JP5223294B2 - Method for producing organic thin film transistor - Google Patents

Description

  The present invention relates to a method for manufacturing an organic thin film transistor.

In recent years, research and development of organic semiconductor materials centering on application to thin film transistors has been actively conducted for the reason that organic electronic devices can be reduced in cost, flexible and large in area. In particular, as organic semiconductor materials, the development of materials of π-conjugated polymers that are soluble in organic solvents and the design of those materials aiming at high performance are attracting attention in order to reduce the film thickness by a low-cost method.
For example, Non-Patent Document 1 shows that poly (3-hexylthiophene) exhibits good solubility and is self-organized due to phase separation of the main chain and side chain of this polymer. It is disclosed that a thin film having regularity is formed and exhibits high mobility.
In Patent Document 1, as a method for producing a polymer film oriented in one direction aiming at higher mobility, a polymer film is provided on a mechanically polished substrate such as polyimide and heated to produce a liquid crystal phase. Then, a method of quenching is disclosed.
Furthermore, in Patent Document 2, an oriented polymer film is obtained by imprinting and transferring a molded body obtained by pressure-molding a polymer to a silicon substrate without using water or an organic solvent, whether soluble or insoluble. A method is disclosed, and an example in which mobility is improved by making the carrier transport direction one direction is shown.

However, in a thin film having local regularity due to self-organization of poly (3-hexylthiophene) as in Non-Patent Document 1, the state of self-organization depends on the type of solvent, coating conditions, etc. when forming the thin film. It is clear that the homogeneity of the organic semiconductor film differs due to the difference, and the mobility varies depending on the film formation conditions. That is, in this thin film, regularity is local and there is no anisotropy in the film surface, and in order to form the regularity uniformly, it is necessary to strictly control the formation environment. It is difficult to manufacture a device with high reproducibility.
On the other hand, the method of Patent Document 1 is an excellent method that makes it easy to align the polymer in one direction. However, since the substrate is mechanically polished, irregularities necessarily exist at the interface of the alignment film. Homogeneous performance cannot be obtained. In addition, the non-uniformity of the film reflecting the unevenness of the substrate may reach the upper part of the film or the film surface, which may make it difficult to manufacture a device having a structure in which thin films are stacked.
Further, the method of Patent Document 2 is a method of forming a polymer film oriented in one direction by pressing and transferring a polymer onto a smooth silicon wafer as a substrate. Depending on the transfer conditions, it is difficult to obtain an appropriate film thickness. In addition, since unevenness occurs on the surface of the transfer film, when used as a transistor, non-uniformity occurs in the bonding with the electrode laminated on the surface of the polymer film, and as a result, uniform performance cannot be obtained. Has a problem.

Japanese translation of PCT publication No. 2003-502874 JP 2004-356422 A Zhenan Bao et al. Applied Physics Letter, Vol. 69, no. 26, p4108-4110 (21996)

  An object of this invention is to provide the method of manufacturing the organic thin-film transistor which can obtain an electrical property with high homogeneity, even if manufacturing conditions are not strictly controlled.

The above problems are solved by the following inventions 1) to 3).
1) on the organic semiconductor film, after planarizing by applying a solvent with a solubility in the organic semiconductor, the organic thin film transistor according to claim Rukoto to have a step of forming an electrode on the organic semiconductor film Manufacturing method.
2) The method for producing an organic thin film transistor according to 1), wherein the organic semiconductor film has an alignment region.
3) The method for producing an organic thin film transistor according to 1) or 2), wherein the solvent soluble in the organic semiconductor contains the same or different organic semiconductor as the organic semiconductor as a solute.

Hereinafter, the present invention will be described in detail.
In the method for producing an organic thin film transistor of the present invention, a solvent that is soluble in the organic semiconductor is applied onto the organic semiconductor film, the surface of the organic semiconductor film is partially dissolved and planarized, and then the organic semiconductor film is formed. An electrode is formed on the semiconductor film . Thereby, an organic thin film transistor with uniform performance can be obtained. Therefore, if this organic thin film transistor is used, a uniform interface can be realized in, for example, a stacked type element. Therefore, when applied to an organic electronic device, it is possible to provide a highly reproducible element with reduced variation in element performance. .
The method for applying the solvent is not particularly limited, but typical examples include spin coating, printing, ink jet, and spray coating.
Although it does not specifically limit as a solvent, As a typical thing, tetrahydrofuran, toluene, xylene, dioxane, chloroform, a dichloromethane, etc., or these mixed solvents can be used.
Said solvent may contain the same or different organic semiconductor as this organic semiconductor as a solute. The concentration of the organic semiconductor in the solution to be applied is not particularly limited, but generally 0.1 to 1% by weight is often used.
After applying the above solvent or organic semiconductor, it is desirable to heat dry at a temperature according to the solvent species and film quality.

The organic thin film transistor of the present invention is usually provided on a substrate. Examples of the substrate include a metal substrate, a glass substrate, a plastic substrate, and a silicon substrate. A substrate with little dimensional change in a series of manufacturing processes can facilitate the manufacturing process. In addition, when a metal thin film or a plastic substrate such as a foldable PES substrate, a polyimide substrate, or a PET substrate is used, flexibility can be given to a completed device.
Moreover, you may provide the organic thin-film transistor of this invention on an insulating film. Thereby, application to various organic electronic devices becomes possible. In particular, since the organic thin film transistor of the present invention has high reproducibility of element performance, even in an electronic device in which these are integrated, it is possible to provide a device with little variation in performance between elements.
Insulating film materials include inorganic insulating films such as silicon oxide, silicon nitride, aluminum oxide and aluminum nitride, as well as organic insulating films such as polyimide, polyvinyl alcohol, polyvinylphenol, polyester, polyethylene, polyphenylene sulfide, polyparaxylene, poly Examples include acrylonitrile, cyanoethyl pullulan, and polymethyl methacrylate.
There is no particular limitation on the method for forming the insulating film, and for example, a CVD method, a plasma CVD method, a plasma polymerization method, an evaporation method, a spin coating method, a dipping method, a printing method, an ink jet method, or the like can be used.

A method for obtaining an organic semiconductor film having an alignment region that can be used in the present invention is not particularly limited, but pressure-molding an organic semiconductor powder and pressing the processed pellet into a thickness of about 1 to 3 mm in one direction of the substrate. It may be formed by sweeping. The pressure molding of the organic semiconductor powder may be performed under vacuum if desired.
The temperature of the substrate during the crimping sweep is preferably equal to or lower than the softening temperature of the organic semiconductor, and is usually in the range from room temperature to the softening temperature, but it is easy to form a thin film and obtains a highly oriented one. A range from a temperature 30 ° C. lower than the temperature to the softening temperature is more preferable.
The organic semiconductor suitable for the present invention is not particularly limited, but preferred examples include homopolymers or copolymers having a skeleton of thiophene and derivatives thereof, homopolymers or copolymers having a skeleton of fluorene and derivatives thereof, and phenylene. -Homopolymer or copolymer having a skeleton of vinylene and its derivatives, homopolymer or copolymer having a skeleton of triarylamine and its derivatives, homopolymer or copolymer having a skeleton of carbazole and its derivatives, vinyl carbazole And a homopolymer or copolymer having a skeleton of a derivative thereof, a homopolymer or copolymer having a skeleton of acetylene and a derivative thereof, and the like.

1 and 2 show a schematic structure of an example of the organic thin film transistor of the present invention.
The organic thin film transistor of the present invention is provided with a first electrode 3, a second electrode 4, and a third electrode 5 that are spatially separated on a substrate 6, and a voltage applied to the third electrode 5. By application, the current flowing in the semiconductor layer 1 made of the organic semiconductor film of the present invention can be controlled.
The first electrode 3 and the second electrode 4 are preferably formed of a material that can make ohmic contact with the organic semiconductor film of the present invention. However, even a material having a Schottky contact can be used as long as its energy barrier is low. Specifically, metals such as gold, platinum, aluminum, nickel, copper, silver, titanium, or poly (styrene sulfonate), poly [2,3-dihydrothieno (3,4-b) -1,4-dioxin ] (PEDOT), organic conductive materials such as polyaniline, and the like.
Furthermore, in order to facilitate carrier injection into the organic semiconductor, it is more preferable that the work function of the electrode is close to the Fermi level of the organic semiconductor.

The third electrode 5 separated from the semiconductor layer 1 by the insulating film 2 can also use the above metal or organic conductive material. Further, an n-type semiconductor or a p-type semiconductor can be used. In the case where a semiconductor is used for the third electrode material, the electrode may be formed using a carrier doped with impurities in advance, or the gate electrode may be formed and then doped with impurities. Furthermore, the third electrode 5 may also serve as a substrate.
The organic thin film transistor of the present invention can be applied to an electronic device by being integrated. For example, it can be used as an element for driving an image display element such as liquid crystal, organic electroluminescence, electrophoresis, and the like, and by integrating them, a so-called “electronic paper” display can be manufactured. In addition, as an electronic device such as an IC tag, an IC in which the organic thin film transistor of the present invention is integrated can be used.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the organic thin-film transistor which can obtain an electrical characteristic with high homogeneity can be provided, even if manufacturing conditions are not strictly controlled.

  EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated in more detail, this invention is not limited by these Examples.

Example 1
Dioctylfluorene-bithiophene copolymer (π-conjugated polymer), which is pressed into pellets, is transferred onto a silicon substrate under pressure to form a uniaxially oriented film, and then spin coated with tetrahydrofuran to partially coat the film surface. The film surface was flattened by being dissolved in and reconstituting the film surface.
FIG. 3 shows an AFM (atomic force microscope) image of the film before spin-coating the solvent, and FIG. 4 shows an AFM image of the film whose surface is flattened by spin-coating the solvent.
As can be seen from FIGS. 3 and 4, it was confirmed that the surface of the organic semiconductor film produced by the method of the present invention was flattened.

Example 2
An organic semiconductor film of the present invention was produced in the same manner as in Example 1 except that a quartz substrate was used instead of the silicon substrate. The polarized ultraviolet absorption spectrum is shown in FIG.
As can be seen from FIG. 5, in the absorption wavelength region derived from the dioctylfluorene-bithiophene copolymer, polarized light having an electric field vector parallel to the sweep direction obtained by pressure-transferring this polymer is strongly absorbed, and vertical polarized light is not absorbed so much. It has become. From this, it was confirmed that the dioctylfluorene-bithiophene copolymer was highly uniaxially oriented in the in-plane direction, and it was confirmed that the spin-coated solvent contributed to the flattening of the film surface.

Example 3
Example 1 is the same as Example 1 except that instead of the silicon substrate, the surface of the silicon substrate acting as a p-doped third electrode is thermally oxidized to form a 200 nm SiO ₂ insulating film. Thus, the organic thin film transistor of the present invention was produced.
Next, a gold film is formed as a first electrode and a second electrode on the surface of the organic semiconductor film by a vacuum deposition method so that the channel length is 30 μm and the channel width is 10 mm, and the organic thin film transistor having the structure of FIG. Created.
Furthermore, in order to confirm the reproducibility of the characteristics of the organic thin film transistor, the same operation was repeated to produce a total of two organic thin film transistors.
When field effect mobility and threshold voltage were measured for these organic thin film transistors, field effect mobility was 1.5 × 10 ⁻³ cm ² / Vs, and 1.4 × 10 ⁻³ cm ² / Vs, threshold voltage. Were -0.5V and -0.6V.
From this, it was confirmed that the organic thin film transistor of the present invention has high reproducibility.

Comparative Example 1
An organic thin film transistor was produced in the same manner as in Example 3 except that tetrahydrofuran was not spin-coated. At this time, in order to confirm the reproducibility, the same operation was repeated to produce a total of two organic thin film transistors.
When field effect mobility and threshold voltage were measured for these organic thin film transistors, field effect mobility was 6.5 × 10 ⁻⁴ cm ² / Vs and 1.1 × 10 ⁻⁴ cm ² / Vs, threshold voltage. Were -2.1V and -7.3V.
It can be seen that if the surface planarization treatment is not performed, variations occur in the junction between the electrode and the organic semiconductor film, resulting in variations in transistor performance.

  As described above, it has been found that the organic thin film transistor of the present invention forms a highly reproducible element. This is because the surface of the organic semiconductor film is flattened and the interface between the electrode and the semiconductor is uniform regardless of location.

The figure which shows schematic structure of an example of the organic thin-film transistor of this invention. The figure which shows schematic structure of the other example of the organic thin-film transistor of this invention. The AFM image of the uniaxially oriented film of Example 1 before spin coating with a solvent. The AFM image of the uniaxially oriented film of Example 1 after spin coating with a solvent. The figure which shows a polarization ultraviolet absorption spectrum of the uniaxially oriented film of Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Semiconductor layer 2 Insulating film 3 1st electrode 4 2nd electrode 5 3rd electrode 6 Board | substrate

Claims (3)

On the organic semiconductor film, after planarizing by applying a solvent with a solubility in the organic semiconductor, manufacturing of the organic thin film transistor according to claim Rukoto to have a step of forming an electrode on the organic semiconductor film Method.   2. The method for producing an organic thin film transistor according to claim 1, wherein the organic semiconductor film has an alignment region.   3. The method for producing an organic thin film transistor according to claim 1, wherein the solvent that is soluble in the organic semiconductor contains, as a solute, an organic semiconductor that is the same as or different from the organic semiconductor.