JP5737849B2 - Organic semiconductor film manufacturing method and organic transistor - Google Patents

Description

  The present invention relates to an organic semiconductor film manufacturing method and an organic transistor.

  In recent years, an organic transistor using an organic semiconductor as a channel layer has attracted much attention. Organic FETs are characterized in that they can be manufactured at a lower cost than conventional field effect transistors using an inorganic semiconductor such as silicon as a channel, are easy to increase in size, and are mechanically flexible.

  In addition, as a method for forming an organic semiconductor film used in an organic FET, a method by vapor deposition is known. However, a method for obtaining a thin film by applying an organic semiconductor material on a substrate and drying it is a method by vapor deposition. In comparison, there is an advantage that the apparatus is simple and can be easily manufactured. However, when an organic semiconductor material is formed on a substrate having high water repellency, there is a problem in that the organic semiconductor material cannot be thinned by repelling.

  Therefore, by adding 10% by mass or 30% by mass of spherical non-porous silica fine particles having a shortest diameter of 30 μm or 0.5 μm in a solution containing an organic semiconductor material, repelling is suppressed and the organic semiconductor is formed on the substrate. It is known to form a thin film of material (for example, Patent Document 1).

JP 2008-311403 A

  However, since the spherical non-porous silica fine particles to be mixed are too large for the thin film made of the organic semiconductor material, the film thickness variation of the thin film formed after the film formation is large, and there are many spherical non-porous silica fine particles to be mixed. There was a problem that it was difficult to obtain good performance as an organic FET.

  Accordingly, an object of the present invention is to provide a method for producing an organic semiconductor film and an organic transistor aimed at solving the above problems.

  Another object of the present invention is to provide a method for producing an organic semiconductor film formed on a highly water-repellent substrate without variation in film thickness, and such an organic transistor.

  In the method for producing an organic semiconductor film according to the present invention, a solution containing an organic semiconductor material is supplied onto a substrate and dried to form a thin film, the substrate has a water contact angle of 50 ° or more, and the solution has a particle size. Insulating fine particles of 10 nm or more and 30 nm or less are contained in an amount of 0.1 wt% or more and 1.0 wt% or less with respect to the total weight of the solution.

  The organic transistor according to the present invention has a thin film composed of a substrate having a water contact angle of 50 ° or more and an organic semiconductor material formed on the substrate, and the thin film has insulating particles having a particle size of 10 nm to 30 nm. Is contained in an amount of 5 wt% to 50 wt% with respect to the weight of the organic semiconductor material.

  In the organic semiconductor film manufacturing method and the organic transistor according to the present invention, it is possible to form an organic semiconductor material applied to a highly water-repellent substrate without variation in film thickness, and it is favorable as an organic semiconductor. It became possible to obtain the characteristic.

It is a schematic sectional drawing of an organic transistor. It is a diagram showing a relationship between the drain current I _D and the gate voltage V _G. It is a diagram showing a relationship between the drain current I _D and the gate voltage V _G.

  Hereinafter, an organic transistor and a method for forming an organic semiconductor film according to the present invention will be described with reference to the drawings. However, it should be noted that the technical scope of the present invention is not limited to these embodiments, but extends to the invention described in the claims and equivalents thereof.

  FIG. 1 is a schematic cross-sectional view of an organic transistor.

  A coating type organic transistor 1 shown in FIG. 1A has a gate electrode 3, a gate insulating film 4, an organic semiconductor film 5, a source electrode 6 and a drain electrode 7 on the surface of a substrate 2. Hereinafter, the manufacturing method of the coating type organic transistor 1 will be described.

  As the substrate 2, it is possible to use a glass substrate or a heat-resistant polymer material such as polycarbonate, polyethylene naphthalate (PEN), polyimide (PI), polyethylene terephthalate (PET).

  Next, the gate electrode 3 is formed on the substrate 2 by a vacuum film forming method using a thin film forming method such as vapor deposition or sputtering, and an electrode shape is formed by a mask film forming method or a photolithographic method. In addition, as materials for the gate electrode, metals such as gold, platinum, chromium, palladium, aluminum, indium, molybdenum, nickel, alloys using these metals, polysilicon, amorphous silicon, tin oxide, indium oxide, indium It is possible to use inorganic materials such as tin oxide (ITO) and indium / zinc oxide (IZO), and combinations of two or more thereof.

  Next, the gate insulating film 4 is formed on the gate electrode 3 by applying a material by spin coating and then heat-curing in an oven, or by chemical vapor deposition. As a material for the gate insulating film, polymethylsilsesquioxane (PMSQ), polyimide, polyvinyl phenol, polyvinyl alcohol, polymethyl methacrylate, polyparaxylene, or the like can be used. Note that PMSQ is cured by heat treatment to form a good insulating film with high water repellency (water contact angle 93 °) and low surface energy.

  Next, the organic semiconductor film 5 is formed on the gate insulating film 4 by applying a solution containing an organic semiconductor material and insulating fine particles by a spin coating method and then naturally drying the solution. Organic semiconductor materials include 6, 13-bis (triisopropylsilylethynyl) pentacene (TIPS-PEN), π-electron conjugated aromatic compounds, chain compounds, organic pigments, organosilicon compounds, charge transfer complexes, etc. Specifically, pentacene, a pentacene derivative in which a bicyclo ring is introduced between the central benzene rings, tetracene, anthracene, thiophene oligomer derivative, phenylene derivative, phthalocyanine derivative, polyacetylene derivative, polythiophene derivative, cyanine dye, etc. can be used. It is. As the insulating fine particles, silica nanoparticles (SNP), regular silica, pigments and the like can be used.

  Insulating fine particles improve the wettability of a solution containing an organic semiconductor material, which has extremely poor wettability and is difficult to apply to an insulating film with high water repellency, and enables the formation of an organic semiconductor film. It has been added. The particle size of the SNP indicates the diameter of the silica sphere when the SNP is dried and then calcined at 800 ° C. for 1 hour to measure the BET specific surface area to obtain a true specific gravity of 2.2.

  For example, when silicon dioxide having a low water repellency (water contact angle 10 °) is used as a gate insulating film, it is possible to form an organic semiconductor material without adding insulating fine particles. Therefore, the present invention is particularly effective for a substrate having a high water repellency (water contact angle of 50 ° or more). The water contact angle is a value obtained by measuring the angle of a portion where a water droplet is dropped on the surface of the insulating film and the water droplet is in contact with the insulating film.

  Next, the source electrode 6 and the drain electrode 7 are formed on the organic semiconductor film 5 by a vacuum deposition method. The source electrode 6 and the drain electrode 7 can be used without particular limitation as long as they are known electrodes used in organic transistors, but most organic semiconductors are P-type in which carriers that transport charges are holes. Since it is a semiconductor, it is preferably formed of a metal having a high work function in order to make ohmic contact with the organic semiconductor. Specifically, gold, platinum, silver, copper, or the like can be used for the source electrode 6 and the drain electrode 7.

  In the coating type organic transistor 1 shown in FIG. 1A, the source electrode 6 and the drain electrode 7 are formed on the organic semiconductor film 5. However, like the coated organic transistor 10 shown in FIG. 1B, the source electrode 6 and the drain electrode 7 may be formed on the gate insulating film 4, and the organic semiconductor film 5 may be formed thereon. . That is, the present invention can be applied to the bottom gate type coating organic transistors 1 and 10.

  Further, like the coated organic transistor 20 shown in FIG. 1C, the organic semiconductor film 5 is formed on the substrate 2, the source electrode 6 and the drain electrode 7 are formed on the organic semiconductor film 5, and the source electrode 6 The gate insulating film 4 and the gate electrode 3 may be formed on the drain electrode 7. 1D, the source electrode 6 and the drain electrode 7 are formed on the substrate 2, and the organic semiconductor film 5 is formed on the source electrode 6 and the drain electrode 7, The gate insulating film 4 and the gate electrode 3 may be formed on the organic semiconductor film 5. That is, the present invention can be applied to the top gate type coating organic transistors 20 and 30.

A gate electrode 3 was formed on the glass substrate 2 having a thickness of 500 μm by patterning ITO having a film thickness of 10 nm and a resistivity of 300 Ω / cm ² by a photolithography method. Further, PMSQ was applied on the gate electrode 3 by spin coating, and then heated in an oven at 200 degrees for 60 minutes to form a gate insulating film 4 having a thickness of 350 nm. After the gate insulating film 4 is formed, a solution obtained by dissolving 2.0 wt% of TIPS-PEN and 0.1 wt% of SNP having a particle diameter of 10 nm in toluene as a solvent with respect to the weight of the entire solution is formed by spin coating. An organic semiconductor film 5 was formed on the film 4 and naturally dried. The formed organic semiconductor film 5 contained 5 wt% SNP with respect to the weight of TIPS-PEN. After the formation of the organic semiconductor film 5, a source electrode 6 and a drain electrode 7 having a thickness of 50 nm are formed on the organic semiconductor film 5 by a vacuum deposition method using gold as a material, and the coating type shown in FIG. An organic transistor was manufactured.

  As described above, the organic semiconductor film was formed using the spin coating method (20 seconds, 500 rpm), and it was visually confirmed whether the organic semiconductor film was formed after the spin coating was completed. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Example 1.

The on / off ratio of the manufactured coated organic transistor was measured. On-off ratio was measured by changing the gate voltage V _G of the organic transistor, the maximum value of the drain current I _D (hereinafter referred to as "ON current") and the minimum value (hereinafter "off-state current of the drain current I _D ")"). In a normal organic transistor, the on / off ratio is preferably 10 ³ or more. In the coating type organic transistor of Example 1, the on / off ratio is 2.3 × 10 ³ , indicating good transistor characteristics. Incidentally, on-off ratio, the curve 41 corresponding to Example 1 of Figure showing the relationship between the drain current I _D and the gate voltage V _G shown in FIG. 2 (in the drain voltage V _D = -30 (V)) Based on.

Further, the obtained organic transistor has a drain voltage V _D , a drain current I _D , a gate voltage V _G , a threshold voltage V _th , a capacitance per unit area of the gate insulating film C 1, a channel length L, If the channel width is W and the mobility of the organic semiconductor film is μ, they can be expressed by the relationship of the following equation (1), and the mobility μ is expressed as a slope in a graph plotting I _D ^1/2 and V _G. Asked.
I _D = [WC / (2L)] ^{_{μ (V G -V th) 2}} (1)
Here, the threshold voltage V _th is set to the value of the voltage V _G when indicating the off current.

By the above method, the mobility μ and the threshold voltage V _th of the manufactured coating type organic transistor were obtained. In the coating type organic transistor of Example 1, the field effect mobility μ was 1.2 × 10 ⁻³ (cm ² / Vs), and the threshold voltage V _th was 2.0 (V).

A coated organic transistor was manufactured in the same manner as in Example 1 except that 1.0 wt% of SNP having a particle diameter of 10 nm was added to the total weight of the solution. The formed organic semiconductor film 5 contained 50 wt% SNP with respect to the weight of TIPS-PEN. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Example 2. The on / off ratio of the coating type organic transistor of Example 2 is 1.8 × 10 ³ , indicating good transistor characteristics. Further, the field effect mobility μ was 2.8 × 10 ⁻⁴ (cm ² / Vs), and the threshold voltage V _th was 1.0 (V). The on / off ratio is a curve 42 corresponding to Example 2 in the diagram showing the relationship between the drain current I _D and the gate voltage V _G shown in FIG. 2 (in the drain voltage V _D = −30 (V)). Based on.

A coated organic transistor was manufactured in the same manner as in Example 1 except that 0.1 wt% of SNP having a particle size of 30 nm was added to the total weight of the solution. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Example 3. The on / off ratio of the coating type organic transistor of Example 3 is 1.3 × 10 ² , indicating good transistor characteristics. Furthermore, the mobility μ was 1.7 × 10 ⁻³ (cm ² / Vs), and the threshold voltage V _th was 8.0 (V). The on / off ratio is a curve 43 corresponding to Example 3 in the diagram showing the relationship between the drain current I _D and the gate voltage V _C shown in FIG. 3 (in the drain voltage V _D = −60 (V)). Based on.

A coated organic transistor was manufactured in the same manner as in Example 1 except that 1.0 wt% of SNP having a particle size of 30 nm was added to the total weight of the solution. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Example 4. The on / off ratio of the coating type organic transistor of Example 4 is 1.5 × 10 ² , indicating good transistor characteristics. Furthermore, the mobility μ was 3.2 × 10 ⁻⁴ (cm ² / Vs), and the threshold voltage V _th was 6.0. The on / off ratio is a curve 44 corresponding to Example 4 in the diagram showing the relationship between the drain current I _D and the gate voltage V _G (in the drain voltage V _D = −60 (V)) shown in FIG. Based on.
(Comparative Example 1)

A coated organic transistor was manufactured in the same manner as in Example 1 except that 0.01 wt% of SNP having a particle diameter of 10 nm was added to the total weight of the solution. As a result, in the coating type organic transistor of Comparative Example 1, an organic semiconductor film could not be formed by spin coating. Therefore, the on / off ratio, mobility μ, and threshold voltage V _th for Comparative Example 1 are not measured.
(Comparative Example 2)

A coated organic transistor was manufactured in the same manner as in Example 1 except that 10 wt% of SNP having a particle diameter of 10 nm was added to the total weight of the solution. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Comparative Example 2. The on-off ratio of the coated organic transistor of Comparative Example 2 is 2.7 × 10 ⁰ , the mobility μ is 3.0 × 10 ⁻⁶ (cm ² / Vs), and the threshold voltage V _th is −1. 0.0 (V). As described above, in Comparative Example 2, the film could be formed, but the on / off ratio was low, and good characteristics as an organic transistor could not be obtained. Incidentally, on-off ratio, based on the drain current I _D and the curve 52 corresponding to Comparative Example 2 in graph showing relationship between a gate voltage V _G and (V _D = at -30 (V)) shown in FIG. 2 Asked.
(Comparative Example 3)

A coated organic transistor was manufactured in the same manner as in Example 1 except that 0.01 wt% of SNP having a particle diameter of 30 nm was added to the total weight of the solution. As a result, in the coating type organic transistor of Comparative Example 3, an organic semiconductor film could not be formed by spin coating. Therefore, the on / off ratio, mobility μ, and threshold voltage V _th for Comparative Example 3 are not measured.
(Comparative Example 4)

A coated organic transistor was manufactured in the same manner as in Example 1 except that 10 wt% of SNP having a particle diameter of 30 nm was added to the total weight of the solution. As a result, it was confirmed that the organic semiconductor film was satisfactorily formed in the coating type organic transistor of Comparative Example 4. The on-off ratio of the coating type organic transistor of Comparative Example 4 is 7.6 × 10 ¹ , the mobility μ is 9.8 × 10 ⁻⁵ (cm ² / Vs), and the threshold voltage V _th is −6. 0.0 (V). As described above, in Comparative Example 4, although film formation was possible, the value of the on / off ratio was low, and good characteristics as an organic transistor could not be obtained. Incidentally, on-off ratio, the drain current I _D and the gate voltage V relationship between _G (drain voltage V _D = -60 (in V)) curve 54 corresponding to Comparative Example 4 shows a shown in FIG. 3 Based on.
(Comparative Example 5)

0.1 wt% of SNP having a particle diameter of 500 nm was added to the weight of the whole solution. As a result, SNP was not uniformly dispersed in the liquid, and an organic semiconductor film could not be formed by spin coating. Therefore, the on / off ratio, mobility μ, and threshold voltage V _th for Comparative Example 5 are not measured.
(Comparative Example 6)

1.0 wt% of SNP having a particle diameter of 500 nm was added with respect to the weight of the whole solution. As a result, SNP was not uniformly dispersed in the liquid, and an organic semiconductor film could not be formed by spin coating. Therefore, the on / off ratio, mobility μ, and threshold voltage V _th for Comparative Example 6 are not measured.

  The results are shown in Table 1. As can be understood from Table 1, the particle size of the insulating fine particles SNP is 10 nm or more and 30 nm or less, and 0.1 wt% or more and 1.0 wt% or less are added to TIPS-PEN. It is necessary for forming an organic semiconductor film and maintaining good characteristics as an organic transistor.

1, 10, 20, 30 Coating type organic transistor 2 Substrate 3 Gate electrode 4 Gate insulating film 5 Organic semiconductor film 6 Source electrode 7 Drain electrode

Claims (4)

In the method of manufacturing an organic semiconductor film in which a thin film is formed by supplying a solution containing an organic semiconductor material onto an insulating film of a substrate and drying it,
The insulating layer is formed by shrink formation,
The water contact angle of the insulating film is 50 ° or more,
The solution contains 0.1 wt% to 1.0 wt% of silica nanoparticles having a particle size of 10 nm to 30 nm ,
The solvent of the solution is toluene, and the organic semiconductor material is triisopropylsilylethynylpentacene.
The manufacturing method of the organic-semiconductor film characterized by the above-mentioned. The method for producing an organic semiconductor film according to claim 1 , wherein the insulating film is polymethylsilsesquioxane (PMSQ), polyimide, polyvinylphenol, polyvinyl alcohol, polymethyl methacrylate, or polyparaxylene. Formed by shrink deposition, a substrate water contact angle has a 50 ° or more insulating film,
A thin film made of triisopropylsilylethynylpentacene formed on the insulating film,
The thin film contains silica nanoparticles having a particle size of 10 nm to 30 nm with respect to triisopropylsilylethynylpentacene in an amount of 5 wt% to 50 wt%.
An organic transistor characterized by that. The organic transistor according to claim 3 , wherein the insulating film is polymethylsilsesquioxane (PMSQ), polyimide, polyvinylphenol, polyvinyl alcohol, polymethyl methacrylate, or polyparaxylene.

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