Nanowire coating

Abstract

A method for providing a coating (2) on a plurality of nanowires (1) on a component (4, 5), comprising the steps of: a) treating each of the nanowires (1) with a reducing agent; b) immersing each of the nanowires (1) in a protective substance; c) drying each of the nanowires (1) to obtain the coating (2) from the protective material; The method includes:

Description

Technical Field

[0001] The present invention relates to a method for providing a coating on a plurality of nanowires on a component, and in particular to a method for connecting two components by means of a plurality of nanowires that can be coated according to the present invention.

Background Art

[0002] It is known to apply a protective paint (Schutzlack) to the grown nanowires. This protective paint temporarily protects the nanowires until each nanowire is used for its intended application. For example, the nanowires can be used to connect two components to each other. The protective paint covers the entire length of each nanowire. Before using each nanowire for its intended application, it is necessary to remove the coating of these nanowires. For this purpose, the protective paint has to be chemically removed. This means that there is an additional method step, which is not desirable in this regard. Furthermore, chemicals, especially those that would be in liquid or gaseous form, are required. In a manufacturing environment, liquid chemicals are usually not desirable. Additionally, the liquid may leave residues on the processed components. When using gaseous chemicals, it is necessary to create a suitable atmosphere, which is cumbersome.

Summary of the Invention

Means for Solving the Problems

[0003] The object of the present invention is to enable the protection of nanowires in a manner that allows for easy removal of the protection without leaving residues, based on the described prior art.

[0004] The aforementioned object is achieved by a method according to the features of the independent patent claims. The dependent claims each show advantageous configurations. The features detailed individually in the claims can be combined with each other in any technically significant manner.

[0005] According to the present invention, a method is provided for providing a coating (2) to a plurality of nanowires (1) on a component. This method is a) A step of treating each nanowire with a reducing substance, b) The step of immersing each nanowire in a protective material, c) A step of drying each nanowire to obtain a coating from the protective material, This includes. Steps a), b), and c) are preferably carried out in the order described above.

[0006] The described method allows each nanowire to be protected with a coating until it is used for its intended purpose. This intended purpose may be connecting a component containing the nanowires to another component. However, the method is also suitable for other applications. The coating obtained by this method is particularly easy to remove, especially without the use of chemicals. In some applications, removal of the coating is not even necessary.

[0007] Each nanowire can be protected in the manner described. In this specification, a nanowire should be understood to mean any wire-like material having a size ranging from several nanometers to several micrometers. The nanowire may have, for example, a circular, elliptical, or polygonal base. In particular, the nanowire may have a hexagonal base.

[0008] The nanowires preferably have a length in the range of 100 nm (nanometers) to 100 μm (micrometers), and more preferably in the range of 500 nm to 60 μm. Furthermore, the nanowires preferably have a diameter in the range of 10 nm to 10 μm, and more preferably in the range of 30 nm to 2 μm. In this specification, the term "diameter" refers to a circular base, and in the case of a base that deviates from this, the same definition of diameter shall be used. It is particularly preferable that all nanowires used have the same length and the same diameter.

[0009] The described method is applicable to various nanowire materials. Conductive materials, particularly metals such as copper, silver, gold, nickel, tin, and platinum, are suitable as nanowire materials. However, non-conductive materials such as metal oxides are also suitable. It is preferable that all nanowires are formed from the same material.

[0010] Nanowires may be formed by galvanic growth on a component. Preferably, the nanowires are grown on a conductive surface of the component. If, however, this surface is part of a non-conductive component, conductivity can be achieved, for example, by metal coating. Therefore, to grow nanowires on a metal thin layer, for example, a non-conductive substrate may be coated with a metal thin layer.

[0011] Preferably, each nanowire is perpendicular to the surface of the component. Preferably, the first end of each nanowire is connected to the surface of the component. Preferably, the second end of each nanowire is located away from this surface. However, this method can also be applied to nanowires lying horizontally on the surface of the component, for example.

[0012] The component may be an electronic component in particular. For example, the component may be a substrate, a silicon chip, or a so-called printed circuit board (PCB). However, this method is applicable to any other type of component.

[0013] In step a), each nanowire is treated with a reducing agent. Any chemical substance that has a reducing effect on the surface of each nanowire can be considered a reducing agent. Alternatively, step a) can be modified so that the surface of each nanowire is reduced. This should be understood as chemical reduction. In step a), oxides on the surface of each nanowire are removed in particular.

[0014] The reducing substance may be in liquid or gaseous form. For example, the reducing substance may be in vapor form. Preferably, the reducing substance is an acid. For example, the reducing substance may be formic acid, and especially formic acid vapor. Alternatively, the reducing substance may be liquid citric acid, a forming gas, or hydrogen plasma.

[0015] In step a), the treatment of each nanowire is preferably carried out by coating each nanowire with a reducing substance. In the case of a liquid or gaseous reducing substance, this treatment may be carried out, for example, by spraying the liquid or gaseous reducing substance onto each nanowire. In the case of a gaseous reducing substance, each nanowire may be exposed to an atmosphere containing the reducing substance.

[0016] In step b), the nanowires are immersed in a protective substance. This protective substance is preferably in liquid form. Any chemical substance that adheres to the surface of each nanowire while it is immersed in the protective substance and then forms a coating on the nanowire by drying is considered the protective substance. Drying is performed in step c), which dries the nanowires. Drying can be performed actively or passively. Active drying is performed when means are taken to act on each nanowire. For example, the nanowires may be exposed to a gas stream, heated, or both. Passive drying is performed when the nanowires are dried by exposing them to their environment without any special means being taken to dry them.

[0017] The method described provides a coating for nanowires. The coating of nanowires should be understood as a layer on the surface of the nanowires. Therefore, the coating conforms to the shape of the nanowires. A coated nanowire represents a structure similarly included within the above-described definition of the term nanowire. This coating is formed such that gaps are created between the coatings of adjacent nanowires. Therefore, the nanowires remain separated from one another despite the presence of this coating. Consequently, a protective coating that encases multiple nanowires together is not a coating of nanowires in the sense used in this specification. Instead, such a protective coating forms a coating on the surface of the component, encasing each nanowire within it.

[0018] This coating can be removed particularly easily when the nanowires are used for their intended purpose. No chemicals are required for this. In this respect, the drawbacks known from the prior art are overcome. In this case, the need for chemicals to form the protection is not significant. Therefore, chemicals can usually be used to form the protection without difficulty. Finally, this protection is applied to the location where the nanowires are also grown. This, in any case, requires the use of chemicals. The problems described in reference to the prior art relate to the disadvantage of removing the protection with chemicals. This is because the protection needs to be removed where the nanowires are used for their intended purpose. According to the described method, this location can be a location where the use of chemicals is impossible or not intended.

[0019] In a preferred embodiment of this method, the protective substance includes an organic substance.

[0020] It has been found that even a small layer of organic molecules is sufficient to protect the surface of nanowires from oxidation.

[0021] In this embodiment, suitable protective substances are benzotriazole, imidazole, polyvinylpyrrolidone, benzimidazole, thiol-based substances, or mercaptobenzimidazole.

[0022] In a further preferred embodiment of the method, the protective substance contains a metal.

[0023] It has been found that even a few atomic layers of a metal are sufficient to protect the surface of the nanowire from oxidation. The metal is preferably a noble metal. In step b), the metal is preferably provided in the form of an immersion bath. This can be done at an appropriate temperature, or by dissolving the metal in a solvent, or both. Therefore, the protective substance preferably contains a solvent. This solvent may be evaporated in step c). In this case, the coating is formed from the part of the protective substance that does not evaporate as a solvent.

[0024] In this embodiment, suitable protective substances are silver and gold.

[0025] In a further preferred embodiment of the method, the protective substance is selected taking into account the material of the nanowire such that in step b) the protective substance adheres at least partially to the nanowire by physical adsorption.

[0026] In physical adsorption, molecules or atoms or both from the protective substance adhere to the surface of the nanowire by van der Waals forces. A case may occur where only a part of the protective substance adheres to the nanowire by physical adsorption in step b). The reason is, for example, that the protective substance contains a solvent and only the remaining part of the protective substance adheres to the surface of the nanowire.

[0027] In a further preferred embodiment of the method, the coating of each nanowire formed by steps a) to c) has an average thickness of at most 20 atoms or 20 molecules, and in particular, an average thickness of at most 10 atoms or 10 molecules.

[0028] If the thickness of the coating is thus thin, the coating can be left on the nanowire when the nanowire is used for its intended application. For example, a component having these nanowires can be connected to another component through these plural nanowires without the need to remove the coating. This connection may be formed through the coating between these nanowires and the surface of another component, or through the coating between these nanowires and plural nanowires on the surface of another component. It is preferable that the plural nanowires on the surface of this another component are also coated so that a connection is formed between the coatings. Alternatively, this coating can be easily removed mechanically. For example, it can be removed by bringing these nanowires into contact with the surface of another component or by bringing them into contact with plural nanowires on the surface of another component. The coating can also be decomposed by heating.

[0029] The aforementioned thin coating can be obtained by steps a) to c). What particularly affects this thickness is the material of the nanowire, the chemical composition of the reducing substance used in step a), the chemical composition of the protective substance used in step b), particularly the concentration of the reducing substance, and parameters in the treatments such as the duration of steps a), b), c) and the temperature of the nanowire during steps a), b), c). How to select these factors for the desired thickness of the coating can be determined by experiments.

[0030] When the coating is formed from atoms, the coating has an average thickness of up to 20 atomic layers, particularly an average thickness of up to 10 atomic layers. When the coating is formed from molecules, the coating has an average thickness of up to 20 molecular layers, particularly an average thickness of up to 10 molecular layers.

[0031] In a further preferred embodiment of the method, the component is rinsed with a rinsing liquid between step a) and b) or between step b) and c) or both. It is preferable that this is done "both".

[0032] Rinsing allows for the acquisition of particularly thin coatings. Solvents such as water are particularly suitable as rinsing solutions. Rinsing between step a) and step b) prevents interaction between the reducing substance and the protective substance. Rinsing between step b) and step c) removes the components of the protective substance, so that these components do not adhere to the nanowires as undesirable residues in step c).

[0033] A further aspect of the present invention provides a method for connecting two components via a plurality of nanowires. This method is A) The step of coating multiple nanowires on at least one of these components, B) The step of bringing these components together so that they are connected to each other via nanowires, This includes.

[0034] The aforementioned advantages and features of the method for coating multiple nanowires on a single component are also applicable and adaptable to methods for connecting two components via multiple nanowires, and vice versa.

[0035] Steps A) and B) are performed in the order described. Step B) is preferably performed immediately following step A). ​​It is particularly preferable that the coating is not removed between steps A) and B). Even if this is done, the coating will be removed by pulling the parts together in step B) or in a step following step B). Therefore, it is preferable that the coating is still present at the start of step B).

[0036] Each nanowire makes it possible to form connections, particularly over large contact areas. As a result, connections that are particularly mechanically stable and possess conductivity, thermal conductivity, or both can be obtained. The method described above can be used to connect, for example, two electronic components to each other. However, the method described above is not limited to applications in the field of electronic equipment.

[0037] The nanowires may be provided on one of the two components. In this case, in step B), each nanowire on the first component contacts the surface of the second component through the coating. It is assumed that the coating remains between each nanowire and the surface of the second component. Alternatively, this coating can be removed in places or completely by bringing the two components together or by subsequent method steps. Where the coating has been removed, there is direct contact between each nanowire and the surface of the second component. Whether and to what extent the coating is removed when the two components are brought together may depend on the thickness of the coating, the material of the coating, the material of the surface of the second component, the material of the nanowires, or at least one of these.

[0038] Alternatively, in step A), multiple nanowires may be provided on each of the two components. Preferably, the nanowires on both components are covered by their respective coatings. In step B), the nanowires on the first component contact the nanowires on the second component through their respective coatings. If each nanowire on both components is coated, contact occurs between the coatings. These coatings may remain between the nanowires. Alternatively, these coatings can be removed in places or completely by bringing the two components together or by subsequent method steps. Where the coatings have been removed, the nanowires are in direct contact with each other. Whether and to what extent the coatings are removed when the two components are brought together may depend on the thickness of the coatings, the material of the coatings, the material of the surface of the second component, the material of the nanowires, or at least one of these.

[0039] In a preferred embodiment, the coating is obtained by the method described above, in step A), which involves coating a plurality of nanowires on the component (4, 5).

[0040] If nanowires are provided on only one component in step A), the aforementioned method for coating multiple nanowires on the component also applies to the nanowires on this component. If nanowires are provided on both components in step A), the aforementioned method for coating multiple nanowires on the components applies to each nanowire on both components.

[0041] The connection between the two components may be formed in advance at room temperature. This is especially true when nanowires are provided on both components.

[0042] In a more preferred embodiment, the method is C) A step of removing at least partially the coating of the nanowire by heating, It also includes.

[0043] Step C) is preferably performed after step B). This heating makes it possible to partially remove the coating, and preferably completely remove it. Preferably, this heating is performed at a temperature of at least 90°C, and particularly in the range of 90 to 150°C.

[0044] This heating is particularly suitable when, in step A), the nanowires are provided on only one of the two components. In this case, the heating is preferably carried out at a temperature of at least 170°C, and particularly in the range of 170 to 230°C. This heating allows each nanowire on the first component to be connected particularly well to the surface of the second component.

[0045] This heating process makes it possible to connect the nanowires together so that they are no longer recognized as nanowires.

[0046] The present invention will be described in more detail below with reference to the drawings. The drawings show particularly preferred exemplary embodiments. However, the present invention is not limited thereto. In particular, the drawings and the size ratios described are schematic. [Brief explanation of the drawing]

[0047] [Figure 1] The results of the method according to the present invention for coating multiple nanowires on a component are shown. [Figure 2] The results of a first embodiment of the method according to the present invention for connecting two components via multiple nanowires are shown. [Figure 3] The results of a second embodiment of the method of the present invention for connecting two components via multiple nanowires are shown. [Figure 4] The results of a third embodiment of the method of the present invention for connecting two components via multiple nanowires are shown. [Modes for carrying out the invention]

[0048] Figure 1 shows a component 4 comprising multiple nanowires 1 having a coating 2. The coating 2 was obtained by the method described below. a) A step of treating each nanowire 1 with a reducing substance, b) The step of immersing each nanowire 1 in a protective material, c) The step is to dry each nanowire 1 to obtain a coating 2 from the protective material.

[0049] This protective substance may contain an organic substance, a metal, or both. This protective substance is selected considering the material of the nanowire 1 so that in step b), the protective substance adheres at least partially to the nanowire 1 by physical adsorption. The coating 2 formed by steps a) to c) has an average thickness of up to 20 atomic or molecular layers on the surface of the nanowire 1. Component 4 is rinsed with a rinsing solution between steps a) and b), or between steps b) and c), or both.

[0050] Figure 2 shows a device 3 having a first component 4 and a second component 5. The two components 4 and 5 are connected to each other via a plurality of nanowires 1. Each nanowire 1 has a coating 2. This device 3 is A) The step of applying a coating 2 to multiple nanowires 1 on two components 4 and 5, B) The step of bringing the two parts 4 and 5 together so that the two parts 4 and 5 are connected to each other via the nanowire 1, It was obtained by a method including [a specific method].

[0051] In the illustrated embodiment, the coating 2 is partially held in place in step B) by adjacent nanowires 1 being connected to each other through the coating 2. However, it is also clear that the coating 2 is cracked in places between the nanowires 1. This cracking is caused by pulling parts 4 and 5 together. Where the coating 2 is cracked, multiple nanowires 1 are held in contact with each other particularly well. Note that these figures are only schematic. In particular, the coating 2 is shown to be thicker than it actually is for illustrative purposes.

[0052] Figure 3 shows another apparatus 3 having a first component 4 and a second component 5. The two components 4 and 5 are connected to each other via multiple nanowires 1. Unlike Figure 2, in this figure, each nanowire 1 has no coating 2 and is directly connected to each other. This can be achieved by the method described with reference to Figure 2. This method is C) A step of removing the coating 2 of the nanowire 1 by heating. It also includes.

[0053] Step C) allows us to obtain the apparatus 3 shown in Figure 3 from the apparatus 3 shown in Figure 2. This heating has the effect of separating the nanowire material so that the nanowires connect with each other. This leads to the situation shown in Figure 3. In this figure, multiple nanowires 1 are shown in a simplified form as a single material layer. Nevertheless, the two parts 4 and 5 are considered to be connected to each other via the multiple nanowires 1.

[0054] Figure 4 shows another device 3. This device 3 is A) A step in which a coating 2 is provided on multiple nanowires 1 on the first component 4, but not on the second component 5, B) The step of bringing the two parts 4 and 5 together so that the two parts 4 and 5 are connected to each other via the nanowire 1, C) A step of removing the coating 2 of each nanowire 1 by heating, It was obtained by a method including the following.

[0055] This heating has the effect of connecting each nanowire 1 to one another, as in Figure 3. However, these nanowires are also connected to the surface of the second component 5. Figure 4 can be achieved by using a higher temperature in step C) than in Figure 3. As a result, the nanowires 1 in Figure 4 are more densely packed than in Figure 3. This is indicated by the fact that the region showing the nanowires 1 has a denser structure. [Explanation of Symbols]

[0056] 1 nanowire 2 Covering 3 equipment 4. First part 5. Second part

Claims

1. A method for connecting two components (4, 5) via multiple nanowires (1), A) The step of providing a coating (2) on a plurality of nanowires (1) on at least one of the components (4, 5), B) The step of bringing the components (4, 5) together so that the components (4, 5) are connected to each other via the nanowire (1), Includes, The coating (2) is removed in places or completely by bringing the two parts (4, 5) together or by a subsequent method step.

2. The method according to Claim 1, The coating (2) in step A) a) a step of treating each nanowire (1) with a reducing substance; b) a step of immersing each nanowire (1) in a protective substance; c) a step of drying each nanowire (1) to obtain the coating (2) from the protective substance; method.

3. The method according to Claim 2, The aforementioned protective substance includes an organic substance. method.

4. The method according to claim 2 or 3, The protective substance includes a metal, method.

5. The method according to any one of Claims 2 to 4, The protective substance is selected considering the material of each nanowire (1) such that in step b), the protective substance adheres at least partially to each nanowire (1) by physical adsorption. method.

6. The method according to any one of claims 2 to 5, The coating (2) of each nanowire (1) formed by steps a) to c) has an average thickness of up to 20 molecules. method.

7. The method according to any one of claims 2 to 6, The aforementioned parts (4, 5) are rinsed with rinsing solution between step a) and b), or between step b) and c), or both. method.

8. The method according to any one of claims 1 to 7, C) A step of removing at least partially the coating (2) of the nanowire (1) by heating, A method that further includes this.

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