WO2001011700A1 - System comprising a transistor function - Google Patents

Abstract

The invention relates to a system comprising a transistor function, especially a component, comprising a gate electrode, a gate dielectric, a source electrode and a drain electrode, as well as a layer comprised of at least one charge transfer organic substance. According to the invention, the charge transfer organic substance can be electrochemically oxidized at least twice in an anodically reversible manner, or can be reduced at least twice in a cathodically reversible manner. In addition, said charge transfer organic substance is at least soluble in a solvent and has a molecular weight of up to 2000 g/mol.

Description

 description

Arrangement with transistor function

The invention relates to an arrangement, in particular a ^component with a transistor function, which has a gate electrode, a gate dielectric, a source and a dram electrode and a layer of at least one charge-transporting organic substance.

Components with a transistor function are known in a wide variety of embodiments. One of these embodiments is the type of field-effect transistor (FET). In the technology of active matrix liquid crystal displays (“Active Matrix Liquid Crystal Displays * = AM-LCDs), one embodiment has attained considerable importance is generally referred to as a thin film transistor ("Thm Film Transistor" = TFT).

In thin film transistors, silicon is usually used as the active semiconductor material in one of its manifestations, for example amorphous silicon in AM LCDs; for example, gallium arsenide can also be used. However, the production of such transistors is comparatively complex and expensive. In addition, high process temperatures that occur during manufacture limit the possible areas of use. In principle, the use of flexible film substrates would allow the production of flexible display films, but suitable films have so far not had the required temperature stability.

Thin film transistors are also known, in which organic materials are used as active semiconductor material. These transistors are usually referred to as “organic transistors ^* (OTs). Because their mode of operation is analogous to the function of conventional field-effect transistors (FETs) made of silicon, the term “organic field-effect transistors ^* (OFETs) is often used for this.

Furthermore, OTs are known in which not only the active semiconductor consists of an organic or polymeric material, but also the other components required for the function, such as electrodes and dielectric, are made up entirely or partially of organic or polymeric materials. If a component with a transistor function consists entirely of organic materials, it is referred to as an “All-Organic Thm Film Transistor”.

Organic transistors can be made on flexible substrates (plastic films). Flexible electronic circuits that can be implemented in this way can be used in a wide variety of applications, such as chip cards or smart cards, transponders and flexible displays. Organic transistors also have other advantages in terms of manufacturing costs: Since their manufacture using the simplest process technology (liquid phase processes such as

Spin coating and printing techniques) bypassing complex vacuum deposition processes, a significant cost reduction can be achieved in particular in the manufacture of simple and simple electronic circuits of low complexity.

Depending on whether positive charges (“holes”) or negative charges (“electrons”) are preferably transported in the semiconductor, p-channel transistors or n-channel transistors are present. Both versions (p-type and n-type) exist both in conventional field-effect transistors made of silicon or gallium arsenide and in organic transistors.

It is known that organic functional layers, in particular the organic semiconductors, can be applied by different deposition processes. For orga- African or polymeric materials, the rings only over a very ge ^¬ or no solubility m grouting a suitable lots agent is preferably used the method of thermal evaporation under high vacuum. The process of thermal vapor deposition is, however, comparatively complex and costly.

Application by known liquid phase processes, such as spin-on of suitable solutions or printing techniques, is much easier and less expensive. A prerequisite for liquid phase processes is sufficient solubility of the organic semiconductor materials in suitable solvents. In this case, the underlying manufacturing processes are particularly simple and therefore inexpensive.

The fact that the components do not yet have sufficient stability for practical use speaks against a commercial use of organic thin film transistors; this fact is known to the person skilled in the art (see, for example: “Applied Physics Letters”, Vol. 71 (1997), pages 3871 to 3873).

The following production methods are known for organic transistors, which relate in particular to the application of the active organic or polymeric semiconductor layer:

- vacuum deposition

Organic semiconductor materials in the form of functional molecules are often used in organic transistors, which are not soluble in suitable solvents and therefore only by vacuum deposition, i.e. Evaporation in a high vacuum, for example by thermal evaporation or by "pulsed laser deposition", can be applied (see, for example: EP-OS 0 825 657; "IEEE Electron Device Letters", Vol. 18 (1997), pages 606 to 608;

"Applied Physics Letters", Vol. 69 (1996), pages 3066 to 3068). However, these production processes are - for reasons process safety and process control and vorran ^¬ gig for cost reasons - for a mass production unsuitable.

- Application from the liquid phase with subsequent chemical conversion

Organic substances, including polymers, can be applied from the liquid phase by known processes (spin coating, printing processes). However, these are materials that do not yet have suitable semiconductor properties in soluble form. The corresponding materials with the required semiconductor properties, on the other hand, are insoluble in suitable solvents. This problem is countered by converting the soluble non-semiconducting substances into insoluble semiconductors by means of a chemical conversion process (see, for example: "Science", Vol. 270 (1995), pages 972 to 974). A disadvantage is here, however, that either aggressive and environmentally harmful process gases, such as hydrogen chloride (HC1), must be used or that toxic reaction products (elimination products) are formed in the conversion process.

- Application from a liquid phase without chemical conversion In particular semiconducting polymers can be made from solutions, i.e. by liquid phase processes such as spin coating, but the achievable transistor properties are not sufficient for practical applications. The reason for this is that so far no high molecular order levels can be achieved with semiconducting plastics. However, high molecular degrees of order are particularly advantageous for the transistor characteristic (see, for example: "Journal of Applied Physics", Vol. 75 (1994), pages 7954 to 7957).

The object of the invention is an arrangement (with transistor function) of the type mentioned with at least one charge transport erenden organic substance, that is an organic semiconductor, indicate that can be provided inexpensively forth ^¬ and good transistor characteristics, the particular ^¬ a high stability, has.

This is achieved according to the invention in that the charge-transporting organic substance is electrochemically reversibly oxidizable at least twice anodically or at least twice reversibly reducible cathodically, is soluble in at least one solvent and has a molecular weight of up to 2000 g / mol.

An organic substance of the type mentioned above, which is capable of transporting electrical charges (holes or electrons), i.e. an organic semiconductor that is p-type or n-type has a certain property profile:

• The substance has sufficient redox stability: For transporting positive charges (punctures), i.e. in the case of a p-channel transistor, the substance must be anodically reversibly oxidizable at least twice. This means that in the cyclic voltammogram, recorded at room temperature in an inert solvent, at least two chemically reversible oxidation waves occur. For the transport of negative charges (electrons), i.e. in the

In the case of an n-channel transistor, the substance must be cathodically reversibly reducible at least twice. This means that in the cyclic voltammogram, recorded at room temperature in an inert solvent, at least two chemically reversible reduction waves occur.

^• The substance has sufficient solubility in at least one solvent and is therefore suitable for liquid phase processing.

^• The substance has a molecular weight of at most 2000 g / mol. Good transistor properties are achieved when the organic semiconductor has a high degree of molecular order. This is functional Substances, the size or molecular weight of which does not exceed the stated value.

Surprisingly, it has been found that the redox stability of the charge-transporting organic substance is an essential criterion for the stability of the arrangement with transistor function. However, this stability criterion was not previously known (cf. “Synthetic Metals”, vol. 87 (1997), pages 53 to 59). The charge-transporting organic substance preferably shows in the

Cyclic voltammogram shows a reversible behavior during at least ten successive oxidation or reduction cycles.

The arrangement (with transistor function) according to the invention is also referred to as an organic transistor. This is understood to be a transistor in which the active semiconductor material consists of an organic sweet dance. The other components, such as electrodes and dielectric, can consist of organic or polymeric substances as well as inorganic substances. The organic transistor according to the invention comprises all arrangements in hybrid technology with organic-inorganic combinations.

The arrangement according to the invention is characterized in that the field effect mobility is at least 110 ^"4 cm ² / Vs. This arrangement has a layer of at least one organic semiconductor. The thickness of this layer is advantageously between 5 nm and 10 µm, preferably between 10 and 100 nm.

The organic semiconductor is advantageously an aromatic hydrocarbon, a heteroaromatic compound or a polyene compound, these substances each having at least one solubility-imparting substituent. The organic semiconductor is preferably a derivative of one of the following compounds: benzene, naphthalene, naph- thacene, pentacene, biphenyl, terphenyl, quaterphenyl, qumque-phenyl, sexiphenyl, triphenylene, chrysene, pyrene, naphthalocyanine, porphyry, perylene, phenanthrene, truxen, fluorene and thiophene or a corresponding aromatic moiety, with one or more ring carbon atoms replaced by oxygen, nitrogen or sulfur. If necessary, one or more double bonds can be hydrogenated.

The solubility-imparting substituent can be one of the following radicals: -C ~ to C ₁₈ alkyl, C ₂ - to -C ₂ alkenyl, C ₃ - to C ₇ cycloalkyl, C-- to C ₅ aralkyl and C ₃ - ois Cιc ~ aryl. These radicals can additionally carry an alkoxy, carbonyl, alkoxycarbonyl, cyano, halogen or amino group, it being possible for the A.lkoxy groups to have 1 to 18 carbon atoms.

The following application options exist in particular for the arrangement with transistor function according to the invention:

^• Electronic circuits

These circuits can possibly perform logical functions (logical AND, logical OR, etc.). If necessary, further electronic components can also be present, for example diodes, transistors made of silicon or gallium arsenide, and passive components, such as coils, resistors and capacitors. This also includes all arrangements that contain transistors of different polarities (n-type, p-type). If necessary, the different polarities can be realized with different transistor arrangements, for example an n-type based on silicon and a p-type according to the invention. Inorganic-organic hybrid circuits are known per se (see, for example: US Pat. No. 5,625,199; "Applied Physics Letters", Vol. 69 (1996), pages 4227 to 4229).

^• Chip cards or smart cards ^• Transponders or ID tags, ie devices for the electronic identification of objects or living things (animals, plants). The invention will be explained in more detail with reference to exemplary embodiments and a figure.

In the figure, an embodiment of the arrangement according to the invention is shown schematically in section, i.e. a thin film transistor. A gate electrode 11 is arranged on a substrate 10. Both rigid supports, such as silicon wafers, and flexible supports, such as plastic films, can be used as the substrate, and the substrate can also be transparent (glass, transparent plastic film). The gate electrode can consist, for example, of a metal, such as gold, or of a conductive plastic, such as polyamine.

The gate electrode 11 is surrounded by a gate dielectric 12. Both inorganic and organic or polymeric materials can be used as the gate dielectric. For example, an inorganic insulator, such as silicon dioxide or silicon nitride, or an insulating plastic, such as poly (4-methylphenol), can be used.

A source electrode 13 and a dram electrode 14 are arranged on the gate dielectric 12. As with the gate electrode, both inorganic materials, for example metals such as gold, and organic or polymeric materials, for example conductive polymers such as polyamine, can be used for these electrodes. The electrodes, including the gate electrode, can also be constructed using the multilayer method and comprise several different components. It is also possible to use different materials for the individual electrodes.

A layer 15 made of a charge-transporting organic substance, ie an organic semiconductor, is arranged between the source electrode 13 and the drain electrode 14. This layer can have one or more of the compounds described in more detail above. example 1

The surface of a silicon wafer is thermally oxidized, so that an oxide layer with a thickness of 400 nm is formed; the silicon wafer acts as the gate electrode and the oxide layer is the gate dielectric. A solution of 4, 4 '''' bis (n-octyl) -qumquephenyl is applied to the preheated wafer (0.5% solution in hot chlorobenzene). After the solvent has dried, gold electrodes parallel to one another are evaporated by means of a shadow mask (length of the gold electrodes: 1 mm; distance between the gold electrodes: 20 μm; pressure during the electrode deposition: 1-10 ^"5 mbar; evaporation rate: 0 , 5 to 1 nm / s; thickness of the gold electrodes: approx. 200 nm).

After the gold electrodes have been applied, the transistor arrangement is contacted with a tip measuring station (gold electrodes as source or drain electrodes, silicon as gate electrode). When a gate voltage of -90 V is applied, the component produced shows the function of a field-effect transistor. The field effect mobility is about 110 ^"4 cm ² / Vs.

Example 2

The surface of a silicon wafer is thermally oxidized, so that an oxide layer with a thickness of 400 nm is formed; the silicon wafer acts as the gate electrode and the oxide layer is the gate dielectric. Gold electrodes parallel to each other are evaporated onto the silicon dioxide layer using a shadow mask (length of the gold electrodes: 1 mm; distance between the gold electrodes: 20 μm; pressure during the electrode deposition: 1-10 ^"5 mbar; vapor deposition rate : 0.5 to 1 nm / s; thickness of the gold electrodes: approx. 200 nm) A solution of 4, 4 '''' bis (n-octyl) - qumquephenyl is applied to the preheated wafer (0 , 25% solution in hot chlorobenzene). After the solvent has dried, the transistor arrangement is contacted with a tip measuring station (gold electrodes as source or drain electrodes, silicon as gate electrode). When a gate voltage of -90 V is applied, the component produced shows the function of a field-effect transistor. The field effect mobility is approximately MO ^-4 cm ² / Vs.

Claims

claims 1. Arrangement with transistor function, in particular component, with a gate electrode (11), a gate dielectric (12), a source and a dram electrode (13, 14) and a layer (15) made of at least one charge-transporting organic substance ^¬ dadurchgekenn characterized in that the charge-transporting organic substance or is at least electrochemically at least twice anodically reversibly oxidizable twice cathodically reversibly reducible, at least one solvent-n soluble and / has a molecular weight up to 2000 g mol. 2. Arrangement according to claim 1, that the layer (15) made of the charge-transporting organic substance has a thickness between 5 nm and 10 μm, preferably between 10 and 100 nm. 3. Arrangement according to claim 1 or 2, that the charge-transporting organic substance is an aromatic hydrocarbon, a heteroaromatic compound or a polyene formation with at least one solubility-imparting substituent. 4. Arrangement according to claim 3, characterized in that the charge-transporting organic substance is a derivative of one of the following compounds: benzene, naphthalene, naphthacene, pentacene, biphenyl, terphenyl, quaterphenyl, qumquephenyl, sexiphenyl, triphenylene, chrysene, pyrene, naphthalocyanine, Porphyrin, perylene, truxen, fluorene and thiophene or a corresponding aromatic compound, which one or more ring carbon atoms are replaced by oxygen, nitrogen or sulfur. 5. Arrangement according to claim 3 or 4, characterized in that the solubility mediator One of the following radicals is a substituent: C 1 -C ₁₈ -alkyl, C ₂ - to C ₂ -alkenyl, C ₃ - to C 7 -cycloalkyl, C-- to C ₁₅ -aryalkyl and C ₆ - to C ₁ -aryl-aryl. 6. Arrangement according to claim 5, that the residues carry an alkoxy, carbonyl, alkoxycarbonyl, cyano, halogen or amino group, the alkoxy groups having 1 to 18 carbon atoms. 7. Electronic circuit comprising at least one arrangement according to one or more of claims 1 to 6. 8. Chip card containing at least one arrangement according to one or more of claims 1 to 6. 9. transponder containing at least one arrangement according to one or more of claims 1 to 6.