JP2006173532A - Organic transistor and method for forming organic transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic transistor which has high mobility of carries and whose threshold voltage and operating voltage are suppressed low. <P>SOLUTION: The organic transistor has a gate electrode formed on a substrate, a gate insulating film formed on the gate electrode, an organic semiconductor film formed on the gate insulating film, and a 1st electrode and a 2nd electrode which are connected to the organic semiconductor film, the organic transistor being characterized in that the gate insulating film includes a 1st gate insulating film and a 2nd gate insulating film contacting the gate electrode and the 1st gate insulating film has a higher specific dielectric constant than the 2nd gate insulating film, which has a larger angle of contact with pure water than the 1st gate insulating film. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an organic transistor having a semiconductor film formed of an organic material.

  In recent years, for example, with the spread of communication devices such as mobile terminals, there is an increasing demand for downsizing and weight reduction of display devices used for the communication devices. In this case, if an organic material such as plastic is used for the substrate used in the display device, the display device can be reduced in weight, and such an organic material further has a feature of excellent flexibility.

For example, an organic transistor using an organic semiconductor material that is excellent in plasticity is attracting attention as a transistor used for a driving element of such a display device. An example of such an organic material transistor is a transistor using pentacene as a semiconductor layer. (For example, refer nonpatent literature 1). The electrical characteristics of such an organic transistor can be analyzed by a field effect transistor model. (For example, refer nonpatent literature 2.)
Further, conventionally, the gate insulating film of a transistor, for example, that the SiO ₂ is used were common, higher relative dielectric constant than SiO _2, and barium strontium titanate, zirconium titanate, barium, etc. An attempt has been made to use a high dielectric constant material for the gate insulating film. (See, for example, Patent Document 1 and Non-Patent Document 3, for example.)
YYLin et at., IEEE Electron Device Letters, Vol.18,606 (1997) S. Sze, "Physics of Semiconductor Devices", Wiley, New York, 1981 CDDimitrakopoulos, SCIENCE, vol.283,822 (1999) JP-A-10-270712

However, in the organic transistor using SiO ₂ as the gate insulating film, the carrier mobility is low, and the threshold voltage and the operating voltage are high. In order to solve these problems, when the gate insulating film is made thin, defects are likely to occur in SiO ₂ , which causes a problem that the breakdown voltage of the gate insulating film is lowered and the leakage current is increased. . In particular, when SiO ₂ is formed by a sputtering method, a layer having many defects is likely to be formed at the initial stage of film formation, so there is a limit to making the gate insulating film thin.

  The use of a high dielectric constant material such as barium strontium titanate or barium zirconate titanate for the gate insulating film is effective in increasing carrier mobility and suppressing threshold voltage and operating voltage. However, since these high dielectric constant films are formed by the sol-gel method, it is necessary to perform heat treatment at a maximum of 400 ° C. Therefore, it is difficult to form on a plastic substrate having a glass transition temperature of 200 ° C. or lower, and for example, it is difficult to use for a control element such as a plastic display device using a plastic substrate. was there.

  Therefore, an object of the present invention is to provide a new and useful organic transistor that solves the above-described problems.

  A specific problem of the present invention is to provide an organic transistor having high carrier mobility and suppressed threshold voltage and operating voltage.

  In a first aspect of the present invention, the above problems are solved by a gate electrode formed on a substrate, a gate insulating film formed on the gate electrode, an organic semiconductor film formed on the gate insulating film, and An organic transistor having a first electrode and a second electrode connected to the organic semiconductor film, wherein the gate insulating film includes a first gate insulating film in contact with the gate electrode, and a second gate The first gate insulating film has a relative dielectric constant higher than that of the second gate insulating film, and the second gate insulating film has a contact angle with respect to pure water higher than that of the first gate insulating film. It is solved by an organic transistor characterized by its large size.

  According to the organic transistor, since the gate insulating film is configured to include the first gate insulating film having a large relative dielectric constant and the second gate insulating film having a large contact angle, the orientation of the organic semiconductor film is good. In addition, the carrier mobility due to the electric field effect is improved, and the threshold voltage and the operating voltage can be suppressed.

  In addition, it is preferable that the first gate insulating film is thicker than the second gate insulating film because the mobility of carriers due to the electric field effect is improved, and at the same time, the breakdown voltage can be improved and the leakage current can be reduced. .

In the second aspect of the present invention, the above-described problem is solved by a gate electrode formed on a substrate, a gate insulating film formed on the gate electrode, and an organic semiconductor formed on the gate insulating film. And an organic transistor having a first electrode and a second electrode connected to the organic semiconductor film, wherein the gate insulating film includes the first gate insulating film in contact with the gate electrode, and the organic transistor. An n-th (n is an integer greater than or equal to 2) gate insulating film in contact with the semiconductor film, the first to n-th gate insulating films,
Among the first to (n-1) th gate insulating films, at least one of the gate insulating films has a relative dielectric constant larger than a relative dielectric constant of the nth gate insulating film, and This is solved by an organic transistor characterized in that the contact angle with pure water is larger than the contact angle of the (n-1) th gate insulating film.

  According to the organic transistor, the relative dielectric constant of at least one of the first to (n−1) th gate insulating films is larger than the relative dielectric constant of the nth gate insulating film, thereby Carrier mobility due to the effect is improved, the threshold voltage and the operating voltage can be suppressed, and the contact angle of the n-th gate insulating film is made larger than the contact angle of the lower layer, and the organic semiconductor The orientation of the film becomes good.

  The contact angle of the nth gate insulating film with respect to pure water is larger than any of the first to (n-1) th gate insulating films, and the first to nth gate insulating films Among them, when the thickness of the gate insulating film having the largest relative dielectric constant is the largest among the first to n-th gate insulating films, the orientation of the organic semiconductor film is further improved, and carriers due to the electric field effect are also obtained. Thus, the threshold voltage and the operating voltage can be suppressed.

  In the third aspect of the present invention, the above-described problem is a method for forming any one of the above organic transistors, wherein the gate insulating film is irradiated with ultraviolet rays having a wavelength of 380 nm or less, and the ultraviolet rays are irradiated. And a step of forming the organic semiconductor film on the gate insulating film.

  According to the formation method, the orientation of the organic semiconductor film is improved, the carrier mobility due to the electric field effect is improved, and the threshold voltage and the operating voltage can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the organic transistor with which the mobility of the carrier was high and the threshold voltage and the operating voltage were suppressed.

  Next, embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a cross-sectional view schematically showing an organic transistor according to Example 1 of the present invention.

  Referring to FIG. 1, a transistor 10 according to this embodiment is formed on a substrate 11 made of a resin material that is an organic material, for example, polycarbonate. The substrate 11 is preferably formed using an organic material such as a resin material because the substrate can be reduced in weight and the flexibility of the substrate becomes good.

  A patterned gate electrode 12 made of a metal such as tantalum is formed on the substrate 11. Further, on the gate electrode 12, a first gate insulating film 13a made of, for example, barium zirconate titanate and a second gate insulating film 13b made of, for example, fluorine polyimide are formed so as to cover the gate electrode 12. A gate insulating film 13 containing is formed.

  An organic semiconductor film 14 made of, for example, pentacene is formed on the gate insulating film 13, and a source electrode 15 and a drain electrode 16 made of, for example, gold (Au) are formed in contact with the organic semiconductor film 14. ing.

  In the organic transistor 10 according to the present embodiment, the gate insulating film 13 includes a first gate insulating film 13a and a second gate insulating film 13b, and the first gate insulating film 13a is the second gate insulating film 13b. The relative permittivity is higher, and the second gate insulating film 13b has a larger contact angle with pure water than the first gate insulating film 13a (hereinafter, the contact angle with pure water is simply referred to as the contact angle). It is formed as follows.

  For this reason, it is possible to improve the carrier mobility and suppress the threshold voltage and the operating voltage. The reason for this will be described in detail below.

For example, in order to improve the carrier mobility of the transistor, it is effective to increase the relative dielectric constant of the gate insulating film. For example, barium zirconate titanate (Ba _x Zr1- _x TiO ₃ ), A material having a large relative dielectric constant such as polyvinyl alcohol generally has a small contact angle and a large surface free energy. For this reason, when an organic semiconductor film is formed on a gate insulating film made of a material having such a high relative dielectric constant, there is a limit to improving the orientation of the organic semiconductor film, and the carrier mobility is reduced. There was a limit to improvement.

  On the other hand, in order to improve the orientation of the organic semiconductor film on the gate insulating film, it is preferable that the contact angle of the gate insulating film in contact with the organic semiconductor film is large. Thus, a large contact angle indicates that the surface free energy of the gate insulating film is small, and the orientation of the organic semiconductor film formed on the gate insulating film becomes good, so that the carrier movement The degree increases, which is preferable. However, such a material having a large contact angle is generally a material having a small relative dielectric constant such as, for example, fluorine polyimide or hydrofluoroether. From the viewpoint of the relative dielectric constant, the carrier mobility is improved. For this purpose, it is not always suitable.

  Therefore, in this embodiment, the gate electrode 13 is configured as follows. First, a first gate insulating film 13a is formed on the gate electrode 12 side using a material having a high relative dielectric constant, and further laminated on the first gate insulating film 13a. A second gate insulating film 13b having a large contact angle, which is a base film for forming the film 14, is formed.

  For this reason, in addition to the good orientation of the organic semiconductor film formed on the second gate insulating film 13b, the relative dielectric constant of the first gate insulating film 13a is further increased. As compared with the conventional organic transistor, the threshold voltage and the operating voltage can be suppressed, and a high-performance organic transistor can be configured.

  In order to achieve the above effect, for example, the relative permittivity of the first gate insulating film 13a is preferably 6 or more, and the contact angle of the second gate insulating film 13b is 70 ° or more. Is preferable.

  The gate insulating film 13 is preferably formed as thin as possible. In that case, it is more preferable that the ratio of the first gate insulating film 13a having a high relative dielectric constant in the gate insulating film 13 is larger. . That is, the thickness t1 of the first gate insulating film 13a having a high relative dielectric constant is more preferably thicker than the thickness t2 of the second gate insulating film 13b, and the relative dielectric constant of the gate insulating film 13 is higher. Therefore, the effect of improving the carrier mobility is increased.

  Further, for example, the modification may be performed by irradiating the gate insulating film 13 with light, an electron beam, an ion beam, plasma, or the like. In this case, by applying the above-described modification treatment to the second insulating film 13b, the orientation of the second insulating film 13b is improved, and therefore the second insulating film 13b is formed on the second insulating film 13b. There is an effect that the orientation of the organic semiconductor film 14 is improved. When such a modification process is performed, the binding energy of the material constituting the second insulating film 13b is E1, and the energy of the light, electron beam, ion beam, plasma, or the like related to the modification process is Es. Then, it is preferable to satisfy E1 <Es. Further, the modification process may be performed by changing the irradiation angle or the polarization direction.

  In addition, when the above-described modification is performed on the first gate insulating film 13a, the relative dielectric constant of the first insulating film 13a is increased.

  For the gate insulating film used in this embodiment, a material that can be formed by a spin coating method, a printing method, an inkjet method, an LB method, or the like can be used, for example. For this reason, it is possible to form the gate insulating film at a low temperature of 200 ° C. or less, which is the glass transition temperature of a resin material such as plastic, and the organic transistor according to this embodiment has a relatively high heat resistance temperature such as an organic material. It is possible to use it in combination with a low material. For this reason, for example, it can be used as a control element of a device required to be plastic, for example, a liquid crystal display device which is a plastic display device, formed on a substrate made of a resin material.

For example, examples of the material constituting the gate insulating film 13 include soluble polyimide, cyclobutane type polyimide, benzophenone type polyimide, BPDA / DPE polyimide, polyimide containing azobenzene in the main chain, polyimide containing a long chain alkyl group, fluorine containing Polyimide, liquid crystalline polyimide, polymer material having one or more functional groups of cinnamoyl group, coumarin group, chalcone group, azo group, polymer material having finylmaleimide-styrene skeleton, polymethacrylate main chain Polymer materials having a high molecular weight, polyvinyl lucinamate resin, polyparaxylene resin, polymethyl methacrylate resin, fluorine-containing polymer material, cellulose, polyvinyl alcohol, polyvinyl phenol, polyamide, epoxy acrylate, polyacrylo It is possible to use any one material selected from the group consisting of tolyl, diphenyl ether phenolic resin, polybenzoxazole, polybenzimidazole, polyvinyl siloxane, cyanoethyl plutene, parylene, and PMMA, or a mixture thereof. . _{Further, SiO 2, Si 3 N 4} , SiON, Al 2 O 3, Ta 2 O 5, ZrO 2, HfO 2, HfSiO x, HfAlO x, HfSiON, La 2 O 3, Ba x Zr 1-x TiO 3 , etc. A material made of any one of the oxide-based and nitride-based inorganic materials, or a mixture thereof may be used.

In addition, among the materials that can form the gate insulating film 13, a material having a high relative dielectric constant is preferable as the material used for the first gate insulating film 13 a, for example, ZrO ₂ , TiO _{2. , HfO 2, Ta 2 O 5} , Al 2 O 3, _{and, Ba x Zr 1-x TiO} 3, any one material selected from the group consisting of or it is particularly preferable to use mixtures thereof.

  Of the above-mentioned materials that can constitute the gate insulating film 13, the material used for the second gate insulating film 13b is preferably a material having a large contact angle. For example, hydrofluoroether, thiol , Aminosilane, cyclobutane-type polyimide, BPDA / DPE polyimide, polyimide containing a long-chain alkyl group, fluorine-based polyimide, polyparaxylene resin, fluorine-containing polymer material, and parylene. It is particularly preferred to use one material or a mixture thereof.

  In FIG. 1, the gate insulating film 13 is described as an example of an organic transistor having a first gate insulating film 13a and a second gate film 13b. However, the present invention is limited to this structure. Instead, for example, as shown in FIG. 2, the gate insulating film may be formed of a multilayer insulating film.

FIG. 2 is a diagram schematically showing another configuration example of the gate insulating film 13 shown in FIG. A gate insulating film shown in FIG. 2, n layers (n is an integer of 2 or more) consists of an insulating film, the first gate insulating film D _1, any number of layers of the gate insulating film is laminated, for example, the until the gate insulating film D _n of n, and is constituted by n-layer laminate. In this case, ₁ the first dielectric constant of the gate insulating film D ₁ of the _epsilon, the thickness d _1, the contact angle and alpha _1, the relative dielectric constant of the gate insulating film D _n epsilon _n, thickness of the n Is d _n , and the contact angle is α _n . In this case, the n-th gate insulating film D _n is formed on the side in contact with the organic semiconductor film, and the first gate insulating film D ₁ is formed on the side in contact with the gate electrode.

If the gate insulating film having a multilayer structure shown in the figure, the gate contact angle alpha _n of the gate insulating film D _n of the n-th, which is formed below the gate insulating film D _n of the n-th, that is, the gate electrode side It is preferable that the contact angle is larger than the contact angle of the insulating film, and among the gate insulating films formed in multiple layers, the contact angle α _{n of the nth} gate insulating film D _n that contacts the organic semiconductor film is the largest. preferable. In this case, the orientation of the organic semiconductor film becomes good.

Further, the lower layer of the gate insulating film _{D n} of the n, i.e., of the gate insulating film _{D n-1} of the first gate insulating film _{D 1} ~ the (n-1), at least one layer, for example, the gate insulating film D _m of the m (m is 1 ≦ m ≦ (n-1 ) to become an integer), it is preferable gate insulating film D _n from the relative dielectric constant of the first n is large, the carrier in this case Increases mobility. Further, it is more preferable that the gate insulating film having a large relative dielectric constant is thick, and in this case, the carrier mobility is increased. Furthermore, among the first gate insulating film D ₁ to the (n−1) th gate insulating film D _n−1 , the thickness of the gate insulating film having the largest relative dielectric constant is the first gate. It is preferable that it is the thickest among the insulating films D ₁ to (n−1) th gate insulating film D _n−1 .

  In addition, when a gate insulating film composed of a plurality of insulating layers is configured, various configurations such as inserting a layer for improving the flatness of an insulating layer to be formed and a layer for improving the adhesion force are included. Can be arbitrarily formed.

  Further, for example, as a material for forming the substrate 11, other than polycarbonate resin, for example, polyester resin, polyacrylate resin, polyimide resin, polyethylene terephthalate resin, polyether sulfone resin, epoxy resin, polymethyl methacrylate resin, cyclic polyolefin resin, It is possible to use an amorphous polyolefin resin, an acrylic UV curable material, or the like. For example, in a liquid crystal display device or the like, when two opposing substrates are formed of an organic material such as a resin material, it is possible to have flexible characteristics such as bending the display device. The substrate 11 can be formed of an inorganic material such as quartz, glass, or silicon.

  Examples of the material used for the organic semiconductor film 14 include naphthalene, anthracene, tetracene, pentacene, rubrene, phenanthrene, pyrene, chrysene, perylene, coronene, oligophenylene (n-phenyl: n = 2-12), oligo Thiophene (n-thiophenyl: n = 2-12), copper phthalocyanine, polythiophene, polyacetylene, poly (2,5-chenylene vinylene), poly (3-alkylthiophene), poly (3-hexylthiophene), fluorene-thiophene It is possible to use any one material selected from the group consisting of a copolymer, a fluorinated product thereof, and a derivative thereof formed by a vacuum deposition method, or a mixture thereof.

  Further, for example, the source electrode 15 and the drain electrode 16 are made of metal such as gold, platinum, chromium, tungsten, tantalum, nickel, copper, aluminum, silver, magnesium, calcium, or an alloy thereof, and polysilicon or amorphous silicon. A film made of any one of graphite, tin-added indium oxide, zinc oxide, and a conductive polymer is formed by a vacuum deposition method, an electron beam deposition method, an RF sputtering method, or a printing method, and an electrode pattern is formed. Thus, it can be formed.

  Next, a specific example in which the organic transistor shown in FIG.

  First, an aluminum film having a thickness of 100 nm to 1000 nm was formed as the gate electrode 12 on the substrate 11 by an RF sputtering method. The material of the gate electrode is not limited to aluminum, and for example, any of titanium, tantalum, or zirconium may be used. Moreover, the formation method of a gate electrode is not limited to RF sputtering method, For example, you may form by an electron beam vapor deposition method or a vacuum evaporation method.

  Next, the first gate insulating layer 13a made of wholly aromatic polyimide (relative dielectric constant 3.4, contact angle 70 to 80 °) is formed uniformly by spin coating so as to have a film thickness of 200 nm. did. Further, the forming method is not limited to the spin coating method, and for example, any one of a dip coating method, a casting method, and a printing method may be used. The formed film was baked at 180 ° C. for 1 hour to be polyimideized.

  Next, on the first gate insulating layer 13a, a second gate insulating layer 13b made of fluorine polyimide (relative dielectric constant 2.6, contact angle 90-100 °) is uniformly applied by spin coating. The film thickness was 80 nm. Further, the forming method is not limited to the spin coating method, and for example, any one of a dip coating method, a casting method, and a printing method may be used. The formed film was baked at 180 ° C. for 1 hour to be polyimideized.

  Next, the organic semiconductor film 14 made of pentacene was formed by vacuum deposition.

Further, the source electrode 15 and the drain electrode 16 connected to the organic semiconductor film 14 were formed on the organic semiconductor film 14 to configure the configuration example 1 of the organic transistor 10 illustrated in FIG. When the mobility characteristic of the organic transistor 10 according to the configuration example 1 was measured, the mobility was 1.5 cm ² / Vs, and it was confirmed that the mobility of the organic transistor according to this example was high.

In the case of forming the organic transistor according to the configuration example 1, the second gate insulating film 13b is not formed, and the organic semiconductor film 14 is in contact with the first gate insulating film 13a. Then, an organic transistor according to Structural Example 2 was formed. When the mobility of the organic transistor according to Structural Example 2 was measured, the mobility was 0.01 cm ² / Vs. For this reason, by comparing the mobility of Configuration Example 1 and Configuration Example 2, the organic semiconductor film 14 is formed by forming the second gate insulating film 13b having a contact angle larger than that of the first gate insulating film 13a. The orientation of the film was improved, and the effect of improving the mobility was confirmed. In addition, the effect of forming the second gate insulating film 13b is not only the improvement of mobility, but also, for example, defects such as pinholes formed in the first gate insulating film are protected. It was confirmed that the current was suppressed.

Next, in the case where the organic transistor according to the structural example 1 is formed, the organic transistor according to the structural example 3 in which the first gate insulating film 13a is changed is formed. In this case, the configuration other than the first gate insulating film 13a was the same as that in the configuration example 1. In the transistor according to Structural Example 3, Ba _x Zr1- _x TiO ₃ (relative dielectric constant 17.3, contact angle 78 °) is formed as the first gate insulating film 13a by magnetron sputtering to a thickness of 200 nm. Formed as follows. When the mobility of the organic transistor according to the configuration example 3 was measured, the mobility was 2.0 cm ² / Vs. From the comparison of the mobility with the configuration example 1, the relative dielectric constant of the first gate insulating film 13a was measured. It was confirmed that the mobility was improved by increasing the height. Thus, the higher the relative dielectric constant of the first gate insulating film 13a, the greater the effect of improving the mobility. In the present invention, while using a gate insulating film having a high relative dielectric constant, which has been difficult in the past, it is possible to further improve the orientation of the organic semiconductor film and to obtain high mobility. .

In the case of forming the organic transistor according to the configuration example 3, the organic transistor according to the configuration example 4 was formed by changing the film thicknesses of the first gate insulating film 13a and the second gate insulating film 13b. In the organic transistor according to the configuration example 4, the gate insulating film 13a has a thickness of 80 nm, and the second gate insulating film 13b has a thickness of 200 nm. That is, the ratio of the film thickness occupied by the first gate insulating film 13a having a high relative dielectric constant was made small while keeping the entire film thickness of the gate insulating film 13 the same as in the case of the configuration example 3. Then, when the mobility by the said structural example 4 was measured, the mobility was 0.5 cm < ² > / Vs. For this reason, compared with the configuration example 3 and the configuration example 4, the thickness of the gate insulating film having a higher relative dielectric constant (in the case of the present configuration example, the first gate insulating film 13a) is the film thickness of the entire gate insulating film. It was confirmed that it is preferable to increase the thickness to increase the mobility.

Next, in the case of forming the organic transistor according to the structural example 1, as an example in which the material used for the gate insulating film is changed, polyvinyl alcohol (relative dielectric constant 7.8, contact angle) is used as the first gate insulating film 13a. 40 °) is formed so as to have a film thickness of 100 nm, and hydrofluoroether (relative dielectric constant 2.6, contact angle 112 °), which is a fluorine-based polymer material, is used as the second gate insulating film 13b. An organic transistor according to Structural Example 5 was formed so as to have a film thickness of 10 nm. When the mobility of the organic transistor according to Structural Example 5 was measured, the mobility was 1.0 cm ² / Vs, and it was confirmed that the mobility was high.

  In the case of forming the organic transistor according to the configuration example 5, the organic transistor according to the configuration example 6 is configured in which the first gate insulating film 13a and the second gate insulating film 13b are interchanged. That is, as the first gate insulating film 13a, hydrofluoroether (relative dielectric constant 2.6, contact angle 112 °), which is a fluorine polymer material, is formed so as to have a film thickness of 10 nm. As the second gate insulating film 13b, polyvinyl alcohol (relative dielectric constant 7.8, contact angle 40 °) was formed to a film thickness of 100 nm.

When the mobility of the organic transistor according to Structural Example 6 was measured, the mobility was 0.01 cm ² / Vs. Therefore, by comparing the mobility of the configuration example 5 and the configuration example 6, the organic semiconductor film 14 is formed by forming the second gate insulating film 13b having a contact angle larger than that of the first gate insulating film 13a. The orientation of the film was improved, and the effect of improving the mobility was confirmed.

Next, in the case of forming the organic transistor according to the structural example 1, as an example in which the material used for the gate insulating film is changed, Ta ₂ O ₅ (relative dielectric constant 25, A contact angle of 80 °) is formed to a film thickness of 100 nm, and a polyimide film CBDA / BAPP (relative dielectric constant of 3.2, contact angle of 90 °) is formed as the second gate insulating film 13b. An organic transistor according to Structural Example 7 formed to have a thickness of 80 nm was formed. When the mobility of the organic transistor according to Structural Example 7 was measured, the mobility was 0.1 cm ² / Vs. The chemical formula of CBDA / BAPP is shown below.

次に、前記構成例７による有機トランジスタを形成する場合において、前記第２のゲート絶縁膜１３ｂを形成後、紫外線（波長３８０ｎｍ以下、照射エネルギー１Ｊ／ｃｍ^２）照射の処理を行った、構成例８による有機トランジスタを形成した。

Next, in the case of forming the organic transistor according to the structural example 7, after the second gate insulating film 13b is formed, the ultraviolet ray (wavelength 380 nm or less, irradiation energy 1 J / cm ² ) irradiation treatment is performed. An organic transistor according to 8 was formed.

When the mobility of the organic transistor according to the configuration example 8 was measured, the mobility was 2 cm ² / Vs, which was higher than that of the transistor according to the configuration example 7. For this reason, from the comparison of the mobility of the configuration example 7 and the configuration example 8, by irradiating the second gate insulating film 13b with ultraviolet rays, the organic semiconductor film formed on the second gate insulating film 13b The effect of improving the orientation and improving the mobility was confirmed.

Next, in the case of forming the organic transistor according to the configuration example 8, as an example in which the material used for the gate insulating film is changed, as the first gate insulating film 13a, a wholly aromatic polyimide (relative dielectric constant 3.4, contact (Angle 70 to 80 °) was formed so that the film thickness was 100 nm, and an organic transistor according to Structural Example 9 was formed. When the mobility of the organic transistor according to Structural Example 9 was measured, the mobility was 1.0 cm ² / Vs, and it was confirmed that the mobility was high.

Next, in the case of forming the organic transistor according to the structural example 9, the first gate insulating film 13a is formed, and then the ultraviolet ray (wavelength 380 nm or less, irradiation energy 1 J / cm ² ) irradiation treatment is performed. 10 organic transistors were formed. In this case, it was confirmed that the relative dielectric constant of the first gate insulating film 13a after the first gate insulating film 13a was irradiated with ultraviolet rays increased to 3.8. Further, when the mobility of the organic transistor according to the configuration example 10 was measured, the mobility was improved to 1.5 cm ² / Vs. For this reason, from the comparison of the mobility of the configuration example 9 and the configuration example 10, by irradiating the first gate insulating film 13a with ultraviolet rays, the dielectric constant of the first gate insulating film 13a increases, and therefore It was confirmed that the mobility was improved.

  In addition, the material used for the gate insulating film is not limited to the above case, and various materials can be used as necessary, and various kinds of surface treatments, heat treatments, and other necessary treatments are performed. It is possible to use as a characteristic.

  The structure of the organic transistor shown in FIG. 1 is an example of the present invention, and is not limited to the case shown in FIG. 1. For example, as shown below, the organic transistor can be used with various modifications and changes. There are the same effects as described in this embodiment.

  3A and 3B are cross-sectional views showing a modification of the organic transistor 10 shown in FIG. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  First, referring to FIG. 3A, in the organic transistor 10 </ b> A shown in this figure, a barrier layer 17 that covers the surface of the substrate 11 is formed on the substrate 11. The barrier layer 17 is made of, for example, a silicon oxide film having a thickness of about 80 nm to 100 nm formed by an RF sputtering method, and has an effect of preventing water and gas from permeating from the substrate toward the organic transistor. Play. Further, the material constituting the barrier layer 17 is not limited to the silicon oxide film, and for example, an inorganic material such as silicon nitride, silicon oxynitride, aluminum oxide, or ITO is preferably used, but polyimide resin, polyvinyl phenol resin, A polymer material such as polyparaxylene resin or polymethylmethacrylate resin may be used, or a laminated structure thereof may be used.

  Further, as shown in FIG. 3B, a barrier layer 18 may be further provided on the back surface of the substrate 11, that is, the surface opposite to the surface on which the transistor is formed. In this case, the barrier layer 18 can be made of the same material as that used for the paria layer 17, and further prevents water and gas from permeating from the substrate toward the organic transistor. The effect to do becomes large.

  Moreover, the organic transistor 10 shown in FIG. 1 can also be configured as shown in FIG. FIG. 4 is a diagram schematically showing a cross section of a transistor 10B, which is another modification of the organic transistor 10 shown in FIG. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  Referring to FIG. 4, the organic transistor 10B according to the present embodiment includes the substrate 11, the gate electrode 12, and the gate insulating film including the first gate insulating film 13a and the second gate insulating film 13b. The structure 13 is the same as that of the organic transistor 10 shown in FIG.

  In this embodiment, the source electrode 15 and the drain electrode 16 are formed on the second gate insulating film 13b, and further cover the source electrode 15 and the drain electrode 16 and the second gate insulating film 13b. Thus, the organic semiconductor film 14A is formed. In this case, the organic semiconductor film 14A can be formed by the same manufacturing method using the same material as the organic semiconductor film 14 shown in FIG. In the case of the present embodiment, the same effect as in the case of the organic transistor shown in FIG.

  5A and 5B are cross-sectional views showing an example in which a barrier layer is formed in the organic transistor 10B shown in FIG. However, in the figure, the same reference numerals are given to the parts described above, and the description will be omitted.

  In the organic transistor 10C shown in FIG. 5A, a barrier layer 17 covering the surface of the substrate 11 is formed on the substrate 11 in the same manner as the organic transistor 10A shown in FIG. The barrier layer 17 has the same structure as that of the organic transistor 10A, and has an effect of preventing water and gas from permeating from the substrate toward the organic transistor.

  Further, as shown in FIG. 5B, a barrier layer 18 may be further provided on the back surface of the substrate 11, that is, the surface opposite to the surface on which the transistor is formed. In this case, the barrier layer 18 can be made of the same material as that used for the paria layer 17, and further prevents water and gas from permeating from the substrate toward the organic transistor. The effect to do becomes large.

  Further, the structure of the organic transistor is not limited to the structure shown in FIG. 1, FIG. 3 (A), (B), FIG. 4, and FIG. 5 (A), (B). The present invention can be applied with modification.

It is sectional drawing which showed typically the organic transistor by Example 1 of this invention. It is the figure which showed typically the example of the structure of the gate insulating film used for the organic transistor of FIG. (A), (B) is a figure (the 1) which shows the modification of the organic transistor of FIG. FIG. 8 is a second diagram illustrating a modification of the organic transistor in FIG. 1. (A), (B) is a figure which shows the modification of the organic transistor of FIG.

Explanation of symbols

10, 10A, 10B, 10C Organic transistor 11 Substrate 12 Gate electrode 13 Gate insulating film 13a First gate insulating film 13b Second gate insulating film 14 Organic semiconductor film 15 Source electrode 16 Drain electrode 17, 18 Barrier layer

Claims (5)

A gate electrode formed on the substrate;
A gate insulating film formed on the gate electrode;
An organic semiconductor film formed on the gate insulating film;
An organic transistor having a first electrode and a second electrode connected to the organic semiconductor film,
The gate insulating film includes a first gate insulating film in contact with the gate electrode and a second gate insulating film, and the first gate insulating film has a relative dielectric constant higher than that of the second gate insulating film. The organic transistor is characterized in that the second gate insulating film has a larger contact angle with respect to pure water than the first gate insulating film.   2. The organic transistor according to claim 1, wherein the first gate insulating film is thicker than the second gate insulating film. A gate electrode formed on the substrate;
A gate insulating film formed on the gate electrode;
An organic semiconductor film formed on the gate insulating film;
An organic transistor having a first electrode and a second electrode connected to the organic semiconductor film,
The gate insulating film is
A first to n-th gate insulating film including a first gate insulating film in contact with the gate electrode and an n-th (n is an integer of 2 or more) gate insulating film in contact with the organic semiconductor film;
Among the first to (n-1) th gate insulating films, at least one gate insulating film has a relative dielectric constant larger than a relative dielectric constant of the nth gate insulating film,
An organic transistor, wherein a contact angle of the nth gate insulating film with respect to pure water is larger than a contact angle of the (n-1) th gate insulating film.   The contact angle of the nth gate insulating film with respect to pure water is larger than any of the first to (n-1) th gate insulating films, and among the first to nth gate insulating films, 4. The organic transistor according to claim 3, wherein the thickness of the gate insulating film having the largest relative dielectric constant is the thickest among the first to n-th gate insulating films. A method for forming an organic transistor according to any one of claims 1 to 4,
Irradiating the gate insulating film with ultraviolet rays having a wavelength of 380 nm or less;
Forming the organic semiconductor film on the gate insulating film irradiated with the ultraviolet rays. A method for forming an organic transistor, comprising:

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