KR20040067047A - Organic thin film transistors and method for manufacturing the same - Google Patents

Abstract

PURPOSE: An organic TFT and a fabricating method thereof are provided to form an organic semiconductor material layer having a large grain size by coating a diluted PMMA coating layer on a source electrode, a drain electrode, and a gate insulating layer and depositing an organic semiconductor material thereon. CONSTITUTION: An organic TFT includes a substrate, a gate electrode, a gate insulating layer, a source electrode, a drain electrode, a diluted PMMA(Poly-Methyl-MethAcrylate) coating layer, and an organic semiconductor material. The gate electrode(20) is formed on the substrate(10). The gate insulating layer(30) is formed on the substrate in order to cover the gate electrode. The source electrode(51) and the drain electrode(52) are formed on the gate insulating layer. The diluted PMMA coating layer(60) is formed on the gate insulating layer in order to cover the source and the drain electrodes. The organic semiconductor material(80) is partially deposited on the source and the drain electrodes and the diluted PMMA coating layer.

Description

Organic thin film transistors and method for manufacturing the same

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic thin film transistor and a method of manufacturing the same. More specifically, a poly- (methyl methacrylate) (PMMA) solution diluted with monochlorobenzen is spin coated on a source, a drain electrode, and a gate insulating film. Thereafter, by depositing an organic semiconductor material, it is possible to form an organic semiconductor material film having a large grain size, to improve the carrier mobility of the device, and to shorten the manufacturing process time, and to a method of manufacturing the organic thin film transistor It is about.

In recent years, interest in organic thin film transistors (OTFTs) has recently grown due to their applicability to new and low-cost applications such as active flexible displays, smart cards, inventory or price indicators. Repeated twice, please delete) It is growing.

In particular, with the recent development of organic EL displays and the low temperature process applicable to plastic substrates, the need for development of active organic EL displays is increasing.

In addition, since an amorphous silicon thin film transistor, which is an active device used in an AMLCD (active matrix liquid crystal display), has a manufacturing temperature of 360 ° C., a plastic substrate required for a high temperature manufacturing temperature is expensive, and it may be broken due to the characteristics of an inorganic device in terms of flexibility. There is a possibility.

Therefore, in recent years, the need for an organic thin film transistor capable of depositing at a temperature near room temperature while ensuring flexibility is increasing.

However, in the organic thin film transistors developed to date, most of the devices exhibiting poor characteristics with mobility of 1 cm 2 / Vsec or less have been pointed out as a problem that stability in air is deteriorated.

In order to solve this problem, studies are being actively conducted to apply pentacene, an organic semiconductor material, to organic thin film transistors.

The reason is that the organic thin film transistors to which pentacin is applied not only exhibit excellent mobility characteristics comparable to those of amorphous silicon thin film transistors, but also exhibit fairly stable characteristics in air.

Meanwhile, in the organic thin film transistor manufactured using the pentacin, a technique in which pentacin having a large grain size can be grown well on the gate insulating film is required to improve mobility.

So far, the results of the research have been shown that pentacin is well grown when the SAM (Self Assembly Monolayer) is coated on the gate insulating layer such as an oxide layer to have hydrophobic characteristics.

However, if the gate insulating film exhibits hydrophilic properties like the oxide film, it exhibits poor characteristics in terms of mobility because the grain size of the pentacin does not grow significantly when the pentacin is deposited.

Therefore, when pentacin is deposited on the gate insulating film, the gate insulating film showing hydrophilicity can be surface treated with OTS (octadecyl trichlorosilane) so that the pentacin can be grown well. .

As a result, the mobility and the on / off ratio of the current of the organic thin film transistor are improved.

However, when processing with OTS, because it is well oxidized in the air, it is inconvenient to proceed in a glove box in an inert gas atmosphere and immersed in various kinds of solutions through several steps, and then hot again. There are problems to perform complex steps such as drying on a hot plate.

In addition, since the characteristics of the gate insulating film exhibits hydrophilicity and have a hydroxyl group (-OH) on the surface, the surface treatment is well performed.

In addition, the pentacin exhibits poor characteristics in terms of mobility because of the relatively inferior characteristics of the source and drain electrodes, the organic thin film transistor adopting the lower electrode structure rather than the organic thin film transistor adopting the upper electrode structure.

Thus, the lower electrode structure is surface-treated with 1-hexadecanethiol or MBN (2-mercapto 5-nitrogenzimidazole) to facilitate pentacin growth on the source and drain electrodes, resulting in mobility characteristics and linear regions. Cases of improvement have been announced.

However, when the material for surface treatment of the source and drain electrodes and the OTS for surface treatment of the gate insulating film are used at the same time, the characteristics are not as good as those of using the OTS alone.

In addition, even if the material to be surface-treated on the source and drain and the OTS can be surface-treated without adversely affecting each other, a complex process of manufacturing an organic thin film transistor by surface-treating the channel portion and the source drain portion with a different material is performed. There was a problem.

Accordingly, the present invention has been made to solve the problems described above, by depositing an organic semiconductor material after spin coating the PMMA solution diluted by monochlorobenzen (monochlorobenzen) on the source and drain electrodes and the gate insulating film, grain SUMMARY OF THE INVENTION An object of the present invention is to provide an organic thin film transistor and a method of manufacturing the same, which can form an organic semiconductor material film having a large size, thereby improving carrier mobility of the device and shortening a manufacturing process time.

A preferred aspect for achieving the above object of the present invention is a gate electrode formed on the substrate;

A gate insulating film surrounding the gate electrode and formed on the substrate;

A source electrode and a drain electrode formed on the gate insulating layer to be spaced apart from each other;

A diluted PMMA coating layer surrounding the source and drain electrodes and coated on the gate insulating layer;

An organic thin film transistor is provided, which is composed of an organic semiconductor material film deposited over the diluted PMMA coating film in some regions and channel regions of the source and drain electrodes.

Another preferred aspect for achieving the above object of the present invention is a first step of forming a gate electrode on top of a substrate;

A second step of surrounding the gate electrode, forming a gate insulating film on the substrate, and forming source and drain electrodes spaced apart from each other on the gate insulating film;

Wrapping the source and drain electrodes and coating a diluted PMMA solution on the gate insulating layer to form a diluted PMMA coating film;

There is provided a method of manufacturing an organic thin film transistor comprising a fourth step of forming an organic semiconductor material film on the diluted PMMA coating layer in a portion of the source and drain electrodes and a channel region.

1A to 1D are cross-sectional views of a manufacturing process of an organic thin film transistor according to the present invention.

2a and 2b are photographs of atomic force microscopy (AFM) for comparing the grain size of pentacin when pentacin was deposited on top of a PMMA coating film diluted with HfO ₂ according to the present invention. .

3a and 3b are photographs observed with an optical microscope to compare the grain size of pentacin when pentacin (pentacene) is deposited on the Si ₃ N ₄ and the diluted PMMA coating film according to the present invention.

4a and 4b are photographs observed with an optical microscope to compare the grain size of pentacin when pentacin (pentacene) is deposited on Ni and diluted PMMA coating film according to the present invention.

<Description of the symbols for the main parts of the drawings>

10 substrate 20 gate electrode

30 gate insulating film 51 source electrode

52 drain electrode 60 diluted PMMA coating film

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings.

1A to 1D are cross-sectional views illustrating a process of manufacturing an organic thin film transistor according to the present invention. First, in FIG. 1A, a material to be used as a gate electrode is formed on a substrate 10 by sputtering or vacuum deposition. It removes using a process and an etching process, and only the desired part is defined as the gate electrode 20. FIG.

At this time, the material to be used as the gate electrode may be a metal such as aluminum, tungsten, chromium, as well as polyaniline (polyanilne) or PEDOT: PSS (polyethylene dioxythiophene (PSS) doped with polyethylenedioxythiophene ( Conductive polymer materials such as PEDOT) can also be used.

In addition, the substrate 10 is applied to any one selected from an inorganic substrate such as a silicon substrate and a glass substrate on which an oxide film is grown and a flexible plastic substrate.

The plastic substrate may be formed of any one material selected from polyethylene terephthalate (PET), polyethylenapthanate (PEN), polycarbonate (PC), polyimide (PI), and polynorborneen (PNB).

Next, the gate electrode 20 is wrapped, a gate insulating film 30 is formed on the substrate 10, and a source electrode 51 and a drain spaced apart from each other on the gate insulating film 30. An electrode 52 is formed (FIG. 1B).

Here, an inorganic insulating film such as SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , HfO ₂ , barium zirconate titanate (BZT), or the like may be used as the gate insulating film.

When the flexible plastic substrate is applied, an organic insulating film is used as the gate insulating film.

The organic insulating layer is selected from poly-4-vinylphenol (PVP), poly- (methylmethacrylate) (PMMA), polyvinylalchol (PVA) added with ammonuym dichromate, polyimide and parylene It is preferable to use either.

In addition, the source and drain electrodes 51 and 52 may be used as any one of gold (Au), platinum (Pt), nickel (Ni), and palladium (Pd), and these metals may not be easily dry or wet etched. Since the metal is deposited on the pattern defined by the photoresist layer, the source and drain electrodes can be defined up to several micrometers by applying a lift-off process.

Subsequently, in FIG. 1C, the PMMA coating layer 60 is formed by wrapping the source and drain electrodes 51 and 52 defined on the gate insulating layer 30 and coating the diluted PMMA solution on the gate insulating layer 30. Form.

The diluted PMMA solution was used by diluting a photosensitive film for E-Beam (monochlorobenzen) in which a molecular weight of 950000 PMMA and a solvent of monochlorobenzene (monochlorobenzen) were mixed in a volume ratio of 1:99. Similar results can be obtained by using an e-photosensitive film of 0.7: 99.3 to 1.3: 98.7.

In addition, the ratio of diluting the e-beam photosensitive film to monochlorobenzene is preferably performed by setting the solvent-containing monochlorobenzene (monochlorobenzen) and the e-beam photosensitive film within a volume ratio of 3: 1 to 12: 1. Do.

In this case, when the surface treatment is performed with the PMMA solution having a dilution ratio of 3: 1 or less, the thickly-covered PMMA insulator layer does not facilitate the injection of holes from the source and the drain, thereby lowering the electrical characteristics of the device. .

In addition, when surface-treated with the PMMA solution having an excessive dilution ratio of 12: 1 or more, pentaccin does not grow well.

On the other hand, the reason for using the diluted PMMA coating film 60, although the hydrophobic properties of the PMMA itself can help the pentacin grow well on the source and drain electrodes, the coated PMMA itself has a good insulator properties, thick PMMA The film, in turn, serves to hinder the injection of holes from the electrode, thereby reducing the mobility of the device. Therefore, the use of diluted PMMA solution is necessary.

Here, after the diluted PMMA solution is coated, a process of baking for 30 minutes to 1 hour at a temperature of 80 ~ 110 ℃ in a convection oven is further provided.

The baking process is most preferably baked for 30 minutes in a convection oven maintained at 110 ℃.

As such, when the ultra thin PMMA layer is covered on the insulator of the source drain electrode and the channel region by performing the baking process, the organic semiconductor material film is formed in the channel portion, the source and the drain electrode when the organic semiconductor material film is deposited in the subsequent process. Can get good growth.

In addition, by coating an extremely thin PMMA film, it is possible to maintain ohmic contact characteristics between the source and drain electrodes and the pentacin.

Finally, in FIG. 1D, an organic semiconductor material layer 80 is formed on the diluted PMMA coating layer 60 in portions of the source and drain electrodes 51 and 52 and the channel 53.

In this case, the organic semiconductor material layer 80 is formed of any one of pentacene, hexithiophene, and polythiophene.

Herein, the organic semiconductor material film 80 is formed on the diluted PMMA coating layer 60 on the partial region of the source and drain electrodes 51 and 52 and the channel 53 region, which are active regions, and is formed on the organic semiconductor material film ( 80 may be used in various ways, such as a conventional photolithography process or using a shadow mask.

2A and 2B are photographic views of atomic force microscopy (AFM) for comparing the grain size of pentacin when pentacin is deposited on top of HfO ₂ and diluted PMMA coating film according to the present invention. First, FIG. 2A is a photographic view of depositing pentacene on top of HfO ₂ , and FIG. 2B is a photographic view of depositing pentacene on top of a diluted PMMA coating film. It can be seen that the grain size of pentacene, in which 2b is relatively deposited, is large.

Here, the diluted PMMA coating film is a film coated with a diluted PMMA solution on top of HfO ₂ .

3A and 3B are photographs observed by an optical microscope in order to compare the grain size of pentacin when the pentacin was deposited on Si ₃ N ₄ and the diluted PMMA coating layer according to the present invention. 3A is a photographic view of depositing pentacene on top of Si ₃ N ₄ , and FIG. 3B is a photographic view of depositing pentacene on top of a diluted PMMA coating film. As a result similar to the comparison of 2a and 2b, it can be seen that when the pentacin is deposited on the diluted PMMA coating film, the grain size of the deposited pentacin is relatively large.

The diluted PMMA coating film is a film coated with a diluted PMMA solution on top of Si ₃ N ₄ .

Therefore, as compared with FIGS. 2A and 2B and FIGS. 3A and 3B, the pentacin grows well when the PMMA diluted in the high dielectric constants HfO ₂ and Si ₃ N ₄ is coated. Irrespective of the coating of diluted PMMA, large grain size pentacins grow.

4a and 4b are photographs observed with an optical microscope to compare the grain size of pentacin when pentacin was deposited on top of a diluted PMMA coating film with Ni according to the present invention, and penta on top of Ni. The grain size of the deposited pentacin is relatively larger than that of FIG. 4A, which is a photograph of when pentacene is deposited, and FIG. 4B, which is a photograph of when pentacene is deposited on a diluted PMMA coating film.

At this time, the diluted PMMA coating film of FIG. 4B is a film coated with the diluted PMMA solution on the top of Ni.

Therefore, when the diluted PMMA solution is coated on the metal layer, and then the pentacin is deposited, the growth is much better than that when the pentacin is deposited on the metal layer. Coating the PMMA solution diluted in, can improve the pentacin growth due to one surface treatment.

Table 1 shows an organic semiconductor material film formed on top of a low temperature oxide (LTO), monochlorobenzene and diluted PMMA coating films (3: 1,6: 1,9: 1,12: 1 PMMA). Is a table comparing organic thin film transistor characteristics.

Mobility (㎠ / V _sec ) Threshold Voltage (V _T ) (V) Saturation Current LTO 0.01 -2 0.9 3: 1 PMMA 0.25 -2.35 14.2 6: 1 PMMA 0.13 -2.05 16.0 9: 1 PMMA 0.23 -0.5 32.3 12: 1 PMMA 0.05 -1.6 10.2 Monochlorbenzene 0.02 -0.55 1.8

(1) mobility

The mobility of the device using LTO and monochlorbenzene (cm 2 / Vsec) is 0.01 and 0.02, and the device is moved using diluted PMMA coatings (3: 1,6: 1,9: 1,12: 1 PMMA). Since the degree (cm 2 / Vsec) is 0.25, 0.13, 0.23, 0.05, it can be seen that the organic thin film transistors having the organic semiconductor material layer formed on the diluted PMMA coating layers have excellent carrier mobility.

(2) Threshold voltage (V _T )

The device using LTO and monochlorbenzene is -2V and -2.35V, and the device using diluted PMMA coatings (3: 1,6: 1,9: 1,12: 1 PMMA) is -2.35V, -2.05 Since it is V, -0.5V, -1.6V, the threshold voltage of the negative voltage characteristic of all around 0V is measured, and it turns out that the characteristic after surface treatment is normal from a threshold voltage viewpoint.

(3) saturation current

This characteristic compares the drain-source saturation current (I _DS-sat ) by applying the same source, drain, and gate voltages of the respective organic thin film transistors.

Here, the saturation current of the device using the diluted PMMA coating films (3: 1,6: 1,9: 1,12: 1 PMMA) is 14.2 ㎂, 16.0 ㎂, 32.3 ㎂, 10.2 ㎂, so that 0.9 ㎂ and 1.8 ㎂ The saturation current of was better than that of LTO and monochlorobenzene.

As described in detail above, the present invention spin-coats a PMMA solution diluted with monochlorobenzene to the source and drain electrodes and the gate insulating layer, and then deposits an organic semiconductor material, thereby forming an organic semiconductor material film having a large grain size. It can be formed, the carrier mobility of the organic thin film transistor can be improved, and the manufacturing process time can be shortened.

Although the invention has been described in detail only with respect to specific examples, it will be apparent to those skilled in the art that various modifications and variations are possible within the spirit of the invention, and such modifications and variations belong to the appended claims.

Claims (14)

A gate electrode formed on the substrate; A gate insulating film surrounding the gate electrode and formed on the substrate; A source electrode and a drain electrode formed on the gate insulating layer to be spaced apart from each other; A diluted poly- (methyl methacrylate) (PMMA) coating film surrounding the source and drain electrodes and coated on the gate insulating film; And an organic semiconductor material deposited over the diluted PMMA coating layer in the partial and channel regions of the source and drain electrodes. The method of claim 1, The diluted PMMA coating film, It is a film coated with a solution diluted with monochlorobenzene (E-Beam) photosensitive film containing a molecular weight of 950000 PMMA and a solvent of monochlorobenzene (monochlorobenzen) in a volume ratio of about 1:99. Organic thin film transistor. The method of claim 2, The ratio of the di-beam photosensitive film diluted in monochlorbenzene is, An organic thin film transistor comprising monochlorobenzene as a solvent and a photoresist for e-Beam in a volume ratio of 3: 1 to 12: 1. Forming a gate electrode on the substrate; A second step of surrounding the gate electrode, forming a gate insulating film on the substrate, and forming source and drain electrodes spaced apart from each other on the gate insulating film; Wrapping the source and drain electrodes and coating a diluted PMMA solution on the gate insulating layer to form a diluted PMMA coating film; And forming an organic semiconductor material film on the diluted PMMA coating film in the partial region and the channel region of the source and drain electrodes. The method of claim 4, wherein The diluted PMMA solution is, Organic thin film, characterized in that the dilution of monochlorobenzene (monochlorobenzen) photosensitive film in which the molecular weight of 950000 PMMA and a solvent of monochlorobenzene (monochlorobenzen) mixed in a volume ratio of about 1:99 Transistor manufacturing method. The method of claim 5, wherein The ratio of diluting the e-beam photosensitive film in monochlorbenzene is, A method for manufacturing an organic thin film transistor, characterized in that the solvent is performed by setting a monochlorobenzene and a photoresist for e-Beam in a volume ratio of 3: 1 to 12: 1. The method of claim 4, wherein Between the third and fourth stages, The organic thin film transistor manufacturing method further comprises the step of baking for 30 minutes to 2 hours at a temperature of 80 ~ 110 ℃ in a convection oven. The method according to any one of claims 4 to 7, The gate electrode, With metals such as aluminum, tungsten and chrome, Organic thin film, characterized in that formed of any one of a conductive polymer material such as polyanilne or PEDOT: PSS (polyethylenedioxythiophene (PEDOT) doped with polyethylenedioctiophene (PSS)) Transistor manufacturing method. The method according to any one of claims 4 to 7, The substrate, A method of manufacturing an organic thin film transistor, characterized in that the oxide film is any one selected from an inorganic substrate such as a silicon substrate and a glass substrate and a flexible plastic substrate. The method according to any one of claims 4 to 7, The plastic substrate, A method of manufacturing an organic thin film transistor, characterized in that formed of any one selected from polyethylene terephthalate (PET), polyethylenapthanate (PEN), polycarbonate (PC), polyimide (PI), and polynorborneen (PNB). The method according to any one of claims 4 to 7, The gate insulating film, A method for manufacturing an organic thin film transistor, characterized in that the film is made of any one selected from SiO ₂ , Si ₃ N ₄ , Al ₂ O ₃ , HfO ₂ and barium zirconate titanate (BZT). The method according to any one of claims 4 to 7, The gate insulating film, Polyvinylalchol (PVA) added with poly-4-vinylphenol (PVP), poly- (methyl methacrylate) (PMMA), ammonium dichromate, polyimide, and parylene It is a film, The manufacturing method of the organic thin-film transistor characterized by the above-mentioned. The method according to any one of claims 4 to 7, The source and drain electrodes, An organic thin film transistor manufacturing method comprising any one of gold (Au), platinum (Pt), nickel (Ni), and palladium (Pd). The method according to any one of claims 4 to 7, The organic semiconductor material film, Method for manufacturing an organic thin film transistor, characterized in that formed of any one of pentacene (pentacene), hexithiophene (hexithiophene) and polythiophene (polythiophene).