the first embodiment, but the top view positions cover both ends of the gate electrode 20. It is the same as that of the organic thin-film transistor which concerns on Embodiment 1 by the point which is such a position.

  For the method of manufacturing the organic thin film transistor according to the second embodiment, the order of the source / drain electrode forming step described in FIG. 2E and the organic semiconductor layer forming step described in FIG. In the formation step, the organic semiconductor layer 51 may be formed on the entire surface of the polymer gate insulating film 32. The other steps are the same as those in the method for manufacturing the organic thin film transistor according to the first embodiment, and thus the description thereof is omitted.

  According to the organic thin film transistor according to the second embodiment, even in an organic thin film transistor having a bottom-gate / top-contact structure, the withstand voltage of the gate insulating film 30 can be improved and the transistor operation can be performed at a low voltage.

[Embodiment 3]
FIG. 4 is a cross-sectional configuration diagram illustrating an example of an organic thin film transistor according to Embodiment 3 of the present invention. In FIG. 4, the organic thin film transistor according to the third embodiment includes a gate electrode 20 formed on an insulating substrate 10, a self-assembled monolayer 31 formed on the gate electrode 20, and a self-assembled monolayer 31. This is the same as the organic thin film transistor according to the first and second embodiments in that the polymer gate insulating film 32 is formed. Therefore, these components are denoted by the same reference numerals as those of the organic thin film transistors according to the first and second embodiments, and the description thereof is omitted.

  In the organic thin film transistor according to the third embodiment, the drain electrode 45 and the organic semiconductor layer 52 are formed on the polymer gate insulating film 32 of the gate insulating film 30, and the source electrode 44 is formed above the organic semiconductor layer 52. It differs from the organic thin-film transistor which concerns on Embodiment 1 and 2 by the point. Note that the top-view positions of the source electrode 44 and the drain electrode 45 are the same as those of the organic thin film transistors according to the first and second embodiments in that they are arranged so as to cover both ends of the gate electrode 20. Note that the positions of the source electrode 44 and the drain electrode 45 may be interchanged as in the organic thin film transistors according to the first and second embodiments.

  The organic thin film transistor according to the third embodiment has a structure called a top & bottom contact structure, and the organic thin film transistor according to the present invention may be configured in such a top & bottom contact structure. Also in the organic thin film transistor according to the third embodiment, the gate insulating film 30 is formed on the gate electrode 20, and the gate insulating film 30 includes the self-assembled monomolecular film 31 formed on the gate electrode 20 and the self-assembled single film. Since it has the laminated structure of the polymer gate insulating film 32 formed on the molecular film 31, the withstand voltage of the gate insulating film 30 is improved, and the transistor operation can be performed at a low voltage.

  In the method of manufacturing the organic thin film transistor according to the third embodiment, the order of the source / drain electrode formation step described in FIG. 2E and the organic semiconductor layer formation step described in FIG. After the formation, the organic semiconductor layer 52 is formed, and finally the source electrode 44 is formed. The other steps are the same as those in the first and second embodiments, and a description thereof will be omitted.

  Thus, as described in the first to third embodiments, the organic thin film transistor according to the present invention has various structures as long as it has a bottom gate structure in which the gate insulating film 30 is formed on the gate electrode 20. Can be applied to.

  Next, the organic thin-film transistor which concerns on the Example of this invention is demonstrated. In the organic thin film transistor according to the present example, the organic thin film transistor having the bottom contact structure according to the second embodiment shown in FIG. The characteristics were compared with those of the thin film transistor. In the following examples, the same reference numerals are assigned to the same components as those of the organic thin film transistor according to the second embodiment, and the description thereof is omitted.

[Example 1]
The organic thin film transistor according to Example 1 of the present invention was manufactured as follows. First, a glass substrate was used as the insulating substrate 10, and Al serving as the gate electrode 20 was formed on the insulating substrate 10 to a thickness of 30 nm by vacuum deposition. This insulating substrate 10 was set in a plasma processing apparatus (manufactured by Samco: PC300), and oxygen plasma processing was performed at 300 W for 10 minutes. The insulating substrate 10 was immersed in a phosphoric acid treatment agent (solution) using isopropyl alcohol as a solvent for several hours to form a phosphoric acid self-assembled monolayer 31.

  Next, after depositing Teflon (registered trademark) AF1600 (manufactured by Mitsui DuPont Fluorochemical) as a gate insulating film material by spin coating, it is baked on a hot plate in order for 30 minutes at 90 ° C. and 2 hours at 120 ° C. Then, a polymer gate insulating film 32 having a thickness of 50 nm was formed.

  The insulating substrate 10 formed up to the polymer gate insulating film 32 was set in a vacuum evaporation apparatus, and pentacene was deposited to a thickness of 50 nm to form the organic semiconductor layer 50.

  A source electrode 42 and a drain electrode 43 were formed thereon by depositing Au with a thickness of 30 nm by mask vapor deposition.

[Comparative Example 1]
The polymer gate insulating film 32 is not formed on the insulating substrate 10 formed up to the self-assembled monolayer 31 by the same manufacturing method as in Example 1, and the organic semiconductor layer 51, the source electrode 42, and the drain electrode 43 are formed. The organic thin film transistor in which was formed was used as Comparative Example 1. The formation method of the organic semiconductor layer 51, the source electrode 42, and the drain electrode 43 is the same as that in the first embodiment.

  In Comparative Example 1, the polymer gate insulating film 32 does not exist and does not correspond to the second embodiment. However, for the sake of easy understanding, the same reference numerals as those in the second embodiment are used for corresponding components. Shall be attached. This also applies to the following comparative examples.

[Comparative Example 2]
The self-organized monomolecular film 31 is not formed on the insulating substrate 10 formed up to the gate electrode 20 by the same manufacturing method as in Example 1, but the polymer gate insulating film 32, the organic semiconductor layer 51, and the source electrode 42 are formed. The organic thin film transistor in which the drain electrode 43 was formed was referred to as Comparative Example 2. The formation method of the polymer gate insulating film 32, the organic semiconductor layer 51, the source electrode 42, and the drain electrode 43 is the same as that in the first embodiment.

[Example 2]
In Example 2, an element for measuring the withstand voltage was created. An Al electrode having a thickness of 30 nm was formed on the insulating substrate 10 formed up to the polymer gate insulating film 32 by the same method as in Example 1. The area where the first Al layer (corresponding to the gate electrode 20) formed on the insulating substrate 10 overlaps with the second Al layer formed last is 0.09 cm ² .

[Comparative Example 3]
An Al electrode having a thickness of 30 nm was formed on the insulating substrate 10 formed up to the self-assembled monolayer 31 by the same method as in Comparative Example 1. The area where the first Al layer (corresponding to the gate electrode 20) formed on the insulating substrate 10 overlaps with the second Al layer formed last is 0.09 cm ² .

[Comparative Example 4]
An Al electrode having a thickness of 30 nm was formed on the insulating substrate 10 formed up to the polymer gate insulating film 32 in the same manner as in Comparative Example 2. The area where the first Al layer (corresponding to the gate electrode 20) formed on the insulating substrate 10 overlaps with the second Al layer formed last is 0.09 cm ² .

  FIG. 5 is a diagram showing the transistor characteristics of the organic thin film transistors according to Example 1 and Comparative Examples 1 and 2. FIG. 5A is a graph showing a change characteristic of the drain current with respect to the gate voltage of the organic thin film transistors according to Example 1 and Comparative Examples 1 and 2. FIG. FIG. 5A shows characteristic curves of the organic thin film transistors according to Example 1, Comparative Example 1, and Comparative Example 2, respectively. The organic thin film transistors according to Example 1 and Comparative Examples 1 and 2 are P-channel type, and are driven by applying a negative voltage to the gate electrode 20. In each characteristic curve of FIG. 5A, the right side from the minimum value indicates the transistor off state, and the left side indicates the transistor on state. In the description here, the polarity is ignored, and the low voltage and high voltage mean the absolute value.

  As shown in FIG. 5A, the organic thin film transistor using the self-assembled monomolecular film according to Comparative Example 1 as the gate insulating film had a low operating voltage, but caused dielectric breakdown at about 4V. Further, when the characteristics of Example 1 and the characteristics of Comparative Example 2 are compared, the minimum value of the characteristic curve of Example 1 is smaller than the minimum value of the characteristic curve of Comparative Example 3. This indicates that the organic thin film transistor according to Example 1 has a characteristic of lower off-current and less leakage current than the organic thin film transistor according to Comparative Example 2. It can also be seen that the organic thin film transistor according to Example 1 can drive the transistor with a slightly lower voltage.

  FIG. 5B is a graph showing the change characteristics of the gate current with respect to the gate voltage of the organic thin film transistors according to Example 1 and Comparative Examples 1 and 2. In FIG. 5B, when the change in the gate current of each characteristic curve is compared, the organic thin film transistor of Example 1 has a lower leakage current because the amount of flowing current is smaller than that of Comparative Example 2. . In addition, the organic thin film transistor according to Comparative Example 1 also has a dielectric breakdown at a low voltage. From this, the operating voltage of the organic thin film transistor can be reduced and the high withstand voltage can be reduced by using the stacked gate insulating film 32 composed of the phosphoric acid self-assembled monolayer 31 and the polymer film shown in the present invention. We were able to demonstrate that

  FIG. 6 is a graph showing measurement results of current-voltage characteristics of organic thin film transistors according to Example 2 and Comparative Examples 3 and 4. The device of Comparative Example 3 caused dielectric breakdown at about 4V. Comparing the elements of Example 2 and Comparative Example 4, it can be seen that the characteristics of Example 2 have less current by one digit or more even at the same voltage, and the insulating characteristics of the organic thin film transistor according to Example 2 are superior. Recognize. In addition, the voltage at which dielectric breakdown occurs is about 10 V higher in the device of Example 2, which also indicates that the withstand voltage is improved. From the above results, it can be seen that the surface treatment of the gate electrode 20 with the self-assembled monomolecular film 31 is effective in increasing the withstand voltage of the polymer gate insulating film 32.

  Thus, according to the organic thin film transistor according to the present invention, the insulation resistance of the insulated gate 30 can be increased, and the transistor operation can be performed at a low voltage.

  The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited to the above-described embodiments, and various modifications and substitutions can be made to the above-described embodiments without departing from the scope of the present invention. Can be added.

  The present invention can be used for transistors and various electronic circuits using the transistors.

DESCRIPTION OF SYMBOLS 10 Insulating substrate 20 Gate electrode 30 Gate insulating film 31 Self-assembled monolayer 32 Polymer gate insulating film 40, 42, 44 Source electrode 41, 43, 45 Drain electrode 50, 51, 52 Organic-semiconductor layer

Claims (5)

An organic thin film transistor having a gate electrode and a gate insulating film formed on the gate electrode,
The organic thin film transistor, wherein the gate insulating film has a laminated structure in which a polymer insulating film is formed on a self-assembled monomolecular film.   The organic thin film transistor according to claim 1, wherein the self-assembled monolayer is a phosphate-based self-assembled monolayer. The phosphate self-assembled monolayer has a long-chain alkyl group represented by n-alkyl-PO (OH) ₂ (n is an integer of 8 or more). Organic thin film transistor.   The organic thin film transistor according to claim 2, wherein the polymer insulating film is a hydrophobic film.   The organic thin film transistor according to any one of claims 1 to 4, wherein the gate electrode is made of aluminum, and a surface thereof is subjected to oxygen plasma treatment.

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