JP2010056484A - Organic transistor, and method of manufacturing organic transistor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic transistor including an electrode which is obtained with the use of a reduced-manufacturing-cost solution method, and which less influences an organic semiconductor layer and is superior in mechanical strength and thermal stability. <P>SOLUTION: The organic transistor includes: an organic semiconductor layer 14; a gate electrode 12 formed in the organic semiconductor layer 14 with a gate insulating layer 13 therebetween; and a source electrode 15 and a drain electrode 16 which are formed in positions facing each other in contact with the organic semiconductor layer 14 and are made of a carbon material. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic transistor using an organic semiconductor material.

In organic field effect transistors (OFETs), the bottom contact type device that forms the organic active layer after forming the source / drain electrodes has a performance drop of one digit or more compared to the top contact type device manufactured in the reverse order. Has been regarded as one of the major technical problems.
This is thought to be due to the fact that when an organic semiconductor thin film is formed on a metal like a bottom contact type device, the energy barrier at the interface between the organic semiconductor and the metal is increased by about 1 eV.
On the other hand, when a metal is applied from the top of an organic semiconductor, such as a top contact type device, the metal penetrates into the organic semiconductor layer and changes its surface state, and the thermal effect during metal deposition , Energy barriers do not occur much.

  However, the bottom contact type device has higher applicability to miniaturization and complex patterns. As solutions to the problems of the bottom contact type device described above, surface treatment with gold thiol, conductive polymer and organic charge transfer complex (TTF) (TCNQ) (tetrathiafuvalene) (tetracyanoquinoji) (Methane) has been reported as an electrode material. (For example, refer nonpatent literature 1, nonpatent literature 2, nonpatent literature 3, nonpatent literature 4).

I. Kismiss, IEEE Trans. Electron Device, 48, 1060 (2001). M. Lefenfeld, G. Blanchet, and J. A. Rogers, Adv. Mater. 15, 1188 (2003). Y. Takahashi, T. Hasegawa, Y. Abe, Y. Tokura, K. Nishimura, G. Saito, Apl. Phys. Lett. 86, 063504 (2007). K. Shibata, K. Ishikawa, H. Takezoe, H. Wada, and T. Mori, Appl. Phys. Lett. 92, 023305 (2008).

  However, the thiol treatment has problems in effect and reproducibility, and conductive polymers and organic charge transfer complexes have many problems as electrode materials. In the conductive polymer, it cannot be said that the conductivity of the polymer itself is so high, and the coating type process using the charge transfer complex requires a plurality of types of solutions, and thus the process is complicated. In addition, these organic electrodes have problems in mechanical strength and thermal stability.

In addition, an electrode made of silver nanoparticles is used as an electrode formed by the solution method, but the same problem as the bottom contact type device using the metal electrode described above in the sense of forming an interface between the organic semiconductor and the metal. Have For this reason, in order to obtain the best performance, for example, it is necessary to produce a top contact type device in which a silver electrode is formed by a printing method or the like after an organic semiconductor thin film is formed.
However, since a silver paste dispersed in a solvent is applied from above the organic semiconductor thin film, the influence on the organic semiconductor thin film becomes a problem.

  In order to solve the above-described problems, in the present invention, an organic transistor including an electrode that can use a solution method with low manufacturing cost and that has less influence on the organic semiconductor layer and excellent mechanical strength and thermal stability. It is to provide.

  The organic transistor of the present invention includes an organic semiconductor layer, a gate electrode formed on the organic semiconductor layer through a gate insulating layer, a source electrode made of a carbon material formed at a position facing and in contact with the organic semiconductor layer, and A drain electrode.

In the organic transistor manufacturing method of the present invention, a gate electrode is formed on a substrate, and a gate insulating layer is formed to cover the gate electrode.
Then, a carbon thin film is formed on the gate insulating layer to form a source electrode and a drain electrode, and an organic semiconductor layer is formed to cover the source electrode and the drain electrode. Alternatively, an organic semiconductor layer is formed on the gate insulating layer, and a carbon thin film is formed on the organic semiconductor layer to form a source electrode and a drain electrode.

  According to the organic transistor of the present invention and the organic transistor provided by the manufacturing method of the present invention, the source electrode and the drain electrode are formed using a carbon material known as a conductive material. Since the carbon material is mainly composed of graphite or the like, the carbon material exhibits high electrical conductivity and is an inexpensive material. Further, from the viewpoint of atmospheric stability, the carbon material is unlikely to oxidize like a metal material, and even if it occurs, the influence on the device is considered to be minimal. Further, since graphite itself is an intermediate between an organic material called a semimetal and a metal material, the energy barrier between the carbon material and the organic semiconductor layer is considered to be smaller than that of the metal material.

  According to the present invention, it is possible to form an electrode of an organic transistor having little influence on the organic semiconductor layer and excellent in mechanical strength and thermal stability by a solution method. For this reason, all the steps for manufacturing the organic transistor can be performed by a wet process.

Hereinafter, specific embodiments of the present invention will be described.
First, FIG. 1 shows a structure of an organic transistor according to the present embodiment of the present invention.
The organic transistor shown in FIG. 1 is a so-called bottom contact element in which a gate electrode 12, a gate insulating layer 13, a source electrode 15 and a drain electrode 16 are sequentially stacked on a substrate 11, and an organic semiconductor layer 14 is stacked thereon. It is a structure called.

  The organic transistor shown in FIG. 1 includes a base 11, a gate electrode 12 formed on the base 11, and a gate insulating layer 13 that covers the gate electrode 12. Further, a source electrode 15 and a drain electrode 16 formed on the gate insulating layer 13 and an organic semiconductor layer 14 covering the source electrode 15 and the drain electrode 16 are provided.

  As the substrate 11 used in the organic transistor, glass, silicon, or a flexible plastic sheet such as polyethylene terephthalate, polycarbonate, polyimide, polysulfone, or polyethersulfone can be used. Moreover, weight reduction and resistance to impact can be improved by using a plastic sheet.

  The gate electrode 12 is formed of, for example, a metal material, a carbon material, a polymer mixture in which conductive particles are dispersed in a liquid together with a polymer, a carbon paste, a conductive polymer, or a conductive material such as highly doped silicon.

Examples of the metal material include metal materials such as Cr, Al, Ta, Mo, Nb, Cu, Ag, Au, Pt, Pd, In, Ni, and Nd, and alloy materials thereof. Examples of the carbon material include carbon black, heat-treated carbon black, glassy carbon, pyrolytic graphite, graphite, scaly graphite, and a mixture thereof.
The gate electrode 12 made of a conductive material such as a metal material and a carbon material is formed to a thickness of about 10 nm to about 500 nm.

  Moreover, as the above-mentioned polymer mixture, for example, conductive particles such as silver ink, graphite ink, silver paste, and carbon paste can be dispersed in a liquid together with a polymer and used. Examples of the conductive polymer include a polyaniline salt, a poly (3,4-ethylene-dioxythiophene) polystyrene sulfonate, or a soluble conductive polymer such as doped polypyrrole. In this case, the gate electrode 12 is formed to a film thickness of about 30 nm to about 1000 nm by applying or printing the polymer mixture, removing the solvent, and drying.

  Further, the above-described highly doped silicon can be formed from a silicon substrate used in a normal LSI process. For example, in a silicon substrate used in an LSI process, the gate electrode layer 12 and the substrate 11 can be formed on the silicon substrate by making the entire silicon substrate or a region in the vicinity where the gate insulating layer is formed highly doped. it can.

  The gate insulating layer 13 covering the gate electrode 12 is formed of various insulating materials such as an inorganic material, an organic material, or an organic low molecular weight amorphous material. Depending on the material, the gate insulating layer 13 can be formed by various film forming methods such as vapor deposition, sputtering, plasma CVD (Chemical Vapor Deposition) gate electrode 12 anodic oxidation, coating, and adhesion from a solution. . The gate insulating layer 13 is formed to a thickness of about 10 nm to about 500 nm.

Examples of inorganic materials include single metal oxides such as SiO ₂ , Al ₂ O ₃ , Ta ₂ O ₅ , and ZrO ₂ , composite oxides such as strontium titanate and strontium barium titanate, nitrides such as SiNx, and oxynitriding And fluoride.

  Examples of the organic material include polyvinylphenol, polymethyl methacrylate, polystyrene, polyimide, benzocyclobutene, cyanoethyl pullulan, polyvinylidene fluoride, vinylidene-4 fluoroethylene copolymer, and other polymer materials. .

  Examples of the organic low molecular weight amorphous material include cholic acid and methyl cholate. In this case, the gate insulating layer 13 is formed to a thickness of about 10 nm to about 500 nm.

  The source electrode 15 and the drain electrode 16 are made of a carbon material. As the carbon material, for example, carbon black, heat-treated carbon black, glassy carbon, pyrolytic graphite, graphite, scale-like graphite, and a mixture thereof can be used.

As a method for forming the source electrode 15 and the drain electrode 16, for example, any method such as an evaporation method, a CVD method, a plasma CVD method, a coating method, a printing method, or a nanoprinting method may be used. In particular, a method of forming and applying or printing a mixture of a carbon material, a binder, and a solvent or a paste-like ink can be used more preferably.
The source electrode 15 and the drain electrode 16 are formed of a carbon paste by dispersing a carbon material in a binder resin. As the binder resin used for the carbon paste, a resin such as a thermosetting resin usually used as a binder for the carbon paste can be used. For example, an acrylic resin, an epoxy resin, a polyamide resin, a polyimide resin, a polyamideimide resin, a polyvinyl alcohol, a phenol resin, a polyester resin, or the like can be appropriately selected and used. The resistance value after drying of the carbon paste is not particularly limited, but is preferably in the range of 10 ⁻³ Ωcm to ¹ Ωcm, and more preferably less than 10 ⁻¹ Ωcm.

A carbon electrode made of a carbon material is formed by, for example, forming an electrode pattern of HMDS (hexamethyldisilazane) self-assembled monolayers (SAMs) on the gate insulating layer 13, applying a carbon paste on the SAMs, and drying. It is formed by doing. At this time, the electrode pattern of the SAMs is formed by forming the SAMs on the entire surface of the gate insulating layer 13, and covering the SAMs with a shadow mask containing the electrode pattern and performing UV irradiation.
Further, the source electrode 15 and the drain electrode 16 are separately formed so as to avoid the portion directly above the gate electrode 12.

The organic semiconductor layer 14 includes, for example, pentacyclic, tetracene, anthracene, perylene, pyrene, coronene, chrysene, decacyclene, violanthrene, and other polycyclic aromatic molecular materials, phthalocyanine, triphenylene, thiophene oligomers and derivatives thereof, benzothiophene derivatives A crystalline organic semiconductor material having electron-donating properties such as tetrathiafulvalenes such as dibenzotetrathiafulvalene, tetrathiotetracene, and regioregular poly (3-alkylthiophene) to form a p-type organic transistor be able to.
The organic semiconductor layer 14 includes perfluorophthalocyanine F ₁₆ CuPc, tetracyanoquinodimethane (TCNQ), dicyanoquinone diimine (DCNQI), fluorothiophene oligomers and derivatives thereof, perfluoropolyacene, naphthalene and perylene. In addition, a crystalline organic semiconductor material having electron accepting properties such as tetracarboxylic acid anhydride, tetracarboxylic acid diimine and derivatives thereof, and fullerene C ₆₀ can be added to form an n-type organic transistor.
Particularly preferably, the following compounds (1) to (6) can be used.

  In addition to the organic semiconductor material described above, any crystalline organic semiconductor material having an electron donating property can be used as the electron donating crystalline organic semiconductor material constituting the organic semiconductor layer 14.

Next, an example of a method for manufacturing the above-described organic transistor will be described with reference to FIGS.
First, as shown in FIG. 2A, a gate electrode 12 and a gate insulating layer 13 are formed on a substrate 11.
The gate electrode 12 is formed by depositing the above-described conductive material to a film thickness of about 10 nm to about 500 nm by, for example, sputtering or vapor deposition. Then, the formed conductive material is patterned into a predetermined gate electrode pattern.
Alternatively, a polymer mixture or a solvent in which metal fine particles having a particle size of several nanometers to several tens of nanometers are applied, and a metal thin film having a film thickness of about 30 nm to about 1000 nm is formed in a process at a substrate temperature of less than 400 ° C. . Then, the formed metal thin film is patterned into a predetermined gate electrode pattern to form the gate electrode 12.

In addition, when an inorganic material is used for the gate insulating layer 13, it is formed by a method such as a vapor deposition method, a sputtering method, or a CVD method.
When an organic material is used for the gate insulating layer 13, a solution in which an insulating organic material or a polymer precursor is dissolved is prepared, and this solution is applied by a spin coating method, a screen printing method, or the like.
Then, the solvent is volatilized to form the gate insulating layer 13 having a film thickness of about 50 nm to about 500 nm. Alternatively, after removing the solvent by volatilization, the gate insulating layer 13 having a film thickness of about 50 nm to about 500 nm is formed by heating to convert the polymer precursor into a desired polymer.

When Ta ₂ O ₅ or Al ₂ O ₃ is used as the gate insulating layer 13, the gate electrode 12 is made of Ta or Al, and the Ta or Al electrode layer is formed using an electrolytic solution such as an ammonium borate aqueous solution. It is formed by anodizing.

Next, after cleaning the surface of the gate insulating layer 13 as necessary, self-assembled monolayers (SAMs) 17 are formed on the gate insulating layer 13 as shown in FIG. 2B.
The SAMs 17 can be formed, for example, by performing a SAMs treatment in which the surface of the gate insulating layer 13 is washed with acetone, 2-propanol and ultrapure water and then exposed to HMDS (hexamethyldisilazane) vapor. .

  Next, as shown in FIG. 2C, a shadow mask 18 containing an electrode pattern is placed on the formed SAMs 17. Then, UV ozone cleaning is performed, and as shown in FIG. 3D, the SAMs 17 in the UV-irradiated portion are decomposed and the decomposed SAMs are removed. By this step, an electrode pattern by SAMs 17 can be formed.

Next, a carbon paste is applied on the SAMs 17 on which the electrode pattern is formed. The carbon pace adjusts the concentration using a solvent such as ethyl acetate as necessary to adjust the viscosity and fluidity.
By this step, as shown in FIG. 3E, the carbon paste spreads only to the portion where the SAMs are removed due to the difference in surface energy between the SAMs 17 and the gate insulating layer 13. A carbon thin film can be formed on the gate insulating layer 13 by drying the carbon paste applied in the air. The carbon thin film becomes the source electrode 15 and the drain electrode 16.

Next, as illustrated in FIG. 3F, the organic semiconductor layer 14 that covers the source electrode 15 and the drain electrode 16 is formed on the gate insulating layer 13. At this time, the organic semiconductor layer 14 is preferably formed directly on the SAMs. By forming the organic semiconductor layer 14 on the SAMs, the molecular arrangement in the organic semiconductor layer 14 is improved.
Alternatively, the organic semiconductor layer 14 can be formed after removing the SAMs. SAMs can be removed by ultrasonic cleaning using an organic solvent such as chloroform or hexane.
The organic semiconductor layer 14 is formed using a wet process such as a spin coating method, a casting method, a screen printing method, an ink jet printing method, or a micro contact printing method using the above-described organic semiconductor material.

Through the above steps, the organic transistor having the structure shown in FIG. 1 can be manufactured.
In the above-described embodiment, the carbon electrode pattern is prepared using carbon paste and SAMs. However, the present invention is not limited to this method, and any method may be used as long as a carbon thin film can be formed. In addition to the above method, for example, CVD (Chemical Vapor Deposition) method, laser ablation method, printing by hand ink jet using carbon paste, and the like can be applied.

(Example)
Hereinafter, the bottom contact type organic transistor shown in FIG. 1 was actually fabricated and the characteristics were investigated.
Example 1
First, the surface of a silicon substrate (SiO ₂ / Si substrate) having a silicon oxide film formed thereon is first washed with acetone, then washed with 2-propanol and ultrapure water, and then dried in an oven. Further, UV ozone cleaning was performed.
Next, the cleaned substrate was exposed to HMDS vapor in an oven at 150 ° C. for 1 hour to perform SAMs treatment on the substrate surface. By this SAMs treatment, HMDS by HMDS was formed on the substrate surface.
After removing the substrate from the oven, excess HMDS on the substrate was washed away with acetone and dried again in an oven at 150 ° C.

  Next, a shadow mask containing an electrode pattern was placed on the substrate on which the SAMs were formed, and UV ozone cleaning was performed, and the SAMs were decomposed only in the UV irradiated portions to form SAMs electrode patterns.

Next, a carbon paste solution obtained by diluting carbon paste (Dotite XC-12, manufactured by Fujikura Co., Ltd., resistance value: 10 ⁻² Ωcm) about 10 times with ethyl acetate was dropped onto the substrate on which the electrode pattern of SAMs was formed. . The dropped carbon paste solution selectively spread the carbon paste solution only to the portion where the SAMs were removed due to the difference in surface energy between SiO ₂ and SAMs on the substrate.
In this state, the carbon paste solution was dried in the air to form a carbon electrode made of carbon paste on the substrate.

  Next, pentacene purified by sublimation purification was used as the organic semiconductor material, an organic semiconductor layer was formed at room temperature on the carbon electrode prepared by the above-described method using a vapor deposition method, and a bottom contact type organic transistor was produced. .

The surface of the carbon electrode of the organic transistor produced in Example 1 was observed by AFM, and an image of the observed carbon electrode is shown in FIG. FIG. 5 shows an image of pentacene formed on the substrate on which the carbon electrode is formed. The carbon electrode of the organic transistor produced in Example 1 was measured by XRD, and the result is shown in FIG.
The following methods were used for AFM and XRD.

AFM (atomic force microscopy)
Using the scanning probe microscope SPA-300 / SPI3800 manufactured by Seiko Instruments Inc. and a Si ₃ N ₄ cantilever, the prepared sample was photographed and the surface shape was evaluated.

XRD (X-ray diffraction)
Using a X-PERT PRO MRD manufactured by Philips, θ-2θscan (2 ° ≦ 2θ ≦ 30 °) is performed on the thin film, and Bragg's law (2 dsin θ = nλ, λ = 1.541838Å (CuKα)) is used. Thus, the lattice spacing (d-spacing) of the sample was determined.

From the image shown in FIG. 4, it can be seen that the carbon electrode has a thin film formed of carbon fine particles having a diameter of about 100 nm. A large number of fine carbon particles gather to form a lump of about 2 μm. Moreover, the boundary between the masses of carbon fine particles is deep, and the surface smoothness is low. Such low smoothness is also disadvantageous for forming an organic semiconductor thin film on a carbon electrode when a bottom contact element is formed. However, as shown in FIG. 5, when a pentacene thin film is deposited on a substrate on which a carbon electrode is actually formed, a morphology unique to pentacene is formed on the carbon electrode. For this reason, it is considered that the film growth of pentacene occurs on the carbon electrode as well as on the silicon substrate. Furthermore, it can be seen that the morphology of pentacene near the carbon electrode continues without breaking down to the immediate vicinity of the electrode.
When a bottom contact type organic transistor using pentacene is formed using a conventional gold electrode, a change in grain size near the electrode has been observed. This change in grain size is considered to be one factor that deteriorates the characteristics of the organic transistor.
In the above-described embodiments, the disorder of the pentacene morphology near the carbon electrode is not observed, which is advantageous in transistor characteristics.

  Further, as shown in FIG. 6 of the XRD result of the carbon electrode, a single peak at 2θ = 30 degrees was observed at 26.5 degrees. This value corresponds to dspace = 3.36 、, which is almost equal to the graphite interlayer distance of 3.35 Å. Therefore, the main component of the carbon electrode is graphite, which mainly indicates that the graphene layer is aligned in parallel with the substrate.

  Next, the stability of the carbon electrode of the organic transistor produced in Example 1 was examined. For comparison, the same measurement was performed in Comparative Example 1 below in which electrodes were formed by (TTF) (TCNQ).

(Comparative Example 1)
An organic transistor of Comparative Example 1 was produced in the same manner as in Example 1 except that the electrode was formed by vapor deposition using (TTF) (TCNQ) instead of the carbon electrode using carbon paste.

For the organic transistors of Example 1 and Comparative Example 1, each electrode was heated in the atmosphere, and the results of examining the temperature change in resistivity are shown in FIG.
As shown in FIG. 7, the carbon electrode of the organic transistor of Example 1 exhibited a resistivity of about 0.4 Ωcm at room temperature. Moreover, the (TTF) (TCNQ) electrode of the organic transistor of Comparative Example 1 exhibited a resistivity of about 0.2 Ωcm. By heating both, the resistance value of the carbon electrode maintained a substantially constant value, whereas the resistivity of the (TTF) (TCNQ) electrode gradually decreased and showed a semiconductor behavior. It was. In addition, the carbon electrode showed an almost constant value even after cooling after heating, whereas the (TTF) (TCNQ) electrode suddenly increased the resistivity from around 360K in the heating process. The increase in the resistivity of the (TTF) (TCNQ) electrode is considered to be due to the decomposition of (TTF) (TCNQ).

Moreover, about the organic transistor of Example 1 and the comparative example 1, the change of the resistivity at the time of keeping under fixed temperature was investigated.
Changes in the resistivity of the carbon electrode of the organic transistor of Example 1 are shown in FIGS. 8A and 8B. 9A and 9B show changes in the resistivity of the (TTF) (TCNQ) electrode of the organic transistor of Comparative Example 1. FIG.

From the results shown in FIGS. 8A and 8B, the carbon electrode of Example 1 showed no significant change at any temperature. On the other hand, as shown in FIGS. 9A and 9B, the (TTF) (TCNQ) electrode of Comparative Example 1 shows a slight increase in resistivity after 16 hours when held at 50 ° C., and when held at 60 ° C. It can be seen that the resistivity increases rapidly. From these results, it can be seen that the carbon electrode is more stable as a conductive material than the conventionally used (TTF) (TCNQ).
For practical use of organic transistors, the service life is one important factor. From the above results, the lifetime of the organic transistor can be improved by using a highly stable carbon electrode as the electrode of the organic transistor.

  Next, the organic semiconductor material applied to the organic transistor was changed, and the organic transistors of Examples 2 to 4 were produced and evaluated. Moreover, the electrode material applied to an organic transistor was changed, the organic transistor of Comparative Examples 1-8 was produced, and evaluation was performed.

(Example 2)
When forming an organic semiconductor layer on the carbon electrode produced by the above-described method using pentacene and using the vapor deposition method, the temperature of the substrate is set to 60 ° C. An organic transistor was fabricated.

(Example 3)
An organic transistor of Example 3 was produced in the same manner as in Example 1 except that the organic semiconductor material was changed from pentacene to F ₁₆ CuPc.

Example 4
An organic transistor of Example 3 was produced in the same manner as in Example 1 except that the organic semiconductor material was changed from pentacene to P3HT and an organic semiconductor layer was formed by using a spin coating method.
Formation of the organic semiconductor layer by spin coating method, distilled the CHCl ₃ was used as a solvent, to prepare a CHCl ₃ solution was dissolved in a proportion of P3HT10mg against CHCl ₃ 1 ml. And this solution was dripped on the board | substrate and the board | substrate was rotated at high speed for 60 seconds at 5000 rpm using the spin coater (Mikasa MS-A100).

(Example 5)
An organic transistor of Example 4 was produced in the same manner as in Example 1 except that the organic semiconductor material was changed from pentacene to DMDCNQI.

(Comparative Example 2)
An organic transistor of Comparative Example 2 was produced in the same manner as Comparative Example 1 except that the electrode material was changed from (TTF) (TCNQ) to gold (Au).

(Comparative Example 3)
An organic transistor of Comparative Example 3 was produced in the same manner as in Example 3 except that the electrode was formed by vapor deposition using (TTF) (TCNQ) instead of the carbon electrode using carbon paste.

(Comparative Example 4)
An organic transistor of Comparative Example 4 was produced in the same manner as Comparative Example 3, except that the electrode material was changed from (TTF) (TCNQ) to gold (Au).

(Comparative Example 5)
An organic transistor of Comparative Example 5 was produced in the same manner as in Example 4 except that the electrode was formed by vapor deposition using (TTF) (TCNQ) instead of the carbon electrode using carbon paste.

(Comparative Example 6)
An organic transistor of Comparative Example 6 was produced in the same manner as Comparative Example 5 except that the electrode material was changed from (TTF) (TCNQ) to gold (Au).

(Comparative Example 7)
An organic transistor of Comparative Example 7 was produced in the same manner as in Example 5 except that the electrode was formed by vapor deposition using (TTF) (TCNQ) instead of the carbon electrode using carbon paste.

(Comparative Example 8)
An organic transistor of Comparative Example 8 was produced in the same manner as Comparative Example 7 except that the electrode material was changed from (TTF) (TCNQ) to gold (Au).

  The characteristics of each organic transistor produced in Examples 1 to 5 and Comparative Examples 1 to 8 were measured using a Keithley 4200 semiconductor parameter analyzer in the air.

Table 1 shows the characteristics of the organic transistors produced in Examples 1 to 5.
FIG. 10 shows output characteristics and transfer characteristics of the organic transistor manufactured in Example 1. FIG. 11 shows the output characteristics and transfer characteristics of the organic transistor manufactured in Example 3, and FIG. 12 shows the output characteristics and transfer characteristics of the organic transistor manufactured in Example 4.

As shown in Table 1, the organic transistor using the carbon electrode of Example 1 showed a carrier mobility of 0.49 cm ² / Vs when the substrate temperature during vapor deposition was room temperature. The substrate mobility was 1.0 cm ² / Vs when the substrate temperature was 60 ^° C.
Pentacene is known as a material exhibiting good p-type transistor characteristics, but in the organic transistors of Examples 1 and 2 described above, high mobility was observed as the bottom contact type.

In a conventional organic transistor, a carrier mobility of 0.49 cm ² / Vs has been reported in a top contact type device using a gold electrode. In addition, in the bottom contact type, a carrier movement path that is an order of magnitude smaller has been reported in a gold electrode that has not been subjected to electrode surface modification or the like. In conventional organic transistors, carrier mobility of about 0.4 cm ² / Vs has been observed in top contact and bottom contact device structures using (TTF) (TCNQ) electrodes.
Thus, it turns out that the organic transistor using the carbon electrode of Examples 1 and 2 has a relatively high value as a bottom contact type element.

Further, as shown in Table 1, in the organic transistor using F ₁₆ CuPc for the organic semiconductor layer of Example 3 and the organic transistor using DMDCCNQI for the organic semiconductor layer of Example 5, n-type carrier mobility is used. Was observed.
Therefore, it is shown that the carbon electrode is effective not only for the p-type transistor but also for the n-type transistor.

Furthermore, in the organic transistor of Example 4, the organic semiconductor layer was formed using P3HT by spin coating. For this reason, a carbon electrode formed using a carbon paste is insoluble in chloroform once formed, and an organic semiconductor layer can be formed by a solution method without dissolving the formed carbon electrode. Become.
Therefore, by applying the carbon electrode in the organic transistor, it is possible to realize a completely coated organic transistor.

  Next, Table 2 shows the carrier mobility of the organic transistors fabricated in Example 1, Examples 3 to 5, and Comparative Examples 1 to 8.

  As shown in Table 2, when the carrier mobility of the organic transistor of Example 1 and Examples 2 to 5 described above is compared with the organic transistor using Au or (TTF) (TCNQ) as an electrode material, the Example 1, Examples 2-5 showed the mobility equivalent to or higher than Comparative Examples 1-8.

Next, FIG. 13A shows changes over time in carrier mobility and threshold voltage of the n-type transistor manufactured in Example 5 using DMDCNQI as the organic semiconductor material. Further, FIG. 13B shows the change over time in the threshold voltage of the organic transistor of Comparative Example 7 in which the electrode material is changed to (TTF) (TCNQ) from Example 5 and Comparative Example 8 in which the material is changed to gold (Au). The time change of the mobility is shown in FIG. 13C.
For comparison, various characteristics of an organic transistor in which the electrode material of the organic transistor of Comparative Example 8 is changed from gold (Au) to silver (Ag) and copper (Cu) are shown in FIGS.

FIG. 13A shows the change in carrier mobility with respect to time after exposure to air (time 0 is under vacuum before exposure to air). From the results shown in FIG. 13A, the organic transistor manufactured in Example 5 has no significant change in both carrier mobility and threshold voltage. Therefore, even in an n-type transistor that is generally low in stability under the atmosphere, an organic transistor having high stability can be configured by using a carbon electrode.
In addition, as shown in FIGS. 13B and 13C, when the organic transistor manufactured in Example 5 is compared with the organic transistor in which the electrode material is changed to another material, the organic transistor manufactured in Example 5 is It can be seen that the stability is equivalent to that of the gold electrode.
This result is presumably because the carbon material forms a stable interface without causing a phenomenon such as complexation at the interface with DMDCNQI.

  From the above results, a coating-type electrode can be manufactured by using a carbon material for the source electrode and the drain electrode. Moreover, in the organic transistor using the coating type carbon electrode, p-type and n-type carrier mobility could be observed for a plurality of organic semiconductor materials including pentacene. In addition, various characteristics of the organic transistor in which a P3HT organic semiconductor layer was fabricated by a coating method were observed, and it was confirmed that the carbon electrode was also effective in the coating method.

In the present invention, in addition to the bottom contact type element described in the above embodiment, for example, a gate electrode 22, a gate insulating layer 23, and an organic semiconductor material are applied on a substrate 21 as shown in FIG. The present invention can also be applied to a so-called top contact element structure in which the organic semiconductor layers 24 are sequentially stacked and the source electrode 25 and the drain electrode 26 are formed on the organic semiconductor layer 24.
Even in the case of a top contact type element, a source electrode and a drain electrode made of a carbon material can be formed by a method similar to the above-described manufacturing method.

In the organic transistor of the present invention, not only can the carbon material be applied to the source electrode and the drain electrode described above, but also the carbon material can be applied to the gate electrode. For this reason, in the organic transistor of this invention, all the electrodes of a gate electrode, a source electrode, and a drain electrode can be comprised from a carbon material.
For example, all the gate electrodes, insulating films, source electrodes, drain electrodes, and organic semiconductor layers constituting the organic transistor by forming the gate electrode by a coating method or a printing method using carbon paste are applied or printed. Can be formed.

  The present invention is not limited to the configuration described in the above-described embodiment, and various modifications and changes can be made without departing from the configuration of the present invention.

It is a figure which shows the structure of the organic transistor of embodiment of this invention. A to C are manufacturing process diagrams of an organic transistor according to an embodiment of the present invention. DF is a manufacturing-process figure of the organic transistor of embodiment of this invention. It is the image which observed the carbon electrode of the organic transistor of Example 1 by AFM. It is the image which observed the carbon electrode of the organic transistor of Example 1, and the organic-semiconductor layer around a carbon electrode by AFM. It is a figure which shows the result of having measured the carbon electrode of the organic transistor of Example 1 by XRD. It is a figure which shows the result of having heated each electrode in air | atmosphere about the organic transistor of Example 1 and Comparative Example 1, and having investigated the temperature change of a resistivity. A and B are diagrams showing the results of examining the change in resistivity when the organic transistor of Example 1 is kept at a constant temperature. A and B are diagrams showing the results of examining the change in resistivity when the organic transistor of Comparative Example 1 is kept at a constant temperature. A and B are diagrams showing output characteristics and transfer characteristics of the organic transistor of Example 1. FIG. A and B are diagrams showing output characteristics and transfer characteristics of the organic transistor of Example 3. FIG. A and B are diagrams showing output characteristics and transfer characteristics of the organic transistor of Example 4. FIG. A is a figure which shows the change of the carrier mobility with respect to the time after the atmospheric exposure of the organic transistor of Example 5. FIG. FIG. 7B is a graph showing changes over time in threshold voltages of the organic transistors of Example 5, Comparative Example 7, and Comparative Example 8. C is a graph showing changes in carrier mobility of the organic transistors of Example 5, Comparative Example 7, and Comparative Example 8 over time. It is a figure which shows the structure of the organic transistor of other embodiment of this invention.

Explanation of symbols

  11, 21 substrate, 12, 22 gate electrode, 13, 23 gate insulating layer, 14, 24 organic semiconductor layer, 15, 25 source electrode, 16, 26 drain electrode, 17 self-assembled monolayers (SAMs), 18 shadow mask

Claims (6)

An organic semiconductor layer;
A gate electrode formed on the organic semiconductor layer via a gate insulating layer;
An organic transistor comprising: a source electrode and a drain electrode made of a carbon material formed at positions facing and facing the organic semiconductor layer.   The organic transistor according to claim 1, wherein the source electrode and the drain electrode are formed by applying a carbon paste to a pattern formed by a self-assembled monolayer. Forming a gate electrode on the substrate;
Forming a gate insulating layer covering the gate electrode;
Forming a carbon thin film on the gate insulating layer to form a source electrode and a drain electrode;
And a step of forming an organic semiconductor layer so as to cover the source electrode and the drain electrode. Forming a gate electrode on the substrate;
Forming a gate insulating layer covering the gate electrode;
Forming an organic semiconductor layer on the gate insulating layer;
The manufacturing method of an organic transistor including the process of forming a carbon thin film on the said organic-semiconductor layer, and forming a source electrode and a drain electrode.   The method for producing an organic transistor according to claim 3 or 4, wherein the carbon thin film is formed by a step of applying a carbon paste and a step of drying the applied carbon paste. In the step of applying the carbon paste,
Forming a self-assembled monolayer on the gate insulating film;
Forming an electrode pattern with the monolayer under self-organization;
The organic transistor manufacturing method according to claim 3, further comprising: applying the carbon paste on the gate insulating film on which the electrode pattern is formed by the self-organized monomolecular film.