JP2004103638A - Organic transistor element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic thin film transistor which is equipped with a gate insulating film that is easily formed, high in carrier mobility, capable of reducing a leakage current, has a high ON/OFF ratio, operates on a low gate voltage, and has a superior device performance. <P>SOLUTION: The organic transistor element is equipped with the gate insulating film that is formed through an atmospheric pressure plasma method, and an organic semiconductor layer is molecularly conformed with an oriented film as the layer is formed adjacent to an oriented film. <P>COPYRIGHT: (C)2004,JPO

Description

【００５３】
【発明の効果】
本発明の有機トランジスタ素子は、ゲート絶縁膜の形成を簡便に行うことが可能で、キャリア移動度が高く、リーク電流が低減され、ＯＮ／ＯＦＦ比が高く、ゲート電圧を低くできデバイス性能に優れる。
【図面の簡単な説明】
【図１】本発明の有機トランジスタ素子の構成をモデル的に示す図である。
【符号の説明】
１　支持体
２　ゲート電極
３　ゲート絶縁膜
４　配向膜
５　有機半導体層
６　ソース電極
７　ドレイン電極
１０　有機トランジスタ素子[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an organic thin film transistor that can easily form a gate insulating film and has excellent device performance.
[0002]
[Prior art]
In recent years, along with research on organic semiconductors, various organic thin film transistors using organic semiconductors have been proposed. Compared to conventional thin film transistors (TFTs) using a-Si (amorphous silicon), they can be manufactured using a low-temperature process, so they can be used for displays with TFTs formed on a flexible polymer support (polymer base). Applications are expected.
[0003]
However, the organic thin film transistor has a problem that the carrier mobility is low and the performance is inferior to those using the Si material.
[0004]
Patent Document 1 discloses that the alignment mobility is improved by bringing an alignment film adjacent to an organic semiconductor layer into molecular alignment to improve the carrier mobility, and Patent Document 2 discloses that heating a semiconductor polymer to a melting point or higher causes a liquid crystal phase. It is described that the mobility of an organic semiconductor channel is improved by performing molecular alignment using an adjacent alignment film by utilizing the alignment.
[0005]
[Patent Document 1]
JP-A-9-232589
[Patent Document 2]
WO 00/79617
[0007]
[Problems to be solved by the invention]
Incidentally, the gate insulating film of the organic thin film transistor is a silicon oxide film formed by thermal oxidation of a silicon substrate, a thin film of metal oxide or metal nitride formed by a dry process such as a sputtering method or a CVD method, or a polymer film formed by coating. However, polymer films have a lower dielectric constant and a weaker electric field effect than metal oxides and metal nitrides, so the gate voltage must be increased and the current ON / OFF ratio in switching is low. Therefore, it is common to employ a dry process that requires a vacuum-based facility that places a large load on manufacturing, and is formed of a metal oxide or metal nitride.
[0008]
The present invention has been made in view of the above circumstances, and can easily form a gate insulating film, have high carrier mobility, reduce leakage current, have a high ON / OFF ratio, and have a high gate voltage. And to provide an organic thin film transistor having excellent device performance.
[0009]
[Means for Solving the Problems]
The above object of the present invention is
1) an organic transistor element having an organic semiconductor layer adjacent to a gate insulating film and an alignment film formed by an atmospheric pressure plasma method;
2) The organic transistor element according to 1), which is formed through a step of performing a heat treatment in a state where the organic semiconductor layer is adjacent to the alignment film.
3) The organic transistor device according to 1) or 2), wherein the organic semiconductor is a π-conjugated polymer compound,
4) An organic transistor device according to 1), 2) or 3) formed on a polymer support.
[0010]
Hereinafter, the present invention will be described in detail.
The organic transistor element according to the present invention is characterized in that the gate insulating film is formed by the atmospheric pressure plasma method, and the organic semiconductor layer is adjacent to the alignment film for molecular matching.
[0011]
In the present invention, the gate insulating film formed by the atmospheric pressure plasma method is not particularly limited, but an inorganic oxide film having a high relative dielectric constant is preferable. As inorganic oxides, silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lanthanum lead titanate, strontium titanate, Examples include barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate bismuth, and yttrium trioxide. Among them, preferred are silicon oxide, aluminum oxide, tantalum oxide and titanium oxide.
Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.
[0012]
Atmospheric pressure plasma method, that is, a method of forming an insulating film by plasma film forming process under atmospheric pressure, discharges under atmospheric pressure or a pressure near atmospheric pressure, excites a reactive gas by plasma, and forms a thin film on a substrate. The forming method is described in JP-A-11-61406, JP-A-11-133205, JP-A-2000-121804, JP-A-2000-147209, and JP-A-2000-185362. Thereby, a highly functional thin film can be formed with high productivity.
[0013]
The thickness of the insulating film is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.
[0014]
As the organic semiconductor material constituting the organic semiconductor layer according to the present invention, a π-conjugated material is used. For example, polypyrroles such as polypyrrole, poly (N-substituted pyrrole), poly (3-substituted pyrrole), poly (3,4-disubstituted pyrrole), polythiophene, poly (3-substituted thiophene), poly (3,4- Poly (diphenylthiophene), polythiophenes such as polybenzothiophene, polyisothianaphthenes such as polyisothianaphthene, polyphenylenevinylenes such as polyphenylenevinylene, poly (p-phenylenevinylene) such as poly (p-phenylenevinylene) Phenylene vinylenes), polyaniline, poly (N-substituted aniline), poly (3-substituted aniline), polyaniline such as poly (2,3-substituted aniline), polyacetylene such as polyacetylene, polydiacetylene such as polydiacetylene , Polyazulene such as polyazulene, polypyrene etc. Polypyrenes, polycarbazoles, polycarbazoles such as poly (N-substituted carbazole), polyselenophenes such as polyselenophene, polyfurans such as polyfuran and polybenzofuran, and poly (p-) such as poly (p-phenylene) Phenylenes), polyindoles such as polyindole, polypyridazines such as polypyridazine, naphthacene, pentacene, hexacene, heptacene, dibenzopentacene, tetrabenzopentacene, pyrene, dibenzopyrene, chrysene, perylene, coronene, terylene, ovalene, Polyacenes such as quaterylene and circum anthracene, and derivatives in which some of the carbons of the polyacenes are substituted with a functional group such as an atom such as N, S or O, or a carbonyl group (triphenodioxazine, triphenodithiazine Hexacene-6,15-quinone, etc.), polyvinylcarbazole, polyphenylene sulfide, or the like can be used polycyclic condensate described in polyvinylene sulfide polymer and JP-like de 11-195790.
[0015]
Further, for example, thiophene hexamer α-sexithiophene α, ω-dihexyl-α-sexithiophene, α, ω-dihexyl-α-quinkethiophene, α, ω-bis ( Oligomers such as 3-butoxypropyl) -α-sexithiophene and styrylbenzene derivatives can also be suitably used.
[0016]
Further, metal phthalocyanines such as copper phthalocyanine and fluorine-substituted copper phthalocyanine described in JP-A-11-251601, naphthalene 1,4,5,8-tetracarboxylic diimide, N, N'-bis (4-trifluoromethylbenzyl) N, N′-bis (1H, 1H-perfluorooctyl), N, N′-bis (1H, 1H-perfluorobutyl) and N, N′- along with naphthalene 1,4,5,8-tetracarboxylic diimide Dioctylnaphthalene 1,4,5,8-tetracarboxylic diimide derivatives, naphthalene tetracarboxylic diimides such as naphthalene 2,3,6,7 tetracarboxylic diimide, and anthracene 2,3,6,7-tetracarboxylic acid Condensed ring tetracarboxylic acids such as anthracenetetracarboxylic diimides such as diimide _Diimides, fullerenes such as _{C 60, C 70, C 76} , C 78, C 84, carbon nanotube, merocyanine dyes, such as SWNT, such as dyes such hemicyanine dyes and the like.
[0017]
Among these π-conjugated materials, thiophene, vinylene, chenylene vinylene, phenylene vinylene, p-phenylene, a substituted product thereof, or two or more of these are used as a repeating unit, and the number n of the repeating unit is 4 to 4. At least one selected from the group consisting of oligomers having 10 or a polymer in which the number n of the repeating units is 20 or more, condensed polycyclic aromatic compounds such as pentacene, fullerenes, condensed ring tetracarboxylic diimides, and metal phthalocyanines Species are preferred.
[0018]
In addition, a material in which a substituent such as a C _{4 to} C ₁₅ alkyl group or the like is added to at least one of the repeating units to form a stereoscopic regular structure is preferable. The addition of a substituent such as an alkyl group enhances the solubility of the organic semiconductor material in an organic solvent, and further provides regularity to the higher-order structure of the polymer when the organic semiconductor layer is formed by forming an ordered structure. it can.
[0019]
Further, among these, a polymer or an oligomer having a chain structure of a thiophene ring is preferable, and it is most preferable to include a 3-alkylthiophene periodic structure. The number of carbon atoms contained in the alkyl group is 4 to 15, and if it is less than 4, the solubility in an organic solvent decreases, and if it is 15 or more, the ordered structure tends to be disordered. Further, in order to make the melting point 240 ° C. or less, the alkyl group preferably has 6 or more carbon atoms. Most preferably, it is an alkyl group having 8 to 15 carbon atoms.
[0020]
In the present invention, for example, a material having a functional group such as acrylic acid, acetamido, dimethylamino group, cyano group, carboxyl group, or nitro group in the organic semiconductor layer, a benzoquinone derivative, tetracyanoethylene, and tetracyanoquinodimethane And materials that have an electron acceptor such as derivatives thereof and materials having functional groups such as amino group, triphenyl group, alkyl group, hydroxyl group, alkoxy group and phenyl group, and substituted amines such as phenylenediamine , Anthracene, benzoanthracene, substituted benzoanthracenes, pyrene, substituted pyrene, carbazole and derivatives thereof, tetrathiafulvalene and its derivatives, etc. Process Good.
[0021]
The doping means that an electron donating molecule (acceptor) or an electron donating molecule (donor) is introduced into the thin film as a dopant. Therefore, the doped thin film is a thin film containing the condensed polycyclic aromatic compound and the dopant. Either an acceptor or a donor can be used as the dopant used in the present invention.
[0022]
_{Cl 2,} Br ₂ as the _{acceptor, I 2, ICl, ICl 3} , IBr, halogen such as _{IF, PF 5, AsF 5,} SbF 5, BF 3, BC1 3, a Lewis acid such as _{BBr 3,} SO 3, HF _{, HC1, HNO 3, H 2} SO 4, HClO 4, FSO 3 H, ClSO 3 H, protonic acids such as _CF 3 SO ₃ H, acetic acid, formic acid, organic acids such as amino _acids, FeCl 3, FeOCl, TiCl _4, Transition metals such as ZrCl ₄ , HfCl ₄ , NbF ₅ , NbCl ₅ , TaCl ₅ , MoCl ₅ , WF ₅ , WCl ₆ , UF ₆ , LnCl ₃ (Ln = La, Ce, Nd, Pr, etc. and lanthanoids) Compound, Cl ⁻ , Br ⁻ , I ⁻ , ClO ₄ ⁻ , PF ₆ ⁻ , AsF ₅ ⁻ , SbF ₆ ⁻ , BF ₄ ⁻ , sulfo And electrolyte anions such as phosphate anions.
[0023]
Examples of the donor include alkali metals such as Li, Na, K, Rb, and Cs; alkaline earth metals such as Ca, Sr, and Ba; Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, and Dy. , Ho, Er, Yb, and other rare earth metals, ammonium ions, R ₄ P ⁺ , R ₄ As ⁺ , R ₃ S ⁺ , and acetylcholine.
[0024]
As a method of doping these dopants, any of a method of preparing a thin film of an organic semiconductor in advance and introducing the dopant later, and a method of introducing a dopant at the time of forming the thin film of the organic semiconductor can be used. As the doping of the former method, gas-phase doping using a gas-state dopant, liquid-phase doping in which a solution or liquid dopant is brought into contact with the thin film, and diffusion doping by bringing a solid-state dopant into contact with the thin film Solid doping method. In liquid phase doping, the efficiency of doping can be adjusted by performing electrolysis. In the latter method, a mixed solution or dispersion of the organic semiconductor compound and the dopant may be simultaneously applied and dried. For example, when a vacuum evaporation method is used, the dopant can be introduced by co-evaporating the dopant together with the organic semiconductor compound. When a thin film is formed by a sputtering method, a dopant can be introduced into the thin film by sputtering using a binary target of an organic semiconductor compound and a dopant. Still other methods include chemical doping such as electrochemical doping and photo-initiated doping, and physical doping such as ion implantation described in, for example, “Industrial Materials”, Vol. 34, No. 4, p. 55 (1986). Any of the conventional dopings can be used.
[0025]
These organic thin films can be prepared by vacuum deposition, molecular beam epitaxy, ion cluster beam, low energy ion beam, ion plating, CVD, sputtering, plasma polymerization, electrolytic polymerization, chemical polymerization, etc. Examples include a synthesizing method, a spray coating method, a spin coating method, a blade coating method, a dip coating method, a casting method, a roll coating method, a bar coating method, a die coating method, and an LB method, which can be used depending on the material. However, in terms of productivity, spin coating, blade coating, dip coating, roll coating, bar coating, die coating, etc., which can easily and precisely form thin films using organic semiconductor solutions, are used. Preferred.
[0026]
The thickness of the organic semiconductor thin film is not particularly limited, but the characteristics of the obtained transistor are often greatly influenced by the thickness of the active layer made of the organic semiconductor. Although it differs depending on the semiconductor, it is generally preferably 1 μm or less, particularly preferably 10 to 300 nm.
[0027]
In addition, heat treatment is preferably performed after the organic semiconductor layer is formed adjacent to the alignment film, so that molecular alignment is promoted and the mobility of the organic semiconductor channel is further improved, which is preferable.
[0028]
As the alignment film, a known technique used for a liquid crystal display or the like, for example, a technique described in JP-A-9-194725 or 9-258229 can be used. Polyimide, a perfluoropolymer, a liquid crystal polymer, or the like is used as a material of the alignment film, and it is preferable to perform a rubbing treatment after forming the film. The method of orientation in an electromagnetic field described in U.S. Pat. No. 5,468,519 may be used.
[0029]
Preferably, the alignment film is photo-aligned, and is an alignment film described in JP-A-8-286180, JP-A-8-313910, JP-A-9-80440, or the like.
[0030]
The thickness of the alignment film is about 1 nm to 5 μm, preferably 5 to 100 nm.
FIG. 1 schematically shows the structure of the organic transistor element of the present invention.
[0031]
In FIG. 1A, an organic transistor element 10a of the present invention has a gate electrode 2 formed on a support 1 and an organic semiconductor layer 5 adjacent to an alignment film 4 with a gate insulating film 3 interposed therebetween. And the drain electrode 7.
[0032]
In FIG. 1B, an organic transistor element 10b of the present invention has a gate electrode 2 formed on a support 1, a gate insulating film 3, an alignment film 4 in this order, and a source electrode 6 and a drain electrode 7 formed in this order. An organic semiconductor layer 5 is formed so as to cover and be adjacent to the alignment film 4 as a channel.
[0033]
In FIG. 1C, an organic transistor element 10c of the present invention has an alignment film 4 on a support 1, and an organic semiconductor layer 5 is adjacent to the alignment film 4 so as to cover the source electrode 6 and the drain electrode 7. The gate electrode 2 is formed as a channel with the gate insulating film 3 interposed therebetween.
[0034]
The material for forming the source electrode 6, the drain electrode 7, and the gate electrode 2 is not particularly limited as long as it is a conductive material. Platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony lead, tantalum, indium , Palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin / antimony, indium tin oxide (ITO), fluorine-doped zinc oxide, zinc, carbon, graphite, glassy carbon, silver paste and carbon Paste, lithium, beryllium, sodium, magnesium, potassium, calcium, scandium, titanium, manganese, zirconium, gallium, niobium, sodium, sodium-potassium alloy, magnesium, lithium, aluminum, magnesium / copper Compounds, a magnesium / silver mixture, a magnesium / aluminum mixture, a magnesium / indium mixture, an aluminum / aluminum oxide mixture, a lithium / aluminum mixture, etc., among which platinum, gold, silver, copper, aluminum, indium, ITO and Carbon is preferred. Alternatively, a known conductive polymer whose conductivity has been improved by doping or the like, for example, conductive polyaniline, conductive polypyrrole, conductive polythiophene, a complex of polyethylene dioxythiophene and polystyrene sulfonic acid, and the like are also preferably used. Among them, those having low electric resistance at the contact surface with the semiconductor layer are preferable.
[0035]
As a method of forming an electrode, a method of forming an electrode using a known photolithographic method or a lift-off method on a conductive thin film formed by using a method such as evaporation or sputtering using the above as a raw material, or a metal foil such as aluminum or copper There is a method of etching using a resist by thermal transfer, ink jet or the like. In addition, a conductive polymer solution or dispersion, or a conductive fine particle dispersion may be directly patterned by ink jet, or may be formed from a coating film by lithography or laser ablation. Further, a method of patterning an ink containing a conductive polymer or conductive fine particles, a conductive paste, or the like by a printing method such as letterpress, intaglio, lithographic, or screen printing can also be used.
[0036]
The support 1 is made of a sheet made of glass or a flexible resin. For example, a plastic film can be used as the sheet. Examples of the plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyether sulfone (PES), polyether imide, polyether ether ketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), Examples include a film made of cellulose triacetate (TAC), cellulose acetate propionate (CAP), and the like. By using such a polymer support, the weight can be reduced, the portability can be improved, and the resistance to impact can be improved as compared with the case where a glass substrate is used. It is preferable that the polymer has a softening point of 110 ° C. or higher, more preferably 150 ° C. or higher.
[0037]
【Example】
Hereinafter, the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0038]
Example 1
An aluminum film having a thickness of 100 nm and a width of 300 μm was formed on a 150 μm-thick PES film (FS-1300 manufactured by Sumitomo Bakelite) by a sputtering method to form a gate electrode. Using a device described in JP-A-2000-80182, a mixed gas of argon (98.2% by volume), tetramethoxysilane (0.3% by volume), and hydrogen gas (1.5% by volume) is formed on the film. Was used to form a silicon oxide film having a thickness of 150 nm by an atmospheric pressure plasma method.
[0039]
Further, a polyimide thin film having a thickness of 20 nm was formed on the silicon oxide film using a commercially available polyimide material, and rubbing treatment was performed by rubbing with a cloth.
[0040]
Next, the content of Zn and Ni were well purified to be 10ppm or less, poly (3-hexylthiophene) for preparing a chloroform solution of regioregular body (Aldrich) in _{N 2} gas atmosphere, the polyimide Was applied using an applicator, dried at room temperature, and then subjected to a heat treatment at 50 ° C. for 30 minutes. At this time, the film thickness of poly (3-hexylthiophene) was 100 nm. Further, gold was deposited on the surface of the poly (3-hexylthiophene) film using a mask to form source and drain electrodes. Source and drain electrodes having a width of 100 μm and a thickness of 100 nm were arranged so as to be orthogonal to the gate electrode, and an organic thin film transistor having a channel width W = 0.3 mm and a channel length L = 20 μm was formed.
[0041]
This organic thin-film transistor exhibited favorable operation characteristics of a p-channel enhancement type FET.
[0042]
The measured values under the following conditions were obtained for the obtained organic thin film transistor.
▲ 1 ▼ gate leakage current _{I g-sd} of; source, short the drain electrode was measured leakage current _{I g-sd} when the gate bias was -30 V.
[0043]
{Circle around (2)} ON / OFF ratio: The ratio of the drain current when the drain voltage is -20 V when the gate bias is -30 V and 0 V.
[0044]
{Circle around (3)} The field effect mobility was calculated from the saturation region of the IV curve by a known method.
[0045]
Example 2
After heating the device of Example 1 together with the film at 230 ° C. in an atmosphere of N ₂ gas replacement, it was cooled to room temperature at a rate of −1 ° C./sec. It was evaluated similarly.
[0046]
Comparative Example 1
A device was prepared and evaluated in exactly the same manner as in Example 1 except that no polyimide film was formed.
[0047]
Example 3
As in Example 1, a 20-nm-thick polyimide film was formed on a 150 μm-thick PES film (FS-1300 manufactured by Sumitomo Bakelite) and rubbed. Next, gold was deposited on the polyimide film using a mask to form source and drain electrodes having a width of 100 μm and a thickness of 100 nm.
[0048]
The content of Zn and Ni were well purified to be 10ppm or less, regioregular of poly (3-octyl thiophene) (Rieke Metals, Ltd. Inc) to prepare a chloroform solution, the solution, _{N 2} gas substitution atmosphere Then, it was applied on the source / drain electrodes and the polyimide film, dried at room temperature, and then subjected to a heat treatment at 50 ° C. for 30 minutes. At this time, the film thickness of poly (3-octylthiophene) was 30 nm.
[0049]
A 130-nm-thick titanium oxide film is similarly formed thereon by the atmospheric pressure plasma method, and then a conductive silver paste is screen-printed so as to overlap the channel portion, and a 30-μm-wide gate electrode is formed. An organic thin film transistor having a length L = 20 μm was prepared.
[0050]
The same evaluation was performed on the obtained organic thin film transistors.
Example 4
After heating the device of Example 3 together with the film at 200 ° C. in an atmosphere of N ₂ gas replacement, it was cooled to room temperature at a rate of −1 ° C./sec. It was evaluated similarly.
[0051]
Comparative Example 2
A device was prepared and evaluated in exactly the same manner as in Example 3, except that no polyimide film was formed.
[0052]
The results of evaluating the above organic thin film transistors are shown.

[0053]
【The invention's effect】
The organic transistor element of the present invention can easily form a gate insulating film, has high carrier mobility, reduces leakage current, has a high ON / OFF ratio, has a low gate voltage, and has excellent device performance. .
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of an organic transistor element of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Support 2 Gate electrode 3 Gate insulating film 4 Alignment film 5 Organic semiconductor layer 6 Source electrode 7 Drain electrode 10 Organic transistor element

Claims (4)

An organic transistor element having an organic semiconductor layer adjacent to a gate insulating film and an alignment film formed by an atmospheric pressure plasma method. 2. The organic transistor element according to claim 1, wherein the organic semiconductor layer is formed through a step of performing heat treatment in a state adjacent to the alignment film. The organic transistor element according to claim 1, wherein the organic semiconductor is a π-conjugated polymer compound. 4. The organic transistor device according to claim 1, wherein the organic transistor device is formed on a polymer support.

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