WO2005001952A1

WO2005001952A1 - Compound for forming a self-organizing monolayer, a layer structure, a semiconductor element and a method for producing a layer structure

Info

Publication number: WO2005001952A1
Application number: PCT/DE2004/001342
Authority: WO
Inventors: Marcus Halik; Günter Schmid; Hagen Klauk; Ute Zschieschang
Original assignee: Infineon Technologies Ag
Priority date: 2003-06-24
Filing date: 2004-06-23
Publication date: 2005-01-06
Also published as: DE10329247A1

Abstract

The invention relates to a compound for forming a self-organizing monolayer, particularly for forming a layer structure for an organic field effect transistor. The inventive compound is characterized by: a) at least one anchor group (1) for binding the molecule (10) to a substrate, particularly an electrode material (6); b) at least one dielectric group (2), and; c) at least one semiconducting group (3). The invention also relates to a layer structure made of the compound, to a semiconductor element, and to a method for producing the layer structure. This makes it possible to facilitate the production of semiconductor components, particularly those for organic field effect transistors.

Description

description

Connection for forming a self-assembling monolayer, a layer structure, a semiconductor component and a method for producing a layer structure

The invention relates to a compound for forming a self-organizing monolayer according to the preamble of claim 1, a layer structure according to claim 15, a semiconductor component with a layer structure according to claim 26 and a method for producing a layer structure according to claim 27.

Systems with integrated circuits based on organic field effect transistors (OFET) represent a promising technology in the mass application area of inexpensive electronics. A field effect transistor is considered organic in particular if the semiconducting layer is made of an organic material.

Since complex circuits can be built with OFET, there are numerous possible applications. For example, the introduction of F-ID (RF-ID: radio frequency identification) systems based on this technology is a potential replacement for the barcode, which is susceptible to faults and can only be used in direct visual contact with the scanner.

Organic field effect transistors normally consist of at least four different layers, one on top of the other: a gate electrode, a dielectric, a source-drain contact layer and an organic semiconductor. The order of the layers can vary. In order for the functionality to be created, the individual layers have to be structured, which is relatively complex. The present invention has for its object to provide means and a method with which the manufacture of semiconductor components, in particular for organic field effect transistors, is simplified.

This object is achieved by a connection according to claim 1. In the connection according to the invention, three different functional chemical groups are matched to one another: at least one anchor group, at least one dielectric group and at least one semiconducting group.

Anchor groups per se are described in the articles by G.M. Whitesides et al. , "Formation of Monolayer Films by the Spontaneous Assembly of Organic Thiols from Solution onto Gold" JACS, vol. 111, p. 321-335 (1989) and ^ on J.H. Menzel et al. , "Mixed silane seifassembled monolayers and their in situ modification" Thin Solid Films, vol. 327-9, p. 199-203 (1998).

Dielectric layers are described in the article by J. Collet, D. Vuillaume, "Nano-field effect transistor with an organic SAM gate insulator" APL vol. 73, p. 2681 (1998).

Organic semiconductors are known in principle, with an overview of the field being given by Katz, H.E., Bao, Z. & Gilat, S.L. "Synthetic chemistry for ultrapure, processable, and high-mobility organic thin film transistor semiconductors". Acc. Chem. Res. 34, 359-369 (2001).

The invention relates to a molecular structure with which the three groups described are integrated in a compound: a) at least one anchor group for binding the connection to a substrate, in particular an electrode material, b) at least one dielectric group, c) at least one semiconducting group.

This makes it possible to build up a self-organizing monolayer in which the individual groups form different layers.

This molecular structure to form a self-assembling monolayer enables e.g. an inexpensive construction of organic field effect transistors, which can be operated at very low voltages due to the extremely thin dielectric layer integrated in the molecule. Organic transistors manufactured in this way can be used to produce integrated circuits with higher performance, as required, for example, in RF-ID applications.

Advantageous embodiments of the compound according to the invention have at least one spacer group and / or at least one crosslinker group.

Crosslinkers are also known in principle (see e.g. B. Vollmert "Polymer Chemistry" Springer Verlag New York, Heidelberg 1973).

Spacer groups are also known in principle. They serve to separate two functional groups in organic compounds so that they do not influence each other.

The at least one spacer group is used for the spatial spacing of adjacent connections of the same type or a different type. The at least one crosslinker group serves to mechanically reinforce one Binding with neighboring connections of the same kind or a different kind.

Advantageously, the connection is essentially linear and has exactly one anchor group, a dielectric group, a semiconducting group, a spacer group and a crosslinking group, the order of the dielectric group, the semiconducting group, the spacer group and the crosslinking group within the Connection is arbitrary. The function of the connection in a monolayer can be specifically influenced by a specific choice of the order of the groups in the connection.

In an advantageous embodiment, as viewed from the substrate, the dielectric group is arranged below the semiconducting group. This order is e.g. well suited for the production of monolayers from the compound for organic field effect transistors.

Furthermore, it is advantageous if the crosslinker group is located at the distal end of the connection, as seen from the substrate, a spacer group being arranged below the crosslinker group. In this order, cross-linking, e.g. easy to carry out due to thermal, chemical or photochemical effects.

At least one anchor group advantageously has a thiol, a chlorosilane, in particular trichlorosilane, an alkoxysilane, in particular trialkoxysilane groups, an amine, an amide and / or a phosphine on.

It is also advantageous if at least one dielectric group has an n-alkyl chain, in particular with n = 6 ... 20. A chain that is too long can cause problems with the

Self-organization lead, a too short chain can lead to poor insulation properties.

In a further advantageous embodiment of the compound according to the invention, at least one semiconducting group (3) has an α, oJ-oligothiopene, a thiophene-phenyl oligomer and / or a condensed aromatic, in particular a pentazene and / or a tetrazene. Also, at least one can be semiconducting

Group have one of the following groups:

As a saver group, at least one -

Alkyl with m = 2 ... 6 used.

A further advantageous embodiment of the compound according to the invention has at least one crosslinker group which has a polymerizable multiple bond, in particular one

Has acrylate, a methacrylate, an activated alkene and / or an activated alkyne and / or has a polymerizable cyclic group.

It is also advantageous if at least one

Crosslinker group has a group that has an intermolecular interaction to form a network with other molecules, in particular contains a group with a possibility of hydrogen bonding and / or a group with a possibility of van der Waals binding and / or that at least one crosslinker group has one of the following groups:

Also, it is advantageous if at least one

Crosslinker group has a carboxylic acid and / or an amide.

The object is also achieved by a layer structure for use in an organic semiconductor component, in particular an organic field effect transistor. According to the invention, this layer structure has a molecular monolayer with compounds according to at least one of Claims 1 to 15.

It is advantageous if the connections in the monolayer are arranged parallel to one another. It is also advantageous if the molecules in the monolayer to form layers have the same groups in the same order, the groups having essentially the same lengths. This results in horizontal layers in the monolayer, in which chemical groups with the same functionality lie (for example a dielectric layer or a semiconducting layer). To form particularly flat semiconductor components, it is advantageous if a layer consisting of the dielectric group (2) and the semiconducting group (3) is between 3 and 10 nm thick.

For the production of a semiconductor component, it is advantageous if a base substrate has a semiconductor wafer, in particular made of silicon, glass, plastic and / or paper. Metallic and / or organic materials can be deposited on these materials.

It is advantageous if the substrate on which e.g. a monolayer is to be deposited, in particular an electrode material or a gate electrode, a metal layer, in particular made of gold, copper, platinum or

Palladium and / or a metal oxide layer, in particular made of titanium and / or aluminum on ice.

It is advantageous if the anchor group of a connection is matched to the substrate, in particular the electrode material. In the case of a substrate with a metallic oxide layer, in particular a titanium or aluminum oxide layer, it is advantageous if at least one anchor group has a chlorosilane and / or an alkoxysilane. In the case of a substrate with a gold layer, it is advantageous if at least one

Anchor group has a thiol. In the case of a substrate with a copper layer, it is advantageous if at least one anchor group has an A in and / or an amide. In the case of a substrate with a palladium layer, it is advantageous if at least one anchor group has a phosphine.

The object is also achieved by a semiconductor component according to claim 24 if it has a layer structure according to at least one of claims 14 to 23. The object is also achieved by a method for producing a layer structure according to at least one of claims 14 to 23 according to claim 25.

A monolayer (11) of a compound according to at least one of Claims 1 to 15 is applied to an assembly with a base substrate (7) by vapor deposition, depositing from a solution and / or an immersion process.

In particular for producing a field effect transistor, it is advantageous if a monolayer is applied to a previously structured substrate, in particular an electrode material.

It is also advantageous if the monolayer after the

Application to a base substrate and / or a substrate is cross-linked by thermal, photochemical and / or chemical action. This mechanically stabilizes the monolayer so that further processing can be carried out on the surface of the monolayer.

A metal layer is advantageously applied to the monolayer as a source-drain layer (8a, 8b), e.g. to obtain a compact field effect transistor structure.

The invention is explained in more detail below with reference to the figures of the drawings using several exemplary embodiments. Show it:

Fig. 1 is a schematic representation of an embodiment of a connection according to the invention;

2 shows a schematic illustration of a plurality of connections arranged parallel to one another to form a layer structure; Fig. 3 general formula of the compound for forming a layer structure;

4a-c chemical formulas for anchor groups (FIG. 4a), semiconducting groups (FIG. 4b) and a crosslinker groups (FIG. 4c);

5 shows a schematic structure of an organic field effect transistor with an embodiment of the layer structure according to the invention;

Fig. 6-b output and pass characteristic of an organic field effect transistor with an embodiment of the layer structure according to the invention.

1 shows an embodiment of a connection 10 according to the invention, with which self-organizing monolayers 11 (see FIG. 2) can be produced. The connection 10 is constructed essentially linearly, an anchor group 1 serving to bind the connection 10 to an electrode material 6, not shown here, as a substrate. The anchor group 1 is designed here as a chlorosilane group. In principle, the monolayer can also be applied to a substrate other than an electrode material 6.

Alternatively, the anchor group 1 can have groups according to FIG. 4a, the first example in FIG. 4a being the chlorosilane group which is also used in the example of FIG. 1. The other groups are alkoxysilanes with n-alkyl radicals (C _x to C _s ), amines, A ide and phosphines. The adaptation of the anchor group 1 to a specific surface material of the substrate 6 is discussed in connection with FIG. 2. A dielectric group 2 is arranged as a non-conductor in the connection 10 above the armature group 1. In the present example, this is an n-alkyl group, with n = 6 ... 20. Chains with n> 20 appear to be inappropriate, since the self-organization of monolayers 11 becomes more difficult with increasing length. Chains with n <6 could lead to a deterioration in the insulation effect.

The length of the dielectric group 2 allows the thickness of the insulator layer to be adjusted in a monolayer 11 (see FIG. 2).

A semiconducting group 3, which here has a polythiophene chain, is arranged above the dielectric group 2. An α, oJ oligothiophene, thiophene-phenyl oligomer and / or condensed aromatics, in particular a pentacene and / or a tetrazene, are particularly suitable. Corresponding semiconducting groups 3 are shown in Fig. 4b.

A relatively short spacer group 4 with an m-alkyl chain (m = 2 ... 6) is arranged above the semiconducting group 3. An alkyl chain with m> 6 does not appear to make sense, since a longer saver group 4 would act as an injection barrier between the top electrode and a semiconductor layer.

At the top is a crosslinker group 5, which can in principle have any polymerizable group.

Examples are acrylates, methacrylates, activatable alkenes and / or activatable alkynes. Possible examples are

Groups for crosslinkers indicated in Fig. 4c. It is also possible that groups are also used which have intramolecular interactions (e.g.

Hydrogen bonds, van der Waals forces) can achieve cross-linking. Examples would be

Carboxylic acids or amides. However, the spatial extent of the crosslinking groups 5 must not be too large, since otherwise the packing of the underlying semiconducting layer, which is mostly based on π-π interaction, could be disturbed in a monolayer 11 (see FIG. 2), thereby reducing the semiconducting effect becomes.

A generalized structure of the connection is shown in FIG. 3. The nomenclature given therein relates to the molecular groups in FIGS. 4a to 4c. X denotes the anchor groups 1, Y the semiconducting groups 3 and Z the crosslinker groups 5.

2 describes how connections 10 can be used to form a layer structure (monolayer 11) which can be used for organic field effect transistors.

For this purpose, a self-organizing structure of connections 10 is selected in FIG. 2, which essentially consists of connection 10 of FIG. 1. The anchor group 1 is bonded to a titanium layer with a natural oxide layer on an electrode material 6. The electrode material 6 here forms an electrode for an organic field effect transistor.

The anchor groups 1 can be adapted to the corresponding surfaces of the electrode material 6. Chlorosilanes and / or alkoxysilanes are preferably used for metal layers, in particular metal layers with natural oxides (titanium, aluminum). For gold layers are preferred

Thiols, amines and / or amides are preferably used for copper layers and phosphines are preferably used as anchor groups 1 for palladium.

In the example, the linear connections 10 are arranged essentially parallel to one another. The lengths of the anchor groups 1, the dielectric groups 2, the semiconducting groups 3, the spacer groups 4 and the crosslinker groups 5 are in each case the same, so that a monolayer with a horizontal layer structure is formed. It is advantageous if all connections 10 of a monolayer 11 are the same.

An organic semiconductor, an organic insulator and mechanical amplifiers (crosslinking) are thus combined in one connection 10. Due to the integrated anchor group 1, the connections 10 bind selectively to a suitable electrode material and, due to their chemical structure, form layers (monolayers) which are arranged over a large area. After cross-linking (mechanical reinforcement

of the layer) further structures can be easily defined (e.g. source-drain electrodes) without destroying the layer.

In the present case, a specific sequence of groups 1, 2, 3, 4, 5 within connection 10 is described in FIGS. 1, 2 and 3. Apart from the anchor group 1, which is always arranged at one end of the connection 10 in the case of linear connections 10, the sequence of the groups 2, 3, 4, 5 within the connection 10 is fundamentally arbitrary. For example, the semiconducting group 3 and the dielectric group 2 are interchanged within the connection 10, so that a different layer sequence results.

The anchor group 1, the dielectric group 2, the semiconducting group 3, the spacer group 4 and the crosslinking group 5 are also those described here

Embodiments each composed homogeneously from a chemical group. In principle, it is also possible that, for example, the semiconducting group 3 is composed of different semiconducting groups 3 (for example thiophenes and aromatics). After a source-drain layer has been applied to this monolayer 11, the arrangement of the field-effect transistor shows characteristics with high charge carrier mobility, namely at very low voltages around 2V.

FIG. 5 shows a schematic sectional view of an organic field effect transistor 100 as an example of a semiconductor component with a self-organized, cross-linked monolayer 11, as was described in FIG. 2.

A method for producing such a field effect transistor 100 is described below.

On a base substrate 7 (e.g. silicon wafer, glass, plastic film, paper) is with the help of

Standard procedures, such as thermal evaporation, sputtering etc.) a metal layer (e.g. titanium, aluminum, palladium, gold etc.) is applied. By means of photolithographic processes, printing techniques and etching processes (dry, wet chemical), structures such as e.g. a gate electrode 6 is introduced.

This assembly (base substrate 7 with gate electrode 6) is immersed for 1 minute in a 1 to 10% solution of the compounds 10 described above to form a self-assembling monolayer 11. The solvent is inert and, depending on anchor group 1, dry. Examples of solvents are Alcohols, toluene, xylene, n-hexane, Acteon and / or PGMEA are suitable.

The coated assembly is then rinsed with pure solvent in order to remove excess, unbound compounds 10. Then the coated assembly is washed with water and dried.

The assembly with the monolayer 11 is stabilized below, ie cross-linked. This will depend on used crosslinker group 5 a thermal initialization (for example at 100 to 200 ° C for 5 minutes). Cross-linking can also be carried out chemically, in particular acid catalytically or photochemically (for example by irradiation with a dose corresponding to UV light).

The monolayer 11 is now mechanically stabilized and the source-drain layer 8a, 8b can be defined.

To complete the field effect transistor 100, a further metal layer (e.g. made of gold, platinum or palladium) is applied. This is structured using standard methods (e.g. photolithography) to form the source-drain layer 8a, 8b. As an alternative to the metal layer, conductive organic materials (e.g. conductive polymers) can also be used for the source-drain layer 8a, 8b.

A connection of the individual contact layers is necessary to produce integrated circuits. For this purpose, contact holes must be defined at the appropriate locations before the source-drain layer 8a, 8b is deposited.

The transistor structure on the base substrate 7 is very simple compared to conventional methods, since the combination of dielectric and semiconductor in a connection 10 eliminates the need to separate the layers.

The deposition of the materials on a previously defined electrode material 6 (gate electrode) can take place both by thermal evaporation and from a solution. This means that these materials can also be deposited using inexpensive processes such as immersion processes. The

Deposition is selective and runs very quickly due to the anchor groups 1, which can be selected specifically for the gate electrode material 6 (see description in connection with FIG. 2). 6a and 6b show current-voltage characteristics which were determined using organic field effect transistors which were provided with embodiments of the monolayers 11 according to the invention. The typical family of output characteristics for an OFET can be seen in FIG. 6a. The gate-source voltage varies between -0.5 and -2 V. The flat pinch-off areas for the drain current are clearly visible.

In the experiments shown in FIGS. 6a and 6b, the charge carrier mobility was 0.2 cm ² / Vs at 1 V

Operating voltage. The subthreshold swing was 240 mV / decade, the on / off ratio was 10 ³ , the threshold voltage was -0.1 V.

The compounds 10 according to the invention and the layer structures produced therefrom essentially offer the following advantages over conventional materials and their processing.

- Only extremely low voltages are required to operate the transistors and circuits (1-2 V; see Fig. 6a, 6b)

- Selective simultaneous deposition of the insulator and semiconductor layers on the substrate (electrode materials).

- The layers are chemically fixed on the substrate (electrode material).

- The process control by immersion processes is inexpensive, whereby the deposition of a layer is saved.

- Mechanically and electrically stable surfaces are obtained by cross-linking, which can be easily structured by subsequent processes. - Due to the thin layers, extremely thin device architectures are possible (insulator and semiconductor layers are typically approx. 3-10 nm thick).

- Due to the existing chemistry, there is a large chemical variation of the connections, so that the electrical properties can be easily varied.

The embodiment of the invention is not limited to the preferred exemplary embodiments specified above. Rather, a number of variants are conceivable which make use of the connection according to the invention, the layer structure according to the invention, the semiconductor component according to the invention and the method according to the invention even in the case of fundamentally different types.

The production of an organic field effect transistor is described below as an example.

LIST OF REFERENCE NUMBERS

1 anchor group

2 dielectric group 3 semiconducting group

4 spacer group

5 crosslinker group

6 electrode material (substrate)

7 base substrate 8a, b source-drain layer

10 compound (molecule)

11 monolayer

100 semiconductor device

Claims

claims

1. Connection to form a self-organizing

Monolayer, in particular to form a layer structure for an organic field effect transistor, characterized by a) at least one anchor group (1) for binding the compound (10) to a substrate, in particular a

Electrode material (6), b) at least one dielectric group (2), c) at least one semiconducting group (3).

2. Connection according to claim 1, characterized by at least one spacer group (4) for the spatial spacing of adjacent connections (10) of the same type or a different type.

3. A compound according to claim 1 or 2, characterized du ch at least one crosslinker group (5) for mechanically strengthening a bond with adjacent compounds (10) of the same type or a different type.

4. Connection according to at least one of the preceding claims, characterized in that the connection (10) is substantially linear and in each case exactly one anchor group (1), a dielectric group (2), a semiconducting group (3), a spacer group ( 4) and a crosslinking group (5), the order of the dielectric group (2), the semiconducting group (3), the spacer group (4) and the crosslinking group (5) being arbitrary within the connection (10).

5. Connection according to at least one of the previous ones

Claims, characterized in that from Seen substrate (6), the dielectric group (2) is arranged below the semiconducting group (3).

6. Connection according to at least one of the preceding claims, characterized in that seen from the substrate (6), the crosslinker group (5) is at the distal end of the connection (10), a spacer group (4) being arranged below the crosslinker group (5) is.

7. Connection according to at least one of the previous ones

/ Claims, characterized in that at least one anchor group (1) has a thiol, a chlorosilane, in particular trichlorosilane, an alkoxysilane, in particular trialkoxysilane groups, an amine, an amide and / or a phosphine.

8. A compound according to at least one of the preceding claims, characterized in that at least one dielectric group (2) has an n-alkyl chain, in particular with n = 6 ... 20.

9. A compound according to at least one of the preceding claims, characterized in that an at least one semiconducting group (3) is an α, α 'oligothiopene, a thiophene-phenyl oligomer and / or a condensed aromatic, in particular a pentacene and / or Tetrazen on ice.

10. Connection according to at least one of the previous ones

Claims, characterized in that at least a semiconducting group (3) one of the following groups:

11. A compound according to at least one of the preceding claims, characterized in that at least one spacer group (4) has an m-alkyl, with m = 2 ... 6.

12. A compound according to at least one of the preceding claims, characterized in that at least one crosslinker group (5) has a polymerizable multiple bond, in particular an acrylate, a methacrylate, an activated alkene and / or an activated alkyne and / or has a polymerizable cyclic group ,

13. A compound according to at least one of the preceding claims, characterized in that at least one crosslinker group (5) has a group which has an intermolecular interaction to form a network with other compounds, in particular a group with a possibility of hydrogen bonding and / or a group with a possibility of van-der-Waals binding.

14. Connection according to at least one of the preceding claims, characterized in that at least one crosslinker group (5) has one of the following groups:

15. A compound according to at least one of the preceding claims, characterized in that at least crosslinker group (5) has a carboxylic acid and / or an amide.

16. Layer structure for use in an organic semiconductor component, in particular an organic field effect transistor, characterized by a molecular monolayer with connection according to at least one of claims 1 to 15.

17. Layer structure according to claim 16, so that the connections (10) in the monolayer (11) are arranged parallel to one another.

18. Layer structure according to claim 16 or 17, characterized in that the connections (10) in the monolayer (11) for forming layers have the same groups in the same order, the groups having essentially the same lengths.

19. Layer structure according to at least one of claims 16 to 18, characterized in that a layer consisting of the dielectric group (2) and the semiconducting group (3) is between 3 and 10 n thick.

20. Layer structure according to at least one of claims 16 to 19, characterized in that a base substrate (7) comprises a semiconductor wafer, in particular made of silicon, glass, plastic and / or paper.

21. Layer structure according to at least one of claims 16 to 20, characterized in that the substrate (6), in particular an electrode material or a gate electrode, a metal layer, in particular made of gold, copper, platinum or palladium and / or

Metal oxide layer, in particular made of titanium and / or aluminum.

22. Layer structure according to at least one of claims 16 to 21, characterized in that a substrate (6), in particular an electrode material with a metallic oxide layer, in particular a titanium or aluminum oxide layer, at least one anchor group (1) with a chlorosilane and / or an alkoxysilane having.

23. Layer structure according to at least one of claims 16 to 22, characterized in that a substrate (6), in particular an electrode material with a gold layer, has at least one anchor group (1) with a thiol.

24. Layer structure according to at least one of claims 16 to 23, characterized in that a substrate (6), in particular an electrode material with a copper layer, has at least one anchor group (1) with an amine and / or an amide.

25. Layer structure according to at least one of claims 16 to 24, characterized in that a substrate (6), in particular an electrode material with a

Palladium layer has at least one anchor group (1) with a phosphine.

26. Semiconductor component, in particular an organic field effect transistor with a layer structure according to at least one of claims 16 to 25.

27. A method for producing a layer structure according to at least one of claims 16 to 25, characterized in that a monolayer (11) of a compound according to at least one of claims 1 to 15 by vapor deposition on an assembly with a base substrate (7) deposit a solution and / or apply a dipping process.

28. The method according to claim 27, characterized in that the monolayer is applied to a previously structured substrate (6), in particular an electrode material.

29. The method according to claim 27 or 28, characterized in that the monolayer (11) after the

Application to a base substrate (7) and / or a substrate (6) is cross-linked by thermal, photochemical and / or chemical action.

30. The method according to at least one of claims 27 to 29, characterized in that after the application of the monolayer (11), a metal layer is applied to the monolayer as a source-drain layer (8a, 8b).