Method for creating and repairing a structure on the surface of a substrate

Abstract

Method for producing a structure on a surface of a substrate (5), wherein a coating material (1) is applied to the surface of the substrate (5), wherein the coating material (1) comprises a binder (3) and a functional filler material (2), and wherein the functional filler material (2) comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, and during and / or after application the coating material (1) is subjected to an alternating magnetic field (6) so that an electrically conductive percolation network of the functional filler material (2) is formed, characterized in that The application material (1) is removed from the substrate (5) after being applied to the substrate (5) and is applied to the same substrate (5) or to a different substrate.

Description

[0001] The present invention relates to a method for producing and repairing a structure on a surface of a substrate and to a corresponding structure.

[0002] Printable electronic structures are typically based on pastes that are provided with functional filler materials such as electrical conductors, semiconductors, or dielectric materials, as well as binders such as polymers, and are applied using various printing techniques. For example, the document DE 10 2019 211970 A1 discloses a method for producing a printed magnetic functional element. US 2014 / 0353540 A1 discloses a method for applying a suspension of a binder and magnetic particles, wherein the particles can be arranged by an alternating magnetic field. US 2012 / 0156391 A1 also discloses a method for producing a structure using magnetic particles and arranging them using an alternating magnetic field. A self-healing mechanism using a static magnetic field is described in US 2019 / 0237228 A1.

[0003] A disadvantage of this is often the formation of a percolation network (i.e. in particular the formation of a network of substances contained in a liquid) of functional filler materials, which determines the performance of the electronic components produced in this way. Two difficulties in particular can arise here: The filler materials are not evenly distributed in the paste, which leads to an insufficient number of contact points. In addition, adjacent particles of the filler material can be (electrically) insulated from one another by the binder and therefore do not form a connection with one another. Due to the large differences in the electrical conductivity of the filler material and binder (e.g. electrically insulating polymers), a comparatively thin binder layer can completely block the electrical path between particles of the filler material.

[0004] The present invention is therefore based on the object of avoiding the disadvantages mentioned and of proposing a method with which structures with the desired properties can be produced in a simple and reliable manner.

[0005] This object is achieved according to the invention by a method and a structure according to the independent claims. Advantageous embodiments and further developments are described in the dependent claims.

[0006] In a method for producing a structure on a substrate surface, a deposition material is applied to the surface of the substrate. The deposition material comprises a binder and a functional filler material. The functional filler material comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order. During application and / or after application, the deposition material is subjected to an alternating magnetic field so that an electrically conductive percolation network of the filler material is formed. After application to the substrate, the deposition material is removed from the substrate and applied to the same substrate or a different substrate.

[0007] The alternating magnetic field, i.e., an oscillating electromagnetic field, moves the particles of the filler material, causing them to self-align on the surface of the substrate. In particular, a more homogeneous distribution is achieved, and the spatial rearrangement generates sufficient contact points to enable an electrical current to flow between the particles. Furthermore, the "shaking" of the particles and the oscillation of the filler material also make it possible to remove electrically insulating layers of the binder or layers formed on the particles due to surface oxidation through friction, thereby establishing direct physical contact between individual particles.These two effects enable the efficient formation of a percolation network, which can be used, for example, to produce printable, electrically conductive structures with high electrical conductivity or printable magnetoresistive sensors. Preferably, the deposited material is applied to the surface of the substrate in a locally defined shape. This locally defined shape—that is, any desired shape limited only by the method of application—also allows the structure to be produced to have virtually any desired shape.

[0008] A material with a magnetic order is understood to mean, in particular, a ferromagnetic material, i.e., in particular, a material with a magnetic permeability that is much greater than 1. However, it is also understood to mean a ferrimagnetic material or an antiferromagnetic material.

[0009] It may also be intended to apply the method to structures already arranged on the substrate, ie to establish an electrical contact between existing electrically conductive structures by means of the method. An electrically conductive material is understood to be a material whose electrical conductivity is at least 10 4 S / m. The conductivity value should be achieved in a temperature range relevant to the application, for example, at room temperature. A semiconducting material is understood to be a material whose electrical conductivity is typically less than 10 4 S / m and more than 10 -8 S / m in the temperature range relevant for the application, for example at room temperature.

[0010] It may be provided that the coating material is removed from the substrate after application to the substrate, i.e., that the structure is separated from the substrate after formation on the surface of the substrate, i.e., the previous direct contact with this surface is eliminated and the structure is further used or processed spatially separated from the substrate. Alternatively or additionally, the structure or the coating material can also be applied to the same substrate or another substrate, for example, made of paper, a ceramic material, a polymer, or a textile, after removal.

[0011] The electrically conductive or semiconducting material with a magnetic order can be composed either of homogeneous particles or of particles that have a core and a shell surrounding the core, typically completely surrounding it. The shell can also be made of a non-magnetic material, i.e., a material without magnetic order, and can comprise, for example, a polymer, a metal, an oxide, or a semiconducting material. In this case, the core can be magnetic, i.e., a material with a magnetic order, and can be electrically conductive (such as cobalt or alloys of iron and nickel) or electrically insulating (such as the magnetic oxide Fe2O3). An electrically insulating material is defined as a material with an electrical conductivity of less than 10 -8S / m in the temperature range relevant for the respective application, for example at room temperature. If the particles are homogeneous, i.e. made of a single material, this material must have a magnetic order and be electrically conductive or semiconducting. The shell can be made of a metal such as gold, silver or carbon, i.e. it can contain or consist of this; if the shell is made of semiconducting materials, this can be made of silicon, ZnO, InGaZnO, GaAs or ZnS, for example. Alternatively or additionally, electrically conductive or semiconducting polymers can also be used for this purpose.

[0012] The binder can preferably be configured as a polymer, particularly preferably as a viscoelastic polymer, to obtain suitable flow properties. As a rule, the binder or binding agent is understood to be a combination of a solvent and a specific polymer. The binder can be formed from an electrically insulating material or an electrically conductive material and can be present, for example, as a gel or liquid metal. Alternatively or additionally, the binder can be formed from a photosensitive material (such as a photoresist used for lithography).

[0013] It can be provided to subject the substrate and the structure applied or deposited thereon to the alternating magnetic field while the deposit material is still liquid, but it can also be provided to first allow the deposit material, i.e. in particular the binder, to dry or harden and then expose the substrate with the deposit material to the alternating magnetic field. The drying or hardening can also take place by thermal processing of the deposit material, for example by heating it with a lamp. In a particularly preferred manner, heating or heating takes place over a period of at least two hours to a temperature of 100 °C to 150 °C in order to solidify the binder, i.e. to remove the solvent. To solidify the binder, the deposit material can in principle be processed at a temperature between 50 °C and 450 °C, whereby the exact parameters depend on the binder.

[0014] The functional filler material is typically selected from iron, nickel, cobalt, and / or alloys of these chemical elements. Alternatively or additionally, the functional filler material may also comprise magnetic oxides, preferably Fe2O3, Cr2O3, Fe3O4, which are coated with an electrically conductive or semiconducting filler material. The functional filler material is particularly preferably Permalloy, ie, in particular Ni 80 Fe 20 , Ni 81 Fe 19 or Ni 78 Fe 22 .

[0015] The coating material can be in the form of a paste, gel, dispersion, or suspension and typically contains the functional filler material in powder form. The average particle size of the filler material is typically between 10 nm and 100 µm, preferably between 100 nm and 10 µm.

[0016] The coating material can be applied to the surface of the substrate using an additive manufacturing process and printing, in particular screen printing, pipetting, painting, dip coating, inkjet printing, spray printing, squeegee printing, three-dimensional filament printing, and / or spin coating. The application can also include pressing, stamping, painting, spreading, spraying, or lithography. If the binder is in the form of a photoresist, the structure can also be structured by lithography as an alternative or in addition to the described processes.

[0017] The deposited material is preferably exposed to an alternating magnetic field with a frequency of 1 mHz to 100 MHz, preferably 40 Hz to 80 Hz, particularly preferably 50 Hz, to enable sufficiently high movement of the filler particles. Typically, the alternating magnetic field is applied for at least 1 millisecond to 10 hours, preferably for 10 seconds. The field strength of the alternating magnetic field is typically 1 µT to 5 T, preferably 100 mT.

[0018] The substrate can be formed from glass, a semiconductor, preferably silicon, a ceramic, paper, a textile, a rubber, and / or a polymer or a composite material. Furthermore, at least one auxiliary layer can be provided on the surface of the substrate, to which the described structure is applied. This auxiliary layer can be, for example, a smoothing layer and / or an intermediate adhesion layer.

[0019] The structure is typically an electrical or electronic structure.

[0020] In addition to the described method, a method for repairing a structure applied to a surface of the substrate can also be performed. The aforementioned properties of the previously explained method are also applicable to the method described in more detail below.The structure, which has been applied to the surface of the substrate in a particularly preferred manner by means of the method already described, in which the application material, which has a binder and a functional filler material with the aforementioned electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, has been applied, can be repaired by applying an alternating magnetic field in the event of mechanical damage to the structure, for example a crack or a scratch, as a result of which in particular the electrical conductivity of the structure is no longer as desired, since the alternating magnetic field closes a percolation network of the functional filler material of the structure in an electrically conductive manner.

[0021] In another method for producing a structure on a substrate surface, a coating material is applied to the surface of the substrate. The coating material comprises a binder and a functional filler material. The functional filler material comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order. During and / or after application, the coating material is subjected to an alternating magnetic field, so that an electrically conductive percolation network of the filler material is formed. The functional filler material is selected from nickel, iron, cobalt, and alloys of these chemical elements, or is selected from magnetic oxides, preferably Fe2O3, Cr2O3, Fe3O4, which are coated with an electrically semiconducting coating material.

[0022] The invention also relates to a structure formed with a coating material, wherein the coating material comprises a binder and a functional filler material. The functional filler material comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order. In addition, the structure has an electrically conductive percolation network of the functional filler material. Typically, this structure is produced by the method explained or repaired by means of the method described. The coating material is typically applied to a surface of a substrate in a locally defined form, i.e., in particular, as a defined structure, but can also be present as a free structure detached from the substrate.If the coating material is applied by spin coating, a continuous, flat coating of the substrate surface to which the coating material is applied can also be achieved. The functional filler material is selected from nickel, iron, cobalt, and alloys of these chemical elements, or is selected from magnetic oxides, preferably Fe2O3, Cr2O3, or Fe3O4, coated with an electrically semiconducting shell material.

[0023] Preferably, the structure is designed as a magnetoimpedance sensor or as a Hall effect sensor, whereby this should be understood in particular as a sensor based on a magnetoimpedance effect, in which an electrical impedance of the respective material changes upon application of a constant or temporally alternating magnetic field, and a measurement can be performed with the sensor when the sensor is supplied with direct current or alternating current or direct voltage or alternating voltage (the choice of supply depends on the selected connection plan). In particular, this should be understood as the ordinary magnetoresistance effect, the anisotropic magnetoresistance effect (AMR effect), the giant magnetoresistance effect (GMR effect), the colossal magnetoresistance effect (CMR effect), the tunneling magnetoresistance effect (TMR effect), as well as the planar Hall effect and magnetoimpedance, as well as the giant magnetoimpedance effect.In addition, this should also be understood to include changes in the electrical voltage due to a normal and / or an anomalous Hall effect when the material is measured in a Hall effect arrangement. However, the structure can also be designed as a temperature sensor, an electrical conductor, a humidity sensor or an electronic structure, preferably as a diode or a transistor.

[0024] Embodiments of the invention are illustrated in the drawings and are described below with reference to Fig. 1 to 3. They show: Fig. 1 a schematic representation of process steps for forming a percolation network; Fig. 2 a schematic representation of process steps for repairing a percolation network and Fig. 3 a schematic representation of the fabrication and repair of a magnetoresistive sensor as well as images and measured values ​​of the sample.

[0025] Fig. Figure 1 shows a schematic view of a method for forming a percolation network. For this purpose, in the process steps running from left to right, a paste is first synthesized as the application material 1 by mixing a functional filler material 2, in the illustrated embodiment an iron powder, with a binder 3 such as a viscoelastic polymer using a stirring rod 4 or another suitable device. The resulting paste is applied to a surface of a substrate 5, for example by printing. On the surface, as shown in Fig. 1, conductor tracks may already be arranged as an electrical structure, with the functional filler material 2 being applied with the aim of enabling electrical contact between the conductor tracks. Subsequently, the paste containing the functional filler material 2 is subjected to an alternating magnetic field 6. As a result, the iron powder particles are arranged through self-alignment in such a way that an electrically conductive percolation network is created.

[0026] In a further embodiment, the paste can also be made of Ni 81 Fe 19-Powder, i.e., permalloy powder, boric acid, hydroxyl-terminated polydimethylsiloxane with a viscosity of 18,000-20,000 cSt, n-hexane, and polydimethylsiloxane (184 silicone elastomer). To prepare the binder or binder 3, 0.9 g of hydroxyl-terminated polydimethylsiloxane, 0.5 mg of boric acid, and 0.1 g of polydimethylsiloxane (with a base:hardener ratio of 10:1) are added to 4 ml of n-hexane. Polydimethylsiloxane serves as a scaffold to create stable structures, while the hydroxyl-terminated polydimethylsiloxane has the potential for self-healing due to its dynamic boron-oxygen bond between adjacent chains. The solvent n-hexane is added to adjust the viscosity of the paste so that the Permalloy microparticles are dispersed as evenly as possible without clumping and thus fully contribute to the formation of an electrically conductive matrix.In addition, the solvent can influence the viscosity of the binder solution so that different viscosity requirements can be met for different application methods.

[0027] The paste can be prepared by magnetic stirring for 30 minutes at room temperature, i.e., at 20 °C. By precisely adding permalloy powder to the binder solution, pastes with different concentrations of magnetoresistive fillers can be obtained for the subsequent printing process.

[0028] Thanks to the intrinsic tackiness of the binder 3, the paste also adheres reliably to different types of substrates 5. For this purpose, the paste can be applied to very different types, for example flat flexible cables, silicon substrates, glass substrates, paper substrates or ceramic substrates, using different printing techniques such as spin coating or screen printing. After evaporation of the n-hexane as a solvent, which occurs within 2 minutes after application, the paste in the printed locally defined form, i.e. as a locally defined structure, is introduced into an alternating magnetic field 6 with a frequency of 50 Hz for 10 seconds. As a result, the particles of the filler material 2 are magnetically guided to form an electrically conductive matrix. The alternating magnetic field 6 is generated by an induction coil in the discussed embodiment.Finally, the structure produced from the paste is heated at 120 °C for two hours to cure the binder 3.

[0029] This method allows printed electronic structures to be easily manufactured and repaired, whereby not only magnetic materials but also magnetic materials that form heterojunctions with non-magnetic materials can be used. In further embodiments, the structure can be Fig. 1 can also be detached from the substrate 5 and reused as a free element or applied to a second substrate.

[0030] Fig. 2 shows in a Fig. 1 shows a method for repairing an electronic structure applied to the substrate 5. Recurring features are provided with identical reference numerals. The Fig. 1 described method can be used in the process described in Fig. 2 The mechanical damage shown on the far left, for example due to a scratch, through which two particles of the percolation network no longer have mechanical contact with each other and thus the electrical conductivity is no longer present, can be repaired by applying the magnetic field 6 again.

[0031] The mobility of the viscoelastic binder 3 (which can be stimulated by heat and / or light) generally guides the particles of the functional filler material 2 to the damaged area of ​​the percolation network. However, due to their density and weight, particles are more difficult to damage, so that only the alternating magnetic field 6 can guide the particles of the filler material 2 to the point of damage. This can also remove any insulating layer of the binder 3, and the percolation network is restored.

[0032] The oscillating magnetic field magnetically polarizes the particles of the filler material 2 and exerts an attractive force on each other, allowing them to arrange themselves as desired without the need for costly manual alignment. By adjusting the maximum field strength and frequency of the alternating magnetic field 6, the process can be tailored to a wide range of practical requirements.

[0033] Fig. 3 shows in Fig. 3a), the top line of the figure, summarizes the manufacturing of an electronic structure using the described method as well as its repair. In Fig. 3b) shows photographs of the magnetoresistive paste in its original state, after cutting, and after repair (from left to right). The repair was performed by exposing it to an alternating magnetic field 6 (also referred to as an alternating magnetic field, AMF; a static magnetic field is abbreviated as "MF") for a period of 20 seconds. Fig. 3c) shows identical figures, but now, in contrast to the 100 mm wide crack in Fig. 3b) a 5 mm wide fracture is present in the layer, which can nevertheless be closed again using the described procedure. Fig. 3b) and Fig. 3c) bars correspond to 400 µm in Fig. 3b) and Fig. 5 mm in Fig. 3c).

[0034] Fig. Finally, Figure 3d shows measurements of electrical resistance over time using known four-point measurement techniques to determine the magnetoresistance of sensors manufactured using the described method. The respective sensor is exposed to an in-plane magnetic field, i.e., one running in the plane of the sensor, and the measurements are performed at room temperature. Fig. 3d) also shows scanning electron microscope images of plasma-etched coating material 1. In the upper image, a static magnetic field was applied, while in the lower image, an oscillating dynamic magnetic field was applied. The bars each correspond to 30 µm.

[0035] Fig. 3e) shows how in Fig. 3d) the electrical resistance is plotted over time, but now a total of four cutting processes are carried out followed by self-healing. Fig.Finally, 3f) shows the magnetoresistance value in percent plotted against the field strength of the alternating magnetic field 6. The two measurement curves show the course of the magnetoresistance value before and after cutting and healing or repair. The measured values ​​are obtained by measuring the change in electrical resistance in a magnetic field and normalizing to the initial resistance value at 0 mT, i.e., (R-R0) / R0.

[0036] Only features of the various embodiments disclosed in the exemplary embodiments can be combined with one another and claimed individually.

Claims

[1] Method for producing a structure on a surface of a substrate (5), in which a coating material (1) is applied to the surface of the substrate (5), wherein the coating material (1) comprises a binder (3) and a functional filler material (2), and wherein the functional filler material (2) comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, and during the application and / or after the application, the application material (1) is subjected to an alternating magnetic field (6) so that an electrically conductive percolation network of the functional filler material (2) is formed, characterized by , that the application material (1) is removed from the substrate (5) after being applied to the substrate (5) and is applied to the same substrate (5) or another substrate. [2] Method according to claim 1, characterized by that the binder (3) is formed as a polymer, preferably a viscoelastic polymer. [3] Method according to claim 1 or claim 2, characterized by that the functional filler material (2) is selected from nickel, iron, cobalt and alloys of these chemical elements or is selected from magnetic oxides, preferably Fe2O3, Cr2O3, Fe3O4, which are coated with an electrically conductive or semiconducting coating material, wherein the functional material (2) is particularly preferably Permalloy. [4] Method according to one of the preceding claims, characterized bythat the application material (1) is applied to the surface of the substrate (5) by means of an additive manufacturing process and printing, in particular screen printing, pipetting, painting, dip coating, inkjet printing, spray jet printing, squeegee printing, three-dimensional filament printing and / or spin coating and / or, if the binder (3) is designed as a photoresist, the application material (1) is structured by lithography. [5] Method according to one of the preceding claims, characterized by that the coating material (1) is subjected to the alternating magnetic field (6) with a frequency of 1 mHz to 100 MHz, preferably 40 Hz to 80 Hz, particularly preferably 50 Hz and / or that the coating material (1) is subjected to the alternating magnetic field (6) for at least 1 ms to 10 hours, preferably for 10 seconds. [6] Method according to one of the preceding claims, characterized bythat the deposit material (1) is processed at a temperature in the range between 50 °C and 450 °C in order to solidify the binder (3). [7] Method for repairing a structure applied to a surface of a substrate (5), which structure has a coating material (1) applied to the surface of the substrate (5), which has a binder (3) and a functional filler material (2), wherein the functional filler material (2) has an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, in which, in the event of mechanical damage to the applied structure, it is subjected to an alternating magnetic field (6) so that a percolation network of the functional filler material (2) is closed in an electrically conductive manner. [8] Method for producing a structure on a surface of a substrate (5), in which a coating material (1) is applied to the surface of the substrate (5), wherein the coating material (1) comprises a binder (3) and a functional filler material (2), and wherein the functional filler material (2) comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, and during the application and / or after the application, the application material (1) is subjected to an alternating magnetic field (6) so that an electrically conductive percolation network of the functional filling material (2) is formed, wherein the functional filler material (2) is selected from nickel, iron, cobalt and alloys of these chemical elements or is selected from magnetic oxides, preferably Fe2O3, Cr2O3, Fe3O4, which are coated with an electrically semiconducting coating material. [9] Structure formed with a coating material (1), wherein the coating material (1) comprises a binder (3) and a functional filler material (2), wherein the functional filler material (2) comprises an electrically conductive or semiconducting material with a magnetic order or consists of the electrically conductive or semiconducting material with the magnetic order, and has an electrically conductive percolation network of the functional filler material (2), wherein the functional filler material (2) is selected from nickel, iron, cobalt and alloys of these chemical elements or is selected from magnetic oxides, preferably Fe2O3, Cr2O3, Fe3O4, which are coated with an electrically semiconducting coating material. [10] Structure according to claim 9, characterized by that the electronic structure is designed as a magnetoimpedance sensor, as a Hall effect sensor, as a temperature sensor, as an electrical line, as a humidity sensor or as an electronic structure, preferably as a diode or as a transistor.

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