WO2011021763A1 - Control method of the overlay accuracy using by self-aligned gravure printing - Google Patents

Control method of the overlay accuracy using by self-aligned gravure printing Download PDF

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Publication number
WO2011021763A1
WO2011021763A1 PCT/KR2010/002639 KR2010002639W WO2011021763A1 WO 2011021763 A1 WO2011021763 A1 WO 2011021763A1 KR 2010002639 W KR2010002639 W KR 2010002639W WO 2011021763 A1 WO2011021763 A1 WO 2011021763A1
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WIPO (PCT)
Prior art keywords
gate electrode
insulation layer
source
light
region
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Application number
PCT/KR2010/002639
Other languages
French (fr)
Inventor
Gyojin Cho
Jaeyoung Kim
Chaemin Lim
Hyungrok Oh
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Paru Co., Ltd.
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Publication date
Application filed by Paru Co., Ltd. filed Critical Paru Co., Ltd.
Publication of WO2011021763A1 publication Critical patent/WO2011021763A1/en

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K71/00—Manufacture or treatment specially adapted for the organic devices covered by this subclass
    • H10K71/60—Forming conductive regions or layers, e.g. electrodes
    • H10K71/611—Forming conductive regions or layers, e.g. electrodes using printing deposition, e.g. ink jet printing
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having potential barriers
    • H10K10/40—Organic transistors
    • H10K10/46—Field-effect transistors, e.g. organic thin-film transistors [OTFT]
    • H10K10/462—Insulated gate field-effect transistors [IGFETs]
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having potential barriers
    • H10K10/40—Organic transistors
    • H10K10/46—Field-effect transistors, e.g. organic thin-film transistors [OTFT]
    • H10K10/462—Insulated gate field-effect transistors [IGFETs]
    • H10K10/468—Insulated gate field-effect transistors [IGFETs] characterised by the gate dielectrics
    • H10K10/471—Insulated gate field-effect transistors [IGFETs] characterised by the gate dielectrics the gate dielectric comprising only organic materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
    • H10K10/00—Organic devices specially adapted for rectifying, amplifying, oscillating or switching; Organic capacitors or resistors having potential barriers
    • H10K10/80—Constructional details
    • H10K10/82—Electrodes

Definitions

  • the present invention relates to a method of fabricating an organic thin film transistor for minimizing an area of a parasitic capacitance generated in an overlap portion between a gate and a drain or a source.
  • Fig. 1 is a sectional view of a transistor when the overlay printing is performed correctly using the conventional printing method. Figs.
  • FIG. 2 to 4 are sectional views showing transistors not printed in the desired position in a case that the overlay accuracy of tens micron is present when the printing is performed using the conventional printing method.
  • the numerical symbol 11 in Fig. 1 indicates a resister mark of a gate electrode and the numerical symbol 12 indicates a resister mark of a source or drain electrode.
  • the patterns are obtained by discharging or transferring an ink containing material for the device and impacting the ink to a predetermined position on the substrate.
  • a hydrophilic transformation layer containing a fluorine based silane coupling agent is applied by a spin coating or a dip coating, dried and then an exposure using UV light or laser beam with a mask pattern is performed for several minutes to obtain the desired patterns.
  • An embodiment of the present invention is directed to providing a method, in which only a portion of an insulation layer except for a previously printed gate is exposed to light and then drain and source electrodes are formed so as to have a gap therebetween corresponding to a critical dimension (CD) of the gate. Also, an embodiment of the present invention is directed to providing, in fabrication of self aligned transistor through a gravure printing method, a method for fabricating a transistor having the same performance as a conventional transistor by reducing overlay accuracy to several microns in consideration that the overlay accuracy of a conventional printing machine is tens microns.
  • an embodiment of the present invention is directed to providing a method of fabricating uniform transistor, in which light is irradiated on a back side of a substrate formed with a gate electrode to surface-reform a portion of an insulation layer to which the light is not irradiated and thus wettablility is enhanced in the surface-reformed portion to allow printing of a drain ink and a source ink thereon.
  • an embodiment of the present invention is directed to providing a method of fabricating a transistor, in which a channel length of drain and source in a printed transistor is formed correspondingly to a CD of a gate.
  • This pattern may be a method of minimizing an area of a parasitic capacitance generated in an overlap portion between the gate and the drain or source which can be seen in a conventional printed transistor.
  • an embodiment of the present invention is directed to providing a method of enhancing, by irradiating light to a back side of a substrate formed with a gate electrode, printability and adhesiveness of an ink for source and drain to be stacked on a second region of an insulation layer which is surface-reformed by irradiation of the light as the gate electrode is not formed thereon.
  • the present invention provides, in fabrication of a organic thin film transistor, a method for fabricating a transistor having the same performance as a conventional transistor by reducing an overlay accuracy of a device to several microns in consideration that the overlay accuracy of a conventional printing machine is tens microns.
  • the present invention provides a method of fabricating uniform transistor, in which light is irradiated on a back side of a substrate formed with a gate electrode to surface-reform a portion of an insulation layer to which the light is not irradiated and thus wettablility is enhanced in the surface-reformed portion to allow printing of a drain ink and a source ink thereon without overlap with the gate.
  • the present invention provides a method of fabricating an organic thin film transistor, which includes a) forming a gate electrode on a transparent substrate; b) forming an insulation layer to cover the gate electrode and irradiating light to a back side of the substrate formed with the gate electrode to form a first region to which the light is not irradiated by the gate electrode and a second region surface-reformed by the irradiation of the light as the gate electrode is not formed thereon; and c) forming drain and source electrodes on the second region.
  • the steps a), b) and c) are implemented by a printing technique respectively, and specifically, the printing technique is used when forming the gate electrode in the step a), when forming the insulation layer in the step b) and when forming the drain and source electrodes in the step c).
  • the printing technique is used when forming the gate electrode in the step a), when forming the insulation layer in the step b) and when forming the drain and source electrodes in the step c).
  • gravure printing may be used as the printing technique.
  • the method of fabricating an organic thin film transistor in accordance with the present can omit various processes compared to a conventional method using lithography and consequently has an effect capable of obtaining a circuit board in an economic cost.
  • the present invention provides a method of fabricating an organic thin film transistor, wherein, in the step c), the source and drain electrodes are printed on the surface-reformed second region and self aligned with the gate.
  • the second region of the insulation layer can become hydrophilic. At this time, adhesiveness and wettability of drain ink and source ink to the second region are enhanced when the drain ink and the source ink are printed on the second region and thus it is possible to form a printed pattern which is not overlapped with the gate.
  • a wavelength of the light in the step b) is 300 to 400 nm and preferably 340 to 380 nm.
  • the form of the light is, but not limited to, a laser beam, which is effective to raise accuracy.
  • a high energy light with a short length of 193 to 248 nm was mainly used.
  • the UV light of a short wavelength has a low penetration power and a resulting low transmittance though it is of a high energy.
  • the substrate and the insulation layer are preferably made of a material with a good transmittance and more preferably a plastic material.
  • the light of a short wavelength is not easily transmitted, it is preferred to use a UV light with a long wavelength of 300 to 400 nm, more preferably 340 to 380 nm.
  • the insulation layer meets the following Equation 1 by the surface-reforming:
  • the second region may have a reduced contact angle of water droplet as it is surface-reformed by the light, and thus has hydrophilicity due to the reduced contact angle and enhanced wettability and adhesiveness with respect to the drain and source ink.
  • an example of a material for the transparent substrate includes polyethylene, polycarbonate, polyethylene terephthalate, polymethamethylacrylate, polytetrafluorethylene, ethylene tetrafluorethylene, polyimide and polyethylenenaphthalate, and polymer or copolymer thereof having high transmittance, but not largely limited thereto.
  • the gate, source and drain electrodes are formed using a water dispersed conductive ink, respectively. More specifically, the gate, source and drain electrodes are formed of a water dispersed conductive ink including metal powder containing one or more selected from the group consisting of silver, copper, nickel, aluminum, tungsten, magnesium, iron and lead; and a hydrophilic solvent, and the water dispersed conductive ink may further include a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylacrylate, polyvinylpyrrolidone, polyvinylalcohol and polyurethane.
  • the metal powder preferably has nano- or micro-sized particles.
  • the gate ink in accordance with the present invention has different physical properties depending on a surface energy of the substrate and has a surface tension lower than the surface energy of the substrate by 1 to 10. If it is difficult to lower the surface tension, a viscosity of the ink can be increased and this can be easily adjusted by adjusting the solvent.
  • a gate line can be realized by a roll to roll printing in accordance with the present invention can be fabricated with a critical dimension of at least 20 micron and preferably has the CD of 100 to 300 micron for application in a device having a gate height of 1 micron or less.
  • the drain and source inks should have good wettability and adhesiveness in the second region and have a repellent force in the first region of the insulation layer on which the light is not irradiated due to the gate electrode.
  • the insulation layer may include a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylacrylate, polyvinylpyrrolidone, polyvinylalcohol, polyinylvhloride, polyacrylonitryl and polyurethane," and a hydrophilic solvent.
  • the insulation layer is preferably further includes 1 to 20 weight% of inorganic substances, and the inorganic substances may contains one or more selected from the group consisting of TiO 2 , SiO 2 , Al 2 O 3 , Nb 2 O 5 , BaTiO 3 , Si 3 N 4 , Ta 2 O 5 , SrTiO 3 , (Ba,Sr)TiO 3 .
  • the insulation layer is made of a material having a high transmittance since it should transmit the light thoroughly. More specifically, it is preferred that the insulation layer is hydrophi lized by the light and the portion of the insulation layer blocked from the light maintains the hydrophobicity.
  • the insulation layer may be fabricated by printing a mixture of polymethacrylate and ethyl carbitol acetate.
  • the solvent usable in the insulation layer, the inks of the gate electrode, drain electrode and source electrode contains one or more selected from the group consisting of water, ethanol, methanol, isopropyl alcohol, hexyl alcohol, octanol, decyl alcohol, ethylene glycol, diethylene glycol, methoxyethanol , acetone, methylethylketone, hexane, cyclohexane, eye1ohexanone, ethyleneglycol monoethylether, diethyleneglycol monobuthylether, N-methylpyrrolidone, pyrrolidine, ethyl acetate, ethyl carbitol acetate and buthyl carbitol acetate.
  • the printing machine used in the present invention is a roll to roll gravure printing machine and is a system in which each printing driver operates between an unwinder for unwinding a plastic foil and a rewinder for rewinding the plastic foil and each driver is provided with a hot wind curing device.
  • a printing speed may be adjustable from 2 to 60 m/min, and roll pressure and web tension are also adjustable.
  • the overlay accuracy of the machine is generally set to 50 micron or more and is varied as the condition of the machine.
  • the physical properties of the ink includes viscosity, kinematic viscosity, rheology, density, surface tension, particle size, size distribution, evaporation speed and etc. and it is preferred that the printing is performed under the condition in that these properties are always equal since variation in any one of these properties makes reproduction of the same fine pattern difficult.
  • a gravure printing cylinder capable of transferring the ink should have uniform grooves and, in order to have the uniform grooves, it is more effective to use hellio and laser stream methods rather than etching corrosion since the former allow finer and uniform etching.
  • the present invention provides an organic thin film transistor, which includes a transparent substrate; a gate electrode formed on the transparent substrate; an insulation layer formed on the gate electrode; and source and drain electrodes formed on the insulation layer and spaced apart from each other,
  • the organic thin film transistor in accordance with the present invention meets the following Equation 2:
  • O ⁇ m ID1-D21 ⁇ 10/a ⁇
  • the method of fabricating an organic thin film transistor in accordance with the present can omit various processes compared to a conventional method using lithography and consequently has an effect capable of obtaining a circuit board in an economic cost.
  • Fig. 1 is a sectional view of a transistor when the overlay printing is performed accurately using a conventional printing method.
  • Fig. 5 is a sectional view illustrating a plastic substrate and a gate electrode printed on the substrate by a gravure printing machine in accordance with an embodiment of the present invention.
  • Fig. 6 is a sectional views illustrating that the gate electrode is firstly printed on the plastic substrate and then an insulation layer is secondly printed.
  • Fig. 7 is a sectional view illustrating a first region 4 to which a UV light is not irradiated by the gate electrode 2 after irradiation of the UV light to a back side of the plastic substrate 1 and a second region 5 which is not formed with the gate electrode and thus is surface-reformed by the irradiation of the UV light.
  • Fig. 8 is a sectional view illustrating that source and drain electrodes are thirdly printed after the irradiation of the UV light.
  • Fig. 9 is an image showing that l ⁇ i of water is dropped in the first region of the insulation layer to which the UV beam is not irradiated due to the gate electrode and a contact angle is then measured.
  • Fig. 10 is an image showing that ⁇ l of water is dropped in the second region of the insulation layer which is surface-reformed by the irradiation of the UV beam as the gate electrode is not formed thereon and the contact angle is then measured.
  • Fig. 11-12 is an image by a microscope after the drain and source electrodes or the channel length are printed, in which Fig. 11 is a microscope image that a gap between the drain and source of Example 1 are printed, and Fig. 12 is a microscope image of channel length of Example 1 are printed
  • Fig. 13-14 is an image by a microscope after the drain and source electrodes or the channel length are printed, in which Fig. 13 is a microscope image that a gap between the drain and source of Example 2 are printed, and Fig. 14 is a microscope image of channel length of Example 2 are printed.
  • Fig. 5 is a sectional view illustrating a plastic substrate and a gate electrode printed on the substrate by a gravure printing machine in accordance with an embodiment of the present invention.
  • Fig. 6 is a sectional views illustrating that the gate is firstly printed on the plastic substrate and then an insulation layer is secondly printed.
  • Fig. 7 is a sectional view illustrating a first region 4 to which a UV light is not irradiated by the gate electrode 2 after irradiation of the UV light to a back side of the plastic substrate 1 and a second region 5 which is not formed with the gate electrode and thus is surface-reformed by the irradiation of the UV light.
  • Fig. 8 is a sectional view illustrating that source and drain electrodes are thirdly printed after the irradiation of the UV light.
  • Ethylene tetrafluoroethylene film available from Asahi glass company (Japan) was used as the plastic substrate 1.
  • Nanosilver was dispersed in ethylene glycol, set to 300cp in viscosity and 44mN/m in surface tension and then used as the gate electrode 2 in a first printing engine of the roll to roll gravure machine (Fig. 5).
  • 2Og of polymethamethylacrylate and 6Og of ethyl carbitol acetate were mixed and diluted to set 250cp in viscosity and used as the insulation layer 3 in a second printing engine.
  • a printing speed of the gate electrode and the insulation layer is 8m/min and curing was performed at 150 0 C for 10 seconds.
  • the gate electrode was 600nm in an average thickness and in a CD.
  • the insulation layer is 2 ⁇ m in an average thickness and is printed so as to cover all of the gate electrode and drain and source regions (Fig. 6).
  • UV light was irradiated to the back side of the substrate formed with the gate electrode at a distance of 10cm for 90 seconds using a mercury UV lamp with 365nm in a main wavelength and 80w/cm2inpower(Fig.7).
  • the ink for the source and drain ink electrodes which was made by dispersing nanosilver in ethylene glycol and was set to 700cp in viscosity and 44mN/m in surface tension, was printed by a roll to plate gravure printing machine (Fig. 8).
  • Fig. 11-12 is an image by a microscope after the drain and source electrodes 7, 6 are printed.
  • Nanosilver was dispersed in ethylene glycol and hexyl alcihol, set to 400cp in viscosity and 37mN/m in surface tension and then used as the gate electrode 2 in the first printing engine of the roll to roll gravure machine (Fig. 5). Also, 2Og of polymethamethylacrylate and 6Og of ethyl carbitol acetate were mixed and diluted to set 250cp in viscosity and used as the insulation layer 3 in a second printing engine. A printing speed of the gate electrode 2 and the insulation layer 3 is 4m/min and curing was performed at 80°C for 60 seconds.
  • the gate electrode was 600nm in an average thickness and 303 ⁇ m in a CD.
  • the insulation layer is 2 ⁇ m in an average thickness and is printed so as to cover all of the gate electrode and drain and source regions (Fig. 6).
  • UV light was irradiated to the back side of the substrate formed with the gate electrode at a distance of 10cm for 90 seconds using a mercury UV lamp with 365nm in a main wavelength and 80w/cm2inpower(Fig. 7).Whenl ⁇ £ of water was dropped in the first region 4 of the insulation layer to which the UV beam is not irradiated due to the gate electrode and a contact angle was measured, the contact angle was 78° .
  • the contact angle was 42° .
  • CAM-MICRO model of Tantec company was used as a measuring equipment for the water contact angle.
  • the ink for the source and drain ink electrodes which was made by dispersing nanosilver in ethylene glycol and was set to lOOOcp in viscosity and 42mN/m in surface tension, was printed by a roll to plate gravure printing machine (Fig.8).

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Thin Film Transistor (AREA)

Abstract

Provided is a method of fabricating an organic thin film transistor, which includes a) forming a gate electrode on a transparent substrate; b) forming an insulation layer to cover the gate electrode and irradiating light to a back side of the substrate formed with the gate electrode to form a first region to which the light is not irradiated by the gate electrode and a second region surface-reformed by the irradiation of the light as the gate electrode is not formed thereon; and c) forming drain and source electrodes on the second region. The method of fabricating an organic thin film transistor overcomes the limitation in an overlay accuracy which is the largest problem of a conventional printed transistor to allow the gate, drain and source electrodes to be printed in a self aligned manner and thus has an advantage that a transistor with reliability and stable performance can be mass- produced in a low cost.

Description

[DESCRIPTION]
[Invention Title]
CONTROL METHOD OF THE OVERLAY ACCURACY USING BY SELF-ALIGNED GRAVURE PRINTING
[Technical Field]
The present invention relates to a method of fabricating an organic thin film transistor for minimizing an area of a parasitic capacitance generated in an overlap portion between a gate and a drain or a source.
[Background Art]
There has been actively developed a printing electronics technology, in which an electronic device is fabricated by forming transistors, capacitors, resistors and wirings directly on a plastic substrate using inkjet and roll to roll printing methods. In the conventional printing electronics technology, various cost consuming processes required in use of photolithography can be omitted and consequently low cost and flexible electronic device can be obtained.
However, in the current printing technologies of inkjet and rotary pressing, it is impossible to lower overlay accuracy to 10 micron or less and thus it is difficult to fabricate a fine printed device. The overlay accuracy is measured as a deviation degree of each device from a desired position when a plurality of the devices is stacked, and it can be found, as seen from Fig. 1 to 4, that the position of each device is deviated from the standard by a value of the overlay accuracy of the printing machine itself as shown in Figs. 2 to 4 although the desired pattern is that shown Fig. 1. Fig. 1 is a sectional view of a transistor when the overlay printing is performed correctly using the conventional printing method. Figs. 2 to 4 are sectional views showing transistors not printed in the desired position in a case that the overlay accuracy of tens micron is present when the printing is performed using the conventional printing method. The numerical symbol 11 in Fig. 1 indicates a resister mark of a gate electrode and the numerical symbol 12 indicates a resister mark of a source or drain electrode. Also, in the case of forming wiring patterns using the inkjet printing and the rotary pressing, the patterns are obtained by discharging or transferring an ink containing material for the device and impacting the ink to a predetermined position on the substrate. When the ink is printed on the substrate as described above, it is difficult to obtain fine patterns as the ink is widely spread or the patterns may not be connected and thus may be separated as the ink is not sufficiently spread due to the properties of the substrate surface. Therefore, there occurs a problem that the desired printed device cannot be obtained.
Therefore, there have been widely tried methods capable of greatly restricting that the ink is spread too much or separated and thus forming desired wiring patterns. For example, it is possible that a hydrophilic transformation layer containing a fluorine based silane coupling agent is applied by a spin coating or a dip coating, dried and then an exposure using UV light or laser beam with a mask pattern is performed for several minutes to obtain the desired patterns.
However, in the fabrication of a printed transistor of a stacked structure, there occurs a problem that it is required to align the mask pattern with a gate portion. Also, though the mask pattern is correctly aligned with the gate portion, the ink for a semiconductor cannot be spread well in the potion where the fluorine based si lane coupling agent is not removed, and this will have a bad influence on the transistor device. Further, most of all, the coating method of the si lane coupling agent is also not suitable for the printing process.
[Disclosure]
[Technical Problem]
An embodiment of the present invention is directed to providing a method, in which only a portion of an insulation layer except for a previously printed gate is exposed to light and then drain and source electrodes are formed so as to have a gap therebetween corresponding to a critical dimension (CD) of the gate. Also, an embodiment of the present invention is directed to providing, in fabrication of self aligned transistor through a gravure printing method, a method for fabricating a transistor having the same performance as a conventional transistor by reducing overlay accuracy to several microns in consideration that the overlay accuracy of a conventional printing machine is tens microns.
Further, an embodiment of the present invention is directed to providing a method of fabricating uniform transistor, in which light is irradiated on a back side of a substrate formed with a gate electrode to surface-reform a portion of an insulation layer to which the light is not irradiated and thus wettablility is enhanced in the surface-reformed portion to allow printing of a drain ink and a source ink thereon.
Furthermore, an embodiment of the present invention is directed to providing a method of fabricating a transistor, in which a channel length of drain and source in a printed transistor is formed correspondingly to a CD of a gate. This pattern may be a method of minimizing an area of a parasitic capacitance generated in an overlap portion between the gate and the drain or source which can be seen in a conventional printed transistor.
Furthermore, an embodiment of the present invention is directed to providing a method of enhancing, by irradiating light to a back side of a substrate formed with a gate electrode, printability and adhesiveness of an ink for source and drain to be stacked on a second region of an insulation layer which is surface-reformed by irradiation of the light as the gate electrode is not formed thereon.
[Technical Solution]
To achieve the objects of the present invention, the present invention provides, in fabrication of a organic thin film transistor, a method for fabricating a transistor having the same performance as a conventional transistor by reducing an overlay accuracy of a device to several microns in consideration that the overlay accuracy of a conventional printing machine is tens microns. Specifically, the present invention provides a method of fabricating uniform transistor, in which light is irradiated on a back side of a substrate formed with a gate electrode to surface-reform a portion of an insulation layer to which the light is not irradiated and thus wettablility is enhanced in the surface-reformed portion to allow printing of a drain ink and a source ink thereon without overlap with the gate.
More specifically, the present invention provides a method of fabricating an organic thin film transistor, which includes a) forming a gate electrode on a transparent substrate; b) forming an insulation layer to cover the gate electrode and irradiating light to a back side of the substrate formed with the gate electrode to form a first region to which the light is not irradiated by the gate electrode and a second region surface-reformed by the irradiation of the light as the gate electrode is not formed thereon; and c) forming drain and source electrodes on the second region.
The steps a), b) and c) are implemented by a printing technique respectively, and specifically, the printing technique is used when forming the gate electrode in the step a), when forming the insulation layer in the step b) and when forming the drain and source electrodes in the step c). In the present invention, gravure printing may be used as the printing technique.
The method of fabricating an organic thin film transistor in accordance with the present can omit various processes compared to a conventional method using lithography and consequently has an effect capable of obtaining a circuit board in an economic cost.
Also, it overcomes the limitation in an overlay accuracy which is the largest problem of a conventional printed transistor to allow the gate, drain and source electrodes to be printed in a self aligned manner and thus has an advantage that a transistor with reliability and stable performance can be mass-produced in a low cost. Therefore, the present invention provides a method of fabricating an organic thin film transistor, wherein, in the step c), the source and drain electrodes are printed on the surface-reformed second region and self aligned with the gate.
The second region of the insulation layer can become hydrophilic. At this time, adhesiveness and wettability of drain ink and source ink to the second region are enhanced when the drain ink and the source ink are printed on the second region and thus it is possible to form a printed pattern which is not overlapped with the gate.
More specifically, a wavelength of the light in the step b) is 300 to 400 nm and preferably 340 to 380 nm. The form of the light is, but not limited to, a laser beam, which is effective to raise accuracy. Conventionally, a high energy light with a short length of 193 to 248 nm was mainly used. However, the UV light of a short wavelength has a low penetration power and a resulting low transmittance though it is of a high energy. In the present invention, the substrate and the insulation layer are preferably made of a material with a good transmittance and more preferably a plastic material. Also, since the light of a short wavelength is not easily transmitted, it is preferred to use a UV light with a long wavelength of 300 to 400 nm, more preferably 340 to 380 nm.
In the step b) the insulation layer meets the following Equation 1 by the surface-reforming:
Equation 1
θl > Θ2 (θl: contact angle of water droplet in the first region, θ 2: contact angle of water droplet in the second region)
The second region may have a reduced contact angle of water droplet as it is surface-reformed by the light, and thus has hydrophilicity due to the reduced contact angle and enhanced wettability and adhesiveness with respect to the drain and source ink.
In the step a), an example of a material for the transparent substrate includes polyethylene, polycarbonate, polyethylene terephthalate, polymethamethylacrylate, polytetrafluorethylene, ethylene tetrafluorethylene, polyimide and polyethylenenaphthalate, and polymer or copolymer thereof having high transmittance, but not largely limited thereto.
Also, the gate, source and drain electrodes are formed using a water dispersed conductive ink, respectively. More specifically, the gate, source and drain electrodes are formed of a water dispersed conductive ink including metal powder containing one or more selected from the group consisting of silver, copper, nickel, aluminum, tungsten, magnesium, iron and lead; and a hydrophilic solvent, and the water dispersed conductive ink may further include a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylacrylate, polyvinylpyrrolidone, polyvinylalcohol and polyurethane.
At this time, the metal powder preferably has nano- or micro-sized particles.
It is preferred that the gate ink in accordance with the present invention has different physical properties depending on a surface energy of the substrate and has a surface tension lower than the surface energy of the substrate by 1 to 10. If it is difficult to lower the surface tension, a viscosity of the ink can be increased and this can be easily adjusted by adjusting the solvent. A gate line can be realized by a roll to roll printing in accordance with the present invention can be fabricated with a critical dimension of at least 20 micron and preferably has the CD of 100 to 300 micron for application in a device having a gate height of 1 micron or less.
It is more preferred that the drain and source inks should have good wettability and adhesiveness in the second region and have a repellent force in the first region of the insulation layer on which the light is not irradiated due to the gate electrode.
In the step b), the insulation layer may include a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylacrylate, polyvinylpyrrolidone, polyvinylalcohol, polyinylvhloride, polyacrylonitryl and polyurethane," and a hydrophilic solvent. At this time, in the step b), the insulation layer is preferably further includes 1 to 20 weight% of inorganic substances, and the inorganic substances may contains one or more selected from the group consisting of TiO2, SiO2, Al2O3, Nb2O5, BaTiO3, Si3N4, Ta2O5, SrTiO3, (Ba,Sr)TiO3 . It is preferred that the insulation layer is made of a material having a high transmittance since it should transmit the light thoroughly. More specifically, it is preferred that the insulation layer is hydrophi lized by the light and the portion of the insulation layer blocked from the light maintains the hydrophobicity. Therefore, it is preferred to select a polymer which can be hydrophi lized by the light in accordance with the present invention and a higher dielectric constant can be obtained when fabricated by mixing an organic material or the binder and an inorganic substance. At this time, since amount and kind of the inorganic substance can have influence on the transmittance by the light, it is preferred to contain the inorganic substance by 1 to 20 weight%. In more specific example, the insulation layer may be fabricated by printing a mixture of polymethacrylate and ethyl carbitol acetate.
In the present invention, it is preferred that the solvent usable in the insulation layer, the inks of the gate electrode, drain electrode and source electrode contains one or more selected from the group consisting of water, ethanol, methanol, isopropyl alcohol, hexyl alcohol, octanol, decyl alcohol, ethylene glycol, diethylene glycol, methoxyethanol , acetone, methylethylketone, hexane, cyclohexane, eye1ohexanone, ethyleneglycol monoethylether, diethyleneglycol monobuthylether, N-methylpyrrolidone, pyrrolidine, ethyl acetate, ethyl carbitol acetate and buthyl carbitol acetate.
In the present invention, as a dispersion method used in the insulation layer, the inks of the gate electrode, drain electrode and source electrode, mechanic stirrer, homogenizer, ultrasonication, bead mill or ball mill may be selectively used and reaction speed and temperature are determined according to a condition of each ink. In order that the dispersed ink as such is used in the high speed roll to roll printing process, it is required a drying time of 10 seconds or less under a predetermined drying condition. Also, a printable viscosity range is not limited, but is required to be adjusted depending on a blading efficiency of a gravure machine. Further, it is preferred to adjust the viscosity depending on a desired pattern since the transfer of the ink upon printing is varied as the viscosity.
The printing machine used in the present invention is a roll to roll gravure printing machine and is a system in which each printing driver operates between an unwinder for unwinding a plastic foil and a rewinder for rewinding the plastic foil and each driver is provided with a hot wind curing device. A printing speed may be adjustable from 2 to 60 m/min, and roll pressure and web tension are also adjustable. The overlay accuracy of the machine is generally set to 50 micron or more and is varied as the condition of the machine.
It is most important for the ink used in the present invention to print the same patterns. The physical properties of the ink includes viscosity, kinematic viscosity, rheology, density, surface tension, particle size, size distribution, evaporation speed and etc. and it is preferred that the printing is performed under the condition in that these properties are always equal since variation in any one of these properties makes reproduction of the same fine pattern difficult. Also, a gravure printing cylinder capable of transferring the ink should have uniform grooves and, in order to have the uniform grooves, it is more effective to use hellio and laser stream methods rather than etching corrosion since the former allow finer and uniform etching.
The present invention provides an organic thin film transistor, which includes a transparent substrate; a gate electrode formed on the transparent substrate; an insulation layer formed on the gate electrode; and source and drain electrodes formed on the insulation layer and spaced apart from each other,
wherein the source and drain electrodes are printed on a portion of the insulation layer which is not formed with the gate electrode and is thus surface-reformed by irradiation of the UV light to a back side of the substrate and are self-aligned with the gate electrode.
Also, the organic thin film transistor in accordance with the present invention meets the following Equation 2:
Equation 2
Oμm = ID1-D21<10/aπ
(Dl:gap between the drain electrode and the source electrode, D2: CD of the gate electrode)
[Advantageous Effects]
The method of fabricating an organic thin film transistor in accordance with the present can omit various processes compared to a conventional method using lithography and consequently has an effect capable of obtaining a circuit board in an economic cost.
Also, it overcomes the limitation in an overlay accuracy which is the largest problem of a conventional printed transistor to allow the gate, drain and source electrodes to be printed in a self aligned manner and thus has an advantage that a transistor with reliability and stable performance can be mass-produced in a low cost .
[Description of Drawings]
The above and other objects, features and advantages of the present invention will become apparent from the following description of preferred embodiments given in conjunction with the accompanying drawings, in which:
Fig. 1 is a sectional view of a transistor when the overlay printing is performed accurately using a conventional printing method.
Figs. 2 to 4 are sectional views showing transistors not printed in the desired position in a case that the overlay accuracy of tens micron is present when the printing is performed using the conventional printing method.
Fig. 5 is a sectional view illustrating a plastic substrate and a gate electrode printed on the substrate by a gravure printing machine in accordance with an embodiment of the present invention.
Fig. 6 is a sectional views illustrating that the gate electrode is firstly printed on the plastic substrate and then an insulation layer is secondly printed.
Fig. 7 is a sectional view illustrating a first region 4 to which a UV light is not irradiated by the gate electrode 2 after irradiation of the UV light to a back side of the plastic substrate 1 and a second region 5 which is not formed with the gate electrode and thus is surface-reformed by the irradiation of the UV light. Fig. 8 is a sectional view illustrating that source and drain electrodes are thirdly printed after the irradiation of the UV light.
Fig. 9 is an image showing that lμi of water is dropped in the first region of the insulation layer to which the UV beam is not irradiated due to the gate electrode and a contact angle is then measured.
Fig. 10 is an image showing that \μl of water is dropped in the second region of the insulation layer which is surface-reformed by the irradiation of the UV beam as the gate electrode is not formed thereon and the contact angle is then measured.
Fig. 11-12 is an image by a microscope after the drain and source electrodes or the channel length are printed, in which Fig. 11 is a microscope image that a gap between the drain and source of Example 1 are printed, and Fig. 12 is a microscope image of channel length of Example 1 are printed
Fig. 13-14 is an image by a microscope after the drain and source electrodes or the channel length are printed, in which Fig. 13 is a microscope image that a gap between the drain and source of Example 2 are printed, and Fig. 14 is a microscope image of channel length of Example 2 are printed.
[Detailed Description of Main Elements]
l: plastic substrate
11: register mark of gate electrode
2' gate electrode
12: register mark of source and drain electrode
3: insulation layer
4: first region of insulation layer to which light is not irradiated due to gate electrode
5: second region of insulation layer which is surface-reformed by irradiation of light as gate electrode is not formed thereon
6: source electrode T- drain electrode
[Best Mode]
Hereinafter, the embodiments of the present invention will be described in detail with reference to accompanying drawings.
Fig. 5 is a sectional view illustrating a plastic substrate and a gate electrode printed on the substrate by a gravure printing machine in accordance with an embodiment of the present invention. Fig. 6 is a sectional views illustrating that the gate is firstly printed on the plastic substrate and then an insulation layer is secondly printed. Fig. 7 is a sectional view illustrating a first region 4 to which a UV light is not irradiated by the gate electrode 2 after irradiation of the UV light to a back side of the plastic substrate 1 and a second region 5 which is not formed with the gate electrode and thus is surface-reformed by the irradiation of the UV light.
Fig. 8 is a sectional view illustrating that source and drain electrodes are thirdly printed after the irradiation of the UV light.
(Example 1)
Ethylene tetrafluoroethylene film available from Asahi glass company (Japan) was used as the plastic substrate 1. Nanosilver was dispersed in ethylene glycol, set to 300cp in viscosity and 44mN/m in surface tension and then used as the gate electrode 2 in a first printing engine of the roll to roll gravure machine (Fig. 5). Also, 2Og of polymethamethylacrylate and 6Og of ethyl carbitol acetate were mixed and diluted to set 250cp in viscosity and used as the insulation layer 3 in a second printing engine. A printing speed of the gate electrode and the insulation layer is 8m/min and curing was performed at 1500C for 10 seconds. The gate electrode was 600nm in an average thickness and
Figure imgf000013_0001
in a CD. The insulation layer is 2μm in an average thickness and is printed so as to cover all of the gate electrode and drain and source regions (Fig. 6). UV light was irradiated to the back side of the substrate formed with the gate electrode at a distance of 10cm for 90 seconds using a mercury UV lamp with 365nm in a main wavelength and 80w/cm2inpower(Fig.7).
When iμJL of water was dropped in the first region 4 of the insulation layer to which the UV beam is not irradiated due to the gate electrode and a contact angle was measured, the contact angle was 77° as shown in Fig. 9. Also, when lμl of water was dropped in the second region 5 of the insulation layer which is surface-reformed by the irradiation of the UV beam as the gate electrode is not formed thereon and the contact angle was measured, the contact angle was 40° as shown in Fig. 9. As a measuring equipment for the water contact angle, CAM-MICRO model of Tantec company was used.
Subsequently, the ink for the source and drain ink electrodes, which was made by dispersing nanosilver in ethylene glycol and was set to 700cp in viscosity and 44mN/m in surface tension, was printed by a roll to plate gravure printing machine (Fig. 8). Fig. 11-12 is an image by a microscope after the drain and source electrodes 7, 6 are printed.
It was found from the printed image that a gap between the drain and source or the channel length was 287.67μm and was different from the gate CD, which was 292.08μm, by less than 10//m as can be seen in Fig. 11 and 12
(Example 2)
Polyethylene film available from Ilshin Chemical Co, Ltd was used as the plastic substrate 1. Nanosilver was dispersed in ethylene glycol and hexyl alcihol, set to 400cp in viscosity and 37mN/m in surface tension and then used as the gate electrode 2 in the first printing engine of the roll to roll gravure machine (Fig. 5). Also, 2Og of polymethamethylacrylate and 6Og of ethyl carbitol acetate were mixed and diluted to set 250cp in viscosity and used as the insulation layer 3 in a second printing engine. A printing speed of the gate electrode 2 and the insulation layer 3 is 4m/min and curing was performed at 80°C for 60 seconds.
The gate electrode was 600nm in an average thickness and 303μm in a CD. The insulation layer is 2μm in an average thickness and is printed so as to cover all of the gate electrode and drain and source regions (Fig. 6). UV light was irradiated to the back side of the substrate formed with the gate electrode at a distance of 10cm for 90 seconds using a mercury UV lamp with 365nm in a main wavelength and 80w/cm2inpower(Fig. 7).Whenlμ£ of water was dropped in the first region 4 of the insulation layer to which the UV beam is not irradiated due to the gate electrode and a contact angle was measured, the contact angle was 78° . Also, when iμA of water was dropped in the second region 5 of the insulation layer which is surface-reformed by the irradiation of the UV beam as the gate electrode is not formed thereon and the contact angle was measured, the contact angle was 42° . As a measuring equipment for the water contact angle, CAM-MICRO model of Tantec company was used.
Subsequently, the ink for the source and drain ink electrodes, which was made by dispersing nanosilver in ethylene glycol and was set to lOOOcp in viscosity and 42mN/m in surface tension, was printed by a roll to plate gravure printing machine (Fig.8).
It was found from the printed image that a gap between the drain and source or the channel length was 297.94μm and was different from the gate CD, which was 292.08μm, by less than lOμm as can be seen in Fig. 13 and 14.
While the present invention has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.

Claims

[CLAIMS]
[Claim 1]
A method of fabricating an organic thin film transistor, comprising-' a)forming a gate electrode on a transparent substrate;
b)forming an insulation layer to cover the gate electrode and irradiating light to a back side of the substrate formed with the gate electrode to form a first region to which the light is not irradiated by the gate electrode and a second region surface-reformed by the irradiation of the light as the gate electrode is not formed thereon; and
c)forming drain and source electrodes on the second region.
[Claim 2]
The method of claim 1, wherein the steps a),b) and c) are implemented by a printing technique respectively.
[Claim 3]
The method of claim 2, wherein, in the step c), the source and drain electrodes are printed on the surface-reformed second region and self aligned with the gate electrode.
[Claim 4]
The method of claim 2, where in the printing technique is a gravure printing.
[Claim 5]
The method of claim 1, wherein, in the step b), the insulation layer meets the following Equation 1 by the surface-reforming:
Equation 1
θl > Θ2 (θl: contact angle of water droplet in the first region, θ 2'- contact angle of water droplet in the second region)
[Claim 6]
The method of claim 5, wherein the gate, source and drain electrodes are formed using a water dispersed conductive ink, respectively.
[Claim 7]
The method of claim 1, wherein, in the step b), a wavelength of the light is 300 to 400nm.
[Claim 8]
The method of claim 7, wherein, in the step b), the light is a laser beam.
[Claim 9]
The method of claim 7, wherein, in the step b), the insulation layer includes a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylaerylate, polyvinylpyrrolidone, polyvinylalcohol , polyinylvhloride, polyacrylonitryl and polyurethane; and a hydrophilic solvent.
[Claim 10]
The method of claim 9, wherein, in the step b), the insulation layer further includes inorganic substances containing one or more selected from the group consisting of TiO2, SiO2, Al2O3, Nb2O5, BaTiO3, Si3N4, Ta2O5, SrTiO3,
(Ba,Sr)TiO3 and a content of the inorganic substances is 1 to 20 weight%.
[Claim 11]
The method of claim 6, the gate, source and drain electrodes are a water dispersed conductive ink including metal powder containing one or more selected from the group consisting of silver, copper, nickel, aluminum, tungsten, magnesium, iron and lead; and a hydrophilic solvent, respectively.
[Claim 12]
The method of claim 11, wherein gate, source and drain electrodes further include a binder containing one or more selected from the group consisting of epoxy, polyvinylphenol , polyester, polymethamethylacrylate, polyvinylpyrrolidone, polyvinylalcohol and polyurethane, respectively.
[Claim 13]
The method of one of claims 9 to 12, wherein the hydrophilic solvent contains one or more selected from the group consisting of water, ethanol, methanol, isopropyl alcohol, hexyl alcohol, octanol , decyl alcohol, ethylene glycol, diethylene glycol, methoxyethanol , acetone, methylethylketone, hexane, cyclohexane, cyclohexanone, ethyleneglycol monoethylether , diethyleneglycol monobuthylether , N-methylpyrrolidone, pyrrolidine, ethyl acetate, ethyl carbitol acetate and buthyl carbitol acetate.
[Claim 141
The method of claim 7, wherein, in the step a), the transparent substrate is made of polyethylene, polycarbonate, polyethylene terephthalate, polymethamethylaerylate, polytetrafluorethylene, ethylene tetrafluorethylene, polyimide or polyethylenenaphthalate.
[Claim 15]
An organic thin film transistor, comprising: a transparent substrate; a gate electrode formed on the transparent substrate; an insulation layer formed on the gate electrode; and source and drain electrodes formed on the insulation layer and spaced apart from each other,
wherein the source and drain electrodes are printed on a portion of the insulation layer which is not formed with the gate electrode and is thus surface-reformed by irradiation of the UV light to a back side of the substrate and are self-aligned with the gate electrode
[Claim 16]
The organic thin film transistor of claim 15, wherein the organic thin film transistor meets the following Equation 2:
Equation 2
Figure imgf000018_0001
(Dl^gap between the drain electrode and the source electrode, D2: CD of the gate electrode)
PCT/KR2010/002639 2009-08-17 2010-04-27 Control method of the overlay accuracy using by self-aligned gravure printing WO2011021763A1 (en)

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