Classifications

• • 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
  • H10K10/40—Organic transistors
  • H10K10/46—Field-effect transistors, e.g. organic thin-film transistors [OTFT]
  • H10K10/462—Insulated gate field-effect transistors [IGFETs]
  • H10K10/466—Lateral bottom-gate IGFETs comprising only a single gate
• • 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]
  • H10K10/484—Insulated gate field-effect transistors [IGFETs] characterised by the channel regions
  • H10K10/488—Insulated gate field-effect transistors [IGFETs] characterised by the channel regions the channel region comprising a layer of composite material having interpenetrating or embedded materials, e.g. a mixture of donor and acceptor moieties, that form a bulk heterojunction
• • 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
  • H10K71/10—Deposition of organic active material
  • H10K71/12—Deposition of organic active material using liquid deposition, e.g. spin coating
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
  • H10K85/00—Organic materials used in the body or electrodes of devices covered by this subclass
  • H10K85/10—Organic polymers or oligomers
  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene

Definitions

• the present invention relates to a method of forming an organic semiconductor thin film used to manufacture an organic thin film transistor, and, more particularly, to a method of simultaneously forming an organic semiconductor thin layer and a dielectric thin layer using vertical phase separation, and a high-performance organic thin film transistor manufactured using the method.
• Organic thin film transistors which are drive elements of next-generation displays, have been actively researched.
• Organic thin film transistors use an organic film as a semiconductor layer instead of a silicon film, and are classified into low-molecular organic thin film transistors, such as oligothiophene, pentacene and the like, and high-molecular organic thin film transistors, such as polythiophene and the like, according to the raw materials of the organic film.
• Organic thin film transistors are chiefly manufactured using a solution process in which a thin film is formed by dissolving an organic semiconductor in a solvent and then applying the organic semiconductor solution onto a substrate.
• a solution process in which a thin film is formed by dissolving an organic semiconductor in a solvent and then applying the organic semiconductor solution onto a substrate.
• a multilayered thin film including a dielectric layer, an organic semiconductor layer and a protective layer is formed using a solution process, there is a problem in that a solvent used in subsequent processes damages the previously-formed lower layer. Therefore, in order to realize a more effective solution process, attempts to form a multilayered thin film in one coating process are being made. Further, in order to decrease the manufacturing cost thereof, methods of manufacturing an organic thin film transistor using a small amount of expensive organic semiconductor is being required.
• this device can be manufactured only when a crystalline polymer, for example, isotactic PS or high-density PE, is used as the insulating polymer.
• a crystalline polymer for example, isotactic PS or high-density PE
• P3HT is crystallized on a substrate, and then an insulating polymer is applied thereon to be vertically separated into a P3HT layer and an insulating polymer layer on the substrate, thereby making a charge transfer channel between source and drain electrodes using a small amount of P3HT.
• this method is difficult to be commercially used because a complicated process of crystallizing P3HT and solidifying an insulating polymer is required. Further, this method is problematic in that it is difficult to make a device by applying a uniform film onto a substrate of a large area because a drop casting process is used in this method.
• the present invention relates to a method of preparing a multilayered thin film having a structure of substrate/insulating polymer layer/organic semiconductor layer, and a method of manufacturing an organic thin film transistor using the prepared multilayered thin film.
• an aspect of the present invention provides a method of forming a multilayered thin film, including: applying a mixed solution of an organic semiconductor and an insulating polymer having different surface energies onto a substrate.
• the multilayered thin film is formed through vertical phase separation while applying the mixed solution.
• a material having the smallest difference in surface energy between the material and the substrate is applied right on the substrate.
• an insulating polymer layer having relatively strong hydrophilicity and high surface energy is formed on the lower end of the multilayered thin film, which is located near the hydrophilic substrate, and an organic semiconductor layer having relatively low hydrophilicity is formed on the upper end of the multilayered thin film.
• the hydrophilic substrate is a substrate having a hydrophilic group, such as -OH or the like, formed on the surface thereof, and, preferably, is a substrate having higher surface energy than an insulating polymer.
• the hydrophilic substrate may be a commonly-used silicon (Si) substrate used as a gate electrode.
• the hydrophilic substrate may be a silicon (Si) substrate coated on the surface thereof with thermally-grown silicon dioxide (SiO 2 ) functioning as a dielectric layer.
• the organic semiconductor is an organic semiconductor having lower surface energy than the insulating polymer.
• organic semiconductors which can be solution-processed may be used as the organic semiconductor.
• the organic semiconductor may be polyalkylthiophene, poly (3, 3-didodecyl-quarterthiophene) (PQT-12) or the like, preferably, P3HT.
• the insulating polymer is an insulating polymer having higher surface energy than the organic semiconductor.
• Various kinds of polymers such as polymethylmethacrylate (PMMA) , polystyrene, polymethylstryrene and the like, which can be dissolved in an organic solvent, may be used as the insulating polymer.
• the difference in surface energy between the organic semiconductor and the insulating polymer is not limited as long as vertical layer separation occurs therebetween. It is preferred that the difference in surface energy therebetween be 2.0 mJ/m 2 or more in order to decrease processing time.
• the difference in surface energy between the organic semiconductor and the insulating polymer be large in order to allow the vertical layer separation to occur easily.
• an insulating polymer having a hydrophilic group for example, polymethylmethacrylate (PMMA) , may be used as the insulating polymer.
• the weight ratio of P3HT and PMMA be 1:99 ⁇ 40:60.
• P3HT content is less than 3 wt%, it is difficult to interconnect the layer- separated P3HT is difficult. Therefore, it is preferred that the P3HT content be 3 wt% or more in order to allow the layer-separated P3HT to form a plane.
• Another aspect of the present invention provides a method of manufacturing an organic thin film transistor, including the steps of: providing a substrate; providing a gate electrode on the substrate; coating the substrate with a mixed solution of an organic semiconductor and an insulating polymer having higher surface energy then the organic semiconductor to form an organic semiconductor thin film on an insulating polymer thin film; and forming drain and source electrodes connected with the organic semiconductor thin film.
• the difference in surface energy between the organic semiconductor and the insulating polymer be large in order to allow the vertical layer separation to rapidly occur during a coating process.
• the mixed solution may be applied on the substrate using spin-coating or ink-jet printing, preferably, spin coating which can be easily used in a substrate of a large area.
• a commonly-used silicon (Si) substrate having a dielectric layer or having no dielectric layer or a hydrophilic flexible substrate may be used as the substrate. It is preferred that the substrate have higher surface energy than the insulating polymer.
• the insulating polymer is PMMA which is a hydrophilic polymer
• the organic semiconductor is P3HT having lower surface energy than the PMMA.
• the source and drain electrodes may be formed on the organic semiconductor layer after the formation of the organic semiconductor layer, and may be formed using an ink-jet printer.
• Still another aspect of the present invention provides a method of manufacturing an organic thin film transistor, including the steps of: providing a substrate; providing a gate electrode on the substrate; forming a dielectric layer on the substrate; coating the dielectric layer with a mixed solution of an organic semiconductor and an insulating polymer having higher surface energy then the organic semiconductor to form an organic semiconductor thin film on an insulating polymer thin film; and forming drain and source electrodes connected with the organic semiconductor thin film.
• the insulating polymer layer is located between the organic semiconductor layer and the dielectric layer because of the difference in surface energy therebetween.
• the insulating polymer layer has hydrophobicity compared to the dielectric layer coated with thermally-grown silicon oxide, thus improving the electrical characteristics of the manufactured organic thin film transistor.
• Still another aspect of the present invention provides an organic thin film transistor, including: a substrate connected with a gate electrode; a first dielectric layer formed on the substrate; a second dielectric layer formed on the first dielectric layer; an organic semiconductor thin film formed on the second dielectric layer; and source and drain electrodes connected with the organic semiconductor thin film.
• the organic thin film transistor of the present invention since the insulating polymer layer is formed on the dielectric layer coated with silicon oxide, the organic thin film transistor can exhibit excellent electrical characteristics .
• the weight ratio of the insulating polymer and the organic semiconductor be 20:80 ⁇ 3:97 in order to improve the charge mobility of the organic thin film transistor.
• the amount of the organic semiconductor is less than 3 wt%, the charge mobility of the organic thin film transistor is decreased.
• the amount of the organic semiconductor is more than 50 wt%, the charge mobility of the organic thin film transistor is also decreased.
• the first dielectric layer such as silicon oxide thermally grown on a silicon (Si) substrate
• the second dielectric layer may have higher surface energy than the first dielectric layer formed thereon, and may be an insulating polymer layer formed by polymerizing polar monomers, for example, hydrophilic monomers, such as methyl methacrylate .
• the organic semiconductor thin film may be made of an organic semiconductor having lower surface energy than the second dielectric layer, and, preferably, may be made of P3HT.
• an insulating polymer and an organic semiconductor can be sequentially vertically applied on a substrate through one solution process.
• an organic thin film transistor according to the present invention in which an insulating polymer thin film and an organic semiconductor thin film are vertically phase-separated, can realize excellent electrical characteristics even when a small amount of organic semiconductor is used. Further, according to the organic thin film transistor of the present invention, since an insulating polymer thin film and an organic semiconductor thin film can be vertically disposed on a substrate using phase separation, the insulation polymer thin film functions as a dielectric layer even when a substrate on which a dielectric layer is not formed is used, and thus the organic thin film transistor can be driven by low voltage and can realize excellent electrical characteristics.
• an organic thin film transistor of the present invention various solution processes, such as spin coating, ink-jet printing and the like, can be applied, and an insulating polymer thin film and an organic semiconductor thin film can be simultaneously formed, thereby efficiently manufacturing the organic thin film transistor.
• FIG. 1 is a schematic view showing a process of forming a multilayered thin film which is vertically separated into a substrate, a PMMA layer and a P3HT layer by spin-casting a blend of P3HT and PMMA on a substrate having an SiO 2 insulator layer or a substrate having no SiO 2 insulator layer;
• FIG. 2 is a graph showing the water contact angle of the multilayered thin film formed using the blend of P3HT and PMMA depending on P3HT content
• FIG. 3A is a graph showing the change in S2p peak of a multilayered thin film having a composition ratio of P3HT:PMMA (20:80) depending on Ar + sputtering time, which was measured using X-ray photoelectron spectroscopy (XPS)
• XPS X-ray photoelectron spectroscopy
• 3B is a graph showing the change in sulfur content of a thin film made of only P3HT (100%) or a multilayered thin film having a composition ratio of P3HT:PMMA (20:80) depending on Ar + sputtering time, which was measured using X-ray photoelectron spectroscopy (XPS) ;
• XPS X-ray photoelectron spectroscopy
• FIG. 4 shows atomic force microscope images of P3HT- PMMA thin films which have different composition ratios of P3HT and PMMA and were formed on a silicon substrate, wherein the composition ratios of P3HT and PMMA are 100:0, 8:92, 5:95, 3:97, 2:98 and 1:99, and the scale bar is 200 nm;
• FIG. 5A is a schematic sectional view showing an organic thin film transistor manufactured using a P3HT-PMMA blend thin film and formed on a substrate having an SiO 2 insulator layer, FIG.
• FIG. 5B is a graph showing the migration characteristics of transistors manufactured using a thin film made of only P3HT (100%) and a P3HT-PMMA blend (5:95) thin film at a V G of -80 V, wherein I D is a drain-source current, V D is a drain-source voltage and V G is a gate voltage,
• FIG. 5C is a graph showing the output characteristics of a transistor manufactured using a thin film made of only P3HT (100%)
• FIG. 5D is a graph showing the output characteristics of a transistor manufactured using a P3HT-PMMA blend (5:95) thin film;
• FIG. 6 is a graph showing the average charge mobility of an organic thin film transistor manufactured using a P3HT-PMMA blend thin film depending on P3HT content, wherein the average charge mobility thereof was measured in a saturated region;
• FIG. 7 shows the performances of an organic thin film transistor which was manufactured using a P3HT-PMMA blend thin film on a substrate having no SiO 2 insulator layer and is used in low-current drive apparatuses
• FIG. 7A is a graph showing the output characteristics of a transistor manufactured using a P3HT-PMMA blend (5:95) thin film, in which the transistor has a channel length of 30 [M and a channel width of 1 mm
• FIG. 7B is a graph showing the migration characteristics and gate leakage current (Igs) of a transistor manufactured using a P3HT-PMMA blend (5:95) thin film.
• a heavily-doped n-type silicon substrate including thermally-grown silicon dioxide (SiO 2 ) and a heavily-doped n-type silicon substrate including no thermally-grown silicon dioxide (SiO 2 ) were washed with a Piranha solution, washed with distilled water, and then left in a vacuum oven.
• a solution (1 wt%) in which P3HT and PMMA were dissolved in chlorobenzene at a predetermined weight ratio was spin-coated on a substrate to form a film.
• the spin- coating of the solution was conducted at a spin rate of 1500 rpm at room temperature.
• the formed film was dried in a vacuum oven at 60 ° C to remove solvent residue therefrom.
• PEDOT/PSS droplets were deposited in line on the dried film using an ink-jet printer .
• TFT The electrical characteristics of TFT were measured in an accumulation mode at room temperature using Keithley 2400 and 236 source measuring apparatuses.
• the water contact angle of a film was measured using a FACE contact angle measuring apparatus (Kyowa Kaimenka gabu Co., Inc.).
• the thickness of a film was measured using an Ellipsometer
• composition of a film in a thickness direction was analyzed by etching the film using an Ar + gun (3.0 KeV) .
• a transistor was manufactured by spin-coating a heavily-doped n-type silicon substrate including thermally- grown silicon dioxide (SiO 2 ) with a mixed solution of P3HT and PMMA. The performance of the transistor was measured while decreasing P3HT content from 100% to about 1%, and the results thereof are shown in FIGS. 5 and 6.
• the charge mobility between source and drain electrodes of a transistor is not greatly different from that of a transistor including pure P3HT.
• the P3HT content thereof is 20 ⁇ 3 wt%, the charge mobility therebetween is greatly increased, and, when the P3HT content thereof is less than 3 wt%, the charge mobility therebetween is greatly decreased.
• a transistor was manufactured by spin-coating a heavily-doped n-type silicon substrate including no silicon dioxide (SiO 2 ) with a mixed solution of P3HT and PMMA. The electrical characteristics of the transistor were measured, and the results thereof are shown in FIG 7.
• a PMMA layer acts as a dielectric layer of an organic thin film transistor, thus manufacturing an organic thin film transistor driven by low power.

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Citations (5)

• 2008
  • 2008-09-11 KR KR1020080090070A patent/KR20100031036A/ko not_active Application Discontinuation
  • 2008-09-12 WO PCT/KR2008/005427 patent/WO2010030050A1/en active Application Filing

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