JP6884348B2 - Organic field effect transistor - Google Patents

Description

The present invention relates to an organic field effect transistor in which a transistor element composed of a gate electrode, a gate insulating film, a source electrode, a drain electrode and an organic semiconductor film is provided on a substrate.

Conventionally, it has been known that the regularity and orientation of the organic semiconductor layer are important for this type of organic field effect transistor. As a method for obtaining an organic semiconductor film having particularly high regularity, the method described in Patent Document 1 has been proposed. Here, in Patent Document 1, a self-assembled monomolecular film made of a silicon compound having a π-electron system is used as an organic semiconductor film to have high regularity, and by printing such as coating with a solution. We have realized an organic semiconductor film that can be easily manufactured.

Japanese Unexamined Patent Publication No. 2004-307847

However, in the case of the organic field effect transistor described in Patent Document 1, since the organic semiconductor film is a monolayer, only the hole movement in the plane is performed, and the influence of the grain boundary is affected as compared with the case where the hole movement is three-dimensional. It becomes large and high mobility cannot be expected. Further, in the case of Patent Document 1, since the silicon compound which is an organic semiconductor film and the substrate are covalently bonded, a distribution occurs in the electron density, and high mobility cannot be expected.

The present invention has been made in view of the above problems, and an object of the present invention is to provide an organic field effect transistor provided with an organic semiconductor film which can be easily formed by printing and is suitable for achieving high mobility.

The present inventor has diligently studied an organic semiconductor material used as an organic semiconductor film. As a result, we have found an organic semiconductor material that can be easily formed by printing and can form a laminated film of 2 to 4 layers having high mobility. The present invention has been created as a result of such studies.

That is, in the invention according to claim 1, the gate insulating film (20), the source electrode (40), and the drain electrode ( An organic field effect transistor provided with a transistor element (100) composed of a 50) and an organic semiconductor film (30).
The organic semiconductor film has a structure forming one surface , and is a crystal film formed by laminating a monomolecular film of an organic semiconductor material in two layers, three layers, or four layers, and the organic semiconductor material has a molecular weight of 1000 or less. , and the chalcogen a polyacene compound, at least one or more benzene rings there between thiophene and thiophene is, chalcogen there is at least one or more benzene rings on the outside of the thiophene having two alkyl groups It is characterized in that it contains a polyacene compound as a main component.

According to this, by using the organic semiconductor material constituting the organic semiconductor film as the above-mentioned chalcogen-containing polyacene compound, the organic semiconductor film is laminated by printing in two layers, three layers or four layers. It can be formed as a crystal film with mobility. Therefore, according to the present invention, it is possible to provide an organic field effect transistor that can be easily formed by printing and has an organic semiconductor film suitable for achieving high mobility.

The scope of claims and the reference numerals in parentheses of each means described in this column are examples showing the correspondence with the specific means described in the embodiments described later.

It is schematic cross-sectional view which shows the cross-sectional structure of the organic transistor which concerns on 1st Embodiment of this invention. It is a figure which shows an example of the chemical structure of the organic semiconductor material which constitutes the organic semiconductor film which concerns on 1st Embodiment. It is a chart which shows the specific effect in 1st Embodiment. It is schematic cross-sectional view which shows the cross-sectional structure of the organic transistor which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each of the following figures, parts that are the same or equal to each other are designated by the same reference numerals in the drawings in order to simplify the description.

(First Embodiment)
The organic field effect transistor S1 according to the first embodiment of the present invention will be described with reference to FIG. The organic field effect transistor S1 is applied to, for example, a transistor provided in a drive circuit of an EL (electroluminescence) element.

The organic field effect transistor S1 of the present embodiment is formed by providing a transistor element 100 on one surface 11 of a substrate 10 having a gate electrode on the one surface 11 side. Here, the number of transistor elements 100 on one surface 11 of the substrate 10 may be plural.

The transistor element 100 is formed by laminating a gate insulating film 20, an organic semiconductor film 30, a source electrode 40, and a drain electrode 50 in this order from the one side 11 side of the substrate 10. As described above, the transistor element 100 of the present embodiment is formed as a bottom gate-top contact type.

Here, in the present embodiment, the substrate 10 also serves as the gate electrode in the transistor element 100. In the present embodiment, the substrate 10 is made of a silicon (Si) wafer and also functions as a gate electrode on one side 11 side. That is, the substrate 10 is configured to have a gate electrode on one side 11 side.

Furthermore, in the present embodiment, the transistor element 100 is composed of a laminate composed of a gate insulating film 20, an organic semiconductor film 30, a source electrode 40 and a drain electrode 50, and a substrate 10 as a gate electrode.

The gate insulating film 20 is formed on one surface 11 of the substrate 10. The gate insulating film 20 is formed of silica (SiO ₂ ) or alumina formed by vapor deposition, sputtering, ALD (atomic layer growth method), or the like. It consists of (Al ₂ O ₃ ) and the like. In the present embodiment, the substrate 10 is made of a silicon wafer, and the gate insulating film 20 for coating the substrate 10 is typically silica.

Then, an organic semiconductor film 30 that functions as a channel layer is formed on the gate insulating film 20. The organic semiconductor film 30 is formed by printing, and is a crystal film formed by laminating a monomolecular film of an organic semiconductor material in two layers, three layers, or four layers. Details of the organic semiconductor film 30 of this embodiment will be described later.

The source electrode 40 and the drain electrode 50 are arranged on the organic semiconductor film 30 so as to be separated from each other. Here, the organic semiconductor film 30 is formed on the gate insulating film 20 so as to connect the source electrode 40 and the drain electrode 50.

The source electrode 40 and the drain electrode 50 are made of, for example, Au (gold) or the like. For example, the source electrode 40 and the drain electrode 50 are formed by forming an Au layer by a vacuum vapor deposition method using a shadow mask or the like.

[Detailed structure of organic semiconductor film 30]
Next, the detailed structure of the organic semiconductor film 30 provided in the transistor element 100 of the organic field effect transistor S1 configured as described above will be described.

The organic semiconductor material constituting the organic semiconductor film 30 is a chalcogen-containing polyacene compound having a molecular weight of 1000 or less and having two alkyl groups, and the carbon number of each alkyl chain is smaller than the number of polyacene rings. The main component is a contained polyacene compound. The chalcogen is a group 16 element in the periodic table such as S (sulfur) and O (oxygen).

As an example of the chalcogen-containing polyacene compound as the main component, 3,12-dihexyl dinaphtho [2,3-d: 2', 3'-d'] naphtho [1,2-b] as shown in FIG. : 6,7-b'] Dithiophene (hereinafter, this is referred to as Material 1) can be mentioned. In this material 1, each alkyl chain has 6 carbon atoms and 8 polyacene rings.

This material 1 is produced by a synthetic method according to the synthetic method described in Example 6 and Example 7 in the International Publication No. 2014/136827 pamphlet (WO2014 / 136827). Specifically, 2-decyl-7-methoxynaphthalene, which is a starting material in the first step of the sixth embodiment, is replaced with 2-hexyl-7-methoxynaphthalene, and the first step and the second step of the sixth embodiment are replaced. If the steps, the first step and the second step of the seventh embodiment are sequentially performed, the material 1 is synthesized.

The chalcogen-containing polyacene compound as the main component is not limited to this material 1, and may be any compound having an alkyl chain having a smaller number of carbon atoms than the number of polyacene rings. For example, the number of polyacene rings is in the range of 4 to 8, and the number of carbon atoms in the alkyl chain can be appropriately changed in relation to the number of polyacene rings.

The organic semiconductor material constituting the organic semiconductor film 30 may contain 100% chalcogen-containing polyacene compound as a main component, but may contain a small amount of another chalcogen-containing polyacene compound as an additive. May be. The content of this additive is 0.1% by weight or more and 5% by weight or less, assuming that the entire organic semiconductor material is 100.

For example, as the organic semiconductor material constituting the organic semiconductor film 30, for example, the material 1 may be 100 wt%, but the material 1 is 99.9 to 95 wt% and the additive is 0.1 to 5 wt%. Something is desirable.

The chalcogen-containing polyacene compound as this additive has the same skeleton as the chalcogen-containing polyacene compound as the main component, and has a small number of carbon atoms in the alkyl chain.

For example, when the chalcogen-containing polyacene compound as the main component is, for example, material 1, the chalcogen-containing polyacene compound as an additive can have the number of carbon atoms of the alkyl chain in the material 1 changed from 6 to 0-4. Furthermore, the additive may have the same skeleton as the skeleton of the material 1 but lack one of the alkyl chains, or may have no alkyl chains on both sides.

The chalcogen-containing polyacene compound as such an additive is contained in the main component in an amount of about 0.1 wt% to 5 wt% as a trace amount of a by-synthesis in the synthesis of the above-mentioned material 1, but separately It may be contained by mixing.

Then, as described above, the organic semiconductor film 30 is formed by printing using the organic semiconductor material described above. Specifically, in this printing, a solution in which an organic semiconductor material is dissolved in a solvent is applied on one surface 11 of the substrate 10 and here on the surface of the gate insulating film 20 by a drop casting method or the like, and this is dried. It is done by.

Here, the solvent is not particularly limited as long as it dissolves the organic semiconductor material, but an organic solvent such as 1-chloronaphthalene is preferable. The concentration of the organic semiconductor material in the solution may be, for example, about 0.03 wt% to 0.13 wt%, as long as it can realize a crystal film in which 2 to 4 layers are laminated. The drying temperature is the volatilization temperature of the solvent, for example, in the case of 1-chloronaphthalene, it is about 160 ° C.

In an organic field effect transistor using a printable organic semiconductor material represented by C8-BTBT (4 ring condensate) and C10-DNTT (6 ring condensate), spherical crystal nuclei are formed when a crystalline thin film is produced. Is formed and crystal grows from the crystal nucleus in a terrace shape, so that the distribution of the thin film is large and the mobility varies greatly. However, each alkyl chain has 6 carbon atoms and 8 condensed rings. When printing is performed using the organic semiconductor material of the present embodiment such as 1, crystals grow from planar crystal nuclei by adjusting the printing temperature, solution concentration, printing speed, etc., and the number of layers is 1, 2. An organic semiconductor film 30 controlled in 3 or 4 layers can be obtained.

Specifically, when the organic semiconductor film 30 has one layer and when the organic semiconductor film 30 is a laminated film in which monomolecular films are laminated in two to four layers, the film thickness distribution of the organic semiconductor film 30 is 1 mm. An organic semiconductor film 30 having a uniform film thickness and excellent flatness, which is as small as 0.3 nm or less per ^{2 is realized.}

Further, when the organic semiconductor film 30 is a laminated film having 2 to 4 layers, the mobility is significantly improved as compared with the case of 1 layer. Further, in the case where the organic semiconductor film 30 is a laminated film of 2 to 4 layers, when a plurality of transistor elements 100 are provided on one surface 11 of the substrate 10, the mobility of each of the plurality of transistor elements 100 varies. It can be as small as 10% or less.

By the way, in the conventional organic field effect transistor, an organic semiconductor film is formed by using a printing type organic semiconductor material represented by C8-BTBT (four-ring condensed ring) and C10-DNTT (six-ring condensed ring). Was there. In the case of these conventional materials, spherical crystal nuclei are formed and crystals grow from the crystal nuclei in a terrace shape, so that the film thickness distribution is large and the mobility varies greatly.

Further, in the present embodiment, when the organic semiconductor film 30 is formed of the organic semiconductor material containing a small amount of the above-mentioned additives, the crystallinity of the organic semiconductor film 30 is less biased than that of the case where no additives are contained. It is easy to form a uniform crystal film. The crystallinity of such an organic semiconductor film 30 can be confirmed by observation with a polarizing microscope or a two-dimensional birefringence evaluation device.

[Verification example]
The effect of this embodiment will be specifically described with reference to the verification example shown in FIG. In this example, as the organic semiconductor material constituting the organic semiconductor film 30, 5 wt of a compound containing the above-mentioned material 1 as a main component and having the same skeleton as the material 1 and having 2 carbon atoms in the alkyl chain as the additive. A solution was prepared in which about 0.03 wt% to 0.13 wt% was dissolved in 1-chloronaphthalene as described above, using the one containing%.

Then, using this solution, an organic semiconductor film 30 controlled into one layer, two layers, three layers or four layers was formed by printing on one surface 11 of the substrate 10 in a size of 20 mm square. Here, for each number of layers, 12 organic field effect transistors S1 were produced in the same 10 planes of the substrate, and for each number of layers, the film thickness distribution and mobility of the organic semiconductor film 30 in the plane were evaluated. Regarding the film thickness distribution, the average film thickness, maximum film thickness, and minimum film thickness of the organic semiconductor film 30 were measured by performing cross-sectional analysis by transmission electron microscopy (TEM) and fitting with a two-dimensional birefringence evaluation device. .. As for the mobility, the average mobility, the maximum mobility, and the minimum mobility of each transistor were obtained.

As shown in FIG. 3, in the case of the one-layer organic semiconductor film 30, the average film thickness: 3.2 nm, the maximum film thickness: 3.3 nm, the minimum film thickness: 3.2 nm, and the average mobility: 0.31 cm ^2. / Vs, maximum mobility: 0.31 cm ² / Vs, minimum mobility: 0.30 cm ² / Vs.

In the case of the two-layer organic semiconductor film 30, the average film thickness: 7.0 nm, the maximum film thickness: 7.1 nm, the minimum film thickness: 6.9 nm, the average mobility: 1.43 cm ² / Vs, the maximum mobility: 1. It was .51 cm ² / Vs and the minimum mobility: 1.38 cm ² / Vs.

In the case of the three-layer organic semiconductor film 30, average film thickness: 10.7 nm, maximum film thickness: 10.8 nm, minimum film thickness: 10.5 nm, average mobility: 2.17 cm ² / Vs, maximum mobility: 2 It was .22 cm ² / Vs and the minimum mobility: 2.10 cm ² / Vs.

In the case of the four-layer organic semiconductor film 30, the average film thickness: 14.3 nm, the maximum film thickness: 14.4 nm, the minimum film thickness: 14.1 nm, the average mobility: 2.45 cm ² / Vs, the maximum mobility: 2. It was .55 cm ² / Vs and the minimum mobility: 2.32 cm ² / Vs.

As described above, according to this verification example, the degree of supersaturation is controlled by optimizing the surface energy, printing temperature, solution concentration, and printing speed of the substrate 10 under the printing conditions of the organic semiconductor film 30, and 1 to 4 are obtained. The film thickness up to the layer can be controlled.

Then, for each number of layers, the organic field effect has a small variation in both the film thickness and the mobility of the organic semiconductor film 30, such as a film thickness distribution of 0.3 nm or less per ^{1 mm 2 and a mobility of 10% or less.} I was able to realize a transistor.

Further, it was clarified that when the organic semiconductor film 30 is controlled to one layer, the mobility is low, and it is useful to control the organic semiconductor film 30 to two to four layers. In the case of one layer, since the organic semiconductor film 30 is a monomolecular layer, only plane hole movement is performed, and it is considered that high mobility cannot be expected for the same reason as in Patent Document 1.

Further, in the verification example of FIG. 3, the case of the material 1 containing the additive is shown, but if the material 1 does not contain the additive, and further, if it is the organic semiconductor material of the above-described embodiment other than the material 1. , The result of the same tendency as in FIG. 3 has been confirmed.

As described above, according to the present embodiment, the organic semiconductor material constituting the organic semiconductor film 30 is made of the chalcogen-containing polyacene compound, so that the organic semiconductor film 30 is printed with two layers of monolayers. It can be formed as a crystal film having high mobility, which is laminated with three or four layers. Therefore, according to the present embodiment, it is possible to provide the organic field effect transistor S1 provided with the organic semiconductor film 30 which can be easily formed by printing and is suitable for realizing high mobility.

Further, according to the present embodiment, the film thickness distribution of the organic semiconductor film 30 as the laminated film is ^{0.3 nm or less per 1 mm 2} , and thus the film thickness distribution is small, the film thickness is uniform, and the film thickness is flat. An organic semiconductor film 30 having excellent properties can be realized.

Further, according to the present embodiment, even when a plurality of transistor elements 100 are provided on the same substrate 10, the variation in mobility between the respective transistor elements can be as small as 10% or less.

(Second Embodiment)
The organic field effect transistor S2 according to the second embodiment of the present invention will be described focusing on the differences from the first embodiment with reference to FIG. The organic field-effect transistor S1 of the first embodiment is of the bottom gate-top contact type, but the organic field-effect transistor S2 may be of the top gate type as of the present embodiment. ..

As shown in FIG. 4, the organic field effect transistor S2 of the present embodiment has an electrically insulating substrate 10. The substrate 10 is made of glass such as non-alkali glass, ceramic, plastic, or the like, and may be a rigid substrate or a flexible substrate.

A source electrode 40 and a drain electrode 50 arranged apart from each other are formed on one surface 11 of the substrate 10. The source electrode 40 and the drain electrode 50 are made of, for example, Au (gold) or the like, as in the first embodiment.

An organic semiconductor film 30 is formed on one surface 11 of the substrate 10 so as to cover the source electrode 40 and the drain electrode 50, and the organic semiconductor film 30 connects the source electrode 40 and the drain electrode 50. .. The organic semiconductor film 30 is the same as that of the first embodiment.

Then, the gate insulating film 20 is formed so as to cover the organic semiconductor film 30 on one surface 11 of the substrate 10. The gate insulating film 20 is the same as that of the first embodiment. A gate electrode 60 made of Cr (chromium) or the like is formed on the gate insulating film 20. The gate electrode 60 is formed by sputtering, photolithography, or the like. With such a structure, the organic transistor S2 according to the present embodiment is configured.

Also in this embodiment, the organic semiconductor material constituting the organic semiconductor film 30 is made of the chalcogen-containing polyacene compound, so that the organic semiconductor film 30 is printed with two layers, three layers or four layers of monomolecular films. It can be formed as a laminated crystal film having high mobility. Therefore, the present embodiment can also provide the organic field effect transistor S2 that has the same effect as that of the first embodiment.

(Other embodiments)
As the bottom gate type transistor element 100, in addition to FIG. 1, a gate electrode made of Cr or the like may be formed on one surface 11 of the substrate 10 in which the substrate 10 is made of an insulating substrate such as glass or plastic. Good. In this case, the gate insulating film 20, the organic semiconductor film 30, the source electrode 40, and the drain electrode 50 may be sequentially formed on the gate electrode formed by sputtering, photolithography, or the like, as in FIG.

Further, the bottom gate type transistor element 100 may be a bottom contact type in addition to the top contact type as shown in FIG. 1 above. That is, as an organic field effect transistor, a transistor element 100 composed of a gate insulating film 20, a source electrode 40, a drain electrode 50, and an organic semiconductor film 30 is formed on the one surface 11 of a substrate 10 having a gate electrode 60 on the one surface 11 side. Anything may be provided.

Further, the present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of the claims. Further, the above-described embodiments are not unrelated to each other, and can be appropriately combined except when the combination is clearly impossible, and the above-mentioned embodiments are not limited to the above-mentioned illustrated examples. Absent. Further, in each of the above embodiments, it goes without saying that the elements constituting the embodiment are not necessarily essential except when it is clearly stated that they are essential and when they are clearly considered to be essential in principle. No. Further, in each of the above embodiments, when numerical values such as the number, numerical values, amounts, and ranges of the constituent elements of the embodiment are mentioned, when it is clearly stated that they are particularly essential, and in principle, they are clearly limited to a specific number. It is not limited to the specific number except when it is done. Further, in each of the above embodiments, when referring to the shape, positional relationship, etc. of a component or the like, the shape, unless otherwise specified or limited in principle to a specific shape, positional relationship, etc. It is not limited to the positional relationship.

10 Substrate 11 One side of the substrate 20 Gate insulating film 30 Organic semiconductor film 40 Source electrode 50 Drain electrode 60 Gate electrode 100 Transistor element

Claims (6)

A gate insulating film (20), a source electrode (40), a drain electrode (50), and an organic semiconductor film (30) are formed on the one surface of a substrate (10) having a gate electrode (60) on the one surface (11) side. An organic field effect transistor provided with a transistor element (100).
The organic semiconductor film has a structure forming one surface , and is a crystal film formed by laminating a monomolecular film of an organic semiconductor material in two layers, three layers, or four layers.
The organic semiconductor material is a molecular weight of 1,000 or less, a chalcogen-containing polyacene compound having two alkyl groups, Ri least one or more benzene rings there between thiophene and thiophene, at least on the outside of the thiophene An organic electric field effect transistor whose main component is a chalcogen-containing polyacene compound having one or more benzene rings. The organic field-effect transistor according to claim 1, wherein the organic semiconductor material has a carbon number of carbon in each alkyl chain of the chalcogen-containing polyacene compound less than the number of rings of the polyacene. The organic semiconductor material contains a chalcogen-containing polyacene compound as an additive of 0.1% by weight or more and 5% by weight or less in addition to the chalcogen-containing polyacene compound as the main component.
Claim 1 or 2 is characterized in that the chalcogen-containing polyacene compound as the additive has the same skeleton as the chalcogen-containing polyacene compound as the main component and has a small number of carbon atoms in the alkyl chain. The organic field effect transistor according to. The organic field effect transistor according to any one of claims 1 to 3, wherein the film thickness distribution of the organic semiconductor film as a laminated film is ^{0.3 nm or less per 1 mm 2.} Any of claims 1 to 4, wherein a plurality of the transistor elements are provided on one surface of the substrate, and the mobility of each of the plurality of transistor elements varies within 10%. The organic field effect transistor according to one. The chalcogen-containing polyacene compound as the main component is 3,12-dihexyl dinaphtho [2,3-d: 2', 3'-d'] naphtho [1,2-b: 6,7-b'] dithiophene. The organic field effect transistor according to any one of claims 1 to 5, wherein the organic field effect transistor is characterized by the above.

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