JP2010212587A - Organic thin film transistor, method for producing organic thin film transistor, organic thin film transistor array and display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an organic thin film transistor, achieving the formation of patterns of an organic semiconductor layer with a high yield by an inkjet method. <P>SOLUTION: The method for producing an organic thin film transistor having a substrate, a gate electrode, a gate insulation film, a source electrode having higher surface free energy than that of the gate insulation film, a drain electrode having higher surface free energy than that of the gate insulation film, and an organic semiconductor layer, includes steps of: forming an island organic semiconductor layer contacting with the source electrode, the drain electrode and the gate insulation film, or the source electrode and the drain electrode by dissolving an organic semiconductor in a first solvent and dripping the solution by an inkjet method; and forming an island organic semiconductor layer contacting with the source electrode, the drain electrode and the gate insulation film by dripping a second solvent which can dissolve the organic semiconductor on the island organic semiconductor layer by the inkjet method. The second solvent has a lower surface tension than that of the first solvent, and a lower boiling point than that of the first solvent. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an organic thin film transistor, a method for manufacturing the organic thin film transistor, an organic thin film transistor array, and a display device.

An organic thin film transistor (TFT) using an organic semiconductor material is
1. High flexibility in material composition, manufacturing method, product form, etc.
2. Easy to increase the area,
3. A simple layer structure is possible and the manufacturing process can be simplified.
4). Can be manufactured using inexpensive manufacturing equipment,
It has been studied energetically because of its advantages.

  When an organic thin film transistor is manufactured, a thin film can be easily formed by a simple method using a wet process such as a printing method, a spin coating method, or a dipping method as a method for forming an organic semiconductor layer. It can be manufactured by orders of magnitude cheaper than TFTs using Si semiconductor materials. The organic TFT has an advantage that the manufacturing process temperature can be lowered. This enables formation on plastic substrates with generally low heat resistance, which can reduce the weight and cost of electronic devices such as displays, and is expected to be used in a variety of ways, including applications that take advantage of the flexibility of plastic substrates. it can.

  When integrating organic TFTs, it is essential to form electrodes. When organic TFTs are integrated without patterning the organic semiconductor layer, an off-current is generated during the operation of the transistor due to the influence of the organic semiconductor layer formed outside the channel region, resulting in an increase in power consumption. In addition, when displaying pixels, it also causes crosstalk. Note that when a TFT using a Si semiconductor material is manufactured, the Si semiconductor material is patterned by photolithography and etching.

  Focusing only on pattern formation of the organic semiconductor layer, a photoresist is applied, a desired pattern is exposed and developed, a resist pattern is formed, etching is performed using this as an etching mask, and the resist is peeled to form a pattern. It is possible. However, when a polymer material is used as the organic semiconductor material, transistor characteristics may be deteriorated if a pattern is formed by applying a photoresist on the polymer material. As the photoresist, a novolac resin having naphthoquinonediazide as a photosensitive group dissolved in an organic solvent such as xylene or cellosolve solvent is used, and the polymer material is an organic solvent contained in the photoresist. Often dissolves in In addition, when a crystalline molecule such as pentacene is used as the organic semiconductor material, the transistor characteristics may be similarly deteriorated although there is a difference in degree. Furthermore, it may be damaged by a stripping solution such as ethylene glycol monobutyl ether or monoethanolamine used when stripping the resist, or may be damaged by pure water rinsing after stripping the resist. From the above, it can be seen that it is difficult to form a pattern of an organic semiconductor layer by conventional photolithography and etching.

For improving such pattern formation, for example, methods described in the following Patent Documents 1 to 4 have been proposed.
That is, in Patent Document 1, a process of forming a wettability changing layer including a material whose critical surface tension changes by application of energy and a smaller critical surface tension by applying energy to a part of the wettability changing layer. A process of forming a pattern having a different critical surface tension composed of a low surface energy part and a high surface energy part having a higher critical surface tension, and a liquid containing a conductive material is formed on the wettability changing layer on which the pattern is formed. A method for producing a laminated structure having a step of forming a conductive layer on a high surface energy part and a step of forming a semiconductor layer on a wettability changing layer by applying to the surface is disclosed.

  In Patent Document 2, a charge is imparted to a predetermined position on the surface to be coated, a charge having a polarity opposite to the charge is imparted to the coating material, and the material to which the charge is imparted by Coulomb force is guided to a predetermined position. A method of forming a pattern, a method of forming a recess at a predetermined position on the surface to be applied, applying a coating material (at least one of an electrode, a semiconductor layer, and an insulating layer) and depositing it on the recess, or applying a material A method for producing an organic transistor by appropriately combining a method of forming a pattern by irradiating the pattern with a laser after evaporation of the solvent is disclosed.

  In Patent Document 3, a conductive layer is provided over a substrate, a mask having at least one window is provided over the conductive layer, the conductive layer is etched through the window, and an opening is formed in the conductive layer. Partially defining the source and drain of the transistor, depositing a conductive material through the window to form the gate of the metal transistor in the opening, and forming a metal oxide dielectric layer over the gate And a method of manufacturing a transistor comprising introducing a semiconductor material between the source and drain, on the gate, and in a space between the source or drain and the gate to form a semiconductor body of the transistor. ing. Etching is performed so as to cause an undercut at the peripheral edge of the window so that the opening has a larger extent than the window in a direction parallel to the surface of the substrate, and the conductive material is deposited at the peripheral edge of the gate. Further, the metal gate deposition is performed so that the peripheral edge of the gate of the transistor is closely aligned with the peripheral edge of the opening so as to be separated from the drain.

  In Patent Document 4, a step of forming a gate electrode, a step of forming a source electrode separated from the gate electrode, a drain electrode facing the source electrode, and an island shape in contact with the source electrode and the drain electrode are disclosed. Forming the organic semiconductor layer, the step of forming the island-shaped organic semiconductor layer includes spraying an organic semiconductor solution, primary drying the organic semiconductor solution, and the dried organic A method of manufacturing a thin film transistor array panel is disclosed which includes a step of redissolving a semiconductor solution and a step of secondarily drying the redissolved organic semiconductor solution.

  However, these methods have problems such as a decrease in throughput due to an increase in process steps and an increase in manufacturing cost.

  On the other hand, as a pattern forming method, an ink jet method and a dispenser method are known. Since the ink jet method and the dispenser method can directly draw a pattern, the material usage rate can be significantly improved. When the organic semiconductor layer is patterned by such an ink jet method or a dispenser method, there is a possibility that the manufacturing process can be simplified and the cost can be reduced. At this time, when a polymer material soluble in an organic solvent is used as the organic semiconductor material, a solution of the organic semiconductor material (organic semiconductor ink) can be prepared. Can do.

However, in order to stably form an organic semiconductor layer in a channel portion including a gate insulating film, a source electrode, and a drain electrode of a transistor by these printing methods, it is important to control ink wettability. In general, the surface of the source and drain electrodes made of metal has high surface free energy, so that the ink is easily wetted. In comparison, the surface of the gate insulating film composed of an organic polymer has a surface free energy relatively lower than that of the electrode. For this reason, the organic semiconductor ink dropped on the channel portion moves onto the electrode that is more likely to get wet after landing, and is formed only on the electrode, so that the channel may not be formed. This tendency becomes more remarkable when the surface free energy of the insulating film is smaller than the surface tension of the ink. If the organic semiconductor layer is not formed in the channel portion, the organic transistor does not operate. In a display device in which an organic transistor array in which a plurality of organic transistors are arranged and a display element are combined, if there is an organic transistor that does not operate due to the above problem, the pixel becomes defective. In a display device, if there is even one pixel defect, the display quality is greatly deteriorated, which is a serious problem.
One way to solve this problem is to adjust the physical properties of the ink. First, by making the surface tension of the solvent as small as possible, it is possible to make the surface of the gate insulating film with low surface free energy easy to get wet. Since the spread after landing becomes large, an organic semiconductor layer is formed in addition to the channel portion, and problems such as an increase in off-leakage and crosstalk may occur.
Or, secondly, by lowering the boiling point of the solvent and drying the ink as soon as possible after landing, it is possible to prevent the ink from moving onto the electrode after landing. In terms of stability, the boiling point of the ink decreases and it becomes easy to dry, so that the ink is dried on the nozzle surface, leading to unstable ejection and non-ejection due to clogging.
From the above, when forming an organic semiconductor layer by an ink jet method or a dispenser method for a channel portion composed of an electrode having a higher surface energy and a gate insulating film having a lower surface energy, stable film forming properties It was difficult to satisfy both the stable discharge characteristics.

  The present invention has been made in view of the above-described problems of the prior art, and an organic transistor that achieves high-yield organic semiconductor layer pattern formation by an inkjet method, an organic transistor manufacturing method, an organic transistor array including a plurality of the organic transistors, and the organic transistor An object is to provide a display device having an array.

The invention described in claim 1 includes a substrate, a gate electrode, a gate insulating film, a source electrode having a higher surface free energy than the gate insulating film, a drain electrode having a higher surface free energy than the gate insulating film, and an organic semiconductor layer A method for manufacturing a thin film transistor, comprising:
A step of forming an island-shaped organic semiconductor layer in contact with the source electrode and the drain electrode and the source electrode and the drain electrode by dissolving the organic semiconductor in the first solvent and dropping by an inkjet method; ,
Dropping a second solvent soluble in the organic semiconductor onto the island-shaped organic semiconductor layer by an ink-jet method to form an island-shaped organic semiconductor layer in contact with the source electrode, the drain electrode, and the gate insulating film; The solvent is characterized in that the surface tension is lower than that of the first solvent, and the second solvent has a boiling point lower than that of the first solvent.

  According to a second aspect of the present invention, in the method of manufacturing an organic thin film transistor according to the first aspect, in the step of forming the organic semiconductor layer, the organic semiconductor contains a polymer material.

  According to a third aspect of the present invention, in the method of manufacturing an organic thin film transistor according to the first or second aspect, the gate insulating film contains a polymer material.

  According to a fourth aspect of the present invention, in the method for manufacturing an organic thin film transistor according to any one of the first to third aspects, at least one of the source electrode, the drain electrode, and the gate electrode is formed by a printing method. It is characterized by that.

  According to a fifth aspect of the present invention, in the method of manufacturing an organic thin film transistor according to the fourth aspect, at least one of the source electrode, the drain electrode, and the gate electrode uses an ink containing metal particles or a metal complex. It is formed.

  A sixth aspect of the present invention is the method for producing an organic thin film transistor according to the fifth aspect, wherein the metal particles are Au, Ag, Cu, or Ni.

  The invention according to claim 7 is the method for manufacturing an organic thin film transistor according to claim 4, wherein at least one of the source electrode, the drain electrode, and the gate electrode contains a conductive polymer. .

  The invention according to claim 8 is the method for producing an organic thin film transistor according to claim 7, wherein the conductive polymer contains polyethylene dioxythiophene.

  The invention described in claim 9 is an organic thin film transistor, which is obtained by the manufacturing method according to any one of claims 1-8.

  A tenth aspect of the present invention is an organic transistor array having a plurality of organic transistors obtained by the manufacturing method according to any one of the first to eighth aspects.

  The invention according to an eleventh aspect is a display device having the organic transistor array according to the tenth aspect.

ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the organic transistor which achieved the pattern formation of the organic-semiconductor layer by the inkjet method with a sufficient yield, the organic transistor array which has multiple this organic transistor, and the display apparatus which has this organic transistor array.
Further, according to the present invention, an organic semiconductor is dissolved in a first solvent and dropped onto a channel portion composed of an insulating film, a source electrode, and a drain electrode by an inkjet method, whereby an island-shaped organic is formed on or near the channel. An organic transistor is formed by forming a semiconductor layer, and subsequently dropping a second solvent, which is soluble in the organic semiconductor, has a lower surface tension than the first solvent, and has a lower boiling point, onto the island-shaped organic semiconductor layer by an inkjet method. It is possible to improve the channel formation yield when the organic semiconductor layer is formed by the inkjet method.
In addition, by including a polymer material in the gate insulating film, the selectivity of a soluble solvent is expanded, the adaptability to the printing process is increased, and the manufacturing process can be further simplified and the cost can be reduced.
In addition, when a metal ink or conductive polymer in which metal fine particles suitable for the ink jet method are dispersed is used as the electrode material, it is possible to further simplify the manufacturing process and reduce the cost.
Furthermore, by combining an organic transistor array composed of the organic thin film transistors of the present invention and a pixel display element, a display device that is inexpensive and excellent in flexibility can be manufactured.

The structure of an organic thin-film transistor is shown, (a) is the top view, (b) is the Ib-Ib sectional view taken on the line of Fig.1 (a). The channel part of an organic thin-film transistor is shown, (a) is the top view, (b) is the IIb-IIb sectional view taken on the line of Fig.2 (a). It is for demonstrating the process in which the organic-semiconductor layer in the manufacturing method of the organic thin-film transistor of this invention is formed, (a) is the figure seen from the side surface, (b) is the figure seen from the upper surface. It is sectional drawing which shows an organic transistor array. It is sectional drawing which shows an example of a display apparatus. It is sectional drawing which shows another example of a display apparatus.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings, but the present invention is not limited to these embodiments.

  FIG. 1 shows an example of the structure of an organic thin film transistor 10 according to the present invention. In FIG. 1A, the gate insulating film 3 is omitted. In the organic thin film transistor 10, a gate electrode 2 and a gate insulating film 3 are sequentially formed on a substrate 1, and a source electrode 4 and a drain electrode 5 are formed on the gate insulating film 3 with a gap therebetween. At this time, a gap separating the source electrode 4 and the drain electrode 5 is formed on the gate electrode 2. An organic semiconductor layer 6 is formed so as to cover a gap separating the source electrode 4 and the drain electrode 5. Furthermore, the electrode and the organic semiconductor layer are formed by a printing method such as an inkjet method.

  In the organic thin film transistor 10, the organic semiconductor layer 6 must be formed in the channel portion C in order to control the current flowing between the source and drain electrodes (between the source electrode 4 and the drain electrode 5) by the gate electrode 2. The channel portion C is a region on the gate electrode 2 in which the source electrode 4 and the drain electrode 5 face each other and are electrically insulated through the gate insulating film 3 as shown by being surrounded by a dotted line in FIG. It is. In FIG. 2A, the gate insulating film 3 is omitted.

  A schematic diagram when the organic semiconductor layer 6 is formed in the channel portion C by the inkjet method is shown in FIG. The organic semiconductor layer 6 needs to be in contact with the source electrode 4, the drain electrode 5, and the gate insulating film 3. However, since the surface of an electrode such as a metal generally has high surface free energy, the source electrode 4 and the drain electrode 5. The surface of the organic semiconductor ink 61 tends to wet and spread. On the other hand, the surface of the gate insulating film 3 using an organic polymer or the like generally has a surface free energy that is relatively lower than the surfaces of the source electrode 4 and the drain electrode 5, and the organic semiconductor ink 61 has a gate insulation. It is difficult to spread on the surface of the film 3. As a result, as shown in FIG. 3, the organic semiconductor ink 61 dripped onto the channel portion C by the ink jet method moves to the surface of the electrode that is more likely to wet and spread after landing, and the organic semiconductor layer yields on the channel portion C. There is a problem that it cannot be formed well (see (1) to (4) in FIG. 3). This becomes more remarkable when the surface free energy of the gate insulating film 3 is smaller than the surface tension of the organic semiconductor ink 61.

  For this purpose, in the present invention, the organic semiconductor constituting the organic semiconductor layer 6 is first dissolved in the first solvent to produce the organic semiconductor ink 61. By dropping this onto the channel portion C by an ink jet method, the organic material is in contact with all of the source electrode 4, the drain electrode 5, and the gate insulating film 3 constituting the channel portion C or only with the source electrode 4 and the drain electrode 5. A semiconductor layer 6 was formed. At this time, the formation of the organic semiconductor layer 6 in the channel portion C is not formed with a high yield, and the case where it is formed in the channel portion and (4) in FIGS. 3A and 3B are shown. Thus, the case where the organic semiconductor layer 6 is formed only on the electrodes 4 and 5 constituting the channel portion C is mixed.

Next, the 2nd solvent 7 is dripped on the channel part C with the inkjet method (refer (5) of Fig.3 (a)). The second solvent dropped here does not contain an organic semiconductor. However, the second solvent can dissolve the organic semiconductor, has a feature that it has a lower surface tension and a lower boiling point than the first solvent. Therefore, nozzle clogging, unstable ejection, and non-ejection due to drying do not occur during ejection of the second solvent droplet. And the droplet by the 2nd solvent 7 melt | dissolves the organic-semiconductor layer 6 on the channel part C or the electrodes 4 and 5 after landing, and since surface tension is smaller than a 1st solvent, surface free energy is low. It is possible to spread and spread even on the gate insulating film 3. Further, since the boiling point is lower than that of the first solvent, the ink can be easily dried, and can be dried before the ink once spread to the gate insulating film 3 moves again to the electrodes 4 and 5. Further, since the drying is fast, it is possible to suppress the ink from spreading too much and prevent the organic semiconductor layer 6 from being formed other than the channel portion C.
For these reasons, it is possible to improve the channel formation yield of the organic semiconductor layer 6.

  As the first solvent, the surface tension is preferably larger than 30 mN / m from the viewpoint of suppressing the ejection stability of the ink jet and the spread after landing. Moreover, it is preferable that a boiling point is 180 degreeC or more, and it is more preferable that it is 200 degreeC or more. Examples of the first solvent include aromatic materials such as benzene, toluene, xylene, mesitylene, cyclohexane, ethyl benzoate, methyl benzoate, acetophenone, and derivatives thereof, ketones, esters, etc. What mixed these two or more is preferable.

  As the second solvent, the surface tension is preferably smaller than 30 mN / m. Moreover, it is preferable that a boiling point is 180 degrees C or less, and it is more preferable that it is 160 degrees C or less. Examples of the second solvent include at least one of aromatic materials such as benzene, toluene, xylene, mesitylene, cyclohexane, ethyl benzoate, methyl benzoate, and acetophenone, and derivatives thereof, or ketones and esters. Or although what mixed these two or more is preferable, the composition differs from a 1st solvent.

As described above, an organic semiconductor ink obtained by dissolving an organic semiconductor material in an organic solvent is used for pattern formation in the present invention.
The organic semiconductor material soluble in the organic solvent is not particularly limited, and high molecular materials, oligomer materials, low molecular materials, and the like can be used. Organic low molecules such as pentacene, anthracene, tetracene, and phthalocyanine; Polyphenylene conductive polymers such as polyparaphenylene and derivatives thereof, polyphenylene vinylene and derivatives thereof; heterocyclic conductive polymers such as polypyrrole and derivatives thereof, polythiophene and derivatives thereof, polyfuran and derivatives thereof; polyaniline And ionic conductive polymers such as derivatives thereof. Among these, a polymer material having a triarylamine skeleton is preferable. Although it does not specifically limit as such a polymeric material, It is preferable to use the material represented by following Chemical formula (1).

  This material is a non-orientated polymer material, and its characteristic variation is very small regardless of the film formation shape and method.

  Moreover, as a material which comprises the gate insulating film 3, polymeric materials, such as polyimide; polyvinylphenol; polyester; acrylic resins, such as polyacrylonitrile and polymethyl methacrylate; epoxy resin; thermosetting resin, are mentioned. The gate insulating film 3 can be formed to a thickness of 400 nm, for example, by spin-coating an NMP (N-methylpyrrolidone) mixed solution of the above polymer material and baking at 180 ° C.

  In addition, at least one of the source electrode 4, the drain electrode 5, and the gate electrode 2 can be patterned by a printing method such as an inkjet method or a dispenser method. At this time, it is preferable to use a metal ink containing metal particles or a metal complex. Examples of the metal particles include, but are not limited to, Au, Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co, Fe, Mn, Cr, Zn, Mo, W, Ru, In, and Sn. Two or more kinds may be used in combination. Of these, Au, Ag, Cu, and Ni are preferable in terms of electrical resistance, thermal conductivity, and corrosion. At this time, it is known that the metal particles have an average particle diameter of about several nm to several tens of nm and are sintered at a significantly lower temperature when uniformly dispersed in the solvent. This is because the influence of highly active surface atoms increases as the particle size of the metal particles decreases. Although it does not specifically limit as a metal complex, The complex etc. which have Au, Pt, Ag, Cu, Pd, In, Cr, Ni etc. as a center metal are mentioned. The gate electrode 2, the source electrode 4, and the drain electrode 5 can be formed by forming a pattern using such a metal ink and then sintering.

  In addition, when the surface tension and viscosity of the metal ink are not suitable, ejection becomes impossible or ejection failure occurs, it is difficult to form round droplets, and ligaments may be lengthened. For this reason, the metal ink has a surface tension of about 30 mN / m and a viscosity of preferably 2 to 13 mPa · sec, more preferably 7 to 10 mPa · sec. Furthermore, when discharging the metal ink, it is necessary to have a drying property so that the solvent is volatilized and the metal particles or the metal complex is not solidified.

  Moreover, when forming such electrodes 2, 4, and 5, a conductive polymer dispersion or the like can be used. Examples of the conductive polymer include polythiophene, polyaniline, polypyrrole, polyparaphenylene, polyacetylene, or those obtained by doping these polymers. Among these, in terms of electrical conductivity, stability, heat resistance, and the like, a complex of polyethylene dioxythiophene (PEDOT) and polystyrene sulfonic acid (PSS) (PEDOT / PSS) is preferable. Conductive polymers are inferior in electrical properties and stability compared to metals, but can improve the electrical properties of the electrode depending on the degree of polymerization and structure, and can be formed at low temperatures because sintering is not required. Excellent in terms.

  Next, an organic thin film transistor array (organic transistor substrate) and a display device will be described.

As shown in FIG. 4, the organic thin film transistor array 20 includes a plurality of organic thin film transistor elements formed on a substrate. The organic thin film transistor array 20 can be manufactured, for example, by the following procedure. First, a scanning wiring (gate electrode) 2 is formed on a substrate 1 such as a glass substrate or a film substrate by an inkjet method using, for example, Ag ink in which Ag fine particles are dispersed. On top of this, a polyimide insulating film as an interlayer insulating film of the gate insulating film 3 and the scanning wiring / signal wiring is formed by spin coating.
Next, a source electrode 4 and a drain electrode 5 made of Au with a film thickness of 50 nm are pattern-formed on the gate insulating film 3 by vacuum evaporation using a shadow mask. Next, on the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, printing is performed by an inkjet method using an ink in which a material represented by the chemical formula (1) is dissolved in a first solvent, An organic semiconductor layer is formed. Then, the 2nd solvent is dripped on an organic-semiconductor layer with the inkjet method, and the organic-semiconductor layer 6 is formed in a channel part. Further, a paraxylylene film having a thickness of 2000 nm is formed on the uppermost layer by a CVD method to form a protective layer (not shown). The organic thin film transistor array is completed by the above process.

  The organic thin film transistor array manufactured as described above can be used for various display devices by combining with various display elements. For example, ITO (Indium Tin Oxide) having a thickness of about 100 nm is formed on the counter substrate by sputtering, polyimide resin is applied thereon by spin coating, and rubbing to form an alignment film with a thickness of about 200 nm. After the alignment treatment, the above-described organic thin film transistor array and a silica spacer are arranged and bonded, and a liquid crystal material is sealed between the gaps, whereby a liquid crystal panel can be manufactured. A configuration example of a typical display device 30 is shown in FIG. In FIG. 5, reference numeral 31 is an interlayer film, 32 is a pixel electrode, and 33 is a display layer.

  As another display panel, an electrophoretic display panel can be formed by arranging and bonding a silica spacer on an opposing substrate on which ITO is formed, and enclosing a microcapsule type electrophoretic element between caps. A configuration example of a typical electrophoretic display device 40 is shown in FIG. In FIG. 6, reference numeral 41 is a film substrate, 42 is an ITO film, 43 is carbon black, 44 is titanium oxide, and 45 is a urethane resin.

  Note that an organic EL panel can also be manufactured by forming an organic EL element as a display pixel and disposing an air shielding shield.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples, but the present invention is not construed as being limited to these examples.

[Comparative Example 1]
An adhesion layer (not shown) made of Cr with a thickness of 3 nm and a gate electrode 2 made of Al with a thickness of 100 nm were formed on the glass substrate 1 by a vacuum deposition method using a shadow mask. Next, Rika Coat SN-20 of polyimide solution (registered trademark, manufactured by Shin Nippon Chemical Co., Ltd., a polyimide resin in which imidization was completed was dissolved in N-methylpyrrolidone) was applied by a spin coating method, prebaked, and then 200 ° C. The gate insulating film 3 having a film thickness of 500 nm was formed by baking. Further, a source electrode 4 and a drain electrode 5 made of Au with a film thickness of 50 nm were pattern-formed on the gate insulating film 3 by a vacuum evaporation method using a shadow mask. Next, the material represented by the chemical formula (1) on the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, has a boiling point of 160 ° C. or less and a surface tension of 30 mN / m or less. Although an attempt was made to print by an ink jet method using an organic semiconductor ink dissolved in 1 wt% in a toluene solvent, stable ejection could not be obtained due to the drying of the ink, and a stable organic semiconductor layer could not be formed.

[Comparative Example 2]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. Next, the material represented by the chemical formula (1) is formed on the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C with a boiling point of 200 ° C. or more and a surface tension of 30 mN / m or more. An attempt was made to print by an inkjet method using an organic semiconductor ink dissolved in 1 wt% in ethyl benzoate. Stable ejection was obtained, but as a result of observation of the organic semiconductor layer 6 with a metal microscope, the organic semiconductor layer 6 was formed on the channel portion C, and was repelled on the gate insulating film 3 to form the electrode 4 5 formed only on top of each other.

[Comparative Example 3]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. Next, the material represented by the chemical formula (1) on the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, has a boiling point of 180 ° C. or more and a surface tension of 30 mN / m or less. Using an organic semiconductor ink dissolved in 1 wt% of a mixed solvent of ethyl benzoate and p-cymene (mixed weight ratio: 0.6 part of p-cymene with respect to 1 part of ethyl benzoate) prepared by an inkjet method Tried to print. As a result of observing the organic semiconductor layer 6 with the forming metal microscope, the organic semiconductor layer 6 was formed on the channel portion C with good yield without being repelled on the gate insulating film 3, but the spread was large and not the channel portion C. A film was also formed between the source and drain electrodes.
When the off-current at the source / drain voltage of −20 V and the gate voltage of +20 V was evaluated in an atmosphere of oxygen <1 ppm and moisture <1 ppm, the off-current of Tr (transistor) increased.

  The results of Comparative Examples 1 to 3 are summarized in Table 1. In these comparative examples, it is necessary to set the boiling point of the solvent used in the organic semiconductor ink to be high for stable ejection in the ink jet method, and the surface tension of the solvent is set to increase the yield of channel formation. Although it is necessary to make it low, the organic semiconductor ink having a high boiling point and a low surface tension is difficult to be patterned because of its large spread.

[Example 1]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink 61 dissolved in 1 wt% in the above ethyl benzoate, printing was performed by an inkjet method to form an organic semiconductor layer. Subsequently, o-xylene having a boiling point of 160 ° C. or lower, lower than the first solvent, and having a surface tension of 30 mN / m or lower and lower than the first solvent as the second solvent is formed on the organic semiconductor layer by an inkjet method. The organic semiconductor layer 6 was formed in the channel part C, and the organic thin-film transistor array 20 was obtained.
When this was observed with a metal microscope, the organic semiconductor layer 6 was formed on the channel with a high yield, and no film formation other than the channel region was observed.

[Example 2]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink 61 dissolved in 1 wt% in the above ethyl benzoate, printing was performed by an ink jet method to form the organic semiconductor layer 6. Subsequently, toluene as a second solvent having a boiling point of 160 ° C. or lower, lower than that of the first solvent, and having a surface tension of 30 mN / m or lower and lower than that of the first solvent is dropped onto the organic semiconductor layer by an inkjet method. And the organic-semiconductor layer 6 was formed in the channel part C, and the organic thin-film transistor array 20 was obtained.
When this was observed with a metallurgical microscope, the organic semiconductor layer 6 was formed on the channel with a high yield, and no film formation other than the channel region was observed.

Example 3
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink 61 dissolved in 30 mN / m in the above acetophenone, printing was performed by an inkjet method to form an organic semiconductor layer. Subsequently, o-xylene having a boiling point of 160 ° C. or lower, lower than the first solvent, and having a surface tension of 30 mN / m or lower and lower than the first solvent as the second solvent is formed on the organic semiconductor layer by an inkjet method. The organic semiconductor layer 6 was formed in the channel part C, and the organic thin-film transistor array 20 was obtained.
When this was observed with a metal microscope, the organic semiconductor layer 6 was formed on the channel with a high yield, and no film formation other than the channel region was observed.

Example 4
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (A) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink 61 dissolved in 1 wt% in the above acetophenone, printing was performed by an inkjet method to form an organic semiconductor layer. Subsequently, toluene as a second solvent has a boiling point of 160 ° C. or lower, lower than that of the first solvent, and has a surface tension of 30 mN / m or lower and lower than that of the first solvent. The organic semiconductor layer 6 was formed in the channel part C, and the organic transistor array 20 was obtained.
When this was observed with a metal microscope, the organic semiconductor layer 6 was formed on the channel with a high yield, and no film formation other than the channel region was observed.

[Comparative Example 4]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink dissolved in 1 wt% in the above ethyl benzoate, printing was performed by an inkjet method to form an organic semiconductor layer. Subsequently, ethyl benzoate having a boiling point of 200 ° C. or higher and a surface tension of 30 mN / m or higher as the second solvent is dropped on the organic semiconductor layer by an ink jet method, and the organic semiconductor layer 6 is connected to the channel portion. Attempted to form C.
As a result of observing this with a metallurgical microscope, the organic semiconductor layer 6 is formed on the channel, and the organic semiconductor layer 6 is repelled on the gate insulating film 3 and formed only on the electrodes 4 and 5. It was accepted.

[Comparative Example 5]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the organic semiconductor ink dissolved in 1 wt% in the above ethyl benzoate, printing was performed by an inkjet method to form an organic semiconductor layer. Subsequently, as a second solvent, acetophenone having a boiling point of 200 ° C. or higher, lower than that of the first solvent, and having a surface tension of 30 mN / m or higher and higher than that of the first solvent is applied onto the organic semiconductor layer by an inkjet method. An attempt was made to form the organic semiconductor layer 6 in the channel portion C by dripping.
As a result of observing this with a metallurgical microscope, the organic semiconductor layer 6 is formed on the channel, and the organic semiconductor layer 6 is repelled on the gate insulating film 3 and formed only on the electrodes 4 and 5. It was accepted.

[Comparative Example 6]
The source electrode 4 and the drain electrode 5 were formed in the same manner as in Comparative Example 1. On the gate insulating film 3 on which the source electrode 4 and the drain electrode 5 are formed, that is, on the channel portion C, the material represented by the chemical formula (1) is used as the first solvent, the boiling point is 200 ° C. or higher, and the surface tension is 30 mN / m. Using the above organic semiconductor ink dissolved in 1 wt% in acetophenone, printing was performed by an ink jet method to form an organic semiconductor layer. Subsequently, as the second solvent, ethyl benzoate having a boiling point of 200 ° C. or higher, higher than that of the first solvent, and having a surface tension of 30 mN / m or higher and lower than that of the first solvent is obtained by the ink jet method. An attempt was made to form the organic semiconductor layer 6 in the channel portion C by dropping it on the top.
As a result of observing this with a metallurgical microscope, the organic semiconductor layer 6 formed on the channel and the one formed on the gate insulating film 3 and formed only on the electrodes 4 and 5 are mixed. It was accepted.

Table 2 summarizes the results of Examples 1 to 4 and Comparative Examples 4 to 6.
From the above, it was proved that the organic semiconductor layer can be formed in the channel portion of the organic transistor with high yield according to the present invention.

Example 5
Using the organic transistor array of Example 1, an active matrix display device (electrophoretic display device) shown in FIG. 6 was produced. Specifically, a resin film (polycarbonate) substrate is obtained by mixing a microcapsule in which carbon black 43 is dispersed and encapsulated in Isopar G (registered trademark, manufactured by ExxonMobil: isoparaffin-based dispersant) and a polyvinyl alcohol aqueous solution. This was applied on a transparent electrode made of ITO 42 provided on 41 to form a layer made of microcapsules and a binder. This and the organic transistor array of Example 1 were bonded via a binder so that the glass substrate 1 and the polycarbonate substrate 41 were the outermost surfaces.
The driver IC for scanning signal is connected to the bus line connected to the gate electrode of the obtained active matrix display device, and the driver IC for data signal is connected to the bus line connected to the source electrode, and the image is switched every 0.5 seconds. As a result, it was possible to display a good still image.

1 Substrate 2 Gate electrode (scanning line)
3 Gate insulating film 4 Source electrode (signal line)
5 Drain electrode 6 Organic semiconductor layer 7 Second solvent 10 Organic thin film transistor 20 Organic thin film transistor array 30 Display device 31 Interlayer film 32 Pixel electrode 33 Display layer 40 Electrophoretic display device 41 Resin film substrate 42 ITO
43 Carbon black 44 Titanium oxide 45 Binder resin C Channel part

JP-A-2005-310962 JP 2004-297011 A Special table 2003-536260 gazette Japanese Patent Laid-Open No. 2008-077865

Claims (11)

A method of manufacturing an organic thin film transistor having a substrate, a gate electrode, a gate insulating film, a source electrode having a higher surface free energy than the gate insulating film, a drain electrode having a higher surface free energy than the gate insulating film, and an organic semiconductor layer ,
By dissolving an organic semiconductor in a first solvent and dropping by an inkjet method, the source electrode, the drain electrode, the gate insulating film, or the island-shaped organic semiconductor layer in contact with the source electrode and the drain electrode are formed. Forming, and
A step of dropping an organic semiconductor-soluble second solvent onto the island-shaped organic semiconductor layer by an ink-jet method to form an island-shaped organic semiconductor layer in contact with the source electrode, the drain electrode, and the gate insulating film; Including
The second solvent has a lower surface tension than the first solvent, and
The second solvent has a lower boiling point than the first solvent,
The manufacturing method of the organic thin-film transistor characterized by the above-mentioned.   The method of manufacturing an organic thin film transistor according to claim 1, wherein in the step of forming the organic semiconductor layer, the organic semiconductor contains a polymer material.   The method of manufacturing an organic thin film transistor according to claim 1, wherein the gate insulating film contains a polymer material.   4. The method of manufacturing an organic thin film transistor according to claim 1, wherein at least one of the source electrode, the drain electrode, and the gate electrode is formed by a printing method.   5. The method for producing an organic thin film transistor according to claim 4, wherein at least one of the source electrode, the drain electrode, and the gate electrode is formed using an ink containing metal particles or a metal complex.   6. The method of manufacturing an organic thin film transistor according to claim 5, wherein the metal particles are Au, Ag, Cu, or Ni.   5. The method of manufacturing an organic thin film transistor according to claim 4, wherein at least one of the source electrode, the drain electrode, and the gate electrode contains a conductive polymer.   The method of manufacturing an organic thin film transistor according to claim 7, wherein the conductive polymer contains polyethylene dioxythiophene.   An organic thin film transistor obtained by the manufacturing method according to claim 1.   An organic transistor array comprising a plurality of organic transistors obtained by the manufacturing method according to claim 1.   A display device comprising the organic transistor array according to claim 10.