JP5733612B2 - Material for organic semiconductor thin film, method of forming organic semiconductor thin film using the material, and organic thin film transistor - Google Patents

Description

  The present invention relates to a material for an organic semiconductor thin film, a method for forming an organic semiconductor thin film using the material, and an organic thin film transistor having an organic semiconductor thin film formed by the forming method. Specifically, it is an organic semiconductor material that can be used as an n-type organic semiconductor element, and when it is heated to a temperature of 80 ° C. to 250 ° C., a material for an organic semiconductor thin film that undergoes a phase transition to a liquid crystal state. The present invention relates to a method for forming an organic semiconductor thin film, and an organic thin film transistor having an organic semiconductor thin film formed by the method.

  The progress of the advanced information society in recent years is remarkable, and the development of digital technology has penetrated communication technologies such as computers and computer networks into daily life. At the same time, flat-screen TVs, notebook computers, and mobile phones have been widely used, and demands for display displays such as liquid crystal displays, organic EL displays, and electronic papers are increasing. In recent years, in particular, the display has become larger and more detailed, and more field effect transistors corresponding to the number of pixels have been required than ever. In a liquid crystal display, a liquid crystal can be driven by disposing a field effect transistor as an active element in each pixel and performing signal on / off control.

  As the field effect transistor used for the active element, a thin film transistor can be used. The performance of thin film transistors depends on the semiconductor material and structure used. In particular, obtaining a large carrier mobility and a high on / off ratio makes it possible to obtain a large current, and not only enables driving of an organic EL or the like, but also miniaturization of a thin film transistor and improvement of contrast. Can do.

  As the thin film transistor used for the active element, a silicon-based semiconductor such as amorphous silicon or polysilicon can be used. Thin film transistors are manufactured by multilayering these silicon semiconductors and forming source, drain and gate electrodes on a substrate.

  Manufacturing a thin film transistor using a silicon semiconductor requires a large-scale and expensive manufacturing facility, and also requires many steps because of using photolithography. is there. In addition, since the manufacturing temperature requires a high temperature of 300 ° C. to 500 ° C. or higher, not only the manufacturing cost is increased, but also the applicability of materials such that it is difficult to form a thin film on a plastic substrate or a flexible plastic film. There is also a problem about.

  On the other hand, an organic thin film transistor using an organic semiconductor thin film made of an organic semiconductor material is produced by a vapor deposition method (vacuum film forming method) or a solution coating method (print film forming method), and is low in cost, large in area, and light in weight. there is a possibility. In addition, since the organic semiconductor thin film can be produced at a lower temperature than the inorganic semiconductor layer, the cost can be reduced. In addition, since an organic semiconductor thin film can be formed on a plastic substrate or a flexible plastic film, the weight can be reduced and application to a flexible electronic device is also possible.

  Many organic semiconductor materials have been studied so far, and those using low molecular compounds and conjugated polymer compounds as organic semiconductor thin films are known. However, although the conjugated polymer compound has excellent solubility in a solvent and can form an organic semiconductor film by a simple solution coating method, the performance in the case of an organic thin film transistor is not sufficiently satisfactory. . On the other hand, the low molecular weight compound shows high performance as an organic thin film transistor, but there is a problem that it is difficult to make a thin film due to poor solubility in a solvent. Here, as a method for producing a semiconductor thin film, there is a method of forming a semiconductor film by a vapor deposition method or an organic semiconductor film by a solution coating method using a dilute solution, and particularly by a simple solution coating method. It is very useful if it can be formed. However, in the solution coating method, since a thin film is formed using a dilute solution obtained by dissolving the above compound in a solvent, it is not possible to stably obtain a film thickness sufficient to obtain stable performance as an organic transistor. There was a problem that it was difficult. That is, an organic semiconductor material having high solubility is desired, but high solubility and high performance are in a trade-off relationship, and a semiconductor thin film material having both high solubility and high performance has not been developed yet.

  Furthermore, the organic semiconductor material includes an n-type semiconductor material for obtaining an n-type semiconductor and a p-type semiconductor material for obtaining a p-type semiconductor. The development of a material that can demonstrate this is awaited. In the n-type semiconductor material, an electric current is generated by moving electrons as main carriers, and in the p-type semiconductor material, an electric current is generated by moving holes (holes) as main carriers. Pentacene-based materials and thiophene-based materials known as organic semiconductor materials exhibiting high performance are semiconductor materials exhibiting p-type characteristics, and reports on high-performance n-type organic semiconductor materials are limited.

  In order for organic electronics to further develop against the above situation, low power consumption and simpler circuits are essential, and organic complementary MOS circuits such as complementary metal oxide semiconductors (CMOS) are required. It becomes. Organic complementary MOS circuits require both an organic thin film transistor having at least one n-type channel and an organic thin film transistor having at least one p-type channel. In such a circuit, it is often required that the organic thin film transistor having an n-type channel and the organic thin film transistor having a p-type channel have the same charge mobility and on / off ratio of electrons and holes. Accordingly, organic semiconductor materials for both an n-type organic thin film transistor having a high electron mobility and on / off ratio and a p-type organic thin film transistor having a high hole mobility and on / off ratio are required. So far, organic semiconductor materials with high mobility such as pentacene and oligothiophene have been reported for p-type organic thin-film transistors, but only n-type organic thin-film transistors with lower mobility than p-type have been reported. Not. For this reason, higher performance n-type organic semiconductor materials are desired than ever before.

  So far, perylene and diimide derivatives thereof, fullerene and derivatives thereof are known as n-type organic semiconductor materials. However, with these n-type organic semiconductor materials, thin film transistors having high transistor performance that satisfy practical aspects such as production cost and productivity of organic semiconductor materials and can be mass-produced by printing and coating methods. There is no report about.

On the other hand, as an organic thin film transistor using a naphthalene tetracarboxylic acid derivative, Patent Document 1 discloses 1,4,5,8-naphthalenetetracarboxylic anhydride (NTCDA), 1,4,5,8-naphthalenetetracarboxyl. It is described that the electron mobility of an organic thin film transistor using an organic semiconductor thin film made of diimide (NTCDI) and tetracyanoquinomethane (TCNQ) is 10 ⁻³ to 10 ⁻⁵ cm ² / Vs.

Further, in Patent Document 2, a thin film transistor including an organic semiconductor material layer including a 1,4,5,8-naphthalenetetracarboxydiimide derivative having an alkyl group and an alkyl group substituted with a fluorine-containing group has a mobility of 0.005. ~0.2cm ² / Vs, the on / off ratio was 10 ⁴ -10 ^5, it is described that show stability in the air, and excellent reproducibility. In Patent Document 3, a thin film transistor including an organic semiconductor thin film layer formed from an organic semiconductor solution containing a 1,4,5,8-naphthalenetetracarboxydiimide derivative having an alkyl group substituted with a fluorine-containing group has a mobility of 0. a 005cm ² /Vs,0.07cm ² / Vs, it is described that show stability in the air, and excellent reproducibility.

In Patent Document 4, a thin film transistor including an organic semiconductor thin film layer formed from an organic semiconductor solution containing a 1,4,5,8-naphthalenetetracarboxydiimide derivative having a cycloalkyl group has a mobility of 0.07 to 2.5 cm. ² / Vs, and an on / off ratio of 10 ⁴ to 10 ⁵ , indicating stability in air and excellent reproducibility. In Patent Document 5, a thin film transistor including an organic semiconductor thin film layer formed from an organic semiconductor solution containing a 1,4,5,8-naphthalenetetracarboxydiimide derivative having a cycloalkyl group has a mobility of 0.07 to 2.5 cm. ² / Vs, and an on / off ratio of 10 ⁴ to 10 ⁵ , indicating stability in air and excellent reproducibility.

Further, Non-Patent Document 1 reports that naphthalene-thiophene derivatives have excellent solubility, and organic thin film transistors produced by a printing method exhibit high transistor characteristics of electron mobility of 0.1 to 0.8 cm ² / Vs. ing. Further, Patent Document 5 also describes a method of forming an organic semiconductor element by heat-treating an organic semiconductor layer made of a liquid crystalline styryl derivative in a temperature range of a smectic liquid crystal state.

  The organic semiconductor thin film formed by a method such as the vacuum film forming method or the printing film forming method (solution coating method) described above generally has a polycrystalline structure in which microcrystals are aggregated, and has many grain boundaries and defects. These grain boundaries and defects hinder charge transport. Therefore, it is difficult to make the organic semiconductor thin film formed by a vacuum film forming method or a printing film forming method uniform over a large area, and these methods produce an organic semiconductor device having stable device performance. That was practically difficult.

In order to solve such a problem, the present inventors have made the following proposals so far. Using an organic semiconductor thin film prepared by vacuum film-forming N, N′-ditridecyl-3,4,9,10-perylenedicarboxylic imide, which is an organic semiconductor material having a thermotropic liquid crystal phase below the decomposition temperature, The organic thin-film transistor heat-processed at the temperature which exhibits a smectic liquid crystal phase is proposed (nonpatent literature 2: electron mobility 2.1cm < ² > / Vs).

European Patent Application Publication No. 1,041,653 US Pat. No. 6,252,245 JP 2000-307173 A JP 2009-516930 A JP 2009-538653 A

H. Yan et al, Nature, 457, 679 (2009) Ichikawa et al, Appl, Phys, Lett, 89 (11), 112108 (2006)

  The present inventors have further studied, and N, N′-dialkyl-1,4,5,8-naphthalenedicarboxylic imide, which is an organic semiconductor material having a thermotropic liquid crystal phase below the decomposition temperature, is used as a liquid medium. High concentration is achieved by forming a fine particle dispersion that is dispersed, and an organic semiconductor thin film formed by a printing film forming method is heat-treated at a temperature exhibiting a smectic liquid crystal phase, thereby achieving high electron mobility and high on-state. / It turned out that it becomes an organic thin-film transistor which has an off value. Based on this knowledge, aiming for further practical technology, by making the naphthalene compound soluble, an organic semiconductor film is formed by a solution coating method, and this is heat-treated at the phase transition temperature of the organic thin film, Further studies are ongoing on application to thin film transistors.

  In the course of proceeding with the above studies, the organic semiconductor material described above has low solubility in a solvent, and in the case of forming an organic semiconductor film by a solution coating method, the film may be non-uniform in the coating process and the drying process. That is, it has been found that it is difficult to obtain a uniform large-area film with the above technique, and in order to obtain a large-area film, it is necessary to form an organic semiconductor film by a vacuum deposition method. As described above, at present, it is an organic semiconductor material that can be formed by a printing film formation method, and it is easy to uniformly produce an organic semiconductor thin film formed by a printing film formation method over a large area. No organic semiconductor material has been found.

  In addition, an organic thin film transistor created using the above-described naphthalene tetracarboxydiimide and its derivative as an organic semiconductor material needs to introduce a thiophene group when synthesizing the material in order to obtain high transistor performance. In addition, it is necessary to introduce a halogen group such as fluorine into the naphthalene skeleton or the alkyl group on the side chain. For this reason, organic semiconductor materials have become expensive due to the complexity and multi-stage manufacturing process, and there has been a practical problem that is important for industrialization, which makes it difficult to produce inexpensive devices. For this reason, manufacture of an organic semiconductor material can be easily performed without passing through many processes, and it can manufacture more cheaply, and at the same time, development of a material having high performance as an organic semiconductor material is desired. Furthermore, in addition to the above, a solution coating method can be used, and an organic semiconductor thin film formed by a printing film forming method can be easily formed uniformly over a large area, and the above-described simple method can be used. The development of technology that can be used as an organic semiconductor layer or an organic thin film transistor having an excellent electron mobility and on / off ratio while being a formed thin film is awaited.

  Therefore, the object of the present invention is to further advance the material for n-type organic semiconductor thin film that has been developed so far, and to obtain a material for organic semiconductor thin film having excellent solubility in a solvent. A solution can be obtained, and by using the organic semiconductor thin film material, an organic semiconductor thin film formed by a printing film forming method can be easily formed uniformly over a large area, and the formed organic thin film However, an object of the present invention is to provide a very useful material for an organic semiconductor thin film, which can form an organic semiconductor thin film having high electron mobility and high on / off value.

  Another object of the present invention is to provide an organic thin film transistor that is excellent in economic efficiency and performance using the organic semiconductor thin film material, in which the electron mobility in the organic thin film transistor is one of the main problems. Another object of the present invention is to provide an organic transistor comprising a stable organic semiconductor film that has been made uniform by heat treatment.

  The above object is achieved by the present invention described below. That is, the present invention is an organic semiconductor thin film material that can be used as an n-type organic semiconductor element, has a phase transition temperature in a temperature range of 80 ° C. to 250 ° C., and has the following general structural formula (1): Provided is a material for an organic semiconductor thin film characterized by including a naphthalenetetracarboxydiimide derivative represented by:

(However, in the formula, R 1 and R 2 are each independently a branched or unbranched alkyl group having 10 to 22 carbon atoms and may further contain N, O, S, and P heteroatoms. X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from a hydrogen atom, a halogen atom and a cyano group.)

The preferred mode of the organic semiconductor thin film material, the general formula (1) R1 and R2 in, C _n H _{2n + 1} where the number of n are different or is mutually identical (n is 10 to 18 The derivative represented by the general structural formula (1) is N, N′-diundecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (1): N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (2), N, N′-dipentadecyl-1,4 represented by the following structural formula (3) Any of 5,8-naphthalenetetracarboxydiimide and N, N′-diheptadecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (4) may be mentioned.

Further, as a preferred form of the organic semiconductor thin film material, the general formula (1) wherein R1 and R2, the number of n are different or is mutually identical _{C n H 2n + 1 -O-} C 3 H ₆ (n represents an integer of 7 to 19); the derivative represented by the general structural formula (1) is N, N′-bis (3- ( n-dodecyloxy) -n-propyl) -1,4,5,8-naphthalenetetracarboxydiimide.

  As another embodiment, the present invention uses, as another embodiment, the organic semiconductor thin film material of any of the above forms, and the material is applied on a substrate in a state of being dissolved or / and dispersed in an organic solvent, followed by drying. Then, the formed coating film is heat-treated at a temperature of 80 ° C. to 350 ° C. to heat the coating film, and the coating film after further cooling has a thickness of 10 nm to 10 μm. A method for forming an organic semiconductor thin film is provided.

Moreover, as a preferable form of the method for forming the organic semiconductor thin film, the coating film is heated to a temperature of 80 ° C. to 250 ° C .; the heat treatment is performed in a reduced pressure atmosphere of 10 ^{−5 to} 50,000 Pa. That said heat treatment is performed in an inert gas atmosphere.

Furthermore, the present invention provides, as another embodiment, an organic thin film transistor in which at least a gate electrode, a gate insulating layer, an organic semiconductor thin film, and a source electrode and a drain electrode are formed on a substrate. An organic thin film transistor is provided which is formed by the method for forming an organic semiconductor thin film. A preferred form of the organic thin film transistor is that its carrier mobility is 0.01 cm ² / Vs or more.

  According to the present invention, by introducing a long-chain alkyl group into the naphthalene diimide skeleton of N, N′-dialkyl-1,4,5,8-naphthalenecarboxydiimide, which can be expected as a useful organic semiconductor material, it is further increased. An organic semiconductor thin film material capable of forming an organic semiconductor thin film having electron mobility and a high on / off value can be provided. Further, according to the present invention, a solution dissolved or dispersed in a solvent by the organic semiconductor thin film material of the present invention having the above-mentioned excellent characteristics can be obtained uniformly and over a large area by a simple printing film forming method using the solution. It is possible to form an organic semiconductor thin film excellent in the above. Furthermore, according to the present invention, it is possible to form a uniform organic semiconductor thin film with a more uniform molecular arrangement by heat-treating the formed organic semiconductor thin film in a phase transition temperature region. According to the present invention, by applying the organic semiconductor thin film described above, it is possible to provide an extremely useful organic thin film transistor that is excellent in economy and transistor performance.

Sectional drawing showing an example of the structure of the bottom contact type organic thin-film transistor of this invention. Sectional drawing showing an example of the structure of the top contact type organic thin-film transistor of this invention. The figure showing the X-ray-diffraction pattern of a N, N'-ditridecyl-1,4,5,8-naphthalene tetracarboxydiimide thin film (after an untreated and heat processing). FIG. 10 is a graph showing the relationship between current modulation characteristics (drain current and drain voltage) in Example 4; FIG. 10 is a graph showing the relationship between current modulation characteristics (drain current and gate voltage) in Example 4; The figure showing the AFM image of a N, N'-ditridecyl-1,4,5,8-naphthalene tetracarboxydiimide thin film. FIG. 4 is a change diagram of heat flow of N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide by scanning calorimetry. The heat flow change figure by DSC of N, N'-dioctadecyl-1,4,5,8-naphthalene tetracarboxydiimide.

  Next, preferred embodiments of the present invention will be described in detail, but the present invention is not limited to the following embodiments, and can be carried out without departing from the gist of the present invention. First, the organic semiconductor thin film material of the present invention will be described.

  The organic semiconductor thin film material of the present invention can be used as an n-type organic semiconductor element, has a phase transition temperature in a temperature range of 80 ° C. to 250 ° C., and is represented by the following general structural formula (1). And naphthalenetetracarboxydiimide derivatives. The organic semiconductor thin film material of the present invention has a thermotropic liquid crystallinity, so that a useful organic semiconductor film with uniform molecular alignment and excellent performance can be formed by a heat treatment process. In addition, in the following general structural formula (1), “may further contain a heteroatom of N, O, S, P” means a heteroatom other than carbon in an alkyl group having 10 to 22 carbon atoms. Means that it may contain.

(However, in the formula, R 1 and R 2 are each independently a branched or unbranched alkyl group having 10 to 22 carbon atoms, and may further contain N, O, S, and P heteroatoms. X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from a hydrogen atom, a halogen atom and a cyano group.)

  Specific examples of the organic semiconductor thin film material that satisfies the above configuration include the following. For example, N, N′-dialkyl-1,4,5,8-naphthalenetetracarboxydiimide, N, N′-dialkylether-1,4,5,8-naphthalenetetracarboxydiimide, and halogenation thereof Compounds, cyanated compounds, and the like.

  The above-mentioned compounds have a π-conjugated skeleton structure and an alkyl group and / or an alkyl ether group. However, as a result of intensive studies, the present inventors have found that such a material is liquid crystal by heating. It has been found that the phase transitions to a state and exhibits thermotropic liquid crystallinity. And, if the material has thermotropic liquid crystallinity, the heat treatment process makes it possible to form a more uniform organic semiconductor thin film with excellent semiconductor characteristics, and such characteristics are considered to be extremely useful industrially. It is done. Therefore, if it is such, it can be used without a problem as an organic-semiconductor thin film of this invention.

  Here, the naphthalene tetracarboxylic acid derivative has two carbonyl groups in which oxygen atoms are bonded to carbon by a double bond at both ends, and a strong electron withdrawing property due to the carbonyl group is generated. It becomes the material which shows the type organic semiconductor characteristic. Therefore, the naphthalene tetracarboxylic acid derivative has a deep HOMO, and there is a possibility of providing an organic thin film transistor that exhibits stable transistor performance despite the presence of impurities such as oxygen and water contained in the atmosphere. is there. In addition, strong stacking can be formed by the strong intermolecular interaction between the naphthalene skeleton structures composed of aromatic rings, and the characteristics can be expressed as an electron transfer material. Furthermore, the naphthalene tetracarboxylic acid derivative having an alkyl group as shown by the general structural formula (1) characterizing the present invention is perpendicular to the substrate in the formation of an organic thin film on the substrate by vapor deposition or solution coating. An organic semiconductor thin film having a proper arrangement is formed, and a high electron mobility is achieved by the horizontal expansion of the naphthalene skeleton structure. Furthermore, since the one having the structure defined in the present invention has thermotropic liquid crystallinity, it becomes possible to homogenize a film with a more uniform molecular arrangement by heating the organic semiconductor film to near the phase transition temperature, Electron mobility also increases, the on / off ratio increases, and the threshold voltage also decreases.

  Substituents R1 and R2 bonded to nitrogen atoms at both ends of the naphthalenetetracarboxydiimide derivative represented by the following general structural formula (1) characterizing the present invention are branched or unbranched alkyl groups having 10 to 22 carbon atoms. It is.

  In the above, when the number of carbon atoms of the alkyl group is less than 10, the effect of molecular arrangement by heat treatment is small, and a uniform film cannot be formed by heat treatment. On the other hand, when the number of alkyl groups exceeds 22, the ratio of the alkyl groups in the compound is increased, the semiconductor characteristics are lowered, and the solubility in the solvent is lowered, so that it is difficult to form a film by a solution coating method. Become.

  Specific examples of the alkyl group include, for example, decyl group, undecyl group, dodecyl group, tridecyl group, tetradecyl group, pentadecyl group, hexadecyl group, heptadecyl group, octadecyl group, nonadecyl group, eicosyl group, heneicosyl group, docosyl group. Examples thereof include a linear alkyl group having 10 to 22 carbon atoms of the group or a branched alkyl group thereof.

Considering the availability of raw materials, the ease of reaction, and the semiconductor characteristics of naphthalene tetracarboxydiimide derivatives, R 1 and R 2 in the general structural formula (1) are the same or different from each other C _n H _{2n +} Those represented by ₁ (n is an integer of 10 to 18) are preferred. Specifically, R 1 and R 2 are a decyl group, an undecyl group, a dodecyl group, a tridecyl group, a tetradecyl group, a pentadecyl group, a hexadecyl group, a heptadecyl group, an octadecyl group, a linear alkyl group having 10 to 18 carbon atoms, or These branched alkyl groups are preferred.

  Furthermore, particularly preferable examples of the naphthalene tetracarboxydiimide derivative represented by the general structural formula (1) characterizing the present invention include, for example, N, N′-diundecyl-1,4 represented by the following structural formula (1). , 5,8-naphthalenetetracarboxydiimide, N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (2), N, represented by the following structural formula (3) N'-dipentadecyl-1,4,5,8-naphthalenetetracarboxydiimide or N, N'-diheptadecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (4) It is done.

  According to the study by the present inventors, the naphthalene tetracarboxydiimide derivatives having an alkyl group having an odd number of carbon atoms listed above are more in phase than the naphthalene tetracarboxydiimide derivatives having an alkyl group having an even number of carbon atoms. Since the temperature range where the transition occurs is wide and the temperature range where the effect of the heat treatment can be obtained is wide, the heat treatment temperature can be easily controlled. For this reason, the effect of molecular arrangement brought about by the heat treatment can be surely obtained, and furthermore, a stable and uniform film can be obtained. For example, the phase transition temperature of N, N′-didecyl-1,4,5,8-naphthalenetetracarboxydiimide having 10 carbon atoms in the alkyl group, which is a material for an organic semiconductor thin film defined in the present invention, is 146 8 ° C and 165.6 ° C. Similarly, the phase transition temperature of N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide, which is an organic semiconductor thin film material defined in the present invention, wherein the alkyl group has 13 carbon atoms and an odd number. Is 109.2 ° C., 144.7 ° C., and 161.3 ° C., and the phase transition temperature region is wider than that in the case where the alkyl group has an even number of carbon atoms. When an organic semiconductor thin film material having a wide phase transition temperature region is used as described above, it is easy to adjust the temperature of the heat treatment step of the organic semiconductor thin film formed by coating the material. Variation in semiconductor characteristics of the organic thin film transistor formed by forming a thin film can be reduced.

  Further, according to the study of the present invention, the dissolution of the derivative represented by the general structural formula (1) in the organic solvent is as described above for each of the nitrogen atoms at both ends of naphthalenetetracarboxydiimide. By having a structure having an alkyl group and / or an alkyl group having a hetero atom selected from N, O, S, P, etc., it has a thermotropic liquid crystallinity and an excellent solution stability Thus, it becomes possible to stably form an organic semiconductor thin film by a coating method.

In addition, the organic semiconductor thin film material of the present invention has the same or different R 1 and R 2 in the general structural formula (1) characterizing the present invention as C _n H _{2n + 1} —O—C ₃ H ₆ ( n represents an integer of 7 to 19). Since the alkyl ether group contains an oxygen atom in the alkyl group, the affinity with the solvent is excellent, so the solubility in the solvent is increased, and a high-concentration solution dissolved in the solvent can be applied. An organic semiconductor thin film having almost no defects or defects can be formed. An organic semiconductor thin film formed using the above materials and an organic thin film transistor using the organic semiconductor thin film can reduce variations in semiconductor characteristics between elements.

  The following are mentioned as an alkyl ether group in the above. For example, 3- (n-heptyloxy) -n-propyl group, 3- (n-octyloxy) -n-propyl group, 3- (n-nonaoxy) -n-propyl group, 3- (n-decyloxy) -N-propyl group, 3- (n-undecyloxy) -n-propyl group, 3- (n-dodecyloxy) -n-propyl group, 3- (n-dodecyloxy) -n-propyl group, 3 -(N-tridecyloxy) -n-propyl group, 3- (n-tetradecaoxy) -n-propyl group 3- (n-eicosaoxy) -n-propyl group, 3- (2-ethylhexyloxy)- Examples thereof include a branched or unbranched alkyl group containing a hetero atom such as an n-propyl group.

Considering the availability of raw materials and the ease of reaction, and the semiconductor characteristics and film forming ability of naphthalenetetracarboxydiimide derivatives, the alkyl ether group in the above is a 3- (n-dodecyloxy) -n-propyl group , 3- (n-tetradecyloxy) -n-propyl group is preferable. Examples of the compound having an alkyl ether group include N, N′-bis (3- (n-dodecyloxy) -n-propyl) -1,4,5, represented by the following structural formula (5). 8-Naphthalenetetracarboxydiimide is mentioned.

  The naphthalene tetracarboxydiimide derivative represented by the general structural formula (1) characterizing the present invention can be synthesized by the following known methods. For example, in a high-boiling organic solvent, naphthalene tetracarboxylic acid anhydride is reacted with a corresponding amine, or once naphthalene tetracarboxylic acid is converted into a potassium salt and then reacted with a corresponding alkyl halide, A naphthalene tetracarboxydiimide derivative represented by the general structural formula (1) can be obtained.

Further, in the derivative represented by the general structural formula (1) characterizing the present invention, X ₁ , X ₂ , X ₃ and X ₄ in the formula (1) may be a hydrogen atom. Independently, a halogen element such as fluorine, chlorine, or bromine or a cyano group can be introduced into the naphthalene skeleton. By introducing a halogen group or a cyano group into the naphthalene skeleton, the solubility in an organic solvent is further increased, and an organic semiconductor thin film can be easily formed by a coating method. Furthermore, according to the organic semiconductor thin film formed of the organic semiconductor thin film material of the present invention, transistor characteristics can be stably realized in the atmosphere. Further, according to the study by the present inventors, in the general structural formula (1) characterizing the present invention, a material in which R1 and R2 in the formula are alkyl groups substituted with fluorine is used. Thus, the formed thin film can prevent impurities such as water, oxygen, and air from entering, and becomes a useful organic semiconductor film that can stably exhibit n-type semiconductor characteristics.

  Examples of naphthalene tetracarboxylic acid anhydrides used when synthesizing a naphthalene tetracarboxydiimide derivative characterizing the material for an organic semiconductor thin film of the present invention include the following. For example, unsubstituted 1,4,5,8-naphthalenetetracarboxylic anhydride, 2,6-dicyano-1,4,5,8-naphthalenetetracarboxylic anhydride, 2,6-dichloro-1,4 , 5,8-naphthalenetetracarboxylic acid anhydride, 2,6-difluoro-1,4,5,8-naphthalenetetracarboxylic acid anhydride, 2,3,6,7-tetrafluoro-1,4,5, Examples include 8-naphthalene tetracarboxylic acid anhydride. Among these, considering the availability of raw materials, the ease of reaction, and the semiconductor properties of the synthesized naphthalenetetracarboxydiimide derivatives, unsubstituted naphthalenetetra which has no substituents introduced into the naphthalene skeleton Preference is given to using carboxylic anhydrides.

  As described above, in the organic semiconductor thin film material of the present invention, in the derivative represented by the general structural formula (1), R1 and R2 in the formula (1) are the same or different alkyl groups. Those having an alkyl ether group can be used, and these can be obtained, for example, as follows. First, the synthesis of a derivative having the same R1 and R2 is a single step, and can be obtained by mixing and heating naphthalenetetracarboxylic acid and the corresponding amine. On the other hand, the synthesis of derivatives in which R1 and R2 are different alkyl groups and alkyl ether groups is a multi-step process, but the obtained derivatives have high solubility in organic solvents due to the asymmetry of the structure, and high concentrations. It can be applied with a high concentration solution dissolved in a solvent. When a film is formed by coating with such a high-concentration solution, the film thickness increases, and an organic semiconductor thin film with almost no film defects or defects can be formed. An organic thin film transistor formed using these films It is possible to reduce variations occurring in the semiconductor characteristics.

  When using the organic-semiconductor film formed with the organic-semiconductor thin-film material of this invention for an organic thin-film transistor, it is preferable to use the compound represented by general structural formula (1) with higher purity. That is, reducing the impurities in the organic semiconductor thin film material can reduce factors that hinder the movement of electrons in the organic semiconductor thin film, increase the electron mobility of the organic thin film transistor, and improve the transistor performance. The method for increasing the purity is not particularly limited, but purification methods such as a chromatographic method, a recrystallization method, a sublimation purification method, a zone refining method, a supercritical method, or a combination of these methods can be used to increase the purity. It is effective to use elevated compounds.

  As described above, since the organic semiconductor thin film material of the present invention is excellent in solubility in a solvent and can obtain a high-concentration solution of the material, an organic semiconductor thin film formed by a printing film forming method can be obtained. It can be easily created uniformly over a large area. Furthermore, the organic semiconductor thin film thus formed can be heat-treated in a temperature region including the phase transition temperature, thereby making it possible to form a uniform organic semiconductor thin film with a more uniform molecular arrangement. That is, the method for forming an organic semiconductor thin film of the present invention uses the organic semiconductor thin film material described above, and the material is applied on a substrate in a state of being dissolved or / and dispersed in an organic solvent, followed by drying. The formed coating film is heat-treated at a temperature of 80 ° C. to 350 ° C., the coating film is heated, and the coating film after being further cooled has a thickness of 10 nm to 10 μm.

  When an organic semiconductor thin film is formed according to the present invention, the film thickness may be 10 nm to 10 μm. When the organic semiconductor thin film formed of the organic semiconductor thin film material of the present invention is used as an organic thin film transistor, semiconductor characteristics can be obtained as long as a monomolecular thin film is formed on the substrate surface. In addition, even when the film thickness is large, the film region functioning as a channel through which electrons move is limited to a few molecules from the substrate. Therefore, the thickness of the organic semiconductor thin film is 10 nm or more, preferably 20 nm or more, and more preferably 50 nm or more, because the thin film thickness increases the probability of film defects / defects. When the film is thick, it functions as an organic thin film transistor without problems, but from the viewpoint of cost, it is 10 μm or less, preferably 1 μm or less.

  The organic thin film transistor of the present invention is characterized by having an organic semiconductor thin film formed of the organic semiconductor thin film material of the present invention described above. The organic semiconductor film is a material for the organic semiconductor thin film of the present invention. The derivative represented by the general structural formula (1) characterizing the above may be formed singly or may be formed by combining a plurality of different types of derivatives. Furthermore, the organic semiconductor thin film material of the present invention used for forming the organic semiconductor thin film is an organic semiconductor thin film exhibiting an n-type semiconductor property that undergoes a phase transition to a liquid crystal state in a temperature range of 80 ° C. to 250 ° C. in addition to the above-described derivatives. It can also be made into the form which used the material for use together. For example, it can be used in combination with perylene diimide and its derivatives. Perylene derivatives that can be used in this case include N, N′-ditridecyl-3,4,9,10-perylenetetracarboxydiimide, N, N′-bis (n-dodecyloxypropyl) -1,4,5. Perylene derivatives having a long-chain alkyl group or a long-chain alkyl ether group, such as 1,8-perylenetetracarboxydiimide, are preferred.

  When the organic semiconductor thin film is formed, when the derivative represented by the general structural formula (1) characterizing the organic semiconductor thin film material of the present invention and the perylene derivative as described above are used in combination, for example, perylene A method of adding a derivative to an organic solvent or a method of dispersing perylene derivative fine particles can be used. In this case, the content of the derivative of the general structural formula (1) in 100% by mass of the material used for forming the organic semiconductor thin film is preferably 20% by mass or more, more preferably 50% by mass or more, and still more preferably. Is 90% by mass or more. If the content is 50% by mass or less, it is difficult to form a uniform film, and a sufficient film thickness as an organic semiconductor film cannot be obtained. If the content is 20% by mass or less, a stable organic semiconductor film is obtained. It becomes difficult.

  The method for forming an organic semiconductor thin film of the present invention for forming an organic semiconductor thin film using the organic semiconductor thin film material of the present invention will be described. First, the organic semiconductor thin film material of the present invention is coated and dried on a substrate in a state of being dissolved or / and dispersed in an organic solvent to form a coated film. Preferably, the organic semiconductor thin film material containing the derivative of the general structural formula (1) described above is dissolved in an organic solvent and coated on the substrate in a solution state, whereby a coating film can be easily formed. . Moreover, when forming an organic semiconductor film using a poor solvent having low solubility, the organic semiconductor thin film material of the present invention is dispersed in a solvent in a solid state, and a coating film is formed by using the dispersion. it can. The organic solvent used at this time is not particularly limited as long as a dispersion or solution having an appropriate concentration can be obtained. For example, halogen hydrocarbon solvents such as chloroform, dichloroethane, chlorobenzene, dichlorobenzene, trichlorobenzene, chloronaphthalene, ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, ester solvents such as ethyl acetate, butyl acetate, methanol, ethanol Alcohol solvents such as n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, tert-butanol, n-hexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, diethylene glycol monomethyl ether , Diethylene glycol monoethyl ether, diethylene glycol monobutyl ether ethylene group Coal, diethylene glycol, triethylene glycol diethyl ether, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, triethylene glycol dimethyl ether, triethylene glycol diethyl ether, triethylene glycol di Ether solvents such as butyl ether, propylene glycol monomethyl ether and propylene glycol dimethyl ether, aromatic hydrocarbon solvents such as toluene, xylene and ethylbenzene, tetrahydrofuran, sulfolane, N, N-dimethylformamide, N-methyl-2-pyrrolidone, Methyl sulfoxide, may be mentioned aprotic polar solvents such as acetonitrile. These solvents may be used alone or in combination. If used together with the organic solvent, water can be used in combination.

  In the preparation of an organic semiconductor solution / dispersion liquid (hereinafter sometimes referred to as a coating liquid) obtained by dissolving or / and dispersing the organic semiconductor thin film material of the present invention in an organic solvent, coating may be applied as necessary. An inorganic compound such as a low molecular surfactant, a high molecular surfactant, a dispersant, and silica can be added to improve the stability of the liquid and the film forming property of the resulting organic semiconductor coating film. Thereby, for example, the dispersion state is stabilized and aggregation can be prevented.

  When the organic semiconductor thin film material is dissolved or / and dispersed in an organic solvent, the concentration of the organic semiconductor thin film material is preferably 0.001% by mass or more with respect to 100% by mass of the total coating liquid, More preferably, it is 0.01 mass% or more. The upper limit of the concentration of the organic semiconductor thin film material with respect to the solvent is not particularly limited, and any concentration can be used as long as the viscosity of the dispersion liquid suitable for a coating machine / printer for forming the organic thin film is obtained.

  The organic semiconductor thin film formed from the material for organic semiconductor thin film of the present invention is obtained by applying the coating liquid obtained as described above to a substrate and drying, and then forming the formed coating film at a temperature of 80 ° C to 350 ° C. By heating the coating film by heat treatment, an organic semiconductor thin film having better performance and excellent performance can be formed. For example, an organic semiconductor thin film that is more uniform and excellent in performance can be formed by printing a dispersion dispersed in a solvent or a solution dissolved in a solvent on a substrate, followed by heating.

  According to the method for forming an organic semiconductor thin film of the present invention, which can be applied to a printing method for applying a coating liquid, further simplification of the apparatus and further cost reduction can be achieved. A uniform, sufficient film thickness can be obtained. As the printing method used in the above, a known printing method can be used. For example, a spin coating method, an ink jet method, a screen printing method, a lithographic printing method, a relief printing method, an intaglio printing method, etc., by a pressurized air An organic semiconductor thin film (coating film) made of an organic semiconductor thin film material can be formed on a substrate by an air spray method, an electrostatic spray method, an airless spray method, or the like that is applied according to the principle of spraying. In addition, as a method of forming an organic semiconductor film using the organic semiconductor thin film material of the present invention, a 100% solid organic semiconductor thin film material that does not use an organic solvent or water is charged and grounded. It is also possible to form an organic semiconductor thin film (coating film) made of an organic semiconductor thin film material by an electrostatic powder coating method that applies static electricity to a substrate (which may be heated). . Such a method is one of the preferred methods in terms of environment and cost in that there is no solvent removal step and there are few steps.

  In the method for forming an organic semiconductor thin film of the present invention, the coating liquid is applied onto the substrate as described above, and after drying, the formed coating film is heated at a temperature of 80 ° C. to 350 ° C. It is necessary to heat the coating film. The phase change of the organic semiconductor thin film material due to the temperature change that is essential for forming a good organic semiconductor thin film by the organic semiconductor thin film material of the present invention is the introduction of an alkyl chain bonded to the naphthalene tetracarboxydiimide group. Alternatively, by introducing an alkyl chain having a hetero atom in the chain, it is considered that a phase transition to a liquid crystal phase (smectic liquid crystal) is exhibited in a temperature range of 80 ° C. to 250 ° C. The phase change of long chain alkylperylene tetracarboxydiimide is described in C.W. Struijk et al., J. Am. Chem. Soc. 122 (2000). From the above, in the method for forming an organic semiconductor thin film according to the present invention, the coating film is heated by performing heat treatment at a temperature of 80 ° C. to 350 ° C. in which the phase change of the organic semiconductor thin film material occurs reliably. did.

  FIG. 7 shows changes in heat flow by scanning calorimetry (hereinafter abbreviated as DSC) of N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide that can be used for the organic semiconductor thin film material of the present invention. showed that. By having a tridecyl group which is a long-chain alkyl group, it is possible to confirm that endotherm occurs near 109 ° C., 145 ° C., and 161 ° C., and phase transition occurs. FIG. 8 shows the change in heat flow by DSC of N, N′-dioctadecyl-1,4,5,8-naphthalenetetracarboxydiimide. By having a tridecyl group which is a long-chain alkyl group, it is possible to confirm that endotherm occurs near 138 ° C. and 149 ° C., and phase transition occurs. On the other hand, in the DSC of N, N′-dioctyl-1,4,5,8-naphthalenetetracarboxydiimide having a short alkyl chain, an endotherm with a melting point was confirmed at around 185 ° C., but no phase transition occurred.

  The present inventors have reported that the transistor performance of an organic thin film transistor is improved by heat-treating an organic semiconductor thin film formed of a perylene tetracarboxydiimide derivative near the phase change temperature (the above-mentioned non-patent document). 2).

  The dispersion film of the organic semiconductor thin film material of the present invention, or a coating film formed by application of a solution, has many crystal grain boundaries and defects, and also has a polycrystalline structure in which microcrystals are aggregated, As it is, many crystal grain boundaries and defects existed, and the organic semiconductor film was inhibited from transporting charges. However, in the present invention, the following remarkable effects are obtained by heat-treating a thin film (coating film) formed of the organic semiconductor thin film material. When the thin film (coating film) is heat-treated, the naphthalene tetracarboxydiimide derivative represented by the general structural formula (1) that characterizes the organic semiconductor thin film material of the present invention becomes a liquid crystal state, thereby forming a uniform coating film. After that, when cooled, it becomes a crystalline state again and exhibits organic semiconductor characteristics. For this reason, [1] formation of a strong stack state by rearrangement of molecules in the crystalline state, [2] impurities are discharged during crystallization, [3] grain size increases, grain boundaries, defects The transistor characteristics are improved, that is, the electron mobility is increased by a combined action such as reduction of defects and improvement of adhesion to the [4] electrode.

  As a result, it is possible to form an excellent organic semiconductor thin film having a large film thickness and almost no film defects or defects. Furthermore, when the organic semiconductor thin film thus formed is used for an organic thin film transistor, variation in semiconductor characteristics between elements can be reduced. In said method, it is preferable to heat-process a coating film at the temperature of 80 to 350 degreeC. By setting the heat treatment temperature in the above range, the phase transition in the derivative of the general structural formula (1) contained in the organic semiconductor thin film material occurs surely, and the above-mentioned [1] By exhibiting the actions [4], an excellent organic semiconductor thin film free from film defects and defects can be obtained.

  Since the organic semiconductor thin film material of the present invention has a thermotropic liquid crystallinity, after printing and coating the organic semiconductor thin film material of the present invention on a substrate, it is further in a temperature region where it becomes a smectic liquid crystal, a nematic liquid crystal, or an isotropic liquid crystal. The film can be further homogenized by the heat treatment step. The material for an organic semiconductor thin film of the present invention is a thermotropic liquid crystal that undergoes a phase transition to a liquid crystal state of either a smectic liquid crystal or a nematic liquid crystal in a temperature range of 80 ° C. to 250 ° C. When the temperature is 80 ° C. or lower, the transistor characteristics may vary greatly depending on the temperature environment used as the organic thin film transistor. When the temperature is 250 ° C. or higher, not only is it difficult to use a plastic substrate, but it is also difficult to manufacture with low-cost and inexpensive manufacturing equipment, which is a merit of the organic semiconductor thin film material. In particular, in addition to cost and transistor performance, an organic transistor may be formed on a flexible plastic substrate. Therefore, it is preferable to have a phase transition temperature in a temperature range of 100 ° C. to 200 ° C.

  Organic semiconductor thin film comprising N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide, which characterizes the material for organic semiconductor thin film of the present invention, which is heat-treated at 100 ° C., 125 ° C. and 150 ° C. The X-ray diffraction pattern of the thin film is shown in FIG. As is clear from FIG. 3, the number of peaks to be confirmed is reduced by the heat treatment, and only the diffraction pattern having a layered structure in which the molecules of the organic semiconductor thin film are aligned is confirmed. An atomic force microscope (AFM) image of this organic semiconductor thin film is shown in FIG. In the untreated (meaning that no heat treatment was performed), a large amount of crystalline substance was confirmed. However, by performing the heat treatment at 125 ° C. and 150 ° C., the size of the crystalline substance was increased. It becomes a thin film like a single crystal in which there is no discontinuous interface (crystal grain boundary) between the two crystals.

The environmental atmosphere for heat treatment in forming the organic semiconductor thin film of the present invention can be performed in the air, in an inert gas, or in a vacuum. It is preferable to perform the heat treatment in a vacuum atmosphere or an inert gas atmosphere because deterioration or oxidation of each material can be prevented. Inert gas used in the heat treatment atmosphere can be used without problems if it does not corrode and deteriorate organic semiconductor thin films such as nitrogen, hydrogen, carbon dioxide, etc. it can. The inert gas needs to contain no gas that degrades the organic semiconductor thin film material such as oxygen, and a high-purity gas is required. Processing in a vacuum is advantageous in terms of cost because it is not necessary to use a high-purity gas. When the heat treatment is performed in a vacuum, it is preferably performed in a reduced pressure atmosphere having a pressure of 10 ^{−5 to} 50,000 Pa. More preferably, it is 1-50,000 Pa, More preferably, it is 100-10,000 Pa. When the degree of vacuum is high, it is effective to install an organic thin film or an organic thin film transistor on the metal plate in order to effectively perform the heat treatment. In this way, heat can be effectively transferred.

  The heat treatment method is not particularly limited, and an oven, a hot roll, a hot press, or the like can be used. Moreover, after forming an organic-semiconductor thin film by the printing method, it can also serve as heat processing and drying in a drying zone. Further, the heat treatment time is not particularly limited as long as the organic semiconductor thin film reaches a predetermined temperature. However, since the heat treatment for a long time promotes the deterioration of the base material, it is preferably within 10 hours.

  The organic semiconductor film made of the material for an organic semiconductor thin film of the present invention is held in the vapor of an organic solvent, so that rearrangement of the organic semiconductor fine particles occurs, and a more uniform and smooth film is provided. As such a solvent, any solvent can be used without any problem as long as it is used for the above-mentioned dispersion. Particularly preferred solvents include organic solvents containing halogen such as chloroform, trichloromethane, and trichloroethylene, pyridine, n-methylpyrrolidone, Examples include toluene and xylene. Examples of the solvent treatment method include a method of holding the organic thin film in a sealed container containing the solvent, and a method of wiping the solvent vapor on the organic thin film.

  The compound represented by the general structural formula (1) characterizing the present invention described above exhibits characteristics as a material for an n-type organic semiconductor thin film, and the compound is used as a material for forming an organic semiconductor thin film. Useful organic thin film transistors can be manufactured. Hereinafter, although the organic type organic thin-film transistor by this invention is demonstrated in detail, this invention is not restricted to these structures.

  In general, an MIS structure (Metal-Insulator-Semiconductor structure) in which a gate electrode is insulated by an insulating film is often used as the structure of the organic thin film transistor. The organic thin film transistor that can be used in the present invention has an organic semiconductor layer made of an organic semiconductor thin film, and further includes a source electrode, a drain electrode, a gate electrode, and a gate insulating layer. In the organic thin film transistor of the present invention, the organic semiconductor thin film is formed of an organic semiconductor thin film material.

  Next, the form of the organic thin film transistor of the present invention will be described. 1 and 2 are cross-sectional views respectively showing examples of the structure of the organic thin film transistor of the present invention. In the form of the organic thin film transistor of FIG. 1, a gate electrode 14 is provided on a substrate 16, an insulating layer 11 is laminated on the gate electrode, and a source electrode 12 and a drain formed on the gate electrode at predetermined intervals. A bottom gate bottom contact type in which an electrode 13 is formed and an organic semiconductor thin film 15 is further stacked thereon is shown. In the form of the organic thin film transistor of FIG. 2, a gate electrode 14 is provided on a substrate 16, an insulating layer 11 is laminated on the gate electrode, an organic semiconductor thin film 15 is laminated thereon, and further thereon. A bottom gate top contact type in which a source electrode 12 and a drain electrode 13 formed at a predetermined interval are formed is shown.

  In the transistor element having such a configuration, a voltage is applied between the gate electrode and the source electrode, the organic semiconductor thin film forms a channel region by the applied voltage, and a current flowing between the source electrode and the drain electrode is controlled. Switching operation is performed.

  Next, the base material which forms the organic thin-film transistor of this invention is demonstrated. The substrate may be an insulating material, and can be manufactured using an inorganic material such as glass or alumina, a plastic substrate such as a polyimide film, a polyester film, a polyethylene film, polystyrene, polypropylene, or polycarbonate. When a plastic substrate is used, a flexible organic thin film transistor that is lightweight and excellent in impact resistance can be manufactured. These substrates may be used alone or in combination. Note that in the case where a conductive substrate, for example, silicon is used for the substrate, the substrate can also serve as the gate electrode.

Next, the insulator layer forming the organic thin film transistor of the present invention will be described. In the present invention, the material constituting the gate insulating layer is not particularly limited, and examples thereof include SiO ₂ , ZrO ₂ , Ta ₂ O ₅ , La ₂ O ₃ , Al ₂ O ₃ , and HfO ₂ . An inorganic material is mentioned. In addition, as the polymer insulating film material, organic materials such as polyimide, polymethyl methacrylate, polyvinyl alcohol, polyvinyl chloride, polyacrylonitrile, polyvinylidene fluoride, polyethylene terephthalate, polyethersulfone, and polycarbonate can be used. The insulating material used for the gate insulating layer may be used alone or in combination.

The method for forming these insulator layers is not particularly limited. For example, a dry process such as a vacuum deposition method, a CVD method, a sputtering method, an atmospheric pressure plasma method, a spray coating method, a spin coating method, Application methods such as blade coating method, dip coating method, cast method, roll coating method, bar coating method, die coating method, air knife method, slide hopper method, and extrusion method, and wet processes such as various printing methods and inkjet methods And can be appropriately selected and applied according to the characteristics of the material to be used. For example, a silicon substrate having a SiO ₂ layer formed by thermal oxidation, steam oxidation or plasma oxidation may be used.

  The gate insulating film is hydrophobized by chemical surface treatment, so that the affinity between the insulator layer and the organic semiconductor thin film is improved, a uniform organic semiconductor thin film can be formed, and leakage current is also suppressed. It becomes possible. Although not particularly limited, for example, gate insulation of silane coupling agents such as OTS (octadecyltrichlorosilane), ODS (octadecyltrimethoxysilane), HMDS (hexamethyldisilazane), and fluorine-containing alkylsilane coupling agents The film is formed by applying a solution or vacuum film formation on the film.

Next, the electrode material for forming the organic thin film transistor of the present invention will be described. As an electrode material used for the source electrode, the drain electrode, and the gate electrode, a conductive material is used. For example, gold, silver, copper, platinum, aluminum, lithium, sodium, potassium, magnesium, calcium, titanium, indium, palladium, manganese molybdenum, magnesium, calcium, barium, chromium, tungsten, tantalum, nickel, cobalt, copper, iron , Lead, tin and other metal materials, and alloys thereof, conductive oxides such as InO ₂ , ZnO ₂ , SnO ₂ , indium tin oxide (hereinafter abbreviated as ITO), and indium zinc oxide (hereinafter abbreviated as IZO) Carbon materials such as carbon black, fullerene, carbon nanotube, and graphite, and conductive polymer compounds can be used. Note that gold, aluminum, magnesium, calcium, ITO, IZO, and a gold / chromium alloy having a low electric resistance at the contact surface with the organic semiconductor thin film are more preferable.

  The method for forming these electrodes is not particularly limited. For example, a printing method using a dispersion in which a conductive material is dispersed in a solution, or a solution in which a conductive material is dissolved in a solution is used. It can be formed by using a printing method, a vapor deposition method, a sputtering method, or the like.

  Further, although the source electrode and the drain electrode are arranged to face each other, the distance (channel length) between the electrodes is one of the factors that determine the transistor characteristics. The distance between the electrodes (channel length) is usually 5,000 μm or less and can be used without any problem, but is preferably 1,000 μm or less, and the width between the source and drain electrodes (channel width) can be used without any particular limitation. However, it is preferably 1 mm or less. The channel width may be longer when the electrode structure is a comb structure. The thickness of the formed source electrode and drain electrode can be used without any problem as long as it is in the range of several nanometers to several hundred micrometers, but 30 nm to 200 micrometers is more preferable.

  Moreover, the organic thin-film transistor of this invention can also provide a gas barrier layer in the whole outer peripheral surface of an organic thin-film transistor, or a part in order to reduce the influence of oxygen, a water | moisture content, etc. in air | atmosphere. Examples of the material for forming the gas barrier layer include polyvinyl alcohol, ethylene-vinyl alcohol copolymer, polyvinyl chloride, polyvinylidene chloride, and polytetrafluoroethylene.

In addition, the organic thin-film transistor of this invention can evaluate a transistor characteristic with an electron (carrier) mobility (cm < ² > / Vs), on / off ratio, and a threshold voltage (V). In particular, it is important that the electron mobility has a large value such that a large current can be obtained in the organic thin film transistor. The electron mobility is desirably 0.001 cm ² / Vs or more. If it is 0.01 cm ² / Vs, it can be used as a drive element for memory and electronic paper, but if it is 0.1 cm ² / Vs or more, it can be used as an active matrix drive element as an alternative to amorphous silicon. Can be used.

Examples of the present invention will be described below.
[Production Example 1: Synthesis of Compound A]
2.23 g of naphthalenetetracarboxylic anhydride and 4.15 g of tridecylamine are dispersed in 20 ml of dimethylformamide and stirred for 6 hours under reflux in a nitrogen stream. After cooling, the mixture is filtered, and the residue is washed with methanol / dilute hydrochloric acid and then water. After washing, drying was performed to obtain 3.27 g of N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide (yield 62%). The resulting compound was collected using column chromatography and purified by recrystallization to obtain NTCDI-C13 (Compound A). Endothermic peaks (measured from room temperature to 250 ° C.) by differential scanning calorimetry thermal analysis (DSC) were present at 109 ° C., 145 ° C., and 161 ° C. (see FIG. 7).

[Production Example 2: Synthesis of compounds BG]
In place of the tridecylamine of Production Example 1, undecylamine, dodecylamine, heptadecylamine, octadecylamine, 3- (dodecyloxy) propylamine, and octylamine were used respectively for compounds B, C, D, E. , F, G were obtained. The obtained compounds A to F were used as examples, and the compound G was used as a compound of comparative examples. The phase transition temperature of the obtained compound is shown in Table 1.

[Evaluation of Thin Film Transistor]
The electrical characteristics of the thin film transistor were measured with a semiconductor device analyzer (B1500A) manufactured by Agilent at room temperature and under vacuum. I _D (drain current) -V _D (source-drain voltage) characteristics (transfer characteristics) are as follows: V _G (gate voltage) is 100 V, 80 V, 60 V, 40 V, 20 V, and the drain voltage under each condition. V _D was measured by sweeping from 0 to 100V. Also, I _D -V _G characteristics (output characteristics), in V _D = 100 V, as measured by sweeping the V _G from 0 to 100 V.
It was calculated mobility from the linear region and the formula (I _D) ^1/2 -V _G characteristics (1).
In the above formula (1), C _i is the capacitance (nF / cm ² ) of the gate dielectric, and V _T is the threshold voltage. Field-effect mobility (mu) is, (I _D) calculated using equation (1) from the slope of ^1/2 -V _G characteristics, the X-intercept of the fitted straight line was calculated threshold voltage (V _T).

[Reference Example 1]
“Preparation of organic thin-film transistors using Compound A (NTCDI-C13)”
A silicon substrate having a silicon oxide film (thickness: 200 nm) on the surface as a gate insulator layer is prepared, ITO (150 nm) is formed by sputtering, and the source electrode and the drain electrode are formed by photolithography and wet etching. Patterned. The channel length and channel width at this time were 100 μm and 2,000 μm, respectively. Thereafter, the compound A obtained in Production Example 1 was dissolved in chloroform so as to have a concentration of 0.50%, and this solution was used on a silicon substrate with a spin coater (1,500 rpm) / 60 s. An organic semiconductor thin film was formed on the substrate and dried under reduced pressure for 1 hour in a vacuum.

With respect to the transistor obtained above, the I _D -V _D characteristic shows that the source-drain voltage (V _D ) is 0 under the respective conditions in which V _G (gate voltage) is applied at 100 V, 80 V, 60 V, 40 V, and 20 V, respectively. Measured by sweeping from 100 to 100V. Also, I _D -V _G characteristics, in V _D = 100 V, a V _G, was measured by sweeping from 0 to 100 V.

[Examples 1 to 3]
Using the device prepared in Reference Example 1, heat treatment was performed for 2 hours at a predetermined temperature shown in Table 1 under a vacuum atmosphere (2,000 Pa), and the processed devices were referred to as devices of Examples 1 to 3. Obtained for each device the (I _D) transistor characteristics calculated from ^1/2 -V _G characteristics shown in Table 2.

The relationship between drain current and gate voltage (output characteristics) obtained as a result of the measurement in Example 3 is shown in FIG. 3, and the relationship between drain current and drain voltage (transfer characteristics) is shown in FIG. As a result, in the I _D -V _D characteristics, a clear saturation region was recognized in the drain current-drain voltage curve, which indicates that the transistor is driven as a field effect transistor having a typical n-type characteristic. (I _D) electron mobility calculated from ^1/2 -V _G ^{characteristics, 2.1 × 10 -1 cm 2 /} Vs, the threshold voltage value is 25V, ON / OFF ratio: 10 ^5. In addition, the grain size growth of the organic semiconductor thin film by heat treatment at this time is shown in FIG.

[Examples 4 to 7]
“Preparation of organic thin-film transistors using Compound A (NTCDI-C13)”
The organic thin film transistor prepared in the same manner as in Reference Example 1 was heat-treated at a predetermined temperature shown in Table 3 for 1 hour in a nitrogen atmosphere (high purity gas: G3) to prepare organic thin film transistors, which were used as devices. . Obtained for each device the (I _D) transistor characteristics calculated from ^1/2 -V _G characteristics shown in Table 3.

[Example 8]
“Preparation of organic thin-film transistor using Compound C (NTCDI-C12)”
A silicon substrate having a silicon oxide film (thickness: 200 nm) as a gate insulator layer on the surface is prepared, ITO (150 nm) is formed by sputtering, and the source and drain electrodes are patterned using photolithography and wet etching. did. The channel length and channel width at this time were 100 μm and 2,000 μm. Thereafter, the compound C obtained in Synthesis Example 3 was dissolved in chloroform so as to have a concentration of 1.0%, and an organic semiconductor thin film was formed on the silicon substrate with a spin coater (1,500 rpm) / 60 s. did. And after drying under reduced pressure at normal temperature, each was heat-processed at 150 degreeC in the vacuum for 1 hour.

With respect to the transistor obtained above, the drain voltage and drain current at different gate voltages were measured. Since a clear saturation region was observed in the drain current-drain voltage curve, it was shown that the transistor was driven as a field effect transistor having typical n-type characteristics.
As a result, in the I _D -V _D characteristics, a clear saturation region was recognized in the drain current-drain voltage curve, which indicates that the transistor is driven as a field effect transistor having a typical n-type characteristic. (I _D) electron mobility calculated from ^1/2 -V _G ^{characteristics, 1.72 × 10 -1 cm 2 /} Vs, the threshold voltage value is 24V, ON / OFF ratio: 10 ^5.

[Example 9]
“Preparation of Organic Thin-Film Transistor Using Compound F (NTCDI-C12-O-C3-)”
An organic thin film transistor was produced in the same manner as in Example 3 except that Compound A in Example 3 was replaced with Compound F. The obtained organic thin film transistor showed high mobility and high on / off ratio, and showed well-balanced transistor characteristics.

[Comparative Example 1]
“Preparation of organic thin-film transistors using Compound G (NTCDI-C8)”
An organic thin film transistor of Comparative Example 1 was produced in the same manner as in Example 1, except that Compound A in Example 1 was replaced with Compound F. The obtained organic thin film transistor was dried in a vacuum oven for 2 hours. The transistor characteristics of the obtained transistor were measured in the same manner as in Example 1. As a result, compared with the example, both the mobility and the on / off ratio were small. This organic thin film transistor was not heat-treated. Table 1, (I _D) electron mobility calculated from ^1/2 -V _G characteristics, 0.005cm ² / Vs, threshold voltage was 43V.

[Evaluation results]
According to the naphthalene tetracarboxydiimide derivative represented by the general structural formula (1) that characterizes the present invention, a favorable organic semiconductor thin film can be formed by a printing method which is a simple method. It has been confirmed that the organic thin film transistor made of the organic semiconductor thin film of the present invention exhibits good transistor characteristics by increasing the electron mobility by one digit or more by performing a heat treatment near the transition temperature to the liquid crystal state. It was.

On the other hand, organic thin film transistors made from naphthalene tetracarboxydiimide derivatives that are not heat-treated have low values for both mobility and ON / OFF ratio, and materials for organic semiconductor thin films that do not undergo phase transition due to heating are treated with heat treatment. The effect was small.
Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above embodiments.

  According to the present invention, an organic semiconductor thin film having a high electron mobility and a high on / off value, and being easily uniform over a large area and excellent in properties by a coating method / printing method using an organic semiconductor thin film material. A useful organic semiconductor thin film material that can be used as an n-type organic semiconductor element that can be formed can be provided. Moreover, the useful organic thin-film transistor manufactured using the said organic-semiconductor thin film material can be provided.

11: Insulating layer 12: Source electrode 13: Drain electrode 14: Gate electrode 15: Organic semiconductor thin film 16: Substrate

Claims (11)

An organic semiconductor thin film material that can be used as an n-type organic semiconductor element, having a phase transition temperature in a temperature range of 80 ° C. to 250 ° C., and represented by the following general structural formula (1) An organic semiconductor thin film material comprising a naphthalenetetracarboxydiimide derivative having a thermotropic liquid crystal phase at a decomposition temperature or lower and having a phase transition to a liquid crystal state .

(However, in the formula, R 1 and R 2 are each independently a branched or unbranched alkyl group having an odd number of carbon atoms of 11, 13, 15 or 17 ; and N, O, S, P (X ₁ , X ₂ , X ₃ , and X ₄ are each independently selected from a hydrogen atom, a halogen atom, and a cyano group.) The derivative represented by the general structural formula (1) is N, N′-diundecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (1), and the following structural formula (2): N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide represented, N, N′-dipentadecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (3) , N represented by the following Symbol structural formula (4), N'Jiheputadeshiru 1,4,5,8-naphthalene tetracarboxylic diimide, or, N represented by the following structural formula (5), N'-bis (3 The material for an organic semiconductor thin film according to claim 1, which is any one of-(n-dodecyloxy) -n-propyl) -1,4,5,8-naphthalenetetracarboxydiimide .
The derivative represented by the general structural formula (1) is N, N′-diundecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (1), and the following structural formula (2): N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide represented, or N, N′-dipentadecyl-1,4,5,8-naphthalenetetra represented by the following structural formula (3) the organic semiconductor thin film material according to claim 1 is either Karubokishijiimi de.
A naphthalene tetracarboxy having a phase transition temperature in a temperature range of 80 ° C. to 250 ° C. and having a thermotropic liquid crystallinity, which is represented by the following general structural formula (1) and undergoes phase transition to a liquid crystal state by heating. Using a material for an organic semiconductor thin film containing a diimide derivative , the material is coated on a substrate in a state of being dissolved or / and dispersed in an organic solvent, and after drying, the formed coating film is 80 ° C to 350 ° C. A method for forming an organic semiconductor thin film, characterized in that the coating film is heated to a temperature to heat the coating film and further cooled to a thickness of 10 nm to 10 μm.

(However, in the formula, R 1 and R 2 are each independently a branched or unbranched alkyl group having 10 to 22 carbon atoms and may further contain N, O, S, and P heteroatoms. X ₁ , X ₂ , X ₃ and X ₄ are each independently selected from a hydrogen atom, a halogen atom and a cyano group.) The method for forming an organic semiconductor thin film according to claim 4, wherein the branched or unbranched alkyl group has an odd number of carbon atoms of 11, 13, 15 or 17. The derivative represented by the general structural formula (1) is N, N′-diundecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (1), and the following structural formula (2): N, N′-ditridecyl-1,4,5,8-naphthalenetetracarboxydiimide represented, N, N′-dipentadecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (3) N, N′-diheptadecyl-1,4,5,8-naphthalenetetracarboxydiimide represented by the following structural formula (4), or N, N′-bis (3- The method for forming an organic semiconductor thin film according to claim 4, which is any one of (n-dodecyloxy) -n-propyl) -1,4,5,8-naphthalenetetracarboxydiimide.
The formation method of the organic-semiconductor thin film of any one of Claims 4-6 which heats the said coating film to the temperature of 80 to 250 degreeC. The method for forming an organic semiconductor thin film according to claim 4 , wherein the heat treatment is performed in a reduced pressure atmosphere of 10 ^{−5 to} 50,000 Pa. The method for forming an organic semiconductor thin film according to any one of claims 4 to 8, wherein the heat treatment is performed in an inert gas atmosphere. On a substrate, a gate electrode, a gate insulating layer, the organic thin-film transistor organic semiconductor thin film and the source electrode and the drain electrode are formed at least, the organic semiconductor thin film, an organic according to any one of claims 1 to 3 An organic thin film transistor characterized by being formed of a semiconductor thin film material . The organic thin film transistor according to claim 10, wherein the carrier mobility is 0.01 cm ² / Vs or more.