WO2009084780A1 - Novel organic passivation layer and organic thin film transistor device using it - Google Patents
Novel organic passivation layer and organic thin film transistor device using it Download PDFInfo
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- WO2009084780A1 WO2009084780A1 PCT/KR2008/003156 KR2008003156W WO2009084780A1 WO 2009084780 A1 WO2009084780 A1 WO 2009084780A1 KR 2008003156 W KR2008003156 W KR 2008003156W WO 2009084780 A1 WO2009084780 A1 WO 2009084780A1
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- Prior art keywords
- thin film
- passivation layer
- film transistor
- organic
- organic thin
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- 238000002161 passivation Methods 0.000 title claims abstract description 169
- 239000010409 thin film Substances 0.000 title claims abstract description 103
- 239000000203 mixture Substances 0.000 claims abstract description 39
- 238000000034 method Methods 0.000 claims abstract description 38
- 230000008569 process Effects 0.000 claims abstract description 29
- 229920003169 water-soluble polymer Polymers 0.000 claims abstract description 27
- 125000002887 hydroxy group Chemical group [H]O* 0.000 claims abstract description 25
- -1 aldehyde compound Chemical class 0.000 claims abstract description 9
- 229920001744 Polyaldehyde Polymers 0.000 claims abstract description 7
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 88
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 87
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 21
- 239000000126 substance Substances 0.000 claims description 19
- 239000010408 film Substances 0.000 claims description 14
- 239000000758 substrate Substances 0.000 claims description 13
- 150000001299 aldehydes Chemical class 0.000 claims description 12
- 125000000732 arylene group Chemical group 0.000 claims description 10
- 125000002947 alkylene group Chemical group 0.000 claims description 8
- 238000000576 coating method Methods 0.000 claims description 7
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000007641 inkjet printing Methods 0.000 claims description 5
- 239000002798 polar solvent Substances 0.000 claims description 5
- 238000004528 spin coating Methods 0.000 claims description 5
- 125000001424 substituent group Chemical group 0.000 claims description 5
- ZNZYKNKBJPZETN-WELNAUFTSA-N Dialdehyde 11678 Chemical group N1C2=CC=CC=C2C2=C1[C@H](C[C@H](/C(=C/O)C(=O)OC)[C@@H](C=C)C=O)NCC2 ZNZYKNKBJPZETN-WELNAUFTSA-N 0.000 claims description 4
- IEQIEDJGQAUEQZ-UHFFFAOYSA-N phthalocyanine Chemical compound N1C(N=C2C3=CC=CC=C3C(N=C3C4=CC=CC=C4C(=N4)N3)=N2)=C(C=CC=C2)C2=C1N=C1C2=CC=CC=C2C4=N1 IEQIEDJGQAUEQZ-UHFFFAOYSA-N 0.000 claims description 4
- 238000007650 screen-printing Methods 0.000 claims description 4
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- 150000001298 alcohols Chemical class 0.000 claims description 3
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- 239000002184 metal Substances 0.000 claims description 3
- 229920002098 polyfluorene Polymers 0.000 claims description 3
- 229920000123 polythiophene Polymers 0.000 claims description 3
- 125000000923 (C1-C30) alkyl group Chemical group 0.000 claims description 2
- 239000002202 Polyethylene glycol Substances 0.000 claims description 2
- 229920000265 Polyparaphenylene Polymers 0.000 claims description 2
- XBDYBAVJXHJMNQ-UHFFFAOYSA-N Tetrahydroanthracene Natural products C1=CC=C2C=C(CCCC3)C3=CC2=C1 XBDYBAVJXHJMNQ-UHFFFAOYSA-N 0.000 claims description 2
- GTDPSWPPOUPBNX-UHFFFAOYSA-N ac1mqpva Chemical compound CC12C(=O)OC(=O)C1(C)C1(C)C2(C)C(=O)OC1=O GTDPSWPPOUPBNX-UHFFFAOYSA-N 0.000 claims description 2
- 125000000217 alkyl group Chemical group 0.000 claims description 2
- 238000007598 dipping method Methods 0.000 claims description 2
- 125000002485 formyl group Chemical group [H]C(*)=O 0.000 claims description 2
- YTVNOVQHSGMMOV-UHFFFAOYSA-N naphthalenetetracarboxylic dianhydride Chemical compound C1=CC(C(=O)OC2=O)=C3C2=CC=C2C(=O)OC(=O)C1=C32 YTVNOVQHSGMMOV-UHFFFAOYSA-N 0.000 claims description 2
- 229920001223 polyethylene glycol Polymers 0.000 claims description 2
- 229920002635 polyurethane Polymers 0.000 claims description 2
- 239000004814 polyurethane Substances 0.000 claims description 2
- IFLREYGFSNHWGE-UHFFFAOYSA-N tetracene Chemical compound C1=CC=CC2=CC3=CC4=CC=CC=C4C=C3C=C21 IFLREYGFSNHWGE-UHFFFAOYSA-N 0.000 claims description 2
- 230000005684 electric field Effects 0.000 claims 1
- 239000004973 liquid crystal related substance Substances 0.000 claims 1
- 125000005582 pentacene group Chemical group 0.000 claims 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 abstract description 16
- 229910052760 oxygen Inorganic materials 0.000 abstract description 16
- 239000001301 oxygen Substances 0.000 abstract description 16
- 239000010410 layer Substances 0.000 description 150
- 235000019422 polyvinyl alcohol Nutrition 0.000 description 83
- SXRSQZLOMIGNAQ-UHFFFAOYSA-N Glutaraldehyde Chemical compound O=CCCCC=O SXRSQZLOMIGNAQ-UHFFFAOYSA-N 0.000 description 42
- 238000001723 curing Methods 0.000 description 33
- 239000000243 solution Substances 0.000 description 23
- 238000006243 chemical reaction Methods 0.000 description 14
- 229920000642 polymer Polymers 0.000 description 12
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- 125000003172 aldehyde group Chemical group 0.000 description 10
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- 230000008859 change Effects 0.000 description 9
- 230000009467 reduction Effects 0.000 description 9
- 230000000903 blocking effect Effects 0.000 description 8
- 238000004519 manufacturing process Methods 0.000 description 8
- SLIUAWYAILUBJU-UHFFFAOYSA-N pentacene Chemical compound C1=CC=CC2=CC3=CC4=CC5=CC=CC=C5C=C4C=C3C=C21 SLIUAWYAILUBJU-UHFFFAOYSA-N 0.000 description 8
- 230000004888 barrier function Effects 0.000 description 7
- 239000003795 chemical substances by application Substances 0.000 description 7
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 6
- FFUAGWLWBBFQJT-UHFFFAOYSA-N hexamethyldisilazane Chemical compound C[Si](C)(C)N[Si](C)(C)C FFUAGWLWBBFQJT-UHFFFAOYSA-N 0.000 description 5
- 239000004065 semiconductor Substances 0.000 description 5
- 230000007246 mechanism Effects 0.000 description 4
- 238000002360 preparation method Methods 0.000 description 4
- 239000002904 solvent Substances 0.000 description 4
- KFZMGEQAYNKOFK-UHFFFAOYSA-N Isopropanol Chemical compound CC(C)O KFZMGEQAYNKOFK-UHFFFAOYSA-N 0.000 description 3
- 239000007864 aqueous solution Substances 0.000 description 3
- 239000003125 aqueous solvent Substances 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 238000004132 cross linking Methods 0.000 description 3
- 230000003247 decreasing effect Effects 0.000 description 3
- 239000010931 gold Substances 0.000 description 3
- 230000000977 initiatory effect Effects 0.000 description 3
- 239000011259 mixed solution Substances 0.000 description 3
- 230000035515 penetration Effects 0.000 description 3
- 239000000377 silicon dioxide Substances 0.000 description 3
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 2
- DHKHKXVYLBGOIT-UHFFFAOYSA-N acetaldehyde Diethyl Acetal Natural products CCOC(C)OCC DHKHKXVYLBGOIT-UHFFFAOYSA-N 0.000 description 2
- 125000002777 acetyl group Chemical class [H]C([H])([H])C(*)=O 0.000 description 2
- JOSWYUNQBRPBDN-UHFFFAOYSA-P ammonium dichromate Chemical compound [NH4+].[NH4+].[O-][Cr](=O)(=O)O[Cr]([O-])(=O)=O JOSWYUNQBRPBDN-UHFFFAOYSA-P 0.000 description 2
- 239000011651 chromium Substances 0.000 description 2
- 229910052681 coesite Inorganic materials 0.000 description 2
- 229910052906 cristobalite Inorganic materials 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000005669 field effect Effects 0.000 description 2
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 2
- 229910052737 gold Inorganic materials 0.000 description 2
- 239000012212 insulator Substances 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
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- 229910052682 stishovite Inorganic materials 0.000 description 2
- 238000001029 thermal curing Methods 0.000 description 2
- 229910052905 tridymite Inorganic materials 0.000 description 2
- 125000006835 (C6-C20) arylene group Chemical group 0.000 description 1
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 1
- 238000005033 Fourier transform infrared spectroscopy Methods 0.000 description 1
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- 238000003848 UV Light-Curing Methods 0.000 description 1
- 241000532412 Vitex Species 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 125000004653 anthracenylene group Chemical group 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 125000004432 carbon atom Chemical group C* 0.000 description 1
- 235000009347 chasteberry Nutrition 0.000 description 1
- 150000001845 chromium compounds Chemical class 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
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- 230000002498 deadly effect Effects 0.000 description 1
- 239000003599 detergent Substances 0.000 description 1
- SWXVUIWOUIDPGS-UHFFFAOYSA-N diacetone alcohol Natural products CC(=O)CC(C)(C)O SWXVUIWOUIDPGS-UHFFFAOYSA-N 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 238000005538 encapsulation Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 125000000524 functional group Chemical group 0.000 description 1
- 238000001879 gelation Methods 0.000 description 1
- 231100000086 high toxicity Toxicity 0.000 description 1
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- 125000004957 naphthylene group Chemical group 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 125000004433 nitrogen atom Chemical group N* 0.000 description 1
- 239000012044 organic layer Substances 0.000 description 1
- 239000003960 organic solvent Substances 0.000 description 1
- 238000000059 patterning Methods 0.000 description 1
- 125000000843 phenylene group Chemical group C1(=C(C=CC=C1)*)* 0.000 description 1
- 238000000016 photochemical curing Methods 0.000 description 1
- ZWLUXSQADUDCSB-UHFFFAOYSA-N phthalaldehyde Chemical compound O=CC1=CC=CC=C1C=O ZWLUXSQADUDCSB-UHFFFAOYSA-N 0.000 description 1
- 229920003229 poly(methyl methacrylate) Polymers 0.000 description 1
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L59/00—Compositions of polyacetals; Compositions of derivatives of polyacetals
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
- C08K5/00—Use of organic ingredients
- C08K5/04—Oxygen-containing compounds
- C08K5/07—Aldehydes; Ketones
-
- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L61/00—Compositions of condensation polymers of aldehydes or ketones; Compositions of derivatives of such polymers
- C08L61/02—Condensation polymers of aldehydes or ketones only
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D129/00—Coating compositions based on homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Coating compositions based on hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Coating compositions based on derivatives of such polymers
- C09D129/02—Homopolymers or copolymers of unsaturated alcohols
- C09D129/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
-
- 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]
Definitions
- the present invention relates to a process for preparing novel organic passivation layer to provide stability of organic thin film transistor devices, which can be applied as operation switching devices of flexible displays for next generation, and manufacturing of organic thin film transistors by using the same. More specifically, the invention relates to a novel process for improving the properties of passivation thin film employed in technical field of forming passivation layer via solution process; compositions for preparing organic passivation layer with reduced penetration of water and oxygen
- passivation thin film was prepared by forming a multi- layer comprising organic layers and inorganic layers by using a vacuum device (J. Vac. Sci. Technol. B 1 Vol. 20, No. 3, 958, 2002, IBM Research Institute and Barix System of Vitex) .
- organic substances which enable solution process are used for passivation layer itself in order to realize all organic devices (UV curable Resin, Appl . Phys. Lett 83, 1644, 2003, Polyvinyl Alcohol, Appl. Phys. Lett 88, 073519, 2006, PMMA, self encapsulation, Adv. Mater. 18, 2900, 2006) .
- the device itself for incorporating an organic passivation layer itself is comprised of organic substances, the organic passivation cannot be formed by using organic solvent.
- water-soluble polymeric materials which do not deteriorate the properties of the organic substances in the device or impair the thin layer, are widely used as an organic passivation thin film.
- Representative examples include water- soluble polyvinylalcohol (PVA) and acrylate resin.
- An organic thin film transistor to which applied is an organic passivation layer primarily exhibits barrier effect against oxygen and water from outside.
- water or oxygen is continuously introduced via minute pinholes or cracks in the passivation layer to induce deterioration of properties of the device.
- the water-soluble polymer is used as a solution in an aqueous solvent due to processability to form a passivation layer, the layer of water-soluble polymer exhibits noticeably poor effect as a water barrier, while it shows the effect as an oxygen barrier to some extent.
- polyvinyl alcohol still contains hydroxyl groups (-0H) , so that the property as a water barrier may be insufficient, and Cr 5+ ion generated during the curing process is deadly harmful to environment .
- the present invention provides a composition for preparing a passivation layer for an organic thin film transistor, which comprises an additive being reactive with hydroxyl groups of water-soluble polymer to cause removal of the hydroxyl groups (which is vulnerable in blocking moisture) , while employing novel curing process wherein cross-linking between the water-soluble polymers is achieved.
- the composition for preparing a passivation layer for an organic thin film transistor can noticeably overcome the problem of disadvantageous device properties.
- the present invention provides an organic thin film transistor which comprises a novel organic passivation layer prepared by using said composition for preparing a passivation layer for an organic thin film transistor, and a display device which comprises said organic thin film transistor.
- the process for forming an organic passivation layer according to the invention does not require usual photoinitiator nor ultraviolet radiation for curing, but the curing reaction proceeds thermally to provide an organic passivation layer.
- the organic passivation layer itself can be formed by various coating processes, since a solution process can be applied thereto.
- the organic thin film transistor comprising an organic passivation layer formed from novel composition for preparing organic passivation layer according to the present invention exhibits enhanced properties of blocking oxygen or moisture, and thereby noticeably overcoming the disadvantageous properties of the device produced therefrom. Thus, reliability of an organic thin film transistor and that of a display device comprising the same can be improved.
- the present invention relates to a composition for preparing a passivation layer for an organic thin film transistor, which comprises water-soluble polymer comprising hydroxyl group; and aldehyde compound selected from dialdehydes and polyaldehydes .
- the invention also relates to an organic thin film transistor comprising an organic passivation layer formed from said composition, and a display device comprising said organic thin film transistor.
- composition for preparing a passivation layer for an organic thin film transistor comprises water-soluble polymer comprising hydroxyl group, and aldehyde compound selected from dialdehydes and polyaldehydes, or a mixture thereof, and it may further comprise solvent.
- solvent polar solvent with low solubility for the organic active layer of the organic thin film transistor is desirable, in order not to cause damage thereof.
- Polar solvent selected from water or alcohols may be used, water or a mixture of water and alcohol being more preferable .
- the water-soluble polymer contained in the composition can be selected from water-soluble polyurethane containing hydroxyl group, polyvinyl alcohol, copolymers of polyvinyl alcohol, water-soluble acrylate resin, polyethylene glycol, or mixtures thereof .
- Polyvinyl alcohol or polyvinyl alcohol copolymer is preferably used.
- the water-soluble polymer preferably has weight average molecular weight of 5,000 to 1,000,000, and more preferably has weight average solubility of 1 to 50% in polar solvent selected from water and alcohols. If the content of the water- soluble polymer is less than 1% by weight, the effect may be insufficient.
- the viscosity of the composition may be abruptly increased and the solubility of the resin may be lowered. If the molecular weight of the water-soluble polymer is less than 5000, properties as passivation layer would be poor, while if it is more than 1,000,000, the solubility and processibility of the polymer would be unfavorable .
- the aldehyde contained in the composition works as a curing agent, which reacts with hydroxyl groups of the water- soluble polymer to cure the organic passivation polymer film.
- the aldehyde can enhance the effect of the organic passivation layer to block moisture and oxygen.
- Water-soluble aldehydes for example dialdehydes or polyaldehydes (which contain two or more aldehyde groups) , or mixtures thereof may be preferably used.
- the aldehyde can be selected from the compounds represented by Chemical Formula (1) or mixtures thereof.
- Group X of Chemical Formula (1) may be further substituted by a functional group or a substituent to improve water-solubility .
- X is selected from a linear or branched (C1-C50) alkylene, (C3-C20) arylene,
- the arylene may be C6-C20 arylene, such as phenylene, naphthylene, anthrylene.
- a carbon atom of the arylene may be replaced by a nitrogen atom.
- the compound of Chemical Formula (1) comprises at least two, specifically from two to ten (2-10) aldehyde groups. The more aldehyde groups, the more the cross-linking reaction with hydroxyl groups. Since too many aldehyde groups may accelerate gelling of the composition itself, it is desirable to control the number of aldehyde groups within the above-mentioned range.
- dialdehydes represented by Chemical Formula (2) or mixtures thereof can be employed as the aldehyde .
- CHO-X-CHO wherein, X is selected from a linear or branched (Cl ⁇ C50)alkylene, (C3-C20) arylene, (C3-20) ar (C1-C30) alkylene, (Cl ⁇ C30)alkyl (C3-C20) arylene, or substituents formed by linkages thereof.
- Speficic dialdehyde compounds include glutaraldehyde and phthaldialdehyde , but are not restricted thereto.
- the aldehyde content contained in the composition for preparing a passivation layer according to the present invention preferably is 1 to 30% by weight of the water- soluble polymer. If the content is less than 1% by weight, the effect of addition of aldehyde may be insufficient. On the other hand, if the content is more than 30% by weight, composition itself may be subjected to gelation, and a uniform thin film to be applied as an organic passivation layer might be difficult to be prepared.
- the present invention also provides an organic thin film transistor which comprises an organic passivation layer prepared by using a composition for preparing a passivation layer of an organic thin film transistor as described above.
- the organic thin film transistor according to the invention comprises a substrate, a gate electrode, an organic insulating film, an organic active layer, a source/drain electrode and an organic passivation layer, and the organic passivation layer is formed by using the composition for preparing a passivation layer for an organic thin film transistor according to the invention, which comprises hydroxyl-containing water-soluble polymer and aldehyde compound selected from dialdehyde and polyaldehyde .
- the organic passivation layer may be formed by coating the composition for preparing a passivation layer for an organic thin film transistor, via a process selected from spin-coating, inkjet printing, roll coating, screen printing and dipping.
- the thickness of the layer preferably is from 0.3 ⁇ m to 5 ⁇ m. If it is less than 0.3 ⁇ m, the effect of blocking permeation of moisture or oxygen may be undesirably poor. On the other hand, if it is more than 5 ⁇ m, improvement in the effect of blocking permeation of moisture or oxygen is not significant, while the thickness would be obstacles for high integration of an organic thin film transistor and preparation of ultra-thin film. Thus, it is desirable to control the thickness within the above-mentioned range.
- the structure of the organic passivation layer which was prepared by using a composition for preparing a passivation layer for a organic thin film transistor according to the present invention was confirmed by NMR, FT-IR, or the like.
- the surface property of the organic passivation layer after curing was evaluated by means of measuring water-contact angle .
- the organic active layer can be formed from pentacene, tetracene, oligo-thiophene, polythiophene, metal phthalocyanine, polyphenylene, polyvinylenephenylene, polyfluorene, C60, phenylenetetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, fluorinated phthalocyanine, or derivatives thereof.
- the organic thin film transistor in which a novel organic passivation layer has been formed according to the present invention exhibits electron mobility in the range of 0.01 to 10 cm 2 /Vs. The range is a common value of electron mobility of conventional organic thin film transistors, and indicates appropriate performance as an organic thin film transistor.
- Fig. 1 shows the mechanism of curing the novel organic passivation layer according to the invention, which comprises reaction between polyvinyl alcohol and glutaraldehyde .
- Fig. 2 shows the change of surface water-contact angle after curing the organic passivation layer.
- Polyvinyl alcohol (PVA) as a water-soluble polymer of powder type (which is commonly used for an organic passivation layer of an organic thin film transistor) , is dissolve in water to prepare an aqueous polyvinyl alcohol solution.
- PVA solution glutaraldehyde (GA) dissolved in water is added in a concentraion of 1-30% by weight on the basis of polyvinyl alcohol to prepare a mixed solution (this is the solution for the organic passivation layer) .
- the organic passivation layer is formed by means of spin coating, inkjet printing, screen printing, or the like, immediately after preparing the solution for organic passivation layer.
- hydroxyl group of polyvinyl alcohol and aldehyde group of glutaraldehyde undergo condensation to eliminate water and form an acetal . Since chemical bonds are formed between the polymeric chains of polyvinyl alcohol, cured polyvinyl alcohol thin film of network structure can be eventually obtained with the hydroxyl groups removed.
- Measurement of water-contact angle is a measure to determine the surface energy of the thin film, as well as to evaluate whether the cured thin film has been well prepared according to the process of the present invention.
- the organic passivation layer according to the present invention is applicable to any transistor such as top gate, bottom gate, top contact or bottom contact type, regardless of the structure of the transistor. It is applicable no matter which organic semiconductor is used, whether it is a vapor- deposition type such as oligothiophene or pentacene, or a solution type polymer such as polythiophene or polyfluorene derivatives.
- the organic passivation layer can be formed by a variety of processes such as spin coating, inkjet printing, roll coating and screen printing. Since the curing process is carried out by means of heat, the problem of damage on the organic semiconductor can be avoided as compared to a photocuring process . Since thermal curing is carried out at a moderate temperature (such as about 100 "C) , the present invention can be applied to an organic thin film transistor comprising a flexible substrate.
- Fig. 3 shows an example of the organic thin film transistors according to the present invention. It is a cross- sectional view of the structure of an organic thin film transistor of bottom gate top-contact type to which an organic passivation layer prepared according to novel curing process of the invention has been applied.
- a gate electrode (2) is formed on a substrate (1) , and an insulating film (3) is formed thereon. Then organic active layer (4) is formed, and a source/drain electrode (5) is formed by using metal.
- an organic passivation layer (6) is formed by using aqueous solution containing water-soluble polymer (e.g. polyvinyl alcohol (PVA) ) (which is widely used as an organic passivation layer) and glutaraldehyde (GA) .
- PVA polyvinyl alcohol
- GA glutaraldehyde
- a substrate wherein SiO 2 as an insulator is placed on a Si wafer is treated with a surface treating agent, HMDS (1, 1, 1, 3 , 3 , 3-hexamethyldisilazane) in order to enhance the surface properties of the insulator, and pentacene having excellent properties as an organic semiconductor layer is then vacuum vapor-deposited.
- HMDS 1, 1, 3 , 3 , 3-hexamethyldisilazane
- gold (Au) is vapor-deposited by using a shadow mask to prepare an organic thin film transistor.
- solution of glutaraldehyde and water-soluble polymer containing hydroxyl groups is spin-coated to form thin film.
- the organic passivation layer is subjected to annealing for removing water in a vacuum oven, and manufacture of an organic thin film transistor wherein the organic passivation layer has been applied by using the novel curing process is completed.
- the electric properties of the organic thin film transistor prepared according to the invention with applying the novel curing process were evaluated by measuring the voltage-drain current property versus gate voltage after applying the passivation layer by using E5272 equipment from Agilent Technology, and mobility of the organic thin film transistor over time.
- Fig. 4 shows current-voltage (I-V) curve of the organic thin film transistor device before and after applying the passivation layer: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
- PVA novel organic passivation layer
- PVA+GA conventional organic passivation layer
- Fig. 5 shows the mobility change of the organic thin film transistor by the lapse of time: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
- PVA+GA novel organic passivation layer
- PVA+GA conventional organic passivation layer
- Fig. 1 illustrates curing mechanism of the novel organic passivation film according to the present invention.
- Fig. 2 illustrates change of surface water-contact angle after curing the novel organic passivation film according to the present invention.
- Fig. 3 is a cross-sectional view showing the structure of an organic thin film transistor to which a novel organic passivation film according to the invention has been applied.
- Fig. 4 shows current-voltage (I-V) curve of an organic thin film transistor device before and after the passivation layer: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
- PVA+GA novel organic passivation layer
- PVA conventional organic passivation layer
- Fig. 5 shows the mobility change of the organic thin film transistor by the lapse of time: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
- PVA+GA novel organic passivation layer
- PVA conventional organic passivation layer
- Powdery polyvinyl alcohol (PVA) (weight average molecular weight 8,000-10,000) polymer was dissolved in water in a concentration of 10% by weight to prepare aqueous polyvinyl alcohol solution.
- the completely dissolved aqueous polyvinyl alcohol solution was filtered by using a membrane filter for aqueous solution having 0.45 ⁇ m of pore size.
- glutaraldehyde (GA) was added in a concentration of 8.25%, 47.37% and 90% by weight, respectively, on the basis of polyvinyl alcohol (PVA) , to prepare polyvinyl alcohol (PVA) -glutaraldehyde mixed solution.
- polyvinyl alcohol (PVA) passivation solution containing 8.25% by weight of glutaraldehyde was prepared.
- the polyvinyl alcohol solution containing glutaraldehyde was spin-coated to obtain thin film with the thickness of about 0.5 ⁇ m, which was then cured at 50 ° C for 2 minutes, and at 100 ° C for 1 hour. In order to remove residual moisture, the film was dried in a vacuum oven at 50 ° C for 12 hours, to obtain the finally cured organic passivation layer.
- Fig. 1 shows the reaction (curing) mechanism of polyvinylalcohol polymer containing hydroxyl groups with glutaraldehyde. Of the finally cured polymer, removed are hydroxyl groups by curing reaction. This results in reduction of moisture transmission, in other word, enhancement of barrier property against moisture.
- the passivation layer according to the invention exhibit far excellent properties in protecting the device properties of organic thin film transistor, as compared to conventional polyvinyl alcohol thin film which does not undergo curing.
- the water-contact angle of the polyvinyl alcohol passivation layer is hardly measurable, since the layer is hydrophilic due to hydroxyl groups being present on the surface. This indicates that moisture is ready to penetrate the passivation layer.
- the water-contact angle is about 50.04° in case of polyvinyl alcohol passivation layer which was cured by means of glutaraldehyde. This means that moisture penetration is relatively suppressed.
- a substrate wherein 60 nm of silicon dioxide is mounted on a p-doped silicon wafer was used.
- the structure of transistor to which the passivation layer would be applied was top-contact and bottom-gate type. Since cleanliness of the substrate is one of the most important factors in manufacturing electronic devices, the substrate was subjected to ultrasonic washing with detergent, distilled water, acetone and isopropyl alcohol and thorough drying in an oven. In order to enhance the surface properties of the well-cleansed substrate, the substrate was coated by using HMDS treating agent, and dried at 120 ° C. On SiO 2 treated with HMDS, pentacene as organic semiconductor was vapor-deposited under vacuum of IxIO "6 torr with a thickness of 50 nm.
- PVA polyvinyl alcohol
- glutaraldehyde prepared from Example 1
- curing was carried out at 50 ° C for 2 minutes and at 100 ° C for 1 hour.
- the transistor was dried in a vacuum oven at 50 ° C for 12 hours to finally incorporate a cured organic passivation layer (thickeness 0.5 ⁇ m) to the organic thin film transistor.
- the properties of the device thus manufactured were measured before and after applying the organic passivation layer, and the change of properties were evaluated.
- Electric properties of the device was measured by drain voltage-drain current versus gate voltage, and gate voltage-drain current versus drain voltage by using E5272 equipment from Agilent Technologies. Properties were evaluated according to the following current-voltage formula in the saturation region on the basis of the above measurements.
- V ⁇ is threshold voltage
- V gs is gate voltage applied
- ⁇ field effect charge mobility
- W and L is the width and length of the channel
- C is capacitance of the insulating film.
- Fig. 4 shows the transfer curve demonstrating the change of properties of a thin film transistor to which general polyvinyl alcohol (PVA) organic passivation layer is applied, and a thin film transistor to which polyvinylalcohol organic passivation layer cured by glutaraldehyde (PVA+GA) is applied, before and after applying the passivation layers.
- PVA general polyvinyl alcohol
- PVA+GA polyvinylalcohol organic passivation layer cured by glutaraldehyde
- the organic thin film transistor device to which a polyvinyl alcohol (PVA) organic passivation layer containing glutaraldehyde was applied showed 0.236 cm 2 /Vs of mobility before incorporating the organic passivation layer, while it showed 0.232 cm 2 /Vs of mobility after applying the polyvinyl alcohol (PVA) passivation layer cured by glutaraldehyde contained therein, showing the result of only 1.7% decrease of the mobility. This is the result of noticeable decrease of deterioration of properties, as compared to the device to which an organic passivation layer without glutaraldehyde was incorporated.
- PVA polyvinyl alcohol
- Fig. 5 shows the result of change of mobility over time in the pentacene organic thin film transistor to which a polyvinyl alcohol organic passivation layer containing glutaraldehyde as curing agent (PVA+GA) was incorporated, and the transistor to which polyvinyl alcohol organic passivation layer without containing glutaraldehyde (PVA) was applied.
- PVA+GA polyvinyl alcohol organic passivation layer containing glutaraldehyde as curing agent
- PVA polyvinyl alcohol organic passivation layer without containing glutaraldehyde
- the result showed only 5.93% reduction of the property in case of the device to which novel organic passivation layer was applied (wherein polyvinyl alcohol had been cured by adding glutaraldehyde as curing agent according to the invention), from 0.236 cm 2 /Vs of initial property to 0.222 cm 2 /Vs.
- This is an excellent property wherein the deterioration of device property over time is decreased to one-fourth (1/4) or less as compared to conventional organic passivation film.
- hydrophilicity is reduced by curing reaction of the organic passivation layer due to glutaraldehyde in the device according to the present invention, as compared to the device using a conventional organic polyvinyl passivation layer, and the film density of the passivation layer itself is increased to result in reduction of free volume, from the viewpoint of shelf life of long period of the organic thin film transistor over time, likewise from the viewpoint of difference of deterioration properties after applying the initial organic passivation layer.
- the present invention relates to a process for preparing novel organic passivation layers with enhanced ability to block moisture and oxygen to ensure long-term reliability of organic thin film transistor devices (OTFT) , which can be applied as operation switching devices of flexible displays and organic electronic devices for next generation, and application thereof to organic thin film transistors.
- OFT organic thin film transistor devices
- the process according to the invention can provide improved device life of organic thin film transistors.
- Organic substances to be employed for organic passivation layer is dissolved in solvent which would not give damage to the underlaid layer of the organic passivation layer.
- water-soluble polymer dissolved in aqueous solvent is employed as the passivation layer.
- Such polymer has poor ability to block moisture, being liable to deterioration of properties owing to moisture penetrated to the device.
- hydroxyl groups possessed by the aqueous polymer used as an organic passivation layer undergo chemical reaction with aldehyde curing agent such as glutaraldehyde to cause curing (bonding with the polymer chains through chemical reaction) .
- aldehyde curing agent such as glutaraldehyde
- the film density of the organic passivation layer itself and free volume are reduced to improve the properties of the passivation layer.
- deterioration of properties such as coating ability, surface roughness and thin film uniformity did not occur. Removal of hydroxyl groups from the passivation layer itself caused decrease in affinity to water, as compared to conventional organic passivation layer, thereby resulting in enhanced properties for preventing moisture and oxygen.
- the novel organic passivation layer was actually applied to an organic thin film transistor, the deterioration of device property of the organic thin film transistor was only 5.93% reduction as compared to the initial value of the property. This is a prominent result of more than 4 times as compared to conventional organic passivation film which was not cured.
- the present process is advantageous in that it does not need to use chromium compound having high toxicity.
- the patterning process of the organic passivation layer can be easily carried out by inkjet printing or the like.
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Abstract
The present invention relates to a composition for preparing a passivation layer for an organic thin film transistor, which comprises water soluble polymer comprising hydroxyl group; and aldehyde compound selected from dialdehydes and polyaldehydes. The invention also relates to an organic thin film transistor comprising an organic passivation layer formed from said composition, and a display device comprising said organic thin film transistor. The present invention relates to a technique which should be essentially applied to a process for applying an organic thin film transistor (OTFT) to an array device. By improving the property of the organic passivation layer to block moisture and oxygen, device reliability of the organic thin film transistor can be enhanced.
Description
[DESCRIPTION]
[invention Title]
NOVEL ORGANIC PASSIVATION LAYER AND ORGANIC THIN FILM TRANSISTOR DEVICE USING IT
[Technical Field]
The present invention relates to a process for preparing novel organic passivation layer to provide stability of organic thin film transistor devices, which can be applied as operation switching devices of flexible displays for next generation, and manufacturing of organic thin film transistors by using the same. More specifically, the invention relates to a novel process for improving the properties of passivation thin film employed in technical field of forming passivation layer via solution process; compositions for preparing organic passivation layer with reduced penetration of water and oxygen
(which is troublesome in view of deteriorate device properties) and minimized damage of the device, and enhanced environmental friendliness, as compared to conventional process for curing polyvinyl alcohol; and organic thin film transistors prepared by using them.
[Background Art]
Techniques of employing passivation thin film have been
applied to organic thin film transistors (OTFT) which are applicable as operation switching devices in flexible displays for next generation, or the like. Conventionally, passivation thin film was prepared by forming a multi- layer comprising organic layers and inorganic layers by using a vacuum device (J. Vac. Sci. Technol. B1 Vol. 20, No. 3, 958, 2002, IBM Research Institute and Barix System of Vitex) . Recently, however, organic substances which enable solution process are used for passivation layer itself in order to realize all organic devices (UV curable Resin, Appl . Phys. Lett 83, 1644, 2003, Polyvinyl Alcohol, Appl. Phys. Lett 88, 073519, 2006, PMMA, self encapsulation, Adv. Mater. 18, 2900, 2006) .
Since the device itself for incorporating an organic passivation layer itself is comprised of organic substances, the organic passivation cannot be formed by using organic solvent. Thus, water-soluble polymeric materials, which do not deteriorate the properties of the organic substances in the device or impair the thin layer, are widely used as an organic passivation thin film. Representative examples include water- soluble polyvinylalcohol (PVA) and acrylate resin. Though such substances for organic passivation layers have surface property with the underlaid organic substances being non-polar, the process for forming the passivation layer was processed in
an aqueous solution by dissolving them in a polar solvent such as water, in order to prevent damage of the underlaid layer.
An organic thin film transistor to which applied is an organic passivation layer primarily exhibits barrier effect against oxygen and water from outside. However, water or oxygen is continuously introduced via minute pinholes or cracks in the passivation layer to induce deterioration of properties of the device. Though the water-soluble polymer is used as a solution in an aqueous solvent due to processability to form a passivation layer, the layer of water-soluble polymer exhibits noticeably poor effect as a water barrier, while it shows the effect as an oxygen barrier to some extent.
Thus, it is necessary to develop novel organic passivation layers which can enhance the effect of water- soluble polymer as a water barrier and eventually suppress the deterioration of device properties, and techniques to apply them.
When using polyvinyl alcohol as an organic passivation layer, a method of adding a small amount of ammonium dichromate (NH4Cr2O7) as a photoinitiator to improve subsequent processes and to enhance the barrier property, and then curing the layer by UV irradiation has been conventionally known.
Though being cured by using photoinitiator as above, polyvinyl alcohol still contains hydroxyl groups (-0H) , so
that the property as a water barrier may be insufficient, and Cr5+ ion generated during the curing process is deadly harmful to environment .
[Disclosure]
[Technical Problem]
The present invention provides a composition for preparing a passivation layer for an organic thin film transistor, which comprises an additive being reactive with hydroxyl groups of water-soluble polymer to cause removal of the hydroxyl groups (which is vulnerable in blocking moisture) , while employing novel curing process wherein cross-linking between the water-soluble polymers is achieved. Eventually, the composition for preparing a passivation layer for an organic thin film transistor can noticeably overcome the problem of disadvantageous device properties.
In addition, the present invention provides an organic thin film transistor which comprises a novel organic passivation layer prepared by using said composition for preparing a passivation layer for an organic thin film transistor, and a display device which comprises said organic thin film transistor.
[Technical Solution]
The present inventors performed intensive studies to overcome the technical problems described above, and found that, if a water-soluble polymer substance containing hydroxyl group dissolved in an aqueous solvent is employed with dialdehyde (containing two aldehyde groups) or polyaldehyde (containing three or more aldehyde groups) , or a mixture thereof, as a novel curing agent, reaction of the hydroxyl groups with the aldehyde groups provides acetal, and cross- linking between the water-soluble polymers by means of two or more aldehyde groups proceeds to form an organic passivation layer; and through the stage of curing the organic passivation layer, an organic passivation layer for an organic thin film transistor with enhanced property of blocking oxygen and moisture can be obtained, which noticeably breaks through the disadvantageous properties of the device produced therefrom.
The process for forming an organic passivation layer according to the invention does not require usual photoinitiator nor ultraviolet radiation for curing, but the curing reaction proceeds thermally to provide an organic passivation layer. Further, the organic passivation layer itself can be formed by various coating processes, since a solution process can be applied thereto. The organic thin film transistor comprising an organic passivation layer formed from novel composition for preparing organic passivation layer
according to the present invention exhibits enhanced properties of blocking oxygen or moisture, and thereby noticeably overcoming the disadvantageous properties of the device produced therefrom. Thus, reliability of an organic thin film transistor and that of a display device comprising the same can be improved.
Now, the present invention is described in more detail. The technical or scientific terms used herein are understood as they are by a person having ordinary skill in the art to which the present invention belongs, if not specifically defined otherwise.
Repeated descriptions regarding the technical constitution and effect which are identical to those of conventional techniques are omitted herein. The present invention relates to a composition for preparing a passivation layer for an organic thin film transistor, which comprises water-soluble polymer comprising hydroxyl group; and aldehyde compound selected from dialdehydes and polyaldehydes . The invention also relates to an organic thin film transistor comprising an organic passivation layer formed from said composition, and a display device comprising said organic thin film transistor.
The composition for preparing a passivation layer for an organic thin film transistor according to the invention
comprises water-soluble polymer comprising hydroxyl group, and aldehyde compound selected from dialdehydes and polyaldehydes, or a mixture thereof, and it may further comprise solvent. As the solvent, polar solvent with low solubility for the organic active layer of the organic thin film transistor is desirable, in order not to cause damage thereof. Polar solvent selected from water or alcohols may be used, water or a mixture of water and alcohol being more preferable .
The water-soluble polymer contained in the composition can be selected from water-soluble polyurethane containing hydroxyl group, polyvinyl alcohol, copolymers of polyvinyl alcohol, water-soluble acrylate resin, polyethylene glycol, or mixtures thereof . Polyvinyl alcohol or polyvinyl alcohol copolymer is preferably used. The water-soluble polymer preferably has weight average molecular weight of 5,000 to 1,000,000, and more preferably has weight average solubility of 1 to 50% in polar solvent selected from water and alcohols. If the content of the water- soluble polymer is less than 1% by weight, the effect may be insufficient. On the other hand, if it is over 50% by weight, the viscosity of the composition may be abruptly increased and the solubility of the resin may be lowered. If the molecular weight of the water-soluble polymer is less than 5000, properties as passivation layer would be poor, while if it is
more than 1,000,000, the solubility and processibility of the polymer would be unfavorable .
The aldehyde contained in the composition works as a curing agent, which reacts with hydroxyl groups of the water- soluble polymer to cure the organic passivation polymer film.
By removing the hydroxyl group and decreasing the free volume of the thin layer of organic passivation layer, the aldehyde can enhance the effect of the organic passivation layer to block moisture and oxygen. Water-soluble aldehydes, for example dialdehydes or polyaldehydes (which contain two or more aldehyde groups) , or mixtures thereof may be preferably used. Specifically the aldehyde can be selected from the compounds represented by Chemical Formula (1) or mixtures thereof. Group X of Chemical Formula (1) may be further substituted by a functional group or a substituent to improve water-solubility .
[Chemical Formula 1]
X- (CHO)n
In Chemical Formula (1) , X is selected from a linear or branched (C1-C50) alkylene, (C3-C20) arylene,
(C3~20)ar (C1-C30) alkylene, (C1-C30) alkyl (C3-C20) arylene, or substituents formed by linkages thereof, and n is an integer from 2 to 10.
The arylene may be C6-C20 arylene, such as phenylene,
naphthylene, anthrylene. A carbon atom of the arylene may be replaced by a nitrogen atom. The compound of Chemical Formula (1) comprises at least two, specifically from two to ten (2-10) aldehyde groups. The more aldehyde groups, the more the cross-linking reaction with hydroxyl groups. Since too many aldehyde groups may accelerate gelling of the composition itself, it is desirable to control the number of aldehyde groups within the above-mentioned range.
More specifically, dialdehydes represented by Chemical Formula (2) or mixtures thereof can be employed as the aldehyde .
[Chemical Formula 2]
CHO-X-CHO wherein, X is selected from a linear or branched (Cl~C50)alkylene, (C3-C20) arylene, (C3-20) ar (C1-C30) alkylene, (Cl~C30)alkyl (C3-C20) arylene, or substituents formed by linkages thereof.
Speficic dialdehyde compounds include glutaraldehyde and phthaldialdehyde , but are not restricted thereto. The aldehyde content contained in the composition for preparing a passivation layer according to the present invention preferably is 1 to 30% by weight of the water- soluble polymer. If the content is less than 1% by weight, the effect of addition of aldehyde may be insufficient. On the
other hand, if the content is more than 30% by weight, composition itself may be subjected to gelation, and a uniform thin film to be applied as an organic passivation layer might be difficult to be prepared. The present invention also provides an organic thin film transistor which comprises an organic passivation layer prepared by using a composition for preparing a passivation layer of an organic thin film transistor as described above.
The organic thin film transistor according to the invention comprises a substrate, a gate electrode, an organic insulating film, an organic active layer, a source/drain electrode and an organic passivation layer, and the organic passivation layer is formed by using the composition for preparing a passivation layer for an organic thin film transistor according to the invention, which comprises hydroxyl-containing water-soluble polymer and aldehyde compound selected from dialdehyde and polyaldehyde .
The organic passivation layer may be formed by coating the composition for preparing a passivation layer for an organic thin film transistor, via a process selected from spin-coating, inkjet printing, roll coating, screen printing and dipping. The thickness of the layer preferably is from 0.3 μm to 5 μm. If it is less than 0.3 μm, the effect of blocking permeation of moisture or oxygen may be undesirably poor. On
the other hand, if it is more than 5 μm, improvement in the effect of blocking permeation of moisture or oxygen is not significant, while the thickness would be obstacles for high integration of an organic thin film transistor and preparation of ultra-thin film. Thus, it is desirable to control the thickness within the above-mentioned range.
The structure of the organic passivation layer which was prepared by using a composition for preparing a passivation layer for a organic thin film transistor according to the present invention was confirmed by NMR, FT-IR, or the like.
The surface property of the organic passivation layer after curing was evaluated by means of measuring water-contact angle .
The organic active layer can be formed from pentacene, tetracene, oligo-thiophene, polythiophene, metal phthalocyanine, polyphenylene, polyvinylenephenylene, polyfluorene, C60, phenylenetetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, fluorinated phthalocyanine, or derivatives thereof. The organic thin film transistor in which a novel organic passivation layer has been formed according to the present invention exhibits electron mobility in the range of 0.01 to 10 cm2/Vs. The range is a common value of electron mobility of conventional organic thin film transistors, and indicates
appropriate performance as an organic thin film transistor.
Now, preferable examples of the present invention are described in detail by referring to the appended drawings. The examples are provided to fully deliver the idea of invention to persons having ordinary skill in the art. Thus, the present invention is not restricted to those examples, but can be specified in other features. The length, thickness, or the like of the layers or areas in the drawings may be exaggerated for the sake of convenience and understanding. Identical reference numbers throughout the specification indicate identical constituents.
Fig. 1 shows the mechanism of curing the novel organic passivation layer according to the invention, which comprises reaction between polyvinyl alcohol and glutaraldehyde . Fig. 2 shows the change of surface water-contact angle after curing the organic passivation layer.
The process for curing the novel organic passivation layer according to the invention is now described. Polyvinyl alcohol (PVA) , as a water-soluble polymer of powder type (which is commonly used for an organic passivation layer of an organic thin film transistor) , is dissolve in water to prepare an aqueous polyvinyl alcohol solution. To the aqueous PVA solution, glutaraldehyde (GA) dissolved in water is added in a concentraion of 1-30% by weight on the basis of polyvinyl
alcohol to prepare a mixed solution (this is the solution for the organic passivation layer) . Since the reaction with glutaraldehyde rapidly progresses in general, the organic passivation layer is formed by means of spin coating, inkjet printing, screen printing, or the like, immediately after preparing the solution for organic passivation layer. As can be seen in Fig. 1, upon preparing the organic passivation layer, hydroxyl group of polyvinyl alcohol and aldehyde group of glutaraldehyde undergo condensation to eliminate water and form an acetal . Since chemical bonds are formed between the polymeric chains of polyvinyl alcohol, cured polyvinyl alcohol thin film of network structure can be eventually obtained with the hydroxyl groups removed.
Measurement of water-contact angle is a measure to determine the surface energy of the thin film, as well as to evaluate whether the cured thin film has been well prepared according to the process of the present invention.
As referring to the results of water-contact angle shown in Fig. 2, it is found that polyvinyl alcohol (PVA) shows very small water contact angle due to existence of hydroxyl groups on the polymer surface, which implies that PVA has high water solubility and that moisture can be easily penetrated to the passivation layer. On the other hand, in case of a cured organic passivation layer, it is thought that penetration of
moisture is inhibited due to removal of hydroxyl groups through the curing mechanism and decrease of the free volume of the organic passivation layer itself by virtue of reaction between the polymer chains. As can be seen from Fig. 2, the water-contact angle of the PVA passivation layer can be hardly measured. However, the PVA passivation layer cured by glutaraldehyde exhibits about 50.04° of water-contact angle.
The organic passivation layer according to the present invention is applicable to any transistor such as top gate, bottom gate, top contact or bottom contact type, regardless of the structure of the transistor. It is applicable no matter which organic semiconductor is used, whether it is a vapor- deposition type such as oligothiophene or pentacene, or a solution type polymer such as polythiophene or polyfluorene derivatives.
The organic passivation layer can be formed by a variety of processes such as spin coating, inkjet printing, roll coating and screen printing. Since the curing process is carried out by means of heat, the problem of damage on the organic semiconductor can be avoided as compared to a photocuring process . Since thermal curing is carried out at a moderate temperature (such as about 100 "C) , the present invention can be applied to an organic thin film transistor comprising a flexible substrate.
Fig. 3 shows an example of the organic thin film transistors according to the present invention. It is a cross- sectional view of the structure of an organic thin film transistor of bottom gate top-contact type to which an organic passivation layer prepared according to novel curing process of the invention has been applied.
As can be seen from Fig. 3, a gate electrode (2) is formed on a substrate (1) , and an insulating film (3) is formed thereon. Then organic active layer (4) is formed, and a source/drain electrode (5) is formed by using metal.
Thereafter, an organic passivation layer (6) is formed by using aqueous solution containing water-soluble polymer (e.g. polyvinyl alcohol (PVA) ) (which is widely used as an organic passivation layer) and glutaraldehyde (GA) . An exemplary process for preparing an organic thin film transistor which employs an organic passivation layer formed by novel curing process for improving the properties of a passivation layer (that is, to block moisture and oxygen) suggested by the present invention is now described by referring to a case using a Si substrate as a gate electrode.
A substrate wherein SiO2 as an insulator is placed on a Si wafer is treated with a surface treating agent, HMDS (1, 1, 1, 3 , 3 , 3-hexamethyldisilazane) in order to enhance the surface properties of the insulator, and pentacene having
excellent properties as an organic semiconductor layer is then vacuum vapor-deposited. In order to introduce a source electrode and a drain electrode, gold (Au) is vapor-deposited by using a shadow mask to prepare an organic thin film transistor. On the top of the organic thin film transistor, solution of glutaraldehyde and water-soluble polymer containing hydroxyl groups is spin-coated to form thin film.
After thermal curing, the organic passivation layer is subjected to annealing for removing water in a vacuum oven, and manufacture of an organic thin film transistor wherein the organic passivation layer has been applied by using the novel curing process is completed. The electric properties of the organic thin film transistor prepared according to the invention with applying the novel curing process were evaluated by measuring the voltage-drain current property versus gate voltage after applying the passivation layer by using E5272 equipment from Agilent Technology, and mobility of the organic thin film transistor over time.
Fig. 4 shows current-voltage (I-V) curve of the organic thin film transistor device before and after applying the passivation layer: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) . When the
conventional organic passivation layer (PVA) was applied, the result shows 15.6% reduction of mobility, while when the novel organic passivation layer (PVA+GA) was applied, it shows only about 1.7% reduction of mobility. This implies noticeable decrease of deterioration of device properties as compared to the device to which an organic passivation layer was applied without incorporation of glutaraldehyde . It is considered that curing reaction occurred between the polymer chains of the polyvinylalcohol passivation layer due to glutaraldehyde incorporated according to the present invention, and consequently, the free volume inside the organic passivation layer was reduced to improve the role of blocking moisture or oxygen at the time of applying the passivation layer.
Fig. 5 shows the mobility change of the organic thin film transistor by the lapse of time: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) . As the result of observing the characteristic change of mobility up to 500 hours, it is found that, the result showed 23.4% reduction of mobility as compared to the initial property when the conventional organic passivation layer (PVA) was applied, while it showed only about 5.93% reduction of mobility as compared to the initial property when the novel organic
passivation layer (PVA+GA) was applied according to the present invention. This is an excellent property wherein the deterioration of device property is decreased to one-fourth (1/4) or less as compared to conventional organic passivation film.
[Description of Drawings]
Fig. 1 illustrates curing mechanism of the novel organic passivation film according to the present invention. Fig. 2 illustrates change of surface water-contact angle after curing the novel organic passivation film according to the present invention.
Fig. 3 is a cross-sectional view showing the structure of an organic thin film transistor to which a novel organic passivation film according to the invention has been applied.
Fig. 4 shows current-voltage (I-V) curve of an organic thin film transistor device before and after the passivation layer: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
Fig. 5 shows the mobility change of the organic thin film transistor by the lapse of time: (a) shows the results from applying a novel organic passivation layer (PVA+GA) according
to the present invention, and (b) shows the results from applying a conventional organic passivation layer (PVA) .
description of symbols of significant parts of the drawing>
1. Substrate
2. Gate electrode
3. Insulating film
4. Organic active layer 5. Source and drain electrodes 6. Organic passivation layer
[Best Mode]
Now, the present invention is more specifically described by referring to Examples, which are provided for illustration only but are not intended to limit the scope of the invention by any means .
[Example 1] Preparation of mixed solution of polyvinylalcohol (PVA) - glutaraldehyde (GA) and cured thin film
Powdery polyvinyl alcohol (PVA) (weight average molecular weight 8,000-10,000) polymer was dissolved in water in a concentration of 10% by weight to prepare aqueous polyvinyl
alcohol solution. The completely dissolved aqueous polyvinyl alcohol solution was filtered by using a membrane filter for aqueous solution having 0.45 μm of pore size. To the solution of polyvinyl alcohol (PVA) thus filtered, glutaraldehyde (GA) was added in a concentration of 8.25%, 47.37% and 90% by weight, respectively, on the basis of polyvinyl alcohol (PVA) , to prepare polyvinyl alcohol (PVA) -glutaraldehyde mixed solution. In case of the organic passivation solution containing glutaraldehyde in a concentration of 47.35% and 90% by weight, the solution itself undergoes reaction prior to forming the thin film and transforms to gel-type, thereby causing problems to form thin film by means of spin coating or the like. Thus, in the present invention, polyvinyl alcohol (PVA) passivation solution containing 8.25% by weight of glutaraldehyde was prepared. The polyvinyl alcohol solution containing glutaraldehyde was spin-coated to obtain thin film with the thickness of about 0.5μm, which was then cured at 50°C for 2 minutes, and at 100 °C for 1 hour. In order to remove residual moisture, the film was dried in a vacuum oven at 50°C for 12 hours, to obtain the finally cured organic passivation layer.
[Comparative Example 1]
Preparation of polyvinyl alcohol (PVA) -containing solution and thin film
Same procedure as described in Example 1 was carried out but without using glutaraldehyde (GA) , to prepare polyvinyl alcohol solution and thin film.
Fig. 1 shows the reaction (curing) mechanism of polyvinylalcohol polymer containing hydroxyl groups with glutaraldehyde. Of the finally cured polymer, removed are hydroxyl groups by curing reaction. This results in reduction of moisture transmission, in other word, enhancement of barrier property against moisture. Thus the passivation layer according to the invention exhibit far excellent properties in protecting the device properties of organic thin film transistor, as compared to conventional polyvinyl alcohol thin film which does not undergo curing.
Referring to the results of water-contact angle shown in Fig. 2, the water-contact angle of the polyvinyl alcohol passivation layer is hardly measurable, since the layer is hydrophilic due to hydroxyl groups being present on the surface. This indicates that moisture is ready to penetrate the passivation layer. On the other hand, the water-contact angle is about 50.04° in case of polyvinyl alcohol passivation layer which was cured by means of glutaraldehyde. This means that moisture penetration is relatively suppressed.
[Example 2] Manufacture of organic thin film transistor
A substrate wherein 60 nm of silicon dioxide is mounted
on a p-doped silicon wafer was used. The structure of transistor to which the passivation layer would be applied was top-contact and bottom-gate type. Since cleanliness of the substrate is one of the most important factors in manufacturing electronic devices, the substrate was subjected to ultrasonic washing with detergent, distilled water, acetone and isopropyl alcohol and thorough drying in an oven. In order to enhance the surface properties of the well-cleansed substrate, the substrate was coated by using HMDS treating agent, and dried at 120°C. On SiO2 treated with HMDS, pentacene as organic semiconductor was vapor-deposited under vacuum of IxIO"6 torr with a thickness of 50 nm. Temperature of the substrate, which significantly affects crystallization of pentacene, was kept constant at 90°C . Finally, gold was vapor-deposited thereon by using a shadow mask with a thickeness of 60 nm to form a source and a drain electrode.
On the pentacene organic thin film transistor, polyvinyl alcohol (PVA) passivation solution containing 8.25% by weight of glutaraldehyde (prepared from Example 1) was spin-coated to form a passivation layer, and curing was carried out at 50 °C for 2 minutes and at 100 °C for 1 hour. In order to remove residual moisture, the transistor was dried in a vacuum oven at 50 °C for 12 hours to finally incorporate a cured organic passivation layer (thickeness 0.5 μm) to the organic thin film
transistor.
[Comparative Example 2] Preparation of organic thin film transistor
According to the same procedure as described in Example 2, an organic thin film transistor was manufactured, but incorporating a passivation layer by using the passivation solution simply containing polyvinyl alcohol (PVA) without glutaraldehyde from Comparative Example 1.
The properties of the device thus manufactured were measured before and after applying the organic passivation layer, and the change of properties were evaluated. Electric properties of the device was measured by drain voltage-drain current versus gate voltage, and gate voltage-drain current versus drain voltage by using E5272 equipment from Agilent Technologies. Properties were evaluated according to the following current-voltage formula in the saturation region on the basis of the above measurements.
I WC1 lds =^i> .Vf
21
In the formula, Vτ is threshold voltage, Vgs is gate voltage applied, μ is field effect charge mobility, W and L is the width and length of the channel, C is capacitance of the insulating film. The threshold voltage is determined as the
gate voltage wherein Ids is 0, from the graph of V ds versus Vgs,
and the field effect charge mobility is calculated from the
slope of the graph of Λ/ ds versus Vg,s •
Fig. 4 shows the transfer curve demonstrating the change of properties of a thin film transistor to which general polyvinyl alcohol (PVA) organic passivation layer is applied, and a thin film transistor to which polyvinylalcohol organic passivation layer cured by glutaraldehyde (PVA+GA) is applied, before and after applying the passivation layers. The device formed from organic passivation layer employing only polyvinyl alcohol (PVA) showed the mobility of 0.372 cm2/Vs before incorporating the organic passivation layer, but the mobility
(0.314 cm2/Vs) was reduced by 15.6% after incorporating the polyvinyl alcohol (PVA) passivation layer. This is usual phenomenon of deterioration of device property after incorporating an organic passivation layer, likely occurring in the process of using water-soluble polymers as considering damage of organic semiconductor. In other word, it is found that crystallinity and orientation of pentacene were damaged by the organic passivation solvent. The organic thin film transistor device to which a polyvinyl alcohol (PVA) organic passivation layer containing glutaraldehyde was applied showed 0.236 cm2/Vs of mobility before incorporating the organic passivation layer, while it
showed 0.232 cm2/Vs of mobility after applying the polyvinyl alcohol (PVA) passivation layer cured by glutaraldehyde contained therein, showing the result of only 1.7% decrease of the mobility. This is the result of noticeable decrease of deterioration of properties, as compared to the device to which an organic passivation layer without glutaraldehyde was incorporated. Thus, it is considered that curing reaction between the polymer chains of the polyvinylalcohol passivation layer occurred by virtue of glutaraldehyde incorporated according to the present invention, and consequently the free volume inside the organic passivation layer was reduced to enhance the role of blocking moisture or oxygen when applying the passivation layer to the device.
Fig. 5 shows the result of change of mobility over time in the pentacene organic thin film transistor to which a polyvinyl alcohol organic passivation layer containing glutaraldehyde as curing agent (PVA+GA) was incorporated, and the transistor to which polyvinyl alcohol organic passivation layer without containing glutaraldehyde (PVA) was applied. As the result of observing the characteristic change of mobility up to 500 hours, it is found that, the result showed 23.4% reduction of mobility in case of the device to which only conventional polyvinyl alcohol was applied as an organic passivation layer, from 0.35 cm2/Vs of initial mobility to
0.268 cm2/Vs after that time. On the other hand, it is found that, the result showed only 5.93% reduction of the property in case of the device to which novel organic passivation layer was applied (wherein polyvinyl alcohol had been cured by adding glutaraldehyde as curing agent according to the invention), from 0.236 cm2/Vs of initial property to 0.222 cm2/Vs. This is an excellent property wherein the deterioration of device property over time is decreased to one-fourth (1/4) or less as compared to conventional organic passivation film. This can be also interpreted that hydrophilicity is reduced by curing reaction of the organic passivation layer due to glutaraldehyde in the device according to the present invention, as compared to the device using a conventional organic polyvinyl passivation layer, and the film density of the passivation layer itself is increased to result in reduction of free volume, from the viewpoint of shelf life of long period of the organic thin film transistor over time, likewise from the viewpoint of difference of deterioration properties after applying the initial organic passivation layer.
[industrial Applicability]
The present invention relates to a process for preparing novel organic passivation layers with enhanced ability to
block moisture and oxygen to ensure long-term reliability of organic thin film transistor devices (OTFT) , which can be applied as operation switching devices of flexible displays and organic electronic devices for next generation, and application thereof to organic thin film transistors. As a novel process for improving the properties of blocking moisture and oxygen of organic passivation layers employed in technical field of forming passivation layer via solution process, the process according to the invention can provide improved device life of organic thin film transistors.
Organic substances to be employed for organic passivation layer is dissolved in solvent which would not give damage to the underlaid layer of the organic passivation layer. In general, water-soluble polymer dissolved in aqueous solvent is employed as the passivation layer. Such polymer has poor ability to block moisture, being liable to deterioration of properties owing to moisture penetrated to the device.
According to the invention, hydroxyl groups possessed by the aqueous polymer used as an organic passivation layer undergo chemical reaction with aldehyde curing agent such as glutaraldehyde to cause curing (bonding with the polymer chains through chemical reaction) . As such, the film density of the organic passivation layer itself and free volume are reduced to improve the properties of the passivation layer.
Throughout the processes for forming and curing the organic passivation layer by using aldehyde according to the present invention, deterioration of properties such as coating ability, surface roughness and thin film uniformity did not occur. Removal of hydroxyl groups from the passivation layer itself caused decrease in affinity to water, as compared to conventional organic passivation layer, thereby resulting in enhanced properties for preventing moisture and oxygen.
When the novel organic passivation layer was actually applied to an organic thin film transistor, the deterioration of device property of the organic thin film transistor was only 5.93% reduction as compared to the initial value of the property. This is a prominent result of more than 4 times as compared to conventional organic passivation film which was not cured. As compared to the process for preparing cured organic passivation layer by means of UV curing with conventional ammonium dichromate, the present process is advantageous in that it does not need to use chromium compound having high toxicity. The patterning process of the organic passivation layer can be easily carried out by inkjet printing or the like.
Practically, applying the novel technique of organic passivation according to the invention to a passivation layer of an organic thin film transistor is a completely novel
technique which has not been disclosed up to now, being essential in applying an organic thin film transistor to an actual device in the field of organic electronics for next generation. In other word, the technique is essential for improving property reliability of devices.
Claims
[CLAIMS]
[Claim l]
A composition for preparing a passivation layer for an organic thin film transistor, which comprises water-soluble polymer comprising hydroxyl group; and aldehyde compound selected from dialdehydes and polyaldehydes .
[Claim 2] A composition for preparing a passivation layer for an organic thin film transistor according to claim 1, wherein said water-soluble polymer is selected from water-soluble polyurethane containing hydroxyl group, polyvinyl alcohol, copolymers of polyvinyl alcohol, water-soluble acrylate resin, polyethylene glycol, or mixtures thereof.
[Claim 3]
A composition for preparing a passivation layer for an organic thin film transistor according to claim 2, wherein said water-soluble polymer has weight average molecular weight of 5,000 to 1,000,000, and weight average solubility of 1 to
50% in polar solvent selected from water and alcohols.
[Claim 4]
A composition for preparing a passivation layer for an organic thin film transistor according to claim 3, wherein said water-soluble polymer is polyvinyl alcohol or copolymer of polyvinyl alcohol .
[Claim 5]
A composition for preparing a passivation layer for an organic thin film transistor according to claim 1, wherein the aldehyde is selected from compounds represented by Chemical Formula (1), or mixtures thereof: [Chemical Formula 1] X- (CHO)n wherein, X is selected from a linear or branched (Cl~C50)alkylene, (C3-C20) arylene, (C3-20) ar (C1-C30) alkylene, (C1-C30) alkyl (C3-C20) arylene, or substituents formed by linkages thereof, and n is an integer from 2 to 10.
[Claim 6]
A composition for preparing a passivation layer for an organic thin film transistor according to claim 5, wherein the aldehyde is selected from dialdehyde compounds represented by Chemical Formula (2), or mixtures thereof: [Chemical Formula 2] CHO-X-CHO
wherein, X is selected from a linear or branched (Cl~C50)alkylene, (C3-C20) arylene, (C3-20) ar (C1-C30) alkylene, (Cl~C30)alkyl (C3-C20) arylene, or substituents formed by linkages thereof.
[Claim 7]
A composition for preparing a passivation layer for an organic thin film transistor according to claim 1, wherein the aldehyde constitutes from 1 to 30% by weight of the water- soluble polymer.
[Claim 8]
An organic thin film transistor comprising a substrate, a gate electrode, an organic insulating film, an organic active layer, source/drain electrodes and an organic passivation layer, wherein the organic passivation layer is formed by using the composition for preparing a passivation layer for an organic thin film transistor according to any one of claims 1 to 7.
[Claim 9]
An organic thin film transistor according to claim 8, wherein said organic passivation layer is formed by coating the composition for preparing a passivation layer for an
organic thin film transistor, via a process selected from spin-coating, inkjet printing, roll coating, screen printing and dipping.
[Claim lθ]
An organic thin film transistor according to claim 8, wherein said organic passivation layer has the thickness from
0.3 μm to 5 μm.
[Claim ll]
An organic thin film transistor according to claim 8, wherein said organic active layer is selected from pentacene, tetracene, oligo-thiophene, polythiophene , metal phthalocyanine, polyphenylene , polyvinylenephenylene, polyfluorene, C60, phenylenetetracarboxylic dianhydride, naphthalenetetracarboxylic dianhydride, fluorinated phthalocyanine, and derivatives thereof.
[Claim 12] An organic thin film transistor according to claim 11, wherein electric field mobility of the organic thin film transistor is within the range of 0.01 to 10 cm2/Vs.
[Claim 13]
A display device comprising an organic thin film transistor according to any one of claims 8 to 12.
[Claim 14] A display device comprising an organic thin film transistor according to claim 13, wherein the display device is selected from organic electroluminescent displays, electronic papers or liquid-crystal displays.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1020070139751A KR100909045B1 (en) | 2007-12-28 | 2007-12-28 | New organic protective film manufacturing method and organic thin film transistor using the same |
| KR10-2007-0139751 | 2007-12-28 |
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| Publication Number | Publication Date |
|---|---|
| WO2009084780A1 true WO2009084780A1 (en) | 2009-07-09 |
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| PCT/KR2008/003156 WO2009084780A1 (en) | 2007-12-28 | 2008-06-05 | Novel organic passivation layer and organic thin film transistor device using it |
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| EP2277944A3 (en) | 2009-07-24 | 2012-01-04 | Electronics and Telecommunications Research Institute | Composition for organic dielectric and organic thin film transistor formed using the same |
Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20050100327A (en) * | 2004-04-13 | 2005-10-18 | 인더스트리얼 테크놀로지 리서치 인스티튜트 | Multi-passivation layer structure for organic thin-film transistors and method for fabricating the same |
| KR20080040877A (en) * | 2006-11-06 | 2008-05-09 | 삼성전자주식회사 | Organic passivation composition |
-
2007
- 2007-12-28 KR KR1020070139751A patent/KR100909045B1/en not_active IP Right Cessation
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2008
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR20050100327A (en) * | 2004-04-13 | 2005-10-18 | 인더스트리얼 테크놀로지 리서치 인스티튜트 | Multi-passivation layer structure for organic thin-film transistors and method for fabricating the same |
| KR20080040877A (en) * | 2006-11-06 | 2008-05-09 | 삼성전자주식회사 | Organic passivation composition |
Non-Patent Citations (1)
| Title |
|---|
| HAN, SEUNG HOON ET AL., APPLIED PHYSICS LETTERS, vol. 88, 2006, pages 73519-01 - 73519-03, XP008067789 * |
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| KR20090071833A (en) | 2009-07-02 |
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