JP4419425B2 - Organic thin film transistor element - Google Patents

Description

【００５１】
【発明の効果】
実施例で実証した如く、本発明の有機薄膜トランジスタ素子によれば、高いＯＮ電流が得られる。
【図面の簡単な説明】
【図１】有機薄膜トランジスタ素子の構成例を示す図である。
【図２】導電性領域の形態を示す図である。
【図３】トランジスタ特性評価回路の模式図。
【符号の説明】
１ 有機薄膜トランジスタ素子
２ ソース電極
３ ドレイン電極
４ 有機半導体層
５ ゲート電極
６ ゲート絶縁層
７ 支持体
８ 導電性領域[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic thin film transistor element capable of obtaining a high ON current.
[0002]
[Prior art]
With the widespread use of information terminals, there is an increasing need for flat panel displays as computer displays. In addition, with the progress of computerization, the information provided by paper media has increased the opportunity to be provided electronically, and as a mobile display medium that is thin, light and easy to carry, electronic paper or digital The need for paper is also increasing.
[0003]
In general, in a flat display device, a display medium is formed using an element utilizing liquid crystal, organic EL, electrophoresis, or the like. In such a display medium, a technique using an active drive element formed of a thin film transistor (TFT) as an image drive element has become mainstream in order to ensure uniformity of screen brightness, screen rewrite speed, and the like.
[0004]
Here, the TFT element is usually formed on a glass substrate, mainly a semiconductor thin film such as a-Si (amorphous silicon) or p-Si (polysilicon), or a metal thin film such as a source, drain, or gate electrode on the substrate. Manufactured by sequentially forming. The production of flat panel displays using TFTs usually requires high-precision photolithographic processes in addition to vacuum equipment such as CVD and sputtering and thin film forming processes that require high-temperature processing processes. The load is very large. Furthermore, along with the recent needs for larger display screens, their costs have become enormous.
[0005]
In recent years, research and development of organic TFT elements using organic semiconductor materials has been actively promoted as a technique to compensate for the disadvantages of conventional TFT elements (see Patent Document 1, Non-Patent Document 1, etc.). Since this organic TFT element can be manufactured by a low-temperature process, it is said that a light and hard-to-break resin substrate can be used, and further, a flexible display using a resin film as a support can be realized (non-patent) Reference 2). Further, by using an organic semiconductor material that can be manufactured by a wet process such as printing or coating under atmospheric pressure, a display with excellent productivity and a very low cost can be realized.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-190001
[Non-Patent Document 1]
Advanced Material 2002 2002 No. 2 page 99 (Review)
[0008]
[Non-Patent Document 2]
SID'02 Digest p57
[0009]
[Problems to be solved by the invention]
However, the conventional organic TFT element has a problem in that the carrier mobility is low, the ON current is small, and the drain bias and gate bias necessary for driving are increased. In order to reduce the drive bias by using an organic semiconductor material having low carrier mobility, for example, an effect can be obtained by shortening the channel length of the element. However, it is complicated to accurately manufacture a TFT element having a small channel length. And a high manufacturing cost is required.
[0010]
The present invention has been made in view of the above circumstances, and an object thereof is to provide an organic TFT element in which a driving bias is reduced and a high ON current can be obtained by a simple manufacturing method.
[0011]
[Means for Solving the Problems]
The above configuration of the present invention is as follows.
1) The organic semiconductor layer connecting the source electrode and the drain electrode contains metal fine particles that are insulated from at least one of the electrodes when no electric field is applied, and the organic semiconductor layer has the metal fine particles dispersed therein. the organic thin film transistor component solution or dispersion of the organic semiconductor material Ru is formed by coated (However, it is not the metal fine particles are silicon particles.)
,
2) The organic thin film transistor element according to 1), wherein the metal fine particles and the organic semiconductor layer form a sea-island structure,
3) An organic thin film transistor element in which, in an organic semiconductor layer that connects a source electrode and a drain electrode, metal fine particles that are in an insulating state with at least one of the electrodes when an electric field is not applied, the organic semiconductor layer includes: a gate insulating film or support member, the organic thin-film transistor element in which the metal fine particles is a layer made of the organic semiconductor material after being coating is characterized in that it is formed by coated (however, the fine metal particles are silicon particles Never.)
,
4) a gate electrode provided through the gate insulating layer and the organic semiconductor layer, any one of the fine metal particles, characterized in that it is formed by joining the gate insulating layer 1) to 3) Organic thin-film transistor element as described in
5) The organic thin film transistor element according to any one of 1) to 4), wherein an average particle diameter of the metal fine particles is 1 μm or less ,
Thus it is achieved.
[0012]
That is, the present inventor reduces the effective channel length by forming a conductive region in an insulating state with at least one of the electrodes when an electric field is not applied in the organic semiconductor layer, thereby reducing the element carrier. The inventors have considered that the mobility can be improved, and have reached the present invention.
[0013]
The present invention will be described in detail below.
An organic thin film transistor element 1 has a source electrode 2 and a drain electrode 3 connected by an organic semiconductor channel (organic semiconductor layer) 4 on a support 7 as shown in a configuration example in FIG. A top gate type having a gate electrode 5 through a layer 6, and a source electrode 2 and a drain electrode 3 having a gate electrode 5 on a support 7 and connected by an organic semiconductor channel 4 through a gate insulating layer 6. The bottom gate type having
[0014]
The organic thin film transistor element 1 of the present invention has a conductive region 8 in an insulating state with at least one of the electrodes when an electric field is not applied in the organic semiconductor layer 4 connecting the source electrode 2 and the drain electrode 3. Features.
[0015]
The form of the conductive region 8 is schematically shown in FIG.
The conductive region 8 of the present invention has various forms as shown in FIG. 2 as long as it is in an insulated state (to ensure the insulation state of both) when at least one of the source electrode 2 and the drain electrode 3 is not applied. Can take.
[0016]
For example, a conductive region patterned after forming a thin film as shown in FIG. 2D may be used, but from the viewpoint of simplification of the process, it is preferable to apply a dispersion of conductive fine particles.
[0017]
Examples of the conductive fine particles used in the present invention include those made of a conductive polymer and metal fine particles. Examples of the conductive polymer include conductive polyaniline, conductive polypyrrole, conductive polythiophene, a complex of polyethylene dioxythiophene and polystyrene sulfonic acid. As metal fine particles, platinum, gold, silver, nickel, chromium, copper, iron, tin, antimony lead, tantalum, indium, palladium, tellurium, rhenium, iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin oxide, etc. 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 mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide mixture And lithium / aluminum mixtures.
[0018]
Metal fine particles are preferable, and metals having a work function of 4.5 to 5.7 eV, such as gold, platinum, and silver, are preferable.
[0019]
The particle diameter of the conductive fine particles is preferably 1 μm or less, more preferably 5 to 50 nm.
[0020]
2 (a) to (c), (e), and (f) are formed by dispersing conductive fine particles in a solution or dispersion of a semiconductor material, coating and drying the semiconductor layer. The semiconductor material may be applied after the dispersion of conductive fine particles is applied. The conductive region may be formed using a sea-island structure formed by dispersing a solution or dispersion of a conductive material in an incompatible solvent. Furthermore, the sea-island structure of the conductive region / organic semiconductor material may be formed using a dispersion obtained by dissolving the organic semiconductor material in an incompatible solvent. FIG. 2F shows an example of a top gate type.
[0021]
In particular, it is preferable that the conductive fine particles are bonded to the gate insulating film, and a larger effect can be obtained by forming the conductive fine particles fused to the gate insulating film.
[0022]
Known organic semiconductor materials are used, preferably π-conjugated materials such as polypyrrole, poly (N-substituted pyrrole), poly (3-substituted pyrrole), poly (3,4-disubstituted pyrrole), etc. Polypyrroles, polythiophene, poly (3-substituted thiophene), poly (3,4-disubstituted thiophene), polythiophenes such as polybenzothiophene, polyisothianaphthenes such as polyisothianaphthene, polychenylene vinylene, etc. Of polychenylene vinylene, poly (p-phenylene vinylene) such as poly (p-phenylene vinylene), polyaniline, poly (N-substituted aniline), poly (3-substituted aniline), poly (2,3-substituted) Aniline), polyacetylenes such as polyacetylene, polydiacetylene, etc. Polyazenes such as lydiaacetylene, polyazulene, polypyrenes such as polypyrene, polycarbazoles such as polycarbazole and poly (N-substituted carbazole), polyselenophenes such as polyselenophene, polyfurans such as polyfuran and polybenzofuran , Poly (p-phenylene) s such as poly (p-phenylene), polyindoles such as polyindole, polypyridazines such as polypyridazine, naphthacene, pentacene, hexacene, heptacene, dibenzopentacene, tetrabenzopentacene, pyrene, Polybenzones such as dibenzopyrene, chrysene, perylene, coronene, terylene, obalene, quaterrylene, and circumanthracene, and some of the carbons of polyacenes are atoms such as N, S, and O, and carbonyl groups. Derivatives substituted with functional groups (triphenodioxazine, triphenodithiazine, hexacene-6,15-quinone, etc.), polymers such as polyvinyl carbazole, polyphenylene sulfide, polyvinylene sulfide, and the like described in JP-A-11-195790 Polycyclic condensates and the like can be used.
[0023]
Further, for example, α-sexual thiophene α, ω-dihexyl-α-sexual thiophene, α, ω-dihexyl-α-kinkethiophene, α, ω-bis (α, which is a thiophene hexamer having the same repeating unit as those polymers. Oligomers such as 3-butoxypropyl) -α-sexithiophene and styrylbenzene derivatives can also be preferably used.
[0024]
Further, metal phthalocyanines such as copper phthalocyanine and fluorine-substituted copper phthalocyanine described in JP-A-11-251601, naphthalene 1,4,5,8-tetracarboxylic acid diimide, N, N′-bis (4-trifluoromethylbenzyl) Along with naphthalene 1,4,5,8-tetracarboxylic acid diimide, N, N′-bis (1H, 1H-perfluorooctyl), N, N′-bis (1H, 1H-perfluorobutyl) and N, N′- Dioctylnaphthalene 1,4,5,8-tetracarboxylic acid diimide derivatives, naphthalene 2,3,6,7 tetracarboxylic acid diimides and other naphthalene tetracarboxylic acid diimides, and anthracene 2,3,6,7-tetracarboxylic acid Anthracene tetracarboxylic acid diimides such as diimides Condensed ring tetracarboxylic acids such as diimides Examples include diimides, fullerenes such as C ₆₀ , C ₇₀ , C ₇₆ , C ₇₈ , and C ₈₄ , carbon nanotubes such as SWNT, merocyanine dyes, and dyes such as hemicyanine dyes.
[0025]
Among these π-conjugated materials, thiophene, vinylene, chelenylene vinylene, phenylene vinylene, p-phenylene, a substituent thereof, or two or more of these are used as a repeating unit, and the number n of the repeating units is 4 to 4 At least 1 selected from the group consisting of an oligomer of 10 or a polymer in which the number n of repeating units is 20 or more, a condensed polycyclic aromatic compound such as pentacene, fullerenes, condensed ring tetracarboxylic diimides, and metal phthalocyanine Species are preferred.
[0026]
Other organic semiconductor materials include tetrathiafulvalene (TTF) -tetracyanoquinodimethane (TCNQ) complex, bisethylenetetrathiafulvalene (BEDTTTTF) -perchloric acid complex, BEDTTTTF-iodine complex, TCNQ-iodine complex. Organic molecular complexes such as can also be used. Furthermore, (sigma) conjugated polymers, such as polysilane and polygermane, and organic-inorganic hybrid material as described in Unexamined-Japanese-Patent No. 2000-260999 can also be used.
[0027]
In the present invention, for example, a material having a functional group such as acrylic acid, acetamide, dimethylamino group, cyano group, carboxyl group, nitro group, benzoquinone derivative, tetracyanoethylene, and tetracyanoquinodimethane are used in the organic semiconductor layer. And materials that can accept electrons, such as derivatives thereof, materials that have functional groups such as amino groups, triphenyl groups, alkyl groups, hydroxyl groups, alkoxy groups, and phenyl groups, substituted amines such as phenylenediamine , So-called doping, containing materials that serve as donors of electrons such as anthracene, anthracene, benzoanthracene, substituted benzoanthracene, pyrene, substituted pyrene, carbazole and its derivatives, tetrathiafulvalene and its derivatives, etc. Processing Good.
[0028]
The doping means introducing an electron-donating molecule (acceptor) or an electron-donating molecule (donor) into the thin film as a dopant. Accordingly, the doped thin film is a thin film containing the condensed polycyclic aromatic compound and the dopant. A well-known thing can be employ | adopted as a dopant used for this invention.
[0029]
Although there is no restriction | limiting in particular as a film thickness of an organic-semiconductor layer, Generally 1 micrometer or less, Especially 10-300 nm is preferable.
[0030]
In the present invention, the material for forming the source electrode 2, the drain electrode 3, and the gate electrode 5 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 oxide / 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, mug Cium / copper mixture, magnesium / silver mixture, magnesium / aluminum mixture, magnesium / indium mixture, aluminum / aluminum oxide mixture, lithium / aluminum mixture, etc. are used, especially platinum, gold, silver, copper, aluminum, indium, ITO and carbon are preferred. Alternatively, a known conductive polymer whose conductivity is improved by doping or the like, for example, conductive polyaniline, conductive polypyrrole, conductive polythiophene, a complex of polyethylenedioxythiophene and polystyrenesulfonic acid, or the like is also preferably used. Among them, those having low electrical resistance at the contact surface with the semiconductor layer are preferable.
[0031]
As a method for forming an electrode, a method for forming an electrode using a known photolithographic method or a lift-off method, using a conductive thin film formed by a method such as vapor deposition 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. Alternatively, a conductive polymer solution or dispersion, or a conductive fine particle dispersion may be directly patterned by ink jetting, or may be formed from a coating film by lithography or laser ablation. Furthermore, 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 relief printing, intaglio printing, planographic printing, or screen printing can also be used.
[0032]
Although various insulating films can be used as the gate insulating layer 6, an inorganic oxide film having a high relative dielectric constant is particularly preferable. Inorganic oxides include silicon oxide, aluminum oxide, tantalum oxide, titanium oxide, tin oxide, vanadium oxide, barium strontium titanate, barium zirconate titanate, lead zirconate titanate, lead lanthanum titanate, strontium titanate, Examples thereof include barium titanate, barium magnesium fluoride, bismuth titanate, strontium bismuth titanate, strontium bismuth tantalate, bismuth tantalate niobate, and yttrium trioxide. Of these, silicon oxide, aluminum oxide, tantalum oxide, and titanium oxide are preferable. Inorganic nitrides such as silicon nitride and aluminum nitride can also be suitably used.
[0033]
Examples of the method for forming the film include a vacuum process, a molecular beam epitaxial growth method, an ion cluster beam method, a low energy ion beam method, an ion plating method, a CVD method, a sputtering method, an atmospheric pressure plasma method, and a spray process. Wet processes such as coating methods, spin coating methods, blade coating methods, dip coating methods, casting methods, roll coating methods, bar coating methods, die coating methods, and other wet processes such as printing and ink jet patterning methods, etc. Can be used depending on the material.
[0034]
The wet process is a method of applying and drying a liquid in which fine particles of inorganic oxide are dispersed in an arbitrary organic solvent or water using a dispersion aid such as a surfactant as required, or an oxide precursor, for example, A so-called sol-gel method in which a solution of an alkoxide body is applied and dried is used.
[0035]
Among these, the atmospheric pressure plasma method is preferable.
The method for forming an insulating film by plasma film formation under atmospheric pressure is a process in which a reactive gas is discharged under atmospheric pressure or a pressure near atmospheric pressure to excite reactive gas to form a thin film on a substrate. The method is described in JP-A-11-61406, JP-A-11-133205, JP-A-2000-121804, 2000-147209, 2000-185362, etc. (hereinafter also referred to as atmospheric pressure plasma method). Accordingly, a highly functional thin film can be formed with high productivity.
[0036]
In addition, as the organic compound film, polyimide, polyamide, polyester, polyacrylate, photo radical polymerization type, photo cation polymerization type photo curable resin, or a copolymer containing an acrylonitrile component, polyvinyl phenol, polyvinyl alcohol, novolac resin, Also, cyanoethyl pullulan or the like can be used.
[0037]
As the method for forming the organic compound film, the wet process is preferable.
An inorganic oxide film and an organic oxide film can be laminated and used together. The thickness of these insulating films is generally 50 nm to 3 μm, preferably 100 nm to 1 μm.
[0038]
The support 7 is made of glass or a flexible resin sheet. For example, a plastic film can be used as the sheet. Examples of the plastic film include polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polyethersulfone (PES), polyetherimide, polyetheretherketone, polyphenylene sulfide, polyarylate, polyimide, polycarbonate (PC), Examples thereof include films made of cellulose triacetate (TAC), cellulose acetate propionate (CAP), and the like. Thus, by using a plastic film, the weight can be reduced as compared with the case of using a glass substrate, the portability can be improved, and the resistance to impact can be improved.
[0039]
【Example】
Example 1
While stirring the aqueous solution of chloroauric acid, dimethylethanolamine was added little by little to prepare an aqueous dispersion 1 of gold fine particles having an average particle diameter of 20 nm.
[0040]
Next, after preparing a chloroform solution of a regioregular body (manufactured by Aldrich) of poly (3-hexylthiophene), which was well purified by a chelate method so that the contents of Zn and Ni were 10 ppm or less, the aqueous dispersion 1 When added to and stirred, some of the gold fine particles were mixed in the chloroform phase. The chloroform phase was dispensed, and further purified by repeating mixing and stirring with ultrapure water and dispensing 5 times to obtain a chloroform dispersion 2.
[0041]
A thermal oxide film having a thickness of 2000 mm was formed on a Si wafer having a specific resistance of 0.01 Ω · cm. The dispersion 2 was applied onto a thermal oxide film using an applicator, and chloroform was dried, followed by heat treatment at 50 ° C. for 30 minutes in an N ₂ gas replacement atmosphere. At this time, the film thickness of the semiconductor layer composed of poly (3-hexylthiophene) and gold fine particles was 30 nm. On top of this, gold having a thickness of 150 nm was deposited using a mask, and source and drain electrodes having a channel length L = 20 μm and a channel width W = 4 mm were formed to obtain an organic thin film transistor element 1.
[0042]
The organic thin film transistor element 1 exhibited good operating characteristics of a p-channel enhancement type FET when driven with a Si substrate as a gate electrode.
[0043]
Example 2
A thermal oxide film having a thickness of 2000 mm was formed on a Si wafer having a specific resistance of 0.01 Ω · cm. The aqueous dispersion 1 was applied onto a thermal oxide film using an applicator and dried, followed by heat treatment at 180 ° C. for 15 minutes. As a result, gold fine particles were fused on the thermal oxide film. This was thoroughly washed with ultrapure water and subjected to ozone treatment by UV light irradiation.
[0044]
Next, a chloroform solution of a poly (3-hexylthiophene) regioregular body (manufactured by Aldrich), which is well purified by a chelate method so that the Zn and Ni contents are 10 ppm or less, is prepared. The applied gold fine particles were coated on the deposited gold fine particles using an applicator, dried chloroform, and then heat-treated at 50 ° C. for 30 minutes in an N ₂ gas replacement atmosphere. At this time, the average film thickness of poly (3-hexylthiophene) was 30 nm. On top of this, gold having a thickness of 150 nm was deposited using a mask to form source and drain electrodes having a channel length L = 20 μm and a channel width W = 4 mm, thereby obtaining an organic thin film transistor element 2.
[0045]
This organic thin film transistor element 2 exhibited good operating characteristics of a p-channel enhancement type FET when driven with a Si substrate as a gate electrode.
[0046]
Example 3
An organic thin film transistor element 3 was produced in the same manner as in Example 1 except that the aqueous dispersion 1 was replaced with the following aqueous dispersion 2. The p-channel enhancement type FET showed good operating characteristics.
[0047]
<Preparation of aqueous dispersion 2>
While stirring the aqueous solution of chloroplatinic acid, dimethylethanolamine was added little by little to prepare an aqueous dispersion 2 of platinum fine particles having an average particle diameter of 20 nm.
[0048]
Comparative Example A thermal oxide film having a thickness of 2000 mm was formed on a Si wafer having a specific resistance of 0.01 Ω · cm. A chloroform solution of a poly (3-hexylthiophene) regioregular body (manufactured by Aldrich), which is well purified by a chelate method so that the content of Zn and Ni is 10 ppm or less, is prepared. After drying with chloroform, heat treatment was performed at 50 ° C. for 30 minutes in an N ₂ gas replacement atmosphere. At this time, the average film thickness of poly (3-hexylthiophene) was 30 nm. On top of this, gold having a thickness of 150 nm was deposited using a mask to form source and drain electrodes having a channel length L = 20 μm and a channel width W = 4 mm to obtain a comparative organic thin film transistor element.
[0049]
The OFF current and the ON current of the organic thin film transistor element fabricated as described above are the circuit configuration shown in FIG. The results of comparison under conditions are shown below.
[0050]

[0051]
【The invention's effect】
As demonstrated in Examples, according to the organic thin film transistor element of the present invention, a high ON current can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of an organic thin film transistor element.
FIG. 2 is a diagram showing a form of a conductive region.
FIG. 3 is a schematic diagram of a transistor characteristic evaluation circuit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Organic thin-film transistor element 2 Source electrode 3 Drain electrode 4 Organic-semiconductor layer 5 Gate electrode 6 Gate insulating layer 7 Support body 8 Conductive region

Claims (5)

The organic semiconductor layer connecting the source electrode and the drain electrode contains metal fine particles that are insulated from at least one of the electrodes when an electric field is not applied, and the organic semiconductor layer is an organic semiconductor in which the metal fine particles are dispersed. the organic thin film transistor component solution or dispersion of the material, characterized in Rukoto formed is coated. (However, it is not the metal fine particles are silicon particles.)   2. The organic thin film transistor element according to claim 1, wherein the metal fine particles and the organic semiconductor layer form a sea-island structure. The organic semiconductor layer connecting the source electrode and the drain electrode, an organic thin film transistor component metal particles in at least one the insulation state of the electrode is contained when no electric field is applied, the organic semiconductor layer, a gate insulating on a membrane or support, the organic thin-film transistor element in which a layer made of the organic semiconductor material after the metal fine particles are coating is characterized in that it is formed by coated. (However, the metal fine particles are not silicon particles.) The organic semiconductor layer and a gate electrode provided through the gate insulating layer, according to claim 1, wherein the metal fine particles are characterized by being formed by joining the gate insulating layer Organic thin-film transistor element.   5. The organic thin film transistor element according to claim 1, wherein an average particle diameter of the metal fine particles is 1 μm or less.

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